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Shamsul Arafin

The Ohio State University, Electrical and Computer Engineering, Faculty Member

University of California, Santa Barbara, Electrical and Computer Engineering, Research Assistant

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Phone: 13106214349
Address: 2015 Neil Avenue, Columbus, OH 43210

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Papers by Shamsul Arafin

Recent progress on GaSb-based electrically-pumped VCSELs for wavelengths above 4 μm

Proc. SPIE 10980, Image Sensing Technologies: Materials, Devices, Systems, and Applications VI, 109800H (13 May 2019), 2019

This paper reports the recent progress on the development of GaSb-based vertical-cavity surface-e... more This paper reports the recent progress on the development of GaSb-based vertical-cavity surface-emitting lasers (VCSELs) with a record-long emission wavelength of above 4 µm using type-II quantum wells. Mid-wave infrared (MWIR) spectral region, covering the 3-6 µm wavelength range, is technologically very interesting for enabling two major application areas such as sensing and defense/security. Among several types of diode lasers, electrically-pumped continuous-wave operating VCSELs seem to be the most attractive choice owing to their low-power consumption, inherent longitudinal single-mode emission, and simple electro-thermal wavelength tunability. The applicability of MWIR VCSELs for these two major areas are also discussed in this paper. Single-mode low-power (a few mWs) VCSEL operating at room-temperature with reasonable tunability is essential for the sensing application. For the advanced military application, high optical power (with at least a few watts), high-efficiency and high-brightness (>1 W/mm 2) MWIR lasers are important. Given that the MWIR wavelength regime is eye-safe and has a low-loss atmospheric window, the development of next-generation MWIR laser sources is currently in high demand.

Optical Frequency Synthesis by Offset-Locking the Tunable Local-Oscillator of a Low-Power Integrated Receiver to a Microresonator Comb

A power-efficient and highly-integrated photonic system, producing low phase-noise coherent optic... more A power-efficient and highly-integrated photonic system, producing low phase-noise coherent optical signal with a wavelength range of 23 nm in the C-band, is presented. The system includes novel InP-photonic integrated coherent receiver circuits that consume record-low (approximately 184 mW) electrical power.

Near-to mid-IR (1–13 μm) III-V semiconductor lasers: introduction to the feature issue

This feature issue reports on the most recent advances in the field of III-V semiconductor lasers... more

Evolution of Chip-Scale Heterodyne Optical Phase-Locked Loops towards Watt Level Power Consumption

Journal of Lightwave Technology, 2017

We design and experimentally demonstrate two chip-scale and agile heterodyne optical phase-locked... more We design and experimentally demonstrate two chip-scale and agile heterodyne optical phase-locked loops (OPLLs) based on two types of InP-based photonic integrated coherent receiver circuits. The system performance of the first generation OPLL was improved in terms of offset-locking range, and power consumption with the use of a power-efficient and compact photonic integrated circuit (PIC). The second generation PIC consists of a 60 nm widely-tunable Y-branch laser as a local oscillator with a 2×2 MMI coupler and a pair of balanced photodetectors. This PIC consumes only 184 mW power in full operation, which is a factor of 3 less compared to the first generation PIC. In addition, the sensitivity of these OPLLs was experimentally measured to be as low as 20 µw. A possible solution to increase the sensitivity of these OPLLs is also suggested.

Advanced InP Photonic Integrated Circuits for Communication and Sensing

IEEE Journal of Selected Topics in Quantum Electronics, 2017

Similar to the area of microelectronics, InP-based photonic integrated circuits (PICs) in the op... more Similar to the area of microelectronics, InP-based photonic integrated circuits (PICs) in the optical domain as a counterpart is also seeing a clear exponential development. This rapid progress can be defined by a number of active/passive components monolithically integrated on a single chip. Given the probability of achieving low-cost, compact, robust and energy-efficient complex photonic systems, there have been significant achievements made in realizing relatively complex InP-PICs in recent years. The performance of these complex PICs is reaching a stage that can enable a whole new class of applications beyond telecom and datacom. A great deal of effort from both academia and industry has made the significant advances of this technology possible. This development has resulted in a positive and profound impact in many areas including sensing, medical diagnostics, metrology, and consumer photonics. This review paper will mainly discuss the recent, in particular since 2012, progress and findings obtained out of current academic and industry research activities for InP-PICs. Major emphasis will be given to the high-performance and complex PICs that have been reported by the scientific community in this time period. A prospect for further development of this photonic integration in InP-platforms is also briefly described.

Heterodyne locking of a fully integrated optical phase-locked loop with on-chip modulators

by Shamsul Arafin and Arda Simsek

We design and experimentally demonstrate a highly integrated heterodyne optical phase locked lo... more We design and experimentally demonstrate a highly integrated heterodyne optical phase locked loop (OPLL) consisting of an InP-based coherent photonic receiver, high-speed feedback electronics and an RF
synthesizer. Such coherent photonic integrated circuits contain two widely tunable lasers, semiconductor optical amplifiers, phase modulators, and a pair of balanced photodetectors. Offset phase locking of the two lasers is achieved by applying an RF signal to an onchip optical phase modulator following one of the lasers and locking
the other one to a resulting optical sideband. Offset locking frequency range >16 GHz is achieved for such a highlysensitive OPLL system which can employ up to the third order harmonic optical sidebands for locking. Furthermore, the rms phase error between the two
lasers is measured to be 8°.

Title: Investigation of Single-mode vertical-cavity surface-emitting lasers with graphene-bubble dielectric DBR

An inter-cavty contact single mode 850 nm VCSEL was fabricated with a graphene assisted self-asse... more An inter-cavty contact single mode 850 nm VCSEL was fabricated with a graphene assisted self-assembly curved dielectric bubble Bragg mirror for the first time. Taking the advantage of graphene’s uniform low surface energy, the low cost dielectric bubble DBR (Si3N4/SiO2) was deposited on top of the graphene/half-VCSEL structure via van der Waals Force (vdWF) without using any additional spacing elements and sacrificial layer release-etch process. The continuous-wave operating VCSELs with an aperture diameter of 7 μm exhibit single-mode output power of more than 1 mW with a slope efficiency of 0.2 W/A. The sidemode suppression ratios are >40 dB. This novel modification into the lasers can also be applied to a variety of other optoelectronic devices, such as resonance photodetecter and super narrow linewidth VCSEL.

Compact Low-Power Consumption Single-Mode Coupled-Cavity Lasers

Ultra-compact, widely-tunable and low-power InP-based four-section couple-cavity lasers are desig... more Ultra-compact, widely-tunable and low-power InP-based four-section couple-cavity lasers are designed and analyzed. Two Fabry-Pérot cavities of unequal lengths, each containing an amplifier and a phase-tuning section are coupled together through low-loss Bragg grating. The theoretical analysis of such multisection lasers starts with calculating the poles of a linear transfer function of the entire resonator in order to obtain resonant wavelengths and wavelength dependent threshold gains. The differential quantum efficiency and the power-current characteristics are then calculated to evaluate the laser performance. The effectiveness of the design procedure is verified by the experimental and proof-of-principle demonstration using simplified three-section lasers. Devices exhibit single-mode operation with a side-mode suppression ratio of over 24 dB and tuning range of 11.2 nm. These telecom-suitable lasers can be used as on-chip local oscillators in low-power integrated optical coherent receivers.

Power-Efficient Kerr Frequency Comb Based Tunable Optical Source

We designed and demonstrated a power-efficient highly-integrated photonic system, requiring a tot... more We designed and demonstrated a power-efficient highly-integrated photonic system, requiring a total power consumption of 1.7 W and producing a spectrally-pure coherent optical signal with a wavelength range of 23 nm in the C-band. The system consists of a compact, low-power InP-based photonic integrated coherent receiver, microresonator-based Kerr frequency comb and agile electronic circuits. The photonic coherent receiver contains a 60-nm widely-tunable Y-branch local oscillator (LO) diode laser, a coupler, and a pair of photodetectors. It consumes a record-low (approximately 184 mW) electrical power. The optical frequency comb reference has excellent spectral purity, <4 kHz optical linewidth and good frequency stability. The spectrally-pure tunable optical source was produced by offset locking the on-chip local oscillator (LO) laser of the integrated receiver to this frequency comb source. A possibility of further stabilization of the frequency comb repetition rate by locking to an external radio frequency synthesizer was demonstrated.

Wavelength dependence of efficiency limiting mechanisms in Type-I Mid-infrared GaInAsSb/GaSb lasers

— The efficiency limiting mechanisms in type-I GaInAsSb-based quantum well (QW) lasers, emitting ... more — The efficiency limiting mechanisms in type-I GaInAsSb-based quantum well (QW) lasers, emitting at 2.3 µm, 2.6 µm and 2.9 µm, are investigated. Temperature characterization techniques and measurements under hydrostatic pressure identify an Auger process as the dominant non-radiative recombination mechanism in these devices. The results are supplemented with hydrostatic pressure measurements from three additional type-I GaInAsSb lasers, extending the wavelength range under investigation from 1.85-2.90 μm. Under hydrostatic pressure, contributions from the CHCC and CHSH Auger mechanisms to the threshold current density can be investigated separately. A simple model is used to fit the non-radiative component of the threshold current density, identifying the dominance of the different Auger losses across the wavelength range of operation. The CHCC mechanism is shown to be the dominant non-radiative process at longer wavelengths (> 2 μm). At shorter wavelengths (< 2 μm) the CHSH mechanism begins to dominate the threshold current, as the bandgap approaches resonance with the spin-orbit split-off band.

Chip-scale frequency synthesizer

Reducing the size of optical frequency synthesizers (OFSs) to the chip scale is technically chall... more Reducing the size of optical frequency synthesizers (OFSs) to the chip scale is technically challenging. Optical frequency comb (OFC) generators are a key element of OFSs, and microresonator-based OFCs lend themselves to on-chip integration. However, even these generators require pump laser powers in the hundred milliwatt range, thus hampering the successful thermal management of integrated OFSs. Now, Shamsul Arafin and co-workers from the USA have demonstrated a chip-scale OFS based on an optical heterodyne phase-locked loop. Light emitted from a semiconductor distributed feedback laser with an output power of 20 mW was sent to a high-Q MgF2 whispering-gallery-mode resonator to generate an optical frequency comb spanning the 1,535–1,575 nm range. The comb lines were used as the reference for the heterodyne optical phase-locked loop, where the latter consisted of a photonic integrated circuit, an electronic integrated circuit and a loop filter. Arbitrary frequency synthesis between the comb lines was demonstrated by tuning the radio frequency offset source, and better than 100 Hz tuning resolution within an accuracy of 5 Hz was achieved.

Towards chip-scale optical frequency synthesis based on optical heterodyne phase- locked loop

An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium p... more An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components. As an input reference, a stable microresonator-based optical frequency comb with a 50-dB span of 25 nm (~3 THz) around 1550 nm, having a spacing of ~26 GHz, was used. A widely-tunable on-chip sampled-grating distributed-Bragg-reflector laser is offset locked across multiple comb lines. An arbitrary frequency synthesis between the comb lines is demonstrated by tuning the RF offset source, and better than 100Hz tuning resolution with ± 5 Hz accuracy is obtained. Frequency switching of the on-chip laser to a point more than two dozen comb lines away (~5.6 nm) and simultaneous locking to the corresponding nearest comb line is also achieved in a time ~200 ns. A low residual phase noise of the optical phase-locking system is successfully achieved, as experimentally verified by the value of 80 dBc/Hz at an offset of as low as 200 Hz. Hall, and S. T. Cundiff, " Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis, " Science 288(5466), 635–639 (2000). 2. J. Castillega, D. Livingston, A. Sanders, and D. Shiner, " Precise measurement of the J = 1 to J = 2 fine structure interval in the 2(3)P state of helium, " Phys.

Nanostructured Optoelectronics: Materials and Devices

The use of nanostructure materials for optoelectronic devices, including light-emitting diodes (L... more The use of nanostructure materials for optoelectronic devices, including light-emitting diodes (LEDs), laser diodes, photodetectors, and solar cells, has recently attracted considerable attention due to their unique geometry. Nanostructures in small dimensions can be perfectly integrated into a variety of technological platforms, offering novel physical and chemical properties for the high performance optoelectronic devices. The exploitation of new nanostructures and their optical and electrical properties is necessary for their emerging practical device applications.

Photoreflectance of a 2.3μm GaInAsSb-based VCSEL structure for gas sensing applications

by Jeff Hosea, Shamsul Arafin, and G. Chai

2nd Annual International Conference on Optoelectronics, Photonics & Applied Physics (OPAP 2014), 2014

Temperature-dependent photo-modulated reflectance (PR) spectroscopy has been applied to study a G... more Temperature-dependent photo-modulated reflectance (PR) spectroscopy has been applied to study a GaSb-based vertical-cavity surface-emitting laser (VCSEL) structure designed to operate at 2.3µm. To investigate the wavelength offset between the quantum well (QW) and cavity mode (CM) features, which determine the device's physical properties and temperature performance, the energies of the QW transitions relative to the VCSEL CM energy were tuned by heating from 9K to 300K. We found that this VCSEL structure has a QW-CM offset of 21meV at room temperature; also, the QW ground-state transition only comes into resonance with the CM at 220±2K. These PR results are closely compared with those obtained in a separate study of actual operating devices.

Temperature stable mid-infrared GaInAsSb/GaSb Vertical Cavity Surface Emitting Lasers (VCSELs)

GaInAsSb/GaSb based quantum well vertical cavity surface emitting lasers (VCSELs) operating in mi... more GaInAsSb/GaSb based quantum well vertical cavity surface emitting lasers (VCSELs) operating in mid-infrared spectral range between 2 and 3 micrometres are of great importance for low cost gas monitoring applications. This paper discusses the efficiency and temperature sensitivity of the VCSELs emitting at 2.6 μm and the processes that must be controlled to provide temperature stable operation. We show that non-radiative Auger recombination dominates the threshold current and limits the device performance at room temperature. Critically, we demonstrate that the combined influence of non-radiative recombination and gain peak – cavity mode de-tuning determines the overall temperature sensitivity of the VCSELs. The results show that improved temperature stable operation around room temperature can only be achieved with a larger gain peak – cavity mode de-tuning, offsetting the significant effect of increasing non-radiative recombination with increasing temperature, a physical effect which must be accounted for in mid-infrared VCSEL design.

First Monolithically Integrated Dual-Pumped Phase-Sensitive Amplifier Chip Based on a Saturated Semiconductor Optical Amplifier

Email Print Request Permissions For the first time, a monolithically integrated photonic phase-s... more Email
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For the first time, a monolithically integrated photonic phase-sensitive amplification chip is fabricated and demonstrated based on an InP/InGaAsP platform. Different semiconductor optical amplifiers have been fabricated as well for characterization. On the chip, two tunable laser pumps that are coherently injection-locked, respectively, from two first-order sidebands of an externally modulated tone are generated to enable signal-degenerate dual-pumped phase-sensitive amplification in a saturated semiconductor optical amplifier. Experiments on different chips are conducted to successfully demonstrate phase-sensitive amplification with approximately 6.3 dB and 7.8 dB extinction of phase-sensitive on-chip gain. Theoretical simulations are performed and agree well with experimental results. The additive noise properties of the phase-sensitive amplification chip are also investigated.

a-Ge and a-Si as dielectric mirror materials for long-wavelength optoelectronic devices: a comparative study

Dielectric mirrors are key components in a number of optoelectronic devices, e.g. vertical-cavity... more Dielectric mirrors are key components in a number of optoelectronic devices, e.g. vertical-cavity surface-emitting lasers (VCSELs) 1 , low-threshold edge-emitting lasers 2 , subwavelength ultrabroadband mirrors 3 and modulators 4 which require very high reflectivity (R > 95%) with low optical losses. In fact, this type of mirrors, such as, distributed Bragg reflectors (DBRs) or Bragg mirrors are composed of stacking alternating thin layers of two different dielectric materials with high and low refractive index. The mirror materials must be chosen in a way that the refractive index contrast, Δn of the constituent materials becomes as high as possible and at the same time the absorption loss becomes very low to reach sufficient reflectivity with a minimum number of layers and interfaces.

Wavelength dependence of the performance of GaInAsSb mid-infrared lasers

Low-resistive ohmic contacts to n-InAs0. 91Sb0. 09 for GaSb-based VCSELs in the mid-infrared range

Temperature dependence of 2.3 μm and 2.6 μm GaInAsSb based BTJ VCSELs and edge emitting lasers

There is a growing interest in electrically pumped lasers that emit in the 2-3μm wavelength regio... more There is a growing interest in electrically pumped lasers that emit in the 2-3μm wavelength region for applications such as gas sensing, pollution monitoring and medical diagnosis. GaSb based type-I quantum well edge-emitting lasers (EELs) provide room temperature continuous wave operation but are limited by Auger recombination and inter-valence band absorption. For most applications, Vertical Cavity Surface-Emitting Lasers (VCSELs) are a preferred option because of lower power consumption, cheaper fabrication and improved beam quality. However, self-heating and the presence of fundamental loss processes necessitate careful design to provide gain peak -cavity mode alignment at a particular temperature and wavelength for optimum performance. In this study we have investigated 2.3µm and 2.6µm VCSELs. Edge-emitting lasers with nominally identical active regions were used to look at the effects of non-radiative recombination and to extract information about the gain peak which was then used to analyse the VCSEL behaviour. A combination of high hydrostatic pressure and temperature dependence techniques were used to investigate the wavelength dependence of non-radiative processes and cavity modegain peak detuning. From these measurements we find that 85% (97 %) of the threshold current of 2.3μm (2.6μm) edge-emitting lasers is due to non-radiative recombination. Our results suggest that temperature insensitive VCSEL operation around room temperature could be achieved with a larger gaincavity de-tuning, offsetting the effect of increasing non-radiative recombination with increasing temperature, as shall be discussed in further detail.

Recent progress on GaSb-based electrically-pumped VCSELs for wavelengths above 4 μm

Proc. SPIE 10980, Image Sensing Technologies: Materials, Devices, Systems, and Applications VI, 109800H (13 May 2019), 2019

This paper reports the recent progress on the development of GaSb-based vertical-cavity surface-e... more This paper reports the recent progress on the development of GaSb-based vertical-cavity surface-emitting lasers (VCSELs) with a record-long emission wavelength of above 4 µm using type-II quantum wells. Mid-wave infrared (MWIR) spectral region, covering the 3-6 µm wavelength range, is technologically very interesting for enabling two major application areas such as sensing and defense/security. Among several types of diode lasers, electrically-pumped continuous-wave operating VCSELs seem to be the most attractive choice owing to their low-power consumption, inherent longitudinal single-mode emission, and simple electro-thermal wavelength tunability. The applicability of MWIR VCSELs for these two major areas are also discussed in this paper. Single-mode low-power (a few mWs) VCSEL operating at room-temperature with reasonable tunability is essential for the sensing application. For the advanced military application, high optical power (with at least a few watts), high-efficiency and high-brightness (>1 W/mm 2) MWIR lasers are important. Given that the MWIR wavelength regime is eye-safe and has a low-loss atmospheric window, the development of next-generation MWIR laser sources is currently in high demand.

Optical Frequency Synthesis by Offset-Locking the Tunable Local-Oscillator of a Low-Power Integrated Receiver to a Microresonator Comb

A power-efficient and highly-integrated photonic system, producing low phase-noise coherent optic... more A power-efficient and highly-integrated photonic system, producing low phase-noise coherent optical signal with a wavelength range of 23 nm in the C-band, is presented. The system includes novel InP-photonic integrated coherent receiver circuits that consume record-low (approximately 184 mW) electrical power.

Near-to mid-IR (1–13 μm) III-V semiconductor lasers: introduction to the feature issue

This feature issue reports on the most recent advances in the field of III-V semiconductor lasers... more

Evolution of Chip-Scale Heterodyne Optical Phase-Locked Loops towards Watt Level Power Consumption

Journal of Lightwave Technology, 2017

We design and experimentally demonstrate two chip-scale and agile heterodyne optical phase-locked... more We design and experimentally demonstrate two chip-scale and agile heterodyne optical phase-locked loops (OPLLs) based on two types of InP-based photonic integrated coherent receiver circuits. The system performance of the first generation OPLL was improved in terms of offset-locking range, and power consumption with the use of a power-efficient and compact photonic integrated circuit (PIC). The second generation PIC consists of a 60 nm widely-tunable Y-branch laser as a local oscillator with a 2×2 MMI coupler and a pair of balanced photodetectors. This PIC consumes only 184 mW power in full operation, which is a factor of 3 less compared to the first generation PIC. In addition, the sensitivity of these OPLLs was experimentally measured to be as low as 20 µw. A possible solution to increase the sensitivity of these OPLLs is also suggested.

Advanced InP Photonic Integrated Circuits for Communication and Sensing

IEEE Journal of Selected Topics in Quantum Electronics, 2017

Similar to the area of microelectronics, InP-based photonic integrated circuits (PICs) in the op... more Similar to the area of microelectronics, InP-based photonic integrated circuits (PICs) in the optical domain as a counterpart is also seeing a clear exponential development. This rapid progress can be defined by a number of active/passive components monolithically integrated on a single chip. Given the probability of achieving low-cost, compact, robust and energy-efficient complex photonic systems, there have been significant achievements made in realizing relatively complex InP-PICs in recent years. The performance of these complex PICs is reaching a stage that can enable a whole new class of applications beyond telecom and datacom. A great deal of effort from both academia and industry has made the significant advances of this technology possible. This development has resulted in a positive and profound impact in many areas including sensing, medical diagnostics, metrology, and consumer photonics. This review paper will mainly discuss the recent, in particular since 2012, progress and findings obtained out of current academic and industry research activities for InP-PICs. Major emphasis will be given to the high-performance and complex PICs that have been reported by the scientific community in this time period. A prospect for further development of this photonic integration in InP-platforms is also briefly described.

Heterodyne locking of a fully integrated optical phase-locked loop with on-chip modulators

by Shamsul Arafin and Arda Simsek

We design and experimentally demonstrate a highly integrated heterodyne optical phase locked lo... more We design and experimentally demonstrate a highly integrated heterodyne optical phase locked loop (OPLL) consisting of an InP-based coherent photonic receiver, high-speed feedback electronics and an RF
synthesizer. Such coherent photonic integrated circuits contain two widely tunable lasers, semiconductor optical amplifiers, phase modulators, and a pair of balanced photodetectors. Offset phase locking of the two lasers is achieved by applying an RF signal to an onchip optical phase modulator following one of the lasers and locking
the other one to a resulting optical sideband. Offset locking frequency range >16 GHz is achieved for such a highlysensitive OPLL system which can employ up to the third order harmonic optical sidebands for locking. Furthermore, the rms phase error between the two
lasers is measured to be 8°.

Title: Investigation of Single-mode vertical-cavity surface-emitting lasers with graphene-bubble dielectric DBR

An inter-cavty contact single mode 850 nm VCSEL was fabricated with a graphene assisted self-asse... more An inter-cavty contact single mode 850 nm VCSEL was fabricated with a graphene assisted self-assembly curved dielectric bubble Bragg mirror for the first time. Taking the advantage of graphene’s uniform low surface energy, the low cost dielectric bubble DBR (Si3N4/SiO2) was deposited on top of the graphene/half-VCSEL structure via van der Waals Force (vdWF) without using any additional spacing elements and sacrificial layer release-etch process. The continuous-wave operating VCSELs with an aperture diameter of 7 μm exhibit single-mode output power of more than 1 mW with a slope efficiency of 0.2 W/A. The sidemode suppression ratios are >40 dB. This novel modification into the lasers can also be applied to a variety of other optoelectronic devices, such as resonance photodetecter and super narrow linewidth VCSEL.

Compact Low-Power Consumption Single-Mode Coupled-Cavity Lasers

Ultra-compact, widely-tunable and low-power InP-based four-section couple-cavity lasers are desig... more Ultra-compact, widely-tunable and low-power InP-based four-section couple-cavity lasers are designed and analyzed. Two Fabry-Pérot cavities of unequal lengths, each containing an amplifier and a phase-tuning section are coupled together through low-loss Bragg grating. The theoretical analysis of such multisection lasers starts with calculating the poles of a linear transfer function of the entire resonator in order to obtain resonant wavelengths and wavelength dependent threshold gains. The differential quantum efficiency and the power-current characteristics are then calculated to evaluate the laser performance. The effectiveness of the design procedure is verified by the experimental and proof-of-principle demonstration using simplified three-section lasers. Devices exhibit single-mode operation with a side-mode suppression ratio of over 24 dB and tuning range of 11.2 nm. These telecom-suitable lasers can be used as on-chip local oscillators in low-power integrated optical coherent receivers.

Power-Efficient Kerr Frequency Comb Based Tunable Optical Source

We designed and demonstrated a power-efficient highly-integrated photonic system, requiring a tot... more We designed and demonstrated a power-efficient highly-integrated photonic system, requiring a total power consumption of 1.7 W and producing a spectrally-pure coherent optical signal with a wavelength range of 23 nm in the C-band. The system consists of a compact, low-power InP-based photonic integrated coherent receiver, microresonator-based Kerr frequency comb and agile electronic circuits. The photonic coherent receiver contains a 60-nm widely-tunable Y-branch local oscillator (LO) diode laser, a coupler, and a pair of photodetectors. It consumes a record-low (approximately 184 mW) electrical power. The optical frequency comb reference has excellent spectral purity, <4 kHz optical linewidth and good frequency stability. The spectrally-pure tunable optical source was produced by offset locking the on-chip local oscillator (LO) laser of the integrated receiver to this frequency comb source. A possibility of further stabilization of the frequency comb repetition rate by locking to an external radio frequency synthesizer was demonstrated.

Wavelength dependence of efficiency limiting mechanisms in Type-I Mid-infrared GaInAsSb/GaSb lasers

— The efficiency limiting mechanisms in type-I GaInAsSb-based quantum well (QW) lasers, emitting ... more — The efficiency limiting mechanisms in type-I GaInAsSb-based quantum well (QW) lasers, emitting at 2.3 µm, 2.6 µm and 2.9 µm, are investigated. Temperature characterization techniques and measurements under hydrostatic pressure identify an Auger process as the dominant non-radiative recombination mechanism in these devices. The results are supplemented with hydrostatic pressure measurements from three additional type-I GaInAsSb lasers, extending the wavelength range under investigation from 1.85-2.90 μm. Under hydrostatic pressure, contributions from the CHCC and CHSH Auger mechanisms to the threshold current density can be investigated separately. A simple model is used to fit the non-radiative component of the threshold current density, identifying the dominance of the different Auger losses across the wavelength range of operation. The CHCC mechanism is shown to be the dominant non-radiative process at longer wavelengths (> 2 μm). At shorter wavelengths (< 2 μm) the CHSH mechanism begins to dominate the threshold current, as the bandgap approaches resonance with the spin-orbit split-off band.

Chip-scale frequency synthesizer

Reducing the size of optical frequency synthesizers (OFSs) to the chip scale is technically chall... more Reducing the size of optical frequency synthesizers (OFSs) to the chip scale is technically challenging. Optical frequency comb (OFC) generators are a key element of OFSs, and microresonator-based OFCs lend themselves to on-chip integration. However, even these generators require pump laser powers in the hundred milliwatt range, thus hampering the successful thermal management of integrated OFSs. Now, Shamsul Arafin and co-workers from the USA have demonstrated a chip-scale OFS based on an optical heterodyne phase-locked loop. Light emitted from a semiconductor distributed feedback laser with an output power of 20 mW was sent to a high-Q MgF2 whispering-gallery-mode resonator to generate an optical frequency comb spanning the 1,535–1,575 nm range. The comb lines were used as the reference for the heterodyne optical phase-locked loop, where the latter consisted of a photonic integrated circuit, an electronic integrated circuit and a loop filter. Arbitrary frequency synthesis between the comb lines was demonstrated by tuning the radio frequency offset source, and better than 100 Hz tuning resolution within an accuracy of 5 Hz was achieved.

Towards chip-scale optical frequency synthesis based on optical heterodyne phase- locked loop

An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium p... more An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components. As an input reference, a stable microresonator-based optical frequency comb with a 50-dB span of 25 nm (~3 THz) around 1550 nm, having a spacing of ~26 GHz, was used. A widely-tunable on-chip sampled-grating distributed-Bragg-reflector laser is offset locked across multiple comb lines. An arbitrary frequency synthesis between the comb lines is demonstrated by tuning the RF offset source, and better than 100Hz tuning resolution with ± 5 Hz accuracy is obtained. Frequency switching of the on-chip laser to a point more than two dozen comb lines away (~5.6 nm) and simultaneous locking to the corresponding nearest comb line is also achieved in a time ~200 ns. A low residual phase noise of the optical phase-locking system is successfully achieved, as experimentally verified by the value of 80 dBc/Hz at an offset of as low as 200 Hz. Hall, and S. T. Cundiff, " Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis, " Science 288(5466), 635–639 (2000). 2. J. Castillega, D. Livingston, A. Sanders, and D. Shiner, " Precise measurement of the J = 1 to J = 2 fine structure interval in the 2(3)P state of helium, " Phys.

Nanostructured Optoelectronics: Materials and Devices

The use of nanostructure materials for optoelectronic devices, including light-emitting diodes (L... more The use of nanostructure materials for optoelectronic devices, including light-emitting diodes (LEDs), laser diodes, photodetectors, and solar cells, has recently attracted considerable attention due to their unique geometry. Nanostructures in small dimensions can be perfectly integrated into a variety of technological platforms, offering novel physical and chemical properties for the high performance optoelectronic devices. The exploitation of new nanostructures and their optical and electrical properties is necessary for their emerging practical device applications.

Photoreflectance of a 2.3μm GaInAsSb-based VCSEL structure for gas sensing applications

by Jeff Hosea, Shamsul Arafin, and G. Chai

2nd Annual International Conference on Optoelectronics, Photonics & Applied Physics (OPAP 2014), 2014

Temperature-dependent photo-modulated reflectance (PR) spectroscopy has been applied to study a G... more Temperature-dependent photo-modulated reflectance (PR) spectroscopy has been applied to study a GaSb-based vertical-cavity surface-emitting laser (VCSEL) structure designed to operate at 2.3µm. To investigate the wavelength offset between the quantum well (QW) and cavity mode (CM) features, which determine the device's physical properties and temperature performance, the energies of the QW transitions relative to the VCSEL CM energy were tuned by heating from 9K to 300K. We found that this VCSEL structure has a QW-CM offset of 21meV at room temperature; also, the QW ground-state transition only comes into resonance with the CM at 220±2K. These PR results are closely compared with those obtained in a separate study of actual operating devices.

Temperature stable mid-infrared GaInAsSb/GaSb Vertical Cavity Surface Emitting Lasers (VCSELs)

GaInAsSb/GaSb based quantum well vertical cavity surface emitting lasers (VCSELs) operating in mi... more GaInAsSb/GaSb based quantum well vertical cavity surface emitting lasers (VCSELs) operating in mid-infrared spectral range between 2 and 3 micrometres are of great importance for low cost gas monitoring applications. This paper discusses the efficiency and temperature sensitivity of the VCSELs emitting at 2.6 μm and the processes that must be controlled to provide temperature stable operation. We show that non-radiative Auger recombination dominates the threshold current and limits the device performance at room temperature. Critically, we demonstrate that the combined influence of non-radiative recombination and gain peak – cavity mode de-tuning determines the overall temperature sensitivity of the VCSELs. The results show that improved temperature stable operation around room temperature can only be achieved with a larger gain peak – cavity mode de-tuning, offsetting the significant effect of increasing non-radiative recombination with increasing temperature, a physical effect which must be accounted for in mid-infrared VCSEL design.

First Monolithically Integrated Dual-Pumped Phase-Sensitive Amplifier Chip Based on a Saturated Semiconductor Optical Amplifier

Email Print Request Permissions For the first time, a monolithically integrated photonic phase-s... more Email
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For the first time, a monolithically integrated photonic phase-sensitive amplification chip is fabricated and demonstrated based on an InP/InGaAsP platform. Different semiconductor optical amplifiers have been fabricated as well for characterization. On the chip, two tunable laser pumps that are coherently injection-locked, respectively, from two first-order sidebands of an externally modulated tone are generated to enable signal-degenerate dual-pumped phase-sensitive amplification in a saturated semiconductor optical amplifier. Experiments on different chips are conducted to successfully demonstrate phase-sensitive amplification with approximately 6.3 dB and 7.8 dB extinction of phase-sensitive on-chip gain. Theoretical simulations are performed and agree well with experimental results. The additive noise properties of the phase-sensitive amplification chip are also investigated.

a-Ge and a-Si as dielectric mirror materials for long-wavelength optoelectronic devices: a comparative study

Dielectric mirrors are key components in a number of optoelectronic devices, e.g. vertical-cavity... more Dielectric mirrors are key components in a number of optoelectronic devices, e.g. vertical-cavity surface-emitting lasers (VCSELs) 1 , low-threshold edge-emitting lasers 2 , subwavelength ultrabroadband mirrors 3 and modulators 4 which require very high reflectivity (R > 95%) with low optical losses. In fact, this type of mirrors, such as, distributed Bragg reflectors (DBRs) or Bragg mirrors are composed of stacking alternating thin layers of two different dielectric materials with high and low refractive index. The mirror materials must be chosen in a way that the refractive index contrast, Δn of the constituent materials becomes as high as possible and at the same time the absorption loss becomes very low to reach sufficient reflectivity with a minimum number of layers and interfaces.

Wavelength dependence of the performance of GaInAsSb mid-infrared lasers

Low-resistive ohmic contacts to n-InAs0. 91Sb0. 09 for GaSb-based VCSELs in the mid-infrared range

Temperature dependence of 2.3 μm and 2.6 μm GaInAsSb based BTJ VCSELs and edge emitting lasers

There is a growing interest in electrically pumped lasers that emit in the 2-3μm wavelength regio... more There is a growing interest in electrically pumped lasers that emit in the 2-3μm wavelength region for applications such as gas sensing, pollution monitoring and medical diagnosis. GaSb based type-I quantum well edge-emitting lasers (EELs) provide room temperature continuous wave operation but are limited by Auger recombination and inter-valence band absorption. For most applications, Vertical Cavity Surface-Emitting Lasers (VCSELs) are a preferred option because of lower power consumption, cheaper fabrication and improved beam quality. However, self-heating and the presence of fundamental loss processes necessitate careful design to provide gain peak -cavity mode alignment at a particular temperature and wavelength for optimum performance. In this study we have investigated 2.3µm and 2.6µm VCSELs. Edge-emitting lasers with nominally identical active regions were used to look at the effects of non-radiative recombination and to extract information about the gain peak which was then used to analyse the VCSEL behaviour. A combination of high hydrostatic pressure and temperature dependence techniques were used to investigate the wavelength dependence of non-radiative processes and cavity modegain peak detuning. From these measurements we find that 85% (97 %) of the threshold current of 2.3μm (2.6μm) edge-emitting lasers is due to non-radiative recombination. Our results suggest that temperature insensitive VCSEL operation around room temperature could be achieved with a larger gaincavity de-tuning, offsetting the effect of increasing non-radiative recombination with increasing temperature, as shall be discussed in further detail.

Graphene gets GaAs onto Silicon

What’s the trick to growing high-quality GaAs on silicon? It’s inserting a layer of graphene betw... more

Non-destructive Photo-modulated Reflectance Study of GaInAsSb-based VCSEL

by Shamsul Arafin and GRACE CHAI TING

Temperature dependent photoreflectance on 2.3µm GaInAsSb ‐based vertical cavity surface emitting ... more

Indium Phosphide Photonic Integrated Circuit Transmitter with Integrated Linewidth Narrowing for Laser Communications and Sensing

An indium phosphide photonic integrated circuit transmitter with integrated linewidth narrowing c... more An indium phosphide photonic integrated circuit transmitter with integrated linewidth narrowing capability is demonstrated. Frequency discrimination is achieved with an asymmetric Mach-Zehnder interferometer. Introduction: Tunable lasers have enabled significant advancements in communications and sensing applications [1]. Semiconductor diode lasers allow for reduced cost, size, weight, and power making them more widely deployable. Widely tunable semiconductor lasers, however, suffer from larger linewidth compared to short-cavity distributed feedback (DFB) lasers or external cavity lasers, thereby limiting their use in high-performance applications. Also for lidar applications, wide wavelength tuning can be utilized for beamsteering. We present an integrated solution for frequency locking and linewidth reduction of a widely tunable sampled grating distributed Bragg reflector (SGDBR) laser based on an indium phosphide (InP) photonic integrated circuit (PIC) platform that includes active/passive integration and two types of ridge waveguides to enable both low-loss and efficient active devices and sharp-bend-radius passive components. An integrated asymmetric Mach-Zehnder interferometer (AMZI) that taps excess light from the back SGDBR mirror is incorporated for frequency discrimination. The AMZI also includes a phase shifter to apply a frequency chirp. The PIC design and fabrication are discussed, and the components for linewidth narrowing are fully characterized including the laser, the AMZI discriminator, and the chirp phase shifter.

Recent Progress on GaSb-based Photonic Integrated Circuits

Despite significant technological achievements in InP-photonic ICs with sampled-grating distribut... more Despite significant technological achievements in InP-photonic ICs with sampled-grating distributed Bragg reflector (SG-DBR) laser tuning technology near 1.55 µm over the past few decades, such platform in the shortwave infrared (SWIR) or mid-infrared (MIR) regimes has not yet reached its full potential. By employing an InGaAsSb/AlGaAsSb/GaSb gain material and necessary processing steps, we aim to develop photonic integrated circuits (PICs) technology in the GaSb material system. The proposed concept for an agile tunable PIC transmitter is shown in Fig. 1. The SG-DBR lasers are the tunable component and each is limited ~6.5% of the center wavelength in order to obtain a good side-mode suppression ratio using a simple cavity geometry; therefore, multiple SG-DBR lasers will be heterogeneously integrated together to cover the entire tuning range. Tunable light output from the SG-DBR cavity will be amplified in the semiconductor optical amplifier (SOA) to increase power to ~10 mW. As can be seen in Fig. 1, the wavelength range from 2.2-2.8 µm can be covered with only four chips using broad bandwidth of the gain materials. Second, we integrate each chip with the desired phase modulator. Light will then be coupled from the GaSb PICs to the SOI combiner planar lightwave circuit (PLC). We suggest a simple non-dispersive 4 × 1 combiner as illustrated in Fig. 1. This combiner could be accomplished by the indicated " y-branch " structures or by 2 × 1 multi-mode interference (MMI) structures. Alternative to the non-dispersive combiner, a wavelength selective 4 × 1 MMI can also be thought of. For the phase modulators, we propose current injection into the passive waveguide regions. The modulation depth is expected to be approximately π radians of phase modulation for a current input of 5 mA with a typical modulator length ~100 µm. The modulation is almost independent of modulator length for current densities in the 0.2-2 kA/cm 2 range. Higher bandwidths are possible by using reverse biased p-n junctions, also using the same passive regions of the platform. The offset quantum-well (OQW) integration platform is chosen for processing SG-DBR lasers and compatible PICs because it requires a relatively simple process. A schematic cross-section of the layer structure of a GaSb-based offset quantum-well (OQW) integration platform is illustrated in Fig. 2(a). After growing the base structures, passive regions were formed by removing the multiple-QW active region from the base structure prior to the regrowth. Atomic steps were observed after MBE regrowth in both active and passive areas with and without MQWs, respectively. The film exhibits atomically smooth surface morphology with root-mean-square (RMS) roughness value of <0.3 nm, as shown in Fig. 2(b)-(c). The presented concepts and encouraging materials growth results pave the way for the realization of transmitter PICs covering a large SWIR wavelength range using GaSb-technology.

Auger recombination in type I GalnAsSb/GaSb lasers and its variation with wavelength in the 2–3 μm range

Semiconductor lasers operating in the 2-3 μm wavelength range are useful for a variety of applica... more Semiconductor lasers operating in the 2-3 μm wavelength range are useful for a variety of applications including environmental monitoring, non-invasive medical diagnosis and industrial processing [1]. While type-I GalnAsSb/GaSb quantum well (QW) lasers have achieved room temperature operation up to 3.73 μm, they are limited by the effects of non-radiative Auger recombination, inter-valence band absorption and carrier leakage due to inadequate hole confinement, all of which induce sensitivity to temperature [2]. Here we report studies of the non-radiative recombination mechanisms in type-I GalnAsSb based lasers, in order to assist device optimisation [3-5].

Offset Locking of a Fully Integrated Optical Phase-Locked Loop Using On-chip Modulators

We demonstrate an integrated heterodyne optical phase-locked loop for potential RF remoting. Offs... more We demonstrate an integrated heterodyne optical phase-locked loop for potential RF remoting. Offset-locking of the two on-chip lasers is achieved by applying a RF signal to an on-chip optical phase modulator and locking to an optical sideband. Over the years, microwave/millimeter wave photonic link technology, supporting the fiber optic remoting of RF signals based on remote heterodyne detection (RHD) [1], has attracted a great deal of attention for a wide range of applications including delay lines over phased-array antenna feeders and backbone networks for cellular phone systems [2]. Such a fiber-optic link at the transmitter or base station requires two widely-tunable lasers with slightly different wavelengths, the phases of which must be strictly correlated. The strict phase correlation between these two lasers can be achieved by using a heterodyne optical phase-locked loop (OPLL) [3] transmitter configuration. There are two techniques that could be adopted for such heterodyne locking. As a first technique, the RF signal can be applied to an electronic mixer following optical detection in such a coherent photonic receiver and the RF difference frequency used for offset locking [4,5]. Another technique is to apply the RF to an on-chip optical modulator monolithically integrated on the photonic receiver following the tunable laser and to achieve the locking using an optical sideband [6]. Use of higher-order sidebands are also possible enabling higher offset frequencies than available from the RF source or the electronics. In this work, we report the second technique using an InP-based photonic integrated circuit with an on-chip optical phase modulator following the LO laser for applying the offset. Outputs from the LO and signal lasers are combined into a pair of photodetectors that provide inputs to agile and highly-sensitive feedback electronics that control the phase section of the LO for locking. A net loop bandwidth of 500 MHz was obtained, and an offset locking frequency range ~16 GHz is achieved in the system, which can employ up to the third-order-harmonic optical sidebands for locking, yielding a locking range as high as 48 GHz. Figure 1(a) shows a schematic of the coherent optical receiver PIC used for OPLL. It includes two widely-tunable sampled-grating distributed Bragg reflector (SG-DBR) lasers that are to be offset locked, MMI couplers, semiconductor optical amplifiers (SOAs), photodetectors, and several RF-modulators. The chip size is 7 mm × 0.5 mm. As can be seen, light from each laser is first equally divided into two paths using 1 × 2 MMIs. One half from each laser is guided into a 2 × 2 MMI, which serves as a 180 degree hybrid to feed the two photodetectors for the feedback loop. Each input arm of the 2 × 2 MMI contains a phase modulator (M) that can be used for applying RF to generate optical sidebands. After adding the fields from these two lasers in the MMI coupler, light is detected in a pair of photodetectors (D) to provide a differential output. The other half from each laser travels through semiconductor-optical-amplifiers (SOAs) to increase their amplitude and modulators for applying possible information. They are then combined in a 2 × 2 MMI at the right side of the OPLL-PIC. In the current experiment this is used for monitoring of the interference between the two SG-DBR lasers by coupling into an optical fiber. An optical microscope photo of the fully-processed PIC on an InGaAsP/InP material platform is shown in Fig. 1(b). The process used to fabricate the devices is quantum-well intermixing (QWI) that creates self-aligned passive regions by intermixing the quantum-wells with their barriers and surrounding waveguide material by a patterned diffusion of implanted phosphorus ions after a first growth. Details of the processing steps for the well-established QWI-based material structure can be found elsewhere [7]. Two widely tunable on-chip SG-DBR lasers along with all of the other optical components were used to form the heterodyne OPLL. One of the lasers was used as a master (or signal) laser, while the other as a slave (or LO) laser to be offset phase-locked to the former. Prior to combining the outputs of these two lasers using a 2 × 2 optical coupler, the output of slave SG-DBR laser is phase-modulated for offset-locking using an integrated on-chip modulator and envelope detected using a pair of balanced on-chip photodetectors. The current output from the

Optical Frequency Synthesis by Offset-Locking to a Microresonator Comb

by Shamsul Arafin and Arda Simsek

We report on the experimental demonstration of a chip-scale microresonator comb enabled optical f... more We report on the experimental demonstration of a chip-scale microresonator comb enabled optical frequency synthesizer using an agile and highly-integrated heterodyne optical phase-locked loop with InP-based photonic integrated circuit and commercial-off-the-shelf electronic components. OCIS codes: (250.5300) Photonic integrated circuits; (060.5625) Radio frequency photonics; (060.2840) Heterodyne (140.0140) Lasers and laser optics; (140.3600) Lasers, tunable; (140.3945) Microcavities; (230.5750) Resonators In recent years, chip-scale and low-power optical frequency synthesizers (OFSs) based on self-stabilization of full-octave microresonator combs are being increasingly investigated for various ultra-high-precision applications in which micro-Hertz levels of stability are sought [1]. However, for many practical applications, including optical spectroscopy [2], optical communication [3], light detection and ranging (LiDAR) [4], and some types of frequency metrology, stabilities in the few Hertz range would be very attractive. In this work, we report on the experimental demonstration of a continuously-tunable, microresonator-enabled, ultra-compact OFS near 1550 nm achieved by using a heterodyne optical phase-locked loop (OPLL) [5]. Figure 1(a) illustrates the basic concept of a compact and chip-scale OFS. A microresonator-based optical frequency comb (OFC) was used as an ultra-stable and narrow linewidth source, serving as a master oscillator (MO) [6]. The comb lines are then used as the reference for the heterodyne OPLL. A RF frequency from a tunable RF synthesizer is applied to feedback electronic circuits of the OPLL to introduce a frequency offset, defined by the frequency difference between the master laser and the local oscillator (LO) laser. By tuning the phase section current of the LO laser as well as f RF , the LO is phase-locked to the comb lines. In order for an OFS to synthesize any arbitrary frequency between comb lines, the heterodyne OPLL offset frequency range must be at least half of the comb's free spectra range (FSR). Also for such continuous tuning, the FSR of the comb must be less than the slave laser's modehop free tuning range.

Coupled-Cavity Lasers for a Low-Power Integrated Coherent Optical Receiver

Compact, tunable, low-power consumption coupled-cavity lasers are designed and experimentally dem... more

A Chip-Scale Heterodyne Optical Phase-Locked Loop with Low-Power Consumption

by Shamsul Arafin, Arda Simsek, Larry Coldren, and Seong-Kyun Kim

A chip-scale heterodyne optical phase-locked loop, consuming only 1.3 W of electrical power, with... more A chip-scale heterodyne optical phase-locked loop, consuming only 1.3 W of electrical power, with a maximum offset locking frequency of 17.4 GHz is demonstrated. The InP-based photonic integrated receiver circuit consumes only 166 mW. 1. Introduction and Design of the Heterodyne OPLL There has been significant effort for realizing highly-integrated chip-scale optical phase-locked loops (OPLLs) in the last decade along with the development in the photonic integration. Traditional free space optics creates loop delays in the order of tens of nanoseconds, which makes the loop bandwidth small. However, with the improvement in photonic integration, OPLLs can be realized with loop bandwidths in the order of hundreds of MHz [1] or even more than 1 GHz [2]. This makes OPLLs attractive and they can be used in a wide range of applications including coherent receivers, high sensitivity detection, laser linewidth narrowing, millimeter and THz wave generation and optical frequency synthesis [3-5]. In previous works, offset locking ranges up to 25 GHz [6], large loop bandwidth exceeding 1 GHz [2] and residual OPLL phase noise variance as low as 0.03 rad 2 [1] were demonstrated for the chip-scale OPLLs. However, these OPLLs consume almost 3 W of electrical power [2], being unsuitable for the real life applications. In this work, a chip-scale heterodyne OPLL with a total power consumption of 1.3 W is designed and demonstrated utilizing a novel indium phosphide (InP)-based photonic integrated circuit (PIC) and commercial-off-the-shelf (COTS) electronic ICs. The PIC receiver contains a widely-tunable (50 nm) compact Y-branch laser, a 180° hybrid (MMI) and two photodiodes. This is offset locked to narrow-linewidth (100 kHz) external-cavity laser (ECL) up to a range of 17.4 GHz with an RF synthesizer. The low power consumption PIC is integrated with COTS electronic ICs in order to realize the highly-integrated OPLL. An optical microscope image and the schematic of the receiver PIC is shown in Fig. 1(a) and (b), respectively. The PIC incorporates a compact Y-branch laser formed between a high-reflectivity coated back mirror and a pair of Vernier tuned front mirrors. The output from one mirror leads to the coherent receiver used for offset locking, while the other output forms the optical output signal from the backend integrated system. The Y-branch laser has a compact cavity with short gain and mirror sections, requiring low current and therefore low drive power. It is tuned via Vernier effect and has been designed for high efficiency at 30º C ambient. The measured tuning range exceeds 50 nm with >50 dB side-mode suppression ratio. The low power receiver PIC is connected with SiGe-based COTS ICs including a limiting amplifier and digital XOR as a mixer/phase detector. The limiting amplifier has a 3-dB bandwidth of 17 GHz with 30 dB of differential gain. The digital XOR operates up to at least 12.5 GHz input RF frequencies. The limiting amplifier limits the signal coming from photodiode pair to logic levels, which enables the system to be insensitive to any optical intensity fluctuations. A second order dual-path loop filter was used to get high loop bandwidth. This was achieved by employing a fast feedforward path which increases the system frequency acquisition range. Fig. 1(b) and (c) displays the architecture and a microscope image of the whole OPLL system, respectively. The PIC, electronic ICs and the loop filter are all integrated on an aluminum nitride (AlN) carrier, and wire-bonded. The system size is approximately 1.8 cm by 1.6 cm. Total delay is less than 300 ps, and the loop bandwidth is approximately 500 MHz.

Wavelength dependence of efficiency limiting mechanisms in Type I GaInAsSb/GaSb lasers emitting in the mid-infrared

Type-I GaInAsSb lasers, emitting between 2-3 µm are investigated using temperature and high press... more Type-I GaInAsSb lasers, emitting between 2-3 µm are investigated using temperature and high pressure characterization techniques. A model of the Auger processes is used to fit the non-radiative component of the threshold current at room temperature, identifying the dominance of different Auger losses across the wavelength range of operation. 1. INTRODUCTION The pursuit of semiconductor lasers in the mid-infrared, operating at ambient temperature with low temperature sensitivity, is motivated by a variety of applications which include environmental monitoring, non-invasive medical diagnosis and industrial processing [1]. Type-I quantum well (QW) laser designs, based on the GaInAsSb/GaSb material system, have received significant attention for this purpose and have reported continuous wave (CW) and room temperature (RT) operation up to 3.73 µm [2]. However, despite these advances the threshold current and external differential efficiency of these devices remain subject to a high degree of temperature sensitivity, confounding the requirement for stability over the operational temperature range. Performance stability of type I infrared inter-band lasers is fundamentally limited by the effects of non-radiative Auger recombination, inter-valence band absorption (IVBA) and carrier leakage. As the spectral range of type-I QW lasers has expanded, these limitations have become more apparent [3]. In this work we report a systematic study of the loss and non-radiative recombination mechanisms affecting the operating characteristics of type-I GaInAsSb based lasers covering the wide spectral range between 2 and 3 µm as well as the extent to which these influence device performance [4].

Physical Properties of Type I GaInAsSb/GaSb lasers emitting in the Mid-infrared range of 2.3-2.9 µm

The pursuit of semiconductor lasers operating at room temperature in the 2-3 µm region is motivat... more The pursuit of semiconductor lasers operating at room temperature in the 2-3 µm region is motivated by a variety of applications which include environmental monitoring, non-invasive medical diagnosis and industrial processing. 1 Type-I quantum well (QW) laser designs, based on the GaInAsSb/GaSb material system have received significant attention for this purpose. The operational instability observed in type-I infrared inter-band lasers are primarily attributable to the effects of non-radiative Auger recombination, inter-valence band absorption and carrier leakage. 2 As the spectral range of type I QW lasers has expanded, these limitations have become more apparent. 3 In this work using high hydrostatic pressure we study the Auger recombination mechanisms affecting the operating characteristics of type-I GaInAsSb based lasers emitting at 2.3 µm, 2.6 µm and 2.9 µm wavelengths and the extent to which these influence device performance. High hydrostatic pressure reversibly alters the fundamental bandgap of semiconductors providing a useful method to investigate bandgap dependent recombination mechanisms such as the Auger processes. In the 2.3-2.9 µm wavelength range the CHCC process is expected to decrease exponentially with the bandgap increase (increasing pressure) while the CHSH process increases exponentially with increasing bandgap as the bandgap approaches resonance with the spin-orbit splitting energy (Δ SO). If either of these processes is a dominant recombination path then the associated bandgap dependent behaviour should be represented in the threshold current density dependence on pressure. The obtained high pressure results (see the figure on the left) have been supplemented with our previous measurements on GaInAsSb lasers to extend the wavelength range from 2.9µm to 1.8 µm (see the figure on the right). The radiative component is removed from the threshold current density using spontaneous emission measurements at atmospheric pressure and assuming í µí°½ í µí±í µí±í µí± ∝ í µí°¸í µí± 2. To account for the structural variability in the devices the nonradiative component of each device was independently normalised to generate a continuous dependence of the threshold current density against the lasing photon energy. A simple model for the CHCC and CHSH processes was used to fit the high pressure measurements. Two important regimes are evident. The nonradiative current decays approximately exponentially with lasing photon energy, before reaching a minimum around 0.6 eV. The non-radiative current then increases exponentially up to 0.67 eV reaching the region where the bandgap is in resonance with Δ SO. This coupled exponential behaviour is indicative of two Auger processes.

Recombination Processes in Type I GaInAsSb Lasers

Mid-infrared optical devices between 2 and 3 µm are motivated by a diverse array of applications ... more Mid-infrared optical devices between 2 and 3 µm are motivated by a diverse array of applications which include trace gas detection and communications [1]. Type-I quantum well (QW) laser structures, based on the GaInAsSb/GaSb material system are the standard approach for this wavelength range. However, loss processes such as Auger recombination, inter-valence band absorption and carrier leakage all effect the temperature stability of these devices. In this work we study the dominant recombination mechanisms affecting the operating characteristics of type-I GaInAsSb based lasers emitting at 2.3, 2.6 and 2.9 µm [2]. The characteristic temperature (T 0) is a measure of the temperature sensitivity of the threshold current density. The temperature dependence of T 0 for the three wavelength devices is presented in Fig. 1. The same qualitative behaviour is observed in each device with T 0 decreasing rapidly (decreasing stability), approaching, and then exceeding the predicted temperature sensitivity of a device dominated by Auger recombination (T 0 ~ T/3). These processes can be explored in more detail using hydrostatic pressure since the different loss processes have distinctive behaviour as a function of pressure. In a device dominated by the CHCC process the threshold current would be expected to decrease exponentially with increasing pressure (increasing bandgap) while a device dominated by the CHSH process is expected to increase exponentially as the bandgap increases and approaches resonance with the spin-orbit splitting energy (Δ SO). This work can be supplemented with previous high hydrostatic pressure measurements on GaInAsSb lasers, extending the wavelength range to 1.83 μm [3]. To account for structural differences the non-radiative component of the threshold current density in each device was independently normalized, generating a smooth dependence with lasing energy. This is shown Fig. 2. Modelling the experimental data provides clear evidence of the dominance of the CHCC process at longer wavelengths and the importance of the spin orbit split off resonance in enhancing the CHSH process.

Toward Hz-level Optical Frequency Synthesis Across the C-band

By using a stable comb as an input reference to an integrated heterodyne optical-phase-locked-loo... more By using a stable comb as an input reference to an integrated heterodyne optical-phase-locked-loop consisting of a coherent receiver photonic IC with a widely-tunable laser, high-speed feedback electronics, and an RF synthesizer, accurate optical frequencies across multiple comb lines can be generated. Initial results will be presented. Beginning with a single stable optical reference tone, it has been shown that a broad comb of lines with similar stability and linewidth can be generated. This has been done by phase locking one line of a mode-locked InP-based photonic IC laser to such a reference with an integrated high-bandwidth optical phase-locked loop (OPLL) [1]. Variations of the mode-locked laser (MLL) also contained a gain-flattening filter that broadened the optical comb into the multi-terahertz range [2]. This comb source is then used as a reference for a second heterodyne OPLL, which contains a widely-tunable laser that can be tuned across the C-band [3,4]. Tuning between comb lines is accomplished with a tunable RF synthesizer for offset locking. Two techniques of offset locking have been demonstrated: (a) the RF was applied to an optical modulator following the tunable laser and an optical sideband was used for locking [5]; (b) the RF was applied to an electronic mixer following optical detection in the heterodyne receiver and the RF difference frequency used for locking [6]. Figure 1 illustrates this system. In this case the MLL is also actively mode locked with a fixed f RF1 for more stability. The tunable frequency f RF2 is varied from a low value to at least half of the comb line spacing for full wavelength coverage.

Heteroepitaxial Growth of III–V Semiconductors on 2D Materials

Quasi van der Waals epitaxy (QvdWE) of III-V semiconductors on two-dimensional layered material, ... more Quasi van der Waals epitaxy (QvdWE) of III-V semiconductors on two-dimensional layered material, such as graphene, is discussed. Layered materials are used as a lattice mismatch/thermal expansion coefficient mismatch-relieving layer to integrate III-V semiconductors on any arbitrary substrates. In this chapter, the epitaxial growth of both III–V nanowires and thin films on two-dimensional layered materials is presented. Also, the growth challenges of thin film on two-dimensional materials using QvdWE are discussed through density functional theory calculations. Furthermore, optoelectronic devices of III-V semiconductors integrated on two-dimensional layered material based on QvdWE are overviewed to prove the future potential and importance of such type of epitaxy.

Photonic Integration and Packaging PIP IEEE Photonics Society

Papers are solicited on the topic of photonic integration and packaging. Photonic devices include... more Papers are solicited on the topic of photonic integration and packaging. Photonic devices include lasers, detectors, filters, couplers, multiplexers and sensors. Many examples are already complex integrated circuits in their own right, and further integration enables even more powerful function for high speed communication, precision metrology, sensing in increasingly diverse market segments. Advances in the different integration platform technologies, including III-V materials, silicon, silica, germanium, chalcogenide glasses, and others, are targeted. Selective area epitaxy, patterned growth, impurity disordering, wafer bonding, active-passive integration, are all techniques used for the integration of optical and electronic devices. Circuits and devices using photonic crystals and plasmonic waveguiding are also welcome. Packaging techniques are also considered, addressing methods for further systems integration and integration with sensoric devices and micro-electro-mechanical devices. The attachment and connection to fiber and polymer waveguides and waveguide arrays, housings and systems on chip. Innovative bonding technologies, encapsulation, and methods for inserting photonic ICs into optical and electronic circuit boards are also considered.

Applied Optics Feature Announcement on "Near- to mid-IR (1-13 µm) III-V Semiconductor Lasers"

Submissions Open: 1 March 2017 Submission Deadline: 1 April 2017 This special issue focuses on r... more Submissions Open: 1 March 2017
Submission Deadline: 1 April 2017

This special issue focuses on recent advances in the field of III-V semiconductor lasers emitting in the near- to mid-infrared spectral regions, with particular emphasis on devices that emit radiation with wavelengths between 1 and 13 µm.

Despite ongoing development of III-V semiconductor lasers operating the near- to mid-infrared spectral region of 1-13 µm over the last few decades, significant improvement in laser performance is still needed to enable applications in optical communication and sensing, spectroscopy, gas sensing, and imaging. Papers representing recent developments of sophisticated and cutting-edge laser technologies with an emphasis on the near- to mid-infrared side of the electromagnetic spectrum are welcome.

This feature issue will cover all aspects of semiconductor lasers including cavity, active region, new laser materials, wavelength tunability, photonic integration, and dimensionality.

Topics of interest include, but are not limited to:

In-plane edge-emitter, DBR, DFB lasers
Widely tunable and photonic-integrated circuit compatible SG-DBR, Y-branch, coupled-cavity lasers
Quantum cascade lasers
Optically or electrically-pumped VCSELs and VECSELs
Silicon photonics compatible lasers
Novel active region including quantum dashes, dots, type-II band alignment, etc. in semiconductor lasers
Nanoscale lasers based on nanowire, plasmonic, random cavities, etc.
Polariton lasers
Photonic crystal, micro- and nano-cavity-based lasers
Multi-segment and ring lasers
High speed lasers
Mode-locked lasers