We show that Parity-time symmetry in matching electric permittivity to magnetic permeability can ... more We show that Parity-time symmetry in matching electric permittivity to magnetic permeability can be established by considering an effective Parity operator involving both mirror symmetry and coupling between electric and magnetic fields. This approach extends the discussion of Parity-time symmetry to the situation with more than one material potential. We show that the band structure of a one-dimensional photonic crystal with alternating purely dielectric and purely magnetic slabs can undergo a phase transition between propagation modes and evanescent modes when the balanced gain/loss parameter is varied. The cross-matching between different material potentials also allows exceptional points of the constitutive matrix to appear in the long wavelength limit where they can be used to construct ultrathin metamaterials with unidirectional reflection.
Complex optical photon states with entanglement shared among several modes are critical to improv... more Complex optical photon states with entanglement shared among several modes are critical to improving our fundamental understanding of quantum mechanics and have applications for quantum information processing, imaging, and microscopy. We demonstrate that optical integrated Kerr frequency combs can be used to generate several bi- and multiphoton entangled qubits, with direct applications for quantum communication and computation. Our method is compatible with contemporary fiber and quantum memory infrastructures and with chip-scale semiconductor technology, enabling compact, low-cost, and scalable implementations. The exploitation of integrated Kerr frequency combs, with their ability to generate multiple, customizable, and complex quantum states, can provide a scalable, practical, and compact platform for quantum technologies.
Using a novel high-index glass material platform, integrated low-loss waveguides were fabricated ... more Using a novel high-index glass material platform, integrated low-loss waveguides were fabricated and are shown to have excellent nonlinear properties. Through self-phase modulation measurements in a 45 cm long spiral waveguide, the Kerr nonlinearity is determined, and is estimated to be more than 200 times larger than that of single mode fibers. The excellent linear transmission together with absence of multi-photon absorption, for peak intensities up to 25 GW/cm 2 , offers a promising alternative for the fabrication of future nonlinear all-optical devices.
Large scale optical integration is enabled by high index contrast materials and building blocks. ... more Large scale optical integration is enabled by high index contrast materials and building blocks. We highlight recent advances in the miniaturization of optical elements and of dense integration of planar lightwave circuits for telecommunications and RF photonic applications.
The employment of single-mode fiber technology, the potentials of coherent optical communication ... more The employment of single-mode fiber technology, the potentials of coherent optical communication systems, and the novel sensor applications have emphasized the need for integrated optical components, such as couplers, modulators, switches, filters, etc., that are reliable, precise, wavelength selective, and even polarization selective. The design of optimized integrated optical components requires a detailed understanding of the various electromagnetic propagation characteristics of the structures defining the devices. Typical optical structures such as dielectric slab waveguides with junctions, rib waveguides, grating structures, and other dielectric waveguiding geometries could also be made from anisotropic materials, and their properties could be electro-optically altered. In addition to providing optimized design, an accurate method that can simulate the operation of the device allows ways of exploring new concepts. The main objective of this paper is to present the use of these simulation techniques. Three methods for the simulation of the propagation of light through dielectric guiding structures have been considered here. These methods are the finite-difference time-domain (FDTD) method, the coupled-mode theory (CMT) and the beam-propagation method (BPM). The time-explicit FDTD method has been demonstrated to be a very powerful tool in the analysis of arbitrary shaped structures, which may contain abrupt discontinuities in both the propagation and the transverse directions. However, solving an optically long structure by the FDTD method will require a large amount of computer resource. Although the CMT and the BPM are not recommended to analyze a structure with large discontinuities in the propagation direction, they can analyze a long structure very effectively if the transition in the propagation direction is adiabatic. Thus, an optically large (thousands of wavelengths long) structure with bends, junctions, discontinuities, and long guiding structures can be partitioned and solved by a combination of these three techniques. After a review of the various simulation methods for optical circuits, this article focuses on the formulation and the implementation of the FDTD method. Examples are presented on simulations of structures of current practical interest.
The Lorentzian-shape filter response of a microring resonator filter is not suitable to the pract... more The Lorentzian-shape filter response of a microring resonator filter is not suitable to the practical use in WDM systems, because of the lack of pass band flatness, high cross talk, and the large wing in the stop band. Therefore, the tailoring of filter response shape is required to improve the performance. In this paper, the authors designed and demonstrated the box-like filter response of microring resonator filter by using the supermodes of stacked double microring resonators. The thicknesses of microrings and the separation between them were optimally designed to give the maximally flat response. A fine fabrication process was developed to achieve the deep and very smooth side wall. The shape factor, which is defined by the ratio of −1 dB bandwidth to −10 dB bandwidth, was successfully improved by three factors from 0.17 of Lorentzian shape to 0.51. key words: ÓÔØ Ð ¬ÐØ Ö¸ÓÔØ Ð Û Ú Ù ¸Ö Ò Ö ×ÓÒ ØÓÖ¸Ô ×× Ò ØØ Ò Ò ¸×Ø ÓÒ¬ ÙÖ Ø ÓÒ
Cleo Qels 2010 Laser Science to Photonic Applications, May 16, 2010
A supercontinuum spectrum of more than 300nm is obtained at 1550nm and 1290nm using doped-silica ... more A supercontinuum spectrum of more than 300nm is obtained at 1550nm and 1290nm using doped-silica glass, 45cm long, integrated spiral waveguides. Different dynamics near two distinct zero dispersion wavelengths are observed and explained theoretically. (C) 2010 Optical Society of America
Reflections that are due to random surface roughness in periodic structures such as dielectric ri... more Reflections that are due to random surface roughness in periodic structures such as dielectric rings and disks inherently phase match forward- and backward-propagating modes. Small reflections are thus considerably enhanced and may impair the performance of traveling-wave resonators. In addition, such contradirectional coupling leads to a splitting of the resonant peak. These effects are studied analytically.
We demonstrated subpicosecond temporal optical imaging based on four wave mixing temporal to freq... more We demonstrated subpicosecond temporal optical imaging based on four wave mixing temporal to frequency domain conversion in a CMOS compatible, high index glass waveguide.
Full C-band tunable filters for 50 GHz channel spacings based on 5/sup th/ order micro-ring reson... more Full C-band tunable filters for 50 GHz channel spacings based on 5/sup th/ order micro-ring resonator filters are described. These filters are tunable over 40 nm and can accommodate one hundred 50 GHz channels.
Nonlinear optical processes are one of the most important tools in modern optics with a broad spe... more Nonlinear optical processes are one of the most important tools in modern optics with a broad spectrum of applications in, for example, frequency conversion, spectroscopy, signal processing and quantum optics. For practical and ultimately widespread implementation, on-chip devices compatible with electronic integrated circuit technology offer great advantages in terms of low cost, small footprint, high performance and low energy consumption. While many on-chip key components have been realized, to date polarization has not been fully exploited as a degree of freedom for integrated nonlinear devices. In particular, frequency conversion based on orthogonally polarized beams has not yet been demonstrated on chip. Here we show frequency mixing between orthogonal polarization modes in a compact integrated microring resonator and demonstrate a bi-chromatically pumped optical parametric oscillator. Operating the device above and below threshold, we directly generate orthogonally polarized beams, as well as photon pairs, respectively, that can find applications, for example, in optical communication and quantum optics.
We show that Parity-time symmetry in matching electric permittivity to magnetic permeability can ... more We show that Parity-time symmetry in matching electric permittivity to magnetic permeability can be established by considering an effective Parity operator involving both mirror symmetry and coupling between electric and magnetic fields. This approach extends the discussion of Parity-time symmetry to the situation with more than one material potential. We show that the band structure of a one-dimensional photonic crystal with alternating purely dielectric and purely magnetic slabs can undergo a phase transition between propagation modes and evanescent modes when the balanced gain/loss parameter is varied. The cross-matching between different material potentials also allows exceptional points of the constitutive matrix to appear in the long wavelength limit where they can be used to construct ultrathin metamaterials with unidirectional reflection.
Complex optical photon states with entanglement shared among several modes are critical to improv... more Complex optical photon states with entanglement shared among several modes are critical to improving our fundamental understanding of quantum mechanics and have applications for quantum information processing, imaging, and microscopy. We demonstrate that optical integrated Kerr frequency combs can be used to generate several bi- and multiphoton entangled qubits, with direct applications for quantum communication and computation. Our method is compatible with contemporary fiber and quantum memory infrastructures and with chip-scale semiconductor technology, enabling compact, low-cost, and scalable implementations. The exploitation of integrated Kerr frequency combs, with their ability to generate multiple, customizable, and complex quantum states, can provide a scalable, practical, and compact platform for quantum technologies.
Using a novel high-index glass material platform, integrated low-loss waveguides were fabricated ... more Using a novel high-index glass material platform, integrated low-loss waveguides were fabricated and are shown to have excellent nonlinear properties. Through self-phase modulation measurements in a 45 cm long spiral waveguide, the Kerr nonlinearity is determined, and is estimated to be more than 200 times larger than that of single mode fibers. The excellent linear transmission together with absence of multi-photon absorption, for peak intensities up to 25 GW/cm 2 , offers a promising alternative for the fabrication of future nonlinear all-optical devices.
Large scale optical integration is enabled by high index contrast materials and building blocks. ... more Large scale optical integration is enabled by high index contrast materials and building blocks. We highlight recent advances in the miniaturization of optical elements and of dense integration of planar lightwave circuits for telecommunications and RF photonic applications.
The employment of single-mode fiber technology, the potentials of coherent optical communication ... more The employment of single-mode fiber technology, the potentials of coherent optical communication systems, and the novel sensor applications have emphasized the need for integrated optical components, such as couplers, modulators, switches, filters, etc., that are reliable, precise, wavelength selective, and even polarization selective. The design of optimized integrated optical components requires a detailed understanding of the various electromagnetic propagation characteristics of the structures defining the devices. Typical optical structures such as dielectric slab waveguides with junctions, rib waveguides, grating structures, and other dielectric waveguiding geometries could also be made from anisotropic materials, and their properties could be electro-optically altered. In addition to providing optimized design, an accurate method that can simulate the operation of the device allows ways of exploring new concepts. The main objective of this paper is to present the use of these simulation techniques. Three methods for the simulation of the propagation of light through dielectric guiding structures have been considered here. These methods are the finite-difference time-domain (FDTD) method, the coupled-mode theory (CMT) and the beam-propagation method (BPM). The time-explicit FDTD method has been demonstrated to be a very powerful tool in the analysis of arbitrary shaped structures, which may contain abrupt discontinuities in both the propagation and the transverse directions. However, solving an optically long structure by the FDTD method will require a large amount of computer resource. Although the CMT and the BPM are not recommended to analyze a structure with large discontinuities in the propagation direction, they can analyze a long structure very effectively if the transition in the propagation direction is adiabatic. Thus, an optically large (thousands of wavelengths long) structure with bends, junctions, discontinuities, and long guiding structures can be partitioned and solved by a combination of these three techniques. After a review of the various simulation methods for optical circuits, this article focuses on the formulation and the implementation of the FDTD method. Examples are presented on simulations of structures of current practical interest.
The Lorentzian-shape filter response of a microring resonator filter is not suitable to the pract... more The Lorentzian-shape filter response of a microring resonator filter is not suitable to the practical use in WDM systems, because of the lack of pass band flatness, high cross talk, and the large wing in the stop band. Therefore, the tailoring of filter response shape is required to improve the performance. In this paper, the authors designed and demonstrated the box-like filter response of microring resonator filter by using the supermodes of stacked double microring resonators. The thicknesses of microrings and the separation between them were optimally designed to give the maximally flat response. A fine fabrication process was developed to achieve the deep and very smooth side wall. The shape factor, which is defined by the ratio of −1 dB bandwidth to −10 dB bandwidth, was successfully improved by three factors from 0.17 of Lorentzian shape to 0.51. key words: ÓÔØ Ð ¬ÐØ Ö¸ÓÔØ Ð Û Ú Ù ¸Ö Ò Ö ×ÓÒ ØÓÖ¸Ô ×× Ò ØØ Ò Ò ¸×Ø ÓÒ¬ ÙÖ Ø ÓÒ
Cleo Qels 2010 Laser Science to Photonic Applications, May 16, 2010
A supercontinuum spectrum of more than 300nm is obtained at 1550nm and 1290nm using doped-silica ... more A supercontinuum spectrum of more than 300nm is obtained at 1550nm and 1290nm using doped-silica glass, 45cm long, integrated spiral waveguides. Different dynamics near two distinct zero dispersion wavelengths are observed and explained theoretically. (C) 2010 Optical Society of America
Reflections that are due to random surface roughness in periodic structures such as dielectric ri... more Reflections that are due to random surface roughness in periodic structures such as dielectric rings and disks inherently phase match forward- and backward-propagating modes. Small reflections are thus considerably enhanced and may impair the performance of traveling-wave resonators. In addition, such contradirectional coupling leads to a splitting of the resonant peak. These effects are studied analytically.
We demonstrated subpicosecond temporal optical imaging based on four wave mixing temporal to freq... more We demonstrated subpicosecond temporal optical imaging based on four wave mixing temporal to frequency domain conversion in a CMOS compatible, high index glass waveguide.
Full C-band tunable filters for 50 GHz channel spacings based on 5/sup th/ order micro-ring reson... more Full C-band tunable filters for 50 GHz channel spacings based on 5/sup th/ order micro-ring resonator filters are described. These filters are tunable over 40 nm and can accommodate one hundred 50 GHz channels.
Nonlinear optical processes are one of the most important tools in modern optics with a broad spe... more Nonlinear optical processes are one of the most important tools in modern optics with a broad spectrum of applications in, for example, frequency conversion, spectroscopy, signal processing and quantum optics. For practical and ultimately widespread implementation, on-chip devices compatible with electronic integrated circuit technology offer great advantages in terms of low cost, small footprint, high performance and low energy consumption. While many on-chip key components have been realized, to date polarization has not been fully exploited as a degree of freedom for integrated nonlinear devices. In particular, frequency conversion based on orthogonally polarized beams has not yet been demonstrated on chip. Here we show frequency mixing between orthogonal polarization modes in a compact integrated microring resonator and demonstrate a bi-chromatically pumped optical parametric oscillator. Operating the device above and below threshold, we directly generate orthogonally polarized beams, as well as photon pairs, respectively, that can find applications, for example, in optical communication and quantum optics.
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Papers by Sai Chu