Papers by Nebojša Stojanović
Optical Fiber Communication Conference, 2018
A 56-Gb/s NRZ direct detection system is demonstrated with record 15.5-dB (16.2-dB) OSNR sensitiv... more A 56-Gb/s NRZ direct detection system is demonstrated with record 15.5-dB (16.2-dB) OSNR sensitivity over 320-km (640-km) SMF. Furthermore, the challenges and recent advances of direct detection systems for DCIs and metro networks are reviewed.
Asia Communications and Photonics Conference 2016, 2016
We experimentally demonstrate the generation and transmission of 56 Gb/s DSB and SSB PAM4 using a... more We experimentally demonstrate the generation and transmission of 56 Gb/s DSB and SSB PAM4 using a DDMZM. DSB outperforms SSB by 6 dB in B2B scenario as well as after 40 km when dispersion pre-compensation is employed in the latter case.
2016 24th Telecommunications Forum (TELFOR), 2016
We propose a novel phase detector (PD) suitable for clock extraction in ultra-fast four-level pul... more We propose a novel phase detector (PD) suitable for clock extraction in ultra-fast four-level pulse amplitude modulation (PAM-4) optical systems that do not utilize digital signal processing (DSP) for clock and data recovery (CDR). The new PD operates with a single sample per symbol and uses simple logical circuits for clock extraction. Excellent performance and low complexity promote the proposed PD and its modifications for the use in future 56 GBaud and beyond PAM-4 systems for data centers' inter/intra connections and short-reach applications like metro networks.
2017 IEEE Photonics Society Summer Topical Meeting Series (SUM), 2017
We discuss the transmission over short-reach networks employing VCSELs for rack-to-rack optical i... more We discuss the transmission over short-reach networks employing VCSELs for rack-to-rack optical interconnects in datacenters. The penalties imposed are compensated by DSP at the receiver. We analyze the DSP complexity and we infer on its impact on the BER performance of the system.
2018 IEEE Optical Interconnects Conference (OI), 2018
We propose a novel clock and data recovery method for high baud rate four-level pulse amplitude m... more We propose a novel clock and data recovery method for high baud rate four-level pulse amplitude modulation format receivers without any digital signal processing. The new phase detector operates with a single sample per symbol and uses only high-speed logical circuits.
2016 21st OptoElectronics and Communications Conference (OECC) held jointly with 2016 International Conference on Photonics in Switching (PS), 2016
We experimentally investigate the impact of different transmitter's pre-distortion techniques... more We experimentally investigate the impact of different transmitter's pre-distortion techniques for 28 Gb/s/λ IM/DD transmissions over 80 km in DCF-free band-limited systems. OSNR requirements of the proposed scheme are presented as well.
Optics Express, 2018
We investigate partial response signaling (PRS) as a way of increasing the transmission length ac... more We investigate partial response signaling (PRS) as a way of increasing the transmission length achievable by direct detection optical systems. The performance of the duobinary and PRS modulations is evaluated against that of conventional on-off-keying (OOK). We prove by simulation and experimentally that duobinary increases the link distance by up to 1.5 times and PRS by up to 3 times, when no signal processing is employed. The gain is preserved even when equalization is used. PRS is employed also with 4-level pulseamplitude modulation (PAM-4) and is shown to improve the transmission distance by almost 3 times.
Photonics, 2017
We experimentally investigate the transmission performance of 56 Gb/s four-level pulse amplitude ... more We experimentally investigate the transmission performance of 56 Gb/s four-level pulse amplitude modulation (PAM-4) over 30-km standard single mode fiber (SMF) using a C-band EML for low-cost metro and short-reach wavelength division multiplexing (WDM) applications. Bit error rate (BER) performance below the HD-FEC threshold is achieved for up to 30-km maximum reported distance without employing dispersion compensation fiber (DCF) in the link.
Journal of Lightwave Technology, 2017
Unlike ultralong coherent optical systems that seriously suffer from fiber nonlinearities, short-... more Unlike ultralong coherent optical systems that seriously suffer from fiber nonlinearities, short-reach noncoherent systems such as data center interconnections, which utilize small, cheap, and low-bandwidth components, are sensitive to nonlinearities that are mainly produced by devices responsible for electrical signal amplification, modulation, and demodulation. One of the most promising schemes for these applications is the four-level pulse amplitude modulation format combined with intensity modulation and direct detection; however, it can be significantly degraded by linear and nonlinear intersymbol interference. Linear and nonlinear signal degradation can efficiently be handled by different types of equalizers. In many cases, the straightforward linear equalizer cannot lower the error rate at the acceptable level. Therefore, much stronger equalizers based on nonlinear models such as the Volterra series are proposed. Volterra filter that can also be orthogonalized by the Wiener model is well described in the existing literature, and, in this paper, we investigate the most critical points related to high-speed Volterra filter design and implementation. Several experiments are carried out in order to indicate filter requirements/complexity, acquisition, and stability. We also provide a simple guidance for filter complexity reduction and useful hints for channel acquisition.
Journal of Lightwave Technology, 2017
In this article, we experimentally demonstrate the transmission of 112 Gb/s four-level pulse ampl... more In this article, we experimentally demonstrate the transmission of 112 Gb/s four-level pulse amplitude modulation (PAM-4) over 100-m OM4 multi-mode fiber (MMF) employing a multi-mode 850-nm vertical-cavity surface-emitting laser (VCSEL) at the transmitter side and equalization techniques at the receiver's digital signal processing (DSP). The penalties imposed by the strong bandwidth limitations due to the optical components as well as the low modal bandwidth of the fiber are compensated by three variant DSP schemes at the receiver i.e., i) a finite-impulse response (FIR) filter, ii) a maximum likelihood sequence estimation equalizer (MLSE), and ii) an FIR filter followed by an MLSE equalizer (FIR/MLSE) in cascaded form. We evaluate all three aforementioned equalization schemes under two different transmitter implementations, i.e., employing a 30-GHz arbitrary waveform generator (AWG) and a lower bandwidth 15-GHz commercially available DAC and we infer about the applicability of each DSP scheme under these implementations. We show that the hybrid implementation of an FIR followed by a 16-state MLSE can enable the 100-m transmission below the 7% hard-decision (HD) forward error correction (FEC) threshold limit and outperforms its other two counterparts for the back-to-back case as well as after 100-m transmission for the high bandwidth transmitter implementation. On the other hand, lower bandwidth DAC implementations i.e., 15 GHz, require an increased states MLSE without the need for a preceding FIR filter to bring the BER below the HD-FEC limit after 100-m OM4 fiber transmission. DSP complexity vs. BER performance is assessed for all aforementioned scenarios evaluating the impact of the transmitter's bandwidth on the overall system's performance. Our proposed solutions show that 112 Gb/s 100-m OM4 multi-mode links based on VCSELs and standard OM4 fiber can enable next generation 100 Gb/s and 400 Gb/s wavelength division multiplexed (WDM) optical interconnects.
Optical Fiber Communication Conference, 2017
A 90 GBaud single sideband duobinary PAM-4 signal is generated using bandwidth pre-compensation a... more A 90 GBaud single sideband duobinary PAM-4 signal is generated using bandwidth pre-compensation and duo-binary pulse shaping employing a 92 GSa/s DAC. Transmission over 13 km of SSMF is achieved in 50 GHz channel enabled by dispersion pre-compensation at the transmitter.
Optics letters, Jan 15, 2016
We experimentally demonstrate the possibility of transmitting 112 Gb/s PAM-4 signals over 30-km ... more We experimentally demonstrate the possibility of transmitting 112 Gb/s PAM-4 signals over 30-km standard single-mode fibers with commercial 20-GHz components. The impact on system performance of three different equalization schemes-feed-forward equalizer (FFE), Volterra filter (VF), and maximum likelihood sequence estimator (MLSE)-is investigated and compared. We prove that the |x| and x|x| components of the VF can efficiently reduce the chirp-induced signal skew distortion, and that an MLSE with only four states can be used to remove the error floor. In contrast, the performance of FFE is worse than that of VF with a 4-state MLSE, even when a 64-state MLSE is used.
Journal of Lightwave Technology, 2016
We investigate two trellis coded modulation (TCM) schemes for use in next generation low-cost 400... more We investigate two trellis coded modulation (TCM) schemes for use in next generation low-cost 400G optical networks. Their performance is evaluated against that of 4-level pulse amplitude modulation (PAM-4). We experimentally demonstrate that TCM outperforms PAM-4 at bit rates between 56 and 80 Gbps and thus is a valid candidate for 8λx50G implementations of future 400G wave division multiplexing (WDM) networks. Due to the severe bandwidth limitations of the experimental setup the feed-forward equalizer (FFE) and the maximum likelihood sequence estimation (MLSE) equalizer are employed in order to achieve bit-error rates (BER) below the KP4 threshold of 3x10-4. We also show that, at 56 Gbps and 1300 nm wavelength, TCM enables optical links of up to 40 km, whereas PAM-4 can only provide transmissions of up to 30 km. We observe that TCM performance degrades faster than that of PAM-4 when we increase the bit rate. For rates higher than 80 Gbps, TCM is not able to improve upon PAM-4 anymore. Thus only PAM-4 is fit for 4λx100G WDM networks, unless higher bandwidth components are used.
2016 IEEE 6th International Conference on Photonics (ICP), 2016
We experimentally demonstrate 56-Gbps optical interconnection over 1 km SSMF by using 10G 1550nm ... more We experimentally demonstrate 56-Gbps optical interconnection over 1 km SSMF by using 10G 1550nm VCSEL. PAM4 and Poly-PAM4 MLSE algorithms are developed to optimize the system performance and overcome the chirp-chromatic-dispersion induced power degradation after 1 km fiber transmission.
Optical Fiber Communication Conference, 2016
We investigate timing recovery schemes for 28 Gb/s NRZ-OOK systems employing inexpensive 1550 nm ... more We investigate timing recovery schemes for 28 Gb/s NRZ-OOK systems employing inexpensive 1550 nm 7-GHz TOSA and ROSA devices in DCF-free links up to 100 km and propose a low-complexity algorithm enabling reliable clock extraction.
Optical Fiber Communication Conference, 2016
4D-PAM-5 trellis coded modulation is experimentally demonstrated and compared with PAM-4 for use ... more 4D-PAM-5 trellis coded modulation is experimentally demonstrated and compared with PAM-4 for use in 8λ×50 Gb/s metro-access optical networks. Power sensitivity gains of up to 2 dB are shown at bit rates of 56 Gb/s.
2015 European Conference on Optical Communication (ECOC), 2015
We experimentally demonstrate Tx DSP-free 112-Gbit/s PAM-4 transmission over 20 km SMF using comm... more We experimentally demonstrate Tx DSP-free 112-Gbit/s PAM-4 transmission over 20 km SMF using commercially available 1298 nm 25-GHz TOSA and ROSA devices. Superior performance is achieved by using timing recovery supported DSP at the receiver.
2015 European Conference on Optical Communication (ECOC), 2015
The performance of two equalization techniques is experimentally compared using a 1530-nm VCSEL, ... more The performance of two equalization techniques is experimentally compared using a 1530-nm VCSEL, 56Gb/s/A PAM-4, and direct detection over 2 km links for datacenter interconnect applications. Results on the performance evaluation in terms of DSP implementation and complexity are presented.
Journal of Lightwave Technology, 2015
We demonstrate the generation and transmission of 28-Gb/s data employing inexpensive, off-the-she... more We demonstrate the generation and transmission of 28-Gb/s data employing inexpensive, off-the-shelf, 10-GHz 3-dB bandwidth optical components, intensity modulation (IM), direct detection (DD), and a digital signal processing-based receiver over uncompensated fiber links. We prove that the proposed technology is an enabler for next-generation 100-G cost-efficient point-to-point dispersion compensation fiber (DCF)-free metro networks up to 80 km, as well as for multispan metro-ring networks up to 400 km, consisting of cascaded erbium-doped fiber amplifiers and DCFs as in real-field implementations. Key techniques to enable transmission are the employment of signal predistortion in the transmitter to compensate for the components' limited bandwidth, a maximum likelihood sequence estimator (MLSE)-based receiver, and a high-performance sampling phase adjustment algorithm. Furthermore, we show that performance can be optimized, while at the same time the complexity of the electronic dispersion compensation part is significantly reduced by exploiting a simplified variant of MLSE that makes use of a reduced number of states. Results in this paper reveal the potentiality of our proposed scheme for a low-cost transition to 100 Gb/s (4 × 28 Gb/s) wavelength division multiplexed, point-to-point, metro-core, and multispan metro-ring networks, employing inexpensive optical components and the traditional cost-efficient IM/DD scheme.
IEEE Photonics Technology Letters, 2015
We demonstrate a 56 Gb/s four-level pulse-amplitude modulation (PAM-4) transmission using direct ... more We demonstrate a 56 Gb/s four-level pulse-amplitude modulation (PAM-4) transmission using direct detection and a long-wavelength 18-GHz bandwidth vertical-cavity surface-emitting laser as directly modulated light source for short-reach inter-and intra-connects in datacenters and short-reach networks. Error-free transmission over 2 km at 7% hard-decision forward-error correction threshold is achieved by applying powerful equalization schemes at the receiver side. Three equalization schemes, i.e., a maximum likelihood estimation (MLSE), a feed-forward equalizer (FFE), and a combination of the FFE and the MLSE are thoroughly investigated, and the performance comparison between them is carried out.
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Papers by Nebojša Stojanović