| 1. |
- Dely, H., et al.
(author)
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High bitrate data transmission in the 8-14 µm atmospheric window using an external Stark-effect modulator with digital equalization
- 2023
-
In: Optics Express. - : Optica Publishing Group (formerly OSA). - 1094-4087. ; 31:5, s. 7259-7264
-
Journal article (peer-reviewed)abstract
- High bitrate mid-infrared links using simple (NRZ) and multi-level (PAM-4) data coding schemes have been realized in the 8 µm to 14 µm atmospheric transparency window. The free space optics system is composed of unipolar quantum optoelectronic devices, namely a continuous wave quantum cascade laser, an external Stark-effect modulator and a quantum cascade detector, all operating at room-temperature. Pre- and post-processing are implemented to get enhanced bitrates, especially for PAM-4 where inter-symbol interference and noise are particularly detrimental to symbol demodulation. By exploiting these equalization procedures, our system, with a full frequency cutoff of 2 GHz, has reached transmission bitrates of 12 Gbit/s NRZ and 11 Gbit/s PAM-4 fulfilling the 6.25 % overhead hard-decision forward error correction threshold, limited only by the low signal-to-noise ratio of our detector.
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| 2. |
- Deng, Qiuzhuo, et al.
(author)
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Quantum Noise Secured Terahertz Communications
- 2023
-
In: 2023 OPTICAL FIBER COMMUNICATIONS CONFERENCE AND EXHIBITION, OFC. - : Optica Publishing Group.
-
Conference paper (peer-reviewed)abstract
- The quantum noise based terahertz signal encryption scheme is proposed, a 16 Gbits(-1) secure terahertz communication system at 300 GHz with the optical communication realms is demonstrated, taking a significant step toward high-security wireless communications.
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| 3. |
- Fan, Yuchuan, et al.
(author)
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A Comparison of Linear Regression and Deep Learning Model for EVM Estimation in Coherent Optical Systems
- 2022
-
In: 2022 Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2022 - Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- We experimentally investigate EVM estimation approaches based on linear regression and deep learning for 28 Gbaud coherent optical systems. We show that the estimation performances are comparable when the modulation format is known.
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| 4. |
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| 5. |
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| 6. |
- Fan, Yuchuan, et al.
(author)
-
Linear Regression vs. Deep Learning for Signal Quality Monitoring in Coherent Optical Systems
- 2022
-
In: IEEE Photonics Journal. - : Institute of Electrical and Electronics Engineers Inc.. - 1943-0655. ; 14:4
-
Journal article (peer-reviewed)abstract
- Error vector magnitude (EVM) is a metric for assessing the quality of m-ary quadrature amplitude modulation (mQAM) signals. Recently proposed deep learning techniques, e.g., feedforward neural networks (FFNNs) -based EVM estimation scheme leverage fast signal quality monitoring in coherent optical communication systems. Such a scheme estimates EVM from amplitude histograms (AHs) of short signal sequences captured before carrier phase recovery (CPR). In this work, we explore further complexity reduction by proposing a simple linear regression (LR) -based EVM monitoring method. We systematically compare the performance of the proposed method with the FFNN-based scheme and demonstrate its capability to infer EVM from an AH when the modulation format information is known in advance. We perform both simulation and experiment to show that the LR-based EVM estimation method achieves a comparable accuracy as the FFNN-based scheme. The technique can be embedded with modulation format identification modules to provide comprehensive signal information. Therefore, this work paves the way to design a fast-learning scheme with parsimony as a future intelligent OPM enabler.
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| 7. |
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| 8. |
- Han, Mengyao, et al.
(author)
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Deep Reservoir Computing for 100 Gbaud PAM6 IM/DD Transmission Impairment Mitigation
- 2023
-
In: 2023 OPTICAL FIBER COMMUNICATIONS CONFERENCE AND EXHIBITION, OFC. - : Optica Publishing Group.
-
Conference paper (peer-reviewed)abstract
- We experimentally evaluate a deep Reservoir Computing (RC)-based post-equalization for 100 Gbaud PAM6 IM/DD transmissions. It achieves similar to 1 dB higher sensitivity than DFE, and similar to 50% implementation complexity reduction compared with the conventional RC configuration.
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| 9. |
- Han, Mengyao, et al.
(author)
-
High Spectral Efficiency Long-wave Infrared Free-Space Optical Transmission with Multilevel Signals
- 2023
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 41:20, s. 6514-
-
Journal article (peer-reviewed)abstract
- This study explores the potential of long-wave infrared free-space optical (FSO) transmission that leverages multilevel signals to attain high spectral efficiency. The FSO transmission system consists of a directly modulated-quantum cascade laser (DM-QCL) operating at 9.15 μm and a mercury cadmium telluride (MCT) detector. To fully understand the system, we conduct measurements on the DM-QCL chip and MCT detector and assess the overall amplitude response of the DM-QCL, MCT detector, and all electrical components. We apply various signals, including on-off keying (OOK), 4-level pulse amplitude modulation (PAM4), 6-level PAM (PAM6), and 8-level PAM (PAM8) to maximize the bit rate and spectral efficiency of the FSO transmission. Through a two-dimensional sweeping of the laser bias current and MCT detector photovoltage, we optimize the transmission performance. At the optimal operation point, the FSO system achieved impressive results which are up to 6 Gbaud OOK, 3.5 Gbaud PAM4, 3 Gbaud PAM6, and 2.7 Gbaud PAM8 signal transmissions, with a bit error rate performance below 6.25% overhead hard decision-forward error correction limit when the DM-QCL operates at 10 °C. We also evaluate the eye diagrams and stability of the system to showcase its remarkable transmission performance. Our findings suggest that the DMQCL and MCT detector-based FSO transceivers offer a highly competitive solution for the next generation of optical wireless communication systems
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| 10. |
- Han, Mengyao, et al.
(author)
-
High Spectral Efficiency Long-Wave Infrared Free-Space Optical Transmission With Multilevel Signals
- 2023
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 41:20, s. 6514-6520
-
Journal article (peer-reviewed)abstract
- This study explores the potential of long-wave infrared free-space optical (FSO) transmission that leverages multilevel signals to attain high spectral efficiency. The FSO transmission system consists of a directly modulated-quantum cascade laser (DM-QCL) operating at 9.15 mu m and a mercury cadmium telluride (MCT) detector. To fully understand the system, we conduct measurements on the DM-QCL chip and MCT detector and assess the overall amplitude response of the DM-QCL, MCT detector, and all electrical components. We apply various signals, including on-off keying (OOK), 4-level pulse amplitude modulation (PAM4), 6-level PAM (PAM6), and 8-level PAM (PAM8) to maximize the bit rate and spectral efficiency of the FSO transmission. Through a two-dimensional sweeping of the laser bias current and MCT detector photovoltage, we optimize the transmission performance. At the optimal operation point, the FSO system achieved impressive results which are up to 6 Gbaud OOK, 3.5 Gbaud PAM4, 3 Gbaud PAM6, and 2.7 Gbaud PAM8 signal transmissions, with a bit error rate performance below 6.25% overhead hard decision-forward error correction limit when the DM-QCL operates at 10 degrees C. We also evaluate the eye diagrams and stability of the system to showcase its remarkable transmission performance. Our findings suggest that the DM-QCL and MCT detector-based FSO transceivers offer a highly competitive solution for the next generation of optical wireless communication systems.
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| 11. |
- Han, Mengyao, et al.
(author)
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Long-Wave Infrared Discrete Multitone Free-Space Transmission Using a 9.15-μm Quantum Cascade Laser
- 2023
-
In: IEEE Photonics Technology Letters. - : Institute of Electrical and Electronics Engineers Inc.. - 1041-1135 .- 1941-0174. ; 35:9, s. 489-492
-
Journal article (peer-reviewed)abstract
- A free-space optical (FSO) transmission system is experimentally demonstrated in the long-wave infrared (LWIR, 9.15μ m ) using a directly modulated quantum cascade laser (DM-QCL) and a commercial mercury-cadmium-telluride infrared photovoltaic detector. At room temperature, the DM-QCL is current-modulated by discrete multitone signals pre-processed with bit-/power-loading. Up to 5.1 Gbit/s data rate is achieved with bit error rate performance below the 6.25% overhead hard-decision forward error correction limit of 4.5× 10-3 , enabled by a frequency domain equalizer. The stability study of the FSO system is also performed at multiple temperature values. This study can provide a valuable reference for future terrestrial and space communications.
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| 12. |
- Joharifar, Mahdieh, et al.
(author)
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16.9 Gb/s Single-Channel LWIR FSO Data Transmission with Directly Modulated QCL and MCT Detector
- 2024
-
In: 2024 Optical Fiber Communications Conference and Exhibition, OFC 2024 - Proceedings. - : Institute of Electrical and Electronics Engineers Inc..
-
Conference paper (peer-reviewed)abstract
- We experimentally demonstrate a room-temperature LWIR FSO link with a 9.1-μm directly modulated QCL and an MCT detector. Net bitrate of up to 16.9 Gb/s is achieved at both 15°C and 20°C over a 1-meter distance.
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| 13. |
- Joharifar, Mahdieh, et al.
(author)
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16.9 Gb/s Single-Channel LWIR FSO Data Transmission with Directly Modulated QCL and MCT Detector
- 2024
-
In: <em>2024 Optical Fiber Communications Conference and Exhibition, OFC 2024 - Proceedings</em>. - : Institute of Electrical and Electronics Engineers Inc.. - 9781957171326
-
Conference paper (peer-reviewed)abstract
- We experimentally demonstrate a room-temperature LWIR FSO link with a 9.1-μm directly modulated QCL and an MCT detector. Net bitrate of up to 16.9 Gb/s is achieved at both 15°C and 20°C over a 1-meter distance.
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| 14. |
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| 15. |
- Joharifar, Mahdieh, et al.
(author)
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High-Speed 9.6-μm Long-Wave Infrared Free- Space Transmission with a Directly-Modulated QCL and a Fully-Passive QCD
- 2023
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 0733-8724 .- 1558-2213. ; 41:4, s. 1087-
-
Journal article (peer-reviewed)abstract
- Free-space optics (FSO) in the mid-infrared (mid- IR) contains rich spectral resources for future ultrahigh-speed wireless communications yet is currently under-exploited. Two atmospheric transmission windows at the mid-IR, namely, the mid-wave IR (MWIR, 3-5 µm) and the long-wave IR (LWIR, 8-12 µm), show great potential in supporting free-space communications for both terrestrial and space application scenarios. Particularly, the LWIR signal with a longer wavelength has high intrinsic robustness against aerosols' scattering and turbulence-induced scintillation and beam broadening effects, which are the main concerns hindering the wide deployment of practical FSO systems. In this context, high-bandwidth semiconductor-based mid-IR FSO transceivers will be desirable to meet the requirements of low energy consumption and small footprints for large-volume development and deployment. Quantum cascade devices, including quantum cascade lasers (QCLs) and quantum cascade detectors (QCDs), appear promising candidates to fulfill this role. In this work, we report a high-speed LWIR FSO transmission demonstration with a 9.6-µm directly-modulated (DM)-QCL and a fully passive QCD without any active cooling or bias voltage. Up to 8 Gb/s, 10 Gb/s, and 11 Gb/s signal transmissions are achieved when operating the DM- QCL at 10°C, 5°C, and 0°C, respectively. These results indicate a significant step towards an envisioned fully-connected mid-IR FSO solution empowered by the quantum cascade semiconductor devices.
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| 16. |
- Li, Lianyi, et al.
(author)
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THz-Over-Fiber System With Orthogonal Chirp Division Multiplexing for Integrated Sensing and Communication
- 2024
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 42:1, s. 176-183
-
Journal article (peer-reviewed)abstract
- To achieve integrated sensing and communication (ISAC) applications with high data rates and high resolution, the terahertz-over-fiber (ToF) system has been recognized as a promising solution. However, the frequency-selective fading would deteriorate the performance of the ToF-based ISAC systems. In this work, we propose the orthogonal chirp division multiplexing (OCDM) waveform-based ToF system for high-performance ISAC applications. The system encodes data with the phase of the sub-chirps and obtains radar images by processing echoes with the zero-padded matched filtering algorithm. We experimentally demonstrate a proof-of-concept OCDM-ToF system, which simultaneously achieves a 32 Gbit/s data rate and 1.875 cm range resolution after transmission over a 10 km optical fiber and a 3.14 m wireless link at the THz band, for the first time. The experimental results indicate that the OCDM-ToF system can enhance robustness against the frequency-selective fading issue, as a benefit improving communication performance with high data rates while preserving the high sensing resolution of OFDM in the THz ISAC applications.
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| 17. |
- Lyu, Zhidong, et al.
(author)
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A Beam-Scannable Photonic THz-ISAC System Based on Risley Prisms
- 2023
-
In: 2023 Asia Communications and Photonics Conference/2023 International Photonics and Optoelectronics Meetings, ACP/POEM 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- We demonstrate a beam-scannable photonic terahertz-integrated sensing and communication (THz-ISAC) system using Risley prisms. 20 Gbps data rate and 1.5 cm resolution are simultaneously achieved at 300 GHz with 40 deg field of view (FoV).
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| 18. |
- Lyu, Zhidong, et al.
(author)
-
Multi-Channel Photonic THz-ISAC System Based on Integrated LFM-QAM Waveform
- 2024
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 0733-8724 .- 1558-2213. ; 42:11, s. 3981-3988
-
Journal article (peer-reviewed)abstract
- The integrated sensing and communication (ISAC) has been envisioned as a promising technology to simultaneously perform high-capacity communication and high-accuracy sensing with efficient resource utilization. Nevertheless, due to the severe mutual constraints between communication and sensing functions, the performance of previously reported ISAC demonstrations notably trails that of individual communication or sensing systems. In this work, an integrated LFM-QAM waveform is proposed and theoretically analyzed by combining linear frequency modulation (LFM) and quadrature amplitude modulation (QAM) formats. Employing the proposed waveform and optical wavelength division multiplexing (WDM) technique, we experimentally implement a multi-channel photonic terahertz (THz)-ISAC wireless system operating at 275 GHz band, simultaneously achieving a communication data rate up to 120 Gbps and a range resolution as high as 2.5 mm. To the best of our knowledge, this is the first time to demonstrate beyond 100 Gbps wireless data rate and mm-scale resolution based on an integrated waveform in the THz region, revealing the potential of THz-ISAC performance.
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| 19. |
- Lyu, Zhidong, et al.
(author)
-
Multi-Channel Photonic THz-ISAC System Based on Integrated LFM-QAM Waveform
- 2024
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 42:11, s. 3981-3988
-
Journal article (peer-reviewed)abstract
- The integrated sensing and communication (ISAC) has been envisioned as a promising technology to simultaneously perform high-capacity communication and high-accuracy sensing with efficient resource utilization. Nevertheless, due to the severe mutual constraints between communication and sensing functions, the performance of previously reported ISAC demonstrations notably trails that of individual communication or sensing systems. In this work, an integrated LFM-QAM waveform is proposed and theoretically analyzed by combining linear frequency modulation (LFM) and quadrature amplitude modulation (QAM) formats. Employing the proposed waveform and optical wavelength division multiplexing (WDM) technique, we experimentally implement a multi-channel photonic terahertz (THz)-ISAC wireless system operating at 275 GHz band, simultaneously achieving a communication data rate up to 120 Gbps and a range resolution as high as 2.5 mm. To the best of our knowledge, this is the first time to demonstrate beyond 100 Gbps wireless data rate and mm-scale resolution based on an integrated waveform in the THz region, revealing the potential of THz-ISAC performance.
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| 20. |
- Lyu, Zhidong, et al.
(author)
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Preamble-Free Synchronization Based on Dual-chirp Waveforms for Photonic THz-ISAC
- 2024
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 42:8, s. 2657-2665
-
Journal article (peer-reviewed)abstract
- The integrated sensing and communication (ISAC) systems based on the linear frequency modulation (LFM) waveforms have attracted substantial attention. However, existing routines suffer from additional synchronization preamble overhead, which limits both communication and sensing performance. This work, using the dual-chirp with opposite slopes, exploits a preamble-free synchronization scheme for the LFM-based ISAC. We first theoretically analyze the quasi-orthogonal property of the proposed dual-chirp LFM waveform and derive its achievable communication rate and range ambiguity function. A photonics-assisted proof-of-concept ISAC experiment is conducted in the 300 GHz frequency band, achieving a 20 Gbps data rate with a distinguished peak sidelobe ratio (PSLR) of up to 29.2 dB and 1.5 cm range resolution. More importantly, less than 0.5% synchronous power overhead is needed in our scheme. In addition, the performance trade-off induced by the data rate and amplitude ratio is validated in the experiment, which is in line with our theoretical analysis. Therefore, the proposed scheme provides a promising solution for synchronizing LFM-based future ISAC systems.
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| 21. |
- Lyu, Zhidong, et al.
(author)
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Radar-Centric Photonic Terahertz Integrated Sensing and Communication System Based on LFM-PSK Waveform
- 2023
-
In: IEEE transactions on microwave theory and techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 71:11, s. 5019-5027
-
Journal article (peer-reviewed)abstract
- The radar-centric terahertz integrated sensing and communication (THz-ISAC) is identified as a significant application in future wireless access networks. Up to date, previously reported demonstrations regarding radar sensing performance lack sufficient support in a complex environment with a strong target masking effect. This work tacks this problem by proposing a radar-centric waveform combining linear frequency modulation (LFM) waveform and phase shift keying (PSK). We first derive sensing metrics of the LFM-PSK waveform through theoretical analysis, including range resolution, peak sidelobe ratio (PSLR), and Cramér-Rao lower bound (CRLB). Then a proof-of-concept experiment on a photonics-assisted integrated sensing and communication (ISAC) system operating at 330 with 18 GHz bandwidth is conducted to verify the performance of the proposed LFM-PSK waveform. In the experiment, the proposed waveform can reach a PSLR of up to 20.9 dB and a range resolution of 1.3 cm, simultaneously accommodating a data transmission of 6 Gbit/s. In addition, the effect of embedding symbols on sensing metrics is also discussed, and by comparing the range solution and PSLR with various data rates, around ∼ 6 dB gain in the PSLR without any deterioration of range resolution is observed.
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| 22. |
- Matsenko, Svitlana, et al.
(author)
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FPGA-Implemented Fractal Decoder with Forward Error Correction in Short-Reach Optical Interconnects
- 2022
-
In: Entropy. - : MDPI AG. - 1099-4300. ; 24:1
-
Journal article (peer-reviewed)abstract
- Forward error correction (FEC) codes combined with high-order modulator formats, i.e., coded modulation (CM), are essential in optical communication networks to achieve highly efficient and reliable communication. The task of providing additional error control in the design of CM systems with high-performance requirements remains urgent. As an additional control of CM systems, we propose to use indivisible error detection codes based on a positional number system. In this work, we evaluated the indivisible code using the average probability method (APM) for the binary symmetric channel (BSC), which has the simplicity, versatility and reliability of the estimate, which is close to reality. The APM allows for evaluation and compares indivisible codes according to parameters of correct transmission, and detectable and undetectable errors. Indivisible codes allow for the end-to-end (E2E) control of the transmission and processing of information in digital systems and design devices with a regular structure and high speed. This study researched a fractal decoder device for additional error control, implemented in field-programmable gate array (FPGA) software with FEC for short-reach optical interconnects with multilevel pulse amplitude (PAM-M) modulated with Gray code mapping. Indivisible codes with natural redundancy require far fewer hardware costs to develop and implement encoding and decoding devices with a sufficiently high error detection efficiency. We achieved a reduction in hardware costs for a fractal decoder by using the fractal property of the indivisible code from 10% to 30% for different n while receiving the reciprocal of the golden ratio.
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| 23. |
- Murnieks, Rihards, et al.
(author)
-
Silica micro-rod resonator-based Kerr frequency comb for high-speed short-reach optical interconnects
- 2023
-
In: Optics Express. - : Optica Publishing Group. - 1094-4087. ; 31:12, s. 20306-20320
-
Journal article (peer-reviewed)abstract
- Conventional data center interconnects rely on power-hungry arrays of discrete wavelength laser sources. However, growing bandwidth demand severely challenges ensuring the power and spectral efficiency toward which data center interconnects tend to strive. Kerr frequency combs based on silica microresonators can replace multiple laser arrays, easing the pressure on data center interconnect infrastructure. Therefore, we experimentally demonstrate a bit rate of up to 100 Gbps/& lambda; employing 4-level pulse amplitude modulated signal transmission over a 2 km long short-reach optical interconnect that can be considered a record using any Kerr frequency comb light source, specifically based on a silica micro-rod. In addition, data transmission using the non-return to zero on-off keying modulation format is demonstrated to achieve 60 Gbps/& lambda;. The silica micro-rod resonator-based Kerr frequency comb light source generates an optical frequency comb in the optical C-band with 90 GHz spacing between optical carriers. Data transmission is supported by frequency domain pre-equalization techniques to compensate amplitude-frequency distortions and limited bandwidths of electrical system components. Additionally, achievable results are enhanced with offline digital signal processing, implementing post-equalization using feed-forward and feedback taps.
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| 24. |
- Murnieks, Rihards, et al.
(author)
-
Silica micro-rod resonator-based Kerr frequency comb for high-speed short-reach optical interconnects.
- 2023
-
In: Optics Express. - : Optical Society of America. - 1094-4087. ; 31:12, s. 20306-20320
-
Journal article (peer-reviewed)abstract
- Conventional data center interconnects rely on power-hungry arrays of discrete wavelength laser sources. However, growing bandwidth demand severely challenges ensuring the power and spectral efficiency toward which data center interconnects tend to strive. Kerr frequency combs based on silica microresonators can replace multiple laser arrays, easing the pressure on data center interconnect infrastructure. Therefore, we experimentally demonstrate a bit rate of up to 100 Gbps/λ employing 4-level pulse amplitude modulated signal transmission over a 2 km long short-reach optical interconnect that can be considered a record using any Kerr frequency comb light source, specifically based on a silica micro-rod. In addition, data transmission using the non-return to zero on-off keying modulation format is demonstrated to achieve 60 Gbps/λ. The silica micro-rod resonator-based Kerr frequency comb light source generates an optical frequency comb in the optical C-band with 90 GHz spacing between optical carriers. Data transmission is supported by frequency domain pre-equalization techniques to compensate amplitude–frequency distortions and limited bandwidths of electrical system components. Additionally, achievable results are enhanced with offline digital signal processing, implementing post-equalization using feed-forward and feedback taps.
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| 25. |
- Ostrovskis, Armands, et al.
(author)
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170 Gbaud On-Off-Keying SiP Ring Resonator Modulator-based Link for Short-Reach Applications
- 2024
-
In: 2024 IEEE Silicon Photonics Conference, SiPhotonics 2024 - Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- We demonstrate a record 170 Gbaud on-off keying C-band silicon photonics ring resonator modulator-based transmitter with performance below the 6.7% overhead HD-FEC threshold after optical back-to-back and transmission over 100 meters of single mode fiber.
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| 26. |
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| 27. |
- Ozolins, Oskars, et al.
(author)
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100 Gbaud On-Off Keying/Pulse Amplitude Modulation Links in C-Band for Short-Reach Optical Interconnects
- 2021
-
In: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:9
-
Journal article (peer-reviewed)abstract
- We experimentally evaluate the high-speed on-off keying (OOK) and four-level pulse amplitude modulation (PAM4) transmitter's performance in C-band for short-reach optical interconnects. We demonstrate up to 100 Gbaud OOK and PAM4 transmission over a 400 m standard single-mode fiber with a monolithically integrated externally modulated laser (EML) having 100 GHz 3 dB bandwidth with 2 dB ripple. We evaluate its capabilities to enable 800 GbE client-side links based on eight, and even four, optical lanes for optical interconnect applications. We study the equalizer's complexity when increasing the baud rate of PAM4 signals. Furthermore, we extend our work with numerical simulations showing the required received optical power (ROP) for a certain bit error rate (BER) for the different combinations of the effective number of bits (ENOB) and extinction ratio (ER) at the transmitter. We also show a possibility to achieve around 1 km dispersion uncompensated transmission with a simple decision feedback equalizer (DFE) for a 100 Gbaud OOK, PAM4, and eight-level PAM (PAM8) link having the received power penalty of around 1 dB.
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| 28. |
- Ozolins, Oskars, et al.
(author)
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106.25 Gbaud 4-Level Pulse Amplitude Modulation Links Supporting (2x)100Gigabit Ethernet on Single Lambda
- 2023
-
In: 2023 OPTICAL FIBER COMMUNICATIONS CONFERENCE AND EXHIBITION, OFC. - : Institute of Electrical and Electronics Engineers Inc..
-
Conference paper (peer-reviewed)abstract
- We experimentally demonstrate and compare EML- and DML-based optical interconnects with 106.25 Gbaud NRZ-OOK and PAM4 for computing applications. The results show that both transmitters can be used to enable optical -amplification-free transmissions with low-complexity DSP.
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| 29. |
- Ozolins, Oskars, et al.
(author)
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High Baudrate Short-Reach Communication
- 2022
-
In: Proceedings OECC/PSC 2022 - 27th OptoElectronics and Communications Conference/International Conference on Photonics in Switching and Computing 2022. - : Institute of Electrical and Electronics Engineers (IEEE). - 9784885523366
-
Conference paper (peer-reviewed)abstract
- We demonstrate a 200 Gbps IM/DD link without any optical amplification using C-band externally modulated laser with 3.3 dBm of modulated output power and O-band directly modulated laser with 7.3 dBm of modulated output power.
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| 30. |
- Ozolins, Oskars, et al.
(author)
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High-Baudrate Silicon Photonics Ring Resonator and Mach-Zehnder Modulators for Short-Reach Applications
- 2023
-
In: 2023 23rd International Conference on Transparent Optical Networks, ICTON 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- Silicon photonics (SiP) is a key enabling technology for high-baudrate communication. It is a key technology for future 800 Gbps and 1.6 Tbps solutions to meet the ever-increasing demands. The 800G pluggable multi-source agreement (MSA) suggests that intensity-modulated direct-detection (IM/DD) is the most sustainable way forward [1]. The high operational bandwidth of each transceiver component is essential. An ultra-compact SiP slow light modulator with record-high bandwidth of 110 GHz shows the potential [2]. Therefore, both multilevel pulse amplitude modulation (PAM) and on-off keying (OOK) should be considered. SiP offers excellent production yield and has a substantial role in optical interconnects. SiP ring resonator modulators (RRM) have unique advantages like a small footprint, simple driver configuration, low power consumption, and suitability for multichannel applications. On the other hand, the SiP Mach-Zehnder modulator (MZM) offers differential drive benefits.
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| 31. |
- Ozolins, Oskars, et al.
(author)
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High-Baudrate Silicon Photonics Ring Resonator Modulators for Short-Reach Applications
- 2023
-
In: 2023 Asia Communications and Photonics Conference/2023 International Photonics and Optoelectronics Meetings, ACP/POEM 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- We demonstrate up to 160 Gbaud on-off keying with first ring resonator modulator and up to 128 Gbaud on-off keying with second ring resonator modulator. Both modulators achieve performance below 6.25% OH HD-FEC threshold.
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| 32. |
- Ozolins, Oskars, et al.
(author)
-
High-Baudrate SiP and InP Modulators for Data Center Interconnects
- 2023
-
In: 2023 31st International Conference on Software, Telecommunications and Computer Networks, SoftCOM 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- The booming internet traffic sets highly challenging requirements for high-speed computing where low latency is required. This leads to a choice of intensity modulation and direct detection system with the highest baudrate possible. Furthermore, record baudrate supporting modulators will be the key technology for future optical interconnect applications. Therefore, we demonstrated silicon photonics and indium phosphide modulators at highest possible sysmbolrate.
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| 33. |
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| 34. |
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| 35. |
- Ozolins, Oskars, et al.
(author)
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Optical Amplification-Free High Baudrate Links for Intra-Data Center Communications
- 2023
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 0733-8724 .- 1558-2213.
-
Journal article (peer-reviewed)abstract
- The enormous traffic growth sets a stringent requirement to upgrade short-reach optical links to 1.6 TbE capacity in an economically viable way. The power consumption and latency in these links should be as low as possible, especially for high-speed computing. This is possible to achieve using high baudrate on-off keying links thanks to a better noise tolerance and a relaxed requirement on linearity for electronics and photonics. In this regard, we demonstrate a 200 Gbaud on-off keying link without any optical amplification using an externally modulated laser with 3.3 dBm of modulated output power operating at 1541.25 nm wavelength. We achieve transmission over 200 meters of single-mode fiber with performance below 6.25% overhead hard-decision forward error correction threshold for each baudrate and all selection of modulation formats. We also show 108 Gbaud on-off keying link with superior performance without decision feedback equalizer up to 400 meters of single-mode fiber. In addition, we benchmark the short-reach optical link with 112 Gbaud four-level pulse amplitude modulation and 100 Gbaud six-level pulse amplitude modulation. For 108 Gbaud on-off keying and 112 Gbaud four-level pulse amplitude modulation, we can achieve an even lower bit error rate.
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| 36. |
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| 37. |
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| 38. |
- Pang, Xiaodan, Dr., et al.
(author)
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200 Gb/s Optical-Amplifier-Free IM/DD Transmissions using a Directly Modulated O-band DFB+R Laser targeting LR Applications
- 2023
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 0733-8724 .- 1558-2213. ; 41:11, s. 3635-
-
Journal article (peer-reviewed)abstract
- We experimentally demonstrate an O-band single-lane 200 Gb/s intensity modulation direct detection (IM/DD) transmission system using a low-chirp, broadband, and high-power directly modulated laser (DML). The employed laser is an isolator-free packaged module with over 65-GHz modulation bandwidth enabled by a distributed feedback plus passive waveguide reflection (DFB+R) design. We transmit high baud rate signals over 20-km standard single-mode fiber (SSMF) without using any optical amplifiers and demodulate them with reasonably low-complexity digital equalizers. We generate and detect up to 170 Gbaud non-return-to-zero on-off-keying (NRZ-OOK), 112 Gbaud 4-level pulse amplitude modulation (PAM4), and 100 Gbaud PAM6 in the optical back-to-back configuration. After transmission over the 20-km optical-amplifier-free SSMF link, up to 150 Gbaud NRZ-OOK, 106 Gbaud PAM4, and 80 Gbaud PAM6 signals are successfully received and demodulated, achieving bit error rate (BER) performance below the 6.25%-overhead hard-decision (HD) forward-error-correction code (FEC) limit. The demonstrated results show the possibility of meeting the strict requirements towards the development of 200Gb/s/lane IM/DD technologies, targeting 800Gb/s and 1.6Tb/s LR applications.
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| 39. |
- Pang, Xiaodan, Dr., et al.
(author)
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Bridging the Terahertz Gap : Photonics-assisted Free-Space Communications from the Submillimeter-Wave to the Mid-Infrared
- 2022
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 0733-8724 .- 1558-2213. ; 40:10, s. 3149-3162
-
Journal article (peer-reviewed)abstract
- Since about one and half centuries ago, at the dawn of modern communications, the radio and the optics have been two separate electromagnetic spectrum regions to carry data. Differentiated by their generation/detection methods and propagation properties, the two paths have evolved almost independently until today. The optical technologies dominate the long-distance and high-speed terrestrial wireline communications through fiber-optic telecom systems, whereas the radio technologies have mainly dominated the short- to medium-range wireless scenarios. Now, these two separate counterparts are both facing a sign of saturation in their respective roadmap horizons, particularly in the segment of free-space communications. The optical technologies are extending into the mid-wave and long-wave infrared (MWIR and LWIR) regimes to achieve better propagation performance through the dynamic atmospheric channels. Radio technologies strive for higher frequencies like the millimeter-wave (MMW) and sub-terahertz (sub-THz) to gain broader bandwidth. The boundary between the two is becoming blurred and intercrossed. During the past few years, we witnessed technological breakthroughs in free-space transmission supporting very high data rates, many achieved with the assistance of photonics. This paper focuses on such photonics-assisted free-space communication technologies in both the lower and upper sides of the THz gap and provides a detailed review of recent research and development activities on some of the key enabling technologies. Our recent experimental demonstrations of high-speed free-space transmissions in both frequency regions are also presented as examples to show the system requirements for device characteristics and digital signal processing (DSP) performance.
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| 40. |
- Pang, Xiaodan, Dr., et al.
(author)
-
Bridging the Terahertz Gap: Photonics-assisted Free-Space Communications from the Submillimeter-Wave to the Mid-Infrared
- 2022
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; , s. 1-1
-
Journal article (peer-reviewed)abstract
- Since about one and half centuries ago, at the dawn of modern communications, the radio and the optics have been two separate electromagnetic spectrum regions to carry data. Differentiated by their generation/detection methods and propagation properties, the two paths have evolved almost independently until today. The optical technologies dominate the long-distance and high-speed terrestrial wireline communications through fiber-optic telecom systems, whereas the radio technologies have mainly dominated the short- to medium-range wireless scenarios. Now, these two separate counterparts are both facing a sign of saturation in their respective roadmap horizons, particularly in the segment of free-space communications. The optical technologies are extending into the mid-wave and long-wave infrared (MWIR and LWIR) regimes to achieve better propagation performance through the dynamic atmospheric channels. Radio technologies strive for higher frequencies like the millimeter-wave (MMW) and sub-terahertz (sub-THz) to gain broader bandwidth. The boundary between the two is becoming blurred and intercrossed. During the past few years, we witnessed technological breakthroughs in free-space transmission supporting very high data rates, many achieved with the assistance of photonics. This paper focuses on such photonics-assisted free-space communication technologies in both the lower and upper sides of the THz gap and provides a detailed review of recent research and development activities on some of the key enabling technologies. Our recent experimental demonstrations of high-speed free-space transmissions in both frequency regions are also presented as examples to show the system requirements for device characteristics and digital signal processing (DSP) performance.
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| 41. |
- Pang, Xiaodan, Dr., et al.
(author)
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Direct Modulation and Free-Space Transmissions of up to 6 Gbps Multilevel Signals With a 4.65-μQuantum Cascade Laser at Room Temperature
- 2022
-
In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 0733-8724 .- 1558-2213. ; 40:8, s. 2370-2377
-
Journal article (peer-reviewed)abstract
- A roadmap for future wireless communications is expected to exploit all transmission-suitable spectrum bands, from the microwave to the optical frequencies, to support orders of magnitude faster data transfer with much lower latency than the deployed solutions nowadays. The currently under-exploited mid-infrared (mid-IR) spectrum is an essential building block for such an envisioned all-spectra wireless communication paradigm. Free-space optical (FSO) communications in the mid-IR region have recently attracted great interest due to their intrinsic merits of low propagation loss and high tolerance of atmospheric perturbations. Future development of viable mid-IR FSO transceivers requires a semiconductor source to fulfill the high bandwidth, low energy consumption, and small footprint requirements. In this context, quantum cascade laser (QCL) appears as a promisingtechnological choice. In this work, we present an experimental demonstration of a mid-IR FSO link enabled by a 4.65-μm directly modulated (DM) QCL operating at room temperature. We achieve a transmission data rate of up to 6 Gbps over a 0.5-m link distance. This achievement is enabled by system-level characterization and optimization of transmitter and receiver power level and frequency response and assisted with advanced modulation and digital signal processing (DSP) techniques. This work pushes the QCL-based FSO technology one step closer to practical terrestrial applications, such as the fixed wireless access and the wireless mobile backhaul. Such a QCL-based solution offers a promising way towards the futuristic all-spectra wireless communication paradigm by potentially supporting the whole spectrum from the MIR to the terahertz (THz).
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| 42. |
- Pang, Xiaodan, Dr., et al.
(author)
-
Free Space Communication Enabled by Directly Modulated Quantum Cascade Laser
- 2024
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In: 2024 Optical Fiber Communications Conference and Exhibition, OFC 2024 - Proceedings. - : Institute of Electrical and Electronics Engineers Inc..
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Conference paper (peer-reviewed)abstract
- We summarize our recent experimental studies of free-space communications enabled by directly modulated quantum cascade lasers at both MWIR and LWIR regions. Different detector types with different characteristics are compared.
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| 43. |
- Pang, Xiaodan, Dr., et al.
(author)
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Short Reach Communication Technologies for Client-side Optics beyond 400 Gbps
- 2021
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In: IEEE Photonics Technology Letters. - : Institute of Electrical and Electronics Engineers Inc.. - 1041-1135 .- 1941-0174. ; 33:18, s. 1046-1049
-
Journal article (peer-reviewed)abstract
- Short reach optical communication technologies are increasingly demanded in several fast-evolving application scenarios in both telecom and datacom. Low-cost and low-complexity intensity modulation and direct detection (IM/DD) technologies are challenged to scale up the link rate beyond 400 Gbps by increasing the single-lane rate towards 200 Gbps, to maintain a low lane count in client-side optics. Limited by the bandwidth of both electronics and optoelectronics, and the more pronounced chromatic dispersion in the fiber, such high baud rate systems require the use of digital signal processing techniques with forward error correction (FEC) coding. Therefore, in this work, we first summarize a few potential alternative technologies to the IM/DD for future development and then focus on extending the IM/DD systems towards 200 Gbps lane rate. We study both their capability and their performance limits using numerical simulations and transmission experiments. CCBY
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| 44. |
- Pang, Xiaodan, Dr., et al.
(author)
-
Up to 6 Gbps Mid-Infrared Free-Space Transmission with a Directly Modulated Quantum Cascade Laser
- 2021
-
In: 2021 European Conference on Optical Communication (ECOC). - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- We report on an experimental demonstration of a mid-infrared free-space communication link enabled by a directly modulated quantum cascade laser operating at room temperature. A record high transmission rate up to 6 Gbps over 50-cm link distance is demonstrated at 4.65 µm wavelength.
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| 45. |
- Puerta, Rafael, et al.
(author)
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Coherent Joint Transmission with 1024-QAM for 6G Distributed-MIMO Networks with Analog Radio-over-LWIR FSO Fronthaul Links
- 2023
-
In: 2023 Asia Communications and Photonics Conference/2023 International Photonics and Optoelectronics Meetings, ACP/POEM 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- Distributed-MIMO (D-MIMO) is a prospective solution for next-generation mobile networks to increase capacity and coverage. We experimentally validate 1024-QAM coherent joint transmissions in a two transmitter D-MIMO network including radio-over-LWIR FSO fronthaul links facilitating deployment and achieving diversity and power gains close to theoretical values.
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| 46. |
- Puerta, Rafael, et al.
(author)
-
Experimental Validation of Coherent Joint Transmission in a Distributed-MIMO System with Analog Fronthaul for 6G
- 2023
-
In: 2023 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 585-590
-
Conference paper (peer-reviewed)abstract
- The sixth-generation (6G) mobile networks must increase coverage and improve spectral efficiency, especially for cell-edge users. Distributed multiple-input multiple-output (D-MIMO) networks can fulfill these requirements provided that transmission/reception points (TRxPs) of the network can be synchronized with sub-nanosecond precision, however, synchronization with current backhaul and fronthaul digital interfaces is challenging. For 6G new services and scenarios, analog radio-over-fiber (ARoF) is a prospective alternative for future mobile fronthaul where current solutions fall short to fulfill future demands on bandwidth, synchronization, and/or power consumption. This paper presents an experimental validation of coherent joint transmissions (CJTs) in a two TRxPs D-MIMO network where ARoF fronthaul links allow to meet the required level of synchronization. Results show that by means of CJT a combined diversity and power gain of +5 dB is realized in comparison with a single TRxP transmission.
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| 47. |
- Puerta, Rafael, et al.
(author)
-
Experimental Validation of Coherent Joint Transmission in a Distributed-MIMO System with Analog Fronthaul for 6G
- 2023
-
In: 2023 Joint European Conference on Networks and Communications & 6G Summit (EuCNC/6G Summit). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 585-590
-
Conference paper (peer-reviewed)abstract
- The sixth-generation (6G) mobile networks must increase coverage and improve spectral efficiency, especially for cell-edge users. Distributed multiple-input multiple-output (D-MIMO) networks can fulfill these requirements provided that transmission/reception points (TRxPs) of the network can be synchronized with sub-nanosecond precision, however, synchronization with current backhaul and fronthaul digital interfaces is challenging. For 6G new services and scenarios, analog radio-over-fiber (ARoF) is a prospective alternative for future mobile fronthaul where current solutions fall short to fulfill future demands on bandwidth, synchronization, and/or power consumption. This paper presents an experimental validation of coherent joint transmissions (CJTs) in a two TRxPs D-MIMO network where ARoF fronthaul links allow to meet the required level of synchronization. Results show that by means of CJT a combined diversity and power gain of +5 dB is realized in comparison with a single TRxP transmission.
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| 48. |
- Salgals, Toms, et al.
(author)
-
Silica Microsphere WGMR-Based Kerr-OFC Light Source and Its Application for High-Speed IM/DD Short-Reach Optical Interconnects
- 2022
-
In: Applied Sciences. - : MDPI AG. - 2076-3417. ; 12:9, s. 4722-
-
Journal article (peer-reviewed)abstract
- Kerr optical frequency combs (OFCs) based on silica microsphere whispering gallery mode resonator (WGMR) have various applications where they are used as a light source. For telecommunication purposes, WGMR-based Kerr-OFC comb generators can be physically realized using silica microsphere resonators and can be used to replace multiple laser arrays. In such a realization, these novel light sources have the potential to demonstrate an attractive solution for intra-datacenter interconnects (DCI). In this paper, we show an experimental demonstration of a silica microsphere WGMR-based Kerr OFC light source where newly generated 400 GHz spaced carriers together with powerful linear equalization techniques, such as a linear symbol-spaced adaptive decision-feedback equalizer (DFE) with feed-forward (FF) and feedback (FB) taps, provide an alternative to individual lasers ensuring low-cost and low-complexity IM/DD scheme for the transmission of NRZ-OOK modulated signals at data rates up to 50 Gbps/lambda over 2 km SMF link. Finally, we demonstrate a record 50 Gbps per lambda transmission of NRZ-OOK modulated signals with a novel silica microsphere WGMR-based Kerr-OFC as a light source operating in the optical C-band, surpassing the previously demonstrated data rate record by five times.
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| 49. |
- Supe, Andis, et al.
(author)
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Cladding-Pumped Erbium/Ytterbium Co-Doped Fiber Amplifier for C-Band Operation in Optical Networks
- 2021
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In: applied sicences. - : MDPI AG. - 2076-3417. ; 11:4
-
Journal article (peer-reviewed)abstract
- Space-division multiplexing (SDM) attracts attention to cladding-pumped optical amplifiers, but they suffer from a low pump power conversion efficiency. To address this issue, ytterbium (Yb3+) and erbium (Er3+) co-doping is considered as an effective approach. However, it changes the gain profile of Er3+-doped fiber amplifiers and induces the gain difference between optical wavelengths in the C-band, significantly limiting the effective band of the dense wavelength-division multiplexed (DWDM) system. This paper is devoted to a detailed study of a cladding-pumped Er3+/Yb3+ co-doped fiber amplifier (EYDFA) through numerical simulations aiming to identify a configuration, before assembling a similar EYDFA in our laboratory premises that ensures the desired performance. The simulation model is based on a commercial double cladding EYDF whose parameters are experimentally extracted and fed to the EYDFA setup for the system-level studies. We investigate the wavelength dependence of the amplifier’s characteristics (absolute gain, gain uniformity, noise figure) and bit error rate (BER) performance for several DWDM channels and their optical power. The obtained results show that a 7 m long EYDF and co-propagating pump direction is preferable for the EYDFA with a 3 W pump source at 975 nm and with the given gain medium characteristics for WDM applications. For instance, it ensures a gain of 19.7–28.3 dB and a noise figure of 3.7–4.2 dB when amplifying 40 DWDM channels with the input power of −20 dBm per channel. Besides, we study EYDFA gain bandwidth and the maximum output power when operating close to the saturation regime and perform a sensitivity analysis showing how the doped fiber’s absorption and emission cross-sections impact the amplification process through energy transfer from Yb3+ to Er3+. Finally, we quantify the power penalty introduced by the EYDFA; the results show that it is not higher than 0.1 dB when amplifying 40 × 10 Gbps non-return-to-zero on-off keying signals from −20 dBm/channel.
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| 50. |
- Udalcovs, Aleksejs, et al.
(author)
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Optical power budget of 25+ Gbps IM/DD PON with digital signal post-equalization
- 2020
-
In: Applied Sciences. - : MDPI AG. - 2076-3417. ; 10:17
-
Journal article (peer-reviewed)abstract
- While infrastructure providers are expanding their portfolio to offer sustainable solutions for beyond 10 Gbps in the access segment of optical networks, we experimentally compare several modulation format alternatives for future passive optical networks (PONs) aiming to deliver 25+ Gbps net-rates. As promising candidates, we consider the intensity modulation direct detection (IM/DD) schemes such as electrical duobinary (EDB) and 4-level and 8-level pulse amplitude modulations (PAM-4/8). They are more spectrally efficient than the conventional non-return-to-zero on-off-keying (NRZ-OOK) used in current 10G PONs. As we move to higher rates, digital equalization enhances the performance by smoothening the systems imperfection. However, the impact that such equalization has on the optical power budget remains unclear. Therefore, in this article, we fairly compare the optical power budget values of a time division multiplexed PON (TDM-PON) exploiting a linear digital signal equalization at the receiver side. We consider the conventional PON configuration (20 km of single-mode fiber (SMF), 1:N optical power splitting) with IM/DD and net-rates above 25 Gbps. Furthermore, we focus on a downstream transmission imposing the bandwidth limitations of 10G components using a digital filter before the detection. The obtained results show that the use of a digital post-equalization with 43 feed-forward (FF) and 21 feedback (FB) taps can significantly improve the signal quality enabling new alternatives and enhancing the optical power budget. © 2020 by the authors.
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