| 1. |
- 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
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In: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 0733-8724 .- 1558-2213. ; 40:10, s. 3149-3162
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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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| 2. |
- Fan, Yuchuan, et al.
(author)
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Feedforward Neural Network-Based EVM Estimation : Impairment Tolerance in Coherent Optical Systems
- 2022
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In: IEEE Journal of Selected Topics in Quantum Electronics. - : Institute of Electrical and Electronics Engineers Inc.. - 1077-260X .- 1558-4542. ; 28:4
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Journal article (peer-reviewed)abstract
- Error vector magnitude (EVM) is commonly used for evaluating the quality of m-ary quadrature amplitude modulation (mQAM) signals. Recently proposed deep learning techniques for EVM estimation extend the functionality of conventional optical performance monitoring (OPM). In this article, we evaluate the tolerance of our developed EVM estimation scheme against various impairments in coherent optical systems. In particular, we analyze the signal quality monitoring capabilities in the presence of residual in-phase/quadrature (IQ) imbalance, fiber nonlinearity, and laser phase noise. We use feedforward neural networks (FFNNs) to extract the EVM information from amplitude histograms of 100 symbols per IQ cluster signal sequence captured before carrier phase recovery. We perform simulations of the considered impairments, along with an experimental investigation of the impact of laser phase noise. To investigate the tolerance of the EVM estimation scheme to each impairment type, we compare the accuracy for three training methods: 1) training without impairment, 2) training one model for all impairments, and 3) training an independent model for each impairment. Results indicate a good generalization of the proposed EVM estimation scheme, thus providing a valuable reference for developing next-generation intelligent OPM systems.
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| 3. |
- Fan, Yuchuan, et al.
(author)
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EVM Estimation for Performance Monitoring in Coherent Optical Systems : An Approach of Linear Regression
- 2022
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In: Optics InfoBase Conference Papers. - : Optica Publishing Group (formerly OSA). - 9781557528209
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Conference paper (peer-reviewed)abstract
- We experimentally demonstrate the effectiveness of a simple linear regression scheme for optical performance monitoring when applied after modulation format identification. It outperforms the FFNN-based benchmark scheme providing 0.2% mean absolute error for EVM estimation., © 2022 The Author(s)
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| 4. |
- Jia, S., et al.
(author)
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Integrated Dual-DFB Laser for 408 GHz Carrier Generation Enabling 131 Gbit/s Wireless Transmission over 10.7 Meters
- 2019
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In: 2019 Optical Fiber Communications Conference and Exhibition, OFC 2019 - Proceedings. - Washington, D.C. : Institute of Electrical and Electronics Engineers Inc.. - 9781943580538
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Conference paper (peer-reviewed)abstract
- A monolithically integrated dual-DFB laser generates a 408 GHz carrier used for demonstrating a record-high single-channel bit rate of 131 Gbit/s transmitted over 10.7 m. 16-QAM-OFDM modulation and specific nonlinear equalization techniques are employed
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| 5. |
- Puerta, Rafael, et al.
(author)
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NR Conformance Testing of Analog Radio-over-LWIR FSO Fronthaul link for 6G Distributed MIMO Networks
- 2023
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In: Opt. Fiber Commun. Conf. Exhib., OFC - Proc.. - : Institute of Electrical and Electronics Engineers Inc..
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Conference paper (peer-reviewed)abstract
- We experimentally test the compliance with 5G/NR 3GPP technical specifications of an analog radio-over-FSO link at 9 μm. The ACLR and EVM transmitter requirements are fulfilled validating the suitability of LWIR FSO for 6G fronthaul. © 2023 The Author(s).
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| 6. |
- Zhang, Lu, et al.
(author)
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Hybrid fiber–THz fronthaul supporting up to 16384-QAM-OFDM with the delta-sigma modulation
- 2022
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In: Optics Letters. - : Optica Publishing Group (formerly OSA). - 0146-9592 .- 1539-4794. ; 47:17, s. 4307-4310
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Journal article (peer-reviewed)abstract
- With the progress of high-capacity radio access networks, ultra-dense small cells are rapidly being deployed in urban areas. As a result, the deployment of a large number of optical fibers in urban areas becomes a severe issue. In this Letter, we propose a hybrid fiber–terahertz (THz) mobile fronthaul system supporting flexible and high-order wireless signal transmission with the delta-sigma modulation. The photonic THz transmission is used as the seamless extension of fiber-based fronthaul in small cells. A 20-Gbit/s digital fiber–THz fronthaul system is experimentally demonstrated to validate the proposed scheme, with 10-km optical fiber transmission and 300-GHz wireless relay. Carrier aggregation of up to 10 40-MHz and 60-MHz 5G-new radio (5G-NR) channels at the radio carrier frequency of 3.9 GHz is reported. The design of quantization noise suppressed delta-sigma modulation enables the system to transmit orthogonal frequency division multiplexing (OFDM) modulation up to 16384 order quadrate amplitude modulation (QAM) mapping with the error vector magnitude (EVM) below 0.5%.
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| 7. |
- Oxenløwe, L. K., et al.
(author)
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100s gigabit/s THz communication
- 2018
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In: Optics InfoBase Conference Papers. - : OSA - The Optical Society. - 9781557528209
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Conference paper (peer-reviewed)abstract
- This paper gives an overview of recent progress on the topic of using around 0.4 THz carriers for communications. Experimental demonstrations will be described, and concepts and pros & cons of various system-platforms discussed.
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| 8. |
- Hu, H., et al.
(author)
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TuB4.1-chip based thz emitter for ultra-high speed THz wireless communication (Invited)
- 2019
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In: IEEE Photonics Society Summer Topical Meeting Series 2019, SUM 2019. - : Institute of Electrical and Electronics Engineers Inc.. - 9781728105970
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Conference paper (peer-reviewed)abstract
- By using a monolithically integrated dual-distributed feedback (DFB) laser chip attached to a photomixing uni-Travelling carrier photodiode (UTC-PD) with a THz antenna, single-channel THz photonic-wireless transmission system with a net rate of 131 Gbit/s over a wireless distance of 10.7 m has been achieved.
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| 9. |
- Lyu, Z., et al.
(author)
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Preamble-Free Synchronization Based on Dual-chirp Waveforms for Photonic THz-ISAC
- 2023
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213.
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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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| 10. |
- Ostrovskis, A., et al.
(author)
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106.25 Gbaud On-Off Keying and Pulse Amplitude Modulation Links Supporting Next Generation Ethernet on Single Lambda
- 2023
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213.
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Journal article (peer-reviewed)abstract
- Development of Data Center based computing technology require energy efficient high-speed transmission links. This leads to optical amplification-free intensity modulation and direct detection (IM/DD) systems with low complexity equalization compliant with IEEE standardized electrical interfaces. Switching from on-off keying to multi-level pulse amplitude modulation would allow to reduce lane count for next generation Ethernet interfaces. We characterize 106.25 Gbaud on-off keying, 4-level and 6-level pulse amplitude modulation links using two integrated transmitters: O-band directly modulated laser and C-band externally modulated laser. Simple feed forward or decision feedback equalizer is used. We demonstrate 106.25 Gbaud on-off keying links operating without forward error correction for both transmitters. We also show 106.25 Gbaud 4-level and 6-level pulse amplitude modulation links with performance below 6.25% overhead hard-decision forward error threshold of 4.5×10-3. Furthermore, for EML-based transmitter we achieve 106.25 Gbaud 4-level pulse amplitude modulation performance below KP-FEC threshold of 2.2×10-4. That shows that we can use optics to support (2x)100 Gbps Ethernet on single lambda at expense of simple forward error correction.
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