FPGA implementation of a coherent optical receiver front-end: High-level design and test methodology

This study evaluated the use of GFDM transmission in passive optical networks (PONs) by comparing the performance of coherent and non-coherent optical receivers using OptSim 2023.12sp2 and Matlab 2018b ®. The study concentrated on transmitting 10 Gb/s radio frequency signals over optical fiber, emphasizing the significance of high-speed fronthaul links for 5G networks. The findings demonstrated that coherent detection markedly enhances receiver sensitivity by approximately 3 dB compared to direct detection, thereby augmenting the capacity of optical fronthaul networks despite the elevated cost. Additionally, the study recommended investigating pre- and post-compensation techniques to mitigate signal dispersion in optical fibers for further performance optimization.

An improved coherent optical receiver architecture that compensates for a random drift in the state of polarization (SOP) of both the signal and the local oscillator (LO) is presented for the first time. The proposed architecture comprises two conventional coherent optical receiver front-ends in tandem, where the SOP of the LO is first divided into its two orthogonal components and then distributed to each coherent optical receiver front-end module. Two distinct methods of polarization diversity recovery of the modulation based on the MRC technique and an eigenvalue-eigenvector decomposition of the covariance matrix have been used to effectively recover the transmitted signal. The concept is validated by numerical simulations, where a differential quadrature phase-shift keyed (DQPSK) modulated signal with a random time-varying SOP is first generated. After its mixing with a LO also possessing a random time-varying SOP, the algorithms that have been developed are provided with eight input variables to be digitally processed. The constellation diagrams corresponding to the recovered DQPSK modulation obtained using the two polarization diversity methods are presented.

We propose a modified method of constant modulus algorithm (CMA) based on polarization demultiplexing in Stokes space for polarization demultiplexing (SS-PDM) in optical coherent receivers. SS-PDM can tolerate chromatic dispersion (CD) and polarization-dependent loss (PDL), but is sensitive to PMD. On the other hand, the CMA with high-order FIR filters could compensate for polarization-mode-dispersion (PMD) effectively, but suffers from the singularity problem which results from PDL. Therefore, we use the polarization rotation matrix estimated by SS-PDM to set the initial center taps of the CMA. The singularity problem of the CMA is avoided effectively in a much wider range of PDL and its convergence speed is also improved. We demonstrate this modified CMA in a simulation of 100-Gbit/s PDM-QPSK with PDL of 1, 3, and 5 dB, respectively. PDL is emulated by attenuating one polarization tributary before polarization multiplexing and the interaction between PDL and PMD is ignored. The singularity problem disappears as expected. Because the tolerance of PDL is affected by DGD, we further investigate the PDL tolerance under different DGD. Finally, we conduct the simulation of 100-Gbit/s PDM-QPSK with PDL of 3 dB over 3000 km SSMF and 4000 km SSMF separately. The convergence speed accelerates indeed compared with that of the conventional CMA.

We propose a self-reconfiguring constant modulus algorithm (CMA) using a constrained mode followed by an unconstrained mode for solving the singularity issue of CMA equalizers in polarization-division-multiplexed coherent receivers.

A highly integrated 40 Gbit/s coherent optical receiver is reported using a Costas loop as a homodyne optical phase locked loop (OPLL). A photonic IC, an electrical IC, and a hybrid loop filter are characterized, and the feedback loop system is fully analyzed to build a stable homodyne OPLL. All components are integrated on a single substrate within the compact size of 10 × 10mm(2), and a 1.1 GHz loop bandwidth and a 120 psloop delay are achieved. The binary phase-shift keying receiver exhibits error-free (BER<10(-12)) up to 35 Gbit/s and BER<10(-7) for 40 Gbit/s with no latency, and consumes less than 3 W power.

The rapid advancement of the thin-film lithium niobate (LiNbO3) platform has established it as a premier choice for high-performance photonics integrated circuits. However, the scalability and cost-efficiency of this platform are hindered by the reliance on chip-level fabrication and integration for passive and active components, necessitating a robust wafer-level LiNbO3 heterogeneous integration platform. Despite its critical role in enabling ultrahigh-speed optical interconnects, as well as optical mmWave/THz sensing and communication, the realization of ultrahigh-speed photodiodes and optical coherent receivers on the LiNbO₃ platform remains an unresolved challenge. This is primarily due to the challenges associated with the large-scale integration of direct-bandgap materials. To address these challenges, we have developed a scalable, high-speed InP-LiNbO₃ wafer-level heterogeneous integration platform. This platform facilitates the fabrication of ultrahigh-speed photodiodes with a bandwidth of 140 GHz, capable of receiving high-quality 100-Gbaud pulse amplitude modulation (PAM4) signals. Moreover, we demonstrate a seven-channel, single-polarization I–Q coherent receiver chip with an aggregate receiving capacity of 3.584 Tbit s-1. This coherent receiver exhibits a balanced detection bandwidth of 60 GHz and a common mode rejection ratio (CMRR) exceeding 20 dB. It achieves receiving capacities of 600 Gbit s-1 λ-1 with a 100-Gbaud 64-QAM signal and 512 Gbit s-1 λ-1 with a 128-Gbaud 16-QAM signal. Furthermore, energy consumption as low as 9.6 fJ bit-1 and 13.5 fJ bit-1 is achieved for 200 Gbit s-1 and 400 Gbit s-1 capacities, respectively. Our work provides a viable pathway toward enabling Pbps hyperscale data center interconnects, as well as optical mmWave/THz sensing and communication.

The resolution of analog to digital converter (ADC) and the power consumption of digital signal processing (DSP) are becoming the bottleneck of optical communication system. To acquire and recover signals with low resolution ADCs, we propose a binarized coherent optical receiver based on opto-electronic neural network, which consists of three layers, the broadcast layer, the optical neural layer, and the electronic neural layer. The broadcast layer that composed of Mach-Zehnder interferometers (MZIs) is to duplicate and select the input optical signal into the opto-electronic neural network. The optical neural layer is constituted by specially designed structures to map the binarized weights into optical domain, which can be integrated on silicon together with the broadcast layer. The one-bit vertical resolution ADCs act as the binarized activation after the optical neural layer. This binarized coherent optical receiver is demonstrated in simulation of 50-Gb/s single polarization (SP) QPSK system and 100-Gb/s polarization multiplexing (PDM) QPSK system. The one-bit vertical resolution ADCs can be utilized to recover the complex modulation format signal successfully. The broadcast layer and the optical neural layer can be integrated based on silicon, which could increase the calculation speed and reduce the energy consumption of the total system.

We analyze and optimize the performance of a single-tap constrained decision-directed least-mean square algorithm for computationally-efficient phase noise estimation in coherent optical intradyne receivers intended for the detection of arbitrary M-QAM constellations.

FSO channel imposes enormous obstacles on adequate attainable performance levels because of its weather dependency which leads to system outages. In this paper a diagnostic methodology is introduced to assess the bit error rate performance of an OFDM FSO link using optical intensity modulation and coherent heterodyne optical detection receiver taking int° consideration the effect of sturdy atmospheric turbulence. The turbulence impact is demonstrated as gamma-gamma distribution and the performances are assessed as far as power penalty, CNR and BER endured by the framework because of the impact of turbulence at a given BER for a few framework parameters like turbulence quality, link separation, local oscillator control and so forth. It is discovered that with 4 subcarriers at 10 Gbps data rate, the power penalty is 6dB at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> for a for a connection separation of 3600 m with 1mW power of both RF and Optical local oscillator. Overall performance may be improved appreciably by way of growing the quantity of ofdm subcarriers.

For the first time, a highly integrated coherent optical receiver is demonstrated using a homodyne OPLL as a Costas loop. The OPLL shows 1.1GHz loop bandwidth, 120ps effective loop delay, and 10×10mm2 compact size of chip integration. The receiver exhibits 40Gbit/s BPSK reception with no latency.

It is generally thought that the maximum signal averaging time for coherent (heterodyne) optical receivers is limited by the aerosol speckle phase decorrelation time. Fortunately, for many applications this is not true. It is demonstrated analytically and confirmed by experimental data that for many applications the signal averaging time is limited by the shorter of the laser transmitter or atmospheric turbulence phase decorrelation times. This can have a significant impact on lowering the threshold for signal detection when the fast Fourier transform (maximum likelihood estimator) is used to detect the signal.

This paper demonstrates digital signal processing (DSP) based chromatic dispersion (CD) reckoning technique for single carrier high speed coherent optical communications. Coherent detection permits the optical field parameters (amplitude, phase and polarization) to be available in the electrical domain enabling new opportunity for multi-level signaling (M-ary PSK and M-ary QAM modulation), as well as the possibility of exploring polarization multiplexing. Again, it enables quasi-exact compensation of linear transmission impairments by a linear filter (equalizer), which can operate adaptively to overcome time-varying impairments. That is why Coherent detection employing QAM modulation formats has become one of the most promising technologies for next generation high speed transmission systems due to the high power and spectral efficiencies. With the development of DSP, coherent optical receivers allow the significant estimation of CD. In recent days, the realizations of these DSP algorithms for mitigating the chromatic dispersion in the coherent transmission systems are the most attractive investigations. In this paper, CD estimation technique has been improved using DSP algorithm and optimal OSNR, BER have been achieved.

In this article the mixing efficiency of an optical coherent receiver is calculated using the Stokes parameter representation for the involved fields. It allows us to obtain formulas of immediate interpretation and computation that can be useful for optical coherent communication system performance evaluation and for the analysis of optical coherent sensors. Moreover, a new scheme for active polarization tracking based on the obtained results is presented that is useful for fiber coherent optical communications.

A novel coherent optical receiver is proposed and experimentally demonstrated by using a feedback technique capable of reducing the nonlinear distortion in a traditional receiver while retaining the signal to noise ratio. Up to 15 dB of SFDR improvement is obtained.

With the fast progress in academic research, the transmission capacity over the single mode fiber (SMF) has been demonstrated more than 100 Tb/s, together with wavelength division multiplexing (WDM), polarization division multiplexing (PDM), coherent detection, and higher-order modulation formats. However, 100 Tb/s is considered as the capacity limit of SMF, which is constrained by the fiber nonlinearity and optical signal to noise ratio. In this paper, using mode division multiplexing combined with coherent WDM PDM-DFTs-OFDM-32QAM, we successfully demonstrate 200-Tb/s (375 × 3 × 178.125-Gb/s) signal over 1-km few mode fiber (FMF) employing both C- and L-bands with 25-GHz channel spacing, achieving a spectral efficiency of 21.375-bit/s/Hz in both C/L-band.