Novel Optical Phase Demodulator Based on a Sampling Phase-Locked Loop

A novel phase-locked coherent demodulator, based on a sampling phase-locked loop, is presented and investigated theoretically. The demodulator is capable of operating at high frequencies, by using optical sampling to downconvert the high-frequency input radio-frequency signal to the frequency range of the baseband loop. We develop a detailed theoretical model of the (sampling) phase-locked coherent demodulator and perform detailed numerical simulations. The simulation results show that the operation of the sampling demodulator resembles the operation of the baseband demodulator for very short optical pulses (<2 ps). Furthermore, we investigate how the signal-to-noise ratio of the demodulator is affected by timing and amplitude jitter of the pulsed optical source     

Highly Linear Coherent Receiver With Feedback

We propose and demonstrate a novel coherent receiver with feedback for high-linearity analog photonic links. In the proposed feedback receiver, a local phase modulator tracks the phase change of the signal and reduces the effective swing across the phase demodulator without reducing the transmitted signal. The signal-to-noise-ratio is thus maintained while linearity is improved. Up to 20-dB improvement in spur-free dynamic range (SFDR) is achieved experimentally. At 3.13 mA of average photocurrent per photodiode, the measured SFDR is 124.3 dBmiddotHz^2/3, which corresponds to an SFDR of 131.5 dBmiddotHz^2/3 when the link is shot-noise-limited     

Experimental 2.5-Gb/s QPSK WDM Phase-Modulated Radio-Over-Fiber Link With Digital Demodulation by a -Means Algorithm

Highest reported bit rate of 2.5 Gb/s for optically phase-modulated radio-over-fiber (RoF) link, employing digital coherent detection, is demonstrated. Demodulation of 3$,times,$ 2.5 Gb/s quadrature phase-shift-keying modulated wavelength-division-multiplexed RoF channels is achieved after 79 km of transmission through deployed fiber. Error-free performance (bit-error rate corresponding to $10^{{-}4}$) is achieved using a digital coherent receiver in combination with a $K$-means algorithm for radio-frequency phase recovery.      

Digital coherent receiver for subcarrier multiplexed phase-modulated radio-over-fibre signals

Digital coherent detection of multi-channel subcarrier multiplexed optically phase-modulated radio-over-fibre signals is experimentally demonstrated. Successful detection after transmission over a 40 kmlong fibre link of four or five 25 Mbaud BPSK/QPSK subcarrier channels in 5 GHz bandwidth is demonstrated using offline digital signal processing.     

Photonic downconversion for coherent phase-modulated radio-over-fiber links using free-running local oscillator

A digital coherent receiver employing photonic downconversion is presented and experimentally demonstrated for phase-modulated radio-over-fiber optical links. Photonic downconversion adds additional advantages to optical phase modulated links by allowing demodulation of signals with RF carrier frequencies exceeding the bandwidth of electrical analog-to-digital converter. High spurious-free dynamic range is observed for RF carriers at 5 GHz photonically downconverted to 1 GHz.     

Low-complexity BCH codes with optimized interleavers for DQPSK systems with laser phase noise

The presence of high phase noise in addition to additive white Gaussian noise in coherent optical systems affects the performance of forward error correction (FEC) schemes. In this paper, we propose a simple scheme for such systems, using block interleavers and binary Bose–Chaudhuri–Hocquenghem (BCH) codes. The block interleavers are specifically optimized for differential quadrature phase shift keying modulation. We propose a method for selecting BCH codes that, together with the interleavers, achieve a target post-FEC bit error rate (BER). This combination of interleavers and BCH codes has very low implementation complexity. In addition, our approach is straightforward, requiring only short pre-FEC simulations to parameterize a model, based on which we select codes analytically. We aim to correct a pre-FEC BER of around \(10^{-3}\). We evaluate the accuracy of our approach using numerical simulations. For a target post-FEC BER of \(10^{-6}\), codes selected using our method result in BERs around 3\(\times \) target and achieve the target with around 0.2 dB extra signal-to-noise ratio.     

The Effect of Timing Jitter on a 160-Gb/s Demultiplexer

For high-speed optical communication systems, timing jitter is a crucial parameter for switching operations between the data and control signal. This is especially the case for the demultiplexer. The effect of timing jitter becomes very important as the bit rate of the data signal increases beyond 100 Gb/s and it is, therefore, essential to quantify its effect. In this letter, the impact of gating timing jitter on a 160-Gb/s demultiplexer is investigated by using two pulse sources with different timing jitter properties. We also investigate the interplay between the control signal pulsewidth and timing jitter. The experiment shows that it is essential to minimize jitter in the 20-kHz to 10-MHz range. Furthermore, we show that the impact of timing jitter can be reduced if the control signal pulses are broader than data signal pulses.