Coherent optical receiver for 680 Mbit/s using phase diversity

ASK multiport optical homodyne receivers

“…Thus, suppression of the BER floor is the major advantage of WIRNA receivers. Initial experiments with multiport homodyne receivers were recently reported [11]- [13], [28], [29]. 'At the same time, the theory of these receivers seems to be lagging behind experimental research: to the best of the authors' knowledge, the performance of the multiport optical homodyne receivers operating under both shot-and phasenoise conditions has never been studied, and laser linewidth requirements for these receivers have not been established.…”

“…where PLo and $Lo are the local oscillator power and phase, respectively. The LO laser frequency is tuned to the frequency of the received signal by means of an AFC loop using temperature and/or current and/or piezoelectric laser mirror [28] control. As usual in coherent systems, an AFC should provide a good frequency control of the center frequency of the LO.…”

“…Practically, K is likely to be small ( 3 or 4); our analysis applies for any value of K. Note that K = 2 leads to 180" phase shift between the output ports; it is easy to show that the resulting receiver does not eliminate phase noise, and has very poor performance. However, a two-port receiver ( K = 2 ) can be used if the phase shift between the output 'It has been shown experimentally [28], 1291 that the frequency control is not critical with multiport receivers: no measurable performance degradation has been observed when the local oscillator laser was detuned by frequency offset from the received signal, with the frequency offset being as large as 50 percent of the bit rate 1291, [30]. The authors of [29], 1301 indicate that the receiver filters were optimized experimentally.…”

Phase diversity techniques for coherent optical receivers

“…Manuscript received May 29, 1986;revised September 30, 1986. The authors are with STC Technology Ltd., Harlow, Essex, U.K. receiver only requires a receiver module of baseband information bandwidth. The two possible modes of "zero IF" operation are homodyne (phase locked) operation [3]- [5] and phase diversity (multiport) techniques [6]- [8]. In this paper, we compare these modes, and show that phase diversity techniques offer robust and practical performance for high bit rate coherent receivers operating at high data rates.…”

ASK Homodyne System Receiver Using a 6-Port Fiber Coupler

“…A novel ASK homodyne system implementation was recently reported by Davis et al [1], which uses a 6-port optical fiber coupler at the receiver in demodulating the data signal directly at baseband without the need for an optical phase-locked loop. This system has some attraction for higher bit rates, avoiding the necessity of a high intermediate frequency as in a heterodyne system.…”