High-Capacity Coherent DCIs Using Pol-Muxed Carrier and LO-Less Receiver

Abstract

A PAM 4 based direct detection system has been standardized for short-distance data center interconnects because of its simple architecture. Performance of the PAM 4 systems is limited for high dispersion values or demands complicated signal processing for further increase in data rates. A polarization multiplexed carrier based self-homodyne (PMC-SH) link with adaptive polarization control is a practical approach with an laser oscillator (LO)-less and carrier phase recovery (CPR)-free coherent receiver that can replace PAM 4 links for achieving high data rates. We analytically find that PMC-SH scheme results in a significantly better BER for a given transmission rate or can achieve doubling of the data rate for given bandwidth of electronics and laser power (when compared with PAM 4). Practical implementation of the proposed system with adaptive polarization control is also discussed. Presented theoretical frame work highlights the advantages of such self-homodyne systems over PAM 4 based systems in terms of SNR requirements and capacity.Index Terms-PAM 4 links, data center interconnects, selfhomodyne system, polarization multiplexed carrier.

An Analog Signal Processing EIC-PIC Solution for Coherent Data Center Interconnects

“…A generic ASP receiver architecture for polarization division multiplexed system with laser phase/frequency offset is detailed in [1,5]. The modulated signal (S) and unmodulated carrier (LO) from the received signal are separated with the aid of an adaptive polarization controller consisting of an electronic polarization controller, polarization beam splitter, power splitter, photodetector, and adaptative polarization control circuit [14]. The polarization segregated optical signals S and LO are given to the ICR.…”

“…Functional validation of the EIC-PIC receiver has been performed for the QPSK homodyne link. This Costas loop aims at removing the time varying phase offset between the modulated and local oscillator signals, for reliable recovery of data in coherent homodyne systems, especially in a polarization multiplexed carrier based selfhomodyne (PMC-SH) links [14]. The EIC-PIC ASP based coherent receiver exhibits an essential step in the direction of achieving highly efficient DCIs.…”

Endless optical phase delay based phase synchronization in low-power coherent DCIs

“…EOPD aided phase synchronization: In PMC-SH links, the modulated signal (S) and the unmodulated carrier (LO) copropagate along the same channel in two orthogonal polarizations and are separated at the receiver for demodulation [16]. Due to the path length difference, laser linewidth, and polarization mode dispersion, time varying phase offset is introduced between S and LO, which has to be removed using phase synchronization.…”

POL-MUX System for Noncoherent Optical Networks

“…Nevertheless, it was not employed in optical data networks and real a comeback occurred with the development of coherent high-speed networks with direct detection system, digital signal processing and multistate modulation formats. Many groups were interested in this topic [14][15][16][17][18], e.g., Bermani et al studied synchronous demodulation of coherent 16-QAM with feedforward carrier recovery [19], El-Nahal et al described coherent 16 quadrature amplitude modulation (16QAM) Optical Communication Systems [20], Gnauck et al examined spectrally-efficient long-haul WDM transmission using 224-Gb/s polarizationmultiplexed 16-QAM [21]. Finally, direct detection systems with digital signal processing and X-QAM modulations were deployed into real high-speed transport optical networks, with high tolerance to negative dispersions effects [22].…”