Frequency Comb-Based WDM Transmission Systems Enabling Joint Signal Processing

Abstract

We review the use of optical frequency combs in wavelength-division multiplexed (WDM) fiber optic communication systems. In particular, we focus on the unique possibilities that are opened up by the stability of the comb-line spacing and the phase coherence between the lines. We give an overview of different techniques for the generation of optical frequency combs and review their use in WDM systems. We discuss the benefits of the stable line spacing of frequency combs for creating densely-packed optical superchannels with high spectral efficiency. Additionally, we discuss practical considerations when implementing frequency-comb-based transmitters. Furthermore, we describe several techniques for comb-based superchannel receivers that enables the phase coherence between the lines to be used to simplify or increase the performance of the digital carrier recovery. The first set of receiver techniques is based on comb-regeneration from optical pilot tones, enabling low-overhead self-homodyne detection. The second set of techniques takes advantage of the phase coherence by sharing phase information between the channels through joint digital signal processing (DSP) schemes. This enables a lower DSP complexity or a higher phase-noise tolerance.

Optical Injection Locking: From Principle to Applications

“…The recovered CW signal then seeded an electro-optic comb generator [107]. In these type of transceivers, the phase-locked nature of the optical carriers are exploited in the DSP for the DWDM signals, showing reduced DSP complexity [5]. OIL is crucial in these systems as it regenerates CW tones with high OSNR.…”

“…Laser synchronization plays important roles in numerous applications. In optical communications, synchronized lasers are used as local oscillators (LOs) to reduce the complexity and latency in coherent receivers [2]- [5]. In conjunction with optical frequency comb, OIL coherently demultiplexes optical tones for dense wavelength division multiplexed (DWDM) systems or super channel transmitters [6]- [9], enabling high spectral efficiency communications.…”

Phase-coherent lightwave communications with frequency combs

“…Having access to multiple channels impaired by the same phase noise means that the phase estimation can be made more efficient in terms of phase tracking capabilities [15][16][17], or power consumption of the digital electronics [18]. It has been suggested that joint phase processing can be implemented with optical frequency comb sources [19][20][21][22] but a proof in a transmission experiment is still outstanding. In the receiver, one even and one odd channel can be picked to be received simultaneously.…”

4:1 Silicon Photonic Serializer for Data Center Interconnects Demonstrating 104 Gbaud OOK and PAM4 Transmission

“…To alleviate this drawback, we investigate the possibility of sharing the laser source over multiple channels. Recent research has illustrated that a frequency comb is a viable alternative as a source for multiple wavelength-division multiplexing (WDM) channels [17]. When expanding our test setup with an optical waveshaper acting as a band pass filter, we could narrow down the spectrum of the frequency comb to less than 2.5 nm without any observable penalty.…”