Performance Oriented DSP for Flexible Long Haul Coherent Transmission

Abstract

In long haul optical fiber communication networks, whichcan span thousands of kilometers, bandwidth is at a premium due to the relatively low availability of optical fibers when compared with network traffic demands. Therefore, these networks require the highest performance in the physical layer, with transceivers that are capable of extracting all the available capacity from each optical fiber. Digital coherent transmitters and receivers, which enhance optical transmission systems by using digital signal processing, are essential for achieving this goal. This tutorial discusses the digital signal processing techniques that are used in the design of high performance coherent modems to compensate for adverse channel effects such as fiber impairments and optoelectronic device nonidealities.

Frame format and DSP receiver design for a 56-GBaud GEO DP-QPSK coherent optical feeder link

“…The driving motivation behind this work was to assess to what extent can one re-use in outer space the coherent DSP algorithms and chips developed either for high-performance, long-haul optical fiber communications [6] or for low-power, short-reach data center optical interconnects [7].…”

“…Accordingly, static equalization reduces to simple matched filtering, and can be efficiently carried out by block-filtering in the frequency domain with the overlap-save trick, see e.g. [6], [7]. We chose to implement matched filtering prior to timing recovery in order to improve SNR for the latter.…”

On the Performance Limits of High-Speed Transmission Using a Single Wideband Coherent Receiver

“…3a. First, it can be noted that the transfer functions of the four channels are all slightly different, and this difference can be compensated as in [21] using a linear filter to further improve performance. In addition, the transfer function is relatively flat up to 25 GHz.…”

“…The Keysight M8196A with a typical bandwidth of 32 GHz, with 8 physical bits resolution, 5 ENOB and a sampling rate of 92 GSa/s was used to convert the digital signal into the electrical domain. An in-depth analysis on how the DAC characteristics impact the quality of the generated transmit signal is conducted in [6], [21], [22]. The outputs of the arbitrary waveform generator (AWG) were amplified by SHF-807 linear broadband amplifiers with a bandwidth of 30 GHz.…”

DSP-free coherent receivers in frequency-synchronous optical networks for next-generation datacenter interconnects

“…The conventional approach typically resolves the above issues through digital signal processing (DSP) and highresolution analog-to-digital converter (ADC). Moreover, coherent detection relies on narrow linewidth and temperature-controlled lasers at both transmitters and receivers [6][7][8][9]. As a result, high speed optical coherent detection is commonly extremely costly and power-hungry.…”