Multi-wavelength coherent transmission using an optical frequency comb as a local oscillator

Abstract

Steadily increasing data rates of optical interfaces require spectrally efficient coherent transmission using higher-order modulation formats in combination with scalable wavelength-division multiplexing (WDM) schemes. At the transmitter, optical frequency combs (OFC) lend themselves to particularly precise multi-wavelength sources for WDM transmission. In this work we demonstrate that these advantages can also be leveraged at the receiver by using an OFC as a highly scalable multi-wavelength local oscillator (LO) for coherent detection. In our experiments, we use a pair of OFC that rely on gain switching of injection-locked semiconductor lasers both for WDM transmission and intradyne reception. We synchronize the center frequency and the free spectral range of the receiver comb to the transmitter, keeping the intradyne frequencies for all data channels below 15 MHz. Using 13 WDM channels, we transmit an aggregate line rate (net data rate) of 1.104 Tbit/s (1.032 Tbit/s) over a 10 km long standard single mode fiber at a spectral efficiency of 5.16 bit/s/Hz. To the best of our knowledge, this is the first demonstration of coherent WDM transmission using synchronized frequency combs as light source at the transmitter and as multiwavelength LO at the receiver.

Chip-scale frequency comb generators for high-speed communications and optical metrology

“…When used as a multi-wavelength optical source at the transmitter, these so-called gain-switched combs sources (GSCS) enable line rates of more than 2 Tbit/s on 24 optical carriers. We also demonstrate that GSCS can not only act as a transmitter light source, but also as multi-wavelength local oscillator, thereby exploiting the scalability advantages of optical frequency combs also at the receiver side [12].…”

Performance of chip-scale optical frequency comb generators in coherent WDM communications

“…Chip-scale comb sources have been used in a variety of WDM transmission experiments, relying on different comb generation approaches and covering a wide range of data rates, channel counts, and line spacings [5][6][7][8][9][10][14][15][16][17][18][19]. A particularly promising option to generate frequency combs in chip-scale devices relies on Kerr comb generation in micro-ring resonators [27].…”

“…A particularly important advantage of frequency combs is the fact that comb lines are inherently equidistant in frequency, hence relaxing the requirements for inter-channel guard bands and avoiding frequency control of individual lines as needed in conventional schemes that combine arrays of independent distributed-feedback (DFB) lasers. Note that these advantages do not apply only to the WDM transmitter, but also to the receiver, where an array of discrete local oscillators (LO) may be replaced by a single comb generator [6,10]. Using an LO comb further facilitates joint digital signal processing of the WDM channels, which may reduce receiver complexity and increase phase noise tolerance [11,12].…”

Frequency Comb-Based WDM Transmission Systems Enabling Joint Signal Processing

“…To obtain the frequency spacing, one could detect the phase variations between the other pilot tone and a carrier of the regenerated comb neighboring or at the same location as this pilot tone. The use of two unmodulated lines at each side of the comb has been used to improve the phase noise of the carriers generated by a gain-switched laser [90]. Similarly in the case of obtaining the frequency spacing from a data channel processed through DSP, this channel is not required to be at any specific location, although its location must be accounted for.…”