Chip-scale frequency comb sources are key elements for a variety of applications, comprising massively parallel optical communications and high-precision optical metrology. In this talk, we give an overview on our recent progress in the area of integrated optical comb generators and of the associated applications. Our experiments cover modulator-based comb sources, injection locking of gain-switched laser diodes, quantum-dash mode-locked lasers, as well as Kerr comb sources based on cavity solitons. We evaluate and compare the performance of these devices as optical sources for massively parallel wavelength division multiplexing at multi-terabit/s data rates, and we report on comb-based approaches for high-precision distance metrology.
Optical frequency combs have great potential for ultra-high bit rate telecommunications e.g. optical orthogonal
frequency-division multiplexing superchannels. For frequency comb generation, monolithic Quantum Dash
semiconductor mode-locked lasers are very attractive candidates owing to their broadband optical spectrum, inherent
intrinsic low noise and compactness. The active region is based on InAs nanostructures grown on InP for operation in
the 1.55 μm window. Owing to enhanced nonlinear effects, a single gain section generates short pulses in the modelocking
regime without resorting to an absorber section. An optical bandwidth over 1.3 THz yielding over 100 channels,
10 GHz spaced, is reported. Mode-locking properties are analyzed in the frequency domain using the concept of supermodes.
An Allan deviation down to ~ 10<sup>-9</sup> is reported for these passively mode-locked lasers. The low timing jitter, longterm
stability and high channel count of these QD based combs are of great potential for Tb/s data transmission with
only one single FP type laser source.
100-Gb/s coherent systems based on polarization-division multiplexed quadrature phase shift keying (PDMQPSK), with aggregate wavelength-division multiplexed (WDM) capacities approaching 10 Tb/s per fibre, are being widely deployed due to the benefits provided by coherent detection. The stringent linewidth requirements for lasers used in these systems only allow optical sources with certain phase noise characteristics to be employed. A major challenge is therefore to produce lasers with the requisite performance at low cost. Discrete mode laser diodes (DMLDs) can be designed for narrow linewidth emission and present an economic approach with a focus on high volume manufacturability of monolithic semiconductor lasers. In this paper the performance of a 112 Gb/s long-haul optical transmission system employing PDM-QPSK is investigated using a range of transmitter lasers with linewidth values ranging from 100 kHz to 5 MHz. A linewidth of 100 kHz was obtained from an external cavity laser (ECL) and linewidths ranging from 200 kHz to 5 MHz were obtained from DMLDs. The performance of the system is analysed through experimental measurements and simulations performed by Virtual Photonics Incorporated Transmission Maker (VPI™). Results are presented for back-to-back operation and after transmission through G.654 pure silica core fibre (PSCF) at distances up to 6930 km.