Generation of ultra-high repetition rate pulses in a highly nonlinear dispersion-tailored compound glass fibre

Abstract

Abstract:The generation of ultrastable optical pulses beyond 160GHz is demonstrated based on two injection-locked CW lasers through nonlinear temporal compression in a high SBSthreshold highly nonlinear dispersion tailored compound glass W-type fibre. IntroductionThe generation of high repetition rate pulses through four-wave-mixing (FWM) based nonlinear temporal compression of a dual-frequency beat signal in a highly nonlinear fibre followed by a linear dispersive medium has proven to deliver high quality pedestal-free (sub-) picosecond signals [1][2][3]. The initially sinusoidal signal can be obtained from the beating of two continuous wave (CW) lasers with a frequency separation corresponding to the desired repetition rate. Usually, independent CW sources are used [1-2] leading to significant timing jitter on the pulses generated over a timescale inversely proportional to the laser linewidths and which can be a significant issue for many applications. In [3] this issue was addressed using stable injection-locking of two semiconductor lasers to an optical comb, then simultaneously performing narrow-bandwidth filtering and amplification. In that case the two phase-locked lasers were then combined together into 2-m-long highly nonlinear bismuth oxide fibre (Bi-NLF), which has high nonlinear coefficient, but also a high dispersion and dispersion slope. Efficient generation of FWM components generally requires a high nonlinear coefficient and a low dispersion and dispersion slope: much higher repetition rates can be envisaged and much higher pulse compression factors can be achieved as the pulses do not temporally broaden in the nonlinear medium. Compound-glass technology has enabled fibres with much higher values of effective nonlinearity than that achievable in silica. However, compound glasses generally suffer from high normal material dispersion around 1.55µm and counter-balancing this with waveguide dispersion is a non-trivial fabrication task. We have recently shown a fibre design with a W-type refractive index profile as a possible solution to this problem [4] and fabricated a fibre with a highly nonlinear coefficient and low and flat dispersion profile at telecom wavelengths.Here we experimentally demonstrate the generation of high repetition rate (160GHz and 200GHz) pulses through stable injection-locking of two semiconductor lasers in a 3m-long sample of the fabricated W-type fibre and investigated the role of the tailored dispersion profile for the generation of ultra-short high repetition rate pulses.

Applications of highly nonlinear dispersion tailored lead silicate fibres for high speed optical communications

“…4 (right)), which showed a power penalty between 0.5dB and 2dB for the three converted channels. Finally, we used another sample (3m-long) of the same W-type fibre to experimentally demonstrate the generation of ultra-high repetition rate (200GHz) pulses through stable injection-locking of two semiconductor lasers [6].…”