Abstract
We present experiments and numerical simulations of optical frequency combs generated by gain-switching a single mode laser diode when subject to optical injection. Our analysis focuses on the combs with a frequency separation fR in the GHz range. We present experimental maps in the parameter space spanned by the detuning and the strength of the optical injection that identify the boundaries between regions with different dynamical states. A rich variety of nonlinear behaviors including injection-locked, unlocked and irregular combs are observed and analyzed. The dynamical state corresponding to an injection locked comb, PN, is characterized by an optical phase oscillation with a well defined amplitude in such a way that repeats or changes in 2π with an N/f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> period, where N is a natural number. Different regions of locked combs with a tongue shape around detuning values given by multiples of f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> appear in the maps. P1 and P2 are the most widespread locked states for large values of the modulation amplitude. As this amplitude decreases a much larger variety of PN states with large values of N appear in small area regions of the map. Our numerical simulations are in very good agreement with experimental results.
Highlights
Optical frequency combs (OFCs) are coherent light sources consisting of evenly spaced discrete spectral components
This redshift is due to the temperature increase caused by the sinusoidal excitation of the bias current in comparison with the constant value corresponding to continuous wave (CW) operation
We have presented an experimental and theoretical study on the effect of optical injection on a high quality OFC generated by gain-switching a single-mode semiconductor laser
Summary
Optical frequency combs (OFCs) are coherent light sources consisting of evenly spaced discrete spectral components. In a recent work we have performed a systematic analysis of the OI conditions for improving the spectral quality of a GS single-mode laser showing a broad noisy spectrum without injection [24]. This theoretical and experimental analysis mainly focused on the 10 dB spectral width and the CNR, that are two of the most important parameters for characterizing the quality of an OFC. In this paper we perform that analysis for the first time to the best of our knowledge This is done by using numerical simulations and experiments on a gain-switched single-mode laser subject to external optical injection. The presented locking scenarios can be used to generate optical combs with different frequency spacing values
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