Abstract
A detailed experimental investigation of the effects of external optical injection on a Fabry Perot laser when in continuous wave (CW) mode and in gain switched mode is presented. Such detailed characterisation can help in optimising operating condition of the transmitters to significantly improve the system performance for dedicated applications. In CW mode, we characterised various performance indicators of a laser such as side mode suppression ratio (SMSR), wavelength, peak power, modulation bandwidth, resonance frequency, optical linewidth, and phase noise under external optical injection with the use of tuning maps. We also present in brief the theoretical origin of these parameters using rate equations. We then investigated the performance of the externally injected Fabry Perot laser under gain switching for optical frequency comb (OFC) generation. We demonstrated the generation of an OFC with a free spectral range of 6.25 GHz to 25 GHz and a quasi-continuous wavelength tunability of 31 nm. The phase noise of the tones of the generated OFC is measured and is found to be similar to that of the externally injected light and the measured optical linewidth was ∼40 kHz. We also presented experimentally the trade-off that exists between bandwidth of the generated OFC and the phase noise of individual comb tones under external optical injection and their optimisation for the application at hand.
Highlights
I N THE last two decades, network traffic has seen a significant increase due to the evolution of the information age
Implementation of such networks calls for specialised transmitters capable of generating number of carriers, with high flatness, flexible channel-spacing, wavelength tunability, high side mode suppression ratio (SMSR), low-noise and cost and power efficiency
We presented an innovative multicarrier transmitter, gain switched optical frequency comb (GS-OFC) utilising external optical injection, which can play a vital role in the implementation of flexible networks
Summary
I N THE last two decades, network traffic has seen a significant increase due to the evolution of the information age. Recent experiments have achieved a record-high of 17.3 bit/s/Hz spectral efficiency transmission over 50 km using probabilistic shaping of polarization division multiplexing (PDM) 4096-QAM [6] Such modulation techniques can operate at closer channel spacing with reduced or no guard bands. Such characterisation can be used to precisely operate the laser subsystem based on master-slave configuration for the application at hand to attain optimum system performance. The effect of external optical injection on the overall bandwidth and the phase noise of the OFC is discussed
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