Soliton Radiation Beat Analysis of Optical Pulses Generated from Two CW Lasers

TL;DR

This paper presents a fibre-based method for generating optical frequency combs using soliton dynamics from two CW lasers, aiming to improve calibration of astronomical spectrographs by analyzing soliton content and formation.

Contribution

It introduces a novel approach combining soliton radiation beat analysis with fibre-based pulse shaping to optimize OFC generation for spectrograph calibration.

Findings

Deeply modulated bichromatic waves produce optimal soliton states for OFC generation.

Soliton crystal formation occurs at low powers, separated solitons at high powers.

Intermediate states combine features of both, suitable for calibration applications.

Abstract

We propose a fibre-based approach for generation of optical frequency combs (OFCs) with the aim of calibration of astronomical spectrographs in the low and medium-resolution range. This approach includes two steps: in the first step, an appropriate state of optical pulses is generated and subsequently moulded in the second step delivering the desired OFC. More precisely, the first step is realised by injection of two continuous-wave (CW) lasers into a conventional single-mode fibre, whereas the second step generates a broad OFC by using the optical solitons generated in step one as initial condition. We investigate the conversion of a bichromatic input wave produced by two initial CW lasers into a train of optical solitons, which happens in the fibre used as step one. Especially, we are interested in the soliton content of the pulses created in this fibre. For that, we study different initial conditions (a single cosine-hump, an Akhmediev breather, and a deeply modulated bichromatic wave) by means of soliton radiation beat analysis and compare the results to draw conclusion about the soliton content of the state generated in the first step. In case of a deeply modulated bichromatic wave, we observed the formation of a collective soliton crystal for low input powers and the appearance of separated solitons for high input powers. An intermediate state showing the features of both, the soliton crystal and the separated solitons, turned out to be most suitable for the generation of OFC for the purpose of calibration of astronomical spectrographs.