Stokes/anti-stokes Raman fiber laser

Abstract

This report discuss on the construction of a fiber-based Stokes and anti-Stokes Raman laser and its applications. The objective of this project is to demonstrate the fiber-based Raman laser. The project also aims to analyse the property of Raman laser generation in optical fiber and the cavity design being used to achieve optimum result.

In this project, we designed and implemented an experimental setup of fiber-based laser structure to produce the Raman fiber lasers (FRL). Prior to the experiment, the proposed designs of the construction of RFL were simulated and analysed for verification with the later practical experiment results. The first Stokes Raman laser and higher order Stokes shift was achieved by using Germanium-doped fiber as a gain medium and the high reflectivity fiber bragg gratings (FBGs) as the filter in the laser cavity. For multiwavelength RFL, multiple FBGs can be cascaded to form a set of cavities linearly. Optimization of the fiber length, cavity reflectivity and the pump laser intensity have been studied and analysed. These parameters were varied for optimised results. An overview of the results concluded that Raman threshold is insensitive to the changes in the fiber length and cavity reflectivity when a long fiber (more than 1km in this project) and high reflectivity output grating were used.

In our experimental setup, an Ytterbium-doped fiber amplifier was constructed to obtain high power pump laser as the Raman threshold is high. RFL with extinction ratios of about 30dB were obtained with a 26dBm pump power. The output power of the RFL is about 17dBm. Besides, an extinction ratio of 40dB Stokes laser was also achieved with double pump source. The output power of the RFL is about 20dBm. The results were comparable to those obtained from simulations and that achieved by others.