FBGs for Laser Diode Wavelength Locking

Introduction

Narrow linewidth and wavelength stabilized lasers play a vital role across various applications and industries, including sensing, medical, spectroscopy, imaging, and telecommunications. Although Distributed Bragg Reflector (DBR) or Distributed Feedback (DFB) lasers have excellent performances, they are more costly to produce than Fabry-Perot laser diodes as they necessitate individual testing before packaging. Furthermore, compared to waveguide gratings used in DFB and DBR lasers, FBGs exhibit superior stability and wavelength precision. Volume Bragg Gratings (VBGs) may be an alternative to FBG in some applications, but FBGs offer several advantages such as thermal stability, simplicity of integration, and versatility.

FBGs for pump wavelength locking

Semiconductor pump lasers with high output power and stable wavelength play a crucial role in modern fiber lasers and amplifiers as well as in Raman fiber amplifiers. Given the amplifying gain medium's sensitivity to pump wavelength fluctuations, the market predominantly favors the use of Fiber Bragg Grating stabilized semiconductor pump lasers. A typical configuration of a FBG locked pump laser module is shown in Figure 1. For this application, the FBG is inscribed in the pump laser pigtail and typically positioned at a distance ranging from 50 cm to 2 meters.

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