Broad-area laser diode with stable single-mode output and wavelength stabilization

Abstract

High power single-mode pump laser diodes operating around 980nm are key components for Erbium-doped devices. Much effort is still currently devoted to improve both their wavelength stability and their achievable output power, while maintaining a stable single-mode operation. Usually, the emission wavelength is stabilized by an external Fiber Bragg Grating (FBG). This configuration requires free-space optics between the laser diode output facet and the fiber or a lensed fiber to ensure an efficient coupling efficiency. This constraint increases fabrication costs, dimensions and mechanical instabilities. Moreover, the maximum achievable output power is limited because a high optical power density can damage the laser facets. To increase the achievable output power, a solution consists in using Broad-Area Laser Diodes (BALD), which are multimode emitters that are composed of large active ribbons with width of some hundreds of micrometers. The objective is then to improve the beam quality by locking the BALD emission on its transverse fundamental mode. We propose in this article to insert an integrated adiabatic transition between the multimode laser and a single-mode FBG. This taper, made by ion-exchange in glass, provides a coupling efficiency of -22.0dB from the multimode laser emission to the single-mode fiber. An optical feedback of -34dB demonstrates the stabilization of the BALD spectrum at the Bragg wavelength. The spectrum of the device is characterized by a maximum side-mode suppression ratio of 35dB, a RMS spectral width of (0.16 ± 0.04) nm and a frequency shift with current of -12GHz/100mA. CONTEXT ApplicationsIon-exchange on glass is a well-established technology for sensor applications. Its compactness and stability allow schemes of integration which often reduce costs of fabrication and improve performances or security. It has already been used for fluorescence detection 1 , chemical and bio-detection 2, 3 , displacement 4 or orientation measurement 5 . Applications in avionics are currently in development since the measurement of an aircraft's True Air Speed (TAS) has been recently demonstrated using a LIDAR containing several ion-exchanged integrated optics elements : seed CW-DFB laser, power splitters etc 6 ... Used for alternative on-board measurement, this system, supported by the European Community, presents modes of failures that are different from the traditional anemo-barometric module. The optical architecture of the micro-LiDAR is presented in Figure 1. The output of the 1.55µm-seed laser made by ion-exchange is split into two parts. The first one is used as a probe beam. It is amplified by a booster and