Anomalous wavelength changes of 980-nm pump laser diodes with antireflection coatings

We have observed abrupt wavelength jumps form 980-nm pump laser diodes with an antireflection (AR) coating when the injection currents were changed. The width of the anomalous jumps becomes wider as the cavity length is shortened. It was clarified from theoretical calculations that the phenomenon is caused by narrow mirror loss distributions. It was also confirmed that wide AR coatings or a long cavity can avoid these abrupt wavelength jumps.

I. Introduction

An erbium-doped fiber amplifier (EDFA) is one of the key components in realizing wavelength-division-multiplexing optical communication systems, and 980-nm laser diodes (LDs) are used as pumping sources for EDFAs [1]– [3]. Fig. 1. Facet reflectivity of 980-nm LDs with an AR coating. Fiber Bragg gratings (FBGs) are also used in order to stabilize the wavelength because the wavelength of 980-nm pump LDs can be easily changed by the atmospheric temperature and/or the injection current. In general, the front facet reflectivity is lower than that of FBGs to overcome the oscillation between front and rear facets of the LDs. Usually the front facet of an LD is coated with an antireflectant [4]. Therefore, it is very important to understand the characteristics of LDs with antireflection (AR) coatings.