1 Sliced fiber Bragg grating used as a laser diode external cavity Pin Long and Justin Carignan O/E LAND INC., 6739 Cordner, LaSalle, Quebec, Canada ABSTRACT A fiber Bragg grating is cut into small segments of 1 to 2mm. Each fiber Bragg grating segment is used as a laser diode external cavity. The laser diode bandwidth can be reduced from 0.19nm to 0.06nm. 1. INTRODUCTION Narrow bandwidth laser sources are important for optical fiber telecommunication applications. The core technology of DWDM is to increase the capacity of single mode fiber by using multiple wavelengths to carry the information. The center wavelength stability of the laser source is very critical for DWDM optical systems. Narrow bandwidth laser sources are also useful devices for instrumentation, sensor, metrology, and biomedical applications. To reduce the bandwidth of a laser diode, you can use technologies like volume holographic gratings, [1-3] and fiber Bragg gratings, [4-7]. Fiber Bragg gratings were used by Pezeshki et al [4] to stabilize the intensity and frequency fluctuations of a laser diode. There are some disadvantages to use fiber Bragg gratings as external cavities to suppress longitude and lateral mode hops: first the light from laser diodes, solid state lasers, or gain mediums must be coupled into the optical fiber with high energy loss; Second, the fiber Bragg grating is usually not located at the fiber end, but at some distance from the fiber end, therefore the length of the optical cavity is longer. Long external cavities makes it difficult to modulate the laser diode at a high frequency; third, there are many applications that need free space laser diodes and do not need light to be coupled into an optical fiber, which limits the use of Fiber Bragg gratings as external cavities. In this paper, we cut fiber Bragg gratings (FBG) into small segments of 1 to 2 mm in length, which we call sliced FBG. The sliced FBG is used as a laser diode external cavity to suppress the laser diode bandwidth and to stabilize the laser diode center wavelength. 2. EXPERIMENT As shown in Fig. 1, a regular Bragg grating written on a fiber is fixed in a ferrule. The fiber Bragg grating within the ferrule is then cut into small slices with a length of 1 to 2 mm as shown in Fig. 2. . Figure 1. FBG in a Ferrule Figure 2. FBG cut into small segment Then both sides of the sliced fiber Bragg grating are polished and are coated with an anti-reflection (AR) coating. A sliced FBG is placed in front of the laser diode emission area as an external cavity shown in Fig. 3. FBG ferrule Slice of FBG