Many applications of Laser diode require antireflection coatings either on one or both the facets of the diode. These include, for example, semiconductor optical amplifiers, optical pumping for solid state lasers and creation of broad band source for tunable external cavity. We have used single layer antireflection coating on the front facet of the laser diode using electron beam evaporation technique to enhance optical power output from the facet. To optimize the coating conditions with precise control over facet reflectance of the laser diode, we have carried out experiment for In-Situ reflectivity measurement. We have used MgF<sub>2</sub> as a low refractive index dielectric material for antireflection coating. The actual single layer AR coating consists of λ/4 thick MgF<sub>2</sub> film. The reflectivity of the film being deposited is measured on GaAs test substrate, kept in close vicinity of the laser diode bar, with the help of a 657 nm (red) laser diode and a photo detector. A LabVIEW programme, called Virtual Instrument (VI), has been prepared to automate the whole experiment. We have also carried out simulation of facet reflectivity subject to the film thickness being deposited.
The power enhancement of laser diodes is achieved by single and multilayer facet coatings such as antireflection and high reflection respectively at the front facet and the back facet of the laser diode. In this work, we have experimented with single layer λ/4 thick Al<sub>2</sub>O<sub>3</sub> film for the Anti Reflection (AR) coating and stack of λ/4 thick Al<sub>2</sub>O<sub>3</sub>/ λ/4 thick Si bi-layers for the High Reflection (HR) coating. The AR/HR coatings were deposited in an electron beam evaporation system. The effect of front and back facet reflectivities on the output power of diode laser has been studied. The highly strained MOVPE grown InGaAs quantum-well edge emitting broad area (BA) diode lasers have been used for this experiments. The light output versus current (L-I) measurements were made on selected devices before and after the coatings. The devices were tested under pulsed operation with a pulse width of 400 ns and a duty cycle of 1:400. We have also carried out the theoretical analysis and simulation of L-I characteristics for this particular diode structure using LabVIEW. The experimental results were compared with simulated results. The effect of facet coating on external differential efficiency of diode laser has also been studied.
Multilayer coatings, such as Antireflection (AR) & High Reflection (HR), are used respectively in front & back facet coatings of diode laser for high power and long life operation. In this paper, we coated single layer AR coating using Al<sub>2</sub>O<sub>3</sub>MgF<sub>2</sub> and multilayer HR coating using Al<sub>2</sub>O<sub>3</sub> and MgF<sub>2</sub> as a low refractive index layer and Si as high refractive index layer on GaAs substrates for optimization of coating conditions and HR coating using Al<sub>2</sub>O<sub>3</sub>\Si and MgF<sub>2</sub>\Si on diode laser chips. AR coating of diode laser is planned.
Conference Committee Involvement (3)
Second International Symposium on Semiconductor Materials and Devices (ISSMD-2)
31 January 2013 |
International Symposium on Semicomductor Materials and Devices (ISSMD 2011)