Semiconductor Laser Engineering, Reliability and Diagnostics: A Practical Approach to High Power and Single Mode Devices

Chapter 4

Optical strength engineering

4.1 Mirror facet properties – physical origins of failure

4.2 Mirror facet passivation and protection

4.2.1 Scope and effects

4.2.2 Facet passivation techniques

4.2.3 Facet protection techniques

4.3 Nonabsorbing mirror technologies

4.3.1 Concept

4.3.2 Window grown on facet

4.3.3 Quantum well intermixing processes

4.3.4 Bent waveguide

4.4 Further optical strength enhancement approaches

4.4.1 Current blocking mirrors and material optimization

4.4.2 Heat spreader layer; device mounting; and number of quantum wells

4.4.3 Mode spot widening techniques

References

Introduction

This chapter is organized as follows. First, we describe the properties of the laser facet after the cleavage procedure and then give the physical origins of facet degradation and failure. A concise yet comprehensive account follows on approaches and techniques to improve and enhance the optical strength in the bulk of the laser and at its mirror facets. This includes a discussion of most different facet passivation techniques, each with its own strengths and weaknesses, nonabsorbing mirror concepts, noninjecting or current blocking mirror technologies, heat spreader layers and laser chip mounting techniques, low optical confinement structures, and other mode spot widening approaches such as thin tapered active layer and flared lateral waveguide configurations.

4.1 Mirror facet properties – physical origins of failure

When a semiconductor laser facet is cleaved, a set of unsaturated ...