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# Optimal Dielectric Layers for Diode Laser Facets

IP.com Disclosure Number: IPCOM000089419D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 27K

IBM

## Related People

McMullin, PG: AUTHOR

## Abstract

The optimal thickness and index of refraction for a protective dielectric coating for diode laser facets have been calculated assuming that the critical factor which results in facet damage failure at high output power is the field strength inside the laser at the facet.

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Optimal Dielectric Layers for Diode Laser Facets

The optimal thickness and index of refraction for a protective dielectric coating for diode laser facets have been calculated assuming that the critical factor which results in facet damage failure at high output power is the field strength inside the laser at the facet.

For simplicity of calculation, the plane wave model shown in the figure has been used for calculating the dielectric layer characteristics even though it is not rigorously applicable to the reflectivity of a slab waveguide. Region I represents the laser with a wave incident on the facet and having strength E(i). E(r) is the strength of the reflected wave, and n(1) is the index of retraction of the laser, which is 3.6 for GaAs. Region II represents the dielectric coating having an index of refraction n(2). E(o) is the strength of the transmitted wave in Region outside of the laser, where the index of retraction n(3) = 1 for air.

It is now assumed that the surface field E(s) = E(i) + E(r) cos Gamma should be minimized, where Gamma is the phase angle between the incident and reflected waves. E(s) is therefore minimum when cos Gamma = -1. It can be shown that when n/2/(2) < n(1)n(3), Gamma is always less than 90 Degrees regardless of the thickness d of the dielectric layer, while for n/2/(2) > n(1)n(3), Gamma = 180 Degrees when d = Lambda/4, where Lambda is the wavelength in the dielectric layer. Thus, cos Gamma = -1 and E(s) is minimum with a quarter-...