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Coupling a Double Heterostructure Injection Laser to an Optical Fiber Waveguide

IP.com Disclosure Number: IPCOM000088985D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 99K

Publishing Venue

IBM

Related People

Comerford, LD: AUTHOR [+2]

Abstract

The illustrated devices exploit the evanescent field in a double heterostructure injection laser to effect direct coupling to an optical fiber waveguide. The laser substrate is thinned across the lasing region so that the evanescent field of the laser radiation is able to penetrate into the optical fiber waveguide. Phase matching of the laser light and the light in the waveguide is effected by canting the axis of the fiber with respect to the propagation axis of the laser cavity.

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Coupling a Double Heterostructure Injection Laser to an Optical Fiber Waveguide

The illustrated devices exploit the evanescent field in a double heterostructure injection laser to effect direct coupling to an optical fiber waveguide. The laser substrate is thinned across the lasing region so that the evanescent field of the laser radiation is able to penetrate into the optical fiber waveguide. Phase matching of the laser light and the light in the waveguide is effected by canting the axis of the fiber with respect to the propagation axis of the laser cavity.

The fundamental concept is best illustrated with the embodiment of Figs. 1 and 1A. The angle Theta between the normal-to-the-lasing axis and the axis of the optical waveguide is given by the expression Cos Theta = n(f) over n(e)

where n(e) = refractive index of the lasing material, and n(f) = refractive index of the optical waveguide.

In this structure the cavity mirrors are made fully reflective, since all radiation exits by evanescent coupling. These surfaces are overcoated with a reflective metal (and possibly a dielectric layer). The waveguide has a lower refractive index than the effective mode index of the laser. Phase matching is achieved by canting the fiber as shown.

The strength of the evanescent coupling can be altered by adjusting the spacing "d" between the active layer and the waveguide. This is most conveniently achieved by controlling the thickness of the buffer layer.

In the embodiment of Fig...