This invention relates to photolithographic techniques and more particularly to the use of such techniques for fabricating so-called microlenses.
The problem of efficiently coupling light from gallium arsenide injection lasers of stripe geometry into the cores of optical fibers is an important one whose solution is being actively sought. By carefully aligning the fiber core with respect to the stripe and by optimizing the air gap spacing between the laser and the fiber, efficiencies of about 8 percent have been achieved.
In "Power Coupling from GaAs Injection Laser into Optical Fibers" by L. G. Cohen, The Bell System Technical Journal, Vol. 51, (March 1972), pages 573-594, the use of a semicylindrical lens is proposed for increasing the power coupling efficiency between a gallium arsenide laser and an optical fiber. The only technique suggested in the cited article for fabricating the lens involves grinding an unclad cylindrical fiber in half.
Lenses with diameters and thicknesses on the order of a few micrometers (.mu.m), hereinafter referred to as microlenses, are required to optimize the aforementioned laser-to-fiber coupling efficiency. Such very small lenses cannot easily and accurately be fabricated by conventional polishing or molding techniques. Moreover, the handling, mounting and alignment of discrete microlenses in a laser-to-fiber system present formidable practical problems.