Abstract

The binary phase gratings (BPGs) for generating multispot array¹ (called Dammann grating) are promising optical fan-out elements for applications including fiber-optic star couplers, free-space optical interconnections, and multiple image arrays. The conventional BPGs, however, have been so far mainly developed for odd numbered spot array generation because of its simplicity of design algorithm.² We present a novel method of designing the BPGs for generating selective order missing (SOM) spot arrays including odd numbered, even numbered³, and irregularly spaced spot array. Gradient descent rule with variable target values in the merit function is introduced as a nonlinear optimization algorithm. The uniformity of the SOM array is very high such that the standard deviation of the beam array intensity is less than 10⁻⁶. It is also found that when the structure of the grating is symmetric in a period, it should be anti-symmetric in each half period in order to get an even numbered spot array, and vice versa. The designed BPGs are also experimentally demonstrated using the conventional e-beam lithographic technique on a quartz substrate. The SOM spot array may be applicable to the digital optical processing systems using S-SEED and smart pixel devices.

© 1993 Optical Society of America