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
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