COMPARISON BETWEEN CONTINUOUS AND DISCRETE SUBWAVELENGTH GRATING STRUCTURES FOR ANTIREFLECTION SURFACES

Both continuously tapered and discrete multilevel subwavelength gratin g structures are examined to determine the optimum method of designing antireflection surfaces. Continuously tapered gratings are designed w ith use of the optimal Klopfenstein graded index technique, while disc rete multilevel stair-step gratings are designed with use of the Tsche byscheff quarter-wave synthesis technique. It is shown that a continuo us design is always deeper than a discrete design. It is determined th at since a subwavelength grating structure produces a bandpass surface , the high-pass (short-wave) performance of the continuous taper desig n cannot be realized. Therefore the discrete method of designing antir eflection subwavelength gratings will always produce a shallower spati al profile or a smaller aspect ratio for any specified maximum reflect ion threshold level over a given passband. (C) 1996 Optical Society of America