Low-loss wavelength-multiplexed optical scanners using volume Bragg gratings for transmit-receive lasercom systems

Low-loss no moving parts free-space wavelength-multiplexed optical scanner (W-MOS) modules for transmit-receive lasercom systems are proposed and experimentally demonstrated. The proposed scanners are realized using volume Bragg gratings stored in dichromated gelatin (DCG) coupled with high-speed wavelength selection such as by a fast tunable laser. The potential speed of these scanners is in the Gigahertz range using present-day state-of-the-art nanosecond tuning speed lasers. A 940-lines/mm volume Bragg grating stored in dichromated gelatin is used to demonstrate the scanners. Angular dispersion and diffraction efficiency of the volume Bragg grating used for demonstration are studied versus wavelength and angle of incidence to determine the free-space W-MOS angular scan and insertion loss, respectively. Experimental results show that a tunable bandwidth of 80 nm, centered at 1560 nm, delivers an angular scan of 6.25 deg. The study also indicates that an in-line scanner design realized using two similar Bragg gratings in DCG delivers 13.42 deg angular scan, which is more than double the angular scan available from the free-space W-MOS using single volume Bragg grating.