1D beam steerer operates at MHz speeds, will go much higher

A high-speed laser-beam steering technique developed at Lincoln Laboratory (Lexington, MA) currently can steer at a 40 MHz speed and has the potential to reach gigahertz steering speeds. The one-dimensional steerer is based on a six-element optical phased array and subsequent coherent beam combining. The total optical output power of the device is now 396 mW and can be scaled to multiwatt output. A stochastic-parallel-gradient-descent (SPGD) algorithm is used to maintain the phase-locking, keeping the on-axis intensity high.

The output from a narrow-linewidth Nd:YAG laser is split and sent to six commercial lithium niobate phase modulators (with phase adjusted by varying the current) and then amplified by an array of diffraction-limited slab-coupled-waveguide semiconductor amplifiers. The SPGD algorithm, which is controlled by real-time Linux software, dithers the phase of the modulators at 1 kHz to obtain the phase corrections needed to maximize the on-axis intensity. A movable fiber-coupled (6.25-μm-diameter fiber tip) high-speed indium gallium arsenide detector is used to sample and measure the beam-steering performance at high speeds. The experimental full-width at half-maximum (FWHM) central lobe width was measured to be 565 μrad (only 5% above the ideal); the steering range was 0.24°, limited by the array diffraction-lobe spacing. Contact W. Ronny Huang at[email protected].