Abstract
Phase control is crucial to the operation of coherent beam combining systems, whether for laser radar or high-power beam combining. We have recently demonstrated a design for a multi-aperture, coherently combined, synchronized- and phased-array slow light laser radar (SLIDAR) that is capable of scanning in two dimensions with dynamic group delay compensation. Here we describe in detail the optical phase locking system used in the design. The phase locking system achieves an estimated Strehl ratio of 0.8, and signals from multiple emitting apertures are phase locked simultaneously to within π/5 radians (1/10 wave) after propagation through 2.2 km of single-mode fiber per channel. Phase locking performance is maintained even as two independent slow light mechanisms are utilized simultaneously.
Highlights
Optical systems that make use of coherent beam combining, including multi-aperture laser radar systems such as ours, depend critically upon having coherent, properly phased signals from each emitter to achieve constructive interference at the target [1,2,3,4,5,6,7]
The theoretically-predicted Strehl ratio due to the RMS residual phase error, according to Eq (16), is about 0.8, comparable to results obtained in several other optical phase locking systems [20,21]
dispersion-compensating fiber (DCF), which is used only for dispersive slow light and not stimulated Brillouin scattering (SBS) slow light, sees the same phase locking performance as unpumped dispersion-shifted fiber (DSF); further, the performance does not vary with wavelength
Summary
Optical systems that make use of coherent beam combining, including multi-aperture laser radar systems such as ours, depend critically upon having coherent, properly phased signals from each emitter to achieve constructive interference at the target [1,2,3,4,5,6,7]. In a multi-aperture laser radar, optical fields from multiple small emitters propagate to a target in the far field, where they overlap and combine coherently, allowing agile beam steering. Slow light can enhance the transverse and longitudinal resolution of a short-pulse, multiaperture, coherently combined laser radar system, as we have recently demonstrated with our SLIDAR (slow-light laser radar) system [8,9,10]. The use of tunable slow-light delay lines in a multi-aperture short-pulse laser radar overcomes the fundamental limitation of group delay mismatch during wide-angle beam steering. A novel fast 2nπ phase snapback circuit overcomes the problem of finite phase actuation range
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
