title: Phase-locking and coherent power combining of broadband linearly chirped optical waves.
abstract: We propose, analyze and demonstrate the optoelectronic phase-locking of optical waves whose frequencies are chirped continuously and rapidly with time. The optical waves are derived from a common optoelectronic swept-frequency laser based on a semiconductor laser in a negative feedback loop, with a precisely linear frequency chirp of 400 GHz in 2 ms. In contrast to monochromatic waves, a differential delay between two linearly chirped optical waves results in a mutual frequency difference, and an acoustooptic frequency shifter is therefore used to phase-lock the two waves. We demonstrate and characterize homodyne and heterodyne optical phase-locked loops with rapidly chirped waves, and show the ability to precisely control the phase of the chirped optical waveform using a digital electronic oscillator. A loop bandwidth of ~ 60 kHz, and a residual phase error variance of < 0.01 rad(2) between the chirped waves is obtained. Further, we demonstrate the simultaneous phase-locking of two optical paths to a common master waveform, and the ability to electronically control the resultant two-element optical phased array. The results of this work enable coherent power combining of high-power fiber amplifiers-where a rapidly chirping seed laser reduces stimulated Brillouin scattering-and electronic beam steering of chirped optical waves.
authors.affiliation: Department of Applied Physics and Materials Science, California Institute of Technology, 1200 E. California Blvd. 136-93, Pasadena, CA 91125, USA. naresh@caltech.edu
authors.forename: Naresh
authors.initials: N
authors.lastname: Satyan
authors.forename: Arseny
authors.initials: A
authors.lastname: Vasilyev
authors.forename: George
authors.initials: G
authors.lastname: Rakuljic
authors.forename: Jeffrey O
authors.initials: JO
authors.lastname: White
authors.forename: Amnon
authors.initials: A
authors.lastname: Yariv