Electronically phase-locked laser systems
View Patent ↗Semiconductor diode lasers are phase-locked by direct current injection and combined to form a single coherent output beam. The optical power is amplified by use of fiber amplifiers. Electronically control of the optical phases of each emitter enables power efficient combining of output beams to be maintained under dynamic conditions.
1. A coherent laser system with enhanced optical power comprised of:
a single reference emitter producing a reference beam at an optical frequency f 1 ;
a multiplicity of tunable optical emitters producing a corresponding number of seed beams, each at an optical frequency f n changeable by an electrical drive signal;
a multiplicity of optical amplifiers producing a corresponding number of amplified beams;
a multiplicity of high-speed photodetectors;
a multiplicity of low-speed photodetectors;
a multiplicity of electronic feedback circuits generating electrical control signals;
whereby the tunable optical emitters and reference emitter are arranged such that each seed beam interferes with a portion of the reference beam to produce an optical beat signal at a frequency f n -f 1 on the high-speed photodetector, wherein the high-speed photodetector transforms the optical beat signal into a high-bandwidth intermediate electrical signal which is input to the electronic feedback circuit, this circuit generating the electrical drive signal which maintains the tunable optical emitter at the precise optical frequency f n , wherein the tunable optical emitter is followed in a series arrangement by an optical amplifier that increases the optical power of the tunable optical emitter, which is then followed by a low-speed photodetector that produces a low bandwidth intermediate electrical signal which is based on the pair wise interference characteristics between amplified beams, this low-bandwidth intermediate electrical signal input to the same electronic feedback circuit to generate the electrical drive signal sufficient to maintain the tunable optical emitter at the precise phase required for efficient coherent power addition of the multiplicity of amplified beams.
2. A coherent laser system in accordance with claim 1 , wherein the optical amplifiers are fiber amplifiers utilizing erbium, praseodymium and/or ytterbium doped active fiber pumped by semiconductor diode lasers.
3. A coherent laser system in accordance with claim 1 , wherein the optical amplifiers are Raman fiber amplifiers.
4. A coherent laser system in accordance with claim 1 , wherein the high-speed photodetectors have an electronic bandwidth in excess of 1 GHz and the low-speed photodetectors have an electronic bandwidth of 1 MHz or less.
5. A coherent laser system in accordance with claim 1 , wherein the tunable optical emitters are single frequency, DFB semiconductor diode lasers emitting in the 1.0-1.7 micron wavelength range with a drive signal tuning response of 0.1 to 10 GHz per mA.
6. A coherent laser system in accordance with claim 1 , wherein the electronic feedback circuit includes an electronic voltage controlled oscillator that generates a changeable frequency offset in the range of 0.1 to 100 GHz.
7. A system in accordance with claim 6 , wherein the frequency offset is identically equal to f n -f 1 .