Coherence Cloning Using Semiconductor Laser Optical Phase-Lock Loops

We demonstrate the concept of coherence cloning where the coherence properties of a high-quality spectrally stabilized fiber laser are transferred to a commercially available high-power DFB semiconductor laser (SCL) using an optical phase-lock loop. The lineshapes and frequency noise spectra of the fiber laser and the free-running and phase-locked SCL are measured and compared. The bandwidth of coherence cloning is limited by physical factors such as the laser frequency modulation response and the loop propagation delay. The effect of this limited bandwidth on the laser field and on self-heterodyne interferometric measurements are analyzed

Sideband locking of a single-section semiconductor distributed-feedback laser in an optical phase-lock loop

The bandwidth and performance of optical phase-lock loops (OPLLs) using single-section semiconductor lasers (SCLs) are severely limited by the nonuniform frequency modulation response of the lasers. It is demonstrated that this restriction is eliminated by the sideband locking of a single-section distributed-feedback SCL to a master laser in a heterodyne OPLL, thus enabling a delay-limited loop bandwidth. The lineshape of the phase-locked SCL output is characterized using a delayed self-heterodyne measurement

Phase noise reduction of a semiconductor laser in a composite optical phase-locked loop

The bandwidth and residual phase noise of optical phaselocked loops (OPLLs) using semiconductor lasers are typically constrained by the nonuniform frequency modulation response of the laser, limiting their usefulness in a number of applications. It is shown in this work that additional feedback control using an optical phase modulator improves the coherence between the master and slave lasers in the OPLL by achieving bandwidths determined only by the propagation delay in the loop. A phase noise reduction by more than a factor of two is demonstrated in a proof-of-concept experiment using a commercial distributed feedback semiconductor laser

Coherent power combination of semiconductor lasers using optical phase-lock loops

Heterodyne optical phase-lock loops (OPLLs) enable the precise electronic control over the frequency and phase of a semiconductor laser (SCL) locked to a ldquomasterrdquo reference laser. One of the more interesting applications of OPLLs is the creation of coherent arrays by locking a number of ldquoslaverdquo SCLs to a common master laser. In this paper, we demonstrate the coherent power combination of various high-power semiconductor lasers using OPLLs in both the filled-aperture and tiled-aperture configurations. We further demonstrate the electronic control over the phase of each individual SCL using a voltage-controlled oscillator. It is feasible to combine a large number of SCLs using this approach, leading to compact, efficient, and cost-effective high-power and high-radiance optical sources

Precise control of broadband frequency chirps using optoelectronic feedback

We demonstrate the generation of wideband frequency sweeps using a semiconductor laser in an optoelectronic feedback loop. The rate and shape of the optical frequency sweep is locked to and determined by the frequency of a reference electronic signal, leading to an agile, high coherence swept-frequency source for laser ranging and 3-D imaging applications. Using a reference signal of constant frequency, a transformlimited linear sweep of 100 GHz in 1 ms is achieved, and real-time ranging with a spatial resolution of 1.5 mm is demonstrated. Further, arbitrary frequency sweeps can be achieved by tuning the frequency of the input electronic signal. Broadband quadratic and exponential optical frequency sweeps are demonstrated using this technique

Coherent beam combining with multilevel optical phase-locked loops

Coherent beam combining (CBC) technology holds the promise of enabling laser systems with very high power and near-ideal beam quality. We propose and demonstrate a novel servo system composed of multilevel optical phase lock loops. This servo system is based on entirely electronic components and consequently can be considerably more compact and less expensive compared to servo systems made of optical phase/frequency shifters. We have also characterized the noise of a 1064 nm Yb-doped fiber amplifier to determine its effect on the CBC and studied theoretically the efficiency of combining a large array of beams with the filled-aperture implementation. In a proof-of-concept experiment we have combined two 100 mW 1064 nm semiconductor lasers with an efficiency of 94%

Coherent power combination of two Master-oscillator-power-amplifier (MOPA) semiconductor lasers using optical phase lock loops

Using heterodyne Optical Phase-Locked Loops (OPLLs), two 1W high power 1550 nm master-oscillator-power-amplifier (MOPA) semiconductor lasers operating as current controlled oscillators are phase-locked to a 1 mW reference laser. The signals of the two MOPAs are then coherently combined and their mutual coherence is studied. In each OPLL, the acquisition range is increased to +/-1.1GHz with the help of an aided- acquisition circuit. Control of the phase of a single slave MOPA is demonstrated using a RF phase shifter. The differential phase error between two MOPAs locked to the common reference laser is typically 22 degrees

Multiple source frequency-modulated continuous-wave optical reflectometry: theory and experiment

We propose and demonstrate a novel approach to increase the effective bandwidth of a frequencymodulated continuous-wave (FMCW) ranging system. This is achieved by algorithmically stitching together the swept spectra of separate laser sources. The result is an improvement in the range resolution proportional to the increase in the swept-frequency range. An analysis of this system as well as the outline of the stitching algorithm are presented. Using three distinct swept-frequency optical waveforms, we experimentally demonstrate a threefold improvement in the range resolution of a three-sweep approach over the conventional FMCW method