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

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

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

High-coherence semiconductor lasers based on integral high-Q resonators in hybrid Si/III-V platforms

The semiconductor laser (SCL) is the principal light source powering the worldwide optical fiber network. The ever-increasing demand for data is causing the network to migrate to phase-coherent modulation formats, which place strict requirements on the temporal coherence of the light source that no longer can be met by current SCLs. This failure can be traced directly to the canonical laser design, in which photons are both generated and stored in the same, optically lossy, III-V material. This leads to an excessive and large amount of noisy spontaneous emission commingling with the laser mode, thereby degrading its coherence. High losses also decrease the amount of stored optical energy in the laser cavity, magnifying the effect of each individual spontaneous emission event on the phase of the laser field. Here, we propose a new design paradigm for the SCL. The keys to this paradigm are the deliberate removal of stored optical energy from the lossy III-V material by concentrating it in a passive, low-loss material and the incorporation of a very high-Q resonator as an integral (i.e., not externally coupled) part of the laser cavity. We demonstrate an SCL with a spectral linewidth of 18 kHz in the telecom band around 1.55 μm, achieved using a single-mode silicon resonator with Q of 10^6

Swept-frequency semiconductor laser coupled to microfabricated biomolecular sensor and methods related thereto

An optoelectronic swept-frequency semiconductor laser coupled to a microfabricated optical biomolecular sensor with integrated resonator and waveguide and methods related thereto are described. Biomolecular sensors with optical resonator microfabricated with integrated waveguide operation can be in a microfluidic flow cell

Compressive sensing optical coherence tomography using randomly accessible lasers

We propose and demonstrate a novel a compressive sensing swept source optical coherence tomography (SSOCT) system that enables high speed images to be taken while maintaining the high resolution offered from a large bandwidth sweep. Conventional SSOCT systems sweep the optical frequency of a laser ω(t) to determine the depth of the reflectors at a given lateral location. A scatterer located at delay τ appears as a sinusoid cos (ω(t)τ ) at the photodetector. The finite optical chirp rate and the speed of analog to digital and digital to analog converters limit the acquisition rate of an axial scan. The proposed acquisition modality enables much faster image acquisition rates by interrogating the beat signal at randomly selected optical frequencies while preserving resolution and depth of field. The system utilizes a randomly accessible laser, a modulated grating Y-branch laser, to sample the interference pattern from a scene at randomly selected optical frequencies over an optical bandwidth of 5 THz , corresponding to a resolution of 30 μm in air. The depth profile is then reconstructed using an l_1 minimization algorithm with a LASSO constraint. Signal-dependent noise sources, shot noise and phase noise, are analyzed and taken into consideration during the recovery. Redundant dictionaries are used to improve the reconstruction of the depth profile. A compression by a factor of 10 for sparse targets up to a depth of 15 mm in noisy environments is shown

A linearly chirped seed suppresses SBS in high-power fiber amplifiers, allows coherent combination, and enables long delivery fibers

When seeding a high power fiber amplifier with a frequency-chirped seed, the backward Brillouin scattering can be kept at the spontaneous level because the coherent laser/Stokes interaction is interrupted. Operating a conventional vertical cavity surface-emitting diode laser in an optoelectronic feedback loop can yield a linear frequency chirp of ~1016 Hz/s at a constant output power. The simple and deterministic variation of phase with time preserves temporal coherence, in the sense that it is straightforward to coherently combine multiple amplifiers despite a large length mismatch. The seed bandwidth as seen by the counter-propagating SBS is large, and also increases linearly with fiber length, resulting in a nearly-length-independent SBS threshold. Experimental results at the 600W level will be presented. The impact of a chirped seed on multimode instability is also addressed theoretically

Using a linearly chirped seed suppresses SBS in high-power fiber amplifiers, allows coherent combination, and enables long delivery fibers

When seeding a high power fiber amplifier with a frequency-chirped seed, the backward Brillouin scattering can be kept at the spontaneous level because the coherent laser/Stokes interaction is interrupted. Operating a conventional vertical cavity surface-emitting diode laser in an optoelectronic feedback loop can yield a linear frequency chirp of ~1016 Hz/s at a constant output power. The simple and deterministic variation of phase with time preserves temporal coherence, in the sense that it is straightforward to coherently combine multiple amplifiers despite a large length mismatch. The seed bandwidth as seen by the counter-propagating SBS is large, and also increases linearly with fiber length, resulting in a nearly-length-independent SBS threshold. Experimental results at the 600W level will be presented. The impact of a chirped seed on multimode instability is also addressed theoretically

A linearly chirped seed suppresses SBS in high-power fiber amplifiers, allows coherent combination, and enables long delivery fibers

When seeding a high power fiber amplifier with a frequency-chirped seed, the backward Brillouin scattering can be kept at the spontaneous level because the coherent laser/Stokes interaction is interrupted. Operating a conventional vertical cavity surface-emitting diode laser in an optoelectronic feedback loop can yield a linear frequency chirp of ~1016 Hz/s at a constant output power. The simple and deterministic variation of phase with time preserves temporal coherence, in the sense that it is straightforward to coherently combine multiple amplifiers despite a large length mismatch. The seed bandwidth as seen by the counter-propagating SBS is large, and also increases linearly with fiber length, resulting in a nearly-length-independent SBS threshold. Experimental results at the 600W level will be presented. The impact of a chirped seed on multimode instability is also addressed theoretically