Single-mode instability in standing-wave lasers: The quantum cascade laser as a self-pumped parametric oscillator

We report the observation of a clear single-mode instability threshold in continuous-wave Fabry-Perot quantum cascade lasers (QCLs). The instability is characterized by the appearance of sidebands separated by tens of free spectral ranges (FSR) from the first lasing mode, at a pump current not much higher than the lasing threshold. As the current is increased, higher-order sidebands appear that preserve the initial spacing, and the spectra are suggestive of harmonically phase-locked waveforms. We present a theory of the instability that applies to all homogeneously broadened standing-wave lasers. The low instability threshold and the large sideband spacing can be explained by the combination of an unclamped, incoherent Lorentzian gain due to the population grating, and a coherent parametric gain caused by temporal population pulsations that changes the spectral gain line shape. The parametric term suppresses the gain of sidebands whose separation is much smaller than the reciprocal gain recovery time, while enhancing the gain of more distant sidebands. The large gain recovery frequency of the QCL compared to the FSR is essential to observe this parametric effect, which is responsible for the multiple-FSR sideband separation. We predict that by tuning the strength of the incoherent gain contribution, for example by engineering the modal overlap factors and the carrier diffusion, both amplitude-modulated (AM) or frequency-modulated emission can be achieved from QCLs. We provide initial evidence of an AM waveform emitted by a QCL with highly asymmetric facet reflectivities, thereby opening a promising route to ultrashort pulse generation in the mid-infrared. Together, the experiments and theory clarify a deep connection between parametric oscillation in optically pumped microresonators and the single-mode instability of lasers, tying together literature from the last 60 years.United States. Defense Advanced Research Projects Agency. Spectral Combs from UV to THz Program (Grant W31P4Q-16-1-0002)National Science Foundation (U.S.) (Awards ECCS-1230477, ECCS-1614631 and ECCS- 1614531)United States. Dept. of Defense. Assistant Secretary of Defense for Research & Engineering (Air Force Contracts FA8721-05-C- 0002 and No. FA8702-15-D-0001

High-Power, Low-Noise 1.5-Μm Slab-Coupled Optical Waveguide (Scow) Emitters: Physics, Devices, And Applications

We review the development of a new class of high-power, edge-emitting, semiconductor optical gain medium based on the slab-coupled optical waveguide (SCOW) concept. We restrict the scope to InP-based devices incorporating either InGaAsP or InGaAlAs quantum-well active regions and operating in the 1.5-μm -wavelength region. Key properties of the SCOW gain medium include large transverse optical mode dimensions (\u3e5 × 5 μm), ultralow optical confinement factor (Γ ∼ 0.25-1%), and small internal loss coefficient (α i ∼ 0.5cm -1). These properties have enabled the realization of 1) packaged Watt-class semiconductor optical amplifers (SOAs) having low-noise figure (4-5dB), 2) monolithic passively mode-locked lasers generating 0.25-W average output power, 3) external-cavity fiber-ring actively mode-locked lasers exhibiting residual timing jitter of \u3c10 fs (1 Hz to Nyquist), and 4) single-frequency external-cavity lasers producing 0.37-W output power with Gaussian (Lorentzian) linewidth of 35kHz (1.75kHz) and relative intensity noise (RIN) \u3c-160dB/Hz from 200kHz to 10 GHz. We provide an overview the SCOW design principles, describe simulation results that quantify the performance limitations due to confinement factor, linear optical loss mechanisms, and nonlinear two-photon absorption (TPA) loss, and review the SCOW devices that have been demonstrated and applications that these devices are expected to enable. © 2006 IEEE

Packaged 1.5- \mu m Quantum-Well SOA With 0.8-W Output Power and 5.5-dB Noise Figure

We report the demonstration of a lensed-fiber-pigtailed InGaAsP-InP quantum-well semiconductor optical amplifier based on the slab-coupled optical waveguide (SCOW) concept. At a 5-A bias current and a wavelength of 1540 nm, the packaged SCOW amplifier (SCOWA) exhibits a record 0.8-W saturation output power, 13.8-dB small-signal gain, 5.5-dB noise figure, and a maximum electrical-to-optical conversion efficiency of 11%. The estimated coupling efficiency between the large (5.6 times 7.5 mum), fundamental SCOWA mode and the lensed fibers (6.5-mum spot size) is 90%.Defense Advanced Research Projects Agency (Air Force Contract FA8721-05-C-0002

Coherently Combined Diode Laser Arrays and Stacks

We have coherently combined up to 7.2 W CW using an individually addressable 10-element-array of 960-nm slab-coupled optical waveguide lasers (SCOWLs). We are currently scaling the phase-locked output power to 100 W using SCOWL stacks.United States. Defense Advanced Research Projects Agency (Air Force Contract No. FA8721-05-C-0002

Coherent combination of slab-coupled optical waveguide lasers

A long-standing challenge for semiconductor lasers is scaling the optical power and brightness of many diode lasers by coherent beam combination. Because single-mode semiconductor lasers have limited power available from a single element, there is a strong motivation to coherently combine the outputs of many elements for applications including industrial lasers for materials processing, free space optical communications, and defense. Despite the fact that such a coherently-combined source is potentially the most efficient laser, coherent combination of semiconductor lasers is generally considered to be difficult, since precise phase control is required between elements. We describe our approach to coherent combination of semiconductor lasers. The Slab-Coupled Optical Waveguide Laser (SCOWL), invented at Lincoln Laboratory, is used as the single-mode diode laser element for coherent combination. With a 10-element SCOWL array, coherently combined output power as high as 7 W in continuous wave using an external cavity has been demonstrated, which is the highest output level achieved using a coherent array of semiconductor lasers. We are currently working on a related approach to scale the coherent power up to 100 W

Optics and Quantum Electronics

Contains table of contents for Section 3, reports on eighteen research projects and a list of publications.Defense Advanced Research Projects Agency Grant F49620-96-0126U.S. Air Force - Office of Scientific Research Grant F49620-98-1-0139Defense Advanced Research Projects AgencyJoint Services Electronics ProgramU.S. Air Force - Office of Scientific ResearchNational Science FoundationU.S. Navy - Office of Naval ResearchCharles S. Draper LaboratoryNational Science Foundation/MRSECJoint Services Electronics Program Grant DAAH04-95-1-0038U.S. Air Force - Office of Scientific Research Contract F49620-95-1-0221U.S. Navy - Office of Naval Research (MFEL) Contract N00014-91-J-1956U.S. Navy - Office of Naval Research (MFEL) Contract N000014-97-1-1066National Institutes of Health Grant 9RO1 EY11289-12National Institutes of Health Grant 1R01 CA75289-01U.S. Navy - Office of Naval Research/MFEL Contract N00014-94-1-071