Direct Frequency Comb Cavity Ring-Down Spectroscopy Using Vernier Filtering.

We present direct frequency comb cavity ring-down spectroscopy with Vernier filtering as a straightforward approach to sensitive and multiplexed trace gas detection. The high finesse cavity acts both to extend the interaction length with the sample and as a spectral filter, alleviating the need for dispersive elements or an interferometer. In this demonstration, a free running interband cascade laser was used to generate a comb centered at 3.

Multi-Gb/s free-space laser communication at 4.6-μm wavelength using a high-speed, room-temperature, resonant-cavity infrared detector (RCID) and a quantum-cascade laser.

Research has shown that free-space laser communication systems may experience fewer outages due to atmospheric impairments such as haze, fog, clouds, and turbulence by operating at a longer wavelength in the mid-wave or long-wave infrared, if disadvantages such as lower-performance transceiver components may be overcome. Here we report a resonant cavity infrared detector (RCID) with 4.6-µm resonance wavelength that enables 20-dB larger link budget than has been reported previously for ∼ 5 Gb/s operation.

Detection of dimethyl methylphosphonate (DMMP) with an interband cascade laser sensor.

We demonstrate the sensitive detection of dimethyl methylphosphonate (DMMP, a hydrogen-bond (HB) basic phosphonate ester) using additional optical loss induced in an interband cascade laser with top optical cladding layer replaced by an exposed sensing window coated by a HB acidic sorbent layer. Thin coatings of the sorbents HCSFA2 and oapBPAF were deposited on the sensing window to allow reversible capture and concentration of DMMP for optical interrogation. Analyte levels down to 0.

Midwave resonant cavity infrared detectors (RCIDs) with suppressed background noise.

We report a resonant cavity infrared detector (RCID) with an InAsSb/InAs superlattice absorber with a thickness of only ≈ 100 nm, a 33-period GaAs/AlGaAs distributed Bragg reflector bottom mirror, and a Ge/SiO/Ge top mirror. At a low bias voltage of 150 mV, the external quantum efficiency (EQE) reaches 58% at the resonance wavelength λres ≈ 4.6 µm, with linewidth δλ = 19-27 nm.

Mid-infrared interband cascade light emitting devices grown on off-axis silicon substrates.

The high-quality growth of midwave infrared light emitters on silicon substrates will advance their incorporation into photonic integrated circuits, and also introduce manufacturing advantages over conventional devices grown on lattice-matched GaSb. Here we report interband cascade light emitting devices (ICLEDs) grown on 4 degree offcut silicon with 12% lattice mismatch. Four wafers produced functioning devices, with variations from wafer to wafer but uniform performance of devices from a given wafer.

Methane detection using an interband-cascade LED coupled to a hollow-core fiber.

Midwave infrared interband-cascade light-emitting devices (ICLEDs) have the potential to improve the selectivity, stability, and sensitivity of low-cost gas sensors. We demonstrate a broadband direct absorption CH sensor with an ICLED coupled to a plastic hollow-core fiber (1 m length, 1500 µm inner diameter). The sensor achieves a 1σ noise equivalent absorption of approximately 0.

Interband Cascade Photonic Integrated Circuits on Native III-V Chip.

We describe how a midwave infrared photonic integrated circuit (PIC) that combines lasers, detectors, passive waveguides, and other optical elements may be constructed on the native GaSb substrate of an interband cascade laser (ICL) structure. The active and passive building blocks may be used, for example, to fabricate an on-chip chemical detection system with a passive sensing waveguide that evanescently couples to an ambient sample gas. A variety of highly compact architectures are described, some of which incorporate both the sensing waveguide and detector into a laser cavity defined by two high-reflectivity cleaved facets.

Near-infrared frequency comb generation in mid-infrared interband cascade lasers.

The interband cascade laser (ICL) is an ideal candidate for low-power mid-infrared frequency comb spectroscopy. In this work, we demonstrate that its intracavity second-order optical nonlinearity induces a coherent up-conversion of the generated mid-infrared light to the near-infrared through second-harmonic and sum-frequency generation. At 1.

Mid-infrared dual-comb spectroscopy with interband cascade lasers.

Two semiconductor optical frequency combs, consuming less than 1 W of electrical power, are used to demonstrate high-sensitivity mid-infrared dual-comb spectroscopy in the important 3-4 μm spectral region. The devices are 4 mm long by 4 μm wide, and each emits 8 mW of average optical power. The spectroscopic sensing performance is demonstrated by measurements of methane and hydrogen chloride with optical multi-pass cell sensitivity enhancement.

Resonant-cavity infrared detector with five-quantum-well absorber and 34% external quantum efficiency at 4 μm.

We report resonant-cavity infrared detectors with 34% external quantum efficiency at room temperature at the resonant wavelength of 4.0 μm, even though the absorber consists of only five quantum wells with a total thickness of 50 nm. The full width at half maximum (FWHM) linewidth is 46 nm, and the peak absorption is enhanced by nearly a factor of 30 over that for a single pass through the absorber.

Two-dimensional plasmonic grating for increased quantum efficiency in midwave infrared nBn detectors with thin absorbers.

We demonstrate a strategy for increasing the operating temperatures of nBn midwave infrared (MWIR) focal plane arrays, based on the use of two-dimensional plasmonic gratings to enhance the quantum efficiency (QE) of structures with very thin absorbers. Reducing the absorber volume correspondingly reduces the dark current in a diffusion-limited photodiode, while light trapping mediated by the plasmonic grating increases the net absorbance to maintain high QE. The plasmonically enhanced nBn MWIR sensors with absorber thicknesses of only 0.

Passively mode-locked interband cascade optical frequency combs.

Since their inception, optical frequency combs have transformed a broad range of technical and scientific disciplines, spanning time keeping to navigation. Recently, dual comb spectroscopy has emerged as an attractive alternative to traditional Fourier transform spectroscopy, since it offers higher measurement sensitivity in a fraction of the time. Midwave infrared (mid-IR) frequency combs are especially promising as an effective means for probing the strong fundamental absorption lines of numerous chemical and biological agents.

Compact photoacoustic module for methane detection incorporating interband cascade light emitting device.

A photoacoustic module (PAM) for methane detection was developed by combining a novel 3.2 μm interband cascade light emitting device (ICLED) with a compact differential photoacoustic cell. The ICLED with a 22-stage interband cascade active core emitted a collimated power of ~700 μW.

Spectral narrowing and stabilization of interband cascade laser by volume Bragg grating.

A volume Bragg grating recorded in photo-thermo-refractive glass was used to spectrally lock the emission from an 18-μm-wide interband cascade laser ridge to a wavelength of 3.12 μm. The spectral width of emission into the resonant mode is narrowed by more than 300 times, and the thermal wavelength shift is reduced by 60 times.

Multi-species sensing using multi-mode absorption spectroscopy with mid-infrared interband cascade lasers.

The application of an interband cascade laser, ICL, to multi-mode absorption spectroscopy, MUMAS, in the mid-infrared region is reported. Measurements of individual mode linewidths of the ICL, derived from the pressure dependence of lineshapes in MUMAS signatures of single, isolated, lines in the spectrum of HCl, were found to be in the range 10-80 MHz. Multi-line spectra of methane were recorded using spectrally limited bandwidths, of approximate width 27 cm, defined by an interference filter, and consist of approximately 80 modes at spectral locations spanning the 100 cm bandwidth of the ICL output.

Interband cascade lasers with long lifetimes.

Narrow-ridge interband cascade lasers were subjected to accelerated aging. The aging curves were statistically evaluated by a log-normal distribution of the failure time, and by the mixed effects of the degradation parameters. Based on 10,000 h of output power trend data for lasers operating at 90°C and the maximum cw power, an unexpectedly long lifetime is predicted.

Gain and loss as a function of current density and temperature in interband cascade lasers.

We characterize the internal efficiency, internal loss, and optical gain versus current density in 7-stage interband cascade lasers operating at λ=3.1 and 3.45 μm using a cavity-length study of the external differential quantum efficiency (EDQE) and threshold current density at temperatures between 300 and 345 K.

Mid-infrared multi-mode absorption spectroscopy using interband cascade lasers for multi-species sensing.

An interband cascade laser (ICL) operating at 3.7 μm has been used to perform multimode absorption spectroscopy, MUMAS, at scan rates up to 10 kHz. Line widths of individual modes in the range 10-80 MHz were derived from isolated lines in the MUMAS signatures of HCl.

High-power continuous-wave interband cascade lasers with 10 active stages.

We report the pulsed and continuous wave (cw) performance of 10-stage interband cascade lasers (ICLs) emitting at both λ ≈3.2 μm and λ ≈3.45 μm.

Pulsed and CW performance of 7-stage interband cascade lasers.

We report a narrow-ridge interband cascade laser emitting at λ ≈3.5 μm that produces up to 592 mW of cw power with a wallplug efficiency of 10.1% and beam quality factor of M(2) = 3.

High-power room-temperature continuous-wave mid-infrared interband cascade lasers.

We demonstrate cw output powers >290 mW into a nearly diffraction-limited (M² ≈2.2) output beam from an interband cascade laser operating at λ = 3.6-3.

Continuous-wave interband cascade lasers operating above room temperature at λ = 4.7-5.6 μm.

We have substantially improved the performance of interband cascade lasers emitting at λ = 4.7 and 5.6 μm, by applying the recently-pioneered approach of heavily doping the injector regions to rebalance the electron and hole concentrations in the active quantum wells.

Rebalancing of internally generated carriers for mid-infrared interband cascade lasers with very low power consumption.

The interband cascade laser differs from any other class of semiconductor laser, conventional or cascaded, in that most of the carriers producing population inversion are generated internally, at semimetallic interfaces within each stage of the active region. Here we present simulations demonstrating that all previous interband cascade laser performance has suffered from a significant imbalance of electron and hole densities in the active wells. We further confirm experimentally that correcting this imbalance with relatively heavy n-type doping in the electron injectors substantially reduces the threshold current and power densities relative to all earlier devices.

Performance characteristics of a continuous-wave compact widely tunable external cavity interband cascade lasers.

We present the design and performance of a novel broadly tunable continuous-wave external-cavity interband cascade laser (ECicL). The ICL die growth and fabrication, as well as the external cavity geometry are described. Tuning across the 3.