Continuous-wave Interband Cascade Laser Research Articles

Continuous wave interband cascade lasers near 13 μm

We report the demonstration of continuous-wave interband cascade lasers (ICLs) near 13 μm. The attained lasing wavelength of 13.2 μm at 92 K stands as the longest cw emission wavelength ever reported for III-V interband lasers. This achievement is attributed to the adoption of an innovative quantum well (QW) active region comprising strained InAs0.5P0.5 layers in contrast to the commonly used “W” QW active region, showing the potential of the modified QW active region with InAsP layers in improving device performance and extending wavelength coverage of ICLs.

A Prototype of ppbv-Level Midinfrared CO2 Sensor for Potential Application in Deep-Sea Natural Gas Hydrate Exploration

For deep-sea natural gas hydrate (NGH) exploration, the highly sensitive detection of dissolved gas in seawater near the seabed is important. A prototype of a midinfrared (MIR) carbon dioxide (CO2) sensing system based on a wavelength modulation spectroscopy (WMS) technique is developed using a thermoelectrically cooled continuous-wave interband cascade laser at 4319.2 nm and an optical multipass cell ( $20\times 7.6\times 10.5$ cm3) with a 24-m effective optical path. A MIR HgCdTe detector and a lock-in amplifier are used to detect and demodulate light source signals. The reported sensing system utilizes a linear optical structure to achieve a highly precision detection performance. The minimum detection limit (MDL) of 48.2 parts per billion (ppb) (at 74 s) at a gas pressure of 20 Torr for the 2f-WMS technique was achieved. The MDL was improved to 38.6 ppbv (at 89 s) at a gas pressure of 20 Torr using the 2f/1f-WMS technique, which reduces the effects of laser power drift. The CO2 sensor was deployed with a gas–liquid separator for CO2 detection in the gas extracted from water. Results validated the reported sensor system’s potential application to deep-sea NGH exploration.

Linewidth broadening factor of an interband cascade laser

This work reports the linewidth broadening factor (LBF) of a continuous-wave interband cascade laser operated both below and above threshold. Using the Hakki-Paoli method, the below-threshold LBFs around the gain peak are determined to be in the range of 1.1–1.4, where the thermal effect is carefully removed. Employing the self-mixing interferometry technique, the above-threshold LBFs are measured to be around 2.2, which do not increase with increasing pump current.

Relative intensity noise of a continuous-wave interband cascade laser at room temperature.

This Letter investigates the relative intensity noise (RIN) characteristics of a continuous-wave 3.4μm interband cascade laser operated at room temperature. The RIN decreases with an increasing pump current and reaches down to -130 dB/Hz at a frequency of 450MHz. In addition, it is proved that the current noise of the laser pump source dominates the RIN for frequencies below 100MHz. The measured RIN is quantitatively in agreement with the theoretical analysis, from which the gain coefficient and the transparent carrier number of the laser are extracted.

ICL-based mid-infrared carbon dioxide sensor system for deep-sea natural gas hydrate exploration.

For deep-sea natural gas hydrate exploration, highly sensitive detection of the dissolved gas in seawater near the seabed is significant because it requires the sensor system to be small in size, low in power consumption, and high in sensitivity. A mid-infrared sensor system was developed to detect dissolved carbon dioxide (CO2) in sea-water, while employing a 4319 nm continuous-wave interband cascade laser (ICL) and a multi-pass gas cell (MPGC) with a 29.8 m optical path length. A compact rectilinear optical structure was proposed by using the free-space-emitting ICL and tunable laser absorption spectroscopy (TLAS). This leads to a minimized sensor size and a simple optical alignment for deep-sea operation. A strong CO2 absorption line, located at 2315.19 cm-1 and a weak 2315.28 cm-1 line and at a low pressure of 40 Torr, was targeted for low- and high-concentration CO2 detection within a concentration range of 0-1000 parts per billion by volume (ppbv) and 0-40 parts per million by volume (ppmv), respectively. The limit of detection (LoD) was assessed to be 0.72 ppbv at an averaging time of 2 s, and the response time was measured to be ~30 s at a flow rate of ~180 standard cubic centimeters per minute (sccm). Deployment of the CO2 sensor combined with a gas-liquid separator was carried out for the CO2 detection in the gas extracted from water, which validated the reported sensor system's potential application for deep-sea natural gas hydrate exploration.

Room-temperature continuous-wave interband cascade laser emitting at 3.45 μm**Project supported by the Major Program of the National Natural Science Foundation of China (Grant No. 61790580), the National Natural Science Foundation of China (Grant No. 61435012), and the National Basic Research Program of China (Grant No. 2014CB643903).

We report a type-II GaSb-based interband cascade laser operating a continuous wave at room temperature. The cascade region of interband cascade laser was designed using the ‘W’ configuration of the active quantum wells and the ‘Carrier Rebalancing’ method in the electron injector. The devices were processed into narrow ridges and mounted epitaxial side down on a copper heat sink. The 25-μm-wide, 3-mm-long ridge without coated facets generated 41.4 mW of continuous wave output power at T = 15 °C. And a low threshold current density of 267 A/cm2 is achieved. The emission wavelength of the ICL is 3452.3 nm at 0.5 A.

A portable low-power QEPAS-based CO2 isotope sensor using a fiber-coupled interband cascade laser

Current field and medical applications demand better quantification of CO2 isotopic ratios with high sensitivity, fast time-response, portable instrument size, and low power consumption. We report such a CO2 isotope sensor using quartz-enhanced photoacoustic spectroscopy (QEPAS) with a continuous-wave interband cascade laser (ICL). The ICL emitting at 4.35μm with a low drive current (35–60mA) and optical power (<2.6mW) covered the P(43) and P(44) lines of 12CO2 and the R(18) line of 13CO2 with a single current scan. The ICL radiation was coupled into a solid-core (100-μm core diameter) indium fluoride optical fiber with a coupling efficiency of 88%. We successfully delivered the single-mode laser beam from the fiber output into the off-beam QEPAS spectrophone enclosed in a compact gas cell. The generated photoacoustic signal was acquired and analyzed by a digital lock-in amplifier to obtain its second harmonic (2f) component. Our sensor is capable of analyzing the CO2 isotopic ratio with an average precision of <1‰, which fulfills the precision requirements of most medical and field applications.

Mid-infrared dual-gas sensor for simultaneous detection of methane and ethane using a single continuous-wave interband cascade laser.

A continuous-wave (CW) interband cascade laser (ICL) based mid-infrared sensor system was demonstrated for simultaneous detection of atmospheric methane (CH4) and ethane (C2H6). A 3.337 µm CW ICL with an emitting wavenumber range of 2996.0-3001.5 cm-1 was used to simultaneously target two absorption lines, C2H6 at 2996.88 cm-1 and CH4 at 2999.06 cm-1, respectively. The sensor performance was first evaluated for single-gas detection by only targeting the absorption line of one gas species. Allan deviations of 11.2 parts per billion in volume (ppbv) for CH4 and 1.86 ppbv for C2H6 with an averaging time of 3.4 s were achieved for the detection of these two gases. Dual-gas detection was realized by using a long-term scan signal to target both CH4 and C2H6 lines. The Allan deviations increased slightly to 17.4 ppbv for CH4 and 2.4 ppbv for C2H6 with an averaging time of 4.6 s due to laser temperature and power drift caused by long-term wavelength scanning. Measurements for both indoor and outdoor concentration changes of CH4 and C2H6 were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost compared to two separate sensor systems.

Ppb-level mid-infrared ethane detection based on three measurement schemes using a 3.34-μm continuous-wave interband cascade laser

A ppb-level mid-infrared ethane (C2H6) sensor was developed using a continuous-wave, thermoelectrically cooled, distributed feedback interband cascade laser emitting at 3.34 μm and a miniature dense patterned multipass gas cell with a 54.6-m optical path length. The performance of the sensor was investigated using two different techniques based on the tunable interband cascade laser: direct absorption spectroscopy (DAS) and second-harmonic wavelength modulation spectroscopy (2f-WMS). Three measurement schemes, DAS, WMS and quasi-simultaneous DAS and WMS, were realized based on the same optical sensor core. A detection limit of ~7.92 ppbv with a precision of ±30 ppbv for the separate DAS scheme with an averaging time of 1 s and a detection limit of ~1.19 ppbv with a precision of about ±4 ppbv for the separate WMS scheme with a 4-s averaging time were achieved. An Allan–Werle variance analysis indicated that the precisions can be further improved to 777 pptv @ 166 s for the separate DAS scheme and 269 pptv @ 108 s for the WMS scheme, respectively. For the quasi-simultaneous DAS and WMS scheme, both the 2f signal and the direct absorption signal were simultaneously extracted using a LabVIEW platform, and four C2H6 samples (0, 30, 60 and 90 ppbv with nitrogen as the balance gas) were used as the target gases to assess the sensor performance. A detailed comparison of the three measurement schemes is reported. Atmospheric C2H6 measurements on the Rice University campus and a field test at a compressed natural gas station in Houston, TX, were conducted to evaluate the performance of the sensor system as a robust and reliable field-deployable sensor system.

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. The slope efficiency is higher while the external differential quantum efficiency per stage remains about the same when comparison is made to earlier results for 7-stage ICLs with similar carrier-rebalanced designs. At T = 25°C, an 18-μm-wide ridge with 4.5 mm cavity length and high-reflection/anti-reflection coatings emits up to 464 mW of cw output power with beam quality factor M(2) = 1.9, for higher brightness than has ever been reported previously for an ICL. When the cavity length is reduced to 1 mm, both the 10-stage and 7-stage devices reach 18% cw wallplug efficiency at T = 25°C.

High-power, high-brightness continuous-wave interband cascade lasers with tapered ridges

We report tapered-ridge mid-infrared (λ = 3.75 μm) interband cascade lasers emitting up to 403 mW of continuous wave output power at T = 25 °C, with beam quality characterized by M2 = 2.3. One index-guided tapered structure consisted of a single 4-mm-long section with ridge width varying linearly from 5 μm to 63 μm. Another device that combined a narrow ridge of uniform width with a tapered section produced slightly lower maximum output power and brightness.

Continuous-wave interband cascade lasers operating above room temperature at λ = 47-56 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. Ridges of ≈10 μm width, 4 mm length, and high-reflectivity back facets achieve maximum continuous wave operating temperatures of 60°C and 48°C, respectively. The threshold power density of ≈1 kW/cm2 at T = 25°C is over an order of magnitude lower than for state-of-the-art quantum cascade lasers emitting in this spectral range.

Materials Evaluation

Current field and medical applications demand better quantification of CO2 isotopic ratios with high sensitivity, fast time-response, portable instrument size, and low power consumption. We report such a CO2 isotope sensor using quartz-enhanced photoacoustic spectroscopy (QEPAS) with a continuous-wave interband cascade laser (ICL). The ICL emitting at 4.35 μm with a low drive current (35–60 mA) and optical power (<2.6 mW) covered the P(43) and P(44) lines of 12CO2 and the R(18) line of 13CO2 with a single current scan. The ICL radiation was coupled into a solid-core (100-μm core diameter) indium fluoride optical fiber with a coupling efficiency of 88%. We successfully delivered the single-mode laser beam from the fiber output into the off-beam QEPAS spectrophone enclosed in a compact gas cell. The generated photoacoustic signal was acquired and analyzed by a digital lock-in amplifier to obtain its second harmonic (2f) component. Our sensor is capable of analyzing the CO2 isotopic ratio with an average precision of <1‰, which fulfills the precision requirements of most medical and field applications.