We present a scheme for homogeneous integration and multiplexing of the outputs of continuous-wave distributed feedback quantum cascade lasers for multi-species gas sensing and similar applications using the concept of monolithic InP-based photonic integrated circuits.
Quantum-cascade-laser-based mid-infrared (mid-IR, wavelengths in the range of approximately 3 microns to 15 microns) Photonic Integrated Circuits (PICs) on the InP platform allow for monolithic integration of high-power laser sources, passive and active photonic elements, and low-loss optical interconnects with transparency in the entire mid-IR spectral region. We will report on our progress in developing InP-based mid-IR PICs, including characterization of linear and nonlinear optical properties of InP/InGaAs waveguides in the mid-IR spectral range, demonstration of low-loss passive mid-IR photonic components, such as ring resonators and wavelength multiplexers, and monolithic integration of these passive components with the active devices.
Photonic integrated circuits (PICs) operating in the mid-infrared spectral range (mid-IR, wavelengths in the range 3-15 micrometers) are of interest for a wide range of applications, including spectroscopy and sensing in the molecular fingerprint region, free-space communication in the atmospheric transparency windows, and infrared countermeasures. InGaAs/AlInAs/InP quantum cascade lasers (QCLs) have been established as the semiconductor laser platform of choice for many mid-IR applications. Efficient utilization of QCL-based mid-IR PICs is largely contingent upon reliability, operating powers, and efficiency of the integrated laser sources as well as the ease of fabrication and integration of the low-loss passive and active photonic components. From these considerations, the development of mid-IR PICs on the InP platform appears to be particularly promising as the platform enables monolithic integration of high-power laser sources and waveguides with transparency in the entire mid-IR spectral region. We will report on our progress in developing InP-based mid-IR PICs, including demonstrations of low-loss passive mid-IR photonic components, such as waveguides, ring resonators, and wavelength multiplexers in InGaAs/InP and their integration with QCLs.
We present terahertz (THz) surface emission by difference frequency generation in nonlinear quantum cascade lasers operating at room temperature. The device comprises two separate, transversely superimposed gratings, one for selective feedback for the midinfrared (MIR) modes and one for normal surface emission of the generated THz radiation. This allows for narrow far-field THz emission with an enhanced extraction over the entire device length with improved electrical and thermal properties compared to previous devices relying on Cherenkov phase matching. The MIR grating is realized as a higher order loss-coupled distributed feedback grating for single-mode emission at two distinct wavelengths. Its position determines the position of the standing wave pattern of the MIR modes and of the nonlinear polarization wave. This allows for a precise placement of the second-order top grating, which leads to perpendicular surface emission. The device emits in a single-lobed far-field with a full width half maximum of 3.5 deg in single-mode operation at room temperature.
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