An etch-free and cost-effective deposition and patterning method to fabricate mid-infrared chalcogenide glass waveguides for chemical sensing applications is introduced. As(2)S(3) raised strip optical waveguides are produced by casting a liquid solution of As(2)S(3) glass in capillary channel molds formed by soft lithography. Mid-IR transmission is characterized by coupling the output of a quantum cascade (QC) laser (lambda = 4.8 microm) into the 40 microm wide by 10 microm thick multi-mode waveguides. Loss as low as 4.5 dB/cm is achieved using suitable substrate materials and post-processing. Optical absorption and surface roughness measurements indicate that the solution-processed films are of sufficient quality for optical devices and are promising for further development of waveguide-based mid-IR elements.

Articles you may be interested inLow divergence single-mode surface emitting quantum cascade ring lasers Appl. Phys. Lett. 93, 161101 (2008); 10.1063/1.3000630 High-power, continuous-wave operation of distributed-feedback quantum-cascade lasers at λ ∼ 7.8 μ m Appl. Phys. Lett. 89, 251119 (2006); 10.1063/1.2408639 Room-temperature, high-power, and continuous-wave operation of distributed-feedback quantum-cascade lasers at λ ∼ 9.6 μ m Appl. Phys. Lett. 88, 201114 (2006); 10.1063/1.2205730High-power, room-temperature, and continuous-wave operation of distributed-feedback quantum-cascade lasers at λ ∼ 4.8 μ m Appl. Phys. Lett.

We characterize the performance of a quantum well infrared photodetector (QWIP), which is fabricated as a photonic crystal slab (PCS) resonator. The strongest resonance of the PCS is designed to coincide with the absorption peak frequency at 7.6 µm of the QWIP. To accurately characterize the detector performance, it is illuminated by using single mode mid-infrared lasers. The strong resonant absorption enhancement yields a detectivity increase of up to 20 times. This enhancement is a combined effect of increased responsivity and noise current reduction. With increasing temperature, we observe a red shift of the PCS-QWIP resonance peak of -0.055 cm(-1)/K. We attribute this effect to a refractive index change and present a model based on the revised plane wave method.

We describe the fabrication and operation of vertically emitting distributed feedback quantum cascade ring lasers operating in the terahertz frequency range. A twofold increase in radiation efficiency is observed as compared to Fabry–Pérot lasers. The emitters exhibit a robust single-mode operation around 3.2 THz with a side mode suppression ratio higher than 30 dB. Modal and threshold characteristics are investigated by performing finite element simulations with results in good agreement with experiments. The ring-shaped resonator facilitates beam collimation which results in a symmetric far-field profile.

We describe the fabrication and operation of surface emitting second-order distributed feedback quantum cascade ring lasers. The devices exhibit single-mode emission at a wavelength of 3.95μm with a side mode suppression ratio of 25dB. A linear tuning coefficient of 0.13cm−1∕K is observed. A single longitudinal mode in the ring shaped resonator results in a highly symmetric far-field pattern and a low beam divergence, represented by a full width at half maximum of ∼3°. Based on these characteristics the presented compact coherent light source may find its way into today’s midinfrared spectroscopy applications.

We report on the fabrication and operation of quantum cascade ring lasers providing grating-coupled surface emission. The devices exhibit tunable far fields, ranging from spot- to ring-shaped symmetric beam cross sections, depending on the grating period. This—along with threshold current densities as low as for comparable Fabry–Pérot lasers—demonstrates the compatibility of reduced beam divergence and two-dimensional integrability, resulting in an attractive light source for applications in midinfrared spectroscopy and imaging.

We present the time-resolved comparison of pulsed 2nd order ring cavity surface emitting (RCSE) quantum cascade lasers (QCLs) and pulsed 1st order ridge-type distributed feedback (DFB) QCLs using a step-scan Fourier transform infrared (FT-IR) spectrometer. Laser devices were part of QCL arrays and fabricated from the same laser material. Required grating periods were adjusted to account for the grating order. The step-scan technique provided a spectral resolution of 0.1 cm(-1) and a time resolution of 2 ns. As a result, it was possible to gain information about the tuning behavior and potential mode-hops of the investigated lasers. Different cavity-lengths were compared, including 0.9 mm and 3.2 mm long ridge-type and 0.97 mm (circumference) ring-type cavities. RCSE QCLs were found to have improved emission properties in terms of line-stability, tuning rate and maximum emission time compared to ridge-type lasers.

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