Detection of volatile organic compounds (VOCs) with particular attention to the BTEX group consisting of benzene, toluene, ethylbenzene, and xylene has risen as an important task in fields as environmental monitoring and breath analysis. Sensors based on optical detection techniques may represent an alternative to traditional approaches. However, optical sensing has been limited in terms of measurements selectivity as BTEX point out absorption features around 3.3 μm, where strong interferences from hydrocarbons occur. This issue can be eliminated operating at longer wavelength in the region from 13 to 15 μm, where BTEX show distinct and isolated absorption features. However, the investigations in this region have been limited by the lack of suitable laser sources as well as by the low performances of commercial detectors. In this work, a new approach to benzene detection is proposed, employing a long wavelength InAs-based QCL as light source and a quartz tuning fork as detector for TDLAS measurements, in light-induced thermoelastic spectroscopy (LITES) detection scheme. Analyte detection in the range of hundreds of part-per-billion with a shoe-box size design is demonstrated.
In this talk we will review our recent demonstrations of mid-IR lasers grown on (001) Si or Ge substrates (diode lasers, interband cascade lasers, quantum cascade lasers) and compare their performance to those grown on their native substrates. We will demonstrate light coupling from lasers grown on patterned Si photonics wafers to passive SiN waveguides, with a coupling efficiency in line with simulations. Finally, we will discuss and evaluate strategies to enhance the coupling efficiency.
InAs-based quantum cascade lasers (QCL) demonstrated high performance in the long-wavelength mid-infrared range. Hard baked photoresist usually employed for electrical insulation in these devices exhibits some drawbacks related to the polymer nature of this material. Wire bonding is difficult because of the mechanical softness of the photoresist. Besides, optical properties of such insulator can be altered when the laser is operated at elevated temperature. Conventional dielectrics with potentially suitable characteristics introduce optical loss and/or current leakage when fabricated using standard deposition techniques. We report manufacturing of InAs-based QCLs using spin-on-glass that ensured high performance of the devices.
We present an investigation on the electrical and optical properties of tapered quantum cascade lasers emitting at 14-15 μm, based on the InAs/AlSb system. In tapered lasers the active zone volume is increased to obtain higher optical power outputs without degrading the beam quality. Devices with three different taper angles of 1°, 2° and 3° were examined in terms of electrical, optical, and spectral properties and were compared with conventional ridge waveguide lasers.
Silicon photonics can have a major impact on the advancement of mid-IR photonics by leveraging the mature and reliable high-volume fabrication technologies already developed for microelectronic integrated circuits. Germanium, already used in silicon photonics, is a promising material for increasing the operating wavelength of Group-IV-based photonic integrated circuits beyond 8 μm and potentially up to 15 μm. High-performance InAs-based quantum cascade lasers grown on Si have been previously reported. In this work, we present InAs-based QCLs directly grown on Ge. The lasers operate near 14 μm with pulsed threshold current densities as low as 0.8 kA/cm2 at room temperature.
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