We present a study on distributed feedback tapered quantum cascade lasers emitting at 14 mu m. The fabricated lasers with taper angles between 0 degrees and 3 degrees exhibited output powers scaling in accordance with the active zone volume increase. Reduced divergence angles as small as 4.2 degrees have been obtained with diffraction limited-beam quality (M2 approximate to 1). With a first order Bragg-grating for single longitudinal mode selection, continuous wave operation was demonstrated up to almost room temperature with side-mode suppression ratios greater than 20 dB.

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.

The precise detection of volatile organic compounds plays a pivotal role in addressing environmental concerns, industrial safety, and medical diagnostics. The accurate identification and quantification of these compounds because of their ubiquity and potential health hazards has fueled the development of advanced sensing technologies. This work presents a sensing system in the realm of long-wavelength infrared spectroscopy for achieving enhanced selectivity and sensitivity of benzene, toluene, and propane detection through quartz-enhanced photoacoustic spectroscopy. High-resolution gas spectroscopy is made possible by the use of specially designed InAs/AlSb-based quantum cascade lasers, emitting in the wavelength range 13–15 μm, and quartz tuning forks. The sensor system, characterized by its robustness and precision, demonstrates exceptional capabilities in benzene, toluene, and propane detection. The system's capacity for practical applications in environmental monitoring and medical diagnostics is demonstrated by its ability to distinguish these volatile organic compounds with a minimum detection limit of 113 ppb, 3 ppb, and 3 ppm for toluene, benzene, and propane at an integration time of 10 s, even in complex gas matrices. This work advances gas sensing technology while also offering insightful information on spectral interferences, a persistent problem in the field. The results usher in a new era of sophisticated and reliable gas sensing techniques meeting the growing demand for precise volatile organic compounds detectors for environmental monitoring purposes.

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 mu m, where strong interferences from hydrocarbons occur. This issue can be eliminated operating at longer wavelength in the region from 13 to 15 mu m, 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.

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.

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 report InAs-based quantum cascade lasers (QCLs) operating near 14 µm with a threshold current density Jth as low as 0.6 kA/cm2 at room temperature. The threshold obtained is lower than the Jth of the best reported InP-based QCLs to date without facet treatment. The achieved performance improvement is partially due to an increased separation between the upper transition level and the next one in the active quantum wells of the employed QCL design.

We present InAs-based quantum cascade lasers (QCLs) operating near 14 µm with a threshold current density as low as 630 A/cm 2 at room temperature, outperforming the best reported to date InP-based QCLs.

Silicon (Si) photonics can have a major impact on the development of mid-IR photonics by leveraging on the reliable and high-volume fabrication technologies already developed for microelectronic integrated circuits. Germanium (Ge), already used in Si photonics, is a prime candidate to extend the operating wavelength of Group IV-based photonic integrated circuits beyond 8 µm, and potentially up to 15 µm. High performance quantum cascade lasers (QCLs) and interband cascade lasers grown on Si have been demonstrated, whereas no QCLs monolithically integrated on Ge have been reported yet. In this work, we present InAs-based QCLs directly grown on Ge by molecular beam epitaxy. The lasers emitting near 14 µm exhibited threshold current densities as low as 0.8-0.85 kA/cm2 at room temperature.

The analysis of Volatile Organic Compounds (VOCs) concentration in exhaled breath can be a promising approach for early and non-invasive diagnosis of different diseases. This work reports the detection of benzene and toluene molecules using a Quartz-Enhanced PhotoAcoustic Spectroscopy (QEPAS) sensor. These two molecules are VOCs commonly found in part-per-billion (ppb) level in the human exhaled breath.

Benzene is a gas known to be highly pollutant for the environment, for the water and cancerogenic for humans. In this paper, we present a sensor based on Quartz Enhanced Photoacoustic Spectroscopy dedicated to benzene analysis. Exploiting the infrared emission of a 14.85 µm quantum cascade laser, the sensor is working in an off-beam configuration, allowing easy alignment and stable measurements. The technique provides a very good selectivity to the sensor and a limit of detection of 30 ppbv in 1 s, i.e. a normalized noise equivalent absorption of 1.95 × 10-8 W.cm-1.Hz-1/2. The achieved performances of the sensor have enabled measurements on several air samples of a gas station showing a non-neglectable risk in case of long exposure.

This article addresses the analysis and design of a high-resolution and temperature-insensitive inclination sensor using fiber Bragg grating (FBG). The sensor uses a pendulum-based structure with FBG attached to its cantilever arm. Initially, strain analysis of the proposed inclination sensor is carried out using the finite-element method (FEM) to optimize the structure and materials for its fabrication. Experimental analysis is carried out on the inclination sensors by varying the inclination angle, and its results are compared with the FEM-based results. The shift in Bragg wavelength of FBG due to the generated strain at the cantilever arm is observed on optical interrogator. To measure the subpicometer wavelength shift with enhanced resolution and lower uncertainty, eigen decomposition of the reflection spectrum using Karhunen–Loève transform (KLT) is implemented. The range of measurement of tilt angle is found to be 0°–3° with a resolution of 0.0008°. The satisfactory linearity of the measured angle versus true angle, excellent repeatability, and very high resolution validates the feasibility of the proposed inclination sensor.

Fiber Bragg Gratings (FBGs) are known for their high sensitivity towards strain and temperature variation. In this manuscript, the strain sensing property of FBG is utilized and explored for measuring weight using a common binocular shaped cantilever type load cell. The shift in Bragg wavelength due to load application is converted into optical power variation using edge filter detection technique. Furthermore, change in optical power is converted into voltage variation and is feed to the Raspberry Pi via analog to digital converter (ADC ADS1115) for real-time and continuous online monitoring of weights. The optical load cell has shown linear response for applied weight up to 8kg. Mechanical properties of optical load cell such as nonlinearity, hysteresis, repeatability, creep and safe over load are studied in detail. Message Queuing Telemetry Transport (MQTT) protocol is used to send data from Raspberry Pi to IoT cloud. The system has achieved resolution of 20g with error of ± 50g.

Psychophysiological measurement can be very crucial in critical conditions faced in aviation, military, hospitals, etc. Respiration rate is one of the primary parameters to determine the psychophysiological condition of a person. An effective respiration rate measurement system is developed using Fiber Bragg Grating (FBG), and a comparison of its response with an electronic sensor is carried out in this paper. An edge filter detection technique is employed to interrogate the optical sensing data. Arduino Uno is used for acquiring data from both electronic and optical sensors simultaneously. Both the electronic and optical sensors are fitted inside the same PVC mask, and their responses are compared. The experiment is carried out on five subjects, and every time it is found, that optical sensor is much more reliable and responsive. Optical sensor has better rise and decay constants for instantaneous temperature sensing making it a superior candidate to diagnose various respiration abnormalities. Respiration rate calculation is also carried out during coughing and headshaking. In the events of coughing, response of the optical sensor is much more prominent as compared to the electronic sensor. However, respiration rate calculation remains unaffected and reliable.