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We propose a sensor for Advance Driver Assistance Systems (ADAS) with unique properties in terms of measuring time and distance that are necessary to predict the pavement condition several meters ahead of a moving vehicle.

Dual comb spectroscopy (DCS) for combustion, industrial, and environmental studies provide transmission spectra of complex mixtures of gases with potentially unknown signatures. We evaluate Independent Component Analysis (ICA) as a processing tool for DCS signals.

We propose an optical thickness measurement device based on electro-optic dual-optical frequency combs (dual-OFCs). Optical frequency combs (OFCs) are light sources that provide an optical signal consisting of many equidistant monochromatic tones. In this paper, we present an agile dual-OFC architecture with adjustable frequency separation of the comb modes and total frequency span, allowing high-resolution measurements of the thickness of transparent thick samples. This architecture is based on a single continuous-wave laser diode and external electro-optic devices to implement the dual-comb sensor, allowing easy control of the optical spectrum of the interrogation source (dual-OFC). As it is characteristic of dual-OFC systems, the optical transmittance function of the sample (etalon) is directly translated to the radiofrequency domain, where detection, demodulation, and processing of signals are performed. The shift in the complexity of implementation from the optical to the electronic domain yields many advantages, as acquisition and signal processing are made independently on the optical characteristics of the sample (thickness). This work was supported by the Spanish Ministry of Economy and Competitiveness under the RTC-2015-4205-4 Salicar and TEC-2014-52147-R Mossi grants.

A fast and reliable photoacoustic (PA) sensor for trace gas detection is reported. The sensor is based on a 3D-printed resonant cell in combination with a continuous wave mode-hop-free external cavity quantum cascade laser to rapidly acquire gas absorption data in the midinfrared range. The cell is designed so as to minimize the window PA background at a selected acoustic resonance. The goal is a resonant PA cell capable of detecting the traces of gases using wavelength modulation of the laser source and second harmonic detection. The versatility and enhancement of the limit of detection at sub-ppm levels are investigated by monitoring specific lines of hydrogen sulfide (H2S). The noise-equivalent absorption normalized to laser-beam power and detection bandwidth is 1.07×10-8 W cm-1 Hz-1/2 for H2S targeting the absorption line at 1247.2 cm−1. These properties make the sensor suitable for various practical sensors for water quality applications.

A photoacoustic gas system has been implemented for comparison of the performance of an electronic and an optical microphone as acoustic sensors. Results show a minimum detectable pressure of 79.5 μPa/Hz1/2 for the optical microphone.

Optical frequency combs (OFCs) generated through the modulation of continuous-wave lasers offer higher power per component, simple comb spacing control, and lower complexity and cost than traditional OFCs. By these reasons, they are an interesting optical source for spectrometers. In this letter, a dual-comb architecture based on two OFCs generated from the same laser using optical phase modulators is presented. The system features a new placement for the spectroscopic sample that increases the versatility, robustness, and stability of the instrument without requiring any reconfiguration for carrying out different types of measurement. Besides this, a self-referenced detection setup based on digital phase sensitive multitone detection improves the SNR of the previous approaches offering more flexibility in its configuration and high data output rate. The proposed architecture is validated by measuring a ro-vibrational absorption feature of HCN at 1544.51 nm and characterizing the spectral response of a fiber-coupled Fabry–Perot filter.

We describe a fiber laser interferometer that has been designed with the purpose of non-invasive continuous fetal heart rate monitoring. The measuring principle is based on the measurement of the arterial wave of a fetus from the arterial pulse wave of a pregnant patient, so the application requires the measurement of arterial pulse waves with very high resolution. The main characteristics of the specific application interferometer are: First, it is based on a common path topology in order to simplify the design of the non-contact optical probe to place on the body of the patient. Second, it uses a low power semiconductor laser at a safe operating wavelength of 1,55 μm. Third, a phase modulation with digital demodulation scheme is used in order to increase range and resolution simultaneously. The resulting interferometer provides up to 1 nm resolution and one millimeter range. Results showing arterial pulse waves measured on the wrist and a finger nail of a patient are presented.

A sensitive optical microphone for photoacoustic spectroscopy based on the common path topology of a fibre laser Doppler vibrometer (FLDV) using phase-generated carrier demodulation and a slim diaphragm as an acoustic wave transducer was demonstrated. A resonant gas cell was adapted to enhance gas-detection performance and simultaneously provide efficient cancellation of the window background acoustic signal. Ammonia (NH3) was selected as the target gas. The absorption line was experimentally identified using a distributed feedback laser diode emitting at 1530 nm. The linearity and sensitivity of the gas sensor were measured using wavelength modulation spectroscopy with second harmonic detection. A Teflon diaphragm was used to implement the optical microphone, along with the FLDV, showing a minimum detectable pressure of 79.5 &mu, Pa/Hz1/2. The noise-equivalent absorption sensitivity for NH3 detection at the absorption line at 1531.7 nm was 1.85 &times, 10&minus, 8 W cm&minus, 1 Hz&minus, 1/2, and the limit of detection was 785 ppbv.

In this paper we describe a fiber-based remote sensing device for the detection of liquid water and ice on the road surface suitable for on-board applications. The system is based on the different optical responses of water and ice to three near infrared wavelengths from low-cost semiconductor laser sources. The design of the sensor is divided in three main parts: The optical fiber-based illumination and collection optics, the optoelectronic system composed by the emitters/detector and the modulation/demodulation electronics and, finally, the data acquisition and digital processing system. The flexible optical design allows both the use of the sensor attached to a post by the road for static measurements, or to be incorporated into a road maintenance vehicle.