Semiconductor optical amplifiers in avionics

RSOAs have been demonstrated to operate within a WDM PON architectures over a >;60nm wavelength range with large path loss capabilities. Two RSOAs enable contiguous operation over the S, C and L bands; results indicate clearly that WDM architectures suitable for avionics with a PLC of >;25dB are possible with only two devices. Performance at extended temperature ranges will be reported later in detai

Intra-cavity spectroscopy using amplified spontaneous emission in fiber lasers

Fiber laser sources offer interesting possibilities for gas sensors since they can operate over an extended wavelength range, encompassing the near-IR absorption lines of a number of important gases but a major problem is that overtone absorption lines of gases in the near-IR are relatively weak. In order to enhance sensitivity, we present here a simple method of intra-cavity absorption spectroscopy (ICAS) which makes use of the amplified spontaneous emission (ASE) already present within a fiber laser cavity. The ASE also provides a convenient broadband source for the simultaneous interrogation of several gases within the gain-bandwidth of the fiber laser. The key principle is based on adjusting the cavity attenuation to select an appropriate inversion level where the fiber gain curve is flat. Under this condition, the ASE undergoes multiple circulations within the fiber laser cavity, enhancing the effective path-length of a gas cell placed within the laser cavity. A theoretical model of system operation is given and we have experimentally demonstrated the principle of operation with acetylene and carbon dioxide using a simple erbium fiber laser system containing a 6 cm path-length, fiber coupled, intra-cavity, micro-optic gas cell. We have experimentally simultaneously observed 16 absorption lines for 1% acetylene gas in the 1530 nm region and detected the very weak carbon dioxide lines in this same wavelength region. A path length enhancement of in the linear regime has been demonstrated transforming the 6 cm micro-optic cell into an effective path length of m. We also demonstrate how the enhancement factor may be calibrated by use of a simple fiber-optic interferometer. Apart from the OSA, all components are inexpensive and the system is very simple to construct and operate

Planting the Seeds for Change: A Case Study from York University’s Knowledge Mobilization Graduate Student Internship Program

This practice-based article describes the academic and non-academic outputs and outcomes of community-academic research collaboration. The collaboration began with a university-sponsored knowledge mobilization internship. A doctoral student spent four months as a knowledge mobilization intern with a youth shelter. With additional funding, the internship evolved into a multi-year collaboration that positively influenced employment opportunities for local youth workers, the shelter’s economic stability and reputation in the local community, young people’s sustained transitions out of the shelter, and academic growth and development on the part of the doctoral student

Recovery of absorption line shapes with correction for the wavelength modulation characteristics of DFB lasers

Tunable diode laser spectroscopy combined with wavelength modulation spectroscopy (WMS) is an important technique for non-invasive measurements of gas parameters such as pressure, concentration and temperature in high noise, harsh environments. A variety of laser types are used for these applications and the modulation characteristics can have significant effects on line shape recovery. Here we identify important characteristics of distributed feedback (DFB) lasers that need to be taken into account in the context of WMS and illustrate the effects with a 2μm wavelength, multi quantum well DFB laser used for CO2 detection. The modulation response of the laser is measured and we demonstrate how the phasor decomposition method (PDM) may be used to obtain accurate line shapes from first harmonic WMS signals by correcting for phase variation across the laser’s low frequency current sweep. We also demonstrate how the PDM approach can be improved by removing the need to pre-set the orientation of the lock-in axis, to isolate the residual amplitude modulation(RAM)component, making it more suitable for field applications

Trace gas sensing using DFB laser and QCL with miniaturized 3D-printed photoacoustic gas cells

Miniaturized 3D-printed photoacoustic trace gas sensors are presented, targeting gas species with absorption features in the telecommunications band as well as the mid-infrared with recovered gas concentrations down to the parts-per-billion range

Recovery of absolute absorption line shapes in tunable diode laser spectroscopy using external amplitude modulation with balanced detection

Accurate recovery of an absorption lineshape is important in many industrial applications for simultaneous measurement of gas concentration and pressure or temperature. Here we demonstrate a method, based on a modification to the Hobbs balanced receiver circuit, for background signal nulling when external amplitude modulation of the laser output is used. Compared with direct or non-nulled detection techniques, we demonstrate that the method significantly improves the signal to noise ratio to a level comparable to that of conventional second harmonic wavelength modulation spectroscopy. Most importantly, normalisation and recovery of the lineshape is straightforward and immune to the difficulties that afflict lineshape recovery with conventional wavelength modulation spectroscopy

Sliding-window analysis tracks fluctuations in amygdala functional connectivity associated with physiological arousal and vigilance during fear conditioning

We evaluated whether sliding-window analysis can reveal functionally relevant brain network dynamics during a well-established fear conditioning paradigm. To this end, we tested if fMRI fluctuations in amygdala functional connectivity (FC) can be related to task-induced changes in physiological arousal and vigilance, as reflected in the skin conductance level (SCL). Thirty-two healthy individuals participated in the study. For the sliding-window analysis we used windows that were shifted by one volume at a time. Amygdala FC was calculated for each of these windows. Simultaneously acquired SCL time series were averaged over time frames that corresponded to the sliding-window FC analysis, which were subsequently associated with the whole-brain seed-based amygdala sliding-window FC using the GLM. Surrogate time series were generated to test whether connectivity dynamics could have occurred by chance. In addition, results were contrasted against static amygdala FC and sliding-window FC of the primary visual cortex, which was chosen as a control seed, while a physio-physiological interaction (PPI) was performed as cross-validation. During periods of increased SCL, the left amygdala became more strongly coupled with the bilateral insula and medial prefrontal cortex, core areas of the salience network. The sliding-window analysis yielded a connectivity pattern that was unlikely to have occurred by chance, was spatially distinct from static amygdala FC and from sliding-window FC of the primary visual cortex, but was highly comparable to that of the PPI analysis. We conclude that sliding-window analysis can reveal functionally relevant fluctuations in connectivity in the context of an externally cued task

An FPGA-based lock-in detection system to enable chemical species tomography using TDLAS

This paper presents the design, implementation and test of a compact, low-cost and fully digital signal recovery system for tunable diode laser absorption spectroscopy (TDLAS) in narrow line-width gas sensing applications. An FPGA-based digital lock-in amplifier (DLIA), in conjunction with TDLAS using the wavelength modulation spectroscopy (WMS) technique, is utilized to demodulate and extract first (1f) and second (2f) harmonic signals for a narrow CO2 feature in the spectrum region of 1997.2nm. The spectrum in this wavelength region shows suitably weak water absorption, enabling CO2 detection with high resolution. Gas-cell experiments were carried out using the DLIA and a conventional rack-mounted commercial lock-in amplifier. The comparison between the two systems shows good agreement, validating the feasibility of this approach and demonstrating the prospect for extension to a massively multichannel system to implement Chemical Species Tomography

Measurement of CO2 concentration and temperature in an aero engine exhaust plume using wavelength modulation spectroscopy

In this paper, the 2f/1f tunable diode laser wavelength modulation technique is used for the simultaneous measurement of concentration and temperature of CO2 in the exhaust plume of an aero engine. The suitability of the R48 spectral feature of CO2 at 1997.2 nm is discussed for this application and for further investigations into the application of CO2 tomographic imaging on large-scale aero-engines. To ensure accurate recovery of gas parameters at the high exhaust temperatures a full spectral characterisation of the spectral feature is presented using direct spectroscopy. The 2f/1f method is validated in the laboratory for controlled gas mixtures and temperatures to recover concentration and temperature, showing good agreement with the actual temperature and concentration values. Finally, single path measurements are presented for an aero engine exhaust showing good correlation with the measured engine conditions

Miniaturized photoacoustic trace gas sensing using a raman fiber amplifier

This paper presents the development of a Raman fiber amplifier optical source with a maximum output power of 1.1 W centered around 1651 nm, and its application in miniaturized 3D printed photoacoustic spectroscopy (PAS) trace gas sensing of methane. The Raman amplifier has been constructed using 4.5 km of dispersion shifted fiber, a 1651 nm DFB seed laser and a commercial 4W EDFA pump. The suppression of stimulated Brillouin scattering (SBS) using a high frequency modulation of the seed laser is investigated for a range of frequencies, leading to an increase in optical output power of the amplifier and reduction of its noise content. The amplifier output was used as the source for a miniature PAS sensor by applying a second modulation to the seed laser at the resonant frequency of 15.2 kHz of the miniature 3D printed gas cell. For the targeted methane absorption line at 6057 cm-1 the sensor system performance and influence of the SBS suppression is characterized, leading to a detection limit (1σ) of 17 ppb methane for a signal acquisition time of 130 s, with a normalized noise equivalent absorption coefficient of 4.1•10-9 cm-1 W Hz-1/2 for the system