QEPAS sensor for breath analysis: a behavior of pressure.

The measurement of trace gases has increasingly become a key technique in healthcare and other medical applications. Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a suitable method that can provide the required characteristics in such applications for a comparatively low cost and small size. The quantitative detection and a low detection limit are also required by applications. In this paper, we present new results on sensing biomedically relevant gases using the on-beam QEPAS technique with some newly developed tunable high-power single-mode laser diodes based on GaSb material. The data processing and detection limit determination are done by a field programmable gate array device, as well as an automatic measurement of the resonance frequency.

Single mode GaSb diode lasers for sensor applications in a long wavelength regime.

The wavelength, λ, range of 1.8 µm≤λ≤3.5 µm contains strong spectral absorption lines of many gases used in health, industry, safety, and medicine and whose sensitive and quantitative detection is desirable. However, the performance of InP diode lasers markedly deteriorates beyond λ∼2 µm. In this paper we present new results on developing tunable high power single mode laser diodes based on the GaSb material system with emission in the wavelength range of 1.8 µm≤λ≤2.2 µm.

Practical and cost-effective high-fidelity optical carrier dissemination using coherent communication techniques.

We report a unidirectional frequency dissemination scheme for high-fidelity optical carriers deployable over telecommunication networks. For the first time, a 10 Gb/s Binary Phase Shift Keying (BPSK) signal from an ultra-narrow linewidth laser was transmitted through a field-installed optical fibre with round-trip length of 124 km between Cork City and town of Clonakilty, without inline optical amplification. At the receiver, using coherent communication techniques and optical injection-locking the carrier was recovered with noise suppression. The beat signal between the original carrier at the transmitter and recovered carrier at the receiver shows a linewidth of 2.8 kHz. Long term stability measurements revealed fractional instabilities (True Allan deviation) of 3.3 × 10(-14) for 1 s averaging time, prior to phase noise cancellation.

Wide temperature range 0 < T < 85 °C narrow linewidth discrete mode laser diodes for coherent communications applications.

Cost effective lasers meeting the linewidth requirements for coherent communication systems are a key element in reducing the overall cost of future coherent systems. We report on monolithic devices with linewidths as low as 138 kHz which operate in a narrow linewidth, single wavelength mode with high sidemode suppression ratio over a wide temperature tuning range of -10 °C < T < 110 °C. A linewidth variation of only 23 kHz was measured at a constant emitted power of 4 mW as the device temperature is varied in the range 0 °C < T < 85 °C.

Phase synchronization scheme for a practical phase sensitive amplifier of ASK-NRZ signals.

We present a phase locking scheme that enables the demonstration of a practical dual pump degenerate phase sensitive amplifier for 10 Gbit/s non-return to zero amplitude shift keying signals. The scheme makes use of cascaded Mach Zehnder modulators for creating the pump frequencies as well as of injection locking for extracting the signal carrier and synchronizing the local lasers. An in depth optimization study has been performed, based on measured error rate performance, and the main degradation factors have been identified.

A practical phase sensitive amplification scheme for two channel phase regeneration.

A "black-box" phase sensitive amplifier is presented achieving simultaneous suppression of deterministic phase distortion on two independent 42.66 Gbit/s DPSK modulated signal wavelengths.

Phase shift keyed systems based on a gain switched laser transmitter.

Return-to-Zero (RZ) and Non-Return-to-Zero (NRZ) Differential Phase Shift Keyed (DPSK) systems require cheap and optimal transmitters for widespread implementation. The authors report on a gain switched Discrete Mode (DM) laser that can be employed as a cost efficient transmitter in a 10.7 Gb/s RZ DPSK system and compare its performance to that of a gain switched Distributed Feed-Back (DFB) laser. Experimental results show that the gain switched DM laser readily provides error free performance and a receiver sensitivity of -33.1 dBm in the 10.7 Gbit/s RZ DPSK system. The standard DFB laser on the other hand displays an error floor at 10(-1) in the same RZ DPSK system. The difference in performance, between the two types of gain switched transmitters, is analysed by investigating their linewidths. We also demonstrate, for the first time, the generation of a highly coherent gain switched pulse train which displays a spectral comb of approximately 13 sidebands spaced by the 10.7 GHz modulation frequency. The filtered side-bands are then employed as narrow linewidth Continuous Wave (CW) sources in a 10.7 Gb/s NRZ DPSK system.

A novel single frequency stabilized Fabry-Perot laser diode at 1590 nm for gas sensing.

A novel single frequency stabilized Fabry-Perot (SFP) laser diode with an emission wavelength of lambda = 1590 nm for H2S gas sensing is reported. Sculpting of the multi-mode spectral distribution of a FP laser to achieve single frequency emission is carried out using post growth photolitographic processing of the device. The resulting longitudinal-mode controlled FP laser has a stabilized single frequency emission with a side mode suppression ratio (SMSR) of 40 dB. The application of this device to spectroscopic based H2S sensing is demonstrated by targeting absorption lines in the wavelength range 1588 < or = lambda < or = 1591 nm. Using wavelength modulation spectroscopy (WMS), a low detection limit of 120 ppm x m x Hz(-1/2) was estimated while targeting the absorption line at 1590.08 nm. These initial results demonstrate the potential of the stabilized FP laser diode at this wavelength as a tunable, single frequency source for spectroscopic based gas sensing.