P. Phelan

H2S and CO2 gas sensing using DFB laser diodes emitting at 1.57 μm

Using wavelength-modulation spectroscopy and harmonic detection, we demonstrate, for the first time, direct optical detection of H 2 S by probing the v 1 + v 2 + v 3 combination absorption band centred at a wavelength λ = 1.59 μm using a distributed feedback (DFB) laser diode. A detection limit of less than 10 ppm at atmospheric pressure over a 5 m path length for the system is inferred from the measured detectivity at higher H 2 S concentrations. This detection sensitivity is at a level below the accepted 10 ppm safe-exposure limit. In addition, we demonstrate the capability of DFB laser diodes for multiple gas sensing in the λ = 1.575 μm region with the same laser by probing the 2v 1 + 2v 2 + v 3 absorption band of CO 2 , achieving a detection limit of about 100 ppm. These results demonstrate the utility of near-infrared laser diodes for industrial applications in the area of toxic- and trace-gas monitoring.

All-optical timing extraction with frequency division using a twin-section laser diode

All-optical timing extraction from a coded line signal with division of the extracted clock frequency is demonstrated using a single twin-section self-pulsating laser diode. Either the bit-rate clock or a submultiple of the bit-rate clock can be extracted, depending only on the DC biases applied to the self-pulsating laser diode. Timing extraction is carried out for the first time without optical injection locking of the self-pulsating laser diode by the optical data source.<<ETX>>

All-optical synchronization and frequency division of mode-locked pulses

The authors report all-optical synchronization and frequency division of mode-locked input signals, using a self-pulsating laser diode. The performances of mode-locked and sinusoidal input signals are compared. Synchronization and frequency division of the mode-locked signals are found to be easier to achieve. This result suggests that significant applications may be found for this system.<<ETX>>

The influence of the unlocked characteristics of a self-pulsating laser diode on synchronization

All-optical synchronization and timing extraction based on self-pulsating twin section lasers are demonstrated. The variation of the unlocked full-width-at-half-maximum (FWHM) of the fundamental of the RF spectrum of a self-pulsating laser diode is investigated. It is shown for the first time that the variation of the FWHM with frequency is dependent on the slope of the absorber bias versus self-pulsation frequency characteristic. The results have important implications for the design and selection of self-pulsating laser diodes for synchronization applications.<<ETX>>

All-optical synchronization and multiplication of the frequency of mode-locked signals

The authors report all-optical synchronized multiplication by rational fractions of the modulation frequency of optical signals in self-pulsing two-section semiconductor laser diodes. The effect is based on the overlap of harmonics of the input signal with harmonics of the self-pulsation. This new generic function is illustrated with mode-locked inputs rich in harmonics, where fractions of 1, 2, and 3/2 are generated, and a number of applications for this effect are identified.<<ETX>>

Novel device for short-pulse generation using optoelectronic feedback

This work describes recent results investigating the operation of a novel device arrangement which is capable of being integrated using present optoelectronic materials. The system utilizes an external cavity laser diode and an avalanche photodiode (APD) in a feedback arrangement and is capable of providing a stable train of picosecond pulses without the use of saturable absorbers or external signal generators. The role of amplification in the electronic feedback circuit is examined in detail.