J. O'Gorman

Generation of Coherent Multicarrier Signals by Gain Switching of Discrete Mode Lasers

The authors demonstrate the generation of a highly coherent multicarrier signal that consists of eight clearly resolved 10.7-GHz coherent sidebands generated within 3 dB of the spectral envelope peak and with an extinction ratio in excess of 45 dB by gain switching a discrete mode (DM) laser. The generated spectral comb displays a corresponding picosecond pulse train at a repetition rate of 10.7 GHz with a pulse duration of 24 ps and a temporal jitter of ~450 fs. The optical spectra and associated pulses of the gain-switched DM laser are subsequently compared with a gain-switched distributed feedback (DFB) laser that generates a spectrum with no discernible sidebands and corresponding pulses with ~3 ps of temporal jitter. By means of external injection, the temporal jitter of the gain-switched DFB laser is then reduced to <; 1 ps, resulting in visible tones on the output spectrum. Finally, a nonlinear scheme is employed and initially tailored to compress the optical pulses, after which, the setup is slightly altered to expand the original frequency comb from the gain-switched DM laser.

Narrow linewidth, tunable Tm/sup 3+/-doped fluoride fiber laser for optical-based hydrocarbon gas sensing

Operation of an efficient continuous-wave (CW) thulium-doped fiber laser emitting at wavelength, /spl lambda/=2.31 /spl mu/m is reported. The fiber laser parameters are optimized with a view to ultimately producing a compact and efficient laser source for optical absorption based gas sensing. A number of fiber laser configurations are investigated to assess their suitability for narrow linewidth, tunable fiber laser operation emitting around /spl lambda/=2.3 /spl mu/m, which is a wavelength region of significant importance for hydrocarbon gas monitoring. Tuning ranges of 140 nm and linewidths of less than 210 MHz have been demonstrated with lasers with bulk external tuning grating. Preliminary hydrocarbon gas sensing investigation confirm the potential of this source for detection of ppb gas concentrations.

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.

Self-pulsating semiconductor lasers: theory and experiment

We report detailed measurements of the pump-current dependency of the self-pulsating frequency of semiconductor CD lasers. A distinct kink in this dependence is found and explained using a rate-equation model. The kink denotes a transition between a region where the self-pulsations are weakly sustained relaxation oscillations and a region where Q-switching takes place. Simulations show that spontaneous emission noise plays a crucial role in the cross-over.

Generation of frequency symmetric signals from a BPSK input for phase sensitive amplification

We report a novel system for simultaneous carrier recovery and frequency symmetric signals generation from a NRZ-BPSK input by exploiting FWM in HNLF for phase sensitive amplification.

A Novel Two-Section Tunable Discrete Mode Fabry-PÉrot Laser Exhibiting Nanosecond Wavelength Switching

A novel widely tunable laser diode is proposed and demonstrated. Mode selection occurs by etching perturbing slots into the laser ridge. A two-section device is realized with different slot patterns in each section allowing Vernier tuning. The laser operates at 1.3 mum and achieves a maximum output power of 10 mW. A discontinuous tuning range of 30 nm was achieved with a side mode suppression greater than 30 dB. Wavelength switching times of approximately 1.5 ns between a number of wavelength channels separated by 7 nm have been demonstrated.

Laser diode based oxygen sensing: A comparison of VCSEL and DFB laser diodes emitting in the 762 nm region

The performance of VCSEL and DFB laser diodes for spectroscopic based high sensitivity oxygen sensing is compared. Detectivities of < 20 ppm m using the DFB laser diode and < 7 × 103 ppm m using the VCSEL were determined utilising wavelength modulation spectroscopy and harmonic detection. We assess factors influencing the relative performance of these devices, including spectral resolution, laser optical power and light current curve linearity.

DPSK Signal Regeneration With a Dual-Pump Nondegenerate Phase-Sensitive Amplifier

We demonstrate, for the first time to our knowledge, regeneration of a 42.66-Gb/s differential phase-shift keyed signal using a dual-pump nondegenerate four-wave-mixing-based fiber-optic parametric amplifier. The regenerative performance of the subsystem is characterized in terms of bit-error rate against narrowband and wideband introduced noise. While a strong receiver sensitivity improvement, up to 20 dB, is noticed against narrowband noise, against quasi-random (wideband) noise we observe a regeneration of 2.7 dB.

Specifying the wavelength and temperature tuning range of a Fabry-Perot laser containing refractive index perturbations (Invited Paper)

The wavelength spectra of ridge waveguide Fabry Perot lasers can be modified by perturbing the effective refractive index of the guided mode along very small sections of the laser cavity. One way of locally perturbing the effective index of the lasing mode is by etching features into the ridge waveguide such that each feature has a small overlap with the transverse field profile of the unperturbed mode, consequently most of the light in the laser cavity is unaffected by these perturbations. A proportion of the propagating light is however reflected at the boundaries between the perturbed and the unperturbed sections. Suitable positioning of these interfaces allows the mirror loss spectrum of a Fabry Perot laser to be manipulated. In order to achieve single longitudinal mode emission, the mirror loss of a specified mode must be reduced below that of the other cavity modes. Here we briefly review one procedure for calculating the mirror loss spectra of devices containing such features. We then go on to describe a method for synthesising onedimensional slot patterns. This technique allows the lasers emission wavelength to be specified to a high degree of accuracy.

All-optical phase regeneration of 40Gbit/s DPSK signals in a black-box phase sensitive amplifier

We present a black-box four wave mixing based bit-rate-flexible phase sensitive amplifier and use it in the first demonstration of 40 Gbit/s DPSK phase regeneration.