Multi-format all-optical processing based on a large-scale, hybridly integrated photonic circuit.

We investigate through numerical studies and experiments the performance of a large scale, silica-on-silicon photonic integrated circuit for multi-format regeneration and wavelength-conversion. The circuit encompasses a monolithically integrated array of four SOAs inside two parallel Mach-Zehnder structures, four delay interferometers and a large number of silica waveguides and couplers. Exploiting phase-incoherent techniques, the circuit is capable of processing OOK signals at variable bit rates, DPSK signals at 22 or 44 Gb/s and DQPSK signals at 44 Gbaud. Simulation studies reveal the wavelength-conversion potential of the circuit with enhanced regenerative capabilities for OOK and DPSK modulation formats and acceptable quality degradation for DQPSK format. Regeneration of 22 Gb/s OOK signals with amplified spontaneous emission (ASE) noise and DPSK data signals degraded with amplitude, phase and ASE noise is experimentally validated demonstrating a power penalty improvement up to 1.5 dB.

40 Gb/s 2R Burst Mode Receiver with a single integrated SOA-MZI switch.

We demonstrate a novel scheme for 2R burst mode reception capable of operating error-free with 40 Gb/s variable length, asynchronous optical data packets that exhibit up to 9 dB packet-to-packet power variation. It consists of a single, hybrid integrated, SOA-based Mach-Zehnder Interferometer (SOA-MZI) with unequal splitting ratio couplers, configured to operate as a self-switch. We analyze theoretically the power equalization properties of unequal splitting ratio SOA-MZI switches and show good agreement between theory and experiment.

Compact all-optical packet clock and data recovery circuit using generic integrated MZI switches.

We present and evaluate a compact, all-optical Clock and Data Recovery (CDR) circuit based on integrated Mach Zehnder interferometric switches. Successful operation for short packet-mode traffic of variable length and phase alignment is demonstrated. The acquired clock signal rises within 2 bits and decays within 15 bits, irrespective of packet length and phase. Error-free operation is demonstrated at 10 Gb/s.

All-optical binary counter.

We experimentally demonstrate an all-optical binary counter composed of four semiconductor optical amplifier based all-optical switching gates. The time-of-flight optical circuit operates with bit-differential delays between the exclusive-OR gate used for modulo-2 binary addition and the AND gate used for binary carry detection. A movie of the counter operating in real time is presented.

Co-ordinated care for women with postnatal depression.

In many cases, postnatal depression is not identified or treated early enough, often as a result of poor co-ordination between the health professionals involved. This article outlines a project to develop multidisciplinary working to improve the care provision for women with postnatal depression.

Measurement of the refractive-index modulation generated by electrostriction-induced acoustic waves in optical fibers.

The refractive-index modulation generated in optical fibers by electrostriction-induced acoustic waves is investigated directly by a pump-probe measurement technique in a 1-km-long fiber Sagnac-loop interferometer. Pump pulses propagating unidirectionally around the loop generate transverse acoustic waves that produce a time-dependent relative phase shift for the probe pulses. The consequent interferometer transmission changes are used as a measure of the acoustic interaction. The acoustic impulse response function of the fiber is measured by use of short optical pulses with a 1-MHz repetition rate. The response consists of a series of peaks separated by ~21 ns with a maximum value of refractive-index modulation of -1.1 x 10(-11) generated by the 230-pJ pump pulses. At a higher pulse repetition rate of 100 MHz additional temporal structure is generated in the 0-5-ns period after the pump pulse, leading to a response similar to that observed in longrange soliton interaction.

Experimental investigation of resonant enhancement of the acoustic interaction of optical pulses in an optical fiber.

The acoustic interaction of optical pulses in optical fibers is investigated directly by time-resolved pump-probe measurements of the transmission of a fiber Sagnac-loop interferometer. Resonant enhancement of the refractive-index change deltan(ac) induced by the acoustic waves is observed when the repetition frequency of the pulse train is close to a vibrational eigenfrequency of the fiber. For standard fiber deltan(ac) is enhanced by a factor of ~3 at the 465-MHz eigenmode frequency, and this factor increases to ~10 when the polymer jacket is removed from the fiber. The guided acoustic wave Brillouin scattering spectrum that arises from spontaneous thermal excitation of the acoustic eigenmodes of the fibers is also measured. The results suggest that the resonant enhancement of deltan(ac) is limited by dampling that is due to the polymer jacket and by inhomogeneous broadening that is due to fiber diameter variations.

Measured reduction of guided-acoustic-wave Brillouin scattering in a fiber interferometer by time-delayed pulses.

We measure the reduction of guided-acoustic-wave Brillouin scattering phase noise in an optical fiber interferometer by varying the time delay between an optical pulse pair. Excellent suppression of the phase noise is achieved when the pulses have parallel polarizations and are delayed by less than 100 ps, but orthogonal polarizations show a residual noise level that is due to the depolarized guided-acoustic-wave Brillouin scattering modes.

Polarization cross saturation in an Er(3+)-doped fiber ring laser.

The cross saturation between the polarization eigenmodes is measured in a unidirectional Er(3+) -doped fiber ring laser in which the population inversions for the polarization components are decoupled only by polarization hole burning. A coupling factor of beta = 0.80 +/- 0.01 is obtained from measurements of the polarization antiphase dynamics in the laser.

Multiwavelength fiber laser using a spatial mode beating filter.

A multiwavelength comb is obtained from Er(3+) - and Nd(3+)-doped fiber lasers by incorporation of a section of multimode optical fiber into an otherwise single-mode fiber ring cavity. This combination of fiber types acts as a wavelength-dependent filter in the laser through spatial mode beating between the LP(01) and LP(11) modes in the multimode fiber.

Guided acoustic-wave Brillouin scattering with optical pulses.

Both continuous-wave and pulsed laser sources have been used to study guided acoustic-wave Brillouin scattering (GAWBS) in optical fibers. Measurements of the scattering process with either a multimode or single-frequency cw source produced similar GAWBS rf spectra. However, with mode-locked pulses the GAWBS rf spectrum extends over a larger frequency range owing to the heterodyning of the laser harmonics with the scattered light. This effect is illustrated by using two mode-locked lasers with different pulse repetition rates of 76 and 980 MHz.

Brown-adipose-tissue mitochondria: the regulation of the 32000-Mr uncoupling protein by fatty acids and purine nucleotides.

The increased proton permeability induced by the addition of a synthetic proton translocator to non-respiring hamster brown-fat mitochondria is unaffected by purine nucleotide addition. In contrast the permeability induced by fatty acids is inhibited by nucleotide, indicating that fatty acids act at the 32000-Mr uncoupling protein. Fatty acids lower the affinity of nucleotide binding to the 32000-Mr protein, but not sufficiently to explain their uncoupling action. The sensitivity of the fatty acid modulation of permeability is dependent on chain length, extent of unsaturation and pH. There is a requirement for an unesterified carboxyl group. In respiring mitochondria fatty acids act in the presence of nucleotide by lowering the 'break-point' potential at which the conductance of the 32000-Mr protein increases. Fatty acids have no effect on the chloride uniport activity of the 32000-Mr protein, but decouple the interference between chloride and protons when the simultaneous transport of both ions is attempted.