Hoang Trung Nguyen

Saturable-Absorber-Based Phase-Preserving Amplitude Regeneration of RZ DPSK Signals

We experimentally investigate a new generation of multiple-quantum-well semiconductor saturable absorber for all-optical phase-shift-keying signal regeneration. The device under study exhibits a reflectivity which decreases when the input signal power increases. This characteristic can be seen as a power limiting function which could be used for phase-preserving amplitude noise reduction, hence preventing from nonlinear phase noise accumulation along a transmission link. The device efficiency is demonstrated at 42.7 Gb/s; a fiber launched power margin of 2 dB and receiver sensitivity improvement up to 5.5 dB are obtained.

All-Optical 2R Regeneration With a Vertical Microcavity-Based Saturable Absorber

This paper gives an overview of recent demonstrations of optical 2R regeneration achieved by vertical microcavity mirror-based multiple-quantum-well saturable absorber (SA). The potential of the device to perform wavelength division multiplexing regeneration is first demonstrated through the first pigtailed SA chip implemented with eight independent fibers using a cost effective coupling technique. The cascadability and wavelength tunability assessment of this module associated with a power limiter fiber-based function has been experimentally demonstrated at 42.6 Gbit/s. Because this method of power limiting is not a suitable solution for all-optical multichannel 2R regeneration, a new SA structure allowing a power limiting function was proposed. We describe and characterize such a structure in this paper. This new SA opens the door to a complete passive all-optical 2R regeneration relying upon a single technology, as shown in this paper through the use of two SA: SA.0 for extinction ratio enhancement and SA.1 for high-power level equalization allowing receiver sensitivity (up to 3.5 dB) and Q-factor (up to 1.4 dB) improvement for a RZ signal at 42.6 Gbit/s. The limitation of SA.1 when the regenerator must be cascaded a large number of times is also described, leading to the observation that SA.1 should be more suitable for phase encoded formats that are more spectrally efficient than ON-OFF keying formats. A SA.1 used as a phase-preserving amplitude regenerator in a 42.6 Gbit/s RZ differential quadrature phase-shift keying transmission system is, therefore, assessed . A fiber launched power margin of 2 dB and a receiver sensitivity improvement of 5.5 dB are obtained. Finally, we use, for the first time an SA.1 as a phase-preserving amplitude regenerator of RZ differential quadrature phase-shift keying signals. The regenerator is assessed in a recirculating loop at 28 Gbaud. The system tolerance to nonlinear phase noise is enhanced by 3 dB and the distance improvement factor was 1.3 for a bit error rate = 10-4.

A Passive All-Optical Device for 2R Regeneration Based on the Cascade of Two High-Speed Saturable Absorbers

We discuss the design and realization of a passive all-optical device for 2R regeneration based on a dual-stage of high-speed microcavity saturable absorbers, one for noise reduction of digital zeros (SA-0), and the other for noise reduction of digital ones (SA-1). The numerical and experimental results showed that by using a simple combination of SA-0 and SA-1 devices, one can obtain an intensity transfer function with a large extinction ratio improvement of low power levels and a strongly nonlinear response reducing the noise of high power levels. The amplitude and phase characterization of a 40-GHz signal transmitted by this device, obtained by frequency-resolved optical gating measurements, reveals the intensity-dependant pulse-compression effect and the low chirp introduced by this device.

All-optical phase-preserving amplitude regeneration of 28-Gbaud RZ-DQPSK signals with a microcavity saturable absorber in a recirculating loop experiment

Microcavity Saturable absorber is used for phase-preserving amplitude regeneration of RZ-DQPSK signals. The regenerator is assessed in a 28 Gbaud recirculating loop showing system tolerance to nonlinear phase noise and distance improvement.

Regeneration and cascadability assessment of a new passive 2R regenerator based on a dual-stage saturable absorber gate

We report on the regenerative properties and on the cascadability assessment of a passive 2R regenerator based on a dual-stage microcavity saturable absorber gate for low and high levels regeneration.

New passive all-optical semiconductor device for bit-1 level noise reduction

This paper proposes and demonstrates a new configuration of SA-based microcavity that can achieve the required bit-1 level stabilisation. It is based on a simple variation of the well-known reflection-mode SA microcavity used for extinction ratio enhancement, with cavity parameters designed for obtaining a decreasing curve of reflectance vs input power, while an increasing curve is obtained with the usual design. Therefore it can be used with similar multiple quantum well (QW) structures, whose carrier lifetime can be reduced by introducing capture and recombination centers via low temperature epitaxy, high-energy ion implantation, Be or Fe doping, etc.

Phase-preserving amplitude regeneration for RZ-DPSK signals at 42.7 Gbit/s using saturable absorber

We experimentally evaluate a novel all-optical phase-preserving amplitude regeneration technique for RZ-DPSK signals using saturable absorber. The devices capacity for amplitude noise reduction, hence preventing from nonlinear phase noise accumulation is demonstrated at 42.7 Gbit/s.

Cascadability assessment of a microcavity-saturable-absorber based phase-preserving amplitude regenerator in a DPSK transmission system

We investigate the cascadability of a microcavity-saturable-absorber-based phase-preserving amplitude regenerator for RZ-DPSK signals. The results show that the tolerance of phase-encoded signals to nonlinear phase noise is increased. A distance improvement ratio up to 1.6 is experimentally demonstrated.

Characterization in intensity and phase of a passive all-optical device based on saturable absorbers for high bit rate 2R regeneration

We discuss the design and characterisations of a passive all-optical device for 2R regeneration based on a dual-stage of high-speed microcavity saturable absorbers. The measurement of signals at 40GHz by FROG technique reveals the low chirp introduced by this device.

Saturable absorber device for high bit rate all-optical regeneration

A new multiple-quantum-well saturable absorber (SA) device allowing power stabilization is described. Combined with the classical SA achieving extinction ratio improvement, it allows all-optical amplitude-shift-keying 2R signal regeneration. Furthermore its phase-preserving characteristics make it potentially useful to prevent phase noise accumulation in RZ DPSK signals.