Quang Trung Le

Quantum-Dash Mode-Locked Laser as a Source for 56-Gb/s DQPSK Modulation in WDM Multicast Applications

We investigate wavelength tunable 56-Gb/s differential quaternary phase-shift keying (DQPSK) systems using comb generation in a quantum-dash mode-locked laser for wavelength-division-multiple access (WDM)-based broadcast application. We present relative intensity noise and bit-error-rate measurements for each mode. We demonstrate error-free operation over nine WDM channels with 100-GHz spacing.

Multi-Data-Rate System Performance of a 40-GHz All-Optical Clock Recovery Based on a Quantum-Dot Fabry–PÉrot Laser

Bit-error-rate assessment of a multi-rate all-optical clock recovery (OCR) based on a narrow linewidth mode-locked quantum-dot (QD) Fabry-Perot laser is presented in this letter. OCR has been achieved without external feedback. We use a QD Fabry-Perot semiconductor laser designed for 40-GHz clock extraction. We then present OCR performance with 40-, 80-, and 160-Gb/s input data signal and demonstrate that clock recovery has been obtained thanks to subharmonic locking process. Results are presented through penalty measurement using an original characterization based on recovered clock remodulation with electrical data from the transmitter. This technique allows us to evaluate the quality of the recovered clock.

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.

Self-phase modulation-based 2R regenerator including pulse compression and offset filtering for 42.6 Gbit/s RZ-33% transmission systems

We report on the experimental and theoretical study of a self-phase-modulation-based regenerator at 42.6 Gbit/s with a return-to-zero 33% format. We point out some detrimental effects such as intrachannel interactions and Brillouin scattering. An efficient solution, relying on a self-phase-modulation-based pulse compressor in combination with the regenerator, is proposed to overcome these detrimental phenomena. The experimental demonstration shows the effectiveness of a wavelength-transparent regenerator at 42.6 Gbit/s with a sensitivity-improvement of more than 5 dB and an eye-opening improvement of 2.3 dB in a back-to-back configuration, as well as a 10 times maximum transmission distance improvement for a BER of 10(-4).

All-optical sampling and spectrographic pulse measurement using cross-absorption modulation in multiple-quantum-well devices

The application of cross absorption modulation for optical sampling and phase sensitive pulse measurement is presented. Both a commercial 40 GHz electroabsorption modulator and a vertical microcavity saturable absorber are used to sample a 2 ps pulse train at 40 GHz. The modulator was then used to make cross-absorption modulation based frequency-resolved optical gating (FROG) measurements. The results were verified by comparison with a commercial optical sampling oscilloscope and the more standard second harmonic generation FROG technique.

Long Distance Transmission Using Optical Regeneration

Principles of 2R and 3R optical regeneration for long haul transmission systems are presented, and recirculation loop assessment experiments of this technique are reviewed and discussed.

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.

Quantum-dash mode-locked laser source for wavelength-tunable 56 Gbit/s DQPSK

We investigate wavelength tunable 56 Gbit/s DQPSK systems using comb generation in a quantum-dash mode-locked laser. Relative intensity noise and bit error rate is measured for each mode. Error-free operation is obtained over 9 WDM channels with 100 GHz spacing.

Noise Tolerance Assessment and System Design Discussion of a Saturable-Absorption-Based All-Optical 2R Regenerator

This letter presents the cascadability assessment and the noise tolerance characterization of an all-optical 2R regenerator based on saturable absorption and nonlinear effects in fiber. The impact of optical signal-to-noise ratio on the 2R regenerator performance is shown, and a regenerator characterization technique that can be used for system design and engineering is discussed.