Didier Erasme

Cross-polarization modulation in semiconductor optical amplifiers

The polarization sensitivity of semiconductor optical amplifiers can be assessed in terms of gain or in terms of induced phase shift. Although the former aspect has received a lot of attention, the latter is rarely mentioned in the literature. Nevertheless, this birefringence leading to a rotation of the lightwave polarization at the output of the device may give rise to some interesting or unwanted effects. An optical control of the birefringence can be applied to wavelength conversion, signal regeneration, all-optical switching or gating. In this letter, the variation of the birefringence with input polarization and input power is measured.

5-Gb/s XOR optical gate based on cross-polarization modulation in semiconductor optical amplifiers

We demonstrate a new design for a XOR optical gate operating in the GHz regime using the cross-polarization modulation effect in a semiconductor optical amplifier. Dynamic and optically controlled polarization rotation in the devices is used to control the output power of the device. Static extinction ratio of the order of 20 dB can be obtained. Bit rate doubling at rate of 1.2 and 2.5 Gb/s have been demonstrated.

All-optical AND gate implementation using cross-polarization modulation in a semiconductor optical amplifier

We demonstrate experimentally a new design for an all-optical AND gate operating in the gigahertz regime. The efficiency of this effect was estimated by measuring the conversion coefficients C/sub TE/TM/ and C/sub TM/TE/ indicating the TE to TM mode conversion and vice versa when the amplifier is perturbed with a wavelength tunable control beam. The all-optical gate here described differ from others developed before using semiconductor optical amplifiers in its ability to operate on nondegenerate input signals and to produce an output signal with an independent wavelength from the wavelengths of the input signals.

Optical injection locking and phase-lock loop combined systems

Optical injection locking and optical phase-lock loops have been used for laser synchronization. The use of a combined optical injection locking and phase-lock loop system is proposed here. We have taken into account the modification of the slave laser phase response induced by the injection locking to calculated the phase-error signal spectrum and the phase-error variance for an optical injection locking and phase-lock system. They show that this system presents both a wide locking range, given by the optical injection locking action, and a low phase error for low frequencies, given by the optical phase-lock loop action. These results can improve the system tracking capability and decrease the final phase-error variance compared with those in isolated systems.

640-Gbit/s Data Transmission and Clock Recovery Using an Ultrafast Periodically Poled Lithium Niobate Device

This paper presents the first demonstration of the use of a periodically poled lithium niobate device for signal processing at 640 Gbit/s. Clock recovery is performed successfully using the lithium niobate device, and the clock signal is used to control a nonlinear fiber-based demultiplexer. The full 640-Gbit/s system gives error-free performance with no pattern dependence and there is less than 1-dB power penalty after 50-km fiber transmission.

Modulation properties of an injection-locked semiconductor laser

The modulation properties of an injection-locked semiconductor laser are investigated using the rate equation formalism. Intensity and phase modulations (IM and PM) are analyzed throughout the locking range where the locked laser is stable. The relaxation oscillation resonance in the IM and PM frequency responses can be dramatically reduced by tuning the injected power and the frequency difference between the master laser and the free-running slave laser. The power spectra under direct modulation are derived throughout the stable locking range. The spreading of the harmonics of the modulated locked laser is strongly affected by the frequency detuning, the injected power, and the injected current modulation. Measurements illustrating the theoretical results are also presented. >

All-optical NOR gates with two and three input logic signals based on cross-polarization modulation in a semiconductor optical amplifier

In this work we present all-optical NOR gates with two and three input logic signals using the cross-polarization modulation (XPolM) effect in a semiconductor optical amplifier (SOA). The gates utilize a single SOA and it needs neither an inversion stage nor an additional synchronized clock. Unlike the gates based on cross-gain and cross-phase modulation in SOAs, the gates presented in this work need neither interforemetric configurations nor input logic signals producing a strong saturation of the amplifier gain. Based on a discussion of the XPolM effect, we present the design criteria allowing the implementation of the all-optical NOR gates with two and three input logic signals.

Analysis of a homodyne receiver using an injection-locked semiconductor laser

The authors study an optical homodyne receiver using an injection-locked semiconductor laser as a local oscillator. The carrier recovery process introduces a phase error, and the calculation of its statistical properties leads to the evaluation of the receiver performance. The analysis shows the dependence of the receiver performance on the injected power and the phase detuning, between the transmitter, and local oscillator electric fields. The receiver performance is affected by the phase noises of the transmitter and local oscillators, by the shot noise of the detectors in the receiver, and by the modulation noise resulting from the injection locking of the local oscillator by a modulated signal. >

10-GHz clock recovery using an optoelectronic phase-locked loop based on three-wave mixing in periodically poled lithium niobate

Clock recovery is a critical function of any digital communications system. To replace the classical electronic phase-locked loops (PLLs) at higher bit rates, several all-optical or optoelectronic clock recovery methods are being studied. This letter presents an optoelectronic PLL where three-wave mixing in a periodically poled lithium niobate (PPLN) device provides the phase comparator. Since PPLN is passive, it generates no amplified spontaneous emission noise; also, the error signal is in the visible (763 nm), therefore easily separated from infrared input signals. Clock recovery is performed on a 10-GHz sinusoidal optical signal. Being based on ultrafast nonlinear effects, this scheme should be able to reach still higher bit rates, on the order of several hundred gigahertz. Also, subclock extraction (e.g., 40-to-10 GHz) should be possible without modifications.

Simple Estimation of Fiber Dispersion and Laser Chirp Parameters Using the Downhill Simplex Fitting Algorithm

We report on a simple and fast method to estimate the fiber dispersion and laser chirp parameters on a dispersive Intensity Modulation and Direct Detection (IM/DD) optical channel. Based on the general IM/DD small-signal frequency response, we use the Downhill-Simplex algorithm to fit the channel measurement retrieved with a network analyzer to a general mathematical model. The method is proven to be quite efficient for light sources of different natures and with different adiabatic and transient chirp characteristics, including a Distributed Feedback (DFB) laser, an Electroabsorption modulator (EAM) and even a Reflective Semiconductor Optical Amplifier with fiber-Bragg grating (RSOA-FBG).