Asier Villafranca

Characterization of the Main Semiconductor Laser Static and Dynamic Working Parameters From CW Optical Spectrum Measurements

We present a complete characterization of the work parameters of several types of semiconductor lasers. Static parameters as: power, linewidth and linewidth enhancement factor and also dynamic parameters such as: relaxation oscillations, relative intensity noise and damping rates are calculated using measurements of the optical spectrum of the lasers operated in continuous-wave mode. Methods for the calculation of these parameters are described and applied to the lasers under test by means of a single general setup and a single set of measurements

Investigations of Repetition Rate Stability of a Mode-Locked Quantum Dot Semiconductor Laser in an Auxiliary Optical Fiber Cavity

We have investigated experimentally the pulse train (mode beating) stability of a monolithic mode-locked multi-section quantum-dot laser with an added passive auxiliary optical fiber cavity. Addition of the weakly coupled (¿ -24 dB) cavity reduces the current-induced shift d¿/dI of the principal peak in the RF spectrum (the effective pulse repetition frequency) by more than an order of magnitude, from -39.5 to -2.3 kHz/mA. The rms timing jitter of the pulse train is simultaneously reduced from 1.4 to 0.9 ps.

Measurement of the linewidth enhancement factor in DFB lasers using a high-resolution optical spectrum analyzer

Linewidth enhancement factor (also know as chirp parameter is calculated for two distributed feedback lasers using the linewidth asymptotic behavior predicted by Schawles-Townes and Henry. A high-resolution optical spectrum analyzer (BOSA) is used to measure power and linewidth. Comparison with widely accepted network analyzer method is performed with very good agreement.

Stimulated Brillouin scattering gain profile characterization by interaction between two narrow-linewidth optical sources

We report on results from the characterization of Stimulated Brillouin Scattering (SBS) spectra for standard single-mode fiber produced by the interaction between two counter-propagating tunable laser sources (TLS) using one as the probe signal to measure and the other as the pump, sweeping a wide span around the signal. Assuming TLS linewidth negligible against SBS gain bandwidth, we measure SBS spectrum for a wide range of pump and probe signal power levels and study the evolution of relevant SBS parameters such as linewidth and gain profile. High signal to noise ratio measurements allows analyzing the evolution of the SBS gain profile from Lorentzian to Gaussian as predicted by current theory of SBS and the use of SBS response for filtering applications.

Precise characterization of the frequency chirp in directly modulated DFB lasers

We report on results from the characterization of the frequency chirp characteristics of distributed feedback (DFB) lasers under direct modulation conditions. Parameters describing transient and adiabatic chirp effects are measured for a DFB laser from the ratio of phase to amplitude modulation factors when modulated with sine waves using a high-resolution optical spectrum analyzer. Transient and adiabatic chirp effects produced under digital non-return to zero (NRZ) amplitude modulation are also analyzed using the emitted optical spectrum. Finally, results from the measurement technique are compared with those obtained from measured optical spectra.

Linewidth Enhancement Factor of Semiconductor Lasers: Results from Round-Robin Measurements in COST 288

Round-robin measurements on the linewidth enhancement factor are carried out within several laboratories participating to EU COST 288 action. The alpha-factor is measured by applying up to 7 different techniques. The obtained results are compared.

Multiple-bit all-optical logic based on cross-gain modulation in a semiconductor optical amplifier

In this paper we have evaluated the non-linear response of a semiconductor optical amplifier (SOA) in terms of Cross Gain Modulation effect (XGM). The different ranges of optical power that make the SOA work as a logic gate have been determined, as well as the optimum relation between inputs to obtain the best response. Taking into account the SOA response, a schematic model for an all-optical 4-input NOR gate using a single SOA has been proposed. Our experimental set-up has been tested with four streams of 10 Gbps RZ data to verify the proper and stable operation of the NOR gate under diverse power levels for each data input. The logic output has been evaluated for different inputs using an optical eye diagram to verify its quality; in addition, the possibility of using the NOR output as the input to other logical semiconductor structures, which would allow to chain multiple gates, has been demonstrated. The concatenation of NOR gates allows to build more complex all-optical devices which will permit the design of advanced mechanisms in the field of transparent networks, such as comparators or look-up tables for switching nodes, without the necessity of optical-electrical conversion.

Time-Resolved Chirp Measurements Using Complex Spectrum Analysis Based on Stimulated Brillouin Scattering

A novel method to measure the complex optical spectrum of digitally modulated signals based on stimulated Brillouin scattering (SBS) is presented. Time resolved chirp measurements of a 10 Gbps modulation is performed using this technique.

Integrated Multi-Bit All-Optical NOR Gate for High Speed Data Processing

In this paper, we study the use of integrated semiconductor optical amplifiers as the basic building block for larger-scale programmable photonic circuits. Making use of the non-linear response of these devices, we study the performance of 4-bit all-optical NOR gates based on fully integrable components for high speed all-optical look up tables. Feasibility of the proposed architecture is demonstrated by proof-of-concept experiments using both commercially available devices and photonic integrated circuits.

Programmable all-optical logic gates based on semiconductor optical amplifiers

In this paper, we discuss the feasibility of optical programmable logic devices based on non-linear processing with semiconductor optical amplifiers. We report results from the simulation of the architecture of an all-optical 4-bit Look-up Table, which is the basic logic element of larger-scale programmable devices, and experimental results from a proof-of-concept setup using commercially available devices. Experimental work with photonic integrated circuits to assess the feasibility of integration of such architectures is also presented.