Severine Philippe

40 GHz mode-beating with 8 Hz linewidth and 64 fs timing jitter from a synchronized mode-locked quantum-dash laser diode

Linewidth narrowing of the radio frequency beat-tones and the optical-modes is experimentally investigated in a ∼40 GHz quantum-dash mode-locked laser diode subject to optical injection of 10 GHz pulses. In comparison to the 75 kHz linewidth exhibited by the beat-tones in passive mode-locking conditions, a remarkable reduction to less than 8 Hz is achieved when the laser is under optical injection. From this beat-tone signal, an integrated root-mean-square timing jitter of 64 fs is calculated. In addition, a quadratic profile of the optical linewidth with the wavelength is observed in active locking, reaching a minimum of 1.7 MHz for the longitudinal modes around 1530 nm and progressively increasing to 37.4 MHz for modes at 1525 nm.

Impact of bias current distribution on the noise figure and power saturation of a multicontact semiconductor optical amplifier

We present an experimental investigation of a multicontact semiconductor optical amplifier. This first-generation device allows for direct control of the carrier density profile along the length of the waveguide. This is used to control the device noise figure, with a minimum value of 5 dB observed at a gain of 15 dB for an optimum carrier density profile. The opposite carrier density profile results in an increase of the power saturation by 3 dB.

Experimental Investigation of Polarization Effects in Semiconductor Optical Amplifiers and Implications for All-Optical Switching

A free-space contra-propagation configuration is implemented and pump-probe studies are undertaken in order to study polarization-dependent gain dynamics in bulk semiconductor optical amplifiers (SOAs) and their application to gain and polarization switching. The polarization dependence of the gain compression shows that the co-polarized case, in which the pump and probe are TE-polarized, is the optimum for gain switching. When injecting light polarized at 45deg, an additional contribution due to the presence of rotating fields is observed, and the cross-polarized case is found to be the most promising for polarization switching. The potential for all-optical switching based on nonlinear polarization rotation (NLPR) induced in the SOA is then assessed through characterization of the dynamics of the state of polarization. It is demonstrated that by careful selection of the orientation of a linear polarizer in front of the detector, it is possible to reduce the recovery time from 100 to 5 ps. The improvement comes about from the selection of the intraband fast gain recovery dynamics. Polarization switching offers potentially faster switching times compared to gain switching as well as an extinction ratio improvement of ~10 dB.

Method to improve the noise figure and saturation power in multi-contact semiconductor optical amplifiers: simulation and experiment

The consequences of tailoring the longitudinal carrier density along the active layer of a multi-contact bulk semiconductor optical amplifier (SOA) are investigated using a rate equation model. It is shown that both the noise figure and output power saturation can be optimized for a fixed total injected bias current. The simulation results are validated by comparison with experiment using a multi-contact SOA. The inter-contact resistance is increased using a focused ion beam in order to optimize the carrier density control. A chip noise figure of 3.8 dB and a saturation output power of 9 dBm are measured experimentally for a total bias current of 150 mA.

Experimental investigation of harmonic and subharmonic synchronization of 40 GHz mode-locked quantum-dash laser diodes

Synchronization of a 40 GHz quantum-dash mode-locked (ML) Fabry-Perot laser diode with optically injected pulse streams is experimentally studied. Injected signals consist of nonmodulated and modulated trains of 1.6 ps pulses at various repetition rates, ranging from 10 to 160 GHz and 10 to 160 Gbps, respectively. Subharmonic, fundamental, and harmonic synchronization of the ML laser allows retrieval of stable 40 GHz clock pulses featuring a width of 1.8 ps. Frequency components at 10 and 20 GHz do not create any amplitude modulation on the recovered 40 GHz clock pulses when injecting signals at 10 and 20 GHz/Gbps. In addition, external synchronization of the laser with pulse streams at 80 and 160 GHz/Gbps is sustained despite the absence of significant components at or below 40 GHz.

Semiconductor optical amplifier-based heterodyning detection for resolving optical terahertz beat-tone signals from passively mode-locked semiconductor lasers

An all-optical heterodyne approach based on a room-temperature controlled semiconductor optical amplifier (SOA) for measuring the frequency and linewidth of the terahertz beat-tone signal from a passively mode-locked laser is proposed. Under the injection of two external cavity lasers, the SOA acts as a local oscillator at their detuning frequency and also as an optical frequency mixer whose inputs are the self-modulated spectrum of the device under test and the two laser beams. Frequency and linewidth of the intermediate frequency signal (and therefore, the beat-tone signal) are resolved by using a photodiode and an electrical spectrum analyzer.

Polarization dependence of non-linear gain compression factor in semiconductor optical amplifier

We investigate the power and the polarization dependence of the intraband dynamics in a bulk semiconductor optical amplifier using both a 2.5-ps pump-probe experimental set-up in contra-propagation and a theoretical model. Our model is based on the rate equations and takes into account the polarization dependence of the gain. By comparing experimental and computational results we are able to highlight the dependences of the intraband dynamics and to extract the non-linear gain compression factor as a function of both pulse energy and polarization of the injected pulses.

Improved Bend Waveguide Design for Terahertz Transmission

Bending waveguides with 90° corners based on a two-dimensional photonic crystal with metallic cylinders arranged in a square lattice are studied for THz wave guiding. Considering single- and double-line defects, five different designs are investigated and assessed in terms of their transmission performance. A better structure is proposed by increasing the number of rods in the bending arc, thus achieving superior performance of the transmission characteristics in comparison to that of the former five designs. A comparison of the improved bend waveguide with a linear waveguide shows a significant reduction of the bending losses. Transmission levels of up to 98% within a 2.5 THz bandwidth (from 1.2 to 3.7 THz) have been accomplished.

Short pulse transmission characteristics in multi-contact SOA

An experimental characterisation of a multi-contact semiconductor optical amplifier using ultrashort optical pulses is presented. The SOA in question allows the injection of bias current through multiple independent electrical contacts, allowing the direct control of the carrier density. Picosecond-scale optical pulses are transmitted through the SOA. The non-linear effects on the pulse shape and spectrum after transmission are determined. It is found that the bias current distribution in the SOA is a significant factor in determining the extent of the non-linearities affecting the pulses. Additionally, amplification of negatively chirped pulses in the saturated SOA is found to reduce the spectral width of the pulses.

Polarization Resolved Four-Wave-Mixing-Based Measurement in Bulk Material Semiconductor Optical Amplifier

The anticipated growth in demand for bandwidth leads to the development of all-optical signal processing techniques at ever increasing data rates. One possible candidate to achieve the required performance is the semiconductor optical amplifier (SOA). It has been demonstrated that ultra-fast gain processes are dominant for pulsewidths below 10 ps. In this paper we present experimental results on the polarization dependence of ultra-fast gain dynamics in InGaAsP/InP bulk material SOA probed using a four-wave mixing technique. Using a standard low-pass filter model it is possible to retrieve information on the polarization dependence of linewidth enhancement factors and the timescales for non-linear phenomena such as carrier density pulsation and carrier heating