Novel design for noise controlled semiconductor optical amplifier

The use of semiconductor optical amplifiers (SOA) in optical communications networks has so far been limited due to their inherent large noise figure (NF) compared to Erbium Doped Fibre Amplifiers. Therefore improvement of the noise performance of SOAs is critical to their widespread adoption in future networks. We propose to reduce the NF of the SOA by introducing a lasing cavity lateral to the axis of amplification of the device. The carrier density within the cavity is clamped at the lasing threshold. It is thus possible to engineer the carrier density distribution along the active waveguide by controlling the cavity design. According to our simulations, some of the cavity designs lead to a reduction of the noise figure in this novel SOA

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 analyze

Heterodyne detection of optical terahertz beat-tones based on semiconductor optical amplifier

In this paper, a detection scheme based on four wave mixing in a semiconductor optical amplifier (SOA) is used to measure the frequency and bandwidth of the optical terahertz beat-tone signal generated by a passively mode locked semiconductor laser. Two signals from external cavity lasers are injected into an SOA, which acts as a local oscillator at their detuning frequency. The device under test is a passively mode locked laser with a beattone frequency in the terahertz spectrum. Its optical signal is injected in the SOA, which also acts as a frequency mixer. The frequency and linewidth of the terahertz signal are then measured by retrieving the intermediate frequency detected by a low bandwidth photodiode and an electrical spectrum analyser

Investigation of optimum wavelength converter based on nonlinear polarisation rotation in a bulk SOA

This work is focused on understanding and optimising the physical mechanisms responsible for wavelength conversion based on cross-polarisation modulation (XPolM) in a bulk semiconductor optical amplifier. A comparison is made between the conversion performance that can be achieved with cross-gain modulation (XGM) and XPolM in co- and counter-propagation configurations. Wavelength independent conversion can be achieved when nonlinear polarisation rotation and XGM effects are balanced in the case of non-inverted wavelength conversion

Experimental investigation of polarisation rotation in semiconductor optical amplifiers

An experimental study of polarisation rotation in a semiconductor optical amplifier is presented. Two techniques are used to investigate the gain and birefringence along the two eigenmodes of the component waveguide, with and without injection. The first investigation is based on the residual reflectivity of the facet mirrors. From the modulation depth of polarisation resolved spectra, the gain and the refractive indices of these modes are determined. The second investigation takes into account the variation of the eigenmode gain and refractive indices as a function of injected power over the range 83.3 to 413 mW. The results of these two experiments are compared, and it is determined that the refractive index and the single-pass gain along the horizontal axis of the waveguide are higher than those along the vertical axis. Both gain and refractive index differences increase as a function of injected power in the sample under test. Furthermore, it is concluded that polarisation rotation in this component is heavily influenced by the power dependence of the relative gain in the TE and TM modes and birefringence

Noise controlled semiconductor optical amplifier based on lateral cavity laser

Experimental characterisation of a novel noise-controlled semiconductor optical amplifier (NCSOA) is presented. The design utilises grooves etched parallel to the active waveguide, at the output sections of the NCSOA, so as to induce lasing laterally to the propagation axis. This clamps the carrier density in a relevant region, allowing for the engineering of a specific longitudinal carrier density profile, corresponding to an improved noise figure performance. Results have demonstrated the effectiveness of carrier density profile engineering as a means of reducing the noise figure in semiconductor optical amplifier

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

We present an experimental investigation of a multi-contact 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

Investigation of polarization dependent gain dynamics in a bulk SOA

The polarization dependence of the gain dynamics in a bulk semiconductor optical amplifier is examined using two experimental setups. The first experimental investigation is based on four-wave mixing. Using a low-pass filter model it is possible to retrieve information on the polarization dependence of the linewidth enhancement factors and recovery timeframes associated with carrier density pulsation and carrier heating, respectively. These experimental results have been confirmed using a second setup. Linearly polarized pulses (2 ps) are launched into the same SOA as a function of the angle of injection. The propagated pulse is analyzed in the frequency and time domains using the frequency resolved optical gating technique. It is found that the SOA presents a polarization dependence when the device is in the non-linear regime

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 pulse