Kevin Carney

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.

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.

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.

Characterization of a multi-electrode bulk-SOA for low NF in-line amplification in passive optical networks

A bulk semiconductor optical amplifier (SOA) utilizing a multi-contact biasing method is characterized as a function of the bias current supplied to each section Firstly, amplified spontaneous emission spectra and characteristic light-current profiles are analyzed. Single-pass gain and noise figure of the SOA are then assessed by injecting a continuous wave input beam. Finally, the amplification of a 10 Gb/s (215-1) long pseudo random bit sequence signal is analysed. The obtained results, particularly at a bias condition of 90mA-50mA-10mA, reveal the potential of this device as a low noise figure in-line amplifier.

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.

Discrete mode laser diodes emitting single wavelength mode at λ∼657 and 689 nm for optical atomic clock applications

Compact monolithic single-mode red emitting diode lasers are still not readily available for many wavelengths in the visible spectrum. Strontium lattice and Calcium clocks are some of the most widely investigated optical clocks worldwide and the pertinent transitions wavelengths required are in the red and blue wavelength spectral region. The current state of the art in laser technology employs external cavity laser diodes and frequency doubling crystals in order to hit the desired wavelength with external amplifiers used to meet the power requirements. Compact rugged monolithic narrow linewidth laser sources operating in the red and blue wavelengths have been identified by the European Space Agency as a key technology that could be used to replace all of these costly, energy inefficient and vibration sensitive components and to one day facilitate the optical clock leaving the laboratory and to eventually end up on a satellite in space.

Characterization of 60GHz quantum well passively mode-locked Fabry-Perot laser for RoF and WPAN applications

Summary form only given. As the frequency spectrum below 10GHz becomes saturated, it will become increasingly difficult to maintain adequate bandwidth provision for the growing customer demand. For this reason, the possibility of utilizing the unlicensed 57GHz-64GHz band for services such as WPAN is an attractive prospect [1]. Furthermore, the advantages of an optical system to realize this prospect are numerous. Extremely low phase noise can be obtained from laser systems used for millimetre-wave applications, relative to the equivalent electronic components. In addition to this, the costs of such a system are much lower and the footprint smaller, not to mention the additional benefits of low loss and easy switching of carrier frequency. In this paper, a multimode quantum well Fabry-Perot laser with potential application as a carrier signal generator for WPAN is characterized. The laser is passively mode-locked, with no saturable absorber, and exhibits pulsed operation at 60GHz with only d.c. bias applied. The InP-based laser is 700μm long and exhibits multimode emission between 1555nm and 1565nm. A typical output spectrum at 70mA bias current is shown in Fig. 1. Also indicated on the graph are the measured values for optical linewidth for each mode. These values were measured using an optical self-heterodyne setup.The linewidth of the beat tone generated at a photodiode was also measured for various values of bias current. In free-running conditions, a linewidth of 1.7MHz is measured at 61.92GHz. A circulator and an optical delay line are then placed after the laser in the setup, in place of the isolator, thus creating an optical feedback loop. A filter is used to isolate two consecutive modes. The linewidth measured for the beat signal is reduced by a factor of 100, to nearly 10kHz, with lower linewidths being for longitudinal modes near to the centre of the optical spectrum. These results indicate that this laser has potential for application in RoF and WPAN areas, due to its low linewidth, cost and the fact that it exhibits 60GHz operation using only d.c. bias.

Characterization of a 60 GHz passively mode locked quantum well laser with applications for radio over fibre

In this paper, a multimode quantum well Fabry-Perot laser with potential application as a carrier signal generator for radio-over-fibre (RoF) is characterized. The laser is passively mode-locked, with no saturable absorber, and exhibits pulsed operation at 60GHz with only d.c. bias applied. The optical spectra, optical linewidth and beat tone linewidth of the laser are all characterized. Due to its pulsed operation at 60GHz and its low linewidth, this laser could be a key low cost component for RoF and WPAN systems.

3.8dB Noise figure in bulk semiconductor optical amplifier

The present paper reports numerical and experimental investigation of noise figure of a multi-section semiconductor optical amplifier. The designed amplifier shows a 3.8dB noise figure, which seems to be the lowest figure reported.

Characterization of 60 GHz multi quantum well passively mode-locked laser under optical self injection locking

The quality and pulse compression of the 60 GHz millimeter wave signals generated by 750 m long InAlGaAs Multi Quantum Well (MQW) passively mode locked laser under free running and optical self-injection locked conditions are experimentally characterized in terms of longitudinal modes under certain bias currents that range from 24 mA to 90 mA. Initially, the MQW laser is characterized in free running condition with no external injection. The measurements reflect that the free spectral range of laser under test is around 61 GHz and exhibit more than 22 lasing modes. The laser is then integrated into low phase noise self-injection locking oscillator by feeding a part of output RF signal back into the laser cavity to enhance passive mode locking. By doing so the microwave line width of our laser is reduced from 900 kHz to 24 kHz with significant increase in output of resultant beat tones which exhibits strong passive mode locking. This is the first time that the free running microwave line width of MQW laser is reduced up to this level. It is evident from our experimental investigation that as we increase the power and phase correlation between different longitudinal modes inside laser cavity through optical self-injection, the strength of the passively mode locked mechanism is significantly increased and the phase noise of radio frequency signal is drastically reduced.