Compressive sampling using a pushframe camera

The recently described pushframe imager, a parallelized single pixel camera capturing with a pushbroom-like motion, is intrinsically suited to both remote-sensing and compressive sampling. It optically applies a 2D mask to the imaged scene, before performing light integration along a single spatial axis, but previous work has not made use of the architecture's potential for taking measurements sparsely. In this paper we develop a strongly performing static binarized noiselet compressive sampling mask design, tailored to pushframe hardware, allowing both a single exposure per motion time-step, and retention of 2D correlations in the scene. Results from simulated and real-world captures are presented, with performance shown to be similar to that of immobile — and hence inappropriate for satellite use — whole-scene imagers. A particular feature of our sampling approach is that the degree of compression can be varied without altering the pattern, and we demonstrate the utility of this for efficiently storing and transmitting multi-spectral images

Frequency modified feedback in external cavity semiconductor laser systems

This thesis presents work done on two external cavity semiconductor laser systems with different types of frequency modified feedback. The first system, based on a vertical-cavity surface-emitting laser (VCSEL) with feedback from a volume Bragg grating, is used to investigate the control of laser cavity solitons (LCSs). The temporal dynamics of a second system, relying on an edge-emitting semiconductor laser (EEL) with frequency-shifted feedback (FSF), is investigated. LCSs are trapped in local minima of a disorder potential landscape which is created by the growth induced inhomogeneities of the cavity resonance. The positions, frequencies and thresholds of the LCSs are dictated by the disorder and as a result LCSs appear at certain locations in the VCSEL aperture. These properties are used to demonstrate a method to quantitatively characterize the disorder in a VCSEL with frequency-selective feedback. LCSs, as any laser, have the freedom to choose their optical phase. The effects of disorder on the interaction of two LCSs are considered. We demonstrate frequency and phase synchronization of paired LCSs as their relative detuning is varied. In both theory and experiment the locking behavior is well described by the Adler model for the synchronization of coupled oscillators. In the case of the second system, dynamics of the output of an EEL with FSF is systematically and comprehensively measured for the first time. Three fundamentally different regimes of operation are identified corresponding to low, medium and high levels of FSF. Low levels of FSF cause the emission spectrum to broaden. Medium levels of FSF are consistent with those found in semiconductor with conventional feedback systems. High levels of FSF result in periodic oscillations on a cw baseline which is similar to the pulsed comb of mode output observed in analogous FSF systems using solid state gain media when the FSF is resonant.This thesis presents work done on two external cavity semiconductor laser systems with different types of frequency modified feedback. The first system, based on a vertical-cavity surface-emitting laser (VCSEL) with feedback from a volume Bragg grating, is used to investigate the control of laser cavity solitons (LCSs). The temporal dynamics of a second system, relying on an edge-emitting semiconductor laser (EEL) with frequency-shifted feedback (FSF), is investigated. LCSs are trapped in local minima of a disorder potential landscape which is created by the growth induced inhomogeneities of the cavity resonance. The positions, frequencies and thresholds of the LCSs are dictated by the disorder and as a result LCSs appear at certain locations in the VCSEL aperture. These properties are used to demonstrate a method to quantitatively characterize the disorder in a VCSEL with frequency-selective feedback. LCSs, as any laser, have the freedom to choose their optical phase. The effects of disorder on the interaction of two LCSs are considered. We demonstrate frequency and phase synchronization of paired LCSs as their relative detuning is varied. In both theory and experiment the locking behavior is well described by the Adler model for the synchronization of coupled oscillators. In the case of the second system, dynamics of the output of an EEL with FSF is systematically and comprehensively measured for the first time. Three fundamentally different regimes of operation are identified corresponding to low, medium and high levels of FSF. Low levels of FSF cause the emission spectrum to broaden. Medium levels of FSF are consistent with those found in semiconductor with conventional feedback systems. High levels of FSF result in periodic oscillations on a cw baseline which is similar to the pulsed comb of mode output observed in analogous FSF systems using solid state gain media when the FSF is resonant

Dynamics of a semiconductor laser with frequency shifted feedback

Dynamics of the output of a semiconductor laser with frequency-shifted optical feedback system is systematically analyzed. Results from experimental studies using an 830 nm, QW, Fabry-Perot cavity, semiconductor laser are reported. The dynamics are mapped as a function of the level of frequency shifted feedback (FSF) and the injection current. The frequency shift of the optical feedback is the fundamental or a sub-harmonic of the external cavity frequency in the experiments. Multi-GHz-bandwidth real time data collection and analysis is used to investigate the temporal and spectral behaviour of the output power of the nonlinear system. The results are contrasted with those from conventional semiconductor laser with optical feedback systems. Three fundamentally different regimes of operation are identified for the FSF system corresponding to low, medium and high levels of FSF. The low and medium level FSF regimes are consistent with those found in the semiconductor with conventional optical feedback system. It is only when high levels of FSF are used that the output gives a noisy, near periodic output which is similar to the pulsed comb of mode output observed in analogous FSF laser systems using solid state gain media when the FSF is resonant.9 page(s

High resolution mapping of the dynamics of a nonlinear semiconductor laser system

Optical feedback is known to cause a range of complex dynamical states in the output power of semiconductor lasers. These types of systems have been much studied [1]. The dynamic state of the laser output can be controlled by varying the level of optical feedback and also the injection current to the laser [2]. Traditionally, analysis of nonlinear dynamics produced by semiconductor lasers has been based on optical and/or RF spectra, due to the high frequencies involved. More recently, the availability of high bandwidth real-time oscilloscopes has facilitated direct measurement of the output power time series and allowed the temporal information, missing from earlier investigations, to be captured. Computer controlled experimental setups have also improved the resolution at which system parameters can be varied and the amount of data that can be captured.1 page(s

BB84 quantum key distribution transmitter utilising broadband sources and a narrow spectral filter

Data for the paper with the same titl