Quaternary pulse position modulation electronics for free-space laser communications

The development of a high data-rate communications electronic subsystem for future application in free-space, direct-detection laser communications is described. The dual channel subsystem uses quaternary pulse position modulation (QPPM) and operates at a throughput of 650 megabits per second. Transmitting functions described include source data multiplexing, channel data multiplexing, and QPPM symbol encoding. Implementation of a prototype version in discrete gallium arsenide logic, radiofrequency components, and microstrip circuitry is presented

Characterizing the Quantum Confined Stark Effect in Semiconductor Quantum Dots and Nanorods for Single-Molecule Electrophysiology

We optimized the performance of quantum confined Stark effect QCSE based voltage nanosensors. A high throughput approach for single particle QCSE characterization was developed and utilized to screen a library of such nanosensors. Type II ZnSe CdS seeded nanorods were found to have the best performance among the different nanosensors evaluated in this work. The degree of correlation between intensity changes and spectral changes of the excitons emission under applied field was characterized. An upper limit for the temporal response of individual ZnSe CdS nanorods to voltage modulation was characterized by high throughput, high temporal resolution intensity measurements using a novel photon counting camera. The measured 3.5 us response time is limited by the voltage modulation electronics and represents about 30 times higher bandwidth than needed for recording an action potential in a neuron.Comment: 36 pages, 6 figure

A power-saving modulation technique for time-of-flight range imaging sensors

Time-of-flight range imaging cameras measure distance and intensity simultaneously for every pixel in an image. With the continued advancement of the technology, a wide variety of new depth sensing applications are emerging; however a number of these potential applications have stringent electrical power constraints that are difficult to meet with the current state-of-the-art systems. Sensor gain modulation contributes a significant proportion of the total image sensor power consumption, and as higher spatial resolution range image sensors operating at higher modulation frequencies (to achieve better measurement precision) are developed, this proportion is likely to increase. The authors have developed a new sensor modulation technique using resonant circuit concepts that is more power efficient than the standard mode of operation. With a proof of principle system, a 93–96% reduction in modulation drive power was demonstrated across a range of modulation frequencies from 1–11 MHz. Finally, an evaluation of the range imaging performance revealed an improvement in measurement linearity in the resonant configuration due primarily to the more sinusoidal shape of the resonant electrical waveforms, while the average precision values were comparable between the standard and resonant operating modes

Towards a FPGA-controlled deep phase modulation interferometer

Deep phase modulation interferometry was proposed as a method to enhance homodyne interferometers to work over many fringes. In this scheme, a sinusoidal phase modulation is applied in one arm while the demodulation takes place as a post-processing step. In this contribution we report on the development to implement this scheme in a fiber coupled interferometer controlled by means of a FPGA, which includes a LEON3 soft-core processor. The latter acts as a CPU and executes a custom made application to communicate with a host PC. In contrast to usual FPGA-based designs, this implementation allows a real-time fine tuning of the parameters involved in the setup, from the control to the post-processing parameters.Comment: Proceedings of the X LISA Symposium, Gainesville, May 18-23, 201

Synchronization tracking in pulse position modulation receiver

A clock pulse generator for decoding pulse position modulation in an optical communication receiver is synchronized by a delay tracking loop which multiplies impulses of a data pulse by the square wave clock pulses from the generator to produce positive impulses when the clock pulse is of one level, and negative impulses when the clock pulse is of another level. A delay tracking loop integrates the impulses and produces an error signal that adjusts the delay so the clock pulses will be synchronized with data pulses. A dead-time tau sub d is provided between data pulses of an interval tau sub p in the data pulse period tau. When synchronized, the average number of positive impulses integrated will equal the average number of negative impulses over the continuous stream of data pulses

Broadband optical chaos for stimulated Brillouin scattering suppression in power over fiber

Broadband chaos generated in an optically injected semiconductor laser is applied for power-over-fiber transmission. By varying the injection power, period-one oscillation, period-two oscillation, and chaotic oscillation are observed in the injected slave laser, indicating a period-doubling route to chaos. Compared to the free-running output of the laser, its chaotic output has a drastically increased signal bandwidth, which leads to a 19 dB increase of the stimulated Brillouin scattering threshold. Using a chaos of 5:2GHz bandwidth, a maximum optical power of 27dBm is obtained after 20km transmission over fiber, which is applicable to optically powering some advanced communication networks. The approach uses the inherent nonlinear laser dynamics, which requires no modulation electronics or microwave signal sources. © 2011 Optical Society of America.published_or_final_versio

Video-rate or high-precision: A flexible range imaging camera

A range imaging camera produces an output similar to a digital photograph, but every pixel in the image contains distance information as well as intensity. This is useful for measuring the shape, size and location of objects in a scene, hence is well suited to certain machine vision applications. Previously we demonstrated a heterodyne range imaging system operating in a relatively high resolution (512-by-512) pixels and high precision (0.4 mm best case) configuration, but with a slow measurement rate (one every 10 s). Although this high precision range imaging is useful for some applications, the low acquisition speed is limiting in many situations. The system’s frame rate and length of acquisition is fully configurable in software, which means the measurement rate can be increased by compromising precision and image resolution. In this paper we demonstrate the flexibility of our range imaging system by showing examples of high precision ranging at slow acquisition speeds and video-rate ranging with reduced ranging precision and image resolution. We also show that the heterodyne approach and the use of more than four samples per beat cycle provides better linearity than the traditional homodyne quadrature detection approach. Finally, we comment on practical issues of frame rate and beat signal frequency selection

Characterizing an image intensifier in an full-field range image system

We are developing a high precision full-field range imaging system. An integral component in this system is an image intensifier, which is modulated at frequencies up to 100 MHz. The range measurement precision is dictated by the image intensifier performance, in particular, the achievable modulation frequency, modulation depth, and waveform shape. By characterizing the image intensifier response, undesirable effects can be observed and quantified with regards to the consequence on the resulting range measurements, and the optimal operating conditions can be selected to minimize these disturbances. The characterization process utilizes a pulsed laser source to temporally probe the gain of the image intensifier. The laser is pulsed at a repetition rate slightly different to the image intensifier modulation frequency, producing a continuous phase shift between the two signals. A charge coupled device samples the image intensifier output, capturing the response over a complete modulation period. Deficiencies in our measured response are clearly identifiable and simple modifications to the configuration of our electrical driver circuit improve the modulation performance

Characterizing an image intensifier in an full-field range image system

We are developing a high precision full-field range imaging system. An integral component in this system is an image intensifier, which is modulated at frequencies up to 100 MHz. The range measurement precision is dictated by the image intensifier performance, in particular, the achievable modulation frequency, modulation depth, and waveform shape. By characterizing the image intensifier response, undesirable effects can be observed and quantified with regards to the consequence on the resulting range measurements, and the optimal operating conditions can be selected to minimize these disturbances. The characterization process utilizes a pulsed laser source to temporally probe the gain of the image intensifier. The laser is pulsed at a repetition rate slightly different to the image intensifier modulation frequency, producing a continuous phase shift between the two signals. A charge coupled device samples the image intensifier output, capturing the response over a complete modulation period. Deficiencies in our measured response are clearly identifiable and simple modifications to the configuration of our electrical driver circuit improve the modulation performance