Experimental investigation of the impact of optical injection on vital parameters of a gain-switched pulse source

An analysis of optical injection on a gain-switched distributed feedback (DFB) laser and its impact on pulse parameters that influence the performance of the pulse source in high-speed optical communication systems is presented in this paper. A range of 10 GHz in detuning and 5 dB in injected power has been experimentally identified to attain pulses, from an optically injected gain-switched DFB laser, with durations below 10 ps and pedestal suppression higher than 35 dB. These pulse features are associated with a side mode suppression ratio of about 30 dB and a timing jitter of less than 1 ps. This demonstrates the feasibility of using optical injection in conjunction with appropriate pulse compression schemes for developing an optimized and cost-efficient pulse source, based on a gain-switched DFB laser, for high-speed photonic systems

An Approach to Assess Solder Interconnect Degradation Using Digital Signal

Department of Human and Systems EngineeringDigital signals used in electronic systems require reliable data communication. It is necessary to monitor the system health continuously to prevent system failure in advance. Solder joints in electronic assemblies are one of the major failure sites under thermal, mechanical and chemical stress conditions during their operation. Solder joint degradation usually starts from the surface where high speed signals are concentrated due to the phenomenon referred to as the skin effect. Due to the skin effect, high speed signals are sensitive when detecting the early stages of solder joint degradation. The objective of the thesis is to assess solder joint degradation in a non-destructive way based on digital signal characterization. For accelerated life testing the stress conditions were designed in order to generate gradual degradation of solder joints. The signal generated by a digital signal transceiver was travelling through the solder joints to continuously monitor the signal integrity under the stress conditions. The signal properities were obtained by eye parameters and jitter, which represented the characteristics of the digital signal in terms of noise and timing error. The eye parameters and jitter exhibited significant increase after the exposure of the solder joints to the stress conditions. The test results indicated the deterioration of the signal integrity resulted from the solder joint degradation, and proved that high speed digital signals could serve as a non-destructive tool for sensing physical degradation. Since this approach is based on the digital signals used in electronic systems, it can be implemented without requiring additional sensing devices. Furthermore, this approach can serve as a proactive prognostic tool, which provides real-time health monitoring of electronic systems and triggers early warning for impending failure.ope

Geometrical jitter and bolometric regime in photon detection by straight superconducting nanowire

We present a direct observation of the geometrical jitter in single photon detection by a straight superconducting nanowire. Differential measurement technique was applied to the 180-{\mu}m long nanowire similar to those commonly used in the technology of superconducting nanowire single photon detectors (SNSPD). A non-gaussian geometrical jitter appears as a wide almost uniform probability distribution (histogram) of the delay time (latency) of the nanowire response to detected photon. White electrical noise of the readout electronics causes broadened, Gaussian shaped edges of the histogram. Subtracting noise contribution, we found for the geometrical jitter a standard deviation of 8.5 ps and the full width at half maximum (FWHM) of the distribution of 29 ps. FWHM corresponds to the propagation speed of the electrical signal along the nanowire of $6.2\times10^{6}$ m/s or 0.02 of the speed of light. Alternatively the propagation speed was estimated from the central frequency of the measured first order self-resonance of the nanowire. Both values agree well with each other and with previously reported values. As the intensity of the incident photon flux increases, the wide probability distribution collapses into a much narrower Gaussian distribution with a standard deviation dominated by the noise of electronics. We associate the collapse of the histogram with the transition from the discrete, single photon detection to the uniform bolometric regim

In-system Jitter Measurement Based on Blind Oversampling Data Recovery

The paper describes a novel method for simple estimation of jitter contained in a received digital signal. The main objective of our research was to enable a non-invasive measurement of data link properties during a regular data transmission. To evaluate the signal quality we estimate amount of jitter contained in the received signal by utilizing internal signals of a data recovery circuit. The method is a pure digital algorithm suitable for implementation in any digital integrated circuit (ASIC or FPGA). It is based on a blind-oversampling data recovery circuit which is used in some receivers instead of a traditional PLL-based clock and data recovery (CDR) circuit. Combination of the described jitter measurement block and the data recovery block forms a very efficient input part of the digital receiver. In such configuration it is able to simultaneously perform both data communication (data recovery) and signal quality estimation (jitter measurement). The jitter measurement portion of the receiver requires no special connection of the received data signal. Thus the measured signal is not influenced by the measurement circuitry at all. To verify the method we performed a measurement on a laboratory free-space optics link. Results of the measurement are satisfactory and can be used for on-line channel analysis

Jitter and Decision-level Noise Separation in A/D Converters

Gaussian aperture jitter leads to a reduced SNR of A/D converters. Also other noise sources, faults and nonlinearities affect the digital output signal. A measurement setup for a new off-chip diagnosis method, which systematically separates the jitter-induced errors from the errors caused by these other factors, is described. Deterministic errors are removed via a subtracting technique. High-level ADC simulations and measurements have been carried out to determine relations between the size of the jitter or decision-level noise and the remaining random errors. By carrying out two tests at two different input frequencies and using the simulation results, errors induced by decision-level noise can be remove

Optimized pulse source employing an externally injected gain-switched laser diode in conjunction with a nonlinearly chirped grating

In this paper, we demonstrate the generation of transform-limited short optical pulses, which display excellent spectral and temporal qualities by employing a novel technology, based on an externally injected gain-switched laser in conjunction with a nonlinearly chirped grating. Using this technique, 3.5-ps optical pulses exhibiting a time-bandwidth product (TBP) of 0.45 are generated, which are suitable for use in high-speed 80 Gb/s optical time-division multiplexing (OTDM) communications systems. The numerical integration of a set of rate equations using suitable parameters for the devices used in the experiments were carried out to further confirm the feasibility of the proposed method for developing an optimized pulse source for high-speed photonic systems