Kambiz Jamshidi

Code Family for Modified Spectral-Amplitude-Coding OCDMA Systems and Performance Analysis

A novel family of codes for modified spectral-amplitude-coding optical code division multiple access (SAC-OCDMA) is introduced. The proposed codes exist for more processing gains than the previously reported codes do. In the network using these codes, the number of users can be extended without any essential changes in the previous transmitters. In this study, we propose a construction method for these codes and compare their performance with previously reported codes.

Bounds for the BER of Codes With Fixed Cross Correlation in SAC-OCDMA Systems

In this paper, two lower and upper bounds for the bit error rate of codes with fixed cross-correlation in spectral-amplitude-coding optical code-division multiple access systems are offered. In this study, we consider only the phase-induced intensity noise and neglect other noises such as shot and thermal noises, in the performance analysis. Also, it is assumed that users are synchronous. This bound is obtained using combinatorics approach and utilizing simple inequalities. In numerical results, the comparison between the upper bound, lower bound, and simulation results for MQC, MFH, BIBD, and Hadamard codes is presented, and the tightness of the bounds is evaluated.

Quasi-Light-Storage based on time-frequency coherence.

We show a method for distortion-free quasi storage of light which is based on the coherence between the spectrum and the time representation of pulse sequences. The whole system can be considered as a black box that stores the light until it will be extracted. In the experiment we delayed several 5 bit patterns with bit durations of 500ps up to 38ns. The delay can be tuned in fine and coarse range. The method works in the entire transparency range of optical fibers and only uses standard components of optical telecommunications. Hence, it can easily be integrated into existing systems.

A Review to the All-Optical Quasi-Light Storage

In this paper, we compare two methods to delay optical signals based on quasi-light storage (QLS). These methods are very simple and offer high-tunable storage times up to several thousand bits. Furthermore, they are transparent to the bit rate and modulation format of the signal. We explore the potentials and limitations of both methods. Fiber-based QLS is useful when high absolute delay is required and no loss or very small amount of attenuation can be tolerated. Frequency-to-time-conversion-based QLS can be used for the delay of very high bandwidth signals.

Widely tunable optical delay generator

We propose and demonstrate a method for quasi storage of light based on periodic spectral filtering realized in the time domain by amplitude modulation using frequency-to-time conversion. The delay can be tuned in a wide range by changing the frequency of an electrical modulation signal. In our experiments, the delay of single 2.5 ps pulses varied by 66 pulse widths. The technique works equally well for more complex optical data packets. Contrary to known approaches, the method has a very large spectral bandwidth and can be implemented by either fiber or integrated solutions using existing technologies. Because of the large bandwidth, fractional delays up to several tens of thousands of pulse widths can be achieved potentially for subpicosecond pulses, which is a tremendous value regarding the implementation simplicity.

Very large, tunable, positive and negative group delay for high-bandwidth signals

A method is proposed to delay optical signals with very large spectral bandwidth based on frequency-to-time conversion and saw-tooth phase modulation. The delay is tunable by modulation slope adjustment. Delay and advancement up to 10 pulse widths are demonstrated experimentally.

Performance Analysis of a Spectrally Phase-Encoded Optical Code Division Multiple Access Packet Network

We analyze the performance of a spectrally phase-encoded optical code division multiple access slotted packet network based on a simple protocol. The steady-state throughput and average packet delay are derived as two measures to assess the performance of the network. First, only multiple access interference is considered and other sources of noise are neglected. In this context, comparing different systems with the fixed bit rate and chip duration leads us to conclude that increasing the code length improves the performance of networks with small average activity; but in highly active networks, decreasing the code length results in a significant improvement in the throughput and average packet delay. Next, Gaussian approximation is used in our performance analysis to consider both shot noise and thermal noise as well as multiple access interference. The packet success probability is derived as a function of transmitted power. It is shown that in a fixed bandwidth and with a fixed bit rate, increasing the code length can lead to better performance in high average powers. But, in the low-power regime, decreasing code length leads to better performance due to the lower level of activity.

Integration of a Tunable, Optical Delay Generator in a Silicon Photonics Platform

We propose an integrated optical delay generator based on Frequency-to-Time conversion. The required dispersions are produced by micro ring resonators based on SOI nano wires. Our design can provide delays up to 500 nanoseconds.