Poorya Saghari

Independent and Simultaneous Monitoring of Chromatic and Polarization-Mode Dispersion in OOK and DPSK Transmission

We propose and demonstrate a novel technique for a simultaneous chromatic and first-order polarization-mode-dispersion (PMD) monitoring method using a partial bit delay Mach-Zehnder interferometer (MZI) with radio-frequency (RF) clock tone monitoring. RF clock tones at the output of the two branches of the MZI behave oppositely with increasing chromatic dispersion (CD) which improves the sensitivity of the measurement. The technique increases CD monitoring sensitivity over standard clock tone methods by a factor of two for a nonreturn-to-zero intensity modulation format and a factor of five for a differential-phase-shift-keying modulation format. The accuracy of PMD monitoring is also enhanced. Moreover, the partial bit delay allows the signal to pass through the constructive branch of the MZI with no observable degradation of the signal quality, allowing it to be normally detected by a receiver

Analytical interference model for two-dimensional (time-wavelength) asynchronous O-CDMA systems using various receiver structures

This paper gives a probabilistic model for the interference in optical code-division multiple access (O-CDMA) systems using a conventional and hard-limiting receiver that relates the code parameters to the system performance. It is shown that for a specified number of wavelengths and chip times, the code weight and maximum collision parameter (MCP) of the code can be optimized in order to maximize the numbers of active and/or potential users. Design rules to maximize the number of active users under certain system constraint are also provided. In this study, the spectral efficiency limits in the O-CDMA system using conventional and hard-limiting receivers are studied. It is worth mentioning that the models offered in this paper do not require the knowledge of the specific codes in the code set and provide the full statistics of the interference under the random code assumption.

Advanced Techniques to Increase the Number of Users and Bit Rate in OCDMA Networks

Optical code-division multiple-access (OCDMA) systems have recently become a topic of interest for their potential application in access points and optical LANs. In this paper, we review OCDMA systems and their limitations, as well as various experimental techniques to increase the number of users and/or bit rate in a system or a network. These techniques include incorporating M-ary modulation formats, hard-limiting receiver, variable thresholding, and orthogonal polarizations as the third dimension. We also discuss some network limitations such as congestion collapse and near-far effect, and we investigate two techniques to overcome them: interference avoidance and missing chip detection.

Fiber Bragg Grating Balanced DPSK Demodulation

We propose and experimentally demonstrate the utilization of a uniform-FBG for balanced DPSK demodulation. The reflection (transmission) is utilized as a bandpass (notch) frequency-discriminator. An approximate 2.8 dB performance increase is achieved in the balanced configuration

Experimental and theoretical analysis of the optimum decision threshold for varying numbers of active users in a 2-D time-wavelength asynchronous O-CDMA system

We experimentally demonstrate the existence of an optimal decision threshold in an optical code-division-multiple-access (O-CDMA) system and show its relation to the number of active users. Our results show that tuning the decision threshold in an O-CDMA receiver to an optimal point based on the number of active users improves receiver sensitivity by > 3 dB. We also demonstrate a monitoring scheme to estimate the number of active users in an O-CDMA system using harmonics of RF clock tones.

Simultaneous Monitoring of Chromatic Dispersion and PMD for OOK and DPSK Using Partial-Bit-Delay-Assisted Clock Tone Detection

We present a simultaneous chromatic and polarization mode dispersion monitoring method using partial bit delay-assisted clock tone monitoring. The method increases clock-tone monitoring sensitivity by a factor of two for NRZ and five for DPSK.

Tolerances and Receiver Sensitivity Penalties of Multibit Delay Differential-Phase Shift-Keying Demodulation

Multibit delay demodulation of differential-phase shift-keying (DPSK) is finding applications in polarization interleaved modulation, optical time-domain multiplexing (OTDM), and multisymbol DPSK demodulation. Little attention has been paid to the degradation in tolerance and power penalty associated with multibit delay demodulation. We assess experimentally, numerically, and analytically the power penalties and tolerances associated with multibit delay DPSK demodulation. Numerical and analytical results show that the power penalty scales by a small factor of 0.2-0.35 dB per integer bit delay due to laser linewidth (LW) while experimental back-to-back results show a significant 1.2 dB per integer bit delay due to frequency offset penalty of longer bit delays. Frequency offset tolerance scales as 1/bit-delay and the delay-mismatch tolerance decreases by 20% for delays longer than 1 bit. A simple analytic model accounts for the combined effect of LW, frequency offset, and amplified spontaneous emission.

Implication of Chromatic Dispersion on Frequency Offset and Bit Delay Mismatch Penalty in DPSK Demodulation

We demonstrate experimentally and numerically the increased penalty due to combination of residual chromatic dispersion and interferometer frequency offset and bit-delay mismatch. The combined penalty is greater than the sum of the individual penalties.

Variable Bit Rate Optical CDMA Networks Using Multiple Pulse Position Modulation

We have demonstrated multiple-pulse position modulation to achieve a variable bit rate OCDMA system, operating at different bit rates of 2.5, 4.3, and 5.7 Gbps, without changing pulse- width, encoders/decoders, and utilized bandwidth.

Experimental Demonstration of an Interference-Avoidance-Based Protocol for O-CDMA Networks

We demonstrate the transmission scheduling algorithm in an O-CDMA network to avoid congestion collapse in an O-CDMA network. Our result shows that transmission scheduling increases the performance of the system by orders of magnitude.