Varghese Baby

All-optical data format conversion between RZ and NRZ based on a Mach-Zehnder interferometric wavelength converter

We demonstrate all-optical conversion between two different data formats: return-to-zero (RZ) and nonreturn-to-zero (NRZ) using a Mach-Zehnder interferometric wavelength converter. For RZ-to-NRZ conversion, a duplication scheme is demonstrated to reduce the ripples caused by the carrier recovery of the semiconductor optical amplifier. The relationship between the ripple-to-signal ratio and the number of pulse duplications is numerically analyzed. For the NRZ-to-RZ conversion, the wavelength converter also shows high performance. The converted RZ signal has a negative power penalty to the NRZ signal due to the change of the data format.

Multiple-wavelength optical orthogonal codes under prime-sequence permutations for optical CDMA

A new family of two-dimensional (2-D) wavelength-hopping time-spreading codes, which employs wavelength hopping algebraically under prime-sequence permutations on top of time-spreading optical orthogonal codes, is studied and analyzed. Different from other 2-D codes, our new codes allow the number of wavelengths and code length to be chosen independently and, at the same time, the code cardinality is a quadratic function of the number of wavelengths without sacrificing the maximum cross-correlation value (i.e., still at most one). They are particularly suitable for high bit-rate optical code-division multiple-access systems with broadband mode-locked lasers, in which the number of time slots is very limited, and system capacity can only be grown by increasing the number of wavelengths, rather than code length. Finally, a novel wavelength-aware detector for wavelength-hopping time-spreading codes is discussed and shown to provide improved code performance.

Experimental demonstration and scalability analysis of a four-node 102-Gchip/s fast frequency-hopping time-spreading optical CDMA network

We present experimental and simulation results from a 102-Gchips/s incoherent wavelength-hopping time-spreading optical code-division multiple-access testbed, utilizing four 50-GHz ITU grid wavelengths. Error-free operation of four users is obtained with an effective power penalty /spl sim/0.5 dB. Simulation studies show scalability to >10 users with an effective power penalty of /spl sim/4 dB. The simulation study of the impact of asynchronous access on the performance allows for a complete network design from an engineering viewpoint.

Performance Analysis of Variable-Weight, Multilength Optical Codes for Wavelength-Time O-CDMA Multimedia Systems

To support multimedia services with different discrete bit-rate requirements, families of multilength optical codes, such as the carrier-hopping prime code (CHPC), extended CHPC, and multiwavelength optical orthogonal code, were recently constructed for wavelength-time optical code-division multiple-access (O-CDMA). In this paper, the performance of these multilength optical codes in a multimedia O-CDMA system with a variable-weight operation are analyzed. Our study shows that short-length codes generate stronger interference than long-length codes. This supports services prioritization in O-CDMA. Our study also shows that code weight is a more important factor than code length in determining code performance (i.e., quality of service).

Suppression of beating noise of narrow-linewidth erbium-doped fiber ring lasers by use of a semiconductor optical amplifier

Beating noise in narrow-linewidth erbium-doped fiber ring lasers puts severe limitations on applications of the lasers. We demonstrate the suppression of beating noise in fiber ring lasers by using a semiconductor optical amplifier in the laser cavity, which acts as a high-pass filter. Two different ring structures are presented as examples to demonstrate this beating noise suppression.

Optical spectral bistability in a semiconductor fiber ring laser through gain saturation in an SOA

We demonstrate the operation of optical bistability in a widely tunable semiconductor fiber ring laser, using a semiconductor optical amplifier (SOA). The laser can be operated in two bistable states: the spectrum of the first state has one main lasing peak with very narrow linewidth, and the second state has simultaneous oscillation of two main peaks at different wavelengths. The two bistable states can be switched to each other using either electrical or optical methods. We further explain the bistable operation using the theory of two-mode competition through gain saturation in the SOA.

Novel Multicode-Processing Platform for Wavelength-Hopping Time-Spreading Optical CDMA: A Path to Device Miniaturization and Enhanced Network Functionality

Cost-effective, robust, code-processing photonic devices are essential for the adoption of optical code-division multiple access in future commercial and military network applications. Progress in several technology platforms for code processing is summarized. In particular, we focus on developments in a technology platform based on holographic Bragg reflectors that allow the processing of multiple codes simultaneously, with low footprint. Results of simultaneous en/decoding of two wavelength-hopping time-spreading codes using a single device are presented. Several applications are presented where multicode-processing capability can result in significant simplification of node and system architectures and, thus, provide feasible implementation of schemes to obtain enhanced network performance such as security and scalability.

Integrated holographic encoder for wavelength-hopping/time-spreading optical CDMA

We report on the application of an integrated holographic device to the generation of two-dimensional (time-frequency) optical codes for use in optical code-division multiplexing based on wavelength encoding/time spreading. The dual code device is based on two holographic Bragg reflectors and allows one to encode data with either one of two complementary diagonal 16-chip temporal-spectral codes.

Multiple access interference (MAI) noise reduction in a 2D optical CDMA system using ultrafast optical thresholding

We demonstrate the reduction of MAI noise due to multiple simultaneous users in a 2D OCDMA system using optical thresholding. The system shows improved performance by reducing the power penalty increase when adding more users.

Continuous-Wave Operation of Semiconductor Optical Amplifier-Based Multiwavelength Tunable Fiber Lasers With 25-GHz Spacing

We demonstrate wide bandwidth operation in a semiconductor optical amplifier (SOA)-based fiber laser with a wavelength spacing of 25 GHz. A broadband multiwavelength filter based on superimposed and chirped fiber Bragg gratings is used for wavelength selection. Three different cavity configurations are presented and compared: 1) a single-SOA standing-wave cavity; 2) a single-SOA ring cavity; and 3) a double-SOA ring cavity. Up to 41 wavelengths are obtained with a signal-to-noise ratio of 35 dB and a wavelength tunability of 10 nm.