Mario A. Santoro

Spread spectrum fiber-optic local area network using optical processing

Spread spectrum code division multiple access (CDMA) allows asynchronous multiple access to a local area network (LAN) with no waiting. The additional bandwidth required by spread spectrum can be accommodated by using a fiber-optic channel and incoherent optical signal processing. New CDMA sequences are designed specifically for optical processing. It is shown that increasing the number of chips per bit, by using optical processing, allows an increase in capacity of a CDMA LAN. An experiment is performed demonstrating the performance of an optical CDMA LAN, operating at 100 Mbd with three users.

Ultrafast All-Optical Synchronous Multiple Access Fiber Networks

Two synchronous multiple access schemes, TDMA and CDMA, are proposed for fiber optic networks using optical signal processing. Network synchronization is achieved by using a central modelocked laser which also serves as the source for each station. The data are converted into a high-bandwidth optical signal using electrooptic modulators. The accessing schemes use optical fiber delay lines. The feasibility of these schemes is discussed.

A mode-filtering scheme for improvement of the bandwidth-distance product in multimode fiber systems

A scheme in which the bandwidth-distance product of a multimode fiber is extended, so that it can nearly support the transmission rate of single-mode systems, is studied. It is based on selective launching of lower order modes into the fiber at the transmitting end and on filtering out at the receiver the fraction of the energy that was coupled into the higher order modes throughout the propagation in the multimode fiber. The power penalty and the dispersion performance of the scheme are investigated. In particular, it is shown that the scheme carries about 6.5 dB penalty, and doubling of the bandwidth*distance value is demonstrated. The effect of splices on the performance is also presented. It is envisioned that this approach may be used to upgrade existing multimode systems without the need for rewiring. For example, it can be used to replace the FDDI (fiber distributed data interface) installations in future high-speed networks, when transmission rates increase from megabits per second to gigabits per second. >

Optical equalization of polarization dispersion

In this paper, we describe a demonstration of the optical equalization of polarization dispersion in direct-detection lightwave systems. We use a polarization controller to adjust the polarization into a fiber to one of the principal states of polarization of the fiber, which eliminates first-order polarization dispersion. Results for a 2.5 Gbps, externally modulated system with a fiber with 120 ps rms of polarization dispersion, show that by using the equalizer we maintain a 10-9 BER, while without the technique the BER varies with time from 10-5 to 10-9. At 10 Gbps, the equalizer allows reliable bit detection even though the eye is closed without equalization, demonstrating an order of magnitude increase in the dispersion-limited B2L product, in agreement with our analytical and computer simulation results. We also describe a demonstration of the technique at the receiver, and show how to implement an adaptive polarization controller to continuously track the principal states using a gradient search algorithm. This technique provides bit-rate-independent equalization of first-order polarization dispersion.

Star-coupler-based optical cross-connect switch experiments with tunable receivers

An optical cross-connect switch using the star-coupler-based frequency-division-multiplex technique are discussed. Two specific tunable receivers have been implanted. The first is a heterodyne receiver with a tunable laser as the local oscillator (LO) and the second is a tunable filter followed by a direct-detection receiver. In the heterodyne receiver, the tunable LO was a monolithic three-section multiple-quantum-well distributed Bragg laser capable of a 1000-GHz tuning range. Receiver sensitivity was measured to be -38 dBm at 1 Gb/s (BER=10/sup -10/). The power margin in the system substantiated feasibility for a 400*400 switch. In the tunable-filter receiver, the tunable filter is a tunable two-stage optical fiber Fabry-Perot filter design consisting of a narrowband filter followed by a wideband filter. The tuning of the filters is computer controlled, and the combined filter has a tuning range of 15000 GHz with a finesse of approximately=5170. Therefore, it is capable of covering over 1000 channels of 2.9 GHz each. >

Polarization scrambling using a short piece of high-birefringence optical fiber and a multifrequency laser diode

Describes a technique for avoiding system performance degradation and outages in an optical fiber system due to state of polarization mismatch between signal and polarization-sensitive system components. The technique uses a short piece of high-birefringence fiber and a multifrequency laser to create a depolarized source that can be used to transmit data without fading. >

Experimental and theoretical performance of ring-shaped passive-bus optical networks

In a ring-shaped passive bus, power-splitting losses of fiber-optic passive taps are exploited so that wavelengths can be reused in different portions of the network. This spatial reuse greatly reduces the number of wavelengths that need to be multiplexed on an optical fiber to yield a large, high-capacity, multichannel network with many concurrent transmissions. Bounds on the power penalty due to interference caused by wavelength reuse (including the self-interference on a ring-shaped passive bus) are presented, and it is experimentally shown that the penalty falls within these bounds for various cases of laser linewidth, ring length, polarization state, and modulation scheme. In all cases, the penalty is below 1.2 dB with 18-dB attenuation between reused wavelengths.<<ETX>>

A multigigabit/second wavelength-division-multiplexing byte-by-byte switch using fast tunable heterodyne receivers

Fast-frequency laser tuning and a 2*2 electrooptic switch have been combined to perform byte-by-byte switching at synchronous optical network (SONET) rates using a wavelength-division-multipling (WDM) architecture. The three-section distributed-Bragg-reflector (DBR) lasers used can be tuned over a 100-GHz range in 5 ns. >

Extending the bandwidth-distance product for multimode fiber systems

Abstract A scheme is investigated by which the bandwidth-distance product of a multimode fiber can be easily extended to support nearly the same transmission rate as the single-mode system. The scheme is based on launching a limited number of modes into the multimode fiber, and extracting a limited number of modes at the receiving end. The power penalty imposed by the scheme and the dispersion performance are investigated. In particular, it is shown that the scheme carries about 6.5-dB penalty, and doubling of the bandwidth × distance value is demonstrated. The proposed scheme facilitates upgrading the existing networks wired with multimode fiber (e.g., FDDI) from hundreds of Mbps to Gbps transmission rates.

Optical FDM switch experiments with tunable fiber Fabry-Perot filters

The authors discuss results of research aimed at understanding the use of monolithic tunable lasers and fiber Fabry-Perot filters in implementing an optical cross-connect switch. The switch architecture uses optical frequency division multiplexing where laser signals are transmitted at different frequencies and then summed in a star coupler. At each star coupler output, a tunable receiver is used to retrieve any input signal of choice. The experimental receiver consists of an optical tunable filter followed by a direct-detection receiver. The laboratory demonstration consists of four frequency-locked transmitters with monolithic tunable lasers, each dithered with a slightly different frequency for the dual purpose of frequency locking and positive channel identification upon signal reception. The tunable filter is a tunable two-stage fiber Fabry-Perot filter design consisting of a narrow filter followed by a wide filter. The tuning of the filters is computer controlled, and the combined filter has a tuning range of 15000 GHz with a finesse approximately=5170. Therefore, it is capable of covering over 1000 channels of 2.9-GHz each. Receiver sensitivity was measured to be -30 dBm at 1.7 Gb/s and -29 dBm at 2.5 Gb/s (bit error rate=10/sup -10/).<<ETX>>