Norman Ashton Whitaker

All-optical arbitrary demultiplexing at 2.5 Gbits/s with tolerance to timing jitter

All-optical demultiplexing has been shown with a full-duty-cycle 2.5-Gbit/s signal in a nonlinear fiber Sagnac interferometer. Complete switching of arbitrary pulse patterns in the data stream has been achieved by using two orthogonal polarization states for the switching and switched pulse trains. The polarization dispersion between the two fiber axes defines a window that allows for switching with timing errors as large as 350 ps.

All-optical, all-fiber circulating shift register with an inverter

An all-optical fiber Sagnac interferometer switch and erbium amplifier have been combined to form an all-optical 254-bit circulating shift register with an inverter. This simple optical loop memory demonstrates the cascadability of Sagnac interferometer switches.

Addressable fiber-loop memory

Optical bits are selectively and nondestructively read out of an all-optical recirculating fiber-loop memory by using a synchronized probe signal at a second wavelength.

Complete switching in a three-terminal Sagnac switch

A three-terminal all-optical fiber switch based on a fiber Sagnac interferometer is described. The use of polarization components allows the construction of a switch in which the control beam and signal beam are isolated (i.e. the device is three terminal) and which is cascadable (the device output can drive its inputs). The interaction length need not be limited by the walkoff length in the fiber, as cross-splices can be made in the birefringent fiber to permit multiple passes. Contrast ratios as high as 40:1 have been demonstrated in a switch driven by an amplified laser diode.<<ETX>>

Sagnac fiber logic gates and their possible applications: a system perspective

The Sagnac all-optical fiber logic gate functions as a two-input AND gate, a two-input AND gate with one inverting input, or both. The fiber logic gate is pipelined and has a fixed latency. This latency has no effect on feed-forward combinatoric circuits. The latency can be used to time multiplex circuits or to time multiplex gates to emulate a circuit. Possible applications such as a bit-jitter-tolerant communications system, an asynchronous communications system, a bit-interleaved self-routing switching system, an exchange/bypass permutation unit, and a folded universal state machine are discussed.

Polarization-independent all-optical switching

A polarization-independent all-optical switch has been demonstrated based on a nonlinear fiber Sagnac interferometer. The control signal is split and recombined with a time delay, producing two linearly polarized pulses that lie within the temporal switching window of the circuit. Less than 10% variation of the switched output signal was observed as the input polarization was varied.<<ETX>>

Low-drift modulator without feedback

A low-drift amplitude modulator has been demonstrated using a fiber Sagnac interferometer with a lithium-niobate phase modulator. Although the fiber-loop length must be adjusted for the modulation rate, this type of modulator structure is inherently insensitive to variations in the voltage bias of the drive signal, as well as to temperature variations.<<ETX>>

Adaptive MAC-layer protocol for multiservice digital access via tree and branch communication networks

Described here is an adaptive MAC-layer protocol that supports multiservice (STM and ATM) applications in the context of subscriber access to tree and branch (e.g., fiber-coaxial cable) networks. The protocol adapts to changing demands for a mix of circuit and cell mode applications, and efficiently allocates upstream and downstream bandwidth to a variety of bursty and isochronous traffic sources. In the case of a hybrid fiber-coaxial (HFC) network the protocol resides in customer premises equipment and a common head-end controller. A medium-access control (MAC) processor provides for dividing the time domain for a given digital bitstream into successive frames, each with multiple STM and ATM time slots. Within the STM region of a frame, variable length time slots are allocated to calls (e.g., telephony, video telephony) requiring different amounts of bandwidth. A contention access signaling channel is also provided in this region for call control and set-up requests. Within the ATM region fixed-length time slots accommodate one individual ATM cell. These ATM time slots may be reserved for a user for the duration of a call or burst of successive ATM cells, or shared via a contention process. At least one contention time slot is available for signaling messages related to ATM call control and set-up requests. Further, the fixed-length ATM time slots may be reserved by a user for the duration of a call, or shared through a contention process. This paper describes the MAC-layer protocol, its relation to circuit- and ATM- amenable applications, and its performance with respect to signaling throughput and latency, and bandwidth efficiency for several service scenarios.