Optical memory for storing data

Details Optical memory for storing data Optical memory for storing data

1997-02-27

1998-04-14

Dinh, Son T.

Static information storage and retrieval

Read/write circuit

Optical

365106, G11C 1930

Patent

active

057401179

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention concerns an apparatus for storing light pulses in a small waveguide memory loop.


BACKGROUND OF THE INVENTION

Photon storage, in analogy to electron storage such as the well known capacitor memory cell, is very difficult because of the physical problem of containment of a photon or photon stream. Up to now, most approaches for storing photons are either based on the effect of optical bistability or on the utilization of long fiber loops.
Devices making use of the optical bistability are usually technologically complex and expensive. Much of the early work on optical bistability was motivated by the idea that optics could avoid some of the intrinsic speed limitations of electronic storage systems. The devices based on the effect of optical bistability rely on electro-optic conversion and hence an electron is stored in this case. A two-dimensional access or emitting function can be implemented with these kind of devices.
Fiber loops exist in the form of sequential storage pipes, where a photon stream, e.g. a sequence of light pulses, flows or recirculates in a first-in first-out (FIFO) fashion. These fiber loops are used as optical delay lines, but do not allow a random-access to the light pulses circulating in such a loop. A typical photon memory device based on a recirculating fiber loop is described in "Programmable Photonic Fiber Loop Memory", A. Dickson et al., Proceedings of the 16th Australian Conference on Optical Future Technology, p. 274-277, 1991. A typical recirculating fiber loop memory 10 is illustrated in FIG. 1. This memory 10 consists of a directional coupler 14 for coupling light into it. This memory 10 comprises an Erbium doped fiber amplifier (EFA) 11 with a 70 meters long Er.sup.+ -fiber, a fiber loop 12 (fiber coil) which is 160 meters long, a semiconductor laser amplifier (SLA) 13 operating as optical switch, and two optical isolators 15, each being depicted as box with a black arrow. These kind of devices are bulky and expensive.
For future functions in optical processing and data communication it is desirable to have a photon storage device in much analogy to a conventional electronic cache memory, i.e. there is a great demand for an optical memory being as easy to use as their electronic counterparts. These kind of devices will most likely be used in many fields of photonics, including telecommunications, packet switching, and optical computing. Usage of an optical memory is foreseen in bit-selective manipulation at high data rates (e.g. 10 Gb/sec), like processing, temporal storage and recognition. It is very important for such a device, that it is capable of storing and manipulating optical bits individually. Ideally it should be integrable to optically perform elemental logical functions. Any conversion of photons into electrons and vice versa should be avoided in order to increase efficiency and to minimize access time to data stored.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus for optically storing light pulses carrying information.
It is another object of the present invention to provide an apparatus for optically storing light pulses carrying information such that each light pulse stored is individually addressable.
The above objects have been accomplished by provision of memory cells comprising a data line, a directional waveguide coupler which can be switched from a `bar-state` to a `cross-state`, and a circular waveguide memory loop for storing a light pulse circulating therein, the data line being optically coupled via the directional waveguide coupler to the loop such that a light pulse on the data line is coupled into said memory loop if the directional waveguide coupler is in the `cross-state`, or passes the directional waveguide coupler--without being coupled into said memory loop--if it is in the `bar-state`. The length L of said memory loop is chosen such that the circulation frequency of said light pulse in the memory loop is equal to the clock frequency of said optical memory

REFERENCES:
patent: 4877952 (1989-10-01), Halemane et al.
patent: 5058060 (1991-10-01), Su

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