JPH0343720B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel dynamic memory type optical memory in which optical signals are sent back and forth to and stored in a polarization-preserving optical fiber.

[Prior Art] A conventional optical memory is a static memory that stores information in a fixed or semi-permanent manner in a storage medium such as an optical disk memory using light irradiation or a pulsed electric field. By shining light onto a storage medium, changes in its reflection, transmission, refraction, etc. are read out. Furthermore, the mainstream storage method for conventional optical memories as well as semiconductor memories is electromagnetic.

[Problems to be Solved by the Invention] However, the electromagnetic memory described above is easily affected by electromagnetic induction and requires shielding to prevent this, resulting in a large device. Furthermore, when data is transferred between computers or between memories using optical fibers, electrical/optical conversion and optical/electrical conversion are always required.

Therefore, in order to solve the above problem, the present inventor developed a third
We proposed an optical dynamic optical memory as shown in the figure. This optical memory consists of an optical switch 1 and a signal storage optical fiber 2 connected in a loop between its input and output terminals.
The optical switch 1 is turned OFF (through state) and the optical signal is transferred to the end 2a before the read optical signal reaches the end 2b. return. In this way, the optical signal is circulated and stored in the closed loop formed by the signal storage optical fiber 2 and the optical switch 1. To read out the stored optical signal, turn on the optical switch 1 and read it from the output fiber 4.

This optical memory has advantages such as non-guidance and easy optical transmission, but its storage capacity is proportional to the length of the signal storage optical fiber 2. That is, if the length of the optical fiber 2 for signal storage is l, the group refractive index is n, the speed of light is C, and the clock frequency that determines the modulation speed of the optical signal is f, then the storage capacity of the optical memory is f・(n・
l)/C[bit]. Therefore, in order to increase the amount of information that can be stored, assuming that f is constant, the length l of the signal storage optical fiber 2 must be increased.

[Object of the Invention] An object of the present invention is to make a memory device lightweight and compact without the need for electric/magnetic shielding, and to enable easy and quick optical transmission without electrical/optical conversion or optical/electrical conversion. An object of the present invention is to provide an optical memory whose storage capacity can be increased without increasing the length of a polarization preserving optical fiber as a storage medium.

[Summary of the invention] In order to achieve the above object, the present invention provides the first
a polarizing prism, a first mirror provided on one side of the first polarizing prism, and a polarizing prism provided in parallel with the first polarizing prism on the reflective side of the first mirror with respect to the first polarizing prism. a second polarizing prism; a second mirror provided on one side of the second polarizing prism on the same side as the first mirror;
a polarization switch provided between the polarization prism and the second polarization prism, and one end of the second polarization prism facing the reflection side or the transmission side of the second mirror, and its inherent polarization axis. A polarization-maintaining optical fiber provided so that the direction of transmitted and reflected polarization matches the direction of transmission and reflection of the second polarizing prism, and a straight line emitted from the other end of the polarization-maintaining optical fiber that faces the other end of the polarization-maintaining optical fiber. Equipped with a 90 degree polarization rotator that rotates the polarization plane of polarized light by 90 degrees and returns it to the other end, it is possible to store signals by switching the polarization switch. The device is configured to perform the following functions: confinement) and readout of the signal.

[Examples] Examples of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, 5 is a 2×2 matrix optical switch having terminals 5a, 5b, 5c, and 5d. This optical switch 5 is of a waveguide type that utilizes an electro-optic effect. When the optical switch 5 is turned on, the terminals 5a and 5d are connected, and between the terminals 5b and 5c, which is a cross state. When the optical switch 5 is turned off, the terminals are connected. The terminals 5a, 5c and the terminals 5b, 5d are switched to a through state in which they are connected. Optical fibers 6, 7, 8, and 9 are connected to the terminals 5a, 5b, 5c, and 5d, respectively.

A collimator 1 is provided at the tip of the optical fiber 9 for inputting a parallel beam to the first polarizing prism 11.
0 is set. Further, a second polarizing prism 12 is provided on the transmission side of the collimator 10 with respect to the first polarizing prism 11 via a polarizing switch 13 . The first polarizing prism 11 and the second polarizing prism 12 are arranged in parallel. When the polarization switch 13 is ON, it rotates the plane of polarization of light passing through it by 90 degrees, and when it is OFF, it passes through the polarization plane as it is without rotating it. Polarization switch 13 with respect to the first polarization prism 11
A first mirror 1 is installed parallel to the reflecting side of the mirror.
4 is provided. In addition, the second polarizing prism 1
2, a second mirror 15 is also provided on the same side of the first mirror 14 with respect to the first polarizing prism 11. Note that the first and second mirrors 14, 1
5 may be formed so that the side surfaces of the first and second polarizing prisms 11 and 12 are mirror surfaces.

Further, one end portion 17a of a polarization preserving optical fiber (hereinafter referred to as SPF) 17 is provided on the transmission side of the polarization switch 13 with respect to the second polarization prism 12 via a collimator 16. The collimator 16 condenses the emitted light that has passed through the second polarizing prism 12 and diverged onto one end portion 17a.
As the collimators 10 and 16, rod lenses or the like are used. As shown in the enlarged view in Figure 2, SPF17 is an elliptical jacket type fiber in which non-isotropic stress is applied to the core, and its characteristic polarization axes X and Y are in the major and minor axes of the ellipse. be.

The intrinsic polarization axes X and Y of one end 17a of the SPF 17 are made to coincide with the reflected polarization direction and the transmitted polarization direction of the second polarizing prism 12. Note that the unique polarization axes X and Y of the one end portion 17a may be made to coincide with the transmission polarization direction and the reflection polarization direction of the second polarizing prism 12. The other end 17b of the SPF 17 has a 1/4 wavelength plate 1.
A mirror 19 is provided via 8. In addition,
The mirror 19 may be formed by silver plating the back surface of the 1/4 wavelength plate 18. One end 17a
The intrinsic polarization axes of the other end portion 17b and the other end portion 17b coincide with each other. Note that the two ends may be twisted by 90 degrees.

Next, the operation of this embodiment will be described.

When the optical switch 5 is turned on, the signal transmitted from the optical fiber 6 is input to the optical fiber 9 via the terminals 5a and 5b, and from the collimator 10 to the first
The light is incident on the polarizing prism 11 of. It is assumed that this incident light is linearly polarized light in the transmission polarization direction of the first polarizing prism 11. Then, this linearly polarized light passes through the first polarizing prism 11, directly passes through the polarization switch 13 in the OFF state, and further passes through the second polarizing prism 12, and then passes through the collimator 16 to one end 17a of the SPF 17. The light is incident in the Y mode, which is one of its intrinsic linear polarization modes. This Y-mode linearly polarized light propagates through the SPF 17 without changing its polarization plane and is emitted from the other end 17b. The emitted Y-mode linearly polarized light is turned into circularly polarized light by the 1/4 wavelength plate 18, reflected by the mirror 19, and turned into reversely rotated circularly polarized light. It is returned to the other end portion 17b in linearly polarized light mode (X mode).

This X-mode linearly polarized light is at one end of SPF17.
7 a to the second polarizing prism 12 , but since the X mode is a total reflection mode of the second polarizing prism 12 , it is totally reflected by the cemented surface of the second polarizing prism 12 and then reflected by the second mirror 15 . After being reflected, it is further totally reflected by the second polarizing prism 12.
It is returned to one end 17a of the SPF 17 again in the X mode. The light then propagates through the SPF 17, is emitted from the other end 17b, passes through the quarter-wave plate 18, mirror 19, and quarter-wave plate 18, becomes Y mode, and returns to the other end 17b. Next, this Y-mode linearly polarized light is emitted from one end 17a and enters the second polarizing prism 12;
Since the light is in the second transmission mode, the light passes through the second polarizing prism 12 and enters the polarizing switch 13.
By this time, the polarization switch 13 has been turned on, and the Y mode linearly polarized light has been turned on by the polarization switch 1.
After passing 3, it becomes X mode. Therefore, it is totally reflected by the first polarizing prism 11 arranged parallel to the second polarizing prism 12 and reflected by the first mirror 14,
Furthermore, it is totally reflected by the first polarizing prism 11 and returned to the polarizing switch 13. This polarization switch 13
The X-mode linearly polarized light returned to polarization switch 1
3, it becomes Y mode and passes through the second polarizing prism 12 and returns to one end 17a of the SPF 17.
is incident on the This completes one cycle of the round-trip transmission of the optical signal in the optical memory optical system, and from now on,
The optical signal repeats the above cycle. In this way, the SPF 17 is stored in the optical signal in a round-trip transmission state.

The amount of information B stored in this optical memory is SPF1
7 is one cycle, so if the length of the SPF 17 is l, the group refractive index is n, the speed of light is C, and the clock frequency that determines the modulation speed of the optical signal pulse train is f, then B = 4. It becomes f・n・l/C. That is, the amount of information four times the fiber length l can be stored. In a specific example, f
=1GHz, n=1.46, l=10Km, C=3× ¹⁰⁸ m/
It turns out that approximately 200kbit of information can be stored if s is used.

When reading out the signal stored in the SPF 17, the polarization switch 13 is turned off. In this way, from the second polarizing prism 12 to the polarizing switch 1
The Y-mode linearly polarized light incident on the optical fiber 9 passes through the polarization switch 13 without changing its mode, and further passes through the first polarization prism 11 and is transmitted through the optical fiber 9.
The signal is read out to the optical fiber 7 via the terminals 5d and 5b of the optical switch 5.

In the above embodiment, if an optical amplifier is provided in the optical path of the optical memory, the limitation on the store time due to attenuation of the optical signal can be eliminated. In this case, there is a method of amplifying using an optical/electrical converter and an electric/optical converter instead of the mirror 19. Furthermore, instead of the quarter-wave plate 18, a magnetic polarizer may be used in which a magnetic field is applied to YIG, so that the plane of polarization is rotated by 90 degrees while the light travels back and forth through this YIG. Furthermore, SPF
One end 17a of the polarizing prism 17 may be provided so as to face the transmission side side of the second mirror 15 with respect to the second polarizing prism 12.

[Effects of the Invention] In summary, the present invention provides the following excellent effects.

(1) Since it is composed only of optical fibers and optical devices, it is less susceptible to electromagnetic induction, eliminates the need for electrical and magnetic shielding, and makes the storage device lighter and smaller.

(2) When transmitting signals between computers or between memories using optical fibers, optical transmission can be performed easily and quickly by switching optical switches without performing electrical/optical conversion or optical/electrical conversion.

(3) Since signals are stored by traveling back and forth through a polarization-preserving optical fiber, storage capacity can be increased without increasing the length of the fiber.

(4) The main parts of optical memory are passive optical devices such as polarization-maintaining optical fibers, polarizing prisms, and mirrors, so they are highly reliable.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an optical memory according to the present invention, FIG. 2 is an end view of a polarization-maintaining optical fiber of the same optical memory, and FIG. 1 is a schematic configuration diagram of a novel optical memory that has been proposed. In the figure, 5 is an optical switch, 6, 7, 8, 9 are optical fibers, 10, 16 are collimators, 11 is a first polarizing prism, 12 is a second polarizing prism, 13
14 is a polarization switch, 14 is a first mirror, 15 is a second mirror, 17 is a polarization maintaining optical fiber, 18
is a quarter wavelength plate, 19 is a mirror, and X and Y are unique polarization axes.

Claims (1)

[Claims] 1 A first polarizing prism, a first mirror provided on one side of the first polarizing prism, and a first polarizing prism provided on the reflection side of the first mirror with respect to the first polarizing prism.
a second polarizing prism disposed in parallel with the polarizing prism; a second mirror disposed on one side of the second polarizing prism on the same side as the first mirror; A polarization switch provided between the second polarization prism and the second polarization prism, with one end of the second polarization prism facing the reflection side or the transmission side of the second mirror, and one end of the second polarization prism facing the reflection side or the transmission side of the second mirror, and the characteristic polarization axis of the second polarization A polarization-maintaining optical fiber is provided to match the transmitted/reflected polarization direction of a polarizing prism, and a polarization-maintaining optical fiber is provided facing the other end of the polarization-maintaining optical fiber to determine the polarization plane of linearly polarized light emitted from the other end. An optical memory characterized by comprising a 90-degree polarization plane rotator for rotating 90 degrees and returning to the other end.