JPH0343719B2 - - 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, the present inventor proposed an optical dynamic optical memory as shown in FIG. 3 in order to solve the above problems. 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.
Turn on optical switch 1 for the optical signal transmitted from
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. Also, reading out the stored optical signal is as follows:
Turn on optical switch 1 and read from 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] The object of the present invention is to make a memory device lightweight and compact without the need for electric/magnetic shielding, and to easily and quickly transmit light without performing electrical/optical conversion or optical/electrical conversion. Moreover, it is an object of the present invention to provide an optical memory that can double the storage capacity without increasing the fiber length by sending signals back and forth through a polarization-preserving optical fiber for signal storage.

[Summary of the invention] In order to achieve the above object, the present invention provides n×
n (n≧2) matrix optical switch, a polarization-maintaining optical fiber for signal input/output connected in a loop between the input and output terminals of the optical switch, and a polarization-maintaining optical fiber provided in this polarization-maintaining optical fiber. a polarization prism, a polarization preserving optical fiber for signal storage with one end thereof facing one side of the polarization prism, and a polarization preserving optical fiber provided with the other end of the polarization preserving optical fiber facing this; 1/ provided between the mirror
The device is equipped with a four-wavelength plate, and is configured to send a signal back and forth to a polarization-maintaining optical fiber for signal storage for storage and to take out the signal by switching an optical switch.

[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, which has input terminals 5a, 5b and output terminals 5c, 5d. This optical switch 5 is of a waveguide type using an electro-optic effect, and when the optical switch 5 is turned on, terminals 5a and 5d are connected, and terminals 5b and 5c are connected.
That is, it becomes a cross state. Also, light switch 5
When turned OFF, between terminals 5a and 5b and between terminals 5b and 5b,
The state switches to a through state in which the terminals 5d and 5d are respectively connected. An input optical fiber 6 is connected to the input terminal 5a of the optical switch 5, and an output optical fiber 7 is connected to the output terminal 5c. In addition, input side terminal 5
A polarization-maintaining optical fiber (hereinafter simply referred to as SPF) 8 for signal input/output is connected in a loop between the polarization-maintaining optical fiber 8 and the output terminal 5d.

The SPF 8 is provided with a polarizing prism 9.
Side surfaces 9a and 9c and side surface 9b of polarizing prism 9
and 9d are on the transmission side, and side surfaces 9a and 9
b and side surfaces 9c and 9d are mutually reflective sides.
On the side surface 9c of the polarizing prism 9, one end 10a of an SPF 10 for signal storage is provided facing the side surface 9c. Further, a quarter wavelength plate 11 is provided at the other end 10b of the SPF 10, and a mirror 12 is provided behind the quarter wavelength plate 11.

SPF10 (also PSF8) is an elliptical jacket type fiber in which non-isotropic stress is applied to the core, as shown in the enlarged view in Figure 2, and the characteristic polarization axes X and Y are in the long axis direction and short direction of the ellipse. It is in the axial direction.
The intrinsic polarization axes of the one end 10a and the other end 10b of the SPF 10 coincide, and are aligned with the transmission polarization direction and the reflection polarization direction of the polarizing prism 9. In addition, the intrinsic polarization axes of the coupling ends on both sides of the polarizing prism 9 of the PSF 8 also match, and they match the transmitted polarization direction and the reflected polarization direction of the polarizing prism 9, but the coupling of the SPF 8 on the side surface 9d of the polarizing prism 9 There is a spatial twist of 90 degrees between the end and the joining end of the SPF 8 of the input terminal 5b.

Next, the operation of this embodiment will be described.

When the optical switch 5 is turned on, the signal transmitted from the input optical fiber 6 is inputted to the SPF 8 via the input terminal 5a and the output terminal 5d of the optical switch 5, and is guided to the SPF 8 and sent to the polarizing prism 9 by the side surface 9a. is incident on the If this incident light is linearly polarized in the transmission polarization direction of the polarizing prism 9, this linearly polarized light passes through the polarizing prism 9, is focused by an appropriate condensing device, and is directed from one end 10a of the SPF 10 to its one characteristic straight line. It is coupled to the polarization mode (temporarily assumed to be Y mode) and transmitted to the other end 10b of the SPF 10. The linearly polarized light emitted from the other end 10b is turned into circularly polarized light by the quarter-wave plate 11, reflected by the mirror 12, and turned into reversely rotated circularly polarized light.
It passes through the 1/4 wavelength plate 11 and becomes the other unique linear polarization mode (X mode) of the SPF 10, and then the other end 10
b. This X-mode linearly polarized light propagates through SPF 10 without changing the plane of polarization, and passes through SPF 10 at one end.
The light enters the polarizing prism 9 from the side a, but since it is linearly polarized in the reflected polarization direction of the polarizing prism 9, it is reflected at the joint surface of the polarizing prism 9 and is transmitted from the side surface 9d to SPF 8.
is incident on the coupled end of the The linearly polarized light (X mode) incident on SPF8 is switched to optical switch 5 by SPF8.
However, since the coupling end of the side surface 9d of the polarizing prism 9 of the SPF 8 and the coupling terminal of the input terminal 5b of the optical switch 5 are spatially twisted by 90 degrees, the input terminal The terminal 5b becomes the Y mode, and the linearly polarized light of the Y mode enters the SPF 10 again via the output terminal 5d, the SPF 8, and the polarizing prism 9. However, after the optical switch 5 turns on and starts reading the signal, the optical switch 5 must be turned off before the optical signal travels back and forth through the SPF 10, passes through the SPF 8, and reaches the input terminal 5b of the optical switch 5. do.

Thus, the optical signal will be stored in the SPF 10, 8 in a transmitted state. The amount of information B stored in this optical memory is as follows: Let l be the fiber length of the long SPF 10, n be the group refractive index, C be the speed of light, and f be the clock frequency that determines the modulation speed of the pulse train of the optical signal. =2・f・n・l/C. Since the optical signal is stored by traveling back and forth through the SPF 10, it is possible to store twice the amount of information as the fiber length l. In a specific example, f=500MHz, n=1.46, l=2Km, C
= 3×10 ⁸ m/s, it was found that approximately 9.7 kbit of information can be stored in memory.

When reading out the signals stored in SPF8 and SPF10, turn on the optical switch 5 and input terminal 5.
b and the output side terminal 5c are connected, and a signal is outputted from the output optical fiber 7. To read the signal,
2(n・l)/from the time when the light switch 5 was turned on
This is the time when an integral multiple of C[SEC] has elapsed.

In the above embodiment, it is also possible to receive a signal from the output optical fiber 7, store it, and read out the stored signal to the input optical fiber 6. In this case, input side terminals 5a, 5b
becomes the output side terminal, and the output side terminals 5c and 5d become the input side terminals. Furthermore, if an optical repeater amplifier is provided in the SPF 8 or the like, the strength of the optical signal can be maintained and the limitation on memory store time can be removed. Also, instead of a 2x2 matrix,
If an optical switch with an n×n (n≧3) matrix is used, the storage capacity can be increased by (n-1) times compared to the optical memory of the above embodiment with a 2×2 matrix. In this case, a polarizing prism 9, a quarter wavelength plate 11,
The mirror 12 may also be shared. Furthermore, instead of the 1/4 wavelength plate 11 in the above embodiment,
A magnetic rotator obtained by applying a magnetic field to YIG may be used as the 90-degree polarized light rotator. in this case,
The plane of polarization is rotated 90 degrees during the round trip. Also,
In the above embodiment, one end portion 10a of the SPF 10 may be provided so as to face the side surface 9b of the polarizing prism 9.

[Effects of the Invention] As is clear from the above description, the present invention can exhibit 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 easily and quickly performed by switching optical switches without performing electrical/optical conversion or optical/electrical conversion.

(3) Since signals are stored by moving the polarization preserving optical fiber back and forth, the storage capacity can be doubled without increasing the fiber length.

(4) The main part of optical memory is polarization preserving optical fiber.
Since it is a passive optical device such as a polarizing prism, it is 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 an optical memory that has been proposed. In the figure, 5 is an optical switch, 6 is an input optical fiber, 7 is an output fiber, 8 is a polarization-maintaining optical fiber for signal input/output, 9 is a polarization prism, and 10 is a polarization-maintaining optical fiber for signal storage. , 11 is 1/4
A wave plate, 12 is a mirror, and X and Y are unique polarization axes.

Claims (1)

[Claims] 1 An optical switch with an n×n (n≧2) matrix in which one of the input side terminals is used as a signal writing terminal and one of the output side terminals is used as a signal reading terminal; A polarization preserving optical fiber for signal input/output connected in a loop between other input/output terminals, a polarizing prism provided on this polarization preserving optical fiber, and the above polarization preserving optical fiber on both sides of the polarizing prism. One end of the optical fiber faces one side of the polarizing prism, which is the transmitting side of the polarizing prism and the other side is the reflecting side, and is used for signal storage for reciprocating signals and storing them. A polarization-maintaining optical fiber and a 90-degree polarization plane that is provided facing the other end of the polarization-maintaining optical fiber and rotates the polarization plane of light emitted from the other end by 90 degrees and returns it to the other end. An optical memory characterized by comprising a polarization plane rotator.