JPS626212B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fiber element for optical logic operations that performs optical input-optical output logic operations using nonlinear optical effects occurring in optical fibers. be.

(Prior art) Conventionally, this type of device uses a Fabry-Perot resonator and inserts a medium with saturable absorption characteristics or optical power (Kerr) effect inside the resonator, thereby achieving optical bistable operation. was used to perform logical operations.

(Problem to be solved by the invention) However, since a Fabry-Perot resonator is used,
High precision is required in selecting the resonator length and aligning the mirrors, and the resonator itself has the disadvantage of being large and inconvenient to handle.

(Means for Solving the Problems) One feature of the present invention is that a polarization-maintaining optical fiber, two optical input ends, a means for multiplexing input pulse light from the input ends, means for optically coupling the input pulsed light as linearly polarized light to the polarization-maintaining optical fiber at an angle other than 45° with respect to the main axis of the polarization-maintaining optical fiber, and detecting the light emitted from the polarization-maintaining optical fiber. It consists of an optical fiber logic element consisting of an analyzer element that emits light and an output end that takes out the output from the analyzer element.

(Operation) With the above configuration, logical operations such as logical product, logical sum, and negation can be performed using the optical force effect, and an optical logic element with high speed operation and high reliability can be obtained.

(Example) Fig. 1 is a block diagram of an experiment conducted to confirm the operation of the optical fiber logic element of the present invention. Pulse light from a single light source 11 is separated into two by a half mirror 4, and then the pulsed light is split into two by a half mirror 4. The waves are combined and input into the optical fiber. 1 is an optical input pulse, 2 is an optical input pulse,
3 is a λ/2 plate phase shifter, 4 is a half mirror, 5 is an attenuator, 6 is an objective lens, 7 is a polarization maintaining optical fiber, 8 is an analyzer (Glan-Thompson prism), 9
1 is a monochromator, 10 is a photodetector, and 11 is a light source. In order to perform an AND (logical product) operation in this system, the polarization plane of the optical input pulse is aligned with the principal axis of the birefringence of the optical fiber 7 through the phase shifter 3, and the polarization plane of the input light is focused using the objective lens 6. and input it into an optical fiber. The polarization direction of the incident light does not need to completely match the principal axis of the optical fiber 7, but if it is 45 degrees to the principal axis, the two polarized waves will propagate uniformly in the directions of the two principal axes of the optical fiber 7. Therefore, the AND operation of the present invention cannot be realized. At this time, the optical input pulses must either have phases that match each other and have sufficiently long coherence lengths so that they mutually reinforce each other, or the coherent lengths must be sufficiently short compared to the optical path length difference between the two input signals so that no interference occurs. is necessary. Furthermore, in the configuration shown in Figure 1, the delay time difference due to the optical path length difference between both inputs corresponds to the time difference between the pulses entering the two input terminals of the element of the present invention, and this must be sufficiently short compared to the input optical pulse width. It won't happen.
When the light intensity of the light pulse incident on the optical fiber 7 is strong, the polarization state of the input light pulse changes after propagation through the optical fiber due to the light intensity dependence of birefringence caused by the optical power effect. . If the analyzer in step 8 is adjusted so that the transmitted light is quenched when the input optical pulse intensity is sufficiently weak, the plane of polarization will rotate when the optical pulse intensity is strong, causing part of the optical pulse to disappear. 8
The light passes through the analyzer and is received by 10 photodetectors. However, in the AND operation, the 9 monochromators are not required. In order to obtain the above-mentioned birefringence characteristics dependent on light intensity, the incident light must be incident such that the plane of polarization is at an angle other than 45° with respect to the main axis of the optical fiber.

FIG. 2 shows experimental results showing the power of the analyzer-transmitted light pulse caused by the above-mentioned nonlinear optical effect with respect to the incident power. The light source is a Nd:YAG laser equipped with a Q switch, and the oscillation wavelength is 1.064μ.
m, and the plane of polarization of the input optical pulse is made to coincide with the main axis of the fiber. The polarization maintaining fiber is a circular core single mode fiber with a fiber length of 11 m. The optical pulse output is 3 times the power of the input optical pulse.
It is proportional to the power. In Figure 2, for example, if the peak power of the input optical pulse is 10W, the transmitted optical power is about 0.9 on the arbitrary scale of the vertical axis when only one of the inputs is input, but if both optical pulses have the same intensity When inputting at the same time, the input power is
Since it is 20W, the output is about 7. This situation is schematically shown in FIG. 3. Therefore, by utilizing the light intensity dependence of birefringence due to the optical power-effect generated in the optical fiber, that is, the phenomenon in which the plane of polarization rotates according to the light intensity, two input light pulses and the transmitted light can be Logical AND operation between pulses
Can perform movements. Figure 4 shows experimental data for this AND operation. From the left, a shows the pulse waveforms of the input light pulse only, the input light pulse only, and the light transmitted through the analyzer for input +, respectively. The states of only input optical pulses and only input optical pulses were realized by blocking one optical path as shown in FIG. The peak power of each input optical pulse is 30 W, and the input pulse waveform is as shown in FIG. 4c. Figure 4a
The output peak value for input + is approximately 10 times the "0" level (OFF state) shown in
When this is regarded as the "1" level (ON state), the ON/OFF ratio is approximately 10 times greater. On the other hand, in the case of Figure 4b where the peak value of the input optical pulse is extremely small at 0.3W, the peak value of the output pulse for the input + is the sum of the outputs for the single inputs, so it is not enough. ON/OFF ratio cannot be obtained and AND operation cannot be performed.

Next, the OR operation shown in FIG. 5 requires saturation of the optical output. Attenuation of the input optical pulse by stimulated Raman scattering can be used as one method to obtain this saturation characteristic. According to the experimental results of another type of polarization maintaining fiber (PANDA fiber) of 5.5 m in length as shown in Fig. 6, the transmitted light intensity becomes saturated when the power of the input optical pulse exceeds 300 W. Furthermore, even if the incident intensity is increased, the input power will shift to Stoke's light of stimulated Raman scattering, so if the wavelength of the analyzer transmitted light is selected with a monochromator and only the power of the input light wavelength is received,
Since the transmitted light intensity does not exceed a certain value,
It can be seen that the required optical input-optical output characteristics suitable for OR operation are actually obtained. Figure 7 is a book
This is an experimental result of the transmitted light pulse waveform of the PANDA fiber, and saturation is clearly seen in the output pulse waveform for input powers of 330W and 480W at fiber length b of 5.5m.

FIG. 8 shows a case in which the elements capable of AND operation are composed only of optical fibers, and 12 is an absolutely single polarization-maintaining optical fiber that functions as an analyzer. If a linearly polarized laser beam is used as a light source as in the above experiment, the polarization plane of the incident light and the main axis of the fiber can be made to coincide by rotating the polarization-maintaining fiber 7, so that the input end of the optical fiber 7 The λ/2 plate retarder can be removed. Further, a monochromator after the analyzer is also unnecessary in the case of AND operation because the influence of stimulated Raman scattered light can be ignored, so the configuration shown in FIG. 8 is possible. FIG. 9 is a cross-sectional view of an absolutely single polarization maintaining fiber (PANDA fiber), where 13 is a core and 14 is a stress applying portion. FIG. 10 shows the measured values of the bending loss wavelength characteristics of two orthogonal polarized waves of this fiber. Bending diameter is approximately 40mm
φ, fiber length is approximately 10 m. used in this experiment
Nd: Y at 1.064μm, which is the wavelength of the YAG laser light source.
Almost no axially polarized waves are transmitted, and only the X-axis polarized waves are transmitted, so by connecting the main axis of the polarization preserving fiber 7 and this fiber together, this fiber can be used as an analyzer. can. 1st
Figures 1a and b show the results for all fiber elements connected to 2m and 6m inertial fibers and this fiber analyzer.
Experimental values for AND operation are shown. Both results a and b are almost the same ON/OFF compared to the results using the Glan-Thompson prism as an analyzer (Figure 4 a).
The ratio has been obtained, and an all-fiber AND element has been realized.

(Effects of the Invention) As explained above, this optical arithmetic element does not use any electrical signals and operates only with optical signals, so the electronic circuit can be eliminated, and the optical force-effect response is reduced.
Since it is extremely fast at about 10 ¹² bit/s, high-speed response is possible, and since a Fabry-Perot resonator is not used, the reliability of the device can be improved. In particular, with all-optical fiber devices, connections between devices can be easily made using optical fibers, so there is almost no delay that occurs in electronic circuits. Furthermore, since it uses optical fiber, it is resistant to external disturbances such as electromagnetic induction, and has the advantage of being small and lightweight, making it promising as an optical logic operation element for use in future optical computers and the like.

Furthermore, although this embodiment shows an example using a silica-based optical fiber, it is possible to reduce the threshold value of input optical power by making the fiber from a material whose optical power-effect constant is larger than that of the silica-based fiber. I can do it. Among the fibers that have actually been realized, for example, germanium core fiber is about 10 times stronger than quartz fiber, and CS2 _- filled liquid core fiber is about 10 times faster than quartz fiber.
There is one with a light power-effect constant of 200.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of the device of this example, Fig. 2 is a diagram showing optical input/output characteristics, Fig. 3 is a schematic diagram of AND operation, Fig. 4 is a diagram showing experimental results of AND operation, and Fig. 5 is a diagram showing the experimental results of AND operation. The figure is a schematic diagram of OR operation, Figure 6 is a diagram showing optical input/output characteristics with saturation, Figure 7 is a transmitted light pulse waveform, Figure 8 is a configuration diagram of all fiber elements, and Figure 9 is an absolute single Figure 10 is a cross-sectional view of the polarization-maintaining fiber, and Figure 11 is a diagram showing the bending loss wavelength characteristics of X and Y polarizations.
The figure shows experimental results of AND operation of all fiber elements. 1... Optical input pulse, 2... Optical input pulse, 3... λ/2 plate phase shifter, 4... Half mirror, 5... Attenuator, 6... Objective lens, 7... Polarization maintaining fiber, 8... Analyzer (Glan-Thompson prism), 9... Monochromator, 10... Photodetector, 11... Light source, 12... Fiber analyzer, 13... Core, 14... Stress applying section.

Claims (1)

[Claims] 1. A polarization-maintaining optical fiber, two optical input ends,
means for multiplexing the incident pulsed light from the input end;
means for optically coupling the combined input pulsed light into the polarization-maintaining optical fiber at an angle other than 45° with respect to the main axis; A detection element that extracts as output a component whose plane of polarization has been rotated due to the force effect;
An optical fiber logic element comprising means for detecting the output from the analyzing element and determining a binary value of 0 or 1 based on the detection level. 2. The optical fiber logic device according to claim 1, wherein the analyzing element is an analyzer and performs an AND operation. 3. The optical fiber logic element according to claim 1, wherein the analyzing element is composed of an analyzer and a monochromator, and performs an OR operation. 4. The optical fiber logic device according to claim 1 or 2, wherein the analyzer is a fiber analyzer.