JPH01210938A - Waveguide type optical logic element and optical limiter - Google Patents

Abstract

PURPOSE:To simultaneously enable the actions of the optical logic operation superior in stability and the optical limiter operation by using the end part of a nonlinear optical material layer brought into contact with the emission end of a waveguide layer as the emission end which has such differential gain characteristic that the optical logic operation is possible for the signal light. CONSTITUTION:A waveguide layer 3 and a clad layer 4 which is brought into contact with the layer 3 and consists of a 4BCMU polymer are provided on an SiO2 buffer layer 2 formed by thermally oxidizing a silicon substrate 1. Since one end 3a of the waveguide layer 3 in the direction of contacting between layers 3 and 4 is used as the incidence end of a signal light Ii(IA, IB), the other end 3b is the emission end which has the optical limiter operation to the signal light. The end part 4b of the layer 4 adjacent to the emission end 3b is the emission end of the evanescent wave which is leaked from the layer 3 and has a differential gain characteristic. Since the layer 4 has high nonlinear susceptibility, the incident light on the layer 3 has the light power transferred to the layer 4 by the effective refractive index because of the increase of the intensity of light. Thus, the emitted light power does not follow up the incident light power in the layer 3 and a saturation phenomenon is shown to indicate the optical limiter operation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention utilizes refractive index changes due to nonlinear optical effects,
The present invention relates to a waveguide type optical logic element and an optical limiter that perform optical limiter operation and optical logic operation in the same element by changing the equipolarized refractive index of incident light depending on the optical intensity.

[Conventional technology] As the practical use of optical communication systems progresses, even higher capacity and
There is a need for multi-functional, advanced optical communication and optical information processing systems. When optical information processing is performed, an optical limiter that adjusts the optical signal pulse trains sent from each channel to a predetermined intensity and an optical logic element that performs logical operations on these pulse trains are required. The optical limiter is also important as a protection circuit that prevents high output light exceeding a threshold value from entering an optical element or an optical circuit.

FIG. 5 is a block diagram of a conventional optical logic element and optical limiter. 7.9 is a reflecting mirror, 8 is an electrode, 10 is a half mirror
111 is an electro-optic crystal, 12 is a photodetector, and 13 is an amplifier. In this conventional example, an electro-optic crystal 11 whose refractive index can be changed by applying a voltage from an electrode 8 is placed in a Fapley-Perot resonator composed of a reflecting mirror 7, 9, etc., and a photodetector 12 and An amplifier 13 feeds back and applies a voltage proportional to the transmitted light intensity IO and the control light intensities IA and IB to the electro-optic crystal 11, thereby forming a (optical-electrical) hybrid optical logic element or optical limiter. .

[Problems to be Solved by the Invention] However, in the optical-electrical hybrid optical logic element or optical limiter in the above-mentioned conventional technology, since a Fapley-Perot resonator is used, adjustment of the optical system is troublesome.
Furthermore, since a device for optical-to-electrical (0/E) conversion is required, there is a drawback that the entire device system becomes large. Furthermore, optical logic elements and optical limiters using resonators have the disadvantage that a single configuration can only perform either a single logic operation or an optical limiter operation.

The present invention was devised to solve the above problems, and its purpose is to have a simple structure, excellent stability, and be able to be configured in a compact size, and to perform optical logic operation and limiter operation in the same element. An object of the present invention is to provide a waveguide-type optical logic element and an optical limiter that can perform simultaneous operation.

[Means for Solving the Problems] The configuration of the waveguide type optical logic element and optical limiter of the present invention to achieve the above object includes a nonlinear optical material layer whose refractive index increases by light irradiation, and a waveguide in contact with the nonlinear optical material layer. one end of the waveguide layer in the direction in which the two layers contact is an input end for signal light, and the other end is an output end that exhibits an optical limiter operation for the signal light, and an output end of the waveguide layer. The end of the nonlinear optical material layer adjacent to the nonlinear optical material layer is used as an output end exhibiting a differential gain characteristic capable of optical logic operation for the signal light, or in the above, two waveguides are provided on both sides of the nonlinear optical material layer. The layers are in contact with each other, and the output end of one waveguide layer that exhibits an optical limiter operation has a differential gain characteristic that enables optical logic operation at the end of the other waveguide layer that is adjacent to the output end of the other waveguide layer across the nonlinear optical material layer. It is characterized by having the output end shown in FIG.

[Function] The present invention uses the nonlinear susceptibility of the nonlinear optical material layer to contact the side surface of the waveguide layer into which the signal light is incident, thereby increasing the equipolarized refractive index as the intensity of the incident light increases. The center of the incident optical power is transferred to the nonlinear optical material layer, causing this waveguide layer to function as an optical limiter. on the other hand,
When the center of the incident light power shifts to the nonlinear optical material layer, the power of the evanescent wave seeping into this layer increases rapidly as the intensity of the incident light increases (differential gain characteristic). Optical logic operation is enabled by determining the light intensity obtained from the output end of the nonlinear optical material layer or other waveguide layer in contact with this layer.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIGS. 1(a) and 1(b) are a plan view (a) and a side view (b) showing the configuration of a first embodiment of an optical logic element and an optical limiter of the present invention. In this embodiment, a waveguide layer 3 of Corning 7059 glass (manufactured by Corning Glass Works, Inc., USA) is formed by RF sputtering on a show buffer layer 2 formed by thermally oxidizing a silicon substrate 1, and a S On the iOt barrier layer 2, the following structural formula (1) is applied.
The structure includes a cladding layer 4 made of 4BCMU polymer having a monomer structure shown in FIG.

R-C=C-C=C-R...(1) R=-+CH, U-. OCNHCH, COC, H.

This cladding layer 4 is the nonlinear optical material layer of the present invention,
The nonlinear optical material forming this layer has a large third-order nonlinear susceptibility χ0 of more than tQ-11esu. The width and thickness of the cross section of the waveguide layer 3 in the direction in which the two layers 3 and 4 are in contact are, for example, approximately 5 μm. Further, the width and thickness of the cross section of the cladding layer 4 in contact with the cladding layer 4 are also formed to be approximately 5 μm.

Here, by setting one end 3a of the waveguide layer 3 in the direction in which the two layers 3.4 are in contact with each other as the input end of the signal light I i (IA, In), the other end 3b is used as the input end of the signal light I1 (IA, In).
, IB), and the end 4b of the cladding layer 4 adjacent to the output end 3b serves as the output end of the evanescent wave that seeps out from the waveguide layer 3 and exhibits a differential gain characteristic. Become.

The type of waveguide used in this embodiment is not particularly limited, but any waveguide can be used as long as it has low loss in the wavelength range used. Specifically, quartz-based (SiOx with Ti or GeOt
(doped) waveguide, the Corning 7059 glass waveguide mentioned above, a Ti or H0 diffused L i N b Os waveguide, and the like.

In addition, the organic nonlinear optical material used for the cladding layer 4 in this example has a critical light intensity (light intensity at which the output light power begins to be saturated in the case of an optical limiter) Ic, which is a practical optical power (approximately I
MW/mm), the nonlinear susceptibility χ
131 is required to exhibit a large value of about l
Polydiacetylene, poly(
Examples include organic polymers such as P-phenylene vinylene) and poly(2,5-chenylene vinylene), and organic single crystals and organic polycrystals such as benzylidene aniline, stilbene, and azo dyes.

The operation of the first embodiment configured as above will be described. The optical logic element and optical limiter according to this embodiment have a simple structure including a cladding layer 4 made of an organic nonlinear optical material and a waveguide layer 3 disposed in contact with the cladding layer 4. The organic nonlinear optical material forming 4 is I
Large third-order nonlinear susceptibility χ greater than O−”e s u
(3). Due to the large nonlinear susceptibility χl) of the cladding layer 4, the equivalent refractive index of the incident light incident on the waveguide layer 3 increases as the light intensity increases.
The center of optical power shifts to the cladding layer 4. Along with this, in the waveguide layer 3, the output light power no longer follows the increase in the incident light power, and a certain critical light intensity is reached! Above c, the output light lot exhibits a saturation phenomenon and exhibits a light limiter operation. On the other hand, in the cladding layer 4, part of the optical power of the waveguide layer 3 seeps out as an evanescent wave, but the seepage of this optical power (the power of the evanescent wave) gradually increases as the equivalent refractive index of the incident light increases. When the center of the incident light power shifts to the cladding layer 4,
It increases rapidly above the critical light intensity 1c. In this way, in the cladding layer 4, the output light lot exhibits differential gain characteristics as the intensity of the light incident on the waveguide layer 3 increases. This differential gain characteristic is a basic characteristic of optical logic gates such as optical OR gates and AND gates (Optics, a magazine published by the Optics Conference of the Japan Society of Applied Physics, Vol. 14).

No. 1, pages 11-18). In this way, compared to conventional (optical-electrical) hybrid optical logic devices and optical limiters that use Fabry bellows type resonators, the device of this embodiment does not require a reflective mirror or optical-electrical limiter that is difficult to adjust. The advantage is that an element with a simple structure can stably perform an optical logic operation and an optical limiter operation simultaneously without using a (0/E) converter, and the same element can perform an optical logic operation and an optical limiter operation simultaneously.

Figures 2 (a) and (b) are an output light intensity characteristic diagram (a) at the output end of the optical waveguide layer and an output light intensity characteristic diagram (b) at the output end of the cladding layer in the first embodiment. An observation example is shown in which the thickness of the waveguide layer 3 is 5 μm, the thickness of the cladding layer 4 is 5 μm, and the wavelength of the incident light 1i at the input end 3a is 1.064 μm. In the figure, both the incident light intensity and the outgoing light intensity are expressed as relative light intensities with respect to the critical light intensity 1c. At the output end 3b of the waveguide layer, as shown in (a), the output light 1o+ is saturated near the critical light intensity Ic (It/Ic=1), indicating an optical limiter operation.

Further, at the output end 4b of the cladding layer, as shown in (b), the output light is near the critical light intensity 1c (Ii/Ic=1). It can be seen that a differential interest time property in which , rises rapidly is obtained.

The optical logic operation of the optical logic element according to this embodiment is based on the above incident light I.
i - Outgoing light I. This is possible by using the differential gain characteristics between the two. As shown in FIG. 1, the signal lights constituting the incident light It entering from the input end 3a are IA and IB,
Let Ioz be the light emitted from the output end 4b, and I. The detection limit of , for example, is set to about 0°lXIc. Based on the differential gain characteristic diagram of FIG. 2(b), this detection limit is set to an output light intensity in the vicinity of If/Ic=1, where the incident light intensity starts to rise rapidly. In this way■. ,
1. The case where can be detected. If the case where it is not possible is set as 0, Table 1
The truth table shown in is obtained. From this table, signal light I
If A and IB are smaller than the rising light intensity 1c of the differential gain characteristic, it is an AND gate.

It can be seen that when it is larger than Ic, it operates as an OR gate.

Table 1 Next, a second embodiment of the present invention will be described. FIG. 3 is a plan view (a) and a side view (b) showing the configuration. In this embodiment, the same members as those in the embodiment shown in FIG. 1 are given the same numbers and will be explained. In this example, two Corning 7059 glass (refractive index n=1°53) waveguide layers 3 and 5 are formed by RF sputtering on a SiO buffer layer 2 formed by thermally oxidizing a silicon substrate 1. The structure is such that an intermediate cladding layer 6 made of a PTS polymer (n=1.58) having a monomer structure of the following structural formula (2) is installed between two waveguide layers 3.5. .

R'-C=C-C=C-R'...(2
)R'=-CHt-0-S-0-CHs This intermediate cladding layer 6 is the nonlinear optical material layer of the present invention. Each waveguide layer 3.5 has a cross-sectional width and thickness of, for example, about 5 μm in the direction in which it contacts the intermediate cladding layer 6ζ. Further, the thickness of the cross section of the intermediate cladding layer 6 is, for example, approximately 0.4 μm. Here, one end 3a of one waveguide layer 3 in the direction in contact with the intermediate cladding layer 6 is set as the input end for the signal light I t (IA, In), and the other end 3b is used as the input end for the signal light I t (IA, In).
, the end 5b of the other waveguide layer 5, which is close to the output end 3b with the intermediate cladding layer 6 in between, serves as an output end that exhibits an optical limiter operation with respect to IF. The output end exhibits differential gain characteristics.

The type of waveguide used in this example is not particularly limited, but any type can be used as long as it has low loss and has a refractive index smaller than that of an organic nonlinear optical material with a large nonlinear susceptibility χ'3' as described below. Available for use. . Specifically, examples include a quartz-based (Sin, doped with Ti or G e O!) waveguide, the Corning 7059 glass waveguide, and a Ti or H diffused LiN b 03 waveguide.

In addition, the organic nonlinear optical material used for the intermediate cladding layer 6 in this embodiment has a critical light intensity (the light intensity at which the output light power begins to be saturated in the case of an optical limiter) and the practical optical power (
The value of the nonlinear susceptibility χf31 is approximately 1
It is desirable to exhibit a large value of e S 11 or more, and to exhibit a refractive index greater than that of the waveguide layer 5 in order to increase the seepage of optical power. There are no particular restrictions on materials that meet these requirements, but specific examples include polydiacetylene, poly(P-phenylenevinylene), and poly(2,5-chenylene), which are known as high χ0 materials. Examples include organic polymers such as vinylene), organic single crystals and organic polycrystals such as benzylizo, vinylene, stilbene, and azo dyes.

The operation of the second embodiment of the present invention constructed as described above will be described. The optical logic element and the optical limiter according to this embodiment have the cladding layer 6 on both sides of the intermediate cladding layer 6 made of an organic nonlinear material. Two waveguide layers 3.
The organic nonlinear material forming the intermediate cladding layer 6 has a refractive index larger than that of the waveguide layer 3.5 and a third-order nonlinear material larger than lO"e s u. It has a susceptibility χ(3). Because of the large nonlinear susceptibility χ<3) of the intermediate cladding layer 6, it is possible to The incident light has an equipolarized refractive index n art that increases as the light intensity increases, and the center of power is located at the intermediate cladding layer 6.
Move to. Along with this, in the waveguide layer 3 on the incident side, the output light power no longer follows the increase in the input light power, and a certain critical light intensity is reached! c or more, the emitted light 1o+ exhibits a saturation phenomenon and exhibits a light limiter operation. On the other hand, in the waveguide layer 5 where no light was incident, the refractive index of the intermediate cladding layer 6 is larger than that of the waveguide layer 5, so the optical power of the waveguide layer 3 on the incident side spreads to the intermediate cladding layer 6. A part of it seeps into this waveguide layer 5 as an evanescent wave. The evanescent wave power (the power of the evanescent wave seeping out of this optical power) gradually increases as the equipolarized refractive index net of the incident light increases, and reaches the critical light intensity ■. The above shows a differential gain characteristic that increases rapidly. As mentioned above, this differential gain characteristic is a basic characteristic of optical logic gates such as optical OR gates and optical AND gates. In this way, this embodiment also uses a reflective mirror and an optical-electrical (optical-electrical) optical limiter, which are difficult to adjust, compared to a conventional (optical-electrical) hybrid optical logic element or optical limiter using a Fabry-Perot type resonator. /E) Without using a conversion device,
The advantage is that an element with a simple structure can stably perform an optical logic operation and an optical limiter operation at the same time.

FIGS. 4(a) and 4(b) show the output light intensity characteristic diagram (a) at the output end of one waveguide layer and the output light intensity at the output end of the other waveguide layer in the second embodiment. In the characteristic diagram (b), the thickness of the waveguide layer 3.5 is 5 μm, and the thickness of the intermediate cladding layer 6 is 0.4 μm.

An observation example is shown in which the wavelength of the incident light if at the input end 3a is L064 μm. In the figure, both the incident light intensity and the output light intensity are critical light intensity I. The relative light intensity is shown. At the output end 3b of one waveguide layer, as shown in (a), the output light 1o1 is saturated near the critical light intensity Ic (I i /Ic = 1), indicating an optical limiter operation. Moreover, at the output end 5b of the other waveguide layer, C
As shown in b), the critical light intensity Ic (I i/Ec = 1)
It can be seen that a differential gain characteristic is obtained in which the output light rot suddenly rises in the vicinity.

The optical logic operation of the optical logic element according to this embodiment is the same as the first embodiment, where the input light 1i minus the output light I is used. This is possible by using the differential gain characteristics between.

Incident light enters from the input end 3a as shown in FIG. 3!
Let the signal lights constituting i be IA and IB, and let the emitted light from the output end 5b be Ion, and the detection limit of this loz is, for example, about 0.04X1. Set it as This detection limit is the fourth
Based on the differential gain characteristic diagram in Figure (b), the incident light intensity when the light starts to rise rapidly is set to the output light intensity near If/Ie=1. In this way, if roz is detected as 1, and if it cannot be detected as 0, the truth table shown in Table 1 described above is obtained. From this table, it can be seen that in this embodiment as well, the signal lights (9) and Ia have the rising light intensity (2) of differential gain characteristics. If it is smaller than re, it can act as an AND gate), and if it is larger than re, it can act as an OR gate.

Note that the present invention is not limited to the above embodiments,
It is a matter of course that the present invention can be applied in various ways and can be implemented in various ways according to its main purpose.

[Effects of the Invention] As is clear from the above description, according to the waveguide type optical logic element and optical limiter of the present invention, the uniform refractive index of incident light is changed by using the change in refractive index due to the nonlinear optical effect. The optical limiter operation and optical logic operation are performed by the same element by varying the intensity, so the structure is simple and highly stable.
It also has the advantage of being able to be configured in a compact size and allowing optical logic operation and optical limiter operation to be performed simultaneously.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are a plan view and a side view showing the configuration of the first embodiment of the present invention, and FIGS. 2(a) and (b) are the optical limiter characteristics in the first embodiment described above. FIG. 3(a) is an output light characteristic diagram showing differential gain characteristics. (b) is a plan view and side view showing the configuration of the second embodiment of the present invention, and FIGS. 4(a) and (b) are outputs showing the optical limiter characteristics and differential gain characteristics in the second embodiment. Light emission characteristic diagram,
FIG. 5 is a block diagram of a conventional optical logic element or optical limiter. 3.5...Waveguide layer, 3a...Incidence end, 3b...
Output end exhibiting optical limiter characteristics, 4... Cladding layer (nonlinear optical material layer), 4b, 5b... Output end exhibiting differential gain characteristics, 6... Intermediate cladding layer. 77 ftJiU to Kankari! E, H/Ic 3 times At)
'lf-strong, ff+1/■c (b) Fig. 2 Relative person n is a blow 1i/Ic (G) Surikarikomito or Ryouguchi i/Ic (b) Fig. 4 Fig. 5

Claims (2)

[Claims] (1) Consisting of a nonlinear optical material layer whose refractive index increases with light irradiation and a waveguide layer in contact with it, one end of the waveguide layer in the direction in which both of the above layers contact is the input end of the signal light, and the other end is the above-mentioned waveguide layer. an output end that exhibits an optical limiter operation for the signal light, and an end of the nonlinear optical material layer adjacent to the output end of the waveguide layer that exhibits differential gain characteristics capable of optical logic operation for the signal light; A waveguide type optical logic element and an optical limiter characterized by the following. (2) It consists of a structure having a nonlinear optical material layer whose refractive index increases by light irradiation and a waveguide layer on both sides in contact with the layer, and one end of one of the waveguide layers in the direction in contact with the nonlinear optical material layer is used for transmitting signal light. The other end is used as an input end, and the other end is used as an output end that exhibits an optical limiter operation for the signal light, and the end of the other waveguide layer that is close to the output end that exhibits an optical limiter operation across the nonlinear optical material layer is used as an input end. A waveguide type optical logic element and an optical limiter, characterized in that the output end exhibits differential gain characteristics capable of optical operation with respect to the signal light.