JPH0336407B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field] The present invention is characterized in that when a single or multiple lights are incident, the refractive index in different crystal axis directions changes differently depending on the light intensity of the lights, and the polarization of the incident light is changed. The present invention relates to an optical nonlinear element using an anisotropic crystal that self-modulates its state, and particularly relates to an optical bistable circuit element capable of ultra-high speed and highly stable operation, which is suitable for an optical logic circuit element.

[Prior art] Conventionally, an electro-optic crystal is inserted between a polarizer and an analyzer, and the rotation of the plane of polarization by applying an external voltage (bias) is used to control the amount of light passing through the crystal and its spectral characteristics. , an OFF type optical shutter is known (see Japanese Patent Application Laid-Open No. 59-49520). However, since this type of car shutter uses an external voltage as a control means, there is a limit to the response speed (speed), which is on the order of several 10 MHz at most, and it is controlled only by light without using electrical signals or circuits. The major drawback was that this was impossible in principle. Furthermore, its operation was limited to ON and OFF operations.

On the other hand, in order to realize ideal optical communication networks and optical computers, there is a strong demand for circuit elements that perform optical logic operations using only light. Here, as an all-optical optical logic operation using a medium having a so-called third-order nonlinear optical effect (x ⁽³⁾ ) in which the refractive index depends on the light intensity, we will use the configuration shown in Figure 2. An optical bistable device can be considered. Second
Figure A shows the basic configuration of an optical bistable element in which a nonlinear medium is inserted inside a Fabry-Perot resonator (or ring resonator) for performing optical feedback. Here, 1 is an optical nonlinear medium, 2 and 3 are reflecting mirrors for a Fabry-Perot cavity, 4 is input light, and 5 is output light. Figure 2B shows the input/output characteristics showing the differential gain characteristics of the element in Figure 1A, and Figure 2C shows the input/output characteristics showing its bistable characteristics. The difference is due to differences in initial detuning. The input/output characteristics of this type of element are expressed by the following formula (1-1)
It is expressed as

Here, P _i = (1 + Fsin ² β) P _p (1-1) β = β _p + KP _p (1-2) F = 4R/(1-R) ² (1-3) β _p = πΔ/( c/2n _p L) (1-4) Δ= _p − (1-5) is defined. P _i is the intensity of the input light, P _p is the intensity of the output light, β is the initial detuning which is the linear phase difference when the light is weak, K is the proportionality constant determined by the magnitude of the nonlinearity of medium 1, and R is the The reflectance of the reflector, c is the speed of light in vacuum, and n _p is the optical nonlinear medium 1 that does not depend on the light intensity.
, L is the length of the medium 1, f _p is the resonant frequency when the optical input is 0, and is the frequency of the input light.

Therefore, from equation (1-1), output light intensity P _p is a polygonal function with respect to input light intensity P _i , and from equation (1-4), the relationship between P _i and P _p is expressed as 2
The characteristics are as shown in Figure B (differential gain characteristic) and Figure 2 C (bistable characteristic), and optical memory, switching, limiter operations, etc. are possible. Therefore, it is theoretically possible to realize various optical logic circuits that utilize such nonlinear characteristics.

However, as is clear from the above equations (1-1) and (1-4), an essentially unavoidable drawback of this type of element is that the input/output characteristics change with respect to changes in the initial detuning β _p . That is, it changes sensitively to changes in Δn _p L. Therefore, it is necessary to suppress temperature changes in the refractive index n _p of the medium 1 and the length L of the medium 1, as well as fluctuations in the frequency of the input light, to an extremely small level, which poses a serious problem in practical use, making it impossible to put it into practical use. It is the cause. In other words, in the configuration shown in Figure 2 A, the refractive index is not compensated for temperature, so the initial detuning β _p changes depending on the temperature, and β _p changes sensitively due to frequency fluctuations of the incident light, so the operation is unstable. There's a problem.

[Objective] In view of the above-mentioned points, an object of the present invention is to provide an optical nonlinear element that is capable of extremely high-speed operation and that greatly reduces the effects of temperature fluctuations of the element and fluctuations of input optical frequency. be.

[Configuration of the Invention] In order to achieve the above object, the first aspect of the present invention is to
An anisotropic crystal that self-modulates the polarization state of the incident light is used as a polarizer for detection. and a photon, the polarization direction by the polarizer is set at 45° with respect to the optical anisotropy axis of the anisotropic crystal, and a single or multiple lights are incident on the anisotropic crystal, It is characterized by self-modulating the polarization state of incident light within the anisotropic crystal.

In addition, the second aspect of the present invention is that when a single or multiple lights are incident, the refractive index in different crystal axis directions changes differently depending on the light intensity of the lights, and the polarization state of the incident light is self-modulated. An anisotropic crystal, a temperature-compensating birefringent crystal that changes the optical path length depending on the temperature to keep the initial detuning constant, and a Babinet Soleil compensator to variably set the initial detuning are combined with a polarizer and an analyzer. and the polarizing direction of the polarizer is set at 45 degrees with respect to the optical anisotropic axis of the anisotropic crystal.

Further, the third aspect of the present invention is that when a single or multiple lights are incident, the refractive index in different crystal axis directions changes differently depending on the light intensity of the lights, and the polarization state of the incident light is self-modulated. An anisotropic crystal, a temperature-compensating birefringent crystal that changes the optical path length depending on the temperature to keep the initial detuning constant, and a Babinet Soleil compensator to variably set the initial detuning are combined with a polarizer and an analyzer. The invention is characterized in that a plurality of optical nonlinear elements are inserted in between and connected in series, and the polarization direction of the polarizer is set at 45 degrees with respect to the optical anisotropy axis of the anisotropic crystal.

Furthermore, the fourth aspect of the present invention is that when a single or multiple lights are incident, the refractive index in different crystal axis directions changes differently depending on the light intensity of the lights, resulting in a self-modulating effect on the polarization state of the incident light. a birefringent crystal for temperature compensation that changes the optical path length according to temperature in order to keep the initial detuning constant, and a Babinet Soleil compensator for variably setting the initial detuning as a polarizer. The polarizer is inserted between the analyzer and the polarization direction of the polarizer relative to the optical anisotropic axis of the anisotropic crystal.
The optical nonlinear element is set at an angle of 45 degrees, and is characterized in that a reflecting mirror is placed next to the analyzer.

[Function] In the present invention, when a single or multiple lights are incident, the refractive index in different crystal axis directions changes differently depending on the light intensity of the lights, and the polarization state of the incident light is self-modulated. An anisotropic crystal is inserted between a polarizer and an analyzer, and the direction of polarization by the polarizer is set at 45 degrees with respect to the optical anisotropic axis of the anisotropic crystal. For example, by injecting light containing control light for controlling switching, etc. and signal light to be controlled into the anisotropic crystal, and utilizing the self-modulation effect in this anisotropic crystal, an all-optical type It performs various operations such as switching operations, optical amplification operations, logical operation operations, and limiter operations. Therefore, according to the optical nonlinear element of the present invention, which performs switching control using only light, the change in optical refraction is much faster than the voltage application, and thus the optical nonlinear element of the present invention provides a change that cannot be obtained with conventional car shutters. High-speed performance of several GHz, which is more than two digits faster, can be achieved. Another advantage is that optical pulses can be compressed by utilizing the self-modulation effect. moreover,
As will be described later, since the initial detuning of the anisotropic crystal itself is very small, it has the characteristic of being tough against temperature fluctuations and frequency fluctuations, and the stability of output is improved.

In addition, the present invention has another configuration including an anisotropic crystal similar to the above, a temperature-compensating birefringent crystal that changes the optical path length depending on the temperature in order to keep the initial detuning constant, and a variable initial detuning. Insert the Babinet Soleil compensator between the polarizer and the analyzer to set it.
By setting the polarization direction of this polarizer at 45 degrees with respect to the optical anisotropy axis of the anisotropic crystal, a remarkable improvement in the stability of the output frequency can be obtained. That is, since the Babinet-Soleil compensator is used, which is made so that the phase change is constant over the entire field of view, the initial detuning can be freely and variably set. By using a temperature-compensating birefringent crystal to change the optical path length according to temperature fluctuations, different thermal expansions in different crystal axis directions are compensated for. The temperature can always be kept constant regardless of temperature fluctuations. The initial detuning generally varies depending on the temperature, and the output frequency fluctuates due to the variation in the initial detuning, but as described above, according to the present invention, the initial detuning can be held constant, so the output frequency The frequency is stabilized and stable output characteristics can be expected.

Furthermore, as another configuration of the present invention, when single or multiple lights are incident, the refractive index in different crystal axis directions changes differently depending on the light intensity of the light, and the polarization state of the incident light is self-modulated. an anisotropic crystal having
In order to keep the initial detuning constant, a temperature-compensating birefringent crystal that changes the optical path length depending on the temperature, and a Babinet Soleil compensator to variably set the initial detuning are inserted between the polarizer and the analyzer. , the polarization direction by this polarizer is set relative to the optical anisotropic axis of the anisotropic crystal.
Multiple optical nonlinear elements set at 45° are connected in series. In this way, since a plurality of optical nonlinear elements are cascaded in multiple stages, nonlinearity is significantly promoted as the number of stages increases. Therefore, by inputting an optical DC bias input pulse to the first-stage optical nonlinear element, various optical logic operations can be performed accurately and easily, and it can be used as an optical logic circuit element.

Further, as still another configuration of the present invention, in an optical nonlinear element having an anisotropic crystal similar to the above, a birefringent crystal for temperature compensation, a Babinet Soleil compensator, a polarizer, and an analyzer, the next stage of the above analyzer is provided. By arranging a reflecting mirror in the material, an asymmetric nonlinear term based on interference that occurs only through the nonlinearity of the material itself is included, and optical bistable characteristics are thereby obtained. Therefore, various applications applying optical bistability,
For example, memory and logical operation can be expected.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the invention. Here, 6
When a single or multiple lights are incident, the refractive index in the direction of the crystal axes orthogonal within the plane changes differently depending on the light intensity of the incident light, thereby modulating the polarization state.
It is an anisotropic crystal (hereinafter referred to as an optical nonlinear crystal) having a so-called self-modulation effect. 7 is a temperature-compensating birefringent crystal that changes the optical path length depending on the temperature in order to keep the initial detuning constant, which will be described later. 8 is a Babinet-Soleil compensation plate for variably setting the initial detuning. 9 is a polarizer, and 10 is an analyzer. The optical nonlinear crystal 6, temperature compensation refractive crystal 7, and Babinet Soleil compensator plate 8 are inserted between the polarizer 9 and the analyzer 10, and the polarization direction by the polarizer 9 is adjusted to the optical anisotropy of the optical nonlinear crystal 6. It is set at 45° to the axis. Further, 11 represents input light, and 12 represents output light.

As is well known, the Babinet Soleil compensator 8 is constructed by arranging a pair of wedge-shaped birefringent crystals (for example, quartz) so that their optical axes are orthogonal to each other, and sliding the crystals to adjust the angle of θ to mutually orthogonal polarized waves. This gives a phase difference θ _p of _p≡2π ( _ne −n _p ) x tan α/λ, and adds a linear initial phase θ _p with respect to the initial detuning in the present invention. Note that x is the sliding distance, α is the wedge angle, and λ
is the wavelength of the incident light, n _e is the refractive index of the crystal for extraordinary rays, and n _p is the refractive index of the crystal for ordinary rays.

The temperature-compensating birefringent crystal 7 compensates for the difference in thermal expansion coefficient β in the crystal axis direction of the birefringent crystal of the nonlinear crystal 6, as will be described later.

It is assumed that the input light 11 propagates in the x-axis direction of the nonlinear crystal 6, and that the y-axis, which is an optical anisotropic axis, and the z-axis, which is an optical axis, are in the plane of the crystal. In addition, the input light 11 is linearly polarized, and the polarizer 9 is used as described above.
and the direction of the analyzer 10 in a parallel Nicol relationship,
If the angle is set at 45 degrees from the y-axis, which is the optical anisotropic axis, the input/output characteristics of the circuit shown in FIG. 1 will be as shown in the following equation (2).

I _t = cos ₂ [(π/2) (I _i /I〓) + (θ/2)] I _i (
2) Here, I _t is the output light intensity, I _i is the input light intensity, θ
is the sum of the initial detuning, which is the linear phase difference when the light is weak, and the phase difference at the Babinet-Soleil compensator, and I is the normalized value of the input and output intensity, that is, the light intensity for rotating the polarization by 90°. is given by the following equation (3).

I〓=λ/2 [(n _y2 −n _z2 )L ₁ +(n′ _y2 −n′ _z2 )L ₂
]
(3) Here, λ is the wavelength of the input light, L ₁ is the length of the crystal 6, L ₂ is the length of the crystal 7, and n _y2 , n _z2 , n' _y2 , n' _z2 are given by the following equation (4) is a coefficient representing the magnitude of the nonlinear refractive index given by χ, and χ is a tensor component of third-order nonlinear susceptibility.

n _y2 ⁽¹⁾ ∝χ ⁽¹⁾ yyyy ⁽³⁾ +2χ ⁽¹⁾ yyzz n _z2 ⁽¹⁾ ∝χ ⁽¹⁾ zzzz ⁽³⁾ +2χ ⁽¹⁾ zzyy (4) Also, the initial The detuning θ is given by the following equation (5).

θ=2π[(n _y0 −n _z0 )L ₁ +(n′ _y0 −n′ _z0 )L ₂ ]/
λ
+θ _p ≡θ _c +θ _p (5) Here, θ _p is the phase difference caused by the Babinet-Soleil compensator 8, n _y0 and n _z0 are linear refractive indices that do not depend on the light intensity in the y and z axis directions of the crystal 6, n′ _y0 , n′ _z0 are crystal 7
is the linear refractive index for

As can be seen from the above formula (2), the output light intensity I _t varies depending on the initial detuning θ, and as can be seen from the above formula (3), the initial detuning θ is the phase difference θ _p caused by the Babinet-Soleil compensator 8.
It is variably set by.

As a specific example, for example, as a nonlinear crystal 6
If LiTaO ₃ is used, n _y2 −n _z2 = 2×10 ^-8
cm ² /MW, where L ₁ = 1 cm, L ₂ = 1 cm,
If λ=1.06μm, the corresponding I〓 is I〓=2.7×
¹⁰³ MW/ ^cm2 .

Further, the lengths L ₁ and L ₂ of the crystals 6 and 7 described above are selected as shown in the following equation (6) in order to perform temperature compensation.

L ₂ /L ₁ =+K ₁ B ₁ /K ₂ B ₂ (6) The above K ₁ , B ₁ , K ₂ , and B ₂ are given by the following equation (7).

K ₁ = (1/B ₁ ) (∂B ₁ /∂T) + α ₁ B ₁ = n _y0 − n _z0 K ₂ = (1/B ₂ ) (∂B ₂ /∂T) + α ₂ (7) B ₂ = n' _y0 - n' _z0 where α is the coefficient of linear expansion and T is the temperature.

For example, when crystal 6 is LiTaO ₃ and crystal 7 is CaCO ₃ , L ₁ /L ₂ =0.292 from the above equations (6) and (7).
Another nonlinear crystal 6 is polydiacetylene polymer (PTS), and when this crystal is used, _ny2 - _nz2 = 1.8 x 10 ^-6 cm ² /MW.

FIG. 3A shows the input/output characteristics of the device of the present invention shown in FIG. 1 described above. However, assuming θ=π, the input and output strengths are
It is normalized and shown as I〓. In this figure, due to the nonlinearity based on the above equations (2) to (5) of the phase difference in the y and z axis directions,
The self-modulation effect of light intensity is evident. Here, if the phase difference θ _p caused by the Babinet-Soleil compensator 8 is changed, the entire characteristic shown in FIG. 3A shifts. Therefore, by utilizing this type of nonlinearity, it is possible to easily compress optical pulses as shown in FIG. 3B.

More specifically, since the present invention performs switching control using only light, it is much faster than voltage application controlled by an electric circuit, so it is more than two orders of magnitude faster than conventional car shutters. For example, high-speed response characteristics on the order of several GHz can be obtained.

FIG. 4A shows another embodiment of the invention. In this embodiment, the optical nonlinear elements shown in FIG. 1 are connected in cascade in multiple stages as shown in the figure. In this case, as the number of stages N increases, nonlinearity is promoted as shown in FIG. 4B. Therefore, by using the nonlinearity shown in Figure 4B, the optical DC bias Pin, _DC ,
By appropriately selecting the peak values Pi and b of the input pulses, if two optical pulses "0" and "1" are incident, various optical logics can be realized as shown in the truth table of Fig. 5 A to D. can perform actions.

Figure 5 A is AND, Figure B is OR, Figure C is
The logical operations of NAND and NOR are shown in FIG. For example, as shown in Figure 5A, the DC bias of the light
Under the condition that Pin, _DC is low and the Hi level of one input pulse does not reach between the threshold Pi,a and Pi,c based on the optical bistable characteristics of the optical nonlinear element shown in Figure 4A, the input pulse ( 0,0), (0,1), (1,0), the output is 0, but when the input pulse is (1,
In case 1), the Hi level of the synthesized input pulse is doubled and reaches between Pi,a and Pi,c, so the output becomes 1. As shown in Figure 5 B, C, and D, similarly to the above, the optical DC bias Pin, _DC and input pulse peak values Pi, b are set appropriately for the above Pi, a and Pi, c. It can be seen that various optical logic operations can be performed by doing this.

FIG. 6 shows yet another embodiment of the invention.
In this embodiment, a reflecting mirror 13 is installed outside the element shown in FIG. In this element, the second
Unlike the conventional example shown in the figure, a Fabry-Perot resonator is not required. In particular, in this case, the incident light I _i and the reflected light I _p interact in the nonlinear crystal 6, so if the transmittance of the reflecting mirror 13 is T, the input/output characteristics of this circuit are expressed by the following equation ( 8).

I _r = cos ² [(π/2) {(1+α)I _i +I _p (1-
T)}/I〓+(θ/2)]I _p (1-T) (8) Here, I _r is the output light intensity, I _i is the input light intensity, and I _p is the reflected light intensity. Expanding the above equation (8), we obtain equation (9).

I _p = cos ² [(π/2) {(I _i + (1+α) I _p (1-
T)}/I〓+(θ/2)]I _i (9) Moreover, the above α and I _p are given by the following equation (10).

I _p = I _p T, α = exp (-4K ² Dτ) (10) Here, k is the wave number, D is the diffusion coefficient of the excited state,
τ is the response time of the crystal permittivity.

This example is characterized by the presence of an asymmetric interaction term (1+α) brought about by the interference of lights traveling in opposite directions included in equations (8) and (9) above, and this is a decisive difference from the conventional car shutter. This appears as a significant difference. That is, when α=0, bistability as shown in FIG. 7B, which will be described later, does not occur.
On the other hand, in conventional car shutters, polarization rotation is brought about by the applied voltage, so there is no asymmetric nonlinear term (1+α) based on interference that occurs only through the nonlinearity of the material itself, and therefore the optical bistable property is essentially unobtainable. Therefore, with conventional car shutters, various applications that apply optical bistability (optical memory, logic operations, etc.) cannot be expected at all, whereas with the configuration of this example, various applications that apply optical bistability can be expected. Applications can be realized.

FIG. 7 shows the input/output characteristics I _r /I vs. I _i /I for various initial detuning θ when T=0 and α=0.5. In the device shown in Fig. 6, the reflected light I _p component produces a positive feedback effect, and as is clear from the above equations (8) and (9), I _r becomes a multivalued function with respect to I _i , and the light Multilevel stability occurs. Further, depending on the difference in the initial detuning θ, differential gain characteristics as shown in FIG. 7A and optical bistability characteristics as shown in FIG. 7B can be obtained.

Finally, in each configuration of the present invention illustrated in FIGS. 1, 4, and 5, the initial detuning determined by the optical nonlinear anisotropic crystal itself is essentially resistant to temperature fluctuations and frequency fluctuations, compared to conventional Fabry-Perot elements. Quantitatively shows that it is stable. First, the initial detuning θ is calculated by ignoring the phase difference θ _p caused by the Babinet-Soleil compensator 8, and by calculating the incident light frequency and the transmission peak frequency when the optical input is O.
Letting _p , it is given by the following equation (11).

θ=2πΔ/[c/{2(n- _{y0 -nz0} )L ₁ +2
(n′ _y0 −n′ _z0 )L ₂ ] (11) However, Δ→Δ+δ→θ+δθ Initial detuning β _p in the conventional Fabry-Perot element shown in the above equation (11) and the above-mentioned equation (1-4) = πΔ/(c/2n _p L) In general, the free spectral range is C/{2(n _y0 −n _z0 )L ₁ +2(n′ _y0 −n′ _z0 )L ₂ } ＞
>C/2n _p L, and it can be seen that this device is much larger than the conventional Fabry-Perot type device.

Therefore, the variation in the initial detuning θ of the device of the present invention with respect to the variation of Δ is much smaller than that of the initial detuning β _p of the conventional device, and the value of the free spectral region itself is used for temperature compensation in the present invention. Since the temperature compensation by the birefringent crystal 7 provides constant stability, extremely stable operation can be obtained overall.

[Effects of the Invention] As explained above, according to the present invention, a polarizer and an analyzer are combined by utilizing the change in the polarization state depending on the light intensity, so that a high ON of the optical signal can be achieved.
This has the advantage of being able to obtain a −OFF ratio.

Furthermore, according to the configuration of the present invention, since the change in the polarization state depending on the light intensity is used as described above, it is essentially different from an element using a Fabry-Perot resonator, and the frequency fluctuation system of the incident light is Changes in initial detuning due to temperature changes can be significantly reduced, allowing stable operation. Furthermore, by using the Babinet Soleil compensator, the initial detuning can be freely and variably set. Furthermore, by using a temperature-compensating birefringent crystal, the initial detuning can be kept constant regardless of temperature fluctuations.

Furthermore, according to the present invention, the response time (dielectric relaxation time) of a change in the dielectric constant of the crystal that causes a change in the polarization state is considered to be short, less than a picosecond, so ultra-high-speed optical logic processing can be realized. .

Furthermore, the present invention has the advantage of having a large beam diameter and being able to perform batch parallel processing of image information in real time.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an example of the basic configuration of the present invention, FIG. 2A is a circuit configuration diagram showing a conventional optical bistable element, and FIG. 2B is a characteristic diagram showing its differential gain characteristics. C is a characteristic diagram showing its optical bistability characteristics,
Figure 3A is a characteristic diagram showing the input/output characteristics of the circuit in Figure 1, Figure 3B is a characteristic diagram showing the optical pulse compression characteristics of the circuit, and Figure 4A is the circuit in Figure 1 connected in multiple stages. A circuit configuration diagram showing another embodiment of the present invention, No. 4
Figure B is its input/output characteristic diagram, Figures 5A to 5D are waveform diagrams explaining the 2-input optical logic operation using the multistage connection circuit of Figure 4A, and Figure 6 is a reflection mirror for the circuit of Figure 1. 1
7 shows the input/output characteristics of the optical bistable circuit of FIG. 6, and A shows the differential gain characteristic. , B is a characteristic diagram showing optical bistability characteristics. DESCRIPTION OF SYMBOLS 1... Nonlinear medium, 2, 3... Reflector for Fabry-Perot resonator, 4... Input light, 5... Output light, 6... Nonlinear crystal, 7... Birefringent crystal for temperature compensation, 8... Babinet Soleil compensator, 9... Polarizer , 10...analyzer, 11
...Input light, 12...Output light, 13...Reflector.

Claims (1)

[Claims] 1. An anisotropy in which the refractive index in different crystal axis directions changes differently depending on the light intensity of the incident light or a plurality of lights, and the polarization state of the incident light is self-modulated. A polarizing crystal is inserted between a polarizer and an analyzer, and the direction of polarization by the polarizer is set at 45 degrees with respect to the optical anisotropic axis of the anisotropic crystal, and the single or multiple lights are inserted into the anisotropic crystal. An optical nonlinear element, characterized in that the incident light enters an anisotropic crystal and self-modulates the incident light within the anisotropic crystal. 2. Initial detuning, an anisotropic crystal that self-modulates the polarization state of the incident light by changing the refractive index in different crystal axis directions depending on the light intensity of the incident light or multiple lights. A temperature-compensating birefringent crystal that changes the optical path length depending on the temperature in order to keep the optical path constant, and a Babinet-Soleil compensator for variably setting the initial detuning are inserted between the polarizer and the analyzer. An optical nonlinear element characterized in that the polarization direction of the polarizer is set at 45 degrees with respect to the optical anisotropy axis of the anisotropic crystal. 3. Initial detuning, an anisotropic crystal that self-modulates the polarization state of the incident light by changing the refractive index in different crystal axis directions depending on the light intensity of the incident light or multiple lights. A temperature-compensating birefringent crystal that changes the optical path length depending on the temperature in order to keep the optical path constant, and a Babinet-Soleil compensator for variably setting the initial detuning are inserted between the polarizer and the analyzer. An optical nonlinear element, characterized in that a plurality of optical nonlinear elements are connected in series, each of which has a polarization direction set by a polarizer at 45 degrees with respect to the optical anisotropy axis of the anisotropic crystal. 4 Anisotropic crystal, initial separation, which has a self-modulating effect on the polarization state of the incident light, in which the refractive index in different crystal axis directions changes differently depending on the light intensity of the incident light or multiple lights. A temperature-compensating birefringent crystal that changes the optical path length depending on the temperature to keep the optical density constant.
and a Babinet Soleil compensator for variably setting the initial detuning is inserted between the polarizer and the analyzer, and the polarization direction by the polarizer is set at 45 degrees with respect to the optical anisotropy axis of the anisotropic crystal. What is claimed is: 1. An optical nonlinear element set as follows, characterized in that a reflecting mirror is disposed at the next stage of the analyzer.