JP2006023334A - Optical switch and its manufacturing method, and optical distributing device and optical multiplexing device using optical switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical switch which is excellent in light resistance, is ultrafast/highly efficient and is low-cost, and its manufacturing method, and to provide an optical distributing device and an optical multiplexing device using the optical switch. <P>SOLUTION: The optical switch 1 has a low reflectance mirror 12, an active film 14 including a nonlinear optical material, and a high reflectance mirror 16 on a substrate 10 in this order. Film thickness of the active film 14 satisfies a resonance condition with respect to a wavelength of at least one out of signal light and control light, or a wavelength between [(λ<SB>1</SB>+λ<SB>2</SB>)/2]-λ<SB>2</SB>when the wavelengths of the signal and control light are represented by λ<SB>1</SB>and λ<SB>2</SB>respectively. Loss of the signal and control light caused by absorption of the substrate 10 is 10% or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical switch that switches signal light at a very high speed with control light, a manufacturing method thereof, and an optical distribution device and an optical multiplexing device that use the optical switch, which are required in optical communication or optical information processing.

For optical switches used in future large-capacity optical communications and ultra-high-speed optical information processing, the method of controlling optical signals with optical signals is not the conventional method of controlling optical signals with electrical signals, and the operating speed and equipment are simplified. This is advantageous from the viewpoint of conversion. The inventors of the present invention have so far conducted studies using an organic nonlinear optical thin film mainly for the purpose of providing an ultrafast optical switch operating in the optical communication wavelength region. As a result, they succeeded in developing an ultrafast optical-optical switch that is easy to increase in area and excellent in productivity (see, for example, Patent Document 1).
The optical switch is an active optical thin-film organic nonlinear optical thin film that changes the refractive index by control light in the vicinity of absorption, and turns the signal light on and off with high efficiency by optical arrangement using the optical Kerr effect. It is.
JP 2003-315857 A

  In addition, the present inventors recently discovered that the performance can be greatly improved by introducing a resonator structure into an optical switch. In the configuration of the invention, a non-linear optical material thin film is used as an active film, a reflective surface (layer) having a high reflectance is provided on one surface of the active film, and a reflective surface (layer) having a low reflectance is provided on the other surface. It will be. One form of the specific configuration is shown in FIG. The optical switch 1 ′ according to FIG. 10 is formed by laminating a high reflectance mirror 16, an active film 14, a low reflectance mirror 12, and a protective layer 18 in this order on a substrate 10. This optical switch has features such as (a) low cost, (b) large area, (c) high-speed response, and (d) low driving energy.

In the optical switch having the above-described configuration, a further excellent optical switch can be obtained by improving the following points.
(1) Although the dielectric multilayer film is suitable as the low reflectance mirror 12 formed on the active film 14, the temperature of the substrate 10 rises during the formation of the dielectric multilayer film, so that it is mainly used for the active film 14. The organic material produced may deteriorate.
(2) The formation of the protective layer 18 is effective for reducing damage to the active layer 14 due to the optical switch operation. However, when the incident light is configured to pass through the protective layer 18, the usable protective layer can be used. There are restrictions on the material, film thickness, etc.
(3) When incident light is collected on the active film 14 using a lens or the like, it is necessary to fix the substrate 10 to a movable pedestal or the like and precisely adjust the distance between the lens and the active film and the angle of rotation, which is practical. The convenience is low.

  The present invention is an optical switch that solves the problems (1) to (3) while maintaining the characteristics (a) to (d) by changing the configuration of an optical switch having a resonator structure, and a method for manufacturing the same. Is to provide. Furthermore, the present invention provides an optical distribution device and an optical multiplexing device using the optical switch.

That is, the present invention
<1> On a substrate, a reflective surface or reflective layer having a low reflectance, an active film containing a nonlinear optical material, and a reflective surface or reflective layer having a high reflectance are arranged in this order, and a signal is transmitted from the substrate side. An optical switch that performs optical switching by irradiating light and control light, and the film thickness of the active film satisfies a resonance condition for at least one of the signal light and the control light, and is due to absorption of the substrate The loss of the signal light and the control light is an optical switch that is 10% or less.

<2> On a substrate, a reflective surface or reflective layer having a low reflectance, an active film containing a nonlinear optical material, and a reflective surface or reflective layer having a high reflectance are arranged in this order, and a signal is transmitted from the substrate side. An optical switch that performs optical switching by irradiating light and control light, and the thickness of the active film is such that the wavelength of the signal light is λ ₁ and the wavelength of the control light is λ ₂ The optical switch satisfies a resonance condition for a wavelength between (λ ₁ + λ ₂ ) / _{2 to} λ _2, and the loss of the signal light and the control light due to absorption of the substrate is 10% or less.

  <3> The active film has a metal layer on a surface opposite to the low-reflectance reflective surface or the surface in contact with the reflective layer, and the high-reflectivity reflective surface includes the active film and the metal layer. <1> or <2>, which is an interface with the optical switch.

  <4> The optical switch according to <1> or <2>, wherein the low-reflectivity reflective layer is a dielectric multilayer film.

  <5> The optical switch according to <1> or <2>, wherein the nonlinear optical material is an organic molecule.

  <6> The optical switch according to <5>, wherein the organic molecule is a squarylium compound.

  <7> The optical switch according to <5>, wherein the organic molecule is a dibenzofuranonyl methanolate compound.

  <8> The optical switch according to <1> or <2>, wherein the optical switching is performed using an optical Kerr effect of the nonlinear optical material.

  <9> A surface of the substrate opposite to the surface having the active film is provided so as to abut a plane portion of a lens having a plane perpendicular to the optical axis, and the thickness of the substrate is set to a focal length of the lens. The optical switch according to <1> or <2>, which is equal to:

  <10> An optical switch manufacturing method in which a dielectric multilayer film, an active film containing a nonlinear optical material, and a metal layer are provided in this order on a substrate.

  <11> An optical distribution device using the optical switch according to any one of <1> to <9>.

  <12> An optical multiplexing device using the optical switch according to any one of <1> to <9>.

According to the present invention, it is possible to provide an ultrahigh-speed and high-efficiency optical switch excellent in light resistance at a low cost. In addition, it greatly contributes to the formation of ultrafast optical switching systems, such as improving module performance and simplifying the manufacturing process at the same time.
Furthermore, since the optical distribution device and the optical multiplexing device of the present invention use the optical switch of the present invention, they can operate at a very high speed.

Hereinafter, an optical switch and a manufacturing method thereof, and an optical distribution device and an optical multiplexing device using the optical switch will be described in detail.
<Optical switch>
The optical switch of the present invention has, on the substrate, a low-reflectivity reflecting surface or reflecting layer, an active film containing a nonlinear optical material, and a high-reflecting reflecting surface or reflecting layer in this order, An optical switch that performs optical switching by irradiating signal light and control light from the substrate side, wherein the thickness of the active film is at least one of the signal light and the control light, or the wavelength of the signal light. When λ ₁ and the wavelength of the control light is λ ₂ , a resonance condition is satisfied with respect to a wavelength between (λ ₁ + λ ₂ ) / _{2 to} λ _2, and the signal light and the signal light due to absorption of the substrate The loss of control light is 10% or less.
In the optical switch of the present invention, an asymmetric resonator is constituted by a reflection surface or reflection layer having a low reflectance, an active film containing a nonlinear optical material, and a reflection surface or reflection layer having a high reflectance. With this asymmetric resonator, an optical switch having high switching efficiency and short response time can be realized.

In the present invention, the loss of the signal light and the control light due to the absorption of the substrate is a value measured by the following method.
The transmittance (T) and reflectance (R) at a desired wavelength are measured, and the loss (1-T ′) is determined from the transmittance T ′ = T / (1-R) corrected for the reflection.
The loss of the signal light and the control light due to the absorption of the substrate is preferably 5% or less, and more preferably 1% or less.

In the case of the optical Kerr effect which is a kind of third-order nonlinear optical effect, the amplitude F of the output signal is proportional to the electric field amplitude E ₁ of the input signal light in the active film and the thickness d of the active film. Is proportional to the square of the electric field amplitude E ₂ of the control light. That is, F is represented by the following formula (1).

In equation (1), χ ⁽³⁾ represents the third-order nonlinear susceptibility of the active film.
Further, since the intensity I of the output signal is proportional to F ² , the output signal intensity is proportional to E ₁ ² and E ₂ ⁴ . When the proportionality coefficient is C, the output signal intensity is expressed by the following equation (2).

Therefore, a large output signal can be obtained by resonating both the control light and the signal light and increasing E ₁ and E ₂ with respect to the amplitude of the incident light. For example, if E ₁ and E ₂ can each be doubled, the output signal will be 64 times.

Next, the operation of the optical switch of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing a first embodiment of the optical switch of the present invention. The optical switch 1 includes a low-reflectivity mirror 12, which is a low-reflectance reflective layer, an active film 14, a high-reflectivity mirror 16, which is a high-reflectivity reflective layer, a protective layer 18, on a substrate 10. Are laminated in this order. Specific materials used for the substrate 10, the low reflectivity mirror 12, the active film 14, the high reflectivity mirror 16, and the protective layer 18 will be described later.
In the optical switch 1, the thickness of the active film 14 is d, the reflectance of the low reflectance mirror 12 is R _1, and the reflectance of the high reflectance mirror 16 is R ₂ . The refractive index of the active film 14 is n. n varies depending on the wavelength λ, and when the nonlinear optical material constituting the active film 14 has absorption, n is a complex number.

When signal light having a wavelength λ is incident on the optical switch 1 perpendicularly, the maximum electric field value in the film changes periodically as shown in FIG. FIG. 2 shows the change in the electric field amplitude with respect to the change in the film thickness d of the active film 14. The wavelength λ _A and the wavelength λ _B are 1550 nm and 1630 nm, respectively.
When the phase changes in reflection by the low reflectance mirror 12 and the high reflectance mirror 16 are φ ₁ and φ ₂ , respectively, the internal electric field is generated by resonance when the wavelength λ and the film thickness d coincide with the following equation (3). Is maximized.

In Equation (3), m represents a positive integer, d ₀ represents the resonant film thickness, and λ ₀ represents the resonant wavelength. That is, the lowest-order (m = 1) resonance occurs in the following formula (4).

High-order resonance occurs at a period of (λ ₀ / 2n). In order to strengthen the internal electric field, the wavelength and the film thickness must satisfy the formula (3) or the formula (4).
Equation (3) is derived from the following equation (6), which is a phase matching condition, with the phase change δ when the light wave reciprocates once in the active film 14 as the following equation (5).

  In a normal Fabry-Perot resonator, the width at which the intensity becomes half of the maximum value on both sides of the resonance point where the transmitted light intensity becomes maximum is called a half-value width (Max Born, Emil Wolff, principle of optics II, p. .515, Tokai University Press). The reflectance at the interface between the air and the active film is R, and the phase δ at the point where the resonance order is m and the intensity is half of the maximum value is expressed by Equation (7).

  In this case, the phase half width ε is expressed by the following formula (8).

Since the phase depends on the film thickness and the wavelength from the equation (5), if the resonance wavelength at the film thickness d ₀ is λ ₀ in the equation (3), the wavelength half width Δλ is approximately expressed by the following equation (9) ).

In the optical switch of the present invention, since the reflectance of the upper and lower mirrors is different, the geometric average of R ₁ and R ₂ , that is, the following formula (10) is used instead of R.

  Therefore, the wavelength half width Δλ of the optical switch of the present invention is approximately given by the following equation (11).

  However, the following symbol in Formula (11) means the fourth root.

  In the present invention, “resonance condition” means that the wavelength λ is within the range of the following formula (12).

    In other words, “resonance condition” in the present invention means that the film thickness d of the active film is in the range of the following formula (12 ′).

For simplicity, it is assumed that the phase change does not occur in the low reflectivity mirror 12, and φ ₁ = 0. The high reflectivity mirror 16 is an ideal metal mirror, the phase change is φ ₂ = π, and the reflectivity is R _2. Assuming that = 1, the wavelength half width Δλ is expressed by the following equation (13).

  Equation (13) indicates that the half-value width of the wavelength decreases as the reflection order increases and the reflectance approaches 100%.

  The electric field at the film thickness under the resonance condition increases as the reflectance of the reflecting surface or the reflecting layer increases. However, when the reflectance of the reflecting surface or the reflecting layer is increased, the time until the internal electric field reaches a steady value increases. Therefore, how the photoelectric field generated inside the optical switch changes with time when an optical pulse enters the optical switch will be described below with reference to FIG. FIG. 3 shows only the main part (active film 14) of the optical switch 1 in FIG.

Consider a case in which a rectangular optical pulse having an amplitude A enters the optical switch 1 from below at time t = 0. Part of the incident light passes through the low reflectivity mirror 12 and enters the active film 14. Let B ₁ be the amplitude of this transmitted light. The transmitted light propagates through the inside of the active film 14 and reaches the high reflectivity mirror 16 at time t = T, and is partially reflected and partially transmitted. The amplitude of the reflected light is C _1. The reflected light propagates downward in the active film 14 and reaches the low reflectivity mirror 12 at time t = 2T, and is partially reflected and partially transmitted. Let B ₂ be the amplitude of the reflected light. Similarly, at time 3T, the high reflectance mirror 16 is reached and upward reflected light C ₂ is generated, and at t = 4T, the low reflectance mirror 12 is reached and downward reflected light B ₃ is generated.
The photoelectric field in the active film 14 immediately above the low reflectivity mirror 12 is 0 at t <0, B ₁ from t = 0 to t = 2T, and B ₁ + C ₁ + B from t = 2T to t = 4T. _{2. From} t = 4T to t = 6T, the time develops as B ₁ + C ₁ + B ₂ + C ₂ + B ₃ . That is, the photoelectric field changes every time the light reciprocates within the active film 14, and the electric field approaches a steady value as the number of reciprocations increases.

Here, (1) when both the low reflectivity mirror 12 and the high reflectivity mirror 16 have a reflectivity R = 99% (high reflectivity), (2) both the low reflectivity mirror 12 and the high reflectivity mirror 16 Is the reflectivity R = 60% (low reflectivity), (3) the low reflectivity mirror 12 is reflectivity R = 60% (low reflectivity), and the high reflectivity mirror 16 is reflectivity R = 99%. FIG. 4 shows the relationship between the number of reciprocations and the photoelectric field inside the active film 14 when the electric field amplitude of incident light is 1 in the case of (high reflectance). The film thickness of the active film 14 satisfies the resonance condition, and the active film 14 does not absorb at the incident light wavelength.
The number of reciprocations until the photoelectric field in the active film 14 reaches 90% of the steady-state value E ₀ is defined as q, and the time constant τ is defined as the time until it reaches 90% of the steady-state value E ₀ . Since the time required for one round trip is 2T, τ = 2qT. T is proportional to the thickness d of the active film 14. Therefore, as d decreases, T decreases and the time constant τ also decreases. In the case of d = λ / 2n, T = λ / 2c = 2.5fs. (However, λ = 1.5 μm and c = 3 × 10 ⁸ m / s)

In FIG. 4, in the case of (1), although E ₀ is large, τ is long. E ₀ = 12.8. The number of round trips until the electric field reaches 90% of the steady value is about 230 (q = 230). Therefore, the time constant is τ = 2qT = 1.15 ps. The steady value reaches 12.8 times the incident light.
In the case of (2), τ is short, but E ₀ is small. E ₀ = 1.8. The number of reciprocations until the electric field reaches 90% of the steady value is about 4 (q = 4). In the case of T = 2.5fs, τ = 10fs. The steady value is 1.8 times the incident light.
In the case of (3), τ is shorter than (1) and E ₀ is larger than (2). E ₀ = 3.5. The number of round trips until the electric field reaches 90% of the steady value is about 9 (q = 9). Assuming T = 2.5fs, τ = 22.5fs. The steady value is 3.5 times the incident light.

In order to increase the internal electric field and shorten the time constant, the reflectance of one reflecting surface or reflecting layer is lowered as in (3) above, and the reflectance of the other reflecting surface or reflecting layer is increased, It has also been found that the thickness of the active film should satisfy the resonance condition.
In the optical switch of the present invention, the signal light and the control light are incident from the reflective surface or the reflective layer side having a low reflectance. The output signal light is also extracted from the reflective surface or the reflective layer side having a low reflectance.

  In the optical switch of the present invention, the reflectance of the reflective surface or the reflective layer having a high reflectance is preferably 90% or more, and is preferably closer to 100%. In addition, the reflectance of the reflective surface or the reflective layer having a low reflectance can be optimized in consideration of the time width of the optical pulse, the time interval of the optical pulse train, the wavelength of the signal light and the control light, etc. In fact. The reflectance of the low reflectance mirror is preferably 10% or more and 90% or less, more preferably 40% or more and 80% or less, and particularly preferably 60% or more and 70% or less.

Next, the characteristics of (3) (when the low reflectance mirror 12 has a reflectance R = 60% and the high reflectance mirror 16 has a reflectance R = 99%), which is an optical switch having an asymmetric reflective layer, Were compared with an optical switch having a symmetric reflective layer (4) having an equivalent time constant τ and an equivalent value (5) having a steady-state value E ₀ . The results are as follows.

(3) Reflective layer with reflectivity of 60% and 99% E ₀ = 3.5, q = 9
(4) When the reflection layers on both sides have a reflectance of 77% E ₀ = 2.5, q = 9
(5) When the reflection layers on both sides have a reflectance of 87.5% E ₀ = 3.5, q = 17

The q in (4) is equivalent to (3), but E ₀ is smaller and inferior than (3).
E ₀ of (5) is equivalent to (3), but q is larger and inferior than (3).
From the above results, it is clear that the optical switch having the asymmetric reflection layer has better characteristics than the optical switch having the symmetric reflection layer.

In general, the wavelength λ _{1 of the} signal light is different from the wavelength λ _{2 of the} control light. Therefore, the resonance condition of the signal light is different from the resonance condition of the control light. In the present invention, since the reflectance of the mirror on one side is low, the wavelength half-value width satisfying the resonance condition is wide, and when λ ₁ and λ ₂ are different by about 10%, both can satisfy the resonance condition. In the present invention, the thickness of the active film may be matched with the resonance condition for a wavelength between (λ ₁ + λ ₂ ) / _{2 to} λ ₂ . From equation (2), depending on the combination of λ ₁ and λ ₂ , the resonant wavelength is set to an optimum value intermediate between λ ₁ and λ ₂ , and a moderate resonant effect is given to both wavelengths. E ₁ ² and E ₂ ⁴ can be made larger than matching with one of ₁ and λ ₂ . Further, according to the equation (2), the output signal strength is proportional to E ₁ ² and E ₂ ⁴ , and therefore, a particularly large output signal strength can be obtained in the above case.
In addition, if the reflection layer with low reflectivity is made to function as a low reflectivity mirror at one of the signal light and control light, and acts as a non-reflective film at the other wavelength, only one of the wavelengths can be obtained. For the other wavelength, the resonance condition can be satisfied and the non-resonance state can be obtained. When the resonance effect acts on only one wavelength, it is possible to suppress the attenuation of the signal light or increase the use efficiency of the control light by making the other wavelength non-reflective.

  When the active film has absorption, the refractive index of the active film becomes a complex number. When the wavelength is λ and the imaginary part of the complex refractive index is k, the absorption coefficient α is α = (4π / λ) k. The intensity of light traveling through the medium having the absorption coefficient α is expressed by the following formula (14).

x is the distance traveled by the incident light through the active film, and I ₀ represents the intensity at the position of x = 0. Strength distance becomes I ₀ /e=0.36I _0, defined as the penetration depth [delta]. It can be expressed as δ = 1 / α = (λ / 4πk). When the thickness d of the active film is d = δ, the intensity of light that has made one round trip through the active film is 1 / e ² = 0.13, and the thickness of the active film is greater than the penetration depth (d For ≧ δ), the resonance effect hardly occurs. That is, the transmittance when the signal light or control light passes through the active film once is preferably 37% (1 / e) or more.

  An optical switch using an asymmetric Fabry-Perot resonator in which the reflectance of the upper reflective surface and the reflectance of the lower reflective surface are different has been reported as an optical switch using absorption saturation of a semiconductor material (Japanese Patent Laid-Open 07-325275), which adjusts the reflectance of the upper and lower mirrors in an absorption saturation type optical switch so that the OFF level of the reflected signal is 0. As in the present invention, the photoelectric field and time constant are adjusted. The purpose is different from the case of measuring.

In the optical switch 1, a multilayer mirror made of a dielectric multilayer film or a metal layer can be used as the high reflectivity mirror 16. When the high reflectivity mirror 16 is a metal layer, the high reflectivity reflecting surface according to the optical switch of the present invention is an interface between the active film and the metal layer.
The dielectric multilayer film, for example TiO ₂ as a material for the high refractive index, the SiO ₂ is used as a low refractive index material, to the incident light wavelength lambda, TiO ₂ and optical thickness of optical thickness λ / 4 λ / 4 SiO ₂ layers can be laminated. The optical thickness is an amount of (refractive index) × (film thickness) expressed in wavelength units. The reflection coefficient of the multilayer mirror in which 6 sets (12 layers) of TiO ₂ / SiO ₂ are laminated is r = 0.0.99.
In the case of a dielectric multilayer film, the phase change upon reflection differs depending on the thickness of each layer constituting the dielectric multilayer film and the laminated structure. In the dielectric multilayer film matched with the incident light wavelength, the phase change is zero. If the phase shift at the low reflectivity mirror 12 is also zero, the resonance condition is nd = m (λ / 2), and the electric field amplitude increases when the optical thickness is an integral multiple of λ / 2.

When the high reflectivity mirror 16 is a metal layer, specific examples of the metal constituting the metal layer include gold, silver, and aluminum. Among these, silver or gold showing high reflectance in the communication wavelength band is preferable.
When the high reflectivity mirror 16 is a metal layer, the phase of the light wave is substantially reversed upon reflection. That is, a phase shift of about 180 ° occurs every reflection. The reflection coefficient at the interface between the active film and the metal is r = (n ₂ −n ₃ ) / (n ₂ + n ₃ ) where n _{2 is} the refractive index of the active film and n ₃ is the refractive index of the metal. .
As an example, if the complex refractive index of the active film is n ₂ = 2.442610 + 0.03381i and the complex refractive index of silver as the metal is n ₃ = 0.32205 + 10.99350i, then r = −0.891−0.413i = 0. .982exp (3.575i). That is, a phase change of φ = 3.575 radians = 204.8 ° occurs.

  The high reflectivity mirror 16 is preferably a metal layer because the temperature rise of the substrate during film formation can be kept low.

In the optical switch 1, a multilayer mirror made of a dielectric multilayer film can be used as the low reflectivity mirror 12. For example, in the case where TiO ₂ and SiO ₂ are laminated one by one with an optical thickness of λ / 4, the reflection coefficient is r = 0.70. The reflection coefficient of the multilayer mirror in which two sets (four layers) of TiO ₂ / SiO ₂ are laminated is r = 0.87.

In the optical switch 1, the active film 14 contains a nonlinear optical material. The nonlinear optical material is not particularly limited, and specific examples thereof include organic molecules, nonlinear optical crystals such as LiNbO _3, and inorganic materials such as metal fine particle-dispersed glass. Among these, the organic material is preferably an organic molecule for reasons such as low cost, large area processability, and excellent nonlinear optical characteristics.
Among the organic molecules, a dibenzofuranonyl methanolate compound represented by the following general formula (1) or a squarylium compound represented by the following general formula (2) is more preferable.

In the general formula (1), R _{1 to} R ₄ may be the same or different and each represents a linear alkyl group or a branched alkyl group, each having a linear alkyl group having 1 to 7 carbon atoms or branched. An alkyl group having 3 to 7 carbon atoms is preferred. Specifically, a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an isopropyl group, an isobutyl group, a sec-butyl group or a tert-butyl group is more preferable, and an n-propyl group, an n-butyl group, An isopropyl group, an isobutyl group or a sec-butyl group is particularly preferred.

  The compound represented by the general formula (1) exhibits a maximum absorption in the vicinity of 1.1 μm, and greatly increases the absorption wavelength without excessively extending the conjugated system as in the case of a conventional long wavelength absorption dye. can do. In addition, it has high thermal stability, good solubility in organic solvents such as acetone and chloroform, and film formability, and is excellent in terms of sublimation.

In addition, the compound represented by the general formula (1) in the present invention can have a structure represented by the following general formula (1 ′).
The compound represented by this structural formula has the same characteristics as those described above for the compound represented by the general formula (1).

In general formula (2), R _{1 to} R ₄ may be the same or different and each represents an alkyl group, preferably a lower alkyl group having 2 to 7 carbon atoms, preferably an n-propyl group, iso- Propyl group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, 2-methylbutyl group, 1-methylbutyl group, 2,2-dimethylpropyl group, 1,2-dimethylpropyl group, 1 , 1-dimethylpropyl group or 1-ethylpropyl group is more preferable, and n-propyl group, n-butyl group, iso-butyl group, sec-butyl group or tert-butyl group is particularly preferable.
In the general formula (2), X _{1 to} X ₈ may be the same or different and each represents H, Cl, OH, CH ₃ , C ₂ H _5, or OCH _{3. 2,} X _4, 1 or 2 or more selected from the group consisting of X ₅ and X ₇ is OH group. In addition, when one or more selected from the group consisting of X ₁ , X ₃ , X ₆ and X ₈ is Cl, a dipole moment can be given to the molecule, and a second-order nonlinear optical effect is exhibited. This is preferable.

  The dye represented by the general formula (2) is a J-aggregate, that is, its absorption band shifts to a longer wavelength side than the absorption band of the dye molecule alone, sharpens, emits fluorescence with a small Stokes shift, and has an absorption peak. It forms an aggregate which has a very large interaction with light of a nearby wavelength and has a property of very fast recovery of absorption saturation, which is a third-order nonlinear optical effect.

  An active film made of organic molecules is prepared by dissolving organic molecules in a suitable solvent to prepare a coating solution, and using this coating solution on a substrate using a bar coating method, a spin coating method, a cast coating method, a dip coating method, or the like. It is obtained by coating and drying the coating solution. Moreover, the active film which consists of other nonlinear optical materials other than an organic molecule is obtained by using the well-known method suitable for the nonlinear optical material to be used.

The optical switching by the optical switch of the present invention is preferably performed using the optical Kerr effect of the nonlinear optical material. By performing optical switching using the optical Kerr effect, the loss of signal light is small because a transparent region of the material is used. High speed operation is possible because there is no actual excitation of electrons. Furthermore, since the wavelength to be used is not limited to the resonance region, specific examples of the nonlinear optical material capable of producing the optical Kerr effect that can be applied to switching in a wide wavelength region include the above-mentioned dibenzofuranonyl methanolate compounds and squares. Lilium compound etc. are mentioned

In the optical switch 1, the protective layer 18 can be provided with any protective layer as long as it does not damage the active film 14 with any material and film thickness. As an example, a metal film, a commercially available sealing material, etc. can be considered, and the light resistance of the optical switch 1 can be greatly improved by optimizing these protective layers. Also, when the temperature rise of the film is suppressed by a heat sink or the like, the effect is great because the heat sink or the like can be brought into direct contact with the film surface.
In the configuration of the optical switch 1 ′ according to FIG. 10, the protective layer 18 is formed on the surface on which the signal light and the control light are incident. Therefore, the protective layer 18 needs to be transparent to control light and signal light. When the protective layer 18 is an antireflection film or when the protective layer 18 is formed in the resonator (between the low reflectance mirror 12 and the high reflectance mirror 16) as shown in FIG. These must be strictly controlled so that the refractive index and film thickness of 18 satisfy the resonance condition. For example, when the protective layer 18 is formed in the resonator, the thickness of the protective layer 18 must be an integral multiple of the wavelength related to resonance. On the other hand, in the configuration of the optical switch of the present invention, the protective layer 18 is formed outside the high reflectivity mirror 16, and thus there is no such limitation.

  In the optical switch 1, the loss of signal light and control light due to absorption of the substrate 10 needs to be 10% or less. If the substrate 10 causes a loss larger than 10% with respect to the signal light and the control light, the signal light is transmitted through the substrate twice, while the control light is squared with respect to the contribution of the Kerr effect. As a result, only a signal intensity of less than 66% can be obtained as compared with the case of no loss. This corresponds to a loss larger than 2 dB, which is a size that cannot be ignored with respect to the driving efficiency of the element. Therefore, the loss due to the substrate 10 needs to be 10% or less. As the substrate that satisfies such conditions, when the signal light and the control light are in the communication wavelength band, optical glass such as fused silica or BK7 and a silicon wafer can be used. In addition, an antireflection layer can be provided on the surface of the substrate 10 on which signal light and control light are incident, so that deterioration in element performance resulting from reflection on the substrate surface can be minimized.

FIG. 5 is a cross-sectional view showing a second embodiment of the optical switch of the present invention. The optical switch 2 according to the second embodiment is provided on the surface opposite to the surface having the active film 14 of the substrate 10 so that the planar portion of the lens 20 having a plane perpendicular to the optical axis is in contact with the substrate 10. The thickness of the substrate 10 is equal to the focal length of the lens 20.
The lens 20 is not particularly limited as long as it has a plane perpendicular to the optical axis, and examples thereof include a gradient index lens and a lens array.
By using a lens having a flat surface, such as the lens 20, and adjusting the thickness of the substrate 10 to match the focal length of the lens 20, adjustment regarding the distance between the lens and the active film can be made unnecessary. Since it is only necessary to directly attach the substrate to the lens surface, which is the light exit surface, the optical switch manufacturing process is greatly simplified, and there are great practical advantages. In addition, since the turning angle is determined by the light emission end face and the flatness of the substrate, higher accuracy can be easily realized as compared with the case of adjusting in free space.

  In addition, the present inventors have developed an element that is smaller and has higher performance by modularizing an optical switch (Japanese Patent Laid-Open No. 2003-149693). If the optical switch of the present invention is applied to the element, the focal length and the tilt angle of the lens can be easily adjusted.

<Manufacturing method of optical switch>
In the method for manufacturing an optical switch of the present invention, a dielectric multilayer film, an active film containing a nonlinear optical material, and a metal layer are provided in this order on a substrate. This method is used for manufacturing an optical switch having a dielectric multilayer film, an active film containing organic molecules as a nonlinear optical material, and a metal layer in this order on a substrate.
According to the method for manufacturing an optical switch of the present invention, the active film containing organic molecules is formed after the formation of the dielectric multilayer film which is a low-reflectance mirror. There is no danger of. The dielectric multilayer film is formed by an electron beam evaporation method or a sputtering method. In this case, the substrate temperature may exceed 200 ° C. When the active film is formed on the substrate prior to the dielectric multilayer film, there is a risk of damaging organic molecules in the active film, but there is no risk in the present invention. On the other hand, such a temperature is not a problem in a glass substrate or the like normally used as a substrate.
Further, since the metal layer can be formed by a normal vacuum deposition method, the increase in the substrate / active film temperature during the metal layer formation can be suppressed to about 40 to 50 ° C. As a result, damage to the active film in the manufacture of the optical switch can be minimized.

<Light distribution device>
The optical distribution device of the present invention uses the optical switch of the present invention. FIG. 6 shows an embodiment of the light distribution apparatus of the present invention. In the optical distribution device according to the present embodiment, the signal light 42 is incident obliquely and the control light 44 is incident vertically on the optical switch 1 of the present invention.
The signal light 42 transmitted through the optical waveguide 46 from the substrate side of the optical switch 1 is incident on an optical system 48 configured by combining lenses, and the surface direction is perpendicular to the traveling direction as outgoing light of the optical system 48. Thus, signal light 42 composed of a row of signal light pulses 42A to 42F whose wavefronts are widened is obtained. The control light 44 synchronized with the signal light 42 is incident on the optical switch 1 over a predetermined width W from the substrate side of the optical switch 1 with its traveling direction perpendicular to the optical switch 1.

Further, in the optical distribution device according to the present embodiment, the optical element 50 in the form of a line or a one-dimensional array is provided at a position after the signal light 42 is reflected by the optical switch 1, and each pixel thereof has each of the signal lights 42. It arrange | positions so that the reflected light of the space position parts 42p-42u may be received. When the signal light pulses 42A to 42F reach the corresponding regions Wp to Wu of the optical switch 1, the control light 44 is changed to the signal light 42 so that the control light pulse 44a reaches the regions Wp to Wu of the optical switch 1. Synchronize.
Thus, the spatial position portion 42p of the signal light pulse 42A, the spatial position portion 42q of the signal light pulse 42B, the spatial position portion 42r of the signal light pulse 42C, the spatial position portion 42s of the signal light pulse 42D, and the spatial position of the signal light pulse 42E. The spatial position portion 42u of the portion 42t and the signal light pulse 42F is cut out as output light pulses 52Ap, 52Bq, 52Cr, 52Ds, 52Et, and 52Fu, respectively, and processed or detected by the corresponding pixel of the optical element 50.

<Optical multiplexer>
The optical multiplexing apparatus of the present invention uses the optical switch of the present invention. FIG. 7 shows an embodiment of the optical multiplexing apparatus of the present invention. In the optical multiplexing apparatus according to the present embodiment, one-dimensional parallel signal light 42 is obliquely incident on the optical switch 1 of the present invention, and control light 44 is incident vertically. In the present embodiment, the parallel signal light 42 includes six-channel signal lights 42A to 42F.
Parallel signal light 42 is incident from the substrate side of the optical switch 1 over a predetermined width W, and control light 44 synchronized with the parallel signal light 42 is light with its traveling direction perpendicular to the optical switch 1. The light is incident on the optical switch 1 over a predetermined width W from the substrate side of the switch 1.

Further, in the optical multiplexing apparatus according to the present embodiment, the condensing optical system 54 and the optical waveguide 46 are disposed at a position after the signal light 42 is reflected by the optical switch 1. When all of the signal lights 42A to 42F reach the areas Wp to Wu corresponding to the signal lights 42A to 42F of the optical switch 1, the control light pulse 44a reaches the areas Wp to Wu of the optical switch 1. The control light 44 is synchronized with the signal light 42.
Thereby, a part of each of the signal lights 42A to 42F is cut out as output lights 56A to 56F each having a short pulse time width, and has a predetermined time difference between them by the condensing optical system 54 and the optical waveguide 46. In the optical waveguide 46, serial signal light 56 in which signal lights (output lights) 56A to 56F are temporally multiplexed is obtained.

EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited by the following Example.
In the following examples, a laser having a pulse width of several hundred femtoseconds (fs = 10 ⁻¹⁵ seconds) is used for signal light and control light, and a dibenzofuranyl methanolate derivative thin film and a squarylium derivative thin film are used as light control units. A resonator structure optical switch having a structure according to the present invention was fabricated, and optical switching was performed for 1.55 (m light in the communication wavelength band and 900 nm light in the near infrared region.

[Example 1]
A dibenzofuranonyl methanolate derivative thin film was used as the active film to form an optical switch having the configuration shown in FIG. The low-reflectivity mirror has a dielectric layer in which a total of four layers of TiO ₂ and SiO ₂ are deposited on a glass substrate with an optical film thickness of 1/4 wavelength by electron beam evaporation (the loss due to absorption is almost 0%). A multilayer film was used. The reflectivity of the dielectric multilayer mirror was 60%. As the dibenzofuranonyl methanolate derivative, a derivative having the following molecular structure was used.

The molecule was dissolved in a tetrahydrofuran solvent at a concentration of 2% by mass and formed into a film by spin coating so as to have a film thickness of about 160 nm. As the high reflectivity mirror, silver having a vacuum deposited of 500 nm was used. Further, a germanium oxide or aluminum vapor deposition film was formed in an arbitrary thickness as a protective layer. The reflection spectrum of the produced optical switch was measured with an ultraviolet-visible spectrometer (Hitachi U-4100). The result is shown in FIG.
From FIG. 8, a decrease in reflectance due to resonance was observed near 1600 nm, and it was confirmed that a resonator structure was formed. With respect to this optical switch, an optical switching experiment was performed using signal light (1550 nm) having a repetition period of 1 kHz and a pulse width of 150 fs and control light (1640 nm) by the following method.
Optical switching experiments were performed with a standard Kerr configuration optical system. A polarizer and an analyzer are arranged in a crossed Nicols state with an optical switch sandwiched between signal lights. In the absence of control light, the signal light cannot pass through the analyzer. Next, control light having a polarization direction of 45 ° with respect to the polarization direction of the signal light is incident on the optical switch in synchronization with the signal light. The signal light becomes elliptically polarized light due to the birefringence induced in the optical switch by the control light, and a part of the signal light passes through the analyzer. This transmitted light is observed as a switching output. As a result, good switching characteristics were obtained, and the optical Kerr rotation angle indicating the performance of the optical switch showed a high value of 2.2 ° when the control light intensity was 5.3 pJ / μm ² .

[Example 2]
An optical switch having the same configuration as in Example 1 was formed using a squarylium derivative thin film as the active film. As the squarylium derivative, a derivative having the following molecular structure was used.

The molecule was dissolved in a propylamine solvent at a concentration of 1% by mass and formed into a film by spin coating so as to have a film thickness of about 60 nm. The type of mirror and the formation method are the same as in Example 1. The reflection spectrum of the optical switch produced by the same method as in Example 1 was measured. The result is shown in FIG. A decrease in reflectance due to resonance was observed near 850 nm, and it was confirmed that a resonator structure was formed.
With respect to this optical switch, an optical switching experiment was performed in the same manner as in Example 1 using signal light (900 nm) having a repetition period of 80 MHz and a pulse width of 150 fs, and control light (850 nm). As a result, good switching characteristics were obtained, and it was confirmed that the Kerr rotation angle per film thickness was 10 times or more compared with the case where the resonator structure was not introduced.

It is sectional drawing which shows 1st embodiment of the optical switch of this invention. It is a figure showing the change of the electric field amplitude with respect to the change of the film thickness of an active film. It is a figure for demonstrating the time change of the photoelectric field which arises inside an optical switch. It is a figure which shows the relationship between the reciprocation number of incident light, and the photoelectric field inside an active film. It is sectional drawing which shows 2nd embodiment of the optical switch of this invention. It is a figure which shows one Embodiment of the optical distribution apparatus of this invention. It is a figure which shows one Embodiment of the optical multiplexing apparatus of this invention. FIG. 3 is a diagram showing a reflection spectrum of the optical switch manufactured in Example 1. 6 is a diagram showing a reflection spectrum of an optical switch manufactured in Example 2. FIG. It is sectional drawing which shows the optical switch which introduce | transduced the resonator structure. It is sectional drawing which shows the optical switch which formed the protective layer in the resonator.

Explanation of symbols

1 optical switch 10 substrate 12 low reflectivity mirror 14 active film 16 high reflectivity mirror 18 protective layer 20 lens

Claims (12)

On the substrate, a reflective surface or reflective layer having a low reflectivity, an active film containing a nonlinear optical material, and a reflective surface or reflective layer having a high reflectivity are arranged in this order, and the signal light and control are performed from the substrate side. An optical switch that performs light switching by irradiating with light,
The thickness of the active film satisfies a resonance condition for at least one of the signal light and the control light,
The loss of the signal light and the control light due to the absorption of the substrate is 10% or less. On the substrate, a reflective surface or reflective layer having a low reflectivity, an active film containing a nonlinear optical material, and a reflective surface or reflective layer having a high reflectivity are arranged in this order, and the signal light and control are performed from the substrate side. An optical switch that performs light switching by irradiating with light,
The thickness of the active film is resonant with respect to a wavelength between (λ ₁ + λ ₂ ) / _{2 to} λ ₂ when the wavelength of the signal light is λ ₁ and the wavelength of the control light is λ _2. Meet the requirements,
The loss of the signal light and the control light due to the absorption of the substrate is 10% or less.   The active film has a metal layer on a surface opposite to the low-reflectance reflecting surface or the surface in contact with the reflecting layer, and the high-reflecting reflecting surface is an interface between the active film and the metal layer. The optical switch according to claim 1 or 2.   The optical switch according to claim 1, wherein the reflective layer having a low reflectance is a dielectric multilayer film.   The optical switch according to claim 1, wherein the nonlinear optical material is an organic molecule.   The optical switch according to claim 5, wherein the organic molecule is a squarylium compound.   The optical switch according to claim 5, wherein the organic molecule is a dibenzofuranonyl methanolate compound.   The optical switch according to claim 1, wherein the optical switching is performed using an optical Kerr effect of the nonlinear optical material.   The surface of the substrate opposite to the surface having the active film is provided so as to abut the flat portion of the lens having a plane perpendicular to the optical axis, and the thickness of the substrate is made equal to the focal length of the lens. The optical switch according to claim 1 or 2.   A method for manufacturing an optical switch, wherein a dielectric multilayer film, an active film containing a nonlinear optical material, and a metal layer are provided in this order on a substrate.   An optical distribution device using the optical switch according to claim 1.   An optical multiplexing device using the optical switch according to claim 1.

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