JP4648788B2 - Gate switch - Google Patents

Description

  The present invention relates to a gate switch, and more particularly to a gate switch that controls an optical signal with an electric signal and is used for optical communication, optical measurement, and a projector, a copier, a printer, a scanner, and the like.

  With the recent development of optical communication technology, a gate switch for turning on / off an optical signal at high speed has become important. This gate switch is not limited to the above-described optical communication, but is applied to other devices (for example, a projector, a copier, a printer, a scanner, etc.), and further development is desired.

  As one method for realizing the gate switch, there is a method of changing the refractive index n of the material constituting the gate switch. As a method for changing the refractive index n, there are mainly a thermo-optic (TO) effect, an acousto-optic (AO) effect, and an electro-optic (EO) effect. Among these effects, the TO effect is not suitable for high-speed operation, and can only achieve a response speed of about several ms at most. In addition, the AO effect is suitable for high-speed operation as compared with the TO effect, but since the amount of change in the refractive index is small, a sufficient change in the refractive index cannot be induced.

  Compared with the above two effects, the EO effect is suitable for high-speed operation and can sufficiently change the refractive index, and is therefore suitable for switching that requires high-speed operation.

  One of the main gate switches using the EO effect that has been conventionally used is one that uses a crystal that exhibits a primary electro-optic effect, such as lithium niobate (LN). However, LN has polarization dependency, and in order to operate (polarization-independent operation) regardless of the polarization state of input light, it is necessary to devise the configuration. Therefore, there is a drawback that the configuration of the switch becomes complicated. In addition, since the primary electro-optic effect of LN or the like is manifested only in a crystal having no central symmetry, polarization dependence always appears. Therefore, this polarization dependence is an issue that cannot be avoided.

  Various reports have been made on how to devise a device configuration for performing polarization-independent operation. In Patent Document 1, the input signal light is first split into a TE mode and a TM mode using a first polarization beam splitter. Next, the TE mode and the TM mode are turned ON / OFF by separate gate switches, and the light that has passed through the switches is multiplexed again by the second polarization beam splitter. With such a configuration, switching is performed for both the TE mode and the TM mode, and as a result, a polarization-independent operation is realized.

JP 2002-228997 A JP 2003-218446 A Yalive Optoelectronics Basics Book 5th Edition Chapter 4 R. L. Prater, et al., “Raman scattering studies of the effects of a symmetry-breaking impurity on the ferroelectric phase transition in K1-xLixTa1-yNbyO3” Solid State Communications, Vol.40, pp.697-701, 1981 S. Toyoda, et al., “Low driving voltage polarization-independent> 3GHz-response electro-optic switch using KTN waveguides,” ECOC-IOOC 2003, Paper MO 4.5.1.

  The apparatus described in Patent Document 1 can certainly perform polarization-independent operation as a result, but in order to perform stable operation, the first polarization beam splitter and the second polarization beam splitter are not connected. It requires high-precision settings such as precisely setting the optical path length between them, and precisely adjusting the mirror angle for bending the optical path.

  Accordingly, there is a problem that it is difficult to realize stable and simple polarization-independent switching in a switch using a crystal that exhibits the primary electro-optic effect.

  In addition, a switch using a crystal that exhibits an electro-optic effect has a temperature dependency on the physical quantity (refractive index, length, etc.) of the crystal, so that the switch operation becomes unstable when the temperature changes. That is, a temperature controller such as a Peltier element is required to keep the temperature of the switch constant in order to avoid unstable operation.

  As an example of a configuration including such a temperature controller, there is a configuration including a temperature controller using a Peltier element as disclosed in Patent Document 2. If such a temperature controller is used, the temperature of the switch can be kept constant. However, there is a problem in that power for operating the temperature controller is necessary, and power consumption increases.

  The present invention has been made in view of such problems. The object of the present invention is to use a structure of an etalon, which can achieve a high-speed response without using a temperature controller, and has no polarization. It is to provide a gate switch capable of realizing dependence.

In order to achieve the above object, the invention according to claim 1 is provided with an optical position shifter having a light input port and a path in which light is output depending on temperature, and the optical position shifter. disposed in the subsequent stage has a secondary electro-optic effect, the phase transition temperature is a temperature at which the phase transition between the paraelectric phase of a ferroelectric phase and a cubic crystal structure is changed in the first plane a dielectric crystal includes a spatial distribution region having to have spatial distribution, the provided on the first surface of the dielectric crystal, the dielectric crystal by applying a voltage, and a predetermined inputted light A voltage is applied to the dielectric crystal provided on a first member that reflects at a reflectance and a second surface facing the first surface of the dielectric crystal, and input light is predetermined. A second member that reflects at a reflectance of the dielectric crystal; and a second member that is disposed after the dielectric crystal, A gate switch and a optical multiplexer for multiplexing the second light emitted from the surface of, and the ambient temperature of the gate switch, said first surface of said dielectric crystal from the optical position shifters the light according to the temperature difference, always change in the environmental temperature to be constant when the temperature changes of the phase transition temperature of said dielectric crystal point where input light passes When the position shifter fluctuates, the light emitted from the optical position shifter is incident on a predetermined point of the spatial distribution region of the dielectric crystal, and the dielectric crystal at the point through which the light passes is made . The phase transition temperature is lower than the environmental temperature, and the dielectric crystal at the point where the light passes is a paraelectric phase .

According to a second aspect of the invention, an input port of the light, a light position displacement instrument route which is the output of the light is determined by the temperature, being disposed downstream of said light position displacement device, the secondary electro-optical effect A spatial distribution region having a spatial distribution in which a phase transition temperature and a refractive index which are a temperature at which a phase transition occurs between a ferroelectric phase and a paraelectric phase having a cubic crystal structure are changed in the first plane a dielectric crystals containing the provided on the first surface of the dielectric crystal, said voltage is applied to the dielectric crystal, and a first member for reflecting the inputted light at a predetermined reflectance A second member provided on a second surface opposite to the first surface of the dielectric crystal, for applying a voltage to the dielectric crystal and reflecting the input light at a predetermined reflectivity; And light emitted from the second surface of the dielectric crystal, which is disposed downstream of the dielectric crystal. A gate switch and a optical multiplexer for multiplexing the point that the environmental temperature of the gate switch, said light position displacement device from said dielectric said first light input to the surface of the crystal passing temperature difference between the phase transition temperature of the dielectric crystal is always to be constant when the temperature changes, and is input from the optical positional displacement device to said first surface of said dielectric crystal the refractive index of the dielectric crystals of the point where light passes was the product of the distance between the first surface and the second surface of the point where the light inputted to the dielectric crystal to pass through as always constant when the temperature changes, by varying the optical positional displacement device in accordance with a change of the environmental temperature, the the predetermined point of the spatial distribution region of the dielectric crystal applying light emitted from the light position displacement device, the light The phase transition temperature of the dielectric crystals of the point where the passage is lower than the ambient temperature, the dielectric crystal point which the light passes is characterized in that it is a paraelectric phase.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the spatial distribution is monotonous and continuous.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the optical position shifter includes a bimetal having one end fixed and an optical fiber disposed at the other end. And

The invention according to claim 5 is the invention according to claim 4 , wherein the optical position displacement device further includes a collimating lens disposed at the other end of the bimetal, and the optical fiber is connected to the collimating lens. It is characterized by being.

According to a sixth aspect of the invention according to any of claims 1 to 5, wherein the first member and the second member, characterized in that it is a thin-film metal electrode.

The invention according to claim 7 is the invention according to any one of claims 1 to 5 , wherein the first member and the second member are a transparent electrode provided on a surface of the dielectric crystal, and the transparent And a dielectric multilayer film mirror made of a dielectric multilayer film provided on the electrode.

The invention according to claim 8 is the invention according to claim 7 , characterized in that a metal thin film electrode is provided between the transparent electrode and the dielectric multilayer mirror.

The invention according to claim 9 is the invention according to any one of claims 1 to 8 , wherein the dielectric crystal is a single crystal, and one of the crystal axes of the single crystal is irradiated to the dielectric crystal. It arrange | positions so that it may correspond with the permeation | transmission direction of this.

The invention of claim 1 0 wherein is the invention according to any one of claims 1 to 8, wherein the dielectric crystal is a polycrystal, at least one crystal axis of the crystal is irradiated on the dielectric crystal It is arranged so as to coincide with the light transmission direction.

The invention of claim 1 1, wherein, in the invention described in any one of claims 1 to 1 0, wherein the dielectric _{crystal, K 1-y Li y Ta} 1-x Nb x O 3 (0 <x <1 , 0 <y <1) or KTa _1-x Nb _x O ₃ (0 <x <1).

Invention of claim 1 wherein, in the invention of any one of claims 1 to 1 0, wherein the dielectric _{crystal, KTa 1-x Nb x O} 3 (0 <x <1) all K in, Or all of K and Li in K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 <y <1) are replaced with at least one element of Ba, Sr, and Ca; It has a composition in which all of Ta and Nb are replaced with Ti.

Invention of claim 1 3, wherein, in the invention of any one of claims 1 to 1 0, wherein the dielectric _{crystal, KTa 1-x Nb x O} 3 (0 <x <1) all K in, Alternatively, all of K and Li in K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 <y <1) are replaced with at least one element of Pb and La, and Ta and It has a composition in which all of Nb is replaced with at least one element of Ti and Zr.

The invention of claim 1 4 wherein, said x as a first composition ratio in the composition of the dielectric crystal in the invention of any one of claims 1 1 to 1 3, 0.1 to 0.5 The y as the second composition ratio in the composition of the dielectric crystal is greater than 0 and less than 0.1.

As described above, according to the present invention, the dielectric crystal has a spatial distribution in at least one of the phase transition temperature and the refractive index, and the ambient temperature of the gate switch and the light input to the dielectric crystal pass through. to, the temperature difference between the phase transition temperature of the region of the dielectric crystal, so that in a certain always, and / or light input to the dielectric crystal through which the environmental temperature of the gate switch has changed , the refractive index of the dielectric crystal region of the dielectric crystals, the product of the thickness of the dielectric crystals, such that a constant always when environmental temperature of the gate switch is changed, the gate switch environmental temperature Since the optical position shifter is changed in accordance with the change, the stability of the operation can be improved without using a temperature controller, and the polarization is independent and a high-speed response is possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.
Before describing the individual embodiments, the filter characteristics of the Fabry-Perot etalon will be described.
A Fabry-Perot etalon (hereinafter referred to as an etalon) has a structure in which a substance having a refractive index n is sandwiched between a pair of mirrors. As main values representing the characteristics of the etalon, there are FSR (Free Spectral Range) and Fines. The center frequency ν _m of the transmission band of the etalon is expressed by the following equation.

In the above formula (1), n is the refractive index of the material sandwiched between the mirrors, d is the resonator length (distance between the mirrors), and θ is the inclination angle of the etalon with respect to the incident light (also called the etalon angle). , C is the speed of light in vacuum. From the equation (1), the center wavelength λ _m of the transmission band of the etalon is expressed by the following equation.

The FSR is an interval between two adjacent sets of the center frequency ν _m of the transmission band expressed by the equation (1), and is expressed by the following equation.

  Fines is a value expressing the extent of the etalon transmission band and is related to the reflectance of the mirror by the following equation.

In the above equation (4), Δν _1/2 is the full width at half maximum of the etalon transmission band, and R is the reflectance of the mirror constituting the resonator.

  When the ratio of the transmitted light intensity to the incident light intensity of the etalon is I (dB), it is expressed by the following formula (see Non-Patent Document 1).

Where δ represents the phase lag within the etalon,

It is.
In order to change the center frequency ν _m of the transmission band of the etalon according to the expression (1), any one of the refractive index n, the resonator length d, and the etalon angle θ of the etalon may be changed. I understand that. Therefore, in order to produce a wavelength tunable filter, it can be expressed by changing these parameters. There are several commercially available wavelength tunable filters, but the mainstream method is to tune the wavelength by changing the resonator length. This is because changing the resonator length d among the above three parameters can maximize the wavelength variable band.

  In order to change the resonator length d and the etalon angle θ, a mechanical operation is required. Therefore, the method for mechanically changing the resonator length d and the etalon angle θ is not suitable for high-speed operation. Compared to them, the method of changing the refractive index n of the substance constituting the etalon can change the center wavelength (center frequency) of the transmission band of the etalon without performing a mechanical operation. As described above, in the case of a change in refractive index using the electro-optic effect, a sufficient amount of change in the refractive index can be obtained and high-speed operation is possible.

  The electro-optic effect includes a primary electro-optic effect (Pockels effect) and a secondary electro-optic effect (Kerr effect). The primary electro-optic effect appears in proportion to the electric field strength, and the refractive index change is expressed by the following equation.

In the above formula (7), n ₀ is the refractive index of a dielectric crystal having a first-order electro-optic effect which is a substance constituting an etalon in the state where no electric field is applied, and r _eff is the first-order The effective value of the electro-optic coefficient, E is the electric field.

  Further, the secondary electro-optic effect appears in proportion to the square of the electric field strength, and the refractive index change is expressed by the following equation.

なお、上記式（８）のｎ₀は電界を印加していない状態での、エタロンを構成する物質である２次の電気光学効果を有する誘電体結晶の屈折率、Ｅは電界であり、ｓ₁₂は下記の式で定義される量である。

In the above formula (8), n ₀ is the refractive index of a dielectric crystal having a secondary electro-optic effect which is a substance constituting the etalon in the state where no electric field is applied, E is an electric field, and s ₁₂ is an amount defined by the following formula.

In the above formula (9), ε ₀ is the dielectric constant of vacuum, ε _r is the specific dielectric constant of the dielectric crystal having the second-order electro-optic effect, and g ₁₂ has the second-order electro-optic effect. This is the electro-optic constant of the dielectric crystal.

Next, consider the temperature dependence of the operation of an etalon composed of a dielectric crystal having a secondary electro-optic effect. Consider a dielectric crystal that has a paraelectric phase and cubic structure at high temperatures and a ferroelectric phase at low temperatures. The temperature that becomes the boundary between the two phases is called the phase transition temperature T _cri . Consider a temperature T (> T _cri ). According to the Curie-Weiss law, the relative permittivity can be written as:

Here, A is a proportionality constant and is called a Curie constant.
That is, from the formulas (8), (9), and (10), the refractive index change is proportional to 1 / (T−T _cri ) ² . Therefore, as the temperature T increases away from the phase transition temperature and becomes higher, the refractive index change becomes smaller and the voltage efficiency becomes worse. Specifically, considering the case of T−T _cri = 1 ° C., the voltage efficiency is 1/9 when the voltage efficiency is 3 ° C. and 1/100 when the voltage efficiency is 10 ° C.

Note that when the temperature is T (<T _cri ), the dielectric crystal becomes a ferroelectric phase, anisotropy occurs in the crystal, and polarization dependence is generated with respect to the operation, which is not preferable.

Therefore, in order to operate the device with a smaller voltage (= without reducing the voltage efficiency) and achieve the polarization-independent operation, as can be seen from the equation (10), the temperature is set to the phase transition temperature T _cri as much as possible. It is necessary to make the dielectric crystal a paraelectric phase. That is, the operating temperature T may be slightly higher than the phase transition temperature T _cri .

In addition, since the refractive index n and thickness d (resonator length) of the material sandwiched between the mirrors are physical quantities that depend on the temperature, the center wavelength λ _m of the etalon transmission band varies depending on the temperature from Equation (2). To do. That is, even if the voltage is fixed to a constant value, the transmittance of light of a certain wavelength varies with temperature, which is not preferable. When the etalon angle θ = 0, the temperature differential of the center wavelength λ _m of the etalon transmission band is expressed by the following equation.

Next, it will be described with reference to FIG. 11 that a gate switch can be realized by using the above etalon. For simplicity of explanation, it is assumed that the temperature is constant and the incident angle θ = 0 of the etalon. Let λ _m (E = 0) be the center wavelength of the transmission band of the etalon when the voltage V is not applied to the dielectric crystal, which is a substance constituting the etalon. Continuous light having a wavelength λ _in equal to λ _m (E = 0) is incident on the etalon. At this time, the incident light passes through 100% etalon except for the loss of etalon. Here, assuming that a voltage V = V ₀ is applied to a dielectric crystal that is a substance that constitutes an etalon, the refractive index of the dielectric crystal that is a substance that constitutes an etalon changes in accordance with Equation (7) or Equation (8). Therefore, the center wavelength λ _m of the transmission band of the etalon changes according to the equation (2). Therefore, the light transmittance at the wavelength λ _in changes. By setting the amount of change in the center wavelength λ _m (center frequency ν _m ) of the etalon transmission band and Fines (see Equation (4)) to an appropriate value, the light transmittance at the wavelength λ _in is set to a desired transmittance. can do. That is, it functions as a gate switch.

  Next, although one embodiment of the present invention is described, the following embodiment is for explanation of the present invention to the last, and does not limit the scope of the present invention. Therefore, those skilled in the art can employ various embodiments including each or all of these elements, and these embodiments are also included in the present invention.

In Figure 1, the etalon-type gate switch 101 includes an optical position shifters 102 route output by the temperature is determined, the etalon 103 disposed behind the light position displacement 102, an optical multiplexer which is subsequent placement of the etalon 103 And a waver 104. Since the etalon 103 functions as a gate switch, it has an electrode for inputting a switching signal, and this electrode is electrically connected to the switching signal transmitter. Continuous light (wavelength λ _in ) is incident on the optical position shifter 102 in which a route output by temperature is determined.

The optical position shifter 102 has a function of changing the incident position on the etalon 103 in accordance with the temperature (environment temperature) of the apparatus. That is, when the temperature changes, the optical position displacement device 102 changes its position, and makes the light emitted from the optical position displacement device 102 enter an appropriate position of the etalon 103. The optical multiplexer 104 has a function of combining and outputting the light emitted from the etalon 103.

The optical position displacement device 102 in which the path output by the temperature is determined is such that the path from which the light is output changes when the temperature changes. The operation is shown in FIG. Consider temperatures T _A , T _B , T _C (T _A <T _B <T _C ). Temperature T _A, T _B, when T _C, respectively light input to the light position displacement 102, is outputted from the point A _1, B _1, C ₁ of the optical positional displacement 102.

That is, when the temperature is T _A , the optical position displacement device 102 fluctuates (at least a part of the optical position displacement device 102 is moved), and light is emitted from the point A ₁ of the optical position displacement device 102. Next, the light emitted from A _{1 of} the optical position shifter 102 enters the point A ₂ of the etalon 103 and exits from the point A _{3 of the} etalon 103. Next, the light emitted from the point A _{3 of the} etalon 103 enters the point A ₄ of the optical multiplexer 104 and exits from the optical multiplexer 104.

When the temperature is T _B , the optical position displacement device 102 fluctuates, and light is emitted from the point B ₁ of the optical position displacement device 102. Next, the light emitted from B _{1 of} the optical position displacement device 102 enters the point B ₂ of the etalon 103 and exits from the point B _{3 of the} etalon 103. Next, the light emitted from the point B _{3 of the} etalon 103 enters the point B ₄ of the optical multiplexer 104 and exits from the optical multiplexer 104.

When the temperature is T _C , the optical position displacement device 102 fluctuates and light is emitted from the point C ₁ of the optical position displacement device 102. Next, the light emitted from C _{1 of} the optical position displacement device 102 enters the point C ₂ of the etalon 103 and exits from the point C _{3 of the} etalon 103. Next, the light emitted from the point C _{3 of the} etalon 103 enters the point C ₄ of the optical multiplexer 104 and exits from the optical multiplexer 104.

When the temperature T is T _A <T <T _B , the optical position displacement device 102 fluctuates, and the light is in an appropriate position according to the temperature between the point A ₁ and the point B ₁ of the optical position displacement device 102. Is output from. When the temperature T changes continuously from T _A to T _B , the point where the light is output changes continuously from the point A ₁ to the point B ₁ .

When the temperature T is T _B <T <T _C , the optical position displacement device 102 fluctuates, and the light is in an appropriate position according to the temperature between the point B ₁ and the point C ₁ of the optical position displacement device 102. Is output from. When the temperature T changes continuously from T _B to T _C , the point where the light is output changes continuously from the point B ₁ to the point C ₁ .

The light output from the optical position shifter 102 whose path is determined by the temperature is input from an appropriate position according to the temperature of the apparatus (environment temperature). That is, the light output from the points A ₁ , B ₁ , C ₁ reaches the points A ₂ , B ₂ , C ₂ , respectively.

FIG. 3 shows a transmission spectrum of the etalon 103 when no voltage is applied to the dielectric crystal that is a substance constituting the etalon 103. As shown in FIG. 3, the center wavelength λ _m of the transmission band of the etalon when no voltage is applied to the dielectric crystal, which is the material constituting the etalon 103, at the points A ₂ , B ₂ and C _2. E = 0) is set to be equal to the wavelength λ _{in of} continuous light at temperatures T _A , T _B , and T _C , respectively.

As mentioned above, in order to operate the device with a lower voltage (= without reducing the voltage efficiency) and achieve polarization independent operation, the operating temperature T is made slightly higher than the phase transition temperature T _cri . The temperature difference is defined as a predetermined temperature difference α (> 0). That is, T _cri = T−α.

Since the light reaches the point A ₂ at the temperature T _A , the phase transition temperature T _CA of the dielectric crystal at the point A ₂ needs to be T _A −α in order to achieve high voltage efficiency. Similarly, the phase transition temperatures T _CB and T _CC of the dielectric crystal at the points B ₂ and C ₂ need to be T _B -α and T _C -α, respectively. That is, when the temperature T varies with T _A ≦ T ≦ T _C , high voltage efficiency can always be achieved by spatially distributing the phase transition temperature of the dielectric crystal.

  In this specification, “spatially distribute the phase transition temperature of the dielectric crystal” means that the phase transition temperature is changed by changing the composition of the dielectric crystal in the dielectric crystal constituting the etalon. This refers to changing in one or two dimensions within the incident plane. This spatial distribution is desirably monotonically and continuously distributed when further improvement in stability is required.

When the dielectric crystal is K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 <y <1) (KLTN), the K · Li ratio and the Ta · Nb ratio should be adjusted. Thus, the phase transition temperature can be set in a wide range (−273 ° C. to + 435 ° C.). Accordingly, by the spatial distribution of the above composition ratio, the point A ₂ at the phase transition temperature T _A-.alpha. next, the point B in ₂ phase transition temperature T _B-.alpha. next, the point in the C ₂ phase transition temperature T _C-.alpha. Thus, the phase transition temperature of the dielectric crystal can be spatially distributed so that the phase transition temperature changes continuously or stepwise between the points. As an example, FIG. 4 shows changes in the phase transition temperature of K _1-y Li _y Ta _1-0.028 Nb _0.028 O ₃ when the K · Li ratio is changed (Non-patent Document 2).

With respect to the etalon 103 having the spatial distribution of the phase transition temperature of the dielectric crystal, the optical position shifter 102 is changed according to the temperature of the device, and light is incident from the optimum position to the temperature of the device. Therefore, it is always possible to operate at a temperature that is a certain temperature difference α away from the phase transition temperature Tcri. Therefore, the polarization independent operation can be stably performed with a smaller voltage. That is, the incident position suitable for each temperature (e.g., point A ₂ in the case of the temperature T _A, the point B ₂ in the case of the temperature T _B, the point C ₂ in the case of the temperature T _C) can incident light into the etalon 103 from Therefore, stable optical switching can be performed without using a temperature controller. In addition, since switching is performed using the electro-optic effect, high-speed operation can be realized.

  In one embodiment of the present invention, in order to stably operate the gate switch regardless of the temperature, the dielectric crystal constituting the etalon 103 has a spatial distribution of the phase transition temperature. You may make it have spatial distribution. Further, a combination thereof, that is, the dielectric crystal constituting the etalon 103 may have both a spatial distribution of phase transition temperatures and a spatial distribution of refractive index.

  In this specification, “split the refractive index of the dielectric crystal” means that the refractive index of the dielectric crystal constituting the etalon is changed by changing the composition of the dielectric crystal. This means changing in one or two dimensions within a plane. This spatial distribution is desirably monotonically and continuously distributed when further improvement in stability is required.

A case where the refractive index of the dielectric crystal constituting the etalon 103 is spatially distributed (the dielectric crystal has a spatial distribution of refractive index) will be described below.
As described above, the refractive index n and the thickness d of the material sandwiched between the mirrors are physical quantities that depend on temperature. Therefore, the center wavelength λ _m of the transmission band of the etalon, which is proportional to the product nd of the refractive index n and the thickness d, varies with temperature (see formula (2)). Since dn / dT and d (d) / dT can take either positive or negative sign, the temperature dependence of the center wavelength λ _m of the transmission band of the etalon can be positive or negative from Equation (11).

As an example, consider the case of d (nd) / dT> 0. The temperature dependence of nd is shown in FIG. The nds at the points A ₂ , B ₂ , and C ₂ are n _A d, n _B d, and n _C d, respectively. When the temperature T _A, the light passes through the point A _2. The product nd at the point A ₂ at the temperature T _A is defined as a product n _A d (T = T _A ). When the temperature T _B, passes through the point B _2. At this time, the product nd at the point B ₂ at the time of temperature T _B is defined as product n _B d (T = T _B ). When the temperature T _C, the light passes through the point C _2. At this time, the product nd at the point C ₂ at the time of temperature T _C is defined as product n _C d (T = T _C ). At this time, if n _A d (T = T _A ) = n _B d (T = T _B ) = n _C d (T = T _C ) is satisfied, at temperatures T _A , T _B , T _C , The central wavelength λ _in of the transmission band of the etalon in the part through which is passed becomes equal. That is, since the refractive index n has a spatial distribution, it is possible to prevent or reduce the temperature fluctuation of the central wavelength of the transmission band of the etalon where light passes.

If the spatial distribution of the refractive index n changes monotonously and continuously, the product nd can be kept substantially constant at all temperatures satisfying T _A ≦ T ≦ T _C. That is, it is possible to prevent or reduce fluctuations in the center frequency (transmission center wavelength) of the transmission band of the etalon when T _A ≦ T ≦ T _C.

When the dielectric crystal is KLTN, the refractive index can be controlled by adjusting the K · Li ratio and the Ta · Nb ratio. The example is shown in FIG. 6 (refer nonpatent literature 3). In other words, by their composition ratios spatial distribution, the point A ₂ in the product n _A d, and the point B ₂ in the product n _B d, and the point C ₂ in the product n _C d becomes continuously in between each point Alternatively, the refractive index of the dielectric crystal can have a spatial distribution so that the refractive index changes stepwise.

For the etalon 103 having the spatial distribution of the refractive index of the dielectric crystal, the output path is determined according to the temperature of the device, and light is incident from the optimum position for the temperature of the device. Therefore, it is possible to operate with the product nd kept substantially constant at all times. Therefore, it is possible to stably perform the polarization-independent operation while preventing or reducing the temperature fluctuation of the central wavelength of the etalon transmittance. That is, the incident position suitable for each temperature (e.g., point A ₂ in the case of the temperature T _A, the point B ₂ in the case of the temperature T _B, the point C ₂ in the case of the temperature T _C) can incident light into the etalon 103 from Therefore, stable optical switching can be performed without using a temperature controller. In addition, since switching is performed using the electro-optic effect, high-speed operation can be realized.

Lights that have passed through the points A ₂ , B ₂ , and C ₂ at temperatures T _A , T _B , and T _C are output from the etalon 103 at the points A ₃ , B ₃ , and C ₃ , respectively. Thereafter, the signals are respectively input from the points A ₄ , B ₄ , and C ₄ to the optical multiplexer 104, combined, and then output from the output unit of the optical multiplexer 104.

Optical position displacement that has a light input port and has a function of determining the route depending on the temperature, that is, a function of changing its position depending on the temperature and inputting light to an appropriate position according to the temperature of the etalon 103 The vessel 102 has a configuration using bimetal. The configuration is shown in FIG.

In FIG. 7, reference numeral 1101 is a bimetal at a temperature T _A , reference numeral 1102 is a bimetal at a temperature T _C , reference numeral 1103 is a collimating lens at a temperature T _A , and reference numeral 1104 is a collimating lens at a temperature T _C , Reference numeral 1105 denotes an optical fiber at a temperature T _A , and reference numeral 1106 denotes an optical fiber at a temperature T _C. In FIG. 7, the optical position shifter according to an embodiment of the present invention includes a bimetal 1101 (1102), a collimator lens 1103 (1104), and an optical fiber 1105 (1106). A collimator lens 1103 (1104) is provided at one end of the bimetal 1101 (1102), and the other end is fixed to an appropriate member around the gate switch such as a housing surrounding the gate switch, which is determined by circuit design. ing. An optical fiber 1105 (1106) is connected to a surface of the collimator lens 1103 (1104) facing the surface on the etalon 103 side.
In FIG. 7, for simplicity of explanation, it is shown in the same figure and a light position displacement unit when the optical position displacer and the temperature T _C in the case of the temperature T _A.

  In FIG. 7, in the etalon 103, the phase transition temperature of the dielectric crystal is spatially distributed. However, the present invention is not limited to this, and the refractive index of the dielectric crystal may be spatially distributed. Further, both the phase transition temperature and the refractive index of the dielectric crystal may be spatially distributed.

Bimetal is a laminate of two types of metal plates having different thermal expansion coefficients. Generally, when the temperature is changed, the metal bends toward a metal having a smaller coefficient of thermal expansion. Therefore, when one end is fixed, the position of the other end changes depending on the temperature. Therefore, by attaching a collimating lens to which an optical fiber is connected to another end, it is possible to realize an optical position shifter whose direction is determined by temperature.

In FIG. 7, since the bimetal 1101 is at the temperature T _A , the phase transition temperature of the dielectric crystal region 71 constituting the etalon 103 is T _A -α. In FIG. 7, since the bimetal 1102 is at the temperature T _C , the phase transition temperature of the dielectric crystal region 72 constituting the etalon 103 is T _C −α. When the temperature changes from T _A to T _C , the bimetal is deformed according to the temperature, the position of the collimating lens is changed with the deformation of the bimetal, and the region incident from the collimating lens is the region 71 to the region 72. Move to. In the region where light is incident when the temperature changes from temperature T _A to T _C , the phase transition temperature of each region is always the temperature obtained by subtracting a predetermined temperature difference α from the temperature of the device (environment temperature). Thus, the composition of the dielectric crystal constituting the etalon 103 is spatially distributed so that the phase transition temperature is spatially distributed.

At this time, the amount of transition with respect to the bimetal temperature (temperature differential of the amount of transition) is set according to the spatial distribution of the phase transition temperature of the dielectric crystal constituting the etalon 103. That is, the light emitted from the collimator lens (light position displacement device), when the temperature T _A in the area 71, the area 72 at the temperature T _C, also between the temperature T _A and the temperature T _C In the case of temperature, the amount of change with respect to the temperature of the bimetal may be set so as to enter the region suitable for the temperature.

  Such adjustment of the shift amount with respect to the temperature of the bimetal can be performed by changing the length and size of the bimetal. The adjustment can also be performed by appropriately selecting the materials of the two metals constituting the bimetal, that is, by adjusting the difference in coefficient of thermal expansion between the two metals.

In FIG. 7, the optical position shifter includes a collimating lens, but may not include a collimating lens. In this case, an optical fiber may be disposed directly at one end of the bimetal.

The configuration of the optical position displacement device 102 whose path is determined by temperature is not limited to the use of bimetal, and any configuration may be used as long as the path of light changes depending on the temperature. By using thermal expansion, the position of a certain part changes depending on the temperature as in the case of bimetal, so by attaching a collimating lens and an optical fiber to that part, it functions as an optical position shifter 102 whose path is determined by the temperature. .

  A configuration diagram of the etalon main body 103 is shown in FIG. Reference numeral 111 is a first mirror, reference numeral 112 is a first electrode, reference numeral 113 is a dielectric crystal made of cubic crystal KLTN having a secondary electro-optic effect, reference numeral 114 is a second electrode, and reference numeral 115 is a second electrode. , The second mirror. The first mirror 111 and the second mirror 115 are arranged substantially in parallel to constitute a resonator. The electrode 112 and the second electrode 114 apply a voltage to the dielectric crystal 113.

  As described above, the first mirror 111 is disposed on one surface of the dielectric crystal 113, and the second mirror 115 is disposed on the surface of the dielectric crystal 113 facing the first mirror 111. The mirror 111 and the second mirror 115 can selectively transmit light in the vicinity of a predetermined frequency at a predetermined transmittance and reflect light in the vicinity of the predetermined frequency at a predetermined ratio.

  As the first mirror 111 and the second mirror 115, a dielectric multilayer mirror, a metal thin film electrode, or both can be used.

  As the first electrode 112 and the second electrode 114, a transparent electrode, a metal thin film electrode, or both can be used.

  When dielectric multilayer mirrors are used as the first and second mirrors and transparent electrodes are used as the first and second electrodes, a metal thin film electrode may be provided between each mirror and the electrode. .

  In this embodiment, an electrode is provided on the dielectric crystal and a mirror is provided on the electrode in order to transmit and reflect predetermined light. However, the present invention is not limited to this. For example, each of the opposing surfaces of the dielectric crystal has the function of both an electrode and a mirror, that is, the function of the electrode and selectively transmit light in the vicinity of a predetermined frequency, and other than the frequency of the transmitted light. An electrode having a function of reflecting light having a frequency may be provided. An example of such a member is a metal thin film electrode. What is important in this embodiment is that, in order to function as an etalon, light in the vicinity of a predetermined frequency is selectively transmitted at a predetermined transmittance, and light other than the predetermined frequency is reflected at a predetermined ratio. is there.

The dielectric crystal constituting the etalon according to the embodiment of the present invention is not limited to KLTN, and any dielectric crystal having a cubic structure and a secondary electro-optic effect may be used. For example, the dielectric crystal according to an embodiment of the present invention may be KTa _1-x Nb _x O ₃ (0 <x <1) (KTN), or KTa _1-x Nb _x O ₃ (KTN). ) Or all of K and Li in K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 <y <1) (KLTN), Ba, Sr, It may have a composition in which at least one element of Ca is replaced and all of Ta and Nb are replaced with Ti.

In addition, the dielectric crystal according to the embodiment of the present invention includes all of K in KTa _1-x Nb _x O ₃ (0 <x <1) (KTN) or K _1-y Li _y Ta _1-x. All of K and Li in Nb _x O ₃ (0 <x <1, 0 <y <1) (KLTN) are replaced with at least one element of Pb and La, and all of Ta and Nb are replaced with Ti It may have a composition replaced with at least one element of Zr.

  Furthermore, in KTN and KLTN, the range of x which is the stoichiometric coefficient of Nb is preferably 0.1 or more and 0.5 or less. In KLTN, the range of y, which is the stoichiometric coefficient of Li, is preferably greater than 0 and less than 0.1.

  In addition, the dielectric crystal according to an embodiment of the present invention may be a single crystal or a polycrystal. However, in the case of a single crystal, one of the crystal axes of the single crystal is made to coincide with the optical axis of light incident on the etalon (the transmission direction of light incident on the etalon). By doing so, the modulation efficiency can be improved and the polarization dependence can be reduced. In the case of a polycrystal, the crystal axis is in various directions, and at least one crystal axis is made to coincide with the optical axis. By adopting such a crystal axis arrangement, the crystal can exhibit an electro-optic effect by applying an electric field, and can realize a modulation operation.

As the optical multiplexer 104, there is a configuration in which the input / output of the optical position shifter 102 whose path is determined by temperature is reversed. The configuration is shown in FIG. In FIG. 9, reference numeral 1201 is a bimetal at a temperature T _A , reference numeral 1202 is a bimetal at a temperature T _C , reference numeral 1203 is a collimating lens at a temperature T _A , and reference numeral 1204 is a collimating lens at a temperature T _C , Reference numeral 1205 denotes an optical fiber at the temperature T _A , and reference numeral 1206 denotes an optical fiber at the temperature T _C. It can be seen that when the temperatures T _A , T _B , and T _C are set so that the positions of the collimating lenses are the points A ₄ , B ₄ , and C ₄ , they operate as an optical multiplexer.

  Note that the configuration of the optical multiplexer 104 is not limited to using a bimetal, and any configuration is possible as long as light can be multiplexed.

In the above description, selects the wavelength lambda _in the input light so that the transmittance is decreased when the transmittance was chosen wavelength lambda _in the input light to maximize, not to apply voltage when unpowered May be. This is shown in FIG.

It is a block diagram of an etalon type gate switch according to an embodiment of the present invention. It is the figure which showed the point through which light passes in each temperature based on one Embodiment of this invention. It is a figure which shows the transmission spectrum of the etalon in each point and each temperature when the voltage is not applied to the dielectric crystal based on one Embodiment of this invention. It is a graph showing the phase transition temperature of the _{K 1-y Li y Ta 1-0.028} Nb 0.028 O 3. It is a graph which shows the temperature dependence of the product of the refractive index n and thickness d based on one Embodiment of this invention. Is a graph showing the refractive index at 1.55μm of _{KTa 1-x Nb x O 3} . It is a block diagram of the optical position displacement device 102 with which the path | route output according to temperature comprised using the bimetal based on one Embodiment of this invention is defined. It is a block diagram of the etalon 103 based on one Embodiment of this invention. It is a block diagram of the optical multiplexer 104 comprised using the bimetal based on one Embodiment of this invention. It is the figure which showed the operation | movement of the gate switch when setting so that the transmittance | permeability of light may become small when a voltage is not applied. It is the figure which showed the operation | movement of the gate switch when setting so that the transmittance | permeability of light may become the maximum when a voltage is not applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Etalon type gate switch 102 Optical position displacement device in which the output path is determined by temperature 103 Etalon 104 Optical multiplexer 111 First mirror 112 First electrode 113 Dielectric crystal 114 Second electrode 115 Second mirror 1101 1102, 1201, 1202 Bimetal 1103, 1104, 1203, 1204 Collimate lens 1105, 1106, 1205, 1206 Optical fiber

Claims (14)

An optical position shifter that has an input port for light and that determines the path in which light is output depending on the temperature;
Disposed downstream of said light position displacement device has a secondary electro-optic effect, a ferroelectric phase and a cubic phase transition temperature is a temperature at which the phase transition between the structures become paraelectric phase first A dielectric crystal including a spatial distribution region having a spatial distribution changing in the plane of
A first member wherein provided on the first surface of the dielectric crystal, wherein a voltage is applied to the dielectric crystal, and for reflecting the input light with a predetermined reflection factor,
A second member provided on a second surface opposite to the first surface of the dielectric crystal, for applying a voltage to the dielectric crystal and reflecting the input light with a predetermined reflectance; ,
A gate switch including an optical multiplexer disposed at a subsequent stage of the dielectric crystal and configured to multiplex light emitted from the second surface of the dielectric crystal;
And the ambient temperature of the gate switch, the temperature difference between the phase transition temperature of the dielectric crystals of the point where the from the optical position shifters dielectric light input to the first surface of the crystal to pass through, The optical position shifter fluctuates in response to the change in the environmental temperature so that the optical position is always constant when the environmental temperature changes, so that the optical position is at a predetermined point in the spatial distribution region of the dielectric crystal. The phase transition temperature of the dielectric crystal at a point where the light emitted from the displacement device is incident and the light passes is lower than the environmental temperature, and the dielectric crystal at the point where the light passes is a paraelectric phase. The gate switch characterized by being.
An optical position shifter that has an input port for light and that determines the path in which light is output depending on temperature,
Disposed downstream of said light position displacement device has a secondary electro-optic effect, a ferroelectric phase and phase transition temperature and refractive index is a temperature at which the phase transition between the paraelectric phase of a cubic system structure A dielectric crystal including a spatial distribution region having a spatial distribution that is changing in the first plane ;
A first member wherein provided on the first surface of the dielectric crystal, wherein a voltage is applied to the dielectric crystal, and for reflecting the input light with a predetermined reflection factor,
A second member provided on a second surface opposite to the first surface of the dielectric crystal, for applying a voltage to the dielectric crystal and reflecting the input light with a predetermined reflectance; ,
A gate switch including an optical multiplexer disposed at a subsequent stage of the dielectric crystal and configured to multiplex light emitted from the second surface of the dielectric crystal;
And the ambient temperature of the gate switch, the temperature difference between the phase transition temperature of the dielectric crystals of the point where the from the optical position shifters dielectric light input to the first surface of the crystal to pass through, The refractive index of the dielectric crystal at a point where light input from the optical position displacement device to the first surface of the dielectric crystal passes so as to be always constant when the environmental temperature changes. The product of the distance between the first surface and the second surface at the point where light input to the dielectric crystal passes is always constant when the environmental temperature changes. By changing the optical position displacement device according to the change in the environmental temperature, the light emitted from the optical position displacement device is incident on a predetermined point of the spatial distribution region of the dielectric crystal, and the light The phase transition temperature of the dielectric crystal at the point where the Lower than the environmental temperature, the gate switch, characterized in that said dielectric crystal point which the light passes is paraelectric phase.
The spatial distribution gate switch according to claim 1 or 2 characterized in that it is a monotonic and continuous. The optical position shifters has one end fixed, the gate switch according to any one of claims 1 to 3 is the optical fiber to the other end, characterized in that it comprises an arrangement bimetallic. The optical position shifter further comprises a collimating lens disposed at the other end of the bimetal,
The gate switch according to claim 4 , wherein the optical fiber is connected to the collimating lens. The gate switch according to any one of claims 1 to 5 , wherein the first member and the second member are metal thin film electrodes. The first member and the second member are composed of a transparent electrode provided on the surface of the dielectric crystal and a dielectric multilayer film mirror made of a dielectric multilayer film provided on the transparent electrode. gate switch according to any one of claims 1 to 5, characterized in. 8. The gate switch according to claim 7 , wherein a metal thin film electrode is provided between the transparent electrode and the dielectric multilayer mirror. Said dielectric crystal is a single crystal, according to claim 1 to 8, characterized in that it is arranged so that one of the crystal axes of the single crystal coincides with the transmission direction of light irradiated to the dielectric crystal The gate switch in any one of. It said dielectric crystal is a polycrystal, claims 1 to 8, characterized in that at least one of the crystal axes of the crystal are arranged to coincide with the transmission direction of the light irradiated to the dielectric crystal The gate switch in any one of. The dielectric crystal has a composition of K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 <y <1) or KTa _1-x Nb _x O ₃ (0 <x < gate switch according to any one of claims 1 to 1 0, characterized in that it has a composition of 1). The dielectric crystal includes all of K in KTa _1-x Nb _x O ₃ (0 <x <1), or K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 < y <all K and Li in 1) Ba, Sr, replacing at least one element of Ca, and claims 1 to 1 0, characterized in that it has a composition obtained by replacing all of the Ta and Nb with Ti The gate switch in any one of. The dielectric crystal includes all of K in KTa _1-x Nb _x O ₃ (0 <x <1), or K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 < and having a composition in which all of K and Li in y <1) are replaced with at least one element of Pb and La, and all of Ta and Nb are replaced with at least one element of Ti and Zr. gate switch according to any one of claims 1 to 1 0. The x as the first composition ratio in the composition of the dielectric crystal is 0.1 or more and 0.5 or less, and the y as the second composition ratio in the composition of the dielectric crystal is greater than 0. gate switch according to any one of claims 1 1 to 1 3, characterized in that at is less than 0.1.

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