JP2007086454A - Liquid crystal wavelength filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal wavelength filter capable of more reducing variation of transmission wavelength due to temperature change than heretofore. <P>SOLUTION: The liquid crystal wavelength filter 10 is provided with: transparent substrates 11, transparent electrodes 12, mirrors 13 and alignment layers 14 which are sequentially formed on the transparent substrates 11; a liquid crystal layer 15 interposed between the transparent substrates 11; and a sealing material 16 provided on the peripheral part of the liquid crystal layer 15. The filter 10 is so constituted that the magnitude of a linear expansion coefficient of the sealing material 16 is limited according to at least one of the thickness of the transparent substrates 11 and the magnitude of the volume expansion coefficient of the liquid crystal layer 15 so that variation of the wavelength of transmission light by the change of the thickness due to temperature change of the liquid crystal layer 15 in an element center part is prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal wavelength filter that extracts an optical signal having a desired wavelength in the field of optical communication, for example.

  Conventionally, as this type of liquid crystal wavelength filter, those shown in Patent Documents 1 and 2 are known.

  First, what was shown by patent document 1 is equipped with a pair of glass substrate which clamps a liquid crystal layer, and the sealing material and coating layer which were provided between the glass substrates around a liquid crystal layer. The thermal expansion coefficient of the sealing material is larger than the thermal expansion coefficient of the liquid crystal layer, and the thickness of the sealing material is thinner than a general one by the amount of the coating layer provided. Patent Document 1 describes that this configuration can suppress a variation in transmission wavelength with respect to a temperature change.

  Next, what is disclosed in Patent Document 2 includes a liquid crystal layer containing bubbles and a pair of transparent substrates sandwiching the liquid crystal layer, and absorbs the volume change of the liquid crystal layer even when the ambient temperature changes. Thus, since the volume of the bubbles changes according to the temperature change, the change in the dimension between the transparent substrates can be suppressed, and the change in the transmission wavelength with respect to the temperature change can be reduced.

JP-A-8-29793 JP 2003-45065 A

  However, the one disclosed in Patent Document 1 does not consider the actual phenomenon that the glass substrate deforms due to the center portion of the liquid crystal layer expanding more than the end face portion as the temperature rises, so the temperature change In some cases, the variation in the transmission wavelength due to the above cannot be reduced.

  In addition, in the case shown in Patent Document 2, bubbles in the liquid crystal layer may move into the light transmission region due to vibration or impact, and in such a case, the transmission wavelength does not reach a predetermined value. There was a problem.

  The present invention has been made in order to solve the conventional problems, and an object of the present invention is to provide a liquid crystal wavelength filter capable of making a variation in transmission wavelength due to a temperature change smaller than that of the conventional one.

  The liquid crystal wavelength filter of the present invention is provided between at least two transparent substrates provided with a transparent electrode and a mirror along the traveling direction of incident light, and the transparent substrate disposed so that the transparent electrodes face each other. In a liquid crystal wavelength filter comprising: a sandwiched liquid crystal layer; and a sealing material that is provided at a periphery of the liquid crystal layer and that joins the transparent substrate that sandwiches the liquid crystal layer, the temperature of the liquid crystal layer at the center of the liquid crystal wavelength filter In order to prevent the wavelength of the transmitted light from fluctuating due to the change in thickness due to the change, the line of the sealing material depends on at least one of the thickness of the transparent substrate and the volume expansion coefficient of the liquid crystal layer. It has the structure which limits the magnitude | size of an expansion coefficient.

  With this configuration, the liquid crystal wavelength filter of the present invention has a thickness of the transparent substrate so as to prevent the wavelength of transmitted light from fluctuating due to a change in thickness due to a temperature change of the liquid crystal layer at the center of the liquid crystal wavelength filter. In addition, since the size of the linear expansion coefficient of the sealing material is limited according to at least one of the volume expansion coefficients of the liquid crystal layer, the variation in the transmission wavelength due to the temperature change can be made smaller than that of the conventional one.

  The liquid crystal wavelength filter of the present invention has a configuration in which the size of the linear expansion coefficient of the sealing material decreases as the thickness of the transparent substrate increases.

  With this configuration, the liquid crystal wavelength filter of the present invention limits the size of the linear expansion coefficient of the sealing material according to the thickness of the transparent substrate, so that the variation of the transmission wavelength due to temperature change is made smaller than that of the conventional one. Can do.

  Furthermore, the liquid crystal wavelength filter of the present invention has a configuration in which the magnitude of the linear expansion coefficient of the sealing material increases as the volume expansion coefficient of the liquid crystal layer increases.

  With this configuration, the liquid crystal wavelength filter of the present invention limits the size of the linear expansion coefficient of the sealing material in accordance with the volume expansion coefficient of the liquid crystal layer. Can also be reduced.

  Further, in the liquid crystal wavelength filter of the present invention, the transparent substrate is a quartz glass substrate, and the sealing material is composed of at least one of an epoxy-based adhesive and an acrylic-based adhesive.

  With this configuration, the liquid crystal wavelength filter according to the present invention includes a generally used quartz glass substrate and a sealing material made of at least one of an epoxy-based adhesive and an acrylic-based adhesive, so that a conventional transparent substrate and a sealing material are formed. Since the manufacturing process can be applied and no new equipment investment is required, the variation in the transmission wavelength due to the temperature change can be made smaller than the conventional one without increasing the manufacturing cost.

Further, in the liquid crystal wavelength filter of the present invention, when the thickness of the quartz glass substrate changes from 0.4 mm to 2.0 mm, the value of the linear expansion coefficient of the sealing material depends on the thickness of the quartz glass substrate. And 3.2 × 10 ⁻⁵ / ° C. to 4.9 × 10 ⁻⁴ / ° C.

  With this configuration, in the liquid crystal wavelength filter of the present invention, when the thickness of the quartz glass substrate is 0.4 mm to 2.0 mm, a sealing material having a linear expansion coefficient corresponding to the thickness is selected. Thus, the variation of the transmission wavelength due to the temperature change can be made smaller than the conventional one.

  Furthermore, the liquid crystal wavelength filter of the present invention has a voltage application state in which a predetermined voltage is applied to the transparent electrode and a voltage non-application state in which the voltage is not applied to the transparent electrode. In a temperature range where the temperature change rate of the wavelength of the transmitted light is from 10 ° C. to 60 ° C., the variation value depending on the temperature of the wavelength has a value of 0 nm / ° C. to 0.1 nm / ° C.

  With this configuration, the liquid crystal wavelength filter of the present invention can keep the fluctuation value due to the temperature of the wavelength within the range of 0 nm / ° C. to 0.1 nm / ° C. in the voltage-free state where the temperature characteristic of the transmission wavelength is maximum. Therefore, the temperature characteristic of the transmission wavelength can be suppressed within a range of ± 0.1 nm / ° C. even in a voltage applied state, and the fluctuation of the transmission wavelength due to a temperature change can be made smaller than the conventional one.

Furthermore, in the liquid crystal wavelength filter of the present invention, when the value of the volume expansion coefficient of the liquid crystal layer changes from 5.2 × 10 ⁻⁵ / ° C. to 2.6 × 10 ⁻⁴ / ° C., the linear expansion of the sealing material. The coefficient value varies from 1.7 × 10 ⁻⁶ / ° C. to 3.9 × 10 ⁻⁴ / ° C. depending on the value of the volume expansion coefficient of the liquid crystal layer.

With this configuration, the liquid crystal wavelength filter of the present invention has a volume expansion coefficient when the value of the volume expansion coefficient of the liquid crystal layer is any of 5.2 × 10 ⁻⁵ / ° C. to 2.6 × 10 ⁻⁴ / ° C. By selecting a sealing material having a linear expansion coefficient corresponding to the rate, the variation in the transmission wavelength due to temperature change can be made smaller than that of the conventional one.

  The present invention can provide a liquid crystal wavelength filter having an effect that the fluctuation of the transmission wavelength due to temperature change can be made smaller than that of the conventional one.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, the configuration of the liquid crystal wavelength filter according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of a liquid crystal wavelength filter according to the present embodiment.

  As shown in FIG. 1, the liquid crystal wavelength filter 10 according to the present embodiment includes a transparent substrate 11, a transparent electrode 12, a mirror 13 and an alignment film 14 that are sequentially formed on the surface of the transparent substrate 11, and a transparent substrate 11. A liquid crystal layer 15 sandwiched between the liquid crystal layer 15 and a sealing material 16 provided at the peripheral edge of the liquid crystal layer 15.

  The transparent substrate 11 is composed of, for example, a quartz glass substrate. The transparent electrode 12 is made of, for example, ITO (Indium Tin Oxide), and is formed on the transparent substrate 11 by, for example, a sputtering method. A voltage having a predetermined frequency is applied to the pair of transparent electrodes 12, and the substantial refractive index of the liquid crystal layer 15 is changed by this voltage.

The mirror 13 is composed of, for example, a multilayer film in which SiO ₂ films and Ta ₂ O ₅ films are alternately stacked, and is formed on the transparent electrode 12 by, for example, a vapor deposition method. The pair of mirrors 13 facing each other constitute an optical resonator, and light having a resonance wavelength corresponding to the interval between the pair of mirrors 13 is generated.

  The alignment film 14 is made of, for example, polyimide, and is formed by applying an alignment treatment agent that determines the alignment of the liquid crystal molecules contained in the liquid crystal layer 15 on the mirror 13.

  The liquid crystal layer 15 is made of, for example, nematic liquid crystal and is enclosed in a region surrounded by the alignment film 14 and the sealing material 16. The sealing material 16 is made of, for example, at least one of an epoxy-based adhesive and an acrylic-based adhesive.

  In the liquid crystal wavelength filter 10 according to the present embodiment, the wavelength of transmitted light fluctuates due to the change in the thickness due to the temperature change of the liquid crystal layer 15 in the central part of the element (the part where the arrow is drawn in FIG. 1). In order to prevent this, the linear expansion coefficient of the sealing material 16 is limited in accordance with at least one of the thickness of the transparent substrate 11 and the volume expansion coefficient of the liquid crystal layer 15.

Specifically, for example, the transparent substrate 11 is composed of a quartz glass substrate having a substrate thickness of 0.8 mm, and the liquid crystal layer 15 is composed of nematic liquid crystal having a volume expansion coefficient of 1.7 × 10 ⁻⁴ / ° C. The sealing material 16 is made of a material having a linear expansion coefficient of 1.9 × 10 ⁻⁴ / ° C. to 2.6 × 10 ⁻⁴ / ° C.

  Since the liquid crystal wavelength filter 10 according to the present embodiment is configured as described above, when light travels in the direction of the arrow shown in FIG. 1, the liquid crystal wavelength filter 10 has a predetermined frequency between the pair of transparent electrodes 12. By applying a voltage, light having a resonance wavelength corresponding to the distance between the pair of mirrors 13 can be output.

  By the way, the liquid crystal wavelength filter 10 configured as described above changes the size of each component in accordance with the ambient temperature, and transmits the wavelength of light transmitted in the direction of the arrow shown in FIG. 1 (hereinafter “transmission wavelength”). Is known to fluctuate.

  Therefore, the inventor of the present invention needs to suppress the thickness fluctuation of the central portion of the liquid crystal wavelength filter 10 in order to suppress the fluctuation amount of the transmission wavelength within the operating temperature range of the liquid crystal wavelength filter 10. By paying attention and calculating the linear expansion coefficient of the sealing material 16 according to the configuration of the transparent substrate 11 and the liquid crystal layer 15, the temperature characteristics of the liquid crystal wavelength filter 10 can be greatly improved compared to the conventional one. Details will be described below.

  First, the temperature characteristics of the liquid crystal wavelength filter 10 configured as described above will be described.

First, the shape of the liquid crystal wavelength filter 10 at a reference temperature (for example, 20 ° C.) is simplified as shown in FIG. 2A, and the thickness of the liquid crystal layer 15 in the direction in which light is transmitted is hereinafter referred to as “cell gap”. . At this reference temperature, the two transparent substrates 11 are parallel to each other, and the transmission wavelength of the liquid crystal wavelength filter 10 is set to a wavelength λ ₀ as shown in FIG.

  When the ambient temperature of the liquid crystal wavelength filter 10 increases, the shape of the liquid crystal wavelength filter 10 changes from the shape shown in FIG. 2A to the shape shown in FIG. 2C or FIG. When the temperature rise is the same, the volume after expansion of the liquid crystal layer 15 in the shape shown in FIGS. 2C and 2E is the same.

FIG. 2C shows the shape change of the liquid crystal wavelength filter 10 when the expansion of the sealing material 16 is smaller than the expansion of the liquid crystal layer 15. In this case, the central portion of the liquid crystal wavelength filter 10 is expanded most, and the cell gap at the central portion is maximized. Here, the size of the cell gap depends on the substrate thickness of the transparent substrate 11, and the cell gap is likely to change as the substrate thickness decreases. The transmission wavelength of the liquid crystal wavelength filter 10 in the shape shown in FIG. 2C is a wavelength λ ₁ shifted to a larger side than the wavelength λ _{0 as} shown in FIG.

On the other hand, FIG. 2 (e) shows a change in the shape of the liquid crystal wavelength filter 10 when the expansion of the sealing material 16 is larger than the expansion of the liquid crystal layer 15. In this case, since the sealing material 16 expands more than the liquid crystal layer 15, the change in the cell gap at the center of the liquid crystal wavelength filter 10 becomes smaller than that shown in FIG. Here, the size of the cell gap also depends on the substrate thickness of the transparent substrate 11. The transmission wavelength of the liquid crystal wavelength filter 10 in the shape shown in FIG. 2 (e) is a wavelength λ ₂ that is substantially equivalent to the wavelength λ _{0 as} shown in FIG. 2 (f).

  As described above, since the size of the cell gap changes according to the temperature change, the transmission wavelength of the liquid crystal wavelength filter 10 also changes according to the temperature change. When the liquid crystal wavelength filter 10 is used, for example, in the optical communication field, the operating temperature range is 10 ° C. to 60 ° C., and the variation value of the transmission wavelength due to the temperature change in this operating temperature range is within ± 0.1 nm / ° C. This is considered sufficient. The fluctuation value of the transmission wavelength due to the temperature change is hereinafter referred to as “transmission wavelength temperature characteristic”.

  In addition, in a voltage application state in which a voltage of a predetermined frequency is applied to the transparent electrode 12, by selecting a frequency, the difference between the maximum value and the minimum value of the temperature characteristic of the transmission wavelength is suppressed to 0.1 nm / ° C. or less. It is known that it can be. Further, it is known that the temperature characteristic of the transmission wavelength is maximized when the applied voltage applied to the transparent electrode 12 is 0 V (hereinafter referred to as “no voltage applied state”). Therefore, if the temperature characteristic of the transmission wavelength satisfies 0 nm / ° C. to 0.1 nm / ° C. in the state where no voltage is applied, the temperature characteristic of the transmission wavelength is suppressed within the range of ± 0.1 nm / ° C. even in the voltage application state. be able to. In addition, the temperature characteristic of the transmission wavelength in the following description refers to the temperature characteristic in a state where no voltage is applied.

  As described above, the temperature characteristic of the transmission wavelength in the liquid crystal wavelength filter 10 is determined by the thickness of the quartz glass substrate used as the transparent substrate 11, the volume expansion coefficient of the liquid crystal material used as the liquid crystal layer 15, and the linear expansion coefficient of the sealing material 16. Is done. Therefore, by calculating the linear expansion coefficient of the sealing material 16 using the thickness of the quartz glass substrate and the volume expansion coefficient of the liquid crystal material as parameters, the temperature characteristic of the transmission wavelength is ± 0.1 nm / ° C. as shown below. Can be kept within the range.

  First, as shown in FIG. 3A, when the cell gap za changes to the cell gap zb after the temperature rises, the shape change z1 is expressed by the following equation.

  z1 = zb-za (1)

  Here, as shown in the right side of FIG. 3A, when the shape of the transparent substrate 11 changes due to the stress when the liquid crystal layer 15 is thermally expanded, the deformed shape of the transparent substrate 11 can be approximated by a quadratic function. It has been experimentally proved that the transparent substrate 11 deforms in a similar form of a quadratic function as the stress applied to the transparent substrate 11 increases.

  Therefore, as shown in FIG. 3B, the shape change of the cell gap due to the temperature rise is modeled and expressed approximately. That is, when the coordinates of the modeled model shown in FIG. 3B (hereinafter referred to as “model 1”) are determined as shown in the figure, the cell gap shape change z1 is expressed by the following equation.

z1 = Ax ² + By ² + C + D (2)

Here, Ax ² + By ² + C represents the deformation of the transparent substrate 11, and D represents the expansion of the sealing material 16. For example, the cell gap difference is C + D in the central portion of the liquid crystal wavelength filter 10, and the cell gap difference is D in the vicinity of the sealing material 16. The central portion of the liquid crystal wavelength filter 10 refers to a portion along the z axis that passes through (x, y) = (0, 0), and the cell gap difference refers to the size and temperature of the cell gap before the temperature rises. The difference from the cell gap dimension after the rise.

  In addition, when the dimension of the cell gap is d, the temperature is T, the transmission wavelength is λ, and the coefficient determined from the material characteristics of the liquid crystal and the substrate, the cell gap, and the like is h, the following relationship is established.

  ∂d / ∂T (nm / ° C.) = H × ∂λ / ∂T (nm / ° C.) (3)

  From equation (3), in order for the temperature characteristic of the transmission wavelength λ to satisfy 0 nm / ° C. to 0.1 nm / ° C., the cell gap temperature change is in the dimension range of 0 nm / ° C. to h × 0.1 nm / ° C. It is shown that it may be contained within. Therefore, the target value is to keep the temperature change C + D in the model 1 within the dimension range of 0 nm / ° C. to h × 0.1 nm / ° C.

  Next, when materials used for actual products are prepared and the transparent substrate 11, the liquid crystal layer 15, and the sealing material 16 are respectively composed of these materials, the linear expansion coefficient of the sealing material 16 is calculated from the equation (2). The results of the study are described. The material of the transparent substrate 11 prepared here is a quartz glass substrate having a substrate thickness of 0.8 mm. The material prepared as the material of the liquid crystal layer 15 is referred to as a liquid crystal material L, and the two types of materials prepared as the sealing material 16 are referred to as sealing materials S1 or S2. Further, since the coefficient h = 10 in the expression (3) in the studied configuration, the target value is to keep the temperature change C + D in the model 1 within the dimensional range of 0 nm / ° C. to 1 nm / ° C.

First, in the case where a quartz glass substrate having a substrate thickness of 0.8 mm, the liquid crystal material L, and the sealing material S1 as the sealing material 16 are used, the in-plane distribution of the cell gap difference from the in-plane distribution of the temperature characteristics of the transmission wavelength. Was approximated by equation (2). In this case, the temperature characteristic of the transmission wavelength in the central portion of the liquid crystal wavelength filter 10 was 0.27 nm / ° C., and the linear expansion coefficient of the sealing material S1 was 5.1 × 10 ⁻⁵ / ° C.

Similarly, when the quartz glass substrate having a substrate thickness of 0.8 mm, the liquid crystal material L, and the sealing material S2 as the sealing material 16 are used, the temperature characteristic of the transmission wavelength is 0 at the central portion of the liquid crystal wavelength filter 10. The linear expansion coefficient of the sealing material S2 was 1.5 × 10 ⁻⁴ / ° C.

  Therefore, it was found that when the sealing material S1 or S2 was used as the sealing material 16, both the temperature characteristics 0 nm / ° C. to 0.1 nm / ° C. could not be satisfied.

  Therefore, the linear expansion coefficient of the sealing material 16 that can satisfy the temperature characteristics of 0 nm / ° C. to 0.1 nm / ° C. is calculated using the new model shown in FIG.

  FIG. 4A shows model 1 from which equation (2) is derived. FIG. 4B shows that the entire volume after expansion is the same as model 1, and the deformation of the transparent substrate 11 and the sealing material. 16 shows different models of expansion (hereinafter referred to as “model 2”). That is, the shape change amount z2 of the liquid crystal wavelength filter 10 in the model 2 is expressed by the following approximate expression by introducing the coefficients s and t into the expression (2).

^{z2 = s (Ax 2 + By} 2 + C) + tD (5)

Here, s (Ax ² + By ² + C) represents the deformation of the transparent substrate 11, and tD represents the expansion of the sealing material 16. For example, in the central portion of the liquid crystal wavelength filter 10, the cell gap difference is sC + tD, and in the vicinity of the sealing material 16, the cell gap difference is tD. Similarly to the model 1, the target value is to keep the temperature change sC + tD in the model 2 within the dimensional range of 0 nm / ° C. to 1 nm / ° C.

When the above-mentioned liquid crystal material L and quartz having a substrate thickness of 0.8 mm are used, the coefficient of equation (5) is obtained under the condition that the cell gap dimension at the center of the liquid crystal wavelength filter 10 is within the target value. seek s and t, the expansion amount tD of the sealing member 16 calculates a result of calculating the linear expansion coefficient range of the sealing member 16, at 1.9 × ^{10 -4} /℃~2.6×10 ^-4 / ℃ If so, it has been found that the temperature characteristics of 0 nm / ° C. to 0.1 nm / ° C. can be satisfied. This result shows that the temperature characteristic target in the central portion of the liquid crystal wavelength filter 10 can be satisfied by using a sealing material having a larger linear expansion coefficient than the sealing materials S1 and S2.

  Next, when a material different from the liquid crystal material L is used as the material of the liquid crystal layer 15, the linear expansion coefficient of the sealing material 16 is calculated based on the volume expansion in the liquid crystal material L.

  The liquid crystal volume expansion due to temperature change is calculated as the liquid crystal volume expansion of the liquid crystal material L × volume expansion coefficient k. When the volume expansion coefficient k = 1, the liquid crystal material L is used. Specifically, using the equation (5), the condition that the volume of the liquid crystal volume expansion due to the temperature change is the volume of the model 1 shown in FIG. t is derived, and the linear expansion coefficient of the sealing material 16 is calculated. The result is shown in FIG. The volume V1 of the model 1 shown in FIG. 3B is expressed by the following equation using the dimensions p and q.

^{V1 = r (4p 3 qA /} 3 + 4pq 3 B / 3 + 4pqC) + 4pqD (6)

  Here, the coefficient r is a coefficient of warpage of the substrate described later, and the coefficient r = 1 when the thickness of the quartz glass substrate is 0.8 mm. Further, the first term on the right side shows the volume of the deformation of the transparent substrate 11, and the second term on the right side shows the volume of the expansion of the sealing material 16.

Figure 5 is a volume expansion of the liquid crystal layer 15 of for the case where the volume expansion coefficient k is changed in 0.1 steps from 0.1 to 1.5, when the temperature changes ^{10 ℃ (μm 3/10 ℃} ) , The volume increase (%), the volume expansion coefficient (/ ° C.), and the linear expansion coefficient range (/ ° C.) of the sealing material 16 are shown. 5, volume expansion of each volume expansion coefficient k is calculated based on the volume expansion "16840.224μm ^3/10 ℃" in volume expansion coefficient k = 1 (when the liquid crystal material L). For example, the volume expansion of the liquid crystal layer 15 when the volume expansion coefficient k = 0.5 is half that when the volume expansion coefficient k = 1.

The value of the volume expansion at the volume expansion coefficient k = 1 indicates the volume expanded with respect to the original volume before the temperature change. When the dimensions p and q shown in FIG. 4B are used, the original volume is 3972000 μm ³ when p = 600 μm, q = 600 μm, and z = 6.8 μm. , volume expansion when a temperature rise of 10 ° C. is 16840.224μm ^3/10 ℃, volume increase is about 0.172%.

  The results shown in FIG. 5 indicate that the linear expansion coefficient of the sealing material 16 must be increased as the liquid crystal volume expansion (coefficient) increases. This means that the cell gap due to the liquid crystal volume expansion is averaged over the entire element so as not to be intensively increased only at the central portion of the liquid crystal wavelength filter 10, or the cell gap is increased in the vicinity of the sealing material 16. ing.

Further, in FIG. 5, when the value of the volume expansion coefficient of the liquid crystal layer 15 changes from 5.2 × 10 ⁻⁵ / ° C. to 2.6 × 10 ⁻⁴ / ° C., the value of the linear expansion coefficient of the sealing material 16. Is shown to change from 1.7 × 10 ⁻⁶ / ° C. to 3.9 × 10 ⁻⁴ / ° C. according to the value of the volume expansion coefficient of the liquid crystal layer 15.

  Next, the linear expansion coefficient of the sealing material 16 is calculated when a quartz glass substrate having a substrate thickness different from the substrate thickness of 0.8 mm is used as the material of the transparent substrate 11.

  Since the substrate deformation is suppressed as the substrate thickness increases, it can be considered that the volume expansion of the liquid crystal layer 15 decreases. At this time, by introducing a substrate warpage coefficient r into the equation (5), the shape change z3 of the liquid crystal wavelength filter 10 is expressed by the following approximate equation. Note that when the thickness of the quartz glass substrate is 0.8 mm, the warp factor r of the substrate is 1.

^{z3 = rs (Ax 2 + By} 2 + C) + tD (7)

  According to the equation (7), when s = 1 and t = 1, the liquid crystal volume expansion is obtained, and the liquid crystal volume expansion is not changed, so that the cell gap dimension at the center of the liquid crystal wavelength filter 10 falls within the target value. By changing s and t, the linear expansion coefficient range of the sealing material 16 is obtained. The result is shown in FIG.

As shown in FIG. 6, when the substrate thickness changes from 0.4 mm to 2.0 mm, the value of the linear expansion coefficient of the sealing material 16 varies from 4.9 × 10 ⁻⁴ / ° C. to 3. It varies between 2 × 10 ⁻⁵ / ° C.

  That is, since the deformation of the substrate with respect to the stress decreases as the substrate thickness increases, the liquid crystal volume expansion can be suppressed to be small. Therefore, it is not necessary to expand the sealing material 16 as the substrate thickness increases, and the linear expansion coefficient of the sealing material 16 It is shown that can be reduced. On the contrary, when the sealant 16 having a linear expansion coefficient larger than that shown in FIG. 6 is used, it is necessary to suppress the change in the cell gap in the central portion of the liquid crystal wavelength filter 10 by deformation of the substrate. It is necessary to form the transparent substrate 11 with a substrate.

  Next, the results calculated in the same manner as described above for the case where the material as the transparent substrate 11 is different from the quartz glass substrate having a substrate thickness of 0.8 mm and the material as the liquid crystal layer 15 is different from the liquid crystal material L are shown in FIG. 7 to 9 show.

FIG. 7 shows a case where the substrate thickness is changed from 0.4 mm to 2.0 mm, and the temperature is changed by 10 ° C. with respect to the case where the volume expansion coefficient k of the liquid crystal layer 15 is changed to 0.5, 1, 1.5. volume expansion of the liquid crystal layer 15 of the ([mu] m ^3/10 ° C.), the volume increase (%) shows the volume expansion coefficient (/ ° C.) and the linear expansion coefficient range of the sealing material 16 (/ ° C.). In FIG. 7, the linear expansion coefficient of the sealing material 16 at each substrate thickness is calculated based on the volume expansion coefficient k = 1 at a substrate thickness of 0.8 mm.

  8 and 9 are graphs of the results shown in FIG. That is, FIG. 8 shows the range of the linear expansion coefficient of the sealing material 16 with respect to the volume expansion coefficient k of the liquid crystal layer 15 using the thickness (t) of the quartz glass substrate as a parameter, and FIG. 9 shows the volume expansion coefficient k as a parameter. The linear expansion coefficient range of the sealing material 16 with respect to the substrate thickness of the quartz glass substrate is shown.

  As shown in FIG. 8, the linear expansion coefficient of the sealing material 16 increases as the volume expansion coefficient of the liquid crystal layer 15 increases. As shown in FIG. 9, the linear expansion coefficient of the sealing material 16 decreases as the thickness of the quartz glass substrate increases. From the graphs shown in FIGS. 8 and 9, the linear expansion coefficient range of the sealing material 16 other than the calculation points shown in FIG. 7 can be known. For example, from the graph shown in FIG. 8, the linear expansion coefficient range of the sealing material 16 when the liquid crystal material having a volume expansion coefficient k of, for example, 0.7 or 1.3 is used is known for each thickness of the quartz glass substrate. it can.

  From the results shown in FIG. 7 to FIG. 9, the temperature characteristic is 0 nm / ° C. by using a sealing material having a linear expansion coefficient corresponding to the combination of the thickness of the quartz glass substrate and the volume expansion coefficient k of the liquid crystal layer 15. A liquid crystal wavelength filter 10 satisfying ˜0.1 nm / ° C. is obtained.

  As described above, according to the liquid crystal wavelength filter 10 of the present embodiment, the transparent substrate 11, the transparent electrode 12, the mirror 13 and the alignment film 14 that are sequentially formed on the surface of the transparent substrate 11, and the transparent substrate 11 The sandwiched liquid crystal layer 15 and a sealing material 16 provided at the peripheral edge of the liquid crystal layer 15 are provided, and the wavelength of transmitted light varies depending on the change in thickness due to the temperature change of the liquid crystal layer 15 in the central portion of the element. In order to prevent this, the linear expansion coefficient of the sealing material 16 is limited according to at least one of the thickness of the transparent substrate 11 and the volume expansion coefficient of the liquid crystal layer 15. The variation of the transmission wavelength due to can be made smaller than that of the conventional one.

Specifically, from the data shown in FIG. 7, for example, a transparent substrate 11 is formed of a quartz glass substrate having a substrate thickness of 1.6 mm, and a nematic liquid crystal having a volume expansion coefficient of 1.2 × 10 ⁻⁴ / ° C. The liquid crystal layer 15 is constituted by the above, and the sealing material 16 is constituted by a material having a linear expansion coefficient of 1.1 × 10 ⁻⁴ / ° C. to 1.9 × 10 ⁻⁴ / ° C. In the temperature range from 10 ° C. to 60 ° C., the wavelength filter 10 can keep the variation value of the transmission wavelength due to temperature change within the range of 0 nm / ° C. to 0.1 nm / ° C.

  Further, according to the liquid crystal wavelength filter 10 of the present embodiment, the transparent substrate 11 is composed of a quartz glass substrate, and the sealing material 16 is composed of at least one of an epoxy-based adhesive and an acrylic-based adhesive. 11 and the conventional manufacturing process for forming the sealing material 16 can be applied, and no new equipment investment is required. Therefore, the variation in the transmission wavelength due to the temperature change can be made larger than that of the conventional one without increasing the manufacturing cost. Can be small.

  In the above-described embodiment, the configuration in which one transparent substrate 11 is provided on each of the light incident side and the light emitting side has been described as an example. However, the present invention is not limited to this, and the transparent substrate 11 is not limited thereto. The same effect can be obtained even if a plurality of is formed.

  As described above, the liquid crystal wavelength filter 10 according to the present invention has an effect that the variation of the transmission wavelength due to the temperature change can be made smaller than that of the conventional one, and an optical signal having a desired wavelength in the optical communication field can be obtained. It is useful as a liquid crystal wavelength filter to be taken out.

Schematic configuration diagram of a liquid crystal wavelength filter according to the present embodiment (A) In the liquid crystal wavelength filter according to the present embodiment, a simplified representation of the configuration of the liquid crystal wavelength filter at the reference temperature. (B) In the liquid crystal wavelength filter according to the present embodiment, the transmission wavelength λ _{0 at the} reference temperature. (C) The liquid crystal wavelength filter which concerns on this Embodiment WHEREIN: The figure which simplified and represented the structure of the liquid crystal wavelength filter when temperature rose from reference temperature (d) The liquid crystal wavelength filter which concerns on this Embodiment in the liquid crystal wavelength filter according to FIG. (e) the present embodiment shows a transmission wavelength lambda ₁ in a case where the temperature from the reference temperature rises, the temperature from the reference temperature by simplifying the structure of the liquid crystal wavelength filter in the case of increased in the liquid crystal wavelength filter according to represent the FIG. (f) embodiment, the transmission in the case where the temperature from the reference temperature increases the wavelength lambda ₂ Figure shows (A) In liquid crystal wavelength filter which concerns on this Embodiment, The figure which shows a shape change when the cell gap za becomes the cell gap zb after a temperature rise (b) In the liquid crystal wavelength filter which concerns on this Embodiment, by temperature rise The figure which shows the model 1 which modeled the shape gap part of the cell gap, and represented it approximately (A) In the liquid crystal wavelength filter according to the present embodiment, a diagram showing model 1 in which the change in the shape of the cell gap due to a temperature rise is modeled and expressed approximately. (B) In the liquid crystal wavelength filter according to the present embodiment FIG. 2 is a diagram showing a model 2 that approximately represents a shape change of a cell gap due to a temperature rise The liquid crystal wavelength filter which concerns on this Embodiment WHEREIN: The figure which shows the linear expansion coefficient range of the sealing material with respect to the volume expansion coefficient k of liquid crystal material The liquid crystal wavelength filter which concerns on this Embodiment WHEREIN: The figure which shows the linear expansion coefficient range of the sealing material with respect to the substrate thickness of transparent substrate material The liquid crystal wavelength filter which concerns on this Embodiment WHEREIN: The figure which shows the linear expansion coefficient range of the sealing material with respect to the substrate thickness of transparent substrate material, and the volume expansion coefficient k of liquid crystal material In the liquid crystal wavelength filter according to the present embodiment, a graph showing the linear expansion coefficient range of the sealing material with respect to the volume expansion coefficient k of the liquid crystal material In the liquid crystal wavelength filter according to the present embodiment, a graph showing the linear expansion coefficient range of the sealing material with respect to the substrate thickness of the transparent substrate material

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal wavelength filter 11 Transparent substrate 12 Transparent electrode 13 Mirror 14 Alignment film 15 Liquid crystal layer 16 Sealing material

Claims (7)

  At least two transparent substrates provided with a transparent electrode and a mirror along the traveling direction of incident light, a liquid crystal layer sandwiched between the transparent substrates disposed so that the transparent electrodes face each other, and In a liquid crystal wavelength filter comprising a sealing material that is provided at a peripheral edge of the liquid crystal layer and that joins the transparent substrate that sandwiches the liquid crystal layer, due to a change in thickness due to a temperature change of the liquid crystal layer in the center of the liquid crystal wavelength filter, The linear expansion coefficient of the sealing material is limited according to at least one of the thickness of the transparent substrate and the volume expansion coefficient of the liquid crystal layer so as to prevent the wavelength of transmitted light from fluctuating. A liquid crystal wavelength filter characterized by the above.   The liquid crystal wavelength filter according to claim 1, wherein the linear expansion coefficient of the sealing material decreases as the thickness of the transparent substrate increases.   3. The liquid crystal wavelength filter according to claim 1, wherein the linear expansion coefficient of the sealing material increases as the volume expansion coefficient of the liquid crystal layer increases.   4. The liquid crystal wavelength filter according to claim 1, wherein the transparent substrate is a quartz glass substrate, and the sealing material is made of at least one of an epoxy-based adhesive and an acrylic-based adhesive. When the thickness of the quartz glass substrate varies from 0.4 mm to 2.0 mm, the value of the linear expansion coefficient of the sealing material is 3.2 × 10 ⁻⁵ / ° C. depending on the thickness of the quartz glass substrate. The liquid crystal wavelength filter according to claim 4, which varies between ˜4.9 × 10 ⁻⁴ / ° C.   It has a voltage application state in which a predetermined voltage is applied to the transparent electrode and a voltage non-application state in which the voltage is not applied to the transparent electrode, and the temperature change rate of the wavelength of light transmitted in the voltage non-application state 6. The liquid crystal wavelength filter according to claim 1, wherein in the temperature range from 10 ° C. to 60 ° C., the fluctuation value of the wavelength depending on the temperature has a value of 0 nm / ° C. to 0.1 nm / ° C. 6. When the value of the volume expansion coefficient of the liquid crystal layer changes from 5.2 × 10 ⁻⁵ / ° C. to 2.6 × 10 ⁻⁴ / ° C., the value of the linear expansion coefficient of the sealing material is the volume of the liquid crystal layer. 7. The liquid crystal wavelength filter according to claim 5, wherein the liquid crystal wavelength filter changes from 1.7 × 10 ⁻⁶ / ° C. to 3.9 × 10 ⁻⁴ / ° C. according to the value of the expansion coefficient.

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