JP2966288B2 - Tunable wavelength filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal etalon type variable wavelength filter for selectively selecting only light having an arbitrary wavelength from light pulses having a large number of wavelengths in wavelength multiplex communication or the like.

[0002]

2. Description of the Related Art A variable wavelength filter 100 shown in FIGS. 4 and 5 is conventionally known as a variable wavelength filter of this kind.

In this tunable wavelength filter 100, a transparent electrode 102 is formed on each opposing surface of a pair of glass substrates 101 by a sputtering method, and a dielectric reflection film 103 is disposed thereon by vapor deposition. A liquid crystal alignment film 104 is disposed on the reflective film 103 by rubbing treatment, and a pair of glass substrates 101 are disposed in parallel with a seal member 105 while maintaining an appropriate interval.
A nematic liquid crystal 106 is sealed between 104, and a non-reflective film 107 is disposed on an outer surface of each of the pair of glass substrates 101 opposite to the opposing surface to constitute a main part.

The tunable wavelength filter 100 changes the refractive index of the liquid crystal 106 by applying a voltage to the transparent electrodes 102, 102, and changes the optical path length between the dielectric reflection films 103, 103 in the Fabry-Perot interference system. By doing so, it is possible to select a resonance wavelength (wavelength of light transmitted through the variable wavelength filter 100).

At this time, as shown in FIG. 7A, the liquid crystal 106 is oriented in the direction of the long axis of the liquid crystal molecules M on the glass substrate 10.
The liquid crystal molecules M have a positive dielectric anisotropy and are oriented so as to be parallel to the first opposing surface.

In general, it can be considered that the liquid crystal molecule M has a long and thin shape as shown in FIG. 6, and has a dielectric constant ε _{e in the} molecular long axis direction and a dielectric constant ε _e in the molecular short axis direction. _o There are two, the dielectric anisotropy [Delta] [epsilon] can be expressed as Δε = ε _e -ε _o.

As described above, the liquid crystal molecules M of the liquid crystal 106 have a positive dielectric anisotropy (Δε> 0), and the dielectric constant ε _{e in the} major axis direction is smaller than the dielectric constant ε in the minor axis direction. _It is larger than _o (ε _e > ε _o ), and as shown in FIG. 7, when no voltage is applied, the liquid crystal molecules M are oriented so that the molecular major axis direction is parallel to the facing surface of the glass substrate 101. (FIG. 7
(A)), when a voltage is applied, the liquid crystal molecules M are oriented such that the long axis direction of the molecule having a large dielectric constant is along the electric field direction (FIG. 7).
(B)). The change in the orientation of the liquid crystal molecules M causes the liquid crystal 10 to change.
6 changes, and as a result, the tunable wavelength filter 100
Can select the resonance wavelength.

[0008] Generally, the refractive index of liquid crystal also changes due to other external factors.

FIG. 8 shows the temperature dependence of the refractive index of a general liquid crystal. Where n _e is the temperature dependence of the molecular long axis direction of liquid crystal molecules, n _o denotes a temperature dependence of the molecular minor axis direction of liquid crystal molecules.

As can be seen from FIG. 8, the temperature change of the refractive index of the liquid crystal is such that the molecular major axis direction is larger than the molecular minor axis direction.

Therefore, the conventional variable wavelength filter 100
Is to change the refractive index of the liquid crystal 106 by changing the alignment of the liquid crystal molecules M in the molecular major axis direction. Therefore, the temperature dependency is high, and the temperature of the liquid crystal 106 is kept constant for accurate selection of the resonance wavelength. Need to be controlled.

Therefore, the conventional variable wavelength filter 100 is provided with a heating mechanism 200 for keeping the temperature of the liquid crystal 106 constant as shown in FIG. This heating mechanism 2
00 denotes a pair of glass substrates 1 of the variable wavelength filter 100.
Temperature sensor 201 and heater 2 provided on
02 and the signal of the temperature sensor 201, the heater 20
2, a temperature control device 203 for controlling the heating temperature. The heater 202 is laminated on the outer surface of the glass substrate 101 so as to surround the light transmitting portion 108 of the variable wavelength filter 100.

The heating mechanism 200 measures the temperature of the tunable filter 100 with the temperature sensor 201, and performs heating in accordance with the measured temperature.

[0014]

However, in the heating mechanism 200 of the tunable wavelength filter 100, the temperature sensor 201 is disposed in a portion completely exposed to the outside of the tunable wavelength filter 100. Since the temperature of the liquid crystal 106 is more susceptible to a change in the environmental temperature than the temperature change of the liquid crystal 106, the heating temperature of the heater 202 is not constant, and the temperature measurement by the temperature sensor 201 is performed externally. Since a large temperature difference is generated, it is difficult to control the temperature of the liquid crystal 106 with high accuracy, and therefore, there is a problem that the selected wavelength fluctuates greatly and the performance as a variable wavelength filter is reduced.

In addition, the heating mechanism 200 includes a temperature sensor 20
1 and the temperature control device 103, there is also a problem that the structure of the tunable wavelength filter 100 becomes complicated and large.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a variable wavelength filter having a simple structure and a small structure, in which the fluctuation of the selected wavelength due to temperature is small, the wavelength selection performance is improved. To offer.

[0017]

Means for Solving the Problems In order to achieve the above-mentioned object, the invention according to claim 1 comprises a pair of glass substrates in which a transparent electrode, a dielectric reflection film, and an alignment film for liquid crystal are formed on opposite surfaces. In a variable wavelength filter which is disposed to face through a sealing member and in which liquid crystal is sealed between the pair of glass substrates surrounded by the sealing member, a positive temperature coefficient of resistance in contact with an outer peripheral portion of the sealing member. And a self-regulating heating resistor having the following characteristics:

According to a second aspect of the present invention, there is provided the variable wavelength filter according to the first aspect, wherein the self-control type heating resistor is formed by adding a conductive material to a synthetic resin having crystallinity to make it conductive. It is characterized by being.

According to a third aspect of the present invention, there is provided the variable wavelength filter according to the first or second aspect, wherein the self-control type heating resistor is continuous in a band along the outer peripheral portion of the seal member. It is characterized by being arranged.

Further, the invention described in claim 4 is the same as the claim 1.
4. The variable wavelength filter according to claim 3, wherein the self-controlling heating resistor is formed as a U-shaped cross-section formed as an opposing surface between the outer peripheral surface of the seal member and the pair of glass substrates. 5. It is characterized by being arranged in.

[0021]

According to the first to fourth aspects of the present invention, the following effects are achieved because of the above-described configuration.

That is, according to the first aspect of the present invention, since the self-control type heating resistor having a positive temperature coefficient of resistance is disposed in contact with the outer peripheral portion of the sealing member having liquid crystal sealed therein.
The heating resistor accurately detects a change in the temperature of the liquid crystal, so that the temperature of the liquid crystal can be accurately controlled.

In addition, since the invention according to claim 1 uses a self-control type heating resistor as the heating element, no additional equipment such as a temperature sensor and a temperature control device is required.

According to a second aspect of the present invention, the self-control type heating resistor is formed by adding a conductive substance to a synthetic resin having crystallinity to make it conductive, so that the synthetic resin used is changed. In addition, it is possible to set an exothermic temperature according to the melting point of the synthetic resin, and it is possible to easily arrange the synthetic resin in the variable wavelength filter by setting it in a fluid state or a film state.

According to the third aspect of the present invention, since the self-control type heating resistor is arranged in a band shape along the outer periphery of the sealing member, a heat transfer area sufficient for heating the liquid crystal is provided. Can be secured.

Further, in the invention according to the fourth aspect, the self-control type heating resistor is arranged in a groove having a U-shaped cross section formed by the outer peripheral surface of the seal member and the opposing surfaces of the pair of glass substrates. The self-control type heating resistor reduces the influence of the ambient temperature and the temperature difference between the liquid crystal and the liquid crystal, thereby accurately detecting the change in the temperature of the liquid crystal and controlling the temperature of the liquid crystal more accurately.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be specifically described based on illustrated embodiments.

FIGS. 1 and 2 show a tunable wavelength filter 1 as one embodiment.

The variable wavelength filter 1 has the same configuration as the above-mentioned conventional variable wavelength filter 100 except for the heating mechanism of the liquid crystal, except for the structure. Therefore, hereinafter, the same components will be described with the same reference numerals.

That is, in the variable wavelength filter 1, a pair of glass substrates 101a and 101b are arranged in parallel and opposed to each other with a seal member 105 interposed therebetween.
A transparent electrode 102, a dielectric reflection film 103, and a liquid crystal alignment film 104 are laminated on each of the opposing surfaces 01a and 101b. Then, the sealing member 105 and the liquid crystal alignment film 1
The liquid crystal 106 is sealed in the space surrounded by the reference numeral 04 and the self-control type heating resistor 2 constituting the heating mechanism is arranged in contact with the outer peripheral portion of the seal member 105 so that the variable wavelength filter 1 is formed. Is roughly configured.

In FIG. 2, reference numeral 107 denotes a reflection film formed on the outer surface of the glass substrate 101a, 101b opposite to the opposite surface, and FIG. 1 shows the anti-reflection film 1 for convenience of explanation.
07, the dielectric reflection film 103, and the liquid crystal alignment film 104 are omitted.

At this time, the transparent electrode 102 and the dielectric reflection film 1
03, the alignment film 104 for liquid crystal, and the sealing member 105 are formed in the same manner as in the related art, and the liquid crystal 106 is a nematic liquid crystal in the same manner as in the related art.

That is, the transparent electrode 102 is made of a glass substrate 10 made of blue plate glass, optical glass, quartz glass or the like.
1a and 101b are formed by sputtering indium tin oxide on the opposing surfaces, and a rectangular voltage applying portion 102a and a belt-like shape from the rectangular voltage applying portion 102a on the non-opposing surfaces of the glass substrates 101a and 101b. And a terminal portion 102b extending therefrom.

The dielectric reflection film 103 is formed of TiO formed on the voltage application portion 102a of the transparent electrode 102 by vapor deposition.
₂ and a multilayer film of SiO ₂ .

Further, the liquid crystal alignment film 104 is formed on the dielectric reflection film 103 by an appropriate alignment treatment agent which is rubbed.

Further, the sealing member 105 is made of an epoxy resin, a phenoxy resin, a polyamide resin, a photocurable resin,
A pair of glass substrates 10 made of an electron beam curable resin or the like.
In order to keep the gap between 1a and 101b constant, a columnar glass spacer having a predetermined diameter may be mixed therein, and may further contain a crosslinking agent, a curing accelerator, a coupling agent, and the like. And this sealing member 105
Is a voltage applying portion 102a of the transparent electrode 102 between the pair of glass substrates 101a and 101b,
3, and a pair of glass substrates 101a, 101
b. The sealing member 105 includes a liquid crystal 1
Injection port 105a for injecting 06 is formed.

Then, the liquid crystal 106 is sealed by the sealing member 105.
Is injected from the injection port 105a, and is sealed in the space between the liquid crystal alignment films 104 surrounded by the seal member 106 by closing the injection port 105a with the sealing material 4.

Further, the self-control type heating resistor 2 is of a self-heating temperature control type having a positive temperature coefficient of resistance, the resistance of which rises according to the heat generation temperature when energized. Specifically, the self-suppressing heating resistor 2 is formed by adding a conductive substance such as carbon black to a synthetic resin having crystallinity such as a polyethylene resin or an ethylene-vinyl acetate copolymer to make it conductive. Can be. The resistance of the self-regulating type heating resistor 2 thus formed increases remarkably at a temperature near the melting point at which the crystal of the synthetic resin is melted, and exhibits self-controllability. For this reason, the self-control type heating resistor 2 can set the heat generation temperature according to the melting point of the synthetic resin by changing the synthetic resin to be used.

The self-control type heating resistor 2 is provided between the outer peripheral surface of the seal member 105 and the pair of glass substrates 101.
a and 101b are arranged in a groove 5 having a U-shaped cross section formed with the opposing surfaces (see FIG. 2), and are arranged so as to surround the seal member 105 in a U-shape. It is connected to a heating terminal portion 3 made of a transparent electrode formed in a strip shape on the upper surfaces of the substrates 101a and 101b. The heating terminals 3 and 3 are connected to a power supply 7 by lead wires 6.

The variable wavelength filter 1 is configured as described above. Next, a specific forming method will be described with reference to FIG. In FIG. 3, for convenience of explanation, the dielectric reflective film 103 and the liquid crystal alignment film 104 are omitted from the laminated structure formed on the glass substrates 101a and 101b.

That is, FIG. 3A shows one glass substrate 101a, and a voltage application section 102a
A self-controlling heating resistor 2 is formed in a U-shape with a margin A where nothing is formed between the transparent electrode 102 and the voltage applying part 102a of the transparent electrode 102. And a heating terminal portion 3 formed of a transparent electrode connected to one end 2a of the self-control type heating resistor 2. This self-control type heating resistor 2 heats and heats the heating resistor 2,
It is formed by applying and drying on the glass substrate 101a by printing or the like, or by sticking the film-shaped heating resistor 2 on the glass substrate 101a.

FIG. 3B shows the other glass substrate 10.
1b, a transparent electrode 102 composed of a voltage applying portion 102a and a terminal portion 102b is formed on an opposing surface thereof, and a seal member 105 is formed so as to surround the voltage applying portion 102a of the transparent electrode 102. A heating terminal 3 made of a transparent electrode connected to the other end 2a of the self-control type heating resistor 2 is formed so as to avoid covering the seal member 105. The sealing member 105 has an injection port 105a for the liquid crystal 106, and the outer periphery of the sealing member 105 is a blank portion B in which nothing is formed.

The pair of glass substrates 101a, 101
Although not shown, the dielectric reflection film 103 and the liquid crystal alignment film 104 are stacked on the voltage application unit 102a of the transparent electrode 102 formed on the opposing surface b as described above.

Then, the other glass substrate 101b is turned upside down, the sealing member 105 is placed in the margin A, the self-control heating resistor 2 is placed in the margin B, and the other end 2a of the self-control heating resistor 2 is placed in the margin B. One glass substrate 10 corresponds to the heating terminal portion 3 provided on the other glass substrate 101b.
1a. This bonding is performed by bonding the sealing member 105 to both glass substrates 101a and 101b. Further, after the liquid crystal 106 is injected from the injection port 105a, the injection port 105a is closed with the sealing material 4 to
Can be obtained.

The tunable wavelength filter 1 thus formed operates as follows.

The tunable wavelength filter 1 is connected to the voltage applying units 102a, 102a via the terminal 102b of the transparent electrode 102.
A voltage is applied between them to change the refractive index of the liquid crystal 106, and the dielectric reflection films 103, 1 in the Fabry-Perot interference system
The resonance wavelength (the wavelength of the transmitted light of the tunable wavelength filter 1) can be selected by changing the optical path length between 03.

Further, since the self-control type heating resistor 2 has a positive temperature coefficient, when energized, it generates heat in accordance with the voltage and resistance, and the temperature rises, and the vicinity of the melting point of the synthetic resin constituting the heating resistor 2 , The resistance increases rapidly and the amount of heat generation is suppressed. When the temperature of the heating resistor 2 decreases, the resistance decreases, the amount of heat generation increases, and the temperature rises. In this way, the self-control type heating resistor 2 maintains the temperature of the liquid crystal 106 constant by self-controlling the amount of heat generated by a change in resistance.

In the variable wavelength filter 1, the self-control type heating resistor 2 is formed in a band shape in a groove 5 having a U-shaped cross section formed by the outer peripheral surface of the seal member 105 and the opposing surfaces of the pair of glass substrates 101a and 101b. Are arranged so that a sufficient heat transfer area can be secured, the influence of the environmental temperature is small, and the temperature difference between the liquid crystal 106 and the liquid crystal 106 is reduced.
The temperature change of the liquid crystal 106 can be accurately controlled by accurately detecting the temperature change of the liquid crystal 106, and thus the fluctuation of the selected wavelength due to the temperature is small, and the wavelength selecting performance is improved.

Further, since the variable wavelength filter 1 uses the self-control type heating resistor 2 as the temperature control means, no additional equipment such as a temperature sensor and / or a temperature control device is required, and the structure is simple and compact. It has become something.

Further, the variable wavelength filter 1 can set the heat generation temperature in accordance with the melting point of the synthetic resin by changing the synthetic resin forming the self-control type heat generating resistor 2, so that the degree of freedom in design is increased. In addition to being enlarged, the self-control type heating resistor 2 can be easily arranged on the tunable wavelength filter 1 by making it into a fluid state or a film state, so that the molding is easy.

[0051]

According to the present invention, as described in detail above, the following effects can be obtained.

That is, according to the first aspect of the present invention,
Since the self-regulating heating resistor having a positive temperature coefficient of resistance is disposed in contact with the outer peripheral portion of the sealing member in which the liquid crystal is sealed, the heating resistor accurately detects a change in the temperature of the liquid crystal and accurately detects the liquid crystal. The temperature can be controlled well, and as a result, it is possible to provide a variable wavelength filter in which the variation of the selected wavelength due to the temperature is small and the wavelength selection performance is improved.

In addition, according to the first aspect of the present invention, since a self-control type heating resistor is used as the heating element, ancillary equipment such as a temperature sensor and a temperature control device becomes unnecessary.
As a result, a compact tunable wavelength filter having a simple structure can be provided.

According to the second aspect of the present invention, the self-control type heating resistor is formed by adding a conductive substance to a crystalline synthetic resin to make it conductive, so that the synthetic resin used is changed. By doing so, it is possible to set the heat generation temperature in accordance with the melting point of the synthetic resin, thereby increasing the degree of freedom of design. As a result, it is possible to provide a tunable wavelength filter that is easier to form in addition to the effects of the second aspect of the present invention.

According to the third aspect of the present invention, since the self-control type heating resistor is arranged so as to be continuous in a band along the outer peripheral portion of the seal member, sufficient heat transfer for heating the liquid crystal is achieved. It is possible to provide a tunable wavelength filter in which the area of the liquid crystal can be kept constant and the temperature of the liquid crystal can be kept constant. Can be.

Further, in the invention according to claim 4, the self-control type heating resistor is arranged in a groove having a U-shaped cross section formed by the outer peripheral surface of the seal member and the opposing surfaces of the pair of glass substrates. The self-regulating heating resistor is less affected by the ambient temperature, reduces the temperature difference with the liquid crystal, accurately detects the temperature change of the liquid crystal, and can control the temperature of the liquid crystal more accurately. As a result, In addition to the effects of the first aspect of the present invention, it is possible to provide a tunable wavelength filter having small temperature dependence and further improved wavelength selection performance.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a variable wavelength filter as one embodiment.

FIG. 2 is a sectional view taken along line II-II in FIG.

3A and 3B are conceptual diagrams of a pair of glass substrates constituting the variable wavelength filter of FIG. 1; FIG.
(B) shows the other glass substrate, respectively.

FIG. 4 is a perspective view of a conventional variable wavelength filter.

FIG. 5 is a sectional view taken along line VV in FIG. 4;

FIG. 6 is a conceptual diagram of liquid crystal molecules.

FIG. 7 is a conceptual diagram of the variable wavelength filter of FIG. 4,
(A) shows the state when no voltage is applied, and (b) shows the state when a voltage is applied.

FIG. 8 is a graph showing the temperature dependence of the refractive index of the liquid crystal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable wavelength filter 2 Self-control type heating resistor 3 Heating terminal 5 Groove 101a, 101b Glass substrate 102 Transparent electrode 103 Dielectric reflective film 104 Liquid crystal alignment film 105 Seal member 106 Liquid crystal

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) G02F 1/13 505 G02F 1/133 G02F 1/1333 G02F 1/1339 G09F 9/30 G09G 3/18 G09G 3 / 36

Claims (4)

(57) [Claims] 1. A pair of glass substrates each having a transparent electrode, a dielectric reflection film, and an alignment film for liquid crystal laminated on an opposing surface are disposed to face each other via a seal member, and the pair of glass substrates surrounded by the seal member. A variable wavelength filter in which a liquid crystal is sealed between glass substrates, wherein a self-control type heating resistor having a positive temperature coefficient of resistance is disposed in contact with an outer peripheral portion of the seal member. 2. The variable wavelength filter according to claim 1, wherein the self-control type heating resistor is formed by adding a conductive substance to a synthetic resin having crystallinity to make the synthetic resin conductive. Variable wavelength filter. 3. The tunable wavelength filter according to claim 1, wherein said self-control type heating resistor is arranged so as to be continuous in a band along an outer peripheral portion of said seal member. Variable wavelength filter. 4. The tunable wavelength filter according to claim 1, wherein the self-control type heating resistor is formed by an outer peripheral surface of the seal member and an opposing surface of the pair of glass substrates. A tunable wavelength filter, which is disposed in a groove having a U-shaped cross section.