JP2002196303A - Wavelength selective module and wavelength selective device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength selective module which enables the switching of selection and non-selection of light of a specified wavelength and a wavelength selective device which can arbitrarily select the light of one kind or more from a optical signal containing plural kinds of light which are different in center wavelength and can suppress the deterioration of intensity of the selected light. SOLUTION: This wavelength selective module 21 which selects the light of specified wavelength from the optical signal is provided with a two-core collimator 23 and a liquid crystal cell 22. The liquid crystal cell 22 divides the light of specified wavelength among the optical signal which is emitted in parallel light from the two-core collimator 23 into left and right circularly polarized light and has cholesteric liquid crystal 26 which changes in accordance with the voltage applied to transparent electrodes 27 between the first state where the circularly polarized light in the direction of optical rotation which is the same as a helical direction is reflected and the second state where the optical signal is transmitted. When the voltage is made so as not to be applied to the cholesteric liquid crystal 26, the same liquid crystal 26 changes into the first state and the light of specified wavelength is reflected by the same liquid crystal 26 and is taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element used for optical communication, for example, wavelength division multiplexing communication, and more particularly, to a wavelength selector for selecting light of a specific wavelength from an optical signal containing a plurality of types of light having different center wavelengths. The present invention relates to a module and a wavelength selection device for selecting one or more types of light having different wavelengths from the same optical signal.

[0002]

2. Description of the Related Art Conventionally, an optical element using an optical fiber or a collimator lens has been used as an optical communication device. As optical communication becomes more widespread in the future, it will become increasingly necessary to downsize and integrate optical communication equipment. Further, optical communication requires a technique for selectively demultiplexing light for each wavelength. As a filter module therefor, a module using a multilayer filter in which high-refractive-index dielectric layers and low-refractive-index dielectric layers are alternately laminated, for example, an edge filter, a narrow band filter, or the like is known (see FIG. 11). ).

The conventional filter module 10 shown in FIG.
Numeral 0 selects light of a specific wavelength from optical signals including a plurality of types of light (light of λ1 to λn) having different center wavelengths.
And a multilayer filter 103 provided between both collimators
Consists of The two-core collimator 101 includes a two-core capillary 104 holding two optical fibers, and a collimator lens 105 including a rod lens or the like. The single-core collimator 102 includes a single-core capillary 106 holding one optical fiber and a collimator lens 107.
Consists of Reference numeral 108 denotes a sleeve. In this filter module 100, the center wavelength is λ1 to λn
Out of the optical signal including the light of the specific wavelength (for example, λ1) is transmitted, and the light of the remaining wavelengths λ2 to λn is reflected.

A plurality of filter modules 100 for transmitting lights having different center wavelengths are prepared, and the plurality of filter modules 100A, 100B,
There is known a wavelength selecting device in which 100C,... Are connected in cascade as shown in FIG. In this device, light having a center wavelength λ1 is selected and transmitted by the filter module 100A, and the remaining light (light having wavelengths λ2 to λn) is reflected.
2 light is selected and transmitted, and the remaining light (light of [lambda] 3 to [lambda] n) is reflected by the filter module 100C.
Only the light having the center wavelength λ3 is selected and transmitted, and the remaining light (λ
4 to λn) are reflected. Hereinafter, similarly, each light having a center wavelength of λ4, λ5,... Λn is sequentially selected.

[0005]

In the above-described conventional filter module 100 shown in FIG. 11, light of a specific wavelength (here, light of λ1) determined by the wavelength selection characteristics of the multilayer filter 103 is always selected. You. For this reason,
When such a filter module is used, there is a problem that selection and non-selection of light of a specific wavelength cannot be switched.

The conventional wavelength selection device shown in FIG. 12 has the following problems. (A) A plurality (n) of filter modules 100A,
100B, 100C,...
The lights of 1, λ2, λ3, ... are always selected,
One or more types of light cannot be arbitrarily selected from optical signals including light of λ1 to λn.

(B) Since an optical signal containing light not selected by each filter module is reflected by the same module and enters the next filter module, there is a loss every time the optical signal is reflected by each filter module. These losses are added. That is, since the intensity of each of the lights λ2 to λn decreases due to the loss when reflected by the filter module 100A, the light of λ2 selected by the filter module 100B is lower than the initial intensity.
Each light of λ3 to λn is transmitted to the filter module 100.
Since the intensity is further reduced due to the loss when the light is reflected by B, the light of λ3 selected by the filter module 100C is further reduced in intensity than the light of λ2. In this way, the intensity of light that is selected later is gradually reduced.

For this reason, there is a problem that as the number of filter modules connected in multiple stages increases, the loss of light of each selected wavelength (attenuation of light intensity) increases. In order to avoid such a problem, it is necessary to devise a way of connecting each filter module, and when the intensity of the selected light becomes smaller than a required value, the intensity of the light is amplified by an amplifier. I needed to. Therefore, when constructing an optical communication system or the like having a large amount of information, it has been a major obstacle.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a wavelength selection module capable of switching between selection and non-selection of light of a specific wavelength. Another object of the present invention is to provide a wavelength selection device which can arbitrarily select one or more types of light from an optical signal including a plurality of types of light having different center wavelengths and can suppress a decrease in intensity of the selected light. It is in.

[0010]

According to a first aspect of the present invention, there is provided a wavelength selection module for selecting light of a specific wavelength from an optical signal including a plurality of types of light having different center wavelengths. A collimator that converts the optical signal into parallel light, and a light that emits a specific wavelength of the optical signal emitted from the collimator into right and left circularly polarized light and reflects circularly polarized light having the same optical rotation direction as the helical direction. A liquid crystal cell having a liquid crystal that changes in accordance with externally applied physical energy between a first state and a second state in which the optical signal is transmitted; and wherein the physical energy applied to the liquid crystal is changed. By changing the liquid crystal to the first state, light of the specific wavelength is reflected by the liquid crystal and taken out.

According to this structure, by changing the physical energy applied to the liquid crystal to change the liquid crystal to the first state, only the circularly polarized light having the same optical rotation direction as the helical direction out of the light of the specific wavelength. It is reflected and the rest of the light is transmitted. Further, by changing the liquid crystal to the second state by changing the physical energy, light of a specific wavelength is not selected, and passes through the liquid crystal together with light of another wavelength. In this manner, selection and non-selection of light of a specific wavelength can be switched, and the optical element can be used in a wide range of applications as an optical element for optical communication. The physical energy applied to the liquid crystal of the liquid crystal cell includes heat, electric field, magnetic field, force, and the like.

According to a second aspect of the present invention, in the wavelength selection module according to the first aspect, the liquid crystal cell has a pair of transparent electrodes provided on opposing surfaces of the liquid crystal and applies the voltage to the transparent electrodes. It is characterized in that the voltage as the physical energy is changed. According to this configuration, the selection and non-selection of the light of the specific wavelength is switched by changing the voltage applied to the transparent electrode, for example, by turning on and off, so that the switching is facilitated. Therefore, it is easier to use the optical element for optical communication in a wide range of applications.

According to a third aspect of the present invention, in the wavelength selection module according to the first or second aspect, the liquid crystal is a cholesteric liquid crystal or a chiral nematic liquid crystal.

According to a fourth aspect of the present invention, in the wavelength selection module according to any one of the first to third aspects, the collimator disposed on the incident side of the liquid crystal cell transmits the optical signal to the liquid crystal cell. Is a two-core collimator that makes the light incident substantially perpendicularly to the collimator. According to this configuration,
The light of a specific wavelength selected by being reflected by the liquid crystal can be condensed and extracted by the two-core collimator, so that the selected light can be easily sent to another optical element for optical communication or the like. Therefore, since the optical coupling with the optical fiber can be realized easily and with high efficiency, it is possible to contribute to facilitating the construction of the optical communication system.

According to a fifth aspect of the present invention, in the wavelength selection module according to any one of the first to fourth aspects, the light transmitted through the liquid crystal cell is condensed on the emission side of the liquid crystal cell. A one-core collimator for coupling to a fiber is provided. According to this configuration, the optical signal can be transmitted to another optical element for optical communication or the like by condensing the transmitted light of the liquid crystal by the single-core collimator and coupling the condensed light to the optical fiber. This also makes it possible to easily and efficiently realize optical coupling with an optical fiber, thereby contributing to facilitating the construction of an optical communication system.

According to a sixth aspect of the present invention, in the wavelength selection module according to any one of the first to third aspects, the collimator disposed on the incident side of the liquid crystal cell transmits the optical signal to the liquid crystal cell. And a single-core collimator for obliquely entering the light into the optical fiber, and a single-core collimator for condensing light of a specific wavelength reflected by the liquid crystal cell and coupling the collected light to an optical fiber. According to this configuration, two collimators arranged on the incident side of the liquid crystal cell use two single-core collimators, but the alignment of the optical fiber becomes easier than when a two-core collimator is used, Manufacturing becomes easier.

According to a seventh aspect of the present invention, in the wavelength selection module according to the sixth aspect, the transmitted light obliquely emitted from the liquid crystal cell is condensed and coupled to the optical fiber on the emission side of the liquid crystal cell. A single-core collimator is disposed. According to this configuration, the transmitted light obliquely emitted from the liquid crystal cell is condensed by the single-core collimator and coupled to the optical fiber, so that an optical signal can be transmitted to another optical element for optical communication or the like. Accordingly, optical coupling with an optical fiber can be realized easily and with high efficiency, which can contribute to facilitation of construction of an optical communication system.

According to an eighth aspect of the present invention, in the wavelength selection module according to any one of the first to seventh aspects, the optical signal is supplied to the incident side of the liquid crystal cell by circularly polarizing in the same optical rotation direction as the helical direction. A wavelength plate for converting the light into a wavelength is disposed. According to this configuration, the optical signal is converted into circularly polarized light having the same optical rotation direction as the helical direction by the wave plate and enters the liquid crystal cell. Therefore, when the liquid crystal is in the first state, all of the light of the specific wavelength converted into the circularly polarized light is reflected by the liquid crystal. Therefore, the reflection efficiency of the selected light having the specific wavelength can be made substantially 100%.

According to a ninth aspect of the present invention, in the wavelength selection module according to the eighth aspect, a wavelength plate for returning the circularly polarized light converted by the wavelength plate to unpolarized light is disposed on the emission side of the liquid crystal cell. It is characterized by being. According to this configuration, light transmitted through the liquid crystal (circularly polarized light) is returned to non-polarized light by the wave plate provided on the emission side of the liquid crystal cell and is emitted through the collimator. There is no need to return circularly polarized light to non-polarized light with a wavelength plate or the like on the optical communication optical element side such as another wavelength selection module that receives the light.

According to a tenth aspect of the present invention, there is provided a wavelength selecting module according to any one of the first to ninth aspects, wherein an optical signal including a plurality of types of light having different center wavelengths is provided.
A wavelength selection device for selecting one or more types of light having different wavelengths, wherein each of the plurality of wavelength selection modules is vertically connected via an optical fiber and the liquid crystal is in the first state. It is characterized in that it is configured to reflect light of different wavelengths.

According to this configuration, of the plurality of wavelength selection modules, physical energy such as a voltage applied to the liquid crystal of the wavelength selection module corresponding to the light of a desired wavelength is changed to change the liquid crystal into the first wavelength. By making the state
One or more types of light having different wavelengths can be arbitrarily selected from an optical signal including a plurality of types of light having different center wavelengths.
Light having a wavelength selected by one of the plurality of wavelength selection modules has some reflection loss when reflected by the liquid crystal, but light having a wavelength not selected has no loss. In other words, the light of each wavelength passes through the liquid crystal of the other wavelength selection module as it is until the light reaches the liquid crystal of the selected wavelength selection module, so that the intensity gradually decreases until the light reaches the liquid crystal of the other wavelength selection module. Never. Therefore, a decrease in the intensity of light of each wavelength can be suppressed. As a result, the present invention is particularly effective when the wavelength selection modules are connected in multiple stages to increase the types of selectable wavelengths and to construct a large-scale optical communication system with a large amount of information.

According to an eleventh aspect of the present invention, in the wavelength selecting device according to the tenth aspect, the voltage applied to each liquid crystal of the plurality of wavelength selection modules is individually changed to thereby select the plurality of wavelength selection modules. At least one liquid crystal of the module is changed to the first state. According to this configuration, the voltage applied to the transparent electrode of the wavelength selection module corresponding to the light of the wavelength desired to be selected among the plurality of wavelength selection modules is changed, for example, turned on and off, and the liquid crystal is changed to the first liquid crystal. By setting the state, one or more types of light having different wavelengths can be easily selected from an optical signal including a plurality of types of light having different center wavelengths.

According to a twelfth aspect of the present invention, in the wavelength selection device according to the tenth or eleventh aspect, the optical signal is applied to the incident side of each liquid crystal cell of the plurality of wavelength selection modules in a helical direction of the liquid crystal. And a wavelength plate that converts the circularly polarized light converted by the wavelength plate back into unpolarized light is disposed on the emission side thereof.

According to this configuration, each of the plurality of wavelength selection modules has a wave plate on each of the entrance side and the exit side of the liquid crystal cell. The reflection efficiency of the selected light that is reflected and selected can be made substantially 100%. Thereby, the loss of light of each wavelength can be further suppressed,
This is even more effective when constructing a large-scale optical communication system. Light transmitted through the liquid crystal is right-circularly polarized light or left-circularly polarized light, but this light is returned to non-polarized light by a wave plate provided on the exit side of the liquid crystal cell and exits through a collimator. Therefore, it is not necessary to return the circularly polarized light to non-polarized light using a wavelength plate or the like on the optical communication optical element side such as another wavelength selection module that receives the emitted light.

According to a thirteenth aspect of the present invention, an optical signal including a plurality of types of light having different center wavelengths is converted into one light having different wavelengths.
A wavelength selecting device for selecting more than one type, comprising: a collimator that converts the optical signal into parallel light; and a liquid crystal cell unit that reflects one or more types of light having different wavelengths among the optical signals emitted from the collimator. A liquid crystal cell unit, wherein the liquid crystal cell unit divides light of a specific wavelength in the optical signal into left and right circularly polarized lights, and reflects a circularly polarized light in the same optical rotation direction as the helical direction of the liquid crystal; The second signal is transmitted
A plurality of sets of a liquid crystal cell comprising a liquid crystal that changes according to physical energy applied from the outside and a pair of transparent electrodes provided on opposing surfaces of the liquid crystal are stacked. The voltage applied to each transparent electrode of the plurality of sets of liquid crystal cells is individually changed to change at least one liquid crystal of the plurality of sets of liquid crystal cells to the first state.

According to this configuration, by individually changing the voltage applied to the transparent electrode of each liquid crystal cell, one or more types of light having different wavelengths can be arbitrarily selected from an optical signal including a plurality of types of light having different center wavelengths. Can be selected. Also,
For light having a wavelength selected by one of the plurality of sets of liquid crystal cells, it is desirable to use a suitable resin or the like to match the refractive index between the liquid crystal cells. In this case, there is some reflection loss when the light is reflected by the liquid crystal, but there is no loss for light of a wavelength not selected. In other words, since the light of each wavelength passes through the liquid crystal of another liquid crystal cell as it is until the light reaches the liquid crystal of the selected liquid crystal cell, the intensity gradually decreases until the light reaches the selected liquid crystal cell. Absent. Therefore, a decrease in the intensity of light of each wavelength can be suppressed. As a result, it is particularly effective when the number of selectable wavelengths is increased by increasing the number of sets of liquid crystal cells to be stacked to construct a large-scale optical communication system with a large amount of information.

According to a fourteenth aspect of the present invention, in the wavelength selection device according to the thirteenth aspect, the optical signal is converted into circularly polarized light having the same optical rotation direction as the helical direction of the liquid crystal on the incident side of the liquid crystal cell unit. It is characterized in that a wavelength plate for conversion is arranged.

According to this structure, since the wavelength plate is provided on the incident side of the liquid crystal cell unit, in each liquid crystal cell, all of the light of each wavelength converted into the circularly polarized light respectively correspond to the corresponding liquid crystal cell. Reflected by the liquid crystal. For this reason, the reflection efficiency of the selected light selected in each liquid crystal cell can be made approximately 100%. At the same time, one wavelength plate may be provided for a plurality of sets of liquid crystal cells constituting a liquid crystal cell unit. Therefore, even when the number of sets of liquid crystal cells is increased, it is not necessary to increase the number of wavelength plates. Therefore, the loss of light of each wavelength selected in each liquid crystal cell can be suppressed, and the large-scale optical communication system described above can be constructed with a small number of components.

According to a fifteenth aspect of the present invention, in the wavelength selection device according to the thirteenth or fourteenth aspect, the circularly polarized light converted by the wavelength plate is converted into a non-polarized light on the emission side of the liquid crystal cell unit. The wave plate for returning to the above is disposed. According to this configuration, the outgoing light of the liquid crystal cell unit can be returned to unpolarized light by the wave plate and sent to another optical element for optical communication or the like. There is no need to convert to light.

The invention according to claim 16 is the invention according to claims 13 to 1
5. In the wavelength selection device according to any one of the items 5,
The collimator disposed on the incident side of the liquid crystal cell unit is a single-core collimator, and the collimator is connected to an optical circulator having at least three terminals via one optical fiber. According to this configuration,
Since the optical circulator and the wavelength selector can be connected by one optical fiber, a single-core collimator may be provided on the incident side of the liquid crystal cell unit instead of a two-core collimator. Therefore, the work of aligning the optical fiber on the incident side becomes easy, and the configuration can be simplified.

[0031] The invention according to claim 17 is the invention according to claims 13 to 1.
7. The wavelength selecting device according to claim 6, wherein a single-core collimator that collects light transmitted through the liquid crystal cell unit and couples the transmitted light to the optical fiber is disposed on an emission side of the liquid crystal cell unit. Features. According to this configuration,
Light emitted from the liquid crystal cell unit is condensed by a single-core collimator and coupled to an optical fiber, whereby an optical signal can be transmitted to another optical element for optical communication or the like. Accordingly, optical coupling with an optical fiber can be realized easily and with high efficiency, which can contribute to facilitation of construction of an optical communication system.

[0032]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] A wavelength selection module according to a first embodiment will be described with reference to FIG. The wavelength selection module 21 includes a plurality of types of light (λ1 to λ
n), light of a specific wavelength (for example, light of λ1) is selected from the optical signal (mixed light) including n). The wavelength selection module 21 includes a liquid crystal cell 22, a two-core collimator 23 arranged on the incident side of the cell, a one-core collimator 24 arranged on the emission side, and a holding member such as a sleeve for holding these. Or case 25).

The liquid crystal cell (LC cell) 22 has a cholesteric liquid crystal 26 and a pair of transparent electrodes 27 provided on opposing surfaces of the liquid crystal 26. Both transparent electrodes 27,
27 are connected to terminals 28 and 28, respectively.
By controlling on / off of a pulse signal as a voltage signal input to these terminals 28, 28, a voltage applied between the transparent electrodes 27, 27 can be turned on / off.

The cholesteric liquid crystal 26 divides the light of a specific wavelength (λ1) of the optical signal emitted from the two-core collimator 23 as parallel light into two circularly polarized lights, left-handed light and right-handed light. And a "selective reflection effect" for selectively reflecting circularly polarized light having the same optical rotation direction as the helical direction for light of the specific wavelength.

That is, the cholesteric liquid crystal 26 divides the light of a specific wavelength in the incident optical signal into left and right circularly polarized light, and selectively reflects circularly polarized light having the same optical rotation direction as the helical direction (planar texture). ) And a second state (homeotropic texture) in which an optical signal is transmitted. The liquid crystal changes according to the voltage applied to the transparent electrodes 27.

Here, assuming that the optical rotation direction of the circularly polarized light is defined toward the incident light, and the cholesteric liquid crystal 26 is a right-handed liquid crystal and its helical direction is right, a left circularly polarized light having an optical rotation direction opposite to the helical direction is provided. Is transmitted, and right-handed circularly polarized light having the same optical rotation direction as the helical direction is selectively scattered and reflected.

The maximum scattering reflection (selective light scattering) occurs at the next wavelength λ0 (the maximum selective light scattering wavelength λ0 shown in FIG. 10). λ0 = n · p (1) where p is the helical pitch of the cholesteric liquid crystal 26. n is an average refractive index in the plane perpendicular to the helical axis of the liquid crystal 26, the refractive index ^{n, n = {(n‖) 2} + (n⊥) 2} 1/2 / 2 ... (2) Equation It is represented by

The wavelength bandwidth Δλ of the scattered reflected light is represented by the following equation: Δλ = Δn · p (3) Here, Δn = n‖−n⊥.

In this embodiment, the maximum selected light scattering wavelength λ
The average refractive index n, the helical pitch p, and the like are set so that 0 becomes the specific wavelength λ1, for example. The cholesteric liquid crystal 26, for example, transmits all light when a voltage is applied between the transparent electrodes 27 and 27, and when no voltage is applied during that time, the cholesteric liquid crystal 26 receives light of a specific wavelength (λ1). The right circularly polarized light having the same optical rotation direction as the helical direction is reflected (scattered and reflected).

The two-core collimator 23 includes a two-core capillary 31 holding two optical fibers 29 and 30 and a collimator lens 32 such as a rod lens. The converted optical signal is vertically incident on the liquid crystal cell 22. The light reflected by the liquid crystal cell 22 is condensed by the collimator lens 32 and is incident (coupled) on the optical fiber 30.

On the other hand, the single-core collimator 24 includes a single-core capillary 34 holding one optical fiber 33 and a collimator lens 35 such as a rod lens.
The light transmitted through 2 is condensed by the collimator lens 35 and enters the optical fiber 33.

According to the first embodiment configured as described above, the following operation and effect can be obtained. (A) Assuming that a voltage is applied between the transparent electrodes 27, the cholesteric liquid crystal 26 is in the second state. Therefore, when an optical signal including a plurality of types of light (light of λ1 to λn) passes through the optical fiber 29, is collimated by the collimator lens 32, and is vertically incident on the liquid crystal cell 22, the optical signal is transmitted to the liquid crystal cell 22. Through the collimator lens 3
The light is condensed at 5 and enters the optical fiber 33. That is,
In this case, light of any wavelength included in the optical signal is not selected.

When no voltage is applied between the transparent electrodes 27, the cholesteric liquid crystal 26 enters the first state. Therefore, when the optical signal is vertically incident on the liquid crystal cell 22, the cholesteric liquid crystal 26 divides the light of the specific wavelength (λ1) of the optical signal into left and right circularly polarized light, and right circularly polarized light having the same optical rotation direction as the helical direction. (Right circularly polarized light of wavelength λ1) is selectively reflected. The light of the selected specific wavelength (λ1) is condensed by the collimator lens 32 and
Incident on.

In this manner, the pulse signal input to both terminals 28, 28 is turned off, and the voltage applied between both transparent electrodes is set to 0, so that light of a specific wavelength (for example, light of λ1) is extracted from optical fiber 30. be able to.

Therefore, selection and non-selection of light having a specific wavelength can be easily switched, and the optical element can be used in a wide range of applications as an optical element for optical communication. (B) By appropriately setting the average refractive index n, the helical pitch p, and the like, the wavelength selection module 21 having different wavelengths of light reflected by the cholesteric liquid crystal 26 can be easily manufactured.

(C) Since the two-core collimator 23 is disposed on the incident side of the liquid crystal cell 22, the cholesteric liquid crystal 2
The light of the specific wavelength reflected by the
And can be extracted from the optical fiber 30.
Therefore, since the optical coupling with the optical fiber can be realized easily and with high efficiency, it is possible to contribute to facilitating the construction of the optical communication system.

(D) Since the single-core collimator 24 is disposed on the emission side of the liquid crystal cell 22, the cholesteric liquid crystal 2
The transmitted light of No. 6 can be collected and made incident on the optical fiber 33. Thus, an optical signal can be easily transmitted to another optical communication optical element such as a wavelength selection module. This also makes it possible to easily and efficiently realize optical coupling with an optical fiber, thereby contributing to facilitating the construction of an optical communication system.

[Second Embodiment] Next, a wavelength selection module according to a second embodiment will be described with reference to FIG. In the wavelength selection module 21A according to the present embodiment, the wavelength plates 40, 4 are provided outside the transparent electrodes 27, 27 of the liquid crystal cell 22.
1 are arranged. The wave plate 40 includes the collimator lens 32 and the transparent electrode 2 on the incident side of the liquid crystal cell 22.
7 is arranged. Further, the wave plate 41 is disposed between the transparent electrode 27 on the emission side of the liquid crystal cell 22 and the collimator lens 35.

The wave plate 40 is a polarizing plate that converts an optical signal collimated by the collimator lens 32 into circularly polarized light having the same optical rotation direction as the helical direction of the cholesteric liquid crystal 26. In this example, since the cholesteric liquid crystal 26 is a dextrorotatory liquid crystal and the helical direction is right, the wave plate 40 converts the optical signal into right circularly polarized light. On the other hand, the wave plate 41 is
It is a polarizing plate for converting right circularly polarized light, which is converted into right circularly polarized light at 0 and transmits through the cholesteric liquid crystal 26, to unpolarized light.

The other structure of this embodiment is the same as that of the first embodiment. According to the second embodiment configured as described above, the following operation and effect can be obtained. (E) In the first embodiment, when the voltage applied between the transparent electrodes 27 and 27 is set to 0, the light reflected by the liquid crystal cell 22 of the cholesteric liquid crystal 26 is changed right and left by the cholesteric liquid crystal 26 in the first state. Since the light of the specific wavelength (λ1) divided into the circularly polarized light is right circularly polarized light, the reflection efficiency of the selected light is about 50%.

On the other hand, according to the second embodiment, the optical signal collimated by the collimator lens 32 is
The light is converted into right circularly polarized light by 0 and enters the liquid crystal cell 22. Therefore, when the applied voltage is set to 0, all of the light of the specific wavelength (λ1) converted into right-handed circularly polarized light is reflected by the liquid crystal cell 22. Therefore, the reflection efficiency of the selected light having the specific wavelength can be made substantially 100%.

(F) The light (right circularly polarized light) of the specific wavelength (λ1) reflected by the cholesteric liquid crystal 26 is returned to non-polarized light by the wave plate 40 and is emitted from the optical fiber 30. There is no need to return the circularly polarized light to non-polarized light with a wave plate or the like on the other optical communication optical element receiving the emitted light. Therefore, since the optical coupling with the optical fiber can be realized easily and with high efficiency, it is possible to contribute to facilitating the construction of the optical communication system.

(G) The light transmitted through the liquid crystal cell 22 is right circularly polarized light. This light is returned to non-polarized light by the wave plate 41 and is emitted from the optical fiber 33.
There is no need to return the circularly polarized light to non-polarized light with a wave plate or the like on the optical communication optical element side such as another wavelength selection module that receives the emitted light. This also makes it possible to easily and efficiently realize optical coupling with an optical fiber, thereby contributing to facilitating the construction of an optical communication system.

[Third Embodiment] Next, a third embodiment will be described with reference to FIG. In the wavelength selection module 21B according to the present embodiment, on the incident side of the liquid crystal cell 22, a single-core collimator 50 that converts an optical signal into parallel light and obliquely enters the liquid crystal cell 22, and a specific wavelength reflected by the liquid crystal cell 22 And a single-core collimator 51 for condensing and emitting the light. Further, a single-core collimator 52 that condenses the light transmitted obliquely through the cholesteric liquid crystal 26 and emits the light obliquely is disposed on the emission side of the liquid crystal cell 22.

The single-core collimator 50 includes a single-core capillary 54 for holding one optical fiber 53 and a collimator lens 55. The single-core collimator 51 includes a single-core capillary 57 that holds one optical fiber 56 and a collimator lens 58. The single-core collimator 52 includes a single-core capillary 60 that holds one optical fiber 59 and a collimator lens 61. Other configurations are the same as those of the first embodiment.

According to the third embodiment configured as described above, the following operation and effect can be obtained. (H) The collimator arranged on the incident side of the liquid crystal cell 22 is
Two single-core collimators are used, but the work of adjusting (aligning) the optical fibers 53 and 56 and the collimator lenses 55 and 58 is easier than in the case of using a two-core collimator, and the manufacturing becomes easier. .

[Fourth Embodiment] Next, a wavelength selector according to a fourth embodiment of the present invention will be described with reference to FIGS.

This wavelength selecting apparatus has the same wavelength selecting modules M1 to M4 as the wavelength selecting module 21A shown in FIG.
(In this example, four), and one or more types of light having different wavelengths are selected from an optical signal including a plurality of types of light (light of λ1 to λ4) having different center wavelengths.

The four wavelength selection modules M1 to M4 are:
They are connected in cascade via optical fibers 65, 66, 67. In addition, four wavelength selection modules M1 to M
Each of the light sources 4 has a different wavelength.

That is, four wavelength selection modules M1
To M4 are the average refractive index n and the helical pitch p of the cholesteric liquid crystal 26 of each liquid crystal cell 22 (LC1 to LC4).
The cholesteric liquid crystal 2
The wavelengths of the light reflected and selected at 6 are different from each other. For example, in this example, each cholesteric liquid crystal 2 of the wavelength selection module M1, M2, M3, M4
6, light of wavelengths λ1, λ2, λ3, and λ4 are respectively reflected and selected.

The four wavelength selection modules M1 to M
4, a pulse signal input to each terminal 28, 28,
A controller 70 for controlling turning off is provided. The four wavelength selection modules M1 to M4 are held in one case 68, thereby forming one modularized wavelength selection device.

According to the fourth embodiment configured as described above, the following operation and effect can be obtained. (I) When selecting only one type of light, for example, light of wavelength λ1, the controller 70 turns off the pulse signal output to the terminals 28, 28 of the wavelength selection module M1, and sets the transparent electrode 27 of the module M1. , 27 are set to zero. Other wavelength selection modules M2 to M
A pulse signal is output to each of the terminals 28, 28. As a result, only the cholesteric liquid crystal 26 of the wavelength selection module M1 enters the first state. Therefore, of the light (λ1 to λ4) converted into right circularly polarized light by the wavelength plate 40, the light of the wavelength λ1 is reflected by the cholesteric liquid crystal 26 of the wavelength selection module M1, and the reflected light is unpolarized by the wavelength plate 40. , And is collected and incident on the optical fiber 30.

When two or more types of light having different wavelengths, for example, light having wavelengths λ1 and λ2, are simultaneously selected, the controller 70 supplies a pulse signal to be output to the terminals 28 and 28 of the wavelength selection modules M1 and M2. Off, and the terminals 28, 28 of the other wavelength selection modules M3, M4.
Outputs a pulse signal. Thereby, each cholesteric liquid crystal 26 of the wavelength selection modules M1 and M2 is
Respectively enter the first state. For this reason, light of wavelengths λ1 and λ2, which are reflected by the cholesteric liquid crystals 26 of the wavelength selection modules M1 and M2 and returned to unpolarized light by the wavelength plate 40, respectively, are individually emitted from the modules M1 and M2. .

When only the light of the wavelength λ3 is selected, the controller 70 turns off the pulse signal output to each terminal 28 of the wavelength selection module M3.
As a result, only the cholesteric liquid crystal 26 of the wavelength selection module M3 enters the first state. Therefore, the light of the wavelength λ3 reflected by the cholesteric liquid crystal 26 of the wavelength selection module M3 is emitted from the module M3.

Therefore, by controlling the voltage applied to the transparent electrode of each wavelength selection module, an optical signal including a plurality of types of light (λ1 to λ4) having different center wavelengths can be obtained.
One or more types of light having different wavelengths can be arbitrarily selected.

In the prior art shown in FIG. 12, as described above, there is a loss each time an optical signal is reflected by each filter module, and such losses are added, and the order of selection is later. The light gradually decreases in intensity. For this reason, the loss (light intensity attenuation) of light of each selected wavelength increases as the number of filter modules connected in multiple stages increases.

On the other hand, according to the fourth embodiment, for light having a wavelength selected by any of the wavelength selection modules M1 to M4, there is some reflection loss when reflected by the cholesteric liquid crystal 26. There is no loss for light of wavelengths not selected. That is, the light of each wavelength passes through the cholesteric liquid crystal 26 of the other wavelength selection module as it is until the light reaches the cholesteric liquid crystal 26 of the wavelength selection module from which the light is selected. It does not decrease gradually.

More specifically, when the light having the wavelength λ1 is selected by the wavelength selection module M1, the light having the other wavelengths λ2 to λ4 is transmitted through the cholesteric liquid crystal 26 of the module M1 without loss. The corresponding modules M2 to M4 are reached. Therefore, a decrease in the intensity of light of each wavelength can be suppressed. As a result, wavelength selection modules are connected in multiple stages to increase the types of wavelengths that can be selected,
This is particularly effective when constructing a large-scale optical communication system having a large amount of information.

(L) Each wavelength selection module M1 to M4
Has the above-mentioned wavelength plates 40 and 41, respectively, so that the reflection efficiency of the selected light selected by each of the modules M1 to M4 can be made approximately 100%. by this,
The loss of light of each wavelength can be further suppressed, which is more effective when constructing the large-scale optical communication system described above.

[Fifth Embodiment] Next, a wavelength selecting apparatus according to a fifth embodiment will be described with reference to FIGS. This wavelength selection device is a wavelength selection module 21 shown in FIG.
A plurality (four in this example) of the same wavelength selection modules M1 to M4, and a plurality of types of light (λ1 to
One or more types of light having different wavelengths are selected from the optical signal including the light of λ4).

(E) According to this embodiment, as compared with the fourth embodiment, the reflection efficiency of the selected light selected by each of the wavelength selection modules M1 to M4 is about 50%. Although it is disadvantageous, it is advantageous in that the number of parts is small because the wave plates 40 and 41 are not provided, and the device can be manufactured at a low cost.

[Sixth Embodiment] Next, a wavelength selecting apparatus according to a sixth embodiment of the present invention will be described with reference to FIGS. This wavelength selection device, similar to the wavelength selection device of the fifth embodiment, has a plurality of types of light (λ1 to
One or more types of light having different wavelengths are selected from the optical signal including the light of λ4).

This wavelength selecting device is provided with a single-core collimator 80 on the input side, a single-core collimator 81 on the output side, and an optical signal which is disposed between both collimators 80 and 81 and emitted from the single-core collimator 80 as parallel light. And a liquid crystal cell unit 82 for selectively reflecting one or more types of light having different wavelengths. The wavelength plates 40 and 41 are disposed on the incident side and the exit side of the liquid crystal cell unit 82, respectively. Further, the wavelength selection device includes both collimators 80 and 81,
The liquid crystal cell unit 82 and a holding member (or case) 25 such as a sleeve for holding the two wavelength plates 40 and 41 are integrated. The wavelength selection device is connected to an optical circulator 84 via one optical fiber 83.

The single-core collimator 80 includes a single-core capillary 85 for holding one optical fiber 83 connected to an optical circulator 84, and a collimator lens 86 such as a rod lens. On the other hand, the single-core collimator 81 includes a single-core capillary 88 for holding one optical fiber 87 and a collimator lens 89 such as a rod lens.

The liquid crystal cell unit 82 comprises a set of liquid crystal cells 2 comprising the cholesteric liquid crystal 26 and a pair of transparent electrodes 27, 27 provided on opposing surfaces of the liquid crystal 26.
2 are stacked and stacked (four sets of LC1 to LC4). Further, the four sets of liquid crystal cells 22 are formed so as to reflect light of specific wavelengths different from each other in the first state. For example, the liquid crystal cells LC1, LC2, LC3, LC4
Reflects the light of the wavelengths λ1, λ2, λ3, λ4 in the first state, that is, the maximum selected light scattering wavelength λ0 is the wavelength λ1, λ2, λ3, λ, respectively.
4 is set. Further, by individually changing (turning on and off) the voltage applied to each transparent electrode 27 of each of the plurality of sets of liquid crystal cells LC1 to LC4, at least one cholesteric liquid crystal 26 of the plurality of sets of liquid crystal cells LC1 to LC4 is changed. Is changed between the first state and the second state.

In this example, as in the above embodiments, in each of the liquid crystal cells LC1, LC2, LC3, and LC4, when a voltage is applied between the transparent electrodes 27, 27, the cholesteric liquid crystal 26 enters the second state. When the voltage is not applied, the cholesteric liquid crystal 26 changes to the first state. Therefore, (wavelength λ
When selecting at least one wavelength from 1 to λ4), the voltage applied to the transparent electrodes 27, 27 corresponding to the wavelength selected from the liquid crystal cells LC1 to LC4 may be set to zero.

The optical circulator 84 transmits an optical signal sent from the light source side or another optical communication optical element and the like to the first terminal 84 a to the single-core collimator 80 via the optical fiber 83 from the second terminal 84 b. The light is emitted. At the same time, the optical circulator 84 converts the light reflected by any one of the liquid crystal cells LC1 to LC4 of the liquid crystal cell unit 82, emitted from the single-core collimator 80, and sent to the second terminal 84b via the optical fiber 83, The light is emitted from the third terminal 84c to a light receiving unit (not shown) or another optical element for optical communication.

According to the sixth embodiment configured as described above, the following operation and effect can be obtained. (C) When selecting only one kind of light, for example, light of wavelength λ2, the pulse signal output to the terminals 28 of the liquid crystal cell LC2 is turned off by the controller 70 and the transparent electrode 27 of the liquid crystal cell LC2 is turned off. , 27 are set to 0 only. As a result, only the cholesteric liquid crystal 26 of the liquid crystal cell LC2 enters the first state, so that the wave plate 40
Of the light (λ1 to λ4) converted into right circularly polarized light, the light having the wavelength λ2 is reflected by the cholesteric liquid crystal 26 of the liquid crystal cell LC2, and the reflected light is returned to the unpolarized light by the wavelength plate 40. The light is condensed by the collimator lens 86 and is emitted to the optical circulator 84 via the optical fiber 83.

When two or more types of light having different wavelengths, for example, light having wavelengths λ1 and λ2 are simultaneously selected, the controller 70 turns off the pulse signals output to the terminals 28 and 28 of the liquid crystal cells LC1 and LC2. A pulse signal is output to the terminals 28 and 28 of the other liquid crystal cells LC3 and LC4. Thereby, the liquid crystal cells LC1,
Since the cholesteric liquid crystal 26 of LC2 is in the first state, light of wavelengths λ1 and λ2 is
The reflected lights are respectively reflected by the cholesteric liquid crystal 26 of C2, and these reflected lights are respectively returned to unpolarized light by the wave plate 40, further condensed, and emitted to the optical circulator 84 via the optical fiber 83.

When only the light of the wavelength λ3 is selected, the controller 70 turns off the pulse signal output to each terminal 28 of the liquid crystal cell LC3. As a result, only the cholesteric liquid crystal 26 of the liquid crystal cell LC3 enters the first state, so that the light having the wavelength λ3 is reflected by the cholesteric liquid crystal 26 of the liquid crystal cell LC3, and the reflected light is returned to unpolarized light by the wavelength plate 40. The light is further condensed and emitted to an optical circulator 84 via an optical fiber 83.

Therefore, by controlling the voltage applied to the transparent electrodes 27, 27 of each of the liquid crystal cells LC1 to LC4, an optical signal including a plurality of types of light (λ1 to λ4) having different center wavelengths can be converted into light having different wavelengths. Can be arbitrarily selected.

(F) Since the wavelength plates 40 and 41 are provided on the incident side and the exit side of the liquid crystal cell unit 82, respectively, the liquid crystal cells LC1 to LC4 convert the light of each wavelength converted to right circularly polarized light. Is reflected by the cholesteric liquid crystal 26 of the corresponding liquid crystal cell. Therefore, each liquid crystal cell L
The reflection efficiency of the selected light selected by C1 to LC4 is approximately 100.
%. At the same time, even when the number of sets of liquid crystal cells constituting the liquid crystal cell unit 82 is increased,
Since only one wave plate 40 or 41 may be provided on each of the incident side and the outgoing side of the liquid crystal cell unit 82, it is not necessary to increase the number of wave plates even if the number of liquid crystal cells is increased. Therefore, the loss of light of each wavelength selected in each liquid crystal cell can be further suppressed, and the large-scale optical communication system can be constructed with a small number of components.

(G) The liquid crystal cell unit 82 constituted by laminating a plurality of sets of liquid crystal cells LC1 to LC4 is disposed between the single-core collimator 80 and the collimator 81. (80) and one (81) on the emission side. Accordingly, even when the number of sets of liquid crystal cells constituting the liquid crystal cell unit 82 is increased, only two collimators 80 and 81 are required, the number of parts is small, the manufacturing cost can be reduced, and the size can be reduced. Can also be achieved.

(T) By using the optical circulator 84, the optical circulator 84 and the wavelength selection device can be connected by one optical fiber 83.
The input side of the unit 82 is not a two-core collimator but
What is necessary is just to provide the core collimator 80. Therefore, the work of aligning the one-core collimator 80 on the incident side and the collimator 81 on the emission side becomes easy, and the configuration can be simplified.

[Modifications] Each of the embodiments described above can be implemented by changing the configuration as follows.

In each of the above embodiments, while the voltage is applied to the transparent electrodes 27 of the liquid crystal cell 22, the liquid crystal cell 22 is in the second state. Are in the first state and reflect light of a specific wavelength. Conversely, the liquid crystal cell 2
2, while no voltage is applied to the transparent electrodes 27, 27,
The liquid crystal cell 22 may be configured to be in the first state when the liquid crystal cell 22 is in the second state and a voltage is applied to the transparent electrode.

In each of the above embodiments, the voltage applied to the transparent electrodes 27 of the liquid crystal cell 22 is changed to change the liquid crystal cell 22 between the first state and the second state. However, the liquid crystal cell 22 may be changed between the two states by changing physical energy other than the voltage applied to the liquid crystal cell 22. Examples of the physical energy include heat, a magnetic field, and a force.

In the above embodiments, the cholesteric liquid crystal is used as the liquid crystal of the liquid crystal cell 22, but a chiral nematic liquid crystal having the same optical characteristics as the cholesteric liquid crystal may be used instead of the cholesteric liquid crystal.

In each of the above embodiments, the cholesteric liquid crystal 26 is a right-handed liquid crystal, that is, the liquid crystal 26 has a helical direction of right. A thing may be used.

In the fourth and fifth embodiments shown in FIGS. 4 and 6, respectively,
However, the number of the modules is not limited to four and may be two or more.

In the sixth embodiment shown in FIGS. 8 and 9, the liquid crystal cells of the liquid crystal cell unit 82 are LC1 to Lc
Although four sets of four are provided, the number of the liquid crystal cells is not limited to four and may be two or more.

[0092]

As described above, according to the first aspect of the present invention, selection and non-selection of light having a specific wavelength can be switched, so that it can be used as an optical element for optical communication in a wide range of applications. it can.

According to the tenth or thirteenth aspect,
One or more types of light having different wavelengths can be arbitrarily selected from an optical signal including a plurality of types of light having different center wavelengths.
Along with this, it is possible to suppress a decrease in the intensity of light of each wavelength, which is particularly effective when increasing the types of selectable wavelengths and constructing a large-scale optical communication system with a large amount of information.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a wavelength selection module according to a first embodiment.

FIG. 2 is a schematic configuration diagram illustrating a wavelength selection module according to a second embodiment.

FIG. 3 is a schematic configuration diagram illustrating a wavelength selection module according to a third embodiment.

FIG. 4 is a schematic configuration diagram illustrating a wavelength selection device according to a fourth embodiment.

FIG. 5 is a schematic configuration diagram showing a part of the wavelength selection device of FIG. 4 in detail;

FIG. 6 is a schematic configuration diagram illustrating a wavelength selection device according to a fifth embodiment.

FIG. 7 is a schematic configuration diagram showing a part of the wavelength selection device of FIG. 6 in detail.

FIG. 8 is a schematic configuration diagram illustrating a wavelength selection device according to a sixth embodiment.

FIG. 9 is a schematic configuration diagram showing a part of the wavelength selection device of FIG. 8 in detail.

FIG. 10 is a graph showing optical properties of a cholesteric liquid crystal.

FIG. 11 is a schematic configuration diagram showing a conventional filter module.

FIG. 12 is a schematic configuration diagram showing a conventional wavelength selection device.

[Explanation of symbols]

21, 21A, 21B, M1 to M4 wavelength selection module, 22, LC1 to LC4 liquid crystal cell, 23 two-core collimator, 24, 50 to 52 single core collimator, 26 cholesteric liquid crystal, 27 transparent electrode, 40 41, a wave plate, 82, a liquid crystal cell unit, 83, an optical fiber, 8
4 ... optical circulator, 84a, 84b, 84c ... terminal.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Manabu Takami 6-7 Nagasaki, Okajima, Fukushima City Nanox Co., Ltd. F-term (reference) 2H049 BA05 BA06 BA43 BA46 BB03 BC25 2H088 EA46 EA47 EA49 2H099 AA01 CA00 DA00

Claims (17)

[Claims] 1. A wavelength selection module for selecting light of a specific wavelength from an optical signal including a plurality of types of light having different center wavelengths, wherein the collimator converts the optical signal into parallel light, and the collimator emitted from the collimator. Light of a specific wavelength in the optical signal is divided into left and right circularly polarized light, and a first state in which circularly polarized light in the same optical rotation direction as the helical direction is reflected, and a second state in which the optical signal is transmitted. A liquid crystal cell having a liquid crystal that changes in accordance with the applied physical energy, and changing the physical energy applied to the liquid crystal to change the liquid crystal to the first state, thereby causing the light of the specific wavelength to change to the first state. A wavelength selection module characterized in that the light is reflected by liquid crystal and taken out. 2. The liquid crystal cell has a pair of transparent electrodes provided on opposite surfaces of the liquid crystal, and changes a voltage as the physical energy applied to the transparent electrodes. 2. The wavelength selection module according to 1. 3. The wavelength selection module according to claim 1, wherein the liquid crystal is a cholesteric liquid crystal or a chiral nematic liquid crystal. 4. The collimator arranged on the incident side of the liquid crystal cell is a two-core collimator that causes the optical signal to be incident on the liquid crystal cell substantially perpendicularly. A wavelength selection module according to claim 1. 5. A one-core collimator for condensing light transmitted through the liquid crystal cell and coupling the light to an optical fiber is disposed on an emission side of the liquid crystal cell. The wavelength selection module according to claim 1. 6. The collimator disposed on the incident side of the liquid crystal cell, a single-core collimator for obliquely entering the optical signal into the liquid crystal cell, and condensing light of a specific wavelength reflected by the liquid crystal cell. The wavelength selection module according to any one of claims 1 to 3, further comprising a single-core collimator coupled to the optical fiber. 7. A one-core collimator for condensing transmitted light obliquely emitted from the liquid crystal cell and coupling the condensed light to an optical fiber is disposed on an emission side of the liquid crystal cell. 2. The wavelength selection module according to 1. 8. A wave plate for converting the optical signal into circularly polarized light having the same optical rotation direction as the helical direction of the liquid crystal is arranged on the incident side of the liquid crystal cell. The wavelength selection module according to any one of the above. 9. The wavelength selection device according to claim 8, wherein a wavelength plate for returning circularly polarized light converted by the wavelength plate to non-polarized light is disposed on an emission side of the liquid crystal cell. module. 10. A plurality of wavelength selection modules according to claim 1, wherein one or more types of light having different wavelengths are selected from an optical signal including a plurality of types of light having different center wavelengths. A wavelength selection device, wherein each of the plurality of wavelength selection modules is vertically connected via an optical fiber, and reflects light of a different wavelength when the liquid crystal is in the first state. A wavelength selecting device, comprising: 11. The method according to claim 1, wherein at least one liquid crystal of the plurality of wavelength selection modules is changed to the first state by individually changing a voltage applied to each liquid crystal of the plurality of wavelength selection modules. Claim 1
0. The wavelength selection device according to 0. 12. A wavelength plate for converting the optical signal into circularly polarized light having the same optical rotation direction as the helical direction of the liquid crystal is provided on an incident side of each liquid crystal cell of the plurality of wavelength selection modules. 12. The wavelength selection device according to claim 10, wherein a wavelength plate for returning the circularly polarized light converted by the wavelength plate to unpolarized light is provided. 13. A wavelength selector for selecting one or more types of light having different wavelengths from an optical signal containing a plurality of types of light having different center wavelengths, comprising: a collimator for converting the optical signal into parallel light; And a liquid crystal cell unit that reflects one or more types of light having different wavelengths in the emitted optical signal, wherein the liquid crystal cell unit converts left and right circularly polarized light of a specific wavelength in the optical signal. And a liquid crystal that changes according to externally applied physical energy between a first state that reflects circularly polarized light having the same optical rotation direction as the helical direction of the liquid crystal and a second state that transmits the optical signal. And a plurality of sets of liquid crystal cells each comprising a pair of transparent electrodes provided on opposing surfaces of the same liquid crystal. The voltage applied to each transparent electrode of the plurality of sets of liquid crystal cells is individually set. Change The wavelength selection device characterized by varying at least one of the liquid crystal of said plurality of sets of liquid crystal cells in the first state. 14. A wavelength plate for converting the optical signal into circularly polarized light having the same optical rotation direction as the helical direction of the liquid crystal on the incident side of the liquid crystal cell unit, and a wavelength plate for converting the optical signal on the output side. 14. The wavelength selection device according to claim 13, further comprising a wavelength plate for returning the circularly polarized light to unpolarized light. 15. The liquid crystal cell unit according to claim 13, wherein a wave plate for returning circularly polarized light converted by the wave plate to non-polarized light is disposed on an emission side of the liquid crystal cell unit. The described wavelength selector. 16. The collimator disposed on the incident side of the liquid crystal cell unit is a single-core collimator.
The wavelength selection device according to any one of claims 13 to 15, wherein the core collimator is connected to an optical circulator having at least three terminals via one optical fiber. 17. The collimator according to claim 13, wherein a single-core collimator for condensing light transmitted through the liquid crystal cell unit and coupling the condensed light to an optical fiber is arranged on an emission side of the liquid crystal cell unit. The wavelength selection device according to claim 1.