JPH0750284B2 - Optical path switch - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical path switcher using a liquid crystal, and more particularly to an optical path switcher suitable for simplifying the structure and improving performance.

[Conventional technology]

Generally, in optical transmission and optical communication systems using an optical fiber, an optical transmission line switching device and an optical path switching device for bypass are required.

The conventional liquid crystal optical path switching device is disclosed in, for example, the literature Optics Letters, Volume 5, 4, (1980), pages 147 to 149 (Optics.
Letters, Vol15, No. 4 (1980) PP147-149).
It can be seen in the paper "A total switching of unpolarized fiber light by a 4-port electro-optical liquid crystal device" published by A. Soref and DHM McMahon. This conventional optical path switching device incorporates a nematic liquid crystal between two glass prisms, and applies an AC electric field between transparent electrodes provided on both sides of the opposing prisms to change the orientation of liquid crystal molecules, thereby refracting light. The incident light is switched in two directions by changing the ratio.

The operation of nematic liquid crystal molecules used in the conventional liquid crystal optical path switching device will be described with reference to FIG. Reference numeral 1 is a nematic liquid crystal layer, and 1'is a nematic liquid crystal molecule. Reference numeral 2 is a transparent electrode provided on a transparent substrate (not shown). 3 is an AC power supply, and 4 is an electric switch provided in the middle of the circuit.
(A) is a case where no electric field is applied between the electrodes 2 (OFF),
Liquid crystal molecules 1'are arranged in parallel. In (b), when an electric field is applied, the liquid crystal molecules 1'are mostly aligned in the direction of the electric field, but the molecules near the upper and lower interfaces remain parallel to the electrodes in the OFF state. Therefore, the use of the nematic liquid crystal causes the following problems. That is, (1) Since the molecules near the interface do not easily respond to the electric field, the transmittance or reflectance is reduced, and it is difficult to reduce crosstalk (crosstalk) as an optical path switch.

(2) In order to improve the above phenomenon, the voltage must be increased and a high driving voltage is required.

(3) The response speed of nematic liquid crystal molecules is slow when the electric field is switched, particularly when the electric field is removed.

Due to such drawbacks, the optical path switching device using nematic liquid crystal has not yet been put to practical use.

In order to improve the above drawbacks, it is necessary to change the liquid crystal material itself to a high performance one. The inventors have proposed to switch the optical path by using a ferroelectric liquid crystal having basic characteristics for improving the above-mentioned drawbacks, sandwiching this liquid crystal with transparent electrodes, and applying a direct current or a pulse voltage between the electrodes. .

A ferroelectric liquid crystal as an element for switching the optical path will be described below. FIG. 3 shows a conceptual diagram of the operation. 11 'is a ferroelectric liquid crystal molecule, and 12 is a spiral axis. Reference numerals 13 and 13 'denote electric fields applied in the direction perpendicular to the spiral axis as shown in FIGS. 3 (a) and 3 (c).

In the case of ferroelectric liquid crystals, the direction of spontaneous polarization is perpendicular to the plane formed by the spiral axis and the long axis of the liquid crystal molecules 11 '. or,
As shown in FIG. 3 (b), when the electric field E = 0, the ferroelectric liquid crystal molecules 11 ′ are oriented in a spiral with an angle θ _t with respect to the spiral axis 12. There is. When an electric field E13 equal to or higher than the threshold electric field E _c is applied to the ferroelectric liquid crystal molecules 11 ′ oriented in this way, the ferroelectric liquid crystal molecules 11 ′ are converted into the electric field E13 as shown in FIG. 3 (a). Orientation is made at an angle of θ _t with respect to the spiral axis 12 on a plane perpendicular to the direction (ie, the paper surface of the figure). When the polarity of the electric field E in FIG. 3 (a) is reversed,
As shown in FIG. 7C, the ferroelectric liquid crystal molecule 11 'has an electric field E1.
Respect et旋軸on the vertical plane (paper surface) in the direction of 3 'theta _t
Have an angle of. In this way, by reversing the electric field E, the molecular orientation can be changed up to twice the tilt angle θ _t with the spiral axis.

Furthermore, when this ferroelectric liquid crystal is driven in the same configuration as in FIG. 2, the liquid crystal layer thickness is reduced (for example, 1.5 μm),
And by adjusting the liquid crystal interface and liquid crystal composition appropriately,
It is possible to give the memory property to the molecular orientation. In this state, the molecules in the vicinity of the interface of the ferroelectric liquid crystal are completely switched to solve the problems (1) and (2) in the liquid crystal for liquid crystal. It should be noted that, compared with a nematic liquid crystal that continuously gives an alternating electric field, it is possible to use only the pulsed applied electric field for switching by utilizing the memory effect of liquid crystal molecules, and it is possible to further reduce the power consumption.

Regarding the response speed of the molecular orientation, in the case of a ferroelectric liquid crystal, the drive mode is to apply positive and negative electric fields that are equal in absolute value, so the response speed is extremely slow when removing the electric field as in the case of nematic liquid crystal. Such a state does not occur, and both switching operations show a response speed equal to or higher than that at the time of applying an electric field in the nematic liquid crystal.

As described above, it is clear that the three problems of the nematic liquid crystal as the optical path switching element can be remarkably improved by using the ferroelectric liquid crystal as the liquid crystal.

4 and 5 show an example of the principle of optical path switching using a ferroelectric liquid crystal. FIG. 4 shows the basic structure of the device, and FIG. 5 shows the molecular alignment state of the ferroelectric liquid crystal by applying two kinds of voltage and the resulting optical path (transmission or total reflection). Here, the incident light 23 is the incident surface (paper surface of the figure)
Light having only an electric field component perpendicular to is considered.

In FIG. 4, the basic structure is the ferroelectric liquid crystal 11, the upper and lower transparent substrates 21 sandwiching the ferroelectric liquid crystal 11, and the transparent solid electrode 2 provided on the boundary surface of the transparent substrate facing the ferroelectric liquid crystal 11. And a DC power supply 22. In addition, in order to obtain the required molecular orientation as shown in FIG.
It is necessary to orient 11 'in a predetermined direction. In reality, an alignment film is provided on the boundary surface with the ferroelectric liquid crystal 11, that is, the electrode surface, but here the drawing becomes complicated. Omitted to avoid.

Generally, when linearly polarized light is incident on an optically uniaxial substance such as liquid crystal, the refractive index is changed by changing the angle formed by the incident direction and the optical axis. FIG. 5 shows that the refractive index of incident light can be changed by changing the molecular long axis direction, that is, the optical axis direction by applying an electric field. As a result, as a typical example, the incident light is totally reflected or transmitted. Indicates that you can

The changes in the molecular orientation shown in FIGS. 5 (a) and 5 (b) correspond to (a) or (c) shown in FIG.
Therefore, the long axis of the molecule is always perpendicular to the direction of the electric field generated by the solid electrode 2. That is, the molecular orientation is always changed in the transparent electrode 2, which is completely different from the optical path switching device using nematic liquid crystal. The angle change of the molecular orientation is equal to twice the tilt angle θ _t from the helix axis as described above. Here, as a typical example, θ _t = 45 °, that is, the angle change is 90 °.
Assuming an alignment state perpendicular to and parallel to the incident surface (paper surface of the drawing) as shown in FIG. 5, the refractive index of the liquid crystal layer 11 in (a) becomes the extraordinary light refractive index ne, and (b) The liquid crystal layer 11 has a refractive index equal to the ordinary light refractive index no (ne> no). Therefore, in this case, the range of the incident angle θ that satisfies the above-mentioned condition is expressed by the following equation.

ng: Refractive index of transparent substrate For example, as an example of using SF10 as the material of the transparent substrate 21, ng = 1.8, ne = 1.7, no = 1.5 and the incident angle θ
= 56.4 to 70.8, with a margin of 14.4 °.

However, in the optical path switcher of the type that applies an electric field only in the thickness direction of the liquid crystal layer described above, only the light (S-polarized light) can be switched as the component perpendicular to the incident surface.
Therefore, it has a drawback that it cannot be applied to light sources such as LEDs having a non-polarized property used in optical LANs such as FA and OA, which have recently been rapidly in demand. Therefore, in order to switch non-polarized light (multimode light), first, P-polarized light having electric field oscillation parallel to the incident surface must be switched. The conditions for that will be described.

In the molecular orientation state of FIG. 5, considering the case where P-polarized light is incident at a critical angle (light travels in the liquid crystal in parallel with the interface), both molecular orientation states of (a) and (b) The refractive index of the liquid crystal is no (the plane of polarization intersects the long axis of the molecule at right angles), the refractive index does not change, and transmission and total reflection cannot be switched. As can be seen from this, the switching of P-polarized light does not occur only by the change of the molecular long axis in the liquid crystal interface, and it is a necessary condition that the liquid crystal is aligned obliquely with respect to the interface.

In order to satisfy this condition, as can be seen from FIG. 3 (b), any electric field application direction other than (a) and (c) may be used, and among them, the angle of intersection with the interface is the largest. This is a case where an electric field is applied in a direction parallel to the liquid crystal interface. Therefore,
If this electric field state is created in the liquid crystal cell, P polarized light can be switched.

Next, the optimum initial arrangement of the helix axis of the ferroelectric liquid crystal and the incident light, including the switching of S-polarized light, is obtained. Here, consider a case in which the incident angle θ is largely selected and light is incident in a direction substantially parallel to the interface. As can be seen from FIG. 6, in the two states on the conical orbit 34 in which the liquid crystal molecules 35 move, the maximum difference in the refractive index for both S-polarized light and P-polarized light is that the helical axis of the ferroelectric liquid crystal.
When 33 is aligned with the incident surface 31, the liquid crystal molecules 35
Is included in a plane 32 parallel to the liquid crystal interface and the position 35a and the incidence plane 3
This is the case at the position 35b included in 1.

In the two states of 35a and 35b, a difference in refractive index is given to the S-polarized light and the P-polarized light, and the optical paths are switched. FIG. 7 shows an example of the configuration of a non-polarized light path switching device using this principle.
This structure consists of two trapezoidal prisms 101 and a ferroelectric liquid crystal 11
And the light is passed through the liquid crystal layer twice as shown in the figure (two cushions). A solid electrode 2 as shown in FIG. 4 is provided on the left half corresponding to the first passage portion (that is, liquid crystal molecules are aligned in the state of 35a in FIG. 6), and light is S-polarized (transmitted). Light) and P-polarized light (reflected light). In the right half including the remaining second passage portion, an electrode structure capable of switching the two states of liquid crystal molecules 35a and 35b shown in FIG. 6 (since this structure is common to the electrode structure of the present invention, (Described later) is provided so that the S-polarized light and the P-polarized light merge with the port of 92b in the orientation state of 35a and to the port of 92d with the orientation state of 35b.

[Problems to be solved by the invention]

In the above-mentioned prior art, high accuracy is required for the degree of area and the angle accuracy of the prism surface forming the optical path.
In particular, in a trapezoidal prism as shown in Fig. 7, in addition to the trapezoidal bottom face that switches between total reflection and transmission by sandwiching the incident and exit faces of light to the prism and liquid crystal, the total reflection of the trapezoidal top face is performed. High precision is also required for the surface that causes In addition, since it is a method of re-combining the separated light into the upper and lower trapezoidal prisms, the deterioration of the dimensional accuracy of the upper and lower trapezoidal prisms directly results in optical axis shift at the recombining portion, resulting in loss and crosstalk. Increase. in this way,
This method using a trapezoidal prism has higher accuracy in terms of surface accuracy, angle accuracy, and dimensional accuracy. Therefore, this method requires high accuracy in assembling the material itself,
Be extremely difficult. Further, even if the propagation optical paths in the prism are simply compared, it is inevitable that the method using the trapezoidal prism has a long optical path and a large propagation loss.

An object of the present invention is to provide an optical path switcher which uses a ferroelectric liquid crystal and can be used for multimode light having a simple structure in order to improve the above problems.

[Means for solving problems]

The above-mentioned object is that in which a ferroelectric liquid crystal is interposed between two transparent substrates arranged to face each other and electrodes provided on each of the facing surfaces of the transparent substrate, the molecules of the ferroelectric liquid crystal are Initially align the helix axis so that it intersects with the plane of incidence of light and the angle that gives the maximum change in refractive index for both S-polarized light and P-polarized light (approximately the tilt angle of the ferroelectric liquid crystal). , The angle between the first orientation in which the molecular long axis of the ferroelectric liquid crystal is substantially parallel to the liquid crystal interface and the interface with the liquid crystal layer gives the maximum change in refractive index for both S-polarized light and P-polarized light. This is achieved by switching between the two orientation states of the angular second orientation.

[Action]

FIG. 8 shows the operating state of the ferroelectric liquid crystal molecules. In this figure, the helical axis 12 'of the liquid crystal molecule shown in FIG.
This corresponds to the state of being rotated by the tilt angle θ _t above.

One molecular long axis 35a 'of the ferroelectric liquid crystal is oriented in a position parallel to the liquid crystal layer interface by an electric field 37a' in the thickness direction of the liquid crystal layer. The other molecular long axis 35b 'is oriented at a position not parallel to the liquid crystal layer interface by an electric field 37b' parallel to the liquid crystal layer interface. The spiral axis 12 'of the ferroelectric liquid crystal molecule is the plane of incidence of light.
Since the initial alignment is offset from the tilt angle θ _t of the liquid crystal material by 31, the light is almost in the long axis direction of the liquid crystal molecules, that is, in the optical axis direction in the molecular alignment state 35a ′ parallel to the liquid crystal layer interface. For example, in the case of a liquid crystal having a positive dielectric anisotropy, both S-polarized light and P-polarized light have the ordinary refractive index no (minimum). In the other molecular alignment state 35b ′ which is not parallel to the liquid crystal layer interface, the liquid crystal molecular long axis is aligned obliquely with respect to both the S polarization direction and the P polarization direction. The refractive index can be increased.

If the former low refractive index state 35a 'is set to the total reflection mode and the latter high refractive index state 35b' is set to the transmission mode,
It becomes possible to switch S-polarized light and P-polarized light, that is, multimode light at a time.

〔Example〕

The first embodiment of the present invention will be described below with reference to FIG.
FIG. 1 (c) shows the crossing state of the light incident surface 31 and the spiral axis 12 '(longitudinal direction of the comb-shaped electrode) of the ferroelectric liquid crystal molecules.
The drawings (a) and (b) are drawn as they are from above.

It has been considered that the crossing angle θ _c is almost equal to θ _t until now, but in reality, the optimum value at which the change in the refractive index is maximum exists at a position shifted by a certain angle Δθ, and the optimum crossing angle θ c _c is represented by θ _c = θ _t + Δθ (2) (where θ _{t is} the tilt angle of the ferroelectric liquid crystal molecule), and Δθ at this time is taken as an example when θ _t = 35 °. I will ask for it. For simplification of calculation, it is approximated that the light rays in the liquid crystal layer travel parallel to the liquid crystal interface, and the ordinary refractive index no of the ferroelectric liquid crystal molecule is 1.5, the extraordinary refractive index ne is 1.7, and the ferroelectric liquid crystal molecule is When the tilt angle θ _{t of is set} to 35 °, the result as shown in FIG. 9 is obtained from the formula of the index ellipsoid. (A) in the graph
8A and 8B correspond to the liquid crystal molecule alignment states a and b in FIG. 8, respectively. From this graph, S polarization and P
The maximum change in refractive index for both polarized light is
It was found that Δθ ≈ 10 °, and from equation (2), θ _c = 35
+ 10 = 45 ° is the optimum value.

The helical axis of the ferroelectric liquid crystal molecules is initially oriented in the direction rotated from the light incident surface by the optimum crossing angle θ _c thus obtained, and the comb-shaped electrodes are arranged in the same direction. I will let you.

As described above, the two states of the ferroelectric liquid crystal molecule, that is, the eighth state
By switching the first orientation 35a 'and the second orientation 35b' in the figure, the optical path switching of the multi-mode light is achieved by a single incidence on the liquid crystal layer. Hereinafter, in FIGS. 1, 10, 11, and 12, FIG.
An example of an electrode structure for creating a'and 37b 'electric field states is shown. As shown in FIG. 1 (c), all of these figures are sectional views seen from the direction in which the light incident surface 31 is rotated by θ _c , and the state of FIG. ) To 3
The states of 5b 'are shown in (b).

First, FIG. 1 shows that a transparent substrate 21 is provided with a comb-shaped transparent electrode 42 and a transparent electrode 43 in which a comb-shaped gap is meandered, and an alignment film for determining the initial alignment of the ferroelectric liquid crystal molecules is formed on the transparent electrode 43. 2 are formed opposite to each other, and the ferroelectric liquid crystal 11 is interposed therebetween.

FIG. 1 (a) shows the liquid crystal layer thickness direction (37a ') due to the upper and lower comb-shaped transparent electrodes 42 and the meandering transparent electrode 43.
An electric field is applied to the film, and the molecular orientation shown in Fig. 35a 'is obtained.
In FIG. 1 (b), an electric field is applied in the direction of 37b 'by only the comb-shaped electrode 42 to obtain the molecular orientation of 35b'.

The problem here is that in Fig. 1 (b), the electric fields of opposite polarities are generated between the adjacent comb-shaped electrodes. For this reason, liquid crystal molecules are vertically oriented between adjacent electrodes, and when a light ray is incident between two or more electrodes, the refractive index may differ between the respective electrodes and the light ray direction may vary. However, the refraction angle in the ferroelectric liquid crystal layer 11 can pass through the liquid crystal layer almost horizontally in consideration of the refraction index ng of the transparent substrate 21. Therefore, it is considered that the refractive index does not change so much even though the liquid crystal molecules are oriented vertically, because they are vertically symmetrical. In addition, since the thickness of the ferroelectric liquid crystal layer 11 is as thin as 1 to 5 μm, it is considered that the variation in the light beam direction due to the change in the refractive index between them is negligible.

This embodiment has a complicated pattern, but is characterized in that the electric field states of (a) and (b) can be obtained only with a single-layer electrode structure.

Next, FIG. 10 shows a second embodiment in which the electrode has a two-layer structure. The structure is such that a transparent solid electrode 2 is vapor-deposited on a transparent substrate 21, and an alignment film 41 (which also serves as an insulating film) that determines the initial alignment of ferroelectric liquid crystal molecules is formed on the transparent solid electrode 2 and the comb is formed thereon. Two liquid crystal-shaped electrodes 42 are opposed to each other, and a ferroelectric liquid crystal is inserted therebetween.

That is, in 10 (a), an electric field is applied by the solid electrode 2 in the thickness direction (37a ') of the liquid crystal layer to obtain a molecular orientation of 35a', and FIG. 10 (b) shows a comb shape. 37 by electrode 42
An electric field is applied in the b'direction to obtain a 35b 'molecular orientation.

Finally, with the comb-shaped electrodes shown in Fig. 1 and 10 (b),
The applied electric field has a curved shape as shown in FIG. 37b ', which may result in incomplete molecular orientation of 35b'.
As a method for preventing this, the embodiment shown in FIGS. 11 and 12 will be described below.

In the embodiment shown in FIG. 11, only the comb-shaped electrode 42 of FIG. 12 is replaced with a strip electrode 51 provided between transparent substrates. As a manufacturing method, a conductive film is formed on the alignment film 41,
Then, a method of removing the portion other than the strip-shaped electrode having a predetermined shape by ion milling or the like can be considered, but it can be said that it is more difficult than the method of manufacturing the comb-shaped electrode. However, the applied electric field is linearly applied as shown in (b), and a perfect molecular orientation state of 35b 'can be expected.

The embodiment shown in FIG. 12 is intended to more easily realize the perfect molecular orientation state of 35b '. That is, instead of the comb-shaped electrodes of FIG. 10 and the strip electrodes of FIG. 11, very thin (for example, about 2 μm) conductive lines are arranged in parallel at a predetermined interval. With this structure, two perfect molecular orientation states as shown in FIG. 12 can be more easily realized.

Next, FIG. 13 and FIG. 14 show a configuration example of a more practical multi-mode optical path switching device using such a principle switching element. The optical path changer shown in FIG. 13 is generally called a bulk type, and has a structure in which the liquid crystal cell structure 75 'shown in FIGS. 1, 10, 11, and 12 is sandwiched by two glass prisms 711 and 712. At this time, as shown in FIG. 1 (c), the light incident surface 31 and the spiral axis 12 'of the liquid crystal are set so as to intersect with each other at θ _c in the equation (2). Further, multi-mode optical fibers 73a to 73d having lenses 74a to 74d are attached as input / output ports. Here, the thickness of the liquid crystal layer 11 needs to be about 5 μm, and in order to keep the space and to confine the liquid crystal layer 11, a thin film punching out a portion where the liquid crystal 11 enters,
For example, insert Myrafilm 72. Further, a non-reflective coating (not shown) is applied to the bottom surface to minimize reflection loss when entering the liquid crystal layer 11.

Now, an operation example will be described with 73a as the incident port.
When single-mode light or multi-mode light enters from the multi-mode light fiber 73a, it is converted into parallel light in the lens 74a and is input into the prism 71. And the ninth
The ferroelectric liquid crystal layer 11 with an incident angle θ that can switch between transmission and total reflection according to the change in the refractive index as shown in the figure.
And is transmitted to 74d or totally reflected to 74b depending on the applied electric field. The emitted light is condensed by the lenses 74b and 74d and output to the emission ports 73b and 73d, respectively. Here, it goes without saying that the four ports 73a to 73d can be used as either the entrance port or the exit port, and thus bidirectional switching is possible.

FIG. 14 shows, as another embodiment, an optical waveguide type optical path switching device that can be integrated as compared with a bulk type. The figure (a) is a top view and the figure (b) is a side view. The basic structure is similar to that of the bulk type shown in FIG.
It has a form in which a liquid crystal cell 75 'is embedded as shown in Figs. That is, the prism 71 and the port portions 73 and 74 of FIG.
However, the optical waveguides 82a to 82d on the substrate 81 are replaced, and optical switching can be performed according to the same principle as described with reference to FIG.

When it is attempted to drive a current ferroelectric liquid crystal material at a practically low voltage level, the electrode application direction interval for applying in the interface direction (37b ′) shown in FIGS. 1, 10, 11, 12 is set. It cannot be larger than the beam diameter of the incident light. Therefore, incident light may hit the electrode portions, which may increase crosstalk. However, if the sensitivity of the liquid crystal material to the electric field increases in the future and the electrode spacing can be made larger than the beam diameter of the incident light, a simple 1-pitch electrode shown in FIGS. 1, 10, 11, and 12 can be used. An optical path switcher with low crosstalk can be constructed with an electrode structure.

[Effect of Example]

The improved actual performance values are shown in Table 1. The composition and phase change of the ferroelectric liquid crystal used is shown in FIG.
Figure 15 shows the temperature dependence of the helical pitch and tilt angle of the ferroelectric liquid crystal molecules.

The nematic liquid crystal (two-cushion) shown in Table 1 is the data of Soref et al. Explained in the conventional example, which is a two-cushion system using a trapezoidal prism as shown in FIG. The ferroelectric liquid crystal (2 cushions) is the same data as described in FIG. 7. The 1 cushion data is the data obtained by incorporating the liquid crystal cell of FIG. 1 into the prism structure of FIG. 13 of the present invention. Is.

As shown in Table 1, by using the ferroelectric liquid crystal, the driving voltage can be reduced to half that of the nematic liquid crystal,
There is no phenomenon corresponding to a significant delay in the switching time (τ _off ) when the voltage is removed in the nematic liquid crystal, and the two switching states are about half the switching time (τ _on ) when the voltage is applied in the nematic liquid crystal.
It can be switched at a high speed of 0.05 mS.

Regarding the crosstalk, in addition to the difference in the performance of the liquid crystal material, the effect due to the simplification (one cushion) of the device structure is remarkably exhibited.

The same applies to the propagation loss, and the effect of shortening the optical path due to the one-cushioning is remarkable.

Also, the drive voltage used for these improved data is
Pulsed (5mS) utilizing the memory property of ferroelectric liquid crystal
This is a significant improvement in terms of driving power as compared with the case where nematic liquid crystal is used. FIG. 16 shows the switching operation state by the pulse voltage.

[Effects of the Invention] As described above, according to the present invention, a ferroelectric liquid crystal having superior properties as compared with a nematic liquid crystal is sandwiched between two transparent substrates, and the ferroelectric liquid crystal is put on a light incident surface to be predetermined. By aligning the helix axis of the liquid crystal in the direction of the angle and devising the electrode structure, both single mode light and multimode light can be operated with a simpler device structure with low crosstalk and low loss. In addition, the switching can be achieved without impairing the high speed and low voltage drivability originally possessed by the ferroelectric liquid crystal.

[Brief description of drawings]

FIG. 1 is a sectional view ((a), (b)) of an optical path switching device provided with a comb-shaped electrode according to an embodiment of the present invention and a view showing an initial orientation direction of ferroelectric liquid crystal molecules ((c)). 2, FIG. 2 is a conceptual diagram showing a molecular alignment state of a conventional nematic liquid crystal, FIG. 3 is a conceptual diagram showing a molecular alignment state of a ferroelectric liquid crystal used in the present invention with respect to various electric fields, and FIG. Of the principle of optical path switching of single-mode light by a liquid crystal, FIG. 5 is a detailed explanatory view of FIG. 4, and FIG. 6 is a view showing two alignment states of ferroelectric liquid crystal molecules used in a conventional optical path switch. FIG. 7 is a diagram showing a configuration example of an optical path switcher for multimode light by a conventional method using a ferroelectric liquid crystal, and FIG. 8 is a view showing two ferroelectric liquid crystal molecules used in the optical path switcher of the present invention. FIG. 9 is a diagram showing an orientation state, FIG. 9 is a diagram showing a calculation example of a refractive index change caused by the method of the present invention, FIG.
FIG. 10 is a sectional view of an optical path switching device having a comb-shaped electrode and a solid electrode according to a second embodiment of the present invention, and FIG. 11 is a third embodiment of the present invention.
Sectional view of an optical path switching device provided with a strip electrode is an example of
FIG. 12 is a cross-sectional view of an optical path switching device using a thin conductive wire as an electrode according to a fourth embodiment of the present invention, and FIG. 13 is a block diagram of a bulk type optical path switching device mounting the electrode structure of the present invention, FIG. 14 is a configuration diagram of an optical waveguide type optical path switch mounted with the electrode structure of the present invention, and FIG. 15 is a diagram showing the temperature dependence of the tilting angle and the tilt angle of the molecules of the ferroelectric liquid crystal actually used. FIG. 16 is a diagram showing a switching operation state by a pulsed voltage, and FIG. 17 is a diagram showing a composition and a phase change of a ferroelectric liquid crystal used in the present invention. 2 ... Solid electrode, 11 ... Ferroelectric liquid crystal, 11 '... Ferroelectric liquid crystal molecule, 12 ... Helical axis of ferroelectric liquid crystal, 21 ... Transparent substrate, 31 ... Light incident surface, 35 ... Helix axis of ferroelectric liquid crystal molecule, 37 ... Electric field, 41 ... Insulating film (alignment film), 42 ... Comb-shaped electrode, 43 ... Meandering electrode, 51 ... Strip electrode, 61 ...
… Thin conductive wire electrodes, 93… Multimode light.

Claims (8)

[Claims] 1. A ferroelectric liquid crystal is interposed between two transparent substrates that are arranged to face each other and electrodes provided on each of the facing surfaces of the transparent substrate, and an optical path that contacts the liquid crystal of the transparent substrate is provided. In the optical path switching device, the refractive index of which is selected to be larger than at least one of the two refractive indexes of the ferroelectric liquid crystal which can be switched from the outside, and the helical axis of the molecules of the ferroelectric liquid crystal is used as the light incident surface. And a means for setting such that they intersect at an angle that gives the maximum change in the refractive index for both S-polarized light and P-polarized light, and the molecular long axis of the ferroelectric liquid crystal is at the interface of the ferroelectric liquid crystal layer. Between the two alignment states of the second alignment in which the angle between the first alignment that is substantially parallel and the interface of the liquid crystal layer is the angle that gives the maximum change in refractive index for both S-polarized light and P-polarized light. And an optical path switching device. 2. The optical path switching device according to claim 1, wherein at least one of the two alignment states is aligned by an electric field generated by electrodes provided between the transparent substrates. . 3. The optical path switching device according to claim 1, wherein the angle between the helix axis and the incident surface is set to be equal to or greater than the angle between the helix axis and the molecular long axis cut by the liquid crystal. 4. The optical path switching device according to claim 1, wherein at least one of the two alignment states is aligned by an electric field generated by electrodes provided between the transparent substrates. 5. The optical path switching device according to claim 1, wherein the electrode provided on one of the facing surfaces of the transparent substrate is a comb-shaped electrode. 6. The electrode comprises a film-like transparent electrode having a uniform thickness provided on each of the opposing surfaces of the transparent substrate, and an insulating film sandwiched between at least one of the transparent electrodes. 2. The optical path switching device according to claim 1, wherein the optical path switching device has a structure in which a shaped electrode is provided. 7. The electrode comprises a film-like transparent electrode having a uniform thickness provided on each of the opposing surfaces of the transparent substrate, and an insulating film provided on each transparent electrode, and between the opposing insulating films. 2. The optical path switching device according to claim 1, wherein the optical path switching device has a structure in which a plurality of strip electrodes are arranged in parallel at predetermined intervals and sandwiched. 8. The electrode comprises a film-like transparent electrode having a uniform thickness provided on each of the opposing surfaces of the transparent substrate, and an insulating film provided on each transparent electrode, and between the opposing insulating films. 2. The optical path switching device according to claim 1, wherein a plurality of thin conductive wires are arranged in parallel at a predetermined interval and sandwiched therebetween.