JP2002031794A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device that uses neither electric field nor electric current, excited only by the intensity of light, can control light, has a light quality display function having a high contrast ratio, can be made a large size screen, can conduct a set light emitting operation, and can greatly improve the efficiency of optical switches. SOLUTION: The device is provided with an optical waveguide (or optical fiber) 1, a transparent electrode 2 which is arranged to be orthogonal or approximately orthogonal to the waveguide (or plural fiber) 1 and a liquid crystal element 3 which is arranged at the crossing point of the waveguide (or optical fiber) 1 and the electrode 2 and responds to the signal of the electrode 2. The difference between the refractive index of the element 3 and the waveguide 1 is set equal to or less than 0.07 or desirably set to zero and at least an optical display function is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type optical device having at least an image display function and a two-dimensional optical operation function.

[0002]

2. Description of the Related Art In recent years, a display device (display device) has become a man-machine interface.
As the inter-face, the demand is increasing more and more, and it is roughly classified into a self-luminous type and a light-receiving type. That is, as a self-luminous type, CRT (cathode ray tube), PDP
(Plasma display), ELD (electroluminescence display), VFD (fluorescent display tube), LED (light emitting diode), etc., and as the light receiving type, LCD (liquid crystal display), ECD (electrochromic display), etc. . All of these displays have been improved in performance due to the development of electronics, and it is expected that both the quality and the price have already reached a mature stage, or will soon enter that stage.

[0003] However, even high-performance displays that make full use of such electronics have not yet sufficiently responded to the changing needs of society and the changing tastes of consumers. For example, in this type of display, an electrode is indispensable because an electric field and a current are used for a screen. However, when an attempt is made to increase the size of a display panel, the electrical resistance due to the electrode or its wiring is inevitably increased. This is the biggest factor preventing the panel from increasing in size, and the screen size of the display is naturally limited. In addition, since the materials used for the display are often hard, it is extremely difficult to make the display a desired size or shape.

[0004] In addition, for example, in the case of a display using electronics such as a large home television, space saving such as a large volume or power consumption and a short response speed when following a high definition signal is required. -There is room for improvement in terms of power saving and high image quality.

Therefore, the present inventor, when developing a display device, fundamentally differs from the conventional technology using electronics, and focuses on full-scale use of photonics (technology that handles optical processes without using an electric field). did.

In the 1970's, a thin display using a combination of an optical waveguide and an optical switch has been proposed as a very low-efficiency one simply using photonics (US Pat. No. 3,838,908, "Guided lilght structures employ").
ing liquid crystal "DJChannin, RCA Corporation,
Oct. 1, 1974). This thin display uses a liquid crystal (nematic) to control the refractive index and change the total reflection of the optical waveguide.
D, etc., there is no good light source, the optical transmission loss of the optical waveguide is large, and the alignment control of the liquid crystal used for the optical switch has not been sufficiently studied.
E. Seiden, "Liquid crystal display device", IBM Te
ch. Disc. bull. Vol. 14, No. 1, p.223, 1971), which lacked practicality and was never commercialized.

Further, in the 1990's after the 1980's, research on lasers began to be actively carried out, and optical waveguide type display devices using the same as light sources were also developed.
It has been proposed. A typical example is to use a gas laser for each of the three primary colors of RGB, one for each light source, guide the laser light therefrom into an optical fiber, and turn on and off the light by a liquid crystal switch. However, this has never been put to practical use.

As described above, although the optical waveguide type display utilizing photonics has a long history of research, it has never been put to practical use or commercialized yet, and its concrete manufacturing method has not been established. Absent.

According to the analysis of the present inventor, the background of such circumstances is that the response speed of the liquid crystal switch is speeded up, its temperature dependence is stabilized, its efficiency is improved, and these three problems are mainly solved. You may not be there. However, according to the study of the present inventors, two of them can be solved by the following measures.

First, the problem of the response speed of the optical switch can be solved by using a ferroelectric liquid crystal in particular, and by not using any memory function unlike the conventional case.

That is, the HDTV of the interlace signal
In the case of (1), when line-sequential driving is performed without using an active element or the like, the display time of one pixel is 1/30 Hz / 1125 line = 29.6 μs.

In the case of UXGA of a progressive signal, the display time of one pixel is 1/60 Hz / 1200 line = 14 μs.

[0013] The ferroelectric liquid crystal is capable of realizing a response speed on the order of microseconds because a permanent dipole of the liquid crystal molecule itself acts on an applied electric field, which is a high definition typified by high definition. This is a response speed that can sufficiently respond to driving of a simple display. (By the way, the response speed of the nematic liquid crystal is on the order of millimeters).

In addition, it is necessary to regulate the orientation of the liquid crystal element not from two surfaces as in the past, but from three or more surfaces. Thereby, the liquid crystal element can be driven in a new mode that does not use the memory property, fluctuations in the bulk characteristic of liquid crystal can be suppressed more than ever, and the temperature dependency itself can be stabilized.

[0015]

The remaining major problem is to improve the efficiency of the optical switch, that is, the optical switch effect as much as possible. However, up to now, how to achieve it has not been known yet, and practical optical devices with satisfactory switching effects have never been developed before. Not even known.

The present invention has been made in order to improve the above circumstances, and an object of the present invention is to add a unique and strict design to the birefringence and alignment method of liquid crystal so that the maximum optical switching effect can be obtained. An optical waveguide type optical device is provided.

[0017]

That is, a first optical device of the present invention comprises: an optical waveguide (or an optical fiber); an electrode intersecting the optical waveguide (or an optical fiber); and the optical waveguide (or an optical fiber). A fiber) and a liquid crystal element arranged at the intersection of the electrodes and responding by the electrodes.
The difference between the refractive index of the liquid crystal element and the refractive index of the optical waveguide is 0.07 or less.

Further, the second optical device of the present invention comprises: an optical waveguide (or an optical fiber); an electrode intersecting the optical waveguide (or the optical fiber); an optical waveguide (or an optical fiber); A liquid crystal element arranged at the intersection and responding by the electrode; and an angle between a liquid crystal molecule of the liquid crystal element and an emission surface (YZ plane) out of the optical waveguide is set to a major axis of the liquid crystal molecule. when the refractive index in the direction and n _e, the refractive index along the short axis and n _o,

[0019]

(Equation 6) Less than.

Further, the third optical device of the present invention comprises: an optical waveguide (or an optical fiber); an electrode crossing the optical waveguide (or the optical fiber); A liquid crystal element arranged at the intersection and responding by the electrode; and an angle formed between a normal direction of the liquid crystal layer of the liquid crystal element and a normal direction of the optical waveguide of the optical waveguide is a major axis direction of the liquid crystal molecules. the refractive index n _e of, when the refractive index along the short axis n _o, the angle a of theta _p of the liquid crystal molecules and the light traveling direction within the optical waveguide, the tilt angle at the time of switching of the liquid crystal molecules was theta,

[0021]

(Equation 7) Or

(Equation 8) It is characterized by being located between.

According to the present invention, in an optical device having a liquid crystal element responding by the electrode at the intersection of the optical waveguide and the electrode, the difference between the refractive index of the liquid crystal element and the refractive index of the optical waveguide is as described above. Or the angle between the liquid crystal molecules and the exit surface out of the optical waveguide is specified as described above, or the angle formed between the liquid crystal layer normal direction and the optical waveguide normal direction is Therefore, the optical switch efficiency can be significantly improved. Therefore, a high degree of practicability can be exhibited, especially when a ferroelectric liquid crystal is used as the liquid crystal, and the memory is not used, and the alignment is regulated from many aspects.

[0023]

In the present invention, it is preferable that the difference between the refractive index of the liquid crystal element and the refractive index of the optical waveguide be as close to zero as possible or zero.

Further, the long axis direction of the refractive index n _e of the liquid crystal molecules, the refractive index n _o of the short axis direction, the angle between the light traveling direction in the liquid crystal molecules and the optical waveguide theta _p, when switching the liquid crystal molecules When the tilt angle of θ is θ, the angle between the liquid crystal layer normal direction of the liquid crystal element and the optical waveguide normal direction of the optical waveguide is:

[0025]

(Equation 9) Or

(Equation 10) Is preferable.

Next, a preferred embodiment of the present invention will be described. FIG. 10 shows an optical device as an optical waveguide display according to a preferred embodiment of the present invention. In each pixel, the optical waveguide 1 and the transparent electrode 2 such as ITO are orthogonal or substantially orthogonal, and a liquid crystal element 3 as an optical switch is disposed at the intersection. The liquid crystal element 3 responds with the electric field intensity, that is, an element that changes the refractive index according to the electric field intensity.
A transparent electrode 3a such as TO, a liquid crystal alignment group 3b, and a liquid crystal 3c.
Consists of The optical waveguide 1 is preferably made of, for example, a plastic fiber or a glass fiber having a high waveguide efficiency. If it is a three-dimensional polymer waveguide, it may be formed on a film by a photolithography method. In addition,
The light source 4 is not particularly limited, but a laser beam such as a semiconductor laser is practical and preferable.

FIG. 11 shows a use form of the above-described optical device. By using a flexible material such as plastic as a constituent material of the device, a powerful screen is provided.
Starting from a 0 degree curved display (A), a hemispherical display (B), a full spherical display (C), a display that can be rolled up when not in use (D), and the surface of articles such as clothes and hats or cups It can be used for various display purposes, up to the adhesive display (E) applied to.

The optical device of the present invention can be made thin, large, and high-definition, and is very bright because it is a self-luminous type that uses a light source efficiently, and the contrast ratio required for a large screen is 500: 1. Can also be easily realized.

Next, the strict design of the liquid crystal birefringence and the alignment method performed by the present inventors will be described in detail.

Liquid crystal molecules have a birefringence in the major axis direction and the minor axis direction, and the value is usually about 1.48 to 1.72.

In the optical waveguide type optical device of the present invention, turning off the outgoing light promotes total reflection of light using the lower refractive index of the liquid crystal switch, and turning on the output light utilizes the higher refractive index of the liquid crystal switch. To transmit light.

FIG. 1 shows a liquid crystal switch according to the present invention when the emitted light is off.

Here, assuming that the refractive index of the optical waveguide is n _f , the refractive index of the liquid crystal switch is n _eff , and the incident angle is θ _in , these relations in the off state satisfy the following equation (1). .

[0034]

[Equation 11] As can be easily predicted from FIG. 1 and equation (1), the difference between the lower effective refractive index during liquid crystal switching and the refractive index of the waveguide is large, based on the total reflection condition. By relaxing the restrictions, switch efficiency is improved.

On the other hand, the transmittance is calculated next in order to estimate the optimum condition of the refractive index of the liquid crystal switch when the emitted light is on.

FIG. 2 shows the liquid crystal switch when the emitted light is on.

A calculation result of the transmittance of Fresnel when the difference between the refractive index of the liquid crystal switch and the refractive index of the waveguide is changed will be described below.

[0038]

(Equation 12)

(Equation 13)In the above equation (2), θ₁Is incident on the waveguide
Angle, n_fIs the refractive index of the waveguide, Δn is the refraction of the liquid crystal switch
Index and the refractive index difference of the waveguide (Δn = n_eff ^on-N_f), T _pIs
Transmittance of p (TE) polarized light, Ts is transmission of s (TM) polarized light
Rate. In order to estimate the tendency, the incident angle was set to 75 ° or
Is 85 ° and the waveguide index is 1.55 or 1.59.
The calculation was performed by fixing each of the two types. Fig.
3 to 6.

In each case, the smaller the value of Δn,
In other words, the closer the refractive index of the liquid crystal switch and the refractive index of the optical waveguide are, the better the transmission efficiency is. That is, in the present invention, the difference between the refractive index of the liquid crystal switch and the refractive index of the optical waveguide is 0.07 or less, preferably zero.

The effective refractive index of the liquid crystal switches, the birefringence of the liquid crystal material itself (n _e: molecular long axis direction, n _o: molecular minor axis direction) and tilt angle (theta), the pretilt angle (theta _p: It is determined by the relationship between the angle between the substrate and the liquid crystal molecules) and the direction of the optical waveguide in the optical waveguide (or optical fiber).

The birefringence of the liquid crystal itself depends on the relationship between the refraction of the liquid crystal molecules and the liquid crystal composition, and the tilt angle and the pretilt angle depend on the anchoring energy with the interface in contact with the liquid crystal molecules. Each can be controlled by selecting the material.

[0042] Given the projection onto the Y-Z plane of the birefringence of the liquid crystal molecules, refractive index of the liquid crystal molecular long axis direction is a n _e cos [theta] _p, the refractive index of the short axis direction is n _o.

As shown in FIG. 7, when the refractive index n _f of the waveguide is less than n _o [quartz optical fiber (n _f 1.45)
And polymethyl methacrylate optical fiber ( _nf 1.4
9) can be used], the pretilt angle θ _p is

[Equation 14] It is necessary to be above. The refractive index n _f of the waveguide n _o
When greater than [polycarbonate (n _f 1.58
5), polystyrene (n _f 1.590) material and the like can be used] is the pretilt angle theta _p is

(Equation 15) Must be less than

From the above equation (1), in order to widen the incident angle condition, it is better that the difference between the effective refractive index of the liquid crystal molecules when the emitted light is on and the effective refractive index when the emitted light is off is large.

Further, in order to realize a high pretilt angle, a cross-linked polyimide rubbing alignment film, an inorganic oblique deposition film, or the like must be used as an alignment film for aligning liquid crystal molecules. Considering that there are still few types of cross-linked polyimide alignment films, the fact that vacuum deposition is costly, and that it is difficult to increase the size, it is not realistic to achieve a high pretilt angle when commercializing. Not a target. Use of a vertical alignment film or the like is not very practical when commercialized. If a vertical alignment film or the like is used, it is immediately understood that the switch for the TM mode, rather than the TE mode, has higher efficiency. FIG. 3-
As can be seen from Fig. 6, from the transmittance surface, T
The E mode is more efficient.

From the above reasons, as the waveguide material selected so as refractive index n _f is between n _e and n _o. In addition, the pre-tilt angle is

(Equation 16) A material having a characteristic of less than 0 °, preferably 0 °, is selected.

[0047] For example, a liquid crystal material _{(n o: 1.50, n e} :
When 1.67) is used, the pretilt angle must be less than 26 °, and polyvinyl alcohol (θ _p :
0 °) or Nippon Synthetic Rubber Polyimide Optmer A
L1000 series (θ _p : 0 to 2 °), JALS-1
46 Series _{(θ p: 1~2 °),} AL3000 series _{(θ p: 2~4 °),} JALS-1082 series _{(θ p: 4~6 °),} JALS-1085 series (θ _p: 5~7 ° ) Can be used.

When the relationship between the switching dynamics of the liquid crystal molecules and the optical waveguide direction Z (TE mode) is determined as shown in FIG. 8, the effective refractive indices (n _eff ¹ , n _eff ² ) of the liquid crystal switch are determined.
Equations (2) and (3) are shown.

In the case of the molecular arrangement (A) of the liquid crystal

[Equation 17]

(Equation 18) For liquid crystal molecular configuration (B)

[Equation 19]

[0050]

(Equation 20) Of n _eff ¹ and n _eff ² , the larger value is the switch position when the emitted light is on, and the smaller value is the switch position when the emitted light is off. The pretilt angle is

(Equation 21) If the condition of less than is satisfied, n _eff ¹ is the switch position when the emitted light is on.

When the molecular arrangement of the liquid crystal is (A), the highest efficiency is obtained when the waveguide refractive index n _f is equal to n _eff ^ON . Therefore, the following conditions are good.

(Equation 22) If the transmission efficiency as a display is 70% or more,
As previously mentioned

(Equation 23) To be

(Equation 24) (See FIG. 9).

Therefore, assuming that the tilt angle at the time of response of the liquid crystal is θ (see FIG. 8), the alignment direction of the liquid crystal is set to a direction inclined by (θ + φ) from the Y-axis direction.

Similarly, when the molecular arrangement of the liquid crystal is (B), the orientation direction of the liquid crystal is set at a direction inclined (θ-φ) from the Y-axis direction.

When it is difficult to make the alignment of the liquid crystal uniform over the entire screen in manufacturing a large display of 40 inches or more, as shown in FIG. Polymer. At this time, the liquid crystal is not injected but is applied in a coating type. Even if it is 100 inches, since the pixel area is about 1 mm ² , the alignment of the liquid crystal becomes easy.

[0055]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

An optical device as shown in FIG. 10 was manufactured as follows. First, as a liquid crystal material, a ferroelectric liquid crystal material M62344 (n _O : 1.48 manufactured by Japan Energy Co., Ltd.) was used.
9, n _e: the 1.666), also in the optical waveguide, Mitsubishi Engineering Plastics Co., Ltd. Iupilon series of polycarbonate (n
_f : 1.585) was selected. A 10 wt% aqueous solution of polyvinyl alcohol (n = 500) was used to form an alignment film, and the baked film was subjected to a rubbing treatment to align the liquid crystal material. When a rectangular wave was applied, the tilt angle of this alignment film was 20 °, and the pretilt angle was 0 °. From the results described above, φ of this liquid crystal material is 40.17 °, that is, the angle between the liquid crystal layer normal direction and the waveguide normal direction is 60.
17 ° (29.83 ° from the waveguide direction).

[0057] Polycarbonate sheets has high very thin flexibility compared to conventional liquid crystal panel, considered necessary to introduce a sufficient spacer to the switch portion, so that 200 to 500 pieces / mm ² , Spacers were sprayed. As a spacer, a 1.5 μm diameter sphere was dispersed in ethanol and spin-coated. The grating for emitting light uses # 2000 file,
It was produced by rubbing in one direction 10 to 20 times.

A red / green / blue semiconductor laser was used as a light source. The polarization direction of these devices is T
They were arranged so as to be incident in the E mode, and were coupled with an optical adhesive.

The liquid crystal was driven by applying a 2 Hz rectangular wave at 10 V. It was confirmed that the guided light from the light source was turned on and off with good contrast in the x-axis direction in accordance with the driving of the liquid crystal.

[0060]

As is apparent from the above description, the optical device of the present invention has a structure in which a liquid crystal element which operates in response to an electric field generated by the electrode is provided at the intersection of the optical waveguide and the electrode. The difference between the refractive index and the refractive index of the optical waveguide, or the angle between the liquid crystal molecules and the exit surface out of the optical waveguide, or the angle formed between the liquid crystal layer normal direction and the optical waveguide normal direction,
Since each is specified as described above, the optical switch efficiency can be significantly improved.

Therefore, if a ferroelectric liquid crystal is selected as the liquid crystal and the alignment is regulated from many sides without using the memory property, a high degree of practicality can be exhibited as a display or a two-dimensional arithmetic device. It is possible to

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a liquid crystal switch in a state where emitted light is off.

FIG. 2 is a schematic configuration diagram showing a liquid crystal switch in an on state of emitted light.

FIG. 3 is a diagram showing the relationship between Δn (the difference between the refractive index of the liquid crystal switch and the refractive index of the optical waveguide) and the relative ratio of transmittance.

FIG. 4 is a diagram showing a relationship when the incident angle θ ₁ is changed.

FIG. 5 is a diagram showing a relationship when the refractive index of the optical waveguide is changed.

FIG. 6 is a diagram showing a relationship when the incident angle is further changed.

FIG. 7 is a diagram showing a relationship between a pretilt angle and birefringence of liquid crystal molecules.

FIG. 8 is a spatial layout diagram showing the relationship between the orientation direction of liquid crystal molecules and the optical waveguide direction Z.

FIG. 9 is a diagram showing a relationship between a refractive index of a liquid crystal switch (when turned on) and a refractive index of an optical waveguide.

FIG. 10 is a schematic perspective view of an optical device (optical waveguide type) showing one embodiment of the present invention.

FIG. 11 is a schematic diagram showing each example of a usage form of the optical device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical waveguide (or optical fiber), 2 ... Transparent electrode, 3
... Liquid crystal switch, 3a ... Transparent electrode, 3b ... Alignment film group, 3
c ... liquid crystal, 4 ... light source

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H088 EA02 EA33 EA63 GA04 GA17 HA11 HA28 HA30 JA17 KA05 KA14 MA02 MA06 2H091 FA19X FA23Z FA24Z FA45Z FA46Z GA02 GA06 HA12 KA01 KA05 LA17 MA10 2K002 AA07 AB07 BA06 CA08 DA06 DA07 HA06 HA07

Claims (5)

[Claims] 1. An optical waveguide (or optical fiber); an electrode intersecting the optical waveguide (or optical fiber); and an intersecting portion between the optical waveguide (or optical fiber) and the electrode, and a response by the electrode. An optical device having at least an optical display function, wherein a difference between a refractive index of the liquid crystal element and a refractive index of the optical waveguide is 0.07 or less. 2. The optical device according to claim 1, wherein a difference between a refractive index of the liquid crystal element and a refractive index of the optical waveguide is zero. 3. An optical waveguide (or optical fiber); an electrode intersecting the optical waveguide (or optical fiber); and an intersecting portion of the optical waveguide (or optical fiber) and the electrode, and a response by the electrode. The angle between the liquid crystal molecules of the liquid crystal element and the exit surface (YZ plane) out of the optical waveguide is such that the refractive index in the major axis direction of the liquid crystal molecules is _ne and the minor axis is when the refractive index of the direction is n _o, [number 1] An optical device having at least an optical display function. 4. An optical waveguide (or optical fiber); an electrode crossing the optical waveguide (or optical fiber); and an intersecting portion between the optical waveguide (or optical fiber) and the electrode, and a response by the electrode. The angle between the liquid crystal layer normal direction of the liquid crystal element and the optical waveguide normal direction of the optical waveguide is such that the refractive index in the major axis direction of the liquid crystal molecules is _ne , and the minor axis direction. Where n _{o is} the refractive index of the liquid crystal, θ _p is the angle between the liquid crystal molecules and the light traveling direction in the optical waveguide, and θ is the tilt angle when switching the liquid crystal molecules. Or, An optical device having at least an optical display function, located between the optical devices. 5. An angle formed between a normal direction of a liquid crystal layer of the liquid crystal element and a normal direction of an optical waveguide of the optical waveguide is expressed as follows: Or The optical device according to claim 4, wherein