JP2001051271A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a device which can save space and electric power and which realizes high image quality by disposing a light emitting element, optical waveguide to guide the light introduced from the light emitting element, optical switch to turn on and off the guided light, and color converting member which is excited by the guided light to emit light. SOLUTION: A short wavelength semiconductor laser or the like is used as a light source, an optical fiber 3 is used as the optical waveguide, a liquid crystal layer 4, especially a ferroelectric liquid crystal, which can perform fast switching and has a large difference in double refraction is used as the optical switch to control total reflection, and a phosphor layer 5 is used as the color converting member. Transparent electrodes 6, 7 are formed, for example, as XY matrix electrodes on both sides of the liquid crystal layer 4 to drive the layer 4. Furthermore, alignment films 8, 9 to align the liquid crystal molecules of the liquid crystal layer 4 are formed. With this structure, since the loss of light is small for increasing the light emission efficiency, the structure is simple and the device can be made large in size and can be made thin, regardless of its size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical waveguide,
The present invention relates to a novel light emitting and display device of an optical waveguide type that excites a phosphor or the like by turning on / off light from a light emitting device.

[0002]

2. Description of the Related Art In recent years, demands for electronic display devices have been increasing as man-machine interfaces.

[0003] Conventional electronic display devices include:
Self-luminous type and light-receiving type are classified, and as a self-luminous type electronic display device, CRT (cathode ray
tube, a plasma display (PDP), an electroluminescence display (ELD), a fluorescent display tube (VFD), a light emitting diode (LED), and the like.

As a light receiving type electronic display device, a liquid crystal display (LCD), an electrochromic display (ECD), an electrophoretic display (ECD)
PID), a dispersed particle oriented display (SPD), a colored particle rotating display (TBD), and the like are known.

However, for example, when the above-mentioned display is considered as a large-sized television receiver for home use, space and power consumption are reduced due to large volume and power consumption and insufficient response speed to follow a high-definition signal. In terms of image quality, it is hard to say that it has been fully completed.

[0006]

In such a situation,
In the 1970's, a thin display combining an optical waveguide and an optical switch was proposed (US Pat. No. 383).
No. 8908).

In this thin display, the refractive index is controlled by the liquid crystal, and the total reflection of the optical waveguide is controlled.

However, at that time, lasers, LEDs, and the like as light sources were not put into practical use, and the optical transmission loss of the optical waveguide was enormous. As it did not exist, it has not been commercialized.

On the other hand, in the 1990's, liquid crystal displays have been put into practical use, and their cost has been reduced.
In addition, as a disadvantage of the liquid crystal display, insufficient color purity and insufficient brightness have been pointed out, but as a means to solve it, using ultraviolet light or blue light instead of white light as the backlight of the liquid crystal, A display in which a liquid crystal panel is used as a shutter and a phosphor is disposed on the front surface has been devised (Japanese Patent Application Laid-Open No. 5-203909, Japanese Patent Application Laid-Open No. 9-1997).
197372).

Further, a laser of three primary colors of RGB is used as a light source,
A display that guides light using an optical fiber and turns it on and off using a liquid crystal switch has also been proposed (J. Viitane
n, et.Al., VTT, “Fiber optical liquid crystal disp
lays ”, SPIE Vol.1976 High-Definition Video, 293,
1993).

However, each of them has advantages and disadvantages and has not yet been put to practical use.

The present invention has been proposed in view of the above circumstances, and an object of the present invention is to provide a novel display element which can realize space saving, power saving, high image quality, and has a sufficient response speed.

[0013]

In order to achieve the above-mentioned object, a display device according to the present invention comprises a light-emitting element and light from the light-emitting element which is introduced and can take out the introduced light from an intermediate portion. An optical waveguide, an optical switch for turning on and off light extracted from the optical waveguide, and a color conversion member that emits light when excited by the light extracted from the optical waveguide.

As the optical waveguide, an optical fiber at least partially having no clad layer or an optical fiber having a clad layer at least partially having the same refractive index as the core layer is used.

The display element of the present invention is a display element having a novel configuration in which a light-emitting element, an optical waveguide, an optical shutter, and a color conversion member such as a phosphor are combined. Since it is a self-luminous type that is frequently used, it has advantages such as being very bright, being thinner, larger, and capable of higher definition.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a display device to which the present invention is applied will be described in detail with reference to the drawings.

The display element of the present invention uses a low-wavelength semiconductor laser or a light-emitting diode as a light source and an optical fiber (wire or rod-shaped) as an optical waveguide, and uses a liquid crystal, particularly a liquid crystal, as an optical switch for controlling total reflection. It uses a ferroelectric liquid crystal capable of high-speed switching and having a large birefringence difference, and is provided with a phosphor on the front surface.

The display element thus configured 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 is required for a large screen. A contrast ratio of 500: 1 can be realized.

FIG. 1 shows an example of a display element to which the present invention is applied, and shows a cross-sectional structure thereof.

In the display device shown in FIG. 1, an optical fiber 3 is fixed on a glass substrate 1 (for example, Corning 7059) by a low refractive index polymer 2, and a liquid crystal layer 4 serving as an optical switch is further provided thereon. A phosphor layer 5 as a color conversion member is formed.

On both sides of the liquid crystal layer 4, transparent electrodes 6 and 7 for driving the liquid crystal layer 4 are formed as, for example, XY matrix electrodes, and an alignment film for aligning liquid crystal molecules of the liquid crystal layer 4. 8, 9 are formed.

The liquid crystal layer 4 must be sealed in a cell. A cell is formed by arranging a glass substrate 10 facing the glass substrate 1 at a predetermined interval, and filling the cell with a liquid crystal material. It is formed by. Therefore, one transparent electrode 7 and the alignment film 9 are formed on the glass substrate 10.

The optical fiber used in the present invention is in the form of a wire or rod made of an inorganic material or an organic material, and is different from a three-dimensional waveguide formed on a substrate. It is a simple substance. The length is sufficiently large as compared with the waveguide diameter.

The cross-sectional shape of the optical fiber is arbitrary and is not particularly limited, but may be, for example, a circle, a polygon, or the like. Ferroelectric liquid crystals can be aligned with good contrast even on a semi-cylindrical shape.

This optical fiber is used by being fixed to a substrate with a polymer having a low refractive index.

The polymer type three-dimensional optical waveguide to be formed on the substrate is uniformly coated in advance to obtain a three-dimensional structure.
It must be etched. Micron-order processing accuracy cannot be obtained by chemical etching, and reactive ion etching (RIE) is required to increase processing accuracy.
However, in this case, the surface of the waveguide is roughened, and the light loss is increased. Actually, when comparing the optical loss between the polymer type three-dimensional waveguide and the polymer type optical fiber, 0.16 dB / cm (at a wavelength of 633 nm) (KS Brown, et. Al., “Characterization of P
oly (Phenylsilsesquixane) Thin-Film Planar optical
Waveguides ”, IEEE Photonics Technology Letters,
Vol. 9, No. 6, 1997) and 0.4 dB / m (wavelength 633)
nm) and the difference is evident.

On the other hand, the liquid crystal material used for the liquid crystal layer is arbitrary, but a ferroelectric liquid crystal or an antiferroelectric liquid crystal is preferable.

Since the ferroelectric liquid crystal has a composition containing a large number of tricyclic molecules, it is characterized in that it has a large birefringence difference, unlike a general nematic liquid crystal in which a large number of bicyclic molecules are contained. In an optical switch that controls total reflection using a change in refractive index, the loss is smaller as the birefringence difference is larger. In particular, a ferroelectric liquid crystal has a response speed of the order of microseconds (the response speed of a nematic liquid crystal is of the order of milliseconds) because the permanent dipole of the liquid crystal molecules itself acts on an applied electric field. It can sufficiently cope with driving of a high-definition display represented by definition.

The display time of one pixel is as follows. In the case of HDTV of an interlace signal, when a simple matrix drive is performed without using an active element or the like, 1/30 Hz / 1125 lines = 29.6 μs. In the case of a UXGA of a progressive signal, 1/60 Hz / 1200 lines = 14 μs.

As shown in FIG. 2, the effective refractive index n _eff of the liquid crystal is represented by the following equation (1), where φ is the angle between the long axis of the liquid crystal molecules and the incident direction of the light beam polarized parallel to the substrate surface. ,
(Y. Sadorihara, et. Al., Technology Report of the
0saka University, Vol. 42, No. 2091, pp. 137, 19
92), by controlling the orientation direction, n⊥ <n _eff <n
Take a value in the range //.

[0031]

(Equation 1)

(N //: refractive index in the major axis direction of liquid crystal molecules, n
⊥: Refractive index in the short axis direction of liquid crystal molecules) The most important point in designing an optical switch is controlling the refractive index of the liquid crystal. on·
In order to optimize the OFF ratio, n _eff in the ON state and the OFF state is selected as follows.

_Assuming that n _eff ^OFF is off and n _eff ^ON is on, the above equation can be rewritten as the following equation (2), where n _eff ^OFF <n _f <n _eff ^ON ( _nf : refractive index of the optical fiber). Here, θ is a tilt angle when a certain liquid crystal composition and an alignment film are used (see FIG. 2).

[0034]

(Equation 2)

The alignment direction of the liquid crystal is (φ + θ). At this time, in order to select φ, the following is considered from the relationship with the refractive index of the optical fiber. As an example, n⊥ is 1.493, n
// is 1.667, θ is 20 °, and the refractive index is 1.
Assuming that 59 optical fibers are used, the relationship between φ and the effective refractive index n _eff is calculated as shown in FIG. Therefore,
When φ is 31 °, the difference from n _f is the largest both on and off. Therefore, the orientation direction may be set to 41 °.

The conditions for the refractive index of the liquid crystal are different depending on the tilt angle and the refractive index of the optical waveguide, but the refractive index n⊥ in the minor axis direction is less than the refractive index of the cladding layer or the core layer of the optical waveguide. It is preferable that the rate anisotropy Δn is 0.1 or more.

As the optical shutter, for example, a mechanical shutter or the like can be used.

As a light source, a near ultraviolet or blue wavelength is used. Low energy ultraviolet light having a large energy is useful for the phosphor, but many liquid crystal and polymer organic substances have ultraviolet absorption, and deterioration is expected. Also, the problem of transparency to ultraviolet light can be avoided.

As the color conversion member, a phosphor is used in consideration of quantum efficiency.

For example, when a blue light emitting element is used,
The conversion efficiency when a green light emitting element is used is compared (assuming that the quantum efficiency of the phosphor is 1).

Blue-green conversion efficiency and blue-red conversion efficiency λB / λG, λB / λR green-blue conversion efficiency and green-red conversion efficiency (1/2) λG / λB, λG / λR red-blue conversion efficiency and Red-green conversion efficiency (1/2) λR / λB, (1/2) λRG / λG Suppose blue 470 nm, green 550 nm, red 620 n
m, 64.8% for both green and red when the light emitting element is blue, 51.9% for both blue and red when the light emitting element is green, and both blue and green when the light emitting element is red. 37.2%. If the wavelength is lower than that of the light emitting element, the conversion efficiency decreases. Therefore, it is preferable to use a light source having a wavelength of blue or less.

When a blue laser is used as the light source, a laser dye organic phosphor may be used for the color conversion member of the blue pixel. This is to avoid the speckle effect which is one of the characteristics of the laser. Organic phosphors are good at color conversion with a wavelength shift of about the Stokes effect, and therefore have a wide range of material choices.

The basic structure of the display element to which the present invention is applied has been described above. A low-wavelength semiconductor laser or a light emitting diode is used as a light source, and an optical fiber (wire or rod) is used as an optical waveguide. Then, the calculation results of the transmission loss of a display using a liquid crystal as the optical switch for controlling total reflection, particularly a ferroelectric liquid crystal capable of being a high-speed switch and having a large birefringence difference, and having a phosphor disposed on the front surface are shown.

Light source coupling 80% × waveguide loss 80% × optical switch efficiency 80% = 51% Ultraviolet-visible conversion efficiency = 90% External light reflection + visible light utilization rate = 70% LD or LED power efficiency = 25% Total = 8% (12.5 times) The required power of the excitation source is π × 200 nit = 628 lm / m ² (683 lm = 1 W at when a display of 100 inch size (3.1 m ² ) at a luminance of 200 nit is considered. R 612 nm Relative luminosity 0.50 205 lm / m ² 0.6 W / m ² 1.86 W G 530 nm Relative luminosity 0.86 353 lm / m ² 0.6 W / m ² 1.86 W B 470 nm Relative luminosity 0.17 70 lm / m ² 0.6 W / m ² 1.86W Total 5.58W. Although it is an ideal value, the efficiency is considerably high. When a ferroelectric liquid crystal is used, it can take only two values because of its greatest feature, ie, memory properties, that is, it is bistable. As a method of displaying the present invention in full color, in addition to the time-resolved method and the area gradation method, light intensity modulation of a laser or LED as a light source can be considered.

In making a large display of 40 inches or more, when it is difficult to uniformly align the liquid crystal over the entire screen, as shown in FIG.
After the low-refractive-index polymer layer 12 is formed thereon, the space 13 may be left only in the pixel portion, and the liquid crystal material 14 may be put in the void 13 and covered with the low-refractive-index polymer. At this time, the liquid crystal is not injected but is applied in a coating type. The pixel area is 10
Even if it is 0 inch, it is about 1 mm ² , so that the alignment of the liquid crystal becomes easy.

The orientation of the ferroelectric liquid crystal in a monostable / hemi-stable state may be selected. In that case, the active element is provided in each pixel without driving in the simple matrix.

[0047]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

First, a low-refractive-index polymer (Cytop: 1.34, trade name, manufactured by Asahi Glass Co., Ltd., having a refractive index of 1.34) was formed on a 40 mm × 25 mm × 1.1 mm glass substrate (manufactured by Corning, trade name: 7059) with a thickness of 50 μm. Was applied using a squeegee.

Next, after precuring at 80 ° C. for 60 seconds, polycarbonate optical fiber (refractive index: 1.59,
Fiber diameter 1 mm: Adjust the refractive index of the cladding layer and the core layer, the difference is 0.01 or less, and arrange 10 lines (Polycarbonate optical fiber has refractive index between birefringence of liquid crystal and heat resistance) And calcined at 120 ° C. for 1 hour.

As shown in FIG. 1, a transparent electrode (ITO) was RF magnetron sputtered to a thickness of 20 nm using the OFF AXIS method so as to form a pixel perpendicular to the optical fiber.

Further, polyvinyl alcohol (P
VA) Spin coat thin film (degree of polymerization 5OO, 1% by weight)
Aqueous solution, 200 rpm 5 seconds + 2000 rpm 20 seconds), 11
It was baked at 0 ° C. for 1 hour. After baking, the rubbing treatment was performed by setting the orientation direction to a direction inclined by (π / 2−θ) from the optical waveguide direction (θ: tilt angle of ferroelectric liquid crystal).

As a counter substrate, 10 lines of I
On a glass substrate with a TO transparent electrode (40 mm x 25 mm x
(0.1 mm) to form a PVA rubbing alignment film.

Further, a fine particle type inorganic phosphor (ZnS: Cu, Al) was formed to a thickness of 50 μm on the glass substrate on which the transparent electrode was not formed by using a sedimentation method.

The two substrates were combined so that the orientation directions were antiparallel, and bonded together with an ultraviolet-curing resin mixed with 0.15% by weight of a 3.0 μm spacer (manufactured by Catalyst Kasei Co., Ltd.). In the gap, a ferroelectric liquid crystal composition of 100
Injected at ° C. Table 1 shows the physical property values of the used ferroelectric liquid crystal composition. Although the cross section of the fiber was circular, good orientation was obtained.

[0055]

[Table 1]

As described above, calculations were performed to determine the optimum φ. The results are shown in FIGS.

Each was calculated as follows to determine the orientation direction.

FLC1 48 ° + 15 ° = 63 ° FLC2 35 ° + 15 ° = 50 ° FLC3 40 ° + 20 ° = 60 ° FLC4 31 ° + 20 ° = 51 ° The wavelength of the incident light is 380 nm, and the polarization direction of the light is It was parallel to the substrate surface. The input / output coupling is TiO ₂
This was performed using a rutile prism.

For the response of the liquid crystal, using a waveform generator,
A 1 kHz rectangular wave ± 5 V was applied.

The switching efficiency of the liquid crystal was measured using an optical power meter (TQ8210: manufactured by Advantest Co.), and the efficiency after forming the liquid crystal layer was calculated by setting the efficiency of the waveguide without the liquid crystal layer to 100%. Table 2 shows the results
Shown in

[0061]

[Table 2]

In the manufactured display,
Light emission of the phosphor was observed.

[0063]

As is clear from the above description, the display device of the present invention has a light-emitting display structure using an optical fiber as an optical waveguide. Since the structure is simple, it is possible to increase the size, and there are many advantages such as a reduction in thickness regardless of the size.

Further, for example, by selecting a film-like material for the optical fiber fixing layer, it is possible to deform (roll, etc.) into a shape that is easy to carry.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing an example of a display element to which the present invention is applied.

FIG. 2 is a schematic diagram showing a relationship between a light guiding direction and a liquid crystal molecule position in a ferroelectric liquid crystal.

FIG. 3 is a characteristic diagram showing φ dependence of an effective refractive index.

FIG. 4 is a schematic diagram showing an example of a large-screen liquid crystal switching element structure.

FIG. 5 is a characteristic diagram showing φ dependence of the effective refractive index when n⊥1.52 and n // 1.62.

FIG. 6 is a characteristic diagram showing φ dependence of the effective refractive index when n⊥1.49 and n / 1.68.

FIG. 7 is a characteristic diagram showing φ dependence of the effective refractive index when n⊥1.484 and n / 1.642.

FIG. 8 is a characteristic diagram showing φ dependence of the effective refractive index when n⊥1.493 and n // 1.667.

[Explanation of symbols]

1,10 glass substrate, 2 low refractive index polymer, 3 optical fiber, 4 liquid crystal layer, 5 phosphor layer, 6,7 transparent electrode, 8,9 alignment film

Continuation of the front page (72) Inventor Shunichi Hashimoto 6-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F-term (reference) 2H038 AA54 BA42 2H091 FA24Y FA24Z FA45Z FA46Z FA50X FB06 FD05 FD06 HA12 LA11 LA16 5C094 AA13 AA15 BA26 ED04 ED20 GA10 JA01 JA20

Claims (9)

[Claims] A light-emitting element, an optical waveguide into which light from the light-emitting element is introduced and capable of extracting the introduced light from an intermediate portion, and an optical switch for turning on and off light extracted from the optical waveguide. A color conversion member that emits light when excited by light extracted from the optical waveguide. 2. The display device according to claim 1, wherein the optical waveguide is at least partially formed of an optical fiber having no cladding layer. 3. The display device according to claim 1, wherein the optical waveguide is made of an optical fiber having a cladding layer having at least a part having a refractive index equivalent to that of the core layer. 4. The display device according to claim 1, wherein the light emitting device is a laser or a light emitting diode, and is optically connected to the optical waveguide. 5. The main light-emitting peak of the light-emitting element has a wavelength of 5
The display element according to claim 4, wherein the thickness is equal to or less than 00 nm. 6. The display device according to claim 1, wherein the optical waveguide has an optical transmission loss at a wavelength of the light emitting device of at least 5 dB / m. 7. The optical fiber, wherein the diameter of the optical fiber is 10% or more of (vertical length of display element) / (vertical resolution) or (horizontal length of display element) / (horizontal resolution). The display element according to claim 2 or 3, wherein 8. The display device according to claim 1, wherein the optical switch comprises a liquid crystal layer driven by applying a voltage. 9. The display device according to claim 8, wherein the liquid crystal material of the liquid crystal layer is a ferroelectric liquid crystal or an antiferroelectric liquid crystal.