JPH071680B2 - Projection CRT device - Google Patents

Description

The present invention relates to a projection type CRT device for enlarging and projecting an image of a phosphor screen on a screen.

[Prior Art] FIG. 3 is a diagram showing a configuration of a typical video projector. In the figure, (1) is a projection type CRT (cathode ray tube) device (hereinafter referred to as “CRT”), and (1R). , (1G), (1
B) are R (red), G (green), and B (blue) monochromatic image light sources, respectively. (2) is a projection lens, and (3) is a screen. A CRT (1) image is enlarged and projected onto a screen (3) placed in front by the projection lens (2) to display a large-screen color image. To be realized.

FIG. 4 is a cross-sectional configuration diagram of the CRT (1), in which (4) is a vacuum envelope, (5) is an electron gun enclosed therein, and (6) is a vacuum envelope (4). A face plate (7) is a phosphor layer formed on the inner surface of the face plate (6). On the phosphor layer (7), a metal back film (8) made of a vapor deposition film of aluminum as a high voltage electrode and a reflective film is formed. ) Has been formed. The CRT (1) emits light when the phosphor (7) is excited by the energy of the electron beam emitted from the electron gun (5) arranged opposite to the metal back film (8).

While video projectors can produce large-screen color images, there is a strong demand for higher brightness. In order to improve the brightness of the video projector, for example, JP-A-58-20775.
As disclosed in Japanese Patent Laid-Open No. 0-331, an optical interference filter (14) (see FIG. 5) is provided on the boundary surface (11) between the face plate (6) and the phosphor layer (7), and the boundary surface (11 ) Has been proposed that increases the transmittance of the light beam that is incident almost perpendicularly (about ± 30 °).

Fig. 7 shows the spectral characteristics (12) of the optical interference filter (14)
It is drawn together with the emission spectrum (13) of the (green) color phosphor, where θ is the incident angle to the face plate (6). The transmittance of a light beam that enters the optical interference filter (14) substantially perpendicularly is close to 100%, but the transmittance decreases drastically as the incident angle increases, and the reflected component light beam increases. The reflected luminous flux is scattered and reflected again by the phosphor layer (7) which is a high-reflectance material, so that the luminous flux incident almost vertically on the face plate (6) increases. FIG. 8 (a) is a diagram showing the luminous intensity distribution from the face plate when the optical interference filter (14) is not present, and FIG. 8 (b) is a diagram showing the luminous intensity distribution when the optical interference filter (14) is present.

As shown in Fig. 5, the video projector has a utilization angle α ₁ of the luminous flux from the phosphor of about ± 3 near the center of the CRT.
As a result, the optical interference filter (14) is less than 0 °.
By adopting, it is possible to obtain a very bright image.

Further, as shown in FIG. 7, in the emission spectrum of the G (green) color phosphor, in addition to the originally necessary spectrum (a),
It has unnecessary spectra of (b) to (d). But,
By using the optical interference filter (14), as is apparent from FIG. 7, the unnecessary spectra of (c) and (d) can be reduced and the saturation of green can be increased.

[Problems to be Solved by the Invention] Although a video projector using an optical interference filter can obtain a very bright image at least near the center of the image,
On the contrary, there was a problem that the periphery of the screen became dark.

In Fig. 5, θ ₂ is the angle of incidence of the principal ray (17) of the effectively utilized light flux from the peripheral part of the CRT on the face plate (6), which is usually about 30 °, and the opening angle of ± α ₂ Since it has it, as is clear from the characteristic diagram of FIG. 7, the transmittance is considerably reduced. As a result, the periphery of the screen becomes very dark.

In order to solve this, there is a plan to make the shape of the inner surface of the face plate (6), that is, the shape of the boundary surface (11) into a curved surface shape as shown in FIG. As a result, the incident angle θ ₂ of the chief ray (17) at the periphery of the CRT becomes smaller than that in the flat case of FIG. 5, and the brightness is improved.

Further, θ ₂ is zero, that is, the normal line (16) at the boundary surface (11) around the CRT is the entrance pupil center (15) of the projection lens (2).
If the face plate (6) is made to have a radius of curvature that passes through, the optical interference filter (14) can obtain a very bright image over the entire area from the center of the screen to the periphery. .

However, in reality, this radius of curvature is extremely small, which makes it extremely difficult to fabricate a CRT.

As described above, the projection type CRT device using the conventional optical interference filter can obtain a very bright image near the center of the screen, but the incident angle to the optical interference filter becomes large in the peripheral part of the screen. However, there was a problem that the transmittance was reduced and a dark image was obtained.

The present invention has been made to solve the above problems, and an object thereof is to obtain a projection type CRT device capable of projecting a bright image over the entire screen.

[Means for Solving the Problem] A projection type CRT device according to the present invention is configured such that the central portion of the screen is thicker toward the peripheral portion so that the transmittance of the principal ray of the light flux does not decrease over the entire area of the screen. It is characterized by having an optical interference filter.

[Operation] Since the optical interference filter according to the present invention transmits the principal ray of the light flux from the peripheral portion of the screen without reducing the transmittance, a bright image can be obtained over the entire screen.

Embodiment of the Invention One embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In the figure, (14) is an optical interference filter,
The thickness t ₁ at the center of the screen and the thickness t ₂ at the periphery are different, and t ₂ is formed thicker.

Here, how to determine the film thickness will be described with reference to FIG.

FIG. 2 is an enlarged sectional view showing the structure of the optical interference filter (14) of this embodiment, where H is a high refractive index layer having a refractive index n _H , L is a low refractive index layer having a refractive index n _L , and H ( It is a laminated structure of LH) N (N is the number of overlapping layers), and is formed between the face plate (6) and the phosphor layer (7) via the adjustment layer (18). d _L is the film thickness of the low refractive index L, and d _H is the film thickness of the high refractive index layer H.

First, the method of designing the center of the screen will be described.

This has the same design as the conventional optical interference filter.

In order to obtain the spectral characteristics as shown in FIG. 7, for example, the desired wavelength at which the transmittance is 50% is λ ₅₀ . Next, the design wavelength of the optical interference filter and the input and _0, is set to _{λ 0 ≒ 4/3 · λ} 50. At this time, the film thickness may be designed to be d _L1 × n _L = λ0 / 4, d _H1 × n _H = λ0 / 4 ... Here, d _L1 and d _H1 are actual film thicknesses near the center of the screen, and d _L1 × n _L and d _H1 × n _H are effective film thicknesses related to the phase difference at the time of multiple reflection of the interference film.

As a specific example, λ ₅₀ = 570 [nm], n _L = 1.45 (SiO ₂ ), n
If _{H = 2.31 (TiO 2),} d L = 131 [nm], d H = 82 [n
m], and if N = 3 to 7, desired characteristics are obtained.

Next, the design method in the peripheral area of the screen will be described. In FIG. 1, the chief ray (17) has an angle of θ _{2 with} respect to the normal line of the surface of the optical interference filter (14) in the peripheral portion. Here, the principal ray is a ray that passes through substantially the center of the effectively used light flux, and this ray passes through the center (15) of the entrance pupil. At this time, the effective film thickness for the chief ray is n _L × d _L2 cos θ _L , n _H × d _H2 cos θ _H ... for the L and H layers, respectively, as is well known in the design method of interference films. Becomes Here, d _L2 and d _H2 are the actual film thickness in the peripheral portion, θ _L and θ _H are the traveling angles when the chief ray passes through the L and H layers, respectively, and the refractive index of the face plate (6) is n _f
Then, there is a relationship of n _f · sin θ ₂ = n _L · sin θ _L = n _H · sin θ _H.

If d _L2 , d _H2 is equal to d _L1 , d _{H1 as} before,
The effective film thickness becomes smaller than the formula, and the condition of the formula, that is, the condition that the effective film thickness is equal to λ0 / 4 is not satisfied,
₅₀ is shorter than the center of the screen. As a result, as described above, the transmittance decreases.

Therefore, in order to obtain the desired characteristics of the chief ray in the peripheral part, if n _L · d _L2 · cos θ _L = λ0 / 4, n _H · d _H2 · cos θ _H = λ 0/4 ... The good is clear.

Therefore, from the equation, the actual film thickness may satisfy the following equation.

d _L1 = d _L2 cos θ _L d _H1 = d _H2 cos θ _{H As} is clear from the equation, the film thicknesses d _L2 and d _H2 at the peripheral portion must be made thicker as θ ₂ becomes larger than at the central portion.

Since the number of repetitions N is naturally the same, the filter thickness is t ₂ > t _{1 in} FIG.

If the film thickness is made thicker toward the periphery so that the formula is satisfied, the chief ray will always appear to be θ = 0 ° in FIG.
Since it has the spectral characteristic of, a bright image can be obtained over the entire area of the screen without becoming dark as in the conventional case.

Although the face plate (6) is a curved surface in the above embodiment, it can be applied to a flat face plate as shown in FIG. 5, and the film thickness can be changed depending on the location so as to satisfy the formula. It is sufficient to obtain the same effect as that of the above embodiment.

If the structure is such that the radius of curvature of the face plate (6) coincides with the center of the entrance pupil (15), then θ ₂ = 0 °
Therefore, it is clear that the film thickness may be constant regardless of the place.

Further, in the above-mentioned embodiment, TiO ₂ is used for the H layer, but Ta ₂ O ₅ may be used, and the adjustment layer (18) may not be provided.

[Effects of the Invention] As described above, according to the present invention, the layer thickness of the optical interference filter is such that the effective film thickness for the chief ray is λ0 / 4,
Since the actual film thickness is increased as it goes to the peripheral portion of the screen, there is an effect that a very bright image can be obtained over the entire screen.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a sectional view showing the construction of an optical interference filter of this embodiment, and FIG. 3 is a diagram showing the construction of this typical video projector. Four
The figure is a cross-sectional view of a conventional projection type CRT device, FIG. 5 and FIG.
FIG. 7 is a cross-sectional view of different projection type CRT devices equipped with a conventional optical interference filter, FIG. 7 is a diagram showing spectral characteristics and phosphor spectrum of the optical interference filter, and FIG. FIG. (1) …… Projection CRT device, (5) …… Electron gun, (6)
…… Face plate, (7) …… Phosphor layer, (14)…
… Optical interference filter, (18) …… Adjustment layer. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A projection type CRT device having a phosphor layer formed on an inner surface of a face plate through an optical interference filter, wherein the inner surface of the face plate has a concave shape when viewed from a projection side, The optical interference filter has a laminated structure of (high refractive index layer) + (low refractive index layer + high refractive index layer) × N (where 3 ≦ N ≦ 7), and k-th (k = 1,2 , ..., (2N + 1))
Let d _k , its refractive index be n _k, and the traveling angle of the chief ray passing through the kth refractive index layer be θ _k , then the kth refractive index layer is on the surface of the above-mentioned phosphor layer. A projection-type CRT device characterized in that it is formed to have a film thickness such that the values of n _k , d _k, and cos θ _k are equal to the principal ray at each position from the central part to the peripheral part.