KR19990018837A - Optical System of Projection Image Display Using AM - Google Patents

Abstract

The present invention relates to an optical system of a projection type image display device using AMA, comprising a light source for emitting light, and selectively reflecting or projecting light emitted from the light source according to a wavelength, and reflecting and An inclined dichroic filter coated with a continuously adjustable coating material is coated, and an optical path control device (AMA) for modulating the light reflected or projected by the inclined dichroic filter according to an applied electric signal. The present invention provides an optical system of a projection image display device using an AMA having a projection lens for projecting light modulated by the optical path control device (AMA) onto a screen.

Therefore, despite the change of the incident angle, the main beams are effectively separated according to the wavelengths, resulting in the effect of improving the color uniformity on the screen.

Description

Optical System of Projection Image Display Using AM

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system of a projection display using an actuated mirror array, and more particularly to a dyke for selectively reflecting or projecting light according to wavelength. In a dichroic filter, a gradient dichroic filter in which a coating material is continuously formed so as to correct it according to an angle of incidence that is changed based on an angle of incidence incident on a center of a dichroic filter. The present invention relates to an optical system of a projection type image display apparatus using AMA which can improve color uniformity.

In general, spatial light modulators, which are devices for projecting optical energy onto a screen, can be applied to various fields such as optical communication, image processing, and information display devices. Typically, such devices are classified into a direct-view image display device and a projection-type image display device according to a method of displaying optical energy on a screen.

An example of a direct-view image display apparatus is a cathode ray tube (CRT), which is a so-called CRT device, which has excellent image quality but increases in weight and volume as the size of the screen increases, leading to an increase in manufacturing cost. There is.

Projection-type image display devices are referred to as liquid crystal displays (hereinafter referred to as LCDs), deformable mirror devices (hereinafter referred to as DMDs), and actuated mirror arrays (hereinafter referred to as AMAs). ). Such projection image display apparatuses can be further divided into two groups according to their optical characteristics. That is, devices such as LCDs can be classified as transmissive spatial light modualators, while DMA and AMA can be classified as reflective spatial light modualators.

Transmission optical modulators, such as LCDs, have a very simple optical structure, which makes them thinner, lighter in weight, and smaller in volume. However, due to the polarity of light, the light efficiency is low, and there is a problem inherent in the liquid crystal material, for example, a slow response speed and a disadvantage in that the inside is easily overheated. In addition, the maximum light efficiency of existing transmission light modulators is limited to a range of 1-2% and requires dark room conditions to provide acceptable display quality.

Optical modulators such as DMD and AMA have been developed to solve the problems of the aforementioned LCD type optical modulators.

DMD shows a relatively good light efficiency of about 5%, but serious fatigue problems are caused by the hinge structure employed in the DMD. In addition, there is a disadvantage that a very complicated and expensive driving circuit is required.

In contrast, AMA is a piezoelectrically driven mirror array that provides light efficiency of 10% or more. In an AMA light modulator, each actuator generates a deformation in accordance with an electric field generated by an applied electric image signal and a bias voltage. When the actuator causes deformation, each of the mirrors mounted on top of the actuator is tilted. Accordingly, the inclined mirrors can reflect light incident from the light source at a predetermined angle. The AMA optical modulator has a simple structure and operation principle, and can obtain high light efficiency compared to LCD or DMD. It also provides enough contrast to provide a bright and clear image under normal room temperature light conditions. Moreover, it is not only affected by the polarity of the incident light, but also by the polarity of the reflected light. In addition, the reflective properties of the AMA are relatively less sensitive to temperature, which has the advantage of improving the brightness of the screen compared to other devices that are easily affected by high power light sources.

Such AMA devices are classified into bulk type devices and thin film type devices. Bulk AMA has a center electrode between two piezoelectric layers. The central electrode is connected to an active matrix having an active epoxy for the signal voltage. On top of the bulk AMA is a mirror layer, which has an inclination angle of +/- 0.25 ° under a voltage of up to 30V. For this reason, bulk AMA requires very high precision in design and manufacture, and there are many difficulties in assembling the structure.

Accordingly, recently, a thin film type AMA (hereinafter referred to as TFAMA) that can be manufactured using a semiconductor manufacturing process has been developed to complete the quality of mirror arrays. The TFAMA is disclosed in Korean Patent Application No. 95-13358 filed on May 26, 1995 by the present applicant.

TFAMA is a reflective light modulator that uses thin film piezo-electric actuators in conjunction with microscopic mirrors to provide uniformity of large scale integration across more than 300,000 pixels of a single-plate mirror. Has been developed. This TFAMA consists of 640x480 pixel panels representing red (R), green (G) and blue (B), respectively. The pixels are designed as cantilever structures to maximize the mirror surface area to increase the light efficiency. The cantilever structure includes an active matrix to which an image signal voltage is applied and a mirror operated by the applied signal voltage.

A conventional optical system using three panel TFAMA is shown in FIG.

Referring to FIG. 1, a conventional optical system includes a light source 11, a source lens 12, a source stop 13, a source mirror 14, a dichroic filter 17, 18, and an optical path control device. 20, 22, 24, field lenses 30, 32, 34, projection stops 15 and projection lenses 16.

In the optical system configured as described above, light of high luminance emitted from the light source 11 is focused by the source lens 12 and passed through the opening of the source stop 13 to be irradiated onto the source mirror 14. As is well known, light consists of three main beams, each of which has a primary color of red (R), green (G), or blue (B) depending on the wavelength. All the light irradiated to the source mirror 14 is reflected and irradiated to the dichroic filters 17 and 18.

The dichroic filters 17 and 18 are optical filters for selectively passing light by wavelength, reflecting only one main beam of red (R), green (G), and blue (B) light, and the other main beam. Transmits.

As shown in FIG. 2, the dichroic filters 17 and 18 are installed to be inclined on the optical axis of the light totally reflected by the source mirror 14 so that the main beam may be selectively reflected and projected on the surface thereof. Coating material 19 is applied. For example, the first dichroic filter 17 reflects only the red beam from the irradiated light and irradiates the R-AMA 20, and the green and blue beams are projected by the coating material to be positioned next to the second dike. The loch filter 18 and the G-AMA 24 are irradiated. The second dichroic filter 18 is also inclined on the optical axis of the light totally reflected by the source mirror 14, the coating material 19 is applied to the surface of the second dichroic filter 17 to Among the projected green and blue beams, only the blue beam is reflected to irradiate the B-AMA 22, and the green beam is projected to irradiate the G-AMA 24.

On the other hand, the main beams irradiated to the optical path control device (20, 22, 24) are field lenses 30, 32, disposed in front of the source stop (13) so that the image can be transmitted to the projection stop 15 without light loss After passing through 34, the optical path is modulated according to the electrical signal applied to the piezoelectric actuator (not shown in the drawing) and irradiated to the dichroic filters 17, 18 through the field lenses 30, 32, 34 again. Then towards the projection stop 15. The red beam passing through the opening of the projection stop 15 enters the projection lens 16.

That is, the red beam reflected by the first dichroic filter 17 is irradiated to the R-AMA 20 through the first field lens 30. The mirror (not shown) of the R-AMA 20 modulates light in accordance with an electrical signal applied to a piezoelectric actuator (not shown) provided thereunder.

On the other hand, the green and blue beams transmitted by the first dichroic filter 17 are reflected by the second dichroic filter 18 and the blue beam is transmitted. The blue beam reflected by the second dichroic filter 18 is irradiated to the B-AMA 22 through the second field lens 32 and enters the projection lens 16 via the path as described above. At this time, the first dichroic filter 17 on the same optical axis transmits the blue beam as it is.

On the other hand, the green beam transmitted through the second dichroic filter 18 is irradiated to the G-AMA 24 through the third field lens 34 and enters the projection lens 16 through the path as described above. . At this time, the first and second dichroic filters 17 and 18 on the same optical axis transmit the green beam as it is.

In this way, the projection lens 16 projects light including a modulated red, green and blue main beam onto the screen to form an image.

On the other hand, in the optical system of the conventional projection type image display device, the light passing through the source stop 13 is separated into the main beam through the dichroic filters 17 and 18, and then each of the optical path control devices 20, 22 and 24 is used. Since the main beam modulated and reflected by H2 must pass through the projection stop 15, the first and second dichroic filters 17 and 18 are inclined so as to have a predetermined inclination in order to construct such an optical system.

However, in the conventional optical system, since the dichroic filters 17 and 18 are inclined at a predetermined inclination, the incident angles of the light incident on the first and second dichroic filters 17 and 18 from the source mirror 14 are different. An error occurs in the optical system configuration that changes toward the upper and lower sides with respect to the center so that the upper side is smaller than the reference incident angle, and the lower side is larger than the reference incident angle. Therefore, the reflection and projection characteristics according to the wavelength is lowered at the upper and lower sides except for the center, and as a result, there is a problem that the color is uneven on the screen.

Accordingly, the present invention is to solve such a conventional problem, the dichroic filter in accordance with the change in the incident angle to correct the change in the incident angle of the light irradiated to the dichroic filter inclined to have a predetermined inclination SUMMARY OF THE INVENTION An object of the present invention is to provide an optical system of a projection type image display device in which a coating material is continuously inclined on the surface of the film.

The present invention for realizing the above object is provided with a light source for emitting light, and the coating material that can reflect or project the light emitted from the light source selectively according to the wavelength, the change and the incident angle is changed A gradient dichroic filter which is continuously adjusted and coated is provided, and an optical path control device (AMA) for modulating the light reflected or projected by the gradient dichroic filter according to an applied electric signal is provided. An optical system of a projection type image display device using an AMA having a projection lens for projecting light modulated by the device (AMA) onto a screen.

According to a preferred embodiment of the present invention, the inclined dichroic filter has a coating material coated on the inclined dichroic filter surface so as to correct an incidence angle that changes according to the inclination based on the incidence angle incident on the center. It is characterized in that the coating on a multi-step basis.

The optical system of the present invention configured as described above is based on the center of the dichroic filter when the light emitted from the light source is incident on the dichroic filter inclined to have a predetermined slope through the source lens, the source stop and the source mirror. Thus, the incident angle incident on the periphery becomes larger or smaller than the incident angle of the central portion. On the other hand, since the inclined dichroic filter is coated with a coating material to compensate for such a change in the incident angle, the main beam is effectively separated according to the wavelength despite the change of the incident angle, thereby improving the color uniformity on the screen. Will bring.

1 is a schematic diagram showing an optical system of a conventional projection type image display apparatus;

Figure 2 is a perspective view of a conventional dichroic filter,

Figure 3 is a perspective view of the gradient dichroic filter in the present invention.

* Explanation of symbols on the main parts of the drawings

11 light source 12 source lens

13: Source Stop 14: Source Mirror

15: projection stop 16: projection lens

20: R-AMA 22: B-AMA

24: G-AMA 30: first field lens

32: second field lens 34: third field lens

117: gradient first dichroic filter

118: gradient second dichroic filter

119: coating material

Hereinafter, an optical system of a projection image display device according to the present invention will be described in detail with reference to the accompanying drawings.

An optical system of a projection image display device according to the present invention will be described with reference to FIGS. 1 and 3.

As shown, the present invention is provided with a light source 11 of 170W to 250W for emitting light, and includes a source lens 12, a source stop 13 and a source mirror 14 on the front thereof. In addition, gradient dichroic filters (117, 118), optical path control devices (AMA, 20, 22, 24), field lenses (30, 32, 34), projection stops (15) and projection lenses (16) Include.

The light source 11 is a broadband source of optical energy and emits long wavelength infrared to ultraviolet rays in the spectrum.

The source lens 12 functions to focus light emitted from the light source 11. The source stop 13 has an opening formed to allow light to pass through the optically opaque member, and the opening is a pin-hole or a slit. The source stop 13 determines the amount of light that forms the image. A source mirror 14 is disposed after the source stop 13, and the source mirror 14 reflects light emitted from the light source 11 and changes the path of the light primarily to incline a dichroic filter. (117, 118).

The gradient dichroic filters 117 and 118 are color separation means for separating light into main beams according to wavelengths. The first gradient dichroic filter 117 reflects a red beam and transmits a green beam and a blue beam. The second dichroic filter 118 reflects the blue beam and transmits the green and red beams.

On the other hand, the light passing through the source stop 13 is separated into the main beam through the gradient dichroic filters 117 and 118, and then modulated by the respective optical path control devices 20, 22 and 24 so as to control the projection stop 15. In order to construct such an optical system, the first and second gradient dichroic filters 117 and 118 are disposed to be inclined so as to have a predetermined slope.

Meanwhile, as shown in FIG. 3, the inclined dichroic filters 117 and 118 according to the characteristic elements of the present invention are inclined so as to correct the incidence angle changed according to the inclination based on the incidence angle incident on the center portion. The coating material 119 coated on the surfaces of the dichroic filters 117 and 118 is coated in multiple stages based on the center of the dichroic filters (117 and 118). The coating material 119 may have the reflection or projection characteristics required by the optical system in response to different incidence angles by changing the coating thickness or changing the light absorption or reflectance of the coating material.

Each of the optical path control devices 20, 22, and 24 includes an actuator (not shown) formed in a cantilever structure so as to be deformed according to an electrical signal applied to the piezoelectric material, and a mirror surface mounted on the actuator. M × N pieces are arranged so as to correspond to the pixels of FIG.

The field lenses 30, 32, and 34 serve to 1: 1 correspond to the projection stop 15 of the image of the source stop 13. That is, the main beams separated by the gradient dichroic filters 117 and 118 through the source stop 13 may be transmitted in parallel to the optical path control devices 20, 22, and 24 corresponding thereto without light loss. It consists of a group of lenses.

The projection stop 15 is made of the same material and shape as the source stop 13 to adjust the amount of light of the main beam projected from the optical path control devices 20, 22, 24 to the projection lens 16. The projection lens 16 is composed of a group of lenses to project an image onto a screen (not shown in the figure).

Hereinafter, the operation of the projection image display device according to the present invention will be described.

First, when the optical system of the present invention is driven, the high luminance light emitted from the light source 11 is focused into parallel light by the source lens 12, and the amount of light is determined by the source stop 13, and the source mirror ( 14) the whole amount is reflected and irradiated onto the gradient dichroic filters 117 and 118 to be separated into three main beams according to the wavelength.

Here, the inclined dichroic filters 117 and 118 are divided into main beams through the dichroic filters 117 and 118 after the light passing through the source stop 13 is applied to the respective optical path control apparatuses 20, 22 and 24. It has been mentioned above that the first and second dichroic filters 117,118 should be inclined so as to have a predetermined inclination in the optical system configuration that must be modulated by and pass through the projection stop 15.

Therefore, the incident angles incident on the first and second gradient dichroic filters 117 and 118 are changed toward the upper and lower sides with respect to the center so that the upper side is smaller than the reference incident angle, and the lower side is larger than the reference incident angle. An error occurs in the system configuration. The gradient dichroic filters 117 and 118 of the present invention have a coating material formed continuously, for example, in three stages, as shown in FIG. The main beam is effectively separated.

Figure 4 shows the color coordinates showing the present invention and a comparative example.

The inclined dichroic filters 117 and 118 of the present invention are controlled by separating the coating material 119 into three stages, and the dichroic filters 17 and 18 of the comparative example are coated with the coating material 19 evenly. In the same optical system, the color on the screen is divided into 9 parts according to the ANSI standard, and the coordinates of the green beam corresponding to each point are checked to compare the JND (just noticable difference) (1 and A, 2 and B…, 9 and I are the same.)

As shown, the dichroic filters 17 and 18 of the comparative example are distributed over a range of approximately 0.05 from 0.30 to 0.35 of the X coordinate, and are considerably deviated from the periphery of the circular arc of 1JND indicated by hidden lines.

On the other hand, the gradient dichroic filters 117 and 118 according to the present invention are distributed over a range of approximately 0.02 from 0.26 to 0.28 of the X coordinate, and are concentrated around 1 JND indicated by a solid line.

The main beams separated by the gradient dichroic filters 117 and 118 are irradiated to the R-AMA 20, the G-AMA 22, and the B-AMA 24, respectively. The mirrors of the optical path control devices 20, 22, and 24 modulate the main beams in accordance with electrical signals applied to the piezoelectric actuators provided thereunder. If an off voltage is applied to the piezoelectric actuator, the mirror does not vibrate, tilt or bend, so that the main beam does not pass through the projection stop 15 even if reflected by the mirror. On the other hand, when the on voltage is applied to the piezoelectric actuator, the strength of the main beam is modulated by vibrating, tilting or bending according to the embodiment in which the mirror is used. As a result, the amount of light is adjusted to enter the projection lens 16 in accordance with the degree of passing through the opening of the projection stop 15.

In this manner, the red, green, and blue beams of which the amount of light is controlled are projected onto the projection lens 16 to form unit pixels, and form an image on a screen on which M × N pixels are arranged.

The foregoing is merely illustrative of a preferred embodiment of the present invention and those skilled in the art to which the present invention pertains may make modifications and changes to the present invention without changing the subject matter of the present invention.

Therefore, according to the present invention, even if the inclined dichroic filter is arranged to change the incident angle due to the optical system configuration, the coating material is continuously coated so that the change of the incident angle can be corrected according to the wavelength despite the change of the incident angle. This effectively separates the main beam, resulting in an improvement in color uniformity on the screen.

Claims (1)

Inclined dichroic filter coated with a light source that emits light, selectively reflecting or projecting the light emitted from the light source according to the wavelength, the coating material is continuously adjusted to vary the reflectance and transmittance according to the incident angle, the gradient dike An optical path control device (AMA) for modulating a main beam reflected or projected by the roic filter according to an applied electrical signal, and a projection stop and projection lens for projecting light modulated by the optical path control device (AMA) onto a screen And an optical system of a projection type image display device using AMA.