JP4918768B2 - Optical screen, projection screen using the same, and method of manufacturing the optical screen - Google Patents

Description

  The present invention relates to an optical screen used in a projection television or the like with high accuracy and thin thickness and reduced light loss of incident light, a projection screen using the same, and a method of manufacturing the optical screen.

  Conventionally, a screen of a projection television or the like has a Fresnel lens sheet and a lenticular lens sheet arranged adjacent to each other. For the purpose of reducing the thickness of the projection television, it is well known that the screen is configured to condense an image with a Fresnel lens sheet and widen a viewing angle with a lenticular lens sheet.

  The lenticular lens initially had only the function of expanding the horizontal viewing angle. Later, in order to enlarge the viewing angle in the vertical direction, devised arrangements of lenticular lenses orthogonal to each other were made, but since the number of sheets increased, the surface reflection of incident light by the increased lenticular lens sheet, the inside of the sheet There was a problem that the transmission efficiency decreased due to scattering and absorption.

  Various lenticular lenses that are perpendicular to each other on a single sheet have been proposed, but are finally becoming established as a microlens array.

  Microlens formation techniques are broadly divided into a refractive index distribution type in which the refractive index of the material is changed in the radial direction and a plurality of minute, substantially hemispherical convex lenses having a diameter of several μm to several 100 μm. The

  As a manufacturing method of the gradient index microlens, an ion exchange method in which ions are diffused to a glass substrate on which a mask matched to a lens shape is formed to cause a stepwise change in refractive index, a laser modification method (Patent Document 1). However, in the gradient index type, the production method by molding cannot be taken, so the cost is inevitably high.

  A method of arranging a plurality of minute, substantially hemispherical convex lenses is more common than the refractive index distribution type, and various manufacturing methods have been proposed.

  For example, after creating a cylindrical photoresist pattern by photolithography, the substrate is heated to cause the resist to flow, and the lens shape is created by surface tension. A method of forming a microlens, a gray scale method in which a resist pattern is formed using a gray scale mask whose transmittance is controlled by the aperture area ratio of a fine pattern, and the shape is transferred to a glass substrate by dry etching (see Patent Document 2) An ink jet method has been proposed in which a small amount of resin material is dropped at a predetermined position using an ink jet printer head, and a lens shape is produced by surface tension. Other methods include X-ray lithography and electron beam lithography.

  However, many methods have the disadvantage that the lens curve cannot be precisely controlled. Otherwise, it requires a complex and delicate processing process.

The manufacturing method of the mold is generally using photolithography, and a mask having a predetermined pattern of openings is manufactured using a laser exposure machine or the like, and then a lens shape is manufactured by etching. As an example, a photomask having a gradation mask pattern formed by electron beam drawing is arranged above the substrate, and an enlarged laser beam is irradiated through the photomask, so that a desired pattern according to the mask pattern is applied on the substrate. There is a technique for forming a three-dimensional pattern by laser ablation (see Patent Document 3). However, in order to reduce the surface roughness, it is necessary to reduce the irradiation energy and gradually ablate over time, and to reduce the level difference, the number of gradations must be increased. As a result, the processing time becomes enormous and the gradation mask manufacturing cost increases.

Patent documents are described below.
JP 2004-184933 A JP 2003-107209 A JP 2005-131940 A

  The quality required for a projection screen is a wide field of view, high brightness, and uniform brightness of the entire screen, but until now the majority of lenses have been focused on wide field of view. The demand for higher brightness is to increase the numerical aperture (NA) of the lens, to reduce the loss of the lens sheet, and to increase the transmission efficiency.

  In order to increase the transmission efficiency while increasing the numerical aperture (NA) of the lens, it is necessary to reduce the thickness of the lens and increase the curvature. As a result, it is essential to control the lens shape.

  The present invention has been made paying attention to the problems of the above-described conventional technology, and is used in a projection television or the like with a high precision, a thin thickness, and a reduced light loss of incident light. It is an object of the present invention to provide a screen, a projection screen using a combination of the optical screen and a Fresnel lens sheet, and a method for manufacturing the optical screen.

In order to achieve the above object, that is, the invention according to claim 1 is an optical screen including a microlens array in which unit lenses are formed on a light-transmitting plastic substrate.
The optical screen is characterized in that the unit lens has a minute concentric Fresnel lens shape whose curved surface shape is controlled.

  As a result, an aspherical lens with good transmission efficiency can be accurately reproduced, and the loss of incident light can be reduced by reducing the thickness of the medium, so that a screen for projection television with higher brightness can be obtained.

  The invention according to claim 2 is a projection screen characterized by using a combination of the optical screen according to claim 1 and a Fresnel lens sheet.

The invention according to claim 3 is the method of manufacturing an optical screen according to claim 1 or 2,
A method of manufacturing an optical screen, wherein unit lens groups having a minute Fresnel lens shape whose curved surface shape is controlled are arrayed by irradiating laser light directly on the light-transmitting plastic substrate. .

  A projection screen including a minute Fresnel lens group is manufactured by direct laser irradiation. This eliminates the need for a complicated and high-cost production line, thereby reducing the manufacturing cost of a small quantity and a wide variety.

  Further, in the invention according to claim 4, the laser is an ultrashort pulse laser having an oscillation pulse width of 1 picosecond or less, and the laser power and the focal position are controlled to be three-dimensionally irradiated. 4. The method of manufacturing an optical screen according to claim 3, wherein unit lens groups each having a fine Fresnel lens shape whose curved surface shape is controlled are arrayed.

  As a result, processing accuracy on the order of nanometers can be obtained, and since there is almost no thermal influence, the screen can be manufactured stably.

The invention according to claim 5 is a method of manufacturing the optical screen,
Using a mold made by directly irradiating a substrate made of a metal material with an ultrashort pulse laser having an oscillation pulse width of 1 picosecond or less with three-dimensional laser power and focal position control Then, a method for producing an optical screen is characterized in that a mold is transferred onto a light-transmitting plastic substrate and unit lens groups each having a fine Fresnel lens shape whose curved surface shape is controlled are arrayed.

  This eliminates the need for an etching process in the mold manufacturing facility, so that the mold can be manufactured in a dry environment with little influence on environmental pollution.

  According to the optical screen of the present invention, the projection screen using the optical screen and the Fresnel lens sheet in combination, and the manufacturing method of the optical screen, the following effects can be obtained.

  First, by processing by controlling the lens shape, it is possible to form a lens with high processing accuracy and thin thickness and good transmission efficiency. By making each minute lens a Fresnel lens, Light loss can be reduced, and a screen for projection television with higher brightness can be obtained.

  Secondly, since the screen can be completed with only the laser device, a complicated and high-cost production line is not required, so that the manufacturing cost for a small quantity and a wide variety can be reduced.

  Thirdly, the etching process is unnecessary, so that there is little adverse effect on the environment. In addition, the transfer mold can be manufactured in a dry environment.

  Fourth, by using an ultra-short pulse laser with an oscillation pulse width of 1 picosecond or less, it is not necessary to select a laser light source according to the light absorption characteristics of materials that has been conventionally performed, and one laser processing system With this, both the production of products and the production of molds can be performed.

  Fifth, since processing is performed with a laser pulse shorter than the thermal relaxation time, processing with extremely little thermal influence is possible, and since the reaction is due to nonlinear phenomena such as multiphoton absorption, the resolution is below the diffraction limit of the irradiation wavelength. And can be finished in the order of 1/10 μm in the atmosphere without using any other additional process.

  Hereinafter, an embodiment as an example of the present invention will be described in detail with reference to the drawings.

  The lens sheet group corresponding to the screen of a projection television is basically aimed at widening the viewing angle of the screen. The function of the projection screen is to suppress the luminance deterioration of the peripheral portion of the image projected from the optical engine and to enlarge the viewing angle. A projection screen implements a function that optically converts a projected image from the optical engine into an observed image.

  In general, a projection screen that has been put into practical use includes an individual Fresnel lens sheet 2 and a lenticular lens sheet 3. The surface of the Fresnel lens sheet 2 on which the Fresnel lens 4 is formed and the surface of the lenticular lens sheet 3 on which the lenticular lens 5 is formed. Are arranged facing each other (see FIG. 2).

  In order to enlarge the viewing angle in the vertical direction, the lenticular lens 5 was changed to a microlens. The front shape and arrangement of the microlens for the projection screen are basically representative of the orthogonal microlens 11 shown in FIG. 3 and the honeycomb microlens 12 shown in FIG.

  On the other hand, the projection screen of the present invention is an optical screen composed of a microlens array in which unit lenses are arranged on the plane of a light-transmitting plastic substrate. It is characterized by a concentric Fresnel lens shape, and the optical design and the shape of the formed lens are complicated, but it is highly accurate, thin, and reduces the loss of incident light. It is an optical screen. A projection screen using a combination of the optical screen and the Fresnel lens sheet is provided.

  First, lens characteristics required for a projection screen are optically designed over the entire screen. This optical design specification is divided into fine areas of the screen and converted into processing information. Finally, laser processing is performed based on this processing information.

  In the present invention, an unnecessary portion of the substrate material is irradiated on one surface of the substrate by irradiating an ultrashort pulse laser having an oscillation pulse width of 1 picosecond or less with three-dimensional control of power and focal position. The projection screen is manufactured by forming a group of non-uniform Fresnel lenses that are removed and combined with the Fresnel lens function and the microlens function. A lenticular lens function can also be produced by forming a direct Fresnel lens.

  In recent years, it has been proposed to use an ultrashort pulse laser having a pulse width of 1 picosecond or less according to the present invention for precise processing of the depth of an organic compound, minute three-dimensional modeling, and the like. In particular, it is possible to perform processing with extremely little heat effect due to the phenomenon that the interaction between light and substance is completed in a shorter time than multiphoton absorption and thermal relaxation time, and processing due to nonlinear response. The resolution is below the diffraction limit of the laser wavelength to irradiate, and high-precision processing is possible compared to various conventional laser devices.

  According to the results of our experiments so far, the minimum processing dimension by the above ultrashort pulse laser can be about 150 nm when the laser oscillation wavelength is around 800 nm, and the processing depth can be several tens of nanometers. It is obvious that finer processing can be performed by shortening the oscillation wavelength of the laser.

  In order to manufacture the mold, it is achieved by obtaining inversion information as compared with the case of directly processing a finished product when converting from optical design information to processing information.

  Hereinafter, the present invention will be described with reference to specific examples.

  FIG. 1 is an example of a method for manufacturing a projection screen using an ultrashort pulse laser according to the present invention, and is a schematic view showing a method for forming a minute Fresnel lens group using an ultrashort pulse laser.

  For processing, a femtosecond laser apparatus having an oscillation wavelength of 775 nm, a peak power of 800 mW, a pulse energy of 800 μJ / pulse, a pulse width of 200 femtoseconds, a pulse repetition frequency of 1 kHz, and an optical diameter of the beam spot 8 of 10 μm was used.

  Laser projection was applied to the plastic sheet according to the following procedure to produce a projection screen.

  First, create a program according to the machining information produced based on the Fresnel lens design information, drive the XYZ three-axis precision stage, and control the laser power and focal position into the minute area divided for each Fresnel surface Thus, one circular micro Fresnel lens 13 having a diameter of 0.1 mm and an individual Fresnel surface height of 4 μm was manufactured. The shape may be elliptical depending on the vertical and horizontal viewing angle requirements, and is not limited to a circular shape.

  Next, a program is created in accordance with the processing information produced based on the lens design information, the XYZ three-axis precision stage is driven, and the step movement is sequentially performed so that the arrangement shown in FIG. All the minute Fresnel lenses 13 were processed so as to be arranged at equal intervals. The arrangement of the individual minute Fresnel lenses 13 may be orthogonal, and is not limited to the arrangement state.

  Finally, near the laser ablation threshold, the entire processed surface was irradiated with laser, and fine processing marks were removed. As a result, the surface roughness was 0.2 μm or less.

  The screen for projection televisions was able to be manufactured with the simplified production process described above.

1 shows an example of arraying minute concentric Fresnel lens-shaped unit lenses whose curved surface shape is controlled on a plane of a light-transmitting plastic substrate in an optical screen according to the present invention. FIG. 6 is a schematic cross-sectional view showing a part of arrayed Fresnel lens-shaped unit lenses. FIG. 4B is a schematic plan view showing an example of an array of Fresnel lens-shaped unit lenses in an enlarged manner. It is a longitudinal direction schematic cross section which shows arrangement | positioning of the conventional common Fresnel lens sheet and a lenticular lens sheet. It is the model top view which shows an orthogonal type | mold microlens array as an example of the shape of the conventional microlens, and its schematic cross section. It is the schematic plan view which shows the honeycomb-type microlens array as another example of the shape of the conventional microlens, and its schematic cross section.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Projection screen 2 ... Fresnel lens sheet 3 ... Lenticular lens sheet 4 ... Fresnel lens 5 ... Lenticular lens 6 ... Laser beam 7 ... Objective Lens 8 ... Beam spot 9 Lens pattern 10 Micro lens 11 Orthogonal micro lens 12 Honeycomb micro lens 13 Micro Fresnel lens

Claims (1)

An optical screen manufacturing method comprising:
Using a mold made by directly irradiating a substrate made of a metal material with an ultrashort pulse laser having an oscillation pulse width of 1 picosecond or less with three-dimensional laser power and focal position control A method for manufacturing an optical screen, comprising: forming a unit lens group having a minute Fresnel lens shape whose surface shape is controlled by transferring a mold onto a light-transmitting plastic substrate.