WO2004104669A1

WO2004104669A1 - Line-at-a-time optical laser display device

Info

Publication number: WO2004104669A1
Application number: PCT/IB2004/050691
Authority: WO
Inventors: Dirk De Bruin; Gerrit Oversluizen; Pieter J. Engelaar; Oscar H. Willemsen; Rogier Winters; Hugo M. Visser; Ruediger J. Lange
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-05-22
Filing date: 2004-05-13
Publication date: 2004-12-02
Also published as: TW200508656A

Abstract

A display device comprising means (1, 2) for guiding at least one laser beam (4) in parallel paths across the display, and light exiting means (5) arranged to extract light from a laser beam out of the display. The display further comprises means (9, 10) for addressing said display by activating said light exiting means along one line (8), perpendicular to said laser beams (4), at a time, and, for each thus selected line, activating a selected number of laser beams (4), to thereby emit light from corresponding intersections with said selected line. This design makes it possible to address the laser display using line-at-a-time addressing. The rows are consecutively selected by addressing the light exiting means, and 10 for each row, laser is directed along the desired columns, so that pixels corresponding to the intersection of the illuminated columns and the selected row will emit light.

Description

Line-at-a-time optical laser display device

The present invention relates to a display device comprising means for guiding a plurality of laser beams in parallel paths across the display, and light exiting means arranged to extract light from a laser beam out of the display.

A particular category of display device comprises a light source and several pixels, each of which can be activated to extract light from the light source. Typically, each pixel can have several different active levels, achieved by controlling the duration of activation (pulse width modulation), or of the intensity of the light source (pulse amplitude modulation). Such displays are normally referred to as "optical" displays, and examples include foil displays and fiber displays.

Optical displays using laser as light source are well know in the art. For example, US 6,453,100 discloses a display where light is directed into an optical guide plate, and is decoupled out of the plate by activation of one pixel at a time. The light maybe generated by a laser.

However, conventional optical laser displays are difficult to address.

The object of the present invention is to provide an optical laser display device which can be more easily addressed.

According to the invention, this and other objects are achieved by a display device of the kind mentioned by way of introduction, further comprising means for addressing the display by activating the light exiting means along one line, perpendicular to said laser beam paths, at a time, and, for each thus selected line, guiding the at least one laser beam in a selected number of the paths, to thereby emit light from corresponding intersections with the selected line.

This design makes it possible to address the laser display using line-at-a-time addressing. The rows are consecutively selected by addressing the light exiting means, and for each row, a laser is directed along the desired columns, so that pixels corresponding to the intersection of the illuminated columns and the selected row will emit light.

The display device preferably comprises a laser unit which can be arranged to emit one laser beam, and to sweep this laser beam through said parallel paths, or arranged to emit one laser beam for each parallel path. The more lasers used, the less power is required from each laser. If considered advantageous, a combination of the above approaches may be chosen, i.e. a plurality of lasers, each being swept over a plurality of columns.

According to a first embodiment, the display comprises a front plate and a back plate, and the laser beam(s) is/are guided between these plates in parallel with the surfaces of the plates, and the light exiting means comprises a flexible foil arranged between the plates. The foil is attached to the front plate in a first area extending across the laser beam(s), and to the back plate in a second area extending across the laser beams. The device further comprises means to control along which row the foil bridges the distance between the plates. Laser beams introduced into the gap between the plates will propagate until they hit the foil crossing, and this crossing can be used to emit light out through the front plate.

The foil can for example be adapted to scatter and/or reflect the laser beam(s), in order to make the display emit light. According to a second embodiment, the laser beam guiding means comprises a wave guide in which the laser beam(s) is/are guided by means of total internal reflection, and the light exiting means are arranged to frustrate said internal reflection locally along a line.

Laser beams introduced into the wave guide will propagate until they reach the line with frustrated internal reflection, and there be decoupled out of the wave guide (and out of the display).

The light exiting means can for example comprise an electromechanically operable foil arranged on one side of the wave guide, and means for bringing this foil into contact with the wave guide. Alternatively, the light exiting means comprise means for electric or accousto-optical switching of the refractive index of the wave guide.

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention. Fig. 1 is a perspective view of a display device according to a first embodiment of the invention

Fig. 2 is a side view of a first variant of the display device in fig 1. Fig. 3 is a side view of a second variant of the display device in fig 1. Fig. 4 is a perspective view of a second embodiment of the invention.

A first embodiment of the invention is illustrated in figs 1 - 3. With reference to fig 1, the display device comprises a back plate 1 and a transparent front plate 2 which are arranged in parallel planes with a gap 3 in between. A laser unit 20 is arranged to emit one or several laser beams 4 in parallel paths into the gap 3, parallel to the surfaces of both plates 1, 2, and these paths define the columns of the display.

Inside the gap 3, which may be provided with a vacuum, a movable foil 5 is arranged. The foil 5 comprises a conducting layer 6, and an insulating layer 7. The foil 5 is attracted to the back plate 1 along a first edge la extending perpendicularly across all columns, and to the front plate 2 along a second edge 2a, likewise extending perpendicularly across all columns. The attraction to the edges la, 2a can be permanent, for example using adhesive, or semi-permanent, for example creating a constant electromagnetic force by applying a suitable voltage. The area between the edges la, 2a define the active display, i.e. the area in which light can be emitted. Somewhere between the two fixed edges, the foil bridges the gap between the plates. Preferably, the angle γ between the foil and the plates at this point of crossing 8 is around 45°.

Further, the plates are provided with electrodes 9, 10 that run perpendicularly to the laser beams. These electrodes define the rows of the display. The foil can be attracted to the electrodes by applying a voltage difference between the conducting foil, here connected to ground potential, and the electrodes 9, 10 on either of the plates. At the side where the laser beams enter the gap 3, the electrodes 9a, 10a are supplied with a voltage such that the foil is attracted to the back plate 1. At the opposite side of the display, i.e. after the crossing 8 of the foil, the electrodes 9b, 10b are applied with a voltage such that the foil is attracted to the front plate 2. At the crossing 8, the foil can be attracted to one of the plates 1 or 2, or be set to a "floating" condition, by applying suitable voltages. The foil crossing 8 can be moved by changing the voltage applied to the appropriate electrodes 9, 10. In fig 1 and 2, the electrodes 10 on the back plate 1 are covered by an insulating layers 11, in order to avoid a short circuit, but alternatively, as illustrated in fig 3, the foil 5 can be provided with two insulating layers 7a and 7b, one on each side of the electrode layer 6. The foil crossing 8, which thus can be moved to any selected row of the display, is used to direct the laser beam out through the front plate 2. To achieve this, the foil is preferably covered with either a light scattering layer 12 or with a light reflecting layer 13, which preferably also forms the insulating layer 7.

In case of a light scattering layer 12, the laser beam 4 is scattered when it hits the foil crossing 8, so that it becomes visible at through the front plate 2, as illustrated in fig 2.

In case of a light reflecting layer 13, the laser beam 4 is reflected out through the front plate 2 when it hits the foil crossing, as illustrated in fig 3. In this latter case, a light scattering layer 15 is preferably deposited on the front plate 2, to provide for a reasonable viewing angle. Diverging lenses could also be used for this purpose.

The display in figs 1 - 3 is addressed by consecutively selecting the rows, one at a time, by applying appropriate voltages or currents to the electrodes 9, 10 as described above. Then, for each selected row, laser beams are directed into selected columns. Light will be emitted from the display from the pixels corresponding to the intersections of these laser beams with the selected row.

A second embodiment of the invention is illustrated in fig 4. According to this embodiment, a laser unit 20 is again arranged to direct one or several laser beams 21 in parallel paths, this time into an optical wave guide 22, here in the form of a thin (preferably 0.01-0.5 mm thickness) transparent plate, e.g. glass. Once coupled into the plate 22, the light reflects with total internal reflection (TIR) and remains confined in the plate. In the plane of the plate, the light travels along the original laser direction, so that the light can be directed along the columns of the display without need for any additional wave guide structure.

The display further comprises means 23, 25 for frustrating the total internal reflection (TIR) along a horizontal line extending across all columns, i.e. a row. In fig 4, a foil 23 is arranged on the surface of the light guide 22, and is arranged to be deformed along a line 24 by applying a voltage 25 to two end points of the line. Such voltage controlled bending of a foil for frustrating an internal reflection has been disclosed in US 5771321, incorporated herewith by reference. Other well known ways to frustrate the TIR are switching the refractive index electrically (US 6141465, US 5647036), and by means of acousto-optic effect (US 5106181), also incorporated herewith by reference.

The display in fig 4 is addressed similarly as the display in figs 1 - 3. The rows are selected consecutively, by frustrating the internal reflection of the plate 22 along a line 24 as described above. Then, for each selected row, laser beams 21 are directed into the plate 22. Light will be emitted from the plate from the pixels corresponding to the intersections of these laser beams with the selected row.

While the horizontal resolution of the display in fig 4 only is determined by the divergence of the laser beam, the vertical resolution is also determined by the size of the area of decoupling, i.e. the size of the area of contact between the foil 23 and the plate 22. While a small contact area improves resolution, it also means that the efficiency of the display is reduced (less light is emitted from each pixel). In order to compensate this reduced efficiency, the wave guide must be made thinner (each laser beam is reflected more often, thereby increasing the chance of the laser beam hitting the contact area). In other words there is a trade off between resolution (contact area) and thickness of the wave guide, which must be determined depending on the implementation. It is estimated that a pixel size of 0.2 mm (i.e. the width of the line 24 in the direction of the laser beam is 0.2 mm) will require a wave guide thickness of about 2 mm or less. To enable addressing of all columns, the laser unit 20 in figs 1 and 4 can include as many lasers as there are columns in the display. Alternatively, the beam of one or several lasers is swept over the columns. In order to reduce the angular sweep required to cover the entire display, the display can be divided into several segments, each addressed by their own laser. The more lasers used, the less power needed per laser, and the less angular sweep needed for each laser.

A lasers beam can be swept by directing it onto e.g. a rotating polygon mirror, an acousto-optic crystal or a vibrating mirror. Before entering the display itself (the gap 3 or the plate 22), the swept laser beam should be redirected to be parallel to the column direction. This could for example be done by means of a lens. Alternatively, a beam is swept using a rotating prism, preferably in the shape of a rectangular parallelepiped.

To produce colors, one or several sets of three different colored lasers may be used, or one or several (near) UV lasers in combination with colored phosphors may be used.

In case of using (at least) three colored lasers, colors may be generated at different times. For example, first the red line is 'written', then the green and then the blue line. However, this is not required: the three lasers generating the colors may also address the same pixels at the same time. The relative powers from the three lasers determines the perceived color of the pixel.

In the above description, the terms columns and rows have been used to distinguish between orthogonal directions in the display device. It should be understood that no limitation is intended regarding which of these directions is horizontal and vertical, respectively.

Claims

CLAIMS:

1. A display device comprising means (1,2; 22) for guiding at least one laser beam in parallel paths (4) across the display, and light exiting means (5; 23) arranged to extract light from a laser beam out of the display, characterized by means (9, 10) for addressing said display by activating said light exiting means along one line (8; 24), perpendicular to said laser beam paths (4), at a time, and, for each thus selected line, guiding said at least one laser beam in a selected number said paths (4), to thereby emit light from corresponding intersections with said selected line.

2. A display device according to claim 1, further comprising a laser unit (20) arranged to emit one laser beam, and to sweep this laser beam through said parallel paths.

3. A display device according to claim 1, further comprising a laser unit (20) arranged to emit one laser beam for each parallel path.

4. A display device according to claims 1-3, further comprising a front plate (2) and a back plate (1), said at least one laser beam (4) being guided between these plates in parallel with the surfaces of said plates, and wherein said light exiting means comprises a flexible foil (5) arranged between said plates, said foil being attached to the front plate in a first area (2a) extending across said paths (4) and attached to the back plate in a second area (la) extending across said paths (4), and means (9, 10) to control along which line (8) the foil bridges the distance between said plates (1, 2).

5. A display device according to claim 4, wherein said foil (5) is adapted to scatter said at least one laser beam.

6. A display device according to claim 4, wherein said foil (5) is adapted to reflect said at least one laser beam.

7. A display device according to claims 1-3, wherein said laser beam guiding means comprise a wave guide (22) in which said at least one laser beam is guided by means of total internal reflection (TIR), and wherein said light exiting means (23) are arranged to frustrate said internal reflection locally along a line (24).

8. A display device according to claim 7, wherein said light exiting means comprise an electromechanically operable foil (23) arranged on one side of the wave guide (22), and means (25) for bringing said foil into contact with the wave guide.

9. A display device according to claim 7, wherein said light exiting means comprise means for electric switching of the refractive index of the wave guide.

10. A display device according to claim 7, wherein said light exiting means comprises means for accousto -optical switching of the refractive index of the wave guide.