JP2005292380A - Display using coherent light - Google Patents

Abstract

A display using coherent light that can reduce speckle without using moving parts.
A display using coherent light includes a coherent light source 105 that can be modulated, main scanning means 101 that performs main scanning of coherent light emitted from the coherent light source 105, and sub scanning that sub-scans the coherent light in the main direction. Means 103, synchronization control means 107 for performing synchronization control of coherent light source 105, main scanning means 101, and sub-scanning means 103; Sub-scanning synchronization signal shifting means 108 is provided for shifting the position of the light spot in the pixel in the sub-direction by shifting it every 103 scanning cycles.
[Selection] Figure 1

Description

The present invention relates to a display using coherent light such as a laser.

  There is known a laser display that forms an image by scanning laser light of three primary colors of red, green, and blue with two optical deflectors in a main scanning direction (usually a horizontal direction) and a sub-scanning direction (usually a vertical direction). ing. Here, the direction of main scanning is the direction of scanning lines, and is usually the horizontal direction. The sub-scanning direction is a direction orthogonal to the scanning line, and is usually the vertical direction. A two-dimensional scanning region (that is, a screen) is formed by these two scans. The directivity and monochromaticity of laser light is suitable for high-resolution and good-quality displays. On the other hand, due to the coherence of the laser light, it appears that fine light dots are superimposed on the image. This is called speckle, and this removal is a major problem for laser scanning displays. Speckle is generated when coherent light scattered at each point on the projection surface interferes with each other in a random phase relationship caused by fine irregularities on the surface.

An example of a speckle removal method will be described. FIG. 6 is a configuration diagram of a non-speckle display using coherent light (see Patent Document 1). In this configuration, the laser beams of the red laser 601, blue laser 602, and green laser 603 are combined by the dichroic beam splitters 605 to 607, modulated by the spatial light modulator 610 via the condenser lens 609, and applied to the observation surface 611. Project. In order to eliminate speckle, the diffusing element 607 is rotated by a coil or a motor 608. As a result, the speckle pattern is split and the speckle on the observation surface 611 disappears.
JP-A-6-208089

  However, the above-described method requires a mechanism for rotating the diffusion element, which is disadvantageous in terms of downsizing the laser display and reducing power consumption.

In view of the foregoing problems, a display using coherent light according to the present invention includes a coherent light source that can be modulated, a main scanning unit that scans coherent light emitted from the coherent light source, a sub-scanning unit that sub-scans coherent light, The synchronization control means for controlling the synchronization of the coherent light source, the main scanning means, and the sub-scanning means, and the sub-scanning synchronization signal of the sub-scanning means output from the synchronization control means are shifted in time for each scanning period of the sub-scanning means. And a sub-scanning synchronization signal shifting means for changing the position of the light spot in the pixel in the sub-scanning direction. In this configuration, the speckle pattern due to coherent light scattered at each point such as the projection surface changes within the afterimage time of the person and is averaged within the pixel, thereby reducing speckle. This is performed by means of electrical processing called sub-scanning synchronization signal shifting means without using a movable mechanism.

  According to the present invention having the above-described configuration, speckle can be reduced without using moving parts. Further, since no moving parts are used, a compact, low power consumption laser scanning display or the like can be realized, and the image quality can be improved.

An embodiment of the present invention will be described below.
In the laser display of the present embodiment, speckle is reduced by changing the position of the light spot in the sub-scanning direction at each pixel formed on the screen for each frame. By changing the position of the light spot for each frame, the speckle pattern changes for each frame, thereby reducing speckle. The position of the light spot in the pixel formed on the screen is changed by shifting the sub-scanning synchronizing signal (sub-scanning synchronizing signal) for each frame.

FIG. 1 is a configuration diagram of a laser display according to the present embodiment. This laser display includes a main scanning direction optical deflector 101, a main scanning direction optical deflector driving circuit 102, a sub scanning direction optical deflector 103, a sub scanning direction optical deflector driving circuit 104, a laser light source 105, and a modulation signal generating circuit 106. , A laser display control circuit 107, and a sub-scanning synchronization signal shift circuit 108. In FIG. 1, the laser beam to be scanned is indicated by a dotted line.

In this configuration, the main scanning direction optical deflector 101 scans the light beam incident from the laser light source 105 to form one-dimensional scanning light. As a small device of the main scanning direction optical deflector 101, there is a resonant type having a double-supported spring structure using single crystal silicon. The driving waveform from the driving circuit 102 to this is a sine wave, a triangular wave, a rectangular wave or the like. The resonance frequency of the optical deflector 101 in the main scanning direction is determined by the number of scanning lines of the laser display, the non-drawing period of sub-scanning, and the frame rate of the screen, and is about 20 kHz. The main scanning direction optical deflector driving circuit 102 drives the main scanning direction optical deflector 101. The main scanning direction optical deflector driving circuit 102 generates a driving signal based on the amplitude of the driving waveform and the synchronizing signal from the laser display control circuit 107 inputted thereto.

The sub-scanning direction optical deflector 103 performs two-dimensional scanning by sub-scanning the scanning line of the light beam incident from the main scanning direction optical deflector 101 in the direction perpendicular to the scanning line. As the sub-scanning direction optical deflector 103, a resonance or non-resonance type having a double-supported spring structure can be used. Generally, it is operated non-resonant and the drive waveform is a triangular wave, a sawtooth wave, or the like. The driving frequency of the optical deflector 103 is determined by the frame rate of the laser display. For example, about 60 Hz. The sub scanning direction optical deflector driving circuit 104 drives the sub scanning direction optical deflector 103. The sub-scanning direction optical deflector drive circuit 104 generates a drive signal based on the amplitude of the drive waveform and the synchronization signal input thereto.

The light source 105 includes a light-emitting element that can be directly modulated, such as a semiconductor laser, and its drive circuit, or a combination of a solid-state laser, an external modulator, and its drive circuit, and a beam forming optical system. For example, red, green and blue lasers are provided. The modulation signal generation circuit 106 generates a modulation signal of the light source 105 based on a video signal input from the outside to the laser display. The modulation synchronization signal and the control signal are input from the laser display control circuit 107.

The laser display control circuit 107 is connected to the main scanning direction optical deflector driving circuit 102, the sub scanning direction optical deflector driving circuit 104, the modulation signal generation circuit 106, and the sub scanning synchronization signal shift circuit 108. The laser display control circuit 107 outputs amplitude setting input signals of the main scanning direction optical deflector driving circuit 102 and the sub-scanning direction optical deflector driving circuit 105, and the main scanning direction optical deflector driving circuit 102 performs horizontal scanning. A synchronization signal is output, and a sub-scanning synchronization signal is output to the sub-scanning synchronization signal shift circuit. The sub-scanning synchronization signal shift circuit 108 generates a signal obtained by shifting the sub-scanning synchronization signal input from the laser display control circuit 107, and outputs this signal to the sub-scanning direction optical deflector driving circuit 104. The shift amount will be described later.

FIG. 2 is a schematic diagram showing the position of the light spot in the pixel of the laser display in this embodiment. The change of the position of the light spot in a certain pixel is divided into four (a) nth frame, (b) n + 1th frame, (c) n + 2 frame, (d) n + 3 frame. Shows the frame. In the figure, reference numerals of pixels are 201 to 204, and reference numerals of light spots are 211 to 214.

  Here, the relationship between the pixels on the screen of the laser display and the scanned light spot will be described. In the laser display, the light spot moves in the main scanning direction by the pixel time. Therefore, the light spot becomes longer in the main scanning direction. The size of the light spot on the screen is inversely proportional to the mirror size of the optical deflector 101 in the main scanning direction. When the size of the mirror in the main scanning direction optical deflector 101 in the main scanning direction is the same as the size in the sub scanning direction, the size of the light spot in the main scanning direction is the same as the size in the sub scanning direction. Considering the above-described spread of the light spot due to the main scanning, if the light spot is made smaller than the pixel, the light spot in the sub-scanning direction becomes smaller than the pixel as shown in FIG. In the present invention, by utilizing this, the position of the light spot in the sub-scanning direction of the pixel is changed for each frame (may be partially overlapped).

  In order to change the position of the light spot in the sub-scanning direction of the pixel, the sub-scanning synchronization signal shift circuit 108 shifts the sub-scanning synchronization signal in units of frames. In FIG. 2, the position of the light spot in the sub-scanning direction of the pixel is changed with 4 frames as one period. The nth frame and the (n + 4) th frame are at the same position. This period is an example, and the number may be another value. Further, if the shift of the position of the light spot in the sub-scanning direction is performed approximately on average within the range of one pixel within the afterimage time of the human eye (that is, the light irradiation amount is approximately average). Therefore, it is not always necessary to have a fixed periodicity (in Example 1, which will be described later, it has a fixed periodicity, but in Example 2, it does not have a periodicity). Further, the change in the shift amount within the period does not need to be monotonous. For example, in FIG. 2, the position of the light spot in the (n + 1) th frame and the position of the light spot in the (n + 3) th frame may be reversed.

  According to this embodiment, by changing the position of the light spot in each pixel in the sub-scanning direction, the speckle pattern due to the coherent light scattered at each point on the projection surface changes within the afterimage time of the person, Speckle can be reduced by averaging within the pixel. And speckle is reduced without using movable parts.

Hereinafter, the present invention will be described with reference to more specific examples.
(Example 1)
In the first embodiment, the sub-scanning synchronization signal shifting unit or circuit 108 includes a plurality of delay units having different delay times, a selection unit that selects signals from the plurality of delay units, and a second scanning synchronization signal. Correspondingly, it comprises counting means for controlling the signal selection by the selection means. The feature of this embodiment is that the control system of the laser display operates with one operation clock, and the shift of the position of the light spot in the sub-scanning direction of the pixel for each frame is performed in synchronization with the operation clock. In the following example, the shift amount makes a round in 4 frames (same as FIG. 2).

  FIG. 3 is a configuration diagram of Embodiment 1 of the sub-scanning synchronization signal shift circuit. The sub-scanning synchronization signal shift circuit 108 includes a delay circuit A301, a delay circuit B302, a delay circuit C303, a delay circuit D304, a frame counter 311 and a selector 312.

  A sub-scanning synchronization signal is input from the laser display control circuit 107 to the delay circuit A301, the delay circuit B302, the delay circuit C303, and the delay circuit D304. A fixed delay amount is set in each delay circuit, and the input sub-scanning synchronization signal is delayed, that is, shifted in time by the delay amount. The frame counter 311 counts the input sub-scanning synchronization signal and controls the selector 312 according to the count number. The counter 311 is reset at 4. Accordingly, the selector 312 has four control states of “0”, “1”, “2”, and “3”. The selector 312 selects an input to be connected (a delay circuit to be connected) in accordance with a control signal from the frame counter 311. The delay circuit A301 is selected by the control state “0” of the selector 312, the delay circuit B302 is selected by the control state “1” of the selector 312, the delay circuit C303 is selected by the control state “2” of the selector 312, and the selector 312 In the control state “3”, the delay circuit D304 is selected. As a result, the sub-scanning synchronization signal corresponding to the delay amount of the selected delay circuit is output from the selector 312.

Here, the delay amount of each delay circuit will be described. The drawing time interval between adjacent pixels in the vertical direction (sub-scanning direction) is the period of main scanning. When this period is Th, the delay amount of each delay circuit is
Delay circuit A301: 0,
Delay circuit B302: 0.2 Th
Delay circuit C303: 0.4 Th
Delay circuit D304: 0.6 Th
It becomes. The reason for setting the delay amount to 5 equal parts (by 0.2 Th) rather than 4 equal parts to Th is to keep the light spot in the pixel.

  In this embodiment, since the shift of the sub-scanning position of the light spot in the pixel is controlled periodically (as determined) based on the operation clock of the control system of the laser display, the system design of the system is easy. is there.

(Example 2)
In the second embodiment, the sub-scanning synchronization signal shifting means or circuit 108 generates a clock independent of the operation clock of the laser display control circuit 107 (the operation clock of the control system of the sub-scanning direction optical deflector driving circuit 104). Generating circuit and logic circuit means for matching the output signal with the input signal according to the input state of the independent clock and then holding it, and inputting the sub-scanning synchronization signal to the logic circuit means as the input signal To do. Therefore, in this embodiment, the shift amount for each frame of the position of the light spot in the pixel in the sub-scanning direction is not fixed.

  FIG. 4 is a configuration diagram of the sub-scanning synchronization signal shift circuit 108 according to the second embodiment. The shift circuit 108 includes a sub-scanning direction optical deflector drive circuit clock generation circuit 401 and a D flip-flop 402. The sub-scanning direction optical deflector driving circuit clock generation circuit 401 generates an operation clock for the sub-scanning direction optical deflector driving circuit 104. The cycle of this clock is set longer than the cycle of the operation clock of the other control system of the laser display (the operation clock of the laser display control circuit 107). The D flip-flop 402 outputs the input signal of the sub-scanning synchronization signal generated from the operation clock of the laser display control circuit 107 at the rising edge of the clock from the clock generation circuit 401.

  FIG. 5 is a timing chart of signals of the D flip-flop 402. Three signals of input, clock, and output are shown for the nth to (n + 3) th frames. This figure shows an example in which the shift amount makes a round in 4 frames. Since the sub-scanning direction optical deflector drive clock is asynchronous with the system clock of the other control system of the laser display (the operation clock of the laser display control circuit 107), the timing shifts. In FIG. 5, since the sub-scanning synchronization signal generated from the operation clock of the control system of the laser display is described as a reference, the timing of the sub-scanning optical deflector drive circuit clock is shifted in each frame. The D Philip flop 402 makes the output signal coincide with the input signal at the rising edge of the sub-scanning optical deflector driving circuit clock, and then holds it until the next rising edge of the sub-scanning optical deflector driving circuit clock. For this reason, a deviation occurs between the output from the D flip-flop 402 and the input. Due to this shift, the delay time changes between the input and output of the D flip-flop 402. Due to this change, the sub-scanning synchronization signal is randomly shifted for each frame. Even in this case, the shift of the position of the light spot in the sub-scanning direction is performed almost on average within the range of one pixel within the afterimage time of the human eye.

  In this embodiment, delay circuits for the number of shifts are not necessary. When the operation clock of the sub-scanning direction optical deflector drive circuit is independent of the operation clocks of other drive / control systems in the apparatus, the circuit scale for applying this method can be reduced.

It is a block diagram of the laser display of embodiment of this invention. It is a figure shown about the shift of the light spot in the pixel in the laser display of embodiment of this invention. FIG. 3 is a configuration diagram of a sub-scanning synchronization signal shift circuit according to the first embodiment. FIG. 6 is a configuration diagram of a sub-scanning synchronization signal shift circuit according to a second embodiment. 6 is a timing chart of the sub-scanning synchronization signal shift circuit according to the second embodiment. It is a block diagram of the laser display of background art.

Explanation of symbols

101: Main scanning direction optical deflector (first scanning means)
102: Main scanning direction optical deflector drive circuit
103: Sub-scanning direction optical deflector (second scanning means)
104: Sub-scanning light deflector drive circuit
105: Light source (coherent light source)
107: Laser display control circuit (synchronous control means)
108: Sub-scanning synchronization signal shift circuit (second scanning synchronization signal shift means)

Claims (3)

A coherent light source that can be modulated, a main scanning unit that main-scans coherent light emitted from the coherent light source, a sub-scanning unit that performs sub-scanning of the coherent light, the coherent light source, the main scanning unit, and the sub-scanning unit. A synchronization control unit that performs synchronization control, and a sub-scanning synchronization signal of the sub-scanning unit that is output from the synchronization control unit are shifted in time for each scanning period of the sub-scanning unit, so that the light spot at the pixel is A display using coherent light, comprising sub-scanning synchronization signal shifting means for changing a position in the sub-scanning direction. The sub-scanning synchronization signal shifting means includes a plurality of delay means having different delay times, a selection means for selecting signals of the plurality of delay means, and a sub-scanning synchronization signal counted by the selection means corresponding to the value. The display using coherent light according to claim 1, comprising: counting means for controlling the signal selection. The sub-scanning synchronization signal shifting means generates clock independent from the operation clock of the display control circuit using coherent light, and matches the output signal with the input signal according to the input state of the independent clock. 2. A display using coherent light according to claim 1, further comprising logic circuit means for holding the sub-scanning synchronization signal as the input signal.

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