Image projection apparatus

Abstract

An image projection apparatus includes a light source, a scanner, and a projection optical system. The light source includes at least one first laser element, at least one second laser element, at least one third laser element, and a drive circuit. The first laser element emits a laser beam having a wavelength from 610 to 680 nanometers and has an oscillation threshold current of 15 milliamperes or less. The second laser element emits a laser beam having a wavelength from 500 to 530 nanometers and has an oscillation threshold current of 25 milliamperes or less. The third laser element emits a laser beam having a wavelength from 430 to 470 nanometers and has an oscillation threshold current of 10 milliamperes or less. The drive circuit pulse-drives the first, second, and third laser elements at a pulse width that is shorter than a pulse width determined by a desired modulation speed of one pixel.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an image projection device, and more particularly, to an image projection device driven with low power consumption. BACKGROUND

[0002] In recent years, an augmented reality (AR) glass as a head-mounted display type augmented reality wearable terminal is being developed as an image projection device.

[0003] An image projection device such as an AR glass requires a small volume, a light weight, a fashionable appearance, and low power consumption.

[0004] A conventional image projection device is configured to guide a laser beam emitted from a laser element to a human eye through a light guide plate having a diffractive optical element (DOE).

[0005] To reduce power consumption, the conventional image projection device drives a semiconductor laser diode (LD) element (hereinafter referred to as a laser element) in a pulse by applying a pulse current higher than an oscillation threshold current to the laser element.

[0006] In terms of reducing power consumption, the pulse driving in the conventional image projection device employs a laser element having a high oscillation threshold current, so that a high slope efficiency, i.e., a ratio of light output to a current value of a pulse current (i.e., a peak current value), is high.

[0007] However, to drive a laser element having a high slope efficiency and a high oscillation threshold current, the conventional image projection device requires a large pulse current value in pulse driving. Since the current value of the pulse current must be increased, the conventional image projection device can cause an increase in power consumption of a driving circuit and a time offset of the pulse current, called jitter. The jitter can cause color shift and image flow, thereby degrading image quality. Therefore, it is desirable that the image projection device reduce power consumption while maintaining good image quality. SUMMARY

[0008] The present disclosure aims to solve at least one technical problem as described above. Therefore, the present disclosure needs to provide an image projection device.

[0009] According to the present disclosure, an image projection device includes: a light source that emits a laser beam; a scanner that scans the laser beam emitted from the light source; and a projection optical system that irradiates the laser beam scanned by the scanner and projects an image to a retina of a user, wherein the light source includes: at least one first laser element that emits a wavelength of the laser beam from 610 nm to 680 nm and has an oscillation threshold current of 15 mA or less; at least one second laser element that emits the wavelength of the laser beam from 500 nm to 530 nm and has the oscillation threshold current of 25 mA or less; at least one third laser element that emits the wavelength of the laser beam from 430 nm to 470 nm and has the oscillation threshold current of 10 mA or less; and a driving circuit that pulse drives the first laser element, the second laser element, and the third laser element with a pulse width shorter than a pulse width determined by a required modulation speed of one pixel. BRIEF DESCRIPTION OF DRAWINGS

[0010] These and / or other aspects and advantages of embodiments of the present disclosure will become more apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: Figure 1 is a diagram illustrating a configuration example of an image projection apparatus according to a first embodiment of the present disclosure; Figure 2 is a diagram illustrating a configuration example of a light source according to the first embodiment of the present disclosure; Figure 3A is a diagram illustrating a current versus light output characteristic of a first laser element according to the first embodiment of the present disclosure; Figure 3B is a diagram illustrating a current versus light output characteristic of a second laser element according to the first embodiment of the present disclosure; Figure 3C is a diagram illustrating a current versus light output characteristic of a third laser element according to the first embodiment of the present disclosure; Figure 4 is a diagram illustrating a driving current of the laser elements according to the first embodiment of the present disclosure; Figure 5 is a diagram illustrating a configuration example of a scanner according to the first embodiment of the present disclosure; Figure 6 is a diagram illustrating a scanning method of the scanner according to the first embodiment of the present disclosure; Figure 7 is a diagram illustrating a configuration example of a tilt mirror module according to the first embodiment of the present disclosure; Figure 8 is a diagram of an operation of the tilt mirror module of the first embodiment of the present disclosure; Figure 9Ais a graph showing the driving conditions of the first laser element (R) according to the first example of the first embodiment of the present disclosure; Figure 9B is a graph showing the driving conditions of the second laser element (G) according to the first example of the first embodiment of the present disclosure; Figure 9C is a graph showing the driving conditions of the third laser element (B) according to the first example of the first embodiment of the present disclosure; Figure 9D is a graph showing the power consumption of the driving conditions of the plurality of laser elements (RGB) according to the first example of the first embodiment of the present disclosure; Figure 10A is a graph showing the driving conditions of the first laser element (R) according to the second example of the first embodiment of the present disclosure; Figure 10B is a graph showing the driving conditions of the second laser element (G) according to the second example of the first embodiment of the present disclosure; Figure 10C is a graph showing the driving conditions of the third laser element (B) according to the second example of the first embodiment of the present disclosure; Figure 10D is a graph showing the power consumption of the driving conditions of the plurality of laser elements (RGB) according to the second example of the first embodiment of the present disclosure; Figure 11A is a graph showing the current and light output characteristics of the first laser element according to the first comparative example; Figure 11B is a graph showing the current and light output characteristics of the second laser element according to the first comparative example; Figure 11C is a graph showing the current and light output characteristics of the third laser element according to the first comparative example; Figure 12A is a graph showing the driving conditions of the first laser element (R) according to the first comparative example; Figure 12B is a graph showing the driving conditions of the second laser element (G) according to the first comparative example; Figure 12C is a graph showing the driving conditions of the third laser element (B) according to the first comparative example; Figure 12D is a graph showing the power consumption of the driving conditions of the plurality of laser elements (RGB) according to the first comparative example; Figure 13A is a graph showing the driving conditions of the first laser element (R) according to the second comparative example; Figure 13Bis a graph showing the driving condition of the third laser element (B) according to the second comparative example; Figure 13C is a graph showing the driving condition of the third laser element (B) according to the second comparative example; Figure 13D is a graph showing the power consumption of the driving condition of the plurality of laser elements (RGB) according to the second comparative example; Figure 14A is a graph showing the driving condition of the first laser element (R) according to the third comparative example; Figure 14B is a graph showing the driving condition of the second laser element (G) according to the third comparative example; Figure 14C is a graph showing the driving condition of the third laser element (B) according to the third comparative example; Figure 14D is a graph showing the power consumption of the driving condition of the plurality of laser elements (RGB) according to the third comparative example; Figure 15 is a graph showing the light source according to the first modification example of the first embodiment of the present disclosure; Figure 16 is a graph showing the scanner according to the second modification example of the first embodiment of the present disclosure; Figure 17 is a graph showing the light source according to the third modification example of the first embodiment of the present disclosure; Figure 18 is a graph showing a configuration example of the light source according to the second embodiment of the present disclosure; Figure 19A is a graph showing the driving condition of the first laser element (R) according to the example of the second embodiment of the present disclosure; Figure 19B is a graph showing the driving condition of the second laser element (G) according to the example of the second embodiment of the present disclosure; Figure 19C is a graph showing the driving condition of the third laser element (B) according to the example of the second embodiment of the present disclosure; Figure 19D is a graph showing the power consumption of the driving condition of the plurality of laser elements (RGB) according to the example of the second embodiment of the present disclosure; Figure 20 is a graph showing the light source according to the modification of the second embodiment of the present disclosure; Figure 21 is a graph showing the light source according to the third embodiment of the present disclosure; Figure 22Ais a graph showing current versus light output characteristics and current versus voltage characteristics of the first laser element according to the third embodiment of the present disclosure; Figure 22B is a graph showing current versus light output characteristics and current versus voltage characteristics of the second laser element according to the third embodiment of the present disclosure; Figure 22C is a graph showing current versus light output characteristics and current versus voltage characteristics of the third laser element according to the third embodiment of the present disclosure; Figure 23A is a graph showing driving conditions of the first laser element (R) according to the first example of the third embodiment of the present disclosure; Figure 23B is a graph showing driving conditions of the second laser element (G) according to the first example of the third embodiment of the present disclosure; Figure 23C is a graph showing driving conditions of the third laser element (B) according to the first example of the third embodiment of the present disclosure; Figure 23D is a graph showing power consumption of driving conditions of the plurality of laser elements (RGB) according to the first example of the third embodiment of the present disclosure; Figure 24A is a graph showing driving conditions of the first laser element (R) according to the second example of the third embodiment of the present disclosure; Figure 24B is a graph showing driving conditions of the second laser element (G) according to the second example of the third embodiment of the present disclosure; Figure 24C is a graph showing driving conditions of the third laser element (B) according to the second example of the third embodiment of the present disclosure; Figure 24D is a graph showing power consumption of driving conditions of the plurality of laser elements (RGB) according to the second example of the third embodiment of the present disclosure; Figure 25A is a graph showing driving conditions of the first laser element (R) according to the third example of the third embodiment of the present disclosure; Figure 25B is a graph showing driving conditions of the second laser element (G) according to the third example of the third embodiment of the present disclosure.

[0011] Figure 25C is a graph showing driving conditions of the third laser element (B) according to the third example of the third embodiment of the present disclosure; Figure 25D is a graph showing power consumption of driving conditions of the plurality of laser elements (RGB) according to the third example of the third embodiment of the present disclosure; Figure 26 is a diagram showing driving conditions of the plurality of laser elements according to the fourth example of the third embodiment of the present disclosure; Figure 27A is a diagram showing driving conditions of the first laser element (R) according to the fourth example of the third embodiment of the present disclosure; Figure 27B is a diagram showing driving conditions of the second laser element (G) according to the fourth example of the third embodiment of the present disclosure; Figure 27C is a diagram showing driving conditions of the third laser element (B) according to the fourth example of the third embodiment of the present disclosure; Figure 27D is a diagram showing power consumption of driving conditions of the plurality of laser elements (RGB) according to the fourth example of the third embodiment of the present disclosure; Figure 28 is a diagram showing driving conditions of the plurality of laser elements according to a fifth example of the third embodiment of the present disclosure; Figure 29A is a diagram showing driving conditions of the first laser element (R) according to the fifth example of the third embodiment of the present disclosure; Figure 29B is a diagram showing driving conditions of the second laser element (G) according to the fifth example of the third embodiment of the present disclosure; Figure 29C is a diagram showing driving conditions of the third laser element (B) according to the fifth example of the third embodiment of the present disclosure; Figure 29D is a diagram showing power consumption of driving conditions of the plurality of laser elements (RGB) according to the fifth example of the third embodiment of the present disclosure; Figure 30 is a diagram showing the light source according to a first modification example of the third embodiment of the present disclosure; and Figure 31 is a diagram showing the light source according to a second modification example of the third embodiment of the present disclosure. DETAILED DESCRIPTION

[0012] Embodiments of the present disclosure will be described in detail, and examples of the embodiments will be illustrated in the accompanying drawings. Throughout the description, the same or similar elements and elements having the same or similar functions are denoted by the same reference numerals. The embodiments described herein with reference to the accompanying drawings are illustrative, and the purpose is to explain the present disclosure, but should not be understood as limiting the present disclosure.

[0013] [First Embodiment] An image projection device according to a first embodiment of the present disclosure will be described below. The image projection device according to the first embodiment is a retinal projection type head-mounted display that projects an image onto a user's retina. More specifically, the image projection device according to the first embodiment is an eye-motion tracking retinal projection type head-mounted display that uses end-face emitting lasers as light sources and projects a plurality of images onto the user's retina by tracking the user's line-of-sight direction. As Figure 1 shown, the image projection device 1 according to the first embodiment includes a light source 11, a collimating optical system 12, a scanner 14, a projection optical system 15, a line-of-sight direction detector 16, an optical system controller 17, and a digital image controller (DIC) 18.

[0014] The light source 11 emits a laser beam to the scanner 14. As Figure 2 shown, the light source 11 includes a first laser element 111, a second laser element 112, a third laser element 113, and a driving circuit (LDD) 117.

[0015] In the first embodiment, each of the first laser element 111, the second laser element 112, and the third laser element 113 is an edge emitting laser. That is, as Figure 2 shown, each of the plurality of laser elements 111, 112, and 113 has a p-type semiconductor layer 101, an n-type semiconductor layer 102, and an active layer 103 between the p-type semiconductor layer 101 and the n-type semiconductor layer 102.

[0016] As Figure 2 shown, the first laser element 111 emits a laser beam Lr of a wavelength from 610 nanometers (nm) to 680 nm (i.e., red). The wavelength of the laser beam Lr can be, for example, 650 nm. The second laser element 112 emits a laser beam Lg of a wavelength from 500 nm to 530 nm (i.e., green). The wavelength of the laser beam Lg can be, for example, 520 nm. The third laser element 113 emits a laser beam Lb of a wavelength from 430 nm to 470 nm (i.e., blue). The wavelength of the laser beam Lb can be, for example, 450 nm.

[0017] The active layer 103 of the first laser element 111 (i.e., the first active layer) contains aluminum gallium indium phosphide (AlGaInP). Each of the active layer 103 of the second laser element 112 (i.e., the second active layer) and the active layer 103 of the third laser element 113 (i.e., the third active layer) contains indium gallium nitride (InGaN).

[0018] Each laser element 111, 112, and 113 is connected to the driving circuit 117 via wiring. The driving circuit 117 is connected to the digital image controller 18. The driving circuit drives the light source 11. Specifically, under the control of the digital image controller 18, the driving circuit 117 applies a driving current between the p-type semiconductor layer 101 and the n-type semiconductor layer 102. When a driving current higher than the oscillation threshold current is applied, each of the plurality of laser elements 111, 112, and 113 emits the plurality of laser beams Lr, Lg, and Lb generated by the recombination of holes and electrons in the active layer 103 from the edge surface (cracked surface) of the active layer 103.

[0019] like Figure 3A As shown, in the first embodiment, when the case temperature (Tc) is between 0°C and 60°C, the oscillation threshold current of the first laser element 111 is 30 mA or less. More specifically, the oscillation threshold current of the first laser element 111 is between 5 mA or more and 25 mA or less when the case temperature is between 0°C and 60°C, and is 15 mA or less when the case temperature is 25°C.

[0020] like Figure 3B As shown, in the first embodiment, when the housing temperature is between 0°C and 60°C, the oscillation threshold current of the second laser element 112 is 35 mA or less. More specifically, the oscillation threshold current of the second laser element 112 is between 15 mA or more and 32 mA or less when the housing temperature is between 0°C and 60°C, and is 25 mA or less when the housing temperature is 25°C.

[0021] like Figure 3C As shown, in the first embodiment, the oscillation threshold current of the third laser element 113 is 15 mA or less when the case temperature is between 0°C and 60°C. More specifically, the oscillation threshold current of the third laser element 113 is between 5 mA or more and 12 mA or less when the case temperature is between 0°C and 60°C, and is 10 mA or less when the case temperature is 25°C.

[0022] These laser elements 111, 112, and 113 have extremely high front surface reflectivity (almost 100%) and low slope efficiency, which reduces the oscillation threshold current.

[0023] like Figure 4As shown, the digital image controller 18 sends a signal (i.e., data) to the drive circuit 117 such that the drive circuit 117 applies a pulse current having a pulse width W and a pulse height H as a drive current to each laser element 111, 112, 113. In other words, the drive circuit 117 pulse-drives each laser element 111, 112, 113. Specifically, the drive circuit 117 pulse-drives each laser element 111, 112, 113 with a pulse width W determined by a required modulation speed of one pixel. The pulse width W determined by the required modulation speed of one pixel can be 11.2 nanoseconds (nsec) (see, for example, the pulse width corresponding to a continuous wave (CW) in Figure 9A to Figure 9C More specifically, the drive circuit 117 pulse-drives each laser element 111, 112, 113 with a pulse width W of 2.2 nanoseconds or less. More preferably, the drive circuit 117 pulse-drives each laser element 111, 112, 113 with a pulse width W of 1.1 nanoseconds or less.

[0024] In other words, the drive circuit 117 pulse-drives each laser element 111, 112, 113 with a sufficiently low oscillation threshold current and a sufficiently short pulse width W. Thus, when the image is projected onto the retina, the laser output is very small, and each laser element 111, 112, and 113 has a lower oscillation threshold current, and thus the drive current is even smaller. As a result, power consumption can be reduced and jitter can be reduced. Furthermore, since the current value generated when the plurality of laser elements 111, 112, and 113 are driven is small, the loss of capacitance and the like (including resistance loss and inductance loss) in the drive circuit 117 is reduced. As a result, the consumed power of the drive circuit 117 itself can be greatly reduced.

[0025] Figure 1 The collimating optical system 12 shown is disposed on the exit side of the plurality of laser beams Lr, Lg, and Lb with respect to the light source 11. The collimating optical system 12 collimates and emits the plurality of laser beams Lr, Lg, and Lb emitted from the light source 11. In the example shown, the collimating optical system 12 includes a single lens. The configuration of the collimating optical system 12 is not limited to the configuration shown. For example, the collimating optical system 12 can include a plurality of lenses. Figure 1 Figure 1

[0026] ​​The scanner 14 is positioned relative to the collimating optical system on the emitting side 12 of the plurality of laser beams Lr, Lg, and Lb. The scanner 14 scans the plurality of laser beams Lr, Lg, and Lb emitted from the light source 11. Specifically, the scanner 14 scans the plurality of laser beams Lr, Lg, and Lb after they have been collimated by the collimating optical system 12.

[0027] like Figure 5 As shown, the scanner 14 includes, for example, a MEMS (Micro-Electro-Mechanical Systems) mirror 141 and an ASIC (Application-Specific Integrated Circuit) (not shown) that drives the MEMS mirror 141. The MEMS mirror 141 has a first rotation axis A1 that rotates the MEMS mirror 141 to scan the plurality of laser beams Lr, Lg, and Lb in a first uniaxial direction. The MEMS mirror 141 also has a second rotation axis A2 that rotates the MEMS mirror 141 to scan the plurality of laser beams Lr, Lg, and Lb in a second uniaxial direction perpendicular to the first uniaxial direction. The ASIC applies a driving current to piezoelectric elements (not shown) disposed around the MEMS mirror 141 to rotate the MEMS mirror 141. The digital image controller 18 controls the rotational drive of the MEMS mirror 141 via the ASIC.

[0028] The MEMS mirror 141 scans the plurality of laser beams Lr, Lg, and Lb by rotating about a first rotation axis A1. The MEMS mirror 141 also scans the plurality of laser beams Lr, Lg, and Lb by rotating about a second rotation axis A2.

[0029] Since a single MEMS mirror 141 scans the plurality of laser beams Lr, Lg, and Lb in mutually orthogonal first and second single-axis directions, it is not necessary to provide separate MEMS mirrors to scan the plurality of laser beams Lr, Lg, and Lb in the main scanning direction and the sub-scanning direction. This allows the image projection system 1 to be miniaturized.

[0030] The MEMS mirror 141 rotates about the first rotation axis A1 using resonance. The MEMS mirror 141 also rotates about the second rotation axis A2 using resonance. Since the MEMS mirror 141 rotates in mutually orthogonal first and second single-axis directions using resonance, the power consumption required to drive the scanner 14 may be reduced.

[0031] like Figure 6As shown, the scanner 14 scans the plurality of laser beams Lr, Lg, and Lb emitted from the light source 11 using a Lissajous scanning method. By scanning the plurality of laser beams Lr, Lg, and Lb using a Lissajous scanning method, high-speed motion image projection with fewer afterimages can be performed on the user's retina. For example, sufficiently fast motion image projection can be performed even at a frame rate of approximately 60 Hz. Furthermore, by using a Lissajous scanning method to scan the plurality of laser beams Lr, Lg, and Lb, the power consumption of the MEMS mirror 141 can be reduced compared to scanning the plurality of laser beams Lr, Lg, and Lb using a raster scanning method.

[0032] The relationship between the scanner 14 and the image resolution is expressed by the following formula.

[0033] N = (θopt * D) / (1.1 * λ) (1) In formula (1), θopt is the optical swing angle of the laser beam emitted from the light source 11, such as... Figure 1 As shown (the same applies below). D is the diameter of the MEMS mirror 141 (the same applies below). λ is the wavelength of the laser beam (the same applies below). Therefore, by increasing θopt * D, an image with higher resolution can be projected onto the retina. For example, the resolution can be improved by increasing the resonant frequencies of the mutually orthogonal first and second single-axis directions and increasing θopt * D in formula (1). It is well known that the highest image quality, such as the image quality in the case of a bitmap display, can be obtained when the GCD (greatest common divisor) of the resonant frequencies in the mutually orthogonal first and second single-axis directions is close to 1.

[0034] The projection optics system 15 is an optical system that projects an image onto the user's retina by illuminating the plurality of laser beams Lr, Lg, and Lb scanned by the scanner 14. For example... Figure 1 As shown, the projection optical system 15 has a first reflector 151, a relay lens 152, and a second reflector 153.

[0035] The first mirror 151 is disposed on the emission side of the plurality of laser beams Lr, Lg, and Lb with respect to the scanner 14. The plurality of laser beams Lr, Lg, and Lb emitted from the scanner 14 are incident on the first mirror 151. The first mirror 151 reflects the plurality of laser beams Lr, Lg, and Lb that are incident. The first mirror 151 is rotated under the control of the optical system controller 17. With the rotation of the first mirror 151, the reflection direction of the plurality of laser beams Lr, Lg, and Lb changes. The optical system controller 17 controls the rotation of the first mirror 151 based on the line-of-sight direction of the user detected by the line-of-sight direction detector 16. Specifically, the optical system controller 17 controls the rotation of the first mirror 151 so that the plurality of laser beams Lr, Lg, and Lb reflected by the first mirror 151 are projected onto the user's retina in accordance with the line-of-sight direction of the user.

[0036] As shown in FIG. 1, the first mirror 151 is constituted by a tilt mirror module. Specifically, the first mirror 151 has a movable body 1541, a gimbal mechanism 1542, a magnetic drive mechanism 1543, a fixed body 1544, a Hall sensor 1545, and a tilt mirror module drive mechanism 1546. Figure 7

[0037] The movable body 1541 includes a tilt mirror 1541a. The movable body 1541 is supported by the fixed body 1544 via the gimbal mechanism 1542 so that the tilt mirror 1541a swings around a center of rotation RC.

[0038] The gimbal mechanism 1542 is constituted by, for example, a metal plate spring. The gimbal mechanism 1542 supports the movable body 1541 with respect to the fixed body 1544 so that the tilt mirror 1541a swings around the center of rotation RC. In the example shown in FIG. 1, the gimbal mechanism 1542 supports the movable body 1541 to the fixed body 1544 so that the tilt mirror 1541a rotates around rotation axes A3, A4. Figure 7

[0039] The magnetic drive mechanism 1543 generates a magnetic drive force between the movable body 1541 and the fixed body 1544. The magnetic drive force causes the movable body 1541 to displace with respect to the fixed body 1544. In the example shown in FIG. 1, the magnetic drive mechanism 1543 includes a coil 1543a and a magnet 1543b. The coil 1543a is disposed on the movable body 1541. The magnet 1543b is disposed on the fixed body 1544 opposite the coil 1543a. Figure 7

[0040] ​​​The fixing body 1544 is configured such that its angle can be changed around the rotation axes A3 and A4. The tilting mirror 1541a projects an image onto the user's retina by changing the angle of the fixing body 1544 around the plurality of rotation axes A3 and A4, based on the user's line of sight.

[0041] The Hall sensor 1545 outputs a detection signal in response to the tilt of the movable body 1541. The Hall sensor 1545 is positioned on the movable body 1541 near the magnet 1543b. Figure 7 In the example shown, the Hall sensor 1545 is disposed inside the coil 1543a. The detection signal output by the Hall sensor 1545 is input to the optical system controller 17. The optical system controller 17 detects the tilt of the movable body 1541 based on the input detection signal. The optical system controller 17 controls the magnetic drive mechanism 1543 to generate a magnetic driving force based on the detected tilt of the movable body 1541. This allows the angle of the tilt mirror 1541a to be quickly and accurately controlled.

[0042] The tilt mirror module drive mechanism 1546 is a drive mechanism that changes the angle of the tilt mirror 1541a based on the line of sight detected by the line of sight direction detector 16. For example, the tilt mirror module drive mechanism 1546 includes a magnetic circuit, a piezoelectric element, and a motor.

[0043] like Figure 1 As shown, the second reflector 153 is disposed on the reflecting side of the plurality of laser beams Lr, Lg, and Lb relative to the first reflector 151. The plurality of laser beams Lr, Lg, and Lb reflected from the first reflector 151 are incident on the second reflector 153 through a relay lens 152. The second reflector 153 reflects the incident plurality of laser beams Lr, Lg, and Lb to the user's retina. The second reflector 153 is, for example, a freeform mirror. The second reflector 153 can be a microstructured diffractive optical element or a holographic optical element.

[0044] The gaze direction detector 16 illuminates infrared light into the user's eyes. To reduce power consumption, the gaze direction detector 16 includes an infrared laser device, such as a vertical-cavity surface-emitting laser (VCSEL) or an infrared LED. The gaze direction detector 16 receives reflected infrared light from the user's eyes. Based on the amount of received reflected light, the gaze direction detector 16 outputs a detection signal for detecting the gaze direction to the optical system controller 17 and the digital image controller 18. The gaze direction detector 16 is, for example, an eye-tracking camera.

[0045] The optical system controller 17 controls the projection optical system 15 based on the line-of-sight direction detected by the line-of-sight direction detector 16. Specifically, as shown in FIG. 6, the optical system controller 17 rotates the first mirror 151 in accordance with a change in the line-of-sight direction detected by the line-of-sight direction detector 16. This enables the laser beams to be focused on the pupil and enables the image to continue to be projected onto the retina regardless of a change in the line-of-sight direction. This enables the user to continue to view the image even after moving the eyes. Figure 8 The optical system controller 17 can control the rotation of the first mirror 151 based on the detection results of the line-of-sight direction detector 16 and the angular velocity sensor (not shown). Specifically, when the angular velocity sensor detects the angular velocity (i.e., vibration) of the image projection apparatus 1, the optical system controller 17 can control the rotation of the first mirror 151 to cancel the detected angular velocity. Thereby, even if the image projection apparatus 1 vibrates, the image can continue to be projected onto the retina according to the line-of-sight direction of the user.

[0046] By projecting the laser beams onto the retina by tracking the line-of-sight direction of the user, the eyebox can be widened. Furthermore, since the flux of the laser beams is narrower than the pupil diameter of the observer, focus adjustment can be omitted. Furthermore, a high-resolution image can be projected, the color gamut of the image can be expanded, and color irregularities in the image can be almost eliminated.

[0047] By projecting the laser beams onto the retina by tracking the line-of-sight direction of the user, the eyebox can be widened. Furthermore, since the flux of the laser beams is narrower than the pupil diameter of the observer, focus adjustment can be omitted. Furthermore, a high-resolution image can be projected. Furthermore, by using RGB lasers, the color gamut of the image can be expanded. Furthermore, since the image is directly projected to the eyes of the user, color irregularities in the image can be almost eliminated.

[0048] The optical system controller 17 can control the rotation of the first mirror 151 based on the detection results of the line-of-sight direction detector 16 and the angular velocity sensor (not shown). Specifically, when the angular velocity sensor detects the angular velocity (i.e., vibration) of the image projection apparatus 1, the optical system controller 17 can control the rotation of the first mirror 151 to cancel the detected angular velocity. Thereby, even if the image projection apparatus 1 vibrates, the image can continue to be projected onto the retina according to the line-of-sight direction of the user.

[0049] The digital image controller 18 controls the light source 11 to emit the plurality of laser beams Lr, Lg, and Lb. Specifically, the digital image controller 18 acquires image data of an image to be projected onto the retina of the user from a memory or a host device. The digital image controller 18 drives the first, second, and third laser elements 111, 112, and 113 through the drive circuit 117 in accordance with pixel values indicated by the image data. As described above, the digital image controller 18 pulse-drives each laser element 111, 112, 113 with a pulse width W of 2.2 nanoseconds or less.

[0050] As described above, in the first embodiment, the projection optical system 15 irradiates the plurality of laser beams Lr, Lg, and Lb scanned by the scanner 14 onto the retina of the user to project an image onto the retina. In the first embodiment, the driving circuit 117 performs pulse driving of the first laser element 111, the second laser element 112, and the third laser element 113 at a pulse width of 2.2 nanoseconds or less. The first laser element 111 has an oscillation threshold current of 15 milliamperes or less and emits a laser beam Lr having a wavelength of from 610 nanometers to 680 nanometers. The second laser element 112 has an oscillation threshold current of 25 milliamperes or less and emits a laser beam Lg having a wavelength of from 500 nanometers to 530 nanometers. The third laser element 113 has an oscillation threshold current of 10 milliamperes or less and emits a laser beam Lb having a wavelength of from 430 nanometers to 470 nanometers.

[0051] Therefore, in the first embodiment, by performing pulse driving of the plurality of laser elements 111, 112, and 113 having good responsivity and sufficiently small oscillation threshold currents at a short pulse width, it is possible to make the pulse current value (i.e., peak current value) of the pulse driving sufficiently small and to reduce power consumption. Since it is possible to make the pulse current value sufficiently small, it is possible to reduce jitter and capacitive loss, etc. of the driving circuit 117.

[0052] This makes it possible to reduce power consumption while maintaining good image quality.

[0053] The plurality of laser elements 111, 112, and 113 having low oscillation threshold currents have low slope efficiency compared to the plurality of laser elements having high oscillation threshold currents. The plurality of laser elements having high slope efficiency can output a laser beam with high efficiency when the driving current is greater than the oscillation threshold current compared to the plurality of laser elements 111, 112, 113 having low slope efficiency. However, in the case of the retinal projection method, as described in the following first comparative example, it was found that the plurality of laser elements having high slope efficiency have high power consumption even when pulse driving is performed because the oscillation threshold current is large. Therefore, it was found that the laser elements 111, 112, and 113 having low slope efficiency and low oscillation threshold currents are more effective in reducing power consumption than the plurality of laser elements having high slope efficiency.

[0054] Since the image projection system 1 according to the first embodiment projects the plurality of laser beams Lr, Lg, and Lb onto the retina, it is possible to significantly reduce the light output required for the image projection compared to conventional image projection systems equipped with a light guide plate and a diffractive optical element. Since the light output can be significantly reduced, it is possible to project a high-quality image without jitter even with a small pulse current value.

[0055] Further, it is found that the light output of the plurality of laser elements 111, 112, and 113 in the first embodiment can be very low, and even if the slope efficiency is low, the power consumption is low when the oscillation threshold current is low. Therefore, it is not necessary to drive the plurality of laser elements 111, 112, and 113 with a drive current near the oscillation threshold current as with the plurality of laser elements having a large oscillation threshold current (i.e., a plurality of laser elements having a high slope efficiency) in order to reduce the power consumption. In other words, in the first embodiment, the plurality of laser elements 111, 112, and 113 can be driven with a drive current sufficiently larger than the oscillation threshold current while reducing the power consumption. This makes it possible to stabilize the light output because it is not easily affected by fluctuations in the oscillation threshold current due to temperature changes and other factors.

[0056] Next, an example showing the power consumption of the image projection system 1 according to the first embodiment will be described and compared with a comparative example.

[0057] [First Example] In the first example of the first embodiment, the plurality of laser elements 111, 112, and 113 having the current-light output characteristics shown in FIG. 1 were driven under four different driving conditions. Figure 3A to Figure 3C

[0058] The four driving conditions are one continuous driving (CW: continuous wave) and three pulse driving. Figure 9A The driving conditions of the first laser element 111 (R) are shown. Figure 9B The driving conditions of the second laser element 112 (G) are shown. Figure 9C The driving conditions of the third laser element 113 (B) are shown. As shown in Figure 9A to Figure 9C The specific parameters of the continuous driving and the pulse driving of each of the plurality of laser elements 111, 112, and 113 are different from each other.

[0059] In Figure 9A to Figure 9C , "LD power (mW)" is the light output of the plurality of laser elements 111, 112, and 113. "Iop" is the drive current of the plurality of laser elements 111, 112, and 113. "PC (CW: mW)" refers to the power consumption when continuously driven with a pulse width identical to that of one pixel, not the power consumption when driven with a shorter pulse width among the pulse widths of one pixel. The pulse width of one pixel is determined by the laser modulation speed (i.e., the modulation frequency) required to project one pixel. In Figure 9A to Figure 9C ​In the example shown in FIG. 6, the pulse width of one pixel is 11.2 ns. "Duty" is the duty obtained when the same light amount is obtained by driving with the shorter pulse within the pulse width of one pixel. "PC (pulse: mW)" is the power consumption when pulse driving is performed. "Power ratio (%) " is the percentage of the ratio of "PC (pulse: mW)" to "PC (CW: mW)". "Pulse width (ns)" is the pulse width set during pulse driving. "Pulse number" is the value obtained by dividing the pulse width required for one pixel by the above "pulse width (ns)", and is the maximum number of pulses per pixel. In order to minimize the power consumption of the plurality of laser elements 111, 112, and 113, it is preferable to output the peak LD power having the same average LD power as the LD power in CW using the set pulse width (ns) and pulse number of 1.

[0060] In the first example of the first embodiment, the power consumption corresponding to the driving conditions of the plurality of laser elements 111, 112, and 113 is calculated by simulation. Figure 9D The power consumption corresponding to the driving conditions of the plurality of laser elements (RGB) is shown. In Figure 9DIn the table, "TPC (100%)" is the total power consumption of the plurality of laser elements 111, 112, and 113 when the pixels are turned on at 100% and when the plurality of pixels are lit white. "TPC (30%)" is the total power consumption of the plurality of laser elements 111, 112, and 113 when the pixels are turned on at 30% of the normal video output. "DIC" is the power consumption required for the digital image controller 18 to perform image processing. "MEMS + ASIC" is the power consumption of the scanner 14, i.e., the MEMS mirror 141 and the ASIC. "Laser module" is the power consumption of the plurality of laser elements 111, 112, and 113 for emitting the plurality of laser beams Lr, Lg, and Lb. The "laser module" matches "TPC (30%)". "LDD" is the power consumption of the driving circuit 117 for controlling the pulse width, frequency, intensity, etc. of the driving signal for the plurality of laser elements 111, 112, and 113. "Pulse generation loss" is the power consumption that is additionally lost for generating a plurality of driving pulses. More specifically, the "pulse generation loss" refers to the power consumption loss generated due to wiring when a pulse current is applied to the plurality of laser elements 111, 112, and 113, and the power consumption loss generated due to transistors when the current is turned on / off. In other words, the "pulse generation loss" is the power consumption lost in the driving circuit 117 and the wiring, which is proportional to the power consumption (= TPC (30%)) applied to the plurality of laser elements 111, 112, and 113, and is independent of the power applied to the plurality of laser elements 111, 112, and 113. "Sum" is the total power consumption of "DIC", "MEMS + ASIC", "laser module", "LDD", and "pulse generation loss".

[0061] The meanings of the terms in the drawings of the first example of the first embodiment are the same in the subsequent examples and comparative examples.

[0062] According to the first example of the first embodiment, the power consumption "sum" can be reduced to 215 mW or less by pulse driving the plurality of laser elements 111, 112, and 113 having the low oscillation threshold current with a pulse width of 2.2 ns or less. The power consumption "sum" can be reduced to 205 mW or less by pulse driving the plurality of laser elements 111, 112, and 113 having the low oscillation threshold current with a pulse width of 1.1 ns. Further, during pulse driving with a pulse width of 1.1 ns, "TPC (30%)" can be reduced to 8.6 mW, which is lower than 10 mW. In particular, since the driving current (Iop) is small, pulse driving of 0.7 ns is feasible, "TPC (30%)" can be set to 6.4 mW, and the power consumption is 201 mW, which is close to the ideal value, and can be achieved.

[0063] According to the first example of the first embodiment, "TPC (30%) " can be reduced to 10 mW or less, which is 1 / 10 of the conventional technology. Thereby, the heat generation of the laser element itself can be eliminated, although the laser element (LD) as a small component generally generates heat locally, thereby causing problems such as the lifetime of the laser element, the output instability, and the local heat dissipation difficulty. Further, according to the first example of the first embodiment, the heat dissipation of the laser element is left to nature, and thus the problems of the reliability and the instability of the laser element are eliminated. This allows the AR glasses to have a fashionable structure.

[0064] In the first embodiment, in order to compare with the first, second, and third comparative examples described later, the device structure of the driving circuit 117 is designed so that "LDD" is 30 mW in all driving conditions, as in the first, second, and third comparative examples. As shown in the second embodiment below, if the logic part is composed of an ASIC, and the peak driving current of the laser is reduced, "LDD" can be reduced to 30 mW or less by optimizing the device structure of the driving circuit 117.

[0065] [Second Example] In the second example of the first embodiment, each of the plurality of laser elements 111, 112, and 113 is driven in the same four driving conditions as in the first example. The parameters of the four driving conditions are the same as in the first example. Figure 3A to Figure 3C

[0066] The first laser element 111 is driven according to the driving conditions shown in Figure 10A The second laser element 112 is driven according to the driving conditions shown in Figure 10B The third laser element 113 is driven according to the driving conditions shown in Figure 10C This results in the power consumption shown in Figure 10D

[0067] In the second embodiment, since the device structure of the driving circuit 117 is optimally designed, the pulse driving current is reduced, and the capacitance loss is reduced, and the like, and thus it is possible to reduce the value of "LDD" compared to the first embodiment. In the optimally designed driving circuit 117, "LDD" can be reduced to about three times "pulse generation loss". As shown in Figure 10D

[0068] As shown in Figure 10D ​​​As shown, in the second example according to the first embodiment, by pulse-driving the plurality of laser elements 111, 112, and 113 with a pulse width of 1.1 nanoseconds or less and a lower oscillation threshold current, the total power consumption can be further reduced than in the first example. Specifically, when pulse-driving with a pulse width of 1.1 nanoseconds is performed, the total power consumption can be reduced to 192 milliwatts or less, which is lower than the ideal value of 200 milliwatts.

[0069] [First Comparative Example] like Figure 11A As shown, in the first comparative example, the same as... Figure 3A The first laser element 111 shown has a larger oscillation threshold current and a higher slope efficiency compared to a red laser element. For example... Figure 11B As shown, in the first comparative example, the same as... Figure 3B The second laser element 112 shown has a larger oscillation threshold current and a higher slope efficiency compared to the green laser element. For example... Figure 11C As shown, in the first comparative example, the blue laser element used has a higher performance than... Figure 3C The third laser element 113 shown has a larger oscillation threshold current and a higher slope efficiency. In the first comparative example, a light guide plate with diffractive optical elements was used instead of the retinal projection method. The efficiency of the light guide plate is poor, thus requiring a large laser power. The red laser element is based on... Figure 12A The green laser element is driven according to the indicated driving conditions. Figure 12B The blue laser element is driven according to the indicated driving conditions. Figure 12C The driving conditions shown are used for driving. This leads to... Figure 12D The power consumption is shown.

[0070] from Figure 12D As can be seen, in the first comparative example, because a retinal projection method that can reduce the required light output was not employed, and the oscillation threshold current of the laser element was relatively large, even with pulse driving at a pulse width of 2.2 nanoseconds or less, the power consumption could not be sufficiently reduced. Specifically, even with pulse driving at a pulse width of 2.2 nanoseconds, the "TPC(30%)" was 53 milliwatts, and the "total" was 280 milliwatts.

[0071] [Second Comparative Example] In the second comparative example, the following was used Figure 3A to Figure 3C The laser elements 111, 112, and 113 are shown, along with a light guide plate having diffractive optical elements. The first laser element 111 is based on... Figure 13A The second laser element 112 is driven according to the driving conditions shown. Figure 13B The third laser element 113 is driven according to the driving conditions shown.Figure 13C The driving conditions shown are used for driving. This leads to... Figure 13D The power consumption is shown.

[0072] from Figure 13D As can be seen, in the second comparative example, since the retinal projection method was not used, even with a pulse drive of 2.2 nanoseconds for the laser element with a small oscillation threshold current, the power consumption could not be sufficiently reduced. Specifically, even with a pulse drive of 2.2 nanoseconds, the "TPC (30%)" was 67 milliwatts, and the "total" could only be reduced to 304 milliwatts. Therefore, it was found that the power consumption and total power consumption of the laser element in the second comparative example were greater than those using the laser element with high slope efficiency. Furthermore, the study found that due to the increased drive current values ​​of the green and blue lasers, if the pulse drive pulse width was shorter than 2.2 nanoseconds, the effect of jitter would increase, image quality would easily degrade, and such a laser with a small oscillation threshold current would be impractical in the case of a light guide plate with diffractive optical elements.

[0073] [Third Comparative Example] In the third comparative example, using Figure 11A The red laser element shown Figure 11B The green laser element shown Figure 11C The blue laser element and the retinal projection system shown.

[0074] The red laser element is based on Figure 14A The green laser element is driven according to the indicated driving conditions. Figure 14B The blue laser element is driven according to the indicated driving conditions. Figure 14C The driving conditions shown are used for driving. This leads to... Figure 14D The power consumption is shown.

[0075] from Figure 14D As can be seen, in the third comparative example, due to the large oscillation threshold current of the laser element, even with pulse driving of a pulse width of 2.2 nanoseconds using the retinal projection method, the power consumption cannot be sufficiently reduced. Specifically, even with pulse driving of a 2.2 nanosecond pulse width, the "TPC (30%)" is still 14 milliwatts, and the "total" can only be reduced to 214 milliwatts. That is to say, when operating low-power laser elements such as retinal projection, due to the large oscillation threshold current, the driving current value increases, and the "TPC (30%)" can only be reduced to 14 milliwatts. Therefore, even with optimal design of the driving circuit 117 (LDD), the total power consumption cannot be reduced.

[0076] According to the example of the above-described first embodiment, it is apparent that, in the case of retinal projection, the power consumption can be effectively reduced by pulse driving the plurality of laser elements 111, 112, and 113 with a short pulse width and a low oscillation threshold current.

[0077] Various modifications as shown below can be applied to the image projection apparatus 1 according to the first embodiment.

[0078] [First Modification Example] In the above-described embodiment, an example in which the plurality of laser elements 111, 112, and 113 are single-beam elements is described.

[0079] In contrast, as shown in Figure 15 In the first modification example, each of the plurality of laser elements 111, 112, and 113 is arranged adjacent to each other.

[0080] Thereby, the plurality of first laser elements 111 emit multi-beams having a wavelength of from 610 nm to 680 nm. The plurality of second laser elements 112 emit multi-beams having a wavelength of from 500 nm to 530 nm. The plurality of third laser elements 113 emit multi-beams having a wavelength of from 430 nm to 470 nm.

[0081] According to the first modification example, by using multi-beams, it is possible to simultaneously display multi-beams, and thus the resonance frequency of the MEMS can be reduced. By reducing the resonance frequency in the first uniaxial direction and the second uniaxial direction that are orthogonal to each other, it is possible to increase θopt * D in Equation (1) so as not to reach the physical limit at which the MEMS mirror 141 is damaged. Since it is possible to increase θopt * D, it is possible to improve the resolution of the image. For example, by increasing the number of beams in the multi-beams, it is possible to further reduce the resonance frequency according to the number of beams and increase θopt * D by a corresponding amount, and thus it is possible to project a plurality of images onto the user's retina at a resolution higher than FHD (Full High Definition), i.e., FHD, 2K, 4K, and 8K resolution.

[0082] Further, since it is possible to increase θopt * D, it is possible to project an image having good visibility onto the user's retina at a higher FOV (field of view), for example, 60°.

[0083] [Second Modification Example] As shown in Figure 16 In the second modification example, the MEMS mirror 141 and the ASIC are vacuum-sealed by a seal 143 arranged above the MEMS mirror 141 and the ASIC.

[0084] According to the second modification, by vacuum sealing the MEMS mirror 141, the power consumption can be further reduced. For example, the power consumption of the MEMS mirror 141 and the ASIC can be reduced to below 10 milliwatts.

[0085] [Third Amendment Example] like Figure 17 As shown, the light source unit 11 may include a collimating lens 118 disposed on the emission side of the plurality of laser elements 111, 112, and 113, and a multiplexing optical system 119 disposed on the emission side of the collimating lens 118. The collimating lens 118 collimates and emits the laser beams Lr, Lg, and Lb emitted from the plurality of laser elements 111, 112, and 113. The multiplexing optical system 119 multiplexes the plurality of laser beams Lr, Lg, and Lb emitted from the collimating lens 118, and reflects them to the scanner 14 side. The collimating lens 118 may be a meta-lens bonded to the plurality of laser elements 111, 112, and 113. The multiplexing optical system 119 may be a dichroic mirror.

[0086] According to the third modification, by including the multiplexing optical system 119, the misalignment of the optical axes of the plurality of laser beams Lr, Lg and Lb can be reduced, thereby enabling the projection of high-quality images with less color shift and image flow.

[0087] [Second Embodiment] Next, the image projection device 1 according to the second embodiment will be described in detail, focusing on its differences from the embodiments described above. Figure 17 An example is shown where the light source 11 uses a dichroic mirror 119 to multiplex the plurality of laser beams Lr, Lg, and Lb. In contrast, in the second embodiment, the light source 11 utilizes a waveguide-type optical multiplexer 134 to multiplex the plurality of laser beams Lr, Lg, and Lb, as shown... Figure 18 As shown.

[0088] like Figure 18 As shown, the waveguide-type optical multiplexer 134 includes multiple waveguides 1341 to 1343 and a transmission outlet 1344.

[0089] The plurality of waveguides 1341 to 1343 respectively propagate the plurality of laser beams Lr, Lg, and Lb emitted from the first laser element 111, the second laser element 112, and the third laser element 113, and multiplex the plurality of laser beams Lr, Lg, and Lb in the multiplexing region 1345. The emission outlet 1344 emits the plurality of laser beams Lr, Lg, and Lb multiplexed in the multiplexing region 1345 to the scanner 14.

[0090] In the second embodiment, the same as the first embodiment, the retinal projection method is employed, and the first laser element 111 having an oscillation threshold current of 30 mA or less, the second laser element 112 having an oscillation threshold current of 35 mA or less, and the third laser element 113 having an oscillation threshold current of 15 mA or less are respectively driven with a pulse width of 2.2 ns or less.

[0091] Therefore, the same as the first embodiment, the power consumption can be reduced while maintaining good image quality.

[0092] Although the waveguide-type light multiplexer 134 can have a low light coupling rate (for example, 20%), by performing pulse driving with a short pulse width, the light output of the image projection system 1 can be stabilized.

[0093] In addition, by performing pulse driving with a short pulse width, the variation in the light coupling ratio of the waveguide-type light multiplexer 134 due to heat generation can be reduced. Therefore, it is not necessary to cool the waveguide-type light multiplexer 134 with a Peltier element or the like, and thus the number of components can be reduced.

[0094] Furthermore, since the waveguide-type light synthesis unit 134 can reduce the misalignment of the optical axes of the plurality of laser beams Lr, Lg, and Lb, a high-quality image with less color deviation and image flow can be projected.

[0095] In the present embodiment, the laser shows an example of an end-face emitting laser, but a vertical resonant surface emitting laser described later can also be used, and when a vertical resonant surface emitting laser is used, the power consumption can be further reduced.

[0096] [Example] Next, an example of the power consumption of the image projection system 1 according to the second embodiment will be described. In the example of the second embodiment, the plurality of laser elements 111, 112, and 113 having the current and light output characteristics shown in FIG. 6 are respectively driven with the same four driving conditions as in the first example of the first embodiment. Figure 3A to Figure 3C The first laser element 111 is driven according to the driving conditions shown in FIG. 7. The second laser element 112 is driven according to the driving conditions shown in FIG. 8. The third laser element 113 is driven according to the driving conditions shown in FIG. 9. This results in the power consumption shown in FIG. 10. Figure 19A The first laser element 111 is driven according to the driving conditions shown in FIG. 7. The second laser element 112 is driven according to the driving conditions shown in FIG. 8. The third laser element 113 is driven according to the driving conditions shown in FIG. 9. This results in the power consumption shown in FIG. 10. Figure 19B The first laser element 111 is driven according to the driving conditions shown in FIG. 7. The second laser element 112 is driven according to the driving conditions shown in FIG. 8. The third laser element 113 is driven according to the driving conditions shown in FIG. 9. This results in the power consumption shown in FIG. 10. Figure 19C The first laser element 111 is driven according to the driving conditions shown in FIG. 7. The second laser element 112 is driven according to the driving conditions shown in FIG. 8. The third laser element 113 is driven according to the driving conditions shown in FIG. 9. This results in the power consumption shown in FIG. 10. Figure 19D The first laser element 111 is driven according to the driving conditions shown in FIG. 7. The second laser element 112 is driven according to the driving conditions shown in FIG. 8. The third laser element 113 is driven according to the driving conditions shown in FIG. 9. This results in the power consumption shown in FIG. 10.

[0097] As shown in FIG. 10, the power consumption of the image projection system 1 according to the second embodiment is lower than that of the image projection system 1 according to the first embodiment. Figure 19DAs shown, according to the example of the second embodiment, by pulse driving the plurality of laser elements 111, 112, and 113 with a pulse width of 1.1 nanoseconds or less and a lower oscillation threshold current, the "sum" can be reduced to 192 milliwatts or less. When pulse driving with a pulse width of 1.1 nanoseconds, the "TPC (30%)" can be reduced to 8.6 milliwatts.

[0098] According to the example of the second embodiment, it is clear that even if the waveguide-type light multiplexer 134 is used, the power consumption can be effectively reduced by pulse driving the plurality of laser elements 111, 112, and 113 with a low oscillation threshold current and a short pulse width.

[0099] [Modification Example] Next, a modification example of the image projection system 1 according to the second embodiment will be described. Figure 18 An example is shown in which the light source 11 includes one waveguide-type light multiplexer 134. In contrast to this, as shown in FIG. 14, the light source 11 of the modification example of the second embodiment has two waveguide-type light multiplexers 134a, 134b. Figure 20 As shown, the light source 11 of the modification example of the second embodiment has two waveguide-type light multiplexers 134a, 134b.

[0100] That is, the light source 11 in the modification example of the second embodiment includes the first laser element 111a, the second laser element 112a, the third laser element 113a, and the waveguide-type light multiplexer 134a in the first group. The light source 11 also includes the first laser element 111b, the second laser element 112b, the third laser element 113b, and the waveguide-type light multiplexer 134b in the second group.

[0101] The waveguide-type light multiplexer 134a of the first group multiplexes the plurality of laser beams Lr, Lg, and Lb emitted from each of the first laser element 111a, the second laser element 112a, and the third laser element 113a of the first group and multiplexes in the multiplexing region 1345a of the plurality of waveguides 1341a to 1343a, and then emits from the emission exit 1344a.

[0102] The waveguide-type light multiplexer 134b of the second group multiplexes the plurality of laser beams Lr, Lg, and Lb emitted from each of the first laser element 111b, the second laser element 112b, and the third laser element 113b of the second group and multiplexes in the multiplexing region 1345b of the plurality of waveguides 1341b to 1343b, and then emits from the emission exit 1344b.

[0103] The emission exit 1344a of the waveguide-type optical multiplexer 134a of the first group and the emission exit 1344b of the waveguide-type optical multiplexer 134b of the second group are arranged at a predetermined angle with respect to the first uniaxial direction and the second uniaxial direction of the MEMS mirror 141.

[0104] That is, in the modified example of the second embodiment, the light source 11 emits a multi-beam from the two emission exits 1344a and 1344b. By emitting a multi-beam, the resonance frequency of the MEMS mirror 141 can be reduced, and thus θopt*D in the above equation (1) can be increased, and thus the resolution can be improved.

[0105] The distance between the plurality of emission exits 1344a and 1344b is preferably less than 20 micrometers (pm), more preferably less than 10 pm, and even more preferably less than 5 pm. Since the waveguide-type coupler does not have thermal interference, the pitch between the emission exits 1344a and 1344b can be reduced. By reducing the pitch between the plurality of emission exits 1344a and 1344b, the light source 11 can emit a high-resolution multi-beam with a small beam pitch.

[0106] In order to reduce the distance between the emission exits 1344a and 1344b, the plurality of waveguides 1341a to 1343a, 1341b to 1343b of the plurality of waveguide-type optical multiplexers 134a, 134b can have a steeper curve than the configuration in Figure 18 Since the image projection system 1 according to the second embodiment employs the retinal projection method, the output of the plurality of laser beams Lr, Lg, and Lb can be small, similarly to the first embodiment. Therefore, even if the plurality of laser beams Lr, Lg, and Lb are lost due to the steep curve of the plurality of waveguides 1341a to 1343a, 1341b to 1343b, an image with good visibility can be projected onto the user's retina. Even if kinks occur in the plurality of laser elements 111, 112, and 113 on the low current side, by driving the plurality of laser elements 111, 112, and 113 at a high current, and causing the plurality of laser beams Lr, Lg, and Lb in the plurality of waveguides 1341a to 1343a and 1341b to 1343b to be lost, the kinks can be avoided, and the plurality of laser beams Lr, Lg, and Lb with appropriate output power can be projected onto the retina.

[0107] [Third Embodiment] Next, the image projection device 1 according to the third embodiment will be described, focusing on the differences from the above-described embodiments. In the above-described embodiments, the example in which the plurality of laser elements 111, 112, and 113 are end-face emitting lasers is described. In contrast, in the third embodiment, the plurality of laser elements 111, 112, and 113 are vertical cavity surface emitting lasers (VCSELs) that emit the plurality of laser beams Lr, Lg, and Lb in a direction perpendicular to a semiconductor substrate (not shown) included in each of the plurality of laser elements 111, 112, and 113. Figure 21 The emission direction of the plurality of laser beams Lr, Lg, and Lb shown is perpendicular to the semiconductor substrate (not shown) included in each of the plurality of laser elements 111, 112, and 113.

[0108] For example, the vertical cavity surface emitting lasers are described in two references: “Kenichi Terao et al (2021). PROCEEDINGS OF THE INTERNATIONAL DISPLAY WORKSHOPS, VOL. 28” and “Tatsushi Hamaguchi et al (2018). Lateral optical confinement of GaN-based VCSEL using an atomically smooth monolithic curved mirror. Scientific Reports”. That is, the semiconductor substrate in each of the laser elements 111, 112, and 113 can be provided between a first high-reflection distributed Bragg reflector (DBR) and a second high-reflection distributed Bragg reflector, with a gain layer therebetween. Alternatively, the semiconductor substrate can be provided outside the first high-reflection distributed Bragg reflector or the second high-reflection distributed Bragg reflector.

[0109] The vertical cavity surface emitting lasers provided with the high-reflection distributed Bragg reflector can effectively expand the color gamut because the desired wavelength can be selected and there is no wavelength variation. Furthermore, the desired oscillation threshold current can be set by adjusting the material composition, reflectivity, and shape of the high-reflection distributed Bragg reflector.

[0110] In the third embodiment, the first laser element 111 has current versus light output (OP) and current versus voltage (V) characteristics as shown in Figure 22A The second laser element 112 has current versus light output (OP) and current versus voltage (V) characteristics as shown in Figure 22B The third laser element 113 has current versus light output and current versus voltage characteristics as shown in Figure 22C

[0111] ​The oscillation threshold current of the first laser element 111 is 1 milliampere or less. The oscillation threshold current of the second laser element 112 is 3 milliampere or less. The oscillation threshold current of the third laser element 113 is 1 milliampere or less. Thus, the oscillation threshold current is significantly reduced compared to an edge emitting laser.

[0112] As shown in Figure 21 Each of the plurality of laser elements 111, 112, and 113 is provided on a plurality of semiconductor chips 114 corresponding to each of the plurality of laser elements 111, 112, and 113, respectively. The plurality of semiconductor chips 114 is provided on the drive circuit 117. By providing each semiconductor chip 114 corresponding to each of the plurality of laser elements 111, 112, and 113 on the drive circuit 117, the wiring of the drive circuit 117 can be shortened. As a result, high frequency characteristics and high gray scale characteristics can be achieved.

[0113] According to the third embodiment, by using the vertical cavity surface emitting laser in which the oscillation threshold current is much lower than that of an edge emitting laser, the power consumption can be significantly reduced.

[0114] Furthermore, since the capacitance loss depending on the drive current can be reduced, the power consumption can be further reduced.

[0115] Since, in the retinal projection system, the plurality of laser elements 111, 112, and 113 can be driven with a low oscillation threshold current, and the required light output is low, the peak current of the drive pulse can be reduced. Since the peak current can be reduced, the pulse driving can be performed with a pulse width of 1 nanosecond or less while reducing the jitter. This further reduces the power consumption.

[0116] Next, an example of the power consumption of the image projection apparatus 1 of the third embodiment will be described.

[0117] [First Example] In the first example of the third embodiment, similarly to the first example of the first embodiment, each of the plurality of laser elements 111, 112, and 113 having the current-light output characteristics shown in Figure 22A to Figure 22C is driven under four different drive conditions. Specifically, the first laser element 111 is driven according to the drive condition shown in Figure 23A . The second laser element 112 is driven according to the drive condition shown in Figure 23B . The third laser element 113 is driven according to the drive condition shown in Figure 23C . This results in the power consumption shown in Figure 23D .

[0118] AsFigure 23D As shown, according to the first example of the third embodiment, by pulse-driving laser elements 111, 112, and 113 with a pulse width of 1.1 nanoseconds or less and a lower oscillation threshold current, the "total" can be reduced to 194 milliwatts. Furthermore, compared to an end-emitting laser, the "TPC (30%)" can be reduced. Specifically, when pulse-driving with a pulse width of 1.1 nanoseconds is performed, the "TPC (30%)" can be reduced to 2 milliwatts.

[0119] In the first embodiment, for comparison with the first, second, and third comparative examples described above, the device structure of the drive circuit 117 is designed such that, as in the first, second, and third comparative examples, the "LDD" is 30 milliwatts under all driving conditions. As shown in the second embodiment below, by optimizing the device structure of the drive circuit 117, the "LDD" can be reduced to below 30 milliwatts.

[0120] [Second Example] In the second example of the third embodiment, using the same four driving conditions as the first example of the first embodiment of the third embodiment, for having Figure 22A to Figure 22C The plurality of laser elements 111, 112, and 113, which exhibit the shown current and optical output characteristics, are driven. The parameters of the four driving conditions are the same as those in the first example of the third embodiment. Specifically, the first laser element 111 is driven according to... Figure 24A The second laser element 112 is driven according to the driving conditions shown. Figure 24B The third laser element 113 is driven according to the driving conditions shown. Figure 24C The driving conditions shown are applied. This leads to... Figure 24D The power consumption is shown. In the second embodiment, the device structure of the drive circuit 117 is optimized so that the value of "LDD" is less than that in the first embodiment. In the optimized drive circuit 117, "LDD" can be reduced to about three times the "pulse generation loss".

[0121] from Figure 24D As can be seen from the second example of the third embodiment, by pulse-driving the plurality of laser elements 111, 112, and 113 with low oscillation threshold currents at a pulse width of 1.1 nanoseconds or less, the total power can be reduced to 169 milliwatts or less. Therefore, most of the power consumption is in the "DIC" and "MEMS+ASIC". Furthermore, since the "LDD" can be reduced to 5 milliwatts during pulse-driving with a pulse width of 1.1 nanoseconds, the "TPC (30%)" can be reduced to 2 milliwatts.

[0122] [Third Example] In the third example of the third embodiment, it hasFigure 22A The first laser element 111 having the current-light output characteristic shown in FIG. 2 is driven according to the driving condition shown in FIG. 3. This results in the power consumption shown in FIG. 4. Figure 25A The second laser element 112 having the current-light output characteristic shown in FIG. 5 is driven according to the driving condition shown in FIG. 6. This results in the power consumption shown in FIG. 7. Figure 22B The second laser element 112 having the current-light output characteristic shown in FIG. 5 is driven according to the driving condition shown in FIG. 6. This results in the power consumption shown in FIG. 7. Figure 25B The third laser element 113 having the current-light output characteristic shown in FIG. 8 is driven according to the driving condition shown in FIG. 9. This results in the power consumption shown in FIG. 10. Figure 22C The third laser element 113 having the current-light output characteristic shown in FIG. 8 is driven according to the driving condition shown in FIG. 9. This results in the power consumption shown in FIG. 10. Figure 25C The third laser element 113 having the current-light output characteristic shown in FIG. 8 is driven according to the driving condition shown in FIG. 9. This results in the power consumption shown in FIG. 10. Figure 25D The third laser element 113 having the current-light output characteristic shown in FIG. 8 is driven according to the driving condition shown in FIG. 9. This results in the power consumption shown in FIG. 10.

[0123] As can be seen from FIG. 11, during the pulse driving with a pulse width of 0.7 nanoseconds, “TPC (30%)” can be reduced to 1 milliwatt or less. In this way, by driving the low-threshold-current laser elements with short pulses in the retinal projection method, the power consumption of the laser elements can be reduced to a negligible level, i.e., 1 / 100 of the conventional technology. Therefore, for example, by vacuum-sealing the MEMS mirror 141 (see FIG. 12) and improving the efficiency of the piezoelectric film, the “MEMS + ASIC” can be reduced to 10 milliwatts. Figure 25D As can be seen from FIG. 11, during the pulse driving with a pulse width of 0.7 nanoseconds, “TPC (30%)” can be reduced to 1 milliwatt or less. In this way, by driving the low-threshold-current laser elements with short pulses in the retinal projection method, the power consumption of the laser elements can be reduced to a negligible level, i.e., 1 / 100 of the conventional technology. Therefore, for example, by vacuum-sealing the MEMS mirror 141 (see FIG. 12) and improving the efficiency of the piezoelectric film, the “MEMS + ASIC” can be reduced to 10 milliwatts. Figure 16 As can be seen from FIG. 11, during the pulse driving with a pulse width of 0.7 nanoseconds, “TPC (30%)” can be reduced to 1 milliwatt or less. In this way, by driving the low-threshold-current laser elements with short pulses in the retinal projection method, the power consumption of the laser elements can be reduced to a negligible level, i.e., 1 / 100 of the conventional technology. Therefore, for example, by vacuum-sealing the MEMS mirror 141 (see FIG. 12) and improving the efficiency of the piezoelectric film, the “MEMS + ASIC” can be reduced to 10 milliwatts.

[0124] According to the third example of the third embodiment, when 10 milliwatts is used as the “MEMS + ASIC”, by pulse driving the plurality of laser elements 111, 112, and 113 having low oscillation threshold currents with a pulse width of 1.1 nanoseconds or less, “TPC (30%)” can be set to a very small value of 1.0 milliwatt. In addition, “Total” can be reduced to 94 milliwatts or less. In this way, by using a VCSEL with a lower oscillation threshold and using the vacuum-sealed MEMS mirror 141, the dominant factor of the power consumption can be made to be only “DIC”, and thus the power consumption can be greatly reduced. If the ASIC constituting the digital circuit of the digital image controller is redesigned using, for example, a fine semiconductor design rule of 20 nanometers, in the future, “DIC” can be reduced to 20 milliwatts or less, and “Total” can be reduced to 34 milliwatts.

[0125] [Fourth Example] As shown in FIG. 13, in the fourth example of the third embodiment, the light source 11 includes each of the plurality of laser elements 111, 112, and 113 having the current-light output characteristic shown in FIG. 2. In other words, in the fourth example of the third embodiment, the light source 11 emits an RGB multi-beam. Figure 26 As shown in FIG. 13, in the fourth example of the third embodiment, the light source 11 includes each of the plurality of laser elements 111, 112, and 113 having the current-light output characteristic shown in FIG. 2. In other words, in the fourth example of the third embodiment, the light source 11 emits an RGB multi-beam. Figure 22A to Figure 22C As shown in FIG. 13, in the fourth example of the third embodiment, the light source 11 includes each of the plurality of laser elements 111, 112, and 113 having the current-light output characteristic shown in FIG. 2. In other words, in the fourth example of the third embodiment, the light source 11 emits an RGB multi-beam.

[0126] In the fourth example of the third embodiment, two first laser elements 111 having the current-light output characteristic shown in FIG. 2 are provided according to the driving condition shown in FIG. 3. In addition, two second laser elements 112 having the current-light output characteristic shown in FIG. 5 are provided according to the driving condition shown in FIG. 6. Furthermore, two third laser elements 113 having the current-light output characteristic shown in FIG. 8 are provided according to the driving condition shown in FIG. 9. This results in the power consumption shown in FIG. 10. Figure 22A In the fourth example of the third embodiment, two first laser elements 111 having the current-light output characteristic shown in FIG. 2 are provided according to the driving condition shown in FIG. 3. In addition, two second laser elements 112 having the current-light output characteristic shown in FIG. 5 are provided according to the driving condition shown in FIG. 6. Furthermore, two third laser elements 113 having the current-light output characteristic shown in FIG. 8 are provided according to the driving condition shown in FIG. 9. This results in the power consumption shown in FIG. 10.Figure 27A driven under the driving conditions shown. This results in Figure 22B The two second laser elements 112 have current-light output characteristics as shown. The two second laser elements 112 are driven under the driving conditions shown. This results in Figure 27B driven under the driving conditions shown. This results in Figure 22C The two third laser elements 113 have current-light output characteristics as shown. The two third laser elements 113 are driven under the driving conditions shown. This results in Figure 27C driven under the driving conditions shown. This results in Figure 27D the power consumption shown.

[0127] From Figure 27D As can be seen, according to the fourth example of the third embodiment, the power consumption of "MEMS + ASIC" is 10 mW by using the vacuum-sealed MEMS mirror 141 and ASIC. In this case, by using the multi-beam of the vertical cavity surface emitting laser, a higher resolution such as FHD / 2K or the like as described above can be achieved. For example, by driving the laser elements 111, 112, and 113 having a low oscillation threshold current with a pulse having a pulse width of 1.1 ns or less, the "total" can be greatly reduced to 93 mW or less. At this time, the dominant factor of the power consumption is only "DIC". Further, "TPC (30%)" can be set to a very small value, for example, 0.61 mW. In this way, by using the VCSEL having a low oscillation threshold and the vacuum-sealed MEMS mirror 141, the dominant factor of the power consumption can be reduced to "DIC" itself, thereby achieving a great reduction in power consumption. Further, by using the VCSEL that is easy to emit a multi-beam, the resolution can be improved while maintaining low power consumption.

[0128] [Fifth Example] As Figure 28 shown, the fifth example of the third embodiment includes a plurality of driving conditions in which the digital image controller 18 projects, to each pixel, two pulses (i.e., multi-pulse) of a pulse current having a pulse width of 0.55 ns to each of the plurality of laser elements 111, 112, and 113. Note that, Figure 28 "0.5 mW" in the "total" is the light output of the second laser element 112 (G).

[0129] In the fifth example of the third embodiment, the first laser element 111 having the current-light output characteristics shown is driven under the driving conditions shown. Further, the second laser element 112 having the current-light output characteristics shown is driven under the driving conditions shown. Further, the third laser element 113 having the current-light output characteristics shown is driven under the driving conditions shown. Figure 22A Figure 29A Figure 22B Figure 29B Figure 22C Figure 29C ​​​​​The driving conditions shown were driven. This resulted in Figure 29D The power consumption shown.

[0130] In Figure 29A to Figure 29C , the driving condition of a pulse width of 1.1 nanoseconds corresponds to a driving condition in which two pulse currents of a pulse width of 0.55 nanoseconds are applied. Figure 28 The driving conditions shown correspond to Figure 29B the driving condition of a pulse width of 1.1 nanoseconds.

[0131] According to the fifth example of the third embodiment, the gray scale can be increased by projecting one pixel by using two driving pulses. For example, 16-bit gray scale can be realized. By projecting one pixel by using three or more driving pulses, the gray scale can be further increased.

[0132] In addition, from Figure 29D it can be seen that, according to the fifth example of the third embodiment, "TPC (30%)" can be reduced to a surprising low power consumption of 1.0 milliwatt. In addition, as described above, if the digital image controller is composed of an ASIC, "DIC" can be reduced to 20 milliwatts, and by using a vacuum-sealed MEMS mirror 141 and an ASIC, "MEMS + ASIC" can be reduced to 10 milliwatts. That is, the total power consumption of "DIC" and "MEMS + ASIC" can be as low as 30 milliwatts. Therefore, "Total" can be 34 milliwatts or less.

[0133] As described above, according to the fifth example of the third embodiment, by driving the laser element with a low threshold current pulse, the power consumption of the laser element and "LDD" can be greatly reduced. Therefore, even if "DIC" and "MEMS + ASIC" can be reduced, "DIC" and "MEMS + ASIC" remain dominant factors of the power consumption.

[0134] That is, in the fifth example of the third embodiment, the power consumption of the laser element can be surprisingly reduced, so that "DIC" and "MEMS + ASIC" become dominant factors.

[0135] As described above, according to the examples of the third embodiment, by pulse driving a vertical cavity surface emitting laser having a low oscillation threshold current with a short pulse width, it can be confirmed that the power consumption can be effectively reduced compared to the case of an edge emitting laser, and a higher gray scale can be realized.

[0136] [MODIFICATION EXAMPLE] Next, a modification example of the image projection apparatus 1 of the third embodiment will be described.

[0137] In Figure 30In the illustrated example, the light source 11 includes four first laser elements 111a to 111d. The four first laser elements 111a to 111d are adjacently staggered. Even if the first laser elements 111a to 111d are distributed around the plurality of emission portions E, this arrangement can make the distance P between the centers of the plurality of emission portions E of the first laser elements 111a to 111d as small as possible. The staggered arrangement of the plurality of first laser elements 111a to 111d can also create an arbitrary pitch P. Therefore, by densely arranging a large number of the plurality of first laser elements 111a to 111d, the light source 11 can be further miniaturized.

[0138] Further, the resonance frequency of the MEMS mirror 141 can be reduced, and θopt * D in Equation (1) can be further increased so as not to reach the physical limit of damage of the MEMS mirror 141. Since θopt * D can be made larger, the image resolution and the FOV can be further improved. For example, by increasing the number of beams in the multi-beam, the resonance frequency can be further reduced according to the number of beams, and θopt * D can be increased by a corresponding amount, so that an image is projected onto the user's retina at a resolution higher than FHD, i.e., FHD, 2K, 4K, and 8K resolution. Further, since θopt * D can be increased, an image with good visibility can be projected onto the user's retina with a high FOV of, for example, 60°.

[0139] The number of the plurality of laser elements is not limited to four, i.e., the number of the plurality of laser elements is arbitrary, and can consist of two or three, or five or more. Specifically, the plurality of first laser elements 111, the plurality of second laser elements 112, and the plurality of third laser elements 113 can be six laser elements staggered as illustrated in Figure 31 According to Figure 31 In the illustrated example, compared with Figure 30 the distance between the centers of the plurality of emission portions E can be further shortened, so the light source 11 can be further miniaturized, and the resolution can be improved.

[0140] In the description of the embodiments of the present disclosure, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise" and "counterclockwise" and the like should be interpreted to refer to the orientation or position as shown or indicated in the drawings under discussion. These relative terms are used only to simplify the description of the present disclosure and do not indicate or imply that the referred device or element must have a particular direction, or be constructed or operated in a particular direction. Therefore, these terms cannot be interpreted as limiting the present disclosure.

[0141] In addition, the terms "first", "second" and the like used herein are only for descriptive purposes and are not intended to indicate or imply relative importance or significance or imply the number of technical features indicated. Therefore, the features defined as "first" and "second" can contain one or more such features. In the description of the present disclosure, the meaning of "multiple" is two or more, unless otherwise specified.

[0142] In the description of the embodiments of the present disclosure, unless otherwise specified or limited, the terms "mounting", "connecting", "coupling" and the like are used in a broad sense, for example, can be fixed connection, detachable connection or integral connection; can be mechanical connection or electrical connection; can be direct connection or indirect connection through intermediate structure; can also be internal communication of two elements, which can be understood by those skilled in the art according to the specific circumstances.

[0143] In the embodiments of the present disclosure, unless otherwise specified or limited, the structure in which the first feature is "on" or "under" the second feature can include the embodiment in which the first feature is in direct contact with the second feature, and can also include the embodiment in which the first feature is not in direct contact with the second feature, but is in contact through additional features formed therebetween. In addition, the "upper", "above" or "top" of the first feature on the second feature can include that the first feature is directly above or obliquely above the second feature, or simply means that the height of the first feature is higher than the height of the second feature; while the "lower", "below" or "bottom" of the first feature on the second feature can include that the first feature is directly below or obliquely below the second feature, or simply means that the height of the first feature is lower than the height of the second feature.

[0144] Various embodiments and examples are provided in the above description for implementing various structures of the present disclosure. To simplify the present disclosure, certain elements and settings are described above. However, these elements and settings are only examples and are not intended to limit the present disclosure. In addition, reference numbers and / or reference letters can be repeated in different examples of the present disclosure. Such repetition is for the purpose of simplification and clarity and does not involve the relationship between different embodiments and / or settings. In addition, the present disclosure provides examples of different processes and materials. However, those skilled in the art should understand that other processes and / or materials can also be applied.

[0145] The reference in the specification to "one embodiment", "some embodiments", "an example embodiment", "an example", "a specific example", or "some examples", means that a particular feature, structure, material, or characteristic being described in connection with the embodiment or example is included in at least one embodiment or example of the disclosure. Therefore, the above-mentioned phrases appearing in the specification do not necessarily refer to the same embodiment or example of the disclosure. In addition, a particular feature, structure, material, or characteristic can be combined in any suitable manner in one or more embodiments or examples.

[0146] Any process or method described in a flow chart or otherwise described herein can be understood as including one or more modules, code segments or portions of executable instructions for implementing the particular logic functions or steps in the process, and the scope of the preferred embodiments of the present disclosure includes other implementations in which the functions can be implemented differently, including according to a substantially identical sequence or in the reverse order, as will be understood by those skilled in the art.

[0147] The logic and / or steps described herein in other descriptions or shown in the flowcharts presented herein, such as a sequence of specific executable instructions for performing logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor- based system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions, or a combination of both. In the context of this specification, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples of the computer-readable medium include, but are not limited to: an electronic connection (electronic device having one or more wires), a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, and a portable compact disc read-only memory (CDROM). In addition, the computer-readable medium can even be paper or other suitable medium capable of printing, because, for example, the paper or other suitable medium can be optically scanned, then, if necessary, the program can be edited, decrypted, or otherwise processed in an appropriate manner, and then electronically obtained, and then the program can be stored in the computer memory.

[0148] It should be understood that various parts of the present disclosure can be implemented by hardware, software, firmware, or a combination thereof. In the above-described embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by an appropriate instruction execution system. For example, if implemented by hardware, the steps or methods can be implemented by one or a combination of the following technologies known in the art: discrete logic circuit with logic gates for implementing data signal logic functions, application specific integrated circuit with appropriate combination logic gates, programmable gate array (PGA), field programmable gate array (FPGA), etc.

[0149] Those skilled in the art should understand that all or part of the steps in the above-described exemplary methods of the present disclosure can be directed by a program to instruct relevant hardware. The program can be stored in the computer-readable storage medium, and when the program is run on the computer, the program includes one of the steps in the method embodiments of the present disclosure or a combination thereof.

[0150] In addition, each functional unit of the embodiments of the present disclosure can be integrated in one processing module, or the units can be physically present separately, or two or more units are integrated in one processing module. The integrated module can be realized in the form of hardware or in the form of a software functional module. When the integrated module is realized in the form of a software functional module and sold or used as an independent product, it can be stored in a computer readable storage medium.

[0151] The storage medium mentioned above can be a read-only memory, a magnetic disk, an optical disk, etc.

[0152] Although the embodiments of the present disclosure have been shown and described, those skilled in the art will understand that the embodiments are illustrative, not limiting, and that changes, modifications, substitutions, and variations can be made to the embodiments without departing from the scope of the present disclosure.

Claims

1. An image projection apparatus characterized by comprising: Comprising: a light source that emits a laser beam; a scanner that scans the laser beam emitted from the light source; and a projection optical system that irradiates the laser beam scanned by the scanner and projects an image onto a retina of a user, wherein the light source comprises: at least one first laser element that emits a wavelength of the laser beam from 610 nanometers to 680 nanometers and has an oscillation threshold current of 15 milliamperes or less; at least one second laser element that emits the wavelength of the laser beam from 500 nanometers to 530 nanometers and has the oscillation threshold current of 25 milliamperes or less; at least one third laser element that emits the wavelength of the laser beam from 430 nanometers to 470 nanometers and has the oscillation threshold current of 10 milliamperes or less; and a driving circuit that pulse drives the first, second, and third laser elements with a pulse width shorter than a pulse width determined by a required modulation speed of one pixel. the driving circuit pulse drives the first, second, and third laser elements with a pulse width of 2.2 nanoseconds or less.

2. The image projection apparatus according to claim 1, characterized by Each of the first, second, and third laser elements is a edge emitting laser diode having a low oscillation threshold current.

3. The image projection apparatus according to claim 1, wherein Each of the first, second, and third laser elements is a vertical cavity surface emitting laser having a low oscillation threshold current.

4. The image projection apparatus according to claim 1, wherein 5. The image projection device according to claim 4, wherein the oscillation threshold current of the first laser element is 1 milliamperes or less, the oscillation threshold current of the second laser element is 3 milliamperes or less, and the oscillation threshold current of the third laser element is 1 milliamperes or less. the light source includes a waveguide-type optical multiplexer that multiplexes the plurality of laser beams emitted from each of the first, second, and third laser elements by causing the plurality of laser beams to be incident on a waveguide.

6. The image projection apparatus according to claim 1, wherein 7. The image projection device according to any one of claims 1 to 6, wherein the first laser element includes a first active layer; the second laser element includes a second active layer; the third laser element includes a third active layer; the first active layer includes aluminum gallium indium phosphide InGaAlP, and the second and third active layers include indium gallium nitride InGaN. the light source includes a plurality of each of the first, second, and third laser elements.

8. The image projection apparatus according to any one of claims 1 to 6, characterized by the scanner scans the laser beam emitted from the light source in a Lissajous scanning method.

9. The image projection apparatus according to claim 1, wherein the scanner reduces a resonance frequency by using a plurality of the first, second, and third laser elements to scan the laser beam at a resolution of FHD or more, and projects the image onto the retina of the user.

10. The image projection apparatus according to claim 8, wherein ​ 11. The image projection apparatus according to claim 1, wherein Also included are: a line-of-sight direction detector that detects a line-of-sight direction of a user of the image projection; and an optical system controller that controls the projection optical system based on the line-of-sight direction detected by the line-of-sight direction detector.

12. The image projection device according to claim 11, wherein The projection optical system includes a tilting mirror module that reflects the laser beams emitted from the light source to the retina of the user, and the optical system controller controls the tilting mirror module to project the laser beams to the retina of the user based on the line-of-sight direction detected by the line-of-sight direction detector.

13. The image projection device of claim 12, wherein, The line-of-sight direction detector is an eye tracking camera.

14. The image projection apparatus according to claim 1, wherein The scanner includes a microelectromechanical system mirror.

15. The image projection apparatus according to claim 14, wherein The scanner also includes an application specific integrated circuit that drives the microelectromechanical system mirror.

16. The image projection apparatus according to claim 14, wherein The microelectromechanical system mirror is vacuum sealed.

17. The image projection apparatus according to claim 14, wherein The microelectromechanical system mirror includes: a first rotation axis for rotation of the microelectromechanical system mirror; and a second rotation axis perpendicular to the first rotation axis for rotation of the microelectromechanical system mirror.

18. The image projection apparatus according to claim 17, wherein The microelectromechanical system mirror rotates about each of the first rotation axis and the second rotation axis using resonance.

19. The image projection apparatus according to claim 1, wherein The drive circuit applies a plurality of drive pulses to each pixel projected to each of the plurality of laser elements.

20. The image projection apparatus according to claim 1, wherein The light source includes a multiplexing optical system that multiplexes the plurality of laser beams emitted from each of the first laser element, the second laser element, and the third laser element.

Images