CN111983806A - Illumination system for wearable display - Google Patents

Abstract

A compact illuminator for a see-through image display system having a highly uniform light distribution is disclosed. The present invention implements a wearable display such as a glasses-type see-through display. The system provides a wide diverging beam from the display device so that the viewer can have a large frame.

Description

Illumination system for wearable display

Cross Reference to Related Applications

This Application is a Non-provisional Application (Non-provisional Application) claiming the benefit of previously filed U.S. provisional Application 62/493,077 filed on 21/6/2016. This application is also a partial continuation application (CIP) of patent application PCT/US2014//000153 filed on 23/6/2014, patent application PCT/US2014//000153 is a non-provisional application of U.S. provisional application 61/957,258 filed on 27/6/2013.

Technical Field

The present invention relates to an illumination system for a wearable display system for projecting an image to a diffractive optical element enabling a see-through display with high resolution and a wide field of view. More particularly, the present invention relates to a very compact illuminator suitable for wearable displays with a very small form factor.

Background

In recent years, wearable displays have received widespread attention after smart phones have become popular and are well accepted by the market. Wearable displays provide the benefits of hands-free operation, as well as show images to the person wearing the display at the same distance as a normal line of sight. Because of these advantages, there is a great need for wearable displays. However, conventional near-eye displays such as head-mounted displays, head-up displays, and eyeglass displays do not provide viewers with a satisfactory wearable display solution because these conventional displays are typically too heavy, large, and too dark. Furthermore, these conventional wearable displays often have low resolution, and many of them do not provide a see-through view, and most are expensive and can only display small-sized images. Accordingly, there is a pressing need for providing a wearable display device that is light, small, bright, and has high resolution with see-through viewing optical paths. Further, it is desirable that new wearable devices be inexpensive, that can display large images, and that can be worn in a discreet manner without others detecting that the person is wearing such a wearable device. Display systems implemented with LEDs and laser light sources typically have the technical problem of non-uniform light intensity distribution, and for display systems, homogenizers (homogenerizers) are typically required to provide uniform image brightness. Three separate color light sources need to be combined into a single light beam before being projected onto the display device. So that a compact glasses type display requires a very small system with both homogenizer and combiner. Several systems have been proposed in the past.

As shown in fig. 1, Takeda et al in patent US8711487 disclose an eyeglass-type display system that utilizes a waveguide and half mirrors to achieve see-through capability. The system comprises a transmissive LCD as the display and the illumination system is a backlight light guide diffusing the light from the light source. The system is suitable for transmissive LCDs, but not necessarily for other display devices (such as LCOS and DMD).

As shown in fig. 2 and 2A, Takahashi et al in U.S. patent application publication US2013/0021581 discloses an illuminator and display for miniaturization. The system includes a polychromatic light source, such as an LED and a laser (11), with microlenses (116) for collimation as shown in fig. 2A, a dichroic mirror (117) for combining the light beams, and polarizing beam splitters (PBS, 16) arranged in a perpendicular direction from the LCOS (17). If it is used in an eyewear display and is embedded in the frame (temple) of the eyewear, the illuminator will protrude from the frame of the eyewear.

As shown in FIG. 3, Katsumata et al discloses a Planar Lightwave Circuit (PLC) in JP 2013-195603. A light beam from a laser diode is introduced into an optical waveguide, and light energy in the optical waveguide can be transferred to an adjacent optical waveguide under certain conditions. This approach is applicable to combiners for laser sources and has great potential, although it requires further investigation before large-scale commercialization.

The present invention provides a practical solution for an illuminator suitable for use in a glasses display.

Disclosure of Invention

It is an object of the present invention to provide a compact illuminator for a see-through near-eye display, the field of view of which is almost the full size of the eyeglasses, although the illuminator, optics and electronics of the system are very compact and can be embedded in the frame of the eyeglasses, such as the eyeglasses in fig. 4 and 5. A display device such as an LCOS, LCD or DMD is used to project an image from its frame towards the lenses of the glasses. Due to the geometric configuration of the glasses and the human eye, an image is projected from the frame of the glasses to the lenses of the glasses and reflected to the human eye. The virtual image is created in the air without any physical screen. The solid screen reflects the projected light at a large divergence angle, and a viewer can see an image at a large viewing angle. But in the case of see-through displays such as glasses displays and flat-view displays, there is no physical screen and the image can only be seen in the so-called "Eyebox" (Eyebox), where the viewer can see the image, but often the image is very small. The bezel of the see-through display must be large enough to allow the viewer to comfortably see the image with some movement of the eyeglass display relative to the eyes. This requires specially designed illuminators to ensure the size of the viewing frame. The size of the viewing frame is closely related to the divergence angle of the light beam from the display device. For conventional projection displays, the divergence angle of the light beam from the display device is kept as small as possible for high resolution and sharp images. But a see-through display requires a large divergence angle of the light beam from the display device and a high resolution virtual image. The illuminator must provide converging light at a large angle to the surface of the display device. This may be achieved with the configuration shown in fig. 7, where the beam expanding lens (1006) expands the incident beam to the collimating lens (1007) and the beam becomes substantially parallel and enters the first microlens array (1008) and creates an image of the light source on the second microlens array (1009), in other words, the image on the second microlens array is conjugate (conjugate) to the light source. The image on the second microlens array is projected by a condenser lens (1010) to a display device (1013) as a conjugate image of the first microlens array. The diameter of the illumination light at the condenser lens and the distance between the condenser lens and the display device determine the convergence angle of the light source and the display device. This is how to ensure a large viewing frame with the illuminator.

Another example of the invention is to reduce the size of the illuminator using an additional 1/4 λ retarder (detarder) that rotates the polarization angle of light located on the opposite side of the display device by 90 degrees, as shown in fig. 10. This configuration reduces the distance between the condenser lens and the display device, which helps to increase the incident light angle. An example of a combination with a homogenizer is shown at figure 11.

It is another aspect of the present invention to provide a light combiner suitable for use in a see-through display having a small form factor. Solid state light sources such as lasers and LEDs are packaged in a unit with a lens array (2002) as in fig. 8 or with a DOE (diffractive optical element 7002) as in fig. 9.

Drawings

Figure 1 is a perspective display configuration shown as disclosed in US8711487 to Takeda et al. A backlight module is used as an illuminator for an LCD display panel.

Fig. 2 and 2A are shown by Takahashi et al in U.S. patent application publication US2013/0021581, in which expanded beam lenses and microlenses are used to provide light to the PBS.

Fig. 3 is a Planar Lightwave Circuit (PLC) disclosed in JP2013-195603 by Katsumata et al. A light beam from a laser diode is introduced into an optical waveguide, and light energy of the optical waveguide can be transferred to an adjacent optical waveguide under certain conditions. This is another way of combining multiple beams into one beam.

Fig. 4 and 5 are examples of eyewear that can embed optical and display systems in a frame.

Fig. 6 shows an example of the invention where the chip of the laser diode is directly packaged with an array of collimating lenses and a dichroic mirror combines the light beam to a beam expanding lens.

Fig. 7 shows an example of a homogenizer using two lenses and two microlens arrays. 7001 is a collimating lens and 7002 is a first Fly-eye lens (which is also referred to as a microlens array). 7003 is a second fly-eye lens. 7004 is a field lens.

FIG. 8 shows an example of the present invention in which optical fibers are used to combine and guide the laser beams into a homogenizer.

Fig. 9 illustrates how a light beam propagates in the components of the luminaire.

Fig. 10 illustrates how light passes in the PBS in combination with a retarder of 1/4 λ to reduce the size of the luminaire.

Fig. 11 illustrates a structure of a reduced-size illuminator.

Fig. 12 illustrates an example of the present invention that uses a microlens array to combine multiple light beams into a light guide (light pipe or optical fiber) and guide to a homogenizer and PBS. Fig. 12A illustrates how a light beam passes through the component.

FIG. 13 illustrates an example of the present invention that uses an array of DOEs to combine the beams into a light pipe and PBS.

FIG. 14 illustrates another exemplary embodiment of a see-through display in combination with an illuminator.

Detailed Description

The following detailed description of various embodiments illustrates various illuminators providing light beams to a display device of a see-through display system having a wide angle (large NA) sufficient for a viewer to ensure a large viewing frame.

Fig. 6 and 7 show an exemplary embodiment of the invention in which a microlens array (1002) collimates multiple light sources (1001) to a set of dichroic mirrors (1005) to combine the light beams into a single light beam. The single light beam is expanded by the beam expanding lens (1006) and directed to the collimating lens (1007). The collimated beam is split into multiple beams by a second microlens array (1008) and focused on a third microlens array (1009) where the image is conjugate to the light source. A condenser lens (1010) is placed next to the third microlens array (1009) and the light beam is passed to the prism (1011) and reflected by the prism (1011) towards the polarizing beam splitter PBS (1012). The reflected light is focused on a display device (1013) to display an image, wherein each pixel corresponds to each microlens of a third microlens array projected on the entire area of the display device (1013), wherein the third microlens array and the display device are optically conjugate.

Fig. 8 shows another embodiment of the present invention, in which a microlens array (2002) is implemented to combine light beams projected from a plurality of light sources (2001) into light to be projected into a light guide (2004) serving as a light pipe, and then the light is transmitted through an optical fiber with a PLC planar lightwave circuit, as in 2006 in fig. 8 and the unit in fig. 3. Fig. 8 further shows a light source unit 2005 and a collimated or condensed light beam 2003. The combined light is expanded by a beam expanding lens (2006) to a collimating lens (2007). The collimated light is then transmitted through the same optical components as shown in fig. 6.

Fig. 9 illustrates in more detail the optical paths for the light beams shown in fig. 6 and 8. The combined light beam (3006) includes multiple wavelengths of light emitted at divergent angles from the edge of the fiber or laser diode/LED. The light source (3006) and the second microlens array (3009) are optically conjugate, and the first microlens array (3008) and the display device (3013) are also optically conjugate. Incident light passes through homogenizers (3007-3010) and is reflected by prism (3011) to polarizer (3015), which reflects the S-wave to light absorber (3014) and passes the P-wave to display device (3013). The display device reflects light with polarization rotation from P-wave to bright image of S-wave, and the S-wave will be reflected by polarizer (3016) in direction (3016) towards the projection lens.

Fig. 10 shows an embodiment of the present invention. Incident light passes through a polarizer plate (4001) which passes only P waves and reflects or absorbs S waves. Light that passes through the polarizer (4002) enters the polarizing beam splitter (PBS, 4011) and hits the polarizer surface (4007, which passes only S-waves and reflects P-waves). Since the light (4002) contains only P-waves, it will be reflected by the PBS (4007) toward the LCOS (4004), and the LCOS changes the polarization of incident light according to an image signal and reflects the S-waves toward the PBS at a bright image. The S-wave will pass through the PBS and through a retarder with 1/4 λ (wavelength) polarization rotation, and will be reflected by the mirror (4006) and pass through the 1/4 λ retarder a second time, which changes the polarization of light 1/2 λ, and the incident light becomes a P-wave and will be reflected by the PBS (4007) towards the exit (4008) of the luminaire. The advantage of this system is that the incoming light (4002) and outgoing light (4009) are in one line, which saves space for the luminaire, rather than the previous example shown in fig. 9, where the incoming light (3006) and outgoing light (3016) are in different levels, which requires more space for the luminaire.

Fig. 11 shows another embodiment of the invention where a laser diode (5001) is packaged in a cell and a microlens array (5002) focuses multiple beams having multiple wavelengths from the laser diode to an optical fiber and a PLC (5015, planar lightwave circuit) (5003,5004,5005 not depicted) combines the multiple beams into a single beam. The beam expanding lens (5006) expands the light beam toward the homogenizer (5007 to 5010). The P wave of the light after the homogenizer will pass through the polarizer (5016) and the residual light containing the S wave is reflected back to the homogenizer. The P-wave light is reflected by the polarizer (5011, Pass-P and reflection-S types) towards the display device (5012). The display device reflects the S-wave light for the image to the polarizer (5011), and it will pass to the retarder (5013) and mirror (5013) of 1/4 λ. The retarder rotates 1/4 λ the polarization of the image light, and the light is reflected by a mirror (5013) and the light is transmitted through the retarder 5013, where the retarder 5013 functions similarly to both the retarder 4005 and the mirror 4006. The beam ends with a rotation of 1/2 λ, again with an additional polarization rotation of 1/4 λ. The incident S wave is converted to a P wave by a retarder and mirror and reflected by a polarizer to the exit of the illuminator (5014, or we may need a new number, such as 4008). Compared to the previous example, the system has an 1/2 distance between the homogenizer and the display device, which provides a larger NA of converging light to the display device. The display system improves the frame size of the image even when the back focal length of the system is two times longer than the size of the PBS because of the repeated optical path of the reflected light through the optical components in the display device.

Fig. 11 shows another embodiment of the invention in which a light source such as a laser diode and LED (6001) is packaged with a microlens array (6002) to focus the beam from the light source to the entrance of a light pipe (6003), which homogenizes the distribution of light intensity. The image at the exit of the light pipe will be projected to a display device (6013). Thus, the light beam at the exit of the light pipe and the light beam projected onto the display device 6013 are optically conjugate. A polarizer (6010) is placed between the light pipe and a crossed PBS (6011) (polarizing beam splitter). The crossed PBS (6011) includes four triangular prisms with polarizing surface coatings with different types (P or S) of polarization in two diagonal directions (6014 and 6015). As shown in fig. 12, the incident beam (6009) is polarized into P-waves by a polarizer (6010) and reflected to the display device (6013) by the polarizer embedded in the PBS (6011). The light beam reflected by the display device containing image light with S-waves will be reflected along direction (6012) towards the projection lens and the residual light with P-waves will pass through the polarizer to the absorber (6016).

Fig. 13 shows an example of the embodiment. Because green is not technically and economically efficient, using LEDs or lasers of all three colors is often neither economical nor practical, and converting the wavelength by phosphors is very useful. 1308 is a blue laser or LED and is used without wavelength conversion because blue is the most efficient. 1307 is a collimating lens, and 131 is a collimated blue beam, and is reflected by dichroic mirror (1306) to output beam (1313). Also as shown in this figure, 1308 is a blue laser or LED, and 1311 is a collimating lens. Reference numeral 1312 denotes a green fluorescent plate which converts blue light into green light 1315 and reflects the green light toward the mirror 1310. 1302 is another blue laser or LED, and 1303 is a collimating lens, and 1304 is a red phosphor plate, which converts blue light to red light (1314).

Fig. 14 shows another example of the embodiment. Three light sources (1405, 1406 and 1407) of different colors are arranged and integrated into one light beam (1411) and directed to the light guide (1401). The light beam (1411) in the light guide is reflected multiple times by the reflector (1402) and the diffuser (1403) and is emitted (1302) substantially towards a normal direction of the diffuser (1403). This example provides a homogenized light distribution from the diffuser surface (1403).

Although specific embodiments of the invention have been illustrated and described herein, it will be appreciated that other modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.

Claims (11)

1. A see-through display system comprising:

display device from the group of LCD, LCOS, micro-mirror and micro-shutter (Microhutter), and

a circuit for driving the display device, and

eyeglass lens and frame, and

a see-through optical element from the group of a Holographic Optical Element (HOE) and a Diffractive Optical Element (DOE) attached to the eyeglass lens, and

projection optics embedded in the frame having at least one lens with at least one free-form surface and at least one mirror that projects an image beam through air onto the glasses, and

Luminaire comprising

Light source(s) of multiple colors with light emitting device(s), from the group of lasers, LEDs, OLEDs and phosphors activated by solid state light sources, and

an optical combiner combining light sources of multiple colors into a single light beam

Wherein the combiner is from the group of dichroic prisms, PBSs, optical fibers, free-form lenses, DOEs, HOEs, and planar optical waveguide circuits, and Total Internal Reflection (TIR) prisms, wherein the angle of incidence of the combined light beams onto the display device is greater than 10 degrees.

2. The combiner for a see-through display system of claim 1, wherein:

the light beams of the light source are combined by the dichroic prism into a light pipe from a set of rectangular tubes having a higher index of refraction than air and optical fibers.

3. The combiner for a see-through display system of claim 1, wherein:

the light beams of the light sources are combined by a polarizing beam splitter into light pipes from a set of rectangular tubes having a higher index of refraction than air and optical fibers.

4. The see-through display system of claim 1, wherein:

a homogenizer from the group of light pipes, microlens arrays, and diffuser plates is placed between the combiner and the display device.

5. The display system of claim 1, wherein:

the display device is an LCOS, an

There is a cubic Polarizing Beam Splitter (PBS) comprising two triangular prisms with a polarizer layer on the beam splitter face, and an 1/4 lambda retarder parallel to the LCOS display surface and located on the opposite side of the face of the PBS from the LCOS so that a single PBS can pass the necessary image light to the projection lens.

6. The display system of claim 1, wherein:

the combiner comprises

An optical element from the group of Diffractive Optical Elements (DOEs) and Holographic Optical Elements (HOE) that directs a light beam from the light source into a light guide from the group of light pipes, optical fibers, and diffuser plates.

7. An illuminator for a wearable display, comprising:

LCOS display device, and

a circuit for driving the display device, and

eyeglass lens and frame, and

luminaire comprising

Light source(s) of multiple colors with light emitting device(s), said light source(s) being from the group of laser, LED and OLED, and

a microlens array for converging a light beam containing a plurality of wavelengths

An optical combiner combining light sources of multiple colors into a single light beam

Wherein the combiner is from the group of dichroic prism, PBS, fiber and planar light waveguide circuit, wherein the angle of incidence of the combined light beams onto the display device is greater than 20 degrees.

8. The luminaire of claim 7, wherein:

the microlens array is a DOE array from the group of holographic and diffractive optical elements.

9. The luminaire of claim 7, wherein:

the microlens array is a DOE array from the group of holographic and diffractive optical elements.

10. The luminaire of claim 7, wherein:

the microlens array is a free-form lens array.

11. The illuminator of claim 7, wherein:

the PBS is a crossed prism having a first polarizer that passes P-waves and reflects S-waves in a diagonal inner surface, and a second polarizer that passes S-waves and reflects P-waves in another diagonal inner surface perpendicular to the first polarizer.

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