WO2014051624A1

WO2014051624A1 - Directional waveguide-based backlight with integrated hybrid lasers for use in a multivew display screen

Info

Publication number: WO2014051624A1
Application number: PCT/US2012/058026
Authority: WO
Inventors: David A FATTAL; Zhen PENG; Di Liang; Raymond G Beausoleil
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2012-09-28
Filing date: 2012-09-28
Publication date: 2014-04-03
Anticipated expiration: 2015-03-28
Also published as: TWI499803B; TW201421075A

Description

DIRECTIONAL WAVEGUIDE-BASED BACKLIGHT WITH INTEGRATED HYBRID LASERS FOR USE IN A MULTIVEW DISPLAY SCREEN

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to PCT Patent Application Serial No. PCT/US2012/035573 (Attorney Docket No. 82963238), entitled "Directional Pixel for Use in a Display Screen", filed on April 27^th, 2012, and to PCT Patent Application Serial No.

(Attorney Docket No. ), entitled "Directional Waveguide-Based

Backlight for Use in a Multiview Display Screen", concurrently filed herewith, and assigned to the assignee of the present application and incorporated by reference herein.

BACKGROUND

[0002] The ability to reproduce a light field in a display screen has been a key quest in imaging and display technology. A light field is a set of all light rays traveling in every direction through every point in space. Any natural, real-world scene can be fully characterized by its light field, providing information on the intensity, color, and direction of all light rays passing through the scene. The goal is to enable viewers of a display screen to experience a scene as one would experience it in person.

[0003] Currently available display screens in televisions, personal computers, laptops, and mobile devices remain largely two-dimensional and are thus not capable of accurately reproducing a light field. Three-dimensional ("3D") displays have recently emerged but suffer from inefficiencies in angular and spatial resolution in addition to providing a limited number of views. Examples include 3D displays based on holograms, parallax barriers, or lenticular lenses.

[0004] A common theme among these displays is the difficulty to fabricate displays for light fields that are controlled with precision at the pixel level in order to achieve good image quality for a wide range of viewing angles and spatial resolutions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present application may be more fully appreciated in connection with the following detailed description taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: [0006] FIG. 1 illustrates a schematic diagram of a top view of a waveguide-based directional backlight with integrated hybrid lasers in accordance with various examples;

[0007] FIGS. 2A-B illustrate schematic diagrams of top views of a waveguide-based directional backlight with integrated hybrid lasers;

[0008] FIG. 3 illustrates different top and side sectional views of a directional backlight;

[0009] FIG. 4 illustrates a schematic diagram of an example hybrid laser;

[0010] FIG. 5 illustrates a schematic diagram of a directional backlight using distributed feedback lasers in accordance with various examples;

[0011] FIG. 6 illustrates different top and side sectional views of a directional backlight of FIG. 5;

[0012] FIG. 7 illustrates a 3D view of a directional backlight in accordance with various examples;

[0013] FIG. 8 illustrates another 3D view of an example directional backlight;

[0014] FIGS. 9A-B illustrate top views of a directional backlight according to various examples;

[0015] FIG. 10 illustrates an example of a waveguide having geometrically distinct regions;

[0016] FIG. 11 illustrates a schematic diagram of a directional backlight having multiple waveguide arrays with waveguides of FIG. 10; and

[0017] FIG. 12 is a flowchart for generating a 3D image with a directional backlight in accordance with various examples.

DETAILED DESCRIPTION

[0018] A directional waveguide-based backlight with integrated hybrid lasers for use in a multiview display screen is disclosed. The directional backlight uses the integrated hybrid lasers to generate a plurality of input planar lightbeams for a waveguide layer consisting of a plurality of waveguide arrays. The hybrid lasers may include hybrid silicon ring lasers and distributed feedback lasers arranged in a silicon/silicon-oxide substrate bonded to the waveguide layer. Each waveguide array is composed of a set of waveguides. Each waveguide is composed of a plurality of directional pixels to guide the input planar lightbeams and scatter a fraction of them into output directional lightbeams. The input planar lightbeams propagate in substantially the same plane as the directional backlight, which is designed to be substantially planar.

[0019] In various examples, the directional pixels have patterned gratings of substantially parallel and slanted grooves arranged in or on top of the waveguides. The waveguides may be, for example, dielectric or polymer waveguides, among others. The patterned gratings can consist of grooves etched in the waveguides or grooves made of material deposited on top of the waveguides (e.g., any material that can be deposited and etched or lift-off, including any dielectrics or metal).

[0020] As described in more detail herein below, each directional pixel may be specified by a grating length (i.e., dimension along the propagation axis of the input planar lightbeams), a grating width (i.e., dimension across the propagation axis of the input planar lightbeams), a groove orientation, a pitch, and a duty cycle. Each directional pixel may emit a directional lightbeam with a direction that is determined by the groove orientation and the grating pitch and with an angular spread that is determined by the grating length and width. By using a duty cycle of or around 50%, the second Fourier coefficient of the patterned gratings vanishes thereby preventing the scattering of light in additional unwanted directions. This insures that only one directional lightbeam emerges from each directional pixel regardless of the output angle.

[0021] As further described in more detail herein below, a directional backlight can be designed with directional pixels that have a certain grating length, a grating width, a groove orientation, a pitch and a duty cycle. Each directional pixel can generate a directional lightbeam having a given view such that the plurality of directional pixels in the plurality of waveguides provides multiple views that form a multiview 3D image. The multiview 3D image can be a red, blue, and green multiview 3D image generated from the directional lightbeams emitted by the directional pixels in the backlight.

[0022] It is appreciated that, in the following description, numerous specific details are set forth to provide a thorough understanding of the examples. However, it is appreciated that the examples may be practiced without limitation to these specific details. In other instances, well known methods and structures may not be described in detail to avoid unnecessarily obscuring the description of the examples. Also, the examples may be used in combination with each other. [0023] Referring now to FIG. 1, a schematic diagram of a top view of a waveguide- based directional backlight with integrated hybrid lasers in accordance with various examples is described. Directional backlight 100 includes hybrid lasers 105a-d arranged in a substrate 110 to generate collimated input planar lightbeams 1 ISa-d and 120a-d for a waveguide array composed of waveguides 125a-d. As generally described herein, a planar lightbeam refers to a beam of light wherein the directions of the light rays in the beam are substantially parallel to each other. Hybrid lasers lOSa-d may be, for example, hybrid silicon ring lasers (described in more detail below with reference to FIG. 4) and arranged to the substrate 110 such as to be bonded to each waveguide. Each hybrid silicon ring laser may be used to generate light of a given color. For example, hybrid silicon laser 105a may be a red laser, hybrid silicon laser 105b may be a green laser, hybrid silicon laser 105c may be a blue laser, and hybrid silicon laser 105d may be a white laser.

[0024] The waveguides 125a-d may be dielectric or polymer waveguides having a plurality of directional pixels arranged thereon, such as, for example, directional pixels 130a- d arranged on waveguide 125a. The directional pixels 130a-d scatter a fraction of the input planar lightbeams 115a-d and 120a-d into output directional lightbeams 135a-d. In various examples, each directional pixel 130a-d has patterned gratings of substantially parallel grooves, e.g., grooves 140a for directional pixel 130a. The thickness of the grating grooves can be substantially the same for all grooves resulting in a substantially planar design. The grooves can be etched in the waveguides or be made of material deposited on top of the waveguides (e.g., any material that can be deposited and etched or lift-off, including any dielectrics or metal).

[0025] Each directional lightbeam 135a-d has a given direction and an angular spread that is determined by the patterned gratings in its corresponding directional pixel 130a-d. In particular, the direction of each directional lightbeam 135a-d is determined by the orientation and the grating pitch of the patterned gratings. The angular spread of each directional lightbeam is in turn determined by the grating length and width of the patterned gratings. For example, the direction of directional lightbeam 135a is determined by the orientation and the grating pitch of patterned gratings 140a.

[0026] It is appreciated that this substantially planar design and the formation of directional lightbeams 135a-d upon input planar lightbeams 1 15a-d and 120a-d requires a grating with a substantially smaller pitch than traditional diffraction gratings. For example, traditional diffraction gratings scatter light upon illumination with lightbeams that are propagating substantially across the plane of the grating. Here, the gratings in each directional pixel 130a-d are substantially on the same plane as the input planar lightbeams USa-d and 120a-d when generating the directional lightbeams 135a-d. This planar design enables illumination with the hybrid lasers lOSa-d.

[0027] In various examples, the directional lightbeams 135a-d are precisely controlled by characteristics of the gratings in directional pixels 130a-d including a grating length L, a grating width W, a groove orientation Θ, and a grating pitch Λ. In particular, the grating length L of grating 140a controls the angular spread ΔΘ of the directional lightbeam 135a along the input light propagation axis and the grating width W controls the angular spread ΔΘ of the directional lightbeam 135a across the input light propagation axis, as follows:

where λ is the wavelength of the directional lightbeam 135a. The groove orientation, specified by the grating orientation angle θ, and the grating pitch or period, specified by Λ, control the direction of the directional lightbeam 135a.

[0028] The grating length L and the grating width W can vary in size in the range of 0.1 to 200 um. The groove orientation angle Θ and the grating pitch Λ may be set to satisfy a desired direction of the directional lightbeam 135a, with, for example, the groove orientation angle Θ on the order of -40 to +40 degrees and the grating pitch Λ on the order of 200-700 nm.

[0029] It is appreciated that directional backlight 100 is shown with a waveguide array of four waveguides 125a-d for illustration purposes only. A directional backlight in accordance with various examples can be designed with many such waveguide arrays (e.g., higher than 100), depending on how the directional backlight 100 is used (e.g., in a 3D display screen, in a 3D watch, in a mobile device, etc.). It is also appreciated that the directional pixels may have any shape, including for example, a circle, an ellipse, a polygon, or other geometrical shape.

[0030] FIGS. 2A-B illustrate schematic diagrams of top views of a waveguide-based directional backlight with integrated hybrid lasers in accordance with various other examples. In FIG. 2A, directional backlight 200 has hybrid lasers 205a-d that are bonded to the substrate 210 such as to be in between each waveguide. In FIG. 2B, directional backlight 2 IS has hybrid lasers 220a-d that are bonded to the substrate 225 such as to be adjacent to the bottom of each waveguide. Hybrid lasers 220a-d are also shown not to be aligned with respect to axis 230 through substrate 220. It is appreciated by one skilled in the art that various other combinations of integrating hybrid lasers arranged in a substrate bonded to a waveguide layer may also be designed without deviating from the principles described herein. For example, the hybrid lasers may be arranged in a substrate such as to be on top or on the bottom of the waveguides.

[0031] Attention is now directed to FIG. 3, which shows different top and side sectional views of a directional backlight in accordance with various examples. Top view 300 shows hybrid laser 30S arranged in substrate 310 and bonded to waveguide 3 IS. Side view 320 shows a cross-sectional side view of a directional backlight (e.g., directional backlights 100, 200, and 2 IS). Hybrid laser 32S is formed of an active material (e.g., a III-V semiconductor material) arranged on a silicon/silicon-oxide substrate formed of a silicon layer 33S and a silicon oxide layer 330. The silicon oxide layer 330 provides a good cladding material for waveguide 340.

[0032] A hybrid laser is described in more detail in FIG. 4. Hybrid laser 400 combines a ΙΠ-IV quantum-well region 405 bonded to a silicon/silicon-oxide layer 410 via a nitride layer 415. An optical waveguide 420 is defined by two trenches in the silicon/silicon- oxide layer 410 such that the hybrid laser 400 behaves like an inverse ridge waveguide. Because the ΙΠ-V region 405 is a hybrid silicon (e.g., indium phosphide ("InP") and aluminum gallium indium arsenide ("AlGalnAs")) slab, the bonding is self-aligned and no alignment step is needed for the bonding between the III-V layer 405 and the silicon/silicon- oxide layer 410. Electrically pumped gain can be achieved from the ΙΠ-V active region 405 since the optical mode of the hybrid laser 405 overlaps both the ΙΠ-V material 405 and the silicon waveguide 420.

[0033] As appreciated by one skilled in the art, hybrid laser 400 is just an example of a hybrid laser that may be integrated into a waveguide layer in a directional backlight. Other types of hybrid laser may be used, such as, for example, distributed feedback lasers. Referring now to FIG. 5, a directional backlight using distributed feedback lasers is described. Directional backlight 500 includes Distributed Feedback Lasers ("DFBs") 505a-d arranged in a substrate 510 to generate collimated input planar lightbeams 515a-d and 520a-d for a waveguide array composed of waveguides 525a-d. The waveguides 525a-d may be dielectric or polymer waveguides having a plurality of directional pixels arranged thereon, such as, for example, directional pixels 530a-d arranged on waveguide 525a. The directional pixels 530a-d scatter a fraction of the input planar lightbeams 515a-d and 520a-d into output directional lightbeams 535a-d that have a direction and angular spread precisely controlled by characteristics of the directional pixels 530a-d.

[0034] FIG. 6 shows different top and side sectional views of a directional backlight of FIG. 5 in accordance with various examples. Top view 600 shows DFB laser 605 arranged in substrate 610 and bonded to waveguide 615 having directional pixels 620a-b. Side view 625 shows a cross-sectional side view of the directional backlight of FIG. 5. DFB laser 630 is formed of an active material (e.g., a III-V semiconductor material) arranged on a silicon/silicon-oxide substrate formed of a silicon layer 640 and a silicon oxide layer 635. The silicon oxide layer 640 provides a good cladding material for a waveguide with directional pixels 645a-b.

[0035] It is appreciated that the examples shown in FIG. 1-7 illustrate various ways to integrate light directly into a waveguide layer. Other examples are also possible, with the goal of having light sources (e.g., the hybrid ring lasers shown in FIGS. 1-4 and the DFB lasers shown in FIGS. 5-6) that are easily fabricated with a waveguide layer having directional pixels as described above.

[0036] While the examples in FIGS. 1-6 are represented in two dimensions, FIG. 7 shows an illustrative 3D view of a directional backlight 700 having hybrid lasers 705a-d arranged in a substrate 710 bonded to waveguides 715a-d. The hybrid lasers 705a-d generate a plurality of input planar lightbeams (illustrated by the arrows in the figure) that get scattered into directional lightbeams having a direction and an angular spread precisely controlled by the directional pixels (e.g., directional pixel 720a in waveguide 715a) in the waveguides 715a-d.

[0037] As appreciated by one skilled in the art, each directional pixel may have different characteristics (e.g., pitch, orientation, grating length, grating width, etc.). Referring now to FIG. 8, a 3D view of an example directional backlight is described. Backlight 800 is shown with a waveguide array composed of waveguides 805a-c. Each waveguide has multiple directional pixels arranged thereon, such as, for example, directional pixel 810a in waveguide 805a, directional pixel 810b in waveguide 805b, and directional pixel 810c in waveguide 805c. The directional pixels 810a-c may be designed to have a different grating pitch and orientation. Each directional pixel 810a-c receives an input planar lightbeam (e.g., lightbeams 815a-c) from a hybrid laser and scatters them into a directional lightbeam (e.g., directional lightbeams 820a-c) according to the grating pitch and orientation of each directional pixel. The directional lightbeams 820a-c, as described above, therefore enable multiple views to be generated into a 3D image. Each directional lightbeam can be precisely controlled by the characteristics of its corresponding directional pixel.

[0038] Attention is now directed to FIGS. 9A-B, which illustrate top views of a directional backlight according to various examples. In FIG. 9A, directional backlight 900 is show with hybrid lasers 905a-d generating input planar lightbeams 910a-d and 91Sa-d, and waveguides 920a-d consisting of a plurality of polygonal directional pixels arranged thereon (e.g., directional pixel 925 in waveguide 920a). Each directional pixel is able to scatter a portion of an input planar lightbeam into an output directional lightbeam (e.g., directional lightbeam 930 scattered by directional pixel 92S). The directional lightbeams scattered by all the directional pixels in the waveguides 920a-d can represent multiple image views that when combined form a 3D image, such as, for example, 3D image 93S.

[0039] Similarly, in FIG. 3B, directional backlight 940 is show with hybrid lasers 945a-d generating input planar lightbeams 950a-d and 955a-d, and waveguides 960a-d consisting of a plurality of polygonal directional pixels arranged thereon (e.g., directional pixel 965 in waveguide 960a). Each directional pixel is able to scatter a portion of an input planar lightbeam into an output directional lightbeam (e.g., directional lightbeam 970 scattered by directional pixel 965). The directional lightbeams scattered by all the directional pixels in the waveguides 960a-d can represent multiple image views that when combined form a 3D image, such as, for example, 3D image 975.

[0040] In various examples, the waveguides in a waveguide array can be designed with geometrically distinct regions. Each geometrically distinct region has a directional pixel that is perpendicular to the region's orientation, thus enabling the directional lightbeams to have different vertical orientations in each region. FIG. 10 shows an example of a waveguide having geometrically distinct regions. Waveguide 1000 has geometrically distinct waveguide regions 1005a-1005e. Each waveguide region may have a single horizontal section such as waveguide region 1005a or multiple sections having different orientations such as waveguide regions 1005b-e. Waveguide regions 1005b-e have an angular section placed between two horizontally oriented sections. For example, waveguide region 1005e has angular section 1010 placed between horizontal sections 1015a-b.

[0041] Each waveguide region has a single directional pixel arranged thereon, such as directional pixels 1020a-e. The directional pixels 1020a-e placed in each waveguide region are oriented perpendicularly to the orientation of the region as shown in the figure. In the case of waveguide regions (e.g., regions 1005b-e) having an angular section between two horizontal sections, the directional pixels (e.g., pixels 1020b-e) are arranged perpendicularly to the orientation of the angular section. This enables the directional lightbeams scattered out of each directional pixel to have different vertical orientations in each region.

[0042] Attention is now directed to FIG. 11, which illustrates a schematic diagram of a directional backlight having multiple waveguide arrays with waveguides of FIG. 10. Directional backlight 1100 is shown with a waveguide layer with multiple waveguide arrays 1 105a-c. Each waveguide array has four waveguides (e.g., one for red light, one for green, one for blue light, and another for white light) with integrated hybrid lasers (e.g., hybrid laser 110) arranged on a substrate 11 IS bonded to the waveguide layer. The waveguide arrays 1105a-c can be designed to form different viewing sections, such as, for example, viewing section 1110. Each viewing section may have directional pixels designed to scatter directional lightbeams into a given image view to generate a 3D image.

[0043] A flowchart for generating a 3D image with a directional backlight in accordance with various examples is illustrated in FIG. 12. First, the characteristics of the directional pixels of the directional backlight are specified (1200). The characteristics may include characteristics of the patterned gratings in the directional pixels, such as, for example, a grating length, a grating width, an orientation, a pitch, and a duty cycle. As described above, each directional pixel in the directional backlight can be specified with a given set of characteristics to generate a directional lightbeam having a direction and an angular spread that is precisely controlled according to the characteristics. Next, a directional backlight is fabricated with the plurality of directional pixels arranged on a plurality of waveguides (1205). The waveguides may be dielectric or polymer waveguides, among others. The directional pixels may be etched in the waveguides or be made of patterned gratings with material deposited on top of the waveguides (e.g., any material that can be deposited and etched or lift-off, including any dielectrics or metal). In various examples, the waveguides may also have geometrically distinct regions as shown in FIGS. 10-11. Light from a plurality of hybrid lasers arranged in a substrate bonded to the plurality of waveguides is input into the directional backlight in the form of input planar lightbeams (1210). Lastly, a 3D image is generated from the directional lightbeams that are scattered by the directional pixels in the directional backlight (12 IS).

[0044] Advantageously, the precise control that is achieved with the directional pixels in the directional backlight enables a 3D image to be generated with an easy to fabricate substantially planar structure. Different configurations of directional pixels can generate different 3D images. The directional backlights described herein can be used to provide 3D images in display screens (e.g., in TVs, mobile devices, tablets, video game devices, and so on) as well as in other applications, such as, for example, 3D watches, 3D art devices, 3D medical devices, among others.

[0045] It is appreciated that the previous description of the disclosed examples is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other examples without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

WHAT IS CLAIMED IS:

1. A directional waveguide-based backlight with integrated hybrid lasers for use in a multiview display screen, comprising:

a waveguide layer having a plurality of waveguide arrays, each waveguide array having a set of waveguides, each waveguide having a plurality of directional pixels to scatter a plurality of input planar lightbeams into a plurality of directional lightbeams, each directional lightbeam having a direction and angular spread controlled by characteristics of a directional pixel in the plurality of directional pixels; and

a plurality of hybrid lasers arranged in a substrate bonded to the waveguide layer to provide the plurality of input planar lightbeams.

2. The directional waveguide-based backlight of claim 1, wherein the plurality of hybrid lasers comprises hybrid lasers selected f om the group consisting of hybrid ring lasers and hybrid distributed feedback lasers.

3. The directional waveguide-based backlight of claim 1 , wherein the plurality of waveguide arrays are substantially planar.

4. The directional waveguide-based backlight of claim 1 , wherein each directional pixel in the plurality of directional pixels comprises patterned gratings with a plurality of substantially parallel and slanted grooves.

5. The directional waveguide-based backlight of claim 4, wherein the characteristics of a directional pixel comprise a grating length, a grating width, a grating orientation, a grating pitch, and a duty cycle.

6. The directional waveguide-based backlight of claim 5, wherein the pitch and orientation of a directional pixel control the direction of a directional lightbeam scattered by the directional pixel.

7. The directional waveguide-based backlight of claim 6, wherein the length and width of a directional pixel control the angular spread of a directional lightbeam scattered by a directional pixel.

8. The directional waveguide-based backlight of claim 1 , wherein a waveguide in the set of waveguides comprises a plurality of geometrically distinct regions, each region having a plurality of sections and a single directional pixel.

9. A method for generating a multiview 3D image with a waveguide-based directional backlight having integrated hybrid lasers, comprising:

specifying a plurality of characteristics for a plurality of directional pixels, each directional pixel composed of a patterned grating having substantially parallel and slanted grooves;

fabricating a directional backlight with the plurality of directional pixels arranged on a plurality of waveguides;

illuminating the plurality of waveguides with light from a plurality of hybrid lasers arranged in a substrate bonded to the plurality of waveguides; and

generating the multiview image with directional lightbeams scattered by the plurality of directional pixels in the directional backlight.

10. The method of claim 9, wherein each directional lightbeam is controlled by the characteristics of a directional pixel.

11. The method of claim 10, wherein the characteristics of a directional pixel comprise a grating length, a grating width, a grating orientation, a grating pitch, and a duty cycle.

12. The method of claim 11, wherein the pitch and orientation of a directional pixel control the direction of a directional lightbeam scattered by the directional pixel.

13. The method of claim 11 , wherein the length and width of a directional pixel control the angular spread of a directional lightbeam scattered by the directional pixel.

14. The method of claim 11, wherein fabricating a directional backlight comprises fabricating a waveguide having a plurality of geometrically distinct regions, each region having a plurality of sections and a single directional pixel.

15. A waveguide, comprising:

a plurality of geometrically distinct regions, each region having a plurality of sections; and

a plurality of directional pixels arranged on the plurality of geometrically distinct regions to scatter input planar lightbeams into a plurality of directional lightbeams, each directional lightbeam having a direction and angular spread controlled by characteristics of a directional pixel in the plurality of directional pixels,

wherein the input planar lightbeams are generated by a plurality of hybrid lasers arranged on a substrate bonded with the waveguide.

16. The waveguide of claim 15, wherein the plurality of sections comprises an angular section placed between two horizontally oriented sections.