WO2019186240A1

WO2019186240A1 - Optoelectronic device

Info

Publication number: WO2019186240A1
Application number: PCT/IB2018/052175
Authority: WO
Inventors: Yuan Gao; George Wong
Original assignee: Compoundtek Pte Ltd
Current assignee: Compoundtek Pte Ltd
Priority date: 2018-03-29
Filing date: 2018-03-29
Publication date: 2019-10-03
Anticipated expiration: 2020-09-29

Abstract

The present invention relates to an optical emitter cell (4), comprising a substrate (10), at least one cladding layer (20) deposited over the substrate (10), and an emitter layer (30) on top of the cladding layer (20) for emitting light. The emitter layer (30) includes at least one emitting port (40) through which the light exits the emitter layer (30). The emitting port (40) is formed by partially etching a top surface of the emitter layer (30), wherein thickness (x) of the emitter layer (30) is greater than that of the emitting port (40).

Description

OPTOE L E CTRONIC DEVIC E

FIE L D OF THE INVE NTION The present invention relates to a semiconductor device, in particular to an optoelectronic device.

BAC KG ROUND OF TH E INVE NTION S ilicon photonics has earned a lot of attention in recent days due to its potential for cost reduction and wide range of applicability. S ilicon Photonic Integrated Circuits (PICs) can be fabricated using standard, wafer scale C MOS technology, which reduces the cost drastically. In addition, using a silicon platform, photonic devices can be integrated with microelectronic circuits. Also, silicon photonics can enable a chip-scale platform for monolithic integration of photonics and micro-electronics for applications of image display devices such as dot projector.

United S tates Patent No. 8,331 ,006 B2 discloses a display device comprising an illuminating unit with a substrate that includes an in-coupling portion and an out-coupling portion. The in-coupling portion and the out-coupling portion are formed by embossing on the surfaces of the substrate, such that light rays can enter/exit the embossed portions, while being subject to total internal reflection in other portions of the substrate.

S imilarly, United States Patent Application No. 13/833,877 discloses an active ophthalmic device based on photonic based projection system, comprising an array of photonic passive emitter cells coupled to a laser source through a network of light pipes. The photonic passive emitter cells provide light patterns or dynamic images from light patterns that may be used to convey information or data through the ophthalmic device to a user's retina in the form of the light patterns. E ach emitter cell includes a control circuit for modulating the light emitted by the corresponding emitter cell. However, the emitting brightness of the emitter cell array is low, and therefore power consumption increases or additional light sources are required.

To counter this problem, a dot projector comprising an array of vertical-cavity surface- emitting lasers (VCS E L) is disclosed in United States Patent Application No. 14/296.463. E ach pixel of the dot project is formed by an active light emitting source such as a VCS E L. However, due to complexity of the fa brication of VCS E L, it poses a constrain to improve fa brication yield of the dot project and lower the cost. T he potential for future scaling up the a rray size (if more pixels are needed) for the dot projectors is also limited.

Hence, there is a need for a passive emitter cell with improved emitting efficiency without increasing power consumption or additiona l light sources. Further there is a need for an optoelectronic device for use as a lighting device in an image display device such as a dot projector, which has improved emitting efficiency while reducing power consumption.

S U MMARY OF TH E INVE NTION

T he present invention relates to a passive optical emitter cell able to operate in near infrared wavelength ra nge from 800 nm to 1000 nm. T he emitter cell comprising a substrate, at least one cladding layer deposited over the substrate, a nd an emitter layer on top of the cladding layer for emitting light. T he emitter layer includes at least one emitting port through which the light exits the emitter layer. T he emitter layer is formed of silicon nitride (S iN) a nd the cladding layer is formed of silicon dioxide (S i0₂).

T he emitting port is formed by partially etching a top surface of the emitter layer, wherein thickness of the emitter layer is greater than that of the emitting port. T hereby, the light rays are directed in the upwa rd direction, a nd thus improving the emitting efficiency (brightness) of the cell without increasing power consumption.

Additional aspects, features a nd advantages of the invention will become a pparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments of the invention in conjunction with the drawings listed below.

B RIE F D E S C RIPTION OF TH E AC C OMPANY ING DRAWING

T he accompanying drawings are included to provide a further understa nding of the present disclosure, and are incorporated in a nd constitute a part of this s pecification. T he drawings illustrate exempla ry embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

FIG UR E 1 displays a diagra mmatic top view of the optoelectronic device, in accordance with an exemplary embodiment of the present invention. FIG UR E 1A displays an enlarged diagrammatic top view of a connector assembly of the optoelectronic device, in accordance with an exemplary embodiment of the present invention.

FIG UR E 2 displays a diagrammatic cross-sectional view of the optical emitter cell of the optoelectronic device, in accordance with an exemplary embodiment of the present invention.

FIG UR E 3 displays a diagrammatic cross-sectional view of a light source assembled with an optical waveguide in the optoelectronic device, in accordance with an exemplary embodiment of the present invention.

FIG UR E 4 displays a diagrammatic top view of the optoelectronic device, in accordance with an alternative embodiment of the present invention.

FIG UR E 5 displays a graphical representation of simulation results for near field emission, in accordance with an exemplary embodiment of the present invention.

FIG UR E 6 displays a graphical representation of simulation results for far field emission, in accordance with an exemplary embodiment of the present invention.

FIG UR E 7 displays a graphical representation of efficiency of the emitter cell in comparison with that of the conventional emitter cell, in accordance with an exemplary embodiment of the present invention.

DETAIL E D DE S C RIPTION OF THE INVE NTION

Detailed description of preferred embodiments of the present invention is disclosed herein. It should be understood, however, that the embodiments are merely exemplary of the present invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and for teaching one skilled in the art of the invention. The numerical data or ranges used in the specification are not to be construed as limiting.

The preferred embodiments will now be described in detail in accordance with the attached drawings. The present invention relates to an optoelectronic device comprising a light source, a connector assembly and an array of optical emitter cells coupled to the light source through a connector assembly. E ach of the emitter cells includes a plurality of emitter ports formed by partially etching a top surface of an emitter layer of the emitter cell. This helps in directing light rays in the upward direction, and thus improving the emitting efficiency without increasing power consumption.

FIG UR E 1 shows a schematic top view of an optoelectronic device, in accordance with an exemplary embodiment of the present invention. The device (1 ) includes a light source (2), a connector assembly (3) and an array of optical emitter cells (4) coupled to the light source (2) through the connector assembly (3). The light source (2) is an edge-emitting laser diode connected to a power supply (5) e.g. AC or DC power supply. In an alternate embodiment, the power supply (5) can be controlled to allow the light source (2) to emit light in a specific sequence.

S imilarly, the light source (2) can also be a surface-emitting laser such as vertical-cavity surface-emitting laser (VCS E L). Commercially available edge-emitting or surface emitting laser diodes and AC or DC power supply can be used as the light source (2) and the power supply (5), respectively. In other embodiments, the light source (2) can be any type of laser capable of operating in near infrared (NIR) wavelength range from 800 nm to 1000 nm)

The connector assembly (3) includes a plurality of connectors (31 ) and optical waveguides (32) in a cascaded arrangement (as shown in FIG UR E S . 1 and 1A), such that a single input light beam is split into multiple equally split output beams. In an exemplary embodiment, the connectors (31) are multimode interference (MMI) coupler, that is commercially available. A coupler (not shown) is used for coupling the light from the light source (2) into the connector assembly (3). In an exemplary embodiment, the coupler is an edge coupler for coupling an edge-emitter laser diode to the connector assembly. In an alternative embodiment, the coupler can also include but not limited to a grating coupler, taper coupler or butt coupler and any other commercially available coupler. The connector assembly (3) includes‘n’ number of splitting stages to provide‘2ⁿ’ number of output light beams, wherein each stage includes Ί’ number of connectors two generate ‘2G number of output light beams which serve as input beams for the next splitting stage.

Each output light beam from the final splitting stage of the connector assembly (3) is fed to a single row of the cells (4). Furthermore, each cell (4) is connected to the corresponding waveguide (32) of the connector assembly (3) through a resistance circuit (not shown) for controlling phase characteristics of the cell (4).

In an exemplary embodiment, the connector assembly (3) includes three stages of splitting, as shown in FIG UR E S 1 and 1A. The connector assembly (3) includes a first stage optical waveguide (32a) that is coupled between the light source (2) and a first stage connector (31 a) which receives the light beam from the first stage optical waveguide (32a). An output side of the first stage connector (31 a) is coupled to two second stage optical waveguides (32b). Each of the second stage optical waveguides (32b) is coupled to an input side of a second stage connector (31 b) whose output end is coupled to two third stage optical waveguides (32c). Further, each of the third stage optical waveguides (32c) is coupled to an input side of a third stage connector (31 c).

The first stage connector (31 a) splits the received light into two light beams and passes the same through the second stage optical waveguides (32b). S imilarly, the second stage connector (31 b) receives and splits the light beam from each second stage optical waveguides (32b) into two light beams and passes the same through the corresponding third stage optical waveguides (32c). Further, each third stage connector (31 c) receives the light beam from the corresponding third stage optical waveguides (32c) and splits the same into two light beams which are finally passed through two output optical waveguides (32d). Thus, the single light beam from the light source (2) is split into eight light beams after three stages of splitting through the connector assembly (3). In an alternate embodiment, the number of stages of s plitting may vary in accordance with requirement.

FIG UR E 2 shows a diagrammatic cross-sectional view of an optical emitter cell, in accordance with an exemplary embodiment of the present invention. E ach cell (4) includes a substrate (10), at least one cladding layer (20) deposited over the substrate (10), and an emitter layer (30) on top of the cladding layer (20). The substrate (10) is a pure silicon substrate and can also include but not limited to quartz and glass. Further, the cladding layer (20) is a silicon dioxide (S i0₂) layer and the emitter layer (30) is a silicon nitride (S iN) layer or a silicon oxide nitride (S iON) layer. In an alternate embodiment, the cladding layer (20) is made of any dielectric material with a refractive index equal to or lower than that of silicon dioxide (S i0₂).

The emitter layer (30) includes one or more emitting ports (40) through which light exits from the emitter layer (30), as shown in FIG UR E 2. The emitting ports (40) are formed by partially etching a top surface of the emitter layer (30), such that thickness (x) of the emitter layer (30) is greater than thickness (y) of the emitting ports (40). As the emitting ports (40) are formed by partial etching, the light exiting the emitting ports (40) in the upward direction is maximized, and thus the emission efficiency of the cell (4) is improved without increasing power consumption. It is to be noted that the position of the emitting ports (40) and the direction of the light are denoted with reference to an arrangement of the cell (4) and can be varied according to the position of the emitter layer (30) with respect to position of the cladding layer (20) and the substrate (10).

A ratio of the thickness (y) of the emitting ports (40) to the thickness (x) of the emitter layer (30) is in within a range of 1/4 - 3/4, more particularly within a range of 1/3.5 - 1/2. T he thickness (y) of the emitting ports (40) is mainly dependent on a cross-sectional profile of the emitting ports (40). In an exemplary embodiment, the cross-sectional profile of the emitting ports (40) is rectangular, as shown in FIG UR E 2. Flowever, in an alternate embodiment, the cross-sectional profile of the emitting ports (40) can also include but not limited to V-shaped, U-shaped and the like.

FIG UR E 3 shows a diagrammatic cross-sectional view of the light source assembled with the optical waveguide in the device, in accordance with an exemplary embodiment of the present invention. The light source (2) is an edge-emitting (M-V) laser diode with a pair of contact pads (2a) for electrical connection with a power supply (5, in FIG UR E 1 ). The light source (2) is aligned with the first stage optical waveguide (32a), such that the light beam emitted by the light source (2) directly enters the first stage optical waveguide (32a). The first stage optical waveguide (32a) is formed of S iN, and both the light source (2) and the first stage optical waveguide (32a) are supported on an S i0₂ layer which itself is supported on a silicon substrate.

The complete functioning of the device (1) is as follows: The power supply (5) energizes the light source (2) to generate a light beam which is then fed to the first stage optical waveguide (32a) of the connector assembly (3). The light beam enters the connector assembly (3) and gets split through‘n’ number of splitting stages into‘2ⁿ‘ number of split light beams. Each of the split light beam is fed to an output optical waveguide (32d) which is coupled to a plurality of emitter cells (4) forming a row of the array of emitter cells (4). Finally, the light beams exit the array of emitter cells (4) to generate a uniform stripe pattern.

Even though only one light source (2) is used in the above embodiment, multiple light sources can be used in the device (1 ) to generate sequential stripe patterns with different spatial periods to resolve the issue of pattern ambiguity in other embodiments. For example, the device (1) includes an array of emitter cells (4) connected to two light sources (2) through two connecting assemblies (3), as shown in FIG UR E 4. Further, light sources capable of operating in a broad wavelength range from ultraviolet, UV, to Mid Infrared, MIR, can also be used.

Returning to FIG UR E 2, the emitter ports (40) in each emitter cell (4) is formed by partially etching a top surface of the emitter layer (30). This helps in directing the light rays in the upward direction, and thus improving the emitting efficiency of the device (1 ) without increasing power consumption, which enables the device (1 ) to support a broad wavelength range from ultra-violet (UV) to Mid-infrared (Mid-IR), and thus allowing future migration from current 800 to 1000 nm wavelength range to other wavelengths, if needed.

FIG UR E S 5 & 6 show a graphical representation of simulation results for near field emission and far field emission, respectively, in accordance with a n exemplary embodiment of the present invention. S uppose a dot projector containing multiple emitter cells, a light dot array can be formed, wherein each dot is the light emitted by a corresponding emitter cell in the array. Therefore, the present invention allows realizing a light dot array with multiple light dots in the dot projector by using a single laser.

FIG UR E 7 displays a graphical representation of efficiency of the present invention in comparison with that of the conventional emitter cell in the wavelength range from 800 nm to 1000 nm. A higher emission efficiency (>70%) is obtained using the partially etched structure as compared to the conventional single etched emitter cells which only reaches an efficiency around 40%.

It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising",

“including”, and “having” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It is also to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. C hanges may be made in the details, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It is further to be understood that use of the expression “at least” or“at least one” suggests the use of one or more elements, as the use may be in one of the embodiments to achieve one or more of the desired objects or results. While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The scope of the disclosure is determined by the claims that follow. The disclosure is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the disclosure when combined with information and knowledge available to the person having ordinary skill in the art.

Claims

C LAIMS

1. A passive optical emitter cell, comprising:

a substrate (10);

at least one cladding layer (20) deposited over said substrate (10); and an emitter layer (30) on top of said cladding layer (20) for emitting light wherein said emitter layer (30) includes at least one emitting port (40) through which the light exits said emitter layer (30),

wherein said emitting port (40) is formed by partially etching a top surface of said emitter layer (30), wherein thickness (x) of said emitter layer (30) is greater than thickness (y) of said emitting port (40).

2. The cell as claimed in claim 1 , wherein said emitting layer (30) is made of silicon nitride. 3. The cell as claimed in claim 1 , wherein said emitting layer (30) is made of silicon oxide nitride.

4. The cell as claimed in claim 1 , wherein a ratio of thickness (y) of said emitting port (40) to thickness (x) of said emitter layer (30) is within a range of 1/4 - 3/4.

5. The cell as claimed in claim 4, wherein said ratio is within a range of 1/3.5 - 1/2.

6. The cell as claimed in claim 1 , wherein a cross-sectional profile of said emitting port (40) is rectangular in shape.

7. The cell as claimed in claim 1 , wherein said cladding layer (20) is made of silicon dioxide.

8. The cell as claimed in claim 1 , further comprising at least one control circuit for controlling phase characteristics of the light emitted from said emitting port (40).

9. An optoelectronic device, comprising: at least one light source (2) emitting a light beam;

at least one connector assembly (3); and

an array (4) of optical emitter cells (4), wherein each optical emitter cell (4), as claimed in claim 1 , is coupled to said connector assembly (3) for receiving at least a portion of said light beam.

10. The device as claimed in claim 9, wherein that said connector assembly (3) includes at least one connector (31) and a plurality of optical waveguides (32), wherein an input end of each connector (31) is connected to one waveguide (32) and an output end of each connector (31 ) is connected to at least two waveguides

(32), such that a light beam inputted to each connector (31) equally split and outputted at each of the corresponding waveguides (32).

11. The device as claimed in claim 9, further comprising at least one control circuit coupled between at least one optical emitter cell (4) and the corresponding optical waveguide (32) for controlling phase characteristics of said cell (4).

12. The device as claimed in claim 9, wherein said connector assembly (3) includes a coupler for coupling light from said light source (2) into said connector assembly (3).

13. The device as claimed in claim 9, wherein each cell (4) includes an emitting layer (30) with at least one emitting port (40), wherein said emitting layer (30) is made of silicon nitride. 14. The device as claimed in claim 9, wherein a ratio of thickness (y) of said emitting port (40) to thickness of (x) of said emitter layer (30) is within a range of 1/4 - 3/4.

15. The device as claimed in claim 14, wherein said ratio is within a range of 1 /3.5 - 1/2.

16. The device as claimed in claim 13, wherein a cross-sectional profile of said emitting port (40) is rectangular in shape.

17. The device as claimed in claim 9, wherein each cell (4) includes an cladding layer (20) made of silicon dioxide.

18. The device as claimed in claim 9, wherein said light source (2) operates in near infrared, NIR, wavelength range from 800 nm to 1000 nm. 19. The device as claimed in claim 9, wherein said light source (2) operates in a broad wavelength range from ultraviolet, UV, to Mid Infrared, MIR.