Optical device and image forming apparatus

Abstract

The present disclosure provides an optical device and the like capable of simply and effectively attenuating stray light from a waveguide layer. The optical device includes: a substrate; a waveguide layer that is formed on the substrate and has an optical waveguide that propagates light; a protective layer provided on the waveguide layer; and a groove extending from the protective layer to the waveguide layer, the groove including a first side surface and a second side surface facing the first side surface, the first side surface and the second side surface exposing end surfaces of the waveguide layer and the protective layer, and the second side surface having a rough surface.

Description

Technical Field

[0001] The present invention relates to an optical device and an image forming apparatus. Background Art

[0002] Optical devices equipped with optical waveguides are connected to laser diodes serving as light sources, optical fibers that transmit communication signals, and other optical devices. In such optical devices, stray light leaking from the waveguide layer can hinder the intended function of the device. Therefore, a common countermeasure to prevent stray light from leaking from the waveguide layer is to provide wall-shaped or columnar wiring electrodes within the optical device (see, for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-205373 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] However, embedding wiring electrodes in optical devices to cut off stray light requires complex processes and costs, and therefore, a simpler and more effective countermeasure against stray light is needed.

[0008] The present disclosure has been made to solve such a problem, and provides an optical device and the like that can simply and effectively attenuate stray light from a waveguide layer.

[0009] Technical solutions to solve problems

[0010] A first aspect of the present invention provides an optical device comprising: a substrate; a waveguide layer formed on the substrate and having an optical waveguide for propagating light; a protective layer provided on the waveguide layer; and a groove extending from the protective layer to the waveguide layer, wherein the groove includes a first side surface and a second side surface opposite to the first side surface, the first side surface and the second side surface exposing end faces of the waveguide layer and the protective layer, and the second side surface has a rough surface.

[0011] Furthermore, a second aspect of the present invention provides an image forming apparatus using the above-mentioned optical device.

[0012] Effects of the Invention

[0013] According to the present invention, it is possible to provide an optical device or the like that can simply and effectively attenuate stray light from a waveguide layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1This is a schematic diagram for explaining the structure of a projector using a light source unit including the optical device according to the present embodiment.

[0015] Figure 2 These are the top view and front view of the light source unit.

[0016] Figure 3 It is a XX cross-sectional view of the groove of the first embodiment.

[0017] Figure 4 It is a XX cross-sectional view of the groove of the second embodiment.

[0018] Figure 5 It is a partial perspective view of the groove of the third embodiment. DETAILED DESCRIPTION

[0019] The embodiments of the present invention are described with reference to the accompanying drawings. In the various figures, portions labeled with the same reference numerals have the same or similar structures. Furthermore, in the various figures, when there are multiple structures having the same or similar structures, sometimes only a portion may be labeled with reference numerals, while the other portions may be omitted from the labeling with the same reference numerals to avoid complexity. Furthermore, the invention described in the claims is not limited to the following embodiments. Furthermore, not all of the structures described in the embodiments are essential for the technical solution to the problem.

[0020] Figure 1 This is a schematic diagram illustrating the structure of a projector 30 that uses a light source unit 10 including an optical device 100 according to this embodiment. Projector 30 uses a MEMS (Micro Electro Mechanical Systems) mirror to reflect and redirect projection light emitted from light source unit 10 over time, scanning the light onto a screen 40 to project an image. Projector 30 is one form of image forming device.

[0021] The light source unit 10 mainly comprises an optical device 100 and a light-emitting device 200. The light-emitting device 200 comprises three components: a red light-emitting module 210, a green light-emitting module 220, and a blue light-emitting module 230. As described later, these components are joined to the end faces of the optical device 100 to form an integral unit. However, in the figures, they are depicted separately from the end faces of the optical device 100.

[0022] The optical device 100 is in the shape of a rectangular parallelepiped. In the figure, the short side direction in the plane direction is defined as the X-axis direction, the long side direction is defined as the Y-axis direction, and the height direction perpendicular to the plane direction is defined as the Z-axis direction. Figure 1 The illustrated method uses the state of the optical device 100 as a reference, and describes the same coordinate axes to indicate the directions of the structures shown in the various figures.

[0023] Optical device 100 includes a waveguide layer 150 parallel to the XY plane. Waveguide layer 150 is formed from an electro-optical material such as a lithium niobate film. A portion of the waveguide layer is partially removed by etching, leaving a ridge that forms a convex shape in the cross section. The ridge acts as an optical waveguide for light to pass through. In this embodiment, three optical waveguides—a first optical waveguide 110, a second optical waveguide 120, and a third optical waveguide 130—are formed on the waveguide layer. Specifically, the optical waveguide layer includes three input waveguides and an output waveguide formed by the confluence of these three input waveguides.

[0024] The first optical waveguide 110 extends in a straight line or a gently curved line from a first incident end face 111 exposed on one side of the optical device 100 to an emission end face 112 exposed on the opposite side of the optical device 100. In other words, light incident on the first incident end face 111 travels through the first optical waveguide 110 and is emitted from the emission end face 112.

[0025] The second optical waveguide 120 extends in a straight line or gently curved line from the second incident end face 121 exposed on one side surface of the optical device 100 provided with the first incident end face 111 to a midpoint where it merges with the first optical waveguide 110. In other words, light incident on the second incident end face 121 travels through the second optical waveguide 120, merges with the first optical waveguide 110 midway, and is emitted from the emission end face 112.

[0026] The third optical waveguide 130 extends in a straight line or gently curved line from the third incident end face 131, which is exposed on one side surface of the optical device 100 provided with the first incident end face 111, to a position where it merges with the middle portion of the first optical waveguide 110. In other words, light incident on the third incident end face 131 travels through the third optical waveguide 130, merges with the first optical waveguide 110 midway, and is emitted from the emission end face 112.

[0027] The three optical waveguide configuration is not limited to the above example; any configuration may be employed in which each optical waveguide has an incident end face, merges midway along the path, and has a common exit end face. Alternatively, a configuration may be employed in which the three optical waveguides branch downstream of the merged location to have two or more exit end faces.

[0028] The red light emitting module 210 mainly comprises a red laser diode 211 and a first carrier 212 supporting the red laser diode 211. The red laser diode 211 is fixed to the first carrier 212. The red laser light emitted from the red laser diode 211 is incident on the first incident end face 111 of the first optical waveguide 110.

[0029] The green light emitting module 220 mainly comprises a green laser diode 221 and a second carrier 222 supporting the green laser diode 221. The green laser diode 221 is fixed to the second carrier 222. The green laser light emitted from the green laser diode 221 is incident on the second incident end face 121 of the second optical waveguide 120.

[0030] The blue light emitting module 230 mainly comprises a blue laser diode 231 and a third carrier 232 supporting the blue laser diode 231. The blue laser diode 231 is fixed to the third carrier 232. The blue laser light emitted from the blue laser diode 231 is incident on the third incident end face 131 of the third optical waveguide 130.

[0031] As described above, second optical waveguide 120 and third optical waveguide 130 merge into first optical waveguide 110. Therefore, when multiple laser diodes emit light simultaneously, mixed light from these laser diodes is emitted from emission end face 112. More specifically, when the red laser diode 211, green laser diode 221, and blue laser diode 231 are individually controlled in their emission intensities and caused to emit light, light of any desired color can be emitted from emission end face 112.

[0032] The optical device 100 includes a groove 140 extending from the protective layer 170 to the waveguide layer 150 (see Figure 3 The groove 140 includes a first side surface 142 and a second side surface 143 opposite to the first side surface 142. The first side surface 142 and the second side surface 143 expose the end surfaces of the waveguide layer 150 and the protective layer 170 (see Figure 3 ). In addition, the second side surface 143 has a rough surface.

[0033] Alternatively, grooves 140 for cutting off stray light propagating through the waveguide layer 150 may be provided at locations that do not divide the optical waveguides. As shown in the figure, grooves 140 may be provided along a curved portion of the optical waveguide (e.g., curved portion 130a of the third optical waveguide 130) or near the emission end face 112. Specifically, grooves 140 are preferably provided near locations along the optical waveguide path where stray light is expected to be more likely to be generated, or near locations where stray light is expected to have a significant impact on emitted light. Grooves 140 may be provided at one or more locations depending on the structure of the optical waveguide, the performance required of the optical device 100, and other factors.

[0034] Figure 2 is a top view of the light source unit 10 ( Figure 2 (A)) and main view ( Figure 2(B)). As shown in the main view, the optical device 100 has a substrate 160, a waveguide layer 150 stacked on the substrate 160, and a protective layer 170 covering the waveguide layer. As the substrate 160, for example, a Si substrate or a sapphire substrate can be used. As the protective layer 170, for example, silicon dioxide (SiO2) can be used. The protective layer 170 can also be set as follows: for example, a buffer layer using a raw material such as aluminum oxide (Al2O3); or, for example, a cladding layer (Cladding Layer) using a raw material such as yttrium oxide (Y2O3). As shown in the top view, in this embodiment, the grooves 140 are provided at multiple locations on the side of the protective layer 170. In this embodiment, each groove 140 is a straight line shape, however, it can also be a curved shape, for example, along the path of the optical waveguide, or it can also be a curved shape such as an L shape.

[0035] Each light-emitting module (red light-emitting module 210, green light-emitting module 220, blue light-emitting module 230) is bonded to substrate 160 via its respective carrier (first carrier 212, second carrier 222, third carrier 232), thereby forming an integral part of optical device 100. Furthermore, an anti-reflection film and a SAC coating may be applied to the side of optical device 100 that is bonded to each light-emitting module, and an anti-reflection film may be applied to the side opposite to the side where emission end face 112 is provided. Furthermore, an Au coating may be applied to the surface of each carrier that is bonded to substrate 160.

[0036] Figure 3 This is an X-X cross-sectional view of groove 140 in the first example of this embodiment. As shown, groove 140 has two side surfaces (a first side surface 142 and a second side surface 143), and may also have a bottom surface 141 connecting first side surface 142 and second side surface 143. For example, the cross-section of groove 140 may be a roughly U-shaped shape open in the Z-axis plus direction. First side surface 142 is the side on which the optical waveguide (in the example, third optical waveguide 130) is provided, while the second side surface is the side on which the optical waveguide is not provided.

[0037] Grooves 140 are provided to attenuate stray light propagating through waveguide layer 150. Therefore, they have a depth sufficient to penetrate protective layer 170 and waveguide layer 150 and reach substrate 160. In particular, in this embodiment, the surface of groove 140 is roughened to appropriately scatter stray light that leaks from waveguide layer 150 into the space within groove 140 on the surfaces (bottom surface 141, first side surface 142, and second side surface 143) of groove 140. Furthermore, groove 140 need not be excavated to reach substrate 160; for example, the depth may be sufficient to separate protective layer 170 and waveguide layer 150 so that the flat surface of substrate 160 is exposed as bottom surface 141.

[0038] The rough surface processing of the surface of the groove 140 is achieved as follows: after the groove is formed, the surface is irradiated with argon (Ar) gas or xenon (Xe) gas using, for example, a milling device. Taking into account the wavelength of light incident on the light waveguide, the arithmetic mean roughness (Ra) of the surface of the groove 140 is preferably greater than 5nm and less than 15nm. In particular, the arithmetic mean roughness (Ra) of the rough surface of the second side 143 is preferably greater than 5nm and less than 15nm. In order to achieve such Ra, for example, when using argon gas in the above-mentioned milling device, it has been confirmed through experiments that it is sufficient to adjust the electron beam voltage within the range of 250V to 450V.

[0039] With the groove 140 having this structure, stray light leaking from the waveguide layer 150 into the space within the groove 140 reaches the bottom surface 141, the first side surface 142, and the second side surface 143, where it is effectively scattered and then repeatedly scattered, thereby attenuating. Alternatively, it is released into the open space above. Therefore, it is expected that stray light will be prevented from returning to the optical waveguide as return light, or from propagating through the waveguide layer 150 and reaching the emission end face 112. In particular, in applications where laser light of various colors is mixed in the optical waveguide and light of a desired color is emitted, as described in this embodiment, it is expected that the color balance may be prevented from being disturbed by stray light.

[0040] To further enhance this effect, the Ra of the two side surfaces (first side surface 142 and second side surface 143) intersecting the waveguide layer 150 is preferably greater than the Ra of the bottom surface 141 parallel to the waveguide layer 150. In particular, the arithmetic mean roughness (Ra) of the second surface 143 is preferably greater than the arithmetic mean roughness (Ra) of the bottom surface 141. With this structure, it is expected that more stray light will be scattered laterally and released into the open space. Furthermore, to release more stray light into the open space, it is preferable that each surface is exposed to the atmosphere rather than filling the space within the groove 140 with other media. In other words, it is preferable that each surface is exposed to the atmosphere.

[0041] Furthermore, as shown in the figure, if a plurality of grooves 140 (three in the example) are provided continuously, even if some stray light enters the waveguide layer 150 in front of the groove, it can be expected that the stray light will be rescattered within the space of the continuous groove 140, thereby significantly reducing the stray light. Furthermore, all of the continuous grooves 140 may have the same structure, or they may have different structures.

[0042] Figure 4It is an X-X cross-sectional view of the groove 140 of the second embodiment in this embodiment. The surface of the groove 140 of the second embodiment is also roughened. In the groove 140 of the second embodiment, the inclination angle of the second side surface 143 is different from that of the first side surface 142. More specifically, the angle formed by the second side surface 143 and the surface direction of the waveguide layer 150 (indicated by θ in the figure) is smaller than the angle formed by the surface direction of the first side surface 142 and the waveguide layer 150. With such a structure, most of the stray light that leaks from the optical waveguide through the waveguide layer 150 to the space inside the groove 140 reaches the second side surface 143 and is scattered and guided to the open space. That is, it can be expected to diffuse the stray light more effectively. At this time, θ is preferably adjusted to be greater than 30° and less than 60°. In addition, although in Figure 4 In the example, the second side surface 143 is further inclined. However, the angle formed by the first side surface 142 and the plane direction of the waveguide layer 150 may be adjusted to be greater than 30° and less than 60°.

[0043] From this point of view, the first side surface 142 is preferably located closer to the optical waveguide than the second side surface 143. For example, when the groove 140 is formed along the optical waveguide, the first side surface 142 may be located on the optical waveguide side.

[0044] Figure 5 This is a partial cross-sectional perspective view of the groove 140 of the third embodiment in this embodiment. The surface of the groove 140 of the third embodiment is also roughened. The groove 140 of the third embodiment may also have ridges 142a and 143a extending in the depth direction on the first side surface 142 and the second side surface 143. Figure 5 In the embodiment, a plurality of ridges 142a and 143a are arranged side by side along the surfaces of the first side surface 142 and the second side surface 143. With the groove 140 having such a structure, stray light leaking from the waveguide layer 150 into the space within the groove 140 is reflected and scattered more in a direction parallel to the surface direction of the waveguide layer 150. Therefore, it can be expected that the stray light will be repeatedly reflected and scattered by the ridges 142a and 143a, and gradually attenuated.

[0045] The groove 140 of the present embodiment described above has a substantially U-shaped cross section having a bottom surface 141 and two side surfaces (a first side surface 142 and a second side surface 143) in all embodiments. However, a substantially V-shaped cross section may be employed without the bottom surface 141. A V-shaped structure can reduce the width of one groove, thereby increasing the number of grooves 140 that can be formed in one location.

[0046] In the embodiment described above, an optical device 100 is described that mixes RGB primary laser light within an optical waveguide and emits light of a desired color. However, the application example of the optical device is not limited to this so-called RGB coupler. In optical devices for other purposes, a single light-emitting module may be used, and in this case, the optical waveguide only needs to be formed by a single path. Similarly, even when multiple light-emitting modules are joined, the number is not limited to three and can be two or four or more. In this case, multiple input end faces corresponding to the number of light-emitting modules are formed together with the optical waveguide. These modules may merge into a single waveguide or have independent output end faces.

[0047] Description of Reference Numerals

[0048] 10: Light source unit, 20: MEMS mirror, 30: Projector, 40: Screen, 100: Optical device, 110: First optical waveguide, 111: First incident end face, 112: Emission end face, 120: Second optical waveguide, 121: Second incident end face, 130: Third optical waveguide, 130a: Bend, 131: Third incident end face, 140: Groove, 141: Bottom face, 142: First side face, 142a: Ridge, 143: Second side, 143a: Ridge, 150: Waveguide layer, 160: Substrate, 170: Protective layer, 200: Light-emitting device, 210: Red light-emitting module, 211: Red laser diode, 212: First carrier, 220: Green light-emitting module, 221: Green laser diode, 222: Second carrier, 230: Blue light-emitting module, 231: Blue laser diode, 232: Third carrier.

Claims

1. An optical device, wherein: have: substrate; a waveguide layer formed on the substrate and having an optical waveguide for propagating light; a protective layer disposed on the waveguide layer; as well as a groove extending from the protective layer to the waveguide layer, The groove comprises a first side and a second side opposite to the first side, The first side surface and the second side surface expose the end surfaces of the waveguide layer and the protective layer. The second side surface has a rough surface.

2. The optical device according to claim 1, wherein The optical waveguide has a bent portion, The groove is provided along the curved portion.

3. The optical device according to claim 1, wherein At least one of the first side surface or the second side surface forms an angle of 30° or more and less than 60° with the plane direction of the waveguide layer. The optical device according to claim 1 , wherein: The first side surface is closer to the optical waveguide than the second side surface. The optical device according to claim 1 , wherein: The groove further has a bottom surface connecting the first side surface and the second side surface, The arithmetic mean roughness Ra of the second side surface is greater than the arithmetic mean roughness Ra of the bottom surface. The optical device according to claim 1 , wherein: The rough surface has an arithmetic mean roughness Ra of 5 nm or more and less than 15 nm.

7. The optical device according to claim 1, wherein The first side surface and the second side surface have ridge portions extending in the depth direction of the groove. The optical device according to claim 1 , wherein: The first side surface and the second side surface are exposed to the atmosphere.

9. The optical device according to claim 1, wherein The optical waveguide includes three input waveguides and an output waveguide formed by merging the three input waveguides.

10. An image forming apparatus, wherein: This image forming apparatus uses the optical device according to claim 9.

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