Optical device and image forming apparatus

Abstract

To provide an optical device that can simply and effectively attenuate stray light from a waveguide layer.SOLUTION: An optical device comprises: a substrate; a waveguide layer that is formed on the substrate and has optical waveguides for propagating light; a protective layer that is provided to cover the waveguide layer; and groove parts that are provided at positions not dividing the optical waveguides so as to have a depth for dividing the protective layer and the waveguide layers, and have a surface subjected to roughening processing.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Optical devices equipped with optical waveguides are used by connecting them to laser diodes serving as light sources, optical fibers for transmitting communication signals, other optical devices, etc. In such optical devices, stray light leaking from the waveguide layer can prevent the optical device from performing its intended function. Therefore, measures such as providing wall-shaped or columnar wiring electrodes within the optical device to block stray light leaking from the waveguide layer are being put into practical use (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-205373 Summary of the Invention [Problem to be solved by the invention]

[0004] However, embedding wiring electrodes in optical devices to block stray light requires complex processes and costs, so a simpler and more effective method of preventing stray light was needed.

[0005] The present invention has been made to solve such problems, and provides an optical device etc. that can simply and effectively attenuate stray light from a waveguide layer. [Means for solving the problem]

[0006] An optical device according to a first aspect of the present invention comprises a substrate, a waveguide layer formed on the substrate and having an optical waveguide for propagating light, a protective layer provided to cover the waveguide layer, and a groove portion having a roughened surface, the groove portion being provided at a position that does not separate the optical waveguide and having a depth that separates the protective layer and the waveguide layer.

[0007] An image forming apparatus according to a second aspect of the present invention employs the above optical device. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an optical device or the like that can easily and effectively attenuate stray light from a waveguide layer. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating the configuration of a projector that employs a light source unit including an optical device according to an embodiment of the present invention. [Figure 2] 3A and 3B are a plan view and a front view of a light source unit. [Figure 3] FIG. 2 is a cross-sectional view of the groove portion according to the first embodiment taken along the line XX. [Figure 4] FIG. 2 is a cross-sectional view of a groove portion according to a second embodiment taken along the line XX. [Figure 5] FIG. 10 is a partial perspective view of a groove portion according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiments of the present invention will be described with reference to the accompanying drawings. In each drawing, components with the same reference numerals have the same or similar configurations. Furthermore, when multiple structures with the same or similar configurations exist in each drawing, some may be referenced with the same reference numerals and others may not be referenced with the same reference numerals to avoid complication. Note that the invention according to the claims is not limited to the following embodiments. Furthermore, not all of the configurations described in the embodiments are necessarily essential as means for solving the problem.

[0011] 1 is a schematic diagram illustrating the configuration of a projector 30 employing a light source unit 10 including an optical device 100 according to this embodiment. The projector 30 reflects projection light emitted from the light source unit 10 by changing its direction over time using a MEMS (Micro Electro Mechanical Systems) mirror and scans the light across the screen 40, thereby projecting an image onto the screen 40. The projector 30 is one form of an image forming apparatus.

[0012] The light source unit 10 is mainly composed of an optical device 100 and a light-emitting device 200. The light-emitting device 200 is composed of three modules: a red light-emitting module 210, a green light-emitting module 220, and a blue light-emitting module 230. As will be described later, these are bonded to and integrated with the end face of the optical device 100, but in the drawing, each is depicted spaced apart from the end face of the optical device 100.

[0013] The optical device 100 has a rectangular parallelepiped shape as a whole, and in the drawings, the short side direction of the planar 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 planar direction is defined as the Z-axis direction. Note that in the subsequent drawings, similar coordinate axes based on the state in which the optical device 100 is installed as in Figure 1 are also included to indicate the orientation of the structure depicted in each drawing.

[0014] The optical device 100 has a waveguide layer 150 parallel to the XY plane. The waveguide layer 150 is formed of an electro-optic material such as a lithium niobate film, and a portion of the waveguide layer 150 is partially removed by etching or the like, leaving a ridge portion that is convex in cross section. The ridge portion functions as an optical waveguide that transmits light, and 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.

[0015] The first optical waveguide 110 is continuous in a straight line or a gentle curve from a first incident end face 111 exposed on one side of the optical device 100 to an exit end face 112 exposed on the opposite side of the optical device 100. That is, light incident on the first incident end face 111 travels through the first optical waveguide 110 and is emitted from the exit end face 112.

[0016] The second optical waveguide 120 continues in a straight line or a gentle curve from the second incident end face 121 exposed on one side of the optical device 100 where the first incident end face 111 is provided, to the point where it joins the middle part of the first optical waveguide 110. That is, light incident on the second incident end face 121 travels through the second optical waveguide 120, joins the first optical waveguide 110 midway, and is emitted from the exit end face 112.

[0017] The third optical waveguide 130 continues in a straight line or a gentle curve from the third incident end face 131 exposed on one side of the optical device 100 where the first incident end face 111 is provided, to the point where it joins the middle part of the first optical waveguide 110. That is, light incident on the third incident end face 131 travels through the third optical waveguide 130, joins the first optical waveguide 110 midway, and is emitted from the exit end face 112.

[0018] The configuration of the three optical waveguides is not limited to the above example, and may be any configuration in which each optical waveguide has an incident end face and joins along the way to form a common exit end face. Alternatively, the three optical waveguides may branch downstream from the joining point to form two or more exit end faces.

[0019] Red light emitting module 210 is mainly composed of red laser diode 211 and first carrier 212 that supports it. Red laser diode 211 is fixed to first carrier 212. Red laser light emitted from red laser diode 211 is incident on first incident end surface 111 of first optical waveguide 110.

[0020] Green light emitting module 220 is mainly composed of green laser diode 221 and second carrier 222 that supports it. Green laser diode 221 is fixed to second carrier 222. Green laser light emitted from green laser diode 221 is incident on second incident end surface 121 of second optical waveguide 120.

[0021] Blue light emitting module 230 is mainly composed of blue laser diode 231 and third carrier 232 that supports it. Blue laser diode 231 is fixed to third carrier 232. Blue laser light emitted from blue laser diode 231 is incident on third incident end surface 131 of third optical waveguide 130.

[0022] As described above, the second optical waveguide 120 and the third optical waveguide 130 merge into the first optical waveguide 110, so when multiple laser diodes emit light simultaneously, a mixture of these lights is emitted from the emission end face 112. More specifically, by controlling the emission intensities of the red laser diode 211, the green laser diode 221, and the blue laser diode 231, it is possible to emit light of any desired color from the emission end face 112.

[0023] The optical device 100 includes grooves 140 for blocking stray light propagating through the waveguide layer 150 at positions that do not divide the optical waveguides. As shown in the figure, the grooves 140 are provided along curved portions of the optical waveguides (e.g., curved portion 130a of the third optical waveguide 130) or near the output end surface 112. That is, the grooves 140 are preferably provided near locations along the optical waveguide path where stray light is likely to occur or where the effect of stray light on output light is likely to be significant. The grooves 140 are provided in one or more locations depending on the configuration of the optical waveguides, the performance required of the optical device 100, and the like.

[0024] 2A and 2B are a plan view (FIG. 2A) and a front view (FIG. 2B) of the light source unit 10. As shown in the front view, the optical device 100 includes a substrate 160, a waveguide layer 150 laminated on the substrate 160, and a protective layer 170 covering the waveguide layer. The substrate 160 may be, for example, a Si substrate or a sapphire substrate. The protective layer 170 may be, for example, silicon dioxide (SiO2). The protective layer 170 may be a buffer layer made of a material such as alumina (Al2O3). Alternatively, the protective layer 170 may be a cladding layer made of a material such as yttrium oxide (YO3). As shown in the plan view, in this embodiment, the grooves 140 are provided at multiple locations on the protective layer 170 side. While each groove 140 is linear in this embodiment, it may also be curved along the path of the optical waveguide, or may have a bent shape such as an L-shape.

[0025] Each light emitting module (red light emitting module 210, green light emitting module 220, blue light emitting module 230) is integrated with the optical device 100 by bonding the respective carriers (first carrier 212, second carrier 222, third carrier 232) to the substrate 160. Note that one side of the optical device 100 to which each light emitting module is bonded may be coated with an anti-reflection film and an SAC coating, and the opposite side to which the emission end surface 112 is provided may be coated with an anti-reflection film. Furthermore, the bonding surface of each carrier to the substrate 160 may be coated with Au.

[0026] 3 is a cross-sectional view taken along line XX of a groove 140 as a first example of this embodiment. As shown in the figure, the groove 140 has a bottom surface 141 and two side surfaces (a first side surface 142 and a second side surface 143), and in its cross section forms a substantially U-shape that is open in the positive direction of the Z axis. The first side surface 142 is the side surface on which an optical waveguide (third optical waveguide 130 in the illustrated example) is provided, and the second side surface is the side surface on which no optical waveguide is provided.

[0027] The groove 140 is provided to attenuate stray light propagating through the waveguide layer 150, and therefore has a depth sufficient to penetrate the protective layer 170 and the waveguide layer 150 and reach the substrate 160. In particular, in this embodiment, the surfaces of the groove 140 (bottom surface 141, first side surface 142, second side surface 143) are roughened so that stray light leaking from the waveguide layer 150 into the space within the groove 140 is appropriately scattered by the surfaces of the groove 140. Note that the groove 140 does not need to be dug all the way to the substrate 160, and may have a depth sufficient to separate the protective layer 170 and the waveguide layer 150 so that the flat surface of the substrate 160 is exposed as the bottom surface 141.

[0028] The surface of the groove 140 is roughened by irradiating the surface with argon (Ar) gas or xenon (Xe) gas using, for example, a milling device after the groove is formed. Considering the wavelength of light incident on the optical waveguide, the arithmetic mean roughness (Ra) of the surface of the groove 140 is preferably 5 nm or more and less than 15 nm. It has been experimentally confirmed that, to achieve such Ra, when using argon gas in the above-mentioned milling device, the beam voltage may be adjusted in the range of 250 V to 450 V.

[0029] With the groove 140 having such a 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 scattered well and further attenuated by repeated scattering. Alternatively, the stray light is emitted into the open space above. Therefore, it is expected that the stray light will be prevented from returning to the optical waveguide as returned light or from propagating through the waveguide layer 150 to the output end surface 112. In particular, in applications where laser light of various colors is mixed in the optical waveguide to emit light of a desired color, as in this embodiment, it is expected that the color balance will be prevented from being impaired by stray light.

[0030] To further enhance this effect, it is preferable that the Ra of the two side surfaces (first side surface 142 and second side surface 143) intersecting with the waveguide layer 150 is greater than the Ra of the bottom surface 141 parallel to the waveguide layer 150. With this configuration, it is expected that more stray light will be scattered by the side surfaces and released into the open space. In order to release more stray light into the open space, it is also preferable that the space within the groove portion 140 is not filled with another medium, and that each surface is in contact with the atmosphere.

[0031] Furthermore, as shown in the figure, if multiple grooves 140 are provided in succession (three in the example shown), even if some stray light enters the waveguide layer 150 beyond, it is expected that the stray light will be scattered again within the space between the continuous grooves 140, and therefore it is expected that the stray light will be significantly reduced. Note that all of the continuous grooves 140 may have the same configuration, but they may also have different configurations.

[0032] FIG. 4 is a cross-sectional view of a groove portion 140 according to a second example of this embodiment, taken along the line XX. The surface of the groove portion 140 according to the second example is also roughened. In the groove portion 140 according to the second example, the inclination angles of the first side surface 142 and the second side surface 143 are different. More specifically, the angle (indicated by θ in the figure) between the second side surface 143 and the surface direction of the waveguide layer 150 is smaller than the angle between the first side surface 142 and the surface direction of the waveguide layer 150. This configuration allows most of the stray light that propagates from the optical waveguide through the waveguide layer 150 and leaks into the space within the groove portion 140 to reach the second side surface 143, where it is scattered and guided to the open space. This means that stray light can be more efficiently diffused. In this case, θ is preferably adjusted to be greater than or equal to 30° and less than 60°. In the example of FIG. 4, the second side surface 143 is more inclined, but the angle that the first side surface 142 makes with respect to the surface direction of the waveguide layer 150 may also be adjusted to be equal to or greater than 30° and less than 60°.

[0033] 5 is a partial cross-sectional perspective view of a groove portion 140 as a third example of this embodiment. The surface of the groove portion 140 as the third example is also roughened. The groove portion 140 as the third example has ridge portions 142a and 143a that are continuous along the depth direction on the first side surface 142 and the second side surface 143. With the groove portion 140 having such a structure, stray light that leaks from the waveguide layer 150 into the space within the groove portion 140 is reflected and scattered more in a direction parallel to the surface direction of the waveguide layer 150, and is therefore expected to be repeatedly reflected and scattered by the ridge portions 142a and 143a, resulting in stepwise attenuation.

[0034] In all of the examples of the present embodiment described above, groove portion 140 has a bottom surface 141 and two side surfaces (first side surface 142 and second side surface 143) and has a substantially U-shaped cross section, but it may also have a substantially V-shaped cross section without bottom surface 141. By adopting a V-shaped configuration, the width of each groove can be narrowed, and therefore the number of groove portions 140 that can be formed in one location can be increased.

[0035] Furthermore, in the above-described embodiment, the optical device 100 is described as mixing RGB primary color laser beams in an optical waveguide to emit light of any desired target color. However, application examples of optical devices are not limited to so-called RGB couplers. Optical devices used for other purposes may include only one light-emitting module, and in that case, the optical waveguide may be formed as a single path. Similarly, even when multiple light-emitting modules are joined, the number is not limited to three, and may be two, four, or more. In this case, multiple input end faces corresponding to the number of light-emitting modules may be formed together with the optical waveguide, and these may merge into a single waveguide, or they may have independent output end faces. [Explanation of symbols]

[0036] 10...light source unit, 20...MEMS mirror, 30...projector, 40...screen, 100...optical device, 110...first optical waveguide, 111...first incident end face, 112...exit end face, 120...second optical waveguide, 121...second incident end face, 130...third optical waveguide, 130a...curved portion, 131...third incident end face, 140...groove portion, 141...bottom surface, 142...first side surface, 143a...ridge portion, 143 ...second side surface, 143a...ridge portion, 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. A substrate; a waveguide layer formed on the substrate and having an optical waveguide for propagating light; a protective layer provided to cover the waveguide layer; a groove portion having a depth sufficient to separate the protective layer and the waveguide layer at a position that does not separate the optical waveguide, the groove portion having a roughened surface; An optical device comprising:

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

3. 2. The optical device according to claim 1, wherein at least one of the two side surfaces of the surface that intersect with the waveguide layer is an inclined side surface that forms an angle of 30 degrees or more and less than 60 degrees with respect to the surface direction of the waveguide layer.

4. 4. The optical device according to claim 3, wherein the inclined side of the two side surfaces is a side surface that intersects with the waveguide layer on a side where the optical waveguide is not provided.

5. 2. The optical device according to claim 1, wherein the arithmetic mean roughness (Ra) of two side surfaces of the surface that intersect with the waveguide layer is greater than the arithmetic mean roughness (Ra) of a bottom surface that is parallel to the waveguide layer.

6. 2. The method according to claim 1, wherein the arithmetic mean roughness (Ra) of the surface is 5 nm or more and less than 15 nm. Optical devices.

7. 2. The optical device according to claim 1, wherein two side surfaces of the surface that intersect with the waveguide layer are provided with ridges that are continuous along the depth direction of the grooves.

8. The optical device of claim 1 , wherein the surface is in contact with the atmosphere.

9. 9. The optical device according to claim 1, wherein the optical waveguide has three input waveguides and one output waveguide where the three input waveguides are joined together.

10. An image forming apparatus employing the optical device according to claim 9.

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