Optical device and image forming apparatus

Abstract

To provide an optical device capable of causing light emitted from a laser diode to be stably incident on an optical waveguide.SOLUTION: An optical device comprises: a waveguide module including a base layer, a cover layer, and a waveguide layer that is formed between the base layer and the cover layer, and has an optical waveguide in which an incident end surface on which a laser beam to be propagated is incident is processed into a curved surface; and a light-emitting module including a laser diode that emits the laser beam and a carrier that supports the laser diode such that an emission surface of the laser beam is arranged to face the incident end surface and be spaced apart from the incident end surface, the carrier being joined to the base layer of the waveguide module and integrated with the waveguide module.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 provided with optical waveguides are used by connecting them to laser diodes that serve as light sources, optical fibers that propagate communication signals, other optical devices, etc. For example, when connecting the end faces of two optical waveguides, an organic adhesive is used (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-142441 Summary of the Invention [Problem to be solved by the invention]

[0004] A portion of traveling light is reflected between different materials. Therefore, when connecting the end faces of optical waveguides with organic adhesive, a lot of reflected light occurs at the interface. It has been found that the occurrence of such reflected light can cause instability, such as wavelength fluctuation, when the output light from a laser diode is guided into an optical waveguide.

[0005] The present invention has been made to solve such problems, and provides an optical device or the like that can stably input light emitted from a laser diode into an optical waveguide. [Means for solving the problem]

[0006] An optical device in a first aspect of the present invention comprises a waveguide module including a base layer, a cover layer, and a waveguide layer formed between the base layer and the cover layer, the waveguide layer having an optical waveguide having an incident end face processed into a curved surface for receiving laser light to be propagated; and a light-emitting module having a laser diode that emits laser light and a carrier that supports the laser diode so that the laser light emission face is positioned opposite to and spaced apart from the incident end face, the carrier being bonded to the base layer of the waveguide module to be integrated with the waveguide module.

[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 stably input light emitted from a laser diode into an optical waveguide. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a projector that employs an optical device according to an embodiment of the present invention. [Figure 2] 1A and 1B are plan and front views of an optical device; [Figure 3] FIG. XX is a cross-sectional view of the first embodiment. [Figure 4] FIG. 2 is a cross-sectional view taken along line XX according to a second embodiment. [Figure 5] FIG. 10 is a partial perspective view of a waveguide module 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. 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 problems.

[0011] 1 is a schematic diagram illustrating the configuration of a projector 30 that employs an optical device 10 according to this embodiment. The projector 30 reflects projection light emitted from the optical device 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.

[0012] The optical device 10 is mainly composed of a waveguide module 100 and a light-emitting module 200. In this embodiment, the light-emitting module 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 waveguide module 100, but in the figure, each is depicted spaced apart from the end face of the waveguide module 100.

[0013] The waveguide module 100 has a rectangular parallelepiped shape as a whole, and in the drawings, the short side direction among the planar directions 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 waveguide module 100 is installed as in Figure 1 are also included to indicate the orientation of the structure depicted in each drawing.

[0014] The waveguide module 100 has a waveguide layer 150 parallel to the XY plane. The waveguide layer 150 is formed of an electro-optical 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 propagates laser 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 as part of 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 waveguide module 100 to an exit end face 112 exposed on the opposite side of the waveguide module 100. That is, the laser light incident on the first incident end face 111 propagates 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 a second incident end face 121 exposed on one side of the waveguide module 100 where the first incident end face 111 is provided, to where it joins the middle part of the first optical waveguide 110. That is, the laser light incident on the second incident end face 121 propagates 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 a third incident end face 131 exposed on one side of the waveguide module 100 where the first incident end face 111 is provided, to where it joins the intermediate portion of the first optical waveguide 110. That is, the laser light incident on the third incident end face 131 propagates 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, the details of which will be described later, is fixed at a predetermined position on 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, the details of which will be described later, is fixed at a predetermined position on 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 at a predetermined position on third carrier 232, as will be described in detail later. Blue laser light emitted from blue laser diode 231 is incident on third incident end surface 131 of third optical waveguide 130. The positional relationship of the light-emitting modules of each color with respect to each optical waveguide is not limited to the above and can be any. For example, red light-emitting module 210 may be arranged to correspond to third optical waveguide 130, and blue light-emitting module 230 may be arranged to correspond to first optical waveguide 110.

[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] 2A and 2B are a plan view and a front view, respectively, of the optical device 10. As shown in the front view, the waveguide module 100 includes a substrate 160 as a base layer, a waveguide layer 150 laminated on the substrate 160, and a buffer layer 170 as a cover layer covering the waveguide layer. The substrate 160 may be, for example, a silicon substrate or a sapphire substrate. The buffer layer 170 is formed of a highly transparent material with a refractive index lower than that of the waveguide layer 150, such as alumina (Al2O3). In this embodiment, the buffer layer 170 fills the space removed from the waveguide layer 150 by etching or other processes to form the optical waveguide. Alternatively, this space may be filled with a protective layer made of, for example, silicon dioxide (SiO2). Although the substrate 160 and the buffer layer 170 are used as the base layer and the cover layer, respectively, in this embodiment, at least one of them may be replaced with a cladding layer or may be configured together with a cladding layer. The cladding layer is formed of a material having a refractive index lower than that of the waveguide layer 150, such as yttrium oxide (Y2O3).

[0024] Each light emitting module (red light emitting module 210, green light emitting module 220, blue light emitting module 230) is integrated with the waveguide module 100 by bonding its respective carrier (first carrier 212, second carrier 222, third carrier 232) to the substrate 160. Note that one side of the waveguide module 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 output end face 112 is provided may be coated with an anti-reflection film. Also, the bonding surface of each carrier to the substrate 160 may be coated with Au.

[0025] 3 is a cross-sectional view taken along line XX of Example 1 of this embodiment. In Example 1, each incident end face (first incident end face 111 is shown in FIG. 3) is curved so as to protrude toward the corresponding laser diode (red laser diode 211 is shown in FIG. 3).

[0026] 3 shows a simplified cross section of red laser diode 211. Red laser diode 211 includes light-emitting unit 213. Red laser light emitted from light-emitting unit 213 is emitted from emission surface 214 of red laser diode 211, travels through air (or a transmission medium), and enters first optical waveguide 110 from first incident end surface 111. When the red laser light enters first incident end surface 111, a portion of the light is reflected by first incident end surface 111. However, because first incident end surface 111 is curved so as to protrude toward red laser diode 211, the amount of light returning directly toward light-emitting unit 213 is significantly reduced compared to when first incident end surface 111 is flat. Most of the reflected light is scattered away from the light-emitting unit 213 in the space between emission surface 214 and first incident end surface 111.

[0027] If first incident end face 111 were flat and much of the reflected light became returned light and reached light-emitting unit 213, this would cause fluctuations in the wavelength and intensity of the red laser light generated by light-emitting unit 213, preventing stable light emission. However, in this embodiment, first incident end face 111 is curved, and output face 214 of red laser diode 211 and first incident end face 111 of first optical waveguide 110 are arranged facing each other but spaced apart, so that much of the reflected light is scattered in the peripheral direction of output face 214 without becoming returned light. Therefore, light-emitting unit 213 can emit red laser light stably.

[0028] Here, the shortest distance d1 between the exit surface 214 of the red laser diode 211 and the first incident end surface 111 of the first optical waveguide 110 is preferably equal to or greater than the thickness d2 of the first optical waveguide 110. Providing such a space is expected to scatter a large amount of reflected light toward the periphery of the exit surface 214. In other words, the curved surface of the first incident end surface 111 may be processed so that a large amount of reflected light is scattered toward the periphery when such a shortest distance is set. Specifically, the curved surface of the first incident end surface 111 is designed so that 10% or more of the reflected light is scattered toward the periphery, more preferably 50% or more. The curved surface of the first incident end surface 111 may be, for example, a spherical surface or a cylindrical surface. If the curved surface is a cylindrical surface, it may be a cylindrical surface whose central axis is parallel to the X-axis as shown in FIG. 3, or a cylindrical surface whose central axis is parallel to the Z-axis. If the curved surface is a cylindrical surface whose central axis is parallel to the Z-axis, it is preferable that a cylindrical surface be formed for each incident end surface.

[0029] The configuration of the second incident end face 121 and the corresponding green light-emitting module 220, as well as the configuration of the third incident end face 131 and the corresponding blue light-emitting module 230, are similar to the configuration of the first incident end face 111 and the corresponding red light-emitting module 210. Therefore, in both cases, it is possible to suppress return light and stably emit the respective laser beams. In particular, in applications such as this embodiment, in which laser beams of different colors are mixed in an optical waveguide to emit light of a desired color, if any of the laser beams becomes unstable, variations in color will occur, and therefore stabilization of the respective laser beams is particularly important.

[0030] 4 is a cross-sectional view taken along line XX of Example 2 of this embodiment. In Example 2, each incident end face (first incident end face 111 is shown in FIG. 4) is curved so as to be excavated on the side opposite to the corresponding laser diode (red laser diode 211 is shown in FIG. 4).

[0031] By processing first incident end face 111 into a curved surface in this manner, even if output face 214 of red laser diode 211 and first incident end face 111 of first optical waveguide 110 are arranged facing each other but spaced apart, most of the reflected light can be scattered toward the periphery of output face 214. Therefore, light emitting unit 213 can emit red laser light stably.

[0032] Even when processing such a curved surface, it is preferable that the shortest distance d1 between the exit surface 214 of the red laser diode 211 and the first incident end surface 111 of the first optical waveguide 110 be equal to or greater than the thickness d2 of the first optical waveguide 110. Providing such a space is expected to scatter a large amount of reflected light toward the periphery of the exit surface 214. In other words, the curved surface of the first incident end surface 111 should be processed so that a large amount of reflected light is scattered toward the periphery when such a shortest distance is set. Specifically, the curved surface of the first incident end surface 111 should be designed so that 50% or more of the reflected light is scattered toward the periphery. The curved surface of the first incident end surface 111 may be, for example, spherical or cylindrical. The configurations of the second incident end surface 121 and the corresponding green light-emitting module 220, and the configurations of the third incident end surface 131 and the corresponding blue light-emitting module 230 are similar to the configurations of the first incident end surface 111 and the corresponding red light-emitting module 210.

[0033] 5 is a partial perspective view of a waveguide module 100 as a third example of the present embodiment. The third example is similar to the second example in that each incident end face (first incident end face 111, second incident end face 121, third incident end face 131) is processed into a curved surface so as to be excavated on the side opposite to the corresponding laser diode, but in particular, this is an example in which the three incident end faces are processed into the same curved surface.

[0034] Specifically, as shown in the figure, a portion of the end face of the substrate 160 and the end face of the buffer layer 170 are processed into a cylindrical curved surface that is continuous with the curved surfaces of the respective incident end faces. In other words, the curved surfaces of the respective incident end faces are realized, for example, by simultaneously performing a grinding process across each layer. This processing method allows curved surfaces to be formed easily and in a short time. Furthermore, if the three incident end faces have the same curved surface, the influence of the return light on each laser diode can be expected to be the same, so the balance of the mixed colors will not be significantly disrupted. Note that, although the example in Figure 5 shows a concave curved surface, it may also be processed into a convex curved surface.

[0035] In the above-described embodiment, the optical device 10 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 the light-emitting modules may have independent output end faces. [Explanation of symbols]

[0036] 10...optical device, 20...MEMS mirror, 30...projector, 40...screen, 100...waveguide module, 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, 131...third incident end face, 150...waveguide layer, 160...substrate, 170...buffer layer, 200...light-emitting module, 210...red light-emitting module, 211...red laser diode, 212...first carrier, 213...light-emitting portion, 214...exit surface, 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 waveguide module including a base layer, a cover layer, and a waveguide layer formed between the base layer and the cover layer, the waveguide layer having an optical waveguide having an incident end face, into which a laser beam to be propagated is incident, the incident end face being processed into a curved surface; a light-emitting module including a laser diode that emits the laser light and a carrier that supports the laser diode so that an emission surface of the laser light is disposed opposite to and spaced apart from the incident end surface, the carrier being bonded to the base layer and integrated with the waveguide module; An optical device comprising:

2. The optical device according to claim 1 , wherein at least a portion of each end surface of the base layer and the cover layer is curved to be continuous with the curved surface of the incident end surface.

3. 2. The optical device according to claim 1, wherein the shortest distance between the exit surface and the incident end surface is equal to or greater than the thickness of the optical waveguide.

4. the waveguide layer has a plurality of the incident end faces, and the optical waveguides continuous with the plurality of the incident end faces are joined together inside the waveguide module and connected to an output end face; 2. The optical device according to claim 1, wherein the light emitting module includes a plurality of the laser diodes corresponding to the plurality of incident end faces, respectively.

5. the waveguide layer has three of the incident end faces, and the optical waveguides continuing to the three incident end faces are joined together inside the waveguide module and connected to an output end face; 2. The optical device according to claim 1, wherein the light emitting module has three laser diodes that emit red, green, and blue light corresponding to the three incident end faces, respectively.

6. 6. The optical device according to claim 5, wherein the three incident end faces are processed to have the same curved surface.

7. An image forming apparatus employing the optical device according to claim 1 .

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