Light Source Module

Abstract

To provide a light source module capable of combining light beams emitted by two semiconductor lasers mounted on the same substrate prior to incidence into a collimator lens and focusing the beams on an image plane.SOLUTION: The light source module comprises first and second semiconductor lasers, and a light beam combining element. The first and second semiconductor lasers are arranged such that their optical axes are parallel to each other. The light beam combining element receives first and second light beams respectively emitted by the first and second semiconductor lasers, and makes the optical axes of the first and second light beams proximate to each other to emit them. An air conversion length of total distance from a first light emission surface of the first semiconductor laser to an emission surface of the light beam combining element and an air conversion length of total distance from a second light emission surface of the second semiconductor laser to the emission surface of the light beam combining element are equal to each other.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a light source module used in an optical scanning device mounted in an image forming apparatus placed in a workplace. [Background technology]

[0002] Conventionally, a light source module having two semiconductor lasers has been known to increase pixel density, and in such a light source module, a polarizing beam splitter is used to combine the light beams emitted by the two semiconductor lasers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 07-181411 Summary of the Invention [Problem to be solved by the invention]

[0004] In a light source module with two semiconductor lasers, the optical path lengths from the light-emitting surfaces of the two semiconductor lasers to the polarizing beam splitter are different. Therefore, when combining the diverging light beams before entering the collimator lens and focusing them on the image plane, it is necessary to make the positions of the light-emitting surfaces of the two semiconductor lasers different. As a result, it is difficult to mount the two semiconductor lasers on the same board.

[0005] The problem that the present invention aims to solve is to provide a light source module that can combine light beams emitted by two semiconductor lasers mounted on the same substrate before they enter a collimator lens and focus them on the same image plane. [Means for solving the problem]

[0006] A light source module according to an embodiment includes first and second semiconductor lasers and a light beam combining element. The first and second semiconductor lasers are arranged so that their optical axes are parallel. The light beam combining element receives the first and second light beams emitted by the first and second semiconductor lasers, respectively, and emits the first and second light beams with their optical axes close to each other. The air-equivalent length of the total distance from the first light-emitting surface of the first semiconductor laser to the emission surface of the light beam combining element is equal to the air-equivalent length of the total distance from the second light-emitting surface of the second semiconductor laser to the emission surface of the light beam combining element. The first light-emitting surface of the first semiconductor laser and the second light-emitting surface of the second semiconductor laser are located on the same plane. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a vertical cross-sectional view of an image forming apparatus equipped with an optical scanning device having a light source module according to an embodiment. [Figure 2] FIG. 2 is a top view of an optical scanning device having a light source module according to the embodiment. [Figure 3] FIG. 3 is a perspective view of an optical scanning device having a light source module according to the embodiment. [Figure 4] FIG. 4 is a perspective view of the optical scanning device according to the embodiment before the light source module is attached to the housing. [Figure 5] FIG. 5 is a cross-sectional view of the housing taken along line DD shown in FIG. [Figure 6] FIG. 6 is a perspective view of the light source module according to the embodiment. [Figure 7] FIG. 7 is a perspective view of the light source module as seen from the opposite side to FIG. [Figure 8] FIG. 8 is a perspective view of the light source module in which the substrate is not shown in FIG. [Figure 9] FIG. 9 is a plan view of the light source module shown in FIGS. [Figure 10A] 10A is a view of the first LD chip in the light source module according to the first embodiment, as viewed in the direction A shown in FIG. [Figure 10B]10B is a view of the second LD chip in the light source module according to the first embodiment, seen from the direction B shown in FIG. [Figure 10C] FIG. 10C is a diagram showing the first LD chip in FIG. 10A and the second LD chip in FIG. 10B superimposed on each other along the optical axis. [Figure 10D] FIG. 10D is a simplified diagram showing an optical system of an optical scanning device related to the light source module according to the first embodiment. [Figure 10E] FIG. 10E is a plan view showing four focused spots formed on the image plane by the light beams emitted from the two LD chips shown in FIG. 10C. [Figure 11] FIG. 11 is a plan view showing four focused spots actually formed on the image plane by two light beams emitted by the light source module according to the first embodiment fixed to the housing after angle adjustment. [Figure 12A] 12A is a view of the first LD chip in the light source module according to the second embodiment, seen from the direction A shown in FIG. [Figure 12B] 12B is a view of the second LD chip in the light source module according to the second embodiment, seen from the direction B shown in FIG. [Figure 12C] FIG. 12C is a diagram showing the first LD chip in FIG. 12A and the second LD chip in FIG. 12B superimposed on each other along the optical axis. [Figure 12D] FIG. 12D is a simplified diagram showing an optical system of an optical scanning device relating to a light source module according to a second embodiment. [Figure 12E] FIG. 12E is a plan view showing four focused spots formed on the image plane by the light beams emitted from the two LD chips shown in FIG. 12C. [Figure 13] FIG. 13 is a plan view showing four focused spots actually formed on the image plane by two light beams emitted by the light source module according to the second embodiment fixed to the housing after angle adjustment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described with reference to the drawings. The scale of each part in each drawing used in describing the embodiments may be changed as appropriate. Furthermore, for the sake of convenience, some configurations and symbols may be omitted in each drawing used in describing the embodiments.

[0009] (Image forming device) First, an image forming apparatus will be described with reference to Fig. 1. Fig. 1 is a vertical cross-sectional view of an image forming apparatus equipped with an optical scanning device having a light source module according to an embodiment. For example, the image forming apparatus is a multifunction peripheral (MFP).

[0010] The image forming apparatus 1 includes an image reading unit 10 and an image forming unit 20. The image reading unit 10 scans and reads images of sheet documents and book documents. The image forming unit 20 forms a developer image on a sheet based on the image read from the document by the image reading unit 10, image data transmitted to the image forming apparatus 1 from an external device, etc.

[0011] The image reading unit 10 includes an automatic document feeder (ADF) 11. The image reading unit 10 reads images of documents conveyed by the automatic document feeder 11 or documents placed on a document table. The image forming unit 20 includes a paper feed cassette 21, a developing unit 22, an optical scanning device 30, a fixing unit 23, and a paper discharge tray 24.

[0012] The operation of the image forming unit 20 will be described.

[0013] A sheet stored in the paper feed cassette 21 is transported to the developing device 22 by a pickup roller and a transport roller. The developing device 22 forms a developer image on the sheet transported from the paper feed cassette 21. Specifically, first, a photosensitive element included in the developing device 22 is exposed to light from the optical scanning device 30, and an electrostatic latent image is formed on the photosensitive surface of the photosensitive element.

[0014] Next, the electrostatic latent image is visualized by supplying a developer to the photosensitive member. A developer image is formed on the photosensitive surface of the photosensitive member, and the developer image on the photosensitive surface is transferred to a sheet transported from a paper feed cassette 21. The sheet onto which the developer image has been transferred is transported to a fixing device 23. The fixing device 23 fixes the developer image to the sheet by heating the sheet. The sheet that has passed through the fixing device 23 is transported to a paper output tray 24. The sheet transported from the fixing device 23 is stacked on the paper output tray 24.

[0015] The structure of the image forming apparatus 1 shown in FIG. 1 is an example, and any structure may be used as long as the apparatus is capable of forming a developer image on a sheet.

[0016] (Optical scanning device) Next, the optical scanning device 30 will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a top view of the optical scanning device 30 having a light source module according to the embodiment. Fig. 3 is a perspective view of the optical scanning device 30 having a light source module according to the embodiment.

[0017] The optical scanning device 30 includes a light source module 100. The light source module 100 emits a diverging light beam. Details of the light source module 100 will be described later. The light source module 100 is attached to the housing 40 so as to be rotatable around the optical axis of the light source module 100, and is fixed to the housing 40 after the rotation angle is adjusted. Here, the optical axis of the light source module 100 refers to an axis that coincides with the chief ray of the light beam emitted from the light source module 100.

[0018] The optical scanning device 30 also includes a collimator lens 31, an aperture plate 32, a cylindrical lens 34, a polygon mirror 35, an fθ lens 37, and a folding mirror 38. The collimator lens 31, the aperture plate 32, the cylindrical lens 34, the polygon mirror 35, the fθ lens 37, and the folding mirror 38 are all fixed to a housing 40.

[0019] The light beam LB emitted from the light source module 100 is incident on the collimator lens 31. The collimator lens 31 converts the divergent light beam emitted from the light source module 100 into a parallel light beam LB.

[0020] As described above, the collimator lens 31 is fixed to the housing 40. For this purpose, the housing 40 has a lens holder 41. The lens holder 41 holds the collimator lens 31 so that the central axis of the collimator lens 31 is positioned on the optical axis of the light source module 100.

[0021] The light beam LB that has passed through the collimator lens 31 is incident on the diaphragm plate 32. As shown in Fig. 3, the diaphragm plate 32 has an opening 33 that shapes the shape of the light beam LB. The diaphragm plate 32 transmits light that enters the opening 33 out of the light beam LB from the collimator lens 31 and blocks light that does not enter the opening 33.

[0022] As described above, the diaphragm plate 32 is fixed to the housing 40. For this purpose, the housing 40 has the diaphragm holder 42. The diaphragm holder 42 holds the diaphragm plate 32 so that the center of the opening 33 is positioned on the optical axis of the light source module 100.

[0023] The light beam LB that passes through the opening 33 of the diaphragm plate 32 is incident on the cylindrical lens 34. The cylindrical lens 34 condenses the light beam LB from the diaphragm plate 32 in the sub-scanning direction. Here, the sub-scanning direction is a direction perpendicular to the main scanning direction. The main scanning direction is the left-right direction in FIG. 2. In other words, the sub-scanning direction is a direction perpendicular to the plane of the paper in FIG. 2.

[0024] As described above, the cylindrical lens 34 is fixed to the housing 40. For this purpose, the housing 40 has a lens holder 43. The lens holder 43 holds the cylindrical lens 34 so that the center of the cylindrical lens 34 is positioned on the optical axis of the light source module 100.

[0025] The light beam LB that passes through the diaphragm plate 32 is incident on the polygon mirror 35. The polygon mirror 35 is fixed to the housing 40. The polygon mirror 35 is rotatable and has multiple reflective surfaces on its outer periphery centered on the axis of rotation. The polygon mirror 35 reflects the light beam LB from the diaphragm plate 32 toward the fθ lens 37. Furthermore, the polygon mirror 35 rotates to cause the light beam LB to scan in the main scanning direction.

[0026] The light beam LB reflected by the polygon mirror 35 is incident on an fθ lens 37. The fθ lens 37 is fixed to a housing 40. The fθ lens 37 extends in the main scanning direction and focuses the light beam LB from the polygon mirror 35 in the sub-scanning direction.

[0027] The light beam LB that passes through the fθ lens 37 is reflected by the folding mirror 38, passes through the cover glass, and heads toward the photosensitive member of the developing unit 22, as shown in Figure 1. The light beam LB forms a focused spot on the surface of the photosensitive member due to the focusing action of the cylindrical lens 34 and the fθ lens 37. The focused spot of the light beam LB scans the surface of the photosensitive member in the main scanning direction due to the scanning action of the polygon mirror 35.

[0028] (light source module) Next, the light source module 100 will be described with reference to Figs. 4 to 9. Fig. 4 is a perspective view of the optical scanning device 30 before the light source module 100 according to the embodiment is attached to the housing 40. Fig. 5 is a cross-sectional view of the housing 40 taken along line DD shown in Fig. 2. Fig. 6 is a perspective view of the light source module 100 according to the embodiment. Fig. 7 is a perspective view of the light source module 100 as seen from the opposite side of Fig. 6. Fig. 8 is a perspective view of the light source module 100 from Fig. 7, with the board not shown. Fig. 9 is a plan view of the light source module 100 shown in Figs. 6 to 8.

[0029] First, the light source module 100 will be described in detail with reference to FIGS. 6 to 9. The configuration of the light source module 100 is shown in most detail in FIG. 9, and in FIGS. 4 to 8, reference numerals are omitted as appropriate for clarity. In addition to the light source module 100, FIG. 9 also shows a collimator lens 31 and an image plane IP. The image plane IP is a surface on which the light beam LB is focused by the optical system of the optical scanning device 30, and corresponds to the surface of the photosensitive member included in the developing unit 22. Strictly speaking, the surface of the photosensitive member is a cylindrical surface; however, because the focused spot of the light beam LB is very small, the curvature of the surface of the photosensitive member can be substantially ignored, and for convenience, the surface is considered to be flat here.

[0030] For ease of explanation, an xyz Cartesian coordinate system is defined for the light source module 100, and an XYZ Cartesian coordinate system is defined for the image plane IP, as shown in FIG. 9. In the xyz Cartesian coordinate system, the zx plane is parallel to the paper surface of FIG. 9, and in the XYZ Cartesian coordinate system, the ZX plane is parallel to the paper surface of FIG. 9. The z axis is parallel to the optical axes LAA and LAB. The optical axis LA is the optical axis of the optical system of the optical scanning device 30, but is simply depicted as a straight line in FIG. 9. The optical axis LA scans along the X axis, which is the main scanning direction, but is depicted in FIG. 9 at the center of the main scanning direction, perpendicular to the image plane IP.

[0031] The light source module 100 includes a first semiconductor laser 110 that emits a first light beam LBA, a second semiconductor laser 120 that emits a second light beam LBB, a holder 160 that holds the first semiconductor laser 110 and the second semiconductor laser 120, and a substrate 170 that includes drive circuits for the first semiconductor laser 110 and the second semiconductor laser 120, etc.

[0032] The first semiconductor laser 110 has a first LD chip 111, and the second semiconductor laser 120 has a second LD chip 121. LD stands for laser diode. The first LD chip 111 has a first light-emitting surface 112, and the second LD chip 121 has a second light-emitting surface 122. The first LD chip 111 emits a first light beam LBA from the first light-emitting surface 112 perpendicular to the first light-emitting surface 112, and the second LD chip 121 emits a second light beam LBB from the second light-emitting surface 122 perpendicular to the second light-emitting surface 122. Both the first light beam LBA and the second light beam LBB are diverging light beams. The first LD chip 111 is sealed in a first CAN package 118, and the second LD chip 121 is sealed in a second CAN package 128. A first connection terminal 119 extends from the first CAN package 118, and a second connection terminal 129 extends from the second CAN package 128.

[0033] The holder 160 has a first hole 161 that accommodates the first semiconductor laser 110 and a second hole 162 that accommodates the second semiconductor laser 120. The first semiconductor laser 110 has a first CAN package 118 accommodated in the first hole 161 of the holder 160, and the second semiconductor laser 120 has a second CAN package 128 accommodated in the first hole 162 of the holder 160. The holder 160 also has two spacer portions 164. The number of spacer portions 164 is not limited to two and may be three or more.

[0034] The substrate 170 is fixed to the spacer portion 164 of the holder 160 by screws 171. The substrate 170 has a first through hole 176 through which the first connection terminal 119 of the first semiconductor laser 110 passes, and a second through hole 177 through which the second connection terminal 129 of the second semiconductor laser 120 passes. The first connection terminal 119 of the first semiconductor laser 110 extends through the first through hole 176 of the substrate 170, and the second connection terminal 129 of the second semiconductor laser 120 extends through the second through hole 177 of the substrate 170. After the positions of the first semiconductor laser 110 and the second semiconductor laser 120 are adjusted, the first connection terminal 119 and the second connection terminal 129 are electrically connected to and fixed to the substrate 170 by soldering.

[0035] The first semiconductor laser 110 and the second semiconductor laser 120 are fixed to the holder 160 so that their respective optical axes LAA and LAB are substantially parallel to each other. Here, the optical axis LAA is substantially perpendicular to the first light-emitting surface 112 of the first LD chip 111 of the first semiconductor laser 110, and the optical axis LAB is substantially perpendicular to the second light-emitting surface 122 of the second LD chip 121 of the second semiconductor laser 120. In other words, both the optical axis LAA and the optical axis LAB are substantially parallel to the z-axis.

[0036] The following describes the light beam combining element 130. The first light beam LBA emitted from the first semiconductor laser 110 and the second light beam LBB emitted from the second semiconductor laser 120 are incident on the light beam combining element 130. The light beam combining element 130 emits the first light beam LBA and the second light beam LBB with their optical axes LAA and LAB positioned close to each other.

[0037] The light beam combining element 130 has a cube-shaped polarizing beam splitter 131 onto which the first light beam LBA emitted from the first semiconductor laser 110 is directly incident, and a prism 136 onto which the second light beam LBB emitted from the second semiconductor laser 120 is directly incident.

[0038] The prism 136 has an incident surface 138 on which the second light beam LBB is incident, a reflecting surface 137 that reflects almost 100% of the second light beam LBB toward the polarizing beam splitter 131, and an exit surface 139 from which the second light beam LBB emerges. The reflecting surface 137 remains as is when the conditions for total reflection are met, but is coated with a reflective film when the conditions for total reflection are not met.

[0039] The polarizing beam splitter 131 has a first incident surface 132 on which the first light beam LBA is incident, a second incident surface 135 on which the second light beam LBB is incident, a bonding surface 134 that transmits almost 100% of the first light beam LBA but reflects almost 100% of the second light beam LBB, and an exit surface 133 from which the first light beam LBA and the second light beam LBB exit.

[0040] Prism 136 is disposed adjacent to polarizing beam splitter 131. More specifically, prism 136 and polarizing beam splitter 131 are disposed so that an exit surface 139 of prism 136 and polarizing beam splitter 131 are in surface contact with each other.

[0041] The light beam combining element 130 also has a half-wave plate 146 provided on the entrance surface 138 of the prism 136 and a quarter-wave plate 141 provided on the exit surface 133 of the polarizing beam splitter 131 .

[0042] The first light beam LBA emitted by the first semiconductor laser 110 and the second light beam LBB emitted by the second semiconductor laser 120 are both linearly polarized light beams. The polarization direction of the first light beam LBA and the polarization direction of the second semiconductor laser 120 are the same. For example, the polarization direction of the first light beam LBA and the polarization direction of the second semiconductor laser 120 are parallel to the x-axis. That is, both the first semiconductor laser 110 and the second semiconductor laser 120 emit P-polarized light beams toward the junction surface 134 of the polarizing beam splitter 131.

[0043] The optical axis of the quarter wave plate 141 is set so as to convert P polarized light and S polarized light into circularly polarized light. That is, the optical axis of the quarter wave plate 141 is set at 45 degrees with respect to the polarization direction of the P polarized light and S polarized light.

[0044] The half-wave plate 146 has its optical axis set so as to convert P-polarized light into S-polarized light.

[0045] The first light beam LBA, which is divergent light emitted from the first semiconductor laser 110 and is P-polarized, enters the polarizing beam splitter 131 from the first entrance surface 132, transmits almost 100% through the junction surface 134, and exits from the exit surface 133. The first light beam LBA, which is P-polarized and exits from the polarizing beam splitter 131, passes through the quarter-wave plate 141 and is converted into a circularly polarized light beam. The first light beam LBA, which is divergent light, then passes through the collimator lens 31 and is converted into a substantially parallel light beam.

[0046] The second light beam LBB, which is a diverging light beam emitted from the second semiconductor laser 120 and is P-polarized, enters the half-wave plate 146 and is converted into an S-polarized light beam by passing through the half-wave plate 146. The second light beam LBB then enters the prism 136 from the entrance surface 138, is reflected almost 100% by the reflecting surface 137, and is emitted from the exit surface 139. The second light beam LBB, which is S-polarized and emitted from the prism 136, enters the polarizing beam splitter 131 from the second entrance surface 135, is reflected almost 100% by the bonding surface 134, and is emitted from the exit surface 133. The second light beam LBB, which is S-polarized and emitted from the polarizing beam splitter 131, passes through the quarter-wave plate 141 and is converted into a circularly polarized light beam. The second light beam LBB, which is a diverging light beam, then passes through the collimator lens 31 and is converted into a substantially parallel light beam.

[0047] The reason why the quarter-wave plate 141 converts the P-polarized first light beam LBA into a circularly polarized light beam and the S-polarized second light beam LBB into a circularly polarized light beam is to make uniform the transmission and reflection characteristics of the first light beam LBA and the second light beam LBB in the optical components (polygon mirror 35, fθ lens 37, folding mirror 38, cover glass) of the optical system of the optical scanning device 30 downstream.

[0048] The first light beam LBA and the second light beam LBB are combined by the junction surface 134 of the polarizing beam splitter 131 and then pass through the collimator lens 31 to become a parallel light beam LB. The light beam LB travels along the optical axis LA of the optical system of the optical scanning device 30 and is focused on an image plane IP with a finite focus. The image plane IP is the surface of a photosensitive member included in the developing unit 22. For convenience, the optical axis LA of the optical system of the optical scanning device 30 is drawn as a straight line in FIG. 9.

[0049] (Air equivalent length) Next, the light source module 100 will be described in more detail with reference to Fig. 9. In the light source module 100, the first light-emitting surface 112 of the first LD chip 111 of the first semiconductor laser 110 and the second light-emitting surface 122 of the second LD chip 121 of the second semiconductor laser 120 are both located substantially on the same plane EP.

[0050] In this configuration in which the first semiconductor laser 110 and the second semiconductor laser 120 are arranged so that the first light-emitting surface 112 and the second light-emitting surface 122 are located approximately on the same plane EP, if the same medium (e.g., air) is used up to the polarizing beam splitter 131, the back focus position of the collimator lens 31 will be significantly different between the first semiconductor laser 110 and the second semiconductor laser 120, resulting in a problem in which images are not formed on the same image plane IP.

[0051] To avoid this problem, in the embodiment, when the first semiconductor laser 110 and the second semiconductor laser 120 are arranged so that the first light-emitting surface 112 and the second light-emitting surface 122 are positioned approximately on the same plane EP, the back focus positions of the collimator lens 31 are aligned between the first semiconductor laser 110 and the second semiconductor laser 120.

[0052] Therefore, in the light source module 100, the air-equivalent length of the total distance from the first light-emitting surface 112 of the first LD chip 111 of the first semiconductor laser 110 to the exit surface 133 of the light beam combining element 130 is equal to the air-equivalent length of the total distance from the second light-emitting surface 122 of the second LD chip 121 of the second semiconductor laser 120 to the exit surface 133 of the light beam combining element 130. This will be explained in detail below.

[0053] 9, the distance from the light-emitting surface 112 of the first semiconductor laser 110 to the first incident surface 132 of the polarizing beam splitter 131 of the optical beam combining element 130 is denoted by La. The distance on the optical axis LAA from the first incident surface 132 of the polarizing beam splitter 131 to the bonding surface 134 is denoted by Lf. Also, the distance on the optical axis LAA from the bonding surface 134 to the exit surface 133 of the polarizing beam splitter 131 is denoted by Lf. The thickness of the quarter-wave plate 141 is denoted by Lg.

[0054] Furthermore, the distance from the light-emitting surface 112 of the second semiconductor laser 120 to the incident surface 147 of the half-wave plate 146 of the optical beam combining element 130 is defined as Lb. The thickness of the half-wave plate 146 is defined as Lc. The distance on the optical axis LAB from the incident surface 138 of the prism 136 of the optical beam combining element 130 to the reflecting surface 137 is defined as Ld. The distance on the optical axis LAB from the reflecting surface 137 of the prism 136 to the exit surface 139 is defined as Le. The optical axis LAB is bent 90 degrees by the reflecting surface 137. The exit surface 139 of the prism 136 coincides with the second incident surface 135 of the polarizing beam splitter 131 of the optical beam combining element 130. The distance on the optical axis LAB from the second incident surface 135 of the polarizing beam splitter 131 to the junction surface 134 is defined as Lf.

[0055] Furthermore, the refractive index of the half-wave plate 146 and the quarter-wave plate 141 is na, the refractive index of the prism 136 is nb, and the refractive index of the polarizing beam splitter 131 is nc.

[0056] The defocus Δα caused by the half wavelength plate 146 is given by the following equation (1).

[0057] Δα=Lc×(1-1 / na) (1) The defocus Δβ caused by the prism 136 is given by the following equation (2).

[0058] Δβ=(Ld+Le)×(1-1 / nb)···(2) The conditions under which the first light emitting surface 112 of the first semiconductor laser 110 and the second light emitting surface 122 of the second semiconductor laser 120 are positioned substantially on the same plane EP are given by the following equations (3) and (4).

[0059] Lb+Lc+Ld+Le=La+Δα+Δβ···(3) La + Lf = Lb + Lc + Ld (4) From equations (1), (2), (3), and (4), the following equation (5) is obtained.

[0060] Ld=(Lf-Lc(1-1 / na)+Le / nb) / (1-1 / nb)...(5) Furthermore, by transforming equation (4), the following equation (6) is obtained.

[0061] Lb = La + Lf - Lc - Ld (6) La is set so that Lb is positive.

[0062] As a calculation example, if La=12, Lc=0.5, Le=3.5, Lf=5, na=1.52, and nb=1.83, we obtain Ld=14.864 and Lb=1.636.

[0063] By setting parameters to satisfy the above conditions, even in a configuration in which the first semiconductor laser 110 and the second semiconductor laser 120 are arranged so that the first light emitting surface 112 and the second light emitting surface 122 are positioned approximately on the same plane EP, the first light beam LBA emitted from the first light emitting surface 112 and the second light beam LBB emitted from the second light emitting surface 122 can be combined by the light beam combining element 130 and then, after passing through a common collimator lens 31, be imaged on the same image plane IP.

[0064] On the other hand, the air-equivalent length is defined as (thickness) / (refractive index at that thickness). The air-equivalent length from the first light-emitting surface 112 of the first semiconductor laser 110 to the exit surface 143 of the quarter-wave plate 141 of the optical beam combining element 130 is defined as the air-equivalent length S1 on the first semiconductor laser 110 side. Furthermore, the air-equivalent length from the second light-emitting surface 122 of the second semiconductor laser 120 to the exit surface 143 of the quarter-wave plate 141 of the optical beam combining element 130 is defined as the air-equivalent length S2 on the second semiconductor laser 120 side. Furthermore, Lg=0.5 and nc=1.52.

[0065] The air-equivalent length S1 on the first semiconductor laser 110 side is expressed by the following formula (7).

[0066] S1=La / 1+Lf / nc+Lf / nc+Lg / na...(7) The air-equivalent length S2 on the second semiconductor laser 120 side is expressed by the following formula (8).

[0067] S2=Lb / 1+Lc / na+Ld / nb+Le / nb+Lf / nc+Lf / nc+Lg / na...(8) Substituting the values ​​from the above calculation example into equation (7), we obtain S1 = 18.907.

[0068] Substituting the values ​​from the above calculation example into equation (8), we obtain S2 = 18.907.

[0069] In this way, S1 = S2. In other words, by making the air-equivalent length S1 from the first light-emitting surface 112 of the first semiconductor laser 110 to the exit surface 143 of the quarter-wave plate 141 of the optical beam combining element 130 and the air-equivalent length S2 from the second light-emitting surface 122 of the second semiconductor laser 120 to the exit surface 143 of the quarter-wave plate 141 of the optical beam combining element 130 equal to each other, it can be rephrased as follows: "Even in a configuration in which the first semiconductor laser 110 and the second semiconductor laser 120 are arranged so that the first light-emitting surface 112 and the second light-emitting surface 122 are positioned substantially on the same plane EP, the first light beam LBA emitted from the first light-emitting surface 112 and the second light beam LBB emitted from the second light-emitting surface 122 can be combined by the optical beam combining element 130, and then transmitted through a common collimator lens 31 to form an image on the same image plane IP."

[0070] Furthermore, the following relational expression (9) can be derived from expressions (7) and (8).

[0071] S1-S2=La-Lb-Lc / na-Ld / nb-Le / nb (9) Substituting equations (5) and (6) into equation (9), we obtain the following equation (10).

[0072] S1-S2=0 (10) That is, S1 = S2. Note that mathematical processing software such as Mathematica (registered trademark) was used to derive equation (9) and calculate equation (10).

[0073] (First Example) A light source module 100 according to a first embodiment will be described with reference to FIGS. 10A to 10E and 11. FIG.

[0074] 10A to 10C are diagrams schematically illustrating a light source module 100 according to a first embodiment. This is an example in which the LD chips 111 and 121 of the semiconductor lasers 110 and 120 have a two-beam array. FIG. 10A illustrates the first LD chip 111 as viewed in direction A, and FIG. 10B illustrates the second LD chip 121 as viewed in direction B. FIG. 10C illustrates the first LD chip 111 in FIG. 10A and the second LD chip 121 in FIG. 10B superimposed on each other along optical axes LAA and LAB. Similar to FIG. 9, FIG. 10D illustrates a simplified optical system of the optical scanning device 30. The optical paths between the first LD chip 111 and the collimator lens 31, and between the second LD chip 121 and the collimator lens 31, are illustrated in terms of air-equivalent lengths. FIG. 10E is a plan view showing four focused spots 115, 116, 125, and 126 formed on the image plane IP by the light beams emitted from the two LD chips 111 and 121 shown in FIG. 10C.

[0075] In the light source module 100 according to the first embodiment, the two light-emitting portions 113 and 114 of the first LD chip 111 are aligned in a straight line parallel to the x-axis, and the two light-emitting portions 123 and 124 of the second LD chip 121 are also aligned in a straight line parallel to the x-axis. The distance along the x-axis between the two light-emitting portions 113 and 114 of the first LD chip 111 and the distance along the x-axis between the two light-emitting portions 123 and 124 of the second LD chip 121 are both Pa. Furthermore, the distance along the x-axis between the inner light-emitting portion 113 of the first LD chip 111 and the inner light-emitting portion 123 of the second LD chip 121 is also Pa. That is, in the x-direction, the four light-emitting portions 113, 114, 123, and 124 of the two LD chips 111 and 121 are aligned at equal intervals Pa.

[0076] The optical axis LAA of the first LD chip 111 passes through the intersection of a line passing through the centers of the light-emitting portions 113 and 114 and a line parallel to the y-axis that bisects the distance in the x-direction between the center of the light-emitting portion 113 inside the first LD chip 111 and the center of the light-emitting portion 123 inside the second LD chip 121. The optical axis LAB of the second LD chip 121 passes through the intersection of a line passing through the centers of the light-emitting portions 123 and 124 and a line parallel to the y-axis that bisects the distance in the x-direction between the center of the light-emitting portion 113 inside the first LD chip 111 and the center of the light-emitting portion 123 inside the second LD chip 121.

[0077] The four light beams emitted from the two LD chips 111 and 121 are focused on an image plane IP by the optical system of the optical scanning device 30, which includes a collimator lens 31, to form four focused spots 115, 116, 125, and 126. The four focused spots 115, 116, 125, and 126 are aligned in a straight line parallel to the X-axis. The spacing between the four focused spots 115, 116, 125, and 126 along the X-axis is Pe. The optical axis LA passes through a point that bisects the distance between the centers of the focused spots 115 and 125. In other words, the optical axis LA passes through the centers of gravity of the four focused spots 115, 116, 125, and 126.

[0078] 11 is a plan view showing four focused spots 115, 116, 125, and 126 that are actually formed on an image plane IP by two light beams LBA and LBB emitted by the light source module 100 according to the first embodiment that is fixed to the housing 40 after angle adjustment. The spacing between the four focused spots 115, 116, 125, and 126 is Pf. Here, Pf does not coincide with Pe because, in the case of a scanning optical system, the magnification of the optical system may differ between the main scanning direction (X direction) and the sub-scanning direction (Y direction).

[0079] When the light source module 100 is fixed to the housing 40, its angle is adjusted around the optical axis LAA. The line passing through the centers of the four focused spots 115, 116, 125, and 126 is adjusted so that it forms an angle θb with respect to the main scanning direction, i.e., the X direction. In one example, θb is the angle Ps by which the four adjacent focused spots 115, 116, 125, and 126 are shifted in the Y direction to obtain the desired resolution in the sub-scanning direction. Ps is 42.3 μm for 600 dpi, 21.2 μm for 1200 dpi, and 10.6 μm for 2400 dpi. In order to obtain such an arrangement of the light-focus spots 115, 116, 125, and 126, when the light source module 100 is fixed to the housing 40, the angle of the light source module 100 around the optical axis is adjusted so that the arrangement of the light-focus spots 115, 116, 125, and 126 shown in Figure 11 is obtained, and then the light source module 100 is fixed to the housing 40 by means of adhesive, screwing, or the like.

[0080] (Second Example) Next, a light source module 100 according to a second embodiment will be described with reference to Figures 12A to 12E and 13. Similar to the first embodiment, the second embodiment is obtained by modifying the layout of the first LD chip 111 of the first semiconductor laser 110 and the second LD chip 121 of the second semiconductor laser 120 on the xy plane.

[0081] 12A to 12E and 13 relating to the second embodiment correspond to Figures 10A to 10E and 11 relating to the first embodiment, respectively. Therefore, the meanings of Figures 12A to 12E and 13 are similar to the meanings of Figures 10A to 10E and 11, respectively. In the following, to avoid redundant explanation, the explanation will focus on the differences from the first embodiment.

[0082] In the light source module 100 according to the second embodiment, the two light emitting portions 113, 114 of the first LD chip 111 are aligned in a straight line parallel to the x-axis, and the two light emitting portions 123, 124 of the second LD chip 121 are also aligned in a straight line parallel to the x-axis. The distance between the two light emitting portions 113, 114 of the first LD chip 111 along the x-axis and the distance between the two light emitting portions 123, 124 of the second LD chip 121 along the x-axis are both Pa. The above is the same as in the light source module 100 according to the first embodiment.

[0083] In the light source module 100 according to the second embodiment, the inner light-emitting portion 113 of the first LD chip 111 is disposed at a position that halves the distance between the centers of the two light-emitting portions 123 of the second LD chip 121 in the x direction. The inner light-emitting portion 123 of the second LD chip 121 is disposed at a position that halves the distance between the centers of the two light-emitting portions 113 and 114 of the first LD chip 111 in the x direction. That is, the four light-emitting portions 113, 114, 123, and 124 of the two LD chips 111 and 121 are arranged at equal intervals of Pa / 2 along the x axis.

[0084] The optical axis LAA of the first LD chip 111 passes through the intersection of a line passing through the centers of the light-emitting portions 113 and 114 and a line parallel to the y-axis that bisects the distance in the x-direction between the center of the light-emitting portion 113 inside the first LD chip 111 and the center of the light-emitting portion 123 inside the second LD chip 121. The optical axis LAB of the second LD chip 121 passes through the intersection of a line passing through the centers of the light-emitting portions 123 and 124 and a line parallel to the y-axis that bisects the distance in the x-direction between the center of the light-emitting portion 113 inside the first LD chip 111 and the center of the light-emitting portion 123 inside the second LD chip 121.

[0085] As in the first embodiment, four light beams emitted from the two LD chips 111 and 121 are focused on an image plane IP by the optical system of the optical scanning device 30, including the collimator lens 31, to form four focused spots 115, 116, 125, and 126. The four focused spots 115, 116, 125, and 126 are aligned on a straight line parallel to the X-axis. However, in the second embodiment, the spacing between the four focused spots 115, 116, 125, and 126 along the X-axis is Pe / 2. The optical axis LA passes through a point that bisects the distance between the centers of the focused spots 115 and 125. In other words, the optical axis LA passes through the center of gravity of the four focused spots 115, 116, 125, and 126.

[0086] 13 is a plan view showing four focused spots 115, 116, 125, and 126 actually formed on an image plane IP by two light beams LBA and LBB emitted by a light source module 100 according to a second embodiment fixed to a housing 40 after angle adjustment. This corresponds to FIG. 11. The intervals between the four focused spots 115, 116, 125, and 126 are all Pi. Pi is approximately Pf / 2.

[0087] As described above, the light source module 100 is angularly adjusted about the optical axis LAA when fixed to the housing 40. The straight line passing through the centers of the four focused spots 115, 116, 125, and 126 is adjusted to form an angle of θc with respect to the main scanning direction, i.e., the X direction. The resolution in the sub-scanning direction and the amount of deviation in the Y direction between two adjacent focused spots 115, 116, 125, and 126 are the same as in the first embodiment.

[0088] In the second embodiment, as shown in FIG. 12C, the four light-emitting units 113, 114, 123, and 124 are arranged in the x direction at intervals Pe / 2, half that of the first embodiment. Therefore, as can be seen by comparing FIGS. 11 and 13, the angle θc by which the light source module 100 is rotated to obtain the same resolution in the sub-scanning direction is approximately twice the angle θb. Therefore, the second embodiment has a lower sensitivity to adjusting the angle of the light source module 100 compared to the first embodiment. This makes it easier to adjust the resolution in the sub-scanning direction. In other words, a small change in angle can be prevented from significantly changing the resolution in the sub-scanning direction.

[0089] (effect) In the light source module 100 according to the embodiment, the air-equivalent length of the total distance from the first light-emitting surface 112 of the first LD chip 111 of the first semiconductor laser 110 to the exit surface 143 of the quarter-wave plate 141 of the light beam combining element 130 is equal to the air-equivalent length of the total distance from the second light-emitting surface 122 of the second LD chip 121 of the second semiconductor laser 120 to the exit surface 143 of the quarter-wave plate 141 of the light beam combining element 130. Therefore, in the light source module 100, the first semiconductor laser 110 and the second semiconductor laser 120 are mounted on the same substrate 170, and the light beam LBA emitted by the first semiconductor laser 110 and the light beam LBB emitted by the second semiconductor laser 120 can be combined before entering the collimator lens 31 and focused on the same image plane IP.

[0090] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. The inventions described in the original claims of this application are set forth below. [1] first and second semiconductor lasers arranged so that their optical axes are parallel; a light beam combining element that receives the first and second light beams emitted by the first and second semiconductor lasers, respectively, and that outputs the first and second light beams with their optical axes adjacent to each other; and an air-equivalent length of a total distance from a first light-emitting surface of the first semiconductor laser to an exit surface of the optical beam combining element and an air-equivalent length of a total distance from a second light-emitting surface of the second semiconductor laser to the exit surface of the optical beam combining element are equal to each other; Light source module. [2] the light beam combining element includes a polarizing beam splitter on which the first light beam is directly incident, and a prism disposed adjacent to the polarizing beam splitter on which the second light beam is directly incident, the prism reflecting the second light beam toward the polarizing beam splitter, and the polarizing beam splitter transmitting the first light beam and reflecting the second light beam; [1] The light source module according to [1]. [3] the first and second semiconductor lasers emit linearly polarized light beams whose polarization directions are the same; The light beam combining element further includes a half-wave plate provided on the incident surface of the prism. [2] The light source module according to [2]. [4] the first and second semiconductor lasers emit P-polarized light beams toward a junction surface of the polarizing beam splitter; [3] The light source module according to [3]. [5] the first light-emitting surface of the first semiconductor laser and the second light-emitting surface of the second semiconductor laser are located on the same plane; [1] The light source module according to [1]. [Explanation of symbols]

[0091] 1...image forming apparatus, 10...image reading unit, 11...automatic document feeder, 20...image forming unit, 21...paper feed cassette, 22...developing unit, 23...fixing unit, 24...paper output tray, 30...optical scanning device, 31...collimator lens, 32...diaphragm plate, 33...opening, 34...cylindrical lens, 35...polygon mirror, 37...fθ lens, 38...folding mirror, 40...housing, 41...lens holder, 42...diaphragm holder, 43...lens holder, 48...bearing, 100...light source module, 110...first semiconductor laser, 111...first LD chip, 112...first light emitting surface, 113, 114...light emitting unit, 115, 116...focus spot, 118...first CAN package, 119...first connection terminal, 120...second semiconductor laser, 121...second LD chip 122...second light-emitting surface, 123, 124...light-emitting portion, 125, 126...light-focus spot, 128...second CAN package, 129...second connection terminal, 130...light beam combining element, 131...polarized beam splitter, 132...first incident surface, 133...exit surface, 134...junction surface, 135...second incident surface, 136...prism, 137...reflecting surface, 138...incident surface, 139 ...exit surface, 141...quarter wave plate, 143...exit surface, 146...half wave plate, 147...incident surface, 160...holder, 161...first hole, 162...second hole, 164...spacer portion, 166...rotation axis, 170...substrate, 171...screw, 176...first through hole, 177...second through hole, S1...air equivalent length on the first semiconductor laser side, S2...air equivalent length on the second semiconductor laser side.

Claims

1. first and second semiconductor lasers arranged so that their optical axes are parallel; a light beam combining element that receives the first and second light beams emitted by the first and second semiconductor lasers, respectively, and that outputs the first and second light beams with their optical axes positioned close to each other; and an air-equivalent length of a total distance from a first light-emitting surface of the first semiconductor laser to an exit surface of the optical beam combining element and an air-equivalent length of a total distance from a second light-emitting surface of the second semiconductor laser to the exit surface of the optical beam combining element are equal to each other; the first light-emitting surface of the first semiconductor laser and the second light-emitting surface of the second semiconductor laser are located on the same plane; Light source module.

2. the light beam combining element includes a polarizing beam splitter on which the first light beam is directly incident, and a prism disposed adjacent to the polarizing beam splitter on which the second light beam is directly incident, the prism reflecting the second light beam toward the polarizing beam splitter, and the polarizing beam splitter transmitting the first light beam and reflecting the second light beam; The light source module according to claim 1 .

3. the first and second semiconductor lasers emit linearly polarized light beams whose polarization directions are the same; the light beam combining element further includes a half-wave plate provided on the incident surface of the prism; The light source module according to claim 2 .

4. the first and second semiconductor lasers emit P-polarized light beams toward a junction surface of the polarizing beam splitter; The light source module according to claim 3 .

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