Optical transmitter

Abstract

A light transmitter of one embodiment includes a housing having an exit end, a light emitting element mounted to a first mounting portion of the housing, and a light receiving element mounted to a second mounting portion of the housing, which monitors output light from the light emitting element. A bracket, a first resin on the lower side of the bracket on the exit end side, and a second resin on the lower side of the bracket on the light emitting element side are provided in the second mounting portion. The thermal expansion rate of the first resin is smaller than the thermal expansion rate of the second resin.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an optical transmitter.

[0002] This application claims priority based on Japanese Application No. 2020-102408 filed June 12, 2020, and the entire disclosure of which is incorporated herein by reference. BACKGROUND

[0003] A semiconductor module is described in Patent Literature 1. The semiconductor module includes a semiconductor laser, a condensing lens that condenses light from the semiconductor laser, a photodiode that monitors light from the semiconductor laser, and a metal case and a metal cover that house the semiconductor laser, the condensing lens, and the photodiode. The metal case and the metal cover include an emission end that has an optical fiber that emits light condensed by the condensing lens to the outside. The photodiode that monitors light from the semiconductor laser is disposed on the opposite side of the emission end when viewed from the semiconductor laser.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. H7-113931 SUMMARY

[0007] One aspect of an optical transmitter includes a housing having an emission end, a light emitting element mounted to a first mounting portion of the housing, and a light receiving element mounted to a second mounting portion of the housing that monitors output light from the light emitting element. A bracket, a first resin on the lower side of the bracket on the emission end side, and a second resin on the lower side of the bracket on the light emitting element side are provided in the second mounting portion. The thermal expansion rate of the first resin is smaller than the thermal expansion rate of the second resin.

[0008] Another aspect of an optical transmitter includes a housing having an emission end, a light emitting element mounted to a first mounting portion of the housing, and a light receiving element mounted to a second mounting portion of the housing that monitors output light from the light emitting element. A bracket and a first resin on the lower side of the bracket are provided in the second mounting portion, and the thermal expansion rate of the first resin is greater than the thermal expansion rate of the bracket. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a perspective view of an optical transmitter according to an embodiment.

[0010] Figure 2 is a perspective view of the optical transmitter of Figure 1 with the cover removed.

[0011] Figure 3 is a perspective view of the optical transmitter of Figure 1A plan view of the light transmitter of the optical communication device 1 in a state where the cover is removed.

[0012] Figure 4 is a plan view schematically showing the positional relationship between the light receiving element and the light emitting element of the optical communication device 1. Figure 1

[0013] Figure 5 is a side view schematically showing the positional relationship between the light emitting element and the light receiving element of the optical communication device 1. Figure 4

[0014] Figure 6 is a graph showing the relationship between the temperature of the housing of the optical communication device 1 and the tracking error. Figure 4

[0015] Figure 7 is a side view showing the bracket of the second mounting portion, the first resin, and the second resin of the optical communication device 1. Figure 4

[0016] Figure 8 is a perspective view showing the bracket of the first modification.

[0017] Figure 9 is a side view showing the bracket, the first resin, and the second resin of the optical communication device 1. Figure 8

[0018] Figure 10 is a plan view schematically showing the optical path of the output light from the light emitting element, the light receiving element, the combiner, and the optical fiber of the optical communication device 1. Figure 4

[0019] Figure 11 is a graph showing the relationship between the temperature of the housing of the optical communication device 1 and the tracking error for each passage of the output light. Figure 4

[0020] Figure 12 is a graph showing the relationship between the temperature of the housing of the optical communication device 1 and the amount of light received by the light receiving element for each inclination angle of the light receiving surface. Figure 4

[0021] Figure 13 is a perspective view showing the bracket of the second mounting portion of the further modification.

[0022] Figure 14 is a graph showing the relationship between the temperature of the housing and the tracking error in the case where the bracket of the optical communication device 1 is used for each passage of the output light. Figure 13 DETAILED DESCRIPTION

[0023] ​​​​​​​​​Further, in order to ensure a wide space inside, a photodiode is sometimes arranged on the emission end side when viewed from the semiconductor laser. In this case, if the light receiving surface of the photodiode is arranged in parallel with the optical axis of the output light from the semiconductor laser, the light receiving sensitivity of the photodiode can be reduced. Therefore, the photodiode is sometimes arranged so that the light receiving surface is inclined with respect to the optical axis of the output light from the semiconductor laser. In this case, the photodiode is arranged on an inclined protrusion provided on the housing.

[0024] However, the housing sometimes warps and the like in a high temperature environment. If warping and the like occur, the output of light from the housing to the outside can be reduced, although the light receiving amount of the photodiode does not change. In a high temperature environment, the optical axis of the output light from the semiconductor laser can also be shifted from the center of the optical fiber, and as a result, the light amount of the output light to the optical fiber can be reduced at high temperatures.

[0025] An object of the present disclosure is to provide an optical transmitter that can suppress reduction in the light amount of output light generated at high temperatures.

[0026] According to the present disclosure, reduction in the light amount of output light generated at high temperatures can be suppressed.

[0027] An embodiment of the present disclosure is described by citing its contents. An optical transmitter of one embodiment has a housing having an emission end, a light emitting element mounted on a first mounting portion of the housing, and a light receiving element mounted on a second mounting portion of the housing that monitors output light from the light emitting element. A bracket, a first resin on the emission end side of the lower side of the bracket, and a second resin on the light emitting element side of the lower side of the bracket are provided in the second mounting portion. The thermal expansion rate of the first resin is smaller than the thermal expansion rate of the second resin.

[0028] In the optical transmitter, the light emitting element is mounted on the first mounting portion of the housing, and the light receiving element that monitors the output light from the light emitting element is mounted on the second mounting portion of the housing. The second mounting portion has a bracket that mounts the light receiving element, a first resin on the emission end side of the lower side of the bracket and the housing, and a second resin on the light emitting element side of the lower side of the bracket and the housing. The thermal expansion rate of the first resin on the emission end side is smaller than the thermal expansion rate of the second resin on the light emitting element side. Therefore, in a high temperature environment, the thermal expansion of the first resin on the emission end side is smaller than the thermal expansion of the second resin on the light emitting element side, and thus the light receiving amount of the light receiving element can be intentionally reduced. As a result, even if the housing warps and the like in a high temperature environment, and the output of light to the outside of the housing is to be reduced, the power of light from the light emitting element can be increased by the reduction in the light receiving amount of the light receiving element. Therefore, even if the housing warps and the like at high temperatures, the influence of the warping can be reduced by the first resin and the second resin, and thus reduction in the light amount of output light to the optical fiber at high temperatures can be suppressed.

[0029] The mounting surface of the light receiving element of the second mounting portion can be disposed obliquely with respect to the optical axis of the output light from the light emitting element. In this case, the thermal expansion of the first resin on the exit end side is smaller than the thermal expansion of the second resin on the light emitting element side in a high temperature environment, and thus the configuration in which the oblique angle is small can be effectively achieved.

[0030] The height of the second resin can be higher than the height of the first resin. In this case, the height of the first resin on the exit end side is made lower than the height of the second resin, and thus the decrease in the light quantity of the output light can be more reliably suppressed even if the housing is warped and the like in a high temperature environment.

[0031] Note that, in the embodiment, different resins are used on the exit end side and the light emitting element side, respectively. However, a resin can be provided only on the light emitting element side. The thermal expansion of the resin on the light emitting element side is larger than the thermal expansion of the bracket on the exit end side in a high temperature environment, and thus the configuration in which the oblique angle is small can be effectively achieved. In this case, the decrease in the light quantity of the output light can be reliably suppressed even if the housing is warped and the like in a high temperature environment.

[0032] The optical transmitter described above can include a plurality of light emitting elements and a plurality of light receiving elements provided corresponding to the plurality of light emitting elements, respectively. The optical path lengths of the plurality of output lights passing through the plurality of light receiving elements from the plurality of light emitting elements can be different from each other. The angle of the mounting surface of the light receiving element that mounts the output light of which the optical path length is short can be larger than the angle of the mounting surface of the light receiving element that mounts the output light of which the optical path length is long. Further, the shorter the optical path length of the output light, the less likely the decrease in the light quantity of the output light occurs. The larger the oblique angle of the mounting surface of the light receiving element, the less likely the decrease in the light receiving quantity at the time of temperature rise occurs. As described above, in the case where the oblique angle of the mounting surface of the light receiving element that receives the output light of which the optical path length is short is larger than the oblique angle of the mounting surface of the light receiving element that receives the output light of which the optical path length is long, the unevenness in the light quantity among the plurality of output lights can be suppressed.

[0033] The bracket can be formed of a material including glass or an alloy of iron, chromium, and nickel.

[0034] The thermal expansion rates of the first resin and the second resin can be larger than the thermal expansion rate of the bracket.

[0035] The housing can include a recess having a bottom at a position lower than the main surface of the housing. The bottom surface of the bracket of the second mounting portion can be mounted to the bottom of the recess.

[0036] Another optical transmitter includes a housing having an emission end, a light emitting element mounted on a first mounting portion of the housing, and a light receiving element mounted on a second mounting portion of the housing to monitor output light from the light emitting element. The second mounting portion has a holder and a first resin on a lower side of the holder. The first resin has a greater thermal expansion rate than the holder.

[0037] In the optical transmitter, the light emitting element is mounted on the first mounting portion of the housing, and the light receiving element to monitor the output light from the light emitting element is mounted on the second mounting portion of the housing. The second mounting portion has the holder and the first resin on the lower side of the holder and on the light emitting element side of the housing. The first resin on the light emitting element side has a greater thermal expansion rate than the holder. Thus, in a high temperature environment, the thermal expansion of the first resin on the light emitting element side is greater than the thermal expansion of the holder, and thus the light receiving amount of the light receiving element can be intentionally reduced. As a result, the power of light from the light emitting element can be increased by the reduction in the light receiving amount of the light receiving element. Thus, even if the housing is warped or the like at high temperatures, the effects of the warp can be reduced by the first resin, and thus the reduction in the light amount of the output light to the optical fiber at high temperatures can be suppressed.

[0038] Hereinafter, specific examples of the optical transmitter of the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited to the examples described below, but is shown by the claims, and is intended to include all modifications within the scope equivalent to the claims and the like. In the description of the drawings, the same reference numerals are attached to the same or equivalent elements, and redundant descriptions are appropriately omitted. In the drawings, in order to facilitate understanding, a part may be simplified or depicted in an exaggerated manner at times, and the dimensional ratio and the like are not limited to the dimensional ratio described in the drawings.

[0039] Figure 1 is a perspective view of the optical transmitter 1 of the present embodiment. As shown in Figure 1 , the optical transmitter 1 includes a housing 2, a cover 3 covering the housing 2, a socket 4 including a cylindrical sleeve, and a wiring board 5. The optical transmitter 1 extends in a long dimension direction D1, and the socket 4, the cover 3 (the housing 2), and the wiring board 5 are arranged in this order.

[0040] Figure 2 is a perspective view of the optical transmitter 1 with the cover 3 removed. As shown in Figure 1 and Figure 2As shown, the housing 2 includes: a lower plate 2A extending in the longitudinal direction D1; and a side wall 2B extending in the height direction D2 from one end of the lower plate 2A in the longitudinal direction D1. The housing 2 is, for example, made of metal. As an example, the material of the housing 2 is Kovar alloy (an alloy obtained by mixing nickel and cobalt with iron) or SUS (Stainless Steel). The housing 2 may also be made of iron, chromium, an alloy of iron and chromium, an alloy of iron and nickel, or plastic.

[0041] The shape of the housing 2, as viewed from the width direction D3 of the light transmitter 1, is L-shaped. The housing 2 is also referred to as an L-shaped base. A socket 4 is inserted into the side wall 2B, and a shape is formed as the output light L (see reference). Figure 4 The outlet end of the socket 4 has an aperture that penetrates the sidewall 2B in the longitudinal direction D1. The socket 4 is formed in a cylindrical shape. The socket 4 has a plurality of flanges 4c. One of the plurality of flanges 4c functions as a guide 4b that determines the position of the socket 4. In the socket 4, when fixed to the housing 2, for example, the guide 4b contacts the outer surface 2f of the sidewall 2B.

[0042] Viewed from the height direction D2, for example, the housing 2 is rectangular. The housing 2 is a component that houses the parts inside the light transmitter 1. Each part of the light transmitter 1 is mounted on the lower plate 2A. The lower plate 2A is a long strip that protrudes from the side wall 2B along the longitudinal direction D1, and each part of the light transmitter 1 is mounted on this long strip. The lower plate 2A includes: a main surface 2b, which faces each part inside the light transmitter 1; a convex mounting surface 2c, which mounts the parts; a guide pin 2d, which determines the position of the cover 3 relative to the housing 2; and an outer surface 2f, which protrudes from the outside of the light transmitter 1.

[0043] The main surface 2b is rectangular, extending in both the longitudinal direction D1 and the width direction D3. The mounting surface 2c is a portion protruding from the main surface 2b along the height direction D2; for example, a combiner 6 for beam combining is mounted on the mounting surface 2c. A guide pin 2d protrudes from the main surface 2b along the height direction D2. The guide pin 2d is, for example, cylindrical. The guide pin 2d is, for example, located on one side in the width direction D3 (offset from the center of the housing 2 in the width direction D3). The cover 3 is a component that covers the housing 2 from the height direction D2, and houses the components of the light transmitter 1 inside the housing 2 and the cover 3. The cover 3 has a protrusion with a hole formed inside for the guide pin 2d of the housing 2 to be inserted. The cover 3 is fixed to the housing 2 by being inserted into the guide pin 2d through the hole of the protrusion.

[0044] The optical transmitter 1 has a wiring substrate 5, a combiner 6, a light receiving element 7, a first lens 8, a light emitting element 9, and a spacer 10 inside the housing 2 and the cover 3. A part of the wiring substrate 5 extends from the housing 2 and the cover 3 to the opposite side of the receptacle 4. The part of the wiring substrate 5 extending to the opposite side of the receptacle 4 protrudes to the outside of the optical transmitter 1.

[0045] Figure 3 is a plan view showing each component mounted on the main surface 2b of the housing 2. As shown in Figure 2 and Figure 3 , the optical transmitter 1 further has a second lens 11 interposed between the receptacle 4 and the combiner 6. For example, the optical transmitter 1 has four light emitting elements 9, four first lenses 8, four light receiving elements 7, the combiner 6, and the second lens 11.

[0046] The optical transmitter 1 is a multi-channel light emitting module including four light emitting elements 9, four first lenses 8, and four light receiving elements 7. Thus, in the optical transmitter 1 having four light paths of the output light L, the light path lengths of the output light L differ from each other for each channel. The receptacle 4 is disposed, for example, at a position deviated from the center in the width direction D3 of the housing 2. The light path of the output light L from the light emitting element 9 at the end portion on the opposite side of the receptacle 4 in the width direction D3 (the lower end portion in Figure 3 ) is the longest. The light path of the output light L from the light emitting element 9 at the end portion on the receptacle 4 side in the width direction D3 (the upper end portion in Figure 3 ) is the shortest.

[0047] The housing 2 has a plurality of light emitting elements 9 and a plurality of light receiving elements 7 mounted thereon. The plurality of light emitting elements 9 are disposed in a side-by-side manner along the width direction D3, and the plurality of light receiving elements 7 are disposed in a side-by-side manner along the width direction D3. For example, each of the four light emitting elements 9 is mounted on the main surface 2b of the housing 2 via a bracket 12 (first mounting portion). Each light emitting element 9 is provided in correspondence with each of the four first lenses 8 and each of the four light receiving elements 7. Each light emitting element 9 is, for example, a semiconductor laser diode (LD: Lasor Diode). The output light L, which is divergent light output from the light emitting element 9, is converted into collimated light by each first lens 8. For example, each of the four light receiving elements 7 is mounted on the main surface 2b of the housing 2 via a bracket 13 (second mounting portion 20). For the bracket 13, a recess (recessed portion) is provided in the main surface 2b. The recess is for adjusting the height. It is also possible that there is no recess in the main surface 2b. Note that the above-mentioned height can be adjusted by the bracket 13.

[0048] The wiring substrate 5 is, for example, an FPC (Flexible Printed Circuit) mounted on the housing 2. The housing 2 has a pair of protrusions 2g protruding upward at the end portion thereof in the longitudinal direction D1 opposite to the side wall 2B. The pair of protrusions 2g are arranged side by side in the width direction D3. The wiring substrate 5 has a first region 5A extending outward from the light transmitter 1, a second region 5B provided with a land 5b, and a connection region 5C connecting the first region 5A and the second region 5B to each other. The first region 5A, the second region 5B, and the connection region 5C are arranged in a "C" shape when viewed in the height direction D2.

[0049] The first region 5A has a recess 5c at each of the both ends thereof in the width direction D3. The first region 5A has a pair of recesses 5c arranged side by side in the width direction D3. The wiring substrate 5 is fixed to the housing 2 by the respective protrusions 2g of the housing 2 being fitted into the respective recesses 5c. The first region 5A is provided with a land 5d electrically connected to the light emitting element 9. Each of the plurality of light emitting elements 9 is electrically connected to the land 5d via an electric wire, for example. The first region 5A is provided at a position higher than the second region 5B (a position separated from the main surface 2b of the housing 2). The height of the first region 5A coincides with the height of the bracket 12 on which the light emitting element 9 is mounted, for example. Thus, the length of the electric wire extending from each light emitting element 9 to the land 5d can be shortened.

[0050] For example, one piece of wiring substrate 5 has the first region 5A as an upper stage and the second region 5B as a lower stage, and is fixed to the housing 2 by adhesion. The second region 5B is provided at a position lower than the first region 5A, and is in contact with the main surface 2b of the housing 2, for example. By thus lowering the position of the second region 5B, the electric wire extending from the wiring substrate 5 or the light receiving element 7 can be prevented from interfering with the output light L passing through the light emitting element 9 and the first lens 8.

[0051] The width (length in the width direction D3) of the connection region 5C of the wiring substrate 5 is narrower than each of the width of the first region 5A and the width of the second region 5B. The connection region 5C is provided at the end portion of the socket 4 side in the width direction D3, for example. The connection region 5C extends from the end portion of the first region 5A in the width direction D3 to the end portion of the second region 5B in the width direction D3. The thickness of the wiring substrate 5 in the first region 5A and the thickness of the wiring substrate 5 in the second region 5B are the same as each other, for example. The connection region 5C extends along the longitudinal direction D1 between the first region 5A and the second region 5B, and is located at the end portion of the housing 2 in the width direction D3, for example.

[0052] The connection region 5C has a step or an inclined portion between the first region 5A and the second region 5B. In the present embodiment, an example is shown in which the connection region 5C has an inclined portion 5f. The wiring substrate 5 can also have an extension region 5D formed in extension of the connection region 5C, with a hole for insertion of a guide pin 2d of the housing 2.

[0053] The spacer 10 is provided between the first region 5A and the housing 2, and the height of the first region 5A is ensured by the spacer 10, for example. Note that instead of the spacer 10, a reinforcing plate formed of an insulating material can be provided in the first region 5A of the wiring substrate 5. In this case, a wiring pattern can also be provided on the lower surface of the first region 5A.

[0054] Figure 4 is a side sectional view of the housing 2 of the light emitting element 9, the first lens 8, the light receiving element 7, the wiring substrate 5, and the combiner 6. As shown in Figure 3 and Figure 4 indicated, the output light L output from the light emitting element 9 via the first lens 8 is input to the combiner 6 by the light receiving element 7. The combiner 6 is, for example, a light combiner that combines the four output lights L. One output light L that is formed by combining the four output lights L inside the combiner 6 is output from the combiner 6 to the second lens 11. The second lens 11 condenses the output light L from the combiner 6 and condenses the output light L to an optical fiber held in the receptacle 4. The output light L is output to the outside of the light transmitter 1 via the optical fiber held in the receptacle 4.

[0055] The light receiving element 7 is a monitoring PD (Photo Diode) that monitors the output light L from each of the plurality of light emitting elements 9. The light receiving element 7 monitors the intensity of the output light L by accepting a portion of the output light L from the light emitting element 9. Each of the four light receiving elements 7 is mounted to the main surface 2b of the housing 2 via a bracket 13 (second mounting portion 20) formed of a material including glass or SUS (an alloy of iron, chromium, and nickel), for example. As one example, the thermal expansion coefficient of glass is 7.1 x 10 -6 / K, and the thermal expansion coefficient of SUS is 11 x 10 -6 / K. Note that the main surface 2b of the housing 2 on which the bracket 13 (second mounting portion 20) is mounted is provided with a recess. Thereby, the height of the light receiving element 7 from the main surface 2b can be adjusted.

[0056] The light-receiving element 7 converts a part of the output light L from the light-emitting element 9 into an electric signal, and outputs the converted electric signal to the land 5b of the wiring substrate 5 via an electric wire (not shown). The light-receiving element 7 and the electric wire extending from the light-receiving element 7 to the land 5b are provided on the light output side (the socket 4 side) of the light-emitting element 9. By the output of the electric signal from the light-receiving element 7, APC control (Auto Power Control) can be performed on the output light L from the light-emitting element 9.

[0057] Figure 5 is a side view schematically showing the light-receiving element 7 and the first lens 8. As Figure 4 and Figure 5 indicated, the second region 5B is a PD wiring FPC having a land 5b for wiring of the light-receiving element 7, and is located on the light output side (the socket 4 side) of the light-receiving element 7. The bracket 13 has a mounting surface 13b on which the light-receiving element 7 is mounted. The mounting surface 13b is obliquely arranged at an inclination angle θ with respect to the optical axis of the output light L (the optical axis extending along the long dimension direction Dl from the light-emitting element 9).

[0058] The light-receiving element 7 is a surface incidence type light-receiving element having a light-receiving surface 7b on a surface. The mounting surface 13b is obliquely arranged with respect to the optical axis of the output light L, and thus the light-receiving surface 7b of the light-receiving element 7 is also obliquely arranged with respect to the optical axis of the output light L. By arranging the light-receiving element 7 so that the light-receiving surface 7b is oblique with respect to the optical axis of the output light L, the light-receiving element 7 receives a part of the output light L.

[0059] Therefore, by arranging the light-receiving element 7 on the light output side of the light-emitting element 9, monitoring of the output light L can be performed on the light output side with a simple configuration. Wiring such as an electric wire for the light-receiving element 7 of the monitoring PD is provided on the light output side of the light-receiving element 7. Therefore, electrical connection with the light-receiving element 7 can be performed without reducing the light-receiving sensitivity of the light-receiving element 7. The light-receiving element 7 is directly wired to the land 5b on the wiring substrate 5, for example, and thus there is no need to separately install a bracket or the like. Therefore, cost reduction is facilitated.

[0060] Figure 6 is a graph showing the relationship between the temperature of the housing 2 and the tracking error. Figure 6 The horizontal axis of the graph of Figure 6 The vertical axis of the graph of Figure 6As shown, if the housing 2 becomes hot, the output of the light L through the optical fiber will decrease. In a high-temperature environment, the housing 2 may warp. Due to the warping of the housing 2, the output light L may sometimes deviate from the center of the optical fiber, thus reducing the amount of light output L and potentially increasing tracking errors.

[0061] In the light transmitter 1 of this embodiment, the bracket 13 is tilted such that the tilt angle θ decreases under high temperature conditions, thereby intentionally reducing the amount of light received by the light-receiving element 7 at high temperatures. Since the amount of light received by the light-receiving element 7 decreases, the current to the light-emitting element 9 increases in order to increase the amount of light reaching the light-receiving element 7, thus increasing the luminous power of the output light L from the light-emitting element 9. As a result, the increase in tracking error is suppressed.

[0062] like Figure 7 As shown, in the light transmitter 1, the second mounting portion 20 that mounts the light-receiving element 7 includes a bracket 13, a first resin 21 located on the lower side (main surface 2b side) and the emission end side (receptor 4 side) of the bracket 13, and a second resin 22 located on the lower side of the bracket 13 and the light-emitting element 9 side. The bracket 13 has the aforementioned mounting surface 13b, a first recess 13c for the first resin 21 to enter, and a second recess 13d for the second resin 22 to enter.

[0063] The mounting surface 13b is inclined upwards towards the emission end side, so that the light-receiving element 7 can receive a portion of the output light L on the light-receiving surface 7b. The first recess 13c is a portion recessed from the side surface 13f on the emission end side of the bracket 13. For example, the first resin 21 fills the first recess 13c to a degree that slightly protrudes from it. The second recess 13d is a portion recessed from the side surface 13g on the light-emitting element 9 side of the bracket 13. For example, the second resin 22 fills the second recess 13d to a degree that slightly protrudes from it.

[0064] The thickness of the first resin 21 (length in the height direction D2) and the thickness of the second resin 22 are, for example, 50 μm. The coefficient of thermal expansion of the first resin 21 is smaller than that of the second resin 22. Therefore, at high temperatures, the thermal expansion of the first resin 21 is smaller than that of the second resin 22, thus reducing the tilt angle θ at high temperatures. As an example, the coefficient of thermal expansion of the second resin 22 is 237 × 10⁻⁶. -6 / K, the thermal expansion coefficient of the first resin 21 is 54×10 -6 / K.

[0065] An effect obtained from the optical transmitter 1 of the present embodiment will be described. In the optical transmitter 1, the light emitting element 9 is mounted on the bracket 12 (first mounting portion), and the light receiving element 7 that monitors the output light L from the light emitting element 9 is mounted on the second mounting portion 20 of the housing 2. The second mounting portion 20 has the bracket 13 that mounts the light receiving element 7, the first resin 21 that is positioned on the lower side of the bracket 13 and on the exit end side of the housing 2, and the second resin 22 that is positioned on the lower side of the bracket 13 and on the light emitting element 9 side of the housing 2. The thermal expansion rate of the first resin 21 on the exit end side is smaller than the thermal expansion rate of the second resin 22 on the light emitting element 9 side. Therefore, in a high temperature environment, the thermal expansion of the first resin 21 on the exit end side is smaller than the thermal expansion of the second resin 22 on the light emitting element 9 side, and thus the light receiving amount of the light receiving element 7 can be reduced. Therefore, when the housing 2 is warped and the like at a high temperature, the light receiving amount of the light receiving element 7 can be reduced and the power of the output light L from the light emitting element 9 can be increased. As a result, the influence of the warping of the housing 2 at a high temperature and the like can be reduced, and the light amount of the output light L to the optical fiber at a high temperature can be suppressed from decreasing.

[0066] The mounting surface 13b of the light receiving element 7 of the second mounting portion 20 is disposed obliquely with respect to the optical axis of the output light L from the light emitting element 9. Therefore, in a high temperature environment, the thermal expansion of the first resin 21 on the exit end side is smaller than the thermal expansion of the second resin 22 on the light emitting element 9 side, and thus the oblique angle θ can be more effectively reduced.

[0067] The housing 2 can be manufactured by MIM (Metal Powder Injection Molding). In this case, the cost of manufacturing the housing 2 can be suppressed. In the housing 2, the side wall 2B in which the socket 4 is fitted and the lower plate 2A in which the components are mounted are integrated, and thus the housing 2 can be formed to be less likely to have component tolerances and to have high rigidity. The housing 2 has a pair of protrusions 2g that protrude upward at the end portion on the side opposite to the side wall 2B in the long dimension direction D1. Therefore, for example, even if the housing 2 in which the components have been mounted is disposed upside down by mistake, the side wall 2B and the protrusions 2g will come into contact with the lower plate and the like, and thus the interference of the mounted components with the lower plate and the like can be avoided.

[0068] The bracket 13 can be formed of a material including glass or SUS (an alloy of iron, chromium, and nickel). The thermal expansion rate of the first resin 21 and the thermal expansion rate of the second resin 22 can be larger than the thermal expansion rate of the bracket 13. The housing 2 can have a recess that has a bottom portion at a position lower than the main surface 2b of the housing 2, and the bottom surface of the bracket 13 of the second mounting portion 20 can be mounted on the bottom portion of the recess.

[0069] In the optical transmitter 1, the first resin 21 on the emission end side has a thermal expansion rate smaller than that of the holder 13. Therefore, in a high-temperature environment, the thermal expansion of the first resin 21 on the emission end side is smaller than that of the holder 13, and thus the light receiving amount of the light receiving element can be intentionally reduced. As a result, even when the housing 2 is warped and the like in a high-temperature environment, the light output to the outside of the housing 2 is reduced, and the power of the light from the light emitting element 9 can be increased by the reduction in the light receiving amount of the light receiving element 7. Therefore, even when the housing 2 is warped and the like in a high-temperature environment, the influence of the warp can be reduced by the first resin 21, and thus the reduction in the light amount of the output light to the optical fiber in a high-temperature environment can be suppressed.

[0070] Reference Figure 8 and Figure 9 The second mounting portion 30 of the optical transmitter of the modified example will be described. Hereinafter, the description overlapping with the above-described optical transmitter 1 will be appropriately omitted in order to avoid repetition. Figure 8 is a perspective view of the holder 33 of the second mounting portion 30. Figure 9 is a side view schematically showing the second mounting portion 30. As shown in Figure 8 and Figure 9 The second mounting portion 30 includes the holder 33 mounting the light receiving element 7, the first resin 31 on the lower side of the holder 33 and on the emission end side, and the second resin 32 on the lower side of the holder 33 and on the light emitting element 9 side. The thicknesses of the first resin 31 and the second resin 32 are different from those of the above-described first resin 21 and the second resin 22.

[0071] The holder 33 has a mounting surface 33b mounting the light receiving element 7, a first recess 33c into which the first resin 31 enters, and a second recess 33d into which the second resin 32 enters. The mounting surface 33b is inclined so as to protrude upward as it goes toward the emission end side. The height (length in the height direction D2) of the first recess 33c is lower than that of the second recess 33d. As one example, the height of the second recess 33d is 300 μm, and the height of the first recess 33c is 50 μm.

[0072] The thickness of the first resin 31 is smaller than that of the second resin 32. For example, the thermal expansion rate of the first resin 31 is smaller than that of the second resin 32. Thus, the thermal expansion of the second resin 32 is larger than that of the first resin 31 in a high-temperature environment, and thus the inclination angle θ can be more effectively reduced in a high-temperature environment. As one example, the thermal expansion rate of the second resin 32 is 237 x 10 -6 / K, and the thermal expansion rate of the first resin 31 is 54 x 10 -6 / K.

[0073] In the light transmitter of the modification, the height of the second resin 32 is higher than the height of the first resin 31. Therefore, by making the height of the first resin 31 on the exit end side lower than the height of the second resin 32, the inclination angle θ can be more effectively reduced. Therefore, even if the housing 2 is warped or the like in a high-temperature environment, the reduction in the light quantity of the output light L can be more reliably suppressed.

[0074] Referring to Figure 10 A light transmitter 41 of another modification will be described. Figure 10 is a plan view schematically showing the light emitting element 9, the first lens 8, the light receiving element 7, the combiner 6, the second lens 11, and the optical fiber 45 held to the socket 4 of the light transmitter 41. As shown in Figure 10 , the light transmitter 41 has four light paths of the output light L similarly to the light transmitter 1 described above.

[0075] In the light transmitter 41, the light path lengths of the output light L differ from each other for each lane. For example, if the lane farthest from the optical fiber 45 is set as Lane 0, the second farthest lane is set as Lane 1, the third farthest lane is set as Lane 2, and the closest lane is set as Lane 3, the output light L of Lane 0 is most easily affected by the tracking error.

[0076] Figure 11 is a graph showing the relationship between the temperature of the housing 2 and the tracking error. Figure 11 The horizontal axis of the graph of Figure 11 indicates the output of the optical fiber 45 when the current of the light receiving element 7 is constant. As shown in Figure 11 , if the housing 2 becomes high temperature, the output is the smallest in Lane 0, and the reduction in the output of Lane 3 is small compared to the other lanes. That is, it is known that the longer the light path length of the lane, the greater the tracking error, and the more easily the reduction in the light quantity of the output light L to the optical fiber 45 occurs.

[0077] Figure 12 is a graph showing the relationship between the temperature of the housing 2 and the light receiving quantity of the light receiving element 7 for each inclination angle θ. Figure 12 The horizontal axis of the graph of Figure 12 indicates the light receiving quantity of the light receiving element 7. As shown in Figure 12 , it is known that the smaller the inclination angle θ, the more easily the light receiving quantity changes depending on the temperature. It is known that the smaller the inclination angle θ, the smaller the light receiving quantity of the light receiving element 7 at high temperature.

[0078] Figure 13 is a perspective view showing the bracket 43 constituting the second mounting portion of the light transmitter 41. As shown in Figure 13As shown, in the bracket 43, the inclination angle θ of the mounting surface 43b differs depending on the passage. The inclination angle θ is the smallest in the passage 0 having the longest optical path length, and the inclination angle θ is the largest in the passage 3 having the shortest optical path length. That is, the inclination angle θ is the smallest in the passage 0 in which the tracking error is likely to become large, and thus the light receiving amount of the light receiving element 7 can be reduced more effectively at high temperatures. As one example, the inclination angle θ of the mounting surface 43b of the passage 0 is 4°, the inclination angle θ of the mounting surface 43b of the passage 1 is 5°, the inclination angle θ of the mounting surface 43b of the passage 2 is 7°, and the inclination angle θ of the mounting surface 43b of the passage 3 is 9°.

[0079] As described above, the optical transmitter 41 is provided with the plurality of light emitting elements 9 and the plurality of light receiving elements 7 provided corresponding to each of the plurality of light emitting elements 9, similarly to the optical transmitter 1 described above. The optical path lengths of the plurality of output lights L passing through the plurality of light receiving elements 7 from the plurality of light emitting elements 9 differ from each other. The angle of the mounting surface 43b (for example, the passage 3) on which the light receiving element 7 receiving the output light L having a short optical path length is mounted is larger than the angle of the mounting surface 43b (for example, the passage 0) on which the light receiving element 7 receiving the output light L having a long optical path length is mounted. As described above, the shorter the optical path length of the output light L, the less likely the light amount of the output light L is reduced. The larger the inclination angle θ of the mounting surface 43b of the light receiving element 7, the less likely the reduction in the light receiving amount at the time of temperature rise occurs.

[0080] Therefore, in a case where the inclination angle θ of the mounting surface 43b of the light receiving element 7 receiving the output light L having a short optical path length is larger than the inclination angle θ of the mounting surface 43b of the light receiving element 7 receiving the output light L having a long optical path length, as Figure 14 As shown, the unevenness in the light amount among the plurality of output lights L can be suppressed. Note that, Figure 14 is a graph showing the relationship between the temperature of the housing 2 and the tracking error in a case where the bracket 43 using the optical transmitter 41 is used. As such, it is known that in the bracket 43, the tracking error can be reduced in each of the plurality of passages.

[0081] As described above, the embodiment of the optical transmitter of the present disclosure has been described. However, the present application is not limited to the above-described embodiment. That is, it is easy for those skilled in the art to recognize that the present application can be variously modified and changed within the scope of the gist recited in the claims. For example, the shape, size, number, material, and arrangement scheme of each component of the optical transmitter are not limited to the above-described content, and can be appropriately changed. For example, in the above-described content, the optical transmitter as the embodiment has been described with respect to the optical transmitter 1 and the optical transmitter 41. However, the optical transmitter can be an optical transmitter in which the configurations of a part of the optical transmitter 1 and the optical transmitter 41 are combined with each other.

[0082] Explanation of Reference Signs:

[0083] 1 …… light transmitter;

[0084] 2 …… housing;

[0085] 2A …… lower plate;

[0086] 2B …… side wall;

[0087] 2b …… main surface;

[0088] 2c …… mounting surface;

[0089] 2d …… guide pin;

[0090] 2f …… outer surface;

[0091] 2g …… protrusion;

[0092] 3 …… cover;

[0093] 4 …… socket;

[0094] 4b …… guide;

[0095] 4c …… flange;

[0096] 5 …… wiring substrate;

[0097] 5A …… first region;

[0098] 5b …… land;

[0099] 5B …… second region;

[0100] 5C …… connection region;

[0101] 5c …… recess;

[0102] 5d …… land;

[0103] 5f …… inclined portion;

[0104] 6 …… combiner;

[0105] 7 …… light-receiving element;

[0106] 7b …… light-receiving surface;

[0107] 8 …… first lens;

[0108] 9 …… light-emitting element;

[0109] 10 …… spacer;

[0110] 11 …… second lens;

[0111] 12 …… bracket (first mounting portion);

[0112] 13 …… bracket (second mounting portion);

[0113] 13b …… mounting surface;

[0114] 13c …… first recess;

[0115] 13d …… second recess;

[0116] 13f, 13g …… side surface;

[0117] 20, 30 …… second mounting portion;

[0118] 21, 31 …… first resin;

[0119] 22, 32 …… second resin;

[0120] 33 …… holder;

[0121] 33b …… mounting surface;

[0122] 33c …… first recess;

[0123] 33d …… second recess;

[0124] 41 …… optical transmitter;

[0125] 43 …… holder;

[0126] 43b …… mounting surface;

[0127] 45 …… optical fiber;

[0128] D1 …… long dimension direction;

[0129] D2 …… height direction;

[0130] D3 …… width direction;

[0131] L …… output light;

[0132] θ …… inclination angle.

Claims

1. An optical transmitter comprising: a housing having an emission end; a light emitting element mounted on a first mounting portion of the housing; and a light receiving element mounted on a second mounting portion of the housing, which monitors output light from the light emitting element, wherein a holder, a first resin on a lower side of the holder on the emission end side, and a second resin on a lower side of the holder on the light emitting element side are provided in the second mounting portion, the thermal expansion rate of the first resin is smaller than the thermal expansion rate of the second resin, and the mounting surface of the light receiving element of the second mounting portion is disposed obliquely with respect to the optical axis of the output light from the light emitting element.

2. The optical transmitter according to claim 1, wherein the height of the second resin is higher than the height of the first resin.

3. The optical transmitter according to claim 1, wherein a plurality of the light emitting elements and a plurality of the light receiving elements corresponding to the plurality of the light emitting elements, respectively, are provided, the optical path lengths of the plurality of the output light from the plurality of the light emitting elements through the plurality of the light receiving elements are different from each other, and the angle of the mounting surface of the light receiving element that receives the output light having a short optical path length is larger than the angle of the mounting surface of the light receiving element that receives the output light having a long optical path length.

4. The optical transmitter according to any one of claims 1 to 3, wherein the holder is formed of a material containing glass or an alloy of iron, chromium, and nickel.

5. The optical transmitter according to any one of claims 1 to 3, wherein the thermal expansion rates of the first resin and the second resin are larger than the thermal expansion rate of the holder.

6. The optical transmitter according to any one of claims 1 to 3, wherein the housing includes a recess having a bottom at a position lower than the main surface of the housing, and the bottom surface of the holder of the second mounting portion is mounted on the bottom of the recess. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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