Optical Transmitter

Abstract

An optical transmitter according to one embodiment comprises a housing having an emission end, a light emitting element mounted on a first mounting portion of the housing, and a light receiving element that is mounted on a second mounting portion of the housing and monitors output light from the light emitting element. The second mounting portion is provided with a carrier, a first resin located on the emission end side on the underside of the carrier, and a second resin located on the light emitting element side on the underside of the carrier. The coefficient of thermal expansion of the first resin is smaller than the coefficient of thermal expansion of the second resin.

Description

[Technical Field]

[0001] The present disclosure relates to optical transmitters. This application claims priority to Japanese Application No. 2020-102408 filed on June 12, 2020, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] Patent Document 1 describes a semiconductor module. The semiconductor module includes a semiconductor laser, a focusing lens that focuses light from the semiconductor laser, a photodiode that monitors the light from the semiconductor laser, and a metal case and metal lid that house the semiconductor laser, the focusing lens, and the photodiode. The metal case and the metal lid include an output end having an optical fiber that emits light focused by the focusing lens to the outside. The photodiode that monitors the light from the semiconductor laser is provided on the opposite side of the output end from the semiconductor laser. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-113931 Summary of the Invention

[0004] An optical transmitter according to one embodiment 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 for monitoring output light from the light-emitting element. The second mounting portion includes a carrier, a first resin positioned on the lower side of the carrier toward the emission end, and a second resin positioned on the lower side of the carrier toward the light-emitting element. The thermal expansion coefficient of the first resin is smaller than the thermal expansion coefficient of the second resin.

[0005] An optical transmitter according to another embodiment 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 for monitoring output light from the light-emitting element. The second mounting portion is provided with a carrier and a first resin positioned below the carrier, and the first resin has a thermal expansion coefficient greater than that of the carrier. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a perspective view showing an optical transmitter according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing the optical transmitter of FIG. 1 with the cover removed. [Figure 3] FIG. 3 is a plan view showing the optical transmitter of FIG. 1 with the cover removed. [Figure 4] 4 is a cross-sectional view showing the housing, the combiner, the wiring board, the light receiving element, and the light emitting element of the optical transmitter of FIG. [Figure 5] FIG. 5 is a side view schematically showing the positional relationship between the light emitted from the light emitting element and the light receiving element in FIG. [Figure 6] FIG. 6 is a graph showing the relationship between the temperature of the housing of FIG. 4 and the tracking error. [Figure 7] 7 is a side view showing the carrier, the first resin, and the second resin of the second mounting portion on which the light receiving element of FIG. 4 is mounted. [Figure 8] FIG. 8 is a perspective view showing a carrier according to a first modified example. [Figure 9] FIG. 9 is a side view showing the carrier, the first resin, and the second resin of FIG. [Figure 10] FIG. 10 is a plan view schematically showing the light path of the output light passing through the light emitting element, the light receiving element, the combiner, and the optical fiber of FIG. [Figure 11] FIG. 11 is a graph showing the relationship between the temperature of the housing and the tracking error for each lane of output light in FIG. [Figure 12] FIG. 12 is a graph showing the relationship between the temperature of the housing in FIG. 4 and the amount of light received by the light receiving element for each inclination angle of the light receiving surface. [Figure 13] FIG. 13 is a perspective view showing a carrier of a second mounting portion according to a further modified example. [Figure 14] FIG. 14 is a graph showing the relationship between the amount of light received by the light receiving element mounted on the carrier of FIG. 13 and the tracking error for each lane of output light. DETAILED DESCRIPTION OF THE INVENTION

[0007] In order to secure a large internal space, a photodiode may be placed on the output end side of the semiconductor laser. In this case, if the photodiode's light-receiving surface is placed parallel to the optical axis of the output light from the semiconductor laser, the light-receiving sensitivity of the photodiode will decrease. For this reason, the photodiode may be placed so that its light-receiving surface is oblique to the optical axis of the output light from the semiconductor laser. In this case, the photodiode is placed on an inclined protrusion provided on the housing.

[0008] However, the housing may warp or the like in a high-temperature environment. When warping or the like occurs, the output of light from the housing to the outside may decrease even though the amount of light received by the photodiode remains unchanged. In a high-temperature environment, the optical axis of the output light from the semiconductor laser may deviate from the center of the optical fiber, which may result in a decrease in the amount of light output to the optical fiber at high temperatures.

[0009] An object of the present disclosure is to provide an optical transmitter that can suppress a decrease in the amount of output light that occurs at high temperatures.

[0010] According to the present disclosure, it is possible to suppress the decrease in the amount of output light that occurs at high temperatures.

[0011] The details of the embodiments of the present disclosure will be described below. An optical transmitter according to one embodiment 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 and monitoring the light output from the light-emitting element. The second mounting portion includes a carrier, a first resin positioned on the lower side of the carrier toward the emission end, and a second resin positioned on the lower side of the carrier toward the light-emitting element. The thermal expansion coefficient of the first resin is smaller than that of the second resin.

[0012] In this optical transmitter, a light-emitting element is mounted on a first mounting section of a housing, and a light-receiving element that monitors the light output from the light-emitting element is mounted on a second mounting section of the housing. The second mounting section includes a carrier that mounts the light-receiving element, a first resin located below the carrier on the light-emitting end side of the housing, and a second resin located below the carrier on the light-emitting element side of the housing. The thermal expansion coefficient of the first resin located on the light-emitting end side is smaller than that of the second resin located on the light-emitting element side. Therefore, in a high-temperature environment, the first resin located on the light-emitting end side thermally expands less than the second resin located on the light-emitting element side, thereby deliberately reducing the amount of light received by the light-receiving element. As a result, even if the housing warps or the like in a high-temperature environment and the optical output to the outside of the housing is likely to decrease, the reduced amount of light received by the light-receiving element can increase the power of the light from the light-emitting element. Therefore, even if the housing warps or the like at high temperatures, the first and second resins can reduce the effect of the warp, thereby preventing a decrease in the amount of light output to the optical fiber at high temperatures.

[0013] The mounting surface of the light-receiving element on the second mounting section may be disposed at an angle to the optical axis of the output light from the light-emitting element. In this case, in a high-temperature environment, the first resin located on the output end side thermally expands less than the second resin located on the light-emitting element side, effectively reducing the angle of inclination.

[0014] The height of the second resin may be greater than the height of the first resin. In this case, by making the height of the first resin located on the emission end side smaller than the height of the second resin, even if the housing warps in a high-temperature environment, it is possible to more reliably suppress a decrease in coupling efficiency.

[0015] In the embodiment, separate resins are used on the light-emitting end side and the light-emitting element side. However, resin may be provided only on the light-emitting element side. In a high-temperature environment, the resin on the light-emitting element side thermally expands more than the carrier on the light-emitting end side, effectively realizing a configuration with a small tilt angle. In this case, even if the housing warps in a high-temperature environment, a decrease in coupling efficiency can be reliably suppressed.

[0016] The optical transmitter described above may include a plurality of light-emitting elements and a plurality of light-receiving elements provided corresponding to the plurality of light-emitting elements. The optical path lengths of the plurality of output light beams passing from the plurality of light-emitting elements through the plurality of light-receiving elements may be different from one another. The angle of the mounting surface on which the light-receiving element that receives the output light beam with a short optical path length is mounted may be larger than the angle of the mounting surface on which the light-receiving element that receives the output light beam with a long optical path length is mounted. Incidentally, the shorter the optical path length of the output light beam, the less likely it is that the amount of light received will decrease when the temperature rises. As described above, when the inclination angle of the mounting surface of the light-receiving element that receives the output light beam with a short optical path length is larger than the inclination angle of the mounting surface of the light-receiving element that receives the output light beam with a long optical path length, the variation in the amount of light among the plurality of output light beams can be suppressed.

[0017] The carrier may be made of glass or a material including an alloy of iron, chromium, and nickel.

[0018] The thermal expansion coefficient of the first resin and the thermal expansion coefficient of the second resin may be greater than the thermal expansion coefficient of the carrier.

[0019] The housing may include a recess having a bottom located lower than the main surface of the housing, and the bottom surface of the carrier of the second mounting portion may be mounted on the bottom of the recess.

[0020] An optical transmitter according to another embodiment includes a housing having an output 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 for monitoring output light from the light-emitting element. The second mounting portion is provided with a carrier and a first resin positioned below the carrier. The first resin has a thermal expansion coefficient greater than that of the carrier.

[0021] In this optical transmitter, a light-emitting element is mounted on a first mounting section of a housing, and a light-receiving element that monitors the light output from the light-emitting element is mounted on a second mounting section of the housing. The second mounting section includes a carrier that mounts the light-receiving element and a first resin that is located below the carrier and on the light-emitting element side of the housing. The thermal expansion coefficient of the first resin located on the light-emitting element side is greater than that of the carrier. Therefore, in a high-temperature environment, the first resin located on the light-emitting element side thermally expands more than the carrier, thereby deliberately reducing the amount of light received by the light-receiving element. As a result, the reduced amount of light received by the light-receiving element can increase the power of the light from the light-emitting element. Therefore, even if warping or the like occurs in the housing at high temperatures, the first resin can reduce the effect of the warping, thereby preventing a decrease in the amount of light output to the optical fiber at high temperatures.

[0022] Specific examples of optical transmitters according to the present disclosure will be described below with reference to the drawings. The present invention is not limited to the examples below, but is defined by the claims, and all modifications within the scope of equivalents to the claims are intended to be included. In the description of the drawings, identical or corresponding elements are designated by the same reference numerals, and redundant descriptions will be omitted as appropriate. For ease of understanding, some parts of the drawings may be simplified or exaggerated, and the dimensional proportions and the like are not limited to those shown in the drawings.

[0023] Fig. 1 is a perspective view showing an optical transmitter 1 according to this embodiment. As shown in Fig. 1, the optical transmitter 1 includes a housing 2, a cover 3 that covers the housing 2, a receptacle 4 with a cylindrical sleeve, and a wiring board 5. The optical transmitter 1 extends along a longitudinal direction D1, with the receptacle 4, cover 3 (housing 2), and wiring board 5 arranged in this order.

[0024] FIG. 2 is a perspective view of the optical transmitter 1 with the cover 3 removed. As shown in FIGS. 1 and 2, the housing 2 includes a bottom plate 2A extending in a longitudinal direction D1 and a side wall 2B extending in a height direction D2 from one end of the bottom plate 2A in the longitudinal direction D1. The housing 2 is made of, for example, metal. Examples of the material for the housing 2 include kovar (an alloy of iron containing at least nickel and cobalt) or SUS (stainless used 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.

[0025] The housing 2 has an L-shape when viewed from the width direction D3 of the optical transmitter 1. The housing 2 is also referred to as an L-shaped base. A hole into which the receptacle 4 is inserted and which serves as the emission end of the output light L (see FIG. 4) is formed in the side wall 2B, and the hole penetrates the side wall 2B in the longitudinal direction D1. The receptacle 4 is formed in a cylindrical shape. The receptacle 4 has multiple flanges 4c. One of the multiple flanges 4c functions as a guide 4b that determines the position of the receptacle 4. When the receptacle 4 is fixed to the housing 2, for example, the guide 4b comes into contact with the outer surface 2f of the side wall 2B.

[0026] When viewed from the height direction D2, for example, the housing 2 has a rectangular shape. The housing 2 is a component that mounts the components housed inside the optical transmitter 1. Each component of the optical transmitter 1 is mounted on a lower plate 2A. The lower plate 2A has an elongated portion that protrudes from the side wall 2B in the longitudinal direction D1, and each component of the optical transmitter 1 is mounted on this elongated portion. The lower plate 2A has a main surface 2b that faces each component inside the optical transmitter 1, a convex mounting surface 2c on which components are mounted, a guide pin 2d that determines the position of the cover 3 relative to the housing 2, and an outer surface 2f that is exposed to the outside of the optical transmitter 1.

[0027] The main surface 2b has a rectangular shape extending in the longitudinal direction D1 and the width direction D3. The mounting surface 2c is a portion that protrudes from the main surface 2b in the height direction D2, and a combiner 6 that combines light is mounted on the mounting surface 2c, for example. The guide pin 2d protrudes from the main surface 2b in the height direction D2. The guide pin 2d is, for example, cylindrical. The guide pin 2d is provided, for example, on one side in the width direction D3 (a position 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 the components of the optical transmitter 1 are housed inside the housing 2 and the cover 3. The cover 3 has a protrusion formed therein with a hole into which the guide pin 2d of the housing 2 fits. The cover 3 is fixed to the housing 2 by fitting the guide pin 2d into the hole in the protrusion.

[0028] The optical transmitter 1 includes a wiring board 5, a combiner 6, a light receiving element 7, a first lens 8, a light emitting element 9, and a spacer 10 inside a housing 2 and a cover 3. A portion of the wiring board 5 extends from the housing 2 and the cover 3 to the side opposite the receptacle 4. The portion of the wiring board 5 extending to the side opposite the receptacle 4 protrudes outside the optical transmitter 1.

[0029] 3 is a plan view showing the components mounted on the main surface 2b of the housing 2. As shown in FIGS. 2 and 3, the optical transmitter 1 further includes a second lens 11 interposed between the receptacle 4 and the combiner 6. For example, the optical transmitter 1 includes four light-emitting elements 9, four first lenses 8, four light-receiving elements 7, the combiner 6, and the second lens 11.

[0030] The optical transmitter 1 is a four-lane multi-channel light emitting module including four light emitting elements 9, four first lenses 8, and four light receiving elements 7. In the optical transmitter 1 having the optical paths of the output light L for four lanes like this, the optical path length of the output light L differs for each channel. The receptacle 4 is disposed, for example, at a position offset from the center of the housing 2 in the width direction D3. The optical path of the output light L from the light emitting element 9 located at the end opposite the receptacle 4 in the width direction D3 (the lower end in FIG. 3) is the longest. The optical path of the output light L from the light emitting element 9 located at the end on the receptacle 4 side in the width direction D3 (the upper end in FIG. 3) is the shortest.

[0031] The housing 2 is mounted with a plurality of light-emitting elements 9 and a plurality of light-receiving elements 7. The light-emitting elements 9 are arranged side by side along the width direction D3, and the light-receiving elements 7 are arranged side by side along the width direction D3. For example, four light-emitting elements 9 are mounted on the main surface 2b of the housing 2 via a carrier 12 (first mounting portion). Each light-emitting element 9 is provided corresponding to one of the four first lenses 8 and one of the four light-receiving elements 7. Each light-emitting element 9 is, for example, a semiconductor laser diode (LD). 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 carrier 13 (second mounting portion 20). The carrier 13 has a recess (concave portion) on the main surface 2b. This recess is for adjusting the height. The main surface 2b may not have a recess. The height can be adjusted by the carrier 13.

[0032] The wiring board 5 is, for example, a flexible printed circuit (FPC) mounted on the housing 2. The housing 2 has a pair of protrusions 2g protruding upward at an end opposite the side wall 2B in the longitudinal direction D1. The pair of protrusions 2g are arranged side by side in the width direction D3. The wiring board 5 has a first region 5A extending outward from the optical transmitter 1, a second region 5B in which pads 5b are provided, and a connection region 5C connecting the first region 5A and the second region 5B to each other. When viewed from the height direction D2, the first region 5A, the second region 5B, and the connection region 5C are U-shaped (C-shaped).

[0033] The first region 5A has recesses 5c at both ends in the width direction D3. The first region 5A has a pair of recesses 5c aligned in the width direction D3. The wiring board 5 is fixed to the housing 2 by fitting each protrusion 2g of the housing 2 into each recess 5c. The first region 5A has pads 5d electrically connected to the light-emitting elements 9. For example, each of the multiple light-emitting elements 9 is electrically connected to the pad 5d via a wire. The first region 5A is provided at a higher position (a position farther from the main surface 2b of the housing 2) than the second region 5B. For example, the height of the first region 5A matches the height of the carrier 12 on which the light-emitting elements 9 are mounted. This allows the length of the wires extending from each light-emitting element 9 to the pads 5d to be shortened.

[0034] For example, one wiring board 5 has a first region 5A as an upper stage and a second region 5B as a lower stage, and is fixed to the housing 2 by adhesive. The second region 5B is provided at a lower position than the first region 5A, and is in contact with, for example, the main surface 2b of the housing 2. By positioning the second region 5B low in this way, it is possible to prevent wires extending from the wiring board 5 or the light receiving element 7 from interfering with the output light L passing through the light emitting element 9 and the first lens 8.

[0035] The width of the connection region 5C of the wiring board 5 (the length in the width direction D3) is narrower than the width of the first region 5A and the width of the second region 5B. The connection region 5C is provided, for example, at the end on the receptacle 4 side in the width direction D3. The connection region 5C extends from the end of the first region 5A in the width direction D3 to the end of the second region 5B in the width direction D3. The thickness of the wiring board 5 in the first region 5A and the thickness of the wiring board 5 in the second region 5B are, for example, the same. The connection region 5C extends in the longitudinal direction D1 between the first region 5A and the second region 5B and is located, for example, at the end of the housing 2 in the width direction D3.

[0036] The connection region 5C has a step or slope located between the first region 5A and the second region 5B. In this embodiment, an example is shown in which the connection region 5C has a slope 5f. The wiring board 5 may also have an extension region 5D on an extension of the connection region 5C, in which a hole into which the guide pin 2d of the housing 2 is inserted is formed.

[0037] The spacer 10 is provided between the first region 5A and the housing 2, and, for example, the height of the first region 5A is ensured by the spacer 10. Note that, instead of the spacer 10, a reinforcing plate made of an insulating material may be provided in the first region 5A of the wiring board 5. In this case, it becomes possible to provide a wiring pattern also on the lower surface of the first region 5A.

[0038] FIG. 4 is a side cross-sectional view of the housing 2, showing the light-emitting element 9, the first lens 8, the light-receiving element 7, the wiring board 5, and the combiner 6. As shown in FIGS. 3 and 4, the output light L output from the light-emitting element 9 via the first lens 8 passes through the light-receiving element 7 and enters the combiner 6. The combiner 6 is, for example, an optical combiner that combines four output light L. The four output light L are combined inside the combiner 6 and output from the combiner 6 to the second lens 11 as a single output light L. The second lens 11 focuses the output light L from the combiner 6 and focuses the output light L on an optical fiber held in the receptacle 4. The output light L is output to the outside of the optical transmitter 1 via the optical fiber held in the receptacle 4.

[0039] The light receiving element 7 is a monitor 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 receiving a portion of the output light L from the light emitting elements 9. For example, each of the four light receiving elements 7 is mounted on the main surface 2b of the housing 2 via a carrier 13 (second mounting portion 20) made of a material containing glass or SUS (an alloy of iron, chromium, and nickel). As an example, the thermal expansion coefficient of glass is 7.1×10 -6 / K, and the thermal expansion coefficient of SUS is 11×10 -6 / K. A recess is provided in the main surface 2b of the housing 2 on which the carrier 13 (second mounting portion 20) is mounted, which allows the height of the light receiving element 7 from the main surface 2b to be adjusted.

[0040] The light receiving element 7 converts a portion of the output light L from the light emitting element 9 into an electrical signal and outputs the converted electrical signal to the pad 5b of the wiring board 5 via a wire (not shown). The light receiving element 7 and the wire extending from the light receiving element 7 to the pad 5b are located closer to the light output side (the receptacle 4 side) than the light emitting element 9. The output of the electrical signal from the light receiving element 7 makes it possible to perform APC (Auto Power Control) on the output light L from the light emitting element 9.

[0041] 5 is a side view schematically showing the light receiving element 7 and the first lens 8. As shown in FIGS. 4 and 5, the second region 5B is a PD wiring FPC having pads 5b for wiring to the light receiving element 7, and is located on the optical output side (receptacle 4 side) of the light receiving element 7. The carrier 13 has a mounting surface 13b on which the light receiving element 7 is mounted. The mounting surface 13b is disposed obliquely so as to form an inclination angle θ with respect to the optical axis of the output light L from the light emitting element 9 (the optical axis extending from the light emitting element 9 along the longitudinal direction D1).

[0042] The light receiving element 7 is a front-illuminated light receiving element and has a light receiving surface 7b on its surface. Because the mounting surface 13b is disposed at an angle to the optical axis of the output light L, the light receiving surface 7b of the light receiving element 7 is also disposed at an angle to the optical axis of the output light L. By disposing the light receiving element 7 so that the light receiving surface 7b is at an angle to the optical axis of the output light L, the light receiving element 7 receives a portion of the output light L.

[0043] Therefore, by arranging the light receiving element 7 on the light output side of the light emitting element 9, it becomes possible to monitor the output light L on the light output side with a simple configuration. Wiring such as wires for the light receiving element 7, which is the monitor PD, is provided on the light output side of the light receiving element 7. This makes it possible to electrically connect the light receiving element 7 without reducing the light receiving sensitivity of the light receiving element 7. The light receiving element 7 is wired directly to, for example, pad 5b on the wiring board 5, so there is no need to mount a separate carrier or the like. This contributes to cost reduction.

[0044] FIG. 6 is a graph showing the relationship between the temperature of the housing 2 and the tracking error. The horizontal axis of the graph in FIG. 6 represents the temperature of the housing 2, and the vertical axis of the graph in FIG. 6 represents the output of the optical fiber when the current of the light receiving element 7 is constant. As shown in FIG. 6, when the temperature of the housing 2 becomes high, the output of the output light L through the optical fiber decreases. When the housing 2 is in a high-temperature environment, warping or the like may occur. In a high-temperature environment, warping of the housing 2 may cause the output light L to deviate from the center of the optical fiber, reducing the amount of output light L and potentially leading to an increase in tracking error.

[0045] In the optical transmitter 1 according to this embodiment, the carrier 13 is tilted so that the tilt angle θ is small in a high-temperature environment, thereby intentionally reducing the amount of light received by the light-receiving element 7 at high temperatures. When the amount of light received by the light-receiving element 7 decreases, the current to the light-emitting element 9 increases to increase the amount of light to the light-receiving element 7, and the light emission power of the output light L from the light-emitting element 9 increases. As a result, an increase in tracking error is suppressed.

[0046] 7, in the optical transmitter 1, the second mounting portion 20 on which the light receiving element 7 is mounted includes a carrier 13, a first resin 21 located on the lower side (main surface 2b side) of the carrier 13 and on the emission end side (receptacle 4 side), and a second resin 22 located on the lower side of the carrier 13 and on the light emitting element 9 side. The carrier 13 has the above-mentioned mounting surface 13b, a first recess 13c into which the first resin 21 fits, and a second recess 13d into which the second resin 22 fits.

[0047] The mounting surface 13b is inclined so as to protrude upward toward the emission end side, which allows the light receiving element 7 to receive a portion of the output light L at the light receiving surface 7b. The first recess 13c is a portion recessed from the side surface 13f of the carrier 13 on the emission end side. For example, the first resin 21 is filled into the first recess 13c to the extent that it slightly protrudes from the first recess 13c. The second recess 13d is a portion recessed from the side surface 13g of the carrier 13 on the light emitting element 9 side. For example, the second resin 22 is filled into the second recess 13d to the extent that it slightly protrudes from the second recess 13d.

[0048] 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 thermal expansion coefficient of the first resin 21 is smaller than that of the second resin 22. As a result, the first resin 21 expands less than the second resin 22 at high temperatures, making it possible to reduce the inclination angle θ at high temperatures. As an example, the thermal expansion coefficient of the second resin 22 is 237×10 -6 / K, and the thermal expansion coefficient of the first resin 21 is 54×10 -6 / K.

[0049] The following describes the effects and advantages of the optical transmitter 1 according to this embodiment. In the optical transmitter 1, the light-emitting element 9 is mounted on the carrier 12 (first mounting portion), and the light-receiving element 7, which 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 includes a carrier 13 on which the light-receiving element 7 is mounted, a first resin 21 located below the carrier 13 on the light-emitting end side of the housing 2, and a second resin 22 located below the carrier 13 on the light-emitting end side of the housing 2. The thermal expansion coefficient of the first resin 21 located on the light-emitting end side is smaller than that of the second resin 22 located on the light-emitting element 9 side. Therefore, in a high-temperature environment, the first resin 21 located on the light-emitting end side thermally expands less than the second resin 22 located on the light-emitting element 9 side, thereby reducing the amount of light received by the light-receiving element 7. Therefore, when warping or the like occurs in the housing 2 at high temperatures, the amount of light received by the light-receiving element 7 can be reduced, thereby increasing the power of the output light L from the light-emitting element 9. As a result, the influence of warping of the housing 2 at high temperatures can be reduced, and a decrease in the amount of output light L to the optical fiber at high temperatures can be suppressed.

[0050] The mounting surface 13b of the second mounting portion 20 for the light receiving element 7 is disposed at an angle with respect to the optical axis of the output light L from the light emitting element 9. Therefore, in a high-temperature environment, the first resin 21 located on the emission end side thermally expands less than the second resin 22 located on the light emitting element 9 side, so that the tilt angle θ can be reduced more effectively.

[0051] The housing 2 may be manufactured by metal injection molding (MIM). In this case, the cost of manufacturing the housing 2 can be reduced. In the housing 2, the side wall 2B to which the receptacle 4 is attached and the bottom plate 2A to which the components are mounted are integrated, which reduces the occurrence of component tolerances and enables the housing 2 to have high rigidity. The housing 2 has a pair of protrusions 2g that protrude upward at the end opposite the side wall 2B in the longitudinal direction D1. Therefore, even if the housing 2 with components already installed is accidentally placed upside down, the side wall 2B and the protrusions 2g will come into contact with the floor or the like, preventing the installed components from interfering with the floor or the like.

[0052] The carrier 13 may be made of a material containing glass or SUS (an alloy of iron, chromium, and nickel). The thermal expansion coefficients of the first resin 21 and the second resin 22 may be greater than the thermal expansion coefficient of the carrier 13. The housing 2 may have a recess having a bottom located lower than the main surface 2b of the housing 2, and the bottom surface of the carrier 13 of the second mounting portion 20 may be mounted on the bottom of the recess.

[0053] In the optical transmitter 1, the thermal expansion coefficient of the first resin 21 located on the emitting end side is smaller than that of the carrier 13. Therefore, in a high-temperature environment, the first resin 21 located on the emitting end side thermally expands less than the carrier 13, so that the amount of light received by the light-receiving element can be intentionally reduced. As a result, even if warping or the like occurs in the housing in a high-temperature environment and the optical output to the outside of the housing 2 is likely to decrease, the amount of light received by the light-receiving element 7 can be reduced, thereby increasing the power of light from the light-emitting element 9. Therefore, even if warping or the like occurs in the housing 2 at high temperatures, the first resin 21 can reduce the effect of the warping, so that a decrease in the amount of light output to the optical fiber at high temperatures can be suppressed.

[0054] A second mounting section 30 of an optical transmitter according to a modified example will be described with reference to FIGS. 8 and 9. Below, to avoid redundancy, descriptions that overlap with those of the optical transmitter 1 described above will be omitted as appropriate. FIG. 8 is a perspective view showing a carrier 33 of the second mounting section 30. FIG. 9 is a side view schematically showing the second mounting section 30. As shown in FIGS. 8 and 9, the second mounting section 30 includes a carrier 33 on which a light-receiving element 7 is mounted, a first resin 31 located below the carrier 33 on the emission end side, and a second resin 32 located below the carrier 33 on the light-emitting element 9 side. The first resin 31 and the second resin 32 have different thicknesses from the first resin 21 and the second resin 22 described above.

[0055] The carrier 33 has a mounting surface 33b on which the light-receiving element 7 is mounted, a first recess 33c into which the first resin 31 fits, and a second recess 33d into which the second resin 32 fits. The mounting surface 33b is inclined so as to protrude upward toward the light-emitting end. The height of the first recess 33c (length in the height direction D2) is shorter than the height of the second recess 33d. As an example, the thickness of the second recess 33d is 300 μm, and the thickness of the first recess 33c is 50 μm.

[0056] The thickness of the first resin 31 is smaller than the thickness of the second resin 32. For example, the thermal expansion coefficient of the first resin 31 is smaller than the thermal expansion coefficient of the second resin 32. As a result, the second resin 32 expands more than the first resin 31 at high temperatures, so that the inclination angle θ can be more effectively reduced at high temperatures. As an example, the thermal expansion coefficient of the second resin 32 is 237×10 -6 / K, and the thermal expansion coefficient of the first resin 31 is 54×10 -6 / K.

[0057] In the optical transmitter according to the modified example, the height of the second resin 32 is greater than the height of the first resin 31. Therefore, the height of the first resin 31 located on the emission end side is less than the height of the second resin 32, so that the inclination angle θ can be more effectively reduced. Therefore, even if warping or the like occurs in the housing 2 in a high-temperature environment, a decrease in the amount of output light L can be more reliably suppressed.

[0058] An optical transmitter 41 according to another modification will be described with reference to Fig. 10. Fig. 10 is a plan view schematically showing the light-emitting element 9, first lens 8, light-receiving element 7, combiner 6, second lens 11, and optical fiber 45 held in the receptacle 4 of the optical transmitter 41. As shown in Fig. 10, the optical transmitter 41 has four optical paths for output light L, similar to the optical transmitter 1 described above.

[0059] In the optical transmitter 41, the optical path length of the output light L differs for each channel. For example, if the lane farthest from the optical fiber 45 is Lane 0, the next farthest lane is Lane 1, the third farthest lane is Lane 2, and the closest lane is Lane 3, the output light L of Lane 0 is most susceptible to the influence of tracking errors.

[0060] Fig. 11 is a graph showing the relationship between the temperature of the housing 2 and the tracking error. The horizontal axis of the graph in Fig. 11 represents the temperature of the housing 2, and the vertical axis of the graph in Fig. 11 represents the output of the optical fiber 45 when the current of the light receiving element 7 is constant. As shown in Fig. 11, when the temperature of the housing 2 becomes high, the output of Lane 0 becomes the smallest, and the output of Lane 3 decreases less than the other lanes. In other words, it can be seen that the longer the optical path length of a lane, the larger the tracking error and the more likely it is that the output light L to the optical fiber 45 will decrease.

[0061] FIG. 12 is a graph showing the relationship between the temperature of the housing 2 and the amount of light received by the light receiving element 7 for each tilt angle θ. The horizontal axis of the graph in FIG. 12 represents the temperature of the housing 2, and the vertical axis of the graph in FIG. 12 represents the amount of light received by the light receiving element 7. As shown in FIG. 12, it can be seen that the smaller the tilt angle θ, the more easily the amount of light received changes with temperature. It can be seen that the smaller the tilt angle θ, the less light is received by the light receiving element 7 at high temperatures.

[0062] FIG. 13 is a perspective view showing a carrier 43 constituting a second mounting portion of an optical transmitter 41. As shown in FIG. 13, the inclination angle θ of the mounting surface 43b of the carrier 43 varies depending on the lane. The inclination angle θ is smallest in Lane 0, which has the longest optical path length, and the inclination angle θ is largest in Lane 3, which has the shortest optical path length. That is, since the inclination angle θ is smallest in Lane 0, which is prone to large tracking errors, it is possible to more effectively reduce the amount of light received by the light receiving element 7 at high temperatures. As an example, the inclination angle θ in Lane 0 is 4°, the inclination angle θ of the mounting surface 43b in Lane 1 is 5°, the inclination angle θ of the mounting surface 43b in Lane 2 is 7°, and the inclination angle θ of the mounting surface 43b in Lane 3 is 9°.

[0063] As described above, the optical transmitter 41, like the optical transmitter 1 described above, includes a plurality of light-emitting elements 9 and a plurality of light-receiving elements 7 provided corresponding to the plurality of light-emitting elements 9. The optical path lengths of the plurality of output light beams L passing from the plurality of light-emitting elements 9 to the plurality of light-receiving elements 7 are different from one another. The angle of the mounting surface 43b (e.g., Lane 3) on which the light-receiving element 7 that receives the output light beam L with a short optical path length is mounted is larger than the angle of the mounting surface 43b (e.g., Lane 0) on which the light-receiving element 7 that receives the output light beam L with a long optical path length is mounted. As described above, the shorter the optical path length of the output light beam L, the less likely a decrease in the amount of the output light beam L occurs. The larger the inclination angle θ of the mounting surface 43b for the light-receiving element 7, the less likely a decrease in the amount of received light occurs when the temperature rises.

[0064] Therefore, when the inclination angle θ of the mounting surface 43b of the light-receiving element 7 that receives output light L with a short optical path length is larger than the inclination angle θ of the mounting surface 43b of the light-receiving element 7 that receives output light L with a long optical path length, it is possible to suppress the variation in the amount of light among the multiple output lights L, as shown in Fig. 14. Note that Fig. 14 is a graph showing the relationship between the temperature of the housing 2 and the tracking error when the carrier 43 of the optical transmitter 41 is used. As such, it can be seen that the carrier 43 can reduce the tracking error in each of the multiple lanes.

[0065] The above describes an embodiment of an optical transmitter according to the present disclosure. However, the present invention is not limited to the above-described embodiment. In other words, those skilled in the art will readily recognize that various modifications and variations are possible within the scope of the claims. For example, the shape, size, number, material, and arrangement of each component of the optical transmitter are not limited to those described above and can be modified as appropriate. For example, the above describes the optical transmitter 1 and the optical transmitter 41 as optical transmitters according to the embodiment. However, an optical transmitter may be formed by combining partial components of the optical transmitter 1 and the optical transmitter 41. [Explanation of symbols]

[0066] 1...Optical transmitter 2. Housing 2A…Lower plate 2B…Side wall 2b…main surface 2c...Mounting surface 2d...Guide pin 2f...Outer surface 2g…Protrusion 3...Cover 4...Receptacle 4b... Guide 4c...Flange 5...Wiring board 5A…First area 5b...pad 5B…Second area 5C…Connection area 5c...recess 5d...pad 5f…slope 6…Synthesizer 7...Photodetector 7b…Light receiving surface 8...First lens 9...Light emitting element 10...Spacer 11...Second lens 12...Carrier (first mounting part) 13...Carrier (second mounting section) 13b...Mounting surface 13c...First recess 13d...Second recess 13f, 13g...side 20,30...Second mounting section 21, 31...First resin 22, 32...Second resin 33...Career 33b…Mounting surface 33c...First recess 33d...Second recess 41...Optical transmitter 43...Career 43b…Mounting surface 45...Optical fiber D1: Longitudinal direction D2: Height direction D3: Width direction L...Output light θ…Inclination angle

Claims

1. a housing having an output end; a light emitting element mounted on a first mounting portion of the housing; a light receiving element mounted on a second mounting portion of the housing and configured to monitor output light from the light emitting element; Equipped with the second mounting portion is provided with a carrier, a first resin positioned on the emission end side of the carrier, and a second resin positioned on the light emitting element side of the carrier, The thermal expansion coefficient of the first resin is smaller than the thermal expansion coefficient of the second resin, a mounting surface of the second mounting portion for the light receiving element is disposed obliquely with respect to the optical axis of the output light from the light emitting element; Optical transmitter.

2. The height of the second resin is greater than the height of the first resin.

2. The optical transmitter according to claim 1.

3. a plurality of light-emitting elements and a plurality of light-receiving elements provided corresponding to the plurality of light-emitting elements, the optical path lengths of the plurality of output lights passing from the plurality of light-emitting elements to the plurality of light-receiving elements are different from one another; an angle of the mounting surface on which the light-receiving element that receives the output light having the short optical path length is mounted is larger than an angle of the mounting surface on which the light-receiving element that receives the output light having the long optical path length is mounted; 2. The optical transmitter according to claim 1.

4. The carrier is made of glass or a material containing an alloy of iron, chromium, and nickel; 4. The optical transmitter according to claim 1.

5. a thermal expansion coefficient of the first resin and a thermal expansion coefficient of the second resin are greater than a thermal expansion coefficient of the carrier; 5. The optical transmitter according to claim 1.

6. the housing includes a recess having a bottom located lower than a main surface of the housing; The bottom surface of the carrier of the second mounting portion is mounted on the bottom of the recess.

6. The optical transmitter according to claim 1.

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