Semiconductor light emitting device and optical subassembly

Abstract

To reduce deterioration of a high frequency property.SOLUTION: A semiconductor light-emitting device 102 includes a submount 10 having a conductive pattern 12 on the upper surface thereof, an optical modulator 36 having a lower electrode 42 facing and connected to the conductive pattern 12, a termination resistor 52 connected to the optical modulator 36 in parallel, and a microstrip substrate 16 having a ground plane 18 facing and connected to the conductive pattern 12. A single-ended transmission line 20 includes a first section 28, and a second section 30 extending from the first section 28 and including a second end 24. The second section 30 has a lower characteristic impedance than the first section 28. A load circuit 58 having a wire 56, the optical modulator 36, and the termination resistor 52 is electrically connected between the second end 24 and the conductive pattern 12. The load circuit 58 has a lower characteristic impedance than the second section 30.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to semiconductor light emitting devices and optical subassemblies. [Background technology]

[0002] An optical modulator for optical communication generates an optical signal according to an input high-frequency electrical signal. Since the quality of the high-frequency electrical signal deteriorates along the transmission line, the optical signal also deteriorates accordingly. Patent Document 1 discloses shortening the bonding wire to reduce the deterioration of high-frequency characteristics. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-275957 Summary of the Invention [Problem to be solved by the invention]

[0004] High-frequency electrical signal sources and transmission lines are generally configured as 50 Ω termination systems for single-ended drive. On the other hand, the characteristic impedance of optical modulators is not always 50 Ω. Therefore, mismatch in characteristic impedance with the optical modulator causes reflection of the high-frequency electrical signal, degrading the quality of the high-frequency electrical signal, and ultimately degrading the quality of the optical signal. For example, the value of the f3 dB band, which indicates the electrical / optical response characteristics, deteriorates.

[0005] The present disclosure aims to reduce the effects of mismatch in characteristic impedance. [Means for solving the problem]

[0006] The semiconductor light emitting device has a submount having a conductive pattern on its upper surface, an optical modulator having an upper electrode on its upper surface and a lower electrode on its bottom surface, the lower electrode being joined opposite the conductive pattern, a termination resistor connected in parallel to the optical modulator, a microstrip substrate having a single-ended transmission line extending from a first end to a second end on its upper surface and a ground plane on its back surface, the ground plane being joined opposite the conductive pattern, and a wire having both ends bonded to the upper electrode of the optical modulator and the second end of the single-ended transmission line, the single-ended transmission line including a first section and a second section extending from the first section and including the second end, the second section having a lower characteristic impedance than the first section, and a load circuit including the wire, the optical modulator and the termination resistor being electrically connected between the second end and the conductive pattern, the load circuit having a characteristic impedance equal to or lower than the second section.

[0007] Since the single-ended transmission line includes a first section and a second section with different characteristic impedances, the influence of mismatch in characteristic impedance with the optical modulator can be suppressed.

[0008] The optical subassembly includes the semiconductor light emitting device and an electrical connector, the electrical connector being electrically connected to the first end of the single-ended transmission line. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram showing the internal configuration of an optical subassembly according to the first embodiment. [Diagram 2] FIG. 2 is a plan view of a submount and components mounted thereon. [Diagram 3] FIG. 3 is a cross-sectional view of the structure shown in FIG. 2 taken along line III-III. [Figure 4] 1 is a diagram showing the response characteristics (optical / electrical response characteristics) of an optical signal to a high-frequency electrical signal. [Diagram 5] FIG. 11 is a plan view of a microstrip substrate according to a second embodiment. [Figure 6] FIG. 11 is a plan view of a microstrip substrate according to a third embodiment. [Figure 7] FIG. 13 is a diagram showing the internal configuration of an optical subassembly according to a fourth embodiment. [Figure 8] FIG. 13 is a plan view of a microstrip substrate according to a fifth embodiment. [Figure 9] FIG. 13 is a plan view of a microstrip substrate according to a sixth embodiment. [Figure 10] FIG. 13 is a plan view of a microstrip substrate according to a seventh embodiment. [Figure 11] FIG. 13 is a plan view of a microstrip substrate according to an eighth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings, the same reference numerals are used to denote the same or equivalent functions, and the repeated description thereof will be omitted. Note that the size of the figures does not necessarily correspond to the magnification.

[0011] [First embodiment] 1 is a diagram showing the internal configuration of an optical subassembly according to a first embodiment. The optical subassembly 100 has a semiconductor light emitting device 102 therein, and is sealed in a box-shaped package 104. An optical signal is output to the outside of the optical subassembly 100 via a lens 106 and an optical connector 108.

[0012] The optical subassembly 100 has an electrical connector 110 on the opposite side of the package 104 to the optical connector 108. The electrical connector 110 electrically connects the inside and outside of the optical subassembly 100, and a flexible substrate (not shown) is connected to the outside of the optical subassembly 100 (the outside of the package 104) to supply power.

[0013] The optical subassembly 100 has a high-frequency connector 112 on the side of the package 104. The high-frequency connector 112 electrically connects the inside and outside of the optical subassembly 100, and is, for example, a GPPO connector. A high-frequency electrical signal of 56 Gbps is input to the high-frequency connector 112.

[0014] [Submount] The semiconductor light emitting device 102 has a submount 10. The submount 10 has a structure in which the surface of a ceramic substrate is metallized. The submount 10 has a conductive pattern 12 on its upper surface. The conductive pattern 12 is at a reference potential (ground potential).

[0015] FIG. 2 is a plan view of the submount 10 and the components mounted thereon. FIG. 3 is a cross-sectional view taken along line III-III of the structure shown in FIG. 2. The entire back surface of the submount 10 is also metallized. Conductive pattern 12 and metal film 14 on the back surface are electrically connected by vias (not shown). The side surfaces of the submount 10 are also metallized, connecting conductive pattern 12 and metal film 14 on the back surface. Here, the lower side surface in FIG. 2 is metallized. Side metallization is not essential.

[0016] [Microstrip board] The semiconductor light emitting device 102 has a microstrip substrate 16. The microstrip substrate 16 has a structure in which electrical wiring is provided on both sides of a ceramic substrate.

[0017] The microstrip substrate 16 has a ground plane 18 on its back surface. The ground plane 18 is bonded to face the conductive pattern 12 of the submount 10, and serves as a reference potential. Solder or a conductive adhesive (not shown) is used for bonding.

[0018] The microstrip substrate 16 has a single-ended transmission line 20 on its upper surface. The single-ended transmission line 20 extends from a first end 23 to a second end 24. The first end 23 and the second end 24 are at both ends of the microstrip substrate 16 along the length of the single-ended transmission line 20. It is not essential that the single-ended transmission line 20 does not completely reach both ends of the ceramic substrate.

[0019] The single-ended transmission line 20 includes an external connection section 22, a first section 28, and a second section 30. The microstrip substrate 16 includes a pair of ground conductors 26 on the upper surface thereof, sandwiching the external connection section 22 of the single-ended transmission line 20. The pair of ground conductors 26 are connected to the ground plane 18 by vias (not shown). A grounded coplanar line is configured by a part of the single-ended transmission line 20, the pair of ground conductors 26, and the ground plane 18. The microstrip line may be a line that does not include the pair of ground conductors 26. The first end 23 is within the region of the external connection section 22. The above-mentioned grounded coplanar line has a line width and the like set to have 50Ω, which is the same characteristic impedance as the driving system of the external electrical signal. Here, the line width of the single-ended transmission line 20 in the region of the external connection section 22 is set to be the same as the line width of the single-ended transmission line 20 in the region of the first section 28 described later, but is not limited to this and may be changed as appropriate. However, it is preferable that the line width of the single-ended transmission line 20 is consistent at the connection point between the external connection section 22 and the first section 28. The first end 23 of the single-ended transmission line 20 and the pair of ground conductors 26 in the external connection section 22 are electrically connected to the high-frequency connector 112 (FIG. 1), and a wire W1 is used for the connection. Specifically, the wire W1 is a GSG line, and the signal wiring is connected to the first end 23 of the single-ended transmission line 20, and the pair of ground wirings are connected to the pair of ground conductors 26, respectively.

[0020] The single-ended transmission line 20 includes a first section 28. The first section 28 has a uniform width and extends linearly. In other words, the first section 28 indicates a region to which the wire W1 is not connected and extends linearly with a uniform width. Since the ground plane 18 is below the first section 28, a microstrip line is formed. The characteristic impedance of the first section 28 is set to 50 Ω, which is the same as that of the external connection section 22 that constitutes the above-mentioned grounded coplanar line. The first section 28 does not include the first end 23. The high-frequency connector 112 and the first section 28 may be connected without the external connection section 22. In this case, the region to which the wire W1 is connected becomes the external connection section 22, and the subsequent region in which the single-ended transmission line 20 extends linearly with a uniform width becomes the first section 28.

[0021] The single-ended transmission line 20 includes a second section 30. The second section 30 extends from the first section 28. The ground plane 18 is below the second section 30, forming a microstrip line. The second section 30 has the same thickness as the first section 28. The second section 30 includes a wide portion 32 that is wider than the first section 28. Therefore, the second section 30 has a lower characteristic impedance than the first section 28. The characteristic impedance of the second section 30 is 45 Ω. The wide portion 32 includes a second end 24, and the second section 30 includes the second end 24. The second end 24 is the other end of the single-ended transmission line 20 and indicates a region of the second section 30 to which a wire 56, which will be described later, is bonded.

[0022] [Semiconductor optical element] The semiconductor light emitting device 102 has a semiconductor optical element 34 (e.g., an EA / DFB laser). An optical modulator 36 (e.g., an electroabsorption modulator (EA modulator) or a Mach-Zehnder modulator (MZ modulator)) and a semiconductor laser 38 (e.g., a distributed feedback (DFB) laser) are both monolithically integrated in the semiconductor optical element 34.

[0023] The semiconductor laser 38 is configured to oscillate continuous light when a direct current is injected into it. The optical modulator 36 absorbs the light from the semiconductor laser 38 in response to the input high-frequency electrical signal, thereby generating a high-frequency optical signal.

[0024] The optical modulator 36 has an upper electrode 40 on its upper surface. The upper surface of the optical modulator 36 is at the same height as the upper surface of the microstrip substrate 16. The optical modulator 36 has a lower electrode 42 on its bottom surface. The lower electrode 42 is bonded to face the conductive pattern 12. Solder (not shown) is used for bonding. The lower electrode 42 of the optical modulator 36 is integrated with the lower electrode (not shown) of the semiconductor laser 38.

[0025] [Capacitor] A capacitor 44 is mounted on the submount 10. A lower electrode 46 of the capacitor 44 is bonded to face the conductive pattern 12. Solder or a conductive adhesive (not shown) is used for bonding. An upper electrode 48 of the capacitor 44 is connected to an upper electrode 50 of the semiconductor laser 38 via a wire W2. Since the capacitor 44 is connected in parallel to the semiconductor laser 38, it is possible to suppress the inflow of high-frequency components into the semiconductor laser 38. The upper electrode 48 of the capacitor 44 is connected to an electrical connector 110 by a wire W3 as shown in FIG. 1.

[0026] [Terminal resistor] The semiconductor light emitting device 102 has a termination resistor 52. The termination resistor 52 is formed by metallization and patterning, and is set to 50 Ω. A pad 54 that is not electrically connected to the conductive pattern 12 is provided on the upper surface of the submount 10, and the termination resistor 52 is connected between the conductive pattern 12 and the pad 54. The pad 54 and the optical modulator 36 are connected by a wire W4. As a result, the termination resistor 52 is connected in parallel to the optical modulator 36. Note that the resistance value is not limited to 50 Ω and may be set to another value as necessary.

[0027] [Wire] The semiconductor light emitting device 102 has a wire 56. Both ends of the wire 56 are bonded to the upper electrode 40 of the optical modulator 36 and the second end 24 of the single-ended transmission line 20, respectively. In the examples of Figures 2 and 3, the wire 56 and the wire W4 are formed into a single continuous wire.

[0028] Since the microstrip substrate 16 has approximately the same height as the semiconductor optical element 34, the wire 56 between the single-ended transmission line 20 and the optical modulator 36 is short. This makes it possible to reduce the inductance component caused by the wire 56. Here, the length of the wire 56 is preferably 150 μm or less. To achieve a length of 150 μm or less, the difference in height between the microstrip substrate 16 and the semiconductor optical element 34 is preferably within ±10%. If the difference in height is large, the wire 56 will be longer than 150 μm, and the inductance of the wire 56 will degrade the high-frequency characteristics.

[0029] [Load circuit] As shown in FIG. 2, a load circuit 58 including a wire 56, an optical modulator 36, and a termination resistor 52 is electrically connected between the second end 24 and the conductive pattern 12. The load circuit 58 also includes a pad 54. The load circuit 58 has a characteristic impedance equal to or less than that of the second section 30. The characteristic impedance of the load circuit 58 is 40 Ω, which is less than 50 Ω. The characteristic impedance varies depending on the frequency, but is defined here as the average value over the entire range of driving frequencies. This definition also applies to the single-ended transmission line 20.

[0030] If the characteristic impedance differs, reflection of the high-frequency electrical signal occurs, degrading the high-frequency characteristics. However, in this embodiment, the characteristic impedance of the single-ended transmission line 20 changes from 50Ω to 45Ω, and is connected to the load circuit 58 of 40Ω. By decreasing the characteristic impedance stepwise in this manner, it becomes possible to reduce the reflection of the electrical signal, and it becomes possible to efficiently transmit the high-frequency electrical signal input to the first end 23 (external connection section 22) to the load circuit 58 and, ultimately, to the optical modulator 36. As a result, it becomes possible to improve the high-frequency characteristics.

[0031] [Characteristics] FIG. 4 is a diagram of the response characteristics (optical / electrical response characteristics) of an optical signal to a high-frequency electrical signal. The high-frequency electrical signal is input to the first end 23. The horizontal axis indicates frequency, and the vertical axis indicates response (S21). The solid line indicates the response characteristics of this embodiment. The dotted line indicates the response characteristics of a comparative example. In the comparative example, the entire single-ended transmission line 20 has a uniform width and a uniform characteristic impedance. The frequency at which the signal becomes -3 dB (f3 dB band) is used as one of the indices of the frequency characteristics of the optical modulator 36. The embodiment showed a characteristic improvement of approximately 5 GHz compared to the comparative example.

[0032] In this embodiment, the characteristic impedances of the first section 28, the second section 30, and the load circuit 58 are 50Ω, 45Ω, and 40Ω, respectively. As a modification, the characteristic impedances of the second section 30 and the load circuit 58 may be the same (40Ω). In this case, it has been confirmed by actual measurements that, despite the large difference in characteristic impedance between the first section 28 and the second section 30, improved high-frequency characteristics are obtained.

[0033] The reason is presumably that the electric field distribution in the single-ended transmission line 20 is relatively uniform, so that the change in the electric field distribution is small and the reflection is also small. On the other hand, the load circuit 58 has a very complicated configuration because it has not only an inductance component and a capacitance component but also a semiconductor region, and the difference in the characteristic impedance at the connection between the two generates a large reflection. It is also important that the wire 56 is short. For example, assume that the microstrip substrate 16 is not arranged and the single-ended transmission line is formed as a pattern on the submount. In this case, a large reflection occurs between the region where the characteristic impedance of the single-ended transmission line is small and the wire 56. By making the wire 56 150 μm or less, the effect of the inductance of the wire 56 on the characteristic impedance can be reduced, and the effect of placing the second section 30 can be obtained.

[0034] [Second embodiment] 5 is a plan view of a microstrip substrate according to the second embodiment. As in the first embodiment, the single-ended transmission line 220 includes an external connection section 222, a first section 228, and a second section 230. The second section 230 includes a bent portion 260. The bent portion 260 extends along a curve that is convex in multiple directions (for example, an S-shaped curve S). The presence of the bent portion 260 expands the electromagnetic field, thereby making it possible to reduce the impedance of the second section 230. The second section 230 has the same width as the first section 228.

[0035] The first end 223 and the second end 224 are located at both ends of the microstrip substrate 216 along the length direction (left and right direction in FIG. 5) of the single-ended transmission line 220. The first end 223 and the second end 224 are shifted from each other in the width direction (up and down direction in FIG. 5) perpendicular to the length direction. In the example of FIG. 1, the optical modulator is placed in front of the high-frequency connector 112, but this embodiment is effective when the two are placed shifted from each other. This makes it possible to increase the degree of freedom in the placement of components in the optical subassembly. The contents described in the first embodiment can be applied to other contents.

[0036] The second section 230 may be bent so that the curvature changes, or may include a portion that extends in a straight line. As a result, the characteristic impedance of the second section 230 varies depending on the position, but in this disclosure, the characteristic impedance of the second section 230 refers to the average characteristic impedance of the entire second section 230. On the other hand, the first section 228 has a constant width and a constant characteristic impedance. This definition is also applicable to the following embodiments.

[0037] [Third embodiment] 6 is a plan view of a microstrip substrate according to the third embodiment. As in the first embodiment, a single-ended transmission line 320 includes an external connection section 322, a first section 328, and a second section 330. The second section 330 includes a wide portion 332 that is wider than the first section 328. The wide portion 332 is gradually wider in the direction away from the first section 328. The wide portion 332 includes a second end 324. The second end 324 is the widest in the second section 330. The rest of the details are applicable to the second embodiment.

[0038] By combining the bent portion 360 and the wide portion 332, it is possible to realize low impedance in a small area. This makes it possible to miniaturize the microstrip substrate 316. As a result, it is possible to miniaturize the optical subassembly itself.

[0039] [Fourth embodiment] FIG. 7 is a diagram showing the internal configuration of an optical subassembly according to a fourth embodiment. In this embodiment, the direction in which a high-frequency electrical signal is input is parallel to the direction in which an optical signal is output. Input and output of both the high-frequency electrical signal and DC current are performed through an electrical connector 410. The electrical connector 410 is adjacent to a microstrip substrate 416 in its length direction (the vertical direction in FIG. 7). The microstrip substrate 416 includes a single-ended transmission line 420. The single-ended transmission line 420 includes an external connection section 422, a first section 428, and a second section 430.

[0040] In contrast, the optical modulator 436 is adjacent to the microstrip substrate 416 in the width direction (the left-right direction in FIG. 7). Therefore, the single-ended transmission line 420 is bent at approximately 90 degrees. More specifically, the second section 430 is bent at 90 degrees with a uniform width. The characteristic impedance of the second section 430 is 43 Ω. The presence of the bent portion 460 realizes a low impedance.

[0041] The first end 423 is located at one of both ends of the microstrip substrate 416 along the length direction of the first section 428. The second end 424 is located at one of both sides of the microstrip substrate 416 along the width direction perpendicular to the length direction. The second section 430 includes a bent portion 460. The bent portion 460 extends along a curved line that is convex in one direction. The rest of the details are applicable to the details described in the first and second embodiments.

[0042] [Fifth embodiment] 8 is a plan view of a microstrip substrate according to the fifth embodiment. The second section 530 includes a wide portion 532 that is wider than the first section 528. The wide portion 532 has a shape in which the width gradually increases. The wide portion 532 includes a second end portion 524. The rest of the details are the same as those described in the fourth embodiment.

[0043] By combining the bent portion 560 and the wide portion 532, it is possible to realize low impedance in a small area. This makes it possible to miniaturize the microstrip substrate 516. As a result, it is possible to miniaturize the optical subassembly itself.

[0044] [Sixth embodiment] FIG. 9 is a plan view of a microstrip substrate according to the sixth embodiment. The single-ended transmission line 620 includes an external connection section 622, a first section 628, and a second section 630. The first end 623 is located at one of both ends of the microstrip substrate 616 along the length direction of the first section 628 (the vertical direction in FIG. 9). The second end 624 is located at one of both sides of the microstrip substrate 616 along the width direction (the horizontal direction in FIG. 9) perpendicular to the length direction. In other words, the single-ended transmission line 620 is bent at a right angle. This allows the electromagnetic field to expand, and the impedance of the second section 630 to be reduced.

[0045] The first section 628 includes a first connecting portion 662 that is connected to the second section 630. The first section 628 extends from the first connecting portion 662 along a first direction D1.

[0046] The second section 630 includes a second connection portion 664 connected to the first section 628. The second section 630 extends from the second connection portion 664 along a second direction D2 that intersects with the first direction D1. The first section 628 and the second section 630 extend in different directions.

[0047] The first connecting portion 662 and the second connecting portion 664 are adjacent to each other in the first direction D1 but not adjacent to each other in the second direction D2. A part of the second connecting portion 664 is thinner than the first connecting portion 662. The rest of the details are the same as those described in the fifth embodiment.

[0048] [Seventh embodiment] 10 is a plan view of a microstrip substrate according to the seventh embodiment. The second section 730 includes a wide portion 732 that is wider than the first section 728. The wide portion 732 includes a second end portion 724. The rest of the details are the same as those described in the sixth embodiment.

[0049] [Eighth embodiment] Fig. 11 is a plan view of a microstrip board according to the eighth embodiment. A part of a second connection part 864 is thinner than a part of a second connection part 664 shown in Fig. 9. This allows the characteristic impedance of a second section 830 to be adjusted. The rest of the details are the same as those described in the sixth embodiment. The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the configurations described in the embodiments can be replaced with substantially the same configurations, configurations that provide the same effects, or configurations that can achieve the same purpose. [Explanation of symbols]

[0050] 10 submount, 12 conductive pattern, 14 metal film, 16 microstrip substrate, 18 ground plane, 20 single-ended transmission line, 22 external connection section, 23 first end, 24 second end, 26 ground conductor, 28 first section, 30 second section, 32 wide portion, 34 semiconductor optical element, 36 optical modulator, 38 semiconductor laser, 40 upper electrode, 42 lower electrode, 44 capacitor, 46 lower electrode, 48 upper electrode, 50 upper electrode, 52 termination resistor, 54 pad, 56 wire, 58 load circuit, 100 optical subassembly, 102 semiconductor light emitting device, 104 package, 106 lens, 108 optical connector, 110 electrical connector, 112 high frequency connector, 216 microstrip substrate, 220 single-ended transmission line, 222 external connection section, 223 First end, 224 Second end, 228 First section, 230 Second section, 260 Bend, 316 Microstrip substrate, 320 Single-ended transmission line, 322 External connection section, 324 Second end, 328 First section, 330 Second section, 332 Widened section, 360 Bend, 410 Electrical connector, 416 Microstrip substrate, 420 Single-ended transmission line, 423 First end, 424 Second end, 428 First section, 430 Second section, 422 External connection section, 436 Optical modulator, 460 Bend, 516 Microstrip substrate, 524 Second end, 528 First section, 530 Second section, 532 Widened section, 560 Bend, 616 Microstrip substrate, 620 Single-ended transmission line, 622 External connection section, 623 First end, 624 Second end, 628 First section, 630 Second section, 662 First connection, 664 Second connection, 724 Second end, 728 First section, 730 Second section, 732 Wide section, 830 Second section, 862 First connection, 864 Second connection, D1 first direction, D2 second direction, W1 wire, W2 wire, W3 wire, W4 wire.

Claims

1. a submount having a conductive pattern on an upper surface thereof; an optical modulator having an upper electrode on an upper surface and a lower electrode on a bottom surface, the lower electrode being bonded to face the conductive pattern; a termination resistor connected in parallel to the optical modulator; a microstrip substrate having a single-ended transmission line extending from a first end to a second end on an upper surface thereof and a ground plane on a rear surface thereof, the ground plane being joined to face the conductive pattern; a wire having both ends bonded to the upper electrode of the optical modulator and the second end of the single-ended transmission line; having the single-ended transmission line includes a first section and a second section extending from the first section and including the second end; the second section has a lower characteristic impedance than the first section; a load circuit including the wire, the optical modulator, and the termination resistor is electrically connected between the second end and the conductive pattern; the load circuit is equal to or less than the second section in characteristic impedance; A semiconductor light emitting device, wherein a difference in height between the upper surface of the microstrip substrate and the upper surface of the optical modulator is within ±10%, and the length of the wire is 150 μm or less.

2. 2. The semiconductor light emitting device according to claim 1, the first end is at one of opposite ends of the microstrip substrate along a length of the first section; The second end is located on one of both sides of the microstrip substrate along a width direction perpendicular to the length direction.

3. A submount having a conductive pattern on an upper surface thereof; an optical modulator having an upper electrode on an upper surface and a lower electrode on a bottom surface, the lower electrode being bonded to face the conductive pattern; a termination resistor connected in parallel to the optical modulator; a microstrip substrate having a single-ended transmission line extending from a first end to a second end on an upper surface thereof and a ground plane on a rear surface thereof, the ground plane being joined to face the conductive pattern; a wire having both ends bonded to the upper electrode of the optical modulator and the second end of the single-ended transmission line; having the single-ended transmission line includes a first section and a second section extending from the first section and including the second end; the second section has a lower characteristic impedance than the first section; a load circuit including the wire, the optical modulator, and the termination resistor is electrically connected between the second end and the conductive pattern; the load circuit is equal to or less than the second section in characteristic impedance; A semiconductor light emitting device, wherein the first end and the second end are located at opposite ends of the microstrip substrate along the length of the single-ended transmission line and are offset from each other in a width direction perpendicular to the length.

4. 4. The semiconductor light emitting device according to claim 1, the single-ended transmission line comprises an external connection section having a first end that connects with the first section; The microstrip substrate has a pair of ground conductors on its upper surface that sandwich the external connection section of the single-ended transmission line, forming a partial grounded coplanar line in the semiconductor light emitting device.

5. 5. The semiconductor light emitting device according to claim 1, Further comprising a semiconductor laser; The optical modulator and the semiconductor laser are both monolithically integrated in a semiconductor optical element.

6. 6. The semiconductor light emitting device according to claim 1, The first section is a semiconductor light emitting device having a uniform width and extending linearly.

7. 7. The semiconductor light emitting device according to claim 1, The second section includes a wide portion that is wider than the first section in width.

8. 8. The semiconductor light emitting device according to claim 7, The wide portion has a shape in which the width gradually increases.

9. 9. The semiconductor light emitting device according to claim 7, The wide portion includes the second end portion.

10. 10. The semiconductor light emitting device according to claim 1 , The second section includes a bend.

11. 11. The semiconductor light emitting device according to claim 10, The bent portion extends along a curved line that is convex in one direction.

12. 11. The semiconductor light emitting device according to claim 10, The bent portion extends along curved lines that are convex in multiple directions.

13. 13. The semiconductor light emitting device according to claim 1, the first section includes a first connection portion connected to the second section, and extends from the first connection portion along a first direction; the second section includes a second connection portion connected to the first section, and extends from the second connection portion along a second direction intersecting the first direction; The semiconductor light emitting device, wherein the first connection portion and the second connection portion are adjacent to each other in the first direction and not adjacent to each other in the second direction.

14. 14. The semiconductor light emitting device according to claim 13, The single-ended transmission line is bent at a right angle.

15. 15. The semiconductor light emitting device according to claim 13, A portion of the second connection portion is thinner than the first connection portion.

16. A semiconductor light emitting device according to any one of claims 1 to 15, An electrical connector; having The electrical connector is electrically connected to the first end of the single-ended transmission line.

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