Optical modulation module and optical transmitter

Abstract

Provided are an optical transmitter and an optical modulation module that are capable of improving a signal path between the optical modulation module and a substrate, that prevents degradation of a modulated signal, and that have a wide frequency band where a good-quality signal can be obtained. An optical transmitter (100) according to the present disclosure comprises: an optical modulation light source chip (4) having upper and lower surfaces; an RF wiring board (2) connected to the optical modulation light source chip (4); and an RF connection substrate (3) having a metal bump (33) for electrically connecting the optical modulation light source chip (4) and the RF wiring board (2). The optical modulation light source chip (4) is configured to include: an n-type semiconductor substrate (41); a p-type semiconductor layer (43); wiring layers (481, 482) electrically connected to the n-type semiconductor substrate (41) and brought into contact with the metal bump (33) on the upper surfaces; and a wiring layer (483) electrically connected to the p-type semiconductor layer (43) and brought into contact with the metal bump on the upper surface.

Description

[Technical field]

[0001] The present disclosure relates to an optical modulation module and an optical transmitter. [Background technology]

[0002] In recent years, data traffic has been increasing exponentially due to the rapid growth of cloud services and wireless applications. This has led to a demand for higher data rates for Ethernet, and 100 Gigabit Ethernet (100GbE) was standardized in 2010. A multi-lane interface with four lanes has been adopted for single mode fiber (SMF) applications. However, an increase in the number of lanes in a multi-lane system is undesirable, and a single light source that can be modulated at 100 Gb / s is required to increase the data rate per single lane. Such a light source is described, for example, in Non-Patent Document 1. Patent Document 1 describes a configuration in which an EADFB laser (Distributed Feedback Laser Integrated with Electro-absorption Modulator) chip and an RF (radio frequency) circuit board are connected by a flip-chip interconnection board consisting of a coplanar waveguide and a termination resistor. The flip-chip interconnection board has a metal bump on the ground part on the side of the signal line, and this metal bump connects the EADFB laser chip and the RF circuit board.

[0003] In the above configuration, the signal line of the RF circuit board is connected to the EADFB laser chip via a metal bump, while the ground part of the flip-chip interconnection board is connected to the ground part on the side of the RF circuit board via a metal bump, and is further connected to the ground electrode on the underside of the EADFB laser chip via the ground electrode on the subcarrier (the substrate under the EADFB laser chip and the RF circuit board). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] S. Kanazawa et. al., “Flip-Chip Interconnection Lumped-Electrode EADFB Laser for 100-Gb / s / λ Transmitter,” IEEE Photon. Technol. Lett., vol. 27, no. 16, pp. 1699-1701, 2015. Summary of the Invention

[0005] However, the signal path of the configuration described in Non-Patent Document 1 passes through the ground part of the subcarrier via the EADFB laser chip, and is connected to the ground part of the flip-chip interconnection board through the RF circuit board. Such a path is so long that it is difficult to handle it as a lumped constant circuit in a frequency band exceeding 60 GHz, and the band is degraded, making it unsuitable for 85 Gbit / s signal transmission. The present disclosure has been made in consideration of such problems, and aims to provide an optical modulation module and an optical transmitter that improve the signal path between the optical modulation module and the board, prevent degradation of the modulated signal, and have a wide frequency band in which a good signal can be obtained.

[0006] In order to achieve the above object, an optical module according to one embodiment of the present invention is an optical modulation module having a first main surface and a second main surface opposite to the first main surface, and connected to a wiring board by a connection board on the side of the first main surface, the optical module including: a first type semiconductor layer doped with an impurity of a first polarity; a second type semiconductor layer doped with an impurity of a second polarity different from the first polarity; a first wiring layer electrically connected to the first type semiconductor layer and electrically connected to a terminal of the connection board at the first main surface; and a second wiring layer electrically connected to the second type semiconductor layer and in contact with the terminal at the first main surface. death , A signal passing through the optical modulation module is transmitted in one transmission direction, and the first wiring layer and the second wiring layer are disposed on the first main surface in a direction intersecting the transmission direction. .

[0007] An optical transmitter according to one embodiment of the present invention is an optical modulation module having a first main surface and a second main surface opposite to the first main surface, and connected to a wiring board by a connection board on the side of the first main surface, the optical modulation module including: a first type semiconductor layer doped with an impurity of a first polarity; a second type semiconductor layer doped with an impurity of a second polarity different from the first polarity; a first wiring layer electrically connected to the first type semiconductor layer and electrically connected to a terminal of the connection board at the first main surface; and a second wiring layer electrically connected to the second type semiconductor layer and in contact with the terminal at the first main surface. ,before The wiring board, the optical modulation module, and the wiring The connection board has terminals that electrically connect to a substrate, and signals are transmitted in one transmission direction, and the first wiring layer and the second wiring layer are arranged in a direction intersecting the transmission direction on the first main surface.

[0008] According to the above-described embodiment, it is possible to provide an optical transmitter and an optical modulation module that improve the signal path between the optical modulation module and the substrate, prevent degradation of the modulated signal, and provide a wide frequency band from which a good signal can be obtained. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a top view of the optical transmitter according to the first embodiment. [Diagram 2] 2A is a diagram showing the bottom surface of the RF connecting board shown in FIG. 1, and FIG. 2B is a vertical sectional view of the optical transmitter shown in FIG. [Diagram 3] FIG. 1A is a diagram showing the top surface of an RF wiring board, and FIG. 1B is a diagram showing the flow of signals in a coplanar waveguide. [Figure 4] 2 is a top view of the optical modulation light source chip shown in FIG. [Diagram 5] 5A is a cross-sectional view taken along a line in FIG. 4, and FIG. 5B is a cross-sectional view taken along another line in FIG. [Figure 6] 5A is a cross-sectional view taken along a line shown in FIG. 4, and FIG. 5B is a cross-sectional view taken along another line shown in FIG. [Figure 7] (a) is a cross-sectional view of an n-side contact groove, and (b) is a cross-sectional view of a p-side contact groove. [Figure 8] FIG. 13 is a top view of an optical transmitter according to a comparative example. [Figure 9] 9(a) is a diagram showing the bottom surface of the RF connecting board shown in FIG. 8, and (b) is a vertical sectional view of the optical transmitter shown in FIG. [Figure 10] 4 is a graph for explaining a frequency response of the first embodiment. [Figure 11] 5 is a graph for explaining the dependency of the 3 dB band of the optical transmitter of the first embodiment on the electrode length. [Figure 12] FIG. 11 is a top view of the optical transmitter according to the second embodiment. [Figure 13] 13(a) is a diagram showing the bottom surface of the RF connecting board shown in FIG. 12, and (b) is a vertical sectional view of the optical transmitter shown in FIG. [Figure 14] 10 is a graph for explaining a frequency response of the second embodiment. [Figure 15] 13 is a graph for explaining the dependency of the 3 dB band of the optical transmitter of the second embodiment on the electrode length. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (First embodiment) 1, 2(a) and 2(b) are schematic diagrams for explaining an optical transmitter 100 according to a first embodiment of the present disclosure. FIG. 1 is a top view of the optical transmitter 100. FIG. 2(a) is a view showing a surface (hereinafter referred to as a "bottom surface") of the RF connection substrate 3 of the optical transmitter 100 facing the optical modulation light source chip 4, and FIG. 2(b) is a cross-sectional view taken along lines IIb and IIb' in FIG. 1. The optical transmitter 100 includes an optical modulation light source chip 4 that is an optical modulation module, an RF wiring substrate 2 that is a wiring substrate connected to the optical modulation light source chip 4, and an RF connection substrate 3 that is a connection substrate having a terminal that electrically connects the optical modulation light source chip 4 and the RF wiring substrate 2. Here, the "optical modulation module" may be any one that has a function of integrating a plurality of elements and modulating input light. The RF wiring substrate 2 and the RF connection substrate 3 may be any substrate that can withstand high frequency use. The terminals of the RF connection substrate 3 are not particularly limited, but metal bumps are used in the first embodiment.

[0011] As shown in FIG. 2(b), the RF wiring board 2 and the optical modulation light source chip 4 are mounted on the subcarrier 1. In the description of the first embodiment and the second embodiment described later, the direction from the subcarrier 1 toward the RF connection board 3 is referred to as "up" or "upward", and the side from the RF connection board 3 toward the subcarrier 1 is referred to as "down" or "downward". Note that such up-down directions are based on the relative positional relationship of the optical transmitter 100 and do not depend on the direction of gravity. The RF connection board 3 is provided on the RF wiring board 2 and the optical modulation light source chip 4 to connect them. In FIG. 1, the RF connection board 3 is indicated by a dashed line, and the RF wiring board 2 and the optical modulation light source chip 4 below the RF connection board 3 are indicated.

[0012] The optical modulation light source chip 4 is, for example, an electroabsorption type optical modulator integrated (EADFB) laser integrating an optical semiconductor amplifier, and includes a plurality of InP-based materials. The subcarrier 1 is a ceramic substrate, and aluminum nitride (AlN) and aluminum oxide (alumina: Al2O3) are used as ceramic materials. The RF wiring board 2 and the RF connection board 3 may be a ceramic substrate, a fluororesin substrate, a PPE (PolyPhenyl Ether) substrate, or a composite material of these. The RF wiring board 2 and the RF connection board 3 are provided with a conductor film on the surfaces facing each other and on the lower surface of the opposite side. The following describes such a configuration in order.

[0013] (RF wiring board) As shown in Fig. 1, the RF wiring board 2 includes a signal line portion 21 that serves as a signal line, and two top-surface ground portions 22 that are arranged on either side of the signal line portion 21, sandwiching the signal line portion 21. The signal line portion 21 and the top-surface ground portion 22 are composed of a conductive film. The signal line portion 21 transmits a signal in the direction indicated by the arrow Ds in the figure. Such an RF wiring board 2 is a grounded coplanar waveguide in which a linear line is formed in a board body that is a plate-shaped dielectric. The conductive film on the bottom surface of the RF wiring board functions as a bottom-surface ground portion 24 (Fig. 3(b)).

[0014] Here, the grounded coplanar waveguide will be described by taking the RF wiring board 2 as an example. FIGS. 3(a) and 3(b) are diagrams for explaining the grounded coplanar waveguide, and FIG. 3(a) is a diagram showing the top surface of the RF wiring board 2, which is a grounded coplanar waveguide, on which wiring is formed. FIG. 3(b) is a schematic diagram for explaining the flow of signals in the grounded coplanar waveguide. In FIG. 3(b), an arrow indicates the direction of the electric field from the signal line portion 21 toward the top-surface ground portion 22, and another arrow indicates the direction of the electric field from the top surface of the RF wiring board 2 toward the bottom-surface ground portion 24. In the grounded coplanar waveguide, the electric field coupling between the signal line portion 21 and the top-surface ground portion 22 is stronger than the electric field coupling between the signal line portion 21 and the bottom-surface ground portion 24, and the signal flow from the signal line portion 21 toward the ground portion is dominated by the path via the top-surface ground portion 22.

[0015] (RF connection board) 2(a), the RF connection board 3 has a signal line formed on the surface of a plate-shaped board body. In the first embodiment, a signal line portion 32 and a bottom ground portion 34 disposed on the side of the signal line 32 are formed on the surface (bottom surface) of the RF connection board 3 facing the RF wiring board 2 and the optical modulation light source chip 4. A termination resistor 31 is formed at the end of the signal line portion 32 to suppress disturbance due to signal reflection.

[0016] The RF connection board 3 also includes six metal bumps 33a, 33b, 33c, 33d, 33e, and 33f. In this specification, when the metal bumps 33a to 33f are not to be distinguished from one another, they are also referred to simply as "metal bumps 33." The metal bumps 33a to 33f are all made of gold (Au). In the first embodiment, the RF wiring board 3 is a grounded coplanar waveguide like the RF wiring board 2. Therefore, in the RF wiring board 3 as well, the flow of a signal from the signal line 32 toward the ground is dominated by the path via the lower surface ground portion 34.

[0017] The number and arrangement of the metal bumps 33a to 33f are not limited to the above. However, it is preferable that the metal bumps 33a to 33f are arranged in a direction intersecting the signal flow direction (the direction indicated by the arrow Ds). In the first embodiment, the metal bumps 33a, 33b, and 33c are arranged in a straight line perpendicular to the signal flow direction, and the metal bumps 33f, 33e, and 33d are arranged in a straight line. As will be described later, the electrodes connected to the metal bumps 33 of the optical modulation light source chip 4 are arranged so that the electrodes connected to the semiconductor layers of different polarities, p-type and n-type, intersect the signal flow direction and are alternately arranged adjacent to each other. The metal bumps 33 connect each of these electrodes to the signal line portion 21 or the upper surface ground portion 22. With this configuration, the RF connection board 3 electrically connects the optical modulation light source chip 4 and the RF wiring board 2.

[0018] In the above configuration, a signal input to the RF connection board 3 is divided into a path that connects to the bottom-surface ground part 34 via the termination resistor 31, and a path that passes through the optical modulation light source chip 4 via the metal bump 33e and is connected to the bottom-surface ground part 34. The RF connection board 3 and the RF wiring board 2 are designed as distributed constant lines, and the electrical path from the signal line part 21 to the ground part via the termination resistor 31 and the optical modulation light source chip 4 needs to be designed as a lumped constant circuit. To design it as a lumped constant circuit, it is necessary to make this path sufficiently short with respect to the signal wavelength and to prevent a phase difference (shift) with the signal passing through the path caused by capacitive coupling from the signal line 31 to the bottom-surface ground 34 from becoming large.

[0019] (Light Modulation Light Source Chip) As shown in FIG. 2(b), the optical modulation light source chip 4 is mounted on the subcarrier 1 together with the RF wiring board 2. The optical modulation light source chip 4 includes a first type semiconductor layer into which an impurity of a first polarity is injected, and a second type semiconductor layer into which an impurity of a second polarity different from the first polarity is injected, and in the first embodiment, the first type is n-type and the second type is p-type. Therefore, as shown in FIG. 2(b), the optical modulation light source chip 4 includes an n-type semiconductor substrate 41, an n-type active layer 46, a p-type semiconductor layer 43, and further includes a semi-insulating semiconductor layer 44 that does not contain impurities, an insulating film 45, and a wiring layer 482.

[0020] A protrusion 42 is formed on the n-type semiconductor substrate 41 by patterning. The active layer 46 is a waveguide for laser light in the optical modulation light source chip 4, and is formed of an n-type semiconductor. The wiring layer 482 is connected to the p-type semiconductor layer 43, and serves as a p-side electrode of the optical modulation light source chip 4. A metal bump 33e on the signal line portion 21 is connected to the wiring layer 482, and the wiring layer 482 and the signal line portion 21 are electrically connected. As shown in FIG. 1, the length of the wiring layer 482 in the direction intersecting with the arrow Ds is defined as the electrode length L. E Such an optical modulation light source chip 4 includes a laser chip, an amplifier, and an optical modulator (not shown), and amplifies and modulates the light emitted from the laser chip and outputs it.

[0021] The n-type semiconductor substrate 41, the semi-insulating semiconductor layer 44, and the p-type semiconductor layer 43 are all InP-based semiconductors, and the active layer 46 contains Ga and As in addition to InP. 1-x Ga x As y P 1-yThe n-type semiconductor substrate 41, the semi-insulating semiconductor layer 44, the active layer 46, the p-type semiconductor layer 43, and the insulating film 45 can all be formed by MOCVD (Metalorganic Chemical Vapor Deposition, MOCVD). The electrical conductivity of each layer is set by the concentration of the dopant contained in each layer. The wiring layer 482 is, for example, an Al wiring, and is formed by, for example, sputtering. After being formed, each of the above layers is patterned into a desired shape by known photolithography. The insulating film 45 is formed by depositing, for example, SiO2, Si3N4, or the like.

[0022] FIG. 4 is a top view of the optical modulation light source chip 4. The optical modulation light source chip 4 of the first embodiment has an upper surface shown in FIG. 4 and a lower surface opposite to the upper surface. The upper surface and the lower surface are the first main surface and the second main surface of the optical modulation light source chip, respectively. Here, the main surface may be any surface that has a relatively large area in the optical modulation light source chip, and there are no limitations on the area or direction. The output direction of light from the optical modulation light source chip 4 is indicated as L in FIG. out It is written as follows.

[0023] On the surface of the optical modulation light source chip 4, an insulating film 45, wiring layers 481, 482, 483, 464, and 485, a p-side contact groove 490b for the wiring layer 482 to contact the p-type semiconductor layer 43, and an n-side contact groove 490a for the wiring layers 481, 483 to contact the n-type semiconductor substrate 41 are formed. In the wiring layer 482, a portion having a wide pattern width is defined as a wide portion 482b, and a portion having a relatively narrow width (length in the longitudinal direction of the optical modulation light source chip 4) is defined as a narrow portion 482a.

[0024] The wiring layers 481 and 483 are n-side electrodes connected to the n-type semiconductor substrate 41, and serve as ground electrodes of the optical modulator mounted on the optical modulation light source chip 4. The wiring layer 482 connected to the signal line portion 21 is a p-side electrode of the optical modulator, and inputs a signal from the RF wiring substrate. The wiring layer 484 is a p-side electrode connected to the p-type semiconductor layer 43, and connects to, for example, a laser chip of the optical modulation light source chip 4. The wiring layer 485 is a p-side electrode connected to the p-type semiconductor layer 43, and connects to, for example, an amplifier of the optical modulation light source chip 4. The wiring layers 484, 482, and 485 serving as p-side electrodes and the wiring layers 481 and 483 serving as n-side electrodes are arranged so as to intersect with the signal transmission direction indicated by the arrow Ds and have different polarities from the adjacent wiring layers. By configuring in this manner, the first embodiment can limit the area in which the p-side electrodes and the n-side electrodes are arranged, and arrange them at a high density to shorten the wiring length between the p-side electrodes and the n-side electrodes.

[0025] In the first embodiment, one wiring layer 482 serving as a p-side electrode and two wiring layers 481 and 483 serving as n-side electrodes are formed on the upper surface, and the wiring layers 481, 482, and 483 are adjacent to each other and arranged alternately on the upper surface. Furthermore, in the first embodiment, the wiring layers 481 and 483 are arranged to sandwich the wiring layer 482 in the planar direction of the upper surface. However, the first embodiment is not limited to this configuration, and multiple wiring layers serving as p-side electrodes and multiple wiring layers serving as n-side electrodes may be arranged.

[0026] 5(a) is a cross-sectional view taken along lines Va and Va' in FIG. 4, FIG. 5(b) is a cross-sectional view taken along lines Vb and Vb' in FIG. 4, FIG. 6(a) is a cross-sectional view taken along lines VIa and VIa' in FIG. 4, and FIG. 6(b) is a cross-sectional view taken along lines VIb and VIb' in FIG. 4. The wiring layer 483 extends from the semi-insulating semiconductor layer 44 toward the n-side contact portion 490a via the insulating film 45, and directly contacts the n-type semiconductor substrate 41. The metal bump 33d of the RF connection substrate 3 is connected to the wiring layer 483, and the n-type wiring substrate 41 is connected to the lower ground portion 34 of the RF connection substrate 3 via the upper ground portion 22. The wiring layer 482 is connected to the p-type semiconductor layer 43, which is connected to the protruding portion 42 of the n-type semiconductor substrate 41 via the active layer 46. Such a wiring layer 482 serves as a p-side electrode of the modulator mounted on the optical modulation light source chip 4 .

[0027] As described above, the optical modulation light source chip 4 has, on one surface (upper surface), the wiring layers 481, 483 which are electrically connected to the n-type semiconductor substrate 41 and connected to the metal bumps 33 on the upper surface, and the wiring layer 482 which is connected to the p-type semiconductor layer 43 and electrically connected to the metal bumps 33 on the upper surface. This configuration is also referred to as a "single-sided pn electrode type" in this specification. As described below, the optical transmitter 100 including the optical modulation light source chip 4 of the single-sided pn electrode type can shorten the signal path passing through the optical modulation light source chip compared to known configurations.

[0028] 7(a) and 7(b) are schematic cross-sectional views for explaining the transmission path of a signal in the optical transmitter 100, where FIG. 7(a) is a cross-sectional view taken along the line segments Vb and Vb' (FIG. 4) of the optical modulation light source chip 4 connected to the RF wiring substrate 2 and the RF connection substrate 3, and FIG. 7(b) is a cross-sectional view taken along the line segments Va and Va' (FIG. 4) of the optical modulation light source chip 4 connected to the RF wiring substrate 2 and the RF connection substrate 3. Note that the signal will be explained here as a current. FIG. 7(a) and FIG. 7(b) explain the path in which a signal is input from the RF wiring substrate 2 to the optical modulation light source chip 4 via the RF connection substrate 3, transmitted within the optical modulation light source chip 4, and output again via the RF connection substrate 3. 7(a), a signal s1 is transmitted from the signal line portion 21 of the RF wiring board 2 to the metal bump 33e via the RF connecting board 3, and enters the n-type semiconductor substrate 41 constituting the optical modulator via the p-type semiconductor layer 43, the active layer 46, and the protruding portion 42 of the n-type semiconductor substrate 41. Furthermore, a signal s2 passes through the n-type semiconductor substrate 41, passes through the wiring layer 483 that contacts the n-type semiconductor substrate 41 in the n-side contact groove 490b, and reaches the bottom ground portion 34 of the RF connecting board 3 (FIG. 2(a)) from the metal bump 33d.

[0029] The signal transmission path in the configuration of the first embodiment is about several tens of μm. Therefore, in the first embodiment, the electrical path due to the capacitive coupling from the signal line portion 21 to the lower surface ground portion 34 can be sufficiently short with respect to the signal wavelength, so that it is possible to suppress the band deterioration. In addition, as described above, the wiring layers 484, 482, 485 serving as the p-side electrodes and the wiring layers 481, 483 serving as the n-side electrodes are arranged so as to be perpendicular to the signal transmission direction (the direction indicated by the arrow Ds), so that it is possible to make the path of the signal passing through the n-type semiconductor substrate 41 the shortest. That is, in the electrical path from the signal line portion 21 to the lower surface ground portion 34, the length of the path through the optical modulation light source chip 4 can be minimized in the first embodiment. Then, the deviation from the wavelength of the signal passing through the electrical path caused by the capacitive coupling between the signal line portion 32 and the lower surface ground portion 34 on the side can be suppressed, and the circuit from the signal line portion 21 to the lower surface ground portion 34 through the optical modulation light source chip 4 can be designed as a lumped constant circuit.

[0030] (Comparative Example) Here, in order to explain the effect of the optical transmitter 100 of the first embodiment described above, a known optical transmitter 200 will be described. FIG. 8, FIG. 9(a), and FIG. 9(b) are schematic diagrams for explaining the known optical transmitter 200, and FIG. 8 is a top view of the optical transmitter 200. The optical transmitter 200 has an RF wiring board 2, an optical modulation light source chip 8, and an RF connection board 9 that connects the RF wiring board 2 and the optical modulation light source chip 8. FIG. 9(a) is a diagram showing the bottom surface of the RF connection board 9 of the optical transmitter 200, and FIG. 9(b) is a cross-sectional view taken along the lines IXb and IXb' in FIG. 8. FIG. 9(b) also shows a signal transmission path s3.

[0031] As shown in FIG. 8, the optical modulation light source chip 8 has wiring layers 881, 884, and 885, and the wiring layers 881, 884, and 885 are all p-side electrodes that contact the p-type semiconductor layer 43. In the known optical transmitter 200, an n-side electrode (not shown) is formed on the lower surface of the n-type semiconductor substrate 41 facing the subcarrier 1. As shown in FIG. 9(a), the RF connection substrate 9 has four metal bumps 33a, 33b, and 33c and a metal bump 83, and the metal bumps 33b and 83 are formed on the signal line portion 32, and the metal bumps 33a and 33c are formed on the lower ground portion 34. Even in the known optical transmitter 200, the RF wiring substrate 2 and the optical modulation light source chip 8 are connected by the RF connection substrate 9.

[0032] In the known optical modulation light source chip 8, as shown in Fig. 9(b), a signal input from the RF wiring board 2 flows to the wiring layer 831 via the metal bump 83, and then flows to the subcarrier 1 via the p-type semiconductor layer 43, the active layer 46, the protrusion 42, the n-type semiconductor substrate 41, and the ground electrode (not shown) on the lower surface of the n-type semiconductor substrate 41. The signal that flows to the subcarrier 1 passes through the subcarrier 1 as it is, and flows again to the lower surface ground portion 34 of the RF connection board 9 via the upper surface ground portion 22 (Fig. 8) of the RF wiring board 2 and the metal bump 33a. It is clear that such a signal transmission path s3 has a length of several hundred µm to about 1 mm, which is about 10 to 100 times longer than the first embodiment, in which the total length of the transmission paths s1 and s2 is several tens of µm.

[0033] In the optical transmitter 200 of the comparative example, the path from the convex portion 43 to the metal bump 33a is longer than that of the optical transmitter 100, and the path from the signal line portion 21 to the metal bump 33 is long enough that it is not visible as a lumped constant circuit in a frequency band exceeding 60 GHz. Therefore, the optical transmitter 200 of the comparative example has poor signal quality in a frequency band exceeding 60 GHz, making it difficult to use the optical transmitter 200 for 85 Gbit / s signal transmission. On the other hand, the optical transmitter 100 of the first embodiment can solve the problem of the optical transmitter 200 by sufficiently shortening the path of the signal from the optical modulation light source chip 4 toward the RF wiring board 2, and can realize 85 Gbit / s signal transmission.

[0034] (effect) Next, the effects obtained by the above-described first embodiment will be described. FIG. 10 is a graph showing the relationship (frequency response) between frequency (GHz) and signal response (dB) obtained by using a subassembly of an optical transmitter 100 equipped with a single-sided pn electrode type optical modulation light source chip 4 of the first embodiment. The horizontal axis of FIG. 10 shows the frequency of the input signal, and the vertical axis shows the normalized fluctuation in gain of the modulated signal. The gain was measured by applying a high-frequency probe to the RF wiring board 2. The inventors also measured the frequency response of the optical transmitter 200 of the comparative example in the same manner, and compared it with the subassembly of the optical transmitter 100 of the first embodiment. In both the optical transmitters 100 and 200, the optical modulation light source chip is an electro-absorption (EA: Electro-Absorption) optical modulator integrated laser in which an optical semiconductor modulator is integrated, and the electrode length L of the EA optical modulator is 100 mm. E In both optical transmitters 100 and 200, metal bump 33 is made of gold, has a diameter of 60 μm and a height of 30 μm, and connects RF connection board 3, RF wiring board 2, and optical modulation light source chip 4 or RF connection board 9, RF wiring board 2, and optical modulation light source chip 8.

[0035] In FIG. 10, the frequency response of the optical transmitter 100 is shown by a line L1, and the frequency response of the optical transmitter 200 is shown by a line L2. Point p1 of the line L1 indicates the point where the frequency response of the optical transmitter 100 shown by the line L1 drops by 3 dB from the maximum value (0), and the wavelength band corresponding to 0 to p1 corresponds to the so-called 3 dB band. Similarly, point p2 of the line L2 indicates the 3 dB band of the optical transmitter 200 shown by the line L2. As shown by the line L2, the frequency response of the optical transmitter 200 of the comparative example deteriorates rapidly when the frequency becomes 60 Hz or higher, and the 3 dB band is 74.6 GHz. In contrast, the optical transmitter 100 of the first embodiment does not deteriorate rapidly in frequency response even when the frequency becomes 60 GHz or higher, and the 3 dB band is 97.8 GHz, as shown by the line L1. From these results, it is clear that the optical transmitter 100 incorporating the optical modulation light source chip 4 of one-sided pn electrode type can improve the frequency response compared to the optical transmitter 200 of the comparative example.

[0036] In addition, the inventors have determined that the electrode length L E The dependence of the modulator on the electrode length L of the optical modulation light source chip was calculated and compared with that of the optical transmitter 200 of the comparative example. E Three types of optical transmitters 100 and 200 with different electrode lengths L were fabricated and the 3 dB bandwidth was measured. E are 50 μm, 100 μm, and 150 μm. Fig. 11 is a graph showing the results, where the plots of "x" show the results for the optical transmitter 100, and the plots of "o" (white circles) show the results for the optical transmitter 200.

[0037] As shown in FIG. 11, the electrode length L E When the electrode length L is 150 μm, the 3 dB bandwidths of the optical transmitters 100 and 200 are approximately the same, but E When the electrode length L is 100 μm, the 3 dB bandwidth of the optical transmitter 100 is slightly longer than that of the optical transmitter 200. In this case, the 3 dB bandwidth of the optical transmitter 100 is 66.7 GHz, and the 3 dB bandwidth of the optical transmitter 200 is 64.7 GHz. Furthermore, E When the electrode length L is 50 μm, the 3 dB bandwidth of the optical transmitter 100 is 109.1 GHz, and the 3 dB bandwidth of the optical transmitter 200 is 79.7 GHz. From these results, it can be seen that the optical transmitter 100 equipped with the optical modulation light source chip 4 of the one-sided pn electrode type has a longer electrode length L than the conventional optical transmitter 200. E It can be said that the frequency response can be improved when the fiber optics has a fiber length of 150 μm or less. As described above, the optical transmitter according to the embodiment of the present invention can improve the bandwidth of the frequency response characteristics by shortening the length of the signal path compared to known optical transmitters.

[0038] [Second embodiment] Next, a second embodiment of the present invention will be described. The optical transmitter 300 of the second embodiment differs from the first embodiment in that, while the optical transmitter 100 of the first embodiment is an electroabsorption optical modulator integrated laser, that is, an electroabsorption optical modulator, the optical transmitter 300 of the second embodiment is equipped with an optical modulation light source chip 5 of a Mach-Zehnder type optical modulator (MZ modulator) equipped with a Mach-Zehnder interferometer 120. Fig. 12 is a top view of the optical transmitter 300, Fig. 13(a) is a view showing the bottom surface of the RF connection substrate shown in Fig. 12, and Fig. 13(b) is a cross-sectional view taken along lines XIIIb and XIIIb' shown in Fig. 12. 13(a), the RF connection substrate 3 also includes six metal bumps 33a to 33f, and the metal bump 33e connects the signal line portion 21 of the RF wiring substrate 2 to the wiring layer 482 that forms an electrode for inputting a signal to the Mach-Zehnder interferometer 120. Note that, even in the second embodiment, the length of the wiring layer 482 shown in FIG. 12 is defined as the electrode length L E Let us assume that.

[0039] 13(b), the metal bump 33 is connected to the p-type semiconductor layer 43 via the wiring layer 482, and the wiring layer 482 functions as a p-side electrode. In the second embodiment, the optical modulation light source chip 5 also includes a wiring layer (not shown) that is connected to the n-type semiconductor substrate 41 and is led out to the upper surface shown in FIG.

[0040] (effect) The inventors fabricated an assembly of the optical transmitter 300 having such a configuration, and measured the frequency response with the frequency as a parameter. The inventors also fabricated an assembly of an optical transmitter equipped with an MZ modulator having a p-side electrode on the upper surface and an n-side electrode on the lower surface (hereinafter, referred to as the "MZ modulator of the comparative example"), measured the frequency response, and compared the results. In fabricating the two optical transmitter assemblies, the electrode length L of the modulator equipped in the optical modulation light source chip was E The metal bumps were made of gold, with a diameter of 65 μm and a height of 30 μm.

[0041] FIG. 14 is a graph showing frequency responses obtained using a subassembly of the optical transmitter 300 equipped with the single-sided pn electrode type optical modulation light source chip 5 of the second embodiment and an assembly of an optical transmitter equipped with an MZ modulator of a comparative example. The horizontal axis of FIG. 14 shows the frequency of the input signal, and the vertical axis shows the normalized fluctuation in the gain of the modulated signal. In FIG. 14, the frequency response of the optical transmitter 300 is shown by line L3, and the frequency response of the optical transmitter equipped with the MZ modulator of the comparative example is shown by line L4. Point p3 of the line L3 shows the 3 dB band of the optical transmitter 300, and point p4 of the line L4 shows the 3 dB band of the optical transmitter equipped with the MZ modulator of the comparative example. As shown in FIG. 14, in the frequency range of 70 Hz or more, the response of the optical transmitter equipped with the MZ modulator of the comparative example deteriorates rapidly, and the 3 dB band is 76.7 GHz. In contrast, the response signal of the optical transmitter 300 of the second embodiment does not deteriorate even after 70 GHz, and the 3 dB band is 103 GHz. From this, the second embodiment shows that the frequency response can be improved by making the optical modulation light source chip a one-sided pn type even in an optical transmitter equipped with an MZ modulator.

[0042] In addition, the inventors of the present invention have determined that the electrode length L E The dependence of the MS modulator on the optical transmitter was calculated and compared with that of the optical transmitter equipped with the MS modulator of the comparative example. In this experiment, as in the first embodiment, E Three types of optical transmitters 300 with different electrode lengths L and an optical transmitter equipped with a comparative MZ modulator were fabricated, and the 3 dB bandwidth was measured. E are 50 μm, 75 μm, 100 μm, and 150 μm. Fig. 15 is a graph showing the results, where the plots of "△" show the results of the optical transmitter 300, and the plots of "●" (black circles) show the results of the optical transmitter equipped with the MZ modulator of the comparative example. As shown in Fig. 15, the electrode length L E When the wavelength is 150 μm, the 3 dB band of the optical transmitter 300 is 66.9 GHz, and the 3 dB band of the optical transmitter equipped with the MZ modulator of the comparative example is 64 GHz.

[0043] Also, according to FIG. 15, the electrode length L EWhen the electrode length L is 75 μm, the 3 dB band of the optical transmitter 300 is 111.3 GHz, whereas the 3 dB band of the optical transmitter equipped with the MZ modulator of the comparative example is 79.3 GHz. E When the electrode length L is 50 μm, the 3 dB band of the optical transmitter 300 is 125.3 GHz, whereas the 3 dB band of the optical transmitter equipped with the MZ modulator of the comparative example is 81.5 GHz. From these results, it can be seen that the second embodiment is a Mach-Zehnder type optical modulator, and E It is therefore possible to improve the frequency response of optical transmitters with a wavelength of 150 μm or less.

[0044] The aspects of the present invention are not limited to the above-described embodiments. That is, the aspects of the present invention have been exemplified as an RF connection substrate using a grounded coplanar waveguide, but the waveguide is not limited to a grounded coplanar waveguide, and may be, for example, a coplanar waveguide without a ground portion on the back side. Furthermore, the aspects of the present invention have been exemplified as an electroabsorption optical modulator and a Mach-Zehnder interference optical modulator as an optical modulation light source chip, but are not limited to such configurations, and may be, for example, a directly modulated laser that directly modulates a semiconductor laser as a light source. The optical modulation module, such as an optical modulation light source chip, used in the optical transmitter of the aspects of the present invention preferably has a 3 dB bandwidth of 60 GHz or more.

[0045] Furthermore, the first and second embodiments described above are not limited to the above-mentioned configuration in which the first type is n-type and the second type is p-type, and the first type may be p-type and the second type may be n-type within the range in which the function of optical modulation is performed. Therefore, in the first embodiment, the signal line portion 21 of the RF wiring substrate 2 may be configured to be connected to the p-side electrode of the optical modulation light source chip 4, or may be configured to be connected to the n-side electrode. In addition, in the first embodiment, the upper surface ground portion 22 of the RF wiring substrate 2 may be configured to be connected to the p-side electrode of the optical modulation light source chip 4, or may be configured to be connected to the n-side electrode. [Explanation of symbols]

[0046] 1 Subcarrier 2. Wiring board 3,9 Connection board 4,5,8 Light Modulation Light Source Chip 21 Signal line section 22 Top ground section 24,34 Bottom ground section 31 Termination resistor 32 Signal line section 33,83 Metal bump 41 n-type wiring board 42 Convex 43 p-type semiconductor layer 44 Semi-insulating semiconductor layer 45 Insulating Film 46 Active layer 100,200,300 Optical Transmitter 464,481,482,483,484,485,881,884,885 wiring layer 490a p-side contact 490b n-side contact groove L E Electrode length

Claims

1. An optical modulation module having a first main surface and a second main surface opposite to the first main surface, the optical modulation module being connected to a wiring board by a connection board on a side of the first main surface, a first type semiconductor layer doped with impurities of a first polarity; a second type semiconductor layer doped with impurities of a second polarity different from the first polarity; a first wiring layer electrically connected to the first type semiconductor layer and electrically connected to a terminal of the connection board on the first main surface; a second wiring layer electrically connected to the second type semiconductor layer and in contact with the terminal on the first main surface; An optical modulation module, wherein a signal passing through the optical modulation module is transmitted in one transmission direction, and the first wiring layer and the second wiring layer are arranged on the first main surface in a direction intersecting the transmission direction.

2. an optical modulation module having a first main surface and a second main surface opposite to the first main surface, and connected to a wiring board by a connection board on the side of the first main surface, the optical modulation module having: a first type semiconductor layer into which an impurity of a first polarity is implanted, a second type semiconductor layer into which an impurity of a second polarity different from the first polarity is implanted, a first wiring layer electrically connected to the first type semiconductor layer and electrically connected to a terminal of the connection board at the first main surface, and a second wiring layer electrically connected to the second type semiconductor layer and in contact with the terminal at the first main surface; The wiring board; the connection board having a terminal for electrically connecting the optical modulation module and the wiring board, An optical transmitter, wherein a signal passing through the optical modulation module is transmitted in one transmission direction, and the first wiring layer and the second wiring layer are arranged on the first main surface in a direction intersecting the transmission direction.

3. 3. The optical transmitter according to claim 2, wherein at least one of the first wiring layer and the second wiring layer is arranged in a plurality of layers on the first main surface, and the first wiring layer and the second wiring layer are adjacent to each other and arranged alternately on the first main surface.

4. 4. The optical transmitter according to claim 2, wherein on the first main surface, the first wiring layer serves as a ground electrode of the optical modulation module, and the second wiring layer serves as an input electrode for inputting a signal from the wiring board via the connection board.

5. 5. The optical transmitter according to claim 2, wherein the first wiring layer is disposed on the first main surface so as to sandwich the second wiring layer in a direction toward the first main surface.

6. 6. The optical transmitter according to claim 2, wherein the connection substrate is a high-frequency substrate, and is a coplanar waveguide or a grounded waveguide having a plate-shaped substrate body and a signal line formed on a surface of the substrate body.

7. 7. The optical transmitter according to claim 2, wherein the optical modulation module is at least one of an electro-absorption type optical modulator, a Mach-Zehnder interference type optical modulator, and a directly modulated laser, and has a modulation electrode having a length of 150 μm or less.

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