Optical modulation module

Abstract

An optical modulation module (1) is provided with: an EML (3) in which an EAM (5) and a DFB laser (4) are integrated; a sub-mount (2) on which the EML (3) is mounted; a termination resistor (11) which is connected to the EAM (5); and a high-frequency substrate (6) which is mounted at a position adjacent to the EML (3) on the sub-mount (2) and has a coplanar line on the front surface thereof. A ground opening (16) is provided on the rear surface of the high-frequency substrate (6), and a ground opening (14) is provided in a region of the sub-mount (2) where the high-frequency substrate (6) is mounted.

Description

Optical modulation module 【0001】 The present disclosure relates to an optical modulation module. 【0002】 An electro-absorption modulator integrated laser (hereinafter referred to as "EML") is used for optical communication and is mounted on a submount such as a ceramic substrate, for example. The operating speed of an electro-absorption modulator (hereinafter referred to as "EAM") included in the EML is determined by the parasitic capacitance, but its mounting form can also be a rate-determining factor. For example, the operating speed of the EAM is also affected by the inductance caused by the gold wire connecting the high-frequency line and the EAM. 【0003】 As a conventional technique for reducing the influence of the above inductance, for example, a semiconductor light-emitting device described in Patent Document 1 has been proposed. In this device, on the submount, the high-frequency substrate has substantially the same height as the EAM, so the wire between the high-frequency line formed on the high-frequency substrate and the EAM becomes short. Therefore, the influence of the inductance component caused by the wire can be reduced. 【0004】 Japanese Unexamined Patent Application Publication No. 2022-80244 【0005】 The conventional technique described in Patent Document 1 has a problem that it is difficult to operate the high-frequency line as a coplanar line with strong lateral electric field confinement due to the influence from the ground plane on the back surface of the high-frequency substrate. For this reason, there is a tendency for electromagnetic field radiation at high frequencies to increase and crosstalk to other channels to increase. 【0006】 The present disclosure solves the above problems and aims to obtain an optical modulation module having a coplanar line with strong lateral electric field confinement. 【0007】The optical modulation module according to this disclosure comprises an EML integrating an EAM and a semiconductor laser, a submount on which the EML is mounted, a termination resistor connected to the EAM, and a high-frequency substrate mounted adjacent to the EML on the submount and having a coplanar line on its surface. The back surface of the high-frequency substrate has a first ground opening, which is a region without a ground conductor, and the region on the submount on which the high-frequency substrate is mounted has a second ground opening, which is a region without a ground conductor. 【0008】 The optical modulation module according to this disclosure has a first ground opening on the back surface of the high-frequency substrate, which is a region without a ground conductor, and a second ground opening in the region where the submount high-frequency substrate is mounted, which is a region without a ground conductor. As a result, the influence of the ground on the back side of the high-frequency substrate is suppressed, so that the coplanar line of the high-frequency substrate in the optical modulation module according to this disclosure can be a high-frequency line with strong lateral electric field confinement. 【0009】 This is an upper perspective view showing an optical modulation module according to Embodiment 1. This is an upper perspective view showing the submount and high-frequency substrate of the optical modulation module according to Embodiment 1. This is a lower perspective view showing the submount and high-frequency substrate of the optical modulation module according to Embodiment 1. This is an upper perspective view showing a modified example of the optical modulation module according to Embodiment 1. This is an upper perspective view showing an optical modulation module according to Embodiment 2. This is an upper perspective view showing an optical modulation module according to Embodiment 3. This is an upper perspective view showing the submount of the optical modulation module according to Embodiment 4. This is an upper perspective view showing the submount and high-frequency substrate of modified example (1) of the optical modulation module according to Embodiment 4. This is an upper perspective view showing the submount and high-frequency substrate of modified example (2) of the optical modulation module according to Embodiment 4. This is an upper perspective view showing an optical modulation module according to Embodiment 5. 【0010】Embodiment 1. The optical modulation module transmits information by modulating the characteristics of the optical signal, such as its intensity, frequency, or phase, according to the electrical signal. The optical modulation module according to Embodiment 1 has a structure in which no ground is formed on the back side of the high-frequency substrate, thereby suppressing the influence of the ground on the back side of the high-frequency substrate. As a result, the coplanar line of the high-frequency substrate can be made into a high-frequency line with strong lateral electric field confinement. 【0011】 (Basic Configuration of Optical Modulation Module) Figure 1 is an overhead perspective view showing an optical modulation module 1 according to Embodiment 1. As shown in Figure 1, the optical modulation module 1 has an EML (Electro-Absorption Modulator Integrated Laser) 3 mounted on a submount 2. The EML 3 integrates a DFB laser 4 and an EAM (Electro-Absorption Modulator) 5. In the optical modulation module 1, a high-frequency substrate 6 is also mounted on the submount 2. A coplanar line consisting of signal lines 7 and ground wiring 10 is formed on the surface of the high-frequency substrate 6. 【0012】 The signal line 7 is connected to the anode of EAM 5 via the first wire 8. The anode of EAM 5 is connected to the termination resistor 11 via the second wire 9. The termination resistor 11 is formed on the submount 2. Furthermore, the DFB laser wiring 12 provided on the submount 2 is connected to the DFB laser 4 of EML 3 via the third wire 13. 【0013】Figure 2 is an upper perspective view showing the submount 2 and high-frequency substrate 6 of the optical modulation module 1. Figure 3 is a lower perspective view showing the submount 2 and high-frequency substrate 6. As shown in Figure 2, the submount 2 has a ground opening 14 (the shaded area in Figure 2) in the region where the high-frequency substrate 6 is mounted, which is a region without a ground conductor. As shown in Figure 3, the high-frequency substrate 6 has a ground opening 16 on its back surface, which is a region without a ground conductor. The ground opening 16 is the first ground opening. The ground opening 14 is the second ground opening. As a result, the influence of the ground on the back side of the high-frequency substrate 6 is suppressed, so that the optical modulation module 1 can use a coplanar transmission line as a high-frequency transmission line with strong lateral electric field confinement. 【0014】 Joint portion 15 is provided in an area of ​​the submount 2 other than the ground opening 14 in the region where the high-frequency substrate 6 is mounted, and is a second joint portion for joining the submount 2 to the high-frequency substrate 6. Joint portion 17 is provided in an area of ​​the back surface of the high-frequency substrate 6 other than the ground opening 16, and is a first joint portion for joining the high-frequency substrate 6 to the submount 2. Joint portions 15 and 17 are metallized portions. By joining joint portion 15 and joint portion 17 using solder or the like, the high-frequency substrate 6 can be firmly joined to the submount 2. 【0015】 The side metallized portion 18 is provided on the side of the high-frequency substrate 6 mounted on the submount 2 that faces the EML 3, and electrically connects the ground wiring 10 of the coplanar line to the cathode of the EML 3. By using the side metallized portion 18, it is possible to electrically connect the ground wiring 10 and the cathode of the EML 3 without joining them. 【0016】 (Submount) Submount 2 is a substrate made of a material that has excellent heat dissipation properties and a coefficient of thermal expansion similar to that of InP (indium phosphide), the material of EML3, such as aluminum nitride. As described above, EML3 and the high-frequency substrate 6 are mounted on submount 2, and the surface on which they are mounted has a termination resistor 11 and DFB laser wiring 12. 【0017】 (EML) EML3 is a device in which a DFB laser 4 and an EAM 5 are integrated onto a single chip. The DFB (Distributed Feedback) laser 4 is a semiconductor laser that serves as a light source for optical signals. The EAM 5 is an optical modulator that modulates light. In EML3, the top surface of the chip is the anode and the bottom surface is the cathode. The thickness of EML3 is generally 100 μm or less. 【0018】 (High-Frequency Substrate) The high-frequency substrate 6 is mounted adjacent to the EML 3 in the submount 2 and is a substrate having a coplanar line on its surface. The distance between the EML 3 and the high-frequency substrate 6 in the submount 2 is 100 μm or less. The high-frequency substrate 6 is made of a material with a lower dielectric constant than aluminum nitride, such as quartz. The coplanar line formed on the surface of the high-frequency substrate 6 is a GSG (ground-signal-ground) coplanar line. The electrical signal propagating through the signal line 7 in the coplanar line is input to the anode of the EAM 5 via the first wire 8, and then output to the terminating resistor 11 via the second wire 9. 【0019】 The ground wiring 10 in the coplanar line is connected to a ground electrode formed on the surface of the submount 2 (the surface on which the EML 3 and the high-frequency substrate 6 are mounted) via the side metallized portion 18 of the high-frequency substrate 6, and is connected to the cathode of the EML 3. Since a ground opening 16 is provided on the back surface of the high-frequency substrate 6, it does not have a ground conductor. Furthermore, since a ground opening 14 is provided on the surface of the submount 2, it also does not have a ground conductor. As a result, the coplanar line of the high-frequency substrate 6 has a strong coupling in the lateral direction. 【0020】Coplanar transmission lines that propagate high-speed signals exceeding 100 GHz require low crosstalk and minimal influence from the dielectric loss of the high-frequency substrate 6. For example, if the thickness of the high-frequency substrate 6 is as thin as 100 μm, equivalent to that of EML3, designing a high-frequency transmission line with a characteristic impedance of 50 Ω will result in the high-frequency transmission line being affected by the back-side ground. In this case, it becomes difficult for the high-frequency transmission line to behave as an ideal coplanar transmission line, which has a strong lateral electric field distribution. Furthermore, the back-side ground layer is prone to resonance in the high-frequency range. As a result, conventional optical modulation modules either experience increased electromagnetic field radiation at high frequencies or bandwidth limitation due to resonance. In contrast, in optical modulation module 1, the coplanar transmission line of the high-frequency substrate 6 operates as an ideal coplanar transmission line due to the ground opening. This reduces electromagnetic field radiation during propagation and minimizes crosstalk to other channels. Also, because there is no ground on the back of the high-frequency substrate 6, high-frequency resonance phenomena originating from the thickness of the substrate on the front and back surfaces do not occur, enabling operation over a wider bandwidth. 【0021】 Next, the operation of the optical modulation module 1 will be described. An electrical signal input to the high-frequency substrate 6 via wire bonding or the like propagates along the coplanar line of the high-frequency substrate 6 and is input to the EAM 5 by the first wire 8. The DFB laser 4 oscillates continuous light when a DC current is injected into it. The EAM 5 generates a high-frequency optical signal by absorbing the light from the DFB laser 4 in response to the input electrical signal. 【0022】 Since the thickness of the EML3 and the high-frequency substrate 6 are equivalent, shortening the length of the first wire 8 reduces the parasitic inductance component generated in the first wire 8, thereby improving the high-frequency characteristics of the optical modulation module 1. For example, if the thickness of the EML3 is 100 μm or less, and the distance between the EML3 and the high-frequency substrate 6 is 100 μm or more, the distance between the signal line 7 on the high-frequency substrate 6 and the pad of the EAM 5 becomes greater, resulting in a longer wire. For this reason, it is preferable that the distance between the EML3 and the high-frequency substrate 6 be 100 μm or less. 【0023】Furthermore, by using a material with excellent heat dissipation properties, such as aluminum nitride, for the submount 2, and a material with low dielectric constant and excellent high-frequency characteristics, such as quartz, for the high-frequency substrate 6, high reliability and excellent high-frequency characteristics can be achieved simultaneously. 【0024】 In Patent Document 1, the submount having a step was constructed using a ceramic laminated substrate. In contrast, the optical modulation module 1 can be realized by combining two substrates with a simple structure, namely the submount 2 and the high-frequency substrate 6, thus enabling inexpensive manufacturing. 【0025】 Furthermore, although an example in which a side metallized portion 18 is provided on the side surface of the high-frequency substrate 6 has been shown, the optical modulation module 1 is not limited to this. For example, the ground wiring 10 and the cathode of the EML 3 may be connected by a through-hole that penetrates the high-frequency substrate 6. 【0026】 Next, a modified example of the optical modulation module 1 according to Embodiment 1 will be described. Figure 4 is an overhead perspective view showing an optical modulation module 1A, which is a modified example of the optical modulation module 1. In the optical modulation module 1, as shown in Figure 1, a high-frequency signal is input from the end of a signal line 7 formed along the longitudinal direction of the high-frequency substrate 6 (the front end in Figure 1). On the other hand, as shown in Figure 4, the optical modulation module 1A has a coplanar line in which ground wiring 10A is formed on both sides of the signal line 7A along the width direction of the high-frequency substrate 6A. The high-frequency signal is input from the end of the signal line 7A along the width direction of the high-frequency substrate 6A. Although the direction of signal input is different for the optical modulation module 1A compared to the optical modulation module 1, all other functions are the same, and therefore the same effects as the optical modulation module 1 can be obtained. 【0027】As described above, the optical modulation module 1 according to Embodiment 1 comprises an EML 3 on which the EAM 5 and DFB laser 4 are integrated, a submount 2 on which the EML 3 is mounted, a termination resistor 11 connected to the EAM 5, and a high-frequency substrate 6 mounted on the submount 2 adjacent to the EML 3 and having a coplanar line on its surface. The back surface of the high-frequency substrate 6 has a ground opening 16, which is a region without a ground conductor, and the region on the submount 2 on which the high-frequency substrate 6 is mounted has a ground opening 14, which is a region without a ground conductor. Since the influence of the ground on the back side of the high-frequency substrate 6 is suppressed, the coplanar line of the high-frequency substrate 6 in the optical modulation module 1 can be a high-frequency line with strong lateral electric field confinement. 【0028】 In the optical modulation module 1 according to Embodiment 1, the high-frequency substrate 6 is a substrate having a lower dielectric constant than the submount 2. As a result, the optical modulation module 1 can simultaneously achieve high reliability and excellent high-frequency characteristics. 【0029】 In the optical modulation module 1 according to Embodiment 1, a side metallized portion 18 is provided on the side of the high-frequency substrate 6 mounted on the submount 2 that faces the EML 3, and electrically connects the ground wiring 10 of the coplanar line to the cathode of the EML 3. It is possible to electrically connect the ground wiring 10 and the cathode of the EML 3 without joining them. 【0030】 In the optical modulation module 1 according to Embodiment 1, a joint portion 17 is provided in an area other than the ground opening 16 on the back surface of the high-frequency substrate 6 for joining the high-frequency substrate 6 to the submount 2, and a joint portion 15 is provided in an area other than the ground opening 14 in the area of ​​the submount 2 on which the high-frequency substrate 6 is mounted, for joining the submount 2 to the high-frequency substrate 6. The joint portion 15 and the joint portion 17 can be joined with solder or conductive adhesive, so that the submount 2 and the high-frequency substrate 6 can be firmly joined. 【0031】 Embodiment 2. Embodiment 2 describes an optical modulation module having a termination resistor on a high-frequency substrate. 【0032】Figure 5 is an overhead perspective view showing the optical modulation module 1B according to Embodiment 2. In Figure 5, the DFB laser wiring 12 and the third wire 13 are omitted from the description. Similar to optical modulation module 1, the optical modulation module 1B has the EML 3 and high-frequency substrate 6B mounted on the submount 2. The EML 3 integrates the DFB laser 4 and the EAM 5. A coplanar line consisting of signal lines 7 and ground wiring 10 is formed on the surface of the high-frequency substrate 6B. 【0033】 The signal line 7 is connected to the anode of the EAM 5 via the first wire 19. The anode of the EAM 5 is connected to a termination resistor 21 provided on the high-frequency substrate 6B via the second wire 20. By providing the termination resistor 21 connected to the EAM 5 on the high-frequency substrate 6B, the width dimension of the submount 2 can be reduced, allowing the EML 3 to be mounted at a narrow pitch. 【0034】 As described above, in the optical modulation module 1B according to Embodiment 2, the high-frequency substrate 6B has a termination resistor 21. As a result, in the optical modulation module 1B, the width of the submount 2 can be narrowed and the EML 3 can be mounted at a narrow pitch, improving the transmission capacity per unit width (Gbps / mm). 【0035】 Embodiment 3. Embodiment 3 describes an optical modulation module in which a driver IC is mounted on a high-frequency substrate. 【0036】 Figure 6 is an overhead perspective view showing the optical modulation module 1C according to Embodiment 3. In Figure 6, the optical modulation module 1C has an EML 3 and a high-frequency substrate 6 mounted on a submount 2. The EML 3 integrates a DFB laser 4 and an EAM 5. A coplanar line consisting of signal lines 7 and ground wiring 10 is formed on the surface of the high-frequency substrate 6. A driver amplifier 22 is mounted on the coplanar line, as shown in Figure 6. 【0037】The driver amplifier 22 is a driver IC that amplifies the input high-speed signal to the amplitude required for modulation by the EAM 5. Driver ICs like the driver amplifier 22 are devices that generate a lot of heat. On the other hand, the optical modulation module 1C uses a substrate 6 made of a material such as quartz, which has a lower dielectric constant and higher thermal resistance compared to aluminum nitride. When the EML 3 gets hot, the optical output decreases and the operating speed also decreases. By mounting the heat-generating driver amplifier 22 on a high-frequency substrate 6 with high thermal resistance, the optical modulation module 1C can reduce the heat inflow to the EML 3 and suppress the performance degradation of the EML 3 due to temperature rise. 【0038】 Furthermore, by mounting the driver amplifier 22 on the high-frequency substrate 6, the driver amplifier 22 can be positioned near the EAM 5, which is a reflection point for high-frequency signals. Since a termination resistor is also mounted on the output of the driver amplifier 22, placing the EAM 5 and the driver amplifier 22 in close proximity reduces multiple reflections originating from the EAM 5. As a result, a smooth frequency response can be achieved even in higher frequency bands. 【0039】 In this embodiment, a configuration in which a driver amplifier 22 is added to that of Embodiment 1 is illustrated, but the same effect can be obtained by applying it to the configuration of Embodiment 2. 【0040】 As described above, in the optical modulation module 1C according to Embodiment 3, the high-frequency substrate 6 is a substrate having a lower thermal conductivity than the submount 2. Furthermore, the optical modulation module 1C includes a driver amplifier 22 provided on the high-frequency substrate 6. This reduces the inflow of heat to the EML 3 and suppresses the performance degradation of the EML 3 due to temperature rise. 【0041】 Embodiment 4. Embodiment 4 describes an optical modulation module in which a recess is provided as a ground opening in the submount or high-frequency substrate. 【0042】FIG. 7 is an upper perspective view showing the submount 2A included in the optical modulation module 1D according to Embodiment 4, and descriptions of components other than the submount 2A are omitted. Also in the optical modulation module 1D, similar to the optical modulation module 1, the EML 3 and the high-frequency substrate 6 are mounted on the submount 2A. On the surface of the high-frequency substrate 6, a coplanar line formed of a signal line 7 and a ground wiring 10 is formed. The signal line 7 is connected to the anode of the EAM 5 via the first wire 8. The anode of the EAM 5 is connected to a termination resistor 11 provided on the submount 2A via the second wire 9. Further, the DFB laser wiring 12 provided on the submount 2A is connected to the DFB laser 4 of the EML 3 via the third wire 13. 【0043】 In the present embodiment, as the submount 2A, a substrate made of a material such as aluminum nitride, which has a thermal expansion coefficient close to that of InP and excellent heat dissipation properties, is used. As shown in FIG. 7, the submount 2A has a recess 23 in a region where the high-frequency substrate 6 is mounted. The recess 23 is a portion where the region of the submount 2A where the high-frequency substrate 6 is mounted is hollowed out and the inside is replaced with air, and is a second ground opening. 【0044】 By providing the recess 23, the influence of the submount 2A having a high dielectric constant on the high-frequency substrate 6 using a low dielectric constant material is reduced. Thereby, the effective dielectric constant that affects the high-frequency signal propagating through the coplanar line is reduced, and the electrical length of the coplanar line can be lengthened. Furthermore, deterioration of high-frequency characteristics such as multiple reflection and resonance can be reduced. 【0045】 Note that even if the recess 23 penetrates to the back surface of the submount 2A or is a hollowing to the middle of the submount 2A, an effect of reducing the effective dielectric constant that affects the high-frequency signal propagating through the coplanar line can be obtained. Also, in order to enhance the shape stability, the inside of the recess 23 may be filled with a resin material or the like. Note that the recess 23 in the optical modulation module 1D can obtain the same effect when applied not only to Embodiment 1 but also to the configurations of Embodiment 2 and Embodiment 3. 【0046】Next, a modified example (1) of the optical modulation module according to Embodiment 4 will be described. Figure 8 is an overhead perspective view showing the submount 2 and high-frequency substrate 6C of the optical modulation module 1E, which is a modified example (1) of the optical modulation module 1D, and the description of components other than the submount 2 and high-frequency substrate 6C has been omitted. In the optical modulation module 1E, as with the optical modulation module 1, the EML 3 and high-frequency substrate 6C are mounted on the submount 2. A coplanar line consisting of a signal line 7 and a ground wire 10 is formed on the surface of the high-frequency substrate 6C. The signal line 7 is connected to the anode of the EAM 5 via the first wire 8. The anode of the EAM 5 is connected to the termination resistor 11 provided on the submount 2 via the second wire 9. Furthermore, the DFB laser wiring 12 provided on the submount 2 is connected to the DFB laser 4 of the EML 3 via the third wire 13. 【0047】 As shown in Figure 8, a recess 24 is provided on the back surface of the high-frequency substrate 6C. By providing the recess 24, the effective dielectric constant that affects the high-frequency signal propagating through the coplanar line is reduced, allowing the electrical length of the coplanar line to be increased. Furthermore, degradation of high-frequency characteristics such as multiple reflections and resonance can be reduced. Note that the recess 24 in the optical modulation module 1E can be applied not only to the configuration of Embodiment 1, but also to the configurations of Embodiments 2 and 3, and similar effects can be obtained. 【0048】Next, a modification example (2) of the optical modulation module according to Embodiment 4 will be described. FIG. 9 is an upper perspective view showing a submount 2 and a high-frequency substrate 6D included in an optical modulation module 1F, which is a modification example (2) of the optical modulation module 1D, and descriptions of components other than the submount 2 and the high-frequency substrate 6D are omitted. Also in the optical modulation module 1F, similar to the optical modulation module 1, an EML 3 and a high-frequency substrate 6D are mounted on the submount 2. On the surface of the high-frequency substrate 6D, a coplanar line formed of a signal line 7 and a ground wiring 10 is formed. The signal line 7 is connected to the anode of the EAM 5 via a first wire 8. The anode of the EAM 5 is connected to a termination resistor 11 provided on the submount 2 via a second wire 9. Further, a DFB laser wiring 12 provided on the submount 2 is connected to the DFB laser 4 of the EML 3 via a third wire 13. 【0049】 On the back surface of the high-frequency substrate 6D, as shown in FIG. 9, a spacer 25 is provided. The spacer 25 is provided. The spacer 25 is a metal spacer joined to a joint portion 15 provided on the submount 2 with solder or the like. The high-frequency substrate 6D is made thinner and adjusted to the same thickness as the EML 3 by the spacer 25. By providing the spacer 25 in this way, the effective dielectric constant that affects the high-frequency signal propagating through the coplanar line can be reduced, and the electrical length of the coplanar line can be lengthened. Further, deterioration of high-frequency characteristics such as multiple reflection and resonance can be reduced. Note that the spacer 25 in the optical modulation module 1F can be applied to the configurations of not only Embodiment 1 but also Embodiment 2, Embodiment 3, and the optical modulation module 1D to obtain similar effects. 【0050】As described above, in the optical modulation module 1D according to Embodiment 4, the ground opening is a recess 23 provided in the region where the high-frequency substrate 6 of the submount 2A is mounted. The recess 23 reduces the influence of the submount 2A, which has a high dielectric constant, on the high-frequency substrate 6, which uses a low dielectric constant material. As a result, the effective dielectric constant that affects the high-frequency signal propagating through the coplanar line is reduced, and the electrical length of the coplanar line can be increased. Furthermore, degradation of high-frequency characteristics such as multiple reflections and resonance can be reduced. 【0051】 In the optical modulation module 1E according to Embodiment 4, the ground opening is a recess 24 provided on the back surface of the high-frequency substrate 6C. The recess 24 reduces the effective dielectric constant that affects the high-frequency signal propagating through the coplanar line, thereby increasing the electrical length of the coplanar line. Furthermore, it can reduce high-frequency characteristic degradation such as multiple reflections and resonance. 【0052】 In the optical modulation module 1F according to Embodiment 4, the high-frequency substrate 6D is thinner than the EML 3. A spacer 25 is provided on the back surface of the high-frequency substrate 6D to lift the back surface of the high-frequency substrate 6D from the submount 2. The spacer 25 reduces the effective dielectric constant that affects the high-frequency signal propagating through the coplanar line, thereby increasing the electrical length of the coplanar line. Furthermore, it can reduce high-frequency characteristic degradation such as multiple reflections and resonance. 【0053】 Embodiment 5. Embodiment 5 describes an optical modulation module in which ground wiring in a coplanar transmission line is electrically connected by wire bonding. 【0054】Figure 10 is an overhead perspective view showing an optical modulation module 1G according to Embodiment 5. As shown in Figure 10, in the optical modulation module 1G, similar to the optical modulation module 1, the EML 3 and high-frequency substrate 6 are mounted on the submount 2. A coplanar line consisting of a signal line 7 and a ground wire 10 is formed on the surface of the high-frequency substrate 6. The signal line 7 is connected to the anode of the EAM 5 via a first wire 8. The anode of the EAM 5 is connected to a termination resistor 11 provided on the submount 2 via a second wire 9. Furthermore, the DFB laser wiring 12 provided on the submount 2 is connected to the DFB laser 4 of the EML 3 via a third wire 13. 【0055】 In this embodiment, the ground wires 10 of the coplanar transmission line formed on the high-frequency substrate 6 are electrically connected by wire bonding 26 using a conductor such as gold wire. The wire bonding 26 shields noise components radiated from the coplanar transmission line, reducing crosstalk to the EML 3 of another adjacent channel. Furthermore, since the electrical connection between the ground wires 10 is strengthened, impedance mismatch caused by the difference in the path length of the return current at the bent portion of the coplanar transmission line can be reduced. This impedance mismatch is caused by a resonance phenomenon at the bent portion of the coplanar transmission line on the high-frequency substrate 6 due to the difference in length between the two ground wires 10. 【0056】 In this embodiment, a configuration in which the ground wirings 10 are connected by wire bonding 26 is illustrated compared to Embodiment 1. However, similar effects can be obtained by applying this configuration not only to Embodiment 1, but also to Embodiments 2, 3, and 4. 【0057】 As described above, in the optical modulation module 1G according to Embodiment 5, the ground wiring 10 in the coplanar line is electrically connected to each other by wire bonding 26. The wire bonding 26 shields the optical modulation module 1G from noise components radiated from the coplanar line, thereby reducing crosstalk to the EML 3 of another adjacent channel. 【0058】 The optical modulation module relating to this disclosure can be used, for example, in optical communications. 【0059】 Furthermore, it is possible to combine each embodiment, modify any component of each embodiment, or omit any component in each embodiment. 【0060】 1. 1A-1G Optical modulation module, 2. 2A Submount, 3 EML (Electromagnetic Wave Lapping Module), 4 DFB laser, 5 EAM (Electromagnetic Wave Absorption Module), 6. 6A-6D High-frequency substrate, 7. 7A Signal line, 8. 19 First wire, 9. 20 Second wire, 10. 10A Ground wiring, 11. 21 Termination resistor, 12 DFB laser wiring, 13 Third wire, 14. 16 Ground opening, 15. 17 Joint, 18 Side metallized section, 22 Driver amplifier, 23. 24 Recess, 25 Spacer, 26 Wire bonding.

Claims

1. An optical modulation module comprising: an EML integrating an electric field absorption modulator and a semiconductor laser; a submount on which the EML is mounted; a termination resistor connected to the electric field absorption modulator; and a high-frequency substrate mounted adjacent to the EML on the submount and having a coplanar line on its surface, wherein the back surface of the high-frequency substrate has a first ground opening which is a region without a ground conductor, and the region on the submount on which the high-frequency substrate is mounted has a second ground opening which is a region without a ground conductor.

2. The optical modulation module according to claim 1, characterized in that the high-frequency substrate is a substrate having a lower dielectric constant than the submount.

3. The optical modulation module according to claim 1 or 2, characterized in that it is provided on the side of the high-frequency substrate mounted on the submount that faces the EML, and comprises a side metallized portion that electrically connects the ground wiring of the coplanar line to the cathode of the EML.

4. The optical modulation module according to any one of claims 1 to 3, comprising: a first joining portion provided in an area other than the first ground opening on the back surface of the high-frequency substrate for joining the high-frequency substrate to the submount; and a second joining portion provided in an area other than the second ground opening in the area of ​​the submount on which the high-frequency substrate is mounted for joining the submount to the high-frequency substrate.

5. The optical modulation module according to any one of claims 1 to 4, characterized in that the high-frequency substrate has the termination resistor.

6. The optical modulation module according to any one of claims 1 to 5, characterized in that the high-frequency substrate is a substrate having a lower thermal conductivity than the submount, and a driver IC is provided on the high-frequency substrate.

7. The optical modulation module according to any one of claims 1 to 6, characterized in that the second ground opening is a recess provided in the region of the submount on which the high-frequency substrate is mounted.

8. The optical modulation module according to any one of claims 1 to 7, characterized in that the first ground opening is a recess provided on the back surface of the high-frequency substrate.

9. The optical modulation module according to any one of claims 1 to 7, characterized in that the high-frequency substrate is thinner than the EML, and a spacer is provided on the back surface of the high-frequency substrate to lift the back surface of the high-frequency substrate from the submount.

10. The optical modulation module according to any one of claims 1 to 9, characterized in that the ground wiring in the coplanar line is electrically connected by wire bonding.

Images