Optical transmission module

Abstract

An optical transmission module (100) is provided with an EML (20) having anode electrodes (21, 22) on the front surface and a cathode electrode on the rear surface and configured to output modulatable laser light, a DC wiring board (40) mounted on the EML (20) and configured to supply power to the EML (20) via the front surface of the EML (20), and a high-frequency board (50) mounted on the DC wiring board (40) and configured to transmit a high-frequency signal to the EML (20) via the front surface of the EML (20).

Description

Optical transmission module

[0001] The present disclosure relates to an optical transmission module.

[0002] An EML (Electro-absorption modulator integrated laser diode) is a semiconductor chip in which a DFB (Distributed Feedback) laser and an EA (Electro-Absorption) modulator are monolithically integrated on a single substrate. Generally, in an EML, an element structure is formed by epitaxial growth on an n-type InP substrate. Therefore, in an EML, an anode electrode is provided on the chip surface, and a cathode electrode is provided on the back surface of the chip.

[0003] Non-Patent Document 1 discloses an optical transmission module including an EML. As shown in Non-Patent Document 1, an optical transmission module generally adopts a configuration in which an EML is mounted on a submount, and a high-frequency signal propagated through a high-frequency line formed on the submount is connected to an anode terminal of an EA modulator via gold wire bonding. The EA modulator is a capacitive element and needs to terminate a high-frequency line with impedance management. The optical transmission module disclosed in Non-Patent Document 1 performs connection using gold wires to a thin film resistor formed on the submount. Also, the back surface of the EML becomes the cathode side and is connected to the ground.

[0004] In recent years, the modulation speed required for optical transmission modules exceeds 100 Gbaud (for example, 113 Gband PAM4). At this time, the inductance caused by gold wire bonding may cause a decrease in the above modulation speed.

[0005] Therefore, Patent Document 1 proposes an optical transmission module in which a high-frequency substrate is flip-chip mounted on an EML. The optical transmission module disclosed in Patent Document 1 aims to improve high-frequency characteristics by eliminating the commonly used gold wire bonding.

[0006] Chengzhi Xu, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 24, NO. 22, 2012

[0007] Japanese Patent Publication No. 2019-33380

[0008] However, the optical transmission module disclosed in Patent Document 1 requires the provision of an anode electrode and a cathode electrode on the surface of the EML. Therefore, the optical transmission module disclosed in Patent Document 1 has the problem of complicating the manufacturing process of the EML.

[0009] Normally, the cathode electrode is located on the back surface of an EML (Electromagnetic Linear Module). If this is done on the front surface, the current will flow laterally from the anode electrode to the cathode electrode. This increases the parasitic resistance of the element and increases the RC time constant. As a result, the high-frequency characteristics deteriorate, or excessive heat is generated due to the parasitic resistance, degrading the element's performance.

[0010] Furthermore, in the optical transmission module disclosed in Patent Document 1, the number of electrodes required on the surface of the EML increases, resulting in a larger surface area for the EML. Consequently, the number of EMLs obtainable per wafer decreases, and the manufacturing cost of the EML increases.

[0011] Furthermore, in the optical transmission module disclosed in Patent Document 1, the anode electrode of the DFB laser is located at the rear of the EML, which may cause physical interference between the anode electrode and the high-frequency transmission line. For this reason, the high-frequency transmission line must be located to the side of the EML. As a result, when such a configuration is applied to an optical transmission module with multiple EMLs arranged in a row, the area required for mounting the EMLs increases, leading to a larger optical transmission module.

[0012] This disclosure was made to solve the above-mentioned problems and aims to provide an optical transmission module that can be constructed without using wire bonding to the EML, even when the EML has an anode electrode on its surface and a cathode electrode on its back surface.

[0013] The optical transmission module according to this disclosure comprises an EML having an anode electrode on its surface and a cathode electrode on its back surface, which outputs modulable laser light; a first wiring board mounted on the EML and supplying power to the EML via the surface of the EML; and a high-frequency board mounted on the first wiring board and transmitting a high-frequency signal to the EML via the surface of the EML.

[0014] According to this disclosure, even when an EML has an anode electrode on its surface and a cathode electrode on its back surface, it can be constructed without using wire bonding to the EML.

[0015] This is an exploded perspective view of the optical transmission module according to Embodiment 1, viewed from the rear upper side. This is an exploded perspective view of the optical transmission module according to Embodiment 1, viewed from the rear lower side. This is a diagram showing the simulation results of the high-frequency characteristics. This is an exploded perspective view of the optical transmission module according to Embodiment 2, viewed from the rear upper side. This is an external perspective view of the optical transmission module according to Embodiment 3, viewed from the front upper side. This is an exploded perspective view of the optical transmission module according to Embodiment 4, viewed from the rear upper side. This is an exploded perspective view of the optical transmission module according to Embodiment 5, viewed from the rear upper side. This is an exploded perspective view of the optical transmission module according to Embodiment 5, viewed from the rear lower side. This is an external perspective view of the optical transmission module according to Embodiment 6, viewed from the front upper side. This is an exploded perspective view of the optical transmission module according to Embodiment 7, viewed from the front upper side. This is an exploded perspective view of the optical transmission module according to Embodiment 7, viewed from the front lower side. This is an external perspective view of the optical transmission module according to Embodiment 7, equipped with an ASIC. Figures 13A and 13B illustrate the case where the EML bumps do not contact the DC wiring board. Figures 14A and 14B illustrate the case where the EML bumps contact the DC wiring board. Figures 15A and 15B illustrate the case where the step dimension between the EML height and the ground block height is manufactured according to the design value. Figures 16A and 16B illustrate the case where the step dimension between the EML height and the ground block height is larger than the design value. Figures 17A and 17B illustrate the case where the step dimension between the EML height and the ground block height is smaller than the design value. This is an external perspective view of the optical transmission module according to Embodiment 9, viewed from the front and above.

[0016] To provide a more detailed explanation of this disclosure, the forms for implementing this disclosure will be described below with reference to the attached drawings.

[0017] Embodiment 1. The optical transmission module 100 according to Embodiment 1 will be described with reference to Figures 1 to 3.

[0018] First, the configuration of the optical transmission module 100 according to Embodiment 1 will be described using Figures 1 and 2. Figure 1 is an exploded perspective view of the optical transmission module 100 according to Embodiment 1, viewed from the rear upper side. Figure 2 is an exploded perspective view of the optical transmission module 100 according to Embodiment 1, viewed from the rear lower side.

[0019] The optical transmission module 100 according to Embodiment 1 shown in Figure 1 is, for example, a module for converting an input high-frequency signal into laser light L and outputting the laser light L. In the optical transmission module 100, the side from which the laser light L is output is the front side, and the opposite side is the rear side.

[0020] As shown in Figures 1 and 2, the optical transmission module 100 includes a submount 11, a ground block 12, an EML 20, a DC wiring board 30 which is a second wiring board, a DC wiring board 40 which is a first wiring board, and a high-frequency board 50.

[0021] The back surfaces of the ground block 12, the EML 20, and the DC wiring board 30 are mounted on the surface of the submount 11. The back surface of the DC wiring board 40 is mounted across the surface of the ground block 12, the EML 20, and the DC wiring board 30. The back surface of the high-frequency board 50 is mounted on the surface of the DC wiring board 40.

[0022] The submount 11 is made of a metal material with excellent heat dissipation properties. An example of a metal material with excellent heat dissipation properties is aluminum nitride. When the ground block 12, EML 20, and DC wiring board 30 are mounted on the submount 11, solder with excellent heat dissipation properties, such as gold or tin, is used. A cooling mechanism (not shown) is thermally connected to the submount 11. The cooling mechanism is an example of a Peltier element, heat sink fins, or water cooling head.

[0023] The DC wiring board 30 is located at the rear of the surface of the submount 11. The DC wiring board 30 has DC wiring 31. The DC wiring 31 is located on the surface of the DC wiring board 30. The DC wiring 31 is a linear wiring extending in the front-rear direction. The DC wiring 31 is electrically connected to the EML 20 via a DC wiring board 40, which will be described later. The DC wiring 31 is also electrically connected to a current source (not shown).

[0024] The ground block 12 and EML 20 are located at the front of the surface of the submount 11. That is, the back surfaces of the ground block 12 and the EML 20 are in contact with the surface of the submount 11. The ground block 12 is positioned on both sides (or left and right sides) in the width direction of the EML 20.

[0025] EML20 is a semiconductor chip manufactured, for example, by epitaxial growth on an n-type InP substrate. EML20 employs a monolithic integration configuration of a DFB laser and an EA modulator (both not shown). EML20 may also be a semiconductor chip manufactured by epitaxial growth on a p-type InP substrate.

[0026] The DFB laser generates laser light L when power is supplied. The EA modulator modulates the laser light L generated by the DFB laser based on a supplied high-frequency signal and outputs it. The DFB laser and EA modulator are installed inside the EML 20. The DFB laser is located at the rear of the EML 20. The EA modulator is located at the front of the EML 20.

[0027] The DFB laser and EA modulator use the front side of the EML 20 as the anode and the back side of the EML 20 as the cathode. The DFB laser has an anode electrode 21. The EA modulator has an anode electrode 22. The anode electrodes 21 and 22 are provided on the front surface of the EML 20. The cathode electrodes of the DFB laser and EA modulator are provided on the back surface of the EML. In other words, the front surface of the EML 20 does not have a cathode electrode; only the anode electrode 21 for power supply and the anode electrode 22 for high-frequency signal supply are provided.

[0028] The ground block 12 has electrical conductivity between its front and back surfaces. The back surface of the ground block 12 and the back surface of the EML 20 are electrically connected via a metal pattern (not shown) provided on the surface of the submount 11. Therefore, the front surface of the ground block 12 is electrically connected to the cathode electrode provided on the back surface of the EML 20.

[0029] The ground block 12 and the EML 20 are formed to the same thickness. That is, the ground block 12 and the EML 20 only need to be designed so that their heights from the surface of the submount 11 are the same. The thickness of the ground block 12 and the EML 20 are set to, for example, 100 μm or less in order to reduce resistance or improve heat dissipation on the cathode side, which is the back side of the EML 20.

[0030] The DC wiring board 40 is used to route the power supply for driving the DFB laser of the EML 20 from the DC wiring board 30 to the DFB laser. The DC wiring board 40 has high-frequency vias 41, a ground layer 42, DC wiring 43, an inductor 44, a termination resistor 45, and a ground layer 46.

[0031] The high-frequency via 41 is provided so as to penetrate the DC wiring board 40 in its thickness direction. That is, one end of the high-frequency via 41 penetrates the surface of the DC wiring board 40, and the other end of the high-frequency via 41 penetrates the back surface of the DC wiring board 40. When the DC wiring board 40 is mounted on the EML 20, the other end of the high-frequency via 41 comes into contact with the anode electrode 22 of the EML 20 and becomes electrically connected to it.

[0032] The ground layer 42 is provided on the surface of the DC wiring board 40. The ground layer 42 is not in contact with one end of the high-frequency via 41, but is arranged to surround that end.

[0033] The DC wiring 43 is provided on the back surface of the DC wiring board 40. When the DC wiring board 40 is mounted on the EML 20 and the DC wiring board 30, the DC wiring 43 comes into contact with the anode electrode 21 of the EML 20 and the DC wiring 31 of the DC wiring board 30, and becomes electrically connected to them.

[0034] The inductor 44 is located on the back surface of the DC wiring board 40. One end of the inductor 44 is electrically connected to the other end of the high-frequency via 41.

[0035] The termination resistor 45 is located on the back surface of the DC wiring board 40. The termination resistor 45 is electrically connected to the other end of the inductor 44.

[0036] The ground layer 46 is provided on the back surface of the DC wiring board 40. The ground layer 46 is located on both the left and right sides of the inductor 44 and the termination resistor 45. When the DC wiring board 40 is mounted on the ground block 12, the ground layer 46 comes into contact with the surface of each ground block 12.

[0037] The high-frequency circuit board 50 is for transmitting high-frequency signals to the EA modulator of the EML 20 via the DC wiring board 40. The high-frequency circuit board 50 has high-frequency vias 51, high-frequency lines 52, ground pads 53, and a ground layer 54.

[0038] The high-frequency via 51 is provided so as to penetrate the high-frequency substrate 50 in its thickness direction. That is, one end of the high-frequency via 51 penetrates the surface of the high-frequency substrate 50, and the other end of the high-frequency via 51 penetrates the back surface of the high-frequency substrate 50. When the high-frequency substrate 50 is mounted on the DC wiring board 40, the other end of the high-frequency via 51 comes into contact with one end of the high-frequency via 41 and becomes electrically connected to it.

[0039] The high-frequency line 52 is provided on the surface of the high-frequency substrate 50. One end of the high-frequency line 52 is electrically connected to one end of the high-frequency via 51. The high-frequency signal is transmitted from the other end of the high-frequency line 52 toward the one end. The high-frequency line 52 is, for example, a microstrip line or a coplanar line.

[0040] The ground pad 53 is provided on the surface of the high-frequency substrate 50. The ground pad 53 does not come into contact with one end of the high-frequency via 51 or the high-frequency line 52, but is positioned to surround them.

[0041] The ground layer 54 is provided on the back surface of the high-frequency substrate 50. The ground layer 54 does not contact the other end of the high-frequency via 51, but is arranged to surround it. When the high-frequency substrate 50 is mounted on the DC wiring board 40, the ground layer 54 comes into contact with the surface of the ground layer 42 of the DC wiring board 40.

[0042] The thinner the DC wiring board 40 and the high-frequency board 50, the shorter the length of the high-frequency vias 41 and 51 can be, which is advantageous in terms of high-frequency characteristics. For this reason, the thickness of the DC wiring board 40 and the high-frequency board 50 are set to, for example, 200 μm or less. Furthermore, when mounting the DC wiring board 40 on the ground block 12, EML 20, and DC wiring board 30, or when mounting the high-frequency board 50 on the DC wiring board 40, gold stud bumps, solder, or copper micropillars are used. In addition, the DC wiring board 40 and the high-frequency board 50 may be pre-laminated and integrated before mounting them on the ground block 12, EML 20, and DC wiring board 30.

[0043] The DC wiring board 40 and the high-frequency board 50 are formed from materials such as quartz, ceramic, or organic materials (polyimide, liquid crystal polymer, etc.). While the DC wiring board 40 is provided with an inductor 44 and termination resistor 45 for peaking, these may also be provided on the high-frequency board 50.

[0044] Therefore, the optical transmission module 100 according to Embodiment 1 supplies power to the anode electrode 21 of the DFB laser via the DC wiring boards 30 and 40, causing the DFB laser to emit light with a constant output. Also, the optical transmission module 100 supplies a high-frequency signal to the anode electrode 22 of the EA modulator via the high-frequency line 52 and the high-frequency vias 41 and 51, causing the EA modulator to modulate the laser light L generated by the DFB laser. The high-frequency signal is, for example, in a modulation format such as 100 GBand PAM4 / NRZ or 200 GBand PAM4 / NRZ.

[0045] At this time, peaking is imparted to the high-frequency signal in the inductor 44 of the DC wiring board 40 and terminated with the termination resistor 45. Further, the heat emitted from the EML 20 is transmitted to the cooling mechanism via the submount 11.

[0046] Also, by having the configuration described above, the optical transmission module 100 according to Embodiment 1 can significantly reduce the inductance component compared to the conventional configuration in which the EML 20 having a front-side anode electrode and a back-side cathode electrode is connected by gold wire bonding, and can improve the high-frequency characteristics. This will be described with reference to FIG. 3.

[0047] FIG. 3 is a diagram showing the simulation results of the high-frequency characteristics. The solid line shown in FIG. 3 represents the simulation results of the high-frequency characteristics in the optical transmission module 100 according to Embodiment 1. The dotted line shown in FIG. 3 represents the simulation results of the high-frequency characteristics in the above conventional configuration. Also, the horizontal axis of FIG. 3 indicates the frequency of the high-frequency signal in the EML 20. The vertical axis of FIG. 3 indicates the passing amplitude of the high-frequency signal in the EML 20.

[0048] As shown in FIG. 3, in the conventional configuration, the 3 dB bandwidth is limited to 75 GHz due to the inductance of the gold wire. In contrast, in the optical transmission module 100 according to Embodiment 1, the 3 dB bandwidth is improved up to about 150 GHz.

[0049] Furthermore, the optical transmission module 100 according to Embodiment 1 includes an EML 20 having a front-side anode electrode and a back-side cathode electrode, which has been commonly used in the past, thereby reducing the complexity of the manufacturing process for the EML 20.

[0050] Furthermore, the optical transmission module 100 according to Embodiment 1 can reduce the parasitic resistance of the element compared to the case where an EML with the anode electrode and cathode electrode on the same plane is provided. As a result, the optical transmission module 100 according to Embodiment 1 can reduce the RC time constant and output laser light L at high speed.

[0051] Furthermore, since the optical transmission module 100 according to Embodiment 1 has the minimum necessary anode electrodes 21 and 22 on the surface of the EML 20, it is possible to suppress an increase in the surface area of ​​the EML 20. In other words, the optical transmission module 100 according to Embodiment 1 can suppress an increase in the manufacturing cost of the EML 20.

[0052] As described above, the optical transmission module 100 according to Embodiment 1 can be configured without using wire bonding to the EML 20, even when it includes an EML 20 having anode electrodes 21 and 22 on its surface and a cathode electrode on its back surface.

[0053] Embodiment 2. The optical transmission module 200 according to Embodiment 2 will be described with reference to Figure 4. Figure 4 is an exploded perspective view of the optical transmission module 200 according to Embodiment 2, viewed from the rear upper side. Components having the same function as those described in the above-described embodiments are denoted by the same reference numerals, and their descriptions are omitted.

[0054] The optical transmission module 100 according to Embodiment 1 comprises one EML 20, whereas the optical transmission module 200 according to Embodiment 2 comprises multiple EMLs 20. Specifically, the optical transmission module 200 arranges multiple EMLs 20 in an array on a single submount 11.

[0055] As shown in Figure 4, the optical transmission module 200 according to Embodiment 2 has a configuration in which a plurality of EMLs 20 are arranged at equal intervals in the width direction. Figure 4 shows an example in which the optical transmission module 200 has four EMLs 20. In this case, the plurality of EMLs 20 and the plurality of ground blocks 12 are arranged alternately in the width direction. When there are four EMLs 20, there are five ground blocks 12. The number of DC wiring boards 30, 40 and the number of high-frequency boards 50 are the same as the number of EMLs 20. The plurality of DC wiring boards 30, 40 and the plurality of high-frequency boards 50 are also arranged at equal intervals in the width direction. The plurality of DC wiring boards 30, 40 and the plurality of high-frequency boards 50 may be separate or integrated. Figure 4 shows an example in which the plurality of DC wiring boards 30, 40 and the plurality of high-frequency boards 50 are each integrated.

[0056] For example, the EML 20 and ground block 12 are arranged at a pitch of 0.25 mm in the width direction. That is, the pitch between adjacent EML 20s is 0.50 mm. When each EML 20 operates with 200 GBand PAM4, communication of 800 Gbps per 1 mm width is possible in the EML 20. This corresponds to 800 Gbps / mm in terms of edge density (transmission capacity per 1 mm width), an index used in products that perform high-density signal wiring, such as semiconductor chips.

[0057] Furthermore, each EML20 can be fitted with a frequency having the same wavelength in the 1310 nm band, or a wavelength corresponding to a LAN-WDM or CWDM grid. When a frequency with the same wavelength is applied to each EML20, a parallel single-mode fiber is used for each EML20. When frequencies with different wavelengths are applied to each EML20, each EML20 is fitted with a wavelength multiplexer that combines beams of different wavelengths onto the same optical axis, and a single-mode fiber for coupling the wavelength-multiplexed light.

[0058] Therefore, even if the optical transmission module 200 according to Embodiment 2 is equipped with multiple EMLs 20, power supply current and high-frequency signals can be supplied to each EML 20 from the rear side. For this reason, the optical transmission module 200 according to Embodiment 2 can suppress an increase in size in the width direction.

[0059] As described above, the optical transmission module 200 according to Embodiment 2 can be configured without using wire bonding to the EML 20, even when it includes an EML 20 having anode electrodes 21 and 22 on its surface and a cathode electrode on its back surface.

[0060] Embodiment 3. The optical transmission module 300 according to Embodiment 3 will be described with reference to Figure 5. Figure 5 is an external perspective view of the optical transmission module 300 according to Embodiment 3, viewed from the front and above. Components having the same functions as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are omitted.

[0061] The optical transmission module 300 according to Embodiment 3 has a configuration that adds two collimating lenses 23 to the configuration of the optical transmission module 200 according to Embodiment 2. The collimating lenses 23 are manufactured, for example, by lens printing technology.

[0062] As shown in Figure 5, the optical transmission module 300 according to Embodiment 3 has an optical fiber (not shown) provided on the output side of each EML 20. One collimating lens 23 is printed on the output section of the EA modulator in the EML 20. The other collimating lens 23 (not shown) is printed on the input section of the optical fiber. The laser light L collimated by the collimating lens 23 of the EML 20 is coupled to the optical fiber core via the collimating lens 23 of the optical fiber.

[0063] When multiple EML20s are separate components, their mounting positions can vary by, for example, several micrometers. This can lead to optical axis misalignment between each EML20 and the integrated optical fiber array facing them. Correcting such optical axis misalignment becomes complicated.

[0064] In contrast, the optical transmission module 300 according to Embodiment 3 can mitigate acceptable positional deviations of the laser beam L by providing collimating lenses 23 on both the EML 20 side and the optical fiber side. Furthermore, the optical transmission module 300 according to Embodiment 3 can mount a compact and high-performance collimating lens 23 with high precision by using printing technology to attach the collimating lens 23. Therefore, the optical transmission module 300 according to Embodiment 3 can improve the efficiency of optical coupling between the EML 20 and the optical fiber.

[0065] As described above, even when the optical transmission module 300 according to Embodiment 3 includes an EML 20 having anode electrodes 21 and 22 on its surface and a cathode electrode on its back surface, it can be constructed without using wire bonding to the EML 20.

[0066] Embodiment 4. The optical transmission module 400 according to Embodiment 4 will be described with reference to Figure 6. Figure 6 is an exploded perspective view of the optical transmission module 400 according to Embodiment 4, viewed from the rear upper side. Components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are omitted.

[0067] The optical transmission module 400 according to Embodiment 4 has a configuration that adds a driver amplifier 60 for driving the EA modulator to the configuration of the optical transmission module 100 according to Embodiment 1.

[0068] As shown in Figure 6, the driver amplifier 60 is connected to the high-frequency transmission line 52 on the surface of the high-frequency substrate 50 so as to cover the transmission line 52. The driver amplifier 60 amplifies the high-frequency signal propagating through the high-frequency transmission line 52 to the voltage level required by the EA modulator. The driver amplifier 60 is positioned such that, for example, the distance from the EML 20 to the EA modulator is 0.5 mm or less.

[0069] As described above, the optical transmission module 400 according to Embodiment 4 has the driver amplifier 60 positioned close to the EA modulator of the EML 20, thereby reducing the effects of multiple reflections occurring between the driver amplifier 60 and the EA modulator. For this reason, the optical transmission module 400 according to Embodiment 4 can improve the high-frequency characteristics of the EML 20.

[0070] Furthermore, the optical transmission module 400 according to Embodiment 4 can shorten the wiring between the driver amplifier 60 and the EA modulator of the EML 20 by shortening the distance between them. Therefore, the optical transmission module 400 according to Embodiment 4 does not require a termination resistor between the driver amplifier 60 and the EA modulator of the EML 20. As a result, the optical transmission module 400 according to Embodiment 4 can reduce power consumption.

[0071] Furthermore, the driver amplifier 60 can also be applied to the optical transmission modules 200 and 300 according to embodiments 2 and 3.

[0072] As described above, even when the optical transmission module 400 according to Embodiment 4 includes an EML 20 having anode electrodes 21 and 22 on its surface and a cathode electrode on its back surface, it can be constructed without using wire bonding to the EML 20.

[0073] Embodiment 5. The optical transmission module 500 according to Embodiment 5 will be described with reference to Figures 7 and 8. Figure 7 is an exploded perspective view of the optical transmission module 500 according to Embodiment 5, viewed from the rear upper side. Figure 8 is an exploded perspective view of the optical transmission module 500 according to Embodiment 5, viewed from the rear lower side. Components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are omitted.

[0074] The optical transmission module 500 according to Embodiment 5 has a configuration in which the DC wiring board 40 is removed from the configuration of the optical transmission module 400 according to Embodiment 4. In addition, the optical transmission module 500 according to Embodiment 5 is equipped with a high-frequency board 50A instead of the high-frequency board 50. Specifically, the optical transmission module 500 according to Embodiment 5 includes a submount 11, a ground block 12, an EML 20, a high-frequency board 50A, and a driver amplifier 60.

[0075] As shown in Figures 7 and 8, the back surface of the high-frequency substrate 50A is mounted across the surface of the ground block 12, the surface of the EML 20, and the surface of the DC wiring board 30. The high-frequency substrate 50A is used to route the power supply for driving the DFB laser of the EML 20 from the driver amplifier 60 to the DFB laser, and to transmit high-frequency signals to the EA modulator of the EML 20. The high-frequency substrate 50A has high-frequency vias 51, a ground layer 54, a power supply via 55, high-frequency lines 56a and 56b, an inductor 57, and a termination resistor 58.

[0076] The power supply via 55 is provided so as to penetrate the high-frequency substrate 50A in the thickness direction. That is, one end of the power supply via 55 penetrates the surface of the high-frequency substrate 50A, and the other end of the power supply via 55 penetrates the back surface of the high-frequency substrate 50A. When the high-frequency substrate 50A is mounted on the EML 20, the other end of the power supply via 55 comes into contact with the anode electrode 22 of the EML 20 and becomes electrically connected to it.

[0077] The high-frequency lines 56a and 56b are provided on the surface of the high-frequency substrate 50A. The high-frequency lines 56a and 56b are arranged in a straight line. A high-frequency signal is transmitted from the high-frequency line 56a to the high-frequency line 56b. A gap is formed between one end of the high-frequency lines 56a and 56b, and one end of the power supply via 55 is located in this gap. That is, the high-frequency lines 56a and 56b and the power supply via 55 are not electrically connected. The other end of the high-frequency line 56b is electrically connected to one end of the high-frequency via 51.

[0078] The inductor 57 is located on the back surface of the high-frequency substrate 50A. One end of the inductor 57 is electrically connected to the other end of the high-frequency via 51.

[0079] The termination resistor 58 is located on the back surface of the high-frequency substrate 50A. The termination resistor 58 is electrically connected to the other end of the inductor 57. The ground layer 54 is arranged to surround the other end of the high-frequency via 51, the inductor 57, and the termination resistor 58.

[0080] The driver amplifier 60 has an added function of supplying power to the DFB laser of the EML 20. Specifically, the driver amplifier 60 amplifies the high-frequency signals propagating through the high-frequency lines 56a and 56b to the voltage level required by the EA modulator, and also supplies power to drive the DFB laser of the EML 20 to the DFB laser via the high-frequency substrate 50A. The driver amplifier 60 is located on the surface of the high-frequency substrate 50A.

[0081] The driver amplifier 60 has a power supply terminal 61, a high-frequency signal input terminal 62, and a high-frequency signal output terminal 63. The power supply terminal 61, the high-frequency signal input terminal 62, and the high-frequency signal output terminal 63 are located on the back surface of the driver amplifier 60.

[0082] When the driver amplifier 60 is mounted on the high-frequency board 50A, the power supply terminal 61 contacts and makes electrical contact with the power supply via 55 of the high-frequency board 50A. When the driver amplifier 60 is mounted on the high-frequency board 50A, the high-frequency signal input terminal 62 contacts and makes electrical contact with one end of the high-frequency line 56a. When the driver amplifier 60 is mounted on the high-frequency board 50A, the high-frequency signal output terminal 63 contacts and makes electrical contact with one end of the high-frequency line 56b. The high-frequency signal input terminal 62 and the high-frequency signal output terminal 63 are electrically connected to each other.

[0083] Therefore, the optical transmission module 500 according to Embodiment 5 supplies power to the anode electrode 21 of the DFB laser via the power supply terminal 61 of the driver amplifier 60 and the power supply via 55 of the high-frequency substrate 50A, thereby causing the DFB laser to emit light at a constant output. Furthermore, the optical transmission module 500 supplies a high-frequency signal to the anode electrode 22 of the EA modulator via the high-frequency lines 56a, 56b and the terminals 62, 63 of the driver amplifier 60, thereby modulating the laser light L generated by the DFB laser using the EA modulator.

[0084] At this time, the high-frequency signal is peaked in the inductor 57 of the high-frequency substrate 50A and terminated by the termination resistor 58. In addition, the heat emitted from the EML 20 is transferred to the cooling mechanism via the submount 11.

[0085] The optical transmission module 500 according to Embodiment 5 does not have a DC wiring board 40, thus reducing the number of components. Furthermore, the absence of the DC wiring board 40 in the optical transmission module 500 according to Embodiment 5 allows for the elimination of the high-frequency vias 41. As a result, the optical transmission module 500 according to Embodiment 5 has only one high-frequency via 51, reducing the number of high-frequency vias from two to one. Consequently, the optical transmission module 500 according to Embodiment 5 can improve the high-frequency characteristics of the EML 20.

[0086] As described above, even when the optical transmission module 500 according to Embodiment 5 includes an EML 20 having anode electrodes 21 and 22 on its surface and a cathode electrode on its back surface, it can be constructed without using wire bonding to the EML 20.

[0087] Embodiment 6. The optical transmission module 600 according to Embodiment 6 will be described with reference to Figure 9. Figure 9 is an external perspective view of the optical transmission module 600 according to Embodiment 6, viewed from the front and above. Components having the same functions as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are omitted.

[0088] While the optical transmission modules 400 and 500 according to embodiments 4 and 5 are equipped with one EML 20, the optical transmission module 600 according to embodiment 6 is equipped with multiple EMLs 20. Specifically, the optical transmission module 600 arranges multiple EMLs 20 in an array and standardizes the driver amplifier 60 on a single submount 11.

[0089] As shown in Figure 9, the optical transmission module 600 according to Embodiment 6 integrates multiple driver amplifiers 60, each corresponding to an EML 20, into a single ASIC (Application Specific Integrated Circuit) 60A. The ASIC 60A is provided across each high-frequency board 50. This ASIC 60A is capable of outputting high-speed high-frequency signals. When an ASIC 60A is provided in this manner, it is preferable for the submount 11 to be a redistribution board with fine wiring for power supply or signal connection to the ASIC 60A.

[0090] As described above, the optical transmission module 600 according to Embodiment 6 has the driver amplifier 60 positioned close to the EA modulator of the EML 20, thereby reducing the effects of multiple reflections occurring between the driver amplifier 60 and the EA modulator. For this reason, the optical transmission module 400 according to Embodiment 4 can improve the high-frequency characteristics of the EML 20.

[0091] As described above, even when the optical transmission module 600 according to Embodiment 6 includes an EML 20 having anode electrodes 21 and 22 on its surface and a cathode electrode on its back surface, it can be constructed without using wire bonding to the EML 20.

[0092] Embodiment 7. The optical transmission module 700 according to Embodiment 7 will be described with reference to Figures 10 to 12. Figure 10 is an exploded perspective view of the optical transmission module 700 according to Embodiment 7, viewed from the front upper side. Figure 11 is an exploded perspective view of the optical transmission module 700 according to Embodiment 7, viewed from the front lower side. Figure 12 is an external perspective view of the optical transmission module 700 according to Embodiment 7, equipped with an ASIC 60A. Components having the same functions as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are omitted.

[0093] As shown in Figures 10 and 11, the optical transmission module 700 according to Embodiment 7 includes a submount 11, a ground block 12, an EML 20, a rewiring board 70, and a termination resistor board 80 which is a high-frequency board.

[0094] The redistribution board 70 is located at the lowest position within the optical transmission module 700. The redistribution board 70 is made of, for example, a resin material. The redistribution board 70 has power supply wiring 71, high-frequency signal wiring 72, and a plurality of bumps 73.

[0095] The power supply wiring 71 and the high-frequency signal wiring 72 penetrate the redistribution board 70 from its back side. Multiple bumps 73 are arranged in an array on the back surface of the redistribution board 70. Each bump 73 is electrically connected to the power supply for the drive current of the DFB laser and to the source of the high-frequency signal.

[0096] The back surface of the termination resistor substrate 80 is mounted on the front surface of the redistribution substrate 70. The termination resistor substrate 80 is made of, for example, ceramics or quartz. The termination resistor substrate 80 has power supply vias 81, an inductor 82, a termination resistor 83, and a high-frequency via 84.

[0097] The power supply via 81 is provided so as to penetrate the termination resistor substrate 80 in the thickness direction. That is, one end of the power supply via 81 penetrates the surface of the termination resistor substrate 80, and the other end of the power supply via 81 penetrates the back surface of the termination resistor substrate 80.

[0098] When the EML 20 is mounted on the termination resistor board 80, one end of the power supply via 81 contacts the anode electrode 21 of the EML 20 and makes electrical contact with it. The other end of the power supply via 81 contacts one end of the power supply wiring 71 of the redistribution board 70 when the termination resistor board 80 is mounted on the redistribution board 70 and makes electrical contact with it.

[0099] The inductor 82 is provided on the surface of the termination resistor substrate 80. It is electrically connected to a high-frequency via 84 that penetrates the termination resistor substrate 80. The termination resistor 83 is provided on the surface of the termination resistor substrate 80. The termination resistor 83 is electrically connected to the other end of the inductor 82.

[0100] When the EML 20 is mounted on the termination resistor board 80, one end of the high-frequency via 84 contacts the anode electrode 22 of the EML 20 and establishes electrical contact with it. The other end of the high-frequency via 84 contacts one end of the high-frequency signal wiring 72 of the redistribution board 70 when the termination resistor board 80 is mounted on the redistribution board 70 and establishes electrical contact with it.

[0101] Therefore, the optical transmission module 700 according to Embodiment 7 supplies power to the anode electrode 21 of the DFB laser via the power supply wiring 71 of the redistribution board 70 and the power supply via 81 of the termination resistor board 80, thereby causing the DFB laser to emit light at a constant output. Furthermore, the optical transmission module 700 supplies a high-frequency signal to the anode electrode 22 of the EA modulator via the high-frequency signal wiring 72 of the redistribution board 70 and the high-frequency via 84 of the termination resistor board 80, thereby modulating the laser light L generated by the DFB laser using the EA modulator.

[0102] At this time, the high-frequency signal is peaked in the inductor 82 of the termination resistor substrate 80 and terminated by the termination resistor 83. In addition, the heat emitted from the EML 20 is transferred to the cooling mechanism via the submount 11.

[0103] It is difficult to provide a thin-film termination resistor on a redistribution board 70 made of resin material. When attempting to provide a thin-film termination resistor on a redistribution board 70, it is necessary to use chip resistors or the like. In contrast, a thin-film termination resistor 83 can be formed by sputtering on a termination resistor board 80 made of ceramics or quartz. In the optical transmission module 700 according to Embodiment 7, by providing a termination resistor board 80 between the redistribution board 70 and the EML 20, the inductor 82 and termination resistor 83, which are passive components essential for driving the EA modulator, can be integrated. For this reason, the optical transmission module 700 according to Embodiment 7 can be miniaturized.

[0104] Furthermore, as shown in Figure 12, the optical transmission module 700 according to Embodiment 7 allows the ASIC 60A, which generates a large amount of heat, to be mounted on the surface of the redistribution board 70. Therefore, by mounting the EML 20 and the ASIC 60A on the surface of the redistribution board 700 according to Embodiment 7, the heat emitted from them can be released from the surface of the redistribution board 70, which has excellent heat dissipation properties.

[0105] As described above, even when the optical transmission module 700 according to Embodiment 7 includes an EML 20 having anode electrodes 21 and 22 on its surface and a cathode electrode on its back surface, it can be constructed without using wire bonding to the EML 20.

[0106] Embodiment 8. The optical transmission module according to Embodiment 8 will be described with reference to Figures 13 to 17.

[0107] Figure 13 illustrates the case where the bump 91 of the EML 20 does not contact the DC wiring board 40. Figure 14 illustrates the case where the bump 91 of the EML 20 contacts the DC wiring board 40.

[0108] In the optical transmission modules 100, 200, 300, 400, 500, 600, and 700 according to Embodiments 1 to 7, the DC wiring board 40 or high-frequency board 50A is joined to the EML 20 and ground block 12 mounted on the submount 11 using metal bumps. As described above, even if an attempt is made to set the height of the EML 20 and the height of the ground block 12 to the same height, they may not be at the same height, as shown in Figure 13.

[0109] Figure 13 shows the case where the height of the ground block 12 is higher than the height of the EML 20. Figure 13A shows the DC wiring board 40 before joining, and Figure 13B shows the DC wiring board 40 after joining. As shown in Figure 13B, the bumps 91 provided on the anode electrodes 21 and 22 of the EML 20 are not in contact with the back surface of the DC wiring board 40 and are not crushed. On the other hand, the bumps 92 provided on the surface of the ground block 12 are in contact with the back surface of the DC wiring board 40 and are crushed.

[0110] Therefore, as shown in Figure 14, in the optical transmission module according to Embodiment 8, the number of stacked bumps 91 is greater than the number of stacked bumps 92. Figure 14 shows an example where there are two stacked bumps 91 and one stacked bump 92. Figure 14A shows the DC wiring board 40 before joining, and Figure 14B shows the DC wiring board 40 after joining. As shown in Figure 14B, both the two bumps 91 and the one bump 92 are in contact with the back surface of the DC wiring board 40 and are crushed.

[0111] The points mentioned above will be explained in detail using Figures 15 to 17. Figure 15 illustrates the case where the step dimension between the height of the EML 20 and the height of the ground block 12 is manufactured according to the design value. Figure 16 illustrates the case where the step dimension between the height of the EML 20 and the height of the ground block 12 is larger than the design value. Figure 17 illustrates the case where the step dimension between the height of the EML 20 and the height of the ground block 12 is smaller than the design value.

[0112] As shown in Figure 15, the height of the EML 20 is set to be 20 μm higher than the height of the ground block 12. The height of one bump 93 is approximately 30 μm. The height tolerance (thickness tolerance) of the EML 20 is ±5 μm, and the height tolerance (thickness tolerance) of the ground block 12 is ±10 μm. Therefore, the maximum height deviation from the set value (20 μm) is 15 μm. The height of the bump 93 after joining is set to 15 μm.

[0113] Therefore, since a height difference of up to 15 μm occurs, if there is only one bump 93 stacked on the anode electrodes 21 and 22 of the EML 20, there is a risk that the bump 93 will not make contact with the back surface of the DC wiring board 40. By increasing the number of bumps 93 stacked on the anode electrodes 21 and 22 of the EML 20 to multiple bumps 93, in all cases from Figure 15 to Figure 17, the bumps 93 stacked on the anode electrodes 21 and 22 of the EML 20 will make contact with the back surface of the DC wiring board 40 and will all be crushed in the same way.

[0114] Therefore, in the optical transmission module according to embodiment 8, even if there is a height difference between the height of the EML 20 and the height of the ground block 12, the EML 20 can always be electrically connected to the DC wiring board 40 by increasing the number of bumps 93 stacked on the anode electrodes 21 and 22 of the EML 20.

[0115] As described above, the optical transmission module according to Embodiment 8 can be configured without using wire bonding to the EML 20, even when it includes an EML 20 having anode electrodes 21 and 22 on its surface and a cathode electrode on its back surface.

[0116] Embodiment 9. The optical transmission module 900 according to Embodiment 9 will be described with reference to Figure 18. Figure 18 is an external perspective view of the optical transmission module 900 according to Embodiment 9, viewed from the front and above. Components having the same functions as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are omitted.

[0117] As shown in Figure 9, the optical transmission module 900 according to Embodiment 9 has a termination resistor 58 on the surface of the high-frequency substrate 50. One end of the high-frequency line 52 and the termination resistor 58 are electrically connected by a gold wire 59.

[0118] As described above, even when the optical transmission module 900 according to Embodiment 9 includes an EML 20 having anode electrodes 21 and 22 on its surface and a cathode electrode on its back surface, it can be constructed without using wire bonding to the EML 20.

[0119] Within the scope of this disclosure, it is possible to freely combine the embodiments, modify any component in each embodiment, or omit any component in each embodiment.

[0120] The optical transmission module according to this disclosure comprises a first wiring board that supplies power to the EML via the surface of the EML and a high-frequency board that transmits a high-frequency signal to the EML via the surface of the EML. This allows the module to be constructed without using wire bonding to the EML, even when the EML has an anode electrode on its surface and a cathode electrode on its back surface, making it suitable for use in optical transmission modules and the like.

[0121] 11 Submount, 12 Ground block, 20 EML, 21 Anode electrode, 22 Anode electrode, 23 Collimating lens, 30 DC wiring board, 31 DC wiring, 40 DC wiring board, 41 High-frequency via, 42 Ground layer, 43 DC wiring, 44 Inductor, 45 Termination resistor, 46 Ground layer, 50, 50A High-frequency board, 51 High-frequency via, 52 High-frequency line, 53 Ground pad, 54 Ground layer, 55 Power supply via, 56a, 56b High-frequency line, 57 Inductor, 58 Termination resistor, 59 Gold wire, 60 Driver amplifier, 60A ASIC, 61 Power supply terminal, 62 High-frequency signal input terminal, 63 High-frequency signal output terminal, 70 Rewiring board, 71 Power supply wiring, 72 High-frequency signal wiring, 73 Bump, 80 Termination resistor board, 81 Power supply via, 82 Inductor, 83 Termination resistor, 84 High-frequency via, 91-93 Bump, 100, 200, 300, 400, 500, 600, 700, 900 Optical transmitter module.

Claims

1. An optical transmission module comprising: an EML having an anode electrode on its surface and a cathode electrode on its back surface, which outputs modulable laser light; a first wiring board mounted on the EML and supplying power to the EML via the surface of the EML; and a high-frequency board mounted on the first wiring board and transmitting a high-frequency signal to the EML via the surface of the EML.

2. An optical transmission module comprising: an EML having an anode electrode on its surface and a cathode electrode on its back surface, which outputs modulable laser light; and a high-frequency substrate mounted on the EML, which supplies power to the EML via the surface of the EML and transmits high-frequency signals to the EML via the surface of the EML.

3. The optical transmission module according to claim 1 or 2, characterized in that it is provided on the submount on which the EML is mounted and comprises a ground block having the same height as the EML.

4. The optical transmission module according to claim 1 or 2, comprising a ground block provided on the submount on which the EML is mounted, having a height greater than the height of the EML, wherein the number of bumps stacked on the EML is greater than the number of bumps stacked on the ground block.

5. The optical transmission module according to claim 1, characterized in that the first wiring board allows high-frequency signals transmitted from the high-frequency board to pass through.

6. The optical transmission module according to claim 5, characterized in that it is provided on a submount on which the EML is mounted, and further comprises a second wiring board on which the first wiring board is mounted and which supplies power to the first wiring board.

7. The optical transmission module according to any one of claims 1 to 6, characterized in that it comprises a collimating lens provided on the output side of the EML and on the input side of the optical fiber facing the EML.

8. The optical transmission module according to any one of claims 1 to 7, further comprising a driver amplifier provided on the high-frequency substrate for amplifying high-frequency signals propagating through the high-frequency substrate.

9. The optical transmission module according to claim 8, characterized in that the distance between the EML and the driver amplifier is 0.5 mm or less.

10. The optical transmission module according to any one of claims 1 to 7, characterized in that it comprises an ASIC provided on the high-frequency substrate and outputting a high-frequency signal.

11. The optical transmission module according to any one of claims 1 to 10, characterized in that the high-frequency substrate has a high-frequency line through which a high-frequency signal is propagated and a termination resistor bonded between the high-frequency line and the substrate.

12. The optical transmission module according to claim 2, characterized in that the high-frequency substrate has high-frequency vias through which high-frequency signals pass, and termination resistors connected to the high-frequency vias.

13. The optical transmission module according to claim 12, comprising a redistribution board on which the high-frequency substrate is mounted and which supplies power and high-frequency signals to the high-frequency substrate, and a plurality of bumps provided on the back surface of the redistribution board.

14. The optical transmission module according to claim 13, characterized in that the surface of the redistribution board is provided with an ASIC that outputs a high-frequency signal.

Images