Modulation circuit

Abstract

The purpose of the present disclosure is to provide a modulation circuit that increases the degree of freedom in arrangement of a wiring configuration on a substrate.　The modulation circuit according to the present disclosure comprises: a subcarrier 1 having a ground pad 2 on an upper surface; and a wiring section 3 including a signal line portion 31 for supplying an electric signal to a modulator 42 for modulating a predetermined signal, the signal line portion 31 extending in a predetermined direction, a termination resistor 32 electrically connected to the signal line portion 31, and a pad portion 33 electrically connected to the termination resistor 32 and the ground pad 2. The signal line portion 31, the termination resistor 32, and the pad portion 33 are arranged in this order on the subcarrier 1 in a direction different from the predetermined direction.

Description

Modulation circuit

[0001] The present disclosure relates to modulation circuits, and more particularly to modulation circuits used in optical transmitters.

[0002] Conventionally, in a modulation circuit, peaking control of the frequency characteristics of a line is performed using a wire (L component) or a capacitor (C component).

[0003] For example, Patent Document 1 discloses a structure in which an RF (Radio Frequency) wiring board and a termination resistor are arranged on one side of an EA-DFB laser chip (modulated laser chip: distributed feedback laser integrated with electro-absorption modulator) equipped with a DFB laser (distributed feedback laser) and an EA modulator (electro-absorption modulator), a capacitor and its ground point are arranged on the other side of the modulated laser chip, and the termination resistor and capacitor are connected using a wire that straddles the modulated laser chip. By adopting this structure, Patent Document 1 aims to improve frequency response characteristics when the wire length varies due to manufacturing errors.

[0004] Japanese Patent Application Laid-Open No. 2020-127168

[0005] However, in the configuration of Patent Document 1, in order to improve frequency characteristics, it is necessary to arrange the wiring configuration over a wide area on the subcarrier (substrate) so as to straddle the modulated laser chip, which reduces the degree of freedom in arranging the wiring configuration.

[0006] Therefore, an object of the present disclosure is to provide a modulation circuit that can improve the degree of freedom in arranging a configuration for wiring on a substrate.

[0007] In order to achieve the above object, the modulation circuit of the present disclosure employs a technique in which the signal line portion, the termination resistor, and the pad portion of the wiring section are arranged in this order in a direction different from the predetermined direction in which the signal line portion extends.

[0008] Specifically, the modulation circuit of the present disclosure comprises: a substrate having a ground pad on its upper surface; a signal line portion that supplies an electrical signal to a modulator that modulates a predetermined signal and extends in a predetermined direction; a wiring portion that includes a termination resistor electrically connected to the signal line portion; and a pad portion electrically connected to the termination resistor and the ground pad; and the signal line portion, the termination resistor, and the pad portion are arranged in this order on the substrate in a direction different from the predetermined direction.

[0009] With this configuration, the signal line portion, the termination resistor, and the pad portion are arranged in a direction different from the direction in which the signal line portion extends, thereby enabling the wiring configuration to be compactly arranged, thereby improving the degree of freedom in the termination of the wiring and allowing the implementation of the termination of the wiring to be arranged according to needs.

[0010] The wiring portion may be surrounded by the ground pad.

[0011] This allows for variations in the mounting configuration of the terminal end of the wiring portion for grounding.

[0012] Furthermore, a modulated laser chip having the modulator and a chip component for controlling the modulated laser chip may be arranged on the substrate, and the chip component may be located symmetrically with respect to the wiring portion with respect to the modulated laser chip.

[0013] According to this, by arranging the wiring configuration and other configuration separately on both sides of the modulated laser chip, there is no interference between the wiring configuration and other configuration, and the degree of freedom in placement can be improved in the space given to each.

[0014] The pad portion may be connected to the ground pad via a plurality of wires.

[0015] This allows peaking control to be performed appropriately.

[0016] The pad portion may be connected to the ground pad via a chip capacitor.

[0017] This allows peaking control to be performed appropriately.

[0018] The ground pad may be provided with a flat-plate capacitor, and the pad portion may be electrically connected to the flat-plate capacitor via a plurality of wires.

[0019] The pad portion may be electrically connected to a capacitor provided outside the substrate.

[0020] This allows peaking control to be performed appropriately.

[0021] The above disclosures can be combined as much as possible.

[0022] According to the modulation circuit of the present disclosure, it is possible to improve the degree of freedom in arranging the wiring configuration on the substrate.

[0023] Fig. 1 is a plan view of an optical transmitter module according to a first embodiment of the present disclosure; Fig. 2 is a diagram illustrating the effect of forming a predetermined gap between a ground and a signal line portion; Fig. 3 is a plan view of an optical transmitter module according to a second embodiment of the present disclosure; Fig. 4 is a plan view of an optical transmitter module according to a third embodiment of the present disclosure; Fig. 5 is a plan view of an optical transmitter module according to a fourth embodiment of the present disclosure;

[0024] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0025] (First Embodiment) An optical transmitter module according to a first embodiment of the present disclosure will be described with reference to FIGS. 1 and 2. FIG. 1 is a plan view of the optical transmitter module according to the first embodiment. FIG. 2 is a diagram illustrating the effect of forming a predetermined gap between the ground and the signal line portion. In the following description, the left side of the figure corresponds to the left side of the module, the right side corresponds to the right side of the module, the up side corresponds to the rear side of the module, and the down side corresponds to the front side of the module. The optical transmitter module functions as a "modulation circuit."

[0026] [Components of the Optical Transmitter Module] In the module of this embodiment, a ground pad 2 and an RF (Radio Frequency) wiring section 3 are formed on a subcarrier 1, and a laser chip 4 and various chip components 5 are mounted in predetermined locations. The subcarrier 1 functions as a "substrate."

[0027] Specifically, the optical transmitter module in this embodiment comprises: a subcarrier 1 having a ground pad 2 on its top surface; a signal line portion 31 that supplies an electrical signal to an EA modulator (Electro-absorption Modulator) 42 that modulates a predetermined signal and extends in a predetermined direction; and a wiring portion 3 that comprises a terminating resistor 32 electrically connected to the signal line portion 31; and a pad portion 33 electrically connected to the terminating resistor 32 and the ground pad 2. The signal line portion 31, the terminating resistor 32, and the pad portion 33 are arranged in this order on the subcarrier 1 in a direction different from the predetermined direction. These will be described in detail below.

[0028] The subcarrier 1 is a flat plate extending in the front-rear and left-right directions. The ground pad 2 is formed so as to cover most of the subcarrier 1. The ground pad 2 is formed on the subcarrier 1 in a roughly U-shape.

[0029] The laser chip 4 is an EA-DFB laser (Distributed Feedback Laser Integrated with Electro-absorption Modulator) and is disposed in the center of the subcarrier 1 so as to extend substantially in the front-to-rear direction. The laser chip 4 includes a DFB laser 41 (Distributed Feedback Laser) and an EA modulator 42. The optical waveguide of the laser chip 4 is a curved waveguide to prevent return light. For this reason, the laser chip 4 is configured to emit light forward at an angle other than 90 degrees relative to the output end face. The laser chip 4 itself is disposed at an oblique angle on the subcarrier 1 so that the emitted light is parallel to the front-to-rear sides of the subcarrier 1, with the emitted light directed forward. The laser chip 4 functions as a "modulated laser chip."

[0030] The DFB laser 41 emits laser light (input light) to the EA modulator 42. The EA modulator 42 modulates the input light from the DFB laser 41 by applying a change in response to a predetermined electrical signal described below. The EA modulator 42 functions as a "modulator."

[0031] The RF wiring section 3 is arranged on the left side of the subcarrier 1 so as to be surrounded by the ground pad 2. The RF wiring section 3 is provided with a signal line section 31, a terminating resistor 32, and a pad section 33. The RF wiring section 3 functions as a "wiring section."

[0032] The signal line portion 31 extends in the left-right direction and is configured to supply a modulated electrical signal input from its left end to the laser chip 4. Specifically, an electrode of the EA modulator 42 of the laser chip 4 and the right end of the signal line portion 31 are electrically connected by a predetermined wire 10. As a result, the modulated electrical signal input from the left end of the signal line portion 31 is supplied to the laser chip 4 (EA modulator 42) via the wire 10. The EA modulator 42 generates output light by changing the input light from the DFB laser 41 in accordance with the modulated electrical signal from the signal line portion 31. The modulated electrical signal is an example of an "electrical signal."

[0033] The signal line portion 31 has a first line 31A and a second line 31B. The first line 31A functions as a coplanar line formed by being sandwiched between the ground pads 2 in the front-to-rear direction. The second line 31B also functions as a coplanar line formed by being sandwiched between the pad portion 33 and the ground pads 2 in the front-to-rear direction. The width of the first line 31A in the front-to-rear direction is wider than the width of the second line 31B in the front-to-rear direction. Specifically, the first line 31A and the second line 31B are formed by providing metal wiring on a ceramic material (such as aluminum nitride) having high thermal conductivity.

[0034] The termination resistor 32 is provided at the rear end of the second line 31B and has a generally rectangular shape. The width of the termination resistor 32 in the front-rear direction is generally the same as the width of the second line 31B and the ground pad 2 in the front-rear direction.

[0035] The pad portion 33 is electrically connected to the rear portion of the termination resistor 32 and has a substantially rectangular shape. The pad portion 33 is formed to have a predetermined area so that various elements can be mounted thereon. Specifically, in this embodiment, the pad portion 33 has a width of 200 μm in the front-to-rear direction and a width of 300 μm in the left-to-right direction. In this embodiment, the pad portion 33 is electrically connected to the ground pad 2 using two wires 13 and 14.

[0036] The relationship between the signal line portion 31, the terminating resistor 32, and the pad portion 33 will be described in detail later.

[0037] The chip component 5 is any chip component, and is, for example, a passive element such as a capacitor or a thermistor. The chip component 5 (capacitor) may be electrically connected to the DFB laser 41 using a wire 11 as shown in the figure, and may be used to control the DFB laser 41. The chip component 5 has, for example, a square shape with sides of approximately 400 μm.

[0038] [Regarding the layout relationship of each component] Next, the layout relationship of each component described above on the subcarrier 1 will be described in detail.

[0039] 1 , the laser chip 4 is mounted in the approximate center in the left-right direction of the subcarrier 1 so as to extend in the approximate front-rear direction. Meanwhile, the signal line portion 31 of the RF wiring unit 3 is disposed to the left of the laser chip 4 and has an approximately rectangular parallelepiped shape extending in the left-right direction. In other words, the signal line portion 31 extends in a different direction from the laser chip 4. In this way, since the signal line portion 31 has an approximately rectangular parallelepiped shape extending in the left-right direction different from the front-rear direction in which the laser chip 4 extends, it is possible to ensure space in front of or behind the signal line portion 31 for arranging the termination resistors 32 and the pads 33 together.

[0040] The signal line portion 31, the terminating resistor 32, and the pad 33 are arranged in this order in the front-to-rear direction. That is, the direction in which the signal line portion 31, the terminating resistor 32, and the pad 33 are arranged is substantially the same as the direction in which the laser chip 4 extends. In other words, the direction in which the signal line portion 31, the terminating resistor 32, and the pad 33 are arranged is substantially perpendicular to the direction in which the signal line portion 31 extends. In this way, by arranging the signal line portion 31, the terminating resistor 32, and the pad 33 in a direction different from the direction in which the signal line portion 31 extends, the configuration for RF wiring can be compactly arranged. This improves the degree of freedom in the termination of the RF wiring, allowing the implementation of the termination of the RF wiring to be arranged according to needs.

[0041] In this embodiment, the signal line portion 31 is arranged to form a substantially rectangular parallelepiped shape extending in a left-right direction different from the front-rear direction along which the laser chip 4 extends, and the space secured thereby is used to appropriately arrange the termination resistor 32 and the pad portion 33. In particular, the provision of the pad portion 33 allows for variations in the mounting form (layout) of the termination portion of the RF wiring portion 3.

[0042] In this embodiment, the pad portion 33 and the ground pad 2 are electrically connected using multiple wires by utilizing the secured space. In this case, peaking control is performed appropriately depending on the length and number of wires. Note that the number of wires is not limited to two. Peaking control may be performed using one wire, or three or more wires.

[0043] Furthermore, in this embodiment, the RF wiring section 3 and the chip components are arranged in positions that are approximately symmetrical with respect to the laser chip 4 (EA modulator 42) in the left-right direction. That is, in this embodiment, the components for RF wiring are arranged together on the left side of the laser chip 4, and components other than the components for RF wiring are arranged in the space created on the right side of the laser chip 4. In other words, in this embodiment, by mounting the components other than the components for RF wiring on the opposite side from the RF wiring section 3, sufficient space is secured for mounting the RF termination section.

[0044] Furthermore, the RF wiring section 3 is surrounded by the ground pad 2. This allows for variations in the mounting form of the terminal end of the RF wiring section 3 for grounding.

[0045] [Gap Between Signal Line Portion and Ground Pad] Next, the gap formed between the signal line portion 31 of the RF wiring unit 3 and the ground pad 2 will be described in detail with reference to Fig. 2. In this embodiment, impedance matching is performed by adjusting the gap between the signal line portion 31 and the ground pad 2.

[0046] 2, the first line 31A of the signal line portion 31 has a width of a μm in the front-to-rear direction. A predetermined gap g1 is formed in the front-to-rear direction between the first line 31A and the ground pad 2. The distance in the front-to-rear direction between the two walls of the ground pad 2 that form the gap g1 is set to b μm.

[0047] On the other hand, the second line 31B has a width of a' μm in the front-rear direction. A predetermined gap g2 is formed in the front-rear direction between the second line 31B and the ground pad 2, and between the second line 31B and the pad portion 33. The distance between the wall of the ground pad 2 and the wall of the pad portion 33 that forms the gap g2 is set to b' μm.

[0048] Generally, the impedance characteristics of a coplanar line are determined by the ratio between the width of the transmission line and the distance between the walls of the ground that sandwich the transmission line. That is, in this embodiment, the impedance characteristics of the first line 31A are determined by the ratio between a μm and b μm, and the impedance characteristics of the second line 31B are determined by the ratio between a′ μm and b′ μm.

[0049] In this embodiment, in order to match the impedance between the first line 31A and the second line 31B, the width of each line and the distance between the walls that form each gap are adjusted to keep the above ratio constant, thereby suppressing signal reflection.

[0050] Second Embodiment A module according to a second embodiment of the present disclosure will be described with reference to Fig. 3. Fig. 3 is a plan view of an optical transmitter module according to the second embodiment. Note that the same reference numerals are used for configurations similar to those in the first embodiment, and descriptions thereof will be omitted. Note that the configuration and arrangement in this embodiment can achieve the same effects as those described in the first embodiment.

[0051] In the second embodiment, the chip capacitor 6 is disposed so as to straddle the pad portion 33 and the ground.

[0052] The chip capacitor 6 is a surface-mount type chip capacitor, and one end of the chip capacitor 6 is electrically connected to the pad portion 33, and the other end of the chip capacitor 6 is electrically connected to and grounded by the ground pad 2. This configuration also has the effect of reducing power consumption by cutting DC (Direct Current).

[0053] (Third Embodiment) A module according to a third embodiment of the present disclosure will be described with reference to Fig. 4. Fig. 4 is a plan view of an optical transmitter module according to the third embodiment. Note that the same reference numerals are used for configurations similar to those in the first embodiment, and descriptions thereof will be omitted. Note that the configuration and arrangement in this embodiment can achieve the same effects as those described in the first embodiment.

[0054] In the third embodiment, a flat chip capacitor 7 is disposed on the ground pad 2 so as to extend in the left-right direction. The chip capacitor 7 is electrically connected to the pad portion 33 using two wires 15, 16. That is, in this embodiment, the pad portion 33 is connected to the ground pad 2 via the two wires 15, 16 and the chip capacitor 7. Note that the number of wires is not limited to two. One wire, or three or more wires may be used, and peaking control may be performed by adjusting the length and number of wires. This configuration also has the effect of reducing power consumption by cutting DC.

[0055] (Fourth Embodiment) A module according to a fourth embodiment of the present disclosure will be described with reference to Fig. 5. Fig. 5 is a plan view of an optical transmitter module according to the fourth embodiment. Note that the same reference numerals are used for configurations similar to those in the first embodiment, and descriptions thereof will be omitted. Note that the configuration and arrangement in this embodiment can achieve the same effects as those described in the first embodiment.

[0056] In the fourth embodiment, a chip capacitor 8 is disposed outside the subcarrier 1 in the vertical and horizontal directions of the figure. The chip capacitor 8 is electrically connected to the pad portion 33 using two wires 17 and 18. The number of wires is not limited to two. One wire, or three or more wires may be used, and peaking control may be performed by adjusting the length and number of wires. This configuration also has the effect of reducing power consumption by cutting DC.

[0057] Other Embodiments It is possible to appropriately combine the above-described mounting modes of the termination portion of the RF wiring portion 3. Furthermore, the package ground pins or the like around the subcarrier 1 may be electrically connected to the pad portion 33.

[0058] Furthermore, the contents of the present disclosure are not limited to optical transmitters, but can be applied to any circuit that uses modulated signals.

[0059] 1: Subcarrier 2: Ground pad 3: RF wiring section 4: Laser chip 41: DFB laser 42: EA modulator 5: Chip component 6, 7, 8: Chip capacitor 10, 11, 12, 13, 14, 15, 16, 17, 18: Wire 31: Signal line section 31A: First line 31B: Second line 32: Terminating resistor 33: Pad section g1: First gap g2: Second gap

Claims

1. A modulation circuit comprising: a substrate having a ground pad on its upper surface; a signal line section that supplies an electrical signal to a modulator that modulates the specified signal and extends in a specified direction; a wiring section that includes a terminating resistor electrically connected to the signal line section; and a pad section that is electrically connected to the terminating resistor and the ground pad; wherein the signal line section, the terminating resistor, and the pad section are arranged in this order on the substrate in a direction different from the specified direction.

2. The modulation circuit according to claim 1, wherein the wiring portion is surrounded by the ground pad.

3. The modulation circuit according to claim 1, wherein a modulated laser chip equipped with the modulator and a chip component for controlling the modulated laser chip are arranged on the substrate, and the chip component is located symmetrically with respect to the wiring portion with respect to the modulated laser chip.

4. The modulation circuit according to claim 1, wherein the pad section is connected to the ground pad via a plurality of wires.

5. The modulation circuit according to claim 1, wherein the pad portion is connected to the ground pad via a chip capacitor.

6. The modulation circuit according to claim 1, wherein a flat-plate capacitor is provided on the ground pad, and the pad portion is electrically connected to the flat-plate capacitor via a plurality of wires.

7. The modulation circuit according to claim 1, wherein the pad portion is electrically connected to a capacitor provided outside the substrate.

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