Optical modulator integrated laser device, optical device, and optical modulator

Abstract

To provide an optical modulator integrated laser device capable of reducing loss of a modulation signal caused by reflection.SOLUTION: An optical modulator integrated laser device comprises a substrate, a laser part, an optical modulation part, a first signal pad, a second signal pad, and a first termination resistance. The laser part is provided on the substrate, and outputs a laser beam. The optical modulation part is provided on the substrate, and has a modulation electrode and modulates the laser beam. The first signal pad is provided on the substrate, a normal phase signal of a differential signal is input thereto, and the pad is connected to the modulation electrode. The second signal pad is provided side by side with the first signal pad on the substrate, and a reverse phase signal of the differential signal is input thereto. The first termination resistance has a first end connected to the first signal pad and a second end connected to the second signal pad, and is provided on the substrate.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to an optical modulator integrated laser element, an optical device, and an optical modulator. [Background technology]

[0002] Patent Document 1 discloses techniques relating to a high-frequency circuit, a module incorporating the high-frequency circuit, and a communication device. In the high-frequency circuit, a signal line transmitting a high-frequency signal is connected to a capacitive element by a first bonding wire. Furthermore, the capacitive element is connected to a termination resistor for impedance matching by a second bonding wire. In the high-frequency circuit, the characteristic impedance of the transmission line formed by the first bonding wire, the second bonding wire, and the capacitive element is larger than the characteristic impedance on the input side of the high-frequency signal. In the high-frequency circuit, the inductance of the first bonding wire is smaller than the inductance of the second bonding wire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-308130 Summary of the Invention [Problem to be solved by the invention]

[0004] As optical communication speeds and capacities increase, broader bandwidth optical modulators are required for optical devices. However, when a modulated signal has a high frequency, such as 100 GHz or higher, electrical reflection of the modulated signal tends to be large. The greater the reflection of the modulated signal, the greater the loss of the modulated signal. This can result in, for example, the modulated signal not being transmitted sufficiently to the optical modulator.

[0005] An object of the present disclosure is to provide an optical modulator integrated laser element, an optical device, and an optical modulator that can reduce loss of a modulated signal due to reflection. [Means for solving the problem]

[0006] An optical modulator-integrated laser device according to an embodiment of the present disclosure includes a substrate, a laser unit, an optical modulation unit, a first signal pad, a second signal pad, and a first termination resistor. The laser unit is provided on the substrate and outputs laser light. The optical modulation unit is provided on the substrate, has a modulation electrode, and modulates the laser light. The first signal pad is provided on the substrate, receives a positive-phase signal of a differential signal, and is connected to the modulation electrode. The second signal pad is provided on the substrate alongside the first signal pad, and receives a negative-phase signal of the differential signal. The first termination resistor has a first end connected to the first signal pad and a second end connected to the second signal pad, and is provided on the substrate. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide an optical modulator integrated laser element, an optical device, and an optical modulator that can reduce loss of a modulated signal due to reflection. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view showing a small optical device for transmission, which is an optical apparatus according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a circuit diagram of a small optical device for transmission. [Figure 3] FIG. 3 is an enlarged perspective view of a part of the small optical device for transmission. [Figure 4] FIG. 4 is an enlarged plan view showing a part of the small optical device for transmission. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV shown in FIG. [Figure 6] 6A to 6C are cross-sectional views showing a part of the process for manufacturing an optical modulator integrated semiconductor laser. [Figure 7] FIG. 7 is a cross-sectional view showing a part of the process for manufacturing an optical modulator integrated semiconductor laser. [Figure 8]FIG. 8 is an enlarged perspective view of a part of a small optical device for transmission according to a first modification. [Figure 9] FIG. 9 is an enlarged plan view showing a part of a small optical device for transmission according to a first modification. [Figure 10] FIG. 10 is an enlarged perspective view of a part of a small optical device for transmission according to a second modification. [Figure 11] FIG. 11 is an enlarged plan view showing a part of a small optical device for transmission according to a second modification. [Figure 12] FIG. 12 is an enlarged plan view showing a part of a small optical device for transmission according to a second modification. [Figure 13] FIG. 13 is a simplified circuit diagram of the circuit of the first embodiment and this modification. [Figure 14] FIG. 14 is a plan view showing a small optical device for transmission as a comparative example. [Figure 15] FIG. 15 is a circuit diagram of a small optical device for transmission. [Figure 16] FIG. 16 is an enlarged plan view showing a part of the small optical device for transmission. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. [1] An optical modulator-integrated laser device according to one embodiment of the present disclosure includes a substrate, a laser unit, an optical modulation unit, a first signal pad, a second signal pad, and a first termination resistor. The laser unit is provided on the substrate and outputs laser light. The optical modulation unit is provided on the substrate, has a modulation electrode, and modulates the laser light. The first signal pad is provided on the substrate, receives a positive-phase signal of a differential signal, and is connected to the modulation electrode. The second signal pad is provided on the substrate alongside the first signal pad, and receives a negative-phase signal of the differential signal. The first termination resistor has a first end connected to the first signal pad and a second end connected to the second signal pad, and is provided on the substrate.

[0010] In the optical modulator-integrated laser device described above in [1], the wire connected to the first signal pad (hereinafter referred to as the first wire) and the wire connected to the second signal pad (hereinafter referred to as the second wire) are arranged side by side. The first wire inputs a modulation signal, and the second wire inputs a signal with a phase opposite to that of the modulation signal, resulting in a virtual reference potential line appearing between the first wire and the second wire. This reduces the mismatch in input impedance of the modulation signal in the first wire. Additionally, the modulation electrode, the first signal pad, and the first termination resistor are arranged on the same substrate. This significantly shortens the distance of the conductive path between the modulation electrode and the first end of the first termination resistor. This reduces electrical reflection of the modulation signal at the first end of the first termination resistor. This reduces loss of the modulation signal due to reflection.

[0011] [2] The optical modulator integrated laser element of [1] above may include: a third signal pad provided on the substrate on the opposite side of the second signal pad across the first signal pad; a fourth signal pad provided on the substrate on the opposite side of the second signal pad across the second signal pad; a second termination resistor provided on the substrate and having a first end connected to the first signal pad and a second end connected to the third signal pad; and a third termination resistor provided on the substrate and having a first end connected to the second signal pad and a second end connected to the fourth signal pad.

[0012] [3] An optical modulator integrated laser element according to another embodiment of the present disclosure includes a substrate, a laser unit provided on the substrate and outputting laser light, an optical modulation unit provided on the substrate and having a modulation electrode and modulating the laser light, a first signal pad provided on the substrate and connected to the modulation electrode to receive a positive-phase signal of a differential signal, a second signal pad provided on the substrate alongside the first signal pad and to receive a negative-phase signal of the differential signal, and a first termination resistor provided on the substrate and having a first end connected to the modulation electrode and a second end connected to the second signal pad.

[0013] [4] An optical device according to one embodiment of the present disclosure includes an optical modulator-integrated laser element selected from the above [1] to [3], a carrier having a first transmission line and a second transmission line on its upper surface and carrying the optical modulator-integrated laser element, a first wire connecting the first signal pad and the first transmission line, and a second wire connecting the second signal pad and the second transmission line.

[0014] [5] An optical modulator according to one embodiment of the present disclosure includes a substrate; an optical modulation unit provided on the substrate, having a modulation electrode, and modulating laser light; a first signal pad provided on the substrate, to which a positive phase signal of a differential signal is input and connected to the modulation electrode; a second signal pad provided on the substrate alongside the first signal pad, to which a negative phase signal of the differential signal is input; and a first termination resistor provided on the substrate, having a first end connected to the first signal pad and a second end connected to the second signal pad.

[0015] [Details of the embodiments of the present disclosure] Specific examples of the optical modulator-integrated laser element, optical device, and optical modulator of the present disclosure will be described below with reference to the drawings. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. In the following description, the same elements in the drawings will be designated by the same reference numerals, and duplicated explanations will be omitted. In the following description, the reference potential may be referred to as the ground potential.

[0016] (First embodiment) Fig. 1 is a plan view showing a small-sized optical device for transmission 1, which is an optical apparatus according to a first embodiment of the present disclosure. Fig. 2 is a circuit diagram of the small-sized optical device for transmission 1. The configuration of the small-sized optical device for transmission 1 will be described with reference to Figs. 1 and 2.

[0017] 1, the small optical device for transmission 1 includes a package 20, a substrate 21 (chip-on-carrier), a substrate 22 (mount carrier), and a substrate 23. The package 20 accommodates the substrates 21, 22, and 23. The substrate 22 is arranged side by side with the substrate 23. The substrate 21 is arranged on the substrate 22. The material of the substrates 21 and 22 is an insulator such as ceramic.

[0018] The small-sized optical device for transmission 1 further includes wiring patterns P1, P2, P3, P4, and P5, ground potential lines P6 and P7, signal lines P8 and P9, and a differential driver IC 24 (differential drive circuit) provided on a substrate 23. The wiring patterns P1, P2, P3, P4, and P5, the ground potential lines P6 and P7, and the signal lines P8 and P9 extend from one side wall of the package 20 toward the substrate 22 and are connected to circuits external to the small-sized optical device for transmission 1 via terminals (not shown). The signal line P8 propagates a high-frequency modulated signal input from outside the small-sized optical device for transmission 1. The signal line P9 propagates a signal input from outside the small-sized optical device for transmission 1 that is opposite in phase to the modulated signal. In other words, the modulated signal propagating through the signal line P8 and the opposite-phase signal propagating through the signal line P9 constitute a differential signal. The ground potential lines P6 and P7 have a ground potential (reference potential) input from a circuit external to the small-sized optical device for transmission 1. The signal lines P8 and P9 and the ground potential lines P6 and P7 form a transmission line.

[0019] The four input terminals of the differential driver IC 24 are connected to the ground potential lines P6 and P7 and the signal lines P8 and P9, respectively. The differential driver IC 24 amplifies the differential signals propagating through the signal lines P8 and P9 and outputs the amplified differential signals (positive phase signal and negative phase signal).

[0020] The small-sized optical device for transmission 1 further includes wiring patterns P10, P11, P12, ground potential lines P13, P14, signal lines P15, P16, a thermistor 25, a monitor photodiode 26, and a lens 27, which are provided on the substrate 22.

[0021] The wiring pattern P10 is connected to the wiring pattern P3 by a wire W1. The wiring pattern P11 is connected to the wiring pattern P4 by a wire W2. The wiring pattern P12 is connected to the wiring pattern P5 by a wire W3. The ground potential line P13 is connected to one of the four output terminals of the differential driver IC24, which has a reference potential, by a wire W4. The ground potential line P14 is connected to the other of the four output terminals of the differential driver IC24, which has a reference potential, by a wire W5. The signal line P15 is connected to one of the four output terminals of the differential driver IC24, which outputs a positive-phase signal, by a wire W6. The signal line P16 is connected to one of the four output terminals of the differential driver IC24, which outputs a negative-phase signal, by a wire W7.

[0022] The thermistor 25 is provided on the wiring pattern P12. The thermistor 25 exhibits a resistance value that depends on temperature. This resistance value is detected by a circuit external to the small-sized optical device for transmission 1 via the wiring pattern P12, the wire W3, and the wiring pattern P5.

[0023] The monitor photodiode 26 is connected between the wiring pattern P10 and the ground potential line P13. In order to maintain a constant average intensity of the emitted light M, the monitor photodiode 26 detects backlight emitted from an optical modulator-integrated semiconductor laser 10 (described later). The monitor photodiode 26 outputs an electrical signal corresponding to the intensity of the backlight to a circuit external to the small-sized optical transmitting device 1 via the wiring pattern P10, wire W1, and wiring pattern P3. The lens 27 is optically coupled to the light-emitting end of the optical modulator-integrated semiconductor laser 10, and collimates the emitted light M emitted from the optical modulator-integrated semiconductor laser 10.

[0024] A thermoelectric cooler (TEC) 28 (shown only in FIG. 2) is provided on the back side of the substrate 22. One electrode of the TEC 28 is connected to the wiring pattern P1 by a wire W8. The other electrode of the TEC 28 is connected to the wiring pattern P2 by a wire W9. Power for driving the TEC 28 is input from a circuit external to the small-sized optical device 1 for transmitting 1 via the wiring patterns P1 and P2. The circuit external to the small-sized optical device 1 for transmitting 1 controls the magnitude of the power for driving the TEC 28 based on the ambient temperature of the optical modulator-integrated semiconductor laser 10 (i.e., the resistance value of the thermistor 25). This maintains the temperature of the optical modulator-integrated semiconductor laser 10 at a predetermined temperature, and the wavelength of the emitted light M at a predetermined wavelength.

[0025] A ground potential line P20, a wiring pattern P21, and a bypass capacitor 29 are provided on the substrate 21. The ground potential line P20 is connected to the ground terminal of the thermistor 25 by a wire W10. The ground potential line P20 is further connected to a ground pattern P19 (described later). The ground potential line P20 has a ground potential (reference potential).

[0026] The bypass capacitor 29 is provided on the ground potential line P20. The bottom electrode of the bypass capacitor 29 is connected to the ground potential line P20. The top electrode of the bypass capacitor 29 is connected to a wiring pattern P21 by a wire W11. The wiring pattern P21 is connected to another wiring pattern P21 by a wire W12.

[0027] Fig. 3 is an enlarged perspective view of a portion of the small-sized optical device for transmission 1. Fig. 4 is an enlarged plan view of a portion of the small-sized optical device for transmission 1. As shown in Figs. 3 and 4, the small-sized optical device for transmission 1 has an optical modulator-integrated semiconductor laser 10, a ground pattern P19, and a transmission line 30. The ground pattern P19 is a metal film provided on a substrate 21. The ground pattern P19 has a ground potential (reference potential).

[0028] The transmission line 30 includes a ground potential line P22, a ground potential line P23, a signal line P24 (first transmission line), and a signal line P25 (second transmission line). The signal line P24 and the signal line P25 are metal films provided side by side in a direction intersecting the direction in which they extend. The ground potential line P22 and the ground potential line P23 are metal films provided at positions sandwiching the signal line P24 and the signal line P25. The ground potential line P22 extends along the signal line P24, and the ground potential line P23 extends along the signal line P25. As shown in FIG. 1, a first end of the ground potential line P22 is connected to the ground potential line P13 by a wire W13. A first end of the ground potential line P23 is connected to the ground potential line P14 by a wire W14. Second ends of the ground potential line P22 and the ground potential line P23 are connected to the ground pattern P19. A first end of signal line P24 is connected to signal line P15 by wire W21. A first end of signal line P25 is connected to signal line P16 by wire W22. A positive-phase signal from differential driver IC24 is transmitted from signal line P24 to signal pad 15 via wire W21. A negative-phase signal from differential driver IC24 is transmitted to signal pad 16 via wire W22.

[0029] The optical modulator-integrated semiconductor laser 10 of this embodiment is an example of an optical modulator-integrated laser element according to the present disclosure. The optical modulator-integrated semiconductor laser 10 is provided on a ground pattern P19. The optical modulator-integrated semiconductor laser 10 includes a substrate 101, a laser section 11, an optical modulation section 12, a terminating resistive film 17 (first terminating resistor), a wire W21 (first wire), and a wire W22 (second wire). The substrate 101 has a rectangular parallelepiped shape. The laser section 11 is disposed in a region on the substrate 101 closer to the substrate 23 than the optical modulation section 12. As shown in FIG. 1 , the laser section 11 is sandwiched between a transmission line 30 and a ground potential line P20. The laser section 11 has an active region, and generates laser light having a constant optical intensity over time when a current is supplied to the active region. The laser section 11 has a drive electrode 14 and a pad 18 on its surface. The drive electrode 14 extends along the laser resonance direction (the direction in which the laser section 11 and the optical modulation section 12 are aligned) and supplies current to the active region. The pad 18 is arranged alongside the drive electrode 14 in a direction intersecting the extension direction of the drive electrode 14 and is connected to the drive electrode 14. The pad 18 is connected to the top electrode of the bypass capacitor 29 by a wire W17. This allows a drive current to be supplied to the drive electrode 14 from outside the small-sized optical device for transmission 1 via the wiring patterns P4, P11, P21, the top electrode of the bypass capacitor 29, and the pad 18.

[0030] The optical modulation unit 12 is located closer to the lens 27 than the laser unit 11. The optical modulation unit 12 has a light absorption layer, modulates the laser light output from the laser unit 11 in the light absorption layer, and outputs modulated emitted light M. The backlight described above is the laser light output from the laser unit 11 without passing through the optical modulation unit 12. The laser unit 11 and the optical modulation unit 12 are monolithically formed on the substrate 101. The optical modulation unit 12 includes a modulation electrode 13, a signal pad 15 (first signal pad), and a signal pad 16 (second signal pad). The optical modulation unit 12 modulates the laser light by transmitting or blocking the laser light in response to the supply of current to the optical absorption layer. The modulation electrode 13 supplies a modulation current (modulation signal) to the optical absorption layer. As a result, the laser light is passed or blocked in the optical absorption layer based on the input modulation signal. The modulation electrode 13 extends in the same direction as the propagation direction of the laser light in a planar view. On the upper surface of the optical modulator integrated semiconductor laser 10, the modulation electrode 13 is provided at approximately the center in the direction perpendicular to the traveling direction of the laser light.

[0031] The signal pad 15 and the signal pad 16 are provided closer to the transmission line 30 than the modulation electrode 13. The signal pad 15 is connected to the modulation electrode 13 and to a first end of a wire W21 for inputting a modulated signal to the optical modulation unit 12. The signal pad 16 is provided alongside the signal pad 16 along the longitudinal direction of the modulation electrode 13. The signal pad 16 is connected to a first end of a wire W22 for inputting an inverted phase signal to the optical modulation unit 12. The signal pad 15 is provided closer to the laser unit 11 than the signal pad 16. The signal pads 15 and 16 are film-like and have a substantially rectangular shape in a planar view. The signal pads 15 and 16 are made of a metal material, such as gold (Au). The film thickness of the signal pads 15 and 16 is, for example, 3 μm to 10 μm.

[0032] A second end of the wire W21 is connected to a second end of the signal line P24 of the transmission line 30. A second end of the wire W22 is connected to a second end of the signal line P25 of the transmission line 30. When viewed from the thickness direction of the substrate 101, the extension direction of the wires W21 and W22 intersects with the extension direction of the modulation electrode 13. The wires W21 and W22 are arranged side by side in the extension direction of the modulation electrode 13. In one example, when viewed from the thickness direction of the substrate 101, the wires W21 and W22 are parallel to each other. The wires W21 and W22 are bonding wires made of, for example, Au. The cross-sectional diameter of the wires W21 and W22 is, for example, 25 μm. The distance between the wires W21 and W22 is, for example, several tens of μm. The difference between the length of wire W21 and the length of wire W22 is less than 1 / 4, less than 1 / 8, less than 1 / 10, or less than 1 / 12 of the wavelength of the modulating signal.

[0033] The termination resistive film 17 is provided between the signal pad 15 and the signal pad 16. The termination resistive film 17 reduces reflection of the modulation signal. A first end 17a (see FIG. 4) of the termination resistive film 17 is connected to the signal pad 15. A second end 17b (see FIG. 4) of the termination resistive film 17 is connected to the signal pad 16. The distance (electrical length) L1 of the conductive path between the connection point of the wire W21 and the signal pad 15 and the first end 17a of the termination resistive film 17 is, for example, less than ¼, less than ⅛, less than ⅙-tenth, or less than ⅛-twelfth of the wavelength of the modulation signal. The distance L1 is, for example, 1 / 1000 or more of the wavelength of the modulation signal. Similarly, the distance (electrical length) L2 of the conductive path between the connection point of the wire W21 and the signal pad 15 and the modulation electrode 13 is, for example, less than ¼, less than ⅛, less than ⅙-tenth, or less than ⅛-twelfth of the wavelength of the modulation signal. Distance L2 is, for example, 1 / 1000 or more of the wavelength of the modulated signal. As a specific example, when the wavelength of the modulated signal is, for example, 1200 μm, distance L1 and distance L2 are less than 300 μm, less than 150 μm, less than 120 μm, or less than 100 μm, and are 1 μm or more.

[0034] The termination resistive film 17 has a rectangular shape. The termination resistive film 17 is made of a metal such as nickel chromium (NiCr), titanium tungsten (TiW), tantalum nitride (TaN), or platinum (Pt). The film thickness of the termination resistive film 17 is, for example, 100 nm to 300 nm. The termination resistive film 17 is made of a thin-film resistive pattern formed by vapor deposition and subsequent lift-off or sputtering. If the resistance value of the termination resistive film 17 is set to, for example, 100 Ω, the termination impedance value becomes 50 Ω. Note that the termination impedance value is generally 50 Ω in many cases, but may differ from 50 Ω by adding a capacitor or inductor, or by adjusting the resistance value.

[0035] FIG. 5 is a cross-sectional view taken along line VV in FIG. 4. The optical modulation unit 12 includes a substrate 101, a passivation film 102, and a seed layer 103. The substrate 101 is in contact with and disposed on the ground pattern P19. The substrate 101 is made of, for example, semi-insulating InP, n-type InP, or a dielectric. The passivation film 102 is disposed on the substrate 101. The passivation film 102 is made of an insulator such as SiO2 or SiN. The thickness of the passivation film 102 is, for example, 300 nm or more and 500 nm or less. The termination resistive film 17 is disposed on the passivation film 102. The signal pads 15 and 16 are disposed on the passivation film 102, and each has a portion that is disposed on the termination resistive film 17 and a portion that is disposed in an area where the termination resistive film 17 is not present. A seed layer 103 is provided between the signal pads 15 and 16 and the passivation film 102, and between the signal pads 15 and 16 and the termination resistive film 17. The seed layer 103 is made of, for example, gold (Au). The seed layer 103 has a thickness of, for example, 100 nm or more and 200 nm or less. The signal pads 15 and 16 are not in contact with each other, and the termination resistive film 17 has a portion exposed from the signal pads 15 and 16.

[0036] 6 and 7 are cross-sectional views showing a part of the manufacturing process of the optical modulator-integrated semiconductor laser 10. A part of the manufacturing process of the optical modulator-integrated semiconductor laser 10 will be described. In the optical modulation section 12, first, a substrate 101 is prepared. Next, a passivation film 102 is formed on the substrate 101. After that, a resist mask (not shown) is formed on the surface of the passivation film 102 by photolithography, and a termination resistive film 17 is formed on the passivation film 102. Next, a seed layer 103 is formed on the surfaces of the termination resistive film 17 and the passivation film 102 by photolithography. After that, a resist mask 104 having openings 104a and 104b is formed on the surface of the seed layer 103 by photolithography. Next, the openings 104a and 104b are gold-plated to form a signal pad 15 in the opening 104a and a signal pad 16 in the opening 104b, as shown in FIG. 7. Finally, the resist mask 104 is removed from the optical modulation unit 12, and the seed layer 103 is removed using the signal pads 15 and 16 as a mask, thereby forming the signal pads 15, the termination resistive film 17, and the signal pads 16 shown in FIG.

[0037] The effects obtained by the small-sized optical device for transmitter 1 and the optical modulator-integrated semiconductor laser 10 having the above configuration will be described in comparison with a comparative example. FIG. 14 is a plan view showing the small-sized optical device for transmitter 2, which is a comparative example. FIG. 15 is a circuit diagram of the small-sized optical device for transmitter 2. FIG. 16 is an enlarged plan view showing a portion of the small-sized optical device for transmitter 2. This small-sized optical device for transmitter 2 differs from the small-sized optical device for transmitter 1 mainly in the following points. The small-sized optical device for transmitter 2 includes an optical modulator-integrated semiconductor laser 10C and a transmission line 30C instead of the optical modulator-integrated semiconductor laser 10 and the transmission line 30. In addition, the small-sized optical device for transmitter 2 includes a termination section 80.

[0038] The optical modulator-integrated semiconductor laser 10C has an optical modulator 12C instead of the optical modulator 12. The optical modulator 12C differs from the optical modulator 12 in that it does not have a signal pad 16 or a wire W22 and that a first end of a wire W41 is connected to the signal pad 15. The terminating resistive film 17 is also not provided on the substrate. The transmission line 30C differs from the transmission line 30 in that it does not have a ground potential line P23 or a signal line P25. The terminating portion 80 is provided on the substrate 21 on the opposite side of the transmission line 30C from the optical modulator-integrated semiconductor laser 10C. The terminating portion 80 has a protruding portion from the ground pattern P19, a pad 81, and a terminating resistive film 82. The pad 81 is connected to a second end of the wire W41. The terminating resistive film 82 has a first end connected to the protruding portion from the ground pattern P19 and a second end connected to the pad 81.

[0039] In the small-sized optical transmitter device 2, the terminating resistive film 82 is provided outside the optical modulator-integrated semiconductor laser 10C, so the transmission path from the second end of the terminating resistive film 82 to the connection point between the wire W21 and the signal pad 15 is long. This increases impedance mismatch, which tends to increase the reflection of the modulated signal at the terminating resistive film 82 as the bandwidth of the optical modulator-integrated semiconductor laser 10C increases. In contrast, in the small-sized optical transmitter device 1 of this embodiment, the modulating electrode 13, the signal pad 15, and the terminating resistive film 17 are provided on the same substrate 101. This significantly shortens the distance of the conductive path between the modulating electrode 13 and the first end 17a of the terminating resistive film 17. This reduces electrical reflection of the modulated signal at the first end 17a of the terminating resistive film 17. This reduces the loss of the modulated signal due to reflection.

[0040] Additionally, in the small optical device for transmission 1 of this embodiment, the wires W21 and W22 are arranged side by side. The wire W21 inputs the modulation signal, and the wire W22 inputs a signal with a phase opposite to that of the modulation signal. This creates a virtual reference potential line between the wires W21 and W22. This reduces the mismatch in the input impedance of the modulation signal at the wire W21, further reducing the loss of the modulation signal due to reflection. Furthermore, this configuration allows the wire spacing to be approximately twice as large as a single-phase drive configuration (a configuration in which a ground potential wire is placed on one or both sides of a single wire transmitting the modulation signal). This allows for a larger wire spacing margin, reducing manufacturing difficulties. Furthermore, in a single-phase drive configuration, the amount of heat generated varies depending on the applied voltage. This change in the amount of heat generated can cause fluctuations in the extinction characteristics, especially when the bit spacing in the modulation signal is close to the thermal response time constant. In contrast, a differential drive configuration like the present embodiment maintains a nearly constant amount of heat generated, thereby suppressing fluctuations in the extinction characteristics.

[0041] As in this embodiment, the distance L1 of the conductive path between the connection point between the wire W21 and the signal pad 15 and the first end 17a of the termination resistive film 17 may be less than ¼ of the wavelength of the modulated signal. Furthermore, the distance L2 of the conductive path between the connection point between the wire W21 and the signal pad 15 and the modulating electrode 13 may be less than ¼ of the wavelength of the modulated signal. According to the inventor's findings, even if the input modulated signal has a high frequency, e.g., 100 GHz or higher, electrical reflection of the modulated signal at the first end 17a of the termination resistive film 17 is unlikely to be significant as long as the distances L1 and L2 are less than ¼ of the wavelength of the modulated signal. Therefore, loss of the modulated signal due to reflection can be effectively reduced. In 100 Gbps communication, the value of ¼ of the wavelength of the modulated signal is, for example, 300 μm, and the distances L1 and L2 are preferably, for example, 100 μm or less.

[0042] As in this embodiment, the wire W21 may be arranged parallel to the wire W22 when viewed in the thickness direction of the substrate 101. In this case, the impedance mismatch of the modulated signal in the wire W21 is more effectively reduced. Therefore, the loss of the modulated signal due to the impedance mismatch is further reduced.

[0043] As in this embodiment, the difference between the length of the wire W21 and the length of the wire W22 may be less than ¼ of the wavelength of the modulated signal, which reduces the skew between the modulated signal and the opposite-phase signal.

[0044] As described above, the termination resistive film 17 may contain at least one material selected from the group consisting of nickel chromium, titanium tungsten, tantalum nitride, and platinum. This improves adhesion between the termination resistive film 17 and the passivation film 102. It also makes it possible to achieve a desired resistance value.

[0045] As in this embodiment, the laser section 11 that outputs laser light may be provided on the substrate 101. This allows the laser section 11 and the optical modulation section 12 to be monolithically configured on the same substrate 101, thereby making it possible to miniaturize the small-sized optical device for transmission 1.

[0046] (First Modification) FIG. 8 is an enlarged perspective view of a portion of the small-sized optical device for transmitting according to the first modified example. FIG. 9 is an enlarged plan view of a portion of the small-sized optical device for transmitting according to the first modified example. The small-sized optical device for transmitting according to this modified example differs from the small-sized optical device for transmitting 1 of the above embodiment in the following points, but is otherwise the same. The small-sized optical device for transmitting according to this modified example includes an optical modulator-integrated semiconductor laser 10A instead of the optical modulator-integrated semiconductor laser 10 of the first embodiment. The optical modulator-integrated semiconductor laser 10A has an optical modulation section 12A instead of the optical modulation section 12 of the first embodiment. The other configurations of the optical modulator-integrated semiconductor laser 10A are the same as those of the optical modulator-integrated semiconductor laser 10.

[0047] The optical modulator integrated semiconductor laser 10A further includes a termination resistive film 43 (second termination resistor) and a termination resistive film 44 (third termination resistor) in addition to the termination resistive film 17. The optical modulation section 12A further includes a reference potential pad 41 (third signal pad) and a reference potential pad 42 (fourth signal pad) in addition to the signal pads 15 and 16. The optical modulation section 12A further includes a wire W23 (third wire) and a wire W24 (fourth wire) in addition to the wires W21 and W22.

[0048] The reference potential pad 41 is provided in an area on the substrate 101 opposite the signal pad 16 with respect to the signal pad 15. The reference potential pad 42 is provided in an area on the substrate 101 opposite the signal pad 16 with respect to the signal pad 15. That is, the reference potential pad 41, the signal pad 15, the signal pad 16, and the reference potential pad 42 are lined up in this order along the extension direction of the modulation electrode 13. The reference potential pad 41 and the reference potential pad 42 are in the form of a film and have a substantially rectangular shape in a plan view. The reference potential pad 41 and the reference potential pad 42 are made of a metal, such as gold (Au). The film thickness of the reference potential pad 41 and the reference potential pad 42 is, for example, 3 μm or more and 10 μm or less.

[0049] A first end of the wire W23 is connected to the reference potential pad 41, and a second end of the wire W23 is connected to the ground potential line P22. A first end of the wire W24 is connected to the reference potential pad 42, and a second end of the wire W24 is connected to the ground potential line P23. This sets the wires W23 and W24 to the reference potential. The wires W23 and W24 are arranged side by side with the wires W21 and W22, sandwiching the wires W21 and W22. That is, the wires W23, W21, W22, and W24 are arranged in this order along the extension direction of the modulation electrode 13. When viewed from the thickness direction of the substrate 101, the wires W23 and W24 may be parallel to the wires W21 and W22. The wires W23 and W24 are bonding wires made of, for example, Au. The cross-sectional diameter of the wires W23 and W24 is, for example, 25 μm. The distance between the wires W21 and W23 and the distance between the wires W22 and W24 are, for example, several tens of μm.

[0050] The termination resistive film 43 is provided between the signal pad 15 and the reference potential pad 41. A first end of the termination resistive film 43 is connected to the signal pad 15. A second end of the termination resistive film 43 is connected to the reference potential pad 41. The termination resistive film 44 is provided between the signal pad 16 and the reference potential pad 42. A first end of the termination resistive film 44 is connected to the signal pad 16. A second end of the termination resistive film 44 is connected to the reference potential pad 42. The termination resistive films 43 and 44 reduce reflection of the modulated signal. The termination resistive films 43 and 44 are rectangular in shape. The termination resistive films 43 and 44 are made of a metal such as nickel chromium, titanium tungsten, tantalum nitride, or platinum. The thickness range and formation method of the termination resistive films 43 and 44 are the same as those of the termination resistive film 17 described above.

[0051] Here, distance L3 is the distance (electrical length) of the conductive path between the connection point of wire W21 and signal pad 15 and the first end of termination resistive film 43. Distance L4 is the distance (electrical length) of the conductive path between the connection point of wire W22 and signal pad 16 and the first end of termination resistive film 44. Distance L5 is the distance (electrical length) of the conductive path between the connection point of wire W23 and reference potential pad 41 and the second end of termination resistive film 43. Distance L6 is the distance (electrical length) of the conductive path between the connection point of wire W24 and reference potential pad 42 and the second end of termination resistive film 44. These distances L3, L4, L5, and L6 are, for example, less than 1 / 4, less than 1 / 8, less than 1 / 10, or less than 1 / 12 of the wavelength of the modulation signal. These distances L3, L4, L5, and L6 are, for example, 1 / 1000 or more of the wavelength of the modulation signal.

[0052] For example, if the differential impedance is 100Ω, the termination resistive film 17 should be 200Ω, and the termination resistive films 43 and 44 should each be 100Ω. The spacing between the wires W23, W21, W22, and W24 should also be adjusted so that the differential impedance approaches 100Ω.

[0053] In the optical modulator-integrated semiconductor laser 10A of this modification, the wires W23 and W24 are set to the reference potential. Therefore, the modulated signal and the reversed-phase signal passing through the wires W21 and W22, respectively, located between the wires W23 and W24, are sandwiched between the ground potential. This further reduces the mismatch in input impedance, thereby further reducing the loss of the modulated signal.

[0054] In addition, the reference potential pad 41, the reference potential pad 42, the termination resistive film 43, and the termination resistive film 44 are provided on the same substrate 101 as the signal pad 15 and the signal pad 16. Therefore, the distance of the conductive path between the signal pad 15 and the first end of the termination resistive film 43, the distance of the conductive path between the reference potential pad 41 and the second end of the termination resistive film 43, the distance of the conductive path between the signal pad 16 and the first end of the termination resistive film 44, and the distance between the conductive path between the reference potential pad 42 and the second end of the termination resistive film 44 can be extremely short. This reduces the reflection of the modulated signal at the termination resistive film 43 and the termination resistive film 44. This further reduces the loss of the modulated signal due to reflection.

[0055] As in this modification, the distances L3, L4, L5, and L6 may be less than ¼ of the wavelength of the modulated signal, thereby reducing the reflection of the modulated signal at the terminating resistive film 43 and the terminating resistive film 44. This further reduces the loss of the modulated signal due to reflection.

[0056] (Second Modification) FIG. 10 is an enlarged perspective view of a portion of a small-sized optical device for transmitting according to the second modified example. FIG. 11 is an enlarged plan view of a portion of a small-sized optical device for transmitting according to the second modified example. The small-sized optical device for transmitting according to this modified example differs from the small-sized optical device for transmitting 1 of the above embodiment in the following points, but is otherwise the same. The small-sized optical device for transmitting according to this modified example includes an optical modulator-integrated semiconductor laser 10B instead of the optical modulator-integrated semiconductor laser 10 of the first embodiment. The optical modulator-integrated semiconductor laser 10B has an optical modulation section 12B instead of the optical modulation section 12 of the first embodiment. The other configurations of the optical modulator-integrated semiconductor laser 10B are the same as those of the optical modulator-integrated semiconductor laser 10.

[0057] The optical modulation section 12B has a termination resistive film 45 (first termination resistor) provided on the substrate 101, instead of the termination resistive film 17 of the first embodiment. The optical modulation section 12B further has a wiring 46 provided on the substrate 101. The wiring 46 is arranged on the opposite side of the signal pad 16 from the signal pad 15. The wiring 46 includes a portion extending along the modulation electrode 13. In one example, that portion of the wiring 46 is parallel to the modulation electrode 13. A first end of the termination resistive film 45 is connected to the modulation electrode 13. A second end of the termination resistive film 45 is connected to the signal pad 16 via the wiring 46. In other words, the wiring 46 connects the signal pad 16 to the termination resistive film 45. The material, thickness, and formation method of the termination resistive film 45 are the same as those of the termination resistive film 17 of the first embodiment.

[0058] The signal pads 15 and 16 of this modification are arranged in a region of the optical modulation section 12B closer to the laser section 11. In contrast, the terminating resistive film 45 is arranged in a region of the optical modulation section 12B closer to the light emitting end. A first end of the terminating resistive film 45 is connected to a portion of the modulating electrode 13 closer to the light emitting end of the optical modulation section 12B.

[0059] In this modification, similar to the first embodiment, the wires W21 and W22 are arranged side by side. The wire W21 receives a modulation signal, and the wire W22 receives a signal of opposite phase to the modulation signal, resulting in a virtual reference potential line between the wires W21 and W22. This reduces the mismatch in input impedance of the modulation signal at the wire W21. Additionally, the modulation electrode 13, the signal pad 16, and the termination resistive film 45 are arranged on the same substrate 101. This significantly shortens the distance of the conductive path between the modulation electrode 13 and the first end of the termination resistive film 45. This reduces electrical reflection of the modulation signal at the first end of the termination resistive film 45. This reduces loss of the modulation signal due to reflection.

[0060] The wire W21 may be arranged parallel to the wire W22 when viewed in the thickness direction of the substrate 101. In this case, the impedance mismatch of the modulated signal in the wire W21 is more effectively reduced.

[0061] As in this modification, the optical modulator integrated semiconductor laser 10B may include a wiring 46 provided on the substrate 101 and connecting the signal pad 16 to the terminating resistive film 45. The wiring 46 may include a portion extending along the modulation electrode 13. In this manner, the portion of the wiring 46 that propagates the opposite-phase signal extends along the modulation electrode 13, thereby reducing the reflection of the opposite-phase signal at the terminating resistive film 45. Therefore, the loss of the modulated signal due to reflection can be further reduced. Note that, as shown in FIG. 12, the wiring 46 may be omitted and the terminating resistive film 45 may be disposed between the signal pad 16 and the modulation electrode 13.

[0062] While a first end of the termination resistive film 17 in the first embodiment is connected to the signal pad 15, in this modification, a first end of the termination resistive film 45 is connected to the modulation electrode 13. FIG. 13(a) is a simplified circuit diagram of the circuit in the first embodiment. FIG. 13(b) is a simplified circuit diagram of the circuit in this modification. Comparing these circuit diagrams, in FIG. 13(a), the modulation electrode 13 is located at a position branching off from the wires W21 and W22 (including the termination resistive film 45), which are signal lines, and forms a stub. This stub appears as a capacitance or inductance depending on the frequency. On the other hand, in FIG. 13(b), the modulation electrode 13 is located between the wires W21 and W22 (including the termination resistive film 45), which are signal lines. This is expected to have the effect of reducing the effect of appearing as a capacitance or inductance depending on the frequency, compared to FIG. 13(a).

[0063] The optical modulator-integrated laser element, optical device, and optical modulator according to the present disclosure are not limited to the above-described embodiments and modifications, and various other modifications are possible. For example, in the above-described embodiments, the wires W21 and W22 are parallel to each other, but the wires W21 and W22 may be inclined relative to each other. Even in this case, the above-described effects can be achieved by arranging the wires W21 and W22 side by side.

[0064] In addition, in the above embodiment, the ground potential lines P22, P23 of the transmission line 30 are provided on the substrate 21 alongside the signal lines P24, P25, but the form of the transmission line is not limited to this. For example, even if the transmission line is configured as a so-called microstrip line in which the ground potential line is provided on the back surface of the substrate 21, the above-mentioned effects can be achieved.

[0065] Furthermore, in the above description, resistive films are used as examples of the first, second and third terminating resistors, but these terminating resistors are not limited to resistive films and may be other resistive elements. [Explanation of symbols]

[0066] 1,2...Small optical devices for transmission 10, 10A, 10B, 10C...Optical modulator integrated semiconductor laser 11...Laser section 12, 12A, 12B, 12C... Optical modulation section 13...Modulation electrode 14...Drive electrode 15...Signal pad (first signal pad) 16...Signal pad (second signal pad) 17…Terminal resistor film (first terminal resistor) 17a...first end 17b…Second end 18...Pad 20…Package 21, 22, 23... Circuit board 24...Differential driver IC (differential drive circuit) 25...Thermistor 26...Monitor photodiode 27...Lens 28...Temperature control element 29...Bypass capacitor 30,30C...Transmission line 41...Reference potential pad (third signal pad) 42...Reference potential pad (fourth signal pad) 43…Terminal resistor film (second terminator) 44…Terminal resistor film (third terminal resistor) 45…Terminal resistor film (first terminal resistor) 46...Wiring 80...Terminal 81...Pad 82...Terminating resistive film 101... Circuit board 102...passivation film 103...Seed layer 104...Resist mask 104a, 104b…Aperture L1, L2, L3, L4, L5, L6...Distance (electrical length) M…Outgoing light P1, P2, P3, P4, P5, P10, P11, P12, P21...wiring pattern P6, P7, P13, P14, P20, P22, P23...Ground potential lines P8,P9,P15,P16,P24,P25...Signal line P19...Ground pattern W1, W2, W3, W4, W5, W6, W7, W8, W9, W10, W11, W12, W13, W14, W17, W41...Wire W21...Wire (first wire) W22...Wire (second wire) W23...Wire (third wire) W24...Wire (4th wire)

Claims

1. A substrate; a laser unit provided on the substrate and configured to output laser light; an optical modulation section provided on the substrate, having a modulation electrode, and modulating the laser light; a first signal pad provided on the substrate, to which a positive phase signal of a differential signal is input and which is connected to the modulation electrode; a second signal pad provided on the substrate alongside the first signal pad, to which an opposite-phase signal of the differential signal is input; a first termination resistor provided on the substrate, the first termination resistor having a first end connected to the first signal pad and a second end connected to the second signal pad; An optical modulator integrated laser device comprising:

2. a third signal pad provided on the substrate on the opposite side of the second signal pad with the first signal pad interposed therebetween; a fourth signal pad provided on the substrate on the opposite side of the first signal pad with the second signal pad interposed therebetween; a second termination resistor provided on the substrate, the second termination resistor having a first end connected to the first signal pad and a second end connected to the third signal pad; a third termination resistor provided on the substrate, the third termination resistor having a first end connected to the second signal pad and a second end connected to the fourth signal pad; The optical modulator integrated laser device according to claim 1 , comprising:

3. A substrate; a laser unit provided on the substrate and configured to output laser light; an optical modulation section provided on the substrate, having a modulation electrode, and modulating the laser light; a first signal pad provided on the substrate, to which a positive phase signal of a differential signal is input and which is connected to the modulation electrode; a second signal pad provided on the substrate alongside the first signal pad, to which an opposite-phase signal of the differential signal is input; a first termination resistor provided on the substrate, the first termination resistor having a first end connected to the modulation electrode and a second end connected to the second signal pad; An optical modulator integrated laser device comprising:

4. The optical modulator integrated laser device according to claim 1 ; a carrier having a first transmission line and a second transmission line provided on an upper surface thereof and on which the optical modulator-integrated laser device is mounted; a first wire connecting the first signal pad and a first transmission line; a second wire connecting the second signal pad and a second transmission line; An optical device comprising:

5. A substrate; an optical modulation section provided on the substrate, having a modulation electrode and modulating laser light; a first signal pad provided on the substrate, to which a positive phase signal of a differential signal is input and which is connected to the modulation electrode; a second signal pad provided on the substrate alongside the first signal pad, to which an opposite-phase signal of the differential signal is input; a first termination resistor provided on the substrate, the first termination resistor having a first end connected to the first signal pad and a second end connected to the second signal pad; An optical modulator comprising:

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