JP6228560B2 - High frequency transmission line and optical circuit - Google Patents

Description

  The present invention relates to a termination technique for an optical device operating at a high frequency, such as an optical transmitter for optical communication, and in particular, a 50 ohm termination of a direct modulation DFB (Distributed Feedback) laser (DML: Direct Modulated DFB Laser). Regarding technology.

  In recent years, the required communication capacity has rapidly increased due to the expansion of use of the Internet, IP telephones, video downloads, etc., and the demand for optical transmitters installed in optical fiber and optical communication equipment is expanding. . The optical transmitter or the components that make it up is called pluggable, and modularization by specifications is rapidly progressing so that it can be easily mounted and replaced.

  XFP (10 Gigabit Small Form Factor Pluggable) is one of the industry standards for 10 Gigabit Ethernet (10 GbE) detachable modules. With this standard, the light source mounted on the optical transmitter module is also modularized. It is out. This is called TOSA (Transmitter Optical Sub-Assembly), and there is a box-shaped TOSA module as a typical module form (Non-patent Document 1).

  In recent years, demand for optical transmitters has increased, but on the other hand, there is an increasing demand for cost reduction while maintaining the performance of optical transmitters. The development of a TOSA module for 100 gigabit per second transmission and standardization activities for ultra-high speed of 400 gigabit per second are also active, and the demand for high performance for TOSA is increasing.

  A configuration of a typical box-type TOSA module will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing an appearance of a typical box-type TOSA module 100. FIG. 2 is a diagram showing a mounting configuration inside the module of the housing shown in FIG.

  As shown in FIG. 1, the housing of the module 100 is made of sintered ceramic or metal according to XFP.

  In the module 100, at least one modulated electric signal power supply wiring terminal 102 penetrating from the terrace portion 101 of the casing toward the inside of the casing is provided. The terrace portion 101 is further provided with a DC power supply wiring terminal.

  In FIG. 1, a ceramic part 103 and a metal part 104 are formed in the module 100.

  A thin plate 201 called a subcarrier is installed apart from the housing. A wiring pattern is formed on the subcarrier 201 by metal plating or vapor deposition on a dielectric material. Furthermore, elements necessary for the optical semiconductor device, such as a laser diode 202, an optical modulator 203, a resistor 204, and a capacitor 205, are mounted on the subcarrier 201.

  The housing is mounted on a metallic small plate called a carrier 206, and a thermoelectric cooling element (TEC) 207 in contact with the lower portion of the housing is mounted under the carrier 206. The TEC 207 absorbs heat generated in the element on the subcarrier 201 and exhausts it from the lower part of the housing. From the viewpoint of power saving and reduction in the number of parts, TOSA has been developed that does not use TEC207.

  A lens 218 (the lens 218 is placed on the carrier 206) or a light extraction window is provided on the side surface of the housing, and the optical semiconductor device is sealed in the package together with the top plate by resistance welding or the like.

  Conventionally, the modulated electric signal power supply wiring 208 and the subcarrier 201 penetrating from the outside to the inside of the housing are electrically connected by the wire-like gold wire 209 and the ribbon-like gold wire 210.

  FIG. 3 shows a connection example between the TOSA module 100 and the driver IC 301 for driving.

  Power supply (not shown) from the driver driver IC 301 or a DC power source is generally performed using the flexible printed circuit board 302.

  The flexible printed circuit board 302 is a printed circuit board that is flexible and can be greatly deformed, and is also referred to as flexible or FPC (Flexible Printed Circuits). Transmission of modulation electrical signals or DC power feeding is performed to the TOSA module 100 via the flexible substrate 302.

  The modulation electrical signal is transmitted from the driver IC 301 for driving to the TOSA module 100 via the flexible substrate 302. In the TOSA module 100, the modulation electrical signal is transmitted to the optical semiconductor element 203 via the modulation electrical signal power supply wiring terminal 102, the transmission line 208, the wires 209 and 210, and the transmission line 211 on the subcarrier. Further, it is transmitted to the terminating resistor 204.

  The driver IC 301 for driving is designed to output a driving waveform with an output impedance of 50 ohms. For this reason, the transmission line 211 and the termination resistor 204 are also normally set to 50 ohms. In this way, it has been the prior art to achieve impedance matching.

  The operating frequency of the XFP-compliant TOSA optical module extends to 10 GHz, and the electric signal behaves as a wave (microwave). That is, at a discontinuous point (reflection point) where impedance matching is not performed, a reflected wave is generated starting from the discontinuous point, and the reflected wave travels toward the drive driver IC 301. Under such circumstances, conventionally, it has been important to eliminate discontinuities (reflection points) between the transmission line 211 and the termination resistor 204.

  4A and 4B are diagrams showing the configuration of a direct modulation DFB laser, where FIG. 4A is a mounting diagram of the direct modulation DFB laser, FIG. 4B is a perspective view of the direct modulation DFB laser, and FIG. FIG. 4A shows the configuration disclosed in Non-Patent Document 2. FIG.

  In the direct modulation DFB laser shown in FIG. 4, a high-frequency wiring (GSG) 401 designed at 50 ohms is connected to a DML electrode 422 by a wire 403, and further connected from the 422 to a termination circuit 404. For example, if the resistance of the DML is 4 ohms, the total resistance is 50 ohms by connecting a 46 ohm termination resistor.

  As can be seen from FIG. 4B, the directly modulated DFB laser 400A is integrated on the p-InP substrate 420.

  The active layer 416 of the DFB laser 400A has an InGaAsP / InGaAsP multi-quantum well (MQW) structure.

  On the active layer 416, there are a diffraction grating for forming a DFB and an n-InP layer 419, which are formed in a mesa shape and then buried with a high-resistance buried layer 421.

  The electrode 423 is provided with a pad electrode 422 for forming a bonding wire or for flip chip bonding. The length of the direct modulation DFB laser 400A is 300 μm.

  In the example shown in FIG. 4, the p-electrode (below the p-InP substrate 420) connected to the ground G of the high-frequency wiring 401 and the electrode 422 connected to the signal S are on different planes of the DML. Shows the case.

  On the other hand, as shown in FIG. 5, DML is also known in which each electrode connected to the ground G and the signal S is provided on the same surface.

FIGS. 5A and 5B are connection modes of high-frequency wiring and DML by flip-chip bonding, in which the electrodes 231 and 240 connected to the ground G and the signal S are provided on the same surface. Show. In FIG. 5A, a p-contact layer 238, a p-InP 237, an active layer 235, an n-InP 234, and an n contact layer 233 are provided on a p-InP substrate 213. Mesa is embedded. The n-electrode 231 connected to the signal S and the p-electrode 240 connected to the ground G are formed on the insulating film (for example, SiO ₂ ) 232. That is, both the p electrode 240 and the n electrode 231 are provided on the same surface.

  An Au bump 215 is formed on each electrode 231, 240, and the DML is connected to the high-frequency wiring board 201 via the Au bump 215, gold-tin solder (bump) 218, and electrode pad 217.

  Recently, there is an increasing demand for ultra-high speed transmitters such as 100 gigabits per second and 400 gigabits per second.

  FIG. 6 shows the configuration of a conventional multi-channel optical transmitter 500, where (a) shows the overall configuration of the multi-channel optical transmitter 500, (b) shows the configuration of one channel, and (c) shows the output of four channels. An overview is shown. The multi-channel optical transmitter 500 is disclosed in Non-Patent Document 3.

  The multi-channel optical transmitter 500 is provided with four DMLs that operate at 25 Gb / s, and operates at 100 Gb / s.

  FIG. 6B corresponds to FIG.

  The wavelengths of the output lights from the four DMLs are different from each other, and are multiplexed by an MMI (Multi-Mode Interference) type optical coupler. A wavelength coupler or a polarization coupler may be used as an optical coupler for multiplexing.

  7A and 7B are diagrams showing a connection form between a 4-channel DML and a high-frequency wiring, where FIG. 7A is a connection form using a conventional wire, FIG. 7B is an equivalent circuit of FIG. 7A, and FIG. (D) shows the equivalent circuit of (b), and (e) shows the high-frequency characteristics of the two connection forms.

  To connect the 4-channel DML shown in FIG. 7 and the high-frequency wiring with wires, for example, a structure as shown in FIG. That is, in FIG. 7A, the DML and the wiring board 604 are connected by the bonding wire 601.

  7A, the multi-channel optical transmitter 600 includes a signal line 602, a DML array 603, a subcarrier 605, and a spacer 606.

The equivalent circuit of the multi-channel optical transmitter 600 in FIG. 7A is a circuit as shown in FIG. The wiring board 604 is connected to the DML via a coil (corresponding to a bonding wire) 6048, and further connected to a termination 6050 via a coil (corresponding to a bonding wire) 6049. For example, when the resistance of the DML is 4 ohms, the total resistance becomes 50 ohms by connecting a termination resistor of 46 ohms to the DML. In the DML 4046 of FIG. 7B, the Rn cladding 6041, the C pad 6042, C active 6043, R active 6044, Rp cladding 6045 and active layer (active layer) 6047 are shown.

  The Rn cladding 6041 described above is the resistance of the cladding layer 419 shown in FIG. 4B, the C pad 6042 is the capacitance of the pad 422 shown in FIG. 4B, and the C active 6043 is shown in FIG. 4B. This corresponds to the capacitance of each active layer 416. The R active 6044 corresponds to the resistance of the active layer 416 shown in FIG. 4B, and the Rp clad 6045 corresponds to the resistance of the substrate 420 shown in FIG. 4B.

  In order to increase the operating band of the DML, the DML electrode 607 and the wiring board 604 are made of gold bumps (example shown in FIG. 5) by flip chip bonding shown in FIG. 5 without using the above-described bonding wires. Then, there is a method of direct connection with Au bumps 215). FIG. 7C is a flip chip bonding connection mode similar to FIG. 5, and FIG. 7D is an equivalent circuit of the connection mode.

  In FIG. 7C, the DML and the wiring board 614 are connected by a gold bump 613.

  In FIG. 7C, the multi-channel optical transmitter 600A includes an upper layer signal line 610, a lower layer signal line 611, an RF via 612, a high frequency circuit board 614, and a subcarrier 615.

  In FIG. 7D, the wiring board 614 is connected to the termination 6050A via the DML 6046A.

  In FIG. 7D, an active layer (active layer) 6047A is shown.

  The flip chip bonding described above is one of the methods for mounting a chip on a mounting substrate. When the chip surface and the substrate are electrically connected, they are not connected by wires as in wire bonding, but in an array form. Connect with gold bumps lined up. As a result, the distance between the chip and the signal line can be shortened as compared with the wire bonding, so that the wiring becomes short. For this reason, as shown in FIG. 7E, the high-frequency characteristics in the case of flip chip bonding are considered to be better than in the case of wire bonding.

  In flip-chip bonding, the high-frequency characteristics gradually deteriorate as the frequency increases, whereas in wire bonding, the frequency is peaked in wire bonding, and the frequency is rapidly increased on the high-frequency side. This is because the characteristics tend to deteriorate.

  Emphasis is placed on improving high-frequency characteristics by reducing parasitic inductance.

  The above-described wiring board is formed by a microstrip line as shown in FIG. In the dielectric substrate of FIG. 8A, the upper surface conductor 701a having a length W is a transmission line, and the lower surface conductor 701b is GND. A dielectric 702 is formed between the conductors 701a and 701b.

As shown in FIG. 8B, the characteristic impedance of the transmission line is determined by the relative permittivity, thickness, conductor thickness and width of the substrate. If a substrate having a high relative dielectric constant is used, the circuit can be reduced in size. In general, it is known that the following substrate materials are used. Glass epoxy substrate (relative permittivity ε _r = 4.8), Teflon substrate (relative permittivity ε _r = 2.6), ceramic substrate (relative permittivity ε _r = 10.0).

  The wiring board is formed of a coplanar line as shown in FIG. In FIG. 8A, one surface of a dielectric substrate having a thickness = h and a relative dielectric constant = εr is defined as a conductor surface, and two slots having a width = S are provided at intervals W on the conductor surface. The dielectric substrate usually has a so-called GSG structure in which the conductor surfaces on both sides are GND and the center conductor is a signal. FIG. 8D shows the characteristic impedance corresponding to the value of s / h in the wiring board with w / h = 1.0.

  FIG. 9 schematically shows a conventional DML termination circuit pattern 800 using flip-chip bonding.

  In the circuit pattern 800 shown in FIG. 9A, the high-frequency line S for sending a signal to the DML 804 and the high-frequency line 801 immediately before the termination resistor 803 have the same 50 ohm design. FIG. 9A shows an example in which both the DML signal electrode and the GND electrode G are on the same surface. The DML signal electrode is connected to the high-frequency line S of the wiring board, and the DML GND electrode is connected to the wiring. Flip chip bonding is performed to the ground line G of the plate.

  The 50 ohm termination resistor 803 may be soldered to the wiring board or built into the wiring board. When the wiring board is built, the terminating resistor 803 is also set to 50 ohms. The termination resistor 803 is made as short as possible in order to reduce parasitic capacitance. The terminal resistor 803 and the ground line G on the right side thereof are directly connected without providing a gap so as not to include a parasitic component.

  When the DML GND electrode is on the opposite side (rear surface) of the signal electrode, only the signal electrode and the high-frequency line 801 of the wiring board are flip-chip bonded as shown in FIG. 9B. In this case, the electrode on the back surface and the ground are connected by a method such as a bonding wire or a via.

  FIG. 10 and FIG. 11 show via connection forms between the DML GND electrode and the ground when the DML GND electrode is on the opposite side (rear surface) of the signal electrode. The connection forms shown in FIGS. 10 and 11 correspond to the circuit pattern 800 of FIG. 9B.

  In FIG. 10, the high frequency wiring board 830 and the DML 804 on the subcarrier 820 are connected by the Au bump 813. Further, the Au bump 815 connects the high-frequency wiring board 830 and the high-frequency wiring board 831 for routing the wiring. In the connection example of FIG. 10, the current path I is a path of flip chip bonding 813 → bottom surface of DML 804 → subcarrier 820 → high frequency wiring board 831.

  As shown in FIG. 11, flip chip bonding 813 is applied to the signal S of the DML 804, and the DML 804 is mounted on the subcarrier 820 by, for example, solder. In general, the thickness of the DML 804 is about 150 μm, and is thinner than the high-frequency wiring board 831. Therefore, the subcarrier 820 is provided with a step as shown in FIG.

  In FIG. 11, two Au electrodes 816a and 816b are connected.

  The Au electrode 816b and the ground G of the high-frequency wiring board 830 are connected by a via 833, and the two high-frequency wiring boards 830 and 831 are connected by flip chip bonding 815.

Dongchurl Kim et.al., “Design and Fabrication of a Transmitter Optical Subassembly in 10-Gb / s Small-Form-Factor Pluggable Transceiver”, IEEE JORNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS. VOL. 12, No. 4, JULY / AUGUST 2006, pp776-782 Chengzhi Xu, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 24, NO. 22, 2012 Shigeru Kanazawa, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 32, NO. 1, 2014

  As in the structure shown in FIG. 9, although there is a conventional high-frequency transmission line that achieves impedance matching by setting the transmission line 801 and the termination resistor 803 to 50 ohms, impedance matching including a direct modulation DFB laser is considered. However, a high-frequency transmission line that improves frequency characteristics has been desired.

A high-frequency transmission line for solving the above problems includes a first conductor line having a predetermined characteristic impedance, a termination resistor connected to the first conductor line, and a second conductor line connected to the termination resistor. the first conductor line, to the terminating resistor and the second conductor line, and a tolyl land lines are opposed at a predetermined distance, the first conductor line path, said terminating resistor side is formed in a tapered line width decreases toward than said predetermined characteristic impedance constitutes a low impedance line portion relatively characteristic impedance is not low, the low impedance line portion, the first conductor Including an impedance transition part including a line, a first low impedance line part including the termination resistor, and a second low impedance line part including the second conductor line, The second low-impedance line portion functions as a stub and is formed so that the amount of frequency peaking is adjusted .

Here, the ground line may be changed by tapered line width increases toward the terminating resistor side.

An optical circuit for solving the above problems includes the high-frequency transmission line. Here, the optical circuit is a directly modulated DFB laser, the DFB section and a signal input electrode and the ground electrodes, even as the signal input electrode is connected to the second conductor line Good.

  The ground electrode may be connected to the ground line.

Connection between said signal input electrode of the first conductor line may be flip-chip connection.

  According to the present invention, high frequency characteristics are improved.

1 is an external view of a typical box-type TOSA module 100. FIG. It is a figure which shows the mounting structure inside the module of the housing shown in FIG. It is a figure which shows the connection aspect of a TOSA module and a driver IC for driving. It is a figure which shows the structure of a direct modulation DFB laser. It is a figure which shows the connection aspect of the high frequency wiring and DML by flip chip bonding. It is a figure which shows the structure of the conventional multichannel optical transmitter. In the conventional multi-channel optical transmitter, it is a figure which shows the connection aspect of the electrode of DML, and a wiring board, an equivalent circuit, and high frequency characteristics. It is a figure which shows the characteristic impedance according to the structure and dielectric constant in the conventional high frequency dielectric plate. It is a figure which shows the outline of the termination | terminus circuit pattern of the conventional DML using flip chip bonding. It is a perspective view which shows the connection form of the GND electrode of DML, and a ground in case the GND electrode of DML exists in the back surface of the electrode for signals. It is sectional drawing which shows the connection form of FIG. It is a figure which shows the structural example of the high frequency transmission line of embodiment of this invention. It is a perspective view which shows an example of a high frequency transmission line. It is a perspective view which shows an example of the DML laser chip connected with a high frequency transmission line. It is a perspective view which shows the example of a combination of a direct modulation | alteration DFB laser chip and a high frequency wiring board. It is a figure which shows an example of the equivalent circuit of FIG.

  Hereinafter, embodiments of the high-frequency transmission line 1 of the present invention will be described. The high-frequency transmission line 1 is configured to transmit a signal to the DFB portion of the direct modulation DFB laser.

[Configuration of high-frequency transmission line]
First, the configuration of the high-frequency transmission line 1 will be described with reference to FIGS. 12 and 13. FIG. 12 is a diagram showing a configuration example of the high-frequency transmission line 1B of the present embodiment in association with a conventional high-frequency transmission line, where (a) is a circuit pattern 1B of the high-frequency transmission line 1B, and (b) is a conventional one. A circuit pattern 800B is shown. FIG. 13 is a perspective view of the high-frequency transmission line 1B.

  As shown in FIG. 12A, the high-frequency transmission line 1B includes a first conductor line 11a, a termination resistor 14 connected to the first conductor line 11a, and a second conductor line 15a connected to the termination resistor 14. And ground lines 12a and 12b disposed to face the first conductor line 11a, the terminating resistor 14 and the second conductor line 15a with a predetermined distance therebetween.

  The conductor lines 11a and 15a are, for example, high-frequency wiring boards. The characteristic impedance of the first conductor line 11a is set to 50Ω, for example, and the second conductor line 15a is set to a value lower than 50Ω, for example.

  Note that the second conductor line 15a constitutes a second low-impedance line portion 423A shown in FIG. 13 in combination with the corresponding ground lines 12a and 12b. The second low-impedance line portion 423A functions as a stub so that the amount of frequency peaking is adjusted.

  The DFB portion 17 is connected between the second conductor line 15a and the ground line 12b. In this embodiment, since the signal electrode and the ground electrode of the DFB portion 17 are both configured on the same surface of the DFB portion 17, the signal electrode of the DFB portion 17 is connected to the conductor line 15a and the DFB portion. The 17 ground electrodes are each flip-chip bonded to the ground line 12b. The connection form of the flip chip bonding is the same as that shown in FIG.

  In FIG. 12A, the first conductor line 11a has bent shapes 16c and 16d that bend inward at the end face on the terminal resistor 14 side. In the example of FIG. 12A, the bent shapes 16c and 16d are, for example, tapered shapes in which the line width is narrowed.

  The ground lines 12a and 12b have bent shapes 16b and 16a that bend toward the first conductor line 11a at positions corresponding to the bent shapes 16c and 16d described above. In the example of FIG. 12A, the bent shapes 16a and 16b are, for example, tapered shapes with a wide GND width.

  Thereby, the characteristic impedance of the bent shape portions 16a to 16d changes toward the termination resistor 14 so as to be smaller than 50Ω. This part constitutes the impedance transition unit 421A shown in FIG.

  Further, the first low impedance line portion 422A shown in FIG. 13 is configured by the lines 11a, 12a, 12b and the termination resistor 14 whose line widths are changed by the taper. The second low-impedance line portion 423A shown in FIG. 13 includes a line 15a adjacent to the termination resistor 14 and ground lines 12a and 12b corresponding thereto.

  On the other hand, as shown in FIG. 12B, the conventional circuit pattern 800 includes a high-frequency line 801b for sending a signal to the DFB unit 805, and two ground lines 801a and 801b. In this case, both the terminating resistor 803a and the high-frequency line 801b connected to the DFB portion have the same 50 ohm design.

  Next, a DFB laser combined with the high-frequency transmission line 1B will be described with reference to FIG. FIG. 14 is a perspective view showing an example of the DFB laser 20.

  As shown in FIG. 14, the DFB laser 20 includes a DFB laser electrode 21, a gold bump 22, a laser chip 24, and a subcarrier 25.

  FIG. 15 is a perspective view showing an example of an optical circuit in which the high-frequency transmission line 1B and the DFB laser 20 are combined.

  In this example, the high-frequency transmission line 1B is connected to the DFB laser 20 shown in FIG.

  In FIG. 15, the DFB laser 20 and the high-frequency transmission line 1B intersect at right angles, but the DFB laser 20 and the high-frequency transmission line 1B may be arranged so as to overlap in the same direction. In particular, when the DFB laser 20 is not a single unit but has an array structure, it is preferable to arrange the DFB laser 20 and the high-frequency transmission line 1B in the same direction.

  The circuit elements 41A, 421A, 422A, and 423A shown in FIG. 15 are respectively the 50Ω line 41a, the impedance transition part 421A, the first low impedance line part 422A, and the second low impedance line part 423A shown in FIG. Corresponding to

  FIG. 16 is an equivalent circuit 40 of the high-frequency transmission line 1.

  The equivalent circuit 40 includes a 50Ω line 41A and an impedance adjustment unit 42A. The impedance adjustment unit 421A is connected in series with the 50Ω line 41A, the impedance transition unit 421A whose impedance is lower than 50Ω, the first low impedance line (including the termination resistor) 422A whose impedance is relatively low, A second low-impedance line 423A having an impedance relatively lower than 50Ω. One end of the DFB portion 424A is connected to the second low impedance line 423A, and the other end of the DFB portion 424A is grounded. The second low-impedance line portion 423A functions as a stub, whereby the amount of frequency peaking is adjusted, and the frequency characteristics in the high-frequency band are improved.

  The circuit elements 41A, 421A, 422A, and 423A shown in FIG. 16 are respectively the 50Ω line 41A, the impedance transition part 421A, the first low impedance line part 422A, and the second low impedance line part 423A shown in FIG. Corresponding to

  Although the embodiment has been described in detail above, the specific configuration is not limited to the embodiment and may be changed.

  For example, the case where the DFB portion 17 is connected between the conductor line 11a and the ground line 12b has been described. However, there may be a case where the signal electrode and the ground electrode of the DFB portion 17 are configured on different surfaces. In such a case, in the high-frequency transmission line, both the signal electrode and the ground electrode of the DFB portion may be flip-chip bonded by the first conductor line 11a.

  The bent shapes (tapered shapes) 16a to 16d described above may be any shape as long as the characteristic impedance is higher than 50Ω, for example, and can be implemented by various other alternative shapes. For example, such a shape may be changed stepwise or continuously in a curved shape.

  In the structure shown in FIG. 12, the tapered shape may be formed only on the first conductor line 11a, and the ground lines 12a and 12b may not be formed.

  The above-described embodiments and modified examples can be implemented in any combination.

1, 1A High-frequency transmission line 11a First conductor line 12a, 12b Ground line 16a to 16d Bending shape (tapered shape)
14 Terminating resistor 15a Second conductor line

Claims (6)

A first conductor line having a predetermined characteristic impedance;
A termination resistor connected to the first conductor line;
A second conductor line connected to the termination resistor;
A ground line disposed opposite to the first conductor line, the termination resistor and the second conductor line with a predetermined distance therebetween;
With
Said first conductor line path, the line width toward the terminating resistor side is formed in a tapered shape that becomes narrow, constitute a low-impedance line portion relatively characteristic impedance is not lower than the predetermined characteristic impedance ,
The low impedance line unit includes an impedance transition unit including the first conductor line, a first low impedance line unit including the termination resistor, and a second low impedance line unit including the second conductor line. ,
The high-frequency transmission line, wherein the second low-impedance line portion functions as a stub and the amount of frequency peaking is adjusted . The high-frequency transmission line according to claim 1, wherein the ground line changes according to a taper shape in which a line width becomes wider toward the termination resistor .   An optical circuit comprising the high-frequency transmission line according to claim 1. It said optical circuit is a directly modulated DFB laser, claim the DFB portion which has a signal input electrode and the ground electrode, the signal input electrode and being connected to the second conductor line 3. The optical circuit according to 3.   The optical circuit according to claim 4, wherein the ground electrode is connected to the ground line. 5. The optical circuit according to claim 4, wherein the connection between the signal input electrode and the first conductor line is a flip-chip connection.

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