JP6770478B2 - Optical transmitter - Google Patents

Description

The present invention relates to an optical transmitter which is a component of a large-capacity optical communication network.

With the explosive increase in data traffic in recent years, there is a demand for larger capacities in optical communication systems, and the optical components used are integrated into more complex configurations, and signals are becoming faster. Has been done. Examples of such an optical transmitter include an optical modulator. Recently, in order to increase the transmission capacity, a polarized multiple optical I / Q modulator using a Mach-Zehnder Modulator (MZM) and in which two optical I / Q modulators are integrated is used. It is becoming like. This modulator integrates four MZMs and supports multi-level modulation such as QPSK (Quadrature Phase Shift Keying) and 16QAM (Quadrature Amplitude Modulation).

As a typical MZM used in the above-mentioned modulator, an LN modulator in which an optical waveguide is configured by using LiNbO ₃ (LN) is widely used. This modulator operates using an electro-optic effect in which the refractive index of the medium changes according to the electric field applied to the LN. However, due to the physical constants of the material, the LN modulator has a relatively long element length.

In recent years, miniaturization of optical transmitter modules and reduction of drive voltage have become issues, and miniaturization of optical modulators and reduction of drive voltage have become indispensable issues. In order to meet these demands, research on semiconductor MZM, which is compact and enables low drive voltage by configuring the optical path from semiconductors, is being energetically promoted.

Here, a typical polarization multiplex IQ modulator using a semiconductor MZM, which is currently being widely used in communication networks, will be described with reference to FIG. 7. This IQ modulator is composed of four child MZM502s and two parent MZM503s each consisting of two child MZM502s on a substrate 501. Each arm of each of the four child MZM502s is provided with a child MZ phase modulation electrode 504.

Further, each arm of the parent MZM503 is provided with a parent MZ phase modulation electrode 505. Further, a phase modulation electrode line 506 is provided on each of the eight arms of each of the four child MZM502s. Further, an RF lead-out line 507 is connected to each phase modulation electrode line 506. An RF signal is input to each arm of the child MZM502 by the RF lead-out line 507 and the phase modulation electrode line 506 to perform a modulation operation.

In most of the polarization multiplex IQ modulators reported so far, the optical waveguide of the optical input / output and the electro-optical modulator are all formed in the same direction, and the high frequency line of the input (output) is orthogonal to the optical input / output direction. The light is supplied externally from the direction in which the light is supplied, and the power is supplied to the modulation region by bending the lead line by approximately 90 ° (see Non-Patent Document 1).

Further, in order to further increase the speed and reduce the power consumption, studies on integration of a driver IC (Integrated circuit) and a modulator are underway (see Non-Patent Document 2). In general, as for the MZ modulator, the differential drive type driver IC is more advantageous than the single end drive type in terms of power consumption. Further, the open collector (open drain) type driver IC has an advantage that the power consumption can be reduced because the back termination is unnecessary and the amount of current can be halved as compared with the conventional back termination type.

Further, when an open collector (open drain) type driver IC is used, the impedance of the connected MZ modulator does not need to be a conventional differential 100Ω line, and is excellent in that it can be an arbitrary impedance. There is. For this reason, recently, studies on reducing power consumption by combining an open collector (open drain) type driver IC and a semiconductor MZM modulator have been actively conducted (see Non-Patent Document 3).

However, in the configuration of Non-Patent Document 3, only the driver IC and the signal (S) electrode of the semiconductor MZ modulator are connected, and the ground (G) electrode is not connected. Therefore, when viewed as a differential line, in the above-mentioned configuration, in-phase signal components are totally reflected at the connection portion, which causes a decrease in the driving force of the driver, deterioration of frequency characteristics, and crosstalk. There are problems such as causing.

S. Lange et al., "Low Power InP-Based Monolithic DFB-Laser IQ Modulator With SiGe Differential Driver for 32-GBd QPSK Modulation", Journal of Lightwave Technology, vol. 34, no. 8, pp. 1678-1682, 2016. Taizo Tatsumi et al., "A Compact Low-Power 224-Gb / s DP-16QAM Modulator Module with InP-based Modulator and Linear Driver ICs", Compound Semiconductor Integrated Circuit Symposium, 2014. N. Wolf et al., "Electro-Optical Co-Design to Minimize Power Consumption of a 32 GBd Optical IQ-Transmitter Using InP MZ-Modulators", Compound Semiconductor Integrated Circuit Symposium, 2015.

By the way, in considering higher speed, it is most important to connect the semiconductor MZ modulator and the driver IC with low loss and without reflection. If the wire length between the driver IC and the modulator is as large as 300 μm or more, reflection and loss will occur in the wire portion due to the influence of the inductance of the wire, and the characteristics at the time of connection will be significantly deteriorated. The desired properties cannot be obtained. Therefore, in order to reduce the inductance for the purpose of higher speed in the above configuration, the wire length should be shortened as much as possible and then connected with a plurality of wires, or a thick wire such as a ribbon bonder or a stitch bonder should be used. It has been devised.

Further, in the semiconductor MZ modulator, it is important to control the temperature by a thermoelectric cooler (TEC) using a Peltier element or the like in principle of operation, and in order to reduce the power consumption of the TEC, the inflow of heat from the driver IC is prevented. It is also important that they are separated to some extent.

However, increasing the distance between the semiconductor MZ modulator and the driver IC contradicts the above-mentioned shortening of the wire length for high speed. As described above, there is a demand for a connection technology capable of satisfying both the high frequency characteristics and the thermal characteristics.

The present invention has been made to solve the above problems, and the inflow of heat from the driver IC into the semiconductor Machzender modulator constituting the optical transmitter can be suppressed without impairing the high frequency characteristics. The purpose is to do so.

The optical transmitter according to the present invention includes a differential drive type Machzenda modulator composed of an optical waveguide made of a semiconductor and having a signal electrode line and a ground electrode line, and an open collector type or open drain type output method. A driver IC for driving the Mach Zender modulator and a wiring board for connecting the Mach Zender modulator and the driver IC by flip-chip mounting are provided.

The above optical transmitter includes a thermoelectric cooler equipped with a Mach zender modulator to cool the Mach zender modulator and a metal block equipped with a driver IC to dissipate heat from the driver IC. The ICs are arranged at a predetermined distance so that the heat generated from the driver IC does not affect the operation of the Machzenda modulator.

In the above optical transmitter, between each terminal at one connection end of the wiring board and the signal terminal and ground terminal of the Machzenda modulator, each terminal at the other connection end of the wiring board, and the signal terminal of the driver IC and Each is connected to the ground terminal by a bump.

In the above optical transmitter, at a plurality of first bumps connecting each terminal at one connection end of the wiring board and between the signal terminal and the ground terminal of the Machzenda modulator, and at the other connection end of the wiring board. A plurality of second bumps connecting each terminal and the signal terminal and the ground terminal of the driver IC are arranged on the same plane, and the plurality of first bumps and the plurality of second bumps are parallel to each other. They are arranged in one column.

In the optical transmitter, the slope of the wiring board with respect to the Mach-Zehnder modulator and driver IC, that is within ± 3 °.

In the above optical transmitter, the signal lead-out line connected to the signal electrode line of the Mach Zenda modulator has a differential coplanar line configuration including a ground line connected to the ground electrode line, and the signal lead-out line is the signal electrode line of the lead-out source. It is preferable that the line length is 700 μm or less so that the signal terminal and the ground terminal are arranged from the to the input end without bending.

The optical transmitter may further include a bias terminal for adjusting the voltage applied to the core made of the semiconductor constituting the optical waveguide of the Machzenda modulator.

As described above, according to the present invention, since the Machzenda modulator and the driver IC are connected by a wiring board connected by flip-chip mounting, the inflow of heat from the driver IC into the MZ modulator by the semiconductor is prevented. An excellent effect of being able to suppress high frequency characteristics without impairing them can be obtained.

FIG. 1 is a configuration diagram showing a configuration of an optical transmitter according to an embodiment of the present invention. FIG. 2A is a plan view showing a partial configuration of an optical transmitter according to an embodiment of the present invention. FIG. 2B is a plan view showing a partial configuration of the optical transmitter according to the embodiment of the present invention. FIG. 3 is a configuration diagram showing a configuration of a conventional optical transmitter. FIG. 4 is a plan view showing a partial configuration of a conventional optical transmitter. FIG. 5A is a plan view showing the configuration of the Machzenda modulator 101. FIG. 5B is a plan view showing the configuration of the Machzenda modulator 101. FIG. 6A is a plan view showing a partial configuration of the Machzenda modulator 101. FIG. 6B is a plan view showing a partial configuration of the Machzenda modulator 101. FIG. 7 is a plan view showing the configuration of a conventional Machzenda modulator.

Hereinafter, the optical transmitter according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 schematically shows a side surface of an optical transmitter. This optical transmitter includes a Mach Zender modulator 101, a driver IC 102, and a wiring board 103 that connects the Mach Zender modulator 101 and the driver IC 102 by flip-chip mounting.

The Machzenda modulator 101 is composed of an optical waveguide made of a semiconductor. Further, the Machzenda modulator 101 is provided with a ground electrode line and a ground electrode, and is a differential drive type. The driver IC 102 is an open collector type or open drain type output system, and drives the Mach Zenda modulator 101.

Here, the Mach Zender modulator 101 is mounted on the thermoelectric cooler 105 that cools the Mach Zender modulator 101. The thermoelectric cooler 105 is composed of a Peltier element as is well known. Further, the driver IC 102 is mounted on a metal block 106 for dissipating heat from the driver IC 102. The Mach Zender modulator 101 and the driver IC 102 of the optical transmitter configured in this way are arranged at a predetermined distance within a range in which the heat generated from the driver IC 102 does not affect the operation of the Mach Zender modulator 101.

Further, as shown in FIGS. 1, 2A, and 2B, the first bump 104a is located between each terminal at one connection end of the wiring board 103 and the signal terminal 111 and the ground terminal 112 of the Machzenda modulator 101, respectively. It is connected with. Similarly, each terminal at the other connection end of the wiring board 103 and the signal terminal 121 and the ground terminal 122 of the driver IC 102 are each connected by a second bump 104b. The first bump 104a and the second bump 104b are, for example, Au bumps having a diameter of 60 μm and a height of 30 μm in a plan view.

Further, the plurality of first bumps 104a and the plurality of second bumps 104b are arranged on the same plane, and the plurality of first bumps 104a and the plurality of second bumps 104b are arranged in a row in parallel with each other. ing. With this configuration, poor connection due to each bump can be suppressed.

According to the embodiment, since the Mach zender modulator 101 and the driver IC 102 are connected by the wiring board 103, the Mach zender modulator 101 and the driver IC 102 are connected in order to suppress the inflow of heat into the Mach zender modulator 101. Even if the space (between chips) is separated, the high frequency characteristics are not impaired. Since it is connected by the wiring board 103, unlike wires, there is no increase in inductance or transmission loss even if the chips are separated to some extent, so that there is no deterioration in frequency characteristics at the time of connection and there is no effect on high-speed operation.

The chips may be separated by, for example, 300 μm or more. With this degree, it is possible to suppress an increase in power consumption of the thermoelectric cooler 105 due to the inflow of heat from the driver IC 102 to the Machzender modulator 101. The wiring board 103 may be composed of an AlN substrate, an alumina substrate, or the like, but since these materials have high thermal conductivity, a SiO ₂ substrate having a lower thermal conductivity, a flexible substrate made of resin, or the like is used. , The conduction of heat between chips can be further prevented.

Further, as shown in FIGS. 3 and 4, in the mounting in which the Mach Zenda modulator 101 and the driver IC 102 are connected by a general wire 131, if the height of each chip is deviated in the mounting, the wire Since 131 draws a large loop and becomes long, it becomes a factor of deterioration of characteristics. On the other hand, according to the embodiment, even if the wiring board 103 is tilted, it can be connected without any problem, so that there is no deterioration in characteristics due to height deviation. However, if the substrate surface of the wiring board 103 is tilted by 3 ° or more with respect to the chip surface of the Mach Zender modulator 101 or the driver IC 102, the connection strength cannot be guaranteed. Therefore, when the flip chip is mounted, the Mach Zender modulator 101 and the driver IC 102 On the other hand, it is important that the inclination of the wiring board 103 is within ± 3 °.

Here, the Machzenda modulator 101 will be described in more detail with reference to FIGS. 5A and 5B. The Machzenda modulator 101 is composed of four child MZM202s and two parental MZM203s each consisting of two child MZM202s. Each arm (core of the optical waveguide) of each of the four child MZM202s is provided with a child MZ phase modulation electrode 204.

Further, each arm (core of the optical waveguide) of the parent MZM 203 is provided with a parent MZ phase modulation electrode 205. Further, a phase modulation electrode line (signal electrode line) 206 is provided on each of the eight arms of each of the four child MZM202s. Further, an RF lead-out line (signal lead-out line) 207 is connected to each phase modulation electrode line 206. A signal terminal and a ground terminal are formed at the input end of the RF lead-out line (signal lead-out line) 207. The RF lead-out line 207 and the phase modulation electrode line 206 input an RF signal to each arm of the child MZM 202 to perform a modulation operation.

In the above configuration, as shown in FIGS. 6A and 6B, the ground electrode line 208 is arranged next to the phase modulation electrode line 206, the ground lead line 209 is arranged next to the RF lead line 207, and the differential coplanar line configuration is provided. It is said that. As shown in FIG. 6A, the ground (G), the signal (S), the ground (G), the signal (S), and the ground (G) may be arranged in this order. Further, as shown in FIG. 6B, the ground (G), the signal (S), the signal (S), and the ground (G) may be arranged in this order. The ground electrode line 208 and the ground lead-out line 209 are not shown in FIGS. 5A and 5B.

Further, the RF lead-out line 207 is arranged in a state where there is no bending from the connection end to the input end with the phase modulation electrode line 206. The same applies to the ground lead-out line 209. The arrangement of the optical waveguide and the high-frequency line of the Mach Zender modulator 101 may be such that the line length of the RF lead-out line 207 (ground lead-out line 209) is the shortest. For example, the RF lead-out line 207 may have a line length of 700 μm or less.

As described above, by connecting the open collector type (open drain type) driver IC 102 having the output PAD of GSGSG to the GSGSG differential coplanar line of the Mach Zender modulator 101 or the differential coplanar line of GSSG, the driver IC 102 The output in-phase signal component is not totally reflected at the connection point and is fed to the Machzenda modulator 101. Therefore, the driving force of the driver IC 102 is not reduced and unnecessary crosstalk does not occur.

Compared with the conventional configuration described in Non-Patent Document 2, the line length of the RF lead-out line 207 can be reduced to 700 μm or less, which is about 1 mm as compared with the conventional configuration, by adopting the configuration of the above-described embodiment.

Further, the structure of the phase modulation unit in the Machzenda modulator 101 may be a capacitive loading structure or another structure in order to realize high speed if it is a differential coplanar line structure.

In the open collector type or open drain type driver IC 102, an arbitrary amount of current is supplied from the Machzenda modulator 101 to the driver IC 102 via the terminal portion of the phase modulation electrode line 206. Therefore, the Mach Zenda modulator 101 is separately provided with a bias terminal for adjusting the voltage applied to the core composed of the semiconductors constituting each arm, and the phase modulation electrode line 206 is provided with an arbitrary voltage for driving the driver IC. Can be applied. In a structure like Non-Patent Document 2, the bias voltage cannot be adjusted through the signal electrode portion, but for example, "n-layer" shown in Fig. 3 of Non-Patent Document 3 is shown. A bias voltage adjustment terminal for applying a bias may be provided separately, such as “bias”.

Unlike the back termination type driver IC, in the case of the open collector type driver IC 102, the impedance of the Machzender modulator 101 may be any impedance (for example, differential 40Ω to 100Ω). Considering the high frequency characteristics of the Machzenda modulator 101 itself, it is desirable that the differential impedance is low, but from the viewpoint of power consumption, the impedance is preferably high.

The connection is not limited to one Mach Zender modulator 101 and one channel driver IC 102. And IQ modulator constructed by two Mach-Zehnder modulator 101, also in connection with two-channel driver IC 102, a described above as well. Further, in the case of connecting the polarization multiplex IQ modulator composed of four Machzenda modulators 101 to the four-channel driver IC 102, the number of connections is only increased, and the wiring board 103 is mounted by flip chip as described above. Can be connected using.

For example, in the case of connecting a polarization multiplex IQ modulator composed of four Machzenda modulators 101 and a four-channel driver IC 102, the wiring board 103 may be separated for each channel and flip-chip mounted. May be collectively connected to one wiring board 103.

Further, in order to realize a wider band modulator by combining the Machzenda modulator 101 and the driver IC 102, it is desirable that the driver IC 102 is provided with a predetermined frequency peaking. For example, 15 to 25 GHz is desirable for 32 GBd, and 30 to 40 GHz is desirable for 64 GBd.

This is because when the driver IC 102 is connected to the Mach Zenda modulator 101 without providing frequency peaking, the loss in the driver IC 102 and the wiring board 103 simply contributes to the deterioration of the modulation band and lowers the band. In addition, by providing frequency peaking, compensation such as covering the loss in the module package can be performed. In this way, by providing frequency peaking and combining the driver IC and the semiconductor MZ modulator, it is possible to further widen the bandwidth.

The Machzenda modulator 101 is composed of an optical waveguide composed of a lower clad layer formed on a substrate, a core formed on the lower clad layer, and an upper clad layer formed over the core. The substrate is composed of, for example, a semi-insulating InP, the lower clad layer is composed of a first conductive InP, the core is composed of non-doped InGaAsP or InGaAlA, and the upper clad layer is a second conductive type. It may be composed of InP. Further, a third clad layer made of a second conductive type InP may be inserted between the lower clad layer and the core.

Further, the core may be composed of a bulk layer made of the above-mentioned quaternary mixed crystal, or may have a multiple quantum well structure. Further, the core may have a multiple quantum well structure, and the upper and lower parts thereof may be sandwiched by a light confinement layer. The optical confinement layer may be composed of a semiconductor having a bandgap energy larger than that of the multiple quantum well structure of the core and a bandgap energy smaller than that of the upper and lower clad layers. The bandgap wavelengths of the quaternary mixed crystal bulk layer and multiple quantum wells that make up the core should be set so that the electro-optic effect works effectively and light absorption does not become a problem at the optical wavelength used. Just do it. Further, the material constituting the Machzenda modulator 101 is not limited to the above-mentioned InP-based material, and for example, a material system matching a GaAs substrate may be used.

As described above, according to the present invention, since the Machzenda modulator and the driver IC are connected by a wiring board connected by flip-chip mounting, heat inflow from the driver IC into the MZ modulator by a semiconductor flows into the MZ modulator. , It becomes possible to suppress without impairing the high frequency characteristics.

The present invention is not limited to the embodiments described above, and many modifications and combinations can be carried out by a person having ordinary knowledge in the art within the technical idea of the present invention. That is clear.

101 ... Mach Zender modulator, 102 ... Driver IC, 103 ... Wiring board, 104a ... First bump, 104b ... Second bump, 105 ... Thermoelectric cooler, 106 ... Metal block.

Claims (6)

A differential drive type Machzenda modulator composed of an optical waveguide made of a semiconductor and having a signal electrode line and a ground electrode line,
A driver IC for driving the Machzenda modulator, which is an open collector type or open drain type output system,
A wiring board for connecting the Machzenda modulator and the driver IC by flip-chip mounting is provided .
The inclination of the substrate surface of the wiring board with respect to the Machzenda modulator and the driver IC is within ± 3 °.
The wiring board, AlN board, the optical transmitter, characterized in that it consists either of S iO ₂ substrate. In the optical transmitter according to claim 1,
A thermoelectric cooler equipped with the Mach zender modulator to cool the Mach zender modulator,
The driver IC is mounted and provided with a metal block for dissipating heat from the driver IC.
The optical transmitter is characterized in that the Mach zender modulator and the driver IC are arranged at a predetermined distance within a range in which heat generated from the driver IC does not affect the operation of the Mach zender modulator. In the optical transmitter according to claim 1 or 2.
Between each terminal at one connection end of the wiring board and the signal terminal and ground terminal of the Machzenda modulator, and each terminal at the other connection end of the wiring board, and the signal terminal and ground terminal of the driver IC. An optical transmitter characterized in that each of them is connected by a bump. In the optical transmitter according to claim 3,
A plurality of first bumps connecting each terminal at one connection end of the wiring board with the signal terminal and the ground terminal of the Machzenda modulator, and
The plurality of second bumps connecting each terminal at the other connection end of the wiring board and the signal terminal and the ground terminal of the driver IC are
Placed on the same plane,
An optical transmitter characterized in that the plurality of first bumps and the plurality of second bumps are arranged in a row in parallel with each other. In the optical transmitter according to any one of claims 1 to 4 .
The signal lead-out line connected to the signal electrode line of the Machzenda modulator has a differential coplanar line configuration including a ground line connected to the ground electrode line.
The signal lead-out line is arranged in a state where there is no bending from the signal electrode line of the lead-out source to the input terminal where the signal terminal and the ground terminal are formed, and the line length is 700 μm or less. Transmitter. In the optical transmitter according to claim 5 ,
An optical transmitter further provided with a bias terminal for adjusting a voltage applied to a core made of a semiconductor constituting the optical waveguide of the Machzenda modulator.

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