JP2002368325A - Light emitting module, optical semiconductor element, and light receiving module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide small-sized optical communication equipment having superior circuit characteristics to high frequencies. SOLUTION: A light emitting module has a transmission line section which transmits high-frequency signals used for modulating light, an optical semiconductor element 20 which receives the high-frequency signals from the transmission line section and outputs modulated light, and a terminating resistance section connected to the element 20. The element 20 is provided with an electrode 22 connected to the transmission line section, a connection pad 25 which connects the electrode 22 to the terminating resistance section, and a conductor pattern 24 which is arranged between the electrode 22 and pad 25 and has a predetermined inductance value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electro-optical converter or an optical-electric converter for an optical communication circuit module.

[0002]

2. Description of the Related Art Data transmission speed is 1 Gbps (giga bit per
Optical communication modules for high-speed transmission exceeding (second) not only need to mount light-emitting elements and light-receiving elements that can operate at high speed, but also need to consider wiring in the module for transmitting high-frequency signals. . For example,
Japanese Patent Application Laid-Open No. 1-192188 and Japanese Patent Application Laid-Open No. 09-172221 disclose that a signal wiring structure in a transmission module for performing electro-optical conversion is constituted by a microstrip line or a transmission line whose impedance is matched, so that the characteristic impedance of the wiring portion is improved. This prevents reflection of high-frequency signals due to mismatching of high-frequency signals, and prevents loss of high-frequency signals and distortion of signal waveforms.

[0003] Japanese Patent Application Laid-Open No. 09-90302 discloses an optical modulator module that reduces the reflection of high-frequency signals by positively utilizing the inductance component of a bonding wire. This optical modulator module uses a modulator that modulates light intensity by applying a high-frequency voltage to an optical waveguide that propagates light emitted from a semiconductor laser. At this time, by disposing the terminating resistor connected to the modulator away from the high-frequency signal source, a first bonding wire connecting the modulator and the high-frequency signal source and a second bonding wire connecting the modulator and the terminating resistor are arranged. The bonding wire forms a circuit existing between the high-frequency signal source and the terminating resistor. Thereby, since the inductance of the first bonding wire and the inductance of the second bonding wire exist between the high-frequency signal source and the terminating resistor, when the frequency of the output signal of the high-frequency signal source increases, the inductance flows through the terminating resistor. The current is reduced and the increase in current through the modulator is compensated. As a result, the frequency dependence of the total current is reduced, and the deviation of the impedance of the circuit from a predetermined value as seen from the signal source is also reduced,
Return loss is reduced. It discloses that the adjustment of the impedance value of the bonding wire is performed by changing the length of the wire by changing the installation location of the terminating resistor.

[0004]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. 09-9030
Using a bonding wire as an inductance for improving the frequency characteristics as in the modulator module disclosed in Japanese Patent Publication No. 2 can easily realize the inductance and is simple. However, in order to realize an inductance having a large value, for example, an inductance exceeding several nH, with a bonding wire, a wiring length of several mm is required, and the size of a wiring pad to be connected to is increased or the bonding wire is arranged. In such a case, it is necessary to provide a space for the substrate, which leads to an increase in the size of the substrate. Further, when the wiring length of the bonding wire is long, it is not ignorable that the wire acts as an antenna, and electrical coupling with other parts is likely to occur.

An object of the present invention is to provide a compact optical communication device having excellent circuit characteristics for high frequencies.

[0006]

According to the present invention, there is provided the following light emitting module. That is, a transmission line unit for transmitting a high-frequency signal, an optical semiconductor element that receives the high-frequency signal from the transmission line unit and outputs modulated light, and a termination resistor unit connected to the optical semiconductor element. The optical semiconductor element has an electrode connected to the transmission line portion, a connection pad for connecting the electrode to the terminating resistor portion, and is disposed between the electrode and the connection pad. And a conductor pattern having a predetermined inductance value.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.

First, an optical transmitter according to a first embodiment of the present invention will be described. The optical transmitter includes a light emitting module 104 having a modulation function (FIG. 4) and a light emitting module 1.
A signal source (not shown) for outputting a signal for operating the C.O.
A control circuit for controlling the operation of the signal source;
And a support portion for supporting an optical fiber for transmitting the optical signal emitted from the optical fiber. The light emitting module 104 having a modulation function has a configuration in which an optical semiconductor element 20 and a bypass capacitor 40 are mounted on a substrate 10 made of ceramics.

As shown in FIG. 1, an optical semiconductor device 20 includes a semiconductor laser portion 101 and a semiconductor laser portion 1 in one device.
And a modulator unit 102 for intensity-modulating the light emitted by the light-emitting device 01. The semiconductor laser unit 101 includes an active layer 27 and an element 20.
And a connection pad 121 connected to the upper electrode 21. On the other hand, the modulator section 102 includes the semiconductor optical waveguide 111 and the element 2
And an electrode 22 for applying a voltage to the optical waveguide 111 disposed on the upper surface of the optical waveguide 111. On the upper surface of the element 20 of the modulator section 102, in addition to the electrode 22, a first connection pad 23 connected to the electrode 22, a meandering conductor pattern 24 connected to the electrode 22, A second connection pad 25 connected to the tip is arranged. The meandering conductor pattern 24 is a pattern called a meander line. In the present embodiment, the meandering conductor pattern 24 is used as an inductance element. A common electrode (not shown) common to the semiconductor laser unit 101 and the modulator unit 102 is arranged on the back surface of the element 20. When a voltage is applied from the electrode 22 to the optical waveguide 111, the absorption edge shifts due to the electro-optic effect of the semiconductor, and the propagating light is absorbed. Thus, the intensity of the light emitted from the semiconductor laser unit 101 is modulated and made incident on an optical fiber (not shown).

On the upper surface of the substrate 10, a common electrode pattern 1
1, a signal transmission pattern 12, and a terminating resistor 13 are formed in advance. The optical semiconductor device 20 and the bypass capacitor 40 are mounted on the common electrode pattern 11, and the common electrode and the bypass capacitor 4 on the back surface of the optical semiconductor device 20 are provided.
One of the electrodes 0 is electrically connected to the common electrode pattern 11. The other electrode of the bypass capacitor 40 is connected to the connection pad 1 of the semiconductor laser unit 101 of the optical semiconductor device 20.
21 and a bonding wire. The connection pad 121 is connected to a signal source (not shown) by a bonding wire (not shown) in order to receive supply of a current for driving the semiconductor laser unit 101. On the other hand, the signal transmission pattern 12 is connected to the first connection pad 23 of the modulator section 102 by a bonding wire 114. The second connection pad 25 of the modulator section 102 is connected to the terminating resistor 13 by a bonding wire 113. The signal transmission pattern 12 is connected to a wiring body of a signal source (not shown), and transmits a high-frequency voltage signal supplied to the electrode 22 of the modulator unit 102. The signal transmission pattern 12 is
It is composed of a 50 ohm grounded coplanar transmission line that is impedance-matched to the signal source wiring body, prevents reflection of high-frequency signals, and suppresses loss and waveform distortion due to reflection.

The modulator section 102 of the light emitting module 104,
FIG. 5 shows an equivalent circuit of a circuit constituted by the signal transmission pattern 12 and the terminating resistor 13. The signal transmission pattern 12 is connected to the modulator unit 102. Since the modulator unit 102 can be regarded as a parallel circuit of a capacitance component and a resistance component,
It is represented by a parallel circuit of a capacitor 102a and a resistor 102b.
The inductance L1 is the inductance of the bonding wire 114. The inductance L2 is determined by the inductance of the conductor pattern 24 and the bonding wire 113.
And the inductance of the above. Note that the resistance value Rt of the terminating resistor 13 is
It is determined to be 50 ohms together with the resistance value of b.

The pattern shape of the conductor pattern 24 is determined as follows. The inductance L2 obtained by combining the inductance of the conductor pattern 24 and the inductance of the bonding wire 113 is as shown in FIG.
The capacitor 102a of the modulator unit 102 forms an LC resonance circuit. The resonance frequency of this LC resonance circuit is
If the frequency band 02 is within the operating frequency band of the high-frequency signal supplied from the signal source via the signal transmission pattern 12, ripples occur in the transmitted high-frequency signal. Therefore, in the present embodiment, the value of the inductance L2 is determined in advance by calculation so that the resonance frequency of the LC resonance circuit is equal to or higher than the upper limit of the frequency used. The capacitance 102a of the modulator unit 102 and the inductance value of the bonding wire 113 required for this calculation are calculated from the structure of the modulator unit 102 and the material and length of the bonding wire 113. Next, the bonding wire 1 is calculated from the value of the inductance L2 determined by calculation.
The inductance value required for the conductor pattern 24 is obtained by subtracting the inductance value of 13 from the inductance value.
The pattern shape of the conductor pattern 24 is determined so as to realize this inductance value.

For example, the upper limit frequency of use of a high frequency signal is 1
At 0 GHz, when the capacitance 102a is 0.5 pF, the capacitance 102a
The value of the inductance L2 for making the resonance frequency of the inductance L2 coincide with the upper limit frequency of use is about 0.5 nH. When the upper limit frequency of use is 2.5 GHz, the value of the inductance L2 is 8 nH. From the value of the inductance L2, the bonding wire 11
By subtracting the value of L of 3, the value of the inductance required for the conductor pattern 24 can be obtained. In order to realize this inductance value, the conductor pattern 2
Design the meander shape and length of 4.

Here, in the circuit of FIG. 5, for the case where the inductance L2 = 0.25 nH and the case where L2 = 0.4 nH, the results obtained by circuit simulation of the S parameters S11 and S21 are shown in FIG. . However,
The capacitance 102a of the modulator unit 102 is 0.5 pF, 0.6 pF,
Three conditions of 0.7 pF were used. The frequency was up to 20 GHz.
Inductance L1 due to bonding wire 114
Was set to L1 = 0.15 nH. As can be seen from FIG.
The inductance L2 is set to 0.2 than when the inductance L2 is 0.25 nH.
When increasing to 4 nH, S in the high frequency band
It can be seen that the increase of No. 11 is small and the return loss can be reduced. Also, it can be seen that the reduction in S21 in the high frequency band is smaller when the inductance L2 is 0.4 nH than when the inductance L2 is 0.25 nH, and that an output can be obtained more efficiently with respect to the input. Also, as shown in FIG. 6, the 3 dB frequency band of S21 when the capacitance 102a of the modulator unit 102 is 0.5 pF and when the capacitance 102a is 0.7 pF,
It can be seen that the case where the inductance L2 is 0.4 nH is wider than the case where the inductance L2 is 0.25 nH, and the circuit characteristics are good.

As described above, the light emitting module 104 shown in FIG.
Since the conductor pattern 24 serving as an inductance is disposed on the upper surface of the optical semiconductor element 20, the inductance L2 can be increased without changing the length of the bonding wire 113. As a result, the resonance frequency of the LC resonance circuit constituted by the inductance L2 and the capacitance 102a of the modulator section 102 can be easily increased. Can be made larger than the upper limit of the working frequency. Therefore, as shown in FIG. 6, the light emitting module 104 with small loss and good circuit characteristics can be obtained. Further, since the conductor pattern 24 is arranged on the upper surface of the optical semiconductor element 20, it is located closest to the modulator section 102. Therefore, the conductor pattern 24 and the modulator section 10
The circuit is hardly affected by the stray capacitance and inductance of the wiring between the first and second wirings, so that good circuit characteristics can be obtained. Further, since the conductor pattern 24 is arranged on the upper surface of the optical semiconductor element 20, it is not necessary to prepare a space for disposing the inductance on the substrate 10, and a small-sized light emitting module 104 having good circuit characteristics can be realized. .

The conductor pattern 24 can be manufactured without any additional steps by patterning the shape of the conductor pattern 24 when patterning the electrode 22 on the upper surface of the optical semiconductor element 20.

In the circuit of FIG. 5, it is desirable that the inductance L1 of the bonding wire 114 is designed to be as small as possible. This is because the inductance L1 and the capacitance 102a of the modulator section 102
This is to say that a low-pass filter is configured to lower the high-frequency band. Therefore, it is preferable to make the signal transmission pattern 12 and the optical semiconductor element 20 as close as possible to reduce the length of the bonding wire 114.

Next, an optical transmitter according to a second embodiment of the present invention will be described.

The optical transmitter according to the second embodiment includes the optical semiconductor element 20 of FIG. 3 as the optical semiconductor element 20 of the light emitting module 104. The optical semiconductor device 20 of FIG.
The configuration of the conductor pattern 24 is different from that of the optical semiconductor element 20 of FIG. The conductor pattern 24 shown in FIG. 3 includes a connection pad 25a arranged at the tip of the meandering pattern,
A connection pad 25b is also provided in the meandering pattern. Therefore, the value of the inductance of the conductor pattern 24 can be selected depending on whether the bonding wire 113 is connected to the connection pad 25a or the connection pad 25b. Actually, when the optical semiconductor element 20 is designed, as described in the first embodiment, the modulator 1
The value of the inductance required for the conductor pattern 24 is obtained by calculation using the value of the capacitance 102a or the like of 02, and the meandering pattern of the conductor pattern 24 that realizes the inductance value or an inductance value in the vicinity thereof is determined. Then, the connection pad 25b is added in the middle of the meandering pattern, and the conductor pattern 24 having a plurality of connection pads is manufactured. Then, the circuit characteristics of the optical transmission module 104 are actually measured when the bonding wire 113 is connected to the connection pad 25a and when the bonding wire 113 is connected to the connection pad 25b. Thereby, for example, data as shown in FIG. 6 is obtained by actual measurement, and the connection pads 25a and the connection pads 25a are obtained.
b, the one with the better circuit characteristics is selected.

As a result, the actual capacitance 102a of the modulator 102 differs from the calculated capacitance 102a due to variations in the doping concentration at the time of manufacturing the optical semiconductor device 20 and differences in the magnitude of the voltage during use. The connection pads 25a and 25b,
Good circuit characteristics can be obtained.

The configuration of the light emitting module 104 excluding the conductor pattern 24 and the configuration of the optical transmitter excluding the light emitting module 104 are the same as those of the first embodiment, and therefore the description is omitted.

In FIG. 3, two connection pads 25 are provided.
Although the conductor pattern 24 having a and 25b is shown, the number of connection pads is not limited to two, and a configuration having three or more connection pads is also possible.

Next, an optical transmitter according to a third embodiment of the present invention will be described.

The optical transmitter according to the third embodiment includes a direct modulation type semiconductor laser 201 shown in FIG. 8 as an optical semiconductor element of a light emitting module. The direct modulation type semiconductor laser 201 of FIG. 8 has an active layer 27, an upper electrode 21, and a back surface electrode (not shown), and is modulated from the semiconductor laser 201 by supplying a high frequency signal to the upper electrode 21. The laser beam is directly emitted. In this case, the peripheral circuit of the electrode 21 has the same configuration as the peripheral circuit of the modulator section 102 of the optical semiconductor device 20 of FIG. 3, as shown in FIG. That is, the bonding wire 1 is
A high-frequency signal is input from the signal transmission pattern 12 via the terminal 14, and the terminating resistor 13 is connected to the bonding wire 113. Therefore, FIG.
As described in the first and second embodiments, the conductor pattern 224 for realizing the inductance is connected to the electrode 21 and the conductor pattern 224 and the terminating resistor 13 are connected by the bonding wire 113 as shown in FIG. A high-frequency circuit with little loss can be realized. At this time,
As shown in FIG. 8, a plurality of connection pads 225a and 225b are provided on the conductor pattern 224 and a pad for connecting the bonding wire 113 is selected, so that the actual connection can be made as in the second embodiment. The inductance can be selected according to the capacitance of the element, and a circuit having excellent high-frequency characteristics can be realized.

Next, an optical receiver according to a fourth embodiment of the present invention will be described with reference to FIGS.

The optical receiver according to the fourth embodiment includes a light receiving module 70 shown in FIG. 7 for receiving an optical signal transmitted through an optical fiber, a discriminating circuit for discriminating a signal from the light receiving module 70, And a support for supporting the optical fiber to the module 70. Light receiving module 70
Has a photodiode chip 30 shown in FIG. The upper surface of the photodiode chip 30 is
A ring-shaped electrode 32 for extracting a signal is provided around the ring-shaped electrode 32, and a part of the ring-shaped electrode 32 is connected to a first connection pad 33 serving as a connection terminal with the outside. Chip 3
On the upper surface of the zero, a meandering conductor pattern 34 connected to the connection pad 33 and a second connection pad 35 arranged at the tip of the conductor pattern 34 are formed. The conductor pattern 34 is used as an inductance.
On the back surface of the photodiode chip 30, a back surface electrode is arranged.

The structure of the light receiving module 70 will be described with reference to FIG. The photodiode chip 30 is represented by a parallel circuit of a signal source 30a and a capacitor 30b. To operate the photodiode chip 30, a bias source 71 and a signal amplifier circuit 72 are connected to the ring-shaped electrode 32. In the present embodiment, the bias source 71 is connected to the second connection pad 35.
And the signal amplifying circuit 72 is connected to the first connection pad 33 by the bonding wire 73.
4 for connection. Therefore, the bias source 71 is connected to the ring-shaped electrode 32 via the conductor pattern 34 acting as an inductance.

Generally, the light receiving module comprises a bias source 7
Conventionally, the signal amplifier circuit 1 and the photodiode chip 3 need to prevent high-frequency signals from flowing into them.
A circuit that separates signals is formed by connecting a resistance element between the circuit element and the element. However, when the signal separating resistor is connected to the input side of the signal amplifier circuit 72, a part of the high frequency signal current is lost due to the capacitance component of the signal separating resistor and the inductance L1 of the bonding wire 74. Since the signal does not reach the signal amplification circuit 72, the characteristics are degraded.

On the other hand, in the present embodiment, the photodiode pattern 30 shown in FIG.
Since the bias source 71 and the photodiode chip 30 are connected via the inductance of No. 4, the bias source 71 can be connected via a large inductance by the conductor pattern 34 and the bonding wire 73. Even without disposing an element, it is possible to prevent a high-frequency signal from flowing into the bias source 71. Therefore, signal deterioration due to the capacitance of the signal separating resistance element does not occur, and characteristics can be improved.

The effect of the conductor pattern 34 increases as the inductance value increases. Therefore, it is desirable to design the conductor pattern 34 so that the inductance value increases as much as possible. On the other hand, the bonding wire 74 connecting the photodiode chip 30 and the signal amplifying circuit 72 desirably has as small an inductance as possible, and is therefore preferably configured to be as short as possible.

As described above, the first to fourth embodiments of the present invention are described.
According to the fourth embodiment, the inductance for improving the high-frequency characteristics of the optical semiconductor device can be realized by the conductor pattern on the upper surface of the optical semiconductor device. Therefore, connection of required inductance can be realized in a small space without connecting an additional inductance element. This has the effect of reducing the cost and size of the optical communication module incorporating the optical semiconductor element.

Further, by forming a conductor pattern for realizing the inductance on the surface of the element, it is not necessary to add an inductance by a bonding wire, and the element can be mounted on the surface. This also has the effect of reducing the cost and size of the optical communication module incorporating the optical semiconductor element. Since the optical semiconductor device of FIGS. 3 and 8 has two connection pads, the connection pad which is not selected is used as an additional connection portion for surface mounting or a connection pad for repair. Can be used. As a result, the effect of improving the reliability of connection at the time of surface mounting and stabilizing the element position / posture can be obtained.

In the first to fourth embodiments,
Although only the meandering pattern is shown as the conductor pattern acting as the inductance, the conductor pattern having the inductance is not limited to this, and it is of course possible to form a spiral pattern as shown in FIG.

[0034]

As described above, according to the present invention,
It is possible to provide a small optical communication device having excellent circuit characteristics for high frequencies.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an optical semiconductor element mounted on a light emitting module of an optical transmitter according to a first embodiment of the present invention.

FIG. 2 is a perspective view illustrating a configuration of a photodiode chip used in an optical receiver according to a fourth embodiment of the present invention.

FIG. 3 is a perspective view showing a configuration of an optical semiconductor element mounted on a light emitting module of an optical transmitter according to a second embodiment of the present invention.

FIG. 4 is a perspective view showing a configuration of a light emitting module of the optical transmitter according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an equivalent circuit of the light emitting module of FIG.

6 is a graph showing a result of a simulation of an S parameter of an equivalent circuit of the light emitting module of FIG. 4;

FIG. 7 is an explanatory diagram illustrating a configuration of a receiving module according to a fourth embodiment of the present invention using an equivalent circuit.

FIG. 8 is a perspective view illustrating a configuration of an optical semiconductor element mounted on a light emitting module of an optical transmitter according to a third embodiment of the present invention.

FIG. 9 shows a conductor pattern 24 of an optical semiconductor device mounted on the light emitting module of the optical transmitter according to the first embodiment of the present invention.
It is a perspective view which shows the structure which made spiral.

[Explanation of symbols]

Reference numeral 10: a substrate on which an optical semiconductor is mounted; 11, a common electrode pattern; 12, a signal transmission pattern; 13, a termination resistor; 20, an optical semiconductor element; 21, an upper electrode of a semiconductor laser unit; Modulator electrode 23, first connection pad 24, meandering conductor pattern 25
... second connection pads, 25a, 25b ... connection pads, 27 ... active layers, 30 ... photodiode chips,
31: light incident surface, 32: signal extraction ring-shaped electrode, 33: first connection pad, 34: meandering conductor pattern, 35: second connection pad, 40:
Bypass capacitor 71 bias source 72 signal amplification circuit 73 74 bonding wire 10
1. Semiconductor laser unit 102 Modulator unit 104
... Light-emitting modules, 112, 113, 114 ... bonding wires, 120 ... optical semiconductor elements, 121 ... connection pads.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F049 MA01 NA03 NA19 NB01 TA14 UA20 5F073 AB28 BA02 FA27 GA24 GA38

Claims (5)

[Claims] 1. A transmission line unit for transmitting a high-frequency signal, and receiving the high-frequency signal from the transmission line unit,
An optical semiconductor element that outputs modulated light; and a terminating resistor connected to the optical semiconductor element. The optical semiconductor element includes an electrode connected to the transmission line, and the electrode connected to the terminal resistor. A light emitting module comprising: a connection pad for connecting to a portion; and a conductor pattern having a predetermined inductance value disposed between the electrode and the connection pad. 2. The light emitting module according to claim 1, further comprising a wiring connecting the connection pad and the terminating resistor, wherein the inductance value of the conductor pattern is an inductance of the conductor pattern and the wiring. And a resonance frequency of a resonance circuit including the capacitance component of the optical semiconductor element is set to a value that is equal to or higher than the frequency of the high-frequency signal. 3. The light emitting module according to claim 1, wherein a plurality of the connection pads are arranged on the upper surface of the element, and the shape of the conductor pattern is different from that of the electrode for each of the plurality of connection pads. A light emitting module, wherein an inductance value between the terminal pad and the connection pad is different from each other, and one of the plurality of connection pads is selectively connected to the terminating resistor. 4. A first connection pad connected to an external wiring, and an electrode for receiving a high-frequency signal from the external wiring via the first connection pad to output modulated light. A second connection pad for connecting the electrode to an external terminating resistor, and a conductor pattern having a predetermined inductance value between the electrode and the second connection pad. An optical semiconductor device comprising: 5. A light receiving element, a bias circuit for applying a bias to the light receiving element, and a receiving circuit for receiving an output signal of the light receiving element, wherein the receiving circuit is connected to the receiving circuit. An electrode, a connection pad for connecting the electrode to the bias circuit, and a conductor pattern having a predetermined inductance value disposed between the electrode and the connection pad. A light receiving module characterized by the above-mentioned.