JPH09307169A - Semiconductor laser module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high modulation degree by a small power signal by restraining power loss caused by a load resistance inserted to a laser diode chip in series in a semiconductor laser module wherein a micro-wave signal is directly input as a modulation signal. SOLUTION: This semiconductor laser module is provided with an input impedance matching circuit 8 wherein a bonding wire 3 and a microstrip line 4 for connecting a laser diode chip 2 and a modulation signal input terminal 6 are incorporated as a part of a constituent element in an inside of a module package 1 which contains a laser diode chip 2 and is provided with a modulation signal input terminal 6. Desirably, capacitance elements 81, 82 are connected between the bonding wire 3 and the microstrip line 4 and a ground. High transmission efficiency is obtained by matching input impedance in one or a plurality of frequency band regions by adjusting a fixed number of the circuit elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser module used in a direct modulation type optical communication system.

[0002]

2. Description of the Related Art In recent years, semiconductor laser modules have been
Applications to communication fields that handle signals in the microwave frequency range, such as TV and public communication, have been actively attempted, and practical use has begun. Among these, in short-to-middle distance transmission of several hundred meters to several kilometers where the accumulation of noise and signal distortion is small, a direct intensity modulation method in which a high frequency signal is directly input to a semiconductor laser module as a modulation signal and converted into an optical signal is known. It is advantageous in terms of facility simplicity and cost.

FIG. 2 shows an electrically equivalent circuit of a first configuration example of a conventional semiconductor laser module. In FIG.
1 is a module package, 2 is a laser diode chip, 3 is a bonding wire, 4 is a microstrip line, 5 is a DC bias circuit, 6 is a modulation signal input terminal, 7 is a transmission line having a specified characteristic impedance, and 10 is input impedance matching. For resistance.

First, a DC drive current is applied from the DC bias circuit 5 to excite and oscillate the laser diode chip 2. Next, a high frequency modulation signal is input from the modulation signal input terminal 6 to directly modulate the laser diode chip 2. Usually, the load of the laser diode chip 2 is several Ω, and the characteristic impedance of the transmission line 7 is 50Ω. Therefore, by inserting the load resistor 10, the transmission line 7
Matches the characteristic impedance of the input impedance and the input impedance of the semiconductor laser module.

Further, in the second configuration example of the conventional semiconductor laser module shown in FIG. 3, by inserting the LC type impedance matching circuit 9 and appropriately setting the LC circuit constant, the transmission line in a desired frequency band is obtained. The characteristic impedance of 7 and the input impedance of the semiconductor laser module are matched.

[0006]

However, in the above-mentioned first conventional structure, since the load resistance inserted in series is several times larger than the load of several Ω of the laser diode chip, a large amount of modulation signal power is required. Is consumed in the load resistance part. For this reason, the input power efficiency converted by the laser diode chip 2 is reduced, and the modulation degree is reduced.

For example, when the load of the laser diode chip is 3Ω and the load resistance is 39Ω, impedance matching is represented by the voltage standing wave ratio VSWR as shown in FIG.
Further, FIG. 5 shows a graph showing the optical output level at this time as a ratio of the modulation signal input current and the optical output power. As can be seen from FIG. 4, the load resistor 1 for input impedance matching
By inserting 0, VSWR becomes low and matching is realized. However, as can be seen from FIG. 5, since the power consumed by the resistor is large, the modulation signal power and output level that can be converted by the laser diode chip are low. Therefore, in order to obtain a desired degree of modulation, it is necessary to input a large modulation signal power, and as a result, it is necessary to newly install a pre-amplifier or to increase the gain of an existing pre-amplifier, resulting in a system complexity. This is a factor in increasing size, size, and cost.

Further, in the second conventional configuration, the bonding wire 2 and the microstrip line 3 function as an inductance component, which limits the frequency range that can be matched by the LC type impedance matching circuit 9 outside the module package. . FIG. 6 is a graph of frequency characteristics showing impedance matching by the voltage standing wave ratio VSWR, and FIG. 7 is a graph of frequency characteristics showing the optical output level at this time by the ratio of the modulation signal input current and the optical output power. is there. Since the impedance matching circuit 9 is inserted, VSWR is lowered and the modulation signal power that can be converted by the laser diode 2 is large.
Fig. 6 shows that a high optical output level can be realized at Hz.
And 7 However, since the bonding wire 3 and the microstrip line 4 have an electric length, due to these influences, a desired frequency range, for example, 120
Input impedance matching at 0 MHz cannot be realized.

Further, it is necessary to transmit signals in a plurality of bands in optical transmission of radio signals, but in this case, matching of input impedance and efficient modulation driving of the laser module become more difficult.

The present invention has been made to solve the above-mentioned conventional problems, and realizes input impedance matching in a single frequency band or a plurality of frequency bands, and obtains a high modulation degree with a small modulation signal power. It is an object of the present invention to provide a semiconductor laser module that can be used.

[0011]

In order to achieve this object, a semiconductor laser module of the present invention includes a laser diode chip and a laser diode chip inside a module package having a modulation signal input terminal. An input impedance matching circuit including a bonding wire connecting to a modulation signal input terminal and a microstrip line as constituent elements is provided.

[0012] Preferably, the input impedance matching circuit further includes a reactance element as a component, and the reactance element is connected between the bonding wire and the microstrip line and the ground side of the laser diode chip. For example, one end of a capacitance element that is a reactance element is
It is connected to the connection point between the bonding wire and the microstrip line, and the other end of the capacitance element is connected to the ground side (that is, the return line side) of the laser diode chip. An inductance element may be used instead of the capacitance element.

An optimum inductance value is obtained by controlling at least one of the wire diameter, the wire length, the number of bonding wires, and the bonding position of the bonding wire, and the input impedance matching circuit sets a desired frequency band. The input impedance matching at is achieved. At this time, not only impedance matching in a single frequency band, but impedance matching may be performed so that transmission efficiency becomes good in a plurality of frequency bands.

Since the input impedance matching circuit further includes a resistance element as a constituent element, and the resistance element is connected in series with the bonding wire and the microstrip line, the impedance of the laser diode chip varies. It is possible to suppress changes in the matching state and the drive current. However, from the viewpoint of suppressing the insertion loss, the resistance value of the resistance element is preferably 10Ω or less.

Furthermore, in addition to the above-mentioned input impedance matching circuit provided inside the module package,
A second input impedance matching circuit may be provided outside the module package, and both input impedance matching circuits may perform impedance matching in one or a plurality of frequency bands.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 shows an equivalent circuit of a semiconductor laser module according to Embodiment 1 of the present invention. In FIG.
The same circuit elements as those in FIG. 2 used to describe the conventional example are denoted by the same reference numerals. FIG. 1 differs from FIG. 2 in the following points. That is, the capacitance elements 81 and 82 as reactance elements are connected between both sides of the bonding wire 3 and the ground. The bonding wire 3 and the microstrip line 4 and the capacitance elements 81 and 82 form the input impedance matching circuit 8.

When a DC drive current is supplied from the DC bias circuit 5, the laser diode chip 2 is excited and oscillates. Then, by inputting a high frequency modulation signal from the modulation signal input terminal 6, the laser diode chip 2 can be directly modulated. Laser diode chip 2
Load of several Ω and characteristic impedance of transmission line 7 50 Ω
The input impedance matching circuit 8 has a function of achieving impedance matching with. That is, the characteristic impedance of the transmission line 7 and the load impedance of the laser diode chip 2 are matched in a desired frequency signal band by appropriately setting the constants of the respective elements forming the input impedance matching circuit 8.

Specifically, by adjusting at least one of the wire diameter, the wire length, the number of bonding wires, and the bonding position of the bonding wire 3, the series inductance value is changed and the characteristics of the input impedance matching circuit 8 are changed. Can be changed. Alternatively, the characteristics of the input impedance matching circuit 8 can be changed by changing the capacitance values of the capacitance elements 81 and 82 and further by changing the bonding wire and microstrip line side connection positions of the capacitance elements 81 and 82.

As a specific example, the capacitance of the capacitance element 81 is 4.5 pF and the capacitance of the capacitance element 82 is 7 pF.
FIGS. 8 and 9 show an example in which the input impedance is set to 1200 MHz and the input impedance is matched at 1200 MHz. FIG. 8 is a graph showing the impedance matching by the voltage standing wave ratio VSWR, and FIG. 9 is a graph showing the optical output level at that time by the ratio between the modulation signal input current and the optical output power. As can be seen from these graphs, VSWR <1.2 was obtained at the desired frequency of 1200 MHz, the optical output was also at a high level, and the modulation signal converted by the laser diode could be increased.

As described above, according to the present embodiment, by providing the input impedance matching circuit 8 inside the module package 1, the impedance is matched in a desired frequency band, and even a low power modulation signal input is performed. It is possible to realize a semiconductor laser module that can obtain a high optical output level and a large modulation degree.

In this embodiment, among the components of the input impedance matching circuit 8 provided inside the module package 1, two capacitances are used as reactance elements connected between the bonding wire 3 and the microstrip line 4 and the ground. Although the elements 81 and 82 are used, the number of reactance elements may be one or three or more, and an inductance element may be used instead of the capacitance element.

(Embodiment 2) Next, Embodiment 2 of the present invention
FIG. 10 shows an equivalent circuit of the semiconductor laser module according to the present invention. This circuit differs from FIG. 1 of the first embodiment in that a resistance element (hereinafter referred to as “load resistance”) 84 is inserted in series between the bonding wire 3 and the laser diode chip 2. The load resistor 84 has a function of suppressing changes in the matching state and changes in the drive current due to changes in the impedance of the laser diode chip 2.
That is, by setting the combined value of the impedance of the laser diode chip 2 and the resistance value of the load resistor 84 to a value that is sufficiently larger than the impedance of the laser diode, the impedance mismatch due to the variation of the impedance of the laser diode chip 2 is caused. Occurrence is suppressed.
In addition, an increase in second-order or third-order intermodulation distortion is suppressed. The value of the load resistance 84 is 10Ω or less, preferably 5Ω
It is better to do the following.

As described above, according to the semiconductor laser module of this embodiment, the input impedance matching circuit 8 including the resistance element 84 connected in series with the bonding wire 3 and the microstrip line 4 is provided inside the module package. As a result, impedance matching is performed in a desired frequency band, a large degree of modulation can be obtained even with a low power modulation signal input, and the occurrence of impedance mismatch when the operating state changes is suppressed.

The load resistance may be inserted not only between the bonding wire 3 and the laser diode chip 2 but also between the microstrip line 4 and the bonding wire 3, for example.

(Third Embodiment) Next, a third embodiment of the present invention.
FIG. 11 shows an equivalent circuit of the semiconductor laser module according to FIG. Compared to FIG. 10 of the second embodiment, in the present embodiment, the capacitance element 83 is further connected between the input side of the microstrip line 4 and the ground. According to such a configuration, by adjusting at least one of the wire diameter of the bonding wire 3, the wire length, the number of bondings, the bonding position, the mounting position and the inserting position of the capacitance elements 81, 82 and 83, two The input impedance can be matched in the frequency band.

As a specific example, the capacitance of the capacitance element 81 is 7 pF and the capacitance of the capacitance element 82 is 2.5 pF.
12 and 13 show an example in which the capacitance of the F and the capacitance element 83 is set to 4.5 pF and the input impedance matching is performed in two regions of 900 MHz and 1500 MHz. FIG. 12 is a graph showing the input impedance matching by the voltage standing wave ratio VSWR, and FIG. 13 is a graph showing the optical output level at that time by the ratio between the modulation signal input current and the optical output power. At 950 MHz, VSWR = 1.
At 6, 1500 MHz, VSWR = 1.4 was obtained, the optical output also became a high output level in both frequency regions, and the modulation signal converted by the laser diode could be increased.

As described above, according to the present embodiment, the input impedance matching circuit 8 is provided inside the package of the semiconductor laser module, and the input impedance matching can be realized so that the transmission efficiency becomes good in the two frequency bands. it can. It is also possible to further add an inductance element and a capacitance element to realize input impedance matching in three or more frequency bands.

(Fourth Embodiment) Next, a fourth embodiment of the present invention.
FIG. 14 shows an equivalent circuit of the semiconductor laser module according to the present invention. This circuit differs from the configuration of the first embodiment shown in FIG. 1 in that
The point is that a second input impedance matching circuit is provided outside the module package 1. In this case, in order to perform the input impedance matching in the desired frequency band, the constants of the input impedance matching circuits both inside and outside the module package 1 are adjusted.

Therefore, impedance matching in a frequency band, which is difficult to adjust only by the input impedance matching circuit inside the module package 1, is facilitated by using the second input impedance matching circuit together. In particular, it is effective when it is desired to realize input impedance matching in two or more frequency bands. in this way,
It is possible to realize a semiconductor laser module in which impedance is matched in any desired frequency band and a large modulation degree can be obtained even with a low power modulation signal input.

In the present embodiment, the second impedance matching circuit 9 provided outside the module package 1 is composed of a π-type circuit including one inductance element and two capacitance elements, but the present invention is not limited to this. A configuration may be adopted.

[0031]

As described above, according to the present invention, the input impedance matching circuit including the bonding wire and the microstrip line as the constituent elements is provided inside the module package, thereby realizing the input impedance matching in the desired frequency band. However, it is possible to provide a semiconductor laser module that can obtain a high degree of modulation with a small amount of modulation signal power.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of a semiconductor laser module according to a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of a semiconductor laser module according to Conventional Example 1.

FIG. 3 is an equivalent circuit diagram of a semiconductor laser module according to Conventional Example 2.

FIG. 4 is a graph showing a relationship between an input modulation signal frequency and VSWR in the semiconductor laser module of Conventional Example 1;

FIG. 5 is a graph showing the relationship between the input modulation signal frequency and the optical output power / input signal current ratio in the semiconductor laser module of Conventional Example 1.

FIG. 6 is a graph showing the relationship between the input modulation signal frequency and the VSWR in the semiconductor laser module of Conventional Example 2;

FIG. 7 is a graph showing the relationship between the input modulation signal frequency and the optical output power / input signal current ratio in the semiconductor laser module of Conventional Example 2.

FIG. 8 is a graph showing a relationship between an input modulation signal frequency and VSWR in the semiconductor laser module according to the first embodiment of the present invention.

FIG. 9 is a graph showing the relationship between the input modulation signal frequency and the optical output power / input signal current ratio in the semiconductor laser module according to the first embodiment of the present invention.

FIG. 10 is an equivalent circuit diagram of the semiconductor laser module according to the second embodiment of the present invention.

FIG. 11 is an equivalent circuit diagram of the semiconductor laser module according to the third embodiment of the present invention.

FIG. 12 is a graph showing the relationship between the input modulation signal frequency and VSWR in the semiconductor laser module according to the third embodiment of the present invention.

FIG. 13 is a graph showing the relationship between the input modulation signal frequency and the optical output power / input signal current ratio in the semiconductor laser module according to the third embodiment of the present invention.

FIG. 14 is an equivalent circuit diagram of a semiconductor laser module according to Embodiment 4 of the present invention.

[Explanation of symbols]

 1 Module Package 2 Laser Diode Chip 3 Bonding Wire 4 Microstrip Line 5 DC Bias Circuit 6 Modulation Signal Input Terminal 7 Transmission Line 8 Input Impedance Matching Circuit 9 Second Input Impedance Matching Circuit 81, 82, 83 Capacitance Element 84 Load Resistance

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Hiroyuki Asakura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (9)

[Claims] 1. A module package containing a laser diode chip and having a modulation signal input terminal includes a bonding wire and a microstrip line for connecting the laser diode chip and the modulation signal input terminal as constituent elements. A semiconductor laser module comprising an input impedance matching circuit. 2. The input impedance matching circuit further includes a reactance element as a constituent element, and the reactance element is connected between the bonding wire and the microstrip line and the ground side of the laser diode chip. 1. The semiconductor laser module described in 1. 3. The semiconductor laser module according to claim 1, wherein the input impedance matching circuit further includes a resistance element as a constituent element, and the resistance element is connected in series with the bonding wire and the microstrip line. 4. The semiconductor laser module according to claim 3, wherein the resistance value of the resistance element is 10Ω or less. 5. The semiconductor laser module according to claim 3, wherein the resistance element is connected between the bonding wire and the microstrip line and the laser diode chip. 6. An optimum inductance value is obtained by controlling at least one of a wire diameter, a wire length, a number of bonding wires, and a bonding position of the bonding wire, and the input impedance matching circuit obtains a desired frequency band. The semiconductor laser module according to any one of claims 1 to 3, wherein the input impedance matching in (3) is realized. 7. The input impedance matching circuit realizes input impedance matching in a desired frequency band by controlling the bonding wire and microstrip line side connection positions of the reactance element. The semiconductor laser module according to claim 1. 8. The semiconductor laser module according to claim 1, wherein the input impedance matching circuit is set to have good transmission efficiency in a plurality of frequency bands. 9. The semiconductor laser module according to claim 1, further comprising a second impedance matching circuit provided outside the module package.