JPH0557748B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device, and particularly to a semiconductor laser device incorporating a thermoelectric cooling element useful as a light source for an optical communication system.

[Conventional technology]

Generally, since a semiconductor laser is a threshold device, the decrease or deterioration of optical output is accelerated as the temperature rises. On the other hand, a change in ambient temperature causes a change in oscillation characteristics, such as murd hopping or a center wavelength shift. Therefore, when used as a light source for an optical communication system, transmission characteristics deteriorate on the high-temperature side or on the low-temperature side.

Conventionally, this type of semiconductor laser device has a temperature range of -10°C to
In order to obtain stable operation in a temperature range of approximately 60℃,
A semiconductor laser device has an electronic cooling element inside it to control the semiconductor laser element and laser light monitoring element to a constant temperature (usually 25°C).

A conventional semiconductor laser device of this type has a structure shown in FIG.

As shown in FIG. 3, the conventional semiconductor laser device includes a semiconductor laser element 4, a laser beam monitor element 5,
It is equipped with an optical fiber coupling lens 3 coupled to an optical fiber 6 and a thermistor 8 for temperature measurement,
semiconductor laser element 4, laser light monitor element 5,
The optical fiber coupling lens 3 and the temperature measurement thermistor 8 are placed at predetermined positions on the mounting block 2, and are in close contact with the cool surface of a thermoelectric cooling element (approximately the same shape as the mounting block, not shown) consisting of a Peltier element. Fixed. On the other hand, the hot surface of the electronic cooling element is tightly fixed to the bottom surface of the airtight package 1.

On the other hand, each terminal of the semiconductor laser element 4, laser light monitoring element 5, thermometer side thermistor 8, and electronic cooling element 7 is connected to each terminal of the confidential package 1.
They are connected as shown in FIG.

[Problem to be solved by the invention]

In the conventional semiconductor laser device described above, the mounting block 2 on which the semiconductor laser element 4 is mounted and the airtight package 1 are connected by a wire rod with a diameter of about 0.2 mm in order to improve the cooling efficiency by the electronic cooling element. , is used as an anode terminal of the semiconductor laser device 4. Therefore, when used as a light source for an ultrahigh-speed optical communication system with an operating speed exceeding 1 Gb/s, parasitic Due to the parallel resonance of the inductance and the impedance of the electronic cooling element 7, the electrical grounding characteristics become insufficient. Therefore, as shown in FIG. 4, in an operating range exceeding 1 GHz, there is a problem that the modulation characteristics (small signal frequency characteristics) are not flat, and the modulation characteristics deteriorate significantly at the parallel resonance frequency.

Conventionally, in a semiconductor laser device having such a thermoelectric cooling element, it is possible to avoid the above-mentioned problems and
As a measure to enable modulation to the ultra-high speed range exceeding Hz, we reduced the lead length of each terminal and internal wiring length to about 2 to 3 mm, suppressed the parasitic inductance of each terminal as much as possible, and installed There have been reports of attempts to reduce the total parasitic inductance as much as possible by increasing the number of grounding wires between the power block and the hermetic package. (For example, Hiroyuki Nakano et al., “Dual-In
−Line Laser Diode Module for Fiber−Optic
"Transmission Up to 4Gb/s" IEEE Journal
of Lightwave Technology, vol.LT-5, No.
10, 1987 pp1403-1411) However, although reducing parasitic inductance by increasing the number of grounding wires as described above is very effective in improving grounding characteristics,
Since the amount of heat radiated by the electronic cooling element that circulates back into the semiconductor laser element 4 via the leads increases, there is a problem in that the cooling efficiency is significantly degraded.

[Means to solve the problem]

According to the present invention, there is provided a semiconductor laser element, a mounting block on which the semiconductor laser element is firmly mounted, an airtight package in which the mounting block is housed and is provided with a plurality of terminals, and a mounting block fixed to the inner surface of the airtight package. , a semiconductor characterized in that the mounting block has an electronic cooling element mounted and fixed thereon, and an anode terminal of the semiconductor laser element and a predetermined terminal of the airtight package are connected via a resistor. A laser device is obtained.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

Referring to FIGS. 1a and 1b, the semiconductor laser element 4, the laser beam monitor element 5, the optical fiber coupling lens 3, and the thermistor 8 for the thermometer side are tightly fixed at predetermined positions on the mounting block 2, and mounted. The bottom surface of the storage block 2 is tightly fixed to the cool surface of the electronic cooling element 7. The hot surface of the electronic cooling element 7 is tightly fixed to the bottom surface of the airtight package 1.

On the other hand, each terminal of the laser light monitoring element 5, the temperature measurement thermistor 8, and the electronic cooling element 7 is connected to a predetermined terminal of the airtight package 1, and the cathode terminal of the semiconductor laser element 4 is connected to a predetermined terminal of the airtight package 1. , Also, the anode terminal of the semiconductor laser element 4 (also serves as the ground for the mounting block 2)
is connected to the lead of the hermetic package 1 via a resistor 9 formed on the connection stitch of the hermetic package 1. In this embodiment, the resistance value of the resistor 9 was set to 15Ω.

Here, an equalization circuit of a conventional semiconductor laser device is shown in FIG. 5a. In Figure 5a, Ll2 is the parasitic inductance of the cathode terminal of the semiconductor laser module, Cp2 is the parasitic capacitance parasitic of the stitch of the cathode terminal of the semiconductor laser module, Lw2
is the parasitic inductance of the internal wiring stitch of the cathode terminal of the semiconductor laser module, Css is the parasitic capacitance of the cathode wiring stitch of the carrier that mounts the semiconductor laser element, Lb2 is the parasitic inductance of the bonding wire for the cathode wiring of the semiconductor laser element, and Ch is the parasitic inductance of the cathode wiring bonding wire of the semiconductor laser element. The parasitic capacitance of the heat sink of the semiconductor laser device, RLD is the resistance (differential resistance) component of the semiconductor laser device, CLD is the capacitance component of the semiconductor laser device, Lb1 is the parasitic inductance of the bonding for the anode wiring of the semiconductor laser device,
Lw1 is the parasitic inductance of the bonding wire connecting the anode of the semiconductor laser module and the package, Ll1 is the parasitic inductance of the anode terminal of the semiconductor laser module, Cp1 is the parasitic capacitance of the stitch of the anode terminal of the semiconductor laser module, Zp is the impedance of the electronic cooling element. Note that the resistor 9 shown in FIG.
Expressed in Rs, this Rs is Lb1 in Figure 5a.
and Lw1.

As shown in FIG. 5b, Zp is represented by the series connection of capacitors C ₁ and C ₂ and resistor R ₁ . Here, C ₁
is the parasitic capacitance of the hot-side substrate of the thermoelectric cooler, C ₂
is the parasitic capacitance of the cool side substrate of the thermoelectric cooler, R ₁
is the resistance component of the metallized pattern and the Peltier element.

Referring now to FIG. 5a, in the conventional semiconductor laser device, the circuit on the anode grounding side of the semiconductor laser element is simplified as shown in FIG. 5c. Here, if the parasitic capacitance of the electronic cooling element is C, then C={(1/C ₁ )+(1/C ₂ )} ⁻¹ . Cp1 is the capacitance parasitic to the stitches of the package,
Since the value is about 0.2 pF, it can be ignored when calculating the approximate formula for parallel resonance. If Cp1 is ignored, the parasitic capacitance C of the electronic cooling element and the grounded anode inductance of the semiconductor laser element will form a parallel resonant circuit. When the impedance at the time of parallel resonance is Z ₁ , Z ₁ approximately becomes (Lw1+Ll1)/R ₁ C.

By the way, in the present invention, in order to suppress parallel resonance, a series resistor Rs is connected between Lw1 and Ll1, so in the present invention, impedance Z ₂ at the time of parallel resonance is approximately Z ₂ = {R ₁ R ₂ / (R ₁ + R ₂ )} + {(Lw1 + Ll1) / C (R ₁ + R ₂ )}.

As an example, Lw1+Ll1=1nH, C=5pF, R ₁
= 2Ω, R ₂ = 10Ω, Z ₁ = 100Ω, Z ₂ = 18.3Ω
becomes. It can be seen that by adding a series resistor as described above, the ground impedance of the semiconductor laser element can be reduced to 1/5 or less during parallel resonance. In this way, by lowering the ground impedance during parallel resonance, it is possible to suppress the depression in the frequency characteristics that has been a problem in conventional semiconductor laser devices.

As shown in FIG. 2, this configuration eliminates the modulation characteristic defects that occurred in the vicinity of 1.5 GHz due to the parasitic inductance of the leads and the parallel resonance of the electronic cooling element 7 in the conventional configuration. We were able to improve the modulation characteristics to a flat one. Furthermore, the cooling efficiency was the same as that of the conventional configuration.

In this embodiment, the resistor 9 is provided at the connecting stitch of the airtight package 1, but the same effect can be obtained even if the resistor is provided on the mounting block side.

Furthermore, as a simple method, a similar improvement effect can be obtained by inserting a chip resistor with good frequency characteristics in series between the anode terminal of the semiconductor laser element 4 and the terminal of the airtight package 1.

Furthermore, if the cooling efficiency is not so important, it is also possible to increase the number of ground wires by arranging the resistors at several locations. in this case,
A semiconductor laser device with even better modulation characteristics can be obtained.

〔Effect of the invention〕

As described above, in the present invention, by connecting the mounting block on which the semiconductor laser element 4 is mounted and the airtight package via the resistor, the parasitic inductance of the connection lead can be reduced without deteriorating the cooling efficiency. This has the effect that poor modulation characteristics caused by parallel resonance of the impedance of the thermoelectric cooling element are improved, the modulation characteristics are flattened, and a semiconductor laser device that can operate up to several GHz can be realized.

[Brief explanation of the drawing]

FIGS. 1a and 1b are a top view and a cross-sectional view, respectively, showing an embodiment of a semiconductor laser device according to the present invention;
FIG. 2 is a diagram showing the frequency characteristics of the semiconductor laser device according to the present invention, FIG. 3 is a diagram showing the conventional semiconductor laser device, FIG. 4 is a diagram showing the frequency characteristics of the conventional semiconductor laser device, and FIG. 5a is a diagram showing an equalization circuit of a conventional semiconductor laser device, FIG. 5b is a diagram showing a Zp equalization circuit in the equalization circuit shown in FIG. 5a,
FIG. 5c is a diagram showing the anode side circuit of the semiconductor laser device in FIG. 5a. DESCRIPTION OF SYMBOLS 1... Airtight package, 2... Mounting block, 3... Optical fiber coupling lens, 4... Semiconductor laser element, 5... Laser light monitoring element, 6...
...Optical fiber, 7...Electronic cooling element, 8...Thermistor for temperature measurement, 9...Resistor.

Claims (1)

[Claims] 1 A semiconductor laser element, a mounting block on which the semiconductor laser element is fixedly mounted, an airtight package in which the mounting block is housed and is provided with a plurality of terminals, and an airtight package fixed to the inner surface of the airtight package, in which the mounting block is fixedly mounted. What is claimed is: 1. A semiconductor laser device comprising a fixed electronic cooling element, wherein an anode terminal of the semiconductor laser element and a predetermined terminal of the airtight package are connected via a resistor.