JPH03201494A - Electronic type cooling element built-in semiconductor laser assembly - Google Patents

Abstract

PURPOSE:To keep a semiconductor laser assembly stable in temperature and high in operation speed by a method wherein not only electrical wire connections are lessened in inductance but also an electronic type cooling element is apparently decreased in parasitic electrostatic capacity. CONSTITUTION:In a semiconductor laser assembly, an LD chip 26 is connected to assembly terminals 28 and 30 with wires 32 and 34 shortened in length. A capacitor 36 smaller than an equivalent electrostatic capacitor Co in capacity is added in series to the capacitor Co, whereby the resultant capacity becomes smaller than that of the capacitor 36, and a resonant frequency induced by the resultant electrostatic capacitor of the equivalent electrostatic capacitor Co and the capacitor 36 and the inductance of the wire 34 can be increased higher than a modulation frequency band. In result, an optical output can be prevented from being distorted in waveform, and a light source can be stabilized in temperature.

Description

[Detailed Description of the Invention] Summary Regarding a semiconductor laser assembly with a built-in electronic cooling element, the present invention aims to provide a semiconductor laser assembly that achieves both temperature stabilization and high speed performance of the semiconductor laser, and the present invention relates to a semiconductor laser assembly with a built-in electronic cooling element. In the semiconductor laser assembly with a built-in electronic cooling element, the conductive member is fixed to one surface of the electronic cooling element, and the other surface of the electronic cooling element is fixed to the inner surface of a metal casing. The wall of the metal casing in which the cooling element is mounted and fixed is divided into three parts: a central part where the electronic cooling element is mounted and a pair of end parts, and a dielectric material is placed between the central part and each end part. Constructed by interposing members.

FIELD OF THE INVENTION The present invention relates to a semiconductor laser assembly with a built-in electronic cooling element.

In an optical communication system, a semiconductor laser (hereinafter referred to as LD) is generally modulated with a time-series electric signal, and the modulated light is guided through a lens system to an optical fiber serving as a transmission path. The LD is usually provided as an LD assembly by being integrated with a lens placed immediately in front of the LD.
The D assembly is integrated with a conventional lens system and a connecting optical fiber and used as an LD module.

Since the characteristics of optical elements such as LDs used in such LD modules are easily affected by temperature, it is desirable to operate them under a constant temperature environment using an electronic cooling element such as a Peltier element.

In addition, with the recent demand for faster optical communication systems, L
It has become necessary to modulate D at a speed of about 10 Gb/S or higher while maintaining its reliability. For this reason, an LD assembly is provided in which an LD, an electronic cooling element such as a Peltier element, and related parts are hermetically sealed inside a single metal casing. Because we prioritized temperature stabilization,
The high-speed modulation characteristics of the LD cannot be said to be good. Therefore, L.D.
There is a need for a semiconductor laser assembly that can achieve both high-speed modulation characteristics and temperature stabilization of the LD using an electronic cooling element.

Conventional technology FIG. 4 shows a cross-sectional view of a conventional LD assembly.

1 is an LD chip, which is mounted and fixed on a stem 2 made of a conductive member such as metal. The stem 2 is mounted on a Peltier element 3. The Peltier element 3 is constructed by forming conductive patterns on two ceramic substrates 4.5, and sandwiching a plurality of semiconductors 6 having the Seebefuch effect between the ceramic substrates 4.5. One ceramic substrate 4 is in surface contact with the stem 2, while the other ceramic substrate 5 is fixed to the inner surface of the metal casing 7 by surface contact. By mecrizing the ceramic substrate 4.5, the metal casing 7 and the ceramic substrate 5 are joined together, and the ceramic substrate 4 and the stem 2 are joined together by soldering.

The metal casing 7 is provided with at least a signal input lead 8 and a ground lead 10 connected to the casing 7, and the signal input lead 8 is connected to an LD drive circuit (not shown). The signal input lead 8 is connected to the LD chimp 1 via a wire 9, and the ground lead 10 is connected to the stem 2 via a wire 11. ↓ 2 is an insulating material such as glass or Teflon for insulating the signal lead 8 from gold and the manufactured housing 7. The LD chip 1 mounted on the stem 2 is driven via the signal human power lead 8, the wire 9.11, and the earth lead IO.

However, when the Peltier element 3 is driven by controlling the voltage and current values applied to the electrodes of the Peltier element 3, thermal energy is carried in one direction by the Peltier element 3, creating a temperature difference between the ceramic substrates 4 and 5. The LD chip 1 is cooled to an appropriate operating temperature.

Problems to be Solved by the Invention However, in a semiconductor laser assembly having the above-mentioned configuration, when the modulation signal of the semiconductor laser is made high-speed, there is a mismatch in electrical impedance caused by the inductance of the electrical connection, and a problem arises between the inductance and the electronic There is a problem in that resonance within the modulation band occurs due to the parasitic capacitance of the type cooling element, and the optical output waveform from the semiconductor laser is disturbed.

To avoid these phenomena, it is possible to shorten the electrical connection and reduce its inductance. but,
With this solution, the parasitic capacitance of the electronic cooling element remains, making it difficult to raise the resonant frequency outside the modulation band. Therefore, simply shortening the electrical connection results in an insufficient optical output waveform.

As explained above, in conventional semiconductor laser assemblies, there is a problem in that when priority is given to stabilizing the temperature of the semiconductor laser, high speed performance has to be sacrificed.

The present invention has been made in view of the above points, and an object thereof is to provide a semiconductor laser assembly with a built-in electronic cooling element that achieves both temperature stabilization and high speed of the semiconductor laser. .

Means for Solving the Problems The present invention not only reduces the inductance of electrical connections as in the past, but also reduces the apparent parasitic capacitance of the electronic cooling element, thereby achieving temperature stability. It is designed to achieve both speed and speed. The principle of the present invention is expressed by the overall circuit diagram of the semiconductor laser assembly of the present invention using the parasitic capacitance equivalent circuit of the electronic cooling element shown in FIG. 2 and this equivalent circuit shown in FIG. explain.

Referring to FIG. 2, the electronic cooling element 14 has p-type and p-type B]2T between the ceramic substrates 16 and 18.
It is configured by alternately disposing semiconductors 20 such as C3, and a conductive pattern for connecting adjacent p-type and p-type semiconductors 20 is formed on the inner surface of the ceramic substrate 16.18. , two electrodes 22,24 are provided for connection to a power source. A current is passed in a fixed direction through the alternately arranged p-type and p-type semiconductors 20 to generate a temperature difference between the upper surface 18a of the ceramic substrate 18 and the lower surface 16a of the ceramic substrate 16 due to the Seebeck effect. That is, when a current is passed in the direction of the arrow shown in the figure, the upper surface 18a
The lower surface 16a can be set as the heat absorbing side and the lower surface 16a as the heat generating side, and by reversing the direction of the current, the relationship between the heat absorbing side and the heat generating side can be reversed.

As mentioned above, when considering the electronic cooling element as a parasitic factor to a high-speed circuit, the ceramic substrate 16°18 is a capacitor with a capacitance C2, C2 determined by the relative dielectric constant ε1, area S, and thickness d. The semiconductor 20 can also be expressed as a series connection of a pure resistor and an inductor. A simple calculation shows that in an actual electronic cooling element, the former is more dominant than the latter, and the equivalent circuit is written as a nearly pure capacitor C8, as shown on the right in Figure 2. can be expressed.

Here, Co = CI C2/ (CI + C2
).

Next, referring to FIG. 3, there is shown an overall equivalent circuit of the semiconductor laser assembly according to the present invention expressed using the equivalent circuit of FIG.
A wire 32. with a shorter connection length is connected between the i-child 28 and 30.
34 are connected to each other. The present invention is characterized in that the high frequency characteristics of the LD assembly are improved by connecting in series a capacitance 36 smaller than C8 to the ground potential side of the equivalent capacitance co of the electronic cooling element. Note that if the capacitor 36 is inserted on the light source side of the equivalent capacitance C8, heat from the LD chip 26 will be transferred via the capacitor 36, but the insulation that forms the capacitor Since the thermal conductivity of the body is low, the temperature stability of the LD chip 26 deteriorates. Therefore, the capacitance 36 needs to be inserted on the ground potential side of the equivalent capacitance C8.

By adding a smaller capacitance 36 in series with the working equivalent capacitance C8, their combined capacitance becomes smaller than the capacitance 36, so the equivalent capacitance C8 and the capacitance It becomes possible to raise the resonant frequency generated by the combined capacitance of the capacitor 36 and the inductance of the wire 34 to outside the modulation band. As a result, disturbances in the optical output waveform can be suppressed, and at the same time, temperature stabilization of the light source can be achieved.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view of an LD assembly 38 according to an embodiment of the present invention, in which an LD chip 40 is mounted and fixed on a stem 42 made of a conductive material such as metal.
is mounted on the Beltier element 44. Beltier element 4
4 forms a conductive pattern connecting adjacent n-type and p-type semiconductors 45 arranged alternately on the inner surfaces of two ceramic substrates 46 and 48, and the ceramic substrates 46 and 48 are semiconductors having a Seebefuch effect. 45 on both sides. One ceramic substrate 48 is in surface contact with the stem 42, while the other ceramic substrate 46 is fixed by surface contact to the inner surface of a metal casing 50 made of Kovar or the like. By metallizing the ceramic substrates 46 and 48, the metal housing 50 and the ceramic substrate 46 can be joined together, and the ceramic substrate 48 and the stem 42 can be joined together.
This is done by soldering.

As shown in the figure, the bottom wall of the metal casing 50 is divided into three parts: a central portion 50a and a pair of end portions 50b.
A dielectric member 52 made of aluminum nitride (AfN4), alumina (A1203), etc. is interposed between the center portion 50a and each end portion 50b. The bonding between the portion 50b and the dielectric member 52 is performed by metallizing the dielectric member 52 and then using, for example, Ag.
- This is done by brazing Cu. Further, a radiation fin 54 is fixed on the outer surface of the central portion 50a.

The metal casing 50 is provided with at least a signal input lead 56 and a ground lead 58 connected to the casing 50, and the signal input lead 56 is connected to an LD drive circuit (not shown). The signal input lead 56 is connected to the LD chip 40 via a wire 60, and the ground lead 58 is connected to the stem 42 via a wire 62. 64 is an insulating material such as glass or Teflon for insulating the signal input lead 56 from the metal casing 50. The LD chip 40 mounted on the stem 42 is driven via a signal human power lead 56, wires 60 and 62, and a ground lead 58.

Further, the end portions 50b of the bottom wall of the metal housing 50 are attached to each of the pair of assembly mounting plates 66, 68 by screws 70 at a sufficient distance from the end surface of the assembly mounting plates 66, 68 to the radiation fins 54. ing. As shown, the end portion 50b is attached to the assembly mounting plate 66 such that the central portion 50a of the bottom wall of the metal housing 50 is galvanically isolated from the end portion 50b by the dielectric member 52.
By attaching it to 68, the dielectric member 52 can function as a capacitor.

Note that the heat passing through the Beltier element 44 is radiated from the heat sink 54. A sufficiently large insulating layer (formed of gas or dielectric material as shown) is formed between the heat sink 54 and the assembly mounting plate 66.68, and the insulation layer is formed between the heat sink 54 and the assembly mounting plate 66.68. It is necessary to prevent direct current coupling between the dielectric members 52 and 52, and to minimize the value of the capacitance that will be added in parallel to the capacitance formed by the dielectric member 52.

In the above-described embodiment, the thermal target of the Bertier element is only a high-speed modulated light source, but for example, when a light source drive circuit is provided near the light source to improve electrical impedance characteristics, heat generated by sources other than the light source may be used. Even when an object is to be treated as a thermal object, the high frequency characteristics of the light source can be maintained at the same level by mounting a better-performing Vertier element and forming the bottom surface of the LD assembly housing exactly the same as in the above-mentioned embodiment. be able to.

Effects of the Invention Since the semiconductor laser assembly of the present invention is constructed as described in detail above, it has the effect of achieving appropriate temperature stabilization of the semiconductor laser without degrading the high-speed modulation characteristics of the semiconductor laser.

[Brief explanation of drawings]

Fig. 1 is a sectional view of an embodiment of the present invention, Fig. 2 is an equivalent circuit diagram of parasitic capacitance of an electronic cooling element, and Fig. 3 shows the principle of the present invention expressed using the equivalent circuit of Fig. 2. The circuit diagram and FIG. 4 are sectional views of a conventional example. 14.44...Electronic cooling element (Peltier element) 26
．． 40... LD chip, co... Parasitic capacitance, 36... Additional capacitance, 50... Metal casing, 50a... Center portion, 50b... End portion, 52 ...Dielectric member, 54...Radiating fin, 66.68... Assembly mounting member.

Claims (1)

[Claims] 1. A semiconductor laser (40) is mounted and fixed on a conductive member (42), and the conductive member (42) is connected to an electronic cooling element (42).
4) and an electronic cooling element (44).
) in a semiconductor laser assembly with a built-in electronic cooling element, the other surface of which is fixed to the inner surface of a metal housing (50), the metal housing (50) has the electronic cooling element (44) mounted and fixed thereon;
) is divided into three parts: a central part (50a) equipped with an electronic cooling element (44), and a pair of end parts (50b);
A semiconductor laser assembly with a built-in electronic cooling element, characterized in that a dielectric member (52) is interposed between the central portion (50a) and each end portion (50b). 2. Heat dissipation fins (
54), and a pair of assembly mounting plates (66, 68), respectively.
2. The method for attaching a semiconductor laser assembly with a built-in electronic cooling element according to claim 1, wherein each of the end portions (50b) is attached at a sufficient distance from the end face of the semiconductor laser assembly (68) to the radiation fin (54).