JP3226696B2 - Semiconductor laser module with thermoelectric cooling element - Google Patents

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 for optical communication, and more particularly to a broadband semiconductor laser module used under high-speed modulation in the gigabit band.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open Nos. 4-267385 and 4-3376 disclose prior art related to a semiconductor laser module for optical communication.
The technology described in Japanese Patent Publication No. 88 and the like is known.

[0003] These prior arts focus only on the reduction of the parasitic inductance of the connection portion of the high-frequency signal input section in a case required for widening the bandwidth of the semiconductor laser module, and particularly under the high-speed modulation in the gigabit band. No consideration has been given to cavity resonances in the case where they occur.

[0004]

In the prior art, when a metal holder for holding an optical isolator or a condensing lens protrudes into a case and approaches a stem on which a semiconductor laser is mounted, a semiconductor laser module is not provided. In the small-signal frequency response characteristic, a capacitive dip of 3 dB or more occurs due to capacitive coupling through the space between the stem and the metal holder and cavity resonance inside the case, and the band is limited by the resonant dip. .

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art without deteriorating a cooling capacity characteristic which is a trade-off with a high frequency characteristic, and to provide a thermoelectric cooling without band limitation by a resonance dip in a small signal frequency response characteristic. An object of the present invention is to provide a semiconductor laser module with an element.

[0006]

According to the present invention, the above object is achieved by connecting a metal holder protruding into a case of a semiconductor laser module and a stem mounting a semiconductor laser with a conductive plate. A Kovar material having a low thermal conductivity is used as the conductive plate material, and a linear distance of 1 mm.
The length was set to 3 mm by making the dimension of mm a key shape.
As a result, the thermal resistance of the conductive plate material is made as large as possible, and the amount of heat flowing into the stem mounted on the thermoelectric cooling element is minimized, so that deterioration of the cooling capacity is minimized. The resonance dip in the small signal frequency response characteristic can be eliminated, and the 3 dB band can be improved.

[0007]

By connecting a metal holder protruding into the case of a semiconductor laser module and a stem on which a semiconductor laser is mounted by a conductive plate material, capacitive coupling via a space generated between the metal holder and the stem during high-frequency modulation, In addition, the cavity resonance inside the case can be prevented, and the 3 dB band can be improved without being limited by the resonance dip in the small signal frequency response characteristics. In addition, since the conductive plate material is made of Kovar material and the dimensions are set so that the thermal resistance is as large as possible, the amount of heat flowing into the stem mounted on the thermoelectric cooling element is minimized, Deterioration of the cooling capacity can be suppressed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a 2.5-inch optical isolator.
FIG. 2 is a cross-sectional view illustrating a configuration of a semiconductor laser module with a thermoelectric cooling element of the present invention for Gb / s.

The beam emitted from the semiconductor laser 1 is a first beam.
The light is converted into a parallel beam or a quasi-parallel beam by a lens 2, condensed by a second lens 4 via an optical isolator 3 for preventing external reflected return light, and is incident on an optical fiber 6 held by a ferrule 5 to be optically coupled. Is done. The semiconductor laser 1 includes a first lens 2, a monitoring photodiode 7 for monitoring backward emission light of the semiconductor laser 1, and a semiconductor laser 1.
Is mounted and fixed on a stem 9 together with a thermistor 8 for detecting the temperature of the light.

A stem 9 is mounted on a thermoelectric cooling element 10 for temperature control, and a holder 12 brazed to the wall of a case 11 by Ag.
Optical isolator 3 hermetically sealed and fixed with solder
The thermoelectric cooling element 10 is adjusted to a position where the optical axes of the second lens 4 and the first lens 2 integrated with each other are aligned, and is fixed in the case 11 by soldering.

The case 11 is a 14-pin butterfly type package using a ceramic substrate 13 for forming leads of a semiconductor laser module used at a modulation speed of 2.5 Gb / s. The RF signal input from the RF lead 14 is transmitted to the semiconductor laser 1 via the RF pattern 15 on the ceramic substrate 13 whose input impedance is set to 25Ω, the impedance matching resistor 16 with the semiconductor laser 1, the connection lead, and the like. Reach. The stem 9 of the semiconductor laser 1 whose p-side is grounded is connected to a ground pattern 17 electrically connected to the case 11 by a ground connection lead 18.

The workability when mounting the stem 9 in the case 11 and the distance between the holder 12 and the stem 9 are minimized so that the distance between the first lens 2 and the second lens 4 is minimized in order to suppress the deterioration of the optical coupling efficiency. The interval is 1 mm. Between the holder 12 and the stem 9, a lead 19 for capacitive coupling and cavity resonance prevention made of Kovar material (hereinafter abbreviated as cavity resonance prevention lead 19) is connected by soldering. This lead for preventing cavity resonance
The shape of No. 19 was key-shaped, 3 mm in length, 0.5 mm in width, and 0.2 mm in thickness.

FIGS. 2 and 3 show measured small signal frequency response characteristics of the semiconductor laser module without the cavity resonance preventing lead 19 (conventional product) and with the cavity resonance preventing lead 19 (this embodiment), respectively. (Laser bias = threshold current + 10 mA). As shown in FIG. 2, when the cavity resonance preventing lead 19 is not provided, the stem 9 on which the semiconductor laser 1 is mounted and the holder 9 are provided.
4dB around 2.2GHz due to cavity resonance between 12
And a 3 dB bandwidth of 2.1 G
3, the resonance dip is eliminated and the 3 dB bandwidth is improved to 4.2 GHz when the cavity resonance preventing lead 19 shown in FIG. 3 is provided.

FIGS. 4 and 5 show light passing through the fourth-order Bessel filter of the semiconductor laser module without the cavity resonance preventing lead 19 (conventional product) and with the cavity resonance preventing lead 19 (this embodiment), respectively. The transmission waveform measurement diagram is shown (2.5
Gb / s, laser bias = threshold current, signal amplitude = 40
mAp-p). Compared to the case without the cavity resonance preventing lead 19 of FIG. 4, the optical transmission waveform with the cavity resonance preventing lead 19 of FIG. 5 has a small rise and fall jitter, a large eye opening, and is improved. I understand.

When the thermoelectric cooling element 10 is cooled, that is, the stem 9 (low temperature side) on which the semiconductor laser 1 is mounted is cooled, the amount of heat absorbed by the thermoelectric cooling element 10 and the thermoelectric cooling element 10 The Joule heat generated
(High temperature side) and is radiated to the external heat sink. The cooling capacity of the semiconductor laser module is represented by the difference between the high temperature and the low temperature. In the case of the present embodiment, as compared with the conventional semiconductor laser module without the cavity resonance preventing lead 19, the holder 12 brazed to the case 11 on the high temperature side by Ag brazing and the low temperature side through the cavity resonance preventing lead 19 The temperature on the low-temperature side rises due to the amount of heat flowing into the stem 9, so that the cooling capacity deteriorates. In order to minimize the deterioration of the cooling capacity, the cavity resonance preventing lead 19 is made of a Kovar material having a low thermal conductivity, and the length dimension is set as described above so that the thermal resistance is as large as possible. The thermal conductivity of Kovar material is 16.7 W / m · ° C., for example, 393 W / m of copper.
-About 1/24 of ° C. The thermal resistance r is calculated by using the length l, thickness t, width W, and thermal conductivity λ of the lead as r = 1 / (tW · λ).
When the length of the cavity resonance preventing lead 19 is set to a key shape and the length is set to 3 mm as in the present embodiment, as compared with the case where the length of the cavity resonance preventing lead 19 is set to 1 mm of the linear distance,
3 times. The amount of heat Q flowing into the stem 9 via the cavity resonance preventing lead 19 is obtained from Q = (Th−Tc) / r using the high temperature side Th, the low temperature side Tc, and the thermal resistance r. When the length of the cavity resonance preventing lead 19 is set to 3 mm from 1 mm, the length is reduced to 1/3. As a result, the measured cooling capacity of the semiconductor laser module of the present embodiment could be kept at 1 ° C. or less as compared with the conventional product without the cavity resonance preventing lead 19.

[0017]

As described above, according to the present invention, the deterioration of the cooling capacity can be kept at 1 ° C. or less, the cavity resonance generated in the case at the time of high frequency modulation can be prevented, and the small signal frequency response characteristic can be improved. The 3 dB band can be improved without being limited by the band due to the resonance dip.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the configuration of one embodiment of the present invention.

FIG. 2 is an actual measurement diagram of a small signal frequency response characteristic of a conventional product.

FIG. 3 is an actual measurement diagram of a small signal frequency response characteristic of the present embodiment.

FIG. 4 is an actual measurement diagram of an optical transmission waveform of a conventional product.

FIG. 5 is an actual measurement diagram of an optical transmission waveform according to the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... 1st lens, 3 ... Optical isolator, 4 ... Second lens, 5 ... Ferrule, 6 ... Optical fiber, 7 ... Monitor photodiode, 8 ... Thermistor,
9 ... stem, 10 ... thermoelectric cooling element, 11 ... case, 12 ... holder, 13 ... ceramic substrate, 14 ... RF lead, 15 ... RF
Pattern, 16: Resistance for impedance matching, 17: Ground pattern, 18: Lead for ground connection, 19: Lead for preventing cavity resonance.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-359207 (JP, A) JP-A-5-323158 (JP, A) JP-A-4-337688 (JP, A) 8511 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/42-6/43 G02B 6/26-6/27 G02B 6/30-6/35

Claims (3)

(57) [Claims] 1. A semiconductor laserWhen, Thermoelectric cooling element for controlling the temperature of the semiconductor laserWhen,  Mounted on the thermoelectric cooling element,The semiconductor laserTo
Equipped stemWhen, Said A lens that collects light emitted from a semiconductor laser
When, The lens is fixed and projects inside the case.
Metal holderWhen,  Conductive plate material for connecting the stem and the metal holderAnd
Have The conductive plate material has a key shape Characterized by semiconductive
Body laser module. 2. The method according to claim 1 , wherein the conductive plate material is 20
A semiconductor laser module with a thermoelectric cooling element, which is formed of a material having a thermal conductivity of W / m · ° C. or less. 3. A process according to claim 1 or in claim 2, the semiconductor laser module with thermionic cooling device, characterized in that the optical isolator is a metal holder which protrudes into the case is inserted and fixed.