Coherent light generators – Particular temperature control
Reexamination Certificate
1998-01-08
2001-01-30
Bovernick, Rodney (Department: 2874)
Coherent light generators
Particular temperature control
C372S038100, C372S038080, C385S092000
Reexamination Certificate
active
06181718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser module with an electronic cooling device, and more particularly to a semiconductor laser module of a direct modulation system in which a high-frequency input signal is modulated directly into an optical signal.
2. Description of the Prior Art
In recent years, the semiconductor laser module has been under energetic attempts for applications to such communication fields as CATV and public communication that deal with signals of microwave/semi-microwave frequency range, giga bit high-speed digital signals, and other high-speed modulation signals, so that the semiconductor laser module has begun to be put into practical use. Particularly for short-and middle-distance transmission ranging from several hundreds of meters to several kilometers involving less accumulation of noise and signal distortions, the direct intensity modulation system in which a high-frequency signal is modulated directly into an optical signal as a modulation signal is suitable. In such a semiconductor laser module, oscillation characteristics of the semiconductor laser have a large temperature dependency, so that shifts of threshold current density or oscillation wavelength may take place depending on temperature variation. Therefore, in order to obtain a stable laser oscillation, it is essential to maintain laser diodes at a constant temperature. Thus, cooling devices such as a Peltier-element electronic cooling device is used to control the temperature of the laser diodes.
In prior-art semiconductor laser modules, module components such as the electronic cooling device and the ground line form a resonance circuit. For example, as shown in
FIG. 20
, the circuit resonates with an input modulation signal in a frequency band around 1.6 GHz, causing in some cases a phenomenon that the optical frequency response level would lower.
For this reason, in public communications in which frequencies close to the aforementioned frequency band such as 1.5 GHz band or 1.9 GHz band are frequently used, or in high-speed digital communications in which transmission rates close to the aforementioned frequency band are used, it has been difficult for such semiconductor laser modules to ensure a sufficient modulation signal.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor laser module with an electronic cooling device in which the resonance frequency of the semiconductor laser module is shifted so as to prevent the lowering of optical frequency response level in bands employed for public communications.
As a result of keen examinations, the inventors have found that the above object can be achieved by changing the inductance of a ground line between a module package and a chip-mounted carrier, thereby shifting the resonance frequency of the resonance circuit including the ground line so as to deviate the resonance frequency from the frequency band of public communications employed by a modulation signal transmission device, and thus completed the present invention.
Therefore, the present invention provides a semiconductor laser module with an electronic cooling device, comprising at least: a semiconductor laser diode; a chip-mounted carrier on which the semiconductor laser diode is mounted; and electronic cooling device on which the chip-mounted carrier is mounted, and which absorbs heat from the chip-mounted carrier; a module package in which the electronic cooling device is mounted on its inner bottom portion and from which the heat absorbed by the electronic cooling device is released; a modulation signal transmitting device operable to an input modulation signal of a specified frequency to the semiconductor laser diode; and a ground line for electronically connecting the module package and the chip-mounted carrier to each other; wherein an inductance of the ground line is changed so that resonance frequency of a resonance circuit made up by including the ground line is shifted so as to deviate from a specified frequency band used by the modulation signal transmitting device.
In the resonance circuit generated in the semiconductor laser module with an electronic cooling device, the resonance frequency of the resonance circuit can be changed by changing the inductance of the ground line that connects the module package and the chip-mounted carrier to each other. As a result, the resonance frequency can be shifted to a higher band or a lower band so as to deviate from the frequency band of public communications used in semiconductor laser module, by which the optical frequency response level in the frequency band used for public communications can be prevented from lowering.
Preferably, the chip-mounted carrier and the module package are electrically conductive.
Also, the present invention provides a semiconductor laser module with an electronic cooling device, wherein the ground line comprises a conductive first connecting device projectively extending from an inner bottom portion of the module package to near the chip-mounted carrier and having a large cross-sectional area, and a conductive second connecting device functioning to connect the first connecting device and the chip-mounted carrier to each other having a small cross-sectional area, and wherein the inductance of the ground line is reduced so that the resonance frequency is shifted to a band higher than the frequency band.
With the arrangement that the ground line comprises a conductive first connecting device projectively extending directly from an inner bottom portion of the module package to near the chip-mounted carrier and having a large cross-sectional area, and a conductive second connecting device operable to connect the first connecting device and the chip-mounted carrier to each other and having a small cross-sectional area, and by virtue of the large cross-sectional area of the first connecting device a parasitic inductance generated in the ground line can be reduced. Besides, since the first connecting device projectively extends to near the chip-mounted carrier, the distance between the first connecting device and the chip-mounted carrier is shortened, so that the second connecting device even with a small cross-sectional area can be reduced in length, with the result of a reduced parasitic inductance. Thus, the parasitic inductance generated in the whole ground line can be reduced, so that the resonance frequency of the resonance circuit made up by including the ground line can be shifted to a higher band so as to deviate from the specified frequency band used by the modulation signal transmitting device.
Meanwhile, by virtue of the small cross-sectional area of the second connecting device, it also becomes possible to suppress the circulating flow of heat that transfers from the module package to the chip-mounted carrier by passing through the first connecting device.
Therefore, by the adoption of such a ground line structure comprising the first connecting device and the second connecting device the parasitic inductance generated in the ground line can be reduced while the circulating flow of heat from the module package to the chip-mounted carrier is prevented. Thus, it becomes possible to shift the resonance frequency of the resonance circuit of the semiconductor laser module to a higher band so as to deviate from the specified frequency band used by the modulation signal transmitting device.
In particular, when the first connecting device is formed on the inner bottom portion of the conductive module package connected directly to the ground surface provided outside, the resonance frequency can be shifted to a higher band with better reproducibility while preventing the occurrence of unnecessary parasitic components in the ground line, as compared with a case where the first connecting device is formed, for example, on the side wall of the module package.
Preferably, the first connecting device is formed integrally with the inner bottom portion of the module package.
Thus, by forming the first con
Asakura Hiroyuki
Iida Masanori
Kobayashi Masaki
Bovernick Rodney
Matsushita Electric - Industrial Co., Ltd.
Stahl Michael J
Wenderoth, Lind & Ponack L.L.P
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