Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
2001-08-31
2004-11-30
Wong, Don (Department: 2828)
Coherent light generators
Particular temperature control
Heat sink
C372S034000, C372S035000, C372S043010, C372S044010, C372S045013, C372S046012, C372S049010, C372S049010, C372S049010, C372S050121
Reexamination Certificate
active
06826212
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a module for optical communication having a semiconductor laser chip region and a modulator. The module for optical communication according to this invention is extremely useful when applied, for example, to an optical transmission module including a temperature controlled electroabsorption type optical modulator integrated laser. It converts electric signals into optical signals in the optical fiber communication.
In a modulator integrated semiconductor laser for use in optical communication (hereinafter referred to as a modulator integrated laser), it has been necessary to keep the chip temperature of the modulator integrated laser constant in order to stably keep the oscillation wavelength of the laser, optical output power, the form of the extinction curve and the chirping characteristics of the modulator in the semiconductor laser for long time even upon change of the environmental temperature or the like.
For instance, in an existent modulator integrated laser, a laser active layer and a modulator absorption layer are constituted with a multiple-quantum well (MQW) comprising InGaAsP (indium-gallium-arsenic-phosphorus) for the laser active layer. Accordingly, in view of the feature of the band structure, it results in a problem of lowering the optical power at high temperature and, at the same time, a problem in view of long time stability of the wavelength. Therefore, optical signals have been transmitted while setting the temperature of the semiconductor laser chip constant at a temperature of 30° C. or at a temperature sufficiently lower than that.
Further, with an aim of efficient operation of optical networks and transmission modules, an optical modulator integrated laser having a wavelength variable function has been known recently. For example, this is described in a document (1): Japanese Patent Published Unexamined Patent Application No. Hei 4-72783 or in the recent document (2); IEEE Photonics Technology Letters, Volume 12, No. 3, p. 242. The wavelength variable function has been attained therein by controlling the temperature of the laser region. In the chip having the wavelength variable function, it is necessary that characteristics other than the oscillation wavelength of the laser, that is, the optical output power and the modulator performance can be kept stably for a long period of time also in a case where the temperature of the laser region is changed within a predetermined range, that is, a temperature range corresponding to the range in which the wavelength of the laser is intended to be changed.
SUMMARY OF THE INVENTION
Subjects will be described below for two cases of a modulator integrated laser having no wavelength variable function (hereinafter referred as a single channel modulator integrated laser) and a modulator integrated laser having a desired wavelength variable function (hereinafter referred to as a wavelength variable modulator integrated laser).
At first, an optical transmission module including a single channel modulator integrated laser is to be described.
FIG. 12
is an example of a constitution for an optical transmitter
75
including a modulator integrated laser. The optical transmitter
75
has mounted therein an optical transmission module
74
(hereinafter referred to as a module) including a modulator integrated laser
1
according to this invention. In addition to the module, there are also mounted, in the optical transmitter
75
, a multiplexer circuit for multiplexing a plurality of electric signals at a low bit rate inputted to the optical transmitter
75
into high bit rate signals, a modulator driver for increasing the amplitude of output signals from the multiplexer circuit such that the module
74
can be driven and a laser driving circuit for driving the three modules, a temperature controller circuit, a multiplexer (MUX) driving circuit and a driver driving circuit. In the example shown in
FIG. 12
, the module
74
and the modulator integrated laser housed therein have to be manufactured considering that the difference between the temperature of the module
74
and that of the outer wall of the module
74
is large (for example, 75° C.). As shown in
FIG. 1
, as the difference between the temperature of the modulator integrated laser
1
and the temperature at the outer wall of the module
74
is larger, the consumption power of a Peltier cooler that controls the temperature of the modulator integrated laser increases abruptly.
FIG. 1
is a graph showing an example of a relation between the difference of the case temperature to the chip temperature of a semiconductor laser chip, and the consumption power by the Peltier cooler.
Further, consumption power for other laser driving is relatively small as about 0.2 W. Accordingly, the consumption power for the entire module increases abruptly as the temperature difference increases.
However, when the temperature of the laser is made higher by using a multiple-quantum well structure constituted with InGaAsP for the laser active layer region, this results in the problem that (1) an optical power is lowered and (2) long-time stability for the oscillation wavelength can not be kept. Accordingly, the setting temperature for the module integrated laser has to be lower than 30° C. On the other hand, in the transmitter, for example, as shown in
FIG. 12
, the consumption power for the modulator driver, the multiplexer (MUX) and the power supplier therefor is large, and the average temperature in the module transmitter is usually about 40° C. or higher. Accordingly, if the setting temperature for the chip can be made higher than usual, it is possible to reduce the difference between the case temperature and the chip temperature of the optical transmission module and, the consumption power for the entire module can be decreased. Further, when it is intended to reduce the size of the optical transmitter (board) incorporated with the module or the optical transmission chip, the module as a heat generating source and other driving IC have to be disposed being close to each other. In this case, the chip environmental temperature will increase further.
In the existent modulator integrated semiconductor laser using InGaAsP for the laser active layer, the two problems described above hinder the rise of the setting temperature and decrease of the module consumption power.
Next, for making the oscillation wavelength of an optical modulator integrated laser variable, it is effective to control the wavelength by the temperature control for the laser region. In the document (2) above, temperature control is conducted not only for the laser region but also for the entire chip. This is a method of changing the temperature near the active layer of the laser thereby varying the oscillation wavelength of the distributed feedback type laser. However, since this results in a problem for the optical power level at high temperature and the long time stability of the oscillation wavelength as described above, it permits only the chip temperature of lower than 30° C. as the operation condition capable of obtaining the longest wavelength right. Therefore, the chip temperature has to be lowered in order to make the wavelength variable range wider. Therefore, there has been a problem that the difference between the temperature of the module and that of the outer wall is large to increase the module consumption power. Further, in the optical modulator, the light wavelength suitable to transmission of optical digital signals for a long distance changes depending on the temperature and the variation coefficient is, for example, at 0.8 nm/° C. On the other hand, the variation coefficient of the laser oscillation wavelength depending on the temperature is, for example, 0.1 nm/° C. For keeping the modulation performance constant, it is necessary to keep the difference between the band gap wavelength of the modulator region and the oscillation wavelength of the laser substantially constant. For example, if the band gap wavelengths of both of them are excessi
Shimizu Junichiro
Shirai Masataka
Tsuji Shinji
Flores Ruiz Delma R.
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Wong Don
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