Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
2002-07-02
2004-04-20
Ip, Paul (Department: 2828)
Coherent light generators
Particular temperature control
Heat sink
C372S034000
Reexamination Certificate
active
06724791
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to method and apparatus for assembling a laser module in a telecommunications network and, more particularly, to a thermoelectric cooling element positioned externally of the laser module for maintaining the operating temperature of the laser module.
2. Description of the Prior Art
In a conventional cable television (CATV) system optical transmitters are used to convert radio frequency (RF) signals to optical signals. The conversion is provided by a laser diode which transmits AM modulated or digitally modulated optical signals for communication over a fiber optic CATV distribution network. The laser diode is coupled to a fiber optic network suitable for use in optical transmissions.
Laser diode devices are sensitive to operating conditions such as temperature, modulating signal level, and the loss or improper application of current which biases the laser diode to its stimulated or laser emission state. As the ambient temperature of the optical transmitter increases or decreases, unequal thermal expansion of the components creates stresses on the components which can alter their optical characteristics. For example, the optical beam emitted from the laser diode is focused to a modulator. Thermal stresses applied to the laser diode misalign the optical beam, resulting in a reduction in the output of the optical transmitter. Therefore, the laser diode must be maintained at a stable operating temperature, i.e. within a range of plus or minus two degrees.
In a conventional optical communications system, the laser diode and the other optical components in the system are buried in underground conduits and the like, exposing them to extreme environmental conditions. The optical elements may be exposed to ambient temperatures ranging from −30° C. to about 50° C. Because the oscillation characteristics of a semiconductor laser diode have a large temperature dependency, if the module is not maintained at a constant temperature. shifts in the threshold current density or oscillation wavelength may take place depending on temperature variation.
In order to accommodate the temperature variations to which the laser diode is exposed and to avoid wavelength shifts, it is the conventional practice to hold the operating temperature of the laser diode by a Peltier-element electronic cooling device. By keeping the operating temperature of the laser diode at a constant temperature, the operating bias and, therefore, the total optical transmission of the optical signal is maintained at a constant level under extreme environmental conditions and in response to electrical disturbances.
An example of the prior art semiconductor laser module using an electronic cooling device in an optical communication system is disclosed in U.S. Pat. No. 6,181,718 in what is commonly referred to as a butterfly-type module package. A semiconductor laser diode is mounted on a carrier which is coupled internally to an electronic cooling device. The cooling device includes a Peltier-element having a pin junction sandwiched between a first dielectric plate substrate and a second dielectric plate substrate. To avoid a temperature increase in the diode, a temperature detector, such as a thermistor-resistor, is installed around the diode. With this arrangement, the temperature around the diode is maintained by the supply current to the Peltier-element. A change in the temperature is detected by the thermistor and in response actuates an increase or decrease of the electric current to the Peltier-element. The current is increased to increase the rate of heat flow from the diode and thereby cool the diode back to the operating temperature. When the temperature measured by the thermistor is lower than the operating temperature, the electric current to the Peltier-element is decreased to decrease the rate of heat flow from the laser diode. The heat generated in the diode raises the temperature thereof back to the operating temperature.
With the above-described butterfly-type module construction, the thermoelectric cooling element is mounted internally within the package in contact with the laser diode. The package is formed by a hermetically sealed metal-ceramic or metal-glass rectangular package with multiple leads protruding from opposite sides of the package. External electronic circuitry is used to control the operation of the internal cooling element. However, this configuration adds significantly to the cost of manufacture of the laser diode module.
Another example of a laser diode module having an internally packaged thermoelectric cooler (TEC) is disclosed in U.S. Pat. No. 5,181,214. All the elements of the laser diode module are mounted to a common, temperature stabilized base plate. The base plate is fabricated of a low thermal expansion material, such as copper-tungsten alloy. The base plate is mounted on a thermoelectric cooler, which in turn is mounted on a heat sink. The thermoelectric cooler controls the rate of heat flow between the base plate and the heat sink in order to maintain the temperature of the laser diode at a predetermined operating temperature.
In U.S. Pat. No. 5,379,145, an optical transmitter for light wave communications utilizes a thermistor thermally coupled with a laser diode in a module. Also, thermally coupled to the laser diode is a thermoelectric cooler. The TEC is connected to a controller responsive to voltage developed across the thermistor to turn current to the TEC on and off to cool the laser diode when its temperature exceeds a certain temperature. The other components are within the package.
In the multichannel analog optical fiber communication system disclosed in U.S. Pat. No. 5,034,334, the laser diode chip is mounted on a metallized carrier. The carrier is in turn attached to a copper stud cooled by a conventional thermoelectric cooling element to maintain the laser diode at about 20° C.
Conventional integrated optical transmitter in a CATV system includes an optical head assembly generating a formed optical beam and an optical modulator which receives the formed optical beam for modulation. An optical head assembly is maintained in a fixed relationship by an epoxy bonding to the modulator. The optical head includes a laser diode that is coupled to the modulator for transmitting an optical beam to the modulator. A thermal transfer plug couples a rear portion of the optical head assembly to a TEC to transfer heat therebetween. A second TEC is coupled by adhesive directly to the optical head. TECs are conventionally operable to remove or add heat from the modulator and optical head assembly to maintain optimum operating temperature. Further, it is disclosed that a thermistor is mounted in the transfer plug to monitor the temperature of the optical head assembly. All these components are contained in an integrated package.
Another example of a butterfly type module package for a semiconductor laser diode in an optical fiber telecommunications system is disclosed in U.S. Pat. No. 6,219,364. A laser diode chip and a thermistor are mounted via a heat sink on a submount. The submount is in turn mounted on a metal substrate. The metal substrate is bonded by a hard metal solder to the top of a Peltier-element. The Peltier-element is in turn sandwiched by ceramic panels so that the cooler element is internally mounted within the module beneath the laser diode.
Another example of a thermoelectric cooling element mounted internally within the laser diode package is disclosed in U.S. Pat. No. 6,018,536. An integrated laser package includes a gain element supported on a high thermal conductive submount in alignment with a fiber of an optical coupling means which is also supported on the submount. The submount is in turn supported on a TEC cooler. Thus, all the elements are heat sunk to the same support in an integrated package and maintained at the same temperature.
One disadvantage of an integrated laser module where the thermoelectric cooling element is contained within the module is the high manufacturing c
Chiappetta Joseph F.
Jamra James
C-COR.net Corp.
Ip Paul
Nguyen Phillip
Price & Adams
LandOfFree
Method and apparatus for controlling the temperature of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for controlling the temperature of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for controlling the temperature of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3199281