Patent Application
20080080575
These and other features and advantages will be better understood by reading the following detailed description, taken together with the drawings wherein:
A laser for use in a laser transmitter or combined transmitter-receiver (usually referred to as a transceiver), consistent with embodiments of the present invention, may be heated to maintain an operating temperature of the laser above a temperature floor such that the operating temperature of the laser is allowed to vary within a reduced operating temperature range. The reduced operating temperature range of the laser thus allows the wavelength emitted by the laser to vary within a reduced range of emission wavelengths. In other words, the temperature floor reduces the temperature range experienced by the laser, which reduces the wavelength excursion. In one embodiment, the operating temperature of the laser is allowed to rise above the temperature floor without cooling the laser to stabilize the operating temperature. Although exemplary embodiments are described herein in connection with particular types of lasers used in laser transmitters in optical communications systems, such as wavelength division multiplexed (WDM) systems, embodiments of the invention may be used with other types of lasers in other types of optical systems.
Referring to
The semiconductor laser 120 may operate at a single wavelength but that wavelength may change due to fluctuations in operating temperature. In particular, the laser 120 may be configured to emit a predefined center wavelength and to have a wavelength temperature fluctuation such that the emission wavelength of the laser 120 varies within a range of wavelengths around the center wavelength. In a WDM system, for example, the laser 120 may be configured to emit a center wavelength within the range of 1271 nm to 1611 nm and may have a wavelength temperature fluctuation of about 0.1 to 0.12 nm per degrees Celsius (nm/° C.).
The laser heating system 130 may include a laser heater 132 positioned sufficiently close to the laser 120 to maintain the operating temperature of the laser 120 above a temperature floor. One example of the laser heater 130 is a resistor heater, which may receive current from the laser circuitry 110. In one embodiment, the laser 120 is uncooled in that there is no cooling element to reduce and stabilize the temperature of the laser 120. In other words, the laser heater 132 maintains the operating temperature of the laser 120 above the temperature floor such that the operating temperature is allowed to rise above the temperature floor without cooling of the laser 120.
The laser heating system 130 may also include a temperature sensor 134 that senses a temperature of the laser 120 or in a region around the laser 120. The temperature sensor 134 may be coupled to the laser heater 132, for example, through laser heater circuitry. The temperature sensor 134 may cause the laser heater 132 to heat the laser 120 when the sensed temperature indicates that the operating temperature of the laser 120 is below the temperature floor and may cause the laser heater 132 to stop heating when the sensed temperature indicates that the operating temperature of the laser 120 is above the temperature floor. To control the heater 132, for example, the temperature sensor 134 may be coupled to a switch 136 that couples the current from the laser circuitry 110 to the laser heater 132. The switch 136 may be used to switch the heater 132 on when the sensed temperature indicates that the operating temperature is below the temperature floor and to switch the heater 132 off when the sensed temperature indicates that the operating temperature is above the temperature floor.
According to one example of a laser 120 having a wavelength temperature fluctuation of about 0.1 to 0.12 nm per degree Celsius, the operating temperature range may be reduced to cover about 90° C. or less to limit the wavelength shift to a maximum of about 11 nm. If the maximum operating temperature is expected to be about 85° C., for example, the heater 132 may be used to maintain an operating temperature above a temperature floor of about −5° C. to limit the operating temperature range to about −5° C. to 85° C. (e.g., as compared to −40° C. to 85° C.). In other words, the laser heater 132 may be switched on when the sensor 134 senses a temperature of below −5° C. and the laser heater 132 may be switched off when the sensor 134 senses a temperature above −5° C. Thus, a conventional wavelength variation of about 13-14 nm for a temperature operating range of −40° C. to 85° C. could be reduced significantly without using a thermoelectric cooler. Other temperature floors (e.g., about 0° C.) and operating temperature ranges may be used depending upon the wavelength temperature fluctuation, manufacturing tolerances, and other characteristics of the laser and depending upon the acceptable amount of wavelength shift that may be tolerated in the optical communications system.
According to one embodiment, as shown in
In the illustrated exemplary embodiment, the laser package 200 is a TO (transistor outline) can laser package and the laser package housing 210 is a TO can housing. The TO can housing 210 aligns and positions the laser 220, fiber 202 and related optical components to each other so that the laser 220 is optically coupled to the fiber 202. In this embodiment, the TO can housing 210 may include a TO can header 214 with a TO can post 216, and the laser 220 is mounted on the laser submount 212 located on the TO can post 216 of the TO can header 214.
In this exemplary embodiment, the laser heater 230 may include a film resistor 232 with electrical terminals or leads 234 coupled to the film resistor 232. The electrical leads 234 may be coupled to a current source (e.g., laser circuitry) for applying current to the film resistor 232. The leads 234 may also be coupled to a temperature sensor and/or switch (not shown) for switching the current to the film resistor 232 on and off in response to sensing an operating temperature below or above a temperature floor, as disclosed above. The relatively small size of the film resistor 232 needed to provide the desired heating (e.g., as compared to a TEC) allows the use of smaller housings, such as the TO can housing. Thus, a heated laser package, consistent with embodiments of the present invention, may reduce temperature drift and wavelength shift while being less expensive, less complex and more compact than conventional temperature-stabilized lasers.
In one embodiment, the film resistor 232 may be formed by a resistance material deposited directly on the laser submount 212, for example, near the location of the laser 220. One advantage of a deposited film resistor is the ability to precisely control resistance, for example, by laser trimming the film resistor using techniques known to those skilled in the art. The resistance material may include a nickel-chromium resistance material, such as NiChrome™, which is a non-magnetic alloy of nickel and chromium. Other film resistors may include, but are not limited to, carbon film resistors, metal film resistors, metal oxide resistors, and metal nitride resistors, such as tantalum nitride. In addition to being formed by depositing a resistance material, the film resistor 232 may be formed as a chip resistor that may be mounted to the submount 212. Other types of resistors that can be used for heaters include, but are not limited to, carbon composition resistors and wire wound resistors.
Because the laser 220 is relatively small and the film resistor 232 can be placed close to the laser 220, a relatively small amount of current is needed to cause the film resistor 232 to generate the desired amount of heat. In one exemplary application, the film resistor 232 may be capable of providing the desired amount of heat from a current (e.g., the operating current of the laser) of less than about 500 mA and with a power consumption of less than about 1.5 W. Those skilled in the art will recognize the desired resistance value of the film resistor based on current, power consumption, and the desired temperature floor for a particular laser and application.
Referring to
If the operating temperature of the laser is determined to fall below the temperature floor 314, the laser is heated 316. The laser may be heated, for example, by switching on a laser heater, as described above. If the operating temperature is not determined to fall below the temperature floor, monitoring of the temperature continues without heating the laser. When the laser is being heated 316, if the operating temperature is determined to rise above the temperature floor 318, heating of the laser is stopped 320. Heating may be stopped 320, for example, by switching off the laser heater, as described above. After heating is stopped 320, the temperature may be allowed to rise above the temperature floor without cooling the laser, but if the temperature again falls below the temperature floor 314, heating 316 is resumed. The monitoring of the temperature, heating and stopping heating may continue during operation of the laser to maintain the operating temperature of the laser above the temperature floor such that the operating temperature of the laser is allowed to vary within a reduced operating temperature range and the wavelength emitted by the laser is allowed to vary within a reduced range of emission wavelengths.
Accordingly, a laser package, laser transmitter and method of reducing an operating temperature of a laser, consistent with embodiments of the present invention, are capable of reducing wavelength excursion or fluctuation of a laser by preventing temperature drift below a temperature floor.
Consistent with one embodiment, a laser package for use in a laser transmitter includes a semiconductor laser configured to emit a predefined center wavelength and a range of wavelengths around the center wavelength. The laser has a wavelength temperature fluctuation such that an emission wavelength of the laser varies with an operating temperature of the laser. The laser package further includes a laser heater for heating the semiconductor laser. The laser heater is configured to maintain the operating temperature of the laser above a temperature floor such that the operating temperature of the laser is allowed to vary within a reduced operating temperature range and the wavelength emitted by the laser is allowed to vary within a reduced range of emission wavelengths.
Consistent with another embodiment, an optical transmitter includes laser circuitry and a laser package coupled to the laser circuitry. The laser package includes a semiconductor laser configured to emit a predefined center wavelength and a range of wavelengths around the center wavelength. The laser has a wavelength temperature fluctuation such that an emission wavelength of the laser varies with an operating temperature of the laser. The laser package further includes a laser heater for heating the semiconductor laser. The laser heater is configured to maintain the operating temperature of the laser above a temperature floor such that the operating temperature of the laser is allowed to vary within a reduced operating temperature range and the wavelength emitted by the laser is allowed to vary within a reduced range of emission wavelengths.
Consistent with a further embodiment, a method is provided for reducing an operating temperature range of a laser. The method includes operating the laser to emit a wavelength that varies with an operating temperature of the laser; monitoring the operating temperature of the laser; heating the laser when the operating temperature falls below a temperature floor; and stopping the heating of the laser when the operating temperature rises above the temperature floor. The operating temperature of the laser is allowed to rise above the temperature floor without cooling the laser.
While the principles of the invention have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the invention. Other embodiments are contemplated within the scope of the present invention in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims.
This application claims the benefit of co-pending U.S. Provisional Patent Application Ser. No. 60/827,331, filed on Sep. 28, 2006, which is fully incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60827331 | Sep 2006 | US |
