Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-10-06
2001-12-04
Scott, Jr., Leon (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S020000, C372S036000, C372S034000, C372S038060
Reexamination Certificate
active
06327287
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to semiconductor lasers, and more particularly to a semiconductor laser diode system with a control loop that provides a controlled output beam of selected wavelength in response to a changes in temperature of the diode or changes in output beam wavelength.
2. Description of Related Art
There are stringent requirements on the stability of the output wavelength and the output power of semiconductor laser units used for optical communication, and specifically for dense wave division multiplexing (DWDM). Typically, the lasers used for these applications are distributed feedback (DFB) semiconductor lasers. At fixed driving current, the output power and wavelength of these devices varies strongly with temperature. Typically the wavelength change is 0.6Å/1C. Over an operating range of 0 to 75 degrees Celsius, this wavelength change is 4.5 nm. In DWDM systems the channel spacing is 0.8 nm or 0.4 nm so this wavelength variation is unacceptable. In addition, aging of the laser will also cause a change in wavelength. To overcome this problem DFB lasers are packaged with a temperature sensor and a cooler which operate in a closed loop to maintain the laser at a fixed temperature. At a fixed temperature the laser wavelength variation is minimized. Thermal control systems used with laser diodes have included the combination of a photodiode, thermoelectric cooler and thermistor. The photodiode receives a portion of the output of the diode laser. The output from the laser diode is stabilized by a feedback drive circuit and a reference adjust variable resistor. A temperature feedback circuit uses a thermistor and the reference adjust resistor to provide feedback stabilization of the laser diode temperature.
U.S. Pat. No. 5,602,860 discloses a cooling system for a laser diode that includes a temperature sensitive switch. When a temperature exceeds a given temperature the switch is open. Coupled to the switch is a thermoelectric cooler that cools the laser diode.
To provide more precise control of the wavelength, the wavelength can be monitored. U.S. Pat. No. 5,867,513 discloses a semiconductor laser unit in which the temperature is controlled in a closed loop which monitors the output wavelength of the laser.
Thermoelectric coolers generally require larger, more expensive power supplies than would otherwise be used. The use of thermoelectric coolers has proven to waste a significant amount of power from the power source. In one device, one or more voltage regulators are used to regulate the power supplied to a thermoelectric cooler. The power used by the voltage regulator is wasted. In addition the thermoelectric cooler itself adds to the cost of manufacturing the laser. U.S. Pat. No. 5,387,974 discloses one embodiment of a temperature insensitive wavelength meter and wavelength compensation for a KrF excimer laser as a method of avoiding the use of costly temperature control. Excimer lasers produce light in the UV wavelength range and are not appropriate for communications applications.
There is a need for a passively cooled wavelength stabilized laser system suitable for use in WDM communication applications and systems.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a laser system.
Another object of the present invention is to provide a wavelength stabilized laser.
A further object of the present invention is to provide a passively cooled wavelength stabilized laser system.
Yet another object of the present invention is to provide a passively cooled wavelength stabilized laser system useful in WDM communications.
Another object of the present invention is to provide a wavelength stabilized laser assembly with a seal cap and seal ring that form a hermetic seal.
Still another object of the present invention is to provide a wavelength stabilized, tunable semiconductor laser assembly that includes a heatsink coupled to a laser and a seal cap with seal ring.
A further object of the present invention is to provide an array of wavelength stabilized, tunable semiconductor laser assemblies with seal caps and rings.
These and other objects of the present invention are achieve in a tunable semiconductor laser assembly. The assembly includes a laser with a seal surface, a semiconductor active region positioned between upper and lower confining regions of opposite type semiconductor material and first and second reflective members positioned at opposing edges of the active and confining regions. A seal cap includes a seal ring. The seal cap seal ring is coupled to the seal surface and forms a hermetic seal. A wavelength tuning member and a temperature sensor is coupled to the laser. A temperature sensor coupled to the laser. A control loop is coupled to the temperature sensor and the tuning member. In response to a detected change in temperature the control loop sends an adjustment signal to the tuning member, and the tuning member adjusts a voltage or current supplied to the laser to provide a controlled frequency and power of an output beam.
In another embodiment of the present invention, a tunable semiconductor laser assembly includes a heatsink coupled to a laser. The laser has a semiconductor active region positioned between upper and lower confining regions of opposite type semiconductor material, and first and second reflective members positioned at opposing edges of the active and confining regions. A seal cap is provide and includes a seal ring. The seal cap seal ring is coupled to the seal surface to form a hermetic seal. A wavelength tuning member and temperature sensor are coupled to the laser. A control loop is coupled to the temperature sensor and the tuning member. In response to a detected change in temperature the control loop sends an adjustment signal to the tuning member and the tuning member adjusts a voltage or current supplied to the laser to provide a controlled frequency and power of an output beam.
In another embodiment of the present invention, a tunable semiconductor laser assembly includes a laser including with an electrically responsive substrate with a substrate seal ring. A support block is positioned on the electrically responsive substrate. Top and bottom reflecting members are included. A cantilever structure has a base section resting on the support block with a deformable section that extends above the electrically responsive substrate. An air gap is created between the deformable section and the electrically responsive substrate. An active head is positioned at a predetermined location on the deformable section and includes at least a portion of the top reflecting member. A seal cap is provided with a seal ring. The seal cap seal ring is coupled to the substrate seal ring and form a hermetic seal. A wavelength tuning member is coupled to the laser. A temperature sensor is coupled to the laser. A control loop is coupled to the temperature sensor and the tuning member. In response to a detected change in temperature the control loop sends an adjustment signal to the tuning member and the tuning member adjusts a voltage or current supplied to the laser to provide a controlled frequency and power of an output beam.
In another embodiment of the present invention, an array of tunable semiconductor laser assemblies includes an array of lasers. Each laser of the array has a seal surface, a semiconductor active region positioned between upper and lower confining regions of opposite type semiconductor materials and first and second reflective members positioned at opposing edges of the active and confining regions. An array of seal caps with seal rings are provided. Each seal cap seal ring is coupled to the seal surface of the laser to form a hermetic seal. A wavelength tuning member and a temperature sensor are each coupled to each laser. A control loop is coupled to the temperature sensor and the tuning member. In response to a detected change in temperature the control loop sends an adjustment signal to the tuning member, and the tuning mem
Kner Peter
Ll Gabriel
Worland Philip
Yu Rang-Chen
Yuen Wupen
Bandwidth 9 Inc
Jr. Leon Scott
Wilson Sonsini Goodrich & Rosati
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