Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2000-10-10
2001-11-20
Scott, Jr., Leon (Department: 2881)
Optical waveguides
With optical coupler
Plural
C372S006000, C372S032000, C372S020000, C372S034000, C372S038060, C385S042000, C385S015000, C385S031000, C359S199200
Reexamination Certificate
active
06321003
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 0.6 A/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 DWDM device, sub-system or system that is tunable.
Yet another object of the present invention is to provide a DWDM device, sub-system or system that is programmably tunable.
A further object of the present invention is to provide a DWDM device, sub-system or system that is flexible and provides for different configuration, different levels of filtration as well as different combinations of wavelengths that are multiplexed and de-multiplexed.
Still another object of the present invention is to provide a tunable DWDM device with one or more filters to reduce crosstalk.
Another object of the present invention is to provide a position independent method and device for combining or separating many wavelengths into or from a single optical fiber.
Yet another object of the invention is to provide a wavelength tunable variable optical tap.
Another object of the invention is to provide a drop and continue network node.
These and other objects of the present invention are achieved in a multiplexer for a wavelength division multiplexed optical communication system. The system includes an optical circulator with at least first, second, third and fourth circulator ports. An optical fiber with a first optical transmission path is coupled to the first circulator port and carries a wavelength division multiplexed optical signal that includes signals
1−n
. A second optical transmission path is in optical communication with the second circulator port. A first laser is coupled to the second optical transmission path. The first laser reflects the
1−n
signals and adds a signal
n+1
. A control loop is coupled to the first laser. In response to a detected change in temperature the control loop sends a signal to adjust a voltage or current supplied to the first laser and provide a controlled frequency and power of an output beam. A third optical transmission path is in optical communication with the third circulator port and transmits the signals
1−n
and the signals
n+1
that are received from the optical circulator. A fourth optical transmission path is in optical communication with the fourth optical circulator port. The fourth optical transmission path is positioned after the second optical transmission path and before the third optical transmission path. A first optoelectronic device is coupled to the fourth optical transmission path.
In another embodiment of the present invention, a multiplexer for a wavelength division multiplexed optical communication system includes a first optical circulator with at least first, second and third circulator ports. An optical fiber with a first optical transmission path is coupled to the first circulator port and carries a wavelength division multiplexed optical signal that includes
1−n
signals. A second optical transmission path is in optical communication with the second circulator port. A first laser is in optical communication with the second optical transmission path. A control loop is coupled to the first laser. In response to a detected change in temperature, the control loop sends a signal to adjust a voltage or current supplied to the first laser and provide a controlled frequency and power of an output beam. A second optical circulator is provided and has at least first, second and third circulator ports. A third optical transmission path is in optical communication with the third circulator port of the first optical circulator and the first circulator port of the second optical circulator. A rejection filter is coupled to the third optical transmission path. The rejection filter drops a signal
1
. A fourth optical transmission path is in optical communication with the second circulator port of the second optical circulator. A first optoelectronic device is in optical communication with the fourth optical transmission path. A fifth optical transmission path is in optical communication with the third circulator port of the second optical circulator.
In another embodiment of the present invention, a multiplexer for a wavelength division multiplexed optical communication system includes a first optical circulator with at least first, second and third circulator ports. An optical fiber with a first optical transmission path is coupled to the first circulator port. The optical fiber carries a wavelength division multiplexed optical si
Kner Peter
Li Gabriel
Worland Philip
Yu Rang-Chen
Yuen Wupen
Bandwidth9 Inc.
Jr. Leon Scott
Wilson Sonsini Goodrich & Rosati
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