Method and system for locking transmission wavelengths for lasers in a dense wavelength division multiplexer
First Claim
1. A system for locking a transmission wavelength of a laser to a selected wavelength comprising:
- a laser wavelength detector for detecting a transmission wavelength of the output beam of the laser;
an etalon for splitting a portion of the output beam of the laser into a series of transmission lines;
an etalon wavelength detector for detecting the etalon transmission lines; and
a control unit for setting the transmission wavelength of the output beam of the laser to a selected wavelength and also for tuning the etalon to align a selected one of the etalon transmission lines to the selected wavelength, the wavelength-locking control unit thereafter detecting any drift of the transmission wavelength of the laser from the selected etalon transmission line and adjusting the laser to compensate for any drift such that the output beam of the laser is locked to the selected transmission wavelength so long as the selected etalon transmission line remains at the selected wavelength.
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Accused Products
Abstract
The method and system operate to calibrate a transmission laser of the dense wavelength division multiplexer (DWDM) and to lock the laser to a selected transmission wavelength. In one example, the transmission laser is a widely tunable laser (WTL) to be tuned to one of a set of International Telecommunications Union (ITU) transmission grid lines for transmission through an optic fiber. To lock the WTL to an ITU grid line, a portion of the output beam from the WTL is routed through the etalon to split the beam into a set of transmission lines for detection by a detector. Another portion of the beam is routed directly to another detector. A wavelength-locking controller compares signals from the two detectors and adjusts the temperature of the etalon to align the wavelength of one of the transmission lines of the etalon with the wavelength of the output beam, then controls the WTL in a feedback loop to lock the laser to the etalon line. The wavelength-locking controller thereafter monitors the temperature of the etalon and keeps the temperature constant to prevent any wavelength drift in the etalon. In one example, the etalon is a silicon etalon configured to have finesse of about 20 and to provide a free spectral range of about 8 GHz. With these parameters, the system is able to lock the wavelength of the WTL to within a precision of about 0.2 GHz.
89 Citations
33 Claims
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1. A system for locking a transmission wavelength of a laser to a selected wavelength comprising:
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a laser wavelength detector for detecting a transmission wavelength of the output beam of the laser;
an etalon for splitting a portion of the output beam of the laser into a series of transmission lines;
an etalon wavelength detector for detecting the etalon transmission lines; and
a control unit for setting the transmission wavelength of the output beam of the laser to a selected wavelength and also for tuning the etalon to align a selected one of the etalon transmission lines to the selected wavelength, the wavelength-locking control unit thereafter detecting any drift of the transmission wavelength of the laser from the selected etalon transmission line and adjusting the laser to compensate for any drift such that the output beam of the laser is locked to the selected transmission wavelength so long as the selected etalon transmission line remains at the selected wavelength. - View Dependent Claims (2, 3, 4, 8, 9, 10, 11, 12, 13, 14, 15)
a gas absorption chamber;
an optical element for routing a portion of the output beam from the laser through the gas absorption chamber to generate gas absorption spectrum; and
a detector for detecting the gas absorption transmission spectrum;
a wavelength-mapping control unit for tuning the laser through a range of tuning parameters while the output beam from the laser is routed through the etalon and through the gas cell to produce an etalon transmission spectrum as a function of the laser tuning parameters and to produce a gas absorption spectrum as a function of the laser tuning parameters; and
an absolute transmission wavelength determination unit operative to compare the detected etalon transmission spectrum with the detected gas absorption spectrum to determine the absolute transmission wavelength of the laser as a function of the laser tuning parameters.
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3. The system of claim 2 wherein the etalon is mounted within the gas absorption chamber and the chamber is filled with acetylene.
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4. The system of claim 2 further including:
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a transmission wavelength input selection unit; and
wherein the absolute transmission wavelength determination unit determines the particular tuning parameters needed to tune the laser to a selected transmission wavelength based on the absolute transmission wavelength of the laser and wherein the control unit operates to tune the transmission laser to the selected wavelength using the particular tuning parameters.
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8. The system of claim 1 wherein the wavelength for transmission is selected from a group of predetermined International Telecommunication Industry (ITU) fiber optic transmission grid lines.
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9. The system of claim 1 wherein the etalon is a temperature-controlled etalon.
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10. The system of claim 9 wherein the temperature-controlled etalon is configured to have a finesse in the range of 15-30 and a free spectral range in the range of 6 GHz to 12 GHz.
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11. The system of claim 10 wherein the temperature-controlled etalon is silicon, sapphire or indium phosphide.
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12. The system of claim 10 wherein the temperature-controlled etalon has an optical axis length of is in the range of about 4 to 7 mm.
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13. The system of claim 10 wherein the temperature-controlled etalon is a silicon etalon having an optical axis length of about 5.36 mm and configured to have a finesse of about 20 and a free spectral range of about 8 GHz.
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14. The system of claim 1 further including a sealed chamber enclosing the etalon, the chamber being filled with a gas including one or more of air, krypton gas, H13CN, or acetylene.
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15. The system of claim 1 wherein the etalon is mounted to a substrate using a bonding material including a binder and a high thermal resistance material.
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5. The system of clam 1 further including a heating element mounted to the etalon and coupled to the wavelength-locking control unit for heating the etalon under control of the wavelength-locking control unit.
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6. The system of clam 5 wherein the heating element includes a first heating strip mounting parallel to an optic axis of the etalon along one side thereof and a second heating strip mounting parallel to an optic axis of the etalon along an opposing side thereof.
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7. The system of clam 6 wherein the etalon has a rectangular cross section and wherein side edges of the heating elements are offset from adjacent corner edges of the etalon.
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16. A method for controlling a laser using a tunable etalon, the method comprising the steps of:
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tuning the laser to transmit at a selected transmission wavelength;
tuning the etalon to align a transmission line of the etalon with the selected transmission wavelength;
detecting any drift of the transmission wavelength of the laser from the etalon transmission line; and
adjusting the laser to compensate for any drift such that the output beam of the laser is locked to the selected transmission wavelength so long as the selected etalon transmission line remains at the selected wavelength. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
routing an output beam from the laser through the etalon while tuning the laser through a range of tuning parameters to produce an etalon transmission spectrum as a function of the laser tuning parameters;
routing an output beam from the laser through a gas cell containing the known gas while tuning the laser through the range of tuning parameters to produce a gas absorption spectrum as a function of the laser tuning parameters;
detecting the etalon transmission spectrum and the gas absorption spectrum; and
comparing the detected etalon transmission spectrum with the detected gas absorption spectrum to calibrate the absolute transmission wavelength of the laser as a function of the laser tuning parameters.
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19. The method of claim 16 wherein the wavelength for transmission is selected from a group of predetermined International Telecommunication Industry (ITU) fiber optic transmission grid lines.
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20. The method of claim 16 further including the initial step of providing a temperature-controlled etalon configured to have a finesse in the range of 15-30 and a free spectral range in the range of 6 GHz to 12 GHz.
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21. The method of claim 20 wherein the temperature-controlled etalon is configured to have a finesse of about 20 and a free spectral range of about 8 GHz.
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22. The method of claim 16 further including the initial step of providing a temperature-controlled etalon formed of silicon, sapphire or indium phosphide.
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23. The method of claim 22 wherein the etalon is fabricated from silicon.
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24. The method of claim 16 further including the initial step of providing a temperature-controlled etalon having an optical axis length in the range of about 4 to 7 mm.
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25. The method of claim 24 wherein the etalon is configured to have an optical axis length of about 5.36 mm.
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26. The method of claim 16 further including the initial step of mounting the etalon to a substrate using a bonding material including a binder and a high thermal resistance material in the form of sieved particles of generally uniform size.
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27. The method of clam 16 further including the initial step of preparing a binder formed of silicone, epoxy or polyimide.
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28. The method of clam 26 further including the initial step of preparing a high thermal resistance material formed of glass microspheres, glass beads, ceramic microspheres, or ceramic beads.
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29. A system for controlling a laser, the system comprising:
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means for tuning the laser to transmit at a selected transmission wavelength;
interference means for splitting a portion of an output beam of the laser into a series of substantially uniformly-spaced transmission lines;
means for adjusting the means for splitting to align a selected transmission line of the series of transmission lines with the selected transmission wavelength;
means for detecting any drift of the transmission wavelength of the laser from the selected transmission line; and
means for adjusting the laser to compensate for any drift such that the output beam of the laser is locked to the selected transmission wavelength so long as the selected transmission line remains at the selected wavelength. - View Dependent Claims (30, 31, 32)
means for routing an output beam from the laser through the interference means while tuning the laser through a range of tuning parameters to produce an interference means transmission spectrum as a function of the laser tuning parameters;
means for routing an output beam from the laser through a gas cell containing the known gas while tuning the laser through the range of tuning parameters to produce a gas absorption spectrum as a function of the laser tuning parameters;
means for detecting the interference means transmission spectrum and the gas absorption spectrum; and
means for comparing the detected interference means transmission spectrum with the detected gas absorption spectrum to calibrate the absolute transmission wavelength of the interference means as a function of the interference means tuning parameters.
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32. The system of claim 29 wherein the interference means is configured to provide a finesse in the range of 15-30 and a free spectral range in the range of 6 GHz to 12 GHz.
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33. The system of claim 36 wherein the interference means is configured to provide a finesse of about 20 and a free spectral range of about 8 GHz.
Specification