Wavelocker for Improving Laser Wavelength Accuracy in WDM Networks
First Claim
1. A method for improving the accuracy of WDM laser frequencies, the method comprising the following steps:
- (a) defining a desired target frequency to which a signal laser is to be tuned, within a predefined acceptable range of system tolerance;
(b) tuning a signal laser to an initial frequency which may or may not fall within the predefined acceptable range of the target frequency;
(c) beating the signal laser with a reference laser by combining and transmitting onto an optical detector, the light emitted by the signal laser at the initial frequency with the light emitted by the reference laser at a reference frequency, thereby creating a beat signal having a beat frequency equal to the difference between the signal laser frequency and the reference laser frequency;
(d) scanning the reference laser across a range of frequencies offset from the target frequency by predetermined amounts, and measuring the amplitude of the beat signal at a plurality of points within the range;
(e) processing the measured amplitudes of the beat signal to determine the actual frequency of the signal laser, and calculating the difference between the actual frequency and the target frequency;
(f) adjusting the frequency of the signal laser to account for the calculated difference; and
(g) repeating steps (c), (d), (e) and (f) to keep the signal laser within the predefined acceptable range of the target frequency.
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Abstract
The present invention includes novel techniques, apparatus, and systems for optical WDM communications. Various wavelocker apparatus and methods are disclosed that measure the frequency offsets between signal lasers and reference lasers. The measured offsets are used to adjust the signal laser frequencies to meet their target frequencies. The absolute accuracy of the reference laser frequency is improved by measuring the absorption of the reference laser by a gas cell with known fixed absorption lines versus the reference laser frequency. Apparatus and methods are disclosed to cover scenarios in which the reference laser polarization is aligned with the signal lasers, as well as those in which the reference laser polarization is not aligned with the signal lasers. The wavelocker apparatus may or may not be located at the same network site as the signal lasers.
118 Citations
18 Claims
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1. A method for improving the accuracy of WDM laser frequencies, the method comprising the following steps:
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(a) defining a desired target frequency to which a signal laser is to be tuned, within a predefined acceptable range of system tolerance; (b) tuning a signal laser to an initial frequency which may or may not fall within the predefined acceptable range of the target frequency; (c) beating the signal laser with a reference laser by combining and transmitting onto an optical detector, the light emitted by the signal laser at the initial frequency with the light emitted by the reference laser at a reference frequency, thereby creating a beat signal having a beat frequency equal to the difference between the signal laser frequency and the reference laser frequency; (d) scanning the reference laser across a range of frequencies offset from the target frequency by predetermined amounts, and measuring the amplitude of the beat signal at a plurality of points within the range; (e) processing the measured amplitudes of the beat signal to determine the actual frequency of the signal laser, and calculating the difference between the actual frequency and the target frequency; (f) adjusting the frequency of the signal laser to account for the calculated difference; and (g) repeating steps (c), (d), (e) and (f) to keep the signal laser within the predefined acceptable range of the target frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A system for improving the accuracy of WDM laser frequencies, the system comprising:
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(a) a signal laser to be tuned to a desired target frequency, within a predefined acceptable range of system tolerance, wherein the signal laser is tuned to an initial frequency which may or may not fall within the predefined acceptable range of the target frequency; (b) a coupler that can combine, and transmit onto an optical detector, the light emitted by the signal laser at the initial frequency with the light emitted by a reference laser at a reference frequency, thereby creating a beat signal having a beat frequency equal to the difference between the signal laser frequency and the reference laser frequency; and (c) control circuitry that can; (i) scan the reference laser across a range of frequencies offset from the target frequency by predetermined amounts; (ii) measure the amplitude of the beat signal at a plurality of points within the range; (iii) process the measured amplitudes of the beat signal to determine the actual frequency of the signal laser; (iv) calculate the difference between the actual frequency and the target frequency; (v) adjust the frequency of the signal laser to account for the calculated difference; and (vi) repeat steps (i)-(v) to keep the signal laser within the predefined acceptable range of the target frequency. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification