Optical: systems and elements – Light interference – Electrically or mechanically variable
Reexamination Certificate
1999-12-13
2001-03-20
Chang, Audrey (Department: 2872)
Optical: systems and elements
Light interference
Electrically or mechanically variable
C359S577000, C359S260000, C359S346000, C359S199200
Reexamination Certificate
active
06204970
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to optical filters, and more particularly to a technique for tuning a dielectric filter in a collimator assembly.
2. Technical Background
Data communication systems increasingly are employing light signals and optical fibers for the transmission of information. The use of optical fibers allows the transmission of large amounts of data at high speeds and with low signal loss over long distances. To increase the data transmission capacity on an optical fiber, a plurality of light signals at different wavelengths are commonly multiplexed with wavelength division multiplexing for transmission through a single optical fiber so that the information is transmitted on multiple wavelengths, i.e., channels. In a wavelength division multiplexed system, the plurality of light signal sources have different wavelengths corresponding to different signal channels. After the multiple channels are transmitted through the optical fiber, the multiple wavelength signals are separated at a receiving end with the use of a demultiplexer to separate the individual signal channels. Select wavelength band filters may be used as one technique to select specific channel wavelengths.
In order to maximize utilization of the available bandwidth, the channel wavelength band and any wavelength separation between adjacent channels should be minimized. Accordingly, to minimize the wavelength band for each signal channel, a narrow band filter is used for accurately selecting the narrow band channel. Such filters are generally fixed, although other filters are tunable to a selected frequency.
One common filter tuning approach is to tune a dielectric filter in a collimator package to resolve a single spectral feature, such as a peak value. The single spectral feature is generally correlated to a specified waveform and serves as the target wavelength for resolving the angle of incidence for that filter. One disadvantage to this approach is that the accuracy for resolving the target wavelength based on a single spectral feature is generally limited such that the per channel wavelength band of the filter is limited. Inaccuracy in resolving the target wavelength may induce significant error for optimal spectral alignment of the dielectric filter. Accordingly, the accuracy of the dielectric filter's initial spectral measurement and optimizing the resulting target wavelength currently limits precise spectral alignment to a collimator assembly's optical axis. For this reason and others, it is desirable to provide a technique and structure for tuning a tunable filter with a high degree of accuracy.
SUMMARY OF THE INVENTION
The present invention provides a tunable filter and method of spectrally tuning a dielectric filter with precise tuning accuracy. To achieve this and other advantages, and in accordance with the purpose of the present invention as embodied and described herein, the present invention provides for a method for tuning a dielectric filter comprising the steps of determining filter characteristics including a cut-on wavelength and a cut-off wavelength at a selected gain level. The filter is aligned with a collimator assembly, and a light source having a wavelength approximately equal to the cut-on frequency is applied as an input to the filter. The collimator assembly is rotated relative to the filter to adjust the filter to the determined cut-on wavelength, the spectral performance is measured, and the measured spectral performance is compared with a cut-on rating value. The method further includes the steps of applying as an input to the filter a light signal having a wavelength set to a cut-off wavelength, rotating the collimator assembly relative to the filter, measuring spectral performance, and comparing the measured spectral performance with a cut-off rating value. The difference in measured spectral performance with the rating values for each of the cut-on wavelength and cut-off wavelength are compared to determine if the difference is within an acceptable range. If the difference is not within an acceptable range, the steps of applying a light signal at the cut-on and cut-off wavelengths and rotating the collimator assembly is repeated until the difference is within an acceptable range. The method advantageously tunes a dielectric filter by utilizing with the cut-on wavelength and a cut-off wavelength to provide precise filter tuning and a resultant filter with a high degree of accuracy.
Additional features and advantages of the invention will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing the invention as described in the description which follows together with the claims and appended drawings.
It is to be understood that the foregoing description is exemplary of the invention only and is intended to provide an overview for the understanding of the nature and character of the invention as it is defined by the claims. The accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute part of this specification. The drawings illustrate various features and embodiments of the invention which, together with their description serve to explain the principals and operation of the invention.
REFERENCES:
patent: 4813756 (1989-03-01), Frenkel et al.
patent: 5361155 (1994-11-01), Chiaroni et al.
patent: 5491582 (1996-02-01), Fujita
patent: 5625613 (1997-04-01), Kato et al.
patent: 5781341 (1998-07-01), Lee
patent: 6040944 (2000-03-01), Pan et al.
Francis Kurt R.
Hellman Scott M.
Chang Audrey
Corning Incorporated
Price Heneveld Cooper DeWitt & Litton
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