Optical waveguides – With optical coupler – Particular coupling function
Reexamination Certificate
2001-06-06
2004-01-20
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling function
C385S015000, C385S039000, C398S085000
Reexamination Certificate
active
06681065
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of filtering and in particular discloses an optical filtering method and apparatus.
BACKGROUND OF THE INVENTION
Photonic processors for microwave signal processing functions are attractive because of their very high time-bandwidth product capabilities. Such processors can remove the bottlenecks caused by limited sampling speeds in conventional electrical signal processors. In addition, they have excellent isolation, immunity to electromagnetic interference (EMI), and remove the limitations of Optical/Electrical and Electrical/Optical conversions for processing high speed signals that are already in the optical domain. Photonic processors also have the ability of attaining extremely high resolution and microwave frequencies.
Recently, there has been considerable interest in photonic processing for microwave filtering applications, and a variety of structures have been reported. A common objective is to increase the Q and frequency selectivity of these filters. This is more difficult to realise for bandpass filters, because it requires an increase in the number of taps in the discrete time signal processor. For this reason, passive structures for photonic processors give limited Q values. Active structures can achieve much higher Q values, but are limited by the requirement that they operate close to the lasing threshold. Also, the fundamental frequency and finesse of these filters is limited because of the minimum length of erbium fibre that can be used. Previously, the present inventors have reported an active photonic signal processor that exhibits a Q of 325, however it is difficult to increase the Q further in this structure because of the onset of lasing.
SUMMARY OF THE PRESENT INVENTION
In accordance with a first aspect of the present invention, there is provided an active-passive signal bandpass filter comprising:
an active filter an active filter arranged in use to operate at a fundamental frequency which is a sub-multiple of a desired filter frequency of the bandpass filter; and
a passive filter arranged in use to eliminate any pass bands in the frequency response of the active filter other than at the desired filter frequency for providing the pass band signal of the bandpass filter.
The active filter can comprise an infinite impulse response filter and the passive filter can comprise a finite impulse response filter.
The active and passive filters can operate on photonic signals and an input signal to the bandpass filter can comprise an optical input signal. The filter preferably operates at microwave frequencies and the input signal can be created via the modulation of the optical signal by a microwave frequency optical oscillator.
The passive filter can comprise a plurality of passive filter elements each comprising a notch filter which, in combination, have high attenuation characteristics for frequencies outside the desired filter frequency and low attenuation of the desired filter frequency. The number of passive filter elements can, for example, be 3.
The passive filter may be formed from optical fibre components.
Alternatively, the passive filter may be formed from optical planar integrated circuits.
A post filter element can be further interconnected to the passive filter, the post filter element providing for further rejection of non desired filter frequencies.
The active filter may comprise an active delay line filter.
The active delay line filter can comprise an optical fibre which comprises two gratings that define a pass length between them, the optical fibre being erbium doped and the active delay filter further comprising a pump laser for providing the gain of the active delay line filter.
Alternatively, the active filter may comprise an optical planar integrated circuit.
The optical planar integrated circuit may comprise optical waveguides for providing the delay function of the active delay line filter and doped optical waveguides for providing the gain function of the active delay line filter; and waveguide gratings in the optical waveguides defining a pass length therebetween.
The active filter may be a tunable active filter for wavelength tuning the filter frequency of the filter.
In one embodiment, the tunable active filter may comprise chirped gratings defining a plurality of path lengths, each path length being associated with a predetermined wavelength of a laser pumping the active delay line filter.
This can enable the filter frequency to be changed.
The present invention may alternatively be defined as providing a photonic processor having a quality factor in excess of about 325.
REFERENCES:
patent: 4692723 (1987-09-01), Fiedziuszko et al.
patent: 4768850 (1988-09-01), Moslehi et al.
patent: 5434937 (1995-07-01), Glance
patent: 5485299 (1996-01-01), Jones
patent: 5513090 (1996-04-01), Bhattacharya et al.
patent: 5548165 (1996-08-01), Mohan et al.
patent: 5567994 (1996-10-01), Davis et al.
patent: 5570440 (1996-10-01), Mizrahi
patent: 5677786 (1997-10-01), Meli
patent: 5822476 (1998-10-01), Jopson
patent: 5825520 (1998-10-01), Huber
patent: 5910889 (1999-06-01), Larsen et al.
patent: 6016371 (2000-01-01), Wickham et al.
patent: 6160660 (2000-12-01), Aina et al.
patent: 6344914 (2002-02-01), Shimojoh et al.
patent: 6445848 (2002-09-01), Islam et al.
patent: 6549701 (2003-04-01), Baney et al.
patent: 2001/0002202 (2001-05-01), Feher
patent: 06334607 (1994-12-01), None
D. Hunter, R. Minasian, “Microwave optical filters using in-fibre Bragg grating arrays,” IEEE Microw. Guided Wave Lett., pp. 103-105, 1996.
F. Coppinger, S. Yegnanararayanan, P.D. Trinh, B. Jalali, and I. L. Newberg, “Nonrecursive Tunable Photonic Filter Using Wavelength-Selective True Time Delay,” IEEE Photon. Technol. Lett., vol. 8, pp. 1214-1216, 1996.
T. Cussick, S. lezekiel, R. Miles, “Al-Optical Microwave Filter Design Employing a Genetic Algorithm,” IEEE Photon, Technol. Lett., vol. 10, pp. 1156-1158, 1998.
Hunter, R. Minasian, “Reflectively tapped fibre optic transversal filter using in-fibre Bragg gratings,” Electron. Lett., vol. 31, pp. 1010-1012, 1995.
IEEE Transactions on Microwave Theory and Techniques, vol. 47, No. 7, issued Jul. 1999, Minasian R A and You N, “A Novel High-Q Optical Microwave Processor using Hybrid Delay Line Filters”, pp. 1304-1308.
D. Hunter, R. Minasian, “Photonic Signal Processing of Microwave Signals Using an Active-Fiber Bragg-Grating-Pair Structure,” IEEE Trans. Microw. Theory Tech., vol. 45, pp. 1463-1466, 1997.
H. Taylor, S. Gweon, S. Fang, C. Lee, “Fiber optic delay-lines for wideband signal processing,” Proc. SPIE, vol. 1562, pp. 264, 1991.
K.P. Jackson, S. A. Newton, B. Moslehi, M. Tur, C.C. Cutler, J.W. Goodman, H.J. Shaw, “Optical Fiber Delay-Line Signal Processing,” IEEE Trans. Microw. Theory Tech., vol. MTT-33, No. 3, pp. 193-209, 1985.
Frankel, R. Esman, “Fibre-optic tunable microwave transversal filter,” IEEE Photon. Technol. Lett., pp. 191-193, 1995.
D. Norton, S. Johns, C. Keefer, R. Soref, “Tunable Microwave Filtering using High Dispersion Fiber Time Delays,” IEEE Photon, Technol. Lett., vol. 6, pp. 831-832, 1994 [5] D.
Foord, P. Davis, A. Greenhalgh, “Synthesis of microwave and millimeter wave filters using optical spectrum slicing,” Electron. Lett. Pp. 390-391, 1996.
Robert A. Minasian, Photonic signal processing of high-speed signals using fibre gratings, Microwave Photonics, 1999. MWP '99. International Topical Meeting on Melbourne, Vic., Australia Nov. 17-19 1999, Piscataway, NJ, USA, IEEE, US, Nov. 17, 1999 pp. 219-222, XPO10367445 ISBN: 0-7803-5558-X.
Jackson K P et al: “Optical Fiber Delay-Line Signal Processing” IEEE Transactions on Microwave Theory and Techniques, IEEE Inc. New York, US, vol. MTT- 33, No. 3,Mar. 1985, pp. 193-210, XP000955400 ISSN: 0018-9480.
Behzad Moslehi et al.: “Novel Amplified Fiber-Optic Recirculating Delay Line Processor” Journal of Lightwave Technology, IEEE. New York, US, vol. 10, No. 8, Aug. 1, 1992, pp. 1142-1147, XP000371909 ISSN: 0733-8724.
Coleman J O: “Choosing Nonuniform TAP Spacing For A Tapped-Delay-Lin
Minasian Robert
You Ningsi
Ladas & Parry
Lee John D.
The University of Sydney
Valencia Daniel
LandOfFree
High Q optical microwave processor using hybrid delay-line... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High Q optical microwave processor using hybrid delay-line..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High Q optical microwave processor using hybrid delay-line... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3197276