CA2059587C - Fiber optic rf signal channelizer - Google Patents
Fiber optic rf signal channelizerInfo
- Publication number
- CA2059587C CA2059587C CA002059587A CA2059587A CA2059587C CA 2059587 C CA2059587 C CA 2059587C CA 002059587 A CA002059587 A CA 002059587A CA 2059587 A CA2059587 A CA 2059587A CA 2059587 C CA2059587 C CA 2059587C
- Authority
- CA
- Canada
- Prior art keywords
- frequency
- channelizer
- fiber optic
- bandpass filter
- cavity
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
- G02B6/29358—Multiple beam interferometer external to a light guide, e.g. Fabry-Pérot, etalon, VIPA plate, OTDL plate, continuous interferometer, parallel plate resonator
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Spectrometry And Color Measurement (AREA)
- Light Guides In General And Applications Therefor (AREA)
Abstract
An array of fiber optic RF filters each responsive to a predetermined wavelength forms a channelizer for a wide bandwidth receiver used in a dense signal environment having complex modulations. Each fiber optic RF filter comprises a resonant cavity formed from a section of multimode optic fiber with a dielectric mirror deposited at each end and wherein the cavity length corresponds to one half the respective modulation signal wavelength of optical energy fed into the filter optic cavity from a laser diode which is modulated by the received RF energy.
Description
~~;'~~5~3'°~
FIELD OF THE INVENTION
This invention relates to the detection of a wide spectrum of radio frequency signals and more particularly to the detection of radio frequency signals in a dense signal environment with complex modulations.
BACKGROUND OF THE INVENTION
Several frequency source identification methods are generally known in the prior art. The mast well known of these is probably what may be termed "standard heterodyning techniques'°. This technique tunes a heterodyne receiver for peak output provides a readout of the frequency in question. This technique is relatively time consuming. and becomes impossible when the signal source is hopping or changing rapidly in frequency. One known technique for signal detection where signal hopping is involved involves the use of a compressive receiver. In this type of receiver, an input signal is mixed with a chirp signal and swept through the intermediate frequency band for a designated time of arrival. The signal's position and time is therefore indicative of its frequency. One example of this type of apparatus is disclosed in U.S. Pat. No. 4,443,801 issued to D.R. Klose et al, which issued on April 17, 1984, and which discloses the use of SAW interferometer processor apparatus which performs high resolution measurements on multiple signals of different frequency.
A SAW channelizer compressive interferometer is a combination of two basic and well known technologies, namely, a SAW channelizer and a compressive interferometer. A conventional SAW channelizer _x_ measures the pulsewidth (PW) , pi.alse ampl~.tude (PA) , arid time of arrival (TOA) while compressive angles of arrival (AOA) channels measure AOA and frequency. A SAW channelizer is comprised of a contiguous bank of SAP7 filters arranged to sort the received signal into frequency bins, with the frequency bin width being selected by the minimum pulsewidths to be intercepted. The filters also have sharp cut off frequencies to enable them to discern strong vs. weak signals in adjacent channels. A compressive interferometer is a spin off of a microscan receiver where AOA is measured from antenna l0 input phase differentials along with the frequency of multiple signals in the IF passband. Conventional SAW based compressive interferometers, however, suffer from having too many filters in the channelizer to measure pulsewidth.
SUMMARY OF THE TNVENTION
It is an object of the present invention, therefore, to detect a wide spectrum of radio frequency signals, whether or not those signals are received coincidentally.
It is a further object of the invention to provide an improvement in a channelized type of RF receiver.
20 It is yet another object of the invention to provide an alternate configuration for a wide band compressive interferometer and SAW channelizer.
Briefly, the,foregoing and other objects of the invention are provided by an array of fiber optic signal filters arranged as bandpass filters to form a channelizer, with each filter being _2_ ~, ...,r~ e,., a.A~ t.°
constructed from a resonant cavity formed from a section of multimode otpic fiber with a dielectric mirror disposed at each end and whose respective cavity length corresponds to one half the center frequency of the filter. Each channel,, moreover, includes a laser diode connected between the RF input and the filter input and a laser detector diode connected between the filter output and a signal output, BRTEF DESCRIPTION OF THE DRAWING
These and other objects, features and details of the invention will become apparent in light of the ensuing detailed disclosure, and particularly in light of the drawings wherein:
Figure 1 is a functional block diagram of a fiber optic filter; and Figure 2 is an electrical block diagram of the preferred embodiment of the invention utilizing fiber optic bandpass filters as shown in Figure 1 in each of the channels.
DETAILED DESCRIPTION
Prior to considering the details of the subject invention, the operation of a compressive receiver will first be described. A
compressive receiver is based upon pulse compression and is formulated on the correlation properties of phase coded waveforms, linear frequency modulation or chirps. SAW technology has typically been used for pulse compression. One approach is to employ a frequency mixer for the RF input and the output of a swept l' ., r". P' t-',' r or chirped local oscillator followed by a compressor implementing what is known as a multiply long, convolve, short (ML-CS) configuration. The chirp slopes of the sweeping local oscillator and the compressor are designed to match so that an output defining a sin x/x function is provided.
In the present invention, the heretofore used SAW filter ban~C
is replaced by an array of fiber optic filters designed as a bank of bandpass filters.
~teferring now to Figure 1, shown thereat is a fiber optic RF
bandpass filter 10 comprised of a predetermined length of multimode optic fiber 12 and a pair of dielectric mirror elements 14 and 16 deposited on each end. Small holes or apertures 18 and 20 are formed in the mirrors 14 and 16 for the passage of optical energy respectively in and out of the cavity 12. The cavity length is chosen to be one half the modulation wavelength ~,m = c/fc where c is the speed of light (3 x 108m/sec) and f~ is the frequency of modulation imposed on the carrier light injected into the cavity 12. The cavity 12, therefore, is not resonant at the frequency of the optical carrier, but to the modulation on the carrier. Thus one would choose the length L to match the center frequency of the band of modulation frequencies fC in accordance with the expression L = c/2nfc where n is the refractive index of the fiber. Operation with non-coherent light and/or a highly multimode fiber results in averaging overoptical resonances within the cavity. Thus the filter acts only on power variations and is independent of the optical wavelength of the light carrier of the energy entering the hole 18 into the cavity 12.
_4_ This now leads to a consideration of the preferred embodiment of the invention which comprises an array of fiber optical bandpass filter channels 1-n. Each of the bandpass filter channels are coupled to an RF input which is receptive to a wide Y~and of frequencies which can be separated into a plurality of spectrum samples or frequency bins distributed over the frequency range of interest.
Accordingly, each channel or frequency bin is comprised of a fiber optic bandpass filter 101 so that the first channel includes the filter 101, while the last channel includes the filter 10n.
Each of the fiber optic bandpass filters 101 - 10n are coupled to the output of a respective laser diode 241 - 24n which is modulated by the RF input at 22. Each of the bandpass filters 101 - 10n have predetermined different center frequencies as determined by the.
respective lengths of the optical fibers 12 from which they are fabricated. Each of the fiber optic bandpass filters 101 - 10n have their respective optical outputs fed to respective laser detector diodes 261 - 26n which in turn output frequencies f1 - fn of the respective frequency bins. When desirable, the n number of laser diodes can be replaced by a single laser diode and modulator element 24 whose output would be commonly coupled to all of the fiber optic bandpass filters 101 - 10n. The frequency outputs f1 -fn when mixed or heterodyned with a swept local oscillator, riot shown, provides IF signals.
Where the array of bandpass filters as shown iri Figure 2 axe included in electronic support measure (ESM) receivers used for electronic waveform applications, for example, there is provided an improved means for detecting radar signals as well as their angles of arrival and also to que direction finders, etc. over a ~fre~c~xency range, for example, between 50oMHz and lBGHz.
Having thus shown and described what is at present considered to be the preferred embodiment of the invention, it should be noted that the same has been made by way of illustration and not limitation. accordingly, all modifications, alterations and changes coming within the spirit and scope of the invention are herein meant to be included.
-6~-
FIELD OF THE INVENTION
This invention relates to the detection of a wide spectrum of radio frequency signals and more particularly to the detection of radio frequency signals in a dense signal environment with complex modulations.
BACKGROUND OF THE INVENTION
Several frequency source identification methods are generally known in the prior art. The mast well known of these is probably what may be termed "standard heterodyning techniques'°. This technique tunes a heterodyne receiver for peak output provides a readout of the frequency in question. This technique is relatively time consuming. and becomes impossible when the signal source is hopping or changing rapidly in frequency. One known technique for signal detection where signal hopping is involved involves the use of a compressive receiver. In this type of receiver, an input signal is mixed with a chirp signal and swept through the intermediate frequency band for a designated time of arrival. The signal's position and time is therefore indicative of its frequency. One example of this type of apparatus is disclosed in U.S. Pat. No. 4,443,801 issued to D.R. Klose et al, which issued on April 17, 1984, and which discloses the use of SAW interferometer processor apparatus which performs high resolution measurements on multiple signals of different frequency.
A SAW channelizer compressive interferometer is a combination of two basic and well known technologies, namely, a SAW channelizer and a compressive interferometer. A conventional SAW channelizer _x_ measures the pulsewidth (PW) , pi.alse ampl~.tude (PA) , arid time of arrival (TOA) while compressive angles of arrival (AOA) channels measure AOA and frequency. A SAW channelizer is comprised of a contiguous bank of SAP7 filters arranged to sort the received signal into frequency bins, with the frequency bin width being selected by the minimum pulsewidths to be intercepted. The filters also have sharp cut off frequencies to enable them to discern strong vs. weak signals in adjacent channels. A compressive interferometer is a spin off of a microscan receiver where AOA is measured from antenna l0 input phase differentials along with the frequency of multiple signals in the IF passband. Conventional SAW based compressive interferometers, however, suffer from having too many filters in the channelizer to measure pulsewidth.
SUMMARY OF THE TNVENTION
It is an object of the present invention, therefore, to detect a wide spectrum of radio frequency signals, whether or not those signals are received coincidentally.
It is a further object of the invention to provide an improvement in a channelized type of RF receiver.
20 It is yet another object of the invention to provide an alternate configuration for a wide band compressive interferometer and SAW channelizer.
Briefly, the,foregoing and other objects of the invention are provided by an array of fiber optic signal filters arranged as bandpass filters to form a channelizer, with each filter being _2_ ~, ...,r~ e,., a.A~ t.°
constructed from a resonant cavity formed from a section of multimode otpic fiber with a dielectric mirror disposed at each end and whose respective cavity length corresponds to one half the center frequency of the filter. Each channel,, moreover, includes a laser diode connected between the RF input and the filter input and a laser detector diode connected between the filter output and a signal output, BRTEF DESCRIPTION OF THE DRAWING
These and other objects, features and details of the invention will become apparent in light of the ensuing detailed disclosure, and particularly in light of the drawings wherein:
Figure 1 is a functional block diagram of a fiber optic filter; and Figure 2 is an electrical block diagram of the preferred embodiment of the invention utilizing fiber optic bandpass filters as shown in Figure 1 in each of the channels.
DETAILED DESCRIPTION
Prior to considering the details of the subject invention, the operation of a compressive receiver will first be described. A
compressive receiver is based upon pulse compression and is formulated on the correlation properties of phase coded waveforms, linear frequency modulation or chirps. SAW technology has typically been used for pulse compression. One approach is to employ a frequency mixer for the RF input and the output of a swept l' ., r". P' t-',' r or chirped local oscillator followed by a compressor implementing what is known as a multiply long, convolve, short (ML-CS) configuration. The chirp slopes of the sweeping local oscillator and the compressor are designed to match so that an output defining a sin x/x function is provided.
In the present invention, the heretofore used SAW filter ban~C
is replaced by an array of fiber optic filters designed as a bank of bandpass filters.
~teferring now to Figure 1, shown thereat is a fiber optic RF
bandpass filter 10 comprised of a predetermined length of multimode optic fiber 12 and a pair of dielectric mirror elements 14 and 16 deposited on each end. Small holes or apertures 18 and 20 are formed in the mirrors 14 and 16 for the passage of optical energy respectively in and out of the cavity 12. The cavity length is chosen to be one half the modulation wavelength ~,m = c/fc where c is the speed of light (3 x 108m/sec) and f~ is the frequency of modulation imposed on the carrier light injected into the cavity 12. The cavity 12, therefore, is not resonant at the frequency of the optical carrier, but to the modulation on the carrier. Thus one would choose the length L to match the center frequency of the band of modulation frequencies fC in accordance with the expression L = c/2nfc where n is the refractive index of the fiber. Operation with non-coherent light and/or a highly multimode fiber results in averaging overoptical resonances within the cavity. Thus the filter acts only on power variations and is independent of the optical wavelength of the light carrier of the energy entering the hole 18 into the cavity 12.
_4_ This now leads to a consideration of the preferred embodiment of the invention which comprises an array of fiber optical bandpass filter channels 1-n. Each of the bandpass filter channels are coupled to an RF input which is receptive to a wide Y~and of frequencies which can be separated into a plurality of spectrum samples or frequency bins distributed over the frequency range of interest.
Accordingly, each channel or frequency bin is comprised of a fiber optic bandpass filter 101 so that the first channel includes the filter 101, while the last channel includes the filter 10n.
Each of the fiber optic bandpass filters 101 - 10n are coupled to the output of a respective laser diode 241 - 24n which is modulated by the RF input at 22. Each of the bandpass filters 101 - 10n have predetermined different center frequencies as determined by the.
respective lengths of the optical fibers 12 from which they are fabricated. Each of the fiber optic bandpass filters 101 - 10n have their respective optical outputs fed to respective laser detector diodes 261 - 26n which in turn output frequencies f1 - fn of the respective frequency bins. When desirable, the n number of laser diodes can be replaced by a single laser diode and modulator element 24 whose output would be commonly coupled to all of the fiber optic bandpass filters 101 - 10n. The frequency outputs f1 -fn when mixed or heterodyned with a swept local oscillator, riot shown, provides IF signals.
Where the array of bandpass filters as shown iri Figure 2 axe included in electronic support measure (ESM) receivers used for electronic waveform applications, for example, there is provided an improved means for detecting radar signals as well as their angles of arrival and also to que direction finders, etc. over a ~fre~c~xency range, for example, between 50oMHz and lBGHz.
Having thus shown and described what is at present considered to be the preferred embodiment of the invention, it should be noted that the same has been made by way of illustration and not limitation. accordingly, all modifications, alterations and changes coming within the spirit and scope of the invention are herein meant to be included.
-6~-
Claims (11)
1. A frequency channelizer for determining the frequency of a plurality of received radio frequency signals over a predetermined bandwidth, comprising:
a plurality of predetermined narrow bandwidth frequency detection channels coupled to an RF signal input, each channel including a fiber optic bandpass filter having a predetermined different center frequency selectively chosen within said predetermined bandwidth for channeling signals for detection within a plurality of frequency bins.
a plurality of predetermined narrow bandwidth frequency detection channels coupled to an RF signal input, each channel including a fiber optic bandpass filter having a predetermined different center frequency selectively chosen within said predetermined bandwidth for channeling signals for detection within a plurality of frequency bins.
2. The frequency channelizer of claim 1 wherein each fiber optic bandpass filter is further comprised of a fiber optic cavity and mirror means having light apertures therein located at opposite ends of said cavity.
3. The frequency channelizer of claim 2 wherein said fiber optic cavity is comprised of a length of optical fiber.
4. The frequency channelizer of claim 3 wherein the length of said optical fiber is a function of the center frequency of the bandpass of the respective filter.
5. The frequency channelizer of claim 3 wherein the length of said optical fiber is substantially equal to one half the wavelength of the respective center frequency.
6. The frequency channelizer of claim 3 and wherein said mirror means comprises a pair of dielectric mirrors secured to each end of said optical fiber.
7. The frequency channelizer of claim 1 and additionally including light modulation means coupled to and responsive to said RF signal input for generating a modulated optical signal which is then coupled to each said fiber optic bandpass filter.
8. The frequency channelizer of claim 7 wherein said light modulation means comprises laser diode means.
9. The frequency channelizer of claim 8 wherein said laser diode means comprises a laser diode coupled between said RF signal input and each said fiber optic bandpass filter.
10. The frequency channelizer of claim 7 and additionally including light demodulation means coupled to each of said fiber optic bandpass filter.
11. The frequency channelizer of claim 10 wherein said light demodulation means comprises a laser detector diode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/656,916 USH1059H (en) | 1991-02-19 | 1991-02-19 | Fiber optic RF signal channelizer |
| US07/656,916 | 1991-02-19 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2059587A1 CA2059587A1 (en) | 1992-08-20 |
| CA2059587C true CA2059587C (en) | 1999-09-07 |
Family
ID=24635093
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002059587A Expired - Fee Related CA2059587C (en) | 1991-02-19 | 1992-01-17 | Fiber optic rf signal channelizer |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | USH1059H (en) |
| CA (1) | CA2059587C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004092809A1 (en) * | 2003-04-16 | 2004-10-28 | Edith Cowan University | Microphotonic filter |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5296860A (en) * | 1991-11-04 | 1994-03-22 | Li Ming Chiang | Optical fiber based bistatic radar |
| US5687263A (en) * | 1995-10-02 | 1997-11-11 | The United States Of America As Represented By The Secretary Of The Navy | Optical RF bandpass filter and method for manufacturing same |
| WO1997043806A2 (en) | 1996-05-17 | 1997-11-20 | Uab Research Foundation | Semiconductor laser with a superbroadband or multiline spectral output |
| US6901224B1 (en) | 2000-02-18 | 2005-05-31 | Northrop Grumman Corporation | Hybrid coherent-optical, RF signal channelizer |
| US7541959B1 (en) * | 2003-04-07 | 2009-06-02 | Photonics Products, Inc. | High speed signal processor |
| US6980147B2 (en) * | 2003-04-07 | 2005-12-27 | Photon Products, Inc. | Channelized analog-to-digital converter |
-
1991
- 1991-02-19 US US07/656,916 patent/USH1059H/en not_active Abandoned
-
1992
- 1992-01-17 CA CA002059587A patent/CA2059587C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004092809A1 (en) * | 2003-04-16 | 2004-10-28 | Edith Cowan University | Microphotonic filter |
Also Published As
| Publication number | Publication date |
|---|---|
| USH1059H (en) | 1992-05-05 |
| CA2059587A1 (en) | 1992-08-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |