PHOTONIC FILTERING OF ELECTRICAL SIGNALS

• US 20100230621A1
• Filed: 03/08/2010
• Published: 09/16/2010
• Est. Priority Date: 03/10/2009
• Status: Active Grant

• Current Assignee: Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Industry, Through The Communications Research Centre Canada
• Original Assignee: Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Industry, Through The Communications Research Centre Canada
• Inventors: LU, Ping, YAO, Jianping, RIDEOUT, Howard, SEREGELYI, Joe, CARON, Mario, OLDHAM, John, PAQUET, Stéphane, MIHAILOV, Stephen J.
• Granted Patent: US 8,768,121 B2
• Time in Patent Office: Days
• US Class Current: 250/551
• CPC Class Codes: G02B 2006/12109 Filter
• CPC Class Codes: G02F 1/01 for the control of the intensity, phase, polarisation or colour G02F1/29, G02F1/35 take precedence
• CPC Class Codes: G02F 2201/16 series; tandem
• CPC Class Codes: G02F 2201/307 Reflective grating, i.e. Bragg grating
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: H04B 2210/006 Devices for generating or processing an RF signal by optical means

Abstract

A filter and a method of filtering a high frequency electrical signal using photonic components is disclosed. The filter has a serially fiber-coupled laser source, a modulator, a filter, and a photodetector. The electrical signal is applied to the modulator. The modulated light propagates through the filter which is constructed to pass not only a modulated sideband, but also at least a fraction of light at the carrier frequency of the laser. The photodetector detects a signal at the beat frequency between the carrier and sideband signals, after both signals have propagated through the filter. As a result, a separate optical branch for light at the carrier frequency is not required, which considerably simplifies the filter construction and makes it more stable and reliable.

Claims

1. A filter for filtering an electrical signal, comprising:

an optical modulator for receiving light at a carrier frequency and for modulating light at a frequency of the electrical signal;

an optical filter for receiving the modulated light arid for selecting light at a first frequency to propagate therethrough with at least a fraction of light at the carrier frequency; and

a photodetector for receiving light filtered by the optical filter and for detecting a signal at a beat frequency between the first frequency and the carrier frequency,

wherein the detected signal at the beat frequency comprises an output signal of the filter.

2. The filter of claim 1, wherein the filter is tunable by tuning at least one of the first frequency of the optical filter or the carrier frequency of light.

3. The filter of claim 1, further comprising a light source for providing light at the carrier frequency.

4. The filter of claim 3, wherein the light source is a laser.

5. The filter of claim 4, wherein the laser is a tunable diode laser.

6. The filter of claim 1, wherein the optical filter comprises a dual-band optical filter having a first passband for light at the first frequency and a second passband for light at the carrier frequency.

7. The filter of claim 6, wherein the optical filter comprises a first fiber Bragg grating having a first transmission band containing the first frequency.

8. The filter of claim 7, wherein the optical filter further comprises a second fiber Bragg grating coupled to the first fiber Bragg grating, the second fiber Bragg grating having a second transmission band,

wherein the first passband comprises an overlap region between the first and the second transmission bands.

9. The filter of claim 8, wherein the first fiber Bragg grating is tunable, whereby a bandwidth of the first passband is tunable.

10. The filter of claim 7, wherein the first fiber Bragg grating is tunable, whereby the first frequency is tunable.

11. The filter of claim 1, wherein the optical filter comprises a dual-band reflection fiber Bragg grating having a first reflection band for light at the first frequency and a second reflection band for light at the carrier frequency and an optical circulator or a beamsplitter coupled to the reflection fiber Bragg grating.

12. The filter of claim 1, wherein the optical filter includes a notch filter for attenuating light at a second frequency different from the first frequency.

13. The filter of claim 1, wherein the optical modulator and the optical filter are coupled by an optical waveguide.

14. The filter of claim 3, wherein the light source, the optical modulator, the filter, and the photodetector are coupled by an optical waveguide.

15. The filter of claim 14, wherein the optical waveguide is an optical fiber.

16. The dual-band optical filter usable in the filter of claim 6, comprising first and second optical sub-filters connected in series, wherein the first and the second optical sub-filters each have first and second passbands,

wherein the first passband of the dual-band optical filter comprises an overlap region between the first passbands of the first and the second optical sub-filters;

wherein the second passband of the dual-band optical filter comprises an overlap region between the second passbands of the first and the second optical sub-filters; and

wherein a central frequency and/or a bandwidth of the first passband of the optical filter is tunable by tuning a central frequency of the first passband of the first optical sub-filter, of the second optical sub-filter, or of both the first and the second optical sub-filters,

whereby the filter for filtering the electrical signal is tunable in frequency and/or bandwidth.

17. The dual-band optical filter of claim 16, wherein the first and the second sub-filters are fiber Bragg gratings.

18. A filter for filtering an electrical signal, comprising:

a first source of light at a carrier frequency modulated at a frequency of the electrical signal; and

an optical filter coupled to the first source of light, for receiving the modulated light and for selecting light at a first frequency to propagate therethrough with at least a fraction of light at the carrier frequency, for subsequent conversion into an output electrical signal at a beat frequency between the first frequency and the carrier frequency.

19. The filter of claim 18, wherein the first source of light comprises a laser source for emitting light at the carrier frequency, wherein the laser source is configured to be directly modulated at the frequency of the electrical signal.

20. The filter of claim 18, wherein the first source of light comprises an optical modulator for receiving light at the carrier frequency and for modulating light at the frequency of the electrical signal.

21. The filter of claim 18, further comprising a photodetector for conversion of light at the carrier frequency co-propagating with the light at the first frequency into the output electrical signal at a beat frequency between the first frequency and the carrier frequency.

22. A method of filtering an electrical signal, comprising:

(a) providing an optical signal at a carrier frequency;

(b) modulating the optical signal of step (a) at a frequency of the electrical signal, so as to generate a modulated optical signal having a sidelobe frequency band;

(c) filtering the optical signal modulated in step (b) using an optical filter having a first passband for passing light at a first frequency within the sidelobe frequency band, and a carrier passband for passing light at the carrier frequency; and

(d) detecting a signal at a beat frequency between the optical signals filtered in step (c).

23. The method of claim 22, wherein a frequency of filtering of the electrical signal is tunable by tuning the carrier frequency or the first frequency or both.