Tunable spectral filter

• US 20040136074A1
• Filed: 01/10/2003
• Published: 07/15/2004
• Est. Priority Date: 01/10/2003
• Status: Active Grant

• Current Assignee: Bookham Incorporated (Lumentum Holdings Inc.)
• Original Assignee: Onetta, Inc. (Lumentum Holdings Inc.)
• Inventors: Wilson, Gordon, Ford, Joseph Earl
• Granted Patent: US 6,891,676 B2
• Time in Patent Office: Days
• US Class Current: 359/572
• CPC Class Codes: G02B 6/2931 Diffractive element operating in reflection
• CPC Class Codes: G02B 6/29313 characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response switching G02B6/35
• CPC Class Codes: G02B 6/29314 by moving or modifying the diffractive element, e.g. deforming
• CPC Class Codes: G02B 6/29361 Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
• CPC Class Codes: G02B 6/29373 utilising a bulk dispersive element, e.g. prism
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35

Abstract

We describe an optical spectral filtering device and associated method for selectively directing a portion of a wavelength multiplexed input signal, entering through an optical fiber, into one or more output signals provided to one or more optical fibers and/or electronic outputs. The optical filtering is accomplished using free-space diffractive wavelength demultiplexing optics combined with a fixed (permanent) patterned structure located in the spectrally dispersed image plane. The structure can block or direct a selected spectral portion of the optical signal to one or more separate outputs, such as an optical fiber or power detector. A single active element in the optical path is used to spatially shift, or steer, the entire input spectrum at the dispersed spectral image plane, to control the portion of the input spectrum illuminating specific features on the permanent patterned structure. In one preferred embodiment, a variable-bandwidth tunable optical spectral power meter is constructed using an optical power detector with a fixed wedge-shaped aperture to detect a portion of a wavelength multiplexed input signal, and a tilting mirror is used to control the signal entering the detector, such that tilting the mirror in one axis will adjust the center wavelength of the signal being detected and tilting the mirror in the orthogonal axis adjusts the spectral bandwidth of the detected signal.

Claims

1. A tunable spectral filter comprising:

a spectral demultiplexer for spatially separating a multiple wavelength input signal;

a beam steerer for laterally shifting the spatially separated multiple wavelength input signal; and

a fixed optical element, positioned in the demultiplexed image plane, capable of selectively reflecting, deflecting, transmitting, and absorbing the laterally shifted, spatially separated wavelength input signal.

2. The tunable spectral filter according to claim 1 further comprising:

a power detector, for measuring the optical power of a controllable portion of the spectrally demultiplexed wavelength input signal.

3. The tunable spectral filter according to claim 1 further comprising:

a position detector, for detecting the position of the spatially demultiplexed signal such that feedback stabilization control is provided.

4. The tunable spectral filter according to claim 1 wherein said beam steerer comprises a reflective grating.

5. The tunable spectral filter according to claim 1 wherein said beam steerer comprises a transmissive grating.

6. The tunable spectral filter according to claim 4 wherein said beam steerer further comprises a mirror, positioned such that the spatially separated multiple wavelength input signal is diffracted by the reflective grating and reflected by the mirror back to the grating.

7. The tunable spectral filter according to claim 4 wherein said beam steerer further comprises a mirror, positioned such that the spatially separated multiple wavelength input signal is reflected by the mirror, diffracted by the reflective grating and then reflected by the mirror again.

8. The tunable spectral filter according to claim 6 wherein said mirror is a MEMS tilt mirror.

9. The tunable spectral filter according to claim 6 further comprising a mirror-controller, for selectively controlling an angle of the mirror.

10. The tunable spectral filter according to claim 4, wherein said grating is capable of selectively tilting.

11. The tunable spectral filter according to claim 10, wherein said selectively tiltable grating is a MEMS tilt grating.

12. The tunable spectral filter according to claim 11, wherein said selectively tiltable grating includes an angle-controller.

13. The tunable spectral filter according to claim 1 wherein said beam steerer is a liquid crystal beam steerer.

14. A tunable spectral filtering apparatus comprising:

means for spatially separating a multiple wavelength input signal;

means for controlling the lateral position of the spatially separated signal; and

means positionally fixed in the demultiplexed image plane, for selectively reflecting, deflecting, transmitting, and absorbing the laterally controlled, spatially separated signal;

such that the apparatus is operable to block or direct a selected spectral portion of the optical signal to one or more outputs.

15. The apparatus according to claim 14 wherein said spatially separating means comprises a reflective grating.

16. The apparatus according to claim 14 wherein said spatially separating means comprises a transmissive grating.

17. The apparatus according to claim 14 wherein said spatially separating means further comprises an additional means for reflecting the spatially separated signal.

18. The apparatus according to claim 14 further comprising a means for opti-mechanical beam steering.

19. A spectral filtering method comprising the steps of:

spatially separating a multiple wavelength input signal;

laterally steering the spatially separated multiple wavelength input signal; and

selectively reflecting, deflecting, transmitting and absorbing the laterally steered, spatially separated multiple wavelength input signal by a fixed optical element positioned in the demultiplexed image plane.

20. The method according to claim 19 further comprising the step of:

detecting, the optical power of a portion of the spectrally demultiplexed signal.

21. The method according to claim 19 further comprising the steps of:

detecting, the position of the spatially demultiplexed signal;

adjusting, the lateral steering of the spatially separated multiple wavelength signal as determined from the position of the spatially demultiplexed signal; and

optionally spatially recombining, the multiple wavelength input signal.