Optical calibration system and method

• US 7,457,547 B2
• Filed: 11/08/2004
• Issued: 11/25/2008
• Est. Priority Date: 11/08/2004
• Status: Active Grant

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Finisar Australia Pty., Ltd. (Coherent Corp.)
• Inventors: Zhou, Hao, Abakoumov, Dmitri, Baxter, Glenn W., Frisken, Steven J.
• Primary Examiner(s): SEDIGHIAN, REZA
• Application Number:
  US10/984,594
• Publication Number:
  US 20060098156A1
• Time in Patent Office: 1,478 Days
• Field of Search: 398/158, 398/159, 398/151, 398/119
• US Class Current: 398/158
• CPC Class Codes: G01M 11/0292 of objectives by measuring the optical modulation transfer function photometry G01J
• CPC Class Codes: G02B 6/29311 Diffractive element operating in transmission
• 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: G02F 2203/12 spatial light modulator
• CPC Class Codes: G02F 2203/50 Phase-only modulation

Abstract

In an optical system including an optical input port for projecting an input optical signal onto an optical phased matrix array, an optical phased matrix array including a plurality of individually addressable pixels thereon, each said pixel being drivable within a prescribed range of levels, and an optical output port for collecting a predetermined fraction of said optical signal received from said optical phased matrix array; a method of compensating for phase distortions including the steps of: (a) determining a plurality of transfer functions relating said level of each said pixel to the phase variation each said pixel introduces to light from said input optical signal which is incident thereon; and (b) controlling the level of selected ones of said pixels in accordance with a corresponding transfer function such that said fractional signal received at said output port is modified in phase to substantially compensate for optical phase distortions arising from said optical phased matrix array.

Claims

1. A method of compensating for phase distortions, in an optical system including:

an optical input port for projecting an input optical signal onto an optical phased matrix array,

an optical phased matrix array including a plurality of individually addressable pixels thereon, each said pixel being drivable within a prescribed range of levels, and

an optical output port for collecting a predetermined fraction of said optical signal received from said optical phased matrix array;

the method including the steps of;

(a) determining a plurality of transfer functions relating said level of each said pixel to the phase variation each said pixel introduces to light from said input optical signal which is incident thereon;

(b) controlling the level of selected ones of said pixels in accordance with a corresponding transfer function such that a fractional signal received at said output port is modified in phase to substantially compensate for optical phase distortions arising from said optical phased matrix array;

(c) determining a transfer function relating a wavelength signal to the pixels they are incident thereon; and

(d) associating selected ones of said pixels in accordance with said transfer function to said wavelength signals such that the phase of selected wavelength signals can be independently modified in accordance with requirements.

2. A method as claimed in claim 1 wherein said transfer functions are implemented in the form of a series of lookup tables relating said level of each said pixel to the phase variation each said pixel introduces to light from said optical signal which is incident thereon.

3. A method as claimed in claim 1 wherein said transfer functions further include substantial compensation for the optical phase distortion arising from the overall optical system.

4. A method as claimed in claim 1 wherein said optical system further includes an optical dispersion element for spatially separating wavelength signals from said optical signal.

5. A method as claimed in claim 1 wherein said optical system includes

a plurality of output ports and aid method further includes the steps of:

(e) determining a plurality of routing transfer functions relating the coupling between said input port and said output ports; and

(f) controlling the level of selected ones of said pixels in accordance with said routing transfer functions such that at least a fraction of selected ones of said wavelength signals is directed to at least one of said output ports.

6. A method as claimed in claim 5 further including the steps of:

(g) determining a transfer function relating an optical power of said wavelength signals that is coupled to optical output ports adjacent the desired output port to the amplitude and phase imparted to said wavelength signals due to multiple reflections in said optical system; and

(h) modifying said routing transfer functions to substantially cancel said optical power on said adjacent output ports.

7. A method as claimed in claim 1 wherein said optical system further includes a plurality of input ports.

8. A method as claimed in claim 1 wherein said method is utilised in a testing phase by testing selected regions of said optical phased matrix array.

9. A method as claimed in claim 1 wherein said optical phased matrix array is a liquid crystal spatial light modulator.

10. A method as claimed in claim 1 wherein said optical phased matrix array is a liquid crystal on silicon spatial light modulator.

11. A method of selecting a desired wavelength signal, in an optical system including:

an optical input port for projecting an input optical signal onto an optical phased matrix array,

an optical phased matrix array including a plurality of individually addressable pixels thereon, each said pixel being drivable within a prescribed range of levels,

an optical dispersion element for spatially separating wavelength signals from said optical signal, and

an optical output port for collecting a predetermined fraction of said optical signal received from said optical phased matrix array;

the method including the steps of;

(a) determining a transfer function relating said wavelength signals to said pixels they are incident thereon; and

(b) associating selected ones of said pixels in accordance with said transfer function to said wavelength signals such that a phase of said selected wavelength signals can be independently modified in accordance with requirements;

(c) determining a transfer function relating said wavelength signals to the pixels they are incident thereon; and

(d) associating selected ones of said pixels in accordance with said transfer function to said wavelength signals such that the phase of selected wavelength signals can be independently modified in accordance with requirements.

12. A method as claimed in claim 11 wherein said wavelength signals are standardized wavelength bands designated for telecommunications networks.

13. A method as claimed in claim 11 wherein said wavelength signals are designated by spacings of one of 200 GHz, 100 GHz, 50 GHz, 25 GHz, or 12.5 GHz.

14. A method as claimed in claim 11 wherein said step of associating selected ones of said pixels with said transfer function are reconfigurable according to requirements.

15. A method as claimed in claim 11 wherein the pixels in a selected region of said optical phased matrix array are associated with wavelength signals separated by a particular spacing and other pixels in other selected regions of said optical phased matrix array are associated with wavelength signals separated by different spacings according to requirements.

16. A method as claimed in claim 15 wherein said particular spacing and said different spacings are each selected from the group of 200 GHz, 100 GHz, 50 GHz, 25 GHz, or 12.5 GHz.

17. A method as claimed in claim 11 wherein said transfer function is implemented in the form of a lookup table relating a predetermined wavelength signal to the corresponding pixel that said predetermined wavelength signal is incident thereon.

18. A method of minimizing power variations in a fractional signal collected by output ports, in an optical system including:

an optical input port for projecting an input optical signal onto an optical phased matrix array,

an optical phased matrix array including a plurality of individually addressable pixels thereon, each said pixel being drivable within a prescribed range of levels, and

a plurality of optical output ports, each for collecting a predetermined fraction of said optical signal received from said optical phased matrix array;

the method including the steps of;

(a) determining a plurality of pixel transfer functions relating said level of each said pixel to a phase variation each said pixel introduces to light from said input optical signal which is incident thereon;

(b) determining a plurality of routing transfer functions relating the coupling between said input port and said output ports by selection of appropriate levels of predetermined ones of said pixels;

(c) determining minimum and maximum levels of said phase variation; and

(d) controlling the level of selected ones of said pixels in accordance with a corresponding routing transfer function, said routing transfer function being constrained between said minimum and maximum levels, to direct at least a fraction of said optical signal to at least one of said output ports such that said power variations in the fraction of light collected by said output port are minimized.

19. A method as claimed in claim 18 wherein said routing transfer functions are substantially insensitive to phase variations in said pixel transfer functions.

20. A method as claimed in claim 18 wherein said minimum and maximum levels are reconfigurable to adjust for phase variations in said pixel transfer functions.

21. A method of minimizing time-varying variations of optical signals in an optical system including:

an optical input port for projecting an input optical signal onto an optical phased matrix array,

an optical phased matrix array including a plurality of individually addressable pixels thereon, each said pixel being drivable within a prescribed range of levels,

an optical output port for collecting a predetermined fraction of said optical signal received from said optical phased matrix array,

a plurality of pixel transfer functions relating said level of each said pixel to a phase variation each said pixel introduces to light from said input optical signal which is incident thereon, and

at least one routing transfer function describing the phase variation to be imparted by selected ones of said pixels to thereby couple said fraction of said optical signal between said input port and said output port, where said routing transfer function is constrained between selected minimum and maximum levels;

the method including the steps of;

(a) providing a detection element at said output port, said detection element providing a detector signal responsive to time-varying variations in said fraction of said optical signal collected by said output port; and

(b) modifying said maximum and minimum levels to substantially minimize said time-varying variations in response to said detector signal thereby substantially optimizing the performance of said optical system.

22. method as claimed in claim 21 wherein said optical system further includes a plurality of optical output ports, each output port including a corresponding detection element, and a plurality of routing transfer functions to couple selected fractions of said optical signal between said input port and at least one selected output ports in accordance with requirements.

23. A method of attenuating a selected fractional wavelength signal in an optical system including:

an optical input port for projecting an input optical signal onto an optical phased matrix array,

an optical phased matrix array including a plurality of individually addressable pixels thereon, each said pixel being drivable within a prescribed range of levels,

an optical output port for collecting a predetermined fraction of said optical signal received from said optical phased matrix array,

a plurality of pixel transfer functions relating said level of each said pixel to a phase variation each said pixel introduces to light from said input optical signal which is incident thereon,

an optical dispersion element for spatially separating wavelength signals from said optical signal,

a wavelength transfer function relating said wavelength signals to said pixels they are incident thereon to defined regions of said pixels for independent modification of said wavelength signals, and

at least one routing transfer function describing a phase variation to be imparted by selected said regions to thereby couple a fraction of said wavelength signal between said input port and said output port;

the method including the steps of;

(a) determining a plurality of equalization transfer functions relating the phase variation of selected pixels in said selected region to the amount of attenuation achieved on a selected wavelength signal;

(b) selecting a suitable equalization transfer function to give the required attenuation on a selected said fractional wavelength signal; and

(c) applying said selected equalization transfer function in conjunction with said routing transfer function to attenuate said fractional wavelength signal in accordance with requirements.

24. An optical system as claimed in claim 23 wherein said selected equalization transfer function causes said fractional wavelength signal to be directed away from said output port by a known distance thereby attenuating the light collected by said output port in accordance with requirements.

25. An optical system as claimed in claim 23 wherein said selected equalization transfer function causes a selected portion of said fractional wavelength signal to be directed away from said output port thereby attenuating the light collected by said output port in accordance with requirements.

26. An optical system as claimed in claim 23 wherein said selected equalization transfer function modifies the phase of selected portions of said wavelength signal such that said modified portions destructively interfere with other portions of said wavelength signal by a known amount thereby attenuating the amount of light collected by said output port in accordance with requirements.

27. An optical system as claimed in claim 23 wherein said optical system includes a plurality of output ports and step (b) further includes selection of an equalization transfer function for attenuation of a selected wavelength signal that does not cause a significant fraction of said optical signal to be collected by another of said optical output ports.

28. A calibration method for an optical device including the steps of:

(a) providing an optical system including at least one optical input port and at least one optical output port, where said input port delivers an optical input signal comprising of a plurality of wavelength signals to a liquid crystal spatial light modulator including a plurality of individually addressable pixels thereon that substantially couples said optical signal to output port;

(b) performing a background calibration of said spatial light modulator and said optical system;

(c) performing an efficiency calibration to optimize the coupling of a selected portion of said optical input signal between said input port and said output port as a function of wavelength;

(d) determining a transfer function relating said wavelength signals to the pixels they are incident thereon; and

(e) associating selected ones of said pixels in accordance with said transfer function to said wavelength signals such that a phase of selected wavelength signals can be independently modified in accordance with requirements;

such that said pixels of said spatial light modulator can be operated as a dynamically reconfigurable grid.

29. A method as claimed in claim 28 wherein the background calibration of step (b) includes analysis of wavefront distortions and optical aberrations of said spatial light modulator and said optical system.

30. A method according to claim 29 wherein said background calibration further includes the correction of said wavefront distortions and aberration by appropriate modification on a pixel-by-pixel basis of the wavefront of light that impinges on said spatial light modulator.

31. A method as claimed in claim 28 wherein steps (a) and (b) result in a plurality of tabulated coefficients describing:

(i) the optical phase response of the individual pixels of said spatial light modulator;

(ii) a plurality of holographic phase modulation functions, which when applied to the pixels of said spatial light modulator, provides directional control of light which is incident on said pixels to couple said light between an input port and an output port of said optical system; and

(iii) a plurality of phase variation functions for control over the coupling efficiency of said light between said input port and said output port.

32. A method as claimed in claim 31 further including a plurality of transfer functions to reconstruct said phase variation functions from said tabulated coefficients in accordance with requirements.

33. A method as claimed in claim 31 wherein said tabulated coefficients describing said optical phase response includes temperature specific information.

34. A method as claimed in claim 28 wherein said calibration method is a self-calibration method.

35. A method as claimed in claim 31 wherein said phase variation functions are formed from a holographic phase function.

36. A method as claimed in claim 28 wherein step (b) includes the steps of:

(b1) Performing a calibration of the phase retardance response to an optical signal of said spatial light modulator on a pixel-by-pixel basis; and

(b2) Performing a calibration of the dispersion characteristics of said optical signal with respect to one axis of said spatial light modulator.

37. A method as claimed in claim 36 where the data obtained from step (b1) is retained and reprocessed using the results of step (b2).

38. A method as claimed in claim 28 wherein said optical system includes a plurality of optical output ports and step (c) includes the steps of:

(c1)determining a further plurality of tabulated coefficients and transfer functions to couple a required fraction of said optical signal to each of said output ports;

(c2)determining a plurality of first modification functions to modify said transfer functions of step (c1) to substantially account for non-uniformity across the surface of said spatial light modulator for each said output port; and

(c3)determining a second modification function to modify said transfer functions of step (c1) to substantially minimise the effect of cross-talk on adjacent ones of said output ports.

39. A method as claimed in claim 28 wherein said spatial light modulator is a liquid crystal spatial light modulator.

40. A method as claimed in claim 28 wherein said spatial light modulator is a liquid crystal on silicon spatial light modulator.

41. A method as claimed in claim 31 wherein said said plurality of phase variation functions are substantially insensitive to variations in the response of said spatial light modulator.

42. A method as claimed in claim 31 further including a detection element at output port to monitor variations in the response of said spatial light modulator.