Compensating for chromatic dispersion in optical fibers

Abstract

An optical chromatic dispersion compensator ( 60 ) betters optical communication system performance. The dispersion compensator ( 60 ) includes a collimating means ( 61 ) that receives a spatially diverging beam of light from an end of an optical fiber ( 30 ). The collimating means ( 61 ) converts the spatially diverging beam into a mainly collimated beam that is emitted therefrom. An optical phaser ( 62 ) receives the mainly collimated beam from the collimating means ( 61 ) through an entrance window ( 63 ), and angularly disperses the beam in a banded pattern that is emitted from the optical phaser ( 61 ). A light-returning means ( 66 ) receives the angularly dispersed light and reflects it back through the optical phaser ( 62 ) to exit the optical phaser near the entrance window ( 63 ) thereof.

1. An optical chromatic dispersion compensator adapted for bettering performance of an optical communication system comprising:
 a collimating means for receiving a spatially diverging beam of light which contains a plurality of frequencies as may be emitted from an end of an optical fiber included in an optical communication system, the collimating means also converting the received spatially diverging beam of light into a mainly collimated beam of light that is emitted from the collimating means; 
 an optical phaser which provides an entrance window for receiving the mainly collimated beam of light from the collimating means and for angularly dispersing the received beam of light in a banded pattern that is emitted from the optical phaser, whereby the received beam of light becomes separated into bands so that light having a particular frequency within a specific band is angularly displaced from light at other frequencies within that same band; and 
 a light-returning means which receives the angularly dispersed light having the banded pattern that is emitted from the optical phaser, and for reflecting that light back through the optical phaser to exit the optical phaser near the entrance window thereof. 
 
     
     
       2. The compensator of  claim 1  wherein the mainly collimated beam of light emitted from the collimating means has a divergence which ensures that more than fifty-percent (50%) of energy in the mainly collimated beam of light impinging upon the entrance window diffracts into fewer than three (3) diffraction orders for any beam of light at a particular wavelength in the angularly dispersed light emitted from the optical phaser in the banded pattern. 
     
     
       3. The compensator of  claim 1  wherein light enters the optical phaser through the entrance window at near normal incidence. 
     
     
       4. The compensator of  claim 1  wherein the entrance window of the optical phaser is at least partially transparent to light impinging thereon. 
     
     
       5. The compensator of  claim 1  wherein the light-returning means includes a light-focusing means and a mirror disposed near a focal plane of the light-focusing means, the light-focusing means collecting the angularly dispersed light having the banded pattern emitted from the optical phaser for projection onto the mirror, the mirror reflecting light impinging thereon back towards the light-focusing means. 
     
     
       6. The compensator of  claim 5  wherein the light-focusing means projects to a distinct location on the mirror each band in the banded pattern of angularly dispersed light generated by the optical phaser. 
     
     
       7. The compensator of  claim 5  wherein a distance between the light-focusing means and the optical phaser is adjustable. 
     
     
       8. The compensator of  claim 5  wherein the mirror is curved. 
     
     
       9. The compensator of  claim 8  wherein curvature of the mirror is adjustable. 
     
     
       10. The compensator of  claim 9  wherein curvature of the mirror is adjusted by bending the mirror. 
     
     
       11. The compensator of  claim 10  wherein force for bending the mirror is selected from a group consisting of mechanical, electrical, magnetic and thermal. 
     
     
       12. The compensator of  claim 9  wherein the mirror has multiple curvatures, and curvature of the mirror is adjusted by translating the mirror. 
     
     
       13. The compensator of  claim 9  wherein the mirror is replaceable, and curvature of the mirror is adjusted by replacing the mirror with another mirror having a different curvature. 
     
     
       14. The compensator of  claim 1  wherein the optical phaser is made from a plate of material having two parallel surfaces between which light after entering the optical phaser through the entrance window reflects, and with the entrance window being formed on an outer surface of the plate. 
     
     
       15. The compensator of  claim 14  wherein the entrance window is formed by a beveled edge of the plate. 
     
     
       16. The compensator of  claim 14  wherein the entrance window is formed by a prism which projects out of one of the two parallel surface surfaces of the optical phaser, and light entering the optical phaser through the entrance window undergoes internal reflection within the prism before impinging upon one of the two parallel surface surfaces. 
     
     
       17. The compensator of  claim 14  wherein one of the two parallel surface surfaces of the optical phaser is partially transparent to allow a portion of light impinging thereon to exit the optical phaser. 
     
     
       18. The compensator of  claim 17  wherein light emitted from the optical phaser through the partially transparent surface detracts at an angle which exceeds forty-five degrees (45°) from a normal thereto. 
     
     
       19. The compensator of  claim 1  wherein the optical phaser is made from a material having an index of refraction which is greater than the index of refraction of medium surrounding the optical phaser. 
     
     
       20. A chromatic dispersion compensation method that is adapted for bettering performance of an optical communication system comprising the steps of:
 collimating into a mainly collimated beam of light a spatially diverging beam of light which contains a plurality of frequencies as may be emitted from an end of an optical fiber included in an optical communication system;   impinging the mainly collimated beam of light onto an entrance window of an optical phaser for angularly dispersing the mainly collimated beam of light into a banded pattern emitted from the optical phaser whereby the mainly collimated beam of light becomes separated into bands so that light having a particular frequency within a specific band is angularly displaced from light at other frequencies within that same band; and   reflecting the angularly dispersed light back through the optical phaser to exit the optical phaser near an entrance window thereof.   
     
     
       21. The method of claim 20 wherein the mainly collimated beam of light has a divergence which ensures that more than fifty-percent (50%) of energy in the mainly collimated beam of light impinging upon the entrance window diffracts into fewer than three (3) diffraction orders for any beam of light at a particular wavelength in the angularly dispersed light emitted from the optical phaser in the banded pattern. 
     
     
       22. The method of claim 20 wherein a light-returning means for reflecting the angularly dispersed light back through the optical phaser includes a light-focusing means and a mirror disposed near a focal plane of the light-focusing means, the method further comprising the steps of:
 the light-focusing means collecting the angularly dispersed light having the banded pattern emitted from the optical phaser for projection onto the mirror; and   the mirror reflecting light impinging thereon back towards the light-focusing means.   
     
     
       23. The method of claim 22 wherein the light-focusing means projects to a distinct location on the mirror each band in the banded pattern of angularly dispersed light generated by the optical phaser. 
     
     
       24. The method of claim 22 further comprising the step of adjusting a distance which separates the light-focusing means from the optical phaser. 
     
     
       25. The method of claim 22 further comprising a step of adjusting a curvature of the mirror. 
     
     
       26. The method of claim 25 wherein curvature of the mirror is adjusted by bending the mirror. 
     
     
       27. The method of claim 26 wherein force for bending the mirror is selected from a group consisting of mechanical, electrical, magnetic and thermal. 
     
     
       28. The method of claim 25 wherein the mirror has multiple curvatures, and curvature of the mirror is adjusted by translating the mirror. 
     
     
       29. The method of claim 25 wherein the mirror is replaceable, and curvature of the mirror is adjusted by replacing the mirror with another mirror having a different curvature. 
     
     
       30. The method of claim 20 wherein light is emitted from the optical phaser through a partially transparent surface thereof, the emitted light being defracted at an angle which exceeds forty-five degrees (45°) from a normal to the partially transparent surface. 
     
     
       31. A chromatic dispersion compensation method that is adapted for bettering performance of an optical communication system comprising the steps of:
 collimating into a mainly collimated beam of light a spatially diverging beam of light which contains a plurality of frequencies as may be emitted from an end of an optical fiber included in an optical communication system;   impinging the mainly collimated beam of light onto an entrance window of an optical phaser (62), the optical phaser (62) having an entrance window (63) for receiving a beam of light, and having opposed parallel surfaces (64, 65) one of which is highly reflective and one of which is at least partially transmissive, and wherein the optical phaser (62) is arranged such that the angle of incidence of the beam's impingement upon the partially transmissive diffractive surface (65) is slightly less than the angle of total internal reflection;   angularly dispersing in the optical phaser the mainly collimated beam of light into a banded pattern emitted from the optical phaser whereby the mainly collimated beam of light becomes separated into bands so that light having a particular frequency within a specific band is angularly displaced from light at other frequencies within that same band; and   reflecting the angularly dispersed light back through the optical phaser to exit the optical phaser near an entrance window thereof.   
     
     
       32. The method of claim 31 wherein the mainly collimated beam of light has a divergence which ensures that more than fifty-percent (50%) of energy in the mainly collimated beam of light impinging upon the entrance window diffracts into fewer than three (3) diffraction orders for any beam of light at a particular wavelength in the angularly dispersed light emitted from the optical phaser in the banded pattern. 
     
     
       33. The method of claim 31 wherein a light-returning means for reflecting the angularly dispersed light back through the optical phaser includes a light-focusing means and a mirror disposed near a focal plane of the light-focusing means, the method further comprising the steps of:
 the light-focusing means collecting the angularly dispersed light having the banded pattern emitted from the optical phaser for projection onto the mirror; and   the mirror reflecting light impinging thereon back towards the light-focusing means.   
     
     
       34. The method of claim 33 wherein the light-focusing means projects to a distinct location on the mirror each band in the banded pattern of angularly dispersed light generated by the optical phaser. 
     
     
       35. The method of claim 33 further comprising the step of adjusting a distance which separates the light-focusing means from the optical phaser. 
     
     
       36. The method of claim 33 further comprising a step of adjusting a curvature of the mirror. 
     
     
       37. The method of claim 36 wherein curvature of the mirror is adjusted by bending the mirror. 
     
     
       38. The method of claim 37 wherein force for bending the mirror is selected from a group consisting of mechanical, electrical, magnetic and thermal. 
     
     
       39. The method of claim 36 wherein the mirror has multiple curvatures, and curvature of the mirror is adjusted by translating the mirror. 
     
     
       40. The method of claim 36 wherein the mirror is replaceable, and curvature of the mirror is adjusted by replacing the mirror with another mirror having a different curvature. 
     
     
       41. The method of claim 31 wherein light is emitted from the optical phaser through a partially transmissive surface thereof, the emitted light being defracted at an angle which exceeds forty-five degrees (45°) from a normal to the partially transmissive surface. 
     
     
       42. An optical chromatic dispersion compensator adapted for bettering performance of an optical communication system comprising:
 an optical phaser (62) having an entrance window (63) for receiving a beam of light, and having opposed parallel surfaces (64,65) one of which is highly reflective and one of which is at least partially transmissive for angularly dispersing the received beam of light in a banded pattern that is emitted from the optical phaser, through the partially transmissive diffractive surface (65), whereby the received beam of light becomes separated into bands so that light having a particular frequency within a specific band is angularly displaced from light at other frequencies within the same band; and   a light-returning means (66) which receives the angularly dispersed light having the banded pattern that is emitted from the partially transmissive diffractive surface (65) of the optical phaser, and for reflecting that light back through the optical phaser to exit the optical phaser near the entrance window thereof;   
       characterized by:
 a collimating means (61) for receiving a spatially diverging beam of light which contains a plurality of frequencies as may be emitted from an end of an optical fiber included in an optical communication system, the collimating means also converting the received spatially diverging beam of light into a mainly collimated beam of light that is emitted from the collimating means and impinges upon the entrance window (63) of the optical phaser (62); and wherein the optical phaser (62) is arranged such that the angle of incidence of the beam's impingement upon the partially transmissive diffractive surface (65) is slightly less than the angle of total internal reflection. 
 
     
     
       43. The compensator of claim 42 wherein the mainly collimated beam of light emitted from the collimating means (61) has a divergence which ensures that more than fifty-percent (50%) of energy in the mainly collimated beam of light impinging upon the entrance window diffracts into fewer than three (3) diffraction orders for any beam of light at a particular wavelength in the angularly dispersed light emitted from the optical phaser (62) in the banded pattern. 
     
     
       44. The compensator of claim 42 wherein light enters the optical phaser (62) through the entrance window at near normal incidence. 
     
     
       45. The compensator of claim 42 wherein the entrance window of the optical phaser (62) is at least partially transparent to light impinging thereon. 
     
     
       46. The compensator of claim 42 wherein the light-returning means (66) includes a light-focusing means (67) and a mirror (68) disposed near a focal plane of the light-focusing means (67) collecting the angularly dispersed light having the banded pattern emitted from the optical phaser for projection onto the mirror, the mirror (68) reflecting light impinging thereon back towards the light-focusing means. 
     
     
       47. The compensator of claim 46 wherein the light-focusing means (67) projects to a distinct location on the mirror (68) each band in the banded pattern of angularly dispersed light generated by the optical phaser (62). 
     
     
       48. The compensator of claim 46 wherein a distance between the light-focusing means (67) and the optical phaser (62) is adjustable. 
     
     
       49. The compensator of claim 46 wherein the mirror (68) is curved. 
     
     
       50. The compensator of claim 49 wherein curvature of the mirror (68) is adjustable. 
     
     
       51. The compensator of claim 50 wherein curvature of the mirror is adjusted by bending the mirror. 
     
     
       52. The compensator of claim 51 wherein force for bending the mirror is selected from a group consisting of mechanical, electrical, magnetic and thermal. 
     
     
       53. The compensator of claim 50 wherein the mirror (68) has multiple curvatures, and curvature of the mirror is adjusted by translating the mirror. 
     
     
       54. The compensator of claim 50 wherein the mirror (68) is replaceable, and curvature of the mirror is adjusted by replacing the mirror with another mirror having a different curvature. 
     
     
       55. The compensator of claim 42 wherein the optical phaser (62) is made from a plate of material having two parallel surfaces (64, 65) between which light after entering the optical phaser through the entrance window reflects, and with the entrance window being formed on an outer surface of the plate. 
     
     
       56. The compensator of claim 55 wherein the entrance window is formed by a bevelled edge of the plate. 
     
     
       57. The compensator of claim 55 wherein the entrance window is formed by a prism which projects out of one of the two parallel surfaces (64, 65) of the optical phaser, and light entering the optical phaser through the entrance window undergoes internal reflection within the prism before impinging upon one of the two parallel surfaces. 
     
     
       58. The compensator of claim 42 wherein light emitted from the optical phaser (62) through the partially transparent surface (65) diffracts at an angle which exceeds forty-five degrees (45°) from a normal thereto. 
     
     
       59. The compensator of claim 42 wherein the optical phaser (62) is made from a material having an index of refraction which is greater than the index of refraction of medium surrounding the optical phaser (62).