Symmetric interferometers unbalanced by using light exposure to tailor the spectral behavior
First Claim
1. A method of making an interferometric optical filter comprising the steps of:
- a) providing a splitter and combiner;
b) providing two arms coupled to the splitter and combiner, the two arms each having a core and a cladding, the arms being substantially same optical path length and having substantially similar mode field diameters along the length thereof; and
, c) irradiating a region of one of the two arms with light of a suitable intensity and duration so as to vary the refractive index n over a region of length L in a substantially uniform manner of said one of the two arms to provide a refractive index difference An and an optical path length difference between the two arms to effect a change Δ
f, where Δ
f is the spacing between a peak and null wavelength of the spectral response of the filter.
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Accused Products
Abstract
Unbalanced Mach-Zehnder interferometers (MZI) are useful for a number of applications including wavelength filters, gain flattening or gain equalization elements, and band splitters or combiners. A MZI is comprised of two couplers surrounding a phase shifting region, which consists of two arms with differential propagation constants. We disclose a means of using light exposure to unbalance a symmetric MZI consisting of substantially the same lengths of substantially the same fiber. In particular, the index of refraction of a fiber can be increased by exposure to ultraviolet light, and the magnitude of the change can be increased by using higher germanium doping or by hydrogen loading the fiber. The magnitude of the phase shift can be controlled accurately by varying the fiber length exposed, the light exposure intensity, the light exposure time, and the hydrogen loading or fiber composition. In addition, exposing the other arm,of the MZI to trim back the phase shift can compensate any over-exposure of the fiber. By starting with a symmetric MZI made from substantially the same fiber, low polarization sensitivity or polarization dependent loss can be achieved, and the device can operate over a wider overall wavelength range. Also, by using a MZI with substantially the same lengths of fibers and by placing those fibers parallel to one another, low environmental sensitivity can be achieved. Moreover, the use of light exposure to unbalance the MZI has the advantage of enabling precise tailoring of the spectral response with ease of manufacturing and high yields. The MZI devices can be cascaded to achieve more complicated filtering functions in lattice devices such as Lyot-Ohman filters or Solc filters.
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Citations
22 Claims
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1. A method of making an interferometric optical filter comprising the steps of:
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a) providing a splitter and combiner;
b) providing two arms coupled to the splitter and combiner, the two arms each having a core and a cladding, the arms being substantially same optical path length and having substantially similar mode field diameters along the length thereof; and
,c) irradiating a region of one of the two arms with light of a suitable intensity and duration so as to vary the refractive index n over a region of length L in a substantially uniform manner of said one of the two arms to provide a refractive index difference An and an optical path length difference between the two arms to effect a change Δ
f, where Δ
f is the spacing between a peak and null wavelength of the spectral response of the filter.- View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of making an optical filter comprising the steps of:
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a) providing an MZI having two substantially similar arms disposed between two optical couplers, the arms each having a core and a cladding and having a substantially same optical path length;
b) irradiating one of the two arms with light of a suitable intensity and duration so as to vary the refractive index of an irradiated region and to provide a relative difference in the optical path lengths between the two arms such that light divided by one of the couplers propagating along the two arms will be phase shifted when combined by the other of the couplers, wherein the refractive index remains varied for a substantial time after the step of irradiating is completed. - View Dependent Claims (8)
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9. A method of making an optical filter comprising the steps of:
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a) providing an optical coupler for splitting and coupling light to or from two arms, the two arms being substantially similar in mode field diameter, the arms each having a core and a cladding and having a substantially same optical path length;
b) irradiating a region of at least one of the arms of the two arms with light of a suitable intensity and duration so as to vary the refractive index of the irradiated region substantially uniformly to vary the optical path length of at least one of the two arms and to provide a phase offset for light propagating within the two arms, wherein the refractive index remains varied for a substantial time after the step of irradiating is completed. - View Dependent Claims (10, 11, 12)
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13. A method of making an optical filter comprising the steps of:
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a) providing an optical coupler for splitting and coupling light to or from two arms, the two arms being substantially similar in mode field diameter, the arms each having a core and a cladding and having a substantially same optical path length;
b) irradiating a region of at least one of the arms of the two arms with light of a suitable intensity and duration so as to vary the refractive index of the irradiated region substantially uniformly to vary the optical path length of at least one of the two arms and to provide a phase offset for light propagating within the two arms; and
irradiating the other of the two arms with light of suitable intensity and duration to lessen the optical path length difference between the at least two arms.
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14. A method of making an optical filter comprising the steps of:
- providing a plurality of waveguide pairs between at least three optical couplers, each of the waveguides within a pair being substantially similar in mode field diameter along their length other than having an optical path length difference between waveguide pairs caused by one or more regions having had a light induced refractive index change.
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15. An optical filter comprising:
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an optical coupler for splitting and coupling light;
two unbalanced optical waveguide arms directly coupled with the optical coupler, the arms being substantially similar along their length other than having a dissimilarity caused by a refractive index change in at least one light irradiated region in at least one of the waveguides providing a difference in optical path length and refractive index between the arms that would otherwise not exist in the absence of light irradiation of at least one of the arms having been performed and which exists for a substantial period of time after the light irradiation is completed.
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16. An optical filter comprising:
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an optical coupler for splitting and coupling light; and
,two unbalanced optical waveguide arms directly coupled with the optical coupler, the arms being substantially similar along their length other than having a dissimilarity caused by a refractive index change in at least one light irradiated region in at least one of the waveguides providing a difference in optical path length and refractive index between the arms that would otherwise not exist in the absence of light irradiation of at least one of the arms, wherein the arms have mode field diameters along their length that are within 30% of each other in regions of the waveguide where the refractive index has not been modified by the use of light. - View Dependent Claims (17, 18, 19, 20, 21, 22)
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Specification