US5625723A — Method for reducing birefringence in optical grat…

Claim 1

Independent Claim 105 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; and selecting the different periods of time so that differences in said differential phase shifts between pairs of adjacent waveguides are substantially equal.

Claim 2

Independent Claim 105 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; and selecting the different periods of time so that differences in said differential phase shifts between pairs of adjacent waveguides are substantially equal.

Claim 3

Dependent Claim 16 words

The method of claim 1 wherein said compensating polarization shift substantially eliminates the inherent polarization shift.

Claim 4

Dependent Claim 35 words

The method of claim 1 wherein the irradiation step comprises the step of illuminating the optical grating by scanning an irradiating beam across the waveguides at a scanning velocity that differs from waveguide to waveguide.

Claim 5

Dependent Claim 31 words

The method of claim 3 further comprising the step of decreasing the scanning velocity as the irradiating beam scans from a shortest of the waveguides to a longest of the waveguides.

Claim 6

Dependent Claim 43 words

The method of claim 3 wherein said irradiating beam has a width in the direction of the scanning velocity that is no greater than approximately one-fifth of the total number of waveguides constituting the optical grating multiplied by the distance between adjacent waveguides.

Claim 7

Independent Claim 130 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; selecting the different periods of time so that the differences in said differential phase shifts between pairs of adjacent waveguides have a prescribed relationship to one another; and annealing the optical grating subsequent to the irradiation step until the compensating polarization shift decays to a substantially stable value.

Claim 8

Independent Claim 130 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; selecting the different periods of time so that the differences in said differential phase shifts between pairs of adjacent waveguides have a prescribed relationship to one another; and annealing the optical grating subsequent to the irradiation step until the compensating polarization shift decays to a substantially stable value.

Claim 9

Independent Claim 119 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; selecting the different periods of time so that the differences in said differential phase shifts between pairs of adjacent waveguides have a prescribed relationship to one another; and annealing the optical grating simultaneously with the irradiation step.

Claim 10

Independent Claim 119 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; selecting the different periods of time so that the differences in said differential phase shifts between pairs of adjacent waveguides have a prescribed relationship to one another; and annealing the optical grating simultaneously with the irradiation step.

Claim 11

Dependent Claim 18 words

The method of claim 6 wherein the annealing step is performed at a temperature of approximately 100-250° C.

Claim 12

Dependent Claim 18 words

The method of claim 7 wherein the annealing step is performed at a temperature of approximately 100-250° C.

Claim 13

Dependent Claim 52 words

The method claim 1 further comprising the steps of: overexposing the waveguides to radiation so that the compensating polarization shift is greater than required to substantially eliminate the inherent polarization shift; annealing the optical grating until the compensating polarization shift decays to a stable value that substantially eliminates the inherent polarization shift.

Claim 14

Dependent Claim 47 words

The method of claim 10 wherein said compensating polarization shift results from differential phase shift induced in the waveguides and wherein the stable value of the compensating polarization shift is selected so that differences in said differential phase shifts between pairs of adjacent waveguides are substantially equal.

Claim 15

Independent Claim 127 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; selecting the different periods of time so that the differences in said differential phase shifts between pairs of adjacent waveguides have a prescribed relationship to one another; and irradiating the waveguides for additional periods of time to reduce transmission spectrum aberrations caused by phase errors.

Claim 16

Independent Claim 127 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; selecting the different periods of time so that the differences in said differential phase shifts between pairs of adjacent waveguides have a prescribed relationship to one another; and irradiating the waveguides for additional periods of time to reduce transmission spectrum aberrations caused by phase errors.

Claim 17

Dependent Claim 25 words

The method of claim 12 wherein said additional periods of time impart an induced phase shift in the waveguides that varies sinusoidally along the waveguides.

Claim 18

Dependent Claim 31 words

The method of claim 13 wherein said induced phase shift varies sinusoidally with a phase selected to minimize the amplitude of sidelines appearing in the transmission spectrum of the optical grating.

Claim 19

Independent Claim 85 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the step of: irradiating the waveguides of the optical grating with spatially nonuniform amounts of radiation by scanning an irradiation beam of substantially constant intensity across the waveguides at a scanning velocity that differs from waveguide to waveguide to induce a compensating polarization shift that substantially reduces the inherent polarization shift.

Claim 20

Independent Claim 85 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides, said method comprising the step of: irradiating the waveguides of the optical grating with spatially nonuniform amounts of radiation by scanning an irradiation beam of substantially constant intensity across the waveguides at a scanning velocity that differs from waveguide to waveguide to induce a compensating polarization shift that substantially reduces the inherent polarization shift.

Claim 21

Independent Claim 146 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides each having a core and cladding, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; selecting the different periods of time so that the differences in said differential phase shifts between pairs of adjacent waveguides have a prescribed relationship to one another; selecting an irradiation energy that induces compaction in the cladding; and irradiating the waveguide structure with radiation having an energy equal to said irradiation energy to induce a reduction in birefringence.

Claim 22

Independent Claim 146 words

A method for reducing the inherent polarization shift caused by birefringence between the TE and TM modes of an optical signal propagating in an optical grating having a plurality of waveguides each having a core and cladding, said method comprising the steps of: irradiating the waveguides of the optical grating at a specifiable wavelength and intensity for different periods of time to induce a compensating polarization shift that substantially reduces the inherent polarization shift, wherein said compensating polarization shift results from differential phase shifts induced in the waveguides; selecting the different periods of time so that the differences in said differential phase shifts between pairs of adjacent waveguides have a prescribed relationship to one another; selecting an irradiation energy that induces compaction in the cladding; and irradiating the waveguide structure with radiation having an energy equal to said irradiation energy to induce a reduction in birefringence.

Claim 23

Dependent Claim 28 words

The method of claim 16 wherein the energy selecting step comprises the step of selecting an irradiation energy sufficient to induce at least 0.1%-0.5% compaction in the cladding.

Claim 24

Dependent Claim 29 words

The method of claim 13 further comprising the step of inserting a mask over the optical grating to produce a periodic variation that approximates the sinusoidal induced phase shift.

Claim 25

Dependent Claim 33 words

The method of claim 6 wherein the waveguides are overexposed to radiation during said irradiating step so that the compensating polarization shift is greater than required to substantially eliminate the inherent polarization shift.

Claim 26

Dependent Claim 18 words

The method of claim 19 wherein at the substantially stable value, the inherent polarization shift is substantially eliminated.

Claim 27

Dependent Claim 53 words

The method of claim 15 wherein the waveguides are overexposed to radiation during said irradiating step so that the compensating polarization shift is greater than required to substantially eliminate the inherent polarization shift, further including a step of annealing the optical grating until the compensating polarization shift decays to a substantially constant value.

Claim 28

Dependent Claim 18 words

The method of claim 21 wherein at the substantially stable value, the inherent polarization shift is substantially eliminated.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	2000-04-28	2000-10-28	2001-04-29	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2004-04-28	2004-10-28	2005-04-29	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2008-04-28	2008-10-28	2009-04-29	$7700.00	Window Closed / Lapsed

Method for reducing birefringence in optical gratings

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