Polarization independent optical isolator

• US 5,774,264 A
• Filed: 09/09/1996
• Issued: 06/30/1998
• Est. Priority Date: 01/28/1994
• Status: Expired due to Term

• Current Assignee: Namiki Precision Jewel Co., Ltd.
• Original Assignee: Namiki Precision Jewel Co., Ltd.
• Inventors: Aoki, Shigeaki, Ikegai, Kazuaki, Konno, Yoshihiro
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): Schuberg, Darren E.
• Application Number:
  US08/709,626
• Time in Patent Office: 659 Days
• Field of Search: 359/484, 359/494, 359/497, 359/282, 359/495, 359/499, 359/298, 359/301, 359/303, 372/703
• US Class Current: 359/484.03
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02B 6/272 comprising polarisation means for beam splitting and combining
• CPC Class Codes: G02B 6/2746 comprising non-reciprocal devices, e.g. isolators, FRM, circulators, quasi-isolators magneto-optic non-reciprocal devices G02F1/093
• CPC Class Codes: G02B 6/2766 Manipulating the plane of polarisation from one input polarisation to another output polarisation, e.g. polarisation rotators, linear to circular polarisation converters
• CPC Class Codes: G02F 1/093 used as non-reciprocal devices, e.g. optical isolators, circulators G02F1/0955 takes precedence
• CPC Class Codes: G02F 2203/06 Polarisation independent

Abstract

A polarization-independent optical isolator having a structure in which polarization dispersion is virtually eliminated by selecting the thickness and optical axis orientations of birefringent crystalline plates used in the isolator. The optical isolator of the present invention employs a combination of birefringent crystalline plates wherein the optical axis orientation of at least one birefringent crystalline plate in the optical isolator is different from the optical axis orientation of the remaining birefringent crystalline plates, and the polarization mode dispersion, which is induced when the beam propagates through the birefringent crystalline plate having a different optical axis orientation, is equal to the dispersion rate of the polarization mode dispersion attributable to the remaining birefringent crystalline plates and in a mutually inverse direction.

Claims

1. A polarization-independent optical isolator which consists of one Faraday rotator and three birefringent crystalline plates, at least one of said three birefringent crystalline plates having an orientation of a crystal optical axis different from an orientation of a crystal optical axis of the other birefringent crystalline plates, said orientation of said crystal optical axis of said at least one of said birefringent crystalline plates arranged to cancel a polarization phase delay arising from different propagation rates between ordinary and extraordinary rays and induced by the propagation of the beams through said other birefringent crystalline plates, wherein said polarization phase delay is suppressed to less than 0.05 picoseconds.

2. The polarization-independent optical isolator of claim I wherein said other birefringent crystalline plates comprise:

a first and second birefringent crystalline plate, said first and second birefringent crystalline plates having the same orientation of the crystal optical axis of said first and second birefringent crystalline plates to a direction normal to the plane of the plates, said orientation of the crystal optical axis of said first and second birefringent crystalline plates set to the direction having the maximum split width between ordinary and extraordinary rays, and said first and second birefringent crystalline plates each having a thickness in said direction normal to the plane of said plates, wherein said thickness of said first plate and said thickness of said second plate are related by a √

2;

1 ratio.

3. A polarization-independent optical isolator which consists of a Faraday rotator with three birefringent crystalline plates having thickness ratios of √

2;

t;

1 or √

2;

1;

t and said Faraday rotator located between the first and the second said birefringent plates, wherein the said birefringent plate thickness indicated by t having an orientation of a crystal optical axis different from an orientation of a crystal optical axis of the other birefringent crystalline plates, said thickness of the said birefringent plate thickness indicated by t having following relation, ##EQU11## in which n_o and n_ei are refractive indexes of ordinary and extraordinary beams and β

and γ

are refractive angle both ordinary and extraordinary beams on said the other birefringent crystalline plates, n_eii and γ

i are the refractive index and refractive angle of the extra-ordinary beam on said birefringent plate thickness indicated by t, arranged to cancel a polarization phase delay induced by said the other birefringent crystalline plates.

4. The polarization independent optical isolator of claim 3 wherein said polarization phase delay is less than 0.05 picoseconds.

5. The polarization independent optical isolator of claim 4, wherein said polarization phase delay arising from different propagation rates between ordinary and extraordinary rays and induced by the propagation of the beams through said other birefringent crystalline plates are suppressed to less than 0.05 picoseconds.

6. A polarization-independent optical isolator which consists of a first birefringent plate, a first Faraday rotator and a second birefringent plate, a second Faraday rotator and a third birefringent plate wherein said first, second and third birefringent plates have a thickness ratio of t:

√

2;

1 wherein said first birefringent plate has an orientation of a crystal optical axis different from said other two birefringent plates, said thickness of said birefringent plate thickness indicated by t having following relation, ##EQU12## in which n_o and n_ei are refractive indexes of ordinary and extraordinary beams and β

and γ

are refractive angle both ordinary and extraordinary beams on said the other birefringent crystalline plates, n_eii and γ

i are the refractive index and refractive angle of the extra-ordinary beam on said birefringent plate thickness indicated by t, arranged to cancel a polarization phase delay induced by said other birefringent crystalline plates.

7. The polarization independent optical isolator of claim 6 wherein said polarization phase delay arising from different propagation rates between ordinary and extraordinary rays and induced by the propagation of the beams through said other birefringent crystalline plates are suppressed to less than 0.05 picoseconds.

8. A polarization-independent optical isolator consists of at least one Faraday rotator with three birefringent crystalline plates, at least one of said three birefringent crystalline plates having an orientation of a crystal optical axis different from an orientation of a crystal optical axis of the other birefringent crystalline plates, said orientation of said crystal optical axis and a thickness of said at least one birefringent crystalline plate arranged to cancel a polarization phase delay induced by the propagation of a beam through said other birefringent crystalline plates.

9. The polarization independent optical isolator of claim 8 wherein said polarization phase delay is less than 0.05 picoseconds.

10. The polarization independent optical isolator of claim 9, wherein said polarization phase delay arising from different propagation rates between ordinary and extraordinary rays and induced by the propagation of the beams through said other birefringent crystalline plates are suppressed to less than 0.05 picoseconds.

11. A polarization independent optical isolator which consists of a Faraday rotator with three birefringent crystalline plates having thickness ratios of t:

1;

√

2or 1;

t;

√

2and said Faraday rotator located between the second and the third said birefringent plates, wherein the said birefringent plate thickness indicated by t having an orientation of a crystal optical axis different from an orientation of a crystal optical axis of the other birefringent crystalline plates, said thickness of the said birefringent plate thickness indicated by t having following relation, ##EQU13## in which n_o and n_ei are refractive indexes of ordinary and extraordinary beams and β

and γ

are refractive angle both ordinary and extraordinary beams on said the other birefringent crystalline plates, n_eii and γ

i are the refractive index and refractive angle of the extra-ordinary beam on said birefringent plate thickness indicated by t, arranged to cancel a polarization phase delay induced by said the other birefringent crystalline plates.

12. A polarization-independent optical isolator which consists of a first birefringent plate, a first Faraday rotator and a second birefringent plate, a second Faraday rotator and a third birefringent plate wherein said first, second and third birefringent plates have a thickness ratio of √

2;

1;

t wherein said first birefringent plate has an orientation of a crystal optical axis different from said other two birefringent plates, said thickness of said birefringent plate thickness indicated by t having following relation, ##EQU14## in which n_o and n_ei are refractive indexes of ordinary and extraordinary beams and β

and γ

are refractive angle both ordinary and extraordinary beams on said the other birefringent crystalline plates, n_eii and γ

i are the refractive index and refractive angle of the extra-ordinary beam on said birefringent plate thickness indicated by t, arranged to cancel a polarization phase delay induced by said the other birefringent crystalline plates.

13. A polarization-independent optical isolator which consists of two Faraday rotators and three birefringent crystalline plates, at least one of said three birefringent crystalline plates having an orientation of a crystal optical axis different from an orientation of a crystal optical axis of the other birefringent crystalline plates, said orientation of said crystal optical axis of said at least one of said birefringent crystalline plates arranged to cancel a polarization phase delay arising from different propagation rates between ordinary and extraordinary rays and induced by the propagation of a beam through said other birefringent crystalline plates, wherein said polarization phase delay is suppressed to less than 0.05 picoseconds.

14. The polarization-independent optical isolator of claim 13 wherein said other birefringent crystalline plates comprise:

a first and second birefringent crystalline plate, said first and second birefringent crystalline plates having the same orientation of the crystal optical axis of said first and second birefringent crystalline plates to a direction normal to the plane of the plates, said orientation of the crystal optical axis of said first and second birefringent crystalline plates set to the direction having the maximum split width between ordinary and extraordinary rays, and said first and second birefringent crystalline plates each having a thickness in said direction normal to the plane of said plates, wherein said thickness of said first plate and said thickness of said second plate are related by a √

2;

1 ratio.