Polarization converter and circuit elements for use in optical waveguides

• US 4,220,395 A
• Filed: 10/17/1978
• Issued: 09/02/1980
• Est. Priority Date: 05/13/1974
• Status: Expired due to Term

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Crow, John D., Shah, Manhar L., Wang, Shyh
• Primary Examiner(s): Levy, Stewart J.
• Application Number:
  US05/952,105
• Time in Patent Office: 686 Days
• Field of Search: 350/96.12, 350/96.13, 350/96.14
• US Class Current: 385/11
• CPC Class Codes: G02F 1/0142 TE-TM mode conversion
• CPC Class Codes: G02F 1/0353 involving an electro-optic TE-TM mode conversion
• CPC Class Codes: G02F 1/095 in an optical waveguide structure
• CPC Class Codes: G11B 11/10532 Heads
• CPC Class Codes: G11C 19/0866 Detecting magnetic domains
• CPC Class Codes: H04B 10/25 Arrangements specific to fibre transmission

Abstract

Wave propagation in thin film optical waveguides using gyrotropic or anisotropic material in either the substrate or adjacent top layer with respect to the thin film waveguide is analyzed and a mode converter capable of converting TE to TM or TM to TE polarization is disclosed. Several mode converters constructed in accordance with the present invention are set forth. Also disclosed are other optical circuit elements constructed from such mode converters including a gyrator, isolator, an optical switch, and a non-destructive optical readout for magnetic memories.

Claims

1. Polarization converter for use in optical waveguide systems, a first layer serving as a substrate and support for said converter and having a predetermined permittivity tensor ε

_s, means forming a thin film optical waveguide disposed in intimate contact on said first layer and having a permittivity tensor ε

_f, means forming a top layer disposed on the other side of the said thin film optical waveguide and having a predetermined permittivity tensor ε

_t, said permittivity tensor ε

_f having certain diagonal elements which control the propagation of a particular wave, said diagonal elements being selected to be greater than the corresponding diagonal elements of permittivity tensors ε

_t and ε

_f, one of said waveguide or adjacent layers being made of a material having propagation characteristics which are polarization dependent for causing the coupling between TE and TM polarizations, said material having a defined interaction length and said film having a thickness constructed and arranged to satisfy the phase-matched conditions over said length and cummulative conversion of TE to TM or TM to TE waves results as such waves are propagated through at least a portion of said length.

2. Polarization converter as in claim 1 in which said thin film waveguide layer thickness is of the order or ten to fifty free space wavelengths.

3. A polarization converter as in claim 1 in which said substrate is made of a material having a propagation characteristic which is polarization dependent.

4. Polarization converter as in claim 3 in which said substrate is anisotropic.

5. Polarization converter as in claim 1 in which said substrate is gyrotropic.

6. Polarization converter as in claim 1 in which said material having propagation characteristics which are polarization dependent is contained within said waveguide layer.

7. Polarization converter as in claim 1 in which said material is anisotropic.

8. Polarization converter as in claim 1 in which said material is gyrotropic.

9. Polarization converter as in claim 1 in which said material having propagation characteristics which are polarization dependent is gyrotropic by induction and further including means for applying a magnetic field to said material.

10. Polarization converter as in claim 1 in which said material is optically active.

11. Polarization converter as in claim 1 in which said material is anisotropic by induction and further including means for applying an electric field to said material.

12. Polarization converter as in claim 1 in which said material is inherently anisotropic.

13. Polarization converter as in claim 1 in which said first, second and third layers have an actual length equal to an integral number of defined interaction lengths.

14. A mode converter as in claim 1 in which said φ

_E =φ

_M condition is unsatisfied by a small amount δ

φ and

further including means for launching microwaves through said converter, the frequency of said microwaves being selected to compensate for said phase-mismatch δ

φ

.

15. A mode converter as in claim 1 in which said φ

_E =φ

_M condition is unsatisfied by a small amount δ

φ and

further including means for launching an acoustic wave through a predetermined length of said converter, the frequency of said acoustic waves being selected to compensate for said phase-mismatch δ

φ

.

16. Polarization converter for use in optical waveguide systems, a first layer serving as a substrate and support for said converter having a predetermined permittivity tensor ε

_s, means forming a thin film optical waveguide disposed in intimate contact on said first layer and having a permittivity tensor ε

_f means forming a top layer disposed on the other side of said thin film optical waveguide and having a predetermined permittivity tensor ε

_t said permittivity tensor ε

_f having certain diagonal elements which control the propagation of a particular wave, said diagonal elements being selected to be greater than the corresponding diagonal elements of permittivity tensors ε

_t and ε

_f one of said waveguide or adjacent layers being made of a material having propagation characteristics which are polarization dependent for causing the coupling between TE and TM polarizations and thereby also establish two eigen modes of propagation through said waveguide, each of said eigen modes being a combination of TE and TM polarization, said eigen modes having different phase velocities, said film having a thickness constructed and arranged to satisfy the phase-matched condition such that φ

E=φ

M and the two eigenmodes contain nearly equal TE and Tm components, said material having an interaction length such that the relative phase of the eigen modes changes over said length to cause mutual cancellation of either the TE or TM components from both of said modes, whereby conversion of TE to TM or TM to TE waves results as they are propagated through said length.

17. In optical switching device for use in optical waveguide ciruits, an electro-optic or magneto-optic mode converter for at least partially changing incoming TE or TM waves to waves of the opposite polarization, means for selectively supplying a bias field to said mode converter said bias field having at least two states, one of which operates to cause operation of said converter.

18. An optical switch as in claim 17 in which said converter is operated at the full conversion point so that an incoming wave of one polarization is either passed unchanged when said signal is absent or changed into a wave of the other polarization when said signal is present.

19. An optical switching device as in claim 17 further including a two-branch circuit forming an output thereof, said branches being constructed and arranged to exclusively propagate TE or TM waves respectively.

20. An optical switching device as in claim 17 in which said converter is operated at the half-conversion point whereby an input of equal strength TE and TM waves of proper phase relationship results in an output of either pure TE or pure TM waves.

21. An optical switch as in claim 17 further including means coupled to the input of said converter for adjusting the relative phase of the input TE and TM waves before passing to said converter.