Tuning the index of a waveguide structure

• US 20030068134A1
• Filed: 09/10/2002
• Published: 04/10/2003
• Est. Priority Date: 09/10/2001
• Status: Active Grant

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Gunn, Lawrence Cary III
• Granted Patent: US 7,120,338 B2
• Time in Patent Office: Days
• US Class Current: 385/50
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 2006/12038 Glass (SiO2 based materials)
• CPC Class Codes: G02B 2006/12061 Silicon
• CPC Class Codes: G02B 2006/12097 Ridge, rib or the like
• CPC Class Codes: G02B 2006/12109 Filter
• CPC Class Codes: G02B 2006/12116 Polariser; Birefringent
• CPC Class Codes: G02B 2006/12145 Switch
• CPC Class Codes: G02B 2006/12147 Coupler
• CPC Class Codes: G02B 6/10 of the optical waveguide type G02B6/02, G02B6/24 take precedence; devices or arrangements for the control of light by electric, magnetic, electro-magnetic or acoustic means G02F1/00; transferring the modulation of modulated light G02F2/00; optical logic elements G02F3/00; optical analogue/digital converters G02F7/00
• CPC Class Codes: G02B 6/12004 Combinations of two or more optical elements
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02B 6/122 Basic optical elements, e.g. light-guiding paths
• CPC Class Codes: G02B 6/1223 high refractive index type, i.e. high-contrast waveguides
• CPC Class Codes: G02B 6/1225 comprising photonic band-gap structures or photonic lattices
• CPC Class Codes: G02B 6/132 by deposition of thin films
• CPC Class Codes: G02B 6/136 by etching
• CPC Class Codes: G02F 1/011 in optical waveguides, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 1/025 in an optical waveguide structure G02F1/017, G02F1/2257 take precedence
• CPC Class Codes: G02F 1/3133 the optical waveguides being made of semiconducting materials
• CPC Class Codes: G02F 2202/10 : semiconductor
• CPC Class Codes: G02F 2203/15 : involving resonance effects, e.g. resonantly enhanced interaction

Abstract

The index of refraction of waveguide structures can be varied by altering carrier concentration. The waveguides preferably comprise semiconductors like silicon that are substantially optically transmissive at certain wavelengths. Variation of the carrier density in these semiconductors may be effectuated by inducing an electric field within the semiconductor for example by apply a voltage to electrodes associated with the semiconductor. Variable control of the index of refraction may be used to implement a variety of functionalites including, but not limited to, tunable waveguide gratings and resonant cavities, switchable couplers, modulators, and optical switches.

Claims

1. An optical waveguide coupler having a tunable coupling coefficient, said coupler comprising:

a first waveguide and a second waveguide, said waveguides juxtaposed for coupling, wherein said first waveguide is comprised of semiconductor having a distribution of free carriers;

a first electrode electrically connected to a first variable voltage source for applying an electric field to said semiconductor of said first waveguide;

wherein said distribution of free carriers is responsive to application of said electric field to change the coupling coefficient between said waveguides from a first value to a second value.

2. The optical waveguide coupler of claim 1, further comprising an insulator juxtaposed with respect to said first electrode and said semiconductor such that said electric field is applied to through said insulator to said semiconductor to alter said distribution of free carriers.

3. The optical waveguide coupler of claim 1, wherein said semiconductor includes n and p type portions forming a junction therebetween, said first electrode electrically connected to one of said portions to induce an electric field across said junction to alter said distribution of free carriers.

4. The optical waveguide coupler of claim 1, wherein said second waveguide comprises semiconductor having a distribution of free carriers.

5. The optical waveguide coupler of claim 4, further comprising a second electrode electrically connected to said variable voltage source to apply an electric field to said semiconductor in said second waveguide.

6. The optical waveguide coupler of claim 4, further comprising a second variable voltage source and a second electrode electrically connected to said second variable voltage source to apply an electric field to said semiconductor in said second waveguide.

7. The optical waveguide coupler of claim 1, wherein said first waveguide comprises an optical path in a resonant cavity.

8. A method of tuning the coupling coefficient of an optical waveguide coupler, comprising:

providing a first waveguide comprising semiconductor containing a distribution of free carriers;

providing a second waveguide juxtaposed to said first waveguide; and

applying an electric field to said semiconductor of said first waveguide to alter the free carrier distribution in said semiconductor, thereby changing the coupling coefficient of said optical waveguide coupler from a first value to a second value.

9. The method of claim 8, wherein said step of providing a second waveguide comprises providing a second waveguide comprising semiconductor.

10. The method of claim 9, further comprising applying said electric field to said semiconductor of said second wavguide to alter the free carrier distribution in said semiconductor, thereby changing the coupling coefficient of said optical waveguide coupler.

11. The method of claim 9, further comprising separately applying an electric field to said semiconductor of said second wavguide to alter the free carrier distribution in said semiconductor, thereby changing the coupling coefficient of said optical waveguide coupler.

12. The method of claim 8, further comprising altering the temperature of said semiconductor of said first waveguide to alter the free carrier distribution in said semiconductor.

13. A waveguide grating comprising a waveguide for propagating light in a longitudinal direction, comprising a plurality of elongate members oriented transverse to said longitudinal direction, said members disposed relative to said waveguide to form a grating for coupling light out of the waveguide, said waveguide having a carrier density at each of said members, said members including respective electrodes for applying an electric field to said waveguide, said electric field altering said carrier density in said waveguide such that said coupling is altered.

14. The waveguide grating of claim 13, wherein the waveguide comprises semiconductor.

15. The waveguide grating of claim 14, wherein the waveguide comprises silicon.

16. The waveguide grating of claim 14, further comprising an insulating layer disposed between said elongated members and said waveguide.

17. The waveguide grating of claim 13, wherein said waveguide comprises a strip loaded waveguide.

18. The waveguide grating of claim 13, wherein said strip loaded waveguide comprises a slab, a strip formed thereon, and an intermediate layer between said strip and said slab.

19. The waveguide grating of claim 18, wherein said slab comprises semiconductor and said intermediate layer comprises dielectric material.

20. The waveguide grating of claim 19, further comprising at least one electrode juxtaposed with respect to said slab to induce an electric field through said dielectric intermediate layer and into said semiconductor slab to alter the distribution of carriers in said semiconductor slab thereby altering the effective index of said strip loaded waveguide.