Diffraction-based optical switch

• US 6,847,749 B1
• Filed: 01/18/2002
• Issued: 01/25/2005
• Est. Priority Date: 01/18/2002
• Status: Expired due to Fees

• Current Assignee: San José State University Research Foundation, The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration, San Josã© State University (US Bancorp)
• Inventors: Spremo, Stevan M., Fuhr, Peter L., Schipper, John F.
• Primary Examiner(s): Glick, Edward J.
• Assistant Examiner(s): Artman, Thomas R
• Application Number:
  US10/058,873
• Time in Patent Office: 1,103 Days
• Field of Search: 385/10, 385 16- 18, 385/37, 359/573, 359/575
• US Class Current: 385/15
• CPC Class Codes: G02B 5/1828 having means for producing variable diffraction controlling the direction of light by means of one or more diffracting elements G02B26/0808; acousto-optical elements G02F1/11, G02F1/33; electro- or magneto-optical diffraction G02F1/292, G02F1/2955

Abstract

Method and system for controllably redirecting a light beam, having a central wavelength λ, from a first light-receiving site to a second light-receiving site. A diffraction grating is attached to or part of a piezoelectric substrate, which is connected to one or two controllable voltage difference sources. When a substrate voltage difference is changed and the diffraction grating length in each of one or two directions is thereby changed, at least one of the diffraction angle, the diffraction order and the central wavelength is controllably changed. A diffracted light beam component, having a given wavelength, diffraction angle and diffraction order, that is initially received at a first light receiving site (e.g., a detector or optical fiber) is thereby controllably shifted or altered and can be received at a second light receiving site. A polynomially stepped, chirped grating is used in one embodiment. In another embodiment, an incident light beam, having at least one of first and second wavelengths, λ1 and λ2, is received and diffracted at a first diffraction grating to provide a first diffracted beam. The first diffracted beam is received and diffracted at a second diffraction grating to produce a second diffracted beam. The second diffracted beam is received at a light-sensitive transducer, having at least first and second spaced apart light detector elements that are positioned so that, when the incident light beam has wavelength λ1 or λ2 (λ1≠λ2), the second diffracted beam is received at the first element or at the second element, respectively; change in a selected physical parameter at the second grating can also be sensed or measured. A sequence of spaced apart light detector elements can be positioned along a linear or curvilinear segment with equal or unequal spacing.

Claims

1. A method for controlling a light beam, the method comprising:

providing a diffraction grating, attached to or part of a piezoelectric substrate, having an initial substrate length and being connected to a controllable voltage source having an initial first voltage difference in a selected direction across the substrate;

directing a beam of light, having at least a selected wavelength λ

, at the grating at a selected incidence angle and receiving a first diffracted light beam component of a selected diffraction order m containing the wavelength λ

at a first light-receiving site;

changing the first voltage difference at the first voltage source by a selected first voltage change amount Δ

V1 and permitting the substrate length to change by a selected first length change amount Δ

L1 in the selected direction,

whereby at least one of the following occurs, after the first voltage change;

(1) the first diffracted light beam component is received at a selected second light-receiving site, different from the first site, (2) a second diffracted light beam component of order m, containing a second wavelength λ

′

but not the wavelength λ

, is received at the first site, (3) a third diffracted light beam component of order m′

, with m′

≠

m, containing at least one of the first and second wavelengths, is received at at least one of the first site and the second site, and (4) a fourth diffracted light beam component, having an incidence angle different from the selected incidence angle and containing at least one of the first and second wavelengths, is received at at least one of the first site and the second site;

providing a second controllable voltage source having an initial second voltage difference across the substrate in a second selected direction that is transverse or perpendicular to the first direction; and

changing the second voltage difference at the second voltage source by a selected voltage change amount Δ

V2 that is chosen so that at leas one of the following occurs;

(i) the substrate length changes by a selected second length change amount Δ

L2 in the second direction, and (2) a selected axis of the grating is rotated by a selected angle change amount Δ

φ

in a selected plane of the substrate.

2. The method of claim 1, further comprising providing said substrate with at least one planar surface, and providing said grating on the at least one planar surface.

3. The method of claim 1, further comprising providing as said piezoelectric substrate a material drawn from the group consisting of quartz, tourmaline, Rochelle salt, ammonium dihydrogen phosphate (ADP), lithium sulphate, lead titanate, lead zirconate titanate, lead metaniobate, lead magnesium niobate, barium titanate (BaTiO_z;

3≦

z≦

4), and modified/unmodified barium strontium titanate (Ba_ySr_1-yTi_xM_1-xO_z;

0≦

x≦

1;

0≦

y≦

1;

3≦

z≦

4), where M is one or a combination of two or more of the following elements;

M=Ta, Zr, Hf, V, Nb, Mo, W, Mn, Sc, Re, Al, Ga and Cr.

4. The method of claim 1, further comprising providing said substrate with a substrate material that is substantially transparent to said wavelength λ

.

5. The method of claim 1, further comprising,

providing a third controllable voltage source having an initial third voltage difference across said substrate in a third selected direction that is transverse or perpendicular to said first direction and said second direction;

and

changing the third voltage difference at the voltage source by a selected voltage change amount Δ

V3 that is chosen so that the substrate length changes by a selected third length change amount Δ

L3 in the third direction.

6. The method of claim 1, further comprising choosing said second voltage change amount Δ

V2 so that said substrate length in a direction of said grating axis is substantially unchanged relative to said substrate length before application of said first and second voltage changes, Δ

V1 and Δ

V2.

7. The method of claim 1, further comprising said grating as a polynomlally stepped, chirped grating.

8. The method of claim 7, further comprising choosing said polynomially stepped grating from a group of gratings consisting of a linearly stepped grating, a quadratically stepped grating and a cubically stepped grating.

9. A system for controlling a light beam, the system comprising:

a diffraction grating, attached to or part of a piezoelectric substrates having an initial substrate length, where the grating is positioned to receive a beam of light, having at least a selected wavelength λ

, at a light-receiving site of the grating at a selected incidence angle and to provide a first diffracted light beam component of a selected order m containing the wavelength λ

; and

a first controllable voltage source, connected in a selected direction across the substrate and having an initial voltage difference, where the voltage difference is changed by a selected fit voltage change amount Δ

V1 to cause the substrate length to change by a selected first length change amount Δ

L1 in the selected direction,

whereby at least one of the following occurs, after the first voltage change;

(1) the first diffracted light beam component is received at a selected second light-receiving site, different from the first site, (2) a second diffracted light beam component of order m, containing a second wavelength λ

′

but not the wavelength λ

, is received at the first site, (3) a third diffracted light beam component of order m′

, with m′

≠

m, containing at least one of the first and second wavelengths, is received at at least one of the first site and the second site, and (4) a fourth diffracted light beam component, having an incidence angle different from the selected incidence angle and containing at least one of the first and second wavelengths, is received at at least one of the first site and the second site;

a second controllable voltage ource having an initial second voltage difference across the substrate in a second selected direction that is transverse or perpendicular to the first direction; and

wherein the second voltage difference at the second voltage source can be changed by a elected voltage change amount Δ

V2 that is chosen so that at least one of the following occurs;

(i) the substrate length changes by a selected second length change amount Δ

L2 in the second direction, and (2) a selected axis of the grating is rotated by a selected angle change amount Δ

φ

in a selected plane of the substrate.

10. The system of claim 9, wherein said substrate is provided with at least one planar surface, and said grating is provided on the at least one planar surface.

11. The system of claim 9, wherein said piezoelectric substrate is drawn from the group or materials consisting of quartz, tourmaline, Rochelle salt, ammonium dihydrogen phosphate (ADP), lithium sulphate, lead titanate, lead zirconate titanate, lead metaniobate, lead magnesium niobate, barium titanate (BaTiO_z;

3≦

5≦

z≦

4), and modified/unmodified barium strontium titanate (Ba_ySr_1-yTi_xM_1-xO_z;

0≦

x≦

1;

0≦

y≦

1;

3≦

z≦

4), where M is one or a combination of two or more of the following elements;

M=Ta, Zr, Hf, Y, Nb, Mo, W, Mn, Sc, Re, Al, Ga and C.

12. The system of claim 9, wherein said substrate is provided with a substrate material that is substantially transparent to said wavelength λ

.

13. The system of claim 9, further comprising:

a third controllable voltage source having an initial third voltage difference across said substrate in a third selected direction that is transverse or perpendicular to said first direction and to said second direction, where the third voltage difference is changed by a selected voltage change amount Δ

V3, chosen so that the substrate length changes by a selected third length change amount Δ

L3 in the third direction.

14. The system of claim 9, wherein said second voltage change amount Δ

V2 is chosen so that said substrate length in a direction of said grating axis is substantially unchanged relative to said substrate length before application of said first and second voltage changes, Δ

V1 and Δ

V2.

15. The system of claim 9, wherein said grating is a polynomially stepped, chirped grating.

16. The system of claim 15, wherein said polynomially stepped grating is chosen from a group of gratings consisting of a quadratically stepped grating and a cubically stepped grating.

17. A method for controlling a light beam, the method comprising:

providing a diffraction grating, attached to or part of a piezoelectric substrate, having an initial substrate length and being connected to a controllable voltage source having an initial voltage difference in a selected direction across the substrate;

providing the substrate with a selected curved surface, and providing the grating on the curved surface;

directing a beam of light, having at least a selected wavelength λ

, at the grating at a selected incidence angle and receiving a first diffracted light beam component of a selected diffraction order m containing the wavelength λ

at a first light-receiving site; and

changing the voltage difference at the voltage source by a selected voltage change amount Δ

V1 and permitting the substrate length to change by a selected length change amount Δ

L1 in the selected direction,

whereby at least one of the following occurs, after the voltage change;

(1) the first diffracted light beam component is received at a selected second light-receiving site, different from the first site, (2) a second diffracted light beam component of order m, containing a second wavelength λ

′

but not the wavelength λ

, is received at the first site, (3) a third diffracted light beam component of order m′

, with m′

≠

m, containing at least one of the first and second wavelengths, is received at at least one of the first site and the second site, and (4) a fourth diffracted light beam component, having an incidence angle different from the selected incidence angle and containing at least one of the first and second wavelengths, is received at at least one of the first site and the second site.

18. A system for controlling a light beam, the system comprising:

a diffraction grating, attached to or part of a piezoelectric substrate, having an initial substrate length, where the grating is positioned to receive a beam of light, having at least a selected wavelength λ

, at a light-receiving site of the grating at a selected incidence angle and to provide a first diffracted light beam component of a selected order m containing the wavelength λ

, wherein the substrate is provided with a selected curved surface, and the grating is provided on the curved surface; and

a controllable voltage source, connected in a selected direction across the substrate and having an initial voltage difference, where the voltage difference is changed by a selected voltage change amount Δ

V1 to cause the substrate length to change by a selected length change amount Δ

L1 in the selected direction,

whereby at least one of the following occurs, after the voltage change;

(1) the first diffracted light beam component is received at a selected second light-receiving site, different from the first site, (2) a second diffracted light beam component of order m, containing a second wavelength λ

but not the wavelength λ

, is received at the first site, (3) a third diffracted light beam component of order m′

, with m′

≠

m, containing at least one of the first and second wavelengths, is received at at least one of the first site and the second site, and (4) a fourth diffracted light beam component, having an incidence angle different from the selected incidence angle and containing at least one of the first and second wavelengths, is received at at least one of the first site and the second site.