Electrostatically deformable single crystal dielectrically coated mirror

• US 5,022,745 A
• Filed: 09/07/1989
• Issued: 06/11/1991
• Est. Priority Date: 09/07/1989
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Zayhowski, John J., Mooradian, Aram
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): Phan, James
• Application Number:
  US07/404,176
• Time in Patent Office: 642 Days
• Field of Search: 350/607, 350/608, 350/609, 350/162.22, 350/612, 350/321, 357/60, 357/89, 250/331, 372/12, 372/19
• US Class Current: 359/847
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G02B 26/0825 the reflecting element being a flexible sheet or membrane, e.g. for varying the focus flexible mirrors for cosmetic use A45D42/24

Abstract

An electrostatically deformable single crystal mirror comprising a highly conducting thick substrate layer and a highly conducting thin membrane layer separated from the thick layer by an insulator is disclosed. The center of the insulating layer is etched to form a cavity. The outer surface of the membrane layer is polished and coated with a dielectric to form a mirror. A voltage is applied between the membrane and the substrate to cause the membrane to deform. Various embodiments of the invention provide for planar translation of the mirror and for convex/concave deformation of the mirror. Incorporation of a deformation sensor in the deformable mirror allows for deformation measurement. In a particular embodiment of the invention, the deformable mirror is used in a tunable etalon for use in an optical filter.

Claims

1. A resonant cavity for a laser formed by two opposing mirrors one of which is an electrostatically deformable single crystal dielectrically coated mirror comprising:

a thick substrate;

an insulating layer on said thick substrate, from which a central region has been removed;

a thin substrate on said insulating layer having at least one polished surface on a side opposite said insulating layer,;

a mirror layer on said polished surface of said thin substrate which thin substrate is substantially thicker than 10 microns and is sufficiently thick to support said mirror layer but thin enough to deform upon application of a potential between said thin and thick substrates; and

at least one electrical contact adapted to provide a potential between said thick substrate and said thin substrate to cause said thin substrate to deform and thereby change the resonance of the cavity to tune the laser frequency.

2. The cavity of claim 1 wherein the thick and the thin substrates are silicon.

3. The cavity of claim 1 wherein said insulating layer further comprises at least one path extending from said central region to an outer edge of the insulating layer.

4. The cavity of claim 1 wherein the insulating layer is an oxide.

5. The cavity of claim 1 wherein the mirror layer is a multilayer dielectric stack deposited onto the polished surface of said thin layer.

6. An electrically translatable mirror comprising:

a thick substrate,

an insulating layer on said thick substrate from which a central region has been removed;

a thin substrate on said insulating layer having at lest one polished surface on a side opposite said insulating layer, said thin substrate having a relatively thicker center portion isolated from a relatively thicker outer portion by a continuous channel portion etched into said thin substrate;

a mirror layer on said polished surface of said thin substrate which thin substrate has a thickness at the relatively thicker portion which is substantially greater than 10 microns and upon application of a potential between said thin and thick substrate the center portion of the thin substrate moves toward the thick substrate in a parallel plane while the channel portions flexes; and

at least one electrode adapted to provide a potential between said thick substrate and said thin substrate to cause said thin substrate to deform.

7. The mirror of claim 6 wherein said insulating layer further comprises at least one path extending from said removed region to an outer edge of the insulating layer.

8. An electrostatically deformable single crystal mirror comprising:

a first highly doped thick, substantially inflexible, substrate layer;

a second highly doped thick, substantially inflexible substrate layer,

a highly doped membrane layer having a polished surface located between said first and second highly doped substrate layers and separated from said first substrate layer by a first insulating layer, said first insulating layer having a central region etched away to form a first cavity between said first substrate and said membrane and separated from said second substrate layer by a second insulating layer, said second insulating layer having a central region etched away to form a second cavity between said second substrate and membrane;

a mirror layer applied to said polished surface of said membrane, and

a plurality of electrodes distributed over each substrate such that an individual electrode may have a potential placed between it and the membrane.

9. An electrostatically deformable single crystal dielectrically coated mirror comprising:

a thick substrate adapted to permit the voltage or charge at one surface to be controlled;

an insulating layer, from which a region has been removed, said insulating layer bonded to said thick substrate;

a thin substrate adapted to permit the voltage or charge at one surface to be controlled, said thin substrate having at least one polished surface, said thin substrate, bonded to said insulating layer such that a polished surface is not bonded to said insulating layer;

a mirror layer applied to said polished unbonded surface of said thin substrate;

at least one electrical contact adapted to control a potential between said thick substrate and said thin substrate; and

a position transducer attached to said mirror for measuring the amount of deformation in said mirror, said position transducer comprising;

(i) a doped region within but electrically isolated from said thick substrate;

(ii) a second doped region within but electrically isolated from said thin substrate;

(iii) a first capacitor electrode connected to said doped region for connection to one terminal of an arm of a high frequency capacitance measurement bridge; and

(iv) a second capacitor electrode connected to said second doped region for connection to a second terminal of an arm of the high frequency capacitance measurement bridge.