# US 8,785,835 B1 · Three-dimensional filter enables adaptive focus sensing

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 8,785,835 B1
- Document ID: US8785835B1
- Status: Granted
- Kind: B1
- Application number: 13/738,358
- Filed: 2013-01-10
- Granted: 2014-07-22
- Earliest claimed: 2013-01-10
- Applicants: Daniel R. Marshall
- Inventors: Daniel R. Marshall
- Web page: https://patentgrep.com/patent/US8785835B1

## CPC

- G02B 7/346: {using horizontal and vertical areas in the pupil plane, i.e. wide area autofocusing}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

This focus sensor is readily usable in a system using pupil obscuration to measure the state of focus of a light beam. A scattering volumetric filter modifies a three-dimensional wavefront so that focus can be detected by a two-dimensional detector for conversion to a one-dimensional signal having values of plus, zero and minus. This diffusing filter comprises sub wavelength particles having a high index of refraction suspended in an adhesive to produce a solid diffuser. This focus sensor enables a well-behaved focus curve having a constant slope near best focus, while maintaining a slope that is either constant or monotonic at a minimal rate over an extended distance to support a long capture-range over which a focus-controlling servo-mechanism can acquire and maintain focus in the presence of corrupting target surface topography or optical defects.

## Claims

### Claim 1

An optical sensor assembly comprising:
a structured filter; and
a detecting surface in intimate contact with the structured filter,
wherein the structured filter comprises:
a transparent medium having a first index of refraction; and
a scattering material comprising suspended particles,
wherein the suspended particles comprise:
greater refractive particles having a second index of refraction that is greater than the first index of refraction; and
lesser refractive particles having a third index of refraction that is less than the first index of refraction.

### Claim 2 (depends on 1)

The optical sensor assembly of claim 1, wherein the structured filter comprises a translucent material that derives its translucence purely from amplitude effects.

### Claim 3 (depends on 1)

The optical sensor assembly of claim 1, wherein the structured filter includes phase changing elements.

### Claim 4 (depends on 1)

The optical sensor assembly of claim 1, wherein the structured filter comprises a translucent material that derives its translucence from reflective effects resulting from a purely imaginary refractive index.

### Claim 5 (depends on 1)

The optical sensor assembly of claim 1, wherein the structured filter comprises a translucent material that derives its translucence from a complex refractive index.

### Claim 6 (depends on 1)

The optical sensor assembly of claim 1, wherein the structured filter comprises a powdered absorber.

### Claim 7 (depends on 1)

The optical sensor assembly of claim 1, wherein the structured filter comprises suspended particles that have a grain size that is selected to suppress artifacts caused by wavefront errors.

### Claim 8 (depends on 1)

The optical sensor assembly of claim 1, wherein the suspended particles comprise titanium dioxide (TiO2).

### Claim 9 (depends on 1)

The optical sensor assembly of claim 1, wherein the suspended particles comprise spherical beads.

### Claim 10 (depends on 1)

The optical sensor assembly of claim 1, wherein the transparent medium is a polymer.

### Claim 11 (depends on 1)

The optical sensor assembly of claim 1, wherein the transparent medium is curable to a solid.

### Claim 12 (depends on 1)

The optical sensor assembly of claim 1, wherein the transparent medium is UV-curable.

### Claim 13 (depends on 1)

The optical sensor assembly of claim 1, wherein the transparent medium is temperature curable.

### Claim 14 (depends on 1)

The optical sensor assembly of claim 1, wherein the transparent medium is self-curing.

### Claim 15 (depends on 1)

The optical sensor assembly of claim 1, wherein the transparent medium is curable by evaporation.

### Claim 16 (depends on 1)

The optical sensor assembly of claim 1 constructed by a method comprising:
producing the structured filter, wherein the step of producing the structured filter comprises:
acquiring the transparent medium;
acquiring a dielectric medium including the suspended particles; and
suspending the dielectric medium in the transparent medium;
mounting a first surface of the structured filter to the detecting surface; and
curing the dielectric medium to a structurally stable state to control a distribution of the suspended particles.

### Claim 17 (depends on 16)

The optical sensor assembly of claim 16, wherein a detector lens is mounted to the structured filter at a second surface of the structured filter that is opposite the first surface of the structured filter.

### Claim 18 (depends on 16)

The optical sensor assembly of claim 16, wherein the step of producing the structured filter further comprises:
shaping the dielectric medium to form a detector lens prior to the step of curing the dielectric medium.