# US 7,466,426 B2 · Phase shifting imaging module and method of imaging

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- Number: US 7,466,426 B2
- Document ID: US7466426B2
- Status: Granted
- Kind: B2
- Application number: 11/300,553
- Filed: 2005-12-14
- Published: 2007-06-14
- Granted: 2008-12-16
- Earliest claimed: 2005-12-14
- Assignees: General Electric Company
- Inventors: Shu-Guo Tang; Kevin George Harding; Robert William Tait; Craig Alan Cantello
- Web page: https://patentgrep.com/patent/US7466426B2

## CPC

- G01B 11/306: {for measuring evenness}
- G01B 9/02007: {Two or more frequencies or sources used for interferometric measurement (using only beat G01B9/02003)}
- G01B 9/0201: {using temporal phase variation}
- G01B 9/02054: {Hand held}
- G01B 9/02081: {simultaneous quadrature detection, e.g. by spatial phase shifting}
- G01B 2290/70: Using polarization in the interferometer
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS

## Abstract

A phase shifting imaging module in a handheld imager is provided. The phase shifting imaging module includes a first beam splitter configured to split an image radiation beam into first and second image radiation beams. It also includes a first prism configured to align the first and second image radiation beams, and a second beam splitter configured to split the first and second image radiation beams into four image radiation beams. A second prism aligns the four image radiation beams. A phase mask introduces phase retardation between the four image radiation beams, resulting in four phase shifted image radiation beams. A pixilated sensor generates image data based upon each of the four phase shifted image radiation beams.

## Claims

### Claim 1

A phase shifting imaging module comprising:
a first beam splitter configured to split an image radiation beam into first and second image radiation beams;
a first prism configured to align the first and second image radiation beams;
a second beam splitter configured to split the first and second image radiation beams into four image radiation beams;
a second prism configured to align the four image radiation beams;
a phase mask that receives the four image radiation beams and is configured to introduce a phase retardation between the four image radiation beams resulting in four phase shifted image radiation beams; and
a pixilated sensor configured to generate image data based upon each of the four phase shifted image radiation beams.

### Claim 2 (depends on 1)

The phase shifting imaging module of claim 1, wherein the phase mask is disposed between the second beam splitter and the pixilated sensor.

### Claim 3 (depends on 1)

The phase shifting imaging module of claim 1, wherein the first or second beam splitter comprises a prism film.

### Claim 4 (depends on 1)

The phase shifting imaging module of claim 1, wherein the first or second beam splitter comprises a prism.

### Claim 5 (depends on 4)

The phase shifting imaging module of claim 4, wherein the prism comprises a right angle prism.

### Claim 6 (depends on 1)

The phase shifting imaging module of claim 1, wherein the pixilated sensor comprises a charge-coupled device.

### Claim 7 (depends on 1)

The phase shifting module of claim 1, wherein the image radiation beam comprises a coherent electromagnetic radiation.

### Claim 8 (depends on 7)

The phase shifting module of claim 7, wherein the image radiation beam comprises a spectral range visible to the human eye.

### Claim 9 (depends on 1)

The phase shifting module of claim 1, wherein the phase mask comprises at least one quarter wave polarizer.

### Claim 10

An imaging system comprising:
at least one radiation source configured to illuminate a part surface to be tested;
at least one lens configured to collimate a radiation beam;
at least one polarizer configured to polarize the radiation beam; and
a phase shifting imaging module configured to split the radiation beam into four aligned radiation beams, and to then phase shift the four aligned radiation beams, the phase shifting imaging module comprising:
a first beam splitter configured to split an image radiation beam into first and second image radiation beams;
a first prism configured to align the first and second image radiation beams;
a second beam splitter configured to split the first and second image radiation beams into four image radiation beams;
a second prism configured to align the four image radiation beams; and
a phase mask that receives the four image radiation beams and is configured to introduce a phase retardation between the four image radiation beams resulting in four phase shifted image radiation beams.

### Claim 11 (depends on 10)

The imaging system of claim 10, wherein the imaging system comprises a handheld imager.

### Claim 12 (depends on 10)

The imaging system of claim 10, further comprising two radiation sources radiating at different wavelengths.

### Claim 13 (depends on 10)

The imaging system of claim 10, wherein the at least one radiation source comprises a diode laser.

### Claim 14 (depends on 10)

The imaging system of claim 10, wherein the at least one polarizer comprises a quarter wave plate, or a half wave plate.

### Claim 15 (depends on 10)

The imaging system of claim 10, wherein the phase shifting imaging module comprises a pixilated sensor to generate an image data based upon each of the four phase shifted image radiation beams.

### Claim 16 (depends on 10)

The imaging system of claim 10, wherein the imaging system is coupled to a workstation.

### Claim 17

A method for measuring a surface feature of a part with a coherent image radiation source, comprising:
irradiating a surface with a coherent electromagnetic radiation beam;
receiving an image radiation beam from the surface;
splitting the image radiation beam into first and second image radiation beams;
aligning the first and second image radiation beams;
splitting the first and the second image radiation beams into four radiation beams;
aligning the four radiation beams;
phase shifting the four radiation beams after alignment; and
generating image data via a pixilated sensor.