# US 10,120,111 B2 · Thin ceramic imaging screen for camera systems

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- Number: US 10,120,111 B2
- Document ID: US10120111B2
- Status: Granted
- Kind: B2
- Application number: 15/379,186
- Filed: 2016-12-14
- Published: 2018-06-14
- Granted: 2018-11-06
- Earliest claimed: 2016-12-14
- Assignees: Google Inc.
- Applicants: Google LLC
- Inventors: Jill D. Berger; Steven M. Swain; Tianran Liang; Kevin Y. Yasumura
- Web page: https://patentgrep.com/patent/US10120111B2

## CPC

- G02B 5/0268: {characterized by the fabrication or manufacturing method}
- C03C 17/007: {containing a dispersed phase, e.g. particles, fibres or flakes, in a continuous phase}
- G02B 5/021: {the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures}
- G02B 5/0242: {by means of dispersed particles}
- G02B 5/0278: {used in transmission}
- G02B 6/359: {of the position of the moving element itself during switching, i.e. without monitoring the switched beams}
- G02B 21/0016: {Technical microscopes, e.g. for inspection or measuring in industrial production processes}
- H04N 23/51: Housings
- H04N 25/76: Addressed sensors, e.g. MOS or CMOS sensors
- C03C 2217/452: Glass
- C03C 2217/485: Pigments
- G02B 6/3512: {the optical element being reflective, e.g. mirror}
- G02B 6/3556: {NxM switch, i.e. regular arrays of switches elements of matrix type constellation}
- G02B 6/356: {in an optical cross-connect device, e.g. routing and switching aspects of interconnecting different paths propagating different wavelengths to (re)configure the various input and output links (switching polarized beams G02B6/3594; power equalizers G02B6/356 and G02B6/3594; path selecting means H04Q11/0001)}
- G02B 26/0833: {the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD (G02B26/0825 takes precedence; micromechanical devices in general B81B)}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- C03C: CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

An apparatus and a camera system are provided. The apparatus includes an imaging screen configured to diffuse incoming light, and a lens system coupled to the imaging screen and configured to focus light from the imaging screen onto a CMOS image sensor. The imaging screen includes a ceramic diffuser layer fused into a surface of a glass substrate, and a thickness of the ceramic diffuser layer is within a range of about 7-10 μm.

## Claims

### Claim 1

An apparatus comprising:
an imaging screen configured to diffuse incoming light; and
a lens system coupled to the imaging screen and configured to focus light from the imaging screen onto a CMOS image sensor, wherein:
the imaging screen comprises a ceramic diffuser layer directly fused into a surface of a glass substrate such that no gap exists between the ceramic diffuser layer and the glass substrate, and
a thickness of the ceramic diffuser layer is within a range of about 7-10 μm.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the ceramic diffuser layer comprises a bismuth-based glass frit and at least one inorganic pigment, including one of silicon dioxide (SiO2), zinc oxide (ZnO), diboron trioxide (B2O3), sodium oxide (Na2O), and bismuth oxide (BiO2).

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein a thermal expansion coefficient (CTE) of the ceramic diffuser layer has a value within about 8% of a CTE value of the glass substrate.

### Claim 4 (depends on 1)

The apparatus of claim 1, further comprising a stainless steel housing coupled to and surrounding the imaging screen using a glass layer including a soda lime float glass material.

### Claim 5 (depends on 4)

The apparatus of claim 4, wherein a thermal expansion coefficient (CTE) of the ceramic diffuser layer has a value within about 10-20% of a CTE value of the stainless steel housing, and wherein a CTE value of the glass substrate is within about 6-7% of the CTE value of the stainless steel.

### Claim 6 (depends on 1)

The apparatus of claim 1, wherein the imaging screen is configured to be thermally stable within a predefined operating temperature range to enable thermal stability of pixel-to-pixel separation of an image formed on the CMOS image sensor.

### Claim 7 (depends on 1)

The apparatus of claim 1, further comprising a processor coupled to the CMOS image sensor, wherein the processor is configured to process an output signal of the CMOS image sensor to determine positions of respective mirrors of an array of MEMS mirrors of an optical circuit switch.

### Claim 8 (depends on 1)

The apparatus of claim 1, wherein the glass substrate comprises a soda lime float glass substrate, and wherein the soda lime float glass substrate comprises a low-iron glass substrate.

### Claim 9 (depends on 1)

The apparatus of claim 1, wherein surface flatness of the glass substrate is characterized by a peak-to-valley value of about λ/4 at a wavelength (λ) of about 633 nm.

### Claim 10

A camera system for monitoring micro electro-mechanical system (MEMS) mirrors, the camera system comprising:
a diffuser comprising a ceramic diffuser layer directly fused into a first surface of a glass substrate such that no gap exists between the ceramic diffuser layer and the glass substrate;
an optical block configured to concentrate light emitted by the diffuser;
an image sensor configured to receive concentrated light from the optical block and to generate electrical signals; and
a processor coupled to the image sensor and configured to produce an image of beams reflected from the MEMS mirrors based on the electrical signals,
wherein a thermal expansion coefficient (CTE) of the ceramic diffuser layer has a value within about 8% of a CTE value of the glass substrate.

### Claim 11 (depends on 10)

The camera system of claim 10, wherein a thickness of the ceramic diffuser layer is within a range of about 7-10 μm.

### Claim 12 (depends on 10)

The camera system of claim 10, wherein the ceramic diffuser layer comprises a bismuth-based glass frit and at least one inorganic pigment, including one of silicon dioxide (SiO2), zinc oxide (ZnO), diboron trioxide (B2O3), sodium oxide (Na2O), and bismuth oxide (BiO2).

### Claim 13 (depends on 10)

The camera system of claim 10, further comprising stainless steel housing coupled to and surrounding the diffuser using a glass layer including a soda lime float glass, and wherein a thermal expansion coefficient (CTE) of the ceramic diffuser layer has a value within about 10-20% of a CTE value of the stainless steel housing, and wherein a CTE value of the glass substrate is within about 6-7% of the CTE value of the stainless steel.

### Claim 14 (depends on 10)

The camera system of claim 10, wherein the image sensor is coupled to the processor and comprises a CMOS image sensor with pixel size of about 6 μm.

### Claim 15 (depends on 10)

The camera system of claim 10, wherein the processor is configured to process the electrical signals to determine positions of respective mirrors of an array of MEMS mirrors of an optical circuit switch.

### Claim 16 (depends on 10)

The camera system of claim 10, wherein the diffuser is configured to be thermally stable within a predefined operating temperature range to enable thermal stability of pixel-to-pixel separation of an image of the beams reflected from the MEMS mirrors.

### Claim 17 (depends on 10)

The camera system of claim 10, wherein the glass substrate comprises a low-iron soda lime float glass substrate.

### Claim 18 (depends on 10)

The camera system of claim 10, wherein the optical block comprises a plurality of lenses configured to have a negative magnification and to concentrate lights from a diffuser spot with a size of about 54 μm into an image sensor pixel of about 6 μm.

### Claim 19 (depends on 10)

The camera system of claim 10, wherein a thickness of the glass substrate is within a range of about 3-4 mm.

### Claim 20 (depends on 10)

The camera system of claim 10, wherein the glass substrate has a surface flatness characterized by a peak-to-valley value of about λ/4 at a wavelength (λ) of about 633 nm.