# US 11,442,314 B2 · Polarization insensitive liquid crystal on silicon (LCOS) phase modulators and related devices and methods

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- Number: US 11,442,314 B2
- Document ID: US11442314B2
- Status: Granted
- Kind: B2
- Application number: 17/393,750
- Filed: 2021-08-04
- Published: 2022-02-17
- Granted: 2022-09-13
- Earliest claimed: 2020-08-11
- Assignees: Chongchang Mao
- Applicants: Chongchang Mao
- Inventors: Chongchang Mao
- Web page: https://patentgrep.com/patent/US11442314B2

## CPC

- G02F 1/133638: {Waveplates, i.e. plates with a retardation value of lambda/n}
- G02F 1/136277: {formed on a semiconductor substrate, e.g. of silicon}
- G02F 1/133553: {Reflecting elements (associated to illuminating devices G02F1/133605)}
- G02F 1/133565: {inside the LC elements, i.e. between the cell substrates}
- G02F 1/13439: {characterised by their electrical, optical, physical properties; materials therefor; method of making}
- G02F 2203/06: Polarisation independent
- G02F 2203/50: Phase-only modulation
- G02F 2413/01: Number of plates being 1
- G02F 2413/05: Single plate on one side of the LC cell
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS

## Abstract

A polarization insensitive optical phase modulator is provided including a glass substrate; a liquid crystal element; a first electrode on a first surface of the liquid crystal element adjacent the glass substrate; a second electrode on a second surface of the liquid crystal element, opposite the first surface, the first and second electrodes supplying an electric potential across the liquid crystal element to drive liquid crystals in a predetermined configuration; and a silicon backplane on the second electrode opposite the liquid crystal element. The first electrode is a transparent electrode to a selected wavelength and is on a surface of the glass substrate. The second electrode includes individually addressable pixels and reflection metal mirrors on pixel surfaces and is on a surface of the silicon backplane. The modulator further includes a polymer quarter-wave plate (QWP) between the second electrode and the liquid crystal element, the polymer QWP having an optical axis at 45 degrees to liquid crystal slow axis.

## Claims

### Claim 1

A polarization insensitive optical phase modulator comprising:
a glass substrate;
a liquid crystal element;
a first electrode on a first surface of the liquid crystal element adjacent the glass substrate;
a second electrode on a second surface of the liquid crystal element, opposite the first surface, the first and second electrodes supplying an electric potential across the liquid crystal element to drive liquid crystals in a predetermined configuration;
a silicon backplane on the second electrode opposite the liquid crystal element;
wherein the first electrode is a transparent electrode to a selected wavelength and is on a surface of the glass substrate; and
wherein the second electrode includes individually addressable pixels and reflection metal mirrors on pixel surfaces and is on a surface of the silicon backplane; and
a polymer quarter-wave plate (QWP) between the second electrode and the liquid crystal element, the polymer QWP having an optical axis at 45 degrees to a liquid crystal slow axis,
wherein reflected light has a 90 degree polarization rotation before traversing the liquid crystal element a second time; and
wherein the reflected light passing through the liquid crystal element the second time has a different phase modulation from that of incident light passing through the liquid crystal element a first time, such that output light has a same phase modulation for both polarization components.

### Claim 2 (depends on 1)

The polarization insensitive optical phase modulator of claim 1, wherein the polymer QWP comprises a quarter-wave plate for the selected wavelength.

### Claim 3 (depends on 2)

The polarization insensitive optical phase modulator of claim 2, wherein selected wavelength has a range of from 0.4 um to 2.0 um for display and/or telecommunication applications.

### Claim 4 (depends on 1)

The polarization insensitive optical phase modulator of claim 1, wherein the polymer QWP comprises a birefringent liquid crystal polymer on a surface of a linear photo-polymerization layer.

### Claim 5 (depends on 4)

The polarization insensitive optical phase modulator of claim 4, wherein the liquid crystal polymer is exposed using an un-polarized ultraviolet (UV) light beam.

### Claim 6 (depends on 5)

The polarization insensitive optical phase modulator of claim 5, further comprising a linear photo-polymerization element on a surface of a silicon backplane and exposed by a polarized UV light beam with a polarization direction at 45° to a slow axis of the liquid crystal element.

### Claim 7 (depends on 1)

The polarization insensitive optical phase modulator of claim 1, wherein the polymer QWP comprise different patterns corresponding with different applications.

### Claim 8 (depends on 1)

The polarization insensitive optical phase modulator of claim 1, wherein liquid crystal element has a thickness of from about 2 um to about 10 um.

### Claim 9 (depends on 1)

The polarization insensitive optical phase modulator of claim 1, wherein the QWP has a thickness of from about 0.4 um to about 4 um.

### Claim 10 (depends on 1)

The polarization insensitive optical phase modulator of claim 1, further comprising a first alignment layer between the first electrode and the liquid crystal element and a second alignment layer between the second electrode and the liquid crystal element.

### Claim 11

A liquid crystal on silicon (LCOS) device providing a substantially polarization independent response to input light, the LCOS device comprising:
a glass substrate having first and second opposing surfaces;
a silicon backplane having first and second opposing surfaces;
a liquid crystal material between the first surface of the glass substrate adjacent the liquid crystal material and the first surface of the silicon backplane adjacent the liquid crystal material;
a first electrode on the glass substrate between the glass substrate and the liquid crystal material, the first electrode being a transparent electrode that provides a common potential voltage Vcom; and
a second electrode on a frame buffer pixel circuit that includes a first electric gate, a source follower, and a second electric gate,
wherein the second electrode in a pixel is not limited to frame buffer pixel circuit.

### Claim 12 (depends on 11)

The LCOS of claim 11, wherein the frame buffer pixel circuit comprises a frame image that is fully displayed while next frame data is loading.

### Claim 13 (depends on 11)

The LCOS of claim 11, wherein the first electrode common potential voltage Vcom operates in a flip-flopped manner in sequential frames to realize alternating current (AC) driving to the liquid crystal element.

### Claim 14 (depends on 11)

The LCOS of claim 11, wherein the first electrode Vcom is provided from an electronic driving board outside of a LCOS panel.

### Claim 15 (depends on 14)

The LCOS of claim 14, further comprising an electronic board configured to provide an adjustable voltage to drive different liquid crystal elements.

### Claim 16

A method of fabricating a polymer quarter-wave plate (QWP) for a polarization insensitive optical phase modulator, the method comprising:
providing a silicon backplane;
forming a second electrode on the silicon backplane, the second electrode including individually addressable pixels and reflection metal mirrors on pixel surfaces;
forming a linear photo-polymerization (LPP) layer on the first electrode;
exposing the LPP layer to polarized ultra-violet (UV) light;
forming a liquid crystal polymer (LCP) layer on the exposed LPP layer; and
exposing the LCP layer to un-polarized UV light to provide the polymer quarter-wave plate (QWP) between the second electrode and a liquid crystal element.

### Claim 17 (depends on 16)

The method of claim 16, wherein the polymer QWP has an optical axis at 45 degrees to a liquid crystal slow axis.

### Claim 18 (depends on 16)

The method of claim 16, wherein reflected light has a 90 degree polarization rotation before traversing the liquid crystal element a second time.

### Claim 19 (depends on 16)

The method of claim 16, wherein the QWP has a thickness of from about 0.4 um to about 4 um.