Method for a holographic projector

Patent metadata

Field	Value
Publication number	US-2020241473-A1
Application number	US-202016752002-A
Country	US
Kind code	A1
Filing date	Jan 24, 2020
Priority date	Jan 25, 2019
Publication date	Jul 30, 2020
Grant date	—

Abstract

A projection system that facilitates the use of in-situ detection of a change in wavelength, thereby enabling appropriate compensation or corrections to be applied on the fly to improve the quality of the image in the primary image region. In-situ detection in this manner can allow wavelength changes due to both temperature fluctuations and hardware variations to be compensated for simultaneously, thereby reducing the time and expense for end of line hardware testing, and removing the need to perform in-situ mapping of the wavelength as a function of temperature. In this way, the quality of the image provided to a user can be improved in a simpler, more efficient manner.

First claim

1 . A holographic projection system arranged to detect a change in a wavelength of light from a light source, the projection system comprising:
a light source arranged to output light having a wavelength; a spatial light modulator arranged to receive the light from the light source and output spatially modulated light in accordance with a diffractive pattern comprising a computer-generated hologram to form an image, wherein the image comprises a primary image region comprising information for a user and first and second control image regions; a detector arrangement configured to detect light travelling to or from the first control image region and output a first signal representative of a position of the first control image region and to detect light travelling to or from the second control image region and output a second signal representative of a position of the second control image region; and a processor arranged to:
cause the spatial light modulator to display the diffractive pattern comprising the computer-generated hologram to form the image, wherein the positions of the first and second control image regions are dependent on the computer-generated hologram and the wavelength;
receive the first and second signals;
determine the relative position of the first and second control image regions based on the first and second signals; and detect a change in the wavelength based on a change in the relative position of the first and second control image regions.

2 . The system of claim 1 , wherein the processor is further arranged to:
calculate a fractional change in the wavelength of the output light from a fractional change in the relative position of the first and second control image regions.

3 . The system of claim 1 , wherein the processor is further arranged to:
calculate a fractional change in the wavelength of the output light from a fractional change in the position of the first control image region.

4 . The system of claim 1 , wherein the diffractive pattern further comprises a grating function.

5 . The system of claim 4 , wherein the processor, configured to detect a change in the wavelength, is configured to:
change the grating function to adjust the position of the first control image region; determine, based on the received first signal, if the position of the first control image region at least partially overlaps with a first detector region of the detector arrangement; determine the grating function which gives rise to the least partial overlap of the first control image region and the first detector region; calculate an angle of diffraction corresponding to said determined grating function based on a position of the first detector region; and calculate the wavelength of the output light based on a diffraction spacing of the grating function and the determined angle of diffraction.

6 . The system of claim 5 , wherein the processor is arranged to determine the position of the first control image region at least partially overlaps with the first detector region of the detector arrangement if an intensity of light detected by the first detector region is above a predetermined intensity threshold set based on an expected intensity of the first control image region.

7 . The system of claim 5 , wherein the processor is further arranged to:
determine, based on the received second signal, if the position of the second control image region at least partially overlaps with a second detector region of the detector arrangement; determine the grating function which gives rise to both the least partial overlap of the first control image region and the first detector region and the at least partial overlap of the second control image region and the second detector region; and calculate an angle of diffraction corresponding to said grating function based on positions of both the first and second detector regions, optionally wherein the processor is arranged to determine the position of the second control image region at least partially overlaps with the second detector region of the detector arrangement if an intensity of light detected by the second detector region is above a predetermined intensity threshold set based on an expected intensity of the second control image region.

8 . The system of claim 7 , where the detector arrangement comprises a first detector comprising the first detector region and a second detector comprising the second detector region.

9 . The system of claim 1 , wherein the processor is further arranged to adjust the light source to compensate for the detected wavelength change.

10 . The system of claim 1 , wherein the processor is further arranged to adjust the computer-generated hologram to compensate for the detected wavelength change.

11 . The system of claim 1 , wherein the positions of the detector arrangement and the spatial light modulator are fixed relative to one another.

12 . The system of claim 1 , wherein the processor is configured to, subsequent to detecting a change in wavelength:
cause the SLM to display a diffraction grating to form an image, wherein a position of a region of the image is dependent on the diffraction grating and the wavelength; receive a signal from the detector arrangement representative of a position of the region of the image, the signal based on detected light travelling to or from the region of the image and detected by the detector arrangement; change the diffraction grating to adjust the position of the region of the image; determine, based on the received signal, if the position of the region of the image at least partially overlaps with a position of the detector arrangement; determine a diffraction spacing of the diffraction grating which gives rise to the least partial overlap; calculate an angle of diffraction corresponding to said determined diffraction grating based on the position of the detector arrangement; and calculate the wavelength of the output light based on the diffraction spacing and the determined angle of diffraction, optionally, wherein the region of the image comprises a diffraction spot.

13 . A method of detecting a change in a wavelength of light from a light source, the method comprising:
receiving light having a wavelength from a light source at a spatial light modulator; displaying a diffractive pattern comprising a computer-generated hologram on the spatial light modulator; spatially modulating the received light in accordance with the displayed diffractive pattern comprising the computer-generated hologram to form an image, the image comprising a primary image region comprising information for a user and first and second control image regions, wherein positions of the first and second control image regions are dependent on the diffractive pattern and the wavelength; detecting at a detector arrangement light travelling to or from the first control image region and light travelling to or from the second control image region; receiving a first signal representative of a position of the first control image region and receiving a second signal representative of a position of the second control image region based on the detected light; determining the relative position of the first and second control image regions based on the first and second signals; detecting a change in the wavelength based on a change in the relative position of the first and second control image regions.

14 . The method of claim 13 , further comprising:
calculating a fractional change in the wavelength of the output light from a fractional change in the relative position of the first and second control image regions.

Assignees

• Dualitas Ltd

Inventors

• Cooney Rory

Classifications

• G01J2009/0249

  with modulation · CPC title

• G01J9/02

  by interferometric methods (using interferometers for measuring optically the linear dimensions of objects G01B9/02) · CPC title

• G01J9/0246 Primary

  Measuring optical wavelength · CPC title

• G03H1/24

  using white light {, e.g. rainbow holograms} · CPC title

• G03H1/0406 Primary

  Image plane or focused image holograms, i.e. an image of the object or holobject is formed on, in or across the recording plane · CPC title