System for acquiring images by means of heterodyne digital holography

Patent metadata

Field	Value
Publication number	US-9958828-B2
Application number	US-201415109108-A
Country	US
Kind code	B2
Filing date	Dec 16, 2014
Priority date	Dec 31, 2013
Publication date	May 1, 2018
Grant date	May 1, 2018

Abstract

A system for acquiring images by means of heterodyne digital holography comprises an image sensor having at least one photodiode coupled to an oversampling analog-digital converter.

First claim

What is claimed is:

1. A system for acquiring images by heterodyne digital holography, comprising:
an image sensor having at least one photodiode coupled to an analog-to-digital converter; and
an optical assembly enabling to simultaneously project on the sensor first and second coherent light beams of different frequencies,
wherein the converter is capable of acquiring, at a first frequency, analog samples representative of an output signal of the photodiode, of generating, at a second frequency equal to the first frequency or to a sub-multiple of the first frequency first digital samples having a first resolution based on said analog samples, and of providing at a third frequency equal to a sub-multiple of the second frequency second digital samples having a resolution greater than the first resolution, generated from the first digital samples,
and wherein the first frequency of the converter is equal to an integral number n of times the system beat frequency (f B ), that is, the absolute value of the difference between the frequencies of the first and second beams.

2. The system of claim 1 , wherein the optical assembly comprises a single acousto-optic modulator.

3. The system of claim 1 , wherein the optical assembly comprises no acousto-optic modulator, and comprises an ultrasound source for exciting an object crossed by the second light beam.

4. The system of claim 3 , wherein the ultrasound source is capable of emitting an ultrasound wave during a first time interval of duration Δt, and wherein the converter is capable of only acquiring samples representative of an output signal of the photodiode during a second time interval of same duration Δt, time-shifted with respect to the first time interval.

5. The system ( 500 ) of claim 3 , wherein the ultrasound source is capable of emitting an ultrasound wave having a first random or pseudo-random sequence of phase jumps by 0 or π, and wherein the converter is capable of receiving a binary signal representative of a second sequence of phase jumps identical to the first sequence but time-shifted with respect to the first sequence, and of modifying an analog sample processing sequence according to this binary signal.

6. The system of any of claim 1 , wherein n is equal to 4.

7. The system of claim 1 , wherein the converter comprises an analog sampling block capable of acquiring n analog samples of an output signal of the photodiode at each beat period of the system.

8. The system of claim 7 , wherein the analog sampling block is capable of analogically performing, for each beat period, one or a plurality of arithmetic operations based on said samples.

9. The system of claim 7 , wherein the converter is capable of providing, after an integral number N of beat periods of the system, a first digital signal over m bits, representative of the real part of the complex field of the second light beam, and a second digital signal over m bits, representative of the imaginary part of the complex field of the second light beam, where m is an integer greater than or equal to 1.

10. The system of claim 9 , wherein m is equal to log 2 (N).

11. The system of claim 1 , wherein the converter comprises an integrator comprising two integration capacitors.

12. The system of claim 1 , wherein the converter comprises two integrators each comprising an integration capacitor.

13. The system of claim 1 , wherein the sensor further comprises a high-pass filtering circuit between the photodiode and the converter.

Assignees

• Commissariat Energie Atomique

Inventors

• Laforest Timothé
• Dupret Antoine
• Verdant Arnaud

Classifications

• H03M3/40

  Arrangements for handling quadrature signals, e.g. complex modulators · CPC title

• G03H2001/0463

  Frequency heterodyne, i.e. one beam is frequency shifted · CPC title

• H03M3/47

  using time-division multiplexing · CPC title

• H03M3/494

  Sampling or signal conditioning arrangements specially adapted for delta-sigma type analogue/digital conversion systems · CPC title

• G03H2226/11

  Electro-optic recording means, e.g. CCD, pyroelectric sensors · CPC title