Method for measuring complex degree of coherence of random optical field by using mutual intensity-intensity correlation

Patent metadata

Field	Value
Publication number	US-11366017-B2
Application number	US-202017252978-A
Country	US
Kind code	B2
Filing date	Jun 8, 2020
Priority date	Aug 26, 2019
Publication date	Jun 21, 2022
Grant date	Jun 21, 2022

Abstract

The invention discloses a method for measuring a complex degree of coherence of a random optical field by using a mutual intensity-intensity correlation, including the steps of: building a test optical path; rotating a quarter-wave plate to enable the fast axis of the quarter-wave plate to be consistent with a polarization direction of reference light, to obtain light intensity distribution information of a first combined light; rotating the quarter-wave plate to enable the slow axis of the quarter-wave plate to be consistent with the polarization direction of the reference light, to obtain light intensity distribution information of a second combined light; blocking the reference light to obtain light intensity distribution information of to-be-tested light; blocking the to-be-tested light to obtain light intensity distribution information of the reference light; and calculating the amplitude and phase of a complex degree of coherence of the to-be-tested light.

First claim

What is claimed is:

1. A method for measuring a complex degree of coherence of a random optical field by using a mutual intensity-intensity correlation, comprising steps of:
building a test optical path comprising a quarter-wave plate, a beam splitter, a condensing element, and a light detector, using a laser as reference light, wherein the reference light is modulated by the quarter-wave plate and then enters the beam splitter, and to-be-tested light enters the beam splitter at the same time, the beam splitter combines the modulated reference light and the to-be-tested light to obtain combined light, and the combined light passes through the condensing element to be imaged on the light detector;
rotating the quarter-wave plate to enable the fast axis of the quarter-wave plate to be consistent with a polarization direction of the reference light to obtain first combined light, and photographing and recording light intensity distribution information I S (1) (r) of the first combined light by using the light detector;
rotating the quarter-wave plate to enable the slow axis of the quarter-wave plate to be consistent with the polarization direction of the reference light to obtain second combined light, and photographing and recording light intensity distribution information I S (2) (r) of the second combined light by using the light detector;
blocking the reference light, and photographing and recording light intensity distribution information I(r) of the to-be-tested light by using the light detector;
blocking the to-be-tested light, and photographing and recording light intensity distribution information S r (r) of the reference light by using the light detector; and
calculating the amplitude and phase of a complex degree of coherence of the to-be-tested light.

2. The method for measuring a complex degree of coherence of a random optical field by using a mutual intensity-intensity correlation according to claim 1 , wherein calculating the amplitude and phase of a complex degree of coherence of the to-be-tested light comprises the following steps:
S61: calculating a mutual correlation G S (1,2) (r 1 ,r 2 ) between the light intensity distribution information I S (1) (r) of the first combined light and the light intensity distribution information I S (2) (r) of the second combined light;
S62: calculating a mutual correlation G B (1,2) (r 1 ,r 2 ) obtained by adding the reference light and the to-be-tested light;
S63: calculating a difference value ΔG (1,2) (r 1 ,r 2 ,Δϕ) between the two mutual correlations G S (1,2) (r 1 ,r 2 ) and G B (1,2) (r 1 ,r 2 ); and
S64: analyzing the difference value ΔG (1,2) (r 1 ,r 2 ,Δϕ) between the two mutual correlations, to obtain the amplitude and phase of the complex degree of coherence of the to-be-tested light.

3. The method for measuring a complex degree of coherence of a random optical field by using a mutual intensity-intensity correlation according to claim 1 , wherein S61 comprises:
according to a second-order coherence matrix in the space-frequency domain, representing, by using a cross-spectral density function, a second-order statistical feature of the to-be-tested light as:
W ( r 1 ,r 2 )= E *( r 1 ) E ( r 2 )   (1),

wherein E(r) represents a random electrical field at a point r in a space, a superscript asterisk represents a complex conjugate, an angle bracket represents ensemble averaging, and in this case, a complex spatial degree of coherence between two points r 1 and r 2 in the space may be defined as:

μ
⁡

(

r
1

,

r
2

)

=

W
⁡

(

r
1

,

r
2

)

S
⁡

(

r
1

)

⁢

S
⁡

(

r
2

)

,

(
2
)

wherein S(r)=W(r,r)= I(r) represents average light intensity of a random optical field at the point r in the space;
in the step of rotating the quarter-wave plate to enable the fast axis of the quarter-wave plate to be consistent with a polarization direction of the reference light, an electrical field of the reference light obtained through modulation by using the quarter-wave plate is denoted as E r (1) (r), in the step of “rotating the quarter-wave plate to enable the slow axis of the quarter-wave plate to be consistent with the polarization direction of the reference light”, an electrical field of the reference light obtained through modulation by using the quarter-wave plate is denoted as E r (2) (r), and an electrical field of the to-be-tested light is denoted as E(r);
there is a phase difference of

π
2

between the electrical fields E r (1) (r) and E r (2) (r), that is:

Δϕ
=

Arg
⁡

[

E
r

(
1
)

Assignees

• Univ Soochow

Inventors

• Chen Yahong
• Huang Zhaofeng
• Wang Fei
• Cai Yangjian

Classifications

• G01J1/42

  using electric radiation detectors (optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10) · CPC title

• G01J2001/4247

  for testing lamps or other light sources · CPC title

• G01J9/00

  Measuring optical phase difference (devices or arrangements for controlling the phase of light beams G02F1/01); Determining degree of coherence; Measuring optical wavelength (spectrometry G01J3/00) · CPC title

• G01J2009/0265

  with phase modulation · CPC title

• G01B2290/70

  Using polarization in the interferometer · CPC title