Measuring optical spectral property of light based on polarization analysis

• US 8,345,238 B2
• Filed: 01/09/2009
• Issued: 01/01/2013
• Est. Priority Date: 02/04/2008
• Status: Active Grant

• Current Assignee: Luna Innovations, Inc.
• Original Assignee: General Photonics Corporation (General Cable Corporation)
• Inventors: Yao, Xiaotian Steve
• Primary Examiner(s): STOCK JR, GORDON J
• Application Number:
  US12/351,294
• Publication Number:
  US 20090207409A1
• Time in Patent Office: 1,453 Days
• Field of Search: None
• US Class Current: 356/364
• CPC Class Codes: G01J 3/1895 using fiber Bragg gratings or gratings integrated in a waveguide
• CPC Class Codes: G01J 3/447 Polarisation spectrometry

Abstract

A device for measuring spectrum of light includes a differential group delay (DGD) device positioned to receive light under measurement and to produce output light with a DGD value representing a difference in the group delay between two orthogonal optical polarizations of the light under measurement. An optical detector is positioned to receive the output light from the DGD device to measure a state and a degree of polarization of the output light. A processing device receives and processes measurements of the state and the degree of polarization from the optical detector. A probe light source produces probe light. An optical sensor receives the probe light and interacts with the probe light at a resonance wavelength of the optical sensor. A processing unit processes the optical spectrum of the returned probe light to extract information on a parameter to change the resonance wavelength.

Claims

1. A method for measuring spectrum of light, comprising:

directing light under measurement through a differential group delay (DGD) device to produce output light with a DGD value representing a difference in the group delay between two orthogonal optical polarizations of the light under measurement;

measuring optical polarization and a degree of polarization of the output light corresponding to the DGD value; and

processing the measured optical polarization and degree of polarization for the output light to produce an optical spectrum of the light under measurement;

wherein the DGD device comprises;

a polarization beam splitter to split the light under measurement into a first optical beam in a first optical polarization along a first optical path and a second optical beam along a second, different optical path in a second optical polarization that is orthogonal to the first optical polarization;

a first Faraday reflector in the first optical path to reflect light in the first optical path back towards the polarization beam splitter;

a second Faraday reflector in the second optical path to reflect light in the second optical path back towards the polarization beam splitter; and

a delay mechanism that changes a relative optical path difference between the first and second optical paths to produce the DGD values;

wherein the polarization beam splitter combines reflected light in the first optical path in the second optical polarization and reflected light in the second optical path in the first optical polarization to produce a combined output beam as the output light.

2. A method for measuring spectrum of light, comprising:

directing light under measurement through a differential group delay (DGD) device to produce output light with a DGD value representing a difference in the group delay between two orthogonal optical polarizations of the light under measurement;

measuring optical polarization and a degree of polarization of the output light corresponding to the DGD value;

processing the measured optical polarization and degree of polarization for the output light to produce an optical spectrum of the light under measurement;

placing an optical sensor at a target location that interacts with light at a resonance wavelength of the optical sensor and responds to a parameter to change the resonance wavelength of the optical sensor;

directing probe light to the optical sensor to interact with the optical sensor to produce returned probe light at the resonance wavelength of the optical sensor associated with the parameter;

directing the returned probe light as the light under measurement into the DGD device; and

processing the optical spectrum of the returned probe light to extract information on the parameter.

3. A method for measuring spectrum of light, comprising:

directing light under measurement through a differential group delay (DGD) device to produce output light with a DGD value representing a difference in the group delay between two orthogonal optical polarizations of the light under measurement;

measuring optical polarization and a degree of polarization of the output light corresponding to the DGD value;

processing the measured optical polarization and degree of polarization for the output light to produce an optical spectrum of the light under measurement;

placing optical sensors at different target locations, the optical sensors interacting with light at different resonance wavelengths, respectively, each responding to a parameter to change a respective resonance wavelength of the optical sensor;

directing probe light to the optical sensors to interact with the optical sensors to produce returned probe light comprising light from the optical sensors caused by interaction with the probe light at the different resonance wavelengths of the optical sensors associated with the parameter;

directing the returned probe light as the light under measurement into the DGD device; and

processing the optical spectrum of the returned probe light to extract information on the parameter at each of the optical sensors.

4. A device for measuring spectrum of light, comprising:

a differential group delay (DGD) device positioned to receive light under measurement and to produce output light with a DGD value representing a difference in the group delay between two orthogonal optical polarizations of the light under measurement;

an optical detector positioned to receive the output light from the DGD device to measure a state of polarization and a degree of polarization of the output light; and

a processing device that receives and processes measurements of the state of polarization and the degree of polarization from the optical detector to produce a spectrum of the light under measurement;

wherein the DGD device comprises;

a polarization beam splitter to split the light under measurement into a first optical beam in a first optical polarization along a first optical path and a second optical beam along a second, different optical path in a second optical polarization that is orthogonal to the first optical polarization;

a first Faraday reflector in the first optical path to reflect light in the first optical path back towards the polarization beam splitter;

a second Faraday reflector in the second optical path to reflect light in the second optical path back towards the polarization beam splitter; and

a delay mechanism that changes a relative optical path difference between the first and second optical paths to produce the DGD values;

wherein the polarization beam splitter combines reflected light in the first optical path in the second optical polarization and reflected light in the second optical path in the first optical polarization to produce a combined output beam as the output light.

5. A device for measuring spectrum of light, comprising:

a differential group delay (DGD) device positioned to receive light under measurement and to produce output light with a DGD value representing a difference in the group delay between two orthogonal optical polarizations of the light under measurement;

an optical detector positioned to receive the output light from the DGD device to measure a state of polarization and a degree of polarization of the output light;

a processing device that receives and processes measurements of the state of polarization and the degree of polarization from the optical detector to produce a spectrum of the light under measurement;

wherein the DGD device comprises;

an optical polarization beam splitter (PBS) having a first port, a second port and a third port, wherein light at a first optical polarization transmits through the PBS between the first port and the second port, and light at a second optical polarization orthogonal to the first optical polarization that enters at either of the second port and the third port is reflected to the other of the second port and the third port;

a first optical path having a first end optically coupled to the second port of the PBS to receive light from the second port and to direct light to the second port;

a polarization reflector coupled to a second end of the first optical path to reflect light received from the first optical path back to the first optical path with a reflected optical polarization that is orthogonal to a polarization of the light that initially enters the first optical path upon exiting the second port of the PBS;

a second optical path having a first end optically coupled to the third port of the PBS to receive light from the second port and to direct light to the third port; and

a reflector coupled to a second end of the second optical path to reflect light received from the second optical path back to the second optical path with a reflected optical polarization that is the same as an optical polarization of the light at the third port when entering the second optical path.

6. The device as in claim 5, wherein, in the DGD device,

the polarization reflector is a Faraday reflector coupled to a second end of the first optical path to reflect light received from the first optical path back to the first optical path with a reflected optical polarization that is, at each location along the first optical path, orthogonal to an optical polarization of the light when traveling in the first optical path from the PBS towards the Faraday reflector prior to the reflection.

7. The device as in claim 5, wherein, in the DGD device,

the polarization reflector comprises a reflector and a quarter wave plate whose one of two orthogonal principal polarization axes is at 45 degrees with a polarization axis of light exiting the second port of the PBS, and

wherein the quarter wave plate is located between the PBS and the reflector.

8. A device for measuring spectrum of light, comprising:

a differential group delay (DGD) device positioned to receive light under measurement and to produce output light with a DGD value representing a difference in the group delay between two orthogonal optical polarizations of the light under measurement;

an optical detector positioned to receive the output light from the DGD device to measure a state of polarization and a degree of polarization of the output light;

a processing device that receives and processes measurements of the state of polarization and the degree of polarization from the optical detector to produce a spectrum of the light under measurement;

a probe light source that produces probe light;

an optical sensor at a target location that receives the probe light and interacts with the probe light at a resonance wavelength of the optical sensor, the optical sensor responding to a parameter to change the resonance wavelength of the optical sensor and to produce returned probe light at the resonance wavelength of the optical sensor associated with the parameter, wherein the returned probe light is directed into the DGD device as the light under measurement; and

a processing unit that processes the optical spectrum of the returned probe light to extract information on the parameter.

9. A device for measuring spectrum of light, comprising:

a differential group delay (DGD) device positioned to receive light under measurement and to produce output light with a DGD value representing a difference in the group delay between two orthogonal optical polarizations of the light under measurement;

an optical detector positioned to receive the output light from the DGD device to measure a state of polarization and a degree of polarization of the output light;

a processing device that receives and processes measurements of the state of polarization and the degree of polarization from the optical detector to produce a spectrum of the light under measurement;

a probe light source to produce probe light;

optical sensors at different target locations, the optical sensors interacting with light at different resonance wavelengths, respectively, each responding to a parameter to change a respective resonance wavelength of the optical sensor, the optical sensors receiving and interacting with the probe light to produce returned probe light comprising light from the optical sensors caused by interaction with the probe light at the different resonance wavelengths of the optical sensors associated with the parameter, wherein the returned probe light is directed into the DGD device as the light under measurement; and

a processing unit processing the optical spectrum of the returned probe light to extract information on the parameter at each of the optical sensors.

10. The device as in claim 9, wherein each optical sensor includes a fiber Bragg grating sensor.

11. A method for measuring optical spectral property of light, comprising:

directing light under measurement to pass through a differential group delay (DGD) device to cause a delay between two orthogonal states of polarization of the light under measurement to produce output light;

measuring a state of polarization of the output light;

processing the measured state of polarization to determine an increase or decrease in frequency of the light under measurement based on a change in the measured state of polarization;

using a wavelength-swept light source to generate the light under measurement;

controlling the DGD device to produce different DGD values on the output light;

at each DGD value, scanning a wavelength of the wavelength-swept light source in a spectral range within a scanning time period to measure values of a state of polarization (SOP) and a degree of polarization (DOP) of the output light at different time instants in the scanning time period;

processing measured SOP and DOP values at each time instant for different DGD values to obtain a center optical frequency or wavelength of the wavelength-swept light source at each time instant;

obtaining a spectral power, which is optical power as a function of the optical wavelength, of the light source at each time instant by Fourier transforming measured DOP values vs. DGD values; and

obtaining a 3-D plot of the optical power as a function of the time instant and as a function of the optical wavelength.

12. The method as in claim 11, further comprising:

converting the 3-D plot into a 3-D plot of the optical power as a function of the center wavelength based on the processing of the measured SOP and DOP values at each time instant for different DGD values as a function of the optical wavelength.