Optical Polarimeter Detecting SOP Rotations

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Solution Overview

Problem

Conventional polarimeters cannot measure rotations of the state of polarization (SOP) string about the average SOP value, especially in cases of large bandwidth or significant time-dependent changes, leading to incomplete measurements.

Innovation Solution

An optical polarimeter is enhanced with a second Stokes measurement arrangement, utilizing a spectral filter and grating with detector pairs, or a single detector/filter pair, to create a condition-dependent Stokes vector, allowing for wavelength-dependent and time-dependent variations to be observed, providing information on polarization transformations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a conventional polarimeter measures only the average Stokes vector, then the measurement is simple and fast, but it cannot detect rotations of the SOP string about the average SOP

Engineering Contradiction:

Improvedetection of polarization transformationsVSAvoidmeasurement arrangement

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The measurement system is segmented into two independent Stokes measurement arrangements: a first arrangement that measures the average Stokes vector, and a second arrangement that measures a condition-dependent Stokes vector. This segmentation allows each arrangement to be optimized for its specific measurement function while together they provide complete polarization transformation detection capability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention adds a new measurement dimension by introducing the condition-dependent Stokes vector measurement that is sensitive to SOP string rotations. This additional measurement dimension (the second Stokes vector) complements the average Stokes vector measurement, enabling detection of polarization transformations that would otherwise be invisible to conventional single-vector measurements.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If spectral filtering is applied to measure wavelength-dependent Stokes vectors, then polarization transformations can be detected, but the measurement speed decreases

Engineering Contradiction:

Improvewavelength-dependent measurementVSAvoidmeasurement speed

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

Spectral filtering is applied in advance to the optical signal before it reaches the detectors in the second Stokes measurement arrangement. This preliminary spectral separation allows the system to simultaneously capture wavelength-dependent information without requiring sequential measurements, thereby maintaining high measurement speed while achieving precise wavelength-resolved Stokes vector measurement.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Enables the detection of polarization transformations by measuring both the average Stokes vector and rotations of the SOP string, enhancing measurement accuracy and efficiency, and allowing for compact, high-speed operation.

Implementation Method 1

utilizing a spectral filter and grating with detector pairs

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

utilizing a spectral filter and grating with detector pairs

Methodology Applied

Scientific EffectOptical filtering: Filter (optical)

Implementation Method 3

An optical sensor, such as a photodetector, is positioned to measure the intensity of light transmitted

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 4

The waveplate is rotatable about the optical axis and is typically a quarter-wave plate

Methodology Applied

Scientific EffectBirefringence: Birefringence

Data Source

PatentUS9116036B2Optical polarimeter

Publication Date: 2015.08.25 OFS FITEL LLC

AI summary

A polarimeter is proposed that utilizes additional Stokes parameter measurements to determine both an average Stokes vector, as well as any rotation of the state of polarization around the Stokes vector. The optical polarimeter is configured to measure the state of polarization (SOP) under multiple, different conditions that yield both averaged Stokes vector and at least one other secondary (filtered) Stokes vector, the latter thus being determined from a subset of the conditions used to create the average Stokes vector. The secondary Stokes vector created from a filtered input will necessarily exhibit changes over time as a function of polarization transformations (based on filter-dependent changes), while the average Stokes vector will retain a constant value. Thus, a comparison of the average Stokes vector to the changing secondary Stokes vector allows for these polarization-dependent transformations to be recognized.