READ ME File For 'Compact, high-resolution spectral interrogator based on laser-written 3D scattering structure inside flat optical fiber - dataset'

Dataset DOI: https://doi.org/10.5258/SOTON/D2441

Date that the file was created: November, 2022

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GENERAL INFORMATION
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ReadMe Author: PRZEMYSLAW FALAK, University of Southampton [ORCID: 0000-0002-2970-0700]

Date of data collection: JULY 2022 - OCTOBER 2022

Information about geographic location of data collection: Southampton, UK

Related projects:
EPSRC grant 'Roll-2-Roll (R2R) manufacture of multilayer planar optics' (EP/V053213/1).
EPSRC grant 'Giant magneto-optic response in rare-earth doped glasses and manufacturing of related devices and sensors’ (EP/S013776/1)
EPSRC grant 'National Hub in High Value Photonic Manufacturing' (EP/N00762X/1).
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SHARING/ACCESS INFORMATION
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Licenses/restrictions placed on the data, or limitations of reuse: No restrictions. Can be used based on CC-BY.

This dataset supports the publication:
AUTHORS: PRZEMYSLAW FALAK, TIMOTHY LEE, SHAHRZAD ZAHERTAR, CHRISTOPHER HOLMES, GILBERTO BRAMBILLA, MARTYNAS BERESNA
TITLE: Compact, high-resolution spectral interrogator based on laser-written 3D scattering structure inside flat optical fiber
JOURNAL: Scientific Reports


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DATA & FILE OVERVIEW
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This dataset contains one archived file .zip with the following content:
1) This README.txt file,
2) Subfolder "01_Wavemeter"
3) Subfolder "02_Stability"
4) Subfolder "03_FBG_interrogation"

This dataset consists of 3 sub-folders titled "01_Wavemeter", "02_Stability" and "03_FBG_interrogation" and 10 .fig files in total.

The "01_Wavemeter" folder contains the following 4 sub-files:

a) "01_Single_wavelength_wavemeters_comparison.fig" - this file contains reconstructed single-peak 1048.65 nm spectra for three devices used: a) solid blue line - flat fiber-inscribed scattering structure; b) dotted red line - 3D scattering chip; c) dashed yellow line - 50 cm MMF (multi-moded fiber; FG105LCA). 
Additionally, the figure contains SNRs (signal-to-noise ratios) for the demonstrated scattering media: 32 for flat fiber matrix; 3.2 for 3D scattering chip and 4.8 for MMF.

b) "02a_MMF_correlation_matrix.fig" - this file contains "correlation matrix" for 50 cm MMF, created by reconstructing single-peak spectrum in range 1040-1056 nm, tuning (shifting) peak position by 45 pm each time (340 peak positions in total).
Note: colorbar scale is uniform for all 3 correlation matrices files (02a-02c).

c) "02b_3D_scattering_chip_correlation_matrix.fig" - as above, but for 3D scattering chip acting as speckle generator.

d) "02c_Flat_fiber_scattering_correlation_matrix.fig" - as above, but using scattering matrix (demonstrated device) inscribed inside the flat fiber as scattering medium (speckle generator).


The "02_Stability" folder contains the following 6 sub-files:

a) "03a_MMF_temporal_stability.fig" - this file contains temporal stability results over 12 hours for 50 cm MMF. The solid blue line is the reconstruction from the tested device, red shaed line - the reference value (Optical Spectrum Analyser Yokogawa AQ6370D). 

b) "03b_3D_scattering_chip_temporal_stability.fig" - temporal stability results over 60 hours for laser-written 3D scattering chip. The blue solid line is the reconstruction result, red dashed - reference device (OSA Yokogawa AQ6370D).

c) "03c_Flat_fiber_temporal_stability.fig" - as above, but for flat fiber-inscribed scattering matrix (array).

d) "03d_MMF_humidity_temp_fluctuations.fig" - this file contains changes in temperature and humidity during MMF stability test (file 03a),

e) "03e_3D_scattering_chip_humidity_temp_fluctuations.fig" - as above, but for 3D scattering chip testing (file 03b),

f) "03f_Flat_fiber_humidity_temp_fluctuations.fig" - as above, but for flat fibre device stability testing (file 03c).


The "03_FBG_interrogation" folder contains the following 4 sub-files:

a) "04a_Microstrain_reconstruction_correlation.fig" - an attempt to recover (reconstruct) the microstrain from the speckles, using linear algebra correlation equation solutions by applying SVD (singular value decomposition).

b) "04b_Microstrain_vs_PCA2.fig" - relation between 2nd principal component (PCA2) and speckle sequence (number) for both calibration (blue dashed line) and testing - solid red line.

c) "04c_Microstrain_reconstruction_PCA2.fig" - as for Fig. 04a, but 2nd principal component (PCA2) projection was used to reconstruct the strain instead of correlation equation solution.

d) "04d_FBG_reflection_spectrum_idle.fig" - the reflection from unstrained (idle) FBG, measured by Yokogawa OSA Aq6370D.

NOTE: the strain change was applied for speckles during calibration (0-200 microstrains with the step of 4 microstrains). 
The calibration was done by one-way sweep from 0 to 200 microstrains and capturing the speckles. 
The measurement was done by three rampings of the strain from 0 to 200 and back to 0 (3 strain "peaks") with the step of 4 microstrains. 

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METHODOLOGICAL INFORMATION
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Description of methods used for collection/generation of data: The raw data was collected as speckle patterns captured by IR camera (.png files) and further processed by MATLAB scripts. 

Methods for processing the data: Generated data was processed by computational MATLAB scripts and saved as MATLAB figure files (.fig).

Software- or Instrument-specific information needed to interpret the data, including software and hardware version numbers: All files within this dataset are MATLAB(C) MathWorks Inc. figure files (.fig). 
All files were created in MATLAB R2021a and shall be opened by any MATLAB version, starting from R2014b.
The .fig files contain the data which can be accessed by using MATLAB commands.

Environmental/experimental conditions: temperature: 22.0 - 23.82C, humidity: 38.5-42%.

People involved with sample collection, processing, analysis and/or submission: PRZEMYSLAW FALAK


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DATA-SPECIFIC INFORMATION 
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Filename: 01_Single_wavelength_wavemeters_comparison.fig

Number of variables: 2

Number of cases: 3

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- wavelength (λ, nanometers),
- Intensity (arbitrary units, dimensionless).
Cases:
a) Reconstructed spectra for wavelength peak at 1048.65 nm using:
- 50 cm of MMF (multi-moded fiber, FG105LCA),
- laser-written 3D scattering chip,
- laser-inscribed scattering matrix inside flat fiber.
b) also Signal-to-noise ratios (SNRs) for each case are displayed

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DATA-SPECIFIC INFORMATION
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Filename: 02a_MMF_correlation_matrix.fig

Number of variables: 2

Number of cases: 1

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- λ reference (nanometers) - known values from the reference device (OSA AQ6370D, Yokogawa),
- λ measured (nanometers) - values recovered from reconstruction algorithm.
Cases:
- 50cm MMF correlation matrix, made by reconstructing spectra with peak wavelength being shifted from 1040 to 1056 nm in 45pm increasements.

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DATA-SPECIFIC INFORMATION
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Filename: 02b_3D_scattering_chip_correlation_matrix.fig

Number of variables: 2

Number of cases: 1

Variable list, defining any abbreviations, units of measure, codes or symbols used:
As above, reference and measured wavelengths in the form of correlation matrix, using 3D laser-written chip as scattering device.

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DATA-SPECIFIC INFORMATION
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Filename: 02c_Flat_fiber_scattering_correlation_matrix.fig

Number of variables: 2

Number of cases: 1

As above, but using flat fiber-inscribed scattering matrix.

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DATA-SPECIFIC INFORMATION
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Filename: 03a_MMF_temporal_stability.fig

Number of variables: 2

Number of cases: 2

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- time (hours),
- wavelength change (delta lambda) in nm
Cases:
- reference (Yokogawa AQ6370D) measurements of wavelength,
- reconstructed wavelength by 50cm MMF (multi moded fibre FG105LCA, Thorlabs) based device.

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DATA-SPECIFIC INFORMATION
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Filename: 03b_3D_scattering_chip_temporal_stability.fig

Number of variables: 2

Number of cases: 2

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- time (hours),
- wavelength change (delta lambda) in nm
Cases:
- reference (Yokogawa AQ6370D) measurements of wavelength,
- reconstructed wavelength by 3D laser-written scattering chip-based device.

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DATA-SPECIFIC INFORMATION
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Filename: 03c_Flat_fiber_temporal_stability.fig

Number of variables: 2

Number of cases: 2

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- time (hours),
- wavelength change (delta lambda) in nm
Cases:
- reference (Yokogawa AQ6370D) measurements of wavelength,
- reconstructed wavelength by flat fiber-inscribed scattering matrix-based device.

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DATA-SPECIFIC INFORMATION
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Filename: 03d_MMF_humidity_temp_fluctuations.fig

Number of variables: 3

Number of cases: 1

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- time (hours),
- temperature (Celsius) and humidity (%) change during fixed-wavelength stability test of MMF

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DATA-SPECIFIC INFORMATION
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Filename: 03e_3D_scattering_chip_humidity_temp_fluctuations.fig
Number of variables: 3

Number of cases: 1

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- time (hours),
- temperature (Celsius) and humidity (%) change during fixed-wavelength stability test of 3D scattering chip

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DATA-SPECIFIC INFORMATION
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Filename: 03f_Flat_fiber_humidity_temp_fluctuations.fig
Number of variables: 3

Number of cases: 1

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- time (hours),
- temperature (Celsius) and humidity (%) change during fixed-wavelength stability test of Flat fiber scattering matrix

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DATA-SPECIFIC INFORMATION
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Filename: 04a_Microstrain_reconstruction_correlation.fig

Number of variables: 2

Number of cases: 2

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- time (minutes),
- strain (microstrain, με)
Cases:
- reference - converted to microstrain translational stage displacement (encoder indications from Thorlabs NANOMAX stage; initial length=12.7 cm),
- correlation-based measurement - reconstruction of microstrain using SVD-based solution of a linear algebra correlation equation.

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DATA-SPECIFIC INFORMATION
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Filename: 04b_Microstrain_vs_PCA2.fig

Number of variables: 2

Number of cases: 2

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- speckle number (dimensionless),
- PCA2 value - 2nd principal component projection value (dimensionless).
Cases:
- calibration - registering PCA2-projected values for microstrain 0-200 with 4 microstrain step,
- testing - PCA2-projected values for microstrain modulation from 0-200 and back to 0 microstrain, 3 times repeated - resulting in 3 "microstrain peaks".

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DATA-SPECIFIC INFORMATION
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Filename: 04c_Microstrain_reconstruction_PCA2.fig

Number of variables: 2

Number of cases: 2

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- time (min),
- strain (microstrain, με)
Cases:
- reference - converted to microstrain translational stage displacement (encoder indications from Thorlabs NANOMAX stage; initial length=12.7 cm),
- PCA-based measurement - reconstruction of microstrain changes using PCA2 (2nd principal component)-based projection.

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DATA-SPECIFIC INFORMATION
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Filename: 04d_FBG_reflection_spectrum_idle.fig

Number of variables: 2

Number of cases: 1

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- Reflection (dBm),
- wavelength (nm)
Cases:
- Measurement of an idle (unstrained) reflection from FBG via OSA Yokogawa AQ6370D.