
READ ME File For 'Dataset to support the publication "An ultra-compact metasurface and specklemeter based chromatic confocal sensor"'

Dataset DOI: 10.5258/SOTON/D2853

Date that the file was created: February, 2024

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GENERAL INFORMATION
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ReadMe Author: Przemyslaw Falak, University of Southampton

Date of data collection: April-June 2023

Information about geographic location of data collection: Southampton, UK; Huddersfield, UK

Related projects:
EP/T02643X/1
EP/P006930/1
EP/S013776/1
EP/N00762X/1
EP/V053213/1
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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, Justin Ho-Tin Chan, James Williamson, Andrew Henning, Timothy Lee, Shahrzad Zahertar, Christopher Holmes, Martynas Beresna, Haydn Martin, Gilberto Brambilla, and Xiangqian Jiang
TITLE: An ultra-compact metasurface and specklemeter based chromatic confocal sensor
JOURNAL: IEEE Transactions on Instrumentation and Measurement

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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) File "Distance_reconstruction.fig"
3) File "Distance_reconstruction.png"
4) File "PCA_values.fig"
5) File "PCA_values.png"
6) File "Reconstruction_error.fig"
7) File "Reconstruction_error.png"
8) File "Metalens_spectradata.mat"
9) File "Metalens_spectradata.png"

Detailed description of the files:

1) "Distance_reconstruction.fig/.png" - this file presents reconstructed relative mirror-metalens separation distance by PCA projection and its comparison to the reference (encoder) position. This file also contains metrics of step size, standard error and maximum deviation of the reconstructed data from the reference.
2) "PCA_values.fig/.png" - this file contains information on the first principal components projection (unitless) of the metalens-mirror separation distance, compared with calibration and measurement datasets. This file also contains metrics of a standard error and maximum deviation.
3) "Reconstruction_error.fig/.png" - this file contains information on the error (i.e. difference between the 'ground truth' encoder position and the reconstructed distance by PCA projection), presented as error value vs. sample number. In addition, the guideline of no error (i.e. error equaled zero) is presented.
4) "Metalens_spectradata.mat/.png" - this file stores the informatrion on reflected light spectrum from metalens-mirror set-up as a function of metalens-mirror separation distance.

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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 CMOS IMX219 camera Raspberry Pi V2 NoIR (.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) and (for one instance) MATLAB datafile (.mat).

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), or MATLAB(C) data file (.mat). 
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.
Alternatively, the files are provided as .png (image) for a preview, but the data underlying these cannot be recovered, unless .fig files are used.

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

People involved with sample collection, processing, analysis and/or submission: P. Falak, J. Ho-Tin Chan, A. Henning, J. Williamson

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DATA-SPECIFIC INFORMATION 
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Filename: Distance_reconstruction.fig/.png

Number of variables: 2

Number of cases: 2

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- Speckle pattern number (number of the sampled speckle pattern, unitless),
- Relative metalens-mirror separation (distance between metalens surface and reflective mirror, expressed as zero for 1 mm separation and is positive for further separation increase and negative for separation decrease, micrometers).
Cases:
a) Reconstructed separation distance by PCA method 
b) Reference separation obtained by querrying translational stage encoder position.

Filename: PCA_values.fig/.png

Number of variables: 2

Number of cases/rows: 2

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- Speckle pattern number (number of the sampled speckle pattern, unitless),
- Projected, unitless dimensionality-reduced metalens-mirror separation by utilising the first PCA (PCA1 value, unitless).
Cases:
a) dimensionality-reduced PCA projection for the first PCA utilising Measurement data 
b) dimensionality-reduced PCA projection for the first PCA utilising Calibration data. 

Filename: Reconstruction_error.fig/.png

Number of variables: 2

Number of cases: 1

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- Speckle pattern number (number of the sampled speckle pattern, unitless),
- Error (difference between reconstructed and reference metalens-mirror separation, micrometers).
Cases:
a) Reconstruction error between PCA-based metalens-mirror reconstruction and reference from translational stage encoder.

Filename: Metalens_spectradata.mat/.png

Number of variables: 2

Number of cases: 1

Variable list, defining any abbreviations, units of measure, codes or symbols used:
- reflected wavelength (λ, nanometers),
- Relative metalens-mirror separation (distance between metalens surface and reflective mirror, expressed as zero for 1 mm separation and is positive for further separation increase and negative for separation decrease, micrometers).
Cases:
a) Metalens-mirror reflected spectra obtained in range 620-720 nm for metalens-mirror separation distances in range -110 to +70 microns, totalling in 228 separation distances. In .mat file, the spectra are labelled 'S2' and corresponding wavelengths 'wl'. In addition, green dashed line indicates relative 'zero' - that is where reflected wavelength peak position equals 660 nm.