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6CCVD Research

Diamond Structures for Tuning of the Finesse Coefficient of Photonic Devices

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-03-31
JournalMaterials
AuthorsMonika Kosowska, A.K. Mallik, MichaƂ Rycewicz, Ken Haenen, MaƂgorzata Szczerska
InstitutionsBydgoszcz University of Science and Technology, Hasselt University
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research investigates the precise tuning of the Finesse coefficient (F) in fiber-optic Fabry-Perot (FP) cavities by utilizing various Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD) diamond structures as reflective mirrors.

  • Core Achievement: Demonstrated the ability to tailor the FP cavity finesse over a wide range (F = 0.3094 to F = 4.4383) simply by exchanging the diamond reflective surface.
  • Materials Used: Boron-doped diamond (BDD), Nitrogen-doped diamond (NDD), and Nanocrystalline diamond (NCD) sheets were synthesized via MPCVD and used as reflective surfaces.
  • Tuning Mechanism: Finesse is controlled by adjusting the reflectivity (R) of the mirrors, which is directly dependent on the refractive index (n) of the diamond film. The index (n) is modified by changing CVD parameters (e.g., dopant type or concentration).
  • Performance Range: BDD films yielded the lowest finesse (F = 0.3094), suitable for two-beam approximation and robust sensing, while the NCD sheet combined with a silver mirror achieved the highest finesse (F = 4.4383), ideal for high-resolution applications.
  • Application Focus: This tailoring capability is critical for optimizing optoelectronic systems, particularly in opto-electrochemical setups, allowing the resonator’s optical parameters to be matched precisely to the properties of the liquid solutions under investigation.
  • System Benefits: The resulting sensor head is compact, robust, immune to electromagnetic interference, and benefits from diamond’s high resistance to chemical and mechanical damage.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Operating Wavelength1550nmCentral wavelength of broadband light source.
Reflective MediumAir (n = 1)DimensionlessMedium filling the external FP cavity gap.
Finesse (F) - BDD Film0.3094DimensionlessBoron-doped diamond (BDD) film (Cavity L = 100 ”m).
Finesse (F) - NDD Film0.3653DimensionlessNitrogen-doped diamond (NDD) film (Cavity L = 150 ”m).
Finesse (F) - Silver Mirror0.4891DimensionlessBaseline comparison (Cavity L = 100 ”m).
Finesse (F) - NCD + Ag Mirror4.4383DimensionlessNanocrystalline diamond sheet with silver mirror (Cavity L = 180 ”m).
Cavity Length (L) Range100 to 180”mUsed in experimental validation (air gap).
Reflectivity (R) Formula((n1 - n2) / (n1 + n2))2DimensionlessReflectivity dependent on refractive indices (n1, n2).
Finesse (F) DefinitionFSR / FWHMDimensionlessRatio of Free Spectral Range (FSR) to Full Width at Half Maximum (FWHM).

Key Methodologies

Section titled “Key Methodologies”
  1. Diamond Film Deposition: Diamond structures (BDD, NDD, NCD) were synthesized using a Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD) system onto silica substrates.
  2. Reflectivity Control: The desired reflectivity (R) of the mirror surfaces was achieved by tailoring the refractive index (n) of the diamond films through precise adjustment of CVD process parameters, including the selection and concentration of dopant elements (Boron or Nitrogen).
  3. Surface Analysis: Scanning Electron Microscopy (SEM) was performed to characterize the surface morphology, confirming uniform crystallite size and distribution across the substrates, which is essential for FP cavity performance.
  4. Interferometer Configuration: A fiber-optic Fabry-Perot interferometer was constructed in a reflective mode. The cavity was formed between the polished fiber end-face (M1) and the investigated diamond structure (M2), separated by an air gap.
  5. Measurement Setup: The system utilized a broadband light source centered at 1550 nm, a 2 x 1 fiber coupler, and an optical spectrum analyzer (OSA). A micromechanical setup ensured precise alignment and stabilization of the parallel reflective surfaces.
  6. Data Processing: Measured optical spectra were normalized and filtered to remove the Gaussian characteristics of the light source, allowing for direct comparison with theoretical transmission models (based on the Airy function) to validate the modeled finesse coefficients.

Commercial Applications

Section titled “Commercial Applications”
  • Opto-Electrochemical Sensing: Development of highly sensitive, customized sensor platforms where the optical resonator properties (finesse, contrast) are optimized to match the specific optical parameters of target analytes (e.g., chemical solutions, biological fluids).
  • Chemical and Biological Monitoring: Utilizing diamond’s chemical inertness and biocompatibility to create robust, long-lifespan sensors for continuous monitoring in harsh chemical processes or in vivo biomedical applications (e.g., measuring hemoglobin concentration).
  • High-Resolution Spectroscopy: Employing high-finesse diamond cavities (F > 4) as high-performance optical filters or resonators for precise gas phase spectroscopy and wavelength stabilization systems.
  • Industrial Process Control: Deploying robust, fiber-optic diamond sensors for real-time, non-destructive monitoring of refractive index and displacement in industrial environments where electromagnetic immunity is required.
  • Quantum Information Systems: Potential application of tailored diamond structures in microcavities for quantum sensing and quantum information processing, leveraging the material’s unique optical and electronic properties.
View Original Abstract

Finesse coefficient is one of the most important parameters describing the properties of a resonant cavity. In this research, a mathematical investigation of the application of diamond structures in a fiber-optic Fabry-Perot measurement head to assess their impact on the finesse coefficient is proposed. We present modeled transmission functions of cavities utilizing a nitrogen-doped diamond, a boron-doped diamond, nanocrystalline diamond sheet and a silver mirror. The diamond structures were deposited using a microwave plasma-assisted chemical vapor deposition system. A SEM investigation of surface morphology was conducted. The modeling took into consideration the fiber-optic Fabry-Perot setup working in a reflective mode, with an external cavity and a light source of 1550 nm. A comparison of the mathematical investigation and experimental results is presented.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2018 - Hybrid Optoelectrochemical Sensor for Superselective Detection of 2,4,6-Trinitrotoluene Based on Electrochemical Reduced Meisenheimer Complex [Crossref]
  2. 2020 - Nanopaper-Based Screen-Printed Electrodes: A Hybrid Sensing Bioplatform for Dual Opto-Electrochemical Sensing Applications [Crossref]
  3. 2013 - Toward Optical Sensors: Review and Applications [Crossref]
  4. 2019 - Multiparameter Fiber-Optic Sensors: A Review [Crossref]
  5. 2019 - Distributed Optical Fiber Sensing: Review and Perspective [Crossref]
  6. 1992 - Optical Fiber Sensing with a Low-Finesse Fabry-Perot Cavity [Crossref]

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