Experimental Realization of Tunable Ferroelectric / Superconductor 1D Photonic Crystals in the Whole Visible Spectrum

Emerging technologies leveraging novel materials and the quantum properties of light states are at the forefront of the race for the physical implementation, encoding, and transmission of information. Photonic crystals (PCs) are central to this paradigm, offering control over light propagation for applications in optical communication and the integration of photonics and electronics. In recent advancements, integrating ferroelectric and superconductor materials into one-dimensional (1D) photonic crystals It has been one of the challenges for researchers for manipulating light across the entire visible spectrum. A notable example is the (BTO/YBCO)N/STO 1D PC structure. For the first time, the researcher from Universidad del Valle experimentally demonstrated the successful incorporation of ferroelectric and superconductor materials into a one-dimensional (1D) PC, specifically composed of (BTO/YBCO)N/STO bilayers. 

In this context, the researcher presents the integration of designer superconductor materials into the fabrication of PCs, leading to a significant reduction in electromagnetic wave damping. This integration allows for optimal propagation and tuning of these waves through the structure at temperatures below the critical superconducting temperature. 

This structure operates across the entire visible spectrum and maintains functionality both below and above the critical superconductor temperature (TC = 80 K). Theoretical calculations corroborate the effectiveness of these 1D PCs across different numbers of bilayers (N), potentially paving the way for advanced optoelectronic integration and information processing in the visible spectrum while preserving their electrical and optical properties [1]. 

Photonic Crystals 

Photonic crystals are structured arrangements, occurring in one, two, or three dimensions, that possess optical characteristics changing at regular intervals, like dielectric constants. This periodicity permits the transmission of electromagnetic waves through materials whose spatial makeup can be finely adjusted based on their composition and design. Consequently, these crystals become invaluable tools for steering the movement and release of photons. The regularity in their structure creates a photonic band structure, influenced by the interaction of light at each interface between the materials forming the periodic framework. This structure facilitates the coherent blending of photons with specific energies, resulting in a spectrum of electromagnetic modes, including those that propagate and those that do not—the latter known as the photonic bandgap. Leveraging these properties, control over light within photonic crystals is achievable, offering novel avenues for applications such as chips, filters, lasers, waveguides, integrated circuits, sensors, and thin-film photovoltaic cells [2]. 

Various types of materials are employed in the creation of tunable photonic crystals (PhCs), including semiconductors, metals, superconductors, metamaterials, and liquid crystals but the combination of high-temperature superconductor (YBCO) and ferroelectric (BTO) thin films is motivated by several technical factors. Firstly, both materials share a perovskite structure, exhibit good lattice matching, and possess chemical similarities. This congruence facilitates the successful growth of high-quality ferroelectric/superconductor thin films through epitaxial processes. Secondly, both materials can endure thermal expansion and contraction, as well as significant mechanical stress, arising from temperature variations between ambient and cryogenic conditions. Thirdly, such a nanosystem aligns with thin film filter technologies utilized in the manufacturing of optical fibers and optoelectronic devices [3], [4]. 

In Figure 1, the researcher observe a schematic representation of three 1D photonic crystals composed of varying numbers of BTO/YBCO bilayers: one, three, and five pairs. These crystals were constructed using a combination of DC and RF sputtering techniques on meticulously polished SrTiO3 (001) substrates [1]. 


Schematic illustration of a (BTO/YBCO)N/STO 1D photonic crystal for N = 1, 3, and 5 periods
Figure 2: Schematic illustration of a (BTO/YBCO)N/STO 1D photonic crystal for N = 1, 3, and 5 periods


Optical Characterization: White Light Laser for Reflectance Measurements 

An older version of our supercontinuum fiber laser Iceblink (Fyla STC 1000) and a monochromator (Fyla TW) were utilized to irradiate the sample within the 400-800 nm spectral range. The beam path includes a telescope arrangement with a 1× magnification factor to collimate the laser and control beam divergence (Figure 2). The light is directed using aluminium mirrors with 95% reflectance, perpendicularly towards a cryostat (Cryostat Advanced Research System) where the sample is placed under a vacuum of 10⁻⁵ bar and maintained at a controlled temperature down to 10 K. The reflection angle is managed with a custom-made copper sample holder inside the cryostat, set at 35° and 65° for different measurement sets. The reflected light is collected with a collimation lens and coupled into a 400 µm diameter multimode optical quartz fiber. This fiber is connected to a spectrometer (HD 4000, Ocean Optics) which displays the spectra on a workstation [1]. 

Supercontinuum laser beam (Fyla STC 1000), spanning wavelengths from 400 to 800 nm
Supercontinuum laser beam (Fyla STC 1000), spanning wavelengths from 400 to 800 nm


Iceblink Supercontinuum Fiber Laser for Tunable Ferroelectric/Superconductor 1D Photonic Crystals

The new version of our supercontinuum laser, the Iceblink could significantly enhance the characterization of tunable ferroelectric/superconductor 1D photonic crystals in several ways: 

  • Broad Spectral Range (450-2300 nm): the extensive spectral range of the supercontinuum laser allows for comprehensive analysis of the photonic crystal’s optical properties across both visible and infrared regions. This enables the study of various photonic bandgaps and resonances within the crystal, providing a deeper understanding of its optical behavior. It facilitates the examination of the material’s response to different wavelengths, helping to identify and optimize the wavelengths where the photonic crystal exhibits maximum efficiency or unique properties. 
  • High Total Power (>3 W) and Visible Range Power (150 mW): the high power output ensures that sufficient light intensity is available for detailed and accurate measurements, even at wavelengths where the material’s reflectivity or transmissivity might be low. The significant power in the visible range is particularly useful for visual inspection and alignment of the optical setup, ensuring precise and reliable characterization. 
  • Excellent Power Stability (<0.5% std dev): the high stability of the laser power ensures that the measurements are consistent and reliable over long periods. This is critical for accurately characterizing the subtle changes in the optical properties of the photonic crystals. Stable power output minimizes the noise in the measurement data, leading to clearer and more precise characterization results.