Observation of SQUID‐Like Behavior in Fiber Laser with Intra‐Cavity Epsilon‐Near‐Zero Effect

Abstract

Establishing relations between fundamental effects in far-flung areas of physics is a subject of great interest in the current research. Realization of a novel photonic system akin to the radio-frequency superconducting quantum interference device (RF-SQUID), in a fiber laser cavity with epsilon-near-zero (ENZ) nanolayers as intra-cavity components is reported here. Emulating the RF-SQUID scheme, the photonic counterpart of the supercurrent, represented by the optical wave, circulates in the cavity, passing through effective optical potential barriers. Different ENZ wavelengths translate into distinct spectral outputs through the variation of cavity resonances, emulating the situation with a frequency-varying tank circuit in the RF-SQUID. Due to the presence of the ENZ element, the optical potential barrier is far lower for selected frequency components, granting them advantage in the gain-resource competition. The findings reported in this work provide a deeper insight into the ultrafast ENZ photonics, revealing a new path toward the design of nanophotonic on-chip devices with various operational functions, and offer a new approach to study superconducting and quantum-mechanical systems.

Manufacturing-Enabled Tunability of Linear and Nonlinear Epsilon-Near-Zero Properties in Indium Tin Oxide Nanofilms

“…To further investigate the SA and RSA effects in ITO samples, a figure-of-9 98 MHz repetition rate fiber laser is utilized to acquire the SA and RSA characteristics, and the schematic diagram of the fiber laser system , is plotted in Figure a, which contains the laser source, isolator, erbium-doped fiber amplifier (EDFA), attenuator, either ITO nanofilm or glass, and power meters to record the experimental data. Consequently, the nonlinear absorption results are displayed in Figure b, where the red circles represent the measured data of unannealed ITO films without annealing process, and the blue triangles denote those with annealing treatments afterward.…”

“…27,28 It has lately been found that an ENZ laser setup can be built with an ITO nanofilm inserted in the laser cavity whose ENZ wavelength λ ENZ (wavelength where the real part of the permittivity reaches zero) is within the laser operating range, providing inter-sample λ ENZ detectability and mode-locking wavelength tunability. 29 However, in Drude or Drude-like models that describe the dispersion of TCOs, it is clear that λ ENZ changes rapidly with the electrical properties of the TCOs, such as free carrier concentration N and mobility μ, which makes λ ENZ hard to tune. Even the advanced techniques introduced in ref 29 require a series of different samples with subsequential λ ENZ .…”

“…Among different optical approaches to achieve ENZ condition, − transparent conducting oxides (TCOs) have been widely explored due to their broad ENZ regions from ultraviolet to near-infrared, lower costs, and simpler structural complexity. ,,, In particular, indium tin oxide (ITO) is the most common sort of TCO with its near-infrared ENZ region and CMOS compatibility, which displays unique linear and nonlinear optical (NLO) properties. , It has lately been found that an ENZ laser setup can be built with an ITO nanofilm inserted in the laser cavity whose ENZ wavelength λ ENZ (wavelength where the real part of the permittivity reaches zero) is within the laser operating range, providing inter-sample λ ENZ detectability and mode-locking wavelength tunability …”

“…However, in Drude or Drude-like models that describe the dispersion of TCOs, it is clear that λ ENZ changes rapidly with the electrical properties of the TCOs, such as free carrier concentration N and mobility μ, which makes λ ENZ hard to tune. Even the advanced techniques introduced in ref require a series of different samples with subsequential λ ENZ . In previous research, TCOs from 12 scalable commercial suppliers were utilized to report their ENZ and NZI properties influenced by λ ENZ .…”