Rectangular SNAP microresonator fabricated with a femtosecond laser

Abstract

SNAP microresonators, which are fabricated by nanoscale effective radius variation (ERV) of the optical fiber with sub-angstrom precision, can be potentially used as miniature classical and quantum signal processors, frequency comb generators, as well as ultraprecise microfluidic and environmental optical sensors. Many of these applications require the introduction of nanoscale ERV with a large contrast α which is defined as the maximum shift of the fiber cutoff wavelength introduced per unit length of the fiber axis. The previously developed fabrication methods of SNAP structures, which used focused CO2 and femtosecond laser beams, achieved α ~ 0.02 nm/µm. Here we develop a new fabrication method of SNAP microresonators with a femtosecond laser which allows us to demonstrate a 50-fold improvement of previous results and achieve α ~ 1 nm/µm. Furthermore, our fabrication method enables the introduction of ERV which is several times larger than the maximum ERV demonstrated previously. As an example, we fabricate a rectangular SNAP resonator and investigate its group delay characteristics. Our experimental results are in good agreement with theoretical simulations. Overall, the developed approach allows us to reduce the axial scale of SNAP structures by an order of magnitude.

Enhancing the impedance matched bandwidth of bottle microresonator signal processing devices

“…( 1) locally, near axial position 𝑧𝑧 2 , by adding Λ 2 𝛿𝛿(𝑧𝑧 − 𝑧𝑧 2 ) with real Λ 2 . In practice, this modification can be introduced, e.g., by a femtosecond laser [16,22], local coating, or an adiabatic phase-unmatched contact with a microfiber to avoid losses and azimuthal reflections. The transmission amplitude in Eq.…”

“…The sharp cut at 𝑧𝑧 = 0 can be introduced, e.g., with a femtosecond laser [16]. Here, for convenience, we introduce the bandwidth of our concern Δ𝜆𝜆 0 starting from wavelength 𝜆𝜆 = 𝜆𝜆 0 so that the cutoff wavelength variation ∆𝜆𝜆 𝑐𝑐 (𝑧𝑧) = 𝜆𝜆 𝑐𝑐 (𝑧𝑧) − 𝜆𝜆 0 and the wavelength variation Δ𝜆𝜆 = 𝜆𝜆 − 𝜆𝜆 0 .…”

Fundamental limit of microresonator field uniformity and slow light enabled ultraprecise displacement metrology

“…Suppressing this ERV is currently challenging for lengthy optical fibers [14]. However, we suggest that it can be reduced to less than 1 Å by surface postprocessing developed in SNAP technology [1,[4][5][6][7]. The unique uniformity of the bat mode amplitude suggests the application of a BatMR as an angstrom-precise translation reference.…”

“…1(b) numerically by varying the size of ears at the edges of the segment 𝑧𝑧 1 < 𝑧𝑧 < 𝑧𝑧 2 until the eigenwavelength 𝜆𝜆 𝑚𝑚𝑚𝑚2 becomes equal to the value of 𝜆𝜆 𝑚𝑚𝑚𝑚 (𝑐𝑐) (𝑧𝑧) at this segment. Experimentally, a BatMR can be created using the SNAP technology [1,4,5,6,7] as follows. First, a BMR with sufficiently large slopes at the edges and uniform center part (e.g., a rectangular BMR [6]) is formed.…”

“…Experimentally, a BatMR can be created using the SNAP technology [1,4,5,6,7] as follows. First, a BMR with sufficiently large slopes at the edges and uniform center part (e.g., a rectangular BMR [6]) is formed. Next, the ears at the BMR edges can be introduced by iterations with CO2 laser beam shots [5], so that 𝜆𝜆 𝑚𝑚𝑚𝑚𝑚𝑚 rises and, finally, coincides with 𝜆𝜆 𝑚𝑚𝑚𝑚 (𝑐𝑐) (𝑧𝑧 𝐶𝐶 ).…”