DISPERSION ENGINEERING OF WHISPERING GALLERY MODE RESONATORS FOR FREQUENCY COMB GENERATION AND TELECOMMUNICATION APPLICATIONS

Kristians Draguns^{1, 2}, Inga Brice¹, Toms Salgals^{2, 3}, Janis Alnis¹

¹ Institute of Atomic Physics and Spectroscopy, University of Latvia, 3 Jelgavas Street, 1004, Riga, Latvia

² AFFOC Solutions Ltd., 17 Andrejostas street, 1045 Riga, Latvia

³ Institute of Telecommunications of the Riga Technical University, 12 Azenes Street, 1048, Riga, Latvia

[email protected]

Whispering gallery mode resonators (WGMRs) are optical devices with axial symmetry, where light is confined within the resonator due to total internal reflection. WGMRs have a typical size of tens to hundreds of micrometers, and experience strong light-matter interaction due to low losses and high mode density. WGMRs can be used to generate Kerr Frequency combs induced by four wave mixing. The frequency combs are generated at anomalous dispersion and it is desirable to have a flat dispersion profile for best results [1]. Thus it is important to engineer the resonator to achieve the dispersion required.

For telecommunication applications the desired free spectral range is around 100 GHz, which translates into a WGMR radius of 332 μm [2]. An interesting geometry is belt type WGMR, where the dispersion profile can be achieved quite flat [3]. The belt resonators are cylindrical structures with an extension with its size characterised by width and height (fig. 1. a).

Computer simulations are made in COMSOL Multiphysics to determine the dispersion. This way we can know at what dimensions we need to make our WGMRs for experiments. For telecommunications the pumping laser should be around 1550 nm at the middle of C-band region (1530 nm – 1565 nm).

[1] S. Fujii, T. Tanabe, Dispersion engineering and measurement of whispering gallery mode microresonator for Kerr frequency comb generation, Nanophotonics 9, 1087-1104 (2020).

[2] E.A. Anashkina, M.P. Marisova, A. V. Andrianov, R.A. Akhmedzhanov, R. Murnieks, M.D. Tokman, L. Skladova, I. V. Oladyshkin, T. Salgals, I. Lyashuk, A. Sorokin, S. Spolitis, G. Leuchs, V. Bobrovs, Microsphere-based optical frequency comb generator for 200 GHz spaced WDM data transmission system, Photonics. 7 (2020).

[3] I. S. Grudinin, N. Yu, Dispersion engineering of crystalline resonators via microstructuring, Optica 2(3), 221-224 (2015).