The University of Southampton
University of Southampton Institutional Repository

Optical characterization of LiNbO3 whispering gallery mode micro-resonators fabricated by surface tension reshaping

Optical characterization of LiNbO3 whispering gallery mode micro-resonators fabricated by surface tension reshaping
Optical characterization of LiNbO3 whispering gallery mode micro-resonators fabricated by surface tension reshaping
Lithium niobate (LN) is an attractive material for high-Q whispering gallery mode (WGM) resonators due to its wide optical transparency window, high electro-optic coefficient and nonlinearity. Recently, LN structures suitable for WGM micro-resonators have been fabricated using surface tension reshaping of a previously microstructured substrates, producing ultra-smooth surfaces while also maintaining the useful crystalline properties of the original material [1]. The method is based on the preferential melting of a surface layer [2] at temperatures close to the melting point for the bulk material. Upon cooling, the melted surface layer re-crystallizes, seeded by the bulk crystal that remains solid during the process, and is reshaped by the surface tension to form ultrasmooth single crystal superstructures. Fig. 1 shows some surface tension reshaped structures which have been obtained by varying the initial microstructure and the thermal treatment conditions, (a): 5µm prolate spheroid, (b): 3µm capsule, (c-e): 7, 30, 80µm diameter pillars. Such structures are suitable for supporting WGMs as the smooth side surface should lead to low scattering loss. Their obtainable small dimensions leads to a small number of supported WGMs and increases the free spectral range (FSR). Both are beneficial for the fabrication of spectral filters and lasers.
Preliminary optical characterisation of the microresonator in Fig. 1e has been conducted. A U-shaped silica fibre taper with a waist diameter of about 2µm was used to couple light in and out of the microresonator. It was observed that when approaching the resonator the fibre taper is attracted by the surface of the structure and loads the cavity. A tunable laser source was used to observe the resonances of the WGM structure. In order to investigate the resonances the light transmitted through the fibre taper and the light scattered from the resonator were monitored during the wavelength scanning process. The scattered light spectrum in Fig. 2 shows a sequence of resonances. A Q factor of 5600 has been calculated by fitting a Lorentzian curve to one of the peaks in the spectrum shown in Fig. 2, which has a corresponding FSR of 4.55nm. The shape of the resonator (Fig. 1e) resembles a truncated microbottle [3]. Such open resonators are known to leak from their two ends [4], and the loss depends on the curvature of the micro-resonator. Leakage from the resonator’s base was experimentally observed. It is expected that higher Q factors will be measured in microresonators with larger curvature.
Ying, C.Y.J.
dc655370-fd93-4a5c-a573-85658ae4f5fa
Murugan, G.S.
a867686e-0535-46cc-ad85-c2342086b25b
Brambilla, G.
815d9712-62c7-47d1-8860-9451a363a6c8
Sones, C.L.
9de9d8ee-d394-46a5-80b7-e341c0eed0a8
Soergel, E.
f4d5aad1-9f81-4877-bceb-33ceed99d9d7
Wilkinson, J.S.
73483cf3-d9f2-4688-9b09-1c84257884ca
Eason, R.W.
e38684c3-d18c-41b9-a4aa-def67283b020
Zervas, M.N.
1840a474-dd50-4a55-ab74-6f086aa3f701
Mailis, S.
233e0768-3f8d-430e-8fdf-92e6f4f6a0c4
Ying, C.Y.J.
dc655370-fd93-4a5c-a573-85658ae4f5fa
Murugan, G.S.
a867686e-0535-46cc-ad85-c2342086b25b
Brambilla, G.
815d9712-62c7-47d1-8860-9451a363a6c8
Sones, C.L.
9de9d8ee-d394-46a5-80b7-e341c0eed0a8
Soergel, E.
f4d5aad1-9f81-4877-bceb-33ceed99d9d7
Wilkinson, J.S.
73483cf3-d9f2-4688-9b09-1c84257884ca
Eason, R.W.
e38684c3-d18c-41b9-a4aa-def67283b020
Zervas, M.N.
1840a474-dd50-4a55-ab74-6f086aa3f701
Mailis, S.
233e0768-3f8d-430e-8fdf-92e6f4f6a0c4

Ying, C.Y.J., Murugan, G.S., Brambilla, G., Sones, C.L., Soergel, E., Wilkinson, J.S., Eason, R.W., Zervas, M.N. and Mailis, S. (2011) Optical characterization of LiNbO3 whispering gallery mode micro-resonators fabricated by surface tension reshaping. CLEO/EQEC 2011: Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, Germany. 22 - 26 May 2011.

Record type: Conference or Workshop Item (Paper)

Abstract

Lithium niobate (LN) is an attractive material for high-Q whispering gallery mode (WGM) resonators due to its wide optical transparency window, high electro-optic coefficient and nonlinearity. Recently, LN structures suitable for WGM micro-resonators have been fabricated using surface tension reshaping of a previously microstructured substrates, producing ultra-smooth surfaces while also maintaining the useful crystalline properties of the original material [1]. The method is based on the preferential melting of a surface layer [2] at temperatures close to the melting point for the bulk material. Upon cooling, the melted surface layer re-crystallizes, seeded by the bulk crystal that remains solid during the process, and is reshaped by the surface tension to form ultrasmooth single crystal superstructures. Fig. 1 shows some surface tension reshaped structures which have been obtained by varying the initial microstructure and the thermal treatment conditions, (a): 5µm prolate spheroid, (b): 3µm capsule, (c-e): 7, 30, 80µm diameter pillars. Such structures are suitable for supporting WGMs as the smooth side surface should lead to low scattering loss. Their obtainable small dimensions leads to a small number of supported WGMs and increases the free spectral range (FSR). Both are beneficial for the fabrication of spectral filters and lasers.
Preliminary optical characterisation of the microresonator in Fig. 1e has been conducted. A U-shaped silica fibre taper with a waist diameter of about 2µm was used to couple light in and out of the microresonator. It was observed that when approaching the resonator the fibre taper is attracted by the surface of the structure and loads the cavity. A tunable laser source was used to observe the resonances of the WGM structure. In order to investigate the resonances the light transmitted through the fibre taper and the light scattered from the resonator were monitored during the wavelength scanning process. The scattered light spectrum in Fig. 2 shows a sequence of resonances. A Q factor of 5600 has been calculated by fitting a Lorentzian curve to one of the peaks in the spectrum shown in Fig. 2, which has a corresponding FSR of 4.55nm. The shape of the resonator (Fig. 1e) resembles a truncated microbottle [3]. Such open resonators are known to leak from their two ends [4], and the loss depends on the curvature of the micro-resonator. Leakage from the resonator’s base was experimentally observed. It is expected that higher Q factors will be measured in microresonators with larger curvature.

PDF
4983.pdf - Other
Download (262kB)

More information

e-pub ahead of print date: 2011
Additional Information: CE5.4W
Venue - Dates: CLEO/EQEC 2011: Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, Germany, 2011-05-22 - 2011-05-26
Organisations: Optoelectronics Research Centre

Identifiers

Local EPrints ID: 343013
URI: https://eprints.soton.ac.uk/id/eprint/343013
PURE UUID: 1c7a5c96-9b29-4ea7-b854-b299d7461df7
ORCID for G.S. Murugan: ORCID iD orcid.org/0000-0002-2733-3273
ORCID for J.S. Wilkinson: ORCID iD orcid.org/0000-0003-4712-1697
ORCID for R.W. Eason: ORCID iD orcid.org/0000-0001-9704-2204
ORCID for M.N. Zervas: ORCID iD orcid.org/0000-0002-0651-4059
ORCID for S. Mailis: ORCID iD orcid.org/0000-0001-8100-2670

Catalogue record

Date deposited: 20 Sep 2012 10:36
Last modified: 02 Oct 2018 00:37

Export record

Contributors

Author: C.Y.J. Ying
Author: G.S. Murugan ORCID iD
Author: G. Brambilla
Author: C.L. Sones
Author: E. Soergel
Author: J.S. Wilkinson ORCID iD
Author: R.W. Eason ORCID iD
Author: M.N. Zervas ORCID iD
Author: S. Mailis ORCID iD

University divisions

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×