Low-loss optical-lattice-like waveguides in lithium niobate by high-repetition-rate femtosecond laser inscription

Teerawat Piromjitpong, Mykhaylo Dubov, Sonia Boscolo

Research output: Contribution to conferencePaper

Abstract

Tightly focused femtosecond laser pulses of 11-MHz repetition rate and 790-nm wavelength were used to fabricate a set of waveguides in a lithium niobate (LiNbO3) crystal. To establish the inscription conditions for optimal low-loss waveguides, within each sample we varied the laser pulse energy, the speed and direction of translation stage movement, and the focus depth of the laser beam. We deployed two new approaches to enhance the inscription results: 1) increase of the laser pulse energy with increasing focus depth inside the material to compensate for the corresponding decrease of the refractive-index contrast between exposed and unexposed areas, and 2) decrease of the laser energy for the modification tracks closer to the waveguide’s core region to reduce the scattering losses due to high-laser-energy driven waveguide’s non-uniformities. All waveguides had an optical-lattice-like hexagonal
packing geometry with a track spacing of 10 μm (optimised for effective suppression of high-order modes). Each structure comprised 84 single-scan Type-II-modification tracks, aligned with the crystalline X-axis of the LiNbO3 wafer. As observed through the optical microscope, the diameters of core and outer cladding of the waveguide were approximately 24 μm and 95 μm, respectively. After thermal annealing at 623K for 3 hours, the minimum attenuation coefficients of (0.4±0.1)dB/cm and (3.5±0.3)dB/cm for the ordinary and extraordinary light polarisation states, respectively, were achieved at the 1550-nm wavelength. These low-attenuation waveguides were obtained with an inscription energy varying between 50.6 nJ and 53.6 nJ and a translation speed of 10 mm/s. The corresponding refractive-index contrast of individual tracks was −(1.55±0.04)×10-3. The waveguides also
showed low attenuation in the visible and near-infrared portion of the spectrum (from 532 nm to 1456 nm).
Our results offer promising means for the development of low-loss, preserved-nonlinearity waveguides that are suitable for several applications, including telecommunications, nonlinear integrated optics and quantum optics.
Original languageEnglish
Pages65-66
Publication statusPublished - Sep 2018
EventPhoton 2018 - Aston University, Birmingham, United Kingdom
Duration: 3 Sep 20186 Sep 2018
http://www.photon.org.uk/home

Conference

ConferencePhoton 2018
CountryUnited Kingdom
CityBirmingham
Period3/09/186/09/18
Internet address

Fingerprint

lithium niobates
repetition
waveguides
lasers
pulses
attenuation
energy
refractivity
quantum optics
integrated optics
attenuation coefficients
optical microscopes
wavelengths
nonuniformity
telecommunication
nonlinearity
spacing
retarding
wafers
laser beams

Bibliographical note

© The Authors

Cite this

Piromjitpong, T., Dubov, M., & Boscolo, S. (2018). Low-loss optical-lattice-like waveguides in lithium niobate by high-repetition-rate femtosecond laser inscription. 65-66. Paper presented at Photon 2018, Birmingham, United Kingdom.
Piromjitpong, Teerawat ; Dubov, Mykhaylo ; Boscolo, Sonia. / Low-loss optical-lattice-like waveguides in lithium niobate by high-repetition-rate femtosecond laser inscription. Paper presented at Photon 2018, Birmingham, United Kingdom.
@conference{83b203f06ea64d678077dc2871b7a538,
title = "Low-loss optical-lattice-like waveguides in lithium niobate by high-repetition-rate femtosecond laser inscription",
abstract = "Tightly focused femtosecond laser pulses of 11-MHz repetition rate and 790-nm wavelength were used to fabricate a set of waveguides in a lithium niobate (LiNbO3) crystal. To establish the inscription conditions for optimal low-loss waveguides, within each sample we varied the laser pulse energy, the speed and direction of translation stage movement, and the focus depth of the laser beam. We deployed two new approaches to enhance the inscription results: 1) increase of the laser pulse energy with increasing focus depth inside the material to compensate for the corresponding decrease of the refractive-index contrast between exposed and unexposed areas, and 2) decrease of the laser energy for the modification tracks closer to the waveguide’s core region to reduce the scattering losses due to high-laser-energy driven waveguide’s non-uniformities. All waveguides had an optical-lattice-like hexagonalpacking geometry with a track spacing of 10 μm (optimised for effective suppression of high-order modes). Each structure comprised 84 single-scan Type-II-modification tracks, aligned with the crystalline X-axis of the LiNbO3 wafer. As observed through the optical microscope, the diameters of core and outer cladding of the waveguide were approximately 24 μm and 95 μm, respectively. After thermal annealing at 623K for 3 hours, the minimum attenuation coefficients of (0.4±0.1)dB/cm and (3.5±0.3)dB/cm for the ordinary and extraordinary light polarisation states, respectively, were achieved at the 1550-nm wavelength. These low-attenuation waveguides were obtained with an inscription energy varying between 50.6 nJ and 53.6 nJ and a translation speed of 10 mm/s. The corresponding refractive-index contrast of individual tracks was −(1.55±0.04)×10-3. The waveguides alsoshowed low attenuation in the visible and near-infrared portion of the spectrum (from 532 nm to 1456 nm).Our results offer promising means for the development of low-loss, preserved-nonlinearity waveguides that are suitable for several applications, including telecommunications, nonlinear integrated optics and quantum optics.",
author = "Teerawat Piromjitpong and Mykhaylo Dubov and Sonia Boscolo",
note = "{\circledC} The Authors; Photon 2018 ; Conference date: 03-09-2018 Through 06-09-2018",
year = "2018",
month = "9",
language = "English",
pages = "65--66",
url = "http://www.photon.org.uk/home",

}

Piromjitpong, T, Dubov, M & Boscolo, S 2018, 'Low-loss optical-lattice-like waveguides in lithium niobate by high-repetition-rate femtosecond laser inscription' Paper presented at Photon 2018, Birmingham, United Kingdom, 3/09/18 - 6/09/18, pp. 65-66.

Low-loss optical-lattice-like waveguides in lithium niobate by high-repetition-rate femtosecond laser inscription. / Piromjitpong, Teerawat; Dubov, Mykhaylo; Boscolo, Sonia.

2018. 65-66 Paper presented at Photon 2018, Birmingham, United Kingdom.

Research output: Contribution to conferencePaper

TY - CONF

T1 - Low-loss optical-lattice-like waveguides in lithium niobate by high-repetition-rate femtosecond laser inscription

AU - Piromjitpong, Teerawat

AU - Dubov, Mykhaylo

AU - Boscolo, Sonia

N1 - © The Authors

PY - 2018/9

Y1 - 2018/9

N2 - Tightly focused femtosecond laser pulses of 11-MHz repetition rate and 790-nm wavelength were used to fabricate a set of waveguides in a lithium niobate (LiNbO3) crystal. To establish the inscription conditions for optimal low-loss waveguides, within each sample we varied the laser pulse energy, the speed and direction of translation stage movement, and the focus depth of the laser beam. We deployed two new approaches to enhance the inscription results: 1) increase of the laser pulse energy with increasing focus depth inside the material to compensate for the corresponding decrease of the refractive-index contrast between exposed and unexposed areas, and 2) decrease of the laser energy for the modification tracks closer to the waveguide’s core region to reduce the scattering losses due to high-laser-energy driven waveguide’s non-uniformities. All waveguides had an optical-lattice-like hexagonalpacking geometry with a track spacing of 10 μm (optimised for effective suppression of high-order modes). Each structure comprised 84 single-scan Type-II-modification tracks, aligned with the crystalline X-axis of the LiNbO3 wafer. As observed through the optical microscope, the diameters of core and outer cladding of the waveguide were approximately 24 μm and 95 μm, respectively. After thermal annealing at 623K for 3 hours, the minimum attenuation coefficients of (0.4±0.1)dB/cm and (3.5±0.3)dB/cm for the ordinary and extraordinary light polarisation states, respectively, were achieved at the 1550-nm wavelength. These low-attenuation waveguides were obtained with an inscription energy varying between 50.6 nJ and 53.6 nJ and a translation speed of 10 mm/s. The corresponding refractive-index contrast of individual tracks was −(1.55±0.04)×10-3. The waveguides alsoshowed low attenuation in the visible and near-infrared portion of the spectrum (from 532 nm to 1456 nm).Our results offer promising means for the development of low-loss, preserved-nonlinearity waveguides that are suitable for several applications, including telecommunications, nonlinear integrated optics and quantum optics.

AB - Tightly focused femtosecond laser pulses of 11-MHz repetition rate and 790-nm wavelength were used to fabricate a set of waveguides in a lithium niobate (LiNbO3) crystal. To establish the inscription conditions for optimal low-loss waveguides, within each sample we varied the laser pulse energy, the speed and direction of translation stage movement, and the focus depth of the laser beam. We deployed two new approaches to enhance the inscription results: 1) increase of the laser pulse energy with increasing focus depth inside the material to compensate for the corresponding decrease of the refractive-index contrast between exposed and unexposed areas, and 2) decrease of the laser energy for the modification tracks closer to the waveguide’s core region to reduce the scattering losses due to high-laser-energy driven waveguide’s non-uniformities. All waveguides had an optical-lattice-like hexagonalpacking geometry with a track spacing of 10 μm (optimised for effective suppression of high-order modes). Each structure comprised 84 single-scan Type-II-modification tracks, aligned with the crystalline X-axis of the LiNbO3 wafer. As observed through the optical microscope, the diameters of core and outer cladding of the waveguide were approximately 24 μm and 95 μm, respectively. After thermal annealing at 623K for 3 hours, the minimum attenuation coefficients of (0.4±0.1)dB/cm and (3.5±0.3)dB/cm for the ordinary and extraordinary light polarisation states, respectively, were achieved at the 1550-nm wavelength. These low-attenuation waveguides were obtained with an inscription energy varying between 50.6 nJ and 53.6 nJ and a translation speed of 10 mm/s. The corresponding refractive-index contrast of individual tracks was −(1.55±0.04)×10-3. The waveguides alsoshowed low attenuation in the visible and near-infrared portion of the spectrum (from 532 nm to 1456 nm).Our results offer promising means for the development of low-loss, preserved-nonlinearity waveguides that are suitable for several applications, including telecommunications, nonlinear integrated optics and quantum optics.

UR - http://www.photon.org.uk/home

M3 - Paper

SP - 65

EP - 66

ER -

Piromjitpong T, Dubov M, Boscolo S. Low-loss optical-lattice-like waveguides in lithium niobate by high-repetition-rate femtosecond laser inscription. 2018. Paper presented at Photon 2018, Birmingham, United Kingdom.