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On the reactive ion etching of RbTiOPO4

On the reactive ion etching of RbTiOPO4
On the reactive ion etching of RbTiOPO4
Summary form only given. RbTiOPO4 (RTP) belongs to the KTiOPO4 (KTP) family of crystals and has similarly useful nonlinear optical properties. In addition, RTP allows higher doping of rare-earth elements, such as Yb3+, when compared to KTP, a 2 times larger damage threshold than KTP, a very large electro-optic coefficient, a low dielectric constant and high chemical stability, which makes these materials very interesting for active photonics applications. In particular, Yb3+-doped RTP exhibits a broad fluorescence spectrum that has been exploited to demonstrate ultrafast operation, with pulses as short as 155fs being generated [1]. Recently, planar waveguiding has been demonstrated in an (Yb3+, Nb5+):RTP film grown by liquid phase epitaxy [2], opening the possibility of planar integrated devices based on this highly functional material.Channel waveguides based on this thin-film technology would be of considerable interest for realising, for example, compact ultrafast lasers with GHz repetition rates [3] with applications in optical frequency metrology, optical sampling and biological imaging, or self-frequency-doubled lasers for visible laser sources. In this work we discuss the reactive ion etching (RIE) of RTP and the process optimisation to fabricate single-mode channel waveguides for lasing application around 1 micron. A 200nm layer of chromium (Cr) was deposited on a number of RTP substrates grown by the top-seeded solution growth method (TSSG), after which it was photolithographically patterned to give a Cr mask with waveguide features of widths 1µm to 10µm. The masked substrates were etched in an OPT Plasmalab 80 plus RIE system (Oxford Instruments) with an RF frequency of 13.56MHz. SF6 and Ar were used to etch the substrates in order to study the interplay between chemical and physical etching processes, respectively. The gas flow rates, gas pressures and RF power were systematically varied to get a good balance between etch rate and RMS surface roughness. The dependence of the etch rate and surface roughness on each parameter is shown in figure 1. Based on these graphs the optimum conditions were chosen to be: RF power of 250W, gas pressure of 40 mTorr and gas flow rate of 10 sccm for both SF6 and Ar (giving a total gas flow rate of 20 sccm). A 6µm-thick (Yb,Nb): RTP thin-film was grown on an undoped RTP substrate by liquid phase epitaxy and then etched for 135 minutes with the optimised conditions. It was then end polished to give a 6mm-long waveguide. An SEM image of the end face of a 9.8µm-wide channel is shown in the inset of figure 1. The sidewall angle was measured to be 63° and the etch depth was 1.4µm. Waveguiding experiments were carried out by end-fire coupling a 981nm fiber-coupled single-mode laser diode into the channels. The output was found to be single-mode, with 1/e2 mode diameters measured to be 16.4µm and 8µm in the x and y directions respectively and is in good agreement with the simulated values of 15.2µm and 6.8µm.
IEEE
Choudhary, Amol
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Cugat, J.
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Pradeesh, Kannan
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Solé, R.
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Díaz, F.
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Aguiló, M.
61fe554a-22ea-43db-9fd3-8d3209bf99ed
Chong, H.M.H.
795aa67f-29e5-480f-b1bc-9bd5c0d558e1
Shepherd, D.P.
9fdd51c4-39d6-41b3-9021-4c033c2f4ead
Choudhary, Amol
a5540b54-f153-43e4-a59a-e3ed9360904b
Cugat, J.
1ae031ce-1563-404b-822f-c4ae2ebd6835
Pradeesh, Kannan
d264c1f5-cbaf-42ac-a939-10fce00fa5cb
Solé, R.
1a1a97ea-3cba-4fa4-b476-1bbbe7ebd9a9
Díaz, F.
babe7378-e970-4195-beab-84f41b1694a4
Aguiló, M.
61fe554a-22ea-43db-9fd3-8d3209bf99ed
Chong, H.M.H.
795aa67f-29e5-480f-b1bc-9bd5c0d558e1
Shepherd, D.P.
9fdd51c4-39d6-41b3-9021-4c033c2f4ead

Choudhary, Amol, Cugat, J., Pradeesh, Kannan, Solé, R., Díaz, F., Aguiló, M., Chong, H.M.H. and Shepherd, D.P. (2013) On the reactive ion etching of RbTiOPO4. In 2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC. IEEE. 1 pp . (doi:10.1109/CLEOE-IQEC.2013.6800965).

Record type: Conference or Workshop Item (Paper)

Abstract

Summary form only given. RbTiOPO4 (RTP) belongs to the KTiOPO4 (KTP) family of crystals and has similarly useful nonlinear optical properties. In addition, RTP allows higher doping of rare-earth elements, such as Yb3+, when compared to KTP, a 2 times larger damage threshold than KTP, a very large electro-optic coefficient, a low dielectric constant and high chemical stability, which makes these materials very interesting for active photonics applications. In particular, Yb3+-doped RTP exhibits a broad fluorescence spectrum that has been exploited to demonstrate ultrafast operation, with pulses as short as 155fs being generated [1]. Recently, planar waveguiding has been demonstrated in an (Yb3+, Nb5+):RTP film grown by liquid phase epitaxy [2], opening the possibility of planar integrated devices based on this highly functional material.Channel waveguides based on this thin-film technology would be of considerable interest for realising, for example, compact ultrafast lasers with GHz repetition rates [3] with applications in optical frequency metrology, optical sampling and biological imaging, or self-frequency-doubled lasers for visible laser sources. In this work we discuss the reactive ion etching (RIE) of RTP and the process optimisation to fabricate single-mode channel waveguides for lasing application around 1 micron. A 200nm layer of chromium (Cr) was deposited on a number of RTP substrates grown by the top-seeded solution growth method (TSSG), after which it was photolithographically patterned to give a Cr mask with waveguide features of widths 1µm to 10µm. The masked substrates were etched in an OPT Plasmalab 80 plus RIE system (Oxford Instruments) with an RF frequency of 13.56MHz. SF6 and Ar were used to etch the substrates in order to study the interplay between chemical and physical etching processes, respectively. The gas flow rates, gas pressures and RF power were systematically varied to get a good balance between etch rate and RMS surface roughness. The dependence of the etch rate and surface roughness on each parameter is shown in figure 1. Based on these graphs the optimum conditions were chosen to be: RF power of 250W, gas pressure of 40 mTorr and gas flow rate of 10 sccm for both SF6 and Ar (giving a total gas flow rate of 20 sccm). A 6µm-thick (Yb,Nb): RTP thin-film was grown on an undoped RTP substrate by liquid phase epitaxy and then etched for 135 minutes with the optimised conditions. It was then end polished to give a 6mm-long waveguide. An SEM image of the end face of a 9.8µm-wide channel is shown in the inset of figure 1. The sidewall angle was measured to be 63° and the etch depth was 1.4µm. Waveguiding experiments were carried out by end-fire coupling a 981nm fiber-coupled single-mode laser diode into the channels. The output was found to be single-mode, with 1/e2 mode diameters measured to be 16.4µm and 8µm in the x and y directions respectively and is in good agreement with the simulated values of 15.2µm and 6.8µm.

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More information

e-pub ahead of print date: May 2013
Additional Information: CE 7.1.
Venue - Dates: 2013 Conference on Lasers and Electro-Optics Europe (CLEO EUROPE/IQEC) and International Quantum Electronics Conference, Munich, Germany, 2013-05-12 - 2013-05-16
Organisations: Optoelectronics Research Centre

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Local EPrints ID: 367505
URI: https://eprints.soton.ac.uk/id/eprint/367505
PURE UUID: e58e8e4c-b2b7-4f58-846c-bc41e48b3ffb
ORCID for H.M.H. Chong: ORCID iD orcid.org/0000-0002-7110-5761
ORCID for D.P. Shepherd: ORCID iD orcid.org/0000-0002-4561-8184

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Date deposited: 31 Jul 2014 09:42
Last modified: 20 Jul 2019 01:25

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Contributors

Author: Amol Choudhary
Author: J. Cugat
Author: Kannan Pradeesh
Author: R. Solé
Author: F. Díaz
Author: M. Aguiló
Author: H.M.H. Chong ORCID iD
Author: D.P. Shepherd ORCID iD

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