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Tunable continuous wave emission via phase-matched second harmonic generation in a ZnSe microcylindrical resonator.

Vukovic N, Healy N, Sparks JR, Badding JV, Horak P, Peacock AC - Sci Rep (2015)

Bottom Line: Whispering gallery mode microresonators made from crystalline materials are of great interest for studies of low threshold nonlinear phenomena.Visible red light is observed when pumped with a telecommunications band source by a process that is phase-matched between different higher order radial modes, possible due to the good spatial overlap between the pump and signal in the small volume resonator.By exploiting the geometrical flexibility offered by the fibre platform together with the ultra-wide 500-22000 nm transmission window of the ZnSe material, we expect these resonators to find use in applications ranging from spectroscopy to quantum information systems.

View Article: PubMed Central - PubMed

Affiliation: Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, UK.

ABSTRACT
Whispering gallery mode microresonators made from crystalline materials are of great interest for studies of low threshold nonlinear phenomena. Compared to amorphous materials, crystalline structures often exhibit desirable properties such as high indices of refraction, high nonlinearities, and large windows of transparency, making them ideal for use in frequency comb generation, microlasing and all-optical processing. In particular, crystalline materials can also possess a non-centrosymmetric structure which gives rise to the second order nonlinearity, necessary for three photon processes such as frequency doubling and parametric down-conversion. Here we report a novel route to fabricating crystalline zinc selenide microcylindrical resonators from our semiconductor fibre platform and demonstrate their use for tunable, low power continuous wave second harmonic generation. Visible red light is observed when pumped with a telecommunications band source by a process that is phase-matched between different higher order radial modes, possible due to the good spatial overlap between the pump and signal in the small volume resonator. By exploiting the geometrical flexibility offered by the fibre platform together with the ultra-wide 500-22000 nm transmission window of the ZnSe material, we expect these resonators to find use in applications ranging from spectroscopy to quantum information systems.

No MeSH data available.


Related in: MedlinePlus

Second harmonic generation.(a) Experimental set-up including a tunable laser source (TLS), ebrium doped fibre amplifier (EDFA), polarization control (PC), tapered coupling fibre (TCF), optical components tester (OCT), and a tapered lensed fibre (TLF). Inset shows a photograph of the generated visible second harmonic light. (b) Measured emission spectrum at 773.9 nm; inset displays the corresponding transmission spectrum showing the pump resonance at λ ~ 1548 nm, with a Q ~ 4.1 × 103 (red fit).
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f2: Second harmonic generation.(a) Experimental set-up including a tunable laser source (TLS), ebrium doped fibre amplifier (EDFA), polarization control (PC), tapered coupling fibre (TCF), optical components tester (OCT), and a tapered lensed fibre (TLF). Inset shows a photograph of the generated visible second harmonic light. (b) Measured emission spectrum at 773.9 nm; inset displays the corresponding transmission spectrum showing the pump resonance at λ ~ 1548 nm, with a Q ~ 4.1 × 103 (red fit).

Mentions: To investigate SHG in the ZnSe resonators we employed the experimental set-up shown in Fig. 2(a). The resonator was pumped with a standard telecommunications band tunable continuous wave source, that was amplified via an erbium doped fibre amplifier (EDFA) to boost the power before coupling into the resonator using a silica tapered coupling fibre (TCF) with a waist diameter of 1–2 μm. In order to observe the second harmonic light, the coupling conditions had to be precisely tuned to locate a resonance close to phase-matching. As well as controlling the polarization of the coupled modes, we found that it was also necessary to slightly tune the angle of the taper with respect to the resonator (by an amount no larger than 2°). As will be discussed below, adjusting the coupling angle essentially allowed us to modify the height of the mode circulating in the cylinder, thus providing an additional degree of freedom to obtain phase-matching over that of the micro-disks. As the second harmonic associated with the telecommunications band pump falls on the red edge of the visible spectrum, it is straightforward to detect when phase-matching has been achieved by imaging the resonator on a CCD camera, as illustrated by the photograph in the inset of Fig. 2(a). To measure the spectral content of the generated light a tapered lensed fibre (TLF) was positioned in close proximity (as labelled). This was necessary as the short wavelength harmonic, which must be in a higher order mode to satisfy phase-matching, did not have sufficient overlap (<1% of the mode energy23) with the micron-sized fibre used to couple the pump. A typical emission spectrum obtained for the SHG process is shown in Fig. 2(b), with the transmission spectrum measured for the coupling conditions displayed in the inset. We note that the coupled resonance has a reduced Ql ~ 103, which broadens the resonance to ~0.2 nm. Accounting for this, the position of the generated light is in excellent agreement with the resonance at 1548 nm, i.e., λS = 1548/2 ~ 773.9 nm. Furthermore, no other emission lines were observed within the range of the spectrometers (350–1700 nm), indicating that SHG was the dominant nonlinear process.


Tunable continuous wave emission via phase-matched second harmonic generation in a ZnSe microcylindrical resonator.

Vukovic N, Healy N, Sparks JR, Badding JV, Horak P, Peacock AC - Sci Rep (2015)

Second harmonic generation.(a) Experimental set-up including a tunable laser source (TLS), ebrium doped fibre amplifier (EDFA), polarization control (PC), tapered coupling fibre (TCF), optical components tester (OCT), and a tapered lensed fibre (TLF). Inset shows a photograph of the generated visible second harmonic light. (b) Measured emission spectrum at 773.9 nm; inset displays the corresponding transmission spectrum showing the pump resonance at λ ~ 1548 nm, with a Q ~ 4.1 × 103 (red fit).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4488835&req=5

f2: Second harmonic generation.(a) Experimental set-up including a tunable laser source (TLS), ebrium doped fibre amplifier (EDFA), polarization control (PC), tapered coupling fibre (TCF), optical components tester (OCT), and a tapered lensed fibre (TLF). Inset shows a photograph of the generated visible second harmonic light. (b) Measured emission spectrum at 773.9 nm; inset displays the corresponding transmission spectrum showing the pump resonance at λ ~ 1548 nm, with a Q ~ 4.1 × 103 (red fit).
Mentions: To investigate SHG in the ZnSe resonators we employed the experimental set-up shown in Fig. 2(a). The resonator was pumped with a standard telecommunications band tunable continuous wave source, that was amplified via an erbium doped fibre amplifier (EDFA) to boost the power before coupling into the resonator using a silica tapered coupling fibre (TCF) with a waist diameter of 1–2 μm. In order to observe the second harmonic light, the coupling conditions had to be precisely tuned to locate a resonance close to phase-matching. As well as controlling the polarization of the coupled modes, we found that it was also necessary to slightly tune the angle of the taper with respect to the resonator (by an amount no larger than 2°). As will be discussed below, adjusting the coupling angle essentially allowed us to modify the height of the mode circulating in the cylinder, thus providing an additional degree of freedom to obtain phase-matching over that of the micro-disks. As the second harmonic associated with the telecommunications band pump falls on the red edge of the visible spectrum, it is straightforward to detect when phase-matching has been achieved by imaging the resonator on a CCD camera, as illustrated by the photograph in the inset of Fig. 2(a). To measure the spectral content of the generated light a tapered lensed fibre (TLF) was positioned in close proximity (as labelled). This was necessary as the short wavelength harmonic, which must be in a higher order mode to satisfy phase-matching, did not have sufficient overlap (<1% of the mode energy23) with the micron-sized fibre used to couple the pump. A typical emission spectrum obtained for the SHG process is shown in Fig. 2(b), with the transmission spectrum measured for the coupling conditions displayed in the inset. We note that the coupled resonance has a reduced Ql ~ 103, which broadens the resonance to ~0.2 nm. Accounting for this, the position of the generated light is in excellent agreement with the resonance at 1548 nm, i.e., λS = 1548/2 ~ 773.9 nm. Furthermore, no other emission lines were observed within the range of the spectrometers (350–1700 nm), indicating that SHG was the dominant nonlinear process.

Bottom Line: Whispering gallery mode microresonators made from crystalline materials are of great interest for studies of low threshold nonlinear phenomena.Visible red light is observed when pumped with a telecommunications band source by a process that is phase-matched between different higher order radial modes, possible due to the good spatial overlap between the pump and signal in the small volume resonator.By exploiting the geometrical flexibility offered by the fibre platform together with the ultra-wide 500-22000 nm transmission window of the ZnSe material, we expect these resonators to find use in applications ranging from spectroscopy to quantum information systems.

View Article: PubMed Central - PubMed

Affiliation: Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, UK.

ABSTRACT
Whispering gallery mode microresonators made from crystalline materials are of great interest for studies of low threshold nonlinear phenomena. Compared to amorphous materials, crystalline structures often exhibit desirable properties such as high indices of refraction, high nonlinearities, and large windows of transparency, making them ideal for use in frequency comb generation, microlasing and all-optical processing. In particular, crystalline materials can also possess a non-centrosymmetric structure which gives rise to the second order nonlinearity, necessary for three photon processes such as frequency doubling and parametric down-conversion. Here we report a novel route to fabricating crystalline zinc selenide microcylindrical resonators from our semiconductor fibre platform and demonstrate their use for tunable, low power continuous wave second harmonic generation. Visible red light is observed when pumped with a telecommunications band source by a process that is phase-matched between different higher order radial modes, possible due to the good spatial overlap between the pump and signal in the small volume resonator. By exploiting the geometrical flexibility offered by the fibre platform together with the ultra-wide 500-22000 nm transmission window of the ZnSe material, we expect these resonators to find use in applications ranging from spectroscopy to quantum information systems.

No MeSH data available.


Related in: MedlinePlus