Fabrication of 1-D Photonic Crystal Cavity on a Nanofiber Using Femtosecond Laser-induced Ablation

Summary

We present a protocol for fabricating 1-D photonic crystal cavities on subwavelength diameter silica fibers (optical nanofibers) using femtosecond laser-induced ablation.

Abstract

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using femtosecond laser-induced ablation. We show that thousands of periodic nano-craters are fabricated on an optical nanofiber by irradiating with just a single femtosecond laser pulse. For a typical sample, periodic nano-craters with a period of 350 nm and with diameter gradually varying from 50 - 250 nm over a length of 1 mm are fabricated on a nanofiber with diameter around 450 - 550 nm. A key aspect of such a nanofabrication is that the nanofiber itself acts as a cylindrical lens and focuses the femtosecond laser beam on its shadow surface. Moreover, the single-shot fabrication makes it immune to mechanical instabilities and other fabrication imperfections. Such periodic nano-craters on nanofiber, act as a 1-D PhC and enable strong and broadband reflection while maintaining the high transmission out of the stopband. We also present a method to control the profile of the nano-crater array to fabricate apodized and defect-induced PhC cavities on the nanofiber. The strong confinement of the field, both transverse and longitudinal, in the nanofiber-based PhC cavities and the efficient integration to the fiber networks, may open new possibilities for nanophotonic applications and quantum information science.

Introduction

Strong confinement of light in nanophotonic devices has opened new frontiers in optical science. Modern nanofabrication technologies have enabled fabrication of 1-D and 2-D Photonic Crystal (PhC) cavities for new prospects in lasing¹, sensing² and optical switching applications³. Moreover, strong light-matter interaction in these PhC cavities has opened new avenues for quantum information science⁴. Apart from PhC cavities, plasmonic nanocavities have also shown promising prospects^5,6,7

Protocol

CAUTION: Wear safety glasses and strictly avoid direct exposure to UV lamp and all lasers including the femtosecond laser. Wear a clean room suit and gloves to avoid contamination. Dispose any fiber trash properly in the designated trash box.

1. Nanofiber Preparation

1. Use a fiber coating stripper to strip the polymer jacket of the single mode optical fiber for a length of 5 mm at two places separated by 200 mm. Clean the two mechanically stripped parts using cleanroom wipe dipped in methanol. Dip the fiber between these two stripped parts in acetone. Wait for 10 - 15 min till the jacket of the fiber fall apart. Take out the fiber....

Results

Figure 2 shows the SEM image of a typical segment of the fabricated nanofiber sample. It shows that periodic nano-craters are formed on the shadow side of the nanofiber, with a periodicity of 350 nm corresponding well to the interference pattern. The inset shows the enlarged view of the sample. The shape of the nano-craters is almost circular and the diameter of a typical nano-crater is around 210 nm.

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Discussion

The lensing effect of the nanofiber plays an important role in the fabrication technique, thereby creating nano-craters on the shadow surface of the nanofiber (shown in Figure 2). The lensing effect of the nanofiber also makes the fabrication process robust to any mechanical instabilities in the transverse direction (Y-axis). Moreover, due to single-shot irradiation, the instabilities along the other axes do not affect the fabrication as the irradiation time is only 120 fs (i.e. pulse width). As.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Femtosecond Laser	Coherent Inc.	Libra HE
Phase Mask	Ibsen Photonics	Custom Made
Optial Nanofiber Manufacturing Equipment	Ishihara Sangyo	ONME
ADC Card	PicoTech	ADC-24
Single mode fiber	Fujikura	FutureGuide-SM
Broadband source	NKT Photonics	SuperK EXTREME
CW Tunable Laser	Coherent Inc.	MBR-110
Spectrum analyser (Transmission spectrum)	Thermo Fisher Scientific	Nicolet 8700
Spectrum analyser (Reflection spectrum)	Ocean Optics	QE65000
CCD Camera	Thorlabs	DCC1545M
Power Meter	Thorlabs	D3MM
Pt-Coater	Vacuum Device Inc.	MSP-1S
Scanning Electron Microscope	Keyence	VE-9800
UV Curable Epoxy	NTT-AT	AT8105
Photodiode	ThorLabs	PDA 36A-EC
Clean room wipe	TExWipe	TX-404
Fiber coating stripper	NTT-AT	Fiber nippers 250 μm
Cover glass	Matsunami Glass IND,LTD	NEO micro cover glass 0.12-0.17 mm
PZT	NOLIAC	NAC 2011-H20
Cylindrical lens stage	NewPort	M-481-A
Y,Z stages	Chuo Precision Industrial Co., LTD.	LD-149-C7
Rotation stage	SIGMA KOKI	KSPB-1026MH
Z-stage(1), Z-stage(2)	NewPort	M-460P