Near-field scanning optical microscopy (NSOM) was used to observe high-resolution images of planar photonic crystal nanocavities fabricated in active InGaAsP material. We have observed the smallest optical cavity modes and dielectric band modes

Gogna, Pawan

Lončar, Marko

Okamoto, Koichi

Qiu, Yueming

Scherer, Axel

Yoshie, Tomoyuki

Caltech Authors - Main

QFA2 
Near-field scanning optical microscopy of photonic crystal 
high-Q nanocavities 
Koichi Okamoto, Marko LonEar, Tom,oyuki Yoshie and Axel Scherer 
Department ofElectrica1 Engineering, C a l f m i a  Insirtute of Technology, Pasadena, CA 91 125-9300 
Yueming Qiu, Pawan Gogna 
In Situ Technology and Experiments System Section, Jet Propulsion Laboratov? California Institute of Technology, 
MS 302-306, 4800 OakGrove Drive, Pasadena, CA 91 I09 
Abstract: Near-field scanning optical microscopy (NSOM) was used to obsenre high-resolution 
images of planar photonic crystal nanocavities fabricated in active InGaAsP material. We have 
observed the smallest optical cavity modes and dielectric band modes. 
02000 Optical Society of America 
OCIS codes: (000.0000) General 
Recently, near-field scanning optical microscopy (NSOM) has been used as a powerful alternative method to 
analyze local electromagnetic field distributions on fabricated nanophotonic structures. Several groups have reported 
NSOM studies of planar photonic crystals (PPC) [l-21, however, high spatially resolved near-field images of modes 
inside the PPC cavities have not so far been reported. We report optical mode images obtained by NSOM on 
compact PPC cavities based on fractional edge dislocations [3-4]. 
A cw light from a He-Ne laser (633nm) and a 20x3 pulsed diode laser (780nm) were used as the excitation laser 
source for illumination mode (I-mode) and the collection mode (C-mode) measurements, respectively. 
Photoluminescence (PL) signals were filtered out from the excitation laser by a low-pass fiter with a cut-off 
wavelength of 850nm, and detected with a high-sensitivity (fW) InGaAs photo-detector. A metal-coated fiber tip, 
with small aperture size, enables us to substantially cut leaky mode light. The best resolution in our system is as 
small as 50nm. By using the shear-force detection, we could also obtain a topographic image of the sample, in 
addition to the near-field optical image. We have also performed micro-PL measurements [3-51 on our structures in 
order to confirm the existence of the localized cavity modes. The photonic crystal nanocavities fabricated in active 
InGaAsP material used in this work are very similar to those used to realize low-threshold lasers described in our 
previous publication 151. 
Fig. 1. (a) Topographic image obtained by the shear-force microscopy. (b) Near-field photoluminescence (PL) 
image. 
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Fig. 1 (a) and (b) show the topographic image and the near-field PL image of the photonic clystal nano-cavity. 
The bright spot seen in NSOM-PL image is located at the center of the PC structure, matching the position of the 
defect cavity, as shown in topographic image. This snnll spot size is an indlcation of a small mode volume, as 
expected from the localized cavity modes. To the best of our knowledge, the optical modes and field distribution 
that we have observed are the smallest reported so far. We also observed the micro-PL analysis of this stmcture. 
Two peaks positioned around h=1450nm correspond to the localized dipole modes 
In addition to localized cavity modes, we have observed dielectric band modes in bulk photonic clystals 
surrounding the nanocavity with C-mode by geometrical tuning for eliminating localized modes out of the emission 
range. Sirmlq results were predicted by theory [6], and profiles of dielectric band modes have been found using 
FDTD analysis of NSOM experiments. Also, spectra obtained using micro PL show the presence of dielectric bands 
at h=1555nm. We conclude that near-field scanning optical microscopy is a powerful tool for investigation of local 
profiles of confined modes in nanocavities. 
[l] D. Gerard, L. Berguigd, F. de Fomel, L. Salomon, C. Seassal, X. Letartre, P. Vilitorovitch, “Near-field probing of active photonic-crystal 
stnictures” Opt. htt. 27, 173 (2002). 
[2] D.-J. Shin, S.-H. Kim, J.-K. Hwang, H.-Y. Ryu, H.-G. Park, D.-S. Song, Y.-H. Lee, “Far- and Near-Field Investigations on the k i n g  Modes 
in Two-Dimensional Photonic Crystal Slab Lasers” IEEE J. Quantum Electronics, 38, 857 (2002). 
[3] J. Sufkovic, M. LonEar, H. Mabuchi, A. Scherer, ‘‘Design of photonic crystal microcavities for cavity QED” Phys. Rev. E. 65, 16608 (2001). 
[4] T. Yoshie, J. VuEkovid, A. Scherer, H. Chen, D. Deppe, “High qualtiy two dimensional photonic crysaal slab cavities” Appl. Phys. Lett. 79, 
4289 (2001). 
[5] M. Lonfar, T. Yoshie, A. Scherer, P. Gogna and Y. Qiu, “Low-threshold photonic crystal laser” Appl. Phys. Lett. 81,2680 (2002). 
[6] S. Fan, A. Ian, J. D. 3oannopoulos, “Near-field scanning optical microscopy as a simultaneous probe of fields and band structure of photonic 
crystals: A computational study” Appl. Phys. Lett. 75, 3461 (1999). 


Near-field scanning optical microscopy of photonic crystal high-Q nanocavities

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Near-field scanning optical microscopy of photonic crystal high-Q nanocavities

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