Supplementary Online Material for
Vertical microgoblet resonator with high sensitivity fabricated by
direct laser writing on a Si substrate
Xiaomei Gao,1,2 Jiafang Li,2,a) Zhenzhong Hao,1 Fang Bo,1,b) Chenyang Hu,2
Jie Wang,1 Zhiguang Liu,2 Zhiyuan Li,2 Guoquan Zhang1 and Jingjun Xu1
1
The MOE Key Laboratory of Weak Light Nonlinear Photonics, TEDA Institute of Applied
Physics and School of Physics, Nankai University, Tianjin 300457, China
2
Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
a) E-mail: [email protected]
b) E-mail: [email protected]
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Water (H2O) was found to be highly absorptive in 1550 nm wavelength band (with absorption
coefficient of ~8.79 cm-1) 1. Therefore, to avoid the water absorption in 1550 nm wavelength
region1, the comparison of RI sensitivity between microdisk and microgoblet microcavities was
conducted in the visible wavelength range, of which the conclusion (i.e., the sensitivity of
microgoblet is higher than that of microdisk with the same thickness) could be reasonably applied
to other wavelength bands. For theoretical demonstration of this point, we conducted numerical
simulation in visible wavelengths, with which refractive index sensitivities of both microgoblets
and microdisks in air and purified water were calculated and compared. It can be seen that Fig.
S1, where the vertical microgoblet resonator has different bottom thickness t with t + h fixed,
shows similar characteristic as that in Fig. 2e of the main text.
Fig.S1. Simulated RI sensitivity of the vertical goblet as a function of the bottom thickness t under r = 20 µm,
w = 1.44 µm and t + h = 4.07 µm in visible wavelengths.
Meanwhile, when the width (w) of the goblet wall is varied while t and h remain unchanged,
as shown in Fig. S2, the change in RI sensitivity show the same trend as in Fig. 3(e) of the main
text.
2
Fig.S2. Simulated RI sensitivity of the mcriogoblet as a function of the wall width w under t = 1.25 µm and h =
2.82µm.
Fig.S3. Simulated mode intensity distributions of vertical goblet microcavities with t = 1.25 µm and w = 1.0
µm under different h. (a) h = 0.42µm, (b) h = 0.82 µm, (c) h =1.62 µm, (d) h = 3.22 µm. (e) RI sensitivity of
the vertical microgoblet as a function of h under w=1.4 µm and t = 1.25 µm.
The RI sensitivity of the microgoblet is also sensitive to h. As shown in Figs. S3(a)-(d), the
TE1, 288 mode is drawn gradually from the microdisk region to the vertical wall as h increases, i. e.
when the resonator changes from a microdisk to the vertical microgoblet resonator. As a result,
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the RI sensitivity shows a general increase with the increase of the wall height, as plotted in Fig.
S3(e). The saturation of the curve above 3.0 µm is because that at this height the TE1, 288 modes
are nearly completely drawn into vertical wall and the interaction region between cavity mode
and outside medium tends to be stable. These properties are also very similar to those in Fig. 4 of
the main text.
It should be mention that the RI sensitivity in visible wavelengths is smaller than that in
near-infrared wavelengths under the same structure parameter, mainly due to the smaller
evanescent field outside the microcavities in visible wavelength region since the structural
parameters were initially designed in 1550 nm wavelength region. Nevertheless, both results in
visible and near-infrared wavelengths have consistently demonstrated that the RI sensitivity of
microgoblet is higher than that of microdisk with the same thickness.
REFERENCES
1
A. M. Armani, D. K. Armani, B. Min, and K. J. Vahala, “Ultra-high-Q microcavity operation in
H2O and D2O,” Appl. Phys. Lett. 87, 151118 (2005).
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