IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 44, NO. 1, JANUARY 2008 75
High Quality Direct Photo-Patterned Microdisk
Lasers With Organic–Inorganic Hybrid Materials
Xiang Wu, Hao Li, Liying Liu, and Lei Xu
Abstract—A direct photo-patterned microdisk-on-chip tech-
nique is used to fabricate 2-D microdisk lasers with various
shapes. High-
morphology-dependent resonances (including
whispering gallery modes and four bouncing reflection modes)
laser emissions from RhB-doped circular and square-shaped
microdisks are observed. A thin polymer cladding on the mi-
crodisk is found to obviously smooth the disk sidewall. As a result,
lowered lasing threshold, increased
-value as high as 12000 and
efficient suppression of h igh-order modes are realized. Lasing
from square-shaped microcavities shows closed and open orbit
resonances separately at different emission directions.
Index Terms—Microdisk lasers, organic–inorganic hybrid mate-
rials, sol-gel processing, whispering gallery modes.
I. INTRODUCTION
O
PTICAL microcavities are widely studied because they
have many applications in fundamental physics [1],
nonlinear optics [2], optical communication [3], and biosensing
[4]. At present, microcavity materials can be classified as two
families: inorganic and organic materials. Different fabrication
technologies have been developed for different materials.
Produced by heating the end of a quartz rod or an optical
fiber, the fused silica microsphere resonators have obtained the
ultrahigh optical quality factors
of nearly 9 billion [5],
[6]. The on-chip silica microtoroids were also processed by
using a combination of lithography, dry etching and a selective
laser reflow process and a very high cavity quality factor
10 has been achieved [7]. On the other hand, organic
microcavities usually have much lower
value. Luminescent
conducting polymers and dye-doped polymer 2-D microdisk
lasers with different shapes were created by microlithography
and
reactive ion etching steps [8]–[10]. So far the achieved
-values from organic microdisk lasers are between several
hundred and 10000. The
factor is limited by the loss in the
microcavity. The main loss mechanisms are due to surface
roughness and less confined optical field. Therefore, high-
microdisks usually rely on complex and precise fabrication
techniques to decrease the roughness, producing thumb-tack
or other types of disks that have high refractive index contrast
Manuscript received June 19, 2007; revised August 27, 2007. This work was
supported in part by the National Natural Science Foundation of China under
Grants 10474015, 60478005, 10574032, and 60638010 and in part by Shanghai
Science and Technology Commission under Grant 06JC14010.
The authors are with the State Key Laboratory for Advanced Photonic Ma-
terials and Devices, Department of Optical Science and Engineering, School
of Information Science and Engineering, Fudan University, Shanghai 200433,
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/JQE.2007.910447
with the surroundings. Polymer microring resonators were
fabricated by a combination of nanoimprint technique and
thermal reflow process [11]. Ultrahigh-
microtoroids were
also applied to produce polymer microresonators with high
-factors of 10 [12].
Recently, the sol-gel technology based on wet processes at
low temperature has proven to be one promising approach to
produce low-cost high quality organic-inorganic glass inte-
grated optical devices [13]. Photosensitive organic–inorganic
hybrid materials can be applied for direct photo-fabrication
of optical waveguides without photoresist lithography. Their
optical properties such as refractive index can be precisely
controlled by selecting the organic constituents and metal oxide
composition. Optical devices such as multimode interference
(MMI) waveguide splitters, Mach–Zehnder (MZ) switches,
distributed Bragg reflector (DBR) lasers, and microring filters
have been fabricated and shown excellent properties [14]–[17].
In addition, the excellent physical and chemical stability of the
organic–inorganic hybrid matrix allow multilayer fabrication,
which offers possibilities for the fabrication of high-
on-chip
microdisk lasers and as the key components in integrated
optical bio–chemical sensor systems.
In this work, sol-gel organic–inorganic hybrid mi-
crodisk-on-chip technique based on the direct UV patterning
and wet etching technique was proposed to fabricate microdisk
lasers on silicon substrate. The device configuration has a usual
three-layer waveguide structure with weak refractive index
contrast in the vertical direction. One-step patterning produces
high quality microlaser arrays. A lowered lasing threshold,
increased
value and suppression of high-order modes were
realized in this 3-layer microcavity structure. We also explored
the lasing from square-shaped microcavities and observed
the closed and open orbit resonances at different emission
directions.
II. M
ICRODISK FABRICATION AND
MICRODISK
LASER PROPERTIES
The organic–inorganic hybrid materials for microcavities
were synthesized in a similar way as described in Ref. [16]
by hydrolysis and polycondensation of methacryloxypropyl
trimethoxysilane (MAPTMS), methacrylic acid (MAA), and
zirconium (IV) propoxide (ZPO). MAPTMS consists a silane
end group and an organic end group with double carbon bond
that can be photo-polymerized under UV exposure. MAPTMS
is hydrolyzed together with ZPO in acidic environment.
ZPO is introduced to adjust the refractive index of the final
product, and ZPO also helps in producing uniform films with
good optical quality. Two types of sol with molar ratios of
(Material 1, ) and
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