International Workshop on Asymmetric Microcavities and their Applications (IWAM)
Takumi Kato, Ryusuke Saito, Tanabe Laboratory
August 2 - August 5, 2013
At FiO2013 (Frontier in Optics) held October 6-10 in Orlando, Florida
I made a poster presentation and attended many of the presentations.
IWAM is a professional research group that gathers only the research in the field of micro optical resonators, under the initiative of the Xiao group of Peking University, and not only high quality presentations from Peking Univ. In spite of the short period of two days, we were able to attend and discuss more than 10 presentations. In addition to the student presentations, the conference was characterized by the participation of major experts in the field, such as Prof. F. Vollmer's keynote lecture on micro-optical resonator sensing and Prof. Chunhua Dong's lecture on optomechanics, both of which were organized by Ph. D. students Xue-Feng jiang and Bei-Bei Li. I was very fortunate to have been able to participate in this advanced experiment in which students took the initiative and actively organized the workshop. If there is any opportunity in the future, I felt that it would be good if Tanabe Lab. could also hold a research group, led by students, inviting students and professors from other universities and foreign universities. Since our presentation had some affinity with the research being conducted at Peking Univ. in the fields of deformed cavity and sensing, we received many active questions during the session.
Research Trend Survey
Biosensing with optical microcavities, F. Vollmer
Sensing using micro optical resonators is moving from the stage of measuring single particles to the next stage. In the direction of single-particle measurement, "plasmon enhancement" techniques such as "applying a metal coating (core-shell) to the WGM resonator to increase sensitivity" and "placing a metal strip close to the WGM resonator to locally induce plasmon resonance to increase sensitivity" have reached a fairly low threshold. The threshold value is considerably lowered by "plasmon enhancement" techniques, such as "increasing the sensitivity by shell" and "locally causing plasmon resonance by placing a metallic strip close to the WGM resonator. The use of prismatic couplings instead of tapered fibers is also thought to have improved the quality and stability of this sensing. The next direction is "DNA nanotechnology," which may be able to detect DNA interactions. Using the fact that combinations such as A-T G-C strongly bind to each other, it is expected that single-stranded DNA will be coated on microspheres in advance, and the resonance spectrum will change when DNA that perfectly binds to the microspheres is attached.
ref: F. Vollmer et al, "Label-free detection with high-Q microcavities: a review of biosensing mechanisms for integrated devices," Nanophotonics 1, 267(2012)
Composite microcavities and their applications in thermal sensing and Raman lasing, Bei-Bei Li, Peking Univ.
The refractive index of silicatroids increases when heated due to the thermo-optic effect; an increase of 1°C changes the refractive index by a factor of 1. The PMDS coating method is very simple: a drop of water is added to the tapered fiber and brought into close proximity to the toroids. The coating is completed by placing a drop of water on the tapered fiber and bringing it into close proximity to the toroid. Since the molecular vibration of silica is different from that of PMDS, different Raman emission was observed. The temperature of the coating seems to be about 1.5 degrees Celsius.
ref: Bei-Bei Li et al, "Low-threshold Raman laser from an on-chip, high-Q, polymer-coated microcavity," Opt. Lett. 38, 1802(2013)
Single nanoparticle and Lentiviruses detection using microcavity resonance broading, Linbo Shao, Peking
The nanoparticles are detected by silicatroids coated with PDMS. The conventional method is to measure the amount of resonance wavelength shift (wavelength shift) or change in mode splitting (mode splitting), but the disadvantage is high noise, and it is difficult to show a constant value over time. Therefore, we are attempting to measure the Q value change due to particle adhesion (mode broading). This method is highly robust over time. It seems to be about 1.5 degrees.
Optical wavelength conversion via optomechanical dark mode, Chunfua Dong
It is well known that OMIT is observed due to the strong coupling between optical resonance and mechanical vibration resonance. These vibrations are directly induced by light. On the other hand, mechanical vibrations in dark mode do not cause OMIT. The advantage of this mode is that it is not directly coupled to light, and thus can store information more stably. These experiments were conducted using silica microspheres. They have demonstrated that wavelength conversion is possible, and are now competing with Painter's group. This work appears to have appeared at about the same time as Painter's Nat. Comm. paper (Painter was first).
ref: Chunhua Dong et al, "Optomechanical Dark Mode," Science 338, 1609 (2012).
Dynamical dissipative cooling of a mechanical resonator in strongly coupled optomechanics, Youg-Chun Liu, Peking
Laser cooling using mechanical vibration of a silicatroid resonator. Laser cooling of a micro optical resonator (only A in the figure is irradiated) has a high temperature limit for cooling due to backaction and swap heating. By adding a cooling-inducing laser (E in the figure), the cooling limit can be dynamically lowered by a few orders of magnitude.
ref: Yong-Chun Liu et al, "Dynamic Dissipative Cooling of a Mechanical Resonator in Strong Coupling Optomechanics," Phy. Rev. Lett. 110, 153606(2013)
A dispersion tuning konb for four wave mixing parametric oscillations based on micro-bubble resonators, Ming Li
The bottle structure is fabricated using silica capillaries. The structure is therefore a micro optical resonator with a hollow structure. The dispersion can be controlled by the thickness and shape of the silica part. Furthermore, by replacing the material in the hollow structure with a gas or liquid, further control is possible, he said. Although FWMs were actually generated, optical combs with such a broad bandwidth had not been realized.
I was told that using a 1.5 ns laser can produce FWM and Raman scattering even at relatively low Q-values.
ref: Ming Li et al, "Kerr parametric oscillations and frequency comb generation from dispersion compensated silica micro-bubble resonators," Optics Express 21, 16908(2013).
Ultrahigh-Q deformed microtoroids and their applications, Xue-Feng Jiang, Peking
When silicatroids are subjected to appropriate distortion, their radiation loss is directional. This is used to realize free-space coupling. They say that if the deformation is less than 15%, the coupling is maintained. They fabricate silica toroids in two steps, first cutting them with XeF2, then laser reflowing them into toroids, and further cutting them with XeF2. The distortion is caused by the photolithography process. Distortion is caused by the photolithography pattern. Basically, this research is for sensing. Free-space coupling is simple and stable, but not so efficient.
This study is an asymmetric structure and is highly related to chaos. It was also discussed that the resonance wavelength is shifted by the coupling with chaos, but I did not understand it well.
ref: Xue-Feng Jiang et al, "Highly Unidirectional Emission and Ultralow-Threshold Lasing from On-Chip Ultrahigh-Q Microcavities," Adv. Mater. 24, (2012)
High-Q on-chip optical microcavities fabricated by femtosecond laser machining, Jintian Lin
Femtosecond laser irradiation modifies the physical properties of silica and accelerates the etching rate against HF etching. Silica disks can be fabricated using this method, and silica toroids can be fabricated by reflow. This method is characterized by its ability to create three-dimensional structures and to broaden the range of materials, and they have also fabricated and achieved toroid structures in Nd:glass and measured lasing. The team did not seem to have a good environment for measurements, so it was thought to be much higher than it actually was.
ref: Jintian Lin et al, "On-chip three-dimensional high-Q microcavities fabricated by femtosecond laser direct writing," Optics Express 20, 10212(2012)