Zhe Ji

Fabrication of Planar Microtoroid Cavities Using High-Power Laser

Planar Microtoroid cavities have important application in many researching and application domains due to their ultrahigh quality factor (Q). But the special toroid structure can not be fabricated through traditional technology. In this paper, a novel processing method for fabricating microtoroid cavities using high-power CO2 laser after a series of traditional processing steps is introduced. The processing details are discussed including light path, focusing system and other important parameters. Test using scanning electronic microscope and laser-Raman spectrum shows that fabrication of planar microtoroid cavity using CO2 laser is feasible. The final microtoroid cavity is fabricated with slight impact to the silicon strut-beam, ensuring excellent optical performance in Planar Microtoroid cavity.

Design and modeling of a novel micro-displacement sensor based optical frequency comb

Pumping a single-mode, tunable, external-cavity laser to excite the whispering gallery modes (WGM) of micro ring resonators (MRRs), a series of equidistant, wide free spectrum range (FSR) can be observed. Frequency shift of FSR can be used to feedback external changes, making MRR very promising in high-sensitivity sensing. In this paper, a novel displacement sensor composed of a micro ring resonator and a waveguide is presented and a designing route for this sensor is discussed. Based on mathematical analysis and the beam propagation methods (BPM), the major parameters including the geometry of MRR and micro cantilever are investigated in detail. Materials selection and fabrication method under current processing technic are also presented. For the typical structure in this paper, the final Q factor is estimated approximately 103 in theory at the wavelength of 1.5μm.Displacement alteration of cantilever is 0.296x10-6m - 0.535x10-5m approximately corresponding 10-8-10-6N force loading. The shift of transmission spectrum is about 3.9nm versus perimeter of MRR changing 1μm.

Integrated micro-and nano optical cavities on a chip for supersensitive sensing

Integrated micro-and nano optical cavities are promising in electro photonic integration devices for their stable performance and compatible potential with optical-fiber technology as well as other electronic photonic integrated circuit. In this paper, we present an optimal design of SOI integrated optical cavities for supersensitive sensing under finite-difference time-domain (FDTD) modeling technique and beam propagation method (BPM). Phase match and coupling distance between the straight waveguide and the cavity are discussed. After showing the optical cavities fabricated with SOI, testing experiment was carried out, obtaining the transmitted spectrum in the near-infrared telecommunication bands. Analyzing transmission peaks using FWHM method, Q about 1000 is estimated. In the last part of this paper, the potential and promising prospective for supersensitive sensing is demonstrated.

A precise measurement of quality factor for Planar Microtoroid Resonators

The quality factor(Q) parameter is the most important parameter for optical micro cavities. In this paper, we present the Planar Microtoroid Resonators fabricated in our laboratory. Then, measuring methods common used are introduced. After that, a precise measurement of quality factor is demonstrated in which the photon lifetime was directly measured by cavity ringdown. This is done by repeatedly scanning the laser into resonance with a mode that was critically coupled to the taper. As the laser scanned into resonance, the power transferred into the cavity increased until the maximal power of the resonant mode was attained. At this moment, an external modulator is used to cut-off the pumping laser. As the resonant power outpouring, a cavity ringdown spectrum is observed and recorded. The cavity lifetime can be obtained through analyzing the spectrum. Finally, the quality factor is estimated from the cavity lifetime which is consistent with the widely used measurement of the frequency line shape.

Water vapor detecting using high-Q microcavity

The target of this paper is to design a novel water-vapor sensor used in humidity transducer system based on high-quality factor (Q) spherical microcavities, which at present obtained the highest Q value induced by surface tension. Sensitive mechanics and its high sensitivity are discussed according to optical loss sensitization to coupling system composed of a microsphere cavity and a tapered fiber. After that, fabrication methods of master parts of the sensor in our lab are introduced. Additionally, a sensing structure composed of a gas-chamber and a vacuum-chamber is also designed. According to water absorption band, telecom band around 1550nm is used to pump the microsphere optical mode. In a vacuum environment, a transmitted spectrum is obtained through output end, revealing some information about the core system including the size of the microcavity and the optical loss of the regime. However, when the core system is placed in a water vapor environment, the transmitted spectrum will change due to extra optical loss induced by water molecules absorption, behaving as spectral shift, free spectrum range (FSR) or line width broadening. Contrasting and analyzing two different spectrums in the two situations, the gas concentration can be deduced. Indispensable experiments were also carried out, showing that, the two spectrums are different from resonance hump, formant strength and formant line width. Even an ultra low water vapor concentration induced a measurable output signal, ensuring a high detecting sensitivity. Certainly, the analyted vapor should not only be water vapor. This kind of sensitive mechanics is versatile. Changing the pumping light corresponding to the analyted absorption band, we are able to detect a series of vapor.

Microsensors based on planar microtoroid cavities

Planar Microtoroid cavities with ultrahigh quality factor have very strong confined function to the electromagnetic wave coupled into them due to their novel ring-like structures. Therefore, they have very good applications in high sensitivity sensors and other micro optics components. In this paper, the Planar Microtoroid cavity and its coupling system constructed together with the tapered fiber are introduced. Then, micro sensors based on the above coupling system are designed. These sensors measure environmental parameters by means of monitoring the changes in the transmission spectrum of the high finesse Planar Microtoroid cavities, obtaining fine resolution and high accuracy due to their ultrahigh quality factor (Q) performance. The sensitive mechanism and the feasibility are demonstrated through optical and mechanical software simulation. With software BeamPROP, the evident resonance and strengthened phenomenon to the electromagnetic wave coupled into the micro-cavity are shown, which have a big relation with the light frequency. The results indicate that, Planar Microtoroid cavity is very promising in designing new micro sensors.