Photonic microring resonators have great potential in the application of highly sensitive label-free biosensors and
detection of high-frequency ultrasound due to high Q-factor resonances. Design consideration, device fabrication
techniques, experimental results are report in this paper.
Multi-dimensional, high frequency ultrasound arrays are extremely difficult to fabricate from conventional piezoelectrics. For over a decade, our lab has explored optical detection as an alternate technology for high frequency applications. We have developed several different types of acoustically coupled optical resonators to provide the sensitivity and bandwidth required for biomedical imaging. Waveguide and fiber lasers, thin Fabry-Perot etalons constructed from polymers, and thin microring resonators imprinted into polymers have all been used as ultrasound transducer arrays. Their performance rivals the theoretical conversion efficiency of piezoelectric devices but with bandwidths approaching 100 MHz, array element dimensions approaching 10 um, and no electrical interconnects. In this paper we present results on several resonant optical ultrasound transducer (ROUT) arrays, emphasizing their potential use in photoacoustic imaging. These results strongly suggest that a high resolution photoacoustic microscope can be constructed using a ROUT in a footprint appropriate for endoscopic and minimally invasive applications.
A novel application of polymer waveguide microring resonator for high-frequency ultrasound detection is presented. The device consists of a microring optical resonator that is coupled to a straight optical waveguide which serves as both input and output ports. Acoustic waves irradiating the ring waveguide induce strain that causes a change in the effective refractive index of optical waves propagating along the ring. The sharp wavelength dependence of the high Q-factor resonator enhances the optical response to the acoustic strain. High sensitivity has been demonstrated experimentally in the detection of broadband ultrasound pulses from a 10MHz transducer. WDM methods are proposed to extend the technique into an array of microrings for ultrasound imaging applications.
Photonic microring resonators have great potential in the application of highly sensitive label-free biosensors due to high Q-factor resonances. Design consideration, device fabrication techniques, methods to increase the resonance Q-factors, and preliminary experimental data on biomolecular detections are discussed in this paper.
We propose to use nonlinear optical (NLO) polymer to fabricate microring resonator device for all-optical switching application. In the proposed device NLO polymer provides the saturable absorption nonlinearity and microring resonator provides the feedback needed for optical bistability. Waveguide confinement and field intensity build-up in the ring resonator both facilitate the nonlinear optical process, making it possible to achieve low switching intensity. Moreover, the size of microrings is in the range of several tens of micro-meters, which is promising for high-speed optical switching as well as for high-density integration. We present detailed analysis of the device operation and identify key facts for the optimization of the devices. We propose to use nanoimprinting lithography technique to create microring resonator structures in NLO polymers, and show our initial results that prove the feasibility of this approach.
Semiconductor surface gratings can find applications in various areas, including optical communications, display, storage, and sensing. The diffraction effects of a surface grating can be used for the operations of various devices. Although semiconductor surface gratings can be fabricated with etching techniques, such a process requires the preparation of a mask and is usually quite complicated. Recently, because of the development of high-power laser, direct writing of surface grating with laser has become an important alternative [1 ,2]. Basically, writing grating with laser is a process of exposing the sample to laser interference fringes. The photons at the bright lines of the fringes interact with the sample material to form periodical corrugations. Because we can control the period of the interference fringe through the interferometer setup and the depth of corrugation through the laser power level, fabrication of surface grating with laser is more flexible than other techniques. In this paper, we investigate the interaction mechanisms between laser photons and semiconductor in fabricating silicon surface gratings with 266 nm laser.