Xiaohua Jian

Wide-spectrum reconstruction method for a birefringence interference imaging spectrometer

We present a mathematical method used to determine the spectrum detected by a birefringence interference imaging spectrometer (BIIS). The reconstructed spectrum has good precision over a wide spectral range, 0.4-1.0 microm. This method considers the light intensity as a function of wavelength and avoids the fatal error caused by birefringence effect in the conventional Fourier transform method. The experimental interferogram of the BIIS is processed in this new way, and the interference data and reconstructed spectrum are in good agreement, proving this method to be very exact and useful. Application of this method will greatly improve the instrument performance.

The data processing of the temporarily and spatially mixed modulated polarization interference imaging spectrometer

Based on the basic imaging theory of the temporally and spatially mixed modulated polarization interference imaging spectrometer (TSMPIIS), a method of interferogram obtaining and processing under polychromatic light is presented. Especially, instead of traditional Fourier transform spectroscopy, according to the unique imaging theory and OPD variation of TSMPIIS, the spectrum is reconstructed respectively by wavelength. In addition, the originally experimental interferogram obtained by TSMPIIS is processed in this new way, the satisfying result of interference data and reconstructed spectrum prove that the method is very precise and feasible, which will great improve the performance of TSMPIIS.

Static dual-channel polarization imaging spectrometer for simultaneous acquisition of inphase and antiphase interference images

The raw data acquired by Fourier-transform imaging spectrometers are the physical superposition of an interferogram and image. To reconstruct an accurate spectrum from a pure interferogram via Fourier transformation and get a pure image that is undisturbed by fringes, the interferogram and the image need to be separated. Although it can be achieved by digital image processing, heavy computations with approximation would be introduced. To overcome these drawbacks and in the meantime avoid the influence of the rapid changes of the observed scene and the perturbations of the rotating elements, a static dual-channel polarization imaging spectrometer that can simultaneously acquire inphase and antiphase interference images is presented. The extraction of a pure image and pure fringe can be simply achieved from the difference and the summation of the two interference images, respectively. The feasibility of the spectrometer and its features are described, and the influence of the polarization direction of the polarizers on the background image and fringe is discussed.

Interferometric verification for the polarization imaging spectrometer

The optical throughput is usually attenuated by the use of two linear polarizers in a polarization imaging spectrometer. To avoid such attenuation, in some special cases to be determined, one may remove a polarizer. Theoretical formulae for different cases are derived by using the matrix representation of the polarizers, Savart plate, and random unpolarized electromagnetic beam. The theoretical and experimental results comply with the Fresnel–Arago polarization interference laws. The normal case, without removing a polarizer, adapted itself to general applications, and the abnormal case, with the fore polarizer removed, was only adapted to polarized scenes.

Electromechanical response of micromachined 1-3 piezoelectric composites: Effect of etched piezo-pillar slope

Micromachined single-crystal piezoelectric 1-3 composites are known for high electromechanical coupling coefficients, low acoustic impedance, high processing precision and uniformity, which are desired for high-frequency ultrasound transducers. In this article, based on Smith and Auld’s 1-3 composite thickness-mode oscillation model, the effect of etched side wall slope on the electromechanical characteristics of micromachined piezoelectric 1-3 composites was studied. In specific, strain constant, stiffness, dielectric constant, electromechanical coupling coefficient, acoustic impedance, longitudinal velocity, and frequency of micromachined 1-3 composites were deduced using the developed model. The analytical model was then verified by a COMSOL simulation and experimental measurements of a micromachined composite sample with pitch of 15.9 µm, thickness of 42.8 µm, and etched pillar slope angle of 83.8°. The measured center frequency was 49.05 MHz, electromechanical coupling coefficient was 0.66, dielectric constant was 1178, and strain constant was 26.90 C/m2, which all agreed well with the analytical calculations. These results will be helpful in design and fabrication of high-frequency micromachined ultrasound transducers.

A dual-layer micromachined PMN-PT 1-3 composite transducer for broadband ultrasound imaging

Broadband ultrasound imaging including tissue harmonic imaging usually captures acoustic information from the frequency higher than that of transmission waves, and has been widely studied in imaging for cardiology, bladder and other fluid-filled or cyst structures. Compared to the conventional pulse-echo method, the broadband imaging possesses the advantages including contrast resolution enhancement, artifacts reduction, and improved signal-to-noise ratio. However, those benefits require broadband ultrasound transducers. In this paper, a micromachined PMN-PT 1-3 composite based dual frequency transducer was designed, fabricated and characterized. The transmitting sensitivity at 17.5 MHz reached 40KPa/V, and the receiving spectra magnitude was compared with a calibrated hydrophone under same test transducer transmitting. These results hold great potential for medical broadband imaging applications.

Multispectral adaptive optics photoacoustic imaging

In this paper a multispectral adaptive optics photoacoustic imaging (MSAOPA) system is proposed. The photoacoustic (PA) signals of MSAOPA generated by irradiating the sample with a tunable optical parametric oscillator (OPO) Lasers emitting light at 600nm–1100nm are received by a broadband ultrasound transducer. The received data are rearranged according to the wavelength sequences and decoded for image reconstruction. Moreover, an adaptive optics sub-system is designed to correct the wavefront errors of the illuminating light for getting high-resolution image of biological tissues. The simulation results demonstrated that when the wavefront errors were corrected by the AO system, the image resolution and quality could be improved significantly.

Automated detection and quantification of early caries lesions on images captured by intraoral camera

In recent years, quantifying the severity of early caries lesions based on white light and/or fluorescence images captured by intraoral camera has been becoming a hot spot in caries research field. In order to quantify the severity of the early caries lesions, it needs to detect and segment the caries lesions accurately first. However, to date, the published methods are mainly based on threshold techniques, and it is difficult to obtain desirable results because the intensity of the teeth changes significantly. To solve this problem, this paper presents an automated detection and quantification algorithm by using a morphological top-hat/bottom-hat method along with a multi-resolution surface reconstruction technique, which is based on local intensity and morphological characteristics of caries images captured by the intraoral oral camera, for early caries lesions. The preliminary experimental results on ex vivo data demonstrated the potential of the proposed algorithm.

High frequency Self-focusing transducer fabricated by a laser engraving technique

High frequency transducers (>15 MHz) have been widely used in small animal ultrasound, ophthalmic ultrasound, skin ultrasound and intravascular ultrasound et. al. The images obtained by a plane transducer have lower resolution and sensitivity compared with a focusing one. It is usually hard to make the focusing transducer with micro size, short focal length and high frequency. For solving these problems, self-focusing transducers were developed, which pattern a Fresnel half-wave bands on the piezoelectric materials surface as the electrode. Using this method can achieve transducers with micro size (∼1–2 mm in diameter), short focal length (∼350 μm) and high frequency (>100 MHz). But this method need wire lead to contact each ring separately, so it is hard to keep every annular ring complete. And the instrument accuracy requirements are quite strict. Therefore, based on recent progress on laser cutting, a high frequency self-focusing piezoelectric transducer using laser cutting technique is developed, which engraved the piezoelectric ceramic into annular rings to form Fresnel half-wave-band sources.

Fabrication and performance of a micro 50-MHz IVUS Transducer based on a 1-3 composite with geometric focusing

In this paper a micro 50-MHz IVUS Transducer based on a 1-3 piezo-composite with geometric focusing was presented. The using 1-3 PZT composite material was developed in our laboratory with 12 um kerfs and 18 um pillars. The transducer was focused in the elevation direction by geometrically shaping the composite material using a PTEF ball with a 5 mm radius. After the silver conductive backing layer was cured, the transducer was divided into the size of 1.0 × 1.0 mm. The final fabricated transducer was fixed in a needle tip, and its diameter is 9F. According to the testing results with our homemade IVUS system, its lateral resolution is about 120 um, which effectively improved the lateral resolution of current IVUS system.