Design and characterization of acoustic 4f imaging system by using an optical microring ultrasound detector

We propose an acoustic 4f imaging system by using a pair of acoustic lens and an optical microring ultrasound detector (OMUD). The system was designed to have a long range imaging, and the signal strength was enhanced by a factor of ∼13 by using an acryl-based acoustic lens at an imaging distance of close to 10 cm. The acoustic signal had a broadband and high frequency spectrum for a given focal distance owing to the unique characteristic of the OMUD. The imaging was obtained without using any reconstruction algorithms. Several performances of the designed system have been investigated by using photo-acoustic microspheres (301 microm in diameter) which are excited by pulsed laser beam. The resolution of images were compared, which consist of full frequency spectrum and harmonic frequency components. With high frequency (10 MHz and 15 MHz), the images showed consistently better resolutions (440 microm and 370 microm) for the microsphere. Frequency analysis of a time-domain signal waveform showed that the signal spectrum of the current system extends up to 20 MHz.