Cameron J. Brooks

High frequency ultrasound imaging using an active optical detector

Optical detection of ultrasound has numerous advantages over traditional piezoelectric methods. These systems offer noncontact inspection, rapid scanning capabilities, fine spatial sampling, and large bandwidths. In addition, difficulties associated with conventional ultrasound imaging systems such as cross-talk between elements, electrical connections, and electromechanical resonances are greatly reduced or even eliminated. Because of this, high frequency phased arrays for ultrasound detection can be emulated by accurately positioning and focusing optical beams on a suitable surface, which defines array elements. However, optical systems have lower sensitivity than their piezoelectric counterparts, limiting their widespread use in ultrasound imaging. Active optical detection offers a solution. An active ultrasound detector consisting of a neodymium-doped glass waveguide laser with an optical demodulation system, was built demonstrating enhanced sensitivity while preserving the benefits of traditional passive optical detection.

Integrated-optic dispersion compensator that uses chirped gratings

An integrated-optic dispersion compensator that uses chirped waveguide gratings is designed and fabricated. The 7-mm-long chirped grating is realized by a recently proposed method of curving a waveguide through a uniform grating. At 800 nm, the fabricated device exhibits a reflection bandwidth in excess of 0.5 nm and a nearly quadratic phase response corresponding to a fiber dispersion–length product of 58 ps/nm. The phase response reported is measured interferometrically with a narrow-band, tunable Ti:sapphire laser. Extending this technology to 5-cm-long gratings should permit dispersion compensation of 50-km-long fiber lengths at 1.55 μm.

Phase response measurement technique for waveguide grating filters

A simple interferometric technique is described which can be used to accurately measure the phase response of waveguide grating filters. A narrowband, tunable Ti:sapphire laser is used in a Michelson interferometer configuration, where light reflected from a waveguide grating filter is combined with a reference beam. The intensity of the combined beams is measured as the wavelength of the Ti:sapphire laser is tuned. The measured intensity exhibits a quasisinusoidal wavelength dependence, from which the phase response of the filter can be deduced. This method is successfully demonstrated using both an integrated optic waveguide grating filter and a bulk grating pair.

An active optical detector for high frequency ultrasound imaging

Optical detection of ultrasound has numerous advantages over traditional piezoelectric methods. These systems offer non-contact inspection, rapid scanning capabilities, fine spatial sampling and large bandwidths. In addition, difficulties associated with conventional ultrasound imaging systems such as cross-talk between elements, electrical connections, and electromechanical resonances are greatly reduced or even eliminated. However, optical systems have lower sensitivity than their piezoelectric counterparts, limiting their widespread use in ultrasound imaging. Active optical detection offers a solution. An active ultrasound detector, consisting of a neodymium-doped glass waveguide laser with an optical demodulation system, was built demonstrating enhanced sensitivity while preserving the benefits of traditional passive optical detection.