Comparison of the state-of-art phase modulators and parametric mixers in time-lens applications under different repetition rates

Ever since the discovery of space-time duality, several methods have been developed to perform temporal imaging, and there are two major categories: the quadratic signal onto the phase modulator and the parametric mixer with a linear chirped pump. The features of each mechanism have been thoroughly and quantitatively explored and optimized for certain kinds of applications, but a comparison of some key parameters, especially in the aspect of the repetition rate, is required. In this paper, we will first review the theoretical models and existing performance of these two mechanisms and, consequently, compare them quantitatively in different aspects: the focal group delay dispersion, the pupil size, the effective duty ratio, and the temporal numerical aperture. All these fundamental parameters are related to the repetition rate. The results obtained in this study would provide some important guidelines for the time-lens design, so as to be optimized in different kinds of applications with different repetition rate requirements, such as ultrafast optical communication and real-time bio-imaging systems.published_or_final_versio

Large area laser scanning optical resolution photoacoustic microscopy using a fibre optic sensor

A laser scanning optical resolution photoacoustic microscopy (LS OR-PAM) system based on a stationary fibre optic sensor is described. The sensor comprises an optically resonant interferometric polymer cavity formed on the tip of a rounded single mode optical fibre. It provides low noise equivalent pressure (NEP = 68.7 Pa over a 20 MHz measurement bandwidth), a broad bandwidth that extends to 80 MHz and a near omnidirectional response. The latter is a significant advantage, as it allows large areas ( > 1cm 2 ) to be imaged without the need for translational mechanical scanning offering the potential for fast image acquisition. The system provides a lateral resolution of 8 µm, an axial resolution of 21 µm, and a field of view up to 10 mm × 10 mm. To demonstrate the system, in vivo 3D structural images of the microvasculature of a mouse ear were obtained, showing single capillaries overlaying larger vessels as well as functional images revealing blood oxygen saturation

All-optical endoscopic probe for high resolution 3D photoacoustic tomography

A novel all-optical forward-viewing photoacoustic probe using a flexible coherent fibre-optic bundle and a Fabry- Perot (FP) ultrasound sensor has been developed. The fibre bundle, along with the FP sensor at its distal end, synthesizes a high density 2D array of wideband ultrasound detectors. Photoacoustic waves arriving at the sensor are spatially mapped by optically scanning the proximal end face of the bundle in 2D with a CW wavelength-tunable interrogation laser. 3D images are formed from the detected signals using a time-reversal image reconstruction algorithm. The system has been characterized in terms of its PSF, noise-equivalent pressure and field of view. Finally, the high resolution 3D imaging capability has been demonstrated using arbitrary shaped phantoms and duck embryo

High-sensitivity polarization gating frequency-resolved optical gating (PG-FROG) using highly-nonlinear dispersion-shifted fiber

We experimentally demonstrate a frequency-resolved optical gating (FROG) system in pulse characterization at 1.55 μm by using cross-phase modulation (XPM) in highly nonlinear dispersion-shifted fiber (HNL-DSF), with over 6-times sensitivity improvement. © 2011 National Sun Yat-Sen Univ.published_or_final_versio

Simultaneous demultiplexing of OTDM channels based on swept-pump fiber-optical parametric amplifier

Session - Quantum Information & Parametric Processing OM3B.2We experimentally demonstrate simultaneous demultiplexing of 80-Gb/s OTDM signal by transforming it into WDM idlers (spaced by 1.15 nm), based on a swept-pump fiber-optical parametric amplifier (FOPA), and 10-dB parametric gain is achieved. © 2012 OSApublished_or_final_versio

Photoacoustic imaging with a multi-view Fabry-Perot scanner

Planar Fabry-Pérot (FP) ultrasound sensor arrays have been used to produce in-vivo photoacoustic images of high quality due to their broad detection bandwidth, small element size, and dense spatial sampling. However like all planar arrays, FP sensors suffer from the limited view problem. Here, a multi-angle FP sensor system is described that mitigates the partial view effects of a planar FP sensor while retaining its detection advantages. The possibility of improving data acquisition speed through the use of sub-sampling techniques is also explored. The capabilities of the system are demonstrated with 3D images of pre-clinical targets

Rapid Spatial Mapping of Focused Ultrasound Fields Using a Planar Fabry-Pérot Sensor

Measurement of high acoustic pressures is necessary in order to fully characterise clinical high-intensity focused ultrasound (HIFU) fields, and for accurate validation of computational models of ultrasound propagation. However, many existing measurement devices are unable to withstand the extreme pressures generated in these fields, and those that can often exhibit low sensitivity. Here, a planar Fabry-Pérot interferometer with hard dielectric mirrors and spacer was designed, fabricated, and characterised and its suitability for measurement of nonlinear focused ultrasound fields was investigated. The noise equivalent pressure of the scanning system scaled with the adjustable pressure detection range between 49 kPa for pressures up to 8 MPa and 152 kPa for measurements up to 25 MPa, over a 125 MHz measurement bandwidth. Measurements of the frequency response of the sensor showed that it varied by less than 3 dB in the range 1 - 62 MHz. The effective element size of the sensor was 65 μm and waveforms were acquired at a rate of 200 Hz. The device was used to measure the acoustic pressure in the field of a 1.1 MHz single element spherically focused bowl transducer. Measurements of the acoustic field at low pressures compared well with measurements made using a PVDF needle hydrophone. At high pressures, the measured peak focal pressures agreed well with the focal pressure modelled using the Khokhlov-Zabolotskaya-Kuznetsov equation. Maximum peak positive pressures of 25 MPa, and peak negative pressures of 12 MPa were measured, and planar field scans were acquired in scan times on the order of 1 minute. The properties of the sensor and scanning system are well suited to measurement of nonlinear focused ultrasound fields, in both the focal region and the low pressure peripheral regions. The fast acquisition speed of the system and its low noise equivalent pressure are advantageous, and with further development of the sensor, it has potential in application to HIFU metrology

Fast swept-source generation based on fiber optical parametric amplifier

We experimentally demonstrate a fast frequency swept-source using the dispersive Fourier transformation-based fiber optical parametric amplifier. The swept rate is as high as 78 MHz, with a linewidth of 0.135 nm. © 2011 OSA.published_or_final_versio

Pencil beam all-optical ultrasound imaging

A miniature, directional fibre-optic acoustic source is presented that employs geometrical focussing to generate a nearly-collimated acoustic pencil beam. When paired with a fibre-optic acoustic detector, an all-optical ultrasound probe with an outer diameter of 2.5 mm is obtained that acquires a pulse-echo image line at each probe position without the need for image reconstruction. B-mode images can be acquired by translating the probe and concatenating the image lines, and artefacts resulting from probe positioning uncertainty are shown to be significantly lower than those observed for conventional synthetic aperture scanning of a non-directional acoustic source. The high image quality obtained for excised vascular tissue suggests that the all-optical ultrasound probe is ideally suited for in vivo, interventional applications