A nonlinear optical image-contrast amplifier

Wei Gao, Sandan Wang, Jinpeng Yuan +3 more

Nonlinear spiral phase contrast imaging serves as a powerful tool for high-performance image edge detection in optical imaging. Compared to conventional computer-based digital imaging methods, it offers numerous possibilities for optical image processing with superior speed, lower energy consumption, and high information capacity. Here, we experimentally demonstrate the high-contrast nonlinear spiral phase contrast imaging in a diamond-type atomic system. A pump vortex-filtered beam (780 nm) and a signal beam with object image (776 nm) simultaneously interact with Rb atomic medium. As a result, a 420 nm beam is generated via the nonlinear four-wave mixing process, carrying the edge information of asymmetric Arabic numeral patterns. The geometric patterns such as triangle, circle, and square are further utilized to validate the effectiveness of nonlinear spiral phase contrast imaging. The high image contrast of ∼95.8% is achieved owing to the stringent phase matching conditions via the atomic four-wave mixing process. Moreover, the directional nonlinear spiral phase contrast imaging of circle and square patterns at 420 nm are realized by employing a Laguerre-Gaussian composite vortex filter on the 780 nm pump beam. This work establishes a versatile platform for multi-wavelength optical image analysis and provides a robust foundation for developing optical information processing methods.

V L Koval'chuk, V P Konarev, V N Lomakin +1 more

An experimental investigation was made of the resolution of a neodymium-activated glass fiber laser image amplifier and of the dependence of the signal/noise ratio at the amplifier output on the signal power at the input. The resolution in the active regime (in the presence of pumping) was not inferior to that in the passive regime (without pumping) and the signal/noise ratio (and, consequently, the contrast of the amplified image) improved, compared with the passive regime.

Antonio Hurtado, Ian D. Henning, M.J. Adams

This paper reports on the experimental observation of power and wavelength optical bistability (OB) and nonlinear gain in a 1550 nm- vertical cavity semiconductor optical amplifier (VCSOA) biased just below threshold and operated in reflection. Two different shapes of power and wavelength OB and nonlinear gain, anticlockwise and clockwise, have been experimentally observed, both with high on-off contrast ratio.

Wolfgang Demtröder