Dongxiong Ling

Dispersion and compensation of optical coherence tomography using double-path rapid scanning optical delay line

Optical coherence tomography (OCT) with advantages of high resolution and high sensitivity is an emerging optical imaging technology that performs cross-sectional tomographic imaging of microstructure in biological system. In spite of the improvement of the longitudinal resolution by using low coherence light source, the dispersion effect aggravates with the increase of spectral bandwidth, which result in serious image blur and loss of image features. We demonstrate a double-path rapid scanning optical delay line (D-RSOD) structure in reference arm that produce the additional phase delay and group delay independent in OCT. The phase delay determined by grating defocus offset (GDO) of D-RSOD is controllable and the system dispersion is compensated by accurate adjustment of GDO in experiment. The full width at half maximum (FWHM) of the interference peak was measured to be 23.2μm and 15.2μm respectively before and after compensation. The experimental results indicate that the interference signal envelops shrink and the tomographic image clarify after dispersion compensation, D-RSOD is an effective means of dispersion compensation in OCT as well.

High-degree low-pedestal pulse compression using cascade of single-mode fibers and an onlinear optical loop mirror

A high-degree low-pedestal pulse compression scheme is presented. The scheme is a three-step compression configuration. It employs an anomalously dispersive single-mode fiber (SMF) as the first compression stage. At the second stage, another anomalously dispersive SMF is used for further compression. After the first two stages of compression, the compressed pulses usually suffer from undesired pedestal generation due to soliton-effect compression. At the final stage, a nonlinear optical loop mirror (NOLM) is adopted for simultaneous compression and pedestal reduction. The numerical results show that the pulse can be effectively compressed through cascaded compression and its pedestal can be efficiently suppressed by the NOLM. The three-stage pulse compression with a NOLM can improve the compressed pulse quality compared to that without a NOLM. The proposed pulse compression method can achieve high-degree low-pedestal pulse compression and provides a feasible and a much simpler design in practice.

Ultra-short pulses in optical fibers with complex parameters

A theory is presented to show the analytic expression of ultra-short pulses existing in a non-instantaneous-response optical fiber with complex parameters. The analytical investigations show that the explicit solitary solutions can be found in form of Jacobi elliptic functions when the imaginary parts of the parameters fulfill a linear relationship. It is found that the single Jacobi elliptic function solutions have two free parameters while hybrid Jacobi elliptic function solutions have only one free parameter.

Simulated annealing method for material parameter extraction with terahertz time-domain spectroscopy

A simulated annealing method for material parameter extraction with terahertz time-domain spectroscopy is introduced to improve the common extraction method. The simulated annealing method seeks the global minimum of the error function to obtain material constants where the characterized material is not constrained by a certain boundary condition. It is shown from the research results that more accurate material parameters can be acquired to meet the actual requirements of material analysis by use of the simulated annealing method.

All-Optical Switches and Y-junction Waveguides Based on the Perpendicular Collisions of Photoisomerization Solitons

A theory is presented to investigate the perpendicular collisions of photoisomerization solitons in a polymer. Some interesting results such as soliton collapse and soliton junction are found by choosing the proper power ratio and relative phase between the signal beam and the pumping beam. The relevant experimental setups are also proposed. These novel results are potoentially useful in forming all-optical switches and Y-junction waveguides.