Fiber-bundle illumination: realizing high-degree time-multiplexed multifocal multiphoton microscopy with simplicity.

High-degree time-multiplexed multifocal multiphoton microscopy was expected to provide a facile path to scanningless optical-sectioning and the fast imaging of dynamic three-dimensional biological systems. However, physical constraints on typical time multiplexing devices, arising from diffraction in the free-space propagation of light waves, lead to significant manufacturing difficulties and have prevented the experimental realization of high-degree time multiplexing. To resolve this issue, we have developed a novel method using optical fiber bundles of various lengths to confine the diffraction of propagating light waves and to create a time multiplexing effect. Through this method, we experimentally demonstrate the highest degree of time multiplexing ever achieved in multifocal multiphoton microscopy (~50 times larger than conventional approaches), and hence the potential of using simply-manufactured devices for scanningless optical sectioning of biological systems.

Long distance fiber Bragg grating strain sensor interrogation using a high speed Raman-based Fourier domain mode-locked fiber laser with recycled residual Raman pump.

We propose a novel fiber Bragg grating (FBG) sensor interrogation using a Raman-based Fourier-domain mode locking (FDML) fiber laser for a high speed and long distance measurement. A residual Raman pump after the generation of the Raman-based FDML fiber laser is recycled for secondary signal amplification in a 2-m erbium-doped fiber (EDF) to further enhance the output power. The chromatic dispersion is precisely controlled to suppress the phase noise in the FDML laser cavity, resulting in the improvement of an R-number of 1.43 mm/dB. After recycling residual pump, we achieve the 40-km round trip transmission of the sensing probe signal with a high scan rate of 30.8 kHz. With 205-mW residual pump power, the bandwidth and the maximum gain are measured to be more than 50 nm, 10.3 dB at 1550 nm, respectively. The sensitivity of the proposed Raman-based FDML fiber laser to strain is also measured, which are 0.81 pm/µstrain in the spectral domain and 0.19 ns/µstrain in the time domain, respectively.

Tunable dispersion slope compensator using two uniform fiber Bragg gratings mounted on S-shape plate.

We propose and experimentally demonstrate a novel method for tunable dispersion slope compensation. We use two uniform fiber Bragg gratings (FBGs), a spatially designed S-bending stage and 4-port circulator. Two FBGs are mounted on each surface of a metal plate along the calculated quadratic curve. The dispersion slope (DS) can be tuned by adjusting a nonlinear strain along two uniform FBGs without changing second order dispersion as well as the central wavelength. In the experiment, a DS tuning range from -13.9 to -54.8 ps/nm(2) is achieved with the bandwidth of larger than 2.0 nm.