Biomedical subjects
Publications and source records attributed to Yoonchan Jeong.
An Er:Yb codoped fiber amplifier chain for the generation of pulses for coherent lidar applications at a wavelength near 1.5 microm is reported. The final 1.8-m-long power amplification stage had a 50-microm core diameter and yielded a 23-dB energy gain, resulting in 0.29-mJ, 100-ns pulses at a repetition rate of 4 kHz with no Brillouin scattering and an M2 of 2.1.
We have demonstrated an ultrashort-pulse Yb3+-fiber laser and amplifier system that produces >400-nJ pulses at a repetition rate of 62 MHz (>25-W average power). The output pulses were recompressed to a duration of 110 fs with good pulse quality by use of a standard bulk grating-based compressor.
We propose the remote multiplexing of holograms with random patterns from a multimode fiber bundle used as the reference beams. The random pattern reference beam is characterized by the superposition and concatenation of propagation modes of multimode fiber and free space. For angle, shift, and wavelength remote multiplexing we compare two methods of laser coupling to the fiber bundle, i.e., direct coupling and lens coupling. A theoretical discussion that uses mode orthogonality is provided to describe multiplexing characteristics, and the theory is verified by experimental results. These remote-multiplexing methods can be applied to general multimode waveguide arrays for construction of compact and integrated optical systems in which multiplexing can be controlled remotely.
We calculate the modal power distribution of a randomly and linearly polarized (LP) multimode beam inside a cylindrical fiber core from knowledge of spatial-intensity profiles of a beam emitted from the fiber. We provide an exact analysis with rigorous proofs that forms the basis for our calculations. The beam from the fiber end is collimated by a spherical lens with a specific focal length. The original LP-mode basis is transformed by the spherical lens and forms another orthogonal basis that describes the free-space beam. By using this basis, we calculate the modal power distribution from the mutual-intensity profile. This is acquired by adopting a well-known mutual-intensity-profile-retrieving technique based on measurements of the intensity patterns several times after two orthogonal cylindrical lenses with varying separation. The feasibility of our decomposition algorithm is demonstrated with simulations.
The polarization-dependent transmission of light through an electrically controllable in-line-type polarizer that is made from polymer-dispersed liquid-crystal spliced optical fibers is discussed experimentally and theoretically. This in-line-type optical splicing method has the advantage of low transmission loss when it is applied in optical fiber communication systems. An anomalous diffraction approach is used to compute the scattering cross section of polymer-dispersed liquid-crystal droplets. The experimental results are supported by a theoretical analysis. This device can be employed in electrically controllable in-line-type polarizers and has the potential to yield electrically controllable polarization-dependent loss compensators.
We demonstrate a multimode-fiber bundle reference scheme in a photorefractive volume hologram and discuss its angular/spatial selectivity both experimentally and theoretically. We measure the angular/spatial selectivity, changing distances between the photorefractive crystal and the output facet of the multimode-fiber bundle. The distance variation leads to a beam-size change in the reference beam, however, the object-beam size was fixed in all cases. The dependence of the angular/spatial selectivity for random-pattern (RP) referencing on a hologram dimension was examined and the characteristics compared with those derived from Gaussian referencing. Experimental results show that the RP referencing makes little contribution to the enhancement in angular selectivity, even though it leads to a considerable enhancement in spatial selectivity. The angular selectivity is mainly dependent on the dimension of a volume hologram, even with RP referencing. It is also noteworthy that the use of an RP beam can cause some high-frequency noise in the angular-multiplexing regime, which should be avoided in a hologram memory system. Nonetheless, the spatial selectivity of the RP referencing shows nearly no dependence on hologram dimension, and is mainly dependent on the transversal speckle size of the random-pattern beam. These characteristics can also be verified by the numerical results presented here, which are in good agreement with the experimental results.
The characteristics of short-period blazed fiber Bragg gratings for use as macro-bending sensors are discussed. This sensor is able to detect macro bending with the transmitted power variation of the first side mode in the blazed fiber Bragg grating. Since an incident ray experiences different variations of tilt angles with respect to bending direction, the blazed fiber Bragg grating has different coupling efficiencies of the first side mode, which can be reduced considerably in the case of twisted blazed fiber Bragg gratings.