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Active gain fiber is a critical component to realize fiber laser sources for various applications such as cutting, welding and other material processing. To meet the requirement for various laser applications, the power scaling of fiber lasers is still concern, where active gain fiber is very important. There are several fabrication technologies for active fibers with low NA, large core diameter and high absorption, which characteristics for high power lasers are typically required. Here, novel fabrication technology based on VAD (Vapor Axial Deposition) for active fibers is introduced.

We demonstrated a novel intensity-modulated interrogation system for an identical weak fiber Bragg grating (FBG) array based on a resonance frequency mapping technique. To compensate for the signal depletion phenomenon because of the increased reflection number of identical weak FBGs, a gain-flattening technique is employed based on the intensity modulation of the applied driving current in the optical fiber laser sensor cavity. Over 60 identical FBGs can be efficiently interrogated by detecting the resonance frequency of each FBG for a distinguished peak position.

We demonstrated the novel quasi-distributed optical fiber sensor with tens of cm spatial resolution based on the wavelength-division resonance frequency mapping technique. To interrogate a weak fiber Bragg grating (FBG) array with a reduced interval length below ~1 m, a wavelength-division optical delay system was employed to separate the adjacent reflections. In our scheme, the sensing head consists of three Bragg wavelengths in the FBG series, which are repeatedly located 15 times along the optical fiber. Thus, 45 weak FBGs can be successfully interrogated using three channels without decreasing the dynamic range of the measured strain or temperature.

Chromatic confocal microscopy (CCM) has been intensively developed because it can exhibit effective focal position scanning based on the axial chromatic aberration of broadband light reflected from a target. To improve the imaging speed of three-dimensional (3D) surface profiling, we have proposed the novel concept of swept-source-based CCM (SS-CCM) and investigated the usefulness of the corresponding imaging system. Compared to conventional CCM based on a broadband light source and a spectrometer, a swept-source in the proposed SS-CCM generates light with a narrower linewidth for higher intensity, and a single photodetector employed in the system exhibits a fast and sensitive response by immediately obtaining spectrally encoded depth from a chromatic dispersive lens array. Results of the experiments conducted to test the proposed SS-CCM system indicate that the system exhibits an axial chromatic focal distance range of approximately 360 μm for the 770–820 nm swept wavelength range. Moreover, high-speed surface profiling images of a cover glass and coin were successfully obtained with a short measurement time of 5 ms at a single position.

VAD technology for laser fibers are offering the extremely large rare-earth doped core, which makes it possible to improve the productivity and reproducibility of laser fibers. At the previous report, Yb:Ce co-doped fibers have shown relatively large background loss and the issues of surface crystallization. In this report, the additional process development for the reduction of the loss and the efficiency improvement has been successful. Based in that, Yb:Ce codoped aluminosilicate PM fiber has been fabricated and it used for power amplification of narrow linewidth source. The slope efficiency was 72.8% w.r.t the absorbed pump power and the output power has been reached to 124W at the initial experiment. The further power scaling will be performed and SBS characterization will be reviewed.

In this study, Cylindrical Diffusing Optical Fiber Probe (CDOFP) is used for tumor treatment using Photolon-based photodynamic therapy induced apoptosis and necrosis in thyroid papillary carcinoma (BCPAP) cells. In conclusion, owing to multiple advantageous properties of Photolon as a PDT agent, including preferential accumulation in tumor, biodegradability and unprecedented photosensitizer packing, we evaluate Photolon mediated PDT as a minimally invasive, tumor specific treatment for thyroid cancer. the Photolon-PDT inhibited the growth of human papilloma thyroid cancer cells and effectively decreased xenograft tumor progression in both 10mm and 15mm diffusing length probe. Therefore, this study preliminarily suggests the use of CDOFP and Photolon-PDT for more effective treatment of human thyroid cancer.

Accurately predicting the peak wavelength and intensity of the electroluminescence spectrum through the photoluminescence method which can be measured without connecting electrodes is not only practically important for the development of micro-LEDs that cannot be fully inspected for device development, but there is also a fundamental importance in understanding the light emitting mechanism of the LEDs. In this study, the correlation and detailed mechanism between PL and EL are systematically analyzed by considering the effects of carrier escape, carrier accumulation, applied bias, leakage current, incident light wavelength and light absorption in order to provide a clear path for all-optical inspection of light emitting diodes and complete understanding of the luminescence mechanism in GaN-related quantum wells.

VAD technology has been proposed for laser fiber fabrication to improve its productivity and reproducibility. Rare-earth ion, Yb3+ has been incorporated with Ce3+ and Al3+ by the conventional solution doping process. In order to obtain a transparent Yb-doped core rod, the pre-sintering and consolidation process for the large volume of silica soot deposited by VAD has been significantly investigated. In addition, 20/400μm Yb-doped fiber with octagonal cladding has been fabricated. The cladding absorption was 0.44dB/m at 915nm, which corresponds to ~ 0.2mol% of Yb concentration and the slope efficiency with respect to absorbed pump power at 976nm was 66.7%.

In this study, cylindrical diffusing optical fiber probe (CDOFP) used for tumor treatment using PDT method is developed and analyzed. Diffusing beam profile of 5mm to 40mm tip length probe is produced and analyzed using laser scribing equipment developed in a previous research. Ball tip at the tip of CDOFP was developed for easier infiltration of tissues and the beam profile of such tip is reviewed. Additionally, CDOFP for PDT tumor treatment was used for laser coagulation test on animal tissue. CDOFP with diffusing tip length 5mm and 15mm was infiltrated inside a cow's liver tissue to process laser coagulation test. Coagulation and thermal damage was measured with twice the maximum intensity of laser, where maximum intensity in-vivo test is 1W 200J.

We have proposed the systematic measurement of coating geometry for specialty fibers based on dark field illumination technique. The measured dark-field projection image shows clear interfaces between different refractive index materials. Using own developed image processing tool, the interfaces automatically detected and analyzed. Every degree of measurements provides circularity of each layer and then shows the center point of individual layer. Using this technique, coating diameter, coating non-circularity and coating ellipticity for double clad fiber were successfully measured and high resolution camera also detected some of existing coating defect and delamination.

This paper proposes the development of cylindrical diffusing optical fiber probe (CDOFP), which possesses a flexible structure and solidity apt to treat cancer during photo-dynamic therapy (PDT). The cylindrical diffusing tip of CDOFP is made from a laser processing system with homogeneity and precision. We fabricated and characterized CDOFP to investigate its clinical feasibility and other possible applications of light therapy using the diffusing optical fiber.

The excessive memory access required to perform motion compensation when decoding compressed video is one of the main limitations in improving the performance of an H.264/AVC decoder. This paper proposes an H.264/AVC decoder that employs three techniques to reduce external memory access events: efficient distribution of reference frame data, on-chip cache memory, and frame memory recompression. The distribution of reference frame data is optimized to reduce the number of row activations during SDRAM access. The novel cache organization is proposed to simplify tag comparisons and ease the access to consecutive 4x4 blocks. A recompression algorithm is modified to improve compression efficiency by using unused storage space in neighboring blocks as well as the correlation with the neighboring pixels stored in the cache. Experimental results show that the three techniques together reduce external memory access time by an average of 90%, which is 16% better than the improvements achieved by previous work. Efficiency of the frame memory recompression algorithm is improved with a 32x32 cache, resulting in a PSNR improvement of 0.371dB. The H.264/AVC decoder with the three techniques is fabricated and implemented as an ASIC using 0.18µm technology.