Jau-Sheng Wang

Preform fabrication and fiber drawing of 300 nm broadband Cr-doped fibers

The fabrication of a Cr-doped fiber using a drawing-tower method with Cr:YAG as the core of the preform is presented. The Cr-doped YAG preform was fabricated by a rod-in-tube method. By employing a negative pressure control in drawing-tower technique on the YAG preform, the Cr-doped fibers with a better core circularity and uniformity, and good interface between core and cladding were fabricated. The amplified spontaneous emission spectrum showed a broadband emission of 1.2 to 1.6 mum with the output power density about a few nW/nm. The results indicate that this new Cr-doped fiber may be used as a broadband fiber amplifier to cover the bandwidths in the whole 1.3-1.6 mum range of low-loss and lowdispersion windows of silica fibers.

Development of Broadband Single-Mode Cr-Doped Silica Fibers

The fabrication of broadband single-mode Cr-doped silica fibers (SMCDSFs) using the fiber drawing-tower method with the modified rod-in-tube technique is demonstrated for the first time. A single-mode characteristic of SMCDSF was observed when the propagation wavelengths were longer than 1310 nm. The transmission loss was about 8 dB/m at 1550 nm. The successful fabrication of SMCDSFs may facilitate the possibility for utilizing the SMCDSFs as a new generation broadband fiber amplifier to cover the bandwidths in the whole 1300- to 1600-nm range of low-loss windows of silica fibers.

Broadband Chromium-Doped Fiber Amplifiers for Next-Generation Optical Communication Systems

We report the first experimental breakthrough of a net gain of optical signals in a broadband chromium-doped fiber amplifier (CDFA) for next-generation optical communication systems. Current fiber amplifiers, including commercial erbium-doped fiber amplifier, cover only a relatively small portion of the entire transmission bandwidths (1300-1600 nm) of the low-loss windows of silica fibers. The newly developed CDFAs have opened up the possibility of utilizing the 300-nm entire spectrum of the low-loss fibers to further increase the transmission capacity. In this paper, we present the experimental demonstration of a net gain of 1.2 dB employing gain enhancement technique. With the help of an optical-fiber system examination for the CDFA, a 40-Gb/s error-floor free data transmission was successfully demonstrated by realizing the high-speed transmission of signal with gain through the chromium-doped fibers (CDFs). Further gain improvement in the CDFAs employing few-mode or single-mode CDFs will be presented and discussed.

Thermal-Stability Comparison of Glass- and Silicone-Based High-Power Phosphor-Converted White-Light-Emitting Diodes Under Thermal Aging

The lumen degradation, chromaticity shift, transmittance loss, and mean-time-to-failure (MTTF) evaluation in glass- and silicone-based high-power phosphor-converted white-light-emitting diodes (LEDs) (PC-WLEDs) under accelerated thermal aging at 150 °C, 200 °C, and 250 °C are presented and compared. The silicone-based PC-WLEDs exhibited less thermal stability than the glass-based PC-WLEDs by 1.86, 2.79, and 4.76 times higher lumen losses, 3.05, 3.26, and 6.84 times larger chromaticity shifts, and 1.82, 2.62, and 6.67 times greater transmittance losses at 150 °C, 200 °C, and 250 °C, respectively. The results also showed that the glass-based PC-WLEDs exhibited higher MTTF than the silicone-based PC-WLEDs by 20 times at room temperature. The peaks of the emission and excitation spectra for both silicone and glass phosphors were not significantly changed after thermal aging, evidenced by fluorescence spectrophotometer analyses. This indicated that the fluorescent ability of Ce:YAG-doped phosphor materials did not change after thermal aging and the transmittance loss was corresponding to the lumen loss and chromaticity shift. The results of the lumen loss, chromaticity shift, transmittance loss, and MTTF investigations clearly demonstrated that the thermal-stability performance of the glass-based PC-WLEDs was better than that of the silicone-based PC-WLEDs. The advantage of employing doped glass encapsulation in high-power PC-WLEDs could be explained: The material property of glass transition temperature of 750 °C was higher than that of silicone transition temperature of 150 °C. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to many applications where the LED modules with high power and high reliability are demanded for use in next-generation solid-state lighting.

Fabrication and characteristics of Cr-doped fibers employing powder-in-tube technique

The fabrication of Cr-doped fibers (CDFs) using fiber drawing-tower combined with non-silica powder-in-tube (PIT) technique to achieve the active application of chromium ions in fiber is demonstrated for the first time. The fluorescence enhancement, transmission loss, and few-mode operation are discussed in the paper. The success in fabrication of CDFs with PIT method may open the possibility for utilizing CDFs as broadband fiber light source.

Fluorescence enhancement in broadband Cr-doped fibers fabricated by drawing tower

The fluorescence enhancement in broadband Cr-doped fibers (CDFs) fabricated by a drawing tower with a redrawn powder-in-tube preform is proposed and demonstrated. The CDFs after heat treatment exhibited Cr⁴⁺ emission enhancement with spectral density of 200 pW/nm, verified by the formation of α-Mg₂SiO₄ nanocrystalline structures in the core of CDFs. The high fluorescence achievement in the CDFs is essential to develop a broadband CDF amplifier for next-generation optical communication systems.

Additional wavelength shift of peak gain due to inhomogeneous distributions of carriers inside semiconductor lasers

According to the traveling wave rate equations, the carrier density inside a semiconductor laser is position dependent. This will introduce an additional wavelength shift for the radiation that experiences the largest gain. Analysis has led to the establishment of the relationship between the shift and the mean square deviation of the carrier density from its mean. Calculations show that under certain circumstances the shift may approach the order of 10/sup -1/ nm.<<ETX>>

Few-Mode Cr-Doped Crystalline Core Fibers for Fiber Amplifier

A few-mode Cr-doped crystalline core fiber (FMCDCCF) is demonstrated. The fiber fabrication is a modified laser-heated pedestal growth (LHPG) technique that consists of over cladding a Cr:YAG crystal rod with silica and then fine tuning its core size with multiple core reduction through the LHPG system. The FMCDCCF exhibits a core diameter of 2 μm and a V-value around 3.77 to provide the few-mode characteristics. The optical properties of the FMCDCCF are similar to that of a pristine Cr4+:YAG crystalline. A gross gain of the FMCDCCF is measured around 2.3 dB at a wavelength of 1.4 μm.

Fabrication and characteristics of ultra-broadband singlemode Cr-doped fibers

The fabrication of ultra-broadband singlemode Cr-doped fibers (SMCDFs) using fiber drawing-tower method is demonstrated for the first time. The success in fabrication of SMCDFs may open the possibility for utilizing SMCDFs as ultra-broadband fiber amplifiers.

Optical Fiber Coupler With a Hollow Core Fiber for Magnetic Fluid Detection

A new type of optical fiber coupler composed of a conventional solid core fiber and a hollow core fiber (HCF) is proposed. The hollow core of the HCF can be filled with various functional liquids and thus provides flexibility in tuning the guiding properties of photons. This enables the proposed coupler to be used as a versatile fiber sensing device. The experimental results revealed its sensitivity to be 73 000 nm/RIU. Compared with a vibrating sample magnetometer with a sensitivity of 10-7 emu and accuracy of ± 1% in the magnetic sensing, the new fiber coupler was estimated to have a higher sensitivity of 2.4 × 10-10 emu and an accuracy of ± 1.3 × 10-2% under an optimal performance condition in a conventional optical spectrum analyzer.