• Journal of the Optical Society of Korea
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• v.13 no.3
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• pp.349-353
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• 2009

We propose a simple in-line variable optical attenuator (VOA) based on the bending effect of tapered single mode fibers. The influence of the taper structure and the reflective index of the external medium surrounding the taper region on the bending loss of the tapered fiber have been investigated experimentally. An attenuation range exceeding 35 dB and a very low excess loss of < 0.2 dB at 1550 nm were achieved. The measured polarization dependent loss of the present VOA at the attenuation level of 10 dB, 20 dB, and 30 dB were 0.1 dB, 0.2 dB, and 0.5 dB, respectively.

• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.337-341
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• 2010

A high sensitivity fiber optic temperature sensor based on a side-polished fiber (SPF) coupled to a tapered multimode overlay waveguide (MMOW) is proposed and studied. Both tapered and non-tapered MMOW were considered to study the effect of tapering of MMOW on the characteristics of the device and to investigate the criticality of the uniformity of the multimode overlay waveguide over the SPF. Present study shows that tapering of the MMOW can be used to tune the desired wavelength range without any loss in the sensitivity. Sensitivity up to 9 nm/$^{\circ}C$ within the temperature range of 25 to $100^{\circ}C$ can be achieved with the proposed sensor, almost 6 times higher compared even to state-of-the-art high-sensitivity grating-based fiber optic temperature sensors.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.22-27
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• 2004

In this paper, we designed a mode size converter to reduce coupling loss between optical waveguide and single mode fiber. The proposed mode converter is composed of periodically segmented tapered waveguide to achieve small size and easy fabrication. For the optimally designed mode size converter at 1550nm, the taper length is 500(equation omitted), the segmentation period 5ß:, the waveguide width of fiber contact section 1.3ß:, and duty cycle 0.95. The coupling loss of the optimized mode size converter is 0.33㏈/point, which is 1.27㏈/point lower than that without the mode size converter.

• Journal of the Optical Society of Korea
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• v.2 no.2
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• pp.80-82
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• 1998

A new fiber coupling scheme using thermally over-expanded core(TOEC) fiber was proposed and demonstrated. In the coupling experiment between 1.3${\mu}{\textrm}{m}$ FP-LD and the proposed TOEC fiber with a tapered hemispherical microlens. superior performances such as a long working distance, a high coupling efficiency, and large misalignment tolerances were verified experimentally.

• Journal of the Optical Society of Korea
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• v.8 no.2
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• pp.90-95
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• 2004

The structure of Ti:LiNbO$_3$optical waveguide with a mode size far different from that of single mode optical fiber has been optimized by tapering the waveguide ends. This work was focused on determining the optimized sets of parameters for the fabrication of low-loss Ti indiffused optical waveguides in LiNbO$_3$. Numerical and analytical modeling were applied to simulate the guiding quality and to determine the mode sizes. Based on these modeling results, new waveguide structures with tapered ends have been defined, fabricated and characterized in the respect of the coupling of fiber to Ti-indiffused LiNbO$_3$waveguide.

• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.326-332
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• 2010

We review the research on specialty fiber couplers with emphasis placed on the characteristics that make them attractive for biomedical imaging, optical communications, and sensing applications. The fabrication of fiber couplers has been carried out with, in addition to conventional single mode fiber, various specialty fibers such as photonic crystal fiber, double clad fiber, and hole-assisted fiber with a Ge-doped core. For the fiber coupler fabrication, the side polishing and the fused biconical tapered methods have been developed. These specialty fiber couplers have been applied to optical coherence tomography, fluorescence spectroscopy, fiber sensors, and optical communication systems. This review aims to provide a detailed statement on the recent progress and novel applications of specialty fiber couplers.

• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.411-417
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• 2000

The waveguide structure effects of a spot-size converter (SSe) of a $1.3\mu{m}$ FP(Fabry-Perot)-LD(Laser Diode) were investigated. Its coupling efficiency and alignment tolerance with a single-mode fiber (SMF) were carefully examined by using a 3dimensional BPM (Beam Propagation Method). It was shown that the fOlmation of enough length of straightened waveguide around the end of the sse region can substantially improve the optical coupling efficiency for a vertically tapered sse. In contrast, a down-taper structure for a laterally tapered sse has superior characteristics to an up-tapered one. We suggested good sse structures which can provide a high coupling efficiency as well as a large alignment tolerance with an .SMF. .SMF.

• Journal of Navigation and Port Research
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• v.26 no.2
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• pp.235-243
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• 2002

Theoretical analysis have been performed to design the high power semiconductor laser for an optical sensor at 1.55${\mu}{\textrm}{m}$ wavelength range which is the lowest loss wavelength in optical fiber. The materials of active region and SCH were $Ln_{1-x}Ga_xAs_yP_{1-y}$. In order to use the light source of optical sensors, it has to satisfy wide spectral width and short coherence length. Therefore, in order to suppress lasing oscillation, we proposed laterally tilted PBH type with a window region. Also, tapered stripe structure was applied for high coupling efficiency into a single mode fiber. From these analyses, the devices of laterally tilted angled and bending structure were fabricated and their characteristics were measured. In the results of the measurement, the fabricated devices have sufficient output power and wide FWHM to apply to the light source of optical fiber sensors.

• ETRI Journal
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• v.38 no.4
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• pp.665-674
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• 2016

We designed and fabricated a semiconductor optical amplifier-integrated dual-mode laser (SOA-DML) as a compact and widely tunable continuous-wave terahertz (CW THz) beat source, and a pin-photodiode (pin-PD) integrated with a log-periodic planar antenna as a CW THz emitter. The SOA-DML chip consists of two distributed feedback lasers, a phase section for a tunable beat source, an amplifier, and a tapered spot-size converter for high output power and fiber-coupling efficiency. The SOA-DML module exhibits an output power of more than 15 dBm and clear four-wave mixing throughout the entire tuning range. Using integrated micro-heaters, we were able to tune the optical beat frequency from 380 GHz to 1,120 GHz. In addition, the effect of benzocyclobutene polymer in the antenna design of a pin-PD was considered. Furthermore, a dual active photodiode (PD) for high output power was designed, resulting in a 1.7-fold increase in efficiency compared with a single active PD at 220 GHz. Finally, herein we successfully show the feasibility of the CW THz system by demonstrating THz frequency-domain spectroscopy of an ${\alpha}$-lactose pellet using the modularized SOA-DML and a PD emitter.