Hyungwoo Kwon

Polarizing properties of optical coupler composed of single mode side-polished fiber and multimode metal-clad planar waveguide

Abstract We report the experimental results for the polarizing properties of an optical coupler made of a single mode side-polished fiber and multimode metal-clad planar waveguide. The experimental results show that the large birefringence of a metal-clad planar waveguide facilitates the effective separation of TE and TM polarization in the spectral domain. Furthermore, through proper control of the planar waveguide parameters, the coupler can be used as either a TE-pass or TM-pass polarizer within a large spectral window (>130 nm). We present an approximated analytical method to calculate resonant wavelengths and demonstrate its validity experimentally.

Tunable gain-flattening filter using microbending long-period fiber gratings

A new type of gain-flattening filter using microbending long-period fiber gratings is presented. The fabrication and characterization of the device are described and its use in an erbium-doped fiber amplifier to flatten the amplified spontaneous emission (ASE) spectrum is demonstrated. The result shows that the ASE variation is less than 1 dB over 33 nm at two different pump powers of 45 and 68 mW.

Performance of a Distributed Simultaneous Strain and Temperature Sensor Based on a Fabry-Perot Laser Diode and a Dual-Stage FBG Optical Demultiplexer

A simultaneous strain and temperature measurement method using a Fabry-Perot laser diode (FP-LD) and a dual-stage fiber Bragg grating (FBG) optical demultiplexer was applied to a distributed sensor system based on Brillouin optical time domain reflectometry (BOTDR). By using a Kalman filter, we improved the performance of the FP-LD based OTDR, and decreased the noise using the dual-stage FBG optical demultiplexer. Applying the two developed components to the BOTDR system and using a temperature compensating algorithm, we successfully demonstrated the simultaneous measurement of strain and temperature distributions under various experimental conditions. The observed errors in the temperature and strain measured using the developed sensing system were 0.6 °C and 50 με, and the spatial resolution was 1 m, respectively.

Narrowband LPFG filter based on a pair of fiber deformers

Summary form only given. Long period fiber gratings (LPFG) are attractive fiber optic devices which have various applications such as gain flattening filters in fiber amplifiers, band rejection filters, mode converters, sensors, etc. The fabrication processes of photoinduced LPFG have been well-established but usually require expensive equipment. The periodic fiber bending technique, which was first demonstrated for mode conversion in a dual mode optical fiber, has been attempted as an alternative to a photoinduced LPFG. The advantageous feature of an LPFG using periodic fiber deformation is its extremely simple fabrication process and coupling strength independent properties of resonant wavelengths. In this paper, we propose a new type of narrowband fiber filter using two identical fiber deformers; connected in series.

Development of a Handheld Line Information Reader and Generator for Efficient Management of Optical Communication Lines

A handheld line information reader and a line information generator were developed for the efficient management of optical communication lines. The line information reader consists of a photo diode, trans-impedance amplifier, voltage amplifier, microcontroller unit, display panel, and communication modules. The line information generator consists of a laser diode, laser driving circuits, microcontroller unit, and communication modules. The line information reader can detect the optical radiation field of the test line by bending the optical fiber. To enhance the sensitivity of the line information reader, an additional lens was used with a focal length of 4.51 mm. Moreover, the simulation results obtained through BeamPROP® software from Synopsys, Inc. demonstrated a stronger optical radiation field of the fiber due to a longer transmission wavelength and larger bending angle of the fiber. Therefore, the developed devices can be considered as useful tools for the efficient management of optical communication lines.

Tunable gain-flattening filter using long-period fiber grating based on periodic core deformation

A new type of gain-flattening filter using long-period fiber gratings (LPFGs) based on periodic microbends is presented. The fabrication and characterization of the device are described and its use in an erbium-doped fiber amplifier (EDFA) to flatten the ASE spectrum is demonstrated. This filter, which is simple and inexpensive, exhibits the unique advantages of being tunable, erasable, and reconfigurable. The result shows that the gain variation over the wavelength range 1525 to 1560nm is less then 1dB when pumped with 45mW and 40mW of pump power at 980nm from a laser diode.

Measurement of Brillouin Backscattering for Distributed Temperature Sensor Applications

We present measurements of the Brillouin frequency shift in an optical fiber using a 1550 nm distributed feedback laser diode(DFB-LD) as a light source. By modulating the probe light with an electro-optic modulator, we confirm the stimulated Brillouin gain spectrum(BGS) and spontaneous BGS using the coherent detection method. We also confirm the applicability of the technique to distributed temperature sensors that measure the change in Brillouin frequency shift due to temperature variations.