Yongmin Jung

Novel hollow optical fibers and their applications in photonic devices for optical communications

Novel photonic devices based on a new type of waveguide, hollow optical fibers (HOF), are described. Utilizing unique three layered structure of HOF, the central air hole, germanosilicate ring core, and silica cladding along with its adiabatic mode transformation capability we demonstrated versatile applications in short-haul, long-haul optical communications, and tunable wavelength selective devices. Detailed design parameters, fabrication arts of the fibers, and operation principles of the devices are discussed.

Optical probe based on double-clad optical fiber for fluorescence spectroscopy

We report an optical probe based on a single double-clad fiber (DCF), which is suitable for fluorescence spectroscopy. The excitation light is delivered through the small diameter core of the DCF and the excited fluorescence light is collected by the large diameter inner cladding of the same fiber. To retrieve the signal beam from the inner cladding, we utilize a DCF coupler that couples only the light beams in the inner claddings of two different pieces of DCF. It was found that the separation of the channel for the excited beam from the channel for the excitation beam in the same piece of fiber could diminish the autofluorescence background noise generated by the fiber itself, while maintaining all the benefits of a single-fiber probe system. The usefulness of the DCF probe and the performance of the DCF coupler are then reported by presenting the fluorescence spectrum of a fresh gingko leaf and comparing it with the spectrum taken with conventional methods. The fabrication process of the DCF fiber and the inner cladding mode coupler for it are also presented.

Optical frequency-domain chromatic dispersion measurement method for higher-order modes in an optical fiber

We propose a new chromatic dispersion measurement method for the higher-order modes of an optical fiber using optical frequency modulated continuous-wave (FMCW) interferometry. An optical fiber which supports few excited modes was prepared for our experiments. Three different guiding modes of the fiber were identified by using far-field spatial beam profile measurements and confirmed with numerical mode analysis. By using the principle of a conventional FMWC interferometry with a tunable external cavity laser, we have demonstrated that the chromatic dispersion of a few-mode optical fiber can be obtained directly and quantitatively as well as qualitatively. We have also compared our measurement results with those of conventional modulation phase-shift method.

Novel all-fiber optic temperature sensors based on hollow optical fibers

Novel all-fiber optic temperature sensors based on hollow optical fibers (HOFs) are presented. The HOFs with an air hole diameter of 8um at the center are fabricated through elaborate controls of MCVD and fiber drawing process. Two types of all-fiber temperature sensors are described. One is an all-fiber temperature sensor composed of a short HOF serially concatenated between a pair of long-period fiber gratings using a B/Ge-codoped core single mode fiber (SMF). The broadband pass-band tuning range of 84.3nm, covering both S and C band, is observed in the range from 25 to 215°C. Transmission peak is linearly shifted showing negative slope of -0.44nm/°C at 1500nm region. Its design, fabrication arts, and device integration are explained with characteristics of output filter spectrum and temperature tuning. The other is an in-line fiber etalon temperature sensor using a short HOF segment fusion-spliced between standard SMFs. This device is characterized in terms of wavelength shift according to temperature for HOFs with and without Ge-doped ring core. Temperature sensitivity of 3.38×10-5/°C and dynamic range of 20dB are observed over the range from 25 to 330°C at 1550nm. It is confirmed that the experimental results for both fiber optical sensors show a good agreement with theoretical analysis.

Mode Analysis and Modal Delay Measurement of a Few-Mode Fiber by Using Optical Frequency Domain Reflectometry

A novel mode analysis method and differential mode delay measurement technique for a multimode optical fiber based on optical frequency domain reflectometry has been proposed for the first time. We have used a conventional OFDR with a tunable external cavity laser and a Michelson interferometer. A few-mode optical multimode fiber was prepared to test our proposed measurement technique. The differential mode delay (DMD) of the sample fiber was measured to be 16.58 ps/m with a resolution of 1.5 ps/m. We have also compared the OFDR measurement results with those obtained using a traditional time-domain measurement method.

Cascaded microoptical waveguide on microactuating platform structure for high-power wideband variable optical attenuator applications

We present a novel cascaded two-stage microoptical waveguide (MOW) on microactuating platform (MAP) structure for applications in high-power ultrawideband variable optical attenuator (VOA). The device consists of a fused biconical taper (FBT) fiber coupler, which acts as a MOW, mounted on an electromechanical system MAP, where an axial stress over the waist of FBT coupler is precisely controlled by a piezoelectric transducer actuator. Cascaded two stages with complementary spectral responses were employed to enhance the spectral flatness and optical extinction ratio, which allowed the maximum attenuation over 60 dB at 1450 nm and a low spectral tilt of < 1 dB over 100 nm for 20-dB attenuation, as well as low polarization-dependent loss of < 0.07 dB. These VOA characteristics were maintained for optical power over 1 W.

P-159: Fiber-Optic Color Synthesizer

Fiber-optic color synthesis (FOCS) was achieved using a novel 3×1 hard polymer clad fiber (HPCF) coupler with red, green and blue primaries. With driving LED electronics, the device rendered micro circular pixel covering extended color gamut.

All-fiber maskless lithographic technology to form microcircular interference pattern on Azo polymer film

We report a novel all-fiber, maskless lithograpic technology to form various concentric grating patterns for micro zone plate on azo polymer film. The proposed technology is based on the interference pattern out of the cleaved end of a coreless silica fiber (CSF)-single mode fiber (SMF) composite. The light guided along SMF expands into the CSF segment to generate various circular interference patterns depending on the length of CSF. Interference patterns are experimentally observed when the CSF length is over a certain length and the finer spacing between the concentric rings are obtained for a longer CSF. By using beam propagation method (BPM) package, we could further investigated the concentric interference patterns in terms of intensity distribution and fringe spacing as a function of CSF length. These intereference patterns are directly projected over azo polymer film and their intensity distrubution formed surface relief grating (SRG) patterns. Compared to photoresist films azo polymer layers produce surface relief grating (SRG), where the actual mass of layer is modulated rather than refractive index. The geometric parameters of the CSF length as well as diameter and the spacing between the cleaved end of a CSF and azo polymer film, were found to play a major role to generate various concentric structures. With the demonstration of the circular SRG patterns, we confirmed that the proposed technique do have an ample potential to fabricate micro fresnel zone plate, that could find applications in lens arrays for optical beam formings as well as compact photonic devices.