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A Development Methodology for Heterarchical Control of Flexible Manufacturing Systems
한영근 한국경영과학회 1995 한국경영과학회 학술대회논문집 Vol.- No.1(2)
This paper presents a methodology for development of a heterarchical control system in Flexible Manufacturing Systems (FMS) environment. A Petri net based model is applied for development of control software. A real-time scheduling methodology for the heterarchical system is also developed and it is used as a software entity in the overall architecture. The partition of generic and specific modules in control software development is emphasized. The control system performs its control tasks in two stages; (1) generation of generic control code and distribution of them to each controller entity prior to system execution; (2) generation of specific control code according to job arrival and its process plan. The control software and the scheduling algorithm are evaluated by a simulation program.
한영근 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.2
A multiwavelength erbium-doped fiber laser based on a nonlinear amplified loop mirror with a highly-nonlinear photonic crystal fiber was proposed and experimentally investigated. The performance of the nonlinear amplified loop mirror was improved by using a single 3-dB coupler and a highly-nonlinear photonic crystal fiber with a length of 100 m. The extinction ratio of the proposed multiwavelength erbium-doped fiber laser was measured to be more than 50 dB. The output power fluctuation was measured to be less than 0.5 dB. The output power difference among multiple peaks was measured to be less than 0.3 dB. A Lyot-Sagnac filter with two segments of polarizationmaintaining photonic-crystal fibers was employed as a multichannel filter, and the wavelength spacing was controlled by changing the polarization states within the Lyot-Sagnac filter. Two different wavelength spacings, 0.6 nm and 0.8 nm, were obtained. The number of channels was also changed:20 for ∆λ = 0.6 nm and 16 for ∆λ = 0.8 nm. In addition, a precisely-interleaved switching based on the proposed multiwavelength erbium-doped fiber laser was realized by changing the polarization states.
Thermally Tunable Multiwavelength Raman Fiber Laser Based on a Novel In-line Interferometer
한영근 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.42
A thermally tunable multiwavelength Raman fiber laser based on a simple in-line interferometer is investigated. A novel in-line interferometer is realized by using a single long-period fiber grating incorporating a core misalignment method. Cladding modes from the guided core mode are excited in the splicing point between two optical fibers when two core regions are misaligned. By removing an external buffer coating layer in the fiber, the cladding modes can be propagated and recoupled to the core mode at a long-period fiber grating. Since the long-period fiber grating couples the core mode to the cladding modes, the interaction between the core mode and the cladding modes induces an interference pattern, which realizes a multichannel filter. Since the transmission characteristics of the long-period fiber grating are effectively controlled by changing the applied temperature, a thermally tunable multichannel filter based on the proposed in-line interferometer can be obtained. When the proposed multichannel filter is inserted within the ring cavity of a Raman fiber laser, a multiwavelength Raman fiber laser is realized. A high extinction ratio of more than 40 dB is achieved. The output power is stable, and the power fluctuation is measured to be less than 0.7 dB, and the proposed multiwavelength Raman laser has a high thermal tunablity of -0.48 nm/℃.
Transmission Characteristics of Multiply-cascaded Phase-shifted Long-period Fiber Gratings
한영근 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.61
The transmission characteristics of multiply-cascaded phase-shifted long-period fiber gratings (LPFGs) are investigated theoretically and experimentally. By including the phase-shift in the middle of a LPFG, an optical filter, such as a bandpass filter can be realized. A wavelength shift of the passband occurs as the amount of phase shift in the middle of a LPFG changes. The bandwidth of the passband in the phase-shifted LPFG is changed by increasing the number of phase-shifted LPFGs. When two -shifted LPFGs with different lengths of gratings are cascaded in series, the bandwidths of the rejection band and the passband can be controlled by using the pristine characteristics of two gratings. We also analyze the transmission characteristics of multiplycascaded phase-shifted LPFGs theoretically by using a transfer matrix method.
한영근 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.3
We experimentally investigated a 320-Gbit/s (32 Chs × 10 Gbit/s) wavelength division multiplexed (WDM) transmission over 1.7 km of a bending-insensitive holey fiber with 10 turns of 5 mm in bending diameter. The holey fiber with a germanium-doped core and with one layer of air holes in the silica cladding region was fabricated by using the thermal expanding technique. The fabricated holey fiber had a low bending loss of less than 0.04 dB for a bending diameter of 5 mm. The 320-Gbit/s optical source consisted of 32 WDM channels with 100-GHz channel spacing in the C-band. After transmission over 1.7 km of the proposed bending-insensitive holey fiber, error free operation of all 32 channels at a bit error rate of 10-9 was achieved.