• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.674-679
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• 2003

We fabricated erbium-doped fiber ring laser with a new structure that can operate in C- & L-band wavelength region. The wave-length of the laser can be tuned continuously over 102 nm between 1510.4-1612.6 nm by insertion of the fiber Fabry-Perot tunable filter (FFP-TF) in the ring cavity. By use of the wavelength tunable characteristics of our fiber laser, we measured absorption spectra of more than fifty transition lines of the acetylene ($^{13}$ C$_2$H$_2$) molecule with high signal to noise ratio (SNR).

• Korean Journal of Optics and Photonics
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• v.28 no.6
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• pp.346-350
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• 2017

A tunable filter incorporating an apodized grating with a high-refractive-index polymer layer is demonstrated. In the apodized tunable filter, the reflectivity is decreased compared to that of a uniform grating, because of the gradually decreased grating depth. To increase the reflectivity of the apodized grating, a polymer of high refractive index is adopted for the apodized grating, and then high reflectivity is obtained while maintaining a narrow bandwidth. The apodized tunable filter exhibits a 3-dB bandwidth of 0.51 nm and a 20-dB bandwidth of 1.05 nm, with 98.5% reflection.

• Proceedings of the Optical Society of Korea Conference
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• 1996.09a
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• pp.66-66
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• 1996

• Korean Journal of Optics and Photonics
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• v.20 no.4
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• pp.217-222
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• 2009

In this paper, a low-cost hybrid-integrated tunable laser is realized using a polymer-ring resonator-based add/drop filter reflector and a reflective semiconductor optical amplifier. The add/drop filter reflector, composed of a double-ring resonator with different radii, can have characteristics of selective wavelength reflection and wide wavelength tuning with an aid of vernier effect derived from the radii difference. By hybrid-integrating the reflective semiconductor optical amplifier with the add/drop filter reflector, a tunable laser can be realized through an active alignment method. The hybrid laser exhibited a single mode lasing with side mode suppression ratio of 26 dB and full width half maximum of 0.03 nm. In addition, applying a low current as small as 25 mA onto electrodes over add/drop filter reflector, a wavelength tuning range of 17 nm could be obtained.

• Current Optics and Photonics
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• v.3 no.2
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• pp.111-118
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• 2019

The optical characteristics of a tunable flattened-pass-band fiber comb filter, based on the polarization-diversified loop configuration, are investigated using the $Poincar{\acute{e}}$-sphere representation. In the design process, the spectral flatness is checked quantitatively, and the tunability of the pass band is demonstrated experimentally. Theoretical calculations show that the filter also exhibits desirable dispersion and polarization properties. The orientation angles of rotatable wave plates for the wavelength tunability of the filter are obtained. Furthermore, we elaborate on the multiple angle loci produced by degeneracies through the combination of optical elements within the loop of the filter.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.36-42
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• 2008

Implementation of a wavelength-swept source with constant tuning rate adopting a PZT-type tunable filter, requires the knowledge of hysteresis of the filter used. The hysteresis must be considered to avoid any degradation in resolution of the optical frequency domain reflectometry (OFDR) system. An optical spectrum analyzer (OSA) could be used to do the hysteresis measurement, but its measurement time is too long for the high-speed driving conditions for the filter. We proposed a new hysteresis measurement method based on OFDR, which could measure the hysteresis in a real driving condition. A hysteresis measurement apparatus consisted of wavelength-swept source, interferometer, signal processing unit, and PC program is built and used to do the measurement. It is concluded that the new method is useful in the measurement of hysteresis at real driving conditions by successfully implementing a swept-wavelength source whose wavelength change is linear in time.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.3
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• pp.39-44
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• 2004

Fiber Bragg grating sensors are fabricated by core index modulation using UV laser and phasemask. Bragg wavelength of the grating is changed by the external strain. In this paper, a signal processing system of fiber Bragg grating sensor has studied in the optical wavelength domain. The system is based on the sweep semiconductor light source that consists of SLD, F-P tunable filter and etalon filter. The hysteresis effects of PZT in the F-P tunable filter are compensated. The long term measurement stability is obtained by controlling the temperature of F-P tunable filter and the SLD. We compare the strain data from fiber Bragg grating sensor and that from strain gauge at concrete hume pipe. We also get very good results for the long gauge displacement using fiber Bragg grating sensor which are identical to the data with short gauge length ordinary displacement sensor.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.6
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• pp.58-64
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• 1997

The wavelengt lockin gsystem of the optical fabry-perot filter theoretially derived and experimentally realized by using the ithering method in order to compensate the laser wavelength drift increasing the BER of the WDM system. The deviation between the laser wavelength and the optical filter center wavelength is compensated by applying a suitable voltage to the PZT. Accordingly, the laser wavelength selected by the fabry-perot filter always maintains the condition of maximum transmission powr. A wavelength locking system has been demonstrated using a fiber fabry-perot filter with a free spectral range of 80nm and an FWH of 1nm. The voltages of the sine wave generated for dithering was 20mV and 10mV, the frequency was 2kHz and center wavelength of the tunable laser was 1550nm. In this paper, the locking system have 20ms of locking time and 2nm of locking range.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.5
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• pp.15-24
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• 1997

We propose a tunable add/drop filter in a form of an all-fiber mach-zehnder interferometer iwth one bragg grating at each arm. This device can be tuned by inducing a strain in the bragg grating. We also theoretically analyze the outut characteristics of the tunable add/drop filter. As a result of simulation, we know that the proposed tunable add/drop filter works well. When 2*10$^{-3}$ of strain is induced, the reflected spectrum shifts about 3nm. And its reflected spectral width is about 0.3nm. In this case roughly 5 channels can be tuned, assuming the channel spacing is 0.3nm. When the pathlengths of the both arms are not the same, the transmissivities at the add and output ports and the reflectivity at the tap port varies sinusoidally with the pthlength difference. To maintain the transmissivities above 90% in the wavelength tuning range of 20nm the pathlength difference less than 16.mu.m is required.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.607-612
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• 2004

Spectral resolution enhancement method of Acousto-Optic Tunable Filter (AOTF) using incident light angle variation is described. AOTF is a small, mechanically rigid, high speed and spectral resolution light tunable filter. The basic theory of AOTF and its experimental verification is described. AOTF can generate two opposite polarized light simultaneously which wavelength can be changed by incident angle variation. We focused on the common region of two filtered light at the specific incident angle. This region can be used to enhance the spectral resolution of AOTF.