• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.37 no.10
• /
• pp.51-56
• /
• 2000

An all fiber coupler-type add/drop filter has been fabricated by writing a Bragg grating in the coupling region of a fused fiber coupler. The fused fiber coupler with 99.8% coupling ratio and 74/m coupling coefficient was used for the add/drop filter. The add/drop filter shows 99% reflectivity and 83% drop efficiency at the operating wavelength of 1536.2nm.

• Journal of the Optical Society of Korea
• /
• v.9 no.4
• /
• pp.135-139
• /
• 2005

We demonstrate a simple and effective wavelength-tunable add/drop filter suitable for coarse wavelength division multiplexing (CWDM) systems. The filter consists of two fibers in contact side by side, with identical long-period fiber gratings (LPG) in each fiber. The LPG couples the power in the fundamental core mode to one of the cladding modes, which is then coupled to the same order cladding mode in the other fiber through evanescent-field coupling between two fibers. Finally, the cladding mode in the second fiber is coupled to its core mode with the help of the other LPG. With an optimal longitudinal offset distance of 10 em, coupling efficiency as high as -1.68 dB and side lobes smaller than -24 dB were experimentally obtained. The experimental results agreed well with the theoretical ones. The operating wavelength of the proposed add/drop filter was tunable by varying the temperature. The temperature sensitivity was measured to be -0.43 nm/$^{\circ}C$.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.29 no.10
• /
• pp.17-24
• /
• 2015

In this paper, we investigated the output polarization of a Lyot-type optical fiber comb filter based on a polarization-diversity loop structure. It was found that the output state of polarization (SOP) of the filter made a wavelength-dependent evolution, and the spectral periods of the output SOP variation in flat-top and lossy flat-top band modes were the channel separation of the filter and its half, respectively. For a certain input SOP, the filter could pass or reject specific spectral sections by adding and controlling an output analyzer. In particular, it was theoretically anticipated that the filter with the output polarizer could provide the fine continuous tuning of its pass band center in a wavelength range corresponding to the ${\pm}9.5%$ of channel spacing(0.8nm) when the input SOP was properly adjusted. It is expected that this tuning function can be effectively applied to suppress unwanted spectral portions in modulated optical signals.

• Journal of the Optical Society of Korea
• /
• v.17 no.4
• /
• pp.312-316
• /
• 2013

A novel fiber-optic sensor system is suggested in which fiber Bragg grating sensors are demodulated by a wavelength-sweeping fiber laser source and a spectrometer. The spectrometer consists of a diffraction grating and a 512-pixel photo-diode array. The reflected Bragg wavelength information is transformed into spatial intensity distribution on the photo-diode array. The peak locations linearly correspond to the Bragg wavelengths, regardless of the nonlinearities in the wavelength tuning mechanism of the fiber laser. The high power density of the fiber laser enables obtaining high signal-to-noise ratio outputs. The improved demodulation characteristics were experimentally demonstrated with a fiber Bragg grating sensor array with 5 gratings. The sensor outputs were in much more linear fashion compared with the conventional tunable band-pass filter demodulation. Also it showed advantages in signal processing, due to the high level of photo-diode array signals, over the broadband light source system, especially in measurement of fast varying dynamic physical quantities.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
• /
• v.8 no.2
• /
• pp.90-95
• /
• 2009

All-optical fiber-type gain flattening filer (GFF) for an EDFA (Erbium doped fiber amplifier) were fabricated by using a FBT (fiber biconical tapered) process and the performance of the GFF was tested and athermal package was proposed. Historically, the chief contributor to gain unevenness has been the EDFA. Due to the inherent gain response of the EDFA's operation, there is always a modest imbalance in the gain applied as a function of wavelength. FBT methods have been used to make fiber type couplers and WDM filter since 1980. Attractivity of this methods was simple, cost effective and thermal stability. Simulation program tool is made to design target GFF profile for this paper. Fiber coupler manufacturing machine is modified for the GFF process. The final GFF is obtained by cascading 4 unit filter that has 6 taper stage. Test result shows 1 dB of wavelength flatness in the C band. Polarization dependent loss is under 0.15dB. The center wavelength variation is below ${\pm}$0.35nm at the temperature range of $20^{\circ}C$ to $70^{\circ}C$.

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

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.23 no.10
• /
• pp.7-13
• /
• 2009

By incorporating a polarization beam splitter and fiber coupler, we propose a fiber-optic multiwavelength-switchable interleaving filter that can function as a polarizaiton-independent transmission or reflection-type one. The proposed filter consists of a polarizaiton beam splitter and a Sagnac birefringence loop that is composed of a 50:50 coupler, polarizaiton-maintaining fibers, and two quarter-wave plates. In the proposed filter, a transmission-type filter with a channel isolation > 18[dB] or a reflection-type one with a channel isolation ~3[dB], whose channel spacing and switching displacement were 0.8 and 0.4[nm] in common, respectively, could be obtained. Channel interleaving operation could be performed by the proper control of waveplates within the Sagnac birefringence loop.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.8 no.6
• /
• pp.1369-1375
• /
• 2007

The recent, a large capacity of telecommunication networks is required in order to it is in proportion to capacity of information communication increase and to satisfy a demand because of the demand about Internet, a multimedia service of internet, Video of internet protocol(VoIP), Audio/Video streaming. As a result, DWDM(Dense Wavelength Division Multiplexing)technologies are emerging to be a prevailing the method of solving it without additional optical fiber network building and high-speed equipment. Therefore this thesis proposed the optical filter of fiber/multilayer slab coupled structure combining it to multilayer slab waveguide by polishing the cladding of one side of fiber to design the optical filter having these functions. When a separation distance of fiber and slab was $3{\mu}m$, The optical filter proposed as the simulation result was satisfied with a DWDM filter characteristic with FWHM of 0.1nm on TM mode and TE mode as 32nm polarization independence in a communication window of $1.3{\mu}m$ when center wavelength was each ${\lambda}_0=1.274755{\mu}m$ and ${\lambda}_0=1.30591{\mu}m$.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.11 no.7
• /
• pp.1359-1366
• /
• 2007

The recent, a large capacity of communication is required in order to it is in proportion to capacity of information communication increase and to satisfy a demand because of the demand about Internet, a multimedia service of Video of internet protocol(VoIP), Audio/Video steaming. DWDM(Dense Wavelength Division Multiplexing) technique has been emerged as the method of solving it without additional optical fiber network building and hish-speed equipment. Therefore this thesis proposed the optical filter of fiber/multilayer slab coupled structure combining it to multilayer slab waveguide by polishing the cladding of one side of fiber to design the optical filter having these functions. The optical filter proposed as the simulation result satisfies DWDM filter characteristic; 1) when the separation distance between fiber and slab is $4.15{\mu}m$ at the communication window of $1.5{\mu}m$, the polarization independence is 65nm, 2) when the center wavelengths about TM mode and TE mode are each ${\lambda}_0=1.54946\;{\mu}m$ and ${\lambda}_0=1.6144\;{\mu}m$ and, FWHM(Full at Half Maximun) is 0.1nm.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.38 no.7
• /
• pp.486-492
• /
• 2001

We propose a novel optical channel-selective filter whose center wavelength and bandwidth can be fully controlled. The Proposed filter consists of three identical chirped fiber Bragg gratings (CFBG’s) with fiber stretchers which is to control the reflection spectra of the CFBG’s. We experimentally demonstrate that the proposed tunable filter can select arbitrary channels from a WDM signal.