• Korean Journal of Materials Research
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• v.6 no.5
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• pp.462-469
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• 1996

1x2 방향성결합형 광 변조기를 LiNbO3 기판상에 양자교환에 의한 자기정렬 방식으로 제작하였다. 양자교환후 광 도파로의 안정을 위해 열처리를 하였다. 본 연구에서는 광 도파로를 제작한 후 열처리 시간에 의한 도파로의 굴절을 변화의 관계에 대하여 연구하였으며 전계효과가 우수한 자기정렬방식을 선택하였다. 제작된 1x2 방향성결합형 광 변조기는 변조전압 8.0V에서 크로스토오크가 -29.5dB의 매우 우수한 특성을 나타내었다.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.8
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• pp.153-165
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• 1995

The design procedure of a GaAs/AlGaAs semiconductor matrix optical switch is presented for a simplified tree architecture in the viewpoint of optical loss. A low loss, 0.537 dB/cm, pin type substrate is designed by considering the loss due to imputity doping at 1.3 $\mu$m wavelength. The operating voltage and the device length of a reversed ${\Delta}{\beta}$ electro-optic directional coupler(EODC) swith which is a cross-point device of the 4${\times}$4 matrix optical switch and the bending loss of rib waveguide are caculated as functions of waveguide parameters and bending parameters. There is an optimum bending radius for some waveguide parameters. It is recommened that higher optical confinement conditions such as wide waveguide width and higher rib-height should be chosen for structural parameters of a low loss and a process insensitive 4${\times}$4 matris optical switch. A 4${\times}$4 optical matrix switch which has a 3 dB loss and a 12 volt operating voltage is designed.

• Korean Journal of Optics and Photonics
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• v.10 no.1
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• pp.40-46
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• 1999

We present a new modified effective index method which can be used to analyze lightwave circuit devices in 3-dimensional structure fast and accruatly using 2-dimensional BPM (beam propagating method). This method can analyze the devices with the cross-section of rectangular, ridge, or similar shapes accurately but more quickly than the 3-dimensional BPM, which is impractical to use on account of long calculating time. As an example, we showed that the calculation error of coupling length in a directional coupler by this method is significantly less than the 2-dimensional BPM using the effective index method.

• Korean Journal of Optics and Photonics
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• v.14 no.5
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• pp.545-554
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• 2003

Design of the optical modulator composed of a three-waveguide coupler and CPW traveling-wave electrodes was carried out. Switching phenomena of three-waveguide couplers were analyzed by using the coupled mode theory, and the coupling-lengths of the devices were calculated by means of the FDM. CPW traveling-wave electrodes were analysed by the CMM and SOR simulation technique in order to find the conditions of phase-velocity and impedance matching. Traveling-wave modulators were fabricated on z-cut LiNbO$_3$ substrate. Ti was in-diffused in LiNbO$_3$ to make waveguides and Au electrodes were built on the waveguides by the electrolyte technique. The fabricated modulator chip was end-polished, pig-tailed and packaged in a brass mount with K-connector. The insertion loss and the switching voltage of the optical modulator were about 4㏈ and 19V, respectively. Network analyzer was used to obtain the S parameter and the corresponding RF response. From the measurement, parameters of the traveling-wave electrodes were extracted to be Z$_{c}$= 45 Ω, N$_{eff}$=2.20, and $\alpha$$_{0}$=0.055/cm√GHZ. The measured optical response R($\omega$) was compared with the theoretically estimated one, showing both responses agree well. The measurement results revealed that 3㏈ bandwidth turned out to be about 13 GHz.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.6
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• pp.61-70
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• 1999

An optical switch composed of three-identical, equally-spaced $Ti:LinbO_3$ waveguides and overlaid Al electrodes of CPW structure was designed and fabricated. Patterned Ti was diffused into z-cut $LinbO_3$ substrates at $1025^{\circ}C$ for 6 hours to make a three-waveguide directional coupler. $SiO_2$ buffer layer of $1.2{\mu}m$ was grown by the PECVD to reduce the propagation loss of TM mode, and Al electrodes were built on the layer for switching the guided beam. For an incident beam of ${\lambda}=1.3{\mu}m$, almost perfect optical coupling between two outer waveguides was observed. When an electric field was applied to detune the three waveguides anti-symmetrically, the optical switching phenomenon was successfully confirmed.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.420-427
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• 1993

Dielectric thin film mirrors are embedded in multimode and single-mode fibers by a fusion splicing technique. The fibers with $45{\circ}$ angled embedded mirrors serve as ultra-compact directional couplers with low excess optical loss of 0.2 dB for multimode and 0.5 dB for single mode at 1.3 ${\mu}m$ and excellent mechanical properties. The reflectance is wavelength dependent and strongly polarization depencient. Far-field scans of the reflected output power measured with a white-light source show a pattern which is almost circularly symmetric with aspect ratio of 1.09 at 5% of the peak power. The splitting ratio in a multimode coupler measured with a diode laser source is much less dependent on input coupling conditions than in conventional fused biconical-taper couplers, indicating that these couplers are less susceptible to modal noise occuring in optical fiber communication systems. Spectral properties of multilayer internal mirrors normal to the fiber axis have been investigated experimentally, and a matrix analysis has been used to explain the results.

• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.423-428
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• 2000

We have demonstrated a -8 dB additional reduction in the intensity sidelobe of an apodized-interaction-strength guide-wave acousto-optic filter with a center passband of 1551.6 nm. Acoustic-intensity weighting was achieved by launching a surface acoustic wave (SAW) beam in a straight acoustic waveguide, and gradually transferring this SAW intensity to the active device, and back out, by evanescent-wave coupling across a 50 !lm barrier over a 19 rom interaction length. The intensity sidelobe was -4.27 dB for an unapodized filter with abmpt onset and cutoff of the interaction, but sidelobes were reduced to at most -12.68 dB for a SAW intensity with raised-cosine weighting. The RF driving power was 17.78 mW. A linear tuning rate of 8.86 nmIMHz and a spectral width of -1.7 nm were demonstrated. rated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.7
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• pp.626-633
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• 2012

In this paper, sound pressure sensitivity of the fiber optic acoustic sensor according to sensor direction and mandrel material were investigated experimentally. Three different directions were selected as stand, lay, and hole. Hollow cylinder type mandrel dimension is 30 mm in outer diameter, 45 mm in length, and 2 mm in thickness, and about 50 m optical fibers were wounded on the surface of the mandrel. Non-directional sound speaker was used as a sound source. Sagnac interferometer and single mode fiber, a laser with 1,550 nm in wavelength, $2{\times}2$ coupler were used. Based on the experimental results, lay direction's sensitivity is the highest in the frequency range of 2 kHz~4 kHz. 'PTFE+carbon' material is more sensitive than PTFE in the frequency range of 5 kHz~20 kHz. Sound pressure detection sensitivity depends on the mandrel direction and material under certain frequency.

• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.169-173
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• 1997

Most conventional lithography systems have been oriented to fabricate electronic devices. Therefore, it is not so easy to fabricate large aspect ratios of waveguide patterns with those systems. When considering costs and efficiencies, a laser lithography system provides number of benefit in realizing waveguide patterns. However, because the conventional laser lithography system could make only positive tone masks, it is inconvenient in determining the direction of the waveguide. A simple and reliable technique to produce negative tone masks was developed by using the laser beam writing. This technique was not sensitive to environmental situations such as dust, vibration, intensity variation. Making use of the technique a variety of device patterns such as Y-branch, directional coupler, and highly smooth S-shape bend could be successfully fabricated with a good contrast.

• Korean Journal of Optics and Photonics
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• v.18 no.6
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• pp.447-451
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• 2007

A triplexer based on a silica planar lightwave circuit Mach-Zehnder nterferometer(MZI) is proposed and its characteristics are analyzed through simulations. To separate 1310 nm band and $1480{\sim}1560nm$ band properly, the path length difference of an MZI is set to be the multiple and half of the wavelength 1310 nm and the balance of the directional coupler is optimized in the $1480{\sim}1560nm$ band. The same MZI is additionally cascaded to provide good crosstalk characteristics. The 1490 nm band and 1550 nm band are further separated using additional two stage MZI's. A three-dimensional BPM and transfer matrix method analysis predicts the low crosstalk characteristics and the fabrication-error-tolerance of the proposed triplexer.