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

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.62 no.12
• /
• pp.1730-1736
• /
• 2013

Slanted and chirp interdigital transducer(IDT) configurations were studied for generating the surface acoustic wave(SAW) with wide bandwidths on a piezoelectric substrate. These devices can be applied to manipulate optical path of light along the waveguide, ultimately used for optical switches and holographic image implementation. Prior to fabrication, the coupling of modes(COM) modeling and simulation were performed to extract optimal design parameters. The optimally designed wideband device showed wide bandwidth of 30MHz, low insertion loss of -25dB, and abrupt side suppression ratio (SSR). Several design conditions were determined during device implementation, such as slanted angle, aperture length, number of fingers, and central frequencies of IDTs. These factors were experimentally analyzed and described in details in this paper.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.8 no.4
• /
• pp.164-171
• /
• 1983

In this paper, angular division multiplexing of the optical multiplexing technique for transmitting several channels using a relatively short step-index fiber is described. Mode coupling and the output power distributionin the fiber for the plane wave excitations is calculated and the crosstalk level determination of the system is proposed. In the presence of the mode coupling, the pulse width in terms of the fiber's length and input condition is calculated in the slab waveguide and the fiber. For the input angles (

• Current Optics and Photonics
• /
• v.1 no.5
• /
• pp.514-524
• /
• 2017

We proposed an integrated wavelength-selective photodetector based on a grating-assisted contradirectional coupler and a graphene absorption layer for a coarse wavelength division multiplexing (CWDM) communication system. The center wavelength of the absorption spectrum of the proposed device can be tuned simply by changing the period of the grating, and the proposed device structure is suitable to forming a cascaded structure. Therefore, an array of the proposed device of different grating periods can be used for simultaneous wavelength demultiplexing and signal detection in a CWDM communication system. Our theoretical study showed that the designed device with a grating length of $500{\mu}m$ could have an absorption of 95.1%, an insertion loss of 0.2 dB, and a 3 dB bandwidth of 7.5 nm, resulting in a -14 dB crosstalk to adjacent CWDM channels. We believe that the proposed device array can provide a compact and economic solution to receiver implementation in the CWDM system by combining functions of wavelength demultiplexing and signal detection.

• ETRI Journal
• /
• v.34 no.3
• /
• pp.361-368
• /
• 2012

A complete high-frequency small-signal circuit model of a 40 Gb/s butterfly electroabsorption modulator integrated laser module is presented for the first time to analyze and optimize its electro-optic (E/O) response and reflection characteristics. An agreement between measured and simulated results demonstrates the accuracy and validity of the procedures. By optimizing the bonding wire length and the impedance of the coplanar waveguide transmission lines, the E/O response increases approximately 5% to 15% from 20 GHz to 33 GHz, while the signal injection efficiency increases from approximately 15% to 25% over 18 GHz to 35 GHz.

• Korean Journal of Optics and Photonics
• /
• v.19 no.3
• /
• pp.219-223
• /
• 2008

To realize a widely tunable laser diode, a polymer coupled-ring reflector is hybrid- integrated with reflective semiconductor optical amplifier. Even though ring-ring and ring-bus coupling ratios are changed by fabrication errors in waveguide width and height, they remain very close to the single peak condition, ensuring high yield in fabrication. The tuning range is observed to be about 35 nm, maintaining the side mode suppression ratio of about 30 dB.

• Journal of the Optical Society of Korea
• /
• v.16 no.3
• /
• pp.305-312
• /
• 2012

We numerically demonstrate the performance of a plasmonic lens composed of an array of nanoslits perforated on thin metallic film with slanted cuts on the output surface. Embedding Kerr nonlinear material in nanoslits is employed to modulate the output beam. A two dimensional nonlinear-dispersive finite-difference time-domain (2D N-D-FDTD) method is utilized. The performance parameters of the proposed lens such as focal length, full-width half-maximum, depth of focus and the efficiency of focusing are investigated. The structure is illuminated by a TM-polarized plane wave and a Gaussian beam. The effect of the beam waist of the Gaussian beam and the incident light intensity on the focusing effect is explored. An exact formula is proposed to derive electric field E from electric flux density D in a Kerr-Dispersive medium. Surface plasmon (SPs) modes and Fabry-Perot (F-P) resonances are used to explain the physical origin of the light focusing phenomenon. Focused ion beam milling can be implemented to fabricate the proposed lens. It can find valuable potential applications in integrated optics and for tuning purposes.

• Korean Journal of Optics and Photonics
• /
• v.16 no.4
• /
• pp.376-383
• /
• 2005

We designed and fabricated integrated-optic tunable polarization controllers based on $LiNbO_3$ with the Ti-indiffused waveguide along the y-axis utilizing the electro-optic effect. The device consists of $TE↔TM$ mode converters and TE/TM phase shifters. We analyzed the operation principles of each device utilizing transfer matrices based on a Jones matrix and simulated shifting of the center wavelength by inducing voltage. We confirmed experimentally that the fabricated devices control the tunability of the center wavelength and the input SOP.

• Current Optics and Photonics
• /
• v.2 no.6
• /
• pp.576-581
• /
• 2018

A new approach for identification of a microwave frequency using an integrated optical waveguide chip, combined with a phase modulator (PM) and two microring resonators (MRRs), is proposed, theoretically deduced, and verified. By wavelength tuning to set the PM under the condition of a double side band (DSB), the measurement range can be started from the dc component, and the measurement range and response slope can be adjusted by designing the radius and transmission coefficient of the MRR. Simulations reveal that the amplitude comparison function (ACF) has a monotonic relationship from dc to 32.5 GHz, with a response slope of 5.15 dB under conditions of DSB modulation, when the radius values, transmission coefficients, and the loss factors are designed respectively as $R_1=400{\mu}m$, $R_2=600{\mu}m$, $t_1=t_2=0.63$, and ${\gamma}_1={\gamma}_2=0.66$. Theoretical calculations and simulation results both indicate that this new approach has the potential to be used for measuring microwave frequencies, with the advantages of compact structure and superior reconfigurability.

• Current Optics and Photonics
• /
• v.5 no.4
• /
• pp.370-374
• /
• 2021

Corals are the remains of animals that grow on warm beaches. They have been used as decorative jewels because of their variety of colors, and as medicinal materials for treating cancers, AIDS, and other therapeutic uses because of their chemical elements. Corals are mainly composed of calcium carbonate (CaCO₃) and have many air pores, tens to hundreds of micrometers in size. The refractive indices and absorption coefficients of dried sliced staghorn corals are investigated using terahertz time-domain spectroscopy. The measured values are similar to those for CaCO₃, as expected. It is observed that a sample with a microstructure formed by air pores can guide terahertz waves. The dispersion, effective index, and loss of the guiding modes of coral core surrounded by five triangular air pores are numerically calculated. The simulated spatial distribution of the electric field of the guide mode at 1.25 THz shows the mode to be tightly confined to the core.