• Korean Journal of Optics and Photonics
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• v.32 no.4
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• pp.180-186
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• 2021

Fluorinated polyimide has excellent light transmittance and a high optical refractive index, and is useful for producing optical-waveguide phase modulators with low optical loss and low electric power consumption. In this work, an optical-waveguide phase modulator is designed and fabricated based on a high-refractive-index fluorinated polyimide, and its characteristics are measured. An efficient protocol for characterizing the loss components of the optical waveguide is proposed, and the propagation loss of the fabricated polyimide optical waveguide is confirmed to be 0.9 dB/cm. The phase modulator requires 9.1 mW of power for phase change of π, and the response time is 290 μs, which is improved by tenfold compared to a previous demonstration of polymeric phase modulators.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.355-358
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• 2003

We report experimental results on the wavelength and polarization selective coupling properties of fiber-to-planar waveguide coupler having a thin metal intermediate layer. The influence of the metal layer thickness and the refractive index of the superstrate on the device properties has been measured and explained. The proposed device exhibited various application possibilities including polarizers, modulators, and sensors.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.10
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• pp.924-930
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• 1998

In this study, we describe the properties of an electro-optical modulator with CPW(coplanar waveguide) electrode fabricated on $LiNvO_3$ optical waveguide, that is applicable to optical communications. These optical modulators have features that use a buffer layer to reduce velocity mismatch between microwaves and optical wave as well as employ CPW to improve impedance and propagation mode mismatch between the electrode and the external circuits. And an annealed proton exchange technique for obtaining low-loss optical waveguides and good reproducibility was employed. Taking into consideration the mentioned background, to achieve the lower driving voltage of optical modulator, we have re-disigned the longer interaction length. And their device properties are discussed also. As a result, fabricated optical modulators of good 10Gps operation and low voltage(5.6V of the halfwave lengfth voltage) at an $1.5{\mu}m$ wavelength are achived with good reproducibility.

• ETRI Journal
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• v.27 no.1
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• pp.95-101
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• 2005

Waveguide structures of the stand-alone electroabsorption (EA) modulator and the electroabsorption modulated laser (EML) are investigated using the 3D beam propagation method. The EA waveguide structures with InP-based passivation layers show saturation in the extinction ratio (ER) due to the stray light traveling through the passivation layers. This paper demonstrates that narrower passivation layers suppress stray-light excitation in the EA waveguide, increasing the ER. A taper structure in the isolation section of the EML waveguide can reduce the mode mismatch and suppress the excitation of the stray light, increasing the ER further. Low-index-polymer passivation layers can confine the mode more tightly in the active waveguide, yielding an even higher ER.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.8
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• pp.731-735
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• 2003

Ti-indiffused LiNbO$_3$waveguide have been used to various high speed optical device based on electro-optic effect such as modulators, switches, and sensor, etc. In order to high speed modulation of optical modulator have, one of the further devices, needed to increasing of electrode surrounding air by LiNbO$_3$dry etching because of impedance matching for optical and RF phase velocity between waveguide and electrode. We studied property of LiNbO$_3$dry etching after waveguide patterning lot optical modulation by using neutral loop discharge (NLD) plasma.

• Korean Journal of Optics and Photonics
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• v.7 no.3
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• pp.280-286
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• 1996

This paper describes operation mechanism of a novel optical waveguide phase modulator with optical bistability characteristics by self electro-optic effect. The fabricated device structure is an optical waveguide modulator, using a refractive index change by an applied electric field, parallel integrated with SEED with an electrical bistability. GaAs/AlGaAs MQW is used as the core layer of the waveguide modulator and the absorption layer of SEED. The absorbed optical power in SEED changes the diode voltage and controls the optical power propagating through the waveguide phase modulator. Optical bistability of waveguide phase modulator is experimentally obtained by using electrical bistability of SEED. Compared to other waveguide modulators, the proposed one has an asset that the lowest optical power is required to generate optical bistability.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.5
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• pp.69-79
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• 1999

In this paper, we proposed a diffuion model of Ti diffused lithium niobate optical waveguide for fabricating waveguides with high refractive index and compared with conventional one. The achivement of low optical insertion loss between waveguide interface and single mode fibers was discussed as a function of Ti thickness for $\lambda$=1.55$\mu\textrm{m}$ The proposed diffusion method exhibited higher refractive index waveguide than conventional one for $\lambda$=0.6328$\mu\textrm{m}$ We have achieved the total fiber-waveguide-fiber insertion loss as low as 0.5dB/cm in z-cut and 1$\pm$0.5dB/cm in x-cut for both TM and TE mode of Mach-Zehnder interferometric waveguide in the range of Ti thickness 1000-1400$\AA$ for $\lambda$=1.55$\mu\textrm{m}$ From these results, this diffusion model for making a low loss waveguide can be used for low-power-modulators and switches.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.7
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• pp.42-49
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• 1999

In this paper, we proposed a simple measurement method to find the behaviors of the fiber-to-waveguide coupler. The polished fiber blocks and planar waveguides on silicon dioxide were fabricated independently and then optically coupled by physical pressure. Several kinds of polymer with different refractive indices were used for waveguide films. The proposed method makes it possible to measure the center wavelength, bandwidth, extinction ratio, and polarization dependence of the coupler during fabrication procedure. The wavelength sensitivity increased with refractive index of polymer. The symmetric planar waveguide structure and isotropic property of guiding materials reduced polarization dependent property. Insertion loss of the coupler was less than 0.5dB. It is expected that our measurement method is useful for developing various optical devices using evanescent coupling between polished fiber and planar waveguide such as optical modulators and filters etc.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.9
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• pp.1782-1792
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• 1994

Ti : $LiNbO_3$ traveling-wave phase optical modulators at wavelength 1.3㎛ have been designed and fabricated, focusing on the optical waveguide and asymmetric coplanar electrode structure. To improve the phase-mismatch of traveling-wave ACPS electrode, the characteristic impedance, effective microwave index, and electrode loss have been presented as a function of geometric parameters including electrode and buffer layer thickness. Low-loss channel optical waveguides on $LiNbO_3$ were fabricated by the Ti diffusion method with $O_2$ water-vapor environment. $2.5{\mu}m$ thick electrode was successfully fabricated by double-spin image reversal process. Modulation bandwidth was limited by a resonance at 2.9 GHz and modulation bandwidth up to 2.5GHz was approxirnately measured.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05b
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• pp.111-118
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• 2002

A new lithium niobate optical modulator with a polymer buffer layer on Ni in-diffused optical waveguide is proposed for the fist time, successfully fabricated and examined at a wavelength of 1.3 mm. By determining the diffusion parameters of Ni in-diffused waveguide to achieve more desirable mode size which is well matched to the mode in the fiber, the detailed results on the achievement of high optical throughput are reported. In addition, the usefulness of polymer buffer layer which can be applicable to a buffer layer in Ni in-diffused waveguide devices is demonstrated. Several sets of channel waveguides fabricated on Z-cut lithium niobate by Ni in-diffusion were obtained and on which coplanar traveling-wave type electrodes with a polymer-employed buffer layer were developed by a conventional fabrication method for characterizing of electro-optical performances of the proposed device. The experimental results show that the measured half-wave voltage is of ~10 V and the total measured fiber-to-fiber insertion loss is of ~6.4 dB for a 40 mm long at a wavelength of =1.3 mm, respectively. From the experimental results, it is confirmed that the polymer-employed buffer layer in LiNbO3 optical modulator can be a substitute material instead of silicon oxide layer which is usually processed at a high temperature of over $300^{\circ}C$. Moreover, the fabrication tolerances by using polymer materials in LiNbO3 optical modulators are much less strict in comparison to the case of dielectric buffer layer.