• Current Optics and Photonics
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• 제6권3호
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• pp.323-331
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• 2022

Electro-optic modulator (EOM) takes a vital role in connecting the electric and optical fields. Here, we present a heterogeneously integrated EOM based on the lithium niobate-on-insulator (LNOI) platform. The key modulation waveguide structure is a field-enhanced slot waveguide formed by embedding silicon nanowires in a thin-film lithium niobate (LN), which is different from the previously reported LN ridge or etchless LN waveguides. Based on such slot structure, optical mode field area is reduced and enhanced electric field in the slot region can interact well with LN material with high Electro-optic (EO) coefficient. Therefore, the improvements in both aspects have positive effects on enhancing the modulation performance. From results, the corresponding EOM by adding such modulation waveguide structure achieves better performance, where the key half-wave-voltage-length product (V_𝜋L) and 3 dB EO bandwidth are 1.78 V·cm and 40 GHz under the electrode gap width of only 6 ㎛, respectively. Moreover, Lower V_𝜋L can also be achieved. With these characteristics, such field-enhanced waveguide structure could further promote the development of LNOI-based EOM.

• 한국광학회지
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• 제19권3호
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• pp.187-192
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• 2008

실리콘과 전광 고분자 물질을 기반으로 한 새로운 광 결정 광변조기를 제안하고, 설계 및 검증을 수행하였다. 이는 실리콘 물질로 된 광 결정 도파로의 중심에 전광 고분자 물질로 된 슬롯 형태의 도파로를 삽입한 구조로 구성된다. 좁은 폭의 전광 고분자 슬롯도파로를 진행하는 광 신호는 주변의 광 결정 구조에 의해 매우 낮은 군속도를 갖게 될 뿐만 아니라, 전광 고분자 내로의 강한 광학적 구속력을 갖게 되어 광-물질 간의 활발한 상호작용과 매우 높은 전기-광학적 효과를 얻을 수 있다.

• Current Optics and Photonics
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• 제3권5호
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• pp.429-437
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• 2019

Temperature adaptability is an important metric for evaluating the performance of an optical system. The temperature characteristics of the optical system are closely related to the material and shape of its lens. In this paper, we establish a mathematical model relating the temperature characteristics to the shape and material of the lens. Then a novel assembly structure that can solve the lens constraint and positioning problem is proposed. From those basics, the correctness of the theoretical model and the effectiveness of the assembly structure are verified through simulated analysis of the imaging quality of the optical system, whose operating temperature range is $-60{\sim}100^{\circ}C$.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2005년도 생물공학의 동향(XVII)
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• pp.730-734
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• 2005

본 연구에서는 광섬유 산소센서를 기반으로 글루코오스 모니터링용 FIA 시스템을 개발하였다. 운반용액의 낮은 유속에서도 검출가능 하였으며, 산소전극을 이용한 글루코오스-FIA 시스템보다 넓은 범위의 글루코오스 농도를 검출할 수 있었다. 향후, 광섬유 센서를 이용하여 생물반응기에서 기질로 사용되는 글루코오스뿐만 아니라 용존산소, pH, $CO_2$와 같이 다양한 인자들의 모니터링 시스템을 개발하고자 한다.

• 한국광학회지
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• 제18권1호
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• pp.50-55
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• 2007

본 연구에서는 광통신 시스템에 있어서 필수적인 기능으로 전망되고 있는 전광 논리소자를 구현하기 위한 집적된 광소자를 제작, 측정 하였다. 유기금속화학증착법(MOCVD)을 이용한 선택영역 성장기술을 이용하여 서로 다른 두 활성영역을 한 기판위에 성장함으로써 능동 반도체 광소자인 반도체 광증폭기와 수동 반도체 광소자인 다중모드 간섭 도파로, S-자 도파로를 집적하였다. 집적된 수동 소자부분의 손실을 측정하고 전광 논리소자를 구현하는 방법 중 하나인 반도체 광증폭기의 cross-gain modulation(XGM)특성을 측정하여 집적된 전광 논리소자로의 사용 가능성을 알아보았다.

• 한국광학회지
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• 제4권3호
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• pp.317-322
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• 1993

본 논문에서는 특성행렬을 사용하여 비선형 집적거울 etalon의 입출력 특성을 해석하는 방법을 제시한다. 빛의 세기에 따른 매질의 굴절률 및 흡수율의 변화 특성을 알면, 관계식과 특성행렬식을 결합하여 집적거울 etalon의 비선형 특성을 해석할 수 있다. 이 방법은 파장에 따른 각 거울의 반사율(크기와 위상)을 일일이 구하지 않고, etalon의 구조가 주어지면 바로 임의의 파장에서의 etalon의 입출력 특성을 해석할 수 있다. 또한, 특성행렬식을 이용하여 비선형 집적거울 etalon에서의 쌍안정성을 보였다.

• Current Optics and Photonics
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• 제3권6호
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• pp.510-515
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• 2019

In this paper, we introduce a 1.3-㎛ 25-GHz waveguide-integrated vertical PIN type Ge-on-Si photodetector fabricated using a multi-project wafers service based on fringing field analysis in the depletion region. In general, 1.3-㎛ photodetectors fabricated using a commercial foundry service can achieve limited bandwidths because a significant amount of photo-generated carriers are located within a few microns from the input along the device length, and they are influenced by the fringing field, leading to a longer transit time. To estimate the response time, we calculate the fringing field in that region and the transit time using the drift velocity caused by the field. Finally, we compare the estimated value with the measured one. The photodetector fabricated has a bandwidth of 20.75 GHz at -1 V with an estimation error of <3 GHz and dark current and responsivity of 110 nA and 0.704 A/W, respectively.

• Journal of the Optical Society of Korea
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• 제19권5호
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• pp.449-455
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• 2015

In this study we propose a new photonic crystal fiber (PCF) design that simultaneously offers broadband single-mode operation, high birefringence, and large normal dispersion in the optical-communication wavelength regime. The waveguide is based on a hybrid square-lattice PCF (HS-PCF) that has circular air holes of two different diameters alternating in the cladding, plus a pure silica defect at the center. The optical properties of the guided modes are analyzed numerically by the finite-element method (FEM) with a perfectly matched layer as the boundary condition. The optimized HS-PCF has a dispersion coefficient of $-601.67\;ps\;nm^{-1}\;km^{-1}$ and a high birefringence of $1.025{\times}10^{-2}$ at $1.55{\mu}m$. In addition, over the S+C+L+U wavelength bands the proposed HS-PCF with ultraflat birefringence with a slope on the order of $10^{-5}$.

• Current Optics and Photonics
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• 제4권4호
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• pp.361-367
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• 2020

An approach based on an integrated photonic Ti:LiNbO₃ Y branch has been proposed, designed, and analyzed for the microwave instantaneous frequency measurement (IFM). By designing the Y branch with length L = 6545 ㎛ and refractive index N_TE - N_TM = 0.0764, a complementary optical filter with free spectral range (FSR) of 600 GHz is constituted, which results in a maximum measureable frequency of 300 GHz being obtained. Theoretical analysis on the temperature stability of the Ti:LiNbO₃ Y branch shows that the FSR variation of the complementary filter is 0.3% for the temperature change of 100 K, which indicates that the IFM approach will have a better stability. All these results demonstrate that the proposed IFM approach has potential capability to be used for the increasingly higher microwave IFM with better stability.

• Current Optics and Photonics
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• 제2권6호
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• pp.576-581
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• 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.