• Current Optics and Photonics
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• 제5권6호
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• pp.711-720
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• 2021

A novel optical hybrid device that doubles the multilevel demodulation resolution by adding the optical interferometer with a waveguide crossover is proposed, theoretically analyzed and experimentally verified. We report two types of all-passive phase control schemes that will be referred to as a phase compensation scheme and a phase optimization scheme. We also apply the proposed phase control schemes to a 45° optical hybrid consisting of two parallel 90° optical hybrids together with the proposed phase control scheme for demodulating 8-level differential phase shift keying optical signals. Octagonal phase response with low wavelength sensitive excess loss of <0.8 dB over 31-nm-wide spectral range will be demonstrated in the InP-based material platform.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.628-632
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• 2005

Remote sensing through atmospheric turbulence had been hard works for a long time, because wavefront distortion due to the Earth's atmospheric turbulence deteriorates image quality. But due to the appearance of adaptive optics, it is no longer difficult things. Adaptive optics is the technology to correct random optical wavefront distortions in real time. For past three decades, research on adaptive optics has been performed actively. Currently, most of newly built telescopes have adaptive optical systems. Adaptive optical system is typically composed of three parts, wavefront sensing, wavefront correction and control. In this work, the wavefront sensing technology for adaptive optical system is treated. More specifically, shearing interferometers and Shack-Hartmann wavefront sensors are considered. Both of them are zonal wavefront sensors and measure the slope of a wavefront. . In this study, the shearing interferometer is made up of four right-angle prisms, whose relative sliding motions provide the lateral shearing and phase shifts necessary for wavefront measurement. Further, a special phase-measuring least-squares algorithm is adopted to compensate for the phase-shifting error caused by the variation in the thickness of the index-matching oil between the prisms. Shack-Hartmann wavefront sensors are widely used in adaptive optics for wavefront sensing. It uses an array of identical positive lenslets. And each lenslet acts as a subaperture and produces spot image. Distortion of an input wavefront changes the location of spot image. And the slope of a wavefront is obtained by measuring this relative deviation of spot image. Structures and measuring algorithms of each sensor will be presented. Also, the results of wavefront measurement will be given. Using these wavefront sensing technology, an adaptive optical system will be built in the future.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2004년도 춘계종합학술대회
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• pp.804-806
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• 2004

인체에 무해하며 고분해능의 단층영상과 저가격 및 소형으로 제작이 가능하여 전세계적으로 많은 연구가 진행중인 광영상 단층촬영기(Optical coherence tomography system : OCT)에 관한 것이다. 샘플에서 흡수와 산란으로 인하여 샘플로부터 반사된 광신호는 매우 미약하다. 게다가 커플러등에 의한 손실로 인하여 광검출기에 도달하는 신호는 매우 미약하다. 이러한 On시스템의 신호대 잡음비를 향상시키기 위하여 기본적인 마이켈슨 간섭계와 마흐젠더 간섭계를 구성하여 시뮬레이션과 기준샘플을 이용하여 측정하였다. 실험결과 마흐젠더 간섭계를 사용한 샘플로 반사된 광신호는 OCT 시스템의 신호대 잡음비 향상시키기 위하여 두 가지 형태의 간섭계를 구성하였으며 시뮬레이션을 통한 비교 분석과 기준 샘플의 측정에 의한 비교분석을 하였다. 실험결과 마흐젠더 간섭계형 OCT 시스템이 신호대 잡음비가 향상됨을 확인 하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.161-164
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• 2002

Optical fiber vibrations sensors (OFVSs) and extrinsic Fabry-Perot interferometer (EFPI) were used in damage monitoring of fiber-metal laminates(FML). The optical fiber vibration sensor and EFPI were applied in order to detect and evaluate the strain, damage and failure of FML. Damages in composites, such as matrix cracks, delamination and fiber breakage may occur as a result of excessive load, fatigue and low-velocity impacts. Tensile test was performed with the measurement of optical signal and acoustic emission (AE). The signals of the optical fiber vibration sensor due to damages were quantitatively evaluated by wavelet transform. EFPI was less sensible to the damage signals compared with the optical fiber vibration sensor. It was found that damage information of comparable in quality to acoustic emission data could be obtained from the optical fiber vibration sensor signals.

• Journal of the Optical Society of Korea
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• 제16권4호
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• pp.354-364
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• 2012

In this paper, a new 2-step quadrature phase-shifting digital holographic optical encryption method using orthogonal polarization is proposed and tolerance errors for this method are analyzed. Unlike the conventional technique using a PZT mirror, the proposed optical setup comprises two input and output polarizers, and one ${\lambda}$/4-plate retarder. This method makes it easier to get a phase shift of ${\pi}$/2 without using a mechanically driven PZT device for phase-shifting and it simplifies the 2-step phase-shifting Mach-Zehnder interferometer setup for optical encryption. The decryption performance and tolerance error analysis for the proposed method are presented. Computer experiments show that the proposed method is an alternate candidate for 2-step quadrature phase-shifting digital holographic optical encryption applications.

• Current Optics and Photonics
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• 제7권2호
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• pp.166-175
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• 2023

We theoretically analyze and experimentally demonstrate a polarization-diversified four-channel optical demultiplexer (DeMUX) comprising a hybrid mode conversion-type polarization splitter rotator (PSR) and delayed Mach-Zehnder interferometer optical DeMUX for use in coarse wavelength division multiplexing (CWDM)-based optical interconnect applications. The Si wire-based device fabricated by a complementary metal-oxide semiconductor-compatible process exhibited nearly the same filter spectral response irrespective of the input polarization state under the PSR. The device had an extremely low insertion loss of <1.0 dB, polarization-dependent loss of <1.0 dB, and interchannel imbalance of <0.5 dB, suppressing unwanted wavelength and polarization crosstalk from neighboring channels of <-20 dB at each peak transmission channel grid.

• Journal of the Optical Society of Korea
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• 제18권6호
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• pp.639-645
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• 2014

In this paper, the scheme of a single module for simultaneous operation of all-optical computing circuits, namely half adder and half subtractor, are realized using semiconductor optical amplifier (SOA) based logic gates. Optical XOR gate by employing a SOA based Mach-Zehnder interferometer (MZI) configuration is used to get the sum and difference outputs. A carry signal is generated using a SOA-four wave mixing (FWM) based AND gate, whereas, the borrow is generated by employing the SOA-cross gain modulation (XGM) effect. The obtained results confirm the feasibility of our configuration by proving the good level of quality factor i.e. ~5.5, 9.95 and 12.51 for sum/difference, carry and borrow, respectively at 0 dBm of input power.

• 한국통신학회논문지
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• 제25권1B호
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• pp.8-14
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• 2000

광여기 MQW(Multiple Quantum Well)면형 광증폭기에 대한 이득해석과 더불어 제작 및 측정을 수행하였다. 제안된 광증폭기는 편광무의존성, 광섬유와의 높은 결합효율, 그리고 동작파장의 자유도가 높다는 등의 장점을 자니고 있다. 본 논문에서는 100내지 200주기 MQW의 이득특성을 격자왜곡과 선택도핑의 효과를 고려해 해석하였다. 그 결과, 3㏈정도의 단일경로이득과 넓은 동작파장특성을 나타내었으며 이 해석 결과는 우리들이 행한 실험결과와 거의 일치하였다. 면형 광증폭기의 단일경로이득이 낮으면 FPI(Fabry-Perot Interferometer)구조로 증폭률을 높이는데는 협대역성의 문제가 발생하나,2-3㏈이상의 적정한 단일경로이득을 가질 경우, FPI 구조로 고이득과 적정한 동작파장특성을 가지게 할 수 있다. 예를 들면 단일경로이득이 3㏈인 MQW를 FPI 구조로 할 경우, 최대이득 10.1㏈, 동작파장대역이 4.6nm의 특성을 가지도록 할 수 있음을 보였다.

• 한국광학회지
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• 제15권5호
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• pp.475-482
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• 2004

Mach-Zehnder 간섭기와 CPW 진행파 전극을 이용한 외부 광변조기를 제작하였다. 유한차분법(FDM)을 이용하여 단일모드를 갖는 Ti:LiNbO$_3$ 광도파를 설계하고 이를 기반으로 M-Z 간섭기를 설계하였다. 또한 도파광과 MW간의 위상속도를 정합시키고 MW의 특성임피던스를 50Ω으로 맞추기 위하여, CPW 전극의 입$.$출력단 및 변조영역을 반복이완법(SOR)으로 수치해석 하였다. 제작된 소자의 삽입손실은 -3.2dB 정도였고, CPW 전극의 S$_{11}$은 12 GHz 이하의 주파수에서 -15 dB이하를 유지하였으며, S$_{21}$은 7 GHz까지 -3dB 이상을 나타내었다. 주파수 응답 측정 결과, 12 GHz에서 3 dB 변조대역폭을 갖는 것으로 측정되었다.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
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• pp.3-6
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• 2005

In this thesis, We researched on the characteristics of optical tunable filter that selects the channel by the wavelength changes of transmission spectrum when we apply outer physical quantities on a fiber bragg grating by using Fabry-Perot Interformer's operational principle.