• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.438-440
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• 2005

광위상변조기를 이용하여 OCT용 초고속 광지연단을 설계하고 수치해석을 수행하였다. 수치해석은 electro-optic 위상 변조기에 1310nm, 10ps의 펄스폭을 갖는 레이저 광원을 적용하여 수행하였다. 수치해석결과로 500MHz의 변조 주파수일때 19ps의 시간 지연을 얻었으며, 이는 기존의 기계적 검출방식(수십kHz)의 OCT장치에 비해 1000배이상 빠른 검출이 가능할 것으로 예상된다.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1597-1598
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• 2006

광간섭계는 물체의 기하학적 구조 및 의료영상계측등 다양한 분야의 광계측에서 매우 일반적으로 사용된다. 이러한 광간섭계에서 광지연단은 측정대상의 기준을 위해 사용되고, 광간섭계의 계측속도는 광지연단에 의해 제한된다. 본 논문에서는 고속 광 지연단을 위해 기존의 기계적 방식을 배제하고, 광학적 방식의 광 간섭계를 구성하였다. 고속 광간섭계의 구성은 1304nm의 10GHz광원을 이용하였으며, 광지연단으로 광위상변조기와 광섬유를 이용하여 안정적이고 고속의 광 간섭계를 구성하였다. 구성된 광간섭계는 광위상변조기의 변조전압, 변조주파수에 의해 광지연시간을 가변할 수 있으며, 10MHz 반복율에 대해 11ps의 광지연시간을 얻을 수 있었다.

• Proceedings of the KIEE Conference
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• 2002.11a
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• pp.230-233
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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 ${\mu}m$. The experimental results show that the measured half-wave voltage is of ${\sim}10$ V and the total measured fiber-to-fiber insertion loss is of ${\sim}-6.4$ dB for a 40 mm long waveguide at a wavelength of 1.3 ${\mu}m$, respectively.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.190-191
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• 2000

종래의 자기광학 디바이스는 자성체막을 빛이 투과할 때 얻어지는 페러데이 회전각을 이용했기 때문에, 페러데이 회전각을 증가시켜서, 광학적 성능을 증가시키려면 자성체막의 두께를 증가시켜야만 했다. 그러나, 자성체막의 두께를 증가시키면, 화소를 자기적으로 분리하기 위하여 자성체 막을 물리적으로 제거 해야하여 깊이가 깊어지고 그 후에 도선막을 구조화하기 위하여 파낸 화소간 갭을 다시 평탄화해야 하는 등의 제조 공정이 기술적으로 매우 어려워진다는 문제점을 가지고 있었다. 또한, 자성체 막의 두께가 증가하면, 도선막에 전류를 흘려 발생하는 자장은 도선막으로부터의 거리의 제곱에 반비례하므로, 두꺼운 자성체 막 전체에 강한 자장을 인가하기 위해서는, 도선막에 흘리는 전류를 증가시켜야만 한다는 문제점을 안고 있었다. (중략)

• Journal of the Optical Society of Korea
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• v.16 no.4
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• pp.401-408
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• 2012

The amplitude error of phase modulator used in closed-loop fiber optic gyroscope has occurred by the temperature dependency of the electro-optic coefficient, and also can be due to the square-wave dither signal which is generally applied for eliminating the deadzone. This error can cause bias drift and scale factor error. This paper analyzes the temperature dependency of the modulation amplitude and the relationship with the scale factor of the gyroscope, and deals with an amplitude control method. The error calculation logic considering the dither signal is implemented on the signal processing module. The result of experiments from a prototype gyroscope shows the effect of the modulation amplitude control and a considerable improvement on performances.

• Journal of IKEEE
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• v.22 no.2
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• pp.316-323
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• 2018

In this paper, we newly introduce the three-level byte-inversion transmission method for preventing LED flicker in visible light communication (VLC). The VLC transmitter sequentially sends the original signal and the inverted signal in byte units using a three-level LED modulator. The average optical power of the LED is kept constant during data transmission, thus flicker-free. In the VLC receiver, the original data is easily recovered using a simple comparator. This structure is very simple because additional clock or carrier is not required for flicker prevention. The developed flicker prevention scheme could be very useful for constructing the flicker-free indoor VLC system in low cost.

• Korean Journal of Optics and Photonics
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• v.8 no.5
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• pp.410-414
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• 1997

Laser projection display is a full color display system for large area. In this system, laser beams are modulated at acousto optic modulators(AOM) according to the video signal. AOM consists of a $TeO_2$ crystal and a $LiNbO_3$ transducer. We calculated the acoustic wave propagating from transducer to acousto optic media and made AOM by the calculated results. We compared calculated results with fabricated AOM by measuring modulation efficiency at various frequency. The modulation efficiency of AOM is 85% at the carrier frequency of 144MHz and the rise time is 41.5 ns.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.1
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• pp.98-105
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• 2000

The projectors using liquid crystal display(LCD) have faults such as low optical efficiency, low brightness and even heat generation. To solve these problems reflective-type spatial light modulators based on MEMS (Microelectromechanical Systems) technology have emerged. Digital Micromirror DeviceTM(DMDTM), which was already developed by Texas Instruments Inc., and Thin-film Micromirror ArrayTM(TMATM), which has been recently developed by Daewoo Electronics Co., are the representative examples. The display using TMATM has particularly much higher optical efficiency than other projectors. But the micromirrors manufactured by semiconductor processes have inevitable distortion because of the limitations of the manufacturing processes, so that the distortions of their surfaces have great influence on the optical efficiency of the projector. This study investigated the effects of mirror flatness on the optical performance, including the optical efficiency, of the TMATM projector. That is to say, as a part of the efforts to enhance the performance of the TMATM projector, how much influence the form errors of a micromirror surface exert on the optical efficiency and the modulation of gray scale of the projector were analyzed through a pertinent modeling and simulations.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.220-220
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• 2013

Surface-normal transmission electro-absorption modulator (EAM) are attractive for high-definition (HD) three-dimensional (3D) imaging application due to its features such as small system volume and simple epitaxial structure [1,2]. However, EAM in order to be used for HD 3D imaging system requires uniform modulation performance over large area. To achieve highly uniform modulation performance of EAM at the operating wavelength of 850 nm, it is extremely important to remove the GaAs substrate over large area since GaAs material has high absorption coefficient below 870 nm which corresponds to band-edge energy of GaAs (1.424 eV). In this study, we propose and experimentally demonstrate a transmission EAM in which highly selective backside etching methods which include lapping, dry etching and wet etching is carried out to remove the GaAs substrate for achieving highly uniform modulation performance. First, lapping process on GaAs substrate was carried out for different lapping speeds (5 rpm, 7 rpm, 10 rpm) and the thickness was measured over different areas of surface. For a lapping speed of 5 rpm, a highly uniform surface over a large area ($2{\times}1\;mm^2$) was obtained. Second, optimization of inductive coupled plasma-reactive ion etching (ICP-RIE) was carried out to achieve anisotropy and high etch rate. The dry etching carried out using a gas mixture of SiCl4 and Ar, each having a flow rate of 10 sccm and 40 sccm, respectively with an RF power of 50 W, ICP power of 400 W and chamber pressure of 2 mTorr was the optimum etching condition. Last, the rest of GaAs substrate was successfully removed by highly selective backside wet etching with pH adjusted solution of citric acid and hydrogen peroxide. Citric acid/hydrogen peroxide etching solution having a volume ratio of 5:1 was the best etching condition which provides not only high selectivity of 235:1 between GaAs and AlAs but also good etching profile [3]. The fabricated transmission EAM array have an amplitude modulation of more than 50% at the bias voltage of -9 V and maintains high uniformity of >90% over large area ($2{\times}1\;mm^2$). These results show that the fabricated transmission EAM with substrate removed is an excellent candidate to be used as an optical shutter for HD 3D imaging application.

• Journal of the Optical Society of Korea
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• v.17 no.2
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• pp.177-181
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• 2013

We present an all-fiberized power-scalable, sub-nanosecond mode-locked laser based on a frequency-shifted-feedback ring cavity comprised of an erbium-doped fiber, a downshifting acousto-optic modulator (AOM), and a bandpass filter (BPF). With the aid of the frequency-shifted feedback mechanism provided by the AOM and the narrow filter bandwidth of 0.45 nm, we generate self-starting, mode-locked optical pulses with a spectral bandwidth of ~0.098 nm and a pulsewidth of 432 to 536 ps. In particular, the output power is readily scalable with pump power while keeping the temporal shape and spectral bandwidth. This is obtained via the consolidation of bound pulse modes circulating at the fundamental repetition rate of the cavity. In fact, the consolidated pulses form a single-entity envelope of asymmetric Gaussian shape where no discrete internal pulses are perceived. This result highlights that the inclusion of the narrow BPF into the cavity is crucial to achieving the consolidated pulses.