• Title/Summary/Keyword: photodetector

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A Wideband Interferometric Wavelength Shift Demodulator of Fiber Bragg Grating Strain Sensor

  • Song, Min-Ho
    • Journal of the Optical Society of Korea
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    • v.3 no.2
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    • pp.64-68
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    • 1999
  • The performance of a fiber Bragg grating strain sensor constructed with 3$\times$3 coupler is investigated. A 3$\times$3 coupler Mach-Zehnder (M/Z) interferometer is used as wavelength discriminator, interrogating strain-induced Bragg wavelength shifts. Two quadrature-phase-shifted intensities are synthesized from the as-coupled interferometer outputs, and digital arctangent demodulation and phase unwrapping algorithm are applied to extract the phase information proportional to strain. Due to the linear relation between the input strain and the output of quadrature signal processing, signal-fading problems eliminated. In the experiment, a fiber grating that was surface adhered on an aluminum beam was strained in different ways, and the photodetector signals were transferred and processed in a computer-controlled processing unit. A phase recovery fo 7.8$\pi$ pk-pk excursion, which corresponds to ~650$\mu$strain pk-pk of applied strain, was demonstrated. The sensor system was stable over the environmental intensi쇼 perturbations because of the self-referencing effect in the demodulation process.

Spectral Characteristics of 50 GHz FSR Etalon for Wide-band DWDM Application

  • Kim, Jong-Deog;Moon, Jong-Tae
    • Journal of the Optical Society of Korea
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    • v.8 no.3
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    • pp.104-107
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    • 2004
  • The periodic transmission spectrum of a solid etalon for wide-band capability is analyzed both theoretically and experimentally. In the transmission spectrum with an incident area of a photodetector, the peak wavelength and transmittance are deeply dependent on the incident angle and the divergence angle of the input laser beam. A thermal adjustment for a solid etalon is an optional way to control the transmission spectrum instead of the inefficient fine-angle alignment. In the result, we present the deviations of free spectral range (FSR) by the change in angle and temperature over wide wavelength range.

Basic Study for the fabrication of Laser Doppler Vibrometer for the Detection of Ultrasonic (초음파 측정용 레이저 도플러 진동계의 제작에 관한 연구)

  • Kim, Seung-Jong;Kim, Myoung-Sun;Kim, Ho-Seong
    • Proceedings of the KIEE Conference
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    • 2000.07c
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    • pp.2195-2197
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    • 2000
  • In order to detect the ultrasonic that is generated by the partial discharge of the heavy electric machinery a Laser Doppler Vibrometer (LDV) is developed. A Michelson type interferometer which employed heterodyne signal process technique is built to measure the frequency and amplitude of vibration. The output signal of the fast photodetector is a frequency modulated signal centered at 40 MHz. The signal from the detector is amplified and converted to intermediate frequency centered at 1 MHz after mixing process. The voltage output that is proportional to the velocity of the moving surface(PZT) is obtained using PLL. The spectrum of the FM signal is analyzed and integration method was introduced to obtain amplitude information. This LDV can be used to measure the vibration of MEMS devices, automobiles, HDD and CDP.

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Measurement of Multimode Fiber Bandwidth by the Fourth-Order Spectra of Amplified Spontaneous Emission

  • Moon, Sucbei;Kim, Dug Young
    • Journal of the Optical Society of Korea
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    • v.18 no.1
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    • pp.15-22
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    • 2014
  • We present a novel bandwidth measurement scheme for multimode optical fibers. Amplified spontaneous emission (ASE) radiation was utilized for a source of intrinsically modulated light with a wide modulation bandwidth. In our measurement scheme, the continuous-wave (CW) ASE light that passed through a multimode fiber (MMF) under test was analyzed by the fourth-order power with a high-speed photodetector and an electric spectrum analyzer. The modulation transfer function of the multimode fiber could be directly measured with the photoelectric spectra in the modulation frequency domain. The measurement result of our method was experimentally compared to that of the conventional measurement scheme based on the impulse response measurement. It has been found that our scheme provides a stable measurement means of MMF characterization that is suitable for the field testing due to the simplicity of the system.

Wide bandgap III-nitride semiconductors: opportunities for future optoelectronics

  • Park, Yoon-Soo
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.12 no.1
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    • pp.11-20
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    • 2002
  • The world at the end of the $20^{th}$ Century has become "blue" Indeed, this past decade has witnessed a "blue rush" towards the development of violet-blue-green light emitting diodes (LEDs) and laser diodes (LDs) based on wide bandgap III-Nitride semiconductors. And the hard work has culminated with, first, the demonstration of commercial high brightness blue and green LEDs and of commercial violet LDs, at the very end of this decade. Thanks to their extraordinary properties, these semiconductor materials have generated a plethora of activity in semiconductor science and technology. Novel approaches are explored daily to improve the current optoelectronics state-of-the-art. Such improvements will extend the usage and the efficiency of new light sources (e.g. white LEDs), support the rising information technology age (e.g. high density optical data storage), and enhance the environmental awareness capabilities of humans (ultraviolet and visible photon detectors and sensors). Such opportunities and many others will be reviewed in this presentation.

Herschel-PACS Observations of YSOs

  • Lee, Jin-Hui;Lee, Jeong-Eun;DIGIT team, DIGIT team
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.1
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    • pp.84.1-84.1
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    • 2011
  • We observed several young stellar objects (YSOs) using the Photodetector Array Camera and Spectrometer (PACS) aboard the Herschel Space Observatory. CO, OH, $H_2O$, [O I], and [C II] lines were detected. CO rotational diagrams show two distinct gas components of ~400 K and ~1000 K with a break around 1500 K of the CO excitation energy, indicative of two different heating mechanisms: PDR and outflow shocks. OH and $H_2O$ line fluxes can be fitted with temperatures different from what are derived from the CO rotational diagrams. In order to understand the physical environment of line formation, the sources were modeled with the 3-D radiative transfer code, LIME. We present the results of observations, simple analysis, and modeling of Herschel-PACS spectra of the YSOs.

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Performance Analysis of Spatial Multiplexing in MIMO Based Visible Light Communication System

  • Mondal, Ratan Kumar;Saha, Nirzhar;Jang, Yeong Min
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38C no.9
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    • pp.797-801
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    • 2013
  • Visible light communication (VLC) is a rapidly growing area of research and applications, due to the potential and predicted high efficiency of bandwidth. One of the key challenges in VLC technology is the choice of devices which are going to be deployed VLC features. Smartphone rationally uses the most widely deployed visible light sensor i.e. image sensor in camera, which could be used to receive the intensity modulated data. Image sensor based VLC system would be the most deployable scenario but initially the capacity was not much attractive compared with photodetector based VLC system. Here, the spatial multiplexing is proposed in MIMO based VLC system to increase the system capacity by utilizing the property of spatial separation of optical light sources in smartphone's camera module. The active pixels of imaging plane act as the multiple receivers which could be able to use on MIMO spatial multiplexing to enhance the system performance.

Implementation of the Variable Output Laser Diode Driver Synchronized with a Pulse Repetition Frequency Code (펄스 반복 주파수 코드에 동기된 출력 가변형 레이저 다이오드 드라이버 구현)

  • Lee, Young-Ju;Kim, Yong-Pyung
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.64 no.5
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    • pp.746-750
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    • 2015
  • In this paper, we propose a simulator to evaluate the performance of the semi-active laser guidance or the quadrant photodetector and to simulate the laser power reflected from a target. The laser pulse repetition frequency was generated and synchronized with the laser pulse repetition(PRF) code. To evaluate the performances of the proposed methods, we implemented a prototype system and performed experiments. As a result, the generated high voltage was variable in the range of DC 3V to 340V and has the rate of change of 2000 V/s. PRF code can be generated within 50ms ∼ 100ms and the error is implemented within 0.3ns. The laser output is synchronized with the PRF code and has a dynamic range of 23.6dB.

Hybrid Transparent Conductor by using Solution-Processed AgNWs for High-Performing Si Photodetectors

  • Kim, Hong-Sik;Kim, Joondong
    • Current Photovoltaic Research
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    • v.3 no.4
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    • pp.116-120
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    • 2015
  • A hybrid transparent conducting layer was applied for Si photodetector. To realize the hybrid transparent conducting layer, a 200 nm-thick ITO layer was deposited onto a Si substrate, following by a solution-processed AgNWs-coating on the ITO. The hybrid transparent conducting layer showed an excellent low electric resistance of $15.9{\Box}/{\Omega}$ with a high optical transparency of 86.89%. Due to these optical and electrical benefits, the hybrid transparent conductor-embedding Si diode provides an extremely high rectifying ratio of 3386. Under light-illumination, the hybrid transparent conductor device provides extremely high photoresponses for broad wavelengths. This implies that a functional design for hybrid transparent conductor is crucial for photoelectric devices and applications.

An Indoor Broadcasting System Using Light-Emitting Diode Lamps Coupled with Power Line

  • Lee, Seong-Ho
    • Journal of Sensor Science and Technology
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    • v.24 no.5
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    • pp.342-347
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    • 2015
  • We introduce an indoor broadcasting system using light-emitting diode (LED) lamps coupled with a 220 V power line. Two couplers connected to the power line constitute a power line communication (PLC) link. The transmission path from an LED lamp to a photodetector forms a visible light communication (VLC) link in free space. When the LED lamp is coupled to the power line, a composite PLC-VLC link is formed, making it possible to transmit a VLC signal beyond line-of-sight. In experiments, a 4 kHz analog signal modulated with a 100 kHz carrier was sent to the power line by a PLC coupler, and LED lamps coupled to the power line detected the signal and radiated it to multiple VLC receivers in the room. This configuration is useful in expanding an indoor VLC sensor network to adjacent rooms or constructing a voice broadcasting system in a building or apartments with existing power lines.