• Title/Summary/Keyword: Optical Pulses

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Improvement of extinction ratio of amplified pulses by incorporating a nonlinear optical loop mirror (EDFA로 증폭된 고출력 펄스 신호의 소광비 향상)

  • Kim, Byung-Jun;Choi, Hyun-Beom;Lee, Han-Hyub;Lee, Dong-Han;Kim, Dae-Yun;Kwon, Il-Bum
    • Korean Journal of Optics and Photonics
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    • v.14 no.2
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    • pp.189-193
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    • 2003

  • A two-stage erbium-doped fiber amplifier (EDFA) with a band pass filter is used to get optical pulses of high peak value. The pulse signal has a 32 ㏈ extinction ratio, 125 W peak power and 79 ㎽ pulse off power. A nonlinear optical loop mirror (NOLM) is used to lower the pulse off power so as to increase the extinction ratio. The pulse signal after the NOLM has a 50.4 ㏈ extinction ratio, 35 W peak power and 0.3 ㎽ pulse off power.

  • https://doi.org/10.3807/KJOP.2003.14.2.189 인용 PDF KSCI

Transition-based Data Decoding for Optical Camera Communications Using a Rolling Shutter Camera

  • Kim, Byung Wook;Lee, Ji-Hwan;Jung, Sung-Yoon
    • Current Optics and Photonics
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    • v.2 no.5
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    • pp.422-430
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    • 2018

  • Rolling shutter operation of CMOS cameras can be utilized in optical camera communications in order to transmit data from an LED to mobile devices such as smart-phones. From temporally modulated light, a spatial flicker pattern is obtained in the captured image, and this is used for signal recovery. Due to the degradation of rolling shutter images caused by light smear, motion blur, and focus blur, the conventional decoding schemes for rolling shutter cameras based on the pattern width for 'OFF' and 'ON' cannot guarantee robust communications performance for practical uses. Aside from conventional techniques, such as polynomial fitting, histogram equalization can be used for blurry light mitigation, but it requires additional computation abilities resulting in burdens on mobile devices. This paper proposes a transition-based decoding scheme for rolling shutter cameras in order to offer simple and robust data decoding in the presence of image degradation. Based on the designed synchronization pulse and modulated data symbols according to the LED dimming level, the decoding process is conducted by observing the transition patterns of two sequential symbol pulses. For this, the extended symbol pulse caused by consecutive symbol pulses with the same level determines whether the second pulse should be included for the next bit decoding or not. The proposed method simply identifies the transition patterns of sequential symbol pulses other than the pattern width of 'OFF' and 'ON' for data decoding, and thus, it is simpler and more accurate. Experimental results ensured that the transition-based decoding scheme is robust even in the presence of blurry lights in the captured image at various dimming levels

  • https://doi.org/10.3807/COPP.2018.2.5.422 인용 PDF KSCI

Midinfrared Pulse Compression in a Dispersion-decreasing and Nonlinearity-increasing Tapered As2S3 Photonic Crystal Fiber

  • Shen, Jianping;Zhang, Siwei;Wang, Wei;Li, Shuguang;Zhang, Song;Wang, Yujun
    • Current Optics and Photonics
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    • v.5 no.3
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    • pp.250-260
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    • 2021

  • A tapered As2S3 photonic crystal fiber (PCF) with four layers of air holes in a hexagonal array around the core is designed in this paper. Numerical simulation shows that the dispersion D decreases and the nonlinearity coefficient γ increases from the thick to the thin end along the tapered PCF. We simulate the midinfrared pulse compression in the tapered As2S3 PCF using the adaptive split-step Fourier method. Initial Gaussian pulses of 4.4 ps and a central wavelength of 2.5 ㎛ propagating in the tapered PCF are located in the anomalous dispersion region. With an average power of assumed input pulses at 3 mW and a repetition frequency of 81.0 MHz, we theoretically obtain a pulse duration of 56 fs and a compression factor of 78 when the pulse propagates from the thick end to the thin end of the tapered PCF. When confinement loss in the tapered PCF is included in the simulation, the minimum pulse duration reaches 72 fs; correspondingly, the maximum compression factor reaches 61. The results show that in the anomalous-dispersion region, midinfrared pulses can be efficiently compressed in a dispersion-decreasing and nonlinearity-increasing tapered As2S3 PCF. Due to confinement loss in the tapered fiber, the efficiency of pulse compression is suppressed.

  • https://doi.org/10.3807/COPP.2021.5.3.250 인용 PDF KSCI