• Journal of Photoscience
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• v.9 no.2
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• pp.9-12
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• 2002

Circadian rhythms can be seen in a variety of physiological functions in insects. Light is a powerful zeitgeber not only synchronizing but also modulating the rhythm to adjust insect's temporal structure to seasonal changes in the environmental cycle. There are two general effects of the length of light phase within 24 hr light cycles on the circadian rhythms, i.e., the modulation of free-running period and the waveform. Since the photoperiodic modulation of the free-running period is induced even in the clock mutant flies, per$\^$s/, the free-running period is not fully determined genetically. In crickets, the ratio of activity (a) and rest phase (p) under the constant darkness (DD) is clearly dependent on the photoperiod under which they have been kept. When experienced the longer photoperiod it becomes smaller. The magnitude of change in a/p-ratio is dependent on the number of cycles they experienced. The neuronal activity of the optic lobe in DD shows the a/p-ratio changing with the preceding photoperiod. These data suggest that a single circadian pacemaker stores and maintains the photoperiodic information and that there is a system that accumulates the effects of single photoperiod to cause greater effects.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.3
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• pp.18-29
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• 1993

In single mode fiber optic transmission systems(FOT's) operated at high modulation rates over long fiber spans, chromatic dispersion can produce distortion in the demodulated waveforms, resulting in intersymbol interference(ISI) in the received signal and a reduction of transmission system performance. In this paper, chromatic dispersion limitations for intensity modulation and direct detection(IM-DD) systems are studied by considering the effect of phase modulation to amplitude modulation (PM-AM) conversion noise. Laser phase noise conversion to amplitude noise due to fiber chromatic dispersion is analyzed by deriving the noise power spectral density. We first derive the noise power spectral density of the laser phase noise to intensity noise conver- sion. Next, also evaluate the system power penalty and the transmitter laser linewidth required to avoid PM-AM conversion noise penalties in long-haul nonregenerative transmission system using an external modulator and optical amplifiers. For such system with optical amplifiers, transmission sys- tem length is limited due to fiber chromatic dispersion, even if an ideal external modulator is used.

• Journal of IKEEE
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• v.13 no.4
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• pp.103-109
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• 2009

We report an efficient jitter reduction technique in an analog fier-optic link employing a Mach-Zehnder modulator followed by an erbium-doped fiber amplifier. By adjusting the modulator-bias to $0.089V_{\pi}$, we could increase the RF gain up to 10.65 dB for 10 GHz RF signal and reduce the random jitter by 46.5%, max, at an input optical power of -0.11 dBm to the EDFA.

• ETRI Journal
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• v.28 no.1
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• pp.103-106
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• 2006

We have fabricated a planar lightwave circuit (PLC) hybrid-integrated optical sub-assembly of a triplexer using a thin film filter (TFF)-attached wavelength division multiplexer (WDM) and photodiode (PD) carriers. Two types of TFFs were attached to a diced side of a silica-terraced PLC platform, and the PD carriers with a $45^{\circ}$ mirror on which pin-PDs were bonded were assembled with the platform. A clear transmitter eye-pattern and minimum receiver sensitivity of -24.5 dBm were obtained under 1.25 Gb/s operation for digital applications, and a second-order inter-modulation distortion (IMD2) of -70 dBc was achieved for an analog receiver.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.35-38
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• 2006

Using the repeaters is indispensable to WiBro services. Repeater types are distinguished by usage, output power and required performance. In the paper, we have studied on the WiBro digital optic repeater design which has excellent performance characteristic than any other repeaters. WiBro has specific characteristic on modulation method TDD(Time Division Duplex)/OFDMA(Orthogonal Frequency Division Multiple Access) so that it demands specified H/W to design WiBro repeater. Switching technique has been introduced because of TDD characteristic in each amplifier on the repeater. Time Advance technique has been considered because of OFDM characteristic among RAS(Radio Access Station) and repeater. In this paper, we have studied on these techniques to increase repeater cell coverage and distance between RAS and repeater.

• Journal of Magnetics
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• v.11 no.3
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• pp.143-146
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• 2006

We attempted to fabricate a new type of magneto optic spatial light modulator (MO-SLM) for multiple-tone modulation by using in-plane magnetization. In the MO-SLM, magnetic property of magneto-optical layer was modified to be suitable for multiple-tone expression by substituting Al in Bi:YIG film. At a driving current to 28 mA in an electrode of the fabricated MO-SLM, changes in brightness of pixels were observed using a polarization microscope.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.154-155
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• 2003

반도체 소자에 있어서 굴절율의 변화는 중요한 역할을 한다. 굴절율을 변화시키는 다양한 요소들은, 전계에 의한 1차 전기광학(linear electro-optic： LEO) 효과와 2차 전기광학 (quadratic electro-optic： QEO) 효과, 자유 운반자에 의한 밴드천이(band-gap shift： BS) 효과와 플라즈마(plasma： PL) 효과 등으로 잘 알려져 있다. 본 논문에서는, 오로지 TE 모드에 대해서만 선택적으로 위상 변화를 주는 P-I-i-I-N GaAs／Al／sub0.35／Ga／sub 0.65／As 도파로 위상변조기를 보고한다. (중략)

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.34-35
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• 2000

A Y-branch phase modulator made of an electro-optic(EO) polymer has been designed and fabricated. An EO polymer, PMMA-DR1, is used for the core layer, and UV-curable polymers, UV-15 and UV-15 LV, for the cladding layers. The rib type polymeric waveguides are fabricated by the reactive ion etching method and their EO effects are obtained by the poling process. The optical properties of the fabricated phase modulator are as follows: the halfwave voltage, $V_{\pi}$, is 25 V, the insertion loss of TM mode is 13.8 dB, and the intensity modulation is 0.17 % (V).

• Korean Journal of Optics and Photonics
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• v.1 no.1
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• pp.58-64
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• 1990

The flow direction in a glass tube is measured by using a forward scattering dual beam laser Doppler velo$.$ cimeter with an acousto-optic modulator. We can determine the flow direction by measuring the shifted Doppler frequency which is dependent on the order of modulation of the laser beam and the fluid flow direction. Also. an electronic amplification circuit which has a bandwidth of 0 . 300 MHz and a gain of 38 dB is designed and fabricated to amplify the high frequency signal.signal.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.8
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• pp.731-735
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• 2003

Ti-indiffused LiNbO$_3$waveguide have been used to various high speed optical device based on electro-optic effect such as modulators, switches, and sensor, etc. In order to high speed modulation of optical modulator have, one of the further devices, needed to increasing of electrode surrounding air by LiNbO$_3$dry etching because of impedance matching for optical and RF phase velocity between waveguide and electrode. We studied property of LiNbO$_3$dry etching after waveguide patterning lot optical modulation by using neutral loop discharge (NLD) plasma.