• Journal of the Optical Society of Korea
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• v.15 no.3
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• pp.227-231
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• 2011

An external optical modulation using absorption s in a Fabry-Perot laser diode (FP-LD), has been proposed and experimentally demonstrated for multicasting in a WDM-PON. The center wavelengths of absorption s in an FP-LD move to short-wavelength rapidly by only a small current (~1 mA) injection. If the current injection is stopped, the s move back to the original position. Such a movement of the s can make the FP-LD act as an external optical modulator, which is found to modulate at a maximum modulation speed of 800 Mbps or more. For a multicasting transmitter in a WDM-PON, the proposed modulator can be cost-effectively applied to a multi-wavelength laser source with the same periodicity of the longitudinal mode. Instead of the multi-wavelength laser source, tunable-LDs are used for experiments. The 32 channel multicasting system with the proposed modulator has been demonstrated, showing power penalties of 1.53~4.15 dB at a bit error rate of $10^{-9}$ with extinction ratios better than 14.5 dB at 622 Mbps.

• Electrical & Electronic Materials
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• v.11 no.11
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• pp.28-36
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• 1998

Widely tunable diodes integrated with periodically sampled and chirped DBR(distributed Bragg reflector) and an EA(electroabsorption) modulator are analyzed dynamically using the improved largesinal time-domain model. The tuning characteristics of sampled- and chirped-grating DBR laser diodes are demonstrated theoretically. The results of the simulation agree well with those of the experiment. And the intensity-modulation properties of the laser diodes integrated with an EA modulator are calculated. It is shown that the external modulation has the lower frequency chirp by 1/20 for the same extinction ratio than the direct modulation, and also the short pulse train can be generated using the optical gating of an EA modulator.

• Journal of the Optical Society of Korea
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• v.18 no.5
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• pp.589-593
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• 2014

Terahertz (THz) communication has important applications in high-speed and ultra broadband wireless access networks. The THz modulator is one of the key devices in a THz communications system. Wavelength division multiplexing (WDM) can expand the capacity of THz communications systems, so research on multi wavelength THz modulators has significant value. By combining photonic-crystal and THz technology, a novel type of multi wavelength THz modulator based on a triple-lattice photonic crystal is proposed in this paper. Compared to a compound-lattice photonic crystal, a triple-lattice photonic crystal has a larger gap width of 0.196. Simulation results show that six beams of THz waves can be modulated simultaneously with high performance. This modulator's extinction ratio is as large as 34.25 dB, its insertion loss is as low as 0.147 dB, and its modulation rate is 2.35 GHz.

• Journal of the Optical Society of Korea
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• v.18 no.5
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• pp.564-568
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• 2014

We present a 25-Gb/s optical transmitter composed of a Si ring modulator and CMOS driver circuit. The Si ring modulator is realized with 220-nm Si-on-insulator process and the driver circuit with 65-nm CMOS process. The modulator and the driver are hybrid-integrated on the printed circuit board with bonding wires. The driver is designed so that the parasitic bonding wire inductance provides enhanced driver bandwidth. The transmitter successfully demonstrates 25-Gb/s operation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.05a
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• pp.698-701
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• 2016

A phase-locked loop(PLL) with effectively increased capacitance by current modulator has been proposed. In this paper, the effective capacitance of loop filter is increased by using current modulator and it results in 1/10 reduction of capacitance in loop filter. It has been designed with a 1.8V $0.18{\mu}m$ CMOS process. The simulation results show that the proposed PLL has the same phase noise characteristic and locking time of conventional PLL.

• International journal of advanced smart convergence
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• v.8 no.3
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• pp.61-68
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• 2019

Spatial modulation (SM) is the first proposed space modulation technique. By further utilizing the quadrature spatial dimension, quadrature spatial modulation (QSM) has been developed as an amendment to SM system to enhance the overall spectral efficiency. Both techniques are capable of entirely eliminating interchannel interference (ICI) at the receiver. In this paper, we propose a simple adaptive hybrid switching transmission scheme to obtain better system performance than SM and QSM systems under a fixed transmission date rate. The presented modulator selection criterion for switching between spatial modulator and quadrature spatial modulator is based on the larger received minimum distance of spatial modulator and quadrature spatial modulator to exploit the spatial channel freedom. It is shown through Monte Carlo simulations that the proposed hybrid SM and QSM switching system yields lower error performance than the conventional SM and QSM systems under the same fixed data rate and thus can provide signal to noise ratio (SNR) gain.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1990-1996
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• 2004

This paper presents a nonlinearly modulated digital actuator (NMDA) for producing nano-precision digital stroke. The NMDA, composed of a digital microactuator and a nonlinear micromechanical modulator, purifies the stroke of the digital actuator in order to generate the high-precision displacement output required for nano-positioning devices. The function and concept of the nonlinear micromechanical modulator are equivalent to those of the nonlinear electrical limiters. The linear and nonlinear modulators, having an identical input and output strokes of 15.2${\mu}{\textrm}{m}$ and 5.4${\mu}{\textrm}{m}$, are designed, fabricated and tested, respectively. The linear and nonlinear modulators are linked to identical digital actuators in order to compare the characteristics of the linearly modulated microactuator (LMDA) and NMDA. In addition, an identical linear modulator is attached to the output ports of LMDA and NMDA. The NMDA shows the repeatability of 12.3$\pm$2.9nm, superior to that of 27.8$\pm$2.9nm achieved by LMDA. When the identical linear modulator is connected to LMDA and NMDA, the final modulated output from NMDA shows the repeatability of 10.3$\pm$7.2nm, superior to that of 15.7$\pm$7.7nm from LMDA. We experimentally verify the displacement purifying capability of the nonlinear mechanical modulator, applicable to nano-precision positioning devices and systems.

• Korean Journal of Optics and Photonics
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• v.7 no.3
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• pp.280-286
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• 1996

This paper describes operation mechanism of a novel optical waveguide phase modulator with optical bistability characteristics by self electro-optic effect. The fabricated device structure is an optical waveguide modulator, using a refractive index change by an applied electric field, parallel integrated with SEED with an electrical bistability. GaAs/AlGaAs MQW is used as the core layer of the waveguide modulator and the absorption layer of SEED. The absorbed optical power in SEED changes the diode voltage and controls the optical power propagating through the waveguide phase modulator. Optical bistability of waveguide phase modulator is experimentally obtained by using electrical bistability of SEED. Compared to other waveguide modulators, the proposed one has an asset that the lowest optical power is required to generate optical bistability.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1779-1781
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• 1997

The 2.0 GeV Pohang Light Source (PLS) is consisted of a full energy Linac and a storage ring. Four kicker magnets are installed in the storage ring tunnel to move the stored beam orbit in the storage ring closer to the injected beam from the beam transfer line. The injected beam then falls into the storage ring beam dynamic aperture. A kicker magnet modulator drives all four kicker magnets to maintain field balance and also synchronized kick of the beam. The kicker modulator can handle 2 GeV full energy beam. The kicker magnet modulator is installed in the storage ring tunnel and under stable operation. Specification of the kicker magnet modulator is ${\sim}6.0{\mu}s$ pulse-width, 200 ns flat-top width with ${\pm}0.2%$ regulation, ${\sim}24\;kA$ peak current, and 10 Hz repetition rate. Two thyratron switches (EEV CX-1536AX) are used in the system. In this article, design, and experimental results of the kicker magnet modulator are discussed.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.507-508
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• 2006

High performance delta-sigma modulator is developed for audio-codec applications(i.e.. 16-bit resolution at a 20kHz signal bandwidth). The modulator is realized with fully-differential switched capacitor integrators. All stages employ a single-stage folded-cascode amplifier. The presented delta-sigma modulator when clocked at 3.2MHz achieves 85.2dB peak-SNDR and 94.8dB SNR. This modulator is designed in a SAMSUNG $0.18{\mu}m$ CMOS process. Finally, this paper shows the test setup and FFT result gained from delta-sigma modulator chip designed for audio applications.