• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.134-141
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• 1997

We design the single mode dispersion-compensating fibers (DCF) which may be necessary for upgrading the previously installed 1.31 ${\mu}{\textrm}{m}$ optical communication system to the 1.55 ${\mu}{\textrm}{m}$ system. To obtain the optimum index profile that allows large negative dispersion at 1.55 ${\mu}{\textrm}{m}$, parabolic-index, double-clad fibers are analyzed by applying the 1-D FEM to the scalar wave equation of optical fibers. In constideration of macro-bending loss, the fibers are designed so that the cutoff wavelength of the $LP_{01}$ mode is greateer than 1.80 ${\mu}{\textrm}{m}$. The computer simulations show that the lower bound of the dispersion at 1.55 ${\mu}{\textrm}{m}$ is limited to about -120 ps/nm . km for the fiber index profiles satisfying the $LP_{01}$'s cutoff condition.

• Korean Journal of Optics and Photonics
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• v.6 no.2
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• pp.156-164
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• 1995

Based on the scalar wave equation of optical fibers, the dispersion characteristics of arbitrarily profiled fibers were analyzed. We used the I-D FEM employing quadratic interpolation fucntions to solve the scalar wave equation. We simulated the DC optical fibers as objects, and searched for the refractive index distribution to minimize the total dispersion. In DC fibers, we found the design parameters for which the total dispersion was almost zero at $\lambda=1.3{\mu}m and 1.55{\mu}m$ simultaneously. We also found the design parameters where the dispersion was flattened, less than 1.0 ps/km.nm for$\lambda=1.4~1.7{\mu}m$1. and the dispersion was as low as 0.65 ps/km.nm at $\lambda=1.55{\mu}m$..

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.335-339
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• 2000

A $1.31/1.55\mu\textrm{m}$ coarse WDM opncal dIrectional coupler that conslsls of two idenlical straight channel waveguides in BK7 glass has been fabricated. The separatIOn between two channel waveguides is $8\mu\textrm{m}$ and the wavegu.ide width is $4\mu\textrm{m}$ . Especlally, we assumed that the index profile is Gaussian function and complementary error function in the width direction and depth direction, respectrvely. This directional coupler operating at $1.31/1.55\mu\textrm{m}$ with crosstalk of 18dB is demonstrated and has the 16 mm long length with 12.6 mm coupling region.region.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.327-332
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• 1997

We fabricated the high speed 1.55${\mu}{\textrm}{m}$ distributed feedback laser diodes (DFB-LD) using both two-step mesa etching process and semi-insulating InP current blocking layers. The devices characteristics were threshold current of ~15mA, slope efficiency of ~0.13mW/mA, and dynamic resistance of ~6.0Ω, with as-cleaved facets. The fabricated DFB-LD showed the single longitudinal mode with more than 40dB up to 6 $I_{th}$(CW condition), emitting at the wavelength of 0.546${\mu}{\textrm}{m}$. The -3dB bandwidth was >10㎓ at the driving current of 27mA, and the maximum -3dB bandwidth was ~18㎓ at 90 mA current, showing the superior frequency response of SI-PBH DFB-LD. In the 10Gb/s transmission experiment for 1.55${\mu}{\textrm}{m}$ DFB-LD module, maximum 10 km of single mode fiber(SMF) or 80 km of dispersion shifted fiber (DSF) could be transmitted with error free.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.120-124
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• 1994

PBH-DFB-LD emitting at $1.55\mu\textrm{m}$ wavelength has been fabricated for 2.5 Gbps optical fiber communications. For fabrication of PBH-DFB-LD. inteference expose for grating formation and 3-step LPE epitaxial growth was used. Fabricated PBH-DFB-LD operates in single longitudinal mode with more than 35dB SMSR and its threshold current is less than 15 mA. The operating wavelength is 1530-1550 nm with the temperature dependence of $0.9\AA/^{\circ}C$. Coupling coefficient(K) was estimated as $$97 cm^{-1} by means of stop-band measurement. PBH-DFB-LD fabricated in this experiment can be applicable as light source for 2.5 Gbps optical fiber communication system. ystem.

• Korean Journal of Optics and Photonics
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• v.22 no.4
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• pp.191-197
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• 2011

In this paper, we have designed an integrated triplexer which is the basic component for a FTTH(Fiber To The Home) system which can transmit CATV and voice/data at the same time in a single fiber. The integrated triplexer can be fabricated with a novel technique of "Micro-Block Stacking (MBS)" method which automatically aligns the optical components in the optical beam pass using accurate ceramic holders. We analyze the displacement of the optical focus according to the tolerances of the component dimensions and the assembly process using code V simulator. For the transmitter, the most serious shift of the focal points is caused by the displacements of the LD spot. So the focal point moves up to $72{\mu}m$ from the center point for ${\pm}25{\mu}m$, ${\pm}25{\mu}m$, ${\pm}30{\mu}m$ displacements. For the receiver the most serious shift of the focal points is caused by the displacements of a 0.8mm ball lens (for the analog receiving part) and a micro ball lens (for the digital receiving part), and the focal point moves up to $55{\mu}$ for ${\pm}55{\mu}m$, ${\pm}5{\mu}m$, ${\pm}55{\mu}m$ micro ball lens displacements.

• Korean Journal of Optics and Photonics
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• v.12 no.1
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• pp.40-47
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• 2001

The structural dependence of the performance of an 1.55 $1.55{\mu}m$ InGaAsPIInGaAsP MQW electro-absorption modulator for highspeed digital fiber communication was systematically investigated. The effects of n-doped SCH region length $t_n$ as well as the general structure parameters including quantum well number $N_w$, well-thickness $t_w$, detuning wavelength $\Delta\lambda$, and device length L were thoroughly analyzed. Thereby, a high-pelfoIDlance electro-absorption modulator with device length L of $100{\mu}m$ was successfully designed. The designed structure showed excellent characteristics that have residual loss less than -1.5 dB, operational voltage from 0 V to -2V, and extinction ratios of -2.92 dB at $V_{\alpha}$=-1 V and -10 dB at $V_{\alpha}$=-2V.X>=-2V.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.183-186
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• 1995

The fabrication of dielectric multilayer mirror(DMM) optimized at the wavelength of 1.55$\mu\textrm{m}$ and its spectral properties were investigated. The materials used in the fabrication of DMM are TiO$_2$-SiO$_2$, which have the advantage of yielding high reflectance for relatively small numbers of layers. The optical constants of TiO$_2$single film were obtained by using a modified envelope method. The reflectances of DMMs with 3,7,11 and 23 layers were 58%, 89%, 97% and 99.9% at the wavelength of 1.55$\mu\textrm{m}$, respectively.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.3
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• pp.60-73
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• 1997

By introducing a compressive-strained quanternary InGaAsP quantum-wells instead of a conventional ternary InGaAs quantum-wells in 1.55.mu.m DFB-LD, the lasing performances canb e improved and the problems caused by the thickness non-uniformity and the compositional abruptness among the hetero-interpaces canb e relaxed. In this paper, we investigated an iptimum InGaAsP/InGaAsP multiple-quantum-well(MQW) structure as an active layer in a direct-modulated 1.55.mu. DFB-LD from the view point of threshold current, chirping charcteristics, and resonance frequency. The optimum compressive-strained MQW structure was revealed as InGaAsP/InGaAsP structure with strain amount of about 1.2%, number of wells $N_{w}$ of 7, well width $L_{w}$ of 58.agns.. The threshold current density J of 500A/c $m^{2}$, the linewidth enhancement factor a of 1.8, and differential resonance frequency of d $f_{r}$/d(I-I)$^{1}$2/=2GHz/(mA)$^{1}$2/(atI=2 $I_{th}$) were expected in 1.55.mu.m .gamma./4-shifted DFB-LD with the cavity length of 400.mu.m long and kL value of 1.25. These values are considerably improved ones compared to those of 1.55um DFB-LD with InGaAs/InGaAsP MQW which have enhancement factor and the resonance frequence frequency by the detuning of lasing wavelength and gain-peak wavelength. It was found that the linewidth enhancement factor of 20% and differential resonance frequency of 35% without the degradation of the threshold current density could be enhanced in the range of -15nm~-20nm detuning which can be realized by controlling the thickness and Incomposition of InGaAsP well. well.and Incomposition of InGaAsP well. well.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.9
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• pp.139-145
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• 1994

InGaAsP/InP PBH-DFB-LD emitting at 1.55${\mu}$m wavelength has been fabricated for 2.5Gbps optical fiber communcations. For fabrication of PBH-DFB-LD, Interference expose for grating formation 3-step LPE epitaxial growth were used. Fabricated PBH-DFB-LD operates in single longitudinal mode with larger than 35dB SMSR and wider than 3dB bandwidth of 3GHz. A 8${\mu}$m mesa structure was introduced by channel etching to reuce parasitic capacitance. To reduce pad capacitance, we designed a small electrode. 0.27mW/mA in the case of spectrum shows single logitudinal mode operation with larger thatn 30dB SMSR measured at 5mW.