• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.8
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• pp.76-85
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• 2000

Effects of the random fluctuation in grating half-period have been studied by an effective index transfer matrix method in DFB lasers. The laser facets are assumed to be perfectly antireflection coated, and the period fluctuation is modeled as a Gaussian random variable. The random fluctuation breaks spectral symmetry in both uniform-grating and quarter-wavelength -shifted(QWS) DFB lasers, and decreases the effective coupling coefficient. This leads to increased average mirror loss of ${\pm}$1 modes and reduced stopband width in uniform grating DFB lasers, and degradation in the wavelength accuracy and the single mode stability in QWS-DFB lasers. Threshold gain difference decreases with increasing period fluctuation irrespective of grating coupling coefficient in QWS-DFB lasers, while spatial hole-burning effect is exacerbated or alleviated when the normalized coupling coefficient is lower and higher than 1.5, respectively.

• ETRI Journal
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• v.25 no.3
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• pp.149-155
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• 2003

A self-pulsating multisection distributed-feedback laser diode (DFB LD) can potentially realize all-optical clock extraction. This device generally consists of three sections, two DFB sections and one waveguide section. The most important variable in this device is detuning, which is the relative spectral position between the stop bands of two DFB sections. We fabricated a novel structure in which two gratings were located one over and one under the active layers. Each grating structure was independently defined in processing so that detuning, which is the prerequisite for self-pulsation, could be easily controlled. Observing various self-pulsating phenomena in these devices under several detuning conditions, we characterized the phenomena as dispersive Q-switching, mode beating, and self-mode-locking.

• Proceedings of the IEEK Conference
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• 2000.11b
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• pp.313-316
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• 2000

Concentric-Circle-Grating (CCG) cavity is analyzed by coupled mode theory. In this case concentric grating is acting as both feedback element and output coupler. In our calculations radiation loss terms are included in guided coupled mode equations. The surface-emitted field distribution is obtained in self-consistent manner.

• Journal of the Optical Society of Korea
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• v.5 no.1
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• pp.5-8
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• 2001

In this work, we studied the effect of chirped grating on optical bistability in λ/4-shifted semiconductor distributed-feedback(DFB) devices, such as an etalon with nonlinear mirrors, a λ/4-shifted DFB waveguide and aλ/4-shifted DFB laser amplifier. We found that chirped DFB devices exhibit bistable switching at a lower input power.OCIS code : 050.2770, 190.1450, 190.5970, 230.0230.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.2
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• pp.48-56
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• 1995

The operating characteristics, such as, the threshold gain, lasing frequency, and longitudinal intensity profile, etc., of 1.55$\mu$m DFB laser diode with index and/or gain grating structures and with one side AR-coated mirror have been analyzed. From this analysis, the optimum design parameters have been shown that ${\Delta}{\Omega}$ (the phase difference between index grating and gain grating) is 0 or ${\pi}$, (xL)$_{r}$=1~3 and (xL)$_{i}$=0.5~0.9. It has been also shown that the modal selectivity and intensity uniformity of the DFB lasers with .DELTA..OMEGA.=0 are ~1.2 times better thatn those of the DFB lasers with ${\Delta}{\Omega}$= ${\pi}$.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.88-89
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• 2003

현대 시대에 광통신 시스템은 안정적이고 높은 단일 모드를 갖는 광원을 필요로 한다. 이 조건을 만족하는 λ／4 phase shifted DFB는 높은 단일모드 생성을 보였으나 high spatial hole burning문제점을 가지고 있다. λ／4 phase shift를 사용하지 않은 dual-pitch grating DFB가 소개되었지만 제작상의 어려움을 가지고 있다. 또 다른 구조인 selection-free tapered stripe DFB lasers가 제안되었는데 제작이 간단하면서도 높은 단일모드 생성을 보였다. (중략)

• Korean Journal of Optics and Photonics
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• v.17 no.6
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• pp.548-555
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• 2006

We investigate the effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection index-coupled (IC) DFB lasers composed of two index-coupled DFB sections and a phase tuning section between them in terms of yield. In the case of weak coupling strength, as the reflectivity of both facets increases, the effect of reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases. Thus the number of mode hoping increases and yield decreases for the variation of phases of both facets. In the case of strong coupling strength, as the reflectivity of both facets increases, the spatial hole burning effect increases, so that the yield decreases. The maximum yield and the range of the phase of a phase tuning section with yield more than 40% decrease as the facet reflectivity increases irrespective of coupling strength. As the coupling strength increases, the variation of yield for the variation of the phase of a phase tuning section increases and the variation of the phase of a phase tuning section with the maximum yield for the variation of the reflectivity of both facets decreases. The yield characteristics of the cases with the coupling strengths of 2 and 3 are better than those with the coupling strengths of 1.2 and 4.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.68-72
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• 1997

Using one of the absorption lines of $^{13}C_2H_2$ molecules near the zero dispersion wavelength(1549.49nm) of dispersion shifted fiber, we stabilized center frequency of an optical fiber Fabry-Perot filter. The free spectral range of the filter is 100 GHz for 100 GHz channel allocation. For equi-spaced three channel multiplexing, channel locking of three DFB-LDs to transmission peaks of the fiber Fabry-Perot filter was tried. To investigate the effect of dithering current applied to each DFB-LD, the change of DFB-LD linewidth was measured.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.7
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• pp.17-28
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• 2000

A novel and efficient approach for the numerical solution of time-dependent coupled-wave equations, which are frequently used for the modeling of DFB(Distributed Feedback), DBR(Distributed Bragg Reflector), and FP(Fabry Perot) laser diodes, is proposed. In this approach, the coupled wave equations are split into two sets of equations. One of two sets of equations contains only the phase factors and the other contains only the coupling terms. The separate equations are solved exactly in their split form successively. This new numerical scheme, which we call the SS-TDM(Split-Step Time Domain Model), is found to require an order of magnitude smaller number of subsections to get accurate results than the previous methods while the computation time for each time step is comparable to the previous methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.12
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• pp.2426-2438
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• 1994

In this paper we present for the first time the electric circuit model for direct frequrncy modulation(FM) response of the conventional distributed-feedback(DFB) semiconductor laser diodes. Especially, in this paper, the proposed model includes not only the carrier density modulation effect, but also the temperature modulation effect determining the DFM characteristics of DFB characteristics of DFB semiconductor lasers. The DFM response due to injection current modulation was obtained as a function of modulation frequency from DC to a few GHz. The circuit model representing the temperature modulation effect is obtained from the structure of DFB LD chip and the simulation results are compared with the published experimental results. The circuit model representing the temperature modulation effect is obtained from the structure of DFB LD chip and the simulation results are compared with the published experimental results. The circuit model representing carrier density modulation effect is obtained from the rate equations of DFB lasers and the simulation results are compared with the results that were obtained by the conventional numerical analysis approach. The results showed good agreements.