• Proceedings of the Optical Society of Korea Conference
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• 2001.08a
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• pp.272-273
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• 2001

Normalized gain difference for index-coupled and quarter wavelength shifted DFB lasers for various facet reflectivities are calculated as a function of facet phases.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.527-534
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• 2005

We investigate the pulsation characteristics in a multi-section DFB laser which is composed of one DFB section, phase tuning section, and gain section. Multi-section DFB lasers with anti-phase (AP) complex-coupled (CC) DFB structure show wide current ranges of gain and phase tuning sections fer stable pulsations compared to those with in-phase CC DFB structure or index-coupled DFB structure. For multi-section DFB lasers with AP CC DFB structure, the current range of a gain section for stable pulsations increases and the tuning range of the pulsation frequency increases as a coupling strength or a gain coupling coefficient increases Also, the tuning range using the phase variation in a phase tuning section increases. For a fixed coupling strength, the current ranges of gain and phase tuning sections for stable pulsations increase and the tuning range of the pulsation frequency increases as the length of a DFB section increases.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.9
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• pp.128-138
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• 1994

In 1.55.mu.m DFB lasers with two non-AR mirrors, I have analyzed the effect of the sturctures of indes and/or gain gratings and mirror positions on the threshold gains, the lasing frequencies, and the beam profiles in longitudinal direction of lasers. I have obtained the optimum condition of static characteristics that ${\Delta}{\Omega}$(the phase difference betweeen index grating and gain grating is 3${\pi}$/4, $({\kappa}L)_{i}$=4~6 in case of $({\kappa}L)_{i}$=0.9 and $({\kappa}L)_{i}$=3~5 in case of $({\kappa}L)_{i}$=0.7. The modal selectivity and intensity uniformity of this optimum condition are 2~2.5 times better than those of the gain-coupled DFB lasers ${\Delta}{\Omega}$=0). The gain-coupled DFB lasers${\Delta}{\Omega}$=0) have 10$^{10) times better modal selectivity and intensity uniformity than the loss-coupled DFB lasers(TEX>${\Delta}{\Omega}$=${\pi}$).

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.191-197
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• 2006

We analyze the self-pulsation(SP) characteristics due to mode beating of two modes emitted in a multi-section complex-coupled (CC) DFB laser composed of two DFB sections and a phase control section between them. SP frequency due to mode beating of the two modes is determined by the difference of grating periods in the two CC DFB regions. As the difference of grating periods in the two CC DFB regions increases, the SP frequency increases from very low frequency to the THz region. In the case of a mode which is not located in the stop band of the other DFB region, the mode propagates into the other DFB region without a high reflection, so that output powers emitted in a multi-section CC DFB laser have high modulation indexes due to the large interaction between the two modes.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.298-305
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• 2003

We have calculated the single mode yield of index-coupled (IC) DFB lasers above threshold for several kL, and facet reflectivity combinations, and investigated the correlation between those results and the single mode yield as a function of f number at the threshold. As a result, there is little correlation between the single mode yield above threshold and the single mode yield as a function of f number at the threshold. The single mode yields above threshold for kL of 0.8 and 1.25 is larger than those for kL, of 2 and 3 due to the spatial hole burning effect. Also, we have investigated the effect of the reflectivity of the AR facet on the single mode yield for AR-HR and AR-CL combinations. For AR-HR combinations, the single mode yield increases as the reflectivity of the AR facet decreases. However, for AR-CL combinations, the reflectivity of the AR facet for the largest single mode yield exists. In the single mode yield calculations for IC DFB lasers in this paper, the single mode yield for kL of 0.8 with AR(1％)-HR combination is largest above threshold.

• Korean Journal of Optics and Photonics
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• v.16 no.1
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• pp.85-98
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• 2005

As the number of compound cavity modes within the stopband of DFB sections decreases, the frequency of mode hopping decreases for the variation of $\Delta$λ$_{B}$, which represents the difference between the Bragg wavelengths of two DFB sections, so that the number of abrupt changes of pulsation frequencies decreases. In addition, the pulsation frequency varies continuously for the variation of the phase in a phase tuning section for a fixed $\Delta$λ$_{B}$. The number of compound cavity modes within the stopband decreases as the length of DFB sections increases and the length of a phase tuning section decreases. Thus stable self-pulsation operations for the variation of $\Delta$λ$_{B}$ and the phase in a phase tuning section could be obtained by proper selection of the coupling strength and the length of each section.ction.

• 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.14 no.4
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• pp.413-422
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• 2003

We have calculated the power extraction efficiency and the lasing wavelength distribution of index-coupled DFB lasers at threshold for various kL and facet reflectivity combinations, and compared with those above-threshold. The power extraction efficiency increases as the asymmetry of the facet reflectivities increases. The power extraction efficiency above-threshold is slightly larger than that at threshold. Since the relative photon density around the center region increases as kL increases, the power extraction efficiency decreases. The uniformity of the distribution of lasing wavelength over the stop band increases due to the relief of mode degeneracy as the asymmetry of the facet reflectivities increases. In the case of AR-HR combination, the lasing wavelength distributions at threshold are similar to those above-threshold. However, in the case of AR-AR combination, the lasing wavelength at threshold is concentrated on both edges of the stop band, while it is concentrated only on the longer wavelength edge above-threshold. As kL increases, the range of the lasing wavelength distribution increases due to the increase of the stop band. The effect of AR reflectivity on the power extraction and the lasing wavelength distribution is very weak.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.7
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• pp.80-91
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• 1999

We present various optimal grating structures which give the low threshold gain, good modulation characteristics, small effective linewidth enhancement factor, and large fabrication tolerance in complex-coupled MQW DFB lasers with absorptive gratings. To obtain these, we calculate the complex coupling coefficients using the extended additional layer method and the threshold gain including the modal loss in the absorptive grating region for rectangular and trapezoidal gratings. Based on the comparison of the results for various possible absorptive grating structures, the design guidelines are presented to obtain the low threshold gain or large fabrication tolerance. Among the grating structures studied, the double grating structure consisting of the absorptive grating on the index grating has the largest fabrication tolerance for the threshold gain and the coupling strength. The fabrication tolerance for the coupling ratio is very large for all the grating structures studied.