• Title/Summary/Keyword: laser oscillation threshold

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Regenerative Erbium-Doped Fiber Ring Amplifier with Unidirectional and Bi-directional Feedbacks

  • Shah, N.S.Mohd.;Teyo, T.C.;Poopalan, P.;Ahmad, H.
    • Proceedings of the IEEK Conference
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    • 2002.07a
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    • pp.540-541
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    • 2002
  • In this paper, the performance of upidirectional and hi-directional regenerative erbium-doped fiber amplifier (EDFA) is compared. The systems are operating above laser oscillation threshold. The experimental results show that the unidirectional regenerative EDFA has a better performance than the hi-directional.

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Lasing mode and Beam Profile Analysis of DFB Laser with an Anti-reflection Coated Mirror (무반사 면을 갖는 DFB 레이저의 발진 모드와 빔 분포 해석)

  • Kwon, Keeyoung
    • The Journal of the Convergence on Culture Technology
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    • v.6 no.4
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    • pp.727-732
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    • 2020
  • In this paper, when a refractive index grating and a gain grating were simultaneously present in a DFB laser having a wavelength of 1.55 ㎛, a dielectric film coating was applied so that reflection did not occur on the right mirror surface, so that 𝜌r=0. In case of δL > 0, the threshold gain and the beam distribution in the longitudinal direction and the radiated power ratio Pl/Pr of the oscillation mode were compared for the cases of the phase of 𝜌l=π and π/2. If the phase of 𝜌l=π, in order to obtain a low threshold current and high frequency stability, κL should be greater than 8. In the case of the phase of 𝜌l= π/2, when κL is larger than 4.0, the oscillation gain starts to be lower than when the phase of 𝜌l=π. In order to lower the threshold current of a oscillation mode and enhance the frequency stability, κL should be greater than 8.

Oscillation Mode and Grating Phase in DFB Laser Diode with an Anti-reflection Coated Mirror (무반사 코팅된 DFB 레이저 다이오드에서 발진 모드와 격자 위상)

  • Kwon, Keeyoung;Ki, Janggeun
    • The Journal of the Convergence on Culture Technology
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    • v.8 no.5
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    • pp.483-488
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    • 2022
  • In this paper, when a gain grating and a refractive index grating exist simultaneously in a DFB laser diode having a wavelength of 1.55 ㎛, an anti-reflection coating is applied to the right mirror surface so that ρr=0. In case of δL<0, the characteristics of the oscillation frequency and oscillation gain have been analyzed. Whenever the phase of the grating on the left side of the mirror continuously decreases by π/2, the δL value of each oscillation mode decreases by about 0.6 to the left of the graph lines of each oscillation mode. The case of the oscillation mode having the lowest threshold gain is the case of κL=10, and in this case, the mode selectivity is relatively low compared to the case of other values of κL. From κL=0.1 to κL=6, the mode selectivity and the frequency stability are excellent. As the mode selectivity is excellent, the frequency stability is excellent. Compared to the case with two cleaved mirrors, the DFB laser diode with anti-reflection coating increases the threshold gain of the oscillation mode by about 2 times, but the mode selectivity becomes about 2 times better.

Effect of Grating Phase in DFB Lasers with an Anti-reflection Coated Mirror (AR 코팅된 DFB 레이저에서 격자 위상의 영향)

  • Kwon, Kee-young;Ki, Jang-geun;Cho, Hyun-mook
    • The Journal of the Convergence on Culture Technology
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    • v.7 no.3
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    • pp.463-468
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    • 2021
  • In this paper, when a refractive index grating and a gain grating were simultaneously present in a DFB laser having a wavelength of 1.55 ㎛, a dielectric film coating was applied so that reflection did not occur on the right mirror surface, so that 𝜌r=0. In case of 𝛿L>0, the characteristics of the oscillation frequency and oscillation gain were analyzed. When the grating phase of the left mirror surface continues to decrease from 𝜋, the graph lines of each mode gradually shift to the left. In case of 𝜅L=10, the threshold gain of the oscillation mode is the lowest. In this case, the mode selectivity is relatively low. From 𝜅L=0.5 to 𝜅L=6, the mode selectivity and the frequency stability are excellent. In the case of DFB lasers with an anti-reflection coated mirror, the threshold gain of the oscillation mode increases but the mode selectivity is about twice as excellent, compared with DFB lasers of having two cleaved facets.

Output characteristics and measurement of the gain coefficient of a pulsed Nd:YAG laser (펄스형 Nd:YAG 레이저의 출력특성과 이득계수 측정)

  • 박대윤
    • Korean Journal of Optics and Photonics
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    • v.10 no.1
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    • pp.53-57
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    • 1999
  • We established the laser oscillator using Nd:YAG crystal grown at Ssang Yong company in Korea and investigated the characteristics of oscillation, Q-switching and wave front of output beam. We measured the single pass gain by controlling the threshold input energy with two output couplers of different output reflectances. Moreover, we compared the gain measured by different output couplers with the gain directly measured by the laser amplifier. The peak power of Q-switching, the pulse width, and the single pass gain coefficient at the threshold energy were 1.5 MW, 30ns, and 0.0958 cm-$^1$ respectively and they were compared with those of the commercial Nd:YAG crystal. Our crystal was proved to be as good as the commercial crystal.

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Nano-Second Periodically Poled Lithium Niobate Optical Parametric Oscillator with Planar Cavity Mirrors

  • Kim, Hong-Ki;Rhee, Bum--Ku
    • Journal of the Optical Society of Korea
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    • v.5 no.4
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    • pp.136-139
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    • 2001
  • We investigated a high-output ower, periodically poled lithium niobate(PPLN) optical parametric oscillator(OPO) pumped by a Q-switched Nd:YAG laser. Given the low optical damage threshold and the limited aperture (0.5mm thick) of PPLN, we tried to maximize the signal output power in a linear cavity consisting of two flat mirrors with a loosely focused pump beam. It is found that this simple cavity structure allowed a robust OPO operation, which was not sensitive to alignment compared with the conventional ones using concave mirrors. A maximum energy of 100$\mu$J/pulse was achieved for the signal at 1.36${\mu}{\textrm}{m}$, while the oscillation threshold was 0.3 mJ/pulse for the pump at 1064 nm.

Lasing Modes of LD-Pumped Fiber Grating Lasers

  • Park, Dong-Wook;Hwang, Joon-Hwan
    • Journal of the Optical Society of Korea
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    • v.6 no.3
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    • pp.108-116
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    • 2002
  • Lasing modes of laser-diode-pumped fiber grating lasers are analyzed by coupled-mode theory. First, a power series solution of the coupled-mode equations is derived under the assumption of an exponentially-decreasing longitudinal modal gain profile for a laser-diode-pumped grating section, followed by determination of the transfer matrix for such a section. Based on these results, an eigenvalue equation for oscillation is then derived and solved numerically for the lasing modes of uniform and phase-shifted fiber grating lasers. Comparisons made with the uniform-gain results indicate that, surprisingly, the lasing mode characteristics are not as significantly altered as might be expected in most cases, even for a highly nonuniform gain profile. In the case of a phase-shifted grating, the phase-shift position appears to have a much greater impact on determining the threshold gain, the modal field distribution, and the front-to-back output power ratio.

Simulation and Examination for Beam Profile of DFB Laser with an Anti-reflection Coated Mirror (무반사 면을 갖는 DFB 레이저의 빔 분포 시뮬레이션과 검정)

  • Kwon, Kee-Young;Ki, Jang-Geun
    • Journal of Software Assessment and Valuation
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    • v.16 no.1
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    • pp.55-63
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    • 2020
  • Lasers for optical broadband communication systems should have excellent frequency selectivity and modal stability. DFB lasers have low lasing frequency shift during high speed current modulation. In this paper, when a refractive index grating and a gain grating are simultaneously present in a DFB laser having a wavelength of 1.55 ㎛, the dielectric film is coated so that reflection does not occur on the right mirror surface, so that ρr=0. For the first mode, which requires a minimum gain at the threshold, the beam distribution of the oscillation mode in the longitudinal direction and the radiated power ratio Pl/Pr were analyzed and compared for the cases of the phase of ρl=π and π/2. If the phase of ρl=π, in order to obtain a low threshold current and high frequency stability, κL should be greater than 8. In the case of the phase of ρl=π/2, for low threshold current, κL is necessary to be 1.0, where the oscillation frequency coincides with the lattice frequency. DFB lasers with an anti-reflection coated mirror have excellent mode selectivity than 1.55um DFB lasers with two mirror facets

Beam Profile Analysis of DFB Laser for High Speed Communications (고속 통신용 DFB 레이저의 빔 분포 해석)

  • Kwon, Keeyoung
    • The Journal of the Convergence on Culture Technology
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    • v.6 no.3
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    • pp.419-425
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    • 2020
  • In this paper, when a refractive index grating and a gain grating are simultaneously present in a DFB (Distributed Feedback) laser for a 1.55 um wavelength with two mirror surfaces without an anti-reflective coating, an analysis program was developed to determine the beam distribution of the oscillation mode in the longitudinal direction. As the phases of the index and gain gratings on the mirror faces are varied, the lasing gain and the beam profiles |R(z)| and |S(z)| of the lasing mode with the emitted power ratio Pl/Pr are analyzed and examined in case of δL<0. In order to reduce the threshold current of a oscillation mode and enhance the frequency stability, κL should be greater than 8, regardless of the grating phase values at the mirror surface.

Circuit Model for the Effect of Nonradiative Recombination in a High-Speed Distributed-Feedback Laser

  • Nie, Bowen;Chi, Zhijuan;Ding, Qing-an;Li, Xiang;Liu, Changqing;Wang, Xiaojuan;Zhang, Lijun;Song, Juan;Li, Chaofan
    • Current Optics and Photonics
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    • v.4 no.5
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    • pp.434-440
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    • 2020
  • Based on single-mode rate equations, we present an improved equivalent-circuit model for distributed-feedback (DFB) lasers that accounts for the effects of parasitic parameters and nonradiative recombination. This equivalent-circuit model is composed of a parasitic circuit, an electrical circuit, an optical circuit, and a phase circuit, modeling the circuit equations transformed from the rate equations. The validity of the proposed circuit model is verified by comparing simulation results to measured results. The results show that the slope efficiency and threshold current of the model are 0.22 W/A and 13 mA respectively. It is also shown that increasing bias current results in the increase of the relaxation-oscillation frequency. Moreover, we show that the larger the bias current, the lower the frequency chirp, increasing the possibility of extending the transmission distance of an optical-fiber communication system. The results indicate that the proposed circuit model can accurately predict a DFB laser's static and dynamic characteristics.