• Advances in nano research
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• v.15 no.1
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• pp.25-34
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• 2023

This paper investigates the dynamics and stability of steady states in a continuous and discrete-time single-mode laser system. By using an explicit criteria we explored the Neimark-Sacker bifurcation of the single mode continuous and discrete-time laser model at its positive equilibrium points. Moreover, we discussed the parametric conditions for the existence of period-doubling bifurcations at their positive steady states for the discrete time system. Both types of bifurcations are verified by the Lyapunov exponents, while the maximum Lyapunov ensures chaotic and complex behaviour. Furthermore, in a three-dimensional discrete-time laser model, we used a hybrid control method to control period-doubling and Neimark-Sacker bifurcation. To validate our theoretical discussion, we provide some numerical simulations.

• Journal of the Optical Society of Korea
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• v.18 no.2
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• pp.167-173
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• 2014

A novel multi-oxide layer structure for vertical cavity surface emitting laser (VCSEL) structures is proposed to achieve higher single mode output power. The structure has four oxide layers with different aperture sizes and thicknesses. The oxide layer thicknesses are optimized simultaneously to reach the highest single mode output power. A heuristic method is proposed for plotting the influence of these variable changes on the operation of optical output power. A comprehensive optical-electrical thermal-gain self-consistent VCSEL model is used to simulate the continuous-wave operation of the multi-layer oxide VCSELs. A comparison between optimized VCSELs with different structures is presented. The results show that by using multi-oxide layers with different thicknesses, higher single-mode optical output power could be achieved in comparison with multi-oxide layer structures with the same thicknesses.

• ETRI Journal
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• v.35 no.3
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• pp.459-468
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• 2013

A novel integrated laser, that is, a distributed reflector laser diode integrated with an electroabsorption modulator, is proposed to improve the output efficiency, single-mode stability, and chirp. The proposed laser can be realized using the selective metalorganic vapor phase epitaxy technique (that is, control of the width of the insulating mask), and its fabrication process is almost the same as the conventional electroabsorption modulated laser (EML) process except for the asymmetric coupling coefficient structure along the cavity. For our analysis, an accurate time-domain transfer-matrix-based laser model is developed. Based on this model, we perform steady-state and large-signal analyses. The performances of the proposed laser, such as the output power, extinction ratio, and chirp, are compared with those of the EML. Under 10-Gbps NRZ modulation, we can obtain a 30% higher output power and about 50% lower chirp than the conventional EML. In particular, the simulation results show that the chirp provided by the proposed laser can appear to have a longer wavelength side at the leading edge of the pulse and a shorter wavelength side at the falling edge.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1874-1876
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• 1997

A fiber optic voltage sensor using photoelastic effect of a single-mode optical fiber, excited with a 632.8 nm He-Ne laser, is developed. The photoelastic effect is produced by piezoelectric effect for the voltage measurement. It is found that the detector output voltage is proportional to the applied voltage. Also, the frequency of the output voltage is equal to that of the applied voltage. Experimental results from a laboratory model demonstrate the feasibility of the sensor for field application in high-voltage systems.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.205-210
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• 2004

The pulse detonation engine (PDE) has recently expected as a new aerospace propulsion system. The PDE system has high thermal efficiency because of its constant-volume combustion and its simple tube structure. We measured thrust of single-tube pulse detonation rocket (PDR) by two methods using the PDR-Engineering Model (full scale model) for ground testing. The first involved measuring the displacement of the PDR-EM by laser displacement meter, and the second involved measuring the time-averaged thrust by combining a load cell and a spring-damper system. From these two measurements, we obtained 130.1 N of time-averaged thrust, which corresponds to 321.2 sec of effective specific impulse (ISP). As well, we measured the heat flux in the wall of PDE tubes. The heat flux was approximately 400 ㎾/$m^2$. We constructed the PDR-Flight Mode] (PDR-FM). In the vertical flight test in a laboratory, the PDR-FM was flying and keeping its altitude almost constant during 0.3 sec.

• 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.