• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7C
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• pp.743-754
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• 2006

In the proposed method, two regular laser working at two different wavelengths perform moving object detection alternatively in time. The laser intensity and the beaming period of each laser is equally maintain as to the single laser radar, hence, externally, dual beam lasers radar works exactly same as the single beam laser radar except that the proposed dual lasers radar needs additional post-processing of received signals in the receiver. To verify the robustness of the proposed method, a set of computer simulation has been performed. The communication channel is assumed to be additive white Gaussian noise, and the perfect synchronization is assumed. All other simulation parameters such as signal power and signalling period are equally maintain in both systems while the signal processing time such as spreading and filtering are expected to be trivial in call cases.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.7
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• pp.31-36
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• 2004

In comparison with in-plane lasers, predicting the output power and differential quantum efficiency of Vertical-Cavity Surface-Emitting Lasers(VCSELs) is very difficult due to the distributed Bragg reflector(DBR) layers. Therefore, effective cavity model and transfer matrix method have been adapted in order to calculate the output power and differential quantum efficiency The effective cavity model is inappropriate to calculate output power and differential quantum efficiency while it is practically adequate to calculate the threshold gain and threshold current density The reason is that the effective cavity model can not take account of the absorption in GaAs stack layer right below the metal aperture. In this paper, we have compared the threshold current and differential quantum efficiency calculated by using transfer matrix method with effective cavity model and we have made a study of the validity of the effective cavity model. Finally, we have confirmed the versatility of the transfer matrix method with these studies.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.5
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• pp.88-98
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• 1999

A refractive index modulated (RIM) DFB laser, in which the refractive index of a center region of the upper cladding layer comprising the grating region is different from that of side regions, is proposed to obtain and effective ${\lambda}$/4 phase shift in the center region. Since the coupling coefficient of a center region in a RIM-DFB laser is larger than that of side regions, a RIM-DFB laser has the effect of a distributed coupling coefficient. Simulation results show that RIM-DFB lasers have better operation characteristics - more uniform photon density profile, less SHB effect, and better single mode operation at high injection currents - compared to those of ${\lambda}$/4 phase-shifted DFB lasers and CPM-DFB lasers. In addition, the effect of the center region on the above threshold characteristics of a RIM-DFB laser is investigated.

• Korean Journal of Optics and Photonics
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• v.18 no.4
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• pp.270-273
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• 2007

We have investigated the output characteristics of the 946 nm Nd:YAG laser which is longitudinally pumped by a fiber coupled laser diode. The temperature of a Nd:YAG crystal mount was kept constant by a controller with thermoelectric cooler. As a result, we measured more intense output at a low temperature, and then the maximum output power was measured to be 870 mW when the pumping power and the temperature were 9.95 W and $5^{\circ}C$, respectively. It appeared that output was decreased above 10 W pump power because of the thermal effects in gain medium.

• Korean Journal of Optics and Photonics
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• v.28 no.6
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• pp.351-355
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• 2017

In this paper, we conduct a simulation of manipulating various pulsed laser operations through tuning the modulation depth of the saturable absorber in a laser cavity. The research, showing that various pulsed operations could be manipulated from Q-switching through Q-switched mode locking to mode locking by tuning the modulation depth of the saturable absorber in a cavity, has been studied by experimental means. We conduct a simulation with the Haus master equation to verify that these experimental results are consistent with expectations from theory. The time dependence of the gain was considered to express Q-switching fluctuation through applying a rate equation with the Haus master equation. Laser operation was manipulated from mode locking through Q-switched mode locking to Q-switching as modulation depth was increased, and this result agreed well with the theoretical expectation.

• 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.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.360-364
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• 2000

We demonstrate self-starting passIve mode locking of a Cr:LiSAF laser, using a SCIDlconduclor Saturable Absorber Mirror (SESAM), Two high-power red semiconductor lasers (Coherent S-67-500C-100-H) of wavelength 667 nm and maximum power of 500 mW were used as pump lasers, The cavity has 10 cm radius-ai-curvature folding minors, two SF 10 prisms, a 99% reflectivity output coupler and a SESAM at dIe focus of a 10 cm radIus-at-curvature mirror. We used the laser crystal in BrewsterBrewster shape with 1 5% $Cr^{+3}$ ion concentration and the length of 6 mm, An X-shaped resonator was used to compensate the astigmatism induced by tile crystal. The structure of the SESAM cOllSists of 30 pmr of $AlAs/Al_{0.15}Ga_{0.85}As$ layer, wi1l1 a 10 nm GaAs quantum well situated in the topmost layer Output spectra were centeled at 833 nm, with 4 nm spectral bandwidth and pulse width was measured to be 220 fs, Output power of 3 mW is obtained at a pump power of 800 mW. 00 mW.

• Journal of KIISE:Information Networking
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• v.29 no.2
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• pp.129-140
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• 2002

In this paper, we consider the problem of packet transmission in a wavelength division multiplexed(WDM) optical network. Our network model assumes that receivers are fixed-tuned and transmitters are tunable such that optical lasers assigned to transmitters have limited access to the network bandwidth: hence each node must be equipped with multiple optical lasers and/or multiple optical filters in order to maintain a single-hop network. We first analyze scheduling all-to-all packet transmissions and present optimum scheduling for all-to-all packet transmissions. We then extend the analysis to the case of arbitrary traffic demands. We show that the scheduling with arbitrary traffic demand is NP-hard. A heuristic algorithm based on list scheduling is presented. The upper bound so obtained is compared with the lower bound and provides performance guarantees with arbitrary demands. The result are applicable to arbitrary tuning delay, arbitrary number of wavelength channels and optical lasers of arbitrary tuning ranges.

• 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 𝜌_r=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.

• Design & Manufacturing
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• v.15 no.4
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• pp.65-71
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• 2021

In the early days of laser invention, it was simply used as a measuring tool, but as lasers became more common, they became an indispensable processing tool in the industry. Short-wavelength lasers are used to make patterns on wafers used in semiconductors depending on the wavelength, such as CO2 laser, YAG laser, green laser, and UV laser. At first, the hole of the PCB board mainly used for electronic parts was not thin and the hole size was large, so a mechanical drill was used. However, in order to realize product miniaturization and high integration, small hole processing lasers have become essential, and pattern exposure for small hole sizes has become essential. This paper intends to analyze the characteristics through patterns by exposing the PCB substrate through DMD and polygon scanner, which are different optical systems. Since the optical systems are different, the size of the patterns was made the same, and exposure was performed under the optimal conditions for each system. Pattern characteristics were analyzed through a 3D profiler. As a result of the analysis, there was no significant difference in line width between the two systems. However, it was confirmed that dmd had better pattern precision and polygon scanner had better productivity.