• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.97-103
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• 2006

This work forcus on the development of gas sensor that measure the concentrations of exhaust gas using diode laser. Each diode laser for exhaust gas measurement is set to work at near-IR using both DA and WMS methods. Also use of fiber-coupled optical elements makes such a sensor rugged and easy to align. On-line data acquisition and processing can be performed with a PC running LabVIEW software, and absorption signals are measured simultaneously by multiplexing method. Finally, It were experimentally compared WMS (Wavelength Modulation Spectroscopy) with DA (Direct Absorption) for the accuracy.

• Journal of the Optical Society of Korea
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• v.8 no.1
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• pp.13-16
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• 2004

A widely tunable SG-DFB (Sampled Grating Distributed Feedback) laser diode is proposed and its feasibility is confirmed through simulation. The new SG-DFB laser diode is composed of a pair of sampled gratings, some parts of which are gain sections and the other parts of which are phase control sections. It is shown that a few tens of nanometers can be tuned through the adjustment of two currents into the phase control sections. Higher output power is expected compared with a SG-DBR laser diode with similar parameters. The dynamic single mode operation is also observed in the time-domain simulation.

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.05a
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• pp.96-99
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• 2005

As the demand of internet networks using backbone communication systems recently increased, the researches on the high-speed wideband optical communication systems are required. For high-speed optical communication systems, asymmetric sampled grating distributed feedback laser diodes (DFB-LDs) are developed and the reliability of DFB-LDs is examined. The reliability of DFB-LDs is performed by monitoring I-V and L-I characteristics and two degradation phenomena related to the electrical characteristics of LDs are observed during the life tests. The first degradation phenomenon by increasing the reverse current is considered as a formation of leakage current path enough to prevent lasing operation in lateral blocking layer near active region of lasers. The second degradation phenomenon by decreasing the forward current is considered as activation of non-radiative Auger recombination process by thermal energy and the second degradation phenomenon is recovered after the off-test period at room temperature Eventually, evaluating the reliability of DFB LDs can allow us to improved the manufacturability in high-volume manufacturing.

• ETRI Journal
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• v.45 no.2
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• pp.193-202
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• 2023

We demonstrate the transmission of uncompressed 4K videos over the photonics-based terahertz (THz) wireless link using a directly modulated distributed feedback laser diode (DFB-LD). For optical heterodyne mixing and data modulation, a DFB-LD was employed and directly modulated with a 5.94-Gb/s non-return-to-zero signal, which is related to a 6G-serial digital interface standard to support ultra-high-definition video resolution. We derived the optimal frequency of the THz carrier by varying the wavelength difference between DFB-LD output and Tunable LD output in the THz signal transmitter to obtain the best transmission performances of the uncompressed 4K video signals. Furthermore, we exploited the negative laser-to-filter detuning for the adiabatic chirp management of the DFB-LD by the intentional discrepancy between the center wavelength of the optical band-pass filter and the output wavelength of the DFB-LD. With the help of the abovementioned methods, we successfully transmitted uncompressed 4K video signals over the 2.3-m wireless transmission distance without black frames induced by time synchronization error.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.113-119
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• 1994

We fabricated and characterized RWG-DFB-LDs emitting at $1.3\mu\textrm{m}$ wavelength. For fabrication of the laser diode, inteference fringe of optical beams was used for grating formation and epi layers were grown by LPE. The fablicated RWG-DFB-LD operated in a single longitudinal mode with more than 30 dB SMSR at 1296.5 nm emitting wavelength and its threshold current was 67 mA. Coupling coefficient (K) was estimated as $40cm^{-1}$ by means of stop-band measurement. Finally, we show that the RWG-DFB-LD fabricated in this experiment can be applicable as light source of 2.5 Gbps optical communication system from the fact that the small signal response of the RWG-DFB-LD rated up to 1.99 GHz at pre-bias level of $1.2 I_{th}$..

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.6
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• pp.108-113
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• 1996

Periodic gratings for 1.55$\mu$m distributed feedback laser diode (DFB LD) have been fabricated by a holographic interference exposure system using an etalon stabilized Ar ion laser. We obtain a good development condition at developer concentration of 65% and obtain etching rate of 1000$\AA$/min at 20.deg. C by the mixed solution HBr:HNO$_{3}$:H$_{2}$O(1:1:10 in volume ratio). We obtain good first order grating with period of 2400${\AA}[\pm}2{\AA}$ at etching time of 45 sec from grating period and diffraction efficiency measurement, and SEM observation of grating fabricated on InP substrate.

• ETRI Journal
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• v.33 no.5
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• pp.810-813
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• 2011

We report the use of a widely tunable detuned dual-mode laser diode (DML) as a compact and portable continuous-wave THz emitter. The wavelength difference between the two lasing modes of this DML can be tuned from 2.4 nm to 9.3 nm by using integrated microheaters. The power difference between these modes is less than 1 dB, and the side-mode suppression ratio is greater than 30 dB over the entire tuning range.

• 한국연소학회:학술대회논문집
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• 2000.12a
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• pp.168-174
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• 2000

A diode laser sensor system based on absorption spectroscopy techniques has been developed to measure $CO_2$ concentration and temperature non-intrusively in high temperature combustion environments using a 2.0 ${\mu}m$ DFB(Distributed Feedback) laser. Two optics was fabricated in pig-tail fashion and all optical components were implemented in a single box. The evolution of measurement sensitivity was done using test cell by changing sweep frequency and $CO_2$ concentration. Gas temperature was determined from the ratio of integrated line strengths. Species concentration was determined from the integrated line intensity and the measured temperature. The result show that the system has 2% error in wide operation frequency range and accuracy of $CO_2$ concentration was about 3%. The system was applied to measure temperature and concentration in the combustion region of a premixed $CH_4$ +air triangular flame. The measurement results of gas temperature agreed well with thermocouple results. Many considerations were taken into account to reduce optical noise, etalon effect, beam steering and base line matching problem. The evaluations results and actual combustion measurement demonstrate the practical and applicability for in-situ and real time combustion monitoring in a practical system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.5
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• pp.1372-1383
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• 1998

In this paper, modeling for DC and AC characteristics analysis of DFB-LD was performed considering effects of .lambda./4-shifted gratingandspatial hole burning within a laser diode cavity. From the simulation for DC characteristics, Light-Current curve, optical power distribution and carrier density distribution within the cavity can be obtained. The simulation for AC characteristics porovides IM response and the amplitude and phase and the amplitude and phase response of FM with excellent accuracy.