• 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.

• Journal of Sensor Science and Technology
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• v.20 no.1
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• pp.8-13
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• 2011

We present measurements of the Brillouin frequency shift in an optical fiber using a 1550 nm distributed feedback laser diode(DFB-LD) as a light source. By modulating the probe light with an electro-optic modulator, we confirm the stimulated Brillouin gain spectrum(BGS) and spontaneous BGS using the coherent detection method. We also confirm the applicability of the technique to distributed temperature sensors that measure the change in Brillouin frequency shift due to temperature variations.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.1-1
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• 2001

Microlasers grown on a chip without any distributed Brags reflectors to provide the feedback are potentially useful for integrated optics, particularly if the laser emission in the plane is unidirectional and this direction can be switched. Microfilters performing as add/drop devices and bandpass units are now considered the most needed optical element for the DWDM field. The talk will concentrate on our research effort in GaN microlasers with non-circular shapes and in dielectric microfilters with oval and square shapes. (omitted)

• Transactions on Electrical and Electronic Materials
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• v.16 no.3
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• pp.117-123
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• 2015

Cholesteric liquid crystals are one dimensional photonic band-gap materials due to their birefringence and periodic structure. Dye doped cholesteric liquid crystals are self-assembling, mirror-less, low threshold laser structures that exhibit distributed feedback. In this review paper, we have presented the development in the field of lasing characteristics of dye doped cholesteric liquid crystals.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.2
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• pp.26-38
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• 1994

We demonstrate a repeatless transmission of 2.5 Gbps digital signal over 98 km opticla filbers using optical transmitter and optcial receiver which are designed and implemented using commercially available devices. The optical transmitter is realized by using a distributed feedback(DFB) laser. Temperature of the laser is thermoelectrically stabilized and the output optical power is also stabilized by using negative feedback. The output power of the transmitter is 0 dBm. The optical receiver consists of an InGaAs avalanche photodiode, a preamplifier. an automatic gain control amplifier, and a clock/data regenerator. We find an optimum decision threshold that gives the best receiver sensitivity form the measured V curve. The best sensitivity is -35.5dBm( BER-1*10S010T, PRBS=2S023T -1 ) and the overload power is -9 dBm. Finally, we achieve error free optical transmission with 98 km optical fibers. The exinction ration penalty of 2 dB. the chromatic dispersion penalty of 1 dB, and the total power penalty of 3.0 dB are measured. These results satisfy CCITT recommendation.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.454-459
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• 2003

We report the first demonstration of 10 Gb/s wavelength conversion in a Mach-Zehnder interferometric wavelength converter monolithically integrated with a loss-coupled DFB probe source. The integrated device is fabricated using a BRS (buried ridge stripe) structure with an undoped InP clad layer on the top of a passive waveguide to reduce high propagation loss. The device exhibited a static extinction ratio of 11 dB. Good performance at 10 Gb/s is obtained with an extinction ratio of 7 dB and a power penalty of 2.8 dB at a 10$^{-9}$ bit error rate.

• Journal of Software Assessment and Valuation
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• v.15 no.2
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• pp.101-109
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• 2019

Lasers for optical broadband communication systems should have excellent frequency selectivity and modal stability. DFB(Distributed Feedback) lasers have low lasing frequency shift during high speed current modulation. In this paper, I have developed a simulation software and analysed threshold gain and lasing frequency of a lasing mode in longitudinal direction of an 1.55um DFB laser with two mirrors and without anti-reflection coatings, that have both an index- and gain-gratings. The grating phase on a left mirror face is fixed as π/2 and the grating phase on a right mirror face is varied. As the phases of the index and gain gratings on the right mirror facet are π and 0, κL should be in the range of 2~6 in order to enhance the frequency stability. In order to reduce the threshold current of a lasing mode, κL should be greater than 8, regardless of the grating phases on the mirror faces.

• 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 the Institute of Internet, Broadcasting and Communication
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• v.14 no.2
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• pp.147-152
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• 2014

A longitudinal modal transmission-line theory(L-MTLT) to analyze the static and dynamic behavior of two-section distributed feedback (DFB) lasers is used. The characteristic impedance and equivalent propagation constant of DFB structure with active layer are derived from L-MTLT. A two-section DFB laser is analogous to a transmission-line network, in which each section is described by transmission-line block corresponding to the equivalent factors. The longitudinal resonant condition of DFB laser based on equivalent transmission-line network is used to reformulate the rate equations so that static and dynamic behavior of two-section DFB lasers with active layer is demonstrated and analyzed accurately.

• ETRI Journal
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• v.29 no.2
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• pp.162-168
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• 2007

A new scheme for bi-directional HDTV/Gigabit Ethernet/CATV transmission over a hybrid dense-wavelength-division-multiplexing passive optical network (DWDM-PON) is proposed and demonstrated. It is based on injection-locked vertical-cavity surface-emitting lasers and distributed-feedback laser diodes as transmitters. Services with 129 HDTV channels, a 1.25 Gbps Gigabit Ethernet connection, and 77 CATV channels are successfully demonstrated over 40 km single-mode fiber links. Good performance of bit error rate, carrier-to-noise ratio, composite second order, and composite triple beat is achieved in our proposed bidirectional DWDM-PON.