• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.399-404
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• 2010

Test results including the variation of propellant-inlet pressure, pulsed thrust, and environment vacuum with the accompanying thermal responses are presented for the pulse-mode operation of a set of monopropellant hydrazine thrusters producing $0.95lb_f$ of nominal steady-state thrust at an inlet pressure of 350 psia. The test data are reduced into the impulse bit, specific impulse, and force centroid that are the factors typically characterizing pulse-mode performance of small rocket engines. With a scrutiny to the performance parameters, their comparison to the reference criteria of 1 lbf standard monopropellant rocket engine are successfully made.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.194-197
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• 2005

Pulse-mode performance evaluation is made for a set of monopropellant hydrazine thrusters producing $0.95 lb_{f}$ of nominal steady-state thrust at an inlet pressure of 350 psia. With a brief description on the hot-firing test matrix, a typical data obtained from pulse-mode firing is given directly showing the variational behavior of propellant supply pressure, vacuum condition, and thrust, in addition to the thermal response of the thruster. The performance features are successfully compared to the reference criteria of 1-lbf standard monopropellant rocket engine.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.6
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• pp.68-74
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• 2014

During the life firing test of 1 N-class thruster development model, pulse mode performance and performance changes were examined. The deviation of pulse mode response time according to thruster feed pressure was relatively small and the resultant ignition delay, response time, tail-off time were 32-35 ms, 86-91 ms, 89-98 ms, respectively. For the stabilized pulse region the impulse bit revealed the outstanding reproducibility of 1.41, 1.32, 2.10% at $3{\sigma}$. During the life firing test, the impulse bit was decreased with limited amounts, therefore the pulse mode performance could be considered to be maintained. The thrust centroid was also maintained during the life firing test.

• Journal of IKEEE
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• v.9 no.2 s.17
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• pp.115-122
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• 2005

We report 400 femto-second highly stable, nearly transform-limited, pulse generation at 10 GHz in $1540{\sim}1550$ nm wavelength region by adiabatic soliton pulse compression of an actively mode-locked fiber ring laser output. Without using any supermode selection device, supermode beating noise has been suppressed below -123 dB/Hz, resulting less than 100 femto-second timing jitters at the noise band of $1\;kHz{\sim}100\;MHz$.

• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.146-151
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• 1999

We demonstrated a harmonic mode locking scheme that used regeneratie phase modulation to get a high and stable repetition rate in a figure-of-eight fiber soliton laser. From the detected beat spectra of the laser output, a sinusoidal clock freguency tone of 400 MHz, the 96th harmonics of the fundamental mode locking frequency, was extracted with a high Q filter and was used to drive the phase modulator, resulting in stable output of soliton pulse train synchronized with the modulation signal. Generated soliton pulses had FWHM pulsewidth of 930 fs and 3.1 nm linewidth, yielding pulsewidth-bandwidth product of 0.359 that was close to the transform limit. As the modulation frequency always followed the beat frequency of laser modes, stable harmonic mode locking was achieved without the adjustment of the cavity length, which has been commonly required in actively mode-locked lasers.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.44-45
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• 2000

GHz 급의 아주 높은 반복율을 가지면서, 피코초 단위의 펄스 열을 발진시키는 레이저를 만들기 위해 능동형 모드록킹 방법을 이용하였다. 이 방법은 공진기안에 광 변조기를 삽입하고, RF 신호를 가하여 시간적으로 공진기내에서의 손실을 변화시키는 방법이다.$^{(1)}$ 공진기 길이를 충분히 길게 하면서도 고 반복율을 가지는 레이저를 만들기 위해 조화 모드록킹 방법을 사용했는데, 이는 레이저 펄스의 반복율을 공진기 길이에 의한 기본 반복율의 정수배가 되도록 하는 방법이다.$^{(2),(3)}$ 3차 조화 모드록킹 방법을 이용한 Nd:YLF 레이저 시스템을 그림 1에서 나타내었다. (중략)

• Korean Journal of Optics and Photonics
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• v.10 no.1
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• pp.58-63
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• 1999

A 10 GHz harmonically mode-locked semiconductor-fiber ring laser was implemented using a semiconductor optical amplifier at $1.5\mu\textrm{m}$ The laser pulse has 13~18 ps pulse duration, 0.4~0.6 nm spectral width and was positively chirped. The output pulse with an average power of 4 dBm was compressed to 6.8 ps using 2 km long standard single mode optical fiber.

• Korean Journal of Optics and Photonics
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• v.21 no.6
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• pp.254-258
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• 2010

We investigate an optical technique for beam shaping and optical amplification of a pulsed laser diode without variation of its original properties, such as repetition rate and pulse duration. The horizontal and longitudinal sizes of the pulsed laser diode are 300 and $2{\mu}m$, respectively, and its output power is $1.1mW/cm^2$. The multimodal and elliptical pulse shape of the laser diode is converted to the single-modal and Gaussian pulse shape by using a lensed optical fiber. Since the single-modal lensed fiber coupling from the multimodal pulsed laser diode degrades the output power severely, the output power of the pulsed laser diode is dramatically enhanced by using an optical amplification method based on master oscillated power amplification (MOPA). The pulse qualities of the laser diode are not changed after amplifying the pulse power and the output power was finally measured to be $29mW/cm^2$.

• Korean Journal of Optics and Photonics
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• v.32 no.2
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• pp.62-67
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• 2021

We have experimentally demonstrated sum-frequency generation (SFG) in a periodically poled lithium niobate (PPLN) crystal, using a mode-locked picosecond-pulsed fiber laser and a continuous-wave (CW) diode laser with a narrow linewidth. The mode-locked fiber laser had a center wavelength of 1560.7 nm and a spectral width of 1.1 nm, and the CW diode laser had a center wavelength of 1551.0 nm and a spectral width of 6 MHz. To effectively realize SFG, both of the spatial modes of the two lasers were made to overlap in the PPLN crystal by using a single-mode optical fiber. The pulse-mode SFG with pulsed- and CW-mode lasers was successfully observed in the spectral and time domains. These results are expected to be applicable in various ways, such as optical frequency measurement and high-resolution laser spectroscopy studies using optical frequency combs.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.250-251
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• 2000

모드록킹된 광섬유 레이저 자이로스코프(ML-FLaG)$^{(1)}$ 는 일반 거울과 Sagnac 루프 거울로 이루어진 공진기 안에 이득 매질이 포함된 광섬유 레이저의 형태를 가진다. Sagnac 루프 거울을 서로 반대 방향으로 진행하는 두 빛 사이의 위상차를 변조시키면 루프 거울의 반사율이 변조되는데, 여기서 위상 변조 주파수를 공진기의 종모드 간격과 일치시키면 공진기 왕복 주기에 두 개의 펄스가 들어가는 모드록킹된 펄스열을 얻을 수 있다. 이 두 펄스 사이의 시간 간격은 회전율에 따라서 변하기 때문에, 두 펄스 사이의 시간 간격 변화를 측정하면 회전 각속도를 알아낼 수 있다. (중략)