• Korean Journal of Optics and Photonics
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• v.23 no.3
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• pp.103-107
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• 2012

We investigate the dependence of the output of a mode locked Yb-doped fiber laser on incident intra-cavity intensity on a semiconductor saturable absorber mirror (SESAM). To vary the incident intra-cavity intensity, we change the beam spot size on a SESAM by varying the focal length of a lens installed in the front of the SESAM.

• Journal of IKEEE
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• v.15 no.4
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• pp.313-318
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• 2011

The effects of external continuous wave optical injection on spectral comb of a 10 GHz harmonically mode-locked semiconductor fiber ring laser have been studied. Greater than 40 dB spectral deeps in the spectral comb and greater than 30 dB reduction of supermode beating noise are achieved by injecting coherent light with ~ 100 KHz spectral width. To examine the possibility of using a low-cost seed source, we replace the seed source by a DFB laser with ~ 10 MHz spectral width. It shows similar spectral deeps, however supermode beating noise enhancement, rather than reduction, is observed.

• Journal of IKEEE
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• v.10 no.2 s.19
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• pp.116-122
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• 2006

We have built a grating-based, high-resolution, spectral line-by-line pulse shaper. By controlling individual spectral lines of a mode-locked laser output, we demonstrate the interesting functionalities of the pulse shaper for arbitrary waveform generation, such as width tunable pulse generation, phase controlled waveform generation, microwave waveform generation, etc.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.276.2-278
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• 2000

In a recent years, a number of approaches have been studied, including passive, active, and hybrid mode-locking of semi-conductor lasers for short pulse generation and research has been devoted to achieve low timing-jitter operation since the timing jitter is unfavorable for system applications. Among the methods of mode locking, passive mode locking does not need external rf drives, and therefore the operation and fabrication procedures are simplified. In spite of these attractive advantages of passive mode-locked laser, it has critical drawbacks such as large timing jitter and the difficulty in synchronization with external circuits. Their inherent large timing jitter value was shown to be suppressed to certain levels by means of hybrid mode-locking technique$^{(1)}$ , where the saturable absorber section was modulated by an external signal with the cavity round trip frequency. Furthermore, the subharmonic mode-locking (SHML) technique alleviates the restrictions of high speed driving electronics. It has been demonstrated experimentally$^{(1)}$ that the hybrid subharmonic mode-locking technique has lead to significant reduction of the timing jitter. (omitted)

• Current Optics and Photonics
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• v.7 no.6
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• pp.738-744
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• 2023

Graphene-based saturable absorbers (SAs) are widely used as laser mode-lockers at various laser oscillators. In particular, transmission-type graphene-SAs with ultrabroad spectral coverage are typically manufactured on transparent substrates with low nonlinearity to minimize the effects on the oscillators. Here, we developed two types of transmitting graphene SAs based on CaF₂ and ZnSe. Using the graphene-SA based on CaF₂, a passively mode-locked mid-infrared Cr:ZnS laser delivers relatively long 540 fs pulses with a maximum output power of up to 760 mW. In the negative net cavity dispersion regime, the pulse width was not reduced further by inhomogeneous group delay dispersion (GDD) compensation. In the same laser cavity, we replaced only the graphene-SA based on CaF₂ with the SA based on ZnSe. Due to the additional self-phase modulation effect induced by the ZnSe substrate with high nonlinearity, the stably mode-locked Cr:ZnS laser produced Fourier transform-limited ~130 fs near 2,340 nm. In the stable single-pulse operation regime, average output powers up to 635 mW at 234 MHz repetition rates were achieved. To our knowledge, this is the first attempt to achieve shorter pulse widths from a polycrystalline Cr:ZnS laser by utilizing the graphene deposited on the substrate with high nonlinearity.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.53-55
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• 2001

A dual probe laser Doppler vibrometer (LDV) that has one laser source and provides two independent object beams has been developed for the first time. An electronic circuit that converts light signal to electronic signal has been also developed using phase locked loop(PLL). It was found that this types of dual probe LDV can be used in differential mode and self-vibration compensation mode.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1838-1840
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• 2001

A dual probe laser Doppler vibrometer (LDV) that has one laser source and provides two independent object beams has been developed for the first time. An electronic circuit that converts light signal to electronic signal has been also developed using digital phase locked loop(DPLL). It was found that this types of dual probe LDV can be used in differential mode and self-vibration compensation mode.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.1
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• pp.119-128
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• 1995

We report hybrid and passive mode-locking results of tilted-stripe AlGaAs semiconductor laser traveling wave amplifiers with saturable absorbers. Dependence ofthe pulse width on the mode locking frequency, the bandwidth of spectral filters, and the bias current of the laser amplifier are investigated. We generate 4 ps optical pulses by using the hybrid mode locking technique. The repetition rate and the peak power of generated pulses are 516 MHz and 170 mW, respectively. The tuning range of uor mode locked laser is 10 nm with the center wavelength of 780 nm. We also generate 2.6 ps optical pulses with peak power of 830 mW by using the passive mode locking technique.

• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.58-64
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• 2002

Using Mach-Zehnder type intensity modulator, we stabilized a 10 GHz harmonically mode-locked dispersion-compensated fiber ring laser using a feedback controlling system, and we measured its stability. The laser was stabilized for more than 16 hours by controlling the cavity length to suppress the relaxation oscillation frequency component which had caused the laser output instability. The ms timing jitter and ms amplitude noise were measured to be 260-524 fsec and 4~11.5%, respectively, and BER test measurement showed a value of 10$^{-13}$ .

• Korean Journal of Optics and Photonics
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• v.25 no.6
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• pp.340-345
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• 2014

We experimentally demonstrate the use of a gold-deposited side-polished fiber as a $2-{\mu}m$-band polarizing device to produce mode-locked pulses from a thulium/holmium-codoped fiber ring cavity. The mode-locking effect was induced by nonlinear transmission caused by the gold-deposited side-polished fiber, due to nonlinear polarization rotation of the oscillated beam within the fiberized cavity. It is also shown that ~558-fs pulses with a peak power of ~6.7 kW could readily be produced at a wavelength of 1935 nm through subsequent thulium/holmium-codoped fiber amplification, due to the higher-order soliton compression effect.