Browsing by Author "Chen, Hou-Ren"

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12 GHz passive harmonic mode-locking in a 1.06 mu m semiconductor optical amplifier-based fiber laser with figure-eight cavity configuration
(2013-03-15)
Chen, Hou-Ren
;
Lin, Kuei-Huei
;
Tsai, Chih-Ya
;
Wu, Hsiao-Hua
;
Wu, Chih-Hsuan
We report the generation of passively harmonic mode-locked pulses using a 1.06 mu m semiconductor optical amplifier (SOA) in a figure-eight laser configuration operated in the all-normal-dispersion regime. Different orders of harmonic mode-locking can be obtained from 30 MHz to 12.02 GHz by changing the injection current of the SOA from 80 to 660 mA together with the adjustment of polarization controllers. The highest pulse repetition rate increases almost linearly with the SOA current. As SOA current is set to 660 mA, we obtain the intracavity power of 46 mW at the highest repetition rate of 12.02 GHz, corresponding to the 1202th harmonic of the fundamental mode-locking frequency. To our best knowledge, this is the lowest intracavity power to generate the highest repetition rate with a passively mode-locked laser in the all-normal-dispersion regime. (C) 2013 Optical Society of America
Generation of chirped long-period gratings in photonic crystal fiber using a constant period corrugated device
(2007)
Chen, Hou-Ren
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Lin, Kuei-Huei
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Lin, Ja-Hon
;
Liu, Wen-Fung
;
Hsieh, Wen-Feng
Chirped long-period fiber gratings (LPGs) are generated in bended photonic crystal fiber (PCF) by using a constant period corrugated device. As the chirping increases, the rejection bandwidth in the transmission spectra of LPGs also increases. Spectral modulation peaks are observed and the modulation depth is increased with the amount of chirping. A chirped dual LPG with rejection bandwidth of about 300 run has been obtained in a bended PCF.
High-power passively continuous-wave and Q-switching mode-locked Nd:LuVO4 laser by few-layer graphene-oxide films
(2016-12-01)
Chen, Hou-Ren
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Tsai, Chih-Ya
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Cheng, Hsin-Ming
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Lin, Kuei-Huei
;
Chen, Chyong-Hua
Using a series of different concentration polymer-free graphene oxide (GO) films as saturable absorbers (SAs), we demonstrate high-power passively continuous-wave modelocking (CW-ML) and Q-switching mode-locking (QS-ML) for a Nd: LuVO4 laser at 1 mu m. CW-ML pulses of 6.62 ps with maximum output power of 3.89 W have been achieved to give the highest pulse peak power of 4.85 kW and pulse energy of 32.14 nJ under 15-W pumping by using SAs of 84.4% transmittance. Using SAs with a lower transmittance having a larger modulation depth of 75.9% and 63.4%, we obtain both the CW-ML pulses of 4.85-ps and QSML pulses with 2.73 W and 1.92 W output powers, respectively. (C) 2016 Optical Society of America
High-power, passively mode-locked Nd:GdVO(4) laser using single-walled carbon nanotubes as saturable absorber
(2011-04-01)
Chen, Hou-Ren
;
Wang, Yong-Gang
;
Tsai, Chih-Ya
;
Lin, Kuei-Huei
;
Chang, Teng-Yao
We use a new (to our knowledge) fabrication method of a single-walled carbon nanotube (SWCNT) absorber without polymer to sustain high-power illumination. Using a series of saturable absorbers (SAs) incorporating different amounts of SWCNTs, we demonstrate mode-locking for a Nd:GdVO(4) laser in the 1 mu m spectral range. Continuous-wave mode-locking (CWML) pulses with a maximum output power of 3.6 W at 1063 nm and high noise extinction of 61 dB has been achieved to give the highest pulse peak power of 3.6 kW and pulse energy of 30 nJ under 15 W pumping. To our knowledge, this is the highest CWML output power with SWCNT-SAs reported. The measured nonlinear absorption of the SWCNT-SAs shows a modulation depth of similar to 3% with subpicosecond recovery time. (C) 2011 Optical Society of America
High-power, passively mode-locked Nd:GdVO4 laser using single-walled carbon nanotubes as saturable absorber
(2011-04-01)
Chen, Hou-Ren
;
Wang, Yong-Gang
;
Tsai, Chih-Ya
;
Lin, Kuei-Huei
;
Chang, Teng-Yao
We use a new (to our knowledge) fabrication method of a single-walled carbon nanotube (SWCNT) absorber without polymer to sustain high-power illumination. Using a series of saturable absorbers (SAs) incorporating different amounts of SWCNTs, we demonstrate mode-locking for a Nd:GdVO4 laser in the 1 mu m spectral range. Continuous-wave mode-locking (CWML) pulses with a maximum output power of 3.6 W at 1063 nm and high noise extinction of 61 dB has been achieved to give the highest pulse peak power of 3.6 kW and pulse energy of 30 nJ under 15 W pumping. To our knowledge, this is the highest CWML output power with SWCNT-SAs reported. The measured nonlinear absorption of the SWCNT-SAs shows a modulation depth of similar to 3% with subpicosecond recovery time. (C) 2011 Optical Society of America
High-quality and Large-size Topological Insulator Bi2Te3-Gold Saturable Absorber Mirror for Mode-Locking Fiber Laser
(2016-12-05)
Chen, Hou-Ren
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Tsai, Chih-Ya
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Cheng, Hsin-Ming
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Lin, Kuei-Huei
;
Yen, Po-Hsiu
A novel high-quality, large-size, reflection-type topological insulator Bi2Te3-Gold (BG) film-based nonlinear optical modulator has been successfully fabricated as a two-dimensional saturable absorber mirror (SAM) by pulsed laser deposition (PLD). This BG-SAM possesses saturation fluence of 108.3 mu J/cm(2), modulation depth (Delta R) of 6.5%, non-saturable loss of 38.4%, high damage threshold above 1.354 mJ/cm(2) and excellent uniformity providing for the generation of passive mode-locked (ML) pulses for erbium-doped fiber lasers (EDFLs) on a large sample area. Under 124 mW 976 nm pumping, We obtained 452-fs continuous-wave ML pulses with pulse energy of 91 pJ and full width at halfmaximum (FWHM) of 6.72-nm from this EDFL. The results clearly evidence that the PLD is an efficient method for fabricating BG-SAM that is suitable for a compact ultrafast ML fiber laser system.
Influence of basal stacking faults on luminescence of m-plane Mg0.19Zn0.81O/ZnO quantum wells grown on a two-step MgZnO-buffer layer
(2019-03-01)
Wu, Yung-Chi
;
Chang, Ning-An
;
Yang, Tsung-Han
;
Tsai, Chih-Ya
;
Chen, Hou-Ren
Different well widths of m-plane Mg0.19Zn0.81O/ZnO multiple quantum wells (MQWs) have been fabricated on the two-step pregrown MgZnO-buffered m-plane sapphires by a pulsed laser deposition and have a narrower linewidth on x-ray diffraction than ZnO-buffered MQWs. By using the variation method to calculate the band diagram and by corroborating the results of temperature-dependent photoluminescence, we confirm the binding energies of free exciton and basal-stacking-fault-bound exciton, which is composed of electrons in the barrier and confined hole in the narrow-width MQWs. The coupling of A1(LO) phonon with excitons in m-MQWs shows more sensitivity toward a decrease in well width than E2(low), due to the crystal symmetry and the reduced Bohr radius. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)
Investigation of Graphene Dispersion From Kelly Sideband in Stable Mode-Locked Erbium-Doped Fiber Laser by Few-Layer Graphene Saturable Absorbers
(2015-11-01)
Chen, Hou-Ren
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Tsai, Chih-Ya
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Chang, Ching-Yang
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Lin, Kuei-Huei
;
Chang, Chen-Shiung
In this paper, stable passively mode-locked fiber lasers (MLFLs) constructed using graphene saturable absorbers (SAs) with different layer numbers of similar to 1 to similar to 15 have been reported. The flat linear transmission spectrum in the range from 1540 to 1580 nm without any distinct absorption peak implies that the graphene SAs exhibit low dispersion in this region. Therefore, stable soliton-like pulses are generated because of negative dispersion provided by the fiber laser cavity, which requires no additional single-mode fiber (SMF) for dispersion compensation. Power-dependent transmission measurements show that the saturation intensity ranges from 1.2 to 3.2 MW/cm(2) and that the modulation depth (MD) of the graphene SAs increases with the number of graphene layers. All the samples were observed to easily mode-lock the laser with a stable mode-locking state persistently operated over hours. By analyzing the soliton Kelly sidebands, we deduced the group delay dispersion (GDD) for different layers of the graphene. The calculated results show that the variation of sample GDD is within the calculation error, indicating that the GDD of graphene is small to be negligible. This result is consistent with the experimental results reported by Chang et al. [Appl. Phys. Lett. 97, 211102 (2010)] using the phase-shift method. This study demonstrates that different layers graphene SAs have different MD contributions to the generation of laser pulses with different pulse widths.
Non-interferometric phase retrieval using refractive index manipulation
(2017-04-07)
Chen, Chyong-Hua
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Hsu, Hsin-Feng
;
Chen, Hou-Ren
;
Hsieh, Wen-Feng
;
光電工程學系
We present a novel, inexpensive and non-interferometric technique to retrieve phase images by using a liquid crystal phase shifter without including any physically moving parts. First, we derive a new equation of the intensity-phase relation with respect to the change of refractive index, which is similar to the transport of the intensity equation. The equation indicates that this technique is unneeded to consider the variation of magnifications between optical images. For proof of the concept, we use a liquid crystal mixture MLC 2144 to manufacture a phase shifter and to capture the optical images in a rapid succession by electrically tuning the applied voltage of the phase shifter. Experimental results demonstrate that this technique is capable of reconstructing high-resolution phase images and to realize the thickness profile of a microlens array quantitatively.
Passive mode locking of ytterbium- and erbium-doped all-fiber lasers using graphene oxide saturable absorbers
(2014-06-02)
Chen, Hou-Ren
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Tsai, Chih-Ya
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Cheng, Hsin-Ming
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Lin, Kuei-Huei
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Hsieh, Wen-Feng
Broadband graphene oxide/PVA films were used as saturable absorbers (SAs) for mode locking erbium-doped fiber laser (EDFL) and ytterbium-doped fiber laser (YDFL) at 1.06 mu m and 1.55 mu m. They provide modulation depths of 3.15% and 6.2% for EDFL and YDFL, respectively. Stable self-starting mode-locked pulses are obtained for both lasers, confirming that the graphene oxide is cost-effective. We have generated mode-locked pulses with spectral width, repetition rate, and pulse duration of 0.75 nm, 9.5 MHz, and 2.7 ps. This is the shortest pulse duration directly obtained from an all-normal-dispersion YDFL with graphene-oxide saturable absorber. (C) 2014 Optical Society of America
Phase retrieval by using the transport-of-intensity equation with Hilbert transform
(2016-04-01)
Li, Wei-Shuo
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Chen, Chun-Wei
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Lin, Kuo-Feng
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Chen, Hou-Ren
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Tsai, Chih-Ya
Phase recovery by solving the transport-of-intensity equation (TIE) is a non-iterative and non-interferometric phase retrieval technique. From solving the TIE with conventional, one partial derivative and Hilbert transform methods for both the periodic and aperiodic samples, we demonstrate that the Hilbert transform method can provide the smoother phase images with edge enhancement and fine structures. Furthermore, compared with the images measured by optical and atomic force microscopy, the Hilbert transform method has the ability to quantitatively map out the phase images for both the periodic and aperiodic structures. (C) 2016 Optical Society of America
Q-switched and mode locked pulses generated from c-cut Nd:LuVO4
(2009)
Song, Kun-Tai
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Lin, Ja-Hon
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Chen, Hou-Ren
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Lin, Kuei-Huei
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Hsieh, Wen-Feng
Q-switched and mode locked pulses have been demonstraed in c-cut Nd center dot LuVO4 laser Using 80% initial transmittance of Cr4+ YAG and output coupler with 70% refleactane, large pulse energy of about 112 mu J has been demonstrated at 18 W pumping.
Room temperature excitonic dynamics of non-polar a-plane ZnO epifilms
(2016-09)
Lin, Ja-Hon
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Liu, Wei-Rein
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Lin, Yi-Chin
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Su, Hsing-Jung
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Chen, Hou-Ren
Pump polarization dependent carrier dynamics, particularly excitonic dynamics, of non-polar a-plane zinc oxide (ZnO) epifilms with two different thicknesses were investigated using time resolved measurements. Unlike the electron and hole dynamics through the above-bandgap excitation, transient differential reflectance (TDR) traces revealed similar trends under two orthogonal pump polarization conditions relative to the c-axis (E-pu +/- c and E-pu vertical bar vertical bar c) of a-ZnO around near-exciton-resonance excitation. By means of a band diagram, the bandgap renormalization (BGR) effect can be reasonably explained by the screening of the Coulomb potential energy due to the accumulation of relaxed free carriers that were initially excited through the absorption of two cascaded pump photons via the excitonic level, a process known as two photon absorption (TPA). Thus, the modulation depths of the TPA around zero time delay, due to simultaneous absorption of one pump and one probe photon via the excitonic level, increased linearly with the pump fluence, proportional to the modulation depth resulting from the BGR effects. (C) 2016 Author(s).
Saturation and beating of acoustic phonon oscillations excited near the exciton resonance of strained polar ZnO/Zn0.8Mg0.2O multiple quantum wells
(2018-01-01)
Liu, Wei-Rein
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Lin, Ja-Hon
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Chen, Jyun-Sian
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Cheng, Hsin-Ming
;
Li, Sheng-Jie
Saturation and beating of coherent acoustic phonon (CAP) oscillations were observed and attributed to the screening of a built-in electric field with increasing pump power using degenerate pump-probe measurements near the exciton resonance of polar ZnO/Zn0.8Mg0.2O multiple quantum wells (MQWs). After purifying the CAP signals by using an empirical mode decomposition, we found not only that the CAP amplitude follows the trend of the band gap renormalization (BGR) and shows saturation at high pump power, but also that the CAP oscillation period coincides with that of the MQWs, consistent with the XRD and TEM results. An additional low-frequency oscillation modifying the CAP signal is revealed due to the negative change in refractive index caused by BGR as the pump power increases.
Stable and Self-Starting Passively Mode-Locked Fiber Laser for 1.06 mu m and 1.55 mu m by Using Graphene Oxide Saturable Absorber
(2013)
Chen, Hou-Ren
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Tsai, Chih-Ya
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Lin, Kuei-Huei
;
Wang, Jing-Yun
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Hsieh, Wen-Feng
Graphene oxide/PVA film is used as saturable absorber for mode locking erbium-doped fiber laser and ytterbium-doped fiber laser. It provides modulation depths of 2.6% and 6% at 1.06 mu m and 1.55 mu m, respectively. Stable mode-locked pulses are obtained for both lasers confirming that graphene oxide is cost- effective for 1.06-mu m and 1.55-mu m pulse generations.
Stable Optical Clock Generation in SOA-Based Fiber Lasers with Figure-Eight Cavity
(2013)
Wang, Jing-Yun
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Lin, Kuei-Huei
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Chen, Hou-Ren
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光電工程學系
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Department of Photonics
Stable optical clocks are obtained from 1.3-mu m and 1.5-mu m SOA-based fiber lasers using passive technology. The waveforms depend on SOA currents, and the repetition rates can be tuned by varying the relative length of sub-cavities.
Stable passive optical clock generation in SOA-based fiber lasers
(2015-02-15)
Wang, Jing-Yun
;
Lin, Kuei-Huei
;
Chen, Hou-Ren
;
光電工程學系
;
Department of Photonics
Stable optical pulse trains are obtained from 1.3-mu m and 1.5-mu m semiconductor optical amplifier (SOA)-based fiber lasers using passive optical technology. The waveforms depend on SOA currents, and the repetition rates can be tuned by varying the relative length of sub-cavities. The output pulse trains of these SOA-based fiber lasers are stable against intracavity polarization adjustment and environmental perturbation. The optical clock generation is explained in terms of mode competition, self-synchronization, and SOA saturation. Without resorting to any active modulation circuits or devices, the technology used here is simple and may find various applications in the future. (C) 2015 Optical Society of America
Stable Q-switched mode-locked Nd3+:LuVO4 laser by Cr4+:YAG crystal
(2008-10-13)
Lin, Ja-Hon
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Chen, Hou-Ren
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Hsu, Hsin-Han
;
Wei, Ming-Dar
;
Lin, Kuei-Huei
In use of saturable Cr4+:YAG crystals, we have demonstrated the stable Q-switched and mode-locked (QML) operation of the Nd:LuVO4 laser. The operation range of QML in use of the Cr4+:YAG is larger than that use of SESAM and NLM. The obtained shape of Q-switched envelope, repetition rate and pulse energy are demonstrated to depend on the initial transmittance of the Cr4+:YAG and reflectivity of the output coupler. Using R = 60% and T-0 = 40%, the highest pulse energy of 77 mu J of each Q-switched envelope, and the highest peak power about 200 kW of Q-switched mode-locked pulses can be obtained at 15 W pump power. It demonstrate the superior characteristic of the Nd:LuVO4 crystal. (C) 2008 Optical Society of America
Stress-Induced Versatile Tunable Long-Period Gratings in Photonic Crystal Fibers
(2008-09-01)
Chen, Hou-Ren
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Lin, Kuei-Huei
;
Lin, Ja-Hon
;
Hsieh, Wen-Feng
;
光電工程學系
We report a method for generating versatile tunable long-period gratings (LPGs) in photonic crystal fibers (PCFs). The central wavelength and rejection bandwidth of LPGs can be tuned over a broad spectral range with adjustable transmission loss. Spectral fringes with uneven spacing are observed in chirped LPGs, depending on the interaction length and the amount of chirping between the two ends of the LPG, and can be removed by reducing the chirping and increasing the grating length. By utilizing a stress-induced LPG, gain flattening of an erbium-doped fiber amplifier has also been demonstrated.
The dominant effect of non-centrosymmetric displacement on the crystal-field energy splitting in the strained a-plane ZnO epi-films on r-plane sapphires
(2017-06-28)
Wu, Yung-Chi
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Liu, Wei-Rein
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Chen, Hou-Ren
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Hsu, Chia-Hung
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Hsieh, Wen-Feng
The polarization-dependent photoluminescence (PL) of the a-plane ZnO (a-ZnO) films grown on r-plane sapphire substrates shows that the crystal-field energy splitting (Delta(CF)) becomes larger with increasing film thickness from 24 nm to 291 nm. In the use of the nonlinear fitting of the stress-strain tensor to the X-ray diffraction data, we found crystal symmetry breaking from wurtzite to monoclinic in these films and determined the corresponding lattice constants and the relaxed lattice constants. With the available lattice variables, we further used the tight-binding method to calculate the band energies and compared with the PL spectra. The results confirm that the crystal deformation and the non-centrosymmetric displacement had opposite effects on the Delta(CF) at the Gamma point and the displacement induced by the strain is the dominant effect on Delta(CF).