Broadband supercontinuum generation in highly GeO2 doped fibers holds significant appeal for researchers due to their distinct advantages. In this study, we propose employing a low repetition rate noise-like pulse mode-locked fiber laser as the pulse seed for mid-infrared supercontinuum generation in such fibers. Utilizing only one amplifier stage to amplify the noise-like pulse, we achieved a broadband supercontinuum with a 20dB bandwidth spanning from approximately 652nm to 3350nm in a highly GeO2 doped fiber with a core GeO2 concentration of 98%, even with an output power as low as 297mW. To the best of our knowledge, this represents the widest supercontinuum achieved in highly GeO2 doped fibers to date. Additionally, we observed that further increases in pump power resulted in damage to the core of the highly GeO2 doped fibers. This posed a challenge in expanding the spectral range of the output supercontinuum by simply increasing the peak pulse power. This conclusion is of significant reference value for research on supercontinuum generation based on highly GeO2 doped fibers.
We experimentally demonstrate, for the first time, a 2.8μm femtosecond mode-locked fluoride fiber laser (MLFFL) with switchable pulsed-state including monopulse, dipulse, harmonic mode-locking and soliton molecules. Specifically, through adjustments to the cavity parameters, the mode-locking operation from monopulse to dipulse within a specific pump power range can be realized, with the maximum output power of 165mW and 175mW, respectively. Further increasing the pump power, the operating regime of the oscillator switches to second-order harmonic mode-locking, where the pulse fundamental repetition rate is ~155MHz with the output power of 330mW. In this case, bound soliton molecule can also be acquired by appropriately optimizing the orientation of the waveplates while keeping the pump power fixed. In particular, with increased pump power, multiple states of bound soliton molecule pairs can be achieved as well. The laser system is simple in structure, self-starting and good stability. Our experimental results may provide solutions for practical applications which requiring different pulse state switchable.
We have successfully demonstrated a high-power erbium-doped fluoride glass fiber laser operating at 2.94 μm. The system achieved continuous operation with an output power of 7.1 W at 2.94 μm. The all-fiber Fabry–Perot laser cavity was constructed using an 11.5 m, 7 mol. % Er3+ :ZBLAN fiber with two fiber Bragg gratings (FBG) having reflectivities of 99.7% and 29.2%. These fiber Bragg gratings were inscribed using a 513 nm femtosecond (fs) laser direct-writing technique. To prevent deterioration at high output powers, an endcap was fused at the output fiber end. The system operated at 2.94 μm exhibited an overall slope efficiency of 20.5% in relation to the launched pump power at 980 nm, and demonstrated a single-mode output beam quality with M2 < 1.2.
In this paper, a high power Tm3+-doped fiber laser (TDFL) based on a monolithic master oscillator power amplifier (MOPA) system with the center wavelength is 1940 nm is demonstrated. The maximum laser power was measured to be 200 W with a slope efficiency of 56.2% at the 793 nm pump power of 368.6 W. Power stability of the laser output over 60 min is measured to be ~0.12%, which indicate a relatively stable laser operation of the TDFL. The output power is limited by the available pump power for the lack of amplified spontaneous emission, parasitic oscillation or self-pulsing effects even at the maximum output power level, showing further power scaling should be possible with increase the pump power.
In this paper, we demonstrate a synchronously pumped 3.5 μm mode-locked fiber laser based on the cross-phase modulation effect. The fiber laser delivered pulses with a central wavelength of 3541.8 nm, 3 dB spectral bandwidth of 5.1 nm, pulse repetition rate of 18.63 MHz, average output power of 50 mW, and signal-to-noise ratio of 68 dB. The Fourier transform limit pulse width is 2.6 ps, estimated by the hyperbolic secant curve.
Graphene is a two-dimensional carbon material which has been extensively studied for its applications in electronic devices due to its fast carrier kinetics. However, the weak photon absorption of graphene limits its application in photodetectors. Transition metal chalcogenides (TMDCs) quantum dots (QDs) have been used to modify the graphene properties since these QDs have abundant active edge sites and specific optoelectronic properties. In this study, we synthesized SnSe2 QDs by the process of sonication and laser ablation. The average size of SnSe2 QDs was characterized by the transmission electron microscopy (TEM). We demonstrated a sensitive ultraviolet (UV) photodetector based on graphene and SnSe2 QDs on a polyethylene terephthalate (PET) substrate. The responsibility of the device was up to 1830 AW-1 when the irradiation density was 155.2 μW/cm2 . The rising time τ𝒓 was 0.26 s. The device showed good stability even after bending 100 times. SnSe2 QDs enhanced the light absorption and the creation of photocarriers which could extend the applications of graphene in flexible optoelectronic devices.
Tin disulfide (SnS2) quantum dots (QDs) have been used in the fields of sensors. However, the reported SnS2 QDs were fabricated by the wet chemical method which was complicated. In this paper, we synthesized SnS2 QDs by a facile ultrasonic probe sonication process. The average size of SnS2 QDs was 3 nm which was observed in the transmission electron microscope (TEM) images. Two vibrational modes of SnS2 QDs were observed at 203 cm-1 (Eg) and 310 cm-1 (A1g) in the Raman spectrum. There was an absorption peak at 320 nm in the UV-Vis spectrum. Excitation wavelength dependent photoluminescence (PL) was measured. The maximum PL intensity of SnS2 QDs was observed at 450 nm under the excitation wavelength of 370 nm. This indicates that the SnS2 QDs have potential applications in optical devices.
KEYWORDS: Femtosecond phenomena, Sensors, Temperature metrology, Structured optical fibers, Temperature sensors, Lithium, Single mode fibers, Michelson interferometers, Interferometers, Head
A 45° fiber cantilever beam for high temperature measurement was fabricated by femtosecond laser in single mode fiber. The temperature sensitivity is obtained to be about 17 pm/℃ at 800 ℃ and 1560 nm. The 45° fiber cantilever beam possesses good repeatability and stability in high temperature. The sensor is small in size, cheap and good stability.
Rotating mirror is not only as an imaging element in optical path of ultra-high speed camera, where imaging quality is affected by surface quality and plane deformation of the rotating mirror, but also as an element to implement ultra-high speed, because performances of the ultra-high-speed camera system are mainly dependent on the static and dynamic mechanical properties of the rotating mirror. In this paper, the static and dynamic properties of magnesium alloy rotating mirror with equilateral-triangle cross-sections were investigated by theoretically and numerically method. At the speed of 2×105 rpm, the maximum lateral deformations of the mirror facet with width 17.32 mm and length 40 mm is 2.476 μm. The maximum von Mises stress is 35.1 MPa. The deformation and stress are less than that of aluminum alloy rotating mirror, which has been successfully applied in many types of RM for ultra-high speed cameras. The first three frequencies of magnesium alloy rotating mirror are 9,539.9 Hz, 9,540.9 Hz and 12,726.0 Hz, respectively. While the first three frequencies of aluminium alloy rotating-mirror are 9,683.9 Hz, 9,685.2 Hz and 11,016.0 Hz. From which it is preliminarily shown that a magnesium alloy rotating mirror can be used as replacement for an aluminium alloy rotating mirror in ultra-high-speed camera.
We describe a quantitative fluorescence projection tomography technique which measures the three-dimensional fluorescence spectrum in biomedical samples with size up to several millimeters. This is achieved by acquiring a series of hyperspectral images, by using laser scanning scheme, at different projection angles. We demonstrate that this technique provide a quantitative measure of the fluorescence signal by comparing the spectrum and intensity profile of a fluorescent bead phantom and also demonstrate its application to differentiating the extrinsic label and the autofluorescence in a mouse embryo.
There is increasing interest in the three-dimensional visualization and quantification of cellular circuits in the brain and therefore optical clearing methods are highly in demand for brain imaging. In particular, clarification without membrane damage is required to image lipophilic tracer-labeled neural tracts. However, previously reported DiI-compatible optical clearing methods are relatively slow and can hinder transparency for imaging. Here, we present DAS, a new, convenient, inexpensive and reproducible aqueous clearing reagent that can efficiently clarify tissues with minimal volume enlargement and reliably preserves emission from fluorescent proteins and lipophilic dyes in membrane integrity preserved tissues.
Optical clearing methods are highly in demand in organism-level biomedical system research since they can facilitate deep optical imaging by reducing light scattering in tissue and then enable three-dimensional signal visualization and quantification of tissues. While the previously reported optical clearing methods have addressed some of six key issues (i.e. transparency, efficiency, reproducibility, preservation of emission from fluorescence proteins, preservation of membrane integrity, and the ease of operation), none has yet addressed all of them. Here, we present a new, convenient, inexpensive and reproducible approach to optical clearing, termed UbasM, providing unprecedented performance in terms of clearing rate, the ease of operation and satisfactory fluorescence protein/membrane integrity preservation while achieving sufficient transparency to permit 3D volumetric imaging.
A superfluorescent fiber source (SFS) with the low Ge-doped and Er/Ce codoped photonic crystal fiber (ECPCF) is proposed to improve the radiation resistance of SFS. The radiation effects of SFSs for an Er/Ce codoped conventional fiber (ECF) and a low Ge-doped and ECPCF are investigated in a Co60 gamma-ray environment. Results show that the low Ge-doped photonic crystal fiber exhibits better radiation tolerance than its counterpart in the Er/Ce codoped fibers, and the attenuation of the power of ECPCF-SFS is significantly smaller than that of ECF-SFS. In addition, the radiation-induced spectral variation of ECPCF-SFS with increased radiation dose is less than that of ECF-SFS. ECPCF-SFS simultaneously exhibits higher recovery performance than ECF-SFS.
We present the design and fabrication approach of a rugate narrow band minus filter. A method for the fabrication of graded-index coatings by rapidly alternating deposition of low (SiO2) and high (Al2O3) refractive index materials is introduced, and this technology was used to fabricate a rugate structure. This paper mainly discusses about rugate narrow band minus filter design and fabrication approach. The experimental results show the measured transmittance spectra are in good agreement with the designed value. The laser-induced damage threshold (LIDT) of the narrow band rugate minus filter is measured.
Acridine orange (AO) molecules were incorporated in AlPO4-5, SAPO-5 and SAPO-47 single crystals by vapor-phase diffusion method. Polarized absorption spectra show that AO molecules are well aligned by the one-dimensional channel systems of AlPO4-5 and SAPO-5 matrices. While the orientation of AO molecules in SAPO-47 crystals is diverse owing to the three-dimensional cage structure of chabazite (structure code CHA). The absorption peak and emission peak of AO/SAPO-5 blue shift compared with that of AO/AlPO4-5 because the channel environment changes from non-polar medium to polar medium when Si substituted in the framework of AlPO4-5. The greater blue shift in absorption band and emission band of AO/SAPO-47 are expected to originate from the polar channel medium and smaller channel size of SAPO-47.
A high power diode-pumped continuous-wave Tm:YAP laser with a piece of silicon chip as the output coupler (Si-OC) is demonstrated. A maximum output power of 13 W with a beam quality of M2 ≤ 1.45 at 1931 nm was obtained, corresponding to an optical-to-optical efficiency of 31%, and a slope efficiency of 33%. To our best knowledge, this is the first report of utilizing silicon as a output coupler on solid Tm:YAP laser system. The mechanism of silicon output coupler on Tm:YAP laser is also discussed in this letter. Because of the intriguing characteristics of silicon, such as high damage threshold, low cost and long-pass filter property, double-sided polishing single crystal silicon chip can perform as a good output coupler in high power laser system near 2 μm region.
An ultra-flat and ultra-broadband supercontinuum (SC) is demonstrated in a 4-m photonic crystal fiber (PCF) pumped by an Yb-doped all-fiber noise-like pulses (NLP) laser. The Yb-doped fiber laser is seeded by a SESAM mode-locked fiber laser, and amplified by cascaded fiber amplifiers, with its center wavelength, repetition frequency and the average noise-like bunch duration of 1064.52 nm, 50.18 MHz, 9.14 ps, respectively. Pumped by this NLP laser, the SC source has a 3 dB bandwidth and a 7 dB bandwidth (ignore the pump residue) of 1440 nm and 1790 nm at the maximum average output power of 6.94 W. To the best of our knowledge, this flatness is significantly prominent for the performance of PCF-based SC sources.
We propose two schemes for achieving tungsten disulfide (WS2)-based saturable absorber (SA) and saturable absorber mirror (SAM). By utilizing the pulsed laser deposition method, we grow the WS2 film on microfiber to form an evanescent field interaction SA device. Incorporating this SA device into a common ring-cavity erbium-doped fiber (EDF) laser, stably passive mode-locking can be achieved with pulse duration of 395 fs and signal-to-noise ratio of 64 dB. We also produce a fiber tip integrated WS2-SAM by utilizing the magnetron sputtering technique (MST). This new type of SAM combines the WS2 layer as SA and gold mirror as high reflective mirror. By employing the WS2-SAM, we construct the linear-cavity EDF lasers, and achieve passive mode-locking operation with pulse duration of ∼1 ns and SNR of ∼61 dB. We further achieve stably passive Q-switching operation with pulse duration of ∼160 ns and pulse energy of 54.4 nJ. These fiber-integrated SAs and SAMs have merits of compactness and reliability, paving the way for the development of new photonic devices such as SAs for pulsed laser technology.
The radiation resistance effect of two superfluorescent fiber sources using Er-doped photonic crystal fiber is studied under 500 Gy gamma-ray irradiation. One is trimmed into a quasi-Gaussian spectrum by a filter and the other is not trimmed. The results show that the SFS with spectrum trimming has a smaller radiation induced attenuation and a higher mean wavelength stability (2.616 dB and 24.803 ppm) than that of the SFS without spectrum trimming (3.187 dB and 611.766 ppm). Therefore, this method has practical use for improving radiation resistance in space environment.
A novel and compact fiber-probe pressure sensor was demonstrated based on micro Fabry-Perot interferometer (FPI). The device was fabricated by splicing both ends of a short section simplified hollow-core photonic crystal fiber (SHCPCF) with single mode fibers (SMFs), and then a micro channel was drilled by femtosecond laser micromachining in the SHC-PCF to significantly enhance the pressure sensitivity. The pressure sensing characteristics based on micro-FPI have been investigated by measuring the signals through the demodulation of phase since the external signal imposing on the interferometer will induce the phase change of interference signal. Then a FBG was cascaded to demodulate the signal. A micro FPI demonstrates a maximum pressure sensitivity of 32 dB/MPa, while a low temperature cross-sensitivity of 0.27 KPa/°C. Hence it may have potential for pressure applications in harsh environment.
A high-stability erbium-doped superfluorescent photonic crystal fiber source (SPCFS) is presented. Optimization of
the high-stable SPCFS is achieved by combining high-performance EDPCF, optimal fiber length, and source
structure with suitable pump power. The result shows a 56.979 ppm mean wavelength stability of a prototype SPCFS
is demonstrated with the temperature varied in the range of −40 °C—70 °C. Especially, in the room temperature, the
mean wavelength stability of a prototype SPCFS is less than 2.59 ppm, which will be approaching the requirement
for inertial-grade fiber optic gyroscopes.
We demonstrate a saturable absorber (SA) based on cladding-filled graphene in a specially designed and manufactured photonic crystal fiber (PCF) for the first time. The saturation absorption property is achieved through the evanescent coupling between the guided light and the cladding-filled graphene layers. To boost the mutual interaction, the PCF is designed to contain five large air holes in the cladding and small-core region. Employing this graphene-PCF SA device, we construct an erbium-doped all-fiber laser oscillator and achieve mode-locked operation. This device can pave the way for high power and all-fiber applications of photonics with graphene with some unique advantages, such as single-mode operation, nonlinearity enhancement, high-power tolerance, environmental robustness, all-fiber configuration, and easy fabrication.
Polarization maintaining (PM) photonic crystal fiber (PCF) and Er-doped PCF technologies are investigated for
interferometer fiber optic gyroscope (IFOG) applications. A PM-PCF optimized to achieve low-loss and high
polarization extinction splice-joints with conventional PM fiber pigtails of a multifunction integrated optical circuit
(MIOC) was drawn and tested under different temperature conditions. The loss and polarization crosstalk
properties of a fiber coil made from the PM PCF were measured and compared with conventional PM fiber. An
erbium-doped PCF was designed and fabricated, with which a superfluorescent fiber source (SFS) was made and tested.
The results show that an IFOG with the PM-PCF coil and the Er-doped PCF source could achieve better temperature
performance. An experimental PCF-based prototype IFOG was built and tested , and preliminary results was obtained.
A high-stable and broadband single-pass backward configuration superfluorescent fiber source based on erbium-doped photonic crystal fiber (EDPCF) is proposed. With the proper EDPCF length, pump power, and a gain flattening filter, we demonstrate that it is possible to create a high-stable and broadband erbium-doped superfluorescent photonic crystal fiber source (SPCFS). This was accomplished by replacing the conventional erbium-doped fiber with the EDPCF, the intrinsic thermal coefficient of which is four times less than the measured conventional erbium-doped fibers. The SPCFS showed that the total output power stability was less than 0.0337%, the 3-dB spectral width was broader than 42 nm, the output spectrum flatness was less than 1 dB, and the mean wavelength stability was less than 2.58 ppm over 6 h at temperatures from 24.3°C to 25.5°C, which approached the requirement for inertial-grade fiber optic gyroscopes.
We investigate on a multi-wavelength operation erbium-doped fiber laser Q-switched by a graphene-based saturable absorber. Stable pulses were generated with the widths from 6.9 to 1.5 μs, energies from 40.4 to 130.2 nJ and repetition rates from 68.32 to 132.9 kHz, when the pump power increased from 142.32 to 441.86 mW. A fiber Bragg grating with five reflective peaks was inserted into the fiber ring through an optical circulator, resulting in a stable output of five-lasing-wavelength output. The laser can perform as a low-cost and easy-built all fiber light source, and has potential applications in the fields where pulses at multi-wavelength operation are needed, i.e., temperature or strain fiber sensors.
A switchable multi-wavelength Erbium-doped photonic crystal fiber (ED-PCF) ring laser based on a length of
polarization-maintaining photonic crystal fiber(PM-PCF) is presented and demonstrated experimentally. A segment of
ED-PCF is used as linear gain medium in the resonant cavity. Due to the polarization hole burning (PHB) caused by the
PM-PCF and a polarization controller (PC), the laser can operate in stable dual- or triple- wavelength modes at room
temperature. The optical signal-to-noise ratio (OSNR) of the laser without any wavelength-selective components is
greater than 30 dB. The amplitude variations of lasing peaks in ten minutes are less than 0.26dB for two different
operating modes.
In this paper, we drew a 500 m-long PCF taper directly on the industry drawing tower. The fiber taper has a uniform
cross-section structure with OD from 170 μm to 70 μm, and demonstrates very good beam quality. The optical
attenuation of PCF taper was measured. The optical attenuation is ~5 dB/km near 1200 nm, but the water absorption
peak around 1400 nm and the attenuation beyond 1600 nm are still large. The zero dispersion wavelength (ZDW) was
calculated to be ~1090 nm at the taper input end, and shifted to ~870 nm at the taper output end. The PCF taper was
pumped with a picosecond laser source at wavelength of 1064 nm, and generated 200 mW output power of SC covering
from ~450 nm to 1600 nm.
A 30-mm-length YVO4/Nd:YVO4/ YVO4 composite crystal was used as self-Raman gain material. Yellow
radiation at 587 nm was obtained by utilizing a 15-mm-length LBO as frequency-doubling crystal. The maximum
average power at 587 nm is up to 8.05 W at the pulse repetition rate of 50 kHz and the pump power of 65 W, with
the corresponding optical conversion efficiency of 12.38%. The shortest pulse width, the highest peak power and the
maximum pulse energy were measured to be 5.57 ns, 22.1 kW, and 161 μJ, respectively.
Long period fiber gratings (LPFGs) with different periods in the standard single mode fiber were
fabricated, using laser direct writing method, by femtosecond laser pulses with pulse width of 200 fs
and the repetition rate of 250 kHz at a center wavelength of 800 nm in air. Comparative with bare
LPFG in temperature sensor, LPFG had been encapsulated using large coefficient of thermal
expansion of epoxy polymer and Aluminum to enhance the temperature sensitivity. The results
showed that the temperature sensitivity of encapsulated LPFG was 2 times than that of bare LPFG.
In addition, we also researched the relationship between resonant wavelength and surrounding
refractive index (SRI) when LPFG immersed in refractive index of solution of different index at
20 degree Celsius.
A 145-m long microstructured optical fiber taper was fabricated on the industry drawing tower. The fiber taper had good uniformity of structure as the outer diameter decreased from 110 to 80 μm. Its optical attenuation was measured 52 dB/km at 1060 nm, and the zero dispersion wavelengths along the slow axis were calculated decreasing from 1000 to 915 nm. Watt-level supercontinuum spanning from 430 to 2050 nm was obtained as the fiber taper pumped by a 1064 nm picosecond laser source. The nonlinear mechanism of spectral broadening is carefully investigated with the support of numerical simulations.
Two kinds of supercontinuum (SC) sources are successfully generated by propagating 200-fs unamplified and amplified
pulses through a 0.85-m long nonlinear photonic crystal fiber (PCF), respectively. The spectra bandwidth of
amplified-femtosecond-pumped SC is about 870 nm spanning 480 nm to 1350 nm, which is flat to 1.2dB over 100 nm
spreading from 550nm to 650 nm. With the same PCF, SC spectra pumped by unamplified-femtosecond-pulses are
narrower and unevener. A detailed simulation is carried out to help us understand the mechanism of supercontinuum
evolution. For pump wavelength located at the zero dispersion wavelength of the PCF, spectra are broadened by the
interaction between SPM and higher-order dispersion at early stage. With increasing the pump power, the spectra are
broadened by fission of higher solitons and parametric four-wave mixing (FWM). When the peak power is up to
mega-watt, FWM plays a notable role in flattening and further broadening the supercontinuum spectra in short
wavelength side. An effective way to generate a flat SC laser source pumped by femtosecond pulses is also
demonstrated.
Real-time terahertz imaging is demonstrated using a 1.63 THz (184.31μm) optically-pumped terahertz
laser (Coherent Sifir-50 FPL) and a 124×124 element room-temperature pyroelectric camera (Pyrocam
III). Transmission-mode THz images are presented with samples hidden in various wrapping materials.
Experimental results show that this THz imaging system has the potential for the application in
real-time mail inspection and non-destructive inspection.
Microchip-laser-pumped supercontinuum (SC) is successfully generated through a 30-m long photonic crystal fiber
(PCF). The spectra bandwidth of SC is 850 nm spanning from 550 nm to 1300 nm. The -15dB-flat bandwidth is 400 nm
spanning from 600 nm to 1000 nm. It is easy to achieve a much more flat SC with the sacrifice of spectra bandwidth. A
detailed simulation is carried out to help us understand more about the supercontinuum generation process. The primary
mechanism of spectral broadening is identified as parametric four-wave mixing (FWM) combined with stimulated
Raman scattering (SRS). These findings also demonstrate an effective way to generate a flat supercontinuum laser source.
LD-pumped all-solid-state yellow laser based on frequency-doubled Nd:YVO4 crystal self-Raman laser was demonstrated. Through extracavity frequency-doubling with KTP crystal, the maximum average output power of the yellow laser was measured to be 495 mW with the incident pump power of 18 W. The corresponding optical conversion efficiency was about 2.75 %. The highest pulse energy, the shortest pulse width and the highest peak power of the yellow laser were obtained to be 19.9 μJ, 4.5 ns and 3.88 kW, respectively.
In this report, a required aperiodically poled structure is designed, where two quasi-phase-matched conditions of optical
parametric oscillator and frequency difference are required to be satisfied simultaneously. By numerical simulation, we
analyze the effects of crystal structure, the cavity parameter of optical parametric oscillator, and terahertz absorption
coefficient on terahertz generation. And, the terahertz wave is generated via cascaded processes, which is of great
interest in fundamental and applied sciences, and is a great demand for many applications in spectroscopy, sensing,
communication, medial diagnoses and biomedical imaging. In addition, the design method for poled ferroelectric crystal
is universal and applicable to many other fields, particularly in those processes where multiple quasi-phase-matched
conditions are required to be satisfied simultaneously.
Raman fiber amplifier (RFA) can be used for amplifying signals in all wavelength bands. To obtain flat Raman gain in considered wavelength range, we can use either more fiber amplifiers for different wave bands or more pump sources combined with appropriate pump powers at appropriate wavelengths. However, appropriate wavelengths and powers make the communication system complex and not easily controlled. Because of its ultra-wide band single mode operation, flexible structure design, their realization of high nonlinearity and overall controlled dispersion properties, photonic crystal fiber (PCF) is recognized as a novel class of fibers and a promising new kind of Raman gain medium. The larger nonlinear coefficient could be obtained by reducing mode area through its air hole microstructure region, thus leading to a greatly improved Raman gain coefficient. In this paper, we have modeled and simulated Raman gain properties of PCFs. Appropriate pump wavelengths and output powers are used as the multi-pump for PCFRAs. Through tuning the pump wavelengths and their output powers we can obtain the gain bandwidth of 40nm (from 1530nm to 1570nm) and the gain value is 14dB with ±0.5dB ripple.
Quantum wire is one of the central subjects of nano-electronics. Quantum wire shows unusual electronic and optical
properties attributed to the following effects: quantum confinement effect, surface effects, and quantum tunneling effect.
Many different kinds of techniques have been developed for researchers to produce quantum wires, such as laser ablation
technique, electrochemical processing, chemical vapor deposition technique, etc. However, controlling the sample size
and orientation distribution is a big challenge in these fabrication methods. One promising technique to prepare monosized
well-aligned quantum wires is using template technique, i.e., deposition of guests into porous matrices.
In this paper, several template synthesis processes for preparations of carbon nanotubes were investigated. The carbon
nanotubes produced by template technique have narrow size distributions and involve fragments of highly ordered
shapes which are due to the limitation of matrix size and channel direction. Because of the restricted dimension of the
matrix, the system shows peculiar properties such as polarization in spectra, strong quantum effects, and faster optical
response. These may be used in electric transport, optic switches, nonlinear optics and lasers.
Femtosecond laser micromachining of solid materials such as Si, GaAs, polymethyl methacrylate (PMMA) and Fused
Silica has been performed in air. Femtosecond (fs) laser pulses with pulse duration of 180 fs and output wavelength of
800 nm is applied for a light source. The relationship between pulse energy and sub-micron scale crater on the surface of
Si, GaAs, PMMA and Fused Silica induced by fs laser pulses has been figured out. The sub-micron void can be
produced in the focal point of fs laser beam. Two kinds of gratings have been fabricated on the surface of Fused Silica by
femtosecond laser machining (FLM). The parameters of one grating such as the length of 20 mm, the width of 1.5 mm
and the period of 2 μm have been obtained. A 20-mm-long and 0.45-mm-wide grating with period of 11 μm has been
also fabricated. The diffraction efficiency of each order has been measured. An elliptical cross section waveguide has
been obtained inside the bulk of Fused Silica. The distance beneath the surface was measured to be 2 mm. The
diffraction rings can be observed in the far field image of the light output from the waveguide.
Rod-type photonic crystal fibers (PCFs) bring enormous advantages in Q-switched fiber laser with high pulse energy, short pulse width and good beam quality for its large mode area and short fiber length. In this paper, an acoustic-optic Q-switched photonic crystal fiber laser was investigated by using a 1m-long Yb-doped large mode area rod-type photonic crystal fiber as gain medium. A maximum pulse energy of 0.78 mJ (21.7 KW peak power) and the shortest pulse width of 20 ns were obtained at low repetition rates. A maximum 1033.6 nm average power of 14.5 W was demonstrated at 65 KHz with a slope efficiency of 56%. Further improvements would be obtained by optimizing the experiment configuration so as to achieve shorter pulse width and higher pulse energy.
Temporal coherence property of supercontinuum (SC) generated in a polarization-maintaining photonic crystal fiber
(PM-PCF) pumped by Ti:sapphire fs laser was experimentally studied by using a modified Michelson interferometer.
The coherence length of supercontinuum light was measured to characterize the temporal coherence property. The
coherence lengths of supercontinuum and pump laser were measured to be 6.5 μm and 59.14 μm, respectively. The
shortened coherence length of supercontinuum output from the PM-PCF was due to the broadened spectrum. Moreover,
the interferogram evolution versus the supercontinuum spectra was also investigated. It was indicated that the flatter the
supercontinuum was, the better the interferogram was.
To our best knowledge, the most supercontinuum sources generated by use of cw pump lasers were obtained with fiber
interaction lengths of the order of 100 m to a few kilometers to enhance the optical nonlinearity. However, the material
loss was accumulated and the price cost was boosted in the long fibers. In this paper, CW supercontinuum generation by
use of a 1480-nm fiber-Raman laser (FRL) in a 100-m high-nonlinear photonic crystal fiber (PCF) together with a 76-km
single mode fiber (SMF) was demonstrated. The broadband supercontinuum was obtained with 10-dB bandwidth of 124
nm spanning from 1476 to 1600 nm. It was shown that the principal mechanism of the broadening could be assigned to
stimulated Raman scattering, four-wave mixing (FWM) and modulation instability (MI).
We report a high-power diode-double-end-pumped Q-switched Nd:YVO4 red laser through intracavity
frequency-doubling with a type-I critical phase-matched LBO crystal. At the repetition frequency of 26 kHz, the
maximum quasi-continuous-wave (QCW) output power at 671 nm was measured to be 9.2 W at the incident pump power
of 62.4 W with the corresponding optical conversion efficiency of 14.7%; the pulse width of about 106 ns; the pulse
energy of 353.8μJ; the peak power of 3.34 kW, respectively. The perfect performance indicated that the
double-end-pumped technique could effectively diminish the thermal lens effect, extend the range of the stable resonator
region and achieve a high optical conversion efficiency to obtain a high output power.
The IP surveillance market is growing significantly and is receiving global attention now. IP camera is the heart of this
new surveillance system. As the key component of IP camera, video capture port contributes greatly to camera's cost.
CCD image sensors are employed in most IP camera for its excellent performance and maturity in the market. In fact,
new types of CMOS image sensors have become possible recent years due to CMOS technology improvements. This
paper presents a design of an IP camera's video capture port using CMOS image sensor based on embedded environment.
Also contained is a brief introduction to the hardware design including the interface and PCB layout. The paper also
provides information on setup of important registers, functions usage and debug tips. The design was tested on an IP
camera which has been on market for three years. The results show that using CMOS image sensor can achieve good
image and save cost. Therefore, it is well suited for the surveillance field where image resolution is not the focus. The
method can easily be extended to any other IP camera design with little change both in hardware and software.
With an acousto-optical Q-switch and Co:LaMgAl11O19(Co:LMA) crystal as the saturable absorber, diode-end-pumped actively and passively Q-switched Nd:GdVO4 lasers at 1.34 μm were demonstrated, respectively. For acousto-optical Q-switched operation, the maximum average output power, the highest pulse energy, the shortest pulse width and the highest peak power were obtained to be 4.54 W, 223 μJ, 19 ns and 11.75 kW, respectively. For passively Q-switched operation with a 0.3-mm-long Co:LMA crystal as the saturable absorber, the maximum average output power, the highest pulse energy, the shortest pulse width and the highest peak power were obtained to be 1.43 W, 112 μJ, 55 ns and 1.95 kW, respectively.
Supercontinuum was generated in a polarization-maintaining (PM) PCF. The main advantage with the PM-PCF is the preservation of the state of polarization of the field propagating. For several applications, it is essential that the output has a well-defined polarization. In addition, the preserved polarization enhances the nonlinear interactions so that less power is required to generate the SC. The field patterns, birefringence and nonlinearity in the PM-PCF were simulated using a full-vector finite element method. Spectral broadening was achieved pumped by the optical parameter amplifier system (OPA). It was concluded that the SC generation was depended on the pump wavelength, and the difference group velocities in the two sides of the zero dispersive wavelength of the PCF and the OH absorption at about 1.4μm in the PCF affected the flatness of the generated supercontinuum. When the pump wavelength lied further away from the zero dispersive wavelength, the flatness was reduced, even in the visible region the blue-shift peaks were separated and didn't come into being supercontinuum. Supercontinuum with a broad bandwidth of 300 nm to 1350 nm was generated when the pump wavelength of 1200 nm, and the generated spectral bandwidth was beyond two octaves.
Raman scattering is an inelastic process, in which we can obtain information about material lattice vibration frequencies. If the wavelength of the excitation laser is within the electronic spectrum of the material, the intensity of some Raman-active vibrations will increase enormously. This resonant Raman effect can be quite useful to explore the electron-phonon coupling in the substance. In this article, we report the investigations on the electron-phonon coupling effect in Se nanoclusters using resonant Raman technique. Up to 10 different laser lines are used in the experiment. The Raman intensity strongly depends on the energy of the laser lines used for excitation. The one-phonon symmetric A1 modes for Se single helix and Se8 rings are enhanced in the vicinity of their absorption bands. Detailed analysis shows that the Raman intensity in the high frequency range 450 - 550 cm-1 is a sum of individual second-order Raman scattering intensities for the confined Se species. These two-phonon Raman shifts occur at twice the frequency shift of the first-order Raman lines, and their intensities are also enhanced when the excitation laser energy matches an electronic transition in Se nanoclusters.
Aluminophosphate AlPO4-5 single crystal is a kind of nanoporous material. Its framework consists of alternative tetrahedra of AlO4 and PO4 which form an array of opened one-dimensional channels and pack in hexagonal structure as two-dimensional photonic crystal. The inner diameter of the channel is 0.73 nm. Since the AlPO4-5 single crystal is electrically insulated and thermally stable up to 900°C, it is an ideal host to incorporate nano-structured species. These guest-host materials are potentially new functional materials in electric transport, optic switches, nonlinear optics and lasers. We have synthesized two different types of guest-host systems, including selenium and carbon nanotube in the channels of AlPO4-5 crystals. Polarized absorption spectra and polarized Raman spectra have been investigated. Both crystals behave as good polarizers with high absorption for the light polarized parallel to the c-axis of the crystal. This anisotropic optical property implies that ordered species with a large aspect ratio are formed in the channel. The
polarization angle dependence of the Raman intensity indicates that the enclosed species are highly oriented in the channels with their dipole transition moment mostly along the channels. These guest-host systems are useful for applications of optical filters or polarizers.
Micro-cavity laser has attracted extensive attentions due to its potential applications in high-speed integrated opto-electronic device and system. In micro-cavity, spontaneous emission process is enhanced or prohibited, and lasing can occur without a visible threshold. In the past, micro-cavity was realized with semiconductors such as microdisks or vertical cavity surface emitting lasers, with organic dyes embedded in planar resonators as Langmuir-Blodgett films or in spheres, and with gain medium in photonic crystals. In this article, we report a new type of micro-cavity laser based on organic dye molecules incorporated in the channels of AlPO4-5 single crystals by physical diffusion method. The optical measurements reveal that the dipole transition moment of the enclosed organic dye molecules is highly oriented in the channels. Due to size confinement of the AlPO4-5 channels, there is a structure deformation of the dye molecules, which leads to a large blue shift in the absorption spectra for the dye/AlPO4-5 crystal. The micro-sized hexagonal AlPO4-5 single crystal serves as a good natural micro-cavity for the lasing action of the adsorbed dye molecules. The micro-cavity mode of the lasing action is demonstrated.
We report a high-power diode-single-end-pumped continuous-wave and Q-switched Nd:GdVO4 red laser through intracavity frequency-doubling with a type-I critical phase-matched LBO crystal. The maximum CW output power at 671 nm was measured to be 2.1 W at the incident pump power of 30 W, with the corresponding optical conversion efficiency of 7%. At the repetition frequency of 47 kHz, the maximum average output power of quasi-CW red light was obtained to be 6 W, with the corresponding optical conversion efficiency of 12.8% and the pulse width of about 97 ns. At the average output power around 5 W, the power stability was better than 5.8% for one hour. The M2 factor increased from 1.33 to 2.47 when the output power was increased from 1 W to 6 W. At the repetition rate of 25 kHz, the maximum pulse energy of 212 μJ was obtained with the corresponding peak power of 3.98 kW.
The absorption spectrum from 300 to 1000 nm and emission spectrum from 960 to 1450 nm of Nd:LuVO4 crystal were measured. A LD-end-pumped passive Q-switched Nd:LuVO4 laser was reported. With a Cr4+:YAG crystal as the saturable absorber, the maximum average output power was measured to be 4.58 W, and the corresponding optical conversion efficiency was 24.0 %, with the pulse energy, peak power, and pulse width being 36.6 μJ, 436.2 W, and 84 ns, respectively.
We investigated the group-velocity dispersion of a one dimensional uniform photonic crystal by the optical transmission method. For application in optical communications, the wavelength should be near one of the two edges of a photonic bandgap. Four kinds of
dispersion-compensation may be obtained with a photonic crystal. Huge negative and positive group-velocity-dispersion (GVD) about a
zero-dispersion-point as large as 5.1 Tera- ps/nm/km by a photonic crystal of 100 periods can be realized. Such a value is about 50 Giga times the GVD of conventional dispersion-compensation fibers. The GVD reaches a maximum when the optical length ratio of the high refractive index material to the low refractive index material is 1.2 for given operating parameters. When we keep the optical length of each layer being constant, the GVD is found to increase rapidly with the refractive index ration of the high refractive index material to the low one and even more rapidly with the number of periods of a photonic crystal. Under quite common operating parameters, a thin piece of photonic crystal of 100 periods may play the role of an ordinary dispersion-compensation fiber with a length over 158
kilo-meters.
We propose a kind of planar photonic crystal micro-cavity which is truly two-dimensional and is composed of a line of periodic air-holes and a set of periodic air grooves both with defect. Unlike the photonic crystal micro-cavity formed by distributed Bragg reflection (DBR) layers and two dimensional holes in a semiconductor substrate, the micro-cavity proposed is a true two-dimensional planar structure that is easy for mass-production through die-press copying. Numerical simulations by the FDTD method show that there exist resonance modes inside the photonic bandgap. The resonance wavelength is mainly decided by the period and radius of the holes. The quality factor of the cavity is mainly decided by the number of periods of the holes and the grooves.
A novel measuring implementation based on second-harmonic generation frequency-resolved optical gating (SHG-FROG) has been presented. Both the intensity and phase of arbitrary-shaped ultra-short laser pulses can be got. According to SHG-FROG, the femtosecond pulse produced by a laser resource is split into two beams which variable time delay one another is controlled by a stepped electromotor. The second-harmonic signal field is generated by focusing these two beams to a 100um BBO crystal. Changing the delay from 0 to N (N is the samples number of time domain or frequency domain) delay units, the two-dimensional spectrum data of the second-harmonic signal field are acquired by PC2000-ISA card spectrometer and OOIwinIP of Ocean Optics. These data are provided to a pulse amplitude and phase retrieval algorithm to retrieve the parameters of the pulse. An experimental system is erected and the all software modules, including spectrum data acquiring, pulse retrieving and displaying, are based on Labwindows/CVI of National Instrument Corp. The stepped electromotor is driven by the commands coming from RS-232 interface. The results show that after 50 times iterations or so, the iterative error of the algorithm can be reduced to an enough small value and then the pulse amplitude, phase and other parameters are the desired parameters. The whole measuring process can be finished in 2~3 seconds while the spectrum data is a 64x64 matrix and the iterative times are set to 50.
We investigate a complex cavity composed of three simple cavities, which are formed by three simple defects in a one-dimensional photonic crystal (PC), by the optical transmission method. We set two of the simple cavities to be the same, and let the cavity-length of the third one vary. Generally, two or more narrow resonant transmission modes emerge in the bandgap region; the position of one of them is basically fixed with different fine structures, in which exists a fixed crest, while the other modes wander in the bandgap region as the cavity-length of the third cavity varies. We find the optimized the relative coupling length being 0.447 for the complex cavity. Introducing the parameter - degree of rectangularity, we find that the complex PC cavity is much more close to an ideal narrow band-pass filter than a simple PC defect cavity. It is surprising that the degree of rectangularity is insensitive to the number of periods in the structures.
Experimental studies on the mode competition in CW fiber laser pumped Raman fiber lasers with two different F-P cavities are carried out. The first cavity consists of a dichroic mirror and a cleaved fiber end and the second of two dichroic mirrors. Results show that there is drastic competition in the first cavity and much less one in the second because of efficient lasing mode selection of two dichroic mirrors. Reasons for mode competition are analyzed. There are two main kinds of competition in the cavity: one exists between the 440cm-1 peak and the 490cm-1 peak in Raman scattering spectrum; and the other is related with long cavity and spatial hole burning. Output characteristic of the laser and probability of different mode wavelengths are also measured.
In this paper, we report the characterization of self-mode- locking femtosecond Cr:forsterite laser, pumped with Nd:YAG laser, generating 36 fs pulse at 1246 nm with 280 mW output power and also research the influence of the crystal cooling temprature vs. output power.
The use of second harmonic generation as a technique for ultrashort optic pulse width measurement is
analyzed to determine in detail the effect of group velocity mismatch (G\TM) between fundamental and second
harmonic fields when considering different pulse shapes. We find that for interferometric autocorrelation and
intensity autocorrelation, GVM has different effects versus different pulseshapes.
In this paper, we report the diode pumped femtosecond Cr:LiSAF laser. Through numerical analysis on the astigmatism, a folded three-mirror cavity is designed. Then we investigate its CW and mode locking operation. When it is pumped by the pulse, the output laser with time duration less than 100 fs is obtained.
In this paper we reported the shortest pulse duration, to our knowledge, from Ti:Sapphire laser in the low gain region. Pumped by 14.5 W from the all-line of Argon-ion laser, a stable laser pulse train centered at 0.94 micrometer, with pulse duration of 37 fs, bandwidth of 33 nm, average power of 80 mW, and a tuning range from 0.9 micrometer to 0.976 micrometer has been obtained.
In chirped pulse amplification system pulse stretching is an important part. To investigate the behavior of an eight-pass single grating pulse stretcher, we examine in two steps: firstly an unchirped ultrashort pulse goes first four-pass through the stretcher, it will be broadened in pulsewidth and provided with amount of positive chirps. Secondly this chirped pulse will has another four-pass experience through the stretcher. Followed by our close calculations, it is clear that stretching factor in the second part is almost 2, and the total stretching factor of this system is equal to the multiplication of the two factors.
The use of second harmonic generation as a technique for ultrashort optical pulse width measurement is analyzed in detail to determine the effect of group velocity mismatch between fundamental and second harmonic fields. We find that for interferometric autocorrelation and intensity autocorrelation type II phase matching, GVM has an appreciable effect. While for intensity autocorrelation type I phase matching, the effect is less noticeable.
A tunable multi-wavelength Ti:sapphire laser with sub-10 femtosecond jitter between the Bi-color pulses has constructed that synchronously generates femtosecond pulse trains at two independent wavelength regions. Two wavelength pulses of duration 26 fs and 29 fs were generated at central wavelength regions from 755 nm to 845 nm. Also, synchronized generation of independent three wavelength pulses has been achieved by fine metallic net slit. Three wavelength pulses of duration 93 fs, 70 fs and 55 fs were generated at central wavelength 755 nm, 808 nm and 821 nm respectively. The jitter between the two color pulses has been obtained using cross-autocorrelation profiles of the two train pulses.
We report the structure and steady-state operating characteristics of the femto-second Ti:sapphire laser. The analytical expression of saturable absorption parameter and selfphase modulation are obtained based on H.A. Haus's self- focusing model and the mode-locked equation by using the self-consistent condition. The relation between the output pulse width and these parameters, the influence of the parameter on the stability of laser are discussed separatively, and to lead some useful conclusions for the optimum design of the fs-laser and how to get as minimum pulse width as possible. By using above results, we have designed the Ti:sapphire laser that it can operate in self- mode locking while the input pump beam from argon-ion-laser is TEMoo mode about a 4 W. The pulse as short as 60 fs duration has been obtained.
The design and performance of a stable Ti:sapphire regenerative amplifier. 7 mJ (800 nm) per pulse at the repetition rate 10 Hz, has been described. The resonator consists of one concave mirror (R equals 4000 mm) and one plane mirror, spaced at a distance of 1.76 m. The two mirrors are coated for high reflection centered at 800 nm. Two Pockel cells, one broadband waveplate and polarizer are used to switch a pulse into and out of the resonator. The Ti:sapphire crystal rod is 6X6X14 mm with an absorption coefficient of 2.6 cm-1 at 490 nm and both sides is cut at Brewster's angle. The pump source is frequency double Nd:YAG laser. For regenerative amplifier, the pump energy which we usually use is 64 mJ per pulse. The seed pulse is from a self-mode-locked Ti:sapphire laser that provides 400 mW of outpower with pulse duration about 80 - 100 fs. After stretching the pulse to about 200 - 300 ps by using the grating stretcher, we inject the pulse into the regenerative amplifier and obtain 7 mJ output energy in single pulse, a net gain of up to 106. This laser system is a pre-amplifier for high energy amplifier.
This paper discusses active mode-locking technique of semiconductor lasers at a
repetition rate of 1GHz.In this work , we use microstrip line matching circuit which
is especially designed to match impedances between an ultrahigh frequency source
and a laser diode . The laser diodes used in our experiments have antireflection
(AR) coatings on one facet . The /4 SlO AR coatings greatly reduce the etalon
effects from the laser diode subcavlty . The reflectivity of one facet of lasers
has less than 0.2 % . Operating characteristics of laser diodes are also described
in this paper
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