The periodical pulse bundles were presented in a Yb-doped double-clad distributed Bragg reflector all-fiber configuration. With a pumped power of 529.2 mW, the periodical pulse bundles is obtained. Furthermore, a single pulse bundle composes of one main pulse and two sub-pulses. The pulse width of the main pulse and the sub-pulse are 2.2 μs and 7.7 μs, respectively. The separations of between main pulse, right sub-pulse and left are 22.70 μs and 22.15 μs, respectively. The average period of the pulse bundle is approximately 75 μs with repetition rate of 13.3 kHz. The number of sub-pulses between adjacent main pulses decreases to one when the pumped power does to 450.2mW. When the pumped power increases to 594.4 mW, the number goes to three.
A Ho3+-doped photonic crystal fiber laser with output wavelength of 2077nm has been demonstrated using a 1992nm Tm3+-doped fiber laser with output wavelength of 1992nm as a pump source. And the optical- optical conversion slope efficiency is 41.3%. In order to optimize the output power of the Ho3+-doped photonic crystal fiber laser, a simple quasi-three level system theoretical modeling is developed in the condition of Stark-splitted energy level diagram of holmium ion. We obtain the theoretical optical- optical conversion slope efficiency 43.5%, which is higher than the experimental 41.3%. Furthermore, the relative deviation of the η is 5%, which shows the theoretical data is good agreement with experimental data. According to the modeling, the influence factors of the output power have been theoretically studied, in detail. The results show that there are an optimal range of Ho3+-doped concentration n0, transmittance of coupled output mirror T2 and length of the PCF L, respectively. Furthermore, the output power is approximately equal to maximum in the range of the optimal value.
In this paper, we present a theoretical model to describe the passively-Q output characteristics of quasi-three level Ho3+-doped Fluorotellurite fiber lasers. According to the model, we have studied the factors impacting on the output characteristics of the laser through numerical simulation method. The calculating program of the theoretical model is written using the Matlab language. We obtain the passively-Q output laser with the pulse repetition rate of 13.1 kHz, pulse width of 28.63ns, peak power of 25W, and pulse energy of 0.34 μJ at the pump power of 0.1W. When the pump power increases, the pulse width of the laser decreases, the pulse repetition rate linearly increases, both the pulse energy and the peak power also increases. The pulse width of the laser linearly increases and the pulse energy increases when the length L does. When the output coupler transmission T increases, both the pulse width and the peak power of the laser decrease. The pulse energy of the laser firstly increases and then decreases when the output coupler transmission T does. We qualitatively analyze what causes the change laws of the outputlaser characteristics, such as the pulse width and the pulse energy.
16-core photonic crystal fiber (PCF) was designed. In order to obtain spatially flat in-phase modes, the super-mode near- field properties were studied through method of numerical simulation calculation and according to coupled mode theory. On the based of the scalar Fraunhofer Diffraction, a far- field in-phase super-mode theoretical modeling was presented. According to the modeling, one discussed the influence of the random phase perturbation, the random amplitude perturbation and the polarization direction perturbation on the far-filed intensity distribution, in detail. The results show that both phase perturbation and amplitude perturbation sharply impact the far-filed distribution of interference intensity and contrast. However, the influence of the polarization direction perturbation is not obvious. When the parameterδ, μ and ▵ increases, the field center intensity decreases and the power of the central spot also does, which means the profile of the spot will blur and the beam quality drop.
A laser-diode-pumped actively Q-switched Yb:NaY(WO4)2 laser operating at around 1040 nm is presented for the first time with acoustic-optic modulator. The dependence of pulse width on incident pump power for different pulse repetition rates is measured. By considering the Guassian spatial distribution of the intracavity photon density and the initial population-inversion density as well as the longitudinal distribution of the photon density along the cavity axis and the turn off time of the acoustic-optic Q-switch, the coupled equations of the actively Q-switched Yb:NaY(WO4)2 laser are given. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.
The gravity acceleration is an important physics constant, which is measured by the rotating liquid as a university physical experiment. However, the present experimental methods have a bigger amount of experimental error. A modified rotating liquid optics method is presented to measure the gravity acceleration, in which an angle measurement instrument with an accuracy of 0.05 degree is introduced. Laser is used to measure the angles of the highest point and the lowest point of the rotating liquid. Then the gravity acceleration can be calculated. The modified method has more little error and makes the experiment easier and more convenient.
The existing problems of the experiment education in colleges and universities are analyzed. Take the science and engineering specialty as example, the idea of the combination with teaching and scientific research is discussed. The key problems are how the scientific research and scientific research achievements are used effectively in the experiment education, how to effectively use scientific research laboratories and scientific researchers. Then, a specialty experiment education system is established which is good for the teaching in accordance of all students’ aptitude. The research in this paper can give the construction of the experiment teaching methods and the experiment system reform for the science and engineering specialties in colleges and universities.
A KTP EOPO pumped by an AO Q-switched and SESAM mode-locked Nd3+: GdVO4 laser is experimentally realized.
The cavity is designed to satisfy synchronously pump. The signal trace and output powers from the OPO are
experimentally measured. Based on the experiment, a dynamical rate-equation model is firstly set to simulate the
operation of the Q-switched and mode-locked OPO. The theoretical values from the rate equations agree with the
experimental results well. The developed model explains the behavior, which is helpful to system optimization.
We investigate a photonic crystal fiber (PCF) which consists of squeezed triangle lattice and elliptical air holes. Birefringence and dispersion properties of this PCF have been numerically estimated by the supercell lattice method. Numerical results show that the birefringence is on the order of 10-2 over ultrabroad wavelength rang from1.3μm to 1.7μm and birefringence can be reached 1.71×10-2 at the operating wavelength of 1.55μm. It is also demonstrated that two near-zero dispersion of -1.75(ps/nm/km) (x-polarized mode) and-0.33(ps/nm/km) (y-polarized mode) at 1.55μm can be achieved. Morever, the fluctuations of the dispersion with fiber parameters are very small. The simulation results show that our proposed PCF are robust to fabrication imperfections.
In order to investigate the power characteristics of the Yb-doped photonic crystal fiber(PCF) laser, we have represented a simple three-level system modeling based on a rate equation model. According to our theoretical modeling, the variation of the output power Pout via the pump power Pp is theoretically studied, which agrees well with experimental data. Then, we have investigated the effects of the doped concentration of Yb ions, the length and the effective mode field area of the PCF on the output power Pout of the Yb-doped PCF laser, respectively. The results show that the output power Pout first increases and then decreases when the doped concentration of Yb ions N0 increases and when the pump power Pp and the length of the PCF L are constant. And the optimal doped concentration Nm exponentially decreases when the length L of the PCF increases and the slope of the optimal doped concentration Nm also decreases when the length L of the PCF increases. The output power Pout first increases and then decreases when the length of the PCF L increases and when the pump power Pp and the doped concentration N0 are constant. And the optimal length Lm of the PCF exponentially decreases when the doped concentration N0 increases and the slope of the length of the PCF also decreases when the doped concentration N0 increases. The output power Pout linearly decreases when the effective mode field area A increases.
Photonic crystal fiber (PCF) with high birefringence and low dispersion is proposed in this work. Both two different sizes of elliptic air holes in the fiber cladding and a small elliptic air hole in the fiber core are used in our proposed PCF. The high birefringence is introduced on the combined effect of elliptical air holes and the squeezed lattice. The birefringence and the dispersion of this PCF have been numerically estimated by the supercell lattice method. The simulation results show that the high birefringence with the order of 10-3and the low dispersion of both x-polarized mode and y-polarized mode at the wavelength of 1.55μm can be obtained. The dependence of both the birefringence and the dispersion on structure parameters is analyzed. The simulation results show that flat birefringence and dispersion can be obtained.
A low-flattened index-guiding photonic crystal fiber (PCF) with high birefringence and low effective mode area is proposed. Elliptical air-holes with different diameters are distributed on the squeezed lattice. With the supercell lattice method, we simulate numerically the dispersion property and the birefringence property of the fundamental modes in this PCF. Simulation results show that the proposed PCF has a total dispersion as low as 0 ±1(ps/nm/ km) over ultra-broad wavelength band from1.3μm to1.6μm . Meanwhile, the birefringence can be reached the order of 10−3 and the low effective mode area is also obtained. Moreover, the influences on the birefringence and dispersion by geometrical parameters have also been discussed in detail.
One provides a simple recipe, which is manipulating refractive of doped region of the MCPCF, to obtain the equal
amplitude distribution of the in-phase supermode for multicores photonic crystal fibers (MCPCFs). Using coupled mode theory and vector finite element method (VFEM), a 7-core PCF is analyzed in detail and the results are applied to 16-,18- and 19-core PCFs, which will find important applications in high-power MCPCF lasers and amplifiers. One shows that it is possible to construct uniformly distributed modes for the nontrivial examples of 7- 16-, 18- and 19-core PCFs. One demonstrates that an equal amplitude distribution of in-phase supermode can be achieved by manipulating refractive of doped region in cores area. This research would provide a theoretical basis for investigating equal amplitude in-phase supermode in the MCPCF.
In this paper, we study the birefringence of polymer photonic crystal fibers with elliptical air holes and squeezed
triangular lattice in the cladding. We use the modified squeezing ratio to describe the squeezed degree reduced by both
squeezed lattice and elliptical air holes. By using the supercell lattice method, the study on the influence of the squeezing
on the birefringence of photonic crystal fibers is given. Studies show that the birefringence on the order of 10-3 can be
easily achieved. Based on these numerical simulations, it is noted that a simple function is given to express the relation
between birefringence and the modified squeezing ratio of polymer photonic crystal fibers in a certain range.
In this paper, we investigate the dispersion and polarization properties of polymer photonic crystal fiber with elliptical air
holes and squeezed lattice using supercell lattice method. We introduce the modified squeezing ratio to describe the
squeezed degree reduced by both squeezed lattice and elliptical air holes. Based on the supercell lattice method, the
highly birefringence and flattened chromatic dispersion can be obtained as the structure parameters of polymer photonic
crystal fiber are appropriate simultaneously.
We study the birefringence characteristics of photonic crystal fiber with squeezed lattice and elliptical air holes in the cladding, based on the supercell lattice method. A definition of modified squeezing ratio is introduced, which describes the complex effect of elliptical air holes and squeezed lattice on the birefringence characteristics. Studies show that the birefringence simply varies with the modified squeezing ratio in a certain range. So the concept of modified squeezing ratio can be used to design the high birefringence photonic crystal fiber.
The squeezed photonic crystal fibers have attracted significant attention, which is a kind of photonic crystal fiber with
squeezed lattice or elliptical air holes in cladding. So far there is no a universal concept to describe the squeezed degree.
We introduce the concept of the modified squeezing ratio to describe the squeezed degree of the squeezed photonic
crystal fibers, and then present a corresponding model. Using this model, we investigate the influence of modified
squeezing ratio on the birefringence characteristics of photonic crystal fibers based on the supercell lattice method.
Furthermore, it is reported for the first time to our knowledge that the complex influence of the lattice squeezing and the
elliptical air holes on the birefringence is discussed.
The impacts of polarization dependence loss (PDL) on the polarization mode dispersion (PMD) compensation in
return-to-zero (RZ) and non-return-to-zero (NRZ) modulated systems are discussed in this paper. PDL affects the degree
of polarization (DOP) feedback PMD compensation only in the presence of PMD. And in the presence of PMD and PDL,
DOP relates not only to both the PMD and the PDL vectors, but also to the signal's polarization states. In the presence of
PDL, DOP-feedback PMD compensation would be more effective in NRZ system than in RZ system.
KEYWORDS: Polarization, Signal attenuation, Time metrology, Picosecond phenomena, Signal detection, Modulation, Sensors, Polarizers, Feedback signals, Analytical research
A novel polarization dependence loss (PDL) measurement approach using the degree of polarization (DOP) feedback
signal has been introduced in this paper. Both the theoretical analysis and the experimental simulation show that, while
maintaining a very acceptable level of measurement accuracy, this PDL measurement method could effectively reduce
the measurement time. In comparison with the current PDL measurement technologies, the most prominent property of
our method is that it could provide different PDL measurement accuracy and range by changing the value of polarization
mode dispersion (PMD) element in the measurement setup.
In this paper, a modified stacking method to fabricate photonic crystal fibers with squeezed lattice is presented, for the first time to our knowledge. This modified method can realize different structures of photonic crystal fibers with different expected squeezing ratios. The influences of the structural parameters on the squeezing ratio and birefringence are separately discussed in detail. Moreover, the birefringence characteristics of such photonic crystal fibers are simulated by using supercell lattice method.
In this paper, several triangular-lattice highly birefringent PCFs are analyzed on the base of the full vector model. Several properties of them, such as the PCF's modal field, the birefringence and the dispersion, are simulated by the supercell lattice method. Moreover, a comparison is made among them to study the impact of air-holes configuration of PCFs on their propagation properties. The simulation results show that air-holes at different position have different impact on the propagation properties of PCFs.
The impact of polarization dependence loss (PDL) on the degree of polarization (DOP) feedback signal in polarization mode dispersion (PMD) compensation is discussed in this paper. PDL affects DOP only in the presence of PMD. And in the presence of PMD and PDL, DOP relates not only to both the PMD and the PDL vectors, but also to the signal's polarization states. The PDL minimum endangering PMD compensation is determined by the step size of the practical PMD compensating algorithm, and the DGD value in optical fiber systems. DOP could no longer act as the feedback signal in PMD compensation unless PDL in the fiber system has been effectively eliminated before PMD compensation.
A model based on rate equations that consider the spatial distribution of photon density and inversion population density, as well as the turnoff time of an acoustic-optical modulator, is developed to perform accurate predictions of the characteristics of a green laser. Numerical solutions are consistent with the experimental results of a diode-pumped acousto optical Q-switched intracavity-frequency-doubled Nd:GdVO4/KTP green laser.
A texton-based texture synthesis algorithm is presented in this paper. Based on the Markov Random Field (MRF) model, the algorithm takes a block randomly from a given sample texture to form a seed area in the center of the synthesized output texture, then synthesizes the output image pixel by pixel spirally along the edge of the seed area. When sampling a pixel from the sample texture in the synthesis procedure, the algorithm adopts so-called candidate search, global search and central search to preserve the integralities of textons in the synthesized output texture. It was practically improved that the algorithm does better than the existing methods in quality for synthesizing most kinds of textures, especially for synthesizing the complex textures.
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