In this paper, we report on a high-energy, high-power quasi-continuous wave (QCW) operation of a double-clad thulium (Tm) fiber laser. We constructed an efficient high-power Tm fiber laser which produced rectangular-shaped pulses at 1940 nm with a > 6 J pulse energy and a 10 ms pulse duration at a 10 Hz repetition rate, corresponding to an average power of > 60 W and a peak power of > 600 W for ~ 110 W of incident pump power at 793 nm. The detailed laser characteristics and the ablation of stones with a constructed laser are discussed.
We report Q-switched operation in a dual-cavity Nd:YAG laser using an acousto-optic modulator. A dual-cavity laser configuration allows selection of the TEM00 mode, LG01 mode, or multimode as a laser output simply by adjusting an aperture size in each cavity. Employing the acousto-optic modulator, the Nd:YAG laser produced Q-switched pulses of a 146 μJ pulse energy in the TEM00 mode, 140 μJ in the LG01 mode, and 160 μJ in the multimode.
We report experimental investigation of PD in Yb-doped fibers. From fluorescence spectra while pumping at 1018 nm and 976 nm, we can attribute the PD to existence of oxygen deficiency centers and its strong dependence on the excited Yb3+ ion density. Furthermore, we investigated the impact of PD on the laser amplification experiment, demonstrating that the tandem pumping at 1018 nm could dramatically reduce the PD-induced background loss compared to the LD pumping at 976 nm due to the low excited Yb3+ density. We will discuss the way to mitigate the PD in high power Yb fiber lasers.
High-power femtosecond (fs) lasers in the visible wavelength regime have numerous applications in areas including micro-machining, medical eye surgery, communication, spectroscopy, etc. To generate this laser beam, frequency conversion, especially second-harmonic generation (SHG), of near-IR lasers using nonlinear optical crystals is known to be the most standard technique. However, the use of a long-length crystal, which is preferred to achieve high SHG conversion efficiency for long-pulse or cw lasers, cannot be applied to the fs laser with broad linewidth due to the tight phase matching condition and the exacerbated walk-off effect. Thus the conditions of the nonlinear optical crystal should be optimized to achieve efficient SHG generation and hence, the high power visible fs laser pulses. There are many reports for the efficient SHG of the fs lasers but not many reports about influence of the crystal length on the SHG process, such as the pulse width and the linewidth and the conversion efficiency.
Here, we report efficient SHG of femtosecond Yb lasers at 1 um by optimizing the conditions of nonlinear optical crystals. The SHG pulse and the conversion efficiency were numerically calculated to find the optimized conditions of the nonlinear optical crystals for the high power fs laser pulses with different pulse widths. Preliminary experiments were conducted using a Type I LBO crystal and the femtosecond Yb laser at 1 um, which was in good agreement with the theoretical results. The theoretical and the experimental results for LBO and BBO crystals will be reported in detail.
This paper presents a sol-gel based 1×2 power splitter for an optical communication based on the plastic
optical fiber. To find out optimum parameters of a power splitter, mode propagation along the splitter
was theoretically analyzed using BPM (Beam Propagation Method) and the results show that the distance
between two arms at the output port of a splitter should be kept below 100μm in order to increase the
output power. The planar lightwave circuit device was fabricated by a nano imprint lithography process
followed by a spin coating process. The core size and the length of a power splitter were 230 μm×230
μm and 2 cm, respectively. The measured surface roughness of core/cladding using the AFM (Atomic
Force Microscope) was under 100nm. The characteristics of a fabricated power splitter were conducted
using an 850nm VCSEL (Vertical Cavity Surface Emission Laser) source and 50:50 power splitting
performance was obtained.
In this letter, we proposed a new method for a variable optical attenuator (VOA) through controlling a mechanical misalignment between 2 single mode fibers using a piezoelectric sheet. A piezoelectric sheet with 3 electrodes is adopted in our proposed structure. We can change amount of the bend of the PZT sheet by controlling the applied voltage on the inner electrode of the PZT sheet, which causes the optical loss to be dependent on the applied voltage. The numerical analysis about the optical loss related to the various mechanical offsets is also investigated. From our experimental results, the dynamic range of the proposed structure is about from 0 to 56 dB when the applied voltage range is from 0 to 22V DC. In our previous work using the piezoelectric tube, the dynamic range is about from 0 to 25dB when it is from 0 to 600V DC. The required voltage to get the same attenuation is dramatically reduced. It can make it more practical in the optical communication field.
KEYWORDS: Magnetism, Finite element methods, Electromagnetism, Microfluidics, Fluid dynamics, Velocity measurements, Power supplies, Digital signal processing, Patents, Particles
This study focuses on the design and analysis of a Rotor type magneto-rheological fluid (MR Fluid) brake and clutch. The brake's braking torque and the clutch's torque output can be easily controlled by adjusting the MR fluid and the configuration of Rotor. Electromagnetic finite element analysis(FEA) is performed, using FEMLAB software of the COMSOL Group, to find out the optimization conditions for the design of the Rotor type MR Fluid clutch and brake. In this paper, the design method of the Rotor type MR Fluid brake and clutch is investigated theoretically. The equation of the torque transmitted by the MR fluid within the Rotor type brake and clutch is derived to provide the theoretical foundation in the rotor design of the brake and clutch. The output torque values are recorded for different input velocities and applied magnetic fields, and the experimental results are compared with the theoretical results. Theoretical and experimental analyses have illustrated that this Rotor type MR fluid brake and clutch can transfer high controllable torques with a very fast time response. It was demonstrated that the Rotor type MR fluid clutch and brake have a strong capability of transmitting and isolating the high torque.
Bare-chip packaging becomes more popular along with the miniaturization of IT components. In this paper, we have studied flip-chip process, and developed automated bonding system. Among the several bonding method, NCP bonding is chosen and batch-type equipment is manufactured. The dual optics and vision system aligns the chip with the substrate. The bonding head equipped with temperature and force controllers bonds the chip. The system can be easily modified for other bonding methods such as ACF. In bonding process, the bonding force and temperature are known as the most dominant bonding parameters. A parametric study is performed for these two parameters. For the test sample, we used standard flip-chip test kit which consists of FR4 boards and dummy flip-chips. The bonding temperatures are chosen between 25°C to 300°C. The bonding forces are chosen between 5N and 300N. To test the bonding strength, a bonding strength tester was designed and constructed. After the bonding strength test, the samples are examined by microscope to determine the failure mode. The relations between the bonding strength and the bonding parameters are analyzed and compared with bonding models. Finally, the most suitable bonding condition is suggested in terms of temperature and force.
In this letter, we proposed a simple and cost-effective variable optical attenuator (VOA) through controlling a mechanical misalignment between 2 single mode fibers. A piezoelectric ceramic tube having 4 electrodes on the surface is the key component in our proposed structure. We can change the deflection of the tube by controlling the applied voltage on the electrodes of the tube, which causes the optical loss to be dependent on the applied voltage. The fact that the piezoelectric ceramic tube can be easily fabricated by using the electro-phoretic deposition processing makes our structure more attractive for mass production. The tube-fabrication processing is out of the range in this paper. So, the detail technical approach of the tube fabrication is excluded intentionally. The numerical analysis about the optical loss related to the various mechanical offsets is also investigated. From our experimental results, the dynamic range of the proposed structure is about from 0 to 25 dB when the applied voltage range is from 0 to 600 V DC. Our proposed structure can be a good candidate for a simple and cost-effective variable optical attenuator in optical communication system field.
We present a novel micro optical waveguide (MOW) on micro actuating platform (MAP) structure that is used for a variable optical attenuator. The device is consists of a fused biconical taper (FBT) coupler mounted on an electromechanical system where an axial stress over the waist of FBT coupler is precisely controlled. Its operation is based on change of coupling constant by compressive stress induced photoelastic effects on the waist zone. We use two FBT couplers to implement an enhanced performance of variable optical attenuator. The couplers are made from a standard single mode fiber and have a circular cross-section in their waist with an enough heating temperature. Each FBT coupler is optimized at 1450nm where total insertion loss is 0.75dB. π phase shifts in the coupling constant have been observed at an axial displacement of 9.5μm. The spectral response between two output ports of the coupler is reciprocal. This allows the proposed device to achieve a high attenuation of >72dB and for 20dB attenuation a flat bandwidth of <1dB over 100nm. Both a low polarization dependent loss (PDL) of <0.07dB and a low operating voltage of 15.3V have been demonstrated with a micro-order actuation.
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