Using an ytterbium-doped fiber with a 50 μm core and 0.028 NA, a pulse energy of 4.8 mJ was achieved directly from a single-mode Q-switched fiber laser. The repetition rate was 10 kHz and the average power was 48.4 W. The slope efficiencies with regard to the absorbed and launched pump power were ~74% and ~59% respectively. The pulse width decreased with increasing pump power. The 4.8 mJ pulse had a FWHM width of ~300 ns. A shorter pulse of ~200 ns FWHM was also achieved at 2.06 mJ in another configuration. The M2 was below 1.3 at all pulse energies. This work demonstrates record pulse energy directly from a single-mode Q-switched fiber laser and the feasibility of operating such laser with high efficiencies.
Under the high energy irradiation, the charges (even little) of molecules of polymer can cause the physical and chemical
characteristics evident changes of polymer. The physics and chemical mechanisms which are responsible for radiation induced loss
was analyzed. The radiation damage of polymethylmethacrylate (PMMA), Polystyrene PS and polycarbonate (PC) optical fiber
under γ-ray irradiation was researched experimentally. The visible light transmission of the POF under different irradiation dose
was measured. The results indicated that the radiation damage of three kinds of POF was wavelength-dependent. Under lower dose
below 1KGy, the transmission rate decreased identical in the whole visible light range. When the irradiation dose exceeded 5KGy, the
transmission rate reduced obviously, and the recovery indicated that the visible light transmission rate of the POF in the range of
400nm to 500nm comparing with 600nm to 800nm, decreased seriously under the irradiation dose exceeded 5kGy. The transmission
rate of both PMMA and PC have an evident peak value at the range 550nm-650m, and that of PS has a wide band at the range
500-700nm. We also measured the recovery of three kinds of POF under different irradiation dose by measuring several times the POF
after stopping irradiating.
The radiation damage and recovery of polymethylmethacrylate (PMMA), Polystyrene PS and polycarbonate (PC) optical
fiber under γ-ray irradiation was researched experimentally. The visible light transmission rate of the POF under
different irradiation dose was measured. The results indicated that the radiation damage of three kinds of POF was
wavelength-dependent. Under lower dose below 1000Gy, the transmission rate decreased identical in the whole visible
light range. When the irradiation dose exceeded 5000Gy, the transmission rate reduced obviously, and the transmission
rate indicated that the visible light transmission rate of the POF at the range of 400nm to 500nm comparing 600nm to
800nm, decreased seriously. The transmission rate of both PMMA and PC have an evident peak value in the range
550nm-650m, and that of PS has wide peak value at the range 500-700nm. In addition, we measured the recovery of
three kinds of POF five times following irradiation at the wavelength 632nm. Under low dose irradiation 100 Gy, the
transmission rate reduced a little, and the irradiation damage can recover during a short time. When the irradiation dose
reached 1000 Gy, the recovery process need longer time. When the irradiation dose exceeded 5000 Gy, the transmission
rate reduced obviously, and the recovery process is slow and the irradiation damage can't recover completely, that
indicated fiber suffered lasting damage.
The Step-index plastic optical fiber (SIPOF) bandwidth calculation model is given. The model includes not only the modal delay but also the attenuation and mode coupling effects. the numerical solution of the power flow equation in Fourier domain which is the main equation in this model is reported. This solution is based on Crank-Nicholson implicit difference method. The frequency response function and bandwidth of four kinds of SIPOFS with different Numerical aperture is researched. The frequency response function and bandwidth under selective excitation is numerically calculated. The results imply that the selective excitation of SIPOF increased effectively the fiber bandwidth. Calculated results are useful for practical application of plastic optical fiber.
Plastic optical fiber (POF) can be taken as short distance transmission system medium for replacing of coaxial cable because of its many excellent characteristics. The bandwidth characteristics of graded-index POF is strongly influenced by the differential mode attenuation (DMA). In this paper, a comprehensive bandwidth calculation model of POF is given. The analytical expression of DMA is fitted by eighth order polynomial from the experimental data, and is used for the calculation of fiber bandwidth. The frequency response function of graded-index plastic optical fiber(GIPOF) is calculated numerically under selective mode excitation condition, and the fiber bandwidth is studied. The calculated results indicated that the selective mode excitation could improve efficiently the fiber 3dB bandwidth. The influence of light source linewidth on fiber bandwidth is also investigated.
We performed some experimental studies on a new type cost-effective power coupling method for large-core POFs, and proposed a novel 1×4 plastic optical fiber (POF) power coupler which is different from fused-taper type and mixing rod POF couplers. Loss factors of this coupler are also analyzed theoretically. This coupler is based on thermal feature of POF, the two end of coupler is composed of fused-drawn tapered fiber and thermal-contracted tapered fiber, respectively, which is characterized as simple configuration and easily fabrication. The performance parameters of this coupler including excess loss, insertion loss, and channel cross-talk were measured. The loss and cross-talk can meet the practical requirement, and the channel uniformity is not desirable. The main issue is technical process. In our experiments, heated-drawing and contracting is controlled manually, the uniformity is deteriorated greatly, moreover, the distortion of POF during drawing and contracting is inevitable, as a result it leads to large bending loss. In addition, the termination of the taper and the alignment of optical path influences seriously on performances. Compared with mixing rod coupler, the coupler has advantages of simple structure, easy fabrication due to the absence of the mixing rod middle component. The further research on this coupler is to draw and contract fiber mechanically rather than manually, to enhance the uniformity, and to reduce loss further.
Optical Burst Switching (OBS) functioning as an IP traffic aggregator at the edge of the Optical Transport Network is provided to enhance network flexibility and efficiency. This paper gives an overview of OBS node and the benefits it will bring about. It explains how an OBS node is modeled and simulated under different traffic conditions and gives the effect of Fiber Delay Line (FDL) in OBS node. Finally, the simulation results are presented and the performances of OBS node are evaluated.
This paper presents a theoretical investigation on the mode coupling and mode coupling induced attenuation in step-index plastic optical fiber under different launching condition. We solved numerically power flow equation of multimode optical fiber by explicit finite difference methods. In our calculation, we adopted mode coupling coefficient measured in Garito’s experiments , and supposed power distribution of incident beam have Gaussin form with respect to angle between beam and optical core axis. Under different incident angle and same beam width, we calculated power distribution at fiber output end when optical fiber length is 1,5,15, 20, 50m respectively. In shorter transmission distance, mode coupling isn’t evident, output power distribution is similar to input ones. With increasing of fiber length, power diffused gradually from high order modes to low order modes, and mode coupling finished in about 20m, where equilibrium mode distribution is achieved. In addition, we calculated mode-coupling induced attenuation of different width and launching angle Gaussin beam, with enhancing of beam width and launching angle , attenuation increased .
In this paper, we described a kind of structures and the principle about a multi-channel optical switch. we designed a novel revolving single mode optical switch, which based on electronically controlled fiber collimators directing the light to desired output fibers, and the movement of fiber collimator is implemented by the rotation of stepping micro-electromotor. The main parts of the optical switch are two cylinders being carrier of fiber collimators, one of which can revolve driven by stepping micro-electromotor which is controlled by micro-computer. With flexibility of structure,it is easy to design the series of 1xN optical switches. Furthermore, by using two or more revolving axes, we can design reasonably the position of the optical collimators, and get no-blocking 2x2 or 4x4 optical switch matrix. We fabricated a 1×8 single1 mode optical switch, and the experiment results indicate that the technical performance of the optical switch can satisfy requires for changing light channel.
In many magneto-optical materials, Faraday rotation is always accompanied by magnetic circular dichroism(MCD, that crystal represents different absorption coefficient of right and left circularly polarization light under magnetic field). In this paper, the theory of (MCD) of magneto-optical materials is introduced. The influence of MCD on polarization dependent optical isolator is analyzed through employing Jones vector and transmission matrix. The analytical formula about the relation of MCD and the insertion loss and isolation ratio of optical isolator is derived. The curve of insertion loss and isolation ratio with respect to MCD demonstrated that MCD degrades much isolation ratio comparing with insertion loss. It is evident from the curve the effect of MCD on isolation ration is general small, but in order to make increase in the isolation as high as possible and the insertion loss as small as possible, crystal with minimum MCD coefficient and maximum rotation coefficient should be chosen. The conclusion is significant to optical isolator optimization designing.
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