Two-dimensional near-wavelength microstructures have been fabricated on a copper film and a silicon wafer by femtosecond vector optical fields with different spatial polarization distribution, at a central wavelength of 800 nm, pulse duration of ∼70 fs, and a repetition rate of 1 kHz. Laser-induced ripples appear at the ablated region on silicon when the laser fluence is above the ablated threshold. When the number of the irradiated pulses increases, ripples with interspace larger than the wavelength could be observed, while the dimension of the ablated region has a slight variation. In the induced microstructures on a copper film, the microstructures in a ring have been observed under the irradiation of a few pulses. Under the irradiation of the multipulse femtosecond vector field, differently from the condition of the silicon, the induced microstructures on the metallic copper surface exhibit the anisotropic extending feature dependent on the polarization distribution of the vector field. The physics behind this unique feature is the anisotropic excitation and propagation of surface plasmon, caused by the coupling of the subsequent irradiation pulses with the existing microstructure. In this case, the surface plasmons resonance in the induced 2D microstructures is closely related to the induced grating structures on the surface.
Orbital angular momentum (OAM), as nature of optical field, has attracted considerable attention, due to its
academic interest and potential applications such as quantum information, atomic manipulation, micromanipulation
and the biosciences. The well-known OAM carried by an optical field originates from the azimuthal phase
gradient of an optical vortex field with a helical phase structure. Here we predict a novel optical OAM, which
is induced by curl of polarization. To demonstrate experimentally the above prediction, we present an idea for
creating a kind of radial-variant vector fields, which could have all local linear polarization and hybrid states of polarization (SoPs). By specifically arranging the SoPs of the vector fields, new effects and phenomena can be anticipated that can expand the functionality and enhance the capability of optical system. The generated vector fields with the radial-variant hybrid SoPs can carry such a novel OAM. Optical trapping experiments validate that the focused vector fields without any additional phase vortex, as the ring optical tweezers, exert torques to drive the orbital motion of the trapped isotropic microspheres.
We constructed a fiber Raman amplifier with an ordinary single-mode fiber in the U-band located on the 1.66μm for the
first time. This paper studies the gain characteristics of FRA by using the pump sources with different property and
different power. Experiments showed the system amplified steadily when pump power was tens of milliwatt. To the
same pump sources, as pump power is increased, the gain of the signal improves obviously. In the case of identical pump
powers, FRA' gain is also concerns with the pump source's type and the pump way. When the double-clad Er-Yb codoped
fiber laser was used as the pump source, though our 1.66μm fiber Raman amplifier, the signal was amplified
effectively and the maximal peak gain reached 5.11dB.
A dual-wavelength narrow-linewidth laser system, with ultranarrow wavelength spacing, is proposed and demonstrated. The operation principle of the laser system is based on the pump-induced thermal effects of the Er-Yb-doped fiber distributed Bragg reflector (DBR) laser. We designed and constructed a common Er-Yb-doped DBR fiber laser with proper parameters. With the pump power of the DBR laser increasing, the Bragg wavelengths and the bandwidths of the two gratings will change unequally. When the laser is pumped with 45 mW, we obtain stable dual-wavelength lasing with a 3-dB bandwidth of 0.014 nm and a wavelength spacing of 0.055 nm.
We present experiments of line and parallel configurations of hybrid erbium-doped fiber amplifiers/fiber Raman amplifiers (EDFAs/FRAs). For the line structure, a gain flatness of ±1.15 dB over a range of 47 nm (1483 to 1530 nm) is obtained. In the parallel configuration, the gain flatness is below ±2 dB for 1487 to 1507 nm and 1520 to 1550 nm. Using a high-birefringence fiber loop mirror as a signal reflector, a noise figure is less than 6 dB in the gain bandwidth. Then performances of different hybrid configurations are compared.
In an intermediate asymptotic propagation distance, pulse's self similar evolution is influenced by the initial pulse width
and chirp, as a result pulses can not completely evolve into a parabolic pulse, which can affect the compression of the
evolved pulse. The self similar evolution results of ultra-short pulse with different width and initial chirp coefficient are
studied by numerical simulation. The study shows the wider the pulse is, the worse the self similar evolution and
compression are; it also shows the initial chirp can greatly hold out the self similar evolution and compression, the larger
the chirp and the wider the pulse, the worse the self similar evolution, and the influence of the positive chirp on the
evolution is bigger than that of negative chirp.
Self similar mode locked fiber laser is studied based on a numerical model. By introducing a dimensionless factor k to
characterize the pulse, the self similar pulse formation and its temporal and spectral changes are investigated throughout
the cavity. The influences of all the elements inside the cavity on the pulse formation are also studied.
In this letter, a S-band discrete Raman fiber amplifier(RFA) with the maximum net gain of 18.3dB was obtained. Using the gain flattening filter based on a cascaded long-period fiber grating (LPFG), the gain profile of this RFA was flattened to within ±1dB in the wavelength range from 1 480 nm to 1 515 nm, and an average gain of 11.3dB was achieved.
We present an all-fiber G-T resonator formed by cascading two fiber loop mirrors. Based on the superposition theory and the transfer function, the wave filtering and nonlinear phase feature of the all-fiber G-T resonator is studied and the related phase shift formula of the output beam is derived. The effect of the parameters on the phase characteristics are analyzed. An novel interleaver based on the all-fiber G-T resonator is designed. The theoretic model is simulated and calculated to meet the need of the flatness and the sharpness in the 50GHZ DWDM systems.
Through analyzing the nonlinear phase feature of the three-mirror G-T cavity, a novel unequal passband interleaver using a Michelson interferometer in which one mirror is replaced by an equally-spaced three-mirror G-T cavity is design by imitation. The device split an input beam with channel spacing of 50GHZ into two beams with channel spacing of 100GHZ. At -1dB, the odd channel and the even channel have unequal passband for transmission speed of 40Gb/s and 10Gb/s, respectively. The isolation is more than 30dB. All the possible reflection coefficients of the three-mirror G-T cavity with which the interleavers meet the above need of the DWDM system are searched out by optimization of the computer.
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