Optimization and comparison of single- and dual-pump fiber-optical parametric amplifiers with dispersion fluctuations

Solutions for fiber-optical parametric amplifiers (FOPAs) with dispersion fluctuations are derived using matrix operators. On the basis of the propagation matrix product and the hybrid genetic algorithm, we have optimized and compared single- and dual-pump FOPAs with zero-dispersion-wavelength variations. The simulations prove that the design of FOPAs involves multimodal function optimization problems. The numerical results show that dual-pump FOPAs are highly sensitive to dispersion fluctuations whereas dispersion variations have less impact on the gain of single-pump FOPAs. To increase signal gain and reduce ripple, dual-pump FOPAs, instead of single-pump FOPAs, have to be carefully optimized with a suitable multisegment fiber structure rather than a one-segment fiber structure. The different combinations of multisegment fibers can provide highly different gain properties. The increase in gain is at the cost of the ripple.

A dual-wavelength sampled fiber Bragg grating and its application in L-band dual-wavelength erbium-doped fiber lasers

A novel dual-wavelength (DW) sampled fiber Bragg grating (SFBG) is proposed and demonstrated for the first time to the author's best knowledge. This kind of SFBG can realize a DW operation with uniform reflection peaks rather than multiple nonuniform peaks shown in conventional SFBGs. Based on the designed SFBG, we have proposed a novel L-band DW erbium-doped fiber laser, which has such a unique merit that the spacing of the two wavelengths keeps unchanged during tuning laser.

Ultra-narrow dual-channel filter based on symmetrical sampled fibre Bragg grating

A kind of ultra-narrow dual-channel filter is proposed in principle and demonstrated experimentally. This filter is designed by means of two sampled fibre Bragg gratings (SFBGs), where one is periodic 0-pi sampling and the other is symmetrical spatial sampling. The former can create two stopbands in the transmission spectra and the latter can produce two ultra-riarrow passbands. Our filter has the 3-dB bandwidth of about 1 pm, whose value is two orders of magnitude less than the bandwidth of the traditional SFBG filters. The proposed filter has a merit that the channel spacing remains unchanged when tuning the filter.

Interactions of three dual-dressing effects of four-wave mixing in a five-level atomic system

We study the four-wave mixing (FWM) in an opening five-level system with two dressing fields. There are three kinds of doubly dressing mechanisms (parallel cascade, sequential cascade, and nested cascade) in the system for doubly dressed four-wave mixing. These mechanisms reflect different correlations between two dressing fields and different effects of two dressing fields to the FWM. Investigation of these mechanisms is helpful to understand the generated high-order nonlinear optical signal dressed by multi-fields.

Identical dual-wavelength fiber Bragg Gratings

In this paper, identical dual-wavelength fiber Bragg, gratings (FBGs) are theoretically proposed and experimentally demonstrated. On the assistance of the Fourier theory, the gratings with symmetrical spectrum are designed in the case of weak refractive-index modulations. With the. perturbation technique, the results achieved in the previous step are modified to meet the strong refractive-index modulation gratings. Based on the coupled-mode theory, we have optimized and achieved the identical dual-wavelength FBGs with two channels that have equal bandwidth and even strength. We have also experimentally demonstrated the proposed FBGs, and the experimental results are compared with theoretical predictions with good agreement.

Dual-wavelength photochromic fulgides for parallel recording memory

Two photochromic fulgides, 2-{2-[4-(N,N-dimethylnilino)-5-methyl-4-oxazoly]}ethylidene-4-(1-methylethylidene) tetrahydrofuran-2,5-dione (A) and 3-(1,2-dimethyl-5-phenyl-3-pyrolloethylidene)-4-(1-methylethylidene)tetrahydrofuran-2,5-dione (B), doped in PMMA as candidates of dual-wavelength optical memory for parallel recording has been investigated. With 488 nm-laser and 650 nm-laser, both "cross" and "star" images are recorded on the fulgides-PMMA film and read out clearly, respectively. Crosstalk between two fulgides in PMMA matrix and nondestructive readout has also been explored. The results show that no significant cross-talk is detected between them, and nondestructive readout is up to 201 times. (C) 2005 Elsevier B.V. All rights reserved.

Room-temperature dual-wavelength erbium-doped fibre laser based on a sampled fibre Bragg grating and a photonic Robin Hood

With the assistance of a kind of photonic Robin Hood that is originated from four-wave mixing in a dispersion-flattened high-nonlinearity photonic-crystal fibre, a novel dual-wavelength erbium-doped fibre (EDF) laser is proposed and demonstrated by using a sampled fibre Bragg grating. The experiments show that, due to the contribution of the photonic Robin Hood, the proposed fibre laser has the advantage of excellent uniformity, high stability and stable operation at room temperature. Our dual-wavelength EDF laser has the unique merit that the wavelength spacing remains unchanged when tuning the two wavelengths of laser, and this laser is simpler and more stable than the laser reported by Liu et al. [Opt. Express, 13 142 (2005)].

A novel dual-wavelength DFB fiber laser based on symmetrical FBG structure

A novel grating structure is proposed and demonstrated to obtain stable dual-wavelength (DW) distributed-feedback (DFB) fiber lasers at room temperature. The proposed grating is based on a symmetrical structure, where one half is periodically sampled by "0"-to-"pi" period and the other half is done by "pi"-to-"0" period. This structure can create two separated resonance cavities and hence achieve the stable DW lasing operation. By fabricating the proposed grating on a piece of Er: Yb-codoped fiber, we experimentally obtain a stable DW-DFB fiber laser with wavelength spacing of similar to 440 pm at room temperature.

STUDY ON PREPARATION OF GAN AND COSI2 EPITAXIAL-FILMS BY MASS ANALYZED LOW-ENERGY DUAL ION-BEAM EPITAXY

The Mass Analyzed Low Energy Dual Ion Beam Epitaxy (MALE-DIBE) system has been designed and constructed in our laboratory. We believe that the system, which was installed and came into full operation in 1988, is the first facility of this kind. With our system we have carried out studies, for the first time, on compound synthesis of GaN and CoSi2 epitaxial thin films. RHEED and AES results show that GaN films, which were deposited on Si and sapphire substrates, are monocrystalline and of good stoichiometry. To our knowledge, GaN film heteroepitaxially grown on Si. which is more lattice-mismatched than GaN on sapphire, has not been reported before by other authors. RBS and TEM investigations indicated a rather good crystallinity of CoSi2 with a distinct interface between CoSi2 and the Si substrate. The channelling minimum yield chi(min) from the Co profile is approximately 4%. The results showed that the DIBE system with simultaneous arrival of two beams at the target is particularly useful in the formation of novel compounds at a relatively low substrate temperature.

A DUAL ION-BEAM EPITAXY SYSTEM

The design and characteristics of a dual ion beam epitaxy system (DIBE) are discussed. This system is composed of two beam lines, each providing a mass-separated ion beam converging finally with the other into the target chamber. The ions are decelerated and deposited on a substrate which can be heated to a temperature of 800-degrees-C. Currents of a few hundred microamperes are available for both beams and the deposit energies are in the range from tens to 1000 eV. The pressure of the target chamber during processing is about 7 x 10(-6) Pa. Preliminary experiments have proved that compound semiconductor materials such as GaN can be synthesized using the DIBE system.