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1.
The generation of spontaneous (noise) gratings during the simultaneous formation of a holographic grating in thin (on the
order of the cutoff thickness of the TE0 waveguide mode) AgCl-Ag films by two laser beams with λ = 532 nm and polarization vectors that make an angle of 45° with
the plane of incidence have been studied. The electron microscopy images and diffraction patterns have revealed a significant
difference of the spontaneous-grating structure from the structure obtained under irradiation by one laser beam. The spontaneous
gratings have a significant spread in the directions of their wave vector, and the diffraction pattern (recorded using a probe
beam with λ = 337 nm) has the form of a bundle of diverging arcs that intersect at one point. This difference is caused by
self-diffraction from the holographic grating, which is responsible for the main diffraction peaks with odd orders, the growth
of spontaneous gratings because of the interference of the beams diffracted by the holographic grating with the waveguide
TE0 modes scattered in the film, and silver transport to the interference minima. The diffraction patterns are quantitatively
analyzed and the period of the new (formed under two-beam irradiation) spontaneous gratings is calculated. The calculation
results are in good agreement with the experimental data. 相似文献
2.
We report on Nd:CNGG active planar waveguides produced by 6.0 MeV carbon ion implantation at fluence from 1 × 1014 ions/cm2 to 8 × 1014 ions/cm2. The refractive index profiles, which were reconstructed according to the measured dark mode spectroscopy, showed that the refractive indices had negative changes in the surface region, forming typical barrier waveguide. The width of waveguide structure induced by carbon ion implantation is ∼3.8 μm. The typical barrier-shaped distribution may be mainly due to the nuclear energy deposition of the incident ions into the substrate. By performing a modal analysis on the observed TE modes, it was found that the TE0 and TE1 modes can be well-confined inside the waveguide. 相似文献
3.
H. Rudolph 《Applied Physics A: Materials Science & Processing》1980,23(4):381-385
The conversion of guided modes (TE0 and TE1) at a rectangular step on a dielectric slab waveguide is investigated with mm microwaves. The power of the modes is measured
from their interference patterns in the evanescent field outside the waveguide slab. The relative power of two modes changes
periodically when the length of the step is varied. In the experiments a change of up to three orders of magnitude was measured.
The step is considered as a sequence of three waveguide sections of different thickness. At the discontinuities the modal
fields are assumed to illuminate the next section. The calculation based on this model agrees with the experimental results. 相似文献
4.
Analysis and design of grating couplers 总被引:5,自引:0,他引:5
Based on an accurate perturbation analysis of the guiding properties of dielectric gratings, simple design criteria are developed
for grating couplers which transfer the energy of a beam into or out of an optical waveguide. Gratings having arbitrary groove
shapes are considered and explicit formulae are given for the leakage parameters of gratings with symmetric profiles. The
results cover TEv and TMv modes and they apply to both shallow and deep grating grooves. The variation of the leakage parameter α in rectangular gratings
is examined in detail; these rectangular gratings are then used as basic configurations for predicting the characteristics
of other grating profiles. Particular attention is given to trapezoidal and triangular profiles and gratings with asymmetric
profiles are also discussed. 相似文献
5.
Yonggang Wu Zihuan Xia Zhenhua Wang Renchen Liu Pinglin Tang Gang Lv Heyun Wu 《Optics Communications》2012,285(12):2840-2845
A perpendicular dual-grating (PDG) guided-mode resonance filter was constructed by placing two identical waveguide gratings close to and their grooves perpendicular to each other. Multilayer waveguide theory was used to estimate the resonant wavelength for the TE and TM polarization incidences, and the rigorous coupled wave analysis (RCWA) was used to investigate the resonant wavelength, the lineshape and linewidth of the resonant peaks for arbitrary polarization incidences. The filter presents identical spectral characteristics for normally incident wave with arbitrary polarization. The separation of the resonant reflection peaks corresponding to the TE0 and TM0 split modes were realized by properly selecting the geometrical and material parameters of the grating layers and the waveguide layers. Measurement of the nano air gap between 0 and 0.4 p by determining one of the two resonant reflection peaks of the TE0/TM0 split modes was achieved without being interfered by the TM0/TE0 split modes. 相似文献
6.
An intricate space-time instability of patterns of small-angle scattering and diffraction of a laser beam on the structures appearing in AgCl-Ag films under exposure to the same beam is investigated. The instability is related to the formation of spontaneous gratings in the film resulting from the interference of the incident beam with the waveguide modes scattered in the film. The existence of a two-dimensional Bragg diffraction on the TE0 and TM0 modes with subsequent formation of secondary spontaneous gratings is revealed and is theoretically substantiated. It is established that the difference in the indicatrices of the radiation scattered into the TE0 and TM0 modes for the s-and p-polarizations manifests itself in different kinds of diffraction and small-angle scattering patterns at the output of illuminated samples. 相似文献
7.
8.
Yi Jiang Chuan-Lei Jia Xue-Lin Wang Ke-Ming Wang Hong-Ji Ma 《Applied Surface Science》2006,253(5):2674-2677
A planar optical waveguide has been formed in a LiB3O5 crystal using 6.0 MeV Cu+-ions with a dose of 1 × 1015 ions/cm2 at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE0 and TM0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change. 相似文献
9.
10.
The spatial-temporal instability of the spontaneous gratings formed in waveguide AgCl-Ag films under irradiation with an S-polarized laser beam is investigated. The studies are based on the simultaneous observation of diffraction (D) patterns formed by the S ? gratings and small-angle scattering (SAS). The transverse instability of D and SAS patterns was found to be associated with excitation of TE0 modes at different angles with respect to the plane of incidence by scattering centers of Rayleigh type with the following formation of microgratings by the scattered modes and with their competition. It is shown that the time evolution of the form and the dynamic shift of the D patterns is also connected with the time dependence of the effective refractive index for TE0 modes. In the case when a focused laser beam was used, the optical turbulence was found in the SAS and D patterns, caused, mainly, by the competition of S ?-and S +-microgratings, which eventually leads to the destruction of the latter. 相似文献
11.
V. Ya. Aleshkin A. A. Biryukov A. A. Dubinov B. N. Zvonkov S. M. Nekorkin 《Technical Physics》2009,54(11):1711-1713
A semiconducting laser diode with an original waveguide structure containing two quantum wells and simultaneously generating
the TE0 and TE
1 modes with wavelengths 1.05 and 0.90 μm, respectively, at liquid nitrogen temperature is developed on the basis of the InGaAs/GaAs/InGaP
heterostructure. 相似文献
12.
B. W. Stallard J. A. Byers M. A. Makowski 《International Journal of Infrared and Millimeter Waves》1990,11(9):1011-1032
A novel device, MAGICTRAC, is described for efficient conversion at millimeter wavelengths of the TE
m,n
whispering-gallery mode into a linearly polarized, free-space Gaussian-like beam. MAGICTRAC uses a mode-converting waveguide taper and three mirror optics, one of which incorporates a twist reflector to linearly polarize the output beam. An example design is presented for the TE15,2 mode at 140 GHz with a calculated efficiency of 96%. Related possible applications include (1) installation of the MAGICTRAC within the vacuum envelope of a gyrotron to separarate the spent e-beam from the generated rf, (2) generation of a whispering-gallery mode by injection of a Gaussian-like beam into the output end, and (3) conversion of TE
m,n
modes into TE0n
modes for low-loss transmission in smooth-wall waveguide.Work performed by LLNL for USDOE under contract W-7405 ENG-48. 相似文献
13.
We study guided modes propagating along a dielectric slab waveguide with a left handed material (LHM) cover or substrate. The dispersion relation is derived by using normalized waveguide parameters. An analytical method is then proposed to calculate the universal dispersion curves. Different from a slab waveguide with a LHM core, we find that guidance properties are strongly dependent on dielectric permittivity ε and magnetic permeability μ of the substrate and cover layers. For oscillating guided modes, fundamental zero order mode is not always absence, sometimes it exists in a restricted range of normalized propagation constant. First order mode behaves as other higher order modes and exists up to infinite high frequency. Higher order modes have no double degeneracy in the case of LHM cover layer. For surface guided modes, the existence and the type of the mode solutions with respect to different parameters are classified systematically and discussed in detail. Unlike a slab waveguide with a LHM core where the dispersion curve of TE1 surface mode continues with that of oscillating TE1 mode, the dispersion curve of TE1 surface mode continues with that of oscillating TE0 mode. It seems that the two different kinds of modes compensate each other to form one whole mode. Both TE and TM guided modes are discussed. 相似文献
14.
15.
16.
M. Imlau S. Haussühl T. Woike R. Schieder V. Angelov R.A. Rupp K. Schwarz 《Applied physics. B, Lasers and optics》1999,68(5):877-885
Elementary holographic phase gratings can be written in single crystals of Na2[Fe(CN)5NO]·2H2O, sodiumnitroprusside, by excitation of metastable electronic states in the blue–green spectral range. For light polarized
parallel to the crystallographic a and b axes of the orthorhombic crystal the light-induced modulation of the refractive index
reaches Δn≈2×10-3 at λ=514.5 nm. Although the largest population of the metastable states is reached for light polarized parallel to the crystallographic
c axis, a photorefractive response is not observed. In contrast to electro-optic photorefractive materials the photorefractive
effect depends mono-exponentially on the exposure and on the modulation of the incident light interference pattern. Beam-coupling
experiments demonstrate that written gratings are in phase with the interference pattern in correspondence with the fact that
the excitation of the metastable electronic states is local. The width of the rocking curve shows that the holographic gratings
are written completely over the volume of the crystal. Variations of the wavelengths within the excitation range as well as
of the crystal thickness do not influence the maximum photorefractive response. Investigations on the grating vector of the
written gratings show unambiguously that charge migration is not responsible for the photorefractive effect.
Received: 18 November 1998 / Revised version: 26 January 1999 / Published online: 12 April 1999 相似文献
17.
We consider the initial stage of formation of photorefractive gratings in planar waveguides based on cubic electrooptic crystals.
We have obtained solutions for the components of the space-charge field for arbitrary ratios between parameters characterizing
the spatial inhomogeneity of the light interference pattern in the waveguide as well as the diffusion length. The dependence
of the component of the space-charge field parallel to the grating vector on its period in the initial section of the recording
is also determined by the sum and difference of the transverse propagation constants of the interacting waveguide modes. We
show that for waveguide interactions characterized by a small transverse scale of spatial inhomogeneity, the distributions
of the space-charge field and the light intensity in the interference pattern are substantially different. These effects must
be considered in analysis of the nonlinear interactions occurring in a refractive index grating due to the electrooptical
effect.
Tomsk University of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika,
pp. 65–73, June, 1997. 相似文献
18.
M.P. Petrov A.P. Paugurt V.V. Bryksin S. Wevering B. Andreas E. Krätzig 《Applied physics. B, Lasers and optics》1999,69(4):341-344
During holographic recording in photorefractive crystals (BSO, BGO, and BTO) by an oscillating interference pattern we observe
a strong dynamic deflection of the laser beams reflected from the crystal’s surface. The theoretical treatment shows that
this new effect is associated with a nonlinear interaction of space charge gratings resulting in a quasi-homogeneous oscillating
space charge field which provides deformations of the crystal via the piezoelectric effect.
Received: 3 August 1999 / Accepted 5 August 1999 / Published online: 8 September 1999 相似文献
19.
L. A. Ageev V. K. Miloslavskii V. I. Lymar V. M. Reznikova 《Optics and Spectroscopy》2013,115(6):843-847
A linearly polarized (E 0) laser beam (λ = 532 nm) causes photoinduced transformations in an AgCl-Ag composition consisting of a thin waveguide AgCl film on glass covered by a layer of Ag nanoparticles. Before the illumination the sample exhibits an absorption band due to localized plasmons in nanoparticles. The illumination excites plasmons and leads to scattering of waveguide TE0 modes. The interference of modes with the incident light beam leads to the development of a periodic structure, the lines of which are formed by Ag particles and directed along E 0. The measured structure period coincides with the result of calculation based on solving the dispersion equation for the TE0-mode. Measurement of absorption in the E ‖ E 0 polarization reveals dichroism and a spectral hole (at λ ≈ nm). It is shown that the structures formed remain on the substrate after removing AgCl in a fixing agent. The dichroism value and dispersion change after fixing. The character of dichroism prior to fixing is recovered after depositing an AgCl layer (with the parameters retained) on the fixed film. 相似文献
20.
A. E. Mandel’ 《Russian Physics Journal》2005,48(2):131-137
An analysis is made of photorefractive nonlinearity resulting from the interaction between the charge gratings formed in a bismuth silicate crystal in an applied meander electric field under illumination by a strong reference and two signal light beams. It is shown that the nonlinear cross interaction between the primary holographic gratings recorded in the crystal should be taken into account where the intensities of the reference and signal light beams differ from one another in magnitude (less than 300 times).__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 24–29, February, 2005. 相似文献