Modal reflection, transmission and loss of deeply etched Bragg waveguide gratings were modelled by six European laboratories using independently developed two-dimensional (2D) numerical codes based on four different methods, with very good mutual agreement. It was found that (rather weak) material dispersion of the SiO2/Si3N4 system does not significantly affect the results. The existence of lossless Floquet–Bloch modes in deeply etched gratings was confirmed. Based on reliable numerical results, the physical origin of out-of-plane losses of 1D or 2D photonic band gap structures in slab waveguides is briefly discussed. 相似文献
The diffraction and refraction of light beam in optical periodic structures can be determined by the photonic band-gap structures
of spatial frequency. In this paper, by employing the equation governing the nonlinear light propagations in photorefractive
crystals, we study the photonic band-gap structures, Bloch modes, and light transmission properties of optically induced planar
waveguide arrays. The relationship between the photonic band-gap structures and the light diffraction characteristics is discussed
in detail. Then the influence of the parameters of planar waveguide arrays on the band-gaps structures, Bloch modes, and linear
light transmissions is analyzed. It is revealed that the linear light transmission properties of waveguide arrays are tightly
related to the diffraction relationships determined by band-gap structures. And the Bloch modes corresponding to different
transmission bands can be excited by different excitation schemes. Both the increases of the intensity and the period of the
array writing beam will lead to the broadening of the forbidden gaps and the concentration of the energy of the Bloch modes
to the high-index regions. Furthermore, the broadening of the forbidden gaps will lead to separation and transition between
the Bloch modes of neighboring bands around the Bragg angle. Additionally, with the increase of the intensity of the array
writing beams, the influences from light intensity will tend to be steady due to the saturation of the photorefractive effect.
Supported by the Youth for Northwestern Polytechnical University (NPU) Teachers Scientific and Technological Innovation Foundation,
the NPU Foundation for Fundamental Research, and the Doctorate Foundation of NPU (Grant No. CX200514) 相似文献
We demonstrate extremely low transmittance characteristics of photonic crystals (PhCs) with a finite thickness in specific photonic bandgaps (PBGs) through numerical simulation, and clarify its origin. Some of the PhCs support decaying Bloch eigenmodes, whose propagation constant (real part of the Bloch wavenumber) as well as their decay constant (imaginary part) changes with frequency inside the bandgap. Such a class of modes can interfere destructively at the exit end of the crystal depending on their round-trip phase change, which creates comb-like valleys in their transmission spectra. 相似文献
Surface Bloch modes induced on three-dimensional dielectric photonic crystals with a complete photonic bandgap are evanescently decaying states at surfaces and have large field overlap with low-index media, resulting in narrow spectrum linewidth and simultaneously a large resonance shift due to a perturbation of the refractive index in the background media. Surface Bloch resonance states are analyzed for (001), (100), and (110) woodpile surface planes. Low-loss, high-sensitivity surface Bloch modes are also analyzed on a flat-top (001) woodpile planar surface. These analyzed surface Bloch modes are confined in a subwavelength scale and are expected to form a basis set used for optical resonance sensing. 相似文献
Planar two-dimensional photonic crystals can be combined with a one-dimensional Bragg mirror to control the quality factor and out-of-plane coupling of optical Bloch modes. We have investigated the optical properties of such structures fabricated on silicon. The photonic crystals are fabricated in the upper Si layer deposited on top of quarter-wave thick SiO2-polycrystalline Si layers. The optical properties are probed by the room-temperature photoluminescence of Ge/Si self-assembled islands as an internal source. We show that an enhancement of the quality factor can be obtained by controlling the thickness of the silicon upper layer in which the two-dimensional photonic crystal is etched and by controlling the air filling factor of the photonic crystal. Quality factors of 2200 around 1100 nm are obtained by this method for defect-free photonic crystals with a square lattice pattern. The experimental results are supported by three-dimensional finite-difference time-domain (FDTD) calculations of the radiated modes for the investigated structures. 相似文献
In a real photonic crystal, there exist three modes: propagation mode, evanescence mode and surface mode. Using ideal modal, semi-infinite photonic crystals, we study their effects on the transmission spectrum of photonic crystals, respectively. Because there exists only one air–crystal interface in a semi-infinite photonic crystal, no multiple reflection occurs and no evanescent modes and backward-propagating modes exist in this structure. The effects of the evanescence modes are studied by comparing the transmission spectrum of a finite-thickness photonic crystal slab and that of a semi-infinite photonic crystal. In addition, the effects of the backward-propagating modes are investigated using a coated semi-infinite photonic crystal structure. Finally, we study the effects of the surface modes, and find that the transmission spectrum of a semi-infinite photonic crystal is strongly dependent on its termination. 相似文献
High power single mode quantum cascade lasers with a narrow far field are important for several applications including surgery or military countermeasure. Existing technologies suffer from drawbacks such as operation temperature and scalability. In this paper we introduce a fabrication approach that potentially solves simultaneously these remaining limitations. We demonstrate and characterize deep etched, buried photonic crystal quantum cascade lasers emitting around a wavelength of 8.5 μm. The active region was dry etched before being regrown with semi‐insulating Fe:InP. This fabrication strategy results in a refractive index contrast of 10% allowing good photonic mode control, and simultaneously provides good thermal extraction during operation. Single mode emission with narrow far field pattern and peak powers up to 0.88 W at 263 K were recorded from the facet of the photonic crystal laser, and lasing operation was maintained up to room temperature. The lasing modes emitted from square photonic crystal mesas with a side length of 550μm, were identified as slow Bloch photonic crystal modes by means of three‐dimensional photonic simulations and measurements.
We present a detailed study of out-of-plane scattering losses in a 1D approximation of 2D photonic crystal slabs. In 2D photonic crystals with a waveguide structure in the third dimension, the periodic structure (in a lot of applications a 2D arrangement of holes etched through the core and cladding) will cause light to scatter out of the waveguide plane. We studied the out-of-plane scattering losses of these holes using a 2D approximation of this 3D structure, with etched slots instead of holes. Our simulation techniques included mode expansion with PML and FDTD. We will present the influence of the refractive index contrast between core and cladding of the layered structure. We show that the losses increase with higher index contrast between core and cladding, but that with very high index contrasts and under the right circumstances light can be coupled into lossless Bloch modes. 相似文献
Enhanced noncollinear second harmonic generation in a finite one-dimensional photonic crystal is analyzed theoretically under conditions of pump field localization near the Bragg reflection. It is shown numerically that phase-matched second-harmonic generation can be implemented in a finite one-dimensional photonic crystal that does not satisfy the conventional phase-matching conditions calculated for effective Bloch modes with narrow spectral lines. The intensity of the generated second-harmonic signal exceeds the second-harmonic intensity attained under the conventional phase-matching conditions by more than an order of magnitude. This phenomenon is explained by interference between Bloch modes having similar amplitudes, wavenumbers, and spectral widths. Since the spatial spectra of waves propagating in a bounded medium have finite widths, the broadened spectral lines of proximate effective Bloch modes resulting from Bragg diffraction of waves tuned to the first transmission resonances near the photonic bandgap edge overlap, merging into a spectral profile with center shifted relative to the original effective Bloch wavevectors. This effect leads to modified phase matching conditions for second harmonic generation in a finite photonic crystal, which are written for the centers of the spectral profiles resulting from modal overlap, rather than for individual effective wavevectors. Substantially different phase matching conditions are obtained for weakly and strongly diffracted beams, whereas conventional phase matching conditions hold only for transmitted signals in the case of weak diffraction. 相似文献
We report experimental results for the band structure of 2-dimensional triangular photonic crystals of air holes in an epitaxial
group III–nitride waveguide film. Surface coupling techniques enable the observation of sharp resonance dips in the transmission
spectra due to a resonance phenomenon between the incident light and Bloch modes of the photonic crystal. The position of
the dips has been measured as a function of angle of incidence and the photonic band structure has been successfully constructed
by the measurement. Corresponding Bloch-mode group velocities have also been obtained.
Received: 28 May 2001 / Published online: 23 October 2001 相似文献