The wavelength dependence of the nonreciprocal phase shift (NPS) in a magneto-optical (MO) waveguide is investigated from the aspect of the geometrical structure. In an MO nonreciprocal waveguide, the effect of the waveguide dispersion on the NPS is being demonstrated to compensate the dispersion of the Faraday rotation coefficients. By accurately controlling the structure parameter of the MO waveguide, the wavelength-insensitive NPS can be obtained. According to this principle, we proposed the dual-wavelength nonreciprocal phase shifter at the wavelengths of 1.31 and 1.55 μm.
Based on the guided-mode propagation analysis method and the self-imaging effect, the general imaging properties of the two-dimensional multimode interference coupler (2-D MMI) are generalized and discussed. The general formulas for the positions, intensities, and phases of the self-images, and for image overlap in 2-D MMIs are derived. The numbers, positions, intensities, and phases of the self-images are directly related to the position of the input field and the positional number. The self-imaging properties of 2-D MMIs can be regarded as the interference superposition of two orthogonal one-dimensional self-imaging effects. These results are verified by guided-mode propagation analysis.
We investigated the group-velocity dispersion of a one dimensional uniform photonic crystal by the optical transmission method. For application in optical communications, the wavelength should be near one of the two edges of a photonic bandgap. Four kinds of
dispersion-compensation may be obtained with a photonic crystal. Huge negative and positive group-velocity-dispersion (GVD) about a
zero-dispersion-point as large as 5.1 Tera- ps/nm/km by a photonic crystal of 100 periods can be realized. Such a value is about 50 Giga times the GVD of conventional dispersion-compensation fibers. The GVD reaches a maximum when the optical length ratio of the high refractive index material to the low refractive index material is 1.2 for given operating parameters. When we keep the optical length of each layer being constant, the GVD is found to increase rapidly with the refractive index ration of the high refractive index material to the low one and even more rapidly with the number of periods of a photonic crystal. Under quite common operating parameters, a thin piece of photonic crystal of 100 periods may play the role of an ordinary dispersion-compensation fiber with a length over 158
We propose a kind of planar photonic crystal micro-cavity which is truly two-dimensional and is composed of a line of periodic air-holes and a set of periodic air grooves both with defect. Unlike the photonic crystal micro-cavity formed by distributed Bragg reflection (DBR) layers and two dimensional holes in a semiconductor substrate, the micro-cavity proposed is a true two-dimensional planar structure that is easy for mass-production through die-press copying. Numerical simulations by the FDTD method show that there exist resonance modes inside the photonic bandgap. The resonance wavelength is mainly decided by the period and radius of the holes. The quality factor of the cavity is mainly decided by the number of periods of the holes and the grooves.
We investigate a complex cavity composed of three simple cavities, which are formed by three simple defects in a one-dimensional photonic crystal (PC), by the optical transmission method. We set two of the simple cavities to be the same, and let the cavity-length of the third one vary. Generally, two or more narrow resonant transmission modes emerge in the bandgap region; the position of one of them is basically fixed with different fine structures, in which exists a fixed crest, while the other modes wander in the bandgap region as the cavity-length of the third cavity varies. We find the optimized the relative coupling length being 0.447 for the complex cavity. Introducing the parameter - degree of rectangularity, we find that the complex PC cavity is much more close to an ideal narrow band-pass filter than a simple PC defect cavity. It is surprising that the degree of rectangularity is insensitive to the number of periods in the structures.
Overlapping-image multimode interference couplers with two-dimensional confinement, a new class of devices, permit uniform and nonuniform two-dimensional power splitting. Based on self-imaging effect, positions, intensities and phases of the overlapping-images are analyzed. The overlapping-imaging properties in multimode interference couplers with two-dimensional confinement are also concluded. And the guided-mode propagation analysis method is used to confirm the analytical results.
Based on self-imaging effect of multimode interference couplers, general self-imaging and overlapping-imaging properties are analyzed. The positions and phases of the self-images are directly related to the position of the input field and positional number. Simple expressions for positions are also derived. And the guided-mode propagation analysis is used to confirm the analytical results.
In order to study the metal target surface in-place deformation induced by the laser beam or other ones effecting upon, three kinds of measuring dynamic in-plane deformation techniques by means of a laser speckle, which are the speckle field time sequence processing (that is the optical flow analysis of speckle pattern), the digital speckle pattern processing (in fact, it is a kind of pattern or picture enhancement technique), and the digital speckle pattern correlation metrology, have been studded and developed. The latter, the correlation metrology, has been made a big progress: better precision and higher processing speed.
In this paper, the new binary optical even device is presented. Whose phase depth exceeded 2(pi) . This device has the characteristics of less weight, convenient adjusting, high utilization rate of energy and well- distributed light beam, which can be used in quasi-molecule laser exposure system.