Showing papers on "Equilibrium mode distribution published in 1992"

Widened output mode semiconductor optical component and method of fabricating it

Abstract: A widened output mode semiconductor optical component such as a laser includes superposed active and passive waveguides. The width of the active waveguide decreases in a rear part of a mode transition section to couple a "narrow" optical mode which is amplified and guided by the active waveguide to a "wide" mode which is guided by the passive waveguide and which has a mode size greater than that of the narrow mode. The width of the passive waveguide then decreases in a front part of this section to couple the wide mode to an even wider circular mode. The invention finds applications in the fabrication of optical heads for optical fiber telecommunication networks.

Measurement of mode splitting in asymmetric Y-junctions

Abstract: A measurement procedure is presented for the determination of mode splitting (or mode sorting) in asymmetric Y-junctions. This procedure avoids measurement errors introduced by bends, tapers, small damages in the waveguides outside the coupling region, variation in fiber-chip coupling, etc. It is based on the analysis of the normalized coupled power in an optical coupler in which a mode splitter is used. The method is illustrated with a mode splitter on lithium niobate. A value of 29.2+or-0.5 dB for the suppression of the unwanted mode is found, showing the applicability of the procedure. >

Optical gates where output signal intensity is independent of phases of input signals

Abstract: A method for amplifying optical signals without dependence of output signal intensity on an input-signal phase is provided. This method is based on nonlinear interaction of three phase-synchronized modes in one core of a waveguide. The method may be realized by passing the above-mentioned signals through an optical element with a waveguide (200) having pulse interaction and propagation portions (205 and 207) which receive impulses in first and second coherent waveguide modes which cause a nonlinear interaction between the first and second waveguide modes and generate a third waveguide mode. This third mode is phase-synchronized with the first and second waveguide modes. The method may be realized in optical amplifiers, switches, as well as logical optical AND gates, OR gates, etc. An optical OR gate which realizes the above principle consists of an input portion (201), a core expansion portion (202) which in addition to the first waveguide mode allows the appearance of a second waveguide mode and a third waveguide mode, a linear mode conversion portion (203), an input impulse portion (204), a first nonlinear interaction and propagation portion (205), a third-mode elimination portion (206), a second nonlinear interaction and propagation portion (207), and an output portion (208, 209) which produces an amplified impulse in a first waveguide mode. Logical AND gate also is described. The elements can be represented in the fiber-optic or integrated-optic version.

Light propagation in thermally fused biconical taper single-mode optical fiber couplers

Abstract: Since the light propagation property of the currently produced single mode optical fiber couplers has not become clarified, there are various problems with their production method, namely in terms of their operability, stability, reproducibility and durability. The main purpose of this paper is to perform quantitative experiment on the major elements which is thought to influence light propagation of thermally fused biconical taper single mode optical fiber couplers. Furthermore, this paper aims to clarify light propagation property of single mode optical fiber couplers by calculating light output using mode coupled theory, in attempt to improving their production method.

Fiber and channel waveguide coupling improvement by mode pattern control

Abstract: In practical applications, the resultant channel waveguide of LiNbO3 substrate should be efficiently coupled to the single mode fiber. The core shape of single mode fiber is a circular distribution, but that of the conventional Ti:LiNbO3 channel waveguide is a semi-elliptical distribution. Optical mode patterns of channel waveguide and single mode fiber can not achieve the mode matching conditions. To improve coupling efficiency between channel waveguide and single mode fiber with arbitrary dimensions, the refractive index profiles and associated fundamental mode patterns of buried Ti/Mg:LiNbO3 channel waveguides are simulated and controlled from fabrication parameters. We have also investigated the dependences of coupling loss on radial and axial offsets.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Analysis of constant phase contours of evaporation duct mode functions for waveguide mode propagation

Abstract: : The M-Layer program tracks the constant phase lines Im(D(q)) = 0 and looks for their intersections with the lines Re(D(q)) = 0 for the locations of the zeros of the mode function D(q). These two types of constant phase lines are tracked and plotted over a search region which contains modes having a range attenuation rate of no more than 5 dB per km. Several new parameters for use in mode search are deduced from the results and some old ones are verified. Future studies is waveguide mode propagation theory pertaining to atmospheric ducts may benefit from this work. An improved mode search strategy is also proposed. Evaporation duct, Waveguide mode propagation.

The TM mode in the self‐focusing dielectric planar waveguide

Abstract: The TM0 guided mode in the self-focusing dielectric planar waveguide and its universal dispersion curves are obtained by an approximation method, The single mode propagation condition of the fundamental mode TE0 in the self-focusing planar waveguide is discussed based on the cutoff wavelengths of the higher-order TE modes and the higher-order TM modes. The coupling between the fundamental mode TE0 and the second mode TM0 is described by the calculation of the birefringence between the TE0 mode and the TM0 mode. It was found that the Kerr effect with α > 0 (α is a parameter which describes the film nonlinearity) causes the fields to be confined in the self-focusing film, which results in the waveguide wavelength decreasing and the cutoff wavelength increasing as α is increased. In addition, the range of the single mode propagation is increased as α is increased. If the self-focusing planar waveguide can support both the TE0 mode and the TM0 mode, then the coupling between the TE0 mode and the TM0 mode is very strong and can be decreased by increasing α. © 1992 John Wiley & Sons, Inc.

Application of the coupled-mode theory to a specialized graded-index optical fiber coupler.

Abstract: A specialized coupler formed by two identical multimode graded-index slab fibers is described. This special coupler can be used to examine the tilt or the roughness of a surface through the reflected beam. It may also find applications as a mode filter, an alignment sensor, or a feed component of an optical monopulse tracking radar. Coupled-mode theory is generalized for this application. The coupling length for maximum power transfer of the higher-order modes from the excited to the coupled fiber, leaving as much power of the lowest mode as possible to continue in the excited fiber, is computed. The fields are computed at the output of the system for incident optical beams with different axial displacements and beams launched on axis with tilted wavefronts. This desired coupling length is shown to be substantially independent of characteristics of the incident light beam. To compute the fields propagated through the tapered section introduced to separate the slab fibers, the stairwise approximation is used, and mode matching is used to connect the fields at the junctions between the successive segments. An optimum taper to separate the coupled fibers, with minimal perturbation of the fields, is present at the right-hand end of the coupling section.