Showing papers on "Coupled mode theory published in 1978"
TL;DR: In this paper, an improved coupled mode theory based on a set of the coupled mode equations for guided modes and radiation continuum was proposed and analyzed for corrugated waveguides and lasers in resonant and nonresonant situations.
Abstract: Corrugated waveguides and lasers in resonant and non-resonant situations are analyzed by an improved coupled mode theory based on a set of the coupled mode equations for guided modes and radiation continuum. The distributed feedback (DFB) coefficient and the radiation loss coefficient are given in closed forms. The formulation can be applicable to arbitrarily shaped gratings and multilayer waveguide structures. The accuracy of the theory is examined by comparing it with Tamir's exact calculation for a nonresonant situation and also with Streifer's one for a DFB structure. Reasonable accuracy is obtained by the proper choice of the unperturbed waveguide parameter. The dependence of the two coefficients on the grating depth, the grating period, the guide layer thickness, and the refractive index difference between core and cladding layers is obtained for all Bragg orders up to the fourth, and for four typical grating shapes, namely, for rectangular, sinusoidal, symmetric triangular, and sawtooth gratings. Both the threshold gain of DFB lasers utilizing higher order Bragg reflection and the output coupling efficiency of grating beam couplers are also calculated for these parameters. A new multilayer structure for controlling the radiation loss is proposed and analyzed. This structure is suitable for the suppression of the radiation loss in DBR reflectors as well as for the improvement of the output coupling efficiency in grating beam couplers.
80 citations
TL;DR: The time independent coupled power equations are derived taking mode losses into account from the beginning, and it is found that the resonator losses are equal to the steady-state losses of randomly coupled modes in the limit of very low and very high differential mode losses.
Abstract: Coupled power equations for multimode fibers were originally derived by neglecting mode losses, loss was later introduced by adding a phenomenological loss factor to the equation system. In this paper the time independent coupled power equations are derived taking mode losses into account from the beginning. The form of the equations so obtained is identical to the well known coupled power equations, but the coupling coefficients are different. The mode losses alter the analytical expressions for the coupling coefficients and cause the matrix of coupling coefficients to be asymmetrical. Some consequences of the coupled power theory incorporating mode losses are discussed for the specific example of a fiber supporting only two guided modes. Finally, we compare the steady-state losses of a fiber with two randomly coupled modes with the corresponding case of a fiber resonator and find that the resonator losses are equal to the steady-state losses of randomly coupled modes in the limit of very low and very high differential mode losses, for all other cases the resonator losses are much higher than the losses of randomly coupled modes.
19 citations
TL;DR: In this article, the possible margin of error on the predicted coupling length according to the coupled-mode theory as applied to fiber and integrated optical guides is inferred based on the solution of a simplified canonical problem.
Abstract: Based on the solution of a simplified canonical problem, the possible margin of error on the predicted coupling length according to the coupled-mode theory as applied to fiber and integrated optical guides is inferred. It was found that coupling length obtained according to the coupled-mode theory is usually accurate to within 20% of the actual value provided that the frequency of operation is above the cutoff frequency of the antisymmetric mode of the coupled structure.
15 citations
TL;DR: Novel optical-waveguide mode filters, based on mode-selective coupling between nonidentical waveguides and attenuation in a lossy waveguide, are proposed and demonstrated.
Abstract: Novel optical-waveguide mode filters, based on mode-selective coupling between nonidentical waveguides and attenuation in a lossy waveguide, are proposed and demonstrated. Both TE0 and TM0 mode filters were fabricated from glass compositions by rf-sputtering. For both the TE0 and TM0 mode filters, insertion losses were 2.1 dB and 1.1 dB, respectively, and attentuations for undesirable modes were 16.8 dB and 21.6 dB, respectively.
11 citations
TL;DR: In this article, the authors consider VHF wave transmission in a straight mine tunnel that contains a braided coaxial cable and show that the optimum lengths for maximum transmission through the leaky cable sections or mode converters predicted here are compatible to those predicted by approximate coupled mode theory.
Abstract: Using an idealized model, we consider VHF wave transmission in a straight mine tunnel that contains a braided coaxial cable. The controlled interchange of energy between the propagation modes can be used to optimize the communication range and allow for coupling to and from portable hand-held antennas. In particular, we show that the optimum lengths for maximum transmission through the leaky cable sections or mode converters predicted here are compatible to those predicted by approximate coupled mode theory.
9 citations
TL;DR: In this paper, the behavior of a fiber laser-amplifier is considered, including the effects of mode coupling, radiation losses, and noise, and a competitive effect between mode coupling and losses is present.
Abstract: The behavior of a fiber laser-amplifier is considered, including the effects of mode coupling, radiation losses, and noise. In the linear regime, a competitive effect between mode coupling and losses is present, in the sense that mode coupling tends to equalize the gains of different modes, while radiation losses favor low-order modes. Thus, single-mode amplification and collective amplification are predominant, respectively, in the weak and strong coupling case. In the saturated regime a mode coupling effect is found that is independent of fiber imperfections and relies on the nonlinear nature of the process.
2 citations
TL;DR: In this article, the reflection and radiation loss characteristics of a periodic grating reflector array for a thin-film Fabry-Perot laser are treated using a perturbation approach combined with the coupled mode theory.
Abstract: The reflection‐ and radiation‐loss characteristics of a periodic grating reflector array for a thin‐film Fabry‐Perot laser are treated using a perturbation approach combined with the coupled mode theory. The present treatment derives the array properties directly in terms of the grating geometry and material constants of the thin‐film guide. It also provides quantitative information on the reflection coefficient and reflector power loss resulting from mode conversion into radiation.
TL;DR: An apparent discrepancy between coupled-mode and ''whisperinggallery'' theories for the radiation of discrete beams from curved single-mode fibres is resolved in this paper, where it is shown that the two formally different approaches are in very good agreement with each other in predicting the periodicity of the radiation.
Abstract: An apparent discrepancy between coupled-mode and `whispering-gallery? theories for the radiation of discrete beams from curved single-mode fibres is resolved. It is shown that the two formally different approaches are in very good agreement with each other in predicting the periodicity of the radiation.