Showing papers on "Equilibrium mode distribution published in 1982"
TL;DR: In this paper, the authors demonstrate wavelength averaging of the power in either mode, permitting a simple measurement of power transfer to the cross-polarized mode as a function of fiber length, and confirm experimentally the theory of random mode coupling between the polarization modes.
Abstract: Perturbations in highly birefringent single-mode fibers couple the two polarization modes and degrade the polarization-holding ability. With a broadband source we demonstrate wavelength averaging of the power in either mode, permitting a simple measurement of the power transfer to the cross-polarized mode as a function of fiber length. Using this technique, we confirm experimentally the theory of random mode coupling between the polarization modes.
93 citations
TL;DR: In this article, the authors reported measurements on mode converters to transform the TE01 mode into HE11 for electron cyclotron heating (ECH) experiments, and the overall efficiency of conversion from TE01 to HE11 exceeds 91% over a measured range of 59.2 to 60.1 GHz.
Abstract: The HE11 mode in corrugated waveguide has a field distribution very close to that of an ideal gaussian mode. Its radiation pattern is symmetric about the waveguide axis and exhibits virtually no cross polarization. This work reports measurements on mode converters to transform the TE01 mode into HE11 for electron cyclotron heating (ECH) experiments. The first mode converter is a 28 degree bend in 1.094-inch I.D. circular waveguide which generates TM11 from TE01 with a measured efficiency of over 95% at 60 GHz. A second converter consists of a straight corrugated waveguide section of the same I.D. in which the corrugation depth increases gradually from zero to nominally a quarter wavelength. This section converts TM11 to HE11 with an efficiency of about 97%. The overall efficiency of conversion from TE01 to HE11 exceeds 91% over a measured range of 59.2 to 60.1 GHz.
89 citations
TL;DR: In this paper, the authors describe the improvement in mode partition noise characteristics when a laser light is injected into a laser diode modulated at 400 Mbits/s, and the relationship between the half-power width of the spectral envelope and signal-to-noise ratio (SNR) degradation is obtained at 20 km fiber length.
Abstract: This paper describes the improvement in mode partition noise characteristics when a laser light is injected into a laser diode modulated at 400 Mbits/s. A single-mode fiber transmission experiment is carried out for the 1.5 μm region. A 20 km repeater spacing at 400 Mbit/s modulation is achieved by LD light injection. The center longitudinal mode power is increased to 94 percent of the total modes. Relative noise in the center longitudinal mode is improved 30 dB by optical injection of -18.2 dBm. However, the mode partition noise generated by noninjected modes is not completely suppressed. The relationship between the half-power width of the spectral envelope and signal-to-noise ratio (SNR) degradation is obtained at 20 km fiber length. If 3 dB excess SNR degradation is allowed for the mode partition noise, then the necessary half-power width of the spectral envelope is less than 0.6 nm.
70 citations
TL;DR: In this article, the mode coupling parameters between the orthogonally polarized HE 11 modes are compared for various kinds of waveguide imperfections and ambient fluctuations in the stress-applied single polarization fibers.
Abstract: Mode coupling effects caused by waveguide imperfections and ambient fluctuations in the stress-applied single polarization fibers have been investigated. Several origins of mode coupling, such as: 1) core deformations, 2) deformation of stress-applying parts, 3) micro-bending, and 4) temperature fluctuations, have been treated. The mode coupling parameters between the orthogonally polarized HE 11 modes are compared for various kinds of waveguide imperfections and ambient fluctuations. It was clarified that the deformation of the stress-applying parts is the dominant factor in the mode coupling effects in stress-applied single polarization fibers.
42 citations
TL;DR: In this paper, the authors reported the measurements of the twist induced circular birefringence in a single mode fiber by direct observation of the scattered light, and an analysis of the evolution of the polarization in a linearly bireringent twisted medium (applicable to weakly guiding single mode (fibers) is given using the coupled mode theory and Poincare sphere representation.
7 citations
TL;DR: In this article, the authors studied the mode selection characteristics of a four-layer dielectric slab waveguide and showed that it can be used as a TE0 mode filter where only TE0 and TM0 modes can propagate without attenuation, provided that the normalized frequency of the waveguide is chosen in the range between two cutoff normalized frequencies.
Abstract: Mode selecting characteristics of four-layer dielectric slab waveguide have been studied, considering its practical application to the optical integrated circuits as a mode filter. The dimensions of the waveguides discussed here are restricted to the cases where only TE0 mode or TE0 and TM0 modes can exist and higher modes are in cutoff region. Cutoff characteristics and attenuation characteristics for TE0 and TM0 modes have been investigated for various waveguide parameters. It has been found from the results of this investigation that the four-layer waveguide can be utilized as a TE0 mode filter where only TE0 mode can propagate without attenuation, provided that the normalized frequency of the waveguide is chosen in the range between two cutoff normalized frequencies for TE0 and TM0 modes. In the latter part of this paper, the four-layer waveguide joined with a three-layer waveguide has been treated, and transmittance and reflectance for transmitted and reflected waves at the junction and also the fields of the transmitted wave in the neighborhood of the junction have been studied.
7 citations
TL;DR: The experiment proved that graded-index and step-index fibers agree in the order of magnitude of parameters representing random bends along the fiber axis, and showed that mode conversion characteristics are affected by structure of the coating and refractive-index depression at the center of the fiber core.
Abstract: Mode conversion coefficients in graded-index fibers with various fiber-coating schemes are measured. The experiment proved that graded-index and step-index fibers agree in the order of magnitude of parameters representing random bends along the fiber axis. It is found that mode conversion coefficients are largely concerned with the structure of the coating. The results show that mode conversion characteristics are affected by structure of the coating and refractive-index depression at the center of the fiber core. The combination of a relatively hard jacket and a thick isolation layer made of soft material is found to be effective in reducing the mode coupling among samples investigated.
5 citations
TL;DR: In this article, a theoretical analysis of the relation between transverse mode control and longitudinal mode behavior in the injection lasers which have undoped active regions was given. And the gain saturation was analyzed on the basis of the density matrix equation.
Abstract: Stabilization and control of the operating field mode in injection lasers are very important problems for wider application of the devices. This paper gives a theoretical analysis of the relation between transverse mode control and longitudinal mode behavior in the injection lasers which have undoped active regions. The guided modes are classified into three types, normal guided mode, active guided mode, and leaky mode, owing to guiding mechanism. Cutoff conditions for all types of modes are mentioned. Gain saturation was analyzed on the basis of the density matrix equation. The so-called weakly (partially) inhomogeneous property of the gain saturation was taken into account. The single longitudinal mode operation is expected when the transverse higher modes are in cutoff condition, because the suppression effect among the resonant modes is promoted. The normal guided mode is the most suitable for the single longitudinal mode operation, because the field profile and diffraction loss are invariable with increasing injection current. The transverse mode control is the most important characteristic in obtaining the single longitudinal mode operation in the injection lasers.
2 citations
TL;DR: In this article, a joint between a single-mode channel waveguide and a singlemode fiber was studied and the measured parameters of the mode field distributions in the waveguide were used to calculate the sensitivity of an end-to-end joint to the magnitude of the gap and to angular transverse displacements between the ends.
Abstract: A study was made of a joint between a single-mode channel waveguide and a single-mode fiber. The measured parameters of the mode field distributions in the waveguide and fiber were used to calculate the sensitivity of an end-to-end joint to the magnitude of the gap and to angular transverse displacements between the ends. The parameters of a channel waveguide fiber should, in principle, allow formation of a joint with an efficiency of 90%. The experimental value of the joint efficiency was 86%.
2 citations
TL;DR: The length dependence (γ value) of the baseband bandwidth measured in a number of fiber systems actually installed is found and an important factor determining junction characteristics is the mode dispersion compensation regulated by the group delay difference among principal mode groups as well as within a principal mode group.
Abstract: It is important in determining system configuration to understand the length dependence of the baseband bandwidth of a graded-index fiber. An actual fiber communication system is constructed from a number of connected fibers with different characteristics. In such cases, the length dependence of the baseband bandwidth becomes very complex due to mode conversion and mode dispersion compensation at the junction and no practical method exists to estimate the characteristics. Therefore, actual systems are approximated by setting an appropriate value of γ in the γth power expression. This paper first finds the length dependence (γ value) of the baseband bandwidth measured in a number of fiber systems actually installed. Next, to analyze factors determining the length dependence, experimental and theoretical investigations are conducted. It is found that an important factor determining junction characteristics is the mode dispersion compensation regulated by the group delay difference among principal mode groups as well as within a principal mode group. It is also found that mode conversion at the junction has a negligible effect. In an actual communication channel employing many fibers, correlation in the group delay difference among the principal mode groups and within the principal mode group of each fiber becomes small and the value of γ is restricted. In practice, it is possible to estimate the average baseband bandwidth by setting γ ∼ 0.6.
TL;DR: In this article, a fiber-optic line consisting of a high-coherence source emitting a linearly polarized spherical wave, a fiber waveguide, and a threshold photodetector is modulated by a simple binary code, and the optimization criteria are the requirement of minimum distortion of the signal waveform at the exit from the fiber and the maximum stability of the communication process.
Abstract: The wave approach is used to solve the problem of design of a fiber-optic line consisting of a high-coherence source emitting a linearly polarized spherical wave, a fiber waveguide, and a threshold photodetector. The intensity of the radiation emitted by the source is modulated by a simple binary code. The optimization criteria are the requirement of minimum distortion of the signal waveform at the exit from the fiber and the maximum stability of the communication process. Allowance is made for all types of dispersion (material, waveguide, and mode), and also for the coupling between the modes because of slight irregularities of the fiber resulting in distortion of the pulse shape. The dependences of the duration of the input pulses and of the photodetector threshold on the wavelength of the radiation emitted by the source are given and analyzed, together with the dependence of the reliability of reception of the transmitted signal on the fiber waveguide length.
02 Aug 1982
TL;DR: In this article, a rib-like waveguide structure consisting of three dielectric films is analyzed, in which properly chosen film thicknesses allow the lateral containment of any selected waveguide mode, with the unselected modes radiating laterally away from the rib structure.
Abstract: A rib-like waveguide structure consisting of three dielectric films is analyzed, in which properly chosen film thicknesses allow the lateral containment of any selected waveguide mode, with the unselected modes radiating laterally away from the rib structure. The wave-guide consists of two high-index films separated by a low index layer in which the fields are evanescent. The lateral guidance method mechanism arises from the joint dependence of the planar waveguide mode propagation constants on the strength of evanescent coupling between the two high-index films, and on the propagation constant difference between the planar wave-guide mode and one with exactly resonant coupling between the high-index layers. Depending on the mode and the film thicknesses, the radiation is guided along a ridge or a trough in the thickness of the low-index layer. Unlike mode-stripping structures based on preferential absorption of the unwanted modes, this all-dielectric structure introduces no loss to the selected mode, other than the unavoidable scattering and residual absorption in the dielectric media, and the reflection and radiation loss at one required longitudinal inteface between adjacent waveguide sections. Also, unlike mode-selecting structures based on Bragg effects, no maintenance of phase-matched conditions over controlled propagation lengths is required.