Showing papers on "Mode scrambler published in 1989"

A novel differential mode rejection network for conducted emissions diagnostics

Abstract: A differential mode rejection network (DMRN), a device which separates common mode noise from differential mode noise in a line impedance stabilization network (LISN)-based conducted emissions setup, is described. Although it is not a filter, its function is analogous to that of a filter. The DMRN filters out differential mode, and passes common mode unfiltered. The differential mode is attenuated by more than 50 dB, and the common mode noise is attenuated by less than 4 dB. Applications of the DMRN are discussed for filter design and troubleshooting, and electromagnetic interference source suppression is briefly described. Mathematical analysis and hardware implementation of the devices are explained. >

Method and apparatus for securing information communicated through optical fibers

Abstract: This invention relates to a technique for protecting information from intrusion that is transmitted through optical fiber. The new method relates to transmitting energy at multiple wavelengths along a single mode optical fiber. The wavelengths can be propagated in single mode or alternatively n single mode or in high order modes. Energy at one or more wavelengths constitutes guard channels which have an enhanced power loss effect by selection of an appropriate cut-off wavelength of the single mode optical fiber. These guard channels can be monitored for power loss to detect intrusion. An apparatus is also described.

Fiber optic intermode coupling single sideband frequency shifter

Abstract: An optical fiber is subjected to a series of traveling flexural waves propagating along a length of the fiber. At least a portion of an optical signal propagating within the optical fiber in a first propagation mode is coupled to a second propagation mode. The optical signal in the second propagation mode has a frequency which is equal to either the sum of or the difference between the frequency of the optical signal in the first propagation mode and the frequency of the traveling flexural waves. The frequency of the optical signal in the second propagation mode is shifted upward or downward from the frequency of the optical signal in the first propagation mode as determined by the direction of propagation of the first optical signal with respect to the direction of propagation of the traveling flexural waves, and as also determined by whether the phase propagation velocity of the optical signal in the first propagation mode is greater than or less than the propagation velocity of the optical signal in the second propagation mode. An acoustic wave is induced in a generator having a gradual tapered cross-section. The generator preferably has the shape of a horn and is coaxially mounted with said optical fiber, so as to suppress the acoustic wave induced in the optical fiber in the reverse direction.

Mode scrambler with non-invasive fabrication in an optical fiber's cladding

Abstract: A mode scrambling arrangement for a multimode optical fiber by irradiating the cladding using an ultra-violet light to change the index of refraction of the cladding. The cladding uses a material whose index of refraction is modified in response to ultra-violet light. The exposure time and intensity of the light required is determined by monitoring the mode pattern in the multimode fiber during the irradiation to provide the desired amount of mode scrambling.

An optical transmission line for use in an optical communication system

Abstract: A mode scrambler (13) is interconnected between a light source (10) and an optical fiber coupler (1) made of a plurality of graded index multi-mode optical fibers (1F) The mode of the input light signals can be converted to a random pattern mode through the mode scrambler (13), so that a steady excitation state of the input light can be realized, including not only dominant lower modes but also higher modes of the input light signals, resulting in enabling to divide the input light signals without any irregularity of the output light power

Frequency dependence of modal noise in multimode optical fibers.

Abstract: When coherent light is launched into a multimode optical fiber, a speckle pattern, namely, modal noise, can be observed at the exit face of the fiber as a result of the random interference of many different propagation modes. Changes in the source frequency can also cause modal noise variations in time at the exit face. The width of the frequency correlation function of a time varying modal noise is directly related to the modal dispersion of light transmission through a multimode optical fiber. In this paper, the frequency correlation functions for both step- and graded-index fibers are analyzed as a function of the source frequency difference. To derive the frequency correlation function, the phase of each mode in fibers is calculated by using the modal delay along the optical path of the geometrical light ray.

Device for optical frequency translation and a modulator in which said device is employed

Abstract: In a device for shifting the frequency of an optical wave, two optical waveguides coupled by an optical wave which propagates in the symmetric mode are excited and subjected to the action of an electromagnetic traveling wave having the effect of shifting the frequency of the optical wave which undergoes a transition from the symmetric mode to the antisymmetric mode. A transfer device supplied with a direct-current voltage V O serves to re-convert the antisymmetric mode to the symmetric mode in order to add the two light signals and to obtain a single output signal translated by the frequency F. This permits the construction of BLU optical modulators.

Nonlinear mode competition and coherence in low gain FEL oscillators

Abstract: A simple, one-dimensional, multimode model for a low-gain FEL oscillator is being used to study numerically the effect of mode competition on the coherency of the radiation. For a beam current smaller than four times the minimum start-oscillation current, many single mode states are possible. However, the time required to reach these states becomes very long for FEL devices described by a small slippage parameter. Two different time scales characterize the process of reaching a single mode state. The shorter time scale is related to an establishment of a relative constant amplitude of the radiation field while the phase of the field is modulated. The relaxation of the phase takes a much longer time. This process can be described analytically by a model that allows for investigation of the effects of noise and mode locking as the relaxation process. >

Modal Characterization Of Fiberoptic Devices Using An Automated Mode Analyzer

Abstract: Characteristics of light, such as intensity, phase, polarization, and wavelength have been exploited for fiber optic devices. Recently, use of the modal characteristic of light in a multimode fiber was demonstrated for sensing and modulating applications. Initial studies, using an Automated Mode Analyzer (AMA), a specially developed experimental system designed for the characterization of devices based on modal power redistribution (MPR), is reported.

Fast evaluation of the characteristics of single-mode optical fibers

Abstract: This paper describes a method for fast engineering evaluation of the transmission characteristics of single-mode optical fibers. A versatile microcomputer program is presented which can be utilized to analyze mode field characteristics of single-mode fibers with arbitrary refractive index profiles. Our computation shows that the mathematical algorithm and the corresponding programs developed in this paper are relatively simple and accurate enough for the engineering design of single-mode fibers for optical communication systems.