52 results about "Modal dispersion" patented technology

The present wavelength multiplexed optical system includes a multimode optical fiber that transmits wavelength multiplexed optical signals and a plurality of multimode modal dispersion compensation optical fibers. Each modal dispersion compensation optical fiber can transmit one of the multiplex wavelengths, and each modal dispersion compensation optical fiber has an optimized index profile such that the modal dispersion for the transmitted wavelength is approximately inversely equal to the modal dispersion induced in the multimode optical fiber. The wavelength multiplexed optical system facilitates an increased bitrate without reducing bandwidth.

A multimode optical waveguide having reduced modal dispersion. The optical waveguide comprises a core, a cladding surrounding the core, and a plurality of optical scattering elements dispersed in the core.

In an optical transmission line consisting of a multimode optical fiber, the mode dispersion of the optical transmission line is reduced in order to permit a wide-band optical signal to be transmitted at high speed, over a long distance and at low costs. When a plurality of multimode optical fibers are connected together to form a transmission line for the purpose of reducing a mode dispersion, length ratios between the respective multimode optical fibers that can maximize the band of this optical transmission are determined, and they are connected together at the length ratios. In addition, a multimode optical fiber having a specific refractive index profile is used as a mode dispersion compensating fiber. Also, a compensated fiber and a compensating fiber each having a specific length are connected together.

The present invention relates to a method for inversing a sea-bottom attenuation coefficient by using a modal dispersion curve energy difference, wherein inversion of a sea-bottom attenuation coefficient is implemented by using amplitude energy information of a modal dispersion curve. The present invention provides a method for inversing a sea-bottom attenuation coefficient by using an energy difference of a modal dispersion curve of two bombs, so as to estimate a sea-bottom attenuation coefficient of an experimental sea area. The method provided by the present invention focuses on inversion of a neritic zone by using a dispersion effect generated by a wide-band explosive sound source during propagation in neritic zones. The method comprises: firstly, placing a receiving hydrophone at a certain depth; then delivering explosive sound sources with the same model number parameter (considered as generating the same signal during explosion) on the same straight line and at different distances, so as to receive time-frequency maps of two explosive sound sources; then processing the time-frequency maps of the two explosive sound sources by using a warping transformation, so as to obtain a transmission energy difference of first four stages of a modal dispersion curve; and finally inversing a sea-bottom attenuation coefficient by using a modal dispersion curve energy difference.

Systems for detection and compensation of modal dispersion in an optical fiber system including a multisegment photodetector coupled to an end of an optical fiber for detecting optical signals exiting the optical fiber and for converting the optical signals to an electrical output are provided. A representative multisegment photodetector includes a plurality of photodetector regions configured such that each of the plurality of photodetectors detects a portion of the plurality of optical signals exiting the end of the optical fiber and modifies the signal to reduce the affects of modal dispersion. Other systems are also provided.

The invention discloses an ultra-miniature broadband polarization beam splitter based on two-slit interference. A medium thin film covers a metal two-slit structure; when an incident light irradiates the metal two-slit structure from the back, each slit is capable of activating a TM mode and a TE mode supported by an air-medium-metal composite waveguide; the total field intensity of the waveguide mode in each direction is the coherent superposition of the separately activated modes of two slits; because two slits are different in width, the interference state in the opposite direction can be opposite and the oriented activation of the waveguide mode can be realized; further, the composite waveguide has great modal dispersion, two polarization modes perpendicular to each other can be propagated along the opposite direction and the polarization beam splitting is realized. A ultra-miniature polarization beam splitter is realized on the metal two-slit structure; the two-slit interference is capable of regulating field distribution in a metal nano structure, is important to the nano surface plasmon polariton devices and is important to an integrated loop.

An optical fiber for reducing modal dispersion and increasing both travel distance and transmission speed. A core center is formed in the core of the optical fiber. The core center is doped with impurities, is hollow, or is pulled at a lower temperature to increase diffraction of the core center. The core center discriminates the low order modes such that only the high order modes are present in the optical fiber. Because the low order modes are absorbed or otherwise discriminated against, the range of propagation constants is reduced and modal dispersion is likewise reduced. High order modes can be launched in the optical fiber using a lens whose center portion is obscured or by using a diffractive lens to couple a source to the optical fiber.

A method for mitigating modal dispersion in a multimode optical fiber involves launching a diffractionless optical beam, such as a Bessel beam, into a multimode optical fiber. A fiber optical transmission system includes a multimode optical fiber transmission medium having an input end and an output end, an optical signal transmitter in communication with the input end of the multimode optical fiber medium, means for converting the optical signal into a diffractionless optical signal, means for launching the diffractionless optical signal in the input end of the multimode optical fiber transmission medium, means for outputting the propagated optical signal from an output end of the multimode fiber transmission medium, and a receiver that receives the optical signal from the output means. Fiber optic communication systems employing the invention embodiments include point-to-point transmission links, local area networks and WDM systems including coarse wavelength division multiplexing and dense wavelength division multiplexing systems.

A method for compensating for both material or chromatic dispersion and modal dispersion effects in a multimode fiber transmission system is provided. The method includes, but is not limited to measuring a fiber-coupled spatial spectral distribution of the multimode fiber laser transmitter connected with a reference multimode fiber optical cable and determining the amount of chromatic dispersion and modal dispersion present in the reference multimode fiber optic cable. The method also includes, but is not limited to, designing an improved multimode fiber optic cable which compensates for at least a portion of the chromatic dispersion and modal dispersion present in the reference multimode fiber optic cable resulting from the transmitter's fiber-coupled spatial spectral distribution.

Multi-mode optical fiber apparatuses, multi-mode optical fibers, and related methods for improving fiber link bandwidth are disclosed. One or more end structures can be disposed on an optical fiber end of a multi-mode optical fiber to improve link bandwidth by reducing and/or eliminating modal dispersion. Modal dispersion can be caused by higher-order modes or modes in an optical fiber being excited by received light. Modal dispersion can limit the bandwidth of an optical fiber link. In certain embodiments, end structures for multi-mode optical fibers are disclosed for reducing the launch angle of light in an optical fiber to reduce modal dispersion. In other embodiments, end structures for multi-mode optical fibers are disclosed for reducing or eliminating coupling astigmatism. In other embodiments, end structures for multi-mode optical fibers are disclosed for directing higher order modes or groups away from an optical detector to reduce or eliminate modal dispersion. In one embodiment, a prism structure is disposed on the source end of the multi-mode optical fiber. In other embodiments a convex profile lens is disposed at the source and detector ends of the fiber.

A parallel optical fiber angled coupling component, which is used for parallel coupling of optical signal between the optical fiber array and the laser array, comprises an optical fiber positioning substrate, a cover plate and a plurality of optical fibers. The end face of the optical fiber is polished into a bevel with an inclination of 42.5° or 47.5°, and the bevel of the optical fiber is coated with a metal reflective film. This invention has the following beneficial effects: The end face of the optical fiber is polished into a bevel with an inclination of 42.5° or 47.5° to reduce inter-modal dispersion and increase the transmission distance of the optical signal in the subsequent optical fiber; the bevel of the optical fiber is coated with a metal reflective film, so as to ensure high reflectivity even if the bevel of the optical fiber is covered with glue.

Multimode optical fiber systems with adjustable chromatic modal dispersion compensation are disclosed, wherein the system includes a VCSEL light source and primary and secondary optically coupled multimode optical fibers. Because the VCSEL light source has a wavelength spectrum that radially varies, its use with the primary multimode optical fiber creates chromatic modal dispersion that reduces bandwidth. The compensating multimode optical fiber is designed to have a difference in alpha parameter relative to the primary multimode optical fiber of −0.1≦Δα≦−0.9. This serves to create a modal delay opposite to the chromatic modal dispersion. The compensation is achieved by using a select length of the compensating multimode optical fiber optically coupled to an output end of the primary multimode optical fiber. The compensating multimode optical fiber can be configured to be bend insensitive.

Covert acoustic communications (CAC) through solid propagation channels that connect node pairs is achieved by encoding signals using spread spectrum coding techniques that position the encoded signal at a center frequency f_c within a narrow frequency bandwidth BW_NB in which the amplitude of the channel response H(f) between each node pair is relatively high. The channel response H(f), bandwidth BW_NB and center frequency f_c, and accordingly the signal data rate will adapt for each node pair and possibly each side of the node pair. A pre-distortion filter 1/H(f) pre-distorts the encoded signal over bandwidth BW_NB to compensate for material and modal dispersion and multipath between the node pair. This technique avoids the problems associated with frequency dependent attenuation of the continuous solid path and allows for simultaneous transmission and reception of signals among the multiple node pairs.

The invention relates to a hybrid optical fiber that includes a multi-segmented optical core exhibiting a refractive graded-index profile typically used to support multimode transmission in which a step-index is added at the center of the optical core, the profile parameters (a s ) and (” s ) of this step-index being tuned so as to provide an optical fiber that transmits both error free multimode optical signals and error free single-mode optical signals. The implementation of such a refractive index profile n(r) of the optical core, as well as the choice of an adequate value of the parameters (a s ) and (” s ) lead to adapt the fundamental mode of the optical fiber such that the optical power coupled into the fundamental mode is maximized at the wavelength of the single-mode transmission, 1550 nm for example, while preserving a relatively reduced modal dispersion at the wavelength of the multimode transmission, 850 nm for example.

The invention relates to the technical field of underwater acoustic signal processing, in particular to a single hydrophone normal wave modal separation method and system based on compressed sensing, and the method comprises: obtaining a horizontal wave value of a broadband normal wave according to an approximate modal dispersion relation; based on a compressed sensing theory, constructing a dictionary matrix of a sparse solving problem by horizontal wave values; according to the dictionary matrix and a broadband frequency domain sound pressure vector received by the single hydrophone, constructing a sparse signal model by adopting a compressed sensing theory, and solving and calculating by utilizing a compressed sensing implementation algorithm to obtain a sparse vector complex coefficient; and, according to the sparse vector complex coefficient and the dictionary matrix, recovering each separated normal wave mode. The method is wider in applicable scene and can be suitable for the condition that refraction type and reflection type normal positive waves exist at the same time under the negative gradient hydrological condition, and the known accurate seawater sound velocity profile and seabed parameters are not needed.