Data rate limiter for optical transmission system
First Claim
1. An optical fiber transmission system bandwidth limiter for operation at a given wavelength comprisinga multimode optical fiber for propagating at said given wavelength a plurality of modes at different velocities, said multimode fiber having first and second ends,means for receiving input light,first transition means located at said first end of said multimode fiber for redistributing energy received by said receiving means and initiating in said multimode fiber for propagation of a plurality of modes which propagate therethrough at different velocities, whereby the reception by said receiving means of a given pulse of light energy having a given time duration width results in the arrival at said second end of said multimode fiber of a plurality of modes, the summation of which would be a light pulse having a width which is greater than said given width by a time interval that is equal to the differential delay time between the slowest and the fastest propagating modes in said multimode fiber, andsecond transition means at said second end of said multimode fiber for converting a portion of the energy in each mode that propagates in said multimode fiber, except the LP01 mode, into at least one lower order mode, whereby an LP01 mode light pulse propagating from said second transition means is broader than said given time duration because of the differences in the propagation times of various modes in said multimode fiber.
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Abstract
A single-mode transmission optical fiber may have a bandwidth much greater than that necessary to transmit a desired predetermined maximum data rate. The single-mode fiber is connected to a bandwidth limiting device comprising the serial combination of an input optical fiber, a mode converter and multimode fiber. If the multimode fiber is capable of propagating two modes, for example, the mode converter converts the LP01 signal from the transmission fiber to the LP01 and LP11 modes. These two modes propagate at different speeds through the multimode fiber. Means connected to the output end of the multimode fiber detects the two modes. If the time delay difference Δt between the two modes is small with respect to the width of a pulse in the transmitted pulse train, the pulse train will be detected without distortion. Transmission at a higher data rate causes Δt to be large with respect to pulse width. Thus, a transmitted pulse causes the generation of a false pulse, whereby operation at the higher data rate is impossible. Also disclosed are methods of making suitable mode converters.
55 Citations
37 Claims
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1. An optical fiber transmission system bandwidth limiter for operation at a given wavelength comprising
a multimode optical fiber for propagating at said given wavelength a plurality of modes at different velocities, said multimode fiber having first and second ends, means for receiving input light, first transition means located at said first end of said multimode fiber for redistributing energy received by said receiving means and initiating in said multimode fiber for propagation of a plurality of modes which propagate therethrough at different velocities, whereby the reception by said receiving means of a given pulse of light energy having a given time duration width results in the arrival at said second end of said multimode fiber of a plurality of modes, the summation of which would be a light pulse having a width which is greater than said given width by a time interval that is equal to the differential delay time between the slowest and the fastest propagating modes in said multimode fiber, and second transition means at said second end of said multimode fiber for converting a portion of the energy in each mode that propagates in said multimode fiber, except the LP01 mode, into at least one lower order mode, whereby an LP01 mode light pulse propagating from said second transition means is broader than said given time duration because of the differences in the propagation times of various modes in said multimode fiber.
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9. An optical fiber transmission system bandwidth limiter comprising
a multimode optical fiber having first and second ends, an input optical fiber joined to the first end of said multimode fiber, and first transition means located at the junction of said input fiber and the first end of said multimode fiber for exciting in said multimode fiber a plurality of modes which is greater in number than the number of modes propagating in said input fiber, said multimode and input optical fibers being laterally and angularly offset with respect to each other at the junction therebetween, the propagation characteristics of said multimode fiber being such that said plurality of modes propagate therethrough at different velocities, whereby the reception by said input fiber of a given pulse of light energy having a given time duration width results in the arrival at said second end of said multimode fiber of a plurality of modes, the summation of which would be a light pulse having a width which is greater than said given width by a time interval that is equal to the differential delay time between the slowest and the fastest propagating modes in said multimode fiber.
- 10. An optical fiber mode converter comprising first and second adjacent sections of optical fiber connected at a junction, the longitudinal axes of said sections being angularly and laterally offset at said junction.
- 15. A mode converter in accordance with claim I4 wherein said first and second sections are optical fibers having different diameters.
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17. A method of making an optical fiber mode converter comprising
providing an optical fiber comprising first and second adjacent sections, said second section being a multimode fiber, heating the junction between said two adjacent sections, and bending said fiber sections at said junction so that the longitudinal axis of said first fiber section is angularly and laterally offset with respect to the longitudinal axis of said second fiber section, the extent of the angular and lateral offsets between the longitudinal axes of said sections being such that the lowest order mode received by said first section is redistributed as a plurality of modes which propagate through said second section at different velocities.
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22. An optical fiber transmission system comprising the serial arrangement of the following components
an optical pulse generator, optical receiving means, at least one single-mode optical transmission fiber connected between said pulse generator and said receiving means, and a bandwidth limiter connected between said at least one single-mode optical transmission fiber and said potical receiving means, said bandwidth limiter being characterized in that it comprises a multimode optical fiber and an input optical fiber which is shorter than said multimode fiber, one end of said input fiber being connected to said multimode fiber, first transition means being located at the junction of said input and multimode fibers for converting energy propagating in said input fiber to a plurality of modes which is greater in number than the number of modes propagating in said input fiber, said plurality of modes propagating through said multimode fiber at different velocities, said multimode and input fibers being laterally and angularly offset with respect to each other at the junction therebetween, means connecting the remaining end of said input fiber to one of said serial arrangement components, and means connecting the remaining end of said multimode fiber to the next mentioned component in said serial arrangement, whereby the reception by said input fiber of a given pulse of light energy having a given time duration width results in the arrival at said next mentioned component of a light pulse having a width greater than said given width.
- 27. An optical fiber mode converter comprising first and second adjacent sections of optical fiber connected at a junction, the longitudinal axes of said sections being angularly and laterally offset at said junction, said junction having been formed by subjecting the ends of said fiber sections to sufficient heat to cause them to soften, whereby said fiber sections are substantially stress-free at said junction.
- 32. An optical fiber mode converter comprising first and second adjacent sections of optical fiber connected at a junction, the longitudinal axes of said sections being angularly and laterally offset at said junction, said fiber sections being substantially stress-free said junction, whereby mode conversion is caused by the lateral and angular offsets of said fibers and is independent of any stress-induced effect.
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37. An optical fiber transmission system comprising the serial arrangement of the following components
an optical pulse generator, optical receiving means, a plurality of single-mode optical transmission fibers connected between said pulse generator and said receiving means, and a bandwidth limiter connected between two of said plurality of single-mode optical transmission fibers, said bandwidth limiter being characterized in that it comprises a multimode optical fiber and an input optical fiber which is shorter than said multimode fiber, one end of said input fiber being connected to said multimode fiber, first transition means being located at the junction of said input and multimode fibers for converting energy propagating in said input fiber to a plurality of modes which is greater in number than the number of modes propagating in said input fiber, said plurality of modes propagating through said multimode fiber at different velocities, said multimode and input fibers being laterally and angularly offset with respect to each other at the junction therebetween, means connecting the remaining end of said input fiber to one of said serial arrangement components, and means connecting the remaining end of said multimode fiber to the next mentioned component in said serial arrangement, whereby the reception by said input fiber of a given pulse of light energy having a given time duration width results in the arrival at said next mentioned component of a light pulse having a width greater than said given width.
Specification