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Generating Fast and Very Slow Propagating Modes to Accommodate Potentially High Dispersive Optical Multi-Mode Waveguides

IP.com Disclosure Number: IPCOM000107308D
Original Publication Date: 1992-Feb-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 66K

Publishing Venue

IBM

Related People

Olsen, CM: AUTHOR

Abstract

A multi-mode waveguide design to be placed prior to a potentially high-dispersive waveguide section (HDWS) is proposed. A HDWS is of interest for reduction of modal noise in multi-mode systems. In such systems an appropriately designed HDWS located on the output of the laser will rapidly separate the waveguide modes (*) and, thus, reduce the speckle contrast on the waveguide output. In principle, an arbitrarily large dispersion can be provided by the waveguide structure in Fig. 1. However, it is not possible to take advantage of this dispersion because modes of arbitrarily high order (i.e., very slow propagating modes) cannot be excited on the input of the waveguide. One can calculate that the maximum useful modal dispersion is 13.8.n1 ps/cm which is obtained for n1/n0 = n1/n2 = 2. Thus, for n0 = 1.

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Generating Fast and Very Slow Propagating Modes to Accommodate Potentially High Dispersive Optical Multi-Mode Waveguides

       A multi-mode waveguide design to be placed prior to a
potentially high-dispersive waveguide section (HDWS) is proposed.   A
HDWS is of interest for reduction of modal noise in multi-mode
systems.  In such systems an appropriately designed HDWS located on
the output of the laser will rapidly separate the waveguide modes (*)
and, thus, reduce the speckle contrast on the waveguide output. In
principle, an arbitrarily large dispersion can be provided by the
waveguide structure in Fig. 1.  However, it is not possible to take
advantage of this dispersion because modes of arbitrarily high order
(i.e., very slow propagating modes) cannot be excited on the input of
the waveguide.  One can calculate that the maximum useful modal
dispersion is 13.8.n1 ps/cm which is obtained for n1/n0 = n1/n2 =  2.
Thus, for n0 = 1.00 (air), the maximum dispersion becomes 20 ps/cm.
To take advantage of a potential dispersion of 20 ps/cm, the beam on
the waveguide  input must have a half width half maximum divergence
of 90o . Typical laser beam divergence is < 30o .

      However, by adding a mode excitation section, as  shown in Fig.
2, wherein all the modes supported by the subsequent HDWS are
excited, one may take full advantage of the potentially
high-dispersive waveguide.  In this waveguide configuration, the
higher order modes are rapidly generated by...