US 6,376,830 B1Granted

System and method for measuring the transfer function of a guided wave device

AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration

InventorsMark E. Froggatt, Turan Erdogan

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Abstract

A method/system are provided for measuring the N×N scalar transfer function elements for an N-port guided wave device. Optical energy of a selected wavelength is generated at a source and directed along N reference optical paths having N reference path lengths. Each reference optical path terminates in one of N detectors such that N reference signals are produced at the N detectors. The reference signals are indicative of amplitude, phase and frequency of the optical energy carried along the N reference optical paths. The optical energy from the source is also directed to the N-ports of the guided wave device and then on to each of the N detectors such that N measurement optical paths are defined between the source and each of the N detectors. A portion of the optical energy is modified in terms of at least one of the amplitude and phase to produce N modified signals at each of the N detectors. At each of the N detectors, each of the N modified signals is combined with a corresponding one of the N reference signals to produce corresponding N combined signals at each of the N detectors. A total of N2 measurement signals are generated by the N detectors. Each of the N2 measurement signals is sampled at a wave number increment Δk so that N2 sampled signals are produced. The N×N transfer function elements are generated using the N2 sampled signals. Reference and measurement path length constraints are defined such that the N combined signals at each of the N detectors are spatially separated from one another in the time domain.

Claims9

Dependent claims

For an N-port guided wave device having a maximum effective path length LD and an effective index n, the guided wave device being defined by a transfer function matrix having N×N scalar transfer function elements, a system for measuring each of the N×N transfer function elements comprising:

a tunable source for generating optical energy of a selected wavelength;
first means coupled to said source for directing said optical energy along N reference paths and for producing N reference signals indicative of amplitude, phase and frequency of said optical energy carried along said N reference paths;
second means coupled to said source for directing said optical energy to the N-ports of the guided wave device, wherein a portion of said optical energy is modified in terms of at least one of said amplitude and said phase to produce N2 modified signals;
third means coupled to said first means and said second means for combining each of said N2 modified signals with a corresponding one of said N reference signals to produce corresponding N2 combined signals;
fourth means coupled to said tunable source and said third means for sampling each of said N2 combined signals at a wave number increment Δk , wherein corresponding N2 sampled signals are produced;
said first means defining N reference path lengths LRi, i=1 to N, and said second means and said third means defining N combined path lengths LMj, j=1 to N, for each of said N reference paths, wherein
|LRi—LMi|>N*LD |j=1,N |i=1,N
and [LeftBracketingBar] L Ri - L Mi [RightBracketingBar] + L D < π 2 ⁢ n ⁢ ⁢ Δ ⁢ ⁢ k [RightBracketingBar] j = 1 , N [RightBracketingBar] i = 1 , N ,
and wherein N combined signals of said N2 combined signals that are associated with said corresponding one of said N reference signals are spatially separated from one another in the time domain;
and
a processor coupled to said fourth means for generating the N×N transfer function elements of the transfer function matrix using said N2 sampled signals.

8 more elements

For an N-port guided wave device having a maximum effective path length LD and an effective index n, the guided wave device being defined by a transfer function matrix having N×N scalar transfer function elements, a method of measuring each of the N×N transfer function elements comprising:

a) generating optical energy of a selected wavelength at a source;
b) directing said optical energy from said source along N reference optical paths having N reference path lengths LRi, i=1 to N, each of said reference optical paths terminating in one of N detectors;
c) producing N reference signals at said N detectors indicative of amplitude, phase and frequency of said optical energy carried along said N reference optical paths;
d) directing said optical energy from said source to the N-ports of the guided wave device and then on to each of said N detectors, wherein N measurement optical paths are defined between said source and each of said N detectors, and wherein a portion of said optical energy is modified in terms of at least one of said amplitude and said phase to produce N modified signals at each of said N detectors;
e) combining, at each of said N detectors, each of said N modified signals with a corresponding one of said N reference signals to produce corresponding N combined signals at each of said N detectors, wherein a total of N2 measurement signals are generated by said N detectors;
f) sampling each of said N2 measurement signals at a wave number increment Δk , wherein N2 sampled signals are produced;
g) defining N measurement path lengths LMj, j=1 to N, of said N measurement optical paths associated with each of said N detectors wherein
|LRi−LMj|>N*LD|j=1,N|i=1,N
and [LeftBracketingBar] L Ri - L Mj [RightBracketingBar] + L D < π 2 ⁢ n ⁢ ⁢ Δ ⁢ ⁢ k [RightBracketingBar] j = 1 , N [RightBracketingBar] i = 1 , N ,
and wherein said N combined signals at each of said N detectors are spatially separated from one another in the time domain;
and
h) generating the N×N transfer function elements of the transfer function matrix using said N2 sampled signals.

9 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/606,120Filed 15 Jun 2000 · us provisional application
Priority: 14 Sep 1999
Granted: 23 Apr 2002
Term ends: Not estimatedThe source records don’t support an estimate.

Classification4 codes

G01M 11/3172
With a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers: reflectometers…
G01M 11/3145
Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR: details of the optoelectronics or data analysis
G01M 11/3181
With a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers: reflectometers…
G01M
Testing static or dynamic balance of machines or structures