RF frequency multiplexed fiber optic data bus

• US 4,726,644 A
• Filed: 07/08/1985
• Issued: 02/23/1988
• Est. Priority Date: 07/08/1985
• Status: Expired due to Fees

• Current Assignee: Tacan Corporation (IPITEK, Inc.)
• Original Assignee: General Dynamics Corporation
• Inventors: Mathis, Ronald F.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): HEALY, BRIAN
• Application Number:
  US06/752,735
• Time in Patent Office: 960 Days
• Field of Search: 350/96.15, 350/96.16, 455/610, 455/612, 455/602, 370/1, 370/3
• US Class Current: 385/24
• CPC Class Codes: G02B 6/2852 using tapping light guides arranged sidewardly, e.g. in a non-parallel relationship with respect to the bus light guides (light extraction or launching through cladding, with or without surface discontinuities, bent structures)
• CPC Class Codes: G02B 6/29335 Evanescent coupling to a resonator cavity, i.e. between a waveguide mode and a resonant mode of the cavity wavelength selective means based on resonator cavity coupled non-evanescently G02B6/29356, G02B6/29358
• CPC Class Codes: G02B 6/29356 Interference cavity within a single light guide, e.g. between two fibre gratings G02B6/29347 - G02B6/2935 take precedence; evanescent coupling to a resonator cavity G02B6/29335
• CPC Class Codes: H04B 10/2725 Star-type networks without a headend
• CPC Class Codes: H04B 10/54 Intensity modulation

Abstract

A fiber optic data bus that includes a multiplexer means for generating a plurality of optical signals and for intensity modulating each of the optical signals in response to a respective one of a plurality of input RF signals each at a different RF carrier frequency to provide a plurality of intensity modulated optical signals. A signal collection means combines the plurality of intensity modulated optical signals into a combined optical signal. A conducting means conducts the combined optical signal to a signal distribution means which distributes the combined optical signal to each of a plurality of output ports. A demultiplexer means extracts from a portion of one of the distributed combined optical signals an output RF signal substantially identical to a predetermined one of the plurality of RF input signals.

Claims

1. A fiber optic data bus for multiplexing, transmitting, and demultiplexing a plurality of input RF signals as a corresponding plurality of output RF signals comprising:

a plurality of modulated light sources, each having an input adapted to receive a respective one of a plurality of input electrical RF signals each at a different RF carrier frequency wherein each modulated light source provides in response to a respective one of said input RF signals at an output a corresponding intensity modulated optical signal;

signal collection means for combining said plurality of intensity modulated optical signals into a combined optical signal, said signal collection means comprising an input star coupler having an output and a plurality of inputs with each input of said input star coupler connected to a respective output of said plurality of modulated light sources;

conducting means conncted to said signal collection means for conducting said combined optical signal, said conducting means comprising an optical fiber having a pair of ends with one end connected to said input star coupler output;

signal distribution means connected to said conducting means for output distribution of said combined optical signal, said signal distribution means comprising an output star coupler having an input and a plurality of outputs with said input of said output star coupler connected to the other end of said optical fiber;

a plurality of optical bandpass filters each having an input and an output, each optical bandpass filter input connected to a different output of said output star coupler, said optical bandpass filter comprising;

a segment of multimode optical fiber of a predetermined length, L,;

an input mirror on one end of said fiber segment;

means for directing intensity modulated light into said fiber segment; and

said fiber segment having a length substantially equal to half the wavelength of the modulation frequency in said fiber segment, with said fiber segment functioning as a resonant cavity and filtered output light exiting through said output mirror;

a plurality of optical detectors each having an input and an output, each optical detector input connected to a different optical bandpass filter output; and

wherein each of said optical filters extracts a predetermined portion of the distributed combined optical signal as an output optical signal which has a frequency corresponding to the modulation frequency of a respective one of said input RF signals and wherein each one of said optical detectors converts a respective output optical signal to an output electrical RF signal.

2. The fiber optic data bus of claim 1 wherein each RF input signal contains information within a predetermined bandwidth centered about an RF carrier of a different predetermined frequency.

3. The fiber optic data bus of claim 1 wherein each one of said modulated light sources comprises a laser diode each having an input adapted to receive a different one of said input RF signals and an output coupled to a respective input of said input star coupler.

4. The fiber optic data bus of claim 1 wherein said plurality of modulated light sources comprises:

a laser; and

a plurality of optical modulators each having an optical input coupled to the output of said laser, a modulation input adapted to receive a different one of said input RF signals and an output coupled to a respective input of said input star coupler.

5. The fiber optic data bus of claim 1 wherein each optical filter comprises a plurality of series connected optical bandpass filters each having an input and an output, the output of each optical bandpass filter connected to the input of another optical bandpass filter, wherein the first optical bandpass filter has an input connected to a respective output of said output star coupler, and a last optical bandpass filter has an output connected to a respective one of said optical detectors.

6. The fiber optic data bus of claim 1 wherein each optical filter input and output mirrors are formed of dielectric material deposited on the respective fiber segment ends.

7. The fiber optical data bus of claim 1 wherein each optical filter light directing means comprises a directional coupler having a single mode injection fiber coupled to a respective fiber segment.

8. The fiber optic data bus of claim 1 wherein each optical filter light directing means comprises an axial hole through a respective input mirror and an injecting fiber axially aligned with and closely adjacent said hole.

9. The fiber optic data bus of claim 1 wherein each optical filter fiber segment comprises a core encased by a cladding each of different refractive indexes.

10. The fiber optic data bus of claim 1 wherein in each optical filter the reflectance of the output mirror is less than the reflectance of the input mirror.

11. The optical fiber data bus of claim 6 wherein in each optical filter the reflectance of the output mirror is less than the reflectance of the input mirror.

12. The fiber optic data bus of claim 1 wherein in each optical filter the reflectances of the respective input and output mirrors are equal.

13. The fiber optic data bus of claim 6 wherein in each optical filter the reflectances of the respective input and output mirrors are equal.

14. The fiber optic data bus of claim 1 wherein the length, L, of said filter is given by the relationship ##EQU6## where λ

is the wavelength of the modulation frequency,

c is the speed of light,

η

is the effective refractive index of said fiber segment, and

f_c is the center modulation frequency.

15. The fiber optic data bus of claim 1 further comprising at least one additional optical bandpass filter each having an additional segment of multimode optical fiber with an input mirror and an output mirror on opposite ends of each additional fiber segment, each additional fiber segment having the respective input mirror coupled adjacent to the respective output mirror of another fiber segment with each adjacently coupled input and output mirrors each having an axially aligned hole therethrough, wherein each additional fiber segment has a length equal to said predetermined length, L, and each additional fiber segment functioning as a resonant cavity with the filtered output light exiting through the output mirror of a last additional segment.