Tunable receiver for a wavelength division multiplexing optical apparatus and method

• US 5,793,912 A
• Filed: 12/18/1996
• Issued: 08/11/1998
• Est. Priority Date: 06/09/1994
• Status: Expired due to Fees

• Current Assignee: APA Enterprises, Inc.
• Original Assignee: Clearfield, Inc
• Inventors: Jain, Anil K., Boord, Warren Timothy
• Primary Examiner(s): Healy, Brian
• Application Number:
  US08/769,459
• Time in Patent Office: 601 Days
• Field of Search: 385/1, 385/2, 385/4, 385/8, 385/9, 385/11, 385/14, 385/15, 385/24, 385/27, 385/28, 385/31, 385/37, 385/40, 385/41, 385/47, 385/49, 385/88, 385/89, 385/129, 385/130, 385/131, 385/132, 359/114, 359/115, 359/130, 359/181, 359/127, 359/124, 359/15, 359/34
• US Class Current: 385/37
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems
• CPC Class Codes: H04J 14/0307 Multiplexers; Demultiplexers

Abstract

A method and apparatus for automatically providing for both multiplexing and independent external modulation of two or more wavelengths emitted by one or more multi-longitudinal mode laser(s) or other light source. The present invention uses an integrated optics device chip to enable coupling of the dispersed wavelengths into separate electro-optic modulators which encode each of the carrier wavelengths with a different signal. Accordingly, the volume of data which can be transmitted over an optical fiber network is increased. The carrier wavelengths can be transmitted over single or multi-mode optical fibers.

Claims

1. An apparatus for receiving and decoding a plurality of wavelength division multiplexed light signals from a single optical fiber, the light signals carrying modulated information in the different wavelengths, comprising:

A) wavelength separation means, for spatially separating the different wavelength light signals from the single optical fiber;

B) a plurality of light detectors for detecting the modulated information in the different wavelength light signals, wherein detected information may be processed, transmitted or stored; and

C) wavelength tuning means, interposed between the wavelength separation means and the plurality of light detectors, for tuning to different wavelengths λ

_c in the optical fiber transmission band, wherein λ

_c is defined as the center wavelength of the light signals, and whereby accommodation is provided to both multi-longitudinal mode laser diodes or distributed feedback (DFB) laser diode arrays as the source of the different wavelength light signals.

2. The apparatus of claim 1, wherein the wavelength tuning means is comprised of a lens assembly.

3. The apparatus of claim 2, wherein the lens assembly includes a divergent lens and a convergent lens, and wherein movement of the divergent lens in a plane generally perpendicular to the direction of the different wavelength light signals corrects the tuning of the receiver.

4. The apparatus of claim 3, wherein the laser is a distributed feedback laser diode array.

5. The apparatus of claim 3, wherein the laser is a multi-longitudinal mode laser.

6. The apparatus of claim 3, wherein the light source is a light emitting diode.

7. The apparatus of claim 2, further comprising a diffraction grating for splitting the light into its constituent components of separate wavelengths and polarizing recovery means, located between the wavelength tuning means and the diffraction grating, for polarizing the collimated light beam perpendicular to the direction of the grating grooves of the diffraction grating.

8. The apparatus of claim 7, wherein the polarizing recovery means is comprised of a polarizing beamsplitter, arranged and configured as a rhomboid prism having an exit port, and including a half wave plate at the exit port, wherein the polarizing beamsplitter and half wave plate polarize the collimated light beam perpendicular to the direction of the grating grooves of the diffraction grating and magnify the beam diameter in the direction parallel to the incidence plane at the diffraction grating, whereby the cross section of the diffracted beam is more closely circular in shape.

9. The apparatus of claim 7, wherein the plurality of light detectors are part of an array and the different wavelengths of light are directed onto the light detector array.

10. The apparatus of claim 7, wherein the different wavelengths of light are directed onto an optical fiber array, including a plurality of optical fibers, each of the plurality of optical fibers terminating at one of the plurality of photodetectors.

11. An apparatus for receiving and decoding a plurality of wavelength division multiplexed light signals from a single optical fiber, the light signals carrying modulated information in the different wavelengths, comprising:

A) wavelength separation means, for spatially separating the different wavelength light signals from the single optical fiber;

B) a physical array including a plurality of light detectors for detecting the modulated information in the different wavelength light signals, wherein detected information may be processed, transmitted or stored; and

C) magnification means, physically interposed between the wavelength separation means and the physical array, for increasing the spatial dispersion of the different wavelength light signals at the physical array to accommodate different wavelength separation Δ

λ

between the carrier wavelengths λ

_i of the wavelength division multiplexed signals.

12. The apparatus of claim 11, wherein the magnification means includes a zoom lens assembly.

13. The apparatus of claim 12, wherein the different wavelength light signals are generated by a laser.

14. The apparatus of claim 13, wherein the laser is a distributed feedback laser diode array.

15. The apparatus of claim 13, wherein the laser is a multi-longitudinal mode laser.

16. The apparatus of claim 13, wherein the light source is a light emitting diode.

17. The apparatus of claim 11, wherein the physical array is a photodetector array.

18. The apparatus of claim 11, wherein the physical array includes an array of optical fibers.

19. A system for transmitting and receiving wavelength division multiplexed signals over a single optical fiber, comprising:

A) transmitter means, including;

i) a single laser for generating a plurality of optical signals of different wavelengths;

ii) external modulator means for modulating the optical signals in accordance with control signals, whereby the optical signals carry information; and

iii) wavelength separation means, for spatially separating the different wavelength signals and directing the signals from the laser to the integrated optic modulator;

B) a multi-mode or single mode optical fiber; and

C) receiver means, including;

i) wavelength separation means, for spatially separating the different wavelength signals transmitted by said optical fiber;

ii) a light detector array or optical fiber array with each fiber terminated at a photodetector, for detecting the modulated information in the different wavelength signals, wherein transmitted information may be processed, transmitted or stored;

iii) wavelength tuning means, interposed between the input optical fiber and the light detector array, for tuning to different center wavelengths λ

_c in the optical fiber transmission band, whereby accommodation is provided to both multi-longitudinal mode laser diodes or distributed feedback (DFB) laser diode arrays; and

iv) magnification means, physically interposed between the wavelength tuning means and the light detector array, for increasing the spatial dispersion of the different wavelength light signals at the light detector array or optical fiber array to accommodate different wavelength separation Δ

λ

between the carrier wavelengths λ

_i of the wavelength division multiplexed signals.

20. A system for transmitting and receiving wavelength division multiplexed signals over a single optical fiber, comprising:

a) transmitter means, including;

i) a plurality of lasers equal to n for generating a plurality m optical signals of different wavelengths, and wherein m is greater than n.

ii) external modulator means for modulating the optical signals in accordance with control signals, whereby the optical signals carry information; and

iii) wavelength separation means, for spatially separating the different wavelength signals and directing the signals from the lasers to the integrated optic modulator;

b) a multi-mode or single mode optical fiber; and

c) receiver means, including;

i) wavelength separation means, for spatially separating the different wavelength signals transmitted by the optical fiber;

ii) a light detector array for detecting the modulated information in the different wavelength signals, wherein transmitted information may be processed, transmitted or stored; and

iii) optical components for tuning the receiver to detect the specific set of wavelengths used in the WDM optical system.

21. The apparatus of claim 20, wherein the lasers are multi-longitudinal mode lasers.

22. The apparatus of claim 20, wherein said wavelength separation means includes a diffraction grating which is a holographic grating.

23. The apparatus of claim 20, wherein:

a) each of the lasers are multi-longitudinal mode lasers;

b) the external modulator means is an integrated optic device, wherein the integrated optic device includes a plurality of directional coupler integrated optic structures, wherein two parallel channel waveguides are provided for each of the directional couplers and control voltages are applied to electrodes overlying the channel waveguides to attenuate or propagate a light wave traveling through the directional couplers; and

c) the wavelength separation means includes a collimating lens for collimating the beam from said laser, a mirror to reflect the collimated beam to a diffraction grating, and a focusing lens to focus the different wavelengths of the beam onto the external modulator means.

24. The apparatus of claim 20, further comprising:

a) a power and temperature controller device cooperatively connected to the lasers, wherein the wavelength shifts of the lasers are minimized;

b) a modulation controller device, operatively connected to the external modulator means, for activating the external modulator to encode information into the different wavelengths of the beam; and

c) detector array controller means, operatively connected to the light detector array, for receiving the detected information and for retransmitting, processing or storing the detected information.

25. The apparatus of claim 20, wherein the optical fiber is a multi-mode fiber.

26. A method of wavelength division multiplexing a plurality of signals over an optical fiber, comprising the steps of:

a) generating a plurality "m" of optical signals of different wavelengths from "n" laser diodes, wherein m is greater than n;

b) spatially separating the different wavelength signals and directing the signals from the laser to an integrated optic modulator;

c) modulating the optical signals with the integrated optic modulator in accordance with control signals, whereby the optical signals carry information;

d) receiving the modulated optical signals; and

e) tuning the receiver to the center frequency λ

_c of the m optical signals.

27. The method of claim 26, further including the step of separating the m optical signals and focusing the signals onto a photodetector array with a zoom lens.