Terrestrial optical communication network of integrated fiber and free-space links which requires no electro-optical conversion between link

Claims

The invention claimed is:

1. A terrestrial optical communication network comprising a plurality of fiber optic links and free-space links between which optical signals are optically coupled by erbium doped fiber amplifiers (ERDAs), and further comprising means for controlling a -power gain of at least one of the ERDAs in response to an optical signal received over one of the free-space links.

2. A terrestrial optical communication network as defined in claim 1 wherein optical signals of the same predetermined fundamental wavelength are communicated over the fiber optic and free-space links by the ERDAs.

3. A terrestrial optical communication network as defined in claim 2 wherein the predetermined fundamental wavelength is the fundamental operating wavelength of the ERDAs.

4. A terrestrial optical communication network as defined in claim 3 wherein at least one fiber optic link also comprises a portion of a fiber optic backbone communication system.

5. A terrestrial optical communication network as defined in claim 3 wherein at least one fiber optic link also comprises a portion of a long-haul fiber optic communication system.

6. A terrestrial optical communication network as defined in claim 1 further comprising a repeater located in at least one of the free-space links, the repeater including ERDAs to amplify the power of the optical signals conducted through the free-space link.

7. A terrestrial optical communication network as defined in claim 1 further including at least one routing switch connected to a plurality of links, and the routing switch including ERDAs to optically couple the optical signals from one of the links connected to the routing switch to another one of the links connected to the routing switch.

8. A terrestrial optical communication network comprising a plurality of fiber optic links and free-space links between which optical signals are optically coupled by erbium doped fiber amplifiers (ERDAs), wherein a transmitting ERDA amplifies the optical signal before its transmission over at least one free-s-pace link, and further comprising a controller connected to the transmitting ERDA to control the optical power gain of the transmitting ERDA, and the control of the optical power gain of the transmitting ERDA adjusts the optical power of the optical signal transmitted over the one free-space link.

9. A terrestrial optical communication network as defined in claim 8 wherein the controller controls the optical power gain of the transmitting ERDA in response to the optical power of the optical signals received over the one free-space link.

10. A terrestrial optical communication network as defined in claim 9 wherein the controller controls the optical power gain in response to the optical power of optical signals received at the location of the transmitting ERDA.

11. A terrestrial optical communication network as defined in claim 9 wherein the controller controls the optical power gain of the transmitting ERDA in response to the optical power of the optical signals received at an opposite end of the one free-space link from which the optical signals were transmitted.

12. A terrestrial optical communication network as defined in claim 11 wherein the controller controls the optical power gain of the transmitting ERDA in response to control information contained in optical signals transmitted from the opposite end of the one free-space link.

13. A terrestrial optical communication network comprising a plurality of fiber optic links and free-space links between which optical signals are optically coupled by erbium doped fiber amplifiers (ERDAs), wherein a receiving ERDA amplifies the optical signal after its reception over at least one free-space link, and further comprising a controller connected to the receiving ERDA to control the optical power gain of the receiving ERDA, and the control of the optical power gain of the receiving ERDA adjusts the optical power of the optical signal delivered by the receiving ERDA.

14. A terrestrial optical communication network as defined in claim 13 wherein the controller controls the optical power gain of the receiving ERDA in response to the optical power of the optical signals received over the one free-space link at the location of the receiving ERDA.

15. A terrestrial optical communication network comprising a plurality of fiber optic links and free-space links between which optical signals are optically coupled by erbium doped fiber amplifiers (ERDAs), wherein a transmitting ERDA amplifies the optical signal before its transmission over at least one free-space link and a receiving ERDA amplifies the optical signal after its reception over the one free-space link, further comprising a controller connected to the transmitting ERDA to control the optical power gain of the transmitting ERDA and connected to the receiving ERDA to control the optical power gain of the receiving ERDA, and the control of the optical power gain of the transmitting ERDA adjusts the optical power of the optical signal transmitted by the transmitting ERDA over the one free-space link and the control of the optical power gain of the receiving ERDA adjusts the optical power of the optical signal delivered by the receiving ERDA.

16. A terrestrial optical communication network as defined in claim 15 wherein the controller controls the optical power gain of each of the transmitting and receiving ERDAs in response to the optical power of the optical signals received over the one free-space link.

17. A terrestrial optical communication network as defined in claim 16 wherein the controller controls the optical power gain in response to the optical power of optical signals received at the location of the transmitting ERDA.

18. A terrestrial optical communication network as defined in claim 16 wherein the controller controls the optical power gain of each of the transmitting and receiving ERDAs to approximately equal amounts.

19. A terrestrial optical communication network comprising a plurality of fiber optic links and free-space links between which optical signals are optically coupled by erbium doped fiber amplifiers (ERDAs), and further comprising transceivers which transmit and receive the optical signals over the free-space links, and a position adjustment mechanism connected to a transceiver of at least one free-space link to adjust the physical position of the transceiver relative to the optical signals transmitted over the one free-space link to optimize an amount of power provided in the one free-space link by one of the ERDAs.

20. A terrestrial optical communication network as defined in claim 19 wherein the position adjustment is determined by the power of optical signals received by the transceiver over the one free-space link.

21. A terrestrial optical communication network as defined in claim 19 wherein the position adjustment is determined by the impingement on the transceiver of optical signals received over the one free-space link.

22. A terrestrial optical communication network as defined in claim 19 wherein the position adjustment is determined based on position control information transmitted optically over the one free-space link by a transceiver located at the other end of the free-space link.

23. A terrestrial optical communication network comprising a plurality of fiber optic links and free-space links between which optical signals are optically coupled by erbium doped fiber amplifiers (ERDAs), and further comprising transceivers which transmit and receive the optical signals over the free-space links, and a position adjustment mechanism connected to a transceiver of at least one free-space link to adjust the physical position of the transceiver relative to the optical signals transmitted over the one free-space link, wherein the transceiver comprises a transmitting ERDA which amplifies the optical signal before its transmission over at least one free-space link, and a controller connected to the transmitting ERDA to control the optical power gain of the transmitting ERDA and adjust the optical power of the optical signal transmitted by the transmitting ERDA over the one free-space link in response to the optical power of the optical signals received over the one free-space link.

24. A terrestrial optical communication network comprising a plurality of fiber optic links and free-space links between which optical signals are optically coupled by erbium doped fiber amplifiers (ERDAs), and further comprising transceivers which transmit and receive the optical signals over the free-space links, and a position adjustment mechanism connected to a transceiver of at least one free-space link to adjust the physical position of the transceiver relative to the optical signals transmitted over the one free-space link, wherein the transceiver comprises a transmitting ERDA which amplifies the optical signal before its transmission over at least one free-space link and a receiving ERDA which amplifies the optical signal after its reception over the one free-space link, and a controller connected to the transmitting ERDA and the receiving ERDA, the controller controlling the optical power gain of the transmitting ERDA to adjust the optical power of the optical signal transmitted by the transmitting ERDA over the one free-space link, the controller controlling the optical power gain of the receiving ERDA to adjust the optical power gain of the optical signal delivered by the receiving ERDA, the controller controlling the optical power gain of at least one of the transmitting and receiving ERDAs in response to the optical power of the optical signals received over the one free-space link.

25. A terrestrial optical communication network comprising a plurality of fiber optic links and free-space links between which optical signals are optically coupled by erbium doped fiber amplifiers (ERDAs), and further comprising a transmitting ERDA and a receiving ERDA at a terminal end of each link, and a controller connected to at least one of the transmitting ERDA or the receiving ERDA to control the connected ERDA, and wherein an optical signal communicated over the link contains information received by the controller to manage the operation of the connected ERDA.

26. A method of terrestrial optical communication comprising the steps of:

establishing a plurality of fiber optic links and free-space links between which optical signals are communicated;

optically coupling the optical signals between the fiber optic and free-space links without electro-optical conversion; and

controlling optical power of an optical signal transmitted over one of the free-space links in response to an optical signal received over the free-space link.

27. A method of terrestrial optical communication as defined in claim 26 wherein the step of optically coupling the optical signals without electro-optical conversion comprises optically coupling the optical signals between the fiber optic and free-space links with erbium doped fiber amplifiers (ERDAs).

28. A terrestrial optical communication network comprising a plurality of links over which optical signals are communicated, comprising a transmitting ERDA which amplifies an optical signal before its transmission over a free-space link and a controller connected to the transmitting ERDA to control the optical power gain of the transmitting ERDA and to adjust the optical power of the optical signal transmitted over the free-space link in response to the optical power of optical signals received over the free-space link.

29. A terrestrial optical communication network as defined in claim 28 wherein the controller controls the optical power gain of the transmitting ERDA in response to the optical power of the optical signals received at an opposite end of the free-space link from which the optical signals were transmitted.

30. A terrestrial optical communication network as defined in claim 29 wherein the controller controls the optical power gain of the transmitting ERDA in response to control information contained in optical signals transmitted from the opposite end of the free-space link.

31. A terrestrial optical communication network as defined in claim 28 further comprising a receiving ERDA which amplifies the optical signal after its reception over the free-space link, and wherein the controller is also connected to the receiving ERDA to control the optical power gain of the receiving ERDA and adjust the optical power of the optical signal delivered by the receiving ERDA.

32. A method of terrestrial optical communication comprising the steps of:

establishing a plurality of links between which optical signals are communicated;

amplifying an optical signal before its transmission over a free-space link;

sensing the optical power of optical signals received over the free-space link;

adjusting the optical power of the optical signal transmitted over the free-space link in response to the sensed optical power of the optical signals received over the free-space link.

33. A method of terrestrial optical communication as defined in claim 32 further comprising the step of:

amplifying an optical signal received over the free-space link before the signal is delivered for use.

34. A terrestrial optical communication network comprising a plurality of links over which optical signals are communicated, comprising a transceiver which transmits and receives optical signals communicated over a free-space link and a controller connected to the transceiver to control the physical position of the transceiver relative to the optical signal path of the free-space link in response to the optical signals received over the free-space link to optimize an amount of power provided in the free-space link by a fiber amplifier.

35. A method of terrestrial optical communication comprising the steps of:

establishing a plurality of links between which optical signals are communicated;

positioning a transceiver at an end of a free-space link;

connecting an adjustment mechanism to the transceiver to adjust the position of the transceiver; and

adjusting the position of the transceiver by controlling the adjustment mechanism in response to the optical signals received by the transceiver over the free-space link to optimize an amount of power provided in the free-space link by a fiber amplifier.

36. A method of communicating optical signals over a free-space link, comprising:

receiving a first optical signal of a predetermined fundamental wavelength used in a long-haul fiber optic communication system from a first fiber optic conductor;

amplifying the first optical signal of the predetermined fundamental wavelength with a fiber amplifier connected in-line with the first fiber optic conductor to form an amplified first optical signal of the predetermined fundamental wavelength;

directing the amplified first optical signal of the predetermined fundamental wavelength through the free-space link with a beam focusing element optically coupled to the fiber amplifier; and

controlling a power gain of the fiber amplifier in response to a second optical signal received over the free-space link.

37. A method in accordance with claim 36, wherein the step of controlling the power gain of the fiber amplifier further comprises the step of:

controlling the power gain of the fiber amplifier in response to a determined strength of the second optical signal.

38. A method in accordance with claim 36, wherein the step of controlling the power gain of the fiber amplifier further comprises the step of:

control the power gain of the fiber amplifier in response to control information contained in the second optical signal.

39. A method in accordance with claim 36, wherein the beam focusing element is optically coupled to the fiber amplifier with a second fiber optic conductor.

40. A method in accordance with claim 36, wherein the fiber amplifier comprises an erbium doped fiber amplifier (ERDA).

41. A method in accordance with claim 36, wherein the predetermined fundamental wavelength is approximately equal to 1.55 micrometer (um).

42. An optical transceiver for communicating optical signals over a free-space link, comprising:

a first fiber optic conductor;

a fiber amplifier connected in-line with the first fiber optic conductor and configured to receive a first optical signal of a predetermined fundamental wavelength used in a long-haul fiber optic communication system from the first fiber optic conductor and amplify its optical signal power to form an amplified first optical signal of the predetermined fundamental wavelength;

a beam focusing element optically coupled to the fiber amplifier and configured to direct the amplified first optical signal of the predetermined fundamental wavelength through the free-space link; and

a controller configured to control a power gain of the fiber amplifier in response to a second optical signal received over the free-space link.

43. An optical transceiver in accordance with claim 42, wherein the controller is further configured to control the power gain of the fiber amplifier in response to a determined strength of the second optical signal.

44. An optical transceiver in accordance with claim 42, wherein the controller is further configured to control the power gain of the fiber amplifier in response to control information contained in the second optical signal.

45. An optical transceiver in accordance with claim 42, wherein the beam focusing element is optically coupled to the fiber amplifier with a second fiber optic conductor.

46. An optical transceiver in accordance with claim 42, wherein the fiber amplifier comprises an erbium doped fiber amplifier (ERDA).

47. An optical transceiver in accordance with claim 42, wherein the predetermined fundamental wavelength is approximately equal to 1.55 micrometer (um).

INTRODUCTION

This invention relates to terrestrial optical communication, and more particularly to a new and improved all-optical terrestrial optical communication network which integrates both fiber and free-space links without requiring electro-optical conversion between the fiber and free-space links, and which achieves a relatively good link power margin for reliable communication in adverse atmospheric conditions, which seamlessly integrates with long-haul fiber backbone links, which provides safety against unintended eye injuries, and which is implemented with relative convenience and cost-effectiveness.

BACKGROUND OF THE INVENTION

Modern society requires that enormous amounts of information be transmitted between users in a relatively error-free manner. Most of the information is communicated as digital information, primarily because digital techniques allow more information to be communicated quickly and reliably, and because a significant amount of the information is transferred between computers. The use of computers and the evolution of computer technology is responsible for much of the increased demand for information communication. The demand for information communication has increased dramatically during the past few years and is expected to continue well into the future.

The typical medium which carries a significant amount of the information is electrical conductors or copper wires. The telephone system, having been installed for many years, is the primary media used for local or localized communications. Using wired media for telecommunications and high speed data communications creates difficulties, and these difficulties arise because of the wires. Electrical wires introduce a practical limit to the physical length or distance over which the information can travel. Lengthy conductors attenuate the signals to the point where the recognition of signals becomes difficult or impossible. Signals conducted over the wires also have a finite limit to the signaling frequency and hence the amount of information which they can carry. Furthermore, noise is relatively easily picked up or induced into the wires, and the noise tends to corrupt the signals carried by the wires. Wire conductor media is also difficult or impossible to install in many situations. Some metropolitan areas simply have no available space to accommodate the additional conductors within utility conduits, and gaining access to buildings and right-of-way to install the conductors is usually difficult or impossible and is certainly costly. For these and other reasons, many of the advancements in communications have focused on wireless media for communicating information.

Radio frequency (RF) transmissions avoid many of the physical problems associated with wired media. The atmosphere becomes the medium for the RF communications, and thus physical limitations associated with access, space, and right-of-way are no longer paramount problems. However, because the atmosphere is freely available for use by all authorized users, the possibility of interference is always present. Various techniques have been devised to minimize RF interference, but those techniques are relatively expensive to implement. Furthermore, even those techniques are not effective to assure that enormous amounts of information can be communicated reliably through RF broadcasts, simply because the information is broadcast and can not be confined to secure communication channels or links which could eliminate sources of interference.

Optical media offers many advantages compared to wired and RF media. Large amounts of information can be encoded into optical signals, and the optical signals are not subject to many of the interference and noise problems that adversely influence wired electrical communications and RF broadcasts. Furthermore, optical techniques are theoretically capable of encoding up to three orders of magnitude more information than can be practically encoded onto wired electrical or broadcast RF communications, thus offering the advantage of carrying much more information.

Fiber optics are the most prevalent type of conductors used to carry optical signals. Although the disadvantage of fiber optic conductors is that they must be physically installed, the fact that an enormous amount of information can be transmitted over the fiber optic conductors reduces the number of fiber optic conductors which must be installed. This avoids some of the problems in metropolitan areas were space for additional cables is difficult to obtain. In those circumstances where the information is communicated over long distances, fiber optic conductors are the typical medium employed for such long-haul transmissions.

Free-space atmospheric links have also been employed to communicate information optically. A free-space link extends in a line of sight path between the optical transmitter and the optical receiver. Free-space optical links have the advantage of not requiring a physical installation of conductors. Free-space optical links also offer the advantage of selectivity in eliminating sources of interference, because the optical links can be focused directly between the optical transmitters and receivers, unlike RF communications which are broadcast without directionality. Therefore, any adverse influences not present in this direct, line-of-sight path or link will not interfere with optical signals communicated.

Despite their advantages, optical free-space links present problems. The quality and power of the optical signal transmitted depends significantly on the atmospheric conditions existing between the optical transmitter and optical receiver at the ends of the link. Rain drops, fog, snow, smoke, dust or the like in the atmosphere will refract or diffuse the optical beam, causing a reduction or attenuation in the optical power at the receiver. The length of the free-space optical link also influences the amount of power attenuation, because longer free-space links will naturally contain more atmospheric factors to potentially diffuse the optical beam than shorter links. Furthermore, optical beams naturally diverge as they travel greater distances. The resulting beam divergence reduces the amount of power available for detection. If the attenuation of the optical beam is sufficiently great, the ability to recognize the information communicated on a reliable basis is diminished, and the possibility that errors in communication will arise is elevated. Atmospheric attenuation particularly diminishes the probabilities of error-free communications at higher transmission frequencies, because atmospheric attenuation naturally occurs to a greater extent at higher optical frequencies, i.e. shorter wavelengths, than at lower optical frequencies.

One approach to reducing the adverse influences of atmospheric attenuation is to use laser beam transmissions in the free-space links at frequencies which are capable of greater penetration and less refraction or diffusion by atmospheric influences. Unfortunately, the more penetrating frequencies are sometimes also the ones which can easily damage hu