WO1987006084A1

WO1987006084A1 - Optical communication system

Info

Publication number: WO1987006084A1
Application number: PCT/US1987/000483
Authority: WO
Inventors: Ernest Eisenhardt Bergmann
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1986-03-27
Filing date: 1987-03-04
Publication date: 1987-10-08
Anticipated expiration: 1988-09-27
Also published as: KR880701500A; EP0261201A1; CA1257652A; US4775971A; KR910003238B1; JPS63502946A

Abstract

A bidirectional optical communication system is capable of sharing a single light source (14), located at a central communication point, among a large plurality of users. Additionally, the system requires only one single mode fiber (18) between each user and the central location to support its bidirectional communication. The system also has the capabilities to control the signal power sent to each subscriber, send more than one signal to each subscriber (voice and/or data and video), and switch to a back-up light source upon failure of the primary light source.

Description

OPTICAL COMMUNICATION SYSTEM

Background of the Invention

1. Field ΩL _ s. Invention

The present invention relates to an optical communication system and, more particularly, to such a communication system capable of sharing a small number of light sources, located at a central communication point, among a plurality of users for providing bidirectional communication, (utilizing optical fibers) between the users and the central communication point.

2. Description oi _h_ι Prior Ad. Light wave communication systems are continuously evolving and becoming more robust. As fiber optics replace conventional copper conductors, the need arises to make these systems economically attractive for the individual subscriber. One method of minimizing cost is to reduce the number of individual fibers needed to provide two-way (i.e. bidirectional) communication between the subscriber and a central communication point (referred to as the central office). The prospect of communicating in both directions on a single optical fiber is attractive for several reasons: (1) lower cost of fiber cable, (2) ease of deployment and retrieval for portable systems, and (3) doubling of traffi capacity on existing cable lines. One such system is described in the article "Two-Way Transmission Experiments Over a Single Optical Fibre at the Same wavelength Using Micro-Optic 3dB Couplers" by K. Minemura et al appearing in Electronics Letters, Vol. 14, No. 11, May 1978 at pp. 340-2. The transmissio system, as described, utilizes micro-optic 3dB couplers, a single pseudo-step- index optical fiber, GaAlAs LEDs, conventional Si PIN photodetectors, and TT interface circuits. Although capable of achieving bidirectional communication, this arrangement requires extensive circuitry at both ends of the communicatio path, each end also requiring its own light source (LED) which can add significantly to the cost of the system. Many other systems exist which share a least some of these same problems (extensive circuitry, light sources at each en a separate fiber for each signal direction, etc.).

A need remains in the prior art, therefore, for a bidirectional communication system which is inexpensive and, ideally, does not require an independent light source at each end of the communication path. Summary of the Invention

The optical system includes a central location comprising a first light source the output of which is subdivided by a power divider arrangement into number of separate output carrier light waves, and a modulation arrangement for adding an information signal to each carrier wave which is then transmitted over an optical fiber to a remote location receiver.

The receiver comprises a detector for recovering the signal transmitted thereto, and means for redirecting the received carrier wave back along the optical fiber to the central location. The receiver includes modulating means fo adding a return signal to the redirected carrier wave. The central location includes means for receiving and recovering the return signal from the receiver. Brief Description of the Drawing

FIG. 1 illustrates in simplified block diagram form an exemplary bidirectional optical communication system utilizing a shared light source formed in accordance with the present invention;

FIG. 2 illustrates an exemplary integrated optical device which may be utilized at a central communication location to provide bidirectional communication in the systems as illustrated in FIG. 1;

FIG. 3 illustrates an exemplary integrated optical device which may be utilized at a remote location to provide bidirectional communication for the system of the present invention as illustrated in FIG. 1; and

FIG. 4 illustrates an alternative optical structure which may be utilized at a central communication location which is capable of sharing, through active and/or passive power division, a single light source among a large multiple of users.

Detailed Description

FIG. 1 illustrates, in simplified block diagram form, an optical communication system 10 formed in accordance with the present invention. A central communication location 12, hereinafter referred to as a central office, utilizes a single light source 14 to communicate with a plurality of N subscribers 16 over a plurality of N optical fibers 18, one fiber associated with each subscriber. Light source 14 may comprise, for example, a solid-state laser (GaAs, GaALAs, InP, etc.), an edge-emitting LED, or any other source capable of providing a carrier signal which can serve as the basis for later modulation in the creation of an information signal. Referring to central office 12, the output carrier light wave I from light source 14 is applied as an input to an optical structure 20, where structure 20 is discussed in greater detail in association with FIGS. 2 and 4. Structure 20 is also responsive to a plurality of N modulation sources 24 which are utilized to impart the desired information 5,- onto carrier light wave I. As shown in block diagram form, structure 20 includes a power divider and modulation network 26 responsive to both light source 14 and modulators 24 for directing the appropriate signal T_{ into the associated fiber 18,- to subscriber 16,-. At subscriber 16,-, a detector 28,- is utilized to recover the modulated signal T.-, where detector 28,- may comprise, for example, a p-i-n photodiode, a phototransistor- or an avalanche photodiode. A modulator 38,- present at subscriber 16,- is then utilized to remodulate the received signal T,- to transmit a return signal R_{ back to central office 12 over fiber 18,-. A detector is included in central office 12 (not shown), similar to detector 38,- at subscriber 16,-, for recovering the return information. Thus, in accordance with the present invention, two-way transmission over a single fiber is achieved between central office 12,- and a subscriber 16,-, where light source 14 is shared among a plurality of subscribers 16.

An advantage of the optical communication system of the present invention is the ability to utilize integrated optical components to perform the functions briefly outlined above. The use of such components results in an extremely compact, relatively low-cost arrangement. Some penalty is paid, however, for complete integration (i.e., all necessary components formed on a single substrate) as is discussed below. FIG. 2 illustrates an exemplary embodiment of a portion of central office

12 where both active power dividers and modulators are formed on a single substrate 39. . .

Incoming carrier light wave I from light source 14 is coupled via a single optical fiber 32 to a waveguide 36 formed in substrate 39. Alternatively, light source 14 may be directly mounted on substrate 39 and would therefore not require the interconnecting fiber. In this example, lithium niobate is the material utilized to form substrate 39 and diffused titanϊa is the material for forming the various waveguides in substrate 39. However, other materials, such as lithium tantalate or strontium-barium niobate with titania diffused waveguides may also be used. Carrier light wave I subsequently travels along waveguide 36 and enters an active power network 38 comprising a plurality of electrode arrays, where these arrays are illustrated in FIG. 2 by single shaded areas for the sake of clarity. It is well known that power dividers utilizing such electrode structures comprise a pair of electrodes, formed to comprise a particular geometry, depending on the crystallographic orientation of the optical substrate. For the arrangement illustrated in FIG. 2, power divider 38 comprises three electrode arrays 40, 42 and 44 utilized to divide carrier light wave I into four output signals, denoted 7₃, J₄, I₅ and I_s, of predetermined power levels. By utilizing an active power divider, as explained in detail hereinafter, the power sent to different subscribers can be continuously adjusted as the nee arises. Alternatively, if a known set of subscribers will never require differing power levels, a passive power divider capable of performing predetermined splitting of the incoming power level can be utilized, as described in detail later in association with FIG. 4.

In order to provide the first step in the desired power division shown in FIG. 2, an additional waveguide 37, formed as shown, is coupled with waveguid 36. An appropriate external control signal G_γ applied to electrode array 40 will modify the index of refraction of substrate 39 in the vicinity of array 40. This modification will cause a change in the coupling of light between waveguides 36 and 37, where the strength of control signal G_x will determine the change in the amount of coupling. Thus for a predetermined value of control signal G carrie light wave I will be partially coupled into waveguide 37, resulting in two output carriers 7_t and I_ of predetermined power levels. The next branch of power division proceeds, as shown in FIG. 2, in two parallel paths. In particular, carrier I_x appearing along waveguide 36 travels along into the vicinity of electrode array 42, where an additional waveguide 46 is utilized to provide coupling with carrier I_x. As explained above, for a predetermined control signal C₂, carrier light wave I_x will partially couple into waveguide 46 to produce two separate output carriers _^" ₃ and _^" ₄ of predetermined power levels. Similarly, carrier light wave I₂ appearing along waveguide 37 enters the vicinity of electrode array 44 and in association with an additional waveguide 48 produces two separate output carriers I_B and /„ of predetermined power levels as controlled by the strength of control signal C₃.

From the above discussion, it is obvious that control signals C , C₂, and C₃ may be utilized to actively optimize the performance of the system. For example, if a subscriber 16_t (not shown) is located relatively close to central office 12 and a subscriber 16₄ is at a rather extreme distance, power divider network 38 may be configured, by modifying the magnitude of control signals C_x, C₂ and C₃ to send a signal J₃ of power 1/8 to subscriber I6_t and a signal I. of power 31/8 to subscriber 16₄ to ensure reception of a strong signal by both subscribers. Additionally, if a particular subscriber is to be totally removed from the system, the adjustment of the appropriate control signals will cause the associated power splitters to provide power only to the remaining subscribers. Thus, as can be seen, the active power switching system of the present invention affords a great deal of continuing flexibility to the central office.^* Further, as stated above, if active monitoring is considered too great a burden for a given central office, passive power division may be employed, where each subscriber will receive a signal of a predetermined power level, regardless of distance from the central office. Such an arrangement might be feasible, for example, when the total communications network is contained within a portion of a large metropolitan area and the most remote subscriber will still be relatively close to the central office.

A modulation arrangement 50 as shown in FIG. 2 may be utilized to impart the desired information signal onto carriers I*- * A plurality of four modulation/information sources 24₁-24₄ provides the information signals. These sources may be, for example, voice, data, and/or video information. As with power divider network 38, electrodes and waveguides may be utilized to couple the desired information into the appropriate waveguide. In particular, a first information signal S is applied to an electrode array 54 which provides coupling between an additional waveguide 56 and carrier I_s traveling along waveguide 46. The application of signal S_x to electrode array 54 will thus modify carrier I_z and provide the desired output signal T_x which is subsequently transmitted over fiber I8_t to subscriber I6_t (not shown). Similarly, information signal S₂ is coupled via an electrode array 58 and waveguide 60 to carrier signal J₄ traveling along waveguide 36 to modulate carrier J₄ and generate output signal T₂. Output signals T₃ and T₄ are produced in a similar manner, where electrode array 62 and waveguide 64 react with carrier signal I₅ traveling along waveguid 37 to produce T₃ and electrode array 66 and waveguide 68 are associated with carrier signal I_s along waveguide 48 to produce output signal T₄. As discussed above, a return signal R from the subscriber (which is usually voice and/or data) travels along the same optical fiber 18 back to central office 12. The arrangement illustrated in FIG. 2 includes components capable of recovering this return signal. As shown in association with return signal R_x, a waveguide 70 is formed to "pick off" a portion of the returning signal which travels back along fiber I8_t and enters waveguide 46. Since the coupling between waveguides 70 and 46 may allow some of return signal R_x to propagate along waveguide 46, the system of the present invention may be designed to prevent an appreciable amount of this propagation. For example, the transmitted signal T_x may be formed to comprise a first polarization, for example, TM (transverse magnetic), and return signal R to comprise the orthogonal TE polarization (transverse electric). Thus, return waveguide 70 would be completely transparent to transmitted signal T_x and would pick off 100% of return signal R . Alternatively, if the polarization of the signals canno be controlled at the subscriber or maintained along the length of fiber 18_! between central office 12 and subscriber 16,., an active polarization controlling component may be included at the coupling between fiber I8_t and waveguide 4 (not shown) to provide the desired polarity to return signal R_x. It is to be understood, however, that these and other means of maintaining a predetermined polarization of signals T and R are utilized only to improve th system performance, since the propagation of a portion of return signal R_x alon waveguide 46 will not destroy the communication path. The only harm to the system is in terms of the power degradation of the return signal coupled into waveguide 70. As shown in FIG. 2, a photodetector 72 is coupled to waveguide 70 to recover signal R_x. As with detectors 28 of FIG. 1, detector 72 may comprise a p-i-n photodiode, a phototransistor, an avalanche photodiode, or any other arrangement capable of converting a received optical signal into an associated electrical signal. In a similar manner, return signal R₂ from subscriber 16₂ may be recovered utilizing a waveguide 74 and detector 76, configured as shown in FIG. 2. Likewise, td recover the signals transmitted by subscribers 16₃ and 16₄, return signal R₃ is coupled via a waveguide 78 to a detector 80 and return signal i?₄ is coupled via a waveguide 82 to a detector 84. As mentioned above, an additional aspect of the present invention is the ability to provide a "spare" light source at the central office which can be switched in when the first fails. Alternatively, this spare light source may be utilized to provide a pair of transmitters which operate simultaneously and may utilize different transmitting wavelengths, for example, to transmit two different messages to one subscriber over the same fiber. Other uses of a spare light source are possible. This provision is illustrated in FIG. 2 by additional light source 90 coupled via an optical fiber 92 to waveguide 37 (where light source 90 may also be directly mounted on substrate 39). Therefore, if light source 14 fails, second source 90 will be activated to provide the input carrier light wave F which will travel through the same waveguide structure as discussed above and subsequently form output signals 7yτ₄. If, as mentioned above, it is desired to operate both sources 14 and 90 simultaneously (source 14 providing an output carrier I_A at a wavelength \_A, source 90 providing an output carrier I_B at a wavelength \_B, \_A ≠ \_B, power divider network 38 may be controlled to actively switch between the two sources. In particular, for the arrangement shown in FIG. 2, control signal C_x is used to control the degree of -coupling between waveguides 36 and 37 and thus provide transmission of either carrier I_A or carrier I₃ along the remaining signal paths. As a further extension of this aspect, it is obvious that yet additional light sources could be incorporated into the system of the present invention as "spares" if it is desired to simultaneously employ both sources 14 and 90.

An exemplary subscriber arrangement 16 for use in accordance with the present invention is illustrated in FIG. 3. As with the central office configuration illustrated in FIG. 2, the subscriber arrangement utilizes an optical substrate 96, for example, lithium niobate, to aid in both recovering the transmitted signal and forming the return information signal. Referring to FIG. 3, transmitted signal T from central office 12 travels along optical fiber 18 whic is coupled at subscriber 16 to a waveguide 98 (preferably comprising diffused titanium) formed in substrate 96. To recover the transmitted information, signal T may travel the length of substrate 96 and be reflected off of a mirror 100 to travel back along coupled waveguides 98 and 102 into detector 28 and toward fiber 18, where the details of detector 28 were previously discussed. In order to impart return information to incoming signal T, external modulator 38 (which is usually a source of voice and/or data information) is applied to an electrode array 104 formed on substrate 96. As with the modulators present at central office 12, the information signal S_R from modulator 38 will alter signal T and form the return information signal R. Thus, by utilizing the incoming signal form central office 12 as the carrier for the return message signal, subscriber 16 does not require a separate light source to generate return signal R. This bidirectional aspect of the present invention realizes a great saving in cost in terms of the equipment needed at the subscriber's location.

As discussed above, it is possible that information from two sources may be broadcast over fiber 18 to subscriber 16. For example, one signal may represent video information and the other represent voice and/or data. In this instance, therefore, subscriber 16 must include additional components capable of handling both incoming signals. One exemplary arrangement capable of performing this task is also illustrated in FIG. 3, where a totally reflective mirror 100 is replaced with a partially reflective mirror 110, also referred to as a dichroic mirror 110. Mirror 110 is chosen such that the wavelength associated with a first of the transmitted signals will be reflected completely and routed over waveguides 98 and 102, as described above, into detector 28 and, also, bac along waveguide 98 to form the carrier for the return signal. However, the second, remaining information signal will pass through unaffected by mirror 11 and into a second photodetector 112, where the information is extracted from the signal. In a practical application, the first signal could be voice and/or data, where the subscriber wishes to send a return signal back to the central office. The second signal, which in the embodiment described above is a one¬ way transmission, could be video, where it is unlikely that a subscriber would want to broadcast video back to the central office. However, additional components, in particular an additional electrode array and modulator, could be added to the arrangement of FIG. 3 to provide a means for bidirectional video communication and such is within the scope of the present invention. In most systems utilizing the teachings of the present invention, the input light source will be a laser, edge-emitting LED, or other high-power device. As previously mentioned, a large portion of this input power could be wasted if off-chip power division methods are not utilized. For example, a high power conventional laser can easily support bidirectional communication with over a hundred separate subscribers. Current techniques of forming integrated optical components, however, limit the number of subscribers which can be supported on a single substrate to approximately eight. Thus, a laser power over ten times that required is transmitted between the central office and t e subscribers. Therefore, to maximize the use of the laser, many sequences of power division may be performed to reduce the input power level to an individual substrate and hence allow a single laser to be shared among a plurality of separate optical substrates.

An exemplary power division arrangement for use at a central office 12 t provide the sharing of a single light source among a plurality of N subscribers, with optical components formed on a plurality of separate substrates, is illustrated in FIG. 4. It is to be understood that the arrangement is exemplary only, for the purposes of illustrating various power division techniques and combinations thereof, and many other variations exist which can be used. The primary light source is a laser 120 which emits a output light of intensity I. This output light is passed through a single mode optical fiber 122 and enters a fused fiber coupler 124 where the power is divided into components of equal value 1/2. Alternatively, fused fiber coupler may be designed to provide any desired power split. Fused fiber couplers themselves are well known in the art, one example being disclosed in U. S. Patent 4,431,260. One of the output light waves from fused fiber coupler 124 subsequently travels along a fiber 126 and enters an integrated power splitter 130, which may be formed on a lithium niobate substrate 131. Power splitter 130 as illustrated in FIG. 4 is a passive device, where the splitting ratio between the two output light waves is fixed when power splitter 130 is formed. Input light wave along fiber 126 enters a first waveguide 132 formed in substrate 131. A second waveguide 134 is also formed in substrate 131 and is positioned relative to waveguide 132 such that a coupling of the light signal takes place, providing a pair of separate output ligh waves, each having a predetermined power level, where equal power levels of 1/ are shown for the sake of illustration in FIG. 4.

The second, remaining output from fused fiber coupler 124 travels along a fiber 128 and enters a second power splitter 136. Like power splitter 130 previously described, second power splitter 136 is an integrated optical device formed on an optical substrate 137. However, unlike power splitter 130, second power splitter 136 is an active device capable of providing any predetermined ratio of power splitting. As shown in FIG. 4, power splitter 136 includes a first waveguide 138 coupled to receive the input light wave traveling along fiber 128. An electrode array 140 is positioned over a portion of waveguide 138 and a second waveguide 142 is formed to couple a portion of the light traveling along waveguide 138, as controlled by the application of a control signal C to electrod array 140. The two output signals from power splitter 136, therefore, will comprise power levels as. controlled by signal C, where these power levels are designated as X and - — in FIG. 4.

_.

For a high power laser source, many further power divisions may be performed before proceeding with the actual modulation to create the information signals sent to the subscribers. One additional branch of power splitting is illustrated in FIG. 4 for the sake of discussion, with the dotted lines indicating the presence of further power splitting. In particular, an additional passive power splitter 146 is illustrated as responsive to a first output from power splitter 130 traveling along a fiber 144, where passive power splitter 146 comprises a set of waveguides 148, 150, 152 and 154 disposed as shown on an optical substrate 155 to form a set of four separate output signals, where in one embodiment each of these signals may have an equal power level of 1/16. Another fused fiber coupler 158 is shown as responsive to remaining 1/4 power level output from power splitter 130 traveling along a fiber 156. As shown, fused fiber coupler 158 provides two separate output light waves of 1/8 power along a pair of fibers 160 and 162. The first output of power X from active power splitter 136 which travels along a fiber 164 is subsequently applied as an input to a passive power splitter 166 including a pair of waveguides 168 and 170 formed on an optical substrate 171. As shown in FIG. 4, this particular power splitter is designed to provide a 1:2 power split. The remaining output from active power splitter 136 is shown as traveling along a fiber 172 and being applied as an input to another active power splitter 174, where power splitter 174 includes a plurality of waveguides 176, 178, 180 and 182 and a plurality of electrode arrays 184, 186 and 188 arranged as shown on an optical substrate 189 to provide four output light waves of controllable power levels, as controlled by a set of signals C',C", and C" connected as shown to electrode arrays 184, 186 and 188.

When a sufficient amount of power division has been performed, the light wave carrier signals are applied as separate inputs to a plurality of modulating components

as shown in FIG. 4, where each modulating component may include a different arrangement, three exemplary arrangements being illustrated in FIG. 4. In particular, modulating component I90_t is illustrated as being similar to optical structure 20 illustrated in FIG. 2, including an active power dividing network 192 and a modulating arrangement 194. As with the arrangement illustrated in FIG. 2, the input light carrier i travels along a single mode fiber 196 and is coupled to the waveguides forming power dividing network 192 and is subsequently modulated using modulating sources (not shown) to provide output transmission signals (_:-{₄. Although not shown, it is to be understood that modulating component 190_1} as well as the remaining modulating components, comprise a demodulating arrangement for recovering the return signal transmitted to central office 12 from each subscriber 16. Modulating component 190₂ is illustrated as a variation of component 190_X, where the active power division is replaced with a passive power dividing arrangement 198. A similar modulating network 200 is utilized to produce a pair of output transmission signals .₆ and t_s. Lastly, a simple modulating component 190_W is illustrated as comprising only a single electrode array 202 formed on an optical substrate 204 and controlled by an external modulation signal to form output transmission signal t_N.

Claims

1. An optical communication system for providing bidirectional communication between a central location and a plurality of remote locations

CHARACTERIZED BY a first shared light source (14) located at said central location and a sin optical fiber (18) between said central location and each remote location, said optical transmission system comprising a central location structure (12) including power dividing means (38) responsive to said first shared light source for providing a plurality of output carrier light waves (I), a plurality of modulating means (54, 58, 62, 66), each responsive to both a carrier light wave and a modulating signal (S) from one of plurality of information sources to produce an output transmission signal to be transmitted to one of said remote locations, and a plurality of detecting means (72, 76, 80, 84) each responsive to a separate one of a return information signal transmitted from said plurality pf remote locations to said central location; an each remote location comprises detection means (102, 104, 28) for recovering the signal from the received output transmission signal; and modulation means (38) responsive to a return signal (SR) for remodulating said output transmission signal to form said return information signal transmitted said central location.

2. An optical communication system as defined in claim 1 wherein the central location further comprises at least one additional shared light source (9 and switching means (40,Cl) capable of coupling said at least one additional shared light source to the power dividing means.

3. An optical communication system as defined in claim 2 wherein the least one additional shared light source operates at a different wavelength tha the first shared light source and both light sources are utilized simultaneously transmit separate information signals to the plurality of remote locations.

4. An optical communication system as defined in claims 1 or 2 wherei the central location power dividing means comprises a plurality of optical waveguides (36, 37, 46, 48) formed on an optical substrate (39), one waveguide (36) responsive to the first shared light source, said plurality of waveguides disposed in a manner to form a plurality of output carrier light waves, each light wave receiving a power fraction of the input power from said first shared light source.

5. An optical communication system as defined in claim 4 wherein the at least one integrated optical power divider is a passive power divider for providing a constant power division throughout the plurality of waveguides such that each output carrier light wave comprises a constant power fraction.

6. An optical communication system as defined in claim 4 wherein the least one integrated optical power divider includes an active power divider capable of changing the power fractions associated with the plurality of output carrier waves, said active power divider further comprises a plurality of electrode arrays (40, 42, 44) disposed on said optical substrate and coupled to the plurality of optical waveguides, control signals (C) connected to said electrode arrays effective to vary the refactive index of said optical substrate in the vicinity of said plurality of electrode arrays so as to control the degree of coupling among the plurality of waveguides and thus modify the power fraction associated with the plurality of output carrier light waves.

7. An optical communication system as defined in claim 1 wherein at least one modulating means comprises a pair (46, 56) of optical waveguides is formed on said optical substrate, one of which waveguides responsive to the carrier light wave output of an associated power dividing means; and an electrode array (54) formed on said substrate responsive to one of said modulating signals, said signals capable of modulating the refractive index of said optical substrate in the vicinity of said electrode array so as to form an ^■ output transmission signal.

8. An optical communication system as defined in claim 1 wherein the detecting means comprises an optical -waveguide (70)-formed on the optical substrate for optical coupling to an associated waveguide (46) along which an outgoing signal is transmitted for receipt of an incoming signal transmitted thereon and a detector (72) for recovering the rejected incoming signal.

9. A central location of an optical communication system for providing bidirectional communication with a plurality of remote locations characterized by: power dividing means (38) for providing a plurality of output carrier light waves (I) from a first light source (14); a plurality of modulating means (54, 58, 62, 66) each responsive to both a carrier light wave output and a modulating signal (S) from one of a plurality of information sources to produce an output transmission signal to be transmitted to one of said remote locations over an optical fiber; and a plurality of detecting means (102, 104, 28) responsive to a separate one of a return information signal transmitted from said plurality of locations to said central location.

10. A central location of an optical communication system as defined in claim 9 wherein said central location further comprises at least one additional shared light source (90) and switching means (40) capable of coupling the second shared light source to the power dividing means.

11. A central location of an optical communication system as defined in claims 9 or 10 wherein the power dividing means comprises a plurality of optical waveguides formed on an optical substrate, one waveguide responsive to the first shared light source, said plurality of waveguides disposed in a manner to form a plurality of output carrier light waves, each light wave receiving a power fraction of the input power from said first light source.

12. A central location of an optical communication system as defined in claim 11 wherein the at least one integrated optical power divider is a passive power divider for providing a constant power division throughout the plurality of waveguides such that each output carrier light wave comprises a constant power fraction as a function of time.

13. A central location of an optical communication system as defined in claim 11 wherein the at least one integrated optical power divider is an active power divider capable of changing the power fractions associated with the plurality of output carrier saves, said active power divider further comprising a plurality of electrode arrays disposed on the optical substrate and coupled to the plurality of waveguides, said plurality of electrode arrays capable of being connected to a plurality of control signals for varying the refractive index of sai optical substrate in the vicinity of said plurality of electrode arrays so as to control the degree of coupling among the plurality of waveguides and thus modify the power fraction associated with the plurality of output carrier light - l -

waves.

14. A central location of an optical communication system as defined in claim 9 wherein at least one modulating means comprises a pair of optical waveguides formed on said optical substrate, one of which waveguides is responsive to the carrier light wave output of an associated power dividing means; and an electrode array formed on said substrate responsive to one of said modulating signals, said signals capable of modulating the refractive index of said optical substrate in the vicinity of said electrode arrays so as to form an output transmission signal.

15. A central location of an optical communication system as defined in claim 9 wherein the detecting means comprises an optical waveguide (70) formed on the optical substrate for optical coupling to an associated waveguide (46) along which an outgoing signal is transmitted for receipt of an incoming signal transmitted thereon, and a detector (72) for recovering the rejected incoming signal.

16. A remote location of an optical communication system capable of receiving information from and transmitting information to a central location, said remote location comprising an optically integrated structure formed on an optical substrate and including detection means for recovering an information signal from the central location transmitted signal; CHARACTERIZED BY modulation means (38) responsive to a modulation signal from an information source (SR) for remodulating said central location transmitted signal to from the return information signal transmitted to said central location.

17. A remote location of an optical communication system as defined in claim 16 wherein the optically integrated structure is CHARACTERIZED BY a first waveguide (98) formed on the optical substrate capable of receiving the central location transmitted signal; first photodetection means (112) for recovering the information present i said central location transmitted signal; a second waveguide formed on said substrate and coupled to the first photodetection means; and reflecting means (100) for reflecting the central location transmitting signal into said second waveguide.

18. A remote location of an optical communication system as defined in claim 17 including second photodetection means (28) for recovering the information present in a second transmitted signal; said reflection means being dichroic for reflectin a first transmitted signal into the first photodetection means and said second transmitted signal into said second photodetection means.

19. A remote location of an optical communication system as defined in claim 16 wherein the modulating means comprises an electrode array (104) disposed on the optical substrate responsive to a return modulation signal from the information source (SR) for modulating the refractive index of said optical substrate in the vicinity of said electrode array to from the return information signal.