EP1044529A1

EP1044529A1 - Optical add-drop multiplexer

Info

Publication number: EP1044529A1
Application number: EP98960669A
Authority: EP
Inventors: Thomas A. Hanson; Mark J. Soulliere
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 1997-12-10
Filing date: 1998-12-03
Publication date: 2000-10-18
Also published as: CN1282473A; CA2312960A1; JP2001526415A; AU1621699A; WO1999030454A1; TW421725B

Abstract

An all optical add-drop multiplexer (ADM) includes nonlinear optical loop mirrors (NOLMs) (302, 304) having signal input (I1), gating input (G1), through output (T1) and drop output (D1) ports. A stream of soliton pulses coupled to the gate input (G1), synchronized with soliton signal pulses coupled to the signal input (I1), directs the signal pulses to the drop output (D1) or to the thro output (T1), depending upon the presence or abscence of solitons in the gate signal. Operations such as logic INVERSION and logic AND are effected by the NOLMs (302, 304) and signals may be added through a combination of operations equivalent to a logic 'OR'. Such combinations are employed to produce one or more drops and one or more adds in an add-drop multiplexer.

Description

OPTICAL ADD-DROP MULTIPLEXER BACKGROUND OF THE INVENTION This application is based upon the provisional application S.N. 60/067,177, filed 12/10/97, which we claim as the priority date of this application. Field of the Invention

The present invention is related generally to improvements in optical data transmission systems and, more particularly, to time division multiplexing of optical soliton signals.

Description of the Related Art

Under certain conditions shape-maintaining pulses of electromagnetic radiation, called solitons, can exist in single mode optical fibers. Soliton-based optical transmission systems offer the potential of extremely high bandwidth and a number of soliton optical transmission systems have been disclosed. See, for example, U.S. Patent No. 4,700,339 entitled Wavelength

Division Mutliplexed Soliton Optical Fiber Telecommunication System, which is hereby incorporated by reference in its entirety. Time division multiplexing (TDM) could be employed to take advantage of the extremely high bandwidth offered by soliton-based communications systems by combining lower bit rate signals into a higher bit rate signal, typically with the presence of a soliton representing a logic " 1 " and the absence representing a logic "0". In such a system, soliton streams of relatively low density, each having a nanosecond time slot for example, could be combined to create a data stream having half-nanosecond time slots, corresponding to a data rate of two gigabits per second (GBs).

In telephony applications, signals are typically added to and deleted from one another in an "Add-Drop Multiplexer" (ADM), as illustrated in FIG. 1. In a digital ADM, a relatively densely packed, or high data rate, stream of electronic pulses enters the ADM 100 at an input labeled Incoming and has a portion of its data, corresponding to a series of time slots, stripped off and routed to an output labeled Drop. The remaining data is routed to another output labeled Outgoing. The data traveling to the outgoing output is combined with data from an input labeled Add. Data from the Add input is inserted into the time slots vacated by the data routed to the drop output. An ADM could be implemented in hybrid form, with light signals converted to digital electronic signals, then dropped and added as desired and, finally, converted from digital electronic signals to optical soliton signals. The disadvantages to such a hybrid system include the introduction of noise and the concomitant increased likelihood of transmission errors, the limited speed of operation of electronic systems, the relatively high cost of operation associated with electronic systems and, particularly for very high speed signals, the relatively high cost of the electronics equipment.

With hybrid optical ADMs probably limited to operation at tens of gigabits per second, it is likely that an all-optical ADM could provide operation at data rates beyond the capability of hybrid ADMs. That is, an all optical system should be able to support data rates of up to 100 GBs in the near term and in excess of one terabit per second

(TBs) in the future, thus increasing operational speed by more than an order of magnitude in comparison with hybrid ADMs. An all-optical ADM which reduces both initial and operating costs, improves reliability, and, perhaps most significantly, provides extremely high-speed operation would therefore be highly desirable and advantageous.

SUMMARY OF THE INVENTION The present invention is directed to an all-optical add-drop multiplexer (ADM) which permits low cost, high reliability data communication at bit rates in the tens of gigabits per second.

In a presently preferred embodiment, an all optical add-drop multiplexer (ADM) includes nonlinear optical loop mirrors (NOLMs) having signal input, gating input, through output, and drop output ports. A stream of soliton pulses coupled to the gate input and synchronized with soliton signal pulses coupled to the signal input, directs the signal pulses to the drop output or to the through output, depending upon the presence or absence of solitons in the gate signal. By directing gating signals to different inputs and by employing different NOLM outputs, operations such as logic INVERSION and logic AND are effected by the NOLMs. Signals may be added through a combination of operations equivalent to a logic "OR" and signals may be dropped by virtue of the NOLM's gating action. NOLMs may be cascaded to add or to drop signals and NOLM combinations are employed to produce one or more drops and one or more adds in an add-drop multiplexer.

These and other features, aspects and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a prior art electronic add-drop multiplexer.

FIGs. 2A, 2B and 2C are a block diagram, a Through output truth table, and a Drop output truth table, respectively, for a nonlinear optical loop mirror (NOLM) in accordance with the present invention.

FIG. 3 is a block diagram illustrating the cascading of NOLMs to produce multiple Drop outputs in accordance with the present invention.

FIG. 4 is a block diagram illustrating another approach to cascading NOLMs to produce multiple Drop outputs in accordance with the present invention. FIGs. 5A and 5B are a block diagram and a truth table, respectively, for a logic

OR function which would prove useful in the implementation of an ADM in accordance with the present invention.

FIG. 6 is a truth table which illustrates the translation between AND and OR logic operations which permits the NOLM to provide Drop and Add multiplexing in accordance with the present invention.

FIG. 7 is a block diagram of an NOLM connected to invert, or negate, an input signal in accordance with the present invention.

FIG. 8 is a block diagram which illustrates a combination of NOLMs connected to yield a one-drop, one-add ADM in accordance with the present invention.

FIG. 9 is a block diagram of another NOLM combination which yields a one- drop, one-add ADM in accordance with the present invention.

FIG. 10 is a truth table used to illustrate an approach to providing multiple adds in an ADM according to the present invention.

FIG. 1 1 is a block diagram of a three-add, three-drop ADM in accordance with the present invention. FIG. 12 is a block diagram illustrating one suitable implementation of an

NOLM for use in conjunction with the present invention.

DETAILED DESCRIPTION OF THE INVENTION An optical demultiplexer in accordance with the present invention may suitably include a nonlinear optical loop mirror having signal input, gating input, through output and drop output ports. A stream of soliton pulses coupled to the gate input, synchronized with soliton signal pulses coupled to the signal input, directs the signal pulses to the drop output or to the through output, depending upon the presence or absence of solitons in the gate signal. Such demultiplexers may be combined to produce an optical add-drop multiplexer (ADM) which offers highly reliable, relatively low cost operation at extremely high data rates, typically in the tens of Gigabits per second.

Optical soliton communication systems employ shape maintaining optical pulses to transmit data, typically with the presence of a soliton interpreted as a logic " 1 " and the absence interpreted as a logic "0". See, for example, U.S Patent No. 5,642,215, entitled Optical Transmission System, U.S. Patent No. 5,471,333 entitled Optical Communication System, U.S. Patent No. 5,530,585 entitled Optical Soliton Transmission System, and U.S. Patent No. 5,523,874 entitled Optical Soliton Pulse Transmission System, all of which are hereby incorporated by reference in their entirety.

The block diagram of FIG. 2A illustrates the operation of a nonlinear optical loop mirror (NOLM) which may be operated in accordance with the present invention. Nonlinear optical loop mirrors are known. See, for example, U.S. Patent No. 5,655,039, which is hereby incorporated by reference in its entirety. An NOLM 200 includes an incoming signal input and a gate input, labeled Incoming and Gate, respectively. Signals introduced to the Incoming input are routed to a Through or a

Drop output, similarly labeled in FIG. 2A, as follows. For a time slot in which a soliton is present at the Gate input, represented by a " 1 ", the signal at the Incoming input is directed to the Drop output. Whenever a time slot at the Gate input does not include a soliton, represented by a "0", the signal at the Incoming input is directed to the Through output. Taking the data streams of the illustration, for example, the first time slot reading from the left includes a 0 at the Incoming input and a 0 at the Gate input. Therefore, the Incoming input, a 0, is routed to the Through output and a 0 is routed to the Drop output. In the second time slot, the signal at the Incoming input is a 0 and that at the Gate input is a 1. Therefore, the Incoming signal, a 0, is routed to the Drop output and a 0 is routed to the Through output. In this, and all subsequent figures, active signals, that is signals derived from the Incoming signal, are represented as bold characters. So that, for example, the second and fourth Drop signals, 0 and 1 respectively are both shown in bold, indicating that the second and fourth Incoming signal values have been routed to the Drop output. Similarly, the first and third Through signal values, 0 and 1, respectively, are also shown in bold to indicate that the first and third Incoming signal values have been routed to the Through output.

FIGs. 2B and 2C are truth tables illustrating the operation of the NOLM 200 relating Incoming, I, and Gate, G, inputs to Through, T, and Drop, D, outputs, respectively. From the truth table point of view, the value of the Drop output is the logical "AND" of the Incoming and Gate signals. The value of the Through output is the logical "AND" of the Incoming value and the negation Gate signal. There is some ambiguity in the output of such a gate. That is, the presence of a logical zero in the bit stream of the Through or Drop signal can indicate either that the corresponding time slot has been "emptied", or "cleared", or that the time slot has a meaningful bit with a logic value of zero for that time slot.

NOLMs, such as NOLM 200 of FIG. 2A, may be cascaded in a cascaded NOLM circuit 300 as illustrated the block diagram of FIG. 3 to obtain a plurality of Drop signals. As shown in FIG. 3, a first NOLM 302 is connected to receive an incoming soliton data stream, labeled I, and a first gating signal Gl . The gating signal Gl routes the incoming signal I as described in relation to FIGs. 2A-2C and as indicated by bold characters in FIG. 3 to produce a first through signal Tl and a first drop signal Dl. The through output Tl of the first NOLM 302 is connected to the incoming signal input 12 of a second NOLM 304 and is also provided as a second gating signal to the gating input G2 of the second NOLM 304. This connection of NOLMs 302 and 304 produces second Through T2 and Drop D2 outputs. The first gate signal Gl routes the Incoming signal in every other time slot, beginning with the second time slot, to the first drop output D 1. The remaining time slots of the incoming signal are further divided between the T2 and D2 outputs by the gating signal G2 which, being equal to 0 in the first time slot, routes the first active time slot of the Tl output to the through output T2 and, being equal to 1 in the third time slot, routes the second active time slot of the through signal Tl, that is time slot three, to the second Drop output D2. In this way, the first Drop signal Dl carries half the incoming signal I while the second drop signal D2 and second through signal T2 each carry one quarter of the Incoming signal I. In general, this approach can be extended to yield N drop signals by routing the (N-l)th Through output to a further cascaded NOLM where it is gated with an Nth Gate signal to produce the Nth Drop signal. It will be recognized that separate gating signals G2 through GN might suitably be provided.

Alternatively, NOLMs may be cascaded through their Drop outputs, to yield a plurality of Drop outputs. In the combination of FIG. 4, the Nth drop signal is created by gating the (N-l)th Drop output with the Nth Gate signal to yield the Drop output. An NOLM 402 receives an incoming data stream at its incoming input II, a Gate input signal at its gating input G(1 :N) and produces through Tl and drop D(1:N) signals, in accordance with the description related to FIG. 2. Again, in this implementation, the Drop output Dl carries the data of every other incoming signal time slot. Outputs D(2:N) and Tl divide the remainder of the incoming signal data. The G(l :N) gate signal indicates the total number of time slots, three in this example, that are to be dropped from the incoming signal to create Dl, D2, . . .DN signals. The G(2:N) signals, of which the G2 could be provided from the Tl output of NOLM 302 of FIG. 3, for example, indicate which time slots should be dropped to create the D2, D3, . . . DN signals.

As illustrated in FIGs. 2-4, an NOLM may be employed in accordance with the present invention to remove bits from an optical bit stream, composed of solitons in the preferred embodiment. That is, an NOLM may be suitably employed to provide the desired "DROP" of an ADM. To produce the ADM's "ADD" function an all-optical logical "OR" circuit, comprising NOLMs, would be highly desirable. The basic functionality of the desired ADD circuit 500 is illustrated in the block diagram of FIG. 5 A. The ADD circuit 500, which would be connected to accept a Through signal in accordance with the presently preferred embodiment, includes an input T and an input A connected to accept Through and Add signals, respectively. It is assumed that signals introduced to the T and A inputs are not overlapping in time. In other words, the active time slots of one signal coincide with inactive time slots of the other signal. Again, active time slots are indicated by bold characters so that the first time slot is active for the T signal and inactive for the A signal, the second time slot is inactive for the T signal and active for the A signal, and so on. The added signal, available at output O, is the logic "OR" of the T and A signals and, since every other time slot was active for each of the added signals, the output signal O is active every time slot, as indicated by the string of bold characters. The truth table of FIG. 5B lists the results of logical combinations at inputs T and A. The combination of 1 + 1 is not allowed as one of the inputs must be inactive and, therefore, at a logic 0.

The truth table of FIG. 6 provides an illustration of a variation on De Morgan's law which indicates that the logic "OR" of signals T and A is equivalent to the logic "AND" of "Not A" and "Not T". As discussed in relation to FIG. 2C, the D output of an NOLM configured in accordance with the present invention provides a logic "AND" of inputs I and G. In the block diagram of FIG. 7, a source of solitons provides a steady stream of logic "Is" for each time slot. This stream of logic "Is" is coupled to the Incoming input of an NOLM 700 and the signal to be inverted, labeled T, is coupled to the Gate input of the NOLM 700. The signal T is available at the Drop output of the

NOLM 700 and its negation, or "NOT T", is produced at the Through output of the NOLM 700.

The block diagram of FIG. 8 illustrates a combination of NOLMs in accordance with the present invention which provides an all-optical ADM implementation preferably for operation with optical solitons. This implementation of the ADM 800 includes a single add input and a single drop output. An NOLM 802 is connected to receive an incoming signal at its input II and a gate signal at its gate input Gl and to produce the ADM's Through and Drop signals. As described above, the NOLM 802 will produce a through signal at its through output Tl and a drop signal at its DROP output Dl. The output signal from the Drop output Dl forms the Drop output of the ADM and the output signal from the Through output Tl forms the input signal T to the gate input G2 of NOLM 804. The Incoming input 12 of the NOLM 804 is connected to receive a steady stream of solitons, as indicated by the " 1 " at the input. As described in relation to FIG. 7, this connection produces a "NOT T" output at the Through output T2 of the NOLM 804. This signal is connected to the Incoming input 15 of a further NOLM 806.

The ADD input of the ADM 800 is formed by the Incoming input 13 of an NOLM 808. The ADD input signal and Incoming input signal are synchronized for proper operation. That is, the ADD signal occupies time slots which are occupied by the DROP signals and the Add signal is preferably gated with the same gate signal as that of the NOLM 802. A gate signal coupled to the input G3 of the NOLM 808 produces a signal A at the drop output D3 of the NOLM 808.

This signal, A, is connected to the gate input G4 of NOLM 810 and a steady stream of "Is" is provided to the Incoming input 14 of the NOLM 810. That is, the NOLM 810 is connected to produce the negation of signal A at its Through output T4. This signal, "NOT A", is connected to the gate input G5 of the NOLM 806. The Drop output D5 of the NOLM 806 produces an output signal "NOT T" AND "NOT A" which is coupled to the gate input G6 of an NOLM 812. A steady stream of "Is" is provided to the Incoming input 16 of the NOLM 812. Consequently, the NOLM 812 provides at its through output T6 the negation of the signal at its gate input, or (NOT T) AND (NOT A), which, by De Morgan's law, is equivalent to T OR A.

In summary, the Incoming signal is stripped of a Drop component which appears at the Drop output Dl of the NOLM 802. The remaining, through signal, is added to a signal Add which is coupled to the Incoming input 13 of NOLM 808 and the resultant, Add OR Through, is provided at the Through output T6 of the NOLM 812. The NOLM NOT circuits, including NOLMs 804, 810, and 812 all receive a steady stream of solitons which may be provided by three generators or a single soliton generator in combination with splitters. The time phasing of all the NOLM inputs are properly matched.

An all-optical ADM, in accordance with a presently preferred embodiment of the invention, is illustrated in the block diagram of FIG. 9. An NOLM 902 splits an incoming signal labeled Incoming, into Through and Drop signals, as described, for example, in relation to FIG. 8. An NOLM 904 is connected to invert the Through signal, thereby producing the output "NOT T" which is coupled to the Incoming input 13 of NOLM 906. An Add signal, labeled Add, is coupled to the Incoming input 14 of the NOLM 908 and is gated by a signal coupled to the gate input G4 of the NOLM 908. In the presently preferred embodiment, the gate signal used at input G4 is the same as that at input G 1. This insures that the Add signal occupies the same time slots as the Drop signal. The gated Add signal A is coupled to the gate input G3 of the NOLM 906 and the through output T3 of the NOLM 906 provides an output signal (NOT T) AND (NOT A). This signal is coupled to the gate input G5 of NOLM 910 which, with a steady stream of "Is" coupled to its Incoming input 15, inverts the signal, thereby providing the desired Outgoing signal which is the logic OR of the Through signal and the Add signal.

As discussed in relation to FIGs. 3 and 4, NOLMs can be cascaded to create multiple drop outputs. Similarly, as indicated by the truth table of FIG. 10, NOLMs may be cascaded to create multiple Add inputs thereby allowing the construction of all- optical ADMs having multiple Drop outputs and multiple Add inputs. The truth table of FIG. 10 illustrates a combination of two Add inputs with a Through input and, generally, the number of Add inputs can be increased by "ANDing" the negative of the first Add signal, labeled Al in the table, with the Through signal. Then, the negative of the next Add signal, labeled A2 in the table, is ANDed" with the result of the previous

AND operation. This step can be repeated until all the desired Add signals have been combined. Then, the result of the previous steps is negated, or inverted. The results labeled NA in the table indicate that no combinations of signals which would overlap " Is", that is which would permit different signals to compete for a time slot, are allowed. The block diagram of FIG. 1 1 illustrates a combination of NOLMs which forms a multi-add, multi-drop-drop all optical ADM 1 100 according to the principles of the present invention. Three NOLMs 1102, 1 104, and 1 106 are cascaded to produce three DROP signals, Drop, Drop, and Drop3, respectively. The Through signal provided by the NOLM 1 106 is provided to an NOLM 1108 which inverts it. An Add signal Addl is received at an NOLM 1110 and gated to produce a signal Al which is passed to the gate input of an NOLM 1116. The NOLM 1116 combines the gated signal Al with the inverted through signal to produce (NOT T) AND (NOT Al). Similarly, a second add signal Add2 is gated through an NOLM 1 1 12 to produce a gated signal A2 which is combined in NOLM 1 1 18 with the resultant output from the NOLM 1 116 to produce an output NOT((NOT T) AND (NOT Al)) AND (NOT A2). N add signals may be combined in this manner, with each previous result ANDed with the gated add signal AN as, provided by the NOLM 1 1 14 to the NOLM 1120. The final resultant is then inverted in the NOLM 1122 to produce the outgoing signal labeled Outgoing.

An NOLM device may be advantageously formed in accordance with the present invention as illustrated in the block diagram of FIG. 12. An NOLM 1200 includes a coupler 1202 attached to a length of optical fiber which forms a loop 1204. The parameters of the loop, such as its length, the effective area of the loop, rate of change of dispersion within the fiber, and the like are selected so that input pulses may be switched or transmitted, depending whether their widths or amplitudes .are above or below predetermined threshold values.

The operation of an NOLM is generally known and can be summarized as follows. If the coupler 1202 divides an input light pulse received at one of its ports 1206 or 1208 into two equal counter-rotating pulses and the loop affects these component pulses symmetrically, the component pulses will interfere constructively on their return to the coupler 1202 and consequently the input pulse will be reflected back through the port through which it entered the loop mirror. If the pulse is divided unevenly and/or if the loop affects the pulses symmetrically, the pulses returning to the coupler may be reflected to the port of entry, transmitted to the coupler s other port, or partly reflected and partly transmitted.

In the presently preferred embodiment of FIG. 12, the loop 1204 is operatively connected to couplers 1210 and 1212 which act as wavelength division multiplexers.

One port of the coupler 1210 acts as the gate input and is labeled accordingly. Input gating pulses are preferably formed of light having a different wavelength than that of the Incoming signal pulses in order to prevent unwanted couplings. Alternatively, the pulses could be of the same wavelength but different polarizations. Incoming signals are received at a port of a 3 dB coupler 1214 labeled Incoming. Alternatively, a circulator could be substituted for the coupler 1214 in order to reduce losses. The NOLM 1200 operates as previously described in relation to the block diagram representations of FIGs. 2A through 2C, with the presence of a gate signal routing the Incoming signal to the Drop output and the absence of a gate signal routing the Incoming signal to the Through output. That is, the output labeled Through is the logical AND of the Incoming input and the inversion of the Gate input. The output labeled Drop is the logical AND of the Incoming and Gate inputs. Pulses presented to the Gate input are coupled out of the loop through the coupler 1212.

The foregoing description of specific embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the .art to best utilize the invention. It is intended that the scope of the invention be limited only by the claims appended hereto.

Claims

We Claim:

1. An optical multi-drop multiplexer, comprising: a first nonlinear optical loop mirror, said first loop mirror having incoming signal input, gating input, through output and drop output ports, said first loop mirror connected to receive an incoming signal and to separate said signal into two signals having non-overlapping time slots, one of the two signals fed to the through output port and the other of the two signals fed to the drop output port, and a second nonlinear optical loop mirror, said second loop mirror having incoming signal input, gating input, through output and drop output ports, said second loop mirror connected to receive one of said two divided signals from said first loop mirror and to divide said divided signal into two further signals having non-overlapping time slots.

2. An optical multi-add multiplexer, comprising: a first nonlinear optical loop mirror, said first loop mirror having incoming signal input, gating input, through output and drop output ports, said first loop mirror connected to receive two incoming signals having non-overlapping time slots and to combine said signals to create at least one of a through signal or drop signal which appear on the through output port or the drop output port, respectively, and a second nonlinear optical loop mirror, said second loop mirror, having incoming signal input, gating input, through output and drop output ports, said second loop mirror connected to receive one of said through or drop signals and a signal whose time slots do not overlap with said received signal and to further combine said received signals and the signal whose time slots do not overlap.

3. An optical add-drop multiplexer, comprising: a first nonlinear optical loop mirror, said first loop mirror having incoming signal input, gating input, through output and drop output ports, said first loop mirror connected to receive an incoming signal and to separate said signal into through and drop signals having non-overlapping time slots, and a second nonlinear optical loop mirror, said second loop mirror having incoming signal input, gating input, through output and drop output ports, said first loop mirror connected to said through signal from said first loop mirror, and an Add signal, said two signals having non-overlapping time slots, said first loop mirror further connected to combine said signals.

4. An optical logic inverter, comprising: a soliton source connected to produce a stream of solitons, and a nonlinear optical loop mirror, said loop mirror having an incoming signal input, a gating input, a through output and a drop output port, said loop mirror connected to receive a first optical signal comprising the stream of solitons and a second optical signal, respectively, at said incoming and gate inputs and to produce the logical AND of said signals at said drop output port and to produce the logical AND of said signal at said incoming input and the inversion of said signal at said gate input at said through output.

5. An optical logic OR gate, comprising: nonlinear optical loop mirrors, said loop mirrors having incoming signal input, gating input, through output and drop output ports, said mirrors connected to produce logic AND gates and logic INVERTER gates and to combine said gates in accordance with De Morgan's law to produce a logic OR gate.

6. An optical multi-drop multiplexer, comprising: a first nonlinear optical loop mirror, said first loop mirror having an incoming signal input, a gating input, and a drop output port, said first loop mirror connected to receive an incoming signal and a gating signal, and to produce a drop signal at the drop output port, and a second nonlinear optical loop mirror, said second loop mirror having an incoming signal input, a gating input and a drop output port, said second loop mirror connected to receive the drop signal from the first nonlinear optical loop mirror on its incoming signal input and to produce a further drop signal on its drop output port.

7. The optical multi-drop multiplexer of claim 6 wherein the incoming signal input of the first nonlinear optical loop mirror comprises a stream of soliton pulses.

8. The optical multi-drop multiplexer of claim 7 wherein the gating signal of the first nonlinear optical loop mirror comprises a stream of alternating soliton pulses synchronized with the incoming signal input of the first nonlinear optical loop mirror so that alternating time slots of the incoming signal input of the first nonlinear optical loop mirror are directed to the drop output port of the first nonlinear optical loop mirror.

9. The optical multi-drop multiplexer of claim 6 wherein one or more additional nonlinear optical loop mirrors are connected in a cascade connection such that a third nonlinear optical loop mirror is connected to receive the further drop signal from the second nonlinear optical mirror and to produce a still further drop signal and so on, whereby any desired number of drop signals may be obtained.

10. An optical multi-through multiplexer, comprising: a first nonlinear optical loop mirror, said first loop mirror having an incoming signal input, a gating input, and a through output port, said first loop mirror connected to receive an incoming signal and a gating signal and to produce a through signal at the through output port, and a second nonlinear optical loop mirror, said second loop mirror having an incoming signal input, a gating input, and a through output port, said second loop mirror connected to receive the through signal from the first nonlinear optical loop mirror on its incoming signal input and to produce a further through signal on its through output.

1 1. The optical multi-through multiplexer of claim 10 wherein the incoming signal input of the first nonlinear optical loop mirror comprises a stream of soliton pulses.

12. The optical multi-through multiplexers of claim 1 1 wherein the gating signal of the first nonlinear optical loop mirror comprises a stream of alternating soliton pulses synchronized with the incoming signal input of the first nonlinear optical loop mirror so that alternating time slots of the incoming signal of the first nonlinear optical loop mirror are directed to the through output port of the first nonlinear optical loop mirror.

13. The optical multi-through multiplexer of claim 10 wherein one or more additional nonlinear optical loop mirrors are connected in a cascade connection such that a third nonlinear optical loop mirror is connected to receive the further through signal from the second nonlinear optical mirror and to produce a still further through signal and so on, whereby any desired number of drop signals may be obtained.

14. The optical multi-through multiplexer of claim 10 wherein the gate input of the second nonlinear optical mirror is connected to receive the through output signal of the first nonlinear optical mirror as its gating signal.

15. The optical multiplexer of any one of claims 1, 2, 3, 6 or 10 wherein the first nonlinear optical mirror comprises a first coupler attached to a length of optical fiber which forms a loop, said loop operatively connected to a second coupler for coupling a gating signal.