CN1237360C - Optical switching system with power balancing - Google Patents

Abstract

A system for switching optical signals from a plurality of input waveguides (102) to a plurality of output waveguides (104), while balancing power in the output waveguides, and a method for its use. The system is based on an optical switch matrix (100) that includes, for each input waveguide and for each output waveguide, one or more attenuators (110, 120) that divert an adjustable portion of the optical energy entering that input waveguide to that output waveguide. Preferably, each input waveguide is coupled to each output waveguide via a pair of 2x2 Mach-Zehnder interferometers, a first of which has an idle input port (112) and a second of which has an idle output port (128). The system also includes a feedback mechanism that taps fixed portions of the power in either the input waveguides or the output waveguides, and adjusts the attenuators accordingly.

Description

Optical switching system and method with power balancing

technical field

The invention relates to an optical signal switching, in particular to an optical switching system which is convenient for output power balance.

Background technique

In an optical communication network based on dense wavelength division multiplexing, signals carried by different wavelength carriers tend to have different optical power due to various reasons. One reason is that such a network uses optical amplifiers to maintain signal power. The optical gain of an optical amplifier is not flat as a function of wavelength. Therefore, even if the input multiplexed signals have equal power, the output multiplexed signals will not have equal power. The second reason is that multiplexed signals usually have different origins, so when these signals reach the optical amplifiers, they experience different propagation losses as a result of traveling different distances. If the signal power range of the multiplexed signal entering the optical amplifier is too large, the amplifier will saturate, resulting in unacceptable data loss.

Two different approaches have been used to solve this problem. The first approach is to flatten the response curve of the system (which is the composite of the response curve of the optical amplifier and that of any other wavelength-dependent components such as filters) by introducing a loss curve that is inverse of the response curve. This can be achieved passively (Y.Li, "Awaveguide EDFA gain equalizer filter", Electronics Letters, vol.33pp.2005-2006, 1995) or dynamically (M.C.Parker, "Dynamic holographic spectral equalization for WDM", IEEE Photon Technology Letters, vol.9pp 529-531, 1997; J.E.ford and J.A.Walker, "dynamic spectral power equalization using micro-opto mechanics", IEEE Photon Technology Letters, vol.10pp.1440-1442, 1998). In this scheme, signals are still multiplexed on ordinary optical waveguides. The second scheme demultiplexes the signal onto individual channels and attenuates each channel using an optical attenuator.

Optical switches such as 2x2 and 1x2 Mach-Zehnder interferometers can be used as attenuators. FIG. 1 shows a Mach-Zehnder interferometer 10 . The interferometer 10 is based on two nearly parallel waveguides, an upper waveguide 12 and a lower waveguide 14 . The waveguides 12 and 14 are coupled to each other in a first 3dB directional coupler 16 and a second 3dB directional coupler 18 . Between directional couplers 16 and 18 , each waveguide 12 and 14 passes through a respective phase shifter 20 and 22 . The left end 24 of the upper waveguide 12 serves as the input to the interferometer 10 . The right end 26 of the upper waveguide 12 serves as the output of the interferometer 10 . The right end 28 of the lower waveguide 14 is a free end.

The operation of interferometer 10 is as follows. The coherent light entering the interferometer 10 at the input end 24 is split by the directional coupler 16 , half of the light continues to propagate to the right in the upper waveguide 12 , and the other half of the light propagates to the right in the lower waveguide 14 . Phase shifters 20 and 22 are used to change the relative phase of the light in waveguides 12 and 14 . Then, according to the phase difference between the light of the upper waveguide 12 and the light of the lower waveguide 14 caused by the phase shifters 20 and 22, the directional coupler 18 causes some or all of the light to pass through the output port 26 and/or the idle port 28 from The interferometer 10 shoots out.

Figure 2 shows the power (dB) leaving a particular Mach-Zehnder interferometer 10 via the output 28 relative to the power entering the interferometer 10 via the input 24 and acting on the phase shifter 20 or a function of the heating power of the phase shifter 22. For 1.55 micron wavelength light, this particular Mach-Zehnder interferometer ₁₀ was fabricated using SiO2 technology on Si. A maximum attenuation of 35 dB is obtained at point I (approximately 50 mW heating power). The minimum attenuation is obtained at point II (nearly 610 mW heating power). Therefore, the Mach-Zehnder interferometer 10 is capable of a 35 dB attenuation range. When the Mach-Zehnder interferometer 10 is used as a switch, point I corresponds to the switch being closed, causing almost all power to leave the switch via the output 26, and point II corresponds to the switch being fully on, causing almost all power to leave the switch via the output terminal 26. The output 28 leaves the switch.

The change in attenuation depends on the change in the heating power used in phase shifters 20 and 22 .

Contents of the invention

2x2 and 1x2 optical switches have also been used as elements of optical switch matrices, such as those taught in PCT application WO 99/60434 and co-pending US patent application 09/696,224, for routing optical signals from input waveguides to Switch to output waveguide. The present invention is an optical switching system based on an optical switch matrix that combines the switching function of an optical switch such as a Mach-Zehnder interferometer 10 with the attenuation function of such an optical switch in a single unit.

Accordingly, in accordance with the present invention there is provided an optical switching system for switching optical energy from a plurality of input waveguides to a plurality of output waveguides comprising: (a) for each output waveguide: for each input waveguide: at least a respective attenuator for diverting an adjustable fraction of the optical energy input via each input waveguide to each output waveguide; said system being characterized in that each said attenuator is adjustable and selectively Let the light energy input to it pass substantially all or not pass or partly pass.

Furthermore, according to the present invention, there is provided a method for switching each of a plurality of optical signals propagating on a corresponding input waveguide from a corresponding input waveguide to a desired one of a plurality of output waveguides, the The method comprises the steps of: (a) providing an optical switch matrix comprising: for each output waveguide: for each input waveguide: at least one corresponding attenuator for converting an adjustable partly diverted to each output waveguide; (b) selecting an attenuator for diverting the optical signal to the intended output waveguide; and (c) adjusting the selected attenuator to balance the power of the optical signal in the output waveguide; the The method is characterized in that each said attenuator adjustably and selectively passes substantially all or substantially none or part of the light energy input thereto.

The optical switching system of the present invention is based on an optical switch matrix comprising a set of one or more optical switches for each input waveguide and each output waveguide for converting an adjustable partially transferred to the output waveguide. At least one optical switch in each switch group is an attenuator, preferably a Mach-Zehnder attenuator. Said switches are preferably 2x2 switches. If there are two switches per switch group, one for input and one for output, the input switch has a free input and the output switch has a free output. The input switch of the last switch group of each input waveguide also has a free output, and the output switch of the first switch group of each output waveguide also has a free input.

The optical switching system of the present invention preferably includes a feedback mechanism for adjusting the attenuators to balance the output power in the output waveguides. The feedback mechanism includes: a power measurement device such as a spectrum analyzer; a set of taps for transferring a fixed portion of the optical energy from the input waveguide or output waveguide to the spectrum analyzer; and a control unit for receiving data from the spectrum analyzer. The analyzer's signals are indicative of the power level in the tapped waveguide, and the attenuators are adjusted based on these signals. Each tap preferably includes a directional coupler coupled to a corresponding input or output waveguide.

"Balancing" the output power in the output waveguides means adjusting the output power in the output waveguides to facilitate the precise transmission of signals downstream from the optical switching system. Typically, this balancing is achieved by equalizing the power in all output waveguides; but there are cases where power balancing is done by adjusting the power to have non-uniform mutual ratios. For example, some signals may point to corresponding destinations further downstream than other signals. If the power of all signals is equalized, signals from far destinations arrive at their destination with lower power than signals from near destinations, since signal attenuation varies in the same sense as propagation distance. In this case, it is generally desirable to adjust the signal power level of the far destination to a higher level than that of the near destination, so that all signals arrive at their respective destinations with equal power.

Description of drawings

The present invention is only described by way of example below in conjunction with accompanying drawing, wherein:

Figure 1 illustrates a Mach-Zehnder interferometer;

Figure 2 shows the relative output power as a function of applied heating power for a particular Mach-Zehnder interferometer;

Fig. 3 illustrates the structure of the optical switch matrix of the present invention;

Fig. 4 illustrates the structure of another optical switch matrix of the present invention;

Figure 5 is a high level block diagram of a complete system of the present invention;

Figure 6 is a high level block diagram of another complete system of the present invention.

Detailed ways

The present invention is an optical switching system that can be used to switch optical signals from input waveguides to output waveguides while balancing the power in the output waveguides.

The principles and operation of the optical switching system of the present invention may be better understood with reference to the drawings and accompanying descriptions.

Referring to the drawings, Fig. 3 shows the structure of an optical switch matrix 100 of the present invention, which is similar to the optical switch matrix taught in WO99/60434. Optical switch matrix 100 connects four input waveguides 102 to four output waveguides 104 . For this purpose, the optical switch matrix 100 includes sixteen input attenuators 110 and sixteen output attenuators 120 . Each attenuator 110 or 120 is a Mach-Zehnder interferometer, which is actually the same as the Mach-Zehnder interferometer 10 . Each input attenuator 110 has an upper input 112 , a lower input 114 , an upper output 116 and a lower output 118 . Likewise, each output attenuator 120 has an upper input 122 , a lower input 124 , an upper output 126 and a lower output 128 . Each input waveguide 102 is coupled to each output waveguide 104 through a respective input attenuator 110 and a respective output attenuator 120 . The input attenuators 110 and output attenuators 120 used to couple a particular output waveguide 102 to a particular output waveguide 104 are designated by corresponding letters: input attenuator 110aa and output attenuator 120aa couple input waveguide 102a to output waveguide 104a; Attenuator 110ab and output attenuator 120ab couple input waveguide 102a to output waveguide 104b, and so on.

Specifically, input waveguide 102 leads into lower input 114 of input attenuator 110 coupled to output waveguide 104a, and output waveguide 104 exits upper output 126 of output attenuator 120 coupled to input waveguide 102d. Each input attenuator 110 is coupled to its corresponding output attenuator 120 by a corresponding intermediate waveguide 132 leading from the upper output 116 of the input attenuator 110 to the lower input 124 of the output attenuator 120 . All upper input ends 112 of the input waveguide 110 are free ends. Likewise, all lower output terminals 128 of the output attenuator 120 are idle terminals. The lower output 118 of the input attenuator 110 coupled to the output waveguide 104d is a free end; a corresponding intermediate waveguide 130 leads from the lower output 118 of each other input attenuator 110 to couple the same input waveguide 102 to the next output waveguide 104 The lower input terminal 114 of the input attenuator 110 . Likewise, the upper input end 122 of the output attenuator 120 coupled to the input waveguide 102a is a free end; the corresponding intermediate waveguide 134 leads to The upper input 122 of each other output attenuator 120 . As in the Mach-Zehnder interferometer 10, the lower input 114 and lower output 118 of each input attenuator 110 are actually opposite ends of the same inner lower waveguide, and the upper input 122 of each output attenuator 120 The upper output end 126 is actually the opposite end of the same inner upper waveguide, so the middle waveguide 130 is actually an extension of the corresponding input waveguide 102 and the middle waveguide 134 is actually an extension of the corresponding output waveguide 104 .

Each attenuator 110 or 120 is considered OFF (closed) in its pass state (point I in FIG. 2 ), wherein all light energy entering via the upper input 112 or 122 exits via the upper output 116 or 126, and All light energy entering via the lower input 114 or 124 exits via the lower output 118 or 128 . With all attenuators OFF, all optical energy entering the matrix 100 via the input waveguides 102 is discarded at the idle output 118 . By increasing the heating power applied to the phase shifters of these attenuators 110 and 120 to point II of FIG. Some or all of the optical energy entering via input waveguide 102 may be diverted to output waveguide 104 .

FIG. 4 shows the structure of another optical switch matrix 200 of the present invention, similar to the optical switch matrix taught in US Patent Application Serial No. 09/696,224. Optical switch matrix 200 connects four input waveguides 202 to four output waveguides 204 . For this purpose, the optical switch matrix 200 includes sixteen input attenuators 210 and sixteen output attenuators 220 . Each attenuator 210 or 220 is a Mach-Zehnder interferometer that is virtually identical to the Mach-Zehnder interferometer 10 . Each input attenuator 210 has an upper input 212 , a lower input 214 , an upper output 216 and a lower output 218 . Likewise, each output attenuator 220 has an upper input 222 , a lower input 224 , an upper output 226 and a lower output 228 . Each input waveguide 202 is coupled to each output waveguide 204 through a respective input attenuator 210 and a respective output attenuator 220 . The input attenuator 210 and output attenuator 220 used to couple a particular input waveguide 202 to a particular output waveguide 204 are labeled by corresponding letters: input attenuator 210ad and output attenuator 220ad couple input waveguide 202a to output waveguide 204d, input attenuator 210ba and output attenuator 210ba couple the input waveguide 202b to the output waveguide 204a, and so on.

Specifically, the input waveguide 202 leads into the upper input end 212 of the input attenuator 210, and the input attenuator 210 is coupled to the output waveguide 204 before the loop; the input waveguide 202a leads into the upper input end 212 of the input attenuator 210ad, and the input waveguide 202b Leads into upper input 212 of input attenuator 210ba, input waveguide 202c leads into upper input 212 of input attenuator 210cb, and input waveguide 202d leads into upper input 212 of input attenuator 210dc. Output waveguides 204 emerge from upper output ports 226 of output attenuators 220 coupled to corresponding input waveguides 202: output waveguides 204a exit from upper output ports 226 of output attenuators 220aa, output waveguides 204b exit from upper output ports 226 of output attenuators 220bb Out, the output waveguide 204c exits the upper output end 226 of the output attenuator 220cc, and the output waveguide 204d exits the upper output end 226 of the output attenuator 220dd. Each input attenuator 210 is coupled to its respective output attenuator 220 by a respective intermediate waveguide 232 leading from the lower output 218 of the input attenuator 210 to the lower input 224 of the output attenuator 220 . All lower ends 214 of the input attenuator 210 are free ends. Likewise, all lower output terminals 228 of output attenuator 220 are idle terminals. The upper output terminals of the input attenuators 210aa, 210bb, 210cc, and 210dd coupling the input waveguide 202 to the corresponding output waveguide 204 are free terminals. A respective intermediate waveguide 230 leads from the upper output 216 of each other input attenuator 210 to the upper input 212 of the input attenuator 210 that couples the same input waveguide 202 to the looping preceding output waveguide 204 . For example, an intermediate waveguide 230 leads from the upper output end 216 of the input attenuator 210cb to the upper input end 212 of the input attenuator 210ca, and another intermediate waveguide 230 leads from the upper output end 216 of the input attenuator 210ca to the upper end of the input attenuator 210cd. Input 212, and a further intermediate waveguide 230 lead from upper output 216 of input attenuator 210cd to upper input 212 of input attenuator 210cc. The upper input terminals 222 of the output attenuators 220ad, 220ba, 220cb, and 220dc that couple the input waveguide 202 to the looping preceding output waveguide 204 are free terminals. A respective intermediate waveguide 234 leads from the upper output 226 of the output attenuator 220 coupling the same output waveguide 204 to the loop preceding input waveguide 202 to the upper input 222 of each other output attenuator 220 . For example, an intermediate waveguide 234 leads from the upper output end 226 of the output attenuator 220dc to the upper input end 222 of the output attenuator 220ac, and another intermediate waveguide 234 leads from the upper output end 226 of the output attenuator 220ac to the upper end of the output attenuator 220bc. Input 222, and an intermediate waveguide 234 leads from upper output 226 of output attenuator 220bc to upper input 222 of output attenuator 220cc. Intermediate waveguide 234 connects output attenuators 220dc, 220db, and 220da to output attenuators 220ac, 220ab, and 220aa, respectively. As indicated by endpoints A, B and C, the intermediate waveguides 234 are connected by wraparound, typically by crossing either the input waveguides 202 or the output waveguides 204 .

As in Mach-Zehnder interferometer 10, upper input 212 and upper output 216 of each input attenuator 210 are actually opposite ends of the same inner upper waveguide, upper input 222 and upper The upper output end 226 is actually the opposite end of the same inner upper waveguide, so the middle waveguide 230 is actually an extension of the corresponding input waveguide 202 and the middle waveguide 234 is actually an extension of the corresponding output waveguide 204 .

Each attenuator 210 or 220 is considered OFF (closed) in its pass-through state (point I in FIG. 2 ), wherein all light energy entering via the upper input 212 or 222 exits via the upper output 216 or 226, and All light energy entering via the lower input 214 or 224 exits via the lower output 218 or 228 . With all attenuators OFF, all optical energy entering matrix 200 via input waveguides 202 is discarded at idle output 216 . By increasing the heating power applied to the phase shifters of these attenuators 210 and 220 to point II of FIG. Some or all of the optical energy entering via the input waveguide 202 may be diverted to the output waveguide 204 .

Figure 5 is a high level block diagram of a complete optical switching system 250 of the present invention. In addition to the 4×4 optical switch matrix 300 for switching optical signals from the four input waveguides 302 to the four output waveguides 304, the system 250 also includes a feedback mechanism for determining the amount of light exiting the matrix 300 via the output waveguides 304. The power of the signal, and adjust the attenuator of the matrix 300 according to the balanced power in the output waveguide 304 in real time. Matrix 300 may be matrix 100 as described above, or matrix 200 as described above. The feedback mechanism includes a spectrum analyzer 310 , a control unit 312 and a set of optical taps 314 . Each tap 314 diverts a small fixed portion of a corresponding one of the output waveguides 304 from that waveguide 304 to the optical spectrum analyzer 310 . An optical spectrum analyzer 310 , represented as a power measuring device, measures the power transferred from each output waveguide 304 and sends a signal representative of these powers to a control unit 312 . Based on these signals, the control unit 312 adjusts the attenuators of the matrix 300 to balance the power in the output waveguides 304 . Tap 314 is preferably based on a directional coupler. Control unit 312 is preferably personal computer based. The control unit 312 also includes an electronic driver for adjusting the heating power applied to the phase shifters of the matrix 300 according to control signals received by the driver from the personal computer.

Figure 6 is a high level block diagram of an alternative optical switching system 350 of the present invention. Similar to system 250, system 350 includes: a 4x4 optical switch matrix 400 for switching optical signals from four input waveguides 402 to four output waveguides 404; a set of optical taps 414; an optical spectrum analyzer 410; A control unit 412 . Optical tap 414 , spectrum analyzer 410 , and control unit 412 are substantially the same as tap 314 , spectrum analyzer 310 , and control unit 312 of system 250 . The main difference between system 250 and system 350 is that in system 350, tap 414 diverts a small, fixed fraction of the power in input waveguide 402 to spectrum analyzer 410, rather than a small amount of power in output waveguide 404. The fixed portion is transferred to the spectrum analyzer 410 . Furthermore, the structure and operation of system 350 are substantially the same as the structure and operation of system 250 . Optical spectrum analyzer 410 measures the power transferred from each input waveguide 402 and sends a signal representative of these powers to control unit 412 . Based on these signals, the control unit 412 adjusts the attenuators of the matrix 400 to balance the power in the output waveguides 404 .

The range over which the system 250 or 350 balances the power in the output waveguide 304 or 404 depends on the resolution of the corresponding electronic driver. There is a tradeoff between the dynamic range of the driver and the accuracy with which the power in the output waveguide 304 or 404 is balanced. Electronic drives are usually digital drives with a fixed predetermined number of steps. An electronic driver with a large step size has a large dynamic range, but at the expense of low precision. Electronic drives with small step sizes provide high precision, but at the expense of limited dynamic range.

Although the invention has been described in connection with a limited number of embodiments, it will be apparent to those skilled in the art that many variations, modifications and other applications of the invention are possible.

Claims (17)

1, a kind of optical switching system is used for the luminous energy from a plurality of input waveguides is switched to a plurality of output waveguides, comprising:

(a) for each output waveguide, and for each input waveguide: at least one corresponding attenuator, but be used for an adjustment member of the luminous energy that enters via described each input waveguide is transferred to described each output waveguide;

Described system is characterised in that, each described attenuator make adjustably and optionally be input to it luminous energy basically all by or basically all not by or partly pass through.

2, system according to claim 1, wherein each described attenuator comprises a Mach-Zedde interferometer.

3, system according to claim 1, wherein for each output waveguide, and for each input waveguide: one of described at least one respective attenuation device comprises the 2x2 switch with an idle output terminal.

4, system according to claim 3, wherein for each output waveguide, one of the described described 2x2 switch of luminous energy being transferred to described at least one respective attenuation device of described each output waveguide from first input waveguide has an idle input end.

5, system according to claim 1, wherein: for each output waveguide, and for each input waveguide: one of described at least one respective attenuation device comprises the 2x2 switch with an idle input end.

6, system according to claim 5, wherein for each input waveguide, one of the described described 2x2 switch of luminous energy being transferred to described at least one respective attenuation device of last output waveguide from described each input waveguide has an idle output terminal.

7, system according to claim 1 also comprises:

(b) feedback mechanism is used to adjust described attenuator, makes the power-balance of luminous energy in the output waveguide.

8, system according to claim 7, wherein said feedback mechanism comprises:

(i) power-measuring device;

(ii) for each output waveguide: a tap is used for a fixed part of the luminous energy of described each output waveguide is transferred to described power-measuring device; With

(iii) control module is used for:

(A) be each output waveguide receives the described power of luminous energy in described each output waveguide of representative from described power-measuring device signal;

(B) adjust described attenuator based on described signal, with the described power of balance.

9, system according to claim 8, wherein said power-measuring device comprises a spectroanalysis instrument.

10, system according to claim 8, wherein each described tap comprises a directional coupler.

11, system according to claim 7, wherein said feedback mechanism comprises:

(i) power-measuring device;

(ii) for each input waveguide: a tap is used for a fixed part of described each input waveguide luminous energy is transferred to described power-measuring device; With

(iii) control module is used for:

(A) be each input waveguide receives the power of luminous energy in described each input waveguide of representative from described power-measuring device signal; With

(B) adjust described attenuator based on described signal, with the described power of luminous energy in the balance output waveguide.

12, system according to claim 11, wherein said power-measuring device comprises a spectroanalysis instrument.

13, system according to claim 11, wherein each described tap comprises a directional coupler.

14, a kind of method is used for each light signal of a plurality of light signals of propagating on corresponding input waveguide is switched to an expection waveguide a plurality of output waveguides from corresponding input waveguide, may further comprise the steps:

(a) provide an optical switch matrix, comprise: for each output waveguide, and for each input waveguide: at least one corresponding attenuator, but be used for an adjustment member of the signal of propagating on described each input waveguide is transferred to described each output waveguide;

(b) selection is used for light signal is transferred to the described attenuator of expection output waveguide; With

(c) attenuator of the described selection of adjustment is with the power of light signal in the balance output waveguide;

Described method is characterised in that, each described attenuator make adjustably and optionally be input to it luminous energy basically all by or basically all not by or partly pass through.

15, method according to claim 14 also comprises step:

(d) the described power of light signal in the measurement output waveguide; Described adjustment is based on that in the output waveguide the described measurement power of light signal carries out.

16, method according to claim 14 also comprises step:

(d) power of light signal in the measurement input waveguide; Described adjustment is based on that in the input waveguide the described measurement power of light signal carries out.

17, method according to claim 14 is wherein implemented described adjustment, with the described power of light signal in the balanced output waveguide.

Images