JP2003529097A - Optical switching system with power balance - Google Patents

Abstract

(57) Abstract: A method for switching an optical signal from a plurality of input waveguides (102) to a plurality of output waveguides (104) while balancing the power in a plurality of output waveguides (104). The system and how to use it. The system includes, for each input waveguide, and for each output waveguide, one or more attenuations that direct an adjustable portion of light energy entering the input waveguide to the output waveguide. It is based on an optical switch matrix (100) that includes devices (110, 120). Preferably, each input waveguide is coupled to each output waveguide via a pair of 2 × 2 Mach-Zehnder interferometers, and the first of the pair of 2 × 2 Mach-Zehnder interferometers. Has an empty input port (112) and the second interferometer has an empty output port (128). The system also includes a feedback mechanism that taps a portion of the power in either the input waveguide or the output waveguide and adjusts the attenuator accordingly.

Description

Detailed Description of the Invention

FIELD AND BACKGROUND OF THE INVENTION The present invention relates to switching optical signals, and more particularly to an optical switching system that facilitates balancing output power. In optical communication networks based on dense wavelength division multiplexing, signals carried on carriers of different wavelengths are likely to have different optical powers for several reasons. One reason is that such networks use multiple optical amplifiers to maintain signal power. The optical gain of an optical amplifier is not flat as a function of wavelength. Therefore, although the incoming multiplexed signals have equal power, the outgoing multiplexed signals generally do not have equal power. The second reason is that since multiplexed signals generally have different sources, they experience different propagation losses as a result of traveling different distances by the time they arrive at an optical amplifier. is there. If the range of signal power between the multiplexed signals entering the optical amplifier is too wide, the amplifier will saturate, resulting in unacceptable data loss.

Two different approaches have been used to solve this problem. The first method is
By introducing a loss curve that is reciprocal to the response curve, the response curve of the system (which is a composite of the response curve of an optical amplifier and the response curves of other wavelength dependent components such as filters) A) is to be flat. This is passively (“A waveguide EDFA gain equalizer filter” by Y.Li), Electronics Letters, vol.31 pp.2005-200.
6, 1995) or dynamically (“Dynamic holographic spectral by MC Parker”
equalization for WDM (Dynamic Holographic Spectral Equalization for Wavelength Division Multiplexing) ”, IEEE Photon Technology Letters, vol.9 pp.529-531, 1997, and JEfo
“Dynamic spectral power equalization using micr” by rd and JA Walker
o-opto mechanics (Dynamic spectrum power equalization using micro optical mechanism) ”,
IEEE Photon Technology Letters, vol.10 pp.1440-1442, 1998). In this approach, the signal remains multiplexed on a conventional optical waveguide. The second approach is to demultiplex the signal into each channel and use an optical attenuator to attenuate each channel.

Optical switches such as 2 × 2 and 1 × 2 Mach-Zehnder interferometers can be used as attenuators. FIG. 1 shows a Mach-Zehnder interferometer 10. Interferometer 10
Is based on two waveguides that are somewhat parallel, an upper waveguide 12 and a lower waveguide 14. The waveguides 12 and 14 include a first 3 dB directional coupler 16 and a second 3 d
They are coupled to each other at the B-directional coupler 18. Directional couplers 16 and 18
In between each waveguide 12 and 14 penetrates a respective phase shifter 20 and 22. The left end 24 of the upper waveguide 12 functions as an input port of the interferometer 10.
The right end 26 of the upper waveguide 12 functions as an output port of the interferometer 10. The right end 28 of the lower waveguide 14 is an empty port.

The operation of interferometer 10 is as follows. The coherent light entering the interferometer 10 from the input port 24 is divided by the directional coupler 16 into half of the light continuing to the right in the upper waveguide 12 and the light propagating to the right in the lower waveguide 14. Split into the other half. Phase shifters 20 and 22 are used to change the relative phase of the light in waveguides 12 and 14. The directional coupler 18 is then connected to the upper waveguide 12
Depending on the phase difference induced by the phase shifters 20 and 22 between the light inside and the light inside the lower waveguide 14, some or all of the light may be output port 26 and / or open port 28. Through the interferometer 10.

FIG. 2 illustrates a power-to-phase shifter in dB leaving the interferometer 10 via the output port 28 for power entering the particular Mach-Zehnder interferometer 10 via the input port 24. 20 or the heat generation power applied to the phase shifter 22. This particular Mach-Zehnder interferometer 10 is manufactured using the SiO ₂ -on-Si (depositing silicon oxide on silicon) technique for light at a wavelength of 1.55 microns. A maximum attenuation of 35 dB is obtained at point I (heating power of about 50 mW). The minimum amount of attenuation is obtained at point II (heating power of about 610 mW). Therefore, the Mach-Zehnder interferometer 10 has the capability of the attenuation range of 35 dB. When this Mach-Zehnder interferometer 10 is used as a switch, point I corresponds to an OFF-state switch in which almost all the power goes out through the output port 26, and point II corresponds through the output port 28. Corresponds to a completely ON switch where all the power goes out. The resolution of the attenuation depends on the resolution of the heating power used in the phase shifters 20 and 22.

SUMMARY OF THE INVENTION 2x2 and 1x2 optical switches are also US patent applications co-pending to PCT application WO99 / 60434 for switching optical signals from an input waveguide to an output waveguide. 09/6
Used as an element in an optical switch matrix such as the optical switch matrix disclosed in US Pat. The present invention is a Mach-Zehnder interferometer 1
An optical switching system based on an optical switch matrix that combines the switching function of optical switches such as 0 and the attenuation function of such optical switches in a single unit. Therefore, according to 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, which is (a) for each output waveguide and for each input waveguide. An optical switching system, characterized in that each tube includes at least one respective attenuator for directing a tunable portion of the optical energy entering through each input waveguide to each output waveguide. Provided.

Further in accordance with the present invention, a method of switching each of a plurality of optical signals traveling on a respective input waveguide from its respective input waveguide to a desired one of a plurality of output waveguides. And (a) for each output waveguide, and for each input waveguide, at least one for directing an adjustable portion of the signal traveling on each input waveguide to each output waveguide. Providing an optical switch matrix including two respective attenuators,
(B) selecting an attenuator that directs the optical signal to the desired output waveguide, and (c)
Adjusting an attenuator selected to balance the power of the optical signal in the output waveguide. The optical switching system of the present invention, for each input waveguide, for each output waveguide,
It is based on an optical switch matrix that includes a set of one or more optical switches for directing a tunable portion of optical energy in an input waveguide to an output waveguide. At least one of the optical switches in each set is an attenuator, preferably a Mach-Zehnder attenuator. Preferably, these switches are 2x2 switches. If there are two switches, one for input and the other for output, per set, this input switch has one empty input port and the output switch has one empty output port. The input switch of the last switch set of each input waveguide also has one free output port, and the output switch of the first switch set of each output waveguide also has one free input port.

[0008] Preferably, the optical switching system of the present invention includes a feedback mechanism for adjusting the attenuator to balance the output power in the plurality of output waveguides. This feedback mechanism includes a power measurement device, such as a spectrum analyzer, a set of taps for directing a portion of the optical energy from either the input or output waveguides to the spectrum analyzer, and the tapped conductors. A controller for receiving signals indicative of power levels in the wave guide from the spectrum analyzer and adjusting the attenuator based on these signals. Most preferably, each tap includes a directional coupler coupled to a respective input or output waveguide. "Balanced" the output power in the output waveguides means adjusting the output power in the output waveguides to facilitate accurate transmission of signals downstream from the optical switching system. Usually this balancing is done by equalizing the power in all the output waveguides, but there is a situation where the power is balanced by adjusting these powers to have a mutual ratio not equal to one. To do. For example, some of the signals may be destined for their respective receiving destinations far downstream than the other signals. If the powers of all signals are equalized, then the signal attenuation changes in the same sense as the mileage, so signals with long-distance destinations have lower power than signals with short-distance destinations. You will have to take it to the destination. In such a case, the power of the signal with the distant receiving destination should be the power of the signal with the distant receiving destination so that all signals arrive at their respective receiving destinations with equal power. It is often desirable to adjust to higher levels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: The present invention relates to an optical switching system that can be used to switch an optical signal from an input waveguide to an output waveguide while balancing the power in a plurality of output waveguides. The principles and operation of an optical switching system according to the present invention may be better understood with reference to the drawings and accompanying descriptions. Referring again to the drawings, FIG. 3 illustrates the architecture of an optical switch matrix 100 of the present invention (similar to the optical switch matrix disclosed in WO99 / 60434).
The basic configuration) is shown. The optical switch matrix 100 has four input waveguides 10.
2 is connected to four output waveguides 104. For this purpose, optical switches
The matrix 100 includes 16 input attenuators 110 and 16 output attenuators 120.
Includes and. Each attenuator 110 or 120 is a Mach-Zehnder interferometer 1
It is a Mach-Zehnder interferometer that is substantially the same as zero. Each input attenuator 110
It has an upper input port 112, a lower input port 114, an upper output port 116 and a lower output port 118. Similarly, each output attenuator 120 includes an upper input port 122, a lower input port 124, an upper output port 126, and a lower output port 128.
Have and. Each input waveguide 102 is connected to each output waveguide 104 by a respective input attenuator 110 and a respective output attenuator 120. The input attenuator 110 and output attenuator 120 coupling a particular input waveguide 102 to a particular output waveguide 104 are labeled with corresponding letters and are labeled as input attenuator 110aa and output attenuator. Device 120aa couples the input waveguide 102a to the output waveguide 104a, input attenuator 110ab and output attenuator 110ab couple the input waveguide 102a to the output waveguide 102b, and so on. is there.

More specifically, the input waveguide 102 leads to a lower input port 114 of an input attenuator 110 that couples to an output waveguide 104 a, and the output waveguide 104 is an input waveguide. It emerges from the upper output port 126 of the output attenuator 120 which is coupled to 102d. Each input attenuator 110 is coupled to its respective output attenuator 120 by a respective intermediate waveguide 132 leading from the upper output port 116 of that input attenuator 110 to the lower input port 124 of its output attenuator 120. Has been done. All upper input ports 112 of the input attenuator 110 are empty. Similarly, all lower output ports 128 of output attenuator 120 are also empty. The lower output port 118 of the input attenuator 110, which is coupled to the output waveguide 104d, is empty and the respective intermediate waveguides 130 are lower than the input attenuator of each of the other input attenuators 110. The output port 118 leads to the lower input port 114 of the input attenuator 110 which couples the same input waveguide 102 to the next output waveguide 104.
Similarly, the upper input port 122 of the output attenuator 120, which is coupled to the input waveguide 102a, is empty, and each intermediate waveguide 134 has a respective input waveguide that precedes the same output waveguide 104. An upper output port 126 of the output attenuator 120 coupled to the wave tube 102 leads to an upper input port 122 of each output attenuator of the other output attenuators 120. As in the Mach-Zehnder interferometer 10, the lower input port 114 and the lower output port 118 of each input attenuator 110 are actually opposite ends of the same inner lower waveguide and each output attenuator 120. The upper input port 122 and the upper output port 126 of are actually opposite ends of the same inner upper waveguide, so the intermediate waveguide 130 is actually an extension of the respective input waveguide 102. Yes, the intermediate waveguides 134 are actually extensions of the respective output waveguides 104. Each attenuator 110 or 120 is OFF in the passing state (point I in FIG. 2).
And in this state all light energy entering through the upper input port 112 or 122 exits through the upper output port 116 or 126 and enters through the lower input port 114 or 124. All light energy exits via the lower output port 118 or 128. In the OFF state of all attenuators, all light energy entering the matrix 100 through the input waveguide 102 is discarded from the empty output port 118. By increasing the heating power applied to the phase shifters of the input attenuator 110 and the output attenuator 120 toward point II in FIG. 2, a particular input waveguide 102 can be converted to a particular output waveguide 104. Turning on the input attenuator 110 and the output attenuator 120, which are coupled to, directs some or all of the light energy entering through its input waveguide 102 to its output waveguide 104.

FIG. 4 illustrates the architecture of another optical switch matrix 200 of the present invention similar to the optical switch matrix disclosed in US patent application Ser. No. 09 / 696,224. The optical switch matrix 200 connects four input waveguides 202 to four output waveguides 204. To this end, the optical switch matrix 200 includes 16 input attenuators 210 and 16 output attenuators 220. Each attenuator 210 or 220 is a Mach-Zehnder interferometer that is substantially the same as the Mach-Zehnder interferometer 10. Each input attenuator 210 includes an upper input port 212, a lower input port 214, an upper output port 216, and a lower output port 2.
I have 18 and. Similarly, each output attenuator 220 has an upper input port 222, a lower input port 224, an upper output port 226, and a lower output port 228. Each input waveguide 202 is connected to each output waveguide 204 by a respective input attenuator 210 and a respective output attenuator 220. The input attenuator 210 and the output attenuator 220 coupling a particular input waveguide 202 to a particular output waveguide 204 are labeled with corresponding letters and are labeled as input attenuator 210ad and output attenuator 210ad. The device 220ad connects the input waveguide 202a to the output waveguide 204d.
And the input attenuator 210ba and the output attenuator 210ba are connected to the input waveguide 2
02b is coupled to the output waveguide 204a, and so on.

More specifically, the input waveguide 202 communicates with an upper input port 212 of an input attenuator 210 that couples to an output waveguide 204 that periodically precedes the input waveguide 2
02a leads to the upper input port 212 of the input attenuator 210ad, and the input waveguide 202b leads to the upper input port 212 of the input attenuator 210ba,
The input waveguide 202c communicates with the upper input port 212 of the input attenuator 210cb, and the input waveguide 202d communicates with the upper input port 212 of the input attenuator 210dc. The output waveguides 204 emerge from the upper output port 226 of the output attenuator 220 that couples to the corresponding input waveguide 202. The output waveguide 204a emerges from the upper output port 226 of the output attenuator 220aa and the output waveguide 204b is
Out of the upper output port 226 of the output attenuator 220bb, the output waveguide 204c
Comes out of the upper output port 226 of the output attenuator 220cc, and the output waveguide 204d comes out of the upper output port 226 of the output attenuator 220dd. Each input attenuator 210 has a respective intermediate waveguide 232 leading from a lower output port 218 of the input attenuator 210 to a lower input port 224 of the output attenuator 220.
Are coupled to their respective output attenuators 220 by. Input attenuator 21
All 0's lower ports 214 are empty. Similarly, output attenuator 220
Of all lower output ports 228 of are empty. Input attenuators 210aa, 210bb, 21 coupling input waveguides 202 to corresponding output waveguides 204
The upper output ports of 0 cc and 210 dd are empty. Each intermediate waveguide 230 is connected to the upper output port 2 of each input attenuator of the other input attenuator 210.
16 leads to the same input waveguide 202 to the upper input port 212 of the input attenuator 210 which couples the same input waveguide 202 to the preceding output waveguide 204. For example, the intermediate waveguide 2
30 is the input attenuator 210ca from the upper output port 216 of the input attenuator 210cb.
Of the other intermediate waveguide 230 to the input attenuator 21.
0ca upper output port 216 to input attenuator 210cd upper input port 21
The second intermediate waveguide 230 leads from the upper output port 216 of the input attenuator 210cd to the upper input port 212 of the input attenuator 210cc.
The upper input ports 222 of the output attenuators 220ad, 220ba, 220cb, 220dc that couple the input waveguide 202 to the preceding output waveguide 204 are empty. Each intermediate waveguide 234 couples from the upper output port 226 of the output attenuator 220 that couples the same output waveguide 204 to the preceding input waveguide 202 periodically to the output attenuation of each of the other output attenuators 220. Upper input port 22
It leads to 2. For example, the intermediate waveguide 234 leads from the upper output port 226 of the output attenuator 220dc to the upper input port 222 of the output attenuator 220ac,
The other intermediate waveguide 234 leads from the upper output port 226 of the output attenuator 220ac to the upper input port 222 of the output attenuator 220bc, and further another intermediate waveguide 2
34 is the output attenuator 220cc from the upper output port 226 of the output attenuator 220bc.
To the upper input port 222 of the. Output attenuators 220dc, 220db, 2
An intermediate waveguide 234 connecting 20da to each of the output attenuators 220ac, 220ab, 220aa is typically wrapped by wraparound, as indicated by terminations A, B and C, to typically input waveguide 202. Or this is done by crossing either of the output waveguides 204.

As in the Mach-Zehnder interferometer 10, the upper input port 212 and the upper output port 216 of each input attenuator 210 are actually the opposite ends of the same inner upper waveguide, and also each output. The upper input port 222 and the upper output port 226 of the attenuator 220 are actually opposite ends of the same inner upper waveguide, so the intermediate waveguide 230 is actually the input waveguide 202 of each respective input waveguide 202. An extension, intermediate waveguide 234 is actually an extension of each output waveguide 204. Each attenuator 210 or 220 is OFF in the passing state (point I in FIG. 2).
And in this state, all light energy entering through the upper input port 212 or 222 exits through the upper output port 216 or 226 and also enters through the lower input port 214 or 224. All light energy exits via the lower output port 218 or 228. In the OFF state of all attenuators, all light energy entering the matrix 200 via the input waveguide 202 is discarded from the empty output port 216. By increasing the heating power applied to the phase shifters of the input attenuator 210 and the output attenuator 220 toward point II in FIG. 2, one particular input waveguide 202 can be coupled to a particular output waveguide 204. Turning on the input attenuator 210 and the output attenuator 220, which are coupled to, directs some or all of the optical energy entering through its input waveguide 202 to its output waveguide 204.

FIG. 5 is a high level block diagram of the overall 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 allows the matrix 300 via the output waveguides 304. A feedback mechanism is included to determine the power of the optical signal emerging from the matrix and adjust the attenuators of the matrix 300 accordingly to balance the power in the output waveguide 304 in real time. The matrix 300 may be the matrix 100 as described above or the matrix 200 as described above. The feedback mechanism includes an optical spectrum analyzer 310, a controller 312 and a set of optical taps 314. Each tap 31
4 directs a small constant portion of the power in each one of the output waveguides 304 from that waveguide 304 to the spectrum analyzer 310. A spectrum analyzer 310, which is an example of a power measurement device, measures the power directed from each output waveguide 304 to this spectrum analyzer and outputs a signal representative of these powers to the controller 3.
Send to 12. Based on these signals, controller 312 adjusts the attenuators of matrix 300 to balance the power in output waveguide 304. Preferably, tap 314 is based on a directional coupler. Preferably, controller 312 is based on a personal computer. The controller 312 also includes an electronic driver for adjusting the heating power applied to the phase shifter of the attenuator of the matrix 300 according to the control signal received by the electronic driver from the personal computer.

FIG. 6 is a high level block diagram of an alternative optical switching system 350 of the present invention. Similar to system 250, system 350 has four input waveguides 402 through 4
The output waveguide 404 includes a 4 × 4 optical switch matrix 400 for switching an optical signal, a set of optical taps 414, an optical spectrum analyzer 410, and a controller 412. Tap 414, spectrum analyzer 410 and controller 41
2 is a tap 314 of the system 250, a spectrum analyzer 310, and a controller 31.
It is substantially the same as 4. The main difference between system 250 and system 350 is that in system 350 tap 414 spectrally analyzes a small constant portion of the power in input waveguide 402 rather than a small constant portion of power in output waveguide 404. It is to turn to the vessel 410. In other respects, the structure and operation of system 350 is substantially the same as the structure and operation of system 250. The spectrum analyzer 410 measures the power directed from each input waveguide 402 to the spectrum analyzer and sends signals representative of these powers to the controller 412. Based on these signals, controller 412 adjusts the attenuators of matrix 400 to balance the power in output waveguide 404. The degree to which the power in the output waveguide 304 or 404 is balanced by the system 250 or 350 depends on the resolution of the respective 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. The electronic drive is typically digital with a fixed, predetermined number of steps.
Electronic drives with large step sizes have large dynamic range at the expense of low accuracy. Electronic drives with small step sizes have high accuracy at the expense of limited dynamic range. Although the present invention has been described with respect to a limited number of embodiments, it will be appreciated that numerous variations and modifications of the invention and other applications can be implemented.

[Brief description of drawings]

[Figure 1]   The figure which shows a Mach-Zehnder interferometer.

FIG. 2 shows the relative output power as a function of the heating power applied for one particular Mach-Zehnder interferometer.

[Figure 3]   The figure which shows the architecture (basic structure) of the optical switch matrix of this invention.

[Figure 4]   FIG. 3 is a diagram showing the architecture of another optical switch matrix of the present invention.

[Figure 5]   FIG. 3 is a high-level block diagram of the overall system of the present invention.

[Figure 6]   FIG. 3 is a high level block diagram of another overall system of the present invention.

[Explanation of symbols]

10 Mach-Zehnder interferometer, 12 upper waveguide, 14 lower waveguide, 16
First 3 dB directional coupler, 18 Second 3 dB directional coupler, 20, 22
Phaser, 24 Left end of upper waveguide (input port), 26 Right end of upper waveguide, 2
8 Right end of lower waveguide (output port, empty port), 100, 200, 300,
400 optical switch matrix, 102, 202, 302, 402 input waveguide, 104, 204, 304, 404 output waveguide, 110, 210 input attenuator, 112 upper input port (empty input port), 114, 124 , 214,
224 lower input port, 116, 126, 226 upper output port, 118,
128 lower output port (empty output port), 120, 220 output attenuator, 1
30, 132, 134, 230, 232, 234 Intermediate waveguide, 218, 228
Lower output port, 250, 350 Optical switching system, 310, 410 Optical spectrum analyzer (spectral analyzer) 312, 412 Controller, 314, 41
4 light taps.

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE, TR), OA (BF , BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, G M, KE, LS, MW, MZ, SD, SL, SZ, TZ , UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, B Z, CA, CH, CN, CO, CR, CU, CZ, DE , DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, I S, JP, KE, KG, KP, KR, KZ, LC, LK , LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, P T, RO, RU, SD, SE, SG, SI, SK, SL , TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW F term (reference) 2H047 KA03 KA12 KB04 MA05 RA08                 2H079 AA12 BA01 BA03 CA05 EA05                 2K002 AA02 AB05 DA08

Claims (17)

[Claims] 1. An optical switching system for switching optical energy from a plurality of input waveguides to a plurality of output waveguides, comprising: (a) each output waveguide and each input waveguide. An optical switching system including at least one respective attenuator for directing a tunable portion of light energy entering through each of the input waveguides to each of the output waveguides. 2. The system of claim 1, wherein each attenuator comprises a Mach Zehnder interferometer. 3. For each output waveguide and for each input waveguide, one of said at least one respective attenuator comprises a 2 × 2 switch having an empty output port. The system according to claim 1. 4. For each output waveguide, said one of said at least one 2 × 2 of said at least one respective attenuator directing optical energy from a first input waveguide to each said output waveguide. 4. The switch according to claim 3, wherein the switch has an empty input port.
The system described in. 5. For each output waveguide and for each input waveguide, one of said at least one respective attenuator comprises a 2 × 2 switch having an empty input port. The system according to claim 1. 6. For each input waveguide, the one 2 × 2 switch of the at least one respective attenuator that directs light energy from each of the input waveguides to a final output waveguide. Has an empty output port.
The system described in. 7. The method of claim 1, further comprising: (b) a feedback mechanism for adjusting the plurality of attenuators to balance the power of the optical energy in the plurality of output waveguides. System. 8. The feedback mechanism comprises: (i) a power measuring device; and (ii) for each output waveguide, directing a fixed portion of the optical energy in each output waveguide to the power measuring device. A tap, and (iii) (A) for each output waveguide, receiving a signal representing the power of the optical energy in each output waveguide from the power measuring device, and (B) based on the signal, 8. A system for adjusting the attenuator to balance the power. 9. The system of claim 8, wherein the power measurement device includes a spectrum analyzer. 10. The system of claim 8, wherein each tap comprises a directional coupler. 11. The feedback mechanism comprises: (i) a power measuring device; and (ii) for each input waveguide, directing a fixed portion of the optical energy in each input waveguide to the power measuring device. A tap and (iii) (A) for each input waveguide, receiving a signal representing the power of the optical energy in each of the input waveguides from the power measuring device, and (B) based on the signal, 8. A system for adjusting the attenuator to balance the power of optical energy in the output waveguide. 12. The system according to claim 11, wherein the power measuring device comprises a spectrum analyzer. 13. The system of claim 11, wherein each tap comprises a directional coupler. 14. A method of switching each of a plurality of optical signals traveling on a respective input waveguide from its respective input waveguide to a desired one of a plurality of output waveguides, the method comprising: ) For each output waveguide, and for each input waveguide, at least one respective one for directing an adjustable portion of the signal traveling on each input waveguide to each output waveguide. Providing an optical switch matrix including an attenuator; (b) selecting the attenuator that directs the optical signal to a desired output waveguide; (c) the power of the optical signal in the output waveguide. Adjusting the selected attenuator to balance the. 15. The method further comprises: (d) measuring the power of the optical signal in the output waveguide, the adjustment being based on the measured power of the optical signal in the output waveguide. 15. The method according to claim 14, characterized in that 16. The method further comprises: (d) measuring the power of the optical signal in the input waveguide, the adjustment being based on the measured power of the optical signal in the input waveguide. 15. The method according to claim 14, characterized in that 17. The method of claim 14, wherein the adjusting is performed to equalize the power of the optical signal in the output waveguide.