MXPA01006352A - Method and apparatus for controlling the ratio of an output signal and an input signal - Google Patents

Abstract

The operating ratio of an input signal and an output signal of a device (for example, the gain of an amplifier) is controlled by the use of two signals having respective levels corresponding to the input and output signal levels. The ratio is controlled to a target value based on a difference between the two signals, without the need for either a reference signal representing the target value or a division operation to calculate the operating ratio. In a preferred mode, the two signals are produced by corresponding amplifier units which have known gains and which are connected, respectively, to the input and the output of the device.

Description

METHOD AND APPARATUS FOR CONTROLLING THE RELATION OF A SALIDAY SIGNAL AND AN INPUT SIGNAL This application claims the benefit of the provisional patent application in E.U.A. with number 60 / 113,083, filed on December 21, 1998.

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for controlling the relationship between an output signal and an input signal of a device. The invention can be instrumented using relatively simple electronic control elements, and is suitable for a wide variety of applications including, for example, electronic control of electric and optical amplifiers and attenuators. Conventional signal ratio control techniques typically involve the monitoring of an output signal or an input signal of a device relative to an external reference signal that is set in accordance with a predetermined target relationship. The device is controlled to operate in an objective relationship based on an error signal representing a difference between the monitored signal and the reference signal.

Another conventional technique involves monitoring both the output signal and the input signal of a device to determine a relationship of the two signals. The ratio determined in this way is compared with an external reference signal corresponding to the objective relation to generate an error signal representing the difference between the determined relation and the objective relation. The device is controlled to work in the target relationship based on the error signal. Figure 1 illustrates the conventional technique just described. In Figure 1 a splitter 12 receives signal levels x and y proportional to the input and output signal levels of a controlled device 10 respectively. That is, x = C? X, ey = C2Y, where X and Y are the levels of the input and output signals, respectively, and Ci and C2 are constants of proportionality dependent on the design of the particular system (often C-). ? = C2). The signal levels x and y can, for example, represent the voltage, current or power levels of the input and output signals. The G ratio of the output signal level to the input signal level can be represented as follows: G = (Y / X) = K (y / x) ... (1) where K = C2 / C ? In this way, signal levels x and y are related as follows: y = Gx / K ... (2) Divider 12 performs a division operation based on inputs x and y, and outputs a proportional relationship signal to the relation G: y / x = G / K ... (3) The relationship signal is provided to a subtracter 14. The subtractor is also provided with a specified reference signal level Gs = Gt / K, where Gt is the objective relationship. The subtractor 14 subtracts the measured relation y / x from the specified relation Gsp to generate an error signal level E: E = Gsp-y / x = (Gt / K) - (G / K) = (Gt-G) / K ... (4) Error E is provided to a controller 16 that adjusts the operation of the device to bring error E to zero. In this state, G becomes equal to GT as will be recognized from equation (4).

DESCRIPTION OF THE INVENTION The present invention reflects a new and unique approach to the ratio control process that does not require an external reference signal or a division operation as in conventional techniques. Briefly, the invention uses first and second signals having levels corresponding to the input signal level and the output signal level of the device, respectively. As will be seen from this moment, by subtracting one of the signals from the other, an error signal is generated to provide a controller that, in turn, controls the operation of the device to provide the level of error signal to zero. In this state, the ratio of the input and output signal levels of the device will be coupled to a predetermined target relationship. As shown in the illustrative modalities of this, the first and second signals may be produced, respectively, using first and second amplifying units of known gains. When the error signal level is zero, the ratio of the input and output signal levels is coupled to a predetermined target ratio based on the known gains of the first and second amplifier units. Figure 2 is a diagram illustrating the basic principles of instrumentation using first and second amplifying units as just described. In Figure 2, an input side amplifier unit 23 having a known gain G i and an output side amplifier unit 25 having a known gain G 0 are connected to the input and output, respectively, of a device 20 which it will be controlled (connections have been omitted from the figures for reasons of simplicity). The input side amplifier unit 23 inputs a signal having a level S i = G x, where X is proportional to the input signal level of the device 20. The output side amplifier unit 25 produces a signal that has a So = Goy level, where y is proportional to the output signal level of the device 20. The signals from the input side and output side amplifier units are provided to a subtracter 24, which has a Sen- level: Serr = So-S¡ - - - (5) The error Sen is provided to a controller 26, which adjusts the operation of device 20 so that it carries the error Sep- to zero and keeps it in this condition. The substitution of S0 and Sj, equation (5) can be rewritten as follows: Serr = G0y-GiX ... (6) Substitution of Gx / K by y (see equation (2)) in the equation (6) produces: Serr = (G0Gx / K) -G¡X = x. { (G0G / K) -G¡} ... (7) The multiplication of right side of equation (7) by G¡ / G¡ produces: Serr = GiX. { (Go / KG¡) G-1} ... (8) As is evident from equation (8), Serr will be zero when G = KG / Go. In other words, the selection of the input side and output side amplifier units, or more precisely, their gains, establish an objective relation AND the control device 10 to keep Sen at zero in this way will result in a constant ratio G = Gt = KG, / Go. The same results are obtained if the minuend and subtrahend in equation (5) are inverted: ^ er ^ p ^ o - "(5) Sen- this way will be expressed more generally as indicated below: How it will be evident from this analysis, the present invention does not require an external reference signal representing the objective input-output signal ratio and does not require a division to determine the actual operational G ratio. in a simple subtraction of signals having levels corresponding to the input and output signal levels, avoiding the need for an external reference signal and a division operation, as is used in conventional techniques, the present invention offers the utilities of the electronic elements with simplified control and high control rates at low cost.In addition, the principles of the invention are not limited to the application to any device articulate or type of devices, or the use of particular components to produce the signals that will be subtracted. In this way it will be understood that the applications mentioned herein, as well as the illustrative modalities, are merely exemplary. The use of amplifying units to produce the signals that will be subtracted may be preferred, as in the illustrative embodiments, due to the advantages in accommodating devices having low levels of input signal (and possibly also low output levels), as well as devices that use non-electrical signals. For example, transimpedance amplifying units can be used in applications involving devices that use optical signals.

BRIEF DESCRIPTION OF THE INVENTION As mentioned in previous paragraphs, the present invention allows the control in relation of an input signal and an output signal of a device without requiring an external reference signal or a division operation. In accordance with one of its main aspects, the invention provides a method for controlling a ratio of an output signal level from a device and an input signal level to the device, comprising: providing a first component connected to an input of the device for producing a first signal having a level corresponding to the level of the input signal; providing a second component connected to an output of a device to produce a second signal having a level corresponding to the output signal level; and adjust the ratio based on the difference between the levels of the first and second signals. In accordance with a preferred mode, the device itself is an amplifying unit, the first and second components are the first and second amplifying units, and the controlled ratio is a gain of the amplifying unit. In a specific instrumentation, the device is a pumped fiber optic amplifier unit, and the controlled ratio is an optical gain of the fiber optic amplifier unit. The optical gain is established by adjusting the pumping power of a laser pump of the fiber optic amplifier unit. The first and second amplifying units are transimpedance amplifying units that are connected by photodetectors corresponding to the input and output of the fiber optic amplifier unit (a transimpedance amplifier provides a functional output voltage signal to an input current signal) . Each of the input signal and the output signal can be a composite signal constituted by a plurality of signals. In such a case, the signal levels of the first and second signals mentioned may correspond to the RMS signal levels of the composite input and output signals, respectively, and the controlled ratio may be an RMS optical gain. In accordance with another of its main aspects, the present invention provides an apparatus for implementing said method. Another aspect of the invention provides a method for controlling a ratio of an output signal level from a device and an input signal level to the device, comprising the production of a first signal having a level corresponding to the signal level input, producing a second signal having a level corresponding to the output signal level, and adjusting the ratio based on a difference between the levels of the first and second signals. The aforementioned and other aspects of the present invention, as well as various features and advantages, will be better understood under the consideration of the following detailed description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram to explain a conventional relationship control technique. Figure 2 is a diagram to explain the control technique in accordance with the present invention. Figure 3 is a diagram illustrating a first apparatus in accordance with the invention. Figure 4 is a diagram illustrating a second apparatus in accordance with the invention. Figure 5 is a diagram illustrating a third apparatus in accordance with the invention. Figure 6 is a diagram illustrating a fourth apparatus in accordance with the invention.

Figure 7 is a diagram of the electronic control elements that are employed in a test apparatus constructed in accordance with Figure 4. Figure 8 is a flow chart of the control operation in the test apparatus. Figure 9 is an oscillograph showing the temporal dynamics of an optical amplifier unit of the test apparatus without the relationship control circuitry in operation. Figures 10 and 11 are oscillographs showing the temporal dynamics of the optical amplifier with the ratio control circuitry in operation.

DETAILED DESCRIPTION OF THE INVENTION Figure 3 is a diagram illustrating a first apparatus 1 in accordance with the present invention. The reference number 30 in the figure represents an electrical device that operates with a G ratio that can be controlled from an input signal and an output signal. In the manner shown, the device 30 is a gain amplifier unit that can be adjusted that includes a single amplifier. However, in practice, the device 30 can be any electrical device having a ratio that can be controlled in terms of its input and output signals (for example, a multi-stage amplifier having cascaded amplifiers, an attenuator single stage or multiple stages, etc.). The input and output signals may be voltage or current signals, for example. A first amplifying unit 33 of known gain Gj, and preferably including a single amplifier, is connected to the input side of the controlled amplifier unit 30. A second amplifying unit 35 of known gain G0, also preferably including a single amplifier, is connects to the output side of the controlled amplifier unit 30. The connections of the amplifier units 33 and 35 to the input and output sides of the amplifier unit 30 can be direct, as shown, or can be indirect (for example, by a current sensor) depending on the requirements of a given instrumentation. The output signals from the amplifier units 33 and 35 are provided to a controller 36 which functions as discussed in detail below, to adjust the operation of the controlled amplifier unit 30 so as to control the ratio G. In the illustrative instrumentation, G is the gain course of the amplifier unit 30. The input side amplifier unit 33 emits a signal level Si = Gxx, where x is an input signal level to the amplifier unit and is proportional to the amplifier unit. input signal level X of the controlled amplifier unit 30. The amplifier unit on the output side 35 emits a signal level S0 = G0y, where y is an input signal level to the output side amplifier unit, in addition , is proportional to the output signal level Y of the controlled amplifier unit 30. The controller 36 checks a subtraction as explained above to determine an error value Serr = ± (S0 -S!), And emits a control signal Scti to the controlled amplifier unit 30 to adjust its gain, so that Serr remains substantially at zero. In this way the amplifying unit 30 is maintained at a substantially constant gain G = GtKGj / G0, that is, an objective gain proportional to the ratio of the known gains of the input side and output side 33 and side amplifier units. 35. To give a more concrete example, suppose that the input and output signals to the controlled amplifier unit are voltage signals having levels Vj and V0 (= GVj), respectively. Assuming sufficiently high input impedances of the amplifying units 33 and 35, the respective input voltage levels thereof will be V, and V0 (corresponding to the case C -? = C2, K = 1). The output voltages of the amplifier units on the input side and output side can be expressed as follows: Si = G¡V¡ So = G0Vc = GoGV¡ In this case G¡ and G0 represent the respective voltage gains of the Amplifying units on the input side and on the side of 1 output 33 and 35, and G represents the voltage gain of the controlled amplifier unit 30. The controller 36 subtracts the voltage Sj from the voltage S0 to determine the error Sen-: ^ err- ^ or "^ ¡= G0GV¡-GiV¡ Based on the error determined in this way, the controller 36 adjusts the gain of the amplifier unit 30 to bring the Serr error to zero and maintain said state, as will be evident from equation (10). The controller 36 may use any suitable control algorithm to control the G ratio based on the Serr error. Proportional-integral (Pl) or proportional-integral-derivative (PID) control algorithms may be preferred for optimal performance. Both controllers, digital and analog, can be used. Suitable algorithms for specific applications can be determined by conventional techniques, for example, by computer simulation and / or empirically. For a more complete analysis of Pl, PID, and other control techniques, see Koenig, D., Control and Analysis of Noisy Processes, Prentice Hall, 1991 (incorporated herein by reference). Figure 4 illustrates a second apparatus 2 according to the present invention for controlling the optical gain (optical power gain) of an optical amplifier unit 40. In this embodiment, the optical amplifier unit 40 is a fiber optic amplifier pumped from a single stage (single coil). Such amplifiers are already well known in the art and will not be discussed in detail here. Briefly, the amplifying unit includes a fiber optic coil 41 doped with ions of a rare earth element (e.g., erbium or praseodymium) and a wavelength-division-multiplex optical coupler (WDM) 42 which couples a signal of optical input with light "pumped" from a laser source controller 44. Note that the thin lines connecting the components in Figure 4 represent the fiber optic connections, while the thick lines connecting the components represent the electrical connections. The laser source or the laser pump unit 44 operates with an optical wavelength that is external to the wavelength band of the optical input signal to the amplifier, but is effective to excite the doped ions in the fiber coil Optics 41. The optical input signal may be composed of a single optical signal at a predetermined wavelength, or may be a material signal composed of a plurality of optical signals at different predetermined wavelengths, as is typical in networks of fiber optic communication WDM. The light of the input signal stimulates the excited ions in the fiber coil 41 to emit additional light of the same wavelengths, effectively amplifying the input optical signal.

The optical power gain G of the amplifier unit 40 depends on the output power of the laser pump unit 44, and can therefore be controlled by adjusting the output power of the laser pump unit. When the input signal will be a composite input, the optical amplifier unit 40 may incorporate a gain leveling filter so that the individual wavelength components of the composite signal experience an equal gain. Otherwise, the optical power gain will be the RMS gain for the collective wavelength components. The optical amplifier unit 40 may also include optical insulators (not shown) on the input and output sides. In the arrangement of Figure 4, a first transimpedance amplifying unit (TIA) 43, preferably including a single amplification stage, has its input connected to an input side of the optical amplifier as a photodetector 47 (for example photodiode) and an optical shunt 48. The optical shunt functions to couple a small portion of the incoming optical signal from the input fiber I of the apparatus to a monitor output 48b that is connected to a photodetector 47. The remaining portion of the optical signal of The input is propagated via a main output 48a of the lead to the input of the optical amplifier unit 40. A second unit TIA 45 has the input connected to an output side of the optical amplifier unit 40 via a corresponding photodetector 47 'and a lead associated optics 48 '. This optical shunt functions to couple a small portion of the output light from the optical amplifier unit to a monitor output 48b 'which is connected to a photodetector 47'. The remnant of the output light is propagated by a main output 48a 'of the branch 48' to an output fiber O of the apparatus. The coupling ratios of the optical branches 48, 48 'can be the same or different. Likewise, these are not restricted to any particular limit. Furthermore, it is generally preferred to use coupling ratios that substantially retain the input and output signal strengths of the apparatus. For example, a coupling ratio of at least 90/10 (meaning that 10% of the light is coupled to the monitor output with 90% of the light propagating to the main output). With reference to Figure 4, the photodetectors 47, 47 'convert the received light from the leads 48, 48' into electrical current signals having levels proportional to the amounts of light received by monitor outputs 48b and 48b '. In this way, the current signals are proportional to the optical power levels of the optical input and output signals of the optical amplifier 40. The ATI 43 and 45 units, in turn, produce output voltage signals proportional to their signals of input current, and these output signals are provided to a controller 46. The respective output voltage signals S i and S 0 of the TIA units 43 and 45 may be represented as follows: S GICIPI So = G0C2P0 = G0C2GP¡ In this, G¡ and G0 respectively represent the transimpedance gains on the input side of the unit TIA 43 and on the output side of the unit TIA 45, P¡ and P0) respectively represent the input optical signal power level and output optical signal power level, G represents the optical power gain of the optical amplifier unit, and Ci and C2 represent the proportionality constants dependent on the coupling ratios of the derivations 48, and 48 'and the responsiveness of the photodetectors 47, 47'. The controller subtracts one of the two voltage signal levels from the other to obtain an error voltage level Serr- err = í (^ or ~ ^ > i) = ± (G0C2Po - G¡C1P¡) = ± (G0C2GP - G¡C? P¡) = ± P¡ (G0C2G - G1C1) = ± PiG¡C ?. { (G0C2 / G1C1) G - 1.}. ... (11) Based on the error voltage, the controller 46 generates a control signal to adjust the operation of the laser pump unit 44, and in this way adjust the optical gain of the amplifying unit 40, to bring Sen to zero and maintain said condition. For example, the laser pump unit may incorporate a pump voltage controller with controlled voltage, if the control signal from the controller 46 can be a voltage set based on a Pl or PID control algorithm using the signal level of Serr error - Again, the control algorithm can be instrumented by digital or analogous circuitry as desired in the particular application. As will be evident from equation (11), when the error If it is zeroed, the optical gain of the amplifying unit 40 will be G = G? = (G | / G0) (C? / C2). When the selected optical leads 48, 48 'have the same coupling relationship and the selected photodetectors 47, 47' have the same response character, Ci and C2 will be equal, so that the target gain is simply GT = G / G0 . By controlling the laser pump to keep Serr at zero, the amplifier unit 40 operates at a constant gain G = Gj. And the target gain is simply a predetermined value based on the known gains of the input side and output side of the amplifying units 43, 45. An external reference signal representing the target gain is not required. As well as a division operation to determine the actual operating gain G. Figure 5 illustrates another embodiment 3 of the invention, in this case to control a multi-stage pumped optical fiber amplifier unit 40 '. The arrangement in Fig. 5 is generally similar to that of Fig. 4, except that the amplifying unit includes a plurality of amplification stages, each including a doped fiber coil 41, a WDM coupler 42, and a control unit. laser pump 44 as described above with respect to figure 4. Here, the number of amplification stages is two, but a greater number of stages can be used. The amplifier coils of the different stages (which can be pumped equally but provide equal or different gains depending on the particular application) are connected in series, as shown. Each stage can also include a gain leveling filter (not shown). As in the embodiment in Figure 4, the controller in Figure 5 subtracts one of the TIA output voltages S i, S 0 from the other to obtain an error signal level Sen. Based on the errors obtained in this way, the controller generates control signals to adjust the outputs of the laser pump units and thus adjust the optical gain of the amplifying optical unit 40 'to bring the error Sep- to zero and maintain said state. In this state, the optical gain of the amplifier unit 40 'will be equal to the target gain, which is based on the known gains of the TIA units on the input side and on the output side, as explained above. The laser pump units can receive identical control signals, even though the two amplification stages may or may not be identical. Of course, in a case where the amplification stages differ and do not provide equal contributions to the general gain, they can be controlled differently, based on the contributions of their respective gain.

Figure 6 shows another embodiment 4, wherein two individually controlled optical amplifier units 40 are connected in series to form a multi-stage amplifier unit. This arrangement allows a more precise control of the overall optical gain than the arrangement of Figure 5, since each amplification stage is monitored and controlled individually. As shown in figure 6, the output side of the unit TIA 45 for the first amplification stage (left) and the output side of the unit TIA 43 for the second amplification stage (right) can have the inputs connected in common with a photodetector 47 '(47). Each amplification stage is controlled separately in the manner described in conjunction with Figure 4. Of course, although the two amplification stages are the same in Figure 6, as are their respective control systems, this is not necessarily the case in the practice. In practice, the two amplification stages may be different, as well as their control systems (for example, the TIA unit pairs may be selected to provide different gains or objectives). An apparatus such as that described in conjunction with Figure 4 was constructed and tested to examine its temporal dynamics. The single coil amplifier unit is composed of 13.7 m of conventional doped fiber, two optical insulators and the input and output, a WDM optical coupler of 1550/980 nm and a standard stabilized laser pump unit of 976 nm grid including a pump current source with voltage control capable of a time of response in submicroseconds (μs). The input signal to the controlled amplifier unit consists of two signals: a continuous wave of -10 dBm (CW) a signal of 1555 nm, and a square wave modulated signal of 500 Hz on / off, 0 dBm of 1553 nm. TIA units were constructed from respective operational amplifiers (with a frequency response of at least 10 MHz), resistors and capacitors that have transimpedance gains of 10,000 for the TIA unit on the input side and 681 for the output side of the unit. TIA unit. These values were determined appropriate based on the typical parameters specific to the system, such as splice losses, characteristics of the laser pump, characteristics of the photodetectors, etc. The TIA units were connected to the input and output sides of the optical amplifier unit by optical couplers 90/10 and substantially identical photodetectors (PIN InGaAs photodiodes with at least a 10 MHz frequency response). In this way, the constants of proportionality C-i and C2 were related as C2 = (9/10) C- |. This is easily derived from the fact that, by virtue of the coupling ratios 90/10, the amount of light coupled to the photodetector on the input side is 1/9 of the light input to the optical amplifier unit, and the amount of light coupled to the photodetector on the output side is 1/10 of the light emitted from the optical amplifier unit. The input and output fibers of the device were standard optical fiber SMF-28. The optical connections between the components of the devices were also made with SMF-28 optical fiber. The signal in the output fiber was measured with a 125 MHz photoreceptor and a 500 MHz digital oscilloscope. To provide a wide margin of control flexibility, a control system based on a digital microprocessor was used, including: two analogue converters to digital (A / D) of 8 bits, (with sampling at 2.5 Mhz). a programmable logic (PAL) grid Mach XL an IBM Power PC microprocessor running at 16 MHz an 8-bit digital to analog (D / A) converter Figure 7 is a block diagram showing the layout of the control system 100 and its connections to the TIA units and the laser pump current controller (pump drive circuitry). The two A / D converters 101 and 102 were used to digitize the electrical output voltages from the TIA units on the input side and the output side 43 and 45, respectively. The PAL 103 performs a rapid subtraction of the computer equipment from the output of the digitized amplifier from the A / D converters. The result of the subtraction, which represents the error Sep-, is used by the microprocessor 104 to execute a control algorithm Pl, and the resulting calculated control signal is then emitted by the D / A converter 105 to the drive circuitry of pump of the laser unit 44.

Figure 8 is a flowchart of the control procedure. From step S1, the PAL reads the digitized TIA outputs (Si, S0) from the A / D converters 101, 102. Then in step S2, PAL 103 calculates the error Serr (n) = S¡-S0, where n denotes the present (nth) control iteration. In step S3, the microprocessor 104 calculates a control movement M (n) to adjust the emission of the laser pump to carry the error Sep- to 0. The calculation is made in accordance with the following control algorithm Pl: M (n) = M (n-1) + l Serr (n) + P (Sßrr (n) -Serr (n-1)) where the coefficients I and P are, respectively, the gains of integral and proportional control and they can be selected and optimized empirically. For a more complete analysis of the Pl control, see the aforementioned Koening text. The optimal values of I and P for the test apparatus were determined empirically at 1 and 500, respectively. Then, in step S4, the value Serr (n-1) to be used in the next iteration is set to the current error Serr (n). Finally, the control movement M (n) is emitted to the pump drive circuitry, and the flow returns to step S1 to perform the next control interaction. The temporal dynamics of the single-coil amplifier described above, but without the automatic gain control system of the invention in operation, are shown in Figure 9. In particular, Figure 9 shows the traces of the input signal of the invention. square wave and the resulting output signal. The relative scales of the two signal strokes are set so that the strokes can be superimposed, as shown for a simpler comparison. A comparison of the signal traces reveals that the emission of the amplifier presents a severe distortion due to the slow gain dynamics associated with the erbium ions in the glass. Figure 10 shows the temporal dynamics with the gain control system on. As seen in Figure 10, the optical output signal has a square waveform with low distortion. The third trace in Figure 10, on those of the input and output, represents the pump control signal and is proportional to the power of the pump. The transient ignition details are shown in Figure 11. The initial rapid increase in the output signal is provided by the initial inversion (inversion refers to the population of helium ions in the excited state). However, the pumping speed is not sufficient to accommodate the increased signal strength. Therefore, after a procedure delay of approximately 5 μs, the gain control circuit increases the power of the pump to the maximum allowed value. The amplifier responds with a gain in temporary increment until the gain is reached. The pump power then decreases to the value required for a steady state operation. The total time required to correct the gain is approximately 25 μs. The response speed of the gain control system can, of course, be increased if a larger amount of pump power is available during transient ignition. Additionally, the response time can be reduced by using faster electronic elements, for example, an analog control circuit instead of a microprocessor-based circuit. It is prudent to repeat that the particular applications of the invention referred to herein, as well as the illustrative modalities, are merely exemplary. Numerous different instrumentations are possible maintaining the basic principles of the invention, seeing established the scope of the invention in the appended claims.

Claims (45)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for controlling a ratio of an output signal level from a device and an input signal level to the device, comprising: providing a first component connected to an input of the device to produce a first signal having a level corresponding to said level of input signal; providing a second component connected to an output of the device to produce a second signal having a level corresponding to said output signal level; and adjusting said ratio based on a difference between the levels of said first and second signals.

2. A method according to claim 1, further characterized in that said device is an amplifying unit and said ratio is a gain of said amplifying unit.

3. A method according to claim 2, further characterized in that each of said output signal and said input signal is a composite signal.

4. A method according to claim 1, further characterized in that said device is an optical device, said input and output signals are optical signals, and said first and second amplifying units are transimpedance amplifier units.

5. The method according to claim 4, further characterized in that each of said output signal and said input signal is a composite signal.

6. A method according to claim 5, further characterized in that said output and input signal levels are RMS levels of the composite signals.

7. A method according to claim 1, further characterized in that said adjustment includes producing a signal level of error Sep, where Serr = ± (S0 - S), S0 is a signal level of said second signal, and Si is a signal level of said first signal, and the use of said level of error signal is a basis for adjusting said relationship.

8. A method according to claim 7, further characterized in that said first signal and said second signal are composite signals and Si and S0 are RMS signal levels.

9. The method according to claim 7, further characterized in that said level of error signal and said first and second signal levels are voltage levels.

10. The method according to claim 1, further characterized in that said adjustment includes adjusting a component of said device that affects said relationship.

11. - A method for controlling an optical gain of an optical amplifying unit, comprising: providing a first transimpedance amplifying unit connected to an input of said optical amplifying unit; providing a second transimpedance amplifying unit connected to an output of said optical amplifying unit; and adjusting the optical gain based on a difference between an output signal of said first transimpedance amplifying unit and an output signal of said second transimpedance amplifying unit.

12. A method according to claim 11, further characterized in that said optical amplifier unit is a pumped fiber optic amplifier unit and said adjustment includes adjusting a pump power of a laser pump of said fiber optic amplifier unit.

13. The method according to claim 12, further characterized in that the optical gain is an RMS optical gain for a plurality composed of wavelengths entering said fiber optic amplifier unit.

14. A method according to claim 12, further characterized in that said pump power is adjusted by adjusting a drive control signal for said laser pump.

15. A method according to claim 12, further characterized in that said adjustment includes producing an error voltage Sen-, where Sen- = ± (S0 - S¡), S0 is an output voltage of said second transimpedance amplifying unit and Sj is an output voltage of said first transimpedance amplifying unit, and using said error voltage as a basis for adjusting the pump power of said laser pump .

16. A method according to claim 15, further characterized in that said first and second transimpedance amplifying units are respectively connected to said input and said output through corresponding photodetectors and S0 and S1 satisfy the following relations: S0 = G0C2GP S i = G, C, P, where G0 and G, are the transimpedance gains of said second transimpedance amplifying unit and said first transimpedance amplifying unit P, is an input optical signal power, G is the gain optics and C2 and Ci are constants.

17. A method according to claim 12, further characterized in that said fiber optic amplifier unit has a simple optical fiber amplification stage.

18. A method according to claim 12, further characterized in that said fiber optic amplifier unit has a plurality of fiber optic amplification stages connected in series.

19. An apparatus for controlling a ratio of an output signal level from a device and an input signal level to the device, comprising: a first component connected to an input of the device for producing a first signal having a level corresponding to that level of input signal; a second component connected to an output of the device to produce a second signal having a level corresponding to said level of output signal; and a controller connected to said first and second amplifier units and said device, said controller operating to adjust said ratio based on a difference between the levels of said first and second signals.

20. An apparatus according to claim 19, further characterized in that said device is an amplifying unit and said ratio is a gain of said amplifying unit.

21. An apparatus according to claim 20, further characterized in that each of said output signal and said input signal is a composite signal.

22. An apparatus according to claim 19, further characterized in that said device is an optical device and said first and second amplifying units are transimpedance amplifying units.

23. A method according to claim 22, further characterized in that each of said output signal and said input signal is a composite signal.

24. - A method according to claim 23, further characterized in that said output and input signal levels are RMS levels of the composite signals.

25. An apparatus according to claim 19, further characterized in that said controller produces a signal level of error Serr, where Serr = ± (S0 - S), S0 is a signal level of said second signal and S It is a signal level of said first signal, and said controller uses said level of error signal as a basis for adjusting said relationship.

26. A method according to claim 19, further characterized in that said controller adjusts a component of said device that affects said relationship.

27.- An optical amplifier apparatus with controlled gain, comprising: an optical amplifier unit; a first transimpedance amplifying unit connected to an input of said optical amplifier unit; a second transimpedance amplifying unit connected to an output of said optical amplifying unit, and a controller connected to said first and second transimpedance amplifying units and said optical amplifying unit, said controller functions to adjust an optical gain of said optical amplifying unit with base in a difference between an output signal of said first transimpedance amplifying unit and an output signal of said second transimpedance amplifying unit.

28. - An apparatus according to claim 27, further characterized in that said optical amplifier unit is a pumped fiber optic amplifier unit that includes a laser pump, and said controller adjusts a pump power of said laser pump.

29. A method according to claim 27, further characterized in that the optical gain is an RMS optical gain for a plurality composed of wavelengths entering said fiber optic amplifier unit.

30. An apparatus according to claim 27, further characterized in that said first and second transimpedance amplifying units are respectively connected to said input and said output through the corresponding photodetectors.

31. An apparatus according to claim 27, further characterized in that said controller produces an error voltage Sen-, where STp- = ± (S0-Sj), Ss is an output voltage of said second transimpedance amplifier. and S i is an output voltage of said first transimpedance amplifier, and said controller uses said error voltage as a basis for adjusting the optical gain.

32.- An apparatus according to claim 31, further characterized in that said first and second transimpedance amplifier units are respectively connected to said input and said output through corresponding photodetectors and S0 and Sj satisfy the following relations: S0 - G0C2GP¡ S | = G, dP? wherein S0 and S1 are the corresponding transimpedance gains of said second transimpedance amplifying unit and said first transimpedance amplifying unit, P1 is an input optical signal power, G is the optical gain, and C2 and Ci are constant .

33.- An apparatus according to claim 32, further characterized in that said optical amplifier unit is a pumped fiber optic amplifier unit that includes a laser pump, and said controller adjusts the power of the pump of said laser pump.

34. An apparatus according to claim 33, further characterized in that said fiber optic amplifier unit has a single stage of fiber optic amplification.

35.- An apparatus according to claim 33, further characterized in that said fiber optic amplifier unit has a plurality of fiber optic amplification stages connected in series.

36.- A method to control a ratio of an output signal level. from a device and an input signal level to the device, comprising: providing a first component connected to an input of the device to produce a first signal having a level corresponding to said input signal level; providing a second component connected to an output of the device to produce a second signal having a level corresponding to said output signal level; and adjusting said ratio based on a difference between the levels of said first and second signals.

37. A method according to claim 36, further characterized in that said device is an amplifying unit and said ratio is a gain of said amplifying unit.

38.- A method according to claim 36, further characterized in that said device is an optical device, said input and output signals are optical signals, and said first and second amplifying units are transimpedance amplifying units.

39.- The method according to claim 36, further characterized in that said adjustment includes producing an error signal level Serr where Serr = ± (S0-S), SQ is a signal level of said second signal, S It is a signal level of said first signal, and using said level of error signal as a basis for adjusting said relationship.

40.- An apparatus for controlling a ratio of an output signal level from a device of an input signal level to the device, comprising: a first component connected to an input of the device to produce a first signal having a level corresponding to said level of input signal; a second component connected to an output of the device to produce a second signal having a level corresponding to said level of output signal; and a controller connected to said first and second amplifier units and said device, said controller operating to adjust said ratio based on a difference between the levels of said first and second signals.

41. An apparatus according to claim 40, further characterized in that said device is an amplifying unit and said ratio is a gain of said amplifying unit.

An apparatus according to claim 40, further characterized in that said controller produces an error signal level Serr, where Serr = ± (S0-S), S0 is a signal level of said second signal and S It is a signal level of said first signal, and said controller uses an error signal level mentioned as the basis for adjusting said relationship.

43.- A method for controlling a ratio of an output signal level from a device and an input signal level to the device, comprising: producing a first signal having a level corresponding to said input signal level; producing a second signal having a level corresponding to said level of output signal; and adjusting said ratio based on a difference between the levels of said first and second signals.

44. An apparatus according to claim 43. further characterized in that said relationship is adjusted so that substantially maintains an objective ratio of said input and output signal levels, said target ratio being based on factors of proportionality with respect to said first and second signal levels at said input and output signal levels, respectively. 45.- An apparatus according to claim 44, further characterized in that said first signal and said second signal are produced, respectively by means of a first amplifying unit and a second amplifying unit, said first and second amplifying units have predetermined gains, and said factors of proportionality are said predetermined gains.