CN1159868C - Control method and device for stable output level of optical receiver - Google Patents

Abstract

The present invention relates to a method for controlling the stability of the output level of an optical receiver, which controls the stability of the output level by detecting optical power and modulation degree. A receiver for implementing the method comprises an optical receiving module, a fixed gain processing circuit, a variable gain processing circuit, a control signal generating circuit, a DC optical detector, a coupler and a network management signal processing unit, wherein the optical power from the DC optical detector and the modulation degree from the coupler are synthesized by the network management signal processing unit for generating signals for sending in the control signal generating circuit; then, a signal is generated for controlling the gain variation of the variable gain processing circuit for keeping the stability of the output level. The present invention does not need a high frequency processing circuit, and has high control precision and good stability.

Description

Control method and device for stable output level of optical receiver

The invention relates to fields using analog optical transmission systems such as radio and television and telecommunications. Specifically, in cable television and other optical transmission systems using analog modulation, the receiver keeps the output level stable when the modulation degree of the transmitter changes and the optical power input to the optical receiver changes.

In the existing field of analog optical transmission such as optical fiber CATV, most of the existing optical receivers do not have the function of automatically controlling the output level stabilization, but the output level is stabilized manually or remotely through the network management system. The above process is done manually. Once the total signal gain of the receiver is determined, it will not change. The output level of the receiver will change due to the change of the received optical power, the change of the modulation degree of the transmitter and the change of the link attenuation. In this way, the output level of the receiver is unstable, or the receiver does not have an automatic output level control function.

For the level stabilization control method with AGC (Automatic Gain Control: AUTO GAIN CONTROL) function, there are comparisons on pages 82 and 182 in the book ""Cable TV Technology", edited by Wang Xisheng, etc., Electronic Industry Press, 1997". detailed introduction. As shown in Figure 1, the existing optical receiver includes an optical receiving module 1, a fixed-gain radio frequency processing circuit 2, a variable gain processing circuit 3 (that is, an AGC amplifier or an electronically adjustable attenuator), a radio frequency detection circuit 4, a control Signal generating circuit 5, DC optical detection unit 6, network management signal processing unit 7, and coupler 8; its working method is: coupler 8 couples out a small part of output level 9, and detects the coupled signal through radio frequency The circuit 4 performs level detection (level detection control mode) or pilot frequency detection (pilot frequency control mode), and uses the detected output signal to generate a control signal through the control signal generation circuit 5, and controls the variable gain processing circuit 3 to realize the output voltage Flat 9 stable. The control signal generating circuit 5 also sends the generated control signal to the network management signal processing unit 7, so as to monitor the working status of the control signal generating circuit 5 and whether the generated control signal is normal.

The main purpose of the DC optical detection unit 6 in Figure 1 is to provide the optical power of the receiver for the network management signal processing unit 7, and generate an alarm when the optical power exceeds a certain range, because only when the optical power is within a certain range, the system transmits indicators to meet the requirements. The existing optical power detection of the receiver is only to intuitively know the size of the received optical power, or inform each receiving point in the network whether the received optical power is normal through the network management; the DC optical detection unit 6 and the network management signal processing unit 7 control the output power Flat 9 stabilization doesn't work. Part of the radio frequency signal coupled by the coupler 8 is sent to the demodulation circuit of the network management signal processing circuit 7, and informs the receiver of the user command sent by the front end, the working status of the transmitter, and the like.

Therefore, in the prior art, in order to solve the problem of receiver output level stability, there are three solutions: level detection control, pilot frequency control and manual (mechanical or electric adjustment) adjustment methods.

For the level detection control method, the receiver is required to firstly perform power detection on the output signal level to generate a control signal, and use the control signal to control the AGC amplifier or the electric attenuator, through the gain change of the amplifier or the attenuation of the electric attenuator change to ensure the stability of the output level. The level detection feedback control method has its advantages, but it also has several disadvantages: high-frequency broadband power detection devices are required, which increases the complexity and cost of hardware; since the detection diodes have different responsivity to different frequency bands, the same level Different detection levels will be generated in different frequency bands, and there will be a large error. This control system can only keep the total power level stable in the whole frequency band, but cannot guarantee the level stability of a single channel. For environments with sudden noise, the level detection part of the control system will mistake the sudden high-amplitude noise as the signal power, and then mistakenly believe that the level is too high and generate an action to reduce the signal level; in addition , the average power detection is limited by the performance of the device, and the control accuracy is limited.

The pilot control method is a better solution. Its essence is to detect the high stability signal sent by the front end at the receiving side, and judge the change of the transmission channel signal gain according to the change of the received signal, and generate a signal according to the change of the channel signal gain. The feedback control signal is used to control the variable gain part in the channel, so as to realize the stabilization of the signal gain of the entire communication channel. However, the pilot control system needs to add pilot devices at the front end and pilot processing devices at the receiving end, which increases the complexity of the network, reduces reliability and increases the cost of the network.

The manual adjustment method can be used to individually adjust each receiving point of the entire network at the beginning of device networking. This method responds slowly to signal changes. It is often discovered after causing undue consequences, and then the problem is solved manually, which in many cases cannot meet the requirements at all.

In the reverse return system, the above three methods have great limitations: the level detection is limited by burst noise, and the difference in the modulation degree of the return image and the digital signal in the return transmitter is also limited. The application of this method is not possible; the pilot method is not realistic at all; manual adjustment is heavy and difficult to implement. The above drawbacks limit the use in reverse backhaul systems, especially in large-scale networking.

The first object of the present invention is to provide a method for controlling the output level stability of a receiver by using an optical power signal. By adopting the present invention, the stability of the output level can be realized without adding any complex hardware devices to the existing network and receiver.

The second object of the present invention is to provide an analog optical receiver using the above output level stabilization control method.

In order to realize the first object of the invention, the steps of the analog optical receiver output level stabilization control method are as follows:

1) Detecting the size of the received optical power of the optical receiver;

2) Judging the change of the output level of the optical receiver according to the size of the received optical power;

3) Generate a control signal according to the above changes to make the output level of the receiver change in the opposite direction to obtain a stable output; return to step 1).

It is also characterized in that, in the above-mentioned step 1), in addition to considering the change factor of the optical power, the modulation degree information or the user command information of the transmitter is also considered, and the above-mentioned step 2) generates a control signal after comprehensive processing to make the output level of the receiver keep it steady.

In order to realize the second object of the invention, the analog optical receiver with stable output level is characterized in that it includes:

The light receiving module is used for photoelectric conversion;

A fixed-gain radio-frequency processing circuit for amplifying and attenuating the electrical signal converted by the optical receiving module;

The variable gain processing circuit is used to amplify, attenuate, etc. the signal sent to the fixed gain radio frequency processing circuit, and control the change of the gain through a control signal;

A control signal generating circuit, used to generate the control signal required by the variable gain processing circuit;

The DC optical detection unit is used to detect the optical power of the optical receiving module and send it to the control signal generating circuit.

It is also characterized in that it also includes a coupler and a network management signal processing unit;

The coupler is used to couple the modulation degree information or user command information from the output signal of the variable gain processing circuit to the network management signal processing unit; the DC optical detection unit also sends the optical power signal to the network management signal processing unit; The network management signal processing unit is used to comprehensively process the received optical power, modulation degree, and user command requirements to generate control signals and send them to the control signal generation circuit.

After adopting the present invention, sum up and have following advantage:

1) It can ensure the stability of the signal level of each channel output by the receiver when the number of channels changes. Since the number of channels of the multi-carrier modulation transmission system such as the optical fiber CATV system is constantly changing, the system using the level detection control method will reduce or increase the actual output level due to the increase or decrease of the number of channels, and cannot maintain the power of each channel. Flat and stable. And the output level stability of each channel is very important in many cases. With the present invention, since the direct current optical signal is used as the control information, the change of the number of channels will not have any influence on the stability of the output level. In a noisy system the situation is similar to a change in the number of channels.

2) The stabilization of the signal level may not be affected by the power of the burst noise. The present invention has more effects in the reverse optical transmission system. Firstly, the detection of optical power avoids the influence of burst noise; This problem may not be considered in the case, only the output level of the receiver needs to be adjusted to a certain fixed value. The use of the present invention in reverse backhaul actually uses optical power as a pilot signal on an optical path. In addition, the received optical power of the reverse receiver varies greatly, so it is necessary to ensure the stability of the output level of the receiver. Using optical power detection to control the stability of radio frequency level is a relatively good method.

3) It can be used to transmit any analog signal optical transmission system with any high frequency and any bandwidth. For example, in the application of ultra-high frequency and ultra-wideband signal optical links such as microwave transmission, since the optical power detection control method does not need to detect radio frequency or microwave signal power or pilot frequency detection, the control method and accuracy are not affected by the transmission bandwidth and frequency. And other factors, so it can be used for analog optical transmission system receiver output level control in various fields from narrow band to wide band, from low frequency to microwave.

4) The feedback control method of optical power detection is very simple, which hardly increases hardware investment and complexity; moreover, it can timely and accurately perform feedback control on signal level changes, and realize the stability of the output level of the optical receiver under various conditions.

The present invention will be described in further detail below through specific embodiments and in conjunction with the accompanying drawings.

Fig. 1 is the principle block diagram of the existing optical receiver using level detection to control output level stability;

Fig. 2 is a schematic block diagram of the optical receiver of the present invention using optical power detection to control output level stability;

Fig. 3 is an application example of the present invention in a bidirectional optical transmission structure.

Figure 1 shows the existing optical receiver, which monitors the output level in real time through the radio frequency detection circuit and keeps the output level stable through the feedback control system.

The output level of the receiver is mainly determined by the received optical power, the modulation degree of the transmitter, the responsivity of the photodiode of the receiver, the resistance value of the load resistor, the gain of the amplifier in the receiver and the insertion loss of each component. The above parameters have a fixed relationship with the output level of the receiver, among which the modulation degree of the transmitter and the received optical power of the receiver are the main ones that change frequently (in fact, if the modulation degree is not artificially changed, the change of the modulation degree is also small, little impact on the output level), other parameters rarely change. Under the condition that the modulation degree and received optical power are constant, the output level of the receiver is fixed. When the modulation degree or received optical power changes, the output level will also change according to a certain relationship.

Fig. 2 shows the optical receiver of the present invention. Compared with the existing receiver shown in Fig. 1, the radio frequency detection circuit 4 is eliminated, instead of directly detecting the output level, the stability of the output level is controlled by detecting changes in optical power and modulation information. The optical receiver includes an optical receiving module 1 , a fixed gain radio frequency processing circuit 2 , a variable gain processing circuit 3 , a DC optical detection unit 6 , a control signal generation circuit 5 , a network management signal processing unit 7 and a coupler 8 .

After the photoelectric conversion of the optical receiving module 1, the radio frequency signal is sent to the fixed gain radio frequency processing circuit 2. The fixed gain radio frequency processing circuit 2 includes a fixed gain amplifier module, a fixed attenuator and other devices that have a constant influence on the signal. This part is a single board It is determined according to the needs during design, and it does not have an automatic control effect on the output level in actual use. The signal processed by the fixed gain radio frequency processing circuit 2 is sent to the variable gain processing circuit 3 .

The variable gain processing circuit 3 is generally an amplifier with an AGC (Automatic Gain Control) function, an electronically adjustable attenuator and other devices with variable gain, which control the change of gain through a control signal.

The control signal generating circuit 5 generates the control signal required by the variable gain processing circuit 3 , and controls the variable gain processing circuit 3 to stabilize the output level 9 . The control signal output by the control signal generation circuit 5 can be controlled by the following factors according to different situations: received optical power, direct requirements of users, transmitter modulation degree, network management signal, or one of the above factors or Several combinations. The received optical power signal comes from the DC optical detection unit 6 , while the user's direct request, modulation degree, and network management signals come from the network management signal processing unit 7 .

The DC optical detection unit 6 detects the magnitude of the DC optical power of the light receiving module 1 and sends it to the network management signal processing unit 7 . In addition to maintaining the original function of the optical power detection in the present invention, the network management signal processing unit 7 can also judge and generate a control signal based on this information and send it to the control signal generating circuit 5 . If only the stability of the output level needs to be considered when the optical power changes (modulation degree is fixed), the control signal generation circuit 5 will directly generate the control signal according to the optical power sent by the DC optical detection unit 6, without the need of the network management signal processing unit 7 Participation.

The radio frequency signal coupled by the coupler 8 is sent to the demodulator in the signal processing circuit 7 of the network management, and informs the receiver of information such as the modulation degree, user commands, and the working status of the transmitter sent from the front end.

The network management signal processing unit 7 processes the signal from the transmitter and manages the signal of the receiver itself, processes the modulation degree of the transmitter, the received optical power and the user's requirements to generate a control signal, and sends it to the control signal generation circuit 5 to generate a control signal that meets the requirements of the user. The control signal required by the user. In fact, in the case where the index requirements are not strict or only the output level is required to be stable but not all receivers have the same output level (it is not necessary to consider that the modulation degrees of different transmitters are slightly different, and the modulation degrees are approximately fixed. change), the network management signal is not required.

The control signal generating circuit 5 also sends the generated control signal to the network management signal processing unit 7, so as to monitor the working status of the control signal generating circuit 5 and whether the generated control signal is normal.

To sum up, the three signals of optical power, modulation degree or user command are all sent to the network management signal processing unit 7 for comprehensive processing. Once any of the user command, optical power or modulation degree changes, such as optical power reduction, modulation degree When the output level required by the user is lowered or the output level is increased, the network management signal processing unit 7 will make the control signal generated by the control signal generating circuit 5 smaller, thereby reducing the attenuation, and finally realizing the stability of the level or reaching a certain value.

The specific application of the present invention in solving the output level stabilization control of the forward receiver and the reverse receiver is introduced below.

Figure 3 is a typical bidirectional optical transmission network structure. In Figure 3, Tx-F, Rx-F, Tx-B, and Rx-B represent the forward transmitter, forward receiver, reverse transmitter, and reverse receiver, respectively, where Tx-F and Rx-B are located in the network The front end, Tx-B and Rx-F are located at the user end (usually an optical node). Tx-F and Rx-F form a forward transmission channel; Tx-B and Rx-B form a reverse transmission channel. For the forward system, usually one forward transmitter Tx-F is transmitted to multiple optical receivers Rx-F through an optical splitter. Due to the influence of various factors, the received optical power of the forward receiver Rx-F located at the optical node will change, which will cause the change of the output signal level, and the change of the output signal level will cause the change of the index in many cases ; In addition, the transmitter with automatic modulation degree control function will cause changes in the output signal level of the receiver when the number of channels changes, the level of individual channels changes, and the noise increases. In the reverse backhaul system, usually the output power of the reverse transmitter Tx-B is the same value, due to the difference in the backhaul distance, the received optical power at the reverse receiver Rx-B will be in a wide range In addition, the modulation degrees of different reverse transmitters are different, and even the signal modulation degrees of different frequency bands of the same transmitter are also different (this situation is very common in reverse transmitters, such as transmitting images and data signals at the same time, The modulation degree of the image signal may be 10dB or even higher than the modulation degree of the digital signal; resulting in a large difference in the output level of the receiver in different frequency bands. This situation limits the use of existing level detection); the result is reverse receiver The output levels also vary widely, which is not conducive to signal processing. The above problems can be well solved by adopting the present invention.

The following facts will be considered during the practical application of the present invention:

1) In an analog modulated optical transmission system, the modulation degree is usually known;

2) The signal gain of the optical receiving module is fixed and can be obtained through manufacturer's information or measurement;

3) Except for the variable part, the signal gain in the receiver circuit is fixed and known.

Due to the above three facts, it is only necessary to consider the received optical power, the modulation degree of the transmitter and the needs of users to control the output level of the receiver to be stable to any value, of course, this value is within the range provided by the receiver. Since the output level of the receiver itself is related to two factors, the received optical power and the degree of modulation, the output level can be controlled to stabilize at a certain range through the received optical power and the degree of modulation.

If the modulation degree of the transmitter is fixed and known, then a fixed optical power will produce a fixed signal level output. The change of the output level can be judged only by detecting the optical power, and the output signal of the receiver can be changed in the opposite direction by generating a control signal, so that the output level of the receiver can be stabilized.

In fact, similar problems are often encountered. The modulation degree of the same transmitter is fixed or variable; the modulation degree of different transmitters may be different; the modulation degree may have a small difference or a large difference difference. The present invention can provide a good solution for the above situations.

(1) The case where the modulation degree of each transmitter is fixed and the modulation degrees of different transmitters are slightly different.

This situation is the simplest, as long as the control signal generating circuit 5 (shown in FIG. 2 ) of the receiver is made fixed, the output level of each receiver can be kept stable. The fluctuations in the output signal levels of different receivers are limited by the small differences in the degree of modulation of the different transmitters, which can be calculated to be small. It is only caused by the difference in the signal gain of the receiving module in the receiver. Subtle differences in parameters such as signal gain in each receiving board can be compensated by fine-tuning the control signal generating circuit.

(2) The modulation degree of each transmitter is fixed but the modulation degree of different transmitters varies greatly.

In this case, in order to ensure that the output level of the receiver is within a certain range, the corresponding receiver output level is adjusted according to the modulation degree of each transmitter during networking so that the output level of the receiver is basically consistent. . Then the control method is not much different from the modulation degree of the above-mentioned transmitter.

(3) The case where the modulation degree of each transmitter is variable.

In this case, due to the change of the modulation degree, even if the input optical power of the receiver remains unchanged, the output signal level of the receiver will also change due to the change of the modulation degree. In order to ensure that the output level of the receiver is stable under the condition of input optical power and modulation degree, each transmitter needs to transmit its own modulation degree and other related information to the receiver network management board through the network management system (that is, the network management board in Figure 2 In the signal processing unit 7), the corresponding control voltage is generated through the control of the network management board and the integrated optical power information, and the gain of the main channel signal is controlled, so that the level output of all receivers can be guaranteed to be stable and equal.

In addition to the modulation problem, the level control problem of the backhaul receiver is that the input optical power of the receiver varies in a wide range because the distances from each point to the front end are different. Using the level control method in the system with variable modulation degree in the forward transmission can solve the above problems well.

The present invention utilizes the optical power of the detection receiver to control the stable method of the output level of the receiver, and has several remarkable features. First, the generation of the control signal only comes from the detection of optical power or the mixed information of the detection of optical power and the degree of modulation, and does not require complex high-frequency signal processing circuits, and the circuits are simple and reliable. The second is high control precision and good output level stability. Its three, the present invention can finish the effect that previous three methods can't reach. For example, when the modulation degree is variable, the use of level detection cannot guarantee the stability of the output signal level at all; through the present invention, it is only necessary to know the modulation degree of the corresponding transmitter to achieve stable and consistent output levels of multiple receivers.

The invention fully utilizes the information resources of the existing transmitter, and can easily realize high-precision output level control without adding additional hardware. And on this basis, its use can be extended to solve the problems that the traditional three methods can't solve or can't solve well. With the development of optical transmission application technology, it will be applicable in more occasions.

Claims (5)

1, a kind of control method of stabilizing output level of light receiver may further comprise the steps:

1) at first detects the size of the received optical power of optical receiver;

2) judge the variation of output level of light receiver according to the size of received optical power;

3) produce control signal according to above-mentioned situation of change the output level of receiver is changed in the opposite direction, to obtain stable output; Return step 1);

It is characterized in that, also detect the information transfer system of transmitter in the described step 1), described step 2) in

Also judge the variation of receiver output level according to the variation of modulation degree.

2, the control method of stabilizing output level of light receiver as claimed in claim 1, it is characterized in that: also detect user's command information in the described step 1), also produce the output level that control signal makes receiver in the described step 3) and reach some determined values according to user command.

3, a kind of optical receiver of realizing stabilizing output level control method as claimed in claim 1 is characterized in that comprising:

Optical Receivers (1) is used for opto-electronic conversion;

Fixed gain rf processing circuitry (2) is used for the amplification of described Optical Receivers (1) electrical signal converted, decay etc.;

Variable gain treatment circuit (3), the signal amplification that is used for described fixed gain rf processing circuitry (2) is sent into, decay etc. come the variation of ride gain by a control signal;

Control signal generation circuit (5) is used to produce the control signal of described variable gain treatment circuit (3) needs;

Direct current optical detecting unit (6) is used to detect the luminous power of described Optical Receivers (1), and sends into described control signal generation circuit (5).

4, optical receiver as claimed in claim 3 is characterized in that: also comprise coupler (8) and webmaster signal processing unit (7),

Described coupler (8) is used for being coupled out information transfer system or user command information is given webmaster signal processing unit (7) from the output signal of variable gain treatment circuit (3);

Described direct current optical detecting unit (6) is also sent into optical power signals webmaster signal processing unit (7);

Described webmaster signal processing unit (7) is used for integrated treatment received optical power, the requirement of percentage modulation user command, sends into described control signal generation circuit (5) to produce control signal.

5, optical receiver as claimed in claim 4, it is characterized in that: described control signal generation circuit (5) is also delivered to webmaster signal processing unit (7) with the control signal that produces simultaneously, so that whether the control signal of the operating state of supervision control signal generation circuit (5) and generation is normal.

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