JP2002084024A - Optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical amplifier for a long-wavelength band (1,580 to 1,610 nm), which can be actualized with simple constitution. SOLUTION: This optical amplifier comprises an optical coupler 2, stages of amplifiers 3, 4, and 7, an equalizer 5, a variable optical attenuator 6, a temperature detecting element such as a thermistor 9, a photodiode(PD) 10, an AD converter 13, an arithmetic unit (CPU) 11, and an external memory 16 between input and output ends. The control signal of the optical attenuator 6 is generated by previously storing an external memory 16 with a 'data table' or 'calculation expression' according to parameters such as input light intensity by the PD 10, and the temperature and wavelength number information (SV signal 12) of an EDF 21 constituting the optical amplifiers 3, 4, and 7 detected by the thermistor and reading it out by the CPU 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier, particularly for a long wavelength band (1580 to 1610 nm) used for optical communication.
It relates to an optical amplifier.

[0002]

2. Description of the Related Art Most of communication is performed by conventional telecommunications because of its many advantages such as a large transmission capacity, being unaffected by external electromagnetic fields, a small signal attenuation, and a light transmission medium. Has been replaced by optical communications using optical fibers. In addition, optical communication is being adopted also in LAN systems in offices and vehicles, due to one or more of the above-mentioned advantages.

[0003] In optical communication using such an optical fiber as a transmission medium, a signal attenuated by long-distance transmission is brought to a predetermined level again or to adjust the amplitude of a signal passing through a plurality of transmission paths. Use an amplifier. In particular, a conventional optical amplifier used for an optical transmission system such as a wavelength division multiplexing (WDM) system or an optical wavelength division multiplexing communication is, for example, an “optical amplifier” in JP-A-10-335722 or “optical amplifier” in JP-A-6-5958. Optical fiber amplifier ".

In conventional optical communication, the wavelength of signal light is 1
Light in the 550 nm band is used. In this wavelength band, EDF (erbium-doped fiber) included in the amplifier
The amplification factor changes depending on the temperature characteristics of the. Therefore, the amplification factor is adjusted by an ALC (automatic level control) circuit for keeping the output light intensity of the amplifier constant. Then, the intensity of the output light is maintained constant by changing the intensity of the excitation light incident on the EDF. However, if only the amplification factor is changed as it is, the light intensity on the long wavelength side and the short wavelength side are not constant in the wavelength multiplex communication, that is, the flatness of the output light is lost. The phenomenon that the flatness of the output light is lost is caused by, for example, FIG.
6 indicates that the light intensity differs depending on the wavelength, as shown in FIG. Therefore,
By connecting an optical attenuator (attenuator) between the EDFs and changing the amount of attenuation, the light intensity of the output light can be kept constant without changing the amplification factor of the entire optical amplifier. As a result, the flatness of the optical output is not lost, and the wavelength multiplex transmission can be performed efficiently.

As a control method of the optical attenuator, EDF is used.
In order to obtain the temperature information, a thermistor whose output voltage value changes depending on the temperature is arranged around the EDF. Then, a change in the thermistor output voltage with respect to the temperature change is input to an operational amplifier (operational amplifier) to form a feedback loop that changes the attenuation of the optical attenuator so that the voltage change becomes zero. The optimum light output flatness is obtained.

[0006]

However, the above-described prior art has the following problems to be solved. First
In the prior art, the signal light in the wavelength band of 1550 nm was used. However, when the signal light in the long wavelength band near 1580 nm to 1610 nm is amplified by the optical amplifier, the output attenuator is controlled only by the EDF temperature to control the optical attenuator. Even if an attempt is made to optimize the degree, there is a problem that the output light flatness is not optimized when the input light intensity to the optical amplifier changes. In the long-wavelength band optical amplifier, it is necessary to simultaneously monitor not only the EDF temperature but also the input light intensity to the optical amplifier, which is a cause of the change in the flatness of the signal light. Therefore, it is necessary to control the attenuation rate of the optical attenuator based on these two monitor values.

Secondly, in the prior art, it is necessary to calculate two monitor values of the EDF temperature and the input light intensity. In addition, the attenuation of the optical attenuator is determined in consideration of other parameters of the EDF characteristic having individual variations. There is a need to.
In the case of using a plurality of these variable data, the conventional method of controlling with an analog circuit not only complicates the circuit scale, but also changes (or replaces) the EDF, which changes the parameters. In such a case, the parts must be changed, and the adjustment requires a great deal of labor.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical amplifier which simplifies the configuration and improves operability, reliability and productivity in order to keep the wavelength flatness of the output light intensity of the optical amplifier constant. It is to provide.

[0009]

An optical amplifier according to the present invention comprises one or more stages of erbium-doped fiber (ED) between input and output.
F) an optical amplifier for optical wavelength division multiplexing communication including an amplifier using F) and an optical attenuator whose attenuation is varied by a control signal, and an optical coupler and a photodiode (PD) for measuring the optical intensity of the optical signal; A temperature detecting element (thermistor) for measuring the temperature of the EDF, an analog-to-digital (AD) converter for converting the detection signals of the PD and the temperature detecting element into digital signals, and a light input intensity and an EDF temperature obtained from the AD converter. An arithmetic unit (CPU) for generating a control signal for the optical attenuator based on the type parameters;

According to a preferred embodiment of the optical amplifier of the present invention, wavelength number information is added as the above-mentioned parameter. The optical attenuator is disposed between a plurality of stages of amplifiers. In addition, an equalizer is provided before the optical attenuator and flattens the optical output with respect to the wavelength. A memory is provided in advance for storing a data table describing the relationship between the above-described parameters and the attenuation of the optical attenuator, and the CPU reads out this data table. Further, a calculation formula for determining the control signal of the optical attenuator is programmed in advance from the above-described parameters, and the calculation is performed in real time by the CPU.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of a preferred embodiment of an optical amplifier according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of a preferred embodiment of an optical amplifier according to the present invention. This optical amplifier includes an input connector 1, an optical coupler (coupler) 2, a pre-amplifier 3, a middle-stage amplifier 4, an equalizer 5, an optical attenuator 6, a post-amplifier 7, an output connector 8, a thermistor 9, and a photodiode (hereinafter referred to as PD). ) 10, SV signal 1
It is composed of an arithmetic unit (CPU) 11 to which 2 is input, an AD (analog / digital) converter 13, a DA (digital / analog) converter 14, an IV (current-voltage) converter 15, and an external memory 16. The CPU 11
Is composed of an arithmetic unit 11a and a memory 11b.

Next, the function and the like of each element constituting the optical amplifier of FIG. 1 will be described. The input connector 1 and the output connector 8 are optical connectors connected to optical fibers (not shown), respectively. The optical coupler 2 branches the wavelength multiplexed signal light input to the optical amplifier. The PD 10 measures the light intensity of the input light and outputs it as a current value. Preamplifier 3
The middle amplifier 4 amplifies the input signal light. The equalizer 5 provides an inverse characteristic to the optical power of each wavelength that is not constant in order to obtain the flatness, and makes the optical power flat. The optical attenuator 6 is a variable optical attenuator whose transmission characteristics change according to the applied drive voltage value. The post-amplifier 7 amplifies the light that has passed through the optical attenuator 6.

FIG. 2 is a configuration diagram of the inside of the front-stage amplifier 3, the middle-stage amplifier 4, and the rear-stage amplifier 7. These amplifiers 3,
4 and 7 include an optical coupler 17, an EDF 21, a laser diode (hereinafter, referred to as LD) 18, an input connector 19, and an output connector 20.

The DEF 21 amplifies the signal light. The thermistor 9 measures the ambient temperature of the EDF 21 and outputs the temperature as an analog voltage value. The IV converter 15 uses P
The current value output from D10 is converted into a corresponding voltage value. The AD converters 13 and 22 convert each input signal into a digital value because the input signal is an analog voltage. The SV signal 12 transmits the number of wavelengths included in the signal light from outside as a digital value because the input signal light is subjected to wavelength multiplex transmission. The CPU 11 determines the control or drive voltage of the optical attenuator 6 that optimizes the flatness of the output light from the three types of information of the EDF temperature, the input light intensity, and the number of wavelengths. The external memory 16 stores information such as “data table” or “calculation formula” for the CPU 11 to refer to. The DA converter 14 is a device that converts a digital value output from the CPU 11 into a corresponding analog voltage value, and amplifies the wavelength multiplexed signal light while maintaining the wavelength flatness of the output light intensity constant.

Next, the operation of the preferred embodiment of the optical amplifier according to the present invention will be described in detail with reference to FIGS. First, the “adjustment stage” will be described. The correlation data of the input light intensity, the EDF temperature, the information on the number of wavelengths of the signal light, and the control (drive) voltage of the optical attenuator 6 for optimizing the flatness of the output light is summarized as a “data table”.

The above-mentioned "data table" is written in the external memory 16 (step S1). This external memory 16
It is preferable to use a memory capable of storing data even when the power is turned off (that is, a nonvolatile memory). When a signal light is input from the input connector 1 (step S2), the optical signal is branched by the optical coupler 2 into N: M. The split light is input to the PD 10, and the PD 10 converts the input light intensity into a corresponding current value (step S3).
The current value at this time represents the light intensity input to the pre-amplifier 3. The current value output from the PD 10 is IV
The voltage is converted into a corresponding voltage value by the converter 15 and output (step S6). This voltage value is supplied to the AD converter 22
Is converted to a corresponding digital value and stored in the memory 11b of the CPU 11 (step S7).

In the temperature measurement of the EDF 21, the temperature around the installation portion of the EDF 21 is set as the EDF temperature. In this example, a thermistor 9 is used as the temperature detecting means, and a voltage value proportional to the temperature value is output by the thermistor 9 (step S4). This voltage value is supplied to the AD converter 13
Is converted to a digital value by the
b. The external memory 16 stores a correspondence table between the voltage value of the input light intensity and the digital value output from the AD converter 13 in advance. Similarly, a correspondence table between the voltage value output from the thermistor 9 and the temperature value of the EDF 21 is stored in the external memory 16.

Next, the "operation state" will be described. C
The PU 11 receives the measured values of the PD 10 and the thermistor 9 and the SV signal 12 (Step S5), and determines whether the monitor value has changed (Step S8). If the monitor value has not changed (step S8: NO), the process proceeds to step S15 described below without performing any processing. On the other hand, if the monitor value has changed (step S8: YE
In S), the "data table" is read from the external memory 16 (step S9). Then, it is determined whether or not the three types of monitor values are in the "data table" (step S10). If not in "data table" (step S
10: NO), the process returns to step S8 described above. On the other hand, if it is in the “data table” (step S1
0: YES), the process proceeds to step S11 described below.

Then, the CPU 11 compares the three types of information with the "data table" and selects a suitable digital value (step S11). Next, the CPU 11 outputs the digital value selected from the "data table" to the outside (step S12). The digital value is converted by the DA converter 14
(Step S13).
Then, the DA converter 14 drives the optical attenuator 6 to change the amount of attenuation of the signal light (Step S14).
Finally, the flatness of the output light output from the post-amplifier 7 via the output connector 8 is kept constant (step S1).
5).

[0021]

Next, a second embodiment of the optical amplifier according to the present invention will be described. The basic configuration is shown in FIG.
And FIG. However, instead of providing the CPU 11 in the above-described first embodiment with a “data table” for determining the drive amount of the optical attenuator 6 or the control signal, three types of parameters of input light intensity, EDF temperature, and wavelength number information are used. The "calculation formula" for determining the attenuator drive amount is programmed in advance. The CPU control unit substitutes three types of parameters stored in the memory 11b of the CPU 11 into the “calculation formula”. And
By calculating the drive amount of the optical attenuator 6, the same effect as the "data table" can be obtained. FIG.
Is a flowchart showing this operation.

The flowchart of FIG.
To S36. Steps S21 to S28 are the same as steps S1 to S8 in FIG. Next, it is determined whether the monitor values of the three types are within the specified values (step S29). If it is not within the specified value (step S29: NO), the process returns to step S28 described above.
On the other hand, if it is within the specified value (step S29: YES), the “calculation formula” is read from the memory (step S3).
0). The three types of variable parameters are substituted into this "calculation formula" (step S31). Next, the CPU 11 calculates the drive amount of the optical attenuator 6 (step S32).
The calculation result is stored in the memory 11b of the CPU 11,
Output to the converter 14 (step S33). Then, the digital value is converted into an analog voltage value by the DA converter 14 (step S34). The optical attenuator 6 is driven to change the amount of signal light attenuation (step S35). Finally,
The flatness of the output light output from the output connector 8 via the post-amplifier 7 is maintained (step S36). When using the "data table", when the number of wavelengths increases,
Since the number of "data tables" increases by the number of wavelengths,
The capacity of the external memory increases. However, in the case of the “calculation formula”, there is an advantage that even if the number of wavelengths increases, only the “calculation formula” needs to be changed, and the capacity of the external memory 16 does not increase.

Hereinafter, the configuration and operation of the preferred embodiment of the optical amplifier according to the present invention have been described in detail. However, it should be noted that such an embodiment is merely an example of the present invention and does not limit the present invention in any way. It will be readily apparent to those skilled in the art that various modifications can be made in accordance with the particular application without departing from the spirit of the invention.

[0024]

As apparent from the above description, the optical amplifier according to the present invention has the following practically significant effects. First, it is easy to change the attenuator drive amount by parameters after the circuit is created. Various information such as alarm information can be managed and controlled by the CPU. The reason is that since all information is digitized, it is possible to centrally manage the information of the whole amplifier by the CPU, and to use the CPU idle time other than the attenuator control, and also to control the alarm information management and the like by the CPU. It is possible.

Second, the use of a CPU makes it possible to reduce the size of a circuit that is complicated in an analog circuit and has a large mounting area. The reason is that since the drive voltage of the optical attenuator is determined from three types of monitor values, it cannot be created by a simple analog circuit as in the case of one type of monitor value, and the circuit scale becomes large. On the other hand, since the driving amount of the optical attenuator is calculated by the CPU, the calculation circuit becomes unnecessary, so that
The circuit itself can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a preferred embodiment of an optical amplifier according to the present invention.

FIG. 2 is a configuration diagram of the inside of a front-stage amplifier, a middle-stage amplifier, and a rear-stage amplifier shown in FIG.

FIG. 3 is a flowchart for obtaining an attenuator drive amount by comparing three types of monitor values and a data table by a CPU.

FIG. 4 is a flowchart for obtaining an attenuator drive amount from three types of monitor values and a given calculation expression by a CPU.

FIG. 5 is a diagram showing an example of an output light flatness characteristic diagram before optical attenuator control when a temperature or the like changes.

FIG. 6 is a diagram illustrating an example of an output light flatness characteristic diagram after optical attenuator control when a temperature or the like changes.

[Explanation of symbols]

 1, 19 Input connector 2, 17 Optical coupler 3, 4, 7 Amplifier 5 Equalizer 6 Optical attenuator 8, 20 Output connector 9 Temperature detection element (thermistor) 10 Photodiode (PD) 11 Processing device (CPU) 12 Wavelength number information ( SV signal) 13, 22 AD converter 14 DA converter 15 IV converter 16 External memory 18 Laser diode (LD) 21 EDF (Erbium-doped fiber)

Claims (6)

[Claims] 1. An optical amplifier for optical wavelength division multiplexing communication, comprising: an amplifier using one or more stages of erbium-doped fiber (EDF) between input and output terminals and an optical attenuator whose attenuation is variable by a control signal. An optical coupler and a photodiode (PD) for measuring the light intensity of the light, a temperature detecting element for measuring the temperature of the EDF, and an analog / digital (AD) for digitally converting detection signals of the PD and the temperature detecting element. An optical amplifier, comprising: a converter; and an arithmetic unit (CPU) that generates a control signal for the optical attenuator based on two parameters of the input light intensity and the EDF temperature obtained from the AD converter. 2. The optical amplifier according to claim 1, wherein wavelength number information is also externally input to said CPU as a parameter. 3. The optical amplifier according to claim 1, wherein the optical attenuator is arranged between a plurality of stages of the amplifiers. 4. The optical amplifier according to claim 1, further comprising an equalizer arranged before the optical attenuator and for flattening an optical output with respect to a wavelength. 5. A memory according to claim 1, further comprising a memory for storing in advance a data table describing the relationship between said parameters and the attenuation of said optical attenuator, wherein said data table is read by said CPU. 5. The optical amplifier according to 4. 6. The optical amplifier according to claim 1, wherein a calculation formula for determining the control signal of the optical attenuator from the parameters is programmed in advance and calculated in real time by the CPU. .