JPH07245599A - Feedforward optical transmitter - Google Patents

Abstract

PURPOSE:To eliminate high order distortion generated in an amplifier section or the like by applying the feedforward system and using wavelength multiplex transmission in the analog optical transmission system. CONSTITUTION:An amplifier 2 amplifies one of input signals distributed by a distributer 1 and a laser diode 3 is used to convert the amplified signal into an optical signal including a main signal component and a harmonic distortion component. The other distributed signal is amplified and delayed and subtracted with a monitor signal of the laser diode 3 at a subtractor circuit 7 to extract only the harmonic distortion signal and it is converted into an optical signal and subject to wavelength multiplexing at a wavelength multiplexer module 10 together with the optical signal of the laser diode 3 and the result is sent to a receiver side. The receiver side uses a wavelength demultiplexer module 11 to demultiplex the optical signal and photo diodes 12, 13 are used to convert the signal into an electric signal and a delay circuit 16 adjusts the phase of the signals and both the signals are synthesized at a subtractor circuit 17 to eliminate the harmonic distortion signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedforward optical transmission device used in an analog optical wavelength division multiplexing transmission system and capable of low distortion transmission characteristics.

[0002]

2. Description of the Related Art FIG. 2 shows the configuration of a conventional feedforward amplifier circuit.

In FIG. 2, reference numeral 1 is a distributor for distributing an input signal applied to an input terminal IN. Reference numeral 2 is an amplifier for amplifying the distributed signal, 3 is a distributor for distributing the signal amplified by the amplifier 2, 4 is a delay circuit for matching the phase with the signal distributed by the distributor 3, and 5 is a delay circuit 4. Of the delay circuit 4 and the attenuator 5, 6 is a subtraction circuit for subtracting the signals of the delay circuit 4 and the attenuator 5, 7 is an amplifier for amplifying the signal of the subtraction circuit 6, and 8 is a phase characteristic generated in the amplifiers 2 and 7. A delay circuit 9 is provided for matching, and a subtraction circuit 9 subtracts the signals of the amplifier 7 and the delay circuit 8.

Next, the operation of the conventional example configured as described above will be described. Higher-order distortion remarkably occurs in an amplifier or the like. Therefore, the output signal of the amplifier 2 contains high-order distortion components. Therefore, in the circuit of the conventional example, the level of the distributed output signal is adjusted by the attenuator 5 so that the output signal distributed by the distributor 3 and the output signal of the delay circuit 4 are at the same level.
The delay circuit 4 delays the signal so that it has the same phase as the signal of the attenuator 5. After that, both output signals from the attenuator 5 and the delay circuit 4 are subtracted by the subtraction circuit 6, so that the amplifier 7 receives the signal of only the high-order distortion component and is amplified. The other signal distributed by the distributor 3 is delayed by the delay circuit 8, is phase-matched with the signal amplified by the amplifier 7, and is then subtracted by the subtraction circuit 9 to suppress high-order distortion components. Output signal OUT
Can be obtained from

[0005]

However, the above-mentioned conventional feedforward method is effective for transmitting electric signals and the like, but in the case of optical transmission, high-order distortion is generated in the amplifier driving the laser diode. However, there is a problem in that the laser diode is driven by the amplified output including the high-order distortion component, and the high-order distortion component cannot be removed.

The present invention solves such a conventional problem, and a feedforward method is applied to use a wavelength division multiplex transmission to cancel a high-order distortion component generated in an amplifier or the like. It is an object to provide an optical transmission system.

[0007]

To achieve the above object, the present invention provides a distributor for distributing an input signal, and a first electric circuit for converting the input signal distributed by the distributor into an optical signal.
An optical conversion element, a monitor element that monitors the optical signal of the first electro-optical conversion element, an attenuator that adjusts the output level of the monitor element, and the monitor element that delays the distributed input signal. A delay circuit for making the output signals from the same phase the same, and a first arithmetic circuit for subtracting the delayed signal and the monitor signal from the attenuator to extract a higher-order distortion component,
A second electric device for converting the signal of the higher-order distortion component into an optical signal-
An optical conversion element, a wavelength multiplexing means for wavelength-multiplexing the optical signals from the first and second electro-optical conversion elements, a wavelength separation means for separating the wavelength-multiplexed optical signal, and the separated main A first opto-electrical conversion element for converting an optical signal containing a signal component and a high-order distortion component into an electric signal, and a second opto-electric conversion element for converting the separated optical signal containing only the high-order distortion component into an electric signal.
Of the opto-electrical conversion element, a delay circuit for adjusting the signals output from the first and second opto-electrical conversion elements and amplified to the same phase, and the signals adjusted to the same phase are combined. And a second arithmetic means for removing higher-order distortion components.

[0008]

Therefore, according to the present invention, the signal containing the main signal component and the high-order distortion component and the signal containing only the high-order distortion component are converted into optical signals by the electro-optical conversion elements, and wavelength-multiplexed and received. To the other side, and at the receiving side, the wavelength-multiplexed optical signal is separated into an optical signal containing the main signal component and the higher-order distortion component and an optical signal containing only the higher-order distortion component, and then converted by the respective opto-electric conversion elements. Signal and convert both signals to the second
By synthesizing by the calculating means of, the higher-order distortion component is canceled and the main signal component is output, so that the higher-order distortion component generated in the amplification section or the like can be surely removed, which is suitable for the analog optical transmission system.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, 1 is a distributor for distributing an input signal input from an input terminal IN, 2 is an amplifier for amplifying one of the distributed input terminals, and this amplifier 2 is Laser diode 3 driven
Are connected. 4 is a delay circuit for adjusting the phase of the other distributed input signal to the phase generated in the amplifier 2,
Reference numeral 5 denotes an amplifier that amplifies the output signal of the photodiode 3a that monitors the output of the laser diode 3, and the output side of the amplifier 5 adjusts the level of the output signal to the same signal level as the output signal of the delay circuit 4. The attenuator 6 is connected. Reference numeral 7 denotes a subtraction circuit for subtracting both output signals of the delay circuit 4 and the attenuator 6 to extract a higher-order distortion component. A laser diode 9 is connected to the output side of the subtraction circuit 7 via an amplifier 8. There is.

Reference numeral 10 denotes a wavelength multiplexing module that multiplexes optical signals transmitted from the laser diodes 3 and 9 through the optical fibers 18a and 18b. The wavelength multiplexing module 10 is connected to the receiving side via an optical fiber cable 19. The wavelength separation module 11 is connected. 12
Is separated by the wavelength separation module 11 and the optical fiber 20a
Photodiode for converting an optical signal, which is a mixture of a main signal component and a higher-order distortion component transmitted through the optical signal, into an electrical signal, 1
3 is separated by the wavelength separation module 11 and the optical fiber 20
b is a photodiode for converting an optical signal of a high-order distortion component transmitted through b into an electric signal, and an output signal of the photodiode 12 is supplied to a subtraction circuit 17 via an amplifier 14.
The output signal of the photodiode 13 is input to the subtraction circuit 1 via the amplifier 15 and the delay circuit 16 that corrects the propagation delay of the amplifier 15 and the amplifier 14.
Input to 7. The subtraction circuit 17 removes a high-order distortion component by synthesizing both signals.

Next, the operation of this embodiment configured as described above will be described. The input signal input from the input terminal IN is distributed by the distributor 1 and then amplified by the amplifier 2, and the laser diode 3 is driven by this amplified output. The amplified output for driving the laser diode 3 contains a main signal component proportional to the input signal and a high-order distortion component due to the amplifier 2.

An optical signal generated by driving the laser diode 3 is transmitted to the wavelength multiplexing module 10 through the optical fiber 18a and monitored by the photodiode 3a. The monitor output is amplified by the amplifier 5 and then attenuated. It is adjusted to the same signal level as the output signal of the delay circuit 4 by the device 6 and supplied to the subtraction circuit 7.

On the other hand, a part of the input signal distributed by the distributor 1 is delayed by the delay circuit 4, so that it is supplied to the subtraction circuit 7 in phase with the output signal of the subtractor 6. In the subtraction circuit 7, only the high-order distortion component is extracted by combining the two signals, and this high-order distortion component is added to the laser diode 9 via the amplifier 8 to add the high-order distortion component to the laser diode. It is converted into an optical signal having a wavelength different from 3.

The optical signal generated from the laser diode 9 is transmitted through the optical fiber 18b to the wavelength multiplexing module 10.
Be transmitted to.

In the wavelength multiplexing module 10, the optical signals generated from the laser diodes 3 and 9 are multiplexed and transmitted to the wavelength demultiplexing module 11 on the receiving side through the optical fiber cable 19.

The wavelength separation module 11 on the receiving side separates the optical signal from the laser diode 3 and the optical signal from the laser diode 9. Laser diode 3 separated
From the optical signal, that is, an optical signal in which a main signal component and a high-order distortion component are mixed, is converted into an electric signal by being applied to the photodiode 12, amplified by the amplifier 14, and then supplied to the subtraction circuit 17. Further, the separated optical signal from the laser diode 9, that is, the optical signal of only the higher-order distortion component is added to the photodiode 13 to be converted into an electric signal, which is amplified by the amplifier 15 and then added to the delay circuit 16. The output signal of the amplifier 14 and the output signal of the delay circuit 16 are brought into phase with each other.

Both signals whose phases are matched are subtraction circuits 17
, The higher-order distortion component is canceled by the subtraction operation, and only the main signal component is output as the output terminal OUT.
Is output from.

As described above, according to the above-described embodiment, one of the input signals distributed by the distributor 1 is amplified by the amplifier 2 and then converted by the laser diode 3 into an optical signal containing a higher-order distortion component. , The monitor signal of the laser diode 3 and the other distributed input signal are added by a subtraction circuit 7 to extract only high-order distortion components, and then converted into an optical signal by a laser diode 8, and each optical signal is converted into a wavelength. The wavelength is multiplexed by the multiplexing module 10 and transmitted to the receiving side. Then, on the receiving side, after being separated into respective optical signals by the wavelength separation module 11, they are converted into electric signals by the respective photodiodes 12 and 13, and the phase adjustment of the respective signals is performed by the delay circuit 16 and then the subtraction circuit. Since the composition is combined in 17, it is possible to cancel the higher-order distortion component generated in the amplification section and the like, and the wavelength-multiplexed optical signal is transmitted, so that the economical efficiency of the transmission line can be improved.

The present invention is not limited to the structure shown in the above embodiment, and various modifications can be made without departing from the scope of the claims.

For example, although the case where a laser diode or a photodiode is used for the electric-optical or optical-electrical conversion element has been described, the present invention is not limited to this.

[0022]

As is apparent from the above embodiment, the present invention converts the signal containing the main signal component and the higher-order distortion component and the signal containing only the higher-order distortion component into optical signals at the receiving side. Since the signal of the higher-order distortion component is canceled at the receiving side, the higher-order distortion component generated in the amplifier or the like can be removed even in the analog optical transmission system.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a feedforward optical transmission system according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram showing a conventional feedforward circuit.

[Explanation of symbols]

 1 Distributor 2 Amplifier 3 Laser diode 3a Monitoring photodiode 4 Delay circuit 5 Amplifier 6 Attenuator 7 Subtraction circuit 8 Amplifier 9 Laser diode 10 Wavelength multiplexing module 11 Wavelength separation module 12 Photodiode 13 Photodiode 14 Amplifier 15 Amplifier 16 Delay circuit 17 Subtraction circuit 18a, 18b Optical fiber 19 Optical fiber cable 20a, 20b Optical fiber IN Data input terminal OUT Data output terminal

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04B 10/18

Claims (1)

[Claims] 1. A distributor for distributing an input signal, a first electro-optical conversion element for converting the input signal distributed by the distributor into an optical signal, and light of the first electro-optical conversion element. A monitor element that monitors a signal, an attenuator that adjusts the output level of the monitor element, a delay circuit that delays the distributed input signal to make the output signal from the monitor element in phase, and the delayed circuit A first arithmetic circuit that subtracts a signal and a monitor signal from the attenuator to extract a higher-order distortion component; and a second electro-optical conversion element that converts the higher-order distortion component signal into an optical signal. , Wavelength division means for wavelength-multiplexing the optical signals from the first and second electro-optical conversion elements, wavelength separation means for separating the wavelength-multiplexed optical signal, the separated main signal component and high Converting an optical signal containing a secondary distortion component into an electrical signal No. 1 optical-electrical conversion element, a second optical-electrical conversion element for converting the separated optical signal of only the higher-order distortion component into an electric signal, and the first and second optical-electrical conversion elements.
A delay circuit for adjusting the signals output from the electric conversion element and amplified to the same phase; and a second arithmetic means for synthesizing the two signals adjusted to the same phase to remove higher-order distortion components Feedforward optical transmission device.