JPH09224002A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical receiver immune to noise with less coupling distortion for converting optical signals modulated by frequency multiplex signals to electric signals. SOLUTION: The received optical signals are provided with orthogonal polarization components and the light of the respective polarization components is modulated by mutually different information signals. Such optical signals are separated for the respective polarization components by a polarization separator 13 and converted into the electric signals respectively in first and second optic/electric conversion means 16 and 17 and the electric signals after conversion are amplified in respective amplifiers 18 and 19. The one for which the output of the amplifiers 18 and 19 is coupled to one electric signal is outputted as an output signal. Thus, since separation is performed for the respective polarization components and light reception and amplification are performed, the coupling distortion is reduced. Also, since the light intensity of the respective polarization components is not lowered before and after being separated even when the separation is performed for the respective polarization components, noise characteristics are not degraded by the separation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver which converts a received optical signal into an electric signal, amplifies and outputs the electric signal, and receives an optical signal modulated by a frequency division multiplexed information signal. Regarding an optical receiver.

[0002]

2. Description of the Related Art As one of methods for transmitting a large number of information through a single optical fiber, a method in which the optical intensity of an optical signal is modulated and transmitted by a modulation signal in which a large number of information signals having different frequency bands are multiplexed There is. A signal in which information is multiplexed for each frequency band in this way is called a frequency division multiplexed signal. When the frequency-multiplexed signal is amplified by the amplifier, the distortion becomes larger than when only the signal in the specific frequency band is amplified. Therefore, various improvements have been made to reduce distortion in an optical receiver that receives an optical signal modulated by a frequency-multiplexed signal.

FIG. 2 shows the configuration of a conventionally used optical receiver that receives an optical signal modulated by a frequency-multiplexed signal by separating it into frequency bands. The optical signal input from the input end 101 is an optical / electrical conversion element 10
2 is received. The electrical signal output from the optical / electrical conversion element 102 is branched into two and input to the low-pass filter 103 and the high-pass filter 104, respectively. The output signal of the low-pass filter 103 is input to the first amplifier 105.
The output signal of the high-pass filter 104 is input to the second amplification 106. The outputs of the first and second amplifiers are
It is input to the coupler 107 that combines the two electrical signals. The output of the coupler 107 is output terminal 1 as an output signal of the optical receiver.
It is taken out from 08.

In this optical receiver, the low-frequency component of the frequency-multiplexed signal transmitted by the optical signal is separately extracted by the low-pass filter 103, and the high-frequency component is extracted by the high-pass filter 104. . And the first and second amplifiers 1
These are individually amplified by 05 and 106, and then combined by the combiner 107. In this way, by separating each frequency band, the number of frequency-multiplexed signals is dispersed into two, and the number of signals amplified by each amplifier can be reduced. For example, the number of signals amplified by one amplifier can be half of the number of frequency-multiplexed signals. This reduces the coupling distortion generated in the amplifier.

FIG. 3 shows the configuration of another optical receiver that has been used conventionally for separating an optical signal modulated by a frequency-multiplexed signal into two and receiving them. The same parts as those of the optical receiver shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be appropriately omitted. The optical signal from the input terminal 101 is input to the optical branching device 111 that branches the optical signal into two. One output of the optical branching device 111 is the first light
The other output is input to the electrical conversion element 112, and is input to the second optical / electrical conversion element 113, respectively.

The output of the first photoelectric conversion element 112 is
After being amplified to a predetermined level by the first amplifier 105, it is input to the coupler 107. The output of the second photoelectric conversion element 113 passes through the second amplifier 106 and then the coupler 1
07. In this way, since the optical signal is separated into two by the optical branching device 111, the amplifiers 105 and 106 are separated.
The signal level of the frequency-multiplexed signal input to is half that of the case where an optical signal is received by one light receiving element, and the coupling distortion in the amplifier can be reduced.

[0007]

In the case of amplifying a frequency-multiplexed signal divided into bands by a low-pass filter and a high-pass filter, since the output impedance of the photoelectric conversion element is high, these filters are Impedance mismatch occurs between and. Therefore, there is a problem that the amplitude frequency characteristic is disturbed in the pass band or the passage loss is increased, and the amplitude characteristic and the noise characteristic are deteriorated. In addition, since the frequency band is limited due to the increase in wiring length, the order of the filter must be reduced, and as a result, the amount of attenuation outside the pass band cannot be secured sufficiently. Therefore, there is a problem that the high frequency signal leaks into the amplifier for the low frequency signal and the low frequency signal leaks into the amplifier for the high frequency signal, and the effect of providing the amplifier individually for each band cannot be sufficiently exerted. .

Further, since an optical signal modulated by signals in all frequency bands of the frequency-multiplexed signal is input to the optical-electrical conversion element, it is possible to reduce the coupling distortion generated in the optical-electrical conversion element. There is a problem that you cannot do it.

In an optical branching device that splits an optical signal into two and receives them by separate optical / electrical conversion elements for amplification, the optical intensity of the optical signal received by each optical / electrical conversion element is branched. It decreases by half before it does. Therefore, there is a problem that the signal level itself of the optical signal received by each optical / electrical conversion element is also halved and is weak against noise.

Therefore, an object of the present invention is to provide an optical receiver which converts an optical signal modulated by a frequency-multiplexed signal into an electric signal, has less coupling distortion, and is strong against noise.

[0011]

According to a first aspect of the present invention, there is provided a polarized light for inputting an optical signal in which two orthogonal polarization components are modulated by different information signals, and separating this into an optical signal for each polarization component. Separation means, first photoelectric conversion means for receiving one optical signal after being separated by the polarization separation means, and outputting an electric signal corresponding to the light intensity, and the first photoelectric conversion means. A first amplifying means for amplifying the output of the second optical signal and a second amplifying means for receiving the other optical signal after being separated by the polarization separating means and outputting an electric signal according to the light intensity thereof.
The opto-electric conversion means, the second amplification means for amplifying the output of the second opto-electric conversion means, and the coupling means for combining the outputs of the first and second amplification means into one electric signal. It is equipped in the receiver.

That is, in the first aspect of the invention, the optical signal to be received has orthogonal polarization components, and the light of each polarization component is modulated by different information signals. Such an optical signal is separated for each polarization component, and each optical / electrical conversion unit converts the optical signal into an electric signal, and the converted electric signal is amplified by each amplification unit. As a result of receiving and amplifying by separating each polarization component,
Coupling distortion can be reduced. Further, even if the light components are separated for each polarization component, the light intensity of each polarization component is hardly decreased before and after the separation, and thus the separation does not weaken the noise.

According to the second aspect of the present invention, an optical signal in which two orthogonal polarization components are modulated by different information signals is input, and the polarization components are rotated in the orthogonal state so that the polarization components have a certain angle. And a polarization state control means for converting the direction of the polarization state and an optical signal output from the polarization state control means in which the direction of the polarization component has a constant angle are input, and this is separated into two optical signals for each polarization component. Polarization separation means, first photoelectric conversion means for receiving one optical signal after being separated by the polarization separation means, and outputting an electric signal according to the light intensity thereof, and this first photoelectric conversion. First amplifying means for amplifying the output of the means, and second photoelectric converting means for receiving the other optical signal after being separated by the polarization separating means and outputting an electric signal according to the light intensity. This second photoelectric conversion means A second amplifier means for amplifying a force, and a coupling means for combining the outputs of the first and second amplifying means into one electric signal is provided to the optical receiver.

That is, according to the second aspect of the present invention, the direction of the polarization component of the input optical signal is converted to an angle suitable for separation, and then the polarization signal is given to the polarization separation means. This makes it possible to appropriately separate the orthogonal components regardless of the direction of the polarization components of the transmitted optical signal.

According to the third aspect of the invention, the optical signal separated by the polarization separating means is modulated by the information signals of the frequency bands in which the two orthogonal polarization components are different from each other.

That is, according to the third aspect of the invention, each polarization component of the input optical signal is modulated by the information signals of different frequency bands. As a result, the information signal can be amplified by the individual amplifier for each frequency band, and the coupling distortion can be reduced.

According to a fourth aspect of the invention, when the input optical signal has two orthogonal polarization components modulated by different information signals, the directions of the two polarization components are the first angle and The polarization plane of the input optical signal is rotated so as to have a second angle orthogonal to this, and when the input optical signal has only one polarization component, the direction of the polarization component is the first The polarization state control means for rotating the polarization plane of the input optical signal so as to have a predetermined angle between the angle and the second angle, and the direction of the polarization component of the output light of the polarization state control means is The light incident at an angle of 1 is output from the first output port, the light having the polarization component of the second angle is output from the second output port, and the direction of the polarization component is the first Incident at a predetermined angle between the angle and the second angle The in ratio corresponding light on the angle 1
And a polarization separating means for dispersing and outputting from the second output port, and a first for receiving an optical signal output from the first output port of the polarization separating means and outputting an electric signal according to the light intensity. Of the photoelectric conversion means, the first amplification means for amplifying the output of the first photoelectric conversion means, and the optical signal output from the second output port of the polarization separation means are received, Second photoelectric conversion means for outputting a corresponding electric signal, second amplification means for amplifying the output of the second photoelectric conversion means, and outputs of the first and second amplification means as one electric signal. The optical receiver is provided with a coupling means for combining the signals.

That is, in the invention described in claim 4, an optical signal having two polarization components is individually amplified by two amplifiers for each polarization component, and an optical signal having only one polarization component is one polarization component. Are separated into two and amplified by two amplifiers.

According to a fifth aspect of the present invention, the polarization state control means sets the direction of the polarization component of the input optical signal to the first angle when the input optical signal has only one polarization component. It is rotated so that it becomes the central angle of the second angle.

That is, according to the fifth aspect of the invention, when the input optical signal has only one polarization component, the plane of polarization is rotated to the center angle between the first angle and the second angle. By doing so, the light intensity is exactly divided by half. This allows the two amplifiers to be evenly distributed and amplified.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of the configuration of an optical receiver in an embodiment of the present invention. Optical signals input from the input terminal 11 have polarization components that are orthogonal to each other, and each polarization component is intensity-modulated by information signals in different frequency bands. The optical signal from the input end 11 is input to the polarization controller 12. The polarization controller 12 is
The direction of the polarization component of the input optical signal is rotated by an arbitrary angle while maintaining the orthogonal state. The output light of the polarization controller 12 is input to the polarization separator 13.

The polarization separator 13 has the first direction of the polarization component.
Is output from the first output port 14, and the direction of the polarization component is shifted by 90 degrees from the first angle.
It is an optical element that outputs a component incident at an angle of from the second output port 15. In addition, regarding the polarization component incident at an angle between the first angle and the second angle, the light incident at a ratio according to the angle is distributed to the first and second ports and output. Has become. For example, the first
The polarization component incident at an angle deviated by 45 degrees from
It is evenly distributed and output to the first and second output ports 14 and 15.

The output light from the first output port 14 is received by the first photoelectric conversion element 16. The output light from the second output port 15 is the second optical-electrical conversion element 1
7 is received. First and second photoelectric conversion element 1
Reference numerals 6 and 17 output electric signals having a magnitude corresponding to the intensity of the received light, and here, photodiodes are used. The electric signal output from the first optical / electrical conversion element 16 is amplified to a predetermined level by the first amplifier 18. The electric signal output from the second optical / electrical conversion element 17 is amplified to a predetermined level by the second amplifier 19.

The output signals of the first and second amplifiers 18, 19 are combined by a combiner 21 into one electrical signal. The electric signal output from the coupler 21 is taken out from the output end 22 as an output signal of the optical receiver.

The polarization controller 12 determines the direction of the polarization component of the optical signal to be output by the polarization separator 13 to determine the direction of the polarization component for each polarization component.
Rotate to an angle that is exactly separated into two lights. That is,
The angle of the polarization plane of the input optical signal is rotated so that the angle of the polarization component becomes the first angle and the second angle. As a result, the polarization splitter 13 separates each orthogonal polarization component and outputs an optical signal. Since the input optical signal is modulated by the information signal of the different frequency band for each polarization component, the first and second amplifiers 18 and 19 individually amplify the electric signals of the different frequency bands. Become.

Further, only half the band component of the transmitted frequency-multiplexed signal is input to each optical-electrical conversion element, and the coupling distortion generated in the optical-electrical conversion element can be reduced. The light intensities of the two optical signals separated for each polarization component are halved compared to before separation, but since the signal in each frequency band is transmitted by one of the polarization components, There is no attenuation of the signal level itself. Therefore, even if the optical signal is separated by the polarization component, the noise characteristic does not deteriorate.

In addition, the optical signal sent from the transmitter is
If it has only one polarization component and is not a composite of two orthogonal polarization components, then by the polarization controller 12,
The plane of polarization of the optical signal is rotated so that it becomes the center angle between the first angle and the second angle. Thus the first angle and 45
After setting the angle of the direction of the polarization component to a deviated angle, when the optical signal is input to the splitting / polarizing means 13, this light is split into just two halves and output from the two output ports 14 and 15. Accordingly, the input optical signal is processed in parallel by the two optical / electrical conversion elements and the amplifier, so that the coupling distortion can be reduced. However, since the intensity of the optical signal is half that before the separation, the noise characteristic is deteriorated.

Depending on whether the optical signal thus input has two orthogonal polarization components or only one polarization component, the optical signal input to the polarization separator 13 By changing the angle of the plane of polarization, it is possible to reduce the coupling distortion in any optical signal.

[0030]

As described in detail above, according to the first aspect of the present invention, the polarized light components are separated and received and amplified, so that the coupling distortion in the optical receiver can be reduced. . Further, even if the light components are separated for each polarization component, the light intensity for each polarization component hardly decreases before and after the separation, so that the noise characteristics do not deteriorate due to the separation.

According to the second aspect of the present invention, the direction of the polarization component of the input optical signal is converted into an angle suitable for separation, and then is given to the polarization separation means. This makes it possible to appropriately separate the orthogonal components regardless of the direction of the polarization components of the transmitted optical signal.

According to the third aspect of the present invention, since the polarization components of the input optical signal are modulated by the information signals of different frequency bands, they are amplified by individual amplifiers for each frequency band of the information signal. It is possible to reduce the coupling distortion.

According to the invention described in claim 4, the optical signal having two polarization components is individually amplified by the two amplifiers for each polarization component, and the optical signal having only one polarization component is one. The polarization component is separated into two and amplified by two amplifiers. Therefore, the coupling distortion can be reduced regardless of whether the optical signal has two polarization components orthogonal to each other or the optical signal has only one polarization component.

Further, according to the fifth aspect of the invention, in the case of the optical signal having one polarization component, the optical signals are separated so that the optical intensities thereof are equalized. Therefore, the optical signal is evenly distributed to the two amplifiers. Can be amplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a configuration of an optical receiver in an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventionally used optical receiver that receives an optical signal modulated by a frequency-multiplexed signal by separating it by frequency band.

FIG. 3 is a block diagram showing a configuration of a conventionally used optical receiver that receives an optical signal that is modulated by a frequency-multiplexed signal by separating it into two.

[Explanation of symbols]

 12 Polarization controller 13 Polarization separator 14 and 15 Output port 16 and 17 Optical / electrical conversion element 18 and 19 Amplifier 21 Coupler

Claims (5)

[Claims] 1. A polarization separation means for inputting an optical signal in which two orthogonal polarization components are modulated by different information signals, and separating this into an optical signal for each polarization component; A first one that receives one of the latter optical signals and outputs an electric signal according to the light intensity
Photoelectric conversion means, a first amplification means for amplifying the output of the first photoelectric conversion means, and the other optical signal after being separated by the polarization separation means, and depending on its light intensity. Second which outputs the electric signal
Photoelectric conversion means, second amplification means for amplifying the output of the second photoelectric conversion means, and coupling means for combining the outputs of the first and second amplification means into one electric signal. An optical receiver characterized by: 2. Polarized light for inputting an optical signal in which two orthogonal polarization components are modulated by different information signals, and rotating the polarization component in an orthogonal state to convert the direction of the polarization component to a certain angle. A state control means, and a polarization separation means for inputting an optical signal in which the direction of the polarization component output from the polarization state control means is at the constant angle and separating the optical signal into two optical signals for each polarization component, A first optical signal that receives one of the optical signals after being separated by the polarization separating means and outputs an electric signal according to the light intensity
Photoelectric conversion means, a first amplification means for amplifying the output of the first photoelectric conversion means, and the other optical signal after being separated by the polarization separation means, and depending on its light intensity. Second which outputs the electric signal
Photoelectric conversion means, second amplification means for amplifying the output of the second photoelectric conversion means, and coupling means for combining the outputs of the first and second amplification means into one electric signal. An optical receiver characterized by: 3. The optical signal separated by the polarization separating means is
The optical receiver according to claim 1 or 2, wherein the two orthogonal polarization components are modulated by information signals in different frequency bands. 4. When the input optical signal has two orthogonal polarization components modulated by different information signals, the directions of the two polarization components are at a first angle and at a second angle orthogonal thereto. The plane of polarization of the input optical signal is rotated so as to have an angle of, and when the input optical signal has only one polarization component, the orientation of the polarization component is the first angle and the second angle. And a polarization state control means for rotating the polarization plane of the input optical signal so that the polarization component of the output light of the polarization state control means has the first angle. The light incident on the first output port is output from the first output port, and the light incident on the second angle is the polarization component of the second output port. And at a predetermined angle between the second angle And a polarization separation means for dispersing and outputting the light from the first and second output ports at a ratio according to the angle, and an optical signal output from the first output port of the polarization separation means, and the light intensity thereof. Output from the second output port of the polarization splitting means; Second optical-electrical conversion means for receiving an optical signal corresponding to the light intensity and outputting an electrical signal corresponding to the light intensity, second amplification means for amplifying the output of the second optical-electrical conversion means, and first and An optical receiver comprising: a coupling means for combining the output of the second amplification means into one electric signal. 5. The polarization state control means sets the direction of the polarization component of the input optical signal to the first angle and the second direction when the input optical signal has only one polarization component. The optical receiver according to claim 4, wherein the optical receiver is rotated so that it becomes an angle at the center of the angles.