JP3003569B2 - Optical receiver - Google Patents

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. It relates to an optical receiver.

[0002]

2. Description of the Related Art As one of systems for transmitting a large amount of information through a single optical fiber, a method of modulating the light intensity of an optical signal with a modulation signal obtained by multiplexing a large number of information signals having different frequency bands is transmitted. There is. A signal in which information is multiplexed for each frequency band in this manner is called a frequency division multiplexed signal. In the case where the frequency multiplexed signal is amplified by the amplifier, the distortion is larger than in the case where only the signal in the specific frequency band is amplified. Therefore, in an optical receiver that receives an optical signal modulated by a frequency multiplexed signal, various improvements for reducing distortion have been made.

FIG. 2 shows the configuration of a conventionally used optical receiver that receives an optical signal modulated by a frequency multiplexed signal by separating the signal by frequency band. The optical signal input from the input terminal 101 is the optical-electrical conversion element 10
2 is received. The electric vibration 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 outputs the first and second amplifier input to the second amplifier 106, these 1
Is input to the combiner 107 that combines the two electric signals. The output of the coupler 107 is output from the output terminal 1 as an output signal of the optical receiver.
08.

In this optical receiver, low-frequency components of a frequency multiplexed signal transmitted by an optical signal are separately extracted by a low-pass filter 103 and high-frequency components are separately extracted by a high-pass filter 104. . And the first and second amplifiers 1
After individually amplifying these in steps 05 and 106, they are combined in the coupler 107. In this manner, by separating the signals into frequency bands, 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 to be amplified by one amplifier can be reduced to half the number of frequency-multiplexed signals. Thereby, the coupling distortion generated in the amplifier is reduced.

FIG. 3 shows the configuration of another conventional optical receiver that separates an optical signal modulated by a frequency multiplexed signal into two and receives it. The same parts as those of the optical receiver shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. The optical signal from the input terminal 101 is input to an optical splitter 111 that splits the optical signal into two. One output of the optical splitter 111 is the first optical
The other output is input to the electric conversion element 112 and the second optical-electric conversion element 113, respectively.

[0006] The output of the first optical-electrical 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 optical-to-electrical conversion element 113 passes through the second amplifier 106 to the coupler 1
07. As described above, since the optical signal is separated into two by the optical splitter 111, each of the amplifiers 105, 106
The signal level of the frequency-division multiplexed signal input to the optical receiver becomes half of the level when the optical signal is received by one light receiving element, so that the coupling distortion in the amplifier can be reduced.

[0007]

In the case where a frequency-division multiplexed signal is amplified by dividing it by a band using a low-pass filter and a high-pass filter, the output impedance of the optical-electrical conversion element is high. And an impedance mismatch occurs. For this reason, there is a problem that the amplitude frequency characteristics in the pass band are disturbed or the passage loss increases, and the amplitude characteristics and the noise characteristics are deteriorated. Further, since the frequency band is limited by the increase in the wiring length, the order of the filter must be reduced, and as a result, the attenuation outside the pass band cannot be sufficiently secured. Therefore, the high-frequency signal leaks into the low-frequency signal amplifier, and the low-frequency signal leaks into the high-frequency signal amplifier, so that there is a problem that the effect of providing individual amplifiers for each band cannot be sufficiently exhibited. .

In addition, since the optical-to-electrical conversion element receives an optical signal modulated by signals in all frequency bands of the frequency multiplexed signal, it is possible to reduce the coupling distortion generated in the optical-to-electrical conversion element. There is a problem that can not be.

In an optical branching device in which an optical signal is split into two optical signals, which are received and amplified by separate optical-electrical conversion elements, the light intensity of the optical signal received by each optical-electrical conversion element is divided. Before decreasing by half. For this reason, there is a problem that the signal level itself of the optical signal received by each optical-to-electrical conversion element is halved, and is weak against noise.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical receiver for converting an optical signal modulated by a frequency multiplexed signal into an electric signal, which has less coupling distortion and is resistant to noise.

[0011]

The [Summary of invention of claim 1, wherein the two orthogonal polarization components enters a light signal modulated by different information signals to each other, to separate it into an optical signal for each polarized component Polarization separating means, first optical-to-electrical converting means for receiving one of the optical signals separated by the polarization separating means, and outputting an electric signal corresponding to the light intensity, and the first photoelectric converting means First amplifying means for amplifying the output of the means, and second photoelectric converting means for receiving the other optical signal separated by the polarization separating means and outputting an electric signal corresponding to the light intensity thereof; The second amplifying means for amplifying the output of the second opto-electrical conversion means and the outputs of the first and second amplifying means are electrically separated from their respective information signals.
The optical receiver is provided with a coupling means for combining the electric signal in the separated state .

That is, according to the first aspect of the present invention, the received optical signal 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, converted into an electric signal by separate optical-electrical conversion means, and the converted electric signal is amplified by individual amplification means. As a result of receiving and amplifying each polarization component separately,
Coupling distortion can be reduced. Further, even if the light is separated for each polarized light component, the light intensity of each polarized light component hardly decreases before and after being separated, so that the light is not weakened by the separation.

[0013] Claim 2 in the invention described, the two orthogonal polarization components enters a light signal modulated by different information signals to each other, polarized in a predetermined angle by rotating remain orthogonal to its polarization component Polarization state control means for converting the direction of the component, and an optical signal output from the polarization state control means and having a predetermined angle of the polarization component direction, which is input into two optical signals for each polarization component A first optical-electrical conversion unit that receives one of the optical signals separated by the polarization separation unit and outputs an electric signal corresponding to the light intensity; First amplifying means for amplifying the output of the photoelectric converting means, and second photoelectric converting means for receiving the other optical signal separated by the polarization separating means and outputting an electric signal according to the light intensity thereof Means,
The second amplifying means for amplifying the output of the second photoelectric conversion means and the outputs of the first and second amplifying means are respectively connected to each other.
The optical receiver is provided with coupling means for combining the information signal with the electrical signal in an electrically separated state . .

That is, 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 is then provided to the polarization separation means. Thereby, it is possible to appropriately separate each orthogonal component irrespective of the direction of the polarization component of the transmitted optical signal.

According to the third aspect of the present invention, the optical signal to be separated by the polarization separation means has two orthogonal polarization components modulated by information signals in different frequency bands.

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

[0017] In a fourth aspect of the present invention, orientation first angle of the two polarization components when the optical signal to be input is one having two orthogonal polarization components modulated with different information signals to each other And rotating the plane of polarization of the input optical signal so as to have a second angle orthogonal thereto, and when the input optical signal has only one polarization component, the direction of the polarization component is the first. Polarization state control means for rotating the polarization plane of the input optical signal so as to be at a predetermined angle between the second angle and the second angle, and the direction of the polarization component in the output light of the polarization state control means is The light incident at the first angle is output from the first port, and the direction of the polarization component is changed to the second.
Is output from the second port, and the direction of the polarized light component is changed to the light incident at a predetermined angle between the first angle and the second angle at a ratio corresponding to the angle. Polarization separating means for dispersing and outputting from the first and second output ports, and a light receiving means for receiving an optical signal output from the first output port of the polarization separating means and outputting an electric signal corresponding to the light intensity. 1 optical-electric conversion means, first amplification means for amplifying the output of the first photoelectric conversion means, and an optical signal output from the second port of the polarization separation means. a second photoelectric conversion means for outputting an electric signal corresponding, second amplifying means for amplifying the output of the second photoelectric conversion unit, the output of the first and second amplifying means, said
The input optical signal is modulated with different information signals
Each information signal is electrically separated when it is
Is combined with the electrical signal in the state of
When the optical receiver has only one polarized light component , the optical receiver is provided with a coupling means for combining into one electric signal.

That is, according to the present invention, 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 converted to one polarization component. Is separated into two and amplified by two amplifiers.

According to the fifth aspect of the present invention, when the input optical signal has only one polarization component, the polarization state control means sets the direction of the polarization component of the input optical signal to the first angle. It is rotated so as to be at the center of the second angle.

That is, in the fifth aspect of the present invention, when the input optical signal has only one polarization component, the polarization plane is rotated to the center angle between the first angle and the second angle. In this way, the light intensity is separated into half and half. As a result, it is possible to amplify the two amplifiers by dispersing them evenly.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

[0022]

FIG. 1 shows an outline of the configuration of an optical receiver according to an embodiment of the present invention. The optical signal input from the input terminal 11 has polarization components orthogonal to each other, and each polarization component is intensity-modulated by an information signal in a frequency band different from each other. The optical signal from the input terminal 11 is input to the polarization controller 12. The polarization controller 12
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 a polarization component of the first direction.
Is output from the first output port 14, and the direction of the polarization component is shifted by 90 degrees from the first angle.
Is an optical element that outputs a component incident at an angle of 2 from the second output port 15. Further, for a polarized light component incident at an angle between the first angle and the second angle, the incident light is distributed to the first and second ports at a ratio corresponding to the angle so as to be output. Has become. For example, the first
The polarization component incident at an angle shifted by 45 degrees from the angle of
The output is distributed equally to the first and second output ports 14 and 15.

The output light from the first output port 14 is received by the first optical / electrical conversion element 16. The output light of the second output port 15 is the second optical-electrical conversion element 1
7 is received. First and second optical-electrical conversion elements 1
Numerals 6 and 17 output electric signals of magnitudes corresponding to the intensity of the received light, and here use photodiodes. 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 and 19 are combined by the combiner 21 into one electric signal. The electric signal output from the coupler 21 is extracted from the output terminal 22 as the output signal of the optical receiver.

The polarization controller 12 determines the direction of the polarization component of the output optical signal by the polarization separator 13 for each polarization component.
Rotate to an angle just 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 separator 13 separates each orthogonal polarization component and outputs an optical signal. Since the input optical signal is modulated by information signals of different frequency bands for each polarization component, the first and second amplifiers 18 and 19 individually amplify electric signals of different frequency bands. Become.

Further, only half the band component of the transmitted frequency-division multiplexed signal is input to each optical / electrical conversion element, so that 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 in this manner are halved compared to those before separation, but since the signal of 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.

The optical signal sent from the transmitter is
If the polarization controller 12 has only one polarization component and is not a composite of two orthogonal polarization components,
The plane of polarization of the optical signal is rotated so as to be at the center of the first angle and the second angle. Thus, the first angle and 45
After setting the direction of the polarization component at an angle shifted by an angle, when an optical signal is input to the separating / polarizing means 13, this light is split exactly by half and output from the two output ports 14 and 15. Thus, the input optical signal is processed in parallel by the two optical-to-electrical conversion elements and the amplifier, so that coupling distortion can be reduced. However, since the intensity of the optical signal is half that before the separation, the noise characteristics are degraded.

Depending on whether the input optical signal has two orthogonal polarization components or has only one polarization component, the optical signal input to the polarization splitter 13 is determined as follows. By changing the angle of the polarization plane, the coupling distortion can be reduced in any of the optical signals.

[0030]

As described in detail above, according to the first aspect of the present invention, since light reception and amplification are performed separately for each polarization component, coupling distortion in the optical receiver can be reduced. . Further, even if the light is 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 is then provided to the polarization separation means. Thereby, it is possible to appropriately separate each orthogonal component irrespective of the direction of the polarization component of the transmitted optical signal.

Further, according to the third aspect of the present invention, since each polarization component of the input optical signal is modulated by the information signal of a different frequency band, it is amplified by an individual amplifier for each frequency band of the information signal. In addition, the coupling distortion can be reduced.

According to the invention, 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 converted into one optical signal. The polarization component is split into two and amplified by two amplifiers. For this reason, the coupling distortion can be reduced regardless of whether the optical signal has two orthogonal polarization components or an optical signal having only one polarization component.

According to the fifth aspect of the present invention, since an optical signal having one polarization component is separated so that its light intensity becomes uniform, the optical signal is evenly distributed to two amplifiers. Can be amplified.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an outline of a configuration of an optical receiver according to an embodiment of the present invention.

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Polarization controller 13 Polarization separator 14, 15 Output port 16, 17 Opto-electric conversion element 18, 19 Amplifier 21 Coupler

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/04-14/06

Claims (5)

(57) [Claims] 1. A two orthogonal polarization components enters a light signal modulated by different information signals to each other, a polarization separating means for separating it into an optical signal for each polarized component are separated by the polarization separator The first optical signal is received after receiving one of the optical signals, and an electrical signal corresponding to the light intensity is output.
And a first amplifying means for amplifying the output of the first photoelectric conversion means; and receiving the other optical signal separated by the polarization separation means, according to the light intensity thereof. Output the second electrical signal
A second amplifying means for amplifying the output of the second photoelectric converting means, and an output of each of the first and second amplifying means as an information signal.
And a coupling means for combining an electric signal with the electric signal in an electrically separated state . 2. A two orthogonal polarization components enter the optical signal modulated by different information signals to each other, to convert the direction of polarization component at an angle by rotating it remains orthogonal to its polarization component Polarization 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 predetermined angle, and separating this into two optical signals for each polarization component. A first optical signal receiving one of the optical signals separated by the polarization separating means and outputting an electric signal corresponding to the light intensity;
And a first amplifying means for amplifying the output of the first photoelectric conversion means; and receiving the other optical signal separated by the polarization separation means, according to the light intensity thereof. Output the second electrical signal
A second amplifying means for amplifying the output of the second photoelectric converting means, and an output of each of the first and second amplifying means as an information signal.
And a coupling means for combining an electric signal with the electric signal in an electrically separated state . 3. An optical signal to be separated by the polarization separation means,
3. The optical receiver according to claim 1, wherein the two orthogonal polarization components are modulated by information signals in different frequency bands. 4. The first optical signal to be input is two orientations of the polarization components that are orthogonal first angle and that this time are those having two orthogonal polarization components modulated with different information signals to each other When the input optical signal has only one polarization component, the direction of the polarization component is changed to the first angle and the second angle. A polarization state control means for rotating the polarization plane of the optical signal input so as to be at a predetermined angle between the first and second angles; The light incident at an angle is output from the first port, the direction of the polarization component is output from the second port at the second angle, and the direction of the polarization component is the same as the first angle. The light incident at a predetermined angle between the second angles is Polarization separating means for dispersing and outputting the light from the first and second output ports at a ratio corresponding to the angle; receiving an optical signal output from the first output port of the polarization separating means; First optical-electrical conversion means for outputting an output electric signal, first amplifying means for amplifying the output of the first optical-electrical conversion means, and an optical signal output from a second port of the polarization splitting means. And outputs an electric signal corresponding to the light intensity.
Of the photoelectric conversion means, second amplifying means for amplifying the output of the second photoelectric conversion unit, the output of the first and second amplifying means, light the input
If the signals are modulated with different information signals
When each information signal is electrically separated,
An optical signal that is synthesized into an electrical signal and has one polarization component
And a combining means for combining the signals into one electric signal when the optical receiver has only one. 5. The polarization state control means, when the input optical signal has only one polarization component, sets the direction of the polarization component of the input optical signal to the first angle and the second angle. 5. The optical receiver according to claim 4, wherein the optical receiver is rotated so that the angle becomes the center of the angle.