JP3730437B2 - Optical signal transmission system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical signal transmission system that transmits a radio signal using an optical fiber, and an apparatus that constitutes the system, and more particularly, to a technique that optimally maintains an output level of a radio signal component detected from an optical modulation signal. .
[0002]
[Prior art]
Wireless communication of information is actively performed due to advantages such as the capability of mobile communication. In familiar examples, pager (pager) systems and mobile phone systems are widely used.
However, such wireless communication systems are easily affected by the communication environment, and communication quality deteriorates due to reflection of radio waves by buildings, shielding of radio waves by buildings and tunnels, interference with other radio waves, etc. Has a weak point that communication is lost.
[0003]
In view of this, it has been studied to use an optical signal transmission system to make up for such a weak point of the wireless communication system, and to convert the wireless signal into an optical signal and transmit it in a place where the communication environment is poor.
For example, in a pager system, an optical signal transmission system as shown in FIG. 4 is provided in an underground shopping area so that a radio paging signal transmitted from a base station can be received by a pager existing in the underground shopping area. Note that the virtual line in the figure is a measure of the boundary between devices constituting the system.
[0004]
That is, the receiving device 1 is installed at a position where the radio signal (RF signal) transmitted from the base station can be received, and the optical signal processing device 2 is installed in the underground shopping area so that the pager in the underground shopping center can receive the wireless signal. Then, the receiving device 1 and the optical signal processing device 2 are connected by an optical communication path 5 including a carrier optical fiber 3 and a communication optical fiber 4 to constitute an optical signal transmission system.
[0005]
In this optical signal transmission system, first, in the optical signal processing device 2, a drive circuit 6 drives a light source (LD: laser diode) 7 to output an optical signal as a carrier wave through the carrier optical fiber 3. In the receiving apparatus 1, the radio signal received from the base station is received by the antenna 8, and the optical carrier wave received through the carrier optical fiber 3 is received by the radio signal received by the antenna 8 in the optical modulator (EOM) 9. The optical signal is modulated and converted into an optical modulation signal, and the optical modulation signal is output to the optical signal processing device 2 through the communication optical fiber 4. In the optical signal processing device 2, a light receiving signal (PD: photodiode) 10 receives an optical modulation signal from the communication optical fiber 4, detects a radio signal component from the optical modulation signal as an electric signal, and detects the electric signal. The signal is amplified by the amplifier 11 and wirelessly transmitted from the antenna 12 into the underground shopping area.
[0006]
[Problems to be solved by the invention]
Here, in the conventional optical signal transmission system as described above, the drive current of the light source 7 is automatically adjusted by the drive circuit 6 so that the output level of the optical carrier wave from the light source 7 is constant.
However, since the level of the radio signal received by the receiving device 1 fluctuates according to the change in the communication environment in which the radio signal has propagated, the optical signal is modulated with this radio signal if the level of the optical carrier wave is constant. The level of the light modulation signal fluctuates, and the detection accuracy of the radio signal component by the light receiver 10 becomes unstable. That is, when the level of the radio signal received by the receiving device 1 is too low, the optical carrier level may greatly exceed the radio signal component, and communication may be disabled. If the level is too high, the waveform of the optical modulation signal may be distorted and communication quality may be significantly reduced.
[0007]
The present invention has been made in view of the above-described conventional circumstances, and by completely adjusting the optical carrier level from the light source, the output level of the radio signal component detected from the light modulation signal is completely different from the conventional idea. Aim to maintain optimal.
Another object of the present invention is to avoid the situation in which an optical carrier wave is modulated with an excessively high level radio signal, and to maintain an optimal output level of a radio signal component detected from the optical modulation signal.
Further objects of the present invention will be apparent from the following description.
[0008]
[Means for Solving the Problems]
First, the present invention relates to a receiving device that outputs an optical modulation signal obtained by modulating an optical carrier wave with a received radio signal, an optical signal processing device that detects a radio signal component from the optical modulation signal, converts the signal into an electric signal, and outputs the electric signal. Is realized as an optical signal transmission system formed by connecting a communication optical fiber and a carrier optical fiber.
Then, the optical signal processing device drives the light source with a driving current and outputs an optical carrier wave to be supplied to the receiving device through the carrier optical fiber, and according to the radio signal component level detected from the optical modulation signal. And a control means for adjusting the light source driving current.
[0009]
This reduces the light source output if the optical carrier level is too high relative to the radio signal level received by the receiving device, and increases the light source output if the optical carrier level is too low. By setting the optical carrier level in accordance with the above, it is possible to prevent the situation where communication is disabled and the deterioration of communication quality.
Further, the present invention is realized as an optical signal processing device for constituting the optical signal transmission system.
[0010]
The present invention also relates to a receiving device that outputs an optical modulation signal obtained by modulating an optical carrier wave with a received radio signal, an optical signal processing device that detects a radio signal component from the optical modulation signal, converts it into an electric signal, and outputs the electric signal. Are realized as an optical signal transmission system in which the optical modulation signals are connected by an optical fiber for transmitting an optical modulation signal.
The receiving apparatus includes an attenuator that attenuates the received radio signal level prior to the modulation process.
[0011]
As a result, when the radio signal level received by the receiving device is too high with respect to the optical carrier level, the radio signal level is lowered, and then the optical carrier is modulated with the radio signal, thereby producing an optical modulation signal. To prevent the waveform quality from being deteriorated.
Further, the present invention is realized as a receiving device for configuring the above optical signal transmission system.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described with reference to the embodiments shown in the drawings.
The same parts as those of the conventional optical signal transmission system shown in FIG.
[0013]
FIG. 1 shows an optical signal transmission system according to an embodiment of the present invention. In addition to the system configuration shown in FIG. 4, in this system, a radio signal component level detected by a light receiver 10 from an optical modulation signal is shown. Accordingly, a control circuit 13 for adjusting a light source driving current output from the driving circuit 6 to the light source 7 is provided in the optical signal processing device 2.
That is, the control circuit 13 receives the radio signal component level detected by the light receiver 10, adjusts and controls the drive current value by the drive circuit 6 according to the radio signal component level, and receives the radio signal received by the receiver 1. Control is performed so that the optical carrier level output from the light source 7 becomes appropriate with respect to the signal level.
[0014]
Specifically, the control circuit 13 performs control processing according to the procedure shown in FIG. 2, and when the optical receiver 10 detects a radio signal component from the optical modulation signal, it determines whether the radio signal component level exceeds a predetermined upper limit value. Judgment (step S1), if it exceeds, the drive current value from the drive circuit 6 to the light source 7 is lowered (step S2), and the optical carrier wave output from the light source 7 to the receiver 1 through the carrier optical fiber 3 Reduce the level. On the other hand, when the upper limit value is not exceeded, it is determined whether the detected radio signal component level is lower than the predetermined lower limit value (step S3), and when it is lower, the drive current value from the drive circuit 6 to the light source 7 is determined. In step S4, the level of the optical carrier wave output from the light source 7 to the receiving device 1 through the carrier wave optical fiber 3 is raised.
[0015]
Therefore, according to the radio signal level transmitted to the optical signal processing device 2 at that time, the optical carrier level modulated by the received radio signal by the optical modulator 9 of the receiving device 1 is adjusted, and the above upper limit value and lower limit value are set. Maintained between values.
Furthermore, the above upper limit value and lower limit value are drive current values for causing the light source 7 to output an optical carrier wave at a level suitable for carrying a certain level of radio signal received by the receiving device 1 at that time. This is a prescribed threshold value, which is set in advance according to the required communication quality.
Accordingly, when the optical carrier level is too high with respect to the radio signal level received by the receiving device 1, the output from the light source 7 is reduced, and when the optical carrier level is too low, the output from the light source 7 is increased. As a result, even if the reception level in the receiving device 1 varies, the optical signal processing device 2 can detect the radio signal component satisfactorily.
[0016]
In the above embodiment, a feedback method is used in which the optical carrier level is automatically adjusted as needed according to the detection level on the optical signal processing device 2 side. However, for example, when the optical signal transmission system is installed in a certain environment where the communication environment does not change so much, the above adjustment may be performed at the time of system installation. A knob that can be operated by the operator is provided, and when the system is installed, the operator operates the control circuit while checking the detection level of the optical signal processing device 2 by the monitor, adjusts the drive current, and is output from the light source 7. The optical carrier level may be adapted to the environment.
[0017]
In the above embodiment, the optical signal processing device is configured by including the optical carrier wave output means including the driving circuit 6 and the light source 7, the light receiver 10, and the control circuit 13, and further this optical signal processing device. In addition, a transmission function including the amplifier 11 and the antenna 12 is also added, but this transmission function portion may be configured as a separate transmission apparatus.
[0018]
FIG. 3 shows an optical signal transmission system according to another embodiment of the present invention. In addition to the system configuration shown in FIG. 4, in this system, a radio received by the receiving apparatus 1 prior to the modulation process is shown. An attenuator (ATT: attenuator) 14 for attenuating the signal level is provided, and the detection level of the optical signal processing device 2 is displayed on the optical signal processing device 2 and the attenuation amount by the attenuator 14 is indicated via the communication line 15. A monitor 16 having a function of remote control is provided.
The monitor 16 may be fixedly provided on the optical signal treatment device 2, but a connection plug is provided on each of the monitor 16 and the optical signal treatment device 2, and the monitor 16 is connected and used when necessary. It may be.
[0019]
In the optical signal transmission system according to the present embodiment, the operator monitors the radio signal level detected by the light receiver 10 with the monitor 16 at the time of system installation, system inspection, and the like. 14 is adjusted to attenuate the level of the radio signal received by the receiver 1 to a value suitable for the optical carrier level output from the light source 7, and the optical signal is modulated by modulating the optical carrier. The reception state in the signal processing device 2 can be adjusted to a normal state. That is, even when the radio signal level at the receiving apparatus 1 is too high, waveform distortion of the optical modulation signal can be prevented and good communication quality can be maintained.
In the above embodiment, the attenuator 14 is remotely operated via the communication line 15. However, an adjustment knob is provided on the attenuator 14 so that the operator can directly adjust the attenuation. Also good.
[0020]
In each of the above-described embodiments, unidirectional communication such as a pager system is taken as an example. However, the present invention can be similarly applied to a bidirectional communication system such as a mobile phone system. Each function shown in the embodiment may be provided in both directions.
[0021]
【The invention's effect】
As described above, according to the present invention, since the optical carrier level from the light source can be adjusted according to the radio signal component level detected from the optical modulation signal, the radio signal component level detected from the optical modulation signal can be adjusted. Can be maintained optimally, and communication quality in the optical signal transmission system can be improved. Further, according to the present invention, it is possible to avoid the situation in which the optical carrier is modulated with an excessive level radio signal in the receiving apparatus, and it is possible to improve the communication quality in the optical signal transmission system.
For this reason, according to the present invention, it is possible to realize good communication using a pager system or a mobile phone system even in a radio wave insensitive zone such as an underground shopping street.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an optical signal transmission system according to the present invention.
FIG. 2 is a flowchart showing a processing procedure according to an embodiment of the present invention.
FIG. 3 is a diagram showing another embodiment of the optical signal transmission system according to the present invention.
FIG. 4 is a diagram illustrating an example of a conventional optical signal transmission system.
[Explanation of symbols]
1: receiver, 2: optical signal processor, 3: optical fiber for carrier wave, 4: optical fiber for communication, 6: drive circuit, 7: light source, 8: antenna, 9: optical modulator, 10: light receiver, 11: Amplifier, 12: Antenna, 13: Control circuit, 14: Attenuator, 16: Monitor,

Claims (4)

Transmits the optical modulation signal between the receiving device that outputs the optical modulation signal obtained by modulating the optical carrier wave with the received radio signal, and the optical signal processing device that detects the radio signal from the optical modulation signal, converts it into an electrical signal, and outputs the electric signal. In an optical signal transmission system connected by a communication optical fiber and a carrier optical fiber that transmits an optical carrier,
  The optical signal processing device
  An optical carrier output means for driving a light source by a drive current and outputting an optical carrier to be supplied to a receiver through a carrier optical fiber;
  Control means for controlling the optical carrier level by adjusting the light source driving current according to the level of the radio signal detected from the optical modulation signal input from the receiving device through the communication optical fiber;
  An optical signal transmission system comprising: The optical signal transmission system according to claim 1,
  An optical signal transmission system, wherein the receiving device includes an attenuator that attenuates the level of a radio signal received prior to modulation processing. The optical signal transmission system according to claim 2,
  An optical signal transmission system further comprising a monitor for displaying the wireless signal component level detected by the optical signal processing device and remotely controlling the attenuation amount of the attenuator via the signal line. The optical signal transmission system according to any one of claims 1 to 3,
  The optical signal processing device includes transmission function means for wirelessly transmitting a wireless signal detected from the optical modulation signal input from the receiving device,
  An optical signal transmission system, wherein the receiving device and the optical signal processing device perform signal relay between a mobile communication base station and a radio signal insensitive zone such as an underground shopping center.

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