JP2003234723A - Optical transmission apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission apparatus in which a communication quality is high, the number of multiplexing signals is large and the cost is reduced. <P>SOLUTION: In the optical transmission apparatus for performing optical modulation by utilizing a multiplex carrier wave acquired by multiplexing a plurality of electric signal carriers of different frequencies in the direction of a frequency axis, and transmitting an optical signal as a result of the relevant optical modulation, this apparatus is provided with a transmission information examination means for examining the presence/absence of transmission information to be transmitted for each electric signal carrier to be multiplexed on the multiplex carrier wave and an attenuation means for attenuating the amplitude of an relevant electric signal carrier in the case of the examined result of the relevant transmission information examination means showing the absence of the relevant transmission information. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission device,
For example, multiplexing multiple types of information using a single optical modulator
This is suitable for application in the case of transmission by transmission. 2. Description of the Related Art An optical transmission system capable of transmitting data over a wide band and a long distance.
Utilizing the transmission path, various signals such as xDSL signal, CA
Frequency multiplexing and transmitting each transmission signal of TV, mobile phone, etc.
Systems have been considered and are being adopted. Such a system
In the system, the transmitted signal is amplitude-modulated and frequency-modulated in advance.
After being modulated and frequency multiplexed, the optical modulation
Used as a modulation signal. [0003] The optical modulation by such a modulation signal
The optical signal generated and output is WDM (wavelength component).
Split multiplexing) or multiple carriers with different frequencies such as optical FDM
It does not use multiple light sources that output waves,
Each of the transmission signals is frequency division multiplexed in the optical signal.
ing. [0004] By the way, each of the above described
Since the transmitted signals have different frequencies, they can be changed simultaneously.
Modulation and demodulation, mixing occurs in the modulation process and demodulation process.
Modulation occurs. When the cross modulation occurs, the target frequency
The optical modulator modulates the transmission signal (for example, f3 shown in FIG. 2).
When the modulation and demodulation are performed by the optical demodulator,
In addition to the original frequency f3 component, other frequencies (for example,
For example, the transmission signal having f1, f2, and f4 in FIG.
Minutes are generated and mixed into the demodulator. In this way,
Intermodulation distortion that undesired frequency components are generated from the wave number
It is called Mi. In FIG. 2, the horizontal axis represents frequency, and the square
Let the locks represent each and every signal spectrum
And the optical signal output from the transmitting side optical modulator has f1 to f1.
Transmission signals having 50 different frequencies of f50 are multiplexed.
Will be. f1 to f50 are the respective signal spectra.
In the center frequency, f1, f2, f3,
..., f50 (the highest frequency is f50). General notation and
Then, each frequency can be expressed as fn (here, n =
1 to 50). [0007] Next, referring to FIG.
Will be described in more detail. Intermixing affecting transmission performance
There are a second-order distortion and a third-order distortion as the key distortion. [0008] Secondary distortion refers to the non-linearity of the input / output characteristics of the optical modulator / demodulator.
Fi-fj (i> j) and fi + generated by linearity
Refers to the component of fj. The third-order distortion has two modes.
Generated from any two of the 50 waves (f1 to f50) described in 2.
| 2 × fi-fj |
| Fi + fj-fk |
There is a minute. [0010] The transmission-side optical modulator uses different transmission frequencies.
Input / output characteristics of the optical demodulator on the receiving side
Has nonlinearity, so that cross-modulation distortion is inevitable.
However, if the influence of cross-modulation distortion is large, communication quality will deteriorate.
Therefore, after all, the number of multiplexed frequencies (f1 to f50),
In other words, communication quality is maintained by reducing the number of multiplexes
Or better for reducing cross-modulation distortion.
Use optical modulators and demodulators with guaranteed high performance
However, reduction of the number of multiplexes is not
Benefits and guaranteed good performance in reducing cross-modulation distortion
Such optical modulators and demodulators are generally expensive. On the other hand, as shown in FIG.
How to arrange the frequencies f1 to f50 without arranging them at equal intervals
To reduce cross-modulation distortion.
In this case, the interval between adjacent frequencies is
The circuit configuration became complicated due to irregular arrangement
In some cases, the multiplex number may not be as large as desired. Means for Solving the Problems The present invention has been made to solve such problems.
In the present invention, a plurality of electric signal carriers having different frequencies are used.
Using multiple carriers obtained by multiplexing waves in the frequency axis direction
Performs optical modulation and transmits an optical signal as a result of the optical modulation.
(1) multiplexing on the multi-carrier
(2) Attempt to transmit for each electrical signal carrier to be transmitted
Transmission information inspection means for inspecting the presence or absence of transmission information; (3)
Inspection by the transmission information inspection means that there is no transmission information
If a result is obtained, the amplitude of the corresponding electrical signal carrier is
It is characterized in that damping means for damping is provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) Embodiment An embodiment of an optical transmitting apparatus according to the present invention will be described below.
I will tell. In this embodiment, the transmission signal is converted into an optical signal.
On the transmitting side for wave number division multiplexing, do not use
By reducing the amplitude of the carrier (of the electrical signal)
It is characterized by reducing the influence of cross-modulation distortion on the receiving side.
You. In this embodiment, the conventional ADSL technology is used for optical fiber.
It is intended to be applied on fiber transmission paths.
You. (A-1) Configuration of Embodiment FIG. 1 shows an overall configuration example of an optical transmission circuit 10 according to this embodiment.
Show. The optical transmission circuit 10 is a telephone network or the Internet.
Fiber optic transmission lines that constitute access lines for
(FB) and telephone lines (copper cable
). The optical transmission times
Route 10 allows multiple copper cables to be
A wideband communication can be performed by being accommodated in a transmission line. For example, for example, a personal
Information processing with network functions such as computers
The device is connected to the xDSL modem via the copper cable.
The optical transmission circuit 10 is connected. The optical transmission circuit 10 is a component for transmission.
Therefore, in order to perform two-way communication, the optical transmission circuit 1
A separate optical receiver circuit with a configuration symmetric to 0 is required.
It is natural. In FIG. 1, the optical transmission circuit 10 includes N
Electric modulation units 11A to 11N and one synthesizer
15 and one optical modulator 16. Of these, the synthesizer 15 and its left in FIG.
The electric modulation units 11A to 11N arranged on the side
The component that processes only the signal
Only the side is the area of the optical signal. Therefore, the transport shown
Transmission waves CA to CN, transmission signals UA to UN, modulator output signal
MA to MN, passing signals SA to SN, switch control signal L
A to LN and the multiplex signal MX are all electric signals,
Only the signal OP is an optical signal. The number N of the electric modulation units 11A to 11N
Means that the effect of the present embodiment is not lost if the minimum is 2 or more.
Therefore, in general, any natural number of 2 or more may be used.
However, here, N = 50 is assumed according to FIG. 2 described above.
I do. Frequency f1 to f to be multiplexed by frequency division multiplexing
Since an electric modulation unit is provided for every 50,
The number of the frequencies f1 to f50 and the electric modulation unit 11
The numbers of A to 11N are the same. In this embodiment,
As in FIG. 2, adjacent frequencies f1 to f50 on the frequency axis
Are arranged at equal intervals. As is apparent from FIG.
The modulation units 11A to 11N all have the same configuration.
However, in the following, the carrier CA having the frequency f1 is mainly used.
Focusing on the electric modulation unit 11A that performs the modulation of
Proceed. The electric modulation unit 11A includes the modulator 1
2A, a switch 13A, and a signal detector 14A.
ing. A type of modulator in which the modulator 12A performs external modulation.
In the case of a modulator, a carrier CA having a frequency f1 is externally provided.
The received carrier wave CA is modulated.
Then, the carrier wave CA is generated inside the modulator 12A.
Shall be. The transmission signal UA is transmitted to the electric modulation unit 11.
A via the copper cable or xDSL modem described above
When connected to a personal computer (this
The connection is made, for example, to a LAN switch located in a general home.
Connection via a switch or router)
Is, for example, a Web access from the personal computer.
Indicate HTTP requests supplied for access
Electrical signal (modem signal). xDSL model
The transmission signal UA
Is an analog signal. The modulator 12A controls the supply of the transmission signal UA.
To the carrier CA of the frequency f1 generated internally.
A circuit that performs modulation in accordance with the transmission signal UA.
Output force signal MA. Even with such a modulation function
If so, what kind of circuit is used as the modulator 12A?
You can also. The modulation method is amplitude modulation,
What kind of method, such as wave number modulation, phase modulation, etc.
I don't know. Further, a different one for each of the modulators 12A to 12N.
A different modulation method may be used. Modulator output signal M output from modulator 12A
The frequency of A is f1 which is the same as the frequency of carrier wave CA
And If the modulation method is amplitude modulation, the amplitude
The modulated modulator output signal MA is transmitted in addition to f1.
To include frequency components corresponding to the frequency of the transmission signal UA
For example, a signal spectrum as shown in FIG. 2 is formed.
However, usually, the frequency of the transmission signal UA which is a modulation signal is
In comparison, the frequency f1 of the carrier CA is much higher.
Here, for the sake of simplicity,
The center frequency of the ram is used to calculate the frequency of the modulator output signal MA.
The number was assumed to be f1. Note that when there is no valid transmission signal UA,
In this case, the unmodulated carrier CA is
Modulator 12A may output as modulator output signal MA.
You. The transmission signal U is transmitted together with the modulator 12A.
The signal detector 14A receiving the supply of the signal A outputs the transmission signal UA.
Inspect whether it is valid and check the scan according to the inspection result.
This is a circuit that outputs the switch control signal LA. The signal detection
Output device 14A uses a detector or A / D converter
It is also possible to configure with. What happens when the transmission signal UA is invalid
Whether to output a bit pattern signal like
The encoding method of the xDSL modem that is the source of the signal UA
Because it depends on which functional specification, the inside of the signal detector 14A
The configuration also differs depending on the function specifications. Although the necessity is thought to be low,
If necessary, whether a valid transmission signal UA is being transmitted
Is the source of the digital signal underlying the transmission signal UA
Terminals (information processing devices such as personal computers)
Or the xDSL modem is connected to the signal detector 14A.
You may make it communicate explicitly. Also, a service equivalent to ADSL described later
When using on the access line, 130 kHz in the uplink
Below, it corresponds to an ADSL signal of 1.1 MHz or less in the downstream
The presence or absence of a signal to be detected is detected by the signal detector 14A.
If detection is performed using a device or A / D converter,
Checking if the sent UA is valid
It is possible. The switch control signal from the signal detector 14A
The switch 13A that receives the signal LA
A circuit that enters a passing state or a blocking state according to the signal LA
It is. From the viewpoint of durability and reliability, the switch 13
A is configured as a contactless switch using a semiconductor
Is considered to be preferable, but the frequency f1 is a high frequency.
, The modulator output signal MA is completely
It can also be difficult to prevent continuity. And
However, even in such cases, the level is small enough.
Can attenuate the amplitude of the modulator output signal MA.
Is enough. As an example, the attenuation in the blocking state is 2
If it is about 0 dB, the effect is sufficient. In the passing state or the blocking state,
A signal that passes through the modulator output signal MA that has passed through the switch 13A
SA. The transmission source xA of the transmission signal UA is xDS.
L modem and the source terminal encoding method and the modulator 12A
Depending on the combination with the modulation method, etc., the switch 13A may be used.
Even if they are not, they are sufficiently small at the stage of the modulator output signal MA.
It can also be amplitude. For example, a source terminal and an xDSL modem
When there is no transmission signal UA for which the encoding method of
Outputs a low level continuously, and the modulator 12A
If the key is to be implemented by a simple multiplier
Indicates that the transmission signal UA is low regardless of the amplitude of the carrier wave CA.
As long as the level is maintained, the amplitude of the modulator output signal MA is
Near to 0 corresponding to the low level value (voltage value, etc.)
Value. However, what kind of coding method is adopted
It depends on the transmission source terminal, and the modulation of the modulator 12A is used.
For the keying method, etc., the demodulation method of the optical demodulator
A valid transfer must be made to determine
The amplitude of the modulator output signal MA when there is no transmission signal UA is always
There is no guarantee that the value can be close to zero. Also, low level
For example, the voltage value is, for example, 0.8 volts,
It is lower than the high level voltage value and close to 0
However, the amplitude of the modulator output signal MA corresponding to this value
Whether it can be said that it is small enough to reduce modulation distortion
Is not always clear. Therefore, when there is no valid transmission signal UA
The amplitude of the modulator output signal MA to a value close to 0 at all times.
It is actually attenuated, and small enough to reduce cross-modulation distortion.
Switch to generate a pass signal SA having a large amplitude.
A switch 13A is required. As described above, the secondary distortion among the intermodulation distortions
Only the components of fi−fj and fi + fj are 3
The | 2 × fi-fj | component and | fi +
fj-fk | component, but the magnitude of intermodulation distortion is actually
And the degree of degradation of communication quality is determined by fi,
The amplitude of each of the passing signals SA to SN having the frequencies fj and fk
It is. Therefore, each switch, including the switch 13A,
Send valid transmission signals using switches 13A to 13N
If not, the amplitude of the passing signals SA to SN is
By doing so, it is possible to reduce cross-modulation distortion and suppress deterioration of communication quality.
It becomes possible. For example, regarding the third-order distortion, each passing signal SA
When all the amplitude levels of .about.SN decrease by 1 dB, the distortion component becomes 3
Decrease (improve) by dB. Distortion when the whole decreases by 10 dB
The minute drops by 30 dB. The electric modulation units 11A to 11N
The switches 13A to 13N to pass or stop
The state is determined based on the data on which the transmission signals UA to UN are based.
The terminal that is the source of the digital signal (the personal computer
Computer, set-top box, etc.)
Is controlled independently according to whether or not to send
It is an event that is defined. The communication supplied from the electric modulation unit 11A
In addition to the excess signal SA, each of the electric modulation units 11B to 11N
That also receives the supply of the pass signals SB to SN supplied from the
The unit 15 frequency-multiplexes these passing signals SA to SN.
And outputs a multiplexed signal MX. To enable such frequency multiplexing,
The frequencies f1 to f50 of the carrier waves CA to CN are shown in FIG.
It is assumed that they are different as shown in FIG. The multiplex signal MX is received as a modulated signal.
The optical modulator 16 performs the optical modulation, and
A circuit for outputting an optical signal OP modulated according to X
You. As the optical modulator 16, for example, a laser diode
Mode can be used. The laser diode as an optical modulator is
Optical modulator that performs external modulation using the above-described electro-optic effect
Unlike, it uses stimulated emission. The optical modulator 16 is a laser
If it is a diode, the multiplex signal MX is the injection current
Hit. Optical signal OP output from optical modulator 16
Is an optical fiber cable F constituting the access line.
B and transmitted. Hereinafter, the present embodiment having the above configuration will be described.
The operation of the state will be described. (A-2) Operation of the Embodiment When the optical transmission circuit 10 is operated, each electric modulation
In the units 11A to 11N, each transmission signal UA to UN
Transmission signal UA from the xDSL modem that is the source of the
Switch 13 according to whether or not
A to 13N are set to a passing state or a blocking state. Then, the switch in the passing state (for example,
For example, from 13A), a passing signal having a sufficiently large amplitude
(For example, SA) is output and the switch is in the blocking state.
(E.g. 13B) pass with a sufficiently small amplitude
A signal (for example, SB) is output. A plurality of optical transmission circuits housed in a single optical transmission circuit 10
Of said source terminals are dynamically used or not used.
Therefore, the number of source terminals used for
Fluctuate. Further, the personal computer and the set
If there are various types of sender terminals such as
Traffic characteristics are diverse and the largest data
The rates are also different. XDSL such as ADSL is basically an optical
Regular telephone lines (copper wires for telephones) instead of fiber transmission lines
Cable) is a technology that uses optical fiber
Even when applied on a transmission line, the basic properties are inherited.
It is. The above-mentioned ADSL is the maximum transmission in the uplink and downlink.
It is characterized by asymmetry with different speeds,
The value of the maximum transmission rate is specified in the ITU-T
Therefore, the specific ADSL service type and connection distance
It depends on the length of separation. But the real ADSL service
Service, the maximum transmission speed of the uplink is about 500 kbps
Degree, the maximum downlink transmission rate is about 1.5Mbps
There are many. In this case, the optical transmission circuit 10
Maximum data rate of accommodated transmission signal UA is 500
kbps. The transmission volume of the Internet will increase in the future.
It can be expected to increase suddenly, and a new communication application
Traffic characteristics are different from the current
But it's a standard data rate
At the moment, about 15 kbps downstream,
It is said that the upstream is about 1.5 kbps. This number is
Average data rate measured over 10 seconds. to this
On the other hand, the maximum transmission speed of ADSL is
1.5 Mbps, and 500 kbps for upstream. Under these conditions, the transmission time rate (line usage
Rate), 1% (= 15 kbp) for downstream
s / 1.5 Mbps), and 0.3% for upstream
(= 1.5 kbps / 500 kbps). As can be seen from the above, the one with a larger transmission time rate
More than 90% of the time is not used for transmission
Will be. The usage rate (transmission time rate) in the time axis direction
It can be used as the usage rate in the frequency axis direction as it is
If we assume that this is
Then, 50 waves multiplexed on the optical signal OP (frequency f1 to frequency f1)
f50) that no more than 45 waves are used
Show. And for 45 waves not used,
Can be attenuated. That is, conventionally, all 50 waves have a large amplitude.
Is there a high possibility that large cross-modulation distortion will occur due to the width?
However, in this embodiment, 45 waves or more are attenuated.
Has only a small enough amplitude and a large amplitude
Less than 5 waves, significantly reducing the magnitude of cross-modulation distortion
Thus, the communication quality can be dramatically improved. Next, this point will be further described with reference to FIGS.
This will be specifically described. FIGS. 3 and 4 show the third-order distortion as an example.
FIG. 3 shows that all of the 50 waves are sufficient.
FIG. 4 shows a case having a large amplitude, and FIG.
The case where only the wave has a sufficiently large amplitude is shown. f1-f
Select any 5 waves out of 50 to give a large amplitude
It is optional, but in FIG. 4, f10,
f22, f28, f35 and f39 are selected. When these are compared, the 50 waves shown in FIG.
When the ratio of the amplitude of the signal (f1 to f50) to the distorted interference wave is 3
While about 5 dB, in the case of five waves shown in FIG.
50 dB or more, and the magnitude of cross-modulation distortion is extremely small.
It turns out that it has improved. 3 and 4
The performance of optical modulation and demodulation was the same. With this improvement, end-to-end communication
It is clear that the actual multiplex number can be increased in
It is. To specify how much can be increased,
The traffic characteristics of the various source terminals
It is necessary to consider in detail the data rate of
Internet usage by users of each source terminal
(For example, users who frequently access the Web using HTTP
Or the user who frequently uses FTP)
However, as can be seen from the above calculation example, 2 to 5
A multiplicity improvement of about twice is sufficiently achievable. In consideration of the above points, the optical transmission
In the case of the transmission circuit 10, the magnitude of the intermodulation distortion on the receiving side
Maximum number of multiplexes (allowable
Multiplex number) is configured to be around 5 waves as an example.
Is considered to be efficient. This configuration includes
Of the performance of the optical modulator 16 and the optical demodulator used on the receiving side
Etc. are included. (A-3) Effects of the Embodiment According to this embodiment, the magnitude of the cross modulation distortion can be reduced.
Communication quality can be improved.
You. In addition, in this embodiment, high communication quality
Substantial multiplicity can be improved while maintaining. Further, the interval between adjacent frequencies is not constant.
These advantages without using the irregular arrays mentioned above
And no complicated circuit configuration is required.
You. (C) Other Embodiments As described above, each of the electric modulation units 11A
Switches 13A to 13N are passed through to 11N
It is determined whether each transmission signal UA-UN is in the blocking state or not.
Valid, invalid, that is, the data underlying the transmission signals UA-UN.
Source terminal of the digital signal (the personal computer
Data, set-top box, etc.)
Is controlled independently according to whether or not to send
It is an event that is defined. Therefore, for an event that is extremely rare in probability,
Even if the number of source terminals exceeds the allowable multiplexing number,
At the same time, valid transmission signals UA to UN are transmitted at the same time.
It can happen. This is extremely rare
Because it usually occurs only momentarily,
Possibility may not be a big problem in practical use
As an example, the optical transmission circuit 20 shown in FIG.
Can prevent the event itself from occurring.
Noh. In FIG. 5, the same reference numerals as in FIG.
The functions of the components and signals added are the same as those shown in FIG.
Same as state. Therefore, the optical transmission circuit 20
The difference from the optical transmission circuit 10 of the embodiment is that the controller
Only the point with 17. The controller 17 controls the allowable multiplexing number.
From the number of source terminals exceeding
Inspect whether sent messages UA-UN have not been sent
It is a component for This controller 17 has
Of the source terminal that sends effective transmission signals at the same
If the number exceeds the allowable number of multiplexes,
By setting 13N to the blocking state, transmitted data
Control to keep the amount of data flowing at the same time constant.
You. Naturally, the thinned data is not transmitted
Is the TCP / IP protocol used on the Internet
In the TCP protocol, the TCP protocol located in the transport layer
Since Tokor performs retransmission control, for some reason data
Even if transmission fails, maintain the reliability of communication and perform desired communication.
It is possible to realize. UDP at the transport layer
Such retransmission control is not performed in communication using
Even in this case, resend is performed as a function of the application.
It is possible. The data to be thinned out is randomly thinned out.
It is fine, and intensively select the crowded band and thin out
You may make it. Further, the effective transmission signal is transmitted to the modulators 12A to 12A-1.
Stage before reaching 2N and signal detectors 14A to 14N
Store each transmission signal in a buffer
The transmission timing of each transmission signal is controlled by controlling the read timing.
Adjust the transmission timing so that a valid transmission signal is
The number of source terminals to send in
It is also possible to do so. In the above embodiment, the effective transmission signal
If UA to UN are not supplied, the switches 13A to 13
N to sufficiently attenuate the amplitude of the passing signals SA to SN
However, for example, the modulators 12A to 12N
In the case of a type of modulator that performs external modulation,
If the transmission signals UA to UN are not supplied, the carrier C
Do not transmit A to CN itself, or
Only the carrier waves CA to CN whose width has been attenuated are modulators 12A to 1A.
By not supplying to 2N, the above-mentioned embodiment and
Similar effects can be expected. In the above embodiment, the interface is mainly used.
The access line for connecting to the network was explained as an example.
However, the present invention is applicable to networks other than the Internet.
This is applicable when transmitting optical signals to
And not only access lines, but also trunk lines and
Sends an optical signal to an optical fiber transmission line as a service line
The present invention can be applied to such cases. For example, a server such as a Web server,
Currently, relay devices such as data
The optical signal received is difficult to perform
Once it needs to be converted to an electrical signal,
Answer, or send an IP packet after routing
When sending to the relevant physical link (optical fiber transmission line)
In this case, an optical transmission circuit 10 similar to that shown in FIG. 1 can be used.
Noh. In the above description, the hardware is mainly used.
Although the present invention has been realized in terms of software,
It is also possible to realize. As described above, according to the present invention,
Optical transmission equipment with high communication quality, low cost,
It is possible to provide an arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a configuration example of a main part of an optical transmission circuit according to an embodiment. FIG. 2 is a schematic diagram showing a frequency arrangement for explaining a problem to be solved by the invention. FIG. 3 is an operation explanatory diagram of the embodiment. FIG. 4 is an operation explanatory diagram of the embodiment. FIG. 5 is a schematic diagram illustrating a configuration example of a main part of an optical transmission circuit according to another embodiment. [Description of Signs] 10, 20: optical transmission circuit, 11A to 11N: detection modulation circuit, 12A to 12N: modulator, 13A to 13N: switch, 14A to 14N: signal detector, 15: synthesizer, 16
... optical modulator, 17 ... controller, CA to CN ... carrier, f1 to f50 ... carrier frequency, UA to UN ... transmission signal, LA to LN ... switch control signal, MX ... multiplex signal,
OP: Optical signal.

Claims (1)

Claims: 1. An optical modulation is performed using a multiplex carrier obtained by multiplexing a plurality of electric signal carriers having different frequencies in a frequency axis direction, and an optical signal is transmitted as a result of the optical modulation. Transmission information inspecting means for inspecting the presence / absence of transmission information to be transmitted for each electric signal carrier multiplexed on the multiplex carrier, and it is assumed that the transmission information inspection means does not have the transmission information. An optical transmission device comprising an attenuating means for attenuating the amplitude of a corresponding electric signal carrier when an inspection result is output.