JPS6219098B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical telephone system in which an exchange and a telephone are connected by an optical fiber. It is related to the method.

In a general telephone system, power is supplied from an exchange to a telephone via a subscriber line, and various signals such as call signals are transmitted via the subscriber line. Furthermore, with the development of low-loss optical fibers, it is conceivable to connect exchanges and telephones using optical fibers, and to transmit various signals such as telephone calls as optical signals. In that case, the power required by the telephone circuit must be converted into an optical signal and transmitted, and power is also required to drive the light emitting element to send out various signals such as call signals from the telephone as optical signals. Therefore, in order to supply that power through optical signals, the exchange must be equipped with a high-output light emitting element.

The present invention reduces the power consumption of the telephone and enables high-quality signal transmission by modulating the optical signal sent from the exchange using dial signals, call signals, etc. of the telephone and returning it to the exchange. The purpose is to Examples will be described in detail below.

FIG. 1 is a block diagram of essential parts of an embodiment of the present invention, in which 1 is an exchange, 2 is an optical fiber, and 3 is a telephone, in which an optical signal from a light emitting element 11 of the exchange 1 is transmitted down an optical fiber 21. The signal is transmitted to the telephone set 3 via the folding section 31 and transmitted to the light receiving element 12 of the exchange 1 via the uplink optical fiber 22. This folding unit 31 modulates the folded optical signal by a signal S such as a call signal or a dial signal, and has, for example, a mechanical or electro-optical configuration in which the degree of optical coupling is controlled by the signal S. It is something. Therefore, a signal from the telephone 3 can be transmitted to the exchange 1 as an optical signal without providing a light emitting element inside the telephone 3.

Since light emitting diodes and the like as light emitting elements do not have sufficient linearity, it is not easy to faithfully convert an analog signal such as a telephone call signal into an optical signal. However, when modulating an optical signal, it is relatively easy to improve the linearity, so by modulating the optical signal at the folding section 31, it is possible to make a high-quality call.

In addition, the light emitting element 11 of the exchange 1 periodically sends out optical pulses as a return optical signal, and for example, when the telephone 3 goes off-hook when making a call, the optical pulse is returned from the return section 31. 3 off-hook can be detected.

FIG. 2 is a block diagram of main parts of an embodiment of the present invention, where _the same reference numerals as in FIG. ₁ indicate the same parts.
13, wavelength multiplexed by a coupler 14,
Send it to the telephone 3 via the downlink optical fiber 21,
In addition, the light reception control unit 15 detects the optical signal that has been returned by the return unit 31 of the telephone 3 and transmitted through the upstream optical fiber 22, and also detects the reception of the optical signal by the light reception control unit 15. Based on the transmission delay time of the optical signal, etc. Control so that the light output is appropriate.

For example, the light emitting element 11 with a wavelength λ ₁ is used to generate a return optical signal, and is controlled to generate light pulses at a predetermined period, and after detecting off-hook of the telephone 3, generates continuous light, and emits light with a wavelength λ ₂ . When driving the element 13 with a call signal and an incoming call signal to generate a call optical signal, the branching filter 32 of the telephone 3 sends the call optical signal to the telephone circuit 33, and sends the return optical signal to the telephone circuit 33. The signals are demultiplexed so as to be respectively input to the folding section 31.

Note that the power required by the telephone circuit 33 is also transmitted as an optical signal from the exchange 1. An optical signal from a light emitting element for power supply of the exchange 1 (not shown) is transmitted by wavelength multiplexing, and the telephone 3 transmits the power as an optical signal. Power is supplied to the telephone circuit 33 by demultiplexing the signal using a demultiplexer and photoelectrically converting the signal.

The telephone circuit 33 photoelectrically converts the optical signal for communication, drives a sound source for displaying an incoming call, and drives the receiver with the photoelectric conversion output by off-hook. Further, the dial signal and the call signal from the transmitter are applied to the return unit 31, the degree of optical coupling is controlled, and the return optical signal is modulated. This modulated optical signal is input to the reception control section 15 of the exchange 1 via the downlink optical fiber 22, and the dial signal is transferred to a common control device etc. by photoelectric conversion, and the call signal is transferred to the other subscriber.

FIG. 3 shows the main part of an example of the folding section 31. The folding section is constructed by optically coupling the downward optical fiber 21 and the upward optical fiber 22 with a mirror 311, and the folding section is constructed by optically coupling the downward optical fiber 21 and the upward optical fiber 22 with a mirror 311. The optical coupling degree is controlled by driving the mirror 311 and using its deflection force to deflect the mirror 311. In this case, the degree of optical coupling is always set to zero, and off-hook information can be transmitted to the exchange 1 using the off-hook as the degree of maximum optical coupling.
Further, it is possible to employ a configuration in which the reflected optical signal is modulated using an electro-optic effect element.

Figure 4 shows the maximum modulation level La by audio signal a.
This is an explanatory diagram of a case where the maximum modulation level Lb of the dial signal b is increased to facilitate reception identification in the exchange 1, and the identification level Th of the dial signal b is set to be higher than the maximum modulation level La of the call signal a. By setting this, dial signal b can be reliably identified. Note that the dial signal b is
It can be applied not only to the rotary dial but also to the multi-frequency signal of the push button dial.

As mentioned above, when the modulation levels of the call signal a and the dial signal b are made different, the dial signal from the telephone circuit 33 is given a large modulation level via the modulation control section 34, as shown in FIG. The call signal is applied to the return unit 31 via the modulation control unit 35 so as to have a modulation level smaller than the modulation level of the dial signal.

FIG. 6 is an explanatory diagram of an example of the operation, and shows the folding part 3
This is for the case where the optical coupling degree of 1 becomes zero on-hook.As shown in Figure a, the return optical signal is sent from exchange 1 at a constant period T, and as shown in Figure b, the return optical signal is transmitted from the telephone The degree of optical coupling in the folding unit 31 is maximized by the off-hook in step 3, and the folded optical signal is transmitted to the exchange 1 via the upstream optical fiber 22 as shown in Figure c. The signal is modulated by the dial signal and transmitted to the exchange 1.

In the case of an incoming call to the telephone 3, as shown in d of Fig. 6, if the incoming call is received at time _t1 , the return optical signal is sent out continuously and the incoming optical signal is also sent out. The response off-hook is t ₂ as shown in figure e.
If this is done at time , as shown in Figure f, the return signal is transmitted to the exchange, off-hook detection is performed, the transmission of the incoming optical signal is stopped, and the connection with the calling party is established by the called party's response. Control etc. are performed.

Light emitting element 1 by light reception control section 15 of exchange 1
As the control means 1 and 13, a means for calculating and controlling the distance of the optical fiber from the transmission delay time of the return optical signal is used. First, we will discuss a general means for detecting and controlling the received light level. explain.

For example, the optical output of the light emitting element 13 is a [dBm],
The loss of the downstream optical fiber 21 or the upstream optical fiber 22 is Lf [dB], the loss of the folding section 31 is Lr [dB], the loss of other connectors, etc. is Lc [dB], and the light reception control section 1
5, the received light level at 31 losses
Lr is known in advance at the time of design, and other losses Lc
is small, so the upstream and downstream optical fibers 2
Including the losses of 1 and 22, we get 2Lf=a-x-Lr (2), and even if this loss 2Lf changes, the received light level x
By controlling the driving current of the light emitting element 13 so that the signal is at a specified level, the modulated optical signal of the optical signal for return by the return unit 31 of the telephone 3, i.e., the call signal of the telephone 3, etc., is controlled regardless of the length of the optical fiber. signals can be reliably transmitted.

When the above-mentioned means for detecting and controlling the received light level is used, the light emitting element is controlled so that the received light level is almost constant, making it difficult to detect deterioration of each part including the folding part 31. be.

The present invention controls the light emitting elements 11 and 13 in accordance with the distance of the optical fiber, and when the above-mentioned deterioration occurs, the received light level is extremely reduced, so it is difficult to detect it easily. can. Further, various known optical signal transmission delay time measuring means can be used to measure the transmission delay time of the optical signal for return. If the time from transmission to reception of this return optical signal is Td [μS], the length of the optical fiber can be determined from the propagation speed of the optical signal υ [μs/Km], and the loss of the optical fiber can be calculated as L [dB/Km]. ], then the loss of the upstream and downstream optical fibers 21 and 22 is
2Lf is expressed as 2Lf=Td/2・1/υ・L (3) By controlling the light output a so that a−2Lf=A becomes the reference, the light reception level of the light reception control unit 15 can be adjusted. It can be kept constant. Such a calculation can be easily obtained using a timer and a table that calculates the loss from the transmission delay time obtained by the timer.

As explained above, the present invention modulates the return optical signal from the exchange 1 in the return unit 31 of the telephone 3 with a signal such as a dial signal or a call signal, and transmits it to the light receiving element of the exchange 1. It transmits
Since there is no need to provide a light emitting element in the telephone 3,
The power consumption of the telephone 3 is reduced, and high-quality signal transmission is possible.

In addition, to detect off-hook when the telephone 3 makes a call, it periodically sends out optical pulses as a return optical signal, and when there is no call, it periodically drives the light emitting element, so it continuously transmits light pulses. Compared to the case where the light emitting elements are driven, this has the advantage that the power consumption in the exchange 1 can be reduced and the life of the light emitting elements can be extended.

In addition, the transmission delay time is measured using the return optical signal, the distance of the optical fiber is calculated from this, and the optical output of the light emitting element is controlled in accordance with the distance of the optical fiber. Since the light output of the light emitting element can be controlled to be automatically optimized in accordance with the distance between the light emitting element and the light emitting element, there is an advantage that stable telephone communication using optical signals is possible.

Furthermore, by increasing the types of multiplexed wavelengths, it becomes possible to transmit not only audio signals but also many more types of signals. Furthermore, in the exchange 1, it becomes easy to detect the received light level and monitor whether or not a failure has occurred, thereby improving reliability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a main part of an embodiment of the present invention, FIG. 2 is a block diagram of a main part of another embodiment of the invention, and FIG. 3 is an explanatory diagram of an example of a folding part of a telephone.
Fig. 4 is an explanatory diagram of the optical modulation level between the call signal and the dial signal, Fig. 5 is a block diagram of the main part when the optical modulation level is different between the call signal and the dial signal, and Fig. 6 is an explanatory diagram of the operation. It is. 1 is an exchange, 2 is an optical fiber, 3 is a telephone, 1
1 and 13 are light emitting elements, 12 is a light receiving element, 14 is a coupler, 15 is a light reception control unit, 21 is a downstream optical fiber, 22 is an upstream optical fiber, 31 is a folding unit, 32
3 is a duplexer, and 33 is a telephone circuit.

Claims (1)

[Scope of Claims] 1. In an optical telephone system in which an exchange and a telephone are connected by an optical fiber, a folding part provided on the optical fiber and the telephone is connected between a light emitting element and a light receiving element provided on the exchange. and periodically transmits a light pulse as a return optical signal from the light emitting element, and after detecting off-hook of the telephone,
The return optical signal is continuously sent out from the light emitting element, modulated by signals such as dial signals and call signals at the return unit of the telephone, and transmitted to the light receiving element of the exchange. Optical signal method. 2. In an optical telephone system in which an exchange and a telephone are connected by an optical fiber, a light emitting element and a light receiving element provided in the exchange are connected via the optical fiber and a folding part provided in the telephone, and after periodically sending out a light pulse as a return optical signal from the light emitting element and detecting off-hook of the telephone,
The return optical signal is continuously sent out from the light emitting element, modulated by a signal such as a dial signal, a call signal, etc. at the return unit of the telephone, and transmitted to the light receiving element of the exchange. An optical signal system, characterized in that the distance of the optical fiber is calculated from the transmission delay time of the optical signal, and the optical output of the light emitting element is controlled.