JPH0444431A - Optical transmitter - Google Patents

Abstract

PURPOSE:To prevent the transmission of interference waves to other stations by adopting the constitution such that a control circuit is used so as to control a controller or a light generator thereby interrupting the transmission of a transmission optical frequency signal or reducing its transmission level. CONSTITUTION:A power supply of an optical transmitter 2 is operated, the power supply is in switching control from the OFF state into the ON state and when the optical transmitter 2 is started, a control circuit 23 as the AFC system acts effectively and while a normal optical transmission frequency signal is stably led out from an optical generator 21, the control circuit 23 controls a controller 24 thereby interrupting the signal from the optical generator 21 so as not to be sent to a transmission optical fiber 4. Thus, an unstable optical transmission frequency signal when the optical transmitter 2 is being started is not leaked externally with the interruption of the transmission by the controller 2 and a leaked wave is prevented from being an interference wave at a transmission or reception frequency band of other terminal stations.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) This invention relates to an optical transmitter used in an optical communication network having frequency division multiplexing functionality.

(Prior art) With recent advances in optical communication technology, an optical communication system has been proposed in which a large number of terminal stations are connected with optical cables to form an optical network, and optical frequency division multiplexing (FDM) communication is performed between the stations. has been done.

That is, as shown in FIG.
~IN are each provided with an optical transmitter 2 and an optical receiver 3, and are connected to each other via an optical star coupler 5 by an optical fiber 4. For example, Hikari Star Kabra 5 is NX
It has a switching function of N.

Each optical transmitter 2 or optical receiver 3 is assigned in advance an optical frequency (channel) unique to that terminal station.

The optical transmitter 2 includes a light generator 21 that has a light emitting diode (LD) or the like and derives a transmission optical frequency signal, a detector 22 that detects the frequency of the generated transmission optical frequency signal, and a detector 22 that detects the frequency of the generated transmission optical frequency signal. For example, the control circuit 23 controls the optical generator 21 so that the optical frequency becomes a predetermined optical frequency previously assigned to that station.

Therefore, if an optical (transmission) frequency is now assigned to the optical transmitter 2 of the terminal station 11, then the terminal station 1
Another terminal station 1 that attempts to receive the transmitted optical signal of 1
2 to IN, the receiving frequency at each receiver 3 is tuned (tuned) to receive the transmitted optical frequency signal from the terminal station 11.

By the way, when the terminal station 11 starts transmission,
When the power of the optical transmitter 2 is operated and the power is switched from OFF to ON, the AFC (automatic frequency control) system by the control circuit 23 functions effectively from the time of startup, and a predetermined signal is transmitted from the optical generator 2I. It takes several milliseconds to several tens of milliseconds until the optical frequency signal is derived.

Although this rise time is short, ranging from several milliseconds to several tens of milliseconds, the frequency during this time is unstable and unsettled, so there is a risk that it will cause interference to the transmission frequency band of other terminal stations.

Particularly, in frequency division multiplex communication where the frequency interval between adjacent channels is relatively narrow in order to effectively utilize the frequency domain, the generation of unnecessary wave signals can be a factor in degrading the quality of communication.

Although the above explanation deals with the case where the optical transmission frequency is assigned to the optical transmitter 2 side, the phenomenon of generation of unnecessary wave signals occurs even when the optical reception frequency is assigned to each terminal station 11 to IN. . In particular, when the optical reception frequency is assigned to each station, not only when the transmitter 2 is activated, but also when the transmitter 2 is activated.
Similarly, an optical transmission signal while scanning frequencies to select a receiving frequency signal (channel) for a specific destination may become an interference wave to other stations.

(Problem to be solved by the invention) In conventional optical transmitters, the optical transmission frequency fluctuates when the power is turned on or when selecting another station, which may cause interference to other communications, so improvements are desired. It will be done.

It is an object of the present invention to provide an optical transmitter that solves the above-mentioned problems and can form a good communication network with few mutual tones.

[Structure of the Invention] (Means for Solving the Problems) A first invention provides an optical transmitter for an optical communication network having a frequency division multiplexing function, including an optical generator for deriving a transmission optical frequency signal, and an optical generator for deriving a transmission optical frequency signal; a detector for detecting the frequency of the optical frequency signal transmitted from the optical generator; a control circuit for receiving the signal from the detector and controlling the output transmission frequency of the optical generator; The present invention is characterized in that it includes a controller capable of blocking the transmission of the transmission optical frequency signal or reducing the transmission level of the transmission optical frequency signal, thereby suppressing the transmission of unnecessary wave signals.

A second invention provides an optical transmitter for an optical communication network having a frequency division multiplexing function, including an optical generator for deriving a transmission optical frequency signal using a semiconductor laser, and the frequency and output of the transmission optical frequency signal from the optical generator. and a control circuit that receives a signal from the detector and controls the semiconductor laser to control its oscillation frequency and output, thereby suppressing the transmission of unnecessary wave signals. It is characterized by

(Operation) The optical transmitter according to the present invention is configured as described above, and in both inventions, the control circuit controls the controller or the light generator to cut off the transmission of the transmitted optical frequency signal or reduce the transmission level. Since the configuration allows this, it is possible to prevent interference waves from being sent to other stations.

(Embodiments) Hereinafter, embodiments of the optical transmitter according to the present invention will be described in detail with reference to FIGS. 1 and 2. Components that are the same as the conventional configuration shown in FIG. 3 are given the same reference numerals, and detailed explanations will be omitted.

FIG. 1 is a circuit diagram showing a first embodiment of an optical transmitter according to the present invention.

That is, the optical transmitter 2 includes an optical generator 21 that has a semiconductor laser or the like and derives a transmission optical frequency signal, a detector 22 that detects the frequency of the generated optical frequency signal, and a detector 22 that detects the frequency of the generated optical frequency signal. A control circuit 23 that receives a signal and controls the transmission optical frequency of the optical generator 21; and a control circuit 23 that receives a signal from the control circuit 23 and can block the transmission of the transmission optical frequency signal or reduce its transmission level as necessary. It is composed of a controller 24.

Therefore, this optical transmitter 2 is incorporated as a transmitter of one terminal station (11) of an optical communication network having a frequency division multiplexing function, and this optical transmitter 2 is preliminarily equipped with optical (transmission)
Assuming that a frequency has been assigned, the other terminal stations (12 to IN) that wish to receive the signal will tune (select) the reception frequency of each receiver 3 and receive the signal from the terminal station (11). will receive the transmitted optical frequency signal.

By the way, when the power of the optical transmitter 2 is operated and controlled to switch from the power OFF state to ON and the optical transmitter 2 is started, the #JIIIJ circuit 23 as an AFC system effectively functions and the light generator 21 The control circuit 23 controls the controller 24 until the regular optical transmission frequency signal is stably derived from
This is to block the data from being transmitted.

Therefore, the unstable optical transmission frequency signal when the optical transmitter 2 is activated does not leak to the outside because the transmission is interrupted by the controller 2, and becomes an interference wave to the transmission or reception frequency band of other terminal stations. is prevented.

Further, the control circuit 23 receives a signal from the detector 22,
Until a predetermined optical transmission frequency is detected, the controller 24
For example, other terminal stations (12 to I
An optical reception frequency (channel) is assigned in advance to N), and even while the optical generator 21 side of the own station (11) sweeps and selects the other channel, the target frequency signal is not detected by the detector 2.
2, the controller 24 can be shut off.

Note that since the controller 24 only needs to have a function of preventing unnecessary optical transmission frequency signals from being sent out, it is not necessary to optically block the transmission optical signals, and for example, in particular, to prevent transmission of unnecessary optical transmission frequency signals. In frequency division multiplexing communication with a narrow frequency interval, the controller 24 is configured with an optical attenuator, and the amount of attenuation is controlled by a signal from the control circuit 22 to substantially prevent interference waves from leaking. Also good. In this case, if there is little variation in the loss of the transmission path due to the star coupler 5 or optical fiber 4 of the optical communication network, it will be attenuated to about 1/10 of the normal transmission level, and it will be transmitted to other terminal stations as a practical interference wave. can prevent the effects of

Moreover, since the controller 24 only has to receive the control signal from the control circuit 23 and substantially suppress the transmission of the interference wave, the controller 24 can directly suppress the transmission of the unnecessary wave signal by controlling the light generator 21 itself. You can also do that.

That is, FIG. 2 is a circuit diagram showing a second embodiment of the optical transmitter according to the present invention. Unlike FIG. 1, the detector 22' detects the optical frequency f of the semiconductor laser in the optical generator 21 and the optical Detect the output ps. Both detected signals are transmitted to the control circuit 2.
3', and is configured to control the oscillation optical frequency of the semiconductor laser and its output. Therefore, first, when turning on the power of the optical transmitter 1 and starting it up, the control circuit 23'
Controls the semiconductor laser of the light generator 21 so that an injection current of a value slightly larger than the threshold value is supplied to the semiconductor laser to oscillate and derive a weak laser light with a level of output that does not cause any disturbance to others. The optical frequency in this state is detected by the detector 22', and the control circuit 23' controls the optical generator 21 so that the optical frequency becomes a predetermined optical transmission frequency.

Next, when the oscillation frequency of the light generator 21, that is, the semiconductor laser reaches a predetermined frequency, the control circuit 23' gradually increases the injection current and controls the output to a predetermined level.

Therefore, until the optical transmission frequency by the optical generator 21 reaches the pre-assigned frequency, the output is controlled to be small regardless of whether the assigned frequency is the transmission frequency or the reception frequency, so that it is not a disturbance wave. It is possible to prevent this from affecting the optical communication of the network.

Note that if the optical transmitter 2 is already in active communication and attempts to switch channels to communicate with another station, the control circuit 23' leaves the optical frequency of the semiconductor laser as it is and changes the optical output. After gradually decreasing the output and suppressing the output so that the injected current is slightly larger than the threshold value, the optical frequency is moved and fixed to a target frequency by AFC, and the optical output is increased to a predetermined level. Note that even in this case, in order to suppress the output, it is sufficient to reduce the injected current to about 1/10 of the predetermined output.

Further, if the control for increasing and decreasing the optical output is performed within a sufficiently gentle range compared to the time constant of the optical frequency control system, smooth frequency switching settings are possible.

In addition, in each of the above embodiments, it has been explained that unnecessary waves are prevented from being transmitted when the power supply is activated to activate the previous transmitter or when selecting a channel. However, if the power is switched from ON to OFF, the optical If there is a possibility that the transmission frequency may fluctuate and cause interference waves, turn off the power.
) may be configured to cut off or reduce the transmission output.

In any case, since the optical transmitter according to the present invention is a simple circuit and does not send out unnecessary optical transmission signals, it can be applied to an optical communication network to obtain remarkable effects.

[Effects of the Invention] The optical transmitter according to the present invention has a simple control circuit configuration that suppresses the transmission of unnecessary optical frequency signals, so it can be applied to high-quality communication networks and is advantageous in practical use. It is very effective.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of an optical transmitter according to the present invention, FIG. 2 is a circuit diagram showing a second embodiment of an optical transmitter according to the present invention, and FIG. 3 is a circuit diagram showing a conventional optical transmitter. FIG. 2 is a circuit configuration diagram showing a state in which the device is incorporated into an optical communication network. 11~IN...Terminal, 2...Optical transmitter, 21
...Previous generator, 22.22'...Detector, 23,
23'...Control circuit, 24...Controller, 3...
Optical receiver, 4... Optical fiber, 5... Optical star coupler. 2: Photodetector 23: Eye-opening circuit 22: Photodetector Agent Patent attorney Norifu Ogo Figure 1 Figure 2

Claims (2)

[Claims] (1) In an optical transmitter of an optical communication network having a frequency division multiplexing function, an optical generator that derives a transmitted optical frequency signal, a detector that detects the frequency of the transmitted optical frequency signal from this optical generator, and a control circuit that receives a signal from a detector and controls the output transmission frequency of the optical generator; and a control circuit that receives a signal from the control circuit and can block transmission of the transmission optical frequency signal or reduce its transmission level as necessary. An optical transmitter characterized in that it is equipped with a controller and can suppress the transmission of unnecessary wave signals. (2) In an optical transmitter of an optical communication network having a frequency division multiplexing function, there is an optical generator that derives a transmitted optical frequency signal using a semiconductor laser, and the frequency and output of the transmitted optical frequency signal from this optical generator are detected. An optical transmitter comprising a detector and a control circuit that receives signals from the detector and controls the oscillation frequency and output of the semiconductor laser, and is capable of suppressing the transmission of unnecessary wave signals.