JPH0380377B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a receiving device for optical pulse signals transmitted through an optical fiber. In particular, it relates to the reception and reproduction of optical pulse frequency modulated signals transmitted through multimode optical fibers.

[Description of prior art]

An optical pulse signal transmitted through a multimode optical fiber is subject to waveform distortion because the wavelength transmission characteristics of the multimode optical fiber are not uniform over a wide band. This waveform distortion is not necessarily the same at the rising point and falling point of the optical pulse signal. Even if a rectangular wave is transmitted on the transmitting side, the received waveform may have large waveform distortion at the falling point, as shown in Figure 1A, or large waveform distortion at the rising point, as shown in Figure 1B. There is. This is thought to occur mainly because multimode optical fibers are manufactured to have uniform attenuation characteristics, but there are no strict manufacturing standards for phase characteristics. Strictly setting standards for phase characteristics naturally increases the manufacturing cost of optical fibers. Therefore, the phase characteristics of the optical signal differ depending on the path it passes.
The difference is whether waveform distortion occurs more at the rising point or the falling point.

In a receiving device for an optical pulse frequency modulation signal, it is necessary to correctly identify the position of the received optical pulse signal from the received optical pulse signal.However, in conventional devices, for example, it is necessary to perform fixed identification at the rising point of the optical pulse signal. Even if the falling point of the optical pulse signal has less waveform distortion than the falling point of the optical pulse signal, this cannot be selected. A pulse signal reproduced from an optical pulse signal with large waveform distortion contains many jitters and has a poor signal-to-noise ratio.

[Objective of the Invention] The present invention improves this, and even if the state of waveform distortion due to the transmission of optical pulse signals through a multimode optical fiber changes, it is possible to identify and reproduce received signals with the best signal-to-noise ratio. The purpose of the present invention is to provide a receiving device that can perform the following functions.

[Features of the invention]

In the present invention, the identification and regeneration circuit selects either the rising point or the falling point of the main electric signal of the photoelectric converter according to the received input waveform,
It is characterized by being configured so that it can be identified.

[Explanation based on examples]

FIG. 2 is a block diagram of a circuit according to a first embodiment of the present invention. The optical pulse signal propagated through the multimode optical fiber 1 is converted into an electrical signal by the photoelectric converter 2,
The signal is amplified by an amplifier 3 and waveform-shaped by a limiter circuit 4. The output signal of the limiter circuit 4 is identified and regenerated by an identification and regeneration circuit 5, passes through a reduction filter 6, and is supplied to a demodulation amplifier circuit (not shown).

The feature of the present invention is that the identification/reproduction circuit 5 is configured to selectively identify the falling point or the rising point of the input signal. That is, the input signal of the discrimination/reproduction circuit 5 is connected to one input of the exclusive OR circuit 8, and its output is connected to the set input of the flip-flop circuit 9. The output of the exclusive OR circuit 8 is branched, passes through a delay circuit 10, and is connected to a reset input of a flip-flop circuit 9. A signal "1" or a signal "0" is continuously applied to the other input terminal 11 of the exclusive OR circuit 8.
Depending on whether the signal ``1'' or the signal ``0'' is applied to this terminal 11, the identification reproducing circuit 5 selects whether to perform identification at the falling point or rising point of the input signal. I can do it.

FIG. 3 is a waveform diagram for explaining the operation of this embodiment circuit. Assuming that the signal shown in FIG. 3N has arrived at the input of the identification/reproduction circuit 5, when the signal "1" is present at the terminal 11, the set input S of the flip-flop circuit 9 has the waveform shown in FIG. 3S. . At this time, since the signal at the reset input R of the flip-flop 9 is a signal delayed by the time t from the signal at the set input S by the delay circuit 10, it has a waveform as shown in FIG. 3R. Therefore, the flip-flop circuit 9 is set at the rising point of the set input S, reset at the rising point of the reset input R, and outputs the input signal N with the waveform shown in FIG. 3Q.
Identification will be performed at the falling point of .

Next, if you apply a signal "0" to terminal 11,
The signal at the set input S of the flip-flop circuit 9 has the waveform shown in FIG. 3 S'. The waveform of the reset input R of the flip-flop circuit 9 is shown in FIG.
The waveform is shown as R′. Therefore, the signal waveform of the output Q of the flip-flop circuit 9 is as shown in FIG.
The waveform becomes Q', and identification is performed at the rising point of the input signal N.

In this way, by selecting whether to give the signal "1" or the signal "0" to the terminal 11 depending on the state of waveform distortion of the received signal, the identification point of the reproduced pulse signal can be set as the rising point or the rising point. You can select the falling point.

FIG. 4 is a circuit diagram of a main part of a circuit according to a second embodiment of the present invention. In this example, the identification and reproducing circuit 5 includes an exclusive OR circuit 8, a D-type flip-flop circuit 15,
and a delay circuit 16. An input signal is applied to the clock input C of the D-type flip-flop circuit 15. The inverted output and input D are combined, the output Q signal is delayed by time t, and the reset input R is
If you give it to , you can perform identification regeneration. The phase of this input signal is inverted depending on whether the signal at the terminal 11 connected to the other input of the exclusive OR circuit 8 is "1" or "0". This results in
Similarly, identify at the rising point of the input signal, or
It is possible to select whether to perform identification at the falling point.

FIG. 5 is a circuit diagram of a main part of a circuit according to a third embodiment of the present invention. This circuit inputs an input signal N to a non-inverting buffer circuit 18 and an inverting buffer circuit 19,
The respective outputs are given to two exclusive OR circuits 20 and 21. The output of this exclusive OR circuit 20 is sent to one input of an AND circuit 23, and the output of the exclusive OR circuit 21 is passed through a delay circuit 24.
By applying this to the other input of the AND circuit 23, the input signal can be identified and reproduced. In this circuit as well, the exclusive OR circuit 2
The phases of the 0 and 21 signals are inverted, and it is possible to select whether to perform identification reproduction at the rising point or the falling point of the input signal.

In addition to the circuits shown in the above examples, circuits that can similarly implement the present invention can be configured in various ways.

The present invention provides a pulse frequency modulation signal in which the pulse width is constant and the pulse repetition frequency changes according to the modulation signal, the pulse duty is about 50%, and the repetition frequency changes according to the modulation signal. It can be applied to any pulse frequency modulated signal.

In addition, "pulse frequency modulation" referred to in this specification
should be understood in a broad sense and includes so-called pulse phase modulation and pulse position modulation.

〔Effect of the invention〕

As explained above, according to the present invention, identification of an optical pulse signal transmitted through a multimode optical fiber is performed using
It is possible to select whether to perform identification at the rising point or at the falling point. Therefore, it is possible to always perform reception with the best signal-to-noise ratio depending on the transmission conditions that vary depending on the path through which the optical signal passes.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a signal waveform that is transmitted to a multimode optical fiber and causes waveform distortion. FIG. 2 is a configuration diagram of a circuit according to a first embodiment of the present invention. FIG. 3 is a waveform diagram for explaining the operation. FIG. 4 is a circuit diagram of a main part of a circuit according to a second embodiment of the present invention, and FIG. 5 is a diagram of a circuit diagram of a main part of a circuit according to a second embodiment of the present invention. 1...Multimode optical fiber, 2...Photoelectric converter, 3...Amplifier, 4...Limiter circuit, 5...
Discrimination regeneration circuit, 6...Low pass filter.

Claims (1)

[Claims] 1. An optical system comprising a photoelectric converter that receives an optical pulse frequency modulation signal transmitted to a multimode optical fiber, and an identification and regeneration circuit that regenerates a pulse signal from the output electrical signal of the photoelectric converter. In the pulse signal receiving device, the identification and regeneration circuit includes an exclusive OR inputted with the output electrical signal and a binary control signal that controls whether the output electrical signal takes a rising point or a falling point. 1. An optical pulse signal receiving device comprising: a circuit; a latch circuit to which the output signal of the exclusive ethical sum circuit is input; and a reset circuit to reset the latch circuit.