JP3340822B2 - Bidirectional optical transmission / reception method and bidirectional optical transmission / reception device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to transmitting digital signals .
And a bidirectional optical transmitting and receiving method.

[0002]

2. Description of the Related Art In optical transmission of digital signals, when a binary signal of "1" and "0" is "1", a light emitting element is driven to emit light, and when it is "0", light is emitted. There is a method of transmitting the NRZ signal as it is, such as not radiating the NRZ signal or treating "1" and "0" in reverse. Further, as shown in the explanatory diagram of FIG.
There is a method of driving the light emitting element such that the Z signal has a pulse width T for the data bit “1” and a pulse width 2T for the data bit “0” by the bi-phase mark modulation method, and these methods are generally used. In this manner, bidirectional optical transmission is also performed, but the transmission rates of transmission / reception 1 and transmission / reception 2 may be the same or different.

[0003]

However, as shown in the characteristic diagram of FIG. 4, the light emitting element has a different peak forward current that can be applied to the light emitting element depending on the duty ratio of the pulse, which results in a difference in light output. I have. For this reason, the transmission by the NRZ signal is inefficient when the signal of “1” is continuous, because a large amount of direct current is included and a current flows to the light emitting element continuously, so that the optical output cannot be increased and the efficiency is low. Further, since the distinction between “1” and “0” is based on the presence or absence of light, the detection sensitivity is directly affected by attenuation.

On the other hand, the bi-phase mark modulation system has
Since the light emitting element is driven by the pulses having the T width and the 2T width, the efficiency is high and the influence of the attenuation is smaller than that of the NRZ signal. However, in either case, the transmitted pulse must be reproduced by accurately detecting the rising and falling periods of the pulse.However, in transmission, the frequency characteristics of the low-frequency part and the high-frequency part are deteriorated. The pulse width increases. This is called “jitter” as a difference between the rising and falling times of the pulse, and causes a code error.

[0005] The rising or falling characteristics of the pulse are also affected by the performance of the light emitting element. The light emitting element has a different response speed depending on the type, and is selected depending on the frequency to be used.In general, the rising of the pulse is steep and the falling is gradual. The difference is great. Therefore, NRZ
For signals, increasing the efficiency of the light emitting element and the common pulse width during transmission for signals using the biphase mark modulation method are common issues during reception and reproduction.

Further, in the case of bidirectional optical transmission, when both clocks have the same period, in reception, the closer to the same phase, the more the reception of the transmission signal on the same side is affected by the interference of the leakage noise, and the weaker the reception is. The more the signal, the greater the effect.Even if you take measures such as light leakage or electromagnetic shielding, it is easy for bit errors in the reproduced signal to occur.Therefore, the bidirectional transmission / reception distance is reduced to less than half compared to one-way optical transmission. There is a problem to do.

[0007]

Therefore, according to the present invention, the pulse is differentiated, the rising portion of the pulse is distinguished from the falling portion of the pulse, the differentiated signal of the falling portion is inverted, and the pulse is multiplexed with the rising portion of the pulse. The rising and falling positions of the pulse coincide with the leading edge of each differential signal. The differentiated signal is optically transmitted as a drive signal for the light emitting element, and in reproduction in reception, a pulse before differentiation in transmission is obtained by a flip-flop circuit whose direction changes for each rising signal. In the case where bidirectional optical transmission and reception are performed using the same clock, if the above-described differential signal transmission is performed with the phase difference between the transmission 1 and the transmission 2 being substantially half of the clock cycle, the pulse of the transmission 1 and the transmission 2 can be obtained. The rising portions of the signals do not coincide with each other, and the received signal can clearly separate the leakage noise of the transmission signal on the same side by the level.

[0008]

Since the pulse width to be transmitted is transmitted only by the rising differential signal, the efficiency of the light emitting element can be increased. Since the rising and falling of the pulse are differentiated in the same direction, the light emitting element can be used. In addition to taking advantage of the steep rising characteristics of, the effects of light emitting element characteristics and deterioration due to transmission are exactly the same as those described above with the NRZ signal and with the biphase mark modulation method, so that the pulse width fluctuation due to transmission is Does not happen. In addition, bidirectional signals do not overlap at a pulse rising portion that is important in transmission, and there is no interference due to leakage noise.

[0009]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention. In transmission 1, the digital signal 10 is a signal obtained by bi-phase mark modulation in the format of CP-1201 of the Electronic Machinery Manufacturers Association, and the pulse period T used in the description of FIG. And the differential signal 11 is obtained by the differentiating circuit. By a separating circuit using a diode or the like, the signal is divided into a positive differential signal 12 and a negative differential signal. The negative differential signal enters an inverting circuit and becomes an inverted differential signal 13,
The light emitting element 15 is driven to emit light to space as a multiplexed differential signal 14 multiplexed with the positive differential signal 12.

In the reception 1, after the light is converted into an electric signal by the light receiving element 16, the reception signal 17 after the E / O is converted by a flip-flop circuit (divided-by-2 circuit) whose direction changes every rising pulse. A reproduction digital signal 18 is obtained. The operation of the flip-flop circuit is shown in the circuit diagram of FIG. 2A and the waveform diagram of FIG. Then, a reproduction clock 19 is generated from the reproduction digital signal 18 by a PLL circuit.

In transmission 2, a digital signal 20 is sent using the reproduction clock 19 as a reference signal, a multiple differential signal 24 is obtained as in transmission 1, and a delay element 25 for giving a delay of half the period of the reproduction clock 19 is provided. Through this, a delayed differential signal 26 is obtained. Thereafter, the same processing as in the transmission 1 is performed for transmission, and the reception 2 reproduces the digital signal 30 by the same configuration as the reception 1. Accordingly, if the transmission 1 and the transmission 2 have a phase difference of half of the time width T, the rising portions of the bidirectional pulses do not overlap, and the same transmission / reception distance as in the unidirectional transmission can be secured.

[0012]

According to the present invention, the light emitting device can be used efficiently. Also, it is possible to reproduce an error-free pulse except for the influence of the time difference between the rise and fall of the pulse response of the light emitting element and the jitter occurring in the transmission system. In addition, since the same transmission / reception distance as in unidirectional transmission can be secured, the number of required circuits is small and the number of light emitting elements can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention.

FIGS. 2A and 2B are flip-flop circuits used in one embodiment of the present invention. FIG. 2A shows a circuit configuration diagram, and FIG. 2B shows a waveform diagram.

FIG. 3 is an explanatory view of a conventional example.

FIG. 4 is a characteristic diagram of a light-emitting element.

[Explanation of symbols]

 Reference Signs List 10 Digital signal 11 Differential signal 12 Differential signal in positive direction 13 Inverted differential signal 14 Multiple differential signal 15 Light emitting element 16 Light receiving element 17 Received signal after E / O 18 Reproduction digital signal 19 Reproduction clock 20 Digital signal 21 Differential signal 22 Forward direction Differential signal 23 Inverted differential signal 24 Multiple differential signal 25 Delay element 26 Delay differential signal 27 Light emitting element 28 Light receiving element 29 Received signal after E / O 30 Reproduction digital signal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04L 25/49 H04L 5/14 H04B 10/00 H04L 7/027

Claims (2)

(57) [Claims] Transmitting 1. A converts the first multiple differential signal <br/> obtained by multiplexing the forward differential signal by inverting the negative differential signal by differentiating the first transmission signal to the light, transmitted Signal
Regenerating the first transmission signal based on the rising edge of the pulse of the received multiple differential signal and reproducing the reproduced first transmission signal
Generating a clock signal based on the signal, before
Differentiating the second transmission signal using the clock signal as a reference signal
Invert the negative differential signal and multiplex it into the positive differential signal
And generating the second multiple differentiated signal, and
Generating a delayed differential signal delayed by approximately one-half the period of the clock signal , converting the delayed differential signal into light, and transmitting the light; and delaying differential obtained by receiving the transmitted signal.
The second transmission signal is restarted based on the rising edge of the signal pulse.
Generating a bidirectional optical signal. 2. A first transmitting means for differentiating a first transmission signal, inverting a negative differential signal and multiplexing the first multiple differential signal multiplexed with a positive differential signal into light and transmitting the light. Regenerating the first transmission signal based on the rising edge of the pulse of the multiple differential signal obtained by receiving the signal transmitted by the first transmission means ,
Second receiving means for generating a clock signal based on the reproduced first transmission signal; and using the clock signal as a reference signal.
To differentiate the second transmission signal and invert the negative differential signal to
Generate a second multiple differential signal multiplexed with the direction differential signal
The second multiple differential signal is approximately 1 / the cycle of the clock signal.
Generating a delayed differential signal delayed by a time of 2
And second transmission means for transmitting by converting No. into light, Pal delay differential signal said second transmitting means is obtained by receiving the transmitted signal
The play of the second transmission signal on the basis of the rise of the scan 1
A bidirectional optical transmission / reception device, comprising: reception means.