JPH0626327B2 - Optical communication device - Google Patents

Description

DETAILED DESCRIPTION [Outline] The forward and reverse outputs of a modulator such as a guide type optical switch are combined with a time difference to increase the optical output on a transmission line and to effectively use the optical output of a light source. To use.

[Industrial application field]

The present invention relates to an optical communication device using an external modulator such as an optical switch, and particularly, to effectively use the other optical output (inverted optical output) of a modulator that has not been used conventionally, and increase the optical communication output. The present invention relates to an optical communication device capable of increasing the level difference between transmission and reception and enabling transmission over a longer distance.

[Conventional technology]

 FIG. 5 shows an example of a conventional modulation method.

FIG. 6 is an explanatory diagram of the circuit operation of FIG.

In the figure, 1 is a light source, 2 is an optical modulator, and 3 is an optical fiber. The same symbols represent the same objects throughout the drawings.

As shown in FIG. 5, the conventional optical communication device using an external modulator is shown in FIG. 6 (a) in which the light source 1 uses a laser or the like.
The optical carrier shown in (1) is input to the optical modulator 2, and the optical carrier is turned on / off by the modulation signal shown in FIG. 6 (b).

As a result, the optical output shown in FIG. 6 (c) was obtained, and the method of guiding this optical output to the optical fiber 3 was adopted.

[Problems to be solved by the invention]

However, in the above-mentioned conventional method, of the optical carriers sent from the light source 1, the signal generated when the modulation signal is off is not used in the optical fiber 3 and is not used. Therefore, there is a problem that only about half of the optical carriers sent from the light source 1 are effectively used.

[Means for solving problems]

The above-mentioned problem is that in an optical communication device that modulates an optical signal by using an external modulator 2a such as an optical switch as shown in FIG. 1 (a), the transmitter side normally outputs the modulated signal of the external modulator 2a. Solved by restoring the original signal by adding and converting the output and the inverted output with a time difference and transmitting them, and performing the sum conversion with the time difference as shown in Fig. 2 (a). To be done.

[Action]

According to the present invention, the light output from the light source is effectively utilized 100% by effectively utilizing the optical output of the light source by performing optical synthesis by providing a time difference (an integer multiple of the data time slot) in the forward and reverse outputs of the guide type optical switch. Since the output can be increased, the effect that longer distance communication can be achieved is produced.

〔Example〕

FIG. 1 (a) is a diagram showing an embodiment of an optical communication device (transmission side) according to the present invention, and FIG. 1 (b) is an operation explanatory diagram of the circuit of FIG. 1 (a).

In the figure, 2a is an optical modulator, 4 is a delay circuit, and 5 is an optical combiner.

In the present invention, as shown in FIG. 1 (a), a guide type optical switch is used as the optical modulator 2a, and the light from the light source 1 is input to the optical modulator 2a and is controlled by a modulation signal so that a normal light is emitted. An output and an inverted optical output are created, and the normal optical output and the inverted optical output delayed by one time slot by the delay circuit 4 are input to the optical combiner 5 to obtain a desired optical output.

FIG. 3 is an explanatory diagram of a guide type optical switch.

In the figure, 20 is a crystal, 21, 22 and 23 are waveguides respectively, 24 and 25 are electrodes respectively, and 26 is a modulation signal source.

Guide optical switch fitted with two electrodes 24, 25 to the waveguide 21 provided in the third Lithium niobate as shown in FIG. L _i N _b of the crystal 20, between the electrodes 24 to the electrodes 25 It has the characteristic that the polarization angle of light passing through the waveguide 21 changes when a voltage is applied.

Therefore, when a modulation signal is applied between the electrodes 24 and 25 by the modulation signal source 26, the non-inverted light output with respect to the modulation signal is the waveguide 22.
Inverted optical outputs for the modulated signals are input to the waveguide 23, respectively.

FIG. 4 is an explanatory diagram of the photosynthesizer.

In the figure, 30 is a polarization filter, 31 and 32 are input rod lenses, 33 is an output rod lens, 34 and 35 are polarization plane preserving fibers, and 36 is a single mode fiber.

The optical combiner shown in FIG. 4 is composed of a polarization filter 30, input rod lenses 31, 32, and an output rod lens 33.
It is assumed that the polarization filter 30 used temporarily passes only vertically polarized waves (S waves).

The vertically polarized wave (S wave) passing through the polarization maintaining fiber 34 enters from the input rod lens 31 and is projected on the polarization filter 30. As described above, since the polarization filter 30 passes only the vertically polarized wave (S wave), it passes through the polarization filter 30 with almost no loss and appears at the output of the output rod lens 33.

On the other hand, the horizontally polarized wave (P wave) enters from the input rod lens 32 through another polarization maintaining fiber 35 and is projected on the polarization filter 30. However, since the polarization plane is different, it is totally reflected and is output to the output rod lens 33. Come out.

Therefore, the S wave entering from the input rod lens 31 and the P wave entering from the input rod lens 32 both come out to the output side of the output rod lens 33 without loss. This is led to a single mode fiber 36 (SMF) and taken out.

By using the polarization filter as described above, a low loss (near lossless) optical combiner can be realized.

The modulator 2a (guide type optical switch) and the optical combiner 5 used in the present invention have been described above, but one embodiment of the optical communication system (transmission side) of the present invention will be further described with reference to FIG. 1 (b). The details will be described.

The light from the light source 1 is input to the optical modulator 2a and is controlled by a modulation signal to generate a normal rotation light output and a reverse rotation light output. The normal rotation light output is an input rod lens of the optical combiner 5 by the polarization maintaining fiber 34. Enter 31. The waveform of this normal light output is shown in Fig. 1 (b).

The inverted optical output of the optical modulator 2a is also a polarization-maintaining fiber.
It enters the delay circuit 4 by 35, is delayed by one time slot here, and again enters the input rod lens 32 of the optical combiner 5 by the polarization-maintaining fiber 35. This input waveform is shown in Fig. 1 (b).
Shown in.

Therefore, the output waveform of the output rod lens 33 of the optical combiner 5 becomes as shown in FIG. 1 (b). As is clear from the figure, both the forward light output and the inverted light output are binary signals of 0 and A ₁ (A ₁ is the amplitude), but the output waveforms are 2A ₁ , A ₁ ,
It becomes a ternary signal of 0. However, the photosynthesizer 5 is lossless.

FIG. 2 (a) is a diagram showing an embodiment of the optical communication device (reception side) according to the present invention, and FIG. 2 (b) is an operation explanatory diagram of the circuit of FIG. 2 (a).

In the figure, 6 is an opto-electric converter (O / E), 7 is an adding circuit,
Reference numeral 8 is a delay circuit.

The transmission waveform shown in FIG. 1 (b) reaches the receiving side via the transmission line. This waveform is shown in Fig. 2 (b).

On the receiving side, the waveform enters the optical-electrical converter 6 and is converted into an electrical signal to become the waveform shown in FIG. 2 (b).
The waveform shown in FIG. 2 (b) is a ternary signal as described above.

The delay circuit 8 is a circuit that delays by one time slot like the delay circuit 4, and the output of the opto-electric converter 6 is input to the adder circuit 7 and added to the output of one time slot before. By performing the sum conversion in this way, the original signal (modulated signal) in the binary signal format as shown in (b) of FIG. 2 can be restored. Incidentally, FIG. 2 (b) shows the output waveform of the delay circuit 8.

Next, the relationship between the optical receiving system and noise will be described.

In FIG. 2 (a), the output signal of the opto-electric converter 6 is input to the adder circuit 7. The input signal of the adder circuit 7 is a ternary signal as described above, It consists of the signal component sent from the and the noise component that enters from the transmission line.

In the input end of the adder circuit 7, the input signal b _n time slot number n, if the a _n and normal signal time slot number n, a _n
= _Bn + an _-1 .

On the other hand, regarding noise, if N _n ′ is the input noise of the time slot number n and N _n is the output noise of the time slot number n, then N _n
= N _n ′ + N _n−1 .

As described above, the signal component is converted from the ternary signal to 2 by the sum conversion.
Although it is a value signal (amplitude A ₂ ), in the case of noise, there is no correlation between the noise of time slot number n and the noise of time slot number n−1. Therefore, (N _n ) ² = 0.5 ·
The relationship of (N _n ′) ² is established, and the output noise amount N _n is halved.

Assuming that the noise in the optical-electrical converter is dominant in terms of noise as described above, the output noise amount is halved as described above due to the sum conversion, and the transmission line loss is reduced by that amount. Since it can be made large, long-distance transmission becomes possible.

〔The invention's effect〕

As described in detail above, according to the present invention, there is a great effect that the light output of the light source can be effectively used 100%.

[Brief description of drawings]

FIG. 1 (a) is a diagram showing an embodiment of an optical communication device (transmission side) according to the present invention, and FIG. 1 (b) is an operation explanatory diagram of the circuit of FIG. 1 (a). FIG. 2 (a) is a diagram showing an embodiment of the optical communication device (reception side) according to the present invention, and FIG. 2 (b) is an operation explanatory diagram of the circuit of FIG. 2 (a). FIG. 3 is an explanatory diagram of a guide type optical switch. FIG. 4 is an explanatory diagram of the photosynthesizer. FIG. 5 shows an example of a conventional modulation method. FIG. 6 is an explanatory diagram of the circuit operation of FIG. In the figure, 1 is a light source, 2 is an optical modulator, 3 is an optical fiber, and 2a.
Is an optical modulator, 4 is a delay circuit, 5 is an optical combiner, 6 is an optical-electrical converter (O / E), 7 is an adder circuit, 8 is a delay circuit, 20
Is a crystal, 21, 22 and 23 are waveguides respectively, 24 and 25 are electrodes respectively, 2
6 is a modulation signal source, 30 is a polarization filter, 31 and 32 are input rod lenses, 33 is an output rod lens, 34 and 35 are polarization-maintaining fibers, and 36 is a single mode fiber.

Claims (1)

[Claims] 1. An optical communication device for modulating an optical signal by using an external modulator, wherein a normal output of the external modulator with respect to a modulation signal,
An optical communication device characterized in that inverted outputs are combined with a time difference and transmitted, and the receiving side restores the original signal by performing a sum conversion with the time difference.