JPH0669167B2 - Switching the optical line without interruption - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for switching a line portion of a switching target section in a working optical line to a switching optical line without interruption.

"Prior art" As is known, tens of percent or more of the communication cables in urban areas have experienced changes to the laying route due to obstacles to this, or due to relocation, there is a high demand for switching to detour routes. .

The outline is shown below in FIG.

In FIG. 8, 1 is an electro-optical converter in the station, 2 is a photoelectric converter in the station, 3 is each line portion (optical cable) 3 ₁ , 3 ₂ , 3 ₃ ...
3n are connected respectively existing (current) of the optical line, 4 cabling point, 5 is switched optical lines (bypass cable), for example when switching line portion 3 ₂ optical line 3 for some reason, The switching optical line 5 has a predetermined cable connection point 4
Connected to.

By the way, since the optical line 3 is currently in use, the switching of the optical line 3 should not hinder the current information transmission. As a countermeasure against this, the hitless switching method described in Japanese Patent Laid-Open No. 59-229938 has already been proposed. Proposed.

This method requires one switching optical line 5 for one line section to be switched, one electro-optical converter 6, two photoelectric converters 7, as shown in FIG. A pilot signal detector 8 for two-route phase difference detection, one comparator 9,
It comprises a variable delay device 10, a combiner 11 and the like.

In the case of the method shown in FIG. 9, the phase caused by the difference in optical path length between the two routes is detected by the pilot signal detector 8, compared by the comparator 9, and the difference is corrected by the variable delay device 10. There is.

The reason for doing this is that the transmission speed of the light in the optical cable is 10
It is as fast as 0 Mbps, and even if the optical path length is only 2 m for one time slot of 10 ns, one cycle (10 ns) as shown in the following formula
This is because there is a shift in the bit and a bit error occurs.

Δτ = NL / C = 1.5 × 2 m / 3 × 10 ⁸ _{(m / s)} = 10 ns Δτ: Difference in delay time N: Refractive index of quartz L: Optical path length C: Speed of light "Problems to be solved by the invention" In the method of FIG. 9 described above, expensive equipment such as the photoelectric converter 7 and the pilot signal detector 8 is required for each optical fiber in the optical cable, and when switching a plurality of optical cables, a large number of optical cables are required for each optical cable. Since expensive equipment is required, the cost required for this becomes enormous.

In addition, there is a method of instantly switching the optical line using a high-speed optical switch, but this is not a non-interruption in principle,
Moreover, with this method, there is a 1/10
Considering the cycle of, the cost requires an expensive optical switch with a switching speed of 1 ns or more for a bit rate of 100 Mbps, and the expensive optical switch must be inserted into all cables in the route in advance, which reduces the cost. It becomes very high, and there is a problem that the insertion loss at this time is high.

In view of the above problems, the present invention aims to provide a method capable of switching optical lines with a small additional cost.

[Means for Solving the Problems] In order to achieve the intended purpose, the present invention inserts a line section provided with a variable optical attenuator and each line section on both sides of the line section between these terminals. While being connected via the optical element for optical multiplexing and demultiplexing, the terminal for turning back the optical signal for operation, which is equipped with a variable optical attenuator, is a current optical line connected to each element for multiplexing and demultiplexing, A line portion with a variable optical attenuator in the working optical line, that is, a line portion in a switching target section, is provided with a variable optical attenuator, a variable optical filter, and a variable delay device by using the optical pulse generating means and the phase difference measuring means. In the above, when switching the line part of the switching target section to the switching optical line in the above, the first step is to adjust the amount of attenuation of each return terminal to the variable optical attenuation provided in these. By vessel Large, separate each folding terminal from each multiplexing / demultiplexing optical element, and the next step is to pass the measurement wavelength light transmission and the working wavelength light non-transmission state through its own variable optical filter and variable optical attenuator. While connecting the switching optical line to the optical element for both optical multiplexing and demultiplexing,
The optical pulse generating means is connected to one of the multiplexing / demultiplexing optical elements, the phase difference measuring means is connected to the other of the multiplexing / demultiplexing optical elements, respectively, and
The working wavelength light is input to the phase difference measuring means via one of the multiplexing / demultiplexing optical elements, and the measuring wavelength light generated by the optical pulse generating means is the other of the multiplexing / demultiplexing optical elements and the switching optical line. , When inputting to the phase difference measuring means via one of the multiplexing / demultiplexing optical elements, the phase difference between these two wavelength lights is measured by the phase difference measuring means, and the phase difference is provided in the switching optical line. Compensation by the variable delay device provided, and as a subsequent step, the optical pulse generating means and the phase difference measuring means are removed from each optical multiplexer / demultiplexer, and the switching optical line is provided with the variable optical A filter and a variable optical attenuator are used to make the operating wavelength light transmissive state.Furthermore, as a subsequent step, the amount of attenuation in the line section of the switching target section is increased by the variable optical attenuator installed in these sections, and the line concerned is changed. Between both optical elements for optical multiplexing and demultiplexing It is characterized in that a terminal for returning the working optical signal is connected to the optical element for optical multiplexing / demultiplexing.

[Examples] Examples of the method of the present invention will be described below with reference to the drawings.

FIG. 1 shows the line portion 21 in the switching target section of the working optical line 20 before switching.

The optical line 20 is configured by connecting optical cables, and a beam splitter 22 as an optical element for multiplexing / demultiplexing is inserted at each connection point thereof.

Therefore, the beam splitter 22 is provided at both ends of the line portion 21.
However, in order to eliminate the insertion loss at this time, a loop-shaped folded terminal 23 is connected to these beam splitters 22.

Further, a variable optical attenuator 2 is provided in the line portion 21 and the folding terminal 23.
4, 25 are provided.

The branching ratio between the input path and the branching path of the beam splitter 22 in the above is 1: x, and when the length of the folding terminal 23 is L, the output side of the terminal 23 has τ = NL / C every , Amplitude 1-x, x ² , x ² (1-x), x ² (1-x) ² , x ² (1-x)
³ ... is output.

At this time, the power (Pou
t) is Pout = 1−x + x ² + x ² (1
^{-X) + x 2 (1-} x) 2 ...... x 2 (1-x) n -1 = 1-x
(1-x) n ^-1 , which is as shown in FIG.

Further, when x = 1/2 and n = 5, the composite power Pout is as shown in FIG.

Assuming that the delay time τ is sufficiently smaller than the pulse time T, all the pulses contribute to the output.

Therefore, when n = ∞, Pout = 1, and in principle, the insertion loss of the beam splitter 23 becomes zero.

For example, T = 10 ns (corresponding to 100 Mbps) and a folded terminal (for example, an optical cord with connectors at both ends) L = 10 cm
Then, τ becomes 0.5 ns, which is sufficiently smaller than the pulse period.

Also, when the pulse is shifted by one cycle (n = 20), the pulse power is about 10 ^-6 and 60 dB down at x = 1/2 with respect to the input pulse, causing a problem such as intersymbol interference. Absent.

However, when the bit rate further increases and T decreases, x is a standard 1/2 (3d using a half mirror
It is necessary to consider the value so that it does not cause intersymbol interference.

As described above, the transmission speed of light in the optical cable is high, and even a slight difference in optical path length causes a cycle shift, resulting in a bit error.

In the present invention, the optical path length difference between the line portion in the switching target section and the switching optical line is measured as follows, and the phase difference caused by the optical path length difference is compensated.

First, the variable optical attenuator 25 provided in the folding terminal 23 of FIG. 1 is gradually increased in attenuation amount, and finally, the folding terminal 23 is separated from the beam splitter 22 with a sufficient attenuation amount.

By doing so, it is possible to avoid a sudden change in the received light power.

Next, as shown in FIG. 4, a switching optical line provided with a variable optical attenuator 26, a variable transmission wavelength type optical filter 27, and a variable delay device 28.
29 is connected across both beam splitters 22, a photoelectric converter 30 and a pulse monitor 31 are connected to one of the beam splitters 22, and an electro-optical converter 32 and a pulse generator 33 are connected to the other beam splitter 22. .

In FIG. 4, it is assumed that the optical filter 27 does not transmit light of the wavelength of the working optical line 20 (at this time, the variable optical attenuator is used).
The attenuation amount of 26 is zero), and the interference of the passing light of the switching optical line 29 with the working light can be suppressed.

On the other hand, when the optical filter 27 transmits the light of the wavelength for phase difference measurement, the delay time τ ₁ in the line portion 21 and the switching optical line 29 in the line portion 21 are monitored by monitoring the pulse of the wavelength. The difference from the delay time τ ₂ , that is, Δτ can be measured.

As the wavelength of the light for measuring the delay period difference, if the active photodetector in the station is insensitive, the light in the active optical line 20 is not adversely affected.

For example, when the working light wavelength is 0.85 μm, a silicon diode is used as the photodetector.
If the delay time difference measurement is performed at 1.3 μm, silicon is not sensitive at this wavelength and has no effect.

Next, when the phase difference due to the optical path length difference can be compensated through the variable delay device 28 of the switching optical line 29, this is carried out.

As the variable delay device 28 at this time, as shown in FIG. 5, the slidable input side optical fiber 34 and the output side optical fiber 34 can be used.
It is conceivable that the device 35 and a reflecting mirror 36 for multiple reflection are provided, and this one shown in the drawing is suitable for accurately compensating for a short optical path length difference.

In addition, for example, if the optical path length difference is 100 m, even if one has experienced multiple reflections 100 times, 1 m is required as the optical path length per time, and it is actually difficult to compensate for a long optical path difference of 100 m. However, in such a case, the plurality of variable delay devices 28 may be arranged at predetermined intervals via the taps for extracting light.

After compensating for the phase difference as described above, the beam splitter 22
Remove the delay time difference measurement system such as photoelectric converter 30 from
Further, the amount of attenuation of the variable optical attenuator 26 in the switching optical line 29 is made sufficiently large to switch the wavelength characteristic of the optical filter 27 to a state where the working wavelength can be transmitted.

For switching the transmission wavelength, a diffraction grating,
There is a type in which the position of these and the optical fiber can be moved relative to an optical filter such as an interference film filter whose wavelength transmission characteristic has an incident angle dependency.

For example, as shown in FIG. 6, a combination of an input side optical fiber 37, an output side optical fiber 38 and a rotary diffraction grating 39 can be cited.

At this time, the power fluctuation due to the switching of the optical filter 27 is suppressed by the attenuation amount of the variable optical attenuator 26.

Therefore, the variable optical attenuator in the switching optical line 29 is
If the attenuation amount of 26 is set to zero, the light receiving end of the station simultaneously receives the two lights that have passed through the working optical line 20 and the switching optical line 29.

As shown in FIG. 7, the variable optical attenuator 24 in the line portion 21 is increased in amount and the line portion 21 is removed so that only the switching optical line 29 is provided. The beam splitter 22 is provided with the folding terminal 44 for the same reason.

Thus, the predetermined hitless switching is completed.

[Effects of the Invention] As described above, in the method of the present invention, the optical path length difference between the line portion of the switching target section and the switching optical line is measured using the phase difference measuring device, and the phase difference caused by the optical path length difference is measured. However, since the phase difference measuring device can be inserted into a predetermined measurement point to measure the optical path length difference and then removed from the measurement point to be used for another measurement point, the optical path is configured. Even if a plurality of optical cables having a plurality of fibers are switched, only one set of the above-mentioned phase difference measuring device is required, and the uneconomical situation of preparing a large number of expensive phase difference measuring devices does not occur.

On the other hand, a variable delay unit is required when inserting it into the switching optical line, but it is inexpensive because it is a single optical component, and switching of the same route occurs multiple times. However, the above optical components can be shared.

In addition, the variable optical filter can be constructed at a low cost and only needs to be inserted into the switching optical line, so that the economical burden is light.

Therefore, when the optical line is switched without interruption by the method of the present invention, the switching can be economically performed at a slight additional cost.

[Brief description of drawings]

1 to 7 show an embodiment of the method of the present invention. FIG. 1 is an explanatory view of an optical line before switching, and FIG. 2 is a folded portion provided on a beam splitter of the optical line. FIG. 3 is an explanatory view of a terminal, FIG. 3 is an explanatory view showing a combined power state of output side pulses in the folded terminal, FIG. 4 is an explanatory view showing an example of phase difference measurement in the method of the present invention, and FIG. FIG. 6 is a schematic diagram showing an example of a delay device, FIG. 6 is a schematic diagram showing an example of an optical filter, FIG. 7 is an explanatory diagram showing a switching completion state of an optical line, and FIG. FIG. 9 is an explanatory diagram showing an outline, and FIG. 9 is an explanatory diagram showing a conventional optical line switching method. 20 …… Current optical line 21 …… Line part of the section to be switched 22 …… Beam splitter which is an optical element 23,44 …… Folding terminal 24,25 …… Variable optical attenuator 26 …… Variable optical attenuator 27 …… Optical Filter 28 …… Variable delay device 29 …… Switching optical line 30 …… Photoelectric converter 31 …… Pulse motor 32 …… Electronic converter 33 …… Pulse generator

Claims (1)

[Claims] 1. A line portion provided with a variable optical attenuator and respective line portions on both sides thereof are connected via an optical element for optical multiplexing / demultiplexing inserted between these respective terminals, Folding terminal of the working optical signal provided with a variable optical attenuator, in the working optical line respectively connected to each of the multiplexing and demultiplexing optical element, using the optical pulse generating means and the phase difference measuring means,
A method of switching a line part with a variable optical attenuator in a working optical line, that is, a line part of a switching target section to a switching optical line provided with a variable optical attenuator, a variable optical filter, and a variable delay device. When switching the line section of the target section to the switching optical line, the first step is to increase the attenuation of each return terminal by the variable optical attenuator installed in them, Separated from the optical device for use as the next step, the optical fiber for switching, which is in the state of transmitting the measuring wavelength light and not transmitting the working wavelength light through its own variable optical filter and variable optical attenuator, is used for both optical multiplexing and demultiplexing. The optical pulse generation means is connected to one of the multiplexing / demultiplexing optical elements and the phase difference measuring means is connected to the other of the multiplexing / demultiplexing optical elements, and the working wavelength light is Wavelength measuring light generated by the optical pulse generating means is input to the phase difference measuring means via the wave optical element, and the other wavelength division optical element, switching optical line, one wavelength division optical When input to the phase difference measuring means via the element, the phase difference between these two wavelength lights is measured by the phase difference measuring means, and the phase difference is compensated by the variable delay device provided in the switching optical line. As a subsequent step, the optical pulse generating means and the phase difference measuring means are detached from each optical element for multiplexing and demultiplexing, and the switching optical line is currently used by the variable optical filter and the variable optical attenuator provided for it. In the state where the wavelength light is transmitted, and in the subsequent process, increase the attenuation of the line sections in the section to be switched by the variable optical attenuator installed in these sections, and increase the line sections for both optical multiplexing and demultiplexing light. Removed from between the elements, and Hitless switching method of the optical line, characterized in that to connect the folded terminal active optical signals to the optical multiplexing and demultiplexing optical element.