JP4603024B2 - Optical pulse speed control device and optical pulse speed control method - Google Patents

Description

  The present invention relates to an optical pulse speed control device and an optical pulse speed control method for controlling the speed of pulsed light in an optical transmission network.

  In an optical transmission network, transmission capacity per fiber is increased by WDM (Wavelength Division Multiplexing) transmission. In routers where these optical fibers are terminated, transmission data is processed from light to electricity. Therefore, the optical-electric conversion processing and the electric signal processing of transmission data in the router are bottlenecks.

  Accordingly, devices that perform processing without converting optical signals into electricity, such as OADMs (Optical Add / Drop Multiplexers) and optical switches, have been used. However, these techniques are limited to path control based on wavelength or static switching processing, and cannot perform flexible control such as routing for each packet which is a unit of transmission data. In particular, since the propagation speed control of pulsed light cannot be flexibly performed, signal collision in the signal processing unit is a problem.

  In order to avoid this, an optical buffer that can hold an optical signal without converting it into electricity is required. In recent years, a slow light phenomenon in which the propagation speed of pulsed light is changed has been studied for realizing this optical buffer. The propagation speed control of pulsed light is realized by changing the group refractive index of the medium through which light propagates, and the group refractive index is controlled by entering light called pump light separately from the signal light to be controlled. It is realized by doing.

  Here, an outline of a method for controlling the speed of pulsed light when a phenomenon called stimulated Brillouin scattering (SBS) is used will be described.

  Stimulated Brillouin scattering is a scattering phenomenon caused by the interaction between incident light and acoustic phonons. When light with a narrow spectral line width is incident on an optical fiber, only the frequency called the Brillouin shift frequency is generated in the direction of propagation opposite to the incident light. Generates Stokes light with a low frequency. At this time, incident light that generates Stokes light is referred to as pump light. That is, when the frequency of the pump light is fp and the Brillouin shift frequency is fb, the frequency of the Stokes light is fp−fb.

  Here, when signal light having a center frequency of fp−fb is incident on the optical fiber so as to face the pump light, the optical power is transferred from the pump light to the signal light in the optical fiber, and the signal light is gained. This gain has Lorentz-type spectral characteristics centered on fp-fb as shown in FIG. 7A, and this gain is also centered on fp-fb from the law called the Kramers-Kronig relationship. The refractive index change shown in 7 (b) occurs.

の関係から求められ、図７（ｃ）に示すスペクトル特性の群屈折率変化が生じ、群屈折率はｆｐ−ｆｂを中心に増加する。パルス光の伝播速度は真空中の光の速度を群屈折率で割ったものになるので、パルス光はゲインされると共に、伝播速度が遅くなる。ゲイン量や群屈折率変化量のピーク値は、ポンプ光強度に比例するため、ポンプ光の強度を制御することによって、パルス光の速度を制御できる。又、ポンプ光周波数がｆｐ、信号光の周波数がｆｐ＋ｆｂである場合、先に説明したゲインとは逆に、パルス光にロスが生じる。このロスのスペクトル特性は、図７（ａ）〜（ｃ）に示した特性の正負反転の特性であり、ロスや群屈折率変化量のピークを示す周波数はｆｐ＋ｆｂとなり、群屈折率はｆｐ＋ｆｂにおいて減少する。つまり、パルス光はロスを受けると共に、パルス光の伝播速度が速くなる。この現象に関しても、ロスや群屈折率変化のピーク値は、ポンプ光強度に比例するため、ポンプ光強度の制御によるパルス光の速度制御が実現できる。 The group index is

The group refractive index change of the spectral characteristics shown in FIG. 7C occurs, and the group refractive index increases around fp−fb. Since the propagation speed of the pulsed light is obtained by dividing the speed of light in vacuum by the group refractive index, the pulsed light is gained and the propagation speed becomes slow. Since the peak value of the gain amount and the group refractive index change amount is proportional to the pump light intensity, the speed of the pulsed light can be controlled by controlling the intensity of the pump light. Further, when the pump light frequency is fp and the signal light frequency is fp + fb, a loss occurs in the pulsed light, contrary to the gain described above. The spectral characteristics of this loss are the characteristics of inversion of the characteristics shown in FIGS. 7A to 7C, the frequency indicating the loss and the peak of the group refractive index change amount is fp + fb, and the group refractive index is fp + fb. Decrease. That is, the pulsed light is lost and the propagation speed of the pulsed light is increased. Also regarding this phenomenon, the peak value of the loss or group refractive index change is proportional to the pump light intensity, so that the speed control of the pulsed light by controlling the pump light intensity can be realized.

Kwang Yong Song et al., "Observation pf pulse delaying and advancement in optical fibers using stimulated Brillouin", Optics Express, Vol. 13, Issue 1, pp.82-88, January 2005

  In order to realize speed control of pulsed light, as shown in FIG. 8, in an optical transmission network in which a transmitter 10 that transmits signal light and a receiver 12 that receives signal light are connected by an optical fiber 14, It is necessary to connect the light source 11 via the optical coupler 13 provided in the optical fiber 14 and to input the pump light. If the frequency of the signal light is fs, pump light having a frequency of fs + fb or fs−fb needs to be incident on the optical fiber 14 so as to face the signal light. Has a problem that its configuration becomes complicated.

  The present invention has been made in view of the above problems, and an object thereof is to provide a light pulse speed control device and a light pulse speed control method with a simple configuration.

An optical pulse velocity control apparatus according to a first invention for solving the above-mentioned problems is as follows.
An optical fiber that connects a transmitter that transmits pulsed light to be signal light and a receiver that receives the pulsed light; and
An optical amplifier that is provided in the optical fiber and amplifies the pulsed light;
By the optical amplifier amplifying and controlling the pulsed light to an incident light intensity greater than the maximum incident light intensity in a region where the transmitted light intensity of the optical fiber linearly changes, the stimulated Brillouin generated in the optical fiber is controlled. The speed of the pulsed light is controlled by controlling the intensity of the backscattered light due to scattering and controlling the magnitude of the change in the group refractive index due to the backscattered light.

An optical pulse speed control device according to a second invention for solving the above-mentioned problems is as follows.
In the optical pulse velocity control device according to the first invention,
A demultiplexer that is provided on the optical amplifier side of the optical fiber and demultiplexes the backscattered light generated in the optical fiber from the optical fiber;
The other optical fiber having one end connected to the duplexer and the other end of the other optical fiber are connected and provided on the receiver side of the optical fiber. And a multiplexer for multiplexing the backscattered light in the opposite propagation direction.
An optical coupler, an optical circulator, or the like can be used as the duplexer and the multiplexer.

An optical pulse speed control method according to a third invention for solving the above-described problems is as follows.
An optical fiber that connects a transmitter that transmits pulsed light to be signal light and a receiver that receives the pulsed light; and
Using an optical amplifier provided in the optical fiber and amplifying the pulsed light,
By the optical amplifier amplifying and controlling the pulsed light to an incident light intensity greater than the maximum incident light intensity in a region where the transmitted light intensity of the optical fiber linearly changes, the stimulated Brillouin generated in the optical fiber is controlled. The speed of the pulsed light is controlled by controlling the intensity of the backscattered light due to scattering and controlling the magnitude of the change in the group refractive index due to the backscattered light.

A method for controlling the speed of an optical pulse according to a fourth aspect of the invention for solving the above-described problem is as follows.
An optical fiber that connects a transmitter that transmits pulsed light to be signal light and a receiver that receives the pulsed light; and
An optical amplifier provided in the optical fiber for amplifying the pulsed light;
A duplexer provided on the optical amplifier side of the optical fiber;
Another optical fiber having one end connected to the duplexer;
With the other end of the other optical fiber connected and a multiplexer provided on the receiver side of the optical fiber,
By the optical amplifier amplifying and controlling the pulsed light to an incident light intensity greater than the maximum incident light intensity in a region where the transmitted light intensity of the optical fiber linearly changes, the stimulated Brillouin generated in the optical fiber is controlled. The intensity of backscattered light due to scattering is controlled, and the backscattered light generated in the optical fiber is demultiplexed from the optical fiber by the duplexer, and the demultiplexed backscattered light is applied to the optical fiber. Re-incident by the multiplexer in the direction of propagation opposite to the pulsed light, and controlling the magnitude of change in the group refractive index due to the backscattered light and the re-incident backscattered light, the speed of the pulsed light It is characterized by controlling.

  According to the first and third inventions, an optical pulse speed control device can be realized by using only an optical amplifier and an optical fiber. Therefore, a mechanism for generating pump light (pump light generation light source and associated equipment) that is essential in the conventional method. ) Can be omitted, the configuration can be simplified, and an economical effect can be obtained. In addition, since the pumping light for the signal light can be generated by the stimulated Brillouin scattering, the frequency control of the pumping light becomes unnecessary and the speed control accuracy of the pulsed light is improved.

  According to the second and fourth inventions, since the duplexer, the multiplexer, and the other optical fiber connecting them are further provided, the stimulated Brillouin scattered light is circulated and incident from the output side of the optical fiber. The ring structure can be used, and the speed control can be realized even when the optical amplifier has a low output.

  An embodiment of an optical pulse speed control device and an optical pulse speed control method according to the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic configuration diagram showing an example of an embodiment of an optical pulse speed control device and an optical pulse speed control method according to the present invention. As shown in FIG. 1, the optical pulse speed control device 16 of this embodiment is an optical device in which a transmitter 10 that transmits pulsed light that is signal light and a receiver 12 that receives pulsed light are connected by an optical fiber 14. In the transmission network, an optical amplifier 15 is provided on the transmitter 10 side of the optical fiber 14 so that the optical pulse speed control device 16 is configured only by the optical fiber 14 and the optical amplifier 15. Thus, the optical pulse speed control device 16 of the present embodiment is realized with a simple configuration.

  In the optical pulse speed control device 16 of the present embodiment, the optical amplifier 15 converts the pulsed light from the transmitter 10 into a threshold for stimulated Brillouin scattering in the optical fiber 14 (in the present invention, the transmitted light intensity of the optical fiber 14 is linear). The maximum incident light intensity in the changing region is defined as a threshold value). The reason for this will be described with reference to FIGS. 2A and 2B show a case where a single mode fiber 25 km is used as the optical fiber 14. When the reflected light intensity and transmitted light intensity at the optical fiber 14 are measured with respect to the emitted light intensity of the optical amplifier 15, that is, the incident light intensity to the optical fiber 14, changes as shown in FIG. . As shown in FIG. 2A, when the incident light intensity to the optical fiber 14 is increased, the reflected light intensity suddenly increases beyond a certain incident light intensity. This is reflected light by stimulated Brillouin scattering.

  On the other hand, there is a phenomenon that the transmitted light intensity does not increase from a certain incident light intensity. This is because loss is caused by the influence of reflected light due to stimulated Brillouin scattering, and as shown in FIG. 2 (b), the advance of the pulse increases as the loss increases. That is, when increasing the intensity of incident light from the optical amplifier 15, if the increase in transmitted light intensity deviates from a linear increase in the log scale, that is, if an output higher than the threshold is incident from the optical amplifier 15, pulse light It becomes possible to control the speed. Then, by utilizing such a phenomenon, the speed of the pulsed light can be controlled by controlling the incident light intensity to the optical fiber 14 with the optical amplifier 15 as shown in FIG. 4 described later. . In addition, since the specific numerical value of a threshold value changes with fiber length, the kind of fiber, the spectrum line width of a pulse light source, etc., a threshold value is calculated | required according to these structures, and the optical amplifier 15 is based on the calculated | required threshold value. The amplification intensity may be controlled.

  As the optical amplifier 15, for example, an EDFA (erbium-doped fiber amplifier), a Raman amplifier, or the like can be used. When the EDFA is used as the optical amplifier 15, the intensity of the excitation light incident on the EDFA is controlled. As a result, the amplification intensity by the EDFA can be controlled, and as a result, the speed of the pulsed light can be controlled.

  Therefore, in the optical pulse speed control device 16 of the present embodiment, the intensity of the pulsed light from the transmitter 10 is amplified to an intensity exceeding the threshold by the optical amplifier 15 before entering the optical fiber 14. Thereafter, when the amplified pulsed light is incident on the optical fiber 14, stimulated Brillouin scattering occurs in the optical fiber 14. The backscattered light generated by this scattering has a frequency that is lower by a shift frequency amount of the Brillouin frequency when viewed from the pulsed light. If the frequency of the backscattered light is fp, the frequency of the pulsed light is fp + fb, the backscattered light plays the role of pump light, and a loss occurs in the frequency where the pulsed light exists. This loss is accompanied by a change in refractive index as described above, thereby reducing the group refractive index. This increases the speed of the pulsed light. The speed of the pulsed light can be controlled by the intensity of the incident pulsed light. This is because increasing the intensity of the incident pulsed light increases the intensity of the backscattered light and increases the amount of change in the group refractive index. Therefore, by controlling the intensity of the pulsed light incident on the optical fiber 14 with the optical amplifier 15, the intensity of the backscattered light due to the stimulated Brillouin scattering generated in the optical fiber 14 is controlled, and the change in the group refractive index due to the backscattered light is controlled. Is controlled to control the speed of the pulsed light.

  FIG. 3 is a graph showing changes in the waveform of pulsed light when a signal having a pulse width of about 20 ns is used. Here, as an example, a pulse waveform when the output power Pin after amplification of the pulsed light by the optical amplifier 15 is set to 3.9 dBm, 18 dBm, and 21.7 dBm is shown. FIG. 4 shows the progress of the pulse with respect to the incident light intensity. As shown in FIGS. 3 and 4, it can be confirmed that when the incident light intensity is increased, the speed of the pulsed light is also increased. By controlling the incident light intensity, the pulse progress, that is, the speed of the pulsed light is controlled. It was confirmed that it could be controlled.

  FIG. 5 is a schematic configuration diagram showing another example of the embodiment of the optical pulse speed control device and the optical pulse speed control method according to the present invention. In FIG. 5, the same components as those in the optical pulse velocity control device shown in FIG.

  As shown in FIG. 5, the optical pulse speed control device 17 of this embodiment is provided on the optical amplifier 15 side of the optical fiber 14 with respect to the optical pulse speed control device 16 shown in FIG. 1 (Example 1). An optical coupler 13a (demultiplexer), another optical fiber 18 having one end connected to the optical coupler 13a, and the other end of the optical fiber 18 connected to the optical fiber 14 and provided on the receiver 12 side. The coupler 13b (multiplexer) is further provided. In other words, optical couplers 13 a and 13 b are provided at both ends of the optical fiber 14, and an optical ring configuration is added by connecting the optical couplers 13 a and 13 b with the optical fiber 18. As described above, the optical pulse speed control device 17 of the present embodiment is also configured by only the optical fibers 14 and 18, the optical amplifier 15, and the optical couplers 13a and 13b, and is realized with a relatively simple configuration. An optical circulator may be used in place of the optical couplers 13a and 13b.

  In an optical ring configuration including the optical couplers 13a and 13b and the optical fiber 18, backscattered light due to stimulated Brillouin scattering generated in the optical fiber 14 by the incidence of pulsed light is demultiplexed from the optical fiber 14 by the optical coupler 13a. The demultiplexed backscattered light wave is propagated to the optical coupler 13b via the optical fiber 18, and is multiplexed by the optical coupler 13b with respect to the optical fiber 14 in the propagation direction opposite to the pulsed light. Then, the light enters the optical fiber 14. With this optical ring configuration, the backscattered light is re-incident on the optical fiber 14 from the side from which the pulsed light is emitted (the optical coupler 13b side).

  Therefore, the pulsed light from the transmitter 10 amplified by the optical amplifier 15 is incident on the optical fiber 14, the backscattered light generated by the stimulated Brillouin scattering is taken out by the optical coupler 13a, and the optical fiber 18 and the optical coupler 13b are used. By being incident on the optical fiber 14, the backscattered light is incident on the pulsed light incident end side from the pulsed light emitting end side of the optical fiber 14, and can function as pump light for the pulsed light. With such a configuration, the backscattered light generated by the stimulated Brillouin scattering is re-incident on the optical fiber 14, so that it is incident as compared with the optical pulse velocity control device 16 shown in FIG. 1 (Example 1). Even if the light intensity is small, the speed of the pulsed light can be controlled, and the incident light intensity required for the speed control can be reduced.

  FIG. 6 is a graph showing the progress of the pulse with respect to the incident light intensity in the case of the first embodiment and the second embodiment. Thus, it can be seen that by providing the ring configuration, the incident light intensity required to realize the advance of the same pulse may be small.

  The present invention has a function of realizing speed control of an optical signal and can be used as an optical buffer or a variable delay circuit.

It is a schematic block diagram which shows an example in embodiment of the optical pulse speed control apparatus which concerns on this invention, and the speed control method of an optical pulse. (A) is a graph which shows the change of the reflected light intensity and the transmitted light intensity with respect to the incident light intensity to the optical fiber, and (b) shows the relationship between the loss due to SBS and the advance of the pulse. It is a graph to show. 2 is a graph showing a change in waveform of pulsed light when the incident light intensity is changed in the optical pulse velocity control apparatus shown in FIG. 1. 2 is a graph showing a pulse advance characteristic with respect to incident light intensity in the optical pulse velocity control apparatus shown in FIG. It is a schematic block diagram which shows another example of embodiment of the optical pulse speed control apparatus which concerns on this invention, and the speed control method of an optical pulse. FIG. 5 is a graph comparing pulse advance characteristics with respect to incident light intensity between the optical pulse speed control device shown in FIG. 1 and the optical pulse speed control device shown in FIG. 4. It is a graph which shows the spectral characteristics of the gain, refractive index change, and group refractive index change which are caused by stimulated Brillouin scattering. It is a schematic block diagram which shows the optical pulse velocity control apparatus at the time of using the conventional stimulated Brillouin scattering.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transmitter 11 Light source 12 Receiver 13, 13a, 13b Optical coupler 14, 18 Optical fiber 15 Optical amplifier 16, 17 Optical pulse rate control apparatus

Claims (4)

An optical fiber that connects a transmitter that transmits pulsed light to be signal light and a receiver that receives the pulsed light; and
An optical amplifier that is provided in the optical fiber and amplifies the pulsed light;
By the optical amplifier amplifying and controlling the pulsed light to an incident light intensity greater than the maximum incident light intensity in a region where the transmitted light intensity of the optical fiber linearly changes, the stimulated Brillouin generated in the optical fiber is controlled. An optical pulse speed control device that controls the speed of the pulsed light by controlling the intensity of backscattered light due to scattering and controlling the magnitude of a change in group refractive index due to the backscattered light. In the optical pulse velocity control device according to claim 1,
A demultiplexer that is provided on the optical amplifier side of the optical fiber and demultiplexes the backscattered light generated in the optical fiber from the optical fiber;
Another optical fiber having one end connected to the duplexer;
The other end of the other optical fiber is connected and provided on the receiver side of the optical fiber, and combines the backscattered light in the propagation direction opposite to the pulsed light with respect to the optical fiber. And an optical pulse velocity control device. An optical fiber that connects a transmitter that transmits pulsed light to be signal light and a receiver that receives the pulsed light; and
Using an optical amplifier provided in the optical fiber and amplifying the pulsed light,
By the optical amplifier amplifying and controlling the pulsed light to an incident light intensity greater than the maximum incident light intensity in a region where the transmitted light intensity of the optical fiber linearly changes, the stimulated Brillouin generated in the optical fiber is controlled. An optical pulse speed control method comprising: controlling the intensity of backscattered light due to scattering; and controlling the magnitude of a change in group refractive index due to the backscattered light to control the speed of the pulsed light. An optical fiber that connects a transmitter that transmits pulsed light to be signal light and a receiver that receives the pulsed light; and
An optical amplifier provided in the optical fiber for amplifying the pulsed light;
A duplexer provided on the optical amplifier side of the optical fiber;
Another optical fiber having one end connected to the duplexer;
With the other end of the other optical fiber connected and a multiplexer provided on the receiver side of the optical fiber,
By the optical amplifier amplifying and controlling the pulsed light to an incident light intensity greater than the maximum incident light intensity in a region where the transmitted light intensity of the optical fiber linearly changes, the stimulated Brillouin generated in the optical fiber is controlled. The intensity of backscattered light due to scattering is controlled, and the backscattered light generated in the optical fiber is demultiplexed from the optical fiber by the duplexer, and the demultiplexed backscattered light is applied to the optical fiber. Re-incident by the multiplexer in the direction of propagation opposite to the pulsed light, and controlling the magnitude of change in the group refractive index due to the backscattered light and the re-incident backscattered light, the speed of the pulsed light A method for controlling the speed of an optical pulse, characterized in that

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