JP2007071614A - Optical gyro and gyro system using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical gyro having a simple structure, concerning the optical gyro capable of detecting a rotation angular speed of a rotator and a gyro system using it. <P>SOLUTION: A semiconductor optical amplifier (SOA) 1 oscillates laser light CW, CCW, amplifies the laser light CW, CCW by induced emission, and radiates the laser light CW, CCW respectively from end faces 1A, 1B into an optical fiber 2. A coupler 3 splits the laser light CW, CCW in the optical fiber 2 at the ratio of 99%:1% into an optical fiber 4. The coupler 3 overlaps the laser light CW, CCW in the optical fiber 4 at the ratio of 50%:50% into an optical fiber 6. A photodetector 7 performs square detection of overlapped light in the optical fiber 6 and generates a beat signal, and a spectrum analyzer 8 detects the frequency f<SB>B</SB>of the beat signal. In this case, the frequency f<SB>B</SB>is changed relative to the rotation angular speed. A detector 9 detects each rotation angular speed of the semiconductor optical amplifier 1 and the optical fiber 2 based on the frequency f<SB>B</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical gyro capable of detecting the rotational angular velocity of a rotating body and a gyro system using the same.

  The gyro is a sensor that can measure rotation with respect to inertial space, and is a sensor that can measure absolute rotation. As such gyros, there are mechanical gyros and optical gyros.

  The mechanical gyro is a gyro that uses the property that the rotating shaft of the rotating body always keeps a fixed direction with respect to the inertial space. However, mechanical gyroscopes require maintenance, are expensive, and are weak in vibration and acceleration, so that their application range is limited to aircraft, ships, rockets, artificial satellites, and the like.

  On the other hand, an optical gyro using the Sagnac effect has recently been put into practical use. This optical gyro propagates clockwise light and counterclockwise light in the optical path, and generates two light (clockwise light and counterclockwise light) caused by the rotation of the rotating body. This is a gyro using the fact that the frequency difference is proportional to the rotational angular velocity.

Optical gyros are roughly classified into optical fiber gyros and ring laser gyros, and there are three types of optical fiber gyros: interference optical fiber gyros, resonant optical fiber gyros, and Brillouin optical fiber gyros (Non-Patent Document 1). ).
Kazuo Hotate, “Practical application of optical fiber gyro and development of next generation technology”, Laser Research, Vol. 26, No. 4, April 1998, p297-303.

  However, in the conventional Brillouin optical fiber gyroscope, in order to amplify the laser light propagating clockwise and counterclockwise in the optical fiber, it is necessary to provide many couplers, resulting in a complicated structure. there were.

  Therefore, the present invention has been made to solve such a problem, and an object thereof is to provide an optical gyro having a simple structure.

  Another object of the present invention is to provide a gyro system having an optical gyro with a simple structure.

  According to this invention, the gyro includes a laser light source, first and second optical fibers, first and second couplers, and detection means. The laser light source oscillates the first and second laser beams and amplifies the oscillated first and second laser beams. The first optical fiber rotates the first laser beam clockwise, and rotates the second laser beam counterclockwise. The first coupler guides a part of the first and second laser beams in the first optical fiber to the second optical fiber. The second coupler emits superposed light obtained by superposing the first and second laser lights in the second optical fiber. The detecting means detects the rotational angular velocities of the laser light source and the first optical fiber based on the frequency of the superimposed light when the laser light source and the first optical fiber are rotating in a predetermined plane.

  Preferably, the laser light source has a first end face and a second end face facing the first end face, and oscillates the first and second laser beams from the first and second end faces, respectively. It consists of a semiconductor laser that emits first and second laser beams to a first optical fiber. The first optical fiber rotates the first laser light emitted from the first end face clockwise to guide it to the semiconductor laser from the second end face, and also emits the second laser emitted from the second end face. The light is rotated counterclockwise and guided from the first end face to the semiconductor laser.

  Preferably, the active layer of the semiconductor laser is in contact with the first and second end faces obliquely.

  Preferably, the wavelength of the first laser light is different from the wavelength of the second laser light.

  According to the invention, the gyro system includes the optical gyro, the transmission device, and the reception device. The optical gyro is the optical gyro according to any one of claims 1 to 4. The transmission means converts the rotational angular velocity detected by the optical gyro detection means into a radio signal and transmits it. The receiving device receives the radio signal transmitted from the transmitting device, decodes the received radio signal, and acquires the rotational angular velocity.

  In the present invention, a first laser beam that rotates clockwise using a laser light source that oscillates a laser beam and amplifies the oscillated laser beam, two optical fibers, and two couplers. And a ring laser that generates a frequency difference between the second laser beam that rotates counterclockwise.

  Therefore, the structure can be simplified as compared with the conventional optical fiber gyro that amplifies the laser light by the amplified light through the coupler.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is a schematic diagram showing the configuration of an optical gyro according to an embodiment of the present invention. Referring to FIG. 1, an optical gyro 10 according to an embodiment of the present invention includes a semiconductor optical amplifier (SOA) 1, optical fibers 2, 4, 6, couplers 3, 5, and optical detection. A detector 7, a spectrum analyzer 8, and a detector 9.

  The semiconductor optical amplifier 1 has an active layer made of indium gallium arsenide (InGaAs). The semiconductor optical amplifier 1 oscillates laser light having a wavelength of 1579 nm, for example, and emits the oscillated laser light from the end faces 1A and 1B as clockwise laser light CW and counterclockwise laser light CCW, respectively. The light is emitted into the fiber 2. Further, the semiconductor optical amplifier 1 amplifies the laser beams CW and CCW that have made one round in the optical fiber 2 by stimulated emission, and emits the amplified laser beams CW and CCW to the optical fiber 2 from the end faces 1A and 1B, respectively.

  The optical fiber 2 is connected to both ends of the semiconductor optical amplifier 1 in a loop shape, and has, for example, a length of 3.03 m and a refractive index of 1.444 (core refractive index). Then, the optical fiber 2 rotates the laser light CW emitted from the end face 1A of the semiconductor optical amplifier 1 clockwise, guides the rotated laser light CW from the end face 1B into the semiconductor optical amplifier 1, and transmits the semiconductor light. The laser light CCW emitted from the end face 1B of the amplifier 1 is rotated counterclockwise, and the rotated laser light CCW is guided from the end face 1A into the semiconductor optical amplifier 1.

  In the coupler 3, the laser beams CW and CCW propagating in the optical fiber 2 are 99%, and the laser beams CW and CCW propagating in the optical fiber 4 are 1% so that the optical fiber 2 is connected to the optical fiber 4. Combine with.

  The optical fiber 4 is coupled to the optical fiber 2 by the coupler 3 and guides a part (1%) of the laser beams CW and CCW propagating through the optical fiber 2 to the coupler 5. The coupler 5 superimposes the two laser beams CW and CCW propagating through the optical fiber 4 at 50%: 50% and guides them to the optical fiber 6.

  The optical fiber 6 guides the superposed light superposed by the coupler 5 to the photodetector 7. The photodetector 7 square-detects the superimposed light in the optical fiber 6 and generates a beat signal that is generated due to the difference between the oscillation frequency of the laser light CW and the oscillation frequency of the laser light CCW.

When the electric field components of the laser beam CW and the laser beam CCW are respectively E _CW and E _CCW ,
E _CW = a _CW cos (2πf _CW t + φ _CW ) (1)
E _CCW = a _CCW cos (2πf _CCW t + φ _CCW ) (2)
It becomes. Here, a _CW and a _CCW are the amplitudes of the laser beams CW and CCW, respectively, and f _CW and f _CCW are the laser beams CW and CCW when the semiconductor optical amplifier 1 and the optical fiber 2 are rotating, respectively. And φ _CW and φ _CCW are the phases of the laser beams CW and CCW, respectively.

  When the two laser beams CW and CCW are overlapped, the detected light intensity I becomes equal to the square of the electric field component, so that the following is obtained.

I = <| E _CW + E _CCW | ² >
= (A ² _CW + a ² _CCW ) / 2 + 2a _CW a _CCW cos {2π (f _CW −f _CCW ) t + (φ _CW −φ _CCW )}
= (A ² _CW + a ² _CCW ) / 2 + 2a _CW a _CCW cos {2πf _B t + Δ} (3)
Note that f _B = f _CW −f _CCW and Δ = φ _CW −φ _CCW . <> Represents a time average.

The DC component of the superimposed light obtained by superimposing the laser beams CW and CCW is (a ² _CW + a ² _CCW ) / 2, and the AC component is 2a _CW a _CCW cos {2πf _B t + Δ}. This AC component is the beat signal, and f _B = f _CW −f _CCW is the frequency of the beat signal.

  Therefore, the photodetector 7 generates the light intensity I shown in the equation (3) by performing the square detection of the superimposed light obtained by superimposing the laser beams CW and CCW, and the beat signal (= the equation (3)). Are detected and output to the spectrum analyzer 8.

The spectrum analyzer 8 detects the frequency f _B of the beat signal detected by the photodetector 7 and outputs the detected frequency f _B to the detector 9.

The detector 9 receives the frequency f _B from the spectrum analyzer 8 and detects the rotational angular velocity of the rotating body based on the received frequency f _B by a method described later.

When an experiment for examining the relationship between the frequency f _B and the rotational angular velocity in the optical gyro 10 is performed, the optical gyro 10 is placed on the table 20. The table 20 is rotated clockwise or counterclockwise by the servo mechanism 30 at various rotational angular velocities. The controller 40 controls the servo mechanism 30 to rotate the table 20 clockwise or counterclockwise at various rotational angular velocities.

  FIG. 2 is a plan view of the semiconductor optical amplifier 1 shown in FIG. Referring to FIG. 2, the semiconductor optical amplifier 1 includes an active layer 11, optical confinement layers 12 and 13, and antireflection films 14 and 15. The active layer 11 is sandwiched between the light confinement layers 12 and 13 and is in contact with the end faces 1A and 1B obliquely.

  The optical confinement layers 12 and 13 are formed of a barrier layer, a cladding layer, and the like, and are provided on both sides of the active layer 11 in contact with the active layer 11. The antireflection films 14 and 15 are formed in contact with the end faces 1A and 1B, respectively.

  As shown in FIG. 2, the structure in which the active layer 11 is disposed obliquely with respect to the end faces 1A and 1B forms a stacked body in which the active layer 11, the optical confinement layers 12 and 13 and the like are stacked, and is formed. The laminate is manufactured by cutting so that the active layer 11 is disposed obliquely.

  When a current is injected into the active layer 11 to cause laser oscillation, the laser light is confined by the optical confinement layers 12 and 13 and propagates in the end faces 1A and 1B in the active layer 11. The laser beam is emitted from the end surface 1A as the laser beam CW and is emitted from the end surface 1B as the laser beam CCW.

  The laser light CW goes around the optical fiber 2 clockwise and is introduced into the active layer 11 from the end face 1B through the antireflection film 15. The laser beam CW introduced into the active layer 11 is amplified by stimulated emission and is emitted from the end face 1A again.

  Further, the laser CCW goes around the optical fiber 2 counterclockwise and is introduced into the active layer 11 from the end face 1A via the antireflection film 14. The laser light CCW introduced into the active layer 11 is amplified by stimulated emission and is emitted from the end face 1B again.

  Thus, the semiconductor optical amplifier 1 oscillates and emits the laser beams CW and CCW into the optical fiber 2, amplifies the laser beams CW and CCW propagated in the optical fiber 2 by stimulated emission, and again, The light is emitted into the optical fiber 2.

Therefore, the laser beams CW and CCW need to pass through the end faces 1A and 1B many times. In order to maintain the intensity of the laser beams CW and CCW, the reflectance of the laser beams CW and CCW at the end faces 1A and 1B is It is set to 10 ⁻⁵ or less.

  Thus, in order to keep the reflectance at the end faces 1A and 1B low, the active layer 11 is disposed obliquely with respect to the end faces 1A and 1B, and the antireflection films 14 and 15 are formed on the end faces 1A and 1B.

  The optical fiber 2 is connected to the antireflection films 14 and 15 of the semiconductor optical amplifier 1 so that the laser beams CW and CCW from the active layer 11 enter the core.

  FIG. 3 is a schematic diagram showing the configuration of the coupler 3 shown in FIG. Referring to FIG. 3, the coupler 3 includes guides 31 and 32. The guides 31 and 32 couple the two optical fibers by sandwiching the two optical fibers in contact with each other.

  When the optical fiber 4 is coupled to the optical fiber 2, the optical fiber 4 is disposed between the guides 31 and 32 so as to contact the optical fiber 2. In this case, the core 21 of the optical fiber 2 is disposed close to the core 41 of the optical fiber 4.

  1% of the laser light CW propagating clockwise in the optical fiber 2 leaks from the core 21 to the core 41 in the vicinity of the core 21 and the core 41. Then, 1% of the laser light CW leaked to the core 41 propagates through the optical fiber 4.

  Further, 1% of the laser light CCW propagating counterclockwise in the optical fiber 2 leaks from the core 21 to the core 41 in the vicinity of the core 21 and the core 41. Then, 1% of the laser light CCW leaked to the core 41 propagates through the optical fiber 4.

  Thus, the laser beams CW and CCW propagating in the optical fiber 4 are part (1%) of the laser beams CW and CCW propagating in the optical fiber 2.

  The optical fibers 4 and 6 are coupled by the coupler 5 by the same method as shown in FIG.

An experimental result of detecting the frequency f _B of the beat signal when the optical gyroscope 10 is placed on the table 20 and the laser beam CW and CCW are superimposed by changing the rotational angular velocity of the table 20 by the servo mechanism 30 and the controller 40 will be described. To do. In the experiment, a current (60 mA) 1.03 times the threshold current was injected to oscillate the semiconductor optical amplifier 1 to generate laser beams CW and CCW.

  FIG. 4 is a diagram showing the relationship between the power and frequency of the beat signal, and FIG. 5 is a diagram showing the relationship between the frequency and power of the beat signal and the rotational angular velocity.

  In FIG. 4, the horizontal axis represents the frequency of the beat signal, and the vertical axis represents the power of the beat signal. In FIG. 5, the horizontal axis represents the rotation angular velocity, and the vertical axis represents the frequency and power of the beat signal.

  Referring to FIG. 4, the peak value of the beat signal is observed at each of the rotation angular velocities of 90 degrees / s, 180 degrees / s, 270 degrees / s, and 360 degrees / s, and the rotational angular velocities are 90 degrees / s, 180 degrees. / S, 270 degrees / s, and 360 degrees / s, the peak value of the beat signal shifts to the high frequency side.

  Therefore, in the optical gyroscope 10, it was found that the beat signal when the laser beams CW and CCW are superimposed can be observed, and the frequency changes depending on the rotational angular velocity.

  Referring to FIG. 5, a straight line k1 indicates the relationship between the frequency and the rotational angular velocity, and a curve k2 indicates the relationship between the power and the rotational angular velocity. The frequency of the beat signal changes linearly with respect to the rotational angular velocity. More specifically, the frequency of the beat signal decreases linearly with respect to the rotational angular velocity in a region where the rotational angular velocity is negative, and linear with respect to the rotational angular velocity in a region where the rotational angular velocity is positive. (See the straight line k1). The proportionality coefficient (scale factor) in the straight line k1 is 4.014 (kHz · sec / deg). On the other hand, the power of the beat signal vibrates with respect to the change in the rotational angular velocity, and the vibration width is relatively stable at 3 dB (see curve k2).

  Therefore, the rotational angular velocity can be detected by detecting the frequency of the beat signal. On the straight line k1, the frequency of the beat signal is not observed in the range of −100 deg / sec to +100 deg / sec, because this is buried in 1 / f noise.

The frequency f _{B of the} beat signal is theoretically expressed by the following equation.

f _B = (4A / (nλP)) Ω (4)
Where A is the area of the region surrounded by the optical fiber 2, n is the refractive index of the optical fiber 2, λ is the wavelength of the laser light CW, CCW, and P is the laser light CW, CCW. Ω is the rotational angular velocity.

In the experiments shown in FIGS. 4 and 5, A = 0.998 m ² , n = 1.444, λ = 1579 nm, and P = 3.03 m. By substituting these values into equation (4) and calculating the proportionality coefficient, a proportionality coefficient of 4.039 (kHz · sec / deg) is obtained.

  Therefore, the error between the experimentally obtained proportionality coefficient (4.012) and the theoretically obtained proportionality coefficient (4.039) is 0.62%, and the optical gyroscope 10 has the Sagnac effect. It turns out that it is a light gyro.

When the detector 9 receives the beat signal from the spectrum analyzer 8, the detector 9 detects the frequency f _B of the received beat signal and detects the rotational angular velocity corresponding to the detected frequency f _B with reference to the straight line k1.

  Thus, the rotational angular velocity can be detected in the optical gyro 10.

  FIG. 6 is a schematic diagram showing a configuration of a gyro system using the optical gyro 10 shown in FIG. Referring to FIG. 6, the gyro system 100 has a configuration in which an optical gyro 10 is configured using a wireless device 60 instead of the photodetector 9, and a remote controller 70 is added to the configured optical gyro 10.

  The wireless device 60 includes a digitizer 61, a controller 62, and an antenna 63. The remote controller 70 includes a personal computer 71 and an antenna 72.

Digitizer 61 receives the beat signal from spectrum analyzer 8 and outputs the received beat signal to controller 62. The controller 62 detects the frequency f _B from the beat signal, and detects the rotational angular velocity by the method described above based on the detected frequency f _B. Then, the controller 62 modulates the detected rotational angular velocity into a predetermined method and transmits it through the antenna 63.

  The antenna 72 receives radio waves from the wireless device 60 and outputs the received radio waves to the personal computer 71. The personal computer 71 obtains the rotational angular velocity detected by the optical gyro 10 by demodulating radio waves from the antenna 72.

  As described above, in the gyro system 100, the optical gyro 10 receives the rotation angular velocity detected by the optical gyro 10 by receiving the radio device 60 that transmits the detected rotation angular velocity by a radio signal and the radio wave from the radio device 60. Therefore, even if the optical gyro 10 rotates at high speed on the table 20, the rotational angular velocity detected by the optical gyro 10 can be acquired by the stationary remote controller 70.

In the optical gyro 10 described above, the frequency f _B of the beat signal cannot be detected in the range of −100 deg / sec to +100 deg / sec. When the cause that the frequency f _B cannot be detected in this range is the lock-in phenomenon, in the optical gyro 10, the semiconductor optical amplifier 1 may be replaced with a semiconductor optical amplifier that oscillates two laser beams having different wavelengths. As a result, it is possible to solve the problem that the frequency f _B cannot be detected in the rotational angular velocity range of −100 deg / sec to +100 deg / sec due to the lock-in phenomenon.

  FIG. 7 is a diagram showing the relationship between the rotational angular velocity in the optical gyro and the frequency difference between the two laser beams. In each of (a), (b), and (c) of FIG. 7, the vertical axis represents the frequency difference Δω between the two laser beams, and the horizontal axis represents the rotational angular velocity Ω.

  In an optical gyro, light of the same frequency is normally propagated clockwise and counterclockwise in the optical fiber 2. In this case, when a rotational angular velocity is given to the optical gyro, a frequency difference is generated between the clockwise light and the counterclockwise light. A proportional relationship is established between the rotational angular velocity Ω to be applied and the frequency difference Δω of light.

  However, since the clockwise light and the counterclockwise light exist in the same optical path, in a region where the rotational angular velocity Ω is small, a lock-in phenomenon occurs where the light is coupled in the optical path and the frequency difference Δω does not occur (FIG. 7). (See (a)).

  Therefore, conventionally, a dither mechanism is used to obtain a frequency difference Δω between two lights even in a region where the rotational angular velocity Ω is small (Non-patent Document 2). This dither mechanism is a method of giving an offset to the rotational angular velocity Ω. That is, a constant angular velocity is applied mechanically at all times. This constant angular velocity is an angular velocity ΔΩ that generates a sufficiently large frequency difference that two lights having the same frequency are not coupled.

  Then, conventionally, even when a small rotational angular velocity (angular velocity in the region REG1 shown in FIG. 7A) that couples two lights is added, the rotational angular velocity Ω generated in the optical gyro is ΔΩ ± Ω. Thus, the frequency difference Δω between the two lights caused by the rotational angular velocity ΔΩ can be detected (see FIG. 7B).

  On the other hand, in an optical gyro using a semiconductor optical amplifier that oscillates two laser beams having different wavelengths, a frequency difference Δk is generated in the optical fiber 2. When the frequency difference between the two laser beams generated by the rotational angular velocity Ω is Δω1, the frequency difference Δω between the two laser beams when the rotational angular velocity Ω is added is Δk ± Δω1.

  This frequency difference Δω = Δk ± Δω1 is a sufficient difference to avoid the coupling of the two laser beams. Therefore, the lock-in phenomenon can be avoided by oscillating two laser beams having different wavelengths.

  As a result, as shown in FIG. 7C, the frequency difference Δω can be detected even in the region where the rotational angular velocity Ω is small, and the accuracy of the optical gyro 10 can be improved.

  In FIG. 7C, there is a rotational angular velocity Ω range in which the frequency difference Δω is zero. This range is normally detected by the optical gyro by controlling the overall dimensions of the semiconductor optical amplifier. Therefore, the optical gyro according to the present invention has no problem in practical use.

  In the present invention, the wireless device 60 constitutes a “transmitting device”.

  Further, the remote controller 70 constitutes a “receiving device”.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  The present invention is applied to an optical gyro having a simple structure. The present invention is also applied to a gyro system having an optical gyro with a simple structure.

It is the schematic which shows the structure of the optical gyro by embodiment of this invention. It is a top view of the semiconductor optical amplifier shown in FIG. It is the schematic which shows the structure of the coupler shown in FIG. It is a figure which shows the relationship between the power and frequency of a beat signal. It is a figure which shows the relationship between the frequency and power of a beat signal, and a rotational angular velocity. It is the schematic which shows the structure of the gyro system using the optical gyro shown in FIG. It is a figure which shows the relationship between the rotation angular velocity in an optical gyro, and the frequency difference of two laser beams.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Semiconductor optical amplifier, 1A, 1B End face, 2, 4, 6 Optical fiber, 3, 5 coupler, 7 Photo detector, 8 Spectrum analyzer, 9 Detector, 10 Optical gyro, 11 Active layer, 12, 13 Optical closed Embedded layer, 14, 15 Antireflection film, 20 Table, 30 Servo mechanism, 31, 32 Guide, 40, 62 Controller, 21, 41 Core, 60 Wireless device, 61 Digitizer, 63, 72 Antenna, 70 Remote controller, 100 Gyro system.

Claims (5)

A laser light source that oscillates the first and second laser beams and amplifies the oscillated first and second laser beams;
A first optical fiber that rotates the first laser light clockwise and rotates the second laser light counterclockwise;
A second optical fiber;
A first coupler for guiding a portion of the first and second laser light in the first optical fiber to the second optical fiber;
A second coupler for emitting superposed light obtained by superposing the first and second laser lights in the second optical fiber;
Detecting means for detecting rotational angular velocities of the laser light source and the first optical fiber based on a frequency of the superimposed light when the laser light source and the first optical fiber are rotating in a predetermined plane; Optical gyro with The laser light source has a first end face and a second end face opposite to the first end face, and oscillates the first and second laser beams from the first and second end faces. Each comprising a semiconductor laser emitting the first and second laser beams to the first optical fiber;
The first optical fiber rotates the first laser beam emitted from the first end face clockwise to guide the semiconductor laser from the second end face, and from the second end face. The optical gyro according to claim 1, wherein the emitted second laser light is rotated counterclockwise and guided from the first end surface to the semiconductor laser.   The optical gyro according to claim 2, wherein an active layer of the semiconductor laser is in contact with the first and second end faces obliquely.   The optical gyro according to any one of claims 1 to 3, wherein a wavelength of the first laser light is different from a wavelength of the second laser light. An optical gyro according to any one of claims 1 to 4,
A transmission device that converts the rotational angular velocity detected by the detection means into a radio signal and transmits the radio signal;
A gyro system comprising: a receiving device that receives a radio signal transmitted from the transmitting device, decodes the received radio signal, and acquires the rotational angular velocity.

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