JP2993582B2 - Optical circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit having a function of controlling, modulating, and sweeping the frequency of a light wave.

[0002]

2. Description of the Related Art Conventionally, the control, modulation and sweeping of the frequency of light have been performed by a direct modulation method by controlling physical parameters of a light source or an external modulation method by controlling a modulation signal of an external modulator. However, it has been difficult to achieve high frequency sweep accuracy with such a conventional method. When this is applied to optical measurement, particularly when applied to an optical frequency domain reflection measurement method, the poor frequency sweep accuracy is an important obstacle.

[0003] Here, the optical frequency domain reflection measurement method is to reflect position information on the carrier frequency of light and to reflect a physical quantity on the reflection intensity, and is one of distributed sensing techniques having high distance resolution. FIG. 21 shows an example of the specific configuration. As shown in FIG.
And the object 2 to be measured are connected by first and second optical directional couplers 3 and 4 connected in series, and a heterodyne receiver 5 is continuously connected to the first and second optical directional couplers 3 and 4. The spectrum analyzer 6 is connected to the heterodyne receiver. With this configuration, a part of the light wave from the light source 1 is guided to the measured object 2 via the first and second optical directional couplers 3 and 4, while the other part of the light wave from the light source 1 is The light wave which enters the heterodyne receiver 5 as the reference light via the first optical directional coupler 3 and is reflected or backscattered in the measured object 2 is converted into the second directional coupler 4.
, And also enters the heterodyne receiver 5.

In such a configuration, a continuous narrow linewidth laser light source is used as the light source 1, and as shown in FIG. 22, the frequency of the light source 1 is linearly changed with time for a certain time T ₁ and a certain sweep rate C. At the heterodyne receiver 5,
The intensity of the light wave (measurement light) reflected or back-scattered in the measured object 2 is measured by heterodyne detection using the reference light also branched from the light source 1 as local light.
Here, as described above, since the frequency of the laser light linearly changes with time, the frequency difference between the measurement light and the reference light has a constant value proportional to the optical path length difference between the two lights. Therefore, the reflection position in the measured object can be known from the frequency difference. In addition, since the reference light intensity is constant, the magnitude of the physical quantity to be measured can be known from the beat signal intensity proportional to the product of the local light and the measured light intensity.

[0005]

In such a conventional optical frequency domain reflection measurement method, when the optical path length difference between the two lights is relatively short (2 to 3 m), the set distance resolution can be obtained. Although it is possible, it generally has the following problems.

When the optical path length difference between the two lights increases, the frequency difference that should correspond to a constant optical path length difference becomes wider due to deviation from the linearity of the frequency sweep. For this reason, the distance resolution is significantly reduced, and a substantial measurable range in which the distance resolution and the loss measurement accuracy are guaranteed cannot be widened.

The upper limit of the measurable range of the optical frequency domain reflection measurement is determined in principle by the coherence length of the light source.
Even when a narrow line width DFB-LD having relatively excellent frequency controllability is used, the measurable range is several tens of meters. Measurement is not possible.

When a light source such as a YAG laser is used, the measurement range can be widened due to a long coherence distance, but a high distance resolution is required over the entire measurement range due to the difficulty of high-precision frequency control. It is difficult to guarantee.

Due to the problems described above, the optical frequency domain reflection measurement method has a high potential as a potential method, but a light source satisfying the required conditions is presently available. However, since it does not exist, it has not been developed as a full-fledged practical technology.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to realize frequency modulation for optical frequency domain reflection measurement which realizes high distance resolution loss distribution measurement over a wide measurement distance range. An object of the present invention is to provide an optical circuit for generating a light wave.

[0011]

According to the present invention, there is provided an optical circuit comprising a first input port, a second input port and a first input port.
An optical directional coupler having a second output port; and a constant frequency shift connected to the second output port of the optical directional coupler for changing a frequency of light output from the second output port. A given frequency shifter, an optical switch connected to the frequency shifter to turn on / off the output of the frequency shifter, and an optical switch connected to the optical switch and the second input port of the optical directional coupler. An optical amplifier for amplifying the transmitted light power constitutes an optical loop circuit whose optical path length is adjusted according to the purpose of use, and continuous light is repeatedly pulsed at a first input port of the optical directional coupling circuit. An external control system, which is connected to an optical modulator that outputs light to the first input port and that temporally synchronizes a pulse signal output from the optical modulator with an on / off state of the optical switch, Ingredient And, a circuit for the output from the first output port of said optical directional coupler with an external output, characterized by comprising multiple stages connected as needs arise.

[0012]

In an optical circuit, when a single pulse light generated by an external control signal is input to a first input port of an optical directional coupler, the pulse light is branched and output from the first and second output ports. Is output. The light output from the second output port enters the optical loop circuit and is shifted by a certain frequency, for example, f [Hz] by the frequency shifter.
It passes through the optical switch, enters the optical amplifier, is amplified by the optical amplifier, and guided to the second input port in a state where the branch loss by the optical directional coupler and the loss and loss by the frequency shifter are compensated, Part is output from the first output port, and the rest again circulates in the optical loop circuit as well. Therefore, according to the optical circuit, a pulse train in which the frequency is shifted by f with respect to the single pulse light input from the first input port is output from the first output port. Further, when the input pulse is a rectangular wave and the optical loop length is equal to the pulse length, an equivalent continuous light whose frequency is swept in a stepwise manner with respect to time can be obtained.

Here, for example, when the repetitive rectangular pulse light from the optical modulator is input to the first input port, the external control system synchronously controls the repetitive rectangular pulse signal and the OFF state of the optical switch to repeat the rectangular pulse. The pulse signal and the off state of the optical switch have the same length, and the rectangular pulse signal is repeatedly delayed at the input end of the optical switch by one pulse from the off state of the optical switch. After that, it is turned on only for a period of (pulse period−pulse length). Then, when the optical path length of the optical loop circuit is adjusted to be equal to the pulse length of the rectangular pulse light, from the first output port,
A pseudo coupled light is obtained in which the original rectangular pulse is at the top and multiple copies of the original pulse are connected backward by (pulse period / pulse length).

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

FIG. 1 shows an optical circuit according to the first embodiment.
As shown in FIG. 1, the optical directional coupler 11 includes first and second optical couplers.
IN which is the input port of₁, IN_TwoAnd the first and second
OUT which is the output port of₁, OUT_TwoAnd the branching ratio
Is 1: 1. This OUT _TwoHas a frequency shifter 12,
The optical switch 13 and the optical amplifier 14 are sequentially connected, and
The optical amplifier 14 is connected to IN_TwoConnected to the
R OUT_TwoTo IN_TwoThe optical loop circuit is connected to
You. Also, IN₁Has a light modulator 15 and a laser light source 16
Are sequentially connected. Further, the optical switch 13 and the optical switch
An external control system 17 for synchronizing the controller 15 is provided.
You. Note that OUT₁Is an external output port.

Here, the frequency shifter 12 has a function of shifting the frequency of light by a fixed value, for example, f [Hz], and specifically, an acousto-optic element or a combination of a plurality of acousto-optic elements. Anything may be used. The optical switch 13 has a function of turning on and off the light from the frequency shifter 12, and is controlled according to an external control signal CS from an external control system 17. Optical amplifier 1
Reference numeral 4 denotes a semiconductor optical amplifier, an optical fiber amplifier or the like, which compensates for a branch loss caused by the directional coupler 11 and an insertion loss of the frequency shifter 12 and the optical switch 13. On the other hand, the laser light source 16 generates continuous light with a narrow line width, and the type thereof is not limited as long as the line width is 1 MHz or less. Further, the optical modulator 15 specifically refers to an acousto-optic device or the like, and the output from the laser light source 16 is a repetitive rectangular pulse (in this embodiment, the pulse width is a second and the repetition period is b second) And is controlled by the external control system 17 in the same manner as the optical switch 13.

In this embodiment, the optical length LR of the above-described optical loop circuit is adjusted to be equal to the pulse length of the repetitive rectangular pulse output from the optical modulator 15. That is, assuming that the pulse length is a, the optical length LR is adjusted as represented by the following equation (1). In addition,
Vg indicates the group velocity of light. LR = a · Vg (1)

In the optical circuit having such a configuration, the external control system 17 controls the optical switch 13 and the optical modulator 15 as shown in FIG. That is, the OFF state of the optical switch 13 is set to the same length as the pulse length a and the ON state is set to the same length as the pulse period b (see FIG. 2B). Considering time, the rectangular pulse signal (see FIG. 2A) is synchronized so that it is delayed by one pulse (a second) with respect to the OFF state of the optical switch 13. As a result, the ON state continues for b-a seconds after the leading edge of the pulse enters the optical switch 13, and then the OFF state continues for a seconds, and this ON / OFF is repeated.

Here, IN through the optical modulator 15₁Niichi
When the next output pulse light OP is input, this pulse light OP
The optical directional coupler 11 allows an optical loop circuit and OUT₁
Demultiplexed with equal intensity to This external output is P₀Toss
You. The light entering the optical loop circuit is the frequency shifter 1
2 receives frequency shift f and is on
After passing through the optical switch 13 and the optical amplifier 14, IN_TwoEnter
Again, the optical loop circuit and OUT₁Is demultiplexed. this
When the external output is P₁And Note that this P₁Is P₀of
Although it is a copy, the optical pulse length LP and the optical loop optical path
Since the length LR is equal to P₀Rear end and P₁Is the tip of
Connected without notice. And the external output is output in the same way
Is done. The external output that has passed the optical loop circuit m times is P_mso
Expressed as P ₀, P₁, P_Two, …… P_m-1, P_m, P_{m + 1}
…… are connected instantaneously as shown in FIG.
It becomes continuous light. In addition, these external outputs P_mThe frequency of
As shown in FIG. 4, the data is discretely shifted by the step f.

For such a primary output pulse light OP,
The replication is performed such that after b seconds, the next primary output pulse light OP '
Until it enters the loop circuit,
N times. n = (b / a) -1 (2) Then, an external output train by the next primary output pulse light OP '
To P₀', P₁', P _Two'… P_n′
P_nAfter the switch, the light switch
After the switch 13 is turned on for b seconds, it is turned off for a seconds.
Control. That is, in the present embodiment, as shown in FIG.
The external output P_nThe rear end of the optical switch 13
The optical switch 13 is turned on from
And keep the off state for a second, and as shown in FIG.
_nP is a copy of_{n + 1}From mixing into the external output
In. Then, as shown in FIG.
The tip of the entered OP 'reaches the input end of the optical switch 13
At this point, the optical switch is turned on again. this
Thus, in the present embodiment, as shown in FIGS.
_nAnd the rear end of OP 'are connected instantaneously, and P_n
P is a copy of_{n + 1}There is no contamination. The light switch
Synchronizes on / off control of switch 13 with primary output pulse light train
Simulated by repeated frequency sweep
And continuous light (see FIGS. 3 and 4). Less than
Below, this is called pulse recombined continuous light.

The intensity of the pulse-recombined continuous light is determined by the optical amplifier 1
4 is automatically stabilized to a constant value determined by the parameter No. 4, and in this embodiment, the loss in the optical loop circuit (the branch loss of the optical directional coupler 11, the frequency shifter 12, and the optical switch 1)
3 and the gain of the optical amplifier 14 are equalized. The effective coherence length LC of the pulse recombined continuous light is determined by the period b of the primary output pulse light as shown by the following equation (3), and can greatly exceed the original coherence distance determined by the line width. . LC〜b · Vg (3) This is the leading portion (P ₀ ) of the pulse recombined continuous light having a length within the original coherence distance (〜a · Vg) determined by the line width.
This is because the replicas (P ₁ ... P _n ) are temporally rearranged, and the phases of P _{0 to} P _n are physically the same. In other words, even if the optical path difference length is considerably long, the light wave will interfere with its own copy, so the substantial optical path difference length from the viewpoint of phase is ~ a · V
This is because it is only about g. Therefore, by using this output light, the measurable range can be made much wider than before.

As shown in FIG. 4, the frequency of the pulse-recombined continuous light changes in a step function having a constant step of time a seconds and a frequency change f [Hz] with respect to time.
This is a constant step over the pulse period b seconds,
This is equivalent to the case where the frequency is swept up to the total frequency shift g [Hz] shown in the following equation (4). g = f · {(b / a) −1} (4) Then, this substantial frequency sweep rate C is kept completely constant as shown in the following equation (5), The problems of distance resolution and loss measurement accuracy due to non-linearity do not occur at all. C = f / a (5) Further, the frequency sweep rate can be any value in principle by selecting the frequency shift f.
The light source used can be arbitrarily selected regardless of its frequency controllability. These are also completely different from the conventional variable frequency light source.

As described above, according to the present embodiment, a pseudo continuous light wave having extremely high frequency sweep accuracy, optional frequency sweep rate selection, wide coherence length, and optional primary light source selection can be obtained. Therefore, by using the pulse-recombined continuous light which is a pseudo continuous light wave, it is possible to realize an optical frequency domain reflection measurement which is excellent in distance resolution and loss measurement accuracy and has a wide measurable range. Therefore,
By using the pulse-recombined continuous light, which is a similar continuous light wave, it is possible to realize an optical frequency domain reflection measurement that is excellent in distance resolution and loss measurement accuracy and has a wide measurable range.

When the optical circuit of the above embodiment is used for the light source in the optical frequency domain reflection measurement system as shown in FIG. 21, the frequency difference between the measurement light (signal light) S and the reference light R is caused by the difference between the optical paths. The length difference is the pulse length L of the primary output pulse light
If it is an integral multiple of P, it uniquely corresponds to the optical path length difference as shown in FIG. However, in general, as shown in FIG. 9, two frequency differences between the signal light S and the reference light R, f ₁ and f ₂ (= f ₁ + f), correspond to a constant optical path length difference. I do.
That is, as illustrated, a constant corresponds and the S 'and the signal light S to the frequency difference f _1, uncertainty time difference corresponds to a certain frequency difference 2a, and the uncertainty of the optical path length difference 2LP
Becomes Therefore, the smallest achievable distance resolution Z
_min is obtained by setting the reception bandwidth B of the heterodyne receiver to the shift amount f of the frequency sister, and
It is represented by Z _min = LP (6) Then, by adjusting the pulse length LP = a · Vg and the optical path length of the optical loop circuit, an arbitrary distance resolution equal to or greater than Z _min can be realized. For example, when achieving a resolution of 1 m, a condition of pulse width a <5 × 10 ⁻⁹ seconds is required.

Further, on the premise that the frequency sweep cycle b is set so that the value of b · Vg becomes larger than the original coherent distance determined by the light source line width, specifically, the following is performed. Is set.

(Method 1) Since the frequency sweep period of the pulse-recombined continuous light is b, the beat signal corresponding to a constant optical path length difference between the reference light R and the signal light S is, as shown in FIGS. A harmonic component based on a frequency of 1 / bHz is involved. In order to prevent a decrease in signal strength due to this harmonic component, it is necessary to set the time during which the signal of the frequency difference f _b is interrupted to be 1/10 or less of the cycle b in FIGS. On the other hand, if the reception bandwidth B is set to f according to the above-described procedure, the distance resolution Z _min is 100
When measuring a section of points, the required bandwidth is 100f. Therefore, on the frequency axis, adjacent 100
In order to avoid the crosstalk of the harmonic component accompanying the signal in the section of the point to the frequency region corresponding to the section of interest, the following equation (7) is assumed as removing the crosstalk up to the 10th harmonic component. The following conditions are required. 1 / b> 10 · (100f) (7) If f = 100 Hz, b <10 ⁻⁵ seconds, and 1
In the case of setting the m resolution, the number n of times of the optical loop circulation is 〜2 × 10 ^{3 according} to the above equation (2). In this case, since the time difference corresponding to 100 points is 10 ⁻⁶ seconds, the time during which the signal of the frequency difference f _b is interrupted in FIG.
It is only the following, and satisfies the above setting conditions. Further, the influence of accumulated noise due to passing through the optical amplifier many times is not so large. However, if f = 10 kHz, b <10 ^-7 and n will be 20 by the same calculation, not only not satisfying the above set conditions, but also only measuring up to 20 points. Therefore, the present method is useful only when the set frequency shift amount f is small.

(Method 2) As a method for preventing the signal strength reduction and the crosstalk due to the harmonic component, in addition to the above-described setting method for b, the following equation (8) is satisfied so as to satisfy the following equation (8). There is also a method of holding down within the reception bandwidth f. 10 · (1 / b) <f (8) In this case, there is no reduction in signal strength due to power distribution. Here, if f = 10 kHz, b> 10 ⁻³ seconds, and 1
For m resolution, the number of turns n is up to 2 × 10 ⁵ ,
This is not preferable because the influence of accumulated noise increases. on the other hand,
Assuming that f = 1 MHz, b> 10 ⁻⁵ seconds, n〜2 × 10 ³ , and the effect of accumulated phase noise can be suppressed. Therefore, this method is effective when the set frequency shift amount f is large.

FIG. 13 shows the configuration of an optical circuit according to the second embodiment. In this embodiment, the optical circuits shown in FIG. 1 are connected in two stages, and members having the same functions as those in FIG. Here, the optical circuit 21
Has a configuration similar to that of the optical circuit shown in FIG. 1, and includes a time width a, a frequency change step f, a repetition period b, and a total frequency shift
= F · {(b / a) −1}. The optical circuit 22
Is the same as the optical circuit 21 except that an optical path length adjusting optical fiber 18 is inserted in order to make the optical path length of the optical loop circuit longer than the optical circuit 21.

When the optical circuit 22 is used alone, that is, when a normal continuous light wave is used as an external light source, the time width a ', the step f' of frequency change, the repetition period b ', and the total frequency shift g'
= F '· {(b' / a ')-1} is generated. In this embodiment, a '= b,
f ′ = g, and the optical path length LR ′ of the optical loop circuit is set to b · Vg. Further, FIG.
As shown in (C), the optical modulator 15 in the optical circuit 22
Are synchronized so as to correspond to one frequency sweep portion of the external output light of the optical circuit 21. At this time, the frequency of the pulse-recombined continuous light output from the optical circuit 22 ranges from the total frequency shift amount g ′ to f · (b ′ / a) while maintaining a constant step f, as shown in FIG. Swept equivalently.

In this case, the maximum value of the number of rounds is the sum of the number of rounds of each optical loop circuit, (b / a) +
(B '/ b), and when realizing a resolution of 1 m, the entire repetition period b' to the pulse width a = 5 × 10 ^-9 seconds
Even if 10 ⁻³ seconds are set (b ′ / a) to 2 × 10 ⁵ ), b
= 10 ^-6 seconds, the total number of laps is up to ~
It can be about 10 ³ . Therefore, the effective repetition period b 'can be increased while suppressing the influence of the accumulated noise. Therefore, the above-described method 2 for reducing the signal strength and removing the crosstalk due to the harmonic component is used.
Can also be applied to a small set frequency shift amount.

FIG. 16 shows the configuration of an optical circuit according to the third embodiment. As shown in the figure, the present embodiment also uses an optical circuit 23 similar to the optical circuit shown in FIG. 1, and members having the same functions are denoted by the same reference numerals, and redundant description will be omitted. In the drawing, reference numeral 18 denotes an optical fiber for adjusting the optical path length of the optical loop circuit. In this embodiment, as a light source connected to the optical modulator 15, a normal frequency-variable narrow-line-width continuous light source 16A is used.
Is used. As the frequency-variable narrow-line-width continuous light source 16A, one that sweeps the frequency by controlling the injection current of the DFB-LD, one that sweeps the frequency by changing the resonator length of a YAG laser or the like depending on the temperature or the like is used. The frequency of the light source 16A is swept at a constant sweep rate (F / T) in a cycle T and a frequency change range F (see FIG. 16B). On the other hand, the optical circuit 23 is set to have a pulse time width a and a repetition period b equal to the frequency sweep period T. However, a / T is set to 10 ^{−2 to} 10 ⁻³ .

In such a configuration, as shown in FIG. 17, the frequency-swept continuous light of the light source 16A is partially cut out as a pulse (pulse length a) by the optical modulator 15 of the optical circuit 23. The frequency of the primary output pulse light continuously changes by (F / T) · a during time a. Therefore, if the frequency shifter amount f of the frequency shifter 12 in the optical circuit 23 is set as shown in the following equation (9), FIG.
A continuous frequency sweep waveform as shown in FIG. 8 is reproduced. f = (F / T) · a (9)

According to this embodiment, the problem of non-linearity of the frequency sweep of the ordinary light source 16A can be solved. When a normal frequency variable light source is used, if the optical path length difference (time difference) between the reference light and the signal light increases due to the nonlinearity of the frequency sweep shown in FIG. 19, the corresponding frequency difference spreads. . However, as shown in FIG. 20, the time dependency of the derivative of the frequency change with respect to time is equivalently removed by the above method, so that a light wave with excellent continuous frequency sweeping accuracy can be recombined. This allows
It is possible to suppress the spread of the frequency difference and realize high distance resolution and high measurement accuracy in the optical frequency domain reflection measurement.

[0034]

According to the present invention, an on / off state of an optical modulator for converting output light from an arbitrary narrow line width continuous light source into a rectangular pulse, and a frequency shifter, an optical switch, and an optical amplifier are internally provided. By controlling the ON / OFF state of the optical switch in the optical circuit in conjunction with the cycle, the frequency sweep accuracy is reliably guaranteed, and the coherence distance is long, and a pulse train or a pseudo continuous light wave is synthesized, An ideal frequency-modulated lightwave for optical frequency domain reflectometry can be provided. As a result, it is possible to realize an optical frequency domain reflection measurement having a high distance resolution, a high loss measurement accuracy, and a wide measurable range, which was impossible with a conventional variable frequency light source.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical circuit according to a first embodiment.

FIG. 2 is an explanatory diagram showing synchronous control of a repetitive rectangular pulse and an ON / OFF state of an optical switch.

FIG. 3 is an explanatory diagram showing external output light of the optical circuit of FIG. 1;

FIG. 4 is an explanatory diagram showing the time dependency of the frequency of the external output light in FIG. 3;

FIG. 5 is an explanatory diagram showing synchronous control of a repeated rectangular pulse and an ON / OFF state of an optical switch.

FIG. 6 is an explanatory diagram showing synchronous control of a repeated rectangular pulse and an ON / OFF state of an optical switch.

FIG. 7 is an explanatory diagram showing synchronous control of a repeated rectangular pulse and an ON / OFF state of an optical switch.

FIG. 8 is an explanatory diagram showing a correspondence between a frequency difference and a time difference (optical path length difference).

FIG. 9 is an explanatory diagram showing a correspondence between a frequency difference and a time difference (optical path length difference).

FIG. 10 is an explanatory diagram showing generation of a high-frequency component accompanying the synchronization of a bead frequency signal.

FIG. 11 is an explanatory diagram showing generation of a high-frequency component accompanying the synchronization of a bead frequency signal.

FIG. 12 is an explanatory diagram showing generation of a high-frequency component accompanying the synchronization of a bead frequency signal.

FIG. 13 is a configuration diagram illustrating an optical circuit according to a second embodiment.

FIG. 14 is an explanatory diagram showing a primary output pulse light (frequency sweep waveform) in the second embodiment.

FIG. 15 is an explanatory diagram showing external output light (frequency sweep waveform) in the second embodiment.

FIG. 16 is a configuration diagram illustrating an optical circuit according to a third embodiment.

FIG. 17 is an explanatory diagram showing synchronization control and the frequency (linear frequency sweep) of the repetitive rectangular pulse light in the third embodiment.

FIG. 18 is a configuration diagram showing a reproduction external output light in the third embodiment.

FIG. 19 is an explanatory diagram showing the synchronization control and the frequency (non-linear frequency sweep) of the repetitive rectangular pulse light in the third embodiment.

FIG. 20 is a configuration diagram showing reproduction external output light in the third embodiment.

FIG. 21 is a basic configuration diagram of an optical frequency domain reflection measurement method.

FIG. 22 is an explanatory diagram showing a conventional frequency sweep in the optical frequency domain reflection measurement method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Optical directional coupler 12 Frequency shifter 13 Optical switch 14 Optical amplifier 15 Optical modulator 16 Narrow line width laser light source 16A Frequency variable narrow line width continuous light source 17 External control system 18 Optical fiber for optical path length adjustment

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G02F 1/00-2/02 H01S 3/10 JICST file (JOIS) WPI (DIALOG)

Claims (1)

(57) [Claims] A first input port and a first input port;
Optical directional coupler having an output port, and a frequency that is connected to the second output port of the optical directional coupler and provides a certain frequency shift to the frequency of light output from the second output port A shifter, an optical switch connected to the frequency shifter for turning on / off an output of the frequency shifter, and a transmitted light of the optical switch connected to the optical switch and a second input port of the optical directional coupler. An optical amplifier for amplifying power constitutes an optical loop circuit in which the optical path length is adjusted according to the intended use, and the first input port of the optical directional coupling circuit converts continuous light into pulsed light repeatedly. An optical modulator connected to the first input port, and an external control system for temporally synchronizing a pulse signal output from the optical modulator with an on / off state of the optical switch. A circuit for an external output the output from the first output port of said optical directional coupler, an optical circuit, characterized by comprising multiple stages connected as needs arise.