JPH09218130A - Method and circuit for detecting frequency sweep error, optical frequency sweep light source, and optical frequency area reflection measuring circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a precise frequency sweep error and perform an optical frequency sweep with high linearity by inputting an output light to a two-optical path interference system, giving a prescribed frequency shift to the light passing one optical path, and selecting either the bead signals of the upper band waves or the bead signals of the lower band waves. SOLUTION: A frequency shift is imparted to the light passing one optical path of a two-optical path interference system 56', and only the bead signals of the primary modulated side band waves are separated on the frequency axis and selected by a band pass filter. Thus, frequency fluctuation can be precisely measured in a frequency fluctuation measuring means 58, and the frequency sweep error of an optical frequency sweep light source 51 can be precisely detected. The frequency sweep error is fed back to the optical frequency sweep light source 51, whereby the optical frequency sweep with good linearity can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical frequency sweep light source for sweeping an output optical frequency of a light source, a frequency sweep error detecting method and circuit for detecting a frequency sweep error, and an optical frequency domain reflection measuring circuit.

[0002]

2. Description of the Related Art An optical frequency domain reflectometry method is known as a method for measuring the loss of optical components and optical transmission lines. FIG. 9 shows an optical frequency domain reflection measuring circuit (O
The basic configuration of FDR) is shown. In the OFDR, the optical frequency sweep light source 51 outputs light whose optical frequency is swept linearly with time, and the measured optical component 5 is output via the optical coupler 52.
3 is input. In the optical coupler 52, part of the output light of the optical frequency sweep light source 51 is branched as reference light. A part of the reflected light at the end face of the measured optical component 53 and inside is measured by the optical coupler 5.
2 and the heterodyne receiver 54 together with the reference light
Is input to The heterodyne receiver 54 obtains beat signals of reflected light and reference light. Since the frequency of this beat signal corresponds to the reflection point position, by inputting the beat signal to the frequency analysis device 55 and performing frequency analysis, it is possible to perform loss measurement and break point diagnosis of the optical component 53 to be measured.

An optical frequency sweep light source 51 is indispensable for such OFDR. As one of the means for sweeping the output light frequency, there is a method of sweeping the frequency of a modulation signal that modulates the output light of the light source. The light modulation method includes a method of directly modulating the semiconductor laser, a method of externally modulating the output light of the laser light source using an optical modulator, and the like. FIG. 10 shows a modulated light spectrum when light having the carrier light frequency W is modulated at the modulation frequency Wm. In the modulated optical spectrum, there are a carrier having an optical frequency W and a modulated sideband having an optical frequency separated from the carrier optical frequency W by N · Wm. However,
N is an integer that is not 0. N is a positive modulation sideband, and N is a negative modulation sideband is called a lower sideband. Here, the optical frequency of the modulation sideband is swept by sweeping the modulation frequency. A voltage controlled oscillator (VCO) or the like is used as a signal source for sweeping the modulation frequency. Since the oscillation frequency of the VCO is almost proportional to the control voltage, the frequency can be relatively easily swept by changing the control voltage to the VCO linearly with time.

By the way, in order to realize a high range resolution in the optical frequency domain reflectometry, an optical frequency sweep with good linearity is required. For that purpose, a method of detecting a deviation of the sweep frequency from a linear sweep (frequency sweep error) and controlling the sweep frequency based on the obtained frequency sweep error is effective. As means for detecting the frequency sweep error, a two-path interference system 56 having an optical path length difference shown in FIG.
There is a way to use. Here, the optical frequency sweep light source 5
The output light of No. 1 is input to the optical receiver 57 via the two-path interference system 56. The optical receiver 57 obtains a beat signal having a frequency proportional to the optical path length difference between the two optical paths.

Now, as a means for sweeping the optical frequency, VC
Consider modulation by O. The frequency f _b (t) of the beat signal and the sweep speed γ (t) are expressed as f _b (t) = f _b0 + δf _b (t) (1) γ (t) = γ ₀ + δγ (t) (2) deep. Here, f _b0 is a beat frequency when the optical frequency is ideally swept linearly with respect to time, γ ₀ is a frequency sweep speed at that time, and δf _b (t) and δγ
(t) represents the fluctuation of the beat frequency and the fluctuation of the sweep speed due to the sweep nonlinearity, respectively.

In FIG. 11, assuming that the optical path length difference between the two optical paths of the two optical path interference system 56 is ΔL, and the group velocity of light in the two optical path interference system 56 is v, the beat caused by the Nth-order modulated sideband wave The frequency f _b (t) of the signal is given by f _b (t) = Nγ (t) · ΔL / v (3), and the frequency fluctuation measuring means 58 causes the frequency fluctuation δf _b (t) of this beat signal. To obtain the frequency sweep error. Further, if the frequency sweep error thus obtained is fed back to the optical frequency sweep light source 51, the optical frequency sweep with good linearity is realized. Thereby, a high distance resolution can be realized in the optical frequency domain reflectometry.

[0007]

However, in the case of the optical frequency swept light source which sweeps the optical frequency by sweeping the modulation frequency, when the conventional two-path interference system is used, the upper sideband and the lower sideband of the same order are used. The waves generate beat frequencies of the same absolute value. Then, the amplitude of the beat signal fluctuates due to the non-coincidence of the phases of the both beat signals, so that it is difficult to correctly detect the frequency sweep error.

The present invention is directed to a frequency sweep error detection method and circuit that enables optical frequency sweep with good linearity by detecting an accurate frequency sweep error, an optical frequency sweep light source, and an optical frequency domain reflection capable of obtaining high distance resolution. The purpose is to provide a measuring circuit.

[0009]

SUMMARY OF THE INVENTION A frequency sweep error detecting method and circuit according to the present invention uses two outputs of an optical frequency sweep light source.
The light is input to the optical path interference system, a predetermined frequency shift is given to the light passing through one of the optical paths, and the beat signal between the Nth upper sidebands and the beat signal between the Nth lower sidebands are separated on the frequency axis. . By selecting one of the beat signals between the upper sidebands or the beat signal between the lower sidebands by the bandpass filter, the amplitude fluctuation caused by the phase difference between the two beat signals is removed. The frequency fluctuation of the beat signal is measured to detect the frequency sweep error of the optical frequency sweep light source (claims 1 and 2).

The optical frequency sweeping light source of the present invention detects the frequency sweeping error of the output light of the laser light source which is modulated by the output signal of the frequency sweeping oscillator by the direct modulation method, and uses the correction signal corresponding to the frequency sweeping error to correct the frequency. The oscillation frequency of the sweep oscillator is adjusted (claims 3 and 5). The optical frequency sweep light source of the present invention detects the frequency sweep error of the output light of the laser light source that is modulated by the output signal of the frequency sweep oscillator by the external modulation method, and uses the correction signal according to the frequency sweep error to detect the frequency sweep oscillator. The oscillation frequency is adjusted (claims 4 and 5).

The optical frequency sweeping light source of the present invention outputs the output light of the laser light source modulated by the output signal of the frequency sweeping oscillator through the optical frequency control means, detects the frequency sweeping error of the output light, and detects the error. The frequency control amount of the optical frequency control means is adjusted by the correction signal according to the frequency sweep error (claim 6). With the above configuration, optical frequency sweeping with good linearity can be realized based on the accurately detected frequency sweeping error. By configuring an optical frequency domain reflectometry circuit using this optical frequency sweep light source, measurement with high distance resolution becomes possible.

Further, instead of controlling the oscillation frequency of the frequency sweep oscillator or the frequency shift amount of the optical frequency control means based on the frequency sweep error, the frequency of the beat signal obtained by the optical frequency domain reflection measurement is corrected by the receiving system. Even with such a configuration, it is possible to perform measurement with a high distance resolution (claim 7). In the optical frequency domain reflection measurement, the frequency f _x (t) of the reflected beat signal at a certain point is given by f _x (t) = γ (t) · ΔL / v (4) ΔL is the optical path length difference between the reference light and the reflected light, and corresponds to the reflection point position.

On the other hand, the frequency f _b (t) of the reference beat signal of the frequency sweep error detection circuit is f _b (t) = γ (t) τ + f _S (5) τ is the delay time due to the difference in optical path length between the two optical paths, f
_S is the frequency shift amount by the optical frequency shifter inserted in the two-path interference system. For simplicity, f _x (t) and f
If _b (t) is assumed to be a positive value, the _{f x (t) / (f} b (t) -f S) = ΔL / vτ ... (6). Therefore, by correcting the frequency of the reflected beat signal as shown in equation (6) with the frequency of the reference beat signal as the frequency reference in the frequency analysis device, the distance resolution in the optical frequency domain reflection measurement can be improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION (Frequency Sweep Error Detection Circuit-Claim 2) FIG. 1 shows a basic configuration of a frequency sweep error detection circuit of the present invention. In the optical frequency sweep light source 51, the VCO gives a modulation signal for modulating the output light of the laser light source, and the optical frequency of the output light is swept by sweeping the oscillation frequency of the VCO. The electric field e (t) of the output light contains a plurality of higher-order modulation sideband components, and e (t) ∝ cos [{2πf ₀ + π (Nγ (t)) t} t + p (t)] ( Given in 7). f ₀ is the carrier frequency of light, γ (t) is the frequency sweep speed, p (t) is the phase noise of the light source, and t is time.
N is an integer, N = 0 is the carrier, N> 0 is the upper sideband,
N <0 corresponds to the lower sideband.

The output light of the optical frequency sweeping light source 51 is input to the optical receiver 57 via the two optical path interference system 56 ', and a beat signal having a frequency proportional to the optical path length difference between the two optical paths is obtained. At this time, of the output signals of the optical receiver 57, the beat signal i (t) between the N-th modulation sidebands is i (t) ∝ cos [2π {Nγ (t)} τt + 2πf _S t + Δp (t, τ )] (8) Δp (t, τ) = p (t) −p (t−τ) (9) The constant phase term is omitted. If the frequency sweep speed is constant, the value of the frequency f _b (t) of the beat signal between the N-th modulation sideband waves is constant. Here, when the constant value of the frequency sweep speed is γ ₀ , the constant value f _b0 of the frequency of the beat signal is given by f _b0 = | Nγ ₀ τ + f _S | (10) On the other hand, when the frequency sweep is not linear with time, the frequency f _b (t) of the beat signal fluctuates with the fluctuation of the frequency sweep speed γ (t). Therefore, the linearity of the frequency sweep can be evaluated from the frequency fluctuation of the beat signal.

In the following, in order to evaluate the linearity of the frequency sweep, consider the case where the beat signal between the primary upper sidebands is measured. In FIG. 1, when the optical frequency shifter 1 is not inserted in the two-path interference system 56 '(conventional configuration), 1
The beat signal between the next upper sidebands and the beat signal between the first lower sidebands have a frequency f _b (t) = having the same absolute value.
Has | γ (t) |. In this state, the optical receiver 57
When the center frequency of the band-pass filter (BPF) 2 connected to the output of is set to f _C = | γ ₀ τ |, its output i ′ (t) is i ′ (t) ∝ cos [Δp (t, τ)] cos [2πγ (t) τt] (11) However, the bandwidth of the bandpass filter 2 is set wider than the fluctuation width of the frequency of the beat signal. here,
The amplitude term cos [Δp (t, τ)] on the right side including the light source phase noise term fluctuates randomly with time, and Δp
When (t, τ) = π / 2 + Mπ, the amplitude becomes 0, and the beat signal cannot be detected. Therefore, if the optical frequency shifter 1 is not inserted in one optical path of the two-optical path interference system 56 ', the frequency fluctuation of the beat signal cannot be correctly detected.

On the other hand, if the optical frequency shifter 1 is used as in this embodiment, the frequency of the beat signal between the primary upper sidebands becomes | γ (t) τ + f _S | The frequency of the beat signal between the waves is | −γ (t) τ + f _S |, and assuming that f _S ≠ 0, the frequencies of the beat signals are different. That is, the beat signal between the primary upper sideband waves and the beat signal between the primary lower sideband waves can be separated on the frequency axis. Here, in order to extract the beat signal between the first-order upper sidebands, when the center frequency of the bandpass filter 2 is set to f _C = | γ ₀ τ + f _S |, its output i ″ (t) is i "(t) α cos [2π {γ (t) τ + f S} t + Δp (t, τ)] ... a (12). As a result, the beat signal between the first-order upper sidebands does not have the amplitude fluctuation caused by the light source phase noise.
The frequency fluctuation measuring means 58 can correctly detect the frequency fluctuation of the beat signal.

Note that (1) L is an integer other than 0 and +1 and a beat signal between L-th modulation sidebands, (2) a beat signal between carrier waves, and (3) a beat signal between modulation-side band waves with different orders. , (4) There are four beat signals other than the reference beat signal: the carrier wave and the beat signal of the modulation sideband. If the frequency of these beat signals is equal to the frequency of the reference beat signal, the crosstalk cannot correctly detect the frequency fluctuation of the reference beat signal. Therefore, the frequency shift amount f _S of the optical frequency shifter 1 needs to be set to a value that does not cause the above crosstalk.

As described above, by giving a certain amount of frequency shift to the light passing through one optical path of the two-optical path interference system 56 ', only the beat signals of the primary modulation sidebands are separated on the frequency axis. The frequency fluctuation measuring means 58 can correctly measure the frequency fluctuation of the beat signal. This is also the case when measuring the frequency fluctuation of the beat signal between the modulation sidebands of a certain order. Thereby, the frequency sweep error of the optical frequency sweep light source 51 can be correctly detected. By feeding back this frequency sweep error to the optical frequency sweep light source 51, an optical frequency sweep with good linearity is realized. An embodiment of this optical frequency swept light source is shown below.

(Optical Frequency Sweep Light Source-Claim 3) FIG.
1 illustrates a first embodiment of an optical frequency swept light source of the present invention. In the figure, the semiconductor laser light source (LD) 12 is directly modulated by the output signal of the frequency sweep oscillator 11, and a part of the output light thereof is transmitted through the optical coupler 24 to the two-path interference system 56 ′.
Is input to The frequency sweep oscillator 11 has a configuration in which the oscillation frequency is controlled by a correction signal externally input to the frequency control terminal. However, when the correction signal is not given, it is assumed that the output signal is frequency-swept at the sweep speed γ = 100 GHz / s. Hereinafter, the two optical path interference system 56 'and the optical receiver 5 which constitute the frequency sweep error detection circuit
7. The beat signal is detected by the bandpass filter (BPF) 2. An acousto-optic modulator can be used as the optical frequency shifter 1 of the two-optical path interference system 56 '.

Here, the sweep speed γ is 100 GHz / s, the delay optical fiber length of the optical path interference system 56 'is 1 km, the frequency shift amount f _S of the optical frequency shifter 1 is 80 MHz, and the group velocity of light in the optical fiber. Assuming that v is approximately 2 × 10 ⁸ m / s, the frequency of the beat signal between the primary upper sidebands and the frequency of the beat signal between the lower sidebands of the beat signals received by the optical receiver 57 are respectively It becomes 80.5MHz and 79.5MHz and can be separated on the frequency axis. It should be noted that carrier waves are 2
The frequencies of the beat signals of the next upper sideband and the second lower sideband are 80.0 MHz, 81.0 MHz and 79.0 MHz, respectively, and these are also separated on the frequency axis. Further, the strength of the beat signal between the higher-order modulated sidebands is sufficiently small and is ignored. Further, when the frequency sweep range is set from 2 GHz to 4 GHz, the frequency of the carrier and the beat signal of the primary modulation sideband is about 2 GHz or more, and these are also separated on the frequency axis. In addition, the frequency of the beat signal between the modulated sidebands having different orders is about 2 GHz or higher.

Therefore, the center frequency f _C of the bandpass filter 2 is set to, for example, 80.5 MHz, and the bandwidth Δf is set to 100 k in consideration of a certain frequency fluctuation of the beat signal.
When set to Hz, only the beat signal between the first upper sidebands is obtained as the output signal of the bandpass filter 2. As a result, the effects of amplitude fluctuations and crosstalk caused by other beat signals are removed, so that the frequency fluctuations of the beat signals between the primary upper sidebands can be accurately measured.

The means for measuring the frequency fluctuation of the beat signal and detecting the frequency sweep error is composed of a frequency discriminator 21 and an integrator (low-pass filter) 22 here. The frequency discriminator 21 converts frequency fluctuations of the beat signal output from the bandpass filter 2 into voltage fluctuations. The voltage fluctuation is proportional to the fluctuation of the sweep speed. Here, since the time integration of the fluctuation of the sweep speed corresponds to the frequency sweep error, the frequency sweep error can be obtained from the fluctuation of the output signal of the integrator 22 due to the low-pass filter or the like.
The correction signal generation circuit 23 generates a correction signal according to this frequency sweep error and controls the oscillation frequency of the frequency sweep oscillator 11. Thereby, the linearity of the frequency sweep can be improved, and an optical frequency swept light source with good sweep linearity can be realized.

(Optical Frequency Sweep Light Source-Claim 4) FIG.
2 shows a second embodiment of the optical frequency swept light source of the present invention. The feature of this embodiment is that the output light of the semiconductor laser light source (LD) 13 is externally modulated. The optical modulator 14 uses, for example, an electro-optical modulator, and modulates the output light of the semiconductor laser light source 13 by the output signal of the frequency sweep oscillator 11. The frequency sweep oscillator 11 has improved frequency sweep linearity as in the first embodiment shown in FIG. 2, and realizes an optical frequency swept light source having good sweep linearity.

(Optical Frequency Sweep Light Source-Claim 5) FIG.
3 shows a third embodiment of an optical frequency swept light source of the present invention. The feature of this embodiment is that the semiconductor laser light source (LD) 12, 15 whose output light is modulated by the output signal of the frequency sweep oscillator 11 is provided in the configuration of the first embodiment shown in FIG. Is used for frequency sweep error detection, and the output light of the semiconductor laser light source 15 is used as the output light of the optical frequency sweep light source. That is, the optical frequency swept light source shown in FIG. 2 can be regarded as a frequency swept signal source for the semiconductor laser light source 15. Since the frequency of the output signal of the frequency sweep oscillator 11 is swept with good linearity by the above configuration, the optical frequency of the modulation sideband wave included in the output light of the semiconductor laser light source 15 is also swept with good linearity.

In such a configuration, as the optical frequency sweep light source, a light source having characteristics such as wavelength and coherence according to the purpose can be arbitrarily selected and easily changed. Note that the same can be applied to the configuration of the second embodiment shown in FIG. 3 according to the external modulation method. Alternatively, the output light of the second semiconductor laser light source 15 may be externally modulated.

(Optical Frequency Sweep Light Source-Claim 6) FIG.
4 shows a fourth embodiment of an optical frequency swept light source of the present invention. In the figure, a semiconductor laser light source (LD) 12 is directly modulated by an output signal of a frequency sweep oscillator 16, and its output light is input to an optical frequency shifter 17. As the optical frequency shifter 17, for example, an acousto-optic modulator is used, and the frequency shift amount (for example, 80 MHz) is set by the output signal of the voltage controlled oscillator (VCO) 18. Voltage controlled oscillator 18
Is a configuration in which the oscillation frequency is controlled by a correction signal input from the correction signal generation circuit 23 to the frequency control terminal. Also with this configuration, the linearity of the optical frequency sweep of the semiconductor laser light source 12 is improved, and an optical frequency sweep light source with good sweep linearity is realized. The same applies to the configuration in which the output light of the semiconductor laser light source 12 is externally modulated.

As described above, the first to fourth embodiments have been shown as the optical frequency sweep light source. However, by constructing the optical frequency domain reflection measuring circuit using such an optical frequency sweep light source, a high distance resolution can be obtained. It becomes possible to measure. An embodiment of an optical frequency domain reflectometry circuit using the optical frequency sweep light source of the present invention will be described below. (Optical Frequency Domain Reflectance Measuring Circuit) FIG. 6 shows a first embodiment of an optical frequency domain reflectance measuring circuit using the optical frequency swept light source of the present invention.

In the figure, an optical frequency sweep light source 1 of the present invention is shown.
0 may be any of the optical frequency sweep light sources shown in FIGS. 2 to 4, but it is necessary to take out the output signal of the frequency sweep oscillator 11 to the outside. Light whose frequency is swept linearly with respect to time is output from the optical frequency sweep light source 10, and is input to the measured optical component 53 via the optical coupler 52. A part of the reflected light at the end face of the measured optical component 53 and inside is branched by the optical coupler 52 and input to the optical receiver 31.
The mixer 32 synthesizes the output signal of the frequency sweep oscillator 11 and the output signal of the optical receiver 31 and outputs a beat signal. The frequency of this beat signal corresponds to the position of the reflection point in the measured optical component 53. The frequency analyzer 55 frequency-analyzes the beat signal, thereby making it possible to measure the loss of the optical component 53 to be measured, diagnose the breaking point, and the like. Since both the output signal of the frequency sweep oscillator 11 and the output light of the optical frequency sweep light source 10 are swept with good linearity, a high distance resolution can be realized.

(Optical Frequency Domain Reflectance Measuring Circuit) FIG. 7 shows a second embodiment of an optical frequency domain reflectance measuring circuit using the optical frequency swept light source of the present invention. In the figure, the optical frequency sweeping light source 10 of the present invention may be any of the optical frequency sweeping light sources shown in FIGS. The output light of the optical frequency sweep light source 10 is input to the measured optical component 53 via the optical couplers 52-1 and 52-2. The optical coupler 52-1 is
A part of the output light of the optical frequency sweep light source 10 is branched as reference light and input to the heterodyne receiver 54. Optical coupler 5
2-2 branches a part of the reflected light on the end face of the measured optical component 53 or inside and inputs the branched light to the heterodyne receiver 54. The heterodyne receiver 54 obtains beat signals of reflected light and reference light. Since the frequency of this beat signal corresponds to the reflection point position, by inputting the beat signal to the frequency analysis device 55 and performing frequency analysis, it is possible to perform loss measurement and break point diagnosis of the optical component 53 to be measured. Since the output light of the optical frequency sweep light source 10 is swept with good linearity, a high distance resolution can be realized.

(Optical frequency domain reflectometry circuit-claim 7)
FIG. 8 shows an embodiment of an optical frequency domain reflectometry circuit using the frequency sweep error detection circuit of the present invention. In the figure,
The frequency sweep error detection circuit 20 of the present invention is the same as the frequency sweep error detection circuit 20 shown in FIG.
The optical path interference system 56 ', the optical receiver 57, and the bandpass filter (BPF) 2 are used. Optical frequency sweep light source 51
Output light is input to the measured optical component 53 via the optical couplers 52-1 and 52-2. The optical coupler 52-1 branches a part of the output light of the optical frequency sweep light source 51 and inputs it to the frequency sweep error detection circuit 20. The frequency sweep error detection circuit 20 outputs a beat signal of predetermined modulation sidebands. In the optical coupler 52-2, part of the output light of the optical frequency sweep light source 51 is branched as reference light. Optical component under test 5
A part of the reflected light on the end face of 3 and inside is branched by the optical coupler 52-2 and input to the heterodyne receiver 54 together with the reference light. The heterodyne receiver 54 obtains beat signals of reflected light and reference light. The frequency of this beat signal corresponds to the position of the reflection point. Here, the frequency analysis device 55 performs frequency analysis of the beat signal from the heterodyne receiver 54 with the frequency of the beat signal output from the frequency sweep error detection circuit 20 as a frequency reference. With this configuration, the fluctuations in the frequency of the beat signal due to the fluctuations in the sweep speed of the light source are canceled out, so that the measured optical component 53 with a high distance resolution.
It is possible to perform the loss measurement and the fracture point diagnosis.

[0032]

As described above, the frequency sweep error detecting method and circuit of the present invention can correctly evaluate the linearity of optical frequency sweep. Further, by using the frequency sweep error detection circuit of the present invention, it is possible to realize a frequency sweep signal source having good linearity or an optical frequency sweep light source having good linearity. Further, by using the optical frequency sweep light source of the present invention, an optical frequency domain reflectometry circuit having a very high distance resolution can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of a frequency sweep error detection circuit of the present invention.

FIG. 2 is a diagram showing a first embodiment of an optical frequency sweep light source of the present invention.

FIG. 3 is a diagram showing a second embodiment of an optical frequency sweep light source of the present invention.

FIG. 4 is a diagram showing a third embodiment of an optical frequency sweep light source of the present invention.

FIG. 5 is a diagram showing a fourth embodiment of an optical frequency sweep light source of the present invention.

FIG. 6 is a diagram showing a first embodiment of an optical frequency domain reflectometry circuit using the optical frequency sweep light source of the present invention.

FIG. 7 is a diagram showing a second embodiment of an optical frequency domain reflectometry circuit using the optical frequency swept light source of the present invention.

FIG. 8 is a diagram showing an embodiment of an optical frequency domain reflectometry circuit using the frequency sweep error detection circuit of the present invention.

FIG. 9 is a diagram showing a configuration example of a conventional optical frequency domain reflectometry circuit.

FIG. 10 is a diagram showing a modulated light spectrum.

FIG. 11 is a diagram showing a configuration example of a conventional frequency sweep error detection circuit.

[Description of Reference Signs] 1 optical frequency shifter 2 bandpass filter (BPF) 10 optical frequency swept light source of the present invention 11, 16 frequency swept oscillator 12, 13, 15 semiconductor laser light source (LD) 14 optical modulator 17 optical frequency shifter 18 Voltage controlled oscillator (VCO) 20 Frequency sweep error detection circuit of the present invention 21 Frequency discriminator 22 Integrator (LPF) 23 Correction signal generation circuit 24 Optical coupler 31 Optical receiver 32 Mixer 51 Optical frequency sweep light source 52 Optical coupler 53 Measured Optical component 54 Heterodyne receiver 55 Frequency analysis device 56 2 Optical path interference system 57 Optical receiver 58 Frequency fluctuation measuring means

Front Page Continuation (72) Inventor Yahei Oyamada 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation

Claims (7)

[Claims] 1. A frequency sweep error in which output light of an optical frequency sweep light source is received by an optical receiver via a two-path interference system, and a frequency sweep error of the optical frequency sweep light source is detected from the obtained frequency fluctuation of a beat signal. In the detection method, a predetermined frequency shift is applied to the light passing through one optical path of the two-path interference system, and a beat signal between N-th order (N is an integer other than 0) upper sideband waves and an Nth-order lower sideband wave The beat signal is separated on the frequency axis, and one of the beat signals between the upper sidebands or the beat signal between the lower sidebands is selected and its frequency fluctuation is measured, and the frequency sweep error of the optical frequency sweep light source is measured. A method for detecting a frequency sweep error characterized by detecting. 2. A two-optical-path interference system that splits the output light of an optical frequency sweep light source into two optical paths, adds a predetermined delay to one of the lights, combines the other light, and outputs the beat signal light. An optical receiver for receiving the beat signal light, and a frequency fluctuation measuring means for measuring the frequency fluctuation of the beat signal output from the optical receiver, and the optical frequency sweep light source of the optical frequency sweep light source from the frequency fluctuation of the beat signal. In a frequency sweep error detection circuit for detecting a frequency sweep error, an optical frequency shifter which is inserted into one optical path of the two optical path interference system and gives a predetermined frequency shift to passing light, and a beat output from the optical receiver A band pass for inputting a signal, selecting one of N-th order (N is an integer other than 0) upper side band wave beat signal or N-th order lower side band wave beat signal, and transmitting the selected signal to the frequency fluctuation measuring means. Frequency sweep error detection circuit, characterized in that a filter. 3. A frequency sweep oscillator in which the oscillation frequency is swept linearly with respect to time, and the oscillation frequency is adjusted according to a correction signal externally input to a frequency control terminal; A laser light source whose output light is modulated by an output signal, a frequency sweep error detection circuit according to claim 2 which detects a frequency sweep error of the output light of the laser light source, and a correction signal according to the frequency sweep error. An optical frequency swept light source, comprising: a correction signal generating means for sending to a frequency control terminal of the frequency swept oscillator; and splitting the output light of the laser light source and outputting the split light to the outside. 4. A laser light source, a frequency sweep oscillator whose oscillation frequency is swept linearly with respect to time, and whose oscillation frequency is adjusted according to a correction signal inputted from the outside to a frequency control terminal, An optical modulator that modulates output light of the laser light source according to an output signal of a frequency sweep oscillator; a frequency sweep error detection circuit according to claim 2 that detects a frequency sweep error of output light of the optical modulator; Correction signal generating means for generating a correction signal according to a sweep error and sending it to the frequency control terminal of the frequency sweep oscillator, and branching the output light of the optical modulator and outputting it to the outside. Optical frequency sweep light source. 5. The optical frequency swept light source according to claim 3 or 4, further comprising a second laser light source whose output light is directly or externally modulated by an output signal of a frequency swept oscillator. An optical frequency sweep light source characterized by outputting the output light of the light source to the outside. 6. A frequency sweeping oscillator whose oscillation frequency is swept linearly with respect to time, a laser light source whose output light is directly modulated or externally modulated by an output signal of the frequency sweeping oscillator, and a frequency control terminal from the outside. The frequency sweep error according to claim 2, wherein an optical frequency control unit that adjusts an output optical frequency of the laser light source according to a correction signal input to the optical frequency control unit, and a frequency sweep error of the output light of the optical frequency control unit is detected. A detection circuit; and a correction signal generation means for generating a correction signal according to the frequency sweep error and sending it to the frequency control terminal of the optical frequency control means, and branching the output light of the optical frequency control means to the outside. An optical frequency sweep light source characterized by outputting to. 7. An optical frequency sweeping light source, an optical coupler that splits the output light of the optical frequency sweeping light source into two, and inputs one of the lights as measurement light to an optical circuit under test, and the optical coupler The frequency sweep error detection circuit according to claim 2, which detects a frequency sweep error of the other light, and an output signal of the frequency sweep error detection circuit for the beat signal of the reflected light from the measurement light and the measured optical circuit. An optical frequency domain reflectometry circuit comprising: a frequency analysis means for performing a frequency analysis with the frequency reference as a frequency reference.