Optical frequency domain reflectometry device and method

Abstract

The present disclosure aims to enable measurement over distances exceeding 1 km with a spatial resolution of less than 100 μm, thereby enabling diagnosis of the health of optical equipment located at such a distance. The device disclosed herein is an optical frequency domain reflectometry device, comprising: a local optical delay fiber for delaying local light; an optical 90-degree hybrid for inputting local light delayed by the local optical delay fiber and backscattered light from a measurement object, causing interference between the local light and the backscattered light to generate an in-phase component and a quadrature component of a beat signal resulting from the interference; and a balanced photodetector for detecting the in-phase and quadrature components of the beat signal. The device measures the optical frequency response of the measurement object relative to the local optical delay fiber.

Description

Technical Field

[0001] The present disclosure relates to optical frequency domain reflectometry technology. Background Art

[0002] In optical frequency domain reflectometry (OFDR), the optical frequency response of the object being measured is measured at an absolute distance z, and its Fourier transform is calculated to obtain a backscattered waveform (for example, see Non-Patent Document 1). In this case, the optical frequency response of the object being measured is sampled at regularly spaced optical frequencies (the FSR of the reference interferometer) using a clock signal obtained from a reference interferometer.

[0003] According to the sampling theorem, the measurable distance in OFDR is determined by the fiber length of the reference interferometer. Furthermore, if the reference interferometer fiber length is longer than the coherence length of the light source, the clock quality deteriorates, making it impossible to sample the beat signal at equal intervals, and thus unable to accurately measure the optical frequency response (and thus, unable to analyze the backscattered light waveform). Consequently, current measurement performance is limited to distances of several tens of meters and spatial resolutions of less than 100 μm (see, for example, Non-Patent Document 2).

[0004] Prior art literature

[0005] Non-patent literature

[0006] Non-patent document 1: U.Glombitza and E.Brinkmeyer, "Cohenret frequency-domainreflectometry for characterization of single-mode integrated-opticalwaveguides", IEEE JLT, vol.11, no.8, pp.1377-1384, Aug.1993.

[0007] Non-patent document 2: BJSoller et al., "High resolution optical frequency domainreflectometry for characterization of components and assemblies", Opt.Exp., vol.13, no.2, pp.666-674, Jan.2005. Summary of the Invention

[0008] Problems to be solved by the invention

[0009] The present disclosure aims to enable measurement of a long distance exceeding 1 km with a spatial resolution of 100 μm or less, thereby enabling diagnosis of the health of an optical device installed at a long distance.

[0010] Means of solving the problem

[0011] The device disclosed herein,

[0012] The optical frequency domain reflectometry device includes:

[0013] Local light delay fiber, which delays the local light;

[0014] an optical 90-degree hybrid that inputs the local light delayed by the local optical delay fiber and the backscattered light from the measurement object, causes the local light and the backscattered light to interfere with each other, and generates an in-phase component and an orthogonal component of a beat signal generated by the interference; and

[0015] a balanced photoelectric detector for detecting an in-phase component and a quadrature component of the beat signal;

[0016] The device measures an optical frequency response of a measurement object with respect to a relative distance with respect to the local optical delay fiber.

[0017] The method disclosed herein is a method performed by an optical frequency domain reflectometry device.

[0018] The optical frequency domain reflectometry device comprises:

[0019] Local light delay fiber, which delays the local light;

[0020] an optical 90-degree hybrid, which inputs the local light delayed by the local optical delay fiber and the backscattered light from the measurement object, and outputs an in-phase component and an orthogonal component of a beat signal generated by the interference of the local light and the backscattered light; and

[0021] a balanced photoelectric detector for detecting an in-phase component and a quadrature component of the beat signal;

[0022] The method measures the optical frequency response of the measurement object with respect to the relative distance with respect to the local optical delay fiber.

[0023] Effects of the Invention

[0024] According to the present disclosure, a long distance exceeding 1 km can be measured with a spatial resolution of 100 μm or less, making it possible to diagnose the health of an optical device installed at a long distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A configuration example of the test system of the present disclosure is shown.

[0026] Figure 2 The beat frequency f corresponding to the absolute distance z is expressed as beat Example of system configuration in the case of .

[0027] Figure 3 An example of the relationship between the beat frequency and the distance disclosed in the present invention is shown.

[0028] Figure 4 Indicates use Figure 2 An example of the relationship between beat frequency and distance measured by the structure.

[0029] Figure 5 Indicates use Figure 2 An example of a spectrum measured for a structure.

[0030] Figure 6 An example of a spectrum measured using the configuration disclosed herein is shown.

[0031] Figure 7 An example of Fresnel reflection measurement results at 3 km is shown. DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, the present disclosure is not limited to the embodiments shown below. These embodiments are merely examples, and the present disclosure can be implemented in various ways, including modifications and improvements, based on the knowledge of those skilled in the art. Furthermore, in this specification and the accompanying drawings, structural elements with the same reference numerals represent structural elements that are identical to one another.

[0033] Figure 1 Figure 2 shows an example configuration of a test system according to the present disclosure. In the test system according to the present disclosure, an optical frequency domain reflectometer 91 is connected to an optical fiber under test 92, which is the measurement target. The optical frequency domain reflectometer 91 includes a wavelength-swept light source (TLS) 11, a coupler 12, a circulator 13, an optical 90-degree hybrid 21, a balanced photodetector (BPD) 22, a low-pass filter (LPF) 23, an A / D converter 24, an auxiliary interferometer 30, and a local delay fiber 40.

[0034] Coupler 12 splits the light from TLS 11 into local light and probe light. Coupler 14 further splits the local light from coupler 12. One local light is input to auxiliary interferometer 30, and the other local light is input to 90-degree hybrid 21. Circulator 13 inputs the probe light to fiber under test 92 and outputs the backscattered light from fiber under test 92 to 90-degree hybrid 21.

[0035] The 90-degree hybrid 21 causes the local light to interfere with the backscattered light, and generates an in-phase component and a quadrature component of a signal (beat signal) generated by the interference.

[0036] The BPD 22 detects the in-phase component and the quadrature component of the beat signal respectively.

[0037] The LPF 23 transmits only the output signal from the BPD 22 , that is, the low-frequency component of the beat signal of the local light and the backscattered light.

[0038] The A / D 124 converts the analog signal output from the LPF 23 into a digital signal according to the sampling clock from the auxiliary interferometer 30 .

[0039] Here, we will refer to Figure 2 , represents the beat frequency f corresponding to the observed absolute distance z beat Example of system configuration in the case of Figure 2 The structure shown does not include the local delay fiber 40 and the optical 90-degree hybrid 21 , but only has one balanced photodetector 122 and an LPF 123 .

[0040] exist Figure 2 In the structure shown, a coupler 121 is included instead of the 90-degree hybrid 21. In this case, a beat signal of local light and backscattered light is generated by the coupler 121 and input to the BPD 122. In addition, the A / D 124 is provided with a delay τ by the auxiliary interferometer 130. AUX The analog signal is converted into a digital signal using a sampling clock of . In this case, the optical frequency response r~(ν) of the measurement object is expressed by the following equation (for example, refer to equation (5) in non-patent document 1).

[0041] [Mathematical formula 1]

[0042]

[0043] The parameters are as follows.

[0044] r(τ): reflection coefficient

[0045] v: light frequency

[0046] τ: The delay caused by the round-trip propagation distance z, which is τ = 2z / c.

[0047] z: Measure the length of the object

[0048] c: Speed ​​of light propagating through the object being measured

[0049] Perform Fourier transform on the optical frequency response r~(ν) to obtain the backscattered light waveform r(τ).

[0050] [Mathematical formula 2]

[0051]

[0052] In addition, the optical frequency response r~(ν) is sampled in the optical frequency domain. For example, the sampling period is 1 / τ Aux = FSR, the maximum measurable delay (Nyquist frequency) is 1 / (2*FSR) = τ Aux . / 2. Therefore, the length of the reference interferometer 130 determines the size of the absolute distance that can be measured.

[0053] exist Figure 2 In the conventional method shown in FIG, since the delay of the local light is zero, Figure 3 As shown in , the beat frequency is distributed according to the delay amount (absolute distance) of the backscattered light. Figure 2 In the illustrated configuration, the 90-degree hybrid 21 is not required.

[0054] (Function of the optical 90-degree mixer 21)

[0055] In the present disclosure, the measurement distance is selected by applying a distance offset to the measurement distance using the delay fiber 40 of the local light. Figure 4 As shown, the backscattered light on the front and rear sides of the local light delay interferes. Although the beat frequency is distributed according to the relative distance, two locations with the same relative distance (two locations in front and behind with the local light delay as the symmetric point) have the same beat frequency. D The reflected light at a short distance has a negative beat frequency and is delayed by τ compared to the local light. D The long distance has a positive beat frequency. Therefore, the present disclosure uses the optical 90-degree hybrid 21 and BPD22 to detect the in-phase component and the orthogonal component of the beat signal respectively. In this way, it is possible to determine whether the beat frequency is positive or negative and whether it is delayed by τ D Short or long.

[0056] The optical frequency response of the present disclosure can be expressed by the following formula:

[0057] [Mathematical formula 3]

[0058]

[0059]

[0060]

[0061] The parameters are as follows.

[0062] r(τ R ): reflection coefficient

[0063] LD : Delay fiber length of local light

[0064] τ R : Relative delay based on the delay imparted by the local optical fiber

[0065] z R : Relative length based on the delay fiber length of the local light

[0066] Therefore, in the present disclosure, the delay amount τ Aux .Determine the maximum relative delay τ that can be measured R The measurable delay range is |τ R |<τ Aux / 2, and the optical frequency response within the range of Mathematical Formula 4 is measured for the relative distance zR.

[0067] [Formula 4]

[0068] |zL D / 2|≤cτ Aux . / 4 (4)

[0069] Thus, in this disclosure, the delay τ in the reference interferometer 30 is referred to as Aux .Determines the size of the measurable relative distance.

[0070] (Function of Local Optical Delay Fiber 40)

[0071] In the present disclosure, not only is a delay τ given to the local light Aux , and also gives the propagation delay τ D The wavelength dispersion at a corresponding fiber length generates a propagation delay τ D By making the copy interfere with the backscattered light in the 90-degree hybrid 21, wavelength dispersion can be compensated and the light from the delay τ can be selectively detected. D A beating signal of the surrounding backscattered light.

[0072] Furthermore, in this disclosure, the delay τ in the reference interferometer 30 is referred to as Aux Determines the relative distance that can be measured. Therefore, even when measuring long distances where the fiber 92 to be measured exceeds the coherence length of the laser, a reference interferometer 30 shorter than the coherence length of the laser can be used. Therefore, the present disclosure does not degrade the quality of the clock signal.

[0073] Figure 5 Indicates the use of Figure 2 An example of a frequency spectrum measured by a structure of . In A / D124, the beat frequency f corresponding to the absolute distance z is observed. beat .

[0074] Figure 6 An example of a spectrum measured using the structure of the present disclosure is shown in FIG. In the present disclosure, the delay τ in the optical fiber 40 is observed with the local light delay. D The beat frequency f corresponding to the relative distance z of the reference beat .

[0075] (Achieve long-distance ultra-high spatial resolution measurement)

[0076] Figure 7 Figure 2 shows an example of Fresnel reflection measurement results at a distance of 3 km. It can be seen that reflections of 40 μm can be detected. Thus, according to the present disclosure, it is possible to measure distances exceeding kilometers with a spatial resolution of 100 μm or less. This makes it possible to diagnose the health of optical equipment installed at long distances.

[0077] (Key Points of This Disclosure)

[0078] Ability to measure backscattered light at a relative distance relative to the local optical delay fiber.

[0079] The delay fiber serves as a reference distance for relative distance measurement and wavelength dispersion compensation.

[0080] By lengthening the local optical delay fiber, it is possible to measure backscattered light at long distances.

[0081] Furthermore, the signal processing device (not shown) included in the optical frequency domain reflectometry device of the present disclosure can be realized by a computer and a program. The program may be stored in a storage medium or provided via a network.

[0082] Possible industrial applications

[0083] The present disclosure can be applied to the information and communication industry.

[0084] Description of Reference Numerals

[0085] 11: TLS

[0086] 12, 14, 31, 34: Coupler

[0087] 13: Circulator

[0088] 21: 90 degree mixer

[0089] 22, 35, 122: BPD

[0090] 23, 123: LPF

[0091] 24, 124: A / D

[0092] 30, 130: Auxiliary interferometer

[0093] 32, 33: Transmission path

[0094] 91: Optical frequency domain reflectometry device

[0095] 92: Optical fiber to be tested.

Claims

1. Optical frequency domain reflectometry device, which is used for optical frequency domain reflectometry technology OFDR. The optical frequency domain reflectometry device includes: Local light delay fiber, which delays the local light; an optical 90-degree hybrid that inputs the local light delayed by the local optical delay fiber and the backscattered light from the measurement object, causes the local light and the backscattered light to interfere with each other, and generates an in-phase component and an orthogonal component of a beat signal generated by the interference; a balanced photoelectric detector for detecting an in-phase component and a quadrature component of the beat signal; an auxiliary interferometer, inputting another local light delayed by the local light delay optical fiber; and, An A / D conversion circuit converts an analog signal into a digital signal according to a sampling clock from the auxiliary interferometer; The device measures an optical frequency response of a measurement object with respect to a relative distance with respect to the local optical delay fiber.

2. The optical frequency domain reflectometry device according to claim 1, Based on the in-phase component and the quadrature component of the beat signal, the positive or negative of the beat frequency is determined.

3. Optical frequency domain reflectometry method, which is a method performed by an optical frequency domain reflectometry device. The optical frequency domain reflectometry device is a device used for optical frequency domain reflectometry technology OFDR, including: Local light delay fiber, which delays the local light; an optical 90-degree hybrid, which inputs the local light delayed by the local optical delay fiber and the backscattered light from the measurement object, and respectively outputs an in-phase component and an orthogonal component of a beat signal generated by the interference of the local light and the backscattered light; a balanced photoelectric detector for detecting an in-phase component and a quadrature component of the beat signal; an auxiliary interferometer, inputting another local light delayed by the local light delay optical fiber; and, An A / D conversion circuit converts an analog signal into a digital signal according to a sampling clock from the auxiliary interferometer; The method measures the optical frequency response of the measurement object with respect to the relative distance with respect to the local optical delay fiber.

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