JP2012150002A - Cutoff wavelength measuring method, operation mode determination method and apparatus for the methods - Google Patents

Abstract

PROBLEM TO BE SOLVED: To specify a cutoff wavelength even in an optical fiber in which a wavelength characteristic of a loss difference between a basic mode and a first higher order mode is easy.SOLUTION: A light wave of a predetermined wavelength is extracted from a light wave generated from a wide band light source 1 by a spectrometer 2, the extracted light wave is made to incident on one end of an optical fiber A to be measured, and based on optical power outputted from a light receiving part 4 when an aperture angle on a variable aperture 3 is successively changed in a state excited in a multimode, a mode field diameter is calculated. The calculation of the mode field diameter is repeated by changing the wavelength extracted by the spectrometer 2 to measure the wavelength characteristics of mode field diameters in multimode excitation. A higher order mode remover 7 is inserted between the spectrometer 2 and one end of the optical fiber A to be measured, the wavelength characteristics of mode field diameters in single mode excitation is similarly measured, and a wavelength indicating that a compared value between both the wavelength characteristics becomes a predetermined value is set as a cutoff wavelength.

Description

  The present invention relates to a technique for measuring a cutoff wavelength of an optical fiber and determining an operation mode of the optical fiber in an arbitrary wavelength band.

  In order to realize high-speed and wide-band optical transmission, a single mode fiber (SMF) that has one propagation mode in the used wavelength band and does not cause mode dispersion is widely used. In SMF, the mode field diameter (MFD), cut-off wavelength, and bending loss determined by the fiber structure are the main parameters, but cut-off wavelength is an important parameter to ensure single-mode transmission. Recently, single-mode characteristics called endlessly single mode, which can guarantee single-mode operation in any wavelength band, are known in optical fibers with a hole structure. Realization of ultra-high-capacity transmission by expanding the transmission wavelength band Is expected.

  Conventionally, a bending method and a multi-mode excitation method have been used to measure the cutoff wavelength. The wavelength characteristic of the loss difference between the fundamental mode and the first higher-order mode in the optical fiber is measured. The wavelength that changes to is specified as the cutoff wavelength. Patent Document 1 proposes a method of performing Far field pattern measurement at the time of off-axis excitation and confirming single mode operability at the measurement wavelength from the shape of the measurement result, and has a low bending loss with reduced bending loss. Applicable to fiber.

  However, in an optical fiber such as an optical fiber having a hole structure in which the leakage loss of the first higher-order mode changes gently with respect to the wavelength, it is difficult to specify the cutoff wavelength, that is, extract the wavelength at which the loss difference changes abruptly. In addition, it is possible to determine the operation mode at the wavelength from the measurement result of an arbitrary wavelength, that is, to determine whether the operation is a single mode (SM) operation or a multi mode (MM) operation. There was a problem that it was difficult. Moreover, when measuring in a wide wavelength band using the method of Patent Document 1, there is a problem that a plurality of light sources are required depending on the wavelength band to be measured.

  In the present invention, the wavelength characteristic of the mode field diameter at the time of single mode excitation and multimode excitation is measured using the well-known Variable Aperture (VA) method, and the both are compared, thereby solving the above-mentioned problem.

  According to the present invention, it is possible to specify a cutoff wavelength even for an optical fiber having a gradual wavelength characteristic of a loss difference between a fundamental mode and a first higher-order mode, such as a hole structure optical fiber, and an operation mode in an arbitrary wavelength band. It is possible to determine whether or not.

It is a block diagram which shows an example of embodiment of the cutoff wavelength measurement of this invention, and an operation mode determination apparatus. It is a characteristic view which shows an example of MFD calculated when the basic mode and 1st high-order mode in this invention apparatus are mixed. It is a characteristic view which shows an example of the measurement result of the cutoff wavelength by this invention apparatus. It is a characteristic view which shows the other example of the measurement result of the cut-off wavelength by this invention apparatus. It is a characteristic view which shows an example of the determination result of the operation mode by this invention apparatus. It is a characteristic view which shows an example of the relationship between the comparison value of MFD in this invention apparatus, and MPI. It is a flowchart which shows an example of the measurement procedure in this invention apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an example of an embodiment of a cutoff wavelength measurement and operation mode determination apparatus according to the present invention. In the figure, 1 is a broadband light source, 2 is a spectroscope, 3 is a variable aperture unit, 4 is A light receiving unit, 5 is a signal processing unit, 6 is a display unit, 7 is a high-order mode remover, 8 is an alignment table, and 9 is a lens.

  The broadband light source 1 generates a light wave over a relatively wide wavelength band, and a white light source, LED, SLD, SC light, or the like can be used. The spectroscope 2 extracts a light wave having an arbitrary wavelength for entering one end of the optical fiber to be measured, for example, A from the light wave emitted from the broadband light source 1.

  The variable opening 3 is installed between the other end of the measured optical fiber A and the light receiving unit 4 and arbitrarily sets the opening angle of the light wave emitted from the other end of the measured optical fiber A. The light receiving unit 4 receives a light wave emitted from the other end of the optical fiber A to be measured through the variable opening 3 and converts the light wave into an electric signal corresponding to the optical power. The signal processing unit 5 records the electrical signal output from the light receiving unit 4 and processes it as described later to perform the cutoff wavelength measurement and the operation mode determination. The display unit 6 displays the result processed by the signal processing unit 5.

  The high-order mode remover 7 is for removing high-order mode light from the output light of the spectroscope 2, and a single-mode optical fiber capable of single-mode operation in the measurement wavelength band can be used. As will be described later, the higher-order mode remover 7 is inserted between the spectroscope 2 and one end of the optical fiber A to be measured only when SM excitation is performed. The alignment base 8 is for aligning the other end of the optical fiber A to be measured to a predetermined position with respect to the variable opening 3, and the lens 9 receives the light wave that has passed through the variable opening 3 as the light receiving unit 4. For condensing light.

  In the above configuration, the light wave emitted from the broadband light source 1 is incident on one end of the optical fiber A to be measured after the spectroscope 2 extracts a light wave having a predetermined wavelength, for example, λ. A light wave propagating through the optical fiber A to be measured and emitted from the other end is narrowed to an arbitrary opening angle by the variable opening 3 and received by the light receiving unit 4, and the optical power at this time is recorded by the signal processing unit 5. The The aperture angle in the variable aperture 3 is sequentially changed, the optical power at each aperture angle is acquired, and based on these, it is converted to MFD at the wavelength λ by the following equations (1), (2), and (3).

Here, θ _i represents the aperture angle (i = 1, 2,... N), P (θ _i ) represents the optical power at the aperture angle θ _i , and 2W (λ) represents the MFD at the wavelength λ. The MFD measurement procedure and calculation procedure by the VA method are described in detail in Non-Patent Document 1.

  In the cutoff wavelength measurement and operation mode determination device of the present invention, the wavelength characteristic of the MFD is measured by changing the wavelength extracted by the spectrometer 2, for example, by changing the wavelength at a predetermined wavelength interval and repeating the same operation.

  Further, in the cutoff wavelength measurement and operation mode determination apparatus of the present invention, only the fundamental mode and the MFD wavelength characteristics in a state in which a plurality of modes can propagate (multi-mode excitation: MM excitation) are used as the wavelength characteristics of the MFD to be measured. The wavelength characteristics of the MFD in a state where propagation is possible (single mode excitation: SM excitation) is measured, and these are compared to identify the cutoff wavelength and determine the operation mode.

  Here, when performing MM excitation, a light wave is directly incident on one end of the optical fiber A to be measured from the spectroscope 2 by spatial coupling, or an optical fiber having a propagation mode number of 2 or more such as a multimode fiber is used. It is inserted between the spectroscope 2 and one end of the optical fiber A to be measured. When performing SM excitation, the higher-order mode remover 7 is inserted between the spectrometer 2 and one end of the optical fiber A to be measured. Here, when the higher-order mode remover 7 is composed of a single mode optical fiber, if the single mode optical fiber is bent, the cladding mode (light propagating through the cladding layer or coating) in the optical fiber is removed. This makes it possible to realize a stable single mode operation in the measurement wavelength band, thereby reducing errors in measurement results.

FIG. 2 is a characteristic diagram showing an example of MFD calculated when the fundamental mode and the first higher-order mode coexist in the cutoff wavelength measurement and operation mode determination device of the present invention. Here, the horizontal axis represents the ratio (P11 / P01) of the power P11 of the first higher-order mode (LP11) to the power P01 of the basic mode (LP01), and the vertical axis (left: solid line) is a mixture of both modes. It is MFD calculated | required by numerical calculation using the FFP moment of following formula (4) using electric field distribution (phi) (x, y). The vertical axis (right: broken line) is obtained at ₁₀ logs (W / W ₀ ) using MFD (2W ₀ ) at SM excitation (P11 / P01 = 0) and MFD (2W) of an arbitrary power ratio. Comparison value.

  The optical fiber to be measured was a single-mode fiber (SMF) having a step-type refractive index distribution with a core diameter 2a of 9.0 μm and a relative refractive index difference Δ of 0.35%, and a wavelength of 1200 nm. At the time of SM excitation where P11 / P01 = 0, the MFD was 8.83 μm.

  Further, FIG. 2 shows that the calculated MFD decreases as P11 / P01 increases. This is because the electric field distribution φ (x, y) in the equation (4) changes due to the addition of the electric field distribution of LP11, and the change in the electric field distribution particularly near the center of the fiber becomes large. Due to the increase. The state where LP01 and LP11 are mixed corresponds to MM excitation in the measurement.

  Here, in the single mode operation region, the higher order mode cannot be propagated, so that it immediately leaks, and even when MM excitation is performed in the wavelength band, only the fundamental mode is emitted at the light receiving end. That is, when MFD is measured by SM excitation and MM excitation, both show the same measurement result in the single mode operation region, and both show different results in the multimode operation region. Therefore, by measuring the MFD in each of the SM excitation and the MM excitation shown in FIG. 1 and detecting the difference between the measured values of each MFD, it is possible to determine single mode operation or multimode operation at the measurement wavelength.

  Next, an example of measuring the cutoff wavelength using the present invention is shown.

  FIG. 3 is a characteristic diagram showing an example of a measurement result obtained by the cutoff wavelength measurement and operation mode determination device of the present invention. Here, the optical fiber to be measured was a general 1.3 μm band SMF, and the length was 22 m.

  FIG. 3A shows a measurement result using the conventional MM excitation method. In the MM excitation method, the output light power of the optical fiber to be measured and the output light power of the multimode fiber are compared, and a straight line that is translated by +0.1 dB is drawn from a straight line approximating the power difference between the two in the long wavelength band. And the intersection of the measurement results is specified as the cutoff wavelength. From FIG. 3A, the cutoff wavelength of the SMF used here is specified as 1184 nm.

FIG.3 (b) shows the measurement result using the cutoff wavelength measuring method of this invention. Here, □ and ◇ in the figure represent MFD measurement results W _SM and W _MM at the time of SM excitation and MM excitation, respectively, and ● represents the ratio 10 log (W _MM / W _SM ) of both measurement results. In FIG. 3B, the same MFD value is obtained under each excitation condition at a wavelength of 1200 nm or more, and the ratio of both represented by ● is 0.1 dB or less, but changes in the wavelength band of 1180 to 1200 nm. It turns out that it grows rapidly.

  In the single-mode operating wavelength band, the same MFD is theoretically obtained for SM excitation and MM excitation. Therefore, the difference in measurement results under each excitation condition is due to measurement accuracy. The accuracy is considered to be 0.1 dB or less. Therefore, it is considered that there is a difference in MFD measurement results due to multimode propagation at wavelengths less than 1200 nm. Accordingly, if the wavelength at which the MFD ratio is −0.1 dB or less is in the multimode region, the cutoff wavelength is obtained as about 1200 nm from the intersection with the straight line having the MFD ratio of −0.1 dB shown by the broken line in FIG. It can be confirmed that the cutoff wavelength can be specified with the same accuracy as the conventional measurement method by the measurement method of the present invention. Although the case where MFD measurement is performed at a wavelength interval of 20 nm is shown here, the cutoff wavelength measurement can be performed with higher accuracy by measuring at a shorter interval.

  FIG. 4 is a characteristic diagram showing another example of a measurement result obtained by the cutoff wavelength measurement and operation mode determination device of the present invention. Here, the optical fiber to be measured is a hole assist type optical fiber in which bending loss is greatly improved by providing holes, and the length is 2 m.

  FIG. 4A shows the measurement result using the conventional MM excitation method. In FIG. 4A, the intersections of the solid line and the broken line are 1200 nm and 1300 nm, and many noise components are superimposed at wavelengths of 1200 to 1300 nm, making it difficult to determine single mode operation and to specify the cutoff wavelength. It is.

  FIG. 4 (b) shows the measurement results using the cutoff wavelength measuring method of the present invention, and the legend in the figure is the same as FIG. 3 (b). In FIG. 4B, on the long wavelength side, the ratio of MFD in SM excitation and MM excitation represented by ● is a difference within the measurement accuracy (± 0.1 dB) obtained in FIG. The MFD ratio monotonously decreased in the wavelength band below 1340 nm. Therefore, as in FIG. 3B, when the wavelength at which the MFD ratio is −0.1 dB or less is considered to be a multimode region, the cutoff wavelength is about 1330 nm in FIG. 4B. Furthermore, compared with the conventional MM excitation method, the noise component near the cutoff wavelength is small, and the error in specifying the cutoff wavelength can be reduced. Therefore, it can be understood that the cutoff wavelength of the low bending loss optical fiber including the hole-assisted optical fiber can be specified with high accuracy by the measurement method of the present invention.

  Next, an operation mode determination method using the present invention and a transmission characteristic estimation method using the determination result will be described.

  FIG. 5 is a characteristic diagram showing an example of the measurement result of the operation mode by the cutoff wavelength measurement and operation mode determination device of the present invention. Here, two types of photonic crystal fibers (PCF) (PCF-1 and PCF-2) having a plurality of holes in uniform pure silica glass were used as the optical fiber to be measured, and the length was 2 m. The ratio d / Λ between the hole diameter d of PCF-1 and the pitch Λ between holes is about 0.31, and the endlessly single-mode condition (d / Λ <0.43) described in Non-Patent Document 2 is satisfied. Fulfill. That is, PCF-1 does not have a cutoff wavelength, and can realize single mode operation at an arbitrary wavelength. On the other hand, d / Λ of PCF-2 is about 0.73, and it is estimated from Non-Patent Document 2 that multimode operation is performed at an arbitrary wavelength. 5 (a) and 5 (b) show measurement results using the conventional MM excitation method and the measurement method of the present invention, respectively.

  In FIG. 5A, the cutoff wavelength cannot be specified because there is no wavelength at which the loss difference between the fundamental mode and the higher-order mode changes in the measurement wavelength band (1000 to 1600 nm) with respect to PCF-1 and PCF-2. Furthermore, single mode operation in the measurement wavelength band cannot be determined. On the other hand, in FIG. 5B, there is no cutoff wavelength in the measurement wavelength band because the wavelength at which the difference in MFD between SM excitation and MM excitation changes does not exist in either PCF-1 or PCF-2.

  In PCF-1, both MFDs coincided over the entire measurement wavelength band, and the MFD ratio was in a range of ± 0.1 dB. However, in PCF-2, MFDs did not coincide at any wavelength, and the MFD ratio was −0.1. It was less than dB. Therefore, it can be determined that PCF-1 is a single mode operation in the measurement wavelength band and PCF-2 is a multimode operation.

  From these results, using the cutoff wavelength measurement and operation mode determination device of the present invention, focusing on the presence or absence of MFD deviation due to the difference in excitation conditions or the change in MFD ratio, determination of the operation mode that could not be determined conventionally It can be performed.

  As described above, high-speed transmission by single mode transmission can be guaranteed in the wavelength band determined to be single mode. On the other hand, in the wavelength band determined to be multimode operation, it is possible to estimate the transmission characteristics using the MFD comparison value. According to Non-Patent Document 3, multi-path interference (MPI) can be calculated by the following equation (5) using a temporal variation amount ΔP of received light power.

Here, it is known that the MPI is related to the transmission characteristic of the optical signal, and the transmission characteristic deteriorates as the MPI increases (for example, see Non-Patent Document 4).

  FIG. 6 shows the multi-path interference (MPI) obtained by calculation. Here, the optical fiber used for the calculation had the same structure as the SMF used for the calculation in FIG. 2, and the wavelength was 1200 nm. In the calculation, it is assumed that power fluctuation occurs between (P01−P11) and (P01 + P11) due to interference between the LP01 mode and the LP11 mode. The horizontal axis corresponds to the vertical axis (right) in FIG. 2, and the vertical axis represents the MPI obtained by the equation (5) using the ratio P11 / P01 between the LP01 mode and the LP11 mode.

  FIG. 6 shows that the MPI value increases as the obtained MFD value deviates from that during SM excitation, and the transmission characteristics deteriorate. Therefore, by using the value obtained by comparing the MFD during MM excitation and SM excitation, the power ratio between the LP01 mode and the LP11 mode is derived from the relationship shown in FIG. 2, and the MPI characteristic is calculated using equation (5). The transmission characteristics can be estimated by the method of the present invention.

  FIG. 7 is a flowchart showing an example of a measurement procedure in the cutoff wavelength measurement and operation mode determination apparatus of the present invention. MM excitation and SM excitation are performed, a light wave is incident on the optical fiber to be measured, and the wavelength characteristics of the MFD are measured using equations (1) to (3) (s1, s2). At this time, the order of measurement may be either MM excitation or SM excitation first. Next, the wavelength characteristics of the MFD obtained by the measurement are compared (s3).

At this time, if the MFD wavelength characteristics in the MM excitation and the SM excitation are 2 W _MM (λ) and 2 W _SM (λ), respectively, as a method of obtaining the comparison value R (λ),
Difference: 2W _MM (λ) -2W _SM (λ) (unit: μm),
Ratio: 2W _MM (λ) / 2W _SM (λ),
Log ratio: 10log10 (2W _MM (λ) / 2W _SM (λ)) (unit is dB),
There is a calculation method.

  In the present invention, since the cut-off wavelength is specified and the operation mode is determined by comparing both, the comparison method is not limited to the above three methods.

After acquiring R (λ), the cutoff wavelength is specified and the operation mode is determined using a predetermined threshold R _th (s4, s5). That is, when there is a wavelength λ that satisfies R (λ) = R _th , the wavelength is specified as λ (s6). Further, the wavelength band where R (λ) <R _th is determined as single mode operation, and the wavelength band where R (λ)> R _th is determined as multimode operation (s7, s8). Here, the threshold value for specifying the cutoff wavelength and the threshold value for determining the single mode operation and the multimode operation may be different values.

  The present invention can be used for a test for determining the cutoff wavelength or the operation mode of an optical fiber.

  1: broadband light source, 2: spectroscope, 3: variable aperture, 4: light receiving unit, 5: signal processing unit, 6: display unit, 7: higher-order mode remover, 8: alignment table, 9: lens, A: Optical fiber to be measured.

Japanese Patent No. 4322630

"Measurement methods and test procedures Mode field diameter," IEC 60793-1-45, 2001. M.Koshiba and K.Saitoh, "Applicability of classical optical fiber theories to holey fibers," Optics Letters, vol.29, no.15, pp.1739-1741, Aug. 2004. S.Ramachandran, etc, "Measurement of multipath interference in the coherent crosstalk regime," IEEE Photon. Technol. Lett., Vol.15, pp.1171-1173, 2003. C. Fukai, etc, "Relationship between optical wiring conditions and MPI degradation," OFC2010, OWA1, 2010.

Claims (4)

A broadband light source;
A spectroscope for extracting a light wave of an arbitrary wavelength to be incident on one end of an optical fiber to be measured from the light wave emitted from the broadband light source;
A variable opening for arbitrarily setting the opening angle of the light wave emitted from the other end of the optical fiber to be measured;
A light receiving unit that receives a light wave emitted from the other end of the optical fiber to be measured through the variable opening, and converts the light wave into an electric signal according to the optical power;
Using at least a signal processing unit that records and processes an electrical signal output from the light receiving unit,
By the signal processing unit,
A light receiving unit when a light wave of a predetermined wavelength is extracted from a light wave emitted from a broadband light source by a spectrograph and incident on one end of an optical fiber to be measured, and the aperture angle in the variable aperture is sequentially changed in a multimode excited state. Calculate the mode field diameter based on the optical power output from, and repeat this by changing the wavelength extracted by the spectrometer, and measure the wavelength characteristics of the mode field diameter during multi-mode excitation,
A light wave of a predetermined wavelength is extracted from the light wave emitted from a broadband light source by a spectrograph and incident on one end of the optical fiber to be measured, and received when the aperture angle at the variable aperture is sequentially changed in a single mode excited state. The mode field diameter is calculated based on the optical power output from the unit, and the wavelength characteristic of the mode field diameter at the time of single mode excitation is measured repeatedly by changing the wavelength extracted by the spectrometer,
Compare the wavelength characteristics of the mode field diameter during multimode excitation with the wavelength characteristics of the mode field diameter during single mode excitation.
A cutoff wavelength measurement method, wherein the cutoff wavelength is measured by measuring a wavelength at which the comparison value is a predetermined value. A broadband light source;
A spectroscope for extracting a light wave of an arbitrary wavelength to be incident on one end of an optical fiber to be measured from the light wave emitted from the broadband light source;
A variable opening for arbitrarily setting the opening angle of the light wave emitted from the other end of the optical fiber to be measured;
A light receiving unit that receives a light wave emitted from the other end of the optical fiber to be measured through the variable opening, and converts the light wave into an electric signal according to the optical power;
Using at least a signal processing unit that records and processes an electrical signal output from the light receiving unit,
By the signal processing unit,
A light receiving unit when a light wave of a predetermined wavelength is extracted from a light wave emitted from a broadband light source by a spectrograph and incident on one end of an optical fiber to be measured, and the aperture angle in the variable aperture is sequentially changed in a multimode excited state. Calculate the mode field diameter based on the optical power output from, and repeat this by changing the wavelength extracted by the spectrometer, and measure the wavelength characteristics of the mode field diameter during multi-mode excitation,
A light wave of a predetermined wavelength is extracted from the light wave emitted from a broadband light source by a spectrograph and incident on one end of the optical fiber to be measured, and received when the aperture angle at the variable aperture is sequentially changed in a single mode excited state. The mode field diameter is calculated based on the optical power output from the unit, and the wavelength characteristic of the mode field diameter at the time of single mode excitation is measured repeatedly by changing the wavelength extracted by the spectrometer,
Compare the wavelength characteristics of the mode field diameter during multimode excitation with the wavelength characteristics of the mode field diameter during single mode excitation.
By determining whether or not the comparison value is a predetermined value or less, it is determined whether the operation mode of the optical fiber under measurement is a single mode operation or a multimode operation in the measurement wavelength band. Judgment method. A broadband light source;
A spectroscope for extracting a light wave of an arbitrary wavelength to be incident on one end of an optical fiber to be measured from the light wave emitted from the broadband light source;
A variable opening for arbitrarily setting the opening angle of the light wave emitted from the other end of the optical fiber to be measured;
A light receiving unit that receives a light wave emitted from the other end of the optical fiber to be measured through the variable opening, and converts the light wave into an electric signal according to the optical power;
A signal processing unit that records and processes an electrical signal output from the light receiving unit;
The signal processing unit extracts a light wave having a predetermined wavelength from a light wave emitted from a broadband light source by a spectroscope, and enters the one end of the optical fiber to be measured. Means for calculating the mode field diameter based on the optical power output from the light receiving unit when it is sequentially changed, and measuring the wavelength characteristics of the mode field diameter during multi-mode excitation by changing the wavelength extracted by the spectrometer When,
A light wave of a predetermined wavelength is extracted from the light wave emitted from a broadband light source by a spectrograph and incident on one end of the optical fiber to be measured, and received when the aperture angle at the variable aperture is sequentially changed in a single mode excited state. Calculating the mode field diameter based on the optical power output from the unit, changing the wavelength extracted by the spectrometer, and repeating the measurement to measure the wavelength characteristics of the mode field diameter during single mode excitation;
Means for comparing the wavelength characteristics of the mode field diameter during multi-mode excitation with the wavelength characteristics of the mode field diameter during single-mode excitation;
And a means for measuring a cutoff wavelength by measuring a wavelength at which the comparison value is a predetermined value. A broadband light source;
A spectroscope for extracting a light wave of an arbitrary wavelength to be incident on one end of an optical fiber to be measured from the light wave emitted from the broadband light source;
A variable opening for arbitrarily setting the opening angle of the light wave emitted from the other end of the optical fiber to be measured;
A light receiving unit that receives a light wave emitted from the other end of the optical fiber to be measured through the variable opening, and converts the light wave into an electric signal according to the optical power;
A signal processing unit that records and processes an electrical signal output from the light receiving unit;
The signal processing unit extracts a light wave having a predetermined wavelength from a light wave emitted from a broadband light source by a spectroscope, and enters the one end of the optical fiber to be measured. Means for calculating the mode field diameter based on the optical power output from the light receiving unit when it is sequentially changed, and measuring the wavelength characteristics of the mode field diameter during multi-mode excitation by changing the wavelength extracted by the spectrometer When,
A light wave of a predetermined wavelength is extracted from the light wave emitted from a broadband light source by a spectrograph and incident on one end of the optical fiber to be measured, and received when the aperture angle at the variable aperture is sequentially changed in a single mode excited state. Calculating the mode field diameter based on the optical power output from the unit, changing the wavelength extracted by the spectrometer, and repeating the measurement to measure the wavelength characteristics of the mode field diameter during single mode excitation;
Means for comparing the wavelength characteristics of the mode field diameter during multi-mode excitation with the wavelength characteristics of the mode field diameter during single-mode excitation;
Means for determining whether the operation mode of the optical fiber under measurement is a single mode operation or a multimode operation in the measurement wavelength band by determining whether or not the comparison value is equal to or less than a predetermined value. An operation mode determination device.

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