JPH0875599A - Device for evaluating polarization characterisitics of polarization-preserving optical fiber - Google Patents

Abstract

PURPOSE: To provide a polarization characteristics evaluation device for quickly and accurately evaluating the polarization characteristics of a polarization- preserving optical fiber. CONSTITUTION: The evaluting device is provided with a light source 21 for emitting continuous light with a wavelength width of 3nm or longer, a polarizer 4 for applying a linear polarization to an optical fiber 5 to be measured with the continuous light as the linear polarization with a specific polarization surface, an analyzer 6 for emitting light by changing the intensity of transmission light of the optical fiber 5 to be measured, and a light intensity detection means 22 for detecting the maximum light intensity and the minimum light intensity of transmission light to be emitted from the analyzer 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization characteristic of a polarization maintaining optical fiber suitable for use in evaluating polarization characteristics such as polarization crosstalk and mode birefringence of a polarization maintaining optical fiber. The present invention relates to a sex evaluation device.

[0002]

2. Description of the Related Art Conventionally, a polarization-maintaining optical fiber has been widely used for connection between a sensing coil of an optical fiber gyroscope and an optical circuit having polarization dependency. Highly accurate evaluation of polarization characteristics such as polarization crosstalk and mode birefringence of this polarization maintaining optical fiber is important for quality control and quality assurance of the polarization maintaining optical fiber.
Further, in order to reduce the manufacturing cost of the polarization maintaining optical fiber, it is necessary to evaluate the polarization characteristics at high speed. In addition, when the polarization-maintaining optical fiber is coiled or the end is processed, the polarization crosstalk generally deteriorates compared to the bare state. And it is important to evaluate with high accuracy.

Polarization crosstalk expresses the linear polarization maintaining ability of a polarization maintaining optical fiber, and has two linear polarization modes of the polarization maintaining optical fiber, namely, HE ^X ₁₁ mode and HE ^Y ₁₁ mode. It is represented by the power ratio of both modes at the exit end of the optical fiber when only one of them is excited. In this polarization crosstalk, a linearly polarized light whose polarization direction is aligned with one principal axis direction of the optical fiber is incident on the incident end of the polarization maintaining optical fiber by using an appropriate polarizer, and the analyzer etc. Is calculated by measuring the intensity ratio of two orthogonal components of linearly polarized light emitted from the emission end of the optical fiber.

FIG. 8 is a schematic configuration diagram showing a conventional polarization crosstalk measuring apparatus (A). In the figure, 1 is a light source for emitting continuous light, 2 is a condenser lens, and 3 is the continuous light. A wave plate (or a phase compensating plate) for converting into circularly polarized light, 4 is a polarizer composed of a Glan-Thompson prism for converting the continuous light into linearly polarized light having a predetermined plane of polarization, and 5 is measured light for measuring polarization characteristics. Reference numeral 6 denotes a fiber, 6 is an analyzer including a Glan-Thompson prism which emits light by changing the light intensity of the transmitted light of the optical fiber 5 to be measured, and 7 is a power meter capable of highly accurate light intensity measurement.

In order to obtain the polarization crosstalk of the polarization maintaining optical fiber by using this polarization crosstalk measuring device (A), first, the optical intensity of the transmitted light of the analyzer 6 is minimized. Rotate the photon 6 and the polarizer 4 and then the polarizer 4
Fixed and rotating the analyzer 6 around the optical axis, and using the power meter 7 the minimum light intensity of the transmitted light passing through the analyzer 6 and the transmitted light when the analyzer 6 is further rotated by 90 degrees. The maximum light intensity is measured and the ratio of this minimum light intensity to the maximum light intensity (this is called extinction ratio) is obtained. This polarization crosstalk measuring device (A) has an advantage that the dynamic range is wide.

FIG. 9 is a schematic configuration diagram showing a conventional polarization crosstalk measuring apparatus (B). The same components as those of the above polarization crosstalk measuring apparatus (A) are designated by the same reference numerals. is there. In the figure, 8 is an optoelectronic (OE) converter. In order to obtain the polarization crosstalk of the polarization-maintaining optical fiber using this polarization crosstalk measuring device (B), the analyzer 6 is transmitted at a constant rotation speed. The polarizer 4 is rotated so that the fluctuation range of the light intensity of the transmitted light is maximized, the maximum value and the minimum value of the light intensity at this time are measured by the photoelectric converter 8, and the ratio of the maximum value and the minimum value is calculated. Ask. This polarization crosstalk measuring device (B) has an advantage that high-speed measurement is possible.

FIG. 10 is a schematic configuration diagram showing a conventional polarization crosstalk measuring apparatus (C). In the figure, 9 is a high coherency light source and 10 is a Stokes analyzer (polarization analyzer). In this polarization crosstalk measuring device (C), when the polarization-maintaining optical fiber is expanded or contracted, points on the Poincare sphere draw a locus of a circle. Therefore, when the polarizer 4 is adjusted so that the radius of this circle is minimized. , R is the radius of this circle, and polarization crosstalk is obtained by the following equation. CT = 10 · log [{1- (1-R ² ) ^1/2 } / {1+ (1 + R ² ) ^1/2 }] (1) This polarization crosstalk measuring device (C) is capable of high-speed measurement. It has the feature of being possible.

On the other hand, the mode birefringence is represented by the difference in equivalent refractive index between the HE ^X ₁₁ mode and the HE ^Y ₁₁ mode which are two linear polarization modes. For example, when both modes are excited at the entrance end of the polarization-maintaining optical fiber, the respective light intensities when the analyzer 6 is set at 45 degrees with respect to the optical axis at the exit end of the optical fiber are I _a and I a. _{Assuming b} , the phase difference φ between the HE ^X ₁₁ mode and the HE ^Y ₁₁ mode at the exit end is expressed by the following formula. cos φ = (I _a −I _b ) / (I _a + I _b ) ... (2) Here, when the mode birefringence is B, the wavelength of light is λ, and the fiber length is 1, the phase difference φ is obtained. The following relationship is established with the mode birefringence B. φ = 2πBl / λ (3) Therefore, the modal birefringence B can be obtained by measuring one cycle of cosφ by changing either the wavelength λ or the fiber length l.

As a method of changing the fiber length l,
Method of actually cutting the fiber (cutback method)
Then, there is a method in which the Faraday effect and the lateral pressure on the fiber cause mode coupling of two orthogonal polarizations, and the position of this mode coupling is changed to change the fiber length equivalently. On the other hand, the wavelength sweep method for changing the wavelength λ is widely used because it is simpler and more reproducible than the above method. At this time, the following relationship is established between the phase change Δφ and the wavelength change Δλ. Δφ = −2πB1 · Δλ / λ ² + (2πl / λ) · (dB / dλ) · Δλ (4) In this equation (3), if the wavelength dependence of the mode birefringence B is ignored, The change Δφ is expressed as Δφ to −2πB1 · Δλ / λ ² (5).

Here, the wavelength interval that gives one cycle of cosφ in equation (1) is Δλ, and in equation (5) Δφ = 2π
Then, B = λ ² / (Δλ · l) (6), and the mode birefringence B can be obtained by measuring the wavelength interval Δλ.

As a method of changing the wavelength λ, the following various methods have been proposed and put to practical use. Method (a): A method of changing the wavelength of light incident on the polarization maintaining optical fiber by using a DFB laser or a wavelength tunable laser. Method (b): A method of performing wavelength sweep by dispersing the emitted light from the white light source through a spectroscope. Method (c): A method of performing wavelength sweep by using a multimode laser and dispersing the transmitted light of the analyzer with an optical spectrum analyzer or the like.

[0012]

The above-mentioned polarization crosstalk measuring device (A) is characterized by the fact that its measuring method is the most faithful to the principle and has a wide dynamic range. There was a problem. 1) In general, since there is mode coupling between the HE ^X ₁₁ mode and the HE ^Y ₁₁ mode, which are two linear polarization modes of a polarization maintaining optical fiber, the polarization crosstalk has a distribution shape of the mode coupling. It depends on the coherency of the light source. Therefore, even when the polarizer and the analyzer are adjusted at high speed to measure the crosstalk, the value fluctuates for each measurement.
Multiple measurements must be taken and these measurements averaged. 2) In order to make the intensity of the light incident on the optical fiber 5 to be measured constant when the polarizer 4 is rotated, a wavelength plate (or a phase compensating plate) 3 is arranged on the incident side of the polarizer 4 and a light source is provided. Although the continuous light emitted from No. 1 is converted into circularly polarized light, the one using the wavelength plate 3 cannot use the light source having a different wavelength, and the one using the phase compensating plate from the light source 1 This must be adjusted each time the wavelength of the emitted continuous light is changed.

Further, in the polarization crosstalk measuring device (B), the crosstalk is -40 dB or less when the polarization maintaining optical fiber is short, but even when the photodetector has a wide dynamic range. However, there is a problem that the change of 40 dB cannot be detected with high accuracy without changing the amplification factor of the amplifier, and the applicable fiber is limited. Also, polarization crosstalk measuring device (C)
Then, there is a problem that the light source 9 having high coherency is required, and the use range of the polarization crosstalk measuring apparatus (C) is limited.

On the other hand, a method (a) for obtaining the mode birefringence
Therefore, DFB lasers or wavelength tunable lasers have high coherency, and when measuring modal birefringence and polarization crosstalk using the same device, it is necessary to replace these lasers with light sources with lower coherence. Adjustments have to be made each time it is changed, which is very troublesome.

In the method (b), since the white light source has a weak light intensity, the wavelength interval Δλ cannot be narrowed. Therefore, the resolution cannot be improved. l needs to be shortened,
There was a problem that it was very inconvenient. Furthermore, when attempting to measure polarization crosstalk using this white light source, the dynamic range is often insufficient. Therefore, when measuring polarization crosstalk using this device, it is necessary to replace the white light source with a light source having a wider dynamic range, and adjustments or the like must be performed each time the light source is changed, which is extremely There was a problem that it took time.

In the method (c), the measurement system is the same as the polarization crosstalk measuring apparatus (A) except for the photodetection system, and both polarization crosstalk and modal birefringence are adjusted without adjustment. However, in order to improve the measurement accuracy of the mode birefringence, the wavelength range should be wide and several cycles should be averaged. There was a problem that it was necessary to do so.

The present invention has been made in view of the above circumstances, and is to evaluate the polarization characteristics of a polarization-maintaining optical fiber in a short time and with high accuracy. The purpose is to provide an evaluation device.

[0018]

In order to solve the above problems, the present invention employs the following polarization characteristic evaluation apparatus for polarization maintaining optical fibers. That is, the polarization characteristic evaluation device for a polarization-maintaining optical fiber according to claim 1 is a light source that emits continuous light with a wavelength width of 3 nm or more, and the continuous light is linearly polarized light having a predetermined polarization plane. Polarizer for inputting polarized light to the optical fiber to be measured, analyzer for emitting by changing the light intensity of transmitted light of the optical fiber to be measured, and maximum and minimum light intensity of transmitted light emitted from the analyzer And a light intensity detecting means for detecting here,
The reason why the wavelength width of continuous light emitted from the light source is limited to 3 nm or more is that the variation of the measured value of the polarization crosstalk cannot be suppressed to about 0.1 dB or less when the wavelength width is less than 3 nm.

According to a second aspect of the present invention, there is provided a polarization characteristic evaluating apparatus for a polarization-maintaining optical fiber, wherein the light source emits continuous light having a wavelength width of 3 nm or more, and the continuous light is linearly polarized light having a predetermined plane of polarization. A polarizer that makes linearly polarized light incident on the optical fiber to be measured, an analyzer that emits light by changing the light intensity of the transmitted light of the optical fiber to be measured, and the transmitted light emitted from the analyzer is wavelength-split and wavelength swept. It is characterized in that it is provided with a wavelength spectroscopic means for performing.

According to a third aspect of the present invention, there is provided a polarization characteristic evaluation apparatus for a polarization maintaining optical fiber, wherein the light source emits continuous light having a wavelength width of 3 nm or more, and the continuous light is linearly polarized light having a predetermined plane of polarization. A polarizer that makes linearly polarized light incident on the optical fiber under measurement, an analyzer that emits light by changing the light intensity of the transmitted light of the optical fiber under measurement, and a maximum light intensity and a minimum light of the transmitted light emitted from the analyzer. A light intensity detecting means for detecting the intensity,
Wavelength spectroscopic means for wavelength-splitting the transmitted light emitted from the analyzer to perform wavelength sweeping is provided.

[0021]

In the polarization maintaining characteristic evaluation apparatus for the polarization maintaining optical fiber according to the first aspect of the present invention, the light source emits continuous light having a wavelength width of 3 nm or more. This averages the variation in the ratio between the minimum light intensity and the maximum light intensity of the transmitted light that passes through the analyzer,
The average value of polarization crosstalk can be measured with good reproducibility. Moreover, since a highly sensitive and highly accurate optical power meter can be used as the light intensity detecting means, the polarization crosstalk of the polarization maintaining optical fiber can be obtained with high accuracy and easily.

In the polarization characteristic evaluation apparatus for a polarization maintaining optical fiber according to a second aspect, the light source emits continuous light having a wavelength width of 3 nm or more. In addition, the wavelength spectroscopic means performs wavelength sweeping on the transmitted light emitted from the analyzer to perform wavelength sweeping. As a result, the sweep wavelengths during the wavelength sweep are continuous, and the mode birefringence can be accurately obtained. Further, since an optical spectrum analyzer with high sensitivity and high accuracy can be used as the wavelength spectroscopic means, the mode birefringence of the polarization maintaining optical fiber can be calculated with high accuracy and easily.

In the polarization characteristic evaluating apparatus for a polarization maintaining optical fiber according to a third aspect, the light source emits continuous light having a wavelength width of 3 nm or more, and the light intensity detecting means emits the transmitted light from the analyzer. The maximum and minimum light intensities of are detected. This makes it possible to obtain the polarization crosstalk of the polarization maintaining optical fiber with high accuracy. In addition, the wavelength spectroscopic means performs wavelength sweeping on the transmitted light emitted from the analyzer to perform wavelength sweeping. This makes it possible to freely select the sweep wavelength at the time of sweeping the wavelength and accurately obtain the mode birefringence.
Moreover, since the polarization crosstalk and the mode birefringence measuring system are the same, the adjustment work or the like that is conventionally required for changing the light source or the like is unnecessary, and the measurement can be performed in a short time.

[0024]

EXAMPLE A polarization characteristic evaluation apparatus for a polarization maintaining optical fiber according to the present invention will be described below. [First Embodiment] FIG. 1 is a schematic configuration diagram showing a polarization characteristic evaluation apparatus according to an embodiment of the present invention. In FIG. 1, the same components as those in FIGS. It is attached.
In the figure, 21 is a light source that emits continuous light having a wavelength width of 3 nm or more, 22 is a high-precision power meter (light intensity detection means), and 23 is a fiber depolarizer (inserted between the light source 21 and the polarizer 4). Depolarizer). When a light emitting diode (LED) is used as the light source 21, the degree of polarization of emitted light is small, and it is not always necessary to insert the fiber depolarizer 23 in adjusting the polarizer and the analyzer. However, in this case, it is necessary to take the average of the crosstalk of the HE ^X ₁₁ mode excitation and the crosstalk of the HE ^Y ₁₁ mode excitation to obtain the crosstalk. Also, the connecting fiber between the LED and the analyzer must not move.

Here, the spectral width of the light source 21 is set to 3 nm.
The reason for the above will be described. Here, taking the length l, a simple mode coupling system connecting a polarization-maintaining optical fiber at both ends of the polarization maintaining optical fiber mode birefringence B at an angle θ to the example, the center wavelength lambda ₀ as the light source 21, wavelength A light source having a Gaussian power spectrum of width δλ is used. In this case, if only the HE ^X ₁₁ mode of the two linear polarization modes is excited at the incident end of the polarization maintaining optical fiber,
The light intensity ratio η between HE ^X ₁₁ mode and HE ^Y ₁₁ mode is

[Equation 1] It is expressed as However,

[Equation 2] Represents the degree of coherence.

For example, since the mode birefringence index B of the stress-applied polarization-maintaining optical fiber has a temperature dependence of about 10 ⁻⁴ / ° C., the value of COSθ in the equation (6) is between 1 and −1. Fluctuates easily. Moreover, | γ | also fluctuates as the wavelength width δλ and the length l of the polarization-maintaining optical fiber fluctuate, and the polarization crosstalk (C
T) also fluctuates. Such polarization crosstalk (CT)
Fluctuations make high-speed polarization crosstalk measurement impossible, so usually, multiple measurements are performed to minimize the effect of this fluctuation, and the average value of polarization crosstalk is calculated. Is taken.

On the other hand, the average value of polarization crosstalk is | γ
It is equal to the polarization crosstalk value when | = 0. Since the mode coupling of an actual optical fiber is an aggregate of such mode coupling, this model is appropriate as the minimum unit that gives the fluctuation of polarization crosstalk.

Here, in order to determine the length 1 of the optical fiber, the terminal processing (connector attachment) of the polarization maintaining optical fiber, which is said to be the most severe condition, will be taken as an example. In a polarization-maintaining optical fiber that is not stressed,
E ^X ₁₁ mode, a normal mode based on the HE ^Y ₁₁ mode both, assuming that the mode coupling in both end portions occurs, short distance mode coupling occurred portions at both ends, with respect to the temperature change of the mode birefringence B And stable polarization crosstalk (CT) cannot be obtained. On the other hand, assuming that both ends are a normal mode system and mode coupling occurs in the intermediate optical fiber part, the length l of the optical fiber is about 1 m. FIG. 2 shows the relationship between the full width at half maximum (wavelength width) of the light source and the crosstalk variation when the length 1 of the optical fiber is 1 m and the angle θ is 5 degrees.

Taking the above into consideration, the spectrum width of the light source 21 for suppressing the fluctuation of the polarization crosstalk within 0.1 dB is obtained by the equations (6) and (7).
It becomes 3.5 nm or more. Therefore, in order to suppress the fluctuation of polarization crosstalk within 0.1 dB, 3.5n
It can be seen that the light source 21 having a spectrum width of m or more is required.

In fact, among easily available light sources, light sources satisfying this condition include a multimode laser diode (LD) and a light emitting diode (LED). In the multimode laser diode, as shown in FIG. 3, the spectrum envelope has a wide wavelength width, but the width of each spectrum is narrow. │γ│ generally indicates a short-period attenuation determined by the interval of the spectrum as the fiber length 1 increases, and the envelope in FIG. 3 is determined by each spectrum width. Therefore, the light source is not always stable. Further, also in the light emitting diode, if the wavelength width becomes too wide, the higher order mode of the polarization maintaining optical fiber is excited, and the polarization crosstalk cannot be accurately measured. As described above, as the light source 21, the edge emitting type light emitting diode (LED) and the wavelength width of 20 to 30 are used.
A combination with a bandpass filter (BPF) of about nm is most suitable.

Table 1 shows the average value and variation range of the polarization crosstalk (CT) when the light source 21 and the optical fiber 5 to be measured are variously changed in the polarization characteristic evaluation apparatus of this embodiment. Is the one that was investigated.

[Table 1]

Here, the light source A (embodiment) is a light emitting diode (LE) having a full width at half maximum (FWHM) of 28.7 nm.
D), the light source B (comparative example) has a full width at half maximum (FWHM) of 3.
Fabry-Perot type laser diode of 9nm (FP-L
D) and the light source C (comparative example) were external cavity laser diodes (FP-LD) with Δf of about 10 MHz. Moreover, as the optical fiber 5 to be measured, three types of optical fibers a, b, and c having different mode couplings were used. The light sources A and B were measured 30 times, and the time average of polarization crosstalk and the fluctuation range were obtained. Regarding the light source C, the time variation of the light intensity was recorded after the polarizer 4 and the analyzer 6 were set to the extinction position with the light source A set, and then the time average and the variation width of the polarization crosstalk were obtained. .

From the above results, it was revealed that the time average value of polarization crosstalk does not depend on the spectral width of the light sources A to C. Regarding the fluctuation range of the polarization crosstalk, the fluctuation range of the light source A is smaller than that of the light sources B and C, and in particular, it is smaller by one digit or more in the case of the fiber c. It was revealed that a stable time average value of polarization crosstalk can be obtained by the measurement.

As described above, according to the polarization characteristic evaluation apparatus of the present embodiment, since the light source 21 which emits continuous light having a wavelength width of 3 nm or more and the high precision power meter 22 are provided, it is possible to detect the polarization characteristic. It is possible to average fluctuations in the ratio of the minimum light intensity and the maximum light intensity of the transmitted light that passes through the photon 6, and obtain a stable average value of polarization crosstalk. Therefore,
Polarization crosstalk of polarization-maintaining optical fiber can be measured with high accuracy. Further, since the fiber depolarizer (depolarizer) 23 is inserted between the light source 21 and the polarizer 4, adjustment is not necessary even when the light source 21 is replaced with another light source having a different wavelength, and the time is short. The measurement can be performed at.

[Second Embodiment] FIG. 4 is a schematic block diagram showing a polarization characteristic evaluation apparatus according to a second embodiment of the present invention. In the drawing, 31 denotes the wavelength of transmitted light emitted from the analyzer 6. It is an optical spectrum analyzer (wavelength spectroscopic means) that performs spectral sweeping.

In addition to the effects of the first embodiment described above, this polarization characteristic evaluation device has a continuous sweep wavelength during wavelength sweep,
It is possible to accurately determine the mode birefringence. Further, by disposing a wavelength multiplexer between the light source 21 and the fiber depolarizer 23, it is possible to save the trouble of changing the light source 21. FIG. 5 is a diagram showing an example in which the mode birefringence B of the measured optical fiber 5 having a fiber length 1 of 520 mm is measured by using this polarization characteristic evaluation apparatus. It is easily required that the refractive index B is 4.64 × 10 ⁻⁴ .

[Third Embodiment] FIG. 6 is a schematic configuration diagram showing a polarization characteristic evaluation apparatus according to a third embodiment of the present invention. In the figure, 41 emits light having a wavelength of 1.3 μm. Light emitting diode (LED), 42 is a light emitting diode (LED) that emits light having a wavelength of 1.55 μm, 43 is a wavelength multiplexing / branching coupler, 44 is a single mode (SM) optical fiber, 4
Reference numerals 5 and 46 are multi-mode (MM) optical fibers, 47 is a light receiving unit, and 48 is a calculation storage unit.

In this polarization characteristic evaluation apparatus, the wavelength multiplexing / branching coupler 43 is used to detect light having a wavelength of 1.3 μm and 1.55 μm.
Of the multi-mode optical fiber 4
Since it is connected to the measurement entrance end by 5, the optical axis adjustment and the adjustment of the wavelength plate, the phase compensation plate, etc. are not required even if the LED 41 and the LED 42 are individually turned on or off and switched. Further, by appropriately connecting the emission end of the multimode optical fiber 45 to either the optical spectrum analyzer 31 or the multimode optical fiber 46,
It is possible to measure the characteristics of either mode birefringence or polarization crosstalk in a short time with high accuracy. As described above, the same device can be used to measure the mode birefringence and polarization crosstalk of the polarization-maintaining optical fiber in a short time and with high accuracy.

[Fourth Embodiment] FIG. 7 is a schematic configuration diagram showing a polarization characteristic evaluation apparatus according to a fourth embodiment of the present invention. In the figure, 51 and 52 are optical switches.

In this polarization characteristic evaluation apparatus, the optical switch 5
1 selects one of the light having a wavelength of 1.3 μm and the light having a wavelength of 1.55 μm, and the fiber depolarizer 23
Since the polarization of the light is canceled by and the multimode optical fiber 45 is connected to the measurement entrance end, the optical axis adjustment,
There is no need to adjust the wave plate or phase compensator. Further, by appropriately connecting the emitting end of the multimode optical fiber 45 to either the optical spectrum analyzer 31 or the multimode optical fiber 46 by using the optical switch 52, either the mode birefringence or the polarization crosstalk can be obtained. The characteristics can be measured with high accuracy in a short time. As described above, the same device can be used to measure the mode birefringence and polarization crosstalk of the polarization-maintaining optical fiber in a short time and with high accuracy.

[0041]

As described above, according to the first aspect of the present invention.
According to the polarization characteristic evaluation device for a polarization-maintaining optical fiber described above, a light source that emits continuous light with a wavelength width of 3 nm or more, and the continuous light as linearly polarized light having a predetermined plane of polarization A polarizer that is incident on a measurement optical fiber, an analyzer that changes the light intensity of the transmitted light of the measured optical fiber and emits the light, and a maximum light intensity and a minimum light intensity of the transmitted light that is emitted from the analyzer are detected. Since the light intensity detection means is provided, it is possible to average fluctuations in the ratio of the minimum light intensity and the maximum light intensity of the transmitted light that passes through the analyzer, and obtain a stable average value of polarization crosstalk. it can. Therefore, the polarization crosstalk of the polarization maintaining optical fiber can be measured with high accuracy.

According to the polarization characteristic evaluation apparatus for a polarization maintaining optical fiber of claim 2, a light source for emitting continuous light having a wavelength width of 3 nm or more and a linearly polarized light having the predetermined polarization plane for the continuous light. And a polarizer that makes the linearly polarized light incident on the optical fiber to be measured, an analyzer that emits light by changing the light intensity of the transmitted light of the optical fiber to be measured, and the transmitted light that is emitted from the analyzer is wavelength-split Since the wavelength spectral means for performing the sweep is provided, the sweep wavelength at the time of wavelength sweep can be freely selected, and the mode birefringence can be accurately obtained.

According to the polarization characteristic evaluation apparatus for a polarization maintaining optical fiber of claim 3, a light source for emitting continuous light having a wavelength width of 3 nm or more, and a linearly polarized light having the predetermined polarization plane for the continuous light. And a polarizer that makes the linearly polarized light incident on the optical fiber to be measured, an analyzer that outputs by changing the light intensity of the transmitted light of the optical fiber to be measured, and a maximum light intensity of the transmitted light that is emitted from the analyzer and Since the light intensity detecting means for detecting the minimum light intensity and the wavelength spectroscopic means for performing wavelength sweeping on the transmitted light emitted from the analyzer are wavelength-swept, the minimum light intensity and the maximum of the transmitted light passing through the analyzer are provided. It is possible to average fluctuations in the ratio of the light intensities and obtain a stable average value of polarization crosstalk. Further, the sweep wavelength at the time of wavelength sweep can be freely selected, and the mode birefringence can be accurately obtained. Therefore, it is possible to measure the polarization crosstalk and the mode birefringence of the polarization maintaining optical fiber in a short time with high accuracy using the same device. Also, 3n
Since continuous light having a wavelength width of m or more is used, polarization crosstalk and modal birefringence can be measured without replacing the light source, and both measurements can be performed in a short time.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a polarization characteristic evaluation apparatus for a polarization maintaining optical fiber according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a full width at half maximum of a light source and a crosstalk fluctuation amount of an optical fiber.

FIG. 3 is a diagram showing a relationship between a standardized light wavelength and a coherence function of a multimode laser diode.

FIG. 4 is a schematic configuration diagram showing a polarization characteristic evaluation apparatus for a polarization maintaining optical fiber according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an example in which the mode birefringence of the optical fiber under test is measured by the polarization characteristic evaluation apparatus for the polarization maintaining optical fiber according to the second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram showing a polarization characteristic evaluation device for a polarization maintaining optical fiber according to a third embodiment of the present invention.

FIG. 7 is a schematic configuration diagram showing a polarization characteristic evaluation device for a polarization maintaining optical fiber according to a fourth embodiment of the present invention.

FIG. 8 is a schematic configuration diagram showing a conventional polarization crosstalk measuring device (A).

FIG. 9 is a schematic configuration diagram showing a conventional polarization crosstalk measuring device (B).

FIG. 10 is a schematic configuration diagram showing a conventional polarization crosstalk measuring device (C).

[Explanation of symbols]

4 ... Polarizer, 5 ... Optical fiber to be measured, 6 ... Analyzer, 21
... light source, 22 ... high-accuracy power meter (light intensity detection means), 23 ... fiber depolarizer (depolarizer), 3
1 ... Optical spectrum analyzer (wavelength spectroscopic means), 4
1, 42 ... Light emitting diode (LED), 43 ... Wavelength multiplexing / branching coupler, 44 ... Single mode optical fiber, 45,
46 ... Multimode optical fiber, 47 ... Light receiving part, 48 ...
Calculation storage unit, 51, 52 ... Optical switch.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryozo Yamauchi 1440 Rokuzaki, Sakura City, Chiba Fujikura Ltd. Sakura Factory

Claims (3)

[Claims] 1. A light source that emits continuous light having a wavelength width of 3 nm or more, a polarizer that makes the continuous light linearly polarized light having a predetermined plane of polarization, and makes the linearly polarized light incident on an optical fiber to be measured, and the measured object. An analyzer that changes the light intensity of the transmitted light of the optical fiber and emits the light, and a light intensity detection unit that detects the maximum light intensity and the minimum light intensity of the transmitted light emitted from the analyzer. Polarization characteristics evaluation device for polarization maintaining optical fiber. 2. A light source that emits continuous light having a wavelength width of 3 nm or more, a polarizer that makes the continuous light linearly polarized light having a predetermined plane of polarization, and makes the linearly polarized light incident on an optical fiber to be measured, Polarization-maintaining characterized by comprising an analyzer that emits light by changing the light intensity of the transmitted light of the optical fiber, and a wavelength spectroscopic means that performs wavelength sweeping of the transmitted light emitted from the analyzer to perform wavelength sweeping. Optical fiber polarization characteristics evaluation device. 3. A light source that emits continuous light having a wavelength width of 3 nm or more, a polarizer that makes the continuous light linearly polarized light having a predetermined plane of polarization, and makes the linearly polarized light incident on a measured optical fiber, and the measured object. An analyzer that changes the light intensity of the transmitted light of the optical fiber and emits the light, a light intensity detection unit that detects the maximum light intensity and the minimum light intensity of the transmitted light that is emitted from the analyzer, and a light transmission that is emitted from the analyzer. A polarization characteristics evaluation device for a polarization-maintaining optical fiber, comprising: a wavelength spectroscopy means for wavelength-splitting light and performing wavelength sweeping.