JPH0763669A - Polarization dependent loss measuring device, light source device for measuring polarization dependent loss and light reception device for measuring polarization dependent loss - Google Patents

Abstract

PURPOSE:To measure at a high-speed and in a high precision the loss which is dependent on polarization of light sources of various optical devices. CONSTITUTION:A light from a light source 1 is converted into a linearly polarized light through a polarizer 4. The linearly polarized light is made incident on a lambda/2 plate 5. The plate 5 is rotated at a constant speed and a lambda/4 plate 6 is rotated by the number of rotations step by step. Through such a operation, an entire polarization state can be obtained on the outgoing side of the plate 6. The optical signal is detected by an optical detector 9 through a measurement object device 8. The detector 9 detects an average level as the direct current element and emphasizes its changing quantity as the alternating signal for amplification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device for measuring a polarization dependent loss of an optical component or an optical transmission line, and a light source device and a light receiving device used for the measuring device.

[0002]

2. Description of the Related Art In recent years, an erbium-doped fiber amplifier (hereinafter referred to as EDFA) has been developed, and optical communication is making a great progress. With the development of this EDFA, a system using the EDFA is being considered not only for a submarine cable that is a long-distance, large-capacity communication line, but also for a terrestrial system that provides services such as CATV and ISDN. EDFA
In the optical communication system using the above, the regenerative repeater is not always necessary, and the relay in the optical form is more advantageous, and therefore, the communication system that directly amplifies and transmits the light is mainly used. However, in order to maintain the transmission characteristics without performing regenerative relay, it is necessary to manage the basic characteristics of the transmission system, which has not been a problem until now. For example, polarization dependent loss (polari
It is necessary to evaluate various basic parameters such as zation dependent loss (hereinafter referred to as PDL), chromatic dispersion, polarization dispersion, and non-linear characteristics for the transmission path, EDFA, optical parts, and the like. In particular, PDL, like PMD, is difficult to manage in terms of performance, so it is necessary to evaluate all of them. Also, not only long-distance and large-capacity transmission lines but also terrestrial systems with multiple branches will greatly affect the characteristics.

As a conventional PDL measuring method, a power meter method, a Poincare method, a Jones matrix method and the like are known as shown below. Here, the loss includes gain.

In the power meter method, a laser light source and a polarization compensator for compensating the plane of polarization of the laser light source and light obtained from the laser light source through the polarization compensator are incident on a measurement target, and an optical output obtained from the output side thereof. Is measured by a power meter, and the PDL is measured by changing the polarization plane of the polarization corrector, which is the most commonly used method. Then, arbitrary polarization is applied to the measurement sample, and the difference (dB scale) between the maximum loss and the minimum loss at that time is defined as PDL.

In the Poincare method, as shown in FIG. 14, the light from the light source 100 is converted into linearly polarized light by the polarizer 101, and is incident on the λ / 4 plate 102. Then, the light transmitted through the λ / 4 plate is incident on the λ / 2 plate 103, and the incident light is applied to the measurement target device 104 to detect its light intensity. Here, the λ / 4 plate and the λ / 2 plate are appropriately rotated to trace the surface on the Poincare sphere. In this way, it is a method of obtaining the difference between the maximum loss and the minimum loss of the polarization by using the real-time monitor using the Poincare sphere and the polarization compensator. In this method, the PD is checked while confirming the polarization state by the real-time monitor.
L can be measured. Then, it is possible to check whether or not the maximum and minimum values are at the opposite poles of the Poincare sphere by the marker.

In the Jones Matrices method, linear polarized waves of 0 °, 45 °, and 90 ° are made incident on an optical element to be tested from a light source, and PDL is calculated from a change in the obtained polarization state using a George matrix. Is a method of obtaining. With this method, high-speed measurement is possible, and since the maximum and minimum values of the loss on the opposite pole are calculated, results equivalent to PDL in all polarization states are obtained. (BL Heffner, “Deterministic, Analytica
lly Complete Measurement of Polarization-Dependent
Transmission Through Optical Devices "IEEE PHOT
ONICS TECHNOLOGY LETTERS. 4: 451-454, MAY, 1992)

[0007]

However, of these conventional methods, in the power meter method, the stability of the light source, the loss and fluctuation of the polarization compensator, the stability of the power meter, etc. are factors of error. Moreover, it is not possible to confirm whether or not all polarization states are obtained. Furthermore, there is a drawback that the measurement takes a long time regardless of whether it is automatic or manual.

On the other hand, in the Poincare method, a λ / 4 plate is generally λ
Since it is placed in front of the / 2 plate, the trajectory of the great circle cannot always be obtained on the Poincare sphere even if the λ / 2 plate is rotated. Further, like the power meter method, it is easily affected by the stability of the light source and the fluctuation of the loss of the polarization corrector. Further, in general, the Stokes analyzer has a lower accuracy than the power meter method and has a drawback that the measurement accuracy is low. Further, in the Jones matrix method, it is difficult to obtain sufficient accuracy because of the accuracy of linearly polarized light incident on the optical element to be tested, the stability of the light source, the accuracy of the detection system, and the error due to calculation. As described above, at present, there is no PDL measuring method that achieves both high speed and high accuracy.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a measuring device for measuring the loss of an optical device depending on the plane of polarization at high speed and with high accuracy. I am trying.

[0010]

According to a first aspect of the present invention, there is provided a polarization-dependent loss measuring device for detecting a polarization-dependent loss of light of an optical element, wherein the light source and the light of the light source are A first polarization controller that converts the polarization state of the incident light into a locus on a great circle represented by a Poincare sphere, and light from the first polarization controller is incident, A second polarization controller that controls the polarization plane of the incident light so as to cover the surface of the Poincare sphere by rotating the angle, and the light that has passed through the second polarization controller is incident on the measurement target, A light receiving unit that detects the intensity of light obtained through the measurement target, and a light receiving unit each time the polarization state of the light emitted from the second polarization controller makes at least one revolution of the great circle on the Poincare sphere. Intensity detecting means for detecting the DC level and the AC level of the signal obtained from the It is characterized in that it comprises a calculating means for calculating a polarization dependent loss based on the maximum value and the minimum value of the obtained by the detection means signals.

According to a second aspect of the present invention, the light source is a light source that generates a linearly polarized wave, and the first polarization controller receives light from the light source and the polarization state of the incident light is expressed by a Poincare sphere. In the invention according to claim 3, the light source is a light source in a specific polarization state that does not change with time, and the first polarization controller is Light from a light source is incident, and the polarization state of the incident light is converted into a locus on a meridian passing through the North Pole and the South Pole including a point represented by a Poincare sphere.

According to the invention of claim 4, the first polarization controller comprises a λ / 2 plate on which light from the light source is incident, and a λ / 2 plate.
A first rotation control means for rotating and driving the plate at that position is provided. In the invention according to claim 5, the first polarization controller applies an electro-optical element and an electro-optical element. Voltage applying means for continuously changing the applied voltage. According to a sixth aspect of the invention, the first polarization controller has a magneto-optical element and a magnetic field applying means for continuously changing the magnetic field applied to the magneto-optical element.
According to a seventh aspect of the present invention, the first polarization controller includes an electro-optical element in which the principal axis of the incident light is inclined by 45 ° with respect to the principal axis direction of the polarized light, and a voltage applied to the electro-optical element. In the invention according to claim 8, the first polarization controller tilts its principal axis by 45 ° with respect to the principal axis direction of the polarization of the incident light. And a voltage applying unit that continuously changes the voltage applied to the liquid crystal. In the invention according to claim 9, the first polarization controller includes a polarization of incident light. It has a Babinet-Soleil compensator whose main axis is inclined by 45 ° with respect to the main-axis direction, and linear driving means for continuously changing the position of the Babinet-Soleil compensator.

According to a tenth aspect of the present invention, the second polarization controller includes a λ / 4 plate on which the light emitted from the first polarization controller is incident, and the first polarization controller. The second rotation control means rotates the predetermined minute angle λ / 4 plate every time the polarized wave of the light emitted from the light rotates the circle on the equator on the Poincare sphere at least once. In the eleventh aspect of the invention, the second polarization controller has an electro-optic crystal on which the light emitted from the first polarization controller is incident, and a polarization of the light on the equator on the Poincare sphere. 13. A voltage applying means for adding a predetermined minute voltage increment to the voltage applied to the electro-optic crystal every time the circuit makes at least one round of the circle.
In the invention described above, the second polarization controller includes the liquid crystal to which the light emitted from the first polarization controller is incident and the polarization of the light at least once around the circle on the equator on the Poincare sphere. Every time
Voltage applying means for adding a predetermined minute voltage increment to the voltage applied to the liquid crystal, and in the invention according to claim 13, the second polarization controller is different from the first polarization controller. A Babinet-Soleil compensator on which the emitted light is incident,
Linear drive control means for changing the position of the Babinet-Soleil compensator by a predetermined minute displacement each time the polarization of the light makes at least one round of the circle on the equator of the Poincare sphere. In a fourteenth aspect of the present invention, the second polarization controller has a point that represents a polarization state represented by the Poincare sphere of the light source and two points where the great circle on the meridian passing through the north pole and the south pole intersects the equator. The electro-optical element is arranged such that its connecting axis and its main axis are aligned with each other, and the electro-optical element is arranged every time the polarization of the light emitted by the first polarization controller makes at least one revolution on the great circle on the meridian. And a voltage applying means for adding a predetermined minute voltage increase to the applied voltage. In the invention according to claim 15, the second polarization controller has a polarization state represented by a Poincare sphere of the light source. The liquid crystal arranged so that its principal axis coincides with the direction connecting the two points where the great circle on the meridian passing through the north pole and the south pole intersects the equator, and the polarization of the light emitted by the first polarization controller. Every time a wave goes around the great circle on the meridian at least once, And a voltage applying means for adding a predetermined minute voltage increase to the applied voltage, wherein the second polarization controller has a polarization state represented by a Poincare sphere of the light source. A point that represents
The Babinet-Soleil compensator whose main axis is arranged so that the great circle on the meridian passing through the North Pole and the South Pole coincides with the direction connecting the two points intersecting the equator, and the light emitted by the first polarization controller There is provided linear drive control means for changing the position of the Babinet-Soleil compensator by a predetermined minute displacement each time the polarized wave makes at least one round of the great circle on the meridian.

According to the seventeenth aspect of the invention, the light intensity detecting means normalizes the output for each polarization state of the light when the light transmitted through the second polarization controller is incident on the light receiving section. ,
It has a memory that holds the reciprocal value as correction data,
The light intensity measuring means includes a multiplying means for multiplying the light intensity output for each polarization state of the light obtained by connecting the measurement object by the correction data, and correcting the polarization dependent loss of the measuring device itself by the light intensity. It is characterized by that.

In the eighteenth aspect of the present invention, the light intensity detecting means normalizes the output for each polarization state of the light when the light transmitted through the second polarization controller is incident on the light receiving section. ,
It has a memory that holds the reciprocal value as correction data,
The light source is characterized by changing the output level of light based on the correction data and controlling so as to cancel the polarization dependent loss peculiar to the polarization dependent loss measuring device.

According to a nineteenth aspect of the present invention, a λ / 2 plate is used as the first polarization controller and a λ / 4 plate is used as the second polarization controller. It has a correction means for correcting.

The invention described in claim 22 is a light source device for polarization dependent loss measurement, which is used for polarization dependent loss measurement for detecting a loss of light dependent on the polarization of light of an optical element.
The light of the light source is incident, the first polarization controller for converting the polarization state of the incident light into a locus on a great circle represented by a Poincare sphere, and the light of the first polarization controller is incident, A second polarization controller for controlling the plane of polarization of the incident light so as to cover the surface of the Poincare sphere by rotating the angle of the great circle.

The invention described in claims 23 to 42 is a light source device for polarization dependent loss measurement, which has the characteristics corresponding to claims 2 to 21, respectively. In the inventions of claims 39 and 42, the measurement data transmission device transmits the measurement data such as rotation angle information indicating the polarization state of light from the light source device side in synchronization with the polarization state of the light source.

In the invention described in Item 43, Item 22
42. A polarization measuring the polarization-dependent loss of the light of the optical element to be measured by receiving the light obtained through the measurement target from the polarization-dependent loss measurement light source device according to any one of claims 42 to 42. A light-receiving device for measuring wave-dependent loss, in which the light-receiving unit that detects the intensity of the received light and the polarization state of light emitted from the light-source device for measuring polarization-dependent loss form a great circle on Poincare. Light intensity detection means for detecting the direct current level and alternating current level of the signal obtained from the light receiving part at least every one rotation, and the polarization dependent loss based on the maximum value and the minimum value of the signal obtained by the light intensity detection means. And a calculating means for calculating.

[0020]

(Function) Claims 1 to 21 of the present application having such characteristics
According to the invention, light from the light source is first incident on the first polarization controller. The first polarization controller converts the polarization state of the incident light into a great circular locus represented on the Poincare sphere. Then, the light emitted from the first polarization controller is further rotated in the polarization direction by the second polarization controller. Here, in the invention of claim 2, the light source is a light source that generates linearly polarized light,
It is converted to a locus on the equator on the Poincare sphere by the first polarization controller. In the invention of claim 3, the first polarization controller converts the locus into a locus on a great circle passing through the north pole and the south pole on the Poincare sphere. Then, the polarization rotation direction of the second polarization controller is stepwise changed to cover all the surfaces on the Poincare sphere at a predetermined interval. In this case, since all the light emitted from the second polarization controller passes through the locus of the great circle of the Poincare sphere, the maximum value and the minimum value of the optical output can be obtained at the specific rotation position. Therefore, if the light source and other optical elements are stable only during the one-rotation locus of the first polarization controller, the maximum value and the minimum value can be obtained sufficiently stably. Further, when the rotation direction of the second polarization controller is within a predetermined range, the direct current level is constant due to the change in the light intensity obtained by the rotation of the first polarization controller.
DC component and AC component can be detected separately. Therefore, the AC component can be detected with a sufficiently high amplification degree and resolution, and by combining with the DC component, the fluctuation of the received light level can be detected with high accuracy. Therefore, PDL is detected with high accuracy in a short time.

Further, in the invention of claims 17, 18, 20 and 21, the light transmitted through the second polarization controller is directly incident on the light receiving portion, and the first and second polarizations obtained at this time are obtained. The reciprocal of the normalized numerical value of the optical output level corresponding to the correction data of the wave controller is held in the memory as correction data.
Therefore, the loss dependent on the polarization peculiar to this device can be detected, and in the actual measurement, the output obtained from the light intensity detecting means is multiplied by this correction value, or the light intensity of the light source is calculated based on this correction value. By correcting, the polarization dependent loss of only the measurement target can be measured excluding the polarization dependent loss unique to this measuring device.

Further, in the inventions of claims 22 to 43 of the present application, this light source portion is used as a device for a light source, and this is connected to a transmission line such as an optical fiber. At this time, by connecting a polarization-dependent loss measuring photodetector to the end of the optical fiber transmission line with branches, the polarization-dependent loss of the entire system including multiple branches and transmission lines in the optical fiber transmission line can be measured. It will be possible.

[0023]

First, the principle of PDL measurement according to the present invention will be described. FIG. 1 is a schematic block diagram showing the basic configuration of a PDL measuring device according to the first embodiment of the present invention. In the figure, a light source 1 is a laser light source having an arbitrary polarization and is given to a polarizer 4 via an optical fiber 2 and a collimator 3. Light may be directly incident on the polarizer 4 without passing through the optical fiber 2 and the collimator 3. The polarizer 4 is a polarizer that converts the polarization of the light source into a linear polarization in a predetermined direction. The polarizer 4 can be replaced with an optical element having a function of converting light of arbitrary polarization into linear polarization, for example, a λ / 4 plate, an electro-optical element, a liquid crystal or the like. Then, a λ / 2 plate 5 and a λ / 4 plate 6 are arranged adjacent to the polarizer 4. In this embodiment, the λ / 2 plate 5 is continuously rotated to continuously change the direction of the linearly polarized wave that has passed through the polarizer 4. And λ /
The 4 plate 6 is rotated stepwise at least every 90 ° of the λ / 2 plate. The rotation driving means 5A drives the λ / 2 plate 5 to rotate, and together with the λ / 2 plate 5 constitutes a first polarization controller. Further, the rotation driving means 6A drives the λ / 4 plate 6 to rotate, and constitutes a second polarization controller together with the λ / 4 plate 6. The light that has passed through the λ / 4 plate 6 is incident on the measurement target device 8 via the collimator 7. The measurement target device 8 is a device for measuring the PDL, and is, for example, an EDFA or other optical component. The light intensity of the light passing through the measurement target device 8 is detected by the photodetector 9. The photodetector 9 detects the light amount level in an alternating current and a direct current.

Here, the relationship between the rotation of these polarization plates and the polarization direction will be described based on the display by the Poincare sphere used for expressing the polarization direction. The Poincare sphere is a globe with a radius of 1 where the amplitudes of the two orthogonal polarizations are X and Y and the phase difference is Ψ. The meridian is α and the latitude is β.
α and β are represented by the following equation α = 2 tan ⁻¹ (| X | / | Y |) β = Ψ, and all polarization states of light are represented by one point on this spherical surface. In FIG. 2, S ₁ , S ₂ , and S ₃ indicate orthogonal axes on the Poincare sphere. In the Poincare sphere, each point on the horizontal plane (that is, on the equator), for example, each point of A, B, C, and D in FIG. 2A corresponds to the linearly polarized wave, and the point E at the top of this sphere and F corresponds to the clockwise and counterclockwise circularly polarized waves, respectively. In the figure, each of these points and the polarization state are schematically shown. The polarization states of two points which are symmetrical with respect to the center point of the sphere are orthogonal to each other. Two points in this relationship are the maximum and minimum positions of the PDL, and in this relationship, lights do not interfere with each other.

The light passing through the polarizer 4 in FIG. 1 is a linearly polarized light in a specific direction, and is shown on the Poincare sphere in FIG.
As shown in (a), it is one point on the horizontal plane (equator) of the circle.
Then, as shown in FIG. 2A, for example, the points A, B, C, and D are successively passed by the half rotation of the λ / 2 plate, and a locus on the equator rotating twice is obtained. That is, the linearly polarized light passes through the λ / 2 plate 5 to become linearly polarized light whose direction is continuously changed. This light is λ
Since it is added to the / 4 plate 6, the angle formed by the main axis of the λ / 4 plate 6 and the linearly polarized wave changes continuously, and the upper and lower poles are formed on the Poincare sphere as shown in FIG. 2 (b). A trajectory on the meridian including is obtained. Therefore, for each angle φ ₁ , φ _2, ... Of the λ / 4 plate 6, the λ / 2 plate is rotated once around the equator on the Poincare sphere. That is, rotate at least 90 ° and λ /
By sequentially changing the rotation of the four plates 6 to 0 to 90 °, all points on the surface of the Poincare sphere are covered at predetermined intervals.

That is, the λ / 2 plate 5 is rotated at a high speed, and λ / 4
By rotating the plate 6 stepwise at a constant angle, an arbitrary polarized wave can be obtained. When the λ / 2 plate 5 makes one revolution, the meridian on the Poincare sphere is always obtained, so the two symmetric points of the great circle forming a certain meridian are shown in FIG. 2 (c).
As shown in, the maximum value MAX and the minimum value M of the polarization dependent loss are
Become IN. That is, the maximum value and the minimum value can be detected within a specific quarter rotation of the λ / 2 plate. PDL here
In order to detect ω with high accuracy, it is preferable that the locus of the light transmitted through the λ / 2 plate 5 on the Poincare sphere has the maximum value and the minimum value of the polarization within at least one rotation. Because the λ / 2 plate 5 makes one revolution (or 1/4 revolution) in a short time.
However, if each element has no drift during this period, it can be detected sufficiently stably. In this case, the λ / 4 plate 6
If the rotation angle is constant, the fluctuation of the received light level (AC signal) mainly represents the loss fluctuation of the polarization corrector and the PDL of the device under test 8, so that the DC component and the AC component will be described later. Therefore, the maximum value and the minimum value can be detected separately by dividing.

FIGS. 3A to 3C show changes in the output of the photodetector 9 when the λ / 2 plate 5 is rotated 180 ° at certain angles φ ₁ , φ ₂ , and φ _3. FIG. As shown in the figure, φ ₁ , φ ₂ , and φ ₃ each provide an output that becomes a sine wave of two cycles, and at any of those angles, in FIG. 3, φ ₃ has a maximum value MAX and a minimum value MIN. Has been obtained. In this way, a signal with a constant frequency that varies according to the rotation angle of the λ / 2 plate can be obtained. Here, since the AC component has a very small level, it is possible to obtain the PDL by adding only the DC level to the AC component by AC amplification as shown in FIG. Since the measurement system itself has a PDL in the embodiment, calibration is performed as described later.

When calculated by such a method, as shown in FIG. 3, the DC component and the AC component excluding the DC component can be detected separately. Therefore, the resolution can be significantly improved as compared with the conventional power meter method. For example, 0.
The PDL of 01 dB is 0.2%, but in the conventional method that directly detects the loss, only 0.2% of the full scale is PDL.
It cannot be used for measurement. However, in the present invention, this fluctuation component is amplified by AC and detected, so that FIG.
The PDL can be detected up to the width of the full scale Fs of the A / D converter shown in (c). Therefore, the resolution can be significantly improved. For example, if PDL is 0.01 dB,
If AC detection is performed, the resolution can be improved about 250 times as compared with the DC method.

In this system, the λ / 2 plate is at least ¼
Since the maximum and minimum values can be detected within the rotation time,
If fluctuations such as the power of the light source, the sensitivity of the photodetector, and other losses are stable within the time for rotating the λ / 2 plate 5 by 1/4, even if there is a drift, it is hardly affected. Therefore, highly accurate measurement is possible. Further, since the λ / 4 plate 6 is stopped while the λ / 2 plate 5 is rotating, the change in loss due to the rotation of the λ / 4 plate 6 is not affected in principle.

Next, a polarization dependent loss measuring apparatus which is a more specific embodiment of the present invention will be described. FIG. 4 is a block diagram showing the configuration of the light source unit of the polarization dependent loss measuring apparatus according to the second embodiment of the present invention. In the figure, the light source 11 is, for example, a laser light source having a constant light intensity, and the laser light source is given to the polarization compensator 12. Polarization corrector 12
Is to manually correct the polarization direction of the light source and convert it to linearly polarized light. This polarized optical signal is incident on the λ / 2 plate driving device 13 via the fiber. In this embodiment, a pulse motor controller (hereinafter referred to as PMC) 14 that generates a clock signal having a constant cycle and controls the pulse motor drivers (hereinafter referred to as PMD) 15 and 16 is used.
have. PMDs 15 and 16 are pulse motors 1 respectively
7, 18 are driven. A pulley 19 is fixed to the pulse motor 17 via a belt. The pulley 19 has a rotary shaft having a U-shaped cross section and is rotatably held by a bearing. A λ / 2 plate 20 is fixed at the center position of the right end of the pulley 19. Then, the laser light obtained from the polarization corrector 12 is made thick by the collimator lens 21 and is incident on the λ / 2 wavelength plate 20.

The pulse motor 18 is a λ / 4 plate driving device 2
The second pulley 23 is driven to rotate. Pulley 23
Similarly to the pulley 19, the rotary shaft is rotatably held coaxially with the pulley 19, and the λ is located at a position facing the λ / 2 plate.
/ 4 plate 24 is provided. The λ / 4 plate 24 is rotated stepwise by the rotational force obtained via the belt. Then, the focusing lens 2 is arranged along the optical axis of the λ / 4 plate 24.
5 are provided. The focusing lens 25 focuses light and makes it enter the optical fiber, and an optical connector serving as an emission terminal 26 of the measuring instrument is connected to an end portion of the optical fiber.

Next, the structure of the light receiving portion of this embodiment is shown in FIG.
Will be described with reference to. The incident terminal 31 is an optical fiber connector connected to this measuring device, and a light receiving element for detecting light, for example, a photodiode 32 is connected to an end portion thereof. The output of the photodiode 32 is I
It is connected to the / V converter 33 and outputs as a voltage signal according to the received light level of the obtained light. The incident terminal 31, the photodiode 32, and the I / V converter 33 configure a light receiving unit that detects the intensity of light that is incident from the light source side through the measurement target. The output of the I / V converter 33 is given to the amplifier 34 via the capacitor C1. A switch 35 controlled by a microcomputer, which will be described later, is connected in parallel to the capacitor C1. When the switch 35 is open, AC amplification is performed, and when the switch 35 is closed, the capacitor 35 is short-circuited so that DC amplification is performed. A digital attenuator 36 is connected to the output side of the amplifier 34, and converts the input signal to a predetermined level according to a control signal from the outside. The output thus obtained is applied to the A / D converter 37. The A / D converter 37 converts the output of the digital attenuator 36 into a digital signal, and its output is given to the CPU 38.
A memory 39 is connected to the CPU 38. As will be described later, the memory 39 holds a two-dimensional correction table for correcting the PDL of the measurement system, and the operation program and the instantaneous value in each cycle at the time of measurement, the average value of the direct current component, and It holds the maximum and minimum values. The CPU 38 is also connected to a display unit 40 for displaying the measurement result and an operation unit 41 for setting the operation mode from the outside. Further, the clock signal from the pulse motor driver 15 described above is input to the CPU 38. Here, the amplifier 34, the condenser 35, the digital attenuator 36, the A / D converter 37 and the CPU 38 constitute a light intensity detecting means for detecting the DC level and the AC level of the signal obtained from the light receiving section. The memory 39 constitutes a calculating means for calculating the polarization dependent loss as will be described later based on the maximum value and the minimum value of the signal thus obtained.

Next, the operation of this embodiment will be described. Before measurement, an optical fiber having a length as short as a dummy is connected in advance between the optical connector of the emitting terminal 26 of the light source section and the incident terminal 31 of the light receiving section, and the PDL specific to this measurement system is measured in advance. Then, it is necessary to hold it as correction data. When obtaining the correction data, the light source 11
More light is generated, and the polarization corrector 12 causes the linearly polarized light beam to enter the λ / 2 plate 20. Here, the angle from the reference position of the λ / 2 plate 20 is θ, and the λ / 4 plate 24 is
The angle from the reference position of is φ. Where specific angle φ
On the other hand, when the λ / 2 plate 20 is rotated 180 ° by driving the pulse motor 17, the output shown in FIG. 6A is obtained. This optical output is, for example, 3.6 for both θ and φ.
Assuming that 180 ° is detected for each angle, the angle θ of the λ / 2 plate 20 is θ = 3.6 to 180 ° for 50 samples of the angle Φ / 4 plate of φ = 3.6 to 180 °. (Θ ₁ = 3.
6, θ ₂ = 7.2 ... θ ₅₀ = 180) up to 50 × 5
Data L _DCR (θ, φ) of 0 will be obtained. The average level L _{DCR (AV)} (φ) shown in FIG. 6A for this specific angle φ of the λ / 4 plate 24 is expressed by the following equation.

[Equation 1] Note that N is the number of samples, and N = 50 here.

As shown in FIG. 6B, the AC component L _ACR (θ, φ) can be detected by using this average level, that is, L _{DCR (AV)} (φ) as a reference level. The correction data C (θ, φ) is calculated from these values by the following equation.

[Equation 2] Here, this correction data is obtained by normalizing the output at each rotation angle and taking the reciprocal value. Thus (50 x
50 =) 2500 correction data C (θ, φ) is calculated and stored in the memory 39. At this time, if the range of the amplifier 34 is different between the detection of the DC component and the AC component, it goes without saying that it is necessary to accurately match the scale of the range.

When measuring an actual object to be measured, for example, a PDL to be measured such as an EDFA, the EDFA is connected between the emission terminal 26 and the incidence terminal 31. Then, as in the case of calibration, light is emitted from the light source 11 with a constant light intensity and is given to the λ / 2 plate 20 via the polarization corrector 12. And λ
The 1/2 plate 20 is rotated twice, and then the λ / 4 plate 24 is rotated by a predetermined step, in this embodiment, 3.6 °, and the same processing is repeated. FIG. 7 is a time chart showing the waveform of each part during PDL measurement. FIG. 7A shows a clock pulse of the pulse motor controller 14, for example, at time t ₁
In the period T1 of ~t ₂ and outputs the 250 pulses,
During this period, the λ / 2 plate 20 rotates 1/2. As shown in FIG. 7B, a divided output obtained by dividing this pulse into ⅕ is output from the pulse motor driver 15, and the A / D converter 37 performs A / D conversion every time this pulse is obtained. Go and capture that data. FIG. 7D shows the output of the amplifier 34, and in the period T1, the switch 35 is closed and the DC level is measured. As shown in the enlarged view in the time axis direction in FIG. 7E, this is the average DC level L _{DC (AV) of the} light intensity when θ is from 0 to 180 ° as in the calibration described above. ₎ (Φ) is calculated based on the following equation.

[Equation 3]

Next, at time t ₂ , the switch 35 is opened to connect the capacitor C1 to the input side of the amplifier 34, and the range of the I / V converter 33 is switched. At this time, the attenuation rate of the digital attenuator 36 is also switched if necessary. Then, the output of the amplifier 34 is shown in FIG.
It changes as shown in (d). Now, the period T from time t _{2 to} t ₃
2 is a waiting period for stabilizing the operation after switching,
Performs amplitude level detection of alternating current period T3 at time t ₃ ~t _4. This is taken in as the value at each θ as L _AC (θ, φ), as shown in the enlarged view in the time axis direction in FIG. Then, the CPU 38, for the specific rotation angle φ of the λ / 4 plate 24 obtained here, sets the above-described correction value C (θ, φ) to the received light level L (θ, φ) within the range of θ of 0 to 180 °. φ)
Is calculated based on the following equation (4).

[Equation 4]

After all the AC level data is captured at time t ₄ , the maximum value L _MAX and the minimum value L _{MAX of the} data L (θ, φ) are obtained with respect to the angle φ of the λ / 4 plate 24 at that time.
_{Find MIN} . Then, PDL (φ) is obtained from the following equation (5).

[Equation 5]

Then, the λ / 4 plate 24 is rotated by a predetermined angle and the same processing is performed. Switching of the time period T4 switch 35 again at time t ₄ ~t ₅ this time to the DC amplifier as off, for switching such a level of the digital attenuator 36. In this way, after the data at the angle φ of the specific λ / 4 plate 24 is obtained between the times t _{1 and} t ₅ , the PDL (φ) at the next rotation angle is calculated. Then, while the λ / 4 plate 24 is rotated by 1/2, the maximum PDL obtained is set as the PDL to be obtained.

In this method, the λ / 2 plate is always rotated at a constant speed of 3.6 °, and the power of the light passing through the object to be measured is detected by high-speed sampling by the photodetector. Despite the method, high-speed measurement is possible.

In this embodiment, the λ / 2 plate and the λ / 4 plate are each rotated by 3.6 °, but this is because the error of the angle step is 1% or less. It goes without saying that a precise value can be obtained by reducing the rotation angle.

In this embodiment, the PD unique to this measuring device is used.
L is calibrated in advance and its correction values are held in a memory as a table, and the level of the optical signal obtained based on this is corrected. However, calibration methods other than such a calibration method are also conceivable. For example, by using a memory holding the correction data, the I / V is set so as to cancel the PDL peculiar to this device in accordance with the rotation angles of the λ / 2 plate and the λ / 4 plate.
The amplification factor of the converter or amplifier is adjusted from the CPU side at each angle (θ,
It may be controlled and changed for each φ). The correction may be performed using a multiplier that multiplies this correction value. Further, it is possible to change the output of the light source based on the data in this memory to cancel the PDL unique to this device. In this case, the light output of the light source 11 itself may be controlled by some method, or the intensity of the light emitted from the light source 11 may be controlled through a light modulator. Particularly, the method of canceling the PDL peculiar to the device by controlling the light intensity on the light source side is the EDFA having the input level dependence of the gain, the multi-channel measurement described later, and the P of the transmission line
Suitable for DL evaluation.

Next, a modified example of the optical system component of the device on the light source side will be described. First, a modification of the first polarization controller will be described. In the first and second embodiments described above, the λ / 2 plate is used to rotate the λ / 2 plate to change the angle of the linearly polarized wave component so as to have a locus corresponding to the equator on the Poincare sphere. However, the configuration is not limited to this, and λ /
Instead of the two plates, as shown in FIG.
It is possible to use the electro-optical element 51 having an electro-optical effect such as NbO ₃ and use the voltage applying means 52 instead of the rotation control means 5A. Liquid crystal may be used instead of the electro-optical element. Also in this case, the light source causes the linearly polarized light to enter the electro-optical element 51 and the like by the polarizer 4. Then, if the voltage is continuously changed, the polarization direction is continuously changed by the applied voltage and can be converted into a locus on the equator on the Poincare sphere.

Further, as shown in FIG. 8B, a magneto-optical crystal 53 such as Faraday glass or YIG is used as shown in FIG.
The same effect can be obtained by rotating the plane of polarization by the Faraday effect by changing the strength of the applied magnetic field using the magnetic field applying means 54. It is also conceivable to rotate the plane of polarization by applying lateral pressure or twist using an optical fiber. Further, the first polarization controller can be configured by using a light source having circular polarization or random polarization and rotating a polarizer that outputs only light of a specific polarization plane.

Next, a fifth embodiment which is a modification of the light source device will be described. In the above-described first to fourth embodiments, the locus on the equator is once formed on the Poincare sphere as shown in FIG. 2A, and the point of circular polarization is formed on the Poincare sphere by the second polarization controller. That is, the surface is traced so as to cover the spherical surface by the meridian passing through the north pole E and the south pole F. However, it is not necessary to trace by meridian, and it is also possible to rotate the angle of the great circle about the axis connecting the arbitrary point on the equator and the point that is the opposite pole to cover the Poincare sphere. It is possible. For example, as shown in FIG. 9, light from the light source 1 is converted into linearly polarized light by the polarizer 4, and the polarization direction is set along the equator on the Poincare sphere by using the λ / 2 plate 5 as in FIG. To rotate. At this time, as shown in FIG.
As shown in (b), an electro-optical element, a liquid crystal, or a magneto-optical element may be used. Then, this light enters the Babinet-Soleil corrector 61. A linear drive control means 62 is connected to the Babinet-Soleil corrector 61, and one wedge-shaped crystal is changed along the vertical direction in the figure. This displacement is such that the locus of light from the λ / 2 plate 5 on the Poincare sphere is at least 1 on the equator.
Each time it rotates, it is changed by a predetermined minute displacement. In this way, the thickness of the crystal changes and birefringence occurs. Other configurations are the same as those in FIG. In this case, the rotation of the λ / 2 plate 5 causes the locus in the polarization direction of the light to change on the equator as shown in FIG. Then, the light enters the Babinet-Soreil compensator 61, and by its linear drive, it passes through two points B and D on the equator on the Poincare sphere, and the angle ψ continuously changes, as shown in FIG. 10B. You can get a great circle. Therefore, the PDL can be obtained with high accuracy by detecting the DC component and the AC component in the same manner as in the above-described embodiment. In this case, the Babinet-Soleil corrector 61 and the linear drive control means 62
Will constitute the second polarization controller.

In the fifth embodiment shown in FIG. 9, the Babinet-Soleil compensator is used. However, as shown in the third and fourth embodiments, the Babinet-Soleille compensator is replaced by the second polarized wave. An electro-optical element or liquid crystal and a voltage applying means may be used as the controller.

In the above-described first to fifth embodiments, FIG.
As shown in (a), the polarization of the incident light is converted into a locus on the equator on the Poincare sphere, and further converted to a locus on the meridian as shown in FIG. 2 (b). The light is first converted into a locus on the meridian by the first polarization controller as shown in FIG. 11 (a), and then the axis connecting two opposite poles on the equator as shown in FIG. 12 (c). It can also be configured to cover the Poincaré sphere by rotating the angle of the great circle as the center. At this time, the light of the light source is not limited to the linearly polarized light, and a light source having an arbitrary polarization state that does not change over time may be used. Then, the light of this light source is once made incident on the first polarization controller, for example, the above-mentioned electro-optical crystal, liquid crystal, or Babinet-Soleil compensator. Here, it is assumed that a point on the Poincare sphere of the light source is an arbitrary position G showing an elliptically polarized wave as shown in FIG. Then, the optical crystal is arranged so that the locus is the meridian, which is a great circle passing through the point G, the north pole point E, and the south pole point F on the Poincare sphere. That is, the locus of the vibration of the electric field of the elliptically polarized wave viewed from the traveling direction of the light is represented as the elliptically polarized wave as shown in FIG. 11B, and the azimuth angle of the principal axis P _{1 of} the ellipse with the X axis is α. Then, if the shaft in the Poincare sphere corresponding axis S ₂ in the X-axis, the main axis P ₁ of the ellipse corresponds to the axis P ₁ on S _1, S ₂ plane apart azimuthal α relative to the axis S ₂ is doing. And S
The directions of the crystal axes of the liquid crystal, the electro-optic crystal, and the Babinet-Soleil compensator are shown in FIG. 11C so that the axis P ₂ orthogonal to the axis P ₁ on the plane of ₁ and S ₂ is the rotation axis. Is arranged at an angle of 45 ° from the main axis. In this way, by continuously applying a voltage to the liquid crystal or the electro-optic crystal, or continuously changing the position of the Babinet-Soleil compensator, the light from the light source can be converted into the Poincare light as shown in FIG. 11 (d). Point G showing the polarization of the light source on the sphere, and North Pole E and South Pole F
It can be converted into a locus of meridians passing through.

Then, the light from the first polarization controller whose locus on the Poincare sphere changes like a meridian is made incident on the second polarization controller, and the inclination angle of this great circle is continuously changed. It is changed to cover the Poincare sphere. Also in this case, an electro-optic crystal, a liquid crystal, and a Babinet-Soleil compensator are used as the second polarization controller. FIG. 12 is an explanatory diagram showing a sixth embodiment in which the light from the first polarization controller having the locus on the meridian thus obtained is changed so as to cover the Poincare sphere. That is, FIG. 12A shows a point G indicating the polarization state in the incident state obtained on the Poincare sphere and a point where the great circle on the meridian passing through the north pole E and the south pole F intersects with the equator, that is, H and I in the figure. If the axis connecting the two is expressed as P ₁ as in FIG. 11, the electro-optical element, the crystal, and the Babinet-Soleil corrector are arranged so that this direction coincides with the main axis as shown in FIG. Thus, the voltage applied to the electro-optical element or the displacement of the Babinet-Soleil compensator is adjusted so that the locus of the light from the first polarization controller on the Poincare sphere is at least 1 on the meridian.
If it is changed by a minute increment or a minute displacement each time it rotates, the meridian tilts through the points H and I of the Poincare sphere as shown in FIG. 12 (c), and the tilt angle depends on the applied voltage or Babinet. Corresponds to the displacement of the Soleil compensator. Therefore, if these are continuously changed, the entire surface of the Poincare sphere can be covered by tilting the meridian. Also in this case, the PDL can be obtained with high accuracy by detecting the DC component and the AC component as in the above-described embodiments.

Further, in this embodiment, the light source side and the light receiving side for receiving the light output and processing the signal are housed in the same housing, and E
Although PDL of optical components such as DFA is measured, when there are many measurement targets, for example, an optical cable is used, and in a transmission system with branches, only the light source side is arranged at the transmitting station and each terminal side is The PDL on the transmission line of the cable can be measured. FIG.
Is a system for measuring the polarization dependent loss of such an optical fiber transmission line. In the figure, reference numeral 70 denotes a light source device for polarization dependent loss measurement. The details are the same as those including the light source 1 to the λ / 2 plate 5, the λ / 4 plate 6 and their rotation control devices shown in FIG. Further, the apparatus of FIG. 4 and the λ / 2 plate 5 and the λ / 4 plate 6 as described above may be replaced with a liquid crystal, an electro-optical element, or a Babinet-Soleil compensator. Then, the light source device 70 is connected to one end of the optical fiber transmission line 71. In this case, it is assumed that a large number of branches are formed on the optical fiber transmission line 71 by, for example, a star coupler or the like. A polarization dependent loss measuring light receiving device 72 is connected to each of the other ends of the optical fiber transmission lines 71. The details are the same as those of the photodetector 9 shown in FIG. 1 and the light receiving unit side device shown in FIG.

In this case, it is necessary to transmit the rotation angle information of the λ / 2 wave plate 5 and the λ / 4 wave plate 6 of the light source device 70 or the polarization state of another polarization corrector to the light receiving device 72 side. . In FIG. 13, the measurement data such as the rotation angle information is displayed as the light source device 7.
It is assumed that the measurement data transmission device 73 in 0 is used for transmission to the light receiving device 72 side via the transmission line 74. Alternatively, the optical fiber transmission line may be used as it is, and the measurement data such as θ and φ may be superposed and transmitted by light having a wavelength different from the wavelength on the light source side to be measured. In this case, it is preferable to correct the output level of the light from the light source by the above-described correction value in order to eliminate the influence of the PDL peculiar to the light source as described above.

Further, in a CATV system or the like in which an optical transmission path is formed by a large number of branch paths, it is conceivable that the light source device side and the light receiving device side are separated by several km or more, and in some cases by several hundreds of km. For this reason, it is difficult to transmit the synchronization signal through another transmission path. Therefore, it is necessary to separately transmit the measurement data such as θ and φ and the synchronization signal by multiplexing the light from the light source side. In this case PDL
It is conceivable to apply modulation to the light source side so as not to affect the measurement itself, to use FM signals, PM signals, AM signals with a constant average level, or to multiplex wavelengths and transmit at different wavelengths. .

[0051]

As described above in detail, according to the inventions of claims 1 to 21 of the present application, the change in the measurement level is detected in an alternating manner as compared with the conventional PDL measuring method. The resolution can be significantly improved as compared with the method of directly detecting the loss using a power meter. Further, the PDL can be detected stably without being affected by the drift of the light source or the measurement system. Furthermore, if the polarization is rotated at a constant speed by the first polarization controller so that it becomes a great circle on the Poincare sphere, and the data is sampled at a high speed, the PDL of the measurement system can be measured in a short time. To be

According to the invention of claims 17, 18, 20 and 21, the correction data is held in the memory based on the light transmitted through the second polarization controller, and the measurement object is connected by this memory. I am trying to correct the output when I do. Therefore, it is possible to remove the influence of the polarization dependent loss unique to this device, and to obtain the effect that only the polarization dependent loss of the measurement target can be measured.

Further, in the inventions of claims 22 to 42 of the present application, the light source unit of the polarization dependent measuring apparatus is independently used as the light source apparatus. Therefore, the PDL of the transmission line can be measured even when the measurement target such as the optical fiber transmission line is distant in distance. Further, in the invention of claim 41 of the present application, since the polarization information of the polarization control device is also transmitted at the same time, the light source device is used for a complicated optical fiber transmission line including a large number of branch routes. Light can be transmitted to the transmission line. Further, in the invention described in Item 40, it is possible to obtain the effect that the PDL of the transmission line can be easily measured by receiving this light.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of a polarization dependent loss measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a locus on a Poincare when the λ / 2 plate and the λ / 4 plate are rotated in the polarization dependent loss measuring apparatus according to the first embodiment of the present invention.

FIG. 3 is a graph showing changes in the output obtained by the photodetector when the λ / 2 plate is rotated in the polarization dependent loss measuring apparatus according to the first embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of a light source section of a polarization dependent loss measuring apparatus according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a light receiving unit side of a polarization dependent loss measuring apparatus according to a second embodiment of the present invention.

FIG. 6 is a time chart showing the operation when obtaining the calibration data for measuring and calibrating the PDL unique to the polarization dependent loss measuring apparatus in the second embodiment of the present invention.

FIG. 7 is a time chart showing waveforms of various parts during measurement of a measurement target according to the second embodiment of the present invention.

8A and 8B are block diagrams showing a configuration of a light source unit of a polarization dependent measurement apparatus according to a third embodiment and a fourth embodiment.

FIG. 9 is a block diagram showing a basic configuration of a polarization dependent loss measuring apparatus according to a fifth embodiment of the present invention.

FIG. 10 is a diagram showing a polarization state at the time of measurement according to the fifth embodiment using a Poincare sphere.

FIG. 11 is a diagram showing a Poincare sphere and a polarization direction in a first polarization controller of a polarization dependent loss measuring apparatus according to a sixth embodiment of the present invention.

FIG. 12 is a diagram showing a polarization state of a second polarization controller of the polarization dependent loss measuring apparatus according to the sixth embodiment of the present invention by means of a polarization state diagram.

FIG. 13 is a diagram illustrating a P of an optical fiber transmission line using the light source device for polarization dependent measurement and the light receiving device for polarization dependent loss measurement of the present invention.
It is a figure which shows the connection at the time of measuring DL.

FIG. 14 is a block diagram showing an outline of a conventional polarization dependent loss measuring apparatus by the Poincare method.

[Explanation of symbols]

 1 Light source 2 Optical fiber 3 Lens 4 Polarizer 5,20 λ / 2 plate 6,24 λ / 4 plate 5A, 6A Rotation control means 7 Device to be measured 8 Optical detector 11 Light source 12 Polarization corrector 13 λ / 2 plate drive Device 14 Pulse motor controller 15, 16 Pulse motor driver 17, 18 Pulse motor 22 λ / 4 plate drive device 26 Emission terminal 31 Incident terminal 32 Light receiving element 33 Head amplifier 34 Amplifier 35 Switch 36 Digital attenuator 37 A / D converter 38 CPU 39 memory 40 display part 41 operation part 51 electro-optical element 52 voltage applying means 53 magneto-optical crystal 54 magnetic field applying means 61 Babinet-Soleil corrector 62 linear drive control means 70 polarization dependent loss measurement light source device 71 optical fiber transmission line 72 Polarization dependent loss measurement photo detector 73 Data transmission equipment

Claims (43)

[Claims] 1. A polarization-dependent loss measuring device for detecting a polarization-dependent loss of light of an optical element, comprising: a light source; and light of the light source being incident on the polarization state of the incident light by a Poincare sphere. The first to transform the represented locus on the great circle
And a second polarization controller for controlling the polarization plane of the incident light so that the light from the first polarization controller is incident and the angle of the great circle is rotated to cover the surface of the Poincare sphere. Polarization controller, a light receiving section that detects the intensity of light obtained through the measurement target by injecting the light that has passed through the second polarization controller into the measurement target, and the second polarization Light intensity detecting means for detecting a DC level and an AC level of a signal obtained from the light receiving section every time the polarization state of the light emitted from the controller makes at least one revolution of the great circle on the Poincare sphere; A polarization dependent loss measuring device, comprising: a calculating means for calculating a polarization dependent loss based on a maximum value and a minimum value of a signal obtained by the intensity detecting means. 2. The light source is a light source that generates a linearly polarized wave, and the first polarization controller receives light from the light source,
The polarization dependent loss measuring apparatus according to claim 1, wherein the polarization state of the incident light is converted into a locus on the equator represented by a Poincare sphere. 3. The light source is a light source having a specific polarization state that does not change with time, and the first polarization controller receives the light of the light source and changes the polarization state of the incident light with a Poincare sphere. The polarization dependent loss measuring device according to claim 1, wherein the polarization dependent loss measuring device converts the locus on a meridian passing through the north pole and the south pole including a point represented by. 4. The first polarization controller includes a λ / 2 plate on which light from the light source is incident, and a first rotation control unit that rotationally drives the λ / 2 plate at that position. The polarization dependent loss measuring apparatus according to claim 2, which is provided. 5. The first polarization controller includes an electro-optical element and a voltage applying unit that continuously changes a voltage applied to the electro-optical element, and makes incident linearly polarized light. 3. The polarization dependent loss measuring device according to claim 2, wherein the polarization direction of is continuously rotated. 6. The first polarization controller includes a magneto-optical element and a magnetic field applying unit that continuously changes a magnetic field applied to the magneto-optical element, and makes incident linearly polarized light. 3. The polarization dependent loss measuring device according to claim 2, wherein the polarization direction of is continuously rotated. 7. The first polarization controller continuously connects an electro-optical element whose main axis is inclined by 45 ° with respect to a main axis direction of polarization of incident light, and a voltage applied to the electro-optical element. 4. A polarization according to claim 3, further comprising: a voltage applying unit that changes the wavelength of the incident light, and continuously converts the incident polarization into a locus on a meridian passing through the North Pole and the South Pole, which is represented by a Poincare sphere. Wave-dependent loss measurement device. 8. The first polarization controller continuously changes a liquid crystal whose main axis is inclined by 45 ° with respect to a main axis direction of polarization of incident light, and a voltage applied to the liquid crystal. 4. The polarization dependent loss measurement according to claim 3, further comprising: a voltage applying means, for continuously converting the incident polarization into a locus on a meridian passing through the north pole and the south pole represented by a Poincare sphere. apparatus. 9. The Babinet-Soleil compensator in which the first polarization controller is arranged with its principal axis inclined by 45 ° with respect to the principal axis direction of the polarization of incident light, and the position of the Babinet-Soleil compensator. And a linear drive control means for continuously changing the incident polarization, and continuously converting the incident polarization into a locus on a meridian passing through the North Pole and the South Pole represented by a Poincare sphere. 3. The polarization dependent loss measuring device according to 3. 10. The second polarization controller is provided with λ to which the light emitted from the first polarization controller is incident.
/ 4 plate, and the polarized light of the light emitted from the first polarization controller rotates the λ / 4 plate by a predetermined minute angle every time the polarization of the light emitted from the first polarization controller makes at least one round of the circle on the equator on the Poincare sphere. 3. The polarization dependent loss measuring device according to claim 2, further comprising two rotation control means. 11. The second polarization controller includes an electro-optic crystal to which the light emitted from the first polarization controller is incident, and a light emitted from the first polarization controller. Each time the polarized wave of (1) makes at least one round of a circle on the equator on the Poincare sphere, a voltage applying means for adding a predetermined minute voltage increase to the voltage applied to the electro-optic crystal. The polarization dependent loss measuring device according to claim 2. 12. The second polarization controller comprises a liquid crystal to which the light emitted from the first polarization controller is incident and a polarization of the light emitted from the first polarization controller. 3. A voltage applying means for adding a predetermined minute voltage increase to the voltage applied to the liquid crystal every time the wave makes at least one round of a circle on the equator on the Poincare sphere. The polarization-dependent loss measurement device described. 13. The second polarization controller includes a Babinet-Soleil compensator into which the light emitted from the first polarization controller is incident, and the light is emitted to the first polarization controller. Linear drive control means for changing the position of the Babinet-Soleil corrector by a predetermined minute displacement every time the polarization of the light makes at least one round of the circle on the equator of the Poincare sphere. The polarization dependent loss measuring device according to claim 2. 14. The second polarization controller connects a point representing a polarization state represented by a Poincare sphere of the light source, and a direction connecting two points where a great circle on a meridian passing through the North Pole and the South Pole intersects with the equator. And an electro-optical element whose principal axes coincide with each other, and a voltage applied to the electro-optical element every time the polarization of the light emitted by the first polarization controller makes at least one round of the great circle on the meridian. 4. A voltage applying means for applying a predetermined minute voltage increase amount.
The polarization-dependent loss measurement device described. 15. The second polarization controller connects a point representing the polarization state represented by the Poincare sphere of the light source and two points where a great circle on the meridian passing through the North Pole and the South Pole intersects the equator. A liquid crystal whose direction coincides with its principal axis and a voltage applied to the liquid crystal each time the polarization of the light emitted by the first polarization controller makes at least one round of the great circle on the meridian, and a predetermined minute voltage. 4. The polarization dependent loss measuring device according to claim 3, further comprising a voltage applying means for adding an increment. 16. The second polarization controller connects a point representing the polarization state represented by the Poincare sphere of the light source and two points where a great circle on the meridian passing through the North Pole and the South Pole intersects the equator. A Babinet-Soleil compensator whose principal axis is arranged so as to coincide with the direction, and the polarization of the light emitted by the first polarization controller at least once per revolution of the great circle on the meridian. 4. The polarization dependent loss measuring device according to claim 3, further comprising linear drive control means for changing the position of the Babinet-Soleil compensator by a predetermined minute displacement. 17. The light intensity detecting means, when the light transmitted through the second polarization controller is incident on the light receiving section,
The output for each polarization state of the light is normalized, and has a memory for holding the reciprocal value as correction data, the light intensity measuring means, the light for each polarization state of the light obtained by connecting the measurement target A multiplication means for multiplying the intensity output by the correction data and the light intensity for correcting the polarization dependent loss of the measuring device itself.
6. The polarization dependent loss measurement device according to any one of 6 above. 18. The light intensity detecting means, when the light transmitted through the second polarization controller is incident on the light receiving section,
It has a memory that normalizes the output for each polarization state of light and holds the reciprocal value as correction data, and the light source changes the output level of light based on the correction data, and a polarization dependent loss measuring device. The polarization dependent loss measuring device according to any one of claims 1 to 16, wherein the polarization dependent loss measuring device is controlled so as to cancel the polarization dependent loss peculiar thereto. 19. A polarization dependent loss measuring device for detecting a polarization dependent loss of light of an optical element, comprising: a light source for generating linearly polarized light; and λ / 2 plates, a first rotation control unit that rotationally drives the λ / 2 plate at that position, a λ / 4 plate on which light transmitted through the λ / 2 plate is incident, and an emission from the λ / 2 plate Second rotation control means for rotating the λ / 4 plate by a predetermined small angle every time the polarization of the reflected light makes at least one revolution of the great circle on the equator on the Poincare sphere; and the second polarization control. The light passing through the measuring device is incident on the measuring object, and the light receiving part for detecting the intensity of the light obtained through the measuring object, and the polarization state of the light emitted from the λ / 4 plate is large on the Poincare sphere. Light for detecting the DC level and AC level of the signal obtained from the light receiving section every time the circle rotates at least once. A polarization dependent loss measuring device comprising: intensity detecting means; and computing means for computing a polarization dependent loss based on a maximum value and a minimum value of a signal obtained by the light intensity detecting means. 20. The light intensity detecting means, when the light transmitted through the λ / 4 plate enters the light receiving portion, the λ /
There is a memory for normalizing the output with respect to the rotation angle θ of the two plates and the rotation angle φ of the λ / 4 plate, and holding a reciprocal value thereof as correction data. 20. The polarization dependent according to claim 19, further comprising: a multiplication means for multiplying the light intensity output for each polarization state of the light with the correction data and correcting the light intensity with the polarization dependent loss of the measuring device itself. Loss measuring device. 21. The light intensity detecting means, when the light transmitted through the λ / 4 plate is incident on the light receiving portion, the λ /
The light source has a memory that normalizes the output with respect to the rotation angle θ of the two plates and the rotation angle φ of the λ / 4 plate, and holds the reciprocal value thereof as correction data. 20. The polarization dependent loss measuring device according to claim 19, wherein the polarization dependent loss measuring device is controlled so as to cancel the polarization dependent loss peculiar to the polarization dependent loss measuring device. 22. A polarization dependent loss measuring light source device used for polarization dependent loss measurement for detecting a polarization dependent loss of light of an optical element, comprising: a light source; Converts the polarization state of incident light into a trajectory on a great circle represented by a Poincare sphere.
And a second polarization controller for controlling the polarization plane of the incident light so that the light from the first polarization controller is incident and the angle of the great circle is rotated to cover the surface of the Poincare sphere. And a polarization controller for measuring polarization dependent loss. 23. The light source is a light source that generates a linearly polarized wave, and the first polarization controller receives the light from the light source, and the polarization state of the incident light is on the equator represented by a Poincare sphere. 23. The polarization-dependent loss measuring light source device according to claim 22, which is converted into a locus of 24. The light source is a light source having a specific polarization state that does not change with time, and the first polarization controller is
23. The light from the light source is incident, and a polarization state of the incident light is converted into a locus on a meridian passing through the North Pole and the South Pole including a point represented by a Poincare sphere. Light source device for polarization dependent loss measurement. 25. The first polarization controller includes: a λ / 2 plate on which light from the light source is incident; and a first rotation control unit that rotationally drives the λ / 2 plate at that position. The light source device for polarization dependent loss measurement according to claim 23, which is provided. 26. The first polarization controller includes an electro-optical element and a voltage applying unit that continuously changes a voltage applied to the electro-optical element, and makes incident linearly polarized light. 24. The polarization direction of is continuously rotated.
The light source device for polarization dependent loss measurement described. 27. The first polarization controller includes a magneto-optical element and a magnetic field applying unit that continuously changes a magnetic field applied to the magneto-optical element, and makes incident linearly polarized light. 24. The polarization direction of is continuously rotated.
The light source device for polarization dependent loss measurement described. 28. The first polarization controller continuously applies an electro-optical element having a main axis inclined by 45 ° with respect to a main axis direction of polarization of incident light, and a voltage applied to the electro-optical element. 26. The polarization according to claim 24, further comprising: Light source device for wave dependent loss measurement. 29. The first polarization controller continuously changes a liquid crystal whose main axis is inclined by 45 ° with respect to a main axis direction of polarization of incident light, and a voltage applied to the liquid crystal. 25. The polarization dependent loss measurement according to claim 24, further comprising a voltage applying means, for continuously converting the incident polarization into a locus on a meridian passing through the north pole and the south pole represented by a Poincare sphere. Light source device. 30. The first polarization controller is a Babinet-Soleil compensator in which the principal axis is inclined by 45 ° with respect to the principal axis direction of the polarization of incident light, and the position of the Babinet-Soleil compensator. And a linear drive control means for continuously changing the incident polarization, and continuously converting the incident polarization into a locus on a meridian passing through the North Pole and the South Pole represented by a Poincare sphere. 24. The light source device for polarization dependent loss measurement according to 24. 31. The second polarization controller has a wavelength λ to which the light emitted from the first polarization controller is incident.
/ 4 plate, and the polarized light of the light emitted from the first polarization controller rotates the λ / 4 plate by a predetermined minute angle every time the polarization of the light emitted from the first polarization controller makes at least one round of the circle on the equator on the Poincare sphere. 24. The polarization-dependent loss measurement light source device according to claim 23, further comprising: two rotation control means. 32. The second polarization controller includes an electro-optic crystal to which the light emitted from the first polarization controller is incident, and a light emitted from the first polarization controller. Each time the polarized wave of (1) makes at least one round of a circle on the equator on the Poincare sphere, a voltage applying means for adding a predetermined minute voltage increase to the voltage applied to the electro-optic crystal. The light source device for polarization dependent loss measurement according to claim 23. 33. The second polarization controller comprises a liquid crystal to which the light emitted from the first polarization controller is incident and a polarization of the light emitted from the first polarization controller. 24. A voltage applying means for applying a predetermined minute voltage increase to the voltage applied to the liquid crystal every time the wave makes at least one round of the circle on the equator on the Poincare sphere. The light source device for polarization dependent loss measurement described. 34. The second polarization controller comprises a Babinet-Soleil compensator into which the light emitted from the first polarization controller is incident, and the light is emitted to the first polarization controller. Linear drive control means for changing the position of the Babinet-Soleil corrector by a predetermined minute displacement every time the polarization of the light makes at least one round of the circle on the equator of the Poincare sphere. The light source device for polarization dependent loss measurement according to claim 23. 35. The second polarization controller connects a point representing a polarization state represented by a Poincare sphere of the light source, and a direction connecting two points where a great circle on a meridian passing through the North Pole and the South Pole intersects with the equator. And an electro-optical element whose principal axes coincide with each other, and a voltage applied to the electro-optical element every time the polarization of the light emitted by the first polarization controller makes at least one round of the great circle on the meridian. 25. The apparatus according to claim 24, further comprising voltage applying means for applying a predetermined minute voltage increment.
The light source device for polarization dependent loss measurement described. 36. The second polarization controller connects a point representing the polarization state represented by the Poincare sphere of the light source and two points where a great circle on the meridian passing through the North Pole and the South Pole intersects the equator. A liquid crystal whose direction coincides with its principal axis and a voltage applied to the liquid crystal each time the polarization of the light emitted by the first polarization controller makes at least one round of the great circle on the meridian, and a predetermined minute voltage. 25. The polarization-dependent loss measuring light source device according to claim 24, further comprising a voltage applying means for applying an increment. 37. The second polarization controller connects a point representing the polarization state represented by the Poincare sphere of the light source and two points where a great circle on the meridian passing through the North Pole and the South Pole intersects the equator. A Babinet-Soleil compensator whose principal axis is arranged so as to coincide with the direction, and the polarization of the light emitted by the first polarization controller at least once per revolution of the great circle on the meridian. 25. The light source device for polarization dependent loss measurement according to claim 24, further comprising linear drive control means for changing the position of the Babinet-Soleil compensator by a predetermined minute displacement. 38. When the light transmitted through the second polarization controller is received, it has a memory that normalizes the output for each polarization state of the light and holds the reciprocal value as correction data. 38. The light source is configured to change the output level of light based on the correction data, and control so as to cancel the polarization dependent loss specific to the polarization dependent loss measuring device. The light source device for polarization dependent loss measurement according to any one of items. 39. The light source device for measuring polarization dependent loss,
39. The polarization according to claim 22, further comprising a measurement data transmission device that simultaneously transmits measurement data indicating polarization states of light of the first and second polarization controllers. Light source device for wave dependent loss measurement. 40. A polarization dependent loss measuring light source device used for polarization dependent loss measurement for detecting a polarization dependent loss of light of an optical element, the light source generating linearly polarized light, A λ / 2 plate on which the light from the light source is incident, a first rotation control unit that rotationally drives the λ / 2 plate at that position, and a λ / 4 on which the light transmitted through the λ / 2 plate is incident. Plate and second rotation control for rotating the λ / 4 plate by a predetermined minute angle every time the polarized wave of the light emitted from the λ / 2 plate makes at least one rotation of the great circle on the equator on the Poincare sphere. Means and
A light source device for polarization dependent loss measurement, comprising: 41. The light intensity detecting means, when receiving the light transmitted through the λ / 4 plate, normalizes the output with respect to the rotation angle θ of the λ / 2 plate and the rotation angle φ of the λ / 4 plate. Turned into
The light source has a memory for holding the reciprocal value as correction data, and the light source changes the output level of light based on the correction data, and controls so as to cancel the polarization dependent loss unique to the polarization dependent loss measuring device. The light source device for polarization dependent loss measurement according to claim 40, characterized in that 42. The light source device for polarization dependent loss measurement,
The light source device for polarization dependent loss measurement according to claim 40 or 41, further comprising a measurement data transmission device that simultaneously transmits measurement data indicating rotation angle information of the first and second rotation control means. 43. The polarization of the light of the optical element to be measured by receiving the light obtained from the polarization-dependent loss measuring light source device according to claim 22 through the measurement target. A light-receiving device for measuring polarization-dependent loss, which measures the loss dependent on the polarization, and a light-receiving part for detecting the intensity of the received light, and a polarization of the light emitted from the polarization-dependent loss measuring light source device. Light intensity detecting means for detecting the DC level and the AC level of the signal obtained from the light receiving section every time the wave state makes at least one revolution of the great circle on Poincare, and the maximum value of the signal obtained by the light intensity detecting means. And a calculation means for calculating a polarization dependent loss based on the minimum value, and a light receiving device for polarization dependent loss measurement.