JP6753581B2 - Optical measuring device - Google Patents

Description

The present invention relates to an optical measuring device and an optical measuring method for measuring the magneto-optical characteristics, non-reciprocal optical characteristics, and nonlinear optical characteristics of the sample to be investigated.

It is important to measure the magneto-optical properties and nonlinear optical properties of substances with high accuracy and high sensitivity in fields such as biology and spintronics. Currently, devices for measuring magneto-optical characteristics such as Faraday rotation angle, car rotation angle, and magnetic circular dichroism are used in biology, spintronics, and other fields.

Measuring the non-reciprocal optical properties of a sample has the advantage of providing important information about the sample, as there is a non-reciprocal response only when the time-reversal symmetry of the sample is broken. However, devices for measuring non-reciprocal optical properties have not yet been developed, and if they are developed, they may be applicable to a wide range of other fields. When the refractive index and absorption coefficient of light traveling in opposite directions in a sample are different, the sample is said to have "non-reciprocal optical properties". Breaking the time-reversal symmetry is important because the sample has a non-reciprocal response. For example, when the sample is a magnetic material, a magnetic field is applied to the sample from the outside, or the light intensity is large and the light response is non-linear, the time reversal symmetry is broken.

The Faraday rotation angle, the car rotation angle, and the magnetic circular dichroism (hereinafter, also referred to as “MCD”) are measured in order to clarify the magneto-optical characteristics of the sample.

FIG. 11 is a conventional device for measuring Faraday rotation. Light enters the sample (“Sample”) 2 from the light source (“Source” in the figure) 1 via the polarizing element (“Analyzer”) 12 in the figure, and the light emitted from the sample 2 enters the sample (“Sample”) 2. It passes through "Analyzer" 13 in the figure and is detected by the detector ("Detector") 3 in the figure. When the polarized light passes through the sample 2 and does not rotate, the light is blocked by the analyzer 13. It does not reach the detector 3. When the polarized light passes through the sample 2 and rotates, a small amount of light passes through the analyzer 13 and is detected by the detector 3.

A polarizer is an optical element that produces linearly polarized light from natural light (non-polarized light) or circularly polarized light. The light transmitted through the polarizer becomes linearly polarized light that oscillates in the polarization axis direction of the polarizer. Further, for this linearly polarized light, it is usual to prepare another polarizer (in this case, referred to as an "inspector") and check whether the linearly polarized light can pass through the analyzer. The angle formed by the polarization axis of the polarizer and the polarization axis of the analyzer is here referred to as the angle between the axes of the polarizer and the analyzer. When the two transmission axes are parallel to each other in the two polarizers, the transmission intensity is maximum, and when the transmission axes are orthogonal to each other, the transmitted light is 0.

FIG. 12 shows the intensity of light passing through a polarizer and an analyzer as a function of the angle formed by the polarization axes of the polarizer and the analyzer. In the figure, when the angle is 90 degrees, the two polarization axes of the polarizer and the analyzer are orthogonal to each other.

FIG. 13 is a conventional device for measuring magnetic circular dichroism (MCD). The apparatus includes a light source 1, a polarizer (Polarizer) 12, a photoelastic modulator (PEM) 14, a pulse generator (Pulse Generator) 6, a lock-in amplifier (Lock-in Amplifier) 5, and a lock-in amplifier (Lock-in Amplifier) 5. It is composed of a detector 3. The photoelastic modulator (PEM) 14 modulates the light into left-handed and right-handed circularly polarized waves. At the timing of the pulse generator 6, the light modulated to left circularly polarized wave or right circularly polarized wave is incident on the sample 2 and partially absorbed. The difference in absorption between the left circularly polarized wave and the right circularly polarized wave is detected by the detector 3 using the lock-in amplifier. Since the lock-in amplifier 5 is used, this device can measure magnetic circular dichroism (MCD) with high sensitivity.

FIG. 14 is a conventional device for measuring the Kerr rotation angle due to the magnetic Kerr effect. The apparatus includes a light source 1, a polarizer (Polarizer) P1, a half mirror 8, an objective optical system (Objective) 9, a polarizer (Polarizer) P2, and a detector 3. To. The light polarized by the polarizer P1 is reflected on the surface of the sample 2 and detected by the detector 3. In front of the detector 3, a polarizer P1 and a polarizer P2 whose polarization axis is rotated by 90 degrees are placed. If there is no polarization rotation on the sample surface, the light is blocked by the polarizer P2 and does not reach the detector. When light is reflected on the surface of sample 2 and the polarized light is rotating, a certain amount of light is detected by the detector. Since the magnitude of the detected light is proportional to the rotation angle (car rotation angle), the rotation angle can be measured. Due to the Kerr effect, reflection occurs on the surface of the sample to convert left circularly polarized light to right circularly polarized light and vice versa.

In addition, the inventors have conducted research and development in the field of magneto-optics (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2014-013318

In the conventional optical measuring device, when measuring the magneto-optical characteristics, non-reciprocal optical characteristics, nonlinear optical characteristics, etc. of the sample to be investigated, the difference in optical characteristics when light travels in the sample in opposite directions is observed. I had to measure. In order to allow light to travel in the opposite direction in the sample, it is necessary to replace the sample or replace the optical fiber etc. at the entrance and exit parts of the sample, resulting in faster measurement and higher accuracy. There was a drawback that it could not be converted.

Further, the conventional device for measuring Faraday rotation (see FIG. 11) has a problem of poor sensitivity.

According to FIG. 12, the first-order differential coefficient of the transmission intensity is 0 when the polarization angle between the polarizer and the analyzer is 90 degrees. This means that the change in transmission intensity depending on the angle formed by the axes of the polarizer and the analyzer is very small. From this, it can be said that the conventional device for measuring the Faraday rotation has very poor measurement sensitivity. The sensitivity of conventional equipment is usually around 10-50 mdeg.

Further, as in FIG. 11, the Kerr effect measuring device (see FIG. 14) also has a drawback that the measurement sensitivity is low. It is considered that the reason why the sensitivity is low is that the differential coefficient of the passing light is 0 when the polarizers are at right angles (see FIG. 12).

Further, in the case of an apparatus for measuring magnetic circular dichroism (MCD), a high signal of magnetic circular dichroism can be obtained only when the wavelength of light is close to the edge of the absorption spectrum of the sample. There is a problem that this limits the information that can be obtained by measuring the magnetic circular dichroism (MCD) of the sample.

An object of the present invention is to solve these problems, and an object of the present invention is to provide an apparatus and a method for measuring a difference in optical characteristics when light travels in opposite directions in a sample to be measured. .. Another object of the present invention is to provide an apparatus and a method for measuring a difference in optical characteristics when traveling by switching the polarization state of light incident on a sample to be measured. Another object of the present invention is to provide an apparatus and a method capable of measuring magneto-optical characteristics, non-reciprocal optical characteristics, and nonlinear optical characteristics with high accuracy and high sensitivity.

The present invention has the following features in order to achieve the above object.
(1) A light source, a detector, and an optical switch that inputs light from the light source and outputs the light to a sample, and inputs light from the sample and outputs the light to the detector. An optical measuring device including an optical switch that switches between two states of the light input / output connection state of the light source.
(2) The optical switch includes a first port for inputting light from the light source, a second port for outputting light to the detector, and a first transmission line for transmitting and receiving a sample and light. It has a third port to be connected and a fourth port to be connected to a second transmission line for transmitting and receiving a sample and light, and the first port and the third port are connected and the third port is connected. There are two states, one in which the second port and the fourth port are connected, and the other in which the first port and the fourth port are connected and the second port and the third port are connected. The optical measuring device according to (1) above, which is an optical switch that switches between states.
(3) The optical measuring device according to (1) or (2), wherein the optical switch is switched and controlled by the pulse generator.
(4) The feature is that the first polarizer is arranged between the first transmission path and the sample, and the second polarizer is arranged between the second transmission path and the sample. The optical measuring device according to (2) or (3) above.
(5) A first quarter wave plate is arranged between the first transmission line and the sample, and a second quarter wave plate is placed between the second transmission line and the sample. The optical measuring apparatus according to any one of (2) to (4) above, which is characterized in that it is arranged.
(6) The optical measurement according to (4) or (5) above, wherein the first polarizing element and the second polarizing element have at least an angle of +45 degrees or −45 degrees for the polarization axes. apparatus.
(7) A first quarter wave plate is arranged between the first polarizer and the sample, and a second quarter wave plate is arranged between the second polarizer and the sample. The optical measuring device according to (4) above, wherein the optical measuring device is arranged.
(8) The polarization axes of the first polarizer, the first quarter wave plate, the second polarizer, and the second quarter wave plate are the light incident on the sample. However, the optical measurement according to (7) above is characterized in that, when the optical switch is switched, the light is set to have the same polarized state, and the switching reverses the relationship with the magnetization direction of the sample. apparatus.
(9) The polarization axes of the first polarizer, the first quarter wave plate, the second polarizer, and the second quarter wave plate are the light incident on the sample. However, the optical measuring apparatus according to (7) above, wherein the polarized light state is switched when the optical switch is switched.
(10) The optical according to any one of (1) to (9) above, wherein the optical measuring device is a device that measures any one or more of a magneto-optical characteristic, a non-reciprocal optical characteristic, and a nonlinear optical characteristic. measuring device.
(11) The optical measuring apparatus according to (1) above, wherein the direction of light passing through the sample is switched by switching the optical switch.
(12) The attenuator is arranged between the optical switch and the sample, and the intensity of the light incident on the sample is switched by switching the direction of the light incident on the sample and transmitted. (11) The optical measuring device according to the above.
(13) The optical measuring device according to (1), wherein the polarization state input to the sample is switched by switching the optical switch.
(14) An optical measurement method for measuring any one or more of magnetic optical characteristics, non-reciprocal optical characteristics, and non-linear optical characteristics, in which light from a light source is input and the light is output to a sample, and the light is output from the sample. It is equipped with an optical switch that inputs the light of the above and outputs it to the detector, and by switching the connection state of the light input / output with the sample between the two states, the direction of the light input to the sample and the direction of the light input to the sample. An optical measurement method characterized by switching any one or more of polarized states.

Since the measuring device of the present invention is provided with an optical switch, it is possible to measure the difference in optical characteristics when light travels in opposite directions in a sample quickly, with high accuracy and high sensitivity. That is, the direction of light propagation can be switched by, for example, a 2 × 2 optical switch without changing any element or device in the assembled optical circuit, so that the characteristics of light propagating in the opposite directions are characteristic. It can measure slight differences with high accuracy.

Further, since the measuring device of the present invention is configured to include an optical switch, the light incident on the sample can be switched. Therefore, the optical characteristics of the reflected light on the surface of the sample due to the difference in the polarization state of the incident light and the like. The difference can be measured quickly, with high accuracy and high sensitivity.

The measuring device of the present invention is particularly suitable for highly accurate and highly sensitive measurement in the measurement of magneto-optical characteristics, non-reciprocal optical characteristics, and nonlinear optical characteristics.

In the measurement method of the present invention, by providing an optical switch to switch, the light can be switched so as to travel in opposite directions in the sample, so that the magneto-optical characteristics, non-reciprocal optical characteristics, nonlinear optical characteristics, etc. can be quickly and It can be measured with high accuracy and high sensitivity.

Further, in the measurement method of the present invention, the light incident on the surface of the sample can be switched to a different polarization state by providing an optical switch to switch the light, so that the reflected light on the surface of the sample due to the difference in the incident light. The difference in optical characteristics can be measured quickly, with high accuracy and high sensitivity. Switching between two states with different polarization states means that, for example, right circularly polarized light and left circularly polarized light can be switched, and linearly polarized light and circularly polarized light can be switched.

In the measuring device or method of the present invention, the differential coefficient is set to +45 degrees or +45 degrees when the polarization angle becomes +45 degrees or +45 degrees by using a polarizer or a quarter wave plate arranged before and after the entrance and exit to the sample. When the maximum is used, more accurate and highly sensitive optical measurement becomes possible.

The figure which shows the apparatus which measures the non-reciprocal loss characteristic of 1st Embodiment. The figure which shows the apparatus which measures the non-reciprocal loss characteristic of the 2nd Embodiment. The figure which shows the apparatus for measuring the Faraday rotation angle of 3rd Embodiment. The figure which shows the apparatus for magnetic circular dichroism measurement of 4th Embodiment. The figure explaining the polarization state in two directions in the apparatus for measuring magnetic circular dichroism of the 4th Embodiment. The figure which shows another apparatus for magnetic circular dichroism measurement of 5th Embodiment. The figure which shows the apparatus which measures the nonlinear absorption characteristic of 6th Embodiment. The figure which shows the apparatus of 7th Embodiment. The figure explaining the polarization state in two directions in the measurement of the Kerr effect using the apparatus of 7th Embodiment. The figure explaining the polarization state in two directions in the magnetic circular dichroism measurement using the apparatus of 7th Embodiment. The figure which shows the conventional Faraday effect measuring apparatus. The figure which shows the relationship between the difference in polarization angles of a polarizer and an analyzer, and the transmitted light intensity. The figure which shows the conventional magnetic circular dichroism measuring apparatus. The figure which shows the device which measures the conventional car rotation angle.

The measuring device according to the embodiment of the present invention includes an optical switch, and the optical switch switches the direction of light propagation to incident light in opposite directions onto the sample to measure the optical characteristics. The direction of light propagation can be changed with, for example, a 2x2 optical switch without changing any of the elements / devices in the assembled optical circuit, so the characteristics of light propagating in the opposite directions are slight. The difference can be measured with high accuracy.

Further, in the measuring device of the embodiment of the present invention, the light propagating direction of the light is switched by the optical switch to switch the polarization state of the light incident on the sample, and the optical characteristics of the sample are measured.

An optical switch is a device mainly used in an optical communication network, and can branch a specific signal or switch a destination as an optical signal without converting it into an electric signal. An optical switch has a plurality of input / output ports, and when the number of input ports is N and the number of output ports is M, it is called an N × M switch. In the present embodiment, since it is necessary to switch so that the traveling directions are opposite to each other, for example, a 2 × 2 switch is used.

The optical measuring device of the present embodiment transmits and receives a light source, a detector, a first port for inputting light from the light source, a second port for outputting light to the detector, and a sample and light. It is provided with an optical switch having a third port connected to a first transmission line for transmitting and receiving light, and a fourth port connecting to a second transmission line for transmitting and receiving light to and from a sample. The optical switch has a state in which the first port and the third port are connected and the second port and the fourth port are connected, and the first port and the fourth port are connected. It is an optical switch that switches between being connected and the state in which the second port and the third port are connected.
The first and second transmission lines are, for example, optical fibers and waveguides.

(First Embodiment)
The present embodiment relates to a measuring device and a method for measuring non-reciprocal loss characteristics. This embodiment will be described with reference to FIG. FIG. 1 is an optical circuit constructed for measuring non-reciprocal loss characteristics. The measuring device of FIG. 1 includes a light source 1, an optical switch 4, and a detector 3. The detector 3 is, for example, a photodetector, and the optical switch 4 is, for example, a 2 × 2 optical fiber switch. 1 (a) and 1 (b) show two states of the optical switch. The light source and photodetector are connected to the same side of the 2x2 fiber optic switch. On the other side of the 2 × 2 fiber optical switch, a surface of the sample 2 in a direction opposite to that in one direction is connected to the optical fiber via a fiber collimator. The fiber collimator located on the surface opposite to the one-way surface of the sample 2 is a component for making the light emitted from the fiber parallel light by a lens and for causing a parallel beam to enter the fiber. The two states of the 2x2 optical fiber switch are exactly the same except that the directions of light incident are opposite. As indicated by arrows in sample 2, light propagation is from top to bottom in FIG. 1 (a) and from bottom to top in FIG. 1 (b). The difference in light detected in the two states of the 2x2 fiber optic switch corresponds to the difference in absorption of light passing through the sample in opposite directions, that is, to the non-reciprocal absorption of the sample. ..

(Second Embodiment)
The present embodiment relates to a non-reciprocal loss characteristic measuring device and method which is the same as the operating principle of the first embodiment and further includes a mechanism for controlling switching of an optical switch. This embodiment will be described with reference to FIG. FIG. 2 is an optical circuit for measuring non-reciprocal loss using a lock-in amplifier. The measuring device of FIG. 2 includes a light source 1, an optical switch 4, and a detector 3 as in the first embodiment, and further includes a lock-in amplifier 5 and a pulse generator (a pulse generator). A Puise Generator) 6 is provided. The continuous electrical pulse generated by the pulse generator 6 activates a 2x2 optical fiber switch to alternately generate the two states. In addition, this electric pulse is used as a reference signal of the lock-in amplifier. A lock-in amplifier is used, and lock-in technology detects only a specific signal with a detector. The detected signal is modulated by a 2x2 fiber optic switch to a frequency that alternately produces two states. The intensity of this modulated optical signal is proportional to the non-reciprocal loss value of the sample. This modulated frequency can be measured with high sensitivity and high accuracy by a lock-in amplifier.

(Third Embodiment)
The present embodiment relates to an apparatus and method for measuring a Faraday rotation angle, in which two polarizers are further arranged in an incident portion and an emitting portion of light of a sample in the same apparatus as in the second embodiment. This embodiment will be described with reference to FIG. FIG. 3 is an optical circuit for measuring Faraday rotation. The measuring device of FIG. 3 includes a light source 1, an optical switch 4, a detector 3, a lock-in amplifier 5, and a pulse generator 6 in the same manner as in the second embodiment, and further comprises light incidence of a sample. Two polarizers (P1, P2) are provided on the surface and the exit surface. In this embodiment, the polarization angles of the two polarizers differ by 45 degrees. That is, the angle of the polarization axes of the two polarizers is 45 degrees. Since the angle between the two polarizers is 45 degrees, the Faraday rotation angle can be measured with high accuracy and high sensitivity. The reason will be briefly explained. Since the Faraday effect is a non-reciprocal effect, polarized light rotates in the opposite direction when light comes in from the opposite direction. For example, when the direction in which light enters is from the direction shown in the figure, the Faraday rotation is +, the polarization of light in the polarizer is 45 degrees or more, and the detected signal is small (see FIG. 12). On the other hand, when the direction in which light enters is from the bottom of the figure, the Faraday rotation is −, the polarization of light in the polarizer is 45 degrees or less, and the detected signal is large. This is because the light curve passing through the two polarizers has the largest differential value at 45 degrees and −45 degrees.
In addition, the Faraday rotation angle can be measured with high accuracy and high sensitivity by detecting the difference in light traveling in opposite directions with a lock-in amplifier.

(Fourth Embodiment)
The present embodiment relates to an apparatus and method for measuring magnetic circular dichroism (MCD). In the present embodiment, a quarter wave plate is arranged in the same apparatus as in the third embodiment, and further in the optical input unit and the optical output unit of the sample. This embodiment will be described with reference to FIG.
FIG. 4 shows an optical circuit for measuring MCD. The optical circuit shown in FIG. 3 is the same as the optical circuit shown in FIG. 3, except that two quarter wave plates (QW1, QW2) are inserted between the sample and the polarizers (P1, P2). .. The polarization axes of the two polarizers are on the same axis. The angle between the axes of the two quarter wave plates is 90 degrees. The angle between the polarizer and the axis of the quarter wave plate is 45 degrees (or -45 degrees). For example, QW1 and P1 have a difference of 45 degrees, and QW2 and P2 have a difference of −45 degrees.

FIG. 5 illustrates the polarization state of light in the propagation directions opposite to each other when the device of FIG. 4 is used. The propagation direction from P1 and QW1 to QW2 and P2 via the sample is described in the upper row, and for convenience, it is referred to as a forward direction, and the opposite direction is described in the lower row and is referred to as a backward direction. The upper part of each of the upper and lower stages of FIG. 5 shows the phase of the x component and the y component of polarized light, and the lower part shows the polarization vector when light propagates along the z-axis. In the forward direction, the z-axis is oriented from the paper surface to the front (viewer), and in the reverse direction, the z-axis is directed from the front (viewer) to the paper surface.

In FIG. 5, the axes of the two polarizers (P1, P2) are each 45 degrees with respect to the x-axis. The low speed axis of the quarter polarizing plate QW1 is the y-axis, and the low speed axis of the quarter polarizing plate QW2 is the x-axis. The forward direction shown in the upper part of the figure will be described. In the forward direction, after the polarizer P1, the light is linearly polarized. The x and y components of polarized light are the same, and the phases are also the same. After the quarter wave plate QW1, the x component of the polarized light advances 90 degrees from the y component, and the polarized light is right-angled. Right-handed circularly polarized light passes through the sample. After passing through the quarter wave plate QW2, the x and y components of polarized light are in phase, and the polarized light is linearly polarized light. The polarization direction is along the polarization axis of the polarizer P2, and light passes through the polarizer P2 without being blocked.

The reverse direction shown in the lower part of the figure will be described. In the opposite direction, the light after passing through the polarizer P2 is linearly polarized. The x and y components of polarized light are equal and their phases are opposite. This means that the x component is 180 degrees ahead of the y component. After passing through the quarter wave plate QW2, the x component of polarized light is 90 degrees slower and 90 degrees ahead of the y component. The polarized light is right-handed circularly polarized light. Right-handed circularly polarized light passes through the sample. After the quarter wave plate QW1, the y component is delayed. The x and y components of polarized light have opposite phases, and the polarized light becomes linearly polarized light. The direction of polarization is along the polarizer P1, and the light passes through the polarizer P1 without being blocked.

Therefore, according to the apparatus of FIG. 4, as shown in FIG. 5, it is possible to measure the difference in absorption when the light of right-handed circularly polarized light propagates in the sample in the forward direction and the reverse direction.

The magnetic circular dichroism of a substance can be measured by the following three methods.
The first method is a method in which the magnetization of a substance and the propagation direction of light are constant, and only the rotation direction of light is changed. For example, light is propagated in the magnetization direction, and the difference in absorption between left-handed and right-handed circularly polarized light is measured.
The second method is a method in which the rotation direction of light and the propagation direction of light are constant and the magnetization of a substance is changed. For example, the difference in light absorption of right-handed circularly polarized light when the sample is magnetized in the same direction as the light propagation direction or in the direction opposite to the light propagation direction is measured.
The third method is a method in which the rotation direction of light and the magnetization of a substance are constant, and the propagation direction of light is changed. For example, the difference in light absorption of right-handed circularly polarized light is measured when the light propagation direction is in the same direction as the magnetization direction of the sample and in the opposite direction.

The device of FIG. 4 uses the third method.

As described above, according to the present embodiment, MCD can be measured with high accuracy and high sensitivity. In this embodiment, a polarizer and a quarter wave plate are arranged at both ends of the sample on both sides of the sample, and the axes of the plurality of polarizers and the axes of the plurality of quarter wave plates are circularly polarized light. Is arranged to pass through the sample.

(Fifth Embodiment)
The present embodiment relates to an apparatus and method for measuring MCD, which is partially different from the fourth embodiment. This embodiment will be described with reference to FIG. The measuring device of FIG. 6 includes a polarizing light source 11, a polarization maintaining fiber, an optical switch 4, a quarter wave plate (QW1, QW2), a detector 3, a lock-in amplifier 5, and a lock-in amplifier 5. A pulse generator 6 is provided. The continuous electric pulse generated by the pulse generator 6 operates the 2 × 2 optical fiber switch 4 to alternately generate two states. The lock-in amplifier 5 is used, and the light from the sample is detected by the detector 3 by the lock-in technique. A quarter wave plate (QW1, QW2) is inserted between the collimator and the sample 2, respectively. When the angle between the axis of the input / output fiber and the axis of the quarter wave plate is rotated by 45 degrees, the absorption of left circularly polarized light can be measured with high accuracy. Further, when this angle is −45 degrees, the absorption of right-handed circularly polarized light can be measured with high accuracy. When this angle is +45 degrees on one side of the sample and -45 degrees on the other side, the difference in absorption between left-handed and right-handed circularly polarized light can be measured.

Compared with the optical circuits of FIGS. 13 and 3, the advantage of the optical circuit of the present embodiment is that the absorption of left-handed circularly polarized light and right-handed circularly polarized light can be measured separately with high accuracy. In the optical circuits of FIGS. 13 and 3, only the difference in absorption between the left circularly polarized light and the right circularly polarized light can be observed.

(Sixth Embodiment)
The present embodiment relates to an apparatus and a method for measuring nonlinear absorption characteristics. This embodiment will be described with reference to FIG. FIG. 7 is an optical circuit for measuring nonlinear absorption. The measuring device of FIG. 7 includes a light source 1, an optical switch 4, and a detector 3 as in the first embodiment, and further includes an attenuator 7. The attenuator 7 is inserted between one side of the sample and the optical switch. (A) and (b) of FIG. 7 show two states of the optical switch 4.

As shown in FIG. 7A, in one state of the optical switch 4, the light passes through the attenuator 7 and then the sample 2. In another state of the optical switch, as shown in FIG. 7B, the light passes through the sample 2 and then through the attenuator 7. Light of different intensities passes through the sample in the two states of the optical switches shown in FIGS. 7 (a) and 7 (b). On the other hand, in FIGS. 7A and 7B, as shown in the figure, the pulse amplitude is almost the same in the detector 3 in the two states of the optical switch. The reason is that in the two states of the optical switch, light exits the light source, passes through the same optical element, and goes to the detector. Here, if the absorption of the sample does not depend on the light intensity, the light intensity of the detector is exactly the same in the two states of the optical switch. When the absorption of the sample depends on the light intensity, there is a small difference in the light intensity in the detector between the two states of the optical switch.

As shown in FIG. 2, this small difference can be measured with high accuracy by using a lock-in amplifier, and the non-linear absorption of the sample can be measured. When a variable attenuator is used as the attenuator, the light intensity dependence of nonlinear absorption can be measured.

(7th Embodiment)
The present embodiment relates to an apparatus and method for measuring magnetic car rotation and measuring MCD in reflection mode. This embodiment will be described with reference to FIG. FIG. 8 is an optical circuit for measuring the car rotation angle or MCD.

The measuring device of FIG. 8 includes a light source 1, an optical switch 4, and a detector 3 as in the first embodiment, and further includes a lock-in amplifier 5 and a pulse generator 6. It includes a first polarizer P1, a first quarter wave plate QW1, a half mirror 8, an objective optical system 9, a second quarter wavelength plate QW2, and a second polarizer P2.

The optical circuit of this embodiment is similar to the conventional optical circuit shown in FIG. 14, but in the optical circuit of this embodiment, the optical switch 4 is placed between the sample 2 and the detector 3 and the sample. The point provided between 2 and the light source 1 is significantly different. Further, by using the lock-in amplifier, the car rotation angle and the MCD can be measured with high accuracy and high sensitivity as compared with the conventional optical circuit.

In the measuring device of FIG. 8, a plurality of polarizers and a plurality of quarter wave plates are inserted after the fiber collimator.

When light is reflected by metal, some of the light is absorbed. In this case, when the metal is a magnetic material or an external magnetic field is applied, the absorption of left polarized light or right polarized light is different after reflection. This effect is called the reflection mode MCD effect. In the apparatus of FIG. 8, when measuring the MCD effect, the angle of the polarization axes of the two polarizers (P1 and P2) is set to 90 degrees. Further, the directions of the axes of the two quarter wave plates (QW1 and QW2) are set to be the same, and the angle between the polarizer and the polarization axes of the quarter wave plates is set to 45 degrees.

In the device of FIG. 8, when measuring the car rotation angle, the angle of the axes of the quarter wave plate QW1 and the quarter wave plate QW2 is set to 45 degrees. The angles of the polarization axes of the two polarizers (P1, P2) are set to be the same.

FIG. 9 illustrates the polarization state of light in the propagation directions opposite to each other when the Kerr effect measurement in the reflection mode is performed using the device of FIG. The propagation direction from P1 and QW1 to QW2 and P2 via the sample is described in the upper row, and for convenience, it is referred to as a forward direction, and the opposite direction is described in the lower row and is referred to as a backward direction. The upper part of each of the upper and lower stages of FIG. 9 shows the phase of the x component and the y component of polarized light, and the lower part shows the polarization vector when light propagates along the z-axis.

In the forward direction, the direction of the z-axis is from the paper surface to the front (viewer) before reflection, and from the front (viewer) to the paper surface after reflection. The x1 axis and the y1 axis are axes rotated by 45 degrees with respect to the x-axis and the y-axis, respectively. The angle between the axes of the quarter wave plate QW1 and the quarter wave plate QW2 is 45 degrees. The polarization angles of the two polarizers (P1, P2) are the same.

FIG. 9 is a diagram showing a simple case when there is no car rotation.
A case where the light propagation direction is the forward direction will be described. In the forward direction, the light after passing through the polarizer P1 is linearly polarized light having the same amplitude of the x component and the y component. The x component and the y component are in phase. After the quarter wave plate QW1, the light becomes right circularly polarized. After normal reflection on the sample, the polarized light changes to left circularly polarized light. The x1 axis and the y1 axis are the low speed axis and the high speed axis of the quarter wave plate QW2, respectively. When light passes through the quarter wave plate QW2, the polarized light becomes linearly polarized light, which is 45 degrees with respect to the polarization angles of the polarizers P1 and P2, respectively. Therefore, only half of the light passes through the polarizer 2.

A case where the light propagation direction is opposite will be described. In the opposite direction, after passing through the polarizer P2, the polarized light is linearly polarized and is along the y1 axis. The polarization direction of the light is not changed by the quarter wave plate QW2, and the incident light and the reflected light are linearly polarized light. The amplitudes of the x-axis and y-axis of polarized light are the same. After the quarter wave plate QW1, the polarized light becomes right circularly polarized. Only half of the light passes through the polarizer P1.

As mentioned above, in the absence of car rotation, the intensity of the output light is the same in both the forward and reverse directions, which is half the intensity of the input light. In the example of the device of FIG. 8, since the difference in light intensity between the opposite directions is measured, there is no difference if there is no car rotation depending on the sample.

When there is car rotation depending on the sample, there is a difference in the measured light intensity between the forward direction and the reverse direction. In the forward direction, circularly polarized light is reflected by the sample. Car rotation does not affect the detection intensity. This is because the polarized light that has already been rotated does not change due to the additional rotation of the car. However, in the opposite direction, the intensity of the output light depends on the car rotation angle. For example, if the polarized light rotates toward the x-axis after reflection, the y component of the polarized light becomes smaller. Therefore, after the quarter wave plate QW1, the polarized light becomes elliptically polarized light. As a result, the intensity of the output light is weakened.

FIG. 10 illustrates the polarization state of light in the propagation directions opposite to each other when the MCD measurement in the reflection mode is performed using the apparatus of FIG. In the forward direction shown in the upper part of the figure, the incident light on the sample is right-handed circularly polarized light. In the opposite direction shown in the lower part of the figure, the incident light is left-handed circularly polarized light. As shown in FIG. 10, the apparatus of FIG. 8 measures the difference in light intensity due to the difference between the left circularly polarized light and the right circularly polarized light in the incident light on the sample. The angle between the polarization axes of the two polarizers (P1, P2) is 90 degrees. In the figure, P1 has a polarization axis of 45 degrees, and P2 has a polarization axis of −45 degrees. Further, the polarization axes of the two quarter wave plates (QW1 and QW2) are the same.

In the above embodiment, the measurement of the non-reciprocal loss characteristic, the measurement of the Faraday rotation angle, the measurement of the photomagnetic circular dichroism (MCD), the measurement of the nonlinear absorption characteristic, and the measurement of the car rotation angle have been described. The measuring device shown in (1) can be used for measurement in which the input of light to the sample is switched by an optical switch.

It should be noted that the examples shown in the above-described embodiments and the like are described for the purpose of making the invention easier to understand, and are not limited to this embodiment.

1 Light source 2 Sample 3 Detector 4 Optical switch 5 Lock-in amplifier 6 Pulse generator 7 Attenuator 8 Half mirror 9 Objective optical system 11 Polarized light source 12 Polarizer 13 Detector 14 Photoelastic modulator P1 First polarizer P2 First Polarizer QW1 1st quarter wave plate QW2 2nd quarter wave plate

Claims (6)

Light source and
With the detector
It is an optical switch that inputs the light from the light source and outputs the light to the sample, and inputs the light from the sample and outputs it to the detector. An optical switch that switches between two states ,
Prepare
The optical switch is
A first port for inputting light from the light source, a second port for outputting light to the detector, and a third port for connecting to a sample and a first transmission line for transmitting and receiving light. It has a sample and a fourth port connected to a second transmission line for transmitting and receiving light, the first port and the third port are connected, and the second port and the fourth port are connected. An optical switch that switches between two states: a state in which a port is connected and a state in which the first port and the fourth port are connected and the second port and the third port are connected. ,
A first polarizer is placed between the first transmission line and the sample, and a second polarizer is placed between the second transmission line and the sample .
The first polarizer and the second polarizer, the first polarizer and the second polarizer polarization axis optical histological measurement device you characterized in that an angle of 4 5 degrees .. Light source and
With the detector
It is an optical switch that inputs the light from the light source and outputs the light to the sample, inputs the light from the sample and outputs it to the detector, and sets the connection state of the input / output of the light with the sample to 2. An optical switch that switches between two states ,
Prepare
The optical switch is
A first port for inputting light from the light source, a second port for outputting light to the detector, and a third port for connecting to a sample and a first transmission line for transmitting and receiving light. It has a sample and a fourth port connected to a second transmission line for transmitting and receiving light, the first port and the third port are connected, and the second port and the fourth port are connected. An optical switch that switches between two states: a state in which a port is connected and a state in which the first port and the fourth port are connected and the second port and the third port are connected. ,
A first polarizer is placed between the first transmission line and the sample, and a second polarizer is placed between the second transmission line and the sample .
A first quarter wave plate is placed between the first polarizer and the sample, and a second quarter wave plate is placed between the second polarizer and the sample .
The polarization axes of the first polarizer, the first quarter wave plate, the second polarizer, and the second quarter wave plate are such that the light incident on the sample is the light incident on the sample. during the switching of the optical switch, it is set to be light of the same polarization state, by the switching, optical histological measurement device you characterized in that the relationship between the magnetization direction of the sample is reversed. Light source and
With the detector
It is an optical switch that inputs the light from the light source and outputs the light to the sample, inputs the light from the sample and outputs it to the detector, and sets the connection state of the input / output of the light with the sample to 2. An optical switch that switches between two states ,
Prepare
The optical switch is
A first port for inputting light from the light source, a second port for outputting light to the detector, and a third port for connecting to a sample and a first transmission line for transmitting and receiving light. It has a sample and a fourth port connected to a second transmission line for transmitting and receiving light, the first port and the third port are connected, and the second port and the fourth port are connected. An optical switch that switches between two states: a state in which a port is connected and a state in which the first port and the fourth port are connected and the second port and the third port are connected. ,
A first polarizer is placed between the first transmission line and the sample, and a second polarizer is placed between the second transmission line and the sample .
A first quarter wave plate is placed between the first polarizer and the sample, and a second quarter wave plate is placed between the second polarizer and the sample .
The polarization axes of the first polarizer, the first quarter wave plate, the second polarizer, and the second quarter wave plate are such that the light incident on the sample is the light incident on the sample. during the switching of the optical switch, an optical histological measurement device you wherein the set so that the polarization state is switched vignetting, is a measure of the reflection mode. Light source and
With the detector
It is an optical switch that inputs the light from the light source and outputs the light to the sample, inputs the light from the sample and outputs it to the detector, and sets the connection state of the input / output of the light with the sample to 2. An optical switch that switches between two states ,
Prepare
The optical switch is
A first port for inputting light from the light source, a second port for outputting light to the detector, and a third port for connecting to a sample and a first transmission line for transmitting and receiving light. It has a sample and a fourth port connected to a second transmission line for transmitting and receiving light, the first port and the third port are connected, and the second port and the fourth port are connected. An optical switch that switches between two states: a state in which a port is connected and a state in which the first port and the fourth port are connected and the second port and the third port are connected. ,
By switching the optical switch, the direction of the light passing through the sample is switched .
Attenuator, arranged between the sample and the optical switch, by switching the direction of the light transmitted incident on the sample, light histological you and switches the intensity of light incident on the sample measuring device. The optical measuring device according to any one of claims 1 to 4, further comprising a pulse generator, wherein the optical switch is switched and controlled by the pulse generator. The optical measuring device according to any one of claims 1 to 5 , wherein the optical measuring device is a device that measures any one or more of a magneto-optical characteristic, a non-reciprocal optical characteristic, and a nonlinear optical characteristic.

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