JPH0821796A - Optical property measuring device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical property measuring device having high measurement reproducibility. [Structure] A light source 1 and a light flux from the light source
A light beam splitting device 4 for dividing the light beam into a light beam or a second light beam, and a first light receiving unit 8 arranged so as to receive a light beam from an object to be measured arranged on the optical axis of the first light beam and convert it into an electric signal.
A second light receiving section 7 for receiving the second light flux and converting it into an electric signal.
And a comparing means 14 for taking a ratio of the outputs from the first light receiving portion and the second light receiving portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring optical characteristics such as transmittance of an object to be measured.

[0002]

2. Description of the Related Art Conventionally, as a device for measuring the transmittance and the like of an object to be measured, there is, for example, a transmittance measuring device defined in JIS B7107-1969. This measuring device is composed of a light source and a photoelectric conversion element, and makes a light beam from the light source enter the object to be measured. The light flux transmitted through the object to be measured is received by the photoelectric conversion element and converted into an electric signal (output) proportional to the amount of incident light. The output of this photoelectric conversion element is used as a measurement signal. Next, the object to be measured is removed, and the light flux from the light source is directly incident on the photoelectric conversion element. The output of the photoelectric conversion element at this time is used as a reference signal. The ratio (percentage) of the obtained measurement signal and the reference signal is calculated and used as the transmittance of the measured object.

[0003]

However, in the conventional measuring apparatus, even if the same object to be measured is repeatedly measured, there is a slight variation in the transmittance between measurements. In short, it is said that "the reproducibility of measurement is low". Further, the conventional device has an inconvenience that the object to be measured must be attached and detached one by one during the measurement of the transmittance.

Further, in order to solve the above-mentioned problems, the present inventor has previously divided the luminous flux into two by using a luminous flux splitting means in the transmittance measuring device, and measures the measuring light transmitted through the measured object and the measured object. The inventors have made an invention to simultaneously measure non-transmitted reference light and improve the measurement accuracy without being affected by the light amount fluctuation of the light source. This invention has been filed in Japanese Patent Application No. 6-37392. This technology is still unpublished at the time of filing the specification of the present application. However, this transmittance measuring device is further provided with a device for performing amplitude modulation on the light source and removing noise by using the modulation frequency. When measuring the transmittance, a chopper or a half mirror is required for amplitude modulation. But,
When the optical members of the chopper and the half mirror are incorporated in the optical system of this device, the structure of the measuring device becomes complicated and the device itself becomes large.

Further, there is also a problem in that positioning of each optical member is carried out at the time of mounting, and it takes a lot of time for adjustment at the time of assembly. The present invention has been made in view of such conventional problems.

[0006]

SUMMARY OF THE INVENTION The present invention provides an optical characteristic measuring apparatus in which a light source and a light source having a reflecting portion for reflecting the light flux from the light source are provided with a first light flux and a second light flux periodically. , A first light receiving part and a second light receiving part for respectively receiving the first light beam and the second light beam and converting them into an electric signal, and outputs from the first light receiving part and the second light receiving part Comparing means for taking the ratio of The object to be measured is arranged on the optical axis of the first light beam, and the first light receiving section is arranged to receive the light beam from the object to be measured (claim 1).

Further, in the light beam splitting device, the first light beam splitting member having a reflecting portion for reflecting the light beam from the light source and the reflecting portion of the first light beam splitting member are caused to periodically appear on the optical axis of the light beam. And a driving member (claim 2). Further, in the light beam splitting device, further, a second light beam splitting member including a reflecting portion that reflects the light flux from the light source, a cutout portion that allows the light flux from the light source to pass therethrough, and the reflecting portion and the cutout portion are periodically described above. And a drive member for causing the light flux from the light source to appear on the optical axis (claim 3). As the second light beam splitting member, a light beam splitting member having an area ratio of 1: 1 between a reflecting portion that reflects the light flux from the light source and a cutout portion that allows the light flux from the light source to pass is used (claim 4).

The optical characteristic measuring device further comprises a computing device for computing the ratio of the outputs of the first light receiving portion and the second light receiving portion based on the information from the comparing means (claim 5). The invention according to any one of claims 1 to 4, further comprising: a frequency detector for reading the temporal cycle in which the luminous flux splitting member divides the luminous flux from the light source into the first luminous flux or the second luminous flux, and outputting a frequency signal relating to the cycle. Optical characteristic measurement in which only a signal corresponding to the frequency signal of the frequency detection unit is selected from the respective electric signals output from the first light receiving unit and the second light receiving unit, and a frequency selection device that outputs the selected signal is added The apparatus is (claim 6). Further, the outputs of the respective signals are compared from the signal corresponding to the first light receiving unit and the signal corresponding to the second light receiving unit output from the frequency selection device, and the DUT received by the first light receiving unit is compared. The optical characteristic measuring device is characterized in that a calculation device for calculating the ratio of the output relating to the luminous flux from the output to the output relating to the luminous flux from the luminous flux splitting member received by the second light receiving section is added (claim 7).

In addition to the above invention, a pinhole for passing a part of the light beam from the light source is added between the light source and the light beam splitting member, and the reduced light beam passing through the pinhole is incident on the light beam splitting member. The optical characteristic measuring device is provided (claim 8).

[0010]

According to the research conducted by the present inventor, it has been found that the cause of slight variations in measured values is the change in the light amount of the light source. According to the present invention, the light flux from the light source is divided into the first light flux and the second light flux in a short time period such that a change in the light amount of the light source can be ignored. The first light flux enters the object to be measured. The first light receiving unit receives the light flux that has transmitted or reflected the object to be measured. The second light receiving unit receives the second light flux. The comparison means takes the ratio of the signals output from the first and second light receiving parts. Therefore, the optical characteristics can be obtained more accurately (the invention of claim 1). A light beam splitting device that splits a light beam from a light source into a first light beam and a second light beam includes a first light beam splitting member having a reflecting portion that reflects the light beam from the light source, and a driving member that drives the first light beam splitting member. Driven by the light source and the reflecting portion for reflecting the light flux from the first light source and the light flux from the light source appear periodically on the optical axis (the invention of claim 2). Alternatively, a second portion having a reflection portion for transmitting the light flux from the light source and a cutout portion for allowing the light flux from the light source to pass therethrough.
The reflecting member and the cutout portion of the second luminous flux member are periodically made to appear on the optical axis of the luminous flux from the light source by the drive member by the driving member (the invention of claim 3). Further, assuming that the ratio of the area of the reflecting portion and the cutout portion of the second light flux member is 1: 1, the light amount of the passing light passing through the cutout portion and the light amount of the reflected light reflected by the reflecting portion are the reflectances of the reflecting portion. Assuming 100%, the ratio is 1: 1 (the invention of claim 4). Further, if the time represented by the reflection part in the luminous flux is equal to the time not represented in the luminous flux, the first luminous flux and the second luminous flux
The amount of light flux becomes equal.

By adding a calculation device for calculating the ratio of the outputs of the first light receiving portion and the second light receiving portion from the information of the comparing means to the configuration of the optical characteristic measuring device, the transmittance or reflection of the object to be measured can be obtained. The optical characteristics such as the ratio are calculated (the invention of claim 5). Alternatively, in the configuration of the optical characteristic measuring device, the light beam splitting member reads a time period in which the light beam from the light source is divided into the first light beam or the second light beam, and outputs a signal relating to the period, and a first light receiving unit. A frequency selecting device for selecting only a signal corresponding to the frequency signal of the frequency detecting section from the respective electric signals output from the second light receiving section and outputting the selected signal is added. The frequency detection unit detects a frequency signal distributed to the first light flux and the second light flux, and outputs the frequency signal to the frequency selection device. The frequency selection device
The frequency signal, the electric signal from the first light receiving unit, and the second signal
The electric signal from the light receiving unit is input. From the electric signal from the first light receiving portion and the electric signal from the second light receiving portion, only the signal corresponding to the frequency signal is selected and the selected signal is output to the comparing means (the invention of claim 6). In the case of such a device, the light beam splitting member has a frequency in the light source so that the frequency selection device can pick it up, and has a function of splitting the light beam from the light source into two. Therefore, it is not necessary to provide a chopper between the light source and the light beam splitting means, and the structure is simplified. Further, the frequency detector may be replaced with the first light receiver or the second light receiver.

Further, an optical characteristic measuring device to which the structure of claim 6 is added is compared with a computing device for computing a ratio of light amounts obtained from signals corresponding to the first light receiving portion and the second light receiving portion from the frequency selecting device. Used instead of means. Therefore, the optical characteristics such as the transmittance of the object to be measured can be automatically and instantly calculated (the invention of claim 7). This is advantageous when continuously measuring different objects to be measured. The calculation result is
It may be displayed as a numerical value or a graph on the display device. However, when the optical characteristic measuring apparatus of the present invention is incorporated in another manufacturing line or inspection line, the electrical signal (output) may be used as a signal for another operation without displaying it.

A pinhole for passing a part of the light beam from the light source is added between the light source and the light beam splitting member in all the optical characteristic measuring devices (the invention of claim 7). When measuring an object to be measured, in order to obtain a more accurate measurement value, it is necessary to narrow the light flux to a minute light flux. For that purpose, the light source itself may emit a minute luminous flux. This way,
This is because the light received by the first light receiving unit and the light received by the second light receiving unit are limited, so that the light amount can be efficiently measured.

Hereinafter, the present invention will be described in more detail by way of examples with reference to the drawings, but the present invention is not limited thereto.

[0015]

EXAMPLE FIG. 1 is a block diagram showing the overall configuration of a transmittance measuring apparatus according to an example. The transmittance measuring apparatus of this embodiment includes a light source 1, a collimator lens 2, a pinhole 3, a rotating mirror 4, a motor 5, a photoelectric switch 6, photodiodes 7 and 8, an object to be measured 9, lock-in amplifiers 10 and 11, It is composed of an arithmetic circuit 12, a digital voltmeter 13, and a computer 14.

The light source 1 is a white light source. The light emitted from the light source 1 is collimated by the collimator lens 2. The light converted into the parallel light flux is made into a narrow light flux by the pinhole 3. The size of the pinhole 3 is smaller than the size of the reflecting portion of the rotating mirror 4. The reason for this is that unless all the light that has passed through the pinhole 3 is received by the photodiode 8 that receives the light that has passed through the rotating mirror and the photodiode 7 that receives the light that has reflected by the rotating mirror 4, the This is because it becomes impossible to compare In short, it is necessary to make the size of the rotating mirror 4 necessary and sufficient together with the size of the pinhole 3.

By further reducing the size of the pinhole 3, the transmittance of a part of the object to be measured can be obtained. Then, by changing the position of the further reduced pinhole, it is possible to obtain the transmittance of each part of the measured object and measure the unevenness of the transmittance of the measured object. The rotating mirror 4 is a kind of light beam splitting member. In this embodiment, it has a shape as shown in FIG. The rotating mirror 4 is made of an aluminum plate, and the blades are mirror-finished on both sides. The blade serves as a reflecting portion that reflects the light flux from the light source. The rotary mirror 4 is provided with four fan-shaped blades radially with respect to the rotation axis. The inside of the dotted line shown in FIG. 2 indicates the mounting portion P. Outside the mounting portion P (outer peripheral side),
The ratio of the area of the blade to the area of the cutout is 1: 1. The light from the light source is divided into the first light flux and the second light flux by the rotating mirror 4. The first light flux is the passing light that has passed through the cutout portion of the rotating mirror 4, and the second light flux is the reflected light that is reflected by the reflecting portion of the rotating mirror 4. Since the areas of the cutout portion and the reflection portion are the same, when the rotating mirror continues to rotate at the same rotation speed, assuming that the reflectance of the rotating mirror is 100%, the reflected light reflected by the rotating mirror is The ratio of the amount of light passing through the cutout portion of the rotating mirror is 1: 1. Therefore, the purpose as a half mirror that divides the amount of light into 1: 1 is achieved,
Further, since the intensity of the passing light or the reflected light is generated in a predetermined cycle, the light of the light source 1 is amplitude-modulated at a predetermined frequency.

The present inventor has previously used a chopper for imparting a predetermined amplitude modulation frequency to light and a half mirror using a metal thin film or a dielectric film for splitting an optical path without using the present rotating mirror. Using. However, since a half mirror using a metal thin film or a dielectric film has an angle characteristic, the ratio of the amount of light transmitted through the half mirror to the amount of light reflected changes when the incident angle of light on the half mirror changes. Therefore, the inventor has to position the half mirror at a position where the influence thereof can be reduced as much as possible, and therefore, it is necessary to perform delicate adjustment, and thus it takes much time to assemble. On the other hand, when the rotating mirror as in this embodiment is used, the influence due to the angle characteristic of the half mirror as described above is eliminated, and the light amounts of the transmitted light and the reflected light are always the same, so that this problem can be solved.

The rotating mirror 4 is attached to the motor 5 with a removable set screw. The rotating mirror 4 is rotated at a constant speed by a motor 5 which is a kind of driving member. The rotating mirror 4 changes the rotating speed of the rotating mirror 4 from 60 to 4500 rpm by the motor 5 so that the signals from the first light receiving unit and the second light receiving unit can be input to the lock-in amplifier under optimum conditions. It is variable. In this embodiment, the rotation speed is around 2700 rpm.
With this rotation speed, even if the light of a fluorescent lamp or the like is input to each light receiving unit, the lock-in amplifier can delete the information of these lights.

The light passing through the cutout portion of the rotary mirror 4 illuminates the object 9 to be measured. The light transmitted through the DUT 9 is captured by the photodiode 8 which is a kind of the first light receiving section. The photodiode 8 detects the transmitted light that has passed through the object to be measured, and outputs a signal corresponding to the amount of light as a measurement signal. The measurement signal may also receive light other than the light passing through from the object to be measured, and thus is input to the lock-in amplifier 11. Further, the reflected light reflected by the rotating mirror 4 is captured by the photodiode 7 which is a kind of the second light receiving section. The photodiode 7 detects the reflected light and outputs a reference signal according to the amount of light. The reference signal is also
Since the light other than the reflected light from the rotating mirror 4 may be received in the same manner as the measurement signal, the lock-in amplifier 10
Is input to The photodiodes 7 and 8 may be other photoelectric conversion elements, integrating spheres, or the like.

In the vicinity of the rotating mirror 4, a photoelectric switch 6 which is a kind of frequency detecting section is installed. The photoelectric switch 6 measures the repetition cycle of the passing light and the reflected light and outputs a predetermined frequency signal. The predetermined frequency signal output from the photoelectric switch 6 is input to the lock-in amplifier 10 and the lock-in amplifier 11. The lock-in amplifier here is a kind of frequency selection device. The lock-in amplifier 10 or the lock-in amplifier 11 is a photoelectric switch 6
, A predetermined frequency signal, a reference signal from the photodiode 7, or a measurement signal from the photodiode 8. The lock-in amplifier 10 outputs a reference signal from which noise components other than a predetermined frequency are removed from the reference signal output from the photodiode 7. Similarly, the lock-in amplifier 11 outputs a measurement signal from which noise components other than a predetermined frequency are removed from the measurement signal output from the photodiode 7. Then, the selected reference signal and measurement signal are output to the comparison means.

The lock-in amplifier will be described below. The lock-in amplifier is often used because high measurement accuracy can be obtained even if the measured signal is a weak signal such that it is buried in noise. Has been done. As an example of the case where it is used for measuring light, a light flux from the light source is given a specific frequency characteristic by a chopper or the like in the middle of the light flux from the light source. The frequency is set to be different from the frequency of the noise light. Further, a frequency detector for measuring the frequency at which the chopper or the like applies amplitude modulation to the light source is provided. The light flux from the light source illuminates the DUT. The light transmitted through the object to be measured is photoelectrically converted by the photoelectric conversion element, and its output is input to the lock-in amplifier as a measurement signal. At this time, in most cases, light (noise) having a different frequency from the light flux from the light source is also received by the photoelectric conversion element. The light of noise is different from the frequency that rushes to the luminous flux, so use it,
The lock-in amplifier removes noise light. In this way, when the measurement is performed using the lock-in amplifier, only the measurement signal can be obtained even if the signal from the photoelectric conversion element has noise having a frequency component different from that of the measurement signal. Therefore, the noise is removed. In other words, it can be said to be a bandpass filter that detects a weak repetitive signal of a certain frequency buried in noise. The structure of the lock-in amplifier will be briefly described. It is composed of a switch for switching between inversion and non-inversion with a frequency signal according to the frequency signal, an averaging circuit, and the like.

The comparison means in this embodiment comprises an arithmetic circuit 12, a digital voltmeter 13 and a computer 14. The arithmetic circuit 12 calculates the value of the voltage Vr of the reference signal and the voltage of the measurement signal Vw, which are obtained from the outputs of the lock-in amplifier 10 and the lock-in amplifier 11, according to Equation 1
Calculate the ratio of two outputs and output as voltage.

[0024]

[Equation 1]

The output converted into voltage is converted from an analog signal to a digital signal by the digital voltmeter 13. The converted digital signal is sent to the computer 14, and the transmittance T is calculated by the computer 2 by the mathematical expression 2, and then displayed on the screen of the computer 14 as a numerical value.

[0026]

[Equation 2]

Note that Rr and Rt represent the ratio of reflection and passage of the rotating mirror 4. Further, k is a coefficient relating to the reflectance of the rotating mirror. The present invention is not limited to the above embodiment, and the light source 1 may be a laser, for example. In this case, the collimator lens 2 becomes unnecessary.
Regarding the rotary mirror 4, the shape of the mirror is not limited to the rotary mirror, and a mirror using a shutter mechanism may be used.
In this case, the shutter is opened and closed with a constant time period.

As a means for obtaining a frequency signal, a U-shaped photosensor in which a light emitting diode is attached to one side and a photodiode is attached to the other side of the U-shaped member other than the photoelectric switch 6 is used. , Or a signal from the photodiode 7 or the photodiode 8. Further, instead of the pinhole 3, the width of light may be limited by a lens or the like.

In this embodiment, the rear surface of the rotating mirror 4 opposite to the light source side is mirror-finished. This detects the light of the photoelectric switch reflected by the rotating mirror 4,
This is because the reflection type photoelectric switch 6 for reading the frequency is attached. However, if the output of the photo sensor 7 or the like is also used for detecting the frequency signal of the lock-in amplifier, the double-sided mirror surface is not always necessary. The same can be said when a U-shaped photo sensor is provided and the frequency is measured by the photo sensor.

The number of blades of the rotary mirror 4 is four in this embodiment, but may be one or five.
There is no particular regulation. For the material of the rotating mirror, iron,
Metal such as stainless steel or glass may be used. In this embodiment, the rotary mirror 4 and the motor 5 are mounted by using a set screw having a detachable mechanism, but other types such as a pin may be used. Further, the rotating mirror 4 may be detachable or non-removable as long as it is not necessary to change the ratio of reflection and transmission. Regarding the shape of the rotating mirror 4,
In this embodiment, the ratio of the area of the blade to the area of the cutout is set to 1: 1, but the ratio of reflection and transmission can be changed by changing the area of the blade and the area of the cutout.
By doing this, when the sensor on the reflection side receives light that is stronger than the allowable value, by reducing the area of the blade, the photodiode on the reflection side can receive light within the allowable value. It is possible to measure various transmittances.

In addition to the motor, the motor 5 may be used in place of the motor as long as it can stably rotate, such as rubber or a spring. In the present embodiment, the comparison means is composed of an arithmetic unit, a digital voltmeter, a computer, etc., but in addition, the photodiode 7 as the first light receiving portion and the photodiode 7 as the second light receiving portion are also provided. Any output can be measured as long as it can be compared with an ammeter or the like.

As described above, in the present embodiment, the measuring device for measuring the transmittance of the object to be measured has been described. However, the device in this embodiment allows the photodiode 7 to receive the amount of light reflected from the object to be measured. By measuring the amount of light reflected from the object to be measured, it can also be used as an apparatus for measuring the reflectance of the object to be measured.

[0033]

As described above, according to the optical characteristic measuring apparatus of the present invention, the light beam from the light source is split into two by the light beam splitting member, and the transmitted light which has passed through the light beam splitting member and passed through the object to be measured. The amount of light and the amount of reflected light reflected by the light beam splitting member are measured at the same time, and the transmittance is obtained.
Further, it is not necessary to attach or detach the DUT during the measurement of the transmittance.

Further, as compared with the measuring device in which the chopper and the half mirror are separately provided, the restrictions on the arrangement of the optical system are lessened and the structure is simplified, so that the measuring device can be miniaturized.
Moreover, since the number of parts that need adjustment is reduced, the adjustment time can be shortened and the assembly cost is not required.

[Brief description of drawings]

FIG. 1 is a device diagram of an embodiment according to the present invention.

FIG. 2 is a diagram of a rotating mirror used in an embodiment relating to the present invention.

[Explanation of symbols]

 1 ... Light source 2 Collimator lens 3 Pinhole 4 Rotating mirror 5 Motor 6 Photoelectric switch 7 Photodiode 8 .. Photodiode 9 ... Object to be measured 10 ... Lock-in amplifier 11 ... Lock-in amplifier 12 ... Arithmetic device 13 ... Digital voltmeter 14 ... Computer P ... Rotation Mirror mount or more

Claims (8)

[Claims] 1. A light source and a light beam from the light source are periodically first
A light beam splitting device for splitting into a light beam or a second light beam;
A first light receiving unit arranged on the optical axis of the light beam so as to receive a light beam from an object to be measured and convert it into an electric signal; and a second light receiving unit for receiving the second light beam and converting it into an electric signal. An optical characteristic measuring device, comprising: a first light receiving unit and a comparing unit that obtains a ratio of outputs from the second light receiving unit. 2. A light flux splitting device comprising: a first light flux splitting member having a reflecting portion for reflecting a light flux from the light source;
The optical characteristic measuring device according to claim 1, further comprising a driving member that causes the reflecting portion of the light beam splitting member to periodically appear on the optical axis of the light beam. 3. The light beam splitting device includes a second light beam splitting member including a reflecting portion for reflecting the light beam from the light source and a cutout portion for passing the light beam from the light source, the reflecting portion and the cutout portion. The optical characteristic measuring device according to claim 1, wherein the optical characteristic measuring device comprises a driving member that periodically appears on the optical axis of a light beam from the light source. 4. The second luminous flux splitting member has an area ratio of 1: 1 between a reflecting portion that reflects the luminous flux from the light source and a cutout portion that allows the luminous flux from the light source to pass therethrough. Item 2. The second light beam splitting member according to item 1 or claim 3. 5. The optical characteristic measuring device according to claim 1, wherein the comparing means comprises an arithmetic device for calculating a ratio of outputs of the first light receiving portion and the second light receiving portion. 6. A frequency detecting section for reading a temporal cycle in which the luminous flux splitting member divides the luminous flux from a light source into the first luminous flux or the second luminous flux, and outputting a frequency signal related to the period, and the first light receiving section. And a frequency selection device that selects only a signal corresponding to the frequency signal of the frequency detection unit from the respective electric signals output from the second light receiving unit, and outputs the selected signal. The optical characteristic measuring device according to claim 1, wherein the output of the above is input to the comparing means. 7. The output of each signal is compared from the signal corresponding to the first light receiving portion and the signal corresponding to the second light receiving portion output from the frequency selection device, and the first light receiving portion receives the signals. 7. An optical characteristic measuring apparatus according to claim 6, further comprising a calculation device for calculating a ratio between an output related to the light flux from the object to be measured and an output related to the light flux from the light flux splitting member received by the second light receiving section. . 8. A pinhole for passing a part of the light beam from the light source is added between the light source and the light beam splitting member, and the reduced light beam passing through the pinhole is made incident on the light beam splitting member. The optical characteristic measuring device according to claim 1.