JP2820659B2 - Ultra-high sensitivity optical rotation measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-high sensitivity optical rotation measuring device for non-invasively measuring the concentration of a rotatory substance in a suspension, in particular, sugar or cholesterol in blood.

[0002]

2. Description of the Related Art Conventionally, as means for measuring the rotation angle of a plane of polarization, that is, the optical rotation generated when linearly polarized light passes through an object to be measured, signal light passing through an analyzer is received by a photodiode. The optical rotation corresponding to the polarization characteristic of the object to be measured is measured based on the photoelectric conversion signal output from the photodiode.

[0003]

In a method for non-invasively measuring the blood glucose level and cholesterol level in a living body from outside the body, if the optical rotation of sugar or cholesterol is to be used, the blood may not be absorbed in the living body. Since the angle of rotation must be measured in the state of coexistence with the tissue, it corresponds to the measurement in the state of low concentration, and furthermore, the light passing through the living body is scattered and is in the same state as the suspension. Therefore, the sensitivity for measuring the blood glucose level and cholesterol level is required to be extremely high. In order to realize such an ultra-high sensitivity, it is necessary to employ a means capable of increasing the sensitivity in principle, and to remove various noises having a high amplification degree and obstructing the optical rotation measurement. Is an essential requirement. In view of this, the applicant of the present invention has disclosed in Japanese Patent Application No. Hei 7-16063, a method in which a polarization signal light that has passed through a measurement object whose rotation angle is to be measured and a polarization reference light that has passed through an optical path that does not pass through the measurement object. Amplifying by outputting an optical rotation angle signal proportional to the first power of the rotation angle of the polarization plane corresponding to the polarization characteristic of the measured object based on the optical heterodyne beat electric signal obtained by photoelectrically converting the frequency difference. An ultra-high sensitivity optical rotation measurement device capable of increasing the degree of rotation and measuring the angle of rotation with high accuracy was provided. In addition, Japanese Patent Application Hei 7-
No. 171004 provided an ultra-high sensitivity optical rotation measuring device capable of realizing high sensitivity by removing noise of a detection system when detecting an optical heterodyne beat electric signal. Another object of the present invention is to eliminate the amplitude fluctuation component of the light contained in the light emitted from the light source in order to increase the sensitivity of the above-mentioned conventional ultra-high sensitivity optical rotation measurement device. .

[0004]

In order to solve the above-mentioned problems, the present invention divides light having temporal coherence emitted from a light source into signal light and reference light, and separates the signal light and reference light. A polarization signal light and a polarization reference light, in which the polarization planes of the modulation signal light and the modulation reference light, each modulated at a predetermined frequency, were respectively polarized in a predetermined direction, were generated, and were passed through an object to be measured for an optical rotation angle. Based on the optical heterodyne beat electrical signal obtained by photoelectrically converting the frequency difference between the polarized signal light and the polarized reference light that has passed through the optical path that does not pass through the device under test, according to the polarization characteristics of the device under test. An ultra-high sensitivity optical rotation measurement device that outputs an optical rotation angle signal proportional to the first power of the rotation angle of the polarization plane, wherein the polarization signal light that has passed through the object to be measured and the optical signal that has passed through an optical path that does not pass through the object to be measured. Combines with polarized reference light A light splitting means for splitting and transmitting light in two directions, a photoelectric conversion means for photoelectrically converting each of the divided lights transmitted from the light splitting means, and an electric signal photoelectrically converted by each of the photoelectric conversion means. A calculating means for outputting the optical heterodyne beat electric signal from which the amplitude fluctuation component of the light contained in the light from the light source is removed by performing a dynamic operation.

[0005] According to the ultra-high sensitivity optical rotation measuring device having the above-mentioned configuration, the optical rotation angle signal proportional to the first power of the rotation angle of the polarization plane corresponding to the polarization characteristic of the measured object based on the optical heterodyne beat electric signal. In the process of outputting the light, when the light splitting unit multiplexes the polarized signal light passing through the object to be measured and the polarized light reference light passing through the optical path not passing through the object to be split and transmits the light in two directions, the photoelectric conversion unit Performs photoelectric conversion of each divided light, and when the photoelectrically converted electric signals are subjected to a differential operation by an arithmetic unit, the amplitude fluctuation component included in the light emitted from the light source is eliminated, and the measured object is Only the optical heterodyne beat electrical signal component proportional to the first power of the rotation angle of the polarization plane corresponding to the polarization characteristic can be output from the arithmetic means.

[0006]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an overall configuration of the ultra-high sensitivity optical rotation measurement device. Less than,
The configuration of this ultra-high sensitivity optical rotation measurement device and its operation will be described. As shown in FIG. 1, a single mode having high temporal coherence
The light P emitted from the laser diode light source 1 which emits the horizontally polarized laser light P of the laser diode is a photo-isolator P. I
Is incident on the beam splitter 2.

The light P incident on the beam splitter 2 is
It is split into transmitted light P1 and reflected light P2. The light P1 serves as reference light that passes through an optical path that does not pass through the object S to be described later, while the light P2 serves as a signal light that passes through an optical path that passes through the object S. The reference light P1 is incident on a first acousto-optic modulator (AOM) 6A. The reference light P <b> 1 incident on the first acousto-optic modulator 6 </ b> A is output from the acousto-optic modulator 6 </ b> A by the output signal of the signal oscillator 15.
Modulated at a frequency of 0.455 MHz. Therefore, the light that has passed through the first acousto-optic modulator 6A is 80.455 MHz.
The reference light is modulated at the frequency of z.

On the other hand, the signal light P2 is incident on a second acousto-optic modulator (AOM) 6B. The signal light P2 incident on the second acousto-optic modulator 6B is 80.000M in the acousto-optic modulator 6B according to the output signal of the signal oscillator 7.
It is modulated at a frequency of Hz. Accordingly, the light that has passed through the second acousto-optic modulator 6B becomes signal light modulated at a frequency of 80.000 MHz.

The reference light P 1 having passed through the first acousto-optic modulator 6 A has its polarization plane rotated by 90 degrees in the process of passing through the half-wave plate 3, becomes vertical polarization, and enters the polarizer 4. Then, by passing through the polarizer 4, the reference light P1A is narrowed down to only the direction in which the polarization direction is necessary.
After being reflected at right angles by the reflector 31, the polarizer 11A
Passes through the beam splitter 5 and is limited to only light having a polarization plane in the vertical direction.

The signal light P2A that has passed through the second acousto-optic modulator 6B and has been modulated at a frequency of 80.000 MHz.
Is reflected by the reflector 8 at right angles, is limited to only horizontally polarized light in the process of passing through the polarizer 9A, and is then subjected to a Faraday rotator (F.
R. ) 10. Faraday rotator 10
The signal from the PID circuit 25 and 1
A signal S obtained by adding the signal from the 100 Hz oscillator 32
Driven by G7.

The signal light P2C whose polarization plane has been rotated by driving the Faraday rotator 10 passes through the measured object S. When the signal light P2C passes through the measurement target S, the polarization of the measurement target S causes the signal light P2C to slightly rotate the plane of polarization. The signal light P2D that has passed through the measured object S is
In a state where a minute vertical polarization component is generated by the rotation of the minute polarization plane based on the polarization property of the measured object S, the polarizer 11
B is incident. Then, the vertical polarization signal light P2E from which most of the horizontal polarization components have been removed through the polarizer 11B is incident on the beam splitter 5.

The beam splitter 5 combines the reference light P1A and the signal light P2E, and splits the light P3A and the light P3A.
B is transmitted to two photodiodes 12A and 12B. Electric fields EP1A, EP of light P1A, P2E, respectively
2E, if the electric field of light is EOP1A, EOP2E,
At a certain time t, EP1A (t) = EOP1Acos ｛(ω0 + ω1) t
+ Φ1｝ EP2E (t) = EOP2Ecos ｛(ω0 + ω2) t
+ Φ2｝. Here, ω0 is the light frequency, ω1 is the reference light modulation frequency, ω2 is the signal light modulation frequency, φ1 is the phase of the reference light, and φ2 is the phase of the signal light. The electric fields EP3A and EP3B of the lights P3A and P3B split by the beam splitter 5 at a certain time t are as follows: EP3A (t) = (1 / √2) · ｛EP1A (t) + E
P2E (t)｝ EP3B (t) = (1 / √2) · ｛EP1A (t) -E
P2E (t)}.

In the photodiodes 12A and 12B, the current I proportional to the square of the absolute value of the electric fields EP3A and EP3B is
Photo-current conversion into SG1 and ISG2
The signals are converted into electric signals SG1 and SG2 corresponding to the currents ISG1 and ISG2 by operational amplifiers (not shown) provided integrally with the nodes 12A and 12B, respectively. Current ISG
The process of converting to ISG2 is as follows. ISG1 = | EP3A | ² = (1/2) · | EOP
1Acos {(ω0 + ω1) t + φ1} | ² + (1 /
2) · | EOP2Ecos {(ω0 + ω2) t + φ2}
│ ² + (1/2) ・ EOP1A ・ EOP2Ecos
{(2ω0 + ω1 + ω2) t + φ1 + φ2} + (1 /
2) EOP1A EOP2Ecosｃｏ (ω1-ω2)
t + φ1-φ2｝ ISG2 = | EP3B | ² = (1/2) · | EOP
1Acos {(ω0 + ω1) t + φ1} | ² + (1 /
2) · | EOP2Ecos {(ω0 + ω2) t + φ2}
| ^2- (1/2) EOP1A EOP2Ecos
{(2ω0 + ω1 + ω2) t + φ1 + φ2} − (1 /
2) EOP1A EOP2Ecosｃｏ (ω1-ω2)
t + φ1−φ2} However, since the term including ω0 of ISG1 and ISG2 exceeds the detection frequency range of the photodiodes 12A and 12B, it is converted as a constant DC component. The difference frequency ｛(ω1-ω) of the signal light P2E
2) An optical heterodyne beat signal of / 2π = 455 KHzＫ is obtained. If the amplitude of the laser light P emitted from the light source 1 is constant, the DC components of ISG1 and ISG2 are constant, and there is no influence on the detection of the rotation angle of the minute polarization plane based on the polarization of the measured object S. The laser light P emitted from the normally used light source 1 contains a time-varying amplitude fluctuation component which is a noise component. The reference light P1A and the signal light P2E also have an amplitude variation component of the laser light P of ISG1 and ISG1.
In the first and second terms of the ISG2 equation,
Most are included. Therefore, as a method of effectively suppressing the amplitude fluctuation of the laser light, the signal S
By performing the differential operation of G1-SG2, the signal SG3
Is EOP1A · EOP from which the first and second terms of ISG1 and ISG2 have been subtracted and the amplitude fluctuation component of the laser light has been removed.
An optical heterodyne beat signal having a frequency difference between the reference light P1A having an amplitude of 2E and the signal light P2E is obtained.

Signal SG output from differential operation circuit 13
Reference numeral 3 denotes an optical heterodyne beat electric signal from which the amplitude fluctuation component has been removed, and passes through the band-pass filter 16. The band pass filter 16 is 455 KHz ± 1.2 KHz
Only signals in the range Bandpass filter 1
The signal SG4 that has passed through the signal generator 6 becomes a DC signal SG5 that has been full-wave rectified by the full-wave rectifier REC and becomes a lock-in amplifier 23.
Is input to This lock-in amplifier 23 has 1100
Hz signal from the oscillator 32 to the reference signal ref. And outputs a signal SG6 obtained by detecting a 1100 Hz component in the DC signal output from the full-wave rectifier REC.

The signal SG6 output from the lock-in amplifier 23 is a signal proportional to the first power of the rotation angle of the minute polarization plane based on the polarization of the object S to be measured. This signal SG6 is input to the PID control circuit 25, and is output as a more precise signal proportional to the first power of the rotation angle of the polarization plane of the measured object S.

The signal OUT output from the PID control circuit 25 becomes an output signal of the ultra-high-sensitivity optical rotation measurement device.

Further, the output signal OUT is the above-mentioned 11
The signal S added to the oscillation signal from the 00 Hz oscillator 32
G7 is fed back to the Faraday rotator 10 described above. The negative feedback signal causes the Faraday rotator 10 to rotate in the opposite direction to cancel the minute rotation of the polarization plane based on the polarization of the object S.

In the above embodiment, the measurement target S is shown as a general multiple scatterer, but a finger or an earlobe is used as the measurement target, and the polarization signal light is transmitted through the measurement target. By measuring the rotation angle of a minute polarization plane based on the polarization of the body, it is possible to non-invasively measure a blood glucose level or a cholesterol level in a living body including a human body. Further, it is possible to precisely measure the rotation angle of a minute polarization plane based on the polarization of a turbid object as well as a transparent object.

[0019]

As described above, according to the present invention, in a state where the amplitude fluctuation component contained in the light from the light source is sufficiently removed, the rotation angle of the minute polarization plane based on the polarization of the object to be measured is reduced. A signal proportional to the first power can be output. Therefore, even if the rotation angle is extremely small, the amplitude fluctuation of the light emitted from the light source is sufficiently removed, so that amplification with low noise is possible, and the rotation angle of the measured object can be measured with high accuracy. can do. Therefore, using this as a basic technique, a prospect for measuring blood glucose level or cholesterol level in a living body including a human body with high accuracy and noninvasively is opened. In addition, the present invention can measure the rotation angle of a minute polarization plane based on the polarization property of multiple scatterers with ultra-high sensitivity, so that it can be applied not only to the medical field, but also to the biotechnology field and the engineering field. It is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 5 Beam splitter 12A, 12B Photodiode 13 Differential operation circuit S DUT P1A Polarization reference light P2E Polarization signal light P3A Division light P3B Division light SG1 Photoelectric conversion signal SG2 Photoelectric conversion signal SG3 Differential operation output signal

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshihide Naito 52, Katasaka-cho, Mizuho-ku, Nagoya-shi, Aichi 52 (56) References JP-A-8-210971 (JP, A) JP-A-9-21746 (JP, A) JP-A-63-44136 (JP, A) JP-A-4-34337 (JP, A) JP-A-4-231848 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) ) G01N 21/00-21/61 G01J 4/04

Claims (1)

(57) [Claims] 1. A modulated signal light and a modulated reference light obtained by dividing light having temporal coherence emitted from a light source into signal light and reference light, and modulating the signal light and the reference light at predetermined frequencies, respectively. A polarization signal light and a polarization reference light are generated by respectively polarizing the polarization planes in predetermined directions, and the polarization signal light passes through the measured object whose rotation angle is to be measured and passes through the optical path that does not pass through the measured object. An optical rotation angle proportional to the first power of a rotation angle of a polarization plane corresponding to a polarization characteristic of the object to be measured based on an optical heterodyne beat electrical signal obtained by photoelectrically converting a frequency difference from the polarization reference light. In the ultra-high-sensitivity optical rotation measurement device that outputs a signal, the polarization signal light that has passed through the object to be measured and the polarization reference light that has passed through an optical path that does not pass through the object to be measured are multiplexed and transmitted in two directions. Light splitting means that emits light and this light component Photoelectric conversion means for photoelectrically converting each of the divided lights transmitted from the means, and a differential operation of the electric signal photoelectrically converted by each of the photoelectric conversion means, thereby performing a light calculation on the light contained in the light from the light source. And a calculating means for outputting the optical heterodyne beat electric signal from which the amplitude fluctuation component has been removed.