KR101282932B1

KR101282932B1 - Visibility Enhanced Low Coherence Interferometer

Info

Publication number: KR101282932B1
Application number: KR1020100104862A
Authority: KR
Inventors: 진종한; 김재완; 강주식; 김종안
Original assignee: 한국표준과학연구원
Priority date: 2010-10-26
Filing date: 2010-10-26
Publication date: 2013-07-05
Also published as: KR20120043526A

Abstract

The present invention relates to a visibility-improved low coherence interferometer, and more specifically, to the injection locking method by using the white light (multi-wavelength) in the injection lock method to measure the amount of reflected light when measuring the step difference due to coherence of low reflectivity materials, such as in a fluid or semi-transparent biosample The present invention relates to a visibility enhancement low coherence interferometer that amplifies without phase distortion and improves visibility by equally or similarly reflecting a reference light signal and a reflected light signal reflected from a reference plane and a measurement plane, respectively.

Description

Visibility Enhanced Low Coherence Interferometer

Optical interferometers using a stabilized laser can be measured due to the speed of light retrospectively to the length standard. The measurement resolution can be obtained below nm, making it suitable for many applications requiring ultra-precision measurements.

Although the optical interferometer is one of the most accurate measurement techniques, it is difficult to measure a material with low reflectivity, which is commonly seen in real life by glass plates, color filters, specimens with rough surfaces, cells or molecules submerged in liquids, etc. .

For reliable measurement, the visibility of interference fringes should be good enough to analyze the received interference fringes. However, when measuring low reflectance materials, the intensity of light reflected from the measurement surface is very small, resulting in rapid visibility. Will fall out. This means that maximum visibility can be obtained when the intensity of light reflected from the reference plane and the measurement plane is the same, but low reflectance material has poor visibility due to the small reflected light.

To prevent this loss of visibility, amplify the intensity of light reflected from the measurement plane to match the intensity of light reflected from the reference plane, or adjust the intensity of light reflected from the reference plane to adjust the intensity of light reflected from the measurement plane. You can use a method to make it equal to the intensity, but there is a limited improvement in visibility.

The latter is a method of increasing the amount of reflected light by allowing more than 90% of the light to proceed to the measurement plane of the amount of light divided into the reference plane and the measurement plane. However, this method is not only troublesome to adjust the amount of light emitted from the measuring plane and the reference plane of the interferometer every time depending on the state of the measuring plane, but also the measurement itself may be impossible when the amount of light is less than the threshold of measurement. There are drawbacks to receiving.

The problem of poor visibility due to the difference in light quantity of the two split light beams has also been shown in low coherence interferometers using white light as the main light, which is used for the optical tomography of living organisms.

For example, low coherence interferometers are mainly used for optical tomography of living organisms by using white light (multi-wavelength) utilizing short interference distance due to wide frequency range as a main light source rather than short wavelength light source. The low coherence interferometer detects the vertices of the interference fringe obtained by precisely transferring the measurement plane or the reference plane in the optical axis direction so that three-dimensional shape measurement of the microsurface is performed.

However, as described above, most of the biosamples to be measured are semi-transparent materials, and thus the amount of reflected light is extremely small.

Therefore, it is necessary to study a device that can improve the accuracy of tomography by improving the visibility of semi-transparent materials while using white light.

The visibility improvement low coherence interferometer of the present invention,

When tomography is performed by varying the measurement plane or reference plane, even if the reflected light has a very small light quantity of nW level, the amplification is performed without changing the phase or time characteristics by the injection locking method using the secondary light source (auxiliary light source). The purpose of the present invention is to improve visibility by matching or making the amount of light reflected by the light reflected from the reference plane equal or similar.

Visibility improvement low coherence interferometer of the present invention for solving the above problems,

A main light source unit for irradiating multi-wavelength light; An optical splitter dividing the irradiated optical signal into two; A reference plane reflecting unit and a measuring plane reflecting unit for reflecting the optical signal separated by the light splitting unit to the reference plane and the measurement plane of the measurement object, respectively; A photodetector configured to combine the optical signals reflected by the reference plane reflector and the measurement plane reflector so that interference is observed and observe the interference; An optical axis fine moving unit for finely moving the reference plane or the measurement plane of the reference plane reflection unit in the optical axis direction; And an auxiliary light source unit for amplifying the reflected light through the injection lock.

The auxiliary light source unit is installed on either side of the reference plane reflection unit or the measurement plane reflection unit to amplify the reflected light signal reflected from the measurement plane reflection unit or the reference light signal reflected from the reference plane reflection unit,

Each of the reference plane reflector and the measurement plane reflector may be installed to amplify the weakly reflected light of the reflected light signal reflected from the measurement plane reflector and the reference light signal reflected from the reference plane reflector.

As described in detail above, the visibility enhancement low coherence interferometer of the present invention,

When measuring the level difference due to coherence of low reflectance materials such as semi-transparent biosample using white light (multi-wavelength), the amount of reflected light is amplified without phase distortion by injection locking method, and the reference light signal reflected from the reference plane and the measurement plane, respectively It is possible to provide a visibility enhancement low coherence interferometer with the same or similar reflected light signal.

1 is a block diagram showing a visibility enhancement low coherence interferometer according to an embodiment of the present invention.
2 to 3 is a block diagram showing a visibility enhancement low coherence interferometer according to another embodiment of the present invention.

Hereinafter, the present invention will be described in detail with the accompanying drawings.

1 is a block diagram showing a visibility-enhanced low coherence interferometer according to an embodiment of the present invention. As described, the visibility enhancement low coherence interferometer according to the present invention is separated by a main light source unit 20 for irradiating multi-wavelength light, an optical splitter 30 for dividing the irradiated optical signal into two, and the light splitter The light reflected from the reference plane reflecting unit 40 and the measuring plane reflecting unit 50, and the reference plane reflecting unit and the measuring plane reflecting unit, respectively, reflecting the reflected optical signal to the reference plane 41 and the measurement plane 51 of the measurement object. The optical detection unit 60, the optical axis micro-movement unit 70, which finely moves the reference plane or the measurement plane of the measurement plane reflection unit in the optical axis direction to observe the interference by synthesizing the signal, and optically amplifies the reflected light. and an auxiliary light source unit 80 for amplifying through an optical amplificaiont.

The main light source unit 20 uses white light for irradiating multi-wavelength light, the light splitter 30 uses a 2 × 2 coupler, and uses a photo detector (PD) as the light detector 60.

The light irradiated from the main light source unit 20, which is the white light, is split in the light splitter 30 and is incident to the reference plane reflecting unit and the measurement plane reflecting unit, respectively.

The reference plane reflection unit 40 and the measurement plane reflection unit 50 include a conventional lens and a reference plane (reference mirror; 41) or a measurement plane (measurement object; 51), and the light incident on the reference plane reflection unit is a reference plane ( 41), the light is reflected back to the incident direction, and the light incident on the measuring surface reflecting portion is reflected back to the measuring surface 51 of the translucent biosample to be measured.

The reference light signal reflected by the reference plane 41 and the reflected light signal reflected by the measurement plane 51 are returned to the light splitter 30. In the light splitter, the reference light signal and the reflected light signal interfere with each other and the photodetector PD. 60) to observe the interference signal.

In this process, the reference plane 41 of the reference plane reflection unit or the measurement plane 51 of the measurement plane reflection unit is provided with an optical axis micro-movement unit 70 for finely moving in the optical axis direction to move one side of the reference plane or the measurement plane in the optical axis direction. Check the interference range for each moving distance to make shape measurement.

The optical axis micro-movement unit enables automatic movement by electronic control to drive the PZT, LM guide or fine adjustment screw in the direction of the optical axis by power means such as a micromotor or a motor, or manually rotates the fine adjustment screw by rotating the fine adjustment screw directly. Conventional methods may be applied, such as to allow movement.

In this operation, tomography (shape measurement) of the low-reflective material, which is a semi-transparent biosample, is because the amount of reflected light is weak, and the auxiliary light source unit 80 is further used as a means for amplifying it.

The auxiliary light source unit 80 may use an optical fiber amplifier (EDFA; Er-doped fiber amplifier) or the like that can amplify the same wide wavelength as the main light source. In this case, the auxiliary light source unit can compensate for the amplified or distorted phase of the optical signal reflected by the injection lock without phase distortion.

As shown in FIG. 2, the auxiliary light source unit 80 is installed only on the reference plane reflection unit 40 (or only on the measurement plane reflection unit; not shown) to amplify the reference light signal reflected on the reference plane 41, or As shown in FIG. 3, both signals are identical by amplifying a weak signal among the reference light signal reflected on the reference plane and the reflected light signal reflected on the measurement plane, provided at both the reference plane reflection unit 40 and the measurement plane reflection unit 50. Or similar light quantity.

The auxiliary light source unit 80 allows current control by the photodetector 60. At this time, the control may be made to maintain a constant visibility by the feedback control (feedback control), this control can be made automatically by the control unit, or the user can be set arbitrarily.

In addition, the auxiliary light source unit 80 may allow the light reflected by the circulator to proceed separately from the incident line of the reference plane reflection unit or the measurement plane reflection unit.

For example, as shown in FIG. 1, two circulators, a first circulator 93 and a second circulator 94, are provided on the measurement surface reflector side, and the incident light signal progress line 91 is reflected from the incident light signal progress line 91. 92 is branched, and the auxiliary light source unit 80 is installed in the branched reflected light signal progress line 92. When the reflected light signal progress lines are connected by the two circulators 93 and 94, the reflected light signal reflected from the measurement surface is changed from the first circulator 93 to the reflected light signal progress line 92. After the amplification is performed by the injection light in the auxiliary light source unit 80 without phase distortion, the second circulator 94 proceeds to return along the incident tube signal progress line 91 to reflect the reference light reflected from the reference plane by the light splitter 30. The interference is combined with the signal.

The interference is observed in the photodetector 60 and provides good visibility since the reflected light signal and the reference light signal have similar amounts of light.

In addition, the reference axis 41 or the measurement plane 51 is moved finely by the optical axis micro-movement unit 70 and the measurement is made through the above process. When the difference in the amount of light between the reflected light signal and the reference light signal is generated, the light detector 60 By controlling the current to the auxiliary light source unit 80 to adjust the amount of light amplified to make the light amount of the two signals to be similar. At this time, the control may be made to maintain a constant visibility by the feedback control (feedback control), this control can be made automatically by the control unit, or the user can be set arbitrarily.

The circulators 93 and 94 may have a variable number of installations depending on the use environment, such as one or a plurality of circulators, in addition to two.

10: Improved visibility Low coherence interferometer
20: main light source
30: light splitting part
40: reference plane reflecting unit
41: reference plane
50: measuring surface reflector
51: measuring surface
60: light detector
70: optical axis fine moving part
80: auxiliary light source
91: incident light signal progress line 92: reflected light signal progress line
93: first circulator 94: second circulator

Claims

A main light source unit 20 for irradiating multi-wavelength light;
An optical splitter 30 dividing the irradiated optical signal into two;
A reference plane reflecting unit 40 and a measuring plane reflecting unit 50 for reflecting the optical signal separated by the light splitting unit to the reference plane and the measurement plane of the measurement object, respectively;
A light detection unit 60 for combining low-coherence interference by observing the optical signals reflected by the reference plane reflection unit and the measurement plane reflection unit, and observing this;
An optical axis fine moving unit 70 for finely moving the reference plane or the measurement plane of the reference plane reflection unit in the optical axis direction;
It is configured to include; a secondary light source unit 80 for amplifying the reflected light through the injection lock,
The auxiliary light source unit 80 is installed in the measurement surface reflector 50, the visibility enhancement low coherence interferometer, characterized in that for amplifying the reflected light signal reflected from the measurement surface reflector without phase distortion.

delete

The method of claim 1,
The auxiliary light source unit (80) is a visibility enhancement low coherence interferometer, characterized in that the feedback control is carried out so that the visibility obtained by the light detector is kept constant.