KR101198013B1 - Multi-wavelength heterodyne interferometer using AOTF - Google Patents

Abstract

PURPOSE: A multi-frequency heterodyne interferometer using an AOTF(Acousto-Optical Tunable Filter) is provided to obtaining a multi-frequency interferometer using an acousto-optical tunable filter, thereby constituting various complex wavelengths by avoiding 2π-ambiguity with an optical system of a simple structure. CONSTITUTION: A multi-frequency heterodyne interferometer using an AOTF comprises a light source(600), a polarization beam splitter(610), an acousto-optical tunable filter(620), an AOTF driving unit(630), a sample stage(640), a second beam route guide unit(650), a quarter wavelength phase-lag plate, a multi-wavelength demodulator(670), and a controlling unit(680). The light source provides multi-wavelength beams. The polarization beam splitter transmits or reflects the beams provided by the light source according to a polarization condition. The acousto-optical tunable filter divides the multi-wavelength beams into first and second beams per wavelengths according to RF frequencies and outputs the second beams by separating the same from the first beams at a different angle according to each frequencies. The AOTF driving unit provides driving RF frequencies to the acousto-optical tunable filter, thereby driving the acousto-optical tunable filter. The sample stage is arranged in a progressive path of the first beams, thereby providing signal beams by reflecting the first beams along an incident route of the first beams. [Reference numerals] (630) AOTF driving unit; (676) Demodulator

Description

Multi-wavelength heterodyne interferometer using AOTF}

The present invention relates to a multi-wavelength heterodyne interferometer using an acoustic light modulation filter, and more specifically, by using a double pass optical alignment of the AOTF, multi-wavelength measurement can be performed with one interferometer without additional complicated optical system configuration. The present invention relates to a multi-wavelength heterodyne interferometer using AOTF, which can extend the measurement range and measure the absolute distance according to two wavelengths by avoiding ambiguity.

An interferometer is an optical system that divides light from the same light source into two or more branches to make a difference in the progress path, and then observes the interference phenomenon when the light meets again. It is widely applied to the device. In general, however, the interferometer is capable of measuring the measurement value up to 1/2 of the wavelength λ without any correction due to the interference phenomenon. Reflective interferometers, in particular, can travel up to one-quarter of the wavelength since they reciprocate the path. For example, in the case of a reflective interferometer using a helium-neon laser with a wavelength of 632 nm as a light source, a threshold occurs around 150 nm, and a repeating pattern appears for each height near 150 nm. This phenomenon is called 2π-ambiguity.

Hereinafter, the relationship between phase and distance and 2π-ambiguity in a reflective interferometer will be described in more detail. 1 is a diagram schematically showing a measurement object having a step. Referring to FIG. 1, when an arbitrary measurement target specimen is held with a reference plane (step difference = 0 nm) and measured with an interferometer, the interference signal is represented as a function of signal light and reference light, and can be represented by Equation 1 below. have.

,

)를 나타내고, Φ는 시스템에 의해 주어지는 준정적인 위상차로 상수값으로 간주할 수 있으며,

는 시편 면에서 반사되어 나오는 신호빛과 기준빛의 광 경로차를 나타낸다. Where Isig and Iref are the intensity of the signal and reference light

,

Is the quasi-static phase difference given by the system and can be regarded as a constant value,

Denotes the optical path difference between the signal light and the reference light reflected from the specimen surface.

In addition, a relationship as shown in Equation 2 below is established between the phase difference and the distance change (or step) of the interference signal given by the optical path difference.

When measuring the surface change, ie, the step, of a specimen with a reflective interferometer, the refractive index of air is 1, and the relative retardation is twice as optical path difference as it feels the difference between two optical paths when entering and exiting the surface. do.

That is, in FIG. 1, the optical path difference measured by an actual reflection type interferometer is twice the actual level because the optical path difference occurs when entering the reference plane and reflecting the point where there is no step, respectively.

Therefore, in the case of the reflective interferometer, the distance change (or step) according to the phase difference is twice the phase change, and is represented by Equation 3 below.

의 최대값이 π가 되어 측정할 수 있는 최대 거리변화는 λ/4가 된다. 이러한 현상을 2π-모호성이라 한다. 2 is a diagram showing an interference signal measured with an oscilloscope. Referring to (1) of FIG. 2, it can be seen that the interference signal is repeated every 2π because the sinusoidal form is a sin wave.

The maximum value of becomes π, and the maximum distance change that can be measured is λ / 4. This phenomenon is called 2π-ambiguity.

In consideration of this 2π-ambiguity, in the case of a scanning interferometer, if the distance between points measured on any specimen is minimized, the step difference is indirectly very small, and thus the distance change is λ / by using this phase unwrapping method. It can be considered as 4 or less.However, even if you maintain a very small measurement interval, if you measure the point where the distance change (or step) is suddenly λ / 4 or more, only the change of λ / 4 or less will be detected even after the phase unfolding. Done. In other words, there is no way to check the value of the cycle.

The most representative method for avoiding this phase ambiguity is a multi-wavelength interferometer. The multi-wavelength interferometer includes a homogeneous method, a multiple wavelength phase-shifting interferometer, a heterodyne method, a wavelength-multiplexed interferometry, a wavelength scanning heterodyne interferometer heterodyne interferometer, superheterodyne interferometer, and the like.

The multi-wavelength (normally two-wavelength) interferometer has the advantage that the measurement range can be widened by using a relatively long synthetic wavelength resulting from the combination of different wavelengths as shown in Equation (1).

는 합성파장을 말한다. 따라서 수학식 2와 같이 합성파장을 이용하면 위상과 거리관의 관계는 수학식 5와 같이 쉽게 나타낼 수 있다.here

Is the synthesized wavelength. Therefore, when the composite wavelength is used as in Equation 2, the relationship between the phase and the distance pipe can be easily expressed as in Equation 5.

In conclusion, as the synthesized wavelength increases, the measurement range also increases. For example, when the multi-wavelength interferometer is composed of 630nm and 530nm wavelength, the synthesized wavelength is about 3.3μm, so the measurement range that can be measured without phase ambiguity is increased.

However, in the conventional multi-wavelength interferometer, since a heterodyne interferometer must have a modulation device for each wavelength in order to modulate and temporally separate light of each wavelength, a complicated optical system is required, and the structure of the beam alignment is complicated. There is a problem that it is not easy. In addition, in the case of a phase shift interferometer, a quadrature signal is obtained using four phase shift signals. However, as the wavelength increases, the number of phase shifts increases and signal processing becomes complicated to obtain quadrature signals corresponding to the respective wavelengths.

An object of the present invention for solving the above-mentioned problems is that the structure of the optical system is very simple, but it is possible to modulate and split each wavelength at the same time, but because the interferometer consisting of all wavelengths form a quadrature state, 2π through a very easy process It is to provide a multi-wavelength heterodyne interferometer using AOTF, a multi-wavelength interferometer that can overcome ambiguity.

A feature of the present invention for solving the above technical problem is a multi-wavelength heterodyne interferometer, a light source for providing light of a multi-wavelength (Multi-Wavelength); A polarization beam splitter (PBS) for transmitting or reflecting light beams provided from the light source according to a polarization state; The light beam provided from the PBS is divided into first and second light beams of a first wavelength according to a driving RF frequency, and the second light beams are formed at different angles from the first light beam according to each wavelength. Acoustic light modulation filter (AOTF) to separate and output; An AOTF driver for driving the AOTF according to a driving RF frequency f _RF ; A sample stage on which a sample to be measured is placed, which is disposed in a propagation path of a first light beam provided from the AOTF, and reflects the first light beam along an incident path of the first light beam to provide a signal beam; A second light path guidance unit disposed on a progress path of second light beams provided from the AOTF, and reflecting the second light beams along each incident path to provide a reference beam; A quadrature phase delay plate (QWP) disposed between the AOTF, the sample stage, and the second light path guidance unit, and converting the incident light beams into circularly polarized light; Detects the interference signal of the signal light and the reference light that is reflected from the PBS after being output from the AOTF according to the wavelength, and receives information about the driving RF frequency from the AOTF driver, and the detection using the driving RF frequency A multi-wavelength demodulator for demodulating and outputting the interference signal; And a controller configured to detect information about a sample using a signal output by the multi-wavelength demodulator, wherein the first light beam is modulated by a driving RF frequency f _RF . It is light, and the second light is characterized in that the unmodulated zero-order light.

In the multi-wavelength heterodyne interferometer using the AOTF having the above-mentioned characteristics, the second light path induction unit comprises: a first mirror for reflecting light incident in parallel again along the incident path; And disposed in a traveling path of second light rays provided from the AOTF, reflecting the second light rays in parallel to each other to provide a first mirror, and second light rays reflected from the first mirror along the incident path, respectively. It is preferably characterized in that it comprises a; paraboloid mirror to reflect back to provide a reference light (Reference beam).

In the multi-wavelength heterodyne interferometer using the AOTF having the above-mentioned characteristics, the second light path induction part is disposed in the progress path of the second light beams provided from the AOTF, and reflects the second light beams along the incident path, respectively. And a spherical mirror to provide a reference beam.

In the multi-wavelength heterodyne interferometer using the AOTF having the above-described characteristics, the AOTF driver is provided to drive the AOTF by time-division a plurality of driving RF frequencies (f _RF ) to the AOTF over time. It is preferable to characterize.

In the multi-wavelength heterodyne interferometer using the AOTF having the above-mentioned characteristics, the multi-wavelength demodulator is a light sword for detecting the interference signal of the signal light and the reference light that is reflected from the PBS after the output from the AOTF according to the wavelength according to the wavelength Exit device; And a demodulator receiving information on a driving RF frequency from the AOTF driver and demodulating and outputting an interference signal provided by the photodetector according to a wavelength according to a wavelength using the driving RF frequency. desirable.

In the multi-wavelength heterodyne interferometer using the AOTF having the above-mentioned characteristics, the AOTF driver is characterized in that to drive the AOTF by simultaneously providing a plurality of driving RF frequencies (f _RF ) to the AOTF.

In the multi-wavelength heterodyne interferometer using the AOTF having the above-mentioned characteristics, the multi-wavelength demodulator is provided by separately separating the interference signal of the signal light and the reference light that is reflected from the PBS after being output from the AOTF according to the wavelength Dispersion device; A plurality of photodetectors disposed in a traveling path of the interference signals separated from the dispersing device and detecting interference signals according to wavelengths; And a plurality of demodulators receiving information on driving RF frequencies from the AOTF driver and demodulating and outputting interference signals provided from the plurality of photodetecting devices, respectively, using the driving RF frequencies. Preferably, the information on the sample is detected using the signals output by the two demodulators.

In the multi-wavelength heterodyne interferometer using the AOTF having the above-mentioned characteristics, the dispersion apparatus is characterized in that it is composed of any one of grating, dispersive prism and dichroic prism. desirable.

In the multi-wavelength heterodyne interferometer using the AOTF having the above-mentioned characteristics, it is preferable that the dispersion apparatus further comprises an optical bandpass filter for selectively transmitting each wavelength only in the path through which the interference signals travel. .

In the multi-wavelength heterodyne interferometer using the AOTF having the above characteristics, the light source is a multi-wavelength laser; And an optical isolator for aligning and outputting the light output from the multi-wavelength laser into P waves.

In the multi-wavelength heterodyne interferometer using the AOTF having the above-mentioned characteristics, the multi-wavelength heterodyne interferometer further comprises a frequency multiplier, the frequency multiplier converts the driving RF frequency provided from the AOTF driver to twice the frequency It is preferable to output to a demodulator.

In the multi-wavelength heterodyne interferometer using the AOTF having the above-mentioned characteristics, the multi-wavelength heterodyne interferometer preferably further comprises a convex lens between the QWP and the sample stage.

The multi-wavelength heterodyne interferometer using the AOTF according to the present invention implements a multi-wavelength interferometer using the AOTF, thereby avoiding 2π-ambiguity through the optical system of a simple structure, and can configure various synthesized wavelengths. It has the advantage of being actively adjustable.

In addition, the multi-wavelength heterodyne interferometer using the AOTF according to the present invention by sequentially providing a plurality of driving RF frequencies for each time through the AOTF driver, one optical sword for the interference signal for the light of the wavelength corresponding to each driving RF frequency It has the advantage that it can be obtained using only the output device and the demodulator.

In addition, since each interference signal outputted by a plurality of wavelengths through a driving RF frequency satisfies the quadrature state simultaneously using the AOTF, phase and amplitude of each wavelength can be simultaneously measured without a separate process. Since the information of the sample for each wavelength can be measured, the dispersion relationship according to the wavelength can be known. In particular, by using a dispersing device such as a grating or a prism, it is possible to stably measure the optical system without the movement of the optical system as compared with a conventional spectrometer which provides different wavelengths to a sample.

1 is a diagram schematically showing a measurement object having a step.
2 is a diagram showing an interference signal measured with an oscilloscope.
3 is a schematic structural diagram of a multi-wavelength heterodyne interferometer using AOTF according to a first embodiment of the present invention.
4 is a diagram showing another embodiment of the multi-wavelength heterodyne interferometer using AOTF according to the first embodiment of the present invention.
FIG. 5 is a diagram illustrating light rays incident to the AOTF and light rays modulated and output by the AOTF.
6 is a schematic structural diagram of a multi-wavelength heterodyne interferometer using AOTF according to a second embodiment of the present invention.
7 is a diagram showing another embodiment of the multi-wavelength heterodyne interferometer using the AOTF according to the second embodiment of the present invention.

Hereinafter, the structure and operation of a multi-wavelength heterodyne interferometer using AOTF according to various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1st Example

In the multi-wavelength heterodyne interferometer using AOTF according to the first embodiment of the present invention, the multi-wavelength heterodyne interferometer using AOTF uses double-beams that travel only in the same path as the incident path among the light rays passing through the AOTF. Pass multi-wavelength heterodyne interferometer, by providing each driving RF frequency (f _RF ) of the number of wavelengths used through the AOTF driver to the AOTF in time domain, thereby providing a plurality of interference signals having different wavelengths according to time. To be detected. The multi-wavelength heterodyne interferometer according to the first embodiment has a characteristic that the size and structure of the multi-wavelength heterodyne interferometer can be independently measured by only a single photodiode and a demodulator, compared to a conventional multi-wavelength system. .

3 is a schematic structural diagram of a multi-wavelength heterodyne interferometer using AOTF according to a first embodiment of the present invention. Referring to FIG. 3, the multi-wavelength heterodyne interferometer 60 according to the first embodiment of the present invention may include a light source 600, a PBS 610, an AOTF 620, an AOTF driver 630, and a sample stage 640. And a second light path guide unit 650, a QWP 660, a multi-wavelength demodulator 670, and a controller 680.

The light source 600 provides light of a multi-wavelength, and is an optical isolator for aligning and outputting the light output from the multi-wavelength laser 602 and the multi-wavelength laser 602 with P waves. 604. In addition, the light source 600 is described as one, but may be composed of a combination of a multi-wavelength laser, several monochromatic lasers, and a white light source.

The polarization beam splitter (PBS) 610 transmits or reflects incident light according to a polarization state. The PBS 610 transmits the P-wave as it is and reflects the S-wave perpendicular to the incident angle. Therefore, the PBS transmits the P wave provided from the light source 600 as it is and provides it to the AOTF 620.

The Acoustic-Optics Tunable Filter (AOTF) 620 serves as an optical band pass filter having a very narrow bandwidth by selecting only a specific wavelength among multiple wavelengths of light incident on the Acoustic-Optics Crystal. Do it. The AOTF 620 vibrates at a driving RF frequency f _RF provided from the AOTF driver 630, and as a result, the AOTF 620 has a first wavelength λ ₁ corresponding to the driving RF frequency f _RF among the incident light beams. The first light is output as first order light modulated by the driving RF frequency f _RF , and the second light is output as zero-order light with the original frequency f _{0 as it} is without modulation. do. At this time, the first light beam and the second light beam are diffracted at a slight angle, unlike the incident path. In particular, the first light beam is output irrespective of the driving RF frequency, that is, all input wavelengths are output by the same path, and the second light beam is diffracted and output at different angles, that is, in a fan shape, according to the driving RF frequency. In addition, the light rays of the P wave incident on the AOTF 620 become the S wave which is a linearly polarized state rotated 90 ° from the P wave by the characteristic of the AOTF as it passes through the AOTF 620.

)를 시간별로 분리시켜 순차적으로 제공하여 상기 AOTF를 구동시킨다. 즉, 일정한 시간 간격에 따라 순차적으로

,

,

를 제공하는 경우, 상기 AOTF로부터 출력되는 1차 빛살은 각각의 구동 RF 주파수에 대응되는 파장과 순차적으로 주파수를 각각

,

,

갖는 빛살이 된다. 상기 AOTF 구동부(630)는 전술한 바와 같이 시간에 따라 변화하는 구동 RF 주파수 정보를 다파장 복조부(670)으로 제공하게 된다.The AOTF driver 630 transmits a plurality of driving RF frequencies to the AOTF 620.

) Is provided sequentially and separated by time to drive the AOTF. That is, sequentially at regular time intervals

,

,

In case of providing the first light beams output from the AOTF, the frequencies corresponding to the respective driving RF frequencies are sequentially converted into frequencies.

,

,

It becomes light to have. As described above, the AOTF driver 630 provides the driving RF frequency information that changes with time to the multi-wavelength demodulator 670.

The multi-wavelength demodulator 670 consists of only one photodetector 674 and one demodulator 676. That is, the photodetector 674 sequentially detects interference signals of the signal light and the reference light, which are output from the AOTF and reflected by the PBS, sequentially according to respective wavelengths, and the demodulator 676 performs the The AOTF driver receives information on a driving RF frequency that changes with time, and demodulates an interference signal corresponding to each wavelength provided by the wavelength according to a wavelength from the photodetector using the information on the driving RF frequencies. To print. The demodulator 676 synchronizes driving RF frequency information that changes with time provided from the AOTF driver 630 and time-dependent interference signals provided from the photodetecting device to separate and demodulate interference signals according to respective wavelengths. To print.

On the other hand, the sample stage 640 is placed on the sample to be measured, and is disposed in the path of the first light beam provided from the AOTF 620, the first light beam is reflected again along the incident path of the first light beam Probe beam is provided.

The second light path guidance unit 650 is disposed on the path of the second light beams provided from the AOTF 620 and reflects the second light beams along the respective incident paths to provide a reference beam. . As shown in FIG. 3, the second light path guide part is disposed in a traveling path of the second light beams provided from the first mirror 652 and the AOTF 620 to reflect light rays incident in parallel again along the incident path. And reflecting the second rays in parallel to each other to provide the first mirror 652, and reflecting the second rays reflected back from the first mirror along the incident path to provide a reference beam. It may be provided as an off-axis parabolic mirror 654. At this time, the parabolic mirror is spaced apart from the AOTF by the focal length of the mirror.

4 is a view showing another embodiment of the multi-wavelength heterodyne interferometer using AOTF according to the first embodiment of the present invention. Referring to FIG. 4, the second light path guide unit 650 is disposed in a path of the second light beams provided from the AOTF 620, and reflects the second light beams along the incidence path, respectively. It may be provided as a spherical mirror 656 providing a reference beam. In the present invention, the spherical mirror 656 may be partially disposed only in the path of the second rays of light, and when the spherical mirror 656 is also disposed in the path of the first rays of light, the portion of the spherical mirror 656 is opened so as not to obstruct the path of the first rays of light. Should be.

On the other hand, since the quarter-wave phase delay plate QWP (Quater-Wave Plate; 660) is aligned at 45 °, when the linearly polarized light of S wave is incident, it is converted into circularly polarized light and outputted. Upon incidence, the light is converted into linearly polarized light of the P wave and output. The QWP 660 is disposed between the AOTF 620, the sample stage 640, and the second light path guide portion 650, and converts linearly varying S-waves provided by the AOTF 620 into circularly polarized light. The circularly polarized light reflected from the sample stage 640 or the second light path guide part 650 is converted into a linearly polarized light of P wave, and then output.

On the other hand, in order to use a multi-wavelength heterodyne interferometer using the AOTF according to the first embodiment of the present invention as a scanning microscope, a lens 665 may be further provided between the QWP 660 and the sample stage 640. . The lens 665 is provided to the sample stage 640 by focusing the light output from the QWP 660.

On the other hand, the signal light and the reference light reflected from the sample stage 640 and the second light path guide unit 650 passes through the QWP 660 and is remodulated in the AOTF 620 to proceed to the PBS (610). The first and second beams reflected by the sample stage 640 and the second beam path guide unit 650 are in a P-polarized state in circular polarization while passing through the QWP. In addition, the light beams re-entered into the AOTF are divided into primary light beams of the first wavelength modulated and modulated zero order light beams corresponding to the driving RF frequency f _RF . Accordingly, as the light beams once frequency-modulated are frequency-modulated again, the frequency difference between the two light beams output from the AOTF 620, that is, the beat frequency, becomes twice the driving RF frequency f _RF of the AOTF 620. In addition, the light beams passing through the AOTF 620 is converted to S-waves by rotating 90 °.

가 제공되는 경우, AOTF를 통과하는 빛살들 중 입사경로와 동일한 경로로 통과하는 빛살들을 도시한 것이며, 도 5의 (b)는 AOTF 구동부(630)로부터 구동 RF 주파수

가 제공되는 경우, AOTF를 통과한 후 거울들에 의해 반사되어 다시 AOTF로 입사되어 입사 경로와 동일한 경로 및 상기 입사경로와 다른 경로로 통과하는 빛살들을 도시한 것이며, 도 5의 (c)는 AOTF 구동부(630)로부터 구동 RF 주파수

,

,

가 동시에 제공되는 경우, AOTF를 통과한 후 거울들에 의해 반사되어 다시 AOTF로 입사되어 입사 경로와 동일한 경로 및 상기 입사경로와 다른 경로로 통과하는 빛살들을 도시한 것이다. 도 5의 (a)를 참조하면, 주파수(

)를 갖는 P편광의 빛살(a1)이 AOTF(50)로 입사되고, AOTF(50)로 입사된 빛살은 제1 빛살(a3) 및 제2 빛살들(a2)로 나뉘어 출력된다. 즉, 1차 빛살(a3)는 주파수(

)를 가지며, 0차 빛살(a2)들은 주파수(

)를 가지게 되며, 상기 0차 빛살들은 각 파장에 따라 1차 빛살과 서로 다른 각도로 분리되어 출력된다. AOTF로부터 출력된 1차 빛살(a3)은 QWP(52)를 통과하면서 45°회전하여 원형편광으로 변환되어 거울(56)으로 입사하게 되며, AOTF로부터 출력된 0차 빛살(a2)들은 QWP(52)를 통과하면서 45°회전하여 원형편광되어 구면거울과 같은 거울(54)로 입사하게 된다. 도 5에서는 설명의 편의상,

에서 i=1,2,3인 빛살만 도시하였다.
FIG. 5 is a diagram illustrating light rays incident to the AOTF and light rays modulated and output by the AOTF, and FIG. 5A illustrates a driving RF frequency from the AOTF driver 630.

When is provided, the light beams passing through the same path as the incident path of the light beams passing through the AOTF is shown, Figure 5 (b) is the driving RF frequency from the AOTF driver 630

If is provided, it shows the rays of light passing through the AOTF and then reflected by the mirrors and incident again to the AOTF to pass on the same path as the incident path and a path different from the incident path, and FIG. 5C shows the AOTF. Driven RF Frequency from Driver 630

,

,

Is provided at the same time, it shows the rays of light passing through the AOTF and then reflected by the mirrors and incident again to the AOTF to pass on the same path as the incident path and on a path different from the incident path. Referring to Figure 5 (a), the frequency (

The light beam a1 of P-polarized light having?) Is incident on the AOTF 50, and the light beam incident on the AOTF 50 is divided into the first light beam a3 and the second light beams a2. That is, the primary light a3 is the frequency (

), The zeroth order rays (a2) have a frequency (

The zeroth order light beams are separated and output at different angles from the first light beam according to each wavelength. The primary light beam a3 output from the AOTF is rotated 45 ° while passing through the QWP 52 to be converted into circularly polarized light and enters the mirror 56. The zeroth light beams a2 output from the AOTF are QWP 52. 45 ° rotates while passing through the circular polarized light is incident to the mirror 54, such as a spherical mirror. In FIG. 5 for convenience of description,

Only the glow with i = 1,2,3 is shown.

)의 0차 빛살(b2)들 및 주파수(

)의 1차 빛살(b1)이 각각 거울(56 및 54)에서 반사되어 QWP(52)를 통과하여 AOTF(50)로 재입사하게 된다. AOTF로 재입사된 1차 빛살(b1)은 AOTF를 그대로 통과하는 0차 빛살(b6)과 AOTF의 구동 RF 주파수(

)로 변조된 1차 빛살(b4)로 나뉘어 서로 일정각도 이격되어 출력된다. 즉, 주파수(

)의 0차 빛살(b6)과 주파수(

)의 1차 빛살(b4)로 나뉘어 출력된다. 한편, AOTF로 재입사된 0차 빛살(b2)은 AOTF를 그대로 통과하는 0차 빛살(b3)와 AOTF의 구동 RF 주파수(

)로 변조된 1차 빛살(b5)로 나뉘어 서로 일정각도 이격되어 출력된다. 즉, 서로 다른 각도로 분리되었던 0차 빛살(b2)들이 다시 AOTF로 재입사되면서 주파수(

)의 0차 빛살(b3)과 주파수(

)의 1차 빛살(b5)로 나뉘어 출력된다. 여기서, 주파수(

)의 1차 빛살(b4)과 주파수(

)의 0차 빛살(b3)은 서로 동일한 제1 경로를 따라 진행하며, 주파수(

)의 1차 빛살(b5)과 주파수(

)의 0차 빛살(b6)도 서로 동일한 제2 경로를 따라 진행하게 되며, 제1 경로와 제2 경로는 서로 일정각도 이격된다. Referring to (b) of FIG. 5, the frequency (

0th order rays b2 and frequency of

) Is reflected by the mirrors 56 and 54, respectively, and passes through the QWP 52 to reenter the AOTF 50. The primary light beam (b1) re-entered into the AOTF is the zeroth light beam (b6) passing through the AOTF as it is and the driving RF frequency of the AOTF (

It is divided into a primary light beam (b4) modulated by) and is output at a predetermined angle apart from each other. That is, frequency (

0th order of light (b6) and frequency (

The primary light beam of b) is divided and output. On the other hand, the zeroth order light beam b2 re-entered into the AOTF is the zeroth order light beam b3 passing through the AOTF as it is and the driving RF frequency of the AOTF (

It is divided into primary light beams b5 modulated by) and is output at a predetermined angle from each other. That is, the 0th order rays b2, which were separated at different angles, are reentered into the AOTF and thus the frequency (

0th order glow (b3) and frequency (

The primary light beam of b) is divided and output. Where frequency (

) 'S primary glow (b4) and frequency (

The zeroth order b3 of) travels along the same first path and has a frequency (

) 'S primary glow (b5) and frequency (

The zero-order light beam b6 of) also travels along the same second path, and the first path and the second path are spaced apart from each other by a predetermined angle.

,

,

가 동시에 제공되는 경우, 각 파장에 따라 주파수(

)의 1차 빛살과 주파수(

)의 0차 빛살들이 서로 다른 각도로 분리되어 진행하게 되므로, Balanced Detection이 가능한 다중파장 헤테로다인 간섭계를 구현하기 위해서는 각 파장에 따라 광검출소자를 각각 배치하거나, 서로 다른 각도로 분리되는 빛들을 하나로 집광시킨 후 그레이팅과 같은 분산장치를 이용하여 다시 분리한 후 광검출소자에 의해 검출할 수 있다. 이와 같이, balanced detection이 가능한 AOTF를 이용한 다중파장 헤테로다인 간섭계의 구현도 가능하나, 본 발명에서는 설명의 편의상 입사경로와 동일한 경로로 진행하는 빛살만을 이용하는 다중파장 헤테로다인 간섭계를 설명하도록 한다.By the way, referring to Figure 5 (c), the driving RF frequency from the AOTF driver 630

,

,

If is provided simultaneously, the frequency (

) 'S primary light and frequency (

Since the 0th order rays of the light beam are separated at different angles, in order to realize a multi-wavelength heterodyne interferometer capable of balanced detection, photodetectors may be arranged according to wavelengths, or light may be separated into one light at different angles. After the separation is performed again using a dispersing device such as a grating, it can be detected by the photodetecting device. As described above, although the implementation of the multi-wavelength heterodyne interferometer using the AOTF capable of balanced detection is possible, the present invention will be described for the convenience of the description of the multi-wavelength heterodyne interferometer using only light rays traveling in the same path as the incident path.

All of the light beams incident on the PBS 610 are S-polarized states, and only the light beams traveling in the first path are detected. The multi-wavelength demodulator 670 detects the interference signal of the signal light and the reference light which is output from the AOTF and reflected by the PBS according to the wavelength, and receives information on the driving RF frequency from the AOTF driver. The detected interference signal is demodulated and output using a driving RF frequency.

)는 체배기(Frequency Doubler; 678)를 통해 2배의 주파수(2

)로 변환되어 순차적으로 복조기(676)로 제공된다. 상기 복조기(676)는 상기 2배의 주파수(2

)를 이용하여 상기 광검출소자로부터 시간별로 제공되는 각각의 간섭신호를 복조하여 신호빛에 대한 I 신호 및 Q 신호를 검출하여 제어부(680)로 출력한다. 여기서, 상기 I값 및 Q 값은 수학식 6 및 7와 같다.The driving RF frequency according to the time provided from the AOTF driver 630 (

) Doubles the frequency (2) via a Frequency Doubler (678).

) Are sequentially provided to the demodulator 676. The demodulator 676 is the frequency twice (2)

) By demodulating each interference signal provided from the photodetecting device by time to detect the I signal and the Q signal for the signal light and output them to the controller 680. Here, the I value and the Q value are as shown in Equations 6 and 7.

Using the above-described I and Q values, it is possible to simultaneously detect amplitude and phase at all wavelengths according to Equations 8 and 9, respectively.

I and Q values corresponding to respective wavelengths over time output from the demodulator are provided to the controller 680 to detect phase and amplitude. The control unit 680 may be composed of an A / D converter 682 and a computer 684 for converting analog signals provided from a demodulator into digital signals, and the computer 684 may include a digital signal provided from an A / D converter. Store the I and Q values of the signal and detect the phase and amplitude from them.

Multi-wavelength heterodyne interferometer using the AOTF according to the first embodiment of the present invention having the above-described configuration by sequentially providing a plurality of driving RF frequencies for each time through the AOTF driver, the light of the wavelength corresponding to each driving RF frequency Has an advantage that the interference signal can be obtained using only one photodetector and a demodulator.

Second Example

The multi-wavelength heterodyne interferometer using AOTF according to the second embodiment of the present invention is a double-pass multi-wavelength heterodyne interferometer that uses only the light rays traveling in the same path as the incident path among the light rays passing through the AOTF. By simultaneously providing a plurality of driving RF frequencies f _RF to the AOTF through the driving unit, a plurality of interference signals having different wavelengths can be detected simultaneously.

 6 is a schematic structural diagram of a multi-wavelength heterodyne interferometer using AOTF according to a second embodiment of the present invention. Referring to FIG. 6, the multi-wavelength heterodyne interferometer 30 using the AOTF according to the second embodiment of the present invention includes a light source 300, a PBS 310, an AOTF 320, an AOTF driver 330, and a sample stage. 340, a second light path guide unit 350, a QWP 360, a multi-wavelength demodulator 370, and a controller 380.

The light source 300, the polarizing beam splitter (PBS) 310, the acoustic-optic tuneable filter (AOTF) 320, and the AOTF driver 330 have the same configuration and operation as those of the first embodiment. Therefore, duplicate descriptions are omitted.

The AOTF driver 330 according to the second embodiment of the present invention may simultaneously drive a plurality of driving RF frequencies f _RF to the AOTF 320 to drive the AOTF 320.

,

,

등의 복수 개의 구동 RF 주파수를 동시에 AOTF(320)로 제공되면, 상기 AOTF(320)는 상기 복수 개의 구동 RF 주파수에 대응하는 제1 파장, 제2 파장, 제3 파장 등을 갖는 제1 빛살들을 동일한 경로로 동시에 출력하게 된다. 이렇게 동시에 제공되는 복수 개의 파장의 신호빛들을 이용하여 본 발명의 제2 실시예에 따른 AOTF를 이용한 다중파장 헤테로다인 간섭계(30)는 신속하게 정보를 처리할 수 있게 된다.In other words, from the AOTF driver 330

,

,

When a plurality of driving RF frequencies, such as a plurality of driving RF frequencies, are simultaneously provided to the AOTF 320, the AOTF 320 may generate first rays having a first wavelength, a second wavelength, a third wavelength, or the like corresponding to the plurality of driving RF frequencies. It will output the same path at the same time. The multi-wavelength heterodyne interferometer 30 using the AOTF according to the second embodiment of the present invention can process information quickly by using the signal lights of the plurality of wavelengths provided at the same time.

On the other hand, since the sample stage 340 and the second light path guide unit 350 are the same as those in the first embodiment, overlapping description is omitted.

7 is a diagram showing another embodiment of the multi-wavelength heterodyne interferometer using the AOTF according to the second embodiment of the present invention. Referring to FIG. 7, the second light path guide unit 350 is disposed on a path of the second light beams provided from the AOTF 320, and reflects the second light beams along the incident path, respectively, to generate a reference light ( It may be provided as a spherical mirror 356 for providing a reference beam. In the present invention, the spherical mirror 356 may be partially disposed only in the path of the second rays of light, and when the spherical mirror 356 is also disposed in the path of the first rays of light, the portion of the spherical mirror 356 is opened so as not to obstruct the path of the first rays of light. Should be.

On the other hand, since the quarter-wave phase delay plate QWP (Quater-Wave Plate; 360) is aligned at 45 °, when the linearly polarized light of the S wave is incident, it is converted into circularly polarized light and outputted. Upon incidence, the light is converted into linearly polarized light of the P wave and output. The QWP 360 is disposed between the AOTF 320, the sample stage 340, and the second light path guide unit 350, and converts linearly varying S-waves provided by the AOTF 320 into circularly polarized light. The circular polarized light reflected from the sample stage 340 or the second light path guide unit 350 is converted into a linearly polarized P wave and output.

On the other hand, in order to use the multi-wavelength heterodyne interferometer using the AOTF according to the second embodiment of the present invention as a scanning microscope, a lens 365 may be further provided between the QWP 360 and the sample stage 340. . The lens 365 is provided to the sample stage 340 by focusing the light output from the QWP 360.

On the other hand, the signal light and the reference light reflected from the sample stage 340 and the second light path guide unit 350 passes through the QWP 360 and is remodulated in the AOTF 320 to proceed to the PBS 310. The first and second beams reflected by the sample stage 340 and the second beam path guide unit 350 pass through the QWP and become P-polarized in circular polarization. In addition, the light beams re-entered into the AOTF are divided into primary light beams of the first wavelength modulated and modulated zero order light beams corresponding to the driving RF frequency f _RF . Accordingly, as the light beams once frequency-modulated are frequency-modulated again, the frequency difference between the two light beams output from the AOTF 320, that is, the beat frequency, becomes twice the driving RF frequency f _RF of the AOTF 320. In addition, the light beams passing through the AOTF 320 are converted to S-waves by rotating 90 °.

The multi-wavelength heterodyne interferometer 30 using the AOTF according to the second embodiment of the present invention is characterized in that a plurality of driving RF frequencies are simultaneously provided to the AOTF, and the multi-wavelength demodulator 370 is a dispersion device ( 372, a plurality of photodetectors 374, and a plurality of demodulators 376.

의 기준빛과 주파수

의 신호빛의 간섭 신호를 파장에 따라 각각 분리하여 다수 개의 광검출소자(374)로 제공한다. 상기 분산장치(372)는 그레이팅(grating), 분산 프리즘(dispersive prism) 및 다이크로익 프리즘(dichroic prism) 중 어느 하나로 구성될 수 있다. 도 6에서는 상기 분산장치(372)를 그레이팅(grating)으로 구성하는 것을 예로 도시하였으며, 도 7에서는 상기 다이크로익 프리즘(dicroic prism)으로 구성하는 것을 예로 도시하였다. 한편, 상기 분산장치(372)와 광검출소자(374) 사이에는 각각의 파장만 선택적으로 투과시키는 광학 밴드패스 필터(373, 379)를 더 구비하는 것이 바람직하다.The dispersing device 372 is a frequency that is reflected from the PBS and proceeds after being output from the AOTF

Reference light and frequency

The interference signal of the signal light of the light source is separated into respective wavelengths and provided to the plurality of photodetecting elements 374. The dispersing device 372 may be composed of any one of grating, dispersive prism, and dichroic prism. In FIG. 6, the dispersing device 372 is configured by grating, and in FIG. 7, the dichroic prism is illustrated by way of example. On the other hand, between the dispersion device 372 and the light detecting element 374 it is preferable to further include optical band pass filter (373, 379) to selectively transmit only each wavelength.

The plurality of photodetectors are respectively disposed in the traveling paths of the interference signals separated from the dispersing device 372 to detect the interference signals according to the wavelengths, and convert them into electrical signals and output them to the plurality of demodulators 376, respectively. do.

)는 체배기(Frequency Doubler; 378)를 통해 2배의 주파수(2

)로 변환되어 다수 개의 복조기(376)로 제공된다. 상기 다수 개의 복조기(376)는 상기 2배의 주파수(2

)를 이용하여 상기 다수 개의 광검출소자로부터 제공되는 각각의 간섭신호를 복조하여 전술한 수학식 6 및 7과 같이 신호빛에 대한 I 신호 및 Q 신호를 검출하여 제어부(380)로 출력한다. 또한 전술한 수학식 8 및 9와 같이 모든 파장에서 진폭 및 위상을 동시에 검출할 수 있다.Driving RF frequency provided from the AOTF driver 330 (

) Is twice the frequency (2) through the Frequency Doubler (378).

) Is provided to a plurality of demodulators 376. The plurality of demodulators 376 has the double frequency (2)

) By demodulating each interference signal provided from the plurality of photodetectors to detect the I signal and the Q signal for signal light as shown in Equations 6 and 7 and output the same to the controller 380. In addition, as shown in Equations 8 and 9, amplitude and phase may be simultaneously detected at all wavelengths.

I and Q values corresponding to the respective wavelengths output from the respective demodulators are provided to the controller 380 to detect phase and amplitude.

The multi-wavelength heterodyne interferometer using AOTF having the above-described configuration has an advantage of enabling accurate measurement by overcoming 2π-ambiguity through a simple optical system by implementing a multi-wavelength interferometer using AOTF.

Although the present invention has been described above with reference to preferred embodiments thereof, this is merely an example and is not intended to limit the present invention, and those skilled in the art do not depart from the essential characteristics of the present invention. It will be appreciated that various modifications and applications which are not illustrated above in the scope are possible. And differences relating to such modifications and applications should be construed as being included in the scope of the invention as defined in the appended claims.

The multi-wavelength heterodyne interferometer using the acoustic light modulation filter according to the present invention can be widely used as a device for overcoming the ambiguity of the interferometer and for scanning the surface of the specimen or detecting the characteristics of the equipment.

30, 60: multi-wavelength heterodyne interferometer
300, 600: light source
310, 610: PBS
320, 620: AOTF
330, 630: AOTF drive part
340, 640: sample stage
350, 650: second light path guide unit
352, 652: first mirror
354: Parabolic Mirror
356: Spherical Mirror
360, 660: QWP
370, 670: multi-wavelength demodulator
372 dispersion device
374, 674: photodetector
376, 676: demodulator
380, 680: control unit

Claims (11)

A light source providing light of multi-wavelength;
A polarization beam splitter (PBS) for transmitting or reflecting light beams provided from the light source according to a polarization state;
The multi-wavelength light beam provided from the PBS is divided into first and second light beams for each wavelength according to a driving RF frequency f _RF , and the second light beams are different from the first light beam according to each wavelength. Acoustic light modulation filter (AOTF) for separating and outputting at an angle;
An AOTF driver providing the AOTF with a driving RF frequency f _RF to drive the AOTF;
A sample stage on which a sample to be measured is placed, disposed in a path of travel of the first rays of light provided from the AOTF, and reflecting the first rays of light along the incident path of the first rays of light to provide a signal beam;
A second light path guidance unit disposed on a progress path of second light beams provided from the AOTF, and reflecting the second light beams along each incident path to provide a reference beam;
A quadrature phase delay plate (QWP) disposed between the AOTF, the sample stage, and the second light path guidance unit, and converting the incident light beams into circularly polarized light;
Detects the interference signal of the signal light and the reference light that is reflected from the PBS after being output from the AOTF according to the wavelength, and receives information about the driving RF frequency from the AOTF driver, and the detection using the driving RF frequency A multi-wavelength demodulator for demodulating and outputting the interference signal; And
A control unit for detecting information about a sample using the signal output by the multi-wavelength demodulator;
Wherein the first rays of light are first-order rays modulated by a driving RF frequency f _RF , and the second rays of light are unmodulated zero-order rays of light. Multiwavelength Heterodyne Interferometer Using Optical Modulation Filter. The method of claim 1, wherein the second light path guide portion
A first mirror for reflecting light rays incident in parallel again along an incident path; And
Disposed in the path of the second rays of light provided from the AOTF, reflecting the second rays of light in parallel to each other to provide a first mirror, and the second rays of light reflected from the first mirror again along the path of incidence; A parabolic mirror that reflects to provide a reference beam;
Multi-wavelength heterodyne interferometer using the acoustic light modulation filter, characterized in that provided with. The method of claim 1, wherein the second light path guide portion
A spherical mirror disposed on a traveling path of second rays provided from the AOTF and reflecting the second rays again along an incident path to provide a reference beam;
Multi-wavelength heterodyne interferometer using the acoustic light modulation filter, characterized in that provided with. The method according to any one of claims 1 to 3, wherein the AOTF driver is provided to the AOTF sequentially by time-division a plurality of driving RF frequencies f _RF to drive the AOTF. A multiwavelength heterodyne interferometer using an acoustic light modulation filter. The method of claim 4, wherein the multi-wavelength demodulation unit
A photodetector for detecting an interference signal of a signal light and a reference light, which are output from the AOTF and reflected by the PBS, according to wavelengths; And
A demodulator receiving information on a driving RF frequency from the AOTF driver, and demodulating and outputting an interference signal provided according to a wavelength according to a wavelength from the photodetector using the driving RF frequency;
Multi-wavelength heterodyne interferometer using the acoustic light modulation filter, characterized in that provided with. The method according to any one of claims 1 to 3, wherein the AOTF driving unit provides the plurality of driving RF frequencies f _RF to the AOTF to drive the AOTF. Wavelength heterodyne interferometer. The method of claim 6, wherein the multi-wavelength demodulation unit
A dispersing apparatus that separates and provides an interference signal of a signal light and a reference light, which are output from the AOTF and reflected by the PBS, according to wavelengths;
A plurality of photodetectors disposed in a traveling path of the interference signals separated from the dispersing device and detecting interference signals according to wavelengths; And
A plurality of demodulators receiving information on a driving RF frequency from the AOTF driver and demodulating and outputting interference signals provided from the plurality of photodetectors using the driving RF frequencies;
Equipped with,
The control unit is a multi-wavelength heterodyne interferometer using an acoustic light modulation filter, characterized in that for detecting information about the sample using the signals output from the plurality of demodulators. 8. The multi-wavelength heterodyne interferometer according to claim 7, wherein the dispersing device is composed of any one of grating, dispersive prism, and dichroic prism. . 8. The multi-wavelength heterodyne interferometer according to claim 7, wherein the dispersing apparatus further comprises an optical band pass filter in a path through which the interference signals travel. The light source according to claim 1,
A multiwavelength laser composed of any one of a multiwavelength laser, a combination of several monochromatic lasers, and a white light source; And
An optical isolator for aligning and outputting light output from the multi-wavelength laser into P waves;
Multi-wavelength heterodyne interferometer using an acoustic light modulation filter, characterized in that consisting of. [2] The acoustic light of claim 1, wherein the multi-wavelength heterodyne interferometer further includes a frequency multiplier, and the frequency multiplier converts the driving RF frequency provided from the AOTF driver into a double frequency and outputs it to a demodulator. Multiwavelength Heterodyne Interferometer Using Modulation Filter.

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