KR20110011052A - Apparatus of controlling speckle contrast of light - Google Patents

Abstract

PURPOSE: An apparatus for controlling the speckle contrast of light is provided to avoid problems generated from single mode optical fiber by guiding light to multi-mode fiber wound around a piezoelectric transducer. CONSTITUTION: A cylindrical piezoelectric transducer is vibrated in a radial direction. Multi mode optical fiber includes light in a plurality of modes which is guided into the core of the optical fiber. The multi mode optical fiber is composed of a glass core and a polymer cladding. The multi mode optical fiber is wound around the piezoelectric transducer. While the piezoelectric transducer is vibrated in the radial direction, light passes through the multi mode optical fiber.

Description

Speckle Contrast Control of Rays {apparatus of controlling speckle contrast of light}

The present invention relates to a speckle contrast control device for light rays, and more particularly, to a speckle contrast control device for light rays in which MMF is wound around a cylindrical PZT vibrating in a radial direction.

The optical fiber is composed of core, cladding, and coating. The core carries the optical signal itself, and the cladding serves to keep the optical signal in the core.

MMF refers to an optical fiber with multiple modes of light guided inside the optical fiber core. The optical fiber usually has a diameter of 50 µm or more, and has a stepped refractive index fiber and a hillside refractive index fiber. SMF refers to an optical fiber that reduces the diameter of the optical fiber core and guides only one mode.

The propagation of light in the optical fiber can be represented by the Maxwell equation. Material constants, such as the index of refraction of the medium through which light propagates, and boundary conditions in the core and cladding of the optical fiber and in the low refractive index surrounding the core in the optical waveguide or optical fiber The wave equation of Solving this wave equation reveals the distribution of the electromagnetic field. The distribution of electromagnetic fields along the optical fiber is called the mode of the optical fiber.

When light is guided through the MMF, spatial coherence control and temporal coherence control are provided as a way to reduce the speckle of speckles generated at the optical fiber output due to the interference between modes. In both cases, a method of controlling coherence in a light source may include 1) applying external perturbation such as vibration to the optical fiber itself, or 2) simultaneously injecting light sources of different frequencies. In the case of 1) to control the spatial coherence, the optical fiber is installed on the rotating plate to change the phase of light to be guided. Then, the randomly distributed speckles will change their position over time and look as if the water is boiling, taking several pictures of that shape over a period of time and averaging them based on luminance You get an image of this reduced form. The process of requesting candidate crystals is not only a fatal disadvantage in laser processing or display applications that require stable light in real time, but also has a saturation effect when a charge-coupled device (CCD) is used as a detector. Cause. In the case of 2), time coherence is controlled by incoherently scanning light sources having different frequencies. Although it has the advantage of being effective for pulsed lasers, it also has a candidate process for averaging multiple images, which is a burden in terms of cost, and also greatly increases the size and complexity of a configuration system, which is a major obstacle to the development of integrated circuits.

Accordingly, the first problem to be solved by the present invention is to provide an apparatus for controlling speckle contrast of light beams capable of forming a homogeneous light beam while being able to integrate into an integrated circuit and avoiding various problems caused by using SMF.

The present invention is a cylindrical PZT vibrating in the radial direction to achieve the first object; And an MMF having at least one mode of light guided in the core of the optical fiber, the MMF wound around the PZT, wherein the light beam passes through the MMF while the PZT vibrates in a radial direction. Provides a speckle contrast control device.

In addition, the MMF may be composed of a glass core and a polymer cladding, typically a hard polymer-clad fiber (HPCF).

According to an embodiment of the present invention, the objective lens for passing the light beam output from the MMF; And a separate MMF for receiving and passing a light beam passing through the objective lens.

In addition, an objective lens for passing the light beam output from the MMF; And a light splitter configured to split the light beam passing through the objective lens into at least two light beams.

According to another embodiment of the present invention, the cross-sectional shape of the multimode optical fiber may have a D-shape.

According to another embodiment of the present invention, the PZT vibrates in the radial direction by applying a sine wave voltage oscillating at a radio frequency (RF) to the PZT.

In addition, the speckle contrast of the light beam is minimized when the RF is a natural frequency of the PZT.

According to the present invention, by guiding the light beam to the MMF wound in the cylindrical PZT vibrating in the radial direction, it is possible to form a homogeneous light beam while avoiding various problems that can be caused by the use of SMF can play an important role in the optical fiber processing industry. have. In addition, the present invention can be effectively applied to color synthesizers and splitters in consideration of the fact that virtual incomplete coherence (VPC) is maintained regardless of branching by the light splitter. The term "virtual" here means a decrease in the spatial coherence of the light source. Furthermore, according to the present invention, the combination of the modes generated when the optical fiber is bent together with the phase change of the guided light produces an effective effect even at high frames per second (fps), thereby eliminating the need for candidate work. A ray homogenizer can be produced. In addition, according to the present invention, the principle is very simple, making it easy to manufacture and the size of the configuration system is quite small, so that it can be developed as an integrated device.

Hereinafter, the present invention will be described in more detail with reference to preferred examples. However, these examples are intended to illustrate the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited thereby.

In the present invention, the MMF is wound around the axis of the cylindrical PZT oscillating in the radial direction, and the PZT is subjected to an electric signal in the form of a sine wave in the RF region and the PZT is vibrated to induce the MMF to receive an aco-optic effect. Acousto-optic effect is an effect of changing the effective refractive index of the material constituting the optical fiber by external perturbation such as shaking. RF is a frequency from about 3 Hz to 300 GHz, and the frequency in this range corresponds to the frequency of the AC electrical signal used to generate / sense the radio wave.

Since the vibrations of the PZT must be well transmitted to the MMF in order to have an effective aco-optic effect, it is important to face the outer wall of the PZT as tightly as possible without the MMF breaking. In this case, in order to allow the MMF to be wound as tightly as possible on the PZT, the cross-sectional shape of the optical fiber may be configured in a D-shape, and the flat surface may face the outer wall of the PZT.

라디안 이상 더 빠르게 변해야 한다. 광도 파로는 광전력(Optical Power)을 도파할 수 있는 구조로서, 광통신에서 광신호를 전달하도록 설계된 광섬유가 대표적이다. When the optical waveguide through which the ray passes is disturbed from the outside, the pattern distribution of the ray at the optical waveguide output is modulated due to the phase modulation and the coupling between the modes of the ray passing through the waveguide. In order to homogenize the spatial modes, the carrier phase is relatively on the time scale rather than the response time of the detection system.

It should change faster than radians. An optical waveguide is a structure capable of guiding optical power, and an optical fiber designed to transmit an optical signal in optical communication is typical.

번째 모드의 전력 변화는 다음의 수학식 1과 같이 나타내어진다.By mode combination

The power change in the first mode is represented by Equation 1 below.

은 광도파로를 지나는 광선들의 모드

과

사이의 전력 결합 계수,

은 모드

의 초기 전력,

은 광도파로에 있는 모드들의 총 수를 의미한다. 만일 전파 위치(Propagation Position)

에 따른 광섬유 변형 함수

가 광섬유 길이

에 대하여 알려져 있는 경우, 길이

에 대한 모드

과

사이의 전력 결합 계수는 다음의 수학식 2와 같이 나타내어진다.here,

Is the mode of rays passing through the optical waveguide

and

Power coupling coefficient between,

Silver mode

Initial power,

Is the total number of modes in the optical waveguide. Propagation Position

Optical fiber strain function

Fiber optic length

Length, if known

Mode for

and

The power coupling coefficient between is represented by Equation 2 below.

은 광섬유 구조에 따른 상수이고,

은 다음의 수학식 3과 같이 나타내어진다.here

Is a constant according to the optical fiber structure,

Is expressed as in Equation 3 below.

과

은 각각 모드

과

의 전파 상수(Propagation Constant)이다. 이상의 수학식 1, 2, 3을 이용하여 도 1에 도시된 압전소자-광섬유 조합(Piezo-Fiber Assembly, PFA)에 진동을 가할 때의 변화를 이하 살펴보기로 한다.here

and

Each mode

and

Propagation constant of. A change in applying vibration to the piezo-fiber assembly (PFA) shown in FIG. 1 using Equations 1, 2, and 3 will now be described.

1 is a conceptual diagram of a PFA according to an embodiment of the present invention and shows a change when applying vibration. Fig. 1 (a) shows the structure and size and refractive index distribution of the HPCF used, and Fig. 1 (b) schematically shows the change in the optical fiber wound on the PZT before and after the PZT expands in the radial direction by the electrical signal. Indicates.

은 다음의 수학식 4와 같이 수정될 수 있다.Therefore, in the PFA shown in FIG.

May be modified as in Equation 4 below.

는 PZT 둘레에 감긴 코일의 총 수이고,

은 PZT에 1회전 감긴 길이에 대한 광섬유 변형 함수이고,

는 PZT의 초기 바깥 반지름이다. 따라서 수학식 4에 포함된

은

로 다시 표현될 수 있다. 이 때

는 광섬유가 원형으로 굽혀짐에 따른 변형 함수이고,

은 PZT 반지름의 증가분이다. PZT에 감긴 광섬유는 전반에 걸쳐 동시에 팽창하기 때문에

은 전파 위치에 독립적인 요소이다. 만일 정현파 전압(

,

는 진폭,

는 각 주파수,

는 시간)을 PZT에 인가하는 경우, PZT의 진동하는 반지름 증가분

은 다음의 수학식 5와 같이 표현된다. here

Is the total number of coils wound around the PZT,

Is the fiber strain function for the length wound one turn on PZT,

Is the initial outer radius of PZT. Therefore, the equation 4

silver

Can be represented again. At this time

Is the deformation function as the optical fiber bends in a circle,

Is the increase in PZT radius. Because the optical fiber wound on PZT expands simultaneously throughout

Is an element independent of the propagation position. If sinusoidal voltage (

,

Is the amplitude,

Is each frequency,

Is the oscillating radius increase of PZT

Is expressed as in Equation 5 below.

은 각주파수

의 함수로서, 단위 전압 당 진폭을 의미한다. 시간에 따른 변화량이 모드간의 결합에 영향을 미치므로

으로부터 시간 독립적인 함수

를 제외하고 수학식 4의

을 다시 표현하면 다음의 수학식 6과 같다.here

Angular frequency

Means the amplitude per unit voltage. The amount of change over time affects the coupling between modes.

Time independent function from

Except for Equation 4

To be expressed again as shown in Equation 6 below.

함수는 정규화(Normalization) 되었다. 수학식 6을 수학식 2에 대입하면 다음의 수학식 7과 같은 결과를 얻는다.here

The function is normalized. Substituting Equation 6 into Equation 2 yields the same result as Equation 7 below.

이다. here

to be.

, PZT의 재료적 및 전기적 특성을 나타내는

, 광섬유를 압전소자에 감은 횟수

, PZT에 인가된 전압의 진폭

와 같은 요소에 의해 모드 결합이 영향 받음을 알 수 있다. 모드 결합 상수

은 전파 상수 차이(

)에 따른

함수에 비례한다. 전파 상수 차이(

)는 고차 모드들 사이에서 작은 값을 가지므로, 변수가 0에 가까울수록 높은 값을 갖는

함수의 성질 때문에 광섬유 내에서 도파된 광선의 모드간 결합은 낮은 차수의 모드들 사이에서보다 높은 차수의 모드들 사이에서 효율적일 것이다.

는

와

에 동시에 의존하므로 모드 결합의 효율을 극대화시키기 위해서는

가 최적화 되어야 한다.According to Equation 7, constant according to the optical fiber structure

Material and electrical properties of PZT

, The number of times the optical fiber is wound on the piezoelectric element

, The amplitude of the voltage applied to the PZT

By elements such as It can be seen that mode combining is affected. Mode coupling constants

Is the propagation constant difference (

)In accordance

Proportional to function Propagation constant difference (

) Has a small value between higher-order modes, so the closer the variable is to 0, the higher the value.

Due to the nature of the function, the intermodal coupling of the light guided within the optical fiber will be more efficient between higher order modes than between lower order modes.

Is

Wow

At the same time, to maximize the efficiency of mode combining

Should be optimized.

This mode combining and phase modulation causes the light rays passing through the PFA to change to have a VPC. As shown in Figure 4, it can be seen that the VPC in the speckle contrast control device of the light beam according to an embodiment of the present invention is kept constant regardless of the length of the optical fiber or the number of branches. This property is particularly useful for laser processing, surgical and display applications.

On the other hand, the more the mode of light guided in the optical fiber, the higher the likelihood that the speckle shapes distributed in the optical fiber output part will be overlapped and homogeneous, so the core diameter of the MMF used is advantageous. In addition to the large core diameters, the interference of the cladding or coating is minimized to induce efficient acoustic and optical effects of the optical fiber, making the optical fiber sensitive to vibrations of the PZT. Commercialized products that serve this purpose include SSCP's HPCF. This optical fiber has a glass core 200 mu m in diameter and is surrounded by a 15 mu m thick polymer cladding. This HPCF is wound around 20 times as tightly as possible without breaking around the axis of cylindrical PZT EC-64 of EDO Corporation of 38mm in outer diameter, 2mm in thickness, and 38mm in height, and then firmly attached with epoxy to make PFA. The applied PZT takes a natural frequency around 24 kHz by theoretical analysis when applying a sinusoidal electrical signal, and trembles with the same frequency with maximum amplitude in the radial direction. This vibration induces an aco-optic effect in the HPCF, resulting in phase shift and mode coupling, resulting in a sufficient average effect even in a very short time, so that a homogeneous light spot without spots can be obtained in real time at the optical fiber output. In fact, in the experiment where a 30 fps CCD camera was used as a detector, homogeneous light beams were observed in real time, and even a human eye that equivalent to 100 fps can identify stable and homogeneous light beams.

FIG. 2 is a graph of contrast value measured by varying the driving frequency of the function generator at 10 peak-voltage (Vpp) near a natural frequency to find the minimum speckle contrast condition.

라 하면, 이의 정현값을 NA라 한다. 일반적인 광섬유가 유리 코어와 유리 클래딩을 갖는 반면, HPCF는 유리 코어와 중합체 클래딩을 갖는다. HPCF가 훨씬 더 큰 직경의 코어 및 더 큰 코어-클래딩 굴절률 차이를 가지기 때문에 일반 광섬유보다 더 많은 모드를 유지한다.The HPCF used in the experiments consisted of a 200 μm diameter glass core, 15 μm thick polymer cladding. HPCF has a stepped refractive index structure with a core refractive index and a cladding refractive index of 1.45 and 1.40, respectively. The numerical aperture (Numerical Aperture, NA) of the HPCF has a value ranging from 0.37 to 0.48. NA is one of the measures which show the property of an optical lens. As in the case of condensing sunlight with a magnifying glass, the brightness increases and the paper can be burned. When a parallel ray is incident on the lens, the light passing through the lens is condensed at a point at the focal point. At this time, the angle between the end of the lens and the line connecting the focal point of the lens

In other words, its sine value is called NA. Typical optical fibers have a glass core and glass cladding, while HPCF has a glass core and polymer cladding. Since HPCF has much larger diameter cores and larger core-cladding refractive index differences, it maintains more modes than ordinary optical fibers.

A 5-meter long HPCF was attached in the manner described above around a cylindrical PZT made of Lead-Zirconate-Titanate. Experimental results show that if the HPCF is wound more than 20 times, a low power Gaussian beam is observed at the output due to optical loss due to strong mode coupling and bending, so that the number of windings is less than 20 times. When the sinusoidal driving signal of the RF region is applied to the PZT, the optical fiber is vibrated by the PZT expanding in the radial direction to receive the aco-optic effect. Thus, phase modulation of the waveguided light and the coupling between modes occur.

Hereinafter, the influence of the speckle reduction according to the driving frequency on the PFA made of HPCF will be described. Contrast is the most used physical quantity as a unit representing the degree of speckle. The standard deviation of the luminance in the selected area is divided by an average value as shown in Equation 8, and the smaller the value, the more uniform the light rays of the output part.

는 광도(Intensity),

는 광도의 평균값,

는 스페클 형상 내에서의 광도의 표준편차이다.

이 증가함에 따라 변조 효과는 증가하고, 스페클 콘트라스트가 감소된다. 실험결과 PZT의 자연 진동수(24.16kHz)에서 스페클 콘트라스트가 최소가 된다. 스페클 콘트라스트와 구동 주파수의 관계를 나타낸 도 2를 참조하면, 근접장 및 원거리장 모두 24.16kHz에서 최소의 콘트라스트 값을 가짐을 알 수 있으나 그 정도를 비교했을 때 근접장에서의 효과가 원거리장에서의 효과보다 훨씬 큰 것을 알 수 있다.here

Is intensity,

Is the mean value of luminosity,

Is the standard deviation of luminous intensity within the speckle shape.

As this increases, the modulation effect increases and the speckle contrast decreases. Experimental results show that the speckle contrast is minimal at the natural frequency (24.16 kHz) of the PZT. Referring to FIG. 2 showing the relationship between the speckle contrast and the driving frequency, it can be seen that both the near and the far field have a minimum contrast value at 24.16 kHz. You can see that it is much larger.

는 녹색 원 안 영역에 해당하는 광도의 콘트라스트 값을 말하며, 도 2와 비교해 봄으로써 구동전압은 10Vpp이건 40Vpp이건 별 차이가 없음을 알 수 있다. 도 3의 아래 부분은 녹색 직선으로 표시된 부분의 20배 확대된 사진인데 주기적인 무늬가 있음을 알 수 있다. 이는 간섭에 의한 결과가 아닌 CCD 카메라 성능으로 인해 발생하는 것으로 고려 대상은 아니지만, 선 광도 분포를 측정하거나 콘트라스트를 계산할 때 품질저하를 일으킬 수 있음을 염두에 두어야 한다.FIG. 3 is an actual photograph of a cross section corresponding to an optical fiber output section in the near and far fields when the natural frequency 24.16 kHz and the driving voltage 40 Vpp were experimentally obtained in the PZT.

Denotes the contrast value of the luminance corresponding to the green circle area, and as compared with FIG. 2, it can be seen that there is no difference in whether the driving voltage is 10 Vpp or 40 Vpp. The lower part of FIG. 3 is a 20 times magnified picture of the part indicated by the green straight line, and it can be seen that there is a periodic pattern. This is not a result of interference, but due to CCD camera performance, but should be taken into account, however, it is important to keep in mind that quality can be degraded when measuring linearity distribution or calculating contrast.

Referring to FIG. 3, when the PZT does not vibrate, a marked speckle with high contrast can be observed at the HPCF output. On the other hand, when PZT oscillates, the speckle contrast is markedly reduced by mode coupling and phase modulation. In the near field, the contrast value decreased from 0.124 to 0.088, which was 29%, and the far field decreased from 0.221 to 0.192, which was 13.1%. The high reduction rate is due to the characteristic that the polymer cladding of HPCF is more sensitive to external vibration than ordinary fiber.

대신에 상대광도

를 사용한다. 광도의 평균값은 도 3에 도시된 녹색 원들 내 영역으로부터 얻을 수 있다.4 is a light intensity distribution of a portion indicated by a green straight line in FIG. 3. The trembling of the PZT causes the messy line luminosity distribution to be soothed that it is flat-top in the near field and Gaussian in the far field. Figure 4 shows the absolute brightness for statistical analysis

Relative brightness instead

Use The average value of the luminous intensity can be obtained from the area in the green circles shown in FIG. 3.

Next, the influence of the coherent light source on the PZT vibration when long-distance waveguide and branching through the HPCF will be described.

FIG. 5 shows the change in the output part according to the PZT oscillation when the ray passing through the PFA is incident on the HPCF having a length of 100 meters through the objective lens.

The output when the ray passing through the PFA is incident again to the 100-meter-long HPCF through the 20x objective lens is shown in FIG. 5. In the absence of vibration, the contrast was 0.135, but in the presence of vibration it was reduced to 0.088.

FIG. 6 shows the change in each output when the light passing through the PFA is incident on a 1 × 3 HPCF beam splitter through a 20x objective lens. It can be seen that when the PZT vibrates, the speckle contrast is reduced compared to the case where the speckle contrast does not vibrate. 5 and 6, when the coherent light source has a VPC through the PFA, it can be seen that the properties are maintained regardless of the waveguide length or branch number.

The biggest feature of the speckle contrast control device of the light beam according to an embodiment of the present invention is that despite the advantages of highly effective spot reduction and homogeneous light beam generation, the constituting system is very small in size. Assuming that the HPCF with a total diameter of 230 µm is wound 20 times, the length of the shaft is 5 mm or less. In the experiment to prove the validity of the present invention, a PZT having a height of 38 mm was used, but as can be seen from a previously published paper, theoretically and experimentally, the height of the cylindrical PZT has no influence on the vibration in the radial direction. Therefore, the designed device can integrate the size of width × length × height into 38mm × 38mm × 5mm.

The speckle contrast control device of the light beam according to an embodiment of the present invention operates after only experimentally determining the frequency representing the lowest contrast value near the theoretical natural frequency, and then applying a constant frequency using a signal generator. The procedure is very simple. Due to the HPCF's structural nature, the strong mode coupling by bending eliminates the need for a high voltage applied to the PZT, as is the case with other conventional multimode optical fibers, thus eliminating the need for an amplifier. In fact, we can see that the results using 40Vpp are the same within the margin of error as the results at 10Vpp.

The speckle contrast control device of the light beam according to an embodiment of the present invention can be utilized for processing using a fiber laser. According to the “Fiber Laser Market Review and Forecast,” fiber-optic laser technology already has a large share of $ 2 billion in the kilowatt (kW) laser market. It is also expected to see an impressive growth rate of 35% in the industrial laser market by 2010. In addition to Erbium doped fiber amplifiers (EDFAs), SMF is generally used for the above-mentioned fiber laser, which has the advantage of having a Gaussian shape at the output. Due to the disadvantages of optical damage and instability of the optical fiber itself due to connection efficiency or high power, there was a limit to its use. The proposed fiber-based light homogenizer solves the problems mentioned above using MMF and solves the speckle problem caused by the interference between modes to increase the degree of freedom of optical fiber available in the fiber laser system. This is expected to be of sufficient value in the ever-growing fiber laser processing market. The use of HPCF rather than SMF allows for homogeneous beam formation and therefore plays an important role in the fiber processing industry. Conventional SMF had a problem that the edge of the light beam is less sharply cut than the center part because the output part is Gaussian, but in the case of the present invention, the flat-top shape will exhibit a homogeneous processing effect over the entire area of the light beam. The experiment was conducted only for helium neon lasers with a wavelength of 635 nm, but the same applies to the green light source at 532 nm wavelength and the blue light source at 473 nm wavelength, so that the VPC is maintained regardless of branching. It can be applied. The recently reported three-output fiber-based color synthesizer produces a much wider range of colors and pure white light sources than the back light unit (BLU) of liquid crystal displays (LCDs) currently used in the market. As a result, it is attracting attention as another alternative to a light-emitting diode (LED) -based BLU. Although only LEDs have been used until now because of the speckle that appeared due to the interference between modes, the proposed technology is expected to expand the breadth of fiber-based display applications by enabling the use of highly coherent lasers and laser diodes (LDs). It is also expected to be used in many other areas where laser light sources are not available due to speckle problems due to coherence.

1 is a conceptual diagram of a PFA according to an embodiment of the present invention and shows a change in optical fiber cross section when vibration is applied.

FIG. 2 is a graph of contrast values measured by varying the driving frequency of the function generator at 10 Vpp near the natural frequency to find the minimum speckle contrast condition.

FIG. 3 is an actual photograph of a cross section corresponding to an optical fiber output section in the near and far fields when the natural frequency 24.16 kHz and the driving voltage 40 Vpp were experimentally obtained in the PZT.

4 is a light intensity distribution of a portion indicated by a green straight line in FIG. 3.

FIG. 5 shows the change in the output part according to the PZT oscillation when the ray passing through the PFA is incident on the HPCF having a length of 100 meters through the objective lens.

Figure 6 shows the change in each output when the light beams passing through the PFA are incident on the 1x3 HPCF light splitter through the objective lens.

Claims (8)

Cylindrical PZT oscillating in radial direction; And A MMF having at least one mode of light waveguided in the core of the optical fiber, And the MMF is wound around the PZT, wherein the light beam passes through the MMF while the PZT vibrates in the radial direction. The method of claim 1, And said MMF is comprised of a glass core and a polymer cladding. The method of claim 1, Speckle contrast control device of the light beam, characterized in that the MMF is HPCF. The method of claim 1, An objective lens for passing the light beam output from the MMF; And Speckle contrast control device of the light beam further comprises a separate MMF for receiving and passing the light beam passing through the objective lens. The method of claim 1, An objective lens for passing the light beam output from the MMF; And And a light splitter for separating the light beams passing through the objective lens into at least two light beams. The method of claim 1, Speckle contrast control device for light rays, characterized in that the cross-sectional shape of the MMF is formed in a D-shape. The method of claim 1, Speckle contrast control device for light rays, characterized in that the oscillating in the PZT radial direction by applying a sine wave voltage oscillating by RF to the PZT. The method of claim 7, wherein Speckle contrast control device of the light beam, characterized in that the speckle contrast of the light beam is minimized when the RF is a natural frequency of the PZT.

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