JP7306907B2 - Phase measurement device and phase compensation device - Google Patents

Description

The present invention is particularly applicable to spatial optical communication, distance sensors, radar, displays, optical switching, optical interconnection, stereolithography, stereoscopic displays, etc., and optical phased arrays constructed using optical waveguides (optical switches The present invention relates to a phase measuring device for measuring phase variations between emitted light beams at respective light emitting ends (including Mach-Zehnder type, etc.) and a phase compensating device for compensating for the phase variations.

In recent years, an optical phased array is known as a device that controls the emission direction and beam shape of emitted light without using a mechanical mechanism.
In the optical phased array, an incident light from the same light source is split by an optical splitter to enter a multi-optical waveguide consisting of two or more optical waveguides. Each optical waveguide constituting the multi-optical waveguide is provided with a phase control section for controlling the phase of light (guided light) propagating in the optical waveguide (see Patent Document 1 below).

By adjusting the phase of each guided light in this phase control unit and changing the state of optical interference between the guided lights, it is possible to control the output direction of the emitted light, the beam shape, the output destination of the light, and the like.
Since the control accuracy of the emitted light depends on the accuracy of the phase control, it is important how the phase control is performed with high accuracy.

The phase difference between the guided lights propagating in the multi-waveguide varies greatly depending on the difference in the length of each optical waveguide. Since it is difficult to completely uniform the processing during manufacturing, the phase of the guided light will inevitably vary.
Therefore, how to accurately measure the phase variation and how to compensate for the measured phase variation are important for improving the control quality of the emitted light.

As a method for measuring and compensating for phase variations, a method for optimizing a light beam phase using a gradient method is known (see Non-Patent Document 1 below).
In the above-described conventional method, when optimizing the amount of compensation given to the phase control section when obtaining a light beam emitted in the direction of 0°, for example, one phase control section first propagates in one optical waveguide. By slightly changing the phase of the guided light, the phase is changed in the direction in which the intensity of the light beam emitted in the direction of 0° increases.
By minutely changing the phase of the guided light, the peak at which the intensity of the light beam emitted in the 0° direction is maximized is found, and the phase value at the peak position is set to the optimum value for compensating for the phase variation. .

By performing such a process of finding the intensity peak of the light beam for all the optical waveguides constituting the multi-waveguide, it is possible to compensate for variations in the initial phase of the multi-waveguide and improve the shape of the light beam. (to be steep) is expected.

Japanese Patent Application Laid-Open No. 2018-10118

D.N. Hutchison et al., "High-resolution aliasing-free optical beam steering," Optica 3, pp.887-890 (2016).

However, since the conventional method uses the gradient method, depending on the initial state, the amount of compensation falls into a local optimum solution, and the optimum solution for compensating the initial phase of the multi-waveguide cannot be obtained. The problem was that there was no

SUMMARY OF THE INVENTION It is an object of the present invention to provide a phase measuring apparatus capable of obtaining, with high accuracy, an optimum solution for compensating the initial phase of a multi-waveguide without the amount of compensation falling into a local optimum solution. It is intended for
Also, a phase compensator capable of obtaining an optimum solution for compensating the initial phase of light emitted from a multi-waveguide with high accuracy and compensating for the initial phase of the emitted light at the output end of the multi-light waveguide using this optimum solution. It is intended to provide

The phase measurement device of the present invention, which can achieve the above object,
A light source that emits coherent light, and the light emitted from the light source is split into a plurality of light beams, at least one of which is used as a light beam related to reference light, and the remaining light beams are used as object light. a light beam splitter;
Each of the plurality of light beams related to the object light split by the light beam splitting unit is incident on the optical phased array to be measured and guided to the corresponding light output end through the corresponding waveguide. , interference fringe information for acquiring interference fringe information generated by the object light flux formed by the light interference effect of the light emitted from these light emitting ends and the reference light split by the light beam splitting unit. an acquisition unit;
a complex amplitude distribution calculation unit that obtains a complex amplitude distribution of the object beam from the interference fringe information acquired by the interference fringe information acquisition unit;
a back-propagation calculation unit that performs calculation for back-propagating the complex amplitude distribution in the interference fringe information acquisition unit obtained by the complex amplitude distribution calculation unit to the light emission end of the optical phased array;
a light emitting end phase distribution calculating unit that obtains the phase distribution of each of the light emitting ends from the complex amplitude distribution of the light emitting ends of the optical phased array obtained by back propagation by the back propagation calculating unit;
with
wherein the light beam splitter comprises a beam splitter that splits the light emitted from the light source into a plurality of light beams related to the object light and a light beam related to the reference light in the optical phased array;
A light beam associated with the reference light passes through a predetermined waveguide of the optical phased array and is emitted from the light emission end of the optical phased array, and interferes with the object light beam emitted from the light emission end of the optical phased array. It is characterized by being forced .
The above-mentioned "object light" includes light in a state capable of carrying object information (optical phase information at the light emitting end of the optical phased array), and the above-mentioned "object light flux" means the object light A light beam in which a plurality of beams of light are multiplexed will be referred to.

Moreover, it is preferable that the complex amplitude distribution calculation unit obtains the complex amplitude distribution of the object light flux using a phase shift digital holography method.
In addition, the phase shift digital holography method acquires the interference fringe information each time the phase of the reference light is shifted multiple times, and the phase shift is performed by a piezoelectric element, a wave plate, an electro-optic effect (EO effect) and It is preferably done using a phase modulator using any of the thermo-optical effects (TO effects).
Further, the computation for backward propagation can be computation using any one of the angular spectrum propagation method, Kirchhoff diffraction integration, Fresnel diffraction integration, Fraunhofer diffraction integration, and inverse Fourier transform method.

Furthermore, the phase compensator of the present invention that can achieve the above object is:
Based on the phase distribution of each of the light emitting ends of the optical phased array obtained by the phase measurement device, the amount of phase variation of each of the light emitting ends is obtained, and the determined amount of phase variation is reduced. and a phase adjustment instructing section for instructing the phase adjustment section of the optical phased array to adjust the phase of each of the light beams.

In the phase measuring apparatus of the present invention, a light source that emits coherent light, the light emitted from the light source is divided into a plurality of beams, at least one of which is used as a reference beam, and the remaining object beams are used as reference beams. are passed through the multi-waveguide of the optical phased array, which is the object of phase measurement, and the object light flux is emitted in the same direction from the light emission end, and interference fringe information is obtained by the reference light and the object light flux. is acquired by the interference fringe information acquisition unit, the complex amplitude distribution of the object light beam is obtained by calculation from this acquired interference fringe information, and then this complex amplitude distribution is calculated to the light output end of the multi-waveguide, and back propagation is performed by calculation. Furthermore, the phase distribution at the light exit end is obtained by calculation.

In this way, the complex amplitude distribution in the interference fringe information acquiring section of the object light flux emitted from the light emitting end of the multi-waveguide of the optical phased array is reversely propagated to obtain the phase distribution at the light emitting end. It is possible to prevent the compensation amount from falling into a local optimum solution, which has been a problem in the conventional technology, and to quantitatively and accurately obtain the optimum solution for compensating the initial phase of the multi-optical waveguide. Is possible.

Also, in the phase compensator of the present invention, it is possible to prevent the amount of compensation from falling into a local optimum solution, and the optimum solution can be used to compensate the initial phase of the multi-waveguide with high accuracy. can be done. That is, by feeding back the amount of compensation based on the results obtained by phase measurement to each phase control section, it is possible to optimize the amount of compensation for compensating for phase variations.

1 is a block diagram showing a schematic configuration of a phase measuring device and a phase compensating device according to Embodiment 1 of the present invention; FIG. 1 is a block diagram specifically showing an optical system of a phase measuring device and a phase compensating device according to Embodiment 1 of the present invention; FIG. 1 is a perspective view showing a general configuration of an optical phased array to be measured/compensated by a phase measuring device and a phase compensating device according to an embodiment of the present invention; FIG. FIG. 4 is a block diagram specifically showing the optical systems of the phase measuring device and the phase compensating device according to the modified example of the first embodiment of the present invention; FIG. 4 is a block diagram showing a schematic configuration of a phase measuring device and a phase compensating device according to Embodiment 2 of the present invention; FIG. 3 is a block diagram showing a schematic configuration of a phase measuring device and a phase compensating device according to Embodiment 3 of the present invention; Four far-field images ((A ), (B), (C), and (D)). 7 is a graph showing a phase distribution at the light exit end calculated by a light exit end phase distribution calculator; Graphs (Embodiment 3 (solid line) and Prior art (dotted line)).

<Embodiment 1>
A phase measuring device and a phase compensating device according to Embodiment 1 of the present invention will be described below with reference to the drawings.
First, the phase measurement device according to Embodiment 1 will be described with reference to FIG.
The phase measuring device is a device for measuring the phase distribution of emitted light at the light emitting end 35 of the optical phased array 30. The light source 10 that emits coherent light and the emitted light from the light source 10 are used as reference light and object light. and the object light enters the optical phased array 30 and is split into a plurality of light beams, which are emitted from the light emission end 35 of the optical phased array 30. an interference fringe information acquisition unit 50 for capturing interference fringe information obtained by interference between the object light flux synthesized by the interference effect and the reference light that has passed outside the optical phased array 30; A computing unit 60 computes a complex amplitude distribution from the fringe information and computes the phase distribution of the emitted light (object beam) at the light exit end 35 of the optical phased array 30 .

Here, the internal configuration of the optical phased array 30 will be described. That is, the optical phased array 30 includes an input unit 31 to which object light incident from the outside (more precisely, light to be referred to as object light) is input, and a plurality of light beams that receive the input object light. a splitter 32 that divides the split light beams into two, and phase control units (1 to N) 33-1 to 33-N that propagate the split light beams through corresponding waveguides and control the phases of the light beams along the way. , and an output section 34 which receives the light beams from the phase control sections (1 to N) 33-1 to 33-N and outputs the light beams (object light) from the light emitting end 35 in the same direction. I have.
Each of the phase control units (1 to N) 33-1 to 33-N is made of an EO material whose light refractive index is changed by voltage application, for example.

The calculation unit 60 includes a complex amplitude distribution calculation unit 61 that obtains the complex amplitude distribution of the object light flux from the interference fringe information obtained by the interference fringe information acquisition unit 50, and an interference fringe distribution obtained by the complex amplitude distribution calculation unit 61. A back-propagation calculation unit 62 that performs a calculation for back-propagating the complex amplitude distribution of the object light flux in the information acquisition unit 50 to the light emitting end 35 of the optical phased array 30, and the light obtained by the back-propagation by the back-propagation calculation unit 62 A light emitting end phase distribution calculator 63 for obtaining the phase distribution of the object light flux at each light emitting end 35 of the optical phased array 30 from the complex amplitude distribution at the light emitting end 35 of the phased array 30 .

In addition to the configuration of the phase measuring device, the phase compensation device according to the first embodiment has a A phase adjustment instruction section 70 is provided for instructing the phase control sections 33-1 to 33-N of the optical phased array 30 to adjust the phase according to the phase compensation amount.
Thus, in the phase measuring device and the phase compensating device according to the first embodiment, the interference fringes of the object light beam emitted after passing through the optical phased array 30 and the reference light passing outside the optical phased array 30 are The complex amplitude distribution of the object light beam is obtained from the interference fringe information in the information acquisition unit 50, and the calculation is performed to propagate it back to the light exit end 35 of the light phased array 30. After that, the phase distribution of the object light beam at the light exit end 35 is obtained. , it is possible to quantitatively and accurately obtain the optimum solution for compensating the initial phase of the multi-waveguide.

A collimator (collimating lens) 41 for converting the reference light into a plane wave and a reference light phase controller 42 for shifting the phase of the reference light are provided on the optical path of the reference light split from the fiber coupler 20. are distributed. Further, in the reference beam phase control unit 42, a process of shifting a predetermined phase amount (for example, (π/2)) at a predetermined timing when obtaining interference fringe information is performed. An instruction may be given from the timing instruction unit (which may be configured by software means arranged in the reference beam phase control unit 42).
In this case, the arrangement order of the collimator 41 and the reference beam phase control unit 42 can be changed, and when obtaining the complex amplitude distribution from the interference fringe information, there is no method of shifting the phase of the reference beam. In this case, it is not necessary to dispose the reference light phase control section 42 .

FIG. 2 is for more specifically explaining the configuration of the optical system of the apparatus of the first embodiment. A case in which the phase shift digital holography method is adopted even in the apparatus configuration of FIG. 2 will be described.
Coherent light output from a laser light source 10a, which is a coherent light source, is split by a fiber coupler 20a into two systems, reference light and object light. The reference light is input to a collimator lens (collimator) 41a, while the object light is It is input to the optical phased array 30a, which is the object to be measured.

A general optical phased array will now be described with reference to FIG. The optical phased array 301 shown in FIG. 3 is constructed as an 8-channel optical waveguide type optical deflection device. That is, this optical phased array 301 is formed by forming each part on a substrate 302, and includes a three-stage beam splitter 304 for splitting light (incident light) incident on a waveguide 303 into eight channels of waveguides 305, It has a phase control section 306 that controls the phase of light in each channel, and a light emission section (light emission end) 307 that emits light from each channel into space.
In FIG. 3, the light emitting portion 307 is the end surface of the substrate on which the optical phased array 301 is formed, but the light emitting portion 307 may have a grating structure (diffraction grating) to output emitted light in the direction perpendicular to the substrate.
The light whose phase is adjusted by the phase control unit 306 and is emitted from each of the eight light emitting ends (pitch is Pr) 307 of the output unit is synthesized by the interference effect, and the light beam is deflected in the direction of the deflection angle θ. can be done.

In the phase control section 306, electrodes 308 are arranged above and below the waveguide 305 of each channel. It is possible to control the phase of the emitted light from. This makes it possible to scan the emitted light beam and the like.
When controlling the phase of the light emitted from the light emitting end 307 of each waveguide 305 by the TO effect, a heater is installed near each waveguide 305 . By controlling the temperature of each waveguide 305, the phase of light emitted from the light emitting end 307 can be controlled.
The optical phased array 30a shown in FIG. 2 is specifically configured like the optical phased array 301 shown in FIG. is irradiated to

On the other hand, as shown in FIG. 2, the reference light incident on the collimating lens 41a is converted into a plane wave (parallel beam), added with a predetermined phase shift amount by the phase adding element 42a, and reflected by the half mirror 80a. , is irradiated onto the image sensor 50a in such a state that it is superimposed on the object beam. As a result, interference fringes of the object light beam and the reference light are formed on the image sensor 50a, the interference fringe information is imaged, and the imaged interference fringe information is output to the computer 60a as a computing unit.

As described with reference to FIG. 1, the computer 60a includes a complex amplitude distribution computing unit 61 for obtaining the complex amplitude distribution of the object light flux at the image sensor 50a from the interference fringe information obtained by the image sensor 50a, and the complex amplitude distribution computing unit 61. From the complex amplitude distribution at the light output end 35 of the optical phased array 30a obtained by the back propagation calculation unit 62 that performs the operation of back propagating the amplitude distribution to the light output end 35 of the optical phased array 30a, the light and a light emitting end phase distribution calculator 63 for obtaining the phase distribution of each of the light emitting ends 35 of the phased array 30a.

The phase distribution of the object light flux at the light emitting end 35 from the light emitting end phase distribution calculator 63 represents the difference from the phase of the reference light. By physically measuring the reference distance from the light output end 35 in advance using another method such as a length measuring instrument, angular spectrum propagation, Kirchhoff diffraction integration, Fresnel diffraction integration, Fraunhofer The complex amplitude distribution on the light emitting section 35 can be obtained from the complex amplitude distribution on the image sensor 50a obtained by calculation such as diffraction integration.

The above description is common to the phase measuring device and the phase compensating device according to this embodiment, but in the case of the phase compensating device, an additional configuration is required. That is, as described above, the object luminous flux at each light emitting end 35 is A compensation amount is obtained so that the phase of . An instruction regarding voltage control is given so as to apply
Further, in the case where the interference information acquisition unit 50 is a far-field image acquisition device composed of an image sensor and a far-field image acquisition optical system (a lens system with a Fourier transform effect), from the interference information acquisition unit 50 to the light exit end 35 can be performed with an inverse Fourier transform operation.

By the way, in the first embodiment, for example, the phase shift digital holography method is used, and the image sensor 50a performs imaging processing of the interference fringes of the object light flux and the reference light each time the phases of the reference light are shifted from each other.
For example, in the well-known 4-step method in the interference fringe analysis method, the shift amount is (π/2), and the imaging process is performed when the phases are 0, π/2, π, and 3π/2. The complex amplitude distribution is obtained from the interference fringe image information (Phase-shifting: Ichirou Yamaguthi et al. OPTICS LETTERS/VOL.22, No.16: August 15, 1997, etc.). That is, a λ/2 plate and a λ/4 plate, which are phase plates, are inserted into the optical path as the phase adding element 42a, and the phase leading axis and the lagging phase are adjusted so as to obtain a phase corresponding to each shift amount. I am trying to change the axis.

This 4-step method is preferable in that the calculation is easy and high-precision results can be obtained, but other step methods such as a 3-step method and a 5-step method (including Hariharan's algorithm, etc.) can be used. It is possible. Alternatively, the phase recovery method may be applied by setting the number of phase shifts to two.
In the above description of the 4-step method, the phase shift amount and the number of times are set to 4 times each of π/2, but they may be set to 3 times each of π/2.

Calculations of the phase shift 4-step method performed in the complex amplitude distribution calculator 61 will be briefly described below using mathematical formulas. The method of obtaining the complex amplitude distribution of the object beam using the phase shift 4-step method is shown in Introduction to Holography (Vincent Toal: September 28, 2011), pages 356-357.
Let A be the amplitude of the object beam, R be the amplitude of the reference beam, φ be the relative phase difference between the object beam and the reference beam, and _I1 , _I2 , _I3 , and _I4 be the intensity patterns of the interference fringes. Assuming that each has four stepped phase differences of 0, π/2, π, and 3π/2, the intensity of these interference fringes is expressed by the following equations (1) to (4). be.

At this time, if the equations are expanded so that only the phase term remains, the following equations (5) and (6) are obtained.

From the above equations (5) and (6), the sine function and cos function including the phase term are expressed by the following equations (7) and (8), respectively.

Using Euler's formula from equations (7) and (8), the complex amplitude distribution of the object luminous flux on the image sensor 50a is expressed by the following equation (9).

In equation (9), the amplitude R of the reference beam can be regarded as a constant by making the reference beam to be used an ideal plane wave, and the complex amplitude distribution in equation (9) represents the phase distribution of only the object beam. can be
In this way, the complex amplitude distribution of the object luminous flux at the image sensor 50a, which is calculated and output by the complex amplitude distribution calculator 61 and is expressed by the above equation (9), is then input to the back propagation calculator 62. Then, a calculation is performed to propagate backward to the light emitting end 35 of the output section 34 of the optical phased array 30 .

ここでx’とy’は、それぞれイメージセンサ５０ａ上の水平方向と垂直方向の位置、xとyはそれぞれ光出射端３５上の水平方向と垂直方向の位置、λは波長、ｋは波数（ｋ＝２π／λ）、ｚはイメージセンサ５０ａと光出射端３５間の距離を表す。 The backpropagation calculation performed in the backpropagation calculator 62 will be briefly described below using mathematical formulas.
Since the light emitting portion 35 is small, even if the propagation distance is several centimeters, the Fraunhofer approximation is established. Let A(x', y') be the complex amplitude distribution on the image sensor 50a represented by the above equation (9), and let U(x, y) be the complex amplitude distribution at the light output end 35 of the optical phased array 30. , the relationship of the following equation (10) holds.

Here, x' and y' are the horizontal and vertical positions on the image sensor 50a, x and y are the horizontal and vertical positions on the light emitting end 35, λ is the wavelength, and k is the wavenumber ( k=2π/λ), and z represents the distance between the image sensor 50a and the light emitting end 35. FIG.

Although the above formula (10) indicates the Fraunhofer diffraction integral, the backpropagation calculation may be performed using the angular spectrum propagation method with less approximation, Kirchhoff diffraction integral, and Fresnel diffraction integral.

ここでuとvは、それぞれ水平方向と垂直方向の空間周波数、xとyはそれぞれ水平方向と垂直方向の位置を示し、FT^-1[ ]は逆フーリエ変換であることを表す。フーリエ変換と逆フーリエ変換は、各々以下の式（１２）、（１３）で表される。

ただし、積分の前の係数（1/(2π)や1/(2π)^1/2など）は省略した。フーリエ変換と逆フーリエ変換の違いはexp内の符号のみであり、本質的な違いは少ない。上式（１１）に関して、複素振幅分布A(u,v)の座標変換次第ではフーリエ変換を適用することで光フェーズドアレイ３０の光出射端３５における複素振幅分布Ｕ(x, y)を取得することができるため、逆フーリエ変換のみに限定されるものではない。 When the interference information acquisition unit 50 is a far-field image acquisition device composed of an image sensor and a far-field image acquisition optical system, the complex amplitude distribution (angular spectrum) on the image sensor 50a represented by the above equation (9) is A(u, v), and the complex amplitude distribution at the light emitting end 35 of the optical phased array 30 is U(x, y), the following equation (11) holds.

where u and v are horizontal and vertical spatial frequencies, x and y are horizontal and vertical positions, respectively, and FT ^-1 [ ] represents inverse Fourier transform. The Fourier transform and the inverse Fourier transform are represented by the following equations (12) and (13), respectively.

However, the coefficients before the integration (1/(2π), 1/(2π) ^1/2, etc.) are omitted. The only difference between the Fourier transform and the inverse Fourier transform is the sign in exp, and there are few essential differences. Regarding the above equation (11), depending on the coordinate transformation of the complex amplitude distribution A(u, v), the complex amplitude distribution U(x, y) at the light exit end 35 of the optical phased array 30 is obtained by applying the Fourier transform. It is not limited to the inverse Fourier transform only, as it can

When the focal length of the far-field image acquisition optical system is f, the horizontal and vertical positions (x', y') on the image sensor 50a and the horizontal and vertical spatial frequencies (u, v) are Between them, the relationship of the following formula (14) is established.

Also, when the far-field image acquisition device acquires the light intensity distribution with respect to angles, it is necessary to perform coordinate transformation from angles (θ _x , θ _y ) to spatial frequencies (u, v). Assuming that the pixel number is (m, n), the number of pixels is M×N, and the horizontal and vertical angular resolutions of the far-field image acquisition device are _δθx and _δθy , respectively, the following equation (15) is obtained.

なお、上記変換を行う際には、線形内挿などにより、実際にはサンプリングされていない角度方向における複素振幅値を内挿してもよい。 Assuming that the wavelength is λ, the following equation (16) holds between the angle (θ _x , θ _y ) and the spatial frequency (u, v). conduct.

It should be noted that when performing the above conversion, the complex amplitude values in the angular directions that are not actually sampled may be interpolated by linear interpolation or the like.

In this way, the complex amplitude distribution of the object light flux at the light exit end 35 expressed by the above equation (11) calculated and output by the backpropagation calculator 62 is then processed by the light exit end phase distribution calculator 63 , and the phase distribution φ(x, y) of the light emitting end 35 is obtained.
Briefly describing the phase distribution calculation performed in the light emitting end phase distribution calculating section 63, the imaginary part The phase distribution φ(x, y) can be obtained from the arctangent of the value obtained by dividing the value of Im[U(x, y)] by the value of the real part Re[U(x, y)].

A computational expression in the light exit end phase distribution computing section 63 is shown in Equation (17).

In addition, the value of the phase distribution φ(x,y) changes in each range of 0 to 2π, and returns to 0 after 2π. Since the phase value becomes discontinuous when it changes from 2π to 0, the phase value may be changed continuously by adding an offset of the period when it becomes 0 from 2π. Therefore, in order to connect the values of each phase distribution φ(x,y), a well-known phase unwrapping method or the like is employed as necessary.

<Modification of Embodiment 1>
In the phase measuring device and the phase compensating device of Embodiment 1 described above, in order to shift the phase of the interference fringes, the wave plate that provides shift amounts of π/2, π, and 3π/2 in the optical path of the reference light. is inserted.

Means for phase-shifting the interference fringes are not limited to this. For example, as shown in FIG. The interference fringes may be phase-shifted by moving in the direction by a minute distance.
Alternatively, a phase modulator using an electro-optical effect (EO effect) or a thermo-optical effect (TO effect) may be used to shift the phase of the interference fringes.
4, the members corresponding to the members in the device shown in FIG. Redundant explanations are omitted.

The object light flux is output from the optical phased array 30b, passes through the half mirror 80b, and is irradiated onto the image sensor 50b. Then, the light is reflected by the reflecting mirror 82b, then enters the half-mirror 81b again, is reflected downward in the drawing, is further reflected rightward in the drawing by the half-mirror 80b, and is irradiated onto the image sensor 50b. Thus, an interference fringe is formed on the image sensor 50b due to the interference effect between the object beam and the reference beam.

In this state, a predetermined voltage is applied from the voltage source 44b to the piezo element 43b capable of moving the reflecting mirror 82b by a very small distance so that shift amounts of π/2, π, and 3π/2 can be obtained. . As a result, a predetermined voltage is applied from the voltage source 44b to the piezo element 43b capable of moving the reflecting mirror 82b by a very small distance, and shift amounts of .pi./2, .pi., and 3.pi./2 are set. Based on the obtained interference fringe image, intensity distributions I ₁ to I ₄ similar to formulas (1) to (4) in the first embodiment can be obtained.

<Embodiment 2>
FIG. 5 is a block diagram showing an outline of a phase measuring device and a phase compensating device according to Embodiment 2 of the present invention. Among the members of the device described in Embodiment 2, the members corresponding to the members in the device described in Embodiment 1 are denoted by 100 added to the reference numerals attached to the members in the device described in FIG. and overlapping descriptions are omitted.

In the apparatus of Embodiment 2, the reference light is not propagated outside the optical phased array 130, but a waveguide for the reference light is produced inside the optical phased array 130, and the reference light propagates inside the phased array 130. is configured as That is, the reference light split from the object light by the fiber coupler 120 is input to the reference light input section 140 of the optical phased array 130, and the wavelength plate 42a and the piezo element 43b described above or the electro-optic effect (EO effect) or thermal It is input to the reference light phase control unit 142 consisting of a phase modulator using an optical effect (TO effect) or the like, and further directed from the light emission end 35 dedicated for the reference light of the output unit 134 to the interference fringe information acquisition unit 150. configured to be emitted.
The waveguide for the reference light is formed using a semiconductor process technology, and by configuring the reference light to pass through the waveguide, it is possible to improve the alignment accuracy compared to the apparatus of the first embodiment. can. In addition, since it is less susceptible to air turbulence, measurement accuracy can be improved.

In addition, the diameter of the optical waveguide is the size of the wavelength order, and the emitted light from each waveguide can be regarded as light from a point light source. can be regarded as
In the case of imaging with a far-field image acquisition device, it may be regarded as a plane wave, or a far-field image may be analytically obtained from the waveguide structure.
Alternatively, a far-field image may be separately photographed in advance and its amplitude distribution may be applied.

In Embodiment 2, the reference light also has phase variations, but the phase distribution of the object light flux obtained by phase shift digital holography is based on the phase distribution of the reference light, so no problem arises.

<Embodiment 3>
FIG. 6 is a block diagram showing an outline of a phase measuring device and a phase compensating device according to Embodiment 3 of the present invention. Among the members of the device described in Embodiment 3, the members corresponding to the members in the device described in Embodiment 1 are denoted by 200 added to the reference numerals attached to the members in the device described in FIG. and overlapping descriptions are omitted.

In the apparatus of Embodiment 3, the i-th one waveguide channel among the N waveguide channels divided by the splitter 232 in the optical phased array 230 is used as the reference light. . That is, one of the beams split by the splitter 232 is used as the reference beam. This light beam used as the reference light is also emitted from the light emitting end 235 of the output section 234 of the optical phased array 230, and is irradiated to the interference fringe information acquiring section (image sensor) 250 together with the object light flux. Obtain the interference pattern.

The light beam used as the reference light is controlled by the phase control unit i for the reference light arranged in the waveguide (the wave plate 42a or the piezo element 43b described above, or the phase modulator using the EO effect or the TO effect). etc.) 233 i performs phase control so that a predetermined amount of shift is obtained, and then outputs to the output section 234 .
According to the present embodiment, the phase control unit for controlling the direction, beam shape, and output destination of the light emitted from the optical phased array 230 can also be used to shift the phase of the reference light. Phase variation can be measured with a simple configuration.
Further, since the reference light is configured to pass through the waveguide, it is possible to improve the alignment accuracy compared to the apparatus of the first embodiment. In addition, since it is less susceptible to air turbulence, measurement accuracy can be improved.

Further, in Embodiment 3, the reference light also has phase variations, but the phase distribution of the object light flux obtained by the phase shift digital holography method is based on the phase distribution of the reference light, so a problem arises. do not have.
In order to minimize adverse effects on the complex conjugate light caused by various errors, the position of the phase control unit used for the reference light is selected from among the waveguides arranged in parallel on the optical phased array 230. , it is desirable to select a waveguide located as close to the end as possible.
Also, the reference light phase control unit may be sequentially switched between 1 to N, and each phase measurement result may be integrated.

<Variation>
The phase measuring device and the phase compensating device of the present invention are not limited to those of the above-described embodiments, and can be modified into other various aspects.
For example, in the above-described embodiment, the analysis of the obtained interference fringes is performed using the phase shift digital holography method. A complex amplitude distribution is obtained by removing the diffracted light component and the DC component.
However, the method of analyzing interference fringes to obtain a complex amplitude distribution is not limited to this. For example, it is also possible to use a Fourier fringe analysis method in which a predetermined frequency component is given to the reference light and one interference fringe intensity I is subjected to Fourier transform to separate unnecessary components and signal components in the frequency space. .

なお、信号光の振幅をＡ、参照光の振幅をＲ、信号光と参照光の相対的な位相差をφ、参照光に付与している傾斜による縞の周波数をf₀ とする。 The interference fringe intensity I obtained using the Fourier fringe analysis method is shown in Equation (18).

Let A be the amplitude of the signal light, R be the amplitude of the reference light, φ be the relative phase difference between the signal light and the reference light, and f ₀ be the fringe frequency due to the tilt given to the reference light.

が示されている。ここで、nは屈折率変化量、dn/dTは屈折率温度係数 (材料固有の値)、ρは比例係数、Rはヒーターの抵抗値、Iは印加電流である（dn/dTとRは温度依存性を有する））。 Each phase control section described above is made of an EO material that changes the refractive index of light by voltage application. A silicon-based material or the like having an effect (TO effect) can also be used.
The thermo-optical effect (TO effect) is described in the following references.
Reference: Shigeru Nakamura, "Integrated Silicon Waveguide Optical Switch Technology," Kogaku Vol.42, No.5, pp.242-248 (2013)

It is shown. where n is the amount of change in refractive index, dn/dT is the temperature coefficient of the refractive index (a material-specific value), ρ is the proportional coefficient, R is the resistance of the heater, and I is the applied current (dn/dT and R are with temperature dependence)).

Experimental results of the third embodiment will be described below. That is, the present invention is applied to an optical phased array 230 composed of 16-channel waveguides. Here, the wavelength of the light source is λ=1.55 μm, and the pitch between the waveguides at the light emitting end 235 is Pr=4 μm.
Of the 16-channel optical waveguides, channel 1 (a channel located at one end) is used as a reference light, and the phase is shifted by 0, π/2, π, and 3π/2, as shown in FIGS. , (C), and (D) were obtained by the interference information obtaining unit 250 .
For the acquired four far-field images, the complex amplitude distribution of the object light flux on the image sensor is obtained by the phase shift digital holography in the complex amplitude distribution calculation unit 261, and the back propagation calculation unit 262 calculates the light emission end 235. A complex amplitude distribution was obtained, and the phase distribution was calculated by the light exit end phase distribution calculator 263 .

The calculated phase distribution at the light exit end 235 is shown in FIG. A solid line is the phase distribution. The phases are aligned (flat) at each position of channels 2 to 16, and it can be estimated that the phases of the respective light emitting ends can be measured.
Here, since the light emitted from channel 1 is used as the reference light, it cannot be calculated by using the method of interfering with the reference light as in the case of the other channels. However, if the phase of channel 1 is treated as zero, there is no problem.

Also, the phase compensation amount was obtained from the phase distribution measured by the third embodiment. In this experiment, the amount of compensation was based on the phase at the center of each waveguide, but the amount of phase compensation may be obtained based on, for example, the average value of the complex amplitude distribution of the emitted light from each waveguide.
FIG. 9 shows the result of compensating for phase variations by feeding back the amount of phase compensation to each of the phase controllers 233-1 to 233-N by the phase adjustment instructing section 270. In FIG. The spectrum shown in the upper part of FIG. 9 represents the light intensity by shading (the higher the light intensity, the closer to white). According to FIG. 9, it is clear that the light beam can be emitted in the direction of 0 degrees in the third embodiment compared to the prior art without phase compensation, and the phase variation can be correctly compensated. it is obvious.

本実験条件に対しては、サイドビーム出射角の理論値は±22.8度となり、本実験により得られた値は、この理論値と略一致していることが検証された。 It is theoretically known that when the main beam is emitted in the direction of 0 degrees, the side beams are emitted in the direction of the following formula (19).

Under this experimental condition, the theoretical value of the side beam output angle was ±22.8 degrees.

10, 110, 210 light source 10a, 10b laser light source 20, 20a, 20b, 120 fiber coupler 30, 30a, 30b, 130, 230, 301 optical phased array 31, 231 input section 131 object light input section 32, 132, 232 splitter 33-1 to 33-N, 133-1 to 133-N, 233-1 to 233-N, 306
Phase control unit 34, 134, 234 Output unit 35, 135, 235 Light emitting end 41 Collimator 41a, 41b Collimator lens 42, 142 Reference light phase control unit 42a Phase addition element 43b Piezo element 44b Voltage source 50, 150, 250 Interference Stripe information acquisition unit 50a, 50b Image sensor 60, 160, 260 Calculation unit 60a, 60b Calculator 61, 161, 261 Complex amplitude distribution calculation unit 62, 162, 262 Back propagation calculation unit 63, 163, 263 Light emission end phase distribution calculation Sections 70, 70a, 70b, 170, 270 Phase adjustment instruction section 80a, 80b, 81b Half mirror 82b Mirror 140 Reference light input section 302 Substrate 303 Waveguide light input section 304 Beam splitter 305 Waveguide 307 Light output section (light output end )
308 electrodes

Claims (5)

A light source that emits coherent light, and the light emitted from the light source is split into a plurality of light beams, at least one of which is used as a light beam related to reference light, and the remaining light beams are used as object light. a light beam splitter;
Each of the plurality of light beams related to the object light split by the light beam splitting unit is incident on the optical phased array to be measured and guided to the corresponding light output end through the corresponding waveguide. , interference fringe information for acquiring interference fringe information generated by the object light flux formed by the light interference effect of the light emitted from these light emitting ends and the reference light split by the light beam splitting unit. an acquisition unit;
a complex amplitude distribution calculation unit that obtains a complex amplitude distribution of the object beam from the interference fringe information acquired by the interference fringe information acquisition unit;
a back-propagation calculation unit that performs calculation for back-propagating the complex amplitude distribution in the interference fringe information acquisition unit obtained by the complex amplitude distribution calculation unit to the light emission end of the optical phased array;
a light emitting end phase distribution calculating unit that obtains the phase distribution of each of the light emitting ends from the complex amplitude distribution of the light emitting ends of the optical phased array obtained by back propagation by the back propagation calculating unit;
with
wherein the light beam splitter comprises a beam splitter that splits the light emitted from the light source into a plurality of light beams related to the object light and a light beam related to the reference light in the optical phased array;
A light beam associated with the reference light passes through a predetermined waveguide of the optical phased array and is emitted from the light emission end of the optical phased array, and interferes with the object light beam emitted from the light emission end of the optical phased array. A phase measuring device characterized in that it is crimped . 2. The phase measuring apparatus according to claim 1 , wherein said complex amplitude distribution calculating section obtains the complex amplitude distribution of said object beam using a phase shift digital holography method. The phase shift digital holography method acquires the interference fringe information each time the phase of the reference light is shifted multiple times, and the phase shift is any one of a piezo element, a wave plate, an electro-optic effect, and a thermo-optic effect. 3. The phase measuring device according to claim 2 , wherein the phase measuring device uses a phase modulator using a . 4. Any one of claims 1 to 3 , wherein the computation for back propagation is computation using any one of the angular spectrum propagation method, Kirchhoff diffraction integration, Fresnel diffraction integration, Fraunhofer diffraction integration, and inverse Fourier transform method. 1. The phase measuring device according to claim 1. A phase measuring device according to any one of claims 1 to 4 , wherein the phase distribution of each of the light emitting ends of the optical phased array obtained by the phase measuring device is obtained. Phase adjustment for determining the amount of phase variation and instructing the phase adjustment unit of the optical phased array to adjust the phase of each of the light beams so that the determined amount of phase variation is reduced. an indicator;
A phase compensator comprising:

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