CN108227334B - Optical phased array - Google Patents
Optical phased array Download PDFInfo
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- CN108227334B CN108227334B CN201711402971.9A CN201711402971A CN108227334B CN 108227334 B CN108227334 B CN 108227334B CN 201711402971 A CN201711402971 A CN 201711402971A CN 108227334 B CN108227334 B CN 108227334B
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
- G02F1/292—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection by controlled diffraction or phased-array beam steering
Abstract
The invention discloses an optical phased array, which consists of N phased array units, wherein each phased array unit comprises 1 phase modulator for adjusting the additional phase of the phased array unit, and the N phase modulators are arranged in a circular ring shape on a planeThe waveguide transmitting unit at one end of each phase modulator faces the outer side of the circle center of the circular ring, and N is a natural number; the working range of the phased array unit isn is an integer, wherein the phase modulator of the nth phased array unit adjusts the additional phase according to the change of the emergent angle omega as follows:d is the distance between adjacent waveguide emission units, and lambda is the wavelength of the light source. The invention realizes 360-degree large-range constant-amplitude scanning. The invention also discloses an optical phased array, thereby realizing multi-point scanning.
Description
Technical Field
The invention relates to the technical field of optical phased arrays, in particular to an optical phased array.
Background
An Optical Phased Array (OPA-Optical Phased Array) which has recently become a research hotspot and is developed rapidly is a new electrically-controlled beam scanning technology, and the working principle of the technology is similar to that of a microwave Phased Array. The core component of the phase modulation device is composed of a plurality of phase modulation units. By controlling the applied voltage of the phase modulators, the additional refractive index inside the modulators can be controlled, and thus the additional phase of the optical field at the exit end of each phase modulator can be controlled, thus realizing the deflection of the propagation direction of the radiation beam. The optical phased array technology is a high-resolution, high-accuracy and rapid light beam control technology, has wide application prospect, and thus becomes a research hotspot in the international recent years.
The conventional optical phased array transmitting unit is arranged in a plane or a linear array, and the schematic diagram is shown in fig. 1. The optical waveguides and the electrode materials are arranged alternately, different voltages are applied to different optical waveguides through electrodes on two sides of the optical waveguides, so that the optical waveguides in different layers have different refractive indexes, different additional phases can be formed at an emergent surface by different optical paths brought by the different refractive indexes, and when the additional phases are linearly arranged, output light beams can deflect in a specific direction, which is the basic working principle of the optical phased array.
As shown in fig. 2, due to the limitation of diffraction envelope, the main lobe of the phased array rapidly decreases and the grating lobe rapidly increases when the light beam deflects, so that the spatial scan angle range of the conventional optical phased array is limited by the intensity of the grating lobe, and the maximum scan angle of the conventional phased array is generally defined as the scan angle when the intensity of the main lobe is equal to that of the grating lobe, and the maximum scan angle range of the conventional phased array is defined as the scan angle when the intensity of the main lobe is equal to that of the grating lobe(d is the period and λ is the wavelength of light).
Although the scanning technology of the optical phased array realizes high resolution, high precision and fast scanning at present, the traditional optical phased array has the following technical bottlenecks to restrict the popularization of the optical phased array:
1. the scanning angle is too small, and most of the optical phased arrays reported in the prior art have the scanning angle of about +/-10 degrees.
2. The waveguide width and period requirements are too stringent resulting in fabrication process difficulties: if the scanning requirement in the +/-90-degree direction is to be realizedIf the minimum grating lobe is required, the duty ratio is requiredClose to 1. (a is the emission cell aperture; λ is the wavelength of the light; d is the period, i.e. the spacing of adjacent waveguide emission cells).
3. The conventional optical phased array grating lobe is large in grating lobe intensity.
4. As shown in fig. 2, in the conventional phased array scanning process, as the scanning angle increases, the intensity of the main lobe gradually decreases, the intensity of the grating lobe gradually increases, and even the intensity of the grating lobe is greater than that of the main lobe, which is obviously undesirable.
Disclosure of Invention
In view of the above, the first invention of the present invention is: breaks through the limit of diffraction envelope and realizes a large-range scanning angle of 360 degrees.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the invention provides an optical phased array, which consists of N phased array units, wherein each phased array unit comprises 1 phase modulator for adjusting the additional phase of the phased array unit, the N phase modulators are arranged in a circular ring shape on a plane, a waveguide transmitting unit at one end of each phase modulator faces the outer side of the circle center of the circular ring shape, and N is a natural number; the working range of the phased array unit isn is an integer, wherein the phase modulator of the nth phased array unit adjusts the additional phase according to the change of the emergent angle omega as follows:d is the distance between adjacent waveguide emission units, and lambda is the wavelength of the light source.
The second object of the present invention is: and multi-point constant-amplitude scanning is realized.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the invention also discloses an optical phased array, which consists of N phased array units, wherein each phased array unit comprises 1 phase modulator for adjusting the additional phase of the phased array unit, the N phase modulators are arranged in a circular ring shape on the plane, a waveguide transmitting unit at one end of each phase modulator faces the outer side of the circle center of the circular ring shape, and N is a natural number;
for theInter-working phased-array units, nPhase modulator of each phased array unit according to m points (omega)1<…<ωj<…ωm) Omega in a scan1、…ωjThe additional phase adjusted in the outgoing direction is:n is an integer, m is a positive integer greater than or equal to 2, and j is a positive integer from 1 to m-1;
for theThe phase modulator of the internal working phased array unit, the nth phased array unit is based on omega in m point scanningj+1、…ωmThe additional phase adjusted in the outgoing direction is:n is an integer, m is a positive integer greater than or equal to 2, and j is a positive integer from 1 to m-1;
for theThe phase modulator of the internal working phased array unit, the nth phased array unit is based on omega in m point scanning1、…ωmThe additional phase adjusted in the outgoing direction is:
n is an integer, m is a positive integer greater than or equal to 2;
d is the distance between adjacent waveguide emission units, and lambda is the wavelength of the light source.
According to the technical scheme, the emission units of the optical phased array are designed to be arranged in a circular ring shape, and coherent superposition of light beams in any angle within a range of 360 degrees can be realized by controlling phase delay of different units, so that large-range scanning of 360 degrees is realized; also, multi-point simultaneous scanning can be realized by controlling the phase delays of different units. Due to the high symmetry of the circular ring type arrangement, the shape of the far-field light intensity can hardly change in the light beam scanning process and only can be translated at different angles, so that the constraint of diffraction envelope of the traditional optical phased array is broken through, and the defects that the main lobe of the traditional optical phased array is greatly attenuated and the grating lobe is greatly increased in the light beam scanning process are overcome.
Drawings
Fig. 1 is a schematic diagram of a prior art optical phased array.
Fig. 2 is a prior art optical phased array beam scan.
Fig. 3a and fig. 3b are schematic diagrams of a one-dimensional circular optical phased array structure according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of phase change of phased array units at observation points along with unit numbers in the + 1-stage grating lobe direction.
FIG. 5 is a far field intensity profile at an exit angle of 0 in accordance with an embodiment of the present invention.
FIG. 6 is a far field intensity plot during a scan with an exit angle of 0 to 0.5rad and an interval of 0.1rad according to one embodiment of the present invention.
FIG. 7 is a schematic diagram of a scanning range of a two-dimensional cylindrical optical phased array according to an embodiment of the present invention.
FIG. 8 is a schematic diagram of a two-dimensional cylindrical optical phased array according to an embodiment of the present invention.
Fig. 9 is a schematic diagram of a three-sphere phased array structure according to an embodiment of the present invention.
Fig. 10 is a schematic diagram of a simulation effect of four-multi-point scanning according to an embodiment of the present invention.
Fig. 11 is a schematic perspective view of a fifth disc waveguide grating coupler inside an optical phased array according to an embodiment of the present invention.
FIG. 12 is a schematic radial cross-sectional view of a five-disk waveguide grating coupler, in accordance with an embodiment of the present invention.
Fig. 13 is a model of a circular waveguide grating coupler built in the five simulation software according to the embodiment of the present invention.
Fig. 14 is a light field distribution diagram after the fifth simulation according to the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and examples.
Example one
Fig. 3a and fig. 3b are schematic diagrams of a one-dimensional circular optical phased array structure according to an embodiment of the present invention. The annular phased array consists of N phased array units, each phased array unit comprises 1 phase modulator 301 for adjusting the additional phase of the phased array unit 300, the N phased modulators are arranged in an annular shape on a plane, a waveguide transmitting unit 302 at one end of each phase modulator faces the outer side of the circle center of the annular shape, and N is a natural number. Fig. 3a is a schematic of the case where the outgoing beam is not deflected and fig. 3b is a schematic of the case where the outgoing beam is deflected. As can be seen from fig. 3a and 3b, the emergent phases of different phased array units are controlled by adjusting the additional phases of different phase modulators, so that the optical phased array realizes coherent superposition at a specific angle. The scanning of the beam is achieved by changing the outgoing phase such that the wavefront changes. The optical phased array can realize 360-degree constant-amplitude scanning, greatly increases the scanning range, and proves that the process is as follows (in all the following formulas, E)n0Is the output amplitude of the nth phased array element and En0N is equal to 1, i.e. equal amplitude emission, and is numbered as shown in fig. 3, N is the number of optical phased array units, and we adopt the case where N is equal to 4k (k is a positive integer) for analysis, but it is concluded that it is applicable to all N being positive integers, a is the emission aperture of the optical phased array unit, d is the adjacent emission unit spacing, λ is the optical wavelength,adding an additional phase, Δ l, to the arraynIs the relative optical path difference of the nth cell from the observation point, R0Phased array to viewpoint distance):
1) according to the light intensity distribution of the optical phased array in the 0-degree observation direction:
when the optical phased array is emitted in the 0 DEG direction, I (0) in the 0 DEG observation direction is maximized
The additional phase for each phased array unit is:
i.e. the maximum I (0) when adding the phase compensation space phase difference is
The optical phased array now exits in the 0 direction.
2) According to the light intensity distribution of the optical phased array in the observation direction with the angle omega:
when the optical phased array is emitted in the ω direction, the I (ω) in the ω observation direction is maximized
The additional phase for each phased array unit is:
i (ω) is the maximum at which the spatial phase difference is compensated for by the additional phase, and is
The optical phased array now exits in the ω direction.
3) According toAndcomparing to obtain the additional phase of the nth phased array unit when the outgoing direction changes by the angle omegaIs adjusted to
4) According to the fact that the maximum value of the light intensity is unchanged I (omega) to I (0) along with the change of the emergent angle in the scanning process, the intensity of a main lobe in the scanning process is determined to be unchanged, and constant-amplitude scanning is achieved;
5) determining the positions of all grating lobes according to the light intensity distribution of the optical phased array in the outgoing direction with the angle of omega and the observation direction with the angle of delta(m＝1,2,…)；
According to
It is determined that the grating lobe intensity is always less than the main lobe intensity as the scan angle changes. Usually, the maximum scanning angle of the optical phased array is defined as the scanning angle when the main lobe intensity is equal to the grating lobe intensity, but the grating lobe intensity is always smaller than the main lobe intensity and cannot reach the intensity equal to the main lobe intensity, so that 360-degree equal-amplitude scanning can be realized.
The above-described proving process is explained in detail below.
As shown in FIG. 3a, it is defined that the vertical direction is an angular direction of 0, the cell number n in the angular direction of 0 is 0, the cell number n to the right is 1,2,3 … … in order, and the cell number n to the left is-1, -2, -3 … … in order.
Wherein,. DELTA.lnIs the relative optical path difference of the nth cell, RnIs the n-th unitDistance to the observation point. Each unit of the optical phased array is regarded as an independent diffraction unit, the light field distribution of each unit in a specific direction is calculated respectively, then the light fields of different units in the specific direction are superposed, and finally the far field light intensity distribution is obtained. The model ignores the physical size of each cell, i.e. assumes it is infinitely small. At 0 deg. distance from 0 th emergent unit R0An observation point is arranged, and the amplitude of the emergent light field of the nth unit is set as En0With an additional phase ofAt an angle theta to the viewing directionnThe closest distance between an observation point and the phased array is R ═ R0Then the field strength of the cell at the observation point is:
wherein
The light field at the observation point in the 0-degree direction obtained by superposing the light intensity of each unit to the observation point is the light field
Then, the light intensity distribution in the 0 ° observation direction is
We observe the phase term of each cell in the formulaThe phase term is made up of two parts,is a phased array unit andthe spatial phase difference generated by the relative distance of observation points is namedIn order to artificially change the additional phase of array elements in the phased array through a phase modulator.
When a reasonable additional phase is added to the phased array unit, the additional phase difference and the space phase difference inside the array unit can be exactly offset, namely the additional phase difference and the space phase difference inside the array unit can be exactly offsetAt the moment, when the light beam emitted by each unit of the phased array reaches an observation point, the coherent superposition condition is met, the maximum value of the light intensity is generated in the direction of 0 degree, and at the moment, the maximum value is generatedSatisfies the following conditions:
when I (0) takes a maximum value
The additional phase distribution of the array elements required for an optical phased array exit angle of 0 is thus determined.
2) If we want to achieve a beam deflection omega. The range of the phased array working unit is fromBecome intoWhen we look at it from the direction of omega,
the light intensity at the observation point is
As mentioned above, in order to achieve a maximum light field intensity observed in the ω direction,
wherein
The spatial phase difference can be compensated by requiring additional phase differences within the array elements, i.e.
Thus, the additional phase distribution of the array element electric control needed when the emergent angle of the optical phased array is omega is determined.
3) According toAndcomparing to obtain the additional phase of the nth phased array unit when the outgoing direction changes by the angle omegaIs adjusted to
I.e. the corresponding cell additional phase profile is shifted to the right along the x-coordinate axis
4) Based on a comparison of the intensity maxima I (ω) and I (0),
wherein
Wherein
It can be derived that I (ω) ═ I (0), i.e. the maximum of the intensity is constant for ω scans over a range of 0 ° to 360 °, i.e. a constant amplitude scan over a range of 360 ° is achieved.
5) After determining the additional phase of each phased array unit, we change the observation direction to delta and calculate the additional phase of the array asThe light intensity in the delta direction of the time far field, and similarly, we can write:
when delta>At the time of the omega, the frequency of the wave,the unit cannot observe, and then the light intensity in the angle of ω emitting direction and the δ observing direction is:
when delta<At the time of the omega, the frequency of the wave,the light intensity in the direction of the angle omega and the angle delta cannot be observedComprises the following steps:
phase term for the whole body for observation points when δ ≠ ωThe coherent superposition condition is not satisfied any more, and from the angle, the maximum value of the optical phased array only in the omega direction can be obtained, namely the emergent direction of the optical phased array is omega.
For any one beam deflection caseThe situation that the phase changes with the element number is roughly shown in fig. 4, and fig. 4 is a schematic diagram that the phase of the phased array element changes with the element number at the observation point in the + 1-stage grating lobe direction. In the figure, the broken line is an auxiliary line. From the formula, it can be seen thatIs a aboutThe symmetric odd function of the first order function,for the derivative of n, i.e. the phase difference of adjacent cells, we are rightFinding the second derivative can find
Namely atSurroundingsApproximately linear distribution, so when(m is 1,2, …),the surrounding cells satisfy a phase difference of approximately ± 2m pi, (m ═ 1,2, …). That is, the coherent superposition condition is approximately satisfied, (m is 0, the main lobe position), which is the reason why the circular optical phased array also has a small grating lobe.
At this time, the grating lobe position is taken into the light intensity formula, and because the grating lobes on the two sides of the main lobe are symmetrical, only the grating lobes on the two sides of the main lobe are symmetrical(m-1, 2, …) grating lobes for analysis
That is, the grating lobe intensity is always less than the main lobe intensity no matter what the scanning angle ω takes any value, and from this point, it can also be shown that the scanning range of 360 ° can be realized by the present invention.
In this embodiment, the waveguide emitting unit selects an SOI waveguide structure, and the wavelength λ is calculated to be 1.55 μm, the thickness of the si waveguide is 0.22 μm, and the width a of the waveguide is λ/4, so that the waveguide satisfies a single-mode transmission condition. The number N of the phased array units is set to 512, and the distance between the adjacent waveguide transmitting units is set to 4 lambda so as to conveniently adjust the phase by applying electrodes between the waveguides. The far field intensity profile at 0 deg. exit angle was plotted by varying the value of the viewing angle delta, as shown in fig. 5.
The effect of plotting the far field intensity profiles during a scan with an optical phased array exit angle ω of 0 to 0.5rad and an interval of 0.1rad is shown in FIG. 6. It can be seen from fig. 6 that the optical phased array of the present invention has no reduction of the main lobe and no increase of the grating lobe during the scanning process, and is not limited by the diffraction envelope of the conventional optical phased array. Large angular equiamplitude scanning over a 360 deg. range is theoretically achieved, which is impossible to achieve with conventional optical phased arrays.
Example two
The one-dimensional circular ring optical phased array in the first embodiment is accumulated in the axial direction, so that an optical phased array with two-dimensional spatial scanning can be obtained, the scanning in the horizontal direction is described above, and the scanning in the vertical direction is achieved by changing the phase difference of the corresponding units of the adjacent layer. The scanning range of the three-two-dimensional cylindrical optical phased array in the embodiment of the invention is shown in fig. 7, the 360-degree large-range scanning can be realized in the horizontal azimuth angle, and the three-two-dimensional cylindrical optical phased array is still limited by the inherent defects of the traditional optical phased array in the pitch angle.
The unique scanning range of the optical phased array makes the optical phased array very suitable for being used for scanning of a vehicle-mounted laser radar, and the detection range of the optical phased array covers the annular periphery of an automatic driving vehicle.
The far-field intensity analysis was performed by the diffraction superposition model, and for the convenience of analysis, the x-axis and the y-axis were set as shown in fig. 8. The short line on the ring is a waveguide transmitting unit, RmnThe distance from the nth unit in the mth column to the observation point. (M is numbered from 0 to M-1 in M rows, M is a positive integer, and n is numbered as in the first embodiment)
Diffraction superposition model of two-dimensional optical phased array:
each unit of the optical phased array is regarded as an independent diffraction unit, the light field distribution of each unit in a specific direction is calculated respectively, then the light fields of different units in the specific direction are superposed, and finally the far field light intensity distribution is obtained. Setting observation points on the horizontal deflection angle and the vertical deflection angle of 0 degreeThe closest distance between the probe and the phased array is R. Let the amplitude of the light field emitted by the nth unit in the mth column be Emn0Electrically controlled additional phase ofAt an angle theta to the observation pointmnA distance of RmnThen the cell is in the 0 ° direction RmnHas a field intensity distribution of
In the formula
The electric field distribution in the far field 0 degree direction of the phased array is
The light intensity distribution is
When the additional phase of the phased array compensates for the spatial phase:
i (0,0) takes the maximum valueNamely, the emergent light with the horizontal deflection angle and the vertical deflection angle of 0 degree is realized. Thereby determining the additional phase distribution of the required array element electrical control.
The x-axis angle at this additional phase is now calculated as delta by changing the angle of the viewpointxAngle of y-axis deltayThe light intensity distribution is similar to the calculation method of the far field light intensity in the 0 degree direction, except the space phaseA change occurs.
Likewise, when deltax>At the time of 0, the number of the first,the unit cannot observe, and the field strength at the observation point is:
the light intensity distribution is
When deltax<At the time of 0, the number of the first,the unit cannot observe, and the field strength at the observation point is:
the light intensity distribution is
In the formula
Two-dimensional cylindrical optical phased array beam deflection:
when we are in (ω)x，ωy) When viewed in the direction, the additional phase of the phased array elements compensates for the spatial phase, i.e.
Can obtain (omega)x，ωy) Field strength maximum in direction, i.e. ω is achievedx，ωyThe light beam is deflected in the direction, and the light intensity after deflection is as follows:
wherein the content of the first and second substances,light intensity at a deflection angle of 0 DEG
Wherein the content of the first and second substances,
a deflection angle of (omega)x，ωy) Comparing the light intensity in the direction with the deflection angle of 0 degrees can obtain:
wherein the content of the first and second substances,
i.e. the light intensity does not change when scanning in the x-direction and the diffraction envelope does when scanning in the y-directionThe limit of (2).
EXAMPLE III
The cylindrical optical phased array can only realize 360-degree large-range scanning in one direction, if the cylindrical optical phased array can realize 360-degree scanning in two directions simultaneously, a plurality of layers of annular optical phased arrays are required to be superposed to be approximately arranged in a spherical shape, namely, the number of phased array units contained in the one-dimensional annular optical phased array on the plane is decreased progressively from the circle center along two axial directions, so that the spherical phased array with unevenly arranged array elements is formed, and the grating lobes are greatly compressed due to the uneven arrangement mode. The theoretical analysis of the spherical optical phased array is still analyzed according to a diffraction superposition model, and the structural schematic diagram of the spherical phased array is shown in fig. 9. The short lines in the figure are phased array transmit units.
Example four
The optical phased array multipoint scanning can realize simultaneous tracking and detection of multiple targets, and has important research value. The optical phased array related by the invention can also realize the function of simultaneously scanning multiple points, and the realization method comprises the following steps:
when the optical phased array scans multiple points, the method is equivalent to overlapping far field intensities emitted at different angles to form two points omega1、ω2(ω2>ω1) Scanning for example, when the scanning angle is ω1When it is neededUnits operating in a range when the scan angle is omega2When it is neededUnit operation within range, overlapping rangeThe additional phase of the inner cell requires a detailed discussion.
For this part of the cell, when we observe at the angle δ, the light field we wish to see is the superposition of the two angularly independent emergent light intensities, that is:
wherein the content of the first and second substances,
is thatWhereinAre respectively two points omega1、ω2Additional phase, E 'of n-th phase control array unit at emission'n0Andthe actual emergent amplitude and the additional phase of the nth phase control array unit. That is, the transmission function of the optical phased array during multi-point scanning is equivalent to the superposition of the transmission functions of the optical phased array corresponding to each point.
Thus can be solvedAdditional phase required for the inner cell:
next, we analyze the far field light intensity distribution after the transmission function is superimposed, and for the above formula
When we get from δ to ω1When the glass is observed in the direction of the glass,
first itemThe maximum value is obtained, and the maximum value,
second itemSince the phase term is irregular, that is, coherent superposition conditions are not satisfied, we can ignore it, so we can approximately consider that
When we get from δ to ω2When the glass is observed in the direction of the glass,
second itemThe maximum value is obtained, and the maximum value,
first itemSince the phase term is irregular, that is, coherent superposition conditions are not satisfied, we can ignore it, so we can approximately consider that
Namely, it isNamely, two-point constant-amplitude scanning is realized.
In summary, because the light field is superimposed before ω1,ω2The maximum values of the light intensity under the deflection angle are the same, so the light intensity of the corresponding angle is also equal when the two points are scanned after being overlapped, namely, the two-point equal-amplitude scanning is realizedDrawing. We get omega1＝0rad，ω20.2rad and ω1＝0rad，ω2The far field pattern was simulated for the two sets of data at 0.5 rad. The resulting effect is schematically shown in FIG. 10, where one point is held stationary at 0rad and the other point produces a deflection from 0.2rad to 0.5 rad.
The above description is made in two-point scanning. Analogize in turn, for the case of m-point scanning (ω)1<ω2<…ωm) To aUnit pair omega in rangejThe directional light intensity (j is a positive integer from 1 to m) contributes, so we can conclude that we needUnits within range operate.
For theInner unit simultaneous pair omega1、…ωjThe light intensity in the direction contributes, m is a positive integer greater than or equal to 2, and j is a positive integer from 1 to m-1;
for theInner unit simultaneous pair omegaj+1、…ωmThe light intensity in the direction contributes, m is a positive integer greater than or equal to 2, and j is a positive integer from 1 to m-1;
for theInner unit simultaneous pair omega1、…ωmEach emission direction contributes, and m is a positive integer greater than or equal to 2.
We next calculate the additional phase required for each cell in regions.
Therefore, forInner cell the light field we wish to see when we look at an angle delta is omega1、…ωjThe light intensity superposition of independent emergent directions is:
wherein
For the phase we finally want to apply to cell n, En′0To finally want the amplitude applied on the cell n,
get it solved
In the same way, forInner cell the light field we wish to see when we look at an angle delta is omegaj+1、…ωmThe light intensity superposition of independent emergent directions is:
wherein
For the phase we finally want to apply to cell n, En′0To finally want the amplitude applied on the cell n,
get it solved
For theInner unit
(in all the above formulae, abs is the amplitude of the complex number and arg is the argument of the complex number)
EXAMPLE five
Fig. 11 is a schematic perspective view of a fifth disc waveguide grating coupler inside an optical phased array according to an embodiment of the present invention. FIG. 12 is a schematic radial cross-sectional view of a five-disk waveguide grating coupler, in accordance with an embodiment of the present invention. The disc waveguide grating coupler can uniformly couple light incident from a light source above the coupler into the annular optical phased array. The circular waveguide grating coupler is arranged on the inner side of the circular optical phased array, the circumference of the circular waveguide grating coupler is connected with the tail end of one side, facing the circle center, of each phase modulator, the circle center of the circular waveguide grating coupler is overlapped with the circle center of the circular optical phased array, annular grooves are formed in the disc of the circular waveguide grating coupler at intervals of preset width along the radius, and the sum of the width of the bottom of each groove and the preset width is equal to the period of the waveguide grating;
the period Λ of the waveguide grating is according to the formula (n)3sinθ-neff) Λ ═ Δ l ═ m λ m ═ 0, ± 1, ± 2 …;
n3represents the refractive index of air; theta represents the included angle between the light source incident on the surface of the disc and the vertical direction; λ represents the light source wavelength; n iseffRepresenting the effective refractive index of the waveguide grating, said neffRefractive index n according to disc waveguide grating coupler material1Refractive index n of substrate material2Refractive index n of air3Height h from the bottom surface of the trench to the substrate1Height h from the top of the recess to the substrate2And the ratio of said predetermined width to the period of the waveguide grating.
Waveguide grating couplers are devices based on the diffraction effect. Due to the periodic modulation of the refractive index of the waveguide by the grating grooves, light incident on the waveguide grating is coupled into the waveguide grating for propagation. The disc waveguide grating coupler of the embodiment of the invention adopts silicon material as n1The substrate adopts silicon dioxide material as n2. The light emitted by the light source is incident perpendicularly, i.e. theta is 0.
Two paths of light beams incident to adjacent periods of the grating have certain optical path difference after entering the waveguide grating:
Δl＝n3Λsinθ-neffΛ
according to the theory of optical interference, where the optical path difference is an integral multiple of the wavelength, the diffraction maximum of light occurs, that is:
(n3sinθ-neff)Λ＝mλm＝0,±1,±2…
according to n1，n2，n3Set up h1＝0.14μm，h20.22 μm and a duty cycle (ratio of the predetermined width to the waveguide grating period) of 0.5, and is calculated by mode solutions software to obtain neff＝2.64，
Thus, a circularly polarized light with θ 0, λ 1.55 μm, m-1, and neff2.64 substituted (n)1sinθ-neff) And lambda is calculated to be 0.587 um.
In this embodiment, after determining the parameters of the disc waveguide grating, the model shown in fig. 13 is established in fdtd, and fig. 13 is a model of the disc waveguide grating coupler established in the five-simulation software in the embodiment of the present invention. The radius of the disc waveguide grating coupler is set to be 10 mu m, the number of output waveguides is 64, the width of each waveguide is 0.4 mu m, and the height of each waveguide is 0.22 mu m so as to ensure single-mode transmission conditions. Circularly polarized light with λ ═ 1.55 μm is incident from above the coupler. A detector is placed on the plane of the coupler to detect the optical field distribution, and it can be seen from the optical field distribution diagram of the coupler after simulation in fig. 14 that the light beams are uniformly coupled into each waveguide unit of the circular optical phased array.
The invention has the beneficial effects that:
1. the emitting unit through with optical phased array designs into the ring shape and arranges the phase place time delay through controlling different units and can realize that the light beam is 360 within range arbitrary angle coherent stack, thereby 360 scanning on a large scale has been realized, because the high symmetry that the ring shape was arranged, the shape of far field light intensity can hardly change at the light beam scanning in-process, only translation on different angles, this constraint of having broken through traditional optical phased array diffraction envelope has overcome traditional optical phased array at the light beam scanning in-process mainlobe and has attenuated by a wide margin, the shortcoming that the grating lobe increases by a wide margin.
2. The invention realizes 360-degree large-range scanning, and the requirement on the distance between adjacent waveguide transmitting units does not need to be met as the prior artThe value of d in the invention can be taken in a large range, such as 4 lambda, 8 lambda and the like.
3. The invention forms the two-dimensional scanning optical phased array by accumulating and arranging the one-dimensional annular optical phased array on M planes in the axial direction. The scanning range is greatly increased in the spatial direction.
4. By designing the emitting units of the optical phased array into circular ring arrangement, multi-point constant-amplitude scanning can be realized by controlling the phase delay of different units.
5. And the disc waveguide grating coupler is arranged on the inner side of the annular optical phased array, annular grooves are formed in the disc at intervals of preset width along the radius, and light beams are uniformly coupled into the annular optical phased array.
6. Because of adopting a circular ring structure, the optical phased array of the invention does not meet the coherent superposition condition at the grating lobe position, so the grating lobe intensity is greatly reduced compared with the traditional optical phased array.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An optical phased array is composed of N phased array units, each phased array unit comprises 1 phase modulator for adjusting the additional phase of the phased array unit, the optical phased array is characterized in that the N phased modulators are arranged in a ring shape on a plane, a waveguide transmitting unit at one end of each phase modulator faces the outer side of the circle center of the ring shape, and N is a natural number; the working range of the phased array unit isn is an integer, wherein the phase modulator of the nth phased array unit adjusts the additional phase according to the change of the emergent angle omega as follows:
d is the distance between adjacent waveguide emission units, and lambda is the wavelength of the light source.
2. The optical phased array as claimed in claim 1, wherein the one-dimensional circular ring-shaped optical phased array on M planes is arranged cumulatively in the axial direction to form a two-dimensional scanning optical phased array, M being a natural number.
3. The optical phased array of claim 2, wherein the one-dimensional circular optical phased array in each plane comprises the same number of phased array elements.
4. The optical phased array as claimed in claim 2, wherein the one-dimensional circular optical phased array on the plane includes phased array elements whose number decreases from the center of the circle in both axial directions.
5. The optical phased array as claimed in claim 1, further comprising a circular waveguide grating coupler disposed inside the circular ring optical phased array, the circular waveguide grating coupler having a circumference connected to a side end of each phase modulator toward a center of the circle, the center of the circular waveguide grating coupler coinciding with the center of the circular ring optical phased array, the circular waveguide grating coupler having circular grooves engraved at every predetermined width along a radius, the width of the bottom of the groove plus the predetermined width being equal to a waveguide grating period;
the period Λ of the waveguide grating is according to the formula (n)3 sinθ-neff) Λ ═ Δ l ═ m λ, m ═ 0, ± 1, ± 2 …;
n3represents the refractive index of air; theta represents the included angle between the light source incident on the surface of the disc and the vertical direction; λ represents the light source wavelength; n iseffRepresenting the effective refractive index of the waveguide grating, said neffRefractive index n according to disc waveguide grating coupler material1Liner for furnitureRefractive index n of the base material2Refractive index n of air3Height h from the bottom surface of the trench to the substrate1Height h from the top of the recess to the substrate2And the ratio of the predetermined width to the waveguide grating period; and delta l represents the optical path difference of two paths of light beams which are incident to adjacent periods of the waveguide grating by the light source.
6. An optical phased array is composed of N phased array units, each phased array unit comprises 1 phase modulator for adjusting the additional phase of the phased array unit, the optical phased array is characterized in that the N phased modulators are arranged in a ring shape on a plane, a waveguide transmitting unit at one end of each phase modulator faces the outer side of the circle center of the ring shape, and N is a natural number;
for theThe phase modulator of the n-th phased array unit is based on m points (omega)1<…<ωj<…ωm) Omega in a scan1、…ωjThe additional phase adjusted in the outgoing direction is:n is an integer, m is a positive integer greater than or equal to 2, and j is a positive integer from 1 to m-1;
for theThe phase modulator of the internal working phased array unit, the nth phased array unit is based on omega in m point scanningj+1、…ωmThe additional phase adjusted in the outgoing direction is:n is an integer, m is a positive integer greater than or equal to 2, and j is a positive integer from 1 to m-1;
for theThe phase modulator of the internal working phased array unit and the n-th phased array unit scans omega according to m points1、…ωmThe additional phase adjusted in the outgoing direction is:
n is an integer, m is a positive integer greater than or equal to 2;
d is the distance between adjacent waveguide emission units, and lambda is the wavelength of the light source.
7. The optical phased array as claimed in claim 6, wherein the one-dimensional circular ring-shaped optical phased array on the M planes is arranged cumulatively in the axial direction to form a two-dimensional scanning optical phased array, M being a natural number.
8. The optical phased array of claim 7, wherein the one-dimensional circular optical phased array in each plane comprises the same number of phased array elements.
9. The optical phased array as claimed in claim 7, wherein the one-dimensional circular optical phased array on the plane includes a decreasing number of phased array elements in both axial directions from the center of the circle.
10. The optical phased array as claimed in claim 6, further comprising a circular waveguide grating coupler disposed inside the circular ring optical phased array, the circular waveguide grating coupler having a circumference connected to a side end of each phase modulator toward a center of the circle, the center of the circular waveguide grating coupler coinciding with the center of the circular ring optical phased array, the circular waveguide grating coupler having circular grooves engraved at every predetermined width along a radius, the width of the bottom of the groove plus the predetermined width being equal to a waveguide grating period;
the period Λ of the waveguide grating is according to the formula (n)3 sinθ-neff)Λ＝△l ═ m λ, m ═ 0, ± 1, ± 2 …;
n3represents the refractive index of air; theta represents the included angle between the light source incident on the surface of the disc and the vertical direction; λ represents the light source wavelength; n iseffRepresenting the effective refractive index of the waveguide grating, said neffRefractive index n according to disc waveguide grating coupler material1Refractive index n of substrate material2Refractive index n of air3Height h from the bottom surface of the trench to the substrate1Height h from the top of the recess to the substrate2And the ratio of the predetermined width to the waveguide grating period; and delta l represents the optical path difference of two paths of light beams which are incident to adjacent periods of the waveguide grating by the light source.
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