Light receiving array and LiDAR device

Abstract

A light receiver array according to the present invention is constituted by array-aligning plural receivers having slow light waveguides of photonic crystals, and a LiDAR device according to the present invention is constituted by linearly arranging a light receiver array and a transmitter. An arranging relationship of plural receivers of the light receiver array is an array-like element formed by array-aligning plural receivers having the slow light waveguides of photonic crystals, and the array alignment is defined by alignment for defining a position relationship between the plural receivers constituting the light receiver array, and orientation for defining a direction of each receiver. A relationship p=λ/sin Δθr is satisfied between the alignment pitch p, wavelength λ of the reception light, and an arrival angle Δθr when a phase difference between reception lights received by waveguide ends of adjacent receivers is one wavelength. Such a constitution that the arrival angle Δθr is equal to a widening angle Δθt of radiation light is suitable.

Claims

1. A light receiver array in which plural receivers having slow light waveguides of photonic crystals are aligned in array, wherein (a) alignment of the respective receivers is linear alignment at an alignment pitch p along one straight line direction, and (b) in orientation of the respective receivers, a traveling direction of a slow light waveguide for reception of each receiver is parallel to an alignment direction of the linear alignment.

2. The light receiver array described in claim 1, wherein length in the traveling direction of the slow light waveguide for reception of each receiver is in an unsaturated range in which reception strength to length of the slow light waveguide monotonously changes.

3. The light receiver array described in claim 1, wherein a relationship p=λ/sin Δθr is satisfied between the alignment pitch p, wavelength λ of the reception light, and an arrival angle Δθr when a phase difference between reception lights received by waveguide ends of adjacent receivers is one wavelength.

4. The light receiver array described in claim 3, wherein the arrival angle Δθr is equal to a widening angle Δθt of radiation light.

5. The light receiver array described in any one of claim 1, wherein each receiver includes photo diodes as a pair, the photo diodes being optically coupled to the waveguide end of each slow light waveguide for reception via a low loss light waveguide, and light waveguide lengths of the receiver and the low loss light waveguide in each pair of photodiodes are equal to each other.

6. The light receiver array described in claim 1, comprising: an emission waveguide connected to the waveguide end of the slow light waveguide for reception of each receiver; a first jointer for jointing the emission waveguide to a connection waveguide; a second jointer for jointing the connection waveguide to other connection waveguide; and a final waveguide for guiding output signals obtained by multiplexing reception outputs of the receivers to an output end, wherein the emission waveguide, the connection waveguide and the final waveguide are low loss light waveguides, and optical path lengths from the respective slow light waveguides for reception to the final waveguide are equal to each other.

7. The light receiver array described in claim 6, wherein the emission waveguide and the waveguide selectively comprise phase adjusters.

8. The light receiver array described in claim 6, wherein the number of the receivers is power-of-two, the first jointer is provided at an equal position of the optical path length between emission waveguides of the adjacent receivers in an array alignment direction, and the second jointer is provided at an equal position of the optical path length between the adjacent connection waveguides in the array alignment direction.

9. A LiDAR device comprising a light receiver array according to claim 1, and one transmitter for emitting radiation light having a slow light waveguide of a photonic crystal, wherein in an alignment direction of the light receiver array, a traveling direction of a waveguide of a receiver is the same as a traveling direction of a waveguide of the transmitter.

10. The LiDAR device described in claim 9, wherein an angle between adjacent radiation lights emitted from the transmitter and a widening angle of the radiation light are the same angle Δθt, and the angle Δθt is equal to an arrival angle Δθr when a phase difference between reception lights received at waveguide ends of adjacent receivers is one wavelength.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram showing one constitution of a LiDAR device using a light deflection device;

(2) FIG. 2 is a diagram showing reception strength to length Lr of a reception wavelength;

(3) FIG. 3 is a diagram for explaining a light reception array according to the present invention;

(4) FIG. 4 is a diagram for explaining a relationship between the number of receivers constituting the light receiver array and signal strength of reception signals;

(5) FIG. 5 is a diagram for explaining constitutions of the receivers of the receiver array and a waveguide;

(6) FIG. 6A is a diagram for explaining a constitution example of the receivers of the receiver array and the waveguide, and shows an example that the light receiver array is constituted by two receivers;

(7) FIG. 6B shows an example that the light receiver array is constituted by eight receivers;

(8) FIG. 6C shows an example that the light receiver array is constituted by sixteen receivers;

(9) FIG. 6D shows an example that the light receiver array is constituted by receivers the number of which is not power-of-two;

(10) FIG. 7A is a diagram for explaining an alignment pitch of plural receivers, and shows when reflected light arrives from a plane vertical direction;

(11) FIG. 7B shows when an incident angle of the reflected light changes, and the light arrives displaced from the plane vertical direction by an angle Δθ;

(12) FIG. 7C is a diagram showing a state that the arrival angle of the reflected light is further increased;

(13) FIG. 7D is a diagram showing a relationship between strength of light signals obtained by multiplexing reception lights of a slow light waveguide for reception of each receiver and the arrival angle Δθ of the reflected light;

(14) FIG. 8A is a diagram for explaining an alignment pitch of plural receivers, and shows a relationship between an angle Δθ.sub.r at which interference for increase occurs, and alignment pitches p, t of the receivers;

(15) FIG. 8B shows when an angle difference Δθ of adjacent radiation lights is larger than a beam widening angle Δθt;

(16) FIG. 8C shows when the angle difference Δθ of the adjacent radiation lights is equal to the beam widening angle Δθt;

(17) FIG. 8D is a diagram chronologically showing radiation light and reflected light when the angle different Δθ of the radiation light is made equal to the beam widening angle Δθt of the radiation light and the arrival angle Δθr of the reflected light;

(18) FIG. 8E is a diagram chronologically showing radiation light and reflected light when the angle different Δθ of the radiation light is made equal to the beam widening angle Δθt of the radiation light and the arrival angle Δθr of the reflected light;

(19) FIG. 8F is a diagram chronologically showing radiation light and reflected light when the angle different Δθ of the radiation light is made equal to the beam widening angle Δθt of the radiation light and the arrival angle Δθr of the reflected light;

(20) FIG. 9 is a diagram for explaining a constitution of the LiDAR device;

(21) FIG. 10A is a diagram for explaining a device structure having a diffraction mechanism in a photonic crystal waveguide, and a brief concept of radiation light;

(22) FIG. 10B shows beam strength distribution in a vertical direction;

(23) FIG. 10C shows beam strength distribution in a horizontal direction; and

(24) FIG. 10D is a diagram showing a constitution for restraining the radiation light from being widened in the horizontal direction.

DETAILED DESCRIPTION

(25) Hereinafter, embodiments of the present invention will be explained in details with reference to the drawings. A brief constitution example of a light receiver array according to the present invention will be explained with reference to FIG. 3, and a relationship between the number of receivers constituting the light receiver array and signal strength of reception signals will be explained with reference to FIG. 4. A constitution example of the light receiver array according to the present invention will be explained with reference to FIGS. 5, 6A-6D, and alignment pitch of plural receivers will be explained with reference to FIGS. 7A-7D, 8A-8F. A constitution of a LiDAR device will be explained with reference to FIG. 9.

(26) (Brief Explanation of Light Receiver Array)

(27) FIG. 3 is a diagram for explaining a light receiver array according to the present invention. A light deflection device includes two light polarizers of a light receiver array 10 including a transmitter 21 and plural receivers 11a-11d. The transmitter 21 and the receivers 11a-11d are constituted by a photonic crystal waveguide. The photonic crystal waveguide is formed by a grating array in which low refractive index portions are periodically arranged in a high refractive index member of a semiconductor material such as Si provided on a clad. The low refractive index portions can be formed, for example, by circular holes provided to the high refractive index member.

(28) A waveguide core for propagating light is formed on the photonic crystal waveguide. The waveguide core is formed by a portion at which circular holes are not arranged at one part of the grating array, in the grating array constituted by alignment of the circular holes. The waveguide core of the transmitter 21 constitutes a slow light waveguide 22 for transmission, and the waveguide cores of the receivers 11a-11d constitute a slow light waveguide 12 for reception.

(29) Incident light incident on the slow light waveguide 22 for transmission of the transmitter 21 is emitted to outside from the slow light waveguide 22 for transmission while being propagated through the slow light waveguide 22 for transmission in a length direction. The slow light waveguide 12 for reception of the receivers 11a-11d receives reflected light, and propagates it in the length direction, and then, outputs reception signals through a low loss light waveguide 13 such as a Si thin line waveguide from a waveguide end.

(30) The transmitter 21 and the light receiver array 10 are linearly and vertically aligned in the length direction of the slow light waveguide 22 for transmission and the slow light waveguide 12 for reception. In the vertical alignment, the transmitter 21 is arranged on a side on which the incident light is incident, and the light receiver array 10 is arranged on a side on which the emission light is received.

(31) The light deflection device includes one cylindrical lens 30 as a collimate lens for converting light into parallel light, in addition to the transmitter 21 and the light receiver array 10. The cylindrical lens 30 is provided on the side of a face for emitting the radiation light and a face for receiving reflected light to the transmitter 21 and the light receiver array 10 vertically aligned, so as to be overlaid along a vertical alignment direction of the light deflection device.

(32) The cylindrical lens 30 has such a size, for example, to have width equal to or larger than width of the transmitter 21 and the light receiver array 10, and length equal to or longer than length of two light deflection devices (10, 21) vertically aligned. Also, the size of the cylindrical lens 30 is not limited to the size almost the same as that of the vertical alignment, and may be optional size, as long as the size is sufficient that the radiation light emitted from the transmitter 21 is converted to parallel beam and emitted to an object (not shown) and the reflected light reflected by the object is collected to the respective receivers 11a-11d of the light receiver array 10.

(33) The light receiver array 10 according to the present invention is constituted by an array-like element formed by array-aligning the plural receivers 11a-11d having photonic crystal slow light waveguides. Also, the light receiver array 10 shown in FIG. 3 has a constitution that four receivers 11a-11d are aligned in array, but the number of the array alignment is not limited to 4, and may be optional. When the number of array-alignment is made power-of-two, a constitution of a waveguide for multiplexing reception signals is made to have a symmetry property to restrain phase displacement of the reception signals when being propagated through the waveguide, so that loss of a jointer caused by the phase displacement can be reduced. The array-alignment of power-of-two will be explained later.

(34) In the light receiver array 10 according to the present invention, by a constitution that a low loss light waveguide 13 such as Si thin line waveguide is connected to a waveguide end of the slow light waveguide 12 for reception of plural receivers 11 to pick up reception light, before the loss by the slow light waveguide of the slow light waveguide 12 for reception, the reception light can be picked up from the slow light waveguide 12 for reception.

(35) FIG. 4 shows reception strength that can be obtained when it is supposed that light picked up from each slow light waveguide for reception can be ideally multiplexed, to the division number of the waveguide. Also, FIG. 4 shows when total extension of the slow light waveguide for reception is 3 mm, and when the waveguide loss is 0 dB/cm, 5 dB/cm, and 10 dB/cm, respectively.

(36) In the case that the waveguide loss is 10 dB/cm, compared to when the light receiver is one slow light waveguide for reception, about 3 times larger reception strength can be obtained when the slow light waveguide 12 for reception is divided into four and the light receiver array 10 is constituted by four receivers 11 (Q in FIG. 4), about 4 times larger reception strength can be obtained when the slow light waveguide 12 for reception is divided into eight and the light receiver array 10 is constituted by eight receivers 11 (R in FIG. 4), and about 5 times larger reception strength can be obtained when the slow light waveguide 12 for reception is divided into sixteen and the light receiver array 10 is constituted by sixteen receivers 11 (S in FIG. 4).

(37) Then, the constitution of the light receiver array according to the present invention will be explained with reference to (a) array alignment, (b) alignment of receivers and (c) orientation of the receivers for defining an arrangement relationship of plural receivers in the array alignment.

(38) (a) Array Alignment

(39) In the array alignment, forms for defining the number of plural receivers include (a1) a form using a short receiver as a starting point, and (a2) a form using a long as a starting point.

(40) (a1) The number of the receivers is set based on signal strength obtained by multiplexing the respective reception signals obtained by the plural short receivers, and signal strength of the reception signals to be obtained by the light receiver array.

(41) (a2) The long receiver is divided into plural receivers, and the division number is set based on the signal strength obtained by multiplexing the reception signals obtained by the plural divided receivers, and the signal strength of the reception signals to be obtained by the light receiver array.

(42) In the form (a1), the number of the receivers is set based on the signal strength of the reception signals obtained by each receiver and the signal strength of the reception signals to be obtained by the light receiver array. When, the signal strength of the reception signals of the receiver is small, the number of the receivers is increased by the number sufficient to satisfy the signal strength of the reception signals of the light receiver array, and when the signal strength of the reception signals of the receiver is large, the number of the receivers is decreased by the number sufficient to satisfy the signal strength of the reception signals of the light receiver array.

(43) In the form (a2), a long receiver is divided into plural receivers, and the division number is set so that the signal strength obtained by multiplexing the reception signals of the plural divided receivers satisfies desired signal strength. When the signal strength obtained by multiplexing the reception signals of the receivers does not satisfy desired signal strength, the division number is increased to increase the number of receivers.

(44) In any of forms (a1) and (a2), the number of the plural receivers is set based on the signal strength of the reception signals obtained by the receiver, and signal strength obtained by the light receiver array. By array-aligning the plural set receivers, larger signal strength than that can be obtained by a single receiver can be obtained.

(45) The arrangement relationship between the plural receivers is defined by (b) alignment for defining such a position relationship between the plural receivers, what relationship the positions of the respective receivers have, and (c) orientation for defining a direction, in what direction each receiver is.

(46) (b) Alignment of Receivers

(47) In the alignment of the receivers, the alignment of each receiver is linear alignment along a one straight line direction at an alignment pitch p in the array alignment of the plural receivers. By making the alignment interval of each receiver correspond to the alignment pitch p, the reflected light with the same phase is received.

(48) (c) Orientation of Receivers

(49) Regarding the orientation of each receiver, a traveling direction of the slow light waveguide for reception of each receiver is parallel to an aligning direction of linear alignment of the plural receivers in its orientation direction.

(50) In the arrangement relationship of each receiver, the alignment of the receiver is linear alignment and the orientation direction of each receiver is parallel to the orientation direction of linear alignment, so that the plural receivers of the light receiver array receive the reflected light with the same arrival angle. The received reflected light is made to have the same phase and the arrival angle is made equal, so as to increase the signal strength of the reception signals of the receiver.

(51) (d) Length Limitation of Slow Light Waveguide for Reception of Receiver

(52) The receiver according to the present invention may be provided with length limitation on the length in the traveling direction of the slow light waveguide for reception of the receiver, in addition to (a) the array alignment, (b) the alignment and (c) the orientation, as mentioned above.

(53) According to a characteristic of reception strength to length Lr of a slow light waveguide for reception shown in FIG. 2, the reception strength of the slow light waveguide has an unsaturated region A monotonously changed according to the length while the propagation loss in the slow light waveguide depends on the waveguide length, and a saturated region B not changed even when the waveguide length is changed by increasing an attenuating amount of propagation light. This characteristic shows that the reception strength is not increased even when the waveguide length is made longer in the saturated region B.

(54) The receiver according to the present invention, in the array alignment of the plural receivers, limits the length in the traveling direction of the slow light waveguide for reception within the unsaturated range A in which the reception strength to the length of the slow light waveguide is monotonously changed. By this length limitation, the propagation loss occurred in the slow light waveguide of the receiver is made an amount according to a length of the slow light waveguide for reception in the traveling direction and the length of the receiver is within effective length, so as to restrain the receiver from having excessive length. When the length of the light deflection device is limited by this length limitation, the substantial propagation loss generated in the slow light waveguide of the receiver is reduced, so as to restrain reduction of the reception strength of the receiver and increase the signal strength of the reception signals of the receiver.

(55) (Constitution of Waveguide of Receiver Array)

(56) FIG. 5 is a diagram for explaining constitutions of a receiver of a receiver array and a waveguide. Also, a waveguide explained here is a member for guiding output signals of each receiver of the receiver array, and includes an emission waveguide connected to each waveguide end of the receiver, a final waveguide for finally outputting output signals, and a connection waveguide constituting an optical path between the emission waveguide and the final waveguide.

(57) FIG. 5 shows a constitution example that light picked up from each waveguide end of the receiver 11 is multiplexed to one emission waveguide. In this constitution example, light picked up from the waveguide ends of four receivers 11a-11d is multiplexed to one final waveguide 13z.

(58) In this constitution, the receivers 11a, 11b and two emission waveguides 13a are jointed to one connection waveguide 13b by a 2×1 (2 inputs/1 output) jointer 14a, the receivers 11c, 11d and two emission waveguides 13a are jointed to one connection waveguide 13b by a first 2×1 jointer 14a, and two connection waveguides 13b are jointed to one final waveguide 13z by a second 2×1 jointer 14b, so as to multiplex final output signals.

(59) At that time, if length from the waveguide end of each slow light waveguide 12 for reception to the final waveguide 13z is the same, optical path length from when the light is emitted from each slow light waveguide 12 for reception until it is jointed to the respective jointers 14a, 14b is equal. Also, if the phase when the light is emitted from each slow light waveguide 12 for reception is the same, the phases at which the light is incident on the jointers 14a, 14b are aligned, so that unnecessary loss by the jointers 14a, 14b is restrained.

(60) A device using a multi-mode interference waveguide has been already developed as such a jointer. Excessive loss evaluated in a test is 0.23 dB, which is small. In the case of the constitution shown in FIG. 5, two jointers 14a, 14b are used to multiplex four slow light waveguide 12 for reception, and the excessive loss is 0.46 dB, which is also small. If it is calculated to transmission ratio from the waveguide end to the final waveguide, it is about 90%.

(61) If the light receiver array is constituted by eight receivers, the loss of the jointer is 0.69 dB when the reception signals are multiplexed by three jointers. If the light receiver array is constituted by sixteen receivers, the loss of jointers is 0.92 dB when the reception signals are multiplexed by four jointers. In any case, the loss of the jointers is not excessive.

(62) Meanwhile, a typical value of propagation loss of a Si thin thine waveguide itself is 2 dB/cm. If total extension of the slow light waveguide for reception is 3 cm, when the waveguide is constituted as shown in FIG. 5, the length from each waveguide end to the final waveguide is about 1.5 cm, which is a half of the total extension of the receiver and the propagation loss is 3 dB.

(63) This propagation loss is excessive for a LiDAR device, and the loss can be made low by enlarging the waveguide width at a straight line portion. For example, normal waveguide width of a Si thin line is 400-450 nm, but if it is extended to about 4 μm, the propagation loss is reduced to about 0.5 dB/cm. The total loss with combination of the above-mentioned jointer loss 0.46-0.92 dB is restrained to 1-2 dB.

(64) In an actual device, even when the optical path lengths are identical to each other from the waveguide end to the jointer, the phase might be displaced by local swing of width and thickness of the waveguide. Phase adjusters 15a, 15b constituted by a heater and the like are arranged on the emission waveguide on a single side of the two emission waveguide 13a incident to the jointer 14a and on the connection waveguide on a single side of the two connection waveguides 13b incident to the jointer 14b, against the phase displacement. By using the phase adjusters, unnecessary phase displacement is compensated.

(65) (Number (Division Number) of Receivers)

(66) Then, the number (division number) of the plural receivers constituting a light receiver array according to the present invention will be explained.

(67) In a form for outputting reception signals per receiver, the number of receivers is optionally set. For example, when the reception signals of the emission waveguide of a low loss light waveguide 13 connected to the waveguide end of the respective receivers 11a-11d are utilized as output signals in FIG. 3, the number of receivers can be optionally defined.

(68) Meanwhile, as shown in FIG. 5, a form for multiplexing reception signals of the respective receivers and outputting one reception signal may include a constitution for using an optional number of receivers, and a constitution for using a power-of-two number of receivers.

(69) In the constitution for using the power-of-two number of receivers, a first jointer is provided at a position of optical path length equal from emission waveguides of adjacent receivers in an array alignment direction to multiplex the reception signals of two receivers to the connection waveguide, and a second jointer is provided at a position of optical path length equal from adjacent connection waveguides in an array alignment direction to multiplex the reception signals of two connection waveguides to the next connection waveguide. The constitutions of the connection waveguide and the second jointer are sequentially repeated, so as to multiplex the reception signals of all receivers to the final waveguide.

(70) The number of the receivers is made power-of-two, so that the jointers for making the reception signals of the two receivers incident are used, and the optical path lengths from each receiver to the final waveguide can be made equal to each other. By making the optical path lengths equal to each other, loss due to phase displacement of the reception signals at each jointer can be reduced.

(71) FIG. 6 shows constitution examples of receivers of receiver array and a waveguide according to the present invention. FIGS. 6A, 6B, 6C show constitution examples that the power-of-two number of receivers are used.

(72) FIG. 6A shows the example that the light receiver array is constituted using two (=2.sup.1) receivers 11a, 11b. In this constitution example, one emission waveguide 13a is connected to a waveguide end of the receiver 11a, the other emission waveguide 13a is connected to the waveguide end of the receiver 11b, the phase adjuster 15a is provided, and the reception signals of the two emission waveguides 13a are jointed to the jointer 14a and multiplexed.

(73) In the constitution example shown in FIG. 5, the light receiver array is constituted using four (=2.sup.2) receivers 11a-11d.

(74) FIG. 6B shows the example that the light receiver array is constituted using eight (=2.sup.3) receivers 11a-11h. In this constitution example, the receiver 11a and the receiver 11b adjacent to each other in an alignment direction are paired, the reception signal of the emission waveguide 13a is jointed to the reception signal of the first jointer 14a, the receiver 11c and the receiver 11d are paired to joint the reception signals, and the connection waveguide 13b is jointed to the second jointer 14b. Also, regarding the receivers 11e-11h, the connection waveguide 13b is jointed to the second jointer 14b in the similar constitution, and the two connection waveguides 13c are jointed to the second jointer 14c, so as to output the output signals from the final waveguide 13z.

(75) FIG. 6C shows the example that the light receiver array is constituted using sixteen (=2.sup.4) receivers 11a-11p. In this constitution example, as is similar to the constitution example of FIG. 6B, two receivers adjacent to each other in the alignment direction are paired, the emission waveguide 13a and the connection waveguides 13b, 13c are jointed to the first jointer 14a and the second jointers 14b, 14c, and the connection waveguide 13d is jointed to the second jointer 14d, so as to output the output signals from the final waveguide 13z.

(76) The number of the receivers 11 is made power-of-two and the jointers are arranged between the receivers adjacent to each other in the alignment direction or the emission waveguide and the connection waveguide, so that it is easy to form a path of a waveguide for making optical path lengths in a corresponding zone from each receiver to the final waveguide equal to each other, so as to restrain phase displacement at the jointer and loss due to the phase displacement.

(77) FIG. 6D shows a constitution example of a waveguide when the number of receivers is not power-of-two. In the constitution example shown here, regarding a set of three receivers (11a-11c, 11d-11f) continued in the alignment direction, emission waveguides 13a1, 13a2, 13a3 are jointed to the first jointer 14a, and the two connection waveguides 13b are jointed to the second jointer 14b, so as to output the output signals from the final waveguide 13z.

(78) In this constitution, a 3×1 (3 inputs/1 output) jointer is used as the first jointer 14a, to respectively multiplex the reception signals of the three receivers 11a-11c and the reception signals of the three receivers 11d-11f. Here, when the first jointer 14a is arranged at a center position of the linear arrangement of the three receivers 11a-11c, the optical path length of the emission waveguide 13a2 becomes different from those of the emission waveguides 13a1, 13a3, so that the optical path lengths are made equal to each other by adjusting the optical path length of the emission waveguide 13a2.

(79) (Alignment Pitch P)

(80) A phase of the reception light emitted from a slow light waveguide end for reception of each receiver is different depending on an alignment pitch p of the receivers and an arrival angle Δθt of arriving reflected light, and it not always equal.

(81) FIGS. 7A-7D show conditions that arriving reflected lights arrive at each slow light waveguide for reception at a similar angle, in a light receiver array in which respective reception waveguides are aligned at the same alignment pitch p.

(82) FIG. 7A shows when the reflected light arrives from a plane vertical direction. In this case, the phases of the reception lights at the waveguide ends of the receivers are equal to each other for all waveguides.

(83) FIG. 7B shows when the incident angle of the reflected light varies and arrives displaced from the plane vertical direction by an angle Δθ. When the incident angle of the reflected light varies, if the phase of the light from a certain slow light waveguide for reception is (+), the phase of the light from the other slow light waveguide for reception might be (−). In this manner, the reception lights with the opposite phases are multiplexed, interference for offsetting the signal strengths occurs. In the worst case, the signal strength of the received outputs finally multiplexed becomes zero.

(84) FIG. 7C shows a state that the arrival angle of the reflected light becomes larger. In this state, such a condition that the phase of the reception light at the waveguide end of the receiver is displaced by one wavelength and aligned again is generated. Under such a state, interference for increasing the light outputs finally multiplexed occurs again. Depending on an angle, such a state is repeated. When an object is measured by a LiDAR device only at such an angle that the multiplexed light outputs are increased by each other, such a problem is solved that the signal strength is attenuated by offsetting the signal strengths with the opposite phases.

(85) FIG. 7D shows a relationship between strength of light signals obtained by multiplexing reception light of a slow light waveguide for reception of each receiver and an arrival angle Δθ of reflected light. The strength of the light signals varies depending on the above-mentioned interference according to the arrival angle Δθ, with Δθr as a cycle.

(86) FIG. 8A shows a relationship between an angle Δθ.sub.r at which interference for increase occurs and alignment pitches p, t of the receivers. When wavelength of the reflected light is λ, the condition for increasing the light signals of the reception light is expressed by the following formula (1) and the alignment pitch p is expressed by a formula (2).
p.Math.sin Δθ.sub.r=λ  (1)
p=λ/sin Δθ.sub.r  (2)

(87) Meanwhile, the beam of radiation light emitted from the transmitter depends on waveguide length and propagation loss of the transmitter, and a widening angle Δθ.sub.t of the beam of the radiation light is determined based on the parameters. For example, when the propagation light is uniformly leaked to form beam using wavelength λ=1.55 μm and the length of the transmitter of 3 mm, the widening angle Δθ.sub.t is about 0.03°. However, actually, the waveguide has the structural fluctuation, so that it is considered that Δθ.sub.t becomes larger. In a scanning operation of the LiDAR device, light beam of the radiation light is sequentially collided to a far object, and a distance is measured using the reflected light reflected and returned by the object.

(88) FIGS. 8B and 8C are diagrams for explaining an angle difference between adjacent radiation lights in a scanning operation. FIG. 8B shows when the angle difference Δθ between the adjacent radiation lights is larger than the beam widening angle Δθt. In this case, a gap is generated between regions in which the adjacent radiation lights are emitted, and leakage is generated in the scanning region. Meanwhile, FIG. 8C shows when the angle difference Δθ between the adjacent radiation lights is equal to the beam widening angle Δθt. In this case, a gap is not generated between regions in which the adjacent radiation lights are emitted, and scanning can be performed without leakage.

(89) Accordingly, in view of the beam widening angle Δθt, it is suitable to set an angle difference between light beam of a certain radiation angle and light beam of the next radiation angle to the beam widening angle Δθt.

(90) Furthermore, the angle difference Δθ is made equal to the arrival angle Δθr of reflected light that is an angle at which reception strength becomes large, so that conditions (Δθt=Δθr) for satisfying both of

(91) a condition of the angle difference Δθ=the beam widening angle Δθt that is a suitable condition of the scanning angle by the radiation light, and

(92) a condition of the angle difference Δθ=the arrival angle Δθr of the reflected light that is a suitable condition of the strength of the reception signal of the receiver can be obtained. At that time, the alignment pitch p is expressed by a formula (3).
p=λ/sin Δθ.sub.t  (3)

(93) FIGS. 8D-8F chronologically and schematically show radiation light and reflected light when the angle different Δθ of the radiation light sequentially emitted is made equal to the beam widening angle Δθt of the radiation light and the arrival angle Δθr of the reflected light.

(94) In the above-mentioned formula (3), when it is supposed as Δθt=0.03°, the alignment pitch p=2.96 mm is satisfied, so that, for example, a receiver array can be constituted by dividing a slow light waveguide for reception of a receiver with total extension of 2.4 cm into eight.

(95) In the constitution of eight receivers obtained by dividing the receiver into eight, the length of each receiver becomes large, and an effect for reducing loss might be limited. In this case, a resolution point is reduced, however, by setting Δθ.sub.t larger to reduce the alignment pitch p, so that the number of receivers is increased to increase the signal strength.

(96) For example, in the case of Δθ.sub.t=0.05° in an actually manufactured slow light waveguide, the alignment pitch p=1.78 mm is satisfied, a receiver array can be constituted with sixteen receivers obtained by dividing a receiver with total extension of 2.8 cm into sixteen. In this constitution, as described above, 5 times larger signal strength can be obtained.

(97) In the constitution in that the division number is made large and the number of the receivers is made large, the phase displacement is restrained using a phase adjuster. For example, when a phase change π is given to a waveguide for emitting reception signals at a (−) phase under a state of FIG. 7B by the phase adjuster, all phases can be made equal to each other. Thereby, the division number can be made twice, and the reception signals can be increased even when the propagation loss of a light polarizer is larger than 10 dB/cm.

(98) (Brief Explanation of LiDAR Device)

(99) Then, the schematic constitution of a LiDAR device according to the present invention will be explained with reference to FIG. 9.

(100) A LiDAR device 50 includes a light receiver array 10 and a transmitter 21 according to the present invention, and emits radiation light A to an object 60 from the transmitter 21 and detects reflected light B reflected and returned by the object 60. By receiving the reflected light B while changing a radiation angle of the radiation light A, the object 60 is scanned to find a distance from the object 60. Also, relative speed of the LiDAR device 50 and the object 60 can be found.

(101) The LiDAR device 50 includes a transmitter 21 and a light receiver array 10 linearly aligned in a vertical direction, and a collimate lens (cylindrical lens 30) arranged above them.

(102) Signal light in incident on the transmitter 21. The signal light incident on the transmitter 21 propagates a waveguide core of a photonic crystal waveguide by slow light. The slow light is leaked to outside while propagating the waveguide core, and emits the radiation light A toward the object 60. The radiation light A is reflected by the object 60. Each receiver 11 (not shown) of the light receiver array 10 receives the reflected light B, and emits detection light from a waveguide end of the waveguide core.

(103) A deflection angle of the transmitter 21 and each receiver of the light receiver array 10 can be changed by wavelength of the incident light or refractive index of the photonic crystal waveguide. A refractive index varying apparatus 56 for making the refractive index of the photonic crystal waveguide variable can be constituted, for example, by a device for making temperature of the photonic crystal waveguide constituting the transmitter 21 and the receiver 11 variable.

(104) The signal light incident on the transmitter 21 uses one light obtained by separating, by a separator 52, a frequency chirp light signal having a frequency that sequentially changes. The light may be amplified by a semiconductor amplifier (SOA) 53. The other light separated by the separator 52 is guided to a mixer 54 as reference light.

(105) A frequency modulator linearly modulates a frequency of laser light generated by a laser source 57 in a constant cycle T, so as to generate the frequency chirp light signal. The signal light and the reference light have the same frequency and phase, because they are obtained by separating the frequency chirp light signal.

(106) The detection light obtained by the light receiver array 10 together with the reference light is guided to the mixer 54, so as to generate beat signals obtained by mixing the reference light and the detection light.

(107) The signal light is delayed by reciprocation of the radiation light A and the reflected light B among the transmitter 21, the light receiver array 10 and the object 60. During that time, the frequency of the reference light is gradually changed by the frequency chirp. In the mixer 54, the signal light received after reciprocation of the light is mixed with the reference light, so as to detect the mixed light. The beat signals corresponding to a frequency difference between the signal light and the detection light are detected by the mixed light. The mixer 54, for example, detects the beat signals with a frequency difference corresponding to a delay time between the detection light and the reference light using a balance type photodiode 54a.

(108) A calculation part 55 finds a distance from the object 60 based on a frequency spectrum of the beat signals obtained by the mixer 54. The calculation part 55 can be constituted, for example, by an A/D converter for A/D converting output signals of the balance type photodiode 54a, and a processor for calculation-processing resultant digital signals.

(109) When a beat frequency of the beat signal is fb, frequency displacement width of the signal light is B, light speed is c, and one modulation cycle required for modulating one cycle of the chirp light signal is T, a distance R from a target is expressed by a following formula (4).
R=(c×fb×T)/(2×B)  (4)

(110) When the relative speed to the object is obtained by the LiDAR device according to the present invention, a relative speed v is expressed by a following formula (5) using a beat frequency fu obtained using up-chirp light signal for increasing a frequency and a beat frequency fd obtained using down-chirp light signal for decreasing a frequency. Also, fo is a center frequency of the chirp light signal.
v=(c/4fo)×(fu−fd)  (5)

(111) In a LiDAR device using a slow light waveguide light polarizer as a transmitter and a receiver, even when there is real loss in a waveguide, strength of reception signals can be improved by making the waveguide length long and increasing a reception area.

(112) As a result, a distance of an object that can be detected by the LiDAR device can be extended. Also, reflection signals can be detected in a shorter time at a higher S/N, so that a three-dimensional image of the object detected by the LiDAR device can be acquired in a shorter time and a frame rate can be improved.

(113) Also, the present invention is not limited to the above-mentioned embodiments. Various changes can be made within the gist of the present invention, and shall not be excluded from the scope of the present invention.

INDUSTRIAL APPLICABILITY

(114) A light deflection device according to the present invention can be mounted to an automobile, a drone, a robot and the like, and can be applied to a 3D scanner that is mounted in a personal computer and a smart phone to handily take peripheral environments, a monitoring system, a space matrix optical switch for optical conversion or a data center, and the like. Also, by applying to a visible optical material as a high refractive index member constituting the light deflection device, it is expected to be applied to a projector, a laser display, a retina display, a 2D/3D printer, a POS, a card reader and the like.

(115) The present application claims the priority of Japanese Patent Application No. 2017-106710 filed on May 30, 2017, and disclosure thereof are entirely incorporated herein.

REFERENCE SIGNS LIST

(116) 10 light receiver array 11, 11a-11h receivers 12 slow light waveguide for reception 13 low loss light waveguide 13a emission waveguide 13a1 emission waveguide 13a2 emission waveguide 13b, 13c, 13d connection waveguide 13z final waveguide 14, 14a, 14b, 14c jointer 15, 15a, 15b phase adjuster 21 transmitter 22 slow light waveguide for transmission 30 cylindrical lens 50 LiDAR device 52 separator 54 mixer 54a balance type photodiode 55 calculation part 56 refractive index varying apparatus 57 laser source 60 object 101 light deflection device 102 photonic crystal waveguide 103 grating array 104 cylindrical lens 105 high refractive index member 106 low refractive index portion (circular hole) 107 waveguide core 108 clad 111 receiver 112 slow light waveguide for reception 121 transmitter 122 slow light waveguide for transmission