JP2017187649A - Optical phased array and optical antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical phased array and an optical antenna in which variation in a deflection angle against change in environment is suppressed and the deflection angle linearly varies stably.SOLUTION: An optical phased array includes: a distribution unit 56 for inputting output light from a laser source from an input port as input light Pin and distributing it into plural to output from a plurality of output ports; a phase modulation unit 54 having a plurality of optical waveguides 64 that are connected with each of the plurality of output ports and extended in a prescribed direction, and a plurality of heating elements 66 that give heat to each of the plurality of optical waveguides 64 to modulate each phase of input light Pin transmitting along the plurality of optical waveguides 64; and a diffraction grating array 52 that includes a plurality of diffraction gratings correspondingly arranged in each of the plurality of optical waveguides 64 and radiates the input light Pin whose phase is modulated as radiation light Pout.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical phased array and an optical antenna.

  An optical phased array is a device that deflects light and is a key device that constitutes an optical antenna. As one form of the optical phased array, an optical phased array as disclosed in Non-Patent Document 1 in which a phase modulator and a diffraction grating are combined is known. The optical phased array disclosed in Non-Patent Document 1 is configured such that the deflection angle can be changed by modulating the phase of light input to each of the diffraction gratings arranged in an array.

Large-scale nanophotonic phased array, Nature, Vol.1943, p195-199, 2013

  In an optical phased array, particularly an optical phased array used for a laser radar or the like of a moving body (automobile or the like), it is important that the deflection angle changes stably and linearly with respect to environmental changes such as ambient temperature. In this regard, in the optical phased array disclosed in Non-Patent Document 1, no measures are taken against the components of the optical phased array, particularly the phase modulator having a large temperature dependence, so that the modulation phase changes when the ambient temperature changes. It will change. Therefore, there is a problem that the deflection angle of the optical phased array changes depending on changes in temperature or the like.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical phased array and an optical antenna in which fluctuation of the deflection angle with respect to environmental changes is suppressed, and the deflection angle changes stably and linearly. And

  In order to achieve the above object, an optical phased array according to claim 1 is provided with a distribution unit that inputs output light from a laser light source as input light from an input end and distributes the output light to a plurality of output ends from a plurality of output ends. A plurality of optical waveguides connected to each of the plurality of output ends and extended in a predetermined direction; and a plurality of heating elements for applying heat to each of the plurality of optical waveguides. A phase modulator that modulates the phase of each of the input light propagating through the light source, and a plurality of diffraction gratings arranged corresponding to each of the plurality of optical waveguides, and emitting the input light whose phase is modulated And a diffraction grating array that radiates as:

  According to a second aspect of the invention, in the first aspect of the invention, each of the plurality of heating elements generates heat proportional to the arrangement order of the plurality of optical waveguides.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein each of the plurality of heating elements has a length in the predetermined direction in an arrangement order of the plurality of optical waveguides. Proportionally and provided with individual electrodes provided in the vicinity of each of the plurality of optical waveguides, the phase modulation section is connected to an electrode region in which the plurality of individual electrodes are connected in series to each other, and to both ends of the electrode region And an electrode pair to which power is applied.

  The invention according to claim 4 is the invention according to claim 1 or 2, wherein each of the plurality of heating elements has a length in the predetermined direction in an arrangement order of the plurality of optical waveguides. Inversely proportional and provided with individual electrodes provided in the vicinity of each of the plurality of optical waveguides, the phase modulation unit is an electrode in which sides of the plurality of individual electrodes in a direction intersecting the predetermined direction are connected to each other And an electrode pair connected to both ends of the electrode region and to which power is applied.

  According to a fifth aspect of the invention, in the invention of the fourth aspect, the electrode region has one end connected at the same position and the other end having a length inversely proportional to the arrangement order of the plurality of optical waveguides. A plurality of the individual electrodes are connected so as to draw a curved line.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the laser light source is a wavelength variable light source.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the laser light source is configured such that one end surface is a first reflecting surface and light is emitted from the other end surface. And an optical filter connected to the optical amplifier, and an outcoupler connected to the optical filter and having an open end that functions as a second reflective surface, the first reflective surface and the A narrow-line-wavelength light source configured to output a light having a wavelength selected by the Fabry-Perot resonator and the optical filter as the output light from the out-coupler. It is.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein a part of the emitted light is received as reference light and the reference light on the light receiving surface is received. A light receiving unit that outputs a position signal for detecting a position, a detection unit that compares the position signal with a target position of the reference light to generate an error signal, and the plurality of heating elements based on the error signal And a drive unit that generates a control signal for controlling the amount of heat generated.

  The invention according to claim 9 is the invention according to claim 8, wherein each of the plurality of optical waveguides includes a core for guiding light and a clad covering the core, and each of the plurality of diffraction gratings. Includes a divided core region obtained by dividing the core into a plurality of portions, and the reference light is emitted in a direction opposite to the direction in which the emitted light is emitted in the divided core region.

  The invention according to claim 10 is the invention according to claim 9, wherein each of the plurality of diffraction gratings includes an adjustment unit that adjusts a ratio between the amount of the emitted light and the amount of the reference light. It is provided inside the cladding along the split core region.

  The invention according to claim 11 is the invention according to claim 9 or 10, wherein each of the plurality of diffraction gratings reflects the reference light between the divided core region and the light receiving unit. The reflection part to be made is provided.

  In order to achieve the above object, an optical antenna according to claim 12 includes a plurality of optical phased arrays according to any one of claims 1 to 7 and a plurality of the optical phased arrays arranged in an array. A plurality of second optical waveguides connected to the input ends of each of the optical phased arrays; and a plurality of second heating elements for applying heat to each of the plurality of second optical waveguides; A plurality of Y branches connected to a second input terminal for bundling the plurality of second optical waveguides and inputting output light from the laser light source; and a second phase modulation unit that modulates each phase of light propagating through the waveguide And.

  According to a thirteenth aspect of the invention, in the invention of the twelfth aspect, a position signal for receiving a part of the radiated light as a reference light and detecting a position of the reference light on a light receiving surface is provided. A light receiving unit that outputs, a detection unit that generates an error signal by comparing the position signal and a target position of the reference light, and a control signal that controls the amount of heat generated by the plurality of heating elements based on the error signal And a drive unit that generates

  According to the present invention, it is possible to provide an optical phased array and an optical antenna in which fluctuation of the deflection angle with respect to environmental changes is suppressed, and the deflection angle is stably and linearly changed.

It is a top view which shows an example of a structure of the optical phased array which concerns on 1st Embodiment. It is a figure explaining the electrode structure of the phase modulation part in the optical phased array which concerns on 1st Embodiment. It is a figure explaining the change of the direction of the wave front of output light by the phase change of the input light of the optical phased array which concerns on 1st Embodiment. It is a figure explaining the change of the direction of the output light in the optical phased array which concerns on 1st Embodiment. It is a top view which shows an example of a structure of the optical phased array which concerns on 2nd Embodiment. It is a figure explaining the electrode structure of the phase modulation part in the optical phased array which concerns on 2nd Embodiment. It is a figure which shows an example of a structure of the two-dimensional optical phased array which concerns on 3rd Embodiment. It is a top view which shows an example of a structure of the optical antenna which concerns on 4th Embodiment. It is a block diagram which shows an example of a structure of the optical phased array which concerns on 5th Embodiment. It is sectional drawing which shows an example of a structure of the diffraction grating which comprises the optical phased array which concerns on embodiment. It is sectional drawing which shows an example of a structure of the diffraction grating which comprises the optical phased array which concerns on embodiment. It is a figure explaining the direction of the projection light of the diffraction grating which comprises the optical phased array which concerns on embodiment, and a reference light. It is a figure explaining the relationship between the phase control in the phase modulation part of the optical phased array which concerns on 5th Embodiment, and the direction of the wave front of output light. It is a figure explaining the direction of the projection light of the laser radar using the optical phased array which concerns on 5th Embodiment. It is a block diagram which shows an example of a structure of the optical antenna which concerns on 6th Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, an optical module that uses a single diffraction grating array to control the wavefront direction of output light in a one-dimensional manner is referred to as an “optical phased array”, and a plurality of optical phased arrays arranged in a planar shape. An optical module that uses an array to two-dimensionally control the direction of the wavefront of output light is referred to as an “optical antenna”.

[First Embodiment]
With reference to FIG. 1 thru | or FIG. 4, the optical phased array which concerns on this Embodiment is demonstrated. As shown in FIG. 1, an optical phased array 50 according to the present embodiment includes a diffraction grating array 52, a phase modulator 54, an MMI (Multimode Interference) coupler 56, and an input waveguide 58. It consists of

  The input light Pin input from the waveguide 58 is branched into a plurality (in FIG. 1 exemplifies eight cases) by the MMI coupler 56 (distribution section), and each of the branched lights is a phase modulation section. At 54, phase modulation is performed. The input light Pin phase-modulated by the phase modulator 54 is input to the diffraction grating array 52 via the eight output waveguides 64-1 to 64-8.

  The phase modulation unit 54 includes eight waveguides 64-1 to 64-8 and an electrode unit 60. The electrode section 60 includes pads 62-1 and 62-2 (electrode pairs), lead wires 61-1 and 61-2 connected to the pads 62-1 and 62-2, and lead wires 61-1 and 61-, respectively. 2, individual electrodes 66-1 to 66-8 (heating elements) connected by wiring. The individual electrodes 66-1 to 66-8 according to the present embodiment are connected in series as shown in FIG. The individual electrodes connected in series are referred to as “electrode regions”.

  The phase modulation unit 54 according to the present embodiment is a phase modulator that uses a thermo-optic effect in which the refractive index changes when the temperature of the substance is raised. That is, individual electrodes 66-1 to 66-8 (hereinafter, collectively referred to as “individual electrodes 66”) functioning as heaters are disposed on the respective upper portions of the waveguides 64-1 to 64-8. A power source is connected between the pads 62-1 and 62-2, and current is passed through the individual electrodes 66-1 to 66-8 to generate heat, thereby heating the waveguides 64-1 to 64-8. The refractive index of the waveguides 64-1 to 64-8 is changed by the heat applied from the individual electrodes 66-1 to 66-8, and the input light Pin transmitted through each of the waveguides 64-1 to 64-8. The phase of is changed.

  The diffraction grating array 52 includes a diffraction grating provided corresponding to each of the waveguides 64-1 to 64-8, and outputs eight input light Pins whose phases are changed by the phase modulation unit 54 to the outside. (Radiated light) Radiated as Pout. Details of the diffraction grating array 52 will be described later.

With reference to FIG. 2, the individual electrodes 66-1 to 66-8 of the electrode unit 60 according to the present embodiment will be described in more detail. The resistance values Ri (i = 1 to 8) of the individual electrodes 66-1 to 66-8 are set as follows. That is, the length of each of the individual electrodes 66-1 to 66-8 is L1 to L8, and the respective resistance values are R1 to R8. In the present embodiment, the length Li is set so as to be proportional to i (that is, the individual electrodes 66 are sequentially lengthened according to the arrangement order of the waveguides). That is, when the proportionality constant is a, Li is expressed by the following (formula 1).

At this time, the resistance values Ri (i = 1 to 8) of the individual electrodes 66-1 to 66-8 (i = 1 to 8) are expressed by the following (formula 2).

However, (rho) is the resistivity of the material (for example, gold | metal | money, aluminum, etc.) which forms the individual electrode 66, S is the cross-sectional area of the YZ plane direction of the individual electrode 66. In the present embodiment, since the thickness of the individual electrode 66 in the Z direction is constant, S is a constant.

Since the currents flowing through the individual electrodes 66-1 to 66-8 are the same, this is assumed to be I (constant), and the amount of heat generated in each of the individual electrodes 66-1 to 66-8 is Pi (i = 1 to 8). The calorific value Pi is expressed by the following (formula 3).

That is, since the heat generation amount Pi is proportional to the position i (= 1 to 8) of the individual electrode 66, the heat generation amount Pi also increases in proportion to the position of the individual electrode 66. Therefore, Pi = c1 · i (c1 is a proportional constant) is set.

  A phase change amount between the phase of the input light Pin and the predetermined reference phase in each of the waveguides 64-1 to 64-8 in which the individual electrodes 66-1 to 66-8 are arranged is represented by Δφ1 to Δφ8 (hereinafter collectively referred to as “general name”). (Phase change amount Δφ)), the phase change amounts Δφ1 to Δφ8 are proportional to the heat generation amount Pi, and can be expressed as Δφi = c2 · Pi (i = 1 to 8, where c2 is a proportional constant). Substituting the above equation Pi = c1 · i and expressing it as Δφi = c1 · c2 · i, it can be seen that the phase change amount Δφi is proportional to the position i.

  That is, according to the optical phased array 50 according to the present embodiment, in the phase modulation unit 54 having a plurality of outputs, the phase change amount Δφ proportional to each position of the plurality of outputs can be easily obtained.

  Next, the relationship between the phase change amount Δφ in the optical phased array 50 and the direction of the output light Pout will be described with reference to FIG. FIG. 3A is a diagram showing the relationship between the phase change amounts Δφa1 to Δφa8 caused by the individual electrodes 66 when the current I is large and the propagation direction of the output light Pout, and FIG. It is a figure which shows the relationship between phase change amount (DELTA) phib1- (DELTA) phib8 by the individual electrode 66, and the direction of the wave front of output light Pout in the case.

  As shown in FIG. 3A, when the current I is constant at a predetermined value, the phase change amount Δφ is proportional to the position i as described above, and thus is emitted from each of the waveguides 64-1 to 64-8. The phase of the emitted light changes linearly (linearly). For this reason, the wavefronts of the light emitted from each of the waveguides 64-1 to 64-8 having the same phase are straight lines and are sequentially emitted as wavefronts Wa1, Wa2, and Wa3. The traveling direction of this wavefront is the propagation direction Da of the output light Pout.

  Next, when the current I is reduced from a predetermined value, as shown in FIG. 3B, the wavefronts connecting the same phases of the light emitted from each of the waveguides 64-1 to 64-8 are represented by wavefronts Wb1, Wb2 and Wb3 are sequentially emitted, and the traveling direction of the wavefront becomes the propagation direction Db of the output light Pout. Since the phase change amount Δφ is proportional to the square of the current I, the inclinations measured from the horizontal direction of the wavefronts Wb1, Wb2, and Wb3 are steeper than the inclinations of the wavefronts Wa1, Wa2, and Wa3, and the inclination of the propagation direction Db is It becomes gentler than the inclination of the propagation direction Da.

  That is, according to the optical phased array according to the present embodiment, the phase modulation unit 54 having a plurality of outputs can easily obtain the phase change amount Δφ proportional to each position of the plurality of outputs. It is possible to change the propagation direction of the output light Pout easily by changing the value of the phase change amount Δφ according to the current to flow.

  Next, the sweeping of the output light Pout in the optical phased array 50 will be described with reference to FIG. 4A is a plan view of the optical phased array 50, FIG. 4B is a side view of the optical phased array 50 viewed from the X direction, and FIG. 4C is a view viewed from the Y direction. Side views of the optical phased array 50 are shown.

  FIG. 4B shows a change in the propagation direction of the output light Pout due to the above-described phase change amount Δφ. As shown in FIG. 4B, when the phase change amount Δφ is changed by the current I, the propagation direction Dy of the output light Pout changes within the angle range Sy in the Y-axis direction. That is, it can be seen that the propagation direction of the output light Pout can be swept in the Y-axis direction by the current I flowing through the electrode portion 60.

  On the other hand, FIG. 4C shows a change in the propagation direction of the output light Pout when the wavelength of the input light Pin is changed. As shown in FIG. 4C, when the wavelength of the input light Pin is changed, the propagation direction Dx of the output light Pout changes within the angle range Sx in the X-axis direction. That is, it can be seen that the propagation direction of the output light Pout can be swept in the X-axis direction depending on the wavelength of the input light Pin.

  As described above in detail, according to the optical phased array according to the present embodiment, since the phase modulation unit in which the individual electrodes for changing the phase change amount individually and linearly are used, the deflection with respect to the environmental change is performed. It is possible to provide an optical phased array in which the variation of the angle is suppressed and the deflection angle is stably and linearly changed.

[Second Embodiment]
The optical phased array 80 according to the present embodiment will be described with reference to FIGS. The optical phased array 80 has a configuration in which the shape of the electrode of the phase modulation unit 54 in the optical phased array 50 is changed. Therefore, since the configuration other than the phase modulation unit is the same as that of the optical phased array 50, the same components are denoted by the same reference numerals and detailed description thereof is omitted.

  As shown in FIG. 5, the optical phased array 80 according to the present embodiment includes a diffraction grating array 52, a phase modulator 90, an MMI coupler 56, and an input waveguide 58. The phase modulation unit 90 includes eight waveguides 64-1 to 64-8 and an electrode unit 92. The electrode portion 92 includes pads 82-1 and 82-2, lead wires 84-1 and 84-2 connected to the pads 82-1 and 82-2, and lead wires 84-1 and 84-2. And individual electrodes 86-1 to 86-8 (hereinafter collectively referred to as “individual electrodes 86”) connected to each other by wiring. The individual electrodes 86-1 to 86-8 according to the present embodiment are connected to each other in the Y direction. The individual electrodes 86-1 to 86-8 to which the sides in the Y direction are connected are referred to as “electrode regions”.

  With reference to FIG. 6, the electrode part 92 which concerns on this Embodiment is demonstrated in detail. Each drawing of FIG. 6 is a diagram in which an individual electrode 86 portion is extracted from the electrode portion 92. In the electrode portion 92, a power source is connected between the pads 82-1 and 82-2, and a current I is passed in the direction shown in FIG.

Next, the relationship between the current I and the positions of the individual electrodes 86-1 to 86-8 will be described. Now, the length of each of the individual electrodes 86-1 to 86-8 is x1 to x8, and the length xi (i = 1 to 8) varies according to the following formula (4) according to the position i. And

However, b is a proportionality constant.

At this time, the resistance values Ri (i = 1 to 8) of the individual electrodes 86-1 to 86-8 are expressed by the following (formula 5).

Here, ρ is the resistivity of the individual electrode 86, d is the length of the individual electrode 86 in the Y direction, and t is the thickness of the individual electrode 86 in the Z direction.

Then, the phase change amount Δφi (i = 1 to 8) corresponding to each of the individual electrodes 86-1 to 86-8 is expressed by the following (formula 6), where α is a proportional constant.

  That is, in the phase modulation unit 90 according to the present embodiment, the phase change amount Δφ is proportional to the position i and proportional to the square of the current. Therefore, also in the optical phased array 80 according to the present embodiment, in the phase modulation unit 90 having a plurality of outputs, the phase change amount Δφ proportional to each position of the plurality of outputs can be easily obtained. It is possible to change the propagation direction of the output light Pout easily by changing the value of the phase change amount Δφ according to the current I flowing.

In the present embodiment, an example in which the shape of the electrode region of the individual electrode 86 is stepped has been described, but the present invention is not limited to this. For example, as shown in FIG. 6C, the electrode region may have a smooth shape such that the length in the X direction is inversely proportional to the position in the -Y direction.
Thus, it is preferable that the electrode region has a smooth shape also from the viewpoint of manufacturing the phase modulation section.

[Third Embodiment]
With reference to FIG. 7, a two-dimensional scanning two-dimensional optical phased array 200 according to the present embodiment will be described. The two-dimensional optical phased array 200 has a form in which a light source is integrated in the optical phased array 50 described above.

  As shown in FIG. 7, the two-dimensional optical phased array 200 includes a light source 250 and an optical phased array 50 connected to the light source 250 via a waveguide 216.

  The light source 250 according to the present embodiment includes an SOA (Semiconductor Optical Amplifier) 202, optical filters 204 and 206, and an out coupler 208. The SOA 202, the optical filters 204 and 206, and the out coupler 208 are included. Are connected by waveguides 210, 212, 214.

  The SOA 202 can change the wavelength by an injection current. Each of the optical filters 204 and 206 is an optical filter using a ring waveguide resonator, and transmits light having a frequency (wavelength) that matches the resonance frequency of the resonator. The out coupler 208 is a coupler having a structure in which two loop mirrors are coupled by a directional coupler, and a portion of the directional coupler has a function of a reflecting surface M2 that reflects incident light. In the present embodiment, the form using two optical filters has been described as an example. However, the present invention is not limited to this. One form may be used, or three or more forms may be used.

  The light source 250 having the above configuration functions as a narrow linewidth wavelength light source. That is, the end surface opposite to the output-side end surface of the SOA 202 is a reflecting surface M1 that reflects light, and the reflecting surface M1 and the reflecting surface M2 constitute a Fabry-Perot resonator. Then, light having a wavelength selected by the Fabry-Perot resonator and the optical filters 204 and 206 is output from the out coupler 208.

  The two-dimensional optical phased array 200 having the above configuration can sweep in the Y direction by changing the current I flowing between the pads 62-1 and 62-2, and changes the wavelength of the SOA 202. As a result, sweeping in the X direction is possible.

[Fourth Embodiment]
With reference to FIG. 8, an optical antenna 300 according to the present embodiment will be described. The optical antenna 300 is an optical antenna configured by using a plurality of the optical phased arrays 50 described above.

  As shown in FIG. 8, the optical antenna 300 includes optical phased arrays 50-1, 50-2, 50-3, 50-4 in which four optical phased arrays 50 are arranged, and Y branches 302-1 and 302-2. , 302-3 and the electrode part 330. In this embodiment, an example using four optical phased arrays 50 will be described as an example. However, the number of optical phased arrays 50 is not limited to four, and is necessary depending on the design conditions of the optical antenna 300 and the like. It is possible to adopt a form using as many as possible.

  The input light Pin input from one end of the waveguide 310 is branched into two by the Y branch 302-1, and propagates to the waveguides 312, 314, respectively. One of the two-branched input light Pin is further branched into two by the Y-branch 302-2 and propagates to the waveguides 316 and 318, respectively, and the other of the two-branched input light Pin is further divided into two by the Y-branch 302-3. It is branched and propagates to the waveguides 320 and 322, respectively.

  The electrode section 330 is provided between the pads 304-1 and 304-2, the lead wires 306-1 and 306-2 connected to the pads 304-1 and 304-2, and the lead wires 306-1 and 306-2, respectively. Are provided with individual electrodes 308-1, 308-2, 308-3, and 308-4 connected by wiring.

  The individual electrodes 308-1, 308-2, 308-3, and 308-4 are disposed above the waveguides 316, 318, 320, and 322, respectively. Then, by causing a current to flow between the pads 304-1 and 304-2, the individual electrodes 308-1, 308-2, 308-3, and 308-4 generate heat, and the waveguides 316, 318, 320, The phase change amount Δφ of 322 can be changed. That is, the region where the individual electrodes 308-1, 308-2, 308-3, and 308-4 are arranged constitutes the second phase modulator.

  As described above, in the optical phased arrays 50-1, 50-2, 50-3, and 50-4, the input light Pin is swept in the X direction by the current Ix that flows through the phase modulator 54 (see FIG. 1). Is possible. Therefore, the wavefronts of the output lights Pout1, Pout2, Pout3, and Pout4 are fixed with the same current value flowing through the phase modulators 54 of the optical phased arrays 50-1, 50-2, 50-3, and 50-4. When the current Iy flowing through the electrode unit 330 is changed, the wavefronts of the output lights Pout1, Pout2, Pout3, and Pout4 are swept in the Y direction.

  In the optical antenna 300 according to the present embodiment, the wavefront of the output light Pout1, Pout2, Pout3, Pout4 is two-dimensionally scanned by combining the sweep in the Y direction by the current Iy and the sweep in the X direction by the current Ix ( Scanning).

  As described in detail above, according to the optical antenna according to the present embodiment, since the phase modulation unit in which the individual electrodes for changing the phase change amount individually and linearly are used, the deflection angle with respect to the change in the environment is used. Thus, it is possible to provide an optical antenna in which the fluctuation of the angle is suppressed and the deflection angle is stably and linearly changed.

[Fifth Embodiment]
The optical phased array according to the present embodiment will be described with reference to FIGS. The optical phased array 10 according to the present embodiment is a mode in which a part of output light is monitored by a sensor and negatively fed back to the phase modulation unit, so that fluctuations in deflection angle due to environmental fluctuations such as temperature can be further suppressed. It is.

  FIG. 9 is a block diagram showing an example of the configuration of the optical phased array 10. As shown in FIG. 9, the optical phased array 10 includes a laser light source 20, an optical integrated circuit 24, and a negative feedback unit 26.

  The laser light source 20 is a generation source for generating output light from the optical phased array 10.

  The optical integrated circuit 24 is an optical waveguide element in which diffraction gratings 120-1 to 120-8 (hereinafter collectively referred to as “diffraction grating 120”) and the phase modulation unit 12 are integrated. Each of the eight diffraction gratings 120 is connected to one end side of the waveguide 30, and the output light of the laser light source 20 is input to the other end side of the waveguide 30. In the optical integrated circuit 24 according to the present embodiment, an example in which the diffraction grating 120 and the phase modulation unit 12 are integrated will be described as an example, but in addition to these, the laser light source 20 and a negative feedback unit to be described later 26 may be integrated.

  The phase modulation unit 12 includes a waveguide 30 connected to each of the diffraction gratings 120 and a heater 28 provided on the top of the waveguide 30. The phase modulation unit 12 heats the eight waveguides 30 by causing the heater 28 to generate heat by a current I flowing from a current driving circuit 18 described later, thereby changing the refractive index.

  As the refractive index of the eight waveguides 30 changes, the phase of the light incident on each of the diffraction gratings 120-1 to 120-8 changes and is output from each of the diffraction gratings 120-1 to 120-8. The direction of light changes. In the optical phased array 10, the direction of the wavefront of the projection light LT output from the optical phased array 10 is changed by changing the direction of the light output from each of the diffraction gratings 120-1 to 120-8. It is comprised so that it can be made to do. That is, since the heat applied to each of the eight waveguides 30 can be controlled by controlling the current I flowing through the heater 28, the direction of the wavefront of the projection light LT can be controlled by the current flowing through the heater 28. it can. In FIG. 9, a single heater 28 is representatively represented to avoid complication, but actually, each of the waveguides 30 is provided with an individual heater.

  As will be described later, the optical phased array 10 according to the present embodiment is configured such that the reference light LR is emitted from a direction (back side) opposite to the direction in which the projection light LT is emitted. The reference light LR is monitor light for generating a negative feedback signal, and forms a light spot on the light receiving surface of a PSD (Position Sensitive Detector). The reference light LR is secondary light to the main light emitted from the diffraction grating 120, as will be described later.

  The negative feedback unit 26 includes a PSD 14 (light receiving unit), a detection circuit 16 (detection unit), and a current drive circuit 18 (drive unit).

  The PSD is an element having two output terminals in which a resistor and a photodiode are combined, and the position of a light spot incident on the PSD can be obtained. That is, when light enters the PSD, carriers are generated at the incident position, and current flows. The current output from the two output terminals changes due to the resistance proportional to the distance from the light incident position to the two output terminals. The position of the center of gravity of the light spot on the sensor can be obtained from the ratio of the currents flowing through the two output terminals.

  In the present embodiment, a PSD having two output terminals is described as an example. However, the present invention is not limited to this. For example, a PSD having four output terminals described later may be used. Further, in the present embodiment, an example in which the position of the light spot is obtained by the PSD 14 will be described. However, the present invention is not limited to this, and any optical element can be used as long as the position can be obtained. Also good.

  As shown in FIG. 9, the detection circuit 16 includes a comparator 160, buffers 162 and 164, and a divider 166.

  The buffers 162 and 164 are circuit elements that buffer the current signals I1 and I2 (position signals) output from the two output terminals of the PSD 14, and the buffers 162 and 164 according to the present embodiment include the current signals I1 and I2, It has a function of converting I2 into voltage signals V1 and V2.

  The divider 166 is a circuit that calculates the current ratio I1 / I2 using the ratio V1 / V2 of the voltage signals V1 and V2.

  The comparator 160 is a circuit that amplifies the difference signal (error signal) between the current ratio I1 / I2 and the reference voltage Vref by inverting the phase, and outputs the amplified signal to the current driving circuit 18. The current ratio I1 / I2 is input, and the reference voltage Vref is input to the non-inverting terminal. The reference voltage Vref is a target value of the current ratio I1 / I2, that is, a target value (target position) of the position of the light spot incident on the PSD 14.

  The current drive circuit 18 (drive unit) outputs a current I that flows through the heater 28 based on the difference signal received from the comparator 160.

  In the optical phased array 10 according to the present embodiment configured as described above, the reference light LR emitted from the back surface is monitored by the PSD 14, and a deviation from the target value of the position on the light receiving surface of the PSD 14 is error-amplified. To generate an error signal. Then, the error signal is converted into a current I by the current driving circuit 18, and the driving current of the phase modulation unit 12 is negatively feedback controlled by the current I, thereby controlling the deflection angle of the projection light LT of the optical phased array 10. doing. Thus, in the optical phased array 10 according to the present embodiment, fluctuations in the deflection angle of the projection light LT due to environmental changes such as ambient temperature are suppressed.

  Next, the diffraction grating 120 according to the present embodiment will be described with reference to FIGS. 10 and 11 are cross-sectional views showing examples of configurations of the diffraction grating 120 of various forms.

  FIG. 10A shows a diffraction grating 120 a which is one form of the diffraction grating 120. As shown in FIG. 10A, the diffraction grating 120a includes a grating part G (divided core region), a core 122, and a clad 124, and is formed on a substrate (not shown).

  The waveguide 122 shown in FIG. 9 is constituted by the core 122 and the clad 124. The light from the laser light source 20 that has propagated through the core 122 is optically coupled to the grating portion G, and is emitted in the + Z direction (surface side) as part of the projection light LT. On the other hand, secondary light is emitted from the grating portion G as the reference light LR in the −Z direction (back side). The reference light LR is condensed as it travels in the optical path direction, and becomes a spot shape when traveling a predetermined distance. As described above, the diffraction grating 120a according to the present embodiment emits the projection light LT from the front surface side, and is a spot-like reference serving as a signal source of the negative feedback signal for the negative feedback control described above from the back surface side. The light LR is emitted.

FIG. 10B shows a diffraction grating 120b which is another form of the diffraction grating. The diffraction grating 120b has a configuration in which the light amount of the reference light LR is decreased and the light amount of the light projection light LT is increased by that amount compared to the diffraction grating 120a. As shown in FIG. 10B, the diffraction grating 120b includes a grating part G, a core 122, a clad 124, and a high refractive index part 126 (adjustment part).

  The refractive index of the high refractive index portion 126 is set larger than that of the clad 124 and smaller than that of the core 122. As described above, by providing the high refractive index portion 126 on the core 122 and the lattice portion G, the ratio of the projection light LT to the reference light LR can be increased. Further, by adjusting the refractive index of the high refractive index portion 126, the ratio of the projection light LT and the reference light LR can be changed.

  FIG. 10C shows a diffraction grating 120c which is another form of the diffraction grating. The diffraction grating 120c is configured to be capable of adjusting the light amounts of the projection light LT and the reference light LR. As shown in FIG. 10C, the diffraction grating 120c includes a grating part G, a core 122, a clad 124, and a reflecting part 128 (adjustment part).

  In the diffraction grating 120c, the distance between the grating part G and the reflecting part 128 is changed, and the phase of the light propagating to the grating part G is adjusted with respect to the reflecting part 128, whereby the light propagating to the grating part G is adjusted. The reflectivity can be changed. Therefore, if the reflectance is increased, the light amount of the projection light LT can be increased, and if the reflectance is decreased, the light amount of the reference light LR can be increased.

  FIG. 11 is a diagram showing a diffraction grating 120d, which is another form of the diffraction grating, together with the PSD 14. In FIG. The diffraction grating 120d has a configuration in which the optical path length of the reference light LR is longer than that of each of the diffraction gratings (diffraction gratings 120a, 120b, 120c). As shown in FIG. 11, the diffraction grating 120 d includes a grating portion G, a core 122, a clad 124, a spacer 130, and a reflective film 134.

  The spacer 130 is formed of a material that is transparent to the input light Pin, and has a function of increasing the optical path length from the grating portion G through which the reference light LR propagates to the PSD 14. A reflective film 134 is formed on one end face of the spacer 130, and the PSD 14 is optically coupled to another end face. The reflective film 134 can be formed by evaporating a metal such as aluminum on the spacer 130, for example.

  In the diffraction grating 120d, the reference light LR that propagates through the core 122 and is radiated to the back surface by the grating portion G is reflected by the reflective film 134, propagates through the spacer 130, and enters the light receiving surface of the PSD 14. Since the diffraction grating 120d is configured to increase the optical path length of the reference light LR, the diffraction grating 120d has a more suitable structure for condensing the reference light LR in a spot shape.

  Next, the direction of the wavefront of the projection light LT in the diffraction grating 120 according to the present embodiment will be described with reference to FIG. In FIG. 12, the diffraction grating 120a is described as an example, but the same concept applies to the diffraction gratings 120b, 120c, and 120d.

  As shown in FIG. 12, a spacer 130 is disposed below a diffraction grating 120 a having a core 122 and a clad 124 formed on a substrate (not shown), and the PSD 14 is optically coupled to the lower portion of the spacer 130.

  As shown in FIG. 12, the angle (deflection angle) in the direction of the projection light LT measured from the normal h passing through the center of the core 122 is θ, and the angle (deflection angle) in the direction of the reference light LR measured from the normal h. ) Is θ ′. In this case, if the phase of the propagation light of the optical phased array 10 is changed by the heater 28, the directions of the wave fronts of the projection light LT and the reference light LR change in the YZ plane in FIG. That is, the deflection angle θ of the projection light LT and the deflection angle θ ′ of the reference light LR change at the same ratio. If the upper and lower structures of the core 122 (lattice part G) are the same, θ≈θ ′, but if they are different, mutual conversion is possible by obtaining mutual conversion coefficients in advance. .

  The reference light LR that has traveled by a predetermined optical path length by the spacer 130 forms a light spot on the light receiving surface of the PSD 14. If the distance from the lower surface of the core 122 to the light receiving surface of the PSD 14 is d, the position of the light spot measured from the intersection O between the normal h and the light receiving surface of the PSD 14 is represented by dsin (θ ′). In this way, the direction of the wavefront of the reference light LR, that is, the direction of the wavefront of the projection light LT can be known from the position of the light spot on the light receiving surface of the PSD 14.

  With reference to FIG. 13, the control of the direction of the wavefront of the projection light LT in the optical phased array 10 will be described in more detail. FIG. 13 illustrates eight waveguides 30 and electrodes 132-1 to 132-8 constituting the heater 28 disposed on each waveguide 30.

  In FIG. 13, the currents flowing through the electrodes 132-1 to 132-8 are made different so that the heat applied to each of the eight waveguides 30 is increased linearly. If the phase plane of the propagation light from the laser light source 20 on the upstream side of the electrodes 132-1 to 132-8 is W0 as shown in FIG. 13, the phase plane of the light emitted from each of the eight waveguides 30 Changes as P1 to P8. The phase planes P1 to P8 are combined to form a wavefront of the projection light LT. As shown in FIG. 13, this wavefront is sequentially propagated to W1, W2, W3, and W4. The propagation direction D of the wavefronts W1 to W4 is the emission direction of the projection light LT. In the optical phased array 10, the propagation direction D of the projection light LT can be changed by changing the current flowing through the electrodes 132-1 to 132-8.

  Next, with reference to FIG. 14, as an example of an application form of the optical phased array 10, a form in the case where the optical phased array 10 is applied to a vehicle-mounted laser radar will be described.

  As shown in FIG. 14A, the laser radar 1 using the optical phased array 10 is installed in front of the vehicle 2, for example. Assuming that the traveling direction of the vehicle is a direction H, the direction of the projection light LT from the laser radar 1 changes at both sides of the direction H with a deflection angle θ. This deflection angle θ is the scanning angle of the laser radar 1, and the deflection angle θ corresponds to the deflection angle θ shown in FIG.

  Here, as shown in FIG. 14B, when the direction H is the origin of the deflection angle θ (θ = 0 °), the deflection angle θ (scanning angle) changes between the maximum value θmax and the minimum value θmin. To do. Specific values of θmax and θmin are, for example, θmax = + 30 ° and θmin = −30 °.

  The scanning angle of the laser radar 1 changes as shown in FIG. 14C with respect to time. In the laser radar 1 according to the present embodiment, since the scanning angle is negatively feedback controlled using the optical phased array 10, it is possible to suppress fluctuations in the scanning angle with respect to environmental changes such as temperature. .

  As described above in detail, according to the optical phased array according to the present embodiment, the phase modulation unit including the individual electrodes that individually and linearly change the phase change amount is provided, and the reference light from the diffraction grating is used. Since the current flowing through the electrode of the phase modulation unit is controlled by negative feedback, it is possible to provide an optical phased array in which the deflection angle variation with respect to environmental changes is further suppressed, and the deflection angle changes more stably and linearly. .

[Sixth Embodiment]
The optical antenna 40 according to the present embodiment will be described with reference to FIG. As shown in FIG. 15A, the optical antenna 40 includes an optical integrated circuit 42, a PSD 14a, a detection circuit 16a, an error amplification circuit 22, and a current driving circuit 18.

  As an example, the optical integrated circuit 42 according to the present embodiment includes a laser light source that generates the input light Pin and an optical antenna 300 shown in FIG.

  The PSD 14a according to the present embodiment is a two-dimensional PSD having four output terminals, and current signals I1, I2, I3, and I4 (position signals) that specify the two-dimensional position of a light spot incident on the PSD 14a. ) From the four output terminals.

  The detection circuit 16a receives the four current signals from the PSD 14a, performs arithmetic processing on the received four current signals I1 to I4, and positional information on the light receiving surface of the PSD 14a (two-dimensional coordinate values X and Y). Is calculated.

  The error amplification circuit 22 receives the coordinate values X and Y from the detection circuit 16a, compares the received coordinate values X and Y with a target value (target position), and generates an error signal e.

  The current drive circuit 18 receives the error signal e from the error amplification circuit 22, and flows it to the electrodes of the heater (the electrode unit 60 (see FIG. 1) and the electrode unit 330 (see FIG. 8)) based on the received error signal e. Generate current.

  With reference to FIG. 15B, the arithmetic processing executed by the detection circuit 16a will be described in more detail. FIG. 15B is a block diagram of the detection circuit 16a together with the PSD 14a. As shown in FIG. 15B, the detection circuit 16a includes four buffers 168 and a calculation unit 170.

  The four buffers 168 buffer each of the current signals I1, I2, I3, and I4 and convert them into coordinate calculation signals UL, UR, LR, and LL, which are voltage signals, respectively.

The calculation unit 170 includes an adder, a divider, and a subtracter as shown in FIG. 15B, and calculates coordinate values X and Y by performing calculation processing on the coordinate calculation signals UL, UR, LR, and LL. The contents of the calculation executed by the calculation unit 170 are as follows. That is, first, ΔX, ΔY, and A are calculated by (Expression 1), (Expression 2), and (Expression 3).
ΔX = (LR + UR) − (LL + UL) (Formula 1)
ΔY = (UL + UR) − (LR + LL) (Formula 2)
A = LR + UR + LL + UL (Formula 3)

Next, coordinate values X and Y are calculated by the following (Expression 4) and (Expression 5).
X = ΔX / A (Formula 4)
Y = ΔY / A (Formula 5)
The coordinate values X and Y calculated by (Equation 4) and (Equation 5) are sent to the error amplification circuit 22 and compared with the target value to generate an error signal e.

  As described above in detail, according to the optical antenna according to the present embodiment, the optical antenna according to the present embodiment includes the phase modulation unit in which the individual electrodes that change the phase change amount individually and linearly are arranged, and the reference light from the diffraction grating. Since negative feedback control is performed on the current flowing through the electrode of the phase modulation unit, it is possible to provide an optical antenna in which fluctuations in the deflection angle with respect to environmental changes are further suppressed, and the deflection angle changes more stably and linearly.

DESCRIPTION OF SYMBOLS 1 Laser radar 2 Vehicle 10 Optical phased array 12, 12a Phase modulation part 14, 14a PSD
16, 16a Detection circuit 18 Current drive circuit 20 Laser light source 22 Error amplification circuit 24 Optical integrated circuit 26 Negative feedback unit 28 Heater 30 Waveguide 40 Optical antenna 42 Optical integrated circuit 50, 50-1 to 50-4 Optical phased array 52 Diffraction Lattice array 54 Phase modulation section 56 MMI coupler 58 Waveguide 60 Electrode sections 61-1, 61-2 Lead wiring 62-1 and 62-2 Pads 64-1 to 64-8 Waveguides 66-1 to 66-8 Individual electrodes 80 Optical phased array 82-1, 82-2 Pad 84-1, 84-2 Lead-out wiring 86-1 to 86-8 Individual electrode 90 Phase modulation part 92 Electrode part 120-1 to 120-8 Diffraction gratings 120a to 120d Diffraction Lattice 122 Core 124 Cladding 126 High refractive index portion 128 Reflecting portion 130 Spacers 132-1 to 132-8 Electrode 134 Reflecting film 160 Comparison 162,164 Buffer 166 divider 168 buffer 170 arithmetic unit 200 the two-dimensional light phased array 202 SOA
204, 206 Optical filter 208 Out coupler 210, 212, 214, 216 Waveguide 250 Light source 300 Optical antenna 302-1, 302-2, 302-3 Y branch 304-1, 304-2 Pad 306-1, 306-2 Lead wirings 308-1, 308-2, 308-3, 308-4 Individual electrodes 310, 312, 314, 316, 318, 320, 322 Waveguide 330 Electrode portion D, Da, Db, Dx, Dy Propagation direction e Error Signal G Lattice part H direction LT Projection light LR Reference light M1, M2 Reflection surface Pin Input light Pout Output light W1-W4, Wa1-Wa3, Wb1-Wb3 Wavefront Sx, Sy Angle range Δφ Phase change amount θ, θ ′ Deflection Corner

Claims (13)

A distribution unit that inputs output light from a laser light source as input light from an input end and distributes the output light to a plurality of outputs from a plurality of output ends; and
A plurality of optical waveguides connected to each of the plurality of output ends and extended in a predetermined direction; and a plurality of heating elements for applying heat to each of the plurality of optical waveguides; A phase modulator for modulating the phase of each of the propagating input light;
A diffraction grating array including a plurality of diffraction gratings arranged corresponding to each of the plurality of optical waveguides and emitting the input light whose phase is modulated as radiation light;
Including optical phased array.   The optical phased array according to claim 1, wherein each of the plurality of heating elements generates heat proportional to an arrangement order of the plurality of optical waveguides. Each of the plurality of heating elements includes an individual electrode provided in the vicinity of each of the plurality of optical waveguides, with the length in the predetermined direction being proportional to the arrangement order of the plurality of optical waveguides,
The phase modulation unit further includes an electrode region in which the plurality of individual electrodes are connected in series to each other, and an electrode pair that is connected to both ends of the electrode region and to which power is applied. The optical phased array described. Each of the plurality of heating elements includes an individual electrode provided in the vicinity of each of the plurality of optical waveguides, with the length in the predetermined direction being inversely proportional to the arrangement order of the plurality of optical waveguides,
The phase modulation unit includes an electrode region in which sides in a direction intersecting the predetermined direction of the plurality of individual electrodes are connected to each other, and an electrode pair connected to both ends of the electrode region and to which power is applied. The optical phased array according to claim 1, further comprising: The electrode region is configured by connecting a plurality of the individual electrodes so that one end is connected at the same position and the other end is drawn in a curve having a length inversely proportional to the arrangement order of the plurality of optical waveguides. Item 5. The optical phased array according to Item 4. The optical phased array according to any one of claims 1 to 5, wherein the laser light source is a variable wavelength light source. The laser light source includes an optical amplifier that has one end surface as a first reflection surface and outputs light from the other end surface, an optical filter connected to the optical amplifier, and a second reflection that is connected to the optical filter. A wavelength selected by the Fabry-Perot resonator and the optical filter, wherein the first reflective surface and the second reflective surface constitute a Fabry-Perot resonator. The optical phased array according to any one of claims 1 to 6, wherein the light is a narrow-line-width wavelength light source that outputs the output light from the outcoupler as the output light. A light receiving unit that receives a part of the radiated light as reference light and outputs a position signal for detecting the position of the reference light on a light receiving surface;
A detection unit that compares the position signal with a target position of the reference light to generate an error signal;
A drive unit that generates a control signal for controlling the amount of heat generated by the plurality of heating elements based on the error signal;
The optical phased array according to any one of claims 1 to 7, further comprising: Each of the plurality of optical waveguides includes a core for guiding light and a clad covering the core,
Each of the plurality of diffraction gratings includes a divided core region obtained by dividing the core into a plurality of parts,
The optical phased array according to claim 8, wherein the reference light is emitted in a direction opposite to a direction in which the emitted light is emitted in the divided core region. 10. The optical phased according to claim 9, wherein each of the plurality of diffraction gratings includes an adjustment unit that adjusts a ratio between the light amount of the radiated light and the light amount of the reference light along the divided core region. array. 11. The optical phased array according to claim 9, wherein each of the plurality of diffraction gratings includes a reflection unit that reflects the reference light between the divided core region and the light receiving unit. A plurality of optical phased arrays according to any one of claims 1 to 7, arranged in an array,
A plurality of second optical waveguides connected to the input ends of each of the plurality of optical phased arrays, and a plurality of second heating elements for applying heat to each of the plurality of second optical waveguides, A second phase modulator for modulating the phase of each of the light propagating through the second optical waveguide;
A plurality of Y branches connected to a second input terminal for bundling the plurality of second optical waveguides and inputting output light from the laser light source;
Including optical antenna. A light receiving unit that receives a part of the radiated light as reference light and outputs a position signal for detecting the position of the reference light on a light receiving surface;
A detection unit that compares the position signal with a target position of the reference light to generate an error signal;
A drive unit that generates a control signal for controlling the amount of heat generated by the plurality of heating elements based on the error signal;
The optical antenna according to claim 12, further comprising: