JP7356918B2 - Small control optical deflector - Google Patents

Description

The present invention relates to an optical deflector that controls the direction of a light beam that is a combination of a plurality of emitted lights, and more particularly to an optical deflector with a small control section.

In recent years, research and development has been progressing on elements that control the direction of light beams (light deflection elements) with the aim of applying them to spatial optical communications, distance sensors, radar, 3D displays, and the like. Among these, optical phased arrays (OPA), whose basic principles are optical phase control and multi-beam interference, can deflect optical beams without mechanical scanning, and can be applied to small and lightweight devices. It is expected that this will be the case (for example, see Patent Document 1).

For example, in a waveguide-type optical phased array, if the radiation ends of each waveguide (hereinafter also referred to as channels) are arranged in a horizontal direction, a light beam is deflected in the horizontal direction from the front of the radiation ends. This waveguide-type optical phased array forms a light beam having strong light intensity at the center of the front surface by controlling the phase of each waveguide with its phase control section.

In the following, an output angle θ is introduced in which the direction in front of the radiation end of the waveguide is 0°, and a value twice the output angle θ is referred to as the deflection angle of the light beam. Here, the conditions under which the output light beam is formed in the direction of the emission angle θ will be explained. This condition is given by assuming that the intensity of light emitted from the radiation end of each waveguide is uniform, the phase difference Δφ between adjacent channels is equal, and the following equation (1) is satisfied. In equation (1), λ represents the wavelength of input light, and pr represents the pitch of the radiation end of the optical waveguide.

The angle at which the value of the output angle θ that satisfies equation (1) is the maximum value is referred to as the maximum output angle θ _max . This maximum output angle θ _max is the output angle θ when the value of Δφ/2π in equation (1) is 1/2, that is, when Δφ=π, and is given as equation (2) below.

Further, the light beam spread angle Φ corresponding to the width of the emitted light beam is approximately given by the following equation (3). In equation (3), N represents the number of radiation ends of the waveguide.

Patent No. 6513885

An important performance index in an optical deflector is the number of rays (hereinafter referred to as NL). The number NL of light rays represents the maximum number of distinguishable light beams emitted in different directions, and also serves as the resolution limit of the optical phased array element. Therefore, in order to improve the performance of the optical deflection device, it is essential to increase the number of light rays NL. The number of light rays NL can be expressed by the following equation (4). In equation (4), θ _max indicates the maximum output angle, and Φ indicates the light beam spread angle. The value twice the maximum output angle θ _max , which is the numerator on the right side of equation (4), will hereinafter be referred to as the maximum deflection angle of the light beam.

According to the above equation (3), it can be seen that as the number N of radiation ends of the waveguide is increased, the light beam spread angle Φ becomes smaller. In other words, the width of the output light beam can be made narrower as the number of channels increases. Furthermore, the following is derived from the relationships among the above-mentioned expressions. For example, according to equation (4), it can be seen that when the maximum deflection angle of the light beam is constant, if the light beam spread angle Φ is made smaller, the number NL of light rays becomes larger. Therefore, in order to increase the number of light rays NL, it is necessary to reduce the light beam spread angle Φ, in other words, it is necessary to increase the number N of radiation ends of the waveguide. Furthermore, according to equations (2) and (4) described above, it is also possible to increase the maximum deflection angle of the light beam by narrowing the pitch pr. As the maximum deflection angle of the light beam increases, the number NL of light rays also increases.

As mentioned above, according to the above equation (3), it is theoretically possible to suppress the spread of the optical beam and make it narrower by increasing the number of optical waveguide channels in the optical deflector. . On the other hand, increasing the number of optical waveguide channels increases the number of optical waveguides whose phase must be controlled. In other words, there is a problem in that the number of operations for performing phase control increases and the phase control becomes complicated. Furthermore, as the number of optical waveguides for which phase control is to be performed increases, the power consumption required for electrical control also increases, which is a problem.

The present invention has been made in view of the above-mentioned problems, and provides an optical deflector with a small number of control units that suppresses the complexity of light phase control and increases in power consumption while improving optical deflection performance. That is the issue.

In order to solve the above problems, an optical deflector with a small control section according to the present invention includes a phase control section in which a plurality of cores on the input side forming an optical waveguide on the input side are arranged in parallel at a first pitch, and a phase control section that forms an optical waveguide on the input side. a light output section in which the radiation ends of a plurality of cores on the output side forming a side optical waveguide are arranged in parallel at a second pitch; In order to enable optical mode coupling between the pitch conversion section in which the optical waveguide is formed, the core on the input side and the core on the output side, a portion of each of the cores on the input side and all of the cores on the light output side are connected. and an optical coupling section in which a portion of the light incident side of each of the emission side cores is disposed, and in the optical coupling section, the one incident side core is disposed between the two emission side cores. The two cores on the output side are arranged between the two cores on the input side that are adjacent to each other in the optical coupling unit, and a crossing optical waveguide that intersects in the pitch conversion unit is formed. It has been said that it has been done.

The present invention has the following excellent effects.
According to the small control part optical deflector, the number of radiation ends of the optical waveguide is increased to improve the performance of optical deflection, while the complexity and consumption of optical phase control due to the increase in the number of radiation ends of the optical waveguide are improved. Increase in power can be suppressed.

1 is a configuration diagram schematically showing a small control unit optical deflector according to an embodiment of the present invention. FIG. FIG. 2 is a cross-sectional view taken along line GG in FIG. 1; FIG. 2 is a partial configuration diagram of the small-control optical deflector of FIG. 1; FIG. 4 is a schematic diagram showing an enlarged view of the region indicated by H in FIG. 3. FIG. FIG. 4 is a schematic diagram showing another example of the configuration of the area indicated by H in FIG. 3; FIG. 4 is a schematic diagram showing another example of the configuration of the area indicated by H in FIG. 3; 4 is a schematic diagram showing the arrangement of cores in a cross section taken along line AA in FIG. 3. FIG. 4 is a schematic diagram showing the arrangement of cores in a cross section taken along line BB in FIG. 3. FIG. 4 is a schematic diagram showing the arrangement of cores in a cross section taken along the line CC in FIG. 3. FIG. 4 is a schematic diagram showing the arrangement of cores in a cross section taken along line DD in FIG. 3. FIG. 4 is a schematic diagram showing the arrangement of cores in a cross section taken along line EE in FIG. 3. FIG. This is a far-field image of a light beam when the phase difference between adjacent optical waveguides is 0. This is a one-dimensional profile when the phase difference between adjacent optical waveguides is 0. This is a far-field image of a light beam when the phase difference between adjacent optical waveguides is π. This is a one-dimensional profile when the phase difference between adjacent optical waveguides is π. It is a graph which shows the relationship between the optical waveguide pitch and the maximum deflection angle in a light emission part. It is a graph showing the relationship between the number of channels and the light beam spread angle in the light emitting section. FIG. 2 is a configuration diagram schematically showing an optical phased array to which the small-control unit optical deflector of FIG. 1 is applied.

[Configuration of light deflector in small control section]
First, the configuration of the small control section optical deflector will be explained with reference to FIGS. 1 to 5. Note that the sizes and positional relationships of members shown in each drawing may be exaggerated for clarity of explanation. The small-control optical deflector 1 shown in FIGS. 1 and 2 is an optical deflector that controls the direction of a light beam that is a combination of a plurality of emitted lights, and is applied to, for example, an optical switch or an optical phased array. be. Here, as shown in Fig. 1, the central axis of the device in the light beam emission direction of the light deflector with a small control section is aligned with the Z-axis, and the positive direction of the Z-axis is the front, and multiple synchrotron beams are emitted. The description will be made assuming that a plurality of radiation ends are arranged on the X axis.

The small-control optical deflector 1 includes an array of a plurality (n) of optical waveguides on the input side and a plurality (n×2) of optical waveguides on the output side. In the following description, it is assumed that n=4. An optical waveguide is also called a channel. The optical waveguide is assumed to propagate light in a single mode, and also propagates polarized light in a TM (Transverse Magnetic) mode. That is, in the propagating light, the amplitude direction of the electric field is perpendicular to the traveling direction. The waveguide is formed from a core and a cladding, and the core has a larger refractive index than the cladding.

The small-control optical deflector 1 includes a cladding around a core forming an optical waveguide, but its illustration is omitted in FIGS. 1, 3, 4, and 5. FIG. 2 is a cross-sectional view including the optical coupling section 70 of the small control section optical deflector 1, and shows cores PSn (n=1 to 4) formed on a predetermined substrate 110 and cores PSn (n=1 4) is a schematic diagram illustrating cores Cn1 and Cn2 (n=1 to 4) and a cladding 90 arranged on both sides.

As shown in FIG. 1, the small-control optical deflector 1 includes a phase control section 10 in which a plurality of optical waveguides on the input side are arranged, a light output section 30 in which a plurality of optical waveguides on the emission side are arranged, and a phase control section 10 in which a plurality of optical waveguides on the emission side are arranged. The pitch converting section 50 is provided between the section 10 and the light emitting section 30, and the optical coupling section 70 is provided between the phase control section 10 and the pitch converting section 50. Note that the adjacent phase control section 10 and light output section 30, the light output section 30 and pitch conversion section 50, and the pitch conversion section 50 and optical coupling section 70 each have a part of the same optical waveguide. Therefore, redundant explanation of the configuration of the optical waveguide shared by adjacent parts will be omitted.

(Phase control section)
The phase control unit 10 includes a plurality of incident side cores PSn (n=1 to 4) that form an incident side optical waveguide and are arranged in parallel at a first pitch. Hereinafter, PSn (n=1 to 4) will be simply referred to as PSn. In the phase control unit 10, cores PSn on the incident side are arranged in parallel at a predetermined first pitch. For example, as shown in FIG. 3, the core PS1 and the core PS2 are arranged in parallel at a pitch p1 in the width direction of the optical waveguide. The phase control unit 10 has an array-shaped optical waveguide that can control the phase of light. The phase control unit 10 changes the refractive index of the core forming the optical waveguide by an external signal such as a voltage or current sent via an electrode wire (not shown).

The material of the cores PS1 to PS4 on the incident side forming the optical waveguide of the phase control unit 10 is a material whose refractive index changes according to the application of an external signal. For example, a liquid crystal material or an electro-optic material whose refractive index changes depending on an applied voltage, or a thermo-optic material whose refractive index changes depending on Joule heat accompanying an applied current can be used. In this embodiment, the material of the core forming the optical waveguide of the phase control section 10 is assumed to be, for example, an electro-optic polymer (EO polymer) that exhibits an electro-optic effect. As the material of the cladding, for example, an oxide such as SiO ₂ or a polymer material can be used. Polymethyl methacrylate (PMMA), polyimide, or the like can be used as the polymer material. Examples of polyimide-based materials include polyimide and fluorinated polyimide.

(Light emitting part)
In the light emitting section 30, the emitting ends On1 and On2 (n=1 to 4) of the plurality of emitting side cores Cn1 and Cn2 (n=1 to 4) forming the emitting side optical waveguide are aligned at a second pitch. It has been established. Hereinafter, Cn1 and Cn2 (n=1 to 4) will be simply written as Cn1 and Cn2, and On1 and On2 (n=1 to 4) will be simply written as On1 and On2. The light emitting section 30 has an array of optical waveguides. As shown in FIG. 3, for example, the radiation end O11 and the radiation end O21 are arranged in parallel at a pitch p2 in the width direction of the optical waveguide. Further, the radiation end O21 and the radiation end O12 are arranged in parallel at a pitch p2, and the radiation end O12 and the radiation end O22 are arranged in parallel at a pitch p2. Note that the pitch p2 is the pitch pr described in equations (1) to (3) above.

The light emitting section 30 has twice the number of emission ends as the number of cores PSn on the incident side forming the phase control section 10 . The material of the cores Cn1 and Cn2 on the emission side is preferably a material having a high refractive index, such as silicon (Si) or silicon nitride (SiN). By doing so, the difference between the refractive index of the cores Cn1 and Cn2 of the optical waveguide and the refractive index of the cladding becomes large, and the effect of confining light inside the cores Cn1 and Cn2 of the optical waveguide can be enhanced. As a result, even if the pitch between the radiation ends On1 and On2 is narrowed, the leakage of light between adjacent optical waveguides can be suppressed and the influence of crosstalk can be suppressed.

(Pitch conversion section)
In the pitch conversion unit 50, the optical waveguide on the output side is formed such that the second pitch (pitch p2) is smaller than the first pitch (pitch p1). The pitch conversion unit 50 has a plurality of emission side cores Cn1 and Cn2. The pitch p2 of the radiation ends On1 and On2 in the cores Cn1 and Cn2 on the output side is formed smaller than the pitch p1 of the core PSn on the input side.

In the pitch converting section 50, the output side optical waveguide includes a bent optical waveguide. As shown in FIG. 3, for example, the core C11 on the output side is a bent optical waveguide. According to this, when setting the desired second pitch (p2), the length of the output side core C11 is shortened compared to the case where the output side core C11 is formed by a linear optical waveguide. This has the effect of downsizing the device.

(Optical coupling part)
The optical coupling unit 70 connects a portion of each light output side of each of the cores PSn on the input side and all output sides so that optical mode coupling can be performed between the core PSn on the input side and the cores Cn1 and Cn2 on the output side. A portion of each of the cores Cn1 and Cn2 on the light incident side is disposed.
Furthermore, in the optical coupling section 70, one core PSn on the input side is arranged between the two cores Cn1 and Cn2 on the output side. In other words, the output side cores Cn1 and Cn2 are arranged in parallel on both sides of the input side core PSn of the phase control unit 10. For example, output side cores C11 and C12 are arranged in parallel, one on each side of the input side core PS1. Furthermore, output side cores C21 and C22 are arranged in parallel, one on each side of the input side core PS2.

In the optical coupling section 70, as shown in FIG. 1, a partial region of the core PSn on the incident side and a partial region of the cores Cn1 and Cn2 on the output side are arranged in parallel. For example, light propagating through one core PS1 on the input side can be transferred to adjacent cores C11 and C12 on the output side, respectively, by mode coupling. In other words, the optical coupling section 70 distributes the light that has propagated through the core of the phase control section 10 to adjacent optical waveguides.

Note that the length of the optical coupling section 70 in the Z-axis direction required for distribution and the length d between opposing optical waveguides (see FIG. 4A) are calculated from spatial overlap integral of optical electromagnetic field distribution and mode coupling theory. be able to. Optical coupling between waveguides depends on the interaction of mode fields (optical amplitude distributions) propagating through the waveguides. The coupling coefficient indicating the degree of coupling is given by the following equation (5) as an overlap integral χ indicating the spatial overlap of modes. In Equation (5), f _EO represents the mode field (light amplitude distribution) in the core PSn on the incident side, and f _SiN represents the mode field (light amplitude distribution) in the cores Cn1 and Cn2 on the exit side.

The cross-sectional structure of the optical coupling section 70 will be explained with reference to FIG. 2. FIG. 2 is a cross-sectional view taken along line GG in FIG. Here, the cladding 90 is formed to cover the entire circumference of the core PSn in the upper, lower, left and right directions, and the entire circumference of the cores Cn1 and Cn2 in the upper, lower, left and right directions. Further, the cladding 90 will be described as including a lower cladding 91, a middle cladding 92, and an upper cladding 93 in this order from the substrate 110 side.

The lower cladding 91 is a cladding placed under the core PSn and the cores Cn1 and Cn2. Here, the cladding provided under the core PSn on the incident side and the cladding provided under the cores Cn1 and Cn2 on the output side are continuously formed with the same thickness. In other words, the lower cladding 91 is shared by the core PSn and the cores Cn1 and Cn2. However, the present invention is not limited to this, and a separate cladding may be provided for each core. Here, the individual clads may be clads of different sizes or clads of different materials.

The middle cladding 92 is a cladding that is laminated on the lower cladding 91 to the height of the core and covers the side surfaces of the core. Here, it is assumed that the height of core PSn is higher than that of cores Cn1 and Cn2, and the intermediate cladding 92 completely covers the upper surfaces of cores Cn1 and Cn2 and is laminated to the same height as the upper surface of core PSn. ing. The space between core PSn and core Cn1 is filled with a cladding material. Further, the space between core PSn and core Cn2 is filled with a cladding material. Furthermore, the gap between the core Cn1 and the core Cn2 is also filled with a cladding material (see FIG. 1).

The upper cladding 93 is a cladding laminated on the middle cladding 92 to a thickness sufficient to completely cover the upper surface of the core and confine light. Here, the upper cladding 93 completely covers the upper surface of the core PSn.

The upper cladding 93 and the middle cladding 92 are formally divided, and can be formed of the same material and at the same timing, as shown by the same hatching, and are collectively referred to as the upper cladding. The hatching of the lower cladding 91 is different from the hatching of the upper cladding, but can be formed of the same material.

As described above, the core PSn on the input side is made of an organic material, and the cores Cn1 and Cn2 on the output side are made of an inorganic material. Specifically, the material of the core PSn on the incident side is, for example, EO polymer. Further, the material of the cores Cn1 and Cn2 on the emission side is, for example, SiN. Further, the cladding is, for example, SiO ₂ .

The planar structure of the optical coupling section 70 will be explained with reference to FIG. 4A. FIG. 4A is a schematic diagram showing an enlarged view of the region indicated by H in FIG. 3. FIG. Output side cores C21 and C22 are arranged in parallel on both sides of the input side core PS2. The cores C21 and C22 on the output side are symmetrically arranged apart from the core PS2 on the input side by a distance d.

As shown in FIG. 4A, in the optical coupling section 70, the cores Cn1 and Cn2 on the output side have a shape with a slope that widens from the end 71 in a plan view as shown in FIG. 4A. For example, the side surface of the core C21 on the output side facing the core PS2 on the input side (lower side in FIG. 4A) is arranged parallel to the side surface of the core PS2 on the input side, and the width of the end portion 71 is the widest. small. In the core C21 on the emission side, the core width gradually increases linearly from the end portion 71 toward the light emission side (right side in FIG. 4A).
In addition, the side surface of the output side core C22 that is disposed on the side facing the input side core PS2 (the upper side in FIG. 4A) is arranged parallel to the side surface of the input side core PS2, and the width of the end portion 71 is the widest. small. In the core C22 on the emission side, the core width gradually increases linearly from the end portion 71 toward the light emission side (right side in FIG. 4A).

In this manner, in the optical coupling section 70, the two output side cores Cn1 and Cn2, which are arranged to sandwich the input side core PSn from both sides, have a tapered end 71 as a whole. In the following, a structure having a shape formed by virtually connecting the slope and the outline of the end 71 of the core C21 on the output side and the outline of the end 71 and the slope of the core C22 on the output side will be referred to as a tapered structure. It is called.

Note that, as shown in FIG. 4B, in the optical coupling section 70, the widths of the two output side cores C21 and C22, which are arranged to sandwich the input side core PS2 from both sides, may be uniform. However, providing a tapered structure at the tips of the cores C21 and C22 on the output side has the effect of increasing the coupling efficiency. Further, in the optical coupling section 70, the cores C21 and C22 on the output side and the core PS2 on the input side may be arranged so as to be in contact with each other. In that case, it is preferable to have a tapered structure as shown in FIG. 4C.

(Light beam shaping)
Light beam shaping in the small control unit optical deflector 1 will be explained with reference to FIGS. 1 and 3. FIG. In a waveguide type optical phased array, one of the conditions for shaping a light beam is that when the light beam is emitted in the direction of the maximum emission angle, the phase difference between adjacent optical waveguides in the light emitting section 30 must be π. No. However, in the optical coupling section 70 of the small control section optical deflector 1, for example, the respective lights branched from the incident side core PS1 to the output side cores C11, C12 have the same phase, and these adjacent cores C11, A phase difference cannot be given between C12. Further, for example, the respective lights branched from the incident side core PS2 to the output side cores C21 and C22 have the same phase, and no phase difference can be given between these adjacent cores C21 and C22.

However, in this embodiment, by applying crossed optical waveguides as shown in FIG. 1, light can be exchanged. That is, the two output-side cores arranged between two adjacent input-side cores in the optical coupling unit 70 form intersecting optical waveguides that intersect in the pitch conversion unit 50 . Furthermore, a pair of intersecting optical waveguides are formed with the Z axis as the axis of symmetry. In other words, with respect to the two output-side cores arranged between the two adjacent input-side cores in the optical coupling section 70, similar two The core on the exit side of the book is formed.

Specifically, a core C12 and a core C21 are arranged between adjacent cores PS1 and PS2 in the optical coupling section 70, and these cores C12 and C21 intersect in the pitch conversion section 50. There is. With this crossed optical waveguide, the position of the radiation end O12 of the core C12 and the position of the radiation end O21 of the core C21 can be exchanged. Therefore, an effect equivalent to providing a substantial phase difference between the cores C11 and C12 and between the cores C21 and C22 can be achieved.
Further, at a position symmetrical to the Z axis from the positions of core PS1 and core PS2, core C32 and core C41 are arranged between adjacent cores PS3 and core PS4 in optical coupling section 70, and core C32 and core C41 are arranged between adjacent cores PS3 and core PS4. The cores C41 intersect at the pitch conversion section 50.

On the other hand, when the two adjacent incident-side cores themselves are arranged at symmetrical positions with respect to the device center axis (Z-axis), the two optical waveguides do not intersect. Specifically, a core C22 and a core C31 are arranged between adjacent cores PS2 and PS3 in the optical coupling section 70, and these cores C22 and C31 intersect in the pitch conversion section 50. do not have.

The two cores Cn1 and Cn2 on the emission side that intersect in the pitch conversion section 50 are formed to have the same thickness including the intersecting portion. A crossed optical waveguide is an optical waveguide structure in which two optical waveguides intersect on the same plane. Depending on the value of the angle θ shown in FIG. 3, the propagating light causes crosstalk. The angle at which crosstalk occurs varies depending on the refractive index and shape of the core and cladding applied to the optical waveguide. Generally, it is known that crosstalk does not occur if the intersecting angle is 20 degrees or more (reference patent document: Japanese Patent No. 3253007). There are also reports on structures that can suppress crosstalk even if the crossing angle is 5 degrees (Reference non-patent literature: Toshikazu Hashimoto, et al., “Optical waveguide shape and device using wavefront matching method”). ”, Laser Research, 2007, Vol. 35, Supplement No., p. 178-179). Therefore, depending on the material and structure of the optical waveguide, it is possible to realize a layout that does not cause crosstalk even if the crossing angle θ is 20 degrees or less. Note that "no crosstalk occurs" means that the light distributed from the core PS1 to the core C21 in the optical coupling section 70, after crossing the waveguide, proceeds to the radiation end O21, and the light from the core C21 travels to the radiation end O12. This means that it will never come out.

In the small control section optical deflector 1, the phase-controlled light propagates from the input side core PSn through the output side cores Cn1 and Cn2 by optical mode coupling, and from the radiation ends On1 and On2 to the outside of each optical waveguide. Emits into free space. An optical interference pattern is generated by diffraction and interference of light emitted into free space. The light beam pattern formed by the small-control optical deflector 1 is an optical interference pattern created by diffraction and interference of the light emitted into this free space. By controlling the phase of each waveguide with the phase control unit 10, the small-control optical deflector 1 can form a light beam having a strong light intensity at the center, for example. Furthermore, by controlling the phase of each waveguide with the phase control unit 10, the small-control optical deflector 1 can emit a light beam in the direction of the maximum output angle, for example.

[Manufacturing method of small control optical deflector]
The small-control optical deflector 1 can be manufactured using a general semiconductor device manufacturing process. For example, the lower cladding 91 is formed on the substrate 110, and materials for the emission side core are laminated and etched to form the emission side cores Cn1 and Cn2. Then, by masking the output side core, materials for the input side core are laminated and etched to form the input side core PSn. Then, by laminating the upper cladding from above the lower cladding 91 and each core, the optical deflector 1 with few control parts can be manufactured.

[simulation]
The inventors of the present application confirmed the effect of the small control section optical deflector 1 by performing the following simulation. First, simulation conditions will be explained with appropriate reference to FIGS. 1 to 5.
<Conditions for overall configuration>
In the small-control optical deflector 1, the number of optical waveguides on the input side was set to n=4, the number of optical waveguides on the output side was set to 8, and N (the number of radiation ends) in the above equation (3) was set to 8. The phase control unit 10 is an optical waveguide consisting of four incident-side cores PSn. Hereinafter, in the simulation, the core on the incident side will be referred to as an organic core. The pitch conversion unit 50 is an optical waveguide consisting of eight output-side cores Cn1 and Cn2. Hereinafter, in the simulation, the core on the output side will be referred to as an inorganic core. The light emitting section 30 is assumed to be the radiation ends On1, On2 of an optical waveguide consisting of eight inorganic cores Cn1, Cn2. The optical coupling unit 70 equally distributes light to two inorganic cores Cn1 and Cn2 with respect to one n-th organic core PSn.

<Conditions of structure and material composition>
(Conditions for phase control unit 10)
Pitch p1 = 10 μm (see Figure 5A)
Material of organic core PSn: EO polymer (refractive index 1.66)
Cross-sectional shape of organic core PSn: square (width 1.5 μm, thickness 1.5 μm)
Material of cladding 90: SiO ₂ (refractive index 1.48)
Thickness of lower cladding 91: 3 μm
Overall thickness of cladding 90: 7μm
Thickness of clad layered on inorganic cores Cn1 and Cn2: 3.5 μm
Thickness of clad layered on lower clad 91: 4 μm
Material of inorganic cores Cn1 and Cn2: SiN (refractive index 2.01)
Cross-sectional shape of inorganic cores Cn1 and Cn2: Rectangular (width 1.0 μm, thickness 0.5 μm)

(Conditions for optical coupling section 70)
The lower cladding 91 was made common to the organic core PSn and the inorganic cores Cn1 and Cn2. Here, each core is on a lower cladding with a thickness of 3 μm, and the core is surrounded by SiO ₂ . Also, the inorganic core is on the same lower cladding as the organic core. The structure was such that inorganic cores Cn1 and Cn2 were arranged in parallel on both sides of an organic core PSn.
Distance d between organic core PSn and inorganic cores Cn1 and Cn2: 0.4 μm (constant)
The tapered structure shown in FIG. 4A was applied to the inorganic cores Cn1 and Cn2 (see FIGS. 5B and 5C).
Width at taper tip: 0.5 μm (see Figure 5B)
Width at taper end: 1.0 μm (see Figure 5C)
Taper length: 500μm
Taper thickness: 0.5μm (constant)
The tapered ends are each connected to the inorganic core of the pitch conversion section 50. The organic core PSn was discontinued at the end point of the taper and did not extend beyond that point.

(Conditions for pitch converter 50)
The inorganic cores Cn1 and Cn2 were made of the same material and cross-sectional shape as the phase control section 10.
Material of inorganic cores Cn1 and Cn2: SiN (refractive index 2.01)
Cross-sectional shape of inorganic cores Cn1 and Cn2: Rectangular (width 1.0 μm, thickness 0.5 μm)
Crossing optical waveguides are structures that intersect in a plane (see FIGS. 5D and 5E). As shown in FIG. 5D, the inorganic core C12 and the inorganic core C21 are integrated with the side surfaces of each waveguide in contact with each other before the intersection point, and are merged in the same layer (see FIG. 5D). Moreover, the arrangement of the inorganic core C12 and the inorganic core C21 in the X-axis direction is reversed on the radiation end side beyond the point where they merge in the same layer (see FIG. 5E).
Crossing angle θ of crossed optical waveguides: 4° (see Figure 3)
In the pitch conversion unit 50, a bent optical waveguide or the like was applied to adjust the length so that all the optical path lengths of the inorganic cores Cn1 and Cn2 were made uniform.
(Conditions for light emitting section 30)
Pitch p2 = 2 μm (see Figure 5E)

<Simulation results>
6A, FIG. 6B, FIG. 7A, FIG. 7B, and the results of a simulation using the Beam Propagation Method (BPM) for the output light beam of the small control unit optical deflector 1 under the simulation conditions described above. This will be explained with reference to FIGS. 8A and 8B (refer to each drawing as appropriate).
(Outline about the direction of light)
The light deflector 1 with a small control section can determine the direction of light depending on the phase distribution of the waveguide in the light emitting section 30. If all the phases between the waveguides are made to be the same, a sharp beam can be emitted at the center, as shown in FIGS. 6A and 6B. Further, by providing a phase difference π (180°) between the waveguides, the beam can be emitted in the maximum direction as shown in FIGS. 7A and 7B. As a result, it was confirmed that the small-control optical deflector 1 can enlarge the deflection surface while shaping the light beam.
Note that the horizontal axis of the graphs shown in FIGS. 6B and 7B indicates the angle of the light emission direction, and the vertical axis indicates the light intensity. Here, the angle of the light emission direction is defined as the positive angle measured in the positive direction of the X-axis from the intersection of the X-axis and the Z-axis in Figure 1, and the negative angle measured in the negative direction of the X-axis. It shows. In addition, regarding the light intensity at each angle of the light emission direction, the value (maximum value) in the direction on the Z axis in FIG. It is expressed in a form.

(When the phase difference between adjacent optical waveguides is 0)
A far-field image of a light beam when the phase difference between adjacent optical waveguides is 0 will be described with reference to FIG. 6A. The image shown in FIG. 6A shows a far-field image of the light beam obtained from the light emitting section 30 when the phase difference between adjacent optical waveguides is 0. In FIG. 6A, the light intensity is shown in shading, and the darker the area, the higher the light intensity. This is the result when light having the same phase is propagated through the organic cores PS1 to PS4 of the phase control unit 10. That is, the phase difference between adjacent optical waveguides such as organic cores PS1 and PS2 is zero. In this case, as shown in FIG. 6A, a light beam with a peak at the center was confirmed. This light beam width, ie, the light beam spread angle, was 7.3°. Here, the value of the light beam spread angle (7.3°) was determined from the half-width of the one-dimensional profile shown in FIG. 6B. A discussion of the results of this light beam spread angle will be given later.

(When the phase difference between adjacent optical waveguides is π)
A far-field image of a light beam when the phase difference between adjacent optical waveguides is π will be described with reference to FIG. 7A. The image shown in FIG. 7A shows a far-field image of the light beam obtained from the light emitting section 30 when the phase difference between adjacent optical waveguides is π. In FIG. 7A, the light intensity is shown in shading, and the darker the area, the higher the light intensity.

In this case, light having a phase of 0.5π is transmitted to the organic cores PS1 and PS3 of the phase control unit 10, and light having a phase of 1.5π is transmitted to the organic cores PS2 and PS4. It is propagating. That is, in the phase control unit 10, the phase difference between the odd-numbered organic cores and the even-numbered organic cores was set to π. As a result, since the intersecting waveguides are present in the pitch converting section 50, the phase difference between all adjacent optical waveguides can be set to π in the light emitting section 30. In this case, as shown in FIG. 7A, a peak of the light beam was observed in the maximum emission direction. The maximum output angle was ±21°, that is, the maximum deflection angle was 42°. Here, the maximum deflection angle (42°) was determined as the angle between two peaks in the one-dimensional profile shown in FIG. 7B.

(About maximum deflection angle)
Here, the relationship between the pitch (p2) of the radiation end of the waveguide in the light output section 30 of the small control section optical deflector 1 and the maximum deflection angle will be explained with reference to FIG. 8A. The horizontal axis of the graph shown in FIG. 8A is the pitch [μm] of the radiation end, and the vertical axis is the maximum deflection angle [°], which is the numerator of the right side of the above equation (4), and the vertical axis is the maximum deflection angle [°], which is the numerator of the right side of the above equation (4) This value is twice the maximum output angle θ _max shown in 2). The graph shown in FIG. 8A illustrates the theoretical values calculated using the above-mentioned equations (2) and (4) under the calculation conditions that the wavelength λ of the input light is 1550 nm. From this graph, it can be seen that the narrower the pitch of the radiation ends of the waveguide, the larger the maximum deflection angle. In this simulation, the pitch p2 = 2 μm is used as the condition for the light emitting section 30, and the maximum deflection angle (42°) of the simulation result closely matches the theoretical value of the maximum deflection angle when the pitch is 2 μm in FIG. 8A. It became a thing.

(About the light beam spread angle)
Here, the relationship between the number of channels and the light beam spread angle in the light emitting section 30 of the small control section optical deflector 1 will be explained with reference to FIG. 8B. The number of channels in the light emitting section 30 refers to the number N of radiation ends On1 and On2 of the waveguide in the light emitting section 30. The horizontal axis of the graph shown in FIG. 8B is the number of channels in the light emitting section, that is, the number N of radiation ends On1 and On2 of the waveguide in the light emitting section 30. Moreover, the vertical axis is the light beam spread angle Φ shown by the above-mentioned equation (3), that is, the beam thinness. The graph shown in FIG. 8B illustrates theoretical values calculated using the above-mentioned equation (3) under various calculation conditions where the input light wavelength λ=1550 nm and the pitch pr=2 μm. From this graph, it can be seen that as the number of channels from which light comes out, ie, the number N of radiation ends, increases, the spread angle decreases and the beam convergence improves. In this simulation, the conditions are that the number of optical waveguides on the input side is 4, and the number of emission ends is 8. This result agrees well with the theoretical value of the light beam spread angle in the case of No. 8.

On the other hand, in an optical deflector having a conventional structure, the number n of optical waveguides on the input side is equal to the number N of emission ends. In an optical deflector with a conventional structure, if the number of optical waveguides in the phase control section is 4, the optical beam spread angle will be the same as the theoretical value (18 degrees or more) when the number of channels is 4 in FIG. 8B. Put it away. On the other hand, even if the optical deflector 1 with a small control section has the same number of optical waveguides in the phase control section as an optical deflector with a conventional structure has, the beam convergence is improved. In other words, the small control unit optical deflector 1 maintains a small number of optical waveguides in the phase control unit 10 to suppress the complexity of optical phase control while increasing the number of channels (the number N of radiation ends). can be secured. In addition, when the phase control unit 10 is equipped with n cores on the incident side, the light deflector 1 with a small control unit has a conventional structure with respect to the spread angle Φ of the light beam emitted from the light output unit 30. It is possible to exhibit performance equivalent to that in which the phase control section is equipped with 2n cores on the incident side.

In addition, the small control unit optical deflector 1 controls the optical beam formed when the number of channels (the number of radiation ends) in the light output unit 30 is N to a phase control unit equipped with N/2 optical waveguides. 10 can be controlled. Here, if the power consumption per time of one optical waveguide in the phase control section 10 is x [W], then if the small control section optical deflector 1 is used, the power consumption of one optical waveguide in the phase control section 10 will be The entire control unit 10 is operable. In other words, it is possible to suppress the power to 1/2 compared to x×N [W] required for an optical deflector with a conventional structure.

Furthermore, the small control unit optical deflector 1 has a tapered structure shown in FIG. We were able to increase the coupling efficiency to 85%. Note that when the structure shown in FIG. 4B was applied to the inorganic cores Cn1 and Cn2, the coupling efficiency was 65%, which was lower than when the tapered structure was applied.

[Application example]
The optical phased array will be explained with reference to FIG. 9. FIG. 9 is a configuration diagram schematically showing an optical phased array to which the small-control unit optical deflector of FIG. 1 is applied. Note that although the optical phased array 100 includes a cladding around the core forming the optical waveguide, illustration thereof is omitted in FIG. 9 . Further, the same components as those of the small-control optical deflector 1 shown in FIG.

The optical phased array 100 is a waveguide type optical phased array, and includes a substrate 110, a light incidence section 120, an optical splitter 130, a plurality of electrode wires 140, and a small control section optical deflector 1. There is.
Substrate 110 can be formed using a variety of materials. For example, the material of the substrate 110 may be soda glass, SiO ₂ , quartz, methyl acrylate, silicon, LiNbO ₃ , LiTaO ₃ , alumina, GaAlAs, InP, or the like. On one surface of the substrate 110, a light incidence section 120, a light splitter 130, a plurality of electrode wires 140, and a small control section light deflector 1 are formed.

The light input section 120 is a section into which light is input from the outside, and is formed from one or more optical waveguides. As the light source, a laser light source, a light emitting diode (LED), or the like can be used. The optical phased array 100 may further include a ball lens, a cylindrical lens, or the like between the light source and the light incidence section 120, if necessary. The optical splitter 130 is an optical element that distributes the light guided through the light incidence section 120 to each optical waveguide arranged in an array. Examples include MMI (Multi Mode Interference) and Y-branching that utilize multimode interference.

The plurality of electrode wires 140 are electrically connected to each channel of the phase control section 10 of the small control section optical deflector 1, respectively. The phase control section 10 can control the phase of light propagating within the optical waveguide of the phase control section 10 by applying voltage or current to each channel from the plurality of electrode wires 140. Note that the required power consumption in the phase control section 10 increases as the number of channels increases, so it is desirable to reduce the power consumption per channel. As the material of the electrode wire 140, for example, metals such as Al, Cu, Au, Ti, and Cr can be used. The electrode wire 140 may be a transparent electrode, and in that case, examples of the material include IZO (Indium Zinc Oxide) and ITO (Indium Tin Oxide).

In an optical phased array, when creating a single beam from multiple radiation ends, narrowing the pitch of the radiation ends increases the maximum deflection angle, and increasing the number of radiation ends narrows the output optical beam. be able to. However, in an optical phased array having a conventional structure, the radiation end of the optical waveguide and the optical waveguide of the phase control section correspond to each other on a one-to-one basis. Therefore, if the pitch of the radiation ends is narrowed, the optical waveguide of the phase control section must be made very precisely, and if the number of radiation ends is increased, the power consumption for phase control in the phase control section will also increase. Resulting in.
On the other hand, the optical phased array 100 has a structure in which the number of emission ends of the optical waveguides in the light emitting section 30 is increased to 2n compared to the number n of optical waveguides in the phase control section 10.

Furthermore, in an optical phased array having a conventional structure, when the light emitting section is provided with N radiation ends, the phase control section also requires N optical waveguides.
On the other hand, even if the number of optical waveguides in the phase control unit 10 is reduced to N/2, the optical phased array 100 produces a beam having the same optical beam spread angle Φ as an optical phased array with N radiation ends. It is possible to exhibit the performance that can be obtained while suppressing power consumption.

[Modified example]
In the optical deflector with a small number of control units according to the embodiment, the intersecting optical waveguides have been described as intersecting in a plane, but it is also possible for one optical waveguide to ride on top of the other optical waveguide and intersect three-dimensionally. However, it is preferable that the intersecting optical waveguides intersect in planes from the viewpoint of ease of manufacture. Furthermore, instead of adjusting the length of the inorganic core in the pitch conversion unit 50, the phase of the propagating light may be adjusted in the phase control unit 10 so that the optical path lengths are equal at the position of the radiation end. . Furthermore, a diffraction grating may be further provided at the radiation end in order to emit the light beam output from the light emitting section 30 upward (in the Y-axis direction) from within the ZX horizontal plane. Furthermore, although the light deflector with a small control section has been described in which the number n of optical waveguides on the incident side is four, the number n is not limited to this, and the number n may be eight, sixteen, or more, for example.

Although the small control unit optical deflector according to the embodiment of the present invention has been described above, the gist of the present invention is not limited to these descriptions, and should not be broadly interpreted based on the description of the claims. No. Furthermore, it goes without saying that various changes and modifications based on these descriptions are also included within the spirit of the present invention.

1 Small control section optical deflector 10 Phase control section 30 Light output section 50 Pitch conversion section 70 Optical coupling section 71 End section 90 Cladding 91 Lower cladding 92 Middle cladding 93 Upper cladding 100 Optical phased array 110 Substrate 120 Light incidence section 130 Optical splitter 140 Electrode wire PS1, PS2, PS3, PS4 Core (core on the incident side)
C11, C12, C21, C22, C31, C32, C41, C42 core (output side core)
O11, O12, O21, O22, O31, O32, O41, O42 Radiation end

Claims (7)

a phase control unit in which a plurality of incident side cores forming an incident side optical waveguide are arranged in parallel at a first pitch;
a light emitting section in which radiation ends of a plurality of emission side cores forming an emission side optical waveguide are arranged in parallel at a second pitch;
a pitch conversion section in which the optical waveguide on the output side is formed such that the second pitch is smaller than the first pitch;
A portion of the light output side of each of the cores on the input side and a portion of each of the cores on the output side so that optical mode coupling can be performed between the cores on the input side and the cores on the output side. an optical coupling part disposed with a part of the side;
In the optical coupling section, one core on the input side is arranged between the two cores on the output side,
A small control unit, wherein a crossing optical waveguide that intersects in the pitch conversion unit is formed by two cores on the output side that are arranged between two cores on the input side that are adjacent to each other in the optical coupling unit. light deflector. 2. The optical deflector with a small control section according to claim 1, wherein the optical waveguide on the output side includes a bent optical waveguide. 3. The small control section optical deflector according to claim 1, wherein the two cores on the emission side that intersect in the pitch conversion section are formed to have the same thickness including the intersecting portion. 4. The small control unit optical deflector according to claim 1, wherein in the optical coupling unit, the core on the output side has a shape with a slope that increases in width from an end. 5. The small control unit according to claim 4, wherein in the optical coupling unit, the two output-side cores arranged to sandwich the input-side core from both sides have tapered end portions as a whole. light deflector. 6. The small control unit optical deflector according to claim 1, wherein the core on the incident side is made of an organic material, and the core on the output side is made of an inorganic material. Any one of claims 1 to 6, wherein the cladding provided under the core on the input side and the cladding provided under the core on the output side are continuously formed with the same thickness. 1. The small control unit optical deflector according to item 1.

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