JP7191720B2 - Isolators, light sources, optical transmitters, optical switches, optical amplifiers, and data centers - Google Patents

Description

The present invention relates to isolators, light source devices, optical transmitters, optical switches, optical amplifiers, and data centers.

A configuration is known in which an isolator having a different transmittance depending on the propagation direction of an electromagnetic wave includes a non-reciprocal phase shifter (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2003-302603

Due to the difficulty of integrating non-reciprocal phase shifters, isolators containing non-reciprocal phase shifters are difficult to miniaturize.

The present disclosure has been made in view of the above points, and aims to provide an isolator, a light source device, an optical transmitter, an optical switch, an optical amplifier, and a data center that can be easily miniaturized.

An isolator according to an embodiment of the present disclosure includes a first waveguide and a second waveguide positioned on a substrate having a substrate surface and aligned along the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the same as that of the first waveguide for the electromagnetic wave propagating from the second end to the first end. It is an odd multiple of the coupling length with the second waveguide.

An isolator according to an embodiment of the present disclosure includes a first waveguide and a second waveguide positioned on a substrate having a substrate surface and aligned along the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L, which represents the length of the second waveguide, is the length of the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the two ends to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
Calculated by

A light source device according to an embodiment of the present disclosure includes an optical isolator and a light source. The optical isolator is arranged on a substrate having a substrate surface and positioned side by side along the substrate surface.
1 waveguide and a second waveguide. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the same as that of the first waveguide for the electromagnetic wave propagating from the second end to the first end. It is an odd multiple of the coupling length with the second waveguide. The light source is optically connected to the port.

A light source device according to an embodiment of the present disclosure includes an optical isolator and a light source. The optical isolator includes a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L representing the length of the second waveguide is the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the second end to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
Calculated by The light source is optically connected to the port.

An optical transmitter according to an embodiment of the present disclosure includes a light source device including an optical isolator and a light source. The optical isolator includes a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the same as that of the first waveguide for the electromagnetic wave propagating from the second end to the first end. It is an odd multiple of the coupling length with the second waveguide. The light source is optically connected to the port. The optical transmitter has an optical modulation function.

An optical transmitter according to an embodiment of the present disclosure includes a light source device including an optical isolator and a light source. The optical isolator includes a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L representing the length of the second waveguide is the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the second end to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
Calculated by The light source is optically connected to the port. The optical transmitter has an optical modulation function.

An optical switch according to an embodiment of the present disclosure comprises an optical isolator. The optical isolator includes a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the same as that of the first waveguide for the electromagnetic wave propagating from the second end to the first end. It is an odd multiple of the coupling length with the second waveguide.

An optical switch according to an embodiment of the present disclosure comprises an optical isolator. The optical isolator includes a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L representing the length of the second waveguide is the coupling between the first waveguide and the second waveguide.
, an equation including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the second end to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
Calculated by

An optical amplifier according to an embodiment of the present disclosure includes an optical isolator. The optical isolator includes a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the same as that of the first waveguide for the electromagnetic wave propagating from the second end to the first end. It is an odd multiple of the coupling length with the second waveguide.

An optical amplifier according to an embodiment of the present disclosure includes an optical isolator. The optical isolator includes a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L representing the length of the second waveguide is the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the second end to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
Calculated by

A data center according to an embodiment of the present disclosure communicates with devices that include optical isolators. The optical isolator includes a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has non-reciprocal members arranged side by side at least partially in the direction in which the second waveguide extends, and has an aspect ratio of 0.8 to 1.2. The polarization direction of the electromagnetic wave input to the first end is parallel to the substrate surface, and the length of the second waveguide is the length of the electromagnetic wave propagating from the second end to the first end. It is an odd multiple of the coupling length between the waveguide and the second waveguide.

A data center according to an embodiment of the present disclosure communicates with devices that include optical isolators. The optical isolator includes a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having the substrate surface. Each of the first waveguide and the second waveguide has a core and a clad. The first waveguide has a first end and a second end, and ports for inputting and outputting electromagnetic waves at the first end and the second end, respectively. The core of the second waveguide has non-reciprocal members arranged side by side at least partially in the direction in which the second waveguide extends, and has an aspect ratio of 0.8 to 1.2. The polarization direction of the electromagnetic wave input to the first end is parallel to the substrate surface, and L representing the length of the second waveguide is the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the second end to the first end in
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
Calculated by

1 is a side view showing a configuration example of an isolator according to one embodiment; FIG. FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1; FIG. 4 is a cross-sectional view showing a configuration example of a non-reciprocal member; 4 is a graph showing an example of phase difference in the non-reciprocal member of FIG. 3; FIG. 4 is a cross-sectional view showing a configuration example of a non-reciprocal member; 6 is a graph showing an example of phase difference in the non-reciprocal member of FIG. 5; FIG. 4 is a cross-sectional view showing a configuration example of a non-reciprocal member; 5 is a graph showing an example of coupling lengths for electromagnetic waves traveling in a first direction; 7 is a graph showing an example of a coupling length for electromagnetic waves traveling in a second direction; 7 is a graph showing an example of simulation results of transmission characteristics; FIG. 4 is a block diagram showing an isolator according to a comparative example; It is a side view which shows the example which equips the both ends of a 2nd waveguide with an antenna. FIG. 11 is a side view showing an example in which electromagnetic wave absorbing members are provided at both ends of the second waveguide; FIG. 11 is a side view showing an example with a plurality of second waveguides; FIG. 4 is a side view showing a configuration example of an isolator having a matching circuit in a waveguide; 2 is a plan view showing a configuration example of a matching circuit; FIG. 7 is a graph showing an example of simulation results of transmission characteristics; FIG. 4 is a side view showing a configuration example of an isolator further including a magnetic field applying section; It is a side view which shows the structural example of the light source device which concerns on one Embodiment. FIG. 4 is a cross-sectional view showing an example of connection between a connection waveguide and a first waveguide; FIG. 4 is a cross-sectional view showing an example of connection between a connection waveguide and a first waveguide; FIG. 11 is a perspective view showing a configuration example of an isolator according to another embodiment; FIG. 11 is a plan view showing a configuration example of an isolator according to another embodiment; FIG. 24 is a cross-sectional view taken along the line BB of FIG. 23; 7 is a graph showing an example of simulation results of transmission characteristics; 4 is a graph showing the relationship between the dielectric constant and the magnitude of non-reciprocity when the aspect ratio of the core is 1; 4 is a graph showing the relationship between the aspect ratio of the core 31 and the magnitude of non-reciprocity.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. The drawings used in the following description are schematic, and the dimensional ratios and the like on the drawings do not necessarily match the actual ones.

As shown in FIG. 1, an isolator 10 according to one embodiment comprises a first waveguide 20 and a second waveguide 30 . The first waveguide 20 and the second waveguide 30 are positioned along the substrate surface 50a on the substrate 50 having the substrate surface 50a and extend in the X-axis direction.

The substrate 50 may include a conductor such as metal, a semiconductor such as silicon, glass, resin, or the like.

Either one of the first waveguide 20 and the second waveguide 30 is in contact with the substrate surface 50a. The second waveguide 30 is located above the first waveguide 20 when the first waveguide 20 contacts the substrate surface 50a. The first waveguide 20 is located above the second waveguide 30 when the second waveguide 30 contacts the substrate surface 50a. It can be said that the first waveguide 20 and the second waveguide 30 overlap each other when viewed from the substrate 50 . Hereinafter, it is assumed that the first waveguide 20 is in contact with the substrate surface 50a. In this case, the second waveguide 30 is located above the first waveguide 20 .

The first waveguide 20 has a first end 201 and a second end 202 on the positive direction side and the negative direction side of the X axis, respectively. The first waveguide 20 has a first port 211 and a second port 212 through which electromagnetic waves are input and output at a first end 201 and a second end 202, respectively. An electromagnetic wave input from the first port 211 to the first waveguide 20 travels along the X-axis toward the second port 212 . An electromagnetic wave input from the second port 212 to the first waveguide 20 travels along the X-axis toward the first port 211 . Each of the first port 211 and the second port 212 may be configured as an end face of the core 21, or may be configured as a coupler that is connected to an external device and capable of propagating electromagnetic waves.

The second waveguide 30 has ends 301 and 302 on the positive and negative sides of the X-axis, respectively. In other words, the second waveguide 30 has two ends. The second waveguide 30 is positioned along the first waveguide 20 and coupled with the first waveguide 20 to each other. The number of second waveguides 30 is not limited to one, and may be two or more.

The first waveguide 20 and the second waveguide 30 may be positioned along each other in at least part of the extending direction. The first waveguide 20 and the second waveguide 30 may be positioned parallel to each other in at least part of the extending direction. The first waveguide 20 or the second waveguide 30 may have a linear structure. The first waveguide 20 and the second waveguide 30 can be easily formed on the substrate 50 by having such simple structures.

Two waveguides lying along each other are also referred to as parallel waveguides. In parallel waveguides, an electromagnetic wave input into one waveguide can migrate to the other waveguide while propagating in that waveguide. That is, electromagnetic waves propagating in the first waveguide 20 can be transferred to the second waveguide 30 . Electromagnetic waves propagating in the second waveguide 30 can pass into the first waveguide 20 .

In parallel waveguides, a parameter representing the proportion of electromagnetic waves that pass from one waveguide to another is also called a coupling coefficient. The coupling coefficient is assumed to be 0 if no electromagnetic wave is transferred from one waveguide to the other. The coupling coefficient is assumed to be 1 if all electromagnetic waves pass from one waveguide to the other. It is assumed that the coupling coefficient can be a value greater than or equal to 0 and less than or equal to 1. The coupling coefficient can be determined based on the shape of each waveguide, the distance between each waveguide, the length along which the waveguides are along each other, and the like. For example, the coupling coefficient can be higher as the shapes of each waveguide are more similar. The distance between each waveguide, for example the distance between the first waveguide 20 and the second waveguide 30 , may be the distance between the cores 21 and 31 . The coupling coefficient can vary depending on the distance an electromagnetic wave travels in the waveguide. That is, in parallel waveguides, the coupling coefficient can be different depending on the position along the direction in which the waveguides extend. The maximum value of the coupling coefficient can be determined based on the shape of each waveguide, the distance between each waveguide, or the like. The maximum value of the coupling coefficient can be a value of 1 or less.

In parallel waveguides, the coupling coefficient is zero at the beginning of the section where the waveguides are along each other. The length from the starting point to the position where the coupling coefficient becomes the maximum value is also called the coupling length. If the length along which the waveguides are along each other is equal to the coupling length, the coupling coefficient at the end of the section along which the waveguides are along each other may be at a maximum value. The coupling length can be determined based on the shape of each waveguide, the distance between each waveguide, or the like.

In the second waveguide 30 , the electromagnetic waves transferred from the first waveguide 20 propagate in the second waveguide 30 in the same direction as in the first waveguide 20 . In the second waveguide 30, when an electromagnetic wave reaches the end 301 or 302, the electromagnetic wave can be radiated from the end 301 or 302 or reflected at the end 301 or 302 to travel in the opposite direction.

As shown in FIG. 2, first waveguide 20 comprises core 21 and clads 22 and 23 . Core 21 and clads 22 and 23 extend in the X-axis direction. The clads 22 and 23 are located on the negative and positive Z-axis sides of the core 21 . The clad 22 is positioned on the substrate 50 side when viewed from the core 21 . The clad 23 is located on the opposite side of the substrate 50 as viewed from the core 21 . It can also be said that the clad 23 is positioned on the second waveguide 30 side when viewed from the core 21 . It can also be said that the clad 22 , the core 21 and the clad 23 are laminated in order when viewed from the substrate 50 . It can also be said that the clads 22 and 23 are positioned with the core 21 interposed therebetween along the direction in which the first waveguide 20 and the second waveguide 30 overlap. It can also be said that the clads 22 and 23 are positioned on both sides of the core 21 along the direction in which the first waveguide 20 and the second waveguide 30 overlap. The core 21 may have a first surface 21a located on the side of the substrate 50 and a second surface 21b located on the opposite side of the first surface 21a. The claddings 22 and 23 may be positioned in contact with the first surface 21a and the second surface 21b, respectively.

The second waveguide 30 comprises a core 31, a non-reciprocal member 32, and claddings 33 and 34. As shown in FIG. Core 31, non-reciprocal member 32, and clads 33 and 34 extend in the X-axis direction. The non-reciprocal member 32 may be positioned on the positive side of the Z-axis with respect to the core 31 . The non-reciprocal member 32 may be positioned on the negative side of the Z-axis with respect to the core 31 . The non-reciprocal member 32 may be positioned side by side with respect to the core 31 in the positive or negative direction of the Y-axis.

As shown in FIG. 2, the shapes of the core 31 and the non-reciprocal member 32 viewed from the cross section intersecting the X-axis are configured so as not to be point symmetrical. The shapes of the core 31 and the non-reciprocal member 32 may be further configured so as not to be line symmetrical. The core 31 and the non-reciprocal member 32 are also collectively referred to as an asymmetric core. The asymmetric core comprises core 31 and non-reciprocal member 32 . The asymmetric core may have non-reciprocal members 32 in at least a portion of the cross-section that intersects the X-axis. Core 31 may be configured to include at least one type of dielectric. The non-reciprocal member 32 may contact the surface of the at least one dielectric substrate 50 or the opposite surface thereof.

The degree of symmetry can be used as an index representing whether or not the cross section of the asymmetric core is close to point symmetry. The degree of symmetry may be expressed by the proportion of matching portions between the cross-sectional shape of the asymmetric core and the cross-sectional shape obtained by rotating the cross-sectional shape by 180 degrees around a predetermined point. A cross-sectional shape with a high degree of symmetry can be said to be close to point symmetry. An asymmetric core may be configured such that its cross-sectional shape is less symmetrical.

In the cross-section of the asymmetric core, the area of core 31 may be configured to be larger than the area of non-reciprocal member 32 . By doing so, most of the electromagnetic waves can propagate inside the core 31 . As a result, electromagnetic wave loss in the second waveguide 30 can be reduced.

The cross-section of the asymmetric core may be configured such that the core 31 is located where the intensity of the electromagnetic wave propagating in the asymmetric core is maximum. By doing so, a portion where the electromagnetic wave has a high intensity can propagate inside the core 31 . As a result, electromagnetic wave loss in the second waveguide 30 can be reduced.

The claddings 33 and 34 are located on the negative and positive Z-axis sides with respect to the asymmetric core. The cladding 33 is located on the substrate 50 side when viewed from the asymmetric core. Cladding 34 is located on the opposite side of substrate 50 from the asymmetric core. It can also be said that the clad 34 is positioned on the second waveguide 30 side when viewed from the asymmetric core. It can also be said that the clad 33 , the asymmetric core, and the clad 34 are laminated in order when viewed from the substrate 50 . It can also be said that the claddings 33 and 34 sandwich the asymmetric core. It can be said that the clads 33 and 34 are located on both sides of the asymmetric core along the direction in which the first waveguide 20 and the second waveguide 30 overlap. The core 31 may have a first surface 31a located on the substrate 50 side and a second surface 31b located on the opposite side of the first surface 31a. The claddings 33 and 34 may be positioned in contact with the first surface 31a and the second surface 31b, respectively.

Cores 21 and 31 and claddings 22, 23, 33 and 34 may comprise a dielectric. The cores 21 and 31 are also called dielectric lines. The dielectric constant of core 21 may be higher than the dielectric constant of each of clads 22 and 23 . The relative permittivity of core 31 may be higher than the relative permittivity of each of clads 33 and 34 . The clad 23 and clad 33 may be made of the same dielectric material. The clad 23 and the clad 33 may be constructed integrally. When clad 23 and clad 33 are integrally formed, formation of isolator 10 can be facilitated. The dielectric constants of cores 21 and 31 and claddings 22, 23, 33 and 34 may be higher than that of air. Leakage of electromagnetic waves from the first waveguide 20 and the second waveguide 30 is suppressed by making the dielectric constants of the cores 21 and 31 and the claddings 22, 23, 33 and 34 higher than the dielectric constant of air. can be As a result, loss due to electromagnetic waves radiated from the isolator 10 to the outside can be reduced.

The core 21 or 31 may be made of silicon (Si), for example. The cladding 22, 23, 33 or 34 may consist of quartz glass (SiO2), for example. The dielectric constants of silicon and fused silica are about 12 and about 2, respectively. Silicon can propagate electromagnetic waves having near-infrared wavelengths from about 1.2 μm to about 6 μm with low loss. If the core 21 or 31 is made of silicon, it can propagate an electromagnetic wave having a wavelength of 1.3 μm band or 1.55 μm band used in optical communication with low loss.

A first waveguide 20 comprising a core 21 and claddings 22 and 23 and a second waveguide 30 comprising an asymmetric core and claddings 33 and 34 meet the waveguide conditions in a single mode. may be satisfied. When the first waveguide 20 and the second waveguide 30 satisfy the waveguide conditions in a single mode, the waveforms of signals propagating through the first waveguide 20 and the second waveguide 30 are less likely to collapse. The isolator 10 that combines the first waveguide 20 and the second waveguide 30 satisfying the waveguiding conditions in a single mode can be suitable for optical communications.

The dielectric constant of the core 21 or 31 may be uniformly distributed along the Z-axis direction, or may be distributed so as to vary along the Z-axis direction. For example, the relative permittivity of the core 21 may be distributed such that it is highest in the central portion in the Z-axis direction and decreases as it approaches the claddings 22 and 23 . In this case, the core 21 can propagate electromagnetic waves on the same principle as a graded-index optical fiber.

An electromagnetic wave input to the core 21 from the first end 201 of the first waveguide 20 via the first port 211 is transmitted to the second end of the first waveguide 20 extending along the X-axis. 202. The direction from the first end 201 to the second end 202 is also called the first direction. Electromagnetic waves propagating in core 21 may migrate to core 31 of second waveguide 30 at a rate dependent on the coupling coefficient based on the distance propagated in core 21 in the first direction. The coupling coefficient when the electromagnetic wave propagates in the core 21 in the first direction is also called the first coupling coefficient.

The electromagnetic wave input to the core 21 from the second end 202 of the first waveguide 20 via the second port 212 is transmitted through the core 21 of the first waveguide 20 extending along the X-axis. 201. The direction from the second end 202 to the first end 201 is also called the second direction. The electromagnetic wave propagating in the core 21 propagates to the core 31 of the second waveguide 30 at a rate corresponding to the coupling coefficient based on the distance propagated in the second direction in the core 21 . The coupling coefficient when the electromagnetic wave propagates in the core 21 in the second direction is also referred to as the second coupling coefficient.

The asymmetric core of the second waveguide 30 may have different propagation characteristics for electromagnetic waves propagating in a first direction and for electromagnetic waves propagating in a second direction. The first coupling coefficient and the second coupling coefficient can be different from each other if the propagation characteristics of the asymmetric core are different based on the propagation direction of the electromagnetic wave. That is, the non-reciprocal member 32 can have the first coupling coefficient and the second coupling coefficient different.

The non-reciprocal member 32 may be made of a material that has different propagation characteristics for electromagnetic waves propagating in the first direction and in the second direction. A material having different propagation characteristics depending on the propagation direction of an electromagnetic wave is also called a non-reciprocal material. The non-reciprocal member 32 may be composed of magnetic material such as magnetic garnet, ferrite, iron, cobalt, or the like. The dielectric constant of the non-reciprocal member 32 can be represented by a tensor as in Equation (1).

テンソルの各要素は、複素数で表されてよい。各要素の添え字として用いられている数字は、Ｘ軸、Ｙ軸及びＺ軸に対応してよい。要素として複素数を有し、比誘電率を表すテンソルは、複素比誘電率テンソルともいう。

Each element of the tensor may be represented by a complex number. The numbers used as subscripts for each element may correspond to the X, Y and Z axes. A tensor that has complex numbers as elements and represents a dielectric constant is also called a complex dielectric constant tensor.

The non-reciprocal member 32 may comprise a concentration of non-reciprocal material. The predetermined concentration may vary in a cross-section intersecting the X-axis. The predetermined concentration may change at least partially along the polarization direction of the electromagnetic waves input to the isolator 10 .

The second waveguide 30 may have the shape shown in FIG. 3 in a cross section that intersects the X axis. Let A be the dimension of the second waveguide 30 in the Y-axis direction. Let B be the dimension in the Z-axis direction of the core 31 and the non-reciprocal member 32 . Let C be the dimension of the non-reciprocal member 32 in the Y-axis direction. It is assumed that the non-reciprocal member 32 is aligned with the core 31 along the Y-axis and is biased toward the negative direction of the Y-axis. It is assumed that the second waveguide 30 extends in the X-axis direction so that the dimension in the X-axis direction has a predetermined length. The non-reciprocal member 32 is assumed to have a dielectric constant represented by a complex dielectric constant tensor.

For the second waveguide 30 illustrated in FIG. 3, the difference between the phase of the electromagnetic wave propagating in the first direction and the phase of the electromagnetic wave propagating in the second direction in the second waveguide 30 can be calculated by simulation. The difference between the phase of the electromagnetic wave propagating in the first direction and the phase of the electromagnetic wave propagating in the second direction is also called phase difference. As shown in the graph of FIG. 4, the phase difference can vary depending on the value of C/A. The value of C/A represents the proportion occupied by the non-reciprocal member 32 when the asymmetric core is viewed along the Z axis. According to the graph of FIG. 4, the phase difference can be large when the value of C/A approaches 0.5. The phase difference can be adjusted by changing the value of C/A. When the phase difference is large, the nonreciprocity of the electromagnetic wave attenuation can be large. That is, the greater the phase difference, the greater the difference between the amount of attenuation when the electromagnetic wave propagates in the first direction and the amount of attenuation when it propagates in the second direction. By adjusting the value of C/A, the second waveguide 30 can be configured to have a property that the amount of attenuation of electromagnetic waves varies according to the propagation direction of the electromagnetic waves. The property that the amount of attenuation of an electromagnetic wave differs depending on the propagation direction of the electromagnetic wave is also called non-reciprocity. When the value of C/A approaches 0.5, it can be said that the asymmetric core has a low degree of symmetry. That is, the non-reciprocity of the second waveguide 30 can be increased by reducing the symmetry of the asymmetric core.

The second waveguide 30 may have the shape shown in FIG. 5 in a cross section that intersects the X axis. Let A be the dimension of the second waveguide 30 in the Y-axis direction and the dimension of the core 31 in the Y-axis direction. Let B be the dimension of the core 31 in the Z-axis direction. Let C and D be the dimensions of the non-reciprocal member 32 in the Y-axis direction and the Z-axis direction, respectively. The non-reciprocal member 32 is located on the positive side of the Z-axis with respect to the core 31 and is biased toward the negative side of the Y-axis in the second waveguide 30 . It is assumed that the second waveguide 30 extends in the X-axis direction so that the dimension in the X-axis direction has a predetermined length. The non-reciprocal member 32 is assumed to have a dielectric constant represented by a complex dielectric constant tensor.

For the second waveguide 30 illustrated in FIG. 5, the difference between the phase of the electromagnetic wave propagating through the second waveguide 30 in the first direction and the phase of the electromagnetic wave propagating in the second direction can be calculated by simulation. As shown in the graph of FIG. 6, the phase difference can vary depending on the value of C/A. The relationship between the phase difference and the value of C/A can change according to the value of D/B. According to the graph of FIG. 6, the phase difference can become large when the value of C/A approaches 0.5. The phase difference can be adjusted by changing the value of C/A. According to the graph of FIG. 6, when the value of D/B increases, the phase difference can increase. The phase difference can be adjusted by changing the value of D/B. The second waveguide 30 can be configured to have nonreciprocity by adjusting the values of C/A and D/B. When the value of D/B increases within the range illustrated in FIG. 6, it can be said that the degree of symmetry of the asymmetric core decreases. That is, the non-reciprocity of the second waveguide 30 can be increased by reducing the symmetry of the asymmetric core.

The second waveguide 30 may have the shape shown in FIG. 7 in a cross section that intersects the X axis. In this case the asymmetric core is not point symmetrical. Therefore, the second waveguide 30 illustrated in FIG. 7 may have non-reciprocity.

The non-reciprocity of the second waveguide 30 also varies depending on the aspect ratio of the core 31 . 26 and 27 show the difference in magnitude of nonreciprocity due to the configuration of the second waveguide 30. FIG. FIG. 26 shows the relationship between the dielectric constant and the magnitude of nonreciprocity when the aspect ratio of the core 31 is 1. In FIG. From this, it can be said that the dielectric constant of the core 31 is desirably 6 or more at the operating frequency. FIG. 27 shows the relationship between the aspect ratio of the core 31 and the magnitude of non-reciprocity. From this, it can be said that the aspect ratio of the core 31 is preferably between 0.8 and 1.2.

When one waveguide of the parallel waveguides has nonreciprocity, the maximum value of the coupling coefficient when the electromagnetic wave propagates in the first direction is different from the maximum value of the coupling coefficient when the electromagnetic wave propagates in the second direction. sell. For example, as shown in FIG. 8, the maximum value of the coupling coefficient between the first waveguide 20 and the second waveguide 30 when the electromagnetic wave propagates in the first direction can be configured to be a value close to 0. . For example, as shown in FIG. 9, the maximum value of the coupling coefficient between the first waveguide 20 and the second waveguide 30 when the electromagnetic wave propagates in the second direction can be configured to be a value close to 1. . Since the maximum value of the coupling coefficient is different for each propagation direction of the electromagnetic wave, the transmittance of the electromagnetic wave can be different for each propagation direction of the electromagnetic wave. In FIGS. 8 and 9, the horizontal axis and the vertical axis respectively represent the traveling distance of the electromagnetic wave in the parallel waveguide and the coupling coefficient.

When the second waveguide 30 has non-reciprocity, the coupling coefficient between the first waveguide 20 and the second waveguide 30 may differ according to the propagation direction of electromagnetic waves. That is, if the second waveguide 30 is non-reciprocal, the first coupling coefficient of the isolator 10 can differ from the second coupling coefficient. By adjusting the magnitude of the non-reciprocity of the second waveguide 30, the second coupling coefficient can be made larger than the first coupling coefficient.

When the electromagnetic wave input from the first port 211 to the first waveguide 20 propagates in the first direction, at least part of the electromagnetic wave transferred to the second waveguide 30 among the input electromagnetic waves reaches the end portion 302 . sell. The electromagnetic wave reaching the end 302 of the second waveguide 30 may be radiated to the outside from the end 302 or reflected at the end 302 without being output from the second port 212 of the first waveguide 20 . When the first coupling coefficient is large, a proportion of electromagnetic waves that are transferred to the second waveguide 30 and reach the end portion 302 of the electromagnetic waves input to the first waveguide 20 may be increased. In this case, the ratio of the electromagnetic wave output from the second port 212 to the electromagnetic wave input to the first waveguide 20 may be reduced. That is, the ratio of the intensity of the electromagnetic wave output from the second port 212 to the intensity of the electromagnetic wave input to the first port 211 can be reduced. The ratio of the intensity of the electromagnetic wave output from the second port 212 to the intensity of the electromagnetic wave input to the first port 211 is also referred to as the transmittance of the isolator 10 with respect to the electromagnetic wave propagating in the first direction. If the first coupling coefficient is large, the transmittance for electromagnetic waves propagating in the first direction may be low. On the other hand, when the first coupling coefficient is small, the proportion of the electromagnetic wave transferred to the second waveguide 30 may be small, so the transmittance of the electromagnetic wave propagating in the first direction may be high.

The electromagnetic wave that is input from the second port 212 to the first waveguide 20 and propagates in the second direction can be affected by the isolator 10 in the same way as the electromagnetic wave that propagates in the first direction is affected by the isolator 10 . Due to this action, part of the electromagnetic wave propagating in the second direction can reach the end 301 of the second waveguide 30 . If the second coupling coefficient is large, the transmittance for electromagnetic waves propagating in the second direction may be low. When the second coupling coefficient is small, the transmittance for electromagnetic waves propagating in the second direction can be high.

If the first coupling coefficient and the second coupling coefficient are different, the transmittance for electromagnetic waves propagating in the first direction may be different from the transmittance for electromagnetic waves propagating in the second direction. In other words, the isolator 10 can function to facilitate the propagation of electromagnetic waves in one direction and to hinder the propagation of electromagnetic waves in the opposite direction by making the first coupling coefficient and the second coupling coefficient different. When the second coupling coefficient is greater than the first coupling coefficient, the isolator 10 can function to facilitate propagation of electromagnetic waves in the first direction and to inhibit propagation of electromagnetic waves in the second direction. When the first coupling coefficient and the second coupling coefficient are approximately 0 and approximately 1, respectively, the difference between the transmittance for electromagnetic waves propagating in the first direction and the transmittance for electromagnetic waves propagating in the second direction can be increased. . As a result, the functionality of the isolator 10 can be improved.

If one of the parallel waveguides has nonreciprocity, the coupling length of the parallel waveguides for electromagnetic waves propagating in the first direction can be different from the coupling length of the parallel waveguides for electromagnetic waves propagating in the second direction. For example, as shown in FIG. 8, the coupling length for electromagnetic waves propagating in the first direction in isolator 10 can be represented as L1. For example, as shown in FIG. 9, the coupling length for electromagnetic waves propagating in the second direction in isolator 10 can be represented as L2. Isolator 10 may be configured such that L1 and L2 are different.

If the length of the two waveguides along each other in parallel waveguides is equal to the coupling length, then the coupling coefficient can reach a maximum value. For example, in parallel waveguides having the relationship shown in the graph of FIG. 8, the coupling coefficient can reach a maximum value if the two waveguides have a length along each other of L1. If the length of the two waveguides along each other is equal to twice the coupling length, the coupling coefficient can be at a local minimum. For example, in parallel waveguides having the relationship shown in FIG. 8, if the two waveguides have a length along each other of 2L 1 , the coupling coefficient can be a local minimum.

The relationship shown in the graph of FIG. 8 can be repeated in regions where the electromagnetic wave travels longer. That is, if the length of the two waveguides along each other is an odd multiple of L1, the coupling coefficient can be maximal. If the length of the two waveguides along each other is an even multiple of L1, then the coupling coefficient can be a local minimum. Even in parallel waveguides having the relationship shown in FIG. can be a value. L1 and L2 are lengths that can be the shortest coupling lengths in parallel waveguides, and are also called unit coupling lengths. That is, the bond length may be an odd multiple of the unit bond length.

The first coupling coefficient and the second coupling coefficient can be adjusted by adjusting the lengths of the first waveguide 20 and the second waveguide 30 along each other. The length of the first waveguide 20 and the second waveguide 30 along each other may be substantially the same as an odd multiple of the unit coupling length for the electromagnetic wave propagating in the second direction. By doing so, the second coupling coefficient can be increased. The length of the first waveguide 20 and the second waveguide 30 along each other may be substantially the same as an even multiple of the unit coupling length for the electromagnetic wave propagating in the first direction. By doing so, the first coupling coefficient can be reduced. By doing so, the second coupling coefficient may be larger than the first coupling coefficient.

Of the electromagnetic waves that are input to one port of the isolator 10, the amount of electromagnetic waves that are not output from the other port is also called attenuation. When the amount of attenuation of electromagnetic waves is large, it can be said that the transmittance of the electromagnetic waves is low. The attenuation of the electromagnetic waves traveling in the first direction and the second direction in the isolator 10 can be calculated by simulation using the finite element method or the like. In FIG. 10, the relationship between the attenuation amount of the electromagnetic wave propagating in the second direction and the frequency of the electromagnetic wave is represented by a solid line graph represented by S12. The relationship between the attenuation amount of the electromagnetic wave propagating in the first direction and the frequency of the electromagnetic wave is represented by a broken line graph represented by S21. The horizontal and vertical axes of the graph represent the frequency of the electromagnetic wave propagating through the first waveguide 20 and the attenuation of the electromagnetic wave, respectively. Attenuation of electromagnetic waves shall be expressed in units of decibels (dB). The upper plot along the vertical axis indicates less electromagnetic wave attenuation. A lower plot along the vertical axis indicates a greater amount of electromagnetic wave attenuation.

As shown in FIG. 10, in a predetermined frequency band represented by fb1, the attenuation of electromagnetic waves propagating in the second direction can be greater than the attenuation of electromagnetic waves propagating in the first direction. In this case, the isolator 10 facilitates the propagation of electromagnetic waves in a predetermined frequency band from the first port 211 to the second port 212, while making it difficult to propagate the electromagnetic waves from the second port 212 to the first port 211. can function. The predetermined frequency band in which the isolator 10 can function to vary the attenuation amount for each propagation direction of the electromagnetic wave is also called the operating frequency of the isolator 10 . The operating frequency of isolator 10 can be arbitrarily determined based on the configuration of isolator 10 . That is, at any operating frequency, the second coupling coefficient can be made larger than the first coupling coefficient.

The isolator 10 according to the present embodiment has a function of varying the transmittance for electromagnetic waves propagating in the first direction and the transmittance for electromagnetic waves propagating in the second direction. Such a function can also be implemented by an isolator 90 according to a comparative example shown in FIG.

The isolator 90 comprises an input 91 , a splitter-coupler 92 , a reciprocal phase shifter 93 , a nonreciprocal phase-shifter 94 , a splitter-coupler 95 and an output 96 . An electromagnetic wave input from input terminal 91 is branched by branch coupler 92 and propagates to reciprocal phase shifter 93 and non-reciprocal phase shifter 94 . The electromagnetic waves are phase-shifted by a reciprocal phase shifter 93 and a non-reciprocal phase shifter 94 respectively, combined by a branch coupler 95 and propagated to an output terminal 96 . Reciprocal phase shifter 93 and non-reciprocal phase shifter 94 may be configured such that an electromagnetic wave input from input terminal 91 is output from output terminal 96 . On the other hand, the electromagnetic wave input from the output terminal 96 is branched by the branch coupler 95 and propagates to the reciprocal phase shifter 93 and the non-reciprocal phase shifter 94 . The electromagnetic waves are phase-shifted by the reciprocal phase shifter 93 and the non-reciprocal phase shifter 94 respectively, coupled by the branch coupler 92 and propagated to the input terminal 91 . The reciprocal phase shifter 93 and the non-reciprocal phase shifter 94 can be configured such that an electromagnetic wave input from the output terminal 96 is not output from the input terminal 91 .

In the isolator 90 according to the comparative example, the loss of electromagnetic waves in the non-reciprocal phase shifter 94 and branch couplers 92 and 95 is relatively large. On the other hand, in the isolator 10 according to this embodiment, electromagnetic waves propagate through the core 31 in principle. As a result, the electromagnetic wave loss in the isolator 10 according to the present embodiment can be smaller than the electromagnetic wave loss in the isolator 90 according to the comparative example. In other words, the isolator 10 according to the present embodiment can function such that the electromagnetic wave can be easily transmitted in one direction and difficult to be transmitted in the opposite direction while reducing the loss of the electromagnetic wave. In the isolator 10 according to this embodiment, the first waveguide 20 and the second waveguide 30 are also referred to as reciprocal lines and non-reciprocal lines, respectively.

In the isolator 90 according to the comparative example, the non-reciprocal phase shifter 94 and the branch couplers 92 and 95 are mounted so as to be connected in series, which makes it difficult to miniaturize. On the other hand, the isolator 10 according to the present embodiment is easily miniaturized on the substrate 50 because the first waveguide 20 and the second waveguide 30 overlap each other. As a result, the isolator 10 according to this embodiment can be integrated and mounted on the substrate 50 . In other words, the isolator 10 according to the present embodiment can function so that electromagnetic waves can be easily transmitted in one direction and difficult to be transmitted in the opposite direction due to the integrated configuration.

As shown in FIG. 12 , the isolator 10 may further include antennas 60 for radiating electromagnetic waves at the ends 301 and 302 of the second waveguide 30 . Antenna 60 can efficiently radiate electromagnetic waves that reach ends 301 and 302 . Antenna 60 makes it difficult for electromagnetic waves to be reflected at ends 301 and 302 . As a result, the functionality of the isolator 10 can be improved.

The second waveguide 30 may have cut surfaces at the ends 301 and 302 . Cut surfaces at both ends of the second waveguide 30 may function as antennas 60 . The normal vector of the cut surface at the ends 301 and 302 of the second waveguide 30 may be configured to point in a direction inclined with respect to the X-axis. The angle between the orientation of the normal vector of the cutting plane and the X-axis direction may be greater than 0 degrees. In other words, the normal vector of the cut surface may have a component in the direction intersecting the propagation direction of the electromagnetic wave in the second waveguide 30 . The angle between the direction of the normal vector of the cutting plane and the X-axis direction may be close to 90 degrees. When the angle between the direction of the normal vector of the cut surface and the X-axis is close to 90 degrees, the second waveguide 30 has a tapered shape in which the thickness gradually decreases at the ends 301 and 302 . As a result, the reflectivity of electromagnetic waves at ends 301 and 302 can be reduced. When the second waveguide 30 is positioned above the first waveguide 20 when viewed from the substrate 50 , the cut surfaces at both ends of the second waveguide 30 are likely to be formed by processing on the substrate 50 .

As shown in FIG. 13 , the isolator 10 may further include electromagnetic wave absorbing members 70 outside the ends 301 and 302 of the second waveguide 30 . The electromagnetic wave absorbing member 70 can absorb electromagnetic waves radiated from the ends 301 and 302 . By doing so, the electromagnetic waves radiated from the isolator 10 are less likely to affect other circuits located around the isolator 10 .

As shown in FIG. 14, the isolator 10 may comprise multiple second waveguides 30 . The number of second waveguides 30 is not limited to two, and may be three or more. Each second waveguide 30 may be coupled in series with the first waveguide 20 . The length of each of the second waveguides 30 and the first waveguide 20 along each other may be substantially the same as the coupling length of the electromagnetic wave propagating in the second direction. By providing the plurality of second waveguides 30 in the isolator 10 , electromagnetic waves propagating in the second direction are more likely to be radiated from the second waveguides 30 and less likely to reach the first end 201 from the second end 202 . As a result, it is possible to improve the function of the isolator 10, which facilitates propagation of electromagnetic waves in one direction and makes it difficult to propagate them in the opposite direction.

As shown in FIG. 15, first waveguide 20 may include match adjustment circuitry 25 . The matching adjustment circuit 25 can adjust the propagation characteristics for each frequency of electromagnetic waves propagating in the first waveguide 20 . The matching adjustment circuit 25 may be provided as a structure in which the core 21 has a plurality of holes 24, as shown in FIG. 16, for example. In FIG. 16, the second waveguide 30 is indicated by a two-dot chain phantom line. The hole 24 may pass through the core 21 in the Y-axis direction. The hole 24 may penetrate from the first surface 21a of the core 21 to the second surface 21b. The hole 24 may penetrate to the claddings 22 and 23 in the Y-axis direction. The holes 24 may be arranged in the X-axis direction. That is, the holes 24 may be arranged in the direction in which the core 21 extends. The number of holes 24 is not limited to nine. The shape of the hole 24 when viewed from the Z-axis direction is not limited to a rectangular shape, and may be a circular shape, a polygonal shape, or other various shapes.

The holes 24 may be periodically arranged in the X-axis direction. When the core 21 has holes 24 periodically arranged in the X-axis direction, the first waveguide 20 including the core 21 can constitute a Bragg diffraction grating. When an electromagnetic wave is input to the first waveguide 20 from the first port 211 , among the input electromagnetic waves, an electromagnetic wave having a wavelength satisfying the Bragg reflection condition may be reflected back to the first port 211 . On the other hand, electromagnetic waves with other wavelengths can propagate towards the second port 212 . That is, the first waveguide 20 having the holes 24 can function as a filter for electromagnetic waves having a predetermined wavelength.

When the first waveguide 20 includes the matching adjustment circuit 25, for example, as shown in FIG. It can be greater than the attenuation of propagating electromagnetic waves. fb2 may be a frequency band different from the frequency band indicated by fb1 in FIG. By adjusting the configuration of the matching adjustment circuit 25, fb2 can be set to a frequency band higher or lower than the frequency band indicated by fb1. Regarding the graph of FIG. 17, the description of matters common to the graph of FIG. 10 is omitted.

Non-reciprocal member 32 may be configured to have non-reciprocal properties when a magnetic field in a predetermined direction is applied. The non-reciprocal member 32 may be configured to be non-reciprocal when a magnetic field having a Z-axis component is applied. The predetermined direction is not limited to the Z-axis direction, and may be various directions. The predetermined direction may be determined based on the cross-sectional shape of the asymmetric core or the degree of symmetry. The non-reciprocity member 32 may be configured to have different magnitudes of non-reciprocity in response to changes in magnetic field strength or orientation. By configuring the isolator 10 in this way, it is possible to control whether or not the non-reciprocity member 32 has non-reciprocity, or the amount of non-reciprocity that the non-reciprocity member 32 has.

As shown in FIG. 18, the isolator 10 may further include a magnetic field application section 80 that applies a magnetic field. The magnetic field applying unit 80 may be positioned in the positive direction of the Z-axis with respect to the second waveguide 30 . The magnetic field applying unit 80 may be positioned on the substrate 50 side with respect to the second waveguide 30 via the first waveguide 20 . The magnetic field applying section 80 may be positioned in a manner different from the manner illustrated in FIG. 18 . The magnetic field applying section 80 may be a permanent magnet such as a ferrite magnet or a neodymium magnet. The magnetic field applying section 80 may be an electromagnet.

Propagation modes of electromagnetic waves in parallel waveguides can include an even mode and an odd mode. The even mode is a mode in which the electric fields of propagating electromagnetic waves are oriented in the same direction in each waveguide that constitutes a parallel waveguide. The odd mode is a mode in which the electric fields of propagating electromagnetic waves are directed in opposite directions in each waveguide that constitutes the parallel waveguides. Electromagnetic waves can propagate in parallel waveguides based on the effective refractive index of the parallel waveguides. The effective refractive index of a parallel waveguide can be determined based on the shape of each waveguide that constitutes the parallel waveguide, the dielectric constant of the material that constitutes the waveguide, the propagation mode of electromagnetic waves, or the like. The effective refractive index of a parallel waveguide when electromagnetic waves propagate in an even mode is also called an even-mode refractive index. The effective refractive index of a parallel waveguide when electromagnetic waves propagate in the odd mode is also called the odd mode refractive index. The even and odd mode indices shall be denoted as neven and nodd, respectively. The coupling length in parallel waveguides can be represented by the following equation (2).

（Ｌ：結合長、ｍ：奇数、λ0：真空中の波長）
アイソレータ１０は、光を入力する構成と組み合わされて使用されうる。この場合、アイソレータ１０は、光アイソレータともいう。図１９に示されるように、光源装置１００は、アイソレータ１０と、光源１１０と、レンズ１１２と、光源１１０に電力を供給する電源１１４とを含む。光源１１０は、例えば、ＬＤ（Laser Diode）又はＶＣＳＥＬ（Vertical Cavity SurfaceEmitting LASER）等の半導体レーザであってよい。光源１１０は、基板５０上に形成されてよい。

(L: bond length, m: odd number, λ0: wavelength in vacuum)
Isolator 10 may be used in combination with a light input configuration. In this case, the isolator 10 is also called an optical isolator. As shown in FIG. 19 , light source device 100 includes isolator 10 , light source 110 , lens 112 , and power supply 114 that supplies power to light source 110 . The light source 110 may be, for example, a semiconductor laser such as an LD (Laser Diode) or a VCSEL (Vertical Cavity Surface Emitting LASER). Light source 110 may be formed on substrate 50 .

The lens 112 converges the light output from the light source 110 to the first port 211 of the first waveguide 20 of the isolator 10 . The shape of the lens 112 is not particularly limited. Lens 112 may be a balllet lens, a biconvex lens, a plano-convex lens, or the like. Lens 112 may be constructed of a material that is optically transparent to the wavelengths of light being propagated.

It can be said that the light source 110 is optically connected to the first port 211 through the lens 112 . The light source 110, the lens 112, and the first port 211 may be fixed in mutual positional relationship so as not to cause misalignment. Light source 110 , lens 112 and first port 211 may be integrally integrated onto substrate 50 . The light source 110 may input into the first port 211 linearly polarized light whose polarization direction is the Y-axis direction. The light source device 100 may not have the lens 112 . If the light source device 100 does not have the lens 112 , the light emitted from the light source 110 may be directly input to the first port 211 .

The method of inputting light from the light source 110 to the first port 211 is not limited to the method of inputting the light from the light source 110 directly or via the lens 112 . Light source 110 may be coupled to first port 211 via an optical fiber. The method of inputting the light propagating through the optical fiber into the first port 211 includes a method of connecting a free space via a lens or the like, a method of directly abutting the output surface of the optical fiber and the first port 211, or a connection guide. Various methods may be included, such as using wave path 120 (see FIG. 20).

By including the light source 110 and the isolator 10 , the light source device 100 can output the light output from the light source 110 in the first direction through the isolator 10 . On the other hand, the light source device 100 can make it difficult for the light returning in the second direction to propagate through the isolator 10 and make it difficult for the light to return to the light source 110 side. As a result, light can be efficiently output.

In the light source device 100, the first waveguide 20 may be configured to be in contact with the substrate surface 50a. That is, the first waveguide 20 may be positioned closer to the substrate surface 50a than the second waveguide 30 is. By doing so, the light source 110 integrated on the substrate 50 and the first port 211 can be easily optically connected.

As shown in FIG. 20, connection waveguide 120 may have core 121 and clads 122 and 123 . The dielectric constant of the core 121 may be substantially the same as the dielectric constant of the core 21 of the first waveguide 20 . Core 121 may be made of the same material as core 21 . The dielectric constant of the claddings 122 and 123 may be lower than that of the core 121 . The relative permittivity of the clads 122 and 123 may be substantially the same as the relative permittivity of the clads 22 and 23 of the first waveguide 20 . Claddings 122 and 123 may be made of the same material as clads 22 and 23 . The end face of the core 121 on the positive side of the X axis is in contact with the first port 211 located on the end face of the core 21 on the negative side of the X axis. The thickness of the core 121 in the Z-axis direction may be greater than the thickness of the core 21 of the first waveguide 20 in the Z-axis direction. The thickness of the core 121 in the Z-axis direction may be substantially the same as the thickness of the core 21 of the first waveguide 20 in the Z-axis direction.

The light input to the core 121 from the negative side of the X-axis may be linearly polarized light with the Y-axis direction as the polarization direction. In other words, the polarization direction of light input to the core 121 from the negative direction side of the X axis may be parallel to the substrate surface 50a. When the light source 110 integrated on the substrate 50 is a semiconductor laser, the polarization direction of the light emitted by the semiconductor laser is parallel to the substrate surface 50a. Semiconductor lasers are easy to integrate on substrate 50 . As a result, formation of the light source device 100 can be facilitated.

At the connecting portion between the core 121 and the core 21 , the width of the core 121 in the Y-axis direction may be substantially the same as the width of the core 21 in the Y-axis direction. When the widths of the cores 121 and 21 in the Y-axis direction change discontinuously at the connecting portion between the cores 121 and 21, the light polarized in the Y-axis direction is likely to be emitted from the connecting portion. At the connecting portion between the cores 121 and 21, the widths in the Y-axis direction of the cores 121 and 21 are substantially the same, so that loss due to radiation can be reduced.

As shown in FIG. 21 , the core 121 of the connection waveguide 120 may be configured in a tapered shape such that the thickness in the Z-axis direction becomes thinner as it approaches the connecting portion with the core 21 of the first waveguide 20 . By doing so, when light whose polarization direction is in the Y-axis direction is input to the connection waveguide 120 , the input light can be matched with the propagation mode of the light in the core 21 . When light is incident on the core 21 from the core 121, mismatching of the propagation mode of light is less likely to occur. As a result, the occurrence of loss when light enters the core 21 from the core 121 can be reduced.

As shown in FIG. 22, an isolator 10 according to another embodiment includes a first waveguide 20 and a second waveguide 20 arranged on a substrate 50 along a substrate surface 50a (see FIG. 1 etc.). and a wave path 30 . The isolator 10 may further comprise a first waveguide 20 and a second surrounding cladding 40 .

As shown in FIG. 23, the first waveguide 20 has a first end 201 and a second end 202 on the positive direction side and the negative direction side of the X-axis, respectively. The first waveguide 20 has a first port 211 and a second port 212 through which electromagnetic waves are input and output at a first end 201 and a second end 202, respectively. An electromagnetic wave input from the first port 211 to the first waveguide 20 travels along the X-axis toward the second port 212 . An electromagnetic wave input from the second port 212 to the first waveguide 20 travels along the X-axis toward the first port 211 . Each of the first port 211 and the second port 212 may be configured as an end face of the core 21 (see FIG. 24), or may be configured as a coupler that is connected to an external device and capable of propagating electromagnetic waves.

The second waveguide 30 has ends 301 and 302 on the positive and negative sides of the X-axis, respectively. In other words, the second waveguide 30 has two ends. The second waveguide 30 is positioned along the first waveguide 20 and coupled with the first waveguide 20 to each other. The number of second waveguides 30 is not limited to one, and may be two or more.

The first waveguide 20 and the second waveguide 30 may be positioned along each other in at least part of the extending direction. The first waveguide 20 and the second waveguide 30 may be positioned parallel to each other in at least part of the extending direction. The first waveguide 20 or the second waveguide 30 may have a linear structure. The first waveguide 20 and the second waveguide 30 can be easily formed on the substrate 50 by having such simple structures.

In the second waveguide 30 , the electromagnetic waves transferred from the first waveguide 20 propagate in the second waveguide 30 in the same direction as in the first waveguide 20 . In the second waveguide 30, when an electromagnetic wave reaches the end 301 or 302, the electromagnetic wave can be radiated from the end 301 or 302 or reflected at the end 301 or 302 to travel in the opposite direction.

As shown in FIG. 24, the first waveguide 20 has a core 21 and clads 22 and 23 . Core 21 and clads 22 and 23 extend in the X-axis direction. The clads 22 and 23 are located on the negative and positive Z-axis sides of the core 21 . The clad 22 is positioned on the substrate 50 side when viewed from the core 21 . The clad 23 is located on the opposite side of the substrate 50 as viewed from the core 21 . It can also be said that the clad 22 , the core 21 and the clad 23 are laminated in order when viewed from the substrate 50 . The core 21 may have a first surface 21a located on the side of the substrate 50 and a second surface 21b located on the opposite side of the first surface 21a. The claddings 22 and 23 may be positioned in contact with the first surface 21a and the second surface 21b, respectively.

The second waveguide 30 comprises a core 31, a non-reciprocal member 32, and claddings 33 and 34. As shown in FIG. Core 31, non-reciprocal member 32, and clads 33 and 34 extend in the X-axis direction. The non-reciprocal members 32 may be positioned side by side with respect to the core 31 in the positive or negative direction of the Y-axis. In other words, the core 31 and the non-reciprocal member 32 may be positioned side by side within the substrate plane. The non-reciprocal member 32 may be positioned on the positive or negative side of the Z-axis with respect to the core 31 .

As shown in FIG. 24, the shapes of the core 31 and the non-reciprocal member 32 viewed from a cross section intersecting the X-axis are configured so as not to be point symmetrical. The shapes of the core 31 and the non-reciprocal member 32 may be further configured so as not to be line symmetrical. The core 31 and the non-reciprocal member 32 are also collectively referred to as an asymmetric core. The asymmetric core comprises core 31 and non-reciprocal member 32 . The asymmetric core may have non-reciprocal members 32 in at least a portion of the cross-section that intersects the X-axis. Core 31 may be configured to include at least one type of dielectric. The non-reciprocal member 32 may contact the surface of the at least one dielectric substrate 50 or the opposite surface thereof.

As shown in FIG. 24, the first waveguide 20 may include a core 21 as a first dielectric and a clad 40 as a second dielectric. The second dielectric may be a different type of dielectric than the first dielectric. The first dielectric and the second dielectric may be arranged in a direction parallel to the substrate surface 50a. The second waveguide 30 may include a core 31 as a third dielectric and a clad 40 as a fourth dielectric. The fourth dielectric may be a different type of dielectric than the third dielectric. The third dielectric, the fourth dielectric, and the non-reciprocal member 32 may be arranged in a direction parallel to the substrate surface 50a. The third dielectric, the fourth dielectric, and the non-reciprocal member 32 may be in contact with each other in the in-plane direction of the substrate surface 50a. At least one of the claddings 22 and 23 of the first waveguide 20 may be integral with at least one of the claddings 33 and 34 of the second waveguide 30 . At least one of the clads 22 and 23 of the first waveguide 20 may be integral with the clad 40 . At least one of the clads 33 and 34 of the second waveguide 30 may be integral with the clad 40 .

Even when the first waveguide 20 and the second waveguide 30 are arranged along the substrate surface 50a, the isolator 10 has the following advantages compared to the isolator 90 according to the comparative example shown in FIG. It can be miniaturized. The reason isolator 10 can be miniaturized is that branch-combiner 92 is not required.

In the present embodiment, as exemplified in FIG. 25, in a predetermined frequency band represented by fb3, the attenuation of electromagnetic waves propagating in the first direction is greater than the attenuation of electromagnetic waves propagating in the second direction. can grow. fb3 may be a frequency band different from the frequency band indicated by fb1 in FIG. 10 or fb2 in FIG. Regarding the graph of FIG. 25, the description of items common to the graphs of FIGS. 10 and 17 is omitted.

In FIG. 22, even if the end of the second waveguide 30 is surrounded by the clad 40, the electromagnetic wave propagating through the second waveguide 30 is radiated from the end of the second waveguide 30 to the clad 40. can be

The isolator 10 and light source device 100 according to the present disclosure may be mounted on an optical transmitter having a modulation function. Isolators 10 according to the present disclosure may be used in optical switches or optical amplifiers. Isolators 10 according to the present disclosure may be used in devices. A device comprising an isolator 10 according to the present disclosure may be used for communication in a data center.

Although the embodiments of the present disclosure have been described with reference to the drawings and examples, it should be noted that those skilled in the art can easily make various variations or modifications based on the present disclosure. Therefore, it should be noted that these variations or modifications are included within the scope of this disclosure. For example, functions included in each component or each step can be rearranged so as not to be logically inconsistent, and multiple components or steps can be combined into one or divided. is. Although the embodiments of the present disclosure have been described with a focus on the apparatus, the embodiments of the present disclosure may also be implemented as a method including steps performed by each component of the apparatus. Embodiments according to the present disclosure can also be implemented as a method, a program, or a storage medium recording a program executed by a processor provided in an apparatus. It should be understood that these are also included within the scope of the present disclosure.

Descriptions such as “first” and “second” in the present disclosure are identifiers for distinguishing the configurations. Configurations that are differentiated in descriptions such as "first" and "second" in this disclosure may interchange the numbers in that configuration. For example, a first port can exchange the identifiers "first" and "second" with a second port. The exchange of identifiers is done simultaneously. The configurations are still distinct after the exchange of identifiers. Identifiers may be deleted. Configurations from which identifiers have been deleted are distinguished by codes. The description of identifiers such as “first” and “second” in this disclosure should not be used as a basis for interpreting the order of the configuration or the existence of lower numbered identifiers.

In the present disclosure, the X-axis, Y-axis, and Z-axis are provided for convenience of explanation and may be interchanged with each other. Configurations according to the present disclosure have been described using a Cartesian coordinate system formed by X, Y, and Z axes. The positional relationship of each configuration according to the present disclosure is not limited to an orthogonal relationship.

REFERENCE SIGNS LIST 10 isolator 20 first waveguide 201 first end 202 second end 21 core 211 first port 212 second port 22, 23 clad 24 hole 25 matching circuit 30 second waveguide 301, 302 end 31 core 32 non Reciprocal member 33, 34 clad 40 clad 50 substrate 50a substrate surface 60 antenna 70 electromagnetic wave absorbing member 80 magnetic field applying unit 100 light source device 110 light source 112 lens 114 power supply 120 connection waveguide 121 core 122, 123 clad

Claims (22)

On a substrate having a substrate surface, comprising a first waveguide and a second waveguide positioned side by side along the substrate surface,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the length of the first waveguide for the electromagnetic wave propagating from the second end to the first end. is an odd multiple of the coupling length between the and the second waveguide ,
isolator. On a substrate having a substrate surface, comprising a first waveguide and a second waveguide positioned side by side along the substrate surface,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L representing the length of the second waveguide is the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the second end to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
calculated by
isolator. 3. The isolator according to claim 1, further comprising a magnetic field applying section that applies a magnetic field in a direction intersecting the substrate surface. 4. The isolator according to any one of claims 1 to 3 , wherein the dielectric constant of the core is higher than the dielectric constant of the cladding. the first waveguide includes a first dielectric and a second dielectric of a different type from the first dielectric arranged in a direction parallel to the substrate surface;
the second waveguide includes a third dielectric, a fourth dielectric different in type from the third dielectric, and the non-reciprocal member arranged in a direction parallel to the substrate surface;
5. The isolator according to claim 1 , wherein said third dielectric, said fourth dielectric and said non-reciprocal member are in contact with each other in an in-plane direction of said substrate surface. 6. The isolator of any preceding claim, wherein the cladding of the first waveguide is integral with the cladding of the second waveguide. 7. The isolator according to claim 1 , wherein both ends of said second waveguide function as antennas for radiating electromagnetic waves transferred from said first waveguide. 8. The isolator according to any one of claims 1 to 7 , wherein electromagnetic waves input to said first end and said second end are propagated in a single mode. 9. The isolator according to any one of claims 1 to 8 , wherein a core of each of said first waveguide and said second waveguide has a dielectric constant higher than that of air. 10. The isolator according to any one of claims 1 to 9 , wherein both ends of said second waveguide have cut surfaces. 11. The isolator according to claim 10 , wherein the normal vector of said cut surface has a component in a direction intersecting with the propagation direction of electromagnetic waves in said second waveguide. an optical isolator having a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having a substrate surface; and a light source,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has non-reciprocal members arranged side by side at least partially in the direction in which the second waveguide extends, has an aspect ratio of 0.8 to 1.2, and has an aspect ratio of 0.8 to 1.2. The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the same as that of the first waveguide for the electromagnetic wave propagating from the second end to the first end. is an odd multiple of the coupling length with the second waveguide,
The light source device, wherein the light source is optically connected to the port. an optical isolator having a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having a substrate surface; and a light source,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has non-reciprocal members arranged side by side at least partially in the direction in which the second waveguide extends, has an aspect ratio of 0.8 to 1.2, and has an aspect ratio of 0.8 to 1.2. The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L, which represents the length of the second waveguide, is the length of the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the two ends to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
calculated by
The light source device, wherein the light source is optically connected to the port. 14. The light source device according to any one of claims 12 and 13 , further comprising a power supply that supplies power to said light source. an optical isolator having a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having a substrate surface; and a light source,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the same as that of the first waveguide for the electromagnetic wave propagating from the second end to the first end. is an odd multiple of the coupling length with the second waveguide,
the light source includes a light source device optically connected to the port;
Optical transmitter with optical modulation function. an optical isolator having a first waveguide and a second waveguide positioned side by side along the substrate surface on a substrate having a substrate surface; and a light source,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L, which represents the length of the second waveguide, is the length of the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the two ends to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
calculated by
the light source includes a light source device optically connected to the port;
Optical transmitter with optical modulation function. On a substrate having a substrate surface, comprising a first waveguide and a second waveguide positioned side by side along the substrate surface,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the length of the first waveguide for the electromagnetic wave propagating from the second end to the first end. an optical switch comprising an optical isolator that is an odd multiple of the coupling length between and said second waveguide . On a substrate having a substrate surface, comprising a first waveguide and a second waveguide positioned side by side along the substrate surface,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L representing the length of the second waveguide is the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the second end to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
An optical switch with an optical isolator, calculated by : On a substrate having a substrate surface, comprising a first waveguide and a second waveguide positioned side by side along the substrate surface,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the length of the first waveguide for the electromagnetic wave propagating from the second end to the first end. optical amplifier comprising an optical isolator that is an odd multiple of the coupling length between the and said second waveguide . On a substrate having a substrate surface, comprising a first waveguide and a second waveguide positioned side by side along the substrate surface,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L representing the length of the second waveguide is the coupling between the first waveguide and the second waveguide. An expression including neven representing the even mode refractive index and nodd representing the odd mode refractive index for the electromagnetic wave propagating from the second end to the first end
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
An optical amplifier with an optical isolator, calculated by : On a substrate having a substrate surface, comprising a first waveguide and a second waveguide positioned side by side along the substrate surface,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and the length of the second waveguide is the length of the first waveguide for the electromagnetic wave propagating from the second end to the first end. a data center that communicates by means of a device comprising an optical isolator that is an odd multiple of the coupling length between the and said second waveguide . On a substrate having a substrate surface, comprising a first waveguide and a second waveguide positioned side by side along the substrate surface,
each of the first waveguide and the second waveguide has a core and a clad;
the first waveguide has a first end and a second end, and has a port for inputting and outputting an electromagnetic wave at each of the first end and the second end;
The core of the second waveguide has an aspect ratio of 0.8 to 1.2, non-reciprocal members are arranged side by side at least partly in the direction in which the second waveguide extends, and the first The polarization direction of the electromagnetic wave input to the end is parallel to the substrate surface, and L representing the length of the second waveguide is the coupling between the first waveguide and the second waveguide. against electromagnetic waves propagating from the second end to the first end
, which includes the even mode index neven and the odd mode index nodd
L=mλ0/2|(neven-nodd)| (m: odd number, λ0: wavelength in vacuum)
A data center that communicates by means of devices with optical isolators, calculated by

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