JP7245744B2 - isolator and optical transmitter - Google Patents

Description

The present disclosure relates to isolators and optical transmitters.

Conventionally, a waveguide type isolator has been proposed (see, for example, Patent Document 1). For example, in Patent Document 1, two waveguides are provided between two three-branch optical couplers, one waveguide includes a 90° reciprocal phase shifter, and the other waveguide includes a 90° phase shifter. An interferometric optical isolator is disclosed that consists of a Mach-Zehnder interferometer that includes a non-reciprocal phase shifter.

Japanese Patent Application Laid-Open No. 2003-302603

However, when the reflected wave of the electromagnetic wave emitted outside from the electromagnetic wave source (light source) through the isolator enters from the end of the isolator on the output side, the electromagnetic wave of a mode different from the emitted electromagnetic wave may be included. An electromagnetic wave having a mode different from that of the emitted electromagnetic wave transmits through the isolator in the opposite direction and is emitted from the incident side end of the isolator, which may cause damage to the electromagnetic wave source or the like.

An object of the present disclosure is to provide an isolator and an optical transmitter capable of reducing transmission of reflected waves including electromagnetic waves of a mode different from that of emitted electromagnetic waves.

The isolator of the present disclosure includes, on a substrate having a substrate surface, a first waveguide located along the substrate surface, a second waveguide located side by side on a first end side of the first waveguide, and the first waveguide. A third waveguide is provided alongside the second end of the waveguide . The first waveguide, the second waveguide and the third waveguide each include a core surrounded by a dielectric. The isolator has a first port for inputting and outputting an electromagnetic wave to and from the first end of the first waveguide, and the second end of the first waveguide or the first waveguide of the third waveguide. A second port for inputting and outputting an electromagnetic wave is provided at an end located on the second end side. The first waveguide and the second waveguide have a first coupling portion forming a first directional coupler acting on electromagnetic waves in a first mode. The first waveguide and the third waveguide form a second coupling that forms a second directional coupler that acts on either one of the first mode and the electromagnetic wave in a second mode different from the first mode. have a part. The second waveguide includes a non-reciprocal member adjacent to the core of the second waveguide at the first coupling portion so that the first directional coupler does not couple electromagnetic waves in the first direction. , to couple electromagnetic waves in a second direction different from the first direction.

The isolator of the present disclosure comprises: three waveguides, a first port and a second port, and a first directional coupler and a second directional coupler. The plurality of waveguides are located on a substrate having a substrate surface along the substrate surface. Electromagnetic waves are input to and output from the first port and the second port. The first directional coupler and the second directional coupler are provided between the first port and the second port and formed between two waveguides, respectively. The first directional coupler and the second directional coupler share one of the three waveguides, and the first directional coupler and the second directional coupler extend in the direction from the first port to the second port. Located in the order of the bidirectional coupler. The first directional coupler has non-reciprocity, transmits an electromagnetic wave of a first mode propagating in a first direction through the same waveguide, and transmits an electromagnetic wave of a first mode propagating in a second direction different from the first direction. Transfer electromagnetic waves to different waveguides. The second directional coupler is an electromagnetic wave in either one of the first mode and a second mode different from the first mode, and transfers the electromagnetic wave propagating in either direction to a different waveguide. .

An optical transmitter of the present disclosure includes a light source, an optical modulator, and an isolator. The optical modulator modulates light emitted from the light source based on a signal to be transmitted. The isolator is arranged downstream of the light source. The isolator comprises, on a substrate having a substrate surface, a first waveguide located along the substrate surface, a second waveguide located side by side on a first end side of the first waveguide, and the first waveguide. a third waveguide positioned side by side on the second end side of the . The first waveguide, the second waveguide and the third waveguide each include a core surrounded by a dielectric. The isolator has a first port for inputting and outputting an electromagnetic wave to and from the first end of the first waveguide, and the second end of the first waveguide or the first waveguide of the third waveguide. A second port for inputting and outputting an electromagnetic wave is provided at an end located on the second end side. The first waveguide and the second waveguide have a first coupling portion forming a first directional coupler acting on electromagnetic waves in a first mode. The first waveguide and the third waveguide form a second coupling that forms a second directional coupler that acts on either one of the first mode and the electromagnetic wave in a second mode different from the first mode. have a part. The second waveguide includes a non-reciprocal member adjacent to the core of the second waveguide at the first coupling portion so that the first directional coupler does not couple electromagnetic waves in the first direction. , to couple electromagnetic waves in a second direction different from the first direction.

An optical transmitter of the present disclosure includes a light source, a driver, and an isolator. The driving section drives the light source based on a signal to be transmitted. The isolator is arranged on the light emitting side of the light source. The isolator comprises, on a substrate having a substrate surface, a first waveguide located along the substrate surface, a second waveguide located side by side on a first end side of the first waveguide, and the first waveguide. a third waveguide positioned side by side on the second end side of the . The first waveguide, the second waveguide and the third waveguide each include a core surrounded by a dielectric. The isolator has a first port for inputting and outputting an electromagnetic wave to and from the first end of the first waveguide, and the second end of the first waveguide or the first waveguide of the third waveguide. A second port for inputting and outputting an electromagnetic wave is provided at an end located on the second end side. The first waveguide and the second waveguide have a first coupling portion forming a first directional coupler acting on electromagnetic waves in a first mode. The first waveguide and the third waveguide form a second coupling that forms a second directional coupler that acts on either one of the first mode and the electromagnetic wave in a second mode different from the first mode. have a part. The second waveguide includes a non-reciprocal member adjacent to the core of the second waveguide at the first coupling portion so that the first directional coupler does not couple electromagnetic waves in the first direction. , to couple electromagnetic waves in a second direction different from the first direction.

According to the embodiments of the present invention, it is possible to reduce transmission of reflected waves including electromagnetic waves in a mode different from that of the emitted electromagnetic waves.

1 is a perspective view of an isolator according to one embodiment; FIG. 2 is a plan view of the isolator of FIG. 1; FIG. FIG. 3 is a cross-sectional view taken along the line AA of FIG. 2; FIG. 3 is a cross-sectional view taken along the line BB of FIG. 2; 4 is a graph showing coupling coefficients for electromagnetic waves propagating in a first direction through a first directional coupler; 4 is a graph showing coupling coefficients for electromagnetic waves propagating in the second direction through the first directional coupler; FIG. 2 is a diagram showing a propagation path of a TE mode electromagnetic wave propagating in a first direction; FIG. 4 is a diagram showing a propagation path of a TE mode electromagnetic wave propagating in a second direction; FIG. 4 is a diagram showing a propagation path of a TM mode electromagnetic wave propagating in a second direction; FIG. 11 is a perspective view of an isolator according to another embodiment; FIG. 2 is a diagram showing a propagation path of a TE mode electromagnetic wave propagating in a first direction; FIG. 4 is a diagram showing a propagation path of a TE mode electromagnetic wave propagating in a second direction; FIG. 4 is a diagram showing a propagation path of a TM mode electromagnetic wave propagating in a second direction; FIG. 8 is a plan view of an isolator according to still another embodiment; FIG. 15 is a cross-sectional view taken along line CC of FIG. 14; 1 is a block diagram showing a schematic configuration of an optical transmitter according to one embodiment; FIG. FIG. 11 is a block diagram showing a schematic configuration of an optical transmitter according to another embodiment;

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

As shown in FIGS. 1-4, the isolator 10 according to one embodiment includes a substrate 50, a first waveguide 20, a second waveguide 30, and a third waveguide . The substrate 50 has a substrate surface 50a (see FIGS. 3 and 4). The first waveguide 20, the second waveguide 30, and the third waveguide 40 are arranged along the substrate surface 50a. The first waveguide 20 and the second waveguide 30, and the first waveguide 20 and the third waveguide 40 are arranged in parallel and partially close to each other. 1 and 2, the portion where the first waveguide 20 and the second waveguide 30 are closely arranged in parallel and the portion where the first waveguide 20 and the third waveguide 40 are closely arranged in parallel are shown. and are facing in the same direction. However, these orientations do not have to be parallel.

For the following description the x-axis, y-axis and z-axis directions are defined respectively. As shown in FIGS. 1 to 3, the x-axis direction is the direction in which the first waveguide 20 extends near the second waveguide 30 and the third waveguide 40 . The positive direction of the x-axis is the direction from one end of the first waveguide 20 (first end 201 described later) to the end of the third waveguide 40 (second end 402 described later). The y-axis direction is a direction along the substrate surface 50a of the substrate 50 and a direction crossing the x-axis direction. The y-axis direction may be substantially orthogonal to the x-axis direction. The positive direction of the y-axis is the direction toward the side where the second waveguide 30 and the third waveguide 40 are located when viewed from the first waveguide 20 . The z-axis direction is a direction perpendicular to the substrate surface 50a. The z-axis direction is orthogonal to the x-axis direction and the y-axis direction. The positive direction of the z-axis is the direction on which the first waveguide 20, the second waveguide 30 and the third waveguide 40 are arranged when viewed from the substrate 50. FIG.

Each component of isolator 10 is described in greater detail below.

Substrate 50 may be constructed from a variety of materials. For example, the substrate 50 may be made of a material selected from materials including metal conductors, semiconductors such as silicon, glass, resin, and the like. The substrate 50 can take various shapes. For example, the substrate 50 may have a rectangular shape having two sides extending in the x-axis direction and the y-axis direction and being long in the x-axis direction.

A first clad 61 common to the first waveguide 20 , the second waveguide 30 and the third waveguide 40 is formed on the substrate surface 50 a of the substrate 50 . The first core 21 , the second core 31 , the third core 41 and the non-reciprocal member 32 are arranged on the upper surface 61 a of the first clad 61 . First waveguide 20 includes a first core 21 . A second waveguide 30 includes a second core 31 and a non-reciprocal member 32 . The non-reciprocal member 32 is arranged in contact with the second core 31 . Third waveguide 40 includes a third core 41 .

As shown in FIGS. 3 and 4, the first core 21, the second core 31, the third core 41 and the non-reciprocal member 32 are surrounded and topped by a second clad 62 formed on the first clad 61. covered. The first clad 61 and the second clad 62 can be collectively called the clad 60 . The first core 21 , the second core 31 , the non-reciprocal member 32 and the third core 41 are surrounded by the clad 60 . The first waveguide 20 includes a first core 21 and a portion of the clad 60 adjacent to the first core 21 . The second waveguide 30 includes a second core 31 and a non-reciprocal member 32 and a portion of the clad 60 adjacent to the second core 31 and the non-reciprocal member 32 . The third waveguide 40 includes a third core 41 and a portion of the clad 60 adjacent to the third core 41 .

The first core 21, the second core 31, the third core 41, and the clad 60 may be configured including a dielectric. The first core 21, the second core 31 and the third core 41 are also referred to as dielectric lines. The dielectric constants of the first core 21 , the second core 31 and the third core 41 may be higher than the dielectric constant of the clad 60 . The first clad 61 and the second clad 62 forming the clad 60 may be made of the same dielectric material. The first clad 61 and the second clad 62 may be configured integrally. When the first clad 61 and the second clad 62 are integrally formed, the isolator 10 can be easily formed. The relative permittivity of the first core 21, the second core 31, the third core 41, and the clad 60 may be higher than that of air. By making the dielectric constants of the first core 21, the second core 31, the third core 41, and the clad 60 higher than the dielectric constant of air, the first waveguide 20, the second waveguide 30, and the , leakage of electromagnetic waves from the third waveguide 40 can be suppressed. As a result, loss due to electromagnetic waves radiated from the isolator 10 to the outside can be reduced.

The first core 21, the second core 31 and the third core 41 may be made of silicon (Si), for example. The clad 60 may be made of quartz glass (SiO ₂ ), 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. When the first core 21 and the second core 31 are made of silicon, they can propagate electromagnetic waves having a wavelength of 1.3 μm band or 1.55 μm band used in optical communication with low loss.

Materials for the first core 21, the second core 31, the third core 41, and the clad 60 are not limited to the materials described above. Any material can be employed for the first core 21, the second core 31, the third core 41, and the clad 60 as long as the function of the isolator 10 of the present disclosure can be obtained. A portion of the second cladding 62 may be air without a layer of a particular material. Air is a dielectric.

The dielectric constants of the first core 21, the second core 31, and the third core 41 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 dielectric constant of the first core 21 may be distributed such that it is highest in the central portion in the z-axis direction and decreases toward the first clad 61 and the second clad 62 . In this case, the first waveguide 20 can propagate electromagnetic waves on the same principle as a graded-index optical fiber.

The first core 21, the second core 31 and the third core 41 covered with the clad 60 propagate electromagnetic waves. In the present disclosure, electromagnetic waves may include electromagnetic waves of various wavelengths. The wavelength of the electromagnetic wave may fall within the band of light from ultraviolet to infrared. When the wavelength of electromagnetic waves is included in the wavelength band of light, the isolator 10 is also called an optical isolator. Also, the electromagnetic wave band may be a wavelength band such as a wavelength of 1.55 μm, which is used in silicon photonics.

The first waveguide 20, the second waveguide 30, and the third waveguide 40 according to the present embodiment can propagate TE mode electromagnetic waves. Electromagnetic waves that do not have an electric field component in the direction of propagation are called TE modes. In the waveguide, the TE mode electromagnetic wave generally oscillates in the horizontal direction with respect to the substrate 50 . Electromagnetic waves in TE mode are also called TE waves. In a device or system utilizing isolator 10, first waveguide 20, second waveguide 30 and third waveguide 40 may be designed to propagate TE mode electromagnetic waves. Therefore, the polarization direction of the electromagnetic waves input to the isolator 10 may be parallel to the substrate 50 . When the electromagnetic wave is light, the polarization direction is also called the polarization direction.

The first waveguide 20, the second waveguide 30 and the third waveguide 40 may satisfy the waveguide condition in single mode. When the first waveguide 20, the second waveguide 30 and the third waveguide 40 satisfy the waveguide condition in a single mode, the signals propagating through the first waveguide 20, the second waveguide 30 and the third waveguide 40 are satisfied. waveform is less likely to collapse. The isolator 10 combining the first waveguide 20, the second waveguide 30 and the third waveguide 40 satisfying the waveguide condition in a single mode can be suitable for optical communication.

Non-reciprocal member 32 comprises a non-reciprocal material. A non-reciprocal material is a material that has different propagation characteristics depending on the propagation direction of electromagnetic waves. The non-reciprocal member 32 may be configured including a magnetic material. Non-reciprocal materials include, for example, magnetic garnets, ferrites, iron, cobalt, and the like. The non-reciprocal material employed for the non-reciprocal member 32 may have the property of absorbing electromagnetic waves.

The first waveguide 20 extends longer in the x-axis direction than the second waveguide 30 and the third waveguide 40 . The first waveguide 20 can be linear in shape. The first waveguide 20 is not limited to a linear shape. The first waveguide 20 may have a bent portion. In the isolator 10 illustrated in FIGS. 1-4, the first waveguide 20 is described as running along the x-axis direction.

As shown in FIGS. 1 and 2, the first waveguide 20 has a first end 201 and a second end 202 on the negative and positive sides of the x-axis, respectively. The first waveguide 20 has a first port 211 at a first end 201 through which electromagnetic waves are input and output. An electromagnetic wave input from the first port 211 to the first waveguide 20 travels along the x-axis in the positive direction of the x-axis. The first port 211 may be configured as an end face of the first core 21, or may be configured as a coupler connected to an external device and capable of propagating electromagnetic waves. The second end 202 may be a flat end, convex, or the like. The first waveguide 20 may curve away from the third waveguide 40 before the second end 202 .

The second waveguide 30 is positioned on the substrate 50 so as to be partially aligned with the first end 201 side of the first waveguide 20 along the substrate surface 50a. As shown in FIGS. 1 and 2, the second waveguide 30 may be straight. Alternatively, the second waveguide 30 may include a portion that is bent in a direction away from the first waveguide 20 with a portion positioned side by side with the first waveguide 20 interposed therebetween. The end of the second waveguide 30 on the negative x-axis side is defined as a first end 301 , and the end on the positive direction side is defined as a second end 302 . In other words, the second waveguide 30 has two ends. The first end 301 and the second end 302 may be flattened or convex.

The third waveguide 40 is located on the substrate 50 so as to be partially aligned with the second end 202 side of the first waveguide 20 along the substrate surface 50a. As shown in FIGS. 1 and 2, the third waveguide 40 may be straight. Alternatively, the third waveguide 40 may include a portion that bends in a direction away from the first waveguide 20 with a portion positioned side by side with the first waveguide 20 interposed therebetween. The end of the third waveguide 40 on the negative x-axis side is defined as a first end 401 , and the end on the positive direction side is defined as a second end 402 . The third waveguide 40 has a second port 412 at the second end 402 through which electromagnetic waves are input and output. An electromagnetic wave input from the second port 412 to the third waveguide 40 travels along the x-axis in the negative x-axis direction. The second port 412 may be configured as an end face of the first core 21, or may be configured as a coupler that is connected to an external device and capable of propagating electromagnetic waves. The first end 401 of the third waveguide 40 may be flat or convex.

The second core 31 of the second waveguide 30 and the first core 21 of the first waveguide 20 have a first coupling portion 71 linearly extending in one direction along each other. The portions of the first waveguide 20 and the second waveguide 30 along each other are also called parallel waveguides. In the first coupling portion 71, the first core 21 and the second core 31 are positioned close enough to couple the electromagnetic field of the near field (evanescent field). , in the first coupling portion 71, an electromagnetic wave input to one of the first waveguide 20 and the second waveguide 30 can move 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, the parameter representing the proportion of electromagnetic waves that pass from one waveguide to the other is called the 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. For the distance between each waveguide, the coupling coefficient can change depending on the distance that the electromagnetic wave propagates 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.

Parallel waveguides with coupling coefficients close to the maximum and with a large proportion of the electromagnetic wave going from one waveguide to the other can be said to form a directional coupler. That is, the first coupling portion 71 can form the first directional coupler 72 . In parallel waveguides, the coupling coefficient and coupling length depend on the mode of the propagated electromagnetic wave. The directional coupler 72 is designed to act on electromagnetic waves in either TE mode or TM mode of a predetermined wavelength. The isolator 10 of this embodiment is designed to act on TE mode electromagnetic waves.

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, the electromagnetic wave propagates through the second core 31 toward the first end 301 or the second end 302 while repeating total reflection. When an electromagnetic wave reaches the first end 301 or the second end 302, the electromagnetic wave is radiated from the first end 301 or the second end 302 or reflected at the first end 301 or the second end 302 to travel in the opposite direction. can be

Unlike a general directional coupler, the first directional coupler 72 of the isolator 10 exhibits nonreciprocity due to the nonreciprocal member 32 adjacent to the second core 31 . The non-reciprocal member 32 is located on the positive direction side of the y-axis with respect to the second core 31 of the second waveguide 30 . The non-reciprocal member 32 may be in contact with the second core 31 over the entire surface of the second core 31 along the x-axis direction. Alternatively, the non-reciprocal member 32 may be in contact with part of the surface of the second core 31 along the x-axis direction. The non-reciprocal member 32 contacts the second core 31 at the second waveguide 30 so that the second waveguide 30 has non-reciprocal properties as described below.

An electromagnetic wave input from the first end 201 of the first waveguide 20 to the first core 21 via the first port 211 is generated in the first core 21 of the first waveguide 20 extending along the x-axis. , propagates toward the second end 202 . In the present application, the direction in which light propagates through each waveguide from the positive x-axis side to the negative x-axis direction is also referred to as the first direction. The electromagnetic wave propagating in the first core 21 can move to the second core 31 at a rate corresponding to the coupling coefficient based on the distance propagated through the first coupling portion 71 in the first core 21 in the first direction. The coupling coefficient when the electromagnetic wave propagates in the first core 21 in the first direction is also referred to as the first coupling coefficient.

In the present application, the direction in which light propagates through each waveguide from the negative x-axis side to the positive x-axis direction is also referred to as the second direction. As will be described later, part of the electromagnetic wave entering from the second port 412 of the third waveguide 40 moves to the first waveguide 20 and propagates in the second direction toward the first end 201 . The electromagnetic wave propagating in the first core 21 can move to the second core 31 at a rate corresponding to the coupling coefficient based on the distance propagated through the first coupling portion 71 in the first core 21 in the second direction. The coupling coefficient when the electromagnetic wave propagates in the second direction inside the first core 21 is also referred to as the second coupling coefficient.

The second core 31 of the second waveguide 30 has nonreciprocity by being in contact with the nonreciprocity member 32 on the positive direction side of the y-axis. Having non-reciprocity means that the effect received by propagating light differs depending on the propagation direction of the light. The second waveguide 30 may have different propagation characteristics depending on whether the electromagnetic wave propagates in the first direction or the electromagnetic wave propagates in the second direction. If the propagation characteristics of the second waveguide 30 differ based on the propagation direction of the electromagnetic wave, the first coupling coefficient and the second coupling coefficient may differ from each other. That is, the non-reciprocal member 32 can have the first coupling coefficient and the second coupling coefficient different.

The non-reciprocity of the second waveguide 30 due to the non-reciprocity member 32 is exhibited by applying a magnetic field from the outside. The direction of the external magnetic field applied to the non-reciprocal member 32 and the polarization direction of the electromagnetic wave propagating through the second waveguide 30 are configured to cross each other. In this embodiment, the polarization direction of the TE mode electromagnetic wave propagating through the second waveguide 30 is substantially parallel to the substrate surface 50a of the substrate 50 (that is, the y-axis direction). In this case, by applying an external magnetic field having a component in the z-axis direction perpendicular to the substrate surface 50a, the non-reciprocity of the non-reciprocal member 32 is exhibited. When the magnitude of the external magnetic field is constant, the non-reciprocity is maximized by applying an external magnetic field substantially in the z-axis direction.

When the non-reciprocal member 32 is a ferromagnetic material, the non-reciprocal member 32 develops non-reciprocity without applying an external magnetic field. When the polarization direction of the electromagnetic wave propagating through the second waveguide 30 is the y-axis direction, the non-reciprocal member 32 is arranged so that the magnetization direction has a component in the z-axis direction. Preferably, the non-reciprocal member 32 is arranged so that the magnetization direction is approximately in the z-axis direction.

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. 5, 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. 6, 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. 5 and 6, the horizontal axis and the vertical axis represent the traveling distance of the electromagnetic wave in the parallel waveguide and the coupling coefficient, respectively.

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.

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. 5, the coupling length for electromagnetic waves propagating in the first direction in the first directional coupler 72 can be represented as _L1 . For example, as shown in FIG. 6, the coupling length for electromagnetic waves propagating in the second direction in the first directional coupler 72 can be represented as _L2 . The first directional coupler 72 may be configured such that L ₁ and L ₂ 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. 5, the coupling coefficient can reach a maximum value if the two waveguides have a length along each other of L ₁ . 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. 5, 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. 5 can be repeated in regions where the electromagnetic waves travel longer distances. That is, if the length of the two waveguides along each other is an odd multiple of L ₁ , the coupling coefficient can be maximal. If the length of the two waveguides along each other is an even multiple of L ₁ , the coupling coefficient can be a local minimum. Even in parallel waveguides having the _relationship shown in FIG _. and can be a local minimum. L ₁ and L ₂ 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.

As described above, in the first directional coupler 72, the first coupling coefficient for the TE mode electromagnetic wave can be set to a small value, preferably close to zero. Also, the second coupling factor can be set to a value that is larger than the first coupling factor, preferably close to one. That is, the transmittance of the first directional coupler 72 with respect to the TE mode electromagnetic wave propagating in the first direction in the first waveguide 20 can be set high. The transmittance of the first directional coupler 72 to the TE mode electromagnetic wave propagating in the second direction in the first waveguide 20 can be set low.

The third core 41 of the third waveguide 40 and the first core 21 of the first waveguide 20 have a second coupling portion 73 linearly extending in one direction along each other. In the second coupling portion 73, the first core 21 and the third core 41 are positioned close enough to couple the electromagnetic field of the near field (evanescent field). In particular, in the isolator 10, the first core 21 and the third core 41 are coupled by an electric field. Therefore, for electromagnetic waves propagating in the TE mode, it can be said that the parallel waveguides form a directional coupler when the coupling coefficient between the first waveguide 20 and the third waveguide 40 is close to the maximum value. That is, the second coupling portion 73 can form the second directional coupler 74 .

Unlike the first directional coupler 72, the third core 41 is not in contact with the non-reciprocal member. Therefore, the second directional coupler 74 has the same coupling coefficient for both the first direction and the second direction. The second directional coupler 74 transfers the electromagnetic wave propagating in the TE mode with a predetermined wavelength that has propagated through the first waveguide 20 in the first direction to the third waveguide 40 . The electromagnetic wave transferred to the third waveguide 40 propagates in the first direction. The second directional coupler 74 transfers the electromagnetic wave propagating in the TE mode with a predetermined wavelength that has propagated through the third waveguide 40 in the second direction to the first waveguide 20 . The electromagnetic wave transferred to the first waveguide 20 propagates in the second direction.

The second directional coupler 74 is configured to function as a directional coupler with respect to electromagnetic waves propagated in TE mode. The second directional coupler 74 has a small coupling coefficient with respect to electromagnetic waves propagating in TM mode. A coupling coefficient of the second directional coupler 74 for electromagnetic waves propagating in the TM mode may be designed to be close to zero.

With the configuration described above, the isolator 10 operates as described below.

As shown in FIG. 7, the TE mode electromagnetic wave incident on the first waveguide 20 from the first port 211 propagates in the first direction. An electromagnetic wave propagating in the first direction is only slightly coupled to the second waveguide 30 in the first directional coupler 72 because the first coupling coefficient is small. Most of the electromagnetic waves propagating in the first direction pass through the first directional coupler 72 and travel through the first waveguide 20 in the first direction. Most of the electromagnetic waves that pass through the first directional coupler 72 and propagate in the first direction are coupled to the third waveguide 40 by the second directional coupler 74 . The electromagnetic wave coupled to the third waveguide 40 travels through the third waveguide 40 in the first direction and exits from the second port 412 . A TE mode electromagnetic wave that enters the first waveguide 20 from the first port 211 propagates through the isolator 10 as generally indicated by the arrows in FIG.

As shown in FIG. 8, the TE-mode electromagnetic wave entering the third waveguide 40 from the second port 412 propagates in the second direction. Most of the electromagnetic waves propagating in the second direction through the third waveguide 40 are coupled to the first waveguide 20 by the second directional coupler 74 . The electromagnetic waves coupled to the first waveguide 20 propagate through the first waveguide 20 in the second direction. Most of the electromagnetic waves propagating in the second direction through the first waveguide 20 are coupled to the second waveguide 30 by the first directional coupler 72 because the second coupling coefficient of the first directional coupler 72 is large. . The electromagnetic wave coupled to the second waveguide 30 travels through the second waveguide 30 in the second direction and is radiated to the outside from the first end 301 of the second waveguide 30 . The TE mode electromagnetic wave incident on the third waveguide 40 from the second port 412 propagates through the isolator 10 as generally indicated by the arrows in FIG.

As shown in FIG. 9, the TM-mode electromagnetic wave entering the third waveguide 40 from the second port 412 propagates in the second direction. Since the coupling coefficient of the second directional coupler 74 for the TM mode electromagnetic wave is small, the electromagnetic wave propagating in the second direction through the third waveguide 40 passes through the first waveguide 20 by the second directional coupler 74 only slightly. do not combine. Most of the electromagnetic waves propagating through the third waveguide 40 in the second direction further propagate through the third waveguide 40 and are radiated to the outside from the first end 401 of the third waveguide 40 . The TM mode electromagnetic wave incident on the third waveguide 40 from the second port 412 propagates through the isolator 10 as generally indicated by the arrows in FIG.

Therefore, in the isolator 10 , when the first port 211 is used as the input port, most of the input TE mode electromagnetic wave is propagated to the second output port 412 . The ratio of the intensity of the electromagnetic wave output from the second port 412 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. On the other hand, when unwanted electromagnetic waves of TE mode and TM mode reflected from the outside are incident on the second port 412 , the unwanted electromagnetic waves are not propagated to the first port 211 , or are propagated only slightly. The ratio of the intensity of the electromagnetic wave output from the first port 211 to the intensity of the electromagnetic wave input to the second port 412 is also referred to as the transmittance of the isolator 10 with respect to the electromagnetic wave propagating in the second direction. The transmittance of isolator 10 for electromagnetic waves propagating in the second direction is much smaller than the transmittance of isolator 10 for electromagnetic waves propagating in the first direction.

As described above, the isolator 10 can reduce the transmission of reflected waves including electromagnetic waves having a mode different from that of the emitted electromagnetic waves. As a result, the isolator 10 can reduce the risk of damage to the electromagnetic wave source (light source) or element (optical element) connected to the input port. In addition, the isolator 10 of the present disclosure can be produced using silicon semiconductor process technology without arranging an optical element such as a polarizer on the substrate. Therefore, the isolator 10 can be expected to be miniaturized and integrated with other optical elements on the substrate.

An isolator 11 according to another embodiment is shown in perspective view in FIG. Isolator 11 of FIG. 10 is similar to isolator 10 shown in FIGS. For this reason, in the following description of the isolator 11, components identical or similar to those of the isolator 10 are denoted by the same reference numerals and names as those of the corresponding components of the isolator 10, and only portions different from the isolator 10 are given. explain.

As shown in FIG. 10, the first waveguide 20 of the isolator 11 has a first port 211 and a second port 212 through which electromagnetic waves are input and output at a second end 202 . The second port 212 may be configured as an end face of the first core 21, or may be configured as a coupler connected to an external device and capable of propagating electromagnetic waves. The first port 211 and the second port 212 may be connected linearly in the x-axis direction by the first waveguide 20 . The first waveguide 20 may include curved portions as well as straight portions.

In isolator 11 , third waveguide 40 has no port at second end 402 . The second end 402 can be flat, convex, or the like. The electromagnetic wave that has propagated through the third waveguide 40 in the first direction and reached the second end 402 is radiated from the second end 402 to the outside of the third waveguide 40 or reflected at the second end 402 to form a third wave. It returns in the waveguide 40 in the second direction.

Unlike the isolator 10, the second directional coupler 74 (see FIGS. 11 to 13) of the isolator 11 has a coupling coefficient between the first waveguide 20 and the third waveguide 40 for electromagnetic waves propagating in the TM mode. is configured to be close to the local maximum. In the isolator 11 , the magnetic field couples the first core 21 and the third core 41 at the second coupling portion 73 . The second coupling section 73, which is a parallel waveguide, forms a second directional coupler 74 acting on TM mode electromagnetic waves. In general, the distance that an electromagnetic wave penetrates a waveguide is greater in a magnetic field than in an electric field. Therefore, the distance between the first core 21 and the third core 41 in the second coupling portion 73 is wider when designed for the TM mode electromagnetic wave than when designed for the TE mode electromagnetic wave. Become.

With the configuration described above, in the isolator 11, the first directional coupler 72 does not couple the TE mode electromagnetic wave in the first direction, but couples the TE mode electromagnetic wave in the second direction. The first directional coupler 72 hardly couples TM mode electromagnetic waves. The second directional coupler 74 does not couple TE mode electromagnetic waves but couples TM mode electromagnetic waves.

Other configurations of the isolator 11 are the same as those of the isolator 10 . Since it is configured as described above, the isolator 11 operates as described below.

As shown in FIG. 11, the TE-mode electromagnetic wave entering the first waveguide 20 from the first port 211 propagates in the first direction. Electromagnetic waves propagating in the first direction are only slightly coupled to the second waveguide 30 in the first directional coupler 72 because the first coupling coefficient is small. Electromagnetic waves propagating in the first direction pass through the first directional coupler 72 and travel through the first waveguide 20 in the first direction. Most of the electromagnetic waves that pass through the first directional coupler 72 and propagate in the first direction pass through the second directional coupler 74 without being coupled to the third waveguide 40 at the second directional coupler 74 . To Penetrate. The electromagnetic wave that has passed through the second directional coupler 74 travels in the first direction through the first waveguide 20 and is emitted from the second port 212 . A TE mode electromagnetic wave that enters the first waveguide 20 from the first port 211 propagates through the isolator 10 as generally indicated by the arrows in FIG.

As shown in FIG. 12, the TE-mode electromagnetic wave entering the first waveguide 20 from the second port 212 propagates in the second direction. Since the coupling coefficient of the second directional coupler 74 for the TE mode electromagnetic wave is small, most of the electromagnetic wave propagating in the second direction through the first waveguide 20 is coupled to the third waveguide 40 by the second directional coupler 74 . , and pass through the second directional coupler 74 . The electromagnetic wave transmitted through the second directional coupler 74 propagates through the first waveguide 20 in the second direction. Most of the electromagnetic waves propagating in the second direction through the first waveguide 20 are coupled to the second waveguide 30 because the second coupling coefficient of the first directional coupler 72 is large. The electromagnetic wave coupled to the second waveguide 30 travels through the second waveguide 30 in the second direction and is radiated to the outside from the first end 301 of the second waveguide 30 . A TE mode electromagnetic wave that enters the first waveguide 20 from the second port 212 propagates through the isolator 10 as generally indicated by the arrows in FIG.

As shown in FIG. 13, the TM-mode electromagnetic wave entering the first waveguide 20 from the second port 212 propagates in the second direction. Since the second directional coupler 74 has a large coupling coefficient for the TM mode electromagnetic wave, most of the electromagnetic wave propagating in the second direction through the first waveguide 20 is transferred to the third waveguide 40 by the second directional coupler 74 . bind to The electromagnetic wave coupled to the third waveguide 40 further propagates through the third waveguide 40 in the second direction and is radiated to the outside from the first end 401 of the third waveguide 40 . The TM-mode electromagnetic wave entering the first waveguide 20 from the second port 212 propagates through the isolator 10 as generally indicated by the arrows in FIG.

Therefore, in the isolator 11, when the first port 211 is used as the input port, most of the input TE mode electromagnetic wave is propagated to the second output port 212. FIG. On the other hand, when unwanted electromagnetic waves of TE mode and TM mode reflected from the outside enter the second port 212 , the unwanted electromagnetic waves are not propagated to the first port 211 or only slightly is propagated to

As described above, the isolator 11, like the isolator 10, can reduce the transmission of reflected waves including electromagnetic waves in a mode different from that of the emitted electromagnetic waves. Thus, the isolator 11 has the same effect as the isolator 10 described above. Further, in the isolator 11, the first port 211 and the second port 212 are provided in the same first waveguide 20, so that the electromagnetic wave is transmitted through the waveguide between the first port 211 and the second port 212. Don't move between. Therefore, the loss of the TE mode electromagnetic wave that is input from the first port 211 and output from the second port 212 is small. Furthermore, the magnetic field couples between the first core 21 of the first waveguide 20 and the third core 41 of the third waveguide 40 . Coupling by a magnetic field can make the distance between the first core 21 of the first waveguide 20 and the third core 41 of the third waveguide 40 wider than coupling by an electric field. Therefore, when the first core 21 of the first waveguide 20 and the third core 41 of the third waveguide 40 are coupled by a magnetic field, the first core 21 of the first waveguide 20 and the third core 41 of the third waveguide 40 The electric fields of the three cores 41 are difficult to couple with each other. Therefore, the coupling coefficient of the TE mode electromagnetic wave between the first core 21 of the first waveguide 20 and the third core 41 of the third waveguide 40 is low. Also from this point, the loss of the TE mode electromagnetic waves input from the first port 211 and output from the second port 212 is small.

An isolator 12 according to yet another embodiment is shown in plan view in FIG. The isolator 12 of FIG. 14 is similar to the isolator 11 shown in FIG. For this reason, in the following description of the isolator 12, components identical or similar to those of the isolator 11 are denoted by the same reference numerals and names as those of the corresponding components of the isolator 11, and only the portions different from the isolator 11 are described. explain.

In the isolator 12, the non-reciprocal member 32 of the second waveguide 30 has an extension on the side opposite to the first waveguide 20 (ie, on the positive direction side of the y-axis). For example, the non-reciprocal member 32 may have a rectangular shape as shown in FIG. 14 when viewed from the direction (z-axis direction) perpendicular to the substrate surface 50a.

Also, the third core 41 of the third waveguide 40 of the isolator 12 includes a first portion 41a and a second portion 41b. The first portion 41 a of the third core 41 and the first core 21 of the first waveguide 20 form the second coupling portion 73 along each other. The second portion 41b of the third core 41 is a portion that is bent and extends in a direction away from the first core 21 on the second direction side of the first portion 41a. The second portion 41b of the third core 41 wraps around the side of the first portion 41a away from the first waveguide 20 (that is, the positive direction side of the y-axis), and the non-reciprocal member 32 of the second waveguide 30 extends into the interior of

As shown in the cross-sectional view of FIG. 15, the vicinity of the tip including the second end 402 of the second portion 41b of the third core 41 has a structure embedded in the non-reciprocal member 32 provided on the first clad 61. It's becoming Thereby, the second portion 41 b of the third core 41 is in surface contact with the non-reciprocal member 32 . The non-reciprocal member 32 has a relatively large absorption coefficient. Therefore, when there is an electromagnetic wave propagating through the second portion 41 b of the third core 41 , the electromagnetic wave is absorbed by the surface in contact with the non-reciprocal member 32 .

Also, the second end 402 of the third core 41 has a tapered shape that tapers in diameter toward the tip. The tapered portion of the third core 41 can be longer than the wavelength of the electromagnetic wave propagating through the isolator 12 . The second end 402 has a tapered cross section taken along a plane parallel to the xy plane. The second end 402 may also taper toward the tip in the z-axis direction. Since the second end 402 is tapered, most of the electromagnetic wave propagating through the third core 41 is radiated from the second end 402 to the outside of the third waveguide 40 without being reflected. .

Other configurations of the isolator 12 are the same as those of the isolator 11 .

With the configuration described above, the isolator 12 has the effect of the isolator 11, and the electromagnetic wave incident from the first port 211 and coupled to the third waveguide 40 by the second directional coupler 74 is transferred to the third waveguide. This has the effect of reducing the amount of light reflected within 40 and returning to the first port 211 again. A more detailed description is given below.

As described with reference to FIG. 11, most of the TE mode electromagnetic wave input from the first port 211 propagates through the first waveguide 20 in the first direction and is output from the second port 212. . However, some electromagnetic waves may couple into the third waveguide 40 at the second directional coupler 74 . When the electromagnetic wave transferred to the third waveguide 40 by the second directional coupler 74 propagates through the third waveguide 40 and is reflected by the second end 402, part of it is transferred to the second directional coupler 74 again. may be coupled to the first waveguide 20 at , return through the first waveguide 20 , and exit from the first port 211 .

According to this embodiment, the third core 41 of the third waveguide 40 contacts the non-reciprocal member 32 at the second portion 41b. When part of the electromagnetic wave propagating through the third waveguide 40 is totally reflected at the interface where the third waveguide 40 contacts the non-reciprocal member 32, part of the electromagnetic wave seeps out to the non-reciprocal member 32 as an evanescent wave. . The electromagnetic waves leaked into the non-reciprocal member 32 are at least partially absorbed by the non-reciprocal member 32 . Therefore, the isolator 11 can attenuate unnecessary electromagnetic waves coupled to the third waveguide 40 . Furthermore, since the second end 402 of the third core 41 has a tapered shape, unwanted electromagnetic waves traveling to the second end 402 are radiated to the outside of the third waveguide 40 . Therefore, electromagnetic waves returning to the first port 211 are reduced.

In the above embodiment, the structure is such that the second end 402 side of the third waveguide 40 is extended to be in contact with the non-reciprocal member 32 . Similarly, any side of the first end 301 and the second end 302 of the second waveguide 30 and the first end 401 of the third waveguide 40 can be extended to contact the non-reciprocal member 32. is.

The isolators 10-12 of the present disclosure can be applied to optical transmitters. An embodiment of an optical transmitter 80 incorporating isolators 10-12 is shown in the block diagram of FIG.

The optical transmitter 80 includes a light source 81 , a DAC 82 (Digital to Analog Converter), a driver 83 , an optical modulator 84 and an isolator 85 .

The light source 81 may employ a laser light source. The laser light source may include a semiconductor laser such as an LD (Laser Diode). The light emitted by the light source 81 may be included in a band from infrared light to ultraviolet light. The light source 81 can continuously emit stable light.

The optical transmitter 80 receives a transmission signal to be transmitted from another device or the like. A transmission signal is converted into an analog signal by the DAC 82 . The driver 83 drives the optical modulator 84 to modulate the light emitted from the light source 81 based on the transmission signal converted to the analog signal. Various modulation schemes such as amplitude modulation and phase modulation can be adopted as modulation schemes for modulating light. As the optical modulator 84, for example, a Mach-Zehnder optical modulator formed by silicon photonics technology can be used. Optical modulator 84 may be formed on the same substrate 50 as isolator 85 .

Isolator 85 may employ an isolator according to the present disclosure. For example, the isolator 85 can be the isolator 10 shown in FIGS. 1-3, the isolator 11 shown in FIG. 10, or the isolator 12 shown in FIG. The isolator 85 is arranged downstream of the light source 81 in the optical path of the light emitted from the light source 81 . For example, as shown in FIG. 16, the isolator 85 is arranged on the light emitting side of the optical modulator 84 and transmits light directed to the outside of the optical transmitter 80 . The isolator 85 reduces the propagation of light that has been reflected outside and returned to the optical transmitter 80 to the optical modulator 84 side, including light of a mode different from that of the transmitted light. Thereby, the isolator 85 reduces the possibility that the reflected light of the emitted light enters the light source 81 and adversely affects the light source 81 such as damage. The isolator 85 may be arranged between the light source 81 and the optical modulator 84 unlike in FIG. In this case, the isolator 85 can reduce the risk of light returning from the outside and return light reflected inside the optical modulator 84 entering the light source 81 .

Another embodiment of an optical transmitter is shown in FIG. The optical transmitter 80 of FIG. 16 employs an external modulation system in which light from a light source 81 is modulated by an optical modulator 84 outside the light source 81 . The embodiment illustrated in FIG. 17 employs a direct modulation scheme that directly controls the light source.

The optical transmitter 90 includes a signal modulator 91 , a driver 92 that is a driver, a light source 93 and an isolator 94 . The signal modulator 91 converts the transmission signal into a binary modulated signal. The driver 92 controls ON/OFF of driving of the light source 93 based on the modulated signal output from the signal modulating section 91 . Isolator 94 may employ an isolator according to the present disclosure. For example, the isolator 94 can be the isolator 10 shown in FIGS. 1-3, the isolator 11 shown in FIG. 10, or the isolator 12 shown in FIG. The isolator 94 is arranged on the light emitting side of the light source 93 and transmits light directed to the outside of the optical transmitter 90 . The isolator 94 reduces the possibility that light, including light in a mode different from the transmitted light, returning to the optical transmitter 90 from the outside due to reflection or the like will enter the light source 93 and have an adverse effect such as damage on the light source 93 . .

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, 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.

The arrangement of the waveguides on the substrate in each of the isolator embodiments described above is merely exemplary. For example, in each of the above-described embodiments, the orientation of the waveguides in the portions where the plurality of waveguides are adjacent to form parallel waveguides is parallel to the longitudinal side of the substrate. However, the shape of the substrate and the orientation and arrangement of the waveguides are not limited to this, and can be set arbitrarily within the range in which the effects of the present disclosure can be obtained. For example, a plurality of waveguides can be arranged not only in the direction along the substrate surface, but also in the direction perpendicular to the substrate surface.

In the above embodiments, an isolator and an optical transmitter for propagating TE mode electromagnetic waves have been described. However, the present disclosure can also be applied to isolators and optical transmitters that propagate TM mode electromagnetic waves. When the present disclosure is applied to an isolator and an optical transmitter that propagate TM mode electromagnetic waves, the arrangement of the non-reciprocal member with respect to the second waveguide and the direction of the applied magnetic field are different from those of the above embodiments. For example, when the present invention is applied to a TM mode isolator and an optical transmitter, the non-reciprocal member is arranged in contact with the direction perpendicular to the substrate surface of the second waveguide (corresponding to the z-axis direction in the above embodiment). sell. Also, at this time, the magnetic field can be applied in a direction orthogonal to the direction in which the second waveguide extends (corresponding to the y-axis direction in the above embodiment).

10, 11, 12 isolator 20 first waveguide 21 first core 201 first end 202 second end 211 first port 212 second port 30 second waveguide 31 second core 32 non-reciprocal member 301 first end 302 Second end 40 Third waveguide 41 Third core 401 First end 402 Second end 412 Second port 50 Substrate 50a Substrate surface 60 Cladding 61 First clad (dielectric)
62 Second clad (dielectric)
71 first coupling unit 72 first directional coupler 73 second coupling unit 74 second directional coupler 80, 90 optical transmitter 81 light source 82 DAC (digital-to-analog converter)
83 driver 84 optical modulator 85 isolator 91 signal generator 92 driver (driving unit)
93 light source 94 isolator

Claims (10)

On a substrate having a substrate surface, a first waveguide located along the substrate surface, a second waveguide located side by side with the first end of the first waveguide, and a second end of the first waveguide. a third waveguide located side by side ;
the first waveguide, the second waveguide, and the third waveguide each include a core surrounded by a dielectric;
a first port for inputting and outputting an electromagnetic wave to and from the first end of the first waveguide, and the second end of the first waveguide or the second end of the first waveguide of the third waveguide a second port for inputting and outputting electromagnetic waves at the end located on the side,
the first waveguide and the second waveguide have a first coupling portion forming a first directional coupler that acts on electromagnetic waves in a first mode;
The first waveguide and the third waveguide form a second coupling that forms a second directional coupler that acts on either one of the first mode and the electromagnetic wave in a second mode different from the first mode. has a part
The second waveguide includes a non-reciprocal member adjacent to the core of the second waveguide at the first coupling portion so that the first directional coupler does not couple electromagnetic waves in the first direction. , an isolator for coupling electromagnetic waves in a second direction different from the first direction. 2. The isolator according to claim 1, wherein said first mode is TE mode, said second mode is TM mode, and said second directional coupler acts only on TE mode electromagnetic waves. The first waveguide has a first port for inputting/outputting an electromagnetic wave at one end, and the third waveguide has a second port for inputting/outputting an electromagnetic wave at an end on a side different from the first port. 3. The isolator of claim 2, comprising ports. 2. The isolator according to claim 1, wherein said first mode is TE mode, said second mode is TM mode, and said second directional coupler acts only on TM mode electromagnetic waves. The first waveguide has a first end and a second end, and each of the first end and the second end has a first port and a second port through which electromagnetic waves are input and output. 5. The isolator according to 4. 6. The core of at least one of the second waveguide and the third waveguide is in contact with the non-reciprocal member at a portion other than the first coupling portion or the second coupling portion. or the isolator according to item 1. 7. The isolator according to any one of claims 1 to 6, wherein an end portion of the core of at least one of the front second waveguide and the third waveguide has a diameter that decreases toward the tip. on a substrate having a substrate surface, three waveguides positioned along the substrate surface;
a first port and a second port for inputting and outputting an electromagnetic wave; and a first directional coupler and a second directional coupler provided between the first port and the second port and respectively formed between two waveguides. a sexual coupler;
The first directional coupler and the second directional coupler share one of the three waveguides, and the first directional coupler and the second directional coupler extend in the direction from the first port to the second port. located in the order of the bidirectional coupler,
The first directional coupler has non-reciprocity, transmits an electromagnetic wave of a first mode propagating in a first direction through the same waveguide, and transmits an electromagnetic wave of a first mode propagating in a second direction different from the first direction. Transfer electromagnetic waves to different waveguides,
The second directional coupler is an electromagnetic wave in either one of the first mode and a second mode different from the first mode, and transfers the electromagnetic wave propagating in either direction to a different waveguide. isolator. a light source;
an optical modulator that modulates light emitted from the light source based on a signal to be transmitted;
an isolator arranged downstream of the light source,
The isolator is
On a substrate having a substrate surface, a first waveguide located along the substrate surface, a second waveguide located side by side with the first end of the first waveguide, and a second end of the first waveguide. a third waveguide located side by side ;
the first waveguide, the second waveguide, and the third waveguide each include a core surrounded by a dielectric;
a first port for inputting and outputting an electromagnetic wave to and from the first end of the first waveguide, and the second end of the first waveguide or the second end of the first waveguide of the third waveguide a second port for inputting and outputting electromagnetic waves at the end located on the side,
the first waveguide and the second waveguide have a first coupling portion forming a first directional coupler that acts on electromagnetic waves in a first mode;
The first waveguide and the third waveguide form a second coupling that forms a second directional coupler that acts on either one of the first mode and the electromagnetic wave in a second mode different from the first mode. has a part
The second waveguide includes a non-reciprocal member adjacent to the core of the second waveguide at the first coupling portion so that the first directional coupler does not couple electromagnetic waves in the first direction. , an optical transmitter for coupling electromagnetic waves in a second direction different from the first direction. a light source;
a driving unit that drives the light source based on a signal to be transmitted;
an isolator arranged on the light emission side of the light source,
The isolator is
On a substrate having a substrate surface, a first waveguide located along the substrate surface, a second waveguide located side by side with the first end of the first waveguide, and a second end of the first waveguide. a third waveguide located side by side ;
the first waveguide, the second waveguide, and the third waveguide each include a core surrounded by a dielectric;
a first port for inputting and outputting an electromagnetic wave to and from the first end of the first waveguide, and the second end of the first waveguide or the second end of the first waveguide of the third waveguide a second port for inputting and outputting electromagnetic waves at the end located on the side,
the first waveguide and the second waveguide have a first coupling portion forming a first directional coupler that acts on electromagnetic waves in a first mode;
The first waveguide and the third waveguide form a second coupling that forms a second directional coupler that acts on either one of the first mode and the electromagnetic wave in a second mode different from the first mode. has a part
The second waveguide includes a non-reciprocal member adjacent to the core of the second waveguide at the first coupling portion so that the first directional coupler does not couple electromagnetic waves in the first direction. , an optical transmitter for coupling electromagnetic waves in a second direction different from the first direction.

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