JP6476265B1 - Optical waveguide device - Google Patents

Abstract

A grating-type optical waveguide device having high polarization conversion efficiency is provided.
A support substrate, an optical waveguide core, and a clad are provided. The optical waveguide core is formed using silicon as a material, and has a thickness larger than 200 nm and smaller than 300 nm. The clad is provided on the support substrate and includes the optical waveguide core. The optical waveguide core includes a rib waveguide portion and a terrace waveguide portion. A grating is formed in the rib waveguide portion. Further, the terrace waveguide portion is formed integrally with the rib waveguide portion on each side surface along the light propagation direction of the rib waveguide portion, with a thickness smaller than that of the rib waveguide portion. This optical waveguide element has a polarization of one of TE polarization and TM polarization in the k-order mode (k is an integer of 0 or more) and the other polarization of the h-order mode (h is an integer of 0 or more). It is converted into a wave and Bragg-reflected, and the other polarization of the p-order mode (p is an integer of 0 or more different from h) is transmitted.
[Selection] Figure 1

Description

  The present invention relates to an optical waveguide device, for example, an optical waveguide device used for wavelength multiplexing or wavelength separation that requires polarization independence.

  In recent years, passive optical networks (PONs) have become mainstream as subscriber optical access systems. In the PON, one station side device (OLT: Optical Line Terminal) and a plurality of subscriber side devices (ONU: Optical Network Unit) are connected via an optical fiber and a star coupler, and one OLT is connected to a plurality of OLTs. Shared by ONU. In PON, the optical signal wavelength used for downlink communication and the optical signal wavelength used for uplink communication are set so that downlink communication from OLT to ONU and uplink communication from ONU to OLT do not interfere with each other. It is wrong.

  Therefore, a multiplexing / demultiplexing element is required to demultiplex and multiplex optical signals having different wavelengths used for downlink communication and uplink communication. In general, an OLT or an ONU has an optical wavelength filter, a photodiode (PD: Photodiode), or a laser diode (LD: Laser Diode) as a multiplexing / demultiplexing element in order to realize a function of transmitting and receiving optical signals having different wavelengths. Composed and configured.

  In order to perform spatial coupling, an alignment operation for aligning the optical axis between the optical wavelength filter, PD, and LD is required. On the other hand, in order to eliminate the work for aligning the optical axis, an optical wavelength filter configured using a waveguide has been developed. Further, in forming this optical wavelength filter, silicon (Si) waveguide using a silicon-based material as a waveguide material has attracted attention because it is excellent in miniaturization and mass productivity (see, for example, Patent Documents 1 to 5). ).

  In the Si waveguide, an optical waveguide core that substantially becomes a light transmission path is formed using Si as a material. Then, the periphery of the optical waveguide core is covered with a clad made of, for example, silica having a refractive index lower than that of Si. With such a configuration, the refractive index difference between the optical waveguide core and the clad becomes extremely large, so that light can be strongly confined in the optical waveguide core. As a result, a small curved waveguide having a bending radius reduced to, for example, about 1 μm can be realized. Therefore, it is possible to create an optical circuit having a size comparable to that of an electronic circuit, which is advantageous for downsizing the entire optical device.

  Further, in the Si waveguide, it is possible to divert the manufacturing process of a semiconductor device such as a CMOS (Complementary Metal Oxide Semiconductor). Therefore, realization of photoelectric fusion (silicon photonics) in which electronic functional circuits and optical functional circuits are collectively formed on a chip is expected.

  By the way, in a PON using a wavelength division multiplexing (WDM) system, a different reception wavelength is assigned to each ONU. The OLT generates a downstream optical signal to each ONU at a transmission wavelength corresponding to the reception wavelength of the transmission destination, and multiplexes and transmits them. Each ONU selectively receives an optical signal having a reception wavelength allocated to itself from downstream optical signals multiplexed at a plurality of wavelengths. In the ONU, a wavelength filter is used to selectively receive a downstream optical signal of each reception wavelength. And the technique which comprises a wavelength filter with the Si waveguide mentioned above is implement | achieved.

  As a wavelength filter using a Si waveguide, for example, there are a filter using a Mach-Zehnder interferometer and a filter using an arrayed waveguide grating. Moreover, as a wavelength filter using a Si waveguide, a ring resonator (see, for example, Patent Documents 6 to 8), a grating type (for example, see Patent Document 9) or a directional coupler type (for example, see Patent Document 10) wavelength filter. There is. These wavelength filters have the advantage of being easy to use because the output wavelength can be made variable and the element structure is simple.

  Among them, ring resonators are often used in this type of device because a plurality of sharp, so-called bimodal wavelength peaks can be obtained. A grating-type or directional coupler-type element can obtain a so-called unimodal wavelength peak having a single wavelength.

U.S. Pat. No. 4,860,294 US Pat. No. 5,764,826 US Pat. No. 5,960,135 US Pat. No. 7,072,541 Japanese Patent Laid-Open No. 08-163028 JP 2003-215515 A JP 2013-093627 A JP 2006-278770 A JP 2006-330104 A JP 2002-353556 A

  In optical communication, since the signal light propagates a long distance in the optical fiber, the polarization state becomes unspecified. For this reason, a wavelength filter that performs wavelength multiplexing or wavelength separation used in optical communication is required to be polarization independent.

  When a grating type element that performs polarization conversion is used in the wavelength filter described above, polarization independence is realized.

  However, the efficiency of polarization conversion in a grating type element is generally low.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a grating-type optical waveguide element having high polarization conversion efficiency.

  In order to achieve the above-described object, the optical waveguide device of the present invention includes a support substrate, an optical waveguide core, and a cladding. The optical waveguide core is made of silicon. The clad is provided on the support substrate and includes the optical waveguide core.

The optical waveguide core includes a rib waveguide portion and a terrace waveguide portion. A grating is formed in the rib waveguide portion. Further, the terrace waveguide portion is formed integrally with the rib waveguide portion on each side surface along the light propagation direction of the rib waveguide portion, with a thickness smaller than that of the rib waveguide portion. Here, the rib is the distance from the contact surface of the rib waveguide with the cladding provided on the lower side of the rib waveguide portion to the contact surface with the cladding provided on the upper side of the rib waveguide portion. The thickness of the waveguide portion is larger than 200 nm and smaller than 300 nm.

  This optical waveguide element has a polarization of one of a TE (Transverse Electric) polarization and a TM (Transverse Magnetic) polarization in the k-order mode (k is an integer of 0 or more), and the h-order mode (h is 0). It is converted into the other polarization of the above integer) and Bragg reflected, and the other polarization of the p-order mode (p is an integer of 0 or more different from h) is transmitted.

In implementing the above-mentioned optical waveguide element, preferably, grating, the diffraction wavelength of the TE polarization and the TM polarization of the h-th order mode of k-order mode lambda _0, TE polarization of k-th order mode in the diffracted wavelength lambda ₀ When the equivalent refractive index of the wave is N _TEk (λ ₀ ), the equivalent refractive index of the TM polarization of the h-order mode at the diffraction wavelength λ ₀ is N _TMh (λ ₀ ), and the grating period is Λ, (N _TEk ( λ ₀ ) + N _TMh (λ ₀ )) Λ = λ ₀ is formed, and the TE polarization of the kth mode is converted to the TM polarization of the _hth mode and Bragg reflected, and p The TM polarization of the next mode is transmitted. Also, the thickness and width of the rib waveguide portion are such that the diffraction wavelength λ ₀ of the TE polarization of the k-order mode to the TM polarization of the h-order mode is the TM of the p-order mode of the TM polarization of the h-order mode. It is formed with a design having a wavelength longer than the diffraction wavelength λ ₁ to the polarization .

Further, according to another preferred embodiment, the grating has a diffraction wavelength of TM polarization of k-order mode and TE polarization of h-order mode as λ. ₀ , Diffraction wavelength λ ₀ The equivalent refractive index of the TM polarization of the k-order mode at N _TMk (Λ ₀ ), Diffraction wavelength λ ₀ The equivalent refractive index of the TE polarized wave of the h-order mode at N _TEh (Λ ₀ ), When the grating period is Λ, (N _TMk (Λ ₀ ) + N _TEh (Λ ₀ )) Λ = λ ₀ The TM polarization of the kth mode is converted into the TE polarization of the hth mode and Bragg reflected, and the TE polarization of the pth mode is transmitted. Further, the thickness and width of the rib waveguide portion are determined by the diffraction wavelength λ from TM polarization of k-order mode to TE polarization of h-order mode. ₀ Is the diffraction wavelength λ from the TE polarization of the h-order mode to the TE polarization of the p-order mode ₁ It is formed with a design having a longer wavelength.

  According to the optical waveguide element of the present invention, since the optical waveguide core includes the rib waveguide portion and the terrace waveguide portion, the electric field distribution of the light propagating through the optical waveguide core is decentered in the thickness direction and is asymmetrical in the vertical direction. Become. As a result, in the grating formed on the optical waveguide core, it is possible to convert one of the input polarized waves into the other polarized wave, perform Bragg reflection, and transmit the other input polarized wave. Therefore, the output light can be aligned with either TE polarization or TM polarization.

  Further, as will be described later, by making the thickness of the optical waveguide core larger than 200 nm and smaller than 300 nm, the coupling coefficient between the TE polarized wave and the TM polarized wave can be increased, and the polarization conversion efficiency can be increased.

It is a schematic diagram for demonstrating an optical waveguide element. It is a figure which shows the light intensity of the transmitted light and reflected light in case the TE polarized wave of a fundamental mode is input into the optical waveguide element. It is a figure (1) which shows the relationship between a coupling coefficient (1 / micrometer), the wavelength difference (micrometer) of a desired diffraction wavelength, and an unnecessary diffraction wavelength, and waveguide thickness (nm). FIG. 6 is a diagram (2) showing a relationship between a coupling coefficient (1 / μm), a wavelength difference (μm) between a desired diffraction wavelength and an unnecessary diffraction wavelength, and a waveguide thickness (nm). It is a figure which shows the relationship between a coupling coefficient (1 / micrometer), the wavelength difference (micrometer) of a desired diffraction wavelength, and an unnecessary diffraction wavelength, and the terrace full width (nm).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

(Constitution)
With reference to FIG. 1, an embodiment of the optical waveguide device of the present invention will be described. FIG. 1 is a schematic diagram for explaining an optical waveguide element. FIG. 1A is a schematic plan view showing an optical waveguide element. FIG. 1B is a schematic end view of the structure shown in FIG. In FIG. 1A, a support substrate and a clad described later are omitted.

  In the following description, for each component, the direction along the light propagation direction is the length direction. The direction along the thickness of the support substrate is the thickness direction. Moreover, let the direction orthogonal to a length direction and a thickness direction be a width direction.

  The optical waveguide element includes a support substrate 10, a clad 20, and an optical waveguide core 30.

  The support substrate 10 is composed of a flat plate made of, for example, single crystal Si.

The clad 20 is provided on the support substrate 10. The clad 20 covers the upper surface of the support substrate 10 and includes the optical waveguide core 30. The clad 20 is formed using, for example, silicon oxide (SiO ₂ ) as a material.

  The optical waveguide core 30 is made of, for example, silicon (Si) having a higher refractive index than that of the clad 20. As a result, the optical waveguide core 30 functions as a light transmission path, and the light input to the optical waveguide core 30 propagates in the propagation direction according to the planar shape of the optical waveguide core 30.

  Here, in order to prevent light propagating through the optical waveguide core 30 from escaping to the support substrate 10, the optical waveguide core 30 is preferably formed at least 1 μm apart from the support substrate 10.

  The optical waveguide core 30 includes a rib waveguide portion 32 and a terrace waveguide portion 38.

  A grating is formed in the rib waveguide portion 32. The rib waveguide portion 32 is configured to integrally include a base portion 34 and projecting portions 36a and 36b. The base portion 34 is formed with a certain width and extending along the light propagation direction, and constitutes a so-called grating. A plurality of protrusions 36 a and 36 b are periodically formed on both side surfaces of the base 34 with the same period Λ.

  The protruding portion 36a formed on one side surface of the base portion 34 and the protruding portion 36b formed on the other side surface are arranged so as to be shifted by a half cycle (ie, Λ / 2). That is, for a certain position in the longitudinal direction, when the projecting portion 36a is disposed on one side surface, the projecting portion 36b is not disposed on the other side surface, and when the projecting portion 36a is not disposed on one side surface. The protrusion 36b is disposed on the other side surface.

In this case, the electric field distribution of light propagating through the optical waveguide core is decentered in the width direction. As a result, mode conversion and polarization conversion can be performed between the TE polarization and the TM polarization. The phase matching condition by the grating is that the Bragg wavelength is λ ₀ , the grating period is Λ, the TE-polarized k-order mode (k is an integer of 0 or more) is equivalent to N _TEk , and the TM-polarized h-order mode (h _N TMh the equivalent refractive index of an integer of 0 or more), the equivalent refractive index of the k-th mode of the TM polarization _N tMK, the equivalent refractive index of the h-th order mode of the TE polarization as _{N TEh,} the following equation (1 ) Or formula (2).

(N _TEk + N _TMh ) Λ = λ ₀ (1)
(N _TMk + N _TEh ) Λ = λ ₀ (2)
If the design satisfies the above formula (1) or formula (2), the polarization of either the TE polarization or TM polarization of the k-order mode (k is an integer of 0 or more) is changed to the h-order mode. It can be converted into the other polarized wave (h is an integer of 0 or more) and Bragg reflected.

  For example, when k = 0 and h = 0, that is, when polarization conversion is performed between a TM polarized wave in the fundamental mode and a TE polarized wave in the fundamental mode, the p-order mode (p is greater than or equal to 0 different from h) The other (integer) polarized wave, for example, the first mode TE polarized wave is transmitted through this optical waveguide element.

  In this optical waveguide element, the base portion 34 and the protruding portions 36a and 36b of the rib waveguide portion 32 are formed with the same thickness. There is a Si portion at the bottom of the grating groove 40 between the protrusions adjacent in the light propagation direction. The base 34 and the protrusions 36a and 36b of the rib waveguide part 32 are formed of Si having the same thickness, and the portion of the grating groove 40 is smaller in thickness than the base 34 and the protrusions 36a and 36b of the rib waveguide part 32. Made of Si.

  As a result, the electric field distribution of the light propagating through the optical waveguide core is decentered in the thickness direction and becomes asymmetric in the vertical direction. Thereby, polarization conversion between the TE polarized wave and the TM polarized wave is efficiently achieved.

  In this optical waveguide element, terrace waveguide portions 38 are further provided on both side surfaces of the rib waveguide portion 32 along the light propagation direction. The terrace waveguide portion 38 has the same thickness as Si of the grating groove 40 and is provided by extending the Si portion of the grating groove 40 in the width direction. That is, the terrace waveguide section 38 is formed integrally with the rib waveguide section 32 on both side surfaces along the light propagation direction of the rib waveguide section 32 with a thickness smaller than that of the rib waveguide section 32. ing.

  As will be described later, the thickness (waveguide thickness) of the base portion 34 and the protrusions 36a and 36b of the rib waveguide portion 32 is set to be larger than 200 nm and smaller than 300 nm, and by providing a terrace waveguide portion 38, TE polarization In addition, the coupling coefficient between the TM polarized wave and the polarization conversion efficiency can be increased.

(Production method)
This optical waveguide device can be easily manufactured by using, for example, an SOI (Silicon On Insulator) substrate. Hereinafter, an example of a method for manufacturing an optical waveguide device will be described.

First, an SOI substrate configured by sequentially laminating a support substrate layer, a SiO ₂ layer, and a Si layer is prepared. Next, for example, dry etching is performed in two stages and the Si layer is patterned to form a base portion and a protruding portion of a rib waveguide portion having a large thickness, a grating groove portion and a terrace waveguide portion having a small thickness. As a result, it is possible to obtain a structure in which the SiO ₂ layer is laminated on the support substrate layer as the support substrate 10 and the optical waveguide core 30 is formed on the SiO ₂ layer.

Next, SiO ₂ is formed so as to cover the optical waveguide core 30 on the SiO ₂ layer by using, for example, a CVD (Chemical Vapor Deposition) method. As a result, the optical waveguide core 30 is included by the clad 20, and an optical waveguide element is obtained.

(Characteristic evaluation)
With reference to FIGS. 2 to 5, a simulation for evaluating the characteristics of an optical waveguide element, which is performed using FDTD (Finite Differential Time Domain), will be described.

  FIG. 2 is a diagram showing the light intensities of transmitted light and reflected light when the fundamental mode TE polarized wave is input to the optical waveguide element. In FIG. 2, the horizontal axis indicates the wavelength (nm) and the vertical axis indicates the light intensity (dB). In FIG. 2, a curve I indicates transmitted light, and a curve II indicates reflected light.

  In the optical waveguide element used here, the thickness of the base portion and the protruding portion of the rib waveguide portion (waveguide thickness) is 300 nm, and the width of the base portion of the rib waveguide portion (hereinafter referred to as waveguide width) is 550 nm. The length of the protruding portion is 125 nm, and the grating groove is formed by carving 80 nm from the upper surface of the optical waveguide core. That is, the thickness of Si in the grating groove portion is 220 nm. The grating period Λ is 300 nm, and the length of the optical waveguide element is 100 μm. Note that the optical waveguide element used in this simulation does not include a terrace waveguide section.

  In FIG. 2, the reflection peak and transmission dip near the wavelength of 1500 nm correspond to the diffraction between the fundamental mode TE polarized wave and the fundamental mode TM polarized wave. In addition to this desired diffraction, unnecessary wavelength peaks and transmission dip are observed near the wavelength of 1400 nm. This corresponds to the diffraction of the TE polarization between the fundamental mode and the first order mode. In practice, it is necessary that the desired diffraction wavelength and the unnecessary diffraction wavelength are as far apart as possible. In order not to affect each other, it is preferable that the diffraction wavelengths are separated by 50 nm or more.

The diffraction wavelength λ ₀ between the fundamental mode TE polarized wave and the fundamental mode TM polarized wave is given by the following equation (3).

2π / Λ = 2π [N _TE0 (λ ₀ ) + N _TM0 (λ ₀ )] / λ ₀ (3)
On the other hand, the fundamental mode of TE polarization and the diffraction wavelength λ ₁ of the first-order mode are given by the following equation (4).

2π / Λ = 2π [N _TE0 (λ ₁ ) + N _TE1 (λ ₁ )] / λ ₁ (4)
From the above formulas (3) and (4), the following formula (5) is obtained.

_{λ 0 -λ 1 = [N TM0} (λ 0) -N TE1 (λ 1)] (1-dN TE0 (λ 0) / dλ) (5)
According to the above equation (5), an unnecessary diffraction wavelength λ ₁ is on the short wavelength side of the desired diffraction wavelength λ ₀ or a long wavelength depending on the sign of N _{T M 0} (λ ₀ ) −N _TE1 (λ ₁ ). It is determined whether it is on the side.

The wider the waveguide width, the greater the refractive index N _TE1 (λ ₁ ) for TE polarized light. On the other hand, the refractive index N _TM0 (λ ₀ ) with respect to the TM polarized wave has a small change due to the waveguide width. Therefore, as the waveguide width becomes wider, the unnecessary diffraction wavelength λ ₁ becomes longer and approaches the desired diffraction wavelength λ ₀ .

On the other hand, the refractive index N _TM0 (λ ₀ ) with respect to the TM polarization increases as the waveguide thickness increases. On the other hand, the refractive index N _TE1 (λ ₁ ) with respect to the TE polarized wave has a small change due to the thickness of the waveguide. Therefore, as the waveguide thickness increases, the desired diffraction wavelength λ ₀ becomes longer and away from the unwanted diffraction wavelength λ ₁ .

  FIG. 3 and FIG. 4 are diagrams showing the relationship between the coupling coefficient (1 / μm), the wavelength difference (μm) between a desired diffraction wavelength and an unnecessary diffraction wavelength, and the waveguide thickness (nm).

  3 and 4, the horizontal axis indicates the waveguide thickness (nm), the vertical axis indicates the coupling coefficient (1 / μm), and the wavelength difference (μm) between the desired diffraction wavelength and the unnecessary diffraction wavelength. Take and show.

  In FIG. 3, curves I, II, and III indicate coupling coefficients when the terrace width (see FIG. 1A) is 0 nm, 25 nm, and 75 nm, respectively. Curves IV, V and VI show the wavelength differences when the terrace width is 0 nm, 25 nm and 75 nm, respectively. Here, the entire terrace width (see FIG. 1A) is 600 nm. Therefore, the waveguide widths when the terrace width is 0 nm, 25 nm, and 75 nm are 600 nm, 550 nm, and 450 nm, respectively.

  As shown by curves I, II and III in FIG. 3, the coupling coefficient increases as the terrace width increases. The maximum value of the coupling coefficient when the terrace width is 75 nm exists where the waveguide thickness is about 250 nm.

  Also, as shown by curves IV, V and VI in FIG. 3, the wavelength difference between the desired diffraction wavelength and the unnecessary diffraction wavelength increases as the waveguide thickness increases.

  In FIG. 4, curves I and II indicate the coupling coefficients when the terrace width is 0 nm and 25 nm, respectively. Curves III and IV show the wavelength differences when the terrace width is 0 nm and 25 nm, respectively. Here, the total terrace width is 450 nm. Therefore, the waveguide widths when the terrace width is 0 nm and 25 nm are 450 nm and 400 nm, respectively.

  Also in FIG. 4, as shown by the curves I and II, the coupling coefficient is larger when the terrace waveguide portion is provided. The maximum value of the coupling coefficient when the terrace width is 25 nm exists where the waveguide thickness is about 250 nm.

  Further, as shown by curves III and IV, as the waveguide thickness increases, the wavelength difference between the desired diffraction wavelength and the unnecessary diffraction wavelength increases.

  FIG. 5 is a diagram illustrating the relationship between the coupling coefficient (1 / μm), the wavelength difference (μm) between a desired diffraction wavelength and an unnecessary diffraction wavelength, and the entire terrace width. In FIG. 5, the horizontal axis represents the entire terrace width (nm), and the vertical axis represents the coupling coefficient (1 / μm) and the wavelength difference (μm) between the desired diffraction wavelength and the unnecessary diffraction wavelength. .

  In FIG. 5, curves I and II show the coupling coefficient and the wavelength difference, respectively. Here, the thickness of the waveguide is 300 nm, and the waveguide width is 550 nm.

  Increasing the terrace width increases the coupling coefficient and decreases the wavelength difference. When the total terrace width is 900 nm (terrace width 175 nm), the coupling coefficient becomes maximum, but the wavelength difference at this time is zero. That is, the desired diffraction wavelength and the unnecessary diffraction wavelength are overlapped. Furthermore, when the terrace width is increased, the coupling coefficient decreases rapidly.

  As shown in FIGS. 3 to 5, when the thickness of the waveguide satisfies the single mode condition, that is, when it is larger than 200 nm and smaller than 300 nm, the coupling coefficient may be increased by providing the terrace waveguide portion. Understood.

  The waveguide width has been confirmed to be effective at least at 450 nm and 550 nm, but 550 nm is more advantageous in consideration of production errors. When the waveguide width is 450 nm, the coupling coefficient is maximized when the waveguide thickness is 250 nm.

  Under the conditions shown in FIGS. 3 and 4, the main diffraction wavelength is longer than the unnecessary diffraction wavelength. For this reason, when the waveguide thickness becomes smaller than 250 nm, the wavelength difference becomes smaller, and when the waveguide thickness becomes larger than 250 nm, the wavelength difference becomes larger. In addition, the coupling coefficient tends to decrease when the waveguide thickness is larger than 250 nm. Therefore, the waveguide thickness is more preferably in a range including 250 nm, for example, 220 nm to 260 nm.

  According to the optical waveguide element of the present invention, since the optical waveguide core includes the rib waveguide portion and the terrace waveguide portion, the electric field distribution of the light propagating through the optical waveguide core is decentered in the thickness direction and is asymmetrical in the vertical direction. Become. As a result, in the grating formed on the optical waveguide core, it is possible to convert one of the input polarized waves into the other polarized wave, perform Bragg reflection, and transmit the other input polarized wave. Therefore, the output light can be aligned with either TE polarization or TM polarization.

  In addition, the coupling coefficient between the TE polarization and the TM polarization can be increased to increase the polarization conversion efficiency.

DESCRIPTION OF SYMBOLS 10 Support substrate 20 Clad 30 Optical waveguide core 32 Rib waveguide part 34 Base part 36a, 36b Protrusion part 38 Terrace waveguide part 40 Grating groove

Claims (2)

A support substrate;
An optical waveguide core made of silicon, and
A clad provided on the support substrate and including the optical waveguide core;
The optical waveguide core is
A rib waveguide portion on which a grating is formed;
A terrace waveguide portion that is smaller than the rib waveguide portion and is formed integrally with the rib waveguide portion on both side surfaces along the light propagation direction of the rib waveguide portion, respectively .
Before Symbol rib waveguide, the distance from the contact surface with the cladding provided on the lower side of the rib waveguide section, to the contact surface with the cladding provided on the upper side of the rib waveguide section, the thickness of the rib waveguide portion is minor than larger 300nm than 200 nm,
(A)
The grating, k order mode (k is an integer of 0 or more) ₀ diffraction wavelength of the TM polarization of the TE polarization and h-th order mode _lambda, the equivalent of TE polarization k-th order mode in the diffracted wavelength lambda ₀ When the refractive index is N _TEk (λ ₀ ), the equivalent refractive index of TM polarization of the h-order mode (h is an integer of 0 or more ) at the diffraction wavelength λ ₀ is N _TMh (λ ₀ ), and the grating period is Λ , (N _TEk (λ ₀ ) + N _TMh (λ ₀ )) Λ = λ ₀ , and converts the k-order mode TE polarization into the h-order mode TM polarization to Bragg reflection And transmit TM polarization of p-order mode (p is an integer of 0 or more different from h),
The thickness and width of the rib waveguide portion are such that the diffraction wavelength λ ₀ of the k-order mode TE polarized wave to the h-order mode TM polarized wave is the p-order of the h-order mode TM polarized wave. It is formed with a design that is longer than the diffraction wavelength λ ₁ to the TM polarization of the mode
Or
(B)
The grating has a diffraction wavelength of TM polarization of k-order mode and TE polarization of h-order mode of λ ₀ , and an equivalent refractive index of TM polarization of k-order mode at the diffraction wavelength λ ₀ of N _TMk (λ ₀ ), _Where the equivalent refractive index of the TE polarized wave of the h-order mode at the diffraction wavelength λ ₀ is N _TEh (λ ₀ ) and the grating period is Λ, (N _TMk (λ ₀ ) + N _TEh (λ ₀ )) Λ Is formed with a design satisfying = λ ₀ , converts TM polarization of k-order mode to TE polarization of h-order mode and makes Bragg reflection, and transmits TE polarization of p-order mode,
The thickness and width of the rib waveguide portion are such that the diffraction wavelength λ ₀ of the TM polarization of the k-order mode to the TE polarization of the h-order mode is the p-order of the TE polarization of the h-order mode. An optical waveguide element characterized by being designed to have a wavelength longer than the diffraction wavelength λ ₁ of the TE polarization mode . The case of (a), the TM polarization equivalent refractive index of the p-th order mode in the diffracted wavelength lambda ₁ as _{N TMp} (λ _1), satisfies the _{N TEk (λ 0)> N} TMp (λ 1) Formed by design,
The case of (b), the TE polarization equivalent refractive index of the p-th order mode in the diffracted wavelength lambda ₁ as _{N TEp} (λ _1), satisfies the _{N TMk (λ 0)> N} TEp (λ 1) The optical waveguide device according to claim 1, wherein the optical waveguide device is formed by design .

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