70 results about "Relative refractive index" patented technology

An MCF includes a plurality of cores each extending in a direction along a central axis and a cladding covering each of the plurality of cores. The cladding includes a low refractive index barrier. The low refractive index barrier includes an alkali metal element. A relative refractive index of the low refractive index barrier is lower than an average value of a relative refractive indices of the cladding overall. The core interval is set such that a total sum of the power coupling coefficients between a specific core among the plurality of cores and each of all remaining cores is 2.3×10−4 / km or less.

The invention discloses a dual-channel all-optical switch device based on two-dimensional Bi2O2Se and a design method of the dual-channel all-optical switch device. The core of the device is an optical interference structure formed by two-dimensional Bi2O2Se nanosheets arranged on a mica substrate. The same group of transient absorption spectrum data is obtained through a pumping-detection system, and is decoupled into two independent switching channels: a channel I is based on carrier relaxation dynamics, and switching is realized by detecting a ground state bleaching signal at a wave band of 560-670 nm; the channel II is based on refractive index modulation caused by a Kramers-Kronig relationship, and realizes switching by analyzing interference fringe signals formed by probe light between the upper surface of the nanosheet and the lower surface of the mica substrate. The invention also provides a quantitative design method of the device, and the method achieves the fitting of an interference fringe signal through building a transient refractive index model, and precisely solves the relative refractive index change dynamics. The dual-channel device realizes picosecond-level ultrafast response (the channel I is 38.1 ps, and the channel II is 65.8 ps) and low-power-consumption operation (mJ / cm < 2 > magnitude), and the channel switch ratios respectively reach 1.74 and 1.93.

The invention relates to a broadband bending-resistant multimode optical fiber and a preparation method thereof, the refractive index profile of a core layer is in a gradually-changed parabola shape, the distribution index alpha is 1.95-2.65, the radius R1 of the core layer is 12-35 microns, the delta 1max is 0.9%-1.4%, the relative refractive index difference delta 1min at the R1 position of the edge of the core layer is-0.16%--0.06%, cladding layers comprise an inner cladding layer, a first sunken cladding layer, a second sunken cladding layer and an outer cladding layer from inside to outside in sequence, the inner cladding layer is sequentially provided with a first inner cladding layer and a second inner cladding layer from inside to outside, the single-side width (R4-R3) of the first sunken cladding layer is 1.5-9.0 [mu] m, delta 4 is-1.1%--0.60%, the single-side width (R5-R4) of the second sunken cladding layer is 1.0-3.0 [mu] m, delta 5 is-1.0%--0.55%, the radius R6 of the outer cladding layer is 60-65 [mu] m, and delta 6 is-0.12-0.12%. The core cladding is reasonable in structural design, has the excellent characteristics of high bandwidth, strong bending resistance and low attenuation, and is high in transmission efficiency and excellent in long-term stability and reliability.

A multicore optical fiber may include a common cladding comprising a radius R4 defining a glass portion of the optical fiber and having a cladding relative refractive index Δ4. At least two waveguides may extend through the common cladding. Each waveguide may include a core region, an inner cladding region, and a depressed cladding region. Each core region may include a maximum relative refractive index Δ1max. Each inner cladding region may include a relative refractive index Δ2. Each depressed cladding region may include a minimum relative refractive index Δ3min and a trench volume from 20-45%µm2 such that Δ1max>Δ2>Δ3min, and Δ4>Δ3min. A cable cutoff wavelength of each waveguide is ≤1150 nm. The co-propagating and counter-propagating inter-waveguide cross talk between each waveguide and a nearest waveguide is <-35 dB at 1310 nm and <-20 dB at 1550 nm for application lengths of 20 m. A mode field diameter of each waveguide is 8.2-9.0 µm at 1310 nm.

The application discloses a bending-insensitive high-bandwidth multi-mode optical fiber, which comprises a core layer, an extension layer, an inner cladding layer, a sunken cladding layer and an outer cladding layer arranged in sequence from inside to outside, the refractive index profile of the core layer is parabolic, the distribution index is 1.9-2.2, the maximum relative refractive index difference of the core layer center position is 0.9%-1.2%, the relative refractive index difference of the extension layer is -0.03% to -0.02%, the difference between the highest relative refractive index difference and the lowest relative refractive index difference of the inner cladding layer is 0.005%-0.03%, the single-side radial width of the inner cladding layer is 0.5-4 mu m, the single-side radial width of the sunken cladding layer is 3-9 mu m, and the relative refractive index difference of the sunken cladding layer is -0.7% to -0.4%. In the application, the optical fiber viscosity is optimized, the sensitivity of the optical fiber bandwidth to wavelength is reduced, the optical fiber has good bending resistance and super high bandwidth performance by reasonably designing the waveguide structure and the doping system.

A polarization maintaining optical fiber (1) has: a core (11); an inner layer (12) that surrounds the core (11) without a gap; a pair of stress applying portions (13) disposed at positions sandwiching the core (11); and a cladding (14) that encloses the inner layer (12) and the pair of stress applying portions (13), a mode field diameter of light of a wavelength of 1.55 μm is 9.3 μm or less in a case where the light propagates in the core (11), a cutoff wavelength is 1.32 μm or more in a case where the optical fiber length is 0.25 m and the stress applying portions (13) are wound one turn around an axis having a radius of 2 mm in a manner that a slow axis of the stress applying portions (13) is perpendicular to a surface of the axis, and a product of an area of a cross section of the inner layer (12) perpendicular to a length direction and an average of relative refractive index differences of the inner layer (12) as a whole with respect to the cladding (14) is -36% μm 2 or more and 0% μm 2 or less.

The object of this invention is to obtain, at a lower cost, an optical glass with a low temperature coefficient of relative refractive index that helps correct the effects of temperature changes on imaging characteristics, and preforms and optical elements using this optical glass. The optical glass, by mass%, contains 1.0% to 27.0% SiO2, 5.0% to 34.0% Ln2O3 (where Ln is one or more selected from the group consisting of La, Gd, Y, and Yb), more than 30.0% to 65.0% BaO, and 25.0% or less B2O3. The temperature coefficient of its relative refractive index (589.29 nm) (40–60 °C) is in the range of +3.0 × 10⁻⁶ to -10.0 × 10⁻⁶ (°C⁻¹).

This disclosure relates to optical integrated devices, optical integrated circuit wafers, and methods for manufacturing optical integrated devices. The optical integrated device includes a substrate and a waveguide having a hollow structure. The waveguide includes a first waveguide and a second waveguide, the second waveguide being optically coupled to the first waveguide and having a relative refractive index difference smaller than that of the first waveguide, and the waveguide converting a mode diameter to the mode diameter of an optical fiber according to the propagation of light. The optical integrated device includes a recessed portion formed near a cleavage line on the substrate, such that, with the cleavage end surface of the substrate protruding further in the axial direction of the optical waveguide than the output end surface of the second waveguide, the width of the output end surface is smaller than the core width of the optical fiber optically coupled to the output end surface.

The optical fiber type light spot homogenizer comprises a machine frame, a laser source is arranged at one end of the machine frame, a multimode optical fiber corresponding to the laser source is arranged at the other end of the machine frame, the laser source emits a laser beam, the multimode optical fiber receives the laser beam, and the multimode optical fiber is connected with the machine frame. The multi-mode fiber laser is characterized in that the relative refractive index difference section of the inner side of the sunken inner cladding of the multi-mode fiber is in a two-stage step decreasing shape, and the center line of the laser beam and the center of the end face of the multi-mode fiber are aligned and offset in parallel by a section of radial offset. The device is small in size, low in cost, compact in structure, good in homogenization effect and stable in performance, and can be directly seamlessly integrated with an input laser source and an output optical fiber system. The optical fiber type light spot homogenizer assembly and the laser beam shaping system can achieve efficient light spot homogenization within the centimeter-level distance. The system can be applied to a vehicle-mounted laser radar, a vehicle-mounted head-up display, a multimode PON optical splitter, laser medical equipment or laser material processing equipment and the like.

This invention belongs to the field of optical fiber communication technology and discloses a low-refractive-index doped mother tube, a capillary, a preparation method, and applications. The invention first deposits a low-refractive-index doped silicon dioxide layer on the inner surface of a pure silicon dioxide liner to prepare a low-refractive-index doped mother tube. Then, the low-refractive-index doped mother tube is heated to its softening temperature and drawn to obtain a low-refractive-index doped capillary. The minimum relative refractive index difference of the low-refractive-index doped silicon dioxide layer in this invention is -1.8% to -2.6%. The low-refractive-index doped capillary designed in this invention can be used to prepare optical fiber power combiners and can improve the performance of the combiners.

The present invention aims to provide a multi-core optical fiber and a design method thereof, which configures four cores of a single-peak type with a standard cladding diameter, satisfies a desired specification, and is excellent in mass productivity, quality, and yield. The multi-core optical fiber of the present invention has four cores of a single-peak type refractive index profile with a radius a arranged in a square lattice shape in a long side direction, and a cladding region with a diameter of 125 ± 1 μm, which has a lower refractive index than the cores, and an absolute value of a relative refractive index difference from the cores is Δ, on an outer peripheral portion of the cores, and the four cores are arranged in a manner that a relationship of a minimum distance (OCT) from a center of the core to an outer periphery of the cladding region, a minimum value Λ of a pitch of the cores, and an MFD at a wavelength of 1310 nm satisfy a number C1, and the relative refractive index difference Δ of the cores and the cladding region and the radius a of the cores are set. [Number C1] OCT ≥ 3.73 MFD + 3.43 Λ ≤ -5.28 MFD + 83.54.

This optical fiber comprises a core, an inner cladding, a trench, and an outer cladding. When the relative refractive index difference of the core is ∆1, the relative refractive index difference of the inner cladding is ∆2, the relative refractive index difference of the trench is ∆3, the relative refractive index difference of the outer cladding is ∆4, the outer diameter of the core is 2r1, the outer diameter of the inner cladding is 2r2, the outer diameter of the trench is 2r3, and the outer diameter of the outer cladding is 2r4, the following relationships are established.　2.2 ≤ r2 / r1 ≤ 3.6; 3μm ≤ r3 － r2 ≤ 12μm; 0.25% ≤ ∆1 － ∆2 ≤ 0.50%; − 0.70% ≤ ∆3 ≤ − 0.10%; A zero-dispersion wavelength is 1296-1306 nm. A zero-dispersion slope is 0.088 ps / nm2 / km or less. A 500-meter cable cutoff wavelength is 1260 nm or less. A bending loss for light with a wavelength of 1310 nm when the optical fiber is wound around a mandrel having a diameter of 15 mm is 0.5 dB or less per turn.

The application discloses a silica ceramic core and a preparation method thereof. The preparation method of the silica ceramic core comprises the following steps: preparing a ceramic slurry, wherein the ceramic slurry comprises ceramic particles, and the ceramic particles comprise silica and silicon nitride; preparing a ceramic matrix blank by means of light-curing 3D printing based on the ceramic slurry; pre-sintering the ceramic matrix blank to obtain a ceramic matrix; preparing an additive solution, impregnating the additive solution into the ceramic matrix, and then performing a heating reaction; and then performing sintering to obtain the silica ceramic core. The application solves the problem of easy scattering caused by the low relative refractive index of the ceramic slurry in the process of preparing the silica ceramic core by means of light-curing 3D printing of the silica ceramic, thereby avoiding the decrease of the forming precision, and the silica ceramic core is easy to demold, and the problem of the rough surface of a casted part caused by the high porosity of the ceramic core during casting is avoided.

An object of the present invention is to achieve a low delay core applicable to a Master channel of a Master-Slave CPE (MS-CPE) transmission method with a general-purpose refractive index distribution structure.An optical fiber according to the present invention is a single-mode optical fiber, and has an SI-type refractive index distribution structure, in which a clad region relative refractive index difference Δ (%) with respect to a core region refractive index, a radius a (μm) of the core region, and a group delay time difference Δτ between the Master channel and the Slave channel satisfy “Mathematical Expression 19” and “Mathematical Expression 20”, orhas a W-type refractive index distribution structure, in which a mode field diameter MFD is 9.5 to 10.1 μm, and a relative refractive index difference Δ1 (%) of a low refractive index layer with respect to a core, a relative refractive index difference Δ2 (%) of the clad region with respect to the core, the core radius a1, and the group delay time difference Δτ between the Master channel and the Slave channel satisfy “Mathematical Expression 41”.

A metamaterial (10) is a terahertz wave control element that optically controls terahertz waves, and has a matrix (20) and a plurality of dielectric fine particles (30) dispersed in the matrix (20). The size of the dielectric fine particles (30) is less than or equal to the wavelength of terahertz waves. The value of the relative refractive index of the matrix (20) for terahertz waves is smaller, by 2.0 or more, than the value of the relative refractive index of the dielectric fine particles (30) for terahertz waves.

The application relates to a method and device for measuring the relative refractive index difference between a fiber core and a cladding. The method comprises: inputting single transverse mode laser beams of different wavelengths in a target application wave band into a fiber to be measured at equal wavelength intervals, obtaining a light spot pattern of the fiber to be measured at each wavelength, and then obtaining a two-dimensional measurement matrix with the row and column sizes being the number of pixel points of the light spot pattern and the number of sampling wavelengths; performing Fourier transform on each row of data of the two-dimensional measurement matrix and adding the results to obtain a differential mode group delay test value of a first high-order mode relative to a base mode; and searching a lookup table of the change of a differential mode group delay theoretical value corresponding to a high-order mode of the fiber to be measured with the core-cladding refractive index difference to find a differential mode group delay theoretical value closest to the differential group delay test value under the core diameter of the fiber to be measured, and obtaining the core-cladding refractive index difference of the fiber to be measured. The method can realize efficient, accurate and non-invasive measurement of the core-cladding refractive index difference of a long link fiber.

The invention belongs to the technical field of few-mode optical fibers, and discloses an ultralow differential mode group delay few-mode optical fiber and a preparation method thereof. The ultralow differential mode group delay few-mode optical fiber provided by the invention comprises a core layer structure, an inner cladding layer structure and an outer cladding layer from inside to outside, the core layer structure comprises a first core layer and a second core layer from inside to outside; the two core layers are provided with gradient sections, the distribution index alpha 1 of the first core layer is 1.5-1.9, and the distribution index alpha 2 of the second core layer is 1.4-1.9; the minimum relative refractive index difference 1 of the first core layer is 0.3% to 0.6%; the maximum relative refractive index difference of the first core layer and the maximum relative refractive index difference of the second core layer are the same and marked as 2, 2 is 0.6%-0.9%, and 2 > 1; the second core layer has a minimum relative refractive index difference 3 of-0.2% to-0.1%. According to the invention, extremely low differential mode group delay can be realized.

To provide an optical fiber that is suitable for reducing transmission loss and is highly manufacturable. [Solution] The optical fiber comprises a core made of silica glass and a cladding portion made of silica glass, surrounding the outer circumference of the core and having a refractive index lower than the maximum refractive index of the core. The core has a center core which has the highest average refractive index within the optical fiber, and the center core does not contain germanium as a dopant to increase the refractive index of the silica glass, and the relative refractive index difference Δclad between the refractive index of the cladding portion and the refractive index of the pure silica glass is 0% or more.

The application relates to a non-zero dispersion-shifted single-mode optical fiber with a low cutoff wavelength and a low macro-bending loss and an application, which comprises a core layer and a cladding layer surrounding the core layer, the cladding layer comprises a depression layer, an inner cladding layer and an outer cladding layer arranged in sequence from inside to outside, the inner cladding layer comprises a first inner cladding layer and a second inner cladding layer arranged in sequence from inside to outside, the relative refractive index difference Delta 1 of the core layer is 0.500% to 0.570%, and the refractive index curve of the core layer is a gradually decreasing parabolic shape, and the refractive index decreases with the increase of the core diameter. The shape of the refractive index profile of the optical fiber is adjusted, the conventional multi-core layer step type design is avoided, the gradually decreasing parabolic design is adopted, compared with the triangular depression core structure, the core center high refractive index range and the effective refractive index area of the application are larger, the waveguide of the light can be effectively bound in the core, and compared with the trapezoidal core, the core layer decreases in a parabolic mode with the radius, the radius of the core layer can be effectively reduced, and the purposes of reducing the cutoff wavelength and the bending loss are achieved.

A multimode optical fiber having a core region. The core region includes silica, has an outer radius r1, and has a maximum relative refractive index of about 1.5% or less. Further, the multimode optical fiber is configured to have an effective bandwidth of about 4.7 GHz-Km or more for an excited portion of the core region having a diameter greater than 50 microns, the effective bandwidth being at a wavelength in a range of about 800 to about 1370 nm.

This invention discloses a fluorine-free, environmentally friendly, bend-insensitive single-mode optical fiber, belonging to the field of optical fiber communication technology. The invention comprises a core layer and an outer cladding arranged sequentially from the inside out. The core layer includes a first recessed core layer and a second protruding core layer, with the second protruding core layer disposed outside the first recessed core layer. The outer cladding is a silica cladding. The refractive index of the core layer is higher than that of the outer cladding, and the refractive index profile of the core layer exhibits a step-like distribution. The relative refractive index difference ΔN1 of the first recessed core layer is smaller than the relative refractive index difference ΔN2 of the second protruding core layer. This invention, through a redesign of the optical fiber's refractive index profile, achieves a bend-insensitive optical fiber that still meets the standards in a fluorine-free state, satisfying the requirements of the G.657.A2 standard. This solves the technical problem of existing technologies using an outer fluorine cladding to reduce bending loss, which fails to meet safety and environmental protection requirements. The invention features a simple structure and excellent performance.

The embodiment of the invention provides an optical fiber preform and a preparation method thereof, an optical fiber and OVD process equipment. The optical fiber preform comprises a core body, an inner cladding, an adjusting layer and an outer cladding which are sequentially arranged from inside to outside, the adjusting layer comprises a first adjusting layer adjacent to the inner cladding layer and a second adjusting layer adjacent to the outer cladding layer; the relative refractive index of the first adjusting layer is smaller than that of the second adjusting layer. The optical fiber preform is used for improving the bending performance of the optical fiber while reducing the transmission loss.

This multicore fiber comprises 2-4 core elements (10), and satisfies Z≤453 when Z=(r1 2πΔ1)(r3 2-r2 2)π|Δ3| / r2, wherein r1 is the radius of a core (11), r2 is the radius of an intermediate layer (12), r3 is the radius of a trench layer (13), Δ1 is the relative refractive index of the core (11), Δ2 is the relative refractive index of the intermediate layer (12), and Δ3 is the relative refractive index of the trench layer (13).

This invention relates to a low-attenuation non-zero dispersion-shifted single-mode optical fiber and its applications. The fiber comprises a first core layer, a second core layer, and a third core layer, a recessed cladding, an auxiliary cladding, and a first outer cladding. The first core layer has a radius R1 of 0.8–1.3 μm and a relative refractive index difference Δ1 of -0.01%–0.05%. The second core layer has a radius R2 of 1.5–1.8 μm and a relative refractive index difference Δ2 of -0.12%–0.15%. The third core layer has a radius R3 of 2.0–2.5 μm and a relative refractive index difference Δ3 of -0.34%–0.30%. The recessed cladding has a radius R4 of 5–6.5 μm and a relative refractive index difference Δ4 of -0.51%–0.57%. The fiber core layer of this invention has a three-core structure, which reduces interlayer stress during fiber drawing. Combined with the near-zero relative refractive index difference of the core layers, it reduces core layer distortion and lowers fiber attenuation.

The invention provides optical glass which has optical characteristics of high refractive index and high dispersion, and is helpful for correcting the influence of temperature change on imaging characteristics. The optical glass contains, in mass%, more than 0% and 35.0% or less of a B2O3 component, 1.0% or more and 50.0% or less of an Ln2O3 component (in the formula, Ln represents one or more elements selected from the group consisting of La, Gd, Y and Yb), and 10.0% or more and 50.0% or less of a BaO component, the sum of mass of TiO2 + ZrO2 + WO3 + Nb2O5 + Ta2O5 is more than 0% and 50.0% or less, and the optical glass has a refractive index of 1.75 or more and an Abbe number (vd) of 18 or more and 42 or less. And the temperature coefficient (40-60 DEG C) of the relative refractive index (589.29 nm) is within the range of + 4.0 * 10 <-6 >-10.0 * 10 <-6 > (DEG C <-1 >).

The multi-core optical fiber includes a plurality of cores, a first cladding, and a second cladding. The second cladding has a refractive index lower than a refractive index of each of the cores and higher than a refractive index of the first cladding. The multi-core optical fiber has a transmission loss of 0.22 dB / km or less. When an effective area of each of the cores is denoted as Aeff, a center-to-center distance between two cores is denoted as Λ, and a relative refractive index difference of each of the cores with respect to the refractive index of the first cladding is denoted as Δcore, Aeff1 is defined byAeff⁢1=18.6-4.63 ln⁢ (Δcore)+1.24Λ+2⁢4.1[ln⁢ (Δcore)]⁢2-6.05×10-3⁢Λ2-0.858Λ⁢ ln⁢ (Δcore),andthe multi-core optical fiber satisfies Condition below by using Aeff1.0.35≤Δcore≤1.25≤Λ≤5⁢00.8Aeff⁢1≤Aeff≤1.35Aeff⁢1

A multimode optical fiber includes a core portion comprising an α-profile, a core maximum relative refractive index ΔCmax, and a core minimum relative refractive index ΔCmin. ΔCmax may be ≤0.85 Δ% and ≥−0.1 Δ%, ΔCmax>ΔCmin, and ΔCmin may be <0 Δ%. A depressed index trench portion surrounds the core portion. The depressed index trench portion has a minimum relative refractive index ΔTmin. A shelf portion surrounds the depressed index trench portion. The shelf portion has a maximum relative refractive index ΔSmax. An outer cladding portion surrounds the shelf portion. The outer cladding portion has a relative refractive index ΔOC. In embodiments, ΔCmin>ΔTmin, ΔCmax>ΔSmax, ΔSmax>ΔTmin, and ΔSmax>ΔOC. Each of the core portion, the depressed index trench portion, and the outer cladding portion may be formed from silica-based glass down-doped with fluorine.

The application relates to an ultra-small-outer-diameter low-attenuation bending-resistant single-mode optical fiber, which comprises a core layer and a cladding layer, the relative refractive index difference Delta n1 of the core layer is 0.3-0.5%, and the diameter D1 is 7-9 mu m; the cladding layer comprises an inner cladding layer, a sunken cladding layer and an outer cladding layer from inside to outside, the inner cladding layer is a transition layer between the core layer and the sunken cladding layer, the relative refractive index difference decreases from inside to outside, the relative refractive index difference Delta n2 is -0.01-0.05%, and the diameter D2 is 14-18 mu m; the relative refractive index difference Delta n3 of the sunken cladding layer is -0.2--0.4%, and the diameter D3 is 28-34 mu m; the outer cladding layer is a pure silica glass layer, the relative refractive index difference Delta n4 is 0, and the diameter D4 is 79-81 mu m. The application can accommodate more fibers in the same volume of optical cable. Through optimization of the fiber profile design and the physicochemical properties of the coating layer, the bending performance, the mechanical performance and the optical transmission performance of the optical fiber can be effectively ensured, and the same communication performance as that of a 125 mu m conventional fiber can be achieved.

This invention relates to a vehicle-mounted multimode optical fiber for communication and power transmission, comprising a core layer and a cladding layer. The core layer has a parabolic refractive index profile. The core layer is characterized by a distribution index α of 2.3–2.7, a core radius R1 of 20–32 μm, and a maximum relative refractive index difference Δ at the core center. 1max The relative refractive index is 0.8%–1.4%, and the relative refractive index difference Δ1 at the core edge R1 is -0.05%–0.05%. The cladding, from the inside out, consists of a first inner cladding, a first depressed cladding, a second inner cladding, a second depressed cladding, and an outer cladding. This invention improves the bandwidth performance of multimode fiber and enhances its differential mode delay (DMD) performance by optimizing the cross-sectional structure design and the amount of multi-element doping. It also reduces the fiber's bandwidth-wavelength sensitivity, achieving both optimized optical transmission bandwidth performance and improved fiber bending insensitivity; thus realizing the integration of high-speed communication and fiber power transmission.

The cladding (12) includes an inner cladding (121) covering the outer periphery of the core (11), a trench (122) covering the outer periphery of the inner cladding, and an outer cladding (123) covering the outer periphery of the trench. The inner cladding has a lower refractive index than the core. The trench has a lower refractive index than the inner cladding. The outer cladding has a higher refractive index than the trench and a lower refractive index than the core. When the relative refractive index difference of the core with respect to the refractive index of pure silica is set as Δ1, the relative refractive index difference of the inner cladding with respect to the refractive index of pure silica is set as Δ2, the relative refractive index difference of the trench with respect to the refractive index of pure silica is set as Δ3, the radius of the outer periphery of the core is set as r1, the radius of the outer periphery of the inner cladding is set as r2, and the radius of the outer periphery of the trench is set as r3, r2 / r1 is 2.2 or more and 3.6 or less, r3-r2 is 3 μm or more and 10 μm or less, Δ1-Δ2 is 0.15% or more and 0.40% or less, and Δ3 is -0.70% or more and -0.10% or less.