Optical waveguide element

Abstract

This optical waveguide element is configured so as to comprise a first optical coupler (1) that demultiplexes a given optical signal into two, a first arm part (2) having a first adjustment section for adjusting the phase of one optical signal after demultiplexing by the first optical coupler (1), a second arm part (3) having a second adjustment section for adjusting the phase of the other optical signal after demultiplexing by the first optical coupler (1), and a second optical coupler (4) that multiplexes the optical signal after phase adjustment by the first arm part (2) and the optical signal after phase adjustment by the second arm part (3). In the optical waveguide element, the respective waveguide widths in the first adjustment section and the second adjustment section and the respective line lengths in the first adjustment section and the second adjustment section are determined on the basis of a predetermined phase difference for the two optical signals multiplexed by the second optical coupler (4).

Description

Optical waveguide element

[0001] This disclosure relates to an optical waveguide element.

[0002] There is an optical waveguide element in which a first optical coupler splits an optical signal into two, a first arm propagates one of the optical signals after splitting by the first optical coupler, a second arm propagates the other optical signal after splitting by the first optical coupler, and the second optical coupler combines the optical signals propagated by the first arm and the optical signals propagated by the second arm. Due to the difference in the optical path length of the first arm and the optical path length of the second arm, the light interferes when the optical signals are combined by the second optical coupler, causing the light to reinforce or cancel each other out. As such an optical waveguide element, for example, Patent Document 1 discloses an optical waveguide element in which the first arm and the second arm each have multiple optical waveguides. The multiple optical waveguides have different waveguide widths according to certain conditions, and the multiple optical waveguides are connected in cascading order. Because the waveguide widths of multiple optical waveguides differ from one another according to certain conditions, the temperature dependence of the optical waveguide element, which fluctuates with changes in ambient temperature, can be reduced.

[0003] Japanese Patent Publication No. 2011-215331

[0004] Although the optical waveguide element disclosed in Patent Document 1 can reduce temperature dependence, it has the problem that if the waveguide widths of multiple optical waveguides are different from each other, the center wavelength of the optical waveguide element may fluctuate due to manufacturing errors in the waveguide width.

[0005] This disclosure was made to solve the above-mentioned problems, and aims to provide an optical waveguide element that can suppress not only the fluctuation of the center wavelength due to temperature changes, but also the fluctuation of the center wavelength due to manufacturing errors in the waveguide width.

[0006] The optical waveguide element according to this disclosure comprises a first optical coupler that splits a given optical signal into two, a first arm portion having a first adjustment section for adjusting the phase of one of the optical signals after splitting by the first optical coupler, a second arm portion having a second adjustment section for adjusting the phase of the other optical signal after splitting by the first optical coupler, and a second optical coupler that combines the optical signal after phase adjustment by the first arm portion and the optical signal after phase adjustment by the second arm portion. Furthermore, the waveguide width in the first adjustment section and the second adjustment section, and the line length in the first adjustment section and the second adjustment section, are determined in advance based on a predetermined phase difference between the two optical signals combined by the second optical coupler.

[0007] According to this disclosure, it is possible to suppress not only the fluctuation of the central wavelength due to temperature changes, but also the fluctuation of the central wavelength due to manufacturing errors in the waveguide width.

[0008] This is a configuration diagram showing an optical waveguide element according to Embodiment 1. This is a configuration diagram showing an optical waveguide element according to Embodiment 2.

[0009] To provide a more detailed explanation of this disclosure, the forms for implementing this disclosure will be described below with reference to the attached drawings.

[0010] Embodiment 1. Figure 1 is a configuration diagram showing an optical waveguide element according to Embodiment 1. The optical waveguide element shown in Figure 1 comprises a first optical coupler 1, a first arm portion 2, a second arm portion 3, and a second optical coupler 4. The first optical coupler 1 is implemented, for example, by an MMIC (Multi-Mode Interface Coupler), a directional coupler, or a Y-branch waveguide. When an optical signal is supplied from the outside, the first optical coupler 1 splits the optical signal into two, outputs one of the split optical signals to the first arm portion 2, and outputs the other split optical signal to the second arm portion 3.

[0011] The first arm section 2 includes, as optical waveguides, a first optical waveguide 11, a second optical waveguide 12, an optical waveguide 13, a fourth optical waveguide 14, and a fifth optical waveguide 15. Each of the first optical waveguide 11, optical waveguide 13, and fifth optical waveguide 15 has a silicon (Si) core and silicon dioxide (SiO₂) ２ This is a waveguide with silicon dioxide as the cladding. Silicon is also called silicon. Silicon dioxide is also called silicon oxide. The second optical waveguide 12 and the fourth optical waveguide 14 each have silicon nitride (SiN) as the core and silicon dioxide (SiO ２ This waveguide has silicon nitride (SiO₂) as its cladding. Silicon nitride is also called silicon nitride. The first arm section 2 is equipped with spot size converters 21 to 32. The cores of the spot size converters 21, 22, 31, and 32 are silicon (Si), and the cladding of the spot size converters 21, 22, 31, and 32 is silicon dioxide (SiO₂). ２ The core of the spot size converters 24, 25, 28, and 29 is silicon nitride (SiN), and the cladding of the spot size converters 24, 25, 28, and 29 is silicon dioxide (SiO₂). ２ The cores of the spot size converters 23, 26, 27, and 30 hold silicon (Si) and silicon nitride (SiN) separated for a certain period of time in the thickness direction of the substrate, and the cladding of the spot size converters 23, 26, 27, and 30 is silicon dioxide (SiO ２ The first arm portion 2 has a first adjustment section (1) for adjusting the phase of one of the optical signals after demultiplexing by the first optical coupler 1. Specifically, the first arm portion 2 has a reference section (1-1), a first adjustment section (1), and a reference section (1-2).

[0012] One end of the first optical waveguide 11 is connected to one output terminal 1a of the first optical coupler 1. The other end of the first optical waveguide 11 is connected to one end of the second optical waveguide 12 via spot size converters 21, 22, 23, and 24. The first optical waveguide 11 is an optical waveguide that forms part of the reference section (1-1). The waveguide width of the first optical waveguide 11 is w １１and the waveguide width w １１ is a waveguide width that satisfies the single-mode condition of the waveguide material of the first arm portion 2.

[0013] One end of the second optical waveguide 12 is connected to the other end of the first optical waveguide 11 via spot size converters 21, 22, 23, 24. The other end of the second optical waveguide 12 is connected to one end of the third optical waveguide 13 via spot size converters 25, 26. The second optical waveguide 12 is an optical waveguide that bears a part of the first adjustment section (1). The waveguide width of the second optical waveguide 12 is w ２２ and the waveguide width w ２２ is a waveguide width different from the waveguide width w ２１ and does not need to satisfy the single-mode condition. The line length of the second optical waveguide 12 is (L + ΔL) / 2. Each of the waveguide width w ２２ and the line length (L + ΔL) / 2 is determined based on a predetermined phase difference for two optical signals multiplexed by the second optical coupler 4. The predetermined phase difference for the two optical signals is the desired phase difference with respect to the phase difference of the two optical signals, and the desired phase difference corresponds to the design value.

[0014] One end of the third optical waveguide 13 is connected to the other end of the second optical waveguide 12 via spot size converters 25, 26. The other end of the third optical waveguide 13 is connected to one end of the fourth optical waveguide 14 via spot size converters 27, 28. The shape of the third optical waveguide 13 is U-shaped so that the second optical waveguide 12 and the fourth optical waveguide 14 are arranged in parallel.

[0015] One end of the fourth optical waveguide 14 is connected to the other end of the third optical waveguide 13 via spot size converters 27, 28 so as to be parallel to the second optical waveguide 12. The other end of the fourth optical waveguide 14 is connected to one end of the fifth optical waveguide 15 via spot size converters 29, 30, 31, 32. The fourth optical waveguide 14 is an optical waveguide that bears a part of the first adjustment section (1). The waveguide width of the fourth optical waveguide 14 is the same w as the waveguide width of the second optical waveguide 12 ２２Therefore, the length of the fourth optical waveguide 14 is the same as the length of the second optical waveguide 12, (L + ΔL) / 2.

[0016] One end of the fifth optical waveguide 15 is connected to the other end of the fourth optical waveguide 14 via spot size converters 29, 30, 31, and 32, so as to be parallel to the first optical waveguide 11. The other end of the fifth optical waveguide 15 is connected to one input terminal 4a of the second optical coupler 4. The fifth optical waveguide 15 is an optical waveguide that forms part of the reference section (1-1). The waveguide width of the fifth optical waveguide 15 is the same as the waveguide width of the first optical waveguide 11. １１ Therefore, the length of the fifth optical waveguide 15 is the same as the length of the first optical waveguide 11.

[0017] The second arm section 3 includes a sixth optical waveguide 16, a seventh optical waveguide 17, an eighth optical waveguide 18, a ninth optical waveguide 19, and a tenth optical waveguide 20 as optical waveguides. Each of the sixth optical waveguide 16, the seventh optical waveguide 17, the eighth optical waveguide 18, the ninth optical waveguide 19, and the tenth optical waveguide 20 has a silicon (Si) core and silicon dioxide (SiO₂) ２ The waveguide has a cladding of ). The second arm section 3 is equipped with spot size converters 41 to 52. The cores of the spot size converters 42, 43, 50, and 51 are silicon nitride (SiN), and the cladding of the spot size converters 42, 43, 50, and 51 is silicon dioxide (SiO ２ The cores of the spot size converters 41, 44, 49, and 52 hold silicon (Si) and silicon nitride (SiN) separated for a certain period of time in the thickness direction of the substrate, and the cladding of the spot size converters 41, 44, 49, and 52 is silicon dioxide (SiO ２ The core of the spot size converters 45-48 is silicon (Si), and the cladding of the spot size converters 45-48 is silicon dioxide (SiO₂). ２The second arm section 3 has a second adjustment section (2) for adjusting the phase of the other optical signal after demultiplexing by the first optical coupler 1. Specifically, the second arm section 3 has a reference section (2-1), a second adjustment section (2), and a reference section (2-2). The sum of the lengths of the reference section (2-1) and the reference section (2-2) is the same as the sum of the lengths of the reference section (1-1) and the reference section (1-2).

[0018] One end of the sixth optical waveguide 16 is connected to the other output terminal 1b of the first optical coupler 1. The other end of the sixth optical waveguide 16 is connected to one end of the seventh optical waveguide 17 via spot size converters 41, 42, 43, 44, and 45. The sixth optical waveguide 16 is an optical waveguide that forms part of the reference section (2-1). The waveguide width of the sixth optical waveguide 16 is w １１ And the waveguide width lol １１ This is the waveguide width that satisfies the single-mode condition for the waveguide material of the second arm portion 3.

[0019] One end of the seventh optical waveguide 17 is connected to the other end of the sixth optical waveguide 16 via spot size converters 41, 42, 43, 44, and 45. The other end of the seventh optical waveguide 17 is connected to one end of the eighth optical waveguide 18 via spot size converter 46. The seventh optical waveguide 17 is an optical waveguide that forms part of the second adjustment section (2). The waveguide width of the seventh optical waveguide 17 is w １２ And the waveguide width lol １２ is waveguide width lol １１ The waveguide width is different, and it does not need to satisfy the single-mode condition. The line length of the seventh optical waveguide 17 is L / 2. Waveguide width w １２ Each of the line length L / 2 is determined based on a predetermined phase difference between the two optical signals combined by the second optical coupler 4.

[0020] One end of the eighth optical waveguide 18 is connected to the other end of the seventh optical waveguide 17 via a spot size converter 46. The other end of the eighth optical waveguide 18 is connected to one end of the ninth optical waveguide 19 via a spot size converter 47. The shape of the eighth optical waveguide 18 is U-shaped so that the seventh optical waveguide 17 and the ninth optical waveguide 19 are arranged in parallel.

[0021] One end of the ninth optical waveguide 19 is connected to the other end of the eighth optical waveguide 18 via a spot size converter 47, so as to be parallel to the seventh optical waveguide 17. The other end of the ninth optical waveguide 19 is connected to one end of the tenth optical waveguide 20 via spot size converters 48, 49, 50, 51, and 52. The ninth optical waveguide 19 is an optical waveguide that forms part of the second adjustment section (2). The waveguide width of the ninth optical waveguide 19 is the same as the waveguide width of the seventh optical waveguide 17. １２ Therefore, the length of the ninth optical waveguide 19 is L / 2, which is the same as the length of the seventh optical waveguide 17.

[0022] One end of the tenth optical waveguide 20 is connected to the other end of the ninth optical waveguide 19 via spot size converters 48, 49, 50, 51, and 52, so as to be parallel to the sixth optical waveguide 16. The other end of the tenth optical waveguide 20 is connected to the other input terminal 4b of the second optical coupler 4. The tenth optical waveguide 20 is an optical waveguide that forms part of the reference section (2-1). The waveguide width of the tenth optical waveguide 20 is the same as the waveguide width of the sixth optical waveguide 16. １１ Therefore, the length of the tenth optical waveguide 20 is the same as the length of the sixth optical waveguide 16.

[0023] Spot size converters 23, 26, 27, 30, 41, 44, 49, and 52 are spot size converters (a). Spot size converters (a) have waveguide width w １１ Waveguide width lol ２１ Transition to, or waveguide width w ２１ Waveguide width lol １１In transitioning to the next mode, it has a mode conversion function that allows transitioning without loss from a Si-core ground mode to a SiN-core ground mode, or from a SiN-core ground mode to a Si-core ground mode. This is usually achieved by adiabatically reducing the waveguide width of the source core material and simultaneously adiabatically increasing the waveguide width of the destination core material. Spot size converters 21, 22, 31, 32, 45, 46, 47, and 48 are spot size converters (b). Spot size converter (b) has a waveguide width w １１ Waveguide width lol １２ Transition to, or waveguide width w １２ Waveguide width lol １１ In transitioning to the waveguide, it has a mode conversion function to transition the ground mode of the waveguide without loss, which is usually achieved by adiabatically changing the waveguide width. Spot size converters 24, 25, 28, 29, 42, 43, 50, and 51 are spot size converters (c). Spot size converter (c) has a waveguide width w ２１ Waveguide width lol ２２ Transition to, or waveguide width w ２２ Waveguide width lol ２１The system has a mode conversion function to transition the waveguide's base mode without loss during the transition, which is usually achieved by adiabatically changing the waveguide width. The number of spot size converters 21 to 32 in the first arm section 2 is the same as the number of spot size converters 41 to 52 in the second arm section 3. As a result, the difference in optical path length between the optical path length of the first arm section 2 and the optical path length of the second arm section 3 can be designed based only on the line length of the optical waveguide in the first adjustment section (1) and the line length of the optical waveguide in the second adjustment section (2). In the optical waveguide element shown in Figure 1, the first arm section 2 has spot size converters 21 to 32, and the second arm section 3 has spot size converters 41 to 52. The number of spot size converters in the first arm section 2 and the number of spot size converters in the second arm section 3 must be the same, and it is not limited to the case where the first arm section 2 has spot size converters 21 to 32 and the second arm section 3 has spot size converters 41 to 52.

[0024] The second optical coupler 4 is implemented, for example, by an MMIC, a directional coupler, or a Y-branch waveguide. One input terminal 4a of the second optical coupler 4 is connected to the other end of the fifth optical waveguide 15. The other input terminal 4b of the second optical coupler 4 is connected to the other end of the tenth optical waveguide 20. The second optical coupler 4 combines the optical signal after phase adjustment by the first arm 2 and the optical signal after phase adjustment by the second arm 3. The second optical coupler 4 outputs the combined optical signal to the outside.

[0025] The waveguide width at the input terminal of the spot size converter 21 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 21 is w １２ Therefore, the waveguide width at the input terminal of the spot size converter 22 is w １２ Therefore, the waveguide width at the output terminal of the spot size converter 22 is w １１ Therefore, the waveguide width at the input terminal of the spot size converter 23 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 23 is w ２１Therefore, the waveguide width at the input terminal of the spot size converter 24 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 24 is w ２２ Therefore, the waveguide width at the input terminal of the spot size converter 25 is w ２２ Therefore, the waveguide width at the output terminal of the spot size converter 25 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 26 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 26 is w １１ That is the case.

[0026] The waveguide width at the input terminal of the spot size converter 27 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 27 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 28 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 28 is w ２２ Therefore, the waveguide width at the input terminal of the spot size converter 29 is w ２２ Therefore, the waveguide width at the output terminal of the spot size converter 29 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 30 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 30 is w １１ Therefore, the waveguide width at the input terminal of the spot size converter 31 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 31 is w １２ Therefore, the waveguide width at the input terminal of the spot size converter 32 is w １２ Therefore, the waveguide width at the output terminal of the spot size converter 32 is w １１ That is the case.

[0027] The waveguide width at the input terminal of the spot size converter 41 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 41 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 42 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 42 is w ２２Therefore, the waveguide width at the input terminal of the spot size converter 43 is w ２２ Therefore, the waveguide width at the output terminal of the spot size converter 43 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 44 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 44 is w １１ Therefore, the waveguide width at the input terminal of the spot size converter 45 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 45 is w １２ Therefore, the waveguide width at the input terminal of the spot size converter 46 is w １２ Therefore, the waveguide width at the output terminal of the spot size converter 46 is w １１ That is the case.

[0028] The waveguide width at the input terminal of the spot size converter 47 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 47 is w １２ Therefore, the waveguide width at the input terminal of the spot size converter 48 is w １２ Therefore, the waveguide width at the output terminal of the spot size converter 48 is w １１ Therefore, the waveguide width at the input terminal of the spot size converter 49 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 49 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 50 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 50 is w ２２ Therefore, the waveguide width at the input terminal of the spot size converter 51 is w ２２ Therefore, the waveguide width at the output terminal of the spot size converter 51 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 52 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 52 is w １１ That is the case.

[0029] Next, the operating principle of the optical waveguide element shown in Figure 1 will be explained. Here, we design an optical waveguide element that generates a constant phase difference between the optical signal output from the first arm 2 and the optical signal output from the second arm 3 to obtain positive interference. Furthermore, the optical waveguide element is designed so that there are no changes in interference conditions due to temperature changes or changes in interference conditions due to manufacturing errors in the waveguide width.

[0030] First, the condition for an optical waveguide element to be independent of the manufacturing error of the waveguide width can be expressed as shown in equation (1) below.

[0031]

[0032] The ΔL shown in equation (1) can be expressed as shown in equation (2) below.

[0033]

[0034] The condition for an optical waveguide element to be independent of temperature changes can be expressed as shown in equation (3) below.

[0035]

[0036] The ΔL shown in equation (3) can be expressed as shown in equation (4) below.

[0037]

[0038] Here, the coefficient of L shown in equation (2) is defined as the width-independent coefficient WIC, as shown in equation (5) below, and the coefficient of L shown in equation (4) is defined as the temperature-independent coefficient TIC, as shown in equation (6) below.

[0039]

[0040] As shown in the following formula (7), when the width-independent coefficient WIC and the temperature-independent coefficient TIC are equal, the change in the interference condition due to the temperature change and the change in the interference condition due to the manufacturing error of the waveguide width do not occur. Therefore, when the width-independent coefficient WIC and the temperature-independent coefficient TIC are equal, not only the fluctuation of the center wavelength due to the temperature change but also the fluctuation of the center wavelength due to the manufacturing error of the waveguide width can be suppressed. Note that since each of the width-independent coefficient WIC and the temperature-independent coefficient TIC is a value that varies depending on the optical waveguide material and the waveguide width, parameters that satisfy the conditions can be designed.

[0041]

[0042] The condition for being independent of the temperature change shown in formula (3) does not include the influence of linear expansion due to the temperature change. The influence of linear expansion due to the temperature change may be included in the condition for being independent of the temperature change. Specifically, if the linear expansion coefficient of the substrate material of the waveguide material i is α ｉ then the change in the length of the waveguide dL / dT with respect to the temperature fluctuation can be expressed as α ｉ Therefore, ΔL shown in formula (4) related to the condition for being independent of the temperature change can be rewritten as shown in the following formula (8).

[0043]

[0044] Here, for example, assume that the waveguide material i = 1 of the Si waveguide on the SOI (Silicon On Insulator) substrate is silicon (Si), and the waveguide material i = 2 of the SiN waveguide on the SOI substrate is silicon nitride (SiN). In this case, since the waveguide material i = 1 of the Si waveguide and the waveguide material i = 2 of the SiN waveguide are different, the linear expansion coefficient α １ of the Si waveguide and the linear expansion coefficient α ２ of the SiN waveguide are strictly different. However, since the volume of the waveguide in the SOI substrate is negligibly small, α １ and α ２ are equal, and the linear expansion coefficient of the Si waveguide and the linear expansion coefficient of the SiN waveguide can be regarded as equal to the linear expansion coefficient of silicon (Si).

[0045] Using equation (8), equation (7) can be rewritten as equation (10) below. If the coefficient of L shown in equation (8) is defined as the temperature-independent coefficient TIC as shown in equation (9) below, then as shown in equation (10) below, when the width-independent coefficient WIC and the temperature-independent coefficient TIC are equal, there will be no change in interference conditions due to temperature changes and no change in interference conditions due to manufacturing errors in waveguide width.

[0046]

[0047] The relationship between the center wavelength λ of an optical waveguide element and the wavelength difference FSR (Free Spectral Range) between adjacent transmittance peaks is expressed by the following equation (11).

[0048]

[0049] After determining the waveguide material and waveguide width that satisfy equation (7) or equation (10), the relationship between L and ΔL for the respective line lengths in the first adjustment section (1) and the second adjustment section (2) can be determined from the simultaneous equations of equation (2) and equation (11), or the simultaneous equations of equation (4) (or equation (8)) and equation (11), which can suppress the variation in wavelength characteristics due to temperature changes and manufacturing errors in waveguide width.

[0050] In the above embodiment 1, the optical waveguide element is configured to include a first optical coupler 1 that splits a given optical signal into two, a first arm portion 2 having a first adjustment section for adjusting the phase of one of the optical signals after splitting by the first optical coupler 1, a second arm portion 3 having a second adjustment section for adjusting the phase of the other optical signal after splitting by the first optical coupler 1, and a second optical coupler 4 that combines the optical signal after phase adjustment by the first arm portion 2 and the optical signal after phase adjustment by the second arm portion 3. Furthermore, the waveguide element has its waveguide width in the first and second adjustment sections, and its line length in the first and second adjustment sections, determined based on a predetermined phase difference between the two optical signals combined by the second optical coupler 4. Therefore, the optical waveguide element can suppress not only fluctuations in the center wavelength due to temperature changes, but also fluctuations in the center wavelength due to manufacturing errors in the waveguide width.

[0051] Embodiment 2. Embodiment 2 describes an optical waveguide element in which the first arm portion 5 comprises a first optical waveguide 61, a second optical waveguide 62, and a third optical waveguide 63, and the second arm portion 6 comprises a fourth optical waveguide 64, a fifth optical waveguide 65, and a sixth optical waveguide 66.

[0052] Figure 2 is a configuration diagram showing an optical waveguide element according to Embodiment 2. In Figure 2, the same reference numerals as in Figure 1 indicate the same or corresponding parts, so a detailed explanation is omitted. The first arm portion 5 includes a first optical waveguide 61, a second optical waveguide 62, and a third optical waveguide 63 as optical waveguides. Each of the first optical waveguide 61, the second optical waveguide 62, and the third optical waveguide 63 has a silicon (Si) core and silicon dioxide (SiO₂) as its core. ２ The waveguide has a cladding of ). The first arm section 5 is equipped with spot size converters 71 to 76. The core of the spot size converters 71 and 74 is silicon nitride (SiN), and the cladding of the spot size converters 71 and 74 is silicon dioxide (SiO ２). The cores of the spot size converters 72 and 73 hold silicon (Si) and silicon nitride (SiN) at a fixed interval in the thickness direction of the substrate, and the clads of the spot size converters 72 and 73 are silicon dioxide (SiO ２ ). The cores of the spot size converters 75 and 76 are silicon (Si), and the clads of the spot size converters 75 and 76 are silicon dioxide (SiO ２ ). The first arm portion 5 has a first adjustment section (1) for adjusting the phase of one of the optical signals after splitting by the first optical coupler 1. Specifically, the first arm portion 5 has a reference section (1-1), a first adjustment section (1), and a reference section (1-2).

[0053] One end of the first optical waveguide 61 is connected to one output end 1a of the first optical coupler 1. The other end of the first optical waveguide 61 is connected to one end of the second optical waveguide 62 via the spot size converters 71, 72, 73, 74, 75. The first optical waveguide 61 is an optical waveguide that forms part of the reference section (1-1). The waveguide width of the first optical waveguide 61 is w １１ and the waveguide width w １１ is a waveguide width that satisfies the single-mode condition of the waveguide material of the first arm portion 5.

[0054] One end of the second optical waveguide 62 is connected to the other end of the first optical waveguide 61 via the spot size converters 71, 72, 73, 74, 75. The other end of the second optical waveguide 62 is connected to one end of the third optical waveguide 63 via the spot size converter 76. The second optical waveguide 62 is an optical waveguide that forms the first adjustment section (1). The waveguide width of the second optical waveguide 62 is w １２ and the waveguide width w １２ is a waveguide width different from the waveguide width w １１ and does not need to satisfy the single-mode condition. The line length of the second optical waveguide 62 is L. The waveguide width w １２ and the line length L are each determined based on a predetermined phase difference for two optical signals combined by the second optical coupler 4.

[0055] One end of the third optical waveguide 63 is connected to the other end of the second optical waveguide 62 via a spot size converter 76. The other end of the third optical waveguide 63 is connected to one input terminal 4a of the second optical coupler 4. The third optical waveguide 63 is an optical waveguide that forms part of the reference section (1-2). The waveguide width of the third optical waveguide 63 is w １１ That is the case.

[0056] The second arm section 6 includes a fourth optical waveguide 64, a fifth optical waveguide 65, and a sixth optical waveguide 66. The fourth optical waveguide 64 and the sixth optical waveguide 66 each have a silicon (Si) core and silicon dioxide (SiO₂) ２ The waveguide has a cladding of ). The fifth optical waveguide 65 has a core of silicon nitride (SiN) and silicon dioxide (SiO ２ The waveguide has a cladding of ). The second arm section 6 is equipped with spot size converters 81 to 86. The cores of the spot size converters 81 and 82 are silicon (Si), and the cladding of the spot size converters 81 and 82 is silicon dioxide (SiO ２ The core of the spot size converters 84 and 85 is silicon nitride (SiN), and the cladding of the spot size converters 84 and 85 is silicon dioxide (SiO₂). ２ The cores of the spot size converters 83 and 86 hold silicon (Si) and silicon nitride (SiN) separated for a certain period of time in the thickness direction of the substrate, and the cladding of the spot size converters 83 and 86 is silicon dioxide (SiO ２ The second arm portion 6 has a second adjustment section (2) for adjusting the phase of the other optical signal after demultiplexing by the first optical coupler 1. Specifically, the second arm portion 6 has a reference section (2-1), a second adjustment section (2), and a reference section (2-2).

[0057] One end of the fourth optical waveguide 64 is connected to the other output terminal 1b of the first optical coupler 1. The other end of the fourth optical waveguide 64 is connected to one end of the fifth optical waveguide 65 via spot size converters 81, 82, 83, and 84. The fourth optical waveguide 64 is an optical waveguide that forms part of the reference section (2-1). The waveguide width of the fourth optical waveguide 64 is w １１ And the waveguide width lol １１ This is the waveguide width that satisfies the single-mode condition for the waveguide material of the second arm portion 6.

[0058] One end of the fifth optical waveguide 65 is connected to the other end of the fourth optical waveguide 64 via spot size converters 81, 82, 83, and 84. The other end of the fifth optical waveguide 65 is connected to one end of the sixth optical waveguide 66 via spot size converters 85 and 86. The fifth optical waveguide 65 is the optical waveguide responsible for the second adjustment section (2). The waveguide width of the fifth optical waveguide 65 is w ２２ And the waveguide width lol ２２ is waveguide width lol ２１ The waveguide width is different from that of the first optical waveguide, and it is not necessary to satisfy the single-mode condition. The line length of the fifth optical waveguide 65 is L + ΔL, and in order to secure a line length of L + ΔL, the fifth optical waveguide 65 is bent in a crank shape. In the example in Figure 2, the fifth optical waveguide 65 has six points where the direction of light propagation is bent at a 90-degree angle. Waveguide width w ２２ The line length L + ΔL is determined based on a predetermined phase difference between the two optical signals combined by the second optical coupler 4.

[0059] One end of the sixth optical waveguide 66 is connected to the other end of the fifth optical waveguide 65 via spot size converters 85 and 86. The other end of the sixth optical waveguide 66 is connected to the other input terminal 4b of the second optical coupler 4. The sixth optical waveguide 66 is an optical waveguide that forms part of the reference section (2-2). The waveguide width of the sixth optical waveguide 66 is the same as the waveguide width of the third optical waveguide 63. １１ That is the case.

[0060] Spot size converters 71, 74, 83, and 86 are spot size converters (a). Spot size converters 75, 76, 81, and 82 are spot size converters (b). Spot size converters 72, 73, 84, and 85 are spot size converters (c). The number of spot size converters 71 to 76 in the first arm section 5 is the same as the number of spot size converters 81 to 86 in the second arm section 6. As a result, the difference in optical path length between the optical path length of the first arm section 5 and the optical path length of the second arm section 6 can be designed based solely on the line length of the second optical waveguide 62 in the first adjustment section (1) and the line length of the fifth optical waveguide 65 in the second adjustment section (2). In the optical waveguide element shown in Figure 2, the first arm portion 5 has spot size converters 71 to 76, and the second arm portion 6 has spot size converters 81 to 86. It is sufficient that the number of spot size converters in the first arm portion 5 and the number of spot size converters in the second arm portion 6 are the same, and it is not limited to the case where the first arm portion 5 has spot size converters 71 to 76 and the second arm portion 6 has spot size converters 81 to 86.

[0061] The waveguide width at the input terminal of the spot size converter 71 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 71 is w ２１ The waveguide width at the input terminal of the spot size converter 72 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 72 is w ２２ Therefore, the waveguide width at the input terminal of the spot size converter 73 is w ２２ Therefore, the waveguide width at the output terminal of the spot size converter 73 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 74 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 74 is w １１ Therefore, the waveguide width at the input terminal of the spot size converter 75 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 75 is w １２Therefore, the waveguide width at the input terminal of the spot size converter 76 is w １２ Therefore, the waveguide width at the output terminal of the spot size converter 76 is w １１ That is the case.

[0062] The waveguide width at the input terminal of the spot size converter 81 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 81 is w １２ Therefore, the waveguide width at the input terminal of the spot size converter 82 is w １２ Therefore, the waveguide width at the output terminal of the spot size converter 82 is w １１ Therefore, the waveguide width at the input terminal of the spot size converter 83 is w １１ Therefore, the waveguide width at the output terminal of the spot size converter 83 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 84 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 84 is w ２２ Therefore, the waveguide width at the input terminal of the spot size converter 85 is w ２２ Therefore, the waveguide width at the output terminal of the spot size converter 85 is w ２１ Therefore, the waveguide width at the input terminal of the spot size converter 86 is w ２１ Therefore, the waveguide width at the output terminal of the spot size converter 86 is w １１ That is the case.

[0063] Next, the operating principle of the optical waveguide element shown in Figure 2 will be explained. Here, we design an optical waveguide element that generates a constant phase difference between the optical signal output from the first arm 2 and the optical signal output from the second arm 3 to obtain positive interference. Furthermore, the optical waveguide element is designed so that there are no changes in interference conditions due to temperature changes or changes in interference conditions due to manufacturing errors in the waveguide width.

[0064] The condition for an optical waveguide element to be independent of the manufacturing error of the waveguide width is expressed as equation (1), similar to the optical waveguide element shown in Figure 1. The ΔL shown in equation (1) is expressed as equation (2). The condition for an optical waveguide element to be independent of temperature changes is expressed as equation (3), similar to the optical waveguide element shown in Figure 1. The ΔL shown in equation (3) is expressed as equation (4) or equation (8). Therefore, for the optical waveguide element shown in Figure 2, similar to the optical waveguide element shown in Figure 1, when the width independence coefficient WIC and the temperature independence coefficient TIC are equal, as shown in equation (7) or equation (10), changes in interference conditions due to temperature changes and changes in interference conditions due to manufacturing errors of the waveguide width will not occur.

[0065] After determining the waveguide material and waveguide width that satisfy equation (7) or equation (10), the relationship between L and ΔL for the respective line lengths in the first adjustment section (1) and the second adjustment section (2) can be determined from the simultaneous equations of equation (2) and equation (11), or the simultaneous equations of equation (4) (or equation (8)) and equation (11), which can suppress the variation in wavelength characteristics due to temperature changes and manufacturing errors in waveguide width.

[0066] In the above embodiment 2, the first arm portion 5 includes a first optical waveguide 61, one end of which is connected to one output terminal 1a of the first optical coupler 1; a second optical waveguide 62, which is responsible for the first adjustment section, one end of which is connected to the other end of the first optical waveguide 61; and a third optical waveguide 63, one end of which is connected to the other end of the second optical waveguide 62, and the other end of which is connected to one input terminal 4a of the second optical coupler 4. Furthermore, the optical waveguide element is configured such that the second arm portion 6 includes a fourth optical waveguide 64, one end of which is connected to the other output terminal 1b of the first optical coupler 1; a crank-shaped fifth optical waveguide 65, which is responsible for the second adjustment section, has a different line length from the second optical waveguide 62, and one end of which is connected to the other end of the fourth optical waveguide 64; and a sixth optical waveguide 66, one end of which is connected to the other end of the fifth optical waveguide 65, and the other end of which is connected to the other input terminal 4b of the second optical coupler 4. Therefore, the optical waveguide element can suppress not only fluctuations in the center wavelength due to temperature changes, but also fluctuations in the center wavelength due to manufacturing errors in the waveguide width.

[0067] Furthermore, this disclosure allows for free combination of each embodiment, modification of any component in each embodiment, or omission of any component in each embodiment.

[0068] The optical waveguide element according to this invention comprises a first optical coupler that splits a given optical signal into two, a first arm portion having a first adjustment section for adjusting the phase of one of the optical signals after splitting by the first optical coupler, a second arm portion having a second adjustment section for adjusting the phase of the other optical signal after splitting by the first optical coupler, and a second optical coupler that combines the optical signal after phase adjustment by the first arm portion and the optical signal after phase adjustment by the second arm portion. This element can suppress not only fluctuations in the center wavelength due to temperature changes but also fluctuations in the center wavelength due to manufacturing errors in the waveguide width, making it suitable for use as an optical waveguide element.

[0069] 1 First optical coupler, 2 First arm section, 3 Second arm section, 4 Second optical coupler, 5 First arm section, 6 Second arm section, 11 First optical waveguide, 12 Second optical waveguide, 13 Third optical waveguide, 14 Fourth optical waveguide, 15 Fifth optical waveguide, 16 Sixth optical waveguide, 17 Seventh optical waveguide, 18 Eighth optical waveguide, 19 Ninth optical waveguide, 20 Tenth optical waveguide, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 Spot size converter, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52 Spot size converter, 61 First optical waveguide, 62 Second optical waveguide, 63 Third optical waveguide, 64 Fourth optical waveguide, 65 Fifth optical waveguide, 66 Sixth optical waveguide, 71, 72, 73, 74, 75, 76 Spot size converter, 81, 82, 83, 84, 85, 86 Spot size converter.

Claims

1. An optical waveguide element comprising: a first optical coupler for splitting a given optical signal into two; a first arm portion having a first adjustment section for adjusting the phase of one of the optical signals after splitting by the first optical coupler; a second arm portion having a second adjustment section for adjusting the phase of the other optical signal after splitting by the first optical coupler; and a second optical coupler for combining the optical signal after phase adjustment by the first arm portion and the optical signal after phase adjustment by the second arm portion, wherein the waveguide width in the first adjustment section and the second adjustment section, and the line length in the first adjustment section and the second adjustment section, are determined based on a predetermined phase difference between the two optical signals combined by the second optical coupler.

2. The first arm section comprises: a first optical waveguide to which one output terminal of the first optical coupler is connected; a second optical waveguide which is part of the first adjustment section and to which one end of the first optical waveguide is connected; a third optical waveguide which is part of the first adjustment section and to which one end of the second optical waveguide is connected; a fourth optical waveguide which is part of the first adjustment section and has the same line length as the second optical waveguide, and to which one end of the third optical waveguide is connected so as to be parallel to the second optical waveguide; and a fifth optical waveguide which has the same line length as the first optical waveguide, and to which one end of the fourth optical waveguide is connected so as to be parallel to the first optical waveguide, and to which one input terminal of the second optical coupler is connected. The second arm section is, The optical waveguide element according to claim 1, comprising: a sixth optical waveguide having the same line length as the first optical waveguide and one end connected to the other output terminal of the first optical coupler; a seventh optical waveguide that forms part of the second adjustment section, has a different line length from the second optical waveguide, and one end connected to the other end of the sixth optical waveguide; an eighth optical waveguide to which one end connected to the other end of the seventh optical waveguide; a ninth optical waveguide that forms part of the second adjustment section, has the same line length as the seventh optical waveguide, and one end connected to the other end of the eighth optical waveguide so as to be parallel to the seventh optical waveguide; and a tenth optical waveguide that has the same line length as the sixth optical waveguide, and one end connected to the other end of the ninth optical waveguide so as to be parallel to the sixth optical waveguide, and the other end connected to the other input terminal of the second optical coupler.

3. The optical waveguide element according to claim 1, wherein the first arm portion comprises a first optical waveguide to which one output terminal of the first optical coupler is connected at one end; a second optical waveguide responsible for the first adjustment section, to which the other end of the first optical waveguide is connected at one end; a third optical waveguide to which the other end of the second optical waveguide is connected at one end, and to which one input terminal of the second optical coupler is connected at the other end; and the second arm portion comprises a fourth optical waveguide to which the other output terminal of the first optical coupler is connected at one end; a fifth crank-shaped optical waveguide responsible for the second adjustment section, having a different line length from the second optical waveguide, to which the other end of the fourth optical waveguide is connected at one end; and a sixth optical waveguide to which the other end of the fifth optical waveguide is connected at one end, and to which the other input terminal of the second optical coupler is connected at the other end.

4. The optical waveguide element according to claim 2 or 3, wherein each of the first arm portion and the second arm portion is equipped with a spot size converter for connecting two optical waveguides, and the number of spot size converters provided in the first arm portion is the same as the number of spot size converters provided in the second arm portion.

5. The optical waveguide element according to any one of claims 1 to 4, characterized in that the core material of the first arm portion is silicon, the cladding material of the first arm portion is silicon oxide, the core material of the second arm portion is silicon nitride, and the cladding material of the second arm portion is silicon oxide.

6. The optical waveguide element according to any one of claims 2 to 5, characterized in that the core material of the optical waveguide in the first adjustment section, the waveguide width of the optical waveguide in the first adjustment section, the core material of the optical waveguide in the second adjustment section, and the waveguide width of the optical waveguide in the second adjustment section are determined to satisfy the following formula (1).

7. The optical waveguide element according to any one of claims 2 to 5, characterized in that the core material of the optical waveguide in the first adjustment section, the waveguide width of the optical waveguide in the first adjustment section, the core material of the optical waveguide in the second adjustment section, and the waveguide width of the optical waveguide in the second adjustment section are determined to satisfy the following formula (2).

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