Waveguide element, supercontinuum light source device, and wavelength dispersion compensator

Abstract

This waveguide element imparts wavelength dispersion characteristics to guided light and comprises: a first waveguide part which imparts a first wavelength dispersion characteristic to the light; a second waveguide part which is disposed so as to be aligned with the first waveguide part along a first direction which is the waveguide direction of the light and imparts a second wavelength dispersion characteristic to the light; and a connecting waveguide part which is disposed between the first waveguide part and the second waveguide part along the first direction and connects the first waveguide part and the second waveguide part. The first waveguide part has, along the first direction, a constant width in a second direction crossing the first direction, and has a first height in a third direction crossing the first direction and the second direction.

Description

Waveguide element, supercontinuum light source device, and wavelength dispersion compensator

[0001] The present disclosure relates to a waveguide element, a supercontinuum light source device, and a chromatic dispersion compensator.

[0002] Non-Patent Document 1 describes a waveguide element that generates mid-infrared supercontinuum light. This waveguide element has a constant thickness (height) along the pulse propagation direction and a tapered shape whose width gradually increases along the pulse propagation direction.

[0003] R. Karim*, Nayem Al Kayed,Nusrat Jahan, M. Shah Alam, Senior Member, IEEE, BMA Rahman, LifeFellow,IEEE, “Study of Highly Coherent Mid-InfraredSupercontinuum Generation in CMOSCompatibleSi-rich SiN Tapered WaveguideM.”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 40, NO. 13, JULY 1, 2022

[0004] According to the findings of the inventors, the wavelength dispersion characteristics imparted to light guided by the waveguide element change depending on the width and height of the waveguide element. In particular, even if the width of the waveguide element is constant along the light guiding direction, by including multiple waveguide portions with different heights, it is possible to impart predetermined wavelength dispersion characteristics according to each waveguide portion. However, in this case, there is a risk of optical loss occurring between the waveguide portions with different heights.

[0005] An object of the present disclosure is to provide a waveguide element, a supercontinuum light source device, and a chromatic dispersion compensator that can impart predetermined chromatic dispersion characteristics while suppressing optical loss.

[0006] The waveguide element according to the present disclosure is [1] "a waveguide element that imparts wavelength dispersion characteristics to guided light, comprising: a first waveguide portion that imparts a first wavelength dispersion characteristic to the light; a second waveguide portion that is arranged alongside the first waveguide portion along a first direction that is a waveguiding direction of the light and that imparts a second wavelength dispersion characteristic to the light; and a connecting waveguide portion that is arranged between the first waveguide portion and the second waveguide portion along the first direction and connects the first waveguide portion and the second waveguide portion, wherein the first waveguide portion has a constant width in a second direction intersecting the first direction along the first direction and a first height in a third direction intersecting the first direction and the second direction; a waveguide element having a width in the second direction that is constant along the first direction and a second height in the third direction that is higher than the first height, wherein the connection waveguide includes a first portion including a first end connected to the first waveguide and a second end connected to the second waveguide, and a second portion provided on the first portion, having a third end connected to the second waveguide and a fourth end closer to the first waveguide than the third end, and having a tapered shape in which the width in the second direction decreases from the third end toward the fourth end, wherein the width of the second portion at the fourth end in the second direction is narrower than the width of the first waveguide in the second direction.

[0007] This waveguide element includes a first waveguide portion and a second waveguide portion, each having a constant width in a second direction intersecting a first direction, which is the light guiding direction. The first waveguide portion has a first height in a third direction intersecting the first and second directions, and the second waveguide portion has a second height in the third direction that is greater than the first height. Therefore, this waveguide element can impart predetermined wavelength dispersion characteristics to light guided by the waveguide element according to the first and second waveguide portions. In particular, this waveguide element further includes a connecting waveguide portion between the first and second waveguide portions, connecting the first and second waveguide portions. The connecting waveguide portion has a first portion connected to the first and second waveguide portions and a second portion provided on the first portion and connected to the second waveguide portion. The second portion has a tapered shape that narrows in a direction from a connection portion (third end) of the second portion with the second waveguide toward the first waveguide, thereby suppressing optical loss between the first and second waveguides.

[0008] The waveguide element according to the present disclosure may be [2] "the waveguide element according to the above [1], wherein a second width, which is the width of the second waveguide portion in the second direction, is wider than a first width, which is the width of the first waveguide portion in the second direction, and the first portion has a tapered portion in which the width in the second direction gradually increases from the first width to the second width as it moves from the first end to the second end." In this case, the width as well as the effective height changes between the first waveguide portion and the second waveguide portion. As a result, it becomes possible to design the wavelength dispersion characteristics imparted to light guided by the waveguide element over a wider range.

[0009] The waveguide element according to the present disclosure may be [3] "the waveguide element according to [1] or [2] above, in which the length of the second portion in the first direction is shorter than the length of the first portion in the first direction." Even in this case, it is possible to guide light while reducing optical loss.

[0010] The waveguide element according to the present disclosure may be [4] "the waveguide element according to the above [1] or [2], in which the length of the second portion in the first direction is longer than the length of the first portion in the first direction." Even in this case, it is possible to guide light while reducing optical loss.

[0011] The waveguide element according to the present disclosure may be [5] "the waveguide element according to [1] or [2] above, in which the length of the second portion in the first direction is equal to the length of the first portion in the first direction." Even in this case, it is possible to guide light while reducing optical loss.

[0012] The waveguide element according to the present disclosure may be [6] "the waveguide element according to the above [1], wherein a second width, which is the width of the second waveguide portion in the second direction, is narrower than a first width, which is the width of the first waveguide portion in the second direction, and the first portion has a tapered portion in which the width in the second direction gradually decreases from the first width to the second width as it moves from the first end to the second end." In this case, not only the effective height but also the width changes between the first waveguide portion and the second waveguide portion. As a result, it becomes possible to design the wavelength dispersion characteristics imparted to light guided by the waveguide element over a wider range.

[0013] The supercontinuum light source device according to the present disclosure is [7] "a supercontinuum light source device comprising the waveguide element according to any one of [1] to [6] above and a light source that outputs pulsed light, wherein the waveguide element guides the pulsed light output from the light source as the light, and imparts to the pulsed light wavelength dispersion characteristics such that the wavelength spectrum of the pulsed light expands stepwise according to the first waveguide portion and the second waveguide portion."

[0014] This supercontinuum light source device includes the above-described waveguide element, and therefore, it is possible to reduce optical loss while imparting wavelength dispersion characteristics to pulsed light guided by the waveguide element such that the wavelength spectrum expands stepwise, thereby obtaining supercontinuum light.

[0015] The supercontinuum light source device according to the present disclosure may be [8] "the supercontinuum light source device according to the above [7], in which the light source outputs ultraviolet pulsed light, visible pulsed light, near-infrared pulsed light, or mid-infrared pulsed light as the pulsed light." In this case, it is possible to impart wavelength dispersion characteristics to the pulsed light guided by the waveguide element such that the wavelength spectrum expands stepwise while reducing optical loss, thereby obtaining supercontinuum light in a desired wavelength range.

[0016] The super-continuum light source device according to the present disclosure may be [9] "the super-continuum light source device according to the above [7], wherein the light source outputs near-infrared pulsed light as the pulsed light, and the waveguide element imparts the wavelength dispersion characteristic to the near-infrared pulsed light while guiding the near-infrared pulsed light, and outputs mid-infrared super-continuum light." In this case, it is possible to impart wavelength dispersion characteristics to the near-infrared pulsed light guided by the waveguide element such that the wavelength spectrum expands stepwise, while reducing optical loss, and to obtain mid-infrared super-continuum light.

[0017] The chromatic dispersion compensator according to the present disclosure is

[10] "a chromatic dispersion compensator comprising: a waveguide element according to any one of the above [1] to [6]; and an input section that inputs the light to the waveguide element, wherein the waveguide element guides the light input by the input section, imparts chromatic dispersion characteristics to the light in stages according to the first waveguide section and the second waveguide section, and outputs the light to which the chromatic dispersion characteristics have been imparted."

[0018] This chromatic dispersion compensator includes the above-described waveguide element, and therefore, while suppressing optical loss, it is possible to impart chromatic dispersion characteristics to light guided by the waveguide element in stages according to the first waveguide portion and the second waveguide portion, thereby obtaining output light having predetermined chromatic dispersion characteristics.

[0019] The chromatic dispersion compensator according to the present disclosure may be

[11] "the chromatic dispersion compensator according to the above

[10] , wherein the waveguide element receives the light input from the input portion at the first waveguide portion and outputs the light from the second waveguide portion." In this case, it is possible to impart chromatic dispersion characteristics to the light guided by the waveguide element in stages according to the first waveguide portion and the second waveguide portion, while suppressing optical loss, and to obtain output light having predetermined chromatic dispersion characteristics.

[0020] The chromatic dispersion compensator according to the present disclosure may be

[12] "the chromatic dispersion compensator according to the above

[10] , wherein the waveguide element receives the light input from the input portion at the second waveguide portion and outputs the light from the first waveguide portion." In this case, it is possible to impart chromatic dispersion characteristics to the light guided by the waveguide element in stages according to the first waveguide portion and the second waveguide portion, while suppressing optical loss, and to obtain output light having predetermined chromatic dispersion characteristics.

[0021] According to the present disclosure, it is possible to provide a waveguide element, a supercontinuum light source device, and a chromatic dispersion compensator that can impart predetermined chromatic dispersion characteristics while suppressing optical loss.

[0022] FIG. 1 is a schematic diagram showing a supercontinuum light source device according to this embodiment. FIG. 2 is a perspective view showing the waveguide element shown in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 4 is a perspective view showing a waveguide element used in the simulation. FIG. 5 is a graph showing the simulation results, illustrating the relationship between wavelength (horizontal axis) and wavelength dispersion (vertical axis) (wavelength dispersion characteristics). FIG. 6 is a graph showing the simulation results, illustrating the relationship between wavelength (horizontal axis) and wavelength dispersion (vertical axis) (wavelength dispersion characteristics). FIG. 7 is a graph showing the simulation results, illustrating the relationship between wavelength (horizontal axis) and wavelength dispersion (vertical axis) (wavelength dispersion characteristics). FIG. 8 is a perspective view showing a waveguide element according to a comparative example. A diagram showing simulation results of the coupling efficiency and light intensity distribution of the waveguide element shown in FIG. 8. FIG. 10 is a perspective view showing a portion (core) of the waveguide element according to this embodiment. FIG. 11 is a graph showing the simulation results. FIG. 12 is a perspective view showing another portion (core) of the waveguide element according to this embodiment. Fig. 13 is a perspective view showing a portion (core) of a waveguide element according to a modified example. Fig. 14 is a graph showing simulation results. Fig. 15 is a perspective view showing a portion (core) of a waveguide element according to another modified example. Fig. 16 is a perspective view showing a portion (core) of a waveguide element according to yet another modified example. Fig. 17 is a graph showing simulation results. Fig. 18 is a perspective view showing a portion (core) of a waveguide element according to yet another modified example. Fig. 19 is a schematic diagram showing a supercontinuum light source device according to a modified example. Fig. 20 is a schematic diagram showing a chromatic dispersion compensator including a waveguide element. Fig. 21 is a perspective view showing a waveguide element according to a modified example.

[0023] An embodiment of the probe unit will be described below with reference to the drawings. In the description of the drawings, identical or corresponding elements are denoted by the same reference numerals, and redundant description may be omitted. Each drawing may also show a Cartesian coordinate system including a first axis defining a first direction D1, a second axis defining a second direction D2 intersecting (orthogonal to) the first direction D1, and a third axis defining a third direction D3 intersecting (orthogonal to) the first direction D1 and the second direction D2.

[0024] FIG. 1 is a schematic diagram showing a supercontinuum light source device according to this embodiment. The supercontinuum light source device 100 shown in FIG. 1 includes a light source 50 that outputs pulsed light and an optical module 60. The light source 50 outputs near-infrared pulsed light L0 (having a center wavelength in a wavelength range of, for example, 0.8 μm to 2.5 μm) as pulsed light. The optical module 60 receives the near-infrared pulsed light L0 output from the light source 50 and expands the wavelength spectrum of the near-infrared pulsed light L0 to generate and output mid-infrared super-continuum light L1 (having a center wavelength in a wavelength range of, for example, 0.9 μm to 25 μm). Note that the supercontinuum light source device 100 is not limited to generating mid-infrared super-continuum light, and may also generate super-continuum light having a wavelength in other wavelength ranges, such as the ultraviolet wavelength range, the visible wavelength range, or the near-infrared wavelength range.

[0025] The optical module 60 includes a waveguide element 1, an input unit 61 that inputs near-infrared pulsed light L0 output from the light source 50 into the waveguide element 1, and a heater control circuit 62 for controlling a heater 4 (see FIG. 2 ) provided in the waveguide element 1. The optical module 60 may be, for example, an optical integrated circuit. The waveguide element 1 guides the near-infrared pulsed light L0 output from the light source 50 and input via the input unit 61, and imparts to the near-infrared pulsed light L0 wavelength dispersion characteristics that gradually expand the wavelength spectrum of the near-infrared pulsed light L0. The heater control circuit 62 controls the heater 4 to control the temperature of the waveguide element 1 so as to obtain desired wavelength dispersion characteristics.

[0026] Fig. 2 is a perspective view showing the waveguide element shown in Fig. 1. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. As shown in Figs. 2 and 3, the waveguide element 1 includes a core 2 and a cladding 3. The cross-section shown in Fig. 3 shows a region of the core 2 where the width in the second direction D2 and the height in the third direction D3 are constant (for example, a waveguide section 22, which will be described later). In this embodiment, as shown in Fig. 3(a), the core 2 has a rectangular cross-section in this region (it is a rectangular waveguide).

[0027] The combination of the material of the core 2 and the material of the clad 3 is as follows: ３ N ４ In this case, the material of the clad 3 is SiO ２ , Air, MgF ２ When the material of the core 2 is Ge or SiGe, the material of the cladding 3 is Air or Si, and the material of the core 2 is As ２ Se ３ In this case, the material of the clad 3 is air, MgF ２ When the material of the core 2 is Si, the material of the clad 3 is SiO ２ , Air.

[0028] 3(b), the core 2 may have a shape in the region in which a first core portion 2a having a rectangular cross section and a second core portion 2b having a rectangular cross section and wider in the second direction than the first core portion 2a are integrally formed below the first core portion 2a (a rib waveguide may be used). Furthermore, as shown in FIG. 3(c), the waveguide element 1 may have a structure in which a base portion 5 made of a material different from that of the core 2 is provided below the core 2 having a rectangular cross section (a strip waveguide).

[0029] 2 , the waveguide element 1 has, as the core 2, a waveguide portion 21 (first waveguide portion), a waveguide portion 22 (second waveguide portion, first waveguide portion), a waveguide portion 23 (second waveguide portion), and connecting waveguide portions 24 and 25. The waveguide portion 21, the waveguide portion 22, and the waveguide portion 23 are arranged in order along the first direction D1. The connecting waveguide portion 24 is arranged between the waveguide portion 21 and the waveguide portion 22 along the first direction D1 and connects the waveguide portion 21 and the waveguide portion 22. In this case (i.e., when focusing on the connecting waveguide portion 24), the waveguide portion 21 serves as the first waveguide portion, and the waveguide portion 22 serves as the second waveguide portion. The connecting waveguide portion 25 is disposed between the waveguide portion 22 and the waveguide portion 23 along the first direction D1 and connects the waveguide portion 22 and the waveguide portion 23. In this case (i.e., when focusing on the connecting waveguide portion 25), the waveguide portion 22 serves as the first waveguide portion and the waveguide portion 23 serves as the second waveguide portion. Note that the waveguide element 1 may propagate light from the waveguide portion 21 to the waveguide portion 23 via the waveguide portion 22 along the first direction D1, or may propagate light from the waveguide portion 23 to the waveguide portion 21 via the waveguide portion 22 along the first direction D1.

[0030] In this embodiment, the waveguide element 1 receives near-infrared pulsed light L0 from the end face 21 s of the waveguide portion 21, and guides the near-infrared pulsed light L0 along the first direction D1 in the order of the waveguide portion 21, the connecting waveguide portion 24, the waveguide portion 22, the connecting waveguide portion 25, and the waveguide portion 23, while imparting wavelength dispersion characteristics to the near-infrared pulsed light L0 such that the wavelength spectrum of the near-infrared pulsed light L0 gradually expands depending on each portion, and emits mid-infrared supercontinuum light L1 from the end face 23 s of the waveguide portion 23.

[0031] Therefore, the first direction D1 is the light guiding direction of the waveguide element 1. The second direction D2 is one direction intersecting the first direction D1, and in this embodiment, this is the width direction. The third direction D3 is another direction intersecting the first direction D1, and in this embodiment, this is the height direction. Note that the width and height are convenient names for the dimensions in the second direction D2 and the third direction D3, and are not associated with the direction of gravity.

[0032] Here, in order to efficiently generate supercontinuum light, it is possible to use a waveguide that exhibits anomalous dispersion characteristics over a wide wavelength range, and to control the wavelength dispersion characteristics of the waveguide. Next, the inventors' findings regarding the control of wavelength dispersion characteristics will be explained.

[0033] Fig. 4 is a perspective view showing a waveguide element used in the simulation. The waveguide element 2A shown in Fig. 4 corresponds to the core 2 of the waveguide element 1. The waveguide element 2A has a constant width WA in the second direction D2 and a constant height HA in the third direction D3. Here, we will consider the case where light is guided from one end to the other end of the waveguide element 2A in the first direction D1.

[0034] 5, 6, and 7 are graphs showing the results of the simulation, showing the relationship between wavelength (horizontal axis) and chromatic dispersion (vertical axis) (chromatic dispersion characteristics). Fig. 5(a) shows multiple graphs for cases where the height HA is constant at 0.8 μm and the width WA is various values ​​from 1.0 μm to 4.5 μm. Fig. 5(b), Fig. 6(a) and (b), and Fig. 7 show similar graphs for cases where the height HA is constant at 1.0 μm, 1.2 μm, 1.4 μm, and 1.6 μm, respectively.

[0035] 5 to 7, it can be seen that the wavelength dispersion characteristics for each wavelength change when the width WA and height HA of the waveguide element 2A are changed. As an example, graph G1 in FIG. 5(a) shows a case where the height HA is 0.8 μm and the width WA is 2.0 μm. For example, the wavelength dispersion at a wavelength of 1.9 μm is about 300 ps / nm / km, but as the wavelength becomes longer, the wavelength dispersion decreases, and sufficient wavelength dispersion characteristics cannot be obtained at wavelengths of 3.0 μm or more.

[0036] On the other hand, even when the width WA is 2.0 μm, by increasing the height HA as shown in graph G1 in Figures 6 and 7, it can be understood that sufficient chromatic dispersion characteristics can be obtained, even for wavelengths of 3.0 μm or more. Therefore, in a waveguide element, appropriate chromatic dispersion characteristics can be imparted by setting the width WA and / or height HA according to the wavelength of the guided light. In other words, since the optimal chromatic dispersion for supercontinuum light generated along the waveguide direction varies, optimal design of chromatic dispersion can be achieved by changing the width and / or height along the waveguide direction.

[0037] Fig. 8 is a perspective view showing a waveguide element according to a comparative example. The waveguide element 2B shown in Fig. 8 corresponds to the core 2 of the waveguide element 1. Based on the above findings, the waveguide element 2B has a plurality of waveguide portions that are different in width in the second direction D2 and in height in the third direction D3 along a first direction, which is the light guiding direction. That is, the waveguide element 2B includes a first waveguide portion 21B, a connection waveguide portion 24B, and a second waveguide portion 22B that are arranged side by side along the first direction D1.

[0038] The first waveguide portion 21B has a constant width WB1 in the second direction D2 and a constant height HB1 in the third direction D3. The second waveguide portion 22B has a constant width WB2 in the second direction D2 that is wider than the width WB1 and a constant height HB2 in the third direction D3 that is higher than the height HB1. The connecting waveguide portion 24B connects the first waveguide portion 21B and the second waveguide portion 22B.

[0039] The connection waveguide 24B includes a first portion 31B and a second portion 32B. The first portion 31B includes a first end E1B connected to the first waveguide 21B and a second end E2B connected to the second waveguide 22B. The first portion 31B has a tapered shape in which a width TB1 of the first portion 31B in the second direction D2 increases from a width WB1 to a width WB2 as it moves from the first end E1B to the second end E2B. The height of the first portion 31B in the third direction D3 is the same as the height HB1 of the first waveguide 21B and is constant along the first direction D1.

[0040] The second portion 32B is provided contiguously on the first portion 31B and has the same shape as the first portion 31B. That is, the second portion 32B includes a third end E3B connected to the second waveguide 22B and a fourth end E4B closer to the first waveguide 21B than the third end E3B. The second portion 32B has a tapered shape in which the width TB2 of the second portion 32B in the second direction D2 increases from width WB1 to width WB2 as it moves from the fourth end E4B to the third end E3B. The height of the second portion 32B in the third direction D3 is constant, such that the sum of the height of the second portion 32B and the height of the first portion 31B is equal to the height HB2 of the second waveguide 22B. As a result, the waveguide element 2B has a structure in which the height changes collectively across the entire width of the first waveguide 21B from the first waveguide 21B to the connecting waveguide 24B.

[0041] As described above, the waveguide element 2B includes the first waveguide portion 21B and the second waveguide portion 22B that have different widths in the second direction D2 and different heights in the third direction D3 across the first direction D1, which is the light guiding direction. This makes it possible to optimally design the wavelength dispersion according to the width WB1 and height HB1 of the first waveguide portion 21B and the width WB2 and height HB2 of the second waveguide portion 22B, respectively.

[0042] On the other hand, as described above, the waveguide element 2B has a structure in which the height changes collectively across the entire width of the first waveguide portion 21B from the first waveguide portion 21B to the connecting waveguide portion 24B (i.e., the second waveguide portion 22B) (i.e., the height changes suddenly in the first direction D1). In this case, as shown in the graph of the simulation results in FIG. 9A, even if the length of the connecting waveguide portion 24B in the first direction D1 (the taper length in the figure) is increased, the maximum coupling efficiency (overlap with the TE00 mode of the second waveguide portion 22B) is approximately 0.84 (84%). In other words, in this case, optical propagation loss occurs. This is thought to be due in part to the intensity of light propagating in the first direction D1 oscillating in the third direction D3, as shown in the light intensity distribution in FIG. 9B.

[0043] The waveguide element 1 according to this embodiment has a structure that can suppress such optical loss while imparting predetermined wavelength dispersion characteristics (i.e., enabling optimal design of wavelength dispersion). Next, a specific structure of the waveguide element 1 according to this embodiment will be described.

[0044] FIG. 10 is a perspective view showing a portion (core) of the waveguide element according to this embodiment. FIG. 10 shows the waveguide portion 21, the waveguide portion 22, and the connecting waveguide portion 24 of the core 2 of the waveguide element 1 shown in FIG. 2 . As shown in FIG. 10 , the waveguide portion 21 has a width W1 (first width) in the second direction D2 and a height H1 (first height) in the third direction D3. The width W1 and the height H1 are constant along the first direction D1. The waveguide portion 22 has a width W2 (second width) in the second direction D2 that is wider than the width W1 and a height H2 (second height) in the third direction D3 that is higher than the height H1. The width W2 and the height H2 are constant along the first direction D1.

[0045] The connecting waveguide 24 comprises a first portion 31 and a second portion 32. The first portion 31 includes a first end E1 connected to the waveguide 21 and a second end E2 connected to the waveguide 22. The first portion 31 has a tapered shape in which the width T1 of the first portion 31 in the second direction D2 gradually increases from width W1 to width W2 as it moves from the first end E1 to the second end E2 (i.e., the first portion 31 has a tapered portion). The height of the first portion 31 in the third direction D3 is the same as the height H1 of the waveguide 21 and is constant along the first direction D1.

[0046] The second portion 32 is integrally formed on the first portion 31. The second portion 32 includes a third end E3 connected to the waveguide 22 and a fourth end E4 closer to the waveguide 21 than the third end E3. The second portion 32 has a tapered shape in which a width T2 of the second portion 32 in the second direction D2 decreases from the third end E3 toward the fourth end E4. In particular, the width of the second portion 32 at the fourth end E4 in the second direction D2 is narrower than the width W1 of the waveguide 21 in the second direction D2. The height of the second portion 32 in the third direction D3 is a value such that the sum of the height of the second portion 32 and the height of the first portion 31 is the same as the height H2 of the waveguide 22, and is constant in the first direction D1.

[0047] As a result, the core 2 of the waveguide element 1 has a structure in which the region where the height changes gradually increases from the waveguide portion 21 to the waveguide portion 22 (i.e., a structure in which the effective height gradually increases). In other words, a height-direction taper is formed in which the effective height of the core 2 gradually increases from the waveguide portion 21 to the waveguide portion 22 for light propagating in the first direction D1. As a result, as shown in the graph of the simulation results in FIG. 11 , by increasing the length of the connecting waveguide portion 24 in the first direction D1 (the taper length in the figure) to a certain extent, the coupling efficiency (overlap with the TE00 mode of the waveguide portion 22) becomes 1.00 (100%). That is, in this case, the optical propagation loss is suppressed.

[0048] As described above, the waveguide element 1 includes the waveguide portion 21 and the waveguide portion 22 that have different widths in the second direction D2 and different heights in the third direction D3 across the first direction D1, which is the light guiding direction. This allows for optimal design of chromatic dispersion according to the width W1 and height H1 of the waveguide portion 21 and the width W2 and height H2 of the waveguide portion 22. Furthermore, optical propagation loss is suppressed during optimal design of chromatic dispersion. While the above description has shown the relationship between the waveguide portion 21, the waveguide portion 22, and the connecting waveguide portion 24, the same applies to the relationship between the waveguide portion 22, the waveguide portion 23, and the connecting waveguide portion 25.

[0049] FIG. 12 is a perspective view showing another portion (core) of the waveguide element according to this embodiment. FIG. 12 shows the waveguide portion 22, the waveguide portion 23, and the connecting waveguide portion 25 of the core 2 of the waveguide element 1 shown in FIG. 2 . As shown in FIG. 12 and as described above, the waveguide portion 22 has a width W2 (first width) in the second direction D2 and a height H2 (first height) in the third direction D3. The width W2 and the height H2 are constant along the first direction D1. The waveguide portion 23 has a width W3 (second width) in the second direction D2 that is wider than the width W2 and a height H3 (second height) in the third direction D3 that is higher than the height H2. The width W3 and the height H3 are constant along the first direction D1.

[0050] The connecting waveguide 25 includes a first portion 41 and a second portion 42. The first portion 41 includes a first end F1 connected to the waveguide 22 and a second end F2 connected to the waveguide 23. The first portion 41 has a tapered shape in which the width Q1 of the first portion 41 in the second direction D2 gradually increases from width W2 to width W3 as it moves from the first end F1 to the second end F2 (i.e., the first portion 41 has a tapered portion). The height of the first portion 41 in the third direction D3 is the same as the height H2 of the waveguide 22 and is constant along the first direction D1.

[0051] The second portion 42 is integrally formed on the first portion 41. The second portion 42 includes a third end F3 connected to the waveguide 23 and a fourth end F4 closer to the waveguide 22 than the third end F3. The second portion 42 has a tapered shape in which a width Q2 of the second portion 42 in the second direction D2 decreases from the third end F3 toward the fourth end F4. In particular, the width Q2 of the second portion 42 in the second direction D2 at the fourth end F4 is narrower than the width W2 of the waveguide 22 in the second direction D2. The height Q2 of the second portion 42 in the third direction D3 is a value such that the sum of the height Q2 and the height of the first portion 41 is the same as the height H3 of the waveguide 23, and is constant in the first direction D1.

[0052] As a result, the core 2 of the waveguide element 1 has a structure in which the region where the height changes gradually increases from the waveguide portion 22 to the waveguide portion 23 (i.e., a structure in which the effective height gradually increases). In other words, a height-direction taper is formed in which the effective height of the core 2 gradually increases from the waveguide portion 22 to the waveguide portion 23 for light propagating in the first direction D1. As a result, similar to the simulation result of FIG. 11 , by increasing the length of the connecting waveguide portion 25 in the first direction D1 to a certain extent, the coupling efficiency (overlap with the TE00 mode of the waveguide portion 23) becomes 1.00 (100%). That is, in this case, the optical propagation loss is suppressed.

[0053] As described above, the waveguide element 1 includes the waveguide portion 22 and the waveguide portion 23 that have different widths in the second direction D2 and different heights in the third direction D3 across the first direction D1, which is the light guiding direction, thereby enabling optimal design of chromatic dispersion according to the width W2 and height H2 of the waveguide portion 22 and the width W3 and height H3 of the waveguide portion 23. Furthermore, optical propagation loss is suppressed during the optimal design of chromatic dispersion.

[0054] Therefore, according to the waveguide element 1, by providing the waveguide portion 21, the waveguide portion 22, and the waveguide portion 23 that have different widths in the second direction D2 and different heights in the third direction D3 across the first direction D1, which is the light guiding direction, it is possible to optimize the chromatic dispersion design in three stages depending on the width W1 and height H1 of the waveguide portion 21, the width W2 and height H2 of the waveguide portion 22, and the width W3 and height H3 of the waveguide portion 23. In this case, the connection waveguide portion 24 suppresses optical loss between the waveguide portion 21 and the waveguide portion 22, and the connection waveguide portion 25 suppresses optical loss between the waveguide portion 22 and the waveguide portion 23. As a result, it is possible to generate supercontinuum light with high efficiency based on the near-infrared pulsed light L0 incident on the end face 21s of the waveguide portion 21 and output it from the end face 23s of the waveguide portion 23.

[0055] In this way, when the waveguide portion 21 is the first waveguide portion and the waveguide portion 22 is the second waveguide portion, the waveguide element 1 imparts a first wavelength dispersion characteristic to light guided through the waveguide portion 21 and imparts a second wavelength dispersion characteristic different from the first wavelength dispersion characteristic to light guided through the waveguide portion 22. Furthermore, when the waveguide portion 22 is the first waveguide portion and the waveguide portion 23 is the second waveguide portion, the waveguide element 1 imparts a different first wavelength dispersion characteristic to light guided through the waveguide portion 22 and imparts a different second wavelength dispersion characteristic different from the different first wavelength dispersion characteristic to light guided through the waveguide portion 23.

[0056] 10 , the length of the second portion 32 in the first direction D1 is equal to the length of the first portion 31 in the first direction D1. That is, when viewed from the third direction D3, the first end E1 of the first portion 31 and the fourth end E4 of the second portion 32 are at the same position in the first direction D1, and the second end E2 of the first portion 31 and the third end E3 of the second portion 32 are at the same position in the first direction D1. The same applies to the length relationship between the second portion 42 and the first portion 41 shown in FIG. 12 .

[0057] 13 , in the waveguide element 1 (core 2), the length of the second portion 32 in the first direction D1 may be shorter than the length of the first portion 31 in the first direction D1. That is, in the waveguide element 1, when viewed from the third direction D3, the second end E2 of the first portion 31 and the third end E3 of the second portion 32 may be at the same position in the first direction D1, while the fourth end E4 of the second portion 32 may be located closer to the waveguide unit 22 than the first end E1 of the first portion 31. The same applies to the relationship in length between the second portion 42 and the first portion 41 shown in FIG.

[0058] 14 , even in this case, by increasing the length of the connecting waveguide 24 in the first direction D1 (the taper length in the figure) to a certain extent, the coupling efficiency (overlap with the TE00 mode of the waveguide 22) becomes 1.00 (100%). That is, even in this case, it is possible to suppress optical propagation loss. Furthermore, in the waveguide element 1 (core 2), the length of the second portion 32 in the first direction D1 may be shorter than the length of the first portion 31 in the first direction D1, and even in this case, it is possible to similarly suppress optical propagation loss.

[0059] 15 , in the waveguide element 1 (core 2), the length of the second portion 32 in the first direction D1 may be longer than the length of the first portion 31 in the first direction D1. That is, in the waveguide element 1, when viewed from the third direction D3, the second end E2 of the first portion 31 and the third end E3 of the second portion 32 may be located at the same position in the first direction D1, while the fourth end E4 of the second portion 32 may be located closer to the waveguide 21 than the first end E1 of the first portion 31. The same applies to the length relationship between the second portion 42 and the first portion 41 shown in FIG. 12 . Even in this case, the coupling efficiency (overlap with the TE00 mode of the waveguide 22) is 1.00 (100%). That is, even in this case, optical propagation loss can be suppressed.

[0060] 16, the width W1 of the waveguide 21, the width T1 of the first portion 31 of the connecting waveguide 24, and the width W2 of the waveguide 22 may be constant along the first direction D1 and have the same value. In this case, the degree of freedom in designing the chromatic dispersion according to the width of each portion is lost, but as shown by comparing the graphs G1 in FIGS. 5 to 7, it is possible to design the chromatic dispersion by changing the height. Therefore, even in this case, an optimal design for chromatic dispersion is possible.

[0061] 17, by increasing the length of the connecting waveguide 24 in the first direction D1 (the taper length in the figure) to a certain extent, the coupling efficiency (overlap with the TE00 mode of the waveguide 22) becomes 1.00 (100%). That is, even in this case, it is possible to suppress the optical propagation loss. The same applies to the width W2 of the waveguide 22, the width Q1 of the first portion 41 of the connecting waveguide 25, and the width W3 of the waveguide 23 shown in FIG.

[0062] 18 , in the waveguide element 1 (core 2), the width W2 of the waveguide portion 22 in the second direction D2 may be narrower than the width W1 of the waveguide portion 21, and the first portion 31 of the connecting waveguide portion 24 may have a tapered portion in which the width T1 in the second direction D2 gradually decreases from the width W1 to the width W2 from the first end E1 to the second end E2. The same applies to the width W2 of the waveguide portion 22, the width Q1 of the first portion 41 of the connecting waveguide portion 25, and the width W3 of the waveguide portion 23 shown in FIG.

[0063] As described above, the waveguide element 1 according to this embodiment includes the waveguide portion 21 and the waveguide portion 22, each having a constant width in the second direction D2 intersecting the first direction D1, which is the light guiding direction. The waveguide portion 21 has a height H1 in the third direction D3 intersecting the first direction D1 and the second direction D2, and the waveguide portion 22 has a height H2 in the third direction D3 that is greater than the height H1. Therefore, the waveguide element 1 can impart predetermined wavelength dispersion characteristics to the waveguide portion 21 and the waveguide portion 22, to light guided by the waveguide element 1.

[0064] In particular, the waveguide element 1 further includes a connecting waveguide portion 24 between the waveguide portion 21 and the waveguide portion 22, connecting the waveguide portion 21 and the waveguide portion 22. The connecting waveguide portion 24 has a first portion 31 connected to the waveguide portion 21 and the waveguide portion 22, and a second portion 32 provided on the first portion 31 and connected to the waveguide portion 22. The second portion 32 has a tapered shape that narrows in a direction from a connection portion (third end E3) of the second portion 32 with the waveguide portion 22 toward the waveguide portion 21. This suppresses optical loss between the waveguide portion 21 and the waveguide portion 22.

[0065] Furthermore, in the waveguide element 1 according to this embodiment, the width W2 of the waveguide portion 22 in the second direction D2 may be wider than the width W1 of the waveguide portion 21 in the second direction D2. The first portion 31 may have a tapered portion in which the width T1 in the second direction D gradually increases from width W1 to width W2 as it moves from the first end E1 to the second end E2. In this case, the width as well as the effective height changes between the waveguide portion 21 and the waveguide portion 22. As a result, it becomes possible to design the wavelength dispersion characteristics imparted to light guided by the waveguide element 1 over a wider range.

[0066] In the waveguide element 1 according to this embodiment, the length of the second portion 32 in the first direction D1 is equal to the length of the first portion 31 in the first direction D1. Even in this case, it is possible to guide light while reducing optical loss.

[0067] In the waveguide element 1 according to this embodiment, the length of the second portion 32 in the first direction D1 may be shorter than the length of the first portion 31 in the first direction D1. Even in this case, it is possible to guide light while reducing optical loss.

[0068] In the waveguide element 1 according to this embodiment, the length of the second portion 32 in the first direction D1 may be longer than the length of the first portion 31 in the first direction D1. Even in this case, it is possible to guide light while reducing optical loss.

[0069] Furthermore, in the waveguide element 1 according to this embodiment, the width W2 of the waveguide portion 22 in the second direction D2 may be narrower than the width W1 of the waveguide portion 21 in the second direction D2. The first portion 31 may have a tapered portion in which the width T1 in the second direction D gradually decreases from width W1 to width W2 as it moves from the first end E1 to the second end E2. Even in this case, the width as well as the effective height changes between the waveguide portion 21 and the waveguide portion 22. As a result, it becomes possible to design the wavelength dispersion characteristics imparted to light guided by the waveguide element 1 over a wider range.

[0070] Here, the supercontinuum light source device 100 according to this embodiment includes the above-described waveguide element 1 (optical module 60 including the waveguide element 1) and a light source 50 that outputs near-infrared pulsed light L0. The waveguide element 1 guides the near-infrared pulsed light L0 output from the light source 50, and imparts to the near-infrared pulsed light L0 wavelength dispersion characteristics such that the wavelength spectrum of the near-infrared pulsed light L0 expands stepwise according to the waveguide portions 21 and 22.

[0071] This supercontinuum light source device 100 includes the above-described waveguide element 1. Therefore, it is possible to reduce optical loss while imparting wavelength dispersion characteristics to the near-infrared pulsed light L0 guided by the waveguide element 1 such that the wavelength spectrum expands stepwise, thereby obtaining mid-infrared supercontinuum light L1.

[0072] However, as described above, the supercontinuum light source device 100 is not limited to generating mid-infrared supercontinuum light, and may also generate supercontinuum light having a wavelength in other wavelength ranges, such as the ultraviolet wavelength range, the visible wavelength range, or the near-infrared wavelength range. In this case, the light source 50 may output ultraviolet pulsed light, visible pulsed light, near-infrared pulsed light, or mid-infrared pulsed light as pulsed light. In this case, it is possible to impart wavelength dispersion characteristics to the pulsed light guided by the waveguide element 1 such that the wavelength spectrum gradually expands while reducing optical loss, thereby obtaining supercontinuum light in a desired wavelength range.

[0073] Furthermore, in the super-continuum light source device 100 according to this embodiment, the light source 50 outputs near-infrared pulsed light L0 as pulsed light, and the waveguide element 1 guides the near-infrared pulsed light L0 while imparting wavelength dispersion characteristics to the near-infrared pulsed light L0, thereby outputting mid-infrared super-continuum light L1. In this case, it is possible to reduce optical loss and impart wavelength dispersion characteristics to the near-infrared pulsed light L0 guided by the waveguide element 1 so that the wavelength spectrum gradually expands, thereby obtaining mid-infrared super-continuum light L1.

[0074] The above embodiment describes one aspect of the waveguide element and the supercontinuum light source device according to the present disclosure. Therefore, the waveguide element and the supercontinuum light source device according to the present disclosure are not limited to the above embodiment.

[0075] Fig. 19 is a schematic diagram showing a super continuum light source device according to a modified example. The super continuum light source device 100A shown in Fig. 19 differs from the super continuum light source device 100 shown in Fig. 1 in that it includes an optical module 60A in which a light source 50 is provided together with a waveguide element 1 (i.e., the light source 50 is formed within the optical module). This type of super continuum light source device 100A can also achieve the same effects as the super continuum light source device 100.

[0076] In the super-continuum light source device 100A, the light source 50 is not limited to outputting near-infrared pulsed light, and may output ultraviolet pulsed light, visible pulsed light, near-infrared pulsed light, or mid-infrared pulsed light as pulsed light. In this case, the super-continuum light source device 100A can output super-continuum light in a wavelength range other than the mid-infrared range.

[0077] Furthermore, in the super-continuum light source devices 100 and 100A, the waveguide element 1 may propagate light from the waveguide portion 21 to the waveguide portion 23 via the waveguide portion 22 along the first direction D1. In this case, super-continuum light having a longer wavelength range than the pulsed light from the light source 50 can be obtained. Furthermore, the waveguide element 1 of the super-continuum light source devices 100 and 100A may propagate light from the waveguide portion 23 to the waveguide portion 21 via the waveguide portion 22 along the first direction D1. In this case, super-continuum light having a shorter wavelength range than the pulsed light from the light source 50 can be obtained. However, the opposite relationship may also occur depending on the parameter settings such as the width, height, and material of the waveguide.

[0078] The above example is an example in which the waveguide element 1 is used as part of a supercontinuum light source device. Alternatively, as shown in Fig. 20 , the waveguide element 1 may be used in a chromatic dispersion compensator 200. That is, the chromatic dispersion compensator 200 differs from the supercontinuum light source devices 100 and 100A in that it does not include a light source 50 and further includes a polarization controller 63.

[0079] The chromatic dispersion compensator 200 can be used, for example, in the field of optical communications, to suppress optical pulse broadening that occurs in an optical fiber transmission line between an optical transmitter and an optical receiver. In this case, the chromatic dispersion compensator 200 is interposed in the optical fiber transmission line and receives an optical signal S0. The chromatic dispersion compensator 200 inputs the optical signal S0 to the waveguide element 1 via the polarization controller 63 and the input unit 61. The waveguide element 1 guides the optical signal S0 input through the input unit 61, imparts chromatic dispersion characteristics to the optical signal in stages according to the waveguide units 21 and 22 (and further the waveguide unit 23), and outputs an optical signal S1 to which the chromatic dispersion characteristics have been imparted. In this case, the waveguide element 1 receives light (optical signal S0) from the input unit 61 at the first waveguide unit (e.g., the waveguide unit 21) and outputs light (optical signal S1) from the second waveguide unit (e.g., the waveguide unit 23). On the other hand, in the chromatic dispersion compensator 200, the waveguide element 1 may be configured to receive light (optical signal S0) from the input portion 61 at the second waveguide portion (e.g., waveguide portion 23) and output light (optical signal S1) from the first waveguide portion (e.g., waveguide portion 21).

[0080] As described above, the chromatic dispersion compensator 200 includes the waveguide element 1. Therefore, while suppressing optical loss, it is possible to impart chromatic dispersion characteristics in stages to the light (optical signal S0) guided by the waveguide element 1 according to the waveguide portions 21 and 22, thereby obtaining the optical signal S1 having predetermined chromatic dispersion characteristics (in which optical pulse broadening is suppressed). As a result, the occurrence of crosstalk due to optical pulse broadening is suppressed.

[0081] 21 is a perspective view showing a waveguide element according to a modified example. The waveguide element 1A shown in FIG. 21 has a silicon oxide layer (SiO ２ The waveguide element 1 differs from the waveguide element 1 in that it further comprises silicon oxide layers 51, 52, and 53. The silicon oxide layers 51, 52, and 53 are each integrally provided on a layer at the same height as the waveguide element 1.

[0082] That is, the silicon oxide layer 51 is formed continuously on the waveguide 21, the first portion 31 of the connecting waveguide 24, the layer of the waveguide 22 at the same height as the waveguide 21, the layer of the connecting waveguide 25 at the same height as the waveguide 21, and the layer of the waveguide 23 at the same height as the waveguide 21. The silicon oxide layer 52 is formed continuously in a layer shape at the same height as the second portion 32 of the connecting waveguide 24, the waveguide 22, the first portion 41 of the connecting waveguide 25, and the waveguide 22 of the waveguide 23. The silicon oxide layer 53 is formed continuously on the second portion 42 of the connecting waveguide 25 and the waveguide 23.

[0083] As described above, the waveguide element 1A including the silicon oxide layers 51, 52, and 53 can also achieve the same effects as the waveguide element 1. Furthermore, like the waveguide element 1, the waveguide element 1A can be applied to the supercontinuum light source devices 100, 100A and the chromatic dispersion compensator 200. Note that for a configuration in which a silicon oxide layer is formed in each layer of a waveguide element, reference can be made to the non-patent document "Pradip Gatkine, Nemanja Jovanovic, Christopher Hopgood, Simon Ellis, Ronald Broeke, Katarzyna Lawniczuk, Jeffrey Jewell, J. Kent Wallace, AND Dimitri Mawet1, "Potential of commercial SiN MPW platforms for developing mid / high-resolution integrated photonic spectrographs for astronomy", APPLIED OPTICS, Vol. 60, No. 19, July 1, 2021", etc.

[0084] 1, 1A...waveguide element, 21...waveguide portion (first waveguide portion), 22...waveguide portion (second waveguide portion, first waveguide portion), 23...waveguide portion (second waveguide portion), 24, 25...connecting waveguide portion, 31, 41...first portion, 32, 42...second portion, 50...light source, 61...input portion, 100, 100A...supercontinuum light source device, 200...chromatic dispersion compensator, E1, F1...first end, E2, F2...second end, E3, F3...third end, E4, F4...fourth end.

Claims

1. A waveguide element that imparts wavelength dispersion characteristics to guided light, comprising: a first waveguide section that imparts a first wavelength dispersion characteristic to the light; a second waveguide section that is arranged alongside the first waveguide section along a first direction that is a waveguiding direction of the light, and that imparts a second wavelength dispersion characteristic to the light; and a connection waveguide section that is arranged between the first waveguide section and the second waveguide section along the first direction, and that connects the first waveguide section and the second waveguide section, wherein the first waveguide section has a constant width in a second direction that intersects with the first direction, and has a first height in a third direction that intersects with the first and second directions; the second waveguide section has a constant width in the second direction along the first direction, and has a second height in the third direction that is greater than the first height; and the connection waveguide section a second portion provided on the first portion, the second portion having a third end connected to the second waveguide portion and a fourth end closer to the first waveguide portion than the third end, the second portion having a tapered shape whose width in the second direction decreases from the third end toward the fourth end, wherein the width of the second portion at the fourth end in the second direction is narrower than the width of the first waveguide portion in the second direction.

2. The waveguide element according to claim 1, wherein a second width, which is the width of said second waveguide portion in said second direction, is wider than a first width, which is the width of said first waveguide portion in said second direction, and said first portion has a tapered portion in which the width in said second direction gradually increases from said first width to said second width as it moves from said first end portion to said second end portion.

3. The waveguide element according to claim 1 or 2, wherein the length of the second portion in the first direction is shorter than the length of the first portion in the first direction.

4. A waveguide element according to claim 1 or 2, wherein the length of the second portion in the first direction is longer than the length of the first portion in the first direction.

5. A waveguide element according to claim 1 or 2, wherein the length of said second portion in said first direction is equal to the length of said first portion in said first direction.

6. The waveguide element according to claim 1, wherein a second width, which is the width of the second waveguide portion in the second direction, is narrower than a first width, which is the width of the first waveguide portion in the second direction, and the first portion has a tapered portion in which the width in the second direction gradually decreases from the first width to the second width as it moves from the first end to the second end.

7. A supercontinuum light source device comprising: a waveguide element according to any one of claims 1 to 6; and a light source that outputs pulsed light, wherein the waveguide element guides the pulsed light output from the light source as the light, and imparts to the pulsed light wavelength dispersion characteristics such that the wavelength spectrum of the pulsed light expands stepwise according to the first waveguide portion and the second waveguide portion.

8. The supercontinuum light source device according to claim 7, wherein the light source outputs ultraviolet pulsed light, visible pulsed light, near-infrared pulsed light, or mid-infrared pulsed light as the pulsed light.

9. The supercontinuum light source device according to claim 7, wherein the light source outputs near-infrared pulsed light as the pulsed light, and the waveguide element guides the near-infrared pulsed light while imparting the wavelength dispersion characteristics to the near-infrared pulsed light, and outputs mid-infrared supercontinuum light.

10. A wavelength dispersion compensator comprising: a waveguide element according to any one of claims 1 to 6; and an input section for inputting the light into the waveguide element, wherein the waveguide element guides the light input by the input section, imparts wavelength dispersion characteristics to the light in stages according to the first waveguide section and the second waveguide section, and outputs the light to which the wavelength dispersion characteristics have been imparted.

11. The chromatic dispersion compensator according to claim 10, wherein the waveguide element receives the light input from the input portion at the first waveguide portion and outputs the light from the second waveguide portion.

12. The chromatic dispersion compensator according to claim 10, wherein the waveguide element receives the light input from the input portion at the second waveguide portion and outputs the light from the first waveguide portion.

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