Photonic crystal resonator

Abstract

The present invention provides a photonic crystal resonator capable of improving the Q value by suppressing overlap between a p-type doping region and an optical resonance mode. The photonic crystal resonator according to the present disclosure comprises a thin film, an active layer embedded in the thin film, and holes periodically disposed in the thin film. The thin film further includes both a p-type doping region adjacent to the active layer and distributed in a trapezoidal shape with respect to the direction of current applied to the active layer, and an n-type doping region distributed in a trapezoidal shape at a position opposite to the p-type doping region. With respect to an array of holes in a region on one side when the center line of the photonic crystal resonator with respect to the direction of the current is defined as a boundary, the array of holes in the region on the opposite side is configured to be an array that is horizontally-shifted in a direction orthogonal to the direction of the current by a distance of 0.1 to 0.5 times a lattice constant.

Description

Photonic crystal resonator

[0001] This disclosure relates to a photonic crystal resonator.

[0002] In recent years, due to the progress of AI technology and IoT technology, the increase in power consumption of information communication devices has become a problem. In order to reduce such power consumption, studies have been underway to replace electrical wiring between chips and within chips of LSIs with optical wiring.

[0003] A photonic crystal resonator is an optical resonator using a photonic crystal and is used in optical devices such as laser light sources. A photonic crystal is a material having a structure in which the refractive index periodically changes in a size on the order of the wavelength of light, and since it can achieve a state where light is not transmitted at all, it is sometimes referred to as an "optical insulator". A photonic crystal resonator using such a photonic crystal has attracted attention in the integration of optical wiring and LSIs and in future optical information processing devices because it can significantly reduce power consumption.

[0004] FIG. 1 is a top view conceptually showing the structure of a photonic crystal resonator 100 according to the prior art. As shown in FIG. 1, the photonic crystal resonator 100 includes an indium phosphide (InP) thin film 101, an active layer 102 embedded in the InP thin film 101, holes 103 periodically arranged in the InP thin film 101, a photonic crystal line defect waveguide 104 corresponding to a region in the InP thin film 101 where the holes 103 are not arranged, and a trench 105 formed in the photonic crystal line defect waveguide 104. Further, the InP thin film 101 is adjacent to the active layer 102 and further includes a p-type doping region 101a distributed in a trapezoidal shape with respect to the direction of the current applied to the active layer 102 (the y direction in FIG. 1), and an n-type doping region 101b distributed in a trapezoidal shape at a position opposite to the p-type doping region 101a.

[0005] For example, in the photonic crystal resonator 100, the active layer 102 may be indium gallium arsenide phosphate (InGaAsP) or indium gallium aluminum arsenide (InGaAlAs), etc. Also, the voids 103 and trenches 105 may be air (i.e., not filled with other materials), or they may be filled with silica (SiO2) or resin.

[0006] A photonic crystal resonator 100 having such a structure achieves optical resonance (laser oscillation) by applying a current to the pn junction between the p-type doping region 101a and the n-type doping region 101b. In other words, the photonic crystal resonator 100 is a current-driven laser (see, for example, Non-Patent Document 1).

[0007] In the integration of optical wiring and LSIs described above, the laser light source is typically integrated near the chip and operated by electronic circuits. Therefore, the laser light source in the integration of optical wiring and LSIs is required to be a current-driven laser. As mentioned above, photonic crystal resonators are current-driven lasers, and this characteristic is one of the reasons why they are attracting attention for their application in the integration of optical wiring and LSIs.

[0008] However, it is known that the p-type InP constituting the p-type doping region 101a has an absorption coefficient that is more than an order of magnitude larger than the n-type InP constituting the n-type doping region 101b. For this reason, in the conventional photonic crystal resonator 100, there is a problem in that the overlap between the p-type doping region 101a and the optical resonance mode causes a deterioration of the Q value based on the absorption loss of the p-type doping region 101a.

[0009] K. Takeda, et al., “Few-fJ / bit data transmissions using directly modulated lambda-scale embedded active region photonic-crystal lasers”, NATURE PHOTONICS Vol. 7, pp569-575 (2013)

[0010] This disclosure has been made in view of the above-mentioned problems, and its purpose is to provide a photonic crystal resonator that can suppress the overlap between the p-type doping region and the optical resonance mode and improve the Q factor.

[0011] To address the above-mentioned problems, this disclosure provides a photonic crystal resonator comprising a thin film, an active layer embedded in the thin film, and periodically arranged vacancies in the thin film, wherein the thin film further comprises both a p-type doping region adjacent to the active layer and distributed trapezoidally with respect to the direction of the current applied to the active layer, and an n-type doping region distributed trapezoidally on the opposite side of the p-type doping region, wherein the arrangement of vacancies in the region opposite to the arrangement of vacancies in the region opposite to the arrangement of vacancies in the region opposite to the arrangement of vacancies in the region opposite to the arrangement of vacancies in the region opposite to the direction of the current is shifted in a direction perpendicular to the direction of the current by a distance of 0.1 to 0.5 times the lattice constant.

[0012] This is a top view conceptually showing the structure of a conventional photonic crystal resonator 100. This is a top view conceptually showing the structure of a photonic crystal resonator 200 according to the first embodiment of this disclosure. This is a contour map showing the simulation results of the magnetic field strength distribution in a model simulating the photonic crystal resonator 200. This is a figure showing the evaluation results of the Q value in the photonic crystal resonator 200, where (a) is a figure conceptually showing the offset d, (b) is a graph plotting the Q value against the offset d in the photonic crystal resonator 100 and the photonic crystal resonator 200 respectively, and (c) is a graph plotting the ratio of the Q value in the photonic crystal resonator 200 to the Q value in the photonic crystal resonator 100 with respect to the offset d. This is a contour map showing the simulation results of the magnetic field strength distribution in a model simulating a photonic crystal resonator 200 when the parallel displacement distance of the vacancies 203 in region 206b is different, where (a) is the contour map when there is no parallel displacement (i.e., corresponding to a photonic crystal resonator 100), and (b)-(f) are the contour maps when the parallel displacement distance is 0.1 times, 0.2 times, 0.3 times, 0.4 times, and 0.5 times the lattice constant, respectively. This is a graph plotting the Q value against the offset d when the parallel displacement distance of the vacancies 203 in region 206b changes. This is a top view conceptually showing the structure of a photonic crystal resonator 700 according to a second embodiment of this disclosure. This is a contour map showing the simulation results of the magnetic field strength distribution in a model simulating a photonic crystal resonator 700. This is a diagram conceptually showing the structure of a photonic crystal resonator 900 according to a third embodiment of this disclosure. This contour plot shows the simulation results of the magnetic field strength distribution in a model that simulates a photonic crystal resonator 900.

[0013] Various embodiments of this disclosure are described below in detail with reference to the drawings. Identical or similar reference numerals indicate identical or similar elements, and redundant descriptions may be omitted. Materials and numerical values ​​are illustrative and are not intended to limit the technical scope of this disclosure. The following description is illustrative and some configurations may be omitted or modified, or implemented with additional configurations, without departing from the gist of one embodiment of this disclosure.

[0014] In the following explanation, the term "lattice constant" refers to the distance between the centers of two vacancies that make up a photonic crystal.

[0015] Unlike the conventional photonic crystal resonator 100, the photonic crystal resonator according to this disclosure has an asymmetric arrangement of vacancies with respect to the center line in the direction of current application (width direction). More specifically, the photonic crystal resonator according to this disclosure is configured such that the arrangement of vacancies in one region with respect to the center line in the direction of current applied to the active layer is shifted in a direction perpendicular to the direction of current by a distance of 0.5 times the lattice constant compared to the arrangement of vacancies in one region 206b.

[0016] In the photonic crystal resonator according to this disclosure, which has such an asymmetrical arrangement of vacancies, the overlap between the p-type doping region and the optical resonant modes is suppressed, and as a result, the Q factor can be improved.

[0017] In one embodiment of the present disclosure, the photonic crystal resonator may include a photonic crystal line defect waveguide corresponding to a region where no vacancies are located, and a trench formed within the photonic crystal line defect waveguide, similar to the prior art photonic crystal resonator 100. However, the photonic crystal resonator according to the present disclosure does not necessarily require a trench, and the same effect is achieved even if the portion where the trench is located is replaced with an InP thin film.

[0018] In another embodiment of the present disclosure, the photonic crystal resonator may differ from the prior art photonic crystal resonator 100 in that it does not include photonic crystal line defect waveguides and trenches, and the portion of the photonic crystal line defect waveguides and trenches 205 is replaced by an InP thin film and vacancies, thus having the form of an Lx-type photonic crystal resonator.

[0019] (First Embodiment) Figure 2 is a conceptual top view showing the structure of a photonic crystal resonator 200 according to the first embodiment of the present disclosure. As shown in Figure 2, the photonic crystal resonator 200 includes an InP thin film 201, an active layer 202 embedded in the InP thin film 201, periodically arranged vacancies 203 in the InP thin film 201, a photonic crystal line defect waveguide 204 corresponding to a region in the InP thin film 201 where no vacancies 203 are arranged, and a trench 205 formed in the photonic crystal line defect waveguide 204. The InP thin film 201 further includes a p-type doping region 201a adjacent to the active layer 202 and distributed in a trapezoidal shape with respect to the direction of the current applied to the active layer 202 (y-direction in Figure 2).

[0020] In addition, the photonic crystal resonator 200 is configured such that, with respect to the center line in the direction of the current applied to the active layer 202 (y-direction in Figure 2), the arrangement of vacancies 203 in one region (the region on which the p-type doping region 201a is formed in Figure 2) 206a is parallel to the arrangement of vacancies 203 in the opposite region (the region on which the p-type doping region 201a is not formed in Figure 2) 206b, by a distance of 0.5 times the lattice constant (corresponding to half a period), in the direction perpendicular to the direction of the current (x-direction in Figure 2). In other words, the photonic crystal resonator 200 has an asymmetric arrangement structure of vacancies 203 with respect to the center line in the direction of the current applied to the active layer 202 (y-direction in Figure 2).

[0021] In Figure 2, the photonic crystal resonator 200 is depicted without including the n-type doping region 101b shown in Figure 1. This is because the n-type doping region was omitted in the simulation for the sake of simplification. As mentioned above, when comparing the absorption coefficients of p-type InP and n-type InP, the former is about an order of magnitude larger, and the aim of the present invention is to create an optical resonance mode that avoids this region. For this reason, the n-type doping region 101b, which is not the main cause of absorption in calculations, is omitted. However, since a pn junction is necessary to construct a current-driven laser, the InP thin film 201 in the photonic crystal resonator 200 needs to have both a p-type doping region 201a and an n-type doping region 101b.

[0022] Figure 3 is a contour map showing the simulation results of the magnetic field strength distribution in a model simulating a photonic crystal resonator 200. In this simulation, the lattice constant a is 420 nm, the vacancy radius is 0.24 a, the thickness of the InP thin film 201 (distance in the z direction in Figure 3) is 250 nm, the length of the active layer 202 (distance in the x direction in Figure 3) is 6 a, the width of the active layer 202 (distance in the y direction in Figure 3) is 300 nm, the thickness of the active layer 202 is 150 nm, and the width of the photonic crystal line defect waveguide 204 is 0.8 mm. (3) 1 / 2 a. A model was used in which the width of the trench 205 was set to 200 nm, and the vacancies 203 and trench 205 were filled with SiO2. In this simulation, the refractive index of the InP thin film 201 was set to 3.17, the refractive index of the vacancies 203 and trench 205 was set to 1.44, and the refractive index of the active layer 202 was set to 3.37. Under these conditions, the magnetic field strength distribution in a model simulating a photonic crystal resonator 200 was calculated using the finite element method (FEM) in this simulation.

[0023] As shown in Figure 3, in the photonic crystal resonator 200, the magnetic field strength is concentrated near the active layer 202, and it was observed that a high light confinement effect is achieved.

[0024] Figure 4 shows the evaluation results of the Q value in the photonic crystal resonator 200. (a) is a conceptual diagram of the offset d, (b) is a graph plotting the Q value against the offset d in the photonic crystal resonator 100 and the photonic crystal resonator 200, and (c) is a graph plotting the ratio of the Q value in the photonic crystal resonator 200 to the Q value in the photonic crystal resonator 100 against the offset d. As shown in Figure 4(a), the offset d is the distance between the active layer 202 and the p-type doping region 201a in the direction in which the current is applied (y-direction in Figure 4(a)). In addition, the Q value corresponding to the vertical axis in Figures 4(b) and (c) is the Q value based on the absorption loss of the p-type doping regions 101a and 201a, and the ratio of the Q values ​​corresponding to the vertical axis in Figure 4(c) is a value normalized to 1, with the Q value in the conventional photonic crystal resonator 100 being 1. In this evaluation, the absorption coefficient of p-type InP constituting the p-type doping regions 101a and 201a is 60 cm². -1 Assuming this, the p-type doping regions 101a and 201a were set as the imaginary part of the refractive index.

[0025] Generally, in optical resonators using two-dimensional photonic crystals, such as photonic crystal resonators 100 and 200, the Q-factor increases with increasing offset d. As shown in Figure 4(b), this trend is also observed in photonic crystal resonators 100 and 200. However, in this evaluation, the Q-factor of photonic crystal resonator 200 was found to be higher than that of photonic crystal resonator 100 in the offset d range of 0-600 nm. Furthermore, as shown in Figure 4(c), it was found that in the offset d range of 0-600 nm, photonic crystal resonator 200 has a Q-factor approximately 1.4-5.8 times higher than photonic crystal resonator 100.

[0026] Thus, it has been found that the photonic crystal resonator 200 according to this disclosure achieves a high light confinement effect and, compared to the conventional photonic crystal resonator 100, suppresses the overlap between the p-type doping region 201a and the optical resonance mode, thereby improving the Q factor.

[0027] Furthermore, in the above description, the photonic crystal resonator 200 was described as being configured such that the arrangement of vacancies 203 in region 206b is shifted in a direction perpendicular to the direction of the current by a distance of 0.5 times the lattice constant. However, the distance by which the vacancies 203 are shifted in a direction perpendicular to the direction of the current is not limited to 0.5 times the lattice constant; a similar effect can be achieved within the range of 0.1 to 0.5 times the lattice constant.

[0028] Figure 5 is a contour map showing the simulation results of the magnetic field strength distribution in a model simulating a photonic crystal resonator 200 when the translational displacement distance of the vacancies 203 in region 206b is different. (a) is the contour map when there is no translational displacement (i.e., corresponding to a photonic crystal resonator 100), and (b)-(f) are the contour maps when the translational displacement distance is 0.1 times, 0.2 times, 0.3 times, 0.4 times, and 0.5 times the lattice constant, respectively.

[0029] As shown in Figure 5, regardless of the translational displacement distance of the vacancies 203 in region 206b, the magnetic field strength is concentrated near the active layer 202, and it was confirmed that a high light confinement effect is achieved.

[0030] Figure 6 is a graph plotting the Q value against the offset d when the parallel displacement distance of the vacancies 203 in region 206b changes. As shown in Figure 6, it was found that the parallel displacement distance of the vacancies 203 in region 206b exhibits a higher Q value than that of the conventional photonic crystal resonator 100 in the range of 0.1 to 0.5 times the lattice constant.

[0031] Thus, in the photonic crystal resonator 200, if the distance over which the vacancies 203 move parallel to the direction perpendicular to the direction of the current is in the range of 0.1 to 0.5 times the lattice constant, a high light confinement effect can be achieved, and it has been found that, compared to the conventional photonic crystal resonator 100, it is possible to suppress the overlap between the p-type doping region 201a and the optical resonance mode and improve the Q factor.

[0032] (Second Embodiment) Figure 7 is a conceptual top view showing the structure of a photonic crystal resonator 700 according to the second embodiment of the present disclosure. As shown in Figure 5, the photonic crystal resonator 700 has a structure in which the trench 205 is removed from the photonic crystal resonator 200 described above, and the portion of the trench 205 is replaced by an InP thin film 701.

[0033] Figure 8 is a contour map showing the simulation results of the magnetic field strength distribution in a model simulating a photonic crystal resonator 700. In this simulation, the element corresponding to the trench 205 in the simulation conditions simulating the photonic crystal resonator 200 shown in Figure 3 was replaced with the InP thin film 701. All other simulation conditions are the same as those for simulating the photonic crystal resonator 200.

[0034] As shown in Figure 8, in the photonic crystal resonator 700 as well, the magnetic field strength was concentrated near the active layer 702, and a high light confinement effect was observed.

[0035] Even with the photonic crystal resonator 700 according to this disclosure having such a configuration, it is possible to achieve a high light confinement effect, similar to the photonic crystal resonator 200 described above, and to suppress the overlap between the p-type doping region 701a and the optical resonance mode, thereby improving the Q factor, compared to the conventional photonic crystal resonator 100.

[0036] (Third Embodiment) Figure 9 is a conceptual diagram showing the structure of a photonic crystal resonator 900 according to the third embodiment of the present disclosure. The photonic crystal resonators 200 and 700 described so far in the present disclosure included photonic crystal line defect waveguides 204 and 704. In contrast, as shown in Figure 9, the photonic crystal resonator 900 has a structure in which the photonic crystal line defect waveguide 204 and trench 205 in the photonic crystal line defect waveguide 204 are removed, and the portions of the photonic crystal line defect waveguide 204 and said trench 205 are replaced by an InP thin film 901 and vacancies 903. In other words, the photonic crystal resonator 900 has the form of an Lx-type photonic crystal resonator in which the periphery of the active layer 902 is covered only by an InP thin film 901 and vacancies 903.

[0037] In Figure 9, the photonic crystal resonator 900 is depicted as having seven missing vacancies, i.e., as an L7 type photonic crystal resonator. However, this is for illustrative purposes only, and the number of missing vacancies may be arbitrarily set according to the design. Similarly, the length of the active layer 902 (distance in the x-direction in Figure 7) may also be arbitrarily set according to the design.

[0038] Figure 10 is a contour map showing the simulation results of the magnetic field strength distribution in a model simulating a photonic crystal resonator 900. In this simulation, the elements corresponding to the photonic crystal line defect waveguide 204 and trench 205 in the simulation conditions simulating the photonic crystal resonator 200 shown in Figure 3 were replaced with the InP thin film 901 and vacancies 903. All other simulation conditions are the same as those for simulating the photonic crystal resonator 200.

[0039] As shown in Figure 10, in the photonic crystal resonator 900 as well, the magnetic field strength was concentrated near the active layer 902, and a high light confinement effect was observed.

[0040] Even with the photonic crystal resonator 900 according to this disclosure having such a configuration, it is possible to achieve a high light confinement effect, similar to the photonic crystal resonators 200 and 700 described above, and to suppress the overlap between the p-type doping region 901a and the optical resonance mode, thereby improving the Q value, compared to the conventional photonic crystal resonator 100.

[0041] The photonic crystal resonators 200, 700, and 900 described in this disclosure have all been described as using InP-based materials. However, as stated above, photonic crystals are materials having a structure in which the refractive index periodically changes in a size that matches the wavelength of light, and are therefore not necessarily limited to InP-based materials. The materials applied to the thin film portions corresponding to the InP thin films 201, 701, and 901, the active layers 202, 702, and 902, the vacancies 203, 703, and 903, and the trenches 205 may be any material depending on the design.

[0042] As described above, the photonic crystal resonator according to this disclosure can suppress the overlap between the p-type doping region and the optical resonant mode, thereby improving the Q factor, compared to the conventional technology. Such a photonic crystal resonator according to this disclosure is expected to be applied to the integration of optical wiring and LSIs, as well as to optical information processing devices.

Claims

1. A photonic crystal resonator comprising: a thin film; an active layer embedded in the thin film; and periodically arranged vacancies in the thin film, wherein the thin film further comprises both a p-type doping region adjacent to the active layer and distributed trapezoidally with respect to the direction of the current applied to the active layer, and an n-type doping region distributed trapezoidally on the opposite side of the p-type doping region, wherein the arrangement of vacancies in the region opposite to the arrangement of vacancies in the region on the opposite side of the boundary with respect to the direction of the current is shifted in a direction perpendicular to the direction of the current by a distance of 0.1 to 0.5 times the lattice constant.

2. The photonic crystal resonator according to claim 1, further comprising a photonic crystal line defect waveguide in a region where no vacancies are located.

3. The photonic crystal resonator according to claim 2, further comprising a trench formed in the photonic crystal line defect waveguide.

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