Optical devices

Abstract

This optical device comprises a first semiconductor layer (102) formed on a clad layer (101), a first core (102a) and a second core (102b) formed such that the first semiconductor layer (102) is positioned therebetween on the clad layer (101), and a plurality of partitioned active layers (103) embedded in the first semiconductor layer (102). The plurality of partitioned active layers (103) are embedded in an active region (131) of the first semiconductor layer (102), and are arranged in a regular cyclic pattern in a waveguide direction. Furthermore, each of the plurality of partitioned active layers (103) has the same length in the waveguide direction. Furthermore, resonators (111) formed such that the active region (131) is positioned therebetween in the waveguide direction are provided. The resonators (111) have a photonic crystal structure formed on the first core (102a) and the second core (102b).

Description

[Technical Field]

[0001] This invention relates to an optical waveguide type optical device. [Background technology]

[0002] Gain-coupled lasers (GC lasers) have been proposed as lasers that achieve superior characteristics by embedding the active region into a heterostructure (BH) and subdividing (dividing) it at a period matching the resonant electric field distribution of light (Non-Patent Literature 1, Non-Patent Literature 2). In GC lasers, the selectively divided active layer is placed in the peak portion of the resonant electric field distribution, i.e., in the region with a strong electric field intensity. This improves optical confinement per volume of each divided active layer (divided active layer), making it possible to efficiently amplify light.

[0003] Furthermore, the active region is subdivided along the optical axis, which reduces the total length of the active region (L BH ) for the current injection region length (L gain The ratio of ) is improved, which reduces the device resistance per divided active layer volume. Reducing device resistance is important for low power consumption operation, high speed operation, and high power operation. In conventional GC lasers, L gain The amplitude is typically around 150 μm to 200 μm, and oscillation threshold values ​​such as 0.7 mA [Non-Patent Literature 1] and 1.5 mA [Non-Patent Literature 2] have been obtained. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] K. Ohira et al., "Stable Single-Mode Operation of Distributed Feedback Lasers With Wirelike Active Regions", IEEE Journal of Selected Topics in Quantum Electronics, vol. 9, no. 5, pp. 1166-1171, 2003. [Non-Patent Document 2] K. Ohira. et al., "Low-Threshold and High-Efficiency Operation of Distributed Reflector Lasers With Width-Modulated Wirelike Active Regions", IEEE Journal of Selected Topics in Quantum Electronics, vol. 11, no. 5, pp. 1162-1168, 2005. [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] The characteristics of the GC laser, such as high optical confinement and low device resistance per divided active layer, are expected to be particularly effective in improving the performance of an extremely low-power laser having an extremely small active region. This is because, generally, as the active volume becomes minute, it becomes difficult to strongly localize light in the active region and to provide a low-resistance current injection channel.

[0006] However, in the prior art, due to its structure, it is not easy to further shorten the gain region length L gain and the total active region length L BH That is, in the prior art, an embedded hetero structure and a distributed Bragg reflector (DBR) composed of InP or the like are used. However, since the coupling constant is small, a DBR length of typically 100 μm or more is required to obtain a sufficient reflectivity, and light cannot be confined in a minute region.

[0007] In particular, when aiming to apply GC lasers to ultra-short distance optical interconnections, L BH It is crucial to achieve extremely low oscillation thresholds (typically on the μA scale) and extremely low power consumption by miniaturizing the laser to a few μm scale while strongly confining light to the active region. However, realizing such lasers is extremely difficult with conventional technology. Thus, it is extremely difficult to shorten GC lasers to an extremely short length with the structure of conventional technology.

[0008] This invention was made to solve the above-mentioned problems and aims to further shorten the length of gain-coupled lasers. [Means for solving the problem]

[0009] The optical device according to the present invention comprises a cladding layer, a first semiconductor layer made of a compound semiconductor formed in an active region on the cladding layer, a first core and a second core formed on the cladding layer with the first semiconductor layer in between, a plurality of segmented active layers embedded in the first semiconductor layer and arranged at a constant period in the waveguide direction with the same length in the waveguide direction, a second semiconductor layer made of an n-type compound semiconductor and a third semiconductor layer made of a p-type compound semiconductor formed on the cladding layer, with the active region in between and in contact with the side surface of the first semiconductor layer, a first electrode connected to the second semiconductor layer, a second electrode connected to the third semiconductor layer, a first passive optical waveguide and a second passive optical waveguide composed of the first core and the second core and connected to the active region, and a resonator formed with the active region in the waveguide direction and composed of a photonic crystal structure formed in the first core and the second core. [Effects of the Invention]

[0010] As described above, the present invention provides a resonator composed of a photonic crystal structure formed in a first core and a second core sandwiching a first semiconductor layer into which a plurality of divided active layers arranged at a certain period are embedded, thus enabling further shortening of the gain-coupled laser. [Brief explanation of the drawing]

[0011] [Figure 1A] Figure 1A is a plan view showing the configuration of an optical device according to an embodiment of the present invention. [Figure 1B] Figure 1B is a cross-sectional view showing a partial configuration of an optical device according to an embodiment of the present invention. [Figure 2] Figure 2 is a plan view showing the configuration of a typical one-dimensional photonic crystal laser. [Figure 3] Figure 3 is a characteristic diagram showing the DFB stopband in the GC-type active region. [Figure 4] Figure 4 is a characteristic diagram showing the deflection angle of the amplitude reflectance of the waveguide mode when looking further out from the endpoint of the active region 131. [Figure 5] Figure 5 is a characteristic diagram showing the deflection angle of the amplitude reflectance of the waveguide mode when looking further out from the endpoint of the active region 131. [Figure 6A] Figure 6A is a characteristic diagram showing the resonant electric field distribution of the resonator 111 of the optical device according to the embodiment. [Figure 6B] Figure 6B is a characteristic diagram showing the resonant electric field distribution of a typical one-dimensional photonic crystal laser. [Figure 6C] Figure 6C is a characteristic diagram showing the resonant electric field distribution of a typical one-dimensional photonic crystal laser. [Modes for carrying out the invention]

[0012] The optical device according to an embodiment of the present invention will be described below with reference to Figures 1A and 1B. Figure 1B shows a cross-section of a plane perpendicular to the waveguide direction. In Figure 1B, the x-axis direction (x direction) is the thickness direction, the y-axis direction (y direction) is the current injection direction, and the z-axis direction (z direction) is the waveguide direction. The optical device according to the embodiment is a gain-coupled laser (GC laser).

[0013] This optical device comprises a cladding layer 101, a first semiconductor layer 102 formed on the cladding layer 101, a first core 102a and a second core 102b formed on the cladding layer 101 with the first semiconductor layer 102 in between, a plurality of segmented active layers 103 embedded in the first semiconductor layer 102, and a second semiconductor layer 104 and a third semiconductor layer 105 formed on the cladding layer 101, parallel to the surface of the cladding layer 101, in a direction perpendicular to the waveguide direction (z direction) (y direction), with an active region 131 in between, and in contact with the side surface of the first semiconductor layer 102.

[0014] The cladding layer 101 can be made of, for example, silicon oxide. For example, a silicon oxide layer formed on a substrate such as Si can be used as the cladding layer 101. The first semiconductor layer 102, the first core 102a, and the second core 102b can be made of, for example, a III-V compound semiconductor such as InP. For example, the first semiconductor layer 102, the first core 102a, and the second core 102b can be formed by depositing InP on the cladding layer 101 using a well-known method such as metal-organic vapor deposition.

[0015] Multiple segmented active layers 103 are embedded in the active region 131 of the first semiconductor layer 102 and are arranged at a constant period in the waveguide direction. Each of the multiple segmented active layers 103 has the same length in the waveguide direction. Each of the multiple segmented active layers 103 can have an external shape, for example, that of a rectangular parallelepiped. The second semiconductor layer 104 and the third semiconductor layer 105 are arranged flanking the active region 131. The second semiconductor layer 104 can be made of an n-type III-V compound semiconductor, such as n-type InP. The third semiconductor layer 105 can be made of a p-type III-V compound semiconductor, such as p-type InP.

[0016] Furthermore, this optical device includes a first electrode 108 electrically connected to the second semiconductor layer 104 and a second electrode 109 electrically connected to the third semiconductor layer 105. In this example, with the cladding layer 101 facing downwards, the upper side of the first semiconductor layer 102 (first core 102a and second core 102b) is cladded with air.

[0017] Furthermore, this optical device may include a fourth semiconductor layer 106 connected to the second semiconductor layer 104, which is formed on the cladding layer 101 and positioned to sandwich the second semiconductor layer 104 between itself and the active region 131. It may also include a fifth semiconductor layer 107 connected to the third semiconductor layer 105, which is formed on the cladding layer 101 and positioned to sandwich the third semiconductor layer 105 between itself and the active region 131.

[0018] If a fourth semiconductor layer 106 is included, the first electrode 108 is connected to the second semiconductor layer 104 via the fourth semiconductor layer 106. If a fifth semiconductor layer 107 is included, the second electrode 109 is connected to the third semiconductor layer 105 via the fifth semiconductor layer 107. The fourth semiconductor layer 106 can be made from an n-type III-V compound semiconductor such as n-type InP. The fifth semiconductor layer 107 can be made from a p-type III-V compound semiconductor such as p-type InP.

[0019] Furthermore, the second semiconductor layer 104 and the third semiconductor layer 105 are formed thinner than the first semiconductor layer 102 (and the first core 102a and the second core 102b). The thinly formed regions can be referred to as "trench regions." In this example, the first semiconductor layer 102, the first core 102a, the second core 102b, the second semiconductor layer 104, the third semiconductor layer 105, the fourth semiconductor layer 106, and the fifth semiconductor layer 107 are formed integrally.

[0020] Furthermore, it includes a first passive optical waveguide 132 and a second passive optical waveguide 133, which are composed of a first core 102a and a second core 102b and connected to the active region 131. The first passive optical waveguide 132 and the second passive optical waveguide 133 are arranged on either side of the active region 131 in the waveguide direction and are optically connected to the divided active layer 103 (active region 131).

[0021] In the active region 131, where the second semiconductor layer 104 and the third semiconductor layer 105 are formed thinner than the first semiconductor layer 102, the second semiconductor layer 104 and the third semiconductor layer 105 form a slab, resulting in a so-called rib-type optical waveguide structure. On the other hand, the first passive optical waveguide 132 and the second passive optical waveguide 133 have a so-called channel-type optical waveguide structure.

[0022] Furthermore, in the optical device according to the embodiment, the second semiconductor layer 104 comprises a first region on the side of the first electrode 108 and a first expanded region on the side of the plurality of divided active layers 103. The first region has a trapezoidal (isosceles trapezoidal) shape, which narrows in width as it moves away from the side of the first electrode 108 in a plan view. The first expanded region has a trapezoidal (isosceles trapezoidal) shape, which narrows in width as it moves away from the side of the plurality of divided active layers 103 in a plan view. The third semiconductor layer 105 also comprises two similar regions (second region and second expanded region).

[0023] Furthermore, in the optical device according to this embodiment, the first passive optical waveguide 132 and the second passive optical waveguide 133, which are arranged on either side of the active region 131 in the waveguide direction, are optically connected to the divided active layer 103 (first semiconductor layer 102) via tapered regions where the core width decreases as it moves away from the active region 131. The core widths of the first core 102a and the second core 102b can also be the same as the width of the first semiconductor layer 102 of the active region 131.

[0024] Furthermore, the optical device according to the embodiment includes a resonator 111 formed with an active region 131 (first semiconductor layer 102) in the waveguide direction. The resonator 111 is composed of a photonic crystal structure formed in the first core 102a and the second core 102b. The photonic crystal structure has multiple through-holes arranged in the waveguide direction, penetrating the first core 102a and the second core 102b of the first passive optical waveguide 132 and the second passive optical waveguide 133 in the thickness direction (nanobeam).

[0025] As described above, by forming a resonator (reflector) 111, sandwiching the active region 131 with the resonator 111, and confining light within the active region 131, the optical device can be operated as a current injection laser. As a mechanism for extracting light, for example, the number of periods of the photonic crystal structure constituting the resonator 111 of the first passive optical waveguide 132 can be reduced, and the resulting transmitted component can be used as the output. Alternatively, for example, a Si core can be formed in the first core 102a of the first passive optical waveguide 132, positioned close enough to allow optical coupling, and the oscillating light can be extracted using the optical waveguide formed by this Si core.

[0026] As is well known, photonic crystals are structures that enable light confinement to extremely small regions ranging from a few micrometers to the wavelength of light (Reference 1). These are structures in which, for example, thin film slabs (2D) made of compound semiconductors such as InP or nanowire waveguides (1D) made of compound semiconductors such as InP have periodically spaced circular holes that penetrate from the top to the bottom. Due to the large refractive index contrast between the low refractive index material such as air or polymer filling the holes and the compound semiconductor, these structures produce strong Bragg reflections. By using such photonic crystals, it is possible to almost completely reflect light within an extremely small region on the wavelength of light and form an extremely small resonator 111.

[0027] Therefore, the length of the active region 131 (active region length L) BHIn order to realize an extremely small GC laser that is miniaturized to the scale of several micrometers to the wavelength scale of light, it is promising to form a resonator 111 that combines a GC-type active region 131 and a photonic crystal. However, the GC-type active region 131 and the photonic crystal are greatly different in both constituent materials and element structures, and significant differences in characteristics as components of the resonator 111 arise therefrom. For this reason, the design of a desired GC laser resonator, that is, a resonator having a GC-type resonant electric field distribution in which the peak position of the electric field intensity of light and the gain position coincide in the active region, while the light is confined within a minute region (divided active layer) by the photonic crystal surrounding the active region, is generally difficult.

[0028] More specifically, in order to realize a desired GC laser resonator, it is necessary to design and optimize the characteristics and relative positional relationship of both so that the electric field distribution in the GC-type active region and the electric field distribution in the photonic crystal region are matched. However, as described above, since both have greatly different structures and characteristics, an appropriate structural design for obtaining this matching of the electric field distribution is not easy, whether by analytical calculation or numerical calculation.

[0029] In contrast, the optical device according to the embodiment has a length L in the waveguide direction in the active region 131 gain In the current injection region, N divided active layers 103 each having a length a are periodically arranged with a period Λ. Note that a typical one-dimensional photonic crystal laser has a structure in which an integrated active layer 203 is embedded in a first semiconductor layer 102 having a rib-shaped core shape, and the front side and the rear side are surrounded by a resonator 111 formed of a photonic crystal structure formed in each of a first core 102a and a second core 102b. [[ID=管理]]

[0030] The optical device according to the embodiment has a current injection region length L in which N divided active layers 103 are arranged gainAssume that the following relationship holds between the N divided active layers 103 and the period Λ. Furthermore, as shown in Figure 1, if the active region 131, in which multiple divided active layers 103 are embedded, is contained within the current injection region sandwiched between the second semiconductor layer 104 and the third semiconductor layer 105, then the following relationship inevitably holds.

[0031]

number

[0032] Furthermore, when N is odd, the active region 131 is positioned such that the center of the (N+1) / 2th divided active layer 103 coincides with the center of the current injection region. Furthermore, when N is even, the active region 131 is positioned such that the center of the first semiconductor layer 102 filling the space between the N / 2th divided active layer 103 and the (N / 2+1)th divided active layer 103 coincides with the center of the current injection region.

[0033] When these conditions are met, the center of the first divided active layer 103 and the point located Λ / 2 outward from the center of the Nth divided active layer 103 (hereinafter referred to as the endpoint of the active region 131) coincide with the endpoint of the current injection region. The amplitude reflectance of the waveguide mode when looking further outward from the endpoint of the active region 131 is given for the front side (left side of Figure 1A) and the rear side (right side of Figure 1A), respectively, r F ,r R Let's assume this amplitude reflectance r F ,r R is, length L tp Waveguide width conversion tapered region, length L ΦF ,L ΦR This provides the characteristics of reflection after passing through the phase adjustment region, the front and rear mirrors made of one-dimensional photonic crystals, and these three regions. F ,r R This can be easily calculated using commonly used commercial 3D finite difference time-domain (3D-FDTD) solvers.

[0034] The active region 131 of the optical device according to this embodiment functions as a uniform distributed feedback (DFB) structure consisting of a first semiconductor layer 102 and a plurality of segmented active layers 103 embedded in the first semiconductor layer 102, and generates a stopband due to the refractive index difference between the plurality of segmented active layers 103 and the first semiconductor layer 102. For the active region 131, the equivalent refractive index of the cross-sectional mode with respect to the average dielectric constant distribution is n eq,ave Let's assume that the equivalent refractive index of the cross-sectional modes in the divided active layer 103 is n eq,BH Let's assume that the equivalent refractive index of the cross-sectional mode in the first semiconductor layer 102 is n eq,semi In this case, the Bragg wavelength λ of the DFB mentioned above is assumed. B This is given by equation (2) below.

[0035]

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[0036] Furthermore, the coupling constant κ at the Bragg wavelength given by equation (2) is given by the following equation (3).

[0037]

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[0038] Furthermore, the equivalent group refractive index of the cross-sectional modes for the average dielectric constant distribution is n g,ave Therefore, the long-wavelength end wavelength of the stopband λ + This is given by equation (4) below.

[0039]

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[0040] In a uniform DFB at infinity, standing wave modes are formed at the long and short wave ends of the stopband, respectively. In this case, the long wave end mode has an electric field distribution such that it has a peak in electric field strength in the high refractive index portion (split active layer 103) and a zero point in electric field strength in the low refractive index portion (first semiconductor layer 102), i.e., a GC-type electric field distribution (Non-Patent Literature 1). Therefore, in order to realize a GC laser, the desired oscillation wavelength λ lasing The long-wave edge wavelength λ is given by equation (4). + Make it equal to . Specifically, based on equations (2)-(4), λ lasing =λ + The DFB can be designed by determining the period Λ and the waveguide length a of each divided active layer 103 such that the above holds true.

[0041] Figure 3 shows the DFB stopband of the GC-type active region designed using the method described above. λ lasing =λ + =1550nm was used. In GC lasers (GC-PhC lasers) with a resonator constructed from a photonic crystal, the length of the GC-type active region is typically on the order of μm, but here, in order to clearly visualize the stopband, the DFB region length was extended to 50 μm, and the transmission spectrum of the enlarged DFB region was calculated and plotted using 3D-FDTD. The wavelength range where the transmittance is almost zero, i.e., the long-wavelength edge wavelength of the stopband λ + It can be confirmed that it is indeed located at approximately 1550 nm. The GC-type active region structure designed here will be used in subsequent GC-PhC laser calculations.

[0042] In the GC-PhC laser, which is an optical device according to the embodiment, in order to obtain a desired GC-type resonant electric field distribution, it is necessary to provide front and rear resonators 111 such that the electric field distribution matches the active region 131 designed as described above. The design method is described below. It is assumed that the structure of the one-dimensional photonic crystal forming the front and rear resonators 111 has been appropriately designed in advance.

[0043]

number

[0044] The above simple three-step design method allows for the creation of a structure exhibiting the desired GC-type resonant electric field distribution (i.e., an appropriate phase adjustment length L). ΦF ,L ΦR Equation (5) allows for precise design of the deflection angle of the reflected wave. F / R )=Φ F / R This is a conditional expression to satisfy "=π". At the endpoint of the active region 131, which is the starting point for calculating the amplitude reflectance, the wavelength λ + Since the electric field amplitude of the long-wave edge mode is zero, when the deflection angle of the reflected wave viewed from this point is π, the respective electric field distributions match, and the desired GC-type resonant electric field distribution is obtained.

[0045] As mentioned above, GC-type active regions and photonic crystal resonators exhibit significantly different optical properties, making coordinated design between the two generally difficult. If the aforementioned calculation method is not used, a computationally intensive design approach is required, such as performing calculations on the entire laser resonator step by step while rapidly sweeping the phase adjustment length. The main reason for this difficulty is the use of photonic crystal resonators, which are difficult to handle analytically.

[0046] In contrast, the design method described above incorporates the reflection characteristics of a complex photonic crystal resonator as a parameter called deflection angle through 3D-FDTD calculations in Step 1, allowing for the application of a semi-analytical calculation method. This significantly reduces the difficulty of the design and the required computational costs, while enabling accurate resonator design.

[0047] A specific example of an optical device (GC-PhC laser) according to the embodiment of the design method described above is shown below. In the following example, for simplicity, the photonic crystal structure of the front resonator 111 is made the same as that of the rear resonator 111, and the structure is symmetrical with respect to the resonator center. At this time, "L ΦF =L ΦR =L Φ ,rF =r R =r=√Rexp(-jΦ)」

[0048] Figure 4 shows the deflection angles of amplitude reflectance calculated under various conditions, and Figure 5 shows the spectrum of power reflectance. L was calculated as the reference phase adjustment length. φ0 Looking at the results at 200 nm, the deflection angle at a wavelength of 1550 nm is slightly smaller than π. Therefore, when we calculate the correction value for the phase adjustment length based on equation (5), we get ΔL φ This results in 64.18 nm. Calculating the reflectance with this phase adjustment length, we can see that the deflection angle at a wavelength of 1550 nm is indeed approximately equal to π, indicating that the desired reflection characteristics are obtained.

[0049] On the other hand, the power reflectivity shown in Figure 5 exhibits almost identical characteristics for all phase adjustment lengths. In other words, the expansion and contraction of the phase adjustment region only adjusts the polarization angle of the reflected wave and does not have a significant effect on the power reflectivity.

[0050] Figure 6A shows the resonant field distribution of the resonator 111 of the optical device (GC-PhC laser) according to an embodiment constructed by combining the active region 131 (Figure 3) whose characteristics were described above with the resonator 111 (Figures 4 and 5) outside it. Table 1 shows the parameters that define the laser structure and the resonator characteristics obtained by calculation. Resonant wavelength λ cav The oscillation wavelength λ set in the above design is lasing This is approximately equal to 1549 nm, which is nearly equal to 1550 nm. At this resonant wavelength, as shown in Figure 6A, a GC-type resonant electric field distribution is obtained in which the peak position of the electric field intensity, shown by the solid line, and the position of the subdivided active layer 103, shown by the dotted line, overlap in a one-to-one correspondence. Therefore, the resonator 111 of the GC-PhC laser exhibiting the desired GC-type resonant electric field distribution can indeed be accurately designed using the simple design method described above. In Figure 6A, the dotted line indicates the presence or absence of the first semiconductor layer 102 (semi) and the subdivided active layer 103 (BH).

[0051] Figures 6B, 6C, and Table 1 also show the resonant field distribution, structural parameters, and resonator characteristics of a conventional one-dimensional photonic crystal laser with an unrefined active region, as shown in Figure 2, for comparison to illustrate the characteristic advantages of the GC-PhC laser. In Figures 6B and 6C, the dotted lines indicate the presence or absence of the first semiconductor layer (semi) and the embedded active layer (BH).

[0052] [Table 1]

[0053] Figure 6B is L gain =L BH This is the case where =5.0μm, and Figure 6C is L gain =L BH This is the case where =2.5μm. Here, Γ shown in Table 1 z This is the optical confinement coefficient of the resonant electric field with respect to the BH in the optical axis direction, and is given by the following equation (6).

[0054]

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[0055] E(z) represents the resonant electric field distribution in the optical axis direction, the subscript BH represents the integral in the divided active layer 103, and the subscript all represents the integral over the entire region. First, Figures 6A and 6B show the nearly common current injection region length L. gain When comparing them, the resonator lengths are almost identical, therefore the resonator Q value is Q cav They are almost equal. On the other hand, the total length of the active region L BH In the proposed structure, L BH =(a / Λ)·L gain = 0.5 × L gain It has been halved, and its active volume has been further reduced.

[0056] Γ zWhile the conventional structure has a larger value when comparing the values ​​of the optical confinement coefficient per active layer length, which is important for laser characteristics, the optical device according to the embodiment shows a significantly larger value, due to the denominator being halved. This reflects the characteristic of GC lasers described above, that "because the active region is selectively located in areas with strong electric field intensity, optical confinement per unit active volume is improved, and efficient amplification of light is possible."

[0057] Next, Figures 6A and 6C show the entire active region L, which is almost the same. BH Comparing them side by side, first, in the structure of the optical device according to the embodiment, the current injection region length L gain is L BH It is twice as long, or 2 times, which results in a significant reduction in element resistance. Also, due to the longer resonator length, the embodiment has a significantly higher Q. cav This indicates that increasing the resonator Q factor is important for reducing the oscillation threshold and improving the optical extraction efficiency. Furthermore, Γ z and Γ z / L BH When comparing the values, the embodiment shows a slightly larger value, confirming the effect of improving optical confinement through GC laser conversion.

[0058] Thus, according to this embodiment, compared to a PhC laser, it brings about improvements in characteristics such as a reduction in the active volume, a reduction in element resistance, an improvement in the resonator Q value, and an improvement in the optical confinement coefficient, making it effective for improving the performance of ultra-low power consumption lasers with an extremely small active region.

[0059] For simplicity, the calculations in this example assume a laser resonator where the structure of the front resonator 111 is identical to that of the rear resonator 111, and light is intentionally not emitted from the front. However, it is clear that the present invention can be applied more generally to laser resonators where the structures of the front and rear resonators 111 are different.

[0060] A particularly typical case is that the rear resonator 111 has a sufficient number of holes to make the light transmittance negligibly small, while the front resonator 111 has an appropriate number of holes to achieve both a low oscillation threshold and high light extraction efficiency, so that a certain proportion of light is transmitted to and output to the front side. In this case, a unidirectional laser light output is obtained only to the front side, which is desirable for applications such as optical interconnections.

[0061] As described above, the present invention provides a resonator composed of a photonic crystal structure formed in a first core and a second core sandwiching a first semiconductor layer into which a plurality of divided active layers arranged at a certain period are embedded, thereby enabling further shortening of the gain-coupled laser.

[0062] According to the present invention, the combination of a GC-type active region and a photonic crystal resonator structure makes it possible to realize a laser that exhibits excellent characteristics while having an extremely small active region, which was difficult to achieve with conventional GC lasers or ordinary PhC lasers. According to the present invention, by appropriately combining numerical calculations such as 3D-FDTD with analytical calculations, accurate resonator design becomes possible using a simple method with low computational costs.

[0063] Some or all of the above embodiments may also be described as follows, but are not limited to the following:

[0064] [Note 1] An optical device comprising: a cladding layer; a first semiconductor layer made of a compound semiconductor formed in an active region on the cladding layer; a first core and a second core formed on the cladding layer, sandwiching the first semiconductor layer; a plurality of segmented active layers embedded in the first semiconductor layer, arranged at a constant period in the waveguide direction and having the same length in the waveguide direction; a second semiconductor layer made of an n-type compound semiconductor and a third semiconductor layer made of a p-type compound semiconductor formed on the cladding layer, sandwiching the active region and in contact with the side surface of the first semiconductor layer; a first electrode connected to the second semiconductor layer; a second electrode connected to the third semiconductor layer; a first passive optical waveguide and a second passive optical waveguide composed of the first core and the second core, connected to the active region; and a resonator formed on either side of the active region in the waveguide direction, composed of a photonic crystal structure formed on the first core and the second core.

[0065] [Note 2] The optical device as described in Appendix 1, comprising: a fourth semiconductor layer made of an n-type compound semiconductor formed on the cladding layer, arranged to sandwich the second semiconductor layer between itself and the active region, and connected to the second semiconductor layer; and a fifth semiconductor layer made of a p-type compound semiconductor formed on the cladding layer, arranged to sandwich the third semiconductor layer between itself and the active region, and connected to the third semiconductor layer, wherein the first electrode is connected to the second semiconductor layer via the fourth semiconductor layer, and the second electrode is connected to the third semiconductor layer via the fifth semiconductor layer.

[0066] [Note 3] An optical device as described in Appendix 1 or 2, wherein the second semiconductor layer and the third semiconductor layer are formed thinner than the first semiconductor layer, the second semiconductor layer comprises a first region having a trapezoidal shape that narrows in width from the side of the first semiconductor layer to the side of the fourth semiconductor layer in a plan view, and a first expanded region having a trapezoidal shape that widens in width from the side of the first region to the side of the fourth semiconductor layer, the third semiconductor layer comprises a second region having a trapezoidal shape that narrows in width from the side of the first semiconductor layer to the side of the fifth semiconductor layer in a plan view, and a second expanded region having a trapezoidal shape that widens in width from the side of the second region to the side of the fifth semiconductor layer, and the first region and the second region are provided with a tapered shape at their ends in the waveguide direction, where the width in a plan view narrows as it moves away from the center of the active region.

[0067] [Note 4] In the optical device described in any one of the appendices 1 to 3, a distributed feedback structure is formed from the first semiconductor layer and the plurality of divided active layers embedded in the first semiconductor layer, and based on the following equations (A), (B), and (C), λ lasing =λ + An optical device characterized in that the period Λ and the length a in the waveguide direction of the divided active layer are determined such that the following holds true.

[0068]

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[0069] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be implemented within the technical concept of the present invention by those with ordinary skill in the art.

[0070] [Reference 1] K. Takeda et al., "Few-fJ / bit data transmissions using directly modulated lambda-scale embedded active region photonic-crystal lasers", Nature Photonics, vol. 7, pp. 569-575, 2013. [Explanation of Symbols]

[0071] 101...Cladding layer, 102...First semiconductor layer, 102a...First core, 102b...Second core, 103...Divided active layer, 104...Second semiconductor layer, 105...Third semiconductor layer, 106...Fourth semiconductor layer, 107...Fifth semiconductor layer, 108...First electrode, 109...Second electrode, 111...Resonator, 131...Active region, 132...First passive optical waveguide, 133...Second passive optical waveguide.

Claims

1. Cladding layer, A first semiconductor layer made of a compound semiconductor formed in the active region on the cladding layer, A first core and a second core are formed on the cladding layer with the first semiconductor layer sandwiched between them, A plurality of segmented active layers are embedded in the first semiconductor layer, arranged at a constant period in the waveguide direction, and have the same length in the waveguide direction, A second semiconductor layer made of an n-type compound semiconductor and a third semiconductor layer made of a p-type compound semiconductor are formed on the cladding layer, sandwiching the active region and in contact with the side surface of the first semiconductor layer. A first electrode connected to the second semiconductor layer, A second electrode connected to the third semiconductor layer, A first passive optical waveguide and a second passive optical waveguide, each composed of the first core and the second core, are connected to the active region. A resonator formed with the active region in the waveguide direction and composed of photonic crystal structures formed in the first core and the second core, Equipped with, An optical device characterized in that a distributed feedback structure is formed from the first semiconductor layer and the plurality of divided active layers embedded in the first semiconductor layer, and the period Λ and the length a in the waveguide direction of the divided active layer are determined based on the following equations (A), (B), and (C) such that a desired oscillation wavelength λ lasing = λ + holds. [Math 1]

2. In the optical device according to claim 1, A fourth semiconductor layer, made of an n-type compound semiconductor, is formed on the cladding layer, is positioned to sandwich the second semiconductor layer between itself and the active region, and is connected to the second semiconductor layer. A fifth semiconductor layer, made of a p-type compound semiconductor, is formed on the cladding layer, is positioned to sandwich the third semiconductor layer between itself and the active region, and is connected to the third semiconductor layer. Equipped with, The first electrode is connected to the second semiconductor layer via the fourth semiconductor layer, The second electrode is connected to the third semiconductor layer via the fifth semiconductor layer. doing An optical device characterized by the following features.

3. In the optical device according to claim 2, The second semiconductor layer and the third semiconductor layer are formed to be thinner than the first semiconductor layer. The second semiconductor layer comprises a first region having a trapezoidal shape that narrows in width from the side of the first semiconductor layer to the side of the fourth semiconductor layer in a plan view, and a first expanded region having a trapezoidal shape that widens in width from the side of the first region to the side of the fourth semiconductor layer. The third semiconductor layer comprises a second region having a trapezoidal shape that narrows in width from the side of the first semiconductor layer to the side of the fifth semiconductor layer in a plan view, and a second expanded region having a trapezoidal shape that widens in width from the side of the second region to the side of the fifth semiconductor layer. The first and second regions have a tapered shape at their ends in the waveguide direction, with the width in plan view becoming narrower as it moves away from the center of the active region. An optical device characterized by the following features.

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