Optical devices

Abstract

This optical device comprises a gain region (101) that constitutes a waveguide-type semiconductor laser and a waveguide-type optical modulation region (102) that modulates laser light from the semiconductor laser. The semiconductor laser is a distributed Bragg reflection laser. The gain region (101) is disposed between a first distributed Bragg reflection mirror region (105) and a second distributed Bragg reflection mirror region (106). The optical modulation region (102) is disposed between the gain region (101) and the first distributed Bragg reflection mirror region (105). The optical modulation region (102) is provided with an optical modulation layer (103) that is disposed in a range in which coupling with transmitted light is possible and is made from a material having an electro-optic effect.

Description

Technical Field

[0001] The present invention relates to an optical device that modulates the frequency of a transmitted laser beam.

Background Art

[0002] To support the continuously increasing information communication traffic, the high-speed and large-capacity of optical communication devices and the long-distance transmission distance have made remarkable progress. Among optical communication devices, an optical transmitter is a key device that supports optical communication. Among them, a directly modulated laser (DML) and an electro-absorption modulator integrated DFB laser (EA-DFB) are widely used in an intensity modulation-direct detection (IMDD) transmission system with a simpler system configuration. However, since DML and EA-DFB generate frequency chirps in principle, there has been a major problem that the transmission distance is limited especially in recent years when a transmission capacity of 100 Gbit / s / λ or higher is realized.

[0003] In response to the above-described problems, a frequency-modulated laser has been proposed as a device that solves the problem of frequency chirp and has an excellent manufacturability by having a device structure similar to DML and EA-DFB (Non-Patent Document 1). The structure of this frequency-modulated laser is shown in FIG. 13. This frequency-modulated laser is a distributed Bragg reflector (DBR) laser, and includes a gain region 702 and a phase shift region 703 of the effective refractive index of the propagating optical mode in a resonance region between two distributed Bragg reflector regions 701a and 701b. By modulating the effective refractive index of the phase shift region 703, the longitudinal mode oscillation wavelength of the DBR laser, that is, the oscillation frequency is modulated.

[0004] In the frequency-modulated laser described above, the frequency-modulated signal light can be subjected to frequency modulation-intensity modulation (FM-AM) conversion by passing through a simple optical filter thereafter, and is also applicable to an IMDD system.

[0005] Furthermore, Non-Patent Document 2 shows that this frequency-modulated laser can operate at high speeds, unlike DMLs, which are largely limited in their operation at low frequencies by the relaxation oscillation frequency. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] S. Matsuo et al., "Extended Transmission Reach Using Optical Filtering of Frequency-Modulated Widely Tunable SSG-DBR Laser", IEEE Photonics Technology Letters, vol. 20, no. 4, pp. 294-296, 2008. [Non-Patent Document 2] T. Kakitsuka and S. MATSUO, "High-Speed ​​Frequency Modulated DBR Lasers for Long-Reach Transmission", IEICE Transactions on Electronics, vol. E92.C, no. 7, p. 929, 2009. [Non-Patent Document 3] S. Matsuo and T. Kakitsuka, "Low-operating-energy directly modulated lasers for shortdistance optical interconnects", Advances in Optics and Photonics, vol. 10, no. 3, pp. 567-643, 2018. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the above-mentioned technology had the following problem: In conventional technology, even if the band gap was controlled to prevent intensity modulation due to the quantum confinement Stark effect or the Franz-Keldysh effect when a modulated electric field was applied to the phase shift region, intensity modulation would still occur for some reason (for example, carriers flowing into and out of the phase shift region), resulting in a decrease in operating speed.

[0008] This invention was made to solve the above-mentioned problems, and aims to modulate frequency while suppressing intensity modulation. [Means for solving the problem]

[0009] The optical device according to the present invention comprises a gain region constituting a waveguide-type semiconductor laser and a waveguide-type optical modulation region for modulating the laser light of the semiconductor laser. The optical modulation region comprises an optical modulation layer made of a material having an electro-optic effect and arranged in a range that can be coupled to the propagating light. By applying a modulation electric field to the optical modulation layer, the effective refractive index of the propagating light mode is modulated, thereby modulating the frequency of the laser light oscillated by the semiconductor laser. [Effects of the Invention]

[0010] As described above, according to the present invention, since the optical modulation region is made of a material having an electro-optic effect, it is possible to modulate the frequency while suppressing intensity modulation. [Brief explanation of the drawing]

[0011] [Figure 1A] Figure 1A is a plan view showing the configuration of an optical device according to Embodiment 1 of the present invention. [Figure 1B] Figure 1B is a cross-sectional view showing a partial configuration of an optical device according to Embodiment 1 of the present invention. [Figure 1C] Figure 1C is a cross-sectional view showing a partial configuration of an optical device according to Embodiment 1 of the present invention. [Figure 1D]FIG. 1D is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 1 of the present invention. [Figure 2A] FIG. 2A is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 1 of the present invention. [Figure 2B] FIG. 2B is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 1 of the present invention. [Figure 2C] FIG. 2C is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 1 of the present invention. [Figure 3A] FIG. 3A is a plan view showing the configuration of the optical device according to Embodiment 2 of the present invention. [Figure 3B] FIG. 3B is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 2 of the present invention. [Figure 3C] FIG. 3C is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 2 of the present invention. [Figure 3D] FIG. 3D is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 2 of the present invention. [Figure 4A] FIG. 4A is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 2 of the present invention. [Figure 4B] FIG. 4B is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 2 of the present invention. [Figure 4C] FIG. 4C is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 2 of the present invention. [Figure 5A] FIG. 5A is a plan view showing the configuration of the optical device according to Embodiment 3 of the present invention. [Figure 5B] FIG. 5B is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 3 of the present invention. [Figure 5C] FIG. 5C is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 3 of the present invention. [Figure 5D] FIG. 5D is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 3 of the present invention. [Figure 6A] FIG. 6A is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 3 of the present invention. [Figure 6B] FIG. 6B is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 3 of the present invention. [Figure 6C] FIG. 6C is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 3 of the present invention. [Figure 7A] FIG. 7A is a plan view showing the configuration of the optical device according to Embodiment 4 of the present invention. [Figure 7B] FIG. 7B is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 4 of the present invention. [Figure 7C] FIG. 7C is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 4 of the present invention. [Figure 7D] FIG. 7D is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 4 of the present invention. [Figure 8A] FIG. 8A is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 4 of the present invention. [Figure 8B] FIG. 8B is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 4 of the present invention. [Figure 8C] FIG. 8C is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 4 of the present invention. [Figure 9A] FIG. 9A is a plan view showing the configuration of the optical device according to Embodiment 5 of the present invention. [Figure 9B] FIG. 9B is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 5 of the present invention. [Figure 9C] FIG. 9C is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 5 of the present invention. [Figure 9D] FIG. 9D is a cross-sectional view showing a partial configuration of the optical device according to Embodiment 5 of the present invention. [Figure 10A] FIG. 10A is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of the optical device according to Embodiment 5 of the present invention. [Figure 10B] Figure 10B is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of an optical device according to Embodiment 5 of the present invention. [Figure 10C] Figure 10C is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of an optical device according to Embodiment 5 of the present invention. [Figure 11A] Figure 11A is a plan view showing the configuration of an optical device according to Embodiment 6 of the present invention. [Figure 11B] Figure 11B is a cross-sectional view showing a partial configuration of an optical device according to Embodiment 6 of the present invention. [Figure 11C] Figure 11C is a cross-sectional view showing a partial configuration of an optical device according to Embodiment 6 of the present invention. [Figure 12A] Figure 12A is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of an optical device according to Embodiment 6 of the present invention. [Figure 12B] Figure 12B is a distribution diagram showing the electromagnetic field distribution of the optical propagation mode of an optical device according to Embodiment 6 of the present invention. [Figure 13] Figure 13 is a cross-sectional view showing the structure of a frequency-modulated laser. [Modes for carrying out the invention]

[0012] The following describes an optical device according to an embodiment of the present invention.

[0013] [Embodiment 1] First, the configuration of the optical device according to Embodiment 1 of the present invention will be described with reference to Figures 1A, 1B, 1C, and 1D. Figure 1B shows a cross-section perpendicular to the waveguide direction along the line aa' in Figure 1A. Figure 1C shows a cross-section perpendicular to the waveguide direction along the line bb' in Figure 1A. Figure 1D shows a cross-section perpendicular to the waveguide direction along the line cc' in Figure 1A. This optical device comprises a gain region 101 that constitutes a waveguide-type semiconductor laser and a waveguide-type optical modulation region 102 that modulates the laser light of the semiconductor laser.

[0014] In Embodiment 1, the semiconductor laser is a distributed Bragg reflector laser, and the gain region 101 is located between the first distributed Bragg reflector region 105 and the second distributed Bragg reflector region 106. The optical modulation region 102 is located between the gain region 101 and the first distributed Bragg reflector region 105. The laser oscillates (outputs) in the direction of the arrow shown in Figure 1A.

[0015] The gain region 101 comprises a p-type semiconductor layer 112a, an i-type semiconductor layer 112, and an n-type semiconductor layer 112b, with an active layer 111 embedded in the i-type semiconductor layer 112. The p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b can be composed of, for example, a III-V compound semiconductor such as InP. The p-type semiconductor layer 112a and the n-type semiconductor layer 112b can be formed by introducing predetermined impurities into the semiconductor layers. The semiconductor layers on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed can be formed on the optical modulation layer 103 via a junction layer 107 composed of, for example, SiO2.

[0016] Furthermore, the active layer 111 can be made of InGaAlAs. Also, the active layer 111 can have a multiple quantum well structure. Using p electrodes 113a and n electrodes 113b, a current is injected through p-type semiconductor layer 112a and n-type semiconductor layer 112b in a direction (lateral direction) that intersects (perpendicular to) the waveguide direction with respect to the i-type semiconductor layer 112 (Reference 1).

[0017] The optical modulation region 102 comprises an optical modulation layer 103 made of a material having an electro-optic effect and arranged in a range that can be coupled to the propagating light. By applying a modulation electric field to the optical modulation layer 103 using electrodes 121a and 121b, the effective refractive index of the propagating light mode is modulated, thereby modulating the frequency of the laser light oscillated by the semiconductor laser. The optical modulation region 102 can be made of, for example, lithium niobate (LN).

[0018] Furthermore, the optical modulation region 102 includes a core 104 formed on the optical modulation layer 103 via a junction layer 107. The core 104 is formed continuously with the i-type semiconductor layer 112 (active layer 111) of the gain region 101. Electrodes 121a and 121b are arranged flanking the core 104. The core 104 can be made of, for example, a III-V compound semiconductor such as InP.

[0019] The first distributed Bragg mirror region 105 and the second distributed Bragg mirror region 106 each include a core 104 formed on the optical modulation layer 103 via a bonding layer 107. The core 104 is continuously formed from the optical modulation region 102 to the first distributed Bragg mirror region 105. The core width is smaller in the optical modulation region 102. In the first distributed Bragg mirror region 105, a diffraction grating 151 is formed on the core 104. Similarly, in the second distributed Bragg mirror region 106, a diffraction grating 161 is formed on the core 104. The diffraction gratings 151 and 161 can also be formed on the sides of the core 104.

[0020] In Embodiment 1, the optical modulation layer 103 and the junction layer 107 are formed in common across the entire areas of the gain region 101, the optical modulation region 102, the first distributed Bragg mirror region 105, and the second distributed Bragg mirror region 106, and the optical modulation layer 103 also functions as a lower cladding layer. Furthermore, an upper cladding layer 108 made of, for example, SiO2 is formed across the entire areas of the gain region 101, the optical modulation region 102, the first distributed Bragg mirror region 105, and the second distributed Bragg mirror region 106. The length of the gain region 101 in the waveguide direction can be 80 μm, and the length of the optical modulation region 102 in the waveguide direction can be 40 μm. Furthermore, the length of the first distributed Bragg mirror region 105 and the second distributed Bragg mirror region 106 in the waveguide direction can be 80 μm.

[0021] Next, the optical propagation modes in the optical device according to Embodiment 1 will be described with reference to Figures 2A, 2B, and 2C.

[0022] First, Figure 2A shows the light propagation modes in the first distributed Bragg mirror region 105 (second distributed Bragg mirror region 106). In the first distributed Bragg mirror region 105, the core 104 has a width of 600 nm and a height of 350 nm, and the junction layer 107 has a thickness of 20 nm. As shown in Figure 2A, the light is almost entirely confined to the core 104.

[0023] Next, Figure 2B shows the optical propagation modes in the optical modulation region 102. The core 104 in the optical modulation region 102 has a width of 350 nm and a height of 350 nm, and the junction layer 107 has a thickness of 20 nm. As shown in Figure 2B, some of the light confined within the core 104 leaks out into the optical modulation layer 103.

[0024] In the optical modulation region 102, it is important to appropriately adjust the cross-sectional size of the core 104 so that the electromagnetic field distribution of the propagating light mode leaks into the optical modulation layer 103. When a modulation electric field is applied from electrodes 121a and 121b positioned on the left and right sides of the core 104, the refractive index in the optical modulation layer 103 is modulated mainly by the electro-optic effect. This modulates the effective refractive index of the propagating light mode in the optical modulation region 102. The cross-sectional size of the core 104, the thickness of the junction layer 107, and the relative positions of electrodes 121a and 121b with respect to the core 104 are appropriately adjusted so that the largest possible change in the effective refractive index is obtained with respect to the applied voltage.

[0025] Next, Figure 2C shows the optical propagation modes of the gain region 101. The thickness of the semiconductor layers on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed is 350 nm, and the width of the active layer 111 is 800 nm. m and The active layer 111 had a thickness of 250 nm. The junction layer 107 had a thickness of 20 nm. As shown in Figure 2C, light is strongly confined within the active layer 111.

[0026] As described above, since the optical modulation region 102 (optical modulation layer 103) is made of a material having an electro-optic effect, it becomes possible to modulate the frequency while suppressing intensity modulation. Regarding the size of the core 104, considering productivity, it is desirable to make the core height (thickness) equal to the thickness of the i-type semiconductor layer 112 of the gain region 101, as described above. Within this range of conditions, it is desirable to appropriately adjust the core width in each region so that the desired optical confinement within the core 104 is obtained, and to connect each region with a tapered structure that gradually changes the width so as not to cause optical emission loss or reflection.

[0027] Furthermore, a compact optical transmitter can be realized by integrating an optical filter for frequency modulation-intensity modulation conversion (FM-AM conversion) beyond the second distributed Bragg reflector region 106. The optical filter described above can be composed of a Mach-Zehnder interferometer (MZI) or a ring resonator using an optical waveguide with an InP core. It is also desirable to appropriately add a wavelength tuning structure, such as a heater, to the optical filter described above. In addition, in order to reduce connection loss to the optical fiber to which the optical device according to the embodiment is connected, a spot size converter, for example, can be integrated beyond the second distributed Bragg reflector region 106.

[0028] [Embodiment 2] Next, the configuration of the optical device according to Embodiment 2 of the present invention will be described with reference to Figures 3A, 3B, 3C, and 3D. Figure 3B shows a cross-section perpendicular to the waveguide direction along the line aa' in Figure 3A. Figure 3C shows a cross-section perpendicular to the waveguide direction along the line bb' in Figure 3A. Figure 3D shows a cross-section perpendicular to the waveguide direction along the line cc' in Figure 3A. This optical device comprises a gain region 101 that constitutes a waveguide-type semiconductor laser and a waveguide-type optical modulation region 102 that modulates the laser light of the semiconductor laser.

[0029] In Embodiment 2 ,halfThe conducting laser is a distributed Bragg reflecting laser, and the gain region 101 is located between the first distributed Bragg reflector region 105 and the second distributed Bragg reflector region 106. The optical modulation region 102 is located between the gain region 101 and the first distributed Bragg reflector region 105.

[0030] The gain region 101 comprises a p-type semiconductor layer 112a, an i-type semiconductor layer 112, and an n-type semiconductor layer 112b, with an active layer 111 embedded in the i-type semiconductor layer 112. The p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b can be composed of, for example, a III-V compound semiconductor such as InP. The p-type semiconductor layer 112a and the n-type semiconductor layer 112b can be formed by introducing predetermined impurities into the semiconductor layers. The semiconductor layers on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed can be formed on the optical modulation layer 103' via a junction layer 107 composed of, for example, SiO2.

[0031] Furthermore, the active layer 111 can be made of InGaAlAs. Also, the active layer 111 can have a multiple quantum well structure. Using p electrodes 113a and n electrodes 113b, a current is injected through p-type semiconductor layer 112a and n-type semiconductor layer 112b in a direction (lateral direction) that intersects (perpendicular to) the waveguide direction with respect to the i-type semiconductor layer 112 (Reference 1).

[0032] The optical modulation region 102 comprises an optical modulation layer 103' made of a material having an electro-optic effect and positioned within a range that can be coupled to the propagating light. By applying a modulation electric field to the optical modulation layer 103' using electrodes 121a and 121b, the effective refractive index of the propagating light mode is modulated, thereby modulating the frequency of the laser light oscillated by the semiconductor laser. The optical modulation region 102 can be made of, for example, lithium niobate.

[0033] Furthermore, the optical modulation region 102 includes a core 104 formed on the optical modulation layer 103' via a junction layer 107. The core 104 is formed continuously with the i-type semiconductor layer 112 (active layer 111) of the gain region 101. Electrodes 121a and 121b are arranged flanking the core 104. The core 104 can be made of, for example, a III-V compound semiconductor such as InP.

[0034] The first distributed Bragg mirror region 105 and the second distributed Bragg mirror region 106 each have a core 104 formed on the optical modulation layer 103' via a bonding layer 107. The core 104 is continuously formed from the optical modulation region 102 to the first distributed Bragg mirror region 105. The core width is smaller in the optical modulation region 102. In the first distributed Bragg mirror region 105, a diffraction grating 151 is formed on the core 104. Similarly, in the second distributed Bragg mirror region 106, a diffraction grating 161 is formed on the core 104. The diffraction gratings 151 and 161 can also be formed on the sides of the core 104.

[0035] In Embodiment 2, the optical modulation layer 103' and the junction layer 107 are commonly formed over the entire areas of the gain region 101, the optical modulation region 102, the first distributed Bragg mirror region 105, and the second distributed Bragg mirror region 106. Furthermore, an upper cladding layer 108 made of, for example, SiO2 is formed over the entire areas of the gain region 101, the optical modulation region 102, the first distributed Bragg mirror region 105, and the second distributed Bragg mirror region 106. The length of the gain region 101 in the waveguide direction can be 80 μm, and the length of the optical modulation region 102 in the waveguide direction can be 40 μm. The length of the first distributed Bragg mirror region 105 and the second distributed Bragg mirror region 106 in the waveguide direction can also be 80 μm.

[0036] The configuration described above is the same as that of Embodiment 1 described above. In Embodiment 2, the optical modulation layer 103' is formed on the lower cladding layer 109 made of SiO2. Furthermore, the optical modulation layer 103' is rib-shaped, having a rib core 103a that is convex on the side where the active layer 111 of the semiconductor laser is formed, when viewed in a cross-sectional view perpendicular to the propagation direction of the propagating light. The slab portion of the optical modulation layer 103' is 100 nm thick, and the rib core 103a can be 1000 nm wide and 200 nm high (thick). The rib-shaped optical modulation layer 103' is formed over the entire area of ​​the gain region 101, the optical modulation region 102, the first distributed Bragg mirror region 105, and the second distributed Bragg mirror region 106.

[0037] Next, the optical propagation modes in the optical device according to Embodiment 2 will be described with reference to Figures 4A, 4B, and 4C.

[0038] First, Figure 4A shows the light propagation modes in the first distributed Bragg mirror region 105 (second distributed Bragg mirror region 106). In the first distributed Bragg mirror region 105, the core 104 had a width of 600 nm and a height of 350 nm, and the junction layer 107 had a thickness of 500 nm. The rib core 103a had a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' was 100 nm. As shown in Figure 4A, the light is almost entirely confined to the core 104.

[0039] Next, Figure 4B shows the optical propagation modes in the optical modulation region 102. The core 104 in the optical modulation region 102 has a width of 250 nm and a height of 350 nm, and the junction layer 107 has a thickness of 500 nm. The rib core 103a has a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' is 100 nm. As shown in Figure 4B, some of the light is confined within the core 104, but the majority has an intensity distribution in the rib core 103a of the optical modulation layer 103'.

[0040] In the optical modulation region 102, it is important to appropriately adjust the cross-sectional size of the core 104 so that the electromagnetic field distribution of the propagating light mode leaks into the rib core 103a. When a modulating electric field is applied from electrodes 121a and 121b positioned on the left and right sides of the core 104 (rib core 103a), the refractive index in the rib core 103a is modulated mainly by the electro-optic effect. This modulates the effective refractive index of the propagating light mode in the optical modulation region 102. The cross-sectional size of the core 104, the thickness of the junction layer 107, and the relative positions of electrodes 121a and 121b with respect to the core 104 are appropriately adjusted so that the largest possible change in the effective refractive index is obtained with respect to the applied voltage.

[0041] Next, Figure 4C shows the optical propagation modes in the gain region 101. The thickness of the semiconductor layers on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed is 350 nm, and the width of the active layer 111 is 800 nm. m and The active layer 111 had a thickness of 250 nm. The junction layer 107 had a thickness of 500 nm. As shown in Figure 4C, the light is strongly confined within the active layer 111.

[0042] As described above, since the optical modulation region 102 (optical modulation layer 103') is made of a material having an electro-optic effect, it becomes possible to modulate the frequency while suppressing intensity modulation. Regarding the size of the core 104, considering productivity, it is desirable to make the core height (thickness) equal to the thickness of the i-type semiconductor layer 112 of the gain region 101, as described above. Within this range of conditions, it is desirable to appropriately adjust the core width in each region so that the desired optical confinement within the core 104 is obtained, and to connect each region with a tapered structure that gradually changes the width so as not to cause optical emission loss or reflection.

[0043] Furthermore, a compact optical transmitter can be realized by integrating an optical filter for frequency modulation-intensity modulation conversion (FM-AM conversion) beyond the second distributed Bragg reflector region 106. The optical filter described above can be composed of a Mach-Zehnder interferometer (MZI) or a ring resonator using an optical waveguide with an InP core. It is also desirable to appropriately add a wavelength tuning structure, such as a heater, to the optical filter described above. In addition, in order to reduce connection loss to the optical fiber to which the optical device according to the embodiment is connected, a spot size converter, for example, can be integrated beyond the second distributed Bragg reflector region 106.

[0044] [Embodiment 3] Next, the configuration of the optical device according to Embodiment 3 of the present invention will be described with reference to Figures 5A, 5B, 5C, and 5D. Figure 5B shows a cross-section perpendicular to the waveguide direction along the line aa' in Figure 5A. Figure 5C shows a cross-section perpendicular to the waveguide direction along the line bb' in Figure 5A. Figure 5D shows a cross-section perpendicular to the waveguide direction along the line cc' in Figure 5A. This optical device comprises a gain region 101 that constitutes a waveguide-type semiconductor laser and a waveguide-type optical modulation region 102 that modulates the laser light of the semiconductor laser.

[0045] In Embodiment 3, the semiconductor laser is a distributed Bragg reflector laser, and the gain region 101 is located between the first distributed Bragg reflector region 105 and the second distributed Bragg reflector region 106. The optical modulation region 102 is located between the gain region 101 and the first distributed Bragg reflector region 105.

[0046] The gain region 101 comprises a p-type semiconductor layer 112a, an i-type semiconductor layer 112, and an n-type semiconductor layer 112b, with an active layer 111 embedded in the i-type semiconductor layer 112. The p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b can be composed of, for example, a III-V compound semiconductor such as InP. The p-type semiconductor layer 112a and the n-type semiconductor layer 112b can be formed by introducing predetermined impurities into the semiconductor layers. The semiconductor layers on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed can be formed on the optical modulation layer 103' via a junction layer 107 composed of, for example, SiO2.

[0047] Furthermore, the active layer 111 can be made of InGaAlAs. Also, the active layer 111 can have a multiple quantum well structure. Using p electrodes 113a and n electrodes 113b, a current is injected through p-type semiconductor layer 112a and n-type semiconductor layer 112b in a direction (lateral direction) that intersects (perpendicular to) the waveguide direction with respect to the i-type semiconductor layer 112 (Reference 1).

[0048] The optical modulation region 102 comprises an optical modulation layer 103' made of a material having an electro-optic effect and positioned within a range that can be coupled to the propagating light. By applying a modulation electric field to the optical modulation layer 103' using electrodes 121a and 121b, the effective refractive index of the propagating light mode is modulated, thereby modulating the frequency of the laser light oscillated by the semiconductor laser. The optical modulation region 102 can be made of, for example, lithium niobate.

[0049] On the other hand, in Embodiment 3, the core 104 is not formed on the optical modulation layer 103' in the optical modulation region 102. The core 104 is formed in the first distributed Bragg mirror region 105 and the second distributed Bragg mirror region 106, as will be described later. The core 104 can be made of, for example, a III-V compound semiconductor such as InP.

[0050] The first distributed Bragg mirror region 105 and the second distributed Bragg mirror region 106 each include a core 104 formed on the optical modulation layer 103' via a bonding layer 107. The core width gradually decreases toward the optical modulation region 102. In the first distributed Bragg mirror region 105, a diffraction grating 151 is formed on the core 104. Similarly, in the second distributed Bragg mirror region 106, a diffraction grating 161 is formed on the core 104. The diffraction gratings 151 and 161 can also be formed on the sides of the core 104.

[0051] In Embodiment 3, the optical modulation layer 103' and the junction layer 107 are commonly formed over the entire areas of the gain region 101, the optical modulation region 102, the first distributed Bragg mirror region 105, and the second distributed Bragg mirror region 106. Furthermore, an upper cladding layer 108 made of, for example, SiO2 is formed over the entire areas of the gain region 101, the optical modulation region 102, the first distributed Bragg mirror region 105, and the second distributed Bragg mirror region 106. The length of the gain region 101 in the waveguide direction can be 80 μm, and the length of the optical modulation region 102 in the waveguide direction can be 40 μm. The length of the first distributed Bragg mirror region 105 and the second distributed Bragg mirror region 106 in the waveguide direction can also be 80 μm.

[0052] Furthermore, similar to the second embodiment described above, the optical modulation layer 103' is formed on the lower cladding layer 109 made of SiO2. In addition, the optical modulation layer 103' is rib-shaped, with a rib core 103a that is convex on the side where the active layer 111 of the semiconductor laser is formed, when viewed in a cross-sectional view perpendicular to the propagation direction of the propagating light. The slab portion of the optical modulation layer 103' is 100 nm thick, and the rib core 103a can be 1000 nm wide and 200 nm high (thick). The rib-shaped optical modulation layer 103' is formed over the entire area of ​​the gain region 101, the optical modulation region 102, the first distributed Bragg mirror region 105, and the second distributed Bragg mirror region 106.

[0053] Next, the optical propagation modes in the optical device according to Embodiment 3 will be described with reference to Figures 6A, 6B, and 6C.

[0054] First, Figure 6A shows the light propagation modes in the first distributed Bragg mirror region 105 (second distributed Bragg mirror region 106). In the first distributed Bragg mirror region 105, the core 104 had a width of 600 nm and a height of 350 nm, and the junction layer 107 had a thickness of 500 nm. The rib core 103a had a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' was 100 nm. As shown in Figure 6A, the light is almost entirely confined to the core 104.

[0055] Next, Figure 6B shows the optical propagation mode in the optical modulation region 102 where the core 104 is not formed. The rib core 103a in the optical modulation region 102 has a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' is 100 nm. As shown in Figure 6B, the light is confined to the rib core 103a of the optical modulation layer 103', and almost all of it has an intensity distribution in the rib core 103a of the optical modulation layer 103'.

[0056] In the optical modulation region 102, it is important that the electromagnetic field distribution of the propagating light mode exists in the rib core 103a. When a modulating electric field is applied from electrodes 121a and 121b positioned on the left and right sides of the rib core 103a, the refractive index in the rib core 103a is modulated mainly by the electro-optic effect. As a result, the effective refractive index of the propagating light mode in the optical modulation region 102 is modulated.

[0057] Next, Figure 6C shows the optical propagation modes of the gain region 101. The thickness of the semiconductor layers on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed is 350 nm, and the width of the active layer 111 is 800 nm. m and The active layer 111 had a thickness of 250 nm. The junction layer 107 had a thickness of 500 nm. As shown in Figure 6C, the light is strongly confined within the active layer 111.

[0058] As described above, since the optical modulation region 102 (optical modulation layer 103') is made of a material having an electro-optic effect, it becomes possible to modulate the frequency while suppressing intensity modulation. Furthermore, by not providing a core 104 in the optical modulation region 102, further light confinement in the rib core 103a becomes possible.

[0059] Furthermore, a compact optical transmitter can be realized by integrating an optical filter for frequency modulation-intensity modulation conversion (FM-AM conversion) beyond the second distributed Bragg reflector region 106. The optical filter described above can be composed of a Mach-Zehnder interferometer (MZI) or a ring resonator using an optical waveguide with an InP core. It is also desirable to appropriately add a wavelength tuning structure, such as a heater, to the optical filter described above. In addition, in order to reduce connection loss to the optical fiber to which the optical device according to the embodiment is connected, a spot size converter, for example, can be integrated beyond the second distributed Bragg reflector region 106.

[0060] [Embodiment 4] Next, the configuration of the optical device according to Embodiment 4 of the present invention will be described with reference to Figures 7A, 7B, 7C, and 7D. Figure 7B shows a cross-section perpendicular to the waveguide direction along the line aa' in Figure 7A. Figure 7C shows a cross-section perpendicular to the waveguide direction along the line bb' in Figure 7A. Figure 7D shows a cross-section perpendicular to the waveguide direction along the line cc' in Figure 7A. This optical device comprises a gain region 101 that constitutes a waveguide-type semiconductor laser and a waveguide-type optical modulation region 102a that modulates the laser light of the semiconductor laser.

[0061] In Embodiment 4, the semiconductor laser is a distributed feedback (DFB) laser and is equipped with a diffraction grating 114 in the gain region 101.

[0062] The gain region 101 comprises a p-type semiconductor layer 112a, an i-type semiconductor layer 112, and an n-type semiconductor layer 112b, with an active layer 111 embedded in the i-type semiconductor layer 112. A diffraction grating 114 can be formed on the active layer 111 in the i-type semiconductor layer 112. The p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b can be composed of, for example, a III-V compound semiconductor such as InP. The p-type semiconductor layer 112a and n-type semiconductor layer 112b can be formed by introducing predetermined impurities into the semiconductor layer. The semiconductor layer on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed can be formed on the optical modulation layer 103' via a junction layer 107 composed of, for example, SiO2.

[0063] Furthermore, the active layer 111 can be made of InGaAlAs. Also, the active layer 111 can have a multiple quantum well structure. Using p electrodes 113a and n electrodes 113b, a current is injected through p-type semiconductor layer 112a and n-type semiconductor layer 112b in a direction (lateral direction) that intersects (perpendicular to) the waveguide direction with respect to the i-type semiconductor layer 112 (Reference 1).

[0064] The optical modulation region 102a comprises an optical modulation layer 103' made of a material having an electro-optic effect and positioned within a range that can be coupled to the propagating light. By applying a modulation electric field to the optical modulation layer 103' using electrodes 121a and 121b, the effective refractive index of the propagating light mode is modulated, thereby modulating the frequency of the laser light oscillated by the semiconductor laser. The optical modulation region 102a can be made of, for example, lithium niobate.

[0065] Furthermore, in Embodiment 4, in the optical modulation region 102a, a diffraction grating 151' is provided on the core 104 formed on the optical modulation layer 103' via a junction layer 107, and the optical modulation region 102a is provided with a distributed Bragg reflection structure. The diffraction grating 151' can be formed on the upper or side surface of the core 104. In Embodiment 4, the optical modulation region 102a also constitutes the distributed Bragg reflector region. The core 104 is formed continuously with the i-type semiconductor layer 112 (active layer 111) of the gain region 101. Electrodes 121a and 121b are arranged flanking the core 104. The core 104 can be made of, for example, a III-V compound semiconductor such as InP.

[0066] In Embodiment 4, the diffraction grating 114 in the gain region 101 is designed to have an appropriate amount of detuning between it and the optical modulation region 102a, which also constitutes the distributed Bragg mirror region.

[0067] Furthermore, in Embodiment 4, an output optical waveguide 106' is formed downstream of the gain region 101. The output optical waveguide 106' includes a core 104 formed on the optical modulation layer 103' via a junction layer 107. The core 104 is formed continuously with the i-type semiconductor layer 112 (active layer 111) of the gain region 101.

[0068] In Embodiment 4, the optical modulation layer 103' and the junction layer 107 are commonly formed throughout the gain region 101, the optical modulation region 102a, and the output optical waveguide 106'. Furthermore, an upper cladding layer 108, for example, made of SiO2, is formed throughout the gain region 101, the optical modulation region 102a, and the output optical waveguide 106'. The gain region 101 can have a length of 80 μm in the waveguide direction, and the optical modulation region 102a can have a length of 40 μm in the waveguide direction. The output optical waveguide 106' can also have a length of 80 μm in the waveguide direction.

[0069] Furthermore, similar to the second embodiment described above, the optical modulation layer 103' is formed on the lower cladding layer 109 made of SiO2. In addition, the optical modulation layer 103' is rib-shaped, with a rib core 103a that is convex on the side where the active layer 111 of the semiconductor laser is formed, when viewed in a cross-sectional view perpendicular to the propagation direction of the propagating light. The slab portion of the optical modulation layer 103' is 100 nm thick, and the rib core 103a can be 1000 nm wide and 200 nm high (thick). The rib-shaped optical modulation layer 103' is formed over the entire area of ​​the gain region 101, the optical modulation region 102a, and the output optical waveguide 106'.

[0070] Next, the optical propagation modes in the optical device according to Embodiment 4 will be described with reference to Figures 8A, 8B, and 8C.

[0071] First, Figure 8A shows the optical propagation mode in the optical modulation region 102a. The core 104 in the optical modulation region 102 has a width of 250 nm and a height of 350 nm, and the junction layer 107 has a thickness of 500 nm. The rib core 103a has a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' is 100 nm. As shown in Figure 8A, almost all of the light is confined to the rib core 103a of the optical modulation layer 103'.

[0072] In the optical modulation region 102a, it is important to appropriately adjust the cross-sectional size of the core 104 so that the electromagnetic field distribution of the propagating light mode leaks into the optical modulation layer 103 (rib core 103a) and the electromagnetic field distribution of the propagating light mode exists in the rib core 103a. When a modulation electric field is applied from electrodes 121a and 121b positioned on the left and right sides of the core 104 (rib core 103a), the refractive index in the rib core 103a is modulated mainly by the electro-optic effect. As a result, the effective refractive index of the propagating light mode in the optical modulation region 102a is modulated.

[0073] Next, Figure 8B shows the optical propagation modes of the gain region 101. The thickness of the semiconductor layers on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed is 350 nm, and the width of the active layer 111 is 800 nm. m andThe active layer 111 had a thickness of 100 nm. The junction layer 107 had a thickness of 500 nm. As shown in Figure 8B, the light is strongly confined within the active layer 111.

[0074] Next, Figure 8C shows the optical propagation modes of the output optical waveguide 106'. In the output optical waveguide 106', the core 104 has a width of 550 nm and a height of 350 nm, and the junction layer 107 has a thickness of 500 nm. The rib core 103a has a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' is 100 nm. As shown in Figure 8C, the light is almost entirely confined to the core 104.

[0075] As described above, since the optical modulation region 102a (optical modulation layer 103') is made of a material having an electro-optic effect, it becomes possible to modulate the frequency while suppressing intensity modulation.

[0076] Regarding the size of the core 104, considering productivity, it is desirable to make the core height (thickness) equal to the thickness of the i-type semiconductor layer 112 of the gain region 101, as described above. Within this range, it is desirable to appropriately adjust the core width in each region so that the desired optical confinement within the core 104 is obtained, and to connect each region with a tapered structure that gradually changes the width so as not to cause optical emission loss or reflection.

[0077] Furthermore, a compact optical transmitter can be realized by integrating an optical filter for frequency modulation-intensity modulation conversion (FM-AM conversion) at the end of the output optical waveguide 106'. The optical filter described above can be composed of a Mach-Zehnder interferometer (MZI) or a ring resonator using an optical waveguide with an InP core. It is also desirable to appropriately add a wavelength tuning structure such as a heater to the optical filter described above. In addition, in order to reduce connection loss to the optical fiber to which the optical device according to the embodiment is connected, a spot size converter, for example, can be integrated at the end of the output optical waveguide 106'.

[0078] [Embodiment 5] Next, the configuration of the optical device according to Embodiment 5 of the present invention will be described with reference to Figures 9A, 9B, 9C, and 9D. Figure 9B shows a cross-section perpendicular to the waveguide direction along the line aa' in Figure 9A. Figure 9C shows a cross-section perpendicular to the waveguide direction along the line bb' in Figure 9A. Figure 9D shows a cross-section perpendicular to the waveguide direction along the line cc' in Figure 9A. This optical device comprises a gain region 101 that constitutes a waveguide-type semiconductor laser and a waveguide-type optical modulation region 102 that modulates the laser light of the semiconductor laser.

[0079] In Embodiment 5, the semiconductor laser is a distributed feedback (DFB) laser and includes a diffraction grating 114 in the gain region 101. Furthermore, in addition to the gain region 101, it also includes a gain region 101' (having two gain regions).

[0080] The gain region 101 comprises a p-type semiconductor layer 112a, an i-type semiconductor layer 112, and an n-type semiconductor layer 112b, with an active layer 111 embedded in the i-type semiconductor layer 112. A diffraction grating 114 can be formed on the active layer 111 in the i-type semiconductor layer 112. The p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b can be composed of, for example, a III-V compound semiconductor such as InP. The p-type semiconductor layer 112a and n-type semiconductor layer 112b can be formed by introducing predetermined impurities into the semiconductor layer. The semiconductor layer on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed can be formed on the optical modulation layer 103' via a junction layer 107 composed of, for example, SiO2.

[0081] Furthermore, the active layer 111 can be made of InGaAlAs. Also, the active layer 111 can have a multiple quantum well structure. Using p electrodes 113a and n electrodes 113b, a current is injected through p-type semiconductor layer 112a and n-type semiconductor layer 112b in a direction (lateral direction) that intersects (perpendicular to) the waveguide direction with respect to the i-type semiconductor layer 112 (Reference 1).

[0082] Gain region 101' has the same configuration as gain region 101 described above. Each diffraction grating can be designed to have an appropriate amount of detuning between the two gain regions 101 and gain region 101'.

[0083] The optical modulation region 102 comprises an optical modulation layer 103' made of a material having an electro-optic effect and positioned within a range that can be coupled to the propagating light. By applying a modulation electric field to the optical modulation layer 103' using electrodes 121a and 121b, the effective refractive index of the propagating light mode is modulated, thereby modulating the frequency of the laser light oscillated by the semiconductor laser. The optical modulation region 102 can be made of, for example, lithium niobate. In Embodiment 5, the optical modulation region 102 is positioned between two gain regions 101 and gain region 101'.

[0084] Furthermore, the optical modulation region 102 includes a core 104 formed on the optical modulation layer 103' via a junction layer 107. The core 104 is formed continuously with the i-type semiconductor layer 112 (active layer 111) of the gain region 101. Electrodes 121a and 121b are arranged flanking the core 104. The core 104 can be made of, for example, a III-V compound semiconductor such as InP.

[0085] Furthermore, in Embodiment 5, an output optical waveguide 106' is formed downstream of the gain region 101. The output optical waveguide 106' includes a core 104 formed on the optical modulation layer 103' via a junction layer 107. The core 104 is formed continuously with the i-type semiconductor layer 112 (active layer 111) of the gain region 101.

[0086] In Embodiment 5, the optical modulation layer 103' and the junction layer 107 are commonly formed throughout the entire area of ​​the gain region 101, the optical modulation region 102, the gain region 101', and the output optical waveguide 106'. In addition, an upper cladding layer 108 made of, for example, SiO2 is formed throughout the entire area of ​​the gain region 101, the gain region 101', the optical modulation region 102, and the output optical waveguide 106'. Furthermore, the length of the gain region 101 and the gain region 101' in the waveguide direction can be set to 80 μm, and the length of the optical modulation region 102 in the waveguide direction can be set to 40 μm. Furthermore, the length of the output optical waveguide 106' in the waveguide direction can be set to 80 μm.

[0087] Furthermore, similar to Embodiment 2 described above, the optical modulation layer 103' is formed on the lower cladding layer 109 made of SiO2. In addition, the optical modulation layer 103' is rib-shaped, with a rib core 103a that is convex on the side where the active layer 111 of the semiconductor laser is formed, when viewed in a cross-sectional view perpendicular to the propagation direction of the propagating light. The slab portion of the optical modulation layer 103' is 100 nm thick, and the rib core 103a can be 1000 nm wide and 200 nm high (thick). The rib-shaped optical modulation layer 103' is formed over the entire area of ​​the gain region 101, the optical modulation region 102, and the output optical waveguide 106'.

[0088] Next, the optical propagation modes in the optical device according to Embodiment 5 will be described with reference to Figures 10A, 10B, and 10C.

[0089] First, Figure 10A shows the optical propagation modes of the gain region 101. The thickness of the semiconductor layers on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed is 350 nm, and the width of the active layer 111 is 800 nm. m and The active layer 111 had a thickness of 100 nm. The junction layer 107 had a thickness of 500 nm. The rib core 103a had a width of 1000 nm and a height of 200 nm, and the slab thickness of the light modulation layer 103' was 100 nm. As shown in Figure 10A, the light is strongly confined within the active layer 111.

[0090] Next, Figure 10B shows the optical propagation modes in the optical modulation region 102. The core 104 in the optical modulation region 102 has a width of 250 nm and a height of 350 nm, and the junction layer 107 has a thickness of 500 nm. The rib core 103a has a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' is 100 nm. As shown in Figure 10B, almost all of the light is confined to the rib core 103a of the optical modulation layer 103'.

[0091] In the optical modulation region 102, it is important that the electromagnetic field distribution of the propagating light mode exists in the rib core 103a. When a modulating electric field is applied from electrodes 121a and 121b positioned on the left and right sides of the rib core 103a, the refractive index in the rib core 103a is modulated mainly by the electro-optic effect. As a result, the effective refractive index of the propagating light mode in the optical modulation region 102 is modulated.

[0092] Next, Figure 10C shows the optical propagation modes of the output optical waveguide 106'. In the output optical waveguide 106', the core 104 has a width of 550 nm and a height of 350 nm, and the junction layer 107 has a thickness of 500 nm. The rib core 103a has a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' is 100 nm. As shown in Figure 10C, the light is almost entirely confined to the core 104.

[0093] As described above, since the optical modulation region 102 (optical modulation layer 103') is made of a material having an electro-optic effect, it becomes possible to modulate the frequency while suppressing intensity modulation.

[0094] Regarding the size of the core 104, considering productivity, it is desirable to make the core height (thickness) equal to the thickness of the i-type semiconductor layer 112 of the gain region 101, as described above. Within this range, it is desirable to appropriately adjust the core width in each region so that the desired optical confinement within the core 104 is obtained, and to connect each region with a tapered structure that gradually changes the width so as not to cause optical emission loss or reflection.

[0095] Furthermore, a compact optical transmitter can be realized by integrating an optical filter for frequency modulation-intensity modulation conversion (FM-AM conversion) at the end of the output optical waveguide 106'. The optical filter described above can be composed of a Mach-Zehnder interferometer (MZI) or a ring resonator using an optical waveguide with an InP core. It is also desirable to appropriately add a wavelength tuning structure such as a heater to the optical filter described above. In addition, in order to reduce connection loss to the optical fiber to which the optical device according to the embodiment is connected, a spot size converter, for example, can be integrated at the end of the output optical waveguide 106'.

[0096] [Embodiment 6] Next, the configuration of the optical device according to Embodiment 6 of the present invention will be described with reference to Figures 11A, 11B, and 11C. Figure 11B shows a cross-section perpendicular to the waveguide direction along the line aa' in Figure 11A. Figure 11C shows a cross-section perpendicular to the waveguide direction along the line bb' in Figure 11A. This optical device constitutes a waveguide-type semiconductor laser and includes a gain region and optical modulation region 101a that serves as a waveguide-type optical modulation region for modulating the laser light of the semiconductor laser. In this optical device, the optical modulation region is arranged to overlap with the gain region.

[0097] In Embodiment 6, the semiconductor laser is a distributed Bragg reflection laser, and the gain region and optical modulation region 101a is located between the first distributed Bragg reflector region 105 and the second distributed Bragg reflector region 106.

[0098] The gain region and optical modulation region 101a comprises a p-type semiconductor layer 112a, an i-type semiconductor layer 112, and an n-type semiconductor layer 112b, with an active layer 111 embedded in the i-type semiconductor layer 112. The p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b can be composed of, for example, a III-V compound semiconductor such as InP. The p-type semiconductor layer 112a and the n-type semiconductor layer 112b can be formed by introducing predetermined impurities into the semiconductor layers.

[0099] Furthermore, the active layer 111 can be made of InGaAlAs. Also, the active layer 111 can have a multiple quantum well structure. Using p electrodes 113a and n electrodes 113b, a current is injected through p-type semiconductor layer 112a and n-type semiconductor layer 112b in a direction (lateral direction) that intersects (perpendicular to) the waveguide direction with respect to the i-type semiconductor layer 112 (Reference 1).

[0100] Furthermore, the gain region and optical modulation region 101a includes an optical modulation layer 103' made of a material having an electro-optic effect and arranged in a range that can be coupled to the propagating light. In the gain region and optical modulation region 101a, a semiconductor layer is formed on the optical modulation layer 103' via a junction layer 107 made of SiO2, in which a p-type semiconductor layer 112a, an i-type semiconductor layer 112, and an n-type semiconductor layer 112b are formed.

[0101] In the gain region and optical modulation region 101a, the optical modulation layer 103' is located outside the formation regions of the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b, and is extracted from the upper part. Electrode 121' a, Electrode 121' b is connected. Electrode 121' a, Electrode 121' By applying a modulation electric field to the optical modulation layer 103' by b, the effective refractive index of the propagating light mode is modulated, thereby modulating the frequency of the laser light oscillated by the semiconductor laser. The optical modulation region 102 can be made of, for example, lithium niobate.

[0102] The first distributed Bragg mirror region 105 and the second distributed Bragg mirror region 106 each include a core 104 formed on the optical modulation layer 103' via a junction layer 107. The core 104 is formed continuously with the i-type semiconductor layer 112. In the first distributed Bragg mirror region 105, a diffraction grating 151 is formed on the core 104. Similarly, in the second distributed Bragg mirror region 106, a diffraction grating 161 is formed on the core 104. The diffraction gratings 151 and 161 can also be formed on the sides of the core 104.

[0103] In Embodiment 6, the optical modulation layer 103' and the bonding layer 107 are commonly formed over the entire areas of the first distributed Bragg mirror region 105, the gain region and optical modulation region 101a, and the second distributed Bragg mirror region 106. Furthermore, an upper cladding layer 108 made of, for example, SiO2 is formed over the entire areas of the first distributed Bragg mirror region 105, the gain region and optical modulation region 101a, and the second distributed Bragg mirror region 106. Additionally, the length of the gain region and optical modulation region 101a in the waveguide direction can be set to 40 μm, while the length of the first distributed Bragg mirror region 105 and the second distributed Bragg mirror region 106 in the waveguide direction can be set to 80 μm.

[0104] Furthermore, the optical modulation layer 103' is formed on the lower cladding layer 109 made of SiO2. In addition, the optical modulation layer 103' is rib-shaped, with a rib core 103a that is convex on the side where the active layer 111 of the semiconductor laser is formed, when viewed in a cross-sectional view perpendicular to the propagation direction of the propagating light. The slab portion of the optical modulation layer 103' is 100 nm thick, and the rib core 103a can be 1000 nm wide and 200 nm high (thick). The rib-shaped optical modulation layer 103' is formed over the entire area of ​​the first distributed Bragg mirror region 105, the gain region and optical modulation region 101a, and the second distributed Bragg mirror region 106.

[0105] Next, the optical propagation modes in the optical device according to Embodiment 6 will be described with reference to Figures 12A and 12B.

[0106] First, Figure 12A shows the light propagation modes in the first distributed Bragg mirror region 105 (second distributed Bragg mirror region 106). In the first distributed Bragg mirror region 105, the core 104 has a width of 550 nm and a height of 250 nm, and the junction layer 107 has a thickness of 500 nm. The rib core 103a has a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' is 100 nm. As shown in Figure 12A, the light is almost entirely confined to the core 104.

[0107] Next, Figure 12B shows the optical propagation modes of the gain region and optical modulation region 101a. In the gain region and optical modulation region 101a, it is important that the optical modes exist in both the rib core 103a and the active layer 111, so that both optical gain and refractive index modulation can be obtained. Electrode 121' a, Electrode 121' When a modulating electric field is applied from b, the refractive index in the rib core 103a is primarily modulated by the electro-optic effect. This modulates the effective refractive index of the propagating light mode in the gain region and optical modulation region 101a. The cross-sectional size of the rib core 103a, the thickness of the bonding layer 107, Electrode 121' a, Electrode 121' The relative position of b with respect to core 104 is adjusted as appropriate to obtain the largest possible change in effective refractive index with respect to the applied voltage.

[0108] The thickness of the semiconductor layers on which the p-type semiconductor layer 112a, i-type semiconductor layer 112, and n-type semiconductor layer 112b are formed is 250 nm, and the width of the active layer 111 is 300 nm. m and The active layer 111 had a thickness of 250 nm. The junction layer 107 had a thickness of 500 nm. The rib core 103a had a width of 1000 nm and a height of 200 nm, and the slab thickness of the optical modulation layer 103' was 100 nm. As shown in Figure 12B, light is mainly confined in the rib core 103a, but is also present in the active layer 111, allowing for optical gain.

[0109] As described above, since the optical modulation layer 103' is made of a material having an electro-optic effect, it becomes possible to modulate the frequency while suppressing intensity modulation. Regarding the size of the core 104, considering productivity, it is desirable to make the core height (thickness) equal to the thickness of the i-type semiconductor layer 112, as described above.

[0110] Furthermore, a compact optical transmitter can be realized by integrating an optical filter for frequency modulation-intensity modulation conversion (FM-AM conversion) beyond the second distributed Bragg reflector region 106. The optical filter described above can be composed of a Mach-Zehnder interferometer (MZI) or a ring resonator using an optical waveguide with an InP core. It is also desirable to appropriately add a wavelength tuning structure, such as a heater, to the optical filter described above. In addition, in order to reduce connection loss to the optical fiber to which the optical device according to the embodiment is connected, a spot size converter, for example, can be integrated beyond the second distributed Bragg reflector region 106.

[0111] As described above, according to the present invention, since the optical modulation region is made of a material having an electro-optic effect, it becomes possible to modulate the frequency while suppressing intensity modulation.

[0112] 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. [Explanation of Symbols]

[0113] 101...Gain region, 102...Optical modulation region, 103...Optical modulation layer, 104...Core, 105...First distributed Bragg mirror region, 106...Second distributed Bragg mirror region, 107...Junction layer, 108...Upper cladding layer, 111...Active layer, 112a...p-type semiconductor layer, 112b...n-type semiconductor layer, 113a...p-electrode, 113b...n-electrode, 121a,121b...Electrodes, 151...Diffraction grating, 161...Diffraction grating.

Claims

1. A gain region comprising a waveguide-type semiconductor laser having a cladding layer made of SiO2, A waveguide-type optical modulation region comprising a cladding layer made of SiO2 for modulating the laser light of the semiconductor laser, Equipped with, The gain region is formed on the optical modulation region, The optical device is characterized in that the optical modulation region comprises an optical modulation layer made of lithium niobate, arranged in a range that can couple to propagating light and having a rib core, and modulates the frequency of the laser light oscillated by the semiconductor laser by modulating the effective refractive index of the propagating light mode by applying a modulation electric field to the optical modulation layer.

2. In the optical device according to claim 1, The aforementioned semiconductor laser is a distributed Bragg reflection laser, The optical modulation region is located between the gain region and the distributed Bragg mirror region. An optical device characterized by the following features.

3. In the optical device according to claim 2, The optical device is characterized in that the optical modulation layer is rib-shaped, convex on the side where the active layer of the semiconductor laser is formed, when viewed in a cross-sectional view perpendicular to the propagation direction of the propagating light.

4. In the optical device according to claim 3, An optical device characterized by comprising a core formed continuously with the active layer of the gain region, extending from the optical modulation region to the distributed Bragg reflector region adjacent to the optical modulation region.

5. In the optical device according to claim 1, The aforementioned semiconductor laser is a distributed Bragg reflection laser, The optical modulation region is arranged to overlap with the gain region, The optical modulation layer is ribbed in a convex shape on the side where the active layer of the semiconductor laser is formed, when viewed in a cross-sectional view perpendicular to the propagation direction of the propagating light. An optical device characterized by the following features.

6. In the optical device according to claim 1, The optical device is characterized in that the semiconductor laser is a distributed feedback type laser.

7. In the optical device according to claim 6, The aforementioned gain region comprises two, The optical modulation region is located between the two gain regions. An optical device characterized by the following features.

8. In the optical device according to claim 6, The optical device is characterized in that the optical modulation region comprises a distributed Bragg reflection structure.

Images