JP5551928B2 - Semiconductor optical device and manufacturing method of semiconductor optical device - Google Patents

Description

  The present invention relates to a semiconductor optical device and a method for manufacturing the semiconductor optical device.

  In recent years, the amount of information transmitted by optical communication has increased dramatically. Supporting such optical communication infrastructure is a semiconductor optical device such as an electroabsorption (EA) modulator integrated DFB (Distributed Feed Back) (EA / DFB) laser. The EA / DFB element performs high-speed modulation by changing the amount of light absorbed by the EA modulator by applying a reverse bias voltage to the EA modulator with light emitted from the DFB laser, with the laser unit in a continuous oscillation state. ing. For this reason, the EA / DFB element has low chirp characteristics as compared with a direct modulation type element that generates modulated light by ON / OFF of the current flowing through the laser, and is inexpensive and low in comparison with an LN modulation type element or the like. Due to its small size, it is frequently used as a semiconductor optical device used for medium and long distance communication.

  By the way, the characteristics of the semiconductor optical device greatly change depending on the state of the internal light. Therefore, when light is input into the semiconductor device from the outside, the operation state changes. It is also sensitive to reflection of light emitted from the element, and the operation state becomes unstable when the emitted light returns into the element. Since a semiconductor has a large refractive index of about 3 and large reflection occurs at the end face of the semiconductor optical element that is a boundary with air, a low-reflection film is usually formed by a dielectric multilayer film on the outgoing end face of the semiconductor optical element. Yes. Furthermore, when it is necessary to reduce the reflected light, a so-called window structure may be employed in which light is not confined in the vicinity of the element end face. FIG. 13 is a plan view showing an example of a state in which the window structure 124 of the semiconductor optical device 100 of the comparative example is viewed from above. In the semiconductor optical device 100 shown in FIG. 13, the optical waveguide portion 116 is not formed up to the end surface of the semiconductor optical device 100, and the beam is expanded by not confining light near the end surface of the semiconductor optical device 100. Therefore, even if light reflection occurs at the end face of the semiconductor optical device 100, the ratio of the return light to the optical waveguide portion 116 is reduced.

  In the DFB laser, when the reflected light returns to the laser, bending (kink) occurs in the light output-current characteristic. In addition, when the reflected light modulated by the EA modulator returns to a continuously oscillating laser such as an EA / DFB element, the DFB laser is swayed by the reflected light and is originally applied to the EA modulator. Since light fluctuations that are different from the electrical signal being generated occur, peaks and dips occur in the frequency response characteristics of the light, light intensity fluctuations and jitter occur in the eye pattern, and as a result, transmission characteristics deteriorate.

  The window structure for reducing the reflectivity is formed by burying and re-growing a low refractive index semiconductor on the extension line of the optical waveguide portion 116. Since the optical waveguide portion 116 (core portion) and the window structure portion 124 have different refractive indexes, light is reflected at the boundary. As a technique for reducing the reflectivity, Patent Document 1 discloses a technique in which the interface between the window structure portion and the core portion is slanted using the crystal plane orientation during crystal growth.

JP 2000-188441 A

  However, when the interface between the window structure portion and the optical waveguide portion (core portion) is inclined using the crystal plane orientation, the angle of the end face of the optical waveguide portion with respect to the optical axis direction of the optical waveguide portion is the crystal plane. Since it is determined by the orientation, it becomes difficult to manufacture the semiconductor optical device so that the effect of reducing the reflectance is maximized when the wavelength band of the light emitted from the laser is changed. In a communication system with a high transmission rate, the influence of reflected light is large. Therefore, in order to maximize the performance of the semiconductor optical device, it is required to reduce the reflected light as much as possible.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor optical device and a method for manufacturing the semiconductor optical device that can reduce reflected light more easily than in the past.

  In order to solve the above-described problems, a semiconductor optical device according to the present invention includes an optical waveguide portion formed of a crystal layer, and the optical waveguide portion has a tapered tip portion, and the optical waveguide portion An end face from which light is emitted is formed at a tip portion of the crystal layer along a direction different from the direction along the crystal plane orientation of the crystal layer.

  The method for manufacturing a semiconductor optical device according to the present invention includes a step of forming an optical waveguide portion constituted by a crystal layer, and a crystal plane orientation of the crystal layer so that a tip portion of the optical waveguide portion is tapered. And a step of forming an end surface along a direction different from the above direction.

  According to the present invention, the angle of the end face of the tip portion of the optical waveguide portion is not limited to an angle determined by the crystal plane orientation, so that the reflected light can be reduced more easily than in the prior art.

  In one aspect of the present invention, the optical waveguide portion is formed on a substrate, and the end surface along a direction corresponding to a direction perpendicular to the surface of the substrate is formed at the tip portion. It is characterized by. By so doing, the end face can be formed more easily than in the prior art.

  In one embodiment of the present invention, the length of the tip portion in the direction along the optical axis of the optical waveguide portion corresponds to a length that is an integral multiple of a half wavelength of light emitted from the optical waveguide portion. It is characterized by that. In this way, the reflectance of light at the end face can be reduced as compared with the prior art.

  In one embodiment of the present invention, the end face is formed so that an incident angle of light passing through the optical waveguide portion to the end face does not exceed a critical angle. By doing so, light is not totally reflected at the end face.

  In one embodiment of the present invention, a window structure portion is formed on the end face side of the optical waveguide portion. In this way, the possibility that the reflected return light is coupled to the optical waveguide can be reduced as compared with the prior art.

  In one embodiment of the present invention, a plurality of end faces are formed at the distal end portion along different directions that are substantially symmetrical with respect to the optical axis of the optical waveguide portion. By so doing, it is possible to reduce the degree of bending of the light emitted from the optical waveguide portion with respect to the optical axis of the optical waveguide as compared with the prior art.

  One embodiment of the present invention is characterized in that the semiconductor laser portion and the light modulation portion are integrated.

  In one embodiment of the present invention, the end surface is formed by dry etching.

1 is a partially cutaway perspective view showing an example of a schematic configuration of a semiconductor optical device according to a first embodiment of the present invention. It is a flowchart which shows an example of the manufacturing process of the semiconductor optical element concerning 1st Embodiment of this invention. It is a perspective view which shows an example of the manufacturing process of the semiconductor optical element concerning 1st Embodiment of this invention. It is a perspective view which shows an example of the manufacturing process of the semiconductor optical element concerning 1st Embodiment of this invention. It is a perspective view which shows an example of the manufacturing process of the semiconductor optical element concerning 1st Embodiment of this invention. It is a perspective view which shows an example of the manufacturing process of the semiconductor optical element concerning 1st Embodiment of this invention. It is a perspective view which shows an example of the manufacturing process of the semiconductor optical element concerning 1st Embodiment of this invention. It is a perspective view which shows an example of the manufacturing process of the semiconductor optical element concerning 1st Embodiment of this invention. It is a top view which shows an example of a mode that the tip part vicinity of the optical-waveguide part of the semiconductor optical element shown in FIG. 8 was seen from the top. It is a figure which shows an example of the relationship between the wavelength of the light oscillated from a semiconductor laser part, and power reflectivity. It is a perspective view which shows an example of the manufacturing process of the semiconductor optical element concerning 2nd Embodiment of this invention. It is a top view which shows an example of a mode that the front-end | tip part vicinity of the optical waveguide part of the semiconductor optical element shown in FIG. 11 was seen from the top. It is a top view which shows an example of a mode that the window structure part of the semiconductor optical element of the comparative example was seen from the upper surface.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a partially cutaway perspective view showing an example of a schematic configuration of a semiconductor optical device 1 (for example, an EA / DFB device) according to the first embodiment. The semiconductor optical device 1 according to the first embodiment is a 1.55 μm band semiconductor optical device 1 using an InGaAsP-based material. As shown in FIG. 1, the semiconductor optical device 1 according to the first embodiment includes a semiconductor laser unit 12 (for example, a DFB laser unit) and an optical modulation unit 14 (for example, an EA modulator) on a semiconductor substrate 10. , Are accumulated. In the first embodiment, the semiconductor laser unit 12 and the light modulation unit 14 constitute an optical waveguide unit 16. A p-cladding layer 18 is formed on the optical waveguide portion 16. The semiconductor laser unit 12, the light modulation unit 14, and the p-cladding layer 18 are embedded in the high resistance semiconductor 20. The upper surface of the p-cladding layer 18 and the upper surface of the high-resistance semiconductor 20 are on the same plane, and two electrodes 22 are provided on the surface.

  In the semiconductor optical device 1 according to the first embodiment, the light oscillated from the semiconductor laser unit 12 is modulated by the light modulation unit 14 and emitted to the outside of the semiconductor optical device 1. The end surface of the semiconductor optical device 1 according to the first embodiment from which light is emitted is coated with a non-reflective coating with a dielectric multilayer film or the like. A window structure 24 is formed in the vicinity of the end surface of the semiconductor optical device 1 from which light is emitted.

  Here, an example of the manufacturing process of the semiconductor optical device 1 according to the first embodiment will be described with reference to the flowchart shown in FIG. 3 to 8 are perspective views showing an example of the manufacturing process of the semiconductor optical device 1.

First, as shown in FIG. 3, a DFB laser multilayer constituting the semiconductor laser unit 12 is crystal-grown on the semiconductor substrate 10 of n-InP (S101). Then, as shown in FIG. 4, the semiconductor laser part 12 is etched leaving only a part of the DFB laser multilayer constituting the semiconductor laser part 12 (S102). Then, as shown in FIG. 5, the EA multilayer constituting the light modulation unit 14 is formed by using the butt joint technique (S103). Then, a diffraction grating is formed in the semiconductor laser unit 12 (S104). Then, as shown in FIG. 6, the p-cladding layer 18 doped with about 10 ¹⁷ cm ^{−3 of} zinc is crystal-grown (S105).

  Then, as shown in FIG. 7, the mesa structure of the semiconductor optical device 1 is formed by dry etching (S106). Thus, the optical waveguide part 16 including the semiconductor laser part 12 and the light modulation part 14 is formed. In the semiconductor optical device 1 according to the first embodiment, the distal end portion 16a of the optical waveguide portion 16 is formed to be tapered. An end face 16b is formed along the direction different from the direction along the crystal plane orientation of the crystal layer (EA multilayer) constituting the EA modulator section 14 at the tip end portion 16a. In the semiconductor optical device 1 according to the first embodiment, the end surface 16b of the tip end portion 16a is formed along a direction corresponding to a direction perpendicular to the upper surface of the semiconductor substrate 10 by dry etching.

  Then, as shown in FIG. 8, a buried crystal is grown around the mesa by a high resistance semiconductor 20 (for example, Fe—InP, Ru—InP, etc.) (S107). And the electrode 22 is arrange | positioned on the upper surface of the semiconductor optical element 1 (S108). Then, non-reflective coating is performed on the end face of the semiconductor optical device 1 from which light is emitted (S109).

  Thus, the semiconductor optical device 1 according to the first embodiment is formed. In the semiconductor optical device 1 according to the first embodiment, the window structure portion 24 is formed on the end face side of the distal end portion 16 a of the optical waveguide portion 16.

  In the semiconductor optical device 1 according to the first embodiment, the light emitted from the semiconductor laser unit 12 is modulated by the light modulation unit 14, and the window structure 24, non-reflective from the end surface 16 b of the tip 16 a of the optical waveguide unit 16. The light is emitted to the outside through the end face of the coded semiconductor optical device 1.

FIG. 9 is a plan view showing an example of a state in which the vicinity of the distal end portion 16a of the optical waveguide portion 16 of the semiconductor optical device 1 shown in FIG. 8 is viewed from above. Here, the length L along the optical axis direction of the optical waveguide portion 16 of the tip portion 16a for reducing the light reflectance at the end surface 16b is set as follows so that the reflected wave at the end surface 16b is canceled. Were determined. When reflected waves whose phases are shifted by 2Nπ (N = 1, 2, 3,...) Are overlapped, the reflectance of light at the end face 16b is minimized. Therefore, the equivalent refractive index _{n _Eff} of the optical waveguide section 16, _{n 1} the refractive index of the high-resistance semiconductor 20, the average refractive index of the tip portion 16a of the optical waveguide section _{16, (n _eff + n 1)} / 2, and to the In order to reduce the reflectance of light at the end face 16b, it is desirable to set the length L along the optical axis direction of the optical waveguide portion 16 of the tip end portion 16a to a value represented by the following equation. In other words, it is desirable to set the length L so as to correspond to a length that is an integral multiple of a half wavelength at the distal end portion 16 a of the light emitted from the optical waveguide portion 16.

  Here, as the value of N increases, the angle formed between the end face 16b and the optical axis of the optical waveguide portion 16 decreases. That is, the incident angle θ of the light passing through the optical waveguide portion 16 to the end face 16b increases. Here, in the semiconductor optical device 1 according to the first embodiment, the length L is based on Snell's law so that the incident angle θ of the light passing through the optical waveguide portion 16 to the end face 16b does not exceed the critical angle. End face 16b is formed so as to satisfy the condition shown in the following equation. In the following equation, Wm represents the width (mesa width) of the optical waveguide portion 16.

  The value of the length L in the semiconductor optical device 1 according to the first embodiment is, for example, 1.45 μm. The length L corresponds to the case where N = 6.

  Here, the reflection at the boundary surface (end surface 16b) between the tip portion 16a and the window structure portion 24 will be described.

  For example, the optical waveguide portion when the end surface 16b is not formed with the tapered tip portion 16a in the optical waveguide portion 16 (for example, when formed so as to be perpendicular to the optical axis of the optical waveguide portion 16). The power reflectivity R at the end face 16b of the 16 tip portions 16a is defined by the following equation from the Fresnel formula. In the following equation, r represents a reflection coefficient.

Here, the equivalent refractive index _{n_eff} of the optical waveguide portion 16 is 3.2, the refractive index n ₁ of the high-resistance semiconductor 20 is 3.167, the width Wm of the tip portion 16a of the optical waveguide portion 16 is 1.3 μm, and the semiconductor laser. When the wavelength λ of the light oscillated from the unit 12 is 1550 nm, the power reflectance R is −45 dB.

  On the other hand, in the semiconductor optical device 1 according to the first embodiment, the tip portion 16a is considered to be equivalent to a multiple reflection structure in which minute regions whose refractive index changes stepwise, and multiple reflection in each minute region is performed. The power reflectance is calculated by calculating the number of layers. For example, FIG. 10 illustrates an example of the relationship between the wavelength λ of the light oscillated from the semiconductor laser unit 12 and the power reflectance R when L = 1.45 μm (corresponding to N = 6). 10 shows the wavelength λ of the light oscillated from the semiconductor laser portion 12 and the distal end portion 16a of the optical waveguide portion 16 when the optical waveguide portion 16 is formed so as to be perpendicular to the optical axis. An example of the relationship (corresponding to the above-mentioned N = 0) with the power reflectivity R at the end face 16b is also shown.

  As shown in FIG. 10, when the wavelength λ of the light oscillated from the semiconductor laser unit 12 is 1500 nm to 1600 nm, the reflectance R is −75 dB or less. Thus, in the semiconductor optical device 1 according to the first embodiment, the reflectance can be greatly reduced as compared with the conventional technique. Further, in the above-described case, the incident angle θ of the light passing through the optical waveguide portion 16 to the end face 16b of the tip end portion 16a has a margin of 33 degrees with respect to the critical angle.

  When the characteristics of the semiconductor optical device 1 according to the first embodiment were evaluated, the semiconductor optical device 1 according to the first embodiment is such that the tip portion 16a of the optical waveguide portion 16 is perpendicular to the optical axis of the optical waveguide portion 16. Compared with the semiconductor optical device 1 manufactured as described above, a reflectance reduction effect of 30 dB or more was obtained. Due to this reflectance reduction effect, the bending of the optical output-current characteristic of the semiconductor optical device 1 and the high level fluctuation and jitter of the eye pattern, which have occurred in the past, are improved as compared with the conventional semiconductor optical device 1. Was confirmed.

  The present invention is not limited to the above embodiment.

[Second Embodiment]
FIG. 11 is a perspective view showing an example of a manufacturing process of the semiconductor optical device 1 according to the second embodiment, corresponding to FIG. FIG. 12 is a plan view illustrating an example of a state in which the vicinity of the distal end portion 16a of the optical waveguide portion 16 of the semiconductor optical device 1 according to the second embodiment is viewed from above corresponding to FIG.

  As shown in FIGS. 11 and 12, in the semiconductor optical device 1 according to the second embodiment, the end surface 16 b of the tip portion 16 a has a shape that is substantially symmetrical with respect to the optical axis of the optical waveguide portion 16. Is formed. In the semiconductor optical device 1 shown in FIGS. 11 and 12, for example, two end surfaces 16 b are formed so that the shape of the distal end portion 16 a is symmetric with respect to the optical axis of the optical waveguide portion 16.

  In the semiconductor optical device 1 according to the first embodiment, there is one end face 16b, and the light is emitted from the optical waveguide portion 16 because the optical waveguide portion 16 is inclined with respect to the optical axis of the optical waveguide portion 16. Bends about 1 degree with respect to 16 optical axes. On the other hand, in the semiconductor optical device 1 according to the second embodiment, light emitted from the optical waveguide portion 16 is emitted along the optical axis of the optical waveguide portion 16. For example, in the semiconductor optical device 1 in which the difference in refractive index between the optical waveguide portion 16 and the high-resistance semiconductor 20 is large and the bending angle of the emitted light is large, as in the semiconductor optical device 1 according to the second embodiment, It is effective to form the end face 16b of the tip portion 16a so that the shape of the tip portion 16a is symmetric with respect to the optical axis of the optical waveguide portion 16.

  The manufacturing process of the semiconductor optical device 1 according to the second embodiment is the same as the manufacturing process of the semiconductor optical device 1 according to the first embodiment, except for S106. In the semiconductor optical device 1 according to the second embodiment, in S106, the two end surfaces 16b are formed so that the shape of the tip portion 16a of the semiconductor optical device 1 is symmetric with respect to the optical axis of the optical waveguide portion 16.

  In order to reduce the reflectance of light at the end face 16b, it is desirable to set the length L of the distal end portion 16a along the optical axis direction of the optical waveguide portion 16 to the value shown in the above-described equation (1).

  Further, in the semiconductor optical device 1 according to the second embodiment, based on Snell's law, the incident angle θ of the light passing through the optical waveguide portion 16 to the end face 16b of the tip portion 16a does not exceed the critical angle. The end face 16b of the tip portion 16a is formed so that the length L satisfies the condition shown in the following equation. In the following equation, Wm represents the width (mesa width) of the optical waveguide portion 16.

  The value of the length L in the semiconductor optical device 1 according to the second embodiment is, for example, 1.45 μm. The length L corresponds to the case where N = 6.

  In the semiconductor optical device 1 according to the second embodiment, for example, when L = 1.45 μm (corresponding to N = 6), the wavelength λ of the light oscillated from the semiconductor laser unit 12 and the power reflectance R Is the same as that of the semiconductor optical device 1 according to the first embodiment (see FIG. 10). In this case, the incident angle θ of the light passing through the optical waveguide portion 16 to the end face 16b of the tip portion 16a has a margin of 16 degrees with respect to the critical angle.

  Also in the semiconductor optical device 1 according to the second embodiment, similarly to the semiconductor optical device 1 according to the first embodiment, the semiconductor optical device 1 in which the tapered tip portion 16a is not formed in the optical waveguide portion 16 (for example, the optical waveguide) Compared with the semiconductor optical device 1) produced so that the tip 16a of the portion 16 is perpendicular to the optical axis of the optical waveguide portion 16, a reflectance reduction effect of 30 dB or more was obtained. Due to this reflectance reduction effect, the bending of the optical output-current characteristic of the semiconductor optical device 1 and the high level fluctuation and jitter of the eye pattern, which have occurred in the past, are improved as compared with the conventional semiconductor optical device 1. Was confirmed.

  The present invention is not limited to the above embodiment.

  For example, the present invention can be applied to a 1.3 μm band that is a communication wavelength band. The present invention is also applicable to the semiconductor optical device 1 using other compound semiconductor materials such as InGaAlAs and GaInNAs. The present invention may be applied to a semiconductor optical device including a semiconductor optical amplifier (SOA) or a semiconductor optical device including a Mach-Zehnder modulator. The basic structure of the semiconductor laser provided in the semiconductor optical device is not limited. The basic structure of the semiconductor laser provided in the semiconductor optical device may be a buried structure or a ridge structure.

  DESCRIPTION OF SYMBOLS 1 Semiconductor optical device, 10 Semiconductor substrate, 12 Semiconductor laser part, 14 Optical modulation part, 16 Optical waveguide part, 16a Tip part, 16b End surface, 18 p-cladding layer, 20 High resistance semiconductor, 22 Electrode, 24 Window structure part, 100 Semiconductor optical device, 116 Optical waveguide part, 124 Window structure part.

Claims (8)

Including an optical waveguide portion constituted by a crystal layer,
The optical waveguide portion is formed with a tapered tip.
The distal end of the optical waveguide section, along said direction different from the direction along the crystal plane orientation of the crystal layer, the end face where the light is emitted is formed,
The length of the tip portion in the direction along the optical axis of the optical waveguide portion corresponds to a length that is an integral multiple of a half wavelength of light emitted from the optical waveguide portion.
A semiconductor optical device. The optical waveguide portion is formed on a substrate;
The end surface is formed at a direction corresponding to a direction perpendicular to the surface of the substrate at the tip.
The semiconductor optical device according to claim 1. The end face is formed so that the incident angle to the end face of the light passing through the optical waveguide portion does not exceed a critical angle.
The semiconductor optical device according to claim 1 or 2, characterized in that. A window structure portion is formed on the end face side of the optical waveguide portion,
A semiconductor optical device according to any one of claims 1 to 3, characterized in that. A plurality of end faces along different directions are formed on the tip portion, which are substantially symmetrical with respect to the optical axis of the optical waveguide portion.
The semiconductor optical device according to claim 1, any one of 4, characterized in that. The semiconductor laser part and the light modulation part are integrated,
The semiconductor optical device according to claim 1, any one of 5, characterized in that. The end face is formed by dry etching;
A semiconductor optical device according to any one of claims 1 to 6, characterized in that. Forming an optical waveguide portion constituted by a crystal layer;
Forming an end surface along a direction different from the direction along the crystal plane orientation of the crystal layer so that the tip of the optical waveguide portion is tapered ,
The length of the tip portion in the direction along the optical axis of the optical waveguide portion corresponds to a length that is an integral multiple of a half wavelength of light emitted from the optical waveguide portion.
The method of manufacturing a semiconductor optical element characterized and this.

Images