Method for manufacturing wavelength-variable laser element

Abstract

A linear waveguide layer (22), a coupling layer (21), and an annular waveguide layer (23) are continuously formed on a semiconductor substrate (9). The annular waveguide layer (23) and the coupling layer (21) are etched to form an annular waveguide (8). The linear waveguide layer (22) is subjected to anisotropic wet etching to form a linear waveguide (7). The ring waveguide (8) and the linear waveguide (7) are optically coupled via a coupling layer (21) to constitute a ring resonator filter (5). When anisotropic wet etching is performed on the linear waveguide layer (22), the linear waveguide layer (22) below the annular waveguide (8) is removed in a region not covered by the linear pattern (25) using a chemical solution having selectivity in the direction in which the linear pattern (25) extends with respect to the linear waveguide layer (22).

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing a wavelength-variable laser element. Background Technology

[0002] A wavelength-variable laser element is proposed, which includes within a laser resonator a gain section, a phase adjustment section, a diffraction grating, and a ring resonator filter optically coupled to the diffraction grating (see, for example, Patent Document 1). The ring resonator filter has two linear waveguides and a ring waveguide formed on these two linear waveguides and optically coupled to the linear waveguides.

[0003] Patent Document 1: Japanese Patent Publication No. 2008-516283

[0004] In conventional methods for manufacturing wavelength-variable laser devices, a linear waveguide is formed by etching a linear waveguide layer, followed by embedding the linear waveguide with a semiconductor layer. A ring-shaped waveguide is then formed by forming a ring layer on top of this semiconductor layer and etching it. However, this method suffers from the following problem: the surface of the semiconductor layer protrudes above the linear waveguide, creating a step difference in the ring-shaped waveguide formed thereon, leading to increased waveguide loss. Summary of the Invention

[0005] This disclosure is made to solve the aforementioned problems, and its purpose is to provide a method for manufacturing a wavelength-variable laser element that can reduce waveguide loss.

[0006] The disclosed method for manufacturing a wavelength-variable laser element comprises a laser resonator in which a gain section, a phase adjustment section, a diffraction grating, and a ring resonator filter optically coupled to the diffraction grating are disposed within the laser resonator. The method is characterized by comprising the following steps: a step of continuously forming a linear waveguide layer, a coupling layer, and a ring waveguide layer on a semiconductor substrate; a step of etching the ring waveguide layer and the coupling layer using a circular pattern as a mask to form a ring waveguide; and a step of anisotropically wet etching the linear waveguide layer using a linear pattern overlapping a portion of the ring waveguide as a mask to form a linear waveguide. The ring waveguide and the linear waveguide are optically coupled via the coupling layer to form the ring resonator filter. During the anisotropic wet etching of the linear waveguide layer, a selective solvent with respect to the direction in which the linear pattern extends is used to remove the linear waveguide layer below the ring waveguide in areas not covered by the linear pattern.

[0007] In this disclosure, a linear waveguide layer, a coupling layer, and a ring waveguide layer are sequentially formed on a semiconductor substrate, and then the ring waveguide layer and the coupling layer are etched to form a ring waveguide. Since the conventional process of burying the linear waveguide with a semiconductor layer is eliminated, no step difference is generated in the ring waveguide. As a result, waveguide loss can be reduced. Attached Figure Description

[0008] Figure 1 This is a perspective view of the wavelength-variable laser element in Embodiment 1.

[0009] Figure 2 It is along Figure 1 A cross-sectional view of the gain section of AA´.

[0010] Figure 3 It is along Figure 1 A cross-sectional view of the BB' diffraction grating.

[0011] Figure 4 It is along Figure 1 A cross-sectional view of a CC' ring resonator filter.

[0012] Figure 5 It is along Figure 1 A cross-sectional view of the DD' amplifier.

[0013] Figure 6 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0014] Figure 7 This is a top view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0015] Figure 8 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0016] Figure 9 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0017] Figure 10 This is a top view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0018] Figure 11 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0019] Figure 12 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0020] Figure 13 This is a top view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0021] Figure 14 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0022] Figure 15 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1.

[0023] Figure 16 This is a top view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2.

[0024] Figure 17 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2.

[0025] Figure 18 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2.

[0026] Figure 19 This is a top view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2.

[0027] Figure 20 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2.

[0028] Figure 21 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2.

[0029] Figure 22 This is a top view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2.

[0030] Figure 23 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2.

[0031] Figure 24 This is a cross-sectional view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2. Detailed Implementation

[0032] The manufacturing method of the wavelength-variable laser element according to the embodiments will be described with reference to the accompanying drawings. The same or corresponding components are labeled with the same reference numerals, and repeated descriptions are sometimes omitted.

[0033] Implementation method 1.

[0034] Figure 1This is a perspective view of the wavelength-variable laser element according to Embodiment 1. Within the laser resonator 1 are arranged a gain unit 2, a phase adjustment unit 3, a diffraction grating 4, a ring resonator filter 5 optically coupled to the diffraction grating 4, and a semiconductor optical amplifier 6. The ring resonator filter 5 has two straight waveguides 7 whose ends are combined and optically coupled to the diffraction grating 4, and a ring waveguide 8 formed on the two parallel straight waveguides 7. The straight waveguides 7 are optically coupled to the ring waveguide 8.

[0035] Gain section 2 provides optical gain. When gain section 2 is positioned between two mirrors, a laser resonator 1 is formed, generating laser oscillation. Phase adjustment section 3 adjusts the phase of the light propagating within the laser resonator 1. By combining a diffraction grating 4 with periodic reflectivity and a ring resonator filter 5 with periodic transmittance, broadband wavelength modulation can be achieved using the vernier effect. Semiconductor optical amplifier 6 is formed to obtain high optical output.

[0036] Figure 2 It is along Figure 1 A cross-sectional view of the gain section of AA'. An n-InP layer 10, an active layer 11, a p-InP layer 12, and a diffraction grating layer 13 are sequentially stacked on an n-type InP semiconductor substrate 9 to form a mesa structure. The active layer 11 is, for example, an MQW (Multiple Quantum Well) structure made of AlGaInAs, including a SCH (Separate Confinement Heterostructure) structure. The diffraction grating 4 is, for example, made of InGaAsP.

[0037] The mesa structure is buried on both sides by Fe-InP buried layers 14 and n-InP buried layers 15. A p-InP layer 16 and a p-InGaAs contact layer 17 are sequentially formed on the mesa structure and the n-InP buried layer 15. An anode electrode 18 is formed above the mesa structure and on the p-InGaAs contact layer 17. A cathode electrode 19 is formed on the lower surface of the semiconductor substrate 9.

[0038] Figure 3 It is along Figure 1 A cross-sectional view of the BB' diffraction grating. As a difference from the gain section 2, a waveguide layer 20 is formed instead of the active layer 11, and the anode electrode 18 and cathode electrode 19 are not formed. The waveguide layer 20 is, for example, made of InGaAsP.

[0039] Figure 4 It is along Figure 1A cross-sectional view of a CC' ring resonator filter. A linear waveguide 7, a coupling layer 21, a ring waveguide 8, and a p-InP layer 16 are sequentially stacked on top of an n-InP layer 10. The ring waveguide 8 and two linear waveguides 7 are optically coupled via the coupling layer 21 to form a ring resonator filter 5. The linear waveguide 7 is, for example, made of AlGaInAs. The coupling layer 21 is, for example, made of InP. The thickness of the coupling layer 21 is, for example, 300 nm. The ring waveguide 8 is, for example, made of InGaAsP. Figure 5 It is along Figure 1 A cross-sectional view of the DD' amplifier. The semiconductor optical amplifier 6 has... Figure 2 The gain section 2 shown has the same structure.

[0040] Next, the manufacturing method of the ring resonator filter of the wavelength-variable laser element of this embodiment will be described. Figure 7 , 10 13 is a top view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1. Figure 6 , 8 9, 11, 12, 14, and 15 are cross-sectional views showing the manufacturing method of the wavelength-variable laser element according to Embodiment 1. Figure 8 It is along Figure 7 A cross-sectional view of AA'. Figure 9 It is along Figure 7 A cross-sectional view of BB'. Figure 11 It is along Figure 10 A cross-sectional view of AA'. Figure 12 It is along Figure 10 A cross-sectional view of BB'. Figure 14 It is along Figure 13 A cross-sectional view of AA'. Figure 15 It is along Figure 13 A cross-sectional view of BB'.

[0041] First, such as Figure 6 As shown, an n-InP layer 10, a linear waveguide layer 22, a coupling layer 21, a ring waveguide layer 23, and a p-InP layer 16 are continuously formed on the (100) surface of an n-type InP semiconductor substrate 9. These crystal structures are zincblende type structures (zinc mixed type structures). In addition, "continuous formation" means that the crystal growth process of multiple semiconductor layers is carried out continuously without interruption, without performing any other processes other than crystal growth in the middle.

[0042] Next, as Figures 7 to 9As shown, a circular pattern 24 is formed on the p-InP layer 16 using a photoresist or the like. Using the circular pattern 24 as a mask, the p-InP layer 16, the annular waveguide layer 23, and the coupling layer 21 are dry-etched or wet-etched to form the annular waveguide 8. Afterward, the circular pattern 24 is removed. At this point, the width of the annular waveguide 8 becomes the target width. The target width is, for example, 1.4 μm.

[0043] Next, as Figures 10 to 12 As shown, two linear patterns 25 are formed on the exposed linear waveguide layer 22 and the p-InP layer 16 on the ring waveguide 8 using a photoresist or the like. When viewed from above, the linear patterns 25 overlap with a portion of the ring waveguide 8. Using the linear patterns 25 as a mask, the linear waveguide layer 22 is anisotropically wet-etched to form the linear waveguide 7.

[0044] At this time, the [0-11] direction (relative to the linear waveguide layer 22 extending in the linear pattern 25) is used. Figure 10 The reagent is selectively applied in the left-right direction. Thus, the linear waveguide layer 22 beneath the annular waveguide 8 is removed in areas not covered by the linear pattern. If the linear waveguide layer 22 is AlGaInAs, a mixture of, for example, tartaric acid and hydrogen peroxide water is used as the reagent. In this case, the

[011] direction ( Figure 10 (up and down directions) and [0-11] directions ( Figure 10 The etching rate of the linear waveguide layer 22 in the left-right direction (of the linear pattern 25) is approximately 1:2~3. Figure 10 The width direction of the straight line pattern 25 is etched on the left and right sides. Figure 10 The width of the straight waveguide 7 is 2 to 3 times that in the vertical direction. However, since side etching is also performed in the width direction of the straight pattern 25, it is difficult to accurately control the width of the straight waveguide 7. Therefore, at this moment, the width of the straight waveguide 7 becomes wider than the target width, for example, 1.8 μm.

[0045] Next, as Figures 13 to 15 As shown, a linear pattern 26 with a target width and a circular pattern 27 covering the annular waveguide 8 are used as masks, and the linear waveguide 7 is patterned by dry etching or wet etching. That is, after forming the linear waveguide 7 with a width wider than the target width, the linear waveguide 7 is patterned to the target width. The target width is, for example, 1.4 μm.

[0046] As explained above, in this embodiment, after the linear waveguide layer 22, coupling layer 21, and ring waveguide layer 23 are continuously formed on the semiconductor substrate 9, the ring waveguide layer 23 and coupling layer 21 are etched to form the ring waveguide 8. Since there is no conventional process of burying the linear waveguide with a semiconductor layer, no step difference is generated in the ring waveguide 8. As a result, waveguide loss can be reduced. In addition, the unwanted linear waveguide layer 22 below the ring waveguide 8 can be removed by using anisotropic wet etching to form the linear waveguide 7.

[0047] The required deviation accuracy for the spacing between the linear waveguide 7 and the ring waveguide 8 is, for example, ±10 nm. In contrast, in this embodiment, the spacing between the linear waveguide 7 and the ring waveguide 8 is determined by the thickness of the epitaxially grown coupling layer 21, thus allowing for high-precision control. Therefore, the coupling loss between the linear waveguide 7 and the ring waveguide 8 can be reduced.

[0048] Implementation method 2.

[0049] Figure 16 , 19 22 is a top view showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2. Figure 17 , 18 20, 21, 23, and 24 are cross-sectional views showing the manufacturing method of the wavelength-variable laser element according to Embodiment 2. Figure 17 It is along Figure 16 A cross-sectional view of AA'. Figure 18 It is along Figure 16 A cross-sectional view of BB'. Figure 20 It is along Figure 19 A cross-sectional view of AA'. Figure 21 It is along Figure 19 A cross-sectional view of BB'. Figure 23 It is along Figure 22 A cross-sectional view of AA'. Figure 24 It is along Figure 22 A cross-sectional view of BB'.

[0050] First, similar to Embodiment 1, an n-InP layer 10, a linear waveguide layer 22, a coupling layer 21, a ring waveguide layer 23, and a p-InP layer 16 are continuously formed on the (100) surface of an n-type InP semiconductor substrate 9.

[0051] Next, as Figures 16 to 18As shown, similarly to Embodiment 1, a circular pattern 24 is used as a mask to dry-etch or wet-etch the p-InP layer 16, the annular waveguide layer 23, and the coupling layer 21 to form the annular waveguide 8. Afterward, the circular pattern 24 is removed. At this point, the width of the annular waveguide 8 becomes wider than the target width, for example, 1.8 μm.

[0052] Next, as Figures 19 to 21 As shown, similarly to Embodiment 1, a straight waveguide 7 is formed by anisotropic wet etching of the straight waveguide layer 22 using a straight pattern 25 as a mask. At this time, the width of the straight waveguide 7 is wider than the target width, for example, 1.8 μm.

[0053] Next, as Figures 22 to 24 As shown, a linear pattern 26 and a circular pattern 27 with a target width are used as masks, and the linear waveguide 7 and the ring waveguide 8 are patterned by dry etching or wet etching. That is, after forming the linear waveguide 7 and the ring waveguide 8 with widths wider than the target width, the linear waveguide 7 and the ring waveguide 8 are patterned to the target width. The target width is, for example, 1.4 μm. In this way, the shape of the linear waveguide 7 and the ring waveguide 8 is finally determined by the patterning, so the shape of the linear waveguide 7 and the ring waveguide 8 becomes accurate. Other structures and effects are the same as in Embodiment 1.

[0054] Explanation of reference numerals in the attached figures

[0055] 1...Laser resonator; 2...Gain section; 3...Phase adjustment section; 4...Diffraction grating; 5...Ring resonator filter; 7...Linear waveguide; 8...Ring waveguide; 9...Semiconductor substrate; 21...Coupled layer; 22...Linear waveguide layer; 23...Ring waveguide layer; 24...Circular pattern; 25...Linear pattern.

Claims

1. A method for manufacturing a wavelength-variable laser element, comprising a laser resonator in which a gain section, a phase adjustment section, a diffraction grating, and a ring resonator filter optically coupled to the diffraction grating are disposed within the laser resonator, characterized in that... It includes the following processes: The process of continuously forming a linear waveguide layer, a coupling layer, and a ring waveguide layer on a semiconductor substrate; The process of forming a ring waveguide by etching the ring waveguide layer and the coupling layer using a circular pattern as a mask; as well as The process of forming a linear waveguide by using a linear pattern overlapping a portion of the ring waveguide as a mask and performing anisotropic wet etching on the linear waveguide layer. The ring waveguide and the straight waveguide are optically coupled via the coupling layer to form the ring resonator filter. During anisotropic wet etching of the linear waveguide layer, a solution selective in the direction of the linear pattern extension relative to the linear waveguide layer is used to remove the linear waveguide layer below the annular waveguide in areas not covered by the linear pattern.

2. The method for manufacturing a wavelength-variable laser element according to claim 1, characterized in that, The linear waveguide layer, the coupling layer, and the annular waveguide layer have a zincblende type structure. The straight line pattern extends along the [0-11] direction.

3. The method for manufacturing a wavelength-variable laser element according to claim 2, characterized in that, The linear waveguide layer is AlGaInAs. A mixture of tartaric acid and hydrogen peroxide water is used as the drug solution.

4. The method for manufacturing a wavelength-variable laser element according to any one of claims 1 to 3, characterized in that, After forming the linear waveguide with a width wider than the target width, the linear waveguide is patterned to the target width.

5. The method for manufacturing a wavelength-variable laser element according to any one of claims 1 to 3, characterized in that, After forming the linear waveguide and the ring waveguide with a width greater than the target width, the linear waveguide and the ring waveguide are respectively patterned to the target width.

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