JP2009222965A - Electric field absorption type modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric field absorption type modulator (EA modulator), having high heat radiation and an superior frequency characteristics. <P>SOLUTION: This EA modulator 10 includes an optical waveguide layer 32, of which the optical absorption amount varies in response to applied electric field, and a p-side electrode 40 for applying the electric field to the optical waveguide layer 32. The p-side electrode 40 has a mesa part 42 which extends along the path of a light input into an input end 32a of the optical waveguide layer 32 and output from an output end 32b thereof; a PAD part 44 connected with an electrical signal line, and a band-like PAD connection part 46 for connecting the PAD part 44 to a partial area in an input end 32a side of the mesa part 42. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electroabsorption modulator, and more particularly to a shape of a signal electrode.

  One of the optical modulators that modulate the intensity of light is an electroabsorption modulator (hereinafter referred to as “EA modulator”) that uses the electroabsorption effect of a semiconductor. The electroabsorption effect is a phenomenon in which, when an electric field is applied to a semiconductor having a quantum well structure, the energy level difference between the conduction band and the valence band changes, and the amount of light absorbed in the quantum well structure changes. is there.

  The EA modulator applies a voltage to a PIN junction having a double hetero structure in which an optical waveguide layer having a multiple quantum well (MQW) structure is sandwiched between a p-type semiconductor and an n-type semiconductor, and the PIN junction. P-side electrode and n-side electrode.

  When a voltage is applied to the PIN junction, an electric field is applied to the optical waveguide layer, so that the light input to the optical waveguide layer is separated into holes and electrons and disappears. As a result, light passing through the optical waveguide layer is reduced, and the optical signal is turned off. Conversely, if no voltage is applied to the PIN junction, the light passes through the optical waveguide layer without being absorbed, so that the on state of the optical signal is realized.

  That is, the EA modulator realizes light intensity modulation by changing the amount of absorption of light propagating through the optical waveguide layer according to the voltage applied to the PIN junction. For this reason, for example, laser light is input to the optical waveguide layer of the EA modulator, and a voltage corresponding to the high-frequency signal is applied to the p-side electrode and the n-side electrode of the EA modulator, thereby modulating the laser light with the high-frequency signal. be able to.

FIG. 5 is a top view of a general EA modulator 50. As shown in the figure, the p-side electrode (signal electrode) 70 of the EA modulator 50 includes a mesa portion 72 formed so as to be positioned above the optical waveguide layer 60 in order to apply an electric field to the optical waveguide layer 60. The PAD unit 74 is connected to an electric signal line that supplies a modulation voltage (signal voltage) that changes the electric field applied to the optical waveguide layer 60 (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2001-117058

  FIG. 6 is a diagram showing the distribution of the amount of light absorption in the optical waveguide layer 60 of the EA modulator 50. As shown in the figure, the amount of absorption of light input to the EA modulator 50 is highest at the input end 60a of the optical waveguide layer 60, and gradually decreases as it approaches the output end 60b.

  When light is absorbed in the optical waveguide layer 60, that is, when light is converted into holes and electrons in the optical waveguide layer 60, a conversion loss always occurs. Since the energy lost here becomes thermal energy, the amount of heat generation increases as the amount of light absorption increases. For this reason, the distribution of the heat generation amount in the optical waveguide layer 60 shows the same tendency as the light absorption amount shown in FIG. That is, the amount of heat generated in the optical waveguide layer 60 is highest at the input end 60a, and gradually decreases as it approaches the output end 60b.

  However, in the conventional EA modulator 50, the electrode width in the vicinity of the input end 60a having the largest amount of heat generation is narrow, and the wide PAD portion 74 to which the electric signal line is connected is disposed near the center of the mesa portion 72. Therefore, heat dissipation through the p-side electrode 70 is not sufficiently performed, and as a result, the frequency characteristics of the EA modulator 50 may be deteriorated (modulation error rate increases due to deterioration of the extinction ratio).

  An object of the present invention is to provide an electroabsorption modulator having high heat dissipation and excellent frequency characteristics.

  In order to solve the above problems, an electroabsorption modulator according to the present invention includes a semiconductor substrate, an optical waveguide layer whose amount of light absorption changes according to an applied electric field, and an input end of the optical waveguide layer. An electric field in which a signal electrode for applying an electric field to the optical waveguide layer having a mesa region extending along a path of light that is input and output from an output end and a pad region to which an electric signal line is connected is formed. In the absorption modulator, the signal electrode has heat conductivity from the partial region on the input end side in the mesa region to the pad region, and from the partial region on the output end side in the mesa region to the pad region. It is characterized by having a shape that is higher than the heat transfer property.

  According to the present invention, heat generated in the vicinity of the input end of the optical waveguide layer that generates a large amount of heat can be efficiently dissipated through the signal electrode (particularly, the pad region to which the electric signal line is connected). Further, the frequency characteristics and the extinction characteristics of the electroabsorption modulator are improved by improving the heat dissipation.

  In one embodiment of the present invention, the signal electrode further includes a band-shaped region that connects the pad region and a partial region on the input end side of the mesa region that is spaced apart from the pad region. . According to this aspect, heat generated in the vicinity of the input end of the optical waveguide layer that generates a large amount of heat is easily conducted to the pad region of the signal electrode, so that the heat dissipation of the electroabsorption modulator is improved.

  In this aspect, the width of the band-like region may be smaller than the width of the pad region. By doing so, an increase in capacitance due to the band-like region of the signal electrode is suppressed, and the high frequency characteristics of the electroabsorption modulator are improved.

  In one embodiment of the present invention, the pad region is disposed closer to the input end than the central portion of the mesa region. According to this aspect, since the distance between the input end of the optical waveguide layer having a large calorific value and the pad region of the signal electrode is reduced, the heat dissipation of the electroabsorption modulator is further improved.

  In one embodiment of the present invention, the pad region is in contact with (directly connected to) the partial region on the input end side of the mesa region. According to this aspect, since the distance between the input end of the optical waveguide layer having a large heat generation amount and the pad region of the signal electrode is minimized, the heat dissipation of the electroabsorption modulator is improved.

  In this aspect, the pad region may be arranged away from the end surface so that the pad region does not contact the end surface on the input end side of the semiconductor substrate. By so doing, it is possible to prevent the pad region from peeling off from the substrate surface.

  According to the present invention, heat generated in the vicinity of the input end of the optical waveguide layer that generates a large amount of heat can be efficiently dissipated through the signal electrode (particularly, the pad region to which the electric signal line is connected). Further, the frequency characteristics of the electroabsorption modulator are improved due to the improvement in heat dissipation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same component and duplication description is abbreviate | omitted.

[Embodiment 1]
FIG. 1 is a top view of an EA modulator 10 according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing a II-II section of the EA modulator 10 shown in FIG.

  As shown in FIG. 2, the EA modulator 10 includes an n-type InP substrate 30 and an optical waveguide layer (mesa) 32 formed on the n-type InP substrate 30 by a known selective growth method using a metal organic vapor phase method. a p-type InP clad layer 34, an InGaAs contact layer 36, a buried layer 38, a p-side electrode (signal electrode) 40 and an n-side electrode (ground electrode) 48 formed by a known vapor deposition method and etching method. Composed. The thickness of the EA modulator 10 is, for example, about 100 μm.

  The optical waveguide layer 32 includes an InGaAsP lower light guide layer, a multiple quantum well layer composed of an InGaAsP well layer and a barrier layer, and an InGaAsP upper light guide layer. Further, as shown in FIG. 2, the optical waveguide layer 32 is sandwiched between the left and right sides by a buried layer 38, and has a width of 1.5 to 3 μm, for example. The optical waveguide layer 32 realizes a PIN junction together with the p-type InP clad layer 34 and the n-type InP substrate. Light is input to the optical waveguide layer 32 from the input end 32a, and signal light is output from the output end 32b.

  As shown in FIGS. 1 and 2, the p-side electrode 40 includes a mesa portion 42 (width 8 to 20 μm) formed to be positioned above the optical waveguide layer 32 in order to apply an electric field to the optical waveguide layer 32. A PAD portion 44 (one side 50-100 μm) to which an electrical signal line (not shown) (diameter of about 25 μm) is connected, and a strip-shaped PAD connection portion 46 that connects the mesa portion 42 and the PAD portion 44 that are arranged apart from each other. (Width 5 to 10 μm), and an electrode having a thickness of about 0.7 μm.

  As shown in FIG. 2, the n-side electrode 48 is formed on the entire back surface of the n-type InP substrate 30 and is an electrode having a thickness of about 0.8 μm to which a ground potential is applied.

  When a modulation voltage (signal voltage) is applied between the p-side electrode 40 and the n-side electrode 48 via an electric signal line, a modulated electric field is applied to the optical waveguide layer 32 from the p-side electrode 40 toward the n-side electrode 48. Is applied. Part or all of the light incident from the input end 32a of the optical waveguide layer 32 is absorbed by the optical waveguide layer 32 by this modulation electric field. As described above (see FIG. 6), the amount of heat generated in the optical waveguide layer 32 due to light absorption is maximized at the input end 32a and gradually decreases as it approaches the output end 32b.

  In the first embodiment, a PAD connection portion 46 that connects a partial region of the mesa portion 42 on the input end 32 a side and the PAD portion 44 is provided on the p-side electrode 40. That is, the p-side electrode is set so that the heat transfer from the partial region on the input end 32 a side of the mesa unit 42 to the PAD unit 44 is higher than the heat transfer from the partial region on the output end 32 b side of the mesa unit 42 to the PAD unit 44. Forty shapes are formed. Thereby, the heat generated near the input end 32a of the optical waveguide layer 32 can be efficiently dissipated through the p-side electrode 40, in particular, the PAD portion 44 to which the electric signal line is connected.

  The PAD portion 44 of the p-side electrode 40 may be disposed on the output end 32b side from the position shown in FIG. 1, but it is desirable that the PAD portion 44 be disposed further on the input end 32a side than the position shown in FIG. By doing so, the distance between the input end 32a of the optical waveguide layer 32 having a large calorific value and the PAD portion 44 is reduced, so that the heat dissipation of the EA modulator 10 is further improved.

  Further, the width of the band-shaped PAD connection portion 46 is not limited to the width shown in FIG. 1, but is desirably at least smaller than the vertical width or the horizontal width of the PAD portion 44. As can be seen from FIG. 2, the p-side electrode 40 and the n-side electrode 48 constitute a capacitor, and the high frequency characteristics of the EA modulator 10 are improved by suppressing an increase in the capacitance of the capacitor. .

[Embodiment 2]
FIG. 3 is a top view of the EA modulator 12 according to the second embodiment of the present invention. The EA modulator 12 has a configuration similar to that of the EA modulator 10 according to the first embodiment, but the shape of the p-side electrode 40 is different from that of the EA modulator 10 as shown in FIG.

  That is, as shown in FIG. 3, the p-side electrode 40 of the EA modulator 12 is a mesa portion 42 (width 8) formed to be positioned above the optical waveguide layer 32 in order to apply an electric field to the optical waveguide layer 32. ˜20 μm) and a PAD portion 44 (one side: 50-100 μm) to which an electric signal line (diameter of about 25 μm) (not shown) is connected, is an electrode having a thickness of about 0.7 μm.

  In the second embodiment, the PAD unit 44 is in contact with the partial region of the mesa unit 42 on the input end 32a side (directly connected) so that the distance between the input end 32a of the optical waveguide layer 32 and the PAD unit 44 is minimized. ing). That is, the p-side electrode is set so that the heat transfer from the partial region on the input end 32 a side of the mesa unit 42 to the PAD unit 44 is higher than the heat transfer from the partial region on the output end 32 b side of the mesa unit 42 to the PAD unit 44. Forty shapes are formed. Thereby, the heat generated near the input end 32a of the optical waveguide layer 32 can be efficiently dissipated through the p-side electrode 40, in particular, the PAD portion 44 to which the electric signal line is connected.

  Note that a gap may be formed between the PAD portion 44 and the end face so that the PAD portion 44 of the p-side electrode 40 does not contact the end face on the input end 32a side of the semiconductor substrate. In this way, it is possible to prevent the PAD part from peeling off from the substrate surface.

  According to the EA modulators 10 and 12 described above, heat generated in the vicinity of the input end 32a of the optical waveguide layer 32 having a large calorific value is transmitted through the p-side electrode 40, particularly, the PAD portion 44 to which the electric signal line is connected. Can be dissipated efficiently. Further, the frequency characteristics of the EA modulator can be improved by improving the heat dissipation.

  The present invention is not limited to the above embodiment, and can be applied to all EA modulators. That is, the structure, material, and dimensions of the EA modulator shown in the above embodiment are merely examples, and the present invention may be applied to an EA modulator configured with other structures, materials, and dimensions. Further, the present invention may be applied to an EA modulator integrated semiconductor laser (see FIG. 4) monolithically integrated with a semiconductor laser.

  Further, the shape of the PAD portion of the signal electrode is not limited to a square as long as an area for connecting the electric signal line is secured, and may be a circle or a triangle, for example.

1 is a top view of an EA modulator according to Embodiment 1 of the present invention. It is sectional drawing which shows the II-II cut surface of the EA modulator shown in FIG. It is a top view of the EA modulator which concerns on Embodiment 2 of this invention. It is a top view of the EA modulator integrated semiconductor laser which concerns on other embodiment of this invention. It is a top view of the conventional EA modulator. It is a figure which shows distribution of the light absorption amount in the optical waveguide layer of an EA modulator.

Explanation of symbols

  10, 12, 16, 50 Electroabsorption modulator (EA modulator), 14 Semiconductor laser unit, 18 EA modulator integrated semiconductor laser, 30 n-type InP substrate, 32, 60 Optical waveguide layer (mesa), 32a, 60a Input end of optical waveguide layer, 32b, 60b Output end of optical waveguide layer, 34 p-type InP cladding layer, 36 InGaAs contact layer, 38 buried layer, 40, 70 p-side electrode (signal electrode), 41 p-side electrode, 42 , 72 Mesa part, 44, 74 PAD part, 46 PAD connection part, 48 n side electrode (ground electrode).

Claims (6)

An optical waveguide layer in which the amount of light absorption changes in accordance with an electric field applied to the semiconductor substrate, and a mesa region that extends along the path of light that is input to the input end of the optical waveguide layer and output from the output end An electroabsorption modulator having a pad region to which an electric signal line is connected and a signal electrode for applying an electric field to the optical waveguide layer,
In the signal electrode, heat transfer from the partial region on the input end side in the mesa region to the pad region is higher than heat transfer from the partial region on the output end side in the mesa region to the pad region. Have a shape,
An electroabsorption modulator characterized by that. The electroabsorption modulator according to claim 1,
The signal electrode further includes a band-shaped region that connects the pad region and a partial region on the input end side of the mesa region that is disposed apart from the pad region.
An electroabsorption modulator characterized by that. The electroabsorption modulator according to claim 2,
The width of the band-like region is smaller than the width of the pad region,
An electroabsorption modulator characterized by that. The electroabsorption modulator according to any one of claims 1 to 3,
The pad region is disposed closer to the input end than the center of the mesa region.
An electroabsorption modulator characterized by that. The electroabsorption modulator according to claim 1,
The pad region is in contact with the partial region on the input end side of the mesa region;
An electroabsorption modulator characterized by that. The electroabsorption modulator according to claim 5, wherein
The pad region is not in contact with the end surface on the input end side of the semiconductor substrate,
An electroabsorption modulator characterized by that.

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