JP6196182B2 - Semiconductor photo detector - Google Patents

Description

  The present invention relates to a semiconductor light receiving device in which a plurality of photodiodes are arranged.

  A photodiode (PD), which is a semiconductor light receiving element, is one of important key devices constituting an optical communication system, and the development of the system is progressing in response to the explosive increase in communication traffic in recent years. Various requests are received including this.

  For example, as an increase in capacity of an optical communication system, differential (differential) phase shift keying (DPSK), differential quadrature phase shift keying (DQPSK), or digital coherent technology is used. Multi-level modulation technology has been actively developed.

  Accordingly, the light receiving device is required to be multi-channeled in which a plurality of photodiodes are arranged and integrated on one chip. In the case of a single photodiode, development toward high speed and high sensitivity is progressing as an improvement in element characteristics. However, in the case of multi-channeling, a new problem of optical mounting will arise.

  Conventionally, photodiodes are arranged for the necessary channels, and light is incident from a multi-core fiber or the like. In order to obtain high coupling efficiency, a microlens array or the like has been used for coupling light (see Non-Patent Document 1). However, these configurations have a problem that the cost of parts is high and mounting is difficult.

  On the other hand, if a single lens having a large diameter is used for light coupling, the component cost can be reduced. However, with a single lens configuration, there is a problem that the tolerance at the time of mounting becomes small and the difficulty of mounting increases.

  Hereinafter, the tolerance at the time of mounting by the single lens mentioned above is demonstrated using FIG. FIG. 5 is a plan view showing a configuration of a multi-channel light receiving device in which four photodiodes 502a, 502b, 502c, and 502d are arranged in a line in the x-axis direction on a chip 501. FIG. The photodiodes 502a, 502b, 502c, and 502d are surface light receiving types, and the effective light receiving surface 512 is circular. This is, for example, a multi-channel light receiving device mounted on a photoelectric conversion module used in a 40 Gbit / s-DQPSK optical communication system. FIG. 5 does not show the lens.

  In the DQPSK system, since I-ch and Q-ch signals are respectively received differentially, a total of four photodiodes are required. As shown in FIG. 5, four photodiodes are included in one chip 501. 502 is integrated.

  Assume that light is incident on a general 4-fiber with a pitch of 250 μm, and light is incident on a single lens in order to reduce the cost of the module. Here, assuming that the focal length of the lens is 150 μm and the distance from the fiber to the lens is 300 μm, light is incident at a multiplication factor of 1 on the center of the light receiving surface of each photodiode with respect to the 4ch photodiode array. Can do. In general, in light mounting, tolerance in the optical axis direction is considered to be large. This is because when the light beam deviates from the optimum position in the optical axis direction, the multiplication factor changes and the light spot size also changes, but the irradiation position of the irradiated spot does not change, so that there is no significant difference in coupling efficiency. .

T. Ohyama et al., "All-in-One 112-Gb / s DP-QPSK Optical Receiver Front-End Module Using Hybrid Integration of Silica-Based Planar Lightwave Circuit and Photodiode Arrays", IEEE PHOTONICS TECHNOLOGY LETTERS, vol.24, no.8, pp.646-648, 2012.

  However, when the light from the multi-core fiber is collected by a single lens, the light spot in the peripheral part away from the central part of the array as illustrated in FIG. 5 due to the shift in the optical axis direction and the change in the multiplication factor. In 512a and 512d, not only the spot size but also the irradiation position is shifted from the center of the corresponding photodiode 502a and 502d.

  For example, if a shift of 5 μm occurs in the optical axis direction when light is incident on the single lens, the multiplication factor is changed from 1 to 1.03. As a result, when the light emitted from the four-core fiber passes through the lens and forms an image, each spot size is only enlarged from 10 μm to 10.3 μm, but the pitch is changed from 250 μm to 257.5 μm. For this reason, the light (spot) from the peripheral fiber away from the center of the array is shifted by 11.25 μm from the center of the light receiving surface of the photodiode. As described above, in the configuration of the single lens, there is a problem that the irradiation position of the light emitted from the peripheral fiber with respect to the central portion of the array is greatly shifted with respect to the central portion of the array due to the shift in the optical axis direction.

  The present invention has been made to solve the above-described problems. In a configuration in which a plurality of arranged photodiodes are optically coupled with a single lens, positional deviation in the optical axis direction occurs. However, it is an object of the present invention to irradiate the photodiodes around the array without shifting light.

A semiconductor light-receiving device according to the present invention includes four or more surface-receiving photodiodes arranged on a substrate, and one lens that couples light to the plurality of photodiodes. The effective light-receiving surface is formed in an isotropic shape as the portion is closer, and the effective light-receiving surface is formed in a longer shape in the arrangement direction as it is farther from the central portion of the array, and the areas of the effective light-receiving surfaces of the plurality of photodiodes are equal. In the photodiode, it is only necessary that the effective light receiving surface be closer to a circle at the center of the array, and that the effective light receiving surface be longer in the array direction as it is farther from the center of the array.

  As described above, according to the present invention, in a configuration in which a plurality of arranged photodiodes are optically coupled with a single lens, even if a positional shift in the optical axis direction occurs, the photodiodes in the periphery of the array On the other hand, it is possible to obtain an excellent effect that light can be irradiated without shifting.

FIG. 1 is a plan view showing a configuration of a semiconductor light receiving device according to an embodiment of the present invention. FIG. 2 is a plan view showing the configuration of the semiconductor light receiving device according to the embodiment of the present invention together with the state of the irradiated light. FIG. 3 is a plan view showing the configuration of the semiconductor light receiving device according to the embodiment of the present invention together with the state of the irradiated light. FIG. 4 is a plan view showing the configuration of the semiconductor light receiving device according to the embodiment of the present invention together with the state of the irradiated light. FIG. 5 is an explanatory diagram for describing tolerance when the semiconductor light-receiving device is mounted using a single lens.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing a configuration of a semiconductor light receiving device according to an embodiment of the present invention.

  This semiconductor light receiving device includes surface-receiving photodiodes 102 and 103 arranged on a substrate 101. Although the case where the four photodiodes 102 and 103 are provided is illustrated in the embodiment, the number of photodiodes may be four or more.

  In the photodiodes 102 and 103, the planar shape of the effective light receiving surface is isotropic at the center of the array, and the planar shape of the effective light receiving surface is longer in the array direction as it is farther from the center of the array. . The “isotropic shape” indicates a point-symmetric shape such as a circle, a square, or a regular hexagon. For example, the effective light receiving surface may have a shape closer to a circle at the center of the array, and the oval shape may be longer in the array direction as the distance from the center of the array increases. In the embodiment, the photodiode 102 at the center of the array has a circular effective light receiving surface 112. On the other hand, in the photodiode 103 that is separated from the central portion of the array, the effective light receiving surface 113 has an oval shape (race track type) that is longer in the array direction (x-axis direction).

  The plurality of photodiodes 102 and 103 have the same effective light receiving surfaces 112 and 113. For example, the effective light receiving surface 112 is circular with a diameter of 20 μm. On the other hand, the effective light receiving surface 113 has a minor axis direction (y-axis direction) of 12 μm and a major axis direction (x-axis direction) of 29 μm. Note that the intervals between the centers of the plurality of photodiodes 102 and 103 are equal, for example, 250 μm.

  As a specific example, in a single lens system having a focal length of 150 μm, light from a four-core fiber having an arrangement interval (pitch) of 250 μm and a core diameter of 10 μm is coupled to the photodiodes 102 and 103 of the semiconductor light receiving device in the embodiment. Think about it. If the distance from the lens to the fiber is 300 μm, light with a mode field diameter of 10 μm is imaged at a pitch of 250 μm at a position 300 μm from the lens. Accordingly, when the photodiodes 102 and 103 are arranged at the light image formation positions, spot lights 201a, 201b, 201c, and 201d having a mode field diameter of 10 μm are arranged at the center positions of the photodiodes 102 and 103 as shown in FIG. Will be incident.

  Here, consider a case where the distance from the lens to the fiber is 295 μm shifted by 5 μm in the optical axis traveling direction. In this case, although the multiplication factor is 1.03, the spot light 201a and 201d emitted from the fiber at the end of the array and imaged has a mode field diameter of 10.6 μm. Further, as shown in FIG. 3, the spot lights 201a and 201d are incident on a position shifted by 11.25 μm from the center of the effective light receiving surface 113 of the photodiode 103 disposed in the peripheral portion to the peripheral side. On the other hand, according to the embodiment, in the photodiode 103, since the planar shape of the effective light receiving surface 113 is longer in the arrangement direction, the spot lights 201a and 201d are contained in the area of the effective light receiving surface 113. Does not cause deterioration of bonding.

  Next, consider a case where the distance from the lens to the fiber is 305 μm, shifted by 5 μm in the direction opposite to the light travel. In this case, although the multiplication factor is 0.97, the spot light 201a and 201d emitted from the fiber at the end of the array and imaged has a mode field diameter of 9.68 μm. As shown in FIG. 4, the spot lights 201a and 201d are incident on a position shifted by 11.25 μm from the center of the effective light receiving surface 113 of the photodiode 103 arranged in the peripheral portion toward the array center. Even in this case, according to the embodiment, since the effective light receiving surface 113 has a longer planar shape in the arrangement direction in the photodiode 103, the spot lights 201a and 201d are within the region of the effective light receiving surface 113. Fits and does not degrade the bond.

  As described above, in the present invention, among four or more surface-receiving photodiodes arranged on a substrate, the effective light-receiving surface is longer in the arrangement direction as the photodiode is farther from the center of the array. Shaped. Thereby, according to the present invention, in the configuration in which the plurality of arranged photodiodes are optically coupled with one lens, even if the positional deviation in the optical axis direction occurs, Light is irradiated (coupled) without shifting.

  The present invention relates to a semiconductor light-receiving device using a photodiode array in which a plurality of photodiodes are integrated on one chip, such as used in a large-capacity optical communication system using a multi-level modulation system. Thus, even when a single lens system is adopted as a cost reduction when assembling the photoelectric conversion module, a high-performance module can be produced without impairing mounting tolerance.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, various structures such as pin-PD and UTC-PD can be applied to the photodiode, and an avalanche photodiode may be used.

  Further, the planar shape of the effective light receiving surface is not limited to a combination of a circle and an ellipse, and may be a square and a rectangle, or a polygon. As long as the effective light receiving surface has a shape closer to point symmetry toward the center of the array and becomes longer in the array direction toward the periphery, any form may be used. However, in general, the light spot system is circular, and considering the ease of manufacturing a photodiode, the combination of circular and oval is efficient.

  DESCRIPTION OF SYMBOLS 101 ... Board | substrate, 102 ... Photodiode, 103 ... Photodiode, 112 ... Effective light-receiving surface, 113 ... Effective light-receiving surface, 201a, 201b, 201c, 201d ... Spot light.

Claims (2)

Four or more surface-receiving photodiodes arranged on a substrate, and one lens for coupling light to the plurality of photodiodes ,
The photodiode is
The effective light receiving surface is isotropic in the center of the array,
The further away from the center of the array, the longer the effective light receiving surface is in the array direction,
The plurality of photodiodes have equal areas of effective light receiving surfaces. A semiconductor light receiving device, wherein: The semiconductor light receiving device according to claim 1,
The photodiode is
The effective light receiving surface is closer to a circle at the center of the array,
A semiconductor light-receiving device, wherein an effective light-receiving surface has an elliptical shape that is longer in the arrangement direction as it is farther from the center of the arrangement.

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