JP2009003007A - Light receiving element module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light receiving element module allowing incidence of light with a substantially uniform intensity distribution in a light receiving diameter and efficiently obtaining high-output RF power. <P>SOLUTION: The light receiving element module is provided with a single-mode optical fiber 2, a step-index multimode optical fiber 3 facingly connected to the single-mode optical fiber, an optical lens 4 transferring an image of light output via the single-mode optical fiber 2 and the step-index multimode optical fiber 3, and a light receiving element 1 receiving light from the optical lens 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light receiving element module that requires high output RF power.

  The light receiving element is used in an optical communication system. For digital signal transmission, it has been mainly used to detect microwatt-level faint light with high sensitivity, and for analog signal transmission, to eliminate distortion of received signals. Has been considered. On the other hand, in recent years, it has been studied that a watt-class light whose intensity is modulated at a high frequency (hereinafter referred to as RF) is incident on a light receiving element to obtain a high-power RF output.

  In a light receiving element module that includes a light receiving element, an optical fiber, and an optical lens system that optically couples them, when the light incident from the optical fiber is imaged on the light receiving surface, the light intensity density near the center of the incident light is Get higher. For this reason, a large amount of heat is intensively generated in the vicinity of the center, and a phenomenon that the received RF power is weakened occurs. Furthermore, the element may be damaged. Further, since the light density of the input light is high, it is greatly affected by the space charge effect.

  Therefore, in the conventional semiconductor light receiving element module, in order to reduce the light intensity density near the center, a lens that is in a non-focal state with respect to the i layer serving as the light absorption layer is formed on the semiconductor substrate. As a result, even when strong light is incident, it is possible to prevent a decrease in internal electric field strength by spreading the incident light over the entire light receiving surface of the light receiving element without concentrating the light from the optical fiber at one point. (For example, refer to Patent Document 1).

JP-A-4-342174

However, the prior art has the following problems.
In the light receiving element module described in Patent Document 1 described above, the incident light spot diameter is defocused and incident on the light receiving unit in order to prevent a decrease in electric field strength. However, the shape of the Gaussian beam itself is not improved, and the spot diameter of the Gaussian beam is only slightly increased, so that there is a difference in intensity distribution between the central portion and the outside within the light receiving diameter.

  Furthermore, if defocusing is performed, it is possible to make light having a substantially uniform intensity distribution within the light receiving diameter. However, in such a case, most of the entire beam deviates from the light receiving diameter, and the efficiency of the output RF power with respect to the entire incident light power becomes very poor.

  The present invention has been made in order to solve the above-described problems, and is a light receiving element capable of receiving light having a substantially uniform intensity distribution within a light receiving diameter and obtaining high output RF power with high efficiency. The purpose is to obtain a module.

  The light receiving element module according to the present invention includes a single mode optical fiber, a step index type multimode optical fiber bonded to face the single mode optical fiber, the single mode optical fiber, and the step index type multimode optical fiber. And an optical lens for image transfer of the output light and a light receiving element for receiving the light from the optical lens.

  According to the present invention, a single mode optical fiber and a step index type multimode optical fiber are joined to form an optical fiber, and a beam incident on the light receiving element from the step index type multimode optical fiber has a substantially uniform intensity. By keeping all incident light within the light receiving diameter and further suppressing the heat generated within the light receiving diameter, light with a substantially uniform intensity distribution is incident on the light receiving diameter and high output RF power is increased. A light receiving element module that can be obtained efficiently can be obtained.

  Hereinafter, preferred embodiments of a light receiving element module of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional structure diagram showing an optical arrangement of a light receiving element module according to Embodiment 1 of the present invention. The light receiving element module of FIG. 1 includes a light receiving element 1, a single mode optical fiber 2, a step index type multimode optical fiber 3, an optical lens 4, and a heat sink 5.

  The light receiving element 1 is a back-illuminated InGaAS / InP PIN photodiode, and has a light receiving diameter of φ50 μm on the light receiving surface. Further, the light receiving surface 1 a side (that is, the back surface side) of the light receiving element 1 is bonded to the heat sink 5.

  The single mode optical fiber (SM fiber) 2 is an optical fiber through which light is transmitted in a single mode, and the step index type multimode optical fiber (SI fiber) 3 has a refractive index only at the interface between the core and the cladding. These optical fibers are continuously changed, and both have a core diameter of 40 to 50 μm and a length of 0.3 to 0.4 mm. Further, the single mode optical fiber 2 and the step index type multimode optical fiber 3 are fused to each other at the joint surface 6.

  The optical lens 4 may be any lens system having a numerical aperture (NA) of 0.2 or more and capable of transferring an image to the same size as the light receiving diameter φ50 μm of the light receiving element. For example, assuming that the beam diameter emitted from the step index type multimode optical fiber 3 is φ40 μm, when a collimating lens having a focal length of 10 mm is used, the step index type multimode optical fiber 3 and the optical lens 4 are arranged. The distance is 8 mm, and the distance between the optical lens 4 and the light receiving element 1 is 10 mm.

  Next, the operation will be described. First, the Gaussian beam having a beam diameter of φ10 μm emitted from the single mode optical fiber 2 is flattened by using the step index type multimode optical fiber 3 as a multimode interference element.

  FIG. 2 is a diagram showing a state of an electric field distribution in the step index type multimode optical fiber 3 of the light receiving element module according to Embodiment 1 of the present invention. A waveform (1) in FIG. 2 is an incident beam from the single mode optical fiber 2. Waveform (2) and waveform (3) are beam shapes at positions of 0.3 mm and 0.4 mm from the incident end, respectively.

  Depending on the position in the step index type multimode optical fiber 3, the shape of the beam changes every moment. Under the present conditions, it is about 0.3 mm to 0.4 mm from the incident end of the step index type multimode optical fiber 3. The incident beam from the single mode optical fiber 2 is most flattened.

  Therefore, the length of the step index type multimode optical fiber 3 is set to 0.3 to 0.4 mm. By transferring an image of the flattened beam with the optical lens 4 in this way, a beam having the same size of φ50 μm can be made incident on the light receiving element 1 having a light receiving diameter of φ50 μm.

  As described above, according to the first embodiment, the periphery of the Gaussian beam emitted from the single mode optical fiber is reflected and combined by the step index type multimode optical fiber, and the light intensity distribution becomes uniform to some extent. An image of the beam is transferred to form an image on the light receiving surface of the back-illuminated light receiving element. As a result, the light intensity density per unit area of the light beam collected within the light receiving diameter is greatly reduced compared to the case where the light beam is collected by the Gaussian beam as it is, and the heat is concentrated. Generation can be suppressed.

  Further, the back side of the light receiving element is bonded to a heat sink. Since the light receiving element is a back-illuminated type, the light absorption layer is close to the heat sink, and the heat exhaust design is excellent. As a result, the obtained received RF power is increased and the element is prevented from being damaged.

  Further, a step index type multimode optical fiber is used as the multimode interference element. Thus, the light receiving element module can be configured only by fusing the step index type multimode optical fiber to the single mode optical fiber. That is, it can be manufactured very easily and is excellent in terms of cost. Furthermore, since both fibers are fused, there is little loss and it is strong against high power incidence.

  Note that the same effect can be obtained by using a hollow fiber or a mirror-like tube capable of reflecting the peripheral portion of the Gaussian beam from the single mode optical fiber instead of the step index type multimode optical fiber.

Embodiment 2. FIG.
FIG. 3 is a cross-sectional structure diagram showing an optical arrangement of the light receiving element module according to Embodiment 2 of the present invention. The light receiving element module of FIG. 3 includes a light receiving element 1, a single mode optical fiber 2, a step index type multimode optical fiber 3, an optical lens 4 a, and a heat sink 5. Compared with the configuration of FIG. 1 in the first embodiment, in the configuration of FIG. 3 in the second embodiment, the optical lens 4 a is bonded to the step index type multimode optical fiber 3, and the optical mode is changed from the single mode optical fiber 2. The difference is that the lens 4a is integrated.

  In the first embodiment, if the position of the optical lens 4 is not strictly determined and there is a desire to change the distance between the step index type multimode optical fiber 3 and the optical lens 4, it is flexible. It is a light receiving element module that can be used. However, since the optical lens 4 is externally provided, it takes time to position the lens.

  On the other hand, in the second embodiment, since the single mode optical fiber 2 to the optical lens 4a are integrated, the distance to the light receiving element 1 is strictly determined, and the lens positioning operation becomes easy.

  As described above, according to the second embodiment, the structure is such that the optical lens is bonded to the step index type multimode optical fiber, and the single mode optical fiber to the optical lens are integrated. As a result, the optical lens can be easily positioned with respect to the light receiving element.

Embodiment 3 FIG.
FIG. 4 is a cross-sectional structure diagram showing an optical arrangement of the light receiving element module according to Embodiment 3 of the present invention. The light receiving element module of FIG. 4 includes a light receiving element 1, a single mode optical fiber 2, a step index type multimode optical fiber 3, and a heat sink 5. Compared with the configuration of FIG. 1 in the previous embodiment 1 or the configuration of FIG. 3 in the previous embodiment 2, the configuration of FIG. 4 in the present embodiment 3 differs in that no optical lens is provided. .

  In the second embodiment, the beam emitted from the step index type multimode optical fiber 3 is directly incident on the light receiving element 1 without passing through the optical lens.

  Since the beam emitted from the step index type multimode optical fiber 3 has a numerical aperture (NA) of about 0.2, a step is required to keep all the light within the light receiving diameter of the light receiving element 1. It is necessary to have a light receiving diameter larger than the diameter of the index type multimode optical fiber 3 and to make the step index type multimode optical fiber 3 and the light receiving element 1 very close to each other.

  Therefore, such a condition can be satisfied by adopting the configuration shown in FIG. 4 without the optical lens. Further, the cost can be reduced by eliminating the optical lens.

  As described above, according to the third embodiment, the same effect as in the first and second embodiments can be realized with the configuration without the optical lens, and the cost of the light receiving element module can be reduced.

Embodiment 4 FIG.
FIG. 5 is a cross-sectional structure diagram showing an optical arrangement of the light receiving element module according to Embodiment 4 of the present invention. The optical element module in FIG. 5 corresponds to a configuration in which the two configurations in FIG. 1 in the first embodiment are connected in parallel.

  The operations of the individual light receiving element modules constituting the parallel circuit are exactly the same as those in the first embodiment. Each received RF power obtained for each module is synthesized by using a matched RF power synthesis circuit 7.

  When the same power as the RF power obtained in the single configuration of FIG. 1 in the first embodiment is obtained by the parallel configuration as in FIG. 5 in the fourth embodiment, per module. The incident light intensity becomes weak, which leads to further prevention of heat generation.

  Further, the received RF power from one light receiving element module reaches saturation when the amount of received light exceeds a certain level. In contrast, by adopting a configuration in which two or more light receiving element modules are connected in parallel as in the fourth embodiment, power equal to or higher than the saturation value of the received RF power obtained by one light receiving element module is obtained. Obtainable.

  As described above, according to the fourth embodiment, the generation of heat can be suppressed by connecting a plurality of light receiving element modules according to the present invention in parallel, and the received RF power exceeding the saturation light receiving amount of one light receiving element module. Can be obtained.

  The light receiving element modules connected in parallel in the configuration of FIG. 5 are not limited to the configuration of FIG. 1 corresponding to the first embodiment, but the configuration of FIG. It is also possible to apply the configuration of FIG. 4 corresponding to the third embodiment.

It is a cross-section figure which shows the optical arrangement | positioning of the light receiving element module in Embodiment 1 of this invention. It is the figure which showed the mode of the electric field distribution in the step index type | mold multimode optical fiber 3 of the light receiving element module in Embodiment 1 of this invention. It is sectional structure drawing which shows the optical arrangement | positioning of the light receiving element module in Embodiment 2 of this invention. It is sectional structure drawing which shows the optical arrangement | positioning of the light receiving element module in Embodiment 3 of this invention. It is a cross-section figure which shows the optical arrangement | positioning of the light receiving element module in Embodiment 4 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Light receiving element (back-illuminated type light receiving element), 2 Single mode optical fiber, 3 Step index type multimode optical fiber, 4, 4a Optical lens, 5 Heat sink, 6 Fiber joint surface, 7 RF power synthetic | combination circuit.

Claims (8)

A single mode optical fiber;
A step index type multimode optical fiber joined to face the single mode optical fiber;
An optical lens for image transfer of light output via the single mode optical fiber and the step index type multimode optical fiber;
A light receiving element module comprising: a light receiving element that receives light from the optical lens. The light receiving element module according to claim 1,
The light-receiving element module is a back-illuminated photodiode or a back-illuminated avalanche photodiode, and is bonded to a heat sink on the light-receiving surface side. In the light receiving element module according to claim 1 or 2,
The step index type multimode optical fiber has a core diameter of 40 to 50 μm and a length of 0.3 to 0.4 mm. In the light receiving element module according to claim 1 or 2,
A light receiving element module comprising a hollow fiber or a mirror-like tube capable of reflecting a peripheral portion of a Gaussian beam from the single mode optical fiber instead of the step index type multimode optical fiber. In the light receiving element module according to any one of claims 1 to 4,
The single-mode optical fiber and the step index type multi-mode optical fiber are fused to each other. In the light receiving element module according to any one of claims 1 to 5,
The step index type multimode optical fiber and the optical lens are bonded to each other;
The light receiving element module, wherein the single mode optical fiber to the optical lens are integrated. In the light receiving element module according to any one of claims 1 to 5,
A light receiving element module, wherein a beam from the step index type multimode optical fiber is directly incident on a light receiving diameter of the light receiving element after removing the optical lens.   8. A light receiving element module comprising: two or more light receiving element modules according to claim 1 arranged in parallel, and a combined output of the light receiving element modules.

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