阅读说明：本技术 光模块及其制造方法 (Optical module and method for manufacturing the same ) 是由 小田拓弥 于 2018-04-02 设计创作，主要内容包括：本发明实现基板型光波导与光纤的耦合效率比以往高的光模块以及对这种光模块进行制造的制造方法。将沿着基板型光波导(11)的芯(111)被进行导波的波导模的端面处的模斑尺寸w1、以及沿着光纤(12)的芯(121)被进行导波的波导模的端面处的模斑尺寸w2设定为：将基板型光波导(11)的芯(111)与光纤(12)的芯(121)的轴偏移量为0时的基板型光波导(11)与光纤(12)的耦合效率η(0)和w2/w1＝1的情况相同的模斑尺寸比w2/w1设为α,满足1＜w2/w1＜α。(An optical module having a higher coupling efficiency between a substrate-type optical waveguide and an optical fiber than conventional optical modules and a method for manufacturing the optical module are provided, wherein a spot size w1 at an end surface of a waveguide guided along a core (111) of the substrate-type optical waveguide (11) and a spot size w2 at an end surface of a waveguide guided along a core (121) of the optical fiber (12) are set such that a spot size ratio w2/w1, which is the same as a case where an axial offset amount of the core (111) of the substrate-type optical waveguide (11) and the core (121) of the optical fiber (12) is 0, between a coupling efficiency η (0) of the substrate-type optical waveguide (11) and the optical fiber (12) and a spot size w2/w1 are equal to 1, is α, and 1 < w2/w1 < α is satisfied.)

1. An optical module is characterized by comprising:

a substrate-type optical waveguide; and

an optical fiber for guiding light inputted to the substrate-type optical waveguide or light outputted from the substrate-type optical waveguide,

a mode spot size w1 at an end face of a waveguide mode guided along a core of the substrate-type optical waveguide and a mode spot size w2 at an end face of a waveguide mode guided along a core of the optical fiber are set so as to satisfy 1 < w2/w1 < α, wherein α is a mode spot size ratio w2/w1 in a case where a coupling efficiency η (0) between the substrate-type optical waveguide and the optical fiber and the coupling efficiency η (0) when w2/w1 is 1 are the same, and the coupling efficiency η (0) is a coupling efficiency when an axial shift amount of the core of the substrate-type optical waveguide and the core of the optical fiber is 0.

2. The light module of claim 1,

the spot size w1 and the spot size w2 are set so as to satisfy β < w2/w1 < α, wherein a spot size ratio w2/w1 at which the coupling efficiency η (0) is maximized is set to β.

3. The light module of claim 1,

the spot size w1 and the spot size w2 are set to: satisfies 1 < w2/w1 < 1.662 xw 1^-3.554+1。

4. The light module of claim 3,

the spot size w1 and the spot size w2 are set to: satisfies 0.058w1⁴-0.668w1³+2.829w1²-5.268w1+4.706＜w2/w1＜1.662×w1^-3.554+1。

5. The light module of claim 1,

the spot size w1 and the spot size w2 are set to: satisfies 1 < w2/w1 < 4.195 xw 1^-3.168+1。

6. The light module of claim 5,

the spot size w1 and the spot size w2 are set to: satisfies 0.070w1⁴-0.827w1³+3.646w1²-7.229w1+6.614＜w2/w1＜4.195×w1^-3.168+1。

7. The light module of claim 1,

the spot size w1 and the spot size w2 are set to: satisfies 1 < w2/w1 < 9.253 xw 1^-2.733+1。

8. The light module of claim 7,

the spot size w1 and the spot size w2 are set to: satisfies 0.093w1⁴-1.097w1³+4.855w1²-9.872w1+9.217＜w2/w1＜9.253×w1^-2.733+1。

9. The light module of claim 1,

z represents a distance between the substrate-type optical waveguide and the end face of the optical fiber,

the spot size w1 and the spot size w2 are set to: satisfies 1 < w2/w1 < (0.506z-0.867) × w1^{(0.0531z-3.7715)}+1。

10. The light module of claim 9,

the spot size w1 and the spot size w2 are set to: satisfies (0.0023z +0.0465) w1⁴-(0.0284z+0.533)w1³+(0.133z+2.2245)w1²-(0.3008z+3.9465)w1+(0.295z+3.4045)＜w2/w1＜(0.506z-0.867)×w1^{(0.0531z-3.7715)}+1。

11. The optical module according to any one of claims 1 to 10,

the spot size w1 is 3 μm or less.

12. A method of manufacturing an optical module including a substrate-type optical waveguide and an optical fiber for guiding light input to or output from the substrate-type optical waveguide,

the manufacturing method is characterized in that the manufacturing method comprises the following steps,

the method includes a setting step of setting a spot size w1 at an end face of a waveguide mode guided along a core of the substrate-type optical waveguide and a spot size w2 at an end face of a waveguide mode guided along a core of the optical fiber to satisfy 1 < w2/w1 < α, wherein α is a spot size ratio w2/w1 when a coupling efficiency η (0) between the substrate-type optical waveguide and the optical fiber is equal to a coupling efficiency η (0) when w2/w1 is equal to 1, and the coupling efficiency η (0) is a coupling efficiency when an axial offset between the core of the substrate-type optical waveguide and the core of the optical fiber is 0.

13. The manufacturing method according to claim 12,

in the setting step, the spot size w1 and the spot size w2 are set to satisfy β < w2/w1 < α, and a spot size ratio w2/w1 at which the coupling efficiency η (0) is maximized is β.

Technical Field

The present invention relates to an optical module including a substrate-type optical waveguide and an optical fiber. The present invention also relates to a method for manufacturing such an optical module.

Background

In recent years, substrate-type optical waveguides such as silicon waveguides and indium phosphide waveguides have been developed with great force. In the above-described substrate-type optical waveguide, since the refractive index difference between the core and the clad is large and the light confinement effect is strong, the mode field diameter of the waveguide mode can be suppressed to 1 μm or less.

An optical fiber is generally used for input and output of light to and from a substrate-type optical waveguide. However, the mode field diameter of a waveguide mode in an optical fiber is generally larger than that of a waveguide mode in a substrate-type optical waveguide. For example, the mode field diameter of a waveguide mode in a typical silicon waveguide is about 0.2 μm, as opposed to about 10 μm in a typical single mode fiber. Therefore, in an optical module including a substrate-type optical waveguide and an optical fiber, it is important to eliminate mismatch in mode field diameter between the substrate-type optical waveguide and the optical fiber and to improve coupling efficiency between the substrate-type optical waveguide and the optical fiber.

As a method of eliminating the mismatch of the mode field diameter between the substrate-type optical waveguide and the optical fiber, there are a method of making the mode field diameter of the waveguide mode in the substrate-type optical waveguide larger near the incident/exit end face and a method of making the mode field diameter of the waveguide mode in the optical fiber smaller near the exit incident end face. As the former technique, for example, a technique is known in which a spot size converter is provided near the entrance/exit end surface of a substrate-type optical waveguide to enlarge the mode field diameter of the waveguide mode to about 3 to 4 μm. In the latter technique, for example, a technique is known in which the mode field diameter of the waveguide mode is reduced by lens processing the exit/entrance end surface of the optical fiber. By using the above-described techniques in combination, the coupling efficiency between the substrate-type optical waveguide and the optical fiber can be improved.

Another important point is to realize an optical module having high coupling efficiency between a substrate-type optical waveguide and an optical fiber. This is important in that the central axis of the core of the substrate-type optical waveguide and the central axis of the core of the optical fiber are aligned with high accuracy. This is because, if a slight axial displacement occurs between the core of the substrate-type optical waveguide and the core of the optical fiber, the coupling efficiency between the substrate-type optical waveguide and the optical fiber is significantly reduced. The axial shift caused by the expansion or contraction of the resin used to fix the optical fiber to the substrate-type optical waveguide causes a decrease in coupling efficiency during use, and therefore attention is required.

In the following equation, w1 is a size of a spot of a waveguide mode near an exit end surface of the substrate-type optical waveguide, and w2 is a size of a spot of a waveguide mode near an entrance end surface of the optical fiber, and z is a distance between an entrance end surface of the substrate-type optical waveguide and an exit end surface of the optical fiber, and x is a distance between a central axis of a core of the substrate-type optical waveguide and a central axis of the core of the optical fiber (hereinafter referred to as an "axial offset amount").

Formula 1

Fig. 8 shows a graph showing the relationship between the axial shift amount x and the coupling efficiency η given by the above expression when λ is 1.55 μm, w1 is 1.5 μm, and z is 5 μm, and it is understood from the graph shown in fig. 8 that if an axial shift of about 1 μm occurs between the core of the substrate-type optical waveguide and the core of the optical fiber, the coupling efficiency η between the substrate-type optical waveguide and the optical fiber decreases by about 2 dB.

In addition, in a conventional optical module, a configuration is generally adopted in which the spot size w1 on the substrate-type optical waveguide side is made larger than the spot size w2 on the optical fiber side (see patent document 1), or a configuration is adopted in which the spot size w1 on the substrate-type optical waveguide side is made close to the spot size w2 on the optical fiber side (see patent document 2), and the spot size w1 on the substrate-type optical waveguide side is made coincident with the spot size w2 on the optical fiber side.

Patent document 1: japanese laid-open patent publication No. 11-218626 "

Patent document 2: japanese laid-open patent publication No. 2001-242337 "

However, in the conventional optical module, there is room for improvement in coupling efficiency between the substrate optical waveguide and the optical fiber. Further, it is desirable to increase a margin for the axial misalignment (hereinafter, also referred to as "axial misalignment margin") with respect to the coupling efficiency so that the axial misalignment between the core of the substrate-type optical waveguide and the core of the optical fiber does not cause a significant decrease in the coupling efficiency.

Disclosure of Invention

The present invention has been made in view of the above-described problems, and an object thereof is to realize an optical module in which the coupling efficiency between a substrate-type optical waveguide and an optical fiber is higher than that of the conventional one.

In order to achieve the above object, an optical module according to one aspect of the present invention includes a substrate-type optical waveguide and an optical fiber for guiding light input to or output from the substrate-type optical waveguide, wherein a spot size w1 at an end surface of a waveguide mode guided along a core of the substrate-type optical waveguide and a spot size w2 at an end surface of a waveguide mode guided along a core of the optical fiber satisfy 1 < w2/w1 < α, wherein α is a coupling efficiency η (0) between the substrate-type optical waveguide and the optical fiber and a spot size ratio w2/w1 when a coupling efficiency η (0) when w2/w1 is 1 is the same, and a coupling efficiency η (0) is a coupling efficiency when an axial offset amount of the core of the substrate-type optical waveguide and a core of the optical fiber is 0.

In order to achieve the above object, a manufacturing method according to one aspect of the present invention is a manufacturing method of an optical module including a substrate-type optical waveguide and an optical fiber for guiding light input to or output from the substrate-type optical waveguide, the manufacturing method including a setting step of setting a spot size w1 of a waveguide mode guided along a core of the substrate-type optical waveguide and a spot size w2 of a waveguide mode guided along a core of the optical fiber to satisfy 1 < w2/w1 < α, where α is a coupling efficiency η (0) between the substrate-type optical waveguide and the optical fiber and a spot size ratio w2/w1 when a coupling efficiency η (0) is equal to w2/w1 ═ 1, and a coupling efficiency η (0) is a coupling efficiency when an axial offset amount of the core of the substrate-type optical waveguide and the core of the optical fiber is 0.

According to one embodiment of the present invention, a substrate-type optical waveguide in which the coupling efficiency η (0) is larger than that of the conventional one when the axial shift amount is 0 can be realized.

Drawings

Fig. 1 is a diagram showing a configuration of an optical module according to an embodiment of the present invention. (a) A plan view of the optical module, and (b) a sectional view of the optical module.

Fig. 2 is a side view of the core of the substrate-type optical waveguide and the core of the optical fiber. The mode distribution of a waveguide mode guided along each core is indicated in (a), and arrows indicating the axial offset x and the distance z between end faces are indicated in (b).

In fig. 3, (a) is a graph showing the coupling efficiency η [ dB ] as a function of the axial shift amount x [ μm ] for the case where the spot size ratio w2/w1 is 1, 1.2, 1.55, 2, 2.41, 2.8, (b) is a graph showing the rate of change d η/dx (1) [ dB/μm ] of the coupling efficiency η [ dB ] as a function of the spot size ratio w2/w1 when the axial shift amount x is 1, (c) is a graph showing the coupling efficiency η (0) [ dB ] as a function of the spot size ratio w2/w1 when the axial shift amount x is 0.

In fig. 4, (a) is a graph showing the coupling efficiency η (0) [ dB ] as a function of the spot size ratio w2/w1 when the axial offset x is 0 for a case where the inter-end surface distance z is 10 μm and the spot sizes w1 are 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, (b) is a graph showing the same spot size ratio α when the axial offset x is 0 and the same spot size ratio β when the axial offset x is 1 as a function of the spot size 96w 37 for a case where the inter-end surface distance z is 10 and the coupling efficiency η (0) when the axial offset x is 0, (c) is a graph showing the maximum spot size ratio η (0) and the maximum spot size ratio 2/w 6338 as a function of the same spot size ratio α and the maximum spot size ratio w η when the axial offset x is 0 and the same spot size ratio 1 and the maximum spot size ratio w η when the axial offset x is 0.

Fig. 5 is a graph of a curve α ═ a × w1 showing a pattern spot size ratio α which optimally approximates the graph shown in fig. 4 (c)^bGraph of the relationship between the coefficients a, b of +1 and the distance z between the end faces.

Fig. 6 is a graph of optimum approximation of the spot size ratio β shown in fig. 4 (c), in which curve β is aw1⁴+bw1³+cw1²Graph of the relationship between the coefficients a, b, c, d, e of + dw + e and the distance z between the end faces.

Fig. 7 is a graph showing the amount of coupling efficiency increase as a function of spot size w 1. (a) The graph is a graph in the case where z is 5 μm, (b) is a graph in the case where z is 10 μm, and (c) is a graph in the case where z is 20.

Fig. 8 is a graph showing a relationship between an axial displacement amount x and a coupling efficiency η of a conventional optical module.

Detailed Description

[ Structure of optical Module ]

A configuration of an optical module 1 according to an embodiment of the present invention will be described with reference to fig. 1. In fig. 1, (a) is a plan view of the optical module 1, and (b) is a cross-sectional view of the optical module 1 in an AA' cross section. In the following description, in the illustrated coordinate system, the positive X-axis direction is referred to as "up", the negative X-axis direction is referred to as "down", the positive Y-axis direction is referred to as "right", the negative Y-axis direction is referred to as "left", the positive Z-axis direction is referred to as "front", and the negative Z-axis direction is referred to as "rear". However, the descriptions of "up", "down", "right", "left", "front", and "rear" are used merely for the sake of simplifying the structure of the optical module 1, and the arrangement of the optical module 1 is not limited at all.

As shown in fig. 1, the optical module 1 includes a substrate-type optical waveguide 11 and an optical fiber 12. The optical fiber 12 is an optical fiber for guiding input light to the substrate-type optical waveguide 11 or guiding output light to be output from the substrate-type optical waveguide 11.

The substrate-type optical waveguide 11 has a core 111 and a recess 112 formed in a substrate. In the present embodiment, a silicon waveguide in which the core 111 and the recess 112 are formed on an soi (silicon on insulator) substrate is used as the substrate-type optical waveguide 11. The substrate-type optical waveguide 11 is arranged such that, in the illustrated coordinate system, two main surfaces (upper surface and lower surface) face in the X-axis positive direction and the X-axis negative direction, and 4 side surfaces face in the Y-axis positive direction, the Y-axis negative direction, the Z-axis positive direction, and the Z-axis negative direction.

The recess 112 is a space formed at the rear end of the upper surface 11U of the substrate-type optical waveguide 11 and in which the distal end portion of the optical fiber 12 is disposed. The recess 112 is a rectangular parallelepiped recess which is open upward and rearward and is surrounded by the end surfaces of the substrate-type optical waveguide 11 downward, forward, rightward, and leftward, and is formed at a corner where the upper surface 11U and the rear surface 11B of the substrate-type optical waveguide 11 intersect.

The core 111 is a region for guiding light formed inside the substrate-type optical waveguide 11, and is made of a material (e.g., silicon) having a higher refractive index than other portions of the substrate-type optical waveguide 11 (e.g., a silica film functioning as a cladding layer). The core 111 is exposed at the end surface 11S of the planar optical waveguide 11 located in front of the recess 112. The center axis of the core 111 in the vicinity of the end face 11S is orthogonal to the end face 11S.

The substrate-type optical waveguide 11 may be provided with a spot size converter for amplifying the spot size of a waveguide mode guided along the core 111. When the spot size converter is provided, the spot size at the end surface 11S of the waveguide mode guided along the core 111 can be enlarged to about 3 μm or 1.5 μm, for example. The path of the core 111 inside the planar optical waveguide 11 is arbitrary in a portion of the planar optical waveguide 11 not shown in fig. 1. The substrate-type optical waveguide 11 may be formed with a functional portion, not shown, that acts on light propagating along the core 111. For example, a modulator that modulates light propagating along the core 111 may be provided.

The optical fiber 12 includes a cylindrical core 121 and a cylindrical cladding 122 covering a side surface of the core 121. In the present embodiment, a single-mode optical fiber including a core 121 made of quartz glass and a cladding 122 is used as the optical fiber 12. Further, a dopant for making the refractive index of the cladding 122 lower than that of the core 121 is added to the core 121 or the cladding 122, and the input light guided along the optical fiber 12 is confined in the core 121 by this refractive index difference. The core 121 is exposed at the end face 12S of the optical fiber 12.

The distal end portion of the optical fiber 12 is disposed in the concave portion 112 of the substrate-type optical waveguide 11 so that the core 121 at the end face 12S of the optical fiber 12 faces the core 111 at the end face 11S of the substrate-type optical waveguide 11. The distal end portion of the optical fiber 12 is fixed to the substrate-type optical waveguide 11 by the resin material 13 injected into the concave portion 112 of the substrate-type optical waveguide 11. At this time, the central axis of the core 121 near the end face 12S of the optical fiber 12 is parallel to the central axis of the core 111 near the end face 11S of the substrate-type optical waveguide 11. The resin material 13 is injected toward the rear of the recess 112 so as not to enter between the end face 12S of the optical fiber 12 and the end face 11S of the substrate-type optical waveguide 11.

The optical fiber 12 may be provided with a spot size converter for reducing the spot size of light guided along the core 121. Examples of usable spot size converters include lens fibers, Grin lens fibers, and high NA fibers. When the spot size converter is provided, the spot size of the end surface 12S of the waveguide mode guided along the core 121 can be reduced to the same size as the spot size of the end surface 11S of the waveguide mode guided along the core 111 of the substrate-type optical waveguide 11. In the present embodiment, the resin material 13 is used as a fixing material for fixing the optical fiber 12 to the substrate-type optical waveguide 11, but the present invention is not limited to this. That is, as a fixing material for fixing the optical fiber 12 to the substrate-type optical waveguide 11, a fixing material other than resin, for example, solder may be used. In the present embodiment, the resin material 13 is injected into the concave portion 112 of the substrate-type optical waveguide 11, but the present invention is not limited to this. That is, instead of the recess, for example, a V-shaped groove may be formed in the substrate-type optical waveguide, and the resin material 13 may be injected into the V-shaped groove. In the present embodiment, the optical fiber 12 is fixed to the substrate-type optical waveguide 11 by a fixing material, but the present invention is not limited to this. That is, the optical fiber may be fixed to the substrate-type optical waveguide by a fixing method other than fixing by a fixing material.

[ setting of the size of the pattern spot ]

Hereinafter, the spot size w1 of a waveguide mode (for example, fundamental mode) guided along the core 111 of the substrate-type optical waveguide 11 and the spot size w2 of a waveguide mode (for example, fundamental mode) guided along the core 121 of the optical fiber 12 are examined. Here, as shown in fig. 2 (a), the spot size w1 of the waveguide mode guided along the core 111 of the substrate-type optical waveguide 11 means that the intensity of the waveguide mode at the end face 11S of the substrate-type optical waveguide 11 is 1/e of the peak intensity²The radius of the above region corresponds to 1/2 which is the mode field diameter of the waveguide mode. Similarly, as shown in fig. 2 (a), the spot size w2 of the waveguide mode guided along the core 121 of the optical fiber 12 means that the intensity of the waveguide mode at the end surface 12S of the optical fiber 12 is 1/e of the peak intensity²The radius of the above region corresponds to 1/2 which is the mode field diameter of the waveguide mode. The ratio w2/w1 of spot size w2 to spot size w1 is described as "spot size ratio".

As shown in fig. 2 (b), the distance from the central axis of the core 111 of the substrate-type optical waveguide 11 to the central axis of the core 121 of the optical fiber 12 is referred to as "axial offset amount" and is denoted by a symbol x. As shown in fig. 2 (b), the distance from the end face 11S of the substrate-type optical waveguide 11 to the end face 12S of the optical fiber 12 is referred to as "distance between end faces" and is denoted by a symbol z. Further, the reference numeral of the axis offset amount x is determined in the following manner. That is, the x axis is taken parallel to the direction in which the optical fiber 12 can be displaced in the direction orthogonal to the center axis of the core 121 of the optical fiber 12, (1) the reference numeral of the axial offset amount x is positive when the center axis of the core 121 of the optical fiber 12 is located on the x-axis positive side with respect to the center axis of the core 111 of the substrate-type optical waveguide 11, and (2) the reference numeral of the axial offset amount x is negative when the center axis of the core 121 of the optical fiber 12 is located on the x-axis negative side with respect to the center axis of the core 111 of the substrate-type optical waveguide 11. The reference sign for the distance z between the end faces is always positive.

Fig. 3 (a) is a graph showing the coupling efficiency η [ dB ] of the core 111 of the substrate-type optical waveguide 11 and the core 121 of the optical fiber 12 as a function of the axial offset amount x [ μm ] for the case where the spot size ratio w2/w1 is 1, 1.2, 1.55, 2, 2.41, 2.8, where the spot size w1 is 1.5 μm, the end face distance z is 10 μm, and the wavelength λ is 1.55 μm, and in any case, the coupling efficiency η is maximized when the axial offset amount x is 0, and the coupling efficiency η decreases as the absolute value | x | of the axial offset amount x increases, and this tendency is established regardless of the spot size w1 and the end face distance z.

Fig. 3 (b) is a graph showing the rate of change d η/dx (1) [ dB/μm ] in the coupling efficiency η [ dB ] when the axis shift amount x is 1 as a function of the spot size ratio w2/w1, here, the spot size w1 is also set to 1.5 μm, the end face-to-end distance z is set to 10 μm, and the wavelength λ is set to 1.55 μm, and as seen from the graph shown in fig. 3 (b), the larger w2/w1 is, the smaller the absolute value | d η/dx (1) | of d η/dx (1) is, which means that the larger w2/w1 is, the larger the axis shift margin (margin of the axis shift amount x relating to the coupling efficiency η) is.

Fig. 3 (c) is a graph showing the coupling efficiency (0) [ dB ] when the axis shift amount x is 0 as a function of the spot size ratio w/w, and in the graph shown in fig. 3 (c), the difference (coupling efficiency increase amount) obtained by subtracting the coupling efficiency (0) when w/w is 1 from the coupling efficiency (0) at each spot size ratio w/w is taken as the vertical axis, and here, the spot size w is also set to 1.5 μm, the inter-end surface distance z is set to 10 μm, and the wavelength λ is set to 1.55 μm from the graph shown in fig. 3 (c), and when w/w is 2.41, (0) is the same as when w/w is 1, when 1 < w/w < 2.41, (0) is larger than w/w 1, and when w/w is 1, it is seen that when w/w is 1.55, (0) takes the maximum value, (0) is larger than when w/w < 1 < 2.41, and when w/w is larger than 1, the second margin w < 2.41 ″, and the range w < 2 is divided into the following "55 w/w < 2 ″.41 ″.55.

The above-described knowledge points obtained from (c) of fig. 3 can be summarized as follows, that is, 1 st, there is a spot size ratio α where the coupling efficiency η (0) when the shaft offset x is 0 is the same as in the case where w2/w1 is 1, and, when 1 < w2/w1 < α, the coupling efficiency η (0) when the shaft offset x is 0 is larger than when w2/w1 is 1, 2 nd, there is a spot size ratio β where the coupling efficiency η (0) when the shaft offset x is 0 takes the maximum value, and further, the range "1 < w2/w1 < 1" where the coupling efficiency η (0) when the shaft offset x is 0 is larger than when the shaft offset x is 1 is divided into two parts, that (1) the shaft tolerance is relatively smaller, "1 < w 1/w < 1".

Therefore, in the optical module 1 according to the present embodiment, it is preferable that the spot sizes W1 and w2. are set so as to satisfy the 1 st condition "1 < W2/W1 < α", and α is a spot size ratio W2/w1. in which the coupling efficiency η (0) when the axial offset x is 0 and the coupling efficiency η (0) when W2/W1 is 1 are the same, whereby the optical module 1 in which the coupling efficiency η (0) when the axial offset x is 0 is larger than W2/W1 when W2/W1 is 1 can be realized.

In the optical module 1 according to the present embodiment, it is more preferable to set the spot sizes W1 and w2. so as to satisfy the 2 nd condition "β < W2/W1 < α", where β is a spot size ratio at which the coupling efficiency η (0) becomes maximum when the axial offset amount x is 0, and thereby, it is possible to realize the optical module 1 in which the coupling efficiency η (0) when the axial offset amount x is 0 is larger than when W2/W1 is 1 and the axial offset margin is large.

The spot size ratios α, β that occur under the above conditions can be expressed as a function of the spot size w1 and the distance z between the end faces.

Fig. 4 (a) is a graph showing, as a function of the spot size ratio w2/w1, the coupling efficiency η (0) [ dB ] when the axis offset amount x is 0 for the case where z is 10, w1 is 0.8, 1.0, 1.5, 2.0, 2.5, and 3.0, in the graph shown in fig. 4 (a), the difference (coupling efficiency increase amount) obtained by subtracting the coupling efficiency η (0) when w2/w1 is 1 from the coupling efficiency η (0) for each spot size ratio w2/w1 is taken as the vertical axis, and here, the distance z between the end faces is 10 μm, and the wavelength λ is 1.55 μm, as can be seen from fig. 4 (a), and as the spot size w1 becomes larger, the coupling efficiency η (0) and the wavelength λ 2/w1 for the case where z is 0, w 638/w is 0, and as can be seen, the maximum value of the coupling efficiency becomes smaller as the spot size w 638 becomes larger, and as the radius size w 6328 becomes smaller, the radius becomes larger, the maximum value of the radius size becomes equal to indicate that the radius of.

Fig. 4 (b) is a graph showing, as a function of w1, a spot size ratio α in which the coupling efficiency η (0) when the axial shift amount x is 0 and the same spot size ratio β in which the coupling efficiency η (0) when the axial shift amount x is 0 take the maximum value, as in the case where z is 10 and w2/w1 is 1, and in the graph shown in fig. 4 (b), the wavelength λ is also 1.55 μm, and in the graph shown in fig. 4 (b), the lower region of the graph showing the spot size ratio α is a region satisfying the above-described 1 st condition, and the region sandwiched between the graph showing the spot size ratio α and the graph showing the spot size ratio β is a region satisfying the above-described 2 nd condition.

Fig. 4 (c) is a graph showing, as a function of w1, a spot size ratio α where the coupling efficiency η (0) when the axis shift amount x is 0 is the same as that in the case where w2/w1 is 1, and a spot size ratio β where the coupling efficiency η (0) when the axis shift amount x is 0 takes the maximum value, in the case where z is 5, 10, and 20, the wavelength λ is also set to 1.55 μm, and in any case, a region on the lower side of the graph showing the spot size ratio α is a region satisfying the above-described 1 st condition, and a region sandwiched between the graph showing the spot size ratio α and the graph showing the spot size ratio β is a region satisfying the above-described 2 nd condition.

The curve α a × w1 can be used^bThe graph of the spot size ratio α shown in fig. 4 (c) is well approximated by +1, and when coefficients a and b that minimize the square error are obtained for the case where z is 5, 10, and 20, the following table 1 shows.

TABLE 1

Coefficient of performance	z＝5	z＝10	z＝20	Linear approximation
					a	1.662	4.195	9.253	a＝0.506z-0.867
b	-3.554	-3.168	-2.733	b＝0.0531z-3.7715

As shown in fig. 5 (a), the coefficient a regarded as a function of z can be linearly approximated. The approximate line that minimizes the squared error is a-0.506 z-0.867. As shown in fig. 5 (b), the coefficient b regarded as a function of z can be linearly approximated. The approximate line that minimizes the squared error is b-0.0531 z-3.7715.

Therefore, the spot size ratio α, in which the coupling efficiency η (0) when the axis offset x is 0 is the same as that in the case where w2/w1 is 1, is approximately expressed as follows.

Case of z ═ 5:

α＝1.662×w1^-3.554+1。

case z is 10:

α＝4.195×w1^-3.168+1。

case of z 20:

α＝9.253×w1^-2.733+1。

the general case is as follows:

α＝(0.506z-0.867)×w1^{(0.0531z-3.7715)}+1。

likewise, curve β ═ aw1 can be used⁴+bw1³+cw1²The graph of the spot size ratio β shown in fig. 4 (c) is well approximated by + dw1+ e, and when coefficients a, b, c, d, and e that minimize the square error are obtained for the case where z is 5, 10, and 20, the results shown in table 2 below are obtained.

TABLE 2

Coefficient of performance	z＝5	z＝10	z＝20	Linear approximation
					a	0.058	0.07	0.093	a＝0.0023z+0.0465
b	-0.668	-0.827	-1.097	b＝-0.0284z-0.533
					c	2.829	3.646	4.855	c＝0.133z+2.2245
d	-5.268	-7.229	-9.872	d＝-0.3008z-3.9465
					e	4.706	6.614	9.217	e＝0.295z+3.4045

As shown in fig. 6 (a), the coefficient a regarded as a function of z can be linearly approximated. The approximate line that minimizes the square error is a ═ 0.0023z + 0.0465. As shown in fig. 6 (b), the coefficient b regarded as a function of z can be linearly approximated. The approximate line that minimizes the squared error is b-0.0284 z + 0.533. As shown in fig. 6 (c), the coefficient c regarded as a function of z can be linearly approximated. The approximate straight line that minimizes the square error is c 0.133z + 2.2245. As shown in fig. 6 (d), the coefficient d, which is regarded as a function of z, can be linearly approximated. The approximate line that minimizes the squared error is d-0.3008 z-3.9465. As shown in fig. 6 (e), the coefficient e, which is regarded as a function of z, can be linearly approximated. The approximate line that minimizes the squared error is e-0.295 z + 3.4045.

Therefore, the spot size ratio β at which the coupling efficiency η (0) takes a maximum value when the axis offset x is 0 is approximately expressed as follows.

Case of z ═ 5:

β＝0.058w1⁴-0.668w1³+2.829w1²-5.268w1+4.706。

case z is 10:

β＝0.070w1⁴-0.827w1³+3.646w1²-7.229w1+6.614。

case of z 20:

β＝0.093w1⁴-1.097w1³+4.855w1²-9.872w1+9.217。

the general case is as follows:

β＝(0.0023z+0.0465)w1⁴

-(0.0284z+0.533)w1³

+(0.133z+2.2245)w1²

-(0.3008z+3.9465)w1

+(0.295z+3.4045)。

finally, the relationship between the maximum value of the coupling efficiency increase amount and the spot size w1 will be described with reference to fig. 7. Fig. 7 is a graph showing the maximum value of the coupling efficiency increase as a function of the spot size w 1. In fig. 7, (a) is a graph in the case where z is 5 μm, (b) is a graph in the case where z is 10 μm, and (c) is a graph in the case where z is 20.

The spot size w1 is preferably 3 μm or less, more preferably 2 μm or less. As can be seen from fig. 3 (a), when z is 5 μm, the coupling efficiency increase amount is 0.001dB or more when the spot size w1 is 3 μm or less, and the coupling efficiency increase amount is 0.01dB or more when the spot size w1 is 2 μm or less. As is clear from fig. 3 (b), when z is 10 μm, the coupling efficiency increase amount is 0.01dB or more when the spot size w1 is 3 μm or less, and the coupling efficiency increase amount is 0.1dB or more when the spot size w1 is 2 μm or less. As is clear from fig. 3 (c), when z is 20 μm, the coupling efficiency increase amount is 0.1dB or more when the spot size w1 is 3 μm or less, and the coupling efficiency increase amount is 1dB or more when the spot size w1 is 2 μm or less.

[ conclusion ]

An optical module (1) according to the present embodiment is characterized by comprising a substrate-type optical waveguide (11), and an optical fiber (12) for guiding light input to the substrate-type optical waveguide (11) or light output from the substrate-type optical waveguide (11), wherein a mode spot size w1 at an end face (11S) of a waveguide mode guided along a core (111) of the substrate-type optical waveguide (11) and a mode spot size w2 at an end face (12S) of a waveguide mode guided along a core (121) of the optical fiber (12) are set so as to satisfy 1 < w2/w1 < α, wherein α is a mode spot size ratio w2/w1 when a coupling efficiency η (0) between the substrate-type optical waveguide (11) and the optical fiber (12) is the same as a coupling efficiency η (0) when w2/w1 is equal to 1, and the coupling efficiency η (360) is an offset of the coupling efficiency between the core (111) of the substrate-type optical waveguide (11) and the core (12) when w 121 is equal to 1.

With the above configuration, a substrate-type optical waveguide having a coupling efficiency η (0) larger than that of the conventional one (when the spot size ratio w2/w1 is 1 or less) can be realized at an axial offset of 0.

In the optical module (1) according to the present embodiment, the spot size w1 and the spot size w2 are preferably set to satisfy β < w2/w1 < α, and a spot size ratio w2/w1 at which the coupling efficiency η (0) is maximized is β.

With the above configuration, the coupling efficiency η (0) when the axial shift amount is 0 can be larger than that of the conventional substrate-type optical waveguide and the axial shift margin is large.

In the optical module (1) according to the present embodiment, the spot size w1 and the spot size w2 are preferably set to: satisfies 1 < w2/w1 < 1.662 xw 1^-3.554+1。

According to the above configuration, when the distance between the substrate-type optical waveguide and the end face of the optical fiber is about 5 μm, the coupling efficiency η (0) when the axial shift amount is 0 can be larger than that of the conventional substrate-type optical waveguide.

In the optical module (1) according to the present embodiment, the spot size w1 and the spot size w2 are preferably set to: satisfies 0.058w1⁴-0.668w1³+2.829w1²-5.268w1+4.706＜w2/w1＜1.662×w1^-3.554+1。

According to the above configuration, when the distance between the substrate-type optical waveguide and the end face of the optical fiber is about 5 μm, the coupling efficiency η (0) when the axial shift amount is 0 can be larger than that of the conventional substrate-type optical waveguide and the axial shift margin is large.

In the optical module (1) according to the present embodiment, the spot size w1 and the spot size w2 are preferably set to: satisfies 1 < w2/w1 < 4.195 xw 1^-3.168+1。

According to the above configuration, when the distance between the substrate-type optical waveguide and the end face of the optical fiber is about 10 μm, the coupling efficiency η (0) when the axial shift amount is 0 can be larger than that of the conventional substrate-type optical waveguide.

In the optical module (1) according to the present embodiment, the spot size w1 and the spot size w2 are preferably set to: satisfies 0.070w1⁴-0.827w1³+3.646w1²-7.229w1+6.614＜w2/w1＜4.195×w1^-3.168+1。

According to the above configuration, when the distance between the substrate-type optical waveguide and the end face of the optical fiber is about 10 μm, the coupling efficiency η (0) when the axial shift amount is 0 can be larger than that of the conventional substrate-type optical waveguide and the axial shift margin is large.

In the optical module (1) according to the present embodiment, the spot size w1 and the spot size w2 are preferably set to: satisfies 1 < w2/w1 < 9.253 xw 1^-2.733+1。

According to the above configuration, when the distance between the substrate-type optical waveguide and the end face of the optical fiber is about 20 μm, the coupling efficiency η (0) when the axial shift amount is 0 can be larger than that of the conventional substrate-type optical waveguide.

In the optical module (1) according to the present embodiment, the spot size w1 and the spot size w2 are preferably set to: satisfies 0.093w1⁴-1.097w1³+4.855w1²-9.872w1+9.217＜w2/w1＜9.253×w1^-2.733+1。

According to the above configuration, when the distance between the substrate-type optical waveguide and the end face of the optical fiber is about 20 μm, the coupling efficiency η (0) when the axial shift amount is 0 can be larger than that of the conventional substrate-type optical waveguide and the axial shift margin is large.

In the optical module (1) according to the present embodiment, it is preferable that z is a distance between the substrate-type optical waveguide (11) and an end surface of the optical fiber (12), and the spot size w1 and the spot size w2 are set to: satisfies 1 < w2/w1 < (0.506z-0.867) × w1^{(0.0531z-3.7715)}+1。

With the above configuration, a substrate-type optical waveguide having a coupling efficiency η (0) larger than that of the conventional one (when the spot size ratio w2/w1 is 1 or less) can be realized at an axial offset of 0.

In the optical module (1) according to the present embodiment, the spot size w1 and the spot size w2 are preferably set to: satisfies (0.0023z +0.0465) w1⁴-(0.0284z+0.533)w1³+(0.133z+2.2245)w1²-(0.3008z+3.9465)w1+(0.295z+3.4045)＜w2/w1＜(0.506z-0.867)×w1^{(0.0531z-3.7715)}+1。

With the above configuration, the coupling efficiency η (0) when the axial shift amount is 0 can be larger than that of the conventional substrate-type optical waveguide and the axial shift margin is large.

In the optical module (1) according to the present embodiment, the spot size w1 is preferably 3 μm or less.

According to the above configuration, the increase amount of the coupling efficiency can be sufficiently increased.

A manufacturing method of an optical module (1) including a substrate-type optical waveguide (11) and an optical fiber (12) for guiding light input to the substrate-type optical waveguide (11) or light output from the substrate-type optical waveguide (11), the manufacturing method including a setting step of setting a spot size w1 of a waveguide mode guided along a core (111) of the substrate-type optical waveguide (11) and a spot size w2 of a waveguide mode guided along a core (121) of the optical fiber (12) so as to satisfy 1 < w2/w1 < α, wherein α is a spot size ratio 2/w1 when a coupling efficiency η (0) between the substrate-type optical waveguide (11) and the optical fiber (12) is the same as a coupling efficiency η (0) when w2/w1 is 1, and the coupling efficiency η (0) is an offset of a coupling efficiency of the core (111) of the substrate-type optical waveguide (11) and the core (12) when a coupling efficiency 121.0 is equal to the core (12).

According to the above-described manufacturing method, a substrate-type optical waveguide having a coupling efficiency η (0) larger than that of the conventional one (when the spot size ratio w2/w1 is 1 or less) when the axial shift amount is 0 can be manufactured.

In the manufacturing method according to the present embodiment, in the setting step, the spot size w1 and the spot size w2 are preferably set to satisfy β < w2/w1 < α, and a spot size ratio w2/w1 at which the coupling efficiency η (0) is maximized is β.

According to the above-described manufacturing method, the substrate-type optical waveguide in which the coupling efficiency η (0) is larger when the axial shift amount is 0 than before and the axial shift margin is large can be manufactured.

[ Note attached ]

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope shown in the claims are also included in the technical scope of the present invention. Further, the method for manufacturing an optical module including the step of setting the spot sizes w1 and w2 by the setting method described in the above embodiment is also included in the scope of the present invention.

Description of reference numerals

1 … light module; 11 … substrate-type optical waveguide; 111 … core; 112 … recess; 12 … optical fiber; 121 … core; 122 … a coating layer; x … axis offset; z … end face distance; w1 … mode spot size (slab-type optical waveguide); w2 … spot size (fiber).