Optical Fiber Array

Abstract

An optical fiber array includes a V-groove substrate in which a V-groove for optical fiber alignment is formed, a pressing plate laminated and bonded on the V-groove substrate, and an optical fiber bonded and fixed in the V-groove of the V-groove substrate, wherein a distance between the optical fiber and the V-groove is less than 20 μm.

Claims

1. An optical fiber array comprising: a V-groove substrate in which a V-groove for optical fiber alignment is formed; a pressing plate laminated and bonded on the V-groove substrate; and an optical fiber bonded and fixed in the V-groove of the V-groove substrate, wherein a distance d between a lower end of the optical fiber and a bottom of the V-groove is less than 20 μm.

2. The optical fiber array according to claim 1, wherein a half angle θ of an opening angle of the V-groove satisfies
θ>sin.sup.−1(r/(r+20)) wherein r is a radius [μm] of the optical fiber.

3. The optical fiber array according to claim 1, wherein a shape of a bottom of a cross section of the V-groove has a substantially arc-shape, and a radius of curvature r.sub.2 [μm] of the substantially arc-shape satisfies
r.sub.1−20sinθ/(1−sinθ)<r.sub.2≤r.sub.1 wherein r.sub.1 is a radius [μm] of the optical fiber, and θ is a half angle of an opening angle of the V-groove.

4. The optical fiber array according to claim 1, wherein a shape of a bottom of a cross section of the V-groove has a straight line shape which is horizontal to the V-groove substrate, and a length w of the straight line shape satisfies
w>2tanθ{r(1/sinθ−1)−20} wherein r is a radius [μm] of the optical fiber, and θ is a half angle of an opening angle of the V-groove.

5. A method for forming a V-groove in a V-groove substrate of an optical fiber array, the method comprising: preparing a mold with a protrusion having a cross-sectional shape corresponding to a cross-sectional shape of the V-groove according to claim 4; and performing molding by forming a release film on the mold and applying pressure, by the mold, to glass preform which is heated.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0042] FIG. 1 is a schematic view of an optical fiber connection structure between a known fiber array and a SiP circuit.

[0043] FIG. 2 is a graph showing a variation in connection loss with respect to an amount of misalignment of an optical axis between cores.

[0044] FIG. 3 is a set of cross-sectional views (a) and (b) of a connection portion between the known fiber array and the SiP circuit.

[0045] FIG. 4 is a cross-sectional view of a connection portion between a fiber array according to Embodiment 1 and a SiP circuit.

[0046] FIG. 5 is a cross-sectional view of a connection portion between a fiber array according to Embodiment 2 and the SiP circuit.

[0047] FIG. 6 is a cross-sectional view of a connection portion between a fiber array according to Embodiment 3 and the SiP circuit.

[0048] FIG. 7 is a diagram explaining steps of forming a V-groove by pressing in Embodiment 3.

DESCRIPTION OF EMBODIMENTS

[0049] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0050] First, because a misalignment of an optical axis between a Si waveguide and an optical fiber is caused by expansion of an adhesive between the optical fiber and a V-groove, it is necessary to reduce a thickness of the adhesive at the corresponding portion.

[0051] In the following Embodiment 1 to 3, as shown in FIGS. 4 to 6, let d be a distance between a lower end of the optical fiber and a bottom of the V-groove, and let θ be an half angle of an equivalent opening angle of the V-groove. In FIGS. 4 to 6, the structure is basically the same except for a cross-sectional shape of the V-groove.

[0052] It is assumed that an operating temperature range to be considered is from −5° C. to 85° C. In addition, because a linear expansion coefficient of the adhesive used when the optical fiber array is assembled is at most 10.sup.−4 [K.sup.−1], it is preferable that d be less than 20 μm.

[0053] In this way, the expansion of the adhesive, that is, a displacement in which the fiber is pushed up is suppressed to less than 0.18 μm at the most, and a variation in the connection loss is less than 0.04 dB from FIG. 2, and the variation in the connection loss is sufficiently suppressed to less than 0.08 dB even in consideration of the two connections for inputting and outputting light to/from a SiP circuit.

Embodiment 1

[0054] FIG. 4 is a connection cross-sectional view of a connection portion between a fiber array 401 of Embodiment 1 of the present invention and the SiP circuit 107. In Embodiment 1 of FIG. 4, the opening angle θ of a V-groove 403 is wider than a normal V-groove, and thus the distance d is shorter than that in the example of known art.

[0055] As shown in FIG. 4, let θ be the half angle of the opening angle of the V-groove 403 and let r [μm] be the radius of the fiber. When a radius of curvature of a bottom portion of the V-groove is neglected, the following equation is derived from a simple geometric calculation.

d=r(1/sinθ−1)

[0056] From a condition of d<20 μm,

θ>sin.sup.−1(r/(r+20))   Expression (1)

is obtained. This gives a condition of the opening angle of the V-groove 403.

[0057] In the case of a fiber with r=62.5 μm, it is required that θ>49.25°, that is, the opening angle is greater than 98.5°.

[0058] In this way, the distance d of a portion of the adhesive 106 which is located between the optical fiber 104 and the V-groove 403 on the lower side of the optical fiber 104 can be less than 20 μm, and a fiber array with a sufficiently small temperature variation in the connection loss with respect to the SiP circuit can be obtained.

Embodiment 2

[0059] FIG. 5 is a connection cross-sectional view of a connection portion between a fiber array 501 according to Embodiment 2 of the present invention and the SiP circuit 107.

[0060] In Embodiment 2 of FIG. 5, the distance d between the lower end of the optical fiber and the bottom of the V-groove 503 is narrowed by rounding a tip end (a bottom) of a cross-sectional shape of the V-groove 503 in a substantially arc shape and increasing the radius of curvature of the tip end. This can be manufactured by grinding the substrate with a blade having a blade shape with a large tip end radius of curvature when the V-groove is formed.

[0061] Similarly, let θ be a half of the opening angle of the V-groove 503, and let r.sub.1 [μm] be the radius of the optical fiber. When the radius of curvature of the tip end of the V-groove is r.sub.2 [μm], d is expressed by the following equation.

d=(r.sub.1−r.sub.2)(1/sinθ−1)   Expression (2)

From 0 μm<d<20 μm,

r.sub.1−20 sinθ/(1−sinθ)<r.sub.2≤r.sub.1   Expression (3)

is obtained for a condition of r.sub.2.

[0062] In the case of r.sub.1=62.5 μm and θ=30°, the relationship 42.5 μm<r.sub.2<62.5 μm is derived. When a V-groove shape satisfies this condition, a fiber array in which the temperature variation of the connection loss with respect to the SiP circuit is sufficiently small can be obtained.

[0063] In particular, when a radius of curvature of the tip end of the V-groove is equal to a radius of the optical fiber 104 (r.sub.2=r.sub.1), a thickness d of the adhesive 106 which causes the optical fiber 104 to rise due to expansion can be minimized.

Embodiment 3

[0064] FIG. 6 is a cross-sectional view of a connection portion between a fiber array 601 according to Embodiment 3 of the present invention and the SiP circuit 107.

[0065] In Embodiment 3 of FIG. 6, it is assumed that the bottom of the V-groove 603 is a flat surface (a flat bottom), and let w be a width thereof. In other words, in Embodiment 3, it is assumed that a bottom shape of a cross section of the V-groove is a straight line which is horizontal to the substrate, and let w be a length (width). Let θ be a half of the opening angle of the V-groove 603, and let r [μm] be the radius of the optical fiber.

[0066] At this time, the following equation is derived.

d=r(1/sinθ−1)−w/2tanθ  Expression (4)

[0067] From d<20 μm,

w>2 tanθ{r(1/sinθ−1)−20}   Expression (5)

is obtained for a condition of w.

[0068] When r=62.5 μm and 0=30°, the relationship w>49.1 μm is obtained.

[0069] When a cross-sectional shape of the V-groove satisfies this condition, a fiber array in which the temperature variation of the connection loss with respect to the SiP circuit is sufficiently small can be obtained.

Steps of Forming V-groove of Embodiment 3

[0070] A shape of the V-groove 603 of Embodiment 3 is suitable for producing a V-groove substrate by pressing instead of directly grinding the substrate with a blade to form a V-groove.

[0071] In other words, as shown in the steps of forming the V-groove of Embodiment 3 of FIG. 7, first, a mold 700 with a protrusion 701 having a cross-sectional shape corresponding to the cross-sectional shape of the V-groove is prepared. Because a shape of the protrusion 701 of the mold 700 coincides with a shape of the V-groove 703, a height h of the protrusion 701 is adjusted so that a width w of an upper surface of the protrusion 701 corresponding to a bottom surface of the V-groove satisfies the above-described relationship w>49.1 μm. This can be conveniently and accurately adjusted by polishing a mold surface.

[0072] Then, molding is performed using the mold 700. Molding is performed by forming a release film on the mold in advance and then applying pressure, by the mold 700, to glass preform 702 which is heated. After molding, cooling is performed while a pressing force is reduced, and a completed V-groove substrate on which the V-groove 703 is formed is taken out from the mold.

INDUSTRIAL APPLICABILITY

[0073] As described above, according to the optical fiber array of the present invention, it is possible to provide an optical fiber array which can suppress a misalignment between a waveguide and a core of an optical fiber when a temperature varies in a SiP circuit, and can reduce temperature dependency of connection loss.