JPH10260338A - Optical transmission module and optical transmission device mounted with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optically communicate high-speed signals by providing a diffraction grating with a specific diffraction grating pattern. SOLUTION: When a light reception point A on a photodiode, the light emission point B of a semiconductor laser, and the diffraction grating 3 are arranged, this diffraction grating 3 has a diffraction pattern satisfying relation, represented as a function (x<2> +y<2> -2yf1 sinθ+f1 <2> )<1/2> -(x<2> +y<2> +f2 <2> )<1/2> =mλ, with the center axis of its diffraction grating surface. Here, f1 is the distance (μm) from the center of the diffraction grating to a 1st light convergence point of the diffraction grating in the end surface direction of a light receiving element or light emitting element, f2 is the distance (μm) from the center of the diffraction grating to a 2nd light convergence point of the diffraction grating in the end surface direction of the light emitting element or light receiving element, θis the angle between the straight line connecting the center of the diffraction grating and the 1st light convergence point of the diffraction grating and the straight line connecting the center and 2nd light convergence point of the diffraction grating, (m) is an integer, λ is the wavelength (μm) of a light beam, and (x) and (y) are the coordinates from the center of a diffraction grating plane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission module and an optical transmission device equipped with the same, and more particularly, to a terminal in which a light emitting element and a light receiving element are provided in one package and connected to an optical fiber cable or the like. The present invention relates to an optical transmission module used for bidirectional optical transmission with an optical transmission device and an optical transmission device equipped with the same.

[0002]

2. Description of the Related Art In an optical communication system or an optical transmission system using an optical transmission line such as an optical fiber cable, a conventional bidirectional optical transmission module used for a signal transmission / reception terminal is disclosed in, for example, An optical transmission module described in JP-A-7-104154 has been proposed. FIG. 13 is a cross-sectional view showing a configuration of a conventional optical transmission module. As shown in FIG.
The light-emitting element 108 and the light-receiving element 106 are housed in the housing 0, and the holographic diffraction grating 103 is provided on the upper or lower surface of the cover glass 104 in the package opening. At the time of transmission, the light beam 1 emitted from the light emitting element 108
09 passes through the diffraction grating 103 and is condensed on the end face of the optical fiber 113 by the lens 101. On the other hand, at the time of reception, the reception light beam emitted from the end face of the optical fiber 113 passes through the lens 101, is diffracted by the diffraction grating 103, and the primary diffracted light 105 is condensed on the light receiving surface of the light receiving element 106 and detected.

[0003]

However, in the optical transmission module described in JP-A-7-104154, the groove of the diffraction grating 103 is focused on the light beam 109 emitted from the light emitting element 108 and the light receiving element 106. The same pattern as the interference fringe pattern generated by the overlapping of the light beam 105 is engraved. Specifically, an interference fringe pattern is calculated based on a difference in optical path length between two light beams, and a diffraction grating is manufactured based on the calculated pattern.

When there is no other optical element such as the cover glass 104 between the diffraction grating and the light emitting element or between the diffraction grating and the light receiving element, the interference fringe pattern can be easily calculated. However, when the cover glass 104 exists between the diffraction grating 103 and the light emitting element 108, the calculation formula of the interference fringe pattern becomes complicated because the light beam is refracted at the glass boundary surface. Therefore, it could not be solved theoretically, and numerical calculations had to be performed for each transmission optical path, which required enormous labor and time for program creation and calculation.

The present invention has been made in view of the above circumstances. For example, by approximating the pattern calculation of the diffraction grating of the optical transmission module by a simple function, the calculation time / labor required conventionally is reduced. An object of the present invention is to provide an optical transmission module capable of performing optical communication of high-speed signals by greatly reducing the light and condensing light sufficiently in a predetermined light receiving area by using the diffraction grating, and an optical transmission device equipped with the optical transmission module.

[0006]

SUMMARY OF THE INVENTION The present invention provides a fiber holder for connecting an optical fiber, a light emitting element for emitting a light beam, a light receiving element for receiving the light beam, and a light receiving element for receiving the light beam. A light-collecting element that guides the end face of the fiber and collects a light beam emitted from the end face of the optical fiber, and at least three or more light-transmitting media between the light-collecting element and the light-emitting element / light-receiving element, An optical transmission module comprising a diffraction grating for diffracting a light beam at a boundary of the medium, a first light-transmitting medium (air), a second light-transmitting medium, and a third light-transmitting medium in order of proximity to the light-emitting element. , Fourth
A light transmitting medium is disposed, and the diffraction grating is provided at a boundary between the second light transmitting medium and the third light transmitting medium or at a boundary between the third light transmitting medium and the fourth light transmitting medium. When the diffraction grating, with respect to the central axis of the diffraction grating surface,
Following function ^{expression, (x 2 + y 2 -2yf} 1 Sinθ + f 1 2) 1/2 - in ^{(x 2 + y 2 + f} 2 2) 1/2 = mλ ( Formula, f ₁ is the diffraction grating The distance [μm] from the center to the first condensing point of the diffraction grating in the direction of the end face of the light receiving element or in the direction of the end face of the light emitting element, f ₂ is in the direction of the end face of the light emitting element or the end face of the light receiving element The distance [μm] to the second converging point of the diffraction grating, θ is a straight line connecting the center of the diffraction grating and the first converging point of the diffraction grating, and the center of the diffraction grating and the second converging point of the diffraction grating. Angle between the connecting straight line and m
Λ is an integer, λ is the wavelength [μm] of the light beam, and x and y are coordinates from the center of the diffraction grating plane).

In the present invention, a semiconductor laser diode is used as the light emitting element, a PIN photodiode is used as the light receiving element, and a convex lens is used as the light collecting element. As a diffraction grating, the pattern calculation of the diffraction grating is approximated by a simple function formula, a photomask is created by electron beam drawing and etching using the function formula, and a light deflection hologram is formed on the flat glass by photolithography. doing.

According to the present invention, by using the above-mentioned function formula for the diffraction grating pattern, there is no need to perform complicated numerical calculations, and the time and labor required for program creation and calculation can be greatly reduced. Further, since the light beam can be efficiently made to enter the light receiving region of the light receiving element, an optical transmission module having high detection sensitivity can be realized. Further, since the light receiving area can be reduced, an optical transmission module capable of detecting a high-speed signal can be realized.

Preferably, the second light transmitting medium and the fourth light transmitting medium are made of flat glass, and the diffraction grating is formed on one of the flat glass.

The second light-transmitting medium and the fourth light-transmitting medium are made of flat glass, and one of the flat glasses hermetically seals an opening of an internal package for housing the light emitting element / light receiving element. Is preferred.

According to the above configuration, a diffraction grating is formed,
Flat glass for adjusting the position of the diffraction grating with respect to the optical axis of the light-emitting element, and flat glass for sealing the opening of the package containing the light-emitting element / light-receiving element (glass without a diffraction grating) Since it is not necessary to perform the position adjustment and the hermetic sealing at the same time, the manufacturing process can be simplified, and the conventional manufacturing apparatus can be used as it is.

The second light transmitting medium and the fourth light transmitting medium are made of flat glass, and the third light transmitting medium made of a light transmitting filler is sandwiched between the two flat glass. You may. According to the above configuration, by using the light-transmitting filler, it is possible to prevent dust and dirt from adhering to the surfaces of the two flat glasses and to further improve the airtightness of the package containing the light emitting element / light receiving element. Becomes possible.

[0013] According to the above configuration, the flat glass is disposed parallel to and substantially perpendicular to the optical axis of the light beam passing through the light-collecting element. It can be configured on the optical axis that satisfies the formula.

If the optical transmission module of the present invention is mounted on an optical transmission device, it can be applied to high-speed signals in bidirectional optical transmission with a terminal connected to an optical fiber cable or the like.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. Note that the present invention is not limited by this.

FIG. 1 is a sectional view showing the structure of an optical transmission module according to a first embodiment of the present invention, and FIG. 2 is a perspective view showing the optical transmission module according to the first embodiment of the present invention.
In FIG. 1, a semiconductor laser 8a as a light emitting element 8 and a photodiode 6a as a light receiving element 6 are mounted on a stem (base) 7, respectively. Semiconductor laser 8
a and the photodiode 6a are housed in an internal package 10, and a cover glass 4 which is a light transmitting body is attached to the opening 10a and hermetically sealed.

The cover glass 4, the lens 1a as the light condensing element 1, and the optical fiber 1
3 are arranged on the optical axis of the semiconductor laser 8a, and the stem 7, the lens 1a, and the fiber holder 12 holding the optical fiber 13 are fixed to the external package 11, respectively, to constitute an optical transmission module. Here, a medium existing between the semiconductor laser 8a and the lens 1a, a first medium (air), a second medium (cover glass 4), and a third medium (air) will be referred to in the order of proximity to the semiconductor laser 8. The diffraction grating 3 is formed on the third medium side surface of the cover glass 4.

At the time of transmission, the light beam 9 emitted from the semiconductor laser 8 enters the cover glass 4, passes through the diffraction grating 3 as 0-order diffracted light, and is condensed on the end face of the optical fiber 13 by the lens 1. The light is transmitted into the optical fiber 13.

On the other hand, at the time of reception, the optical fiber 13
Is transmitted in the opposite direction to that at the time of transmission, is condensed by the lens 1 and enters the diffraction grating 3. The first-order diffracted light 5 generated by the diffraction grating 3 is collected on the light receiving surface of the photodiode 6a, and a signal is detected. Note that x,
y and z indicate the coordinates on the diffraction grating 3 and the coordinates of the optical axis.

A method for calculating the pattern of the diffraction grating 3 will be described. The pattern of the diffraction grating 3 is a semiconductor laser 8a
A spherical wave centered on the light emitting point of the
This is obtained by calculating the pattern of interference fringes generated when two light beams of a spherical wave centered on one point above interfere with each other on the surface of the diffraction grating 3.

FIG. 3 is an explanatory diagram showing a method of calculating a diffraction grating pattern according to the present invention when only air exists between the diffraction grating and the semiconductor laser and between the diffraction grating and the photodiode. The case where the light receiving point A on the photodiode, the light emitting point B of the semiconductor laser 8a, and the diffraction grating 3 are arranged as shown in FIG. 3 will be described. Receiving point A, the phase phi ₁ of the light divergent spherical wave centered on the light emitting point B, and the _{φ 2, φ 1 = kn (} x 2 + y 2 -2yf 1 Sinθ + f 1 2) 1/2 ...... (1) φ ₂ = kn (x ² + y ² + f ₂ ² ) ^1/2 ... (2)

In equations (1) and (2), k: 2π / λ λ: wavelength of light n: refractive index of medium (here, air, n = 1) x, y: center on diffraction grating surface 3 F ₁ : distance from the center of the diffraction grating 3 to the light receiving point A f ₂ : distance from the center of the diffraction grating 3 to the light emitting point B θ: a straight line connecting the center of the diffraction grating 3 and the light receiving point A; It is an angle formed by a straight line connecting the center of the diffraction grating 3 and the light emitting point B.

From the phase difference φ ₁ −φ ₂ between the two light beams, the (x, y) of the pattern of the diffraction grating 3 becomes φ ₁ −φ ₂ = 2mπ (3) (m = integer), and the equation is transformed. ^{results, (x 2 + y 2 -2yf} 1 Sinθ + f 1 2) 1/2 - represented by ^{(x 2 + y 2 + f} 2 2) 1/2 = mλ ...... (4). For any m, satisfying equation (4), (x,
There is one curve y), which is composed of m
It becomes the pattern of.

[0024] In _{^{(4), a 2 2 = f 2 2}} - {f 1 2 -f 2 2 -m 2
^{λ 2} 2 / {4 (} m 2 λ 2 -y 1 2)} b 2 = (y 1 2 -m 2 λ 2) / m 2 λ 2 c = y 1 (f 1 2 -f 2 2 -m ² λ ² ) / {2 (m ² λ ² -y ₁ ² )} y ₁ = f ₁ Sinθ and substituting:-(x / a) ² + ｛(y + c) / (a / b)｝ ² = 1 …… (5) It can be seen that it is hyperbolic.

Only in the case shown in FIG. 3, it is possible to easily and accurately calculate the pattern of the diffraction grating from the equation (4). However, in the optical path having the configuration shown in FIG.
When the cover glass 4 exists between the semiconductor laser 8 and the diffraction grating 3 and the photodiode 6, the light beam is refracted at the boundary between the cover glass 4 and the air.
Equations (1) and (2) cannot be directly applied to the phases φ1 and φ2 of the spherical wave. Therefore, the present invention uses the following calculation method.

FIG. 4 is a diagram showing a method of calculating a diffraction grating pattern in the first embodiment of the present invention. FIG. 4 (a)
The light emitting point B of the semiconductor laser 8a, the light receiving point A of the photodiode 6a, the cover glass 4, and the positional relationship of the lens 1a are shown. First, the optical path length of the cover glass 4 was replaced by an optical path length converted into an air medium (= glass thickness d / glass refractive index n). As a result, as shown in FIG. 4B, the optical system is condensed to almost one point in the air. The focal point is defined as a point B ′.

Next, as shown in FIG. 4C, it is considered that the light emitting point is located at the position of the point B ', and the position of the photodiode 6a at that time is assumed to be the point A'. (The positional relationship between points A ′ and B ′ is the same as that of points A and B before replacement with the air equivalent optical path length.
And the same positional relationship). A diffraction grating pattern is calculated as a pattern of interference fringes of two spherical waves having the points A ′ and B ′ as condensing points. In this case, since the refractive indexes are all uniform (air), equation (4) can be used as it is.

However, a feature of the present embodiment is that the values of FIG. 4C are used as the values of f ₁ , f ₂ and θ. FIG. 4D shows a configuration in which the diffraction grating 3 is manufactured based on the calculated diffraction grating pattern and is incorporated in the original optical system. As shown in FIG.
The first-order diffracted light slightly spreads on the photodiode point A without being converged on one point. The reason is that the produced diffraction grating pattern is a pattern for condensing only one point on the point A ′ of the photodiode in the arrangement of FIG. This is because an aberration is generated in the first-order diffracted light because it is approximately substituted.

FIG. 5 is an explanatory view showing an example of a diffraction grating pattern in the first embodiment of the present invention. Here, λ =
1.31 μm, cover glass 4 thickness d = 0.25 mm, f ₁ = 1.1 m
m, f ₂ = 1.2 mm, θ = 34 °. The spacing between the diffraction grating patterns is on the order of μm.
It is thinned out every other book.

A diffraction grating pattern is drawn by an electron beam drawing apparatus controlled by a computer programmed with the calculated diffraction grating pattern, a photomask is produced by an etching process or the like, and a diffraction grating 3 is formed on the flat glass by photolithography. I do. At this time, the formed diffraction grating pattern has a cross-sectional shape such as a trapezoid, a rectangle, or a sawtooth shape. The position of the cover glass 4 is adjusted so that the diffraction grating 3 formed on the cover glass 4 is at a predetermined position, and the cover glass 4 is fixed to the inner package 10 in that state.

FIG. 6 is an explanatory diagram showing a light beam shape on a light receiving element in the first embodiment of the present invention. The light beam shape 15 on the photodiode 6 when the diffraction grating 3 shown in FIG. 5 is used is not completely condensed at one point due to the influence of aberration, but is not focused on the light receiving region 14 of φ80 μm. It is small enough to condense and poses no practical problem. Generally, in high-speed signal transmission, the light receiving area cannot be made too large in order to reduce the rise and fall of the element. However, if the light receiving area is φ80 μm, signal transmission up to several tens of Mbps is possible.

Note that the diffraction grating 3 is formed by the first cover glass 4.
When provided on the surface on the medium side, the diffraction grating 3 and the light emitting element 8
Since the refractive index between the diffraction grating 3 and the light receiving element 6 is uniform due to the presence of only air,
It is possible to directly calculate a precise diffraction grating pattern.

FIG. 7 is a sectional view showing the structure of an optical transceiver module according to a second embodiment of the present invention. In FIG.
The same components as those in the first embodiment are denoted by the same reference numerals. In the second embodiment, a glass optical block 2 is disposed between a cover glass 4 and a lens 1a.
Here, the first medium (air), the second medium (cover glass 4), the third medium (air), the fourth medium (optical block 2), and the fifth medium (air) are expressed in order from the light emitting element. .
The diffraction grating 3 is formed on the surface of the optical block 2 on the third medium side.

The reason why the optical block 2 is provided is that the diffraction grating 3 and the cover glass 4 are formed as separate components, so that the position of the diffraction grating with respect to the optical axis of the light emitting element can be adjusted by a flat glass (with a diffraction grating provided). This is because the functions are divided into a flat glass (a flat glass having no diffraction grating) and a flat glass (a flat glass having no diffraction grating) for hermetically sealing the light emitting element and the light receiving element. When the position adjustment and the hermetic sealing are performed at the same time, the manufacturing apparatus becomes complicated. However, if the steps are performed separately, the manufacturing steps can be simplified, and the conventional manufacturing apparatus can be used as it is. Therefore, a diffraction grating 3 is provided on the optical block 2. After correcting the cover glass 4 by replacing the optical path length with an optical path length converted into an air medium in the same manner as in the first embodiment, the pattern of the diffraction grating 3 was calculated by the functional equation (4).

FIG. 8 is an explanatory diagram showing a light beam shape on a light receiving element in the second embodiment of the present invention. As shown in FIG. 8, the light beam shape 16 on the light receiving element 6 can be condensed in the light receiving area 14 of φ80 μm as in the first embodiment, and sufficient signal light intensity can be ensured and a high-speed optical signal can be received. It is.

FIG. 9 is an enlarged view showing a partial configuration of an optical transceiver module according to a third embodiment of the present invention. The third embodiment is a modification of the second embodiment, and differs from the second embodiment in that an ultraviolet curable resin 18 is filled between the cover glass 4 and the optical block 2. In FIG. 9, components having the same components as in the second embodiment have the same reference numerals. Accordingly, it is possible to prevent dust and dirt from adhering to the surfaces of the second and fourth media, and to further improve the airtightness of the light emitting element and the light receiving element. Further, by irradiating and curing the ultraviolet ray, the fixing strength of the optical block 2 to the internal package 10 can be increased. The filler may be a light transmitting body, and for example, may be a liquid having no curing properties, such as silicone oil.

FIG. 10 is an explanatory view showing a light beam shape on a light receiving element in the third embodiment of the present invention. As shown in FIG. 10, when the ultraviolet curing resin 18 is used, the light beam shape 17 on the light receiving element 6 is φ8 as in the second embodiment.
The light is condensed in the light receiving region 14 of 0 μm, so that sufficient signal light intensity can be ensured and a high-speed optical signal can be received.

FIG. 11 is a sectional view showing a comparative example with respect to the embodiment. FIG. 12 is an explanatory diagram showing the shape of the light beam on the light receiving element in FIG. Here, a comparative example with the embodiment will be supplementarily described. As shown in FIG.
An optical block 102 and a cover glass 104 exist between the light emitting element 3 and the light emitting element 108, and a diffraction grating 103 is provided on a surface of the optical block 102 on the side of the fifth light transmitting medium. In this case, the diffraction grating is calculated in the same manner as in the first to third embodiments of the present invention. However, as shown in FIG. 12, the light beam is not sufficiently focused in the light receiving region. When the size of the light receiving region 114 is increased, the signal intensity increases, but the rise / fall time increases, so that a high-speed signal cannot be accurately received. For this reason, when a diffraction grating is provided on the optical block 2, the third light-transmitting medium is used instead of the fifth light-transmitting medium.
It can be seen that it is desirable to provide on the light transmitting medium side (light emitting element side).

[0039]

According to the present invention, it is possible to easily calculate a diffraction grating pattern without performing complicated numerical calculations in forming a diffraction grating pattern, and to use the diffraction grating to collect a light beam sufficiently small in a light receiving region. By light, an optical transmission module capable of transmitting and receiving high-speed signals can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an optical transmission module according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing an optical transmission module according to a first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a diffraction grating pattern calculation method according to the present invention.

FIG. 4 is a diagram showing a calculation method of a diffraction grating pattern in the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an example of a diffraction grating pattern according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a light beam shape on a light receiving element according to the first embodiment of the present invention.

FIG. 7 is a sectional view showing a configuration of an optical transceiver module according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a light beam shape on a light receiving element according to a second embodiment of the present invention.

FIG. 9 is an enlarged view showing a partial configuration of an optical transceiver module according to a third embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a light beam shape on a light receiving element in a third embodiment of the present invention.

FIG. 11 is an explanatory diagram showing a comparative example with respect to the embodiment.

12 is an explanatory diagram showing a shape of a light beam on a light receiving element in FIG.

FIG. 13 is a cross-sectional view illustrating a configuration of a conventional optical transmission module.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Condensing element 1a Lens 2 Optical block 3 Diffraction grating 4 Cover glass 5 Light beam incident on a light receiving element 6 Light receiving element 6a Photodiode 7 Stem 8 Light emitting element 8a Semiconductor laser 9 Light beam emitted from a light emitting element 10 Internal package 11 External Package 12 Fiber holder 13 Optical fiber 14 Light receiving area of light receiving element 15, 16, 17 Light beam on light receiving element 18 UV curable resin

Claims (6)

[Claims] 1. A fiber holder for connecting an optical fiber, a light emitting element for emitting a light beam, a light receiving element for receiving a light beam, an optical fiber for guiding a light beam emitted from the light emitting element to an end face of the optical fiber. A condensing element for condensing a light beam emitted from the end face of the light-emitting element, at least three or more light-transmitting media between the condensing element and the light-emitting element / light-receiving element, and a light beam at a boundary of the medium. In a light transmission module including a diffraction grating, a first light transmitting medium (air), a second light transmitting medium, a third light transmitting medium, and a fourth light transmitting medium are arranged in order of proximity to the light emitting element. When the diffraction grating is provided at a boundary between the second light transmitting medium and the third light transmitting medium or at a boundary between the third light transmitting medium and the fourth light transmitting medium, With respect to the central axis of the diffraction grating surface, Serial function ^{expression, (x 2 + y 2 -2yf} 1 Sinθ + f 1 2) 1/2 - in ^{(x 2 + y 2 + f} 2 2) 1/2 = mλ ( Formula, f ₁ is the diffraction grating The distance [μm] from the center to the first condensing point of the diffraction grating in the direction of the end face of the light receiving element or in the direction of the end face of the light emitting element, f ₂ is in the direction of the end face of the light emitting element or the end face of the light receiving element The distance [μm] to the second converging point of the diffraction grating, θ is a straight line connecting the center of the diffraction grating and the first converging point of the diffraction grating, and the center of the diffraction grating and the second converging point of the diffraction grating. Angle between the connecting straight line and m
Is an integer, λ is the wavelength [μm] of the light beam, and x and y are the coordinates from the center of the diffraction grating plane). 2. The apparatus according to claim 1, wherein the second light transmitting medium and the fourth light transmitting medium are made of flat glass, and the diffraction grating is formed on one of the flat glass.
The optical transmission module as described in the above. 3. The second light-transmitting medium and the fourth light-transmitting medium are made of flat glass, and one of the flat glasses hermetically seals an opening of an internal package that houses the light emitting element / light receiving element. The optical transmission module according to claim 1, wherein the optical transmission module is stopped. 4. The second light transmitting medium and the fourth light transmitting medium are made of flat glass, and the third light transmitting medium made of a light transmitting filler is sandwiched between the two flat glass. The optical transmission module according to claim 1, wherein: 5. The light according to claim 2, wherein the flat glass is disposed in parallel and substantially perpendicular to an optical axis of the light beam transmitted through the light-collecting element. Transmission module. 6. An optical transmission device comprising the optical transmission module according to claim 1.