JPH07104154A - Optical transmission module and optical transmitting device - Google Patents

Abstract

PURPOSE:To provide a two-way optical transmission module which is effective in miniaturizing the device and also reducing the cost by a simple constitution and an optical transmitting device using the module. CONSTITUTION:A light emitting element 1 and a light receiving element 2 are stored in the same package 12, a holographic diffraction grating 6 is installed on the upper, or lower surface of a cover glass 2 arranged on a package opening part. At the time of transmitting, light beams 100 emitted from the light emitting element 1 are transmitted through the diffraction grating 6 and condensed on the end face 5 of an optical fiber 4 by a lens 3. Meanwhile, at the time of receiving, receiving light beams 105 emitted from the end face 5 of the optical fiber 4 reach the diffraction grating 6 through the lens 3, and the beams 105 are diffracted by the diffraction grating 6, and + 1st order diffracted light beams 108 are condensed on the photodetecting surface of the light receiving element 7. Thus, a transmission signal is received from signal light transmitted through the optical fiber 4.

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 used for transmitting and receiving information signals by connecting to a terminal such as an optical fiber cable, and particularly to a light emitting element and a light receiving element in one package. The present invention relates to an optical transmission module for providing bidirectional transmission 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 (hereinafter referred to as an optical fiber for simplification), a bidirectional optical transmission module used as a signal transmitting / receiving terminal ( Hereinafter, as a conventional example of an optical module for the sake of simplicity), there is a technique described in JP-A-62-229206, for example. This is to collimate the light emitted from the light emitting element and the collimating lens for collimating the light emitted from the light emitting element, the light receiving element and the condensing lens for coupling the light to the light receiving element, and the optical fiber terminal and the light emitted from the optical fiber. The common port lens and the pentaprism block equipped with a filter for demultiplexing and multiplexing light according to wavelength are housed or connected in one metal case.

[0003]

However, the optical module disclosed in the above-mentioned prior art has a problem that the number of optical components housed in one metal case increases. Further, since the transmitted light and the received light are separated by using the pentaprism block, it is necessary to dispose the light emitting element and the light receiving element in positions spatially separated from each other and in directions orthogonal to each other. Is an obstacle to.

The object of the present invention is to solve the above problems,
An object of the present invention is to provide an optical module suitable for downsizing and cost reduction, and an optical transmission device using the module.

[0005]

In order to achieve the above object, in the present invention, a light emitting element, a light receiving element, and an optical element (for example, a lens) for guiding a light beam emitted from the light emitting element to a predetermined optical fiber are provided. An optical module including at least the light emitting element and the light receiving element, and a package having a window portion provided with a transparent member (hereinafter, referred to as a cover glass for simplicity), wherein an upper surface or a lower surface of the cover glass is provided. A diffraction grating having a grating groove with a linear or curved locus was provided.

Further, the optical element is held in the package.

Further, at least the diffraction grating and the cover glass can be rotated about a predetermined rotation axis substantially parallel to the optical axis of the light beam passing through the cover glass.

As the light receiving element, a light receiving element having a rectangular, trapezoidal or oval light receiving surface having a longitudinal direction substantially parallel to a straight line connecting the light receiving element and the light emitting element is used.

Further, the grating groove of the diffraction grating has a substantially sawtooth cross-sectional shape.

Further, a wavelength selective filter for selectively transmitting a light beam having a specific wavelength is provided in the optical path from the optical fiber to the light receiving element.

Further, the grating groove depth d of the diffraction grating, the refractive index n _{0 of the} members constituting the diffraction grating, and the refractive index n ₁ of the surrounding medium in contact with the diffraction grating are determined by the wavelength λ of the predetermined light beam. On the other hand, the following equation d≈m · λ / (n ₀ −n ₁ ) (where m is an integer) ...

Further, the function of emitting a light beam to the light emitting means including the light emitting element and the components attached thereto according to a predetermined electric signal and, conversely, a predetermined amount according to the light quantity of the light beam incident on the light emitting element. It also has a light detection function that outputs the electric signal of.

Furthermore, an optical module having each of the above-described configurations is mounted on an optical transmission device used in an optical communication system or an optical transmission system.

[0014]

With the above construction, the received light beam guided from the optical fiber into the optical module is diffracted by the diffraction grating provided on the upper surface or the lower surface of the cover glass, and is placed in the vicinity of the light emitting element. The signal can be received by being incident on the light receiving element. Therefore, the light emitting element and the light receiving element can be provided at positions significantly closer to each other than the conventional optical module, and each optical component in the optical module can be linearly arranged. This is extremely advantageous for downsizing and simplification of the optical module.

When the optical element for guiding the transmission light emitted from the light emitting element to the optical transmission line is fixed in the package, a holder member for holding the optical element can be omitted and the holder member can be omitted. Since it is possible to omit the step of axially aligning the package with the package and further fixing the package, it is more advantageous for the cost reduction of the optical module.

Further, the diffraction grating is rotated around an axis substantially parallel to the optical axis together with the cover glass on which the diffraction grating is installed, so that the diffraction grating diffracts the diffraction grating and enters the light receiving element. The position can be easily adjusted.

Further, by making the light receiving surface of the light receiving element rectangular, trapezoidal or oval, good reception performance is always obtained even if the light beam condensing position on the light receiving surface is displaced due to the wavelength shift of the received light. Obtainable.

Further, if the grating groove of the diffraction grating has a substantially sawtooth cross-sectional shape, the light utilization efficiency of the received light diffracted by the diffraction grating and incident on the light receiving element can be improved.

If a wavelength selective filter for selectively transmitting a light beam of a specific wavelength is provided in the optical path from the optical fiber to the light receiving element, a plurality of signal lights having different wavelengths are transmitted in the optical fiber. In such a case, so-called crosstalk in which signal light other than the received light leaks into the light receiving element can be reduced.

Further, when the grating groove depth d of the diffraction grating is defined by the above relational expression, the diffraction efficiency can be made almost zero for the light beam having the wavelength λ in the expression. Therefore, if such a diffraction grating is used and an optical module is configured with a light beam having a wavelength λ as a transmitted light and a light beam having a wavelength λ ′ different from λ as a received light, as a result, the light utilization efficiency of the transmitted / received light is increased. It is possible to perform bidirectional optical transmission in which the crosstalk with respect to received light is sufficiently reduced.

Further, when the light emitting means having a light detecting function for the incident light beam is used, the first light beam received by the light receiving element and the second light beam transmitted / received by the light emitting element are simultaneously multiplexed and transmitted. be able to.

[0022]

The present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a sectional view of an optical module according to the first embodiment of the present invention. In the figure, 1 is a light emitting element such as a semiconductor laser element. This light emitting element 1
Emits a light beam 100 having a predetermined wavelength by a driving current modulated according to a transmission signal. Light emitting element 1
The light beam 100 emitted from the laser beam reaches the lens 3 through the cover glass 2. Then, the light beam 10 transmitted through the lens 3
4 is condensed on the end face 5 of the optical fiber 4 and is transmitted into the optical fiber 4 (hereinafter, this light beam 104
Is referred to as a transmitted light beam).

On the other hand, a light beam 105 transmitted from another optical module or the like through the optical fiber 4 to reach this optical module and emitted from the end face 5 of the optical fiber (hereinafter, this light beam 105 is distinguished from the transmission light beam 104, The received light beam) follows an optical path opposite to that of the transmitted light beam 104, passes through the lens 3, and reaches the cover glass 2. On the upper surface or the lower surface of the cover glass 2, a phase type diffraction grating 6 having a predetermined grating groove is provided.

FIG. 2 is a perspective view showing an example of a grating groove formed in the diffraction grating 6. Further, FIG. 3 is a plan view showing an example of the loci of the lattice grooves (trajectories at the center of the lattice grooves are shown by solid lines drawn every several lines in the square frame of FIG. ). That is, in the diffraction grating 6, for example, a grating groove having a rectangular or trapezoidal cross-sectional shape as shown in the example of FIG. 2 and having a curved or linear locus at unequal intervals as shown in the example of FIG. Twenty is engraved. When the light beam transmitted through the lens 3 enters such a diffraction grating 6, the diffraction grating 6 diffracts the light beam and generates a + 1st order diffracted light beam 108. The + 1st order diffracted light beam 108 is condensed on the light receiving surface of the light receiving element 7 such as a photodiode provided in the vicinity of the light emitting element 1. The diffraction grating 6 having such a function is generally called a holographic diffraction grating, and an interference fringe produced by the light beam 100 emitted from the light emitting element 1 and the light beam 108 condensed on the light receiving element 7 overlapping each other. Lattice grooves are engraved along.

When the light beam (+ 1st-order diffracted light beam) 108 generated by the diffraction grating 6 is incident on the light receiving surface of the light receiving element 7, a predetermined detection signal corresponding to the intensity of the incident light is output and this detection is performed. The received signal is demodulated from the signal.

The light emitting element 1 and the light receiving element 7 are fixed to a columnar base 11 (hereinafter referred to as a submount) as shown in FIG.
Is fixed on the same base 10 (hereinafter, referred to as a stem) together with the light receiving element 8 (hereinafter, referred to as a monitor diode) used for monitoring the optical output of the light emitting element 1.
The light emitting element 1, the light receiving element 7, the submount 11 to which they are fixed, and the monitor diode 8 are sealed by a package 12 in which a cover glass 2 is provided in the opening. The lens 3 is attached to the lens holder 13,
The optical fiber 4 is fixed to a fiber holder 14, and the holders 13 and 14 are sequentially stacked on the package 12 as shown in FIG. 1, and are joined and fixed by means such as welding.

Next, the function of the diffraction grating 6 of this embodiment will be described with reference to FIGS. 4 and 5. 4 and 5
FIG. 4 is a schematic cross-sectional view in which a main part of the optical module of this embodiment is extracted.

First, the state during transmission will be described with reference to FIG. The light beam 100 emitted from the light emitting element 1 passes through the cover glass 2 and the diffraction grating 6. Then, at that time, the 0th-order light beam 101 which is diffracted by the diffraction grating 6 and advances straight as it is, and the + 1st-order diffracted light beam 102 and the -1st-order diffracted light beam 103 which are deflected by a predetermined angle and proceed
The light beam is separated into a plurality of light beams (strictly speaking, high-order diffracted light beams of ± 2nd order or higher exist, but they are omitted here for convenience of description). Of these, the 0th-order light beam 101 is condensed on the end surface 5 of the optical fiber 4 by the lens 3 and transmitted into the optical fiber 4. This 0th-order light beam 1
The light quantity ratio of each of the 01 and + 1st order diffracted light beams 102 and −1st order diffracted light beams 103 to the light beam 100, so-called diffraction efficiency, is determined by the grating pitch P of the diffraction grating 6, the grating groove width W, the grating groove depth d, and the grating groove. Engraved substrate member (cover glass when engraving lattice grooves directly on the cover glass)
N ₀ , the refractive index n ₁ of the medium (eg, air) around the diffraction grating, and the wavelength λ of the light beam 100 incident on the diffraction grating. For example, the wavelength of the incident light beam is 1.3 μm, the average grating pitch is 2 μm on a glass substrate having a refractive index n ₀ = 1.51, and the grating groove width W is half the grating pitch P, that is, W / P = 0.5. When the diffraction grating 6 is arranged in the air (n ₁ = 1) and the grating groove depth d is set to about 0.7 μm, the 0th order light beam of the incident light beam incident on the diffraction grating 6 is About 40% of light intensity, ± 1
The light quantity of the second-order diffracted light can be about 20%. Therefore, when such a diffraction grating 6 is used, about 40% of the light amount of the light beam 100 emitted from the light emitting element 1 is
The transmitted light can be condensed on the end surface 5 of the optical fiber 4.

Next, the state of reception will be described with reference to FIG. The received light beam 105 transmitted through the optical fiber 4 and emitted from the optical fiber end face 5 in the optical module passes through the lens 3 and is then converted into a converged light beam 106 to reach the diffraction grating 6. Then, as in the case of transmission, the 0th-order light beam 107 that is diffracted by the diffraction grating 6 and travels straight
+ 1st order diffracted light beam 108 and −
It is separated into a first-order diffracted light beam 109. At this time, the diffraction efficiency of each diffracted light beam with respect to the light beam 106 incident on the diffraction grating 6 becomes the same value as at the time of transmission. That is,
Since the wavelength of the received light beam 105 is 1.3 μm, which is the same as in the above-described transmission example, and the diffraction grating 6 is the same grating as in the above example, the light quantity of the + 1st-order diffracted light beam 108 is
It is about 20% of 06. The + 1st-order diffracted light beam 108 is received by the light-receiving element 7 provided near the light-emitting element 1.
The received signal is collected and demodulated on the light receiving surface of.

In this embodiment having such a configuration, the received light beam guided from the optical fiber is diffracted by the diffraction grating provided on the cover glass and is incident on the light receiving element arranged in the immediate vicinity of the light emitting element. Therefore, the light emitting element and the light receiving element can be arranged much closer to each other than the conventional optical module, and each optical component in the optical module can be linearly arranged. It greatly contributes to the miniaturization and simplification of modules.

FIG. 6 is a sectional view of an optical module according to the second embodiment of the present invention. In FIG. 6, the same components as those of the first embodiment of FIG. 1 are designated by the same reference numerals. . The basic configuration and function of this embodiment are almost the same as those of the first embodiment shown in FIG. The difference from the first embodiment is that the lens 3 is fixed in the package 12, and the lens holder 13
It is the point that omitted. With such a configuration, the number of components can be further reduced as compared with the first embodiment, and the axial alignment / joining process of the lens holder can be omitted. Further, there is an advantage that the optical fiber 4 and the fiber holder 14 can be shared with a conventional one-way optical transmission module (optical module in which a light emitting element and a lens are housed in one package).

Next, a case of actually assembling the optical module as described in FIG. 1 or 6 will be described. In this case, in order for the + 1st-order diffracted light beam 108 diffracted by the diffraction grating 6 to be correctly focused on the light receiving surface of the light receiving element 7, its diffraction direction needs to be adjusted. For such adjustment, the position of the focused spot may be adjusted by rotating the diffraction grating 6 around the optical axis of the light beam incident on the diffraction grating or an axis parallel thereto. Since the diffraction grating 6 is fixed to the upper surface or the lower surface of the cover glass 2 as described above, it is sufficient to rotate the cover glass 2 when rotating the diffraction grating 6.

FIG. 7 is a diagram showing an example of such a state.
In particular, it is a schematic plan view in which only the cover glass 2, the diffraction grating 6 and the light receiving element 7 are extracted and drawn. Since the light beam 106 is incident on the diffraction grating 6 from a direction perpendicular to the paper surface, the + 1st order diffracted light beam 108 is viewed in the XY plane as shown in FIG. The light travels in a substantially vertical direction and is focused on the light receiving surface of the light receiving element 7. Therefore, as shown by the arrow in the figure, the cover glass 2 is rotated by a slight angle in the XY plane (that is, the light beam 10
6 Rotate a small angle around the optical axis or an axis parallel to the optical axis)
Then, the diffraction grating 6 fixed on the cover glass 2 is also rotated at the same time, and as a result, the focused spot 110 on the light receiving element 7 is moved in a predetermined direction (direction substantially coincident with the Y-axis direction in the example of FIG. 7). Can be displaced. As a result, the relative displacement of the focused spot 110 with respect to the light receiving element 7 can be initially adjusted. When the cover glass 2 is fixed to the package 12, first, the package 12 may be rotationally adjusted with respect to the stem 10 and then bonded and fixed.

By the way, +1 when the light is collected on the light receiving element 7.
The order diffracted light beam 108 is diffracted by the change in the wavelength, that is, the diffraction angle (± 0 with the optical axis of the 0th order light beam).
The angle formed by the optical axes of the first-order diffracted light beams changes. For this reason, when the wavelength of the received light beam 105 changes due to factors such as temperature fluctuations, as shown in FIG. 8, the focused spot 110 on the light receiving element 7 connects the diffraction grating 6 and the light receiving element 7 in the direction (in FIG. 8). It will be displaced in the X direction). Therefore,
Even if the focused spot 110 is displaced due to the wavelength shift,
In order to prevent the light-receiving element 7 from protruding from the light-receiving surface, a light-receiving element having a sufficiently long light-receiving surface in at least the displacement direction of the focused spot 110, that is, the direction connecting the diffraction grating 6 and the light-receiving element 7 is required. . 8 and 9 are plan views showing one example thereof. In the example of FIG. 8, the light receiving element 7
Has a rectangular light receiving surface in which the side length a in the X direction is sufficiently longer than the side length b in the Y direction. However, the shape of the light receiving surface is not limited to the rectangular shape, and may be, for example, a trapezoidal shape as shown in FIG. 9 or an oval (elliptical) shape.

Further, the position itself of the light receiving element 7 is not limited to the embodiment shown in FIGS.
It may be arranged at any position as long as it can be stored in 2. Further, the number of light receiving elements 7 is not limited to one, and two or more light receiving elements may be provided. For example, if the light receiving element 7 is 2
The individual + 1st order diffracted light beams 108 and − shown in FIG.
If each of the first-order diffracted light beams 109 is received, the light utilization efficiency at the time of reception can be further improved.

FIGS. 10 and 11 show the configurations of the optical modules of the third and fourth embodiments of the present invention in which two light receiving elements are provided, respectively. However, FIG. 10 and FIG.
1 is a schematic plan view in which only main components are extracted and drawn to show the arrangement of the light receiving elements 7a and 7b.
In FIG. 1, the same components as those in the above-described embodiments are designated by the same reference numerals.

In the third embodiment shown in FIG. 10, the first light receiving element 7a is arranged on the submount 11 shown in each of the embodiments of FIGS. 1 and 6, and the opposite side with the light emitting element 1 sandwiched therebetween. The second light receiving element 7b is arranged at. And the first
The focused spot 110 of the + 1st-order diffracted light beam 108 is incident on the light receiving element 7a of, and the second light receiving element 7b is
A condensing spot 111 of the first-order diffracted light beam 109 is configured to enter. On the other hand, in the fourth embodiment shown in FIG. 11, the two light receiving elements 7a and 7b are arranged at positions rotated by 90 ° from the arrangement of FIG.

The plurality of light receiving elements thus arranged are
Any arrangement may be used as long as they are arranged in substantially symmetrical positions with the light emitting element 1 interposed therebetween. If the arrangement direction of the light receiving element changes, it is naturally necessary to rotate the diffraction grating 6 accordingly, and adjust so that each diffracted light beam is focused on a predetermined light receiving element.

12 and 13 relate to the fifth embodiment of the present invention. FIG. 12 is a perspective view of a main part of a diffraction grating used in the optical module of this embodiment. FIG. 13 shows the diffraction grating. It is a schematic sectional drawing of the optical module of the present Example used. Note that, in FIGS. 12 and 13, the same components as those of the embodiments described above are denoted by the same reference numerals.

In this embodiment, the grating groove 21 of the diffraction grating 6'is
However, it is not a rectangular cross-sectional shape like the grating groove 20 shown in FIG. 2, but a sawtooth-shaped cross-sectional shape asymmetric with respect to the incident optical axis. When the grating groove 21 has such an asymmetrical cross-sectional shape (hereinafter, this is referred to as blazing), the diffraction efficiency of the ± 1st-order diffracted light beams becomes nonuniform, and one of the diffracted light beams (see FIG.
In the example of 2, the light quantity of the + 1st order diffracted light beam 108) increases. For example, the wavelength of the light beam 106 incident on the diffraction grating 6 ′ is 1.3 μm, the average grating pitch is 2 μm on a glass substrate having a refractive index n ₀ = 1.51, and the cross-sectional shape is a substantially right triangle. Blazed lattice grooves 21
In the case of engraving, if the grating groove depth d is about 1.3 μm, about 40% of the light quantity of the incident light beam 106 can be converted into the + 1st order diffracted light beam 108. This is about twice as efficient as when the rectangular lattice groove 20 as shown in FIG. 2 is provided. On the other hand, the light quantity of the −1st order diffracted light beam 109 is reduced to about 5% of the incident light beam 106. In addition, at this time, the amount of light of the 0th-order light beam 107 that proceeds without diffraction is still about 40% of the amount of light of the incident light beam 106. This is the same value as when the rectangular lattice groove 20 is used.

Therefore, as shown in FIG. 13, in the optical module of the present embodiment equipped with the blazed diffraction grating 6 ', the reception light beam 105 of the reception light beam 105 can be obtained without lowering the light utilization efficiency during transmission. About 40% of the amount of light can be guided to the light receiving element 7, and the light utilization efficiency at the time of reception is significantly improved.

The cross-sectional shape of the blazed grating groove 21 is not limited to the right triangle as shown in FIG. 12, and any triangle other than the right triangle may be used as long as it is asymmetric with respect to the incident optical axis. The shape may be a trapezoid.

By the way, in each of the embodiments described above, the wavelength of the transmission light beam guided from the light emitting element 1 to the optical fiber 4 and the wavelength of the reception light beam transmitted through the optical fiber 4 into this optical module are as follows. Not limited at all. That is, the optical module of the present invention can be used without any problem not only when the wavelengths of both light beams match but also when the wavelengths differ.

In each of the above embodiments, the optical fiber 4
Although the case where one type of signal light is transmitted inside is described, the optical module of the present invention can also be used when two or more types of signal light are transmitted. However, in such a case, each signal light may act as stray light with respect to the other signal light, and as a result, so-called crosstalk characteristics (crosstalk characteristics) of the received signal may deteriorate,
There is a need for means to prevent it.

FIG. 14 and FIG. 15 respectively show the essential parts of the optical modules of the sixth and seventh embodiments of the present invention in which two or more types of signal light are transmitted, and the above mentioned crosstalk characteristic deterioration. Have taken preventive measures against. Note that, in FIGS. 14 and 15, the same components as those in each of the embodiments described above are denoted by the same reference numerals.

In the sixth embodiment and the seventh embodiment, the two kinds of signal lights transmitted in the optical fiber 4 have wavelengths λ1 and λ2 which are different from each other. Then, in the optical module, the received light beam of wavelength λ1 (106a in the example of FIGS. 14 and 15) is transmitted, and the light beam of other wavelength λ2 (FIGS. 14 and 15).
In this example, the wavelength selective filter 30 is provided so that 106b) is reflected. The wavelength selective filter 30 is provided on the lower surface of the cover glass 2 in the sixth embodiment of FIG. 14 and on the upper surface of the light receiving element 7 in the seventh embodiment of FIG. Filter 30
May be provided anywhere in the optical path from the end face 5 of the optical fiber 4 to the light receiving element 7.

Further, in the sixth and seventh embodiments of FIGS. 14 and 15, in order to selectively receive a plurality of signal lights transmitted in one optical fiber, the wavelengths of the respective signal lights are different from each other. However, other than that, for example, there is a method of selecting by utilizing the difference in the polarization direction of light. That is, if a polarization-preserving type optical fiber is used as the optical fiber 4 and a polarization filter is used instead of the wavelength selective filter 30 described above, a specific signal light is selected from a plurality of signal lights having different polarization directions. Can be received.

On the other hand, when the signal lights transmitted through the optical fiber have different wavelengths, when they are diffracted by the diffraction grating, a difference in the wavelength causes a difference in the diffraction angles of the ± first-order diffracted light beams. So if you use the difference in the diffraction angles,
Each signal light can be received independently. Figure 1
FIG. 6 is a schematic cross-sectional view of an optical module according to an eighth embodiment of the present invention, which receives each signal light independently by utilizing the difference in diffraction angle. Note that, in FIG. 16, the same components as those in the above-described embodiments are designated by the same reference numerals.

In this embodiment, two received light beams 105a and 105b having different wavelengths are converted into light beams 106a and 106b by the lens 3 and reach the diffraction grating 6. Then, they are diffracted together by the diffraction grating 6 and separate the + 1st order diffracted lights 108a and 108b. However, in general, when light beams with different wavelengths are incident on the same diffraction grating, the light beam with the longer wavelength is ±
The diffraction angle of the first-order diffracted light beam is large. Therefore, FIG.
, The + 1st-order diffracted light beam 108b having the longer wavelength λ2 has the shorter wavelength λ1 than λ2 +1.
The second-order diffracted light beam 108a is condensed at a position farther from the light emitting element 1. Therefore, by arranging the light receiving elements 7a and 7b so that the + 1st-order diffracted light beams 108a and 108b are incident on different light receiving elements, the respective received light beams can be received independently.

By the way, in the above-mentioned sixth and seventh embodiments of FIGS. 14 and 15, the example in which the wavelength selective filter 30 is provided in order to selectively receive a plurality of signal lights having different wavelengths has been shown. Other than that, for example, by controlling the groove depth of the diffraction grating 6, the diffraction grating itself can have the same wavelength selection function as the wavelength selective filter. Examples in which the diffraction grating itself has a wavelength selection function will be described below.

FIG. 17 shows a diffraction grating 6 having a grating groove 20 having a rectangular cross-sectional shape as shown in FIG. 2 formed on a substrate having a refractive index n ₀ = 1.51. The relationship is as follows: light beam with wavelength λ1 = 1.3 μm and wavelength λ2 =
It is a graph figure which shows the result calculated about the light beam of 1.55 micrometer. As is clear from the figure, the grating groove depth d
Is about 2.5 to 2.6 μm, the wavelength λ1 = 1.3
The light beam of μm is hardly diffracted, and the light amount is almost 100.
% Passes through the diffraction grating 6 as it is as a 0th-order light beam. On the other hand, a light beam with a wavelength λ2 = 1.55 μm is about 1
There is a diffraction efficiency of 0%. This is expressed by the following equation (n ₀ −n ₁ ) · d≈m · λ for a wavelength λ having a grating groove depth d, where n ₀ : refractive index n _{1 of} a member constituting the diffraction grating. : Refractive index of the medium (eg, air) around the diffraction grating m: When the relation of any integer is satisfied, this diffraction grating is equivalent to the case where there is no grating groove for the light beam of wavelength λ. It has the property that

18 and 19 are schematic sectional views of an optical module according to the ninth embodiment of the present invention using the diffraction grating 6 having such a wavelength selecting function. FIG. 18 shows a state at the time of transmission. FIG. 19 shows the state at the time of reception. Note that, in FIGS. 18 and 19, the same components as those of the embodiments described above are denoted by the same reference numerals.

In this embodiment, the wavelength λ1 =
A light emitting element 1 that emits a 1.3 μm light beam is provided. As described above with reference to FIG. 17, assuming that the grating groove depth d of the diffraction grating 6 is about 2.5 to 2.6 μm, the wavelength λ1
The diffraction grating 6 hardly functions as a diffraction grating for a light beam of 1.3 μm. Therefore, at the time of transmission shown in FIG. 18, the light beam 100a emitted from the light emitting element 1 is
Almost 100% of the light amount passes through the diffraction grating 6 as it is to become a light beam 101a, which is condensed by the lens 3 on the end face 5 of the optical fiber 4. Therefore, very high light utilization efficiency can be obtained during transmission.

At the time of reception shown in FIG. 19, the light beam 105a of wavelength λ1 = 1.3 μm is emitted from the end face 5 of the optical fiber 4 as in the sixth and seventh embodiments shown in FIGS. Light beam 105 with wavelength λ2 = 1.55 μm
b and b are emitted at the same time, and they reach the diffraction grating 6 through the lens 3. However, the diffraction grating 6 diffracts only the light beam 106b having the wavelength λ2, and the + 1st order diffracted light beam 1
08b is focused on the light receiving element 7. On the other hand, the light beam 106 a having the wavelength λ1 directly passes through the diffraction grating 6 and the cover glass 2 to become the light beam 107 a, which reaches the light emitting element 1. Therefore, the light receiving element 7 selectively receives only the light beam of the wavelength λ2, and the same good crosstalk characteristics as those obtained when the wavelength selective filter is used can be obtained.

As described above, when the grating groove depth of the diffraction grating 6 is set in accordance with the wavelength of the predetermined signal light transmitted in the optical fiber, the diffraction grating itself can have a wavelength selecting function. It is possible to obtain high light utilization efficiency at the time of transmission and good crosstalk characteristics at the time of reception at the same time without using the above filter.

Further, as shown in the following embodiments, light emitting means including the light emitting element 1 and the monitor diode 8 (the light emitting element and the light receiving element for monitoring the output of the light emitting element are usually paired to emit light). (Constituting means) has a light detecting function similar to that of the light receiving element 7, so that the signal is transmitted independently through the diffraction grating 6 and receives the signal independently from the light beam 107a having the wavelength λ1 reaching the light emitting element 1. can do.

FIG. 20 shows the configuration of an optical transmission device equipped with an optical module according to the tenth embodiment of the present invention, which uses a light emitting means having a light detecting function. Also in FIG. 20, the same numbers are assigned to the same components as those in each of the above-described embodiments.

The optical components used in this embodiment are the same as those in the ninth embodiment shown in FIGS. 18 and 19 except for the light emitting element 1 '. Therefore, at the time of reception, as in the ninth embodiment,
The + 1st order diffracted light beam 108b having the wavelength λ2 is received by the light receiving element 7
Is condensed on the light receiving surface of. The signal photoelectrically converted therein is supplied to the current-voltage converter 50b provided in the transmitter / receiver 60, and the waveform shaper 51b and the demodulator 5 are supplied.
The reception signal (2) is obtained through 2b and the like. On the other hand, the light beam 10 having the same wavelength λ1 as the transmitted light beam 104
The light 6a passes through the diffraction grating 6 and the cover glass 2 and becomes a light beam 107a, which is incident on the light emitting element 1 '. By the way, in an optical communication system or an optical transmission system in which a bidirectional optical transmission module such as the present invention is used, a time division transmission / reception method in which signal transmission and reception are alternately repeated so as not to overlap each other is a general signal transmission method. Is. Therefore,
If the time division transmission / reception method is used also in this embodiment,
When the light beam 107a is incident on the light emitting element 1, the light emitting element 1'is turned off or is in a rest state. Here, the light emitting element 1 ′ of the present embodiment emits a light beam having a wavelength λ1 = 1.3 μm at the time of transmission, and detects the light beam incident on the light emitting element 1 ′ at the time of turning off or at the rest state at the time of reception ( Here it has a function of guiding.
As a specific example of a light emitting element having such a light detection function, for example, when the light is off or in a rest state, it functions as a simple optical waveguide, and a part of the light beam incident on the front end face is guided to the rear end face and is guided to the rear part. There is a semiconductor laser device having a function of irradiating the provided monitor diode 8.

When the semiconductor laser device as described above is used as the light emitting device 1 ', at the time of transmission, a light beam of a predetermined light amount is emitted from the front end face at the time of transmission, and a predetermined light amount proportional to the light amount is emitted. Light beam is radiated to the monitor diode 8 from the rear end face. Then, the output from the monitor diode 8 is fed back to the semiconductor laser driving device 54 as a light emission output control signal of the semiconductor laser element 1 ′ through the current-voltage converter 50a provided in the transmitter / receiver 60. A transmission signal modulated by the modulator 53 is input to the semiconductor laser driving device 54, and a semiconductor laser driving current is supplied from the semiconductor laser driving device 54 to the semiconductor laser element 1'in accordance with this signal. As a result, the semiconductor laser device 1 ′ emits the modulated transmission light beam.

On the other hand, at the time of reception, as described above, a part of the light beam 107a incident on the end face of the semiconductor laser device 1'is guided inside the semiconductor laser device 1 ', and further the monitor diode 8 from the rear end face. Is irradiated. Then, a signal corresponding to the amount of light is output from the monitor diode 8, and the current-voltage converter 50a and the waveform shaper 51 are output.
The received signal (1) is obtained through a and the demodulator 52a. The semiconductor laser driving device 54 and the demodulator 52a are controlled by the control device 55, and the control device 55 automatically switches the transmission / reception process.

In addition to the light beam 107a, the 0th-order light beam 1 of wavelength λ2 is formed on the front end face of the semiconductor laser device 1 '.
Since 07b also enters, the crosstalk characteristic of the received signal (1) may be deteriorated by this. In this case,
If a wavelength selective filter that transmits the light beam of wavelength λ1 and reflects the light beam of wavelength λ2 is provided on the front end face of the semiconductor laser device 1 ′, sufficiently good crosstalk characteristics can be obtained.

The light emitting element used in this embodiment is
The element is not limited to the above-mentioned semiconductor laser element, and any element having both the light emitting function and the light detecting function as described above may be used. Further, as long as it is an element having a light emitting function and a light detecting function at the same time, it is possible to use a free transmission method without being limited to the time division transmission / reception method described above.

By the way, in any of the embodiments described so far, the 0th-order diffracted light beam that has been transmitted through the diffraction grating as it is is used as a transmission light beam at the time of transmission, and at least the + 1st-order diffracted light beam diffracted by the diffraction grating is received at the time of reception. It is configured. However, the present invention is not limited to such a configuration. For example, FIG. 21 and FIG.
2 is a schematic sectional view showing an optical module according to an 11th embodiment and a 12th embodiment of the present invention, respectively.

First, in the eleventh embodiment of FIG. 21, of the plurality of light beams emitted from the light emitting element 1 and diffracted by the diffraction grating 6, the + 1st order diffracted light beam 102 is converted into the transmission light beam 104 by the lens 3. is doing. Therefore, the light emitting element 1 is arranged to be inclined with respect to the optical axis of the lens 3,
The optical axis of the first-order diffracted light beam 102 is substantially aligned with the optical axis of the objective lens. On the other hand, at the time of reception, similarly to each of the above-described embodiments, the + 1st order diffracted light 108 generated by being diffracted by the diffraction grating 6 is incident on the light receiving element 7 to receive a signal.

On the other hand, in the twelfth embodiment shown in FIG.
The 0th-order light beam 107 of the received light beam 105 that has been transmitted straight through the diffraction grating 6 is configured to enter the light-receiving element 7. That is, among the plurality of light beams emitted from the light emitting element 1 and diffracted by the diffraction grating 6, the + 1st-order diffracted light beam 102 is used as a transmission light beam, and the reception light beam 105 is diffracted by the diffraction grating 6. Of the light beams of
7 is received as a signal by the light receiving element 7.

As described above, any of the + 1st-order diffracted light beam, the -1st-order diffracted light beam, and the 0th-order light beam diffracted by the diffraction grating 6 may be used for the transmission / reception. Furthermore, a high-order diffracted light beam of ± 2nd order or higher may be used for transmission / reception.

Further, although all the above-mentioned embodiments have one light emitting element and transmit the light beam emitted from the light emitting element into one optical fiber, of course, it is limited to such a structure. Not done. That is, it does not matter even if a plurality of light emitting elements are provided in one optical module or a plurality of optical fibers are connected. As an example of such a configuration, for example, a semiconductor laser array is used as a light emitting element, each lens array is connected to a separate optical fiber, or a ± 1st order diffracted light beam generated from one light beam is used by a diffraction grating. There is a configuration in which a separate optical fiber is connected to each of the 0th-order light beams.

Furthermore, it goes without saying that the optical module (bidirectional optical transmission module) of each of the embodiments described above can be mounted on various optical transmission devices.

[0070]

As described above, according to the present invention, a bidirectional optical transmission module can be obtained with a simple structure.
It is very effective in reducing the size and cost of the bidirectional optical transmission module.

[Brief description of drawings]

FIG. 1 is a sectional view of a bidirectional optical transmission module according to a first embodiment of the present invention.

FIG. 2 is one of the diffraction gratings used in the first embodiment of the present invention.
It is a principal part perspective view which shows an example.

3 is a schematic plan view showing an example of a grating groove locus of the diffraction grating of FIG.

FIG. 4 is a cross-sectional view of essential parts showing a state of a bidirectional optical transmission module at the time of transmission according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional view of essential parts showing a state of the bidirectional optical transmission module at the time of reception according to the first embodiment of the present invention.

FIG. 6 is a sectional view of a bidirectional optical transmission module according to a second embodiment of the present invention.

FIG. 7 is a plan view of relevant parts for explaining an example of a light spot position adjusting method applied in each embodiment of the present invention.

FIG. 8 is a plan view of a principal portion showing an example of a light receiving surface of a light receiving element applied in each embodiment of the present invention.

FIG. 9 is a main-portion plan view showing another example of the light-receiving surface of the light-receiving element applied in each embodiment of the present invention.

FIG. 10 is a plan view of a principal part of a bidirectional optical transmission module according to a third embodiment of the present invention.

FIG. 11 is a plan view of a principal part of a bidirectional optical transmission module according to a fourth embodiment of the present invention.

FIG. 12 is a perspective view of a principal part showing an example of a diffraction grating used in a bidirectional optical transmission module according to a fifth embodiment of the invention.

FIG. 13 is a cross-sectional view of essential parts of a bidirectional optical transmission module according to a fifth embodiment of the present invention.

FIG. 14 is a cross-sectional view of essential parts of a bidirectional optical transmission module according to a sixth embodiment of the present invention.

FIG. 15 is a cross-sectional view of essential parts of a bidirectional optical transmission module according to a seventh embodiment of the present invention.

FIG. 16 is a cross-sectional view of essential parts of a bidirectional optical transmission module according to an eighth embodiment of the present invention.

FIG. 17 is an explanatory diagram showing the relationship between the grating groove depth and diffraction efficiency in an example of the diffraction grating used in the present invention.

FIG. 18 is a cross-sectional view of essential parts showing the state of a bidirectional optical transmission module during transmission according to the ninth embodiment of the present invention.

FIG. 19 is a sectional view of a key portion showing a state of the bidirectional optical transmission module at the time of reception according to the ninth embodiment of the present invention.

FIG. 20 is a configuration diagram of an optical transmission device equipped with an optical module according to a tenth embodiment of the present invention.

FIG. 21 is a cross-sectional view of essential parts of a bidirectional optical transmission module according to an eleventh embodiment of the present invention.

FIG. 22 is a cross-sectional view of essential parts of a bidirectional optical transmission module according to a twelfth embodiment of the present invention.

[Explanation of symbols]

 1, 1'Light emitting element 2 Cover glass 3 Lens 4 Optical fiber 6,6 'Diffraction grating 7, 7a, 7b Light receiving element 8 Monitor diode 30 Wavelength selective filter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Fukui 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Ltd.

Claims (9)

[Claims] 1. A light emitting device, a light receiving device, and an optical device for guiding a light beam emitted from the light emitting device to a predetermined optical transmission path.
An optical transmission module comprising a package having at least the light emitting element and the light receiving element and having a window portion provided with a transparent member, wherein a lattice groove having a linear or curved locus is provided on an upper surface or a lower surface of the transparent member. An optical transmission module having a diffraction grating. 2. The optical transmission module according to claim 1, wherein the optical element is held in the package. 3. The device according to claim 1, wherein at least the diffraction grating and the transparent member are rotatable about a predetermined rotation axis substantially parallel to the optical axis of the light beam passing through the transparent member. Characteristic optical transmission module. 4. The light receiving element according to claim 1, wherein the light receiving element has a rectangular or trapezoidal or oval light receiving surface having a longitudinal direction in a direction substantially parallel to a straight line connecting the light receiving element and the light emitting element. Characteristic optical transmission module. 5. The optical transmission module according to claim 1, wherein the grating groove of the diffraction grating has a substantially sawtooth cross-sectional shape. 6. The light according to claim 1, wherein a wavelength selective filter that selectively transmits a light beam of a specific wavelength is provided in an optical path from the optical transmission path to the light receiving element. Transmission module. 7. The diffraction groove depth d of the diffraction grating, the refractive index n _{0 of} a member forming the diffraction grating, and the refractive index n ₁ of a surrounding medium in contact with the diffraction grating are set to predetermined values according to claim ₁ . The optical transmission module is characterized by satisfying the following expression d≈m · λ / (n ₀ −n ₁ ) (where m is an integer) with respect to the wavelength λ of the light beam. 8. The light emitting means according to claim 1, wherein the light emitting means includes the light emitting element and components attached thereto.
An optical transmission module having a function of emitting a light beam in response to a predetermined electric signal and a light detection function of outputting a predetermined electric signal in accordance with the amount of light beam incident on a light emitting element. 9. An optical transmission device comprising the optical transmission module according to claim 1.