JP3728594B2 - 2-wavelength optical multiplexer / demultiplexer module - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a two-wavelength optical multiplexer / demultiplexer module, and more particularly to a two-wavelength optical multiplexer / demultiplexer module used for single-core bidirectional communication.
[0002]
[Prior art]
A conventional example of an optical transceiver module will be described with reference to FIG.
In the field of optical communication technology, signal light having a wavelength of λ ₁ : 1.31 μm and signal light having a wavelength of λ ₂ : 1.55 μm are transmitted through one optical fiber 8. Specifically, in a terminal that accesses signal light of wavelength λ ₁ and signal light of wavelength λ ₂ , both signal lights are transmitted and reflected by an optical filter 3 made of a dielectric multilayer filter and separated. To do. That is, the signal light having the wavelength λ ₂ transmitted through the optical fiber 131 reaches the optical filter 3 through the Y-branch optical waveguide 22, passes through the optical filter 3, and accesses the light receiving element 4 made of a photodiode. . On the other hand, the signal light having the wavelength λ ₁ emitted from the laser diode 5 reaches the optical filter 14 via the Y-branch optical waveguide 22, is reflected thereby, and is transmitted to the outside via the optical fiber 8. As described above, both the signal light having the wavelength λ _{1 and} the signal light having the wavelength λ ₂ can be transmitted and received by the single optical fiber 8.
[0003]
[Problems to be solved by the invention]
In the prior art, since the incident angle of light with respect to the optical filter 3 is as shallow as about 10 °, there is almost no difference in the reflection characteristics of p-polarized light and s-polarized light and the transmission characteristics of p-polarized light and s-polarized light. The wave dependent characteristic PDL is good. However, since the laser diode 5 and the light receiving element 4 are arranged to face each other via the linear optical waveguide 21, the optical filter 3 has the signal light having the wavelength λ ₁ emitted from the laser diode 5 incident on the light receiving element 4. Therefore, it is necessary that the signal light having the wavelength λ _{1 and} the signal light having the wavelength λ ₂ exhibit high isolation of about 60 dB. It is not easy to design and manufacture the optical filter 3 exhibiting high isolation of about 60 dB.
[0004]
Since the Y-branch optical waveguide 22 is configured to be curved as necessary, an advanced design and manufacturing technique that suppresses light leakage outside the optical waveguide due to bending of the optical waveguide is required.
The present invention provides a two-wavelength multiplexer / demultiplexer module that has a simple optical waveguide structure and easily realizes high isolation between a laser diode and a light receiving element.
[0005]
[Means for Solving the Problems]
An optical waveguide substrate having an end face 12 inclined by about 45 ° with respect to a light incident / exit axis on an extension of an optical axis of an optical fiber fixed in a V-shaped groove 13 in a two-wavelength optical multiplexer / demultiplexer module 1, the cross-sectional V-shaped groove 13 formed to the vicinity of the 45 ° inclined end surface of the surface 11 of the optical waveguide substrate 1, the optical fiber 131 fixed to the cross-sectional V-shaped groove 13, and the end surface of the optical waveguide substrate 1 An optical filter 3 composed of a dielectric multilayer filter disposed on the optical input / output axis extension line 12 and close to the vicinity of the optical fiber ; One of the elements 4 and the other of the laser diode 5 or the light receiving element 4 disposed opposite to the optical filter 3 in a direction orthogonal to the light incident / exit axis extending line, And one and the optical waveguide 6 in a straight line interposed to form a little raised on the surface of the optical waveguide substrate between the optical fiber 131 of the The diode 5 or the light receiving element 4, of the laser diode 5 or the light receiving element 4 A two-wavelength optical multiplexer / demultiplexer module including a straight optical waveguide 6 ′ formed between the other and the optical filter 3 so as to be slightly raised and formed on the surface of the optical waveguide substrate is formed .
[0006]
Further, in the two-wavelength optical multiplexer / demultiplexer module according to the second aspect of the present invention, the two-wavelength optical multiplexer / demultiplexer in which both of the two straight optical waveguides 6 and 6 ′ are constituted by the optical fibers 131 and 131 ′. Configured the module.
A third aspect of the present invention relates to the two-wavelength optical multiplexer / demultiplexer module according to any one of the first and second aspects, wherein the light receiving element 4 disposed opposite to the optical filter 3 on the light incident / exit axis extension line and The laser diode 5 is disposed opposite to the optical filter 3 in a direction perpendicular to the light incident / exit axis extension line, and the transmittance of the p-polarized light and the s-polarized light incident on the light receiving element 4 is substantially equal . A two-wavelength optical multiplexer / demultiplexer module comprising a high dielectric multilayer filter of 5 dB or less was constructed.
[0007]
Further, in the dual wavelength optical multiplexer / demultiplexer module according to any one of claims 1 and 2, the laser diode 5 disposed opposite to the optical filter 3 on the light incident / exit axis extension line and The light receiving element 4 is disposed opposite to the optical filter 3 in a direction orthogonal to the light incident / exit axis extension line, and the reflectance of p-polarized light and s-polarized light incident on the light receiving element 4 is substantially equal and the reflectance is 0. A two-wavelength optical multiplexer / demultiplexer module comprising a high dielectric multilayer filter of 5 dB or less was constructed.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the example of FIG.
In FIG. 1, 10 is a base part. The optical waveguide substrate 1 and the submount 2 are attached and fixed to the surface of the base portion 10. The optical waveguide substrate 1 is composed of a silicon wafer. Between the surface 11 of the optical waveguide substrate 1 and the surface of the base portion 10, there is about 45 with respect to the light incident / exit axis direction that coincides with the core of the optical fiber fixed to the V-shaped groove 13, which will be described later. The end face 12 inclined by a degree is formed with a step from the surface of the base portion 10. The surface 11 and the end face 12 are orthogonal to each other at an angle of 90 °. A cross-section V-shaped groove 13 for fixing an optical fiber is formed on the surface 11 of the optical waveguide substrate 1 along the light incident / exit axis direction. An optical fiber 131 is positioned and bonded to the V-shaped groove 13 with its core line aligned with the light incident / exit axis.
[0009]
Reference numeral 3 denotes an optical filter composed of a dielectric multilayer filter. The optical filter 3 is positioned and fixed in correspondence with the light incident / exit axis on an end face 12 inclined by about 45 ° with respect to an extension line of the light incident / exit axis. The optical filter 3 has unique light transmittance characteristics and light reflectance characteristics which will be described later with reference to FIGS.
The submount 2 fixed to the base portion 10 is positioned and fixed facing the optical filter 3 on the extension line of the light incident / exit axis. A light receiving element 4 is positioned and fixed to the submount 2 so as to face the optical filter 3 on the extension line of the light incident / exit axis.
[0010]
A laser diode 5 is positioned and fixed on the surface 11 of the optical waveguide substrate 1 so as to face the optical filter 3 in a direction orthogonal to the light incident / exit axis. In this embodiment, the laser diode 5 will be described as emitting signal light having a wavelength λ ₁ .
A very short first straight optical waveguide 6 is interposed between the optical fiber 131 fixed to the V-shaped groove 13 and the optical filter 3, and extremely between the laser diode 5 and the optical filter 3. A short second straight optical waveguide 6 'is interposed. The first linear optical waveguide 6 and the second linear optical waveguide 6 ′ are formed so as to slightly protrude from the surface using the optical waveguide substrate 1 as a silicon wafer. FIG. 2 shows an embodiment in which these very short optical waveguides 6 and 6 'are constituted by optical fibers. That is, the very short first straight optical waveguide 6 is formed by extending the tip of the optical fiber 131 fixed to the V-shaped groove 13 in a very short direction, as shown in the drawing, and the very short second straight line. The optical waveguide 6 ′ is constituted by a second optical fiber 131 ′.
[0011]
In the above two-wavelength multiplexer / demultiplexer module, the signal light having the wavelength λ ₂ transmitted to the module via the optical fiber 131 reaches the optical filter 3 via the very short first linear optical waveguide 6. Then, the light receiving element 4 is accessed through this. On the other hand, the signal light having the wavelength λ ₁ emitted from the laser diode 5 reaches the optical filter 3 through the very short second linear optical waveguide 6 ′, and is reflected by this to pass through the optical fiber 131 to the outside of the module. Is emitted. By the way, the optical filter 3 must originally exhibit high isolation so that the signal light having the wavelength λ ₁ emitted from the laser diode 5 cannot be incident on the light receiving element 4. Since the laser diode 5 is positioned and arranged in a direction perpendicular to the light incident / exit axis of the laser diode 5, an optical filter having a slightly lower isolation may be used. That is, it is not always necessary for the optical filter 3 itself to have a high isolation characteristic for the signal light having the wavelength λ ₁ , thereby facilitating the design and manufacture of the optical filter 3.
[0012]
Here, the optical filter 3 will be described with reference to FIGS. 3 and 4. FIG. 3 is a diagram showing the transmittance of the optical filter 3 with an emphasis on isolation between the signal light having the wavelength λ _{1 and} the signal light having the wavelength λ _{2 at} an incident angle of 45 °. FIG. 4 is a diagram showing the reflectivity of the optical filter 3 with an emphasis on isolation between the signal light having the wavelength λ _{1 and} the signal light having the wavelength λ _{2 at} an incident angle of 45 °.
Since the incident angle of 45 ° of the signal light with respect to the optical filter 3 is a large incident angle, even if the optical filter 3 is designed according to a normal design, in principle, a large difference occurs between p-polarized light and s-polarized light. Thus, the optical filter 3 that can sufficiently achieve transmission isolation of the signal light having the wavelength λ ₁ with respect to the signal light having the wavelength λ ₂ cannot be obtained. That is, in the case of the laser diode 5 in which the p-polarized light accounts for most of the emitted light energy, there is a particularly large transmission isolation between the signal light of wavelength λ _{2 and} the signal light of wavelength λ ₁ as shown in FIG. It is not guaranteed. Then, referring to FIG. 4, the wavelength regard to the reflection isolation wavelength lambda ₂ of the signal light with respect to lambda ₁ of the signal light, p-polarized light and s-polarized light of a wavelength in both lambda ₁ of the signal light and the wavelength lambda ₂ of the signal light It does not mean that a very large isolation of reflection is ensured.
[0013]
Another optical filter will be described with reference to FIGS. FIG. 5 is a diagram showing the transmittance of the optical filter 3 with an emphasis on the transmittance of the signal light having the wavelength λ _{2 at} an incident angle of 45 °. FIG. 6 is a diagram showing the reflectance of the optical filter 3 with an emphasis on the reflectance of the signal light having the wavelength λ _{2 at} an incident angle of 45 °.
For SiO ₂ / Ta ₂ O ₅ and then only deposited laminated 58 layers alternately 15. 3 [mu] m optical filter 3 made of a dielectric multilayer film filter obtained by laminating, FIG. 5 shows the transmission characteristics, the wavelength lambda ₂ of the signal light The transmittance is about 0.5 dB or less. On the other hand, the transmittance of the signal light having the wavelength λ ₁ , in particular, the transmittance of the p-polarized light that occupies most of the emission energy of the laser diode 5 is increased. As described above, the emission optical axis and the light receiving element of the laser diode 5 4 is arranged so as to be orthogonal to the light receiving axis 4, the signal light having the wavelength λ ₁ emitted from the laser diode 5 may be transmitted through the optical filter 3 even though it is large, so that it is not received by the light receiving element 4. Absent. On the other hand, since the transmittance of the signal light having the wavelength λ ₂ is improved, the isolation of reflection is improved to 20 dB or more. That is, the transmission isolation of the light having the wavelength λ ₁ is not a problem because the laser diode 5 and the light receiving element 4 are not arranged to face _each other, but the reflection isolation of the signal light having the wavelength λ ₂ is a problem. Therefore, if the transmission characteristics of the p-polarized light and the s-polarized light of the signal light having the wavelength λ ₂ are reduced, the reflection isolation of the light having the wavelength λ ₂ is also improved.
[0014]
In the above embodiment in which the light receiving element 4 is disposed on the extension axis of the light incident / exit axis and behind the optical filter 3, the optical filter 3 is designed with an emphasis on the optical characteristics of the light receiving element 4 as the light receiving element. The design of FIGS. 5 and 6 is such that the transmittance of the p-polarized light and the s-polarized light of the signal light having the wavelength λ ₂ incident on the light receiving element 4 is substantially equal and high. In this embodiment, in particular p-polarized light of the wavelength lambda ₁ of the signal transmitted through the optical fiber 131 is transmitted through the optical filter 3 are received by the light receiving element 4, the wavelength lambda ₂ of the signal transmitted in the same manner It can be recognized from FIG. 5 that light also passes through the optical filter 3 and is received by the light receiving element 4. It can be recognized from FIG. 6 that the signal light having the wavelength λ ₁ emitted from the laser diode 5 is reflected by the optical filter 3 and emitted to the outside of the module.
[0015]
Here, in FIGS. 1 and 2, the light receiving element 4 and the laser diode 5 are exchanged, the laser diode 5 is disposed instead of the light receiving element 4, and conversely, the light receiving element 4 is disposed instead of the laser diode 5. A second embodiment will be described. That is, when the light receiving element 4 is arranged in a direction perpendicular to the light incident / exit axis with respect to the optical filter 3, the reflectance of the p-polarized light and the s-polarized light incident on the light receiving element 4 are substantially equal and the reflectance is high. The design shown in FIG. The amount of transmission of the signal light of wavelength λ ₁ emitted from the laser diode 5, in particular, p-polarized light, which is transmitted through the optical filter 3 is large as shown in FIG. 3, but the light receiving element 4 is perpendicular to the light incident / exit axis by the optical filter 3. Since it is arranged in the direction, there is no problem. However, the reflection isolation of the optical filter 3 composed of the dielectric multilayer filter in which only 76 layers of SiO ₂ / Ta ₂ O ₅ are alternately deposited and laminated to 16.9 μm does not reach 20 dB. In summary, in the case of the second embodiment, the signal of wavelength λ ₁ transmitted through the optical fiber 131 is reflected by the optical filter 3 and received by the light receiving element 4 and transmitted in the same manner. It can be recognized from FIGS. 3 and 4 that the signal light having the wavelength λ ₂ is also reflected by the optical filter 3 and received by the light receiving element 4. It can be recognized from FIG. 3 that the signal light having the wavelength λ ₁ emitted from the laser diode 5 passes through the optical filter 3 and is emitted to the outside of the module.
[0016]
【The invention's effect】
As described above, according to the present invention, the signal light having the wavelength λ ₂ transmitted to the module via the optical fiber 131 is transmitted to the optical filter 3 via the very short first linear optical waveguide 6. The light receiving element 4 is accessed through this. On the other hand, the signal light having the wavelength λ ₁ emitted from the laser diode 5 reaches the optical filter 3 through the very short second linear optical waveguide 6 ′, and is reflected by this to pass through the optical fiber 131 to the outside of the module. Is emitted. Here, a configuration is adopted in which both optical waveguides 6 and 6 ′ are inclined at 45 ° with respect to the optical filter 3, and an extremely short linear optical waveguide can be obtained, resulting in bending of the optical waveguide. Thus, it is possible to suppress the loss of light leaking out of the optical waveguide. The optical filter 3 must originally exhibit high isolation so that the signal light having the wavelength λ ₁ emitted from the laser diode 5 is not allowed to enter the light receiving element 4. Since it is positioned and arranged in a direction perpendicular to the light emission axis of the diode 5, an optical filter with somewhat low isolation may be used. That is, it is not always necessary for the optical filter 3 itself to have a high isolation characteristic for the signal light having the wavelength λ ₁ , thereby facilitating the design and manufacture of the optical filter 3. That is, in order to prevent interference between the light emitting element and the light receiving element at a normal incident angle of 0 °, an optical filter with good isolation is necessary. However, according to the configuration of the present invention, the isolation is poor and the transmittance is low. A high optical filter can be used, and the design and manufacture of the optical filter is facilitated.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a first embodiment;
FIG. 2 is a diagram illustrating a second embodiment.
FIG. 3 is a diagram showing transmission characteristics of an optical filter that places importance on isolation of signal light having a wavelength λ _{1 at} an incident angle of 45 °.
FIG. 4 is a diagram showing reflection characteristics of an optical filter that places importance on isolation of signal light having a wavelength λ _{1 at} an incident angle of 45 °.
FIG. 5 is a graph showing the transmission characteristics of an optical filter with an emphasis on the transmittance of signal light of wavelength λ _{2 at} an incident angle of 45 °.
FIG. 6 is a diagram showing the reflection characteristics of an optical filter that places importance on the transmittance of signal light of wavelength λ _{2 at} an incident angle of 45 °.
FIG. 7 illustrates a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical waveguide board | substrate 10 Base part 11 Surface 12 End surface 13 Sectional V-shaped groove 131 Optical fiber 131 '2nd optical fiber 2 Submount 3 Optical filter 4 Light receiving element 5 Laser diode 6 1st linear optical waveguide 6' 2nd Straight optical waveguide

Claims (4)

In the two-wavelength optical multiplexer / demultiplexer module,
An optical waveguide substrate having an end face 4 5 DEG inclined relative to the optical input and output shaft on the extension of the optical axis of the optical fiber to be fixed in a V-shaped groove,
And a V-shaped groove formed on Symbol 4 5 ° inclined end Menma surface of the optical waveguide substrate,
An optical fiber fixed in a V-shaped cross section;
An optical filter made of dielectrics multilayer filter disposed on the light incidence and emission axis extension on the end face of the optical waveguide substrate,
Any one of the laser diode and the light receiving element disposed on the light incident / exit axis extension line and facing the optical filter, and the laser diode or the light receiving element disposed on the optical filter in the direction orthogonal to the light incident / exit axis extension line One of the other,
A linear optical waveguide interposed between one of the laser diode or the light receiving element and the optical fiber and formed on the surface of the optical waveguide substrate on the light incident / exit axis extension line;
A linear optical waveguide formed on the surface of the optical waveguide substrate between the other of the laser diode or the light receiving element and the optical filter, and formed on an extension line orthogonal to the light incident / exit axis extension line. 2 wavelength optical multiplexer / demultiplexer module. The two-wavelength optical multiplexer / demultiplexer module according to claim 1,
A two-wavelength optical multiplexer / demultiplexer module characterized in that both of the two straight optical waveguides are constituted by optical fibers. In the two-wavelength optical multiplexer / demultiplexer module according to any one of claims 1 and 2,
A light receiving element disposed opposite to the optical filter on the light incident / exit axis extension line, and a laser diode disposed opposite to the optical filter in a direction orthogonal to the light incident / exit axis extension line;
2. A two-wavelength optical multiplexer / demultiplexer module comprising a dielectric multilayer filter having substantially the same transmittance for p-polarized light and s-polarized light incident on the light receiving element and having a transmittance of 0.5 dB or less. In the two-wavelength optical multiplexer / demultiplexer module according to any one of claims 1 and 2,
A laser diode disposed opposite to the optical filter on the light incident / exit axis extension line and a light receiving element disposed opposite to the optical filter in a direction perpendicular to the light incident / exit axis extension line;
2. A two-wavelength optical multiplexer / demultiplexer module comprising a dielectric multilayer filter having substantially the same reflectance of p-polarized light and s-polarized light incident on the light receiving element and having a reflectance of 0.5 dB or less.

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