JP3964768B2 - Optical module - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical module in which an optical waveguide circuit and an optical semiconductor element are integrated, and more particularly to an optical module adapted to an optical circuit in which optical components having a multimode optical waveguide structure such as a light receiving element are integrated.
[0002]
[Prior art]
In an optical module in which a single-mode optical waveguide and an optical semiconductor element are hybrid-integrated, a structure has been adopted in which light is guided to the optical semiconductor element by a single-mode optical waveguide and optically coupled to the optical waveguide and the optical semiconductor element. For example, refer nonpatent literature 1).
[0003]
FIG. 7 shows an example of the prior art. Reference numeral 71-1 in the figure denotes a single mode optical waveguide core. A part of the optical waveguide on the optical waveguide substrate is removed and a recess is provided, and a laser diode (hereinafter also referred to as LD (laser diode)) 72-1 and a receiving photodiode (hereinafter referred to as PD (hereinafter referred to as PD)) are provided as optical semiconductor elements. 72-2 is fixed on the substrate and combined with the Y branch circuit 73-1 of the optical waveguide 71-1, thereby constituting an optical transceiver.
[0004]
In general, in a single-mode optical waveguide, light is radiated to a clad with a large loss in an optical circuit portion or an optical coupling portion. Also in FIG. 7 of the conventional example, radiation of light appears and becomes a loss at the Y branch portion. Reference numeral 710-2 is stray light.
In the X-crossing waveguide as shown in FIG. 8, when one waveguide light crosses the other waveguide region in the X-crossing circuit 83-2 at the crossing portion, the light is radiated at that portion. If the optical waveguide ahead has the same structure as the incident side, light that does not couple exists and is inefficient, and extra stray light is generated in the waveguide. Reference numeral 810-2 is stray light.
[0005]
[Non-Patent Document 1]
Junichi Yoshida et al., “Technological Outlook for Economics of Components for Optical Access Systems”, NTT R & D, 1997, Vol.46, No.5, pp467-472
[0006]
[Problems to be solved by the invention]
In the optical module as described above, stray light is generated at the Y branch of the optical waveguide, at the intersection of the optical waveguide, and at the optical coupling portion between the optical waveguide and the semiconductor element.
[0007]
For this reason, there existed the subject which should be solved that the light which should be light-received by PD reduces or a stray light couple | bonds with other PD.
[0008]
The present invention has been made in view of such problems, and an object of the present invention is to provide an optical module capable of increasing the coupling efficiency of the entire module and suppressing stray light.
[0009]
[Means for Solving the Problems]
In order to achieve such an object, an optical module of the present invention is an optical module in which a single mode optical waveguide and an optical element corresponding to a multimode are integrated, and the single mode optical waveguide has a Y branching and crossing circuit. An optical circuit portion including at least one of a directional coupler and a star coupler, a multimode optical waveguide is provided in the vicinity of the optical circuit portion, and optically coupled to the optical element through the multimode optical waveguide. The multi-mode optical waveguide has an opening angle toward the optical element , and the opening angle is tan Θ = λ / (πw) (λ: wavelength in the medium, w: field radius, π: pi The angle Θ satisfies the relationship:
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the location which has the same function in each drawing, and duplication of description is abbreviate | omitted.
[0025]
In all of the embodiments, the optical waveguide is made of silica and has a step index type core structure. However, in the present invention, the optical waveguide may not be silica, and the waveguide core structure may not be a step index type.
[0026]
[Embodiment 1]
FIGS. 1A and 1B show that an optical element mounting portion is provided on an optical waveguide substrate having a Y branch circuit to provide an optical element mounting portion, and a laser diode (LD) and a photodiode (PD) are integrated in a hybrid manner. It is a figure of an optical module. FIG. 1A shows a case where a multimode waveguide core is used. FIG. 1B is a diagram in the case where a part of the cladding is removed to obtain a waveguide structure. In FIG. 1A, a laser diode (LD) 12-1a and a photodiode (PD) 12-2a are hybrid-integrated. In FIG. 1B, a laser diode (LD) 12-1b and a photodiode (PD) 12-2b are integrated in a hybrid manner.
[0027]
In FIGS. 1A and 1B, reference numerals 11-3a and 11-3b in the drawings are clads. Since the Y branch portions 13-1a and 13-1b are normally demultiplexed into two waveguides, unlike the waveguide mode transmitted by one, light that is not coupled like stray light 710-2 shown in FIG. appear. On the other hand, with the PD 12-2a and PD 12-2b, the absorption layers 12-2a-1 and 12-2b-1 can receive light even if they are not in single mode, and light is guided to the PD by a single mode waveguide as an optical waveguide. There is no need.
[0028]
Therefore, in the first embodiment, as shown in FIG. 1A, one circuit of the Y branch circuit 13-1a is a multimode optical waveguide 11-2a, and a photodiode is disposed at the end thereof. In addition, when the optical waveguide is suddenly changed as a multimode optical waveguide, a large number of higher-order modes are generated, making it difficult to completely confine the light. Only the higher-order mode is generated. As a result, the excess loss that has been about 1 dB in the Y branch can be suppressed to about 1 dB.
[0029]
As an optical module having this configuration, as shown in FIG. 1B, a structure in which stray light is guided may be removed from the cladding 11-3b. In this case, the waveguide core 11-4 connected to the PD 12-2b may not be used, or a single mode or other mode waveguide may be used.
[0030]
Further, FIGS. 2A and 2B are diagrams of an optical module using a bent waveguide. FIG. 2A is an explanatory diagram of light emission by the bent waveguide. FIG. 2B is a diagram in the case where the radiation light of the bent waveguide is guided and incident on the PD.
[0031]
In FIG. 2A, reference numeral 21-1a denotes a single mode optical waveguide core, 21-3a denotes a cladding, and 210-1a denotes propagating light. When the optical waveguide is bent sharply, stray light 210-2a is generated from the bent portion. To do.
[0032]
In FIG. 2B, reference numeral 21-1a denotes a single mode optical waveguide core, 21-3b denotes a cladding, 22-1b-1 denotes a laser diode element active layer, and 22-2b-1 denotes a multimode photodiode element. The absorption layer 220-3 is a conventional optical waveguide track with a radius of curvature. If there is no problem even if the amount of light entering the PD is very small, a multimode waveguide structure 21-2b that couples with the leaked light may be provided as shown in FIG. 2B to guide the light to the PD. . This makes it possible to reduce the radius of curvature when the waveguide is bent. In the first embodiment, it is necessary to open a distance of about 1 mm between the LD 22-1b and the PD 22-2b in order to take an electrode. In order to increase the distance between them, the conventional Y branch circuit has a horizontal direction on the drawing. Required about 3 mm. In the embodiment of FIG. 2 (b), the distance in the vertical direction on the drawing of the distance between the LD and the PD can be increased to about 2 mm, so that the required horizontal distance on the drawing can be shortened.
[0033]
The branch circuit is the same in the following second to fourth embodiments, but may be a directional coupler or a star coupler in addition to the Y branch in the first embodiment.
[0034]
[Embodiment 2]
3 and 8 show an X-crossing circuit 33- using an X-crossing optical waveguide and a 1.3-micron 1.55-micron wave filter (33-4, 83-4) made of a dielectric multilayer film formed on a polyimide film. 2 is a diagram of an optical module in which an optical waveguide having a wavelength branching circuit integrated in 2 and 83-2, LDs 32-1 and 82-1 and PDs 32-2 and 82-2 corresponding to a multimode are hybrid-integrated.
[0035]
FIG. 8 is a diagram of a conventional structure of a wavelength division multiplexing optical transceiver using an X-crossing waveguide and a filter. Reference numeral 81-1 is a single mode optical waveguide core, and 81-3 is a cladding. The film 83-4 has a thickness of about 20 microns, but the light is diffracted in this portion, and the transmitted light causes a relatively large diffraction loss in the optical waveguide whose exit side waveguide is the same thickness as the incident side optical waveguide. To do.
[0036]
Therefore, FIG. 3 shows a case where the PD output side optical waveguide is a multimode optical waveguide 31-2. Reference numeral 31-1 denotes a single mode optical waveguide core, and 31-3 denotes a clad.
[0037]
Here, assuming that a radiating angle is a Gaussian beam, the waveguide width w320-2 (field diameter corresponding to the radiating angle determined by the distance from the radiating portion (radiation angle × distance), field radius in the single mode waveguide) In contrast, the angle Θ satisfying the relationship of tan Θ = λ / (πw) using the wavelength λ in the medium is expressed, so that the expansion ratio of the width of the multimode optical waveguide (the elevation angle of the side surface of the waveguide with respect to the optical axis) The same level. As a result, the stray light 810-2 by the conventional diffraction is confined in the core portion, and the PD coupling ratio is improved by about 0.2 dB.
[0038]
Further, FIG. 4 shows the structure of a multi-channel wavelength division multiplexing optical transceiver in which a plurality of optical modules having the configuration of FIG. 3 are formed on the same substrate. Here, the filter circuit 43-4 is inserted over a plurality of unit modules having the above circuit (the circuit of FIG. 3) as one unit, and suppresses the LD emission side light from leaking to the PD side. Reference numeral 41-3 is a cladding, 43-2 is an X-cross circuit, 42-1a to 42-1d are laser diode elements, and 42-2a to 42-2d are multi-mode photodiode elements.
[0039]
On the other hand, FIG. 9 shows the structure of a conventional multi-channel wavelength division multiplexing optical transceiver in which a plurality of optical modules having the configuration shown in FIG. 8 are formed on the same substrate. Here, the filter circuit 93-4 is inserted over a plurality of unit modules having the above circuit (the circuit of FIG. 8) as one unit, and suppresses the LD emission side light from leaking to the PD side. Reference numeral 91-3 is a cladding, 93-2 is an X-crossing circuit, 92-1a to 92-1d are laser diode elements, and 92-2a to 92-2d are photodiode elements.
[0040]
With respect to incident light on the PD side, light having substantially the same wavelength is incident on the PD 92-2a via, for example, the optical waveguide core 91-1, so that the light that has not been combined becomes stray light 810-2. When entering PD 92-2b to 92-2d, it becomes crosstalk noise 910-3.
[0041]
However, in FIG. 4 of the second embodiment, light that has been conventionally stray light in the optical waveguide to the PD 42-2a is confined in the optical waveguide core 41-2 and propagates to the PD (propagating light 410-1). Crosstalk can be suppressed. This makes it possible to suppress the level of light crosstalk from about 30 dB in the past to about 40 dB.
[0042]
[Embodiment 3]
FIG. 10 is a configuration diagram of a conventional LD module with a monitor, and FIG. 5 is a diagram of an optical module in which an LD and a PD are integrated in an optical waveguide according to the third embodiment.
[0043]
In FIG. 10, reference numeral 102-2 is a photodiode element, 1010-1 is propagating light, and optical coupling between the optical waveguide 101-1 and the LD 102-1 usually has a different field diameter, so that coupling loss occurs, and the optical waveguide A large amount of uncoupled light 1010-2 is generated in the vicinity of the end face.
[0044]
Therefore, as shown in FIG. 5, in the third embodiment, a PD 52-2 that supports multimode is used for output monitoring in order to make the emission intensity of the LD 52-1 constant. In FIG. 5, reference numeral 510-1 is propagating light, 510-2 is uncoupled light, 520-1 is a radiation angle, and 51-3 is a cladding. Here, in the vicinity of the coupling portion between the LD 52-1 and the optical waveguide 51-1, a light guide structure is provided by removing a part of the clad (such as 51-4) as a multimode optical waveguide.
[0045]
The PD 52-2 used here is called a refraction type PD, which refracts incident light from the side surface of the chip on the oblique wall surface of the chip and takes out the light to the chip surface and receives it by a surface type absorption layer. . For this reason, the area of the light receiving portion is large and is about 100 μmφ. Since the size of the light guide structure by the clad is about 20 μm square, the spot is sufficiently small with respect to the light receiving diameter of the PD 52-2, and a sufficient output monitor of 100 μA at a module output of 0 dBm was possible.
[0046]
Further, since the optical waveguide cannot be interrupted when the PD 52-2 is arranged, it is necessary to sufficiently separate it from the optical axis of the LD. On the other hand, in order to reduce the decrease due to scattering of the monitor light, it is necessary to arrange the PD as close to the LD as possible. Therefore, in the third embodiment, the direction of the optical waveguide structure is such that the structure is provided in a range where light does not decrease in accordance with the radiation angle of the LD, and the distance from the LD is as close as possible. In this structure, when the end face of the waveguide is inclined in consideration of the light returning to the LD by the end face of the optical waveguide, the direction of refraction may be taken in accordance with Snell's law as with the optical axis of the waveguide. In this case, since the radiation angle 520-1 of the end face of the LD 52-1 was 25 degrees, it was tilted to about 25 degrees, and the clad wall was directed to the PD so that total reflection was established at the glass-air interface. The structure was constricted into a shape.
[0047]
[Embodiment 4]
FIG. 11 shows a configuration example of a conventional optical monitor circuit, and FIG. 6 shows a configuration example of the optical monitor circuit according to the fourth embodiment. In the fourth embodiment, in FIG. 6, a part of the light incident on the waveguides 61-1a to 61-1c from the left through the optical fibers 61-5a to 61-5c is reflected by the filter 63-4. The light intensity is monitored by the PDs 62-2a to 62-2c corresponding to the multimode.
[0048]
Conventionally, as shown in FIG. 11, a single mode waveguide is used for the waveguide 111-1, and the tolerance of the reflection part of the filter 113-4 is strict, and good optical coupling is obtained with respect to the PD 112-2 a. Is difficult, and the leaked light is incident on the other optical elements 112-2b to 112-2d to generate crosstalk light 111--3. Reference numeral 1110-1 denotes propagation light, 113-2 denotes an X-crossing circuit, and 111-3 denotes a cladding.
[0049]
Therefore, in the fourth embodiment, as shown in FIG. 6, the PD 62-2a to 62-2b side optical waveguides 61-2a to 61-2b are multimode waveguides (lower waveguide circuit in FIG. 6). . Thus, as in the second embodiment, the light that has been reflected to the PD and has become stray light without being coupled to the conventional optical waveguide is guided by the waveguide and coupled to the PD, resulting in high efficiency. Optical coupling is obtained. Furthermore, since the light 1110-3 that has become the stray light and the crosstalk light in FIG. 11 is confined in the core portions 61-2a to 61-2b, the crosstalk to other elements can be suppressed. Reference numeral 610-1 is propagation light, 63-2a to 63-2c are X-crossing circuits, and 61-3 is a cladding.
[0050]
Further, as shown in the upper waveguide circuit of FIG. 6, a waveguide structure excluding a part of the cladding may be used. Reference numerals 61-4a and 61-4b are cladding removal portions. In the fourth embodiment, a refraction type PD having a light receiving surface of about 100 μmφ is used as the PD 62-2c so that there is no problem even if light spreads to a cladding height of 50 μm.
[0051]
Furthermore, a guide structure is provided from the vicinity of the fiber and reflected by the filter 63-4 so that the light leaked by the coupling between the fiber 61-5c and the optical waveguide 61-1c can be received by the PD 62-2c. When this structure is used, the amount of light entering the PD 62-2c can be adjusted by intentionally shifting the fiber 61-5c from the waveguide 61-1c.
[0052]
[Effect of the embodiment]
As described above, according to the present embodiment, the coupling efficiency of the entire module is increased by using a multimode-compatible optical element and a multimode optical waveguide as part of the optical module. Since the light thus formed is coupled with the multimode optical waveguide, stray light can be suppressed at the same time. Furthermore, by optimizing the structure of the optical waveguide for the field diameter and the emission direction, it becomes possible to enhance the optical coupling between the multimode and the emitted light.
[Conclusion]
According to the present embodiment, an optical module including a single-mode optical waveguide and an optical component corresponding to a multimode and including an optical element having a planar device structure is provided in the vicinity of an optical circuit portion including the single-mode optical waveguide. Are provided with a multimode optical waveguide and optically coupled to the optical component through the multimode optical waveguide (corresponding to Embodiments 1, 2, and 4, FIGS. 1 to 4 and 6).
For this reason, the coupling efficiency as a whole module increases, and it becomes possible to suppress stray light.
In addition, according to the present embodiment, an optical module including a single-mode optical waveguide and an optical component that supports multi-modes and integrated with an optical element having a planar element structure has a field diameter different from that of the single-mode optical waveguide. Are coupled to each other, and a cladding structure capable of confining light is provided in the vicinity of the coupling portion, and the optical component is optically coupled through the cladding structure (Embodiment 3, FIG. 5).
For this reason, the coupling efficiency as a whole module increases, and it becomes possible to suppress stray light.
More specifically, in order to solve the conventional problems and achieve the object, the optical module of this embodiment includes a single-mode optical waveguide and an optical component corresponding to multimode, and has a planar element structure. An optical module in which elements are integrated, wherein a multimode optical waveguide is provided in the vicinity of an optical circuit portion composed of the single mode optical waveguide, and is optically coupled to the optical component through the multimode optical waveguide. (Corresponding to Embodiments 1, 2, and 4, FIGS. 1-4, and 6).
Here, the vicinity of the optical circuit portion can be characterized by being a subsequent stage of the Y branch circuit (Embodiment 1, FIG. 1).
The vicinity of the optical circuit portion is a cross circuit, and the transmitted light of the cross circuit is optically coupled to the optical component (Embodiment 2, FIGS. 3, 4).
The vicinity of the optical circuit portion is a cross circuit, and the reflected light of the cross circuit can be optically coupled to the optical component (Embodiment 4, FIG. 6).
The multimode optical waveguide has an opening angle toward the optical component, and the opening angle is tan Θ = λ / (πw) (λ: wavelength in the medium, w: field radius, π: circumference The angle Θ satisfies the relationship of (rate) (Embodiment 2, FIGS. 3 and 4).
Further, the light to be optically coupled to the optical component can be characterized by leakage light of the single mode optical waveguide (Embodiments 1, 2, and 4, FIGS. 1-4, and 6).
Further, the single mode optical waveguide may be a bent waveguide (Embodiment 1, FIG. 2).
Further, in place of the multimode optical waveguide, a clad structure capable of confining light can be provided (Embodiment 1, FIG. 1, Embodiment 4, and FIG. 6).
In addition, the vicinity of the optical circuit portion may be a rear stage of the directional coupler (Embodiment 1, 2, or 4).
In addition, the vicinity of the optical circuit portion may be a subsequent stage of the star coupler (Embodiment 1, 2, or 4).
In order to solve the conventional problems and achieve the object, the optical module of the present embodiment includes a single-mode optical waveguide and an optical component compatible with multimode, and integrates optical elements having a planar element structure. an optical module, and the single-mode optical waveguide to the single-mode optical waveguide is coupled different optical elements of the field diameter, comprising a cladding structure capable confine light in the vicinity of the binding portion, thereof cladding The optical component is optically coupled to the optical component through a structure (Embodiment 3, FIG. 5).
Here, the axis of the cladding structure may be characterized by being along a predetermined radiation angle of light from the coupling portion to the optical component (Embodiment 3, FIG. 5).
Further, the light to be optically coupled to the optical component may be leakage light of the single mode optical waveguide (Embodiment 3, FIG. 5).
With the above configuration, in an optical module having a planar optical waveguide circuit mainly composed of a single mode and a multimode optical waveguide structure in the component, the multimode optical waveguide is located near the multiplexer / demultiplexer or the optical coupling portion of the optical waveguide circuit. A structure is formed and the waveguide is optically coupled to a multimode optical component.
A multi-mode optical waveguide generally has a large field diameter, and light that is not coupled in a single-mode waveguide structure can be propagated. Therefore, by using the above configuration, light generated in the optical multiplexing / demultiplexing circuit and normally leaking light can be easily guided to the optical component, and the optical component is multimode, so that the entire circuit is efficient. It becomes possible to produce a good optical component.
[Brief description of the drawings]
FIG. 1 shows a hybrid integration of a laser diode (LD) and a photodiode (PD) by removing a part of a waveguide from an optical waveguide substrate having a Y branch circuit according to Embodiment 1 of the present invention and providing an optical element mounting portion. FIG. 5A is a diagram of a case where a multimode waveguide core is used, and FIG. 5B is a diagram of a case where a waveguide structure is removed by removing a portion of the cladding.
FIGS. 2A and 2B are diagrams of an optical module using a bent waveguide according to the first embodiment of the present invention, in which FIG. 2A is an explanatory diagram of light emission by the bent waveguide, and FIG. 2B is a diagram illustrating the light emitted from the bent waveguide; It is a figure in the case of making it wave and incident on PD.
FIG. 3 is a diagram when a multimode waveguide is used on the PD side according to the second embodiment of the present invention.
FIG. 4 is a structural diagram of a multi-channel wavelength division multiplexing optical transceiver according to the configuration of Embodiment 2 of the present invention.
FIG. 5 is a diagram of an LD module with a monitor having a structure in which uncoupled light is guided by a clad according to a third embodiment of the present invention.
FIG. 6 is a diagram illustrating a configuration example of an optical monitor circuit according to a fourth embodiment of the present invention, which collectively represents a case using a waveguide core and a case using a clad.
FIG. 7 is a diagram of an optical transceiver having a conventional Y branch circuit.
FIG. 8 is a structural diagram of a wavelength division multiplexing optical transceiver using a conventional X-crossing waveguide and a filter.
FIG. 9 is a structural diagram of a conventional multi-channel wavelength division multiplexing optical transceiver.
FIG. 10 is a configuration diagram of a conventional LD module with a monitor.
FIG. 11 is a diagram illustrating a configuration example of a conventional optical monitor circuit.
[Explanation of symbols]
71-1, 21-1a, 81-1, 31-1, 91-1, 101-1, 51-1, 61-1a to 61-1c, 111-1 single mode optical waveguide core 11-2a, 21- 2b, 31-2, 41-2, 61-2a to 61-2b multimode optical waveguide core 11-4 waveguide core 1-3, 91-3, 51-3, 111-3, 61-3 clad 51- 4, 61-4a, 61-4b Clad removing portions 61-5a to 61-5c Optical fibers 72-1, 12-1a, 12-1b, 22-1b, 32-1, 82-1 and 42-1a to 42 -1d, 92-1a to 92-1d, 102-1, 52-1 Laser diode element 22-1b-1 Laser diode element active layer 72-2, 12-2a, 12-2b, 22-2b, 32-2 , 82-2, 42-2a to 42-2d, 2-2a to 92-2d, 102-2, 52-2, 62-2a to 62-2c, 112-2a to 112-2d Photodiode elements 12-2a-1, 12-2b-122-2b-1 Photo Diode element absorption layers 73-1, 13-1a, 13-1b Y branch circuits 83-2, 33-2, 43-2, 93-2, 113-2, 63-2a to 63-2c X-crossing circuit 33- 4, 83-4, 43-4, 93-4, 63-4, 113-4 Dielectric multilayer filter 210-1a, 410-1, 1010-1, 510-1, 1110-1, 610-1 Propagation Light 710-2, 810-2, 210-2a, 1010-2, 510-2 Stray light 910-3, 1110-3 Crosstalk light 520-1 Radiation angle 320-2 Field radius 220-3 in single mode waveguide Conventional Half curvature The trajectory of the optical waveguide by

Claims (1)

In an optical module that integrates single-mode optical waveguides and multi-mode optical elements,
The single mode optical waveguide includes at least one optical circuit portion of a Y branch, a cross circuit, a directional coupler, and a star coupler,
A multimode optical waveguide is provided in the vicinity of the optical circuit portion,
While optically coupled to the optical element through the multimode optical waveguide,
The multimode optical waveguide has an opening angle toward the optical element , and the opening angle is tan Θ = λ / (πw) (λ: wavelength in the medium, w: field radius, π: pi) An optical module characterized in that the angle Θ satisfies the following relationship.

Images