JP3594510B2 - Optical module - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical module suitable for a transmitting and receiving module having an optical fiber and a semiconductor optical element, and more particularly to a hybrid optical module assembled by a passive alignment method using a marker.
[0002]
[Prior art]
FIG. 1 schematically shows a conventional module manufacturing method by a passive alignment method using a marker. FIG. 1 is a conceptual diagram of a mounting method including a semiconductor optical device 1 and a mounting substrate 2 thereof. The back surface of the semiconductor optical device 1 is sucked by vacuum tweezers 9 or the like, and is held above the mounting substrate 2. The alignment mark 5 on the semiconductor optical element 1 and the alignment mark 7 on the mounting substrate 2 are aligned using an infrared microscope or the like. An alloy is formed by bringing the solder 6 on the substrate 2 into contact with the solder 6 and heating by the heater 11 in the mounting substrate fixing base 10, thereby obtaining an electrical and mechanical connection. Thereafter, an optical fiber (not shown) is placed in a V-shaped groove (not shown) for fixing an optical fiber formed in advance on the mounting substrate 2, and these are fixed with an adhesive or the like to mount the optical module. Make it.
[0003]
When an optical fiber and a semiconductor photodetector are coupled by such a passive alignment method, a photodetector having a large light receiving surface is effective for efficiently receiving light. However, in general, when the light receiving surface is enlarged, the band becomes narrow, and the sensitivity to high-speed signals deteriorates. Therefore, a semiconductor photodetector called a refraction photodiode has been developed as a photodetector having a large coupling tolerance (tolerance) with an optical fiber, high sensitivity, and a wide bandwidth.
[0004]
FIG. 2 shows a sectional view of the refraction photodiode. Here, 12 is a semi-insulating InP substrate, 13 is an n-type InP layer, 14 is an InGaAs light absorbing layer, 15 is a p-type semiconductor layer (InP layer), 16 is a p-type InGaAsP contact layer, and 17 is an insulating film (nitride). Film, 18 is a p-side ohmic electrode, 19 is an n-side ohmic electrode, 20 is a p-side electrode, 21 is an n-side electrode, and 22 is an anti-reflection film (anti-reflection film; light-receiving region). When light is incident on the inclined light refracting portion 22 from the right direction in FIG. 2, the light is bent downward in FIG. Therefore, if the light incident position is set to a position higher than the light absorbing layer 14, the light always reaches the light absorbing layer 14. The ordinary waveguide structure photodetector has a small coupling tolerance because light must be directly incident on the light absorption layer portion, but this refraction type photodiode can be used if light is incident on the light absorption layer 14 above. Good, has high coupling tolerance. Further, in order to improve the tolerance of the ordinary waveguide structure photodetector, the volume of the light absorbing layer may be increased, but in this case, the traveling time of the carrier generated inside becomes long, and the high speed signal Can not respond. On the other hand, the refraction photodiode only needs to have the light absorbing layer 14 only in the portion where the bent light passes, and its thickness may be about 2 μm, which is sufficient to absorb the light. It has the feature of being responsive.
[0005]
[Problems to be solved by the invention]
However, when the above-described refraction photodiode is mounted on the substrate by the mounting method shown in FIG. 1, the light absorbing portions 14 to 20 protruding from the surface thereof are mounted on the mounting substrate (the semiconductor optical device mounting substrate). 2) The groove for accommodating the projecting portion such as the light absorbing portion must be formed in advance on the mounting substrate 2 side because it hits the surface of 2). there were.
[0006]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a semiconductor optical device having a projection on a surface and a projection on a normal surface, including a refraction photodiode, without increasing the number of manufacturing steps. It is an object of the present invention to provide an optical module that can mount all semiconductor optical devices without any components on a mounting substrate on the same optical axis.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes an optical element mounting substrate in which one or more optical fiber fixing guide grooves are formed, and one or more optical fibers fixed in the guide grooves. An optical element having at least one optical element mounted on the optical element mounting board, and an optical element having an active region disposed right above the guide groove and optically coupling with the optical fiber; In the optical module included, the optical element in which the active region is disposed directly above the guide groove and optically couples with the optical fiber has a region including the active region protruding from the surface of the optical device. An optical element in which at least a part of a region including the active region is housed in the guide groove, the optical element has a light refractive index portion having an inclined end surface, and the incident light is the light Bent at the index of refraction to pass through the light absorbing layer Characterized in that it comprises a refractive photodiode least.
[0010]
Also, the semiconductor optical amplifier and the refraction photodiode as the optical element may be housed in the same guide groove.
[0011]
Further, a semiconductor light emitting element as the optical element and a refraction photodiode are housed in the same guide groove.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
(1st Embodiment)
The optical module according to the first embodiment of the present invention includes a combination of a substrate having a guide groove for fixing an optical fiber, an optical fiber, and a refraction photodiode. FIG. 3 shows the basic structure of the optical module. FIG. 3A is a diagram illustrating a cross-sectional structure of a receiving module (optical module) including an optical fiber, a refraction photodiode, and a mounting substrate, and FIG. 3B is a diagram illustrating a surface of the mounting substrate directly above. FIG. FIG. 3C is a view of the surface of the refraction photodiode as viewed from directly above.
[0014]
As shown in the cross-sectional view of FIG. 2 described above, the refraction photodiode 23 is composed of a semi-insulating InP substrate 12, an n-type InP layer 13, an InGaAs light absorbing layer 14, and a p-type semiconductor layer 15 formed thereon. It has a structure in which the end face is inclined by wet etching using the crystal orientation. As shown in the top view of the refraction photodiode 23 in FIG. 3C, the p-side electrode 20 and the n-side electrode 21 are taken out from the p-layer and the n-layer, respectively. An alignment mark 5 at the time of passive alignment is formed in a portion without a layer.
[0015]
An example of a method of manufacturing such a refraction photodiode 23 and the semiconductor optical element mounting substrate 2 will be described below.
[0016]
First, a manufacturing process of the refraction photodiode 23 will be described with reference to FIG.
[0017]
First, on the semi-insulating InP substrate 12, the n-type InP layer 13 is 1.0 μm, the non-doped InGaAs light absorbing layer 14 is 2.0 μm, the non-doped InP layer 15 is 2.0 μm, and the forbidden band width is A non-doped InGaAsP contact layer 16 having a wavelength of 1.5 μm and a thickness of 0.5 μm are sequentially grown. Thereafter, a nitride film is formed on the entire surface, and the nitride film is etched only in a portion used as a light absorbing layer. Thereafter, zinc is diffused by a diffusion method, and only the portion where the nitride film is etched is made to be p-type. After removing the nitride film, the photoresist is left in an island shape only in a portion used as a light absorbing layer, and the n-type InP layer 13 is exposed by etching. A nitride film 17 is formed again on the entire surface, and a part of the p-type InGaAsP contact layer 16 and a part of the n-type InP layer 13 on the light absorption layer are exposed.
[0018]
Next, Ni (10 nm), Zn (30 nm), and Au (100 nm) are formed on the p-type InGaAsP contact layer 16 by vapor deposition. At this time, the alignment mark 5 is formed in a portion where there is no InGaAsP contact layer 16 by the resist pattern formed at the same time. Similarly, AuGe (100 nm), Ni (20 nm), and Au (500 nm) are deposited on the n-type InP layer 13. Then, the temperature is raised to 420 ° C. in a hydrogen atmosphere to form a p-side ohmic electrode 18 and an n-side ohmic electrode 19. Further, Ti (50 nm), Pt (100 nm), and Au (800 nm) are deposited on the p-side ohmic electrode 18 by vapor deposition, and the p-side electrode 20 is manufactured. Similarly, Ti (50 nm), Pt (100 nm), and Au (300 nm) are deposited on the n-side ohmic electrode 19 to form the n-side electrode 21. Then, the photoresist is left in a portion other than the end surface portion that becomes the light incident portion, and wet etching is performed to form a light refraction portion having an inclined end surface. Finally, the substrate is cleaved to a size of 500 μm × 350 μm, and an antireflection film 22 is formed on the surface of the light refraction portion, thereby manufacturing the refraction type photodiode 23.
[0019]
Next, a manufacturing process of the mounting substrate will be described with reference to FIGS.
[0020]
First, a 1 μm thick SiO ₂ film (insulating film) 25 is formed by thermally oxidizing the p-type Si substrate 24. Thereafter, a guide groove pattern for fixing the fiber is formed using a photoresist. After etching the SiO ₂ film 25 by dry etching, the photoresist is removed, and etching is performed in an aqueous potassium hydroxide solution to form a V-groove 29. Then, an electrode pattern and a pattern for an alignment mark are formed using a photoresist. Then, a current injection electrode 26 and an alignment mark 27 are formed by depositing Cr (50 nm) and Au (500 nm) by vapor deposition. Further, on the current injection electrode 26, AuSn solder 28 is vapor-deposited in a thickness of 2.5 μm on a portion in contact with the electrodes 20 and 21 of the refraction photodiode 23. Finally, after removing the photoresist, a mounting substrate 2 having a size of 3 mm × 7 mm is manufactured using a dicing saw.
[0021]
Using the refraction type photodiode 23 and the mounting substrate 2 manufactured as described above, mounting is performed as follows.
[0022]
First, the mounting substrate 2 is fixed to a pedestal 10 having a heater 11 (see FIG. 1). Next, the refraction type photodiode 23 is placed so that the p side faces downward, and the semi-insulating substrate 12 side is sucked by the vacuum tweezers 9 (see FIG. 1). Then, the refraction photodiode 23 is moved onto the mounting substrate 2, and alignment is performed while viewing the alignment marks 5 on the refraction photodiode 23 and the alignment marks 27 on the mounting substrate 2 with an infrared microscope. Then, as shown in FIG. 3A, the semi-refractive photodiode 23 is pressed onto the mounting substrate 2 and heated to 300 ° C. to bond the refracting photodiode 23 to the mounting substrate 2. I do. Then, the optical fiber 30 is inserted into the V-groove 29 of the mounting substrate 2, a UV curable resin is poured into a gap in the V-groove 29, and the resin is cured by irradiating UV light (ultraviolet light). The fiber 30 is fixed in the V-groove 29.
[0023]
When the characteristics of the receiving module manufactured as described above were examined, when the positional deviation between the optical fiber 30 and the refraction type photodiode 23 was ± 15 μm in the horizontal direction, 1 dB degradation in the receiving sensitivity was observed. Similarly, when the position of the optical fiber 30 and the position of the refraction photodiode 23 are displaced by ± 7 μm in the vertical direction and by 100 μm in the optical axis direction, 1 dB of reception sensitivity degradation was observed.
[0024]
In the present embodiment, the case where the refractive photodiode 23 is an InP-based light emitting element has been described, but a GaAs-based or II-VI group semiconductor may be used. Further, in the present embodiment, the Si substrate is used as the mounting substrate 2, but it goes without saying that an insulator such as ceramic, glass, plastic, or a metal may be used. As the electrodes, Ti / Pt / Au was used for the electrodes 20 and 21 on the semiconductor optical element side, and Cr / Au was used for the electrode 26 on the mounting substrate side. However, a combination of these metals and other materials may be used. Alternatively, a metal such as Ni may be combined to improve the adhesion. In the present embodiment, the SiO ₂ film 25 on the mounting substrate is manufactured by thermal oxidation, but may be manufactured by a sputtering method, a plasma CVD method, or the like. Further, the guide groove 29 for fixing the optical fiber is formed by wet etching, but may be formed by machining by dicing, and the shape may be not only V-shaped but also rectangular or semi-circular. When an insulator or metal such as ceramic, glass, or plastic is used as the mounting substrate, a guide groove for fixing the optical fiber may be formed by molding using a mold.
[0025]
(Second embodiment)
Next, FIG. 4 shows a configuration of an optical module according to a second embodiment of the present invention. The optical module according to the second embodiment of the present invention includes a substrate having a guide groove for fixing an optical fiber, an optical fiber, a combination of a semiconductor optical amplifier and a refraction photodiode. FIG. 4A is a diagram showing a cross-sectional structure of a receiving module including an optical fiber, a semiconductor optical amplifier, a refraction photodiode, and a mounting substrate. FIG. 4B is a diagram showing the mounting substrate surface from directly above. FIG. 4C is a diagram in which the surface of the semiconductor optical amplifier is viewed from directly above.
[0026]
As shown in FIG. 4A, the semiconductor optical amplifier 45 includes an n-type InP substrate 31, an InGaAsP active layer 32 formed thereon, a p-type InP cladding layer and a p-type InGaAsP contact layer. Type semiconductor layer 33. Further, on both sides of the InGaAsP active layer 32, vertical tapered spot size conversion regions 34 are integrated. In a section perpendicular to this, a current confinement layer is formed around the InGaAsP active layer 32. A p-side electrode 35 is formed on the p-type InGaAsP contact layer of the p-type semiconductor layer 33, and an n-side electrode 36 is formed on the n-type InP substrate 31. This semiconductor optical amplifier 45 is joined to the mounting substrate 2 side by solder 28. Alignment marks 37 for alignment are formed on portions of the surface of the semiconductor optical amplifier 45 which are not covered by the p-side electrode 35. Reference numeral 40 denotes a dummy electrode for supporting the element. On the other hand, a V-groove 29 for fixing an optical fiber, an electrode 26 for current injection, a solder 28 for bonding for mounting a semiconductor optical element, and an alignment mark 39 for a semiconductor optical amplifier are formed on the surface of the substrate 2 for mounting a semiconductor optical element. ing.
[0027]
An example of a method for manufacturing the semiconductor optical amplifier 45 and the semiconductor optical element mounting substrate 2 as described above will be described below.
[0028]
First, the manufacturing steps of the semiconductor optical amplifier 45 will be described with reference to FIGS.
[0029]
First, on the n-type InP substrate 31, the non-doped InGaAsP active layer 32 whose forbidden band width corresponds to 1.55 μm in wavelength and the p-type InP layer 33 are grown to 0.5 μm and 0.1 μm, respectively. Thereafter, a SiO ₂ film is deposited on the surface, and a resist pattern having a length of 600 μm corresponding to the length of the light emitting region is formed. The SiO ₂ film and the semiconductor are etched using the photoresist as a mask. After removing the photoresist, by growing InGaAsP, the vertical tapered spot size conversion regions 34 are integrated on both sides of the InGaAsP active layer 32. After removing the SiO ₂ film, a SiO ₂ film is deposited again on the entire surface. A stripe having a width of 0.5 μm is formed thereon with a photoresist, and the SiO ₂ film and the semiconductor are etched. After the removal of the resist, the p-InP layer 33 and the n-InP layer 31 are grown and buried around the InGaAsP active layer 32 with this. After removing the SiO ₂ film, a p-InP layer 33 of 1.5 μm and a 0.3 μm p-type InGaAsP layer 32 are sequentially grown on the entire surface, whereby the p-type semiconductor layer 33 is formed, and the embedded structure is completed. .
[0030]
Then, after removing the 1 nGaAsP contact layer above the spot size conversion region 34, a SiO ₂ film is deposited on the entire surface, and then the SiO ₂ film is etched only on the active layer. Next, Ni (10 nm), Zn (30 nm), and Au (100 nm) are formed on the InGaAsP contact layer and near the end face by vapor deposition. At this time, the alignment marks 37 are simultaneously formed by lift-off using a photoresist. Then, the n-type InP substrate 31 is polished to a thickness of about 100 μm, and then AuGe (100 nm), Ni (20 nm), and Au (500 nm) are deposited on the n-type InP substrate 31 by vapor deposition. accumulate. At this time, the spot size conversion area 34 is protected with a photoresist so that the electrode metal is not attached. After removing the photoresist, the temperature was raised to 420 ° C. in a hydrogen atmosphere, and Ti (50 nm), Pt (100 nm), and Au (800 nm) were deposited on the p-side and n-side by vapor deposition, and the p-side electrode 35 and the n-side An electrode 36 is formed. Finally, the semiconductor optical amplifier 45 is manufactured by cleaving to a size of 500 μm in width and 1200 μm in length, and depositing an antireflection film 38 on both end surfaces by an electron beam evaporator.
[0031]
The method of manufacturing the mounting substrate 2 is the same as that of the above-described first embodiment of the present invention.
[0032]
The semiconductor optical amplifier 45 manufactured in this manner is positioned so that the alignment marks 37 and 39 match each other, and mounted on the mounting substrate 2 as in the first embodiment. After that, the refraction photodiode 23 is aligned so that the alignment marks 5 and 27 are aligned, and is mounted on the mounting substrate 2. Finally, the optical fiber 30 is inserted into the V-groove 29, and the optical fiber 30 is fixed to the V-groove 29 using a UV curable resin.
[0033]
When the characteristics of the receiving module manufactured as described above were examined, when the positional deviation between the optical fiber 30 and the semiconductor optical amplifier 45 was ± 2 μm in the horizontal direction, 1 dB degradation in the receiving sensitivity was observed. Similarly, when the positions of the optical fiber 30 and the semiconductor optical amplifier 45 are shifted by ± 1.5 μm in the vertical direction and by 10 μm in the optical axis direction, 1 dB of reception sensitivity degradation was observed. When a current of 70 mA was supplied to the semiconductor optical amplifier 45, the reception sensitivity at a bit error rate of 10 ⁻¹⁰ was −30.5 dBm for a signal of 2.5 Gbps.
[0034]
(Third embodiment)
As shown in FIG. 5, the optical module according to the third embodiment of the present invention includes a substrate having a guide groove for fixing an optical fiber, an optical fiber, a semiconductor laser (semiconductor light emitting element), and a refraction type photo diode. It is composed of a combination with a diode. FIG. 5A is a diagram illustrating a cross-sectional structure of a transmission module including an optical fiber, a semiconductor laser, a refraction photodiode, and a mounting substrate. FIG. FIG. 5C is a diagram in which the surface of the semiconductor laser is viewed from directly above.
[0035]
An example of a method for manufacturing the optical module of the present embodiment will be described below.
[0036]
The refractive photodiode 23 is manufactured in the same manner as in the first embodiment of the present invention.
[0037]
The semiconductor laser 46 is manufactured in the same process as the method of manufacturing the semiconductor optical amplifier 45 according to the above-described second embodiment of the present invention, and is cleaved to a half size before an antireflection film is formed on an end face. It is manufactured by setting the reflectance of the film (dielectric film) 41 formed on both end surfaces to 30% or more in geometric mean.
[0038]
The semiconductor optical laser 46 manufactured in this manner is positioned such that the alignment mark 42 of the semiconductor laser 46 and the alignment mark 43 of the mounting substrate 2 match, as in the above-described second embodiment of the present invention. After the alignment, the semiconductor laser 46 is mounted on the mounting substrate 2. After that, the refraction photodiode 23 is aligned so that the above-mentioned alignment marks 5 and 27 are aligned, and the refraction photodiode 23 is mounted on the mounting substrate 2. Finally, the optical fiber 30 is inserted into the V-groove 29, and the optical fiber 30 is fixed to the V-groove 29 using a UV curable resin.
[0039]
When the characteristics of the transmission module manufactured as described above were examined, a degradation of 1 dB in the coupling efficiency was observed when the displacement between the optical fiber 30 and the semiconductor laser 46 was ± 2 μm in the horizontal direction. Similarly, when the positions of the optical fiber 30 and the semiconductor laser 46 are displaced by ± 1.5 μm in the vertical direction and by 10 μm in the optical axis direction, a decrease in the coupling efficiency of 1 dB was observed. Further, the output of the semiconductor laser 46 was monitored by the refraction photodiode 23, and by applying an electrical feedback corresponding to the output to the semiconductor laser 46, a constant optical output could be obtained from the optical fiber 30.
[0040]
(Other embodiments)
In each of the above embodiments of the present invention, the case where the number of optical fiber fixing guide grooves formed on the substrate for mounting a semiconductor optical element is one is illustrated, but the present invention is not limited to this, and a plurality of optical fibers This also includes the case where the fixing guide groove is formed in the semiconductor optical element mounting substrate.
[0041]
【The invention's effect】
As described above, according to the present invention, without increasing the number of manufacturing steps, it is possible to mount a semiconductor optical device having a projection on a surface and a semiconductor optical device having no projection on a normal surface, including a refraction photodiode. Passive alignment using alignment marks, because it can be mounted on the same optical axis on a substrate for mounting, and a refraction photodiode with a large position tolerance can be mounted on the substrate for mounting optical elements without increasing the manufacturing process. The method becomes easy, and the module manufacturing cost can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a conventional mounting method, and is a conceptual diagram showing a cross-sectional structure of an optical module and a mounting substrate.
FIG. 2 is a conceptual diagram showing a configuration of a refraction photodiode.
3A and 3B are conceptual diagrams illustrating a configuration of an optical module according to a first embodiment of the present invention, wherein FIG. 3A is a cross-sectional view of the optical module, and FIG. 3B is a top view illustrating a configuration of a surface of a mounting substrate; And (c) is a top view showing the configuration of the surface of the refraction photodiode.
4A and 4B are conceptual diagrams illustrating a configuration of an optical module according to a second embodiment of the present invention, wherein FIG. 4A is a cross-sectional view of the optical module, and FIG. 4B is a top view illustrating a configuration of a surface of a mounting substrate. FIG. 2C is a top view showing the configuration of the surface of the semiconductor optical amplifier.
FIGS. 5A and 5B are conceptual diagrams illustrating a configuration of an optical module according to a third embodiment of the present invention, in which FIG. 5A is a cross-sectional view of the optical module, and FIG. 5B is a top view illustrating the configuration of the surface of a mounting substrate; FIG. 2C is a top view showing the configuration of the surface of the semiconductor laser.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 semiconductor optical device 2 semiconductor optical device mounting substrate 3 metal for electrode
4 Metal for electrode 5 Alignment mark 6 Solder,
7 Alignment mark 8 Electrode metal 9 Vacuum tweezers 10 Mounting base fixing base 11 Heater 12 Semi-insulating InP substrate 13 n-type InP layer 14 InGaAs light absorption layer 15 p-type semiconductor layer (InP layer)
16 p-type InGaAsP contact layer 17 insulating film (nitride film)
18 p-side ohmic electrode 19 n-side ohmic electrode 20 p-side electrode (Ti / Pt / Au electrode)
21 n-side electrode (Ti / Pt / Au electrode)
22 Anti-reflection film 23 Refractive photodiode 24 Si substrate 25 Insulating film (SiO ₂ film)
26 Current injection electrode (Cr / Au electrode)
27 Alignment mark 28 Solder 29 Optical fiber fixing guide groove (V groove)
Reference Signs List 30 optical fiber 31 n-type InP substrate 32 InGaAsP active layer 33 p-type semiconductor layer 34 spot size conversion region 35 p-side electrode 36 n-side electrode 37 alignment mark 38 antireflection film 39 alignment mark 40 element supporting dummy electrode 41 dielectric film 42 Alignment mark 43 Alignment mark 45 Semiconductor optical amplifier 46 Semiconductor laser

Claims (3)

An optical element mounting substrate having at least one guide groove for fixing an optical fiber,
One or more optical fibers fixed in the guide groove,
And one or more optical elements mounted on the optical element mounting substrate,
An optical module, wherein the optical element includes an optical element in which an active region is disposed right above the guide groove and optically couples with the optical fiber .
The optical element in which the active region is disposed directly above the guide groove and optically couples with the optical fiber has a region including the active region protruding from the surface of the optical device, and a region including the active region. An optical element at least partially housed in the guide groove,
The optical element has a light refractive index portion having an inclined end surface, and at least includes a refractive photodiode that is bent so that incident light passes through the light absorbing layer at the light refractive index portion. Optical module. The optical module according to claim 1 , wherein the semiconductor optical amplifier as the optical element and the refraction photodiode are housed in the same guide groove. 2. The optical module according to claim 1 , wherein the semiconductor light emitting element as the optical element and the refraction photodiode are housed in the same guide groove. 3.

Images