JP3224203B2 - Optical module - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module having a bidirectional optical transmission / reception function used in an optical subscriber system. In the optical subscriber system, development of a low-cost optical module is indispensable.

[0002]

2. Description of the Related Art FIG. 12 shows a block diagram of a WDM transmitting / receiving module. This optical module is 1.3 / 1.55μ
It comprises a WDM circuit for multiplexing / demultiplexing m optical signals and a bidirectional optical transmitting / receiving circuit for transmitting / receiving 1.3 μm optical signals. In order to reduce the cost of such an optical module, it is effective to use a hybrid integrated optical module in which an optical functional element such as a semiconductor laser or a light receiving element is directly mounted on a quartz optical waveguide substrate.

FIG. 13 shows an example of the configuration of a conventional hybrid integrated optical module (Yamada et al., “Filter-Reflection WDM Transmit / Receive Optical Circuit (SC) Using PLC Platform”).
-2-5), Proceedings of the 1996 IEICE Spring Conference, p.
p.439-440). This hybrid integrated optical module is a WDM that multiplexes and demultiplexes 1.3 / 1.55 μm optical signals.
Circuit and a bidirectional optical transmitting and receiving circuit for transmitting and receiving 1.3 μm optical signals.

A quartz optical waveguide 2 formed on a silicon substrate 1 having a step is referred to as a platform. On the silicon substrate recess of this platform,
Filter insertion groove 1 of quartz optical waveguide 2 as WDM circuit
And a Y-branch circuit 1 for a 1.3 μm optical signal as a part of a bidirectional optical transmitting and receiving circuit.
02 is formed. As a result, the input / output optical fiber 4a common to 1.3 / 1.55 μm optical signals and the output optical fiber 4b for 1.55 μm optical signals can both be connected to the same end face of the platform via the optical fiber block 5.

Further, the feature of the present optical module is that the transmission wavelength is set on the silicon terrace (silicon substrate convex portion) 6 near the end of the input waveguide and the output waveguide of the Y branch circuit 102.
A 1.3 μm semiconductor laser (LD) 31, a monitoring light receiving element (M-PD) 32, and a 1.3 μm receiving light receiving element (R-PD) 33 are directly mounted.
With such a configuration, the number of components constituting the optical module can be significantly reduced.

Here, the reason for using the silicon substrate 1 having a step will be described with reference to FIG. The silicon terrace 6 functions as a height reference plane for the LD and PD and a heat sink. For this purpose, the optical function element (L
D31, M-PD32, R-PD33) 3 are the active layers 3
It is mounted on the silicon terrace 6 via the solder joint 40 in the form of “junction down” with “a” facing downward. At this time, the center of the optical waveguide core 2b is
Is set to match the height of the active layer 3a.

The height from the surface of the silicon terrace 6 to the center of the optical waveguide core 2b is typically about 10 to 12 μm. Therefore, if the thickness of the core layer is 8 μm, the thickness of the lower cladding layer 2 c on the surface of the silicon terrace 6 is only about 6 to 8 μm at most. On the other hand, in the optical waveguide formed on the silicon substrate 1, when the thickness of the lower clad layer is small, the influence of the silicon substrate appears and the propagation loss increases. Therefore, in order to realize a high-quality optical waveguide, a lower clad layer having a sufficient thickness is required. Therefore, in the platform of the conventional hybrid integrated optical module, the silicon substrate in the portion to be the optical waveguide is dug down in a concave shape so that the lower clad layer having a sufficient thickness is formed.

[0008]

The conventional optical module shown in FIG. 13 uses a platform in which a silica-based optical waveguide is formed on a silicon substrate having a step to greatly reduce the number of parts and reduce the number of assembly steps. Can be simplified,
The cost can be significantly reduced. However, in order to construct an optical subscriber system at lower cost, it is necessary to reduce the cost of the optical module as much as possible. From this viewpoint, the conventional optical module shown in FIG.
There is still room for cost reduction. For this purpose, it is necessary to solve the following problems.

First, the cost of a platform using a silicon substrate having a step is slightly higher than that of a platform using a normal flat silicon substrate. Therefore, a module configuration using a flat silicon substrate and capable of directly mounting an optical functional element is desired. Second, in the conventional optical module, since the optical functional element mounting portion and the filter mounting portion are provided on the same substrate, it is necessary to design a process and select a material in consideration of a heat treatment temperature. FIG. 15 shows a manufacturing process of a conventional optical module. (1), (2a), and (3a) are steps in the case of mounting in ascending order of processing temperature. That is, after forming the filter insertion groove 14 on the substrate ((1) filter groove forming step),
The optical functional elements (31 to 33) are mounted ((2a) optical functional element mounting step), and finally, the interference film filter 15 is inserted and fixed ((3a) filter inserting step). In this case, the high temperature at the time of mounting the optical functional element is not applied to the filter and the adhesive for fixing the filter, so that the requirement for heat resistance of these materials is eased. However, since the filter groove forming step and the filter inserting step are not continuous, there is a high possibility that dust adheres to the filter inserting groove 14. Therefore, sufficient care must be taken to prevent the generation of dust during the mounting process.

In the steps (1), (2b), and (3b), after the interference film filter 15 is inserted and fixed ((2b) filter insertion step), the optical functional elements (31 to 33) are mounted ((3b) ) Optical functional element mounting process). In this case, the filter and the adhesive for fixing the filter are exposed to a high temperature. Therefore, when selecting these materials, it is necessary to select a material having sufficient heat resistance.

Third, since the conventional optical module shown in FIG. 13 is a so-called pigtail type in which the optical fiber is connected and fixed to the end of the platform, care must be taken in handling the optical fiber. It was difficult to automate the process of mounting on an electric wiring board. For this reason, a configuration in which an optical fiber connected to an optical module is detachable, that is, a receptacle type is desired. By the way, in the pigtail type module, the optical fiber is connected and fixed after the optical axis of the optical fiber and the optical waveguide are aligned.
The connection loss can be reduced to almost the ideal value of about 0.1 dB. However, in the case of the receptacle type, a certain amount of connection loss is inevitable, and at present, a connection loss of about 0.5 to 1 dB occurs. Such a connection loss is an unacceptably high value for a 1.55 μm optical signal. Generally, LD
In a passive optical circuit that does not include an active optical element such as an optical fiber or a PD and is composed of an optical fiber-silica optical waveguide-optical fiber system, the fiber connection loss needs to be suppressed to about 0.1 dB.

The present invention provides an optical module in which a flat silicon substrate can be used for cost reduction in a hybrid integrated optical module and the passive optical circuit section can be reduced in loss while having a receptacle type configuration. The purpose is to:

[0013]

According to a first aspect of the present invention, there is provided an optical module comprising: an optical waveguide formed on a first substrate; and an optical waveguide formed on the first substrate while maintaining optical coupling with the optical waveguide. A hybrid optical circuit including an optical functional element having an operating wavelength of 1.3 μm mounted thereon, and a hybrid optical circuit formed on a second substrate;
And a passive optical circuit made of a light waveguide circuit the optical signal to demultiplexing of 1.3μm band and 1.55μm band, said hybrid <br/> mode optical circuit and the passive optical circuit, the hybrid optical circuit
From the center of the active layer of the optical functional device
The height of the solder joint is added to the height to the element surface.
Shall have a thin lower cladding layer,
Relative refractive index difference and core size of the passive optical circuit
With that the spot size is reduced, is set to a characteristic optical waveguide structure and parameters are required for each of the circuits, the optical waveguide circuit of the passive optical circuit, the optical waveguide of the hybrid optical circuit at one end face In this configuration, it is directly connected to the circuit in a detachable state, and is fixedly connected to the optical fiber with a fixing agent at the other end surface.

With this, in order to mount the optical function element,
Hybrid optical circuits that require high temperature soldering
When a molecular filter element is included, the heat resistance is relatively high.
A weak passive optical circuit is manufactured as a separate substrate configuration, and heat treatment is performed.
The effect can be cut off. Further, by using the hybrid optical circuit and the passive optical circuit as separate substrates, the respective optical waveguide structures and parameters can be optimally selected and manufactured. For example, the hybrid optical circuit has a priority on reducing the coupling loss with the optical functional element, and is composed of a silica-based optical waveguide with a relative refractive index difference of 0.75% and a core size of 6 μm square. The passive optical circuit has a reduction in the loss of the optical waveguide circuit. Priority, relative refractive index difference 0.3
%, And a quartz optical waveguide having a core size of 8 μm square, and an optical module can be realized by a combination of both.

Further, the thickness of the lower cladding layer is set to be thin.
So the optical function element is junction-down on the board
To achieve alignment with the optical waveguide circuit
be able to. However, such a thin lower cladding layer
Is remarkable for a 1.55 μm optical signal.
1.3 μm optical signal with increased propagation loss
, A slight propagation loss occurs. But hive
The allowable propagation loss for the optical waveguide of the lid optical circuit is
Be slightly larger than the propagation loss required for optical circuits.
Considering the above, the length of the optical waveguide circuit of the hybrid optical circuit
By setting the height to the minimum necessary, this optical waveguide
The effect of loss can be minimized. On the other hand, high quality
Passive optical circuits that require high quality optical waveguide characteristics are hybrid
Separated from the optical circuit.
It can be formed using an optical waveguide having the same.

Further, the optical module of the present invention has an operating wavelength
Equipped with 1.3μm band optical function element, and used for passive optical circuit
In both the 1.3 μm and 1.55 μm wavelength bands
An operating optical waveguide circuit is formed. This gives 1.55
Passive optical circuits that need to operate in the μm band
An optical waveguide having a partial cladding layer can be used.
On the other hand, a hybrid that only needs to operate in the 1.3 μm band
The optical circuit uses a thin lower cladding layer formed on the substrate.
Can be. For this reason, the hybrid optical circuit
Despite waveguide formed on thin lower cladding layer
And the effect of increased propagation loss can be almost ignored.
You. Therefore, a high-performance and low-cost optical module
Can be manufactured.

The hybrid light of the optical module according to claim 2
The circuit is a lower clad formed on a flat silicon substrate
A silica-based optical waveguide having a layer thickness of 5 to 10 μm;
Directly on a silicon substrate while maintaining optical coupling with a silica-based optical waveguide
It is composed of optical function elements mounted in close contact. Also, passive optical circuits
Is the lower cladding layer formed on a flat silicon substrate.
Constructed using a silica-based optical waveguide with a thickness of 15 μm or more
Is done.

Therefore, according to the structure of the present invention, the flat
Using a quartz optical waveguide on a silicon substrate
An optical module with an hybrid configuration can be realized.
You.

Further, the optical module according to the present invention is a
By using a separate board for the lid optical circuit and the passive optical circuit,
The direct connection between the passive optical circuit and the hybrid optical circuit.
Passive optical circuit and optical fiber fixed while detachable
Connection loss can be minimized by the fixed connection with the agent.
Wear. That is, in a passive optical circuit in which connection loss needs to be reduced to the limit, the optical fiber and the optical waveguide can be connected to the optical fiber with ultra-low loss by fixing the optical fiber and the optical waveguide with an adhesive or the like after alignment. . On the other hand, in the hybrid optical circuit, since the tolerance of the connection loss is relatively large, there is no problem even if the connection with the passive optical circuit is detachable.

With this configuration, in the process of mounting the optical module on the electric wiring board, the hybrid optical circuit for making an electrical connection to the board can be handled without the fiber pigtail. This process can be automated. The passive optical circuit with the fiber pigtail can constitute an optical module by mounting the hybrid optical circuit on a board and then attaching the hybrid optical circuit to the hybrid optical circuit. Therefore, this configuration can realize low loss of the passive optical circuit while being a receptacle type configuration.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 shows a first embodiment of the optical module of the present invention. The optical module of the present embodiment is composed of three parts, a passive optical circuit 10, a hybrid optical circuit 20, and an optical fiber block 5, and has a configuration in which they are combined.

The passive optical circuit 10 includes a 1.3 / 1.55 μm input / output waveguide 11, a 1.55 μm output waveguide 12, and a 1.3 / 1.5 μm output waveguide 12, which are formed using a quartz optical waveguide 2 on a silicon substrate 1.
The input / output waveguide 13 and the interference film filter 15 inserted in the filter insertion groove 14 of the silica-based optical waveguide 2 function as a WDM circuit for multiplexing and demultiplexing 1.3 / 1.55 μm optical signals. The hybrid optical circuit 20 forms a Y-branch circuit using the quartz-based optical waveguide 2 on the silicon substrate 1.
1.3 μm input / output waveguide 21, semiconductor laser (LD) 31 having a transmission wavelength of 1.3 μm mounted on the same substrate, monitoring photodiode (M-PD) 32, and reception wavelength 1.3
A receiving photodiode (R-PD) 33 of μm functions as a bidirectional optical transmitting / receiving circuit.

Both ends of the passive optical circuit 10 and the hybrid optical circuit 20 are directly connected while the 1.3 μm input / output waveguide 13 and the 1.3 μm input / output waveguide 21 maintain optical coupling.
The other end of the passive optical circuit 10 is fixedly connected via an optical fiber block 5 to an input / output optical fiber 4a common to 1.3 / 1.55 μm optical signals and an optical fiber 4b for outputting 1.55 μm optical signals. With such a configuration, the whole functions as a bidirectional WDM transmission / reception circuit.

The optical module of this embodiment has a configuration in which the passive optical circuit 10 and the hybrid optical circuit 20 are formed on different substrates, respectively, and thereafter are connected to each other. Therefore, different optical waveguide parameters are employed. be able to. As described above, in the passive optical circuit 10, since it is necessary to reduce the fiber connection loss and the optical circuit loss to the minimum, an optical waveguide having a relative refractive index difference of 0.3% between the core and the clad and a core size of 8 × 8 μm was used. By doing so, the connection loss between the optical fiber and the optical waveguide can be reduced to 0.1 dB or less per point, and the propagation loss of the optical waveguide can be reduced to 0.
It can be reduced to about 05dB / cm. As a result, the insertion loss of the optical module for a 1.55 μm optical signal can be reduced to 0.8 dB or less.

On the other hand, in the hybrid optical circuit 20, reducing the coupling loss between the optical functional element and the optical waveguide is given top priority. For this purpose, the spot size of the optical waveguide needs to be smaller than that of the passive optical circuit 10. Therefore, an optical waveguide having a relative refractive index difference of 0.75% and a core size of 6 × 6 μm was used. Further, as the LD 31, a spot size conversion laser (SS-LD) provided with a spot magnifying section in the light output section was used. As a result, the optical coupling loss between the optical waveguide and the LD 31 could be reduced to 3 dB.

As described above, the first embodiment of the optical module of the present invention
Is that the passive optical circuit 10 and the hybrid optical circuit 20 can be realized using optical waveguides having optimal parameters. Note that this effect can be sufficiently exerted even when the quartz optical waveguide formed on the stepped silicon substrate described in the related art is used as the substrate (platform) of the hybrid optical circuit 20.

Further, when a polymer material is used for the interference film filter 15 and its fixing agent as in the passive optical circuit 10 of the present embodiment, the problem of the heat treatment temperature in the manufacturing process of the optical module can be easily reduced. Can be solved. Here, a manufacturing process of the optical module of the present embodiment will be described with reference to FIG. In the present embodiment, since the optical module is divided into the passive optical circuit 10 and the hybrid optical circuit 20, both can be manufactured in different processes. After forming the filter insertion groove 14 in the quartz optical waveguide 2 on the silicon substrate 1 ((1a) filter groove formation step), the passive optical circuit 10 inserts the interference film filter 15 into the filter insertion groove 14, Fix with an adhesive ((1b) filter insertion step). Further, glass plates 8 are bonded to both ends of the silicon substrate 1 and polished so as to form an oblique end surface of 8 °. In the figure, the end face is not slanted, but is formed so that either the vertical direction or the horizontal direction is slanted.

On the other hand, the hybrid optical circuit 20 has an optical function element (LD31, M-PD3) independent of the passive optical circuit 10.
2, R-PD33) can be mounted ((2) optical function element mounting step). At this time, to mount and fix each optical function element,
In order to melt the solder joint 40, it is necessary to raise the substrate temperature to 300 ° C. or more. However, since it is completely separated from the filter insertion step in the passive optical circuit 10, there is no influence on the interference film filter 15. Has no effect. Further, a glass plate 8 is adhered to an end of the silicon substrate 1 and polished so as to have an oblique end face of 8 ° in the vertical or horizontal direction.

Further, the input / output optical fiber 4a and the output optical fiber 4b are fixed to the optical fiber block 5, and one end surface thereof is similarly polished so as to be an oblique end surface. Finally, the oblique end faces of the optical fiber block 5, the passive optical circuit 10, and the hybrid optical circuit 20 are connected by using, for example, an ultraviolet curing adhesive, and an optical module is manufactured ((3) optical module assembly process). In the above process, both ends of the passive optical circuit 10, one end of the hybrid optical circuit 20, and one end of the optical fiber block 5 are polished obliquely in order to prevent reflection at the connection. Further, the reason why the glass plate 8 is bonded to each end is to increase the area of each connecting portion and increase the bonding strength.

(Second Embodiment) FIG. 3 shows a second embodiment of the optical module of the present invention. The module configuration of the present embodiment is the same as that of the first embodiment shown in FIG.
The feature of the present embodiment lies in that the optical waveguide structures of the passive optical circuit 10 and the hybrid optical circuit 20 are as shown in FIGS. 3 (a) and 3 (b).

As shown in FIG. 3A, the quartz optical waveguide 2 of the passive optical circuit 10 according to the present embodiment transmits 1.3 / 1.55 μm optical signals and requires a sufficiently small propagation loss. A structure in which a core layer 2b is buried with a sufficiently thick lower clad layer 2c and an upper clad layer 2a formed on a silicon substrate 1 is used. Here, the thicknesses of the lower cladding layer 2a and the upper cladding layer 2b were both set to 20 μm, the core size was set to 7 × 7 μm, and the relative refractive index difference was set to 0.45%.

On the other hand, the silica-based optical waveguide 2 of the hybrid optical circuit 20 has the flexibility that only the 1.3 μm optical signal propagates and that a slight increase in the propagation loss can be compensated for by finely adjusting the operating conditions of the optical functional element. Then, as shown in FIG. 3 (b), a quartz optical waveguide 2 is formed on a flat silicon substrate 1, and the optical functional element 3 is directly mounted. Here, the thickness of the lower cladding layer 2a is 7.5 μm, and the thickness of the upper cladding layer 2b is 20 μm.
μm, the core size was set to 7 × 7 μm, and the relative refractive index difference was set to 0.45%.

As described above, in the hybrid optical circuit 20 of the present embodiment, since the lower cladding layer 2c is set to be thin, a flat silicon substrate can be used instead of the conventional stepped silicon substrate. Further, in the passive optical circuit 10, since the optimal parameters can be set for the optical waveguide, the loss can be reduced. As a result, a high-performance and low-cost optical module can be realized.

Here, the basis of the above design conditions in the hybrid optical circuit 20 will be described with reference to FIG. When the optical function element 3 is mounted on the silicon substrate 1 in a junction-down form, in order to match the height of the core layer 2b of the quartz optical waveguide and the active layer 3a of the optical function element 3, the lower clad layer 2c The thickness is D, the thickness of the core layer 2b is d, the height from the center of the active layer 3a of the optical function element 3 to the element surface is H, and the solder joint 4 on the surface of the silicon substrate 1 is formed.
Assuming that the thickness of 0 is h, it is necessary to satisfy the following relationship: D + d / 2 = H + h (1) Generally, in the optical function device 3, the height H from the center of the active layer 3a to the device surface is 7 to
It is not easy to set the thickness to 8 μm or more. In consideration of the positioning accuracy of the optical functional element, it is desirable that the thickness h of the solder joint 40 be set to 5 μm or less including the thickness of the electric wiring layer. Further, the core layer 2 of the silica-based optical waveguide
The thickness d of b is usually about 6 to 8 μm. Taking these into consideration, the upper limit of the thickness D of the lower cladding layer 2c that can be achieved is substantially determined from the equation (1). That is, it is understood that D should be set to about 10 μm or less.

FIG. 5 shows the relationship between the lower cladding layer thickness D and the optical waveguide propagation loss. Here, the quartz optical waveguide on the silicon substrate has a core size of 7 × 7 μm and a relative refractive index difference of 0.45%.
And When the thickness of the lower cladding layer is 15 μm or more, the propagation loss is 0.1 dB / cm or less, which is low, regardless of the wavelength and polarization of the propagating light. When the thickness of the lower cladding layer becomes 15 μm or less, the loss of 1.55 μm TM mode propagating light starts to increase,
When the lower cladding layer thickness is 7.5 μm, the loss is 1.5 dB / cm.
On the other hand, for a 1.3 μm optical signal, the propagation loss of both the TE mode and the TM mode is 0.1 when the lower cladding layer thickness is 10 μm.
It is less than dB / cm, but if the layer thickness is less than this, the loss of the TM mode increases remarkably, and the lower cladding layer thickness is 7.5 μm.
Will result in a loss of 0.3 dB / cm.

From FIG. 4 and FIG. 5 described above, the conditions under which the quartz optical waveguide of a flat silicon substrate can be used as a substrate of a hybrid optical circuit are defined. That is, if the relative refractive index difference of the optical waveguide is 0.45%, the core size is 7 × 7 μm, the wavelength used is limited to the 1.3 μm band, and the propagation loss of 0.5 dB / cm is allowed, the lower cladding layer thickness D is 7 to 10 μm. It can be seen that it should be set to.

In the above description, the relative refractive index difference is 0.45%.
The case where the optical waveguide of was used was shown, but the relative refractive index difference was 0.75.
%, When an optical waveguide having a core size of 6 × 6 μm is used,
When the lower cladding layer thickness D is set to 5 μm or more, an optical waveguide having a loss of about 0.5 dB / cm with respect to a 1.3 μm optical signal can be realized. As described above, if the core size of the optical waveguide is set to 6 to 8 μm and the thickness of the lower cladding layer is set to 5 to 10 μm, at least
It can be seen that a hybrid optical circuit can be formed using a quartz optical waveguide on a flat silicon substrate for a transmitting / receiving module for 1.3 μm optical signals.

(Third Embodiment) FIG. 6 shows a third embodiment of the optical module of the present invention. The functions of the passive optical circuit 10 and the hybrid optical circuit 20 in this embodiment are the same as those in the first and second embodiments. The feature of this embodiment resides in that a Mach-Zehnder interference circuit 16 is used as a WDM circuit in the passive optical circuit 10. In this embodiment, the output section of the 1.55 μm output waveguide 12 is set to 1.3 / 1.55 μm
It is arranged on the same end face as the input / output waveguide 11.

By using the Mach-Zehnder interference circuit 16, the passive optical circuit 10 can be composed of only an optical waveguide. This is advantageous compared to the first and second embodiments because there is no filter groove processing or post-processing, but the size is increased by the complexity of the optical waveguide. Therefore, in practice, the configuration of the first or second embodiment or the configuration of the third embodiment is selected depending on whether there is a strong demand for miniaturization or a strong demand for simplifying the assembling process.

In this embodiment, the hybrid optical circuit 20
Is the same as in the first and second embodiments. This is because, in the first to third embodiments, the hybrid optical circuit 20
It is shown that can be shared. In other words, if you prepare optical circuits commonly used in various optical modules,
Various optical modules can be manufactured at low cost only by changing the combination. The hybrid optical circuit 20 can be used as a single-wavelength bidirectional optical transmitting / receiving module by directly connecting optical fibers via the optical fiber block 5 as shown in FIG.

(Fourth Embodiment) FIG. 8 shows an optical module according to a fourth embodiment of the present invention. This embodiment and first to first
The difference from the third embodiment lies in the way of dividing the functions of the passive optical circuit 10A and the hybrid optical circuit 20A. The passive optical circuit 10A has a WDM circuit 101 and a Y branch circuit 102. The hybrid optical circuit 20A includes a semiconductor laser (L
D) 31 and monitor photodiode (M-PD) 3
2, a receiving photodiode (R-PD) 33, a transmitting output waveguide 22, and a receiving input waveguide 23. Furthermore, in the present embodiment, the hybrid optical circuit 20
The optical function element mounting portion A is covered with a sealing lid 34, and the sealing lid 34
Are fixed by soldering and locally airtightly sealed.

With such a configuration, the optical waveguide length in the hybrid optical circuit 20A can be reduced to a necessary minimum. As a result, in a hybrid optical circuit using a flat silicon substrate, even in a region where the propagation loss increases due to the reduction in the thickness of the lower cladding layer, the overall increase in loss is sufficiently reduced by shortening the optical waveguide length. Can be suppressed. Further, in the hybrid optical circuit, the hermetic sealing can be locally realized as described above. For this reason, when installing the optical module in the package, the package structure can be simplified, and the module cost can be reduced. The local sealing can be applied not only to this embodiment but also to other embodiments.

(Fifth Embodiment) FIG. 9 shows a fifth embodiment of the optical module of the present invention. The optical module of the present embodiment includes a passive optical circuit 10B and a hybrid optical circuit 2B.
OB and three parts of the optical fiber block 5, which are combined.

The passive optical circuit 10B comprises a Mach-Zehnder interference circuit 16 and functions as a 1.3 / 1.55 μm WDM circuit. The hybrid optical circuit 20B has a transmission wavelength of 1.
It comprises a 55 μm semiconductor laser (LD) 35, a monitoring photodiode (M-PD) 36, and a receiving photodiode (R-PD) 33 having a receiving wavelength of 1.3 μm, and functions as a bidirectional optical transmitting / receiving circuit. .

By the way, the hybrid optical circuit 20B comprises:
As in the second embodiment, the lower clad layer formed on the flat silicon substrate 1 has a thickness of 7.5 μm and a core size of 7 × 7 μm.
m, a quartz optical waveguide 2 having a relative refractive index difference of 0.45% is used. As shown in FIG. 5, an optical waveguide of this size has a thickness of 1.55 μm.
A propagation loss of about 1.5 dB / cm occurs for the mTM mode. On the other hand, the propagation loss for a 1.3 μm optical signal is 0.5 dB /
cm or less. Therefore, in the hybrid optical circuit 20B, the 1.55 μm LD 35 is arranged closer to the end of the substrate than the 1.3 μm R-PD 33, and the length of the optical waveguide through which the 1.55 μm optical signal propagates is shortened as much as possible (optical waveguide length to 5 m).
m). Thereby, the influence of the thin lower cladding layer was suppressed. That is, even when a silica-based optical waveguide having a thin lower cladding layer on a flat silicon substrate 1 is used, an optical functional element for 1.55 μm can be mounted by shortening the optical waveguide length. Since the passive optical circuit 10B uses the silica-based optical waveguide 2 formed on the silicon substrate 1 and having a lower cladding layer thickness of 20 μm, a core size of 7 × 7 μm, and a relative refractive index difference of 0.45%, the propagation loss is 0.1 dB / cm. The following excellent optical waveguide characteristics have been realized.

(Example of Mounting Form) FIG. 10 shows an example of a mounting form of the optical module of the present invention. The optical module shown here is of the first embodiment shown in FIG. After the passive optical circuit 10 and the optical fiber block 5 are aligned and fixed with an adhesive to be integrated, the entire package 5 is formed.
0. On the other hand, the hybrid optical circuit 20 is disposed in the package 51. Prior to this, it is desirable that the optical functional element of the hybrid optical circuit 20 be locally sealed. For the local sealing, for example, the method described in the fourth embodiment is used. The package 50 and the package 51 are detachably connected to each other using the guide pins 52.

As described above, since the passive optical circuit 10 and the optical fiber block 5 are aligned and fixed to be integrated, the connection loss of the input and output optical fibers for a 1.55 μm optical signal that requires particularly low loss is reduced. It can be reduced to 0.1dB / cm. On the other hand, since the passive optical circuit 10 with the optical fiber and the hybrid optical circuit 20 are detachably connected to each other, the step of mounting this optical module on the electric mounting board can be greatly simplified. it can.

Here, a step of mounting the optical module on the electric mounting board 60 will be described with reference to FIG. Since the optical module can be detachably detached from the package 50 including the passive optical circuit with the optical fiber,
As shown in (1), only the package 51 including the hybrid optical circuit can be mounted in the same process as the normal electronic circuit 61 without the pigtail. And
As shown in (2), if the package 50 including the passive optical circuit with the optical fiber is finally connected, the optical module can be easily mounted on the electrical mounting board 60. As described above, the optical module of the present invention can realize a low loss of the passive optical circuit while having the receptacle type configuration, and can greatly simplify the mounting process on the electric mounting board.

[0049]

As described above, in the optical module of the present invention, the passive optical circuit and the hybrid optical circuit are formed on different substrates, respectively, and the two are coupled to each other. And parameters can be optimally selected and manufactured. Further, in the present invention, focusing on the fact that the allowable propagation loss for the optical waveguide of the hybrid optical circuit is slightly larger than the propagation loss required for the passive optical circuit, the lower part of the quartz-based optical waveguide formed on a flat silicon substrate is considered. The thickness of the cladding layer was set in the range of 5 to 10 μm. As a result, a hybrid optical circuit can be configured using a silica-based optical waveguide on a flat silicon substrate without using a silicon substrate having a step. In addition, a passive optical circuit that requires high-quality optical waveguide characteristics may be set with optimal parameters, so that a high-quality and low-cost optical module having a hybrid configuration can be realized.

Further, according to the present invention, 1.3 / 1.55 μm WD
In a WDM transmission / reception module composed of an M circuit and a 1.3 μm bidirectional optical transmission / reception circuit, a WDM circuit that propagates an optical signal of 1.55 μm and requires low propagation loss requires a lower cladding layer having a sufficient thickness. A passive optical circuit having the same can be used. On the other hand, a bidirectional optical transmitting / receiving circuit (a circuit composed of a branch circuit, a semiconductor laser, and a light receiving element) that only needs to operate in the 1.3 μm band is a hybrid optical circuit having a thin lower cladding layer formed on a flat silicon substrate. Can be used. As a result, the loss of the 1.55 μm optical signal is sufficiently low, and an optical module having a hybrid configuration using a flat silicon substrate can be realized at low cost.

Further, it is possible to align the passive optical circuit and the optical fiber, further fix them with an adhesive and integrate them, and directly connect the connection end faces of the hybrid optical circuit and the passive optical circuit in a detachable state. it can. As a result, in the process of mounting an optical module on an electrical wiring board, a hybrid optical circuit that needs to realize electrical connection to this board can be handled without a fiber pigtail, and then the fiber An optical module can be configured by attaching a passive optical circuit with a pigtail. Therefore, this configuration can realize low loss of the passive optical circuit while being a receptacle type configuration.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an optical module of the present invention.

FIG. 2 is a view showing a manufacturing process of the optical module of the first embodiment.

FIG. 3 is a diagram showing a second embodiment of the optical module of the present invention.

FIG. 4 shows a hybrid optical circuit 2 according to a second embodiment.
FIG.

FIG. 5 is a diagram showing a relationship between a lower cladding layer thickness D and an optical waveguide propagation loss.

FIG. 6 is a diagram showing a third embodiment of the optical module of the present invention.

FIG. 7 is a diagram showing a modification of the third embodiment of the optical module of the present invention.

FIG. 8 is a diagram showing a fourth embodiment of the optical module of the present invention.

FIG. 9 is a diagram showing a fifth embodiment of the optical module of the present invention.

FIG. 10 is a diagram showing an example of a mounting mode of the optical module of the present invention.

FIG. 11 is a view showing a step of mounting the optical module of the present invention on a board.

FIG. 12 is a diagram showing a block configuration of a WDM transmission / reception optical module.

FIG. 13 is a diagram showing a configuration example of a conventional hybrid integrated optical module.

FIG. 14 is a diagram showing a cross-sectional structure of a conventional optical module.

FIG. 15 is a diagram showing a manufacturing process of a conventional optical module.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Quartz optical waveguide 2a Upper cladding layer 2b Core layer 2c Lower cladding layer 3 Optical functional element 3a Active layer 4a Input / output optical fiber 4b Output optical fiber 5 Optical fiber block 6 Silicon terrace 8 Glass plate 10 Passive light Circuit 11 1.3 / 1.55 μm input / output waveguide 12 1.55 μm output waveguide 13 1.3 μm input / output waveguide 14 Filter insertion groove 15 Interference film filter 16 Mach-Zehnder interference circuit 20 Hybrid optical circuit 21 1.3 μm input / output waveguide 31 Transmission wavelength 1.3 μm semiconductor laser (LD) 32 monitor light receiving element (M-PD) 33 receiving wavelength 1.3 μm receiving light receiving element (R-PD) 34 sealing lid 35 semiconductor laser (LD) with transmission wavelength 1.55 μm 36 monitor Light receiving element (M-PD) 40 Solder joint 50, 51 Package 52 Guide pin 60 Gas mounting board 61 the electronic circuit 101 WDM circuit 102 Y branch circuit

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiro Yanagisawa 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Kuniharu Kato 3--19, Nishishinjuku, Shinjuku-ku, Tokyo No. 2 Within Nippon Telegraph and Telephone Corporation (56) References JP-A-8-190026 (JP, A) JP-A-8-94870 (JP, A) JP-A 8-304645 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/24-6/43 G02B 6/12-6/14

Claims (2)

(57) [Claims] 1. An optical waveguide circuit formed on a first substrate, and light of an operating wavelength of 1.3 μm mounted on the first substrate via solder while maintaining optical coupling with the optical waveguide circuit. A hybrid optical circuit comprising functional elements, and a 1.3 μm band and 1.55 μm formed on a second substrate.
A passive optical circuit composed of an optical waveguide circuit for multiplexing / demultiplexing an optical signal in a band , wherein the hybrid optical circuit and the passive optical circuit have an optical waveguide structure of the hybrid optical circuit, and the optical function
Solder bonding to the height from the center of the active layer of the device to the surface of the device
With a lower cladding layer thin enough to add the thickness of the part
And the relative refractive index difference between the core and the clad and the core dimensions
The spot size is smaller than the passive optical circuit.
By setting , the optical waveguide structure and parameters are set to characteristics required for each circuit, and the optical waveguide circuit of the passive optical circuit is detachable from the optical waveguide circuit of the hybrid optical circuit at one end face. An optical module, wherein the optical module is directly connected in a state, and is fixedly connected to the optical fiber with a fixing agent at the other end face. 2. The substrate in the hybrid optical circuit is a flat silicon substrate, and the optical waveguide circuit in the hybrid optical circuit is formed using a silica-based optical waveguide in which the thickness of the lower cladding layer is set in the range of 5 to 10 μm. The optical functional element is mounted directly on the silicon substrate while maintaining optical coupling with the quartz optical waveguide, and the substrate in the passive optical circuit is a flat silicon substrate,
2. The optical module according to claim 1, wherein the optical waveguide circuit in the passive optical circuit is formed using a silica-based optical waveguide in which a thickness of a lower cladding layer is set to 15 μm or more.