Mounting structure for optical module

A mounting structure for an optical module includes a light emitting element, a submount board on which the light emitting element is mounted, a main board on which the submount board is mounted, a light guide member provided on the main board, and a diffraction grating optical coupler provided on the main board and connected to the light guide member. The submount board and the main board are bonded to each other on a surface of the submount board different from a surface on which the light emitting element is mounted.

TECHNICAL FIELD

The technical field relates to amounting structure for entering laser light from a light emitting element into a minute waveguide in an optical module.

BACKGROUND

In recent years, utilization of light has been studied in the fields of high-speed and large-capacity communication and optical sensing. In the fields of large-capacity communication and optical sensing, it is necessary to allow laser light from a light emitting element such as a semiconductor laser to enter a light guide member such as an optical fiber in a device. Then, miniaturization of the light guide member is progressing due to the necessity of integration. Therefore, high position accuracy of the semiconductor laser with respect to the light guide member has been demanded.

Japanese Patent Unexamined Publication No. 2018-84778 discloses a technique using a diffraction grating optical coupler in order to allow laser light of a semiconductor laser (hereinafter, referred to as “laser light” unless otherwise specified) to enter an optical fiber.

Japanese Patent Unexamined Publication No. 2018-84778 describes a technique that can reduce the position accuracy required for a semiconductor laser as compared with a case where a diffraction grating optical coupler is used and laser light is directly incident on an optical fiber.

However, in a case where the miniaturization of the optical fiber progresses and the position accuracy of the optical fiber is required on a micrometer order, there is the following problem when laser light is incident on the optical fiber.

In a method in which laser light is directly incident on an optical fiber, the optical fiber is mounted on a board with fine position accuracy on a micrometer order. For an optical waveguide that requires micrometer-order position accuracy, a semiconductor laser that enters laser light into the optical waveguide is required to have position accuracy on several tens to several hundreds of nanometer order with respect to the board. Therefore, it is difficult to mount a semiconductor laser for technical reasons.

In the method of Japanese Patent Unexamined Publication No. 2018-84778 in which laser light is incident on an optical fiber mounted with high position accuracy via a diffraction grating optical coupler, the edge emitting laser light has a large spread angle and spreads about 30° in the vertical direction. In a case of using a reflection mirror, the distance from an emission port of the laser light to the diffraction grating optical coupler is long, and a light incident range is widened. Therefore, in order to receive the spread laser light, an enlarged diffraction grating optical coupler is necessary. The enlarged diffraction grating optical coupler has a problem that optical efficiency is lowered because the incident laser light is re-emitted after the laser light is incident.

SUMMARY OF THE INVENTION

To solve the above problem, there is provided a mounting structure for an optical module. The mounting structure includes a light emitting element, a submount board on which the light emitting element is mounted, a main board on which the submount board is mounted, a light guide member provided on the main board, and a diffraction grating optical coupler provided on the main board and connected to the light guide member. The submount board and the main board are bonded to each other on a surface of the submount board different from a surface on which the light emitting element is mounted.

According to the present disclosure, it is possible to provide an optical module structure that enters laser light from a light emitting element into a fine waveguide having high position accuracy in an optical module.

DESCRIPTION OF EMBODIMENTS

First Embodiment

FIG.1is a schematic sectional view showing a mounting structure according to a first embodiment of the present disclosure. Edge emitting semiconductor laser101which is a light emitting element has emission port102. Semiconductor laser101is mounted on a first surface of submount board103. Submount board103has electrode109on the first surface for bonding semiconductor laser101. Semiconductor laser101and submount board103are bonded to each other via a bonding member. Examples of the bonding member include gold tin, solder, and gold stud bump. Main board104is provided with light guide member105for receiving laser light from semiconductor laser101.

Light guide member105has diffraction grating optical coupler106for coupling laser light. Diffraction grating optical coupler106couples the laser light according to an incident angle of the laser light. Main board104and submount board103are bonded to each other on an inclined side (second) surface of submount board103via adhesive material107so that laser light can be incident on diffraction grating optical coupler106at a predetermined angle. Adhesive material107is, for example, a UV curable resin. As shown inFIG.1, the second surface of the submount board103is different from (not the same surface as) the first surface on which the light emitting element101is mounted.

Angle108between main board104and submount board103may be any degree of angle because diffraction grating optical coupler106can be designed according to the angle. However, in order to form the mounting structure with high accuracy, it is preferable to use anisotropic etching in which submount board103is formed of a single crystal of silicon and can be processed according to the crystal orientation of silicon. When silicon is formed by anisotropic etching, the angle of the edge of submount board103, that is, angle108is 54.74°. Here, this angle has a variation of ±5° or less depending on, for example, whether or not a wafer is sliced from a silicon ingot with high accuracy.

Angle108is an angle formed between a surface of main board104on which diffraction grating optical coupler106is mounted and a surface of submount board103on which semiconductor laser101is mounted. Angle108is the angle formed between the surfaces, and the angle formed between normal vectors perpendicular to each surface.

When submount board103is mounted on main board104, the position at which the laser is incident on diffraction grating optical coupler106is affected. Therefore, the mounting accuracy of submount board103in the vertical direction of main board104needs to be high. When only adhesive material107is present between main board104and submount board103, adhesive material107is generally a non-rigid material. Accordingly, a gap (interval) between main board104and submount board103cannot be set to a predetermined value. Therefore, as shown inFIG.2, it is better to form spacer201on main board104and to position main board104and submount board103in the vertical direction via spacer201. Thereafter, it is preferable to bond and mount main board104and submount board103with adhesive material107.

Spacer201is formed by a semiconductor process performed when main board104is formed, so that spacer201can be adjusted in thickness with high accuracy. Therefore, the gap formed between main board104and submount board103can be set to a predetermined value. Spacer201is formed of, for example, metal or resin. When the spacer is formed of an elastic resin, a small gap due to dust or unevenness can be absorbed. In order to allow the laser light to enter diffraction grating optical coupler106without spreading as much as possible, it is preferable that a distance between semiconductor laser101and diffraction grating optical coupler106is close. Therefore, it is preferable that the position where semiconductor laser101is mounted on submount board103is close to a tip portion processed by anisotropic etching.

When it is desired to stop the laser light and make it incident on diffraction grating optical coupler106, as shown inFIG.3, lens301may be provided between semiconductor laser101and diffraction grating optical coupler106, and the laser light may be stopped by lens301.

Spacer201and lens301described above may be used in combination.

Second Embodiment

Also in the above-described embodiment, the laser light can be incident on diffraction grating optical coupler106at a predetermined angle, and the distance between semiconductor laser101and diffraction grating optical coupler106can be reduced. For further miniaturization of light guide member105, a second embodiment is preferable. Matters not described are the same as those in the above-described embodiment.

Even in the case where semiconductor laser101is mounted on the tip of submount board103as in the embodiment described above, depending on the thickness of semiconductor laser101and the thickness of submount board103, the distance between emission port102of semiconductor laser101and diffraction grating optical coupler106is increased, and the laser light spreads. Even when a lens is provided between semiconductor laser101and diffraction grating optical coupler106, the position where the lens is installed is required to have high accuracy. Accordingly, the lens cannot be mounted.

The second embodiment will be described with reference toFIG.4.FIG.4is a schematic sectional view showing a mounting structure according to the second embodiment of the present disclosure. The configuration between semiconductor laser101and diffraction grating optical coupler106is different from the above-described embodiment.

In the second embodiment, core401is provided between semiconductor laser101and diffraction grating optical coupler106as a high refractive member having a high refractive index with respect to laser light and clad402is provided as a low refractive member having a lower refractive index than core401with respect to laser light. Semiconductor laser101as the light emitting element and diffraction grating optical coupler106are connected by core401as the high refractive member and clad402as the low refractive member. Core401and clad402are self-forming optical waveguides formed of a self-forming optical waveguide material. The self-forming optical waveguide is formed from a self-forming optical waveguide material containing two photocurable resins. The self-forming optical waveguide is, for example, a light guide member such as an optical fiber. One of the two photocurable resins is cured at the wavelength of laser light of the semiconductor laser. The other photocurable resin is cured at a wavelength different from the wavelength of the previous laser light.

The photocurable resin cured at the wavelength of the laser light of semiconductor laser101has a higher refractive index of the laser light than the photocurable resin cured at the wavelength different from the wavelength of the laser light of semiconductor laser101.

The curing with the two photocurable resins is preferably a photocurable resin having a different polymerization method such as radical polymerization and cationic polymerization. As an example of these materials, Aronix M-1100 (manufactured by Toagosei Co., Ltd.) is used as a photocurable resin having a high refractive index with respect to laser light, and OXT-101 (manufactured by Toagosei Co., Ltd.) is used as a photocurable resin having a low refractive index with respect to laser light.

The portion between semiconductor laser101and diffraction grating optical coupler106is filled with the self-forming optical waveguide material. By irradiating the portion filled with the self-forming optical waveguide material with laser light, the high refractive index component of the photocurable resin is cured, and core401is formed. By simultaneously emitting the laser light and laser light from another semiconductor laser (not shown) from light guide member105side, the laser light in the portion where the respective laser lights overlap becomes strong. Core401is formed around the portion where the laser lights overlap. Therefore, even in a case where the coupling position between the laser of semiconductor laser101and diffraction grating optical coupler106is shifted, when there is a portion where each laser overlaps, core401is formed following the overlapping portion. The above-described other semiconductor laser may not be mounted on main board104or submount board103. The above-described semiconductor laser may be disposed outside main board104or submount board103, and for example, the fiber of a fiber laser may be brought close to the outside of emission port102to irradiate the self-forming optical waveguide material with laser light. The above-described other semiconductor laser may be mounted on either main board104or submount board103.

The other photocurable resin that cures at a wavelength different from the wavelength of the laser of semiconductor laser101is cured to form clad402. Core401has a higher refractive index of laser light than clad402. By forming such a self-forming optical waveguide having core401and clad402, the laser light of semiconductor laser101can be incident on diffraction grating optical coupler106without being diffused.

Third Embodiment

A third embodiment differs from the first embodiment and the second embodiment (FIGS.1to3) in the angle of the laser light incident on diffraction grating optical coupler106. Matters not described are the same as those in the first embodiment and the second embodiment.

When the laser light is incident on diffraction grating optical coupler106at predetermined angle108as in the first embodiment and the second embodiment, light guide member105receives the laser light in the direction of the horizontal component at angle108. On the other hand, when the laser light is perpendicularly incident on diffraction grating optical coupler106, the laser light is coupled to light guide member105in the incident direction and in the opposite direction.

When the light guide member is not formed in the opposite direction, the laser light is reflected at the end of diffraction grating optical coupler106, and the reflected light and the laser light incident on light guide member105interfere with each other.

When the light guide member branches into two by using this phenomenon and the branched light guide member is used, the laser light of semiconductor laser101may be perpendicularly incident on diffraction grating optical coupler106.

The third embodiment will be described with reference toFIG.5.FIG.5is a schematic sectional view showing a mounting structure according to the third embodiment. Electrode109for bonding semiconductor laser101is formed on the front surface of submount board501. The side surface of submount board501is perpendicularly cut. Semiconductor laser101is mounted on submount board501. Submount board501and main board104are bonded to each other via adhesive material107. In order to shorten the distance between semiconductor laser101and diffraction grating optical coupler106, it is preferable to mount semiconductor laser101on the end of submount board501on the surface side bonded to main board104. In consideration of optical efficiency, the bonding angle between main board104and submount board103is preferably 90°±5°.

FIG.6is a plan view of the mounting structure showing a configuration in which light guide member105is branched when viewed from above. Light guide member105and diffraction grating optical coupler106are formed on main board104. Light guide member105branches from diffraction grating optical coupler106in two directions.

A configuration for reducing the distance between semiconductor laser101and diffraction grating optical coupler106will be described with reference toFIG.7. Semiconductor laser101is mounted on submount board501so that the surface bonded to main board104corresponds to the emission surface of semiconductor laser101. The distance between semiconductor laser101and diffraction grating optical coupler106is adjusted by the height of spacer201. The reason why the gap between submount board501and main board104can be adjusted with high accuracy by spacer201is the same as that described with reference toFIG.2in the embodiment described above.

The mounting structure for the optical module according to the present disclosure can be used to create an optical sensing device using silicon photonics or laser light in which miniaturization of the light guide member will proceed in the future.