WO2014199831A1

WO2014199831A1 - Optical path conversion element, connection structure for optical path conversion element, light source device, and optical mounting device

Info

Publication number: WO2014199831A1
Application number: PCT/JP2014/064180
Authority: WO
Inventors: 近藤　順悟; 山口　省一郎; 隆史吉野; 武内　幸久
Original assignee: 日本碍子株式会社
Priority date: 2013-06-11
Filing date: 2014-05-28
Publication date: 2014-12-18
Also published as: JP6379090B2; JPWO2014199831A1

Abstract

This optical path conversion element (4) is provided with: a support substrate (5); a thin layer (6) comprising an optical crystal formed on the support substrate, the thin layer having a first principal surface side (6a) situated on the support substrate side, and a second principal surface side (6b) situated on the opposite side from the support substrate; and a ridge optical waveguide (8) partitioned by at least a pair of ridge grooves (7) formed in the thin layer (6), the ridge optical waveguide having a light entrance face (8a) and a reflecting face (8b) for reflecting light propagated through the optical waveguide (8). Light reflected by the reflecting face exits the surface through the thin layer.

Description

Optical path changing element, optical path changing element connection structure, light source device and optical mounting device

The present invention relates to an optical path changing element, an optical path changing element connection structure, a light source device, and an optical mounting device.

Data processing speed has been dramatically increased with the progress of information communication. In data centers, optical interconnection for optical transmission between devices such as network devices and servers is being introduced, and the development of active optical cables (AOC: "Active Optical Optical Cable"), which are key parts, has been activated. Three-dimensional optical mounting technology using AOC technology is being considered for use in multimedia transmission equipment in homes and indoor wiring, and in the future for use in information communication terminals such as personal computers and mobile phones.

In order to realize three-dimensional optical mounting, a technique for bending light at 90 degrees and optically connecting optical components is required. Regarding this, there are conventional techniques shown in Patent Documents 1 to 6.

Patent Documents 1 to 3 disclose a technique (reflection element) using a polymer waveguide and having a function of converting an optical path by 90 degrees.

In Patent Document 1, a polymer optical waveguide module having a light emitting element, a lower clad, a core, and an upper clad, having an optical path conversion mirror surface at one end thereof, and a light receiving element for monitoring light from the light emitting element Is disclosed.

Patent Document 2 discloses an optical waveguide film that does not require a microlens by processing it into a 45 ° mirror surface on the end face of the optical waveguide film and directly adhering it to a flat light emitting element such as VECSEL. The core size is about 10 μm square in the case of a single mode optical waveguide, and 50 to 100 μm square in the case of a multi mode. The cladding is at least 20 μm or more in order to maintain mechanical strength.

Patent Document 3 discloses an optical waveguide film in which a mirror is formed by forming a metal film on a 45 ° groove processed surface. When the cladding thickness is 5 μm or more, the cladding thickness necessary for light confinement can be secured, and when it is 500 μmμ or less, the film thickness can be easily controlled uniformly. From the above viewpoint, the thickness of the lower cladding layer is more preferably in the range of 10 to 100 μm.

JP2006-011210 JP2006-017885 JP2012-150242 JP 04-24610 JP 05-34526 Japanese Patent Application 2008-276657

When the direction of the light emitted from the light source is changed and optically coupled to the optical waveguide device, when the waveguide of the optical waveguide device is a single mode waveguide, the core size is about 10 μm square. For this reason, a coupling loss becomes large in a butt joint.

In addition, when a butt joint is formed directly under the mirror, the polymer waveguide has a cladding thickness of at least 5 μm, so that the beam expands and coupling loss due to mode mismatch increases. Even when the optical path is changed by bending the optical fiber, it is difficult to fix the optical component because the outer peripheral portion is curved.

For 45 ° mirrors, in the case of polymer optical waveguides and optical fibers, the conditions for total reflection at the interface with air are satisfied, but the refractive index is as low as about 1.5. The rate difference is reversed and the total reflection condition may not be satisfied, and the reflectivity varies greatly. In order to prevent this, a material with a lower refractive index is required for coating, but it is difficult to select an appropriate material because the SiO2 film cannot be used.

An object of the present invention is an optical path changing element for changing an optical path of light oscillated from a light source and making it incident on an optical waveguide element, which can increase and stabilize the coupling efficiency of light from the light source to the optical waveguide element An optical path changing element is provided.

The present invention is an optical path changing element that changes the propagation direction of light,
Support substrate,
A thin layer made of an optical crystal and formed on the support substrate, the first layer having a first main surface on the support substrate side and a second main surface on the opposite side of the support substrate; And a ridge-type optical waveguide defined by at least a pair of ridge grooves formed in a thin layer, the ridge-type optical waveguide having a light incident surface and a reflective surface that reflects light propagating through the ridge-type optical waveguide With
The light reflected by the reflecting surface is emitted from the second main surface side through the thin layer.

Further, the present invention is a connection structure between the optical path changing element and an optical waveguide element having a channel type optical waveguide,
The exit surface of the optical path changing element and the channel type optical waveguide are butt-jointed.

Further, the present invention relates to a light source device comprising a light source that oscillates light and the optical path changing element.

The optical mounting device according to the present invention is
A mounting substrate having a top surface, a bottom surface and a side surface between the top surface and the bottom surface;
The optical path changing element fixed to the upper surface of the mounting substrate,
It is fixed to the upper surface of the mounting board, and includes a light source that oscillates light, and an optical waveguide element that is fixed to the side surface of the mounting board and has another channel-type optical waveguide
The exit surface of the optical path changing element and the channel type optical waveguide are butt-jointed.

According to the present invention, in the optical path changing element for changing the optical path of the light oscillated from the light source and making it incident on the optical waveguide element, the coupling efficiency of light from the light source to the optical waveguide element can be increased and stabilized.

1 is a perspective view schematically showing an optical mounting device 1. FIG. It is a schematic diagram which shows the coupling | bonding state of the light source 3 and the optical path changing element 4. FIG. 2 is a schematic diagram showing a coupling state of a light source 3, an optical path changing element 4 and an optical waveguide element 10. FIG. 3 is a perspective view of an optical path changing element 4. FIG. 3 is a cross-sectional view schematically showing an optical path changing element 4. FIG. It is a cross-sectional view schematically showing the optical path changing element 4A. It is a perspective view which shows typically other optical mounting devices 1A. It is a schematic diagram which shows the coupling | bonding state of the light source 3 and the optical path changing element 4B. 3 is a schematic diagram showing a coupling state of a light source 3, an optical path changing element 4B, and an optical waveguide element 10. FIG. It is a perspective view of the optical path changing element 4B. In the optical path changing element of an Example, it is a graph which shows the relationship between the angle of a reflective surface, and the reflectance of s polarization | polarized-light and p deflection | deviation.

First, referring to the drawings, a specific structure of the optical mounting device of the present invention will be exemplified, and then various embodiments will be described.

As shown in FIG. 1, the mounting substrate 2 has an upper surface 2a, a bottom surface 2d, and

side surfaces

2b and 2c. In this embodiment, the upper surface 2a and one side surface 2b are used for mounting.

The light source 3 is fixed to the upper surface 2 a of the mounting substrate 2. For example, as shown in FIGS. 2 and 3, light is emitted as indicated by an arrow A from the active layer 3 a of the light source 3.

Further, the optical path changing element 4 is fixed to the upper surface 2 a of the mounting substrate 2. In the optical path changing element, as shown in FIGS. 4 and 5, the support substrate 5 and the thin layer 6 are joined and integrated with each other. For example, a pair of ridge grooves 7 are formed on the first main surface 6 a on the support substrate side of the thin layer 6, and a ridge-type optical waveguide 8 is formed between the ridge grooves 7. In this example, the lower buffer layer 21 is formed on the main surface 6 a of the thin layer 6, and is bonded to the support substrate 5 via the adhesive layer 22. On the other hand, the second main surface 6b opposite to the support substrate 5 of the thin layer 6 is flat, and the buffer layer 20 is formed on the main surface 6b side. In this case, the buffer layer 20 itself may function as an antireflection film for the emitted light, or an antireflection film may be provided on the buffer layer 20.

The incident surface 4 a of the optical path changing element 4 is flat, and is substantially perpendicular to the top and bottom surfaces of the optical path changing element 4. On the other hand, the exit surface 4b of the optical path changing element 4 is inclined at an angle θ with respect to the bottom surface. The light oscillated from the light source enters the incident surface 8a of the channel-type optical waveguide 8, propagates in the optical waveguide 8 as indicated by arrow B, and is then reflected by the reflecting surface 8b facing the exit surface of the optical path changing element. . Then, the light propagates through the thin layer 6 as indicated by an arrow C, and is emitted as indicated by an arrow C from the emission surface 4c on the bottom side.

In this example, a Bragg grating 9 is formed in the optical waveguide 8. It is preferable to provide a propagation part without a diffraction grating between the incident surface 8 a of the optical waveguide 8 and the Bragg grating 9. Further, it is preferable to provide a non-reflective layer on the incident surface side 8a and the output surface side 4c of the optical waveguide. The Bragg grating and the light source constitute an external resonator and stabilize the wavelength of the oscillating laser beam. This makes it possible to provide a stable laser light source with a changed optical path.

In this example, as shown in FIG. 1, the optical waveguide element 10 is fixed on the side surface 2 b of the mounting substrate 2, and the channel type optical waveguide 11 is formed in the optical waveguide element 10. The incident surface 10a of the optical waveguide element 10 faces the bottom surface of the optical path changing element 4, and the output surface 10b of the optical waveguide element 10 is provided on the opposite side.

As shown in FIGS. 3 and 4, the exit surface 4 c of the optical path changing element 4 is butt-jointed with the channel type optical waveguide 11 of the optical waveguide element 10, and a gap with a dimension G is provided therebetween. . A butt joint refers to a joint structure in which end faces of optical waveguides having different refractive index distributions are brought into contact with each other in the optical axis direction. In this example, there is no optical waveguide opening on the emission surface 4c, but the light reflected by the reflection surface 8b propagates and emits a thin layer for a short distance while maintaining the beam shape, so the shape of the light beam is For this reason, a butt joint is established.

In the present invention, as in the above-described embodiment, the light propagating in the channel type optical waveguide (ridge optical waveguide) defined by the ridge groove in the thin layer provided on the support substrate is converted into the thin layer end face. And is emitted from the bottom side of the thin layer. At this time, unlike the diffusion optical waveguide, the ridge-type channel optical waveguide formed in the thin layer can strengthen the confinement and there is no scattering on the surface of the optical waveguide. It is possible to prevent a decrease in the coupling efficiency due to scattering of. Furthermore, since the light emitted from the bottom surface of the optical path changing element can be coupled to a separate optical waveguide element by the butt joint method, high coupling efficiency can be realized with a small number of parts without requiring a lens. . Further, by using a birefringent material for the thin layer, the polarization of the light source can be maintained, and it can be coupled to the optical waveguide element while maintaining high polarization crosstalk.

In the example of FIG. 5, the Bragg grating 9 may be formed on the first main surface 6a side where the ridge groove of the thin layer 6 is provided, or may be formed on the flat second main surface 6b. The Bragg grating is preferably formed on the flat second main surface side (in this example, the side opposite to the support substrate 5). That is, by forming the ridge groove 7 and the Bragg grating 9 on the main surface on the opposite side of the thin layer, variation in the shapes of the Bragg grating and the ridge groove can be further reduced.

Also in the element 4A shown in FIG. 6, the thin layer 6 is provided on the support substrate 5. For example, a pair of ridge grooves 7 are formed on the second main surface 6 b side of the thin layer 6, and a ridge type optical waveguide 8 is formed between the ridge grooves 7. In this example, the lower buffer layer 21 is formed on the first main surface 6 a of the thin layer 6 on the support substrate side, and is bonded to the support substrate 5 via the adhesive layer 22. On the other hand, an upper buffer layer 20 is formed on the second main surface 6b of the thin layer 6 having the ridge groove. In this case, the upper buffer layer may function as an antireflection film for the emitted light, or an antireflection film may be formed on the upper buffer layer.

In the example of FIG. 6, the Bragg grating 9 may be formed on the second main surface 6b side where the ridge groove of the thin layer 6 is provided, or may be formed on the flat first main surface 6a. The Bragg grating is preferably formed on the flat first main surface side (the support substrate 5 side in this example). That is, by forming the ridge groove 7 and the Bragg grating 9 on the opposite surface of the thin layer, the shape variation of the Bragg grating and the ridge groove can be further reduced.

In the absence of the upper buffer layer 20, the air layer can directly contact the grating. As a result, the difference in refractive index can be increased without the presence of a grating groove, and the reflectance can be increased with a short grating length. In this case, it is preferable that the non-reflective film is formed only on the optical path portion of the emitted light.

Further, in the optical path changing element, it is preferable to form an antireflection film (AR coating) on the incident surface 8a of the optical waveguide. Further, it is preferable that an antireflective film (AR coating) is also formed on the exit surface 6b side. The buffer layer substantially functions as a clad for the optical waveguide, and may function as a non-reflective film for the emitted light. The non-reflective film for the emitted light may be formed by being formed on the buffer layer on the emission surface 6b side. The buffer layer is preferably 5 μm or less from the viewpoint that the spot size of the reflected light does not expand. From this viewpoint, the optical path may not have a buffer layer.

The mounting device 1A shown in FIGS. 7 to 10 is similar to the device shown in FIGS. 1 to 6, except that no Bragg grating is formed in the ridge type optical waveguide of the optical path changing element.

As shown in FIG. 7, the mounting substrate 2 has an upper surface 2a, a bottom surface 2d, and

side surfaces

2b and 2c. A light source 3 is fixed to the upper surface 2 a of the mounting substrate 2. For example, as shown in FIGS. 8 and 9, light is emitted as indicated by an arrow A from the active layer 3 a of the light source 3.

Further, the optical path changing element 4B is fixed to the upper surface 2a of the mounting substrate 2. In the optical path changing element, as shown in FIGS. 9 and 10, the support substrate 5 and the thin layer 6 are joined and integrated with each other. For example, a pair of ridge grooves 7 are formed in the thin layer, and a ridge-type optical waveguide 8 is formed between the ridge grooves 7.

In addition, the structure of the cross section of the optical path changing element may be as shown in FIG. 5 or as shown in FIG.

The incident surface 4a of the optical path changing element 4B is flat, and is substantially perpendicular to the top and bottom surfaces of the optical path changing element 4B. On the other hand, the exit surface 4b of the optical path changing element 4B is inclined at an angle θ with respect to the bottom surface. The light oscillated from the light source enters the incident surface 8a of the channel-type optical waveguide 8, propagates in the optical waveguide 8 as indicated by arrow B, and is then reflected by the reflecting surface 8b facing the exit surface of the optical path changing element. . Then, the light propagates through the thin layer 6 as indicated by an arrow C, and is emitted as indicated by an arrow C from the emission surface 4c on the bottom side.

Also in this example, for the reasons described above, it is possible to provide a stable laser light source with a changed optical path.

Further, in this example, as shown in FIG. 7, the optical waveguide device 10 is fixed on the side surface 2 b of the mounting substrate 2, and the channel type optical waveguide 1 is formed in the optical waveguide device 10. The incident surface 10a of the optical waveguide element 10 is opposed to the bottom surface of the optical path changing element 4B, and the output surface 10b of the optical waveguide element 10 is provided on the opposite side.

As shown in FIGS. 9 and 10, the exit surface 4c of the optical path changing element 4B is butt-jointed with the channel-type optical waveguide 11 of the optical waveguide element 10, and a gap with a dimension G is provided therebetween. .

The thickness of the thin layer is preferably 8 μm or less, more preferably 5 μm or less, from the viewpoint of the coupling efficiency of the optical waveguide element to the channel type optical waveguide. In addition, the thickness of the thin layer is preferably 0.5 μm or more because it reduces the propagation loss of the optical waveguide.

The optical crystal forming the thin layer preferably has a refractive index of 1.9 or more, and more preferably has a refractive index of 1.95 or more, from the viewpoint of tolerance of reflectance.

Preferable examples of the optical crystal forming the thin layer are gallium arsenide, lithium niobate single crystal, tantalum oxide, zinc oxide, and alumina oxide. Further, by making the optical crystal birefringent, the polarization plane of the laser light can be maintained.
Further, the thin layer can be formed by bonding by bonding, but can also be formed by sputtering, vapor deposition, or film formation by CVD on a support substrate.

In the thin layer, one or more metal elements selected from the group consisting of magnesium (Mg), zinc (Zn), scandium (Sc), and indium (In) are used to further improve the optical damage resistance of the optical waveguide. In this case, magnesium is particularly preferable. The crystal can contain a rare earth element as a doping component. As the rare earth element, Nd, Er, Tm, Ho, Dy, and Pr are particularly preferable.

It is not necessary to provide a reflective film on the reflective surface of the optical path changing element, but a reflective film may be provided.

Examples of such a reflective film include the following. That is, a metal film such as gold or aluminum is preferable. In order to improve the adhesion of these metals, the buffer layer may have a multilayer structure of metal films such as Ti, Pt, Ni, and Cr.

A ridge-type optical waveguide is obtained by physically processing and molding an optical crystal by, for example, machining or laser processing.

As the light source, a laser with a highly reliable GaAs-based or InP-based material is suitable. As an application of the structure of the present application, for example, when a green laser that is the second harmonic is oscillated using a nonlinear optical element, a GaAs laser that oscillates near a wavelength of 1064 nm is used. Since GaAs-based and InP-based lasers have high reliability, a light source such as a one-dimensionally arranged laser array can be realized. It may be a super luminescence diode or a semiconductor optical amplifier (SOA). In addition, the material and wavelength of the active layer can be selected as appropriate.

The Bragg grating can be formed by physical or chemical etching as follows.
As a specific example, a metal film such as Ni or Ti is formed on a high refractive index substrate, and windows are periodically formed by photolithography to form an etching mask. Thereafter, periodic grating grooves are formed by a dry etching apparatus such as reactive ion etching. Finally, it can be formed by removing the metal mask.

The material of the adhesive layer may be an inorganic adhesive, an organic adhesive, or a combination of an inorganic adhesive and an organic adhesive.

The specific material of the support substrate is not particularly limited, and examples thereof include glass such as lithium niobate, lithium tantalate, and quartz glass, quartz, and Si.

The reflectance of the non-reflective layer must be less than or equal to the grating reflectivity. As the film material to be formed on the non-reflective layer, a film laminated with an oxide such as silicon dioxide or tantalum pentoxide, or metal is also used. Is possible.

Further, each end face of the light source, the optical path changing element, and the optical waveguide element may be cut obliquely in order to suppress end face reflection. Further, the thin layer and the support substrate are bonded and fixed in the above example, but may be directly bonded.

In the ridge-type optical waveguide in the optical path changing element, the angle θ with respect to the bottom surface of the reflecting surface is usually 45 °, so that the light is bent at a right angle. However, it is not limited to this. θ can be selected from 42 to 48 °, for example.

Also, the processing method for providing an angle to the reflection surface of the ridge-type optical waveguide may be polishing or processing by dicing or a micro grinder.

The configuration of the optical waveguide element is not particularly limited as long as the channel type optical waveguide is formed. The optical waveguide element may be a monolithic substrate, for example, but preferably includes a support substrate and a thin layer made of an optical crystal bonded on the support substrate, and a channel-type optical waveguide is included in the thin layer. Is formed. The channel type optical waveguide is preferably a ridge type optical waveguide, but may be a diffusion type optical waveguide.

The size G of the gap between the exit surface of the optical path changing element and the entrance surface of the channel type optical waveguide of the optical waveguide element is preferably 1 μm or more, and preferably 9 μm or less, depending on the design.

(Example A)
The devices shown in FIGS. 1 to 4 and FIG. 5 were produced.
Specifically, in order to form a y-axis propagating optical waveguide in a z-plate MgO-doped lithium niobate crystal, an excimer laser was used to form a groove with a width Wm of 3 μm and a Tr of 1 μm to form an optical waveguide. Further, an SiO2 film was formed to a thickness of 0.5 [mu] m by a sputtering apparatus, and the optical waveguide forming surface was bonded using a black LN substrate as a support substrate.

Next, the black LN substrate side was attached to a polishing surface plate, and the back surface of the LN substrate on which the optical waveguide was formed was precisely polished to a thickness Ts of 2 μm. Then, it was removed from the surface plate, and an AR coating was formed on the entire polished surface.

Then, it was cut into a bar shape with a dicing machine, one end face was optically polished vertically, the opposite end face was optically polished at 45 °, and an AR coating of 0.1% or less was formed on the vertical polished end face. Finally, the chip was cut so that the element size was 1 mm wide and 3 mm long.

In order to evaluate the characteristics of the optical path reflection element, the reflectance was 100% for both p-polarized light (TM wave) and s-polarized light (TE wave) when measured with a semiconductor laser having a wavelength of 800 nm. Moreover, the polarization crosstalk was 20 dB or more, and no deterioration due to reflection was observed.

In addition, in FIG. 11, the simulation result of angle (theta) of a reflective surface and an output surface and a reflectance is shown.

Next, using this optical waveguide reflecting element, a module shown in FIGS. 1 to 4 was manufactured by optically aligning an 800 nm wavelength semiconductor laser and a spot size 3 × 2 μm optical waveguide element. An optical waveguide element was disposed directly under the mirror, and the gap G with the reflection waveguide was 3 μm. As a result of measuring the coupling efficiency after mounting, it was about 80%.

When a light source and an optical waveguide element similar to those described above are directly butt-joined without going through an optical path conversion element, the coupling efficiency is about 80%. Therefore, it was confirmed that the present invention can be combined with an excess loss of 5% or less.

In the above example, the coupling efficiency was measured by changing the gap G with the optical waveguide directly under the mirror. Table 1 shows the loss fluctuation when the temperature is changed from -20 ° C to 70 ° C after mounting.

As can be seen from the table, according to the present invention, a butt joint can be achieved with high coupling efficiency over a wide gap range.

(Example B)
In Example A, as shown in FIG. 6, the flat main surface 6a side without a thin ridge groove was used as the bonding surface. Other than this, an optical path changing element and an optical mounting device were produced in the same manner as in Example A, and evaluated in the same manner as in Example A. The results are shown in Table 2.

(Comparative example)
In Example A, a ridge waveguide was not formed. Instead, a channel type optical waveguide was formed by a titanium diffusion method. The channel type optical waveguide side was used as the bonding surface. Other than this, an optical path changing element and an optical mounting device were produced in the same manner as in Example A, and evaluated in the same manner as in Example A. The gap G of the butt joint was 3 μm. As a result, the coupling efficiency was 50%, and the temperature fluctuation was 1 dB. Since the diffusion waveguide has a small difference in refractive index, the light confinement effect is weak, and it is difficult to reduce the spot size.

Claims

An optical path changing element that changes the propagation direction of light,
Support substrate,
A thin layer made of an optical crystal and formed on the support substrate, the first layer having a first main surface on the support substrate side and a second main surface on the opposite side of the support substrate; And a ridge type optical waveguide defined by at least a pair of ridge grooves formed in the thin layer, wherein the ridge has an incident surface for the light and a reflective surface for reflecting the light propagating through the ridge type optical waveguide. Type optical waveguide,
The light path changing element, wherein the light reflected by the reflecting surface is emitted from the second main surface side through the thin layer.
The element according to claim 1, wherein the refractive index of the optical crystal is 1.9 or more.
3. The element according to claim 1, wherein the optical crystal is birefringent.
The element according to any one of claims 1 to 3, wherein a Bragg grating is formed in the ridge-type optical waveguide, and the Bragg grating and the light source constitute an external resonator.
The element according to any one of claims 1 to 4, wherein the ridge groove is provided on the first main surface side of the thin layer.
A connection structure between the optical path changing element according to any one of claims 1 to 5 and an optical waveguide element having a channel-type optical waveguide,
The connection structure according to claim 1, wherein the output surface of the optical path changing element and the channel type optical waveguide are butt-jointed.
A light source device comprising: a light source that oscillates the light; and the optical path changing element according to any one of claims 1 to 5.
A mounting substrate having a top surface, a bottom surface and a side surface between the top surface and the bottom surface;
The optical path changing element according to any one of claims 1 to 5, which is fixed to the upper surface of the mounting substrate.
It is fixed to the upper surface of the mounting substrate, a light source that oscillates the light, and is fixed to the side surface of the mounting substrate, and includes an optical waveguide element having a channel type optical waveguide,
An optical mounting device, wherein an exit surface of the optical path changing element and the channel type optical waveguide are butt-jointed.