JP2579906B2 - Optical coupling device - Google Patents

Description

The present invention relates to the fields of optical fiber communication, optical applied measurement and control, and optical information processing.

Prior Art FIGS. 4 and 5 are a side view and a front view showing a conventional technique. In FIGS. 4 and 5, between the bottom surface of the prism 3 pressed (pressed) onto the optical waveguide 2 formed on the substrate 1 and the substrate 1, an epoxy-based adhesive or an ultraviolet curing resin is used. Filling agent 11
After adjusting the air gap so as to obtain the highest optical coupling efficiency, curing was performed, and the prism 3 was fixed. Also,
An adhesive 12 was applied to the side surface of the prism 3 for reinforcement.

Problems to be Solved by the Invention In the conventional technology, the gap between the prism and the optical waveguide changes due to the contraction and expansion when the adhesive 11 is cured, so that the correction is impossible and the optical coupling efficiency is reduced. Had become. Further, since the optical coupling efficiency is fluctuated with respect to external force, vibration, and temperature due to fixation with an adhesive, there has been a problem.

Means for Solving the Problems In order to solve the above problems, an optical coupling device of the present invention performs optical coupling between an optical waveguide provided on a substrate and the outside by a prism pressed against the optical waveguide. In the optical coupling device, the side surface of the prism is fixed on a substrate via a fixing base. More specifically, as a fixing means, polyester resin, or soldering, or characterized by using laser welding, the gap between the prism bottom and the optical waveguide, as it is, or a transparent resin, or transparent It is characterized by being filled with grease and using a material having a linear expansion coefficient substantially equal to that of the prism as a material of the fixing base.

Action Since the side surface of the prism and the substrate are fixed via the fixing plate, the fixing of the prism is firm, and the prism is stable against external force and vibration. Some polyester-based adhesives have a shrinkage rate of 0.1 to 0.2% upon curing, and a displacement of 1 μm or less can be easily obtained at the time of fixing, and a decrease in bonding efficiency is slight and causes no problem. In addition, quick fixing can be realized by soldering,
There is an effect that readjustment is possible by increasing the temperature. In addition, fixing by laser welding can achieve fixing in less than a second, and extremely quick and firm fixing is possible. Further, by filling the gap between the prism bottom surface and the optical waveguide with a transparent resin, it is possible to prevent dust from entering from outside into the portion where the optical coupling of the gap is performed, to reduce the light scattering loss, Serves as a protective layer over time. Filling the gap with transparent grease has the effect of preventing intrusion of dust and reducing light scattering loss without causing stress in the gap of the prism. Further, by using a material in which the linear expansion coefficient of the fixing base is substantially equal to that of the prism, the gap between the prism and the optical waveguide hardly changes even with a temperature change, and stable optical coupling can be realized.

Embodiment FIGS. 1 and 2 are a side view and a front view, respectively, showing a first embodiment of the present invention. Here, for the sake of explanation, an example in which sapphire is used for the substrate 1 and a PLZT-based thin film is used for the material of the optical waveguide 2 will be described. The prism 3 has a refractive index of 3.3
The GaP right-angle prism 3 was used. The edge of the prism 3 is pressed against the optical waveguide 2, the gap 8 formed between the bottom surface of the prism 3 and the optical waveguide 2 is adjusted, and the input light 6 is collected.
The light was guided into the optical waveguide 2 as the guided light 7 when the light was incident on the prism 3 at a waveguide angle θ 角 40.7 degrees in the vicinity of the edge. The gap 8 and the beam incident position were adjusted. At the time of the highest coupling efficiency, the fixed base 4 was fixed to the substrate 1 and then fixed to the prism 3. The size of the gap 8 can be known by measuring the interval between stripes due to interference between the bottom surface of the prism 3 and the optical waveguide 2. Soda glass was used as the material of the fixing base 4. For fixing, both the fixing portions 5a and 5b were completely cured in about 15 minutes using a polyester-based resin (Technovit 4000 (registered trademark), manufactured by Kulzer Co., Ltd., with a shrinkage of 0.1 to 0.2% during curing). Almost no change was observed in the voids 8 during curing.
This is because the resin shrinkage rate at the time of curing is extremely small, 0.2% or less, and the fixing base 4 is fixed to the prism 3 from the side, and the fixing is performed simultaneously from both side surfaces. It is considered that the inclination and the ups and downs of the prism 3 have disappeared. The direction of the coordinate axis is shown below in the figure.

FIG. 3 is a side view showing a second embodiment of the present invention.
In FIG. 3, the side surface of the prism 9 is fixed by the fixed base 4, and the bottom surface 5 b of the fixed base 4 is fixed on the surface of the substrate 1. The fixing between the prism 9 and the fixing base 4 and the fixing between the bottom surface 5b of the fixing base 4 and the surface of the substrate 1 are performed as in the above-described first embodiment of the present invention.

The present embodiment is different from the first embodiment in that the shape of the bottom surface of the prism 9 (on the side in contact with the surface of the substrate 1) is not a plane, but as shown in FIG. It is a point that is configured. These two planes respectively make a slight gap angle ε ₁ and a small gap angle ε ₂ with the surface of the substrate 1, and form a dihedral angle θ (θ = 180 ° −ε ₁゜ −ε ₂₎ sandwiching the ridge line 10.
゜) is obtuse (90 ° <θ <180 °). The experiment was conducted using an obtuse angle θ of 175 °.

The ridge line 10 on the bottom surface of the prism was pressed against the ultra-thin optical waveguide 2 formed on the surface of the substrate 1, and the incident light 6 was squeezed and applied to this portion.

In the case of the prism 9, the optical coupling efficiency is adjusted by adjusting the distance between the ridge line 10 and the optical waveguide 2 (actually, it is almost constant and a value close to zero), and the gap angle ε ₁ on the waveguide light 7 side (accordingly, By adjusting the gap angle ε ₂ ) on the opposite side, higher efficiency can be obtained than in the case of the prism 3 of the first embodiment.

Also in the case of the prism 9, as in the first embodiment, before and after the fixing of the prism 9 and the fixing table 4 and between the fixing table 4 and the substrate 1, the gap between the ridge 10 and the optical waveguide 2 and the gap angle ε _1. Little change was seen. Therefore, there was almost no change in optical coupling efficiency.

Further, as another fixing method, a method by soldering and a method by laser welding were also tried.

In the soldering method, a copper block was used as a fixing base, In was vapor-deposited on the fixing base and the fixing surface of the GaP prism, and the prism was alloyed by raising the temperature in advance. Then, as shown in FIG. 1, after the prism position is adjusted, the fixing portion 5b of the fixing base 4 and the substrate 1 is fixed with a polyester resin, and then the fixing portion 5a of the prism 3 and the fixing base 4 is fixed.
Was heated, and the In solder was melted and soldered.
Almost no misalignment due to soldering was observed.

In addition, a thin metal film with strong adhesion, such as chrome or gold, is formed on the prism, fixing base, substrate, etc. in advance by vacuum evaporation or sputter evaporation, and then solder plating and soldering is performed. Therefore, the number of types of materials to be joined can be increased.

In laser welding, using glass or metal for the fixing base material, after adjusting the prism position, placing the fixing base in contact with the substrate and the prism, focusing the laser beam on the fixing part 5b with the substrate and welding, The laser beam was focused on the fixing part 5a of the prism and the fixing base for welding. Q switch YAG for light source
A laser was used. There was almost no change in the prism gap due to fixation, and the change in coupling efficiency was less than 0.5 dB.
In the case of laser welding, unlike the case of soldering, there is no undoing, but the firmest fixation is possible, and the most stable connection to external force and vibration is obtained.

Further, dust from the outside may enter the gap between the bottom surface of the prism and the optical waveguide, which induces scattering of the extruded guided light and lowers the optical coupling efficiency. In order to prevent this, the space was previously filled with a transparent epoxy resin or an ultraviolet curable resin and fixed, and then the resin was cured. The change in prism gap due to contraction and expansion due to curing is
Since the prism was fixed in advance by the fixing base, there was almost no change, and the scattering of the optical waveguide was reduced, and the loss was slightly reduced. Also, the change in the refractive index due to curing was slight, and the change in the light coupling efficiency was suppressed to 0.5 dB or less. In addition, when a similar experiment was conducted with transparent grease filled in the voids instead of resin, stable binding was obtained, and the change in binding efficiency due to immobilization was almost as small as when not filled with grease. there were.

Further, an experiment was conducted using a material having the same linear expansion coefficient as that of the prism as a material of the fixing table. Specifically, when a fixing base was formed and fixed using GaP of the same material as the prism, it was confirmed that an optical coupling efficiency characteristic extremely stable with respect to a temperature change was obtained.

In the description of this embodiment, the input unit has been described. However, it is obvious that the same effect can be obtained when the direction of the optical path is reversed, that is, the output unit.

Although described PLZT-based thin-film optical waveguide to the optical waveguide, which of course other optical waveguide, for example, Ti diffusion, or LiNbO ₃ waveguide proton exchange, YIG thin film optical waveguide, Ya optical waveguide such as a glass optical waveguide It is obvious that a similar effect can be obtained even with prism materials other than GaP.

In addition, although glass, copper, GaP, and the like have been described as materials for the fixing base, it is obvious that similar effects can be obtained with other materials. It is obvious that the solder material and the material of the metal thin film for soldering are not limited to those described in the embodiments of the present invention as long as the effects can be obtained.

Effect of the Invention According to the configuration of the present invention, the direction of the stress generated when fixing the fixed portion by fixing the side surface of the substrate and the prism via the fixing base is changed to a direction substantially orthogonal to the optical coupling, It is possible to prevent a decrease in optical coupling efficiency due to fixation. Therefore, it is possible to easily increase the optical coupling efficiency, which has been greatly deteriorated in the past when fixing the prism. In addition, since the rigidity of the fixed base is strong, stable optical coupling can be obtained even with external force and vibration. Furthermore, by using a material having a similar linear expansion coefficient to that of the prism material for the fixing base, a change in the prism gap due to a temperature change is scarcely observed, so that an extremely stable temperature characteristic of optical coupling can be obtained.

[Brief description of the drawings]

1 and 2 are a side view and a front view showing a first embodiment of the optical coupling device of the present invention, FIG. 3 is a side view showing a second embodiment of the optical coupling device, and FIGS. FIG. 5 is a side view and a front view showing a technical example of the conventional device. 1 ... substrate, 2 ... optical waveguide, 3,9 ... prism, 4 ...
... Fixing base, 5a, 5b ... Fixed part, 6 ... Incident light, 7 ... Guided light, 8 ... Void, 10 ... Twill wire

Claims (8)

(57) [Claims] 1. An optical coupling device in which optical coupling between an optical waveguide provided on a substrate and the outside is performed by a prism pressed against the optical waveguide, wherein a side surface of the prism is placed on the substrate via a fixing base. An optical coupling device which is fixed. 2. The optical coupling device according to claim 1, wherein an adhesive made of a polyester resin is used for fixing the fixing base and the side surfaces of the prism and the fixing base and the substrate. 3. The optical coupling device according to claim 1, wherein soldering is used for fixing the fixing base and the side surfaces of the prism and the fixing base and the substrate. 4. The optical coupling device according to claim 3, wherein a metal thin film is interposed when the fixing base and the side surfaces of the prism and the fixing base and the substrate are fixed by soldering, respectively. 5. The optical coupling device according to claim 1, wherein each of the fixing base and the side surface of the prism and the fixing base and the substrate are fixed by laser welding. 6. The optical coupling device according to claim 1, wherein a gap between the bottom surface of the prism and the substrate is filled with a transparent resin. 7. The optical coupling device according to claim 1, wherein a gap between the bottom surface of the prism and the substrate is filled with transparent grease. 8. The optical coupling device according to claim 1, wherein a material having a linear expansion coefficient substantially equal to that of the prism is used as a material of the fixing base.