JPH0822499B2 - Method for polishing end face of single crystal substrate for optical element - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a method for polishing an end face of a single crystal substrate for an optical element.

2. Description of the Related Art Generally, in a bar code reader, a laser printer, or the like, light that enters from one end surface of a single crystal substrate having an optical waveguide on one surface and passes through the substrate is deflected based on an electro-optical effect or the like. An optical element for deflecting light of the type that is emitted from the end face is used. In the single crystal substrate used for such an optical element, both end faces on which light enters and exits are provided with an optical flat surface in an accurate and smooth state so as not to affect the traveling direction of the light when entering and exiting. In order to do so, so-called optical polishing is performed.

However, since such a single crystal substrate is made of lithium niobate (LiNbO ₃ ) single crystal or the like and is a relatively fragile material, the edge of the end face, that is, the corner of the substrate, etc. is formed by performing the above-mentioned optical polishing. The inconvenience of chipping occurred.

On the other hand, by superposing one surface of the single crystal substrate to be polished on the side where the optical waveguide is provided and one surface of the auxiliary substrate and fastening and fixing them, both end surfaces of each substrate are pressed simultaneously against the polishing surface. Therefore, a method of polishing while preventing at least one edge portion of both end surfaces, that is, the edge portion on the side where the optical waveguide is formed, is considered.

Problems to be Solved by the Invention However, such a method is to perform polishing simultaneously by superposing and tightening a single crystal substrate and an auxiliary substrate. The side that is displaced and faces the auxiliary board,
That is, the edge portion of the substrate on the side where the optical waveguide is formed may be chipped. In addition, after polishing, when handling such as releasing the fastening to both substrates, there is a risk that the edge portion of the single crystal substrate may come into contact with the fastening jig and be chipped.

On the other hand, it is also conceivable to perform optical polishing in a state where both the single crystal substrate and the auxiliary substrate are bonded with an adhesive, and then remove the adhesive to separate the two substrates. However, with such a method, it is extremely difficult to elute the adhesive once cured between both substrates, and even if it is possible, it requires a special expensive resin and a long elution work time. However, practical application was difficult. Also, as in the case described above, when handling such as releasing the cured adhesive between both substrates after polishing, the edge portion of the single crystal substrate may come into contact with the fastening jig and may be chipped. There was a risk of it.

Means for Solving the Problems The present invention has been made against the background of the above circumstances, and the gist thereof is to provide an optical device in which an end face of a single crystal substrate for an optical element having an optical waveguide on one face is optically formed. A method of polishing to a flat surface, comprising: (a) an auxiliary substrate having substantially the same polishing characteristics as that of the substrate and a refractive index lower than that of the optical waveguide on one surface of the substrate and having a refractive index lower than that of the optical waveguide. To include an adhering step of adhering using an adhesive having a ratio, and (b) a polishing step of simultaneously polishing both end surfaces of the substrate and the auxiliary substrate by pressing the end surfaces of the substrate and the auxiliary substrate against a polishing surface. is there.

According to the method and the effect of the invention, since the substrate having the optical waveguide and the auxiliary substrate are bonded to each other on one surface, the substrate on the side having the optical waveguide does not shift from each other during polishing. The effect that no chipping of the edge is generated can be obtained, and since the auxiliary substrate and the substrate have substantially the same polishing property, the polishing operation becomes easy.

Further, since the auxiliary substrate whose refractive index is lower than that of the optical waveguide of the single crystal substrate is similarly bonded to one surface of the optical waveguide side of the single crystal substrate using an adhesive whose refractive index is lower than that of the optical waveguide of the substrate, The light propagating in the optical waveguide does not leak to the adhesive or the auxiliary substrate side, and the single crystal substrate can be used as an optical element without peeling and removing the auxiliary substrate. Therefore, according to the method of the present invention, since it is not necessary to peel and remove the auxiliary substrate, it is extremely difficult to elute the adhesive once cured between both substrates, and a special expensive resin or a long time The adhesive elution work, which requires a time for elution work, is not required, and at the same time when the adhesive that has hardened between the two substrates is released after polishing, the edge of the single crystal substrate is a jig for fastening. It is possible to suitably eliminate the possibility that it may come into contact with and be chipped.

Embodiment Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a substrate 10 used for an optical element for deflecting light. A substrate 10 made of lithium niobate (LiNbO ₃ ) single crystal has a thickness of about 0.5 mm, and a two-dimensional optical waveguide 12 is provided on one surface thereof. The two-dimensional optical waveguide 12 has a refractive index of, for example, about 2.2 to 2.22, and the refractive index thereof is made larger than that of the other portions of the substrate 10 so that the light is preferably guided by the characteristic of confining the light in the thickness direction. From the surface of the substrate 10
Diffusion of (titanium) forms a relatively thin layer of about several μm. The substrate 10 and the two-dimensional optical waveguide 12 only have different refractive indexes, and the refractive indexes thereof continuously change. Therefore, the boundaries between them are shown by broken lines.

In order to perform so-called optical polishing on both end surfaces of the substrate 10, that is, the light incident surface and the light emitting surface, one surface of the substrate 10 on which the two-dimensional optical waveguide 12 is provided, as shown in FIG. A pair of auxiliary substrates 16 are bonded using an adhesive agent 14 along the edges of both end surfaces facing each other above. The adhesive 14 is made of an ultraviolet curable resin such as trichlorpropane triacrylate or pentaerythritol triacrylate, and has a lower refractive index than the two-dimensional optical waveguide 12 and little light attenuation after curing. Is. The auxiliary substrate 16 is made of the same material as the substrate 10 and has substantially the same abradability as that of the substrate 10, and has a thickness of about 0.5 mm made of, for example, LiNbO ₃ single crystal.
Since one surface thereof is a mirror surface and no optical waveguide is formed, it has a lower refractive index than the two-dimensional optical waveguide 12. Then, after both end surfaces of the substrate 10 to which the auxiliary substrate 16 is adhered and one end surface of the pair of auxiliary substrates 16 are subjected to chamfering and cutting processing in order to make them smooth with respect to each other, both end surfaces thereof are used for optical polishing. The polishing surface 18 of a lapping machine or the like is pressed to perform polishing.

At this time, the LiNbO ₃ single crystal that is the material of the substrate 10 has a relatively fragile property with respect to polishing, but the two edges of the substrate 10 on the one surface side where the two-dimensional optical waveguide 12 is provided are adhesive respectively. Since it is protected by the auxiliary substrate 16 and the auxiliary substrate 16, the edge of the substrate 10 on the side where the two-dimensional optical waveguide 12 is formed will not be chipped off even if the above optical polishing is performed.

When the substrate 10 that has been optically polished as described above is used for a deflecting optical element, a semiconductor laser 20 is attached to one end surface of the substrate 10 as shown in FIG.
Light is incident on the two-dimensional optical waveguide 12 in the substrate 10 through one end surface of 10. At this time, the adhesive 14 and the auxiliary substrate 16 remain adhered to one surface of the substrate 10 on the side where the two-dimensional optical waveguide 12 is formed, but the refractive index of the adhesive 14 is, for example, about 1.5. Since the refractive index is lower than that of the two-dimensional optical waveguide 12, incident light passing through the two-dimensional optical waveguide 12 hardly leaks toward the adhesive 14. Then, when a control voltage is applied by a plurality of electrodes (not shown) in the process of the incident light being guided through the two-dimensional optical waveguide 12, an electric field formed in the substrate 10 according to the control voltage is formed based on the electro-optic effect. The incident light is deflected at a desired angle due to the refractive index distribution. The light deflected in the substrate 10 is emitted from the other end surface of the substrate 10 which has been optically polished as described above.

As described above, by applying the end face polishing method of the present embodiment, the pair of auxiliary substrates 16 are two-dimensional optical waveguides with the adhesive 14 when the incident surface and the emission surface of the substrate 10 used for the optical element are optically polished. Since it is adhered to one surface of the side on which 12 is provided along both edges, polishing is performed by overlapping and tightening one surface of the substrate on the side on which the optical waveguide is provided and one surface of the auxiliary substrate. Compared with the method described above, it is possible to obtain an effect of preventing the edge of the substrate 10 from being chipped due to the displacement of the auxiliary substrate 16 during polishing or the like. Further, since the auxiliary substrate 16 and the substrate 10 are made of substantially the same material, the same grindability can be obtained, and the polishing work becomes easy.

Further, the adhesive 14 has a refractive index lower than that of the two-dimensional optical waveguide 12, and even if light is incident on the substrate 10 while the adhesive 14 is still attached, the light will be adhesive 14 Since it hardly refracts toward and affects the traveling direction of light, after the optical polishing, the adhesive 14 and the auxiliary substrate 16 are formed on the substrate.
No need to remove from 10. Therefore, by applying the method of the present embodiment, compared with the conventional method that was difficult to handle when removing the fastening jig or the like to release the fastening to the substrate and the auxiliary substrate after polishing, The edge of the substrate 10 is protected by the adhesive 14 and the substrate 10 after polishing
Is easy to handle. In addition, compared to the conventional method of peeling the auxiliary substrate adhered to the single crystal substrate after polishing, it is extremely difficult to elute the adhesive once hardened, and a special expensive resin or long elution work is required. The time-consuming adhesive elution work is not required, and the edge of the single crystal substrate comes into contact with the fastening jig when handling, such as releasing the cured adhesive between both substrates after polishing. It is possible to preferably eliminate the possibility of chipping.

In the above embodiment, the adhesive 14 is made of an ultraviolet curable resin such as trichloropropane triacrylate and pentaerythritol triacrylate, but other types of adhesives may be used. In short, the adhesive
It suffices that 14 has a refractive index lower than that in the two-dimensional optical waveguide 12 and has little light attenuation.

In addition, as shown in FIG. 4, the two-dimensional optical waveguide of the substrate 10 is
12 above, that is, between the two-dimensional optical waveguide 12 and the adhesive 14,
A Huffer layer 22 such as a SiO ₂ layer may be provided. By doing so, the influence of the refractive index of the adhesive on the guided light can be eliminated, and the selection range of the adhesive can be expanded.

Further, as the auxiliary substrate 16, not only the same material as the substrate 10 but also substrates made of other materials can be adopted as the auxiliary substrate as long as the abradability is substantially the same.

The above description is merely one embodiment of the present invention, and the present invention can be variously modified without departing from the spirit thereof.

[Brief description of drawings]

FIG. 1 is a perspective view of a substrate for an optical element to which the method of one embodiment of the present invention is applied. FIG. 2 is a partially enlarged view of a state where an auxiliary substrate is bonded to the substrate of FIG. 1 as seen from a side surface. FIG. 3 is a side view showing a state in which the substrate after polishing is used for an optical element. FIG. 4 is a side view showing a state in which an auxiliary substrate is bonded to a substrate in another embodiment of the present invention. 10: Substrate 12: Two-dimensional optical waveguide (optical waveguide) 16: Auxiliary substrate 18: Polished surface

Claims (1)

[Claims] 1. A method of polishing an end surface of a single crystal substrate for an optical element having an optical waveguide on one surface into an optical plane, wherein one surface of the substrate has substantially the same polishing characteristics as the substrate and the optical property. A bonding step of bonding an auxiliary substrate having a refractive index lower than that of the waveguide with an adhesive having a refractive index lower than that of the optical waveguide, and an end surface of the substrate and an end surface of the auxiliary substrate to a polishing surface. And a polishing step of polishing both end surfaces at the same time by pressing, thereby polishing the end surface of the single crystal substrate for an optical element.