JP7018082B2 - Drawing device and drawing method - Google Patents

Description

The present disclosure relates to a drawing apparatus and a drawing method for drawing an optical waveguide on a glass substrate by irradiating light.

With the expansion of demand for communication networks, the demand for larger capacity of optical communication networks is becoming stronger along with the demand for smaller optical components and lower power consumption. In order to solve such demands, multiplexing and densification of optical transmission are being promoted, and the key device thereof is an optical waveguide device equipped with a functional circuit.

Conventionally, the optical waveguide and the functional circuit of the optical waveguide device have been formed by etching the core layer laminated in the form of an underclad layer on the Si substrate by a flame hydrolysis method or the like, but it is limited to two dimensions. Attempts have also been made to three-dimensionally form the optical waveguides and optical circuits that have been used (see, for example, Patent Document 1). As shown in FIG. 4, this is a technique for continuously changing the refractive index inside the glass material by condensing and irradiating the laser beam to form a waveguide.

Japanese Unexamined Patent Publication No. 09-31237

Variable beam splitter "https://bit.ly/2OaXze2", January 31, 2020 search

However, since Patent Document 1 draws an optical waveguide using one laser beam, only one optical waveguide can be drawn one by one, and it is not suitable for forming an optical circuit having a large number of channels. That is, this technique has the first problem that the drawing time increases according to the number of optical waveguides to be formed and the drawing efficiency is poor.

Further, the technique of Patent Document 1 can form an optical waveguide in a layered manner on a glass substrate. However, since the optical waveguide is drawn using one laser beam, when the optical waveguide is drawn on a plurality of layers, the optical waveguide on the upper layer may be affected when the optical waveguide on the lower layer is drawn. FIG. 5 is a Mach-Zehnder interferometer (MZI) formed by drawing an optical waveguide on a glass substrate with a laser beam L. An optical waveguide Gu was previously formed on the upper layer of the MZI on the glass substrate. When the optical waveguide Gl is formed in the lower layer, the refractive index of the optical waveguide Gu (core waveguide) is different from that of the surrounding clad layer. The light-collecting position of the light is shifted, and the optical waveguide Gl is shifted. In MZI, the difference between the lengths of the two waveguides is important, and when the optical waveguide shifts as shown in the partial T of FIG. 5, the waveguide length differs from the design value, and interference does not occur at a desired wavelength.
As described above, Patent Document 1 has a second problem that the optical waveguide in the upper layer may be affected when the optical waveguide is formed in a layer on the glass substrate.

Therefore, in order to solve the above problems, the present invention provides a drawing device and a drawing method that can improve the drawing efficiency of the optical waveguide and are not easily affected by the optical waveguide in the upper layer even when the optical waveguide is formed in layers. The purpose.

In order to achieve the above object, the drawing apparatus according to the present invention is to branch a high-intensity laser beam for drawing into a plurality of paths and irradiate the glass substrate.

Specifically, the drawing apparatus according to the present invention is
A beam splitter that splits the laser beam from a short pulse laser into multiple pieces,
A lens that concentrates the branched laser beam on a predetermined area inside the glass substrate, and
A stage that moves the glass substrate with a desired motion,
The optical waveguide is drawn on the locus of the predetermined region due to the movement of the stage.
Here, the first drawing apparatus according to the present invention is characterized in that the lens collects a plurality of branched laser beams into each predetermined region.

Further, the drawing method according to the present invention is a drawing method for drawing an optical waveguide on a glass substrate.
Dividing the laser beam from a short pulse laser into multiple parts,
Focusing the branched laser beam on a predetermined area inside the glass substrate,
It is characterized by moving the glass substrate with a desired motion and forming the optical waveguide in a locus of the predetermined region.
Here, the drawing method is characterized in that a plurality of branched laser beams are focused on each predetermined region.

If the laser beam is branched into a plurality of paths (the branched laser beam is referred to as "branched laser beam") and the glass substrate is irradiated with each branched laser beam, a plurality of optical waveguides can be drawn at the same time. Therefore, the drawing time is constant regardless of the number of optical waveguides formed. Therefore, the drawing apparatus and drawing method according to the present invention can improve the drawing efficiency and solve the first problem.
Therefore, the present invention can provide a drawing apparatus and a drawing method capable of improving the drawing efficiency of the optical waveguide.

Further, the beam splitter of the drawing apparatus according to the present invention is characterized in that the branching ratio of the laser beam is changed according to the motion of the stage.
The drawing apparatus and drawing method according to the present invention can have the characteristics of a plurality of optical waveguides for drawing at the same time.

On the other hand, the second drawing apparatus according to the present invention is characterized in that the lens collects a plurality of branched laser beams into one predetermined region.

Since one optical waveguide is formed by a plurality of branched laser beams, a desired optical waveguide can be drawn by another branched laser beam even if one of the branched laser beams shifts the condensing position due to the upper layer optical waveguide. Therefore, the drawing apparatus and the drawing method according to the present invention are less likely to be affected by the optical waveguide in the upper layer when the optical waveguide is formed in a layer on the glass substrate, and can solve the second problem.
Therefore, the present invention can provide a drawing apparatus and a drawing method that are not easily affected by the upper layer optical waveguide even when the optical waveguide is formed in layers.

Further, it is preferable that the lens of the drawing apparatus according to the present invention is located at a position where the laser beam is irradiated so as not to face each other. Here, the opposite means a perpendicular line drawn from the center point of the condensing region to the surface of the glass substrate on the surface of the glass substrate on the lens side, where the incident points of all the branched laser beams are in the same straight line. The intersection of light and the surface is on the straight line. It is possible to prevent a plurality of branched laser beams from being affected by the upper optical waveguide at the same time.

The above inventions can be combined as much as possible.

INDUSTRIAL APPLICABILITY The present invention can improve the drawing efficiency of an optical waveguide, and can provide a drawing device and a drawing method that are not easily affected by the upper layer optical waveguide even when the optical waveguide is formed in layers.

It is a figure explaining the drawing apparatus which concerns on this invention. It is a figure explaining the drawing apparatus which concerns on this invention. It is a figure explaining the light-collecting area of the drawing apparatus which concerns on this invention. It is a figure explaining the related drawing apparatus. It is a figure explaining the problem of the drawing apparatus which concerns on this invention. It is a figure explaining the problem of the drawing apparatus which concerns on this invention. It is a figure explaining the light-collecting area of the drawing apparatus which concerns on this invention. It is a figure explaining the problem of the drawing apparatus which concerns on this invention.

An embodiment of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In addition, the components having the same reference numerals in the present specification and the drawings shall indicate the same components.

(Embodiment 1)
FIG. 1 is a diagram illustrating a drawing apparatus 301 of the present embodiment. The drawing device 301 is
A beam splitter 12 that splits the laser beam Lm from the short pulse laser 51 into a plurality of pieces, and
A lens 13 that concentrates the branched laser beam (branched laser beam Ls) on a predetermined region inside the glass substrate 50, and
A stage 11 that moves the glass substrate 50 with a desired motion, and
Equipped with
It is characterized in that an optical waveguide is drawn on a locus of the predetermined region due to the movement of the stage 11.
In the drawing device 301, the lens 13 concentrates the branched laser beam Ls on each predetermined region (Aa, Ab, Ac, Ad).

The drawing device 301 is an example of a device capable of drawing four optical waveguides at the same time. The drawing apparatus according to the present invention does not limit the number of optical waveguides that can be drawn simultaneously to four.

The short pulse laser light source 51 includes a short pulse laser and a power source for driving the short pulse laser. As the short pulse laser, for example, a titanium sapphire laser can be used. It is necessary to optimize the laser irradiation conditions in advance, and the optimization parameters include wavelength, average intensity, pulse width, repetition frequency, substrate moving speed, and substrate material. In this embodiment, the center wavelength is set to 800 nm, the repetition frequency is set to 2 MHz, the pulse width is set to 140 fs, and the average intensity is set to 120 mW. The moving speed of the stage 11 is set to 500 μm / s.

The glass substrate 50 may be a material other than glass as long as it is a material through which laser light is transmitted. For example, optical glass such as quartz, borosilicate glass, and BK7, crystalline materials such as lithium niobate and YVO4, and organic polymer materials such as polymethylmethacrylate (PMMA) may be used as a substrate for forming an optical waveguide. The optical waveguide can be drawn by adjusting the light intensity of the laser beam under the condition of inducing a change in the refractive index of the substrate material.

The laser beam Lm emitted from the short pulse laser light source 51 is branched into four branches by the three broadband beam splitter cubes (12a, 12b, 12c) and the wide band total reflection mirror 12d. In the present embodiment, a beam splitter 12 in which three wideband beam splitter cubes (12a, 12b, 12c) are connected and a wideband total reflection mirror 12d correspond to the beam splitter 12.

The widespread beam splitter cube 12a has a demultiplexing ratio of 3: 1, the widespread beam splitter cube 12b has a demultiplexing ratio of 2: 1, and the wideband beam splitter cube 12c has a demultiplexing ratio of 1: 1. Therefore, the light intensities of the four branched laser beams Ls demultiplexed by the beam splitter 12 are 1/4 of the laser light Lm, respectively, and have the same light intensity.

The branched laser light Ls is focused on four focusing regions (Aa, Ab, Ac, Ad) of the glass substrate 50 fixed on the stage 11 by the lens 13 in each optical path.
The stage 11 is a 3-axis stage, and the motion is controlled by a control device such as a computer. If the stage 11 is moved to move the condensing region (Aa, Ab, Ac, Ad), four continuous optical waveguides (Ga, Gb, Gc, Gd) are formed at the same time.

In FIG. 1, four optical waveguides are drawn in parallel, but the light is focused by controlling the individual wideband beam splitter cubes (12a, 12b, 12c) and the wideband total reflection mirror 12d separately to change the reflection direction. Since the positions of the regions (Aa, Ab, Ac, Ad) can be freely changed, it is possible to form four non-parallel optical waveguides.

When changing the position of the condensing region in the thickness direction of the glass substrate 50, lenses having different focal lengths may be used. When the number of waveguides to be formed is large, the integrated value of the light intensity in the condensing region (light intensity x irradiation time) is increased by increasing the light intensity of the laser beam Lm or slowing down the moving speed of the glass substrate 50. Should be maintained at a value that changes the refractive index of the glass substrate.

The beam splitter 12 may change the branching ratio of the laser beam Lm according to the motion of the stage 11.
In order to draw a linear optical waveguide, if the operation of the stage 11 is a linear motion, the light intensities of the branched laser beams Ls may be the same. That is, the beam splitter 12 equally branches the laser beam Lm and outputs the branched laser beam Ls. However, in order to draw a curved optical waveguide, when the stage 11 makes a rotational motion, if the light intensity of the branched laser beam Ls is the same, the light energy is generated in the condensing region on the center side of the rotation and the condensing region on the outside. There is a difference in the integrated value of. Specifically, in the condensing region on the center side of rotation, the integrated value of light energy is large and the optical waveguide becomes thick, and in the condensing region outside the rotation, the integrated value of light energy is small and the optical waveguide becomes thin. If the thickness of the optical waveguide changes, the characteristics of the optical waveguide will differ. Therefore, when the operation of the stage 11 is a rotational motion, the beam splitter 12 splits the laser beam so that the integrated values of the light energies in all the focusing regions are equal.
In such a case, as the beam splitter 12, a beam splitter (for example, see Non-Patent Document 1) that changes the transmittance and the reflectance to change the branch ratio by changing the incident angle can be used. can.

(effect)
The drawing device 301 can draw a plurality of waveguides at once by splitting the laser beam Lm by the beam splitter 12 and irradiating the plurality of condensing regions (Aa, Ab, Ac, Ad). At that time, an arbitrary waveguide can be drawn on the glass substrate by individually moving the split portion (splitter cube).

(Embodiment 2)
FIG. 2 is a diagram illustrating the drawing apparatus 302 of the present embodiment. The drawing device 302 includes a beam splitter 12, a lens 13, a stage 11, a reflection mirror (21a, 21b, 21c), and a prism (22a, 22b, 22c). The beam splitter 12 is composed of wideband beam splitter cubes (12a, 12b) and a total reflection mirror 12d. The lens 13 is composed of lenses (13a, 13b, 13c) corresponding to the individual branched laser beams Ls. In FIG. 2, the short pulse laser light source 51 and the glass substrate 50 are not included in the drawing device 302.

The drawing device 301 of the first embodiment draws an optical waveguide with each demultiplexing laser beam. That is, four optical waveguides were drawn simultaneously with four demultiplexing laser beams. On the other hand, the drawing device 302 differs from the drawing device 301 in that the three demultiplexing laser beams Ls are focused on one focusing region At to form one optical waveguide. That is, the lens 13 concentrates a plurality of branched laser beams Ls on one focusing region At.

The drawing device 302 splits the laser beam Lm emitted from one short pulse laser light source 51 into three branched laser beams Ls by the beam splitter 12. The branched laser light Ls is reflected by the reflection mirrors (21a, 21b, 21c), respectively, and is one condensing region of the glass substrate 50 fixed on the stage 11 via the prisms (22a, 22b, 22c) and the lens 13. It is focused on At.

The movement of the stage 11 is controlled by a control device 20 such as a computer, and the glass substrate 50 can be moved by a desired movement. Therefore, if the stage 11 is moved to move the condensing region At, one continuous optical waveguide is formed. By moving the stage 11 in the thickness direction of the glass substrate 50, the optical waveguide can be drawn in a plurality of layers in the glass substrate 50. In the case of FIG. 2, the upper layer optical waveguide Gu and the lower layer optical waveguide Gl are formed in the glass substrate 50.

The drawing device 302 sets the light intensity when the two branched laser beams Ls are superimposed to be less than the light intensity at which the refractive index of the glass substrate 50 changes, and the light intensity when the three branched laser beams Ls are superimposed to the glass substrate 50. The short pulse laser light source 51 is controlled so that the refractive index of the light is equal to or higher than the changing light intensity, and the light intensity of the laser light Lm is adjusted.

That is, the refractive index of the glass substrate 50 changes in the region where three or more demultiplexing laser beams Ls overlap, and the refractive index of the glass substrate 50 does not change in the region where the two branched laser beams Ls are superimposed and irradiated. This will be described with reference to FIG. Ls1, Ls2, and Ls3 indicate the focusing position of each branched laser beam Ls.

FIG. 3A shows a state in which the condensing positions of the respective branched laser beams Ls do not overlap. The focusing region of the laser resembles the shape sandwiched between hyperbolas, and is schematically represented by a drum shape in FIG. FIG. 3B shows a state in which the beam splitter 12, the reflection mirror 21, the prism 22, and the lens 13 are adjusted so that the three focusing positions of the respective branched laser beam Ls are superimposed. If the light collection positions overlap, the light intensity increases, the refractive index of the glass substrate 50 can be changed, and an optical waveguide can be drawn.

FIG. 3C shows a state in which the focusing position of one branched laser beam Ls1 is displaced and is at the position of Ls1'. Even in such a state, the position and shape of the region (Ls1'+ Ls2 + Ls3) where the focused positions of the three branched laser beams Ls overlap are almost unchanged from the original region ((Ls1 + Ls2 + Ls3). Even if the condensing position of the branched laser light is deviated, the refractive index of the glass substrate 50 can be changed at the same position as in FIG. 3 (B) where there is no misalignment, and the optical waveguide can be drawn.

Therefore, if the refractive index of the glass substrate 50 can be changed only when the laser beams branched into a plurality of branches are superimposed, there is almost no effect even if the focusing position of the laser beam shifts.

One of the causes of the shift of the condensing position of the branched laser beam Ls is that the optical waveguide Gu exists above the condensing region At (in the direction of the light source) as shown in the glass substrate 50 in FIG. As described above, since the refractive index of the optical waveguide Gu (core waveguide) is different from that of the surrounding clad layer, the focal length shifts when the branched laser beam Ls crosses the optical waveguide Gu (see FIG. 6). ..

FIG. 6 describes a case where the branched laser beam Ls is vertically incident on the surface of the glass substrate 50 for the sake of simplicity. In this case, the optical waveguide Gu moves the condensing position upward from the original position. When the branched laser beam Ls is incident from a direction that is not perpendicular to the surface of the glass substrate 50, the optical waveguide Gu moves the condensing position not only upward but also horizontally.

In this way, even when the focal length of the branched laser light Ls shifts in the upper optical waveguide Gu, the focused shape (drum shape) of the laser light extends in the optical axis direction, so that there are three branches. Since the superimposed position of the laser beam Ls and its shape are almost the same, even if the focal length of the branched laser beam Ls is deviated by crossing the optical waveguide Gu, the optical waveguide is placed at the same position as when the optical waveguide Gu does not exist. Can be drawn.

Although the case where the number of branched laser beams Ls is 3 has been described in the present embodiment, the drawing apparatus according to the present invention does not limit the number of branched laser beams Ls to 3. The number of branched laser beams Ls may be 2 or 4 or more.

Further, it is preferable that the lens 13 is in a position to irradiate the branched laser beam Ls so as not to face each other. That is, the optical axes of at least two branched laser beams Ls are set to face each other by non-180 degrees. Here, the opposite (180 degree facing) means that the incident points Pins of all the branched laser light Ls are on the same straight line and are collected on the surface 50s on the lens 13 side of the glass substrate 50 as shown in FIG. This is a state in which the intersection Pat of the perpendicular line drawn from the center point Atc of the optical region At to the surface 50s and the surface 50s exists on the straight line. FIG. 7A is a cross-sectional view of the glass substrate 50 cut in the thickness direction, and FIG. 7B is a view of the glass substrate 50 seen from the lens 13 side. Here, FIG. 7 shows a case where there are two branched laser beams, but the same applies to three or more branched laser beams.

The radius of curvature (R ≧ several hundred μm) of the optical waveguide is large with respect to the laser irradiation system, and the optical waveguide Gu in the upper layer can be regarded as almost a straight line for the branched laser light.
If the optical axes of the two branched laser beams Ls face each other by 180 degrees, the two optical axes may be accidentally affected by the optical waveguide Gu as shown in FIG. In general, the distance between adjacent optical waveguides is wider than 50 μm, which is sufficiently coarser than the thickness of the optical waveguide (≈ the diameter of the condensing region At) of several μm. Therefore, the two branched laser beams Ls. This is because if the optical axes of the above are arranged non-180 degrees, two or more branched laser beams Ls are hardly affected by the optical waveguide Gu at the same time. In order to avoid such a state, the number of branched laser beams should be 3 or more, and the position of the branched laser beams should be adjusted so that all the branched laser beams are not affected by the optical waveguide in the upper layer. preferable. Even when two branched laser beams Ls cross the optical waveguide Gu at the same time, the influence is small. This is because the focal shape of the laser beam extends in the optical axis direction, so even if the two focusing positions move in the optical axis direction at the same time, the superposition position of the three branched laser beams and their shape are almost the same. be.

(effect)
The drawing device 302 synchronously irradiates the branched laser light Ls in a plurality of passes, and adjusts the condensing region At below the optical waveguide Gu in the upper layer to the lower layer without being affected by the optical waveguide Gu. The optical waveguide Gl can be drawn.

11: Stage 12: Beam splitter 21a, 12b, 12c: Broadband beam splitter Cube 12d: Wideband total reflection mirror 13, 13a, 13b, 13c: Lens 21a, 21b, 21c: Reflection mirror 22a, 22b, 22c: Prism 50: Glass Substrate 51: Short pulse laser light source 301, 302: Drawing device

Claims (2)

A beam splitter that splits the laser beam from a short pulse laser into multiple pieces,
A lens that is in a position to irradiate the plurality of branched laser beams so as not to face each other, and concentrates the plurality of branched laser beams to the same predetermined area inside the glass substrate.
A stage that moves the glass substrate with a desired motion,
Equipped with
A drawing device characterized in that an optical waveguide is drawn on a locus of the predetermined region due to the movement of the stage.
However, the opposite means that on the surface of the glass substrate on the lens side, the incident points of all the branched optical axes of the laser beam are on the same straight line, and the intersection is lowered from the center point of the predetermined region to the surface. It is a state in which the intersection of the vertical line and the surface exists on the straight line. It is a drawing method that draws an optical waveguide on a glass substrate.
Dividing the laser beam from a short pulse laser into multiple parts,
Condensing a plurality of branched laser beams into the same predetermined area inside the glass substrate so as not to face each other.
A drawing method comprising moving the glass substrate with a desired motion and forming the optical waveguide in a locus of the predetermined region.
However, the opposite means that the incident points of all the branched optical axes of the laser beam are on the same straight line on the surface of the glass substrate on the side where the plurality of laser beams are incident , and the predetermined region. A state in which the intersection of the perpendicular line drawn from the center point to the surface and the surface exists on the straight line.

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