JPH01238624A - Optical waveguide element - Google Patents

Abstract

PURPOSE:To suppress the spreading angle of an exit beam to a lower angle by parting the light exit end face of an optical waveguide from a substrate end face, then forming the part of the optical waveguide adjacent to the light exit end face thicker than the other part of the optical waveguide. CONSTITUTION:The light exit end face 11b of the optical waveguide 11 formed on the transparent substrate 16 is positioned apart from the end face 16a of the substrate 16 toward the inner side and the part adjacent to this light exit end face 11b is formed thicker than the other part 11 of the optical waveguide. The laser beam 13 emitted from the light incident end face of the optical waveguide 11 into the optical waveguide progresses in the optical waveguide 11, is emitted once from the light exit end face 11b to the part of the substrate 16 and is emitted from the substrate end face 16a to the outside of the substrate 16. The spreading angle phi3 the light beam 13B to be emitted at this time decreases as the spreading is suppressed and, therefore, the use of an inexpensive cylindrical lens 25 having a smaller aperture diameter is possible. The light intensity distribution in the spreading angle phi3 can be the distribution approximate to a Gauss distribution.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an optical waveguide device, and more particularly, to an optical waveguide device that allows a light beam guided in the optical waveguide to be emitted from the end face of the optical waveguide with a small divergence angle. This relates to wave path elements.

(Prior Art) Conventionally, various optical waveguide elements have been provided in which an optical waveguide is formed on a substrate. In this type of optical waveguide element, the light beam guided in the guide waveguide is often extracted to the outside of the optical waveguide, for example, directly from the end face of the optical waveguide or via a prism coupler or a diffraction grating (grating coupler).

On the other hand, as shown in Japanese Patent Application Laid-Open No. 62-77761, attempts have been made to form an optical deflector using a guiding waveguide element, and in that case, the optical beam emitted from the optical waveguide is focused into a small spot. I often let them do it.

(Problems to be Solved by the Invention) When the light beam is directly emitted from the end face of the optical waveguide as described above, the output efficiency is good, but on the other hand, due to the diffraction of the light at the end face of the optical waveguide, As shown in 1), the problem arises that the output beam 50 tends to spread widely. In FIG. 3, 51 is a substrate and 52 is an optical waveguide. When converging the light beam 50 as described above, the larger the divergence angle φ1 of the light beam 50, the more necessary it is to focus the light beam 50 using the cylindrical lens 53 with a larger NA (numerical aperture). For example, φ1=1
When the angle is 6°, a lens with an NA of about -0.14 is required.

As is well known, a cylindrical lens with a large NA is expensive, so the use of such a cylindrical lens increases the cost of an optical deflection device or the like constituted by an optical waveguide element. Note that the divergence angle here is the light intensity or 1/e
It is defined in the range that decreases to 2. In addition, in this case, the above-mentioned divergence angle φ1 may be approximately 35° if there is a so-called "sag" on the end surface of the optical waveguide 52 (the edge portion indicated by the arrow H in FIG. 3(1) is rounded). Because of the large size, there is also the problem that the end face must be polished extremely carefully.

On the other hand, when the light beam 50 is emitted out of the optical waveguide 52 using the prism coupler 54 as shown in FIG. is shown by curve E, and the beam 5
There is a problem in that it cannot become a zero or Gaussian beam (a beam whose light intensity distribution is a Gaussian distribution). When the light beam 50 with the above-mentioned light intensity distribution is focused as described above, the light intensity distribution of the beam spot will have side lobes, making it difficult to record or read a precise image by scanning the light beam. It becomes impossible to do anything. Furthermore, when using this prism coupler 54, the output efficiency varies depending on the gear between the prism coupler 54 and the optical waveguide 52, so if this gap cannot be controlled extremely precisely to within a deviation of 10 μm, the light intensity distribution will change. There is also the problem that it becomes extremely non-uniform.

Further, even when the diffraction grating 55 is used as shown in (3) of FIG. 3, the output beam 50 cannot become a Gaussian beam (the distribution of the light intensity I is shown by the curve F in the figure).

In addition, when using such a diffraction grating 55,
The output efficiency of the guided light is about 70% at most, which is considerably lower than in the case of edge emission.

Therefore, as a method for emitting guided light that can solve the various problems described above to some extent, the document Be1l Sys.

Tech, J., 50. p43. Jan, 1971 “E.
xcitation of Waveguides
for integrated 0ptics wi
th La5er Beam”-D, Marcu
se & E, A, J, Marcat
The method shown in illi- is being considered. This method is as shown in FIG.
The light passes through the substrate and is then emitted to the outside of the device. In this case, the light beam 50 that is about to spread upward in the drawing and exit from the light emitting end face 52a is totally reflected by the upper surface 51b in the drawing of the substrate 51 and travels downward. Compared to the case of end emission shown in (1), the divergence angle φ2 is smaller.

Further, in this case, the output beam 50 becomes a substantially Gaussian beam, and the output efficiency thereof is also comparable to that in the case of end emission shown in FIG. 3(1). Furthermore, in this case, the edge of the board (
Even if there is the above-mentioned "sag" or chipping in the portion shown by arrow J in FIG. 3 (4), there is little effect on the spread angle φ2.

Note that the above-mentioned document only discloses that a light beam is made to enter an optical waveguide using the configuration shown in FIG. 3 (4); It is obvious that it can be emitted outside.

An object of the present invention is to provide an optical waveguide element that can further reduce the divergence angle of the emitted beam by basically using the configuration shown in FIG. 3 (4) having the above-mentioned features. be.

(Means for Solving the Problems) The guiding waveguide element of the present invention is an optical waveguide element in which the light beam emitted from the light emitting end face of the optical waveguide is emitted after passing through the substrate portion as described above. It is characterized in that the portion of the optical waveguide adjacent to the light output end face is formed thicker than the other portions of the optical waveguide.

(Function) As described above, if the portion of the optical waveguide adjacent to the light emitting end face is made thicker than the other parts of the optical waveguide, the diffraction of the light beam emitted from the end face will be weakened, resulting in the above-mentioned spread. The corners become smaller.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIGS. 1 and 2 show a guiding waveguide element IO according to an embodiment of the present invention. This leading waveguide element 10 is -
As an example, it constitutes an optical deflector for image recording,
An optical waveguide 11 formed on a transparent substrate 16 and a pair of crossed comb-shaped electrodes (I
inter D 1g1tal Transdu
cer % or less referred to as IDT) 15, a semiconductor laser 18 directly coupled to one end surface (light incident end surface) lla of the optical waveguide 11, and a waveguide formed in the optical waveguide ll at a position close to the one end surface 11a. It has a lens 19. This optical deflector also includes a drive circuit 17 that applies a high frequency alternating voltage to the IDT 15, and a semiconductor laser 1.
8, a cylindrical lens 25, and a plane scanning lens 26.

In this embodiment, as an example, the substrate 16 is made of LiNbO.
The optical waveguide 11 is formed by using three wafers and providing a Ti diffusion film on the surface of the wafer. Note that substrate 1
As the material 6, a crystalline substrate made of sapphire, Si, etc. may also be used. Regarding optical waveguides, for example, see "Integrate Optics" edited by T. Tamir.
0ptics ) J (Tobitkusin Applied Physics (Topics 1nApplied)
Physics) Volume 7) Published by Springer-Verlag (19
75): There is a detailed description in the published works such as "Optical Integrated Circuits" co-authored by Nishihara, Makishin, and Suhara, published by Ohmsha (1985), and in the present invention, any of these known optical waveguides can be used as the optical waveguide 11. . However, in this embodiment, this optical waveguide 11
is formed from a material such as the Ti diffusion film described above that allows surface acoustic waves to be propagated, which will be described later. Further, the optical waveguide may have a laminated structure of two or more layers.

As a feature of the present invention, the other end surface (light emitting end surface) 11b of the optical waveguide 11 is located away from the end surface lea of the substrate 16 inwardly, as shown in FIG. 2, and is adjacent to this light emitting end surface 11b. The portion is formed thicker than the other portions of the optical waveguide. Leading waveguide 11 having such a shape
For example, as shown in FIG. 4(1), Ti is deposited on the substrate 16.
(Titanium: thickness 400A), a first diffusion treatment (1000°C, 8 hours in nitrogen, 1 hour in oxygen) is performed to spread the Ti into the substrate 16 as shown in FIG. 4(2). Then, as shown in Figure 4 (3), Ti (thickness 2
5OA) and then the second diffusion treatment (950℃
(3 hours in nitrogen and 1 hour in oxygen), and the Ti is diffused into the substrate 16 continuously with the Ti as shown in FIG. 4 (4). In addition, if T1 is arranged in a tapered cross-section as shown in FIG. 4(1) during the first Ti diffusion, as shown in FIG. 4(4), the optical waveguide 11 is The thickness of the portion adjacent to the light emitting end surface 11b changes gently and continues to the other relatively thin portion.

If this is done, it is possible to prevent a large radiation loss of the guided light at a portion where the thickness changes stepwise.

Note that the optical waveguide 11 as described above can be produced more easily than the above-described diffraction grating for light beam emission.

The aforementioned semiconductor laser 18 emits a laser beam (radiation beam) 13'' from one end surface (light incident end surface) 11a of the optical waveguide 11 into the guiding waveguide 11. This radiation beam 13'' is transmitted to the waveguide lens 19. parallel beam 1 by
3, and this light beam 13 travels in the direction of arrow A in FIG. 1 in a waveguide mode within the optical waveguide 11. Note that the semiconductor laser 18 is not directly coupled to the light incident end face 11a as described above, but the light beam 13° is made to enter the leading waveguide ll via a lens, a coupler prism, a diffraction grating (grating coupler), etc. You can.

When recording an image, the photoreceptor 23 is set on a transport means 22 such as an endless belt.

Then, the semiconductor laser 18 is driven by the laser drive circuit 20.
The IDT 15 is driven to emit a laser beam of 13°, and at the same time, an alternating voltage whose frequency changes continuously is applied from a drive circuit 17 to the IDT 15 . Note that the laser drive circuit 20 is controlled by a modulation circuit 24 to change the optical output according to the image signal S (i.e., the light beam 13'
The semiconductor laser 18 is driven so as to change the intensity of the light beam 13' and the number of pulses and pulse width when emitting the light beam 13' in a spiral pattern.

By applying the voltage as described above to the IDT 15, the surface acoustic wave 12 travels on the surface of the optical waveguide 11 in the direction of arrow B in FIG. The IDT 15 uses this surface acoustic wave 1
2 is arranged so as to travel in a direction intersecting the optical path of the guided light (parallel beam) 13.

Therefore, the guided light 13 travels across the surface acoustic wave 12, and at this time, the guided light 13 undergoes Bragg diffraction due to acousto-optic interaction with the surface acoustic wave 12. As is well known, the deflection angle of the guided light 13 due to this diffraction is approximately proportional to the frequency of the surface acoustic wave 12. As described above, the drive circuit 17 applies an alternating voltage whose frequency changes continuously to the IDT 15, so that the frequency of the surface acoustic wave 12 changes continuously and the deflection angle changes continuously. Therefore, this guided light 13 is deflected as shown by arrow C. The guided light 13 deflected in this way is transmitted from the light output end face 11b of the optical waveguide 11 to the substrate 16.
The light is emitted from the substrate end surface lea, and is emitted from the substrate end surface lea.

The light beam 13B thus emitted outside the optical waveguide element IO
has a vertical spread in FIG. When the light beam 13B is emitted from the end face 11b, the diffraction becomes weaker, so the angle of spread φ3 is
This is smaller than the divergence angle φ2 when the light beam is emitted as shown in FIG. 3(4). The emitted light beam 13B is corrected for the above-mentioned spread by a cylindrical lens 25, and then passes through a plane scanning lens 26 made of, for example, an fθ lens, and is focused on a small beam spot P. Specifically, the divergence angle φ3 of the light beam 13B can be, for example, about 5°, and in that case, the cylindrical lens 25 has an NA of 0.0.
4 or so can be used. Furthermore, the output efficiency of the light beam 13B is approximately 10, excluding loss due to Fresnel reflection.
The light intensity distribution becomes sufficiently high as about 0%, and the light intensity distribution over the direction of the spread angle φ3 can become a distribution close to the Gaussian distribution as described above.

This light intensity distribution and output efficiency are determined by the edge of the substrate 16 (
Even if there is some chipping or ``sagging'' at the location indicated by arrow J in Figure 2, it will not have much of an effect.

The light beam 13B focused on the beam spot P scans the photoreceptor 23 in the direction of arrow X (main scan).

At the same time, the photoreceptor 23 is transferred by the transfer means 22 in the direction of the arrow y, which is substantially perpendicular to the main scanning direction, to perform sub-scanning, so that the photoreceptor 23 is two-dimensionally scanned by the light beam 13B. As mentioned above, this light beam 13B
is modulated based on the image signal S, so the photoreceptor 2
3, an image carried by this image signal S is recorded.

Note that in order to synchronize the image signal S for one main scanning line with the main scanning of the light beam 13B, the blanking signal sb included in this image signal S is used as a trigger signal.
The timing of voltage application to the IDT 15 may be controlled.

Furthermore, by controlling the driving timing of the transfer means 22 using this blanking signal sb, the main scanning and sub-scanning can be synchronized.

Although the guiding waveguide element 10 of the embodiment described above is formed as an optical deflector, the present invention is not limited to such an optical deflector, but is applicable to guiding light guided within an optical waveguide. The present invention is applicable to any optical waveguide device in which the light is emitted from the end face into the substrate, and after passing through the substrate, the light is emitted from the end face of the substrate to the outside of the device.

(Effects of the Invention) As explained in detail above, in the optical waveguide device of the present invention, the light output end face of the optical waveguide is separated from the substrate end face, and the light beam is emitted outside the element through these both end faces. The efficiency is high, the light intensity distribution of the emitted beam can be made into a Gaussian distribution, and it is easier to fabricate than an optical waveguide element in which a diffraction grating is provided on the surface of the guiding waveguide. It will be difficult to be affected by this.

Furthermore, in the optical waveguide device of the present invention, the light output end face of the optical waveguide is separated from the substrate end face as described above, and the portion of the optical waveguide adjacent to the light output end face is made thicker than the other optical waveguide portions. By forming this, it becomes possible to weaken the diffraction when the light beam is emitted from the optical waveguide and to suppress the spread angle of the emitted beam to a small value. Therefore, according to this guiding waveguide element, the spread of the emitted beam can be adjusted to NA
It becomes possible to perform correction using an inexpensive cylindrical lens with a relatively small numerical aperture, and it is possible to reduce the cost of an optical scanning recording device or the like constructed using the optical waveguide element.

[Brief explanation of the drawing]

1 and 2 are respectively a perspective view and a side view showing an optical waveguide device according to an embodiment of the present invention, and FIGS.
, (3) and (4) are schematic diagrams showing the structure of the light beam emitting part in a conventional guiding waveguide element, and FIG. 4 (1), (
2), (3), and (4) are explanatory diagrams illustrating the method of manufacturing the optical waveguide device of the above embodiment. 10. Optical waveguide element 11. Optical waveguide 11b... Light output end face of optical waveguide 12... Surface acoustic wave 13... Guided light 13B
...Light beam 15...IDT16--Board
lea... End face of the board Figure 3 l

Claims (1)

[Claims] An optical waveguide for guiding a light beam is formed on a transparent substrate, a light output end face of the optical waveguide is located apart from the substrate end face, and the light beam emitted from the output end face is directed to a portion of the substrate. An optical waveguide element in which light is emitted from an end face of a substrate through a substrate, characterized in that a portion of the optical waveguide adjacent to the light emitting end face is formed thicker than other parts of the optical waveguide.