JPH07141688A - Optical waveguide and converging device - Google Patents

Abstract

PURPOSE:To efficiently convert an incident beam to a waveguide beam and to provide a circular spot excellently converged on one focal point by equalizing an equivalent refractive index of a TM mode waveguide beam propagating through a waveguide layer with the equivalent refractive in-dex of a TE mode waveguide beam. CONSTITUTION:A transparent substrate 1, a phase correction layer 2, a buffer layer 3, the waveguide layer 4 and a grating coupler 6 formed on the waveguide layer 4 and constituted of a concentric circular rugged structure are all provided with an axis L orthogonally intersecting with the waveguide layer 4 as a central axis. The coupler 5 is formed on a circular area around the axis L, and the coupler 6 is formed on a ring-shaped area surrounding the coupler 5. A beam 7 incident on the coupler 5 along the axis L excites the waveguide beam 8. The waveguide beam 8 is radiated from the grating coupler 6 propagating from the center to an outer periphery. Then, the equivalent difractive index of the TM mode waveguide beam propagating through the waveguide layer 4 is made equal to the equivalent difractive index of the TE mode waveguide beam by the phase correction layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide for transmitting light in a thin film and a light condensing device for converging light at one point.

[0002]

2. Description of the Related Art The conditions for injecting light into a waveguide layer and exciting the guided light using an optical coupler such as a grating coupler are related to the polarization state of the incident light. FIG. 4 shows a state of light input to the waveguide layer in the conventional example. In FIG. 4, 1 is a transparent substrate, 4 is a waveguiding layer, and 13 is a grating coupler (the fringe direction of the grating is orthogonal to the plane of the drawing) having a linear concavo-convex structure with a pitch Λ formed on the waveguiding layer. The condition for exciting the guided light 12 by the light 11 that enters the grating coupler 13 at an angle θ with the waveguiding layer normal L is given by the following equation.

Sin θ = N−λ / Λ (Equation 1) where N is the equivalent refractive index of the guided light 12, λ is the wavelength of the laser light 11, and the incident optical axis and the guided optical axis are parallel to the paper surface. .

When the electric vector of the incident light is orthogonal to the paper surface like 11a, TE mode guided light parallel to the surface of the waveguiding layer is excited like the electric vector 12a, and when parallel to the paper surface like 11b. , TM-mode guided light whose electric vector is orthogonal to the surface of the waveguiding layer 12b is excited. Since the magnitude of the equivalent refractive index N differs depending on whether the guided light 12 is the TE mode or the TM mode, the incident angle θ also differs according to Expression 1 depending on whether the TE mode or the TM mode is excited.

FIG. 5 is equivalent to the film thickness of the waveguide layer in FIG. 4 where the refractive index of the waveguide layer 4 is 1.85, the refractive index of the transparent substrate 1 is 1.45, and the wavelength of the laser beam 11 is 0.82 μm. The relationship with the refractive index (dispersion property) is written using the guided mode as a parameter. When the film thickness is fixed, the TE mode equivalent refractive index is T for each order (0th order, 1st order, 2nd order).
It is larger than the equivalent refractive index of M mode.

FIG. 6 is a block diagram of a light collecting device using the above-described conventional waveguide layer. In FIG. 6, 1 is a transparent substrate, 4
Is a waveguide layer, and 5 and 6 are grating couplers having a concentric concavo-convex structure formed on the waveguide layer.
A central axis is an axis L orthogonal to. The coupler 5 is formed in a circular region around the axis L, and the coupler 6 is formed in a ring-shaped region surrounding the coupler 5. The light 7 incident on the grating coupler 5 along the axis L excites the guided light 8. However, the pitch Λ of the grating coupler 5 satisfies the following equation.

Λ / Λ = N (Equation 2) N is the equivalent refractive index of the guided light 8 and λ is the wavelength of the laser light 7.

The guided light 8 propagates from the center toward the outer circumference and is emitted from the grating coupler 6. The pitch Λ of the grating coupler 6 is such that f is the focal length, r is the emission position radius of the radiated light 9, and θ is the opening angle at the emission position.
The following simultaneous equations are satisfied.

Sin θ = λ / Λ−N (Equation 3) tan θ = r / f (Equation 4) When the above two expressions are satisfied (that is, the pitch Λ changes as a function of r), the radiated light 9 is one point. The light 11 that is focused on the laser light and reflected by the reflecting surface 10 placed at the focal position can excite the guided light 12 again by the grating coupler 6.

FIG. 7 shows the relationship between the polarization state and the light input, light guide, and light output in the light collecting device shown in FIG. The light incident on the grating coupler 5 is linearly polarized light, and the electric vector is parallel to the y-axis like 7A, 7B, 7C and 7D.

If the coupler 5 is large, then in equation 2, N
Is equal to the equivalent refractive index for the TE mode (N is T
Even if the equivalent refractive index for M mode is equal, TE and TM
Except that the electric vector direction is changed and the following circumstances are the same), and the TE mode guided light 8a, 8b propagating in the x-axis direction by the coupler 5 and propagating in the azimuth forming a deviation angle of φ with the x-axis. The guided light 8e is excited.

The electric vectors of the guided lights 8a, 8b and 8e are in the tangential direction of the circle concentric with the coupler 5, and the optical amplitude of the guided light 8e is the magnitude of cosφ standardized by the amplitude of the guided light 8a.

Therefore, the amplitude of the light 9e emitted from the grating coupler 6 depends on the deviation angle φ of the emission position, and
proportional to the size of φ. The polarization direction of the emitted light is in the tangential direction of the circle whose electric vector is concentric with the coupler 5.

For example, the electric vectors of the radiated lights 9A and 9B on the x-axis are parallel to the y-axis, and the electric vector of the radiated light 9e is in the direction inclined by the angle φ with respect to the y-axis.

Therefore, of the light 9e emitted from the coupler 6, the light amplitude of the component that interferes with each other at the focal point F1 (that is, the component whose electric vector is in the y-axis direction) is cos ²
proportional to the size of φ. Therefore, the emitted light is equivalently subjected to aperture restriction such that it is shielded in a region having a small deviation from the y-axis, and the focused spot at the point F1 is an elliptical spot spread in the y-axis direction.

When the coupler 5 is sufficiently small, the conditions for pumping guided light shown in formula 2 are relaxed, and in addition to the above-described pumping of TE mode light, the equivalent refractive index of TM mode is slightly smaller than N of formula 2. Guided lights 8c 'and 8d' (both guided lights propagating in the y-axis direction) and 8e '(guided light propagating in an azimuth forming an angle of φ with the x-axis) are also excited.

The electric vectors of the guided lights 8c ', 8d', and 8e 'are all in the normal direction to the surface of the waveguide layer, and the optical amplitude of the guided light 8e' is the magnitude of sin φ of the optical amplitude of the guided light 8c '. is there.

The emission angle of the light emitted from the grating coupler 6 is smaller in N of the equation 3 than in the TE mode.
The radiation angle (angle formed by the radiation and the normal to the waveguide layer, that is, the opening angle θ) becomes large, and the focal point F2 of the TM mode radiation is obtained.
Is closer to the coupler 6 side than the point F1 due to the TE mode radiation.

The amplitude of the TM mode radiated light 9e 'is proportional to the magnitude of sin φ, and its electric vector is in the radial direction of the circle concentric with the coupler 5 (that is, the direction forming an angle φ with the x axis) (strictly speaking). Is the polarization direction of the emitted light, whose electric vector is the emission direction and the guiding direction (the radial direction of the circle concentric with the coupler 5).
Is in the plane including and is in the direction orthogonal to the radial direction,
Here we use an approximate expression).

Therefore, the optical amplitude distribution of the components that interfere with each other (that is, the component whose electric vector is in the y-axis direction) is si
It is proportional to the size of n ² φ (strictly speaking, sin ² φcos θ). Therefore, the emitted light is equivalently subjected to aperture restriction such that it is shielded in a region having a small deviation angle from the x-axis, and the focused spot at the point F2 is an elliptical spot extending in the x-axis direction.

That is, when the coupler 5 is sufficiently small, the elliptical spot spread in the y-axis direction at the point F1, the point F2.
Gives an elliptical spot spread in the x-axis direction.

[0022]

The above-mentioned conventional optical waveguide and light condensing device have the following problems. When the coupler 5 is large, the light incident on the region having a small deviation angle with the x-axis by the coupler 5 excites the guided light strongly, but the excitation is weak in the region having a small deviation angle with the y-axis, and the incident light is effective. Not used.

Further, in addition to the declination dependence of the guided light amount, the polarization direction of the radiated light is in the circular tangential direction,
The radiated light is equivalently blocked by an aperture that is shielded in a region having a small deviation from the y-axis, and the focused spot is an elliptical spot spread in the y-axis direction.

When the coupler 5 is sufficiently small, the TM mode light is excited in the region where the deviation angle from the y axis is small in addition to the above-described excitation of the TE mode light, so that there is no problem regarding effective use of the incident light. However, there remains a problem with the ability to collect emitted light.

That is, since the TE mode and the TM mode have different equivalent refractive indices, the emission angles of the TE mode radiation and the TM mode radiation are different, and the focused spot is an elliptical spot spread in the y-axis direction by the TE mode radiation. And an elliptical spot spread in the x-axis direction by the TM mode radiation light are obtained separately on the optical axis.

In any case, since the aperture is equivalently applied as a light-collecting element, a circularly condensed light-collecting spot cannot be obtained.

In view of the above problems, the present invention efficiently guides guided light in all directions regardless of the size of the coupler 5, and makes the amplitude and polarization direction of the emitted light uniform regardless of the direction and provides a focused spot. It is an object of the present invention to provide an optical waveguide and a light condensing device capable of narrowing a circular shape.

[0028]

In order to solve the above-mentioned problems, an optical waveguide of the present invention comprises a laser light source, a waveguide layer formed of a transparent layer, and a laser beam emitted from the laser light source. And an input means for exciting guided light propagating in the waveguide layer, the waveguide layer sandwiching a first transparent layer having a lower refractive index than the waveguide layer and having a higher refractive index than the waveguide layer. It is characterized by being laminated on two transparent layers.

Further, the second transparent layer is laminated on the fourth transparent layer having a refractive index higher than that of the waveguide layer with the third transparent layer having a refractive index lower than that of the waveguide layer being sandwiched therebetween. The lamination may be repeated once or more.

In particular, the input means is composed of an uneven periodic structure formed on the waveguide layer, the periodic structure forms a concentric circle, and the laser light is incident along the central axis A of the concentric circle. Which further comprises an output means for radiating the guided light to the outside of the waveguide layer, the output means being constituted by a concave-convex periodic structure formed on the waveguide layer,
The periodic structure forms a concentric circle about the central axis A, and the period of the periodic structure becomes denser toward the outer circumference, so that the light emitted to the outside of the waveguide layer is condensed at one point. It is a light collector.

[0031]

According to the present invention, with the above structure, the equivalent refractive index of the TM mode guided light propagating in the waveguide layer can be made equal to the equivalent refractive index of the TE mode guided light, and the light is radiated to the outside of the waveguide layer. The emission direction and phase of light and the polarization direction can be aligned.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical waveguide and a light collecting device according to embodiments of the present invention will be described below with reference to the drawings. The same members as those in the conventional example are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 shows the construction of an optical waveguide and a light collecting device in an embodiment of the present invention. In FIG. 1, 1 is a transparent substrate, 2 is a phase correction layer, 3 is a buffer layer, 4 is a waveguiding layer, and 5 and 6 are grating couplers having a concentric concavo-convex structure formed on the waveguiding layer. The axis L orthogonal to the wave layer 4 is the central axis.

The coupler 5 is formed in a circular area around the axis L, and the coupler 6 is formed in a ring-shaped area surrounding the coupler 5. The light 7 incident on the grating coupler 5 along the axis L excites the guided light 8. However, the pitch Λ of the grating coupler 5 satisfies Expression 2 where N is the equivalent refractive index of the guided light 8 and λ is the wavelength of the laser light 7.

The guided light 8 propagates from the center toward the outer circumference and is emitted from the grating coupler 6. The pitch Λ of the grating coupler 6 is such that f is the focal length, r is the emission position radius of the radiated light 9, and θ is the opening angle at the emission position.
The simultaneous equations of Equations 3 and 4 are satisfied. By satisfying the expressions 3 and 4 (that is, the pitch Λ changes as a function of r), the emitted light 9 is condensed at one point, and the light 11 reflected by the reflecting surface 10 placed at the focal position is the grating coupler 6. The guided light 12 can be excited again by.

In FIG. 2, the refractive index of the waveguiding layer 4 in FIG. 1 is 1.85, the refractive index of the transparent substrate 1 is 1.45, the refractive index of the phase correction layer 2 is 2.4, and the film thickness is 0.11 μm. , The buffer layer 3 has a refractive index of 1.45, the film thickness is 0.15 μm, and the wavelength of the laser light 7 is 0.82 μm. It is written using the mode as a parameter.

[0037] Although thing seen when increasing the thickness of the phase correction layer 2 continuously from 0 to 0.11μm by observing the dispersion characteristic diagram, TE _0, TE ₁ of 2 TE ₁ in FIG. 5, T
Since E ₂ is changed and TE ₀ in FIG. 5 is degenerated and does not appear in the dispersion characteristic diagram (a waveguide mode exists in the phase correction layer 2 but does not exist in the waveguide layer 4), the order is Has been postponed.

The fact that TM ₀ exists even when the film thickness is zero in FIG. 2 is due to the existence of the TM mode that guides the phase correction layer. As can be seen from the comparison with FIG. 5, the dispersion characteristics greatly change due to the presence of the phase correction layer, and the waveguide layer film thickness of 0.
At 9 μm (indicated by a broken line), the TE mode equivalent refractive index and the TM mode equivalent refractive index are equal in both 0th and 1st orders, and the respective curves (TE ₀ and TM ₀ , TE ₁ and TM ₁ ) are asymptotic to each other. Since they intersect, the equivalent refractive index difference that occurs even if there is an error in the thickness of the waveguide layer is small.

As shown in FIG. 2, the equivalent refractive index of TE mode and T
The condition for making the equivalent refractive index of the M mode equal is obtained when the refractive index of the phase correction layer is higher than that of the waveguide layer and the refractive index of the buffer layer is lower than that of the waveguide layer. .

FIG. 3 shows the relationship between the polarization state and the light input, light guide, and light output in the light collecting device of the present invention shown in FIG. The light incident on the grating coupler 5 is linearly polarized light, and the electric vector is parallel to the y-axis like 7A, 7B, 7C and 7D.

As shown in FIG. 2, since the equivalent refractive index of the TE mode is equal to the equivalent refractive index of the TM mode due to the existence of the phase correction layer, N in the formula 2 is equivalent to the TE mode (that is, the TE mode). Equivalent refractive index for
If they are equal to each other, the coupler 5 excites the TE mode guided lights 8a and 8b propagating in the x-axis direction and the TE mode guided light 8e propagating in an azimuth forming a deviation angle of φ with the x-axis, and at the same time propagates in the y-axis direction. TM mode guided light 8c ', 8d' and x-axis and φ
The TM mode guided light 8e 'propagating in the azimuth forming the declination angle is excited.

The electric vectors of the guided lights 8a, 8b and 8e are in the tangential direction of the circle concentric with the coupler 5, and
The electric vectors of c ', 8d', and 8e 'are all in the direction normal to the waveguiding layer.

The optical amplitude of the guided light 8e is standardized by the amplitude of the guided light 8a and has a magnitude of cosφ, and the optical amplitude of the guided light 8e ′ is also standardized by the amplitude of guided light 8c ′ and has a magnitude of sinφ. Is.

Therefore, the amplitudes of the lights 9e and 9e 'emitted from the grating coupler 6 depend on the deviation angle φ of the emission position. In the TE mode (9e), the amplitude is proportional to the magnitude of cosφ, and in the TM mode. (9e ′) is proportional to the size of sin φ.

The polarization direction of the emitted light is TE mode emitted light (9
(A, 9B, 9e, etc.), the electric vector is the coupler 5.
Is in the tangential direction of the circle concentric with the
In the case of C, 9D, 9e ′, etc.), the radial direction of the circle concentric with the coupler 5 (strictly speaking, the electric vector is in the radial direction and the waveguide direction (the radial direction of the circle concentric with the coupler 5)). It is in the plane that includes and is in the direction orthogonal to the radial direction, but here we use an approximate representation).

Since the equivalent refractive index of the TE-mode guided light and the equivalent refractive index of the TM-mode guided light are equal, the phase of the TE-mode radiated light and the phase of the TM-mode radiated light are the same, and from the formula 3, the TE-mode radiated light The emission angle and the emission angle of the TM mode emission light match.

Therefore, the TE mode radiation light and the TM mode radiation light can be combined into a linearly polarized light. 9e and 9
Taking the radiated light of e ′ as an example, the vibration azimuths are orthogonal, and the propagation azimuth is in phase with each other. Therefore, 9E, which is a composite wave, is linearly polarized light, and the polarization direction is 9e and 9e ′ has an amplitude ratio of cos φ. :
If sin φ (that is, if the amplitudes of 9A and 9D are equal), it will be perfectly aligned in the y-axis direction, and y will be present even if the amplitude ratio is slightly shifted
The deviation from the axial direction is small.

Therefore, the amplitude of the combined light emitted from the coupler 6 has a substantially uniform distribution regardless of the emission position (declination position), and the emission angles of the TE mode emission light and the TM mode emission light are the same. Since they coincide with each other, a double focus unlike the conventional example does not occur, and a well-focused circular spot is obtained at the focus F.

In the above embodiment, the phase correction layer and the buffer layer were considered to be laminated only once before forming the waveguide layer. However, the TE mode equivalent refractive index and the TM mode equivalent refractive index are If they are equal, it may be repeated multiple times.

Of course, the stacking order of the phase correction layer, the buffer layer and the waveguide layer may be reversed. Further, in the above embodiment, the example in which the waveguiding layer is formed after the lamination of the phase correction layer and the buffer layer is shown, but the lamination of the buffer layer and the phase correction layer may be further added thereto once or more.

Further, in FIG. 2 of the above embodiment, the TE mode equivalent refractive index and TM are simultaneously obtained for a plurality of orders (0th order and 1st order).
An example in which the equivalent refractive indices of the modes are equal has been shown, but the effect of the present embodiment is the same even if only a single order is matched, such as TE ₀ and TM ₀ at point A in FIG. is there.

[0052]

As described above, the optical waveguide and the light concentrating device of the present invention make the equivalent refractive index of the TE mode and the equivalent refractive index of the TM mode equal to each other, so that the incident light can be efficiently converted into the guided light and one focal point can be obtained. A well-focused circular spot can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical waveguide and a light collecting device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a waveguide layer film thickness and an equivalent refractive index of an optical waveguide in an example of the present invention.

FIG. 3 is an explanatory diagram showing the relationship between the polarization state of the light collecting device and the light input, light guide, and light output in the embodiment of the present invention.

FIG. 4 is an explanatory cross-sectional view showing light input to an optical waveguide layer in a conventional example.

FIG. 5 is a diagram showing a relationship between a waveguide layer film thickness and an equivalent refractive index of an optical waveguide in a conventional example.

FIG. 6 is a configuration diagram of an optical waveguide and a condensing device using the same in a conventional example.

FIG. 7: Polarization state and light input of the light collector in the conventional example,
Explanatory diagram showing the relationship between optical waveguide and optical output

[Explanation of symbols]

 1 Transparent Substrate 2 Phase Correction Layer 3 Buffer Layer 4 Waveguide Layer 5 Input Grating Coupler 6 Output Grating Coupler 7 Incident Light 8 Guided Light 9 Emitted Light 10 Reflected Surface 11 Reflected Light 12 Returned Guided Light

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kiyoko Oshima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A laser light source, a waveguide layer formed of a transparent layer, and input means for guiding laser light emitted from the laser light source into the waveguide layer and exciting guided light propagating in the waveguide layer. The waveguide layer has a second transparent layer having a higher refractive index than the waveguide layer with a first transparent layer having a lower refractive index interposed therebetween.
Which is laminated on the transparent layer of the TM and propagates in the waveguide layer
An optical waveguide, characterized in that the equivalent refractive index of mode-guided light is made equal to the equivalent refractive index of TE-mode guided light. 2. The second transparent layer is laminated on a fourth transparent layer having a higher refractive index than the waveguide layer with a third transparent layer having a lower refractive index than the waveguide layer sandwiched therebetween, 2. The optical waveguide according to claim 1, wherein the lamination is repeated one or more times. 3. A sixth transparent layer having a higher refractive index than the waveguide layer is laminated on the waveguide layer with a fifth transparent layer having a lower refractive index interposed therebetween, and the above lamination is performed once or more. The optical waveguide according to claim 1, which is repeated. 4. The input means is composed of a concave-convex periodic structure formed on a waveguide layer, the periodic structure forms concentric circles, and laser light is incident along a central axis A of the concentric circles. The optical waveguide according to claim 1. 5. An output means for radiating guided light to the outside of the waveguide layer is provided, and the output means is constituted by an uneven periodic structure formed on the waveguide layer, and the periodic structure defines the central axis A. 5. The collection according to claim 4, wherein the light radiated to the outside of the waveguide layer is condensed at one point by forming concentric concentric circles and making the period of the periodic structure denser toward the outer periphery. Light equipment.