JP3200007B2 - Optical coupler and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupler used for inputting light to an optical waveguide device, and a method for manufacturing the same.

[0002]

2. Description of the Related Art As an optical coupler used for inputting light to an optical waveguide element, for example, there is a prism coupler formed by pressing a prism against an optical waveguide and closely attaching the prism. In a prism coupler, when light enters near a boundary between a portion having a prism and a portion having no prism (hereinafter, referred to as an “edge” of the prism), an air gap between the prism and the optical waveguide is formed at the portion having the prism. The phenomenon that light that has passed through the tunnel and entered the optical waveguide does not exit the optical waveguide because the prism does not exist after the light is reflected on the substrate side, and propagates inside the optical waveguide. Use.

[0003] In a prism coupler, although the tolerance to the wavelength change of incident light is large, it is difficult to integrate the prism coupler and the optical waveguide. Therefore, conventionally, a prism coupler is formed by bonding a prism onto an optical waveguide with an adhesive.

FIGS. 12 (a) to 12 (c) show Japanese Unexamined Patent Publication No.
FIG. 1 is a cross-sectional view illustrating a configuration of a prism coupler described in Japanese Patent No. 9503.

In the configuration shown in FIG. 12A, a waveguide layer 202 of an optical waveguide is formed on a substrate 201, and further thereon,
Equivalent gap layer 203 having a lower refractive index than waveguide layer 202
To form Then, the prism 204 is bonded onto the equivalent gap layer 203 with an adhesive 205. In this case, light (not shown) incident on the prism 204 is effectively tunneled from the bonding portion 205 to the equivalent gap layer 203.
And enters the waveguide layer 202 and propagates through the waveguide layer 202.

[0006] In the configuration of FIG.
In the configuration shown in FIG. 7A, a light-shielding layer 207 made of a dielectric thin film is formed at an end of the bonding portion 205. FIG.
12C, the light shielding layer 206 made of a metal thin film is replaced with the equivalent gap layer 20 in the configuration of FIG.
3 is formed. These light shielding layers 207 and 20
6 has openings 211 and 212 of appropriate size. In each configuration, the light 209 incident on the prism 204 passes through the equivalent gap layer 203 from the bonding portion 205 in a tunnel effect, enters the waveguide layer 202, and propagates through the waveguide layer 202.

[0007] On the other hand, FIG.
Is a configuration of a prism coupler integrated with an optical waveguide element disclosed in Japanese Patent Application Laid-Open Publication No. H11-163,036. In this prism coupler, the dielectric film (second gap layer) 305 causes the light 30
A straight edge 309 is formed at the portion where the light 8 enters. The second gap layer 305 also has a function of suppressing the recombination of light from the optical waveguide, that is, the light coupled from the prism to the optical waveguide from returning to the prism side.

[0008] The optical waveguide included in the prism coupler of FIG. 13 is formed as follows. That is, the substrate 301
Is used, and an SiO ₂ layer is formed as a buffer layer 302 on the surface thereof. On the buffer layer 302, a SiON layer is formed as a core layer 303. Further, a first gap layer 304 and a second gap layer 305 each made of SiO ₂ are formed on the core layer 303. Thus, an optical waveguide is formed. Also,
A photocurable adhesive 306 is injected into a groove formed by not providing the second gap layer 305, and the prism 307 made of flint glass having a high refractive index is bonded to the optical waveguide by the adhesive 306. I have.

Next, the coupling principle of the prism coupler constructed as described above is as follows. The light 308 that has entered the prism 307 passes through the first gap layer 304 in a portion where the second gap layer 305 does not exist, and enters the core layer 303. The light entering the core layer 303 is reflected at the boundary between the buffer layer 302 and the core layer 303,
It proceeds again toward the surface of the optical waveguide. However, since the second gap layer 305 is present, the thickness of the film existing on the core layer 303 becomes relatively large, so that light cannot be transmitted out of the core layer 303. As a result, light is transmitted to the core layer 3 of the optical waveguide.
03, the light recombination decreases.

A photodiode 310 is provided at a predetermined position on the substrate 301. On the photodiode 310, a groove is provided in the buffer layer 302, and the core layer 303 is in direct contact with the substrate 301.
Light that has propagated inside the core layer 303 is guided to the photodiode 310 through this portion.

First gap layer 304 and second gap layer 3
05, the SiO ₂ layer forming these layers
Is etched at a predetermined location by an amount corresponding to the thickness of the second gap layer 305 to determine the thickness of the first gap layer 304, whereby the boundary between the portion where the second gap layer 305 exists and the portion where the second gap layer 305 does not exist is determined. Form.

[0012]

In the configuration shown in FIG. 12A, since the edge portion of the bonding portion 205 is not linear,
Even if an attempt is made to optimize an incident position (determined by a distance from the edge to the center of the spot) in the major axis direction of the incident light spot (an elliptical shape in which the incident direction is the major axis on the optical waveguide 202), the coupling efficiency ( The conversion efficiency from the incident light to the guided light inside the optical waveguide) changes according to the position in the minor axis direction. Therefore, it is difficult to accurately determine the incident position of the light at which the coupling efficiency is maximized. Even if the light incident position is determined at a certain position, the maximum coupling efficiency cannot always be obtained.

The requirement for the linearity of the line of intersection of the edge surface is determined relatively to the major axis of the incident beam spot. For example, for an incident beam having an incident beam spot having a major axis of about 10 μm, the coupling efficiency is reduced to 90% of the maximum efficiency with a displacement of ± 2.5 μm. For this reason, the straight line here is a straight line that can be regarded as a straight line even for a small incident beam, that is, a straight line having linearity obtained by photolithography. More specifically, it means a straight line having a degree of linearity and a deviation from the center line of about ± 0.5 μm or less.

On the other hand, in the configuration shown in FIG. 12B or 12C, a linear edge is formed in the bonding portion 205 by providing the light shielding layers 207 and 206.
However, for example, in the configuration of FIG.
Since only the equivalent gap layer 203 exists between the light shielding layer (metal thin film) 206 and the light shielding layer (metal thin film) 206, light propagating through the waveguide layer 202 is absorbed by the metal thin film 206 and gradually attenuated, thereby substantially reducing the coupling efficiency. To decline.

In the configuration of the prism coupler shown in FIG. 13, the refractive indices of the first gap layer 304 and the second gap layer 305 existing between the core layer 303, which is a waveguide layer, and the adhesive 306 are different from those of the first coupler. The difference from the refractive index of the layer 303 is relatively small. By providing the second gap layer 305, the core layer 303 existing on the second gap layer 305 can be formed.
High refractive index region having a higher refractive index (specifically,
Core layer 303 with adhesive 306 and prism 307)
Of the optical waveguide around the core layer 303 is hardly emitted to the outside. However, the core layer 303 where the power of the guided light is concentrated and the high refractive index region are different from the second gap layer 30.
5 also did not completely separate. Therefore, light loss due to recombination occurs as much as the high refractive index region protrudes from the light incident position in the light propagation direction. This recombination is
Theoretically, the second gap layer 305 can be completely removed by making the thickness sufficiently large. But the second
Thickening the gap layer 305 may cause undesired effects such as an increase in film stress or a change in the characteristics of the optical waveguide element in which the optical coupler is integrated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has the following objects. (1) Coupling efficiency by recombination without increasing the thickness of a film laminated on an optical waveguide device. And (2) to provide a method for manufacturing such an optical coupler.

[0017]

An optical coupler according to the present invention comprises a substrate and an optical waveguide structure laminated on the substrate,
At least a first dielectric layer laminated on the substrate;
An optical waveguide structure including a second dielectric layer laminated on the dielectric layer, light incident means provided on the optical waveguide structure, and bonding the light incident means to the optical waveguide structure a bonding portion, an optical coupler having a refractive index of the adhesive portion n _b, the refractive index n ₁ of the first dielectric layer, and between the refractive index n ₂ of the second dielectric layer _{, n b> n 1> n} 2 the relationship is satisfied, the adhesive portion has an edge surface intersecting the surface of the optical waveguide structure, line of intersection between the edge surface and the surface of the optical waveguide structure is linear The light incident means protrudes from the edge surface by a length P _L in the light traveling direction in the optical waveguide structure, and is provided between the protrusion and the surface of the optical waveguide structure. An air gap having a height equal to or higher than the height of the edge surface is provided, thereby achieving the above object.

[0018] Preferably, the height h of the edge surface, the refractive index of air n _a, the refractive index n _s of the substrate, the refractive index n _b of the adhesive portion, the refractive index n ₁ of the first dielectric layer , The refractive index n ₂ of the second dielectric layer, the thickness t of the first dielectric layer, the thickness u of the second dielectric layer, and the length P of the projection of the light input means.
_L is set so as to satisfy the following relational expressions (1) and (2) (where α _{r in the} relational expression (1) is a function of h, and The imaginary part of the imaginary solution of the equation (2) has the larger absolute value).

[0019]

(Equation 3)

[0020]

(Equation 4)

Preferably, the effective refractive index for TE light and the effective refractive index for TM light are substantially equal. For example, the refractive index of the substrate n _s = about 1.44, the refractive index of the bonding portion n _b = about 1.57, and the refractive index of the first dielectric layer n ₁
= About 1.53, the refractive of the second dielectric layer constant n ₂ = approximately 1.
43, the thickness t of the first dielectric layer is about 570 nm, and the thickness u of the second dielectric layer is about 100 nm.

In one embodiment, the light incident means is a prism.

In another embodiment, the light incident means is a dielectric plate bonded to the substrate at a predetermined angle.

Preferably, the refractive index of the light incidence means is substantially equal to the refractive index of the bonding portion.

According to another aspect of the present invention, there is provided a method for manufacturing an optical coupler having the above configuration. Forming the optical waveguide structure on the substrate; applying a photoresist to a surface of the optical waveguide structure; forming a groove in the photoresist; Disposing the light incident means, bonding the light incident means to the optical waveguide structure with an adhesive, and removing the photoresist, thereby achieving the object. Achieved.

Preferably, the adhesive is a photo-curable adhesive.

In one embodiment, the light incident means is a prism, and the bonding and fixing step includes a step of disposing the prism on the groove and a step of injecting the adhesive into the groove to form the prism. Adhesively fixing the optical waveguide structure;
Further included.

In another embodiment, the light incident means is a dielectric plate, and the bonding and fixing step holds the dielectric plate at a predetermined angle with respect to the surface of the optical waveguide structure. And supplying the adhesive so as to cover the groove, and bonding and fixing the dielectric plate to the optical waveguide structure.
Further included.

Preferably, in the step of forming a groove in the photoresist, RIE is performed as a post-process of forming the groove.
The method further includes a step of performing a treatment (oxygen plasma treatment).

Hereinafter, the operation will be described.

The optical coupler of the present invention having the above-described structure is
It is formed integrally with an optical waveguide element having an optical waveguide structure. At this time, the adhesive forming the bonding portion bonds the optical waveguide structure and the light incident means (that is, the prism or the dielectric plate), and at the same time, the edge surface formed on the bonding portion performs a bonding function. As a result, the optical coupler can be integrated with the optical waveguide element without increasing the thickness of the second dielectric layer included in the optical waveguide structure without obstructing the function thereof, and the increase in film stress can be prevented. Problems can be avoided.

Also, by appropriately setting the height of the edge surface of the bonding portion from the surface of the optical waveguide structure (for example, the surface of the second dielectric layer), the position of the edge surface above the second dielectric layer can be reduced. Regions (prisms and adhesive portions) having a higher refractive index than one dielectric layer can be completely separated from the optical waveguide structure.
Thus, the loss due to the recombination can be fundamentally removed, and the recombination can be reduced without increasing the thickness of the optical waveguide when the optical coupler is integrated with the optical waveguide element.

Further, by appropriately setting the thickness and the refractive index of the film of each part constituting the optical coupler, the coupling efficiency for TE light and TM light can be made substantially equal. Furthermore, by making the refractive index of the bonding portion equal to that of the light incident means (prism or dielectric plate), the reflectance at the interface between them can be minimized. When a prism is used, multiple reflections caused by the adhesive acting like a thin film due to the small thickness of the adhesive existing between the prism and the optical waveguide can be almost completely removed.

In the method for manufacturing an optical coupler according to the present invention,
The edge surface of the bonding portion that performs the optical coupling function is formed by transferring the shape of the groove formed by the photoresist, and its height is determined by the thickness of the photoresist. Therefore, if the photoresist is thickened, the optical waveguide structure (second
Dielectric layer) As the height of the edge surface of the bonding part from the surface,
A height sufficient to completely eliminate the effects of recombination can be secured.

If a photo-curable adhesive is used, the manufacturing time can be shortened, and the displacement of the light incident means (prism or dielectric plate) in the process of solidifying the adhesive is suppressed, and the coupling efficiency is reduced. Contributes to prevention of deterioration. In addition, since the dielectric plate is easier to process than the prism, if the optical coupler is formed using the dielectric plate, the manufacturing cost can be reduced as compared with the case where the prism is used.

Further, before adhering the light incident means (prism or dielectric plate) to the surface of the optical waveguide, as a post-processing of the groove forming step, an organic solvent of the resist developing solution generated on the surface of the optical waveguide in the groove forming process. If RIE processing (oxygen plasma processing) is performed to remove the residue or remove the altered layer on the surface of the optical waveguide, the adhesive strength at the time of bonding the light incident means to the optical waveguide is increased.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a sectional view showing a configuration of an optical coupler 100 according to a first embodiment of the present invention.

In the optical coupler 100 shown in FIG. 1, the first dielectric layer 1 and the second dielectric layer 2 are laminated on the substrate 3 to form the optical waveguide 6. On the second dielectric layer 2, the prism 4 is provided with an adhesive portion 5 on which an edge surface 7 for coupling is formed.
Is glued through. Here, it is preferable that the adhesive used as the bonding part 5 is transparent. Edge surface 7 of bonding portion 5
Intersects the surface of the optical waveguide 6, and the line of intersection between the edge surface 7 and the surface of the optical waveguide 6 is a straight line. The prism 4 protrudes from the edge surface 7 by a certain length in the light traveling direction in the optical waveguide 6, and a predetermined distance equal to the height of the edge surface 7 is provided between the protrusion and the surface of the optical waveguide 6. Is provided.

In the configuration shown in FIG. 1, the prism 4 is connected to the optical waveguide 6
The optical coupler 100 is formed by adhering to the optical coupler 100. The prism 4 plays a role of guiding incident light from the air to a region having a higher refractive index than the waveguide 6.
On the other hand, what actually relates to the light coupling is the edge surface 7 of the bonding portion 5. The light coupling principle will be described below. Edge surface 7 of bonding portion 5 from inside prism 4
Is incident on the boundary between the bonding portion 5 and the second dielectric layer 2 at an incident angle of total reflection, and passes through the second dielectric layer 2 in a tunnel effect. It enters the first dielectric layer 1. However, the light does not pass through the substrate 3 but is totally reflected at the boundary between the substrate 3 and the first dielectric layer 1 and travels toward the surface of the optical waveguide 6. However, this time the first dielectric layer 1
Since there is no bonding portion 5 in contact with the second dielectric layer 2 above, the light is totally reflected in the direction of the substrate 3. Thereafter, the light propagates inside the optical waveguide 6 while repeating such total reflection at the upper and lower boundaries of the optical waveguide 6.

Hereinafter, constituent materials of the optical coupler 100 of FIG. 1 will be described.

The constituent material of the substrate 3 is appropriately selected depending on the use of the optical waveguide element in which the optical coupler 100 is integrally formed. Specifically, in addition to being able to use a simple dielectric substrate such as a glass substrate, when used as an optical coupler for an optical waveguide element integrated with a light receiving element, a dielectric layer is formed on a Si substrate. Substrates that have been used can be used. As the dielectric layer, SiO
_Two layers, a phosphorus-doped silicate glass (PSG) layer, a spin-coatable glass material (SOG) layer, or the like is formed.

The constituent material of the first dielectric layer 1 is the optical coupler 1
Although 00 changes depending on the material of the waveguide layer of the optical waveguide element formed integrally, SiON known as a constituent material of the waveguide layer, or # 7059 glass manufactured by Corning Incorporated is used. Can be. In the present embodiment, # 7059 glass manufactured by Corning is used as the first dielectric layer 1.

As the constituent material of the second dielectric layer 2, a material having a lower refractive index than that of the first dielectric layer 1 is used. For example, when # 7059 glass manufactured by Corning is used as the first dielectric layer 1 as described above, Si
O ₂ or SOG is used.

Referring to FIGS. 2A and 2B and FIG. 3, the optical coupler 100 shown in FIG. 1 is replaced with an optical waveguide shown in FIGS. 2A and 2B in top view and sectional view. A configuration formed integrally with the element will be described. The optical coupler 100 has the configuration shown in FIG.
It is formed in a region shown as “A” in FIG. In addition,
In the following description, the prism 104, the bonding portion 105, the first
Dielectric layer 101, second dielectric layer 102, and substrate 103
(However, when the substrate 3 is a substrate in which a dielectric layer is formed on the surface of a semiconductor substrate such as Si or a metal substrate, the dielectric layer is set to n _p , n _b , n _1). , N ₂ and n _s .

As shown schematically in the top view of FIG. 2 (a), this optical waveguide element has
The two kinds of polarized light of the E light and the TM light are separated into each other by the polarization separating unit 109, and thereafter, the different photodiodes 10 are used.
It is configured to receive light at 8a and 108b. Also,
In this optical waveguide device, as shown in the cross-sectional view of FIG. 2B, a Si substrate 111 on which a photodiode 108 (generally showing 108a and 108b in FIG. 2A) is formed.
A substrate 103 having a dielectric layer 110 formed on the surface thereof is used. On a surface of the substrate 103 corresponding to the polarization separating portion 109, a height of about 80 having a tapered end portion is provided.
A Ta ₂ O ₅ layer 109 a of nm is formed. further,
On their outermost surface, a Corning #
A 7059 glass layer 101 (refractive index n ₁ = about 1.53) is laminated to a thickness of about 570 nm. Thus, the optical waveguide 106 is configured. In the above configuration, the Si substrate 1
As the dielectric layer 110 on the surface of 11, an SiO ₂ layer having a refractive index n _s = about 1.44 is provided. Each of the above refractive index values is a measured value with respect to light having a wavelength of 780 nm.

FIG. 3 is a sectional view showing a configuration in which the optical coupler 100 of FIG. 1 is formed in the region A (see FIG. 2A) of the optical waveguide device having the above configuration. In this case, the # 7059 glass layer 101 functions as the first dielectric layer 1 in the configuration of FIG. 1 and further has a refractive index n _{2 of} about 1 that functions as the second dielectric layer 2 of FIG. forming a SiO ₂ layer 102 having a .43. And then,
The prism 104 is connected to the second dielectric layer 1 via the bonding portion 105.
02 to form the optical coupler 100. The refractive index value n of the second dielectric layer (SiO ₂ layer) 102
₂ is smaller than the refractive index values n ₁ , n _p and n _b of the first dielectric layer 101, the prism 104 and the bonding portion 105.

The refractive index n _p of the prism 104 is n ₁ , n ₂
And n _s . In particular, in order to suppress the reflection of light at the interface between the prism 104 and the bonding portion 105, it is desirable that the refractive index is equal to or close to the refractive index n _b of the bonding portion 105. For example, prism 1
04 and the angle of incidence of the light on the interface theta _bi between the adhesive portion 105
In order to suppress the reflectance at the interface between the prism 104 and the bonding portion 105 to a desired value R or less, the bonding portion 1
It is necessary to set the refractive index n _{b of} 05 so as to satisfy the following two conditional expressions.

[0048]

(Equation 5)

[0049]

(Equation 6)

For example, when the prism 104 is formed of a material having a refractive index n _p = about 1.57 (for example, glass material LF5), the reflection at the interface between the prism 104 and the bonding portion 105 is reduced to almost zero. For this purpose, the refractive index n of the prism 104
_The bonding portion 105 is formed by a UV-curable adhesive having a refractive index n _b close to _p = 1.57. Specifically, LX-2310C manufactured by Loctite Co., Ltd. can be used.

Next, a method for setting the thickness of the second dielectric layer 102 will be described.

In order to make the coupling efficiency for the TE polarized light and the coupling efficiency for the TM polarized light approximately equal and close to the maximum value as much as possible in the prism coupler of this embodiment,
As almost equal to the optimum incidence angle theta _TM for the optimum incidence angle theta _TE and TM light to TE light, constituting the optical coupler 100. Here, using the effective refractive indices N _TE and N _TM (the value obtained by dividing the phase constant of each mode in the optical waveguide by the wave number k _o = 2π / λ (λ is the wavelength)) for the TE light and the TM light,

[0053]

(Equation 7)

[0054]

(Equation 8)

Considering the following relational expression, the condition for making θ _TE and θ _TM substantially equal is N _TE ≒ N _TM .

The effective refractive indices _NTE and _NTM are the refractive indices of air, the bonding portion 105, the first dielectric layer 101, the second dielectric layer 102, and the substrate 103, respectively, n _a , n _b , n ₁ , n ₂ ,
And n _s, and the first dielectric layer 101 and the second dielectric layer 1
02 are t and u, respectively, and the height of the edge surface of the bonding portion 105 from the surface of the second dielectric 102 is h, the complex solution of the equation contained in the following relational expression (2) It can be obtained as the real part of β _TE and β _TM .

[0057]

(Equation 9)

In the equation in the above relational expression (2), h = 0 in a portion where light enters. The refractive index and the thickness of the film of each part constituting the optical coupler 100 are respectively n _a =
When 1.0, n _b = about 1.57, n ₁ = about 1.53, n ₂ = about 1.43, n _s = about 1.44, and t = about 570 nm, u = about 100 nm. Solving the above equation gives N _TE = 1.4852 and N _TM = 1.4842
And _NTE ≒ _NTM is satisfied. Therefore, the thickness and the value of the refractive index of each part constituting the optical coupler 100 may be set as described above.

Next, the shape of the prism 104 will be described.

When a trapezoidal prism is used as the prism 104, the base angle φ of the prism 104 shown in FIG.
By making approximately equal to the angle θ _op shown below,
The inclined surface of the prism 104 is substantially perpendicular to the optimal incident direction of each of the TE polarized light and the TM polarized light, so that the coupling efficiencies for both polarized lights are substantially equal and approach the maximum value.

[0061]

(Equation 10)

N _TE = 1.4852 and N _TM determined earlier
= 1.4842, from the above equation, θ _op = about 71 °. Therefore, the base angle of the prism 104 is about 71 °.
In addition to the setting of the shape, by applying an anti-reflection coating to the surface of the prism 104, the prism 1
04, the reflectance at the incident surface can be further reduced.

The shape of the prism may be determined so that the loss due to reflection in the light incident direction is minimized. For example, in addition to the shape shown in FIG. 1, a prism 4a having a shape in which incident light is once totally reflected on a surface and then made incident on an optical waveguide, such as an optical coupler 150 shown in FIG. 4, may be used. Note that, in FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

Next, a method of determining the height h of the edge surface of the bonding portion 105 from the surface of the second dielectric layer 102 will be described with reference to FIG.

In the optical coupler 100 of the present embodiment, if the height h of the edge surface is not sufficient, the optical coupler 100 is directed toward a high refractive index region such as the prism 4 existing above the optical waveguide 6 by a distance h. As shown in FIG. 5, the guided light propagating through the optical waveguide 6 is transmitted (recombined), and the coupling efficiency is reduced. Accordingly, the length of the prism 4 protruding from the light incident position shown in FIG. 5 is represented by P _L, and the radiation coefficients (the imaginary parts of the complex solutions β _TE and β _TM of the above-described equations) for both TE and TM polarized light are represented by P _L. When the larger absolute value is α _r (a function of h), the height h of the edge surface of the bonding portion 5 from the surface of the optical waveguide 6 (specifically, the second dielectric layer) is It is desirable to satisfy the following expression.

[0066]

[Equation 11]

FIGS. 6A to 6C show that the wavelength of light is 780.
nm, the substrate 103 has a refractive index of about 1.44, the first dielectric layer 101 has a refractive index of about 1.53, and the second dielectric layer 102 has a refractive index of about 1.53.
11 is a graph showing the relationship between the height h of the edge surface at the bonding portion 105 and the normalized transmission power when the prism 104 is bonded to the optical waveguide 106 having a refractive index of about 1.43. Here, the normalized transmission power is the recombination loss
Loss from the maximum coupling efficiency due to loss (
(Equivalent to the left side) is subtracted from the maximum coupling efficiency . The vertical axes in FIGS. 6A to 6C are for 1 mm propagation (PL = 1 m
m), the closer the value is to 1, the smaller the decrease in coupling efficiency due to recombination.
FIGS. 6A, 6B and 6C are graphs when the refractive index n _{p of the} prism is 1.58, 1.57 and 1.56, respectively. However, it is assumed that the refractive index of the bonding portion 105 is substantially equal to the refractive index of the prism. FIG. 6 (a)
In the graphs of (c) to (c), when the thickness of the first dielectric layer 101 is about 100 nm when the TE polarized light is incident, and when the thickness of the first dielectric layer 101 is about 50 nm when the TE polarized light is incident. Shows data when the thickness of the first dielectric layer 101 is about 100 nm when the TM polarized light is incident, and shows data when the thickness of the first dielectric layer 101 is about 50 nm when the TM polarized light is incident.

As shown in FIGS. 6A to 6C, even if the refractive index of the bonded portion changes, the height h of the edge surface of the bonded portion is changed.
Is about 0.6 μm or more, recombination can be completely suppressed, and a decrease in coupling efficiency can be suppressed.

Next, the optical waveguide of the optical input section (portion for forming the optical coupler) in FIG.
With reference to (a) to (g), a method for manufacturing the optical coupler in the present embodiment will be described.

First, as shown in FIG. 7A, a photoresist 51 is applied on the optical waveguide 52. here,
The thickness w of the photoresist 51 corresponds to the height h of the edge surface. As described above, the height h of the edge surface is about 0.6.
If it is not less than μm, a decrease in the coupling efficiency due to recombination can be almost eliminated. Therefore, the thickness w of the photoresist 51 also needs to be at least about 0.6 μm or more. However, since the refractive index of the adhesive changes under various conditions such as the ambient temperature, the height h of the edge surface of the bonding portion is determined so that the adhesive between the prism 54 and the optical waveguide 52 does not function as a thin film. The thickness w of the photoresist 51 is
It is preferable that the thickness be sufficiently thicker than 0.6 μm. Here, the condition that the adhesive between the prism 54 and the optical waveguide 52 does not function as a thin film is to determine the thickness w of the photoresist 51 so as to suppress multiple reflection,
The effect can be almost completely eliminated by removing multiple reflections in the range based on the beam diameter L. Therefore, the setting condition of the thickness w of the photoresist 51, that is, the height h of the edge surface in consideration of the influence of multiple reflection is

[0071]

(Equation 12)

Is as follows.

Next, a sectional view of FIG. 7B and FIG.
As shown in the top view, a photoresist 51 is patterned to form a groove 53 for injecting an adhesive. On this occasion,
Before the prism 54 is bonded, as a post-processing of the step of forming the groove 53, removal of the organic residue of the resist developing solution generated on the surface of the optical waveguide 52 in the process of forming the groove 53 and the optical waveguide 5
It is preferable to perform RIE processing (oxygen plasma processing) for removing the deteriorated layer on the surface of No. 2. Thereby, the adhesive force when bonding the prism 54 to the optical waveguide 52 is increased.

Subsequently, the sectional view of FIG.
As shown in the top view of (e), the position of the prism 54 is
The position is adjusted using the position adjusting device 57 so that the edge B is parallel to the edge C of the groove 53 on the photoresist 51. After the adjustment, the prism 54 is pressed against the photoresist 51 applied on the optical waveguide 52 while holding the adjustment device 57 at the adjusted position. At this time, as shown in FIG.
When the optical waveguide 52 is disposed, the prism 54 comes into contact with the surface of the photoresist 51 at two places.
Of the prism 54 and the bottom surface of the prism 54 are improved. As a result, when the light is incident at the optimum incident angle at which the coupling efficiency to the optical coupler is maximized, the optical waveguide 5 at the base angle of the prism 54 determined to minimize the reflection at the incident surface is minimized.
2 can be minimized from the angle between the surface and the angle of incidence. As a result, it is possible to suppress a decrease in coupling efficiency due to a shift of the incident angle to the optical coupler from the optimum incident angle. The above effect can be enhanced by pressing the prism 54 against the surface of the optical waveguide 52 when fixing the prism 54.

Subsequently, as shown in FIG.
A photo-curable adhesive 55 such as UV-curable is injected into the substrate. Then, light such as UV light is irradiated to solidify the adhesive 55, and the prism 54 is fixed. Here, the adhesive 55 to be used may be other than a photo-curable one. However, if a photo-curable adhesive is used, the time required for fixing is reduced, and the displacement of the prism 54 at the time of fixing may be reduced. It is possible to reduce the decrease in the coupling efficiency caused by this. In addition, as for the selection of the adhesive 55 and the photoresist 51, a combination that is chemically stable when both are in contact with each other is selected. For example, when LX-2310C manufactured by Loctite is used for the adhesive 55, the photoresist 51 may be selected from a positive type photoresist PMER manufactured by Tokyo Ohka Co., Ltd.

After fixing the prism 54, FIG.
The photoresist 51 is removed as shown in FIG. here,
The removal of the portion of the photoresist 51 sandwiched between the adhesive 55 and the optical waveguide 52 proceeds faster as the gap between the adhesive 55 and the optical waveguide 52 is wider. Therefore, in order to facilitate removal of the photoresist 51 in this portion, it is preferable to apply the photoresist 51 thickly. For example, a thick photo-resist 51 is applied. Specifically, a positive photoresist P manufactured by Tokyo Ohka Co., Ltd.
MER is applied in a layer of about 15 μm, and the total thickness w is set to about 30 μm (one layer is applied, baked and the next layer is applied again). As a result, the height h of the edge surface 56 of the bonding portion 55 of the optical coupler is about 30 μm.

Through the above steps, the photoresist 51
The edge surface 56 corresponding to the edge of the prism 54 is formed by the adhesive 55 in a manner in which the groove shape is transferred. Here, the line of intersection between the edge surface 56 and the surface of the optical waveguide 52 is a straight line.

When defining the height h of the edge surface 56, the edge surface 56 of the photoresist 51 intersects the surface of the optical waveguide 52 at 90 °, but this is not necessarily required to be 90 °. There is no. For example, this angle can be smaller than 90 ° (70 ° in FIG. 8A) depending on the conditions at the time of exposure and development of the resist, as in the optical coupler 170 shown in FIG. 8A. . In this case, the edge surface 56 of the bonding portion 55 of the optical coupler 170 is connected to the optical waveguide 5.
Make an angle of about 70 ° with the surface of the second. Thus, even if the edge surface 56 is inclined with respect to the surface of the optical waveguide 52, the propagation length is short at the inclined portion, so that the coupling efficiency of the optical coupler does not decrease. Further, even if the inclination direction is reversed, no problem occurs similarly.

In the manufacturing process, it is difficult to bring the prism 54 and the photoresist 51 into complete close contact with each other. Therefore, the adhesive flows into the gap between the photoresist 51 and the prism 54, and The final shape after the removal may be as shown in FIG. 8B. However, in the optical coupler 180 of FIG. 8B, only a part of the prism 54 involved in the recombination is replaced by the adhesive, and if the difference in the refractive index between the adhesive and the prism is small, the optical coupling 180 The characteristics of the vessel do not change significantly. Further, if the height h of the edge surface 56 of the bonding portion 55 is sufficiently high, no inconvenience occurs. FIG. 8 (b)
The height h of the edge surface 56 in the optical coupler 180 is as shown in the figure.

8A and 8B, FIG.
The same components as those in (a) to (g) are denoted by the same reference numerals, and a detailed description thereof will be omitted here.

Next, the coupling efficiency of the optical coupler according to the present embodiment will be described.

The major diameter of the beam spot (L in FIG. 3) is about 1
The incident light of 0 μm is converted to an optimum incident angle (the incident angle θ in FIG. 3).
_i coincides with θ _op ), and is approximately 4
The coupling efficiency when the incident beam is incident such that the center of the incident beam is positioned at a distance of μm is about 80% for each of the TE polarized light and the TM polarized light. It should be noted that the coupling efficiency is _expressed by exp for the imaginary parts α _r of the complex solutions β _TE and β _TM of the above equation.
Field distribution in the x direction on the optical waveguide is represented by _{(-k o α r x) (} x -direction is perpendicular to the optical waveguide, the traveling direction of light) and, overlapping the x-direction of the Gaussian distribution shape of the incident light It can be obtained by integration.

(Second Embodiment) FIG. 9 shows a second embodiment of the present invention.
It is sectional drawing which shows the structure of the optical coupler 200 in embodiment.

In the optical coupler 200 shown in FIG. 9, the first dielectric layer 11 and the second dielectric layer 12 are laminated on the substrate 13 to form the optical waveguide 16. Second dielectric layer 12
On top of this, a dielectric plate 14 is bonded via a bonding portion 15 on which an edge surface 17 for coupling is formed. here,
It is preferable that the adhesive used as the bonding portion 15 is transparent. The edge surface 17 of the bonding portion 15 intersects the surface of the optical waveguide 16, and the line of intersection between the edge surface 17 and the surface of the optical waveguide 16 is a straight line. The bonding portion 15 protrudes from the edge surface 17 by a certain length in the light traveling direction in the optical waveguide 16, and is equal to the height of the edge surface 17 between the protrusion and the surface of the optical waveguide 16. An air gap of a predetermined height or more is provided.

The dielectric plate 14 is perpendicular to the incident direction defined by the incident angle θ _OP of the optical coupler 200 determined from the effective refractive indexes N _TE and N _TM of the TE light and TM light in the optical coupler 200. In other words, the position is adjusted so that the angle φ formed by the dielectric plate 14 with respect to the surface of the optical waveguide 16 is substantially equal to the incident angle θ _OP . After the adjustment of the position, the dielectric plate 14 is bonded to the optical waveguide 16 with the adhesive 15 as described above.

The incident light transmitted through the bonding portion 15 from the dielectric plate 14 and reaching the vicinity of the edge surface 17 of the bonding portion 15 is
The light enters the boundary between the bonding portion 15 and the second dielectric layer 12 and further passes through the second dielectric layer 12 in a tunnel effect and enters the first dielectric layer 11. The light does not pass through the substrate 13 but is totally reflected at the boundary between the substrate 13 and the first dielectric layer 11 and travels toward the surface of the optical waveguide 16. However, the light is totally reflected in the direction of the substrate 13 because there is no bonding portion 15 in contact with the second dielectric layer 12 on the optical waveguide 16 this time. Thereafter, the light propagates inside the optical waveguide layer 16 while repeating such total reflection at the upper and lower boundaries of the optical waveguide layer 16.

Hereinafter, constituent materials of the optical coupler 200 shown in FIG. 9 will be described.

The constituent material of the substrate 13 is appropriately selected depending on the use of the optical waveguide device forming the optical coupler 200. Specifically, in addition to being able to use a simple dielectric substrate such as a glass substrate, in addition to using an optical coupler for an optical waveguide element integrated with a light receiving element, S
A substrate in which a dielectric layer is formed on an i-substrate can be used. As the dielectric layer, an SiO ₂ layer, a phosphorus-doped silicate glass (PSG) layer, a spin-coatable glass material (SOG) layer, or the like is formed.

In the present embodiment, a substrate 13 having a surface on which a SiO ₂ layer having a refractive index n _{s of} about 1.44 is formed is used.

The constituent material of the first dielectric layer 11 changes depending on the material of the waveguide layer of the optical waveguide element in which the optical coupler 200 is integrally formed, and is known as the constituent material of the waveguide layer. SiON or # 7059 glass manufactured by Corning Incorporated can be used. In the present embodiment, Corning # 7059 glass having a refractive index n _{1 of} about 1.53 is used as the first dielectric layer 11. Further, the thickness t of the first dielectric layer 11 is about 570 nm.

The constituent materials of the second dielectric layer 12 include:
A material having a lower refractive index than the first dielectric layer 11 is used. For example, when Corning # 7059 glass is used as the first dielectric layer 11 as described above,
SiO ₂ or SOG is used.

Referring to FIG. 10, optical coupler 2 shown in FIG.
00 is integrated with the optical waveguide device whose top view and cross-sectional view are shown in FIGS. 2A and 2B. FIG. 10 is a cross-sectional view showing a configuration in which the optical coupler 200 of FIG. 9 is formed in a region A (see FIG. 2A) of the optical waveguide element. The configuration of the optical waveguide element is the same as that described in the first embodiment, and the same components are denoted by the same reference numerals, and the detailed description thereof will not be repeated.

Next, a method for setting the thickness of the second dielectric layer 102 will be described.

In the prism coupler of this embodiment, as in the first embodiment, the coupling efficiency for TE polarized light and the coupling efficiency for TM polarized light are made substantially equal and as close as possible to the maximum value. The optical coupler 200 is configured so that the incident angle θ _TE and the optimum incident angle θ _TM for TM light are substantially equal. As described above, in order to achieve this object, the thickness of the second dielectric layer 102 is set so that the effective refractive indexes N _TE and N _TM for TE light and TM light satisfy N _TE ≒ N _TM. decide. For example, the second dielectric layer 102 is formed using an SiO ₂ layer having a refractive index n ₂ = about 1.43, and optically coupled using a UV curable adhesive LX-2310C manufactured by Loctite as the adhesive 15. When forming the container 200, the thickness u of the second dielectric layer 102 is set to about 100 nm.

At this time, as in the first embodiment, N _TE = 1.4852 and N _TM = 1.4842, and N _TE ≒ N _TM is satisfied. Also, at this time, since the optimal incident angle θ _op to the optical coupler 200 is about 71 °, the reflection on the surface of the dielectric plate 114 when the light is incident at the optimal incident angle The position is adjusted by inclining about 71 ° with respect to the surface of the optical waveguide so that the adhesive 11
Adhere with 5. In addition to such settings, the dielectric plate 11
By applying an anti-reflection coating to the surface of No. 4, the reflectance at the incident surface of the dielectric plate 114 can be further reduced.

The second dielectric layer 1 on the edge surface of the bonding portion 115
The height h from the surface of No. 02 is determined in the same manner as in the first embodiment. Specifically, the wavelength of light is set to 780
nm, the substrate 103 has a refractive index of about 1.44, the first dielectric layer 101 has a refractive index of about 1.53, and the second dielectric layer 102 has a refractive index of about 1.53.
Has a refractive index of about 1.43, and the bonding section 115 has a refractive index of about 1.
57, and the thicknesses t and u of the first and second dielectric layers 101 and 102 are t = about 570 nm and u = about 1 respectively.
00 nm, the height h of the edge surface of the bonding portion 115
Is about 0.6 μm or more, recombination can be completely suppressed, and a decrease in coupling efficiency can be suppressed.

Further, it is preferable that the difference in the refractive index between the bonding portion 115 and the dielectric plate 114 is small. For example, the bonding portion 1
15 at a boundary between the dielectric plate 114 and the dielectric plate 114 is a predetermined value R
In order to make the following, since light is incident on the dielectric plate 114 almost perpendicularly, the refractive index n _b of the adhesive forming the bonding portion 115 and the refractive index n _p of the dielectric plate 114

[0098]

(Equation 13)

The following relationship is set.

For example, Loctite L is used as an adhesive.
When X-2310C is used, its refractive index is about 1.57, so in order to minimize the reflectance R,
It is preferable to use a material having a refractive index of about 1.57 for the dielectric plate 114. Since the processing of the dielectric plate is easier than the processing of the prism, the optical coupler 200 of the present embodiment shown in FIG. 9 is lower in cost than the optical coupler 100 of the first embodiment shown in FIG. It can be manufactured by

Next, referring to FIGS. 11A to 11F, the optical waveguide of the optical input section (portion for forming the optical coupler) in FIG. Will be described.

First, as shown in FIG. 11A, a photoresist 51 is applied on the optical waveguide 52. Here, the thickness w of the photoresist 51 is the height h of the edge surface.
Corresponding to As described above, when the height h of the edge surface is about 0.6 μm or more, it is possible to almost eliminate the decrease in coupling efficiency due to recombination. Therefore, the photoresist 5
The thickness w of 1 also needs to be at least about 0.6 μm or more. However, since the refractive index of the adhesive changes under various conditions such as ambient temperature, the thickness w of the photoresist 51 that determines the height h of the edge surface of the bonding portion is set so that the adhesive does not function as a thin film. It is preferable that the thickness be sufficiently thicker than 0.6 μm.

Next, as shown in the sectional view of FIG. 11B, the photoresist 51 is patterned to form a groove 53 for injecting an adhesive. At this time, before bonding the dielectric plate 61, as a post-processing of the step of forming the groove 53, removal of the organic residue of the resist developing solution generated on the surface of the optical waveguide 52 in the process of forming the groove 53 and removal of the optical waveguide 52 It is preferable to perform RIE processing (oxygen plasma processing) for removing the altered layer on the surface. Thereby, the adhesive force when bonding the dielectric plate 61 to the optical waveguide 52 is increased.

Subsequently, the sectional view of FIG.
As shown in the top view of (d), the position of the dielectric plate 61 is
The position is adjusted using the position adjusting device 62 so that the edge B ′ is parallel to the edge C ′ of the groove 53 on the photoresist 51. After the adjustment, the adjusting device 6 is moved to the adjusted position.
The dielectric plate 61 is placed on the surface of the photoresist 51 applied on the optical waveguide 52 while holding the substrate 2. In this state, photocurable (for example, UV curable) so as to cover the groove 53.
An adhesive 63 is injected to bond the dielectric plate 61.

Subsequently, as shown in FIG.
The adhesive 63 is solidified by light irradiation such as light, and the dielectric plate 61 is fixed. Here, the adhesive 63 to be used may be other than a photo-curable one. However, if a photo-curable adhesive is used, the time required for fixing is shortened, and the displacement of the dielectric plate 61 during fixing is reduced. Thus, it is possible to reduce a decrease in coupling efficiency caused by the above. The selection between the adhesive 63 and the photoresist 51 is based on the fact that the adhesive does not dissolve the photoresist and changes other than solidification of the adhesive 63 by irradiation with UV light (for example, generation of gas at the boundary between the two). ) Does not occur, and a combination that is chemically stable when both come into contact with each other is selected. For example, when LX-2310C manufactured by Loctite is used as the adhesive 63, a positive photoresist PMER manufactured by Tokyo Ohka Co., Ltd. may be selected as the photoresist 51.

After fixing the dielectric plate 61, FIG.
The photoresist 51 is removed as shown in FIG. Here, the removal of the portion of the photoresist 51 sandwiched between the adhesive 63 and the optical waveguide 52 proceeds faster as the gap between the adhesive 63 and the optical waveguide 52 is wider. Therefore, in order to facilitate removal of the photoresist 51 in this portion, it is preferable to apply the photoresist 51 thickly. For example, a thick photo-resist 51 is applied. Specifically, a positive photoresist PMER manufactured by Tokyo Ohka Co., Ltd. is applied in a layer of about 15 μm, and the total thickness w is set to about 30 μm. Do). As a result, the height h of the edge surface 64 of the bonding portion 63 of the optical coupler is about 30 μm.

Through the above steps, the photoresist 51
The edge surface 64 is formed by transferring the groove shape of
3 is formed. Here, the edge surface 64 and the optical waveguide 52
The line of intersection with the surface of is a straight line.

The edge surface 64 of the photoresist 51 does not necessarily need to be 90 ° with respect to the surface of the optical waveguide 52. Even if the edge surface 64 is inclined with respect to the surface of the optical waveguide 52, the coupling efficiency of the optical coupler does not decrease.

Note that the optical coupler of this embodiment also
The incident light whose major diameter (L in FIG. 10) of the beam spot is about 10 μm is converted into an optimum incident angle (the incident angle θ _{1 in} FIG. 10 is θ _op).
), The coupling efficiency is approximately 80% for each of the TE-polarized light and the TM-polarized light when the incident beam is incident such that the center of the incident beam is located at a position about 4 μm away from the edge surface of the bonding portion.

[0110]

As described above, in the optical coupler of the present invention,
At the same time as the adhesive bonds the optical waveguide and the light incident means (prism or dielectric plate), the bonding function is performed by the edge surface formed on the adhesive. Thus, the second dielectric layer can be integrated without increasing the thickness of the second dielectric layer without hindering the function of the optical waveguide element, and problems such as an increase in film stress can be avoided.

Further, by appropriately setting the height of the edge surface of the bonding portion from the surface of the second dielectric layer, a higher refraction than the first dielectric layer, which is located above the second dielectric layer. The area having the refractive index (prism or adhesive) can be completely separated from the optical waveguide. Thus, the loss due to the recombination can be fundamentally removed, and the recombination can be reduced without increasing the thickness of the optical waveguide when the optical coupler is integrated with the optical waveguide element.

Further, by appropriately setting the thickness and the refractive index of the film of each part constituting the optical coupler, the coupling efficiency for TE light and TM light can be made substantially equal. Further, by making the refractive index of the adhesive equal to the refractive index of the prism or the dielectric plate, the reflectance at the interface between them can be minimized. When a prism is used, multiple reflections caused by the adhesive acting like a thin film due to the small thickness of the adhesive existing between the prism and the optical waveguide can be almost completely removed.

In the method for manufacturing an optical coupler according to the present invention,
The edge surface of the bonding portion that performs the optical coupling function is formed by transferring the shape of the groove formed by the photoresist, and its height is determined by the thickness of the photoresist. Therefore, if the thickness of the photoresist is increased, the height of the edge surface of the bonding portion from the surface of the second dielectric layer can be secured to a value that can completely eliminate the influence of recombination.

If a photo-curable adhesive is used, the manufacturing time can be reduced, and the displacement of the prism or the dielectric plate during the solidification of the adhesive is suppressed, contributing to the prevention of a decrease in the coupling efficiency. . In addition, since the dielectric plate is easier to process than the prism, if the optical coupler is formed using the dielectric plate, the manufacturing cost can be reduced as compared with the case where the prism is used.

Further, before bonding the prism or the dielectric plate to the surface of the optical waveguide, as a post-process of the groove forming step, removal of organic residues of the resist developing solution generated on the surface of the optical waveguide in the process of forming the groove and light guide. By performing RIE processing (oxygen plasma processing) for removing the degenerated layer on the surface of the waveguide, the adhesive strength at the time of bonding the prism or the dielectric plate to the light incident means to the optical waveguide is increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an optical coupler according to a first embodiment of the present invention.

FIGS. 2A and 2B are a top view and a cross-sectional view illustrating a configuration of an optical waveguide element in which the optical coupler of FIG. 1 is integrally formed.

FIG. 3 is a cross-sectional view showing a configuration in which the optical coupler of FIG. 1 and the optical waveguide device of FIG. 2 are integrally formed.

FIG. 4 is a cross-sectional view illustrating another configuration of the optical coupler according to the first embodiment of the present invention.

FIG. 5 is a sectional view of the optical coupler of FIG. 1;

6 (a) to 6 (c) are graphs showing the relationship between the height of the edge surface of the junction in the optical coupler of FIG. 1 and the normalized transmission power.

FIGS. 7A to 7G are a cross-sectional view and a top view illustrating a manufacturing process of the optical coupler of FIG. 1;

FIGS. 8A and 8B are cross-sectional views illustrating another configuration of the optical coupler according to the first embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating a configuration of an optical coupler according to a second embodiment of the present invention.

10 is a cross-sectional view showing a configuration in which the optical coupler of FIG. 9 is formed integrally with an optical waveguide element.

FIGS. 11A to 11F are a cross-sectional view and a top view showing a manufacturing process of the optical coupler of FIG. 9;

FIGS. 12A to 12C are cross-sectional views respectively showing the configurations of a conventional optical coupler.

FIG. 13 is a cross-sectional view showing another configuration of a conventional optical coupler.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, 11 1st dielectric layer 2, 12 2nd dielectric layer 3, 13 Substrate 4, 4a Prism 5, 15 Bonding part 6, 16 Optical waveguide 7, 17 Edge surface 14 Dielectric board 51 Photoresist 52 Optical waveguide 53 Groove 54 Prism 55, 63 Bonding portion 56, 64 Edge surface 57, 62 Position adjusting device 61 Dielectric plate 101 First dielectric layer 102 Second dielectric layer 103 Substrate 104 Prism 105, 115 Bonding portion 106 Optical waveguide 108, 108a , 108b Photodiode 109 Polarization Separating Section 109a Ta ₂ O ₅ Layer 110 Dielectric Layer 111 Si Substrate 114 Dielectric Plate

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshio Yoshida 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Yukio Kurata 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Sharp (56) References JP-A-3-87705 (JP, A) JP-A-4-289531 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/122 G02B 6 / 34

Claims (11)

(57) [Claims] 1. An optical waveguide structure laminated on a substrate, comprising: a first dielectric layer laminated on at least the substrate; and a first dielectric layer laminated on the first dielectric layer. An optical coupler comprising: an optical waveguide structure including two dielectric layers; a light incident unit provided on the optical waveguide structure; and an adhesive unit for adhering the light incident unit to the optical waveguide structure. there are the refractive index of the adhesive portion n _b, the refractive index n ₁ of the first dielectric layer, and between the refractive index n ₂ of the second dielectric layer, n _b> n _1> n ₂
The bonding portion has an edge surface intersecting with the surface of the optical waveguide structure, and the line of intersection between the edge surface and the surface of the optical waveguide structure is a straight line, and the light incident means includes: Projecting from the edge surface toward the traveling direction of light in the optical waveguide structure by a length P _L ,
An air gap having a predetermined height equal to or higher than the height of the edge surface is provided between the protrusion and the surface of the optical waveguide structure, and the height h of the edge surface is determined by the refractive index of air. n _a, the substrate
Refractive index n _s, a refractive index n _b of the adhesive portion, the first dielectric
Refractive index n ₁ of the layer, the refractive index n ₂ of the second dielectric layer, said first
The thickness t of the dielectric layer, the thickness u of the second dielectric layer,
With respect to the length P _{L of the} protrusion of the force means , the following relational expression
(1) and (2) are set (however,
Α _r in the relational expression (1) is a function of h,
Imaginary number of the equation of relational expression (2) for each of
The imaginary part of the solution is the one with the larger absolute value), the optical coupler. (Equation 1) (Equation 2) 2. The optical coupler according to claim 1 , wherein an effective refractive index for the TE light is substantially equal to an effective refractive index for the TM light. 3. The refractive index of the substrate n _s = about 1.44, the refractive index of the bonding portion n _b = about 1.57, the refractive index of the first dielectric layer n ₁ = about 1.53, Refractive index n ₂ of the second dielectric layer = about 1.43, thickness t of the first dielectric layer = about 570
The optical coupler of claim 2 , wherein nm and the thickness u of the second dielectric layer is about 100 nm. Wherein said light incident means is a prism, an optical coupler according to any of claims 1-3. Wherein said light incident means is a dielectric plate which is adhered at a predetermined angle to the substrate, the optical coupler according to any of claims 1-3. 6. A refractive index of the adhesive portion and the refractive index of said light projecting means are substantially equal, the optical coupler according to any of claims 1-5. 7. A method of manufacturing an optical coupler according to any one of claims 1 to 3, the method comprising the step of forming the optical waveguide structure on the substrate, the optical waveguide structure A step of applying a photoresist on the surface; a step of forming a groove in the photoresist; and disposing the light incident means on the photoresist, and bonding the light incident means to the optical waveguide structure with an adhesive. A fixing method, and a step of removing the photoresist. 8. The adhesive according to claim 1, wherein the adhesive is a photo-curable adhesive.
The method according to claim 7 . 9. The method according to claim 9, wherein the light incident means is a prism, and the bonding and fixing step includes a step of arranging the prism on the groove and a step of injecting the adhesive into the groove to connect the prism to the optical waveguide. The method according to claim 7 , further comprising the step of bonding and fixing to a structure. 10. The light incident means is a dielectric plate,
The bonding and fixing step, a step of holding the dielectric plate at a predetermined angle with respect to the surface of the optical waveguide structure,
9. The method according to claim 7 , further comprising: supplying the adhesive so as to cover the groove to adhesively fix the dielectric plate to the optical waveguide structure. 10. 11. forming a groove in the photoresist, further comprising the step of RIE process (oxygen plasma process) as a post-treatment of the formation of the groove, claim 7-1
0. The production method according to any one of the above.