JPH05114767A - Manufacture of photocoupler - Google Patents

Abstract

PURPOSE:To enable functional elements where devices are integrated to be optically coupled together small in loss. CONSTITUTION:An SiO2 selective growth mask 413 is formed on the (100) plane of an InP semiconductor substrate 401. At this point, a mask gap stripe (light propagating direction of optical waveguide) is set in orientation to a [011] direction. Next, a clad layer 408 is selectively grown as thick as tc through an epitaxial growth method. Furthermore, a core layer 409 is made to grow. After the selective growth mask 413 is removed, a clad layer 410 is formed on all the surface of the semiconductor substrate 401.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical coupling device for converting a spot diameter of a light wave propagating through an optical waveguide with low loss.

[0002]

2. Description of the Related Art In the case of optically coupling a semiconductor laser diode (LD) and a single mode fiber, if the LD element end face and the fiber are directly butt-coupled (butt joint), the optical waveguide light wave spot size of each other. However, the coupling loss of the direct butting part becomes a problem because of the difference. Usually, LD light wave spot size (mode radius:
W) is about 1 μm, and the spot size of the fiber is about 5 μm, the coupling loss in this case is about 10 d.
Become B. Therefore, a method is generally used to reduce the coupling loss by converting the spot size with a lens.

FIG. 6 shows an example of a conventional configuration in the case of optically coupling an optical fiber having a plurality of laser diodes (LD) and an array fiber with a single lens. In FIG. 6, 604 is a semiconductor substrate and 605 is an LD.
Active region (optical waveguide part), 614 is a lens, 606 is a fiber, and 607 is a V-groove array for fixing the fiber 606 at regular intervals.

In such a configuration, as the LD integration scale increases, the coupling loss increases due to the effects of lens aberrations and the like, so that the number of LDs that can be integrated on one semiconductor substrate is limited.

An optical coupling device for converting the spot size of light by means of a tapered optical waveguide as shown in FIG. 7 is used as a substitute for a lens to optically couple the LD and the fiber with low loss. is there. Figure 7 (a)
Is a plan view of the conventional optical coupling device seen from above, and FIG.
7B is a sectional view, and FIG. 7C is a diagram for explaining the operation principle. That is, as can be seen from FIG. 7C, the refractive index difference Δn [= (n ₂ −n of the core layer 709 of the optical waveguide.
₁ ) / n ₁ , n _{1 is} the refractive index of the cladding layers 701 and 710, and n ₂ is the refractive index of the core layer 709, the size of the core layer 709, that is, the thickness When t and the width w are gradually increased from 0, the spot size W of the guided light (fundamental mode light) is gradually decreased from the infinite size, and after reaching the minimum value, there is a relation that it is increased again. Here, if the thickness t and the width w become too large, a multimode waveguide is formed, and the loss due to the higher-order mode conversion becomes large, so that the size of this region is not usually used. Utilizing this relationship, the core layer 70 of the optical coupling device
9 is the size, that is, in the design of thickness t and width w,
On the light incident end side (the side coupled to the LD), a dimension w _i and a thickness t _i (= several hundred nm to several μm) that give a spot size W _i approximately the same as the LD light spot size (about 1 μm).
At the light emitting end side, the fiber spot size (about 5
size μm) to give the same degree of size W _o t _o, w _o
(= Several tens to several hundreds nm). The length l of the region where the size of the core layer 709 is tapered is
Several hundred μm to several m to reduce loss due to radiation
It is necessary to make the length m or more.

[0006]

However, when the above-mentioned conventional photolithography / etching technique is used, the dimension of the emitting end side, that is, the thickness t _o and the width w _o are designed especially because of the limitation of the resolution in manufacturing. It was difficult to realize a low-loss optical coupling device because it was difficult to make the value sufficiently small.

Therefore, the present invention has been made in order to solve the above-mentioned conventional problems, and an object thereof is to provide the above-mentioned two different optical functional elements, especially between the optical functional elements in which a plurality of devices are integrated. An object of the present invention is to provide a method of manufacturing an optical coupling device capable of optical coupling with low loss.

[0008]

In order to achieve such an object, the present invention uses a selective growth mask having a tapered interval width when epitaxially growing a semiconductor layer which becomes a core portion of an optical waveguide. is there.

[0009]

In the present invention, the thickness and width of the core portion are tapered by using the selective growth mask.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is an application example of the optical coupling device according to the present invention, and is a diagram showing a configuration in which the optical coupling device according to the present invention is inserted between an array LD element and a fiber to achieve optical coupling with low loss. is there. FIG. 2 is a diagram for explaining the configuration of the optical coupling device according to the present invention shown in FIG.
1A is a plan view seen from above, and FIG. 1B is a sectional view. In the figure, 101 is a semiconductor substrate of an optical coupling device according to the present invention, 102 is a spot size conversion waveguide, 103 is an antireflection film, 104 is a semiconductor laser substrate,
Reference numeral 105 is an LD active layer (optical waveguide portion), 106 is a single mode optical fiber, and 107 is a V-groove array.

In such a structure, since the light wave spot size of the LD is converted to the spot size of the fiber by the optical waveguide of the optical coupling device, the LD and the single mode optical fiber 106 are optically coupled with low loss. You can

FIG. 2 (a) is a plan view of the optical coupling device according to the present invention as seen from above, and FIG. 2 (b) is A- of FIG. 2 (a).
FIG. 2C is a cross-sectional view of the line A '(light incident end).
It is sectional drawing of the BB 'line part (light emission edge part) of (a).
In the figure, 201 is a semiconductor substrate made of InP, which serves as a clad portion of the optical waveguide. 208 is InP or I
A clad layer made of nGaAsP or the like, 209 is InG
a core layer made of aAsP, InAlAs, or the like, 210
Is a clad layer made of InP or the like. Reference numeral 211 is incident light, and 212 is outgoing light. The width w and the thickness t of the core layer 209 are w _i and t _i at the light incident portion and w _o and t _o at the light emitting portion, respectively. The width w and the thickness t of the cladding layer 208 are w _mi , t _c , w _mo , and t _c in the light incident / exiting portion, respectively. The clad layer 208 and the core layer 209 have refractive indices of n ₁ and n ₂ respectively.
Is. When InP is used for the cladding layer 208, n ₁ = 3.166 for light in the wavelength λ = 1.55 μm band. Further, the refractive index of InGaAsP can be set to an arbitrary value from about 3.2 to 3.5 depending on its composition.

In such a structure, the optical waveguide
The size of the light wave spot is as shown in Fig. 7 (c).
The respective dimensions w and t of the rud layer 208 and the core layer 208
Since it depends on the size of the refractive index n, for example, LD and optical flux
When the optical coupling with the fiber is taken, for example, in the configuration of FIG.
And the spot size on the light incident side is the LD spot size.
Size (usually the mode radius W is about 1 μm)
To become w_i , T _i The size of the
On the shooting side, the fiber spot size (W ~ 5 μm)
W that gives the same spot size_o , T_o Set
There is. For example, the refractive index difference Δn of the core layer is about 5 to 10%.
If, w_i , T_i From several 100 nm to several μm
W_o , T_o Is several tens to several hundreds of nm
become. Also, the length l of the region where the waveguide layer is tapered is
Reduces the radiation loss due to mode size conversion
It is sized like this. For example, l = several 100 μm to several
It becomes about mm. In this region, the waveguide layer
The sizes w and t are stepwise w_i , T_i From w_o , T_o To
You can change it.

Next, the principle for manufacturing the above-mentioned t and w to the design values will be described with reference to the sectional view of the semiconductor substrate shown in FIG. As shown in FIG. 3, when the semiconductor layers 308 and 309 are epitaxially grown in the stripe-shaped gaps of the selective growth mask 313 made of an insulator such as SiO ₂ or SiN formed on the crystal (100) surface of the semiconductor substrate 301, For example, when the stripe direction is the [011] direction, the semiconductor layers 308 and 309 grow in a shape such that the angle θ is about 55 degrees with respect to the substrate surface, and the thickness thereof is h _max shown in the figure. It is known that the growth rate is extremely slow after reaching, and the growth is substantially stopped. Therefore, when the growth time is set to be sufficiently long, the thickness h _max of the semiconductor layers 308 and 309 becomes about h _max = w _m tan θ / 2 and is determined by the gap width w _m of the mask.

On the other hand, the minimum manufacturable width of the mask gap width w _m is limited by the spatial resolution of the photolithography technique used. For example, when the ordinary ultraviolet exposure technique is used, the size is about 1 μm, and In the case of the beam exposure drawing technique, it is around 100 nm. However, as shown in FIG. 2, the cladding layer 208 is epitaxially grown to an appropriate thickness t _c (<h _max ) with respect to the gap width w _m of the manufactured mask, and then the core layer 209 is formed to form the core layer 209. The thickness t is t = w _m tan θ / 2−t _c . Therefore, the thickness t _{c with} respect to the manufacturable width w _m
In principle, the size of t and w can be made as small as possible by setting the thickness to an appropriate value.

FIG. 4 is a diagram for explaining a process according to an embodiment of a method for manufacturing an optical coupling device according to the present invention.
FIG. 4A is a plan view seen from above the optical coupling device, FIG.
4B to 4D are cross-sectional views. In the figure, first, as shown in FIGS. 4A and 4B, the SiO ₂ selective growth mask 41 is formed on the (100) plane of the InP semiconductor substrate 401.
3 is formed. At this time, the stripe direction of the mask gap (light propagation direction of the optical waveguide) is set to the [011] direction. Next, as shown in FIG. 4C, the cladding layer 408 is selectively grown by the epitaxial growth method to the thickness t _c . Further, the core layer 409 is grown. Next in FIG.
After removing the selective growth mask 413 as shown in (d), a cladding layer 410 is formed on the entire surface of the semiconductor substrate 401.

FIG. 5 is a diagram for explaining a process according to another embodiment of the method of manufacturing an optical coupling device according to the present invention.
FIG. 5A is a plan view seen from above the optical coupling device, FIG.
5B is a cross-sectional view of the line AA '(light incident end) of FIG. 5A, and FIG. 5C is the line BB' of FIG. 5A (light emitting end). FIG. In this figure, this optical coupling device can be manufactured by stopping the epitaxial growth when the thickness t _i ′ of the core layer 509 at the light incident end is smaller than h _max as shown in FIG. 5B. Since the core layer 509 has a trapezoidal shape, the field pattern of the guided light has an elliptical shape. In the embodiment of FIG. 2, the field pattern of the guided light has a circular shape. Normally, the field pattern of the output light from the LD is elliptical,
With this structure, the effect of reducing the coupling loss due to the field pattern deviation can be obtained.

In the present invention, for example, the core layer 5
It is also possible to fabricate the core width w _i to an arbitrary size by a usual etching technique after selectively growing 09.

Although the case where the spot size conversion waveguide layer is formed on the InP substrate has been described above, it is obvious that other semiconductor materials such as GaAs can be similarly manufactured.

Since this optical coupling device is made of a semiconductor material, the present coupling device is formed on the same substrate at the light input / output end of an optical functional element such as an LD element or an optical switch using the semiconductor material. It is also possible to produce monolithically integrated optical devices according to the invention. For example, when forming an optical functional device waveguide on a semiconductor substrate,
The optical coupling waveguides may be formed so that the main coupling waveguides are formed at the same time or the optical functional element portion is formed, and then the mutual waveguides are directly abutted to each other.

[0021]

As described above, according to the present invention,
The width and thickness of the core portion can be tapered by using a selective growth mask having a tapered gap width when epitaxially growing a semiconductor layer to be the core portion of the optical waveguide. In addition, an extremely small waveguide can be formed without being limited by the spatial resolution of the photolithography technique used for mask formation. 2 from this
It is possible to produce one optical functional element, in particular, an optical coupling device in which a plurality of devices are integrated and optical coupling is performed with low loss between the optical functional elements.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example in which an optical coupling device according to the present invention is inserted between an array LD element and a fiber.

FIG. 2 is a diagram illustrating a configuration of an optical coupling device according to the present invention.

FIG. 3 is a diagram illustrating the principle of a method of manufacturing the optical coupling device shown in FIG.

FIG. 4 is a process diagram for explaining an example of a method for manufacturing an optical coupling device according to the present invention.

FIG. 5 is a process drawing for explaining another embodiment of the method of manufacturing the optical coupling device according to the present invention.

FIG. 6 is a diagram showing a conventional optical coupling method between an optical functional element and an array fiber.

FIG. 7 is a diagram showing a configuration of a conventional optical coupling device.

[Explanation of symbols]

 101 semiconductor substrate 102 spot size conversion waveguide 103 antireflection film 104 semiconductor laser substrate 105 LD active layer 106 optical fiber 107 V-groove array 201 semiconductor substrate 208 clad layer 209 core layer 210 clad layer 211 incident light 212 emitted light 301 semiconductor substrate 308 semiconductor layer 309 semiconductor layer 313 selective growth mask 401 semiconductor substrate 408 clad layer 409 core layer 410 clad layer 413 selective growth mask 501 semiconductor substrate 508 clad layer 509 core layer 510 clad layer

Claims (2)

[Claims] 1. In the epitaxial selective growth of at least one optical waveguide layer performed on a semiconductor substrate on which a selective growth mask made of an insulator is formed, a gap width of the selective growth mask and a selective growth orientation plane of the optical waveguide layer. The method of manufacturing an optical coupling device, characterized in that the thickness of the optical waveguide layer is controlled by the angle of and the optical waveguide layer is formed so as to have a tapered thickness along the optical waveguide direction. 2. In the epitaxial selective growth of at least one cladding layer and an optical waveguide layer performed on a semiconductor substrate on which a selective growth mask made of an insulator is formed, a gap width of the selective growth mask and selection of the optical waveguide layer. The thickness of the optical waveguide layer is controlled by the angle of the growth azimuth plane and the thickness of the cladding layer, and the optical waveguide layer is formed to have a tapered thickness along the optical waveguide direction. A method for manufacturing a featured optical coupling device.