JPH07168146A - Spot conversion optical waveguide - Google Patents

Abstract

PURPOSE:To improve the single mode, the productivity and the conversion loss of spot size of a spot conversion optical waveguide. CONSTITUTION:This spot conversion optical waveguide is equipped with an optical waveguide for propagation, a spot conversion part and an enlarged spot optical waveguide. The guided wave light propagated through the enlarged spot optical waveguide is shut up in a horizontal direction by the ridge of the enlarged spot optical waveguide, and clad does not exist on the core of the enlarged spot waveguide other than the ridge part, and further the core of the enlarged spot waveguide is thinned to enlarge a spot diameter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot conversion optical waveguide which is small in size, low in loss and easy to manufacture.

[0002]

2. Description of the Related Art First, for convenience of later description, a spot size will be defined. When the field distribution of light is fitted with a Gaussian distribution, the width (half width) where the power distribution becomes 1 / e ² of the peak value is the spot size. Further, in the following, the spot size is about 1 μm or less in the optical function part and the propagation optical waveguide part, and the spot size is about 4 μm in the expanded spot optical waveguide part, and the single mode optical fiber (hereinafter referred to as SMF).
Abbreviated).

First, a conventional ridge optical waveguide having a large spot size will be described.

44 and 45, the ridge size is as large as 6 to 8 μm, and the first and second conventional examples (RG Wal) of the optical waveguide having a large spot size are shown.
ker et al., Electron. Lett. , Vol. 1
9, no. 15, pp. 590-592,1983) (FIG. 44 (A), FIG. 45 (A)) and diagrams showing the distribution of the equivalent refractive index with respect to the respective lateral coordinates (FIG. 44 (B), FIG. 45 ( B)). In the figure, the power distribution of light is indicated by F. Here, 1 and 3 are clad (AlG
aAs, refractive index = 3.34), 2 is a core (GaAs, refractive index = 3.41). The clad 1 has a height of 6 to 8 μm
It has a ridge shape. In the first conventional example of FIG. 44, the core 1 has a large thickness of 1.4 μm. Therefore, as shown in the schematic diagram, light leaks into the left and right cores of the ridge 1. The light leaked to the left and right feels the air directly above the core 2. Therefore,
The equivalent refractive index of the regions on the left and right of the ridge is considerably lower than that of the ridge region where the cladding 1 is present, and the lateral refractive index difference Δn in the distribution of the equivalent refractive index is relatively large. As a result, as described in this document, there is a drawback that it becomes a multimode optical waveguide.

Further, in FIG. 45, since the core 2 exists only directly under the ridge-shaped clad, there is no exudation of light in the lateral direction other than the ridge, but the thickness of the core 2 is the same as in FIG. Since the thickness is as thick as 4 μm, the lateral refractive index difference Δn in the distribution of the equivalent refractive index becomes extremely large, and there is a drawback that a multimode optical waveguide is obtained.

Next, the spot conversion will be described.

Generally, in the case of a semiconductor optical waveguide, since the difference in refractive index between the core and the clad is large, the spot size of the light propagating through the semiconductor optical waveguide is as small as submicron in order to propagate the light of a single mode. . The coupling efficiency η when two Gaussian beams with spot sizes w ₁ and w ₂ are coupled is

[0008]

Η = 4 / (w ₁ / w ₂ + w ₂ / w ₁ ) ² (1)

From the equation (1), it can be seen that the spot sizes should be matched to reduce the coupling loss between the optical waveguides. When the SMF is used as the light receiving optical waveguide, its spot size w ₂ is about 4 μm, and if it is directly coupled with the semiconductor optical waveguide, the coupling loss becomes extremely large. For example, when the spot size w ₁ of the semiconductor optical waveguide is 1 μm and the spot size w ₂ of the SMF is 4 μm, the coupling loss (−10 · log (η)) is 6.5 dB.
Becomes Therefore, as described below, a so-called front-end processing single-mode optical fiber (hereinafter abbreviated as front-end SMF) is used in which the tip is polished to give a lens effect to reduce the spot size. However, if the spot size of the front spherical SMF is reduced to the submicron order, there arises a problem of tolerance of misalignment. That is, the coupling efficiency η in the case where two Gaussian beams having the spot size w are coupled by being displaced by x in the direction perpendicular to the optical axis is

[0010]

[Equation 2] η = exp (−x ² / w ₂ ) (2), and when the spot size w is as small as submicron, the coupling loss increases significantly, and the tolerance of axis misalignment becomes extremely severe. In fact, even if the radius of curvature R1 of the tip of the front spherical SMF is made small, it is very difficult to reduce the spot size to about 0.5 μm due to the processing accuracy during polishing (above reference: Kono). Kenji, "Fundamentals and Applications of Optical Coupling Systems for Optical Devices" (Hyundai Engineering Co.).

Therefore, it is necessary to increase the spot size of the semiconductor optical waveguide. FIG. 46 is a perspective view illustrating a conventional example of spot size conversion in a semiconductor optical waveguide. Here, I is an optical function part, II is a propagation optical waveguide part, and III is a spot conversion part. Reference numerals 4 and 5 are a clad and a core of an optical function part such as a semiconductor laser. 6 and 7 are the cladding and core of the propagation optical waveguide, and 8
Is the core of the spot converter. 47 and 48 are cross-sectional views taken along the lines AA 'and BB' of FIG. 46, respectively.

The operation principle of this conventional example will be described. As can be seen from FIG. 46 or 47, the width of the tip of the core 8 of the spot converting portion is gradually tapered. Therefore, when the light propagating through the core 7 of the optical waveguide for propagation reaches the core 8 of the spot converter, the amount of light leaking into the clad increases and the field distribution of the light spreads. As a result, the spot size becomes large, and the coupling loss given in equation (1) can be reduced.

In this conventional spot conversion optical waveguide, the core is tapered to be thin. However, if the width of the core becomes too thin, light leaks into the clad, and the spot size becomes too large and the force for guiding the light is increased. (Waveguide power) becomes too loose. Therefore, there is a problem that the insertion loss of light increases due to the coupling loss due to the spot size mismatch with the optical fiber, or the scattering loss and the radiation loss due to the waveguide fluctuation in the narrow portion.

FIG. 49 shows a perspective view of a fourth conventional example (E).
electron. Letters, vol. 28, p
p. 631-632, 1922). Here, II is a propagation optical waveguide portion, III is a spot conversion portion, and IV is an enlarged spot optical waveguide. This example is proposed for the case where the propagation optical waveguide and the core of the spot converter are completely embedded. In this conventional example, the core 9 of the optical waveguide for propagation (here, the bandgap wavelength λg = 1.
3 μm), the waveguide power of the core 9 of the propagation optical waveguide is gradually weakened so that the guided light leaks to the clad and is finally emitted. Along with that,
The width of the core 10 of the enlarged spot optical waveguide deposited under the core 9 of the propagation optical waveguide is gradually widened so that the vertical direction is the thickness of the core 10 and the lateral direction is the width of the core 10. Here, 11 is an upper clad, 12 is a lower clad, and 13 is an InP substrate.

In this conventional example, the core 9 of the propagation optical waveguide is used.
Is a completely buried type optical waveguide, the core 10 of the enlarged spot conversion portion is also completely buried, and the lateral light is confined by defining the width of the core 10. Therefore, this conventional example is suitable for a buried optical waveguide, but it is difficult to apply because the ridge structure has a different shape like an optical switch. There are drawbacks such as a large conversion loss at the time of size conversion, a large propagation loss due to the embedded waveguide, and an extremely flat light power distribution, which deteriorates the coupling efficiency with the SMF.

[0016]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve these problems and to provide a spot conversion optical waveguide excellent in single mode property, manufacturability and spot size conversion loss. is there.

[0017]

In order to achieve the above-mentioned object, a spot conversion optical waveguide according to the present invention is a propagation optical waveguide having a first core through which guided light of a small spot size propagates, In a spot conversion optical waveguide including a spot conversion unit having a second core for converting a spot size and an enlarged spot optical waveguide having a third core through which guided light having a large spot size propagates, the third core is a thin film. The expanded spot optical waveguide has a ridge structure for laterally confining propagating guided light, and the power of light in the expanded spot optical waveguide is a peak value of the power distribution of light in the depth direction. The second-order differential according to the depth-direction coordinate of the power distribution is positive in at least a part between the half value of the peak value and the depth direction. Gaussian the power distribution than narrow of fitting full width at half maximum of definitive the power distribution, and the full width at half maximum of the power distribution than the full width at half maximum of the Gaussian distribution of fitting in with the value of 1 / e ² of the peak value It is characterized in that it has a narrow distribution, and that the guided light propagates in a substantially single mode in the enlarged spot optical waveguide.

Here, the ridge structure may include an upper clad formed on the third core, and the ridge structure has a third core formed on a lower clad and the third core.
It may consist of an upper clad formed on the core.

A side cladding may be further provided on a side surface of the ridge structure.

At least one of the thickness and the width of the second core of the spot conversion portion may change toward the tip of the waveguide.

The first core and the second core may be laminated with the third core, and at least one semiconductor layer is provided between the first core and the second core and the third core. May be.

The first core, the second core, and the third core may be formed on the same plane of a common lower clad.

The bottom surface of the second core may be arranged above the bottom surface of the first core, or the center of the second core in the thickness direction may be arranged above the center of the first core in the thickness direction. Of course, a thin film-shaped fourth core may be provided at least above the second core.

[0024]

According to the present invention, since light is confined vertically by a thin core as a structure of an enlarged spot optical waveguide and confined in a lateral direction by a ridge structure, light leakage in the lateral direction is small, As a result, a single mode optical waveguide having a large spot size can be realized. In the structure in which the core thickness of the spot conversion unit is thin, the conversion loss during conversion of the spot size is particularly small, and since the enlarged spot waveguide has the ridge structure, the waveguide type optical device having the ridge structure is used. When applied to a device, there are advantages that the manufacturability is good and the spot size conversion loss can be reduced.

Furthermore, since the center of the field distribution of the light propagating through the second core and the center of the field distribution of the light propagating through the first core can be made to coincide with each other in the thickness direction, the second core portion and the first core portion can be made. Connection loss due to axial misalignment in the thickness direction of the core at the connection part of the above, or the center of the field distribution of the light propagating in the second core and the light propagating in the third core and the fourth core. Since the centers of the field distribution can be made to coincide with each other, it is possible to reduce the connection loss due to the axial deviation of the second core portion and the cores of the third core portion and the fourth core portion in the thickness direction. is there.

[0026]

Embodiments of the present invention will be described in detail below with reference to the drawings.

First, in order to explain the principle of the present invention, the cross-sectional structure of the enlarged spot optical waveguide in one example of the spot conversion optical waveguide according to the present invention, the light power distribution (F), and the equivalent refractive index with respect to the lateral coordinate are shown. The distributions are shown in FIGS. 1 (A) and 1 (B), respectively. In the figure, 14 is a ridge-shaped In
P-clad (refractive index 3.17), 15 is InGaAsP
Core (bandgap wavelength = 1.1 μm, refractive index = 3.
28) and 16 are InP clads. One of the characteristics of the present invention is to reduce the confinement rate (Γ factor) of the optical power in the core by reducing the thickness of the core. Therefore, the width of the ridge, that is, the InP clad 1
Although the width of 4 is as wide as 10 μm, the thickness of the InGaAsP core 15 is as thin as about 0.08 μm.
Extrusion of the guided mode to the InGaAsP core 15 other than the region where 4 exists is so small that it can be ignored. As a result, the equivalent refractive index of this region is almost the same as that of the InP clad 16. On the other hand, as described above, the thickness of the InGaAsP core 15 is extremely thin and the Γ factor to the core is small, so that the equivalent refractive index of the ridge portion is also low. That is, as shown in FIG. 1, the refractive index difference Δn in the lateral direction is smaller than that in the conventional example shown in FIGS. As a result, even when the ridge width is as wide as 10 μm, it is possible to realize single mode propagation, which was difficult in the conventional example.

FIG. 2 shows the power distribution of the guided light of the present invention (solid line) and the Gaussian distribution (dotted line) of the conventional example fitted with the peak value and its half value. In the present invention, since a large amount of light leaks from the core 15 to the claddings 14 and 16, between the peak value of the power distribution of light in the depth direction and the half value thereof, except in the vicinity of the peak of the power distribution, the depth direction The second derivative of the power distribution of the guided light according to the coordinates is positive. Also, it can be seen that the power distribution of the guided light is narrower than the Gaussian distribution fitted with the full width at half maximum of the power distribution of the guided light. Further, as shown in FIG. 3, it is found that the full width at half maximum of the power distribution of the guided light (solid line) is narrower than the full width at half maximum of the Gaussian distribution (dotted line) fitted with the value of 1 / e ² of the peak value of the guided light. Such a difference in the shape of the field distribution occurs when the thickness of the InGaAsP core 15 is 0.7 μm or less, and shows a remarkable spot conversion characteristic according to the present invention. However, if the core 15 is too thin, the light confinement efficiency becomes small, and in extreme cases, it becomes impossible to guide light.

As described with reference to the example of FIG. 1, since the core 15 is thin in the present invention, the Γ factor of light to the core 15 is small, and in the example of FIG. 1, light leaks out to the core other than the ridge portion. It was extremely small. Therefore, in the example of FIG. 1, the core beside the ridge may be eliminated. That is, in the present invention, the core adjacent to the ridge may be removed by etching. The cross-sectional structure and the distribution of the equivalent refractive index with respect to the horizontal coordinate in that case are shown in FIG.
Shown in (A) and (B). As can be seen from the figure, the distribution of the equivalent refractive index with respect to the abscissa is almost the same as the example of FIG. 1, and as a result, the power distribution of the guided light is almost the same as that of the example of FIG. realizable.

(Embodiment 1) Here, the manufacturing procedure of the spot conversion optical waveguide of the present invention will be described, taking as an example the case where the optical function section constitutes an optical phase modulator, and the structure of the present invention will be described in the description. .

FIG. 5 is a perspective view of the first embodiment of the present invention.
FIG. 6 shows a sectional view taken along the line BB '. For simplicity, the case of an optical phase modulator as an optical function unit is shown. In the figure,
I is an optical phase modulator, II is a propagation optical waveguide, III is a spot converter, and IV is an enlarged spot optical waveguide. 21 is a p-side electrode, 22 is an InGaAs cap layer, and 23 is p-
InP clad, 24 is i-InP side clad, 2
5 is, for example, i-InGaAlAs (well) / InAl
As (Barrier) Multiple Quantum Well (MultipleQua)
nTum Well: MQW) and the well thickness is 9n
m, and the barrier thickness is 5 nm, the exciton peak wavelength is 1.44 μm, which is suitable for operation at 1.55 μm. The thickness of the MQW layer 25 is about 0.4 μm. The MQW layer 25 is tapered in the spot conversion part III. 26 is a common core of the spot conversion optical waveguide, for example, i having a bandgap wavelength λg of 1.1 μm.
The InGaAsP layer has a thickness of 0.08 μm.
The core 26 may be n-InGaAsP, and MQW
The layer 25 may have the same composition as the layer 25, or may have a multilayer structure in which different materials are laminated to adjust the refractive index. 27 is n
-InP clad, 28 is an n-InP substrate, 29 is an n-side electrode, 30 is a clad for the spot conversion portion and the enlarged spot optical waveguide. Here, p-InP is used, but i-InP may be used. F indicates the field distribution of the guided light.

FIG. 6 is a sectional view taken along line BB 'in FIG. Field distribution of guided light, that is, from F ₁ spot size optical phase modulator section I and propagation optical waveguide section II, is expanded to F _2, further enlarged spot waveguide IV of F ₃ in the spot conversion section III .

As can be seen from FIG. 5, the optical phase modulator section I
In the propagation optical waveguide section II, the optical waveguide is not a buried type but a ridge type. FIG. 7 is a diagram for explaining the manufacturing process of the first embodiment of the present invention. n-InP substrate 28
An n-InP clad 27, an i-InGaAsP common core 26, and an i-MQW core 25 are deposited on this (at this time,
In addition to protecting the i-MQW layer 25, In described later
A thin i-InP layer may be deposited over the i-MQW layer 25 to facilitate P regrowth). A photoresist 31 is spin-coated on the entire surface, and then patterned as shown in FIG. 7 (at this time, when viewed from above, FIG.
The photoresist is tapered in the spot conversion part III so that it can be easily inferred. Then, the i-MQW layer 25 is dry-etched into a tapered shape as shown in FIG. 5 to remove the photoresist. FIG. 8 is a transverse sectional view at this time.

In the case of the long-wavelength semiconductor described here, by using a sulfuric acid-based etchant, i-
It is possible to etch the InGaAlAs well and the i-InAlAs barrier and stop the etching with i-InP (referred to as selective etching technique). Therefore, i-MQ
5 nm or 1 between the W layer 25 and the i-InGaAsP layer 26
If an i-InP layer with a thickness of about 0 nm is inserted, it will function as an etch stop layer, and the i-M of the spot converter will be formed.
The QW layer can be processed into a tapered shape. Further, similarly, the core 26 of the spot converting portion can be processed into a tapered shape.

The next fabrication process is shown in FIG. Here, the area selective growth technique disclosed in Japanese Patent Laid-Open No. 5-82909 is used. FIG. 9 is a top view when the SiO ₂ mask 32 for selective growth is formed on the chip of FIG. In the selective region growth, the source atoms attached to the place without the SiO ₂ mask 32 contribute to the growth as they are, but the source atoms coming on the SiO ₂ mask are Si.
It does not adhere to the O ₂ mask and moves to a place without the SiO ₂ mask. Therefore, as shown in FIG. 9, there is no SiO ₂ mask in the optical phase modulator I and the propagation optical waveguide II,
When the SiO ₂ mask 32 is formed on the spot conversion section III and the enlarged spot optical waveguide IV, the spot conversion section III and the InP clad 23 of the optical phase modulator section I and the propagation optical waveguide section II have a thickness smaller than that of the spot conversion section III. Expanded spot optical waveguide
The IV InP clad 30 can be formed to be several times thicker.
That is, I in the optical phase modulator I and the optical waveguide II for propagation
If the thickness of the nP clad 23 is 1.5 μm, the thickness can be 4.5 to 6 μm in the spot converter III and the enlarged spot optical waveguide IV. At the tip of the element from the spot conversion section III to the enlarged spot optical waveguide IV, the spot size of the guided light is as large as about 5 μm, so a thick clad is required, but it can be formed by this manufacturing method. The final ridge processing is performed by dry etching or wet etching.

Now, the operation of this embodiment will be described.
First, the role of the i-InP side cladding 24 will be briefly described with reference to FIG. Guided light is InP clad 2
Although it propagates in the vicinity of the core immediately below 3, the guided light also leaks above and below the core. I if the side cladding 24 is thin
In the place where the nP clad 23 is not present, the guided light feels the low refractive index (1.0) of air, and the equivalent refractive index in that place decreases. On the other hand, in the place where the p-InP clad 23 is present, the light leaked onto the core feels its refractive index (3.17), so that the equivalent refractive index becomes high and the lateral light confinement becomes possible. Here, in the enlarged spot optical waveguide IV, the core is i-
A thin layer of InGaAsp layer 26 (here, 0.08 μm)
And)), and the field distribution spreads up and down. Since the InP clad 30 has a large width in this region, it is necessary to reduce the difference in refractive index in the lateral direction in order to realize single mode propagation. Therefore, in FIG. 5, the thickness of the side clad 24 ′ of the spot converter and the enlarged spot optical waveguide is set to, for example, 0.5 μm, and the region I,
It is thicker than the thickness of the side clad in II (for example, 0.1 μm).

In this embodiment, as shown in FIG. 6, the guided light F propagating through the optical function part I and the propagation optical waveguide part II.
₁ enters the spot converter III. Spot converter II
At I, the width of the core is tapered, so F
As shown by ₂ , the confinement of light becomes loose, and the spot size is increased not only in the left and right but also in the vertical direction, and finally emitted. This emitted light is common core 2
It is confined vertically by 6. When the core is made thin, the confinement of guided light in the vertical direction becomes loose,
As a result, it is enlarged like F ₃ . FIG. 10 shows the relationship between the thickness of the common core 26 and the spot size in the thickness direction. As shown in FIG. 10, the spot size in the vertical direction of the guided light can be greatly enlarged as compared with that of the optical phase modulator section or the propagation optical waveguide section. On the other hand, as shown in FIG. 11, the lateral spot size is extremely widened by making the width Ws of the clad of the ridge in the spot converter and the expanded spot optical waveguide wider than the width Wp of the clad of the propagation optical waveguide. It can be greatly enlarged (Ws is set to about 14 μm in FIG. 5). The width of the ridge of the spot conversion section and the enlarged spot optical waveguide may be tapered toward the tip of the waveguide as shown in FIG. 5, or may be constant.

As described above, in this embodiment, since the spot converter and the enlarged spot optical waveguide have the ridge structure,
It has good manufacturability in that the optical function part is structurally the same as the optical device having the ridge structure, and because of the similarity in the shape of the field distribution, it is possible to use the propagation optical waveguide part and the spot conversion part as an enlarged spot optical waveguide. It is possible to realize a large spot while having the advantage that the bonding property is good at the time of bonding. As a result, the coupling with the single-mode optical fiber has a low loss and the tolerance of the axis deviation is large, and the connection can be easily performed.

In this embodiment, the width of the taper portion of the spot converting portion is not changed and only the width is reduced, but the thickness may be reduced at the same time. Further, the width may be widened while reducing the thickness. Further, in FIG. 5, the taper of the spot conversion portion is cut off before reaching the element end surface. However, if the spot size of the guided light is designed to match the spot size of the fiber, the MQW core 25 is tapered. It goes without saying that it may exist until reaching the end face of the element.

Furthermore, in the above description, the method of converting a small spot in the propagation optical waveguide portion into a large spot has been described. However, if the incident light and the outgoing light are exchanged and the large spot is made incident from the right side of FIG. It is possible to convert a large spot of a single-mode optical fiber into a small spot, perform a function such as an optical switch and an optical modulation, and then enlarge the spot again to be coupled to the single-mode optical fiber. Therefore, by forming the spot conversion optical waveguide of this embodiment on both sides of an optical device having a light input / output unit such as a waveguide type optical switch, a module to which a single mode optical fiber is connected can be easily manufactured. become.

As a result of the experiment, it is confirmed that the coupling efficiency of the single mode optical fiber is relatively high on the light emitting side even if the expanded spot optical waveguide is not the single mode. The thickness of the side cladding of the spot converter and the enlarged spot optical waveguide (0.
5 μm) may be the same as the thickness of the side cladding of the light propagating portion (0.1 μm in the above description).

(Embodiment 2) FIG. 12 shows a second embodiment of the present invention. In the present embodiment, the spot is expanded vertically by merely gradually reducing the thickness of the core 25 of the spot conversion unit. In this embodiment, the lateral expansion of the spot is performed only by the width of the ridge 30. Therefore, although the effect is not as great as that of the first embodiment, a small spot of the optical function portion can be converted into a large spot. Further, the width of the ridge 30 may be widened in a tapered shape or may be constant.

(Embodiment 3) FIG. 13 shows a perspective view of a third embodiment of the present invention, and FIG. 14 shows a sectional view taken along line BB '. The main difference between this embodiment and the first embodiment shown in FIG. 5 is the shapes of the common core 26 and the clad 30 in the spot converter III and the enlarged spot optical waveguide IV. In the first embodiment, the common core 26 is n
-InP clad 27 is formed on the entire surface and clad 30
Was formed on the common core 26 also in areas other than the ridge portion. In this embodiment, the common core 26 and the clad 30 form a ridge. The material system used is as described in Example 1.

The manufacturing process of this embodiment is the same as the method described in the first embodiment up to the process of FIGS. 7 and 9. Also in this case, the SiO ₂ mask 32 for the area selective growth technique is formed as shown in FIG.

As described above, as shown in FIG. 9, the optical phase modulator section I and the propagation optical waveguide section II have no SiO ₂ mask, and the spot conversion section III and the enlarged spot optical waveguide IV have SiO 2. _{If the two} masks 32 are formed, the optical phase modulator portion I and the propagation optical waveguide portion II can be formed by the area selective growth.
Than the thickness of the InP cladding 23 of
I and the InP clad 30 of the enlarged spot optical waveguide IV can be formed to be several times thicker. That is, assuming that the thickness of the InP clad 23 in the propagation optical waveguide section is 1.5 μm, the spot conversion section and the enlarged spot optical waveguide have 4.5 to 6 μm.
It can be m. In the spot converter III and the enlarged spot optical waveguide IV, since the spot size of the guided light is as large as about 5 μm, a thick clad is required, but this can be formed by this manufacturing method. The final ridge processing is performed by dry etching or wet etching. Then, i-InGa outside the ridge
The AsP layer 26 may be removed with a sulfuric acid-based etchant, or the i-InGaA under the SiO ₂ mask 32 may be removed.
If the sP layer 26 is removed before depositing the mask 32, the width of the ridge can be formed in the spot conversion portion by a region selective growth technique.
The etching process of 6 becomes unnecessary.

Now, the operation of this embodiment will be described.
First, the role of the i-InP side cladding 24 in the optical phase modulator section I and the propagation optical waveguide section II will be briefly described with reference to FIG. The guided light propagates near the core immediately below the InP clad 23, but at this time, the guided light also leaks above and below the core. InP when the side cladding 14 is thin
In the place where the cladding 23 is not present, the guided light feels the low refractive index (1.0) of air, and the equivalent refractive index in that place is lowered. On the other hand, in the place where the p-InP clad 13 is present, the light leaked onto the core feels its refractive index (3.17), so that the equivalent refractive index becomes high and the lateral light confinement becomes possible.

In this embodiment, as shown in FIG. 14, the guided light (F ₁ ) propagated through the optical phase modulator section I and the propagation optical waveguide section II enters the spot conversion section III. Since the width of the core is tapered in the spot conversion section III, the light confinement is loosened, and the spot size is increased not only in the left and right but also in the vertical direction (F ₂ ) and finally emitted. The emitted light is vertically confined by the common core 26. When the core is made thin, the confinement of guided light to the core in the vertical direction becomes loose, and as a result, the spot size is enlarged (F ₃ ). FIG. 15 shows the relationship between the thickness of the core of the enlarged spot optical waveguide and the spot size in the thickness direction in this example. As shown in FIG. 15, the vertical spot size of the guided light is significantly larger than that of the optical phase modulator section or the propagation optical waveguide section (the vertical spot size of these sections is about 0.3 μm). Can be expanded to. On the other hand, as for the lateral spot size, as shown in FIG. 16, the width Ws of the clad of the ridge in the spot converter is the width W of the clad of the optical waveguide portion for propagation.
Compared with p (about 2 μm), the width can be made extremely large (Ws is set to 10 μm in FIG. 13).

As described above, in this embodiment, since the spot conversion portion and the enlarged spot optical waveguide have the ridge structure,
Good manufacturability in that the optical function part is structurally the same as the optical device having a ridge structure, and the coupling of the propagation optical waveguide part with the spot conversion part and expanded spot optical waveguide due to the similarity in the shape of the field distribution. A large spot can be realized while having the advantage of good characteristics. As a result, the coupling with a single mode optical fiber (spot size is about 4 μm) also has low loss as shown in FIG. Further, since the spot size is enlarged, the tolerance of the axis deviation is large and the optical device and the fiber can be easily connected.

FIG. 17 shows the clad width (ridge width: Ws) of the ridge upon coupling with the single-mode optical fiber, using the thickness of the common core of the spot conversion optical waveguide as a parameter.
And the coupling loss.

(Embodiment 4) In the spot conversion portion of the third embodiment, the core is only a thin layer of the i-InGaAsP layer 26 (here, 0.08 μm), and the field distribution greatly spreads vertically. In the third embodiment, the ridge 3
Although the portion other than 0 is etched right above the n-InP clad 27, the thickness of the i-InGaAsP layer 26 is as thin as about 0.08 μm, so that the lateral bleeding of the guided mode to this portion is small. Few. Therefore, as shown in FIG. 18, which is the fourth embodiment of the present invention, i-InGaAsP is used.
The core 26 may be left.

In the above embodiment, only the width of the taper portion of the core 25 in the spot conversion portion is reduced without changing the thickness, but the thickness may be reduced at the same time. Further, the width may be widened while reducing the thickness. Further, in the example of FIG. 13, the taper of the spot conversion portion is cut off before reaching the end face of the element, but if the spot size of the guided light is designed to match the spot size of the fiber, the core 25 is tapered. May exist until the end face of the element is reached. The structure in this case is shown in FIG. In this example, the core 25 is continuous with the spot converter III and the enlarged spot optical waveguide IV.

In the above description, the method of converting a small spot of the propagation optical waveguide portion into a large spot has been described. However, if the incident light and the outgoing light are exchanged and the large spot is made incident from the right side of FIG. It is possible to convert a large spot of an optical fiber into a small spot, perform a function such as an optical switch and an optical modulation, and then enlarge the spot again to be coupled to a single mode optical fiber.
Therefore, by forming the spot conversion optical waveguide of this embodiment on both sides of an optical device having a light input / output unit such as a waveguide type optical switch, a module to which a single mode optical fiber is connected can be easily manufactured. become.

(Embodiment 5) FIG. 20 is a perspective view showing a fifth embodiment of the present invention. In the present embodiment, the spot is expanded vertically by simply gradually thinning the thickness of the core 25 in the spot converter. In this embodiment, the lateral expansion of the spot is performed only by the width of the ridge 30. Therefore, although the effect is not as great as that of the first embodiment, a small spot of the optical function portion can be converted into a large spot.

(Sixth Embodiment) FIG. 21 is a perspective view showing a sixth embodiment of the present invention. In this embodiment, the width of the core 25 of the spot conversion portion is tapered to widen the field distribution in the vertical and horizontal directions, and the core 26 is tapered toward the distal end of the waveguide, so that the lateral direction is increased. The spot size has been further expanded.

(Embodiment 7) FIG. 22 is a perspective view of a seventh embodiment of the present invention, in which the thickness of the core 25 of the spot conversion portion III is reduced toward the tip of the waveguide and the enlarged spot optical waveguide is used. The spot size in the lateral direction is further expanded by widening the IV core 26 in a tapered shape toward the tip of the waveguide.

In the sixth embodiment shown in FIG. 21 and the seventh embodiment shown in FIG. 22, the width of the core 26 of the enlarged spot optical waveguide is widened toward the tip of the waveguide so that the spot is laterally moved. Since the width of the core 26 is increased and the width of the core 26 is increased, the manufacturing tolerance of the width of the core 26 is increased. On the contrary, even if the width of the core 26 is narrowed toward the tip of the waveguide, the field distribution of the guided light is small. Since it leaks to the left and right, the spot size can be increased. Further, even when the width of the core 25 of the spot conversion unit is constant, a spot defined by the width of the core 25 or the width of the core 25 and the width of the ridge 30 can be realized.

Further, in each of the embodiments of the present invention, the ridge width of the spot conversion portion and the enlarged spot optical waveguide has been described as being constant (Ws), but it may be changed by widening in a taper shape toward the tip of the waveguide. May be. Furthermore, although the core 25 and the core 26 have been described as different materials, it is needless to say that the same material, that is, a part of the core 25 may be used as the core 26.

Since one feature of the present invention is that the common core 26 is thin, the enlarged spot has a Gaussian distribution fitted with the peak value and the value at 1 / e ² as shown in FIG. It is narrower near the half value than. Furthermore, the present invention can be applied not only to semiconductors but also to dielectric optical waveguides such as quartz optical waveguides.

(Embodiment 8) FIG. 24 shows a perspective view of an eighth embodiment of the present invention, and FIG. 25 shows a sectional view taken along the line BB '. For simplicity, an optical phase modulator is used as an example of the optical function unit. As can be seen from FIG. 24, in the optical phase modulator section I and the propagation optical waveguide section II, the i-MQW core is not a buried type but a ridge type. In the figure, I is an optical phase modulator section, II is a propagation optical waveguide section, III is a spot conversion section, and IV is an enlarged spot optical waveguide section. 21 is a p-side electrode, 22 is an InGaAs cap layer, and 23 is p-InP
Clad, 24 is i-InP side clad, 25 is, for example, i-InGaAlAs (well) / InAlAs
(Barrier) It is a multiple quantum well (MQW), and if the well thickness is 9 nm and the barrier thickness is 5 nm, the exciton peak wavelength is 1.44 μm, which is suitable for operation at 1.55 μm. The thickness of MQW25 is about 0.4 μm. Reference numeral 26 denotes a common core of the spot conversion optical waveguide, for example, i-InG having a bandgap wavelength λg of 1.1 μm.
It is an aAsP layer and has a thickness of 0.08 μm. The thickness may be slightly thicker or thinner, or may be another material such as InAlAs (since the refractive index of InGaAsP and InAlAs are different, the thickness of the core 26 in this case is naturally different). 27 is an n-InP clad, 2
Reference numeral 8 is an n-InP substrate, and 29 is an n-side electrode. 3
Reference numeral 0 denotes the cladding of the expanded spot optical waveguide as described above, and p-InP is used here, but i-InP may be used. Furthermore, as can be seen from FIGS. 24 and 25,
Unlike the above-described embodiment, in this embodiment, the thickness D of the core 25a of the spot conversion portion III is different from the thickness of the core 25 of the propagation optical waveguide portion. As will be described later, this makes it possible to reduce conversion loss during spot conversion.

26 to 29 are views for explaining the manufacturing process of the eighth embodiment of the present invention. As shown in FIG. 26, n
On the InP substrate 28, n-InP clad 27, i-
An InGaAsP core 26 and an i-MQW core 25 are deposited (at this time, the i-M is formed to protect the i-MQW layer 25 and facilitate InP regrowth described later.
A thin i-InP layer may be deposited on the QW layer 25). Then, a photoresist 31 is spin-coated on the entire surface, and the i
-Dry etching or wet etching is performed while leaving the MQW 25 by the thickness D. Next, the resist is spin-coated again on the entire surface and then patterned as shown in FIG. 27 (at this time, the patterning is tapered so that it can be easily inferred from FIG. 24 when viewed from the upper surface). Then, the i-MQW layer 25 is dry-etched or wet-etched into a taper shape as shown in FIG.
FIG. 28 is a transverse sectional view at this time.

In the case of the long-wavelength semiconductor described here, by using a sulfuric acid-based etchant, i-
The InGaAlAs well and i-InAlAs can be etched, and the etching can be stopped by i-InP (referred to as selective etching technique). Therefore, in the i-MQW layer 25, the i-InP having a thickness of about 5 nm to 10 nm is formed.
If a layer is added, it can be made to function as an etch stop layer, leaving a thickness D as shown in FIG. In addition, if an i-InP layer is inserted between the i-MQW layer 25 and the i-InGaAsP core layer 26, the i-InP layer functions as an etch stop layer, and the i-M of the spot converter is formed.
The QW layer can be processed into a tapered shape. Alternatively, this i
If the thickness of the nP layer is set to about 0.2 μm, the dry etching can be performed in a tapered shape without etching the core 26 of the enlarged spot optical waveguide at the time of etching the i-MQW layer of the spot conversion section III. Providing this layer is also a feature of the present invention.

The next fabrication process is shown in FIG. Here, the region selective growth technique described above is used.
FIG. 29 shows the SiO ₂ mask 32 for selective growth in FIG.
It is a top view at the time of forming in the chip of FIG. Therefore, as described in the first embodiment, as shown in FIG. 29, the optical phase modulator section I and the propagation optical waveguide section II have no SiO ₂ mask, and the spot conversion section III and the enlarged spot optical waveguide IV are not provided. If the SiO ₂ mask 32 is formed, the In of the optical phase modulator portion I and the optical waveguide portion II for propagation can be obtained by the area selective growth.
The thickness of the spot conversion portion III and the InP cladding 30 of the enlarged spot optical waveguide IV can be formed several times thicker than the thickness of the P cladding 23. That is, In in the optical waveguide portion for propagation
If the thickness of the P clad 23 is 1.5 μm, the thickness of the InP clad can be 4.5 to 6 μm in the spot converter III and the enlarged spot optical waveguide IV. Since the spot size of the guided light is as large as about 5 μm at the tip of the element of the spot size conversion unit III, a thick clad is required, but it can be formed by this manufacturing method. The final ridge processing is performed by dry etching or wet etching.

Now, the operation of this embodiment will be described.
First, the role of the i-InP side cladding 24 in the optical phase modulator section I and the propagation optical waveguide section II will be briefly described with reference to FIG. As described in Example 1,
If the side clad 24 is thin, the guided light feels a low refractive index of air in a place where the InP clad 23 does not exist, and the equivalent refractive index in that place decreases. On the other hand, at the location where the p-InP clad 19 is present, the light leaked onto the core feels its refractive index, so that the equivalent refractive index becomes high and lateral light confinement becomes possible.

In the present embodiment, as shown in FIG. 25, the guided light F ₁ propagated through the optical phase modulator section I and the propagation optical waveguide section II is incident on the spot conversion section III. Since the width of the core is tapered in the spot conversion section III, the light confinement becomes loose as shown by F ₂ , and the spot size is increased not only in the left and right but also in the up and down direction and finally emitted. . The emitted light is vertically confined by the common core 26. However, since the core 26 is thin, the vertical confinement of the guided light in the core becomes loose, and as a result, as shown by the spot size F ₃ of the guided light in the vertical direction, the optical phase modulator section and the optical waveguide for propagation are propagated. The size can be greatly enlarged as compared with the parts (the vertical spot size in these parts is about 0.3 μm). On the other hand, the lateral spot size is shown in FIG.
As shown in FIG. 0, the width Ws of the clad of the ridge in the spot conversion part is equal to the width Wp of the clad of the optical waveguide part for propagation.
Compared with (about 2 μm), the width can be made extremely large (Ws is set to about 10 μm in FIG. 26).

As described above, in this embodiment, since the enlarged spot optical waveguide has the ridge structure, the optical function part is structurally the same as the optical device having the ridge structure, and thus the manufacturability is good, and the shape of the field distribution is good. Due to the similarity of the above, the coupling characteristics of the propagation optical waveguide portion, the spot conversion portion, and the enlarged spot optical waveguide are also good. Further, since the enlarged spot optical waveguide has a ridge structure, it has an advantage that the propagation loss is small, and a large spot can be realized. As a result, the coupling with the single mode optical fiber (spot size is about 4 μm) also has low loss as shown in FIG. Furthermore, since the spot size has been expanded, the tolerance of misalignment is large,
The optical device and the fiber can be easily connected.

Now, the spot converter III shown in FIG.
The influence of the thickness D of the core 25a in FIG.
Generally, the conversion loss from a large spot to a small spot is larger than the conversion loss from a small spot to a large spot. Therefore, here, the spot conversion loss in the spot conversion unit III when the eigenmode of the enlarged spot optical waveguide IV is converted into the eigenmode of the propagation optical waveguide unit II will be considered. FIG. 32 shows the calculated value and the experimental value of the spot conversion loss with the thickness D of the core 25a of the spot conversion section III as a parameter. Since the thickness of the core 25 of the propagation optical waveguide section II is 0.4 μm, D = 0.4 μm in the figure means that the propagation optical waveguide section II and the spot conversion section III have the same core thickness. From the figure,
It can be seen that the spot conversion loss can be significantly reduced by making the thickness of the core of the spot conversion portion III 0.15 μm, which is smaller than the thickness (0.4 μm) of the core of the propagation optical waveguide portion II. The physical meaning of this result will be discussed below. Since the optical function part I and the propagation optical waveguide part II have a ridge structure, if the thickness of the side clad 24 is set to about 50 nm, the phase modulation characteristic will be obtained even though the core 25 has a large thickness of 0.4 μm. Ridge width W to ensure
Single mode propagation can be realized even if p is as wide as 2 μm.
However, since the spot converter is an embedded waveguide, multi-mode propagation occurs when the thickness is 0.4 μm and the core width is 2 μm. In order to solve this, if the core width in the spot converter is narrowed to allow single mode propagation, the width becomes narrower, making it difficult to fabricate, and the spot size of the spot converter III becomes smaller. The coupling loss with the optical waveguide section II becomes large. Therefore, it is better to reduce the thickness of the core 25a of the spot converter III as in the present embodiment. In addition,
In the above description, it is assumed that D = 0.15 μm is preferable, but this is the case when compared with D = 0.4 μm. Although the characteristics may change, other thicknesses may be used, and the core 25 of the optical waveguide portion II for propagation may have a different thickness. It goes without saying that the preferable value of D differs depending on the thickness and the refractive index. Also spot conversion unit III
Needless to say, the taper shape of the core 25a may be not only a straight line but also a curved line or a polygonal line not only in the present embodiment but also in the embodiments described later.

In the enlarged spot optical waveguide of the eighth embodiment, the core is only a thin layer of the i-InGaAsP layer 26 (here, it is 0.08 μm), and the field distribution spreads largely up and down. In this eighth embodiment, the ridge 3
Although the portion other than 0 is etched right above the InGaAsP core 26, the thickness of the i-InGaAsP core layer 26 is as thin as about 0.08 μm, so that the lateral protrusion of the guided mode to this portion is small. .

(Embodiment 9) As shown in FIG. 33, which is the ninth embodiment of the present invention, the i-InGaAsP core 26 other than the ridge portion in the spot conversion portion and the enlarged spot optical waveguide is removed with a sulfuric acid-based etchant. May be. Alternatively, i-InG under the SiO ₂ mask 32 (see FIG. 29) is used.
If the aAsP layer 26 is removed before depositing the SiO ₂ mask 32, the width of the ridge can be formed in the spot conversion portion by the area selective growth technique.
The etching process of the AsP layer 26 becomes unnecessary.

(Embodiment 10) As described above, the Γ factor of the power of the guided light to the core 26 of the spot conversion portion is small, so that in the expanded spot optical waveguide IV, as shown in FIG. It may be provided. The width of the side clad may be changed, and the side clad may be provided on the entire surface of the core 26.

(Embodiment 11) FIG. 35 shows a spot converter.
An example is shown in which the core 25b of III is left even on the end face of the enlarged spot waveguide section IV. Even with such a structure, the spot can be enlarged.

(Embodiment 12) In this embodiment, in the expanded spot optical waveguide IV, lateral light is confined by a ridge, and the propagation optical waveguide portion II and the spot conversion portion are used.
The thickness of the cores 25 and 25b is changed at the connection point between III. FIG. 36 eliminates the common core 26 in FIG.
Tapered core 25 left on the end surface of the enlarged spot
b is the core of the enlarged spot optical waveguide.

(Embodiment 13) FIG. 37 shows a thirteenth embodiment of the present invention. In the present embodiment, the spot is expanded vertically by merely gradually thinning the thickness of the core 25c in the spot conversion unit. In this embodiment, the lateral expansion of the spot is performed only by the width of the ridge 30. Therefore, the effect is not as great as that of the eighth embodiment, but the small spot of the optical function portion can be converted into a large spot.

(Embodiment 14) FIG. 38 shows a fourteenth embodiment of the present invention. In the present embodiment, the core 25 of the spot conversion unit
The width of “a” is tapered to expand the field distribution vertically and horizontally, and the core 26a of the expanded spot optical waveguide IV is formed.
The width of the spot in the lateral direction is further increased by widening the area toward the tip of the waveguide in a tapered shape.

(Embodiment 15) FIG. 39 shows a fifteenth embodiment of the present invention in which the core 25c of the spot conversion portion is made thinner toward the tip of the waveguide, and the core 26a of the enlarged spot optical waveguide is formed. The spot size in the lateral direction is further expanded by widening the width toward the tip of the waveguide in a tapered shape.

Further, the core of the propagation optical waveguide section and the core of the spot conversion section may be made of the same material or different materials. In the above description, the optical function part is the ridge waveguide, but the present invention can be applied to a buried waveguide such as a semiconductor laser. It goes without saying that the present invention can be applied not only to the semiconductor optical waveguide but also to the silica optical waveguide.

(Embodiment 16) Now, for example, the eighth embodiment of the present invention described above will be described. As can be seen from the cross-sectional view of FIG. 25, the core 25 of the optical waveguide portion II for propagation and the spot conversion portion. The thickness of the III core 25a is different,
Moreover, the bottom surface of the core 25 of the propagation optical waveguide portion and the bottom surface of the core 25a of the spot conversion portion are in the same plane. Therefore, the center of the core 25 of the optical waveguide section II for propagation and the spot conversion section II
The centers of the cores 25a of I 2 do not coincide with each other in the thickness direction, and the lights propagating through the propagation optical waveguide section II and the spot conversion section III are vertically off-axis. As a result, equation (2)
Accordingly, a connection loss occurs due to the axis deviation (about 0.7 dB when the thickness of the core 25 of the propagation optical waveguide section II is 0.4 μm and the thickness of the core 25a of the spot conversion section III is 0.15 μm). It will be a degree of coupling loss).

FIG. 40 is a perspective view of a sixteenth embodiment of the present invention, which is for eliminating the axial misalignment of the core in the thickness direction. 41 is a sectional view taken along the line BB ′ of FIG. As can be seen from FIGS. 40 and 41, in this embodiment, a buffer layer 33 such as InP is newly provided on the substrate 28, and the thickness of the core in the spot conversion portion III is set to the optical waveguide portion II for propagation (and Even if the thickness is smaller than the core thickness in the optical phase modulator section I), the thickness of the buffer layer 33 in the propagation optical waveguide section II is different from that in the spot conversion section III.
5a and the center of the core 25 in the propagation optical waveguide portion II in the thickness direction can be aligned. Therefore, by using the structure of the present embodiment, it is possible to eliminate the coupling loss due to the different thicknesses of the cores in the propagation optical waveguide section II and the spot conversion section III. In addition,
In addition to providing the buffer layer 33, the optical waveguide portion for propagation II
And the thickness of the buffer layer 33 in the spot conversion section III is different, instead of the substrate 28 of the optical waveguide section II for propagation.
Etching has the same effect.

(Embodiment 17) FIG. 42 is a perspective view of a seventeenth embodiment of the present invention, and FIG. 43 is a sectional view taken along the line BB '. In this embodiment, the thin film core 34 is also provided above the core 25a of the spot converter. In the present embodiment, since the light is distributed to the common core 26 and the thin film core 34 in the expanded spot optical waveguide IV, the centers of the light field distributions in the expanded spot optical waveguide IV and the spot conversion unit III are also aligned in the thickness direction. It is possible to further reduce the loss.

[0079]

As described above, according to the present invention, as the optical waveguide structure of the enlarged spot optical waveguide portion, light is confined vertically with a thin core and laterally confined with a ridge structure. , There is little light bleeding in the lateral direction,
As a result, a single mode optical waveguide having a large spot size can be realized. Furthermore, in the structure in which the core of the spot conversion unit is thin, the conversion loss during conversion of the spot size is particularly small, and the expanded spot optical waveguide has a ridge structure. With respect to the waveguide device having the ridge structure in the waveguide portion, there is an effect that a particularly excellent spot conversion optical waveguide can be realized from the viewpoints of manufacturability, spot size conversion characteristics, and propagation loss. Furthermore, by arranging the center of the second core in the thickness direction so as to coincide with the center of the first core in the thickness direction, or by disposing at least the fourth core above the second core.
By providing the thin film core, the center of the field distribution of light propagating through the second core in the thickness direction can be aligned with the center of the field distribution of light propagating through the first core in the thickness direction. It is possible to reduce the connection loss due to axial misalignment in the thickness direction of the core in the connection portion between the core portion and the first core portion, or to reduce the center of the field distribution of light propagating through the second core in the thickness direction. Since the centers of the field distributions of the light propagating through the third core and the fourth core can be matched in the thickness direction, the guided light in the thickness direction of the second core portion and the cores of the third core portion and the fourth core portion There is an advantage that the connection loss due to the axis shift can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic cross section and a refractive index distribution for explaining the principle of the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of the spot conversion optical waveguide of the present invention.

FIG. 3 is a characteristic diagram illustrating an operation of the spot conversion optical waveguide of the present invention.

FIG. 4 is a diagram showing a schematic cross section and a refractive index distribution for explaining the principle of the present invention.

FIG. 5 is a perspective view of the first embodiment of the present invention.

FIG. 6 is a cross-sectional view of the first embodiment of the present invention.

FIG. 7 is a cross-sectional view illustrating the manufacturing procedure of the first embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating the manufacturing procedure of the first embodiment of the present invention.

FIG. 9 is a top view illustrating the manufacturing procedure of the first embodiment of the present invention.

FIG. 10 is a characteristic diagram showing the relationship between the thickness of the common core and the size of the converted spot size in the thickness direction.

FIG. 11 is a characteristic diagram showing the relationship between the clad width of the ridge and the lateral size of the converted spot size.

FIG. 12 is a perspective view of a second embodiment of the present invention.

FIG. 13 is a perspective view of a third embodiment of the present invention.

FIG. 14 is a cross-sectional view of the third embodiment of the present invention.

FIG. 15 is a characteristic diagram showing the relationship between the thickness of the spot size conversion core and the spot size in the thickness direction.

FIG. 16 is a characteristic diagram showing a relationship between a clad width of a ridge and a spot size.

FIG. 17 is a characteristic diagram showing a relationship between a ridge width and a coupling loss in coupling with a single mode fiber.

FIG. 18 is a perspective view of the fourth embodiment of the present invention.

FIG. 19 is a perspective view of a modification of the fourth embodiment of the present invention.

FIG. 20 is a perspective view of the fifth embodiment of the present invention.

FIG. 21 is a perspective view of a sixth embodiment of the present invention.

FIG. 22 is a perspective view of a seventh embodiment of the present invention.

FIG. 23 is a diagram showing a power distribution of light in the depth direction.

FIG. 24 is a perspective view of an eighth embodiment of the present invention.

FIG. 25 is a sectional view of an eighth embodiment of the present invention.

FIG. 26 is a sectional view for explaining the manufacturing method according to the eighth embodiment of the present invention.

FIG. 27 is a cross-sectional view illustrating the manufacturing method of the eighth example of the present invention.

FIG. 28 is a sectional view for explaining the manufacturing method according to the eighth embodiment of the present invention.

FIG. 29 is a cross-sectional view explaining the manufacturing method of the eighth example of the present invention.

FIG. 30 is a characteristic diagram illustrating an operation of the eighth embodiment of the present invention.

FIG. 31 is a characteristic diagram illustrating an operation of the eighth embodiment of the present invention.

FIG. 32 is a characteristic diagram illustrating the operation of the eighth embodiment of the present invention.

FIG. 33 is a perspective view of the ninth embodiment of the present invention.

FIG. 34 is a perspective view of a tenth embodiment of the present invention.

FIG. 35 is a perspective view of an eleventh embodiment of the present invention.

FIG. 36 is a perspective view of a twelfth embodiment of the present invention.

FIG. 37 is a perspective view of a thirteenth embodiment of the present invention.

FIG. 38 is a perspective view of a fourteenth embodiment of the present invention.

FIG. 39 is a perspective view of a fifteenth embodiment of the present invention.

FIG. 40 is a perspective view of a sixteenth embodiment of the present invention.

FIG. 41 is a sectional view of a sixteenth embodiment of the present invention.

FIG. 42 is a perspective view of a seventeenth embodiment of the present invention.

FIG. 43 is a sectional view of a seventeenth embodiment of the present invention.

FIG. 44 is a diagram showing a schematic cross section and a refractive index distribution of a first conventional example.

FIG. 45 is a diagram showing a schematic cross section and a refractive index distribution of a second conventional example.

FIG. 46 is a perspective view of a third conventional example.

FIG. 47 is a top view of a third conventional example.

FIG. 48 is a sectional view of a third conventional example.

FIG. 49 is a perspective view of a fourth conventional example.

[Explanation of symbols]

1 clad 2 core 3 clad 4 clad of optical function part 5 core of optical function part 6 core of optical waveguide for propagation 7 clad of optical waveguide for propagation 8 core of optical waveguide for spot size conversion 9 core of optical waveguide for propagation 10 spots Conversion optical waveguide core 11 Upper clad 12 Lower clad 13 InP substrate 14 Upper clad 15 Thin film core 16 Lower clad 21 p-side electrode 22 InGaAs cap layer 23 p-InP clad 24 i-InP side clad 25 i-MQW 26 Spot conversion Common core for use 27 n-InP clad 28 n-InP substrate 29 n-side electrode 30 Spot conversion optical waveguide clad 31 Photoresist 32 Region selective growth SiO ₂ mask 33 Buffer layer 34 Thin film core

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroaki Takeuchi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (10)

[Claims] 1. A propagation optical waveguide having a first core through which guided light with a small spot size propagates, a spot converter having a second core that converts the spot size of the guided light, and guided light with a large spot size. In the spot conversion optical waveguide including the enlarged spot optical waveguide including the third core that propagates, the third core has a thin film shape, and the enlarged spot optical waveguide includes a ridge for lateral confinement of the propagated guided light. The power of light in the expanded spot optical waveguide having a structure has a coordinate in the depth direction of the power distribution in at least part of a peak value of the power distribution of the light in the depth direction and a half value of the peak value. The power distribution is more positive than the Gaussian distribution fitted with the full width at half maximum of the power distribution in the depth direction, in which the second derivative is positive. Is narrow, and 1 of the peak value
/ E ² value, the full width at half maximum of the power distribution is narrower than the full width at half maximum of the Gaussian distribution, and the guided light propagates substantially in a single mode in the expanded spot optical waveguide. A spot conversion optical waveguide characterized by: 2. The ridge structure comprises an upper clad formed on the third core.
Spot conversion optical waveguide described in. 3. The spot conversion optical waveguide according to claim 1, wherein the ridge structure includes a third core and an upper clad formed on the third core. 4. The spot conversion optical waveguide according to claim 1, further comprising a side cladding on a side surface of the ridge structure. 5. The spot according to claim 1, wherein at least one of the thickness and the width of the second core of the spot conversion section changes toward the tip of the waveguide. Conversion optical waveguide. 6. The spot conversion optical waveguide according to claim 1, wherein the first core and the second core are laminated with the third core. 7. The first and second cores and the third core
The spot conversion optical waveguide according to claim 6, wherein at least one semiconductor layer is provided between the cores. 8. The spot conversion optical waveguide according to claim 1, wherein the second core and the third core are formed on the same plane of a common lower cladding. 9. The bottom surface of the second core is arranged above the bottom surface of the first core.
9. The spot conversion optical waveguide according to any one of 1 to 8. 10. The spot conversion optical waveguide according to claim 1, wherein at least a thin film-shaped fourth core is provided above the second core.