KR101160246B1 - Resonator of Hybrid LASER Diode - Google Patents

Abstract

A resonator of a hybrid laser diode is provided. The resonator is provided on a hybrid waveguide, a substrate including a semiconductor layer consisting of a multimode waveguide and a single mode waveguide in series, and a hybrid waveguide of the semiconductor layer, the tapered form overlapping a portion of the multimode waveguide. And a compound semiconductor waveguide comprising a coupling structure at one end, and a reflecting portion provided at one end of the single mode waveguide. The multimode waveguide has a narrower width than the hybrid waveguide, and the single mode waveguide has a narrower width than the multimode waveguide.

Laser, diode, resonator, hybrid, single mode

Description

Resonator of Hybrid LASER Diode

The present invention relates to a hybrid laser diode, and more particularly to a resonator of a hybrid laser diode.

The present invention is derived from a study conducted as part of the IT source technology development project of the Ministry of Knowledge Economy and the Ministry of Information and Telecommunication Research and Development. [Task management number: 2006-S-004-03, Title: Silicon substrate ultra-high speed optical interconnection IC] .

Hybrid laser diodes using heterogeneous coupling of silicon and group III-V compound semiconductors have attracted attention as a light source for silicon photonics technology in which optical devices and electronic devices are fused.

When such a hybrid laser diode is used as a light source for information transmission, it is required to implement a laser diode operating in a single mode in order to improve transmission quality.

The emergence of Silicon On Insulator (SOI) substrates allows the construction of silicon optical waveguides. Accordingly, the optical device can be integrated into the electronic device of the silicon substrate. This new field of research is called silicon photonics. However, since silicon itself cannot gain in the wavelength band for optical communication, the use of an external light source is inevitable. In order to overcome these difficulties, hybrid laser diodes using wafer bonding between compound semiconductors and silicon have recently been studied.

In the case of hybrid laser diodes, they are manufactured through wafer bonding technology, and thus, a technique for creating various types of structures by the regrowth method used in compound semiconductor laser diodes cannot be used in hybrid laser diodes.

The part of the hybrid laser diode that determines its performance is the structure of the compound semiconductor waveguide. Structures that can be used as the structure of the compound semiconductor waveguide include a ridge waveguide and a slab waveguide. In the case where the structure of the compound semiconductor waveguide is a ridge waveguide, a single mode waveguide can be formed even when the cross-sectional area of the silicon waveguide is small, and there is an advantage of having a high current confinement characteristic. However, the leakage current due to the surface recombination effect on the surface of the compound semiconductor waveguide exposed to the outside has a big disadvantage. On the other hand, when the structure of the compound semiconductor waveguide is a slab waveguide, the slab waveguide is basically a waveguide that supports multiple modes, and in order to increase the current binding characteristic, an impurity region that binds the current must be formed using ion implantation technology. Since it is difficult to form the width of the impurity region accurately and accurately, there is a disadvantage that stable fundamental mode oscillation is difficult.

An object of the present invention is to provide a hybrid laser diode capable of stable basic mode oscillation while minimizing the effect of surface coupling generated in a compound semiconductor waveguide of a resonator.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, the present invention provides a resonator of a hybrid laser diode. The resonator is provided on a hybrid waveguide, a substrate including a semiconductor layer consisting of a multimode waveguide and a single mode waveguide in series, and a hybrid waveguide of the semiconductor layer, the tapered form overlapping a portion of the multimode waveguide. The compound semiconductor waveguide including a coupling structure at one end, and a reflecting portion provided at one end of the single mode waveguide. The multimode waveguide may have a narrower width than the hybrid waveguide, and the single mode waveguide may have a narrower width than the multimode waveguide.

The compound semiconductor waveguide may have a width of 5 μm or more.

The compound semiconductor waveguide may include a III-V compound semiconductor.

The substrate may be a silicon-on-insulator (SOI) substrate comprising a base semiconductor layer, an insulator layer on the base semiconductor layer, and a semiconductor layer on the insulator layer. The compound semiconductor waveguide may be formed by bonding with the semiconductor layer of the substrate.

The apparatus may further include a mode selector provided between the multimode waveguide and the single mode waveguide. The mode selector may be a multimode interference waveguide.

The reflector may use a waveguide or facet reflection in which a diffraction grating is formed.

The hybrid waveguide, the multimode waveguide and the single mode waveguide may be connected in series by the transition region waveguides provided therebetween. The transition region waveguide may have a width that narrows from the hybrid waveguide to the multimode waveguide and from the multimode waveguide to the single mode waveguide.

As described above, according to the problem solving means of the present invention, the semiconductor layer of the resonator is composed of a waveguide for hybrid, multi-mode waveguide, single-mode waveguide to eliminate the higher-order mode, propagating and amplifying only the basic mode, so that only the basic mode oscillates Can be. Accordingly, even if the compound semiconductor waveguide has a wide width, a hybrid laser diode capable of basic mode oscillation can be provided.

In addition, according to the problem solving means of the present invention, since the compound semiconductor waveguide of the resonator has a wide width, the effect of the surface coupling is minimized, the threshold current can be lowered. Accordingly, by minimizing leakage current, a hybrid laser diode having improved stability may be provided.

In addition, according to the problem solving means of the present invention, the semiconductor layer of the resonator includes a hybrid waveguide and a multi-mode waveguide having a wide width, and the compound semiconductor waveguide has a wide width, so that between the semiconductor layer and the compound semiconductor waveguide Precise processing for optical coupling may not be required. Accordingly, a hybrid laser diode which can be manufactured in an easy process with low precision can be provided.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in different forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the invention to those skilled in the art, and the invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. As used herein, the terms 'comprises' and / or 'comprising' mean that the stated element, step, operation and / or element does not imply the presence of one or more other elements, steps, operations and / Or additions. In addition, since they are in accordance with the preferred embodiment, the reference numerals presented in the order of description are not necessarily limited to the order. In addition, in the present specification, when it is mentioned that a film is on another film or substrate, it means that it may be formed directly on the other film or substrate or a third film may be interposed therebetween.

In addition, the embodiments described herein will be described with reference to cross-sectional and / or plan views, which are ideal exemplary views of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for effective explanation of technical content. Accordingly, shapes of the exemplary views may be modified by manufacturing techniques and / or tolerances. Accordingly, the embodiments of the present invention are not limited to the specific forms shown, but also include variations in forms generated by the manufacturing process. For example, the etched area shown at right angles may be rounded or may have a shape with a certain curvature. Accordingly, the regions illustrated in the figures have schematic attributes, and the shape of the regions illustrated in the figures is intended to illustrate a particular form of region of the device and not to limit the scope of the invention.

1 is a graph illustrating a change in light binding coefficient of an active layer according to a thickness of a silicon layer in a general hybrid laser diode.

Referring to FIG. 1, in a hybrid laser diode including a silicon slab waveguide and a compound semiconductor ridge waveguide, the active layer of the first higher mode in the basic mode and the vertical direction according to the thickness of the silicon slab waveguide is shown. The light bond coefficient is shown.

In the form of the waveguide mode for the three cases (a, b and c), the thinner the thickness of the silicon slab waveguide, the more the waveguide mode distribution shifts toward the compound semiconductor ridge waveguide. At this time, the first higher order mode does not exist when the thickness of the silicon slab waveguide is very thin (in case of c). However, as the thickness of the silicon slab waveguide becomes thicker, the entire waveguide guides the higher order mode, and the optical bond coefficient of the compound semiconductor ridge waveguide increases (in the case of b). At this time, the silicon slab waveguide guides the basic mode, but the light binding coefficient of the silicon slab waveguide is reduced (in case of a).

This tendency is the same when the silicon waveguide is a ridge waveguide. In other words, the silicon waveguide must be thin in order for the basic mode to be oscillated. This means that the distribution of the waveguide modes in the left and right directions is determined by the width of the compound semiconductor ridge waveguide, and in order to guide only the single mode, the width of the compound semiconductor ridge waveguide should be a small value around 1 μm.

As described above, when the compound semiconductor ridge waveguide has a narrow width of about 1 μm, in a hybrid laser diode that cannot use the regrowth method, the leakage current due to the surface coupling effect on the surface of the compound semiconductor ridge waveguide exposed to the outside is very large. do.

As a method for minimizing the surface coupling that causes the leakage current, which is the problem described above, the compound semiconductor ridge waveguide is widened and impurities are injected into the compound semiconductor ridge waveguide except the region overlapping with the basic mode to suppress oscillation in the higher order mode. can do. However, it is difficult to set a gain region having a width of about 3 μm because of the problem of precision that the interface between the impurity region and the gain region is difficult to be clearly defined in both the vertical direction and the horizontal direction.

2A is a plan view illustrating a resonator of a hybrid laser diode according to an exemplary embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along the line II ′ of FIG. 2A.

2A and 2B, a resonator of a hybrid laser diode includes a substrate 110 including a base silicon layer 112, an insulator layer 114, and a silicon layer 116, and a silicon layer 116 of the substrate 110. The compound semiconductor waveguide 210 is provided on the (), and the reflector 128 provided at one end of the silicon layer 116.

The resonator of the hybrid laser diode is configured to provide an optical path through which light of a particular wavelength can reciprocate so that light of the same phase can be amplified. The optical path of the resonator of the hybrid laser diode according to the embodiment of the present invention is the silicon layer 116 of the substrate 110, the compound semiconductor waveguide 210 provided on the silicon layer 116 and one end of the silicon layer 116. It may be composed of a reflector 128 provided in.

2A and 2B show part of a resonator of a hybrid laser diode. This is for convenience of description, and the resonator of the actual hybrid laser diode according to the embodiment of the present invention may be an intact structure further including a mirror symmetrical portion with respect to the right side of the drawings. The structure of the resonator of such a hybrid laser diode is taken for granted to those skilled in the art having ordinary skill in the art.

That is, the resonator of the hybrid laser diode according to the exemplary embodiment of the present invention may include a substrate 110 including a base silicon layer 112, an insulator layer 114, and a silicon layer 116, and a silicon layer 116 of the substrate 110. The compound semiconductor waveguide 210 is provided on the (), and the reflecting portion 128 provided at both ends of the silicon layer 116.

The substrate 110 may be an SOI substrate. The silicon layer 116 may be formed by connecting the hybrid waveguide 120h, the multimode waveguide 122, and the single mode waveguide 126 in series. The multimode waveguide 122 may have a narrower width than the hybrid waveguide 120h, and the single mode waveguide 126 may have a narrower width than the multimode waveguide 122.

The hybrid waveguide 120h, the multimode waveguide 122, and the single mode waveguide 126 may be connected in series by the transition region waveguides provided therebetween. The transition region waveguide may have a gradually narrower width from the hybrid waveguide 120h to the multimode waveguide 122 and from the multimode waveguide 122 to the single mode waveguide 126.

The compound semiconductor waveguide 210 may be provided on the hybrid waveguide 120h of the silicon layer 116 of the substrate 110. One end of the compound semiconductor waveguide 210 may be a tapered shape coupling structure 210t overlapping a portion of the multi-mode waveguide 122 of the silicon layer 116. The region provided with the tapered coupling structure 210t may be referred to as an optical coupling region f.

The compound semiconductor waveguide 210 may be formed by bonding with the silicon layer 116 of the substrate 110. The compound semiconductor waveguide 210 is formed by patterning the silicon layer 116 of the substrate 110 by a photolithography process, so that the hybrid waveguide 120h and the multi-mode waveguide in which the silicon layer 116 is connected in series. Forming a substrate comprising a compound semiconductor waveguide 210 patterned on the substrate 110 for hybridization of the silicon layer 116 of the substrate 110. Bonding the waveguide 120 and the compound semiconductor waveguide 210 of the other substrate to face each other, and removing other substrates except the compound semiconductor waveguide 210.

The compound semiconductor waveguide 210 may include a III-V compound semiconductor. The compound semiconductor waveguide 210 may include InP, InGaAs, InGaAsP, AlGaInAs, or the like. Accordingly, the hybrid waveguide 120h and the compound semiconductor waveguide 210 may constitute a gain region h of the resonator of the hybrid laser diode. The compound semiconductor waveguide 210 may have a width of about 5 μm or more. The hybrid waveguide 120h may have the same width as the compound semiconductor waveguide 210 or may have a wider width. This may be to ensure sufficient misalignment margin in the process of bonding the compound semiconductor waveguide 210 to the hybrid waveguide 120h of the silicon layer 116 of the substrate 110.

The tapered coupling structure 210t, which is one end of the compound semiconductor waveguide 210, overlaps a portion of the multi-mode waveguide 122 of the silicon layer 116 in the optical coupling region f, thereby including a higher order mode. The waveguide mode can be easily propagated to the multi-mode waveguide 122 of the silicon layer 116.

The reflector 128 may be a distributed Bragg reflector (DBR) that is a waveguide in which a diffraction grating is formed. Alternatively, the reflector 128 may use facet reflection. The reflector 128 using surface reflection may be fabricated in a mirrored state at one end of the single mode waveguide 126 of the silicon layer 116. Accordingly, the basic mode propagated by the single mode waveguide 126 is the gain region h of the resonator of the hybrid laser diode composed of the hybrid waveguide 120h and the compound semiconductor waveguide 210 by the reflector 128. Can be fed back.

Operation of the resonator of the hybrid laser diode according to the embodiment of the present invention is as follows. The hybrid waveguide 120h and the compound semiconductor waveguide 210 include a higher-order mode generated in the gain region h of the resonator of the hybrid laser diode. The waveguide mode is the compound semiconductor waveguide 210 in the optical coupling region f. Propagates through the tapered coupling structure 210t to the multimode waveguide 122 of the silicon layer 116, and the waveguide mode including the higher order mode passes through the multimode waveguide 122 to the single mode waveguide 126. The higher order modes that are propagated and included in the waveguide mode propagated to the single mode waveguide 126 are eliminated due to the extreme loss through the single mode waveguide 126, and only the basic mode included in the waveguide mode is removed. The resonator of the hybrid laser diode is a waveguide mode that propagates to the reflector 128 provided at one end of 126 and includes only the basic mode reflected by the reflector 128. It is fed back to the gain region (h).

In addition, the waveguide mode including only the fundamental mode precious to the gain region h of the resonator of the hybrid laser diode is a multimode waveguide (not shown), a single mode waveguide included in a mirror symmetrical part with respect to the right side of the drawings. As propagated and returned through the (not shown) and the reflector (not shown), its modal gain can be relatively increased. Accordingly, the resonator of the hybrid laser diode according to the embodiment of the present invention can oscillate only the basic mode in which the modal gain is relatively increased.

Although the higher order modes included in the waveguide mode are lost as they pass through the single mode waveguide 126, this may be possible when the single mode waveguide 126 has a sufficient length. That is, it is necessary to reduce the length of the single mode waveguide 126 to form a resonator of a smaller size hybrid laser diode.

Accordingly, the resonator of the hybrid laser diode according to the exemplary embodiment of the present invention may further include a mode selector 124 provided between the multi mode waveguide 122 and the single mode waveguide 126. The mode selector 124 may be a multimode interference (MMI) waveguide. The multi-mode interference waveguide may be focused at different positions according to the mode refractive indices of the basic mode and the higher order mode included in the waveguide mode. That is, by arranging the single mode waveguide at the point of the focusing multi-mode interference waveguide of the basic mode included in the waveguide mode, only the basic mode included in the waveguide mode may propagate to the single mode waveguide 126.

By arranging the mode selector 126 having such a mode selection function between the multi-mode waveguide 122 and the single-mode waveguide 126, the hybrid laser diode composed of the hybrid waveguide 120h and the compound semiconductor waveguide 210 is provided. Although the gain region h of the resonator does not generate a waveguide mode including only the basic mode, the resonator of the hybrid laser diode may relatively increase the modal gain of the basic mode. Accordingly, the resonator of the hybrid laser diode according to the embodiment of the present invention can smoothly oscillate in the basic mode.

As a result, since the resonator of the hybrid laser diode according to the embodiment of the present invention may include the compound semiconductor waveguide 210 having a wide width, the effect of surface coupling may be reduced. Accordingly, the threshold current of the hybrid laser diode can be lowered.

In addition, since the resonator of the hybrid laser diode according to the embodiment of the present invention is an optical coupling between the multi-mode waveguide 122 and the compound semiconductor waveguide 210 having a sufficient width, the tapered form of the compound semiconductor waveguide 210 is provided. The process for forming the coupling structure 210t does not require precision of submicron precision. As a result, a process for manufacturing a hybrid laser diode may be easier.

The resonator of the hybrid laser diode according to the embodiment of the present invention is composed of a hybrid waveguide, a multimode waveguide, a single mode waveguide, and has a silicon layer that removes the higher-order mode and propagates and amplifies only the basic mode. Can be oscillated. Accordingly, even if the compound semiconductor waveguide has a wide width, a hybrid laser diode capable of basic mode oscillation can be provided.

In addition, the resonator of the hybrid laser diode according to the embodiment of the present invention has a wide compound semiconductor waveguide, thereby minimizing the effect due to surface coupling, thereby lowering the threshold current. Accordingly, by minimizing leakage current, a hybrid laser diode having improved stability may be provided.

In addition, the resonator of the hybrid laser diode according to the embodiment of the present invention has a silicon layer including a wide waveguide for hybrid and a multimode waveguide, and a wide compound semiconductor waveguide, thereby providing a silicon layer and a compound semiconductor waveguide. Precise processes for optical coupling between may not be required. Accordingly, a hybrid laser diode which can be manufactured in an easy process with low precision can be provided.

FIG. 3A is a plan view of a device structure modified to examine the fundamental mode oscillation characteristics of a resonator of a hybrid laser diode according to an embodiment of the present invention, and FIGS. 3B and 3C are respectively the basic mode and the higher order in the device of FIG. 3A. Figures showing the propagation characteristics of the mode.

Referring to FIG. 3A, the device for recognizing the fundamental mode oscillation characteristics of the resonator of the hybrid laser diode is defined by a single waveguide region 126 such that two devices having the resonator structure of the hybrid laser diode shown in FIG. 2A are mirror symmetric. It may be composed of two devices connected to each other and sharing a single waveguide region 126. These two devices may be composed of a first device and a second device, respectively, in which the reflector (see 128 in FIG. 2A) is omitted in the resonator structure of the hybrid laser diode shown in FIG. 2A. It can have a structure. In addition, the first device and the second device may have a structure in which a mode selector (see 124 of FIG. 2A) is omitted from the resonator structure of the hybrid laser diode illustrated in FIG. 2A.

The first apparatus includes a first multi-mode waveguide connected in series by a transition region waveguide to a first gain region consisting of a first hybrid waveguide 120ha and a first compound semiconductor waveguide 210a, and a first hybrid waveguide 120ha. 122a), and a single waveguide region 126 connected in series by the transition region waveguide to the first multi-mode waveguide 122a. The tapered coupling structure 210ta of the first compound semiconductor waveguide 210a may partially overlap the first multi-mode waveguide 122a.

The second device includes a second gain region composed of a second hybrid waveguide 120hb and a first compound semiconductor waveguide 210b, and a second multi-mode waveguide connected in series by a transition region waveguide to the second hybrid waveguide 120hb. 122b), and a single waveguide region 126 connected in series by the transition region waveguide to the second multi-mode waveguide 122b. The tapered coupling structure 210tb of the second compound semiconductor waveguide 210b may partially overlap the second multi-mode waveguide 122b.

3B and 3C, on the assumption that the waveguide mode is generated in the first gain region, when the waveguide mode is applied to the first gain region, the fundamental mode oscillation characteristics of the resonator of the hybrid laser diode are described. The results of measuring the propagation characteristics of the basic mode and the higher order mode in the device are shown. When the waveguide mode is applied to the second gain region, a result of inverting the top and bottom of FIGS. 3B and 3C may be seen.

As shown in FIG. 3B, when the basic mode is applied to the first gain region, the basic mode passes through the tapered coupling structure 210ta of the first compound semiconductor waveguide 210a to the first multi-mode waveguide 122a. Propagated, the basic mode propagates through the first multi-mode waveguide 122a to the single mode waveguide 126, and the basic mode propagates through the second multi-mode waveguide 122b through the second multi-mode waveguide 122b. It can be seen that it propagates to the second gain region through the tapered coupling structure 210ta of the two-component semiconductor waveguide 210b.

Alternatively, as shown in FIG. 3C, when a higher order mode is applied to the first gain region, the higher order mode passes through the tapered coupling structure 210ta of the first compound semiconductor waveguide 210a. 122a), and the higher order mode propagates through the first multi-mode waveguide 122a to the single mode waveguide 126, while the higher order mode undergoes extreme loss as it passes through the single mode waveguide 126 and is removed, It can be seen that the second multi-mode waveguide 122b and the second compound semiconductor waveguide 210b do not propagate to the tapered coupling structure 210ta and thus do not reach the second gain region.

In conclusion, the resonator of the hybrid laser diode according to the embodiment of the present invention includes a basic mode and a higher order mode in a gain region composed of a hybrid waveguide (see 120h of FIG. 2A) and a compound semiconductor waveguide (see 210 of FIG. 2A). Although the waveguide mode is generated, only the basic mode may be propagated by the multi-mode waveguide (see 122 of FIG. 2A), the single mode waveguide (see 126 of FIG. 2A), and the reflector 128. Accordingly, the resonator of the hybrid laser diode according to the embodiment of the present invention can smoothly oscillate only the basic mode in which the modal gain is increased.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. You will understand that. It is therefore to be understood that the above-described embodiments are illustrative and not restrictive in every respect.

1 is a graph for explaining the change of the optical binding coefficient of the active layer according to the thickness of the silicon layer in a typical hybrid laser diode;

2A is a plan view illustrating a resonator of a hybrid laser diode according to an exemplary embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along the line II ′ of FIG. 2A;

3A is a plan view of a device structure modified to examine the fundamental mode oscillation characteristics of a resonator of a hybrid laser diode according to an exemplary embodiment of the present invention, and FIGS. 3B and 3C are respectively a basic mode and a higher order mode in the apparatus of FIG. 3A. Figures showing the propagation characteristics of the.

* Description of the symbols for the main parts of the drawings *

110: SOI substrate 112: base silicon layer

114: insulator layer 116: silicon layer

120h, 120ha, 120hb: Waveguide for Hybrid

122, 122a, 122b: multi-mode waveguide 124: mode selector

126: single mode waveguide 128: reflector

210, 210a, 210b: compound semiconductor waveguide

210t, 210ta, 210tb: coupling structure

Claims (10)

A substrate including a semiconductor layer having a hybrid waveguide, a multimode waveguide and a single mode waveguide connected in series; A compound semiconductor waveguide provided on the hybrid waveguide of the semiconductor layer, the compound semiconductor waveguide having a tapered coupling structure overlapping a portion of the multimode waveguide; And A reflector provided at one end of the single mode waveguide, The multimode waveguide has a narrower width than the hybrid waveguide, and the single mode waveguide has a narrower width than the multimode waveguide. The method of claim 1, The compound semiconductor waveguide has a width of 5㎛ or more, the resonator of a hybrid laser diode. The method of claim 1, The compound semiconductor waveguide comprises a group III-V compound semiconductor resonator of a hybrid laser diode. The method of claim 1, And the substrate is a silicon on insulator (SOI) substrate comprising a base semiconductor layer, an insulator layer on the base semiconductor layer, and the semiconductor layer on the insulator layer. The method of claim 4, wherein And the compound semiconductor waveguide is formed by bonding the semiconductor layer of the substrate to the semiconductor layer. The method of claim 1, And a mode selector provided between the multimode waveguide and the single mode waveguide. The method of claim 6, And the mode selector is a multi-mode interference waveguide. The method of claim 1, And the reflector uses a distributed Bragg reflector or facet reflection, which is a waveguide in which a diffraction grating is formed. The method of claim 1, And wherein the hybrid waveguide, the multimode waveguide and the single mode waveguide are connected in series by transition region waveguides respectively provided therebetween. 10. The method of claim 9, And the transition region waveguide has a narrower width from the hybrid waveguide to the multimode waveguide and from the multimode waveguide to the single mode waveguide.

Images