WO2018163076A1

WO2018163076A1 - System and method for coupling light into a slot waveguide

Info

Publication number: WO2018163076A1
Application number: PCT/IB2018/051459
Authority: WO
Inventors: Shankar Kumar Selvaraja; Viphretuo MERE
Original assignee: Indian Institute Of Science
Priority date: 2017-03-07
Filing date: 2018-03-07
Publication date: 2018-09-13

Abstract

The present disclosure relates to a new and improved optical coupling system which can efficiently couple light into a slot waveguide. The optical coupling system disclosed herein is simple, does not require sharp transitions and complicated structures or fabrication, yet provides a high coupling efficiency, e.g., over 99%. Further, the disclosed optical coupling system can reduce optical losses due to mode-mismatch and light scattering. In an aspect, the present disclosure provides an optical coupling system for coupling a light into a slot waveguide, the system can include: a waveguide configured to receive an input light; a splitter configured to receive the input light from the waveguide and to split the input light into a first light and a second light each having a power level; a first waveguide arm configured to propagate the first light; a second waveguide arm configured to propagate the second light; a waveguide taper configured at an output end of the first waveguide arm and the second waveguide arm; and a slot waveguide coupled to the waveguide taper.

Description

SYSTEM AND METHOD FOR COUPLING LIGHT INTO A SLOT WAVEGUIDE

FIELD OF THE INVENTION

[0001] The present disclosure pertains to the technical field of optical waveguides. In particular, the present disclosure pertains to a system and method for optically coupling light from an optical source into slot waveguide.

BACKGROUND OF THE INVENTION

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Slot waveguides are used to confine light in a low-index material between two high- index strip waveguides by varying the gap and dimensions (width and height) of strip waveguides (see, FIG. 1). In operation, the normal component of the electric field (quasi-TE) undergoes very high discontinuity at the boundary between a high- and a low-index material, which results into higher amplitude in low-index slot region. The amplitude is proportional to the square of the ratio between the refractive indices of high-index material (Si, Ge, S13N4) and the low-index slot material (air). On the other hand, the effect of the presence of slot is minimal on quasi-TM mode, which is continuous at the boundary. When the gap distance between the slot waveguides is within the decay length of the field the slot section has high field confinement [See, 1. Xu, Qianfan, et al. "Experimental demonstration of guiding and confining light in nanometer-size low -refractive-index material. " Optics letters 29.14 (2004): 1626-1628], which results into the propagation of light in the slot section; unlike in a conventional strip waveguide, where the propagating light is confined mainly inthe high-index medium.

[0004] An advantage of a slot waveguide is high-field confinement in slot section, which normally cannot be achieved using a simple strip- or a ridge-based waveguide, making it a potential candidate for applications that require light-matter interaction such as sensing and nonlinear photonics [See, 2. Passaro et al. "Optimizing SOI slot waveguide fabrication tolerances and strip-slot coupling for very efficient optical sensing" Sensors 12.3 (2012): 2436-2455; 3. Dell' Olio Francesco et al. "Optical sensing by optimized silicon slot waveguides" Optics Express 15.8 (2007): 4977-4993; 4.Z. Wang et al. "Ultracompact low-loss coupler between strip and slot waveguides" Opt. Lett. 34(10), 1498-1500(2009)]. Launching of light into a slot waveguide is normally done by phase matching the propagation constant of strip waveguide and slot waveguide. However, efficient coupling still remains a challenge because of scattering loss and mode mismatch of slot and strip waveguides, with a reported loss of 2-10 dB/cm [See, For Example, 5.Baehr- Jones, Tom, et al. "High-Q optical resonators in silicon-on-insulator-based slot waveguides" Applied Physics Letters 86.8 (2005): 081101 ; 6.Saynatjoki, A., et al. "Low-loss silicon slot waveguides and couplers fabricated with optical lithography and atomic layer deposition" Optics express 19.27 (2011): 26275-26282]. Coupling efficiencies in excess of 96% have also been achieved in the art [See, 4. Z. Wang et al, "Ultracompact low-loss coupler between strip and slot waveguides" Opt. Lett. 34(10), 1498-1500(2009); 7. Han, Kyunghun, et al. " Strip-slot direct mode coupler" Optics express 24.6 (2016): 6532-6541].

[0005] Insertion loss of a slot waveguide realized in a highly transparent high-index material is constituted by propagation loss, which results from scattering of light from sidewalls of waveguide and mode coupling mismatch. The modal mismatch between an optical fiber, wire/strip waveguide with slot waveguide is a fundamental limitation. A simple end-fire coupling, due to mismatch would result in large reflection and radiation loss. To overcome this issue, various proposals have been made to increase the coupling efficiency. However, such coupling mechanisms suffer from a number of disadvantages which are illustrated in below

Table 1.

Table 1

Coupler Design Technology Limitations

I. Polymer waveguides Mode size conversion using Sharp tips width in order of

[8. Sun, Haishan, et al. "Efficient inverted tappers 30 nm and 250 μηι taper fiber coupler for vertical silicon length

slot waveguides" Optics express

17.25 (2009): 22571-22577]

II. Strip to slot taper coupler Adiabatically pushes the Asymmetry in the coupling [6.Saynatjoki, A., et al. "Low -loss mode into the slot section results into higher silicon slot waveguides and waveguides substrate losses due to couplers fabricated with optical thinner lines.

lithography and atomic layer

deposition" Optics express 19.27

(2011): 26275-26282]

III. Direct strip to slot Input waveguide width = Slot width 50 nm, which [7. Han, Kyunghun, et al. "Strip- (2*W_siot+ gap) and small requires electron beam slot direct mode coupler" Optics foot print

express 24.6 (2016): 6532-6541]

IV. MMI(Multimode interference) Multimode interference to Higher order modes require [9.Deng, Qingzhong, et al. "Strip- focus the images into the longer taper lengths slot waveguide mode converter slot to waveguide

based on symmetric multimode

interference" Optics letters 39.19

(2014): 5665-5668]

[0006] Accordingly, it would be advantageous to provide an optical coupling system that efficiently couples light into a slot waveguide, does not require sharp transitions and complex fabrication process, and reduces optical losses due to mode-mismatch and scattering. Another advantage would be to provide a simple and highly efficiently method for coupling light into slot waveguide.

[0007] The present invention satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.

[0008] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0009] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability.

OBJECTS OF THE INVENTION

[0010] It is an object of the present disclosure to provide a new and improved optical coupling system that overcomes one or more disadvantages associated with previously known waveguide couplers. [0011] It is a further object of the present disclosure to provide an optical coupling system that efficiently couples light into a slot waveguide.

[0012] It is another object of the present disclosure to provide an optical coupling system that efficiently couples a mode from a strip waveguide or high-index guided mode into a slot waveguide or low-index guided mode.

[0013] It is another object of the present disclosure to provide an optical coupling system that can achieve a coupling efficiency of >99% from a waveguide mode to a slot mode.

[0014] It is another object of the present disclosure to provide an optical coupling system that does not require complicated structures or fabrication.

[0015] It is another object of the present disclosure to provide an optical coupling system that does not require sharp transitions.

[0016] It is another object of the present disclosure to provide an optical coupling system that reduces optical losses due to mode-mismatch and light scattering.

[0017] It is yet another object of the present disclosure to provide a method that efficiently couples a mode from a strip waveguide or high-index guided mode into a slot waveguide or low- index guided mode.

SUMMARY

[0018] Aspects of the present disclosure relate to a new and improved optical coupling system which can efficiently couple light into a slot waveguide. The optical coupling system disclosed herein is simple, does not require sharp transitions and complicated structures or fabrication, yet provides a high coupling efficiency, e.g., over 99%. Further, the disclosed optical coupling system can reduce optical losses due to mode-mismatch and light scattering.

[0019] In an aspect, the present disclosure provides an optical coupling system for coupling light into a slot waveguide, the system can include:

a waveguide configured to receive an input light;

a splitter configured to receive the input light from the waveguide and to split the input light into a first light and a second light each having a power level;

a first waveguide arm configured to propagate the first light;

a second waveguide arm configured to propagate the second light;

a waveguide taper configured at an output end of the first waveguide arm and the second waveguide arm; and

a slot waveguide coupled to the waveguide taper. [0020] In an embodiment of the present disclosure, the waveguide can have a width appropriate for single or multimode transmission.

[0021] In another embodiment, the splitter can split the input light into first and second light in a ratio of 50:50.

[0022] In an embodiment, each of the first and second waveguide arms can have a width appropriate for single mode propagation, and each of the first and second waveguide arms can have equal length and width or phase matched.

[0023] In certain preferred embodiments, each of the first and second waveguide arms can have a bent portion with a radius of curvature with low bend loss.

[0024] In some embodiments, the waveguide taper can have linear configuration with an adiabatic taper.

[0025] In a preferred embodiment, the slot waveguide can have a slot gap that can support slot mode at an operating wavelength.

[0026] In another preferred embodiment, the slot waveguide can have a width of 0.5 μηι.

[0027] According to embodiments of the present disclosure, the waveguide, the first and second waveguide arms and the waveguide taper can be formed of an optically transparent material in an operating wavelength, such as Silicon, Silicon Nitride, Silicon Carbide, Germanium, III-V compound semiconductor or dielectrics.

[0028] In another aspect, the present disclosure provides a method for coupling a light into a slot waveguide, the method can include the steps of:

receiving an input light using an input waveguide;

splitting the input light into a first light and a second light in a ratio of 50:50 using a splitter;

propagating the first light and the second light through a first waveguide arm and a second waveguide arm, respectively, wherein each of the first waveguide arm and the second waveguide arm can have a bent portion; and

passing the first light and the second light into a slot waveguide through a linear waveguide taper.

[0029] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0031] FIG. 1 shows cross sectional view of a slot waveguide and a strip waveguide.

[0032] FIG. 2A schematically shows an exemplary design of an optical coupling system, in accordance with embodiments of the present disclosure.

[0033] FIG. 2B shows 3D view of the optical coupling system shown in FIG. 2A, in accordance with embodiments of the present disclosure.

[0034] FIG. 3 illustrates strip waveguide and fundamental TE mode profile, in accordance with embodiments of the present disclosure.

[0035] FIG. 4 shows 3D view of an exemplary splitter, in accordance with embodiments of the present disclosure.

[0036] FIG. 5 illustrates exemplary configuration of a phase matched waveguide arm having 10 μπι radius curvature and 1 μιη width, in accordance with embodiments of the present disclosure.

[0037] FIG. 6 illustrates exemplary configuration of a tapered slot waveguide coupler, in accordance with embodiments of the present disclosure.

[0038] FIGs. 7A and 7B are graphs showing Neff and fraction of Evanescent field outside a slot waveguide at different slot widths, in accordance with embodiments of the present disclosure.

[0039] FIGs. 8A -8C illustrate Quasi-TE field distribution in a slot waveguide; width and height of 0.5 μηι each, and different gap width, in accordance with embodiments of the present disclosure.

[0040] FIG. 9 shows simulated E-field (V/m) distribution (3D FDTD) (Full design with 100 nm gap), in accordance with embodiments of the present disclosure.

[0041] FIGs. 10A and 10B are graphs showing normalized power at an output of a slot waveguide (gap width 200 nm): (10A) Different arm length of the bend waveguides; (10B) Different arm width of the bend waveguide. DETAILED DESCRIPTION OF THE INVENTION

[0042] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[0043] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0044] Unless the context requires otherwise, throughout the specification which follow, the word "comprise" and variations thereof, such as, "comprises" and "comprising" are to be construed in an open, inclusive sense that is as "including, but not limited to."

[0045] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0046] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. It should also be noted that the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

[0047] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.

[0048] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. "such as") provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0049] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0050] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.

[0051] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0052] The present disclosure relates to a new and improved optical coupling system which can efficiently couple light into a slot waveguide. The optical coupling system disclosed herein is simple, does not require sharp transitions and complicated structures or fabrication, yet provides a high coupling efficiency, e.g., over 99%. Further, the disclosed optical coupling system can reduce optical losses due to mode-mismatch and light scattering.

[0053] In an aspect, the present disclosure provides an optical coupling system for coupling a light into a slot waveguide, the system can include:

a waveguide configured to receive an input light;

a first waveguide arm configured to propagate the first light;

a second waveguide arm configured to propagate the second light;

a slot waveguide coupled to the waveguide taper.

[0054] In an embodiment of the present disclosure, the input waveguide can have a width appropriate for single or multimode transmission.

[0055] In another embodiment, the splitter can split the input light into first and second lights in a ratio of 50:50. [0056] In an embodiment, each of the first and second waveguide arms can have a width appropriate for single mode propagation, and each of the first and second waveguide arms can have equal length and width or phase matched.

[0057] In certain preferred embodiments, each of the first and second waveguide arms can have a bent portion with a radius of curvature with low bend loss.

[0058] In some embodiments, the waveguide taper can have linear configuration with an adiabatic taper.

[0059] In a preferred embodiment, the slot waveguide can have a slot gap that can support slot mode at an operating wavelength.

[0060] In another preferred embodiment, the slot waveguide can have a width of 0.5 μηι.

[0061] According to embodiments of the present disclosure, the waveguide, the first and second waveguide arms and the waveguide taper can be formed of an optically transparent material in an operating wavelength, such as Silicon, Silicon Nitride, Silicon Carbide, Germanium, III-V compound semiconductor or dielectrics.

[0062] In another aspect, the present disclosure provides a method for coupling a light into a slot waveguide, the method can include the steps of:

receiving an input light using an input waveguide;

propagating the first and second lights through a first waveguide arm and a second waveguide arm, respectively, wherein each of the first waveguide arm and the second waveguide arm can have a bent portion; and

passing the first and second lights into a slot waveguide through a linear waveguide taper.

[0063] FIG. 2A shows exemplary design of an optical coupling system 100 (also referred to as "tapered slot waveguide coupler") for coupling light into a slot waveguide, constructed in accordance with one preferred embodiment of the present disclosure. The coupling system 100 can include an input waveguide 102 for receiving an input light, a splitter 104 coupled to the input waveguide, a first waveguide arm 106, a second waveguide arm 108, a waveguide taper 110 and a slot waveguide 112. According to this embodiment, Germanium (n = 4.204) and CaF2 (n = 1.4096) can be used as core and substrate material. Design and simulations can be performed at 4 μηι wavelength using commercial FDTD EM solver. A 3D view of the optical coupling systemlOO is shown in FIG. 2B. [0064] The input waveguide 102 can be a single mode waveguide; strip or shallow-etched, which can be used for launching input light into the system. Waveguide width and thickness for single mode operation can depend on the waveguide, cladding material and wavelength. For 4000 nm wavelength, the width (W) and thickness (T) of the strip waveguide can be 1 μιη and 0.5 μηι respectively. FIG. 3 shows cross-section schematic of a strip waveguide and fundamental TE mode profile.

[0065] The splitter 104 (also referred to as "power splitter") can have a Y-branch configuration and a splitting ratio of 50:50. Power form the input waveguide 102 can be equally split by the splitter into two identical strip waveguides as shown in FIG. 4. The splitter 104 can be provided with an input waveguide wide of 1000 nm; same as the waveguide which expands to -2200 nm wide waveguide. The expansion width W_RHS can be calculated as 2* W_LHS + Gap. Length, width and gap of the splitter 104 can be optimized to yield low insertion loss and better splitting ratio between the two arms.

[0066] Power split by the splitter can be guided through the first and second phase-matched single-mode waveguide arms (106 and 108). The first and second waveguide arms each can have a bent portion with a radius of curvature of 10 μηι. In a high-refractive index contrast platform such as SOI or Ge-on-Glass, the minimum bending radius with acceptable loss can be as small as 5000 nm. Smaller bend radii of the waveguide arms can greatly enhance the performance of waveguide device, as well as allow for a greatly decreased device footprint. FIG. 5 illustrates exemplary configuration of a phase matched waveguide arm having 10 μηι radius curvature and 1 μιη width.

[0067] The two phase-matched waveguide arms 106 and 108 can be brought together to form a slot waveguide 112 through a waveguide taper 110. The starting and ending width of the waveguide taper 110 can be dictated by the phase-matched waveguide arms and slot waveguide width, respectively. In certain preferred embodiments, the input side waveguide width (W_LHS) can be equal to the width of bent waveguide arms (e.g. 1.0 μιη). While, the right hand side can be equal to the width of the slot waveguide W_si_ot (e.g. 0.5 μηι). An exemplary configuration of the tapered slot waveguide coupler is shown in FIG. 6.

[0068] The slot waveguide 112 can include two identical strip waveguides with a fixed gap width as shown in FIG. 6. The slot waveguide 112 can extend out from the system for connection with a device or circuit. Unlike conventional core guided waveguide geometry, light can be confined within the gap of the slot waveguide. The graph in FIG. 7 A shows the simulated effective index of the TE guided mode in the slot for various slot gap and waveguide width. From FIG. 7 A, it can be observed that smallest gap of 100 nm results in higher mode confinement inside the slot gap. FIG. 7B shows the mode confinement in a slot waveguide with 100 nm, 200 nm, and 300 nm gap. FIGs. 8A -8C illustrate Quasi-TE field distribution in a slot waveguide; width and height of 0.5 μηι each, and different gap width.

Coupling Between a Strip and Slot Waveguide:

[0069] FIG. 9 shows a 3D FDTD simulation of the present coupling scheme. TE fundamental mode was launched into the strip waveguide (left side), which was then split and combined at the right side to form slot waveguide. Table-2 below summarizes the coupling efficiency of the system 100 of the present disclosure. From Table-2, it can be observed that coupling efficiency as high as 99% can be achieved with the coupling system 100 of the present disclosure.

TABLE-2

Sensitivity and Tolerance:

[0070] This section presents the sensitivity and tolerance of the disclosed coupling scheme towards fabrication imperfections. The effect of variation in dimensional variation such as length and width of the split waveguide, which is one of the critical elements on the coupling efficiency, was calculated.

[0071] FIG. 10A shows the effect of coupling efficiency when the length of one of the waveguide arms is changed while rest of the parameters are kept optimal and constant. The change in the length creates a phase imbalance and results in non-optimal excitation or coupling of the slot mode. However, the phase imbalance vanishes when the length of the waveguide accumulates 0° phase. As a result, when the length of the upper arm is increased from 0 to 1.8 μιτι, the phase difference introduced decreases the coupling efficiency by -50 %. [0072] The tolerance towards the waveguide width variation was simulated by introducing a 2% variation in width of one of the waveguide arms while rest of the parameters were kept optimal and constant. The outer-width was decreased by 5 to 20 nm. Like length variation, the change in width resulted in change in the propagation constant and phase which eventually resulted in drop in coupling efficiency by 4% (FIG. 10B). Table-3 below summarizes the effect of width variation on the coupling efficiency.

TABLE-3

Tunable Coupling:

[0073] The coupling method disclosed herein, unlike other coupling schemes, can be tuned using thermo-optic or electro-optic methods to overcome fabrication and design imperfections. The phase of light propagating through the two waveguide arms can be tuned using thermo-optic or electro-optic effect. This tunability can enable to compensate phase imbalances in the waveguide arms or the splitter.

[0074] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE PRESENT INVENTION

[0075] The present disclosure provides an optical coupling system that efficiently couples light into a slot waveguide. [0076] The present disclosure provides an optical coupling system that efficiently couples a mode from a strip waveguide or high-index guided mode into a slot waveguide or low-index guided mode.

[0077] The present disclosure provides an optical coupling system by which a coupling efficiency of >99% from a waveguide mode to a slot mode can be achieved.

[0078] The present disclosure provides an optical coupling system that does not require complicated structures or fabrication.

[0079] The present disclosure provides an optical coupling system that does not require sharp transitions.

[0080] The present disclosure provides an optical coupling system that reduces optical losses due to mode-mismatch and light scattering.

[0081] The present disclosure provides a simple, economic and highly efficient method for coupling light into a slot waveguide.

[0082] The present disclosure provides a system for coupling light into a slot waveguide, wherein the system increases power density in slot section while maintaining coupling efficiency.

[0083] Another advantage of present coupling system is the flexibility of the width of the slot waveguides for a given slot gap width, which will be more tolerant to fabrication errors.

Claims

We Claim:

1. A system for coupling a light into a slot waveguide, comprising:

a waveguide configured to receive an input light;

a first waveguide arm configured to propagate the first light;

a second waveguide arm configured to propagate the second light;

a slot waveguide coupled to the waveguide taper.

2. The system as claimed in claim 1, wherein the waveguide has a width appropriate for single or multimode transmission.

3. The system as claimed in claim 1, wherein the splitter splits the input light into first and second lights in a ratio of 50:50.

4. The system as claimed in claim 1, wherein each of the first and second waveguide arms has a width appropriate for single mode transmission.

5. The system as claimed in claim 1, wherein each of the first and second waveguide arms has an equal length and width or phase matched waveguide.

6. The system as claimed in claim 1, wherein each of the first and second waveguide arms has a bent portion.

7. The system as claimed in claim 1, wherein the waveguide taper comprises an adiabatic or low-loss linear taper.

8. The system as claimed in claim 1, wherein the slot waveguide has an appropriate slot gap width.

9. The system as claimed in claim 1, wherein a slot gap of the slot waveguide is in a range of lOOnm to 300nm.

10. The system as claimed in claim 1, wherein the waveguide, the first and second waveguide arms and the waveguide taper are formed of an optically transparent material selected from the group consisting of Silicon, Silicon Nitride, Silicon Carbide, Germanium, III-V compound semiconductor and dielectrics.

11. A method for coupling a light into a slot waveguide, comprising the steps of:

receiving an input light using an input waveguide;

propagating the first and second lights through a first waveguide arm and a second waveguide arm, respectively, wherein the first waveguide arm and the second waveguide arm each has a bent portion; and

passing the first light and the second light into a slot waveguide through a linear waveguide taper, wherein the slot waveguide.