Patent Publication Number: US-2021191039-A1

Title: Optical device and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 62/698,587 filed on Jul. 16, 2018 and U.S. Non-Provisional application Ser. No. 16/238,969 filed on Jan. 3, 2019, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates to an optical device and, more particularly, to an optical device including a waveguide, a taper and an attenuator, and a method of forming the optical device. 
     Optical waveguides are often used as components in optical circuits having multiple photonic functions. A waveguide is used to confine and guide light from a first point on an integrated chip (IC) to a second point on the IC. In addition, a taper is used to facilitate a high coupling efficiency between the waveguide and another optical device. Unwanted optical signal may be radiated from the taper and cause interference with other optical devices. An attenuator may be used to degrade unwanted optical signal from a taper. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1A  is a schematic diagram of an optical device, in accordance with an embodiment of the present disclosure. 
         FIG. 1B  is a cross-sectional view of an attenuator of the optical device illustrated in  FIG. 1A , taken along a line AA, in accordance with an embodiment of the present disclosure. 
         FIG. 1C  is a schematic diagram of an optical device, in accordance with another embodiment of the present disclosure. 
         FIG. 1D  is a schematic diagram of an optical device, in accordance with yet another embodiment of the present disclosure. 
         FIG. 1E  is a schematic diagram of an optical device, in accordance with still another embodiment of the present disclosure. 
         FIG. 2A  is a schematic diagram of an optical device, in accordance with an embodiment of the present disclosure. 
         FIG. 2B  is a cross-sectional view of an attenuator of the optical device illustrated in  FIG. 2A , taken along a line BB, in accordance with an embodiment of the present disclosure. 
         FIG. 2C  is a schematic diagram of an optical device, in accordance with another embodiment of the present disclosure. 
         FIG. 2D  is a schematic diagram of an optical device, in accordance with yet another embodiment of the present disclosure. 
         FIG. 2E  is a schematic diagram of an optical device, in accordance with still another embodiment of the present disclosure. 
         FIG. 3A  is a schematic diagram of an optical device, in accordance with an embodiment of the present disclosure. 
         FIG. 3B  is a schematic diagram of an optical device, in accordance with another embodiment of the present disclosure. 
         FIG. 3C  is a schematic diagram of an optical device, in accordance with yet another embodiment of the present disclosure. 
         FIG. 3D  is a schematic diagram of an optical device, in accordance with still another embodiment of the present disclosure. 
         FIG. 3E  is a schematic diagram of an optical device, in accordance with yet still another embodiment of the present disclosure. 
         FIG. 4A  is a schematic diagram of an optical device, in accordance with an embodiment of the present disclosure. 
         FIG. 4B  is a cross-sectional view of an attenuator of the optical device illustrated in  FIG. 4A , taken along a line CC, in accordance with an embodiment of the present disclosure. 
         FIG. 4C  is a schematic diagram of an optical device, in accordance with another embodiment of the present disclosure. 
         FIG. 4D  is a schematic diagram of an optical device, in accordance with yet another embodiment of the present disclosure. 
         FIG. 4E  is a schematic diagram of an optical device, in accordance with still another embodiment of the present disclosure. 
         FIG. 5A  is a schematic diagram of an optical device, in accordance with an embodiment of the present disclosure. 
         FIG. 5B  is a schematic diagram of an optical device, in accordance with another embodiment of the present disclosure. 
         FIG. 5C  is a schematic diagram of an optical device, in accordance with yet another embodiment of the present disclosure. 
         FIG. 5D  is a schematic diagram of an optical device, in accordance with still another embodiment of the present disclosure. 
         FIG. 5E  is a schematic diagram of an optical device, in accordance with yet still another embodiment of the present disclosure. 
         FIGS. 6A to 6H  are cross-sectional views showing a method of forming the optical device illustrated in  FIG. 1C , taken along a line XX, in accordance with some embodiments of the present disclosure. 
         FIGS. 7A and 7B  are cross-sectional views showing a method of forming the optical device illustrated in  FIG. 2C , taken along a line YY, in accordance with some embodiments of the present disclosure. 
         FIG. 8  is a cross-sectional view showing a method of forming the optical device illustrated in  FIG. 4C , taken along a line ZZ, in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     The present disclosure provides an optical device including an attenuator to degrade unwanted optical signal transmitted between optical ports or interfaces. With the attenuator, isolation between optical ports may be enhanced and interference can be reduced. The attenuator may include one of a conductive structure, a doped structure and a refractive structure. These structures are all available in fabrication processes. 
       FIG. 1A  is a schematic diagram of an optical device  101 , in accordance with an embodiment of the present disclosure. 
     Referring to  FIG. 1A , the optical device  101  includes a waveguide  12 , a taper  14  and an attenuator  161 . In an embodiment, the optical device  101  may include a directional coupler, which may serve as a power combiner, a power divider, an add-drop multiplexer or a switch. The waveguide  12  is used to confine and guide light. The taper  14 , which is integrated with the waveguide  12 , is used to couple the waveguide  12  to, for example, another waveguide. The taper  14  during operation may radiate unwanted optical signal, for example, signal reflected from other optical devices. However, unwanted signal radiated from the taper  14  may cause interference with other optical devices such as optical splitters or optical modulators. The attenuator  16  functions to degrade unwanted optical signal from the taper  14  in order to alleviate the impact. The waveguide  12 , taper  14  and attenuator  161  may be formed on a substrate  134 , for example, a semiconductor-on-insulator (SOI). An SOI substrate includes a layered silicon-insulator-silicon, which helps reduce parasitic device capacitance, thereby improving performance. In addition, the waveguide  12 , taper  14  and attenuator  161  are disposed in a dielectric layer  120 , for example, an oxide layer on the substrate  134 . 
     The attenuator  161  includes a conductive structure  136 , which will be discussed in detail by reference to  FIG. 1B . Moreover, the attenuator  161  extends along a first side  141  of the taper  14 , and is spaced apart from the taper  14  by a first gap d 1 . In an embodiment, the first gap d 1  ranges from approximately 100 to 2,000 nanometers (nm). In another embodiment, the first gap d 1  is approximately 150 nm. The relatively small gap d 1  and the conductive structure  136  facilitate degradation or attenuation of unwanted signal radiated from the taper  14 . 
       FIG. 1B  is a cross-sectional view of the attenuator  161  of the optical device  101  illustrated in  FIG. 1A , taken along a line AA, in accordance with an embodiment of the present disclosure. 
     Referring to  FIG. 1B , the attenuator  161  includes conductive vias  137  on the substrate  134 , and a metal layer  138  disposed on the conductive vias  137  and extending along the first side  141  of the taper  14 . In an embodiment, copper is a suitable material for the conductive vias  137  and the metal layer  138 . 
       FIG. 1C  is a schematic diagram of an optical device  102 , in accordance with another embodiment of the present disclosure. 
     Referring to  FIG. 1C , the optical device  102  is similar to the optical device  101  described and illustrated with reference to  FIG. 1A  except that, for example, the optical device  102  includes a second attenuator  162  in additional to a first attenuator  161 . The second attenuator  162  extends along a second side  142 , opposite to the first side  141 , of the taper  14 . Moreover, the second attenuator  162  includes a conductive structure similar to that of the first attenuator  16 . Furthermore, the second attenuator  162  is spaced apart from the taper  14  by a second gap d 2 . In an embodiment, the second gap d 2  ranges from approximately 100 to 2,000 nanometers (nm). In another embodiment, the second gap d 2  is approximately 150 nm. 
       FIG. 1D  is a schematic diagram of an optical device  103 , in accordance with yet another embodiment of the present disclosure. 
     Referring to  FIG. 1D , the optical device  103  is similar to the optical device  101  described and illustrated with reference to  FIG. 1A  except, for example, an attenuator  163 . In  FIG. 1A , the attenuator  161  of the optical device  101  extends along substantially the full length of the first sides  141  of the taper  14 . By comparison, the attenuator  163  of the optical device  103  extends along a portion of the first side  141  of the taper  14 . Moreover, the attenuator  163  includes a conductive structure similar to that of the first attenuator  161 . 
     In other embodiments, like the optical device  102  illustrated in  FIG. 1C , the optical device  103  may further include a second attenuator (not shown) that extends along the second side  142  of the taper  14 . The second attenuator of the optical device  103  may extend along a full length or a portion of the second side  142 , and includes a conductive structure similar to that of the first attenuator  161 . 
       FIG. 1E  is a schematic diagram of an optical device  104 , in accordance with still another embodiment of the present disclosure. 
     Referring to  FIG. 1E , the optical device  104  is similar to the optical device  103  described and illustrated with reference to  FIG. 1D  except that, for example, the optical device  104  includes a second attenuator  164  in additional to the first attenuator  163 . The second attenuator  164  is separated from the first attenuator  163  and extends along another portion of the first side  142  of the taper  14 , and includes a conductive structure similar to that of the first attenuator  161 . 
     In other embodiments, like the optical device  102  illustrated in  FIG. 1C , the optical device  104  may further include a third attenuator (not shown) that extends along the second side  142  of the taper  14 . The third attenuator of the optical device  104  may extend along a full length or a portion of the second side  142 , and includes a conductive structure similar to that of the first attenuator  163 . In the case of a third attenuator extending along a portion of the second side  142 , the optical device  104  may further include a fourth attenuator (not shown) that is separated from the third attenuator and extends along another portion of the second side  142  of the taper  14 . 
       FIG. 2A  is a schematic diagram of an optical device  201 , in accordance with an embodiment of the present disclosure. 
     Referring to  FIG. 2A , the optical device  201  is similar to the optical device  101  described and illustrated with reference to  FIG. 1A  except that, for example, an attenuator  261  replaces the attenuator  161 . The attenuator  261  includes a doped structure  236 , which will be discussed in detail by reference to  FIG. 2B . Moreover, the attenuator  261  extends along a first side  141  of the taper  14 , and is spaced apart from the taper  14  by the first gap d 1 . 
       FIG. 2B  is a cross-sectional view of an attenuator of the optical device  201  illustrated in  FIG. 2A , taken along a line BB, in accordance with an embodiment of the present disclosure. 
     Referring to  FIG. 2B , the attenuator  261  may be formed on a substrate  134 , for example, a semiconductor-on-insulator (SOI). The SOI substrate  134  includes a first silicon layer  342 , a buried oxide layer (BOX)  345  on the first silicon layer  342 , and a second silicon layer  348  on the BOX  345 . In the present embodiment, the doped structure  236  is formed by doping the second silicon layer  348  with an n-type or a p-type impurity. 
       FIG. 2C  is a schematic diagram of an optical device  202 , in accordance with another embodiment of the present disclosure. 
     Referring to  FIG. 2C , the optical device  202  is similar to the optical device  201  described and illustrated with reference to  FIG. 2A  except that, for example, the optical device  202  includes a second attenuator  262  in additional to a first attenuator  261 . The second attenuator  262  extends along a second side  142 , opposite to the first side  141 , of the taper  14 . Moreover, the second attenuator  262  includes a doped structure similar to that of the first attenuator  261 . Furthermore, the second attenuator  262  is spaced apart from the taper  14  by the second gap d 2 . 
       FIG. 2D  is a schematic diagram of an optical device  203  accordance with yet another embodiment of the present disclosure. 
     Referring to  FIG. 2D , the optical device  203  is similar to the optical device  201  described and illustrated with reference to  FIG. 2A  except, for example, an attenuator  263 . In  FIG. 2A , the attenuator  261  of the optical device  201  extends along substantially the full length of the first sides  141  of the taper  14 . By comparison, the attenuator  263  of the optical device  203  extends along a portion of the first side  141  of the taper  14 . Moreover, the attenuator  263  includes a doped structure similar to that of the first attenuator  261 . 
     In other embodiments, like the optical device  202  illustrated in  FIG. 2C , the optical device  203  may further include a second attenuator (not shown) that extends along the second side  142  of the taper  14 . The second attenuator of the optical device  203  may extend along a full length or a portion of the second side  142 , and includes a doped structure similar to that of the first attenuator  161 . 
       FIG. 2E  is a schematic diagram of an optical device  204 , in accordance with still another embodiment of the present disclosure. 
     Referring to  FIG. 2E , the optical device  204  is similar to the optical device  203  described and illustrated with reference to  FIG. 2D  except that, for example, the optical device  204  includes a second attenuator  264  in additional to the first attenuator  263 . The second attenuator  264  is separated from the first attenuator  263  and extends along another portion of the first side  142  of the taper  14 , and includes a doped structure similar to that of the first attenuator  161 . 
     In other embodiments, like the optical device  202  illustrated in  FIG. 2C , the optical device  204  may further include a third attenuator (not shown) that extends along the second side  142  of the taper  14 . The third attenuator of the optical device  204  may extend along a full length or a portion of the second side  142 , and includes a doped structure similar to that of the first attenuator  261 . In the case of a third attenuator extending along a portion of the second side  142 , the optical device  204  may further include a fourth attenuator (not shown) that is separated from the third attenuator and extends along another portion of the second side  142  of the taper  14 . 
       FIG. 3A  is a schematic diagram of an optical device  301 , in accordance with an embodiment of the present disclosure. 
     Referring to  FIG. 3A , the optical device  301  includes a taper  24  that is doped with impurity (hereinafter the “doped taper”). The doped taper  24  facilitates alleviation of unwanted signal radiated therefrom. Since the doped taper  24  also functions as an attenuator, as a result, an attenuator disposed along the taper  24  may be eliminated. In the present embodiment, the taper  24  is wholly doped with impurity. In other embodiments, however, only a portion or portions of the taper  24  are doped. 
       FIG. 3B  is a schematic diagram of an optical device  302 , in accordance with another embodiment of the present disclosure. 
     Referring to  FIG. 3B , the optical device  302  is similar to the optical device  201  described and illustrated with reference to  FIG. 2A  except, for example, the doped taper  24 . In addition to the doped first attenuator  261 , the doped taper  24  also functions to degrade unwanted signal. 
       FIG. 3C  is a schematic diagram of an optical device  303 , in accordance with yet another embodiment of the present disclosure. 
     Referring to  FIG. 3C , the optical device  303  is similar to the optical device  202  described and illustrated with reference to  FIG. 2C  except, for example, the doped taper  24 . In addition to the doped first attenuator  261  and the doped second attenuator  262 , the doped taper  24  also functions to degrade unwanted signal. 
       FIG. 3D  is a schematic diagram of an optical device  304 , in accordance with still another embodiment of the present disclosure. 
     Referring to  FIG. 3D , the optical device  304  is similar to the optical device  203  described and illustrated with reference to  FIG. 2D  except, for example, the doped taper  24 . In addition to the doped first attenuator  263 , the doped taper  24  also functions to degrade unwanted signal. 
     In other embodiments, like the optical device  303  illustrated in  FIG. 3C , the optical device  304  may further include a second attenuator (not shown) that extends along the second side  142  of the taper  24 . The second attenuator of the optical device  304  may extend along a full length or a portion of the second side  142 , and includes a doped structure similar to that of the first attenuator  261 . 
       FIG. 3E  is a schematic diagram of an optical device  305 , in accordance with yet still another embodiment of the present disclosure. 
     Referring to  FIG. 3E , the optical device  305  is similar to the optical device  204  described and illustrated with reference to  FIG. 2E  except, for example, the doped taper  24 . In addition to the doped first attenuator  263  and the doped second attenuator  264 , the doped taper  24  also functions to degrade unwanted signal. 
     In other embodiments, like the optical device  303  illustrated in  FIG. 3C , the optical device  305  may further include a third attenuator (not shown) that extends along the second side  142  of the taper  24 . The third attenuator of the optical device  305  may extend along a full length or a portion of the second side  142 , and includes a doped structure similar to that of the first attenuator  261 . In the case of a third attenuator extending along a portion of the second side  142 , the optical device  305  may further include a fourth attenuator (not shown) that is separated from the third attenuator and extends along another portion of the second side  142  of the taper  24 . 
       FIG. 4A  is a schematic diagram of an optical device  401 , in accordance with an embodiment of the present disclosure. 
     Referring to  FIG. 4A , the optical device  401  is similar to the optical device  201  described and illustrated with reference to  FIG. 2A  except that, for example, an attenuator  361  replaces the attenuator  261 . The attenuator  361  includes a refraction structure  336 , which will be discussed in detail by reference to  FIG. 4B . Moreover, the attenuator  361  extends along a first side  141  of the taper  14 , and is spaced apart from the taper  14  by the first gap d 1 . 
       FIG. 4B  is a cross-sectional view of an attenuator of the optical device  401  illustrated in  FIG. 4A , taken along a line CC, in accordance with an embodiment of the present disclosure. 
     Referring to  FIG. 4B , the attenuator  361  may be formed on a substrate  134 , for example, a semiconductor-on-insulator (SOI). The SOI substrate  134  includes a first silicon layer  342 , a buried oxide layer (BOX)  345  on the first silicon layer  342 , and a second silicon layer  348  on the BOX  345 . In an embodiment, the refraction structure  336  may be formed by nitrogen implantation into the second silicon layer  342 , resulting in a silicon nitride layer. Suitable materials, such as the exemplary silicon nitride, for the refraction structure  336  include those having an index of refraction larger than that of silicon, which in turn is larger than that of silicon oxide. As a result, the materials have an index larger than that of the substrate  134 . With a larger index of refraction, the refraction structure  336  creates a total reflection environment and facilitates refracting away unwanted signal. 
       FIG. 4C  is a schematic diagram of an optical device  402 , in accordance with another embodiment of the present disclosure. 
     Referring to  FIG. 4C , the optical device  402  is similar to the optical device  401  described and illustrated with reference to  FIG. 4A  except that, for example, the optical device  402  includes a second attenuator  362  in additional to a first attenuator  361 . The second attenuator  362  extends along a second side  142 , opposite to the first side  141 , of the taper  14 . Moreover, the second attenuator  362  includes a refraction structure similar to that of the first attenuator  361 . Furthermore, the second attenuator  362  is spaced apart from the taper  14  by the second gap d 2 . 
       FIG. 4D  is a schematic diagram of an optical device  403 , in accordance with yet another embodiment of the present disclosure. 
     Referring to  FIG. 4D , the optical device  403  is similar to the optical device  401  described and illustrated with reference to  FIG. 4A  except, for example, an attenuator  363 . In  FIG. 4A , the attenuator  361  of the optical device  401  extends along substantially the full length of the first sides  141  of the taper  14 . By comparison, the attenuator  363  of the optical device  403  extends along a portion of the first side  141  of the taper  14 . Moreover, the attenuator  363  includes a refraction structure similar to that of the first attenuator  361 . 
     In other embodiments, like the optical device  402  illustrated in  FIG. 4C , the optical device  403  may further include a second attenuator (not shown) that extends along the second side  142  of the taper  14 . The second attenuator of the optical device  403  may extend along a full length or a portion of the second side  142 , and includes a refraction structure similar to that of the first attenuator  361 . 
       FIG. 4E  is a schematic diagram of an optical device  404 , in accordance with still another embodiment of the present disclosure. 
     Referring to  FIG. 4E , the optical device  404  is similar to the optical device  403  described and illustrated with reference to  FIG. 4D  except that, for example, the optical device  404  includes a second attenuator  364  in additional to the first attenuator  363 . The second attenuator  364  is separated from the first attenuator  363  and extends along another portion of the first side  142  of the taper  14 , and includes a refraction structure similar to that of the first attenuator  361 . 
     In other embodiments, like the optical device  402  illustrated in  FIG. 4C , the optical device  404  may further include a third attenuator (not shown) that extends along the second side  142  of the taper  14 . The third attenuator of the optical device  404  may extend along a full length or a portion of the second side  142 , and includes a refraction structure similar to that of the first attenuator  361 . In the case of a third attenuator extending along a portion of the second side  142 , the optical device  404  may further include a fourth attenuator (not shown) that is separated from the third attenuator and extends along another portion of the second side  142  of the taper  14 . 
       FIG. 5A  is a schematic diagram of an optical device  501 , in accordance with an embodiment of the present disclosure. 
     Referring to  FIG. 5A , the optical device  501  includes a taper  34  having a refraction structure (hereinafter the “refractive taper”). The refractive taper  34  facilitates alleviation of unwanted signal radiated therefrom. Since the refractive taper  34  also functions as an attenuator, as a result, an attenuator disposed along the taper  34  may be eliminated. In the present embodiment, the taper  34  is wholly provided with a material having an index of refraction larger than that of the substrate. In other embodiments, however, only a portion or portions of the taper  34  are provided with the material. 
       FIG. 5B  is a schematic diagram of an optical device  502 , in accordance with another embodiment of the present disclosure. 
     Referring to  FIG. 5B , the optical device  502  is similar to the optical device  401  described and illustrated with reference to  FIG. 4A  except, for example, the refractive taper  34 . In addition to the refractive first attenuator  361 , the refractive taper  34  also functions to degrade unwanted signal. 
       FIG. 5C  is a schematic diagram of an optical device  503 , in accordance with yet another embodiment of the present disclosure. 
     Referring to  FIG. 5C , the optical device  503  is similar to the optical device  402  described and illustrated with reference to  FIG. 4C  except, for example, the refractive taper  34 . In addition to the refractive first attenuator  361  and the refractive second attenuator  362 , the refractive taper  34  also functions to degrade unwanted signal. 
       FIG. 5D  is a schematic diagram of an optical device  504 , in accordance with still another embodiment of the present disclosure. 
     Referring to  FIG. 5D , the optical device  504  is similar to the optical device  403  described and illustrated with reference to  FIG. 4D  except, for example, the refractive taper  34 . In addition to the refractive first attenuator  363 , the refractive taper  34  also functions to degrade unwanted signal. 
     In other embodiments, like the optical device  503  illustrated in  FIG. 5C , the optical device  504  may further include a second attenuator (not shown) that extends along the second side  142  of the taper  34 . The second attenuator of the optical device  504  may extend along a full length or a portion of the second side  142 , and includes a refractive structure similar to that of the first attenuator  361 . 
       FIG. 5E  is a schematic diagram of an optical device  505 , in accordance with yet still another embodiment of the present disclosure. 
     Referring to  FIG. 5E , the optical device  505  is similar to the optical device  404  described and illustrated with reference to  FIG. 4E  except, for example, the refractive taper  34 . In addition to the refractive first attenuator  363  and the refractive second attenuator  364 , the refractive taper  34  also functions to degrade unwanted signal. 
     In other embodiments, like the optical device  503  illustrated in  FIG. 5C , the optical device  505  may further include a third attenuator (not shown) that extends along the second side  142  of the taper  34 . The third attenuator of the optical device  505  may extend along a full length or a portion of the second side  142 , and includes a doped structure similar to that of the first attenuator  361 . In the case of a third attenuator extending along a portion of the second side  142 , the optical device  505  may further include a fourth attenuator (not shown) that is separated from the third attenuator and extends along another portion of the second side  142  of the taper  34 . 
       FIGS. 6A to 6H  are cross-sectional views showing a method of forming the optical device  102  illustrated in  FIG. 1C , taken along a line XX, in accordance with some embodiments of the present disclosure. 
     Referring to  FIG. 6A , a substrate  134 , for example, an SOI substrate, is provided. The substrate  134  includes a first silicon layer  342 , a second silicon layer  348 , and a BOX layer  345  between the first silicon layer  342  and the second silicon layer  348 . 
     Referring to  FIG. 6B , the second silicon layer  348  is patterned, exposing portions of the BOX layer  345 . 
     Next, referring to  FIG. 6C , a dielectric layer  110  is formed on the BOX layer  345  and the patterned second silicon layer  348  by using, for example, a deposition process. Suitable materials for the dielectric layer  110  include silicon oxide. In  FIG. 6D , openings  610  are then formed in an etching process to expose portions of the patterned second silicon layer  348 . The openings  610  define locations where conductive vias to be subsequently formed. 
     Referring to  FIG. 6E , conductive vias  137  are formed on the patterned second silicon layer  348  by, for example, forming a conductive layer on the dielectric layer  110  in a plating process, filling the openings  610 , followed by a chemical-mechanical polish (CMP) process. Suitable materials for the conductive vias  137  include, for example, copper. 
     Next, referring to  FIG. 6F , another dielectric layer (not numbered) is formed on the conductive vias  137  and the dielectric layer  110 , resulting in a dielectric layer  120 . In  FIG. 6G , the dielectric layer  120  is patterned, exposing the conductive vias  137  through openings  620 . 
     Subsequently, referring to  FIG. 6H , a conductive layer  138  is formed on the conductive vias  137  by using, for example, a deposition process, resulting in a conductive structure  136  as illustrated in  FIG. 1B . The conductive layer  138  may include copper. As a result, a first attenuator  161  and a second attenuator  162  are formed. 
       FIGS. 7A and 7B  are cross-sectional views showing a method of forming the optical device  202  illustrated in  FIG. 2C , taken along a line YY, in accordance with some embodiments of the present disclosure. 
     Referring to  FIG. 7A , similar to the method described and illustrated with reference to  FIGS. 6A to 6C , an SOI substrate  134  is provided. The second silicon layer  348  is patterned and then a dielectric layer  120  is formed on the BOX layer  345 . The dielectric layer  120  exposes the pattered second silicon layer  348 . 
     Referring to  FIG. 7B , doped structures  236  are formed by, for example, a doping process. As a result, a first attenuator  261  and a second attenuator  262  are formed. In some embodiments, the concentration of a dopant for the doping process may range from approximately 10 19  to 10 20  cm −3 . In an embodiment, the tapper  14  may also be doped with the dopant in the doping process, resulting in a doped taper  24  as described and illustrated in  FIG. 3C . In another embodiment, the optical device, such as the optical device  301  described and illustrated with reference to  FIG. 3A , is free of attenuators and includes a doped structure for degrading unwanted signal. 
       FIG. 8  is a cross-sectional view showing a method of forming the optical device  402  illustrated in  FIG. 4C , taken along a line ZZ, in accordance with some embodiments of the present disclosure. 
     Referring to  FIG. 8 , similar to the method described and illustrated with reference to  FIGS. 6A to 6C , an SOI substrate  134  is provided. The second silicon layer  348  is patterned and then a dielectric layer  120  is formed on the BOX layer  345 . The dielectric layer  120  exposes the pattered second silicon layer  348 . Subsequently, refraction structures  336  are formed by, for example, an implanting process. As a result, a first attenuator  361  and a second attenuator  362  are formed. In an embodiment, the tapper  14  may also be implanted with nitride in the implanting process, resulting in a refractive taper  34  as described and illustrated in  FIG. 5C . In another embodiment, the optical device, such as the optical device  501  described and illustrated with reference to  FIG. 5A , is free of attenuators and includes a refractive structure for degrading unwanted signal. 
     Embodiments of the present disclosure provide an optical device. The optical device includes a waveguide configured to guide light, a taper integrated with the waveguide on a substrate and configured for optical coupling, and a first attenuator extending along a first side of the taper. The first attenuator includes a conductive structure on the substrate. The conductive structure includes conductive vias on the substrate; and a metal layer, on the conductive vias, extending along the first side of the taper. 
     Embodiments of the present disclosure also provide an optical device. The optical device includes a waveguide configured to guide light, a taper integrated with the waveguide on a substrate and configured for optical coupling, and a first attenuator extending along a first side of the taper. The first attenuator includes a doped structure in the substrate to facilitate degrading unwanted optical signal from the taper. 
     Some embodiments of the present disclosure provide an optical device. The optical device includes a waveguide configured to guide light, a taper integrated with the waveguide on a substrate and configured for optical coupling, and a first attenuator extending along a first side of the taper. The first attenuator includes a refractive structure in the substrate to facilitate degrading unwanted optical signal from the taper. The refractive structure has an index of refraction larger than that of the substrate. 
     Some embodiments of the present disclosure provide an optical device. The optical device includes a waveguide disposed on an oxide layer and configured to guide light; a taper disposed on the oxide layer, integrated with the waveguide, and configured for optical coupling; and a first attenuator extending along a first side of the taper, including a doped structure spaced apart from the taper and configured to facilitate degrading unwanted optical signal from the taper. 
     Some embodiments of the present disclosure provide an optical device. The optical device includes a waveguide disposed on an oxide layer and configured to guide light; a taper disposed on the oxide layer, integrated with the waveguide, and configured for optical coupling; and a first attenuator extending along a first side of the taper, including a refractive structure configured to facilitate degrading unwanted optical signal from the taper, and having an index of refraction larger than that of the oxide layer. 
     Some embodiments of the present disclosure provide an optical device. The optical device includes a waveguide disposed on an oxide layer and configured to guide light; a doped taper integrated with the waveguide, and configured for optical coupling and facilitating alleviation of unwanted optical signal radiated therefrom; and a first attenuator extending along a first side of the taper, including a first doped structure configured to facilitate degrading unwanted optical signal from the doped taper. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.