US20090016680A1 - Method and apparatus for minimizing propagation losses in wavelength selective filters - Google Patents
Method and apparatus for minimizing propagation losses in wavelength selective filters Download PDFInfo
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- US20090016680A1 US20090016680A1 US11/777,023 US77702307A US2009016680A1 US 20090016680 A1 US20090016680 A1 US 20090016680A1 US 77702307 A US77702307 A US 77702307A US 2009016680 A1 US2009016680 A1 US 2009016680A1
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- coupling
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- wavelength selective
- light
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/12007—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer
Definitions
- the invention relates generally to optics, and relates more particularly to optical interconnects.
- FIG. 1A illustrates a top view of one example of a conventional wavelength selective filter 100 (e.g., such as those used for wavelength division multiplexing).
- FIG. 1B illustrates a cross sectional view of the filter 100 of FIG. 1A , taken along line A-A′.
- the filter 100 includes a ring resonator 102 side-coupled to an access straight waveguide (or waveguide bus) 104 .
- the ring resonator 102 is tuned to a wavelength channel of interest, such that the ring resonator 102 filters this channel from the bus 104 .
- the coupling gap 106 i.e., the distance that separates the ring resonator 102 from the bus 104 ) is typically on the order of a micrometer and controlled within a few nanometers of precision. Such control, however, is difficult to achieve by typical lithography methods.
- FIG. 2A illustrates a top view of an alternative example of a conventional wavelength selective filter 200 .
- FIG. 2B illustrates a cross sectional view of the filter 200 of FIG. 2A , taken along line A-A′.
- the filter 200 includes a ring resonator 202 coupled to a waveguide bus 204 .
- the ring resonator 202 is formed in a high refractive index waveguiding layer that is separate from the layer in which the bus 204 is formed.
- the coupling gap 206 is vertically disposed and can be precisely controlled by an amount of gap material grown, for example, by molecular-beam epitaxy (MBE).
- MBE molecular-beam epitaxy
- FIGS. 1A and 1B For silicon on insulator (SOI)-based planar lightwave circuits based on strip silicon single-mode waveguides with sub-micron cross sections, the approach illustrated in FIGS. 1A and 1B results in a coupling gap on the order of 100 nanometers, which should be controlled with nanometer precision. This makes fabrication tolerances very difficult to maintain.
- Applying the alternative approach illustrated in FIGS. 2A and 2B would require the growth of an oxide or other low refractive index material on top of the SOI structure to form the coupling gap, followed by growth of an additional top silicon layer for the ring resonator.
- an apparatus includes a waveguide bus defined in a first crystalline layer of the apparatus, for receiving incoming light, a resonator defined in the first crystalline layer, and a coupling structure defined in a second polysilicon or amorphous silicon layer of the apparatus, for coupling a selected wavelength of the incoming light from the waveguide bus to the resonator.
- FIG. 1A illustrates a top view of one example of a conventional wavelength selective filter
- FIG. 1B illustrates a cross sectional view of the filter of FIG. 1A , taken along line A-A′;
- FIG. 2A illustrates a top view of an alternative example of a conventional wavelength selective filter
- FIG. 2B illustrates a cross sectional view of the filter of FIG. 2A , taken along line A-A′;
- FIG. 3A is a top view of one embodiment of a wavelength selective filter, according to the present invention.
- FIG. 3B is a cross sectional view of the filter of FIG. 3A , taken along line A-A′;
- FIG. 3C is a cross sectional view of the filter of FIG. 3A taken along line B-B′.
- the present invention is a method and an apparatus for minimizing propagation losses in wavelength selective filters.
- Embodiments of the present invention vertically couple a waveguide bus to a resonator using a straight polysilicon waveguide section with lateral tapers, where the waveguide bus and the resonator are located on a common crystalline layer of an SOI wafer.
- FIG. 3A is a top view of one embodiment of a wavelength selective filter 300 , according to the present invention.
- FIG. 3B is a cross sectional view of the filter 300 of FIG. 3A , taken along line A-A′.
- FIG. 3C is a cross sectional view of the filter 300 of FIG. 3A taken along line B-B′.
- the filter 300 comprises a resonator (e.g., a ring resonator) 302 , a waveguide bus 304 and a coupling structure 308 .
- a resonator e.g., a ring resonator
- the resonator 302 and the waveguide bus 304 are defined in a first, common crystalline layer 312 of the SOI wafer of the filter 300 .
- the coupling structure 308 is defined in a second layer 314 of the filter 300 , located in one embodiment above the first layer 312 .
- the second layer comprises polysilicon or amorphous silicon.
- the coupling structure 308 comprises a substantially straight waveguide having lateral adiabatic tapers 310 1 - 310 2 (hereinafter collectively referred to as “tapers 310 ”) at each end.
- the tapers 310 are configured for coupling incoming light between the coupling structure 308 and the waveguide bus 304 or the resonator 302 .
- incoming light is received in the first layer 312 of the filter 300 by a first section of the waveguide bus 304 .
- the light propagates through the waveguide bus 304 , it is coupled to the coupling structure 308 in the second layer 314 of the filter 300 , via a first taper 310 1 .
- the light then propagates through the coupling structure 308 until the light reaches the resonator 302 , where the selected wavelength is coupled to the resonator 302 .
- the remainder of the light i.e., wavelengths other than the selected wavelength
- the filter 300 is thereby configured to control the coupling gap 306 between the resonator 302 and the waveguide bus 304 by growth (e.g., of oxide or other low refractive index material).
- growth e.g., of oxide or other low refractive index material.
- propagation losses in this case are minimized because the optical mode of incoming light propagates in the polysilicon or amorphous silicon top layer (i.e., second layer 314 ) for only a very short relative distance, and no further substantial losses due to the resonator 302 occur.
- Embodiments of the present invention represent a significant advancement in the field of optics.
- Embodiments of the present invention provide a coupling section (e.g., a straight poly-silicon waveguide section with lateral tapers) by which a waveguide bus is vertically coupled to a resonator.
- the gap between the bus and the resonator can be tightly controlled, while propagation losses are minimized.
Abstract
Description
- The invention relates generally to optics, and relates more particularly to optical interconnects.
-
FIG. 1A illustrates a top view of one example of a conventional wavelength selective filter 100 (e.g., such as those used for wavelength division multiplexing).FIG. 1B illustrates a cross sectional view of thefilter 100 ofFIG. 1A , taken along line A-A′. Thefilter 100 includes aring resonator 102 side-coupled to an access straight waveguide (or waveguide bus) 104. Thering resonator 102 is tuned to a wavelength channel of interest, such that thering resonator 102 filters this channel from thebus 104. For high refractive index contrast planar lightwave waveguides and circuits, the coupling gap 106 (i.e., the distance that separates thering resonator 102 from the bus 104) is typically on the order of a micrometer and controlled within a few nanometers of precision. Such control, however, is difficult to achieve by typical lithography methods. -
FIG. 2A illustrates a top view of an alternative example of a conventional wavelengthselective filter 200.FIG. 2B illustrates a cross sectional view of thefilter 200 ofFIG. 2A , taken along line A-A′. Like thefilter 100, thefilter 200 includes aring resonator 202 coupled to awaveguide bus 204. However, as illustrated inFIG. 2B , thering resonator 202 is formed in a high refractive index waveguiding layer that is separate from the layer in which thebus 204 is formed. In this case, thecoupling gap 206 is vertically disposed and can be precisely controlled by an amount of gap material grown, for example, by molecular-beam epitaxy (MBE). - For silicon on insulator (SOI)-based planar lightwave circuits based on strip silicon single-mode waveguides with sub-micron cross sections, the approach illustrated in
FIGS. 1A and 1B results in a coupling gap on the order of 100 nanometers, which should be controlled with nanometer precision. This makes fabrication tolerances very difficult to maintain. Applying the alternative approach illustrated inFIGS. 2A and 2B would require the growth of an oxide or other low refractive index material on top of the SOI structure to form the coupling gap, followed by growth of an additional top silicon layer for the ring resonator. This is likely to result in a polycrystalline or amorphous silicon structure on top of the silicon layer, which can lead to significant propagation losses (e.g., approximately twenty dB/cm) due to scattering on the grain boundaries. Losses are increased proportionally to the photon lifetime (inverse of the ring resonator quality factor) if the ring resonator or other resonator structure is located on the top layer of the circuit. - Thus, there is a need for a method and an apparatus for minimizing propagation losses in wavelength selective filters.
- The present invention is a method and an apparatus for minimizing losses in wavelength selective filters. In one embodiment, an apparatus includes a waveguide bus defined in a first crystalline layer of the apparatus, for receiving incoming light, a resonator defined in the first crystalline layer, and a coupling structure defined in a second polysilicon or amorphous silicon layer of the apparatus, for coupling a selected wavelength of the incoming light from the waveguide bus to the resonator.
- So that the manner in which the above recited embodiments of the invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be obtained by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
-
FIG. 1A illustrates a top view of one example of a conventional wavelength selective filter; -
FIG. 1B illustrates a cross sectional view of the filter ofFIG. 1A , taken along line A-A′; -
FIG. 2A illustrates a top view of an alternative example of a conventional wavelength selective filter; -
FIG. 2B illustrates a cross sectional view of the filter ofFIG. 2A , taken along line A-A′; -
FIG. 3A is a top view of one embodiment of a wavelength selective filter, according to the present invention; -
FIG. 3B is a cross sectional view of the filter ofFIG. 3A , taken along line A-A′; and -
FIG. 3C is a cross sectional view of the filter ofFIG. 3A taken along line B-B′. - To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.
- In one embodiment, the present invention is a method and an apparatus for minimizing propagation losses in wavelength selective filters. Embodiments of the present invention vertically couple a waveguide bus to a resonator using a straight polysilicon waveguide section with lateral tapers, where the waveguide bus and the resonator are located on a common crystalline layer of an SOI wafer.
-
FIG. 3A is a top view of one embodiment of a wavelengthselective filter 300, according to the present invention.FIG. 3B is a cross sectional view of thefilter 300 ofFIG. 3A , taken along line A-A′.FIG. 3C is a cross sectional view of thefilter 300 ofFIG. 3A taken along line B-B′. Referring simultaneously toFIGS. 3A-3C , thefilter 300 comprises a resonator (e.g., a ring resonator) 302, awaveguide bus 304 and acoupling structure 308. - The
resonator 302 and thewaveguide bus 304 are defined in a first,common crystalline layer 312 of the SOI wafer of thefilter 300. Thecoupling structure 308 is defined in asecond layer 314 of thefilter 300, located in one embodiment above thefirst layer 312. In one embodiment, the second layer comprises polysilicon or amorphous silicon. Thecoupling structure 308 comprises a substantially straight waveguide having lateral adiabatic tapers 310 1-310 2 (hereinafter collectively referred to as “tapers 310”) at each end. Thetapers 310 are configured for coupling incoming light between thecoupling structure 308 and thewaveguide bus 304 or theresonator 302. - Specifically, incoming light is received in the
first layer 312 of thefilter 300 by a first section of thewaveguide bus 304. As the light propagates through thewaveguide bus 304, it is coupled to thecoupling structure 308 in thesecond layer 314 of thefilter 300, via afirst taper 310 1. The light then propagates through thecoupling structure 308 until the light reaches theresonator 302, where the selected wavelength is coupled to theresonator 302. The remainder of the light (i.e., wavelengths other than the selected wavelength) continues to propagate along thecoupling structure 308 until the light reaches asecond taper 310 2, by which the remainder of the light is coupled back to thewaveguide bus 304. - The
filter 300 is thereby configured to control thecoupling gap 306 between theresonator 302 and thewaveguide bus 304 by growth (e.g., of oxide or other low refractive index material). However, propagation losses in this case are minimized because the optical mode of incoming light propagates in the polysilicon or amorphous silicon top layer (i.e., second layer 314) for only a very short relative distance, and no further substantial losses due to theresonator 302 occur. - Thus, the present invention represents a significant advancement in the field of optics. Embodiments of the present invention provide a coupling section (e.g., a straight poly-silicon waveguide section with lateral tapers) by which a waveguide bus is vertically coupled to a resonator. The gap between the bus and the resonator can be tightly controlled, while propagation losses are minimized.
- While foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims (5)
Priority Applications (4)
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US11/777,023 US7469085B1 (en) | 2007-07-12 | 2007-07-12 | Method and apparatus for minimizing propagation losses in wavelength selective filters |
CN2008101302785A CN101344615B (en) | 2007-07-12 | 2008-06-23 | Method and apparatus for minimizing propagation losses in wavelength selective filters |
TW097125812A TWI421552B (en) | 2007-07-12 | 2008-07-09 | Method and apparatus for minimizing propagation losses in wavelength selective filters |
US12/211,645 US7567738B2 (en) | 2007-07-12 | 2008-09-16 | Method and apparatus for minimizing propagation losses in wavelength selective filters |
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US11/777,023 US7469085B1 (en) | 2007-07-12 | 2007-07-12 | Method and apparatus for minimizing propagation losses in wavelength selective filters |
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US12/211,645 Continuation US7567738B2 (en) | 2007-07-12 | 2008-09-16 | Method and apparatus for minimizing propagation losses in wavelength selective filters |
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US20090016680A1 true US20090016680A1 (en) | 2009-01-15 |
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US12/211,645 Active US7567738B2 (en) | 2007-07-12 | 2008-09-16 | Method and apparatus for minimizing propagation losses in wavelength selective filters |
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DE102012209250A1 (en) * | 2012-05-31 | 2013-12-05 | Protected-Networks.Com Gmbh | security system |
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US7469085B1 (en) * | 2007-07-12 | 2008-12-23 | International Business Machines Corporation | Method and apparatus for minimizing propagation losses in wavelength selective filters |
JP6010275B2 (en) * | 2010-03-15 | 2016-10-19 | セイコーエプソン株式会社 | Optical filter and analytical instrument and optical instrument using the same |
JP2012049597A (en) * | 2010-08-24 | 2012-03-08 | Nikon Corp | Imaging apparatus |
CN104242052B (en) * | 2013-06-18 | 2018-01-19 | 中国科学院苏州纳米技术与纳米仿生研究所 | Ring cavity device and preparation method thereof |
CN104062712A (en) * | 2014-07-17 | 2014-09-24 | 广东威创视讯科技股份有限公司 | Smoothing structure applied to LED and LED display screen |
US10114173B2 (en) * | 2017-03-14 | 2018-10-30 | Huawei Technologies Co., Ltd. | Optical device |
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US7469085B1 (en) * | 2007-07-12 | 2008-12-23 | International Business Machines Corporation | Method and apparatus for minimizing propagation losses in wavelength selective filters |
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2008
- 2008-06-23 CN CN2008101302785A patent/CN101344615B/en active Active
- 2008-07-09 TW TW097125812A patent/TWI421552B/en not_active IP Right Cessation
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US6665476B2 (en) * | 2000-09-29 | 2003-12-16 | Sarnoff Corporation | Wavelength selective optical add/drop multiplexer and method of manufacture |
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Publication number | Publication date |
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US20090016677A1 (en) | 2009-01-15 |
US7567738B2 (en) | 2009-07-28 |
TWI421552B (en) | 2014-01-01 |
CN101344615B (en) | 2010-06-02 |
TW200921168A (en) | 2009-05-16 |
CN101344615A (en) | 2009-01-14 |
US7469085B1 (en) | 2008-12-23 |
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