Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0221—Power control, e.g. to keep the total optical power constant
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/20—Filters
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
  • G02F2201/17—Multi-pass arrangements, i.e. arrangements to pass light a plurality of times through the same element, e.g. by using an enhancement cavity
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F2203/00—Function characteristic
  • G02F2203/58—Multi-wavelength, e.g. operation of the device at a plurality of wavelengths
  • G02F2203/585—Add/drop devices

Definitions

• This invention relates generally to an optical transmission system, and, more particularly, to an electro-optically tunable optical filter for use in an optical transmission system.
• Photonics the use of light to store, transmit, and/or process information, is rapidly penetrating the market for commodity and high technology products.
• optics is the transmission medium of choice for many metropolitan and local-area networks.
• optical transmission networks typically use sophisticated optical filters that may dynamically equalize the power on the wavelength, or frequency, channels of the networks.
• Exemplary optical filters that dynamically equalize power on a broad spectral feature basis include Mach-Zehnder filters, acousto-optic filters, holograms, and micro-mechanically driven mirrors.
• Exemplary optical filters that may dynamically equalize the power on a channel-by- channel basis include demultiplexers, arrays of programmable attenuators, multiplexers, and the like.
• Optical filters may include one or more waveguides for transmitting light, as well as one or more elements that may adjust the phase of the light propagating in the waveguides.
• a Joule heater is deployed proximate the waveguides and used to vary the temperature of the optical waveguide.
• the effective refractive index of the optics waveguide depends on the temperature of the waveguide, so varying the temperature changes the optical path length of the waveguide and thereby varies the phase of the light traveling in the optical waveguide.
• Thermo-optic phase adjustment is used in optical attenuators, spectrally selective filters, interferometers, and the like.
• Doerr U.S. Patent No. 6,212,315) describes a channel power equalizer that uses thermo-optic phase adjustment in a plurality of phase shifters.
• thermo-optic phase adjustment may not be well-suited for spectral filtering applications.
• the sensitivity of temperature-dependent phase controllers may be limited by the relatively small thermo-optic coefficient of silica. Although other materials may exhibit larger thermo-optic coefficients, these may be difficult to form into low-loss single mode waveguides.
• thermo-optic methods of phase control may not respond fast enough to be integrated tightly with other electronic devices in the optical transmission network.
• thermal crosstalk may also reduce the range of phase expression of the temperature-dependent phase controller. Although the reduction in the range of phase expression may be, at least in part, compensated for by increasing the range of temperatures applied to the phase controllers, increasing the temperature range typically results in a corresponding increase in power consumption of the device. Furthermore, the polarization independence of orthonormal modes may be reduced by thermal crosstalk.
• a method is provided for filtering an optical signal.
• the method includes receiving at least one input optical signal, forming first and second optical signals using the at least one input optical signal, and modifying at least one portion of the first optical signal using a plurality of non-waveguiding electro-optic phase adjusters.
• the method also includes forming an output optical signal by combining the first optical signal, including the at least one modified portion of the first optical signal, with the second optical signal.
• an apparatus in another aspect of the instant invention, includes an optical demultiplexer, a plurality of non-waveguiding electro-optic phase adjusters optically coupled to the optical demultiplexer, and an optical multiplexer optically coupled to the plurality of electro-optic phase adjusters.
• an electro-optically tunable optical filter in yet another aspect of the instant invention, includes a first optical transmission medium, a second optical transmission medium, and a first optical coupler for coupling portions of the first and second optical transmission media.
• the electro-optically tunable optical filter also includes an optical demultiplexer coupled to the second optical transmission medium, a plurality of non-waveguiding electro-optic phase adjusters optically coupled to the optical demultiplexer, and an optical multiplexer optically coupled to the plurality of non- waveguiding electro-optic phase adjusters.
• the electro-optically tunable optical filter further includes a third optical transmission medium optically coupled to the optical multiplexer and a second optical coupler for coupling portions of the second and the third optical transmission media.
• FIGS. 1A and IB conceptually illustrate two exemplary embodiments of a dynamically and chromatically variable transmissivity apparatus, such as a dynamic gain flattening filter;
• Figure 2 conceptually illustrates a plurality of electro-optic phase adjusters that may be used in the dynamically and chromatically variable transmissivity apparatus shown in Figures 1 A and IB;
• Figure 3 conceptually illustrates a perspective view of one embodiment of the electro- optic phase adjusters shown in Figure 2;
• Figure 4 illustrates one embodiment of an exemplary method of filtering an optical signal using the dynamically and chromatically variable transmissivity apparatus shown in Figures 1A and IB.
• Figure 1 A conceptually illustrates a first exemplary embodiment of a dynamically and chromatically variable transmissivity apparatus, such as a dynamic gain flattening filter 100.
• a dynamically and chromatically variable transmissivity apparatus such as a dynamic gain flattening filter 100.
• the variable transmissivity apparatus 100 may be one of variety of optical elements known to those of ordinary skill in the art.
• the variable transmissivity apparatus 100 may be a channel equalizer for controlling channel powers in wavelength-division multiplexed systems, a Mach-Zehnder filter, a Michelson interferometer, and the like.
• the first exemplary embodiment of the dynamic gain flattening filter 100 includes first and second optical transmission media 101, 102.
• the first and second optical transmission media 101, 102 are waveguides.
• a first optical signal may enter the dynamic gain flattening filter 100 through a first port 105 in a non-reciprocal device 110.
• the non-reciprocal device 110 is a circulator 101 that may be formed using materials having a high Nerdet constant, as will be appreciated by those of ordinary skill in the art.
• the non-reciprocal device 110 may be optically coupled to the waveguide 101 so that the first optical signal may be transmitted to the waveguide 101 and then enter the dynamic gain flattening filter 100 through a first port 115 in a first optical coupler 120.
• the first optical signal may enter the dynamic gain flattening filter 100 without passing through the non-reciprocal device 110.
• a second optical signal propagating along the waveguide 102 may enter the dynamic gain flattening filter 100 through a second port 125 in the first optical coupler 120.
• the first optical signal and, if present, the second optical signal are wavelength division multiplexed optical signals.
• the first optical coupler 120 may split and/or combine the first and second optical signals to form two signal components that are transmitted to upper and lower arms 125, 130 of the waveguides 101, 102, respectively. For example, if no second optical signal is provided to the dynamic gain flattening filter 100 via the waveguide 102, the first optical coupler 120
• the two signal components, VR and _/ ' Vl - R are
• the upper and lower arms 125, 130 are waveguides.
• the upper arm 125 may be waveguide.
• a first portion 133(1-2) of the lower arm 130 may be a waveguide.
• the first portion 133(1) of the lower arm 130 is optically coupled to an optical demultiplexer 135.
• the optical demultiplexer 135 receives the signal
• the signal component J ⁇ JI - R may have a bandwidth of 60nm and be demultiplexed
• component _/ Vl - R into portions corresponding to the plurality of selected frequency and/or
• wavelength bands may include, but are not limited to, optical splitters, prisms, gratings, and the like.
• the optical demultiplexer 135 provides the portions of the signal component j* ⁇ - R
• electro-optic phase adjusters 140 which are optically coupled to the optical demultiplexer 135.
• the number of electro-optic phase adjusters 140 is a matter of design choice.
• three electro-optic phase adjusters 140 are shown in Figure 1, alternative embodiments of the present invention may include more or fewer electro-optic phase adjusters 140.
• the plurality of electro-optic phase adjusters 140 are optically coupled to a mirror 145.
• the upper arm 125 is also optically coupled to the mirror 145.
• a wave plate 150 may be deployed adjacent the mirror
• a quarter-wave plate 150 may be deployed between the mirror and the upper arm 125 and electro-optic phase adjusters 140. Incorporating the quarter-wave plate 150 may reduce, or null, birefringence in the portions of the signal
• the optical path length of the upper and lower arms 125, 130 may, in one embodiment, be approximately equal.
• the optical path length of the upper arm 125 and lower arm 130, including the optical demultiplexer 135, the electro-optic phase adjusters 140, and the wave plate 150 may be equal to within about a few wavelengths of the first and, if present, the second optical signal.
• the effective optical path length of the electro-optic phase adjusters 140, and consequently the optical path length of portions of the lower arm 130 may be controlled, or tuned, to modify the portions of the signal
• the electro-optic phase adjusters 140 may be varied so that one or more relative phase
• a phase difference of ⁇ /4 may be introduced between two of the portions of the
• component j Vl - R introduced by the electro-optic phase adjusters 140 may be approximately
• the optical demultiplexer 135 may also function as
• an optical multiplexer for the reflected portions of the signal component y ' Vl - R .
• the optical demultiplexer 135 may combine to reflected portions of the signal
• signal component y ' Vl - R may interfere destructively and/or constructively to form a filtered
• the filtered output signal may be provided to the non- reciprocal device 110 and may then exit the dynamic gain flattening filter via a second port 155.
• the non-reciprocal device 110 is optional and may be omitted in alternative embodiments of the present invention.
• Figure IB shows a second exemplary embodiment of the dynamic gain flattening filter 100.
• the plurality of electro-optic phase adjusters 140 are optically coupled to an optical multiplexer
• Portions of the signal component j Vl - R may be
• the optical multiplexer 160 may be any optical multiplexer 160.
• the optical multiplexer 160 may be any optical multiplexer 160.
• the optical multiplexer 160 may be any optical multiplexer 160.
• the signal component VR and the modified signal component y ' Vl - R may interfere destructively and/or constructively to form a filtered output
• the first and second optical couplers 120, 165 have the same splitting ratio, R, although this is not necessary for the practice of the present invention. Furthermore, the second optical coupler 165 may be omitted in various alternative embodiments of the present invention.
• the optical path length of the upper and lower arms 125, 130 may, in one embodiment, be approximately equal.
• the optical path length of the upper arm 125 and lower arm 130, including the optical demultiplexer 135, the electro-optic phase adjusters 140, and the optical multiplexer 145 may be equal to within about a few wavelengths of the first and, if present, the second optical signal.
• the effective optical path length of the electro-optic phase adjusters 140, and consequently the optical path length of portions of the lower arm 130 may be controlled, or tuned, to modify the portions of the
• electro-optic phase adjusters 140 may be varied so that one or more relative phase
• a phase difference of ⁇ /4 may be introduced between two of the portions of the
• one or more components of the dynamic gain flattening filter 100 may be formed on a single planar waveguide platform (not shown).
• the optical demultiplexer 135, the plurality of electro-optic phase adjusters 140, and the mirror 150 or the optical multiplexer 160 may be formed on the planar waveguide platform.
• the planar waveguide platform may be formed of a polymer, silica-on-silicon, a semiconductor, or like materials.
• the two embodiments of the dynamic gain flattening filter 100 shown in Figures 1 A and IB may be integrated tightly with other electronic devices.
• the number of electro-optic phase adjusters 140 that may be formed on a single platform may be increased because thermal crosstalk between multiple electro-optic phase adjusters 140 may be reduced relative to, e.g., a plurality of thermo-optic phase adjusters.
• the electro-optic phase adjusters 140 may also have an increased range of phase expression and/or reduced power consumption compared to, e.g., a plurality of thermo-optic phase adjusters.
• FIG. 2 conceptually illustrates the plurality of electro-optic phase adjusters 140, in accordance with one embodiment of the present invention. As discussed above, in one
• the signal component y ' Vl - R is provided to the optical demultiplexer 135 via
• the optical demultiplexer 135 is optically coupled to a plurality of optical transmission media, such as waveguides 200, which may be deployed proximate a corresponding plurality of slots 210.
• a plurality of optical transmission media such as waveguides 200
• an end of the waveguide 200 may be deployed proximate the slot 210 so that the waveguide 200 is optically coupled to the slot 210 and may provide portions of the signal
• each of the waveguides 200 may provide a
• An electro-optically active phase adjusting element 220 may be positioned in at least a portion of the slot 210.
• the electro-optically active phase adjusting element 220 may be an electro-optically active material such as a liquid crystal, a polymer- dispersed liquid crystal, a birefringent material, and the like, which may be located in the slot 210.
• any desirable type of electro-optically active phase adjusting element 220 may be used.
• the electro-optically active phase adjusting element 220 may be a silicon substrate having an opening that is filled with an electro-optically active material.
• the electro-optically active phase adjusting element 220 may be formed separately and subsequently inserted into the electro-optic phase adjusters 140.
• One or more electrodes 230 are deployed proximate the slot 210.
• two electrodes 230 are deployed near the slot and above at least a portion (drawn in ghosted lines) of the waveguide 200.
• the present invention is not so limited. In alternative embodiments, more or fewer electrodes 230 may be deployed proximate the slot 210. Furthermore, in other alternative embodiments, at least a portion of the electrodes 230 may be deployed within the slot 210.
• the electrodes 230 are coupled to a control unit 240 via lines 250.
• the lines 250 may be wires, conductive traces, and the like.
• the control unit 240 may provide selected signals, such as voltages and/or currents, to the electrodes 230.
• the signals provided by the control unit 240 may be used to vary the optical path length of the electro-optically active phase adjusting element 220. For example, applying a voltage to one or more of the electrodes 230 may create an electric field, and at least a portion of the electric field may penetrate into the slot 210. Varying the strength of the signal, e.g. the voltage, may change the amplitude and/or orientation of the electric field, which may change the optical path length of the electro-optically active phase adjusting element 220.
• a phase of one or more of the portions of the signal component y ' Vl - R may be
• optically active phase adjusting element 220 In one embodiment, a relative phase difference
• Another plurality of optical transmission media such as waveguides 260, may be deployed proximate the slot 210.
• an end of the waveguide 260 may be deployed proximate the slot 210 so that the waveguide 260 is optically coupled to the slot 210
• a portion (drawn in ghosted lines) of the waveguide 260 may be positioned beneath one or more of the electrodes 230.
• the waveguides 260 may be optically coupled to the mirror 145 and/or the wave plate 150.
• the waveguides 260 may be optically coupled to the multiplexer 160, which may, as discussed above, split and/or combine
• the slot 210 and the electro-optically active phase adjusting element 220 are, in one embodiment, non-waveguiding.
• waveguiding elements such as the waveguides 200, 260
• the electro-optic phase adjusters 140 are referred to hereinafter as "non-waveguiding" electro- optic phase adjusters 140.
• FIG. 3 conceptually illustrates a perspective view of one embodiment of the electro- optic phase adjuster 140.
• one or more waveguide portions 305(1-2) are formed within a dielectric layer, commonly referred to in the art as a cladding layer 310, which is formed above a semiconductor substrate 320, such as silicon.
• a dielectric layer commonly referred to in the art as a cladding layer 310
• semiconductor substrate 320 such as silicon.
• the configuration of the electro-optic phase adjuster 140 is exemplary in nature, and that in alternative embodiments, the electro-optic phase adjuster 140 may include other components not shown in Figure 3.
• the waveguide portions 305(1-2) shown in the illustrated embodiment are formed of material having a refractive index that is larger than a refractive index of the cladding layer 310.
• the waveguide portions 305(1-2) may be formed of un-doped silica having a refractive index of about 1.4557 and the cladding layer 310 may be formed of doped or un- doped silica having a refractive index of about 1.445.
• the waveguide portions 305(1-2) and the cladding layer 310 may be formed of any desirable materials.
• the cladding layer 310 may include an under cladding layer (not shown) formed, at least in part, in a region 315 beneath the waveguide portions 305(1-2) and an upper cladding layer (not shown) formed, at least in part, in a region 320 above the waveguide portions 305(1- 2).
• the upper cladding layer and the under cladding layer do not have the same refractive index.
• the upper cladding layer may have a refractive index of about 1.4448 and the under cladding layer may have a refractive index of about 1.4451.
• a slot 330 is incised in the cladding layer 310 so that the waveguide portions 305(1-2) terminate proximate the slot 330.
• the waveguide portions 305(1-2) may not terminate proximate the slot 330.
• a part of the waveguide portions 305(1-2) may be proximate the slot 330 even though the waveguide portions 305(1-2) terminate at a location spaced from the slot 330.
• the slot 330 is incised so that an evanescent field amplitude due to the signals propagating in the waveguide portions 305(1-2) at transverse edges 350(1-2) of the slot 330 is less than -40dB of the peak value.
• the precise location of the slot 330 and the desired evanescent field amplitude at the transverse edges 350(1-2) are matters of design choice.
• the slot 330 is depicted as rectangular in Figure 3, the geometry of the slot 330 is a matter of design choice, taking on any of a variety of geometric cross sectional configurations and even varying in cross sectional configuration along its length.
• Figure 4 illustrates one embodiment of an exemplary method of filtering an optical signal using, for example, the dynamic gain flattening filter 100 shown in Figures 1A and IB.
• the illustrated embodiment of the method includes receiving (at 400) at least one input optical signal.
• First and second optical signals are then formed (at 410) using the at least one input optical signal.
• the optical coupler 110 shown in Figures 1A and IB may form
• At least one portion of the first optical signal may be modified (at 420) using a plurality of electro-optic phase adjusters, such as the electro-optic phase adjusters 140 shown in Figures 1 A and IB.
• An output optical signal may then be formed (at 430) by combining the first optical signal, including the at least one modified portion of the first optical signal, with the second optical signal.
• the accuracy, finesse, and control of the dynamic gain flattening filter 100 may be increased relative to, e.g., thermo- optic phase controllers.
• a larger number of electro-optic phase adjusters 140 may be included in a dynamic gain flattening filter 100 that is formed on, a single semiconductor substrate.
• the range of phase expression of the electro-optic phase adjusters 140 may also be increased without necessarily requiring a corresponding increase in power consumption of the device.
• the polarization independence of orthonormal modes of signals propagating in the dynamic gain flattening filter 100 may also be improved.
• variable transmissivity apparatus 100 is, at least in part, likely to be driven by the increasing sophistication of signaling paradigms adopted for use in access and metropolitan networks, as well as transmission backbones. It is anticipated that the current invention, perhaps in conjunction with other developments, foreseen and unforeseen, may permit a much greater range of these applications to be addressed. In particular, the greater finesse and lower power requirements may facilitate the adoption of this approach in highly functional assemblies in access and metropolitan networks, as well as transmission backbones.

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• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
• Optical Integrated Circuits (AREA)
• Liquid Crystal (AREA)
• Lasers (AREA)
• Optical Communication System (AREA)

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• 2003
  • 2003-07-17 GB GB0316824A patent/GB2404034A/en not_active Withdrawn
• 2004
  • 2004-07-15 WO PCT/GB2004/003090 patent/WO2005011171A1/en not_active Ceased
  • 2004-07-15 KR KR1020067001127A patent/KR20060061795A/ko not_active Withdrawn
  • 2004-07-15 AT AT04743429T patent/ATE421197T1/de not_active IP Right Cessation
  • 2004-07-15 US US10/564,134 patent/US7558449B2/en not_active Expired - Fee Related
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  • 2004-07-15 DE DE602004019099T patent/DE602004019099D1/de not_active Expired - Lifetime
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