WO2001011419A2 - Dynamic spectral shaping in optical fibre communication - Google Patents

Dynamic spectral shaping in optical fibre communication Download PDF

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Publication number
WO2001011419A2
WO2001011419A2 PCT/US2000/021662 US0021662W WO0111419A2 WO 2001011419 A2 WO2001011419 A2 WO 2001011419A2 US 0021662 W US0021662 W US 0021662W WO 0111419 A2 WO0111419 A2 WO 0111419A2
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WO
WIPO (PCT)
Prior art keywords
wavelength
controllable
dispersive element
grating
fiber optic
Prior art date
Application number
PCT/US2000/021662
Other languages
French (fr)
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WO2001011419A3 (en
WO2001011419A9 (en
Inventor
Asif A. Godil
David M. Bloom
Original Assignee
Lightconnect, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/372,649 external-priority patent/US6169624B1/en
Priority claimed from US09/548,788 external-priority patent/US6501600B1/en
Priority claimed from US09/549,781 external-priority patent/US6826330B1/en
Application filed by Lightconnect, Inc. filed Critical Lightconnect, Inc.
Priority to AU16537/01A priority Critical patent/AU1653701A/en
Priority to JP2001516015A priority patent/JP2003506988A/en
Priority to EP00979122A priority patent/EP1203463A2/en
Publication of WO2001011419A2 publication Critical patent/WO2001011419A2/en
Publication of WO2001011419A3 publication Critical patent/WO2001011419A3/en
Publication of WO2001011419A9 publication Critical patent/WO2001011419A9/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
    • H01S3/10023—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by functional association of additional optical elements, e.g. filters, gratings, reflectors
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0808—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more diffracting elements
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/264—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting
    • G02B6/266—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting the optical element being an attenuator
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/2931—Diffractive element operating in reflection
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/29313—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/29395—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device configurable, e.g. tunable or reconfigurable
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/27—Optical coupling means with polarisation selective and adjusting means
    • G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
    • G02B6/2793—Controlling polarisation dependent loss, e.g. polarisation insensitivity, reducing the change in polarisation degree of the output light even if the input polarisation state fluctuates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S2301/00—Functional characteristics
    • H01S2301/04—Gain spectral shaping, flattening
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06754—Fibre amplifiers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping

Definitions

  • the present invention relates to dynamically shaping the spectral response with high resolution for fiber-optic applications. More particularly, the present invention relates to dynamic gain or channel equalization for erbium doped fiber amplifiers (EDFA) used in WDM networks.
  • EDFA erbium doped fiber amplifiers
  • the EDFA gain is highly non-uniform across the EDFA spectral band. Therefore gain flattening is an important part of good EDFA design and operation. Presently this is accomplished using a static gain flattening filter based on thin film filter technology or more recently on fiber bragg gratings. The dynamic aspect is covered by using a variable optical attenuator between the two stages of an EDFA.
  • An object of the present invention is to provide controllable transmission in a communications system.
  • Another object of the present invention is to provide controllable transmission in a communications system as a function of wavelength.
  • a further object of the present invention is to provide controllable compensation for the wavelength dependent gain of EDFA' s.
  • Yet another object of the present invention is to provide controllable and dynamic compensation for the dynamic wavelength dependent gain of EDFA' s.
  • an optical system includes an EDFA system with at least one amplifier stage.
  • a spectral shaping device is coupled to the EDFA system.
  • the spectral shaping device includes a fiber optic input port that provides an input beam.
  • a wavelength dispersive element is coupled to the input port. The wavelength dispersive element spreads the input beam in at least one dimension as a function of wavelength and generates a dispersed beam.
  • a controllable grating reflects the dispersed beam to the wavelength dispersive element and generates a recombined beam. The controllable grating provides a controllable reflectivity as a function of wavelength.
  • a fiber optic output port is positioned to receive the recombined beam.
  • the optical system provides a desired controllable wavelength flatness.
  • an optical system includes a fiber optic input port providing an input beam and a wavelength dispersive element coupled to the input port.
  • the wavelength dispersive element spreads the input beam in at least one dimension as a function of wavelength and generates a dispersed beam.
  • a controllable grating reflects the dispersed beam to the wavelength dispersive element and generates a recombined beam.
  • the controllable grating provides a controllable reflectivity as a function of wavelength.
  • a fiber optic output port is positioned to receive the recombined beam.
  • An EDFA is coupled to the fiber optic input port.
  • the optical system provides a desired controllable wavelength flatness.
  • Figure 1(a) is a schematic top view of one embodiment of an optical system of the present invention that is utilized for dynamic spectral shaping.
  • Figure 1(b) is a schematic side view of the Figure 1(a) optical system.
  • Figure 2(a) is a schematic top view of a deformable grating, modulator array utilized in one embodiment of the present invention.
  • Figure 2(b) is a schematic side view of the Figure 2(a) deformable grating, modulator array.
  • Figure 3(a) is a schematic top view of a modified Figure 1(a) optical system that includes a circulator to extract the output light.
  • Figure 3(b) is a schematic side view of the Figure 3(a) optical system with circulator.
  • Figure 4(a) is a schematic top view of a modified Figure 1(a) optical system that includes of a quarter- wave plate to minimize PDL.
  • Figure 4(b) is a schematic side view of the Figure 4(a) optical system.
  • Figure 5 is a schematic top view of one embodiment of an optical system of the present invention that is utilized for dynamic spectral shaping and incorporates an array waveguide grating.
  • FIGURE 1 illustrates one embodiment of an optical system 100 of the present invention for the dynamic spectral shaping. Its comprised of an input optical fiber 105, an output optical fiber 115, an input collimating lens 110 of focal length fl, an output collimating lens 120 of focal length fl, a walkoff birefringent plate 130 on the input side, a walkoff birefringent plate 135 on the output side, a half wave plate 140, a grating 150 to diffract the light onto a focusing lens 160 of focal length f2, and then onto the device array 200.
  • an input optical fiber 105 comprised of an input optical fiber 105, an output optical fiber 115, an input collimating lens 110 of focal length fl, an output collimating lens 120 of focal length fl, a walkoff birefringent plate 130 on the input side, a walkoff birefringent plate 135 on the output side, a half wave plate 140, a grating 150 to diffract the light onto a focusing
  • the broadband light from the input optical fiber 105 is collimated by lens 110 which may be a GRIN lens, spherical lens or any other suitable lens.
  • lens 110 which may be a GRIN lens, spherical lens or any other suitable lens.
  • the collimated light passes through a walkoff birefringent plate 130 such as YVO4, calcite or LiNbO3.
  • the ordinary polarization goes straight through while the extraordinary polarization is displaced downwards by an amount, which if designed properly, should be greater than the beam size.
  • the polarization of one of the displaced beams is rotated by using a half wave plate (HWP) 140 and made the same as the other beam. Now both beams are either vertically or horizontally polarized.
  • HWP half wave plate
  • the polarization direction is chosen to maximize the diffraction efficiency of the grating 150 which may be a holographic grating or a blazed grating.
  • Two parallel beams impinge on the grating which diffracts the light towards the upper half of a focusing lens 160 of focal length f2 which is placed a distance f2 away from the grating.
  • This telecentric use walks the focused beam across the device array 200 as a function of wavelength.
  • the two polarization paths come together on the device array which is segmented to cover different spectral slices.
  • the reflected light from the device goes through the bottom half of the lens 160 and impinges on the grating which puts all the wavelengths back to gather.
  • the polarization is combined again using the HWP and the output birefringent plate 135 which is oriented opposite from the input birefringent plate.
  • the beam is focused into the output fiber 115 using another collimating lens 120.
  • the device array 200 may be an array of LCD elements, a suitable MEMS device array such as micro mirrors or cantilevers, an array of electro- optic modulators, an array of acousto-optic modulators or any light controlling device array.
  • the preferred embodiment is based on using a deformable grating modulator array invented by Bloom et. al. (patent no. 5,311,360) as shown in FIG. 2A,B.
  • the device is comprised of ribbons 199 of width w suspended above the substrate 198.
  • the top surface of the ribbon is a height d above the substrate. Ribbons are electrically connected and driven in pairs. Each pair controls a spectral slice.
  • 201 controls ⁇ l
  • 202 controls ⁇ 2, and so on till 20n controls ⁇ n.
  • the gap between the ribbons is also w. All ribbons and gaps are covered with a reflective layer which may be aluminum or gold.
  • a reflective layer which may be aluminum or gold.
  • d m ⁇ l/2.
  • d 2362 nm.
  • the shorter wavelength elements will start out with the ribbons already slightly pulled in.
  • the spectral resolution of the system is determined by fl, f2, grating pitch and the grating incident angle. The resolution should be such that going from ⁇ l to ⁇ 2 moves the spot across the device array by w.
  • An alternate embodiment of the optical system 300 is shown in FIG. 3A,B, which is the same as system 100 in FIG. 1, except a circulator 103 is used to separate out the light in the input fiber 101 from the output fiber 102.
  • FIG. 400 Yet another embodiment of the optical system 400 is shown in FIG.
  • dispersive element 150 is an arrayed waveguide grading ("AWG").
  • a suitable AWG 150 is manufactured by Lightwave Microsystems, San Jose, California.
  • device array 200 which can be a controllable, deformable grating modulator, can be placed in close proximity to the dispersed output at AWG 150. This proximity is selected to provide good coupling efficiency back into the waveguides of AWG 150.
  • the maximum distance depends on the size of the waveguides of AWG 150. In a preferred embodiment, the distance is 10 microns or less and can be butt-coupled.
  • AWG 150 disperses the light from the input optical fiber 105 and spreads the input beam in at least one dimension as a function of wavelength where it impinges on device array 200.
  • the spatially dispersed light is reflected back into AWG 150 which subsequently recombines the light into optical fiber 105 but in a counterpropagating direction to the input.
  • the output light can be extracted by circulator 103.
  • Other embodiments can include a separate output port and do not require the circulator.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optical Couplings Of Light Guides (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
  • Mechanical Light Control Or Optical Switches (AREA)
  • Optical Communication System (AREA)
  • Light Guides In General And Applications Therefor (AREA)

Abstract

The present invention is directed towards dynamic spectral shaping. Using a grating (150), the spectral band is spread across a diffractive MEMS (200) or other suitable device operable as a controllable grating providing a controllable reflectivity as a function of wavelength. The device may be the deformable grating modulator invented by Bloom et. al. (US patent no. 5,311,360) or other suitable device. The invention also includes the coupling in and out of the fiber (105) and may use polarization optics (130, 140) to ensure the grating is used in only one polarization where the diffraction efficiency is higher.

Description

DYNAMIC SPECTRAL SHAPING FOR FIBER-OPTIC APPLICATION
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to dynamically shaping the spectral response with high resolution for fiber-optic applications. More particularly, the present invention relates to dynamic gain or channel equalization for erbium doped fiber amplifiers (EDFA) used in WDM networks.
Description of Related Art
The EDFA gain is highly non-uniform across the EDFA spectral band. Therefore gain flattening is an important part of good EDFA design and operation. Presently this is accomplished using a static gain flattening filter based on thin film filter technology or more recently on fiber bragg gratings. The dynamic aspect is covered by using a variable optical attenuator between the two stages of an EDFA.
However the previous approach is inadequate for very long links where cascading of many EDFAs and components cannot ensure adequate spectral flatness. In addition, for dynamically reconfigurable networks a static approach is inadequate. Therefore there is a need for dynamically shaping the spectral response at various points in the network for maintaining adequate end to end spectral flatness. A device for accomplishing this was invented by B. Y. Kim and others based on exciting an acoustic flexure wave along the length of a bare fiber. However this approach gives limited spectral control and the bare fiber is affected by shock and vibration. Work done at Lucent is based on spreading the wavelengths in space using a grating, followed by an array of MARS
(mechanical anti-reflection switch) micromechanical modulators. This approach is limited by the fabrication difficulty and performance limitation of the MARS device. Accordingly, there is a need for a simple but powerful means of dynamic spectral shaping. The ideal system should have low insertion loss, fine spectral resolution, large dynamic range, low polarization dependent loss (PDL) and simple control.
SUMMARY OF THE INVENTION An object of the present invention is to provide controllable transmission in a communications system.
Another object of the present invention is to provide controllable transmission in a communications system as a function of wavelength.
A further object of the present invention is to provide controllable compensation for the wavelength dependent gain of EDFA' s.
Yet another object of the present invention is to provide controllable and dynamic compensation for the dynamic wavelength dependent gain of EDFA' s. These and other objects of the present invention are achieved in a dynamic spectral shaping device with a controllable transmission as a function of wavelength that includes a fiber optic input port providing an input beam. A wavelength dispersive element is coupled to the input port. The wavelength dispersive element spreads the input beam in at least one dimension as a function of wavelength and generates a dispersed beam. A controllable grating reflects the dispersed beam to the wavelength dispersive element and generates a recombined beam. The controllable grating provides a controllable reflectivity as a function of wavelength. A fiber optic output port is positioned to receive the recombined beam. In another embodiment of the present invention, an optical system includes an EDFA system with at least one amplifier stage. A spectral shaping device is coupled to the EDFA system. The spectral shaping device includes a fiber optic input port that provides an input beam. A wavelength dispersive element is coupled to the input port. The wavelength dispersive element spreads the input beam in at least one dimension as a function of wavelength and generates a dispersed beam. A controllable grating reflects the dispersed beam to the wavelength dispersive element and generates a recombined beam. The controllable grating provides a controllable reflectivity as a function of wavelength. A fiber optic output port is positioned to receive the recombined beam. The optical system provides a desired controllable wavelength flatness. In another embodiment of the present invention, an optical system includes a fiber optic input port providing an input beam and a wavelength dispersive element coupled to the input port. The wavelength dispersive element spreads the input beam in at least one dimension as a function of wavelength and generates a dispersed beam. A controllable grating reflects the dispersed beam to the wavelength dispersive element and generates a recombined beam. The controllable grating provides a controllable reflectivity as a function of wavelength. A fiber optic output port is positioned to receive the recombined beam. An EDFA is coupled to the fiber optic input port. The optical system provides a desired controllable wavelength flatness.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1(a) is a schematic top view of one embodiment of an optical system of the present invention that is utilized for dynamic spectral shaping. Figure 1(b) is a schematic side view of the Figure 1(a) optical system. Figure 2(a) is a schematic top view of a deformable grating, modulator array utilized in one embodiment of the present invention.
Figure 2(b) is a schematic side view of the Figure 2(a) deformable grating, modulator array.
Figure 3(a) is a schematic top view of a modified Figure 1(a) optical system that includes a circulator to extract the output light.
Figure 3(b) is a schematic side view of the Figure 3(a) optical system with circulator.
Figure 4(a) is a schematic top view of a modified Figure 1(a) optical system that includes of a quarter- wave plate to minimize PDL. Figure 4(b) is a schematic side view of the Figure 4(a) optical system. Figure 5 is a schematic top view of one embodiment of an optical system of the present invention that is utilized for dynamic spectral shaping and incorporates an array waveguide grating.
DETAILED DESCRIPTION OF THE INVENTION
FIGURE 1 illustrates one embodiment of an optical system 100 of the present invention for the dynamic spectral shaping. Its comprised of an input optical fiber 105, an output optical fiber 115, an input collimating lens 110 of focal length fl, an output collimating lens 120 of focal length fl, a walkoff birefringent plate 130 on the input side, a walkoff birefringent plate 135 on the output side, a half wave plate 140, a grating 150 to diffract the light onto a focusing lens 160 of focal length f2, and then onto the device array 200.
The broadband light from the input optical fiber 105 is collimated by lens 110 which may be a GRIN lens, spherical lens or any other suitable lens. The collimated light passes through a walkoff birefringent plate 130 such as YVO4, calcite or LiNbO3. The ordinary polarization goes straight through while the extraordinary polarization is displaced downwards by an amount, which if designed properly, should be greater than the beam size. The polarization of one of the displaced beams is rotated by using a half wave plate (HWP) 140 and made the same as the other beam. Now both beams are either vertically or horizontally polarized. The polarization direction is chosen to maximize the diffraction efficiency of the grating 150 which may be a holographic grating or a blazed grating. Two parallel beams impinge on the grating which diffracts the light towards the upper half of a focusing lens 160 of focal length f2 which is placed a distance f2 away from the grating. This telecentric use walks the focused beam across the device array 200 as a function of wavelength. The two polarization paths come together on the device array which is segmented to cover different spectral slices. The reflected light from the device goes through the bottom half of the lens 160 and impinges on the grating which puts all the wavelengths back to gather. The polarization is combined again using the HWP and the output birefringent plate 135 which is oriented opposite from the input birefringent plate. The beam is focused into the output fiber 115 using another collimating lens 120.
The device array 200 may be an array of LCD elements, a suitable MEMS device array such as micro mirrors or cantilevers, an array of electro- optic modulators, an array of acousto-optic modulators or any light controlling device array. The preferred embodiment is based on using a deformable grating modulator array invented by Bloom et. al. (patent no. 5,311,360) as shown in FIG. 2A,B. The device is comprised of ribbons 199 of width w suspended above the substrate 198. The top surface of the ribbon is a height d above the substrate. Ribbons are electrically connected and driven in pairs. Each pair controls a spectral slice. 201 controls λl, 202 controls λ2, and so on till 20n controls λn. The gap between the ribbons is also w. All ribbons and gaps are covered with a reflective layer which may be aluminum or gold. For operation at a given wavelength λ, d = mλ/2 where m is an integer. Now light reflected from the ribbons and the gaps is in phase and device looks like a mirror. By applying a voltage to the ribbons, the electrostatic force starts pulling the ribbons downwards and light starts diffracting. At a maximum deflection of λ/4, all the light is diffracted out and the element is effectively off. Two pairs of ribbon/gap provides enough isolation for a single-mode fiber. However more pairs can also be used. For a range of wavelength, λl-λn, d is chosen based on the longest wavelength, λl, i.e. d = mλl/2. In practice, m=3 is a suitable choice. For the EDFA application λl=1575 nm, therefore d=2362 nm. The shorter wavelength elements will start out with the ribbons already slightly pulled in. In FIG. 1, the choice of focal lengths fl, f2 and the grating use determines the spot size on the device array which in turn determines the ribbon width w, i.e. spot size = 4w. The spectral resolution of the system is determined by fl, f2, grating pitch and the grating incident angle. The resolution should be such that going from λl to λ2 moves the spot across the device array by w. An alternate embodiment of the optical system 300 is shown in FIG. 3A,B, which is the same as system 100 in FIG. 1, except a circulator 103 is used to separate out the light in the input fiber 101 from the output fiber 102.
Yet another embodiment of the optical system 400 is shown in FIG.
4A,B. This is again similar to system 100 shown in FIG 1 except that polarization splitting is not employed. Since both polarizations are impinging on the grating 150, it is desirable that the grating have high diffraction efficiency for both polarizations. After diffracting from the grating, a quarter wave plate (QWP) 140 is employed to flip the vertical and horizontal polarizations on the return path. This reduces the polarization dependent loss (PDL) for the overall system assuming the device array 200 does not have any significant PDL. If PDL from the device array needs to be minimized further, the polarization independent grating modulator invention of Godil et. al. (include by cross- reference) can be used here configured as an array of elements. Another variation of this embodiment would be to use a circulator on the input side to separate out the output fiber from the input without creating a separate path.
Another embodiment of the present invention is disclosed in Figure 5. In this embodiment, dispersive element 150 is an arrayed waveguide grading ("AWG"). A suitable AWG 150 is manufactured by Lightwave Microsystems, San Jose, California. In this embodiment, device array 200, which can be a controllable, deformable grating modulator, can be placed in close proximity to the dispersed output at AWG 150. This proximity is selected to provide good coupling efficiency back into the waveguides of AWG 150. The maximum distance depends on the size of the waveguides of AWG 150. In a preferred embodiment, the distance is 10 microns or less and can be butt-coupled. With this combination, AWG 150 disperses the light from the input optical fiber 105 and spreads the input beam in at least one dimension as a function of wavelength where it impinges on device array 200. The spatially dispersed light is reflected back into AWG 150 which subsequently recombines the light into optical fiber 105 but in a counterpropagating direction to the input. The output light can be extracted by circulator 103. Other embodiments can include a separate output port and do not require the circulator.
The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art.
What is claimed is:

Claims

1. A dynamic spectral shaping device with a controllable transmission as a function of wavelength, comprising: a fiber optic input port providing an input beam; a wavelength dispersive element coupled to the input port, the wavelength dispersive element spreading the input beam in at least one dimension as a function of wavelength and generating a dispersed beam; a controllable grating reflecting the dispersed beam to the wavelength dispersive element and generating a recombined beam, the controllable grating providing a controllable reflectivity as a function of wavelength; and a fiber optic output port positioned to receive the recombined beam.
2. The device of claim 1, wherein the controllable grating is an array with a diffraction efficiency that is controlled as a function of position on the array.
3. The device of claim 1, wherein the controllable grating is an array of ribbons.
4. The device of claim 1, wherein the controllable grating is a micromachined grating device.
5. The device of claim 1, further comprising: a first lens positioned between the fiber optic input port and the wavelength dispersive element.
6. The device of claim 1, further comprising: a second lens positioned between the wavelength dispersive element and the controllable grating.
7. The device of claim 1, further comprising: a birefringent plate positioned between the fiber optic input port and the wavelength dispersive element.
8. The device of claim 1 , further comprising: a half- wave plate positioned between the fiber optic input port and the wavelength dispersive element.
9. The device of claim 1, further comprising: a quarter-wave plate positioned between the wavelength dispersive element and the controllable grating.
10. The device of claim 1, further comprising: a second birefringent plate positioned between the wavelength dispersive element and the fiber optic output port.
11. An optical system, comprising: an EDFA system including at least one amplifier stage; a spectral shaping device coupled to the EDFA system, the spectral shaping device including: a fiber optic input port providing an input beam; a wavelength dispersive element coupled to the input port, the wavelength dispersive element spreading the input beam in at least one dimension as a function of wavelength and generating a dispersed beam; a controllable grating reflecting the dispersed beam to the wavelength dispersive element and generating a recombined beam, the controllable grating providing a controllable reflectivity as a function of wavelength; a fiber optic output port positioned to receive the recombined beam; and wherein the optical system provides a desired controllable wavelength flatness.
12. The system of claim 11, wherein the at least one amplifier stage of the EDFA system is coupled to the fiber optic output port.
13. The system of claim 11 , wherein the at least one amplifier stage of the EDFA system is coupled to the fiber optic input port.
14. The system of claim 11, wherein at least a portion of the spectral shaping device is incorporated in the EDFA system.
15. An optical system, comprising: a fiber optic input port providing an input beam; a wavelength dispersive element coupled to the input port, the wavelength dispersive element spreading the input beam in at least one dimension as a function of wavelength and generating a dispersed beam; a controllable grating reflecting the dispersed beam to the wavelength dispersive element and generating a recombined beam, the controllable grating providing a controllable reflectivity as a function of wavelength; a fiber optic output port positioned to receive the recombined beam; and an EDFA coupled to the fiber optic input port, wherein the optical system provides a desired controllable wavelength flatness.
PCT/US2000/021662 1999-08-11 2000-08-08 Dynamic spectral shaping in optical fibre communication WO2001011419A2 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
AU16537/01A AU1653701A (en) 1999-08-11 2000-08-08 Dynamic spectral shaping for fiber-optic application
JP2001516015A JP2003506988A (en) 1999-08-11 2000-08-08 Dynamic spectral shaping for application to optical fibers
EP00979122A EP1203463A2 (en) 1999-08-11 2000-08-08 Dynamic spectral shaping in optical fibre communication

Applications Claiming Priority (10)

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US37271299A 1999-08-11 1999-08-11
US09/372,649 1999-08-11
US09/372,649 US6169624B1 (en) 1999-08-11 1999-08-11 Achromatic optical modulators
US09/372,712 1999-08-11
US17168599P 1999-12-21 1999-12-21
US60/171,685 1999-12-21
US09/548,788 2000-04-13
US09/548,788 US6501600B1 (en) 1999-08-11 2000-04-13 Polarization independent grating modulator
US09/549,781 2000-04-14
US09/549,781 US6826330B1 (en) 1999-08-11 2000-04-14 Dynamic spectral shaping for fiber-optic application

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EP1377858A1 (en) * 2001-03-19 2004-01-07 Capella Photonics Inc. Reconfigurable optical add-drop multiplexers
WO2002082165A2 (en) * 2001-04-03 2002-10-17 Cidra Corporation Dynamic optical filter having a spatial light modulator
WO2002082166A3 (en) * 2001-04-03 2003-07-03 Cidra Corp Variable optical source
US7126740B2 (en) 2001-04-03 2006-10-24 Cidra Corporation Multifunctional optical device having a spatial light modulator with an array of micromirrors
WO2002082165A3 (en) * 2001-04-03 2003-10-30 Cidra Corp Dynamic optical filter having a spatial light modulator
WO2002082166A2 (en) * 2001-04-03 2002-10-17 Cidra Corporation Variable optical source
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EP1386194A1 (en) * 2001-04-13 2004-02-04 Corning Incorporated High contrast reflective lcd for telecommunications applications
EP1386194A4 (en) * 2001-04-13 2005-07-27 Corning Inc High contrast reflective lcd for telecommunications applications
WO2003017537A1 (en) * 2001-08-16 2003-02-27 Telefonaktiebolaget Lm Ericsson (Publ) Optical amplifier
US7202996B2 (en) 2001-08-16 2007-04-10 Telefonaktiebolaget Lm Ericsson (Publ) Optical amplifier
US7046410B2 (en) 2001-10-11 2006-05-16 Polychromix, Inc. Actuatable diffractive optical processor
WO2003060591A3 (en) * 2002-01-15 2003-12-04 Analog Devices Inc Optical switching system and apparatus with integral covering lens
WO2003060591A2 (en) * 2002-01-15 2003-07-24 Analog Devices, Inc. Optical switching system and apparatus with integral covering lens
WO2003065097A2 (en) * 2002-01-28 2003-08-07 Cidra Corporation Multifunctional optical device having a spatial light modulator with an array of micromirrors
WO2003065097A3 (en) * 2002-01-28 2003-12-18 Cidra Corp Multifunctional optical device having a spatial light modulator with an array of micromirrors
US6818959B2 (en) 2002-03-12 2004-11-16 Btg International Limited MEMS devices with voltage driven flexible elements
US6985308B1 (en) 2002-05-28 2006-01-10 Polychromix Corporation Telecommunications optical processor
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US6842556B2 (en) 2002-09-10 2005-01-11 Analog Devices, Inc. Two input, two output optical switch using two movable mirrors
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JP2003506988A (en) 2003-02-18

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