0001
`
`Capella 2004
`Cisco v. Capella
`IPR2014-00894
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`

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`Method of Payment:
`A cheque is enclosed to cover the Provisional Filing Fee in the amount of $150.00 US.
`
`The invention was not made by an agency of the United States Government or under contract with an
`agency of the United States Government
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`Please change any additional fees or credit overpayment to Deposit Account No: 20-0345.
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`:2.g\2’@
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`Date:
`
`Respectfully submitted,
`
`Q10 . gang
`
`Randy W. Lacasse
`Regn No: 34,368
`
`2001 Jefferson Davis Highway
`Efsuite 806
`j="-fAr1ington, VA 22202
`j:.:U.s.A.
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`(703)4151o15
`(703)4-151017
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`The basic arrangement of proposed COADM module is shown in Figure 1.
`A pair of circulators is used to separate input I output and addldrop signals
`(not shown).
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`Diffraction
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`Mirror
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`grazing
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` Figure 1.
` The front end micro-optics design is shown in Figures 2a, b.
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` Inputioutput
`Add!Drop
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`compensation
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`The light from input fiber is collimated with a microlens. The polarization
`diversity arrangement is used to provide two sub beams at the same
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`(horizontal) polarization. A plate, made of the same material as the
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`birefringent element, is inserted into upper sub beam for PMD
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`compensation. An alternative PMD free front end design is shown in
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`Figure 2b.
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` Half wave
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`Figure 2b.
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`In the following Figure 3, the optical layout is explicitly shown. A single mirror
`is used to provide light focussing I collimation. The diffraction grating is
`located at the focus of the mirror. Since the input beams are collimated, the
`light is essentially focussed on the grating. The 1le2 spot size at the grating,
`2:91, and the 1le2 beam diameter, 20);, at the microcollimator are related in the
`following way:
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`calm; : }L*f /1:
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`(1)
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`It follows from Eq. (1) that one can tune the spot size on the grating and the
`resulting spectral resolution by changing the beam size at microcollimator.
`should also be kept in mind that, by symmetry, the spot size at LC array is
`equal to the spot size at microcellimator; that, in its turn, dictates
`requirements on the LC array pixel size.
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`It
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`More detailed design exists and can be provided if needed.
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`Microcollirnator
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`Diffraction grating
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` Mirror
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`Liquid crystal array
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`Figure 3.
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`Figures 4a and 4b below illustrate how the LC array can be used to provide
`switching between pass through and add I drop states. The optical system
`shown in Figures 1 and 3 delivers the light beams from microcollimators to
`the LC array with no or little additional spot expansion. Since there is a
`diffraction grating in the intermediate focal plane, the light at LC plane will be
`dispersed in wavelength.
`In Figures 4a and 4b, the dispersion direction is
`perpendicular to the plane of paper.
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`in “ON” state,
`The LC cell in “OFF” state rotates polarization by 90 degrees.
`polarization is not rotated. It is seen from Figures 4a and 4b that in “OFF"
`state the light paths of two ports are interchanged.
`In “ON” state of LC pixel,
`the light is reflected back into respective port. Since every spectral channel is
`passed through an independently controlled pixel, a full reconfigurability of all
`40 or more channels is obtained. Further, the arrangement of Figure 4b has
`additional advantage of low PMD since the respective positions of two sub
`beams originating from each port does not change upon switching.
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`With respect to LC cell type, the twisted nematic (TN) cell is a preferable
`candidate since it has a very small residual birefringence in “ON” state. Since
`birefringence is small, a very high contrast ratio (>35 (13) can be obtained and
`maintained over the wavelength and temperature range.
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`Another embodiment of the switch geometry is shown in Figure 5.
`the birefringent element is placed before the LC cell.
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`In Figure 5,
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`ADDIDROP
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`Polafizatign djvgrsity
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`Polarization diversity
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`Figure 5.
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`LC cell works as a reflective variable retarder.
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`This invention relates to an add-drop multiplexing circuit that in a first
`preferred embodiment is based on a system that utilizes polarized light. A
`front end described heretofore in Figs. 2a and 2b serves to provide the
`required polarized light. The system shown in Fig. 3 is a preferred
`embodment wherein light is launched and received from two microlenses
`which serve as input {output ports. The system is a 4-f system and a curved
`mirror has at its focal plane the microlenses, a reflective diffraction grating,
`and an array of element in the form of switches. Although the priniciple
`embodiment described relates to an multiplexorfdemultiplexor circuit in the
`form of an addldrop circuit, the invention also lends itself to being used in
`equalization schemes. in such an embodiment an array of detectors (not
`shown) is provided about or near to the switches. The switches described
`heretofore serve to route an incoming signal back to one of the ports from
`which it was launched or alternatively to the other port in dependence upon
`control signals provided to the switch.
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`Although it is preferred to have a single mirror as shown in the embodiment of
`Fig. 3 more than one mirror can be used. Notwithstanding, if a single mirror is
`used the device will have fewer alignment problems and wilt have less loss.
`In fact much of the advantage of this design versus a conventional 4f system
`using separate lenses is afforded due to the fact that critical matching of
`components is obviated. A single mirror is used in both directions to and from
`the ports via the switch. Furthermore, if the mirror is mounted to a fused
`silica base and it itself is made of fused silica the entire structure will be quite
`insensitive to small temperature fluctuations.
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`0006
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`Although a single mirror and a reflective grating is preferred, using a
`transmissive grating with a second mirror is possible.
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`0007
`0007
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`CLAIMS
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`1. A 4-f optical system for multiplexing or demultiplexing an optical signal comprising:
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`reflective means having a focal plane;
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`at least two ports disposed to provide or receive the optical signal or a portion thereof to or
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`from said reflective means;
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`a diffractive element for diffracting the signal or a portion thereof; and
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`an array of elements for receiving at least a portion of the signal after it has been diffracted
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`by said diffractive element, wherein the at least two ports, the diifractive means and the array
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`of elements are disposed substantially in the focal plane of said reflective means.
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`2. A 4-f optical system as defined in claim 1 wherein the array of optical elements are
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`switches for switching a signal incident thereon from a first direction to another
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`independence upon a control signal.
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`3. A 4-f optical system as defined in claim 3, wherein the switches are polarization dependent
`switches.
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`4. A 4-f optical system as defined in claim 2 wherein the difiactive element is a reflective
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`diffractive element and wherein the reflective means is a single curved mirror.
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`5. A 4-f optical system as defined in claim 1 wherein the switch is disposed to receive light
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`from a second focal plane for selectably switching light received from one of the first and
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`second ports to be directed to the other of the first and second ports or back to a same port
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`from which it originated.
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`6. A 4-f optical system as defined in claim 1 wherein the array of elements includes a
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`polarization dependent switch, for reflecting light backwards when the light is of a first
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`polarization and for switching light to another location when the light is of a second
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`orthogonal polarization.
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`0008
`0008
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`7. A 4-f optical system for multiplexing an optical signals comprising:
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`a first poit for transmitting a Gaussian beam of light;
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`a second port for receiving a demultiplexed beam of light;
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`a reflective-focusing element for focusing the beam of light received from at least one of the
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`first and second ports at a first focal plane;
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`a reflective diffractive optical element at the first focal plane; and,
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`a switch disposed to receive light from the reflective-focusing element after having been
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`dispersed in a wavelength dependent manner from the reflective diifractive element for
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`selectably switching light received from the first to be directed to one of the first second port.
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`8. A 4-f optical system as defined in claim 7, wherein a diameter of the Gaussian beam at the
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`first port is substantially the same as a diameter of the beam at the switch, and wherein the
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`diameter of the Gaussian beam incident upon the diffiactive element is substantially less than
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`the diameter incident upon the switch.
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`9. A 4-f optical system as defined in claim 8, wherein the switch is a polarization dependent
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`switch for switching light of a first polarization in a first direction and for switching light
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`having a second orthogonal polarization in a second direction.
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`10. A-4f optical system as defined in any of the preceding claims, wherein the signal
`launched from one of the ports directed to the array of elements is incident upon the
`reflective means at two separate locations, and wherein the reflective means is a single
`curved mirror.
`
`1.
`
`An addidrop comprising:
`-
`two ports with split polarized sub beams each
`—
`focussing elements arranged as a reflective 4f system , see Figure
`1
`
`—
`—
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`-
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`a diffraction grating in the first focal plane
`an array of reflective 2x2 switches in the wavelength dispersed
`second focal plane
`two circulators connected to the above mentioned ports for output
`of reflected signals
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`[1] in which polarization splitting at the front end is realized using a
`microlens, a birefringent element, and a half wave plate, see Figures 2a
`and 2b
`
`[1] in which a single mirror is used as focussing elements, see Figure 3
`[1] in which a diffraction grating is a high efficiency, high dispersion
`diffraction grating
`[1] in which the array of reflective 2x2 switches is realized using a liquid
`crystal array and a pair of polarization beam splitters attached to the
`rear side of the array, see Figure 4a and 4b. The arrangement of Figure
`4b has an additional advantage of low PllllD for both addidrop and pass
`through states.
`[1] in which the array of reflective 2x2 switches is realized using a liquid
`crystal array and a birefringent element attached to the front side of the
`array, see Figure 5
`[1] in which there are two devices in one, one being for C and the other
`for L band. Ecah device has its own inioutladdidrop ports that are
`conveniently shifted with respect to each other as to cover the
`respective spectral band. The common optical elements are mirror,
`diffraction grating, and LC array having at least two rows of pixels
`[5] in which the liquid crystal array is twisted nematic liquid crystal
`array
`[8] in which the “ON” state of the liquid crystal is used in “addIdrop"
`mode, and “OFF” state of liquid crystal is used in "inlout" mode
`[8] in which the inter pixel areas of liquid crystal array are covered by a
`black grid
`[5] or [6] in which the liquid crystal array "is pi cell array
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`:"*S*’
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`10.
`
`11.
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`NOTE: claims for channel equalizer are same except: 1) there is one port, not
`two, and one circulator is connected to that port, and 2) there is no need in
`claim 8. Alternatively, channel equalizer can be realized on the basis of pass-
`through state of the above described addldrop module with no circulators.
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`D. How does your solution differ from known solutions to the same
`problem?
`
`
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`Other COADM I channel equalizer devices are based either on waveguide
`or free space optics. The free space optics approaches include diffraction
`
`grating and MEMS (Lucent), or diffraction grating and LC (). The
`advantages of the present approach over early designs are much smaller
`amount of optical elements, ease of alignment, thermal stability, and high
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`channelcount
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