Patent Application: US-201514806273-A

Abstract:
the present invention generally relates to the field of fiber optics , and more particularly , to apparatuses , systems , and methods directed towards improving effective modal bandwidth within a fiber optic communication environment . in an embodiment , a multimode optical fiber in accordance with the present invention comprises a core and cladding material system where the refractive indices of the core and cladding are selected to modify the shape of the profile dispersion parameter , y , as a function of wavelength in such a way that the alpha parameter , which defines the refractive index profile , produces negative relative group delays over a broad range of wavelengths . the new shape of the profile dispersion parameter departs from traditional fibers where the profile dispersion parameter monotonically decreases around the selected wavelength that maximizes the effective modal bandwidth .

Description:
a cross - sectional view of an exemplary multimode optical fiber ( mmf ) in accordance with the present invention is shown in fig7 . this fiber includes a core region having a center and a radius a , and a cladding region surrounding the core . both the core and the cladding are comprised of optically conductive materials such that the refractive index at the center of the core ( n 1 ) is greater than the refractive index of the cladding ( n 2 ), and the distribution of the refractive indices throughout the optical fiber is generally referred to as the fiber &# 39 ; s refractive index profile . in an embodiment , the mmf of the present invention includes a dispersion parameter profile having a concave or a convex shape with minimum / maximum value at or near to the wavelength which has the peak emb or λ p . such an mmf can have a refractive index profile that includes a generally parabolic shape as shown in fig8 . this refractive index profile can be attained by including , in the core , one or more dopants in respective concentrations , and it can be defined by equation ( 1 ) where the α - value is selected pursuant the fiber &# 39 ; s α opt profile . an α - value selected pursuant to the present invention may be referred to as α d through this specification . instances of exemplary characteristics of an mmf provided in accordance with some embodiments of the present invention are shown in fig9 a - 10b . fig9 a and 9b illustrate exemplary characteristics of an mmf that uses dopants such as , for example , boron ( b ) to decrease the refractive index of the core and / or cladding and fluorine ( f ) to decrease the refractive index of the cladding . certain combination of concentrations of these dopants in the core and cladding can produce concave like functions for the alpha optimum profile as shown by the solid line in fig9 a . by designing the fiber to have a refractive index profile with a power exponent of α d & lt ; α opt , it is possible to maintain negative relative group delays over a broad spectral region while maintaining a high modal bandwidth as illustrated in fig9 b . fig1 a and 10b illustrate exemplary characteristics of another mmf that is doped with , for example , phosphorous ( p ) to increase the refractive index of the cladding . small amounts of phosphorous , or other dopants , in the core in combination with dopant ( s ) such as fluorine in the cladding can produce convex like functions for the alpha optimum profile as shown in fig1 a . by designing the fiber to have a refractive index profile with a power exponent of α d & lt ; α opt , it is possible to maintain negative relative group delays in a broad spectral region while maintaining a high modal bandwidth as illustrate in fig1 b . fig1 illustrates a flow chart outlining the process for determining α d and developing an mmf profile according to an embodiment of the present invention . this embodiment can be used in a design and / or manufacturing process for an mmf with one or more dopants , where the concentration profile of each dopant is based on the same α d value . it is to be understood that the same α d value does not require the same dopant concentration value . in step 100 , the initial parameters are selected for the mmf . these parameters can include , but are not limited to , numerical aperture , index contrast δ , core and cladding dimensions , peak emb , maximum coupling loss , chromatic dispersion parameters ( e . g ., chromatic dispersion coefficient d , zero dispersion wavelength λ z ), manufacturing tolerances , and / or desired spectral windows for a minimum value of the effective modal bandwidth emb 0 . once the initial parameters are provided , one or more dopants together with their respective concentrations are selected in step 105 . the selection in step 105 may be based on some pre - existing criteria , such as , for example , a library of dopants compatible for the fabrication of sio 2 fiber core and cladding . a very brief example of such a library is provided in table iii . the range of combinations among these and other dopants is very extensive , and can be computed numerically from the sellmeier coefficients . alternatively , the selection in step 105 may be random . upon the selection of the dopant ( s ) and respective concentration ( s ), an initial verification step 110 is performed where the basic characteristics such as , but not limited to , numerical aperture , δ , d , and λ z are computed . the initial verification can allow for a relatively early determination of whether the selected material ( s ) will result in an mmf that falls within some desired guidelines . this can be especially useful in determining whether the mmf will satisfy certain standards characteristics such as those defined by the om3 and om4 standards . this determination can be made in step 115 where if it is determined that the mmf will not satisfy some predetermined criteria , a new selection of a dopant ( s ) and concentration ( s ) must be made in step 105 . while this verification and comparison process embodied in the two steps 110 and 115 is performed immediately after the dopant selection step of 105 , this is not a requirement . instead it may be performed during any time following step 105 . however , for practical purposes , early determination of a non - compatible selection in step 105 may provide time , computing , and / or cost savings . if at step 115 it is determined that the selected material ( s ) and respective concentration ( s ) are satisfactory , in step 120 the profile of the dispersion parameter y ( λ ) and the optimum α - value α opt ( δ ) are calculated using equations ( 3 ) and ( 4 ), and in step 125 the concavity of the dispersion parameter y ( λ ) around the peak emb λ p is evaluated . note that the term “ concavity ” as used herein refers to both a concave and a convex shape . if the profile of the dispersion parameter is not concave or convex around the peak emb , steps 105 - 125 are repeated with a new dopant ( s ) and / or concentration ( s ). if , on the other hand , the profile of the dispersion parameter does exhibit desired concavity around the peak emb value , the method proceeds to step 130 where an α d value is chosen based on the optimum α - value at peak emb α opt ( λ p ) and the manufacturing tolerances . in an embodiment , α d follows the following equation : α d = α opt ( λ p )+ b · abs ( t α )/ 2 ( 6 ) where t α is a manufacturing tolerance for the α - parameter which depends on manufacturer ( e . g ., ± 0 . 01 ) and parameter b is utilized to increase the broadband windows for high emb , relax the conditions for relative negative mode group delay tilt , to include the small dependence of alpha with wavelength , or to adjust for the different process used by fiber manufacturers . in order to produce an mmf which exhibits the l - mmf condition , the sign of b must be negative . in some cases , for example multicomponent fiber , it may not be possible to find relatively simple analytical expressions such as equations ( 6 ). in those cases , use of a full numerical model to find the optimum α d value for each component may be required . after determining the α d value , the relative mode group delays t g ( λ ) are derived in step 135 by using equation ( 2 ) and substituting α d in place of α ; the differential mode delay ( dmd ) profiles are computed in step 140 from the earlier - derived mode group delays t g ( λ ); and the effective modal bandwidth emb ( λ ) is computed in step 145 from the earlier computed dmd profiles . thereafter , a final verification of performance compliance is made in step 150 where the values obtained in steps 135 - 145 are evaluated . in one example , the evaluation in step 150 can be limited to the evaluation of the emb ( λ ) to verify that it is in compliance with the minimum required value emb 0 for the spectral window originally defined in step 100 . in other examples , the values derived in steps 135 and 140 can also be evaluated . for instance , the maximum values for the relative mode group delays are checked to fall within some predetermined range group ( e . g ., a range specified by the om3 or om4 standard ). furthermore , the sign ( e . g ., positive versus negative ) of the relative mode group delay values can also be evaluated to confirm the presence of an l - mmf condition for at least some of the operating wavelengths . in another instance , the dmd plots can be evaluated for visual confirmation of fiber &# 39 ; s transmission characteristics ( e . g ., the presence of a left shift of the majority of peak pulse at increasing radial offsets at various wavelengths ). moreover , the plots can be used to measure the dmd value at various operating wavelengths which in it of itself can be a prerequisite to meeting some preexisting standard . note that the recitation of verification processes is not meant to be limiting and / or exhaustive . if the verification process returns a favorable result , the mmf parameters are saved in step 155 for later use such as , for example , the manufacture of the mmf . if , on the other hand , the verification step 150 fails , steps 105 - 145 are repeated for new dopant ( s ) and / or concentration ( s ). as an example , the method described in fig1 may be used to produce a broadband mmf that uses b 2 o 3 and small amounts of geo 2 . the addition of b 2 o 3 dopant to the fiber &# 39 ; s core has the effect of reducing the refractive index and therefore reducing the λ , increasing phase velocity and group velocity relative to pure si , and varying the shape of the dispersion parameter y ( λ ) and α opt . in order to maintain δ ≈ 1 % at an operating wavelength of about 850 nm to reduce coupling losses when mated with legacy fibers , modeling results indicate that fluorine doping in the cladding and / or combined doping of geo 2 — b 2 o 3 in the core may be desired . the effect of b 2 o 3 on α opt is shown in fig1 where the wavelength - dependent α opt profiles are modeled for three dopant concentrations . the ( a ) α opt profile is based on a concentration of 13 . 3 mol % of b 2 o 3 ; the ( b ) α opt profile is based on a concentration of 4 . 1 mol % of geo 2 and 7 . 7 mol % of b 2 o 3 ; and the ( c ) α opt profile is based on a concentration of 0 . 1 mol % of geo 2 and 5 . 5 mol % of b 2 o 3 . to produce a broadband mmf with high modal bandwidth and negative group delays the required concentration of dopants should be precisely controlled . this may allow the negative group delay condition to be maintained for at least 200 nm for emb & gt ; 4 . 7 ghz · km , and over 300 nm for om3 fibers . in an embodiment , the fibers that satisfy the requirements for high emb and negative group delays can have a core with geo 2 dopant concentration between 3 to 6 mol % and b 2 o 3 dopant concentration between 4 and 9 mol %. for such fiber the cladding includes a less than 4 wt % dopant concentration of b 2 o 3 and / or f . for example of the α opt value of an mmf co - doped with 4 . 1 mol % ge and 7 . 7 mol % b 2 o 3 in the core , and 3 wt % f in the cladding is shown in fig1 as the parabolically shaped solid line . the ideal designed alpha ( α d ) for the profile shape is 2 . 1147 and is equivalent to the α value at the vertex of the parabolic plot . for this example , it is assumed that tolerances of ± 0 . 005 in the α d value ( with respect to the ideal α d value ) are permissible in order to remain within the desired emb limits . given the potential α d values shown in fig1 , it is possible to derive the maximum values for the relative mode group delays using equation ( 2 ). these results are provided in fig1 where the maximum relative group delays are plotted as a function of wavelength for the three separate target α d values ( α d = 2 . 1197 for triangle markers ; α d = 2 . 1147 for dot markers ; and α d = 2 . 1097 for square markers ). the dotted horizontal lines represent the range limits of maximum delays for emb & gt ; 4 . 7 ghz · km . based on these results it is possible to tell that all three instances remain within the maximum delay limits over a relatively broad range of wavelengths . furthermore , it is possible to tell that for mmfs having α d = 2 . 1147 or 2 . 1097 , the maximum relative mode group delays within the region of interest have a negative value . this provides an indication of an l - mmf condition occurring throughout the range of interest for the respective fibers . on the other hand , for an mmf having α d = 2 . 1197 , at least some maximum relative group delays will have a positive value . while this may not be desirable in some cases , in other cases the positive values may form a part of an overall analysis of the performance resulting from a fiber with a certain α d value . in other words the existence of positive α d values does not necessarily take the resulting fiber or the process by which that fiber was made outside the scope of the present invention . this , as further described later in the specification , is because at higher wavelengths , mcdc may not be of such high concern . as such , a fiber which meets the l - mmf condition over only a part of its operational wavelength window may still be desirable . the results provided in fig1 highlight the potential need for selecting an appropriate α d value so as to remain within appropriate operational limits considering potential manufacturing tolerances . given the maximum relative group delays , it is then possible to determine a series of dmd plots for a respective fiber . fig1 - 17 show the dmd plots computed for the maximum relative group delays of the fiber with α d = 2 . 1147 . the dmd pulses in these plots were computed using tia &# 39 ; s procedure described in the fotp - 220 standard , which is incorporated herein by reference in its entirety . these plots simulate the measured dmd pulses at each wavelength as indicated at the top of each figure . having a dmd plot for a given wavelength , it is then possible to compute the emb for that respective wavelength . for the examples of fig1 - 17 the respective emb values are provided at the top of each dmd plot , and a summary of the emb values as a function of wavelength is provided in fig1 . as another example , the method described in fig1 may also be used to produce a broadband mmf that uses p 2 o 5 as the core dopant and f as the cladding dopant . the addition of p 2 o 5 dopant to the fiber &# 39 ; s core has the effect of increasing the refractive index and therefore increasing the δ , i . e ., the difference in core - cladding refractive index , reducing phase velocity and group velocity relative to pure si , and varying the shape of the dispersion parameter y ( λ ) and α opt . in order to maintain δ ≈ 1 % at an operating wavelength of about 850 nm to reduce coupling losses when mated with legacy fibers , modeling results indicate that fluorine doping in the cladding and / or combined doping of geo 2 — p 2 o 5 in the core may be preferred . this may allow the negative group delay condition to be maintained for at least 200 nm for emb & gt ; 4 . 7 ghz · km , and over 300 nm for om3 fibers . in an embodiment , the fibers that satisfy the requirements for high emb and negative group delays can have a core with p 2 o 5 dopant concentration between 6 to 10 mol %. fig1 illustrates an α opt profile for a fiber having a 9 . 1 mol % concentration of p 2 o 5 and 90 . 9 mol % concentration of sio 2 . based on this profile , an α d is selected to be 2 . 01205 ( illustrated in fig1 via a dashed line ). the selected α d provides a basis for deriving the maximum values for the relative mode group delays using equation ( 2 ). the maximum relative group delays as a function of wavelength for the target α d are shown in fig2 , with the horizontal dotted lines representing represent the range limits of maximum delays for emb & gt ; 4 . 7 ghz · km . from the derived group delays , it is then possible to determine a series of dmd plots for a respective fiber . fig2 - 23 show the dmd plots computed for the maximum relative group delays shown in fig2 . the dmd pulses in these plots were computed using tia &# 39 ; s procedure described in the fotp - 220 standard . these plots simulate the measured dmd pulses at each wavelength as indicated at the top of each figure . having a dmd plot for a given wavelength , it is then possible to compute the emb for that respective wavelength . for the examples of fig2 - 23 the respective emb values are provided at the top of each dmd plot , and a summary of the emb values as a function of wavelength is provided in fig2 . another method for designing an mmf according to an embodiment of the present invention is outlined in the flow chart of fig2 . this embodiment can be especially applicable in design and / or manufacturing processes of mmfs with two or more dopants where the α - value of at least one dopant concentration profile is different from the α - value of at least one other dopant concentration profile . an exemplary representation of a fiber having dopant concentration profiles differing with respect to their power exponent a is illustrated in fig2 . however , this method can still be used to design fibers using only a single primary dopant also . in step 200 , the initial parameters are selected for the mmf . these parameters can include , but are not limited to , numerical aperture , index contrast δ , core and cladding dimensions , peak emb , maximum coupling loss , chromatic dispersion parameters ( e . g ., chromatic dispersion coefficient d , zero dispersion wavelength λ z ), manufacturing tolerances , and / or desired spectral windows for a minimum value of the effective modal bandwidth emb 0 . once the initial parameters are provided , the dopants together with respective concentrations are selected in step 205 . the selection in step 205 may be based on some pre - existing criteria , such as , for example , a library of dopants compatible for the fabrication of sio 2 fiber core and cladding . alternatively , the selection in step 205 may be random . upon the selection of the dopants and respective concentrations , an initial verification step 210 is performed where the basic characteristics such as , but not limited to , numerical aperture and λ are computed for the selected materials and concentrations . the initial verification can allow for a relatively early determination of whether the selected material will result in an mmf that falls within some desired guidelines . this can be especially useful in determining whether the mmf will satisfy certain standards characteristics such as those defined by the om3 and om4 standards . this determination can be made in step 215 where if it is determined that the mmf will not satisfy some predetermined criteria , a new selection of a dopants and concentration profiles must be made in step 205 . while this verification and comparison process embodied by the two steps 210 and 215 is performed immediately after the dopants selection step of 205 , this is not a requirement . instead it may be performed during any time following step 205 . however , for practical purposes , early determination of a non - compatible selection in step 205 may provide time , computing , and / or cost savings . if at step 215 it is determined that the selected materials and concentrations are satisfactory , in step 220 the spectral characteristics of the fiber with the selected materials are modeled using the sellmeier coefficients given by : n 2 ⁡ ( λ ) = 1 + ∑ i = 1 3 ⁢ ⁢ a i ⁢ λ 2 λ 2 - b i 2 ( 7 ) because the concentrations of the dopants vary along the radial position of the fiber &# 39 ; s core , modeling of the spectral characteristics is achieved by taking this radial variance into consideration . consequently , equation ( 7 ) becomes a function of λ and r , and also takes into consideration that more than one dopant may be used . after determining the spectral characteristics for the mmf , the relative mode group delays t g ( λ ) are derived in step 225 by using numerical models , such as for example wentzel - kramer - brillouin or finite time domain difference ; the differential mode delay ( dmd ) profiles are computed in step 230 from the earlier - derived mode group delays t g ( λ ); and the effective modal bandwidth emb ( λ ) is computed in step 235 from the earlier computed dmd profiles . thereafter , a final verification of performance compliance is made in step 240 where the values obtained in steps 225 , 230 and / or 235 are evaluated . in one example , the evaluation in step 240 can be limited to the evaluation of the emb ( λ ) to verify that it is in compliance with the minimum required value emb 0 for the spectral window originally defined in step 200 . in other examples , the values derived in steps 230 can also be evaluated . for instance , the dmd plots can be evaluated for visual confirmation of fiber &# 39 ; s transmission characteristics ( e . g ., the presence of a left shift of the majority of peak pulse at increasing radial offsets at various wavelengths ). moreover , the plots can be used to measure the dmd value at various operating wavelengths which in it of itself can be a prerequisite to meeting some preexisting standard . note that the recitation of verification processes is not meant to be limiting and / or exhaustive . if the verification process returns a favorable result , the mmf parameters are saved in step 245 for later use such as , for example , the manufacture of the mmf . if , on the other hand , the verification step 240 fails , steps 205 - 240 are repeated for a new dopant and / or concentration . as an example , the method described in fig2 may be used to produce a broadband mmf that uses ge and f as its dopants . fig2 illustrates exemplary concentration profiles for the ge and f dopants , with ge mol % concentration being represented via the solid line and f mol % concentration being represented via the dotted line . both of these concentrations can be represented with the following equations as a function of radial offset r from the center of the core : for ⁢ ⁢ ge ⁢ : ⁢ ⁢ x ge ⁡ ( r ) = x ge max ⁡ ( 1 - ( r a ) α d ge ) ( 8 ) for ⁢ ⁢ f ⁢ : ⁢ ⁢ x f ⁡ ( r ) = x f max ⁡ ( ( r a ) α d f ) ( 9 ) where α d ge and α d f are parameters which determine the shape of the respective dopant concentration profile and x ge max and x f max are parameters that define the maximum concentrations of respective dopants at some radial offset position . the values for these parameters can be selected based on some pre - existing criteria , such as , for example , generally known dopant concentrations and concentration profile shapes , or at random . in the example of fig2 , the α d values are selected to be α d ge = 1 . 9963 and α d f = 2 . 0093 . taking equations ( 8 ) and ( 9 ) into consideration it is then possible to generate the spectral characteristics of the fiber as a function of radial offset r and wavelength λ . expanding on equation ( 7 ), the resultant refractive index profile is computed using : n 2 ⁡ ( r , λ ) = 1 + ∑ i = 1 3 ⁢ ⁢ ( a i + x ge ⁡ ( r ) ⁢ da i ge + x f ⁡ ( r ) ⁢ da i f ) ⁢ λ 2 λ 2 - ( b i + x ge ⁡ ( r ) ⁢ db i ge + x f ⁡ ( r ) ⁢ db i f ) ( 10 ) where x ge and x f are the mole fractions , and da i the db i the material specific variation terms . given the result - set of equation ( 10 ), it is possible to derive the maximum values for the relative mode group delays , and then using those values to determine a series of dmd plots for the respective fiber as shown in fig2 - 29 . the dmd pulses in these plots were computed using tia &# 39 ; s procedure described in the fotp - 220 standard . these plots simulate the measured dmd pulses at each wavelength as indicated at the top of each figure ( 825 nm to 1175 nm ). having a dmd plot for a given wavelength , it is then possible to compute the emb for that respective wavelength . for the examples of fig2 - 29 the respective emb values are provided at the top of each dmd plot , and a summary of the emb values as a function of wavelength is provided in fig3 . in these figures it is observed that the negative dmd tilt ( e . g ., the l - mmf ) and the emb ≧ 4 . 7 ghz · km conditions can be maintained from 850 nm to 950 nm . these results indicate that using the mmf of the currently described embodiment can be especially advantageous in the shorter wavelengths region of about 850 nm to about 950 nm . at longer wavelengths ( e . g ., & gt ; 975 nm ) the attenuation and chromatic dispersion can be significantly lower accounting for a least 2 db reduction in transmission penalties compared with the penalties at 850 nm . therefore , at those longer wavelengths mcdc may not be required . by modifying the exponents in the dopant concentration functions shown in equations ( 8 ) and ( 9 ), the peak emb wavelength or λ p can be shifted either to the left or to the right . for example by using α d ge = 1 . 9963 and α d f = 2 . 0163 , λ p becomes ˜ 900 nm . concepts disclosed herein can be applied to designing optical fibers for use with laser transceivers emitting multiple transverse modes ( e . g ., vcsel transceivers ). this fiber can be used in channels requiring the transmission and receiving of multiple signals over a broad range of wavelengths . concepts embodied by the present invention may be applicable in unidirectional and / or bidirectional cwdm ( coarse wavelength - division multiplexing ). it has been recognized that performance of cwdm systems depend not only on modal bandwidth , but also on the total bandwidth resulting from the modal and chromatic dispersion interaction . in order to equalize the reach or performance of the transmitter wavelength in a cwdm channel as illustrated in fig3 , mcdc ( modal - chromatic dispersion compensation ) should preferably be applied to the shorter wavelength of the utilized spectra in such a way that the penalties due to dispersion and attenuation are balanced . for example , fig3 shows the case where n = 8 wavelengths separated by δs = 40 nm . this configuration may allow 100 gbps or 128 gbps bidirectional transmission per fiber by multiplexing different wavelength vcsels with serial rates of 25 gbps or 28 gbps . it may also enable 200 gbps bidirectional transmission per fiber using vcsel transceivers with serial rates of 50 gbps . transceivers operating with the first 4 shorter wavelengths ( i . e ., 850 nm to 970 nm ) are subject of significantly more attenuation ( as shown in fig3 ) and chromatic dispersion ( as shown in fig3 ) than transmitters operating with the longer wavelengths . therefore , the impact of mcdi ( modal - chromatic dispersion interaction ) described herein can be more significant for the shorter wavelengths than the longer wavelengths . additionally , design techniques described herein may be combined with any known fiber manufacturing techniques to the extent necessary . for example , those of ordinary skill will be familiar with the general concept of manufacturing optical fibers where in a first stage a preform is produced and in a second stage a fiber is drawn from that preform . those familiar with the relevant art will also be familiar with the techniques used to introduce / add one or more dopants during the manufacturing stages . this step typically occurs during the preform formation stage where a controlled introduction of dopants results in a preform having some desired dopant concentration profile . in some embodiments , it is at this stage that the selected dopants can be controlled in accordance with the design parameters of the present invention . furthermore , in some embodiments , the reference to a “ broad spectral region ” may be understood to refer to a region that is at least 50 nm , at least 100 nm , at least 150 nm , at least 200 nm , at least 250 nm , and / or at least 300 nm . however , this should not be interpreted as limiting the meaning of the term “ broad spectral region ,” as in some embodiments this term may also have a customary meaning as would be understood by those of ordinary skill in the relevant art . note that while this invention has been described in terms of several embodiments , these embodiments are non - limiting ( regardless of whether they have been labeled as exemplary or not ), and there are alterations , permutations , and equivalents , which fall within the scope of this invention . additionally , the described embodiments should not be interpreted as mutually exclusive , and should instead be understood as potentially combinable if such combinations are permissive . it should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention . for example , while extensive references have been made to vcsel systems throughout the specification , the present invention may be implemented with other , non - vcsel optical sources . it is therefore intended that claims that may follow be interpreted as including all such alterations , permutations , and equivalents as fall within the true spirit and scope of the present invention . furthermore , the subject matter described herein , such as for example the methods for designing and / or manufacturing an mmf in accordance with the present invention , can be implemented at least partially in software in combination with hardware and / or firmware . for example , the subject matter described herein can be implemented in software executed by a processor . in one exemplary implementation , the subject matter described herein can be implemented using a non - transitory computer readable medium having stored thereon computer executable instructions that when executed by the processor of a computer control the computer to perform steps of a method or process . exemplary computer readable media suitable for implementing the subject matter described herein include non - transitory computer - readable media , such as disk memory devices , chip memory devices , programmable logic devices , and application specific integrated circuits . in addition , a computer readable medium that implements the subject matter described herein may be located on a single device or computing platform or may be distributed across multiple devices or computing platforms . devices embodying the subject matter described herein may be manufactured by any means , such as by semiconductor fabrication or discreet component assembly although other types of manufacturer are also acceptable , and can be manufactured of any material , e . g ., cmos . jack jewell , “ extended wavelength receivers for forward compatibility ,” presented in t11 pi6 , june 2013 ftp :// ftp . t10 . org / t11 / document . 13 / 13 - 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