CA2221859A1

CA2221859A1 - Optical filter for spectroscopic measurement and method of producing the optical filter

Info

Publication number: CA2221859A1
Application number: CA002221859A
Authority: CA
Inventors: James M. Lepper, Jr.; Mohamed Kheir Diab
Original assignee: Masimo Corporation; James M. Lepper, Jr.; Mohamed Kheir Diab
Current assignee: Masimo Corp
Priority date: 1995-06-07
Filing date: 1996-06-04
Publication date: 1996-12-19
Also published as: CN1192808A; DE69628005T2; EP0830625A1; EP0830625B1; AU706049B2; US6278522B1; AU6036796A; ATE239924T1; WO1996041218A1; JPH11507143A; US5940182A; DE69628005D1; US5760910A

Abstract

An optical filter used in applications involving spectroscopic measurements is fabricated by depositing layers of optical coatings onto a substrate. The layers are deposited so as to have a substantially constant thickness in a first direction along the surface of the substrate, and a gradually increasing thickness along a direction perpendicular to the first direction. The structure of the optical filter allows for large scale production of the filter so that costs in producing the filter are greatly reduced. The filter may be used in a variety of applications including, but not limited to chemical analysis, blood glucose monitoring, and the like.

Description

-CA 022218~9 1997-11-18 WO 96/41218 PCTAU~ vG~7 OPTICAL FILTER FOR SF.."hOSCOrlC MEASUREMENT
AND METHOD OF PRODUCING THE OPTICAL FILTER
kl . ' of the Invention Field of the Invention The present invention relates to optical filters which are used in 3,,' : where - _ are used to dL ~ the p ., li~s of h ~~ such as N ~ ' and other ':
D~a~.H: of the Related Art Optical filters are well known in .,' IS involving ~, t,,s ~, measurement. Sr t~- . is used to d: the . ., li_~ and chemical c , of various ~: in a sample basedupon the opticaM.hala.. t.niali.,a of the sample. In a typical t,, 1, t, light lin the visible and - .- ' ' range) is used to illuminate the sample over multiple ~ spectra. More than one optical r, (~ a~ .lh) is used to more precisely ': . ~ the optical chàla..l~.ialil.s of the sample and also to subtract out t~, In some 3~, ~' ' , the light reflected from the sample is detected, while in other 3~ r~' light 1,. ' through the sample is detected to ' the optical chala~.t~,.iali~.a of the sample. In addition, a - ' of the l,_ ~ through the sample and the ,~,' - from the filter may be employed.
The detected light is usually, " ' to provide an indication of the ''t,l, ~ response" of the sample at each of the r,l, y spectra. As is well known in the art, each ' has definable optical, " li_., :' ' by the r,. at which the ' reflects and absorbs light. Thus, the optical chala~.lt~.ialiL.s of a given: L e may be, lir;od (e.g., plotted as intensity of reflected or 1, ' light versus r,l . r) 20 to provide an indication of the optical cha.aLteHali~.a of that - ' - :r Since different ' typically have distinct optical r,ha-_: ialil.a, 1 I,.. _ata of the optical, ~r li~a of a sample ~ - " several - ' - can serve as the basis for ": ' " among or making other I - I relating to the several - within a sample. Precise of the reflected or 1, t~ ' light can be used to d the precise c .: of the various c ' -Y within a sample.
Some present . t~- - )r' I I systems use multiple light emitting diodes (LEDs) or laser sources to provide light at the desired ~ u.. ~,Ih... However, very expensive, high precision ~ u.. ' ~Ih light sources must be employed in order to '~: ~ such a system with the y ~ u~ ~,Ih accuracy for each of the sources.
One ' llali._ method of ~, light at multiple H" involves rotating an optical filter between the sample to be measured and a 1,1. " ' light source. Current optical ~ , devices, as identified by the 30 inventor for use in the present i ~. . often require expensive ~ : ' filters which are used to generate a pattern of optical signals to be ll ' One such filter, ~ '~ known as a dichroic filter, L , iaeS a rotating optically coated disk which includes regions of varying optical i' ' - As the wheel spins, light from the bl Jr ' ' light source passes through different portions of the wheel so that light of various r,. are passed by the filter to illuminate the sample. That is, the regions on the dichroic filter are formed in a pattern so that 35 rotation of the optical disk results in the ll of selected optical bands. In many previous P .' involving precise Y, e ~,- , I :, optical filters have been designed with very high ' _ CA 022218~9 1997-11-18 WO96/41218 PCTrUS96/08627

-2-r. i , t, the methods for I - ' such filters have often precluded the ~ y of ' the filters by mass ".. ' : Thus, even optical filters of this kind may be ~ to fabricate.
Summarv of the Invention The present invention provides a rotating dichroic filter for ~, . , I I wherein the cost of the filter is a,, . '~ 100 times less than r ~ " ' rotating dichroic filters. This is a~l ' d by first relaxing the, ' of the filter and ~ - _ for the n' - of filter ' through more intensive signal I Jr:~ _ steps. In addition, the filter is ~ d in a manner which allows for easier , .~ The filter r : l ~ed in ~ ~~ with the present invention allows from 10 to 100 times as much light to pass while I the r y precision throuyh signal r ~
One aspect of the present invention involves a method of ~a _ an optical filter. The method involves a number of steps. An optical substrate is provided having a top surface and a bottom surface, and layers of optical coating are deposited on the top surface such that the layers vary in thickness across the top of the substrate in a first direction. The thickness of the layers is ' ~ constant in a second direction - ' : 11~
r I " ' to the first direction. In one ' - " t, the method further involves creating a mounting hole in the center of the substrate. In addition, an opaque strip along at least a portion of the substrate is deposited in one bc"
Another aspect of the present invention involves an optical filter. The optical filter has a substrate having a top surface and a bottom surface. The filter also has a plurality of optical coatings deposited on the top surface of the substrate such that the coatings vary in thickness in a first direction across the top surface. The coatings are - ' : 11~ constant in thickness across the top surface in a second direction - ' 'I~ I I " ' to the first direction.
Another aspect of the present invention r , i~ an optical filter having a generally a generally circular substrate. Layers of optical coatings deposited on the substrate provide a - 19 _ I~.l : wherein h~ one-half of light incident upon the coatings passes throuah the coatinas over the entire surface of the substrate.
Yet another aspect of the present invention involves an optical filter. A substrate having a top surface and a bottom surface has a plurality of layers of optical coatings varying in thickness in a first direction across the substrate. The layers provide optical ll_ ~.halablL.i;~ for the optical filter to provide an optical filter which transmits more than one . .... ....................' Jtll through the filter at all locations across the surface of the filter.
Brief D~""i,.; of the Drawinas Figure 1 depicts an: . ' y dichroic filter as - t....,l~d by r ~liullal methods.Figure 2 depicts ~ ' i 'I~ the general method used in accu,.' with the present invention to F~ - e a lot~t ' optical filter.
Figure 3 depicts the dichroic filter of the present invention depicted in Figure 2 in a blood glucose, 35 _, , ':

CA 022218~9 1997-11-18

-3 Fi~qure 4A - 4C depict in graph form the optical t- ~ ~.hala~.tL.i;~tiL.~ for an , ' y dichroic filter over different degrees of rotation in a , with the present invention.
Figure 4D i" dte~ a matrix used to specify the optical ~.hala~.lcsl;~ .s of an - . ' y dichroic filter in r-- .' with the present invention.
Figure 5 depicts in Ograph form the optical ll . cha, à.,t~ liL;, of an y r , _ " ' dichroic ~ filter over different deOqrees of rotation in ae ~' with the present invention.
Figure 6 depicts a ~qeneral flow chart of the signal, ~ ~ L, , which are used to compensate for the lower optical t ' . of the filter of the present invention.
Fi~qure 7 i" ~te~ a flow chart which sets forth the Oqeneral steps of obtainin~q the optical Lha,a,.t~ ti~.
10 matrix of Figure 4D.
Figure 8 I, t~...t~ a 1L :' ' block diaOqram of the general steps of using the filter of the present invention in - ; with signal I ~ g to a~c d , I
Detailed DC~L~. of the Invention Figurè 1 shows an exemplary dichroic filter ldL~ alcid accordinOq to: ._ ' methods. Previous methods 15 employed to fabricate such optical filters typically involved laying out a circular substrate and then ;.~IL~
;..~,l - _ the coating ' ' on the surface of the circular substrate as the substrate is rotated with unUorm speed.
Such a filter 150 is depicted in Figure 1 as havinOq coating layers 152, 154, 156, etc., of s _ ~ ~, i' ' e to form a spiral r Sil, ~ as the filter 150 is rotated. 0f course, it should be ~ ' ~d that the 20 coating :' ' depicted in Figure 1 are; ~O alcsd for ease of " ~, This method of optical coatinOq is carried around ' ~ the entire ~ l 'eSIl of the circular substrate so that as the coated substrate revolves, the thickness of the optical coating grows i' ~ _' the entire r~ and then suddenly drops back from the thickest coating to the thinnest coating at the end of one ,~.. ' It has been found, however, that such methods of optical coating require high precision and are extremely 25 costly. Fi ' c" '~ these filters is typically carried out - b, . . since ".. ' : methods do not allow for laying out several disks on a single sheet for mass, . ~ purposes.
In addition, cr ., " ' filters of the type depicted in Figure 1 Onenerally have many layers (e.Oq., 100 or more layers is common). The number of layers in ! .. " ' filters are provided to provide very precise pass bands (for a bandpass filter). Figure 5 depicts an ' y l,_ LhalaLIclio~ for a ~ .. ' rotational dichroic filter versus degrees of rotation for a selected .. ' Jth. As :" dll,d in Figure 5, the pass band of the filter is very precise for the selected ~ ~..' _ h, generally without ' ! ' ee and also provides 11~ zero l._ outside the pass band. A very high number of layers is required to obtain a filter with this near ideal o precision. It should be . ' -d, that this very narrow passband is in different rotational positions for different ~, ~,.c' _lhs. In other words, a r . ' dichroic filter can be l~hdla~lcliLcid as a I - ' . : which passes 35 a different ~ .... ' oth at different rotational positions.

CA 022218~9 1997-11-18 W O 96/41218 PCT~US96/08627

-4-Creating each layer is r ~ _ due to the . rotational variation from thin to thicker. Thus, when many layers are created (e.g., 100 or more for good ".. ~ ~, such . .. - ' filters are very costly.
In a~ u with the present invention, a dichroic filter is disclosed which differs sig, t; 1~ from r .. ' dichroic filters. Figure 2 depicts a filter 120 alon~ with the steps followed in the method of producing

5 a filter in a ' e with the teachings of the present invention.
The dichroic filter according to the present invention is made in a novel manner in which the multiple optical coatinys are created on a substrate to form a ~ _ 15 ' substrate. For a rotational filter, the substrate is then cut to forrn a IJtL: ' disk filter.
In addition, according to one aspect of the present invention, the dichroic filter has fewer layers than 10 r . ~' filters. This provides for less precision in the ll_ Lhala~ ti~. of the filter. Figure 4A - 4C
depict the optical 1- ~ chd~a~.lu.i~liLs for selected ~ h~ of an ~ ' y rotational filter made in .' with the present invention having only 17 optical coating layers. As " - all.d in Figures 4A - 4C, the ,hala~ , is not as precise as the ll ~ ~,hala~.lL.i~ti~. of the filter ..,,,.~ ' in Figure 5.
As depicted in Figures 4A4C, the dichroic filter of the present invention has a several pe~rt ' for each 15 ~ .... ' ~ll. depicted. In addition, outside the pass-bands, the l-_ does not fall ' '~ to zero, as with the - .. ' precision filters. The reduced precision in the p ' ' is due to the reduced number of layers in the filter. It should be _ ' .: -d, that the reduced precision explained above is not limited to .ui ' dichroic filters, but could also be _ 1~ with dichroic filters that are vibrated (e.g., through ~ " or the like), and for any other optical filter which; .~..; 'l~ involves high precision in the pass-bands. The d....~LaSL
20 precision of the filter of the present invention is _ ' ' with signal . 9 as further explained below to obtain the required precision. In this manner, the cost of the filter can be reduced.
When both aspects of the filter in _ .' with the present invention are used (layering process and reduced number of layers), the resulting filter is much less expensive to construct than c .. ' dichroic filters.
However, it should be noted that using either aspect of reducing cost is 1~. ~ in itself. For instance, a 25 ~ .. ' .ui ' filter could be ~ alud with far fewer layers, but using: .. ' layering i such that the filter increases in thickness through the entire revolution of the filter. Al~ , the method of l_' i ~- disclosed herein could be used to form a rotational filter with .. ' precision (e.g., many layers) at reduced 'a~,ll..i"~ costs due to the improved ~a~,ll,. ~ method.
In the method which reduces the cost of layering the optical filter, a flat substrate 110 (Figure 2) is coated with optical coatings of ~ , ~ thickness to form a wedge-shaped coated layer 111. It should be noted that for purposes of clearly i" ~ali"9 the present invention, the thickness of the optical coating 111 has been e ~ ut~d, and in practical ~,' : the thickness of the optical layer 111 varies from roughly 1.66 ~ , to about 3.33 . : ~, with an average thickness of about 2.35 . ~. It should also be ' ~- -d that these t i' ' are ~ and may vary .' ' ~ upon the index of 1.,1-_ of the layer ~ i ' Therefore, 35 in a"l,c.da"..e with one aspect of the present invention, the optical coatings which define the filter are applied across CA 022218~9 1997-11-18 W O 96/41218 PCTAJ596~'~8~7 a substrate rather than r 'l~ applying coatings L;~ thus, _ l~ reducin~q the cost of the filter. The filter at this point provides a dichroic filter which could be used in ~ " _ filter type 3~,"
For a rotational filter, once the optical layers 111 have been applied to the substrate 111, a c~" ~ iLdl portion 112 is cut from the ~ . ~f~ ' ,fcd slab formed by the optical layer 111 together with the substrate 110.
A ~1- ' iLdl aperture is then formed in the center of the L~" ' iLdl portion 112 to form a mountin~q hole. In certain , ' it is desirable to form an optically opaque strip such as a brass strip 122 over a portion of the optical filter disk 120. The brass strip provides a zero-transmission reference portion of the disc 120 which may be helpful for noise: " in certain si~qnal I _ ,"
The above ' ,: provides ease of " for I ' " _ one aspect of the present invention.
10 However, it should be ' Jd that the method may, in practice, involve first cutting the substrate into a disk.
Thereafter, the optical coatings are applied onto the disk as though the disk were still square so that the excess falls onto the platform (not shown) -,, _ the disk within the vacuum tank. In this manner the wedge is formed on the surface of the disk 120 as shown in Fi~qure 10.
It will be . ' : -d that the disk 120 does not '1~ increase in thickness through the entire 15 c;,-.uff-,- of the wheel, but increases in thickness and then ' La5Ls in i' ' However, both halves of the circumference can be utilized as further described below.
In addition to the reduced '~ _ cost of the filter described above, in i~ . with a further aspect of the present invention, a minimal number of optical coating layers are ', ' In one preferred b~ " :, only 17 layers are - y to obtain the desired ll ' Althougfh reducing the number of layers results in less precise filters, such , f~ can be ' in digital signal I ~ g steps. For example, as explained above, ........... ' dichroic filters typically pass a single l-., y band at a time (Figure 5), while the filter of the preferred i ' " may allow for multiple bands to pass, since this is _ - ' for, and can be s t~,d through si~qnal "., It should be noted here that the resolution typically ~~ y for 3" " involving more expensive l~ or - ~ ~ is typically not y for analyzing liquids. However, additional layers can be added at gfreater spacing intervals in order to increase ll ' - of the filter.
COMPENSATING DIGITAL SIGNAL PkOCt~SlNG
As briefly set forth above, the " of a filter made in a~ d with the present invention having a minimal number of optical coatings can be ' ' through signal, .
Figure 6 is a data flow diagram which details the method used to r , for the , of the filter made in a . with the present invention. It should be ' -d, however, that prior to run-time, " i is F l~ . ' PRE-RUN-TIME INITIALIZATION
The " is ~ I ~ at the factory or other time prior to use. In general, a filter LLIaL~ Ii matrix is t~. l 1, as described in greater detail below with reference to Figure 7. The filter c halaLh,.i~liu~
matrix ll, t.. ~ i the l- LhalaLI~ liLs of the dichroic filter 120 at different portions of the filter 120 CA 022218~9 1997-11-18 WO 96/41218 PCT~US96/08627

-6-and for various ~ .,.. ' ' of light. The filter cLa~ 6L~ matrix is used in order to extract portions of the electrical signal ~, alcd by a detector which are due simply to the optical _ caused by the filter 120.
In other words, by knowing the filter cha~a~.t~..iaLi~.~, the , l of the filter can be ~ ' for.
The filter ~.halal,lcli~, matrix is a i ~, d' ' ' matrix. The filter L.hala~ r;alil~ matrix includes one 5 column for each ~ ~.. ' ' of light which is r,hala~.ll,.iLcd and one row for each position (-: ' in the present .. ' of the filter 120, at which chalal,l-,. (of the filter ch~ ; ) is I 1~ ' Thus, in one ! 'JC" t, the filter l,halaLII,.iali~. matrix includes 16 columns and 256 rows when 16 ~ are chala..lcHLcd and 256 positions of the filter 120 are defined. It should be . ' : ' here that it is not r y that 16 different ~ ~.. ' Jth;. be used; the use of additional ~ Ihi~ is pal~ _ for i 10 the signal-to-noise ratio. Since about half of the incident light is ll. ' through the filter at each position of the filter, the same ~ .,.. ~, ' is detected multiple times (although in a unique c~ ' with other 1, _. ' Jth~
each time) so that the overall signal intensity is from 10 to 100 times the intensity of any single .... ' _Ih and much higher than the noise floor. This is c 1~ referred to as Felgate's ~ " In this manner the spectral response of the entire filter 120 over the expected measured ~ ... ' _Ihs is ~ ': ~ Lhala~.lcHLcd. The method 15 employed to construct the filter chala~ liL~ matrix is described in detail below with reference to Figure 7.
DERIVATIQN OF THE FILTER CHARA~; I t.~ C MATRIX
Figures 4A4D, together with Figure 7, illustrate in greater detail, the method employed to obtain the filter Lha-a..lc-i,li-, matrix. The ' i. routine is " - all!d in Figure 7 and starts with a begin block 800.
The activity blocks 830-845, together with Figures 4A4D, illustrate the method used in a~ ,' with 20 the present invention to construct the filter ~dlàldl,ldli~ .s matrix. The filter 120 reflects and transmits optical radiation in different ,u.., ~ for different . ~... ' Ih~ at different places on the filter disk 120. This is clearly dl~d in Figure 4A4C, wherein Figure 4A .., t.._.~t~ the optical l, of light at â ~ . .. ' "lh of 850 r - ~ plotted versus each of a possible 256 disk rotational positions (for one i ' " ~; As shown in Figure 4A, when the disk 120 is in the initial starting position (i.e., ~ - O where O ..,, the r~ ' position of 25 the filter 120), the l,_ of light at 850 ~ is 3~ 10% through the filter 120, while when the disk 120 is rotated so that ~ - 32, the optical ll. of light at 850 ~ : ~ through the filter 120 is p, o,.illlal~l~ 25%. Again, between the disk rotational positions of ~ - 128 to ~t~ - 160, the transmission of light at 850 ~ Ih through the filter 120 is ,, '~ 75%. Thus, the optical 1, for A - 850 . aiS entirely ~.hala~.lcliLcd over 256 rotational positions of the disk filter 120, as depicted 30 in Figure 4A.
Figure 4B depicts the optical ll _ I,hala~lcH ,li-.~ of light at 1,150 - ~ over the same 256 .u ' positions of the disk 120. Similarly, Figure 4C depicts a plot of the optical ll of light at 1,350 - ~ through the disk filter 120 at each of the 256 rotational positions of the disk 120. In one actual bc " of the invention, the optical ll .,hala..lcli~liLa of the filter 120 are described for 256 rotational 35 positions at each of 16 ~ ~.. ' "ll.~ between 850, ~ and 1,400 e ~.

CA 022218~9 1997-11-18 WO 96/41218 PCT/U~,G~ 7

-7-Thus, from these I a filter Lhdla~lu.ialiL matrix may be c I d, as shown in Figure 4D.
The filter Lhala..l~,iali~, matrix d ~ ' in Figure 4D as F(~"l) includes 256 rows and 16 columns. Each column of the filter chala~ liali., matrix: , ia~S the spectral 1- chalal,t~.ial;..a of the disk 120 at each of the ~ 256 lUt ' positions of the disk 120 for the selected ~ ' for that column.
In order to construct the filter chalaLItlialil, matrix depicted in Fi~ure 4D, the filter 120 is illuminated at a first l.,l ' position over each of the 16 ~ ~.. ' " ' to obtain spectral tra ~e '" for each of the 16 wavelengths, as indicated within an activity block 830. Once the spectral ll . c 'fiL;~.Ita have been determined for the first rotational position as indicated within the activity block 830, the filter is illuminated at a second .ui ' position (i.e., ~ - 1) over the 16 selected ~ u.. '~ Jth~ to obtain spectral 1- ~ D ~ 'ril,;...lta 10 for the second ~. ' position, as ll, ~ d in an activity block 835. This method is carried on for each of the possible rui ' positions of the disk 120 until, as indicated within an activity block 840, the filter is illuminated at the "mth," or last, .ui ' position (i.e., position 256) of the disk filter 120 over the 16 selected Ihs to obtain the spectral ll c '~ ts for the last rotational position. In one preferred G ' -'~' 1, where a stepper motor is used, the rotational positions will be precise from l~.. ' to l~... ' of 15 the disk 120. Of course, a computer disc motor with salient poles and run at a constant speed could be used provided that phase dithers are ' to less than one part in 256.
Once spectral t- ~ e'liL; ..Ia have been :' ~ 3d for all 16 ~ _. ' ' of all 256 ~-~positions of the disk 120, the filter chalal,t~,.;ali.,a matrix is r t~u: d, as indicated within an activity block 845.
The matrix defined by column and row where columns represent c~ and row .~;, t_~..ts the . ~ Ih by 20 putting c 'ri~,k,.~ta. Once the filter Lha,a..te.ialb,s matrix is c t,- d, the system has the y: ~.
for ,1,., ~.
It should be . ' -d that ' i . of a filter chalal,t~.ialiL matrix has been described for purposes of the ..: ' filter 120. However, an " ~ filter, or any filter with defined positions on the filter such as Fabry-Perot type filters and even fixed filters such as those used in CCD 3~,' ' can also be ~.hala~ HL~d in 25 accu~da.,~,e with the d- above.
RUN-TIME PROCESSING
D of the overall, ~ " in r- , with the present invention in order to account for G~a;ua of the filter through the use of the filter chd.aLI~ dliu.. matrix is made with reference to Figures 3, 7 and 8.
Figure 3 " atbS the use of the filter 120 in a system for ~ blood ~ Figure 6 " t.dl~a a general flow diagram for the steps of a " for the , ~.,;;,;un in the filter to obtain the Lhala~ Hali~.~ of a medium under test. Figure 8 " : altS a general i. ' diagram of the process of _ for filter; I through signal r e E As depicted in Figure 6, the start of I I ~ is .l, t .,.,t~d in a begin block 300. First, I ' , " and self-testing I ~ e ' ~a are r r. ~ I, as ~-, .,_e.~t~,d in an activity block 305. Briefly, ' ' , ~ and self testing involves boot llr _ti and r . ' " a self testing.
For example, the system first ' if there is a sufficient signal intensity to take an accurate reading. After CA 022218~9 1997-11-18 W O 96/41218 PCT~US96/08627

-8-h ' , _ and self testing is ~ ' I, the light source 110 (Figures 3 and 8) is activated to transmit light 115 through the filter 120, as,, bvv.~tvd in an activity block 310. Initially, the light source 110 is activated while no test medium 131 is r ~ between the filter 120 and the detector 140. Thus, the light which is detected by a detector 140 (Figure 3) ~m a baseline light intensity (IO) which can be used as a test to insure that a bulb 5 which is too dim or too bright is not inserted as a ..,' bulb for example. In one ' " t, a lens 117 (Figure 8) can be provided between the light source and the filter 120 to provide focused light 115 on the filter 120.
Once the initial baseline light intensity constant has been l: - d, the medium 131 under test is inserted as indicated in an activity block 312.
As indicated within an activity block 315, the light which is incident upon the detector 140 is converted 10 to an electrical signal and this signal is amplified in a pre-amp (not shown), filtered with the band pass filter (not shown), and sampled by an analog-to-digital converter 142. Since the filter 120 is rotating (at 3~ 78.125 ,~.. ' per second in one actual ' " t, although other rotational rates could be ? 1~ 1~, as called for by the particular 1"' ), samples of the electrical signal output by the detector 140 are indicative of the light intensity detected at various rotational positions of the filter 120. In one ul~ ' t, one complete rotation (i.e., 360~) of the filter 120 L ll, ' to 512 digital samples. That is, 512 samples are taken within the period L 1., "V to one IVG~-~ of the filter 120. Thus, for example, if the filter 120 rotates at 78.125 ,~..' per second, then 512 samples will be taken within ~,, I - 1~ 1178th of a second, so that the sampling rate of the analog-to-di~ital converter 142 will be 3" 1 ~ 40,000 samples per second.
As 1~ i' I, the filter 120 r , ' in accu, d - - with the present invention includes, _ ' ' : regions 20 within an entire ,v.~' Sr " 'I~, the filter 120 is symmetrically layered so that the first half-revolution of the filter provides a mirror of the signal of the second half-revolution of the filter 120. That is to say, as depicted in Figure 2, the filter is formed in a wedge shape so that the thickness in one direction is constant and the thickness in the r , direction increases linearly. Thus, the second half-,... ' of the filter 120 is ,l ' ' For tbis reason, digital samples taken for one-half of the rG.. ' of the filter 120 could be discarded so that in each rotation of the filter 120 there are 256 samples used for purposes of digital signal I r ' _ rather than 512 samples in the - ' " described above. AIIGIIIaI;~ all 512 samples can be used for r I ' _ by averaging cv.,l, " _ values. In yet an ~ ali.~ ' " t, the ,l ' ' I half of the filter may be used for filter and source '' Each of the 256 samples (if only half are used) ~I, I a different portion of the filter 120 having different optical ll -vhala-vlGli~livv~
Ac~ , the filter 120 is specially designed to include an opaque strip (i.e., the brass strip 122).
The digital signal processor 145 detects when the opaque strip 122 of the filter 120 is ~ i between the light 115 and the detector 140 by i " the intensity output from the detector 140. This intensity is Gffvvli.vl~
zero when the light is blocked by the opaque strip 122. Since the opaque strip 122 blocks ' 'l~ all of the optical radiation ll_ ' from the source 110, any signal output from the optical detector 140 when the light is blocked (e.~q., from ambient li~ht, thermal effects, etc.), will be - I etGd as electrical noise which is not due to either the spectral ' ~.i cLàlavl~l;;.liv~ of the medium under test 131 or the spectral l-CA 022218~9 1997-11-18 W O 96/41218 PCT~US96'~8'?7

9.
.,I.a~ .s of the filter 120. Thus, the digital signal, 1 145 interprets the signal present at the output of the optical detector 140 when the brass strip 122 is , v ' between the light source 110 and the optical detector 140 as s ' - noise which is ' , ~a~ d from all signals output from the optical detector 140. In one ' - " t, this is simply . " ' d by . ' '._ ~ the digital value . ,c, " ~. to the detected 5 noise level from each of the digital values s ~ pr " to the detected signal samples obtained within the activity block 315. AlLI,.llal~ , a shutter r' ~ could be ~v d within the light path, or the lamp 110 could be turned off il~ to provide the same effect. In this manner, the electrical noise inherent within the system is removed so that those electrical signals due to the optical l~_ Lha.a..h.i~ti..~ of the filter 120 (and the test medium 130) are ' .,d in the further p ~ ~ steps.
Once the ~lr 1' - 1;- noise inherent within the system has been extracted, control passes from the activity block 315 to an activity block 323. Within the activity block 323 the signal is divided by l~ to normalize the signal.
The ' ' signal is ' , ~ !d within an activity block 325 to construct a signal intensity matrix, or vector, from the sample values obtained within the activity block 315 (taking into ' the ' IdLliun of the electrical noise, and the signal " ~ ~ ' in the activity block 323) Figure 8 " : ales a signal intensity matrix Iqb, The signal intensity matrix 1000 (Figure 8) is a one column matrix 's :- referred to as a vector) including 256 signal intensity valyes (e.g., one value for each sampled rotational position of the filter 120 in the present . bc " ~: Thus, the signal intensity vector 1000 is obtained by direct ~ . ~ of the optical signal which passes through both the filter 120 and the test medium 131 and is detected by the optical detector 140.
Of course, the values used to form the signal intensity vector 1000 are taken from the amplitude of the signals output from the detector 140 after ' i~ of the noise from each sample. D~ ;gr " each ~ui ' position of a filter 120 which is sampled by the analog to digital converter 170 by the symbol ~, then ~, will -- ,., to the first ,.: ' position of the filter 120, ~2 will ~ J to the second ,.te ' position of the filter 120, to ~25B~ which ~ ,., ' to the last ,ut: ' position of the filter 120 before ~1 is taken again. Using this notation,1,p1 r ,., ' to the intensity of light detected by the optical detector 140 when the filter 120 is in the first rotational position ~ 2 Culll, ' to the intensity of light detected by the detector 140 when the filter 120 is in the second rotational position 5jb2~ etc. Thus, the signal intensity matrix , i~e~ a single column matrix having 256 digital values from Ig,l to Iq~256~ which o ,., ' to the optical detected at each of the rotational positions of the filter 120. In one ' ~ " t, the intensity values for several ,. .' are averaged to form the signal intensity matrix.
- Once the signal intensity vector has been obtained activity block 325 (Figure 6), hl . 'Ibl ;' _ ' ' as l(~), and the filter Lha-a.,lb-iali.,s matrix, hbll' 'Ibl d '" ' ' as F(~,A), has been obtained as explained above and ,~, c~ d as a data input in a block 333, the signal intensity matrix togetherwith the filter Lhalal~lL.i;~
matrix may be used to obtain a matrix indicative only of the optical -bc ,ui chalaLI~ l;L;~ of the test medium 131, as n, . ' in activity blocks 330, 331. That is, since the overall optical ' ,ui is known as measured within the signal intensity matrix, I(~), and the optical 1, Chalal.lbli;~ ,s of the filter 120 are known as CA 022218~9 1997-11-18 W O 96/41218 PCT~US9G,!c~ 7

-10-, e~ t~d by the filter cha,al.tL.i~lil,~ matrix, F(~,A) the optical a' ~ of the detected liyht due to the chalal.lv,,i ,ti.,:. of the test medium 131 may be d~: ' by removiny the optical ll_ Lha~al~lv~ due to the filter from the overall intensity vector l(~) - ' ' This is 1c~ by first takiny the inverse of the filter matrix, as ~m I - ' in the activity block 331, and ' , '~ 'ti, 1~; v the siynal 5 intensity vector l(~) by the inverse filter matrix, as ~I, I ' in the activity block 330.
If the l._ throuyh the test medium 131 is ~ ,, ' as TU) wherein the ll_ of liyht throuyh the test medium 131 is defined as a function of the ~ ~..' ":h, and the ll of liyht throuyh a selected rui ' ' position (e.y., when ~ - 0, s .l, " _ to 0~) of a filter 120 is ! d as a function of Ib and is ' _ - ' by the function F(st~,A), the r ' . or - .. ' of the optical ~' v~ due to the test medium 131 and the filter 120 is !' '_ 3d over the same ~ ~.. ' "Ihs by the function ll~). To obtain T(A) from the intensity vector l(~) and the filter ll. matrix F(~,A), the intensity vector l(~) and the inverse F '(~A) are ' .i, " ' The functions l(~) and F(S~,A) may be ~-, I ' by the siynal intensity and filter chalal,teli:,ti~. matrices, ~-v~ ly. Thus, since I(O = F(/~,~) X T(~

and l(~ v~ a: s ' matrix (vector) ~, an intensity value for each rotational position value ~, while F(~"l) ,., t~.,t~ a two :" ' matrix _ a filter ll_ c~ 'li..i~.,~ value for each value of ~ and each value of A (Fiyure 4D), then the function T(A), I~".t~ ali.~ of optical l. throuyh the test medium 131, may be ,l, ci~ Ld as a one column matrix having values for each of the various ~ Ih values, Z0 A.
In _ ,' with one ' " of the present invention, 16 ~ ~.. 1( lh.. are selected overthe ranye of 850 - _ to 1,400 ~ for purposes of clLIa.. lv,li ~ the spectral chala.lL.i~lil,~ of the test medium 131 as well as the filter 120.
The matrix form of equation (1) above is shown below:

CA 0222l8~9 l997-ll-l8 W O 96/41218 PCTAUS96i'~8~-7 I(O F(~ ) T(~) ~1 f~lAl f~lA2 f<l)lAn tll I~2 b ~.......... . tA2 (2) ~--I~m f~4mAl fd~mln tAn As shown in Equation (2), the signal intensity matrix l(~) is equal to the product of the two d- ' filter chala.,l~liali~. matrix, F(~.~l), and the single column test medium matrix TU). In this equation, two of the matrices are given fi.e., I(~) and F(~,A)). Thus, the third matrix, T(~l), which ~ _.,t~ the optical ll_ cha~acleli;,L.. ~ of the test medium 131 for the 16 selected ~ "' between 850 ~ and 1,400 ~, may be obtained by simply . "i, 1~; ~ the inverse of the filter ~.hal : i,li~. matrix, d ~ ' as F-,A), by the signal intensity matrix, I(~), using r .. ' matrix inversion and 'ti," ~ ' , as shown below.
T(~) F l(~?P,~) I(O

tAl f~lAl f~212 f~lAm I~l t f I (3) A2 ~2A 1 <~2 tAN f~mA 1 f~mA,n I~m 10 Thus, as indicated in an activity block 331, the inverse ll '~ is taken of the filter l,halaLLI,.i;,li,, matrix, F '(~"l), and then this inverse matrix is multiplied by the signal intensity matrix, I(O, within the activity block 330 to obtain the r.l ~ response of the test medium 131 as ~ .,t~ d by the test medium cllalàtl~ . matrix, or Il vector TU).
Figure 8 " : al~.~ this operation in pictorial form. As shown in Figure 8, the light source 110 emits light which passes through the lens 117 and the filter 120 to provide filtered optical radiation 125. The optical radiation 125 passes through the medium under test 131 to provide an optical signal used to generate the signal intensity matrix 1000.

CA 0222l8~9 l997-ll-l8 WO 96/41218 PCT~US96iC~ 7 The signal intensity matrix 1000 is multiplied by the inverse of the filter cl~dla~ ib matrix 1010 as indicated within a block 1005. As shown in Figure 9, the filter Lhalablerialil. matrix 1010 is derived from an analysis of the filter 120, as described above. The inverse ll c~ of the filter ..ha,~ . matrix 1010 is multiplied by the signal intensity vector 1000 to obtain the optical r,l ; response matrix, or l-_ ~ vector, 1015.
Further, s~ " depends on the desired analysis of the test medium.
APPLICATIONS OF THE FILTER
The optical filter of the present invention has uses in various ~ In practice, the optical filter could be used with any 3,," " where optical radiation is d ' ' into multiple spectra. For example, 10 pali ' benefits of the invention may be exhibited in on-line, in-stream chemical process analyzers, or industrial 3"'- i' where fast, small, low-cost I are needed. It should be noted that the circular scanning t~ ' , used with a rotating dichroic filter provides a ' : ' ' N. _ which provides for an increased scanning speed over linear sinusoidal D "' " or a sawtooth scan. Thus, the, '~ filter wheel 120 has many 3"" " in the process control industry, where rapid, real-time spectra are desired for on-line 15 process control. Specific ~"" include F '~ s where different , - of h~dl~ - i are to be I d, drug and alcohol in vivo blood testing, etc.
APPLICATIONS INVOLVING BLOOD GLUCOSE MONITORING
One pal i- ' I, _ N. _ 3"" ~ of the filter of the present invention involves i"g blood glucose levels within a patient, such as a diabetic, without requiring the bAll_: of blood. This e,,' i is 20 described briefly below.
Figure 3 ' ~I~ depicts the filter 120 in operation as an optical filter within a blood glucose monitor.
Optical radiation 115 emitted from a light source 110 is focused via a lens assembly 117 (which may comprise fiber optics or the like) and passes through the filter 120. The dichroic filter 120 ~ . an optically ll rotatable disk substrate which is layered with optical coatings having different i' ' s so as to modulate the 25 b.. - " ' optical radiation 115 through a spectrum from the near infrared (NIR) (e.g., 700 nm) to the infrared (IR) (e.g.r 1,400 nm). The filter 120 further includes the optically opaque strip 122 which may, for example, comprise brass or some other metal which is deposited radially outward from the center of the filter disk 120. The opaque strip provides â "O" location indicator and zero optical intensity, or electrical offset. The filter disk 120 is driven in a circular motion by a smooth, disk drive motor in one preferred ~ , however, a stepper motor could be 30 used - ~ for its known phase e " - Filtered optical radiation 125 passes from the filter 120 through a fleshy medium, perfused with blood such as a finger tip 130. In some 3p,' - it may be desirable to provide a focusing lens, or other optical conduit, between the filter 120 and the finger 130. The light which passes through the finger 130 is detected by a detector 140. In general, the detection signal is ~ " ~ and L .~ d to digital form in the analog to digital .~._ circuit 142. The digital signal ~ ~ 145 accepts the digital signals and 35 ' for the ~ in the dichroic filter.

CA 0222l8~9 l997-ll-l8 W O 96/41218 PCT~US9G/0~7 ln o~ . when light 115is emitted from the broadband light source 110 over a ~ ' "lh range of 3~ 700 a to 1,400 a, (or 850-1700- a in another ' ~ ' where the upper and lower ~ h~ have a ratio of 3~ 2:1) this broadband light 115 shines through the rotating dichroic filter 120. It should be noted that the light 115 is focused onto a portion of the filter 120 by means of fiber optics, a lens assembly (e.g., the lens 117), or the like. As the dichroic filter 120 rotates, the broadband light - 115 is filtered through a portion of the dichroic filter 120 producin~ the filtered optical radiation 125. As indicated above, the dichroic filter 120is coated with optical layers of varying thickness so that different portions of the dichroic filter 120 pass different ~ ' of light. Thus, as the filter 120 rotates, the optical radiation 125 output from the filter includes optical radiation of various ~ u..' ~,lhs. In one ' ' t, a fiber optic is used to couple the optical radiation 125 emitted from a portion of the filter 120 to the patient's finger 120. It should be noted here, that since the optical ckalaLI~Iial;l.s of the filter 120 can be carefully measured and the rotational speed of the dichroic filter 120is known, the time-varying pattern of optical radiation 125 emitted from the filter 120 to illuminate the finger 130is well defined, and therefore, may be used during signal, ~ ~ ~ to ' the amount of ~i which is due to the optical filter 120.
The optical radiation 125 which is used to illuminate the finger 130 passes through the finger 130 to produce the ': - ' ' light 135. As is well known in the art, some of the optical radiation 125 passes . 'e~
through the finger 130, some of the optical radiation 125is reflected within the finger 130 to produce scattering.
The scattered radiation which is 1~ ' through the finger 130, together with the light which passes ~ d through the finger 130, make up the light 135. Some of the optical radiation 125is absorbed by c : within the finger 130.
The finger 130is known to include a fingernail, skin, bones, flesh, and blood. The blood itself primarily .iaea water, o..~b ~ ' ' . Iipids, protein and glucose. Each of these - within the finger (e.g., nerves, muscle tissue, etc.) c~ tS- to the .' ~ and 5(,alt~.. ,. of the optical radiation 125 through the finger 130. The _' ~.i of optical radiation through a ~ ' _ medium typically follows well defined laws in relation to the optical cLa~aLI~.ialiLa of each of the ~ taken , dl '~. App,l - to these laws are . tssod in the equations for Beer-Lambert's law, where low SLall~ , . ' - most closely follow the Beer-Lambert;, - The light 135 which passes through the finger 130is incident upon the optical detector 140. The optical detector 140 ~, al~:a an electrical signal r I ~ to the overall intensity of the light 135.
Although the light 135 typically has different i at different .. ' ' the optical detector 140 9 dltS an electrical signal which is, ~ t to the area contained under the spectral response curve of the Iight 135 within the optical band detected by the detector 140. That is, the optical detector 140 receives light having different at different .... ' "lhs. The detected ~ ~.. '( ~:hs are restricted over a band of ..I ~ ~1~850 nm to 1,700 nm due to the chalaLI~.ialiLa of the detector 140,so that, if intensity is plotted as a function of . .,. '~ " ' to obtain a spectral response curve, the area under the spectral response curve will be indicative of the average optical radiation intensity incident upon the detector 140. Thus, the electrical signal produced by the detector 140is~ to the overall (i.e., average) intensity of the light 135.

CA 022218~9 1997-11-18 The filter 120 r , ' in accu-ddnLe with the present invention includes .l ' ' : regions within an entire ~ S~ , the filter 120 is ~ layered so that the first half-,.,.~' of the filter is ~ ': 11~ , ' to the signal of the second half--L.. ' of the filter 120. That is to say, as depicted in Figure 13, the filter is formed in a wed9e shape so that the thickness in one direction is constant and the 5 thickness in the I I ' ' direction increases linearly. Thus, the second half-~ ' of the filter 120 is ., ' ' : For this reason, digital samples taken for one-half of the ~L.. ' '- of the filter 120 could be discarded so that in each rotation of the filter 120 there are 128 samples used for purposes of digital signal 1 ~ ~ _ rather than 256 samples in one: ' ' Of course, it will be a" LL;atl.d that some of the samples are lost due to the opaque strip. A' ~ _I~, all 256 samples can be used for I ~~ ~ _ by averaging ..;~ ' ~ values. In 10 yet an all~ . ' ~ ' t, the r- ' ' half of the filter may be used for filter and source ~ '', Each of the 128 samples (if only half are used) ~-, ~"ls a different portion of the filter 120 having different optical Il. LllalabL~ I;LJ~.
PRODUCTION SPECIFICATIONS FOR THE OPTICAL FILTER
In one ~ N~ b- ' ~ for blood glucose ........... _e.~ t, the ".. ' :- . 'i~_: for the filter 15120 are as follows:

SIZE: 20 mm wide x 20 mm ~ ~. ' _0~ span, linear ' ' ,~. coating SUBSTRATE: 25 mm OD glass disc with 7.5 mm shaft hole in center WAVELENGTH PASSED: 700-1400 ~
20 112 BANDWIDTH: 50 to 200 1 : ~, bands may repeat BLOCKING: none ENVIRONMENT: Survive ~ humidity, 0-70 c The pass band edges are produced so as to ' '~ lllial~ a 20 ~ band edge.
The pass band may repeat within the window at as ]ittle as 400 cm~1 spacing, or 17-18 periods within the window. The pass band center 1. ~ ~ should approach 100%, and the re~ion between pass bands should approach 100% ...I~
Blocking .,, ~ . outside of the window are no~ critical. They may be limited by t 1-e '5 materials such as RG660, R6700, or ~ ' ~ s, or O-H bands typically found in glass below 7100 cm-'.
Only the ability to resolve wave number bands near 200 cm-1 with one or more band edges should limit the cost.
CHARAC I thl~ I ICS FOR PRESENT EMBODIMENT
r,~r~ , the filter will not have a window narrower than 8,000 to 11,000 cm1 or about 910 to 1,250 nm. The ' '~ his N _ ~ 1~ widerthan 200 cm-t, and the bandedge is 8d~ narrowerthan200 35 cm'. The 1. ~ ~ maximum of the primary band is 1~ above 80%, and the l._ ~ ~ minimum CA 022218~9 1997-11-18 WO 96/41218 PCTAUS9bi'C~ 7 is '-_ _ ly below 20%. Any other bands should be 1., ' ' . unit to unit; but if they are not, a '' ROM could be used in e:r ~ with the DSP to perform initial ~ of individual filters.
MECHANICAL BOUNDARIES AND CHARAL;IL...~IICS FOR THE PRESENT EMBODIMENT
The linear filter is - N. ~ 1~ rotated about its center at less than 4,800 RPM for portable in vivo ,," -(although near 48,000 RPM mi~ht be suitable in certain industrial ,, ' ;), with an aperture centered at a radius of minimum 9 mm to maximum 45 mm, with a clear aperture diameter of 1 mm to 3 mm and a numerical aperture of .12 to A0. The light path passes through a small circular portion traveling along an annular region of the rotating filter, causing a - ' ' scan of the ~, ~..' _Ih~, although they are deposited linearly.
For dynamic balance and low L ' . the linear filter is deposited on a circular substrate. Since the 10 center is not used optically, a standard diameter shaft mounting hole is . ~I~.",d, most of the present hardware in the invention use either 0.5000-.000, +.0005" diameter, or 7.5-0.0+.1 mm. For a small filter, e.g., 20 mm diameter, bonding to the uncoated side would be ' ,,d. Note that the filter mount does not have spokes or other sl" dl .,. of the optical path.
Initial Optir~ ~ ' alignment of the coating on the glass is not critical beyond 0.5 mm and will be e '''-'el~ . Some marking of the deposit alignment at the edge or center is desired.
Although the preferred - ~ " of the present invention has been described and i" ~.dl~d above, those skilled in the art will 1~, I,.,;al~ that various changes and ~ "" to the present invention do not depart from the spirit of the invention. A- d _'~, the scope of the present invention is limited only by the scope of the following appended claims.

Claims

1. An optical system comprising:
a generally circular substrate having a top surface and a bottom surface; and a plurality of optical coatings deposited on said top surface of said substrate said coatings varying in thickness in a first direction across said top surface, said coatings substantially constant in thickness across said top surface in a second direction substantially perpendicular to said first direction.
2. The optical system of Claim 1, further comprising:
a detector positioned to receive light incident upon said detector and filtered by said optical filter, said detector configured to provide an output signal in response to the received light which is a sum of all incident light within the response of the detector; and a signal processor coupled to said detector, said signal processor responsive to said output signal to decode the output signal into components parts, wherein one part represents the optical characteristics of the light incident on the detector with the properties of the filter removed.3. The optical system according to Claim 1 further comprising a cylindrical portion circumferentially disposed about a centered, cylindrical aperture such that said filter is rotatably mountable about a shaft disposed through said aperture.
4. The optical system according to Claim 3 further comprising an optically opaque radial strip.
5. The optical system according to Claim 4 wherein there are no more than 17 of said coatings.
6. The optical system according to Claim 1 wherein said coatings are configured to provide optical transmission characteristics that are redundant within a region of an entire revolution of said filter.
7. The optical system according to Claim 6 wherein said transmission characteristics are substantially symmetrical between a first half-revolution and a second half-revolution of said filter.
8. The optical system according to Claim 7 wherein the plurality of coatings are selected such that a particular wavelength has a plurality of transmission passbands over said first half-revolution.
9. The optical filter according to Claim 7 wherein there are transmission passbands for a plurality of wavelengths at each rotational position of said filter.
10. The optical filter according to Claim 9 wherein approximately one-half of the incident light is transmitted through said coatings at each rotational position of said filter.
11. The optical filter according to Claim 9 wherein a ratio of overall transmitted signal intensity to transmitted signal intensity for any particular wavelength is in the range of 10 to 100 at each rotational position of said filter.
12. The optical system of Claim 1, wherein said optical coatings deposited on said surface are configured to provide transmission characteristics as a function of wavelength and said rotational positions.
13. The optical system according to Claim 12 wherein said transmission characteristics include a plurality of passbands for a particular wavelength.
14. The optical system according to Claim 13 wherein said transmission characteristics include a plurality of passbands for each of a plurality of wavelengths.

15. The optical system according to Claim 14 wherein said wavelengths are in a range from 700 to 1,400 nanometers.
16. The optical filter according to Claim 15 wherein said wavelengths are in a range no narrower than 910 to 1,250 nanometers 17. The optical filter according to Claim 12 wherein said transmission characteristics include multiple passbands at each of said rotational positions.
18. The optical filter according to Claim 17 wherein approximately one-half of the incident light is transmitted through said coatings at each of said rotational positions.
19. The optical filter according to Claim 17 wherein a ratio of overall transmitted signal intensity to transmitted signal intensity for any particular wavelength is in the range of 10 to 100 each of said rotational positions.
20. An optical filter comprising:
a substrate having a top surface and a bottom surface; and a plurality of layers of optical coatings varying in thickness in a first direction along said substrate, said layers adapted to provide optical transmission of more than one wavelength passband at locations through said plurality of layers.
21. An optical filter according to Claim 20 wherein a ratio of overall transmitted signal intensity to transmitted signal intensity for any particular wavelength is in the range of 10 to 100 at each location across the surface of said filter.
22. An optical filter according to Claim 21 wherein approximately one-half of the incident light is transmitted through said layers at each location across the surface of said filter.
23. A method of manufacturing a rotating optical filter, said method of manufacturing comprising the steps of:
providing an optical substrate having a top surface and a bottom surface; and depositing layers of optical coatings on said top surface such that said layers are of varying thicknesses across said top of said substrate in a first direction and such that the thickness of the layers is substantially constant in a second direction substantially perpendicular to said first direction.
24. The method of Claim 23, further comprising the step of creating a mounting hole in the center of the substrate.
25. The method of Claim 24, further comprising the step of depositing an opaque strip along at least a portion of said substrate.