# Patent

## Title
Low cost filter for fluorescence systems

## Abstract

Consistent with the present disclosure, a filter is provided by depositing a coating a substrate. The coating, which may include a plurality of hard-coating layers, has an associated transmission characteristic having a passband, as well as extended blocking.

## Background
This application claims the benefit of U.S. Provisional Application No. 60/841,552 filed Sep. 1, 2006, and U.S. Provisional Application No. 60/842,950 filed Sep. 8, 2006, the contents of both of which are incorporated herein by reference.


The present disclosure is directed toward optical filters. In particular, the present disclosure relates to optical filters which may be incorporated into fluorescence imaging and/or quantification systems.
Fluorescence systems are often employed to analyze or image biological samples. In such systems, the sample is typically exposed to light from a broadband or laser source at a wavelength at which a material of interest in the sample, such as a fluorophore or a naturally occurring substance in the material, absorbs light causing it to fluoresce or emit light at a different (typically longer) wavelength. Light emitted from the sample is then detected so that the location, amount, and other properties associated with the material of interest, as well as the sample, can be determined. In addition, an image of the sample can be constructed based on the detected fluorophore, for example.
In many fluorescence systems, light at a given wavelength excites an atom in the material of interest. The atom then relaxes to a lower energy state, and, in doing so, emits light at a different wavelength. Fluorescence systems typically include an optical source, such as a bright arc lamp or a laser, to generate the excitation light, and a photodetector for sensing light emitted by the sample. The photodetector may include a digital camera or the eyes of an observer. In order to reduce the amount of other light reaching detector, such as light from the source, filters are typically employed which are transmissive at wavelengths of light emitted by the sample, but reflective and/or absorbing at other wavelengths. If light at such other wavelengths is adequately suppressed, a so called “spectral darkfield” situation can be achieved in which an image is black or dark when no features of interest are present. Image quality can thus be improved. Without this spectral darkfield property, in most samples no fluorescence could be observed.
Optical filters are also used to direct the excitation light to the sample, and if highly reflective or absorbing at wavelengths associated with the emitted light, can efficiently direct the excitation light at the desired wavelengths to the sample while blocking light from the source at the emitted wavelengths.
Some optical filters include coatings of metal oxides and are physically hard (“hard coatings”), while others include coatings of softer materials, such as sodium aluminum fluoride (“cryolite”) and/or zinc sulfide (“soft coatings”). Filters including soft coatings are commercially available from Omega Optical, Inc.
With improved optical filters, more photons of emitted light and fewer photons of undesired light (e.g., the excitation light) are fed to the photodetector. Thus, weaker signals can be detected, or less excitation light is required to generate a given emitted optical signal, thereby minimizing damage to the sample by intense light from the source. Or, an image can be detected in less time leading to faster measurements. In addition, a higher signal-to-noise ratio (and therefore better resolution) can be achieved in the image, since, for example, the filter can block more excitation light from reaching the photodetector, while transmitting a given intensity of emitted light.
For an optical filter to be useful as a fluorescence filter, it preferably should be able to transmit light with high efficiency over a well-defined band of wavelengths (passband). The spectrum associated with an optical passband filter typically has reduced transmission over a limited range of wavelengths above the high wavelength edge of the passband, as well as a limited range of wavelengths below the lowest wavelength edge. For fluorescence spectroscopy applications, however, the filter spectrum should have substantial blocking of light over a broad range of wavelengths extending well beyond the limited ranges associated with the passband. Generally these two requirements (high transmission in the passband and extended blocking) are at least somewhat mutually exclusive. That is, providing more blocking generally occurs at the expense of reduced transmission in the desired passband. As explained below, wide-band blocking or extended blocking can be enhanced by colored (or absorbing) filter glass. Even with such enhancements, however, typically the most effective means to provide high blocking is with dielectric thin-film reflecting layers—generally the more layers, the more blocking is achievable. Because there tend to be limitations on the number of layers that can be successfully deposited in a single coating run, this requirement means that conventional fluorescence filters to-date have typically required multiple thin-film coatings per filter. For example, filters fabricated by ion-beam sputtering, which deposit many hard coating layers have to-date been made with at least two coatings per filter. Such filters include BrightLine® fluorescence filters commercially available from Semrock, Inc. Filters are disclosed in U.S. Pat. Nos. 6,809,859, 7,068,430, 7,119,960, and 7,123,416, as well as application Ser. No. 10/953,483, all of which are incorporated herein by reference.
As noted above, colored filter glass has been implemented in order to obtain greater blocking over a wider spectrum. Typically, colored filter glass is often combined with filters formed of soft-coated layers (discussed in U.S. Pat. No. 6,809,859) for such purposes. For example, the long-wave pass emission filters of very low-cost fluorescence filter sets are comprised of a single piece of colored filter glass.
In most soft-coated filters, however, extended-blocking multiple optical coatings are typically provided, each of which blocks light over a band of wavelengths determined by the “stopband width” of a characteristic quarter-wave stack of thin-film layers. Thus, wider blocking ranges require more quarter-wave stack coatings and are thus more difficult to fabricate.
Hard-coated filters are more robust than soft-coated filters and usually achieve blocking via dielectric reflection. Some hard-coated filters are based on a long-wave-pass coating on one side of a single substrate and a short-wave-pass coating on the opposite side, thus producing a bandpass filter, where one or both of the coatings also has built-in extended blocking reflection layers. Other conventional hard-coated filters have been made that have a bandpass filter on one side of a substrate based on a multi-cavity Fabry-Perot type filter coating (quarter-wave-based structure), and then one or more additional coatings with extended blocking layers on the opposite side of the substrate and any additional needed substrates (when there is more than one additional coating). Such filters are described in U.S. Pat. No. 7,119,960 and typically have a narrow passband, which, when measured at the optical density 5 points on the spectral curve, is less than 2% of the center wavelength of the passband. It would be desirable, however, to provide a filter with a wider passband.
Conventional filters typically have limited performance due to the high losses and poor edge steepness associated with colored filter glass or require multiple coating runs leading to higher filter cost. Furthermore, conventional filters that are able to be made at reasonable costs (targeted at more cost-conscious markets like clinical microscopy) typically suffer from poor brightness, poor contrast, and poor reliability and durability. The lower brightness results from the use of colored filter glass in some instances, or from thinner and fewer coatings to reduce coating time, which lead to less steep filter edges (and thus wider exciter-emitter passband separation). Poorer contrast also results from the inability to position the edges optimally (due to poor steepness) as well as lower overall blocking when the coating thickness and the number of coatings are limited. Poor reliability and durability results from the use of soft coatings, which until now have been the only means by which low-cost fluorescence filters could be produced. These filters tend to “burn-out” when exposed to intense radiation for extended periods of time, and because the coatings are porous and absorb water vapor, they can degrade over time, especially in hot, humid, and corrosive environments. In addition, coatings that are not protected from physical contact by an extra glass substrate (such as those found on dichroic beamsplitters) are susceptible to damage when handled or when normal optics cleaning procedures are used.
Accordingly, there is a need for optical fluorescence filters having reduced cost for clinical microscopy applications, for example. There is also a need for such low cost filters to provide more brightness, a lower background light level and/or better contrast. In addition, there is a need for filters that have extremely high reliability and durability, especially in clinical applications, in which doctors and medical technicians must make repeated diagnoses of identical tissue samples, for example, even years after the samples are taken.
SUMMARY OF THE INVENTION
Consistent with an aspect of the present disclosure, an optical device is provided which comprises a substrate having a surface and a plurality of hard-coating layers provided on the surface of the substrate. The plurality of hard-coating layers includes alternating first and second layers. The first layers have a first refractive index, nL, and the second layers having a second refractive index, nH, greater than the first refractive index. In addition, the plurality of hard-coating layers has a spectral characteristic, which has a passband. The passband is defined by a first passband wavelength λ1passband and a second passband wavelength λ2passband. The passband has a center wavelength and the minimum spectral distance between the optical density 4 points on the spectral curve is greater than 2% of the center wavelength. The spectral characteristic also has an average transmissivity at least equal to 80% over the passband. Further, the spectral characteristic has an average optical density greater than 4 over a first blocking band of wavelengths extending from a first blocking wavelength, λ1block, to a second blocking wavelength, λ2block, whereby the second blocking wavelength satisfies:

λ2block<0.9*((1−x)/(1+x))*λ1block,

Alternatively, the spectral characteristic has an average optical density greater than 4 over a second blocking band of wavelengths extending from a third blocking wavelength λ3block to a fourth blocking wavelength, λ4block, the fourth blocking wavelength satisfies:

λ4block>1.1*((1+x)/(1−x))*λ3block,

where





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A first edge band of wavelengths is associated with a first edge portion of the spectral characteristic adjacent the passband. The first edge band of wavelengths extends from λ1passband to λ1block, such that, at a first transmission wavelength, λ1-50%, within the first edge band of wavelengths, the coating has a transmissivity of 50%.

    
    
        λ1passband, λ1block, and λ1-50%, satisfy:

(λ1passband−λ1block)/)λ1-50%<2%, and

    
    


A second edge band of wavelengths is associated with a second edge portion of the spectral characteristic adjacent the passband. The second edge band of wavelengths extends from λ2passband to λ3block, such that, at a second transmission wavelength, λ2-50%, within the second edge band of wavelengths, the coating has a transmissivity of 50%,

    
    
        λ2passband, λ3block, and λ2-50%, satisfy:

(λ3block−λ2passband)/λ2-50%<2%.

    
    





BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.
FIG. 1 illustrates a cross-sectional view of a filter consistent with an aspect of the present disclosure;
FIGS. 2a-2c illustrate spectral characteristics associated with examples of the filter shown in FIG. 1;
FIG. 3 illustrates a fluorescence spectroscopy system consistent with a further aspect of the present disclosure;
FIG. 4 illustrates a cross-sectional view of a dichroic beamsplitter consistent with an additional aspect of the present disclosure;
FIG. 5 illustrates a cross-sectional view of a filter consistent with the present disclosure;
FIG. 6 illustrates a spectral characteristic associated with the filter shown in FIG. 5;
FIGS. 7a-7c illustrate filter sets consistent with additional aspects of the present disclosure; and
FIGS. 8-15 illustrate spectral plots in connection with filters consistent with the present disclosure.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Consistent with the present disclosure, a filter having high transmission, steep edges, and extended blocking is realized with a single coating provided on one side of a substrate. Instead of providing a plurality of quarter-wavelength-based Fabry-Perot type cavities, the single coating includes a portion that serves as a first edge filter for blocking wavelengths exceeding some predetermined wavelength, and another portion that acts as a second edge filter to block wavelengths below another wavelength. When these coating portions are formed on one another, their corresponding spectra are superimposed, and the resulting spectrum includes a wide passband (greater than 2% the center wavelength, measured as the minimum spectral distance between the optical density 4 points on the spectral curve) with blocking on either side. The coating also includes at least one additional portion for extended blocking. As a result, a filter having a spectrum with high transmissivity in the passband, steep passband edges, and extended blocking can be obtained in a single coating without the need to provide additional coatings on multiple substrates. Accordingly, multiple conventional filters are not necessary to obtain these desirable spectral characteristics. Overall costs are therefore reduced. In addition, a filter set (including an exciter filter, beam splitter and emission filter) having just three filter components can be realized, leading to a simpler system design with improved reliability.
Reference will now be made in detail to various exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
An exemplary filter 100 in accordance with the present disclosure is shown in FIG. 1. Filter 100 includes a plurality of layers of alternating high (nH) and low (nL) refractive index, which constitute a coating 111 having a plurality of alternating refractive index hard coating layers on a first surface 120 of substrate 110. Typically, coating 111 includes hard coating layers, although soft coatings may also be employed. Substrate 110 typically includes a float glass or an optical glass. The low refractive index layers, if made of hard materials, typically include one of SiO2, Ta2O5, Nb2O5, HfO2, TiO2, and Al2O5., while the high refractive index layers, if made of hard materials, include another one of SiO2, Ta2O5, Nb2O5, HfO2, TiO2, and Al2O5 (each of the materials that either the high or low refractive index layers is physically hard and thus forms a “hard coating” layer). Coating 111 includes a first coating portion 112 having some of the alternating layers of high and low refractive index materials, which are configured to transmit shorter wavelengths and provide extended blocking at long wavelengths. A second coating portion 114, typically including those materials of first portion 112, is provided on first coating portion 112. Second portion 114 is configured to act as an edge filter to pass shorter wavelengths, and thus may be termed a “short-wave-pass layer.” A third coating portion 116, including other hard-coating layers, is next provided on second coating portion 114. Third coating portion 116 is configured as an edge filter to have high transmissivity at longer wavelengths and provide blocking over a limited range of shorter wavelengths. Third coating portion 116 may thus be termed a “long-wave-pass” layer. Fourth coating portion 118, also including hard-coating layers, may further be deposited on third coating portion 116. Fourth coating portion 118 is configured to provide extended blocking at shorter wavelengths. Third coating portion 116 and fourth coating portion 118 typically include those materials forming the alternating layers of first and second coating portions 112 and 114, respectively.
The first (112), second, (114), third (116), and fourth (118) coating portions are typically formed with high-precision, ion-assisted, ion-beam sputtering thin-film deposition techniques. Such known techniques, which may include optical monitoring, can be used to accurately deposit hundreds of layers. In particular, deposition of the first (112) and second (114) coating portions may be controlled in accordance with known algorithms and may be further controlled with known optical monitoring of the deposited materials. Deposition of the third (116) and fourth (118) coating portions may also be controlled with known algorithms. Optical monitoring of the deposition of the materials that constitute the third (116) and fourth (118) coating portions, however, may not be necessary. Rather, these depositions may be timed for specified periods of time instead of being subject to continuous optical monitoring. Known optimization algorithms may also be applied to further adjust the overall thickness of each of coating portions 112, 114, 116, and 118 and/or the thicknesses of individual high and low refractive index layers that constitute coating portions 112, 114, 116, and 118. In addition, consistent with the present disclosure, first coating portion 112 may be omitted if extended blocking (described in greater detail below) at longer wavelengths is not required. In that case, coating 111 includes coating portions 114, 116, and 118. Alternatively, if extended blocking at shorter wavelengths is not required, fourth coating portion 118 may be omitted, such that coating 111 includes coating portions 112, 114, and 116.
An exemplary spectral characteristic 200-3 of filter 100 consistent with the present disclosure is shown in FIG. 2c. The spectral characteristic has a passband 205, which is defined by a first passband wavelength λ1passband and a second passband wavelength λ2passband. Spectral characteristic 200-3 has an average transmissivity at least equal to 80% over passband 205 and an average optical density greater than 4, and may be more than 5, over first blocking band of wavelengths 215 extending from a first blocking wavelength, λ1block, to a second blocking wavelength, λ2block. As shown in FIG. 2c, λ1block is less than λ1passband. Here, “optical density” (OD) is defined as OD=−log10(T), T being an average transmission measured between 0 and 1, and “average optical density” is defined as the optical density where T is the transmission averaged over a band of wavelengths,. Preferably, the second blocking wavelength satisfies:

λ2block<0.9*((1−x)/(1+x))*λ1block,

where





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A value for λ2block as determined by the above equations typically indicates that the blocking on the short-wavelength side of the passband occurs over a wider region than that which would result from a single quarter-wave stack of layers. The equations are adapted from the analysis in Section 5.2 (specifically Equations 5.15) from the text book Thin-Film Optical Filters (Third Edition, H. A. Macleod, Institute of Physics Publishing, Bristol and Philadelphia, 2001), which is incorporated herein by reference. Blocking beyond that which would result from a single quarter-wave stack of layers (which itself is present due to function of the quarter-wave stack in forming the filter edge) is referred to as “extended blocking.” Such extended blocking over a wavelength region results from a more complex layer structure than merely a quarter-wave stack, and includes, for example, multiple quarter-wave stacks optimally combined into a single coating, or a “chirped” quarter-wave stack in which each of the high and low index layer thicknesses are monotonically increasing or decreasing over at least a portion of the coating.
In addition, spectral characteristic 200-3 has an average optical density greater than 4, and may be more than 5, over second blocking band of wavelengths 225 extending from a third blocking wavelength λ3block to a fourth blocking wavelength, λ4block, the fourth blocking wavelength satisfies:

λ4block>1.1*((1+x)/(1−x))*λ3block,

Theoretically, the factors 0.9 and 1.1 in the above formulas do not define the upper and lower bounds of λ2block and λ4block, respectively. In practice, however, due to uncertainties in the precise values of the refractive indexes of the deposited layers that constitute coating 111 (such as inability to measure the index precisely and slight variations of the index with wavelength and environmental conditions) and other non-idealities (such as measurement uncertainty), the values of λ2block and λ4block that are actually observed can extend slightly below and above, respectively, that which is theoretically predicted. Accordingly, the above formulas take into account such non-idealities by incorporating a factor of 0.9 in the formula for λ2block and a factor of 1.1 in the formula for λ4block.in order to reflect that which may actually be observed.
A value for λ4block as determined by the equation above may ensure that the blocking on the long-wavelength side of the passband is comprised of extended blocking, or blocking over a wider range than would result from a single quarter-wave stack of layers, in analogy to the description of short-wavelength-side extended blocking above.
A first edge band of wavelengths 230 is associated with first edge portion 210 adjacent passband 205. First edge band of wavelengths 230 extends from λ1passband to λ1block, such that, at a first transmission wavelength, λ1-50%, within first edge band of wavelengths 230, coating 111 has a transmissivity of 50%, and λ1passband, λ1block, and λ1-50%, satisfy:

(λ1passband−λ1block)/λ1-50%<2%.

Further, a second edge band of wavelengths 240 is associated with a second edge portion 220 of spectral characteristic 200 adjacent passband 205. Second edge band of wavelengths 240 extends from λ2passband to λ3block, and, as shown in FIG. 2c, λ3block is greater than λ2passband. In addition, at a second transmission wavelength, λ2-50%, within second edge band of wavelengths 240, coating 111 has a transmissivity of 50%, and λ2passband, λ3block, and λ2-50%, satisfy:

(λ3block−λ2passband)/λ2-50%<2%.

A first portion 201 of spectral characteristic 200-3 extending from λ2block to λ1EB has reduced transmission and constitutes a range of extended blocking associated with first coating portion 118. A second portion 202 of spectral characteristic 200 extending from λ1EB to a center wavelength λ0 of passband 205 constitutes part of a long-wave-pass edge filter spectrum attributable to third coating portion 116, and a third portion 203 extending from center wavelength λ0 to λ2EB constitutes part of a short-wave pass edge filter spectrum attributable to second coating portion 114. Extended blocking of portion 204 of spectral characteristic 200-3 extends from λ2EB to λ4block, and is attributable to coating portion 112.
In the above exemplary transmission characteristic 200-3, λ2block may be substantially equal to 400 nm and λ4block may be substantially equal to 700 nm. In addition, spectral characteristic 200-3 may have an average OD greater than 2 over a band of wavelengths extending from λ4block (e.g., 700 nm) to 1000 nm or 1100 nm. λ4block may also be substantially equal to 900 nm. Further, consistent with the present disclosure, the passband may have a bandwidth, measured as the minimum spectral distance between λ1block and λ3block,(both of which typically having an associated optical density of 4, and being referred to as “OD 4 points”), which is greater than 2% of the center wavelength λ0. Accordingly, for example, for a center wavelength λ0 of 550 nm, the passband bandwidth (i.e., the minimum spectral distance between λ1block and λ3block) is greater than 11 nm. Exemplary passband bandwidths may be between 10 nm and 80 nm and exemplary center wavelengths may be within 380 nm to 700 nm.
As noted above, first coating portion 112 may be omitted. In that case, the resulting spectral characteristic will lack extended blocking over longer wavelengths beyond λ2EB (see spectral characteristic 200-1 in FIG. 2a). Also, if fourth coating portion 118 were omitted, the resulting spectral characteristic would not provide extended blocking at shorter wavelengths less than λ1EB (see spectral characteristic 200-2 in FIG. 2b).
Returning to FIG. 1, consistent with a further aspect of the present disclosure, an anti-reflection coating 124 may be provided on a second surface 122 of substrate 110 opposite first surface 120. Anti-reflection coating 124 is typically configured to substantially prevent reflection of light having a wavelength within passband 205.
FIG. 3 illustrates a fluorescence spectroscopy system 300, such as a fluorescence microscope, consistent with a further aspect of the present disclosure. System 300 includes a source 305, which may be a broadband optical source or a laser. Light from source 305 is directed toward a collimating lens or lens group 310 and passed to an exciter filter 315, which may have a construction similar to that discussed above in regard to FIG. 1 and a spectral characteristic similar to that shown in FIG. 2. Filtered light transmitted through filter 315 is next reflected off of dichroic beamsplitter 320, and passed through lens or lens group 322 to sample 324. In response to such excitation light, sample 324 fluoresces and emits or outputs light at a wavelength different than the excitation light. Such emitted light passes through lens 322 and dichroic beamsplitter 320. The emitted light next passes through emission filter 326, which also has a similar construction as filter 100 but a transmission characteristic 600 (see FIG. 6, which is discussed in greater detail below) that differs from that shown in FIG. 2. The filtered emission light passes through lenses or lens groups 328 and 330 and is then sensed by visual inspection or with a detector 332, which, for example, may generate an image of a portion of sample 324. As further shown in FIG. 3, filters 315, 320, and 326 may be mounted in housing 380.
Filters consistent with the present disclosure may be incorporated into commercially available fluorescence microscopes, such as the BX41 microscope available from Olympus America Inc.
FIGS. 4 and 5 show dichroic beam splitter 320 and emission filter 326, respectively, in greater detail. Dichroic beam splitter 320 includes a hard-coating 412 including a plurality of hard alternating refractive index layers provided on substrate 410, and emission filter 326 has a coating 511, which includes first (512), second (514), third (516), and fourth (518) coating portions, each of which including alternating hard-coating refractive index layers. Coating portions 512, 514, 516, and 518 have a similar structure as coating portions 112,114,116, and 118, respectively. The individual high (nH2) and low (nL2) refractive index layers that make up each of layers coating portions 512, 514, 516, and 518 may have the same or different refractive indices as layers coating portions 112, 114, 116, and 118.
The spectral characteristic 600 of emission filter 326 is shown in FIG. 6 and is similar in shape to spectral characteristic 200 shown in FIG. 2. Spectral characteristic 600 has a passband 605, which is defined by passband wavelengths λ1-2passband and λ2-2passband. Spectral characteristic 600 has an average transmissivity at least equal to 80% over passband 605, and an average optical density greater than 4 over a lower blocking band of wavelengths 615 extending from wavelength λ1-2block to wavelength λ2-2block. Preferably, λ2-2block satisfies:

λ2block<0.9*((1−x)/(1+x))*λ1block,

In addition, spectral characteristic 600 has an average optical density greater than 4 over an upper blocking band of wavelengths 625 extending from wavelength λ3-2block to wavelength, λ4-2block, λ4-2block satisfying:

λ4block>1.1*((1+x)/(1−x))*λ3block,

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A lower edge band of wavelengths 630 is associated with a lower edge portion 610 adjacent passband 605. Lower edge band of wavelengths 630 extends from λ1-2passband to λ1-2block, such that, at wavelength λ1-2-50%, within lower edge band of wavelengths 630, coating 111 has a transmissivity of 50%, and λ1-2passband, λ1-2block, and λ1-2-50%, satisfy:

(λ1-2passband−λ1-2block)/λ1-2-50%<2%.

Further, an upper edge band of wavelengths 640 is associated with an upper edge portion 620 of spectral characteristic 600 adjacent passband 605. Upper edge band of wavelengths 640 extends from λ2-2passband to λ3-2block, such that, at wavelength λ2-50%, within upper edge band of wavelengths 640, coating 511 (FIG. 5) has a transmissivity of 50%, and λ2-2passband, λ3-2block, and λ2-2-50%, satisfy:

(λ3-2block−λ2-2passband)/λ2-2-50%<2%.

A first portion 601 of spectral characteristic 600 extending from λ2-2block to λ1-2EB has reduced transmission and constitutes a range of extended blocking associated with coating portion 518. A second portion 602 of spectral characteristic 600 extending from λ1-2EB to a center wavelength λ2-0 of passband 605 constitutes part of long-wave-pass edge filter spectrum attributable to third coating portion 516, and a third portion 603 extending from center wavelength λ2-0 to λ2-2EB constitutes part of a short-wave pass edge filter spectrum attributable to second coating portion 514. Extended blocking of portion 604 of spectral characteristic 600 extends from λ2-2EB to λ4-2block, and is attributable to coating portion 512. Passband 605, measured as the minimum spectral distance between λ1-2block and λ3-2block, has a bandwidth similar to that of the passband bandwidth of spectral characteristic 200-3 discussed above in connection with FIG. 2c. Both λ1-2block and λ3-2block are OD 4 points.
It is noted that if extended blocking is not required at longer wavelengths, coating portion 512 may be omitted, such that extended blocking of portion 604 would not be provided for wavelengths greater than λ2-2EB. In that case, spectral characteristic 600 would resemble spectral characteristic 200-1 shown in FIG. 2a. Likewise, if desired, coating portion 518 may be omitted, such that extended blocking would not be provided at wavelengths less than λ1-2EB, and the resulting spectral characteristic would be similar to spectral characteristic 200-2 shown in FIG. 2b. 
Returning to FIGS. 3-5, layer 412 of dichroic beam splitter 320 is configured to reflect light within the passband of exciter filter 315 (corresponding to passband 205 discussed above). In that case, the excitation light wavelength is preferably within the lower blocking band of wavelengths 615, and coating 511 is configured to pass light emitted from the sample at a wavelength within second blocking band of wavelengths 225 (see FIG. 2). In addition, layer 412 is configured to pass the emission light. Preferably, the emission light has a wavelength within passband 605. With filters 315, 320, and 326 so configured, relatively little excitation light from 305 reaches detector 332, thereby improving the quality of the image output by fluorescence spectroscopy system 300.
Alternatively, the locations of detector 332 and source 305 may be switched, as well as the locations of filters 315 and 326. In this example, dichroic beam splitter 320 passes excitation light, which has a wavelength within passband 205, and reflects light at the emission light wavelength (in passband 605), such that the emission light is reflected toward detector 332.
In FIG. 3, each of filters 315, 320, and 326 may be considered as constituting a filter set 382. Accordingly, since each filter has an associated substrate, filter set 382 has three substrates. Consistent with an additional aspect of the present disclosure, however, the number of substrates in a filter set may be reduced by providing multiple coatings on a single substrate. Examples of alternative filter sets 701-703 will next be described with reference to FIGS. 7a-7c, respectively.
FIG. 7a illustrates a filter set 701 including right-angle prisms constituting substrates 705 and 710. Coating 111 of filter 100 may be provided in contact with side surface 720 of substrate 705, while coating 412 of filter 320 may be provided on hypotenuse surface 721. In addition, coating 511 of filter 326 may be provided on side surface 724 of substrate 710. As further shown in FIG. 7a, coating 412 is spaced from hypotenuse surface 722 of substrate 710 by an air gap 715.
Filter set 702 shown in FIG. 7b is similar to filter set 701, however, air gap 715 is filled with a conventional optical cement 716. Further, in filter set 703 shown in FIG. 7c, coating 412 contacts both hypotenuse surfaces 721 and 722 of substrates 705 and 710, respectively. In each of FIGS. 7a-7c, surfaces 721 and 722 face one another so that filters sets 701-703 have a substantially cubical structure.
Exemplary spectra associated with filter sets consistent with the present disclosure will next be described with reference to FIGS. 8-15. FIG. 8 is a composite of measured exciter filter (dashed curve), dichroic beamsplitter (dotted curve), and emitter filter (solid curve) spectra over a wavelength range of 300 nm to 1100 nm, and FIG. 9 shows an enlarged view of these spectra over a range of 350 nm-500 nm. In FIGS. 8 and 9, transmission (%) is plotted as a function of wavelength. FIG. 10 is equivalent to FIG. 8, but optical density (“OD”, where OD=−log10(T), T being a transmission measured between 0 and 1) is plotted instead of transmission. FIG. 11 illustrates theoretical OD plots which closely approximate the measured OD plots shown in FIG. 10. The curves shown in FIGS. 8-11 are associated with filters to be used in connection with a sample including a known Calcofluor White dye.
Similar plots were obtained in connection with a filter set suitable for use with samples including fluorescein isothiocyanate (FITC), as shown in FIGS. 12-15. Namely, measured transmission vs. wavelength plots over 300 nm-1100 nm and 400 nm-600 nm are shown in FIGS. 12 and 13, respectively. Here also, the dashed curve in FIGS. 12 and 13 corresponds to the exciter filter spectrum, the dotted curve in these figures corresponds to the dichroic beam splitter spectrum, and the solid curve in these figures corresponds to the emitter filter spectrum. An OD plot equivalent to FIG. 12 is shown in FIG. 14, which closely tracks the theoretical OD plot shown in FIG. 15.
As discussed above, the present disclosure describes a filter in which a coating, preferably provided on a single substrate, has sharp passband edges as well as extended blocking. Filter sets employing such filters can be realized with three or fewer substrates, thereby simplifying system design and reducing costs.
Tables 1 and 2 below list exemplary individual layer thicknesses associated with the exciter filter, dichroic beamsplitter, and emitter filter spectra discussed above. Tables 1 and 2 correspond to the above described filter sets for use in connection with Calcofluor White and FITC dyes, respectively.
It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.











TABLE 1









Exciter
Dichroic
Emitter



Thickness (μm): 
Thickness (μm): 
Thickness (μm): 



18.10235289
4.30942641
15.30518641



Total Layers: 252
Total Layers: 42
Total Layers: 194













Layer
Material
Thickness (nm)
Material
Thickness (nm)
Material
Thickness (nm)
















1
Ta2O5
21.542528
Ta2O5
18.000001
Nb2O5
15


2
SiO2
55.843133
SiO2
45.229547
SiO2
53.841577


3
Ta2O5
30.894336
Ta2O5
143.803044
Nb2O5
26.05551


4
SiO2
53.362462
SiO2
198.835667
SiO2
59.414165


5
Ta2O5
35.710448
Ta2O5
120.273508
Nb2O5
30.883961


6
SiO2
52.515375
SiO2
180.766523
SiO2
60.058802


7
Ta2O5
32.47336
Ta2O5
126.919956
Nb2O5
30.839114


8
SiO2
56.175247
SiO2
209.7412
SiO2
60.260543


9
Ta2O5
37.12421
Ta2O5
140.751131
Nb2O5
29.978574


10
SiO2
52.311916
SiO2
216.766227
SiO2
60.230434


11
Ta2O5
38.088323
Ta2O5
141.535809
Nb2O5
36.339558


12
SiO2
55.228444
SiO2
219.386661
SiO2
60.128235


13
Ta2O5
36.11487
Ta2O5
141.508871
Nb2O5
33.433398


14
SiO2
56.085383
SiO2
219.067385
SiO2
60.27866


15
Ta2O5
35.883605
Ta2O5
143.744437
Nb2O5
32.321118


16
SiO2
53.428594
SiO2
217.84547
SiO2
60.290167


17
Ta2O5
38.749063
Ta2O5
142.615164
Nb2O5
32.971644


18
SiO2
55.005335
SiO2
219.96471
SiO2
60.084473


19
Ta2O5
33.125595
Ta2O5
148.345141
Nb2O5
38.854117


20
SiO2
53.620042
SiO2
74.853541
SiO2
60.333791


21
Ta2O5
38.709828
Ta2O5
27.5237
Nb2O5
30.131382


22
SiO2
55.970609
SiO2
63.705179
SiO2
60.213917


23
Ta2O5
35.304189
Ta2O5
50.085785
Nb2O5
36.413843


24
SiO2
55.767196
SiO2
82.713346
SiO2
60.250527


25
Ta2O5
36.78825
Ta2O5
18.867521
Nb2O5
34.726858


26
SiO2
55.150101
SiO2
87.295223
SiO2
60.257074


27
Ta2O5
35.74457
Ta2O5
57.591256
Nb2O5
32.771514


28
SiO2
57.804198
SiO2
48.795137
SiO2
60.214228


29
Ta2O5
36.902705
Ta2O5
31.273588
Nb2O5
35.342404


30
SiO2
55.763948
SiO2
87.382707
SiO2
60.189456


31
Ta2O5
35.352542
Ta2O5
57.951009
Nb2O5
37.402842


32
SiO2
56.062901
SiO2
25.668132
SiO2
60.117843


33
Ta2O5
34.279367
Ta2O5
54.839717
Nb2O5
30.870974


34
SiO2
57.80494
SiO2
78.482223
SiO2
60.43428


35
Ta2O5
35.60142
Ta2O5
38.818646
Nb2O5
35.537588


36
SiO2
56.591019
SiO2
46.407176
SiO2
60.037206


37
Ta2O5
33.656702
Ta2O5
51.138684
Nb2O5
36.374396


38
SiO2
57.143868
SiO2
82.982884
SiO2
60.214403


39
Ta2O5
35.719864
Ta2O5
26.708898
Nb2O5
34.3149


40
SiO2
58.257933
SiO2
51.859533
SiO2
60.235292


41
Ta2O5
36.531073
Ta2O5
61.104302
Nb2O5
33.271157


42
SiO2
56.307264
SiO2
108.277778
SiO2
60.168732


43
Ta2O5
32.680998


Nb2O5
36.119813


44
SiO2
50.733023


SiO2
60.207085


45
Ta2O5
28.023277


Nb2O5
33.464954


46
SiO2
51.196887


SiO2
60.149693


47
Ta2O5
19.142286


Nb2O5
36.00308


48
SiO2
50.629785


SiO2
60.403769


49
Ta2O5
26.716951


Nb2O5
34.160149


50
SiO2
55.850154


SiO2
60.124751


51
Ta2O5
29.863823


Nb2O5
35.2811


52
SiO2
55.110524


SiO2
60.26672


53
Ta2O5
35.894137


Nb2O5
32.10233


54
SiO2
47.843927


SiO2
60.193407


55
Ta2O5
37.041665


Nb2O5
37.316571


56
SiO2
45.381408


SiO2
60.137124


57
Ta2O5
29.600061


Nb2O5
35.867151


58
SiO2
40.860677


SiO2
60.39107


59
Ta2O5
29.372521


Nb2O5
31.036834


60
SiO2
46.399012


SiO2
60.174082


61
Ta2O5
22.842174


Nb2O5
36.978492


62
SiO2
49.815853


SiO2
60.319609


63
Ta2O5
36.274424


Nb2O5
33.374732


64
SiO2
54.324142


SiO2
60.181133


65
Ta2O5
40.458827


Nb2O5
35.861868


66
SiO2
75.141758


SiO2
60.307815


67
Ta2O5
54.975978


Nb2O5
33.59944


68
SiO2
80.679719


SiO2
60.193744


69
Ta2O5
54.217618


Nb2O5
33.456941


70
SiO2
78.526051


SiO2
60.489912


71
Ta2O5
55.168441


Nb2O5
36.443989


72
SiO2
71.834635


SiO2
59.841639


73
Ta2O5
48.329459


Nb2O5
26.27951


74
SiO2
72.58696


SiO2
60.075569


75
Ta2O5
43.503151


Nb2O5
38.213174


76
SiO2
73.635288


SiO2
60.821373


77
Ta2O5
49.566789


Nb2O5
85.270905


78
SiO2
72.455856


SiO2
92.173209


79
Ta2O5
51.439232


Nb2O5
54.480764


80
SiO2
75.609158


SiO2
96.399518


81
Ta2O5
52.108783


Nb2O5
56.282028


82
SiO2
71.153379


SiO2
89.371698


83
Ta2O5
53.7385


Nb2O5
59.277907


84
SiO2
73.672009


SiO2
86.689226


85
Ta2O5
48.097387


Nb2O5
55.262139


86
SiO2
75.728818


SiO2
92.000607


87
Ta2O5
48.340231


Nb2O5
59.871431


88
SiO2
73.564619


SiO2
91.317968


89
Ta2O5
50.903301


Nb2O5
49.138615


90
SiO2
74.184541


SiO2
91.944998


91
Ta2O5
45.757418


Nb2O5
59.19566


92
SiO2
71.307732


SiO2
90.656734


93
Ta2O5
52.953195


Nb2O5
55.054019


94
SiO2
75.18989


SiO2
90.676684


95
Ta2O5
51.368575


Nb2O5
55.917677


96
SiO2
70.218863


SiO2
92.214702


97
Ta2O5
50.998686


Nb2O5
53.847302


98
SiO2
77.100628


SiO2
90.031406


99
Ta2O5
49.206599


Nb2O5
57.238435


100
SiO2
72.037935


SiO2
94.243958


101
Ta2O5
47.827542


Nb2O5
55.83927


102
SiO2
75.489039


SiO2
87.603422


103
Ta2O5
47.501052


Nb2O5
53.717509


104
SiO2
75.590678


SiO2
93.646056


105
Ta2O5
54.441313


Nb2O5
57.562274


106
SiO2
72.561606


SiO2
92.557977


107
Ta2O5
46.160845


Nb2O5
57.247855


108
SiO2
75.730994


SiO2
94.723869


109
Ta2O5
49.702663


Nb2O5
64.04146


110
SiO2
73.981934


SiO2
140.276505


111
Ta2O5
49.986898


Nb2O5
81.152058


112
SiO2
74.587345


SiO2
88.362474


113
Ta2O5
45.299428


Nb2O5
61.31521


114
SiO2
75.231447


SiO2
100.353597


115
Ta2O5
54.377292


Nb2O5
57.315144


116
SiO2
74.795316


SiO2
97.686937


117
Ta2O5
46.568703


Nb2O5
74.336194


118
SiO2
74.454398


SiO2
132.284981


119
Ta2O5
51.044388


Nb2O5
71.632993


120
SiO2
75.266462


SiO2
100.249233


121
Ta2O5
47.624753


Nb2O5
61.480426


122
SiO2
72.993341


SiO2
105.27203


123
Ta2O5
47.964037


Nb2O5
73.607006


124
SiO2
74.330836


SiO2
127.441961


125
Ta2O5
54.166437


Nb2O5
70.243021


126
SiO2
78.83242


SiO2
99.79181


127
Ta2O5
46.652477


Nb2O5
70.395986


128
SiO2
69.698416


SiO2
120.687337


129
Ta2O5
49.419439


Nb2O5
80.646146


130
SiO2
74.878913


SiO2
105.629715


131
Ta2O5
48.650384


Nb2O5
66.512313


132
SiO2
77.469953


SiO2
127.300651


133
Ta2O5
53.886899


Nb2O5
90.342434


134
SiO2
78.690787


SiO2
109.779167


135
Ta2O5
58.564139


Nb2O5
64.40587


136
SiO2
80.162979


SiO2
99.077318


137
Ta2O5
71.78323


Nb2O5
68.822795


138
SiO2
86.102169


SiO2
134.415894


139
Ta2O5
55.204927


Nb2O5
81.319024


140
SiO2
87.572558


SiO2
102.463352


141
Ta2O5
50.601814


Nb2O5
67.198258


142
SiO2
68.136137


SiO2
123.365193


143
Ta2O5
50.349154


Nb2O5
87.583061


144
SiO2
86.178214


SiO2
121.883831


145
Ta2O5
58.186181


Nb2O5
75.342968


146
SiO2
73.681454


SiO2
133.570567


147
Ta2O5
70.259044


Nb2O5
82.365214


148
SiO2
98.260809


SiO2
102.90187


149
Ta2O5
56.657859


Nb2O5
87.2159


150
SiO2
79.960814


SiO2
168.316217


151
Ta2O5
61.9969


Nb2O5
86.089948


152
SiO2
85.68654


SiO2
143.549416


153
Ta2O5
58.487597


Nb2O5
81.55587


154
SiO2
78.844243


SiO2
119.358623


155
Ta2O5
70.784963


Nb2O5
87.987123


156
SiO2
89.081327


SiO2
150.803977


157
Ta2O5
56.026038


Nb2O5
90.977229


158
SiO2
83.635559


SiO2
156.064747


159
Ta2O5
65.467321


Nb2O5
90.759677


160
SiO2
89.225853


SiO2
135.613339


161
Ta2O5
71.020416


Nb2O5
78.077551


162
SiO2
89.115342


SiO2
125.232036


163
Ta2O5
64.229848


Nb2O5
83.932929


164
SiO2
88.504899


SiO2
148.934923


165
Ta2O5
56.637385


Nb2O5
95.680094


166
SiO2
86.461303


SiO2
148.743293


167
Ta2O5
59.587057


Nb2O5
87.985304


168
SiO2
90.374743


SiO2
151.172071


169
Ta2O5
62.67727


Nb2O5
94.80538


170
SiO2
97.243763


SiO2
155.204918


171
Ta2O5
65.378098


Nb2O5
90.204983


172
SiO2
93.196831


SiO2
132.993524


173
Ta2O5
74.062652


Nb2O5
81.763033


174
SiO2
95.769772


SiO2
147.14212


175
Ta2O5
63.635611


Nb2O5
103.569699


176
SiO2
95.215149


SiO2
161.029059


177
Ta2O5
59.20011


Nb2O5
99.402575


178
SiO2
98.399319


SiO2
154.260901


179
Ta2O5
74.275704


Nb2O5
102.986509


180
SiO2
101.091627


SiO2
165.499705


181
Ta2O5
69.877353


Nb2O5
111.317219


182
SiO2
106.71887


SiO2
167.574838


183
Ta2O5
71.073631


Nb2O5
115.804816


184
SiO2
104.115398


SiO2
166.510097


185
Ta2O5
69.662266


Nb2O5
112.668699


186
SiO2
100.11951


SiO2
162.864546


187
Ta2O5
69.377336


Nb2O5
103.082378


188
SiO2
104.399829


SiO2
153.116153


189
Ta2O5
75.096851


Nb2O5
108.040025


190
SiO2
105.517552


SiO2
164.27813


191
Ta2O5
70.843547


Nb2O5
114.895638


192
SiO2
111.700199


SiO2
162.726583


193
Ta2O5
76.455848


Nb2O5
111.21254


194
SiO2
100.059876


SiO2
78.946972


195
Ta2O5
73.523768


196
SiO2
104.669083


197
Ta2O5
63.613775


198
SiO2
120.318062


199
Ta2O5
89.34781


200
SiO2
110.531615


201
Ta2O5
74.655493


202
SiO2
109.966102


203
Ta2O5
73.48166


204
SiO2
119.086024


205
Ta2O5
83.73169


206
SiO2
100.309196


207
Ta2O5
75.324665


208
SiO2
97.320858


209
Ta2O5
69.045354


210
SiO2
107.551845


211
Ta2O5
91.440427


212
SiO2
119.775905


213
Ta2O5
66.670026


214
SiO2
118.637034


215
Ta2O5
79.590138


216
SiO2
129.284989


217
Ta2O5
96.234672


218
SiO2
125.081023


219
Ta2O5
82.820693


220
SiO2
129.361088


221
Ta2O5
73.167236


222
SiO2
122.415306


223
Ta2O5
86.141677


224
SiO2
137.47071


225
Ta2O5
91.663801


226
SiO2
123.466319


227
Ta2O5
88.789668


228
SiO2
142.853947


229
Ta2O5
82.699299


230
SiO2
112.973376


231
Ta2O5
75.808449


232
SiO2
116.289632


233
Ta2O5
103.393429


234
SiO2
131.623678


235
Ta2O5
135.874235


236
SiO2
139.086712


237
Ta2O5
110.938326


238
SiO2
148.137695


239
Ta2O5
119.290778


240
SiO2
148.727869


241
Ta2O5
109.294552


242
SiO2
158.719661


243
Ta2O5
104.603832


244
SiO2
153.67652


245
Ta2O5
114.623631


246
SiO2
152.308865


247
Ta2O5
102.906211


248
SiO2
160.394283


249
Ta2O5
100.052054


250
SiO2
154.428969


251
Ta2O5
99.935121


252
SiO2
69.518357




















TABLE 2









Exciter
Dichroic
Emitter



Thickness (μm):
Thickness (μm): 
Thickness (μm): 



15.46312828
4.78682926
16.51720336



Total Layers: 195
Total Layers: 32
Total Layers: 199













Layer
Material
Thickness (nm)
Material
Thickness (nm)
Material
Thickness (nm)
















1
Nb2O5
103.020435
Nb2O5
19.755258
Nb2O5
120.520412


2
SiO2
184.969867
SiO2
249.436778
SiO2
208.471674


3
Nb2O5
105.65992
Nb2O5
102.667383
Nb2O5
98.844384


4
SiO2
177.696611
SiO2
226.406451
SiO2
149.332901


5
Nb2O5
111.787595
Nb2O5
53.47712
Nb2O5
98.279852


6
SiO2
166.111328
SiO2
240.811076
SiO2
162.657065


7
Nb2O5
175.482955
Nb2O5
70.760978
Nb2O5
111.307612


8
SiO2
152.596466
SiO2
232.649733
SiO2
182.747042


9
Nb2O5
99.839977
Nb2O5
74.140776
Nb2O5
101.10863


10
SiO2
162.547624
SiO2
231.888658
SiO2
165.814661


11
Nb2O5
117.107037
Nb2O5
77.34542
Nb2O5
107.951598


12
SiO2
166.03817
SiO2
230.346511
SiO2
165.702027


13
Nb2O5
105.336144
Nb2O5
77.00804
Nb2O5
110.77163


14
SiO2
168.556027
SiO2
230.522453
SiO2
164.502195


15
Nb2O5
105.872654
Nb2O5
75.358277
Nb2O5
104.819083


16
SiO2
160.59604
SiO2
232.094873
SiO2
173.543722


17
Nb2O5
101.415851
Nb2O5
75.480988
Nb2O5
93.246141


18
SiO2
162.822862
SiO2
231.775947
SiO2
166.941351


19
Nb2O5
100.420397
Nb2O5
77.171654
Nb2O5
110.454611


20
SiO2
154.47743
SiO2
231.110905
SiO2
156.201891


21
Nb2O5
88.909405
Nb2O5
76.930145
Nb2O5
118.86173


22
SiO2
130.390877
SiO2
231.405803
SiO2
168.680866


23
Nb2O5
81.697069
Nb2O5
75.551257
Nb2O5
68.573262


24
SiO2
141.646947
SiO2
230.497556
SiO2
152.615185


25
Nb2O5
82.555605
Nb2O5
75.62217
Nb2O5
77.401487


26
SiO2
145.341923
SiO2
233.252254
SiO2
149.403322


27
Nb2O5
114.93102
Nb2O5
70.037093
Nb2O5
76.636857


28
SiO2
154.548707
SiO2
252.562806
SiO2
155.659656


29
Nb2O5
94.476203
Nb2O5
47.366784
Nb2O5
126.190604


30
SiO2
136.529517
SiO2
264.999891
SiO2
177.406209


31
Nb2O5
66.101724
Nb2O5
44.978082
Nb2O5
118.182198


32
SiO2
119.076319
SiO2
143.416145
SiO2
134.96742


33
Nb2O5
79.729322


Nb2O5
82.964814


34
SiO2
130.874119


SiO2
134.253757


35
Nb2O5
77.992525


Nb2O5
99.632888


36
SiO2
107.485394


SiO2
136.967071


37
Nb2O5
65.800567


Nb2O5
84.309472


38
SiO2
128.134247


SiO2
125.187075


39
Nb2O5
90.910325


Nb2O5
91.372536


40
SiO2
130.795882


SiO2
151.253421


41
Nb2O5
77.295454


Nb2O5
77.281077


42
SiO2
112.503147


SiO2
123.411921


43
Nb2O5
84.909856


Nb2O5
87.053171


44
SiO2
120.81689


SiO2
157.742993


45
Nb2O5
59.418177


Nb2O5
90.646247


46
SiO2
112.953288


SiO2
123.049582


47
Nb2O5
61.10262


Nb2O5
76.703209


48
SiO2
111.503659


SiO2
116.839938


49
Nb2O5
65.958775


Nb2O5
80.310636


50
SiO2
127.125449


SiO2
153.946123


51
Nb2O5
85.430322


Nb2O5
78.805046


52
SiO2
112.775188


SiO2
117.543485


53
Nb2O5
56.630195


Nb2O5
79.153398


54
SiO2
105.40047


SiO2
118.904155


55
Nb2O5
78.765413


Nb2O5
95.762182


56
SiO2
110.84542


SiO2
149.672109


57
Nb2O5
95.071038


Nb2O5
81.465016


58
SiO2
113.979483


SiO2
115.576654


59
Nb2O5
54.909864


Nb2O5
73.183432


60
SiO2
109.144907


SiO2
115.54896


61
Nb2O5
61.138387


Nb2O5
90.276731


62
SiO2
101.5793


SiO2
157.761513


63
Nb2O5
63.953512


Nb2O5
76.449894


64
SiO2
115.694758


SiO2
110.97485


65
Nb2O5
92.745136


Nb2O5
66.878672


66
SiO2
117.584656


SiO2
109.007813


67
Nb2O5
65.394942


Nb2O5
76.535182


68
SiO2
97.007268


SiO2
101.204588


69
Nb2O5
63.950919


Nb2O5
73.043965


70
SiO2
99.003518


SiO2
63.705658


71
Nb2O5
53.62224


Nb2O5
80.258136


72
SiO2
98.115648


SiO2
103.316583


73
Nb2O5
60.656343


Nb2O5
69.991268


74
SiO2
89.521684


SiO2
105.298699


75
Nb2O5
63.642403


Nb2O5
60.098474


76
SiO2
95.056625


SiO2
107.357243


77
Nb2O5
58.955796


Nb2O5
72.011096


78
SiO2
94.019429


SiO2
101.801649


79
Nb2O5
59.79292


Nb2O5
68.272344


80
SiO2
95.337034


SiO2
106.96859


81
Nb2O5
58.781


Nb2O5
72.521376


82
SiO2
92.690163


SiO2
89.234517


83
Nb2O5
62.99268


Nb2O5
58.598235


84
SiO2
94.153333


SiO2
115.600753


85
Nb2O5
55.447279


Nb2O5
69.202224


86
SiO2
98.487741


SiO2
107.014337


87
Nb2O5
60.725646


Nb2O5
72.455308


88
SiO2
89.544252


SiO2
97.342236


89
Nb2O5
63.601086


Nb2O5
63.113257


90
SiO2
100.274483


SiO2
135.724689


91
Nb2O5
52.206565


Nb2O5
46.793414


92
SiO2
87.663852


SiO2
72.010233


93
Nb2O5
64.740092


Nb2O5
80.56155


94
SiO2
101.752041


SiO2
123.411312


95
Nb2O5
55.720872


Nb2O5
76.424644


96
SiO2
96.903455


SiO2
64.204657


97
Nb2O5
56.692561


Nb2O5
102.34953


98
SiO2
91.511539


SiO2
71.179041


99
Nb2O5
61.22283


Nb2O5
57.076149


100
SiO2
96.596527


SiO2
72.559939


101
Nb2O5
62.779161


Nb2O5
33.97113


102
SiO2
89.93581


SiO2
72.734555


103
Nb2O5
62.534761


Nb2O5
39.740447


104
SiO2
92.739907


SiO2
73.051133


105
Nb2O5
54.171416


Nb2O5
45.354032


106
SiO2
96.849103


SiO2
74.135476


107
Nb2O5
63.939278


Nb2O5
49.428548


108
SiO2
80.191432


SiO2
73.556512


109
Nb2O5
65.397114


Nb2O5
45.257904


110
SiO2
105.817135


SiO2
74.133337


111
Nb2O5
60.031711


Nb2O5
49.200523


112
SiO2
75.121866


SiO2
73.628251


113
Nb2O5
59.984846


Nb2O5
39.769374


114
SiO2
103.875707


SiO2
73.346996


115
Nb2O5
59.988706


Nb2O5
49.874938


116
SiO2
90.589629


SiO2
72.872096


117
Nb2O5
53.800292


Nb2O5
46.727442


118
SiO2
96.321289


SiO2
72.439376


119
Nb2O5
77.09225


Nb2O5
46.257557


120
SiO2
73.185234


SiO2
73.803087


121
Nb2O5
61.726588


Nb2O5
49.63358


122
SiO2
110.071331


SiO2
73.440207


123
Nb2O5
58.450469


Nb2O5
42.555636


124
SiO2
52.926246


SiO2
73.900884


125
Nb2O5
81.093005


Nb2O5
48.92588


126
SiO2
39.60735


SiO2
73.476829


127
Nb2O5
30.972587


Nb2O5
45.373354


128
SiO2
63.717129


SiO2
74.350068


129
Nb2O5
28.812372


Nb2O5
45.205053


130
SiO2
65.726825


SiO2
75.271069


131
Nb2O5
51.930921


Nb2O5
47.340812


132
SiO2
62.658775


SiO2
75.510507


133
Nb2O5
44.689331


Nb2O5
45.316969


134
SiO2
61.304026


SiO2
74.669696


135
Nb2O5
38.032444


Nb2O5
46.348844


136
SiO2
60.894131


SiO2
73.954689


137
Nb2O5
49.786027


Nb2O5
47.590089


138
SiO2
63.123868


SiO2
73.988145


139
Nb2O5
36.831253


Nb2O5
41.787049


140
SiO2
65.654231


SiO2
73.831633


141
Nb2O5
37.365471


Nb2O5
49.757488


142
SiO2
65.629594


SiO2
73.720914


143
Nb2O5
44.090334


Nb2O5
48.296369


144
SiO2
65.669747


SiO2
73.061434


145
Nb2O5
40.460522


Nb2O5
45.376895


146
SiO2
65.039624


SiO2
73.641224


147
Nb2O5
43.94835


Nb2O5
47.904826


148
SiO2
64.973048


SiO2
74.358153


149
Nb2O5
39.135381


Nb2O5
43.689922


150
SiO2
65.675389


SiO2
74.667973


151
Nb2O5
35.757871


Nb2O5
48.432513


152
SiO2
65.175315


SiO2
74.459908


153
Nb2O5
45.600403


Nb2O5
43.394492


154
SiO2
65.847471


SiO2
73.891471


155
Nb2O5
41.851528


Nb2O5
47.151012


156
SiO2
65.7225


SiO2
73.265274


157
Nb2O5
37.057438


Nb2O5
47.944367


158
SiO2
66.186088


SiO2
72.970548


159
Nb2O5
41.607851


Nb2O5
50.739433


160
SiO2
65.499169


SiO2
73.294839


161
Nb2O5
43.656602


Nb2O5
43.792746


162
SiO2
64.882681


SiO2
74.191749


163
Nb2O5
34.963028


Nb2O5
42.503653


164
SiO2
65.276026


SiO2
73.823048


165
Nb2O5
42.46295


Nb2O5
50.548065


166
SiO2
66.08707


SiO2
72.500106


167
Nb2O5
45.406729


Nb2O5
44.227006


168
SiO2
65.656958


SiO2
72.028742


169
Nb2O5
39.090325


Nb2O5
52.30712


170
SiO2
64.649759


SiO2
72.564394


171
Nb2O5
35.493024


Nb2O5
43.051055


172
SiO2
65.234651


SiO2
73.124878


173
Nb2O5
43.949858


Nb2O5
50.009649


174
SiO2
65.772432


SiO2
72.960645


175
Nb2O5
40.226738


Nb2O5
43.067512


176
SiO2
66.337577


SiO2
72.434957


177
Nb2O5
40.886654


Nb2O5
42.759632


178
SiO2
65.82086


SiO2
72.609111


179
Nb2O5
38.368344


Nb2O5
51.113242


180
SiO2
64.442884


SiO2
72.310448


181
Nb2O5
43.148079


Nb2O5
49.032682


182
SiO2
60.270591


SiO2
73.161244


183
Nb2O5
36.174955


Nb2O5
38.189301


184
SiO2
60.597924


SiO2
71.289535


185
Nb2O5
42.938963


Nb2O5
40.751881


186
SiO2
62.107829


SiO2
72.554329


187
Nb2O5
43.297542


Nb2O5
44.046474


188
SiO2
63.033125


SiO2
71.462947


189
Nb2O5
18.612166


Nb2O5
27.650176


190
SiO2
59.632382


SiO2
69.256787


191
Nb2O5
39.684558


Nb2O5
37.674692


192
SiO2
62.537565


SiO2
67.540846


193
Nb2O5
28.592641


Nb2O5
31.042601


194
SiO2
47.574953


SiO2
57.342841


195
Nb2O5
26.307995


Nb2O5
49.926189


196




SiO2
62.411325


197




Nb2O5
43.555442


198




SiO2
60.999258


199




Nb2O5
20.686301

## Claims

1. An optical device, comprising:
a substrate having a surface; and
a plurality of layers provided on the surface of the substrate, the plurality of layers including alternating first and second layers, the first layers having a first refractive index, nL, and the second layers having a second refractive index, nH, greater than the first refractive index,
wherein the plurality of layers has a spectral characteristic, the spectral characteristic having a passband, which is defined by a first passband wavelength λ1passband and a second passband wavelength λ2passband, the spectral characteristic having a center wavelength between λ1passband and λ2passband and having an average transmissivity at least equal to 80% over the passband,
the spectral characteristic having an average optical density greater than 4 over at least one of first and second blocking bands of wavelengths, wherein the first blocking band of wavelengths extends from a first blocking wavelength, λ1block, having an associated optical density equal to 4 to a second blocking wavelength, λ2block, the second blocking wavelength satisfying:


λ2block<0.9*((1−x)/(1+x))*λ1block,


wherein the second blocking band of wavelengths extends from a third blocking wavelength, λ3block, having an associated optical density equal to 4 to a fourth blocking wavelength, λ4block, the fourth blocking wavelength satisfying:


λ4block>1.1*((1+x)/(1−x))*λ3block,



where




  
    x
    =
    
      
        2
        π
      
      ⁢
      arc
      ⁢
      
        
      
      ⁢
      
        sin
        ⁡
        
          (
          
            
              
                n
                H
              
              -
              
                n
                L
              
            
            
              
                n
                H
              
              +
              
                n
                L
              
            
          
          )
        
      
    
  
  ,



wherein a first edge band of wavelengths is associated with a first edge portion of the spectral characteristic adjacent the passband, the first edge band of wavelengths extending from λ1passband to λ1block, such that, at a first transmission wavelength, λ1-50%, within the first edge band of wavelengths, the coating has a transmissivity of 50%,


λ1passband, λ1block, and λ1-50%, satisfy:



(λ1passband−λ1block)/λ1-50%<2%, and


wherein a second edge band of wavelengths is associated with a second edge portion of the spectral characteristic adjacent the passband, the second edge band of wavelengths extending from λ2passband to λ3block, such that, at a second transmission wavelength, λ2-50%, within the second edge band of wavelengths, the plurality of layers has a transmissivity of 50%,


λ2passband, λ3block, and λ2-50%, satisfy:



(λ3block−λ2passband)/λ2-50%<2%, and


a minimum spectral distance between λ1block and λ3block is greater than 2% of the center wavelength.

2. An optical device in accordance with claim 1, wherein the plurality of layers includes a plurality of hard-coating layers.

3. An optical device in accordance with claim 2, wherein the spectral characteristic has an average optical density greater than 5 over at least one of the first and second blocking bands of wavelengths.

4. An optical device in accordance with claim 2, wherein λ4block is between 700 nm to 900 nm, and the spectral characteristic has an average OD greater than 2 over a band of wavelengths extending from λ4block to wavelength greater than 1000 nm.

5. An optical device in accordance with claim 2, wherein the center wavelength is within 380 nm to 700 nm.

6. An optical device in accordance with claim 2, wherein the spectral distance between λ1block and λ3block is between 10 nm and 80 nm.

7. An optical device in accordance with claim 2, wherein the plurality of hard coating layers includes two or more of: SiO2, Ta2O5, Nb2O5, HfO2, TiO2, and Al2O5.

8. An optical device in accordance with claim 2, wherein the substrate includes one of a float glass and an optical glass.

9. An optical device in accordance with claim 2, wherein the surface of the substrate is a first surface of the substrate, the substrate further comprising a second surface opposite the first surface, the optical device further comprising:
an anti-reflection coating provided on the second surface of the substrate, the anti-reflection coating substantially preventing reflection of light having a wavelength within the passband.

10. An optical device in accordance with claim 2, wherein the substrate is a first substrate, the plurality of layers is a first plurality of layers, the spectral characteristic is a first spectral characteristic, the passband is a first passband, and the center wavelength is a first center wavelength, the optical device further comprising:
a second substrate;
a second plurality of layers provided on the second substrate, the second plurality of layers being configured to reflect first light at a first wavelength, the first wavelength being within said first passband;
a third substrate having a surface;
a third plurality of layers provided on the surface of the third substrate, the third plurality of layers including alternating third and fourth layers, the third layers having a refractive index, nL2, and the fourth layers having a refractive index, nH2, greater than nL2,
wherein the third plurality of layers has a second spectral characteristic, the second spectral characteristic having a second passband, which is defined by passband wavelengths λ1-2passband and λ2-2passband, the second spectral characteristic having an average transmissivity at least equal to 80% over the second passband, and the second passband having a second center wavelength between λ1-2passband and λ2-2passband,
the second spectral characteristic having an average optical density greater than 4 over at least one of a lower blocking band of wavelengths and an upper blocking band of wavelengths, the lower blocking band of wavelengths extends from wavelength λ1-2block, which has an associated optical density equal to 4, to wavelength λ2-2block, λ2-2block satisfying:


λ2-2block<0.9*((1−x2)/(1+x2))*λ1-2block,


wherein the upper blocking band of wavelengths extends from wavelength λ3-2block, which has an associated optical density equal to 4, to wavelength λ4-2block, λ4-2block satisfying:


λ4-2block>1.1*((1+x2)/(1−x2))*λ3-2block,



where




  
    
      x
      2
    
    =
    
      
        2
        π
      
      ⁢
      arc
      ⁢
      
        
      
      ⁢
      
        sin
        ⁡
        
          (
          
            
              
                n
                
                  H
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
              -
              
                n
                
                  L
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
            
              
                n
                
                  H
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
              +
              
                n
                
                  L
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
          
          )
        
      
    
  
  ,



wherein a lower edge band of wavelengths is associated with a lower edge portion of the spectral characteristic adjacent the second passband, the lower edge band of wavelengths extending from λ1-2passband to λ1-2block, such that, at wavelength λ1-2-50%, within the lower edge band of wavelengths, the second coating has a transmissivity of 50%,


λ1-2passband, λ1-2block, and λ1-2-50%, satisfy:



(λ1-2passband−λ1-2block)/λ1-2-50%<2%,


wherein an upper edge band of wavelengths is associated with an upper edge portion of the second spectral characteristic adjacent the second passband, the upper edge band of wavelengths extending from λ2-2passband to λ3-2block, such that, at wavelength, λ2-2-50%, within the upper edge band of wavelengths, the second coating has a transmissivity of 50%,


λ2-2passband, λ3-2block, and λ2-2-50%, satisfy:



(λ3-2block−λ2-2passband)/λ2-2-50%<2%, and


wherein the first wavelength is within the lower blocking band of wavelengths, the third plurality of layers being configured to pass second light having a second wavelength, the second wavelength being within the second blocking band of wavelengths, the second plurality of layers being configured to pass third light, the third light having a third wavelength, which is within the second passband, and a minimum spectral distance between λ1-2block and λ3-2block is greater than 2% of the second center wavelength.

11. An optical device in accordance with claim 2, wherein the substrate is a first substrate, the plurality of layers is a first plurality of layers, the spectral characteristic is a first spectral characteristic, the passband is a first passband, and the center wavelength is a first center wavelength, the optical device further comprising:
a second substrate;
a second plurality of layers provided on the second substrate, the second plurality of layers being configured to transmit first light at a first wavelength, the first wavelength being within said first passband;
a third substrate having a surface;
a third plurality of layers provided on the surface of the third substrate, the third plurality of layers including alternating third and fourth layers, the third layers having a refractive index, nL2, and the fourth layers having a refractive index, nH2, greater than nL2,
wherein the third plurality of layers has a second spectral characteristic, the second spectral characteristic having a second passband, which is defined by passband wavelengths λ1-2passband and λ2-2passband, the second spectral characteristic having an average transmissivity at least equal to 80% over the second passband, and the second passband having a second center wavelength between λ1-2passband and λ2-2passband,
the second spectral characteristic having an average optical density greater than 4 over at least one of a lower blocking band of wavelengths and an upper blocking band of wavelengths, the lower blocking band of wavelengths extends from wavelength λ1-2block, which has an associated optical density equal to 4, to wavelength λ2-2block, λ2-2block satisfying:


λ2-2block<0.9*((1−x2)/(1+x2))*λ1-2block,


wherein the upper blocking band of wavelengths extends from wavelength λ3-2block, which has an associated optical density equal to 4, to wavelength λ4-2block, λ4-2block satisfying:


λ4-2block>1.1*((1+x2)/(1−x2))*λ3-2block,



where




  
    
      x
      2
    
    =
    
      
        2
        π
      
      ⁢
      arc
      ⁢
      
        
      
      ⁢
      
        sin
        ⁡
        
          (
          
            
              
                n
                
                  H
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
              -
              
                n
                
                  L
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
            
              
                n
                
                  H
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
              +
              
                n
                
                  L
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
          
          )
        
      
    
  
  ,



wherein a lower edge band of wavelengths is associated with a lower edge portion of the spectral characteristic adjacent the second passband, the lower edge band of wavelengths extending from λ1-2passband to λ1-2block, such that, at wavelength λ1-2-50%, within the lower edge band of wavelengths, the second coating has a transmissivity of 50%,


λ1-2passband, λ1-2block, and λ1-2-50%, satisfy:



(λ1-2passband−λ1-2block)/λ1-2-50%<2%,


wherein an upper edge band of wavelengths is associated with an upper edge portion of the second spectral characteristic adjacent the second passband, the upper edge band of wavelengths extending from λ2-2passband to λ3-2block, such that, at wavelength, λ2-2-50%, within the upper edge band of wavelengths, the second coating has a transmissivity of 50%,


λ2-2passband, λ3-2block, and λ2-2-50%, satisfy:



(λ3-2block−λ2-2passband)/λ2-2-50%<2%, and


wherein the first wavelength is within the lower blocking band of wavelengths, the third plurality of layers being configured to pass second light having a second wavelength, the second wavelength being within the second blocking band of wavelengths, the second plurality of layers being configured to reflect third light, the third light having a third wavelength, which is within the second passband, and a minimum spectral distance between λ1-2block and λ3-2block is greater than 2% of the second center wavelength.

12. An optical device in accordance with claim 2, wherein the surface of the substrate is a first surface of the substrate, the substrate being a first substrate further having a second surface, the plurality of layers is a first plurality of layers, the spectral characteristic is a first spectral characteristic, the passband is a first passband, and the center wavelength is a second center wavelength, the optical device further comprising:
a second substrate having a first surface and a second surface;
a second plurality of layers provided between the second surface of the first substrate and a first surface of the second substrate, the second plurality of layers being configured to reflect first light at a first wavelength, the first wavelength being within said passband;
a third plurality of layers provided on the second surface of the second substrate, the third plurality of layers including alternating third and fourth layers, the third layers having a refractive index, nL2, and the fourth layers having a refractive index, nH2, greater than nL2,
wherein the third plurality of layers has a second spectral characteristic, the second spectral characteristic having a second passband, which is defined by passband wavelengths λ1-2passband and λ2-2passband, the second spectral characteristic having an average transmissivity at least equal to 80% over the second passband, the second passband has a second center wavelength between λ1-2passband and λ2-2passband,
the second spectral characteristic having an average optical density greater than over at least one of a lower blocking band of wavelengths and an upper blocking band of wavelengths, the lower blocking band of wavelengths extends from wavelength, λ1-2block, which has an associated optical density equal to 4, to wavelength, λ2-2block, λ2-2block satisfying:


λ2-2block<0.9*((1−x2)/(1+x2))*λ1-2block,


wherein the upper blocking band of wavelengths extends from wavelength λ3-2block, which has an associated optical density equal to 4, to wavelength, λ4-2block, λ4-2block satisfying:


λ4-2block>1.1*((1+x2)/(1−x2))*λ3-2block,



where




  
    
      x
      2
    
    =
    
      
        2
        π
      
      ⁢
      arc
      ⁢
      
        
      
      ⁢
      
        sin
        ⁡
        
          (
          
            
              
                n
                
                  H
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
              -
              
                n
                
                  L
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
            
              
                n
                
                  H
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
              +
              
                n
                
                  L
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
          
          )
        
      
    
  
  ,



wherein a lower edge band of wavelengths is associated with a lower edge portion of the spectral characteristic adjacent the second passband, the lower edge band of wavelengths extending from λ1-2passband to λ1-2block, such that, at wavelength λ1-2-50%, within the lower edge band of wavelengths, the second coating has a transmissivity of 50%,


λ1-2passband, λ1-2block, and λ1-2-50%, satisfy:



(λ1-2passband−λ1-2block)/λ1-2-50%<2%,


wherein an upper edge band of wavelengths is associated with an upper edge portion of the second spectral characteristic adjacent the second passband, the upper edge band of wavelengths extending from λ2-2passband to λ3-2block, such that, at wavelength, λ2-2-50%, within the upper edge band of wavelengths, the second coating has a transmissivity of 50%,


λ2-2passband, λ3-2block, and λ2-250%, satisfy:



(λ3-2block−λ2-2passband)/λ2-2-50%<2%, and


wherein the first wavelength is within the lower blocking band of wavelengths, the third plurality of layers being configured to pass second light having a second wavelength, the second wavelength being within the second blocking band of wavelengths, the second plurality of layers being configured to pass third light, the third light having a third wavelength, which is within the second passband, and a minimum spectral distance between λ1-2block and λ3-2block is greater than 2% of the second center wavelength.

13. An optical device in accordance with claim 12, wherein the second plurality of layers is in contact with the second surface of the first substrate and spaced from the first surface of the second substrate.

14. An optical device in accordance with claim 12, wherein the second plurality of layers is in contact with the first surface of the second substrate and spaced from the second surface of the first substrate.

15. An optical device in accordance with claim 12, wherein the second plurality of layers is in contact with the first surface of the second substrate and with the second surface of the first substrate.

16. An optical device in accordance with claim 12, wherein the optical device includes an adhesive, the second plurality of layers is attached to one of the first surface of the second substrate and the second surface of the first substrate by the adhesive.

17. An optical device in accordance with claim 2, wherein the surface of the substrate is a first surface of the substrate, the substrate being a first substrate further having a second surface, the plurality of layers is a first plurality of layers, the spectral characteristic is a first spectral characteristic, the passband is a first passband, and the center wavelength is a first center wavelength, the optical device further comprising:
a second substrate having a first surface and a second surface;
a second plurality of layers provided between the second surface of the first substrate and a first surface of the second substrate, the second plurality of layers being configured to pass first light at a first wavelength, the first wavelength being within said passband;
a third plurality of layers provided on the second surface of the second substrate, the third plurality of layers including alternating third and fourth layers, the third layers having a refractive index, nL2, and the fourth layers having a refractive index, nH2, greater than nL2,
wherein the third plurality of hard coating layers has a second spectral characteristic, the second spectral characteristic having a second passband, which is defined by passband wavelengths λ1-2passband and λ2-2passband, the second spectral characteristic having an average transmissivity at least equal to 80% over the second passband,
the second spectral characteristic having an average optical density greater than 4 over at least one of a lower blocking band of wavelengths and an upper blocking band of wavelengths, the lower blocking band of wavelengths extends from wavelength, λ1-2block, which has an optical density equal to 4, to wavelength, λ2-2block, λ2-2block satisfying:


λ2-2block<0.9*((1−x2)/(1+x2))*λ1-2block,


wherein the upper blocking band of wavelengths extends from wavelength λ3-2block, which has an associated optical density equal to 4, to wavelength, λ4-2block, λ4-2block satisfying:


λ4-2block>1.1*((1+x2)/(1−x2))*λ3-2block,



where




  
    
      x
      2
    
    =
    
      
        2
        π
      
      ⁢
      arc
      ⁢
      
        
      
      ⁢
      
        sin
        ⁡
        
          (
          
            
              
                n
                
                  H
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
              -
              
                n
                
                  L
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
            
              
                n
                
                  H
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
              +
              
                n
                
                  L
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
          
          )
        
      
    
  
  ,



wherein a lower edge band of wavelengths is associated with a lower edge portion of the spectral characteristic adjacent the second passband, the lower edge band of wavelengths extending from λ1-2passband to λ1-2block, such that, at wavelength λ1-2-50%, within the lower edge band of wavelengths, the second coating has a transmissivity of 50%,


λ1-2passband, λ1-2block, and λ1-2-50%, satisfy:



(λ1-2passband−λ1-2block)/λ1-2-50%<2%,


wherein an upper edge band of wavelengths is associated with an upper edge portion of the second spectral characteristic adjacent the second passband, the upper edge band of wavelengths extending from λ2-2passband to λ3-2block, such that, at wavelength, λ2-2-50%, within the upper edge band of wavelengths, the second coating has a transmissivity of 50%,


λ2-2passband, λ3-2block, and λ2-250%, satisfy:



(λ3-2block−λ2-2passband−)/λ2-2-50%<2%, and


wherein the first wavelength is within the lower blocking band of wavelengths, the third plurality of layers being configured to pass second light having a second wavelength, the second wavelength being within the second blocking band of wavelengths, the second plurality of layers being configured to reflect third light, the third light having a third wavelength, which is within the second passband, and a minimum spectral distance between λ1-2block and λ3-2block is greater than 2% of the second center wavelength.

18. An optical device in accordance with claim 17, wherein the second plurality of layers is in contact with the first surface of the first substrate and spaced from the first surface of the second substrate.

19. An optical device in accordance with claim 17, wherein the second plurality of layers is in contact with the first surface of the second substrate and spaced from the first surface of the first substrate.

20. An optical device in accordance with claim 17, wherein the second plurality of layers is in contact with the first surface of the second substrate and with the first surface of the first substrate.

21. An optical device in accordance with claim 17, wherein optical device includes an adhesive, the second plurality of layers is attached to one of the first surface of the second substrate and the first surface of the first substrate by the adhesive.

22. An optical device in accordance with claim 17, wherein the first substrate includes a first right angle prism and the second substrate includes a second right angle prism, the first and second right angle prisms being oriented relative to one another to constitute a substantially cubical structure.

23. A fluorescence spectroscopy system, comprising:
a source configured to supply light;
an optical filter configured to transmit said light, such that said light is directed toward a sample, the optical filter including:
a substrate having a surface; and
a plurality of layers provided on the surface of the substrate, the plurality of hard-coating layers including alternating first and second layers, the first layers having a first refractive index, nL, and the second layers having a second refractive index, nH, greater than the first refractive index,
wherein the plurality of hard-coating layers has a spectral characteristic, the spectral characteristic having a passband, said light having a wavelength within the passband, the passband being defined by a first passband wavelength λ1passband and a second passband wavelength λ2passband, the spectral characteristic having an average transmissivity at least equal to 80% over the passband and the passband having a center wavelength between λ1passband and λ2passband,
the spectral characteristic having an average optical density greater than 4 over at least one of first and second blocking bands of wavelengths, wherein the first blocking band of wavelengths extends from a first blocking wavelength, λ1block, having an associated optical density equal to 4 to a second blocking wavelength, λ2block, the second blocking wavelength satisfying:


λ2block<0.9*((1−x)/(1+x))*λ1block,


wherein the second blocking band of wavelengths extends from a third blocking wavelength, λ3block, having an associated optical density equal to 4 to a fourth blocking wavelength, λ4block, the fourth blocking wavelength satisfying:


λ4block>1.1*((1+x)/(1−x))*λ3block,




where




  
    x
    =
    
      
        2
        π
      
      ⁢
      arc
      ⁢
      
        
      
      ⁢
      
        sin
        ⁡
        
          (
          
            
              
                n
                H
              
              -
              
                n
                L
              
            
            
              
                n
                H
              
              +
              
                n
                L
              
            
          
          )
        
      
    
  
  ,




wherein a first edge band of wavelengths is associated with a first edge portion of the spectral characteristic adjacent the passband, the first edge band of wavelengths extending from λ1passband to λ1block, such that, at a first transmission wavelength, λ1-50%, within the first edge band of wavelengths, the coating has a transmissivity of 50%,


λ1passband, λ1block, and λ1-50%, satisfy:



(λ1passband−λ1block)/λ1-50%<2%, and


wherein a second edge band of wavelengths is associated with a second edge portion of the spectral characteristic adjacent the passband, the second edge band of wavelengths extending from λ2passband to λ3block, such that, at a second transmission wavelength, λ2-50%, within the second edge band of wavelengths, the plurality of layers has a transmissivity of 50%,


λ2passband, λ3block, and λ2-50%, satisfy:



(λ3block−λ2passband)/λ2-50%<2%, and


a minimum spectral distance between λ1block and λ3block is greater than 2% of the center wavelength; and

a detector configured to sense emitted light from the sample in response to said light supplied by the source.

24. A fluorescence spectroscopy system, comprising:
a source configured to supply first light, said first light being directed toward a sample such that the sample emits second light;
an optical filter configured to transmit said second light, the optical filter including:
a substrate having a surface; and
a plurality of layers provided on the surface of the substrate, the plurality of hard-coating layers including alternating first and second layers, the first layers having a first refractive index, nL, and the second layers having a second refractive index, nH, greater than the first refractive index,
wherein the plurality of hard-coating layers has a spectral characteristic, the spectral characteristic having a passband, the second light having a wavelength within the passband, the passband being defined by a first passband wavelength λ1passband and a second passband wavelength λ2passband, the spectral characteristic having an average transmissivity at least equal to 80% over the passband, and the passband having a center wavelength between λ1passband and λ2passband,
the spectral characteristic having an average optical density greater than 4 over at least one of first and second blocking bands of wavelengths, wherein the first blocking band of wavelengths extends from a first blocking wavelength, λ1block, having an associated optical density equal to 4 to a second blocking wavelength, λ2block, the second blocking wavelength satisfying:


λ2block<0.9*((1−x)/(1+x))*λ1block,


wherein the second blocking band of wavelengths extends from a third blocking wavelength, λ3block, having an associated optical density equal to 4 to a fourth blocking wavelength, λ4block, the fourth blocking wavelength satisfying:


λ4block>1.1*((1+x)/(1−x))*λ3block,




where




  
    x
    =
    
      
        2
        π
      
      ⁢
      arc
      ⁢
      
        
      
      ⁢
      
        sin
        ⁡
        
          (
          
            
              
                n
                H
              
              -
              
                n
                L
              
            
            
              
                n
                H
              
              +
              
                n
                L
              
            
          
          )
        
      
    
  
  ,




wherein a first edge band of wavelengths is associated with a first edge portion of the spectral characteristic adjacent the passband, the first edge band of wavelengths extending from λ1passband to λ1block, such that, at a first transmission wavelength, λ1-50%, within the first edge band of wavelengths, the coating has a transmissivity of 50%,


λ1passband, λ1block, and λ1-50%, satisfy:



(λ1passband−λ1block)/λ1-50%<2%, and


wherein a second edge band of wavelengths is associated with a second edge portion of the spectral characteristic adjacent the passband, the second edge band of wavelengths extending from λ2passband to λ3block, such that, at a second transmission wavelength, λ2-50%, within the second edge band of wavelengths, the plurality of layers has a transmissivity of 50%,
λ2passband, λ3block, and λ2-50%, satisfy:


(λ3block−λ2passband)/λ2-50%<2%, and



a minimum spectral distance between λ1block and λ3block is greater than 2% of the center wavelength; and
a detector configured to sense the second light.