# Patent

## Title
Optical thin-film polarizing bandpass filter

## Abstract

Optical components and their methods of manufacture are provided, including a first stack of layers configured to exhibit a first stop band for s-polarized radiation and a second stop band for p-polarized radiation incident on the first stack of layers at an oblique angle, a second stack of layers configured to exhibit a third stop band for s-polarized radiation and a fourth stop band for p-polarized radiation incident on the second stack of layers at the oblique angle, where the cut-on wavelength for the first stop band is approximately equal to or larger than the cut-off wavelength for the third stop band. Optical components are further provided to include extended blocking functionality, and to permit stress balancing in thin-film coatings on opposite sides of a substrate.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 61/161,984, filed Mar. 20, 2009, the contents of which are incorporated herein by reference.


DESCRIPTION
1. Field
This disclosure relates to materials, components, and methods directed to the fabrication and use of polarizing bandpass filters.
2. Background
Often it is useful to isolate a polarization state of light or other radiation in a system. For example, and without limitation, many interferometric and spectroscopic systems are sensitive to light polarization. In addition, some detectors in optical systems are highly sensitive to light polarization. Polarization can even play a role in laser-based cutting, for example, in which the shape of the cutting region becomes highly anisotropic when polarized light is used. Linear or even elliptical (including circular) states of polarization can be obtained using a “polarizer,” or a component that transmits an identified state of polarization while absorbing, reflecting, or deviating light with an orthogonal state of polarization to that state identified. A perfect polarizer exhibits 100% transmission of the desired state of polarization and complete extinction of the undesired state. Real polarizers exhibit less than 100% transmission of the desired state and incomplete blocking of the undesired state. Often the most important parameter that describes a polarizer is the “contrast ratio,” or the ratio of the transmission through a pair of identical aligned polarizers to that through the same pair of polarizers with their polarization axes crossed. The inverse of the contrast ratio is called the “extinction ratio.” Conventional contrast ratios can vary from less than 100:1 to as high as 100,000:1. (As used herein, the value of base 10 logarithms of the contrast ratio or, equivalently, −1×base 10 logarithm of the transmission of a filter (measured between 0 and 1), is referred to as “Optical Density” or “OD.”)
Often, it is also useful to isolate a certain wavelength band of light in the system. For example, often it is desirable to configure a system such that a detector that is intended to detect only certain wavelengths receive as input only a narrow range of wavelengths, while eliminating, as input to the detector, as much light at other wavelengths as possible, as such other light is considered “noise.” Optical components that isolate one or more bands of wavelengths are called “bandpass filters.” The width of the band for conventional near-UV, visible, and near-IR optical bandpass filters can range from less than 1 nm to a few nm (or less than about 1% of the center wavelength of the band) for so-called “narrowband” filters to several tens of nm (about 1 to 10% of the center wavelength) for most bandpass filters—such as those used in fluorescence detection and imaging systems. Some bandpass filters can even be several tens of % of the center wavelength wide. Filters much wider than several tens of % are possible, but are not typically referred to as bandpass filters. The blocking might cover only a limited range of wavelengths on either side of the band, or it might cover a very wide range of wavelengths. For example, a bandpass filter designed to transmit the laser line of a semiconductor laser but block the broader spontaneous emission noise on either side of the laser line needs to block light only over the range of spontaneous emission—typically about 100 nm—and thus might have a limited range of blocking. However, a bandpass filter used in front of a silicon-based detector (such as a photodiode or CCD camera) often needs to cover the entire range of sensitivity of the detector—from the UV up to about 1100 nm. The level of blocking is also application dependent—in some cases an OD of 2 to 4 is sufficient, but for applications like fluorescence spectroscopy and imaging, where the signal can be many orders of magnitude smaller than the excitation light intensity as well as surrounding ambient light noise, often an OD of 6 or even higher is necessary.
Conventionally, in order to achieve both a polarization function and a bandpass filtering function, it has been necessary to use two separate optical components: a polarizer and a bandpass filter.
Considering first the polarization function, one common type of polarizer is a stretched polymer film polarizer, which may be understood as a function of the charge conduction. For example, an array of aligned polymers that efficiently conduct charge is understood to substantially absorb light with its electric field vibrating in the direction parallel to the alignment direction of the polymers, and to transmit light with its electric field vibrating in the orthogonal direction. The result of the interaction is that the transmitted light is linearly polarized in the direction orthogonal to the alignment direction of the array of stretched polymers.
For exemplary purposes only, other types of conventional polarizers include: a metal-based wire-grid polarizer used for the visible and NIR (“near infra-red”) wavelength regions; a “POLARCOR” linear polarizer, which utilizes absorption from aligned silver nano-particles in glass; a dichroic sheet polarizer, constructed by laminating a thin, stretched, and dyed polymer film between two polished, antireflection-coated glass windows, which—similar to the stretched polymer film polarizers—are based on preferential absorption of one linear polarization; a birefringence-based crystal polarizer, which is most commonly made with calcite crystals, but may also made with BBO and YVO4 crystals, including Glan-Laser and Glan-Thompson polarizers. A Glan-Thompson polarizer utilizes epoxy to bond together two birefringent prisms, whereas a Glan-Laser polarizer uses an air-space between the two prisms to enable higher laser damage thresholds. These polarizers operate on the principle that the light is incident at certain angles of incidence on the two interfaces formed by a gap between two identical birefringent crystals. In a Glan-Thompson polarizer these angles are sufficiently large that p-polarized light is totally internally reflected and thus rejected, whereas s-polarized light is transmitted. In a Glan-Laser polarizer, these angles are near or equivalent to Brewster's angle for p-polarized light, which is therefore highly transmitted, whereas s-polarized light is totally internally reflected and thus highly rejected. There are also other types of birefringent polarizers, all of which operate on the principle that light rays of one polarization—incident upon birefringent material—will be deviated from rays of the orthogonal polarization.
As a further example, optical thin-film polarizers are understood to achieve discrimination using interference from a dielectric optical thin-film coating. These polarizers operate near the edge of a “stop band” region of high reflection (as may result from a quarter-wave stack of layers, or a nearly quarter-wave stack of layers). For example, when an optical thin-film polarizer is used at an oblique angle of incidence (“AOI”), the performance for each plane of polarization differs. For a quarter-wave (QW) stack consisting of multiple layers with each layer having optical thickness equal to a quarter-wavelength of some reference wavelength and refractive index alternating between a high and a low value, the most prominent difference appears close to edge of the fundamental stop band (the highly reflective region approximately centered on the reference wavelength). While the effective phase thickness at an oblique angle is independent of polarization, the width of the fundamental stop band for p-polarized light becomes narrower, while the width of the fundamental stop band for s-polarized light becomes wider, such that each edge of the stop band “splits.” Such a “split” is illustrated in FIG. 1. Curve 100 (solid line) is an exemplary stop band associated with light at normal incidence on a QW stack. Curves 110 (dashed line) and 120 (dotted line) illustrate the same stop band for light incident at 45 degrees on the QW stack. In changing the AOI from 0 degrees to 45 degrees, the stop band (curve 100) shifts toward shorter wavelengths, and becomes narrower for p-polarized light (dashed curve 110 depicting a fundamental p-polarized stop band 107 bounded by cut-off wavelength 102 and cut-on wavelength 101) and wider for s-polarized light (dotted curve 120 depicting a fundamental s-polarized stop band 117 bounded by cut-off wavelength 112 and cut-on wavelength 111). As used herein, the width of the fundamental stop band is defined as the difference between the corresponding cut-on and cut-off wavelengths. Moreover, as used herein, the cut-on (cut-off) wavelength is defined as the first wavelength above (below) the reference wavelength that reaches 50% transmission. Also, it should be noted that the spectrum associated with a QW stack comprised of exactly quarter-wavelength-thick layers exhibits significant “ripple,” or rapid variation of the transmission, in the regions outside the stopband, which is not illustrated in FIG. 1. This ripple can be almost eliminated by optimizing the layer thicknesses as described in U.S. Pat. Nos. 7,068,430 and 7,123,416, both herein incorporated by reference, resulting in layers that are approximately, but not exactly, a quarter-wavelength thick. Herein, the term “QW stack” is understood to include both stacks of exactly quarter-wavelength-thick layers and stacks that have been optimized to eliminate ripple outside the stopband and are thus comprised of approximately quarter-wavelength-thick layers.
Within the above described split, there is a narrow range of wavelengths for which there is both high-transmission of p-polarized light (just outside the stop band for p-polarized light) and high reflection/attenuation of s-polarized light (just inside the stop band for s-polarized light). Beyond the cut-on edge of the fundamental stop band for s-polarized light, the plate polarizer generally has high transmission for both polarizations. Coatings that achieve such an effect can be applied to a single substrate (a so-called “plate polarizer”) or to the hypotenuse of a right-angle prism, which when combined with a second such prism, create a cube (a so-called “cube beamsplitter polarizer”).
Many conventional polarizers are understood to exhibit limited contrast ratios. For example, a metal-based wire-grid polarizer used for the visible and NIR wavelength regions will typically have a contrast ratio of about a few hundreds-to-one. The typical contrast ratio for polymer-based linear polarizers is typically less than a few thousands-to-one at best. A “POLARCOR” linear polarizer can achieve a contrast ratio of up to 10,000:1. A dichroic sheet polarizer can exhibit a contrast ratio up to 10,000:1. Birefringence-based Calcite crystal polarizers, including Glan-Laser and Glan-Thompson Calcite polarizers, can also achieve contrast ratios better than 100,000:1. All of these examples achieve polarization discrimination either by preferential absorption or by birefringence. In addition, commercially available thin-film-based plate polarizers and cube beamsplitters have contrast ratios from a few hundreds-to-one up to about 1000:1.
Moreover, conventional polarizers known to exhibit high contrast ratios are understood to have limited acceptance angles. For example, birefringence-based polarizers, which are known to offer the highest contrast ratios available, operate with high contrast and simultaneously high transmission of the desired polarization over only a narrow range of angles of incidence. In other words, there exists a trade-off between contrast ratio and acceptance angle. Typical acceptance angles (as used herein, the half-angle, measured from the nominal AOI) can range from less than about 10 degrees for Glan-Thompson polarizers to less than 1 to several degrees for Glan-Laser polarizers. The reason for this limitation in Glan-Laser polarizers, for example, is that at lower AOIs the s-polarized light is no longer totally internally reflected, whereas at higher AOIs the transmission of the p-polarized light decreases substantially. As a result, some of the light outside of the acceptance angle range is transmitted as unpolarized light, and some of the light outside of the acceptance angle range is reflected as unpolarized light. This behavior can present problems in systems where even small amounts of signal light or stray light are present at higher angles of incidence, since the undesired polarization leaks through.
In addition, conventional polarizers known to exhibit high contrast ratios are understood to have limited clear apertures. Again, birefringence-based polarizers have maximum clear apertures substantially less than 1 inch (typically 15 mm maximum), due to the difficulty and cost of producing high-quality, uniform, single-crystal Calcite.
Moreover, conventional polarizers offer poor control over beam deviation: All non-thin-film based polarizers (those based on selective absorption and birefringence) have limited control over the transmitted wavefront of an optical beam, and in particular tend to cause the beam to deviate from the optical axis. Most conventional polarizers cannot achieve a specification of better than one to several arc minutes of beam deviation.
Further, conventional polarizers do not offer convenient collection of the orthogonal polarization. For example, in many systems it is desirable not only to eliminate one polarization of light to achieve a polarized transmitted beam, but to split the light into two orthogonal polarizations. This function cannot be performed with polarizers based on absorption of the undesired, orthogonal polarization. Such “polarizing beamsplitters” are possible with birefringent and thin-film-interference-based polarizers. However, for birefringent polarizers, in general the deviation angle of the orthogonal polarization is an unusual angle determined by the birefringence of the prisms and the index of refraction—rarely if ever can it be made to equal 90 degrees, which is a convenient angle for the compact alignment of an optical system. Thin-film polarizers can be designed to be used a 45 degrees AOI, thus deviating the orthogonal light 90 degrees, both in plate and cemented (or air-spaced) right-angle prism cube configurations.
A paper which discusses development of optimization strategy for dielectric thin-film coatings, and which further discloses an example of a thin-film polarizing beamsplitter and mirror is H. Fabricius, “Synthesis and functioning of SMART coatings for application in compact instruments and sensors,” DOPS-Nyt 1-2001, p. 28-38, 2001 (The Quarterly Journal of the Danish Optical Society). This paper discloses, in part, the use of merit function optimization in the design of thin-film coatings. In particular, this paper discloses use of a linear summation merit function to include different properties of a thin film coating. This paper also discloses application of the first-order optimization technique (simplex) and the second-order optimization technique (Newton) for coating design—which includes calculation of up to the second-order derivative of the disclosed merit function. As acknowledged in the paper, however, it becomes increasingly difficult, if not impossible, to guess at a suitable initial structure in order to arrive at a final coating with complex functionalities. For a coating that is intended to exhibit complex functionality, referred to as SMART coatings, the paper suggests that a synthesis technique rather than optimization technique is needed. To that end, the paper discloses and applies the so-called “needle-synthesis” technique, developed by A. V. Tichonravov. Pursuant to this technique, a designer conventionally starts with a single thick layer. Then, one or more near zero-thickness layers, so-called “needle layers,” are inserted into the coating design. The position at which a needle layer is inserted may be selected according to whether the value of a function (which is connected to a derivative of the merit function) is less than zero at that position. Once inserted, optimization routines may be used to improve the design. As a result, the thicknesses of these needle layers are allowed to grow if helpful to improving the design. Under the needle-synthesis technique, the process is repeated until the design meets the requirement or some other termination criterion. Depending upon the design requirements or termination criterion, accordingly, the resulting structure can include a wide diversity of layer thicknesses—including many relatively thick layers and many relatively thin layers. The paper discloses a thin-film polarizing beamsplitter designed by application of the needle-synthesis technique, second-order optimization of the reflection and the transmission in the spectral range from 600 nm to 740 nm, and is based on a material set of TiO2 and SiO2. The resulting polarizing beamsplitter is disclosed as having a layer count of 53. At 45 degrees AOI, the paper discloses that the filter exhibits high transmission for p-polarization from 620 nm to about 640 nm, and exhibits less than 1% transmission for s-polarization over the same wavelength range. The design of the polarizing beamsplitter disclosed in the paper further achieves a contrast ratio of approximately 1000:1, and requires approximately 10 nm for the p-polarization edge to change from 90% transmission to 0.1%. The out-of-band blocking exhibited by the disclosed polarizing beamsplitter extends from 600 nm to 740 nm.
It is desirable, however, for a combined polarizing bandpass filter to exhibit a contrast ratio over 1,000,000:1, to exhibit steep edges, and to exhibit extended blocking over a wide range of wavelengths. Moreover, a design which includes a wide diversity of layer thicknesses—including many relatively thick layers and many relatively thin layers—is more difficult to manufacture than, for example, a design made up entirely of approximate quarter-wave thick layers. Further, when designing a polarizing bandpass filter intended to exhibit such specific, combined, complex functionalities, it is desirable to utilize a technique that allows for smaller perturbations in the design steps than that permitted by the needle-synthesis technique.
Furthermore, polarizers are understood to have limited transmission of p-polarized light: Most polarizers, especially those based on absorption, have difficulty achieving transmission of even 90% (for the best, dichroic sheet polarizers). Thin-film and birefringence-based polarizers can achieve transmission above 90%, but generally, at best, no more than between 90 and 95%. For birefringence-based polarizers, such as the Glan-Laser polarizers, s-polarized light must be totally reflected, which occurs over a particular range of angles, and generally the Brewster's angle where p-polarized light is completely transmitted does not coincide with this range of angles, thus limiting the transmission of the desired p-polarized light.
Further still, polarizers are understood to have limited laser damage thresholds (LDT). Most polarizers cannot withstand continuous-wave (cw) laser intensities in excess of about 1 W/cm2, nor can most polarizers withstand pulsed laser energy densities (for low repetition rate,  ̃10 ns pulses) above nJ/cm2. Certain polarizers specially designed to have no absorptive materials in the laser path, such as Glan-Laser Calcite polarizers, can have higher LDT values (up to kW/cm2 for cw lasers and J/cm2 for pulsed lasers).
Yet further, polarizers typically have poor physical durability and optical quality. Most absorption-based polarizers are based on plastics or hybrid glass-plastic laminated structures, and thus have limited environmental durability. Furthermore, birefringent crystal polarizers have limited durability since crystals like calcite are very soft and easily cleave or break. These components also tend to have limited optical quality, since defects in bulk crystals like calcite lead to bubbles, striae, and other optical inhomogeneities, which cause degradation of the polarization, transmission loss due to scattering, and distortion of an optical beam, especially when used for imaging applications.
More information on polarizers can be found in numerous text books (such as Polarized Light in Optics and Spectroscopy, by David S. Kliger and James W. Lewis, Academic Press, 1990) or internet-accessible on-line resources that describe available products (such as the website of Meadowlark Optics, Inc.).
Considering next a conventional bandpass filtering function, thin-film bandpass filters capable of performing bandpass filtering functionality have been previously described in, for example, U.S. Pat. No. 6,809,859, which disclosure is incorporated herein in its entirety by reference. For example, filter 1900 illustrated in FIG. 19 includes a long-wave-pass filter 1902 deposited directly on a first surface 1904 of a colored glass substrate 1906 and a short-wave-pass filter 1908 deposited directly on a second surface 1910 of the colored glass substrate. Advantageously, the filters 1902 and 1908 are each formed from “hard coatings.” With reference also to FIG. 20, for example, the long-wave-pass filter 1902 may be formed by depositing alternating hard coating layers of high 2000-1, 2000-2 . . . 2000-n and low 2002-1, 2002-2 . . . 2002-x index of refraction material. It is to be understood that the short-wave-pass filter will have a similar construction, i.e. alternating high and low index hard coating layers. The colored glass substrate absorbs light at wavelengths well removed from the bandpass region or filter edges, and is used to extend the spectral region of high blocking (high optical density) if desired; for example, the colored glass might absorb UVwavelengths, or IR wavelengths, or both. Such substrates are commercially available from such vendors as Schott Glass Corp. Each of the layers 2000-1, 2000-2 . . . 2000-n and low 2002-1, 2002-2 . . . 2002-x has an associated optical thickness, defined by the product of its physical thickness times its refractive index. Although the embodiments shown in the drawings are not drawn to scale, the hard coating layers illustrated in FIG. 19 may be, for example, one quarter wavelength in optical thickness. Depending on desired transmission characteristics, however, non-quarter-wave optical thicknesses and/or varying optical thicknesses may also be provided.
Bandpass filters are not known to function as polarizers. Specifically, bandpass filters are not known to offer any substantial polarization contrast. As a result, and as stated above, optical systems that require both bandpass and polarizer functionality at the same location have used at least two separate components, leading to increased optomechanical system complexity (additional mounting requirements, alignment considerations, stray-light control problems, etc.), lower overall transmission, increased system weight, and, as a result, increased overall cost (because of the need for multiple components as well as the increased complexity and weight).
Accordingly, there is a need to provide a solution for systems and operations that benefit from both a polarizing function and a bandpass filtering function with reduced system complexity, increased transmission, and/or decreased system weight.
SUMMARY
In an embodiment consistent with the present disclosure, the above need can be achieved by the manufacture and use of an optical thin-film filter that operates at an oblique angle of incidence and exhibits high transmission of light with p-polarization and simultaneously deep attenuation of light with s-polarization within a certain wavelength range, with a p-to-s polarization contrast ratio better than 1,000,000:1. Outside of the same wavelength range, materials and components consistent with the present disclosure exhibit deep blocking—better than optical density (OD) 6—for light with all states of polarization. The blocking region can be further expanded by the use of extended blocking, as previously described in U.S. Pat. No. 6,809,859, incorporated herein above by reference, to enhance performance and/or incorporate additional desirable functionality. Therefore, materials and components consistent with the present disclosure function as both a bandpass filter for p-polarization and a broadband blocking filter for s-polarization.
Materials and components consistent with the present disclosure are configured to function as a polarizer with a very high contrast ratio between the desired state of polarization and the undesired state of polarization. Furthermore, materials and components consistent with the present disclosure also are configured to function as a bandpass filter, simultaneously and/or cooperatively with its function as a polarizer.
Materials and components consistent with the present disclosure comprise two QW stacks, configured such that the cut-on wavelength of the fundamental stop band for s-polarization associated with the first QW stack is approximately equal to or longer than the cut-off wavelength of the fundamental stop band for s-polarization associated with the second QW stack, and thereby configured such that a bandpass filter is formed for p-polarization while light with s-polarization is blocked inside this passband subject to a relatively high contrast ratio.
Furthermore, materials and components consistent with the present disclosure comprise two QW stacks configured as described above and further configured using conventional optimization routines known to those skilled in the art of thin-film design (such as TFCalc) to—among other things and without limitation—optimize the layer structure to further improve transmission and also to minimize passband ripple for p-polarization.
Consistent with the present disclosure, two thin-film QW stacks 2102 and 2108 as configured above can be deposited on the opposite sides of a single substrate 1906 as depicted in FIG. 21. They can also be deposited on the same side of substrate 1906 as a single coating consistent with the present disclosure. The single-sided coating approach of FIG. 22 eliminates beam walk-off between light reflected from opposite sides of the substrate. It also makes it possible to leave the uncoated side of the substrate 1906 available for another coating to further enhance the performance (e.g., an antireflection coating) or to provide additional functionality. In one embodiment consistent with the present disclosure, as shown in FIG. 23, the second side of the substrate is coated with an extended blocking coating 2300, as previously described in U.S. Pat. No. 6,809,859, herein above incorporated by reference, to further expand the blocking region. For exemplary purposes only, a typical Si photodiode has a sensitivity to wavelengths spanning from the UV up to about 1100 nm. By applying an extended blocking coating 2300 to cover the entire range of sensitivity of such a detector, the performance of materials and components consistent with the present disclosure is further enhanced in connection with such an exemplary Si photodiode. As a further example, and without limitation, it can be desirable to suppress the residual intensity from additional laser wavelengths or wavelength harmonics present in a system, such as the 1064 nm fundamental wavelength of a frequency-doubled 532 nm Nd:YAG laser. Consistent with the present disclosure, this can be achieved by designing the coating on the second side of the substrate as illustrated in the exemplary 532 nm filter as discussed further below.
Additional functionality—such as resistance to substrate bending—can also be provided through the application of such a coating on the second side of a substrate. By way of example only, coatings that are generated using energetic ion-beam sputtering processes typically exhibit a relatively high compressive stress. Such stress in the coating can further cause bending of the substrate. For imaging applications, and when applied to a reflected beam, bending of the underlying substrate in the filter can contribute to the wavefront error and degradation of the image quality. When applied to a transmitted beam, the effect of an underlying bent substrate in a filter component is equivalent to an effective substrate wedge, which can give rise to beam deviation. Consequently, it can be desirable to minimize substrate bending. Consistent with the present disclosure, a coating on the second side of the substrate, which can provide enhanced performance and/or additional functionality, also can be configured to balance the coating stress on the underlying substrate from the first side—where a polarizing bandpass filter consistent with the present disclosure may be deposited. In one embodiment, the coating on the second side is configured to exhibit a coating stress on the underlying substrate that matches the coating stress from the first side. Consistent with the present disclosure, such a balanced design strategy can reduce substrate bending and minimize reflected wavefront error in reflection and beam deviation in transmission. The performance of materials and components consistent with the present disclosure may be further enhanced by selecting a quality glass substrate, chosen to have a very small substrate wedge, as previously described in U.S. Pat. No. 7,411,679, herein incorporated by reference. As described herein and utilizing a balanced design approach and a glass substrate with a wedge less than 4.4 arc second, materials and components consistent with the present disclosure can achieve less than 10 arc seconds beam deviation over the entire range of their operation.
As described herein, in an embodiment, materials and components consistent with the present disclosure combine the functions of a polarizer and bandpass filter in a single component utilizing a single substrate of glass with one or both sides coated with numerous discrete multi-layer thin films. The thin film layers may be deposited using any of a number of conventional thin-film deposition techniques capable of making highly multi-layer optical coatings, such as ion-assisted ion-beam sputtering.
Materials and components consistent with the present disclosure can be a valuable component in any optical system that requires isolation of a single-state of polarization and a band of wavelengths of light. Without limitation, examples of systems that can benefit from materials and components consistent with the present disclosure include: (a) fluorescence detection systems as described below; (b) laser clean-up filters; (c) laser communication detection systems; (d) harmonic-generation imaging systems; and (e) polarization and wavelength multiplexing systems.
For example, a fluorescence detection system which measures the degree of polarization of fluorescence emission can benefit from the present disclosure. Such measurements can indicate whether or not one chemical species binds to another species with a fluorescent label attached. By way of example only, a polarized excitation source can excite a certain orientation (dipole moment) of a fluorescent molecule under study. Ideally, such an excited molecule would also emit polarized fluorescence, except that such molecules may be very quickly “depolarized” due to motion. However, when another species binds to the labeled target, the target becomes much less mobile so that the degree of polarization of the emitted light increases (i.e., the degree of “depolarization” of the labeled target is reduced). Consequently, valuable information can be obtained by measuring the degree of polarization of the target as a function of time. This technique is known to be used in both high-speed fluorescence detection (so-called microplate readers) as well as in microscopy.
Furthermore, a complete laser clean-up filter can benefit from the present disclosure by passing a single, desired polarization output from a laser at the desired laser wavelength while blocking both light at the laser wavelength of the orthogonal polarization as well as light of all polarization states at wavelengths adjacent to the laser line. The blocked light is considered “noise” in systems based on such lasers, and the better these noise sources can be blocked, the better the signal-to-noise ratio of the system.
Moreover, a laser communication detection system can benefit from the present disclosure, where such a system is designed to receive a laser-based signal of a single polarization, in which it is useful to block incident light at wavelengths other than the laser wavelength (such as ambient light from the sun and other sources), as well as undesired orthogonally polarized light at the laser wavelength. In such systems, for example, a large ratio between filter transmission and blocking, as well as a high polarization contrast ratio, lead directly to improved signal-to-noise ratio of the communication system.
Further, a harmonic-generation imaging system, such as may be used for material characterization or biological research, can benefit from the present disclosure. For example, in second-harmonic-generation (SHG) microscopy for biological imaging, a laser may be used to illuminate a sample of interest (e.g., at around 810 nm), and a microscope may be used to collect and image the light at one half of the illumination wavelength (e.g., at around 405 nm). The efficiency of the SHG process can benefit from the present disclosure. For example, the polarization dependence can be used to determine unique characteristics of the biological material not easily measurable with standard or even fluorescence microscopy. Moreover, high-fidelity images require isolation of the frequency-doubled wavelength as well as relatively high polarization contrast from a component that does not distort the high-quality imaging path.
Further still, a simultaneous polarization and wavelength multiplexing system can benefit from the present disclosure. For example, high-power laser applications such as laser materials processing can be limited by power scaling characteristics of the laser—in which obtaining higher and higher total power may sacrifice brightness (where brightness is the power per unit area, per unit wavelength interval, per unit beam solid angle). One way to increase brightness is to combine many laser beams together, each with a slightly different wavelength (so-called “wavelength multiplexing”), and using two orthogonal polarizations at each wavelength (so-called “polarization multiplexing”). Materials and components consistent with the present disclosure are ideal components for achieving simultaneous polarization and wavelength multiplexing.
A polarizing bandpass filter (PBF) consistent with the present disclosure may be used at an oblique AOI, such as 45 degrees, where for many applications only the transmitted light is of interest. There will, however, also be a reflected beam, deviating from the transmitted beam by two times the angle of incidence, or 90 degrees in the case of a filter used at a 45 degree AOI. Thus, a PBF consistent with the present disclosure can act like a beamsplitter for some applications—where it transmits p-polarization within a band and reflects s-polarization within the same band. Consequently, some applications can also take advantage of this reflected beam, even though the reflected beam, while primarily s-polarized, may also contain p-polarized light (that is, it may contain approximately 1% of the p-polarized incident light), and thus may not have the same s-to-p contrast ratio in the reflected beam as the p-to-s contrast ratio in the transmitted beam. However, if a second PBF consistent with the present disclosure is used in series in the reflected path of the first PBF consistent with the present disclosure, aligned so that the s-polarization reflected off of the first PBF becomes p-polarization when transmitted through the second PBF consistent with the present disclosure, then the combination of the two PBFs can yield two output beams containing the orthogonal polarizations of the input beam and with greater than 1,000,000:1 contrast ratio for both beams. For the simultaneous polarization and wavelength multiplexing system, a PBF consistent with the present disclosure acts like a beam combiner.
Additional features and advantages will be set forth in part in the description which follows, being apparent from the description of or learned by practice of the disclosed embodiments. The features and advantages will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the scope of the embodiments, as claimed.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments and, together with the description, serve to explain the features, advantages, and principles of the disclosed embodiments.
FIG. 1 is an exemplary illustration of an edge split associated with light at an oblique AOI on a QW stack;
FIG. 2 is an exemplary illustration of two different stop bands associated with light at a 45° AOI from two different thin-film coatings or from two different portions of the same thin-film coating consistent with an embodiment of the present disclosure;
FIG. 3 is an exemplary illustration of the net result of combining the two different thin-film coatings or combining two different portions of the same thin-film coating from FIG. 2 consistent with an embodiment of the present disclosure;
FIG. 4 depicts the calculated transmission percentage for both s-polarization and p-polarization of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1;
FIG. 5 depicts the calculated Optical Density (OD) for both s-polarization and p-polarization of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1;
FIG. 6 depicts both the calculated and measured p-polarization transmission percentage of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1;
FIG. 7 depicts both the calculated and measured p-polarization Optical Density (OD) of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1;
FIG. 8 depicts both the calculated and measured s-polarization transmission percentage of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1;
FIG. 9 depicts both the calculated and measured s-polarization Optical Density (OD) of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1;
FIG. 10 depicts the calculated Optical Density (OD) for both s-polarization and p-polarization of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1, with curves plotted for light incident at 11 different angles ranging from 40 to 50 degrees;
FIG. 11 depicts the calculated transmission percentage for both s-polarization and p-polarization of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2;
FIG. 12 depicts the calculated Optical Density (OD) for both s-polarization and p-polarization of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2;
FIG. 13 depicts the calculated transmission percentage for both s-polarization and p-polarization of a 1064 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 3;
FIG. 14 depicts the calculated Optical Density (OD) for both s-polarization and p-polarization of a 1064 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 3;
FIG. 15 depicts both the calculated and measured p-polarization transmission percentage of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2;
FIG. 16 depicts both the calculated and measured p-polarization Optical Density (OD) of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2;
FIG. 17 depicts both the calculated and measured s-polarization transmission percentage of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2;
FIG. 18 depicts both the calculated and measured s-polarization Optical Density (OD) of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2;
FIGS. 19 and 20 depict a conventional thin-film bandpass filter of the prior art; and
FIGS. 21-23 depict embodiments consistent with the current disclosure.



DETAILED DESCRIPTION
Reference will now be made in detail to the one or more embodiments, characteristics 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.
As has been described above in connection with FIG. 1, when light is incident on a thin-film at an oblique AOI the performance for each plane of polarization differs from that for a normal AOI. Specifically, while the effective phase thickness at an oblique angle is independent of polarization, the width of the fundamental stop band for p-polarized light can become narrower (curve 100 to curve 110), while the width of the fundamental stop band for s-polarized light can become wider (curve 100 to curve 120). Again, as used herein, the width of the fundamental stop band is defined as the difference between the corresponding cut-on and cut-off wavelengths. Moreover, as used herein, the cut-on (cut-off) wavelength is defined as the first wavelength above (below) the reference wavelength that reaches 50% transmission.
Materials and components consistent with the present disclosure exploit this performance difference. For example, FIG. 2 illustrates two different stop bands (each stop band including both a fundamental s-polarization stop band and a fundamental p-polarization stop band) associated with light incident at 45 degrees from two different thin-film coatings or from two different portions of the same thin-film coating consistent with the present disclosure. Specifically, and for exemplary purposes only, referring to the two different thin-film coatings or two different portions of the same thin-film coating as a first QW stack 2102 and a second QW stack 2108, dashed curve 200 is an exemplary p-polarization transmission characteristic for the first QW stack 2102 (with a first fundamental stop band for p-polarization 207 bounded by cut-off wavelength 202 and cut-on wavelength 201), dotted curve 210 is an exemplary s-polarization transmission characteristic for the first QW stack 2102 (with a first fundamental stop band for s-polarization 217 bounded by cut-off wavelength 212 and cut-on wavelength 211), solid curve 230 is an exemplary p-polarization transmission characteristic for the second QW stack 2108 (with a second fundamental stop band for p-polarization 237 bounded by cut-off wavelength 232 and cut-on wavelength 231), and dotted-dashed curve 240 is an exemplary s-polarization transmission characteristic for the second QW stack 2108 (with a second fundamental stop band for s-polarization 247 bounded by cut-off wavelength 242 and cut-on wavelength 241). In FIG. 2, the second fundamental stop band for p-polarization 237 (associated with the second QW stack 2108) is at a longer wavelength than the first fundamental stop band for p-polarization 207 (associated with the first QW stack 2102). Consistent with the present disclosure, the cut-on wavelength 211 of the fundamental stop band for s-polarization 217 associated with the first QW stack 2102 (that is, a first stop band for s-polarization) is equal to or slightly longer than the cut-off wavelength 242 of the fundamental stop band 247 for s-polarization associated with the second QW stack 2108 (that is, a third stop band for s-polarization). In this manner, consistent with the present disclosure, a bandpass filter is formed for p-polarization—due to the relative positions of the cut-off wavelength 232 of the fundamental stop band for p-polarization associated with the second QW stack 2108 (that is, a fourth stop band for p-polarization) and the cut-on wavelength 201 of the fundamental stop band for p-polarization associated with the first QW stack 2102 (that is, a second stop band for p-polarization)—while light with s-polarization is blocked inside this passband.
Considering the first and second QW stacks described above in connection with FIG. 2 as a unitary structure, FIG. 3 depicts the net result of combining the two different coatings or portions of a coating. Specifically, FIG. 3 depicts a passband for p-polarized light (dashed curve 310) while s-polarized light is blocked over the entire passband region 300 as well as within the blocking range for p-polarized light (dotted curve 320).
Table 1 below depicts the material, sequence of layers, and layer thickness of a thin-film design of an exemplary 633 nm polarization bandpass filter consistent with the present disclosure. This design has a total coating thickness of 13.566 micrometers and a total layer count of 140. It does not incorporate an extended blocking design on the second side of the substrate. Instead, an AR coating is used.









TABLE 1





Layer 
Material
Thickness (nm)

















1
Nb2O5
10.511629


2
SiO2
107.82405


3
Nb2O5
74.186108


4
SiO2
95.459275


5
Nb2O5
48.58121


6
SiO2
95.990325


7
Nb2O5
63.937908


8
SiO2
107.814673


9
Nb2O5
60.806319


10
SiO2
107.174089


11
Nb2O5
60.784994


12 
SiO2
107.23574


13
Nb2O5
62.68626


14
SiO2
106.417737


15
Nb2O5
70.891225


16
SiO2
106.746457


17
Nb2O5
56.328244


18
SiO2
106.217109


19
Nb2O5
58.898732


20
SiO2
107.039902


21
Nb2O5
67.178682


22
SiO2
107.436006


23
Nb2O5
60.100543


24
SiO2
106.511113


25
Nb2O5
66.444396


26
SiO2
107.220078


27
Nb2O5
66.543654


28
SiO2
106.999487


29
Nb2O5
65.094616


30
SiO2
106.333156


31
Nb2O5
62.297208


32
SiO2
107.416353


33
Nb2O5
57.45066


34
SiO2
106.475994


35
Nb2O5
56.992719


36
SiO2
106.675666


37
Nb2O5
77.407889


38
SiO2
107.36145


39
Nb2O5
59.970505


40
SiO2
106.965326


41
Nb2O5
63.469101


42
SiO2
107.699656


43
Nb2O5
72.402873


44
SiO2
107.085062


45
Nb2O5
60.647687


46
SiO2
106.251434


47
Nb2O5
59.818188


48
SiO2
106.637492


49
Nb2O5
64.612124


50
SiO2
105.898804


51
Nb2O5
54.229638


52
SiO2
106.360016


53
Nb2O5
68.023714


54
SiO2
107.07246


55
Nb2O5
68.151692


56
SiO2
106.828688


57
Nb2O5
69.680628


58
SiO2
108.329967


59
Nb2O5
69.15047


60
SiO2
107.333285


61
Nb2O5
58.692006


62
SiO2
106.890455


63
Nb2O5
62.129245


64
SiO2
106.862369


65
Nb2O5
61.899899


66
SiO2
105.417729


67
Nb2O5
50.156398


68
SiO2
105.20167


69
Nb2O5
57.618227


70
SiO2
108.74548


71
Nb2O5
69.643752


72
SiO2
136.862518


73
Nb2O5
77.285109


74
SiO2
140.700876


75
Nb2O5
82.664222


76
SiO2
141.126887


77
Nb2O5
87.061513


78
SiO2
143.252888


79
Nb2O5
91.04546


80
SiO2
142.968658


81
Nb2O5
85.847561


82
SiO2
139.818176


83
Nb2O5
82.407398


84
SiO2
136.405591


85
Nb2O5
79.332196


86
SiO2
135.493958


87
Nb2O5
78.104676


88
SiO2
139.685085


89
Nb2O5
79.825172


90
SiO2
142.414738


91
Nb2O5
83.363033


92
SiO2
142.97985


93
Nb2O5
90.355012


94
SiO2
141.912028


95
Nb2O5
85.758544


96
SiO2
138.163627


97
Nb2O5
78.97733


98
SiO2
137.523583


99
Nb2O5
77.488072


100
SiO2
140.615754


101
Nb2O5
81.961683


102
SiO2
142.226302


103
Nb2O5
81.727777


104
SiO2
141.725388


105
Nb2O5
89.985913


106
SiO2
139.749915


107
Nb2O5
86.049916


108
SiO2
137.324146


109
Nb2O5
75.760851


110
SiO2
135.413425


111
Nb2O5
77.200681


112
SiO2
139.650493


113
Nb2O5
100.342915


114
SiO2
140.088335


115
Nb2O5
75.85867


116
SiO2
141.013069


117
Nb2O5
72.228282


118
SiO2
137.111591


119
Nb2O5
101.656208


120
SiO2
137.368209


121
Nb2O5
84.248349


122
SiO2
135.060635


123
Nb2O5
68.794123


124
SiO2
139.726061


125
Nb2O5
81.333468


126
SiO2
141.572455


127
Nb2O5
90.661852


128
SiO2
140.345522


129
Nb2O5
101.240754


130
SiO2
138.356661


131
Nb2O5
73.798415


132
SiO2
136.397037


133
Nb2O5
76.291838


134
SiO2
141.837171


135
Nb2O5
73.060248


136
SiO2
148.130077


137
Nb2O5
122.304111


138
SiO2
137.701563


139
Nb2O5
66.584428


140
SiO2
37.252111









FIGS. 4, 5, and 10 depict the theoretical design spectra for p- and s-polarized light associated with the exemplary 633 nm polarizing bandpass filter of Table 1. This exemplary filter may be used, for example, as a laser clean-up filter for a 632.8 nm helium-neon (HeNe) laser, or a 635 nm diode laser, in which both polarization and spectral clean-up functions are performed. FIG. 4 depicts the calculated transmission percentage and FIG. 5 depicts the calculated OD of the structure of Table 1 for “s” and p-polarizations. FIG. 10 depicts the calculated OD for both s- and p-polarizations at 11 different angles of incidence ranging from 40 to 50 degrees. (As used herein, the 10 degree range between 40 degrees and 50 degrees illustrated in FIG. 10 corresponds to an acceptance angle range of 10 degrees, i.e., an acceptance angle of at least ±5 degrees.) The curves show that at a particular wavelength (for example 642 nm), the high transmission of p-polarization and high contrast ratio are maintained over this full angular range.
FIGS. 6 to 9 depict a comparison between the calculated characteristics depicted in FIGS. 4 and 5, and the measured characteristics of the embodiment described in Table 1 consistent with the disclosure and comprising a thin-film that was coated using an ion-assisted ion-beam sputtering deposition system. The thin-film coating method and equipment used to create the embodiment measured in FIGS. 6-9 is described in more detail in, for example, U.S. Pat. No. 7,068,430, herein incorporated by reference. The measurements on the resulting filter depicted in FIGS. 6-9 were obtained from a home-built spectrophotometer.
FIG. 6 depicts both the calculated (dotted curve 610) and measured (curve 620) p-polarization transmission percentage of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1.
FIG. 7 depicts both the calculated (dotted curve 710) and measured (curve 720) p-polarization Optical Density (OD) of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1. The measurement noise floor in FIG. 7 is different at different wavelengths. In general it is limited to about OD 4 (−40 dB), although it is lower at some wavelengths, particularly those further away from wavelengths of higher transmission (for either polarization).
FIG. 8 depicts both the calculated (dotted curve 810) and measured (curve 820) s-polarization transmission percentage of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1. Note that the measured data ranges from only about 500 to 830 nm, and therefore is not distinguishable from the calculated data on this linear-scale plot.
FIG. 9 depicts both the calculated (dotted curve 910) and measured (curve 920) s-polarization Optical Density (OD) of a 633 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 1. As with FIG. 7, the measurement noise floor in FIG. 9 is limited to about OD 4 (−40 dB)), particularly within the filter passband region. Thus the apparent passband at approximately 630 nm with a peak value of approximately OD 4 is an artifact of the measurement system, and is not representative of the actual value of transmission of s-polarized light near these wavelengths.
Further to the discussion above regarding the interpretation of the measured spectra shown in FIGS. 6-9, a more precise measurement of the contrast ratio at a single wavelength within the passband has been made. The beam from a 30 mW 632.8 nm HeNe laser was directed through two “clean-up” filters to eliminate any noise away from the laser wavelength (Semrock LL01-633 and FF01-633/22 filters). The beam was then passed through a one of the polarizing bandpass filters with the laser polarization axis approximately aligned with the p-polarization axis of the filter to achieve maximum transmission, and then through a neutral density filter with an OD of 1. The resulting beam was detected by a standard Si photodiode. The output voltage, after a transimpedance amplifier with the gain set to 105, was measured to be 7.70 V. Next, a second polarizing bandpass filter was placed after the first, the ND filter was removed, and the gain on the amplifier was increased to 107. The second filter was rotated about the laser beam (optical) axis to minimize the signal at the detector in order cross the polarization axes of the two filters. The output voltage was then measured to be 3.07 mV. The ratio of the unattenuated laser beam intensity to the attenuated intensity was thus (7.70/3.07×10−3)×103=2,510,000, where the factor 103 arises because of the removal of the ND filter (101) and the increase in gain of 107/105=102. Thus, the contrast ratio is at least 2,510,000:1, or OD 6.4. In fact it is believed to be appreciably higher than this value, which represents the noise-floor limit of this measurement system.
While the noise floor of the measurement system is insufficient to measure accurately the attenuation of light greater than a blocking level of about optical density (OD) 4 in FIGS. 7 and 9, the measured results are consistent with the theoretical prediction that the contrast ratio of the embodiment of Table 1 is greater than 1,000,000:1.
Table 2 below depicts the material, sequence of layers, and layer thickness of a thin-film design of an exemplary 532 nm polarization bandpass filter consistent with the present disclosure. The design for the polarizing bandpass filter has a total coating thickness of 14.369 um and a total layer count of 180. The design for the extended blocking has a total coating thickness of 14.382 um and a total layer count of 100.








TABLE 2







Polarizing Bandpass Filter
Extended Blocking












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















1
Nb2O5
45.517007
1
Nb2O5
127.620061


2
SiO2
76.497209
2
SiO2
245.676701


3
Nb2O5
35.246569
3
Nb2O5
113.011088


4
SiO2
80.870653
4
SiO2
221.244963


5
Nb2O5
47.444038
5
Nb2O5
138.961562


6
SiO2
95.149124
6
SiO2
237.879919


7
Nb2O5
47.488064
7
Nb2O5
129.562555


8
SiO2
92.190326
8
SiO2
222.787409


9
Nb2O5
48.177733
9
Nb2O5
135.207074


10
SiO2
86.842561
10
SiO2
215.626118


11
Nb2O5
48.418622
11
Nb2O5
139.159423


12
SiO2
82.330305
12
SiO2
216.113506


13
Nb2O5
47.997723
13
Nb2O5
135.483154


14
SiO2
84.015724
14
SiO2
212.349376


15
Nb2O5
46.075392
15
Nb2O5
148.216423


16
SiO2
88.613824
16
SiO2
214.953982


17
Nb2O5
52.552005
17
Nb2O5
132.826807


18
SiO2
91.850761
18
SiO2
217.493559


19
Nb2O5
52.750536
19
Nb2O5
130.989100


20
SiO2
91.063983
20
SiO2
217.301824


21
Nb2O5
46.873211
21
Nb2O5
140.022924


22
SiO2
88.206144
22
SiO2
222.256337


23
Nb2O5
46.623818
23
Nb2O5
110.913500


24
SiO2
84.089545
24
SiO2
222.196761


25
Nb2O5
47.418478
25
Nb2O5
122.895058


26
SiO2
83.010887
26
SiO2
182.737041


27
Nb2O5
52.421141
27
Nb2O5
136.192334


28
SiO2
86.692413
28
SiO2
233.981119


29
Nb2O5
54.379124
29
Nb2O5
126.498452


30
SiO2
90.713816
30
SiO2
204.653354


31
Nb2O5
51.622008
31
Nb2O5
135.221433


32
SiO2
92.557823
32
SiO2
206.407022


33
Nb2O5
45.132714
33
Nb2O5
115.859735


34
SiO2
87.025291
34
SiO2
230.581090


35
Nb2O5
46.081098
35
Nb2O5
117.600326


36
SiO2
84.501341
36
SiO2
205.983660


37
Nb2O5
50.276398
37
Nb2O5
141.546161


38
SiO2
84.090050
38
SiO2
230.652288


39
Nb2O5
54.575001
39
Nb2O5
118.350672


40
SiO2
82.330892
40
SiO2
228.600987


41
Nb2O5
55.896536
41
Nb2O5
123.708933


42
SiO2
83.939394
42
SiO2
178.811917


43
Nb2O5
52.492803
43
Nb2O5
118.283157


44
SiO2
86.209621
44
SiO2
190.750734


45
Nb2O5
48.570611
45
Nb2O5
112.363206


46
SiO2
88.058789
46
SiO2
165.555652


47
Nb2O5
47.210881
47
Nb2O5
111.857736


48
SiO2
87.257202
48
SiO2
201.048157


49
Nb2O5
49.225311
49
Nb2O5
107.523225


50
SiO2
84.648390
50
SiO2
186.805699


51
Nb2O5
52.363218
51
Nb2O5
121.987324


52
SiO2
80.794510
52
SiO2
180.321392


53
Nb2O5
56.236364
53
Nb2O5
113.854714


54
SiO2
78.232594
54
SiO2
186.340605


55
Nb2O5
57.902087
55
Nb2O5
105.534075


56
SiO2
79.174775
56
SiO2
165.796870


57
Nb2O5
55.102816
57
Nb2O5
114.031310


58
SiO2
82.788632
58
SiO2
184.355737


59
Nb2O5
49.611691
59
Nb2O5
97.351208


60
SiO2
86.717248
60
SiO2
159.150405


61
Nb2O5
45.931399
61
Nb2O5
94.120768


62
SiO2
88.838206
62
SiO2
185.274946


63
Nb2O5
46.984899
63
Nb2O5
103.044863


64
SiO2
89.127167
64
SiO2
161.070097


65
Nb2O5
51.335178
65
Nb2O5
110.134530


66
SiO2
86.852511
66
SiO2
178.503328


67
Nb2O5
55.760855
67
Nb2O5
105.683945


68
SiO2
82.023160
68
SiO2
92.434142


69
Nb2O5
56.138740
69
Nb2O5
110.025307


70
SiO2
78.046585
70
SiO2
84.621624


71
Nb2O5
54.260380
71
Nb2O5
118.292110


72
SiO2
78.068458
72
SiO2
220.070560


73
Nb2O5
50.208171
73
Nb2O5
102.243249


74
SiO2
81.888826
74
SiO2
147.382546


75
Nb2O5
48.488523
75
Nb2O5
79.887915


76
SiO2
85.652353
76
SiO2
173.723465


77
Nb2O5
50.322784
77
Nb2O5
82.819916


78
SiO2
87.624614
78
SiO2
136.807258


79
Nb2O5
55.435470
79
Nb2O5
98.298746


80
SiO2
85.285377
80
SiO2
127.750476


81
Nb2O5
57.459590
81
Nb2O5
74.594761


82
SiO2
77.534958
82
SiO2
136.823902


83
Nb2O5
57.387896
83
Nb2O5
94.549683


84
SiO2
74.177464
84
SiO2
127.016818


85
Nb2O5
51.486178
85
Nb2O5
95.814915


86
SiO2
70.551633
86
SiO2
158.214426


87
Nb2O5
46.522439
87
Nb2O5
70.561785


88
SiO2
68.962169
88
SiO2
170.061455


89
Nb2O5
56.083587
89
Nb2O5
61.721530


90
SiO2
81.317827
90
SiO2
115.250711


91
Nb2O5
76.847578 
91
Nb2O5
85.292596


92
SiO2
96.284372 
92
SiO2
136.934598


93
Nb2O5
77.696133 
93
Nb2O5
80.258324


94
SiO2
121.901395
94
SiO2
104.875444


95
Nb2O5
69.290744
95
Nb2O5
94.859929


96
SiO2
131.082679
96
SiO2
118.023369


97
Nb2O5
64.230428 
97
Nb2O5
15.889228


98
SiO2
127.887643
98
SiO2
40.932894


99
Nb2O5
61.656274 
99
Nb2O5
52.216434


100
SiO2
125.348733
100
SiO2
124.495443


101
Nb2O5
62.539181





102
SiO2
118.802007





103
Nb2O5
67.192927





104
SiO2
115.192558





105
Nb2O5
70.745710





106
SiO2
115.252739





107
Nb2O5
70.783244





108
SiO2
118.794014





109
Nb2O5
67.288583





110
SiO2
121.796117





111
Nb2O5
65.310838





112
SiO2
119.865138





113
Nb2O5
66.926840





114
SiO2
114.446735





115
Nb2O5
70.215057





116
SiO2
109.615559





117
Nb2O5
74.263947





118
SiO2
108.652702





119
Nb2O5
73.694911





120
SiO2
112.826536





121
Nb2O5
69.982383





122 
SiO2
116.268381





123 
Nb2O5
67.233507





124
SiO2
118.360159





125 
Nb2O5
66.920745





126 
SiO2
117.343641





127 
Nb2O5
68.835408





128 
SiO2
111.834397





129 
Nb2O5
73.537417





130 
SiO2
106.446264





131 
Nb2O5
76.919693





132
SiO2
109.747676





133 
Nb2O5
70.616072





134 
SiO2
117.327515





135 
Nb2O5
58.088006





136
SiO2
118.645878





137 
Nb2O5
79.545339





138
SiO2
114.083793





139 
Nb2O5
64.761010





140
SiO2
108.468007





141 
Nb2O5
70.848541





142 
SiO2
108.884220





143 
Nb2O5
78.750872





144 
SiO2
109.301275





145 
Nb2O5
75.510093





146 
SiO2
113.041103





147 
Nb2O5
60.611943





148 
SiO2
117.606548





149 
Nb2O5
62.743487





150 
SiO2
119.179805





151 
Nb2O5
77.985917





152 
SiO2
112.635280





153
Nb2O5
73.903519





154
SiO2
106.977138





155
Nb2O5
68.913057





156
SiO2
107.890171





157
Nb2O5
73.766677





158
SiO2
110.703528





159
Nb2O5
69.077871





160
SiO2
117.279097





161
Nb2O5
71.021381





162
SiO2
119.349301





163
Nb2O5
71.748821





164
SiO2
110.691409





165
Nb2O5
72.251591





166
SiO2
104.627478





167
Nb2O5
74.003889





168
SiO2
109.431170





169
Nb2O5
71.624679





170
SiO2
118.654920





171
Nb2O5
71.030166





172
SiO2
127.327127





173
Nb2O5
67.425738





174
SiO2
124.646495





175
Nb2O5
65.102421





176
SiO2
101.322126





177
Nb2O5
95.564315





178
SiO2
112.097613





179
Nb2O5
81.053508





180
SiO2
71.248600









FIGS. 11 and 12 depict the theoretical design spectra for p- and s-polarized light associated with the exemplary 532 nm polarizing bandpass filter of Table 2. This exemplary filter may be used, for example, as a laser clean-up filter for a frequency doubled 532 nm Nd:YAG, in which both polarization and spectral clean-up functions are performed. FIG. 11 depicts the calculated transmission percentage for s-polarization (dotted curve 1110) and p-polarization (curve 1120) and FIG. 12 depicts the calculated OD of the structure of Table 2 for s-polarization (dotted curve 1210) and p-polarization (curve 1220). The example illustrates the use of the extended blocking on the second side of the substrate to further expand the blocking range of the polarizing bandpass filter to cover the entire range of sensitivity of a typical Si photodiode detector. The extended blocking also offers additional functionality by providing OD 5 blocking for p-polarization and OD 6 blocking for s-polarization over the fundamental wavelength of a frequency doubled 532 nm Nd:YAG laser at 1064 nm. Furthermore, the coatings on opposite sides of the substrate are configured to exhibit approximately the same coating stress in order to minimize substrate bending.
Table 3 below depicts the material, sequence of layers, and layer thickness of a thin-film design of an exemplary 1064 nm polarization bandpass filter consistent with the present disclosure. The design for the polarizing bandpass filter has a total coating thickness of 25.944 um and a total layer count of 158. The design for the extended blocking has a total coating thickness of 25.937 um and a total layer count of 214.








TABLE 3







Polarizing Bandpass Filter
Extended Blocking












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















1
Nb2O5
76.269680
1
Nb2O5
24.017568


2
SiO2
175.873885
2
SiO2
72.505701


3
Nb2O5
81.855957
3
Nb2O5
34.038790


4
SiO2
177.833901
4
SiO2
68.918568


5
Nb2O5
97.588287
5
Nb2O5
48.082415


6
SiO2
182.251856
6
SiO2
61.260696


7
Nb2O5
100.291445
7
Nb2O5
35.040893


8
SiO2
185.784944
8
SiO2
64.884759


9
Nb2O5
101.393477
9
Nb2O5
33.660408


10
SiO2
182.261530
10
SiO2
69.429266


11
Nb2O5
104.143546
11
Nb2O5
49.042511


12
SiO2
179.259236
12
SiO2
62.770267


13
Nb2O5
111.304569
13
Nb2O5
42.036900


14
SiO2
174.471870
14
SiO2
60.614197


15
Nb2O5
110.491593
15
Nb2O5
36.782341


16
SiO2
169.568408
16
SiO2
63.141080


17
Nb2O5
100.628981
17
Nb2O5
46.965337


18
SiO2
169.275661
18
SiO2
60.459907


19
Nb2O5
113.023407
19
Nb2O5
43.826132


20
SiO2
173.796847
20
SiO2
63.617501


21
Nb2O5
120.712498
21
Nb2O5
37.731486


22
SiO2
179.266481
22
SiO2
63.573651


23
Nb2O5
110.794679
23
Nb2O5
41.152106


24
SiO2
182.015345
24
SiO2
61.375091


25
Nb2O5
95.620691
25
Nb2O5
15.090968


26
SiO2
183.080081
26
SiO2
70.048312


27
Nb2O5
99.652939
27
Nb2O5
42.243729


28
SiO2
183.121005
28
SiO2
66.290824


29
Nb2O5
111.420681
29
Nb2O5
47.237748


30
SiO2
180.715424
30
SiO2
74.594613


31
Nb2O5
116.457865
31
Nb2O5
47.781563


32
SiO2
175.889789
32
SiO2
70.165998


33
Nb2O5
100.927838
33
Nb2O5
35.545157


34
SiO2
172.868995
34
SiO2
69.796697


35
Nb2O5
112.922033
35
Nb2O5
51.218382


36
SiO2
171.907336
36
SiO2
73.574028


37
Nb2O5
111.144934
37
Nb2O5
56.931993


38
SiO2
174.881267
38
SiO2
81.111366


39
Nb2O5
109.407350
39
Nb2O5
50.608482


40
SiO2
178.835664
40
SiO2
86.951447


41
Nb2O5
110.996851
41
Nb2O5
55.272387


42
SiO2
183.107314
42
SiO2
83.604089


43
Nb2O5
106.058571
43
Nb2O5
46.872214


44
SiO2
184.401057
44
SiO2
76.894926


45
Nb2O5
102.002680
45
Nb2O5
25.040071


46
SiO2
183.676346
46
SiO2
71.601668


47
Nb2O5
102.109305
47
Nb2O5
54.544201


48
SiO2
179.389432
48
SiO2
89.350081


49
Nb2O5
108.012853
49
Nb2O5
53.453774


50
SiO2
171.502266
50
SiO2
94.841758


51
Nb2O5
114.845235
51
Nb2O5
43.424327


52
SiO2
169.066522
52
SiO2
89.709506


53
Nb2O5
119.728433
53
Nb2O5
55.995009


54
SiO2
169.172212
54
SiO2
93.250233


55
Nb2O5
117.016762
55
Nb2O5
59.296262


56
SiO2
170.534551
56
SiO2
98.915777


57
Nb2O5
110.244732
57
Nb2O5
53.536737


58
SiO2
174.758914
58
SiO2
93.090994


59
Nb2O5
104.190735
59
Nb2O5
64.308972


60
SiO2
180.880028
60
SiO2
91.709614


61
Nb2O5
100.859964
61
Nb2O5
65.940442


62
SiO2
185.352085
62
SiO2
89.607012


63
Nb2O5
101.585471
63
Nb2O5
54.125273


64
SiO2
184.663108
64
SiO2
94.091782


65
Nb2O5
105.418473
65
Nb2O5
57.506857


66
SiO2
181.349453
66
SiO2
96.091395


67
Nb2O5
112.591504
67
Nb2O5
65.489312


68
SiO2
175.972741
68
SiO2
96.118785


69
Nb2O5
119.697424
69
Nb2O5
51.265493


70
SiO2
167.348353
70
SiO2
88.735083


71
Nb2O5
120.346495
71
Nb2O5
56.843423


72
SiO2
158.028639
72
SiO2
94.685492


73
Nb2O5
112.908639
73
Nb2O5
66.495671


74
SiO2
154.524230
74
SiO2
93.247781


75
Nb2O5
103.079890
75
Nb2O5
54.678349


76
SiO2
158.307329
76
SiO2
95.080386


77
Nb2O5
104.555945
77
Nb2O5
62.407787


78
SiO2
149.894095
78
SiO2
99.304635


79
Nb2O5
133.744076
79
Nb2O5
59.647837


80
SiO2
157.238880
80
SiO2
109.564913


81
Nb2O5
157.307257
81
Nb2O5
62.376800


82
SiO2
222.421365
82
SiO2
100.732925


83
Nb2O5
164.978387
83
Nb2O5
68.651293


84
SiO2
243.442190
84
SiO2
104.238212


85
Nb2O5
146.108167
85
Nb2O5
51.501480


86
SiO2
257.982159
86
SiO2
106.578758


87
Nb2O5
128.513473
87
Nb2O5
60.370934


88
SiO2
258.795726
88
SiO2
99.078531


89
Nb2O5
125.796396
89
Nb2O5
60.395578


90
SiO2
251.547528
90
SiO2
107.873882


91
Nb2O5
130.824772
91
Nb2O5
58.365952


92
SiO2
241.243358
92
SiO2
103.836848


93
Nb2O5
139.284763
93
Nb2O5
59.074118


94
SiO2
231.725020
94
SiO2
104.419870


95
Nb2O5
146.396928
95
Nb2O5
61.098665


96
SiO2
226.514970
96
SiO2
101.356843


97
Nb2O5
150.465432
97
Nb2O5
65.338759


98
SiO2
226.562033
98
SiO2
101.783813


99
Nb2O5
148.377656
99
Nb2O5
64.561088


100
SiO2
230.672338
100
SiO2
109.847541


101
Nb2O5
142.433993
101
Nb2O5
63.376546


102
SiO2
235.783824
102
SiO2
104.451557


103
Nb2O5
137.750861
103
Nb2O5
67.732729


104
SiO2
239.522217
104
SiO2
111.209044


105
Nb2O5
135.363863
105
Nb2O5
63.884836


106
SiO2
238.499326
106
SiO2
118.263053


107
Nb2O5
140.704385
107
Nb2O5
64.403140


108
SiO2
232.901602
108
SiO2
107.722446


109
Nb2O5
147.066765
109
Nb2O5
66.921505


110
SiO2
224.559510
110
SiO2
114.222833


111
Nb2O5
152.917026
111
Nb2O5
81.043909


112
SiO2
219.188397
112
SiO2
119.079233


113
Nb2O5
153.316877
113
Nb2O5
75.048831


114
SiO2
219.076154
114
SiO2
127.631515


115
Nb2O5
146.824224
115
Nb2O5
79.697160


116
SiO2
221.821296
116
SiO2
129.232124


117
Nb2O5
142.055954
117
Nb2O5
75.689855


118
SiO2
226.394113
118
SiO2
124.377047


119
Nb2O5
141.260286
119
Nb2O5
73.324674


120
SiO2
229.844594
120
SiO2
129.389361


121
Nb2O5
164.281663
121
Nb2O5
72.158316


122
SiO2
231.310045
122
SiO2
122.156334


123
Nb2O5
130.264386
123
Nb2O5
72.711426


124
SiO2
228.799850
124
SiO2
146.819015


125
Nb2O5
153.232261
125
Nb2O5
77.931869


126
SiO2
224.589667
126
SiO2
137.556689


127
Nb2O5
136.665820
127
Nb2O5
70.401333


128
SiO2
221.051085
128
SiO2
141.079211


129
Nb2O5
147.060919
129
Nb2O5
72.030535


130
SiO2
219.903957
130
SiO2
134.882298


131
Nb2O5
176.451217
131
Nb2O5
80.575108


132
SiO2
223.193355
132
SiO2
132.855800


133
Nb2O5
130.286602
133
Nb2O5
86.349552


134
SiO2
227.797986
134
SiO2
162.604521


135
Nb2O5
126.377815
135
Nb2O5
83.706143


136
SiO2
231.344348
136
SiO2
150.860663


137
Nb2O5
161.185802
137
Nb2O5
88.308783


138
SiO2
230.196868
138
SiO2
151.580754


139
Nb2O5
160.891759
139
Nb2O5
86.137495


140
SiO2
222.354947
140
SiO2
145.467726


141
Nb2O5
127.934270
141
Nb2O5
93.823618


142
SiO2
220.428832
142
SiO2
145.692395


143
Nb2O5
151.698692
143
Nb2O5
88.638113


144
SiO2
223.641545
144
SiO2
166.522326


145
Nb2O5
159.459213
145
Nb2O5
82.758192


146
SiO2
230.335517
146
SiO2
162.437548


147
Nb2O5
146.210897
147
Nb2O5
102.722876


148
SiO2
242.848429
148
SiO2
158.591803


149
Nb2O5
133.369419
149
Nb2O5
89.013031


150
SiO2
255.250171
150
SiO2
172.028574


151
Nb2O5
128.530552
151
Nb2O5
93.019817


152
SiO2
255.413595
152
SiO2
162.373266


153
Nb2O5
154.028764
153
Nb2O5
100.767844


154
SiO2
236.989414
154
SiO2
168.402745


155
Nb2O5
172.327509
155
Nb2O5
90.165787


156
SiO2
209.578318
156
SiO2
165.029500


157
Nb2O5
188.157719
157
Nb2O5
98.282752


158
SiO2
116.530002
158
SiO2
161.905593





159
Nb2O5
93.909673





160
SiO2
165.503978





161
Nb2O5
97.410323





162
SiO2
163.508848





163
Nb2O5
81.461916





164
SiO2
160.847345





165
Nb2O5
90.821141





166
SiO2
167.418231





167
Nb2O5
254.442506





168
SiO2
253.216268





169
Nb2O5
177.126935





170
SiO2
196.325506





171
Nb2O5
200.553685





172
SiO2 
253.922016





173
Nb2O5
146.371458





174
SiO2
281.770599





175
Nb2O5
168.294617





176
SiO2
269.510376





177
Nb2O5
188.346604





178
SiO2
271.106979





179
Nb2O5
182.796162





180
SiO2
274.135359





181
Nb2O5
172.174666





182
SiO2
279.869089





183
Nb2O5
152.030745





184
SiO2
276.406444





185
Nb2O5
177.759023





186
SiO2
269.816222





187
Nb2O5
180.876591





188
SiO2
288.212703





189
Nb2O5
177.589573





190
SiO2
308.111767





191
Nb2O5
175.497904





192
SiO2
370.663757





193
Nb2O5
231.124138





194
SiO2
333.667322





195
Nb2O5
180.729220





196
SiO2
309.172085





197
Nb2O5
197.765045





198
SiO2 
292.830833





199
Nb2O5
209.833715





200
SiO2
340.313926





201
Nb2O5
249.167243





202
SiO2
348.525419





203
Nb2O5
166.141222





204
SiO2
308.318764





205
Nb2O5
186.006142





206
SiO2
240.504569





207
Nb2O5
271.452540





208
SiO2
432.259920





209
Nb2O5
154.228513





210
SiO2
344.869009





211
Nb2O5
179.508473





212
SiO2
410.522423





213
Nb2O5
214.030115





214
SiO2
171.750331









FIGS. 13 and 14 depict the theoretical design spectra for p- and s-polarized light associated with the exemplary 1064 nm polarizing bandpass filter of Table 3. This exemplary filter may be used, for example, as a laser clean-up filter for a 1064 nm Nd:YAG, in which both polarization and spectral clean-up functions are performed. FIG. 13 depicts the calculated transmission percentage for s-polarization (dotted curve 1310) and p-polarization (curve 1320) and FIG. 14 depicts the calculated OD of the structure of Table 3 for s-polarization (dotted curve 1410) and p-polarization (curve 1420). The example illustrates the use of the extended blocking on the second side of the substrate to further expand the blocking range of the polarizing bandpass filter from UV up to 1800 nm, to cover the entire combined range of sensitivity of a typical Si photodiode and an InGaAs detector. The extended blocking also offers additional functionality by providing better than OD 6 blocking for both states of polarization over the second and the third harmonic wavelengths of 532 nm and 355 nm respectively. Furthermore, the coatings on opposite sides of the substrate are configured to exhibit almost the same coating stress in order to minimize substrate bending.
FIGS. 15 to 18 depict a comparison between the calculated characteristics depicted in FIGS. 11 and 12, and the measured characteristics of the embodiment described in Table 2 consistent with the disclosure and comprising a thin-film that was coated using an ion-assisted ion-beam sputtering deposition system. The thin-film coating method and equipment used to create the embodiment measured in FIGS. 15-18 is described in more detail in, for example, U.S. Pat. No. 7,068,430, herein incorporated by reference. The measurements on the resulting filter depicted in FIGS. 15-18 were obtained from a home-built spectrophotometer.
FIG. 15 depicts both the calculated (dotted curve 1510) and measured (curve 1520) p-polarization transmission percentage of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2. The extended blocking is apparent in this figure.
FIG. 16 depicts both the calculated (dotted curve 1610) and measured (curve 1620) p-polarization Optical Density (OD) of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2. The measurement noise floor in FIG. 16 is different at different wavelengths. In general it is limited to about OD 4 (−40 dB), although it is lower at some wavelengths, particularly those further away from wavelengths of higher transmission (for either polarization).
FIG. 17 depicts both the calculated (dotted curve 1710) and measured (curve 1720) s-polarization transmission percentage of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2. Note that the measured data and calculated data are both shown but are not distinguishable on this linear-scale plot.
FIG. 18 depicts both the calculated (dotted curve 1810) and measured (curve 1820) s-polarization Optical Density (OD) of a 532 nm Polarization Bandpass Filter consistent with an embodiment of the present disclosure and consistent with the structure identified in Table 2. As with FIG. 16, the measurement noise floor in FIG. 18 is limited to about OD 4 (−40 dB), particularly within the filter passband region. Thus the apparent passband at approximately 532 nm with a peak value of approximately OD 4 is an artifact of the measurement system, and is not representative of the actual value of transmission of s-polarized light near these wavelengths.
In order to assess the laser damage threshold (LDT) of the filter produced and whose spectra are plotted in FIGS. 15-18, a filter was analyzed by a commercial test laboratory (Spica Technologies, Inc.). A pulsed 532 nm laser with 10 ns pulse widths and a 20 Hz repetition rate was used. The p-polarized laser beam was focused to a spot size (1/e2) of 623 micrometers on the surface of the sample (the Polarizing Bandpass Filter coating side) at a 45 degree angle of incidence. 110 test sites were exposed on a single filter with 200 pulses per site. The testing concluded that the laser damage threshold was >1.75 J/cm2; no damage was observed on 10 sites irradiated with this fluence, nor at any sites irradiated with fluence values below 1.75.
Materials and components consistent with the present disclosure, such as the exemplary PBF described above, offer solutions to all of the problems that have been identified. For example, they offer a contrast ratio equivalent to or higher than any other known available polarizer (>1,000,000:1). The acceptance angle range can be 10 degrees or more, and therefore is larger than that of comparative birefringence-based, high-contrast, high-LDT polarizers (Glan-Laser type). Additionally, light at angles of incidence outside of the acceptance angle range is extinguished for both polarizations, thus ensuring that no light of undesired polarization leaks through the polarizer, in contrast to birefringence-based polarizers which may allow unpolarized light to leak through at angles outside of the acceptance angle range. Furthermore, the clear aperture of a PBF consistent with the present disclosure can exceed 75 mm using existing manufacturing techniques, and in principle could be scaled even larger. Due to a simple, single-substrate configuration such as described above in the exemplary embodiment, the beam deviation of a PBF consistent with the present disclosure is limited by the quality of the underlying substrate, which can be readily held to tolerances below even a few arc seconds, compared to the few arc minute tolerances of many other polarizers. As discussed above, beam deviation due to bending of the substrate can be almost eliminated by implementing a balanced design strategy where the coating stresses on opposite sides of the substrate are configured to match to each other. Because of the flexibility of the AOI for a PBF consistent with the present disclosure, it can be chosen to be 45 degrees, thus enabling the orthogonal polarization of light to be deviated at a 90 degree angle, which enables convenient and compact optical system arrangement. The transmission characteristics of a PBF consistent with the present disclosure may be similar to that of other high-layer-count thin-film bandpass filters, which can approach 100%, for example, limited only by the quality of the anti-reflection (AR) coating performance. Similarly, the LDT of a PBF consistent with the present disclosure may be similar to that of other high-layer-count thin-film bandpass filters, which can be kW/cm2 for cw laser light and >1 J/cm2 for pulsed laser light. PBFs made from high-quality substrate glass with one or two hard, ion-beam-sputtered optical coatings can have excellent physical durability as well as optical quality, causing almost no distortion to a transmitted optical beam.
Further still, materials and components consistent with the present disclosure, offer the very unique spectral property in which it combines a polarizer and a bandpass filter together in one, single-substrate component. Linear polarization with a contrast ratio better than 1,000,000:1 is realized over a desired wavelength range, outside of which materials and components consistent with the present disclosure have deep attenuation better than OD 6 for both polarizations. Such a unique spectral property has a variety of applications. For example, materials and components consistent with the present disclosure can be placed at the output of a diode laser to clean up both background noise and at the same time works as a high-quality linear polarizer to improve polarization purity of output laser beam. In LIDAR and laser-based fluorescence microscope, polarization is also often utilized to provide further discrimination of background noise for enhancement of signal contrast. As pointed out above these applications and others can benefit from reduced optomechanical system complexity, higher overall transmission, decreased system weight, and, as a result, lower overall cost.
Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. 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.

## Claims

1. A bandpass filter and polarizer, comprising:
a first stack of layers, wherein the first stack of layers is configured to exhibit a first stop band for s-polarized radiation incident on the first stack of layers at an oblique angle between a first cut-on radiation wavelength and a first cut-off radiation wavelength, and wherein the first stack of layers is further configured to exhibit a second stop band for p-polarized radiation incident on the first stack of layers at said oblique angle between a second cut-on radiation wavelength and a second cut-off radiation wavelength; and
a second stack of layers, wherein the second stack of layers is configured to exhibit a third stop band for s-polarized radiation incident on the second stack of layers at said oblique angle between a third cut-on radiation wavelength and a third cut-off radiation wavelength, and wherein the second stack of layers is further configured to exhibit a fourth stop band for p-polarized radiation incident on the second stack of layers at said oblique angle between a fourth cut-on radiation wavelength and a fourth cut-off radiation wavelength;
wherein said second cut-on radiation wavelength is less than said first cut-on radiation wavelength;
wherein said third cut-off radiation wavelength is less than said fourth cut-off radiation wavelength;
wherein said first cut-on radiation wavelength is approximately equal to or larger than said third cut-off radiation wavelength; and
wherein said second cut-on radiation wavelength is less than said fourth cut-off radiation wavelength.

2. The bandpass filter and polarizer of claim 1, wherein:
said first stack of layers comprises alternating first and second layers, the first layers having a first refractive index and the second layers having a second refractive index.

3. The bandpass filter and polarizer of claim 2, wherein:
said second stack of layers comprises alternating third and fourth layers, the third layers having a third refractive index and the fourth layers having a fourth refractive index.

4. The bandpass filter and polarizer of claim 2, wherein:
said first layer comprises Nb2O5.

5. The bandpass filter and polarizer of claim 2, wherein:
said second layer comprises SiO2.

6. An optical filter in accordance with claim 2, wherein:
said first layer includes at least one compound selected from: tantalum pentoxide (Ta2O5), hafnium oxide (HfO2). and titanium dioxide (TiO2).

7. The bandpass filter and polarizer of claim 1, further comprising:
a substrate.

8. The bandpass filter and polarizer of claim 7, wherein:
said substrate is between said first stack of layers and said second stack of layers.

9. The bandpass filter and polarizer of claim 7, wherein:
said first stack of layers and said second stack of layers are on the same side of said substrate.

10. The bandpass filter and polarizer of claim 9, further comprising:
an extended-blocking filter on the opposite side of said substrate from said first stack of layers and said second stack of layers.

11. The bandpass filter and polarizer of claim 10, wherein:
said extended blocking filter is configured to block a first range of radiation wavelengths that lie less than said second cut-off radiation wavelength, and configured to block a second range of radiation wavelengths that lie greater than said fourth cut-on radiation wavelength, and
wherein said first range and said second range are substantially larger than said second stopband and said fourth stopband.

12. The bandpass filter and polarizer of claim 10, wherein:
said extended blocking filter is configured to exhibit a blocking of at least optical density (OD) 2 for all radiation wavelengths that lie between an ultraviolet wavelength and approximately 1100 nm.

13. The bandpass filter and polarizer of claim 10, wherein:
said extended blocking filter is configured to exhibit a blocking of at least optical density (OD) 2 for all radiation wavelengths that lie between an ultraviolet wavelength and approximately 1800 nm.

14. The bandpass filter and polarizer of claim 7, wherein:
said substrate comprises glass.

15. The bandpass filter and polarizer of claim 7, wherein:
a component comprising said first stack of layers, said second stack of layers, and said substrate exhibits an acceptance angle range with a magnitude of at least 10 degrees.

16. The bandpass filter and polarizer of claim 7, wherein:
a component comprising said first stack of layers, said second stack of layers, and said substrate exhibits a clear aperture of at least 25 mm.

17. The bandpass filter and polarizer of claim 7, wherein:
a component comprising said first stack of layers, said second stack of layers, and said substrate exhibits a clear aperture of at least 20 mm.

18. The bandpass filter and polarizer of claim 7, wherein:
a component comprising said first stack of layers, said second stack of layers, and said substrate exhibits a laser damage threshold (LDT) for cw laser radiation of at least 1 kW/cm2.

19. The bandpass filter and polarizer of claim 7, wherein:
a component comprising said first stack of layers, said second stack of layers, and said substrate exhibits a laser damage threshold (LDT) for pulsed laser radiation of at least 1 J/cm2.

20. The bandpass filter and polarizer of claim 7, wherein:
a component comprising said first stack of layers, said second stack of layers, and said substrate exhibits a contrast ratio of at least 1,000,000:1.

21. The bandpass filter and polarizer of claim 7, wherein:
a component comprising said first stack of layers, said second stack of layers, and said substrate exhibits a laser damage threshold (LDT) for cw laser radiation of at least 1 kW/cm2.

22. The bandpass filter and polarizer of claim 7, wherein:
a component comprising said first stack of layers, said second stack of layers, and said substrate exhibits a laser damage threshold (LDT) for pulsed laser radiation of at least 1 J/cm2.

23. The bandpass filter and polarizer of claim 1, wherein:
said oblique angle is approximately 45 degrees.

24. The bandpass filter and polarizer of claim 1, wherein:
at least one set of wavelengths approximately equal to a wavelength value lie between said second cut-on radiation wavelength and said fourth cut-off radiation wavelength; and
wherein said wavelength value is a value selected from: 325 nm, 375 nm, 405 nm, 440 nm, 488 nm, 515 nm, 532 nm, 543 nm, 561 nm, 568 nm, 591 nm, 633 nm, 647 nm, 670 nm, 780 nm, 808 nm, 830 nm, 980 nm, and 1064 nm.

25. The bandpass filter and polarizer of claim 1, wherein:
said first stop band, said second stop band, said third stop band, and said fourth stop band exhibit an optical density (OD) of at least 5.

26. The bandpass filter and polarizer of claim 25, wherein:
a component comprising said first stack of layers, said second stack of layers, and a substrate exhibits a transmission characteristic of at least 98%.

27. A method of making a bandpass filter and polarizer comprising:
providing a substrate;
depositing a plurality of first and second layers on said substrate to form a first stack of layers of alternating first and second layers, the first layers having a first refractive index and the second layers having a second refractive index;
depositing a plurality of third and fourth layers on said substrate to form a second stack of layers of alternating third and fourth layers, the third layers having a third refractive index and the fourth layers having a fourth refractive index;
configuring said first stack of layers such that said first stack of layers exhibits a first stop band for s-polarized radiation incident on the first stack of layers at an oblique angle between a first cut-on radiation wavelength and a first cut-off radiation wavelength, and further wherein the first stack of layers exhibits a second stop band for p-polarized radiation incident on the first stack of layers at said oblique angle between a second cut-on radiation wavelength and a second cut-off radiation wavelength;
configuring said second stack of layers such that said second stack of layers exhibits a third stop band for s-polarized radiation incident on the second stack of layers at said oblique angle between a third cut-on radiation wavelength and a third cut-off radiation wavelength, and further wherein the second stack of layers exhibits a fourth stop band for p-polarized radiation incident on the second stack of layers at said oblique angle between a fourth cut-on radiation wavelength and a fourth cut-off radiation wavelength; and
configuring said first stack of layers and said second stack of layers such that said second cut-on radiation wavelength is less than said first cut-on radiation wavelength, said third cut-off radiation wavelength is less than said fourth cut-off radiation wavelength, said first cut-on radiation wavelength is approximately equal to or larger than said third cut-off radiation wavelength, and said second cut-on radiation wavelength is less than said fourth cut-off radiation wavelength.

28. The method of making a bandpass filter and polarizer of claim 27, wherein:
said substrate is between said first stack of layers and said second stack of layers.

29. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first stack of layers and said second stack of layers are on the same side of said substrate.

30. The method of making a bandpass filter and polarizer of claim 29, further comprising:
depositing an extended-blocking filter on the opposite side of said substrate from said first stack of layers and said second stack of layers.

31. The method of making a bandpass filter and polarizer of claim 30, wherein:
said extended blocking filter is configured to block a first range of radiation wavelengths that lie less than said second cut-off radiation wavelength, and configured to block a second range of radiation wavelengths that lie greater than said fourth cut-on radiation wavelength, and
wherein said first range and said second range are substantially larger than said second stopband and said fourth stopband.

32. The method of making a bandpass filter and polarizer of claim 30, wherein:
said extended blocking filter is configured to exhibit a blocking of at least optical density (OD) 2 for all radiation wavelengths that lie between an ultraviolet wavelength and approximately 1100 nm.

33. The method of making a bandpass filter and polarizer of claim 30, wherein:
said extended blocking filter is configured to exhibit a blocking of at least optical density (OD) 2 for all radiation wavelengths that lie between an ultraviolet wavelength and approximately 1800 nm.

34. The method of making a bandpass filter and polarizer of claim 27, wherein:
said substrate comprises glass.

35. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first layer comprises Nb2O5.

36. The method of making a bandpass filter and polarizer of claim 27, wherein:
said second layer comprises SiO2.

37. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first layer includes at least one compound selected from: tantalum pentoxide (Ta2O5), hafnium oxide (HfO2), and titanium dioxide (TiO2).

38. The method of making a bandpass filter and polarizer of claim 27, wherein:
said oblique angle is approximately 45 degrees.

39. The method of making a bandpass filter and polarizer of claim 27, wherein:
at least one set of wavelengths approximately equal to a wavelength value lie between said second cut-on radiation wavelength and said fourth cut-off radiation wavelength; and
wherein said wavelength value is a value selected from: 325 nm, 375 nm, 405 nm, 440 nm, 488 nm, 515 nm, 532 nm, 543 nm, 561 nm, 568 nm, 591 nm, 633 nm, 647 nm, 670 nm, 780 nm, 808 nm, 830 nm, 980 nm, and 1064 nm.

40. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first stop band, said second stop band, said third stop band, and said fourth stop band are configured to exhibit an optical density (OD) of at least 5.

41. The method of making a bandpass filter and polarizer of claim 40, wherein:
said first stack of layers, said second stack of layers, and said substrate exhibits a transmission characteristic of at least 98%.

42. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first stack of layers, said second stack of layers, and said substrate are configured as a component to exhibit an acceptance angle range with a magnitude of at least 10 degrees.

43. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first stack of layers, said second stack of layers, and said substrate are configured as a component to exhibit a clear aperture of at least 75 mm.

44. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first stack of layers, said second stack of layers, and said substrate are configured as a component to exhibit a clear aperture of at least 20 mm.

45. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first stack of layers, said second stack of layers, and said substrate are configured as a component to exhibit a clear aperture of at least 25 mm.

46. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first stack of layers, said second stack of layers, and said substrate are configured as a component to exhibit a contrast ratio of at least 1,000,000:1.

47. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first stack of layers, said second stack of layers, and said substrate are configured as a component to exhibit a laser damage threshold (LDT) for cw laser radiation of at least 1 kW/cm2.

48. The method of making a bandpass filter and polarizer of claim 27, wherein:
said first stack of layers, said second stack of layers, and said substrate are configured as a component to exhibit a laser damage threshold (LDT) for pulsed laser radiation of at least 1 J/cm2.