Patent Publication Number: US-10317279-B2

Title: Optical filtration system for diamond material with nitrogen vacancy centers

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is related to U.S. Patent Provisional Application No. 62/343,746, filed May 31, 2016, entitled “DNV DEVICE INCLUDING LIGHT PIPE WITH OPTICAL COATINGS”, the entire contents of which are incorporated by reference herein in its entirety. 
     This application is related to U.S. patent Provisional application No. 62/343,750, filed May 31, 2016, entitled “DNV DEVICE INCLUDING LIGHT PIPE”, the entire contents of which are incorporated by reference herein in its entirety. 
     This application claims priority to U.S. patent Provisional application No. 62/343,758, filed May 31, 2016, entitled “OPTICAL FILTRATION SYSTEM OR DIAMOND MATERIAL WITH NITROGEN VACNCY CENTERS,” the entire contents of which are incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The present disclosure generally relates to a method and system for transmitting light fluoresced from materials with vacancy centers (e.g., nitrogen vacancy (NV) diamond material) to an optical collector. The transmission of light fluoresced from NV diamond material to an optical collector impacts the efficiency by which fluoresced light is directed to the optical collector and detected. 
     SUMMARY 
     Some embodiments relate to a system that may comprise: an optical excitation source configured to generate light corresponding to a first wavelength; a vacancy center material comprising a plurality of vacancy centers, the vacancy center material configured to: receive radio frequency (RF) excitation; receive optical excitation based, at least in part, on the generation of the light corresponding to the first wavelength; and generate light corresponding to a second wavelength responsive to the RF excitation and the optical excitation received; a plurality of optical collectors configured to receive at least a first portion of the light corresponding to the second wavelength; and an optical filter configured to provide at least a second portion of the light corresponding to the second wavelength to the plurality of optical collectors. 
     Other embodiments relate to a system that may comprise: an optical excitation source configured frequency (RF) excitation; receive optical excitation based, at least in part, on the generation of the light corresponding to generate light corresponding to a first wavelength; vacancy center material comprising a plurality of vacancy centers, the vacancy material configured to: receive radio frequency (RF) excitation, receive optical excitation based, at least in part, on the generation of light corresponding to the first wavelength, and generate light corresponding to a second wavelength responsive to the RF excitation and the optical excitation received, a plurality of optical collectors configured to receive at least a first portion of the light corresponding to the second wavelength; and a plurality of optical filters configured to provide at least a second portion of the light corresponding to the second wavelength to the plurality of optical collectors. 
     Other embodiments relate to a system that may comprise: an optical excitation source configured to generate light corresponding to a first wavelength; a vacancy center material comprising a plurality of vacancy centers, the vacancy material configured to: receive radio frequency (RF) excitation; receive optical excitation based, at least in part, on the generation of the light corresponding to the first wavelength; and generate light corresponding to a second wavelength responsive to the RF excitation and the optical excitation received; an optical collector configured to receive at least a first portion of the light corresponding to the second wavelength; and an optical filter configured to provide at least a second portion of the light corresponding to the second wavelength to the optical collector. 
     These and other features of the implementations described herein, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the several drawings described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the disclosure will become apparent from the description, the drawings, and the claims, in which: 
         FIG. 1  illustrates an orientation of an NV center in a diamond lattice. 
         FIG. 2A  illustrates an energy level diagram of energy levels of spin states for an NV center. 
         FIG. 2B  illustrates an energy level diagram in the absence of an external magnetic field. 
         FIG. 2C  illustrates an energy level diagram and the excitation of the NV center in the presence of an external magnetic field. 
         FIG. 2D  illustrates an energy level diagram with energy levels of spin states for an NV center. 
         FIG. 3  is a schematic block diagram of some embodiments of an optical filtration system. 
         FIG. 4  is a schematic block diagram of some embodiments of an optical filtration system. 
         FIG. 5  is a diagram of an optical filter according to some embodiments. 
         FIG. 6  is a diagram of an optical filter according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Vacancy Center, its Electronic Structure, and Optical and RF Interaction 
     The vacancy center in diamond comprises a substitutional nitrogen atom in a lattice site adjacent a carbon vacancy as shown in  FIG. 1 . The NV center may have four orientations, each corresponding to a different crystallographic orientation of the diamond lattice. 
     The vacancy center may exist in a neutral charge state or a negative charge state. Conventionally, the neutral charge state uses the nomenclature NV 0 , while the negative charge state uses the nomenclature NV, which is adopted in this description. 
     The vacancy center has a number of electrons including three unpaired electrons, one from each of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron. 
     As shown in  FIG. 2A , the vacancy center is illuminated by green light. The vacancy center pair of electrons photo luminesce in the red spectrum responsive to illumination by green light. Green photons are absorbed thereby exciting the electrons from the ground Ms 0 state to the excited Ms 1 state. In turn, the electrons move to the ground state emitting the red light. In some embodiments, the photo luminescence occurs responsive to a consistent excitation (e.g., a continuous green light excitation). Alternatively or additionally, the photo luminescence may occur responsive to an intermittent excitation (e.g., a pulsed green light excitation according to pulsed sequences such as Ramsey, Hahn Echo, CPMG sequences, etc.). During intermittent excitation, the timing of the green emissions can be adjusted or otherwise scaled to maximize the population (probability) of electrons transitioning between the ground state and the excited state. 
     In the absence of an external magnetic field as shown in  FIG. 2B , radio frequency (RF) excitation transitions electrons from the ground state to the +1 and −1 spin state at, for example, a slightly increased energy level responsive to the electrons experiencing spin-spin interaction with the RF magnetic field. The consistent excitation (e.g., a continuous green light excitation) transitions the +/−1 spin electrons to the excited Ms1 state where some of them move to the Ms 0 state. The remaining electrons transition from the excited state to the ground Ms 0 state based, at least in part, on an inter-system crossing (ISC) that does not emit red light. Alternatively, equivalent heat (1˜1042 nm) is emitted. In turn, the “dark” electrons create a reduction in red intensity at 2.89 GHz that looks like a “notch” as depicted in  FIG. 2B . 
       FIG. 2C  illustrates the excitation of the NV center according to an example embodiment. When an external magnetic field of magnitude B [Ts] is applied to an NV axis, the external magnetic field causes the energy to express an indirect relationship such that the energy increases for the +1 spin electron and decreases (e.g., by the same amount) for the −1 spin electron. Energy is related to frequency according to the equation 
     
       
         
           
             
               
                 
                   
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     such that one or more “notches” (e.g., two notches) result on the vacancy axis. For example, two notches result equally separated in frequency and linearly proportional to the strength of the magnetic field vector projected on that particular vacancy axis according to the equation
 
δ f= 2 gμB   (2)
 
     The higher frequency notch corresponds to the dark +1 spin electrons depleting through the ISC, and the lower frequency notch from the −1 spin electrons. Advantageously, electron population densities (e.g., probabilities) behave according to the algorithms above resulting in the conservation of each electron. 
     In some embodiments as shown in  FIG. 2D , the vacancy center has rotational symmetry and has a ground state, which is a spin triplet with  3 A 2  symmetry with one spin state ms=0, and two further spin states ms=+1, and ms=−1. In the absence of an external magnetic field, the ms=±1 energy levels are offset from the ms=0 due to spin-spin interactions, and the ms=±1 energy levels are degenerate, i.e., they have the same energy. The ms=0 spin state energy level is split from the ms=±1 energy levels by an energy of 2.87 GHz for a zero external magnetic field. 
     Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the ms=±1 energy levels, splitting the energy levels ms=±1 by an amount 2gμ B Bz, where g is the g-factor, μB is the Bohr magneton, and Bz is the component of the external magnetic field along the NV axis. This relationship is correct for a first order and inclusion of higher order corrections is a straight forward matter and will not affect the computational and logic steps in the systems and methods described below. 
     The vacancy center electronic structure further includes an excited triplet state  3 E with corresponding ms=0 and ms=±1 spin states. The optical transitions between the ground state  3 A 2  and the excited triplet  3 E are predominantly spin conserving, meaning that the optical transitions are between initial and final states which have the same spin. For a direct transition between the excited triplet  3 E and the ground state  3 A 2 , a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions. 
     There is, however, an alternate non-radiative decay route from the triplet  3 E to the ground state  3 A 2  via intermediate electron states, which are thought to be intermediate singlet states A, E with intermediate energy levels. Significantly, the transition rate from the ms=±1 spin states of the excited triplet  3 E to the intermediate energy levels is significantly greater than that from the ms=0 spin state of the excited triplet  3 E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet  3 A 2  predominantly decays to the ms=0 spin state over the ms=±1 spin states. These features of the decay from the excited triplet  3 E state via the intermediate singlet states A, E to the ground state triplet  3 A 2  allows that if optical excitation is provided to the system, the optical excitation will eventually pump the vacancy center into the ms=0 spin state of the ground state  3 A 2 . In this way, the population of the ms=0 spin state of the ground state  3 A 2  may be “reset” to a maximum polarization determined by the decay rates from the triplet  3 E to the intermediate singlet states. 
     Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet  3 E state is less for the ms=±1 states than for the ms=0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the ms=±1 states of the excited triplet  3 E state will decay via the non-radiative decay path. The lower fluorescence intensity for the ms=±1 states than for the ms=0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the ms=±1 states increases relative to the ms=0 spin, the overall fluorescence intensity will be reduced. 
     With reference to  FIG. 3 , some embodiments of an optical filtration system  300  is illustrated. In these embodiments, the optical filtration system  300  includes an optical excitation source  310 , a vacancy material  305  with vacancy centers, a RF excitation source  320 , optical guide  330 , and a optical filter  350 . 
     The optical filter  350  is configured to provide at least a second portion of light corresponding to a second wavelength W 2  to a plurality of optical collectors  330  as described herein. 
     The optical excitation source  310  may be a laser or a light emitting diode. The optical excitation source may be configured to generate light corresponding to a first wavelength W 1 . For example, the optical excitation source  310  may emit light corresponding to green. 
     The vacancy material  305  may be configured to receive optical excitation based, at least in part, on the generation of light corresponding to the first wavelength W 1 . In some further embodiments, the NV diamond material  305  may be configured to receive radio frequency (RF) excitation provided via the RF excitation source as described herein above. 
     In turn, the vacancy material  305  may be configured to generate light corresponding to a second wavelength W 2  (e.g., a wavelength corresponding to red) responsive to the RF excitation and the optical excitation received. In this regard, the optical excitation source  310  induces fluorescence by the vacancy material  305  corresponding to the second wavelength W 2 . The inducement of fluorescence causes an electronic transition from the excited state to the ground state. The optical excitation source  310 , in addition to exciting fluorescence in the NV diamond material  305 , also serves to reset the population of the ms=0 spin state of the ground state  3 A 2  to a maximum polarization, or other desired polarization. 
     The optical filtration system  300  includes a plurality of optical collectors  330  configured to receive at least a first portion of light corresponding to the second wavelength W 2 . The optical collectors may take the form of light pipes, light tubes, lenses, optical fibers, optical waveguides, etc. For example, as the vacancy material  305  generates light corresponding to the second wavelength W 2  (e.g., red light), a first portion of the light corresponding to the second wavelength W 2  may enter or is otherwise received by the optical collectors  330 . The light corresponding to the wavelength W 2  may be received by the receiving ends  332  of each respective optical collector  330 . In some embodiments, the receiving ends  332  may be disposed proximate to (e.g., adjacent to or otherwise near) the vacancy material  305 . Although a plurality of optical collectors  330  is depicted, in some embodiments, one optical collector  330  (as depicted in  FIG. 4 ) may be configured to receive at least a first portion of light corresponding to the second wavelength W 2 . 
     As illustrated in  FIG. 3 , the NV diamond material  305  is disposed between the receiving ends  332  such that the optical collectors  330  are configured to form a gap G. A second portion of the light corresponding to the wavelength W 2  may be directed beyond the gap G and/or the optical collectors  330 . For example, the light directed beyond the gap G may not enter or otherwise be received by the optical collectors  330 . The gap G may include an adhesive material such as a gel or an epoxy. Although a gap G is depicted, the gap G may be filled or otherwise inexistent such that the NV diamond material  305  may generate light without the gap G as described herein. 
     The optical filtration system  300  further includes the optical filter  350 . The optical filter  350  is configured to provide at least a second portion of light corresponding to the second wavelength W 2  to the plurality of optical collectors  330 . As used herein, the term “optical filter” may be used to refer to a filter configured to transmit (e.g. pass) light corresponding to one or more predetermined wavelengths (e.g., a first wavelength corresponding to green) while reflecting light corresponding to other predetermined wavelengths (e.g., a second wavelength corresponding to red). In some embodiments, the optical filter  350  may take the form of a dichroic filter, interference filter, thin-film filter, dichroic mirror, dichroic reflector, or a combination thereof. The optical filter  350  (e.g., a dichroic filter) may be configured to reflect light corresponding to the second wavelength W 2  (e.g., light in the red fluorescence band) from the vacancy material  305  which, in turn, is received by the optical collectors  330 . For example, the optical filter  350  may reflect the light directed beyond the gap G to the optical collectors  330  that would otherwise not enter or be received by the optical collectors  330 . 
     Alternatively or additionally, light corresponding to the first wavelength W 1  from the vacancy material  305  may be directed through the optical filter  350  to filter out the light corresponding to the first wavelength W 1  (e.g., in the green fluorescence band). Although a single optical filter  350  is depicted, in some embodiments, a plurality of optical filters  350  (as depicted in  FIG. 4 ) may be configured to provide at least a second portion of light corresponding to a second wavelength W 2  to one or more optical collectors  330 . 
     In some embodiments, the optical filter  350  includes an optical coating (e.g., an anti-reflection coating, high reflective coating, filter coating, beamsplitter coating, etc.) configured to facilitate transmission of light corresponding to the first wavelength W 1  (e.g., light corresponding to green) through the optical filter  350 . The optical coating may include at least one of a soft coating (e.g., one or more layers of thin film) or a hard coating. The optical coating may be made of a material such as zinc sulfide, cryolyte, silver, and/or any other like suitable material, or a combination thereof. 
     The optical coating (e.g., the anti-reflective coating) is further configured to facilitate the provision of the light corresponding to the second wavelength W 2  to the optical collectors  330 . For example, the optical coating facilitates the reflection of the light corresponding to the second wavelength W 2  from the vacancy material  305  to the optical collectors  330 . 
     As illustrated in  FIG. 5 , the optical coating may include a substrate S and one or more layers Ln configured to at least one of transmit or reflect light according to at least one refractive index which describes how light propagates through the optical filter  350 . In this regard, the phase shift between the light corresponding to the second wavelength W 2  reflected, for example, at the first and second points P 1 , P 2  of the layer Ln is 180°. In turn, the reflections R 1 , R 2  (e.g., the reflected rays) are cancelled responsive to interference such as, but not limited to, destructive interference. Advantageously, the optical coating increases transmission, efficiency by which the light corresponding to the second wavelength W 2  is received by the optical collectors  330  and resists environmental damage to the optical filter  350 . 
     With reference back to  FIG. 3 , the optical filter  350  may be disposed at least one of above, beneath, behind, or in front of the vacancy material  305  to receive and, in turn, provide the light corresponding to the second wavelength W 2  (e.g., light in the red fluorescence band) to the optical collectors  330 . As illustrated, the optical filter  350  is disposed behind the NV diamond material  305  such that the optical filter  350  reflects light corresponding to the second wavelength W 2  from the vacancy material  305 . In some embodiments, the optical filter  350  may be configured to enclose or otherwise surround the vacancy material  305 . The enclosing of the vacancy material  305  increases the reflection of light corresponding to the second wavelength W 2  from the vacancy material  305  to the optical collectors  330 . 
     In some embodiments, the optical filter  350  is disposed proximate to the plurality of optical collectors  330 . The optical filter  350  may be disposed within a predetermined distance to the optical collectors  330 . For example, the optical filter  350  may be disposed next to the optical collectors  330  as depicted. The optical filter  350  may be disposed at least one of above, beneath, behind, or in front of the plurality of optical collectors  330 . As depicted, the optical filter  350  is disposed behind the plurality of optical collectors  330 . Advantageously, disposing the optical filter  350  behind the plurality of optical collectors  330  facilitates the removal of light corresponding to the first wavelength W 1  (e.g., light corresponding to green) by the optical filter  350  which reduces noise and/or other errors introduced by W. 
     In further embodiments, a predetermined dimension (e.g., length, width, height, etc.) corresponding to the optical filter  350  may be configured to extend beyond a predetermined dimension (e.g., length, width, height, etc.) corresponding to the gap G and/or the optical collectors  330 . For example, the width of the optical filter  350  may be configured to be greater than the width of the gap G to compensate for over tolerances in manufacturing such that the optical filter  350  covers the gap G. As the light corresponding to the second wavelength W 2  makes contact C with or otherwise hits the optical filter  350 , the light W 2  is reflected (as illustrated in  FIG. 6 ) from the optical filter  350  to the optical collectors  330 . The light ray W 2  R is reflected at an angle of incidence a and an angle of reflection β as depicted across the normal N. The angle of incidence may equal the angle of reflection. Each respective angle may measure between 0 degrees and 180 degrees based on one or more refractive indices corresponding to the optical filter  350 . Alternatively or additionally, the height of the optical filter  350  may be configured to be greater than the height of the optical collectors  330  to compensate for over tolerances in manufacturing such that the optical filter  350  receives light (e.g., light corresponding to the second wavelength W 2 ) directed beyond the optical collectors  330 . In turn, the optical filter  350  reflects or otherwise provides the light corresponding to the second wavelength W 2  to the optical collectors  330 . 
     The dimensional variations are not limited to those included in the respective illustrations. Such dimensional variations may be increased, decreased, adjusted or otherwise scaled depending on the application of the optical filtration system  300 . 
     The embodiments of the inventive concepts disclosed herein have been described in detail with particular reference to preferred embodiments thereof, but it will be understood by those skilled in the art that variations and modifications can be effected within the spirit and scope of the inventive concepts.