Patent Publication Number: US-10330744-B2

Title: Magnetometer with a waveguide

Description:
BACKGROUND 
     Magneto-optical defect center materials such as diamonds with nitrogen vacancy centers can be used to determine an applied magnetic field by transmitting light into the diamond and measuring the responsive light that is emitted. The loss of light in such systems may be detrimental to measurements and operations. 
     SUMMARY 
     An illustrative magneto-optical defect center material may include a first portion comprising a plurality of defect centers dispersed throughout the first portion. The magneto-optical material also may include a second portion adjacent to the first portion. The second portion may not contain significant defect centers. The second portion may be configured to facilitate transmission of light generated by the defect centers of the first portion away from the first portion. 
     Some illustrative magneto-optical defect center materials may include a first portion that can have a plurality of defect centers dispersed throughout the first portion. The materials may also include a second portion adjacent to the first portion. The second portion may not contain defect centers. The second portion may be configured to facilitate transmission of light generated by the defect centers of the first portion away from the first portion. 
     Some illustrative magnetometers may include a diamond. The diamond may include a first portion and a second portion. The first portion may include a plurality of nitrogen vacancy (NV) centers, and the second portion may not have substantial NV centers. The second portion may be configured to facilitate transmission of light generated from the NV centers of the first portion away from the first portion. The magnetometer may further include a light source that may be configured to transmit light into the first portion of the diamond. The magnetometer may further include a photo detector configured to detect light transmitted through at least one side of the second portion of the diamond. The magnetometer may also include a processor operatively coupled to the photo detector. The processor may be configured to determine a strength of a magnetic field based at least in part on the light detected by the photo detector. 
     Some illustrative magneto-optical defect center materials include means for absorbing first light with a first frequency and transmitting second light with a second frequency. The materials may also include means for directing the second light that may be adjacent to the means for absorbing the first light and transmitting the second light. The means for directing the second light may not absorb the first light. The means for directing the second light may be configured to facilitate transmission of the second light away from the means for absorbing the first light and transmitting the second light. 
     Some illustrative methods include receiving, at a plurality of defect centers of a first portion of a magneto-optical defect center material, first light with a first frequency. The plurality of defect centers may be dispersed throughout the first portion. The method can also include transmitting, from the plurality of defect centers, second light with a second frequency. The method may further include facilitating, via a second portion of the magneto-optical defect center material, the second light away from the first portion. The second portion may be adjacent to the first portion. The second portion may not contain defect centers. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the following drawings and the detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an NV center in a diamond lattice in accordance with some illustrative embodiments. 
         FIG. 2  illustrates an energy level diagram showing energy levels of spin states for an NV center in accordance with some illustrative embodiments. 
         FIG. 3  is a schematic diagram illustrating a NV center magnetic sensor system in accordance with some illustrative embodiments. 
         FIG. 4  is a graph illustrating the fluorescence as a function of an applied RF frequency of an NV center along a given direction for a zero magnetic field in accordance with some illustrative embodiments. 
         FIG. 5  is a graph illustrating the fluorescence as a function of an applied RF frequency for four different NV center orientations for a non-zero magnetic field in accordance with some illustrative embodiments. 
         FIG. 6  is a schematic diagram illustrating a magnetic field detection system in accordance with some illustrative embodiments. 
         FIG. 7  is a diagram illustrating possible paths of light emitted from a material with defect centers in accordance with some illustrative embodiments. 
         FIG. 8A  is a diagram illustrating possible paths of light emitted from a material with defect centers and a rectangular waveguide in accordance with some illustrative embodiments. 
         FIG. 8B  is a three-dimensional view of the material and rectangular waveguide of  FIG. 8A  in accordance with some illustrative embodiments. 
         FIG. 9A  is a diagram illustrating possible paths of light emitted from a material with defect centers and an angled waveguide in accordance with some illustrative embodiments. 
         FIG. 9B  is a three-dimensional view of the material and angular waveguide of  FIG. 9A  in accordance with some illustrative embodiments. 
         FIG. 10A  is a diagram illustrating possible paths of light emitted from a material with defect centers and a three-dimensional waveguide in accordance with some illustrative embodiments. 
         FIG. 10B  is a three-dimensional view of the material and a three-dimensional waveguide of  FIG. 10A  in accordance with some illustrative embodiments. 
         FIGS. 10C-10F  are two-dimensional cross-sectional drawings of a three-dimensional waveguide in accordance with some illustrative embodiments. 
         FIG. 11  is a diagram illustrating a material attached to a waveguide in accordance with some illustrative embodiments. 
         FIG. 12  is a flow chart of a method of forming a material with a waveguide in accordance with some illustrative embodiments. 
         FIG. 13  is a flow chart of a method of forming a material with a waveguide in accordance with some illustrative embodiments. 
     
    
    
     The foregoing and other features of the present disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure. 
     Magneto-optical defect center materials such as diamonds with nitrogen vacancy (NV) centers can be used to detect magnetic fields. Green light which enters a diamond structure with NV centers interacts with NV centers, and red light is emitted from the diamond. The amount of red light emitted can be used to determine the strength of the magnetic field. The efficiency and accuracy of sensors using magneto-optical defect center materials such as diamonds with NV centers (DNV sensors) is increased by transferring as much light as possible from the NV centers to the photo sensor that measures the amount of red light. Magneto-optical defect center materials include but are not be limited to diamonds, Silicon Carbide (SiC) and other materials with nitrogen, boron, or other chemical defect centers. 
     In various embodiments described herein, the material with the defect centers may be formed in a shape that directs light from the defect centers towards the photo diode. When excited by the green light photon, a defect center emits a red light photon. But, the direction that the red light photon is emitted from the defect center is not necessarily the direction that the green light photon was received. Rather, the red light photon can be emitted in any direction. When the red photon reaches the interface between the diamond and the surrounding medium, the photon may transmit through the interface or reflect back into the diamond, depending, in part, on the angle of incidence at the interface. The phenomenon by which the photon may reflect back into the diamond is referred to as total internal reflection (TIR). Thus, the sides of the diamond can be angled and polished to reflect red light photons towards the photo sensor. 
     The NV center in a diamond comprises a substitutional nitrogen or boron 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 NV 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 NV center has a number of electrons, including three unpaired electrons, each one from the vacancy to a respective 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. 
     The NV center has rotational symmetry, and as shown in  FIG. 2 , has a ground state, which is a spin triplet with  3 A 2  symmetry with one spin state m s =0, and two further spin states m s =+1, and m s =−1. In the absence of an external magnetic field, the m s =±1 energy levels are offset from the m s =0 due to spin-spin interactions, and the m s =±1 energy levels are degenerate, i.e., they have the same energy. The m s =0 spin state energy level is split from the m s =±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 m s =±1 energy levels, splitting the energy levels ms=±1 by an amount 2gμ B B z , where g is the g-factor, μ B  is the Bohr magneton, and B z  is the component of the external magnetic field along the NV axis. This relationship is correct to a first order and inclusion of higher order corrections is a straightforward matter and will not affect the computational and logic steps in the systems and methods described below. 
     The NV center electronic structure further includes an excited triplet state  3 E with corresponding m s =0 and m s =±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 that 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 alternative 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 m s =±1 spin states of the excited triplet  3 E to the intermediate energy levels is significantly greater than the transition rate from the m s =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 m s =0 spin state over the m s =±1 spins 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 NV center into the m s =0 spin state of the ground state  3 A 2 . In this way, the population of the m s =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 m s =±1 states than for the m s =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 m s =±1 states of the excited triplet  3 E state will decay via the non-radiative decay path. The lower fluorescence intensity for the m s =±1 states than for the m s =0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the m s =±1 states increases relative to the m s =0 spin, the overall fluorescence intensity will be reduced. 
       FIG. 3  is a schematic diagram illustrating a conventional NV center magnetic sensor system  300  that uses fluorescence intensity to distinguish the m s =±1 states, and to measure the magnetic field based on the energy difference between the m s =+1 state and the m s =−1 state. The system  300  includes an optical excitation source  310 , which directs optical excitation to an NV diamond material  320  with NV centers. The system further includes an RF excitation source  330 , which provides RF radiation to the NV diamond material  320 . Light from the NV diamond may be directed through an optical filter  350  to an optical detector  340 . 
     The RF excitation source  330  may be a microwave coil, for example. The RF excitation source  330 , when emitting RF radiation with a photon energy resonant with the transition energy between ground m s =0 spin state and the m s =+1 spin state, excites a transition between those spin states. For such a resonance, the spin state cycles between ground m s =0 spin state and the m s =+1 spin state, reducing the population in the m s =0 spin state and reducing the overall fluorescence at resonances. Similarly, resonance occurs between the m s =0 spin state and the m s =−1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the m s =0 spin state and the m s =−1 spin state, or between the m s =0 spin state and the m s =+1 spin state, there is a decrease in the fluorescence intensity. 
     The optical excitation source  310  may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source  310  induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material  320  is directed through the optical filter  350  to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the detector  340 . The optical excitation light source  310 , in addition to exciting fluorescence in the diamond material  320 , also serves to reset the population of the m s =0 spin state of the ground state  3 A 2  to a maximum polarization, or other desired polarization. 
     For continuous wave excitation, the optical excitation source  310  continuously pumps the NV centers, and the RF excitation source  330  sweeps across a frequency range that includes the zero splitting (when the m s =±1 spin states have the same energy) photon energy of 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material  320  with NV centers aligned along a single direction is shown in  FIG. 4  for different magnetic field components B z  along the NV axis, where the energy splitting between the m s =−1 spin state and the m s =+1 spin state increases with B z . Thus, the component B z  may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation. Examples of pulsed excitation schemes include Ramsey pulse sequence, and spin echo pulse sequence. The excitation scheme utilized during the measurement collection process (i.e., the applied optical excitation and the applied RF excitation) may be any appropriate excitation scheme. For example, the excitation scheme may utilize continuous wave (CW) magnetometry, pulsed magnetometry, and variations on CW and pulsed magnetometry (e.g., pulsed RF excitation with CW optical excitation). In cases where Ramsey pulse RF sequences are used, pulse parameters u and T may be optimized using Rabi analysis and FID-Tau sweeps prior to the collection process, as described in, for example, U.S. patent application Ser. No. 15/003,590, which is incorporated by reference herein in its entirety. 
     In general, the diamond material  320  will have NV centers aligned along directions of four different orientation classes.  FIG. 5  illustrates fluorescence as a function of RF frequency for the case where the diamond material  320  has NV centers aligned along directions of four different orientation classes. In this case, the component B z  along each of the different orientations may be determined. These results, along with the known orientation of crystallographic planes of a diamond lattice, allow not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field. 
     While  FIG. 3  illustrates an NV center magnetic sensor system  300  with NV diamond material  320  with a plurality of NV centers, in general, the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. Magneto-optical defect center materials include but are not be limited to diamonds, Silicon Carbide (SiC) and other materials with nitrogen, boron, or other defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material. 
       FIG. 6  is a schematic diagram of a system  600  for a magnetic field detection system according to some embodiments. The system  600  includes an optical excitation source  610 , which directs optical excitation to an NV diamond material  620  with NV centers, or another magneto-optical defect center material with magneto-optical defect centers. An RF excitation source  630  provides RF radiation to the NV diamond material  620 . A magnetic field generator  670  generates a magnetic field, which is detected at the NV diamond material  620 . 
     The magnetic field generator  670  may generate magnetic fields with orthogonal polarizations, for example. In this regard, the magnetic field generator  670  may include two or more magnetic field generators, such as two or more Helmholtz coils. The two or more magnetic field generators may be configured to provide a magnetic field having a predetermined direction, each of which provide a relatively uniform magnetic field at the NV diamond material  620 . The predetermined directions may be orthogonal to one another. In addition, the two or more magnetic field generators of the magnetic field generator  670  may be disposed at the same position, or may be separated from each other. In the case that the two or more magnetic field generators are separated from each other, the two or more magnetic field generators may be arranged in an array, such as a one-dimensional or two-dimensional array, for example. 
     The system  600  may be arranged to include one or more optical detection systems  605 , where each of the optical detection systems  605  includes the optical detector  640 , optical excitation source  610 , and NV diamond material  620 . Furthermore, the magnetic field generator  670  may have a relatively high power as compared to the optical detection systems  605 . In this way, the optical systems  605  may be deployed in an environment that requires a relatively lower power for the optical systems  605 , while the magnetic field generator  670  may be deployed in an environment that has a relatively high power available for the magnetic field generator  670  so as to apply a relatively strong magnetic field. 
     The system  600  further includes a controller  680  arranged to receive a light detection signal from the optical detector  640  and to control the optical excitation source  610 , the RF excitation source  630 , and the second magnetic field generator  675 . The controller may be a single controller, or multiple controllers. For a controller including multiple controllers, each of the controllers may perform different functions, such as controlling different components of the system  600 . The second magnetic field generator  675  may be controlled by the controller  680  via an amplifier  660 , for example. 
     The RF excitation source  630  may be a microwave coil, for example. The RF excitation source  630  is controlled to emit RF radiation with a photon energy resonant with the transition energy between the ground m s =0 spin state and the m s =±1 spin states as discussed above with respect to  FIG. 3 . 
     The optical excitation source  610  may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source  610  induces fluorescence in the red from the NV diamond material  620 , where the fluorescence corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material  620  is directed through the optical filter  650  to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector  640 . The optical excitation light source  610 , in addition to exciting fluorescence in the NV diamond material  620 , also serves to reset the population of the m s =0 spin state of the ground state  3 A 2  to a maximum polarization, or other desired polarization. 
     The controller  680  is arranged to receive a light detection signal from the optical detector  640  and to control the optical excitation source  610 , the RF excitation source  630 , and the second magnetic field generator  675 . The controller may include a processor  682  and a memory  684 , in order to control the operation of the optical excitation source  610 , the RF excitation source  630 , and the second magnetic field generator  675 . The memory  684 , which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical excitation source  610 , the RF excitation source  630 , and the second magnetic field generator  675  to be controlled. That is, the controller  680  may be programmed to provide control. 
       FIG. 7  illustrates a magneto-optical defect center material  720  with a defect center  715  and an optical detector  740 . In an illustrative embodiment, the magneto-optical defect center material  720  is a diamond material, and the defect center  715  is an NV center. In alternative embodiments, any suitable magneto-optical defect center material  720  and defect center  715  can be used. An excitation photon travels along path  705 , enters the material  720  and excites the defect center  715 . The excited defect center  715  emits a photon, which can be in any direction. Paths  710 ,  711 ,  712 ,  713 , and  714  are example paths that the emitted photon may travel. In the embodiments of  FIG. 7 , one defect center  715  is shown for illustrative purposes. However, in alternative embodiments, the material may include multiple defect centers  715 . Also, the angles and specific paths in  FIG. 7  are meant to be illustrative only and not meant to be limiting. In alternative embodiments, additional, fewer, and/or different elements may be used. 
     In the embodiments illustrated in  FIG. 7 , there is no object between the material  720  and the optical detector  740 . Thus, air or a vacuum is between the material  720  and the optical detector  740 . The air or vacuum surrounds the material  720 . In alternative embodiments, objects such as waveguides may be between the material  720  and the optical detector  740 . Regardless of whether an object is between the material  720  and the optical detector  740 , the refractive index of the material is different than the refractive index of whatever is between the material  720  and the optical detector  740 . 
     In the embodiments shown in  FIG. 7  in which the same material (e.g., air or a vacuum) surrounds the material  720  on all sides and has a different refractive index than the material  720 , the path of the emitted light may change direction at the interface between the material  720  and the surrounding material depending upon the angle of incidence and the differences in the refractive indexes. In some instances, depending upon the differences in the refractive indexes, the angle of incidence, and the surface of the interface (e.g., smooth or rough), the photon may reflect off of the surface of the material  720 . In general, as the angle of incidence becomes more orthogonal, as the differences in the refractive indexes gets closer to zero, and as the surface of the interface is more rough, the higher the chance that the emitted photon will pass through the interface rather than reflect off of the interface. In the examples of  FIG. 7 , all of paths  710 ,  711 ,  712 ,  713 , and  714  travel through the interface (i.e., a side surface of the material  720 ). However, in other instances, the photon may reflect off of one or more surfaces of the material  720  before passing through the interface. Because the emitted photon can be emitted in any three-dimensional direction, only a small fraction of the possible beam paths exit the surface of the material  720  facing the optical detector  740 . 
       FIG. 8A  is a diagram illustrating possible paths of light emitted from a material with defect centers and a rectangular waveguide in accordance with some illustrative embodiments.  FIG. 8A  illustrates a material  820  with a defect center  815  and an optical detector  840 . In an illustrative embodiment, the magneto-optical defect center material  820  is a diamond material, and the defect center  815  is an NV center. In alternative embodiments, any suitable magneto-optical defect center material  820  and defect center  815  can be used. Attached to the material  820  is a waveguide  822 . An excitation photon travels along path  805 , enters the material  820  and excites the defect center  815 . The excited defect center  815  emits a photon, which can be in any direction. Paths  810 ,  811 ,  812 ,  813 , and  814  are example paths that the emitted photon may travel. In the embodiments of  FIG. 8A , one defect center  815  is shown for illustrative purposes. However, in alternative embodiments, the material may include multiple defect centers  815 . Also, the angles and specific paths in  FIG. 8  are meant to be illustrative only and not meant to be limiting.  FIG. 8B  is a three-dimensional view of the material and rectangular waveguide of  FIG. 8A  in accordance with an illustrative embodiment. As shown in  FIG. 8B , the material  820  and the waveguide  822  are a cuboid. In alternative embodiments, additional, fewer, and/or different elements may be used. 
     The embodiments shown in  FIG. 8A  includes a waveguide  822  attached to the material  820 . In an illustrative embodiment, the waveguide  822  is a diamond, and there is no difference in refractive indexes between the waveguide  822  and the material  820 . In alternative embodiments, the waveguide  822  may be of any material with the same or similar refractive index as the material  820 . Because there is little or no difference in refractive indexes, light passing through the interface  824  does not bounce back into the material  820  or change velocity (e.g., including direction). Accordingly, because light passes freely through the interface  824 , more light is emitted from the material  820  toward the optical detector  840  than in the embodiments of  FIG. 7 . That is, light emitted in a direction toward a side of the material  820  that is not the interface  824  may bounce back into the material  820  depending upon the angle of incidence, etc., as described above. Such light, therefore, has a chance to be bounced into the direction of the interface  824  and toward the optical detector  840 . In general, light (e.g., via path  812 ) that contacts a sidewall of the waveguide  822  will be reflected back into the waveguide  822  as opposed to transitioning outside of the waveguide  822  because of the angle of incidence. That is, such light will generally have a low angle of incidence, thereby increasing the chance that the light will bounce back into the waveguide  822 . Similarly, light that hits the end face of the waveguide  822  (i.e., the face of the waveguide  822  facing the optical detector  840 ) will generally have a high angle of incidence, and, therefore, a higher chance of passing through the end of the waveguide  822  and pass onto the surface of the optical detector. 
     In some illustrative embodiments, the material  820  includes NV centers, but the waveguide  822  does not include NV centers. Light emitted from an NV center can be used to excite another NV center. The excited NV center emits light in any direction. Accordingly, if the waveguide  822  includes NV centers, light that passed through the interface  824  may excite an NV center in the waveguide  822 , and the NV center may emit light back towards the material  820  or in a direction that would allow the light to pass through a side surface of the waveguide  822  (e.g., as opposed to the end face of the waveguide  822  and toward the optical detector  840 ). In some instances, light may be absorbed by defects that are not NV centers, and such defects may not emit a corresponding light. In such instances, the light is not transmitted to a light sensor. 
     Accordingly, efficiency of the waveguide  822  is increased when the waveguide  822  does not include nitrogen vacancies. In this context, efficiency of the system is determined by the amount of light that is emitted from the defect centers compared to the amount of light that is detected the optical detector  840 . That is, in a system with 100% efficiency, the same amount of light that is emitted by the defect centers passes through the end face of the waveguide  822  and is detected by the optical detector  840 . In an illustrative embodiment, a system with the waveguide  822  that has nitrogen vacancies has a mean efficiency of about 4.5%, whereas a system with the waveguide  822  that does not have nitrogen vacancies has a mean efficiency of about 6.1%. 
       FIG. 9A  is a diagram illustrating possible paths of light emitted from a material with defect centers and an angled waveguide in accordance with some illustrative embodiments.  FIG. 9A  illustrates a material  920  with a defect center  915  and an optical detector  940 . In an illustrative embodiment, the magneto-optical defect center material  920  is a diamond material, and the defect center  915  is an NV center. In alternative embodiments, any suitable magneto-optical defect center material  920  and defect center  915  can be used. The material  920  with the waveguide  922  has a higher efficiency than the embodiments of  FIG. 8 . In an illustrative embodiment with a diamond and waveguide similar to the material  920  and the waveguide  922  of  FIG. 9 , the system has a mean efficiency of about 9.8%. 
     In an illustrative embodiment, the shape of the material  920  and the waveguide  922  in  FIG. 9A  is two-dimensional. That is, the surfaces of the material  920  and the waveguide  922  that are orthogonal to the viewing direction of  FIG. 9  are flat with each side in a plane that is parallel to one another, and each side spaced from one another.  FIG. 9B  is a three-dimensional view of the material and angular waveguide of  FIG. 9A  in accordance with an illustrative embodiment. 
     As shown in  FIG. 9A , the material  920  and the waveguide  922  are defined, in one plane, by sides  951 ,  952 ,  953 ,  954 ,  955 , and  956 . The angles between sides  951  and  952 , between sides  952  and  953 , between sides  953  and  954 , and between sides  956  and  951  are obtuse angles (i.e., greater than 90°). The angles between sides  954  and  955  and between sides  955  and  956  are right angles (i.e., 90°). The material  920  with nitrogen vacancies does not extend to sides  954 ,  955 , and  956 . In alternative embodiments, any suitable shape can be used. For example, the waveguide can include a compound parabolic concentrator (CPC). In another example, the waveguide can approximate a CPC. 
       FIG. 10A  is a diagram illustrating possible paths of light emitted from a material with defect centers and a three-dimensional waveguide in accordance with some illustrative embodiments.  FIG. 10A  illustrates a material  1020  with a defect center  1015  and an optical detector  1040 . In an illustrative embodiment, the magneto-optical defect center material  1020  is a diamond material, and the defect center  1015  is an NV center. In alternative embodiments, any suitable magneto-optical defect center material  1020  and defect center  1015  can be used. Attached to the material  1020  is a waveguide  122 . An excitation photon travels along path  1005 , enters the material  1020 , and excites the defect center  1015 . The excited defect center  1015  emits a photon, which can be in any direction. Paths  1010 ,  1011 ,  1012 , and  1013  are example paths that the emitted photon may travel. In the embodiments of  FIG. 10 , one defect center  1015  is shown for illustrative purposes. However, in alternative embodiments, the material may include multiple defect centers  1015 . Also, the angles and specific paths in  FIG. 10  are meant to be illustrative only and not meant to be limiting. In alternative embodiments, additional, fewer, and/or different elements may be used. 
     In an illustrative embodiment, the material  1020  includes defect centers, and the waveguide  1022  is made of diamond but does not include defect centers. In an illustrative embodiment, the angles formed by sides  1055  and  1056  and by sides  1056  and  1057  are right angles, and the other angles formed by the other sides are obtuse angles. In an illustrative embodiment, the cross-sectional shape of the material  1020  and the waveguide  1022  of  FIG. 10A  is the shape of the material  1020  and the waveguide  1022  in two, orthogonal planes. That is, the material  1020  and the waveguide  1022  have one side  1052 , one side  1056 , two sides  1051 , two sides  1053 , two sides  1054 , two sides  1055 , two sides  1057 , and two sides  1058 . The three-dimensional aspect can be seen in  FIG. 10B . 
       FIGS. 10C-10F  are two-dimensional cross-sectional drawings of a three-dimensional waveguide in accordance with some illustrative embodiments. The three-dimensional waveguide in  FIGS. 10C-10F  can be the same waveguide as in  FIGS. 10A and/or 10B . Dimensions  1061 ,  1062 ,  1063 ,  1064 ,  1065 ,  1066 ,  1067 ,  1068 ,  1069 , and  1070  are provided as illustrative measurements in accordance with some embodiments. In alternative embodiments, any other suitable dimensions may be used. In an illustrative embodiment, the dimension  1061  is 2.81 mm, the dimension  1062  is 2.00 mm, the dimension  1063  is 0.60 mm, the dimension  1064  is 1.00 mm, the dimension  1065  is 3.00 mm, the dimension  1066  is 0.50 mm, the dimension  1067  is 1.17 mm, the dimension  1068  is 2.0 mm, the dimension  1069  is 0.60, and the dimension  1070  is 1.75 mm. 
     In an illustrative embodiment, the three-dimensional material  1020  and waveguide  1022  of the system of  FIGS. 10A-10F  had a mean efficiency of 55.1%. The shape of the configuration of  FIGS. 10A and 10B  can be created using diamond shaping and polishing techniques. In some instances, the shapes of  FIGS. 10A-10F  can be more difficult (e.g., more steps, more sides, etc.) than other configurations (e.g., those of  FIGS. 8A, 8B, 9A, and 9B ). As explained above, the material and the waveguide of the configurations of  FIGS. 8A, 8B, 9A, 9B, and 10A-10F  include the material with the defect centers and the material without the defect centers (i.e., the waveguide). In some embodiments, the material with the defect centers is synthesized via any suitable method (e.g., chemical vapor deposition), and the waveguide is synthesized onto the material with the defect centers. In alternative embodiments, the material with the defect centers is synthesized onto the waveguide. 
     In alternative embodiments, the material and the waveguide can be synthesized (or otherwise formed) independently and attached after synthesis. For example,  FIG. 11  is a diagram illustrating a material attached to a waveguide in accordance with some illustrative embodiments. The material  1120  can be fused to the waveguide  1122 . In an illustrative embodiment, the material  1120  and the waveguide  1122  are fused together using optical contact bonding. In alternative embodiments, any suitable method can be used to fuse the material  1120  and the waveguide  1122 . 
     In an illustrative embodiment, the refractive index of the material  1120  and the waveguide  1122  are the same. Accordingly, as discussed above, more of the light that is emitted from the defect centers is directed towards the optical detector  1140  with the waveguide  1122  than without. 
     In an illustrative embodiment, because the waveguide  1122  is synthesized separately from the material  1120 , the waveguide  1122  can be manufactured into any suitable shape. In the embodiments shown in  FIG. 11 , the waveguide  1122  is a paraboloid. For example, the waveguide  1122  can be a compound parabolic concentrator. In an illustrative embodiment, the material  1120  is a cube. In such an embodiment, the length of the diagonal of one of the sides is the same as the length of the diameter of the paraboloid at the end of the waveguide  1122  attached to the material  1120 . In alternative embodiments, any other suitable shape can be used, such as any of the shapes shown in  FIGS. 8A, 8B, 9A, 9B, and 10A-10F . 
     In the embodiments of  FIGS. 7, 8A, 9A, and 10A , the light used to excite the corresponding defect centers is orthogonal to the respective side of the material that the light enters. In some instances, light entering the material through the interface at an orthogonal angle is the most efficient direction to get the light into the material. In other instances, a larger incidence angle may be more efficient than an orthogonal angle, depending upon the polarization of the light with respect to the surface orientation. In alternative embodiments, the light can enter the material at any suitable angle, even if at a less efficient angle. For example, the angle of the light entering the material can be parallel to a plane of the respective optical detector (e.g., as in  FIG. 7 ). Such an angle can be chosen based on, for example, a configuration of a magnetometer system (e.g., a DNV system) or other system constraints. 
       FIG. 12  is a flow chart of a method of forming a material with a waveguide in accordance with an illustrative embodiment. In alternative embodiments, additional, fewer, and/or different operations may be performed. Also, the use of a flow chart and/or arrows is not meant to be limiting with respect to the order or flow of operations. For example, in alternative embodiments, two or more operations may be performed simultaneously. 
     In an operation  1205 , a material with defect centers is synthesized. For example, the material can be a diamond material, and the defect centers can be NV centers. In an illustrative embodiment, chemical vapor deposition can be used to create the material with defect centers. In alternative embodiments, any suitable method for synthesizing the material with defect centers can be used. 
     In an operation  1210 , a waveguide is synthesized. For example, the waveguide can be the same material as the material with the defect centers but without the defect centers (e.g., diamond material without NV centers or other defect centers). In an illustrative embodiment, chemical vapor deposition is used to synthesize the waveguide onto the material with defect centers. For example, chemical vapor deposition can be used to form the material in the operation  1205  in the presence of nitrogen or other element or material, and the waveguide can be synthesized by continuing to deposit carbon on the material but without the nitrogen or other element or material. 
     In an operation  1215 , the material and waveguide can be cut and polished. For example, the material and waveguide can be cut and polished into one of the shapes shown in  FIGS. 8A, 8B, 9A, 9B, 10A-10F . In an illustrative embodiment, after the material and waveguide is cut and polished, the material and waveguide can be used in a magnetometer such as a DNV sensor. 
       FIG. 13  is a flow chart of a method of forming a material with a waveguide in accordance with some illustrative embodiments. In alternative embodiments, additional, fewer, and/or different operations may be performed. Also, the use of a flow chart and/or arrows is not meant to be limiting with respect to the order or flow of operations. For example, in alternative embodiments, two or more operations may be performed simultaneously. 
     In an operation  1305 , a material with defect centers is synthesized. In an illustrative embodiment, the material is diamond and the defect centers are NV centers. For example, a material can be formed using chemical vapor deposition in the presence of nitrogen or other defect material, thereby forming a material with defect centers. In alternative embodiments, any suitable method can be used to create a material with defect centers. In an operation  1310 , the material with defect centers is cut and polished. The material with defect centers can be cut into any suitable shape, such as a cube, a cuboid, etc. 
     In an operation  1315 , a waveguide is synthesized. For example, a material without defect centers can be formed using any suitable method, such as chemical vapor deposition. In an operation  1320 , the waveguide can be cut and polished. For example, the waveguide can be cut into the shape of the waveguide  822  of  FIGS. 8A and 8B , the waveguide  922  of  FIGS. 9A and 9B , the waveguide  1022  of  FIGS. 10A-10F , or the waveguide  1122  of  FIG. 11 . In alternative embodiments, the waveguide can be cut into any suitable shape. 
     In an operation  1325 , the material with the defect centers is fused to the waveguide. For example, optical contact bonding can be used to fuse the material with the defect centers with the waveguide. In alternative embodiments, an adhesive or other suitable bonding agent can be used to attach the material with the defect centers to the waveguide. In such embodiments, the substance used to fix the material with the defect centers to the waveguide can have a refractive index that is the same as or similar to the refractive index of the material. In an illustrative embodiment, after the material and waveguide are fixed together, the material and waveguide can be used in a magnetometer such as a DNV sensor. 
     In an illustrative embodiment, any of the operations described herein can be implemented at least in part as computer-readable instructions stored on a computer-readable memory. Upon execution of the computer-readable instructions by a processor, the computer-readable instructions can cause a node to perform the operations. 
     The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components. 
     With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” Further, unless otherwise noted, the use of the words “approximate,” “about,” “around,” “substantially,” etc., mean plus or minus ten percent. 
     The foregoing description of illustrative embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.