this description may use relative spatial and / or orientation terms in describing the position and / or orientation of a component , apparatus , location , feature , or a portion thereof . unless specifically stated , or otherwise dictated by the context of the description , such terms , including , without limitation , top , bottom , above , below , under , on top of , upper , lower , left of , right of , in front of , behind , next to , adjacent , between , horizontal , vertical , diagonal , longitudinal , transverse , etc ., are used for convenience in referring to such component , apparatus , location , feature , or a portion thereof in the drawings and are not intended to be limiting . furthermore , unless otherwise stated , any specific dimensions mentioned in this description are merely representative of an exemplary implementation of an optical isolation element and are not intended to be limiting . unless otherwise indicated or the context suggests otherwise , as used herein , “ a ” or “ an ” means “ at least one ” or “ one or more .” fig1 and 2 are an exploded perspective view and partial side perspective view , respectively , showing an optical sensor 100 of the type in which an optical isolation element embodying aspects disclosed herein may be employed . fig3 is a side view of a sensor 100 with an exemplary optical isolation element 150 mounted thereon . fig4 is a side view of the internal components of the sensor and the optical isolation element 150 is shown in cross - section . fig5 is a transverse cross - sectional view of the sensor 100 and optical isolation element 150 . the sensor 100 may include a sensor housing 102 ( i . e ., body , shell , sleeve , or capsule ). see , for example , fig1 - 3 . the sensor housing 102 may include an end cap 113 . in exemplary embodiments , sensor housing 102 may be formed from a suitable , optically transmissive polymer material , such as , for example , acrylic polymers ( e . g ., polymethylmethacrylate ( pmma )). the sensor 100 may include an indicator matrix layer 106 ( e . g ., graft or gel ) coated on or embedded in at least a portion of the exterior surface of the sensor housing 102 . the sensor 100 may include indicator molecules 104 , such as fluorescent indicator molecules or absorption indicator molecules distributed throughout all or a portion of the indicator matrix layer 106 . the indicator matrix layer 106 may cover the entire surface of sensor housing 102 or only one or more portions of the surface of housing 102 . furthermore , as an alternative to coating the indicator matrix layer 106 on the outer surface of sensor housing 102 , the indicator matrix layer 106 may be disposed on the outer surface of the sensor housing 102 in other ways , such as by deposition or adhesion . in some sensors including an indicator matrix layer 106 , the indicator matrix layer 106 may comprise a biocompatible polymer matrix that is prepared according to methods known in the art and coated on the surface of the sensor housing 102 . in certain sensors , the biocompatible matrix materials are permeable to an analyte or substance of interest . exemplary biocompatible matrix materials that may be used include some methacrylates ( e . g ., hema ) and hydrogels that , advantageously , can be made selectively permeable — particularly to the analyte — so as to perform a molecular weight cut - off function . in a sensor that does not include an indicator matrix layer 106 , instead of being distributed throughout an indicator matrix layer 106 , the indicator molecules 104 could simply be coated on the surface of the sensor housing 102 . the sensor 100 includes one or more light sources 108 ( a single light source is shown in the figures ), which may , for example , comprise a light emitting diode ( led ) or other light source that emits radiation , including radiation over a range of wavelengths that interact with the indicator molecules 104 . for example , in the case of a fluorescence - based sensor , light source 108 emits radiation at a wavelength which causes the indicator molecules 104 to fluoresce when the indicator molecules are in the presence of an analyte or substance of interest . however , other leds or light sources may be used depending on the specific indicator molecules applied to sensor 100 and the specific analytes or substances of interested to be detected . sensor 100 also includes one or more photodetectors 110 ( e . g ., photodiodes , phototransistors , photoresistors or other photosensitive elements ) which , in the case of a fluorescence - based sensor , is sensitive to fluorescent light emitted by the indicator molecules 104 such that a signal is generated by the photodetector 110 in response thereto that is indicative of the presence or level of fluorescence of the indicator molecules . the illustrated sensor 100 includes a first photodetector 224 and a second photodetector 226 . the sensor 100 may include one or more optical filters 112 , such as high pass or band pass filters . the one or more optical filters 112 may cover a photosensitive side of the one or more photodetectors 110 . the one or more optical filters 112 may prevent or substantially reduce the amount of radiation generated by the light source 108 from impinging on a photosensitive side of the one or more photodetectors 110 . at the same time , the one or more optical filters 112 may allow light ( e . g ., fluorescent light ) of a specified wavelength , or within a specified range of wavelengths , emitted by indicator molecules 104 to pass through and strike the photosensitive side of the one or more photodetectors 110 . this reduces “ noise ” attributable to incident radiation from the light source 108 in the light measurement signals output by the one or more photodetectors 110 . an optical isolation element such as described herein may be used in conjunction with or as an alternative to such optical filters 112 . sensor 100 may be wholly self - contained . in other words , the sensor may be constructed in such a way that no electrical leads extend into or out of the sensor housing 102 to supply power to the sensor ( e . g ., for driving the light source 108 ) or to transmit signals from the sensor 100 . instead , in one embodiment , the sensor 100 may be powered by an internal , self - contained power source , such as , for example , microbatteries , micro generators and / or other power sources . however , in one preferred embodiment , sensor 100 may be powered by an external power source ( not shown ). for example , the external power source may generate a magnetic field to induce a current in an inductive element 114 ( e . g ., a coil or other inductive element ). additionally , the sensor 100 may use the inductive element 114 to communicate information to an external data reader ( not shown ). in some embodiments , the external power source and data reader may be the same device . sensor 100 may include a semiconductor substrate 116 . in an illustrated embodiment , the circuitry is fabricated in the semiconductor substrate 116 . the circuitry may include analog and / or digital circuitry . in a non - limiting embodiment , the circuitry may be formed in the semiconductor substrate 116 using a complementary metal oxide semiconductor ( cmos ) process . however , other formation processes ( e . g ., n - type metal - oxide - semiconductor ( nmos ) or n - type metal - oxide - semiconductor ( pmos )) may alternatively be used . the one or more photodetectors 110 may be mounted on the semiconductor substrate 116 , or , alternatively , the one or more photodetectors 110 may be fabricated in the semiconductor substrate 116 . for example , in a non - limiting embodiment , the one or more photodetectors 110 may be monolithically formed in the semiconductor substrate 116 . for instance , in one embodiment , the one or more photodetectors 110 may be monolithically formed in the semiconductor substrate 116 using a complementary metal oxide semiconductor ( cmos ) process ( e . g ., using diffusions from the cmos process ). however , other formation processes ( e . g ., nmos or pmos ) alternatively may be used . the light source 108 may be mounted on the semiconductor substrate 116 . for example , in a non - limiting embodiment , the light source 108 may be flip - chip mounted on the semiconductor substrate 116 . alternatively , the light source 108 may be fabricated in the semiconductor substrate 116 . sensor 100 may also include one or more capacitors 118 . the one or more capacitors 118 may be , for example , one or more antenna tuning capacitors and / or one or more regulation capacitors . further , the one or more capacitors 118 may be in addition to one or more capacitors fabricated in the semiconductor substrate 116 . an application for which the sensor 100 was developed — although by no means the only application for which it is suitable — is measuring various biological analytes in the living body of an animal ( including a human ). for example , sensor 100 may be used to measure glucose , oxygen , toxins , pharmaceuticals or other drugs , hormones , and other metabolic analytes in , for example , the human body . the specific composition of the indicator matrix layer 106 and the indicator molecules 104 may vary depending on the particular analyte the sensor is to be used to detect and / or where the sensor is to be used to detect the analyte ( e . g ., in the blood or subcutaneous tissues ). preferably , however , indicator matrix layer 106 , if present , should facilitate exposure of the indicator molecules to the analyte . also , it is preferred that the optical characteristics of the indicator molecules ( e . g ., the level of fluorescence of fluorescent indicator molecules ) be a function of the concentration of the specific analyte to which the indicator molecules are exposed . to facilitate use in - situ in the human body , the sensor housing 102 , in one embodiment , is preferably formed in a smooth , oblong or rounded shape . other shapes and configurations could be used as well . advantageously , in certain embodiments , the sensor 100 is on the order of approximately 500 microns to approximately 0 . 85 inches in length l and on the order of approximately 300 microns to approximately 0 . 3 inches in diameter d . in certain embodiments , the sensor 100 may have generally smooth , rounded surfaces . this configuration facilitates the sensor 100 to be implanted into the human body , i . e ., dermally or into underlying tissues ( including into organs or blood vessels ) without the sensor interfering with essential bodily functions or causing excessive pain or discomfort . however , given its small size , the sensor 100 may have different shapes and configurations and still be implantable within a human without the sensor interfering with essential bodily functions or causing excessive pain or discomfort . in exemplary configurations , a preferred length of the housing is approximately 0 . 5 inches to 0 . 85 inches and a preferred diameter is approx . 0 . 1 inches to 0 . 11 inches . however , in other embodiments , the housing may be even smaller . fig3 and 4 are side views of the sensor 100 with an optical isolation element 150 mounted thereon . the optical isolation element 150 is mounted onto an end portion of the substrate 116 projecting from the inductor 114 and partially surrounds the light source 108 , photodetectors 110 , and optical filters ( if present in the sensor ) 112 . details of an exemplary optical isolation element 150 are shown in fig6 and 8 . the configuration of the optical isolation element is largely dependent upon the configuration and arrangement of the various components of the sensor , such as the inductor 114 , the substrate 116 , the light source 108 , the photodetectors 110 , and the filters 112 , as well as the internal shape of the housing 102 . the optical isolation element 150 shown in the figures is specifically configured so as to be compatible with the arrangement of the sensor 100 . the configuration of the optical isolation element and the sensor are exemplary and are not intended to be limiting . referring to fig6 and 8 , the optical isolation element 150 includes a first end wall 152 , an opposed second end wall 154 , a first sidewall 156 extending between the first end wall 152 and the second end wall 154 and an opposed second sidewall 164 also extending between the first end wall 152 and the second end wall 154 . an opening 172 is formed in a top portion of the optical isolation element 150 . in one exemplary embodiment , the second end wall 154 has a generally circular shape , and the first end wall 152 has a partial circular shape with a flat bottom edge 176 . the first sidewall 152 has a first sidewall extension 158 extending from a lower edge of the sidewall 152 and a cutout 162 adjacent to the extension 158 . similarly , the second sidewall 164 has a second sidewall extension 166 extending from a lower edge of the second side wall 164 and a cutout 174 adjacent to the extension 166 . the first and second sidewalls 156 , 164 have a curved , generally circular shape . as shown in fig6 ( b ) and 7 , the first sidewall extension 158 has a flattened surface 160 , and the second sidewall extension 166 has a flattened surface 168 . fig4 and 5 show further details of an embodiment of the installation of the optical isolation element 150 on the sensor 100 . in the illustrated embodiment , optical isolation element 150 is mounted on a portion of the semiconductor substrate 116 extending from the inductive element 114 . the first end wall 152 is disposed against an end of the inductive element 114 with the flat edge 176 resting on the top surface of the semiconductor substrate 116 . the second end wall 154 is disposed at an end of the semiconductor substrate 116 and includes a lower portion 174 extending below a top surface of the semiconductor substrate 116 . end walls 152 , 154 are generally parallel to each other and perpendicular to a longitudinal axis of the cylindrical sensor housing 102 . as shown in fig5 , the first sidewall 156 and the second sidewall 164 are disposed on opposite sides of the optical elements ( photodetectors 224 , 226 and light source ( led ) 108 ) of the sensor 100 and partially enclose the photodetectors 226 and 224 and the light source 108 . the sidewalls 156 , 164 are generally circular in shape so as to conform to the circular cross - sectional shape of the housing 102 . as shown in fig5 , the first sidewall extension 158 extends alongside the first photodetector 224 with the flattened portion 160 of the extension 158 providing a light - tight fitting between the sidewall 156 and the photodetector 224 . similarly , the sidewall extension 166 of the second sidewall 164 is disposed against the second photodetector 226 , and the flattened surface 168 of the second extension 166 provides a light - tight fitting between the sidewall 164 and the photodetector 226 . as shown in fig3 , in accordance with one non - limiting embodiment , the cutouts 162 and 170 of the first and second sidewalls 156 , 164 , respectively , rest upon the top surface of the substrate 116 . the optical isolation element can be machined or molded , and it can be made from any suitable material that is sufficiently opaque , is moldable or machinable , and is nonreactive with other components or materials within the sensor 100 . suitable materials include plastic , metal , acrylic , glass , porcelain , epoxies , nylon or delrin . undesired light paths between the optical isolation element 150 and the electronic components of the sensor 100 can be blocked or filled with opaque materials , such as overfills , underfills , epoxies , or paints . as can be appreciated from fig5 and 6 , any light emitted by the light source 108 can only escape the optical isolation element 152 through the top opening 172 of the optical isolation element . thus , light from the light source 108 impinges substantially only on the indicator matrix 106 and does not disperse into other portions of the sensor 100 . similarly , substantially the only light that will impinge upon the photodetectors 224 , 226 can reach the photodetectors only through the opening 172 of the optical isolation element 150 . extraneous light from other sources , such as ambient light , is substantially prevented from reaching the photodetectors 224 and 226 by the optical isolation element 150 . while an optical isolation element has been described and shown in considerable detail with reference to certain illustrative embodiments , including various combinations and sub - combinations of features , those skilled in the art will readily appreciate other embodiments and variations and modifications thereof as encompassed within the scope of the present disclosure . moreover , the descriptions of such embodiments , combinations , and sub - combinations is not intended to convey that an optical isolation element requires features or combinations of features other than those expressly recited in the claims . accordingly , the present disclosure is deemed to include all modifications and variations encompassed within the spirit and scope of the following appended claims .