Abstract:
Flexible, low-cost, physically robust optical coupling patches for use in spectrophotometric patient monitoring, and methods of fabrication thereof, are described. The optical coupling patch comprises a flexible base layer having a skin-contacting surface and a first aperture formed therethrough that establishes an optical interface with a skin surface when the base layer is placed against the skin surface. The optical coupling patch further comprises an elastomeric waveguiding member laterally disposed on a surface of the base layer opposite the skin-contacting surface. The optical coupling patch guides optical radiation between a laterally propagating state at a first location laterally distal from the first aperture and a generally vertically propagating state at the first aperture.

Description:
FIELD 
       [0001]    This patent specification relates to non-invasive spectrophotometric patient monitoring in which optical radiation, such as near-infrared optical radiation, is directed onto a skin surface of the patient, migrates through at least a portion of a tissue sample underlying the skin surface, and then is measured as it emanates outwardly again from the skin surface. More particularly, this patent specification relates to an optical coupler for directing the optical radiation onto the skin surface and collecting for measurement the resultant outwardly emanating optical radiation. 
       BACKGROUND 
       [0002]    Spectrophotometric systems based on visible and/or near infrared (NIR) optical radiation for achieving various non-invasive physiological measurements, such as transcranial measurements of oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (Hb) concentrations, have been in various stages of proposal and development for an appreciable number of years. Examples include continuous wave (CWS) spectrophotometric systems as discussed in WO1992/20273A2 and WO1996/16592A1, phase modulation (PMS) spectrophotometric systems as discussed in U.S. Pat. No. 4,972,331, U.S. Pat. No. 5,187,672, and WO1994/21173A1, time resolved (TRS) spectrophotometric systems as discussed in U.S. Pat. No. 5,119,815, U.S. Pat. No. 5,386,827, and WO1994/22361A1, and phased array spectrophotometric systems as discussed in WO1993/25145A1, each of these disclosures being incorporated by reference herein. It is to be appreciated that while an optical coupler according to one or more of the preferred embodiments described infra is particularly suitable for use in a non-invasive cerebral oxygenation monitoring context, the scope of the present teachings is not so limited, with one or more of the described optical couplers being readily adapted for use on other parts of the anatomy, such as the neck, the abdomen, the arms, and the legs. 
         [0003]      FIG. 1A  illustrates one prior art optical coupling configuration in which source radiation is guided from an external optical source into a tissue sample  4  by a source fiber optic cable  1 , and in which detected radiation is guided to one or more external measurement devices by return fiber optic cables  2 , wherein the source and return fiber optic cables are cemented into a rigid holder  3  for direct perpendicular abutment against the skin surface. Although perhaps suitable for laboratory experiments, the configuration of  FIG. 1A  becomes impractical in real-world clinical settings in which patients, who may be lying, sitting, or standing in various positions, require monitoring over a substantial period of time. In such cases, unfavorable leverages make it difficult to maintain the holder  3  in a secured position relative to the skin surface over a period of time in a reasonably comfortable manner as would be needed for consistency of measurement and prevention of ambient light intrusion. 
         [0004]      FIG. 1B  illustrates a different prior art approach to optical coupling as discussed in U.S. Pat. No. 5,584,296, in which both the optical sources and the optical detectors are integrated into a deformable coupling patch. External cabling requirements are made easier since only electrical power and electrical information signals need be carried to and from the device, and in view of its relative flatness and conformability, the device can be secured to the patient in a more stable and comfortable manner. One particular advantage is the ability for the cable leads to lie flat against the body, so that the both the cable leads and the patch can be readily secured in place. However, the semiconductor photodiodes needed for the on-patch optical detection are substantially less sensitive than off-patch detection solutions such as photomultiplier tubes (PMTs), resulting in lower signal-to-noise performance than if PMTs were used. Likewise, due to size and heat restrictions, the on-patch optical sources are of lesser precision and power than can be supplied using larger and more powerful off-patch sources. Electromagnetic shielding problems due to the presence of radio frequency (RF) radiation also become problematic. Moreover, the complexity brought about by the various electrical connections and RF shielding hardware reduce the mechanical flexibility and robustness of the device, such that it needs to be treated rather tenderly to reduce the risk of malfunction. Finally, the complexity of the device also increases the fabrication cost such that disposability is not a realistic option, thus bringing about the need for costly decontamination procedures between patients and/or the need for awkward, performance-reducing prophylactic sheathing measures. 
         [0005]      FIG. 1C  illustrates another prior art approach to optical coupling as discussed in U.S. Pat. No. 7,313,427, in which an optical detector is integrated into the deformable coupling patch, but in which the source optical signal is provided externally. The optical signal is guided laterally over a fiber optic cable from an edge of the coupling patch to the location at which light insertion is desired, and then is redirected vertically by use of a prism into the skin at that location. Although source precision and power issues may be improved over the configuration of  FIG. 1B , supra, many of the other disadvantages remain, such as lower signal-to-noise ratios associated with the photodiode detectors, electromagnetic shielding problems, device cost, device complexity, and reduced mechanical flexibility and robustness. 
         [0006]      FIG. 1D  illustrates another prior art approach to optical coupling as discussed in U.S. Pat. No. 4,510,938, in which both the optical sources and the optical detectors are provided externally. A first optical fiber bundle is used to transfer the source radiation laterally across a coupling structure to the desired location of light insertion, at which point the first optical fiber bundle is bent at a right angle to direct the source radiation downward onto the skin surface. A second optical fiber bundle is similarly configured for receiving the outwardly emanating radiation and transferring that radiation to an external optical detector. Disadvantageously, a substantial amount of device height in a direction outward from the skin surface (i.e., a substantial amount of overall device thickness) is needed to accommodate the bending of the optical fiber bundles. The larger size brings about positional stability issues, and the presence of the optical fiber bundles contributes to reduced device flexibility/conformability as well as physical robustness issues. 
         [0007]      FIG. 1E  illustrates another prior art approach to optical coupling as discussed in U.S. Pat. No. 6,556,851, in which both the optical sources and the optical detectors are provided externally, and in which prisms are used to avoid the need for right-angle bending of the optical fiber cables. Although the overall device can be flatter than that of  FIG. 1D , supra, the optical fiber cables can limit flexibility and conformability, as well as bring about problems with device robustness against rough handling. By way of example, a substantial degree of device bending can damage the optical fiber cables and/or disturb their physical relationship to the prisms at one or more failure points, causing a reduction in performance and/or device failure. 
         [0008]    It would be desirable to provide an optical coupling device for use in non-invasive spectrophotometric patient monitoring that provides an advantageous combination of physical robustness, relatively low fabrication cost, minimal profile thickness, disposability, and durability, while also providing for effective optical coupling with good signal to noise performance. Each of the above-described prior art optical coupling configurations is believed to bring about one or more disadvantages and/or to contain one or more shortcomings that is avoided by one or more devices or techniques according to one or more of the preferred embodiments described hereinbelow. Other issues arise as would be apparent to one skilled in the art upon reading the present disclosure. 
       SUMMARY 
       [0009]    According to one preferred embodiment, a flexible, low-cost, physically robust optical coupling patch is provided for use in spectrophotometric patient monitoring. The optical coupling patch comprises a flexible base layer having a skin-contacting surface and a first aperture formed therethrough, the flexible base layer comprising a first elastomeric material having a first refractive index, the first aperture establishing an optical interface with a skin surface when the flexible base layer is placed against the skin surface. The optical coupling patch further comprises an elastomeric waveguiding member laterally disposed on a surface of the flexible base layer opposite the skin-contacting surface. The elastomeric waveguiding member comprises a second elastomeric material having a second refractive index greater than the first refractive index and is configured to guide optical radiation between (i) a laterally propagating state at a first location laterally distal from the first aperture, and (ii) a generally vertically propagating state at the first aperture. The elastomeric waveguiding member includes a substantially planar reflecting surface shaped integrally thereinto near the first aperture. The reflecting surface is oriented at an angle that causes reflective redirection of the optical radiation between the laterally propagating state and the vertically propagating state. The optical coupling patch further comprises a flexible cladding material having a third refractive index less than the second refractive index. The flexible cladding material selectively covers the elastomeric waveguiding member such that a cavity is formed directly adjacent the integrally formed reflecting surface of the elastomeric waveguiding member, wherein the cavity is occupied by either air or a low-index material having a fourth refractive index less than the third refractive index, whereby the reflective redirection of the optical radiation is facilitated. 
         [0010]    Also provided according to a preferred embodiment is an optical coupling patch for use in spectrophotometric patient monitoring having a bottom surface for contacting a skin surface of a patient and a side edge including first and second end facets. The optical coupling patch is operable to guide source radiation received at the first end facet to a downward facing first aperture formed in the bottom surface for downward introduction into the patient. The coupling patch is further operable to receive radiation emanating upwardly from the patient at a second aperture formed in the bottom surface and to guide the received radiation from the second aperture to the second end facet. The optical coupling patch comprises a flexible base layer, first and second elastomeric waveguiding members disposed on the base layer and extending from the first and second end facets, respectively, to the first and second apertures, respectively. The optical coupling patch further comprises a flexible first cladding layer disposed on the base layer and extending alongside the first and second elastomeric waveguiding members, and a flexible second cladding layer disposed atop the first cladding layer and the first and second elastomeric waveguiding members. The base layer, the first cladding layer, and the second cladding layer each have an index of refraction less than that of either of the first and second elastomeric waveguiding members. The first and second elastomeric waveguiding members each include a substantially planar surface shaped integrally thereinto near its respective aperture that is oriented at an angle between about 35 and 55 degrees relative thereto, whereby the source radiation propagating laterally in the first elastomeric waveguiding member is reflectively redirected downward toward the first aperture, and whereby the upwardly emanating radiation received at the second aperture is reflectively redirected to propagate laterally in the second elastomeric waveguiding member toward the second end facet. 
         [0011]    Also provided according to another preferred embodiment is a method for fabricating a flexible, slab-like optical coupling patch for use in spectrophotometric patient monitoring, the optical coupling patch having a bottom surface for contacting a skin surface of a patient, and a side edge. The method comprises providing a flexible base layer comprising an elastomeric material, the base layer extending to the side edge and having a lower surface corresponding to the bottom surface of the optical coupling patch and an upper surface opposite the lower surface, the base layer having an opening extending through the lower and upper surfaces thereof. The method further comprises forming an elastomeric waveguiding member on the upper surface of the base layer extending laterally thereacross between the side edge and the opening, the elastomeric waveguiding member comprising a first end facet facing in a lateral direction at the side edge, a second end facet facing downwardly into the first opening, and a substantially planar surface integrally formed into the first elastomeric waveguiding member by virtue of its outer shape at a location directly above the second end facet, the substantially planar surface being oriented at an angle between about 35 and 55 degrees relative to the second end facet. The method further comprises forming at least one flexible cladding layer that covers the base layer and the elastomeric waveguiding member. 
         [0012]    Also provided according to another preferred embodiment is a flexible, slab-like optical coupling patch for use in spectrophotometric patient monitoring. The optical coupling patch has a bottom surface for contacting a skin surface of a patient and a downward facing first aperture formed in the bottom surface. The optical coupling patch is operable to guide optical radiation between (i) a laterally propagating state at a first location laterally distal from the first aperture, and (ii) a generally vertically propagating state at the first aperture. The optical coupling patch comprises a flexible base layer including the skin-contacting surface and a first opening formed therethrough that establishes the first aperture. The first aperture establishes an optical interface with the skin surface when the flexible base layer is placed thereagainst. The optical coupling patch further comprises a light deflecting member disposed above the first opening and configured to deflect optical radiation between a generally vertically propagating state thereat and a laterally propagating state thereat. The optical coupling patch further comprises an elastomeric waveguiding member disposed on a surface of the flexible base layer opposite the skin-contacting surface and extending laterally across the optical coupling patch from the light deflecting member to the first location laterally distal from the first aperture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIGS. 1A-1E  each illustrate an optical coupler according to the prior art; 
           [0014]      FIG. 2  illustrates a non-invasive spectrophotometric patient monitoring system including an optical coupling assembly according to a preferred embodiment; 
           [0015]      FIGS. 3A-3B  illustrate perspective views of an optical coupling patch according to a preferred embodiment; 
           [0016]      FIG. 4A  illustrates a bottom view of an optical coupling patch according to a preferred embodiment; 
           [0017]      FIGS. 4B-4D  illustrate side cut-away views of the optical coupling patch of  FIG. 4A ; 
           [0018]      FIGS. 5A-5B  illustrate exploded perspective views of the optical coupling patch of  FIG. 4A ; 
           [0019]      FIG. 6  illustrates a side cut-away view of an optical coupling assembly according to a preferred embodiment; 
           [0020]      FIGS. 7A-7B  illustrate perspective views of an optical coupling patch according to a preferred embodiment; 
           [0021]      FIG. 8  illustrates a bottom view of an optical coupling patch according to a preferred embodiment; 
           [0022]      FIG. 9  illustrates an exploded perspective views of the optical coupling patch of  FIG. 8 ; 
           [0023]      FIG. 10  illustrates a perspective view of an optical coupling patch according to a preferred embodiment; 
           [0024]      FIG. 11  illustrates a side cut-away view of an optical coupling patch according to a preferred embodiment; 
           [0025]      FIG. 12  illustrates a side cut-away view of an optical coupling patch according to a preferred embodiment; 
           [0026]      FIG. 13  illustrates a side cut-away view of an optical coupling patch according to a preferred embodiment; 
           [0027]      FIG. 14  illustrates a side cut-away view of an optical coupling patch according to a preferred embodiment; and 
           [0028]      FIG. 15  illustrates a side cut-away view of an optical coupling patch according to a preferred embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 2  illustrates a spectrophotometric patient monitoring system including a console unit  211  and an optical coupling apparatus  202  according to a preferred embodiment. The optical coupling apparatus  202  is entirely passive, containing no optical signal generation devices or electrooptical detection devices, but rather is configured to transfer source optical radiation from the console unit  211  into a skin surface of a patient P, and to receive and transfer optical radiation emanating outwardly from the skin surface back to the console unit  211  for measurement. Optical coupling apparatus  202  comprises a fiber optic cable assembly  206  including a source fiber optic cable  206 S and a return fiber optic cable  206 R, each preferably containing a bundle of optical fibers. The source and return fiber optic cables  206 S and  206 R are coupled at one end to the console unit  211  and at the other end to an optical coupling patch  204  via an edge adapter  208 . 
         [0030]    The console unit  211  includes one or more optical sources, such as a laser source, and one or more optical detectors, such as a photomultiplier tube (PMT), along with associated control, processing, and display circuitry as may be used with any of a variety of spectrophotometric techniques. One wavelength range for which the optical coupling apparatus  202  is suitable is the 500 nm-1000 nm range. The optical coupling apparatus  202  is particularly suitable for use with optical radiation in the range of 690 nm-830 nm, although the scope of the preferred embodiments is not so limited. 
         [0031]    Optical coupling patch  204  comprises a flexible, thin, low-profile, generally slab-like body designed to be easily brought into contact with the skin surface of the patient and maintained thereagainst over a relatively long time period while also being comfortable. Any of a variety of methods, or combination of methods, for maintaining the optical coupling patch  204  in contact with the skin surface are within the scope of the preferred embodiments including, but not limited to: directly adhering a bottom surface of the optical coupling patch  204  to the skin using an adhesive; adhering the optical coupling patch  204  to the skin around a periphery thereof using an oversized adhesive patch; and using various elastic wrap or ACE® bandaging configurations. In one preferred embodiment that is particularly applicable to cerebral spectrophotometric monitoring, the optical coupling patch  204  can be affixed on the inside of an headband assembly, a wearable hat assembly, or helmet assembly that is worn by the patient during the monitoring session. 
         [0032]    As used herein with respect to optical coupling patch  204 , the term lateral direction refers to a direction generally parallel to or along the patient&#39;s skin surface when the optical coupling patch  204  is positioned thereagainst, while the term vertical direction refers to a direction generally normal to the skin surface when the optical coupling patch  204  is positioned thereagainst (i.e., an inward/outward direction with respect to the skin surface). Thus, it is to be appreciated that the terms “lateral” and “vertical” as used herein with respect to optical coupling patch  204  do not imply any particular direction with respect to gravity or other fixed frame of reference in the surrounding clinical environment. It is to be further appreciated that the term “lateral” as used herein with respect to optical coupling patch  204  does not imply restriction to a single geometric plane, which is particularly relevant for cases in which the optical coupling patch  204  is applied for monitoring of the neck, arms, legs, feet, or fingers, or when the optical coupling patch  204  is only partially supported or lying on a non-planar surface. 
         [0033]    Integrally formed into optical coupling patch  204  is a source elastomeric waveguiding member  210  configured and dimensioned to transfer source optical radiation laterally from an edge of the optical coupling patch  204  to an emitting aperture  212  that faces downwardly into the skin surface. Also integrally formed into optical coupling patch  204  is a detection elastomeric waveguiding member  216  configured and dimensioned to receive radiation emanating upwardly at a detection aperture  214  and to transfer that radiation laterally to the edge of the optical coupling patch  204 . Although the source elastomeric waveguiding member  210  and detection elastomeric waveguiding member  216  preferably terminate near each other along a common side of the optical coupling patch  204 , thereby simplifying optical fiber cabling requirements, the scope of the present teachings is not so limited and includes configurations in which the source elastomeric waveguiding member  210  and detection elastomeric waveguiding member  216  terminate along different sides of the optical coupling patch  204 . 
         [0034]      FIGS. 3A and 3B  illustrate perspective views of the optical coupling patch  204  as held in a hand, with edge adapter  208  and fiber optic cable assembly  206  omitted. In one exemplary preferred embodiment, the optical coupling patch  204  has lateral dimensions of about 3 inches (7.62 cm) by 1.5 inches (3.81 cm), and a thickness of about 0.15 inches (3.8 mm). In one preferred embodiment, the optical coupling patch  204  is entirely elastomeric in construction, with no optical fiber bundles and no rigid components contained therein, for providing an advantageous combination of conformability, durability, and low fabrication cost. In alternative preferred embodiments to be described further infra (see  FIGS. 11-15 ) a rigid reflective optical component, such as a prism or a planar mirror element, can be positioned near each elastomeric waveguiding member, but that element is sufficiently small such that the overall flexible, bendable, and “floppy” physical character of the optical coupling patch is not substantially affected. 
         [0035]    In accordance with a preferred embodiment, the optical coupling patch  204  comprises a multilayer structure in which each layer is formed from a thermally curable polysiloxane elastomer having a Shore OO durometer hardness in the range of 25 to 95. In another preferred embodiment, the polysiloxane elastomer exhibits a Shore A durometer hardness in the range of 20 to 60. In other preferred embodiments, the polysiloxane elastomer exhibits a Shore A durometer hardness in the range of 10 to 90. In addition to flexibility, durability, and low cost, the class of preferred polysiloxane elastomers further exhibits chemical inertness, water repellency, electrical insulation properties, and biocompatibility. Other classes of elastomeric materials that may be usable in conjunction with one or more of the preferred embodiments include certain flexible polybutadienes, epoxy resins, and polyurethanes, and more generally any elastomeric material known or hereinafter developed that possesses equivalent optical and mechanical properties to the described polysiloxane elastomers while being sufficiently safe for placement on human skin. 
         [0036]      FIG. 4A  illustrates a bottom view of the optical coupling patch  204 , and  FIGS. 4B-4D  illustrate side cutaway views of the optical coupling patch  204  along respective cutting planes as positioned along a skin surface.  FIGS. 5A-5B  illustrate perspective exploded views of the optical coupling patch  204 . Optical coupling patch  204  comprises a base layer  426  through which is formed the emitting aperture  212  and the detection aperture  214 . The source elastomeric waveguiding member  210  extends laterally across the base layer  426  between a laterally facing end facet  418  and the downwardly facing emitting aperture  212 . The detection elastomeric waveguiding member  216  extends laterally across the base layer  426  between a laterally facing end facet  420  and the downwardly facing detection aperture  214 . A first cladding layer  424  is formed on the base layer  426  and extends alongside the elastomeric waveguiding members  210 / 216 , and a second cladding layer  422  is formed thereover. Each of the apertures  212  and  214  is laterally distal from its associated end facet  418  and  420 , respectively. By laterally distal, it is meant that the optical radiation needs to be laterally guided over a substantial distance relative to the thickness of the optical coupling patch to get from the point of introduction (e.g., the end facet) over to the point of exit (the aperture), consistent with the purpose and form factor of the device. Thus, for example, if the thickness of the optical coupling patch is about 0.15 inches (3.8 mm), then the features and advantages according to the preferred embodiments become especially apparent when the lateral propagation distance of the optical radiation is at least several times that thickness, e.g. at least about 0.60 inches (1.5 cm), although the scope of the preferred embodiments is not so limited. 
         [0037]    In accordance with a preferred embodiment, the source elastomeric waveguiding member  210  includes a substantially planar reflecting surface  428  shaped integrally thereinto directly above the emitting aperture  212 . The planar reflecting surface  428  can be formed, for example, by virtue of an appropriate mold shape during mold-based formation of the source elastomeric waveguiding member  210 , or by using a precision slicing step. Preferably, an air cavity  430  is formed directly adjacent to the planar reflecting surface  428  to facilitate reflection. The reflecting surface  428  is formed at a 45-degree angle relative to the vertical such that source optical radiation that is laterally propagating from the end facet  418  is reflectably redirected in a generally downward direction into the skin surface through the emitting aperture  212 . In other preferred embodiments, the angle of the reflecting surface  428 , which could alternatively be referred to as a reflective elbow feature, is between about 35 and 55 degrees relative to the vertical. Detection elastomeric waveguiding member  216  is similarly formed with a substantially planar reflecting surface  432  that is molded, sliced, or otherwise fabricated integrally thereinto, whereby radiation that is upwardly emanating at the detection aperture  214  is reflectively redirected to propagate laterally in the detection elastomeric waveguiding member  216  toward the end facet  420 . In one preferred embodiment, a reflective coating can be placed on the planar reflective surfaces  428  and  432  for further facilitating the reflective redirection of the optical radiation. In one preferred embodiment, the air gaps  430  and  434  can be filled with a low-index material having a refractive index substantially lower than any of the base layer  426 , the cladding layers  422 / 424 , and elastomeric waveguiding members  210 / 216 . 
         [0038]    For one exemplary preferred embodiment suitable for spectrophotometric monitoring in the wavelength range of 690 nm-830 nm, the elastomeric waveguiding members  210 / 216  are formed using a polysiloxane elastomer that exhibits an optical loss of less than 0.3 dB/cm and an index of refraction greater than 1.45 over that wavelength range, while the base layer  426  and cladding layers  422 / 424  comprise optically opaque polysiloxane elastomers exhibiting indices of refraction less than 1.42 over that wavelength range. For another preferred embodiment, the elastomeric waveguiding members  210 / 216  are formed using a polysiloxane elastomer that exhibits an optical loss of less than 0.2 dB/cm and a refractive index greater than 1.54 for that wavelength range. 
         [0039]    Examples of suitable polysiloxane elastomers for the elastomeric waveguiding members  210 / 216  are described, for example, in U.S. Pat. No. 7,160,972, which is incorporated by reference herein. Another example of a suitable polysiloxane elastomer for the elastomeric waveguiding members  210 / 216  is LS-6257 LIGHTSPAN® Optical Thermoset available from NuSil Technology LLC of Carpinteria, Calif., which exhibits a Shore A durometer hardness of 35 (corresponding to a Shore OO durometer hardness of about 83), a refractive index between about 1.55-1.56 for all wavelengths between 690-830 nm, and an optical loss of below 0.2 dB/cm for all wavelengths between 690-830 nm. An example of a suitable polysiloxane elastomer for the base layer  426  and cladding layers  422 / 424  is NuSil LS-6941 LIGHTSPAN® Optical Thermoset, which exhibits a Shore A durometer hardness of 50 (corresponding to a Shore OO durometer hardness of about 90) and a refractive index between about 1.40-1.41 for all wavelengths between 690-830 nm. Preferably, the NuSil LS-6941 LIGHTSPAN® Optical Thermoset is pigmented with a black pigment for opaqueness, such as MED-4900-2 color masterbatch, also available from NuSil. Another example of a suitable polysiloxane elastomer for the base layer  426  and cladding layers  422 / 424  is a similarly pigmented version of SILBIONE® RTV 4410 QC A/B Elastomer available from Bluestar Silicones USA Corporation of East Brunswick, N.J., having a Shore A durometer hardness of 10 (corresponding to a Shore OO durometer hardness of about 55). The preferred cladding materials preferably demonstrate adequate biocompatibility and suitability for contact with human skin in accordance with appropriate evaluation standards such as EN/ISO 10993 and appropriate regulatory classifications such as 93/42/CEE European Directive (Class I) or US Pharmocopeia (Class VI). 
         [0040]    Fabrication of the optical coupling patch  204  can proceed as follows. The base layer ( 426 ) is formed by flowing a thermally curable elastomer into a mold, and then thermally curing the flowed layer. The downward facing apertures ( 212 / 214 ) are formed into the base layer  426  either by virtue of the base layer mold design or by a stamping/cutting process subsequent to base layer cure. Elastomeric waveguiding members ( 210 / 216 ) are then formed upon the base layer ( 426 ) either by a molding step or by placing separately prefabricated versions (e.g., separately molded versions) of the elastomeric waveguiding members thereon in appropriate alignment with the apertures. As mentioned previously, the substantially planar reflecting surfaces ( 428 / 432 ) can be formed by virtue of the mold shape (e.g., having appropriately slanted mold sidewalls at those locations), or in a precision post-cure slicing step. The cladding layers ( 422 / 424 ) are then formed atop the base layer/elastomeric waveguiding member assembly in a manner that results in the presence of the air gaps ( 430 / 434 ) next to the planar reflecting surfaces, which can be achieved in a variety of ways. In one example, the first cladding layer ( 424 ) is flowed while removable stoppers are positioned over the planar reflecting surfaces ( 428 / 432 ). After curing of the first cladding layer ( 424 ), the removable stoppers are removed to expose the air gaps in uncovered form. Finally, a separately prefabricated version (e.g., separately molded version) of the second cladding layer ( 422 ) is adhered over the top of the first cladding layer to enclose the air gaps ( 430 / 434 ). 
         [0041]      FIG. 6  illustrates a side cut-away view of the optical coupling assembly  202  at an interface between the optical coupling patch  204  and the source fiber optic cable  206 S, which are mechanically and optically coupled by the edge adapter  208 . The source fiber optic cable  206 S comprises an outer sheath  606  and a plurality of optical fibers  604 . In one preferred embodiment, the edge adapter  208  is configured with a channel  610  through which the optical fibers  604  are inserted and brought into abutment with the edge facet  418  of the source elastomeric waveguiding member  210 . Edge adapter  208  comprises a body made of stainless steel or other rigid material formed into a slot-like shape as shown that compressibly holds the optical coupling patch  204  to maintain the abutment of the edge facet  418  and the optical fibers  604 , optionally using an acrylic or epoxy adhesive to further secure the optical coupling patch  204 . Optionally, index-matching adhesives or other index-matching methods can be used to reduce reflective losses at the interface between the optical fibers  604  and the source elastomeric waveguiding member  210 . Similar interfacing is provided between the return fiber optic cable  206 R and the detection elastomeric waveguiding member  216 . It is to be appreciated that  FIG. 6  represents but one example of a variety of different configurations that can be used to mechanically and optically connect the optical coupling patch  204  with the source/return fiber optic cables  206 S/ 206 R as could be achieved by a person skilled in the art without undue experimentation in view of the present disclosure. 
         [0042]    For one preferred embodiment, the fiber optic cable assembly  206  and edge adapter  208  can be reusable while the optical coupling patch  204  is disposable, in which case a small, disposable prophylactic (not shown) can be used to cover the edge adapter  208  during each use. In other preferred embodiments, the entire optical coupling assembly  202  including the fiber optic cable assembly  206 , the edge adapter  208 , and the optical coupling patch  204  are disposable, an option which is made more practical in view of the relatively low material and fabrications cost of the optical coupling patch  204 . In still other preferred embodiments, the edge adapter  208  is replaced by a non-rigid, permanent coupling scheme between the fiber optic cable assembly  206  and optical coupling patch  204 , the entire optical coupling assembly again being disposable. 
         [0043]      FIGS. 7A-7B  illustrate top and bottom perspective views, respectively, of an optical coupling patch  704  that is similar to the optical coupling patch  204  of  FIGS. 2-6 , supra, except that multiple source and detection elastomeric waveguiding members are provided. The optical coupling patch  704  represents but one of a rich variety of design possibilities for all-elastomeric optical couplers (or virtually all-elastomeric optical couplers, see  FIG. 11  and associated description infra) that are within the scope of the preferred embodiments.  FIG. 8  illustrates a bottom view, and  FIG. 9  illustrates an exploded perspective view, of the optical coupling patch  704 . Optical coupling patch  704  includes source elastomeric waveguiding members  710 , emitting apertures  714 , detecting apertures  716 , detection edge facets  718 , source edge facets  720 , a first cladding layer  724 , a second cladding layer  722 , and a base layer  726 . Source elastomeric waveguiding members  710  each include an angled, substantially planar reflecting surface  930  formed integrally thereinto, and detection elastomeric waveguiding members  716  each include an angled, substantially planar reflecting surface  934  formed integrally thereinto. In one exemplary preferred embodiment, the optical coupling patch  704  has lateral dimensions of about 3 inches (7.62 cm) by 1.5 inches (3.81 cm), and a thickness of about 0.15 inches (3.8 mm). One exemplary size for each of the emitting apertures  714  is about 0.08 inches (2 mm) square, these dimensions also describing the cross-sectional shape of each source elastomeric waveguiding member  710 . One exemplary size for each of the detection apertures  716  is about 0.08 inches (2 mm) by 0.24 inches (6 mm), these dimensions also describing the cross-sectional shape of each detection elastomeric waveguiding member  716 . 
         [0044]    Using the term longitudinal to refer to the general lateral direction between the emitting/detecting apertures  712 / 714  and the source/detection edge facets  720 / 718  (i.e., the “y” direction in  FIGS. 7A-9 ), and using the term side-to-side to refer to the lateral direction perpendicular to the longitudinal direction (i.e., the “x” direction in  FIGS. 7A-9 ), the source elastomeric waveguiding members  710  are adiabatically routed in the side-to-side direction as they extend longitudinally between their respective emitting apertures  712  and source edge facets  720 , for accommodating a larger cross-sectional size for the detection elastomeric waveguiding members  716 . By adiabatically routed, it is meant that any side-to-side routing in the source elastomeric waveguiding members  710  is implemented gradually over a long longitudinal distance as compared to their cross-sectional dimension, for reducing optical loss associated with the side-to-side routing. Because detected photons are precious and few in comparison to source photons in spectrophotometric techniques, it is preferable to make the detection apertures  716  larger in size, rather than the emitting apertures  714  larger in size, in the event such size variation is permitted by the particular spectrophotometric technique being used. For similar reasons, it is preferable that any side-to-side routing that is needed to accommodate the desired device dimensions and aperture patterns be applied to source elastomeric waveguiding members rather than detection elastomeric waveguiding members. 
         [0045]      FIG. 10  illustrates a perspective view of an optical coupling patch  1004  according to another preferred embodiment, with cladding layers omitted for clarity of presentation. Shown in  FIG. 10  is a base layer  1026  upon which is disposed source elastomeric waveguiding members  1010  including planar reflective surface features  1030  and detection elastomeric waveguiding members  1014  including planar reflective surface features  1034 . The detection elastomeric waveguiding members  1016  are adiabatically tapered in a side-to-side cross-sectional dimension and the source elastomeric waveguiding members  1010  are adiabatically routed in the side-to-side direction in order to accommodate a long, slender shape for the optical coupling patch  1004  as may be useful for various monitoring applications. 
         [0046]      FIG. 11  illustrates a side cut-away view of an optical coupling patch  1104  according to a preferred embodiment that is similar to the optical coupling patch  204  of  FIGS. 2-6 , supra, except that one or more rigid reflective optical components is included to facilitate the reflective redirection of the propagating radiation between the lateral and generally vertical directions. Shown in  FIG. 11  is a side cut-away view along a detection elastomeric waveguiding member  1116  of the optical coupling patch  1104 , which also includes a detection aperture  1114 , a base layer  1126 , and lower/upper cladding layers  1124 / 1122 , the detection elastomeric waveguiding member  1116  including a substantially planar surface  1132  oriented an angle (e.g., 45 degrees) relative to the vertical. According to the preferred embodiment of  FIG. 11 , instead of an air gap adjacent to the planar surface  1132 , a planar mirror element  1150  is positioned directly adjacent the planar surface  1132  for facilitating the reflective redirection of the optical radiation. In another preferred embodiment shown in  FIG. 12 , a planar mirror element  1250  is implemented as a silvered (or otherwise reflectively coated) surface of a prism-shaped solid  1251 , which could provide for easier manipulation and placement of the planar mirror element in some fabrication scenarios. 
         [0047]    Fabrication of the optical coupling patch  1104  can proceed in a manner similar to that of optical coupling patch  204 , supra, except that instead of a removable stopper being placed on the planar surface  1132  prior to flowing the lower cladding layer  1124 , the planar mirror element  1150  is instead placed there at that time. Also, for the preferred embodiment of  FIG. 11 , the upper cladding layer  1122  can be formed integrally with the lower cladding layer  1124  in a common flowing and curing step. 
         [0048]      FIG. 13  illustrates a side cut-away view of an optical coupling patch  1304  according to a preferred embodiment that is similar in many respects to the optical coupling patch  204  of  FIGS. 2-6 , supra, except that an internally reflecting prism  1360  is used to deflect the light between vertically and horizontally propagating states. Shown in  FIG. 13  is a side cut-away view along a detection elastomeric waveguiding member  1316  of the optical coupling patch  1304 , which also includes a detection aperture  1314 , a base layer  1326 , and lower/upper cladding layers  1324 / 1322 . Here, however, the detection elastomeric waveguiding member  1316  only extends from an end facet  1318  to the prism  1360 , rather than having an elbow and extending all the way to the downward-facing detection aperture  1314 . The optical radiation is deflected between vertically and horizontally propagating states by the prism  1360 . 
         [0049]    In the preferred embodiment of  FIG. 13 , an air gap  1330  is formed adjacent to the internally reflecting surface of the prism  1360  to further facilitate the total internal reflection of the optical radiation. In the preferred embodiment of  FIG. 13 , an opening  1362  in the base layer  1326  located immediately below the prism  1360  is occupied by air. In the preferred embodiment of  FIG. 14  there is no air gap above the prism  1360 , but rather the cladding layer  1324  occupies that space. In other preferred embodiments (not shown) a different low-index material can be used to occupy that space. For the preferred embodiment of  FIG. 14 , total internal reflection can be achieved by using a prism material of sufficiently high index relative to the cladding material for total internal reflection. In the preferred embodiment of  FIG. 15  the opening  1362  immediately below the prism  1360  is occupied by the same elastomeric material as the detection elastomeric waveguiding member  1316 . In other preferred embodiments (not shown) different materials, such as index-matching materials, can be used to occupy the opening  1362 . 
         [0050]    Whereas many alterations and modifications of the preferred embodiments will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that the particular embodiments shown and described by way of illustration are in no way intended to be considered limiting. By way of example, although the optical coupling patches according to one or more of the preferred embodiments described supra are bidirectional in function (i.e., providing both optical source coupling and optical detection coupling functions), optical coupling patches that are unidirectional in function (i.e., providing only optical source coupling, or only optical detection coupling) are also within the scope of the preferred embodiments. 
         [0051]    By way of further example, although the source radiation (detected radiation) is illustrated in one or more of the preferred embodiments supra as entering (exiting) the optical coupling patch at a laterally facing end facet, in alternative preferred embodiments the source radiation (detected radiation) may enter (exit) the optical coupling patch along a vertically facing facet. In such cases, the optical radiation would be deflected near the entry facet (exit facet) between vertically and horizontally propagating states using a deflection scheme similar to one or more of the above-described deflection schemes (for example, the deflection scheme near apertures  212 / 214  of  FIG. 2 , supra). Thus, in such cases, the optical radiation would be deflected twice inside the optical coupling patch, at respective locations that are laterally distal from each other, with the optical radiation being laterally guided between those locations by an elastomeric waveguiding member. Thus, reference to the details of the described embodiments are not intended to limit their scope, which is limited only by the scope of the claims set forth below.