HK1151351B - Optical device components - Google Patents

Description

Optical device assembly

This non-provisional application claims priority to U.S. provisional patent application No.60/977,467, filed on 4.10.2007, which is incorporated herein by reference in its entirety.

Background

Whether the sample is a gas, liquid or solid, its basic property is that it is prone or not to absorb or scatter light of a particular wavelength. Characterization of the propensity of a sample to absorb, scatter or transmit is the basis for many optical measurements and instruments (e.g., spectrophotometry). The accuracy and repeatability of measurements made using optical means involves many factors, including the strength of the signal reaching one or more detectors. The optical device may be used to measure the presence and amount of a component in human or animal blood or interstitial fluid. In one example, a non-invasive (non-invasive) optical device may use some form of spectroscopy to acquire a signal or spectrum from a target region of a user's body.

Diabetes is a chronic disease that, when uncontrolled, can cause serious damage to many body systems over time, including nerves, blood vessels, eyes, kidneys and the heart. The national institute for diabetes, digestive system disease, and renal disease (NIDDK) estimates that 2360 million people in the united states or 7.8% of the total population in the united states have diabetes in 2007. Worldwide, the World Health Organization (WHO) estimates that more than 1.8 million people have diabetes, and by 2030 they expect this number to increase to 3.66 million, with 3030 million in the united states. According to WHO, it is estimated that 110 million people die from diabetes in 2005. They predict that diabetes mortality will increase by more than 50% overall and by more than 80% in middle-upper income countries by 2006 to 2015.

Diabetes is a significant economic burden to individuals and the whole society. According to the American diabetes Association, the total annual economic cost of diabetes in the United states in 2007 is estimated to amount to $ 1740 million. This figure has increased by $ 420 million since 2002. This 32% increase means that the dollar amount is rising above 80 billion dollars per year.

One important element of diabetes management is that diabetic patients self-monitor blood glucose (SMBG) concentrations in a home environment. By frequently testing blood glucose levels, diabetics can better manage medication, diet, and exercise to continuously control and prevent long-term adverse health outcomes. Indeed, 1441 diabetic patients have been closely focused on diabetes control and complications experiments (DCCT) for several years and the results indicate that only 1/4, 1/2, 1/3 of those patients who were tested daily for multiple blood glucose levels according to the intensive control regimen developed diabetic eye disease, renal disease, and neurological disease, and very few of those patients who had the early forms of these three complications had worsened compared to the standard treatment group.

However, current monitoring techniques prevent normal use because it is inconvenient and painful to draw blood through the skin prior to analysis, which makes many diabetics less diligent than they should do to control blood glucose well. As a result, non-invasive measurement of glucose concentration is an attractive and advantageous development of diabetes management. Non-invasive monitoring would make multiple tests per day painless and more popular with pediatric diabetics. According to a study published in 2005 (J, Wagner, c.malchoff, and g.abbott, diabetes technology & Therapeutics, 7(4)2005, 612-.

There are many non-invasive methods for blood glucose determination. A non-invasive blood chemistry detection technique involves the collection and analysis of spectral data. Since other components (e.g. skin, fat, muscle, bone, interstitial fluid) are present in addition to blood in the region being sensed, extracting information about blood characteristics (e.g. blood glucose concentration) from spectral or other data obtained from spectroscopy is a complicated problem. Such other components can affect these signals in such a way as to change the reading (reading). In particular, the amplitude of the resulting signal may be much greater than the amplitude of the portion of the signal corresponding to blood, thus limiting the ability to accurately extract blood characteristic information.

Disclosure of Invention

Embodiments of the present invention relate to an apparatus comprising a light source generating a plurality of light beams, each of the plurality of light beams having a different wavelength range. The device further comprises a light tunnel (light tunnel) for directing the plurality of light beams to the target area, an aperture (aperture) for directing the plurality of light beams emitted from the target area to a lens configured for collecting (collect) the light beams emitted from the target area. Further, the apparatus includes a detector including a plurality of light sensing devices, each light sensing device configured to detect a light beam and generate an output signal indicative of a detected light intensity, and a processor for determining a blood characteristic as a function of each generated output signal.

Embodiments relate to a light collection system including a lens positioned adjacent a target area, an aperture positioned between the lens and the target area and configured to direct a plurality of light beams emitted from the target area, and one or more filters.

Drawings

In the drawings, which are not necessarily drawn to scale, like reference numerals describe substantially similar components throughout the several views. Like reference numerals having different letter suffixes represent different instances of substantially similar components. The accompanying drawings illustrate, by way of example and not by way of limitation, various embodiments discussed herein.

Fig. 1A-B illustrate plots of pulse waves corresponding to light absorption by arterial blood, according to some embodiments.

FIG. 2 illustrates an optical construction according to some embodiments.

Fig. 3 illustrates an existing optical configuration for performing optical measurements of biological samples, according to some embodiments.

Fig. 4A-B illustrate optical configurations for performing optical measurements of biological samples, according to some embodiments.

Fig. 5 illustrates a cross-sectional view of a light funnel according to some embodiments.

FIG. 6 illustrates components of a light source according to some embodiments.

Fig. 7 illustrates a cross-sectional view of a light funnel having a matrix of infrared emitting diode (IRED) arrays disposed therein, according to some embodiments.

Detailed Description

The following detailed description includes a discussion of the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments, which are also referred to herein as "examples," are described in sufficient detail to enable those skilled in the art to practice the invention. These embodiments may be combined, other embodiments may be utilized, or structural and logical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

As used herein, the terms "a" or "an" are intended to include one or more than one, and the term "or" is intended to mean a non-exclusive "or," unless otherwise indicated. Also, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Further, all publications, patents, and patent documents cited herein are incorporated by reference in their entirety. In the event of inconsistencies between the documents so incorporated by reference and used herein, the usage in the incorporated references shall be considered to be complementary to the usage in the present document; for inconsistent inconsistencies, the definitions are used in this document.

Embodiments of the present invention relate to optical assemblies, such as light funnels for illumination and measurement of optical properties of samples. Although illustrated with respect to spectroscopic samples of human or animal body regions, embodiments are directed to all types of optical instruments, including optical detectors, microscopes, spectrometers, and the like. Spectroscopy can be used to determine the amount of light absorbed by a biological sample (e.g., a human finger). By measuring the amount of light absorbed by the finger, the glucose, cholesterol and hemoglobin levels of a person can be determined non-invasively. Fingertip measurements are generally preferred because of the high concentration of capillaries in the fingertip and the conversion from arterial to venous blood that occurs in the fingertip.

When light is transmitted through a biological sample, such as a human finger, the light is absorbed and scattered by various components of the finger, including skin, muscle, bone, fat, interstitial fluid, and blood. However, it was observed that light absorption by a human finger exhibits a small range of cyclic patterns corresponding to the heartbeat. Fig. 1A depicts a plot 102 of a pulse wave corresponding to light absorption of arterial blood in a capillary due to a user's heartbeat. Although the amplitude of the cyclic pattern is small compared to the total current produced by the detector, considerable information can be extracted from the cyclic pattern of the plot 102. For example, assuming a person's heart rate is 60 beats per minute, the time between the start of any pulse beat and the end of that pulse beat is one second. During this one second period, the plot will have a maximum or peak 104 reading and a minimum or valley 106 reading. The peak 104 reading of the plot corresponds to when the blood in the capillary is at a minimum and the valley 106 reading corresponds to when the blood in the capillary is at a maximum. By using the optical information provided by the peaks and valleys of the circulation plot, light absorption and scattering by major finger components not in the capillaries (e.g. skin, fat, bone, muscle and interstitial fluid) is excluded. These main components that are not in the capillaries are excluded since they are unlikely to change during the one second interval. In other words, light absorbed by blood may be detected based on the peaks and valleys of the plot 102.

Assuming that the peak value of the circulating photocurrent generated by the photo-sensing device is I_pAdjacent valley of circulating photocurrent is I_vThe photocurrent generated by the light sensing device under the condition of no finger of a person is I₀Then, the transmittance corresponding to the peak photocurrent and the valley photocurrent may be defined as follows:

and

the corresponding peak absorbance (absorbance) and valley absorbance are:

A_V＝-log(T_V) (3); and

A_p＝-log(T_p)(4)。

A_vand A_pThe difference reflects the light absorption and scattering only by the blood in the finger:

the algorithm shown in equation (5) only requires monitoring the photocurrent variation to determine the optical power variation transmitted through the finger. As a result, it is not necessary to determine the photocurrent generated by the light sensing device in the absence of a human finger.

Unfortunately, since the cyclic mode is a very small signal, the amplitude of the cyclic mode (i.e., the difference between the peak and valley) is typically 1% to 3% of the total optical power transmitted through the finger. Fig. 1A shows a cyclic pattern on an enlarged scale. FIG. 1B depicts a more accurate reflection of a cyclic pattern in terms of signal amplitude. To obtain when determining Δ ASignal-to-noise (S/N) ratio of 100: 1, the absorbance (peak-to-peak) of the baseline noise (baseline noise) of the device used to measure light absorption through the finger should not be greater than 3.0X 10 in the 10Hz bandwidth^-5。

However, it is difficult to obtain 3.0 x 10 within the 10Hz bandwidth with low optical power levels used by some batteries powering the handheld non-invasive blood chemistry measurement device^-5Absorbance (peak-to-peak) baseline noise level. One solution involves increasing the illumination power. However, due to size limitations of some devices, the illumination power may not be increased to achieve the desired baseline noise level (e.g., battery drain), or may not be increased enough to achieve the desired baseline noise level. Thus, the systems and methods described require an increase in the amount of optical power that can be detected by such devices without significantly increasing device size and battery power consumption.

Fig. 2 is a simplified block diagram illustrating components of a current optical measurement system 200, the optical measurement system 200 using the "pulsation" concept to determine the amount of light absorbed and scattered only by blood in a human finger. A power source 201, such as a battery, supplies power to a light source 202 that produces a plurality of light beams 204, 206, 208, 210 that are directed toward the top of the user's finger. According to one aspect of the optical measurement system 200, the light beams 204, 206, 208, 210 each have a different wavelength or different wavelength range, typically within 800nm to 1600 nm. For example, first light beam 204 may have a wavelength range between 850nm and 900nm, second light beam 206 may have a wavelength range between 875nm and 940nm, third light beam 208 may have a wavelength between 920nm and 980nm, and fourth light beam 210 may have a wavelength between 950nm and 1050 nm. Although the optical measurement system 200 is described herein as producing four (4) beams, in other embodiments, it is contemplated that the light source 202 may be modified to produce fewer beams or additional beams.

The first aperture 212 ensures that the beams 204, 206, 208, 210 are incident on the target area of the finger. The second aperture 214 ensures that the beam is transmitted through a portion of the finger to be incident on the lens 216. The components of the finger and optical measurement system 200 attenuate the beams 204, 206, 208, 210, and thus, the attenuated beams 218, 220, 222, 224 are emitted from the finger. The attenuated beams 218, 220, 222, 224 are incident on the lens 216, and the lens 216 collects the attenuated beams 218, 220, 222, 224 so that they are more efficiently incident on the detector block 226.

The detector block 226 is positioned directly below the lens 216 and includes a plurality of Light Sensing Devices (LSDs) 228, 230, 232, 234, such as photodiode arrays. In accordance with one aspect of the optical measurement system 200, each of the light sensing devices 228, 230, 232, 234 respectively detects a particular wavelength of light defined by a corresponding Interference Filter (IF)236, 238, 240, 242. Interference filters transmit one or more spectral bands or light and block other spectral bands or light.

Each of the light sensing devices 228, 230, 232, 234 generates a corresponding current signal proportional to the power of light received by the particular light sensing device. The current signal generated by the photodiode may be converted to another form of signal, such as an analog voltage signal or a digital signal.

The processor 243 is coupled to the detector block 226 and is configured to calculate the change in the photocurrent signals 244, 246, 248, 250.

According to one aspect, the processor 243 executes an algorithm such as that shown in equation (5) to calculate the change in light absorption (Δ a) caused only by blood in the finger. This quantitative calculation of the light absorption of the blood can then be used to determine the properties of the blood. For example, by comparing the calculated optical absorption value to predetermined values corresponding to different glucose levels stored in a memory (not shown), the user's glucose level may be determined.

Referring now to fig. 3, a configuration of a conventional apparatus for measuring the amount of light absorbed by a human finger. An infrared light emitting diode ("IRED") block 302 includes multiple IRED that generate near infrared ("NIR") radiation or a 850nm to 1100nm beam. The generated NIR beam enters an entrance aperture (entry aperture)304 and passes through the finger. The NIR light beam transmitted through the finger passes through an exit aperture (exit aperture)306 onto a lens 308. The lens 308 collimates the beams and projects them onto a filter array 310 and then onto a detector array 312. The device further comprises a wall housing 314 for preventing stray light from reaching the light detector.

In this optical configuration, the light beams passing through the exit aperture 306 are thoroughly mixed in wavelength. More specifically, the entire optical power distribution of 850nm to 1100nm is transmitted to each detector in the detector array 312.

As described below, the problem with the device configuration depicted in fig. 3 is that the effectiveness of the device is hampered, resulting in potentially high baseline noise.

Low power of illumination

To accommodate the small finger size of a child, light should enter the finger through an entrance aperture 304 that is about 0.25(1/4) inches or less in diameter, and light transmitted through the finger should be collected through an exit aperture 306 that is about 0.25(1/4) inches or less in diameter. However, the number of IRED that can be placed into a 0.25 inch diameter region is limited. For example, only four 3 millimeter (mm) diameter IREDs may be effectively placed into a 0.25 inch diameter area of the entrance aperture 304. Since the average power from each IRED is about 2.5 milliwatts (mW) at half-power emission angles of fifteen (15) to twenty (20) degrees, the total available power from each IRED into the finger is about fifty percent (50%) or 1.25 mW. Thus, for four (4) IRED's, the total available power is about five (5) mW (e.g., 4 × 2.5mW x. 50) over the entire wavelength range covered by the four IRED's, typically 850nm to 1100 nm.

Absorption and scattering by human fingers

Typically, as mentioned above, skin, fat, muscle, blood and bone will attenuate the light entering the finger. For example, it was observed that absorption and scattering of light by a human finger can reduce the power of transmitted light in the NIR region of 850nm to 1100nm by a factor of about 200. As a result, the total IR power transmitted through the finger is only about 25 microwatts (μ W) (e.g., 5mW/200) over the entire wavelength region covered by the four IRED's, typically 850nm to 1100 nm.

Small collection cube corner for coupling optics

Light is emitted from the exit aperture 306 in all directions in a 2 pi solid angle under the finger. In conventional optical designs, it is difficult to collect most of the optical power transmitted through the finger, since the exit aperture 306 cannot be treated as a point source of light. Typically, the total optical power collected using the optical layout shown in fig. 3 is only about 10%, or the power decreases by a factor of 10, i.e. becomes 2.5 μ W, over the entire wavelength region covered by four IREDs, typically 850nm to 1100 nm. Note that this is the optical power sent to all detectors in fig. 3.

Number of detectors

Moreover, an optical system, such as that shown in fig. 3, may require twenty (20) to thirty (30) so many diode detectors to obtain accurate information about the chemical composition in the blood. Thus, the optical power entering each detector will be about 125nW or less.

Narrow band pass filter

The interference filter placed on top of each detector typically has a full width at half maximum (FWHM) bandwidth of 10nm, which reduces the optical power by a factor of 25, i.e. to 5nW, assuming a uniform power distribution over the entire wavelength region of 850nm to 1100 nm. Further, the peak transmittance of each interference filter is about 50% or less. Thus, the optical power received by each detector is reduced to about 2.5nW or less.

Photoelectric conversion efficiency

The photoelectric conversion efficiency of silicon diode detectors ranges from 0.1 ampere/watt (A/W) at 1100nm to about 0.5A/W at 900 nm. As a result, for each detector, the intermediate wave according to the corresponding interference filterLong (center wavelength), each detector generates a photocurrent in the range of 0.25 nanoamperes (nA) or less to 1.25nA or less. The corresponding high-end shot noise within the 10Hz bandwidth is about 2.0 x 10^-4An absorbance (p-p) or more exceeding 6 times an absorbance required for accurately determining the value of Δ a defined by equation (5) at an S/N ratio of 100. In other words, to achieve the desired S/N ratio of 100: 1 for Δ A, the optical power received by the detector should be increased by more than 40 times.

Fig. 4A illustrates an optical configuration for performing optical detection of a biological sample according to one aspect of the present optical measurement system 400. The light source 402 generates a plurality of light beams 404, 406, 408, 410. The light source 402 may be, for example, an incandescent light source or an infrared light emitting diode. According to one aspect of the optical measurement system 400, each of the beams 404, 406, 408, 410 has a different wavelength or a different range of wavelengths. For example, first light beam 404 may have a wavelength range between 850nm and 920nm, second light beam 406 may have a wavelength range between 900nm and 980nm, third light beam 408 may have a wavelength between 970nm and 1050nm, and fourth light beam 410 may have a wavelength between 1030nm and 1100 nm. The total wavelength range may include, for example, from about 800nm to about 1600 nm. Although the optical measurement system 400 is described herein as producing four (4) beams, it is contemplated that the light source may be modified to produce fewer beams or additional beams in other embodiments.

Light beams 404, 406, 408, 410 from the light source 402 enter the illumination funnel 412 through an inlet 414 and exit the illumination funnel 412 through an outlet 416. The diameter of the outlet 416 of the illumination funnel 412 is less than or equal to the diameter of the inlet 414. For example, according to one embodiment, the diameter of the inlet 414 is about 0.625(5/8) inches and the diameter of the outlet 416 is about 0.25(1/4) inches. Thus, unlike the configuration depicted in FIG. 3, the illumination funnel 412 focuses the light beams 404, 406, 408, 410 in the same general direction toward the top of the user's finger. The illumination funnel can significantly increase the total optical power received by the target area compared to the configuration of fig. 3, thus substantially increasing the signal-to-noise ratio.

Fig. 5 depicts a cross-sectional view of the illumination assembly or funnel 412. According to one aspect, the illumination funnel 412 has a substantially cylindrical outer wall 502 with a diameter D1; and a central cavity (central cavity) defined by an inner wall 506 shaped as a truncated cone and two light inlets/outlets 508 and 504. Opening 508 (second opening) has a smaller diameter D3 and opening 504 (first opening) has a larger diameter D2. The separation distance between the two light openings is L and the half angle of the frustum of the inner surface is α. According to one embodiment of the invention, the value of the half angle α ranges from 10 to 15 degrees. The half angle may, for example, be less than about 25 degrees. The illumination funnel 412 may be formed from a plastic, metal, or other suitable material or compound/layer of materials having any desired index of refraction. According to one aspect, the illumination funnel 412 is formed of metal and may make the surface of the inner wall 506 highly reflective. When configured appropriately, the light intensity at the exit 508 may be increased by a factor of 50 to 100 relative to the light intensity at the entrance 504.

FIG. 6 depicts components of a light source 402 according to one aspect of an optical measurement system 400. The circuit board may be positioned adjacent to or in contact with the first opening of the funnel and may include a light source mounted on or in contact with the circuit board. In one example, multiple IREDs 602, 604, 606, and 608 are mounted to a Printed Circuit Board (PCB) 610. The PCB 610 receives power through a power line 612 connected to a power source (e.g., the power source 201) such as a battery. When power is supplied through power line 612, each of IREDs 602, 604, 606, and 608 receives power and generates multiple light beams (e.g., light beams 404, 406, 408, 410). It is apparent that IREDs with similar operating currents can be connected in series to increase battery life. The light source may be mounted in or above the funnel, for example by surrounding the light source with, for example, a housing.

According to one aspect, the light funnels 412 may be mounted to the PCB 610 by screws, posts, or other connection means. The frustoconical shape of the inner surface of the illumination funnel 412 serves to focus and focus the light beams 404, 406, 408, 410 from the IREDs 602, 604, 606, 608 into a generally conical beam toward the finger.

FIG. 7 depicts a cross-sectional view of another embodiment of an illumination funnel 412 having a three-dimensional (3-D) IRED array matrix 702 disposed therein. Multiple light sources, such as IREDs, may be positioned in a three-dimensional layer and arranged to optimize light intensity. The light sources may be positioned in, for example, a horizontal layer and a vertical layer. According to this embodiment, there are a total of twenty-six (26) IREDs included in the 3-D array matrix. IRED is arranged in four (4) layers. The first row, as shown at 704, includes four (4) IRED's (two IRED's not shown), the second layer, as shown at 706, includes five (5) IRED's (two IRED's not shown), the third layer, as shown at 708, includes seven (7) IRED's (four IRED's not shown), and the fourth layer, as shown at 710, includes ten (10) IRED's (six IRED's not shown). Power line 712 supplies all IREDs. According to other embodiments, other IRED patterns (patterns) may also be utilized. Any number of light sources or layers may be utilized to optimize light intensity.

Since IRED is optically transparent to infrared light, the light loss due to blocking effects within the funnel cavity should be low, and the structure shown in fig. 7 is expected to collect more than 85% of the optical power emitted from the IRED 3-D array in the light funnel cavity. As a result, the total optical power of 0.25 inch diameter transmitted through the outlet 416 of the illumination funnel 412 should be about 55mW (e.g., 26X 2.5mW X0.85). Thus, the total optical power transmitted through the 0.25 inch opening above the finger in the present optical measurement system 400 is approximately eleven (11) times the corresponding power (e.g., 5mW) to reach the aperture 306 of the configuration described with reference to FIG. 3. Also, the increased optical power received at the finger will increase the amount of optical power that can be transmitted through the finger, thus increasing the optical power that is detectable at the detector block 428.

Referring back to FIG. 4A, the beams 404, 406, 408, 410 are attenuated by the finger and components of the optical measurement system 400. The attenuated light beam then passes through an exit aperture 418 and is collected by an aspheric lens 430. Light beam 432 exiting lens 430 may then pass through filter 426 to detector 428.

The main advantage of using an aspheric lens 430 for light collection is that its solid angle for light collection is much larger. When the configuration is appropriate, the total optical power received by each detector can be increased by a factor of 3 to 4 when the light exiting the target area is collected using aspheric lens 430, as compared to the light collection configuration shown in fig. 3. The combination of using illumination funnel 412 and aspheric lens 430 as a light collector can increase the optical power received by each detector by a factor of about 20 to about 40 compared to the optical configuration shown in fig. 3.

The detection block 428 is positioned below the aspheric lens 430 and may include a plurality of light sensing devices, such as photodiode arrays. In accordance with one aspect of the optical measurement system 400, each light sensing device detects a specific wavelength of light defined by a corresponding interference filter 426 placed on top of the detector.

A processor, such as processor 243, may be coupled to detector module 428 and configured to calculate a change in the current signal generated by the light sensing device. For example, as described above with reference to fig. 2, the processor 243 executes an algorithm (e.g., shown in equation (5)) to calculate the change in light absorption (Δ a) caused only by blood in the finger. This quantitative calculation of the light absorption of the blood can then be used to determine the properties of the blood.

Fig. 4B illustrates another optical configuration for performing optical detection of a biological sample according to an aspect of the present optical measurement system 400. The light source 402 generates a plurality of light beams 404, 406, 408, 410. For example, the light source 402 may be an incandescent light source or an infrared light emitting diode. In accordance with one aspect of the optical measurement system 400, each of the beams 404, 406, 408, 410 has a different wavelength or a different range of wavelengths. For example, the wavelength of first light beam 404 may range between 850nm and 920nm, the wavelength of second light beam 406 may range between 900nm and 980nm, the wavelength of third light beam 408 may range between 970nm and 1050nm, and the wavelength of fourth light beam 410 may range between 1030nm and 1100 nm. For example, the total wavelength range may include from about 800nm to about 1200 nm. Although the optical measurement system 400 is described herein as producing four (4) beams, it is contemplated that the light source may be modified to produce fewer beams or additional beams in other embodiments.

Light beams 404, 406, 408, 410 from the light source 402 enter the illumination funnel 412 through an inlet 414 and exit the illumination funnel 412 through an outlet 416. The diameter of the outlet 416 of the illumination funnel 412 is less than or equal to the diameter of the inlet 414. For example, according to one embodiment, the diameter of the inlet 414 is about 0.625(5/8) inches and the diameter of the outlet 416 is about 0.25(1/4) inches. Thus, in contrast to the configuration depicted in FIG. 3, the illumination funnel 412 focuses the light beams 404, 406, 408, 410 in the same general direction toward the top of the user's finger. The illumination funnel can significantly increase the total optical power received by the target area compared to the configuration of fig. 3, thus substantially increasing the signal-to-noise ratio.

As shown in FIG. 4B, the beams 404, 406, 408, 410 are attenuated by the finger and components of the optical measurement system 400. The attenuated NIR beam of light then passes through an exit aperture 418, is collected by a condenser lens 420, and is projected onto a transmission grating arrangement 422.

As shown in fig. 4B, the transmission diffraction grating 422 angularly decomposes the various wavelength components of the mixed NIR light beam into spectra as the wavelengths monotonically increase as indicated by the arrows. In other words, each beam may be separated by wavelength because the diffraction angle of a particular beam depends on the wavelength of that beam. The spectrum 424 produced from the transmission diffraction grating 422 is then narrowed by the interference filter array 426 to be detected by the diode array 428. The center wavelength of each interference filter in the filter array 426 is set to monotonically increase so as to coincide with the corresponding wavelength component of the spectrum from the transmission diffraction grating 422.

In the collection optical configuration of fig. 3, a total optical power distribution from 850nm to 1100nm is sent to each detector, in contrast to which the method using a transmission diffraction grating would only send wavelength components to each detector that are close to the center wavelength of the corresponding filter. As a result, the amount of light loss is significantly reduced and the optical power received by the photodiode is increased by a factor of 10 to 20, relative to the light collection configuration described with reference to fig. 3. Thus, the optical power received by the photodiode may be increased by a factor of about 100 to 200 using a combination of the illumination funnel 412, the aspheric lens 420 as a condenser, and the transmission grating 422 as a wavelength separation device, as compared to the optical configuration shown in fig. 3.

Embodiments of the invention may also include methods of using the above-described apparatus or light collection system, with a light source that may be in contact with a target through an illumination funnel sufficient to produce transmitted, transflective, or reflected light. For example, transmitted, transflective, or reflected light may enter the light collection system and be directed to one or more detectors.

Claims (15)

1. A light collection device, comprising:

a light source for generating a plurality of light beams, each of the plurality of light beams having a different wavelength range;

a frusto-conical light funnel for collecting the plurality of light beams through an inlet having a first diameter and directing the plurality of light beams to a target area through an outlet having a second diameter, wherein the second diameter is smaller than the first diameter;

an aperture for directing the plurality of light beams emitted from a target area;

a lens configured to collect the plurality of light beams directed from the aperture;

a detector comprising a plurality of light sensing devices, each light sensing device being configured to detect a light beam passing through the lens and to generate an output signal indicative of the intensity of the detected light; and

a processor for determining a blood characteristic from each of the generated output signals.

2. The apparatus of claim 1, further comprising a plurality of interference filters, each configured to pass a different one of the plurality of light beams emitted from a target area according to a wavelength range, wherein the plurality of interference filters are positioned between the lens and the detector.

3. The apparatus of claim 2, further comprising a transmission grating positioned between the lens and the detector.

4. The apparatus of claim 1, wherein the light source comprises one or more light emitting diodes.

5. The apparatus of claim 1, wherein the light source comprises one or more incandescent light sources.

6. The apparatus of claim 1, wherein the wavelength range comprises a different wavelength range between 800nm and 1600 nm.

7. The apparatus of claim 1, wherein the light source is positioned at an entrance of the light funnel.

8. A light collection device, comprising:

a light source for generating a plurality of light beams, each of the plurality of light beams having a different wavelength range;

a frusto-conical light funnel for collecting the plurality of light beams through an inlet having a first diameter and directing the plurality of light beams to a target area through an outlet having a second diameter, wherein the second diameter is smaller than the first diameter;

an aperture for directing the plurality of light beams emitted from a target area;

a lens configured to collect the plurality of light beams directed from the aperture;

one or more detectors, each detector configured to detect a beam of light passing through the lens and to generate an output signal indicative of the intensity of the detected light;

one or more filters positioned between the lens and the detector; and

a processor for determining a blood characteristic as a function of each generated output signal.

9. The apparatus of claim 8, further comprising a transmission grating positioned between the lens and the one or more filters.

10. The apparatus of claim 8, wherein the one or more filters are interference filters.

11. The apparatus of claim 10, wherein the one or more interference filters are each configured to pass a different one of the plurality of light beams emitted from a target area according to a wavelength range.

12. The apparatus of claim 8, wherein the one or more detectors are positioned adjacent to or in contact with the one or more filters.

13. The apparatus of claim 8, wherein the one or more detectors comprise a detector array.

14. The apparatus of claim 8, wherein the plurality of light beams are produced by an incandescent light source.

15. The apparatus of claim 8, wherein the plurality of light beams are generated by infrared light emitting diodes.