An optical spectrometer having a multi-wafer structure. The structure may be fabricated with MEMS technology. The spectrometer may be integrated with a fluid analyzer. A reflective grating such as a diffraction or holographic grating situated on the circumference of a Rowland circle along with a point of light emission and a detector may be a configuration of the spectrometer. Some configurations may use an external light source where the light may be optically conveyed to the point of emission on the circle. There may be a Raman configuration where an interaction of light with a sample or an interactive film of a channel in a fluid analyzer is the point of light emission for the spectrometer. In some configurations of the spectrometer, the grating and/or the film may be reflective or transmissive.

BACKGROUND

The present invention pertains to spectrometers and particularly to micro spectrometers. More particularly, the invention pertains to micro spectrometers for fluid analyses.

SUMMARY

The present invention is an optical micro spectrometer using a grating and compact light source, which is applicable to fluid composition analysis.

DESCRIPTION

FIGS. 1aand1bshow an edge view and a top view of a two wafer spectrometer, device or configuration10.FIG. 1ais a cross section at a line18of the spectrometer or device10inFIG. 1b. A bottom wafer11is a substrate with the top wafer12situated on it. The top wafer12has a flow channel13. The spectrometer may be based on a concave diffraction grating14or other similar wavelength sensitive reflective mechanism, mounted proximate to a circle15, such as a classic Rowland circle. A light16may be emitted by a light source17such as a micro discharge device (MDD). The light16may proceed through a portion of the flow channel13to a grating14. Grating14may reflect the light16at an angle down another portion of the flow channel13towards a photodiode array and/or CCD detector19. The detector may be an array. Light source17and detector19may be situated proximate to the Rowland circle15. So the light path may go from source17to grating14and from grating14to detector19. All three items17,14and19may be situated near or on circle15.

The grating or reflector14may be a concave diffraction grating, a holographic concave reflective grating, or a focusing transmission grating. Source17may be a micro discharge device or a bright surface reflection from a laser focused onto that surface.

The location of a particular wavelength λ on the Rowland circle may be give by the equation nλ=d(sin θ+sin δ), where n is the order, g is the grating spacing, θ is the angle of incidence of light on the grating and δ is the angle of reflection off the grating. If the angle of incidence is zero, then the equation may be nλ=g·sin δ.FIG. 2illustrates an example grating14, grooves23, incidence and reflected light16, and some related parameters.

A characteristic of the spectrometer10may reside in its wafer-level (11,12) manufacture (wafer of gratings and wafer of photo-detector arrays19(image intensifier arrays, CCDs or charge-injection detectors (CIDs)), which would be compatible with a fluid analyzer, such as a phased heater array structure for enhanced detection (PHASED) micro gas analyzer (MGA). The spectrometer10may provide excellent compactness (1-60 mm3), affordability, flexibility and response speeds than possible with interference filters or commercial mini-spectrometers to process spectro-chemical emission from a micro discharge device (MDD)17. The term “fluid” may refer to a gas or a liquid, or both.

This invention may provide clear analytical-capability advantages to PHASED, μRaman, MDD-based NOx/O2/NH3/SO2sensors, and other like sensors, and other applications of MDDs17in industry and government to monitor concentrations of Cl—, F—, P—, Hg—, Cd—, and so on, containing compounds with specific MDLs in the ppb-ppm range. Presently available analyses of micro discharge device (MDD)17optical emissions may require either a number of discrete, narrow band-pass optical filters, poorly-reproducible sliding transmission band-pass filters, or costly and complex chip-level, but still relatively bulky, optical spectrometers. None appears to lend itself to easy integration into NOxsensors or PHASED MGAs based on MDDs.

The spectrometer of the present invention may leverage available sample gas flow channels in NOxsensors or in wafer-to-wafer bonded MEMS (micromachined electro mechanical system) structures such as PHASED MGAs to support an MDD light source17, a single reflective surface (grating)14, and an array19of photo detectors (diodes or transistors) coupled to a CCD array. It may support a reasonable numerical aperture of 1/5 and feature a standard CCD output, with spectral resolutions below 5 nm/pixel. The invention make fabrication possible including micromachining (i.e., etching) a set of grating grooves14with a grating constant of 0.250-1 μm and having the photo detector-CCD array19on the same chip11,12as the MDD17electrodes21and22. The spectrometer10may be viewed as a functional, low-cost MDD17sensor of NOx—O2—NH3—CO2—SO2for combustion exhaust (automotive and stationary) as well as a detector for the PHASED micro gas analyzer.

One may provide multiple detector channels for 5-10 wavelength bands via discrete interference filters deposited at the ends of polished optical fibers or on individual photodiodes. This may be an alternative of a low-cost spectrometer. Small, pocket size spectrometers and chip-level spectrometers may be available. However, a related-art “integrated” spectrometer may need a CCD camera placed at a distance of 35 cm from the MDD.

A related-art grating spectrometer may have a resolution of 3 pixels/nm but not a known good dispersion (in nm/μm). Other features and requirements that are to be achieved with the present device may include, for example, a large aperture to maximize S/N. Spectral resolution may be Δλ≦5 nm half-width, so that λ/Δλ≧300/5=60. There may be a sufficient number of grating grooves, N, (in grating14) to achieve a λ/Δλ≦n·N resolution that is greater than the one given by the image of the slit+MDD+optical fiber on the CCD pixels, where n is the order of the observed grating spectrum. Blazing of the grooves may be consistent with the desired observation order. Observation order and spectral- and detector-range may be provided to minimize interference among different orders at the detector array19. There may be diffraction-limited resolution and focusing on the PDs (photo diodes). The overall small overall volume may enable wafer-level, high-volume and low-cost fabrication. Detection of spectral MDD emission may be in the 200-400 nm range.

A grating spectrometer may have a resolution of 3 pixels/nm (nm may be used to designate the dimension of the used wavelength, while mm may be for the spatial dimension of the detector array) but not a known good dispersion (in nm/mm). Other items that may be achieved with the present device may include, for example, a large aperture to maximize S/N. Spectral resolution may be D1*5 nm half-width, so that 1/D1*300/5=60. There may be a sufficient number of grating grooves, N, (in grating14) to achieve a 1/D1*n*N resolution (where n=grating dispersion order), that is greater than the one given by the image of the slit+MDD+optical fiber on the CCD pixels, where n is the order of the observed grating spectrum.

Sources of cameras and PD (photo diode) arrays with CCDs for detector19may include a Kodak KAF1401E CCD camera with pixel size 6.8 μm, Sony DXC-107 CCD Camera with 768×494 pixels of 8×9.5 μm, Marconi CCD37 camera with pixels of 15.0 μm, and a CCD by E2V Technologies model CCD38-20, having 44 μm square pixels and a 456×684 μm pixel image area with a 100 μm thick Gadox (Gd2O2S) scintillator.

An approach taken to achieve satisfactory operation and satisfy the requirements listed above may be illustrated inFIGS. 1a,1b,5a,5b,6and9.FIGS. 1aand1bshow the feasibility of fabricating a spectrometer within the two-wafer (11,12) structure of PHASED.FIG. 5ais side view of a spectrometer, device or configuration20with a top view at about line24shown inFIG. 5b, including views of the grating14and detector19. A feature is the integration of the fabrication of sub-micron, smooth and concave grating grooves (via DRIE into the grating wafer31) and the PD-CCD array (photo-detector-charge-coupled device)19into the wafer32. The dimensions of device20may stay within an acceptable 1×1×1 mm volume, assuming that the size of the MDD source17(≦electrode (21,22) gap=8 μm) and its image on the PD-CCD array (11.3 μm)19are small enough to achieve the desired resolution.

FIGS. 5aand5bshow a solution the integration challenge by allowing for separate wafers31and32to hold the grating14with its grooves23and concave surface, and the PD-CCD array19, respectively.

Bonding a stack with a greater number of wafers, including wafers33and34as the channel wafer and the heater wafer, respectively, along with grating wafer31and detector wafer32, is one approach for integrating a small-sized spectrometer into an MGA. The volume requirements of device20appear to be similar to those of device10shown inFIGS. 1aand1b, again assuming that the size of the MDD source (≦electrode gap=8 μm) and its image on the PD-CCD array (11.3 μm) are small enough to achieve the desired resolution. The focal distance26between grating14and detector or receptor19may be about 1000 microns.

FIG. 6may preserve the configuration ofFIGS. 5aand5bwith a spectrometer, device or configuration30to allow separate fabrication of grating14and PD-CCD19, and additionally overcome the MDD17size limitation, which may be relaxed to a 30 μm size gap, resulting in a 42.43 μm image size and a grating-to-PD-CCD array distance 25 of f ˜=7500 μm (7.5 mm). The overall volumetric size may be increased from the herein noted ˜1 mm3to ˜18 mm3. The main geometrical/fabrication difference between the devices20and30represented inFIGS. 5aand6may be the extra “spacer wafer”35, between the “grating” and the “channel wafers”31and33, respectively, inFIG. 6. The “spacer”35inFIG. 6may have a thickness of about 6 mm on top of the wafer36that supports the MDD or light source17, which may have a thickness37of sw=1.5 mm. Layer35may also be situated on the channel wafer33can be on a heater wafer34. Wafers33and34may together have about the same thickness as wafer36.

From a set of specific characteristics, one may derive the following general step-by-step guidelines for the making of the subject low-cost spectrometer10,20and/or30, as illustrated by specifications in the first table ofFIG. 4, with inputs encompassed by dashed boxes. An initial step may be scaling. Here, one may determine the image or focal distance d (25,26) between the grating14and the PD-CCD array19(and as provided by the diameter of the Rowland Circle15), equating the dispersion Di, (needed for the finite image of the light source to achieve the desired spectral resolution, Δλ), with that generated by the grating, Dg. Dimay be governed by geometrical optics of imaging the source (slit or MDD17) onto the PD-CCD array19of total length p·Np, to cover the λ-range λ2−λ1:
Di=(λ2−λ1)/p·Np=(λ2−λ1)/{p·(λ2−λ1)/Δλ}=Δλ/p,
where Np=(λ2−λ1)/Δλ=(400−200)/3=200/3=67; and p=pixel size in μm. On the other hand, Dgmay be given by the grating groove width, g, the spectral order, n, the diffraction angle, δ, and the focal distance, f:
Dg=(λ2−λ1)/(s2−s1)=(λ2−λ1)/{f·(sin δ2−sin δ1)}=g/(f·n)
where s1,2=distances on the PD-CCD array19focal plane corresponding to the wavelengths λ1,2, and sin δ1,2=n·λ1,2/g. Therefore, with g=1342 nm, p=42.4 μm, n=2 and Δλ=3.79 nm, one may achieve,
f≧g·p/n·Δλ=7500 μm.

The next step may be the grating14. Fabrication of the grating grooves23spaced at g=850 nm (see the first table inFIG. 4) may tax fabrication capabilities. To ease fabrication of wider grooves23, the second table inFIG. 4is based on g=1342 nm, which may result in a focal distance of f=7500 μm as shown herein.

An additional step may be a blazing of the grooves23consistent with the desired observation order. For the devices10and20ofFIGS. 1a,1b,5aand5b, this may mean an angle of 45/2=22.5°. For the device30ofFIG. 6, the blazing angle may have to be δ/2=13.3°.

A further step may be the aperture. Considering the center incident beam16to the grating14, the aperture may be A=(g·N/√2)/(f/√2)=g·N/f. For the device30ofFIG. 6, to achieve A=1/5, it may be required that N=A·f/g=(1/5)·7500/1=1,118 grooves.

Another step may be the diffraction-limited resolution and focusing on the PDs19. One may achieve this by checking that the diffraction limit given by Ld=0.61·λ/A=915 nm=0.915 μm, does not exceed the optical resolution or definition of the present PD-CCD array19, which may be represented by the pixel size, 11≦p≦43 μm, to cover the resolution range from that inFIGS. 1a,1b,5aand5bto that ofFIG. 6.

A subsequent step may be separation of grating orders. By observing the 200-400 nm MDD emission spectrum at the 2ndorder (n=2), one may also cover the 777 nm O-lines in the 1storder, provided that the two are kept apart, which one may do by covering the PD-CCD pixels for the 777 nm lines with a UV-blocking filter such as glass, so that the complete spectrometer detection range does not need to be extended to ˜800 nm in the second order.

A process for a making of the device30inFIG. 6may be modified to enable input the desired aperture and the MDD17position (up from the PD-CCD32wafer in μm and on the Rowland circle15) and is captured in the second table inFIG. 4, with inputs highlighted with dashed-line boxes. One may input aperture and distance25between grating14and PD-CCD array19, f, and calculate W. One may input the MDD-support wafer36thickness37, sw, and calculate the diffraction angle, δ, and wavelength positions on the PD-CCD array19, s, and the corresponding dispersion in nm/μm. One may input the MDD17gap size and calculate the MDD image size (assumed to be equivalent to one pixel) and the spectral resolution in nm/pixel. If the latter is larger than the desired 3-5 nm/pixel, one may adjust f, sw, and/or the MDD gap, until the desired resolution is achieved.

There may be assembly and operation of the micro-spectrometers10,20and30. The assembly may be shown byFIGS. 1a,1b,5a,5band6. An attachment of an optical fiber27carrying the optical emission from an MDD17, at a remote location, e.g., exposed to sample gases from a harsh car exhaust at that remote location, may need to be carefully made. Such a fiber27may be made to end at nearly exactly the same point at whichFIGS. 1a,1b,5a,5band6show the MDD17gap, through as many wafer thicknesses as needed, preferably at an angle that points to the center of the grating14. If a hole28is etched that is larger than the optical fiber27, fastening and sealing the fiber27at such an angle may be possible due to the extra dead-space. The use of such an optical fiber27may be better than having the sample gases enter the grating cavity29, in order to maintain long term, maintenance-free operation.

There may be a need to align the spectrometer elements relative to one another, such as the light source (MDD)17, grating14and PD-CCD array19. During operation, the MDD-source17may be ultimately imaged on the PD-CCD array19. The outputs of array19may then be further processed (i.e., amplified, digitized, integrated and displayed) as needed.

Some recommended wavelength bands for monitoring and quantifying NOx, O2, SO2, NH3, CO2, and H2O in combustion engine exhaust are listed in a table inFIG. 3. The detection of CWA (chemical warfare agent) simulants with gas chromatography (GC) or PHASED MGA with, for instance, an Ocean Optics Co. spectrometer, used as indicated here is illustrated inFIG. 7. The graph ofFIG. 7shows GC elution times in minutes of various simulants. The MDD outputs shown inFIG. 7are for a chromatogram of diesel fuel with CWA simulants, at twelve wavelengths.

The ˜2×3×4″ size of the Ocean Optics spectrometer may represent the state-of-the-art of commercial spectrometers, which is not large relative to desk-top conventional units, but is rather large relative to the size of the present devices10,20and30.

As mentioned herein, and in order to observe the 777 nm lines of O (representing O2concentration) without having to extend the wavelength range in the 2ndorder to 777 nm, one could place a UV-blocking filter such as glass on the pixels corresponding to the 2ndorder range of 77/2=388.5±2 nm. Conversely, broad filters blocking the 400-800 nm of the 1storder may reduce potential interferences between the two orders.

To minimize light scattering, suitable light-absorbing coatings may be applied to the walls of the channel or column, and consideration be given to place light-stopping blends, although a coating consisting of carbon nanotube (CNT) grass may obviate this need.

In the fabrication of the present device, the specifications noted here may be for a differential MDD17design in a 100×100 micron channel, to operate in air, and be duty-cycled as much as possible but able to follow GC peaks of >15 ms half-width. Measurements may include MDD impedance, current or voltage and an optical output into 3-8 channels selected via interference filters.

One may attain a glass wafer, such as Pyrex™ (to host the PHASED channels), which might also support MDD17electrodes21and22and transmit MDD light16through it (poorly in UV but acceptable in visible light). A small “interference gradient” filter may be placed on the outside surface of the glass wafer, with a small-pitch photo-CCD or channeltron array situated on top of the CCD or array19. One may obtain the wafer, put the channels into it and provide the optics. The glass thickness at the MDD17may be thin. One may “seal” the MDD electrodes21and22into the glass with a thick dielectric coating applied on the optical output side, so that the plasma does not light up on the detector side.

FIGS. 8aand8bshow cross-sectional views of a fabrication of a concave micro grating array14.FIG. 8amay be approximately to scale andFIG. 8bmay have an enlarged view of a preformed epoxy42and a shaping of a film or membrane43for the grating14. A spherical surface shape may be made with a hard surface41(a stainless ball bearing) pressing into a soft surface42(epoxy), and then shaping the membrane43over the “dimple” made by the ball bearing41. The grating14may be written on the membrane43surface while it is still flat. Then the membrane43may be formed into the dimple (possibly with air pressure). In this approach, one may have to eliminate the air behind the membrane43through some vent pore or porous surface, possibly in the epoxy42. The membrane43may be attached to the silicon wafer45with an adhesive46.

The “grated” film43should be deformed without squashing the grating grooves. One may, for example, press 7.5 mm OD ball-bearings41onto the deformable film43). This may be an alternative to the use of pressure (which requires an extra fixture), since the pressing of a bearing41onto the film43provides a sure shot at getting the right spherical curvature. As to material, one may place a free Si3N4membrane43over an array of 1.5-2 mm ID holes44in a Si wafer45, which can be marked holographically on a photoresist, and etched with the grating grooves while in the “flat” state before being deformed by pressure. The deformation “depth” of that spherical shell of about 1.5 mm OD, with a 3.75 radius of curvature may be:
3.75−(3.75^2−0.75^2)^0.5=0.07576 mm,
or 76 microns in the middle of 1500 microns. This may correspond to a strain of 3.75*(arcsin(0.75/3.75)−0.75)/0.75=0.0067896, i.e., 0.679% and below the break point. The nitride fracture strength=5.87±0.62 GPa and Young's modulus=255±5 GPa, which indicates that the yield strain is 1.12%. Although the grooves may “initiate” fracture before 1.12% or even before 0.679%.

The grating14membrane may mimic the master grating (but in an inverted fashion). So if the master is blazed to a particular angle, so will be the duplicate be blazed as such. One may determine what type of lift-off film should be used, and how much the liftoff would tend to planarize the grating surface. However, even the first tries may be blazed the same as the master grating. Along with an epoxy42, one may use a thermal deformation process to create the spherical shape, and then cool it to maintain the shape.

As part of the fabrication process, the thin membrane43may be deformed into a spherical shape (like a soap bubble) under gas or liquid pressure on one side, and an epoxy42on the other, which would solidify when one wants it, and then be bonded to the membrane (without deformation as it hardens).

The present device or micro-spectrometer10,20,30may reside in the design and its guidelines. The device may have truly integrated optics with an MDD light source17, sealed optics (with the MDD operating in a sample gas stream and sending its emission via an optical “fiber”, e.g., fiber27, to a sealed optical device), a concave grating14and an array19of photo-detectors (PD-CCD). Optics56may facilitate the light movement within the device30. The device may have wafer-level assembly and very extreme compactness (1-60 mm3), but also low-cost of fabrication, by virtue of merging an independent, SOA fabrication of gratings14and of PD-CCD arrays19. The device may meet the resolution needs for MDD17emission spectroscopy and provide a large optical aperture for a high signal/noise ratio and at high-speed (low integration time requirements) detection/measurements. The device may be fabricated with processes for the grating14, MDD17and photo-detector arrays19. It may use CNT grass as a very effective optical anti-reflector on spectrometer walls to minimize scattered light.

The emission spectrometer10,20,30may have great ruggedness reliability resulting from the presently noted fabrication and size features. This spectrometer may have very short response time (short signal integration time need) and a high S/N, due to large aperture of 1/5. The present spectrometer may have greater reliability and a higher S/N than the interference-filter-based approaches, due to the filter's center wavelength shift with temperature and incident angle, and an attempted cure of the latter by limiting the angle of incidence may reduce the light input and S/N.

There may be easy coupling between one or more optical fibers27(carrying the MDD17output) into the sealed micro-spectrometer, where the end(s) of the fibers function as a “point” or “slit” light source (seeFIG. 6). The spectrometer may achieve better S/N due to use of CNT grass on internal surfaces to minimize noise caused by scattered light.

An issue that may be contended with is that the related art compact MGAs (micro gas analyzers) or fluid composition analyzers either require sophisticated, high-speed data processing to output species concentrations and use of energy-consuming pumps to transport and/or thin-out sample gas (required for micro mass spectrometers and micro gas chromatographs), and/or exclude a host of gases of interest such as O2, N2and H2(as with IR or NDIR analyzers), and/or are too unstable to reliably serve in critical industrial processing or safety-related applications (polymer and SAW sensors; and MOS and electrochemical gas sensors, of which some are intrinsically un-safe by requiring≧300° C. for operation).

A fluid composition micro-analyzer40ofFIG. 9may leverage the Raman scattering signature that each component of a mixture provides without regard to its molecular symmetry (so that symmetrical zero-dipole gases such as O2, N2and H2are not excluded), and the availability of chip-level, low-cost lasers (VCSELs) as light sources. Also, may leverage the possibility of increasing the aperture of the photo-detectors and thus the optical efficiency and minimum detection limit (MDL) of the whole MGA by using a (chip-level) micro spectrometer rather than a limited number of individual, rigid and fixed wavelength detectors behind small aperture and lossy interference filters.

The principle of the spectrometer40may involve a micro Raman scattering fluid analyzer, coupled to a μspectrometer with possible coupling to a PHASED MGA. Aspects of the present spectrometer40may include a micro Raman gas or liquid analyzer of revolutionary compactness, high aperture and thus high S/N and low MDL, short response time, and low-power consumption. The lasing cavity beam may operate as an entrance slit light source into a sealed μspectrometer (after turning the image inFIG. 9by 90°).

The capability for the Raman spectrometer40to simultaneously sense O2, CO, CO2, NO and NO2, coupled to its low cost, may make this device useful for internal and external combustion applications, besides its use in medical, industrial and government applications.

As stated herein, GC-MS analyzers may require significant data processing to identify and quantify the one or more analytes present in an unknown sample gas. Especially computation-intensive may be analyte mixtures, which consume time and electric power. Such computing power needs might not be much reduced with IR absorption analyzers, especially with analyte gas mixtures.

However, overwhelming computing requirements to identify and quantify analytes are not necessarily needed with Raman spectroscopy, because Raman scattering spectra appear much simpler than the signatures of GC-MS or IR analyzers, except possibly the simple NDIR analyzers with just a few (and therefore less reliable) wavelength-band channels.

The simplicity of Raman scattering spectra is illustrated with the few Raman lines graphed inFIG. 10, which are in units of cm−1, for phosgene, CO2, cyanide and O2. The plot inFIG. 10shows a material versus an increasing Raman frequency shift of the scattered-light output, relative to the frequency of the input light. Measurement of this shift appears easier to achieve with low-resolution (λ/Δλ) in the IR than in the visible or UV, although the scattering intensity or efficiency may be higher at shorter wavelengths. Besides the scarcity of lines compared to an IR spectrum or even the mass fragments of a MS (mass spectrometer) signature, another striking feature seems to be the capability to select the wavelength region of operation by choosing the input laser wavelength, of which the resulting and plotted Raman shifts are not dependent on. More complex molecules may have a few more lines than simpler ones. Furthermore,FIG. 10shows that diatomic molecules such as O2(or H2, N2) may have well-defined and observable line shifts, which spectrometry in the near IR would not provide.

The application of these fundamental aspects of Raman spectro-meters may be hindered by the presently available and relatively bulky and not portable Raman MGA versions. The present spectrometer40may reveal how to micro-miniaturize as well as increase the functionality of known Raman spectrometers on several levels, besides size reduction. One part of the present spectrometer40may include using an optical detector19that is more versatile than the few optical bands defined by discrete optical narrow-band-pass filters used in the related art.FIG. 9shows one version of a Raman spectrometer40, in which the detector19may provide compactness, a 10-50 times increase in the number of optical detection channels relative to the related art, and a very high numerical aperture or f-number. The photo-detectors on the CCD array19may enable advantageous signal integration and processing. A VCSEL (vertical-cavity surface-emitting laser) light source41may be much more compact than gas lasers. To maximize service life, the sample gases do not come in contact (avoiding the risk of optical surface contamination) with the grating14of spectrometer40, since there may be a window57between the light cavity42where the light source41and its mirror43are situated. However, the sample58may enter the external laser cavity42and interact with the light44for maximum Raman scattering output light16. The heart of the Raman MGA spectrometer40may be the laser cavity42. Especially, by the positioning of an external VCSEL41-to-mirror43multi-reflection beam44, which is not quite positioned as shown (but it is positioned as such for illustrative purposes) inFIG. 9, but beam44may be parallel to the grating14grooves23. This configuration of device40may increase the S/N by at least another factor of 10, which in turn may increase the MDL by an equivalent amount. The Raman (scattered) light may then be generated from a line that is positioned as if it were the entrance slit of a spectrometer, and imaged onto similar shaped elements of the CCD photo-detector array19(unless provided with an appropriate cylindrical lens to focus the image line down to a “point”, i.e., to a CCD array19of point-shaped detectors). The present Raman spectrometer40may be compatible with the sample gas outputs of pre-concentrated and component-separated analytes provided by a PHASED MGA via micro channels of about 100 μm ID.

Aspects of the present micro Raman (gas or liquid) spectrometer40may be combined with an MGA to result in a compact micro Raman analyzer using compact VCSEL light source41technology. The spectrometer use photo detectors19with a CCD array for optical detection, integration and a step of signal processing.

The advantages of the present micro Raman spectrometer40over the related art may include a 10-20 times reduction of reduced outer package dimensions (1000-8000 times in volume and weight reduction) and it may use an optical detector that is more versatile than the few optical bands defined by discrete optical narrow-band-pass filters. Also, the spectrometer40may have a 10-50 times increase in the number of optical detection channels relative to the related art. The present spectrometer40may have a very high (about 1/10) numerical aperture or f-number (coupled with a line-shaped scattering source) which may increase the S/N and cannot be used with narrow-band-pass interference filters because of their angular sensitivity (the passed wavelength is dependent on the angle of incidence). The high aperture of the present analyzer40may enable shorter integration time and thus overall faster total response time.

FIG. 11shows an illustrative example of a surface-enhanced Raman spectrometer, configuration or device50relative to a PHASED detector structure47. A VCSEL light source41may emit a light beam48which impinges a film49situated on a PHASED heater membrane51and is reflected to a grating14. Grating14may reflect light48, in part, through a notch or edge filter52to be detected by a micro CCD array19. The film49may be regarded as a surface-enhanced Raman spectrometer film. The source of light may be for providing Raman scattering from a fluid adsorbed on the film-surface illuminated by the light.

FIG. 12shows an illustrative example of a surface-enhanced Raman spectrometer, configuration or device60relative to a PHASED detector structure47. A VCSEL41may emit light48which may, via possible optics54, impinge a surface-enhanced Raman spectrometer film49situated on a heater membrane51. Heater membrane49may be part of a PHASED structure47. Light48may be reflected by film49to a notch or edge filter53which may or may not have the properties of a splitter. Filter53appears to have the properties of a splitter for the illustrative example inFIG. 12. Filter53may reflect certain light48in accordance with the specifications of the filter to through a transmissive grating55. In some configurations, this grating may be reflective. From grating55, light48may continue on to a micro CCD array19, via possible optics. Array19may have a TE cooler, if needed. PHASED structure47may have a TE cooler, if needed.

A fluid analyzer which may be used in conjunction with the spectrometers10,20,30,40,50and60may include a channel or channels for a flow of a sample along a membrane that supports heaters and a stationary phase for sample analysis. The channel or channels may be an integral part of the micro fluid analyzer. The analyzer may have the pre-concentrator (PC)101(viz., concentrator) and chromatographic separator (CS)102that incorporates the channel or channels.FIG. 13is a system view of an example fluid analyzer which may be a phased heater array structure for enhanced detection (PHASED) micro gas analyzer (MGA)110. It reveals certain details of the micro gas apparatus110which may encompass the specially designed channel described herein. The PHASED MGA110, and variants of it, may be used for various fluid chromatography applications.

Sample stream111may enter input port112to the first leg of a differential thermal-conductivity detector (TCD) (or other device)115. A pump116may effect a flow of fluid111through the apparatus110via tube117. There may be additional pumps, and various tube or plumbing arrangements or configurations for system110inFIG. 13. Fluid111may be moved through a TCD115, concentrator101, flow sensor122, separator102and TCD118. Controller119may manage the fluid flow, and the activities of concentrator101and separator102. Controller119may be connected to TCD115, concentrator101, flow sensor122, separator102, TCD118, and pump116. Data from detectors115and118, and sensor122may be sent to controller119, which in turn may process the data. The term “fluid” may refer to a gas or a liquid, or both.

FIG. 14is a schematic diagram of part of the sensor apparatus110representing a portion of concentrator101and/or separator102inFIG. 13. This part of sensor apparatus110may include a substrate or holder124and controller119. Controller119may or may not be incorporated into substrate124. Substrate124may have a number of thin film heater elements125,126,127, and128positioned thereon. While only four heater elements are shown, any number of heater elements may be provided, for instance, between two and one thousand, but typically in the 20-100 range. Heater elements125,126,127, and128may be fabricated of any suitable electrical conductor, stable metal, alloy film, or other material. Heater elements125,126,127, and128may be provided on a thin, low-thermal mass, low-in-plane thermal conduction, membrane or support member124, as shown inFIGS. 14 and 15.

Substrate130may have a well-defined single-channel phased heater mechanism131having a channel132for receiving the sample fluid stream111, as shown inFIG. 15. The channels may be fabricated by selectively etching silicon channel wafer substrate130near support member124. The channel may include an entry port133and an exhaust port134.

The sensor apparatus110may also include a number of interactive elements inside channel132so that they are exposed to the streaming sample fluid111. Each of the interactive elements may be positioned adjacent, i.e., for closest possible contact, to a corresponding heater element. For example, inFIG. 15, interactive elements135,136,137, and138may be provided on a surface of support member124in channel132, and be adjacent to heater elements125,126,127, and128, respectively. There may be other channels with additional interactive film elements which are not shown in the present illustrative example. The interactive elements may be formed from any number of films commonly used in liquid or gas chromatography. Furthermore, the above interactive substances may be modified by suitable dopants to achieve varying degrees of polarity and/or hydrophobicity, to achieve optimal adsorption and/or separation of targeted analytes.

Controller119may be electrically connected to each of the heater elements125,126,127,128, and detectors115and118as shown inFIG. 14. Controller119may energize heater elements125,126,127and128in a time phased sequence (see bottom ofFIG. 16) such that each of the corresponding interactive elements135,136,137, and138become heated and desorb selected constituents into a streaming sample fluid111at about the time when an upstream concentration pulse, produced by one or more upstream interactive elements, reaches the interactive element. Any number of interactive elements may be used to achieve the desired concentration of constituent gases in the concentration pulse. The resulting concentration pulse may be provided to detector118, for detection and analysis.

FIG. 16is a graph showing illustrative relative heater temperatures, along with corresponding concentration pulses produced at each heater element. As indicated above, controller119may energize heater elements125,126,127and128in a time phased sequence with voltage signals150. Time phased heater relative temperatures for heater elements125,126,127, and128may be shown by temperature profiles or lines151,152,153, and154, respectively.

In the example shown, controller119(FIG. 14) may first energize first heater element125to increase its temperature as shown at line151ofFIG. 16. Since first heater element125is thermally coupled to first interactive element135(FIG. 15), the first interactive element desorbs selected constituents into the streaming sample fluid111to produce a first concentration pulse161(FIG. 16) at the heater element125, if no other heater elements were to be pulsed. The streaming sample fluid111carries the first concentration pulse161downstream toward second heater element126, as shown by arrow162.

Controller119may next energize second heater element126to increase its temperature as shown at line152, starting at or before the energy pulse on element125has been stopped. Since second heater element126is thermally coupled to second interactive element136, the second interactive element also desorbs selected constituents into streaming sample fluid111to produce a second concentration pulse. Controller119may energize second heater element126such that the second concentration pulse substantially overlaps first concentration pulse161to produce a higher concentration pulse163, as shown inFIG. 16. The streaming sample fluid111may carry the larger concentration pulse163downstream toward third heater element127, as shown by arrow164.

Controller119may then energize third heater element127to increase its temperature as shown at line153inFIG. 16. Since third heater element127is thermally coupled to third interactive element137, third interactive element137may desorb selected constituents into the streaming sample fluid to produce a third concentration pulse. Controller119may energize third heater element127such that the third concentration pulse substantially overlaps larger concentration pulse163provided by first and second heater elements125and126to produce an even larger concentration pulse165. The streaming sample fluid111carries this larger concentration pulse165downstream toward an “Nth” heater element128, as shown by arrow166.

Controller119may then energize “N-th” heater element128to increase its temperature as shown at line154. Since “N-th” heater element128is thermally coupled to an “N-th” interactive element138, “N-th” interactive element138may desorb selected constituents into streaming sample fluid111to produce an “N-th” concentration pulse. Controller119may energize “N-th” heater element128such that the “N-th” concentration pulse substantially overlaps larger concentration pulse165provided by the previous N-1 interactive elements. The streaming sample fluid may carry the resultant “N-th” concentration pulse167to either a separator102or a detector118.

Nomenclature used in here may include CCD (charge-coupled device), MDD (micro discharge device) and PD (photo detector). The symbols may include A (aperture or f-number, N·g/f=W/f), d (distance (light source to grating) in μm), Di(dispersion of wavelengths of the image on the PD-CCD array, in nm (wavelength)/μm (length)), Dg(dispersion of light generated by the grating, Dg=(λ2−λ1)/(s2−s1)=(λ2−λ1)/{f·(sin δ2−sin δ1)}=g/(f·n)), f (distance between grating and PD-CCD array, concave grating focal distance and diameter of the Rowland circle), g (grating groove center-center spacing in nm), N (number of grating grooves), Np(number of pixel elements in the PD-CCD array), p (pixel size in μm), s (space variable on the PD-CCD plane, s2−s1corresponding to λ2−λ1), sw(thickness of the support of the MDD source, above the PD-CCD surface), W (width of the grating), δ (angle between rays incident to and output from the grating, i.e., diffraction angle as defined inFIG. 5and inFIG. 2, δ=arcsin{(sw/f)0.5}), Δλ (wavelength range covered by each pixel, in nm), and λ (wavelength in nm, λ1=smallest and λ2=longest wavelength of a used range)

Although the invention has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.