Systems and methods for a multi-band position sensor and a multi-band optical detector are disclosed. This system comprises a dual-axis, lateral-effect position sensor for locating spots of light that has energy in two wavelength bands. This sensor senses the time-varying intensities of the light in each of the two wavelength bands. This sensor also provides the location of the spot of light on the light-detecting plane of the sensor. Examples are provided for light of two mid-wave infrared (MWIR) wavelength bands or of a short-wave infrared (SWIR) and a MWIR band. This sensor approach, could be applied to detect light of other wavelength bands, such as a combination of a MWIR and a long-wave infrared (LWIR) band. This concept is extended to an array of detectors for multi-band optical detection and multi-source location and tracking. Monolithic chip level fabrication of the multi-band detectors is also discussed.

TECHNICAL FIELD

The present disclosure is directed in general to the field of optical sensors and in particular to dual band light sensors and position sensors.

BACKGROUND OF THE DISCLOSURE

There is a compelling need in the field of optical sensors for a fast response dual band position sensor that can detect energy in two different spectral bands, are fast enough to track time varying intensities of light, and at the same time can track the location of the source of the light as that source moves at high velocities. Such a need exists for both commercial and military applications.

A variety of optical position sensors are known. Some of these include sensor systems that can locate the spot of illumination using imaging cameras, but suffer from a relatively slow response time. Some of the sensor systems sense multiple spectral bands by using multiple cameras to view the scene, with a different camera sensing each of the spectral bands. These systems are much larger and more complex, and the images they produce must be spatially aligned with each other. Because of their slow response, these imaging cameras cannot distinguish between the flashes that are characteristics of different small-caliber weapons.

Prior position sensing detectors, such as lateral-effect position sensing detectors, can have fast response and provide information on the location of a spot of light. However, these detectors cannot distinguish between multiple spectral bands. The existing sensors that cover a larger field of view often require large and slow mechanical gimbals to move their narrow field of view (FOV) detectors.

SUMMARY OF THE DISCLOSURE

To address one or more of the above-deficiencies of the prior art, one embodiment described in this disclosure provides for a dual-axis, lateral-effect position sensor for locating spots of light that has energy in two wavelength bands. This sensor senses the time-varying intensities of the light in each of the two wavelength bands. This sensor also provides the location of the spot of light on the light-detecting plane of the sensor.

An embodiment of the sensor comprises a detector that has two absorber regions, a first region absorbing light of the first wavelength band and a second region absorbing light of the second wavelength band, with each absorbing region generating holes and electrons associated with the light absorbed in each band. The detector has an energy barrier that blocks the flow of one electrical carrier type (i.e., blocking either the holes or the electrons) but that permits the flow of the other carrier type. The detector has a first pair of electrodes, which are located on opposite sides of the detector, that produce output currents associated with the blocked carrier type associated with absorbed light of the first wavelength band. The detector also has a second pair of electrodes, which are located on opposite sides of the detector, that produce output currents associated with the blocked carrier type associated with absorbed light of the second wavelength band. The detector also has a fifth electrode that produces an output current associated with the unblocked carrier type associated with absorbed light of both wavelength bands. In some embodiments, this fifth electrode provides a common or return path for the electrical currents generated from absorption of the light. The first pair of electrodes is located on different sides of the detector from the second pair of electrodes. In an embodiment of the detector, the detector has a square or a rectangular shape and the four electrodes of the two pairs of electrodes are located on the four sides of the detector.

Some embodiments of the sensor make use of the fact that the dual-band light of the spot illuminating the detector and whose position is to be determined is produced by the same source. Thus, at least for a part of the time interval when the spot is illuminating the detector, that spot comprises light of both wavelength bands. When both wavelengths of light are in the illuminating spot, the sensor can determine the position of the spot in both orthogonal directions defined by the detector. The detector, in combination with a signal-processing circuit, also provides outputs associated with the time-varying intensities of the light in each of the two wavelength bands.

In some embodiments, the sensor further comprises a signal-processing circuit. This circuit amplifies the photocurrents associated with the absorbed light. For each of two directions defined by the detector, this circuit determines a difference value associated with the photocurrents from the electrodes of a pair of electrodes and a sum value associated with the photocurrents from the electrodes of that same pair of electrodes. This circuit then determines a location value for the spot of light along that direction, for example, by dividing the difference value by the sum value. The sum value for each electrode pair, which could vary with time, indicates the intensity of the absorbed light in the band associated with that electrode pair. In some embodiments, the circuit also has a switch associated with each electrode pair that suppresses the output of the location value when the sum value for that electrode pair is below a threshold set-point.

In one embodiment of the detector, the barrier blocks the flow of holes between the two absorber regions. For that embodiment, the photo-generated hole-currents are used to determine the location of the spot. In another embodiment, the barrier blocks the flow of electrons between the two absorber regions. For that embodiment, the photo-generated electron-currents are used to determine the location of the spot.

Examples are provided for light of two mid-wave infrared (MWIR) wavelength bands or of a short-wave infrared (SWIR) and a MWIR band. This sensor approach, could be applied to detect light of other wavelength bands, such as a combination of a MWIR and a long-wave infrared (LWIR) band. This concept is extended to an array of detectors for multi-band optical detection and multi-source location and tracking. Monolithic chip level fabrication of the multi-band detectors are also discussed.

Certain embodiments may provide various technical features depending on the implementation. For example, a technical feature of some embodiments may include the capability to provide position sensing while other embodiments provide for multi-band optical detection.

Although specific features have been enumerated above, various embodiments may include some, none, or all of the enumerated features. Additionally, other technical features may become readily apparent to one of ordinary skill in the art after review of the following figures and description.

DETAILED DESCRIPTION

It should be understood at the outset that, although exemplary embodiments are illustrated below, the present invention may be implemented using any number of techniques, whether currently known or not. The present invention should in no way be limited to the examples, implementations, drawings, and techniques illustrated below. Additionally, the drawings are not necessarily drawn to scale.

Multi-wavelength observation of the light emitted from an object can be useful for determining the temperature of the object, since the spectral shape of its black-body radiation depends on its temperature. Also, the light from an object can be produced by other effects such as emission due to chemical reaction products.FIG. 1aillustrates an example of the emission spectra of the plume from various rockets andFIG. 1billustrates the emission spectra of the chemical products associated with various spectral features.FIGS. 1aand 1billustrates that the comparison of the intensities of light in two different wavelength bands such as the SWIR band of 2.0-2.5 μm, the MWIR band of 3.4-4.1 μm or the MWIR band of 4.5-5.0 μm can enable one to distinguish between different sources of a plume.

FIG. 2aillustrates the spectral emission of a blast from a gunshot. The emitted light has spectral components due to the gases produced by the gunshot and also spectral components due to the hot soot produced. Different weapons have different ratios of the chemical versus temperature components of the emitted spectrum. Also, these spectral components could have different time variations for different weapons. An example of the time varying light of the blast from a weapon is illustrated inFIG. 2bfor several spectral components.

An embodiment of the disclosed sensor includes a lateral-effect position sensing detector (LEPSD). The LEPSD can detect the location of a spot of light that illuminates the detector. In general, the size of that spot of light is smaller than the size of the detector. When used in a sensor, the LEPSD is coupled to a lens that focuses input light from a distant source onto the LEPSD. This assembly can sense the angle-of-arrival of the light, which illuminates the lens and which is projected as a spot onto the LEPSD. Thus, the LEPSD can be used to locate the source of the light. As discussed above, it is helpful in some cases to be able to distinguish between different spectral components of the light from a distant source. A LEPSD sensor that can detect light in two wavelength bands, that can provide the time-variation of the two spectral components of light and that can locate the source of that light is useful for identifying, locating and tracking the motion of sources such as rockets, projectiles and gunshots.

FIG. 3illustrates a schematic depiction of a dual-band lateral-effect position sensing detector300. In typical operation, a spatially non-uniform intensity distribution of light is incident upon a side (or face) of the LEPSD. This light intensity distribution may resemble a focused or nearly focused spot of light, whose size is much smaller than the size of the LEPSD. The LEPSD has four signal contacts (306,308,309and310) with each contact producing an output photo-current. The LEPSD also has a common contact307that produces a return photo-current that is equal to the sum of the photo-current from the other four contacts. The collector304serves to collect the return current and coupled that current to the common contact307. The LEPSD has two absorber regions—Absorber1(301) and Absorber2(303)—that are separated by a barrier layer302. These two absorber regions301and303selectively absorb the two wavelength bands of the incident light. When the incident light is absorbed in an absorber region, each photon of incident light can result in the generation of an electron charge-carrier and a hole charge-carrier. The barrier layer302selectively blocks the flow of one carrier type (e.g., either the electrons or the holes) and permits the flow of the other carrier type.FIG. 3illustrates an example of a LEPSD that provides location in regards to two orthogonal axes of X and Y. As depicted inFIG. 3, two contacts X1310and X2308are coupled to the first absorber layer (Absorber1) and two contacts Y1306and Y2309are coupled to the second absorber layer (Absorber2). The incident light illuminates the detector from the side closer to Absorber1. Buffer305is of suitable material to pass the light through it to Absorber1. Light of the shorter-wavelength band (i.e., Band1) sensed by this detector is absorbed in Absorber1. Light of the longer-wavelength band (i.e., Band2) sensed by this detector passes through Absorber1and is absorbed in Absorber2. For the example illustrated, the side of the detector closer to Absorber2and farther from the incident light has a common contact307that also can serve as an optical reflector of the light illuminating the detector and passing through the detector layers. The reflector allows that longer-wavelength light to make two passes through Absorber2so that the thickness of Absorber2can be smaller and still absorb the same amount of light as a thicker absorber. In some embodiments, the signal contacts are accessed from the side of the detector closer to Absorber2, as illustrated in theFIG. 3. However, in other embodiments of the detector, the signal contacts are accessed from the side of the detector closer to Absorber1.

System400ainFIG. 4aillustrates the electronic function of the dual-band LEPSD, in the form of an equivalent electrical circuit. Each of the two absorber layers generates a photo-current that is proportional to the intensity of the light of the associated wavelength band. The light is in a spot that is smaller than the size of the detector. Thus, the photo-currents are produced in only a portion of the detector area. For the photo-current associated with each of the two wavelength bands (e.g., IP1or IP2), the current flows to two contacts (e.g., X1and X2or Y1and Y2, respectively) that are located on opposite sides of the detector and that are associated with the absorber region for that wavelength band. The detector acts like a resistive divider for this current. The resistances (e.g., RX1and RX2or RY1and RY2) depend on the distance from the location of the spot of light to the contact. The resistance (e.g., RX1) is smaller when the spot is closer to the contact (e.g., X1).

System400binFIG. 4billustrates the function of an electronic signal-processing circuit that is coupled to the dual-band LEPSD. When a spot of light is incident upon the LEPSD, photo-currents can be produced at the four contacts—X1, X2, Y1and Y2—which are the electrical outputs of the LEPSD. The four photo-currents—I1X1, I1X2, I2Y1and I2Y2—are derived from the photo-currents IP1and IP2resulting from absorption of the incident light by absorber regions Absorber1and Absorber2, respectively. Contacts X1and X2are configured to determine the offset or relative displacement of the spot of incident light (or the centroid of the illumination pattern) from the center of the detector along the x-axis. Contacts Y1and Y2are configured to determine the offset or relative displacement of the spot of incident light (or the centroid of the illumination pattern) from the center of the detector along the y-axis. The position of the illuminated spot X(t) and Y(t) is determined by processing the four photo-currents as indicated by the following equations:

In an exemplary embodiment, KX=LX/2 and KX=LY/2, with LXand LYbeing the nominal widths of the LEPSD (i.e., the distances between the oppositely located contacts) along the x-axis and along the y-axis, respectively. If the illuminated spot is located at the center of the LEPSD, values of zero are produced for the y-position offset and for the x-position offset. For this example, if the illuminated spot is located adjacent the contact Y2, the y-position offset would have a value of +0.5LY. And, if the illuminated spot is located adjacent the contact Y1, the y-position offset would have a value of −0.5LY. As the illuminated spot moves closer to contact Y2, the value of resistance RY2becomes smaller and the value of resistance RY1becomes larger. Likewise, as the illuminated spot moves closer to contact X1, the value of resistance RX1becomes smaller and the value of resistance RX2becomes larger. In the example depicted in thisFIG. 42a, the positive photo-current IP1is divided through resistances RX1and RX2and the positive photocurrent IP2is divided through resistances RY1and RY2as shown below:
IY2=IP2·RY1/(RY1+RY2).

In one embodiment, the four output currents from the LEPSD are connected to trans-impedance amplifiers (TIAs), as illustrated inFIG. 4b. Various known circuit designs could be used for the TIAs. Also, various known circuit designs, such as those based on operational amplifiers, could be used to implement the subtracting operation, the summing operation and the dividing operation. In some designs, the signal provided to the denominator input of the dividing circuit should have a positive value. There is a separate set of operational amplifiers, subtracting circuitry, summing circuitry and dividing circuitry for each of the two photo-currents, IP1and IP2. The circuitry associated with IP1produces the time-varying X-position offset X(t) from the center of the detector. The circuitry associated with IP2produces the time-varying Y-position offset Y(t) from the center of the detector. The summing circuitry for each photo-current, e.g., IP1, produces an output waveform (e.g., A1IP1(t)) that is related to the time-variation of that photo-current. The processing circuit for the LEPSD has four outputs. Two outputs provide the location of the dual-band illuminating spot, along two reference axes (e.g., X and Y). One other output provides the time-variation of light in the first wavelength band of the illuminating spot. Another output provides the time-variation of light in the second wavelength band of the illuminating spot.

Another embodiment500inFIG. 5illustrates a material structure for the LEPSD. For this example, Absorber1(501) absorbs from incident light511, light of SWIR and MWIR bands that have wavelength between approximately 2 and 4 μm and Absorber2(503) absorbs light of a MWIR band that has wavelength shorter than 5 μm. Absorber1is transparent to the longer wavelength light having wavelength greater than the 4 μm cutoff of the Absorber1material. Thus, light having wavelength between 4 and 5 μm would be absorbed by Absorber2as well as any remaining light of 2 to 4 μm wavelength that passes through Absorber1without being absorbed. In an exemplary embodiment, Absorber1comprises n-type GaInAsSb and Absorber2comprises n-type InAsSb. These two absorber regions are separated by a p-type GaAlAsSb barrier layer502that imposes a high energy barrier in the conduction band to block the flow of electrons between the two absorber regions. That barrier layer502, however, imposes no energy barrier or only a small energy barrier in the valence band to the flow of holes between the two absorber regions. InFIG. 5, 518represents the Fermi level,512represents the edge of the conduction band and519represents the edge of the valence band. The material structure illustrated inFIG. 5also has a buffer layer505located on the side of Absorber1that is opposite the side adjacent to the barrier layer. The energy bandgap of this buffer layer (i.e., the energy difference between the edges of the valence band and the conduction band) is sufficiently wide to pass light having wavelength longer than 2 μm, which would be detected by the detector. In an exemplary embodiment of the structure illustrated inFIG. 5, the buffer layer comprises p-type AlAsSb. The buffer layer imposes a barrier in the conduction band that blocks the flow of electrons from Absorber1into that buffer layer. Thus, those electrons generated as a result of light absorption in Absorber1remain in that absorber region and flow to the two electrical contacts coupled to Absorber1. The buffer layer also imposes a barrier in the valence band that blocks the flow of holes from Absorber1into that buffer layer. But since the barrier layer between the two absorber regions does not block the flow of holes, those holes generated as a result of light absorption in Absorber1can flow into Absorber2.

The material structure illustrated inFIG. 5also has a p-type collector layer504located on the side of Absorber2that is opposite the side adjacent to the barrier layer502(and also opposite the side of the detector that has the buffer layer505). The energy bandgap of this collector layer504(i.e., the energy difference between the edges of the valence band and the conduction band) is sufficiently wide to pass light having wavelength longer than 4.0 μm, which would be detected by Absorber2of the detector. However, the collector layer504could absorb light that otherwise would be absorbed by Absorber1if that light made a second pass through those regions. In an exemplary embodiment of the structure inFIG. 5, the collector layer504comprises p-type GaInAsSb. The collector layer imposes a barrier in the conduction band that blocks the flow of electrons from Absorber2into that collector layer. Thus, those electrons generated as a result of light absorption in Absorber2remain in that absorber region and flow to the two electrical contacts coupled to Absorber2. The collector layer does not impose a barrier in the valence band but establishes a potential gradient that aids the flow of holes from Absorber2into that collector layer. Thus, those holes generated as a result of light absorption in Absorber1and in Absorber2can flow into the collector layer.

In an embodiment600,FIG. 6aandFIG. 6billustrates Cx and Cy cross-sectional views of the LEPSD ofFIG. 5for the X-position cross-section and for the Y-position cross-section, as viewed from cut lines drawn along the X-axis and along the Y-axis, respectively. These two cut lines are indicated in the illustration ofFIG. 3by Cx and Cy. The incident light is represented by611, Band1absorber is601, Band2absorber is603, the Barrier layer is602and the Buffer layer is605. The dielectric area is represented by621and the ion-implanted doping areas by622. The bottom metal interconnects and pads are represented by607. Two electrical signal contacts608and610located on opposite edges of the detector are coupled to the Band1absorber601(or Absorber1). These two contacts (visible in the Cx view) extract the photo-generated electron currents resulting from absorption of the shorter-wavelength, Band V1light. Two other electrical signal contacts606and609located on opposite edges of the detector are coupled to the Band2absorber (or Absorber2). These two contacts (visible in the Cy view) extract the photo-generated electron currents resulting from absorption of the longer-wavelength, Band2light. The relative levels of those four currents depend on the location of the illuminating spot of light, as discussed above with reference toFIGS. 4aand4b.

Several electrical common contacts607located on the side of the detector opposite the side from which the light is incident are coupled to the collector layer604. The collector layer can be separated into multiple collector regions, as illustrated inFIGS. 6aand 6b. The detector has a total of five electrical contact pads613,614,615,616and617that are located on the back side of the device, which is the side opposite the side from which the light is incident. These pads can be electrically coupled to the electronic circuit, as illustrated inFIG. 4and also with reference toFIG. 3. For example, contact pad613is electrically coupled to the X1signal contact610and supplies current I1X1to the electronic circuit. Contact pad614is electrically coupled to the X2signal contact608and supplies current I1X2to the electronic circuit. Contact pad615is electrically coupled to the Y1signal contact606and supplies current I2Y1to the electronic circuit. Also, contact pad616is electrically coupled to the Y2signal contact609and supplies current I2Y2to the electronic circuit. Contact pad617is electrically coupled to the common contacts607and provides a path for the return current (or ground) of the electronic circuit. The combined current from the common contacts607coupled to the multiple collector regions604equals the sum of the currents IP1and IP2respectively produced as a result of absorption of light by the Band1absorber1601and coupled through contacts610,608as well as absorption of light by the Band2absorber2603and coupled through contacts606,609.

In some embodiments, these pads613,614,615,616and617also can serve as optical reflectors that reflect the portion of Band2light which is not absorbed from one pass through the Band2absorber region (Absorber2) back again through that absorber region to be absorbed, in a second pass. This two-pass operation allows the thickness of the Band2absorber region to be smaller.

In another embodiment700illustrated inFIG. 7, the LEPSD is implemented with a different material structure. In this embodiment, the incident light is represented by711, the band1absorber is represented by701, the band2absorber by703, the collector1by704, the collector2by727and the barrier in the valence band by728. An optional conduction band barrier is represented by726. The conduction band edge for these various material layers is indicated by712and the valence band edge is indicated by719in the energy diagram shown in the figure. The Fermi level is illustrated by the dashed line718. Like the embodiment500, Absorber1absorbs light of SWIR and MWIR bands that have wavelength between approximately 2 and 4 μm and Absorber2absorbs light of a MWIR band that has wavelength shorter than 5 μm. Absorber1is transparent to the longer wavelength light having wavelength greater than the 4 μm cutoff of the Absorber1material. Thus, light having wavelength between 4 and 5 μm would be absorbed by Absorber2as well as any remaining light of 2 to 4 μm wavelength that passes through Absorber1without being absorbed. For the embodiment700, the exemplary material for the Absorber1comprises p-type GaInAsSb and Absorber2comprises n-type InAsSb. These two absorber regions are separated by an n-type InAs barrier layer that imposes a sufficiently high energy barrier in the valence band to block the flow of holes between the two absorber regions. That barrier layer728, however, imposes no energy barrier or only a small energy barrier in the conduction band to the flow of electrons between the two absorber regions. The energy structure facilitates the flow of electrons from Absorber1(701) into Absorber2(703).

The embodiment700illustrated inFIG. 7also has a collector layer704, Collector1, located on the side of Absorber1that is opposite the side adjacent to the barrier layer728. The energy bandgap of this collector layer is sufficiently wide to pass light having wavelength longer than 2 μm, which would be detected by the detector. For the embodiment700, the exemplary material for Collector1comprises p-type GaAlAsSb. Alternatively, this collector layer also could comprise p-type AlInSb. This collector layer imposes a barrier in the conduction band that blocks the flow of electrons from Absorber1into Collector1. Thus, those electrons generated as a result of light absorption in Absorber1remain in that absorber region or flow into Absorber2. Collector1permits the flow of holes from Absorber1into that layer and collects those holes generated as a result of light absorption in Absorber1.

The embodiment700also has a second p-type collector layer727, Collector2, located on the side of Absorber2(703) that is opposite the side adjacent to the barrier layer728(and also opposite the side of the detector that has the first collector layer704, Collector1). The energy bandgap of this second collector layer727(i.e., the energy difference between the edges of the valence band and the conduction band) is sufficiently wide to pass light having wavelength longer than 4 μm, which would be detected by Absorber2of the detector. However, this collector layer might absorb some shorter-wavelength light that otherwise would be absorbed by Absorber1. In the exemplary structure, this collector layer comprises p-type AlInSb. Collector2(727) imposes a barrier in the conduction band that blocks the flow of electrons from Absorber2into that collector layer. Thus, those electrons generated as a result of light absorption in Absorber2remain in that absorber region and flow to electrical contacts coupled to Absorber2. Collector2does not impose a barrier in the valence band but establishes a potential gradient that aids the flow of holes from Absorber2into that collector layer, which collects those holes generated as a result of light absorption in Absorber2. An additional barrier layer726can be included in the material structure that further blocks the flow of electrons from Absorber2into the second collector layer727but does not impede the flow of holes from Absorber2into that collector layer.

System800illustrated inFIG. 8aandFIG. 8billustrates Cx and Cy cross-sectional views of a detector embodiment that makes use of the material structure in the embodiment700(FIG. 7). Please refer toFIG. 3for the cross-sectional cuts Cx and Cy. The incident light is represented by811, the barrier by828, the common contact areas by807, the dielectric area by821, and the ion implanted doping areas by822. Two electrical signal contacts808and810located on opposite edges of the detector are coupled to the Band1absorber801(or Absorber1) through Collector1,804. These two contacts (visible in the Cx view) extract the photo-generated electron currents resulting from absorption of the shorter-wavelength, Band1light. Two other electrical signal contacts806and809located on opposite edges of the detector are coupled to the Band2absorber803(or Absorber2) through Collector2,827. These two contacts (visible in the Cy view) extract the photo-generated electron currents resulting from absorption of the longer-wavelength, Band2light. The relative levels of those four currents depend on the location of the illuminating spot of light, as discussed above with reference toFIGS. 4aand4b.

Multiple electrical common contacts807located on the side of the detector opposite the side from which the light811is incident are coupled to Absorber2(803). The photo-generated electrons that are produced as a result of the absorption of the Band1light and the Band2light are extracted through these common contacts807. Multiple via holes are formed in Collector2(827). These via holes are filled with metal posts837that conduct currents from the common contacts807to a metal pad817for the common current associated with absorption of light in both wavelength bands. The detector has a total of five electrical contact pads813,814,815,816and817that are located on the back side of the device, which is the side opposite the side from which the light is incident. These pads can be electrically coupled to the electronic circuit, as illustrated inFIGS. 4aand 4b. These pads813,814,815,816and817have the same electrical connections as the corresponding pads613,614,615,616and617shown inFIGS. 6aand 6b. In some embodiments, these pads also can serve as optical reflectors that reflect the portion of Band2light which is not absorbed from one pass through the v Band2absorber region (Absorber2) back again through that absorber region to be absorbed, in a second pass. This two-pass operation allows the thickness of the Band2absorber region to be smaller.

The embodiment900inFIG. 9illustrates the pattern of electrical contacts made to the backside of the detector structure ofFIGS. 7 and 8. The four signal contacts are located at the four edges of the detector. Two signal contacts910,908are coupled to Collector1(904) and two other signal contacts906,909are coupled to Collector2(927). Although via holes are formed in Collector2, that collector layer927is still contiguous and provides paths for currents to flow to the two signal contacts coupled to that layer. Each metal post937in a via hole is in direct contact only with the Ohmic contacts formed in Absorber2and is separated from the material of Collector2by some dielectric material921filling the spaces in the via hole. The metal posts937in the via holes make contacts with the Band2absorber layer. The X1and X2contacts are represented by910and908, respectively, while the Y1and Y2contacts are represented by906and909, respectively, inFIG. 9.

For the embodiments500and600ofFIGS. 5 and 6, which illustrate a detector suitable for dual-band detection of SWIR and MWIR light, the currents to the four signal contacts flow through n-type materials that have fairly high electrical conductivity, because the electrons have high mobility. For the embodiments ofFIG. 7throughFIG. 9, the currents to the four signal contacts flow through heavily doped p-type materials, which although having lower carrier mobility than n-type materials can have high electrical conductivity because of its high doping level.

The thickness of Absorber1should be sufficiently large to enable most (e.g., >90-95%) of the Band1light to be absorbed in a single pass through that region. In general, a thickness of 2 μm to 5 μm may be acceptable, although even greater thickness could be used, too. Any Band1light not absorbed by Absorber1could then become absorbed by Absorber2and result in currents from the Absorber2region that do not represent the Band2light. The thickness of Absorber2preferably is sufficiently large to enable most (e.g., >90-95%) of the Band2light to be absorbed in two passes through that region. In general, a thickness of 3 μm to 5 μm may be acceptable, although even greater thickness could be used, too. As illustrated inFIGS. 6 and 8, the metal reflectors are separated from the absorber materials by a spacer of dielectric material621,821that has sufficiently large thickness (e.g., >0.2 μm) and sufficiently low refractive index (e.g., <2.4) to reduce the absorption of the Band2light by those metal reflectors. The term “minimally” absorbing is used in the context of what amount of absorption is acceptable in the ‘other’ band that is not supposed to be absorbed by this absorber. The acceptable amount of absorbed light in the other band depends on the specific application. For J example, having absorption below 25% in the wrong band may be acceptable for some applications. For other applications, this wrong band absorption may have to be less than 5%.

The specific compositions of the materials in the detector structure can be adjusted to achieve absorption of light over a desired range of wavelengths at a given operating temperature. This material can be grown on substrate materials such as GaSb and GaAs. The materials do not need to have the same lattice constant as that of the substrate. In some embodiments, it is preferable that the lattice constants of the materials in the various layers and regions of the detector structure are similar.

Although binary, ternary and quaternary bulk materials have been described in the examples discussed above, it also is possible to use superlattices of several binary materials for the various layers and regions of the detector structure. For example, short-period superlattices of InAs/GaSb can be used to achieve absorbers that absorb light at wavelengths ranging from MWIR bands to LWIR bands.

The embodiment1000ofFIG. 10illustrates an alternate architecture for the detector that also can provide position location of a spot of illuminating light along two axes defined by the detector. In this embodiment, the position location can be provided separately for light of the two wavelength bands. Thus, even when the illuminating spot contains light in only one wavelength band, the detector still can locate that spot. InFIG. 10, the absorber-1is represented by1001, the absorber2by1003, the barrier layer by1002, the collector layer by1004, the buffer layer by1005, the common contact layer by1007, and the signal contacts by1010a,1008a,1008b,1008c,1009a,1009b,1009c,1006a,1006band1006c. (Signal contacts1010band1010care hidden from view in this drawing). The detector separates each group of signal contact into three portions. For example, two of those portions (1009a,1006a) and (1009b,1006b) are located near corners of the detector, as shown in theFIG. 10. The other portions (1009c,1006c) are located between those corner-located portions and near an edge of the detector. The X1and X2contacts (1010cand1008c, respectively) and Y1and Y2contacts (1006cand1009c, respectively) are as discussed earlier.

Four contacts1010a,1010b,1008a,1008blocated near the four corners of Absorber1are coupled to Absorber1. Likewise, four contacts1006a,1006b,1009a,1009blocated near the four corners of Absorber2are coupled to Absorber2. The four contacts associated with each absorber in combination with that absorber, which acts like a four-part resistive divider, can function like a quadrilateral position sensing detector. The detector1000ofFIG. 10thus has two quadrilateral position sensing detectors that are stacked above each other V and that are spatially aligned with each other, with one quadrilateral position sensing detector sensing light of Band1and the other quadrilateral position sensing detector sensing light of Band2. When used as quadrilateral position sensing detectors, the centroid of the Band1light and the centroid of the Band2light could be at different spatial locations. The detector1000can separately locate the Band1light and the Band2light. Each of the corner contacts (e.g.,1006a,1006b,1009a,1009b) would be connected to a input of an electronic circuit that processes the signal currents from those contacts and determines the location of the spot of light sensed by the associated absorber layer.

Though figures are illustrated for a rectangular detector, the detector as well as the Absorber1, Absorber2and the barrier can be of any shape, such as any polygon, a square or even a circle. The detectors can also be cascaded along the X and Y directions to form an array of detectors supporting different wavelength absorptions on one or more detectors. Such array of detectors can detect optical intensities on several bands from one or more incident light and can also detect the locations of multiple light sources. Such an array of detectors can be fabricated on a monolithic substrate. Any single layer can also contain more than one Absorber type and in which case, each Absorber type will have its own set of electrodes. Additional Absorber layers can also be stacked vertically to detect intensities of light at additional wavelength bands or to locate multiple sources. Also, each Absorber can absorb more than one wavelength (such as a band of wavelengths) and in which case, the sensor detection will be for the band as opposed to a single wavelength. Additionally, the light or radiation sources that are detected can be in any wavelength band (SWIR, MWIR or LWIR).

The various embodiments of the disclosed sensor can be part of an optical angle-of-arrival sensor that determines the incidence angle of the dual-band light produced by a transient event (such as a muzzle flash) or a rapidly moving object (such as a projectile or missile). Such events and moving objects produce MWIR radiation because of the heat and gas-compression generated and also could produce MWIR radiation as a result of chemical reactions (e.g., exhaust gas from gun blasts or fuel combustion). The sensor can locate and track the object producing the dual-band light. The sensor also can determine the time-variation of the light in each wavelength band. Different objects that could produce the dual-band light generally would have different characteristic time variations of the intensities in the two bands. Thus, this sensor can not only locate the light but also provide information about the source of that light. This sensor also can provide information on how the source of light changes as its position changes. For example, the source of light could change from having substantial contribution from chemical combustions reactions to having more contributions from heating and J compression effects.

The concepts represented here for the dual band sensor can be extended to three v bands and beyond by stacking up the properly chosen absorbers and with appropriate barriers. The mathematics can be extended as a system of matrix equations to identify intensities of light at multi-bands as well as to locate and track multiple sources. This disclosure includes such extensions to the concepts presented here.

Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set.

To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke paragraph 6 of 35 U.S.C. Section 112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.