TRACKING AND DETECTOR DEVICE FOR OPTICAL SYSTEMS

A tracking detector device for use in a free-space optics (FSO) system includes a position sensor and an optical receiver coupled to the bottom surface of the position sensor. The position sensor has an optical aperture configured to allow a portion of incoming light to pass through the position sensor and a plurality of position receivers located adjacent to the optical aperture and configured to sense portions of the incoming light. The tracking detector device may also include a focusing optic disposed adjacent to the bottom surface of the position sensor and configured to focus the portion of the incoming light that passed through the position sensor onto the optical receiver. The tracking detector may advantageously be employed in FSO communications systems and provide fully automated alignment with an incoming light beam under computer control.

TECHNICAL FIELD

The subject matter described herein relates to systems, methods, and structures providing integrated optical tracking and detection that may be utilized in a variety of optical systems including free space optics (“FSO”) communications systems—among others.

BACKGROUND

The background description provided is to present a general context of the disclosure. Work of the inventor, to the extent it may be described in this background section, and aspects of the description that may not otherwise qualify as prior art at the time of filing are neither expressly nor impliedly admitted as prior art against the present technology.

Optical systems are essential for many technologies. As such, optical systems are used in a wide variety of applications, including astronomy, medicine, industry, and consumer electronics. Free-space optics generally refers to optical technologies that transmit modulated visible or infrared (IR) light beams through air or space from source to destination rather than guided through an optical waveguide, e.g., optical fiber. FSO communications is a communications technology that utilizes light propagating in free-space, e.g., air, vacuum, outer space, to wirelessly transmit data for communications such as computer networking. Moreover, the light, which may be in the form of an encoded visible or infrared (IR) beam, is directed towards a receiver. Upon receiving the encoded light beam, the receiver outputs an electric al signal, such as a digital signal, that represents data encoded in the received light. FSO communications systems are particularly useful where such waveguide optical connections are impractical due to high costs or other considerations.

However, as those skilled in the art will understand and appreciate, many optical systems—and FSO communications in particular—require proper alignment of an incoming light beam with respect to a receiver. If the alignment is not sufficient, the receiver may not be able to receive and digitize the incoming light beam, resulting in lost data and reduced bandwidth.

Prior art alignment approaches have utilized a beam splitter to split an incoming light beam into a first light beam used for communication purposes and a second light beam used for alignment purposes. The first light beam is directed towards a receiver that digitizes the incoming light beam for the communications purposes. The second light beam is directed towards another receiver that acts as an alignment sensor to determine an overall alignment of the beam. Based on this overall alignment information, one or more components of an optical assembly may be adjusted to change the alignment of the incoming beam. Unfortunately, such prior art approaches are complex optically and mechanically and require multiple beam paths for detection and alignment purposes.

SUMMARY

An advance in the art is made according to aspects of the present disclosure directed to an optical tracking and detector device for use in optical systems such as a FSO communication systems—among others. In sharp contrast to the prior art, optical systems including our inventive optical tracking and detector device exhibit position sensor elements that are configured to detect any misalignment of incoming/received light.

Viewed from a first illustrative aspect, the optical tracking and detector device according to aspects of the present disclosure generally includes a position sensor having an optical aperture configured to allow a portion of incoming light to pass through the position sensor; a plurality of position receivers positioned adjacent to the optical aperture, the plurality of position receivers configured to sense portions of the incoming light; and an optical detector configured to detect the portion of the incoming light that passes through the position sensor aperture.

Viewed from another—more specific, illustrative aspect, the optical tracking and detector device according to aspects of the present disclosure includes a position sensor, a focusing optic disposed adjacent to the position sensor, and an optical receiver device coupled to the bottom of the optical device. Advantageously, the optical receiver device could be any one of several different optical receiver devices, such as optical detectors, optical waveguides, and the like. The optical aperture is configured to allow a portion of incoming light to pass through, as well as a plurality of position receivers located adjacent to the optical aperture and configured to sense portions of the incoming light that strike a top surface of the position sensor. The focusing optic focuses the portion of the incoming light that passed through the position sensor onto the optical device.

In some embodiments, the optical tracking and detector device may advantageously be fabricated as a pair of sub-assemblies—including an upper sub-assembly and a lower sub-assembly. When so fabricated, a common upper sub-assembly may be paired with any one of several lower sub-assemblies each of which exhibit—for example—a specific detector type, a specific detector arrangement, or a specific optical coupling arrangement or combinations thereof.

In yet another illustrative example, a device for use in a FSO system includes a position sensor having an optical aperture extending from the top surface to a bottom surface of the position sensor and an optical detector coupled to a bottom surface of the position sensor. The position sensor also has a plurality of position receivers located adjacent to the optical aperture and configured to sense portions of the incoming light that strike the top surface of the position sensor. The optical aperture allows a portion of incoming light to pass through the position sensor and be received by the optical detector.

Further areas of applicability and various methods of enhancing the disclosed technology will become apparent from the description provided. The description and specific examples in this summary are intended for illustration only and are not intended to limit the scope of the present disclosure.

This SUMMARY is provided to briefly identify some of aspects of the present disclosure that are further described in the DESCRIPTION. This SUMMARY is not intended to identify key or essential features of the present disclosure, nor is it intended to limit the scope of any claims.

The term “aspects” is to be read as “at least one aspect”. The aspects described above, and other aspects of the present disclosure described herein are illustrated by way of illustrative examples(s) and not limited to the accompanying drawing.

The drawing figures, which are incorporated in and constitute a part of the specification, illustrate various systems, methods, and other illustrative embodiments of the disclosure. It will be appreciated that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the drawing figures represent one embodiment of the boundaries. In some embodiments, one element may be designed as multiple elements or multiple elements may be designed as one element. In some embodiments, an element shown as an internal component of another element may be implemented as an external component and vice versa. Furthermore, elements may not be drawn to scale.

DESCRIPTION

The following merely illustrates principles of this disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its spirit and scope.

Described herein are devices that can be utilized with a variety of optical systems such as FSO systems. In particular, the devices described herein are designed to decrease the size, weight, cost, and complexity of an optical head for an optical system, for example, a FSO communications system.

Referring toFIG.1, illustrated is a perspective view of one illustrative example of an illustrative device100that—as previously noted—may be utilized as part of a link or node in an FSO communications system. As its primary components in this example, device100includes a position sensor110attached to an optical detector unit130. The optical detector unit130—which may include a slab of InP or other suitable material along with a lens or other light-focusing/directing element—can be further coupled to a substrate150, such as an alumina substrate or other type of substrate.

As illustratively shown, position sensor110is formed on a substrate111, having a top surface112and a bottom surface114(best shown inFIG.2). The position sensor110may be constructed from indium phosphide (“InP”) or any other suitable material. When configured according to aspects of the present disclosure, position sensor110detects the relative alignment of a light beam160projected onto the top surface112of the position sensor110and thereby acts as an alignment sensor. Position sensor110may include a plurality of position receivers118A-118D formed on the top surface112of position sensor110. In particular, the position receivers118A-118D may be in the form of a quad-cell detector. However, and as will be understood and appreciated by those skilled in the art, the position receivers118A-118D may take any one of several different forms and arrangements.

Further still, while four position receivers118A-118D are shown, any number of position receivers may be utilized in a variety of arrangements. For example, instead of a quad-cell arrangement such as illustratively shown, the arrangement may include any number individual position receivers such as hex-cell detector, (6receivers), hepto-cell detector (7receivers), octo-cell detector (8receivers), etc. Additionally, such position receivers may be arranged in an inner/outer ring arrangement wherein an outer ring of position receivers may surround an inner ring of position receivers which in turn surround an aperture.

Further still, while four position receivers118A-118D are shown, any number of position receivers may be utilized. In one illustrative example, position receivers118A-118D may be in the form of PIN photodetectors and/or avalanche photodiodes (“APDs”). However, it should be understood any type of suitable photodetectors, or combinations thereof, may be utilized to act as the position receivers118A-118D.

Each of the position receivers118A-118D may have anode pads120A-120D and cathode pads122A-122D, respectively, also formed on the top surface112of the position sensor110. The anode pads120A-120D are connected to the anodes of the position receivers118A-118D, respectively, while the cathode pads122A-122D are connected to the cathodes of the position receivers118A-118D, respectively. In some cases, the anode pads120A-120D or the cathode pads122A-122D may be connected to each other. However, in these situations, only one of the anode pads120A-120D or the cathode pads122A-122D may be connected to one another.

Signals output by the position receivers118A-118D can be utilized to determine a general alignment of the light beam160. The light beam160is a light beam that has been encoded to communicate information optically over a free space. The free space acts as a communication channel that allows the transmission of information from one location to another. In some cases, the free space may be in the form of a gas, such as air, or a vacuum, such as outer space. As those skilled in the art will understand and appreciate, the general alignment of the light beam160is important because if the light beam160is not aligned correctly, detection may be imperfect, and information encoded within the light beam160may be lost.

As best shown inFIG.2, located within position sensor110is aperture116, which allows a portion of the light beam160to pass through the position sensor and be received by the optical detector130. As will be described in more detail, aperture116may be an InP substrate with an antireflection coating or other sufficiently optically transparent material, depending upon the transmission wavelength of the light beam160. In one illustrative example, the aperture116may be made from the same material used to form the substrate of the position sensor110, such as InP. Alternatively, the aperture116may be an empty cavity. In another illustrative example, the aperture may have straight sidewalls such that an entrance and exit are the same diameter or have tapered sidewalls such that an entrance has a greater diameter than an exit. As will be explained later, aperture116allows portions of the light beam160to pass through the position sensor110and be received by the optical detector130.

Advantageously, aperture116may be located within position sensor110such that portions of the aperture116adjacent to the top surface112of the position sensor110are adjacent to the position receivers118A-118D. Moreover, since the alignment of the light beam160should be such that the light beam160is projected to the aperture116, surrounding the aperture116with position receivers118A-118D allows for a determination regarding if the alignment of the light beam160with respect to the aperture116is proper and/or desired.

For example, in situations where the position receivers118A-118D are a quad-cell, the general alignment of the light beam160can be determined based on the comparison of the signals output from the position receivers118A-118D. For example, as illustratively shown inFIG.1, the displacement of the light beam160in x-direction (left/right) is the signal difference from the signal outputs of the position receivers118A and118C minus the signal outputs of the position receivers118B and118D divided by the total signal outputs. This x displacement (xdisp) can be expressed as follows:

Similarly, the displacement of the light beam160in the y-direction (up/down) is the signal difference from the signal outputs of the position receivers118A and118B minus the signal outputs of the position receivers118C and118D divided by the total signal outputs. This y displacement (ydisp) can be expressed as follows:

Once the general displacement of the light beam160is determined, an optical assembly170, which may include one or more optical components172, can be adjusted to better project the light beam160onto the top surface112of the position sensor110so that enough light from the light beam160reaches and optical receiver and the optical detector unit130via the aperture116. Those skilled in the art will understand and appreciate that a “sufficient amount of light” for the optical receiver and/or optical detector is merely a detectable amount of light from which data may be extracted and/or informational determinations may be made.

The optical components172making up the optical assembly170can include any one of a number of different optical components and combinations thereof. As such, the optical components172can include lenses, diffusers, etc., as well as actuators that can effectively change the projection of the beam160by adjusting the optical components172.

The optical detector unit130that receives the light from the light beam160generally includes a top surface132and a bottom surface134. Such optical detector unit may include a slab of InP or other suitable material along with a light focusing element including a lens.

Shown further in this figure is optical detector136which receives at least a portion of light that traverses the aperture and optical detector unit130. Those skilled in the art will understand and readily appreciate that the optical detector136can be any type of optical detector, such as a PIN photodetector, an APD, a P-N junction device, a charge-coupled device detector, a cadmium sulfide photocell, a metal-semiconductor-metal (“MSM”) detector, and the like. Additionally, optical detector136may include a plurality of PIN photodetectors, APDs, P-N junction devices, cadmium sulfide photocells, MSM, etc. and have such plurality arranged as a 1-dimensional or multi-dimensional array. When configured in this manner, information pertaining to light striking the optical detector136asymmetrically may be obtained and useful for certain applications such as determining a direction from which a light beam originates.

Similarly, an optical fiber or other optical receiver structure such as fiber or semiconductor waveguides may be employed to receive the light beam that traverses the aperture, with such received light being directed via the waveguide to another structure that may include an optical detector such as those noted above.

In this illustrative example, the optical detector136is an APD. As is known, APDs are highly sensitive semiconductor photodiode detectors that exploit the photoelectric effect to convert light into electricity. As such, APDs can convert received light portions of the light beam160into an electrical signal that represents data transported by the light beam160. APDs may generally exhibit an absorber-multiplier structure wherein incident photons are absorbed in an absorber region and undergo avalanche multiplication in the multiplication region.

In this illustrative example, the optical detector136includes contact pads138A and138B and a contact area. The contact pads138A and138B are connected to contact pads152A and152B, respectively, of the substrate150. The contact pads152A and152B are connected to traces154A and154B, respectively, that may be connected to other electrical components that can utilize the signals generated by the optical detector130in response to receiving the beam160.

In this example, the top surface132of the optical detector unit130is directly adjacent to and attached to the bottom surface114of the position sensor110. The optical detector unit130may be attached to the position sensor110through a number of different methodologies, such as using a low viscosity optical adhesive or utilizing a wafer bonding technique.

Additionally, to better project portions of the beam160received by the optical detector onto contact area136, a focusing optic180may be utilized. In this example, the focusing optic180is positioned adjacent to the top surface132of the optical detector unit130. Additionally, because it is located adjacent to the top surface132of the optical detector unit130, the focusing optic180is also adjacent to the bottom surface114of the position sensor110.

The focusing optic180may be coated with an anti-reflective coating182. The antireflective coating182may match the index of refraction of any adhesive used to bond the position sensor110to the optical detector unit130and/or the index of refraction of air or whatever medium the light beam160is being transported through.

As illustratively shown inFIG.2, the top surface112of the position receiver generally defines a first plane190, while the bottom surface134of the optical detector unit130defines a second plane192. A third plane194is generally defined by the bottom surface114of the position sensor110and/or the top surface132of the optical detector unit130. The planes190,194may be substantially parallel to one another.

In this illustrative example, the focusing optic180may be located anywhere between the first plane190and the second plane192such that the focusing optic180can focus portions of the light beam160that passed through the aperture116onto appropriate areas of the optical detector unit130, such as the optical detector136.

As such, in the example shown inFIG.2, the focusing optic180may be integrated within portions of the die that forms the optical detector unit130. In this example, the focusing optic180is located between the second plane192and the third plane194but is still located between the first plane190and the second plane192.

However, the focusing optic180can be in other areas between the first plane190and the second plane192. For example, referring toFIG.3, another example of the device100is shown. The same reference numerals have been utilized to refer to the same components. Any previous description regarding these components is equally applicable to the example of the device100ofFIG.3.

In the example of the device100ofFIG.3, the focusing optic180is still located between the first plane190and the second plane192. However, in this example, the focusing optic180is located between the first plane190and the third plane194. This differs from the example ofFIG.2, wherein the focusing optic180was located between the second plane192and the third plane194. In the example of the device100ofFIG.3, the focusing optic180can be integrated within the die of the position sensor110. Again, the purpose of the focusing optic180is to focus light that has been received by the aperture116onto the appropriate area of the optical detector unit130, such as the optical detector136.

Referring now toFIG.4, there is shown another illustrative example of device100. Like before, the same reference numerals have been utilized to refer to the same components. As such, any previous description regarding these components is equally applicable to the example of the device100ofFIG.4. The device100ofFIG.4foregoes the use of the focusing optic180altogether. Moreover, due to the closeness of the position sensor110with respect to the optical detector130, the distance that the light beam travels after exiting aperture116is short. Due to the short distances, in this example, portions of the light beam160that pass through the aperture116can be directly projected onto appropriate portions of the optical detector unit130, such as the optical detector136, without intervening optics located between the first plane190and the second plane192. Of course, this can vary from application to application. In some applications, the focusing optic180may be desirable as it may improve the functioning of the optical detector unit130. In other applications, the focusing optic180can be foregone altogether.

While the illustrative example shown inFIGS.1-4illustrate examples wherein the position sensor110is directly adjacent and/or attached to the optical detector unit130, it is noted that the position sensor110need not be directly adjacent and/or attached to the optical detector unit130. For example,FIG.5illustrates another example of device100. Like before, the same reference numerals have been utilized to refer to the same components. As such, any previous description regarding these components is equally applicable to the example of device100ofFIG.5.

In the illustrative example of device100ofFIG.5, position sensor110is not connected to the optical detector unit130. Portions of the light beam that pass-through position sensor110are focused onto the appropriate portion of the optical detector unit130using the focusing optic180, which is shown to be separate from the position sensor110and the optical detector unit130. In particular, the focusing optic180, in this example, is located between a plane194A, defined by the bottom surface114of the position sensor110and a plane194B, defined by the top surface132of the optical detector unit130. As such, the focusing optic180is still located between the first plane190and the second plane192.

Additionally, while the focusing optic180is separated from the position sensor110and the optical detector130in this example, it is possible that the focusing optic180may be attached to the position sensor110and/or the optical detector unit130. For example, the focusing optic180could be located between the first plane190and the plane194A, defined by the bottom surface114of the position sensor110or could be located between the second plane192and the plane194B, defined by the top surface132of the optical detector unit130. Further still, while the focusing optic180is shown as a single lens, the focusing optic180could be broken up into several optical components located between the first plane190and the second plane192.

The focusing optic180in this example could be freely positioned with respect to the position sensor110and/or the optical detector unit130. Alternatively, the position of the focusing optic180in this example could be fixed based on the position of the position sensor110and/or the optical detector unit130.

It is noted that the examples illustrated inFIGS.1-5show that portions of the light beam160pass through the aperture116of the position sensor110and are received by an optical detector unit130. However, as mentioned earlier, optical detector unit130can be replaced with virtually any other type of optical device.

For example,FIG.6illustrates another example of the device100. Like before, the same reference numerals have been utilized to refer to the same components. As such, any previous description regarding these components is equally applicable to the example of the device100ofFIG.6.

In the example shown inFIG.6, optical detector unit130has been replaced with a different optical device, in this case, an optical fiber assembly200. In this illustrative example, the optical fiber assembly200can receive portions of the beam160that have passed through the position sensor110. The optical fiber assembly200includes an optical coupler202connected to an optical fiber204. The optical coupler202, in coordination with the focusing optic180, directs portions of the beam160that passed through the position sensor110into the optical fiber204. The optical fiber204can be any type of optical fiber, such as single-mode optical fiber, hollow-core optical fiber, and the like.

The optical fiber204can then transport the light beam160to a different location. In particular, the optical fiber204may transport portions of the light beam160to an optical detector (not specifically shown) that can then convert the light beam160that was transported by the optical fiber204into an appropriate electrical signal.

FIG.7is a cut-away view of an illustrative TO packaging including tracking and detector device for free-space optical systems that includes a position sensor and detector according to aspects of the present disclosure. As illustratively shown in that figure, our tracking and detector device for free-space optical systems may be advantageously packaged into familiar shaped transistor outline packages that provide a robust, manufacturable package that is compatible with a variety of manufacturing technologies. Shown further in the figure is the relative position of the tracking and detector device relative to the TO cap and window that permits the entrance of a light beam that is subsequently tracked and detected.

FIG.8is close-up of the cut-away view ofFIG.7showing an illustrative TO packaging including tracking and detector device for free-space optical systems that includes a position sensor and detector according to aspects of the present disclosure.

FIG.9is top view of an illustrative TO packaging with cap removed revealing a tracking and detector device for free-space optical systems that shows a schematic of the detector and wire bonds to component and package leads according to aspects of the present disclosure.

FIG.10is top view of an illustrative TO packaging with cap removed revealing a tracking and detector device for free-space optical systems that shows a schematic of a quad-cell position sensor/detector and wire bonds to component and package leads according to aspects of the present disclosure.

FIG.11is top view of an illustrative TO packaging including cap window/optic revealing a tracking and detector device for free-space optical systems that shows a schematic of a quad-cell position sensor/detector and central aperture through which light beam is configured to be directed to an underlying light beam detector/sensor according to aspects of the present disclosure.

FIG.12(A)is a top view schematic of an illustrative octo-cell position sensor arrangement andFIG.12(B)is a top view schematic of an illustrative inner-outer position sensor arrangement according to aspects of the present disclosure. As illustratively shown inFIG.12(A)an 8-segment octo-cell position sensor arrangement is employed and contained in a TO packaging. A TO package window formed in a TO package cap provides optical access to the position sensor contained therein.FIG.12(B)shows an alternative position sensor arrangement namely and inner/outer ring arrangement where two position sensor “rings” are positioned substantially concentrically within a TO package. In this illustrative arrangement, the outer position sensor ring is a quad-cell arrangement while the inner ring is a octo-cell arrangement and surrounds the aperture. While not specifically shown from this view, the two concentric position sensor rings may be at the same elevation—or not—relative to an underlying optical receiver.

FIG.13is a schematic diagram of an illustrative free-space optical system including tracking and detector device for free-space optical systems including servo-controlled coupler and controller configured to receive alignment information from the tracking and detector device and mechanically move the tracking and detector device to a desired location for reception of light beam according to aspects of the present disclosure. As illustratively shown in the figure, the tracking detector is shown positioned on X-Y positioning table or other adjustable structure that is under computer control. Operationally, the computer/controller receives tracking data from the tracking detector and interactively adjusts X and/or Y position of the tracking detector to desirably align a received light beam with a central aperture of the tracking detector.

As those skilled in the art will readily appreciate, such an arrangement may be employed in virtually any free-space optical arrangement where the alignment of a light beam with a detector is critically important including line-of-sight optical communications and applications thereof such as:Backhaul—providing high-speed backhaul connections between data centers, cell towers and other network nodes;Enterprise networks—providing connections between buildings or campuses as an alternative to fiber optic cable;Wireless broadband—providing wireless broadband access to homes and businesses as an alternative to optical fiber, cable, and DSL;Military and government—providing communications, surveillance, and targeting. As those skilled in the art will readily appreciate, such free-space applications provide a number of advantages over other technologies including high bandwidth, low latency, and high reliability.

FIG.14is a schematic flow diagram of an illustrative method for controlling a free-space optical system including tracking and detector device for free-space optical systems including servo-controlled coupler and controller configured to receive alignment information from the tracking and detector device and mechanically move the tracking and detector device to a desired location for reception of light beam according to aspects of the present disclosure. As illustratively shown, a controller receives position output signals from position sensor at block1301. At Block1302, and Block1303, X and Y displacement(s) is/are determined from the received position sensor output signals. At Block1304, a determination is made whether X or Y position adjustment is required and, if so, at Block1305, the X and/or Y positions of the sensor/detector is/are adjusted. The process repeats until no further adjustment is necessary. This overall process is repeated such that a desired alignment is continuously realized.

The following includes definitions of selected terms employed herein. The definitions include various examples and/or forms of components that fall within the scope of a term and may be used for various implementations. The examples are not intended to be limiting. Both singular and plural forms of terms may be within the definitions.

References to “one embodiment,” “an embodiment,” “one example,” “an example,” and so on, indicate that the embodiment(s) or example(s) so described may include a feature, structure, characteristic, property, element, or limitation, but that not every embodiment or example necessarily includes that feature, structure, characteristic, property, element or limitation. Furthermore, repeated use of the phrase “in one embodiment” does not necessarily refer to the same embodiment, though it may.