Abstract:
A compact, integrated LIDAR system utilizes SOI-based opto-electronic components to provide for lower cost and higher reliability as compared to current LIDAR systems. Preferably, an SOI-based LIDAR transmitter and an SOI-based LIDAR receiver (both optical components and electrical components) are integrated within a single module. The various optical and electrical components are formed utilizing portions of the SOI layer and applying well-known CMOS fabrication processes (e.g., patterning, etching, doping), including the formation of additional layer(s) over the SOI layer to provide the required devices. A laser source itself is attached to the SOI arrangement and coupled through an integrated modulation device (such as a Mach-Zehnder interferometer, i.e., MZI) to provide the scanning laser output signal (the scan controlled by, for example, an electrical (encoder) input to the input to the MZI). The return, reflected optical signal is received by a photodetector integrated within the SOI arrangement, where it is thereafter converted into an electrical signal and subjected to various types of signal processing to perform the desired type(s) of signal characterization/signature analysis.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/762,994, filed Jan. 27, 2006. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention is related to a “LIght Detection And Ranging” (LIDAR) system and, more particularly, to a compact, integrated LIDAR system utilizing SOI-based opto-electronic components to provide for lower cost and higher reliability as compared to current LIDAR systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    LIDAR systems are known to be utilized in a number of different arrangements including, but not limited to, “radar guns” as used by police to monitor traffic speeds, ground-based surveying, underwater scanning, airborne geo-mapping arrangements, aerosol monitoring, and the like. LIDAR systems may operate on the basis of various types of optical output signals, including continuous wave (CW) Doppler, pulsed Doppler, CW phase-shift keying (CW-PSK), pulsed PSK, and the like. In one exemplary arrangement, the LIDAR device emits a short pulse of infrared light that is directed in a narrow beam toward a selected target. The light pulse strikes the target and is typically reflected back towards the LIDAR device. This return energy is then captured by an optical receiving element and converted from light energy to an electrical signal. A high speed clock is used to determine the total trip time, which can then be used to calculate the range to the target. For speed calculations, multiple ranges are taken and the change in range over a short period of time is determined. Typically, police LIDAR speed guns and survey range finders use stripe array laser diode emitters to emit the pulse of infrared energy required to measure the distance to targets at significant ranges. The maximum range that a system can achieve is proportional to the amount of energy emitted per pulse by the laser. The amount of energy that is emitted from these lasers is typically limited by the laser safety regulations of the country where the LIDAR units are sold, impacting the maximum range over which these devices may be used. 
         [0004]    LIDAR units are also starting to be used in automotive applications for driver assistance situations. Typically, these units have a range and field of view to detect objects, such as other automobiles, at an appropriate distance to take any necessary action, such as warning the driver or changing the speed of the automobile. In order to obtain the required field of view, prior art systems use two methods. One prior art LIDAR system consists of a phased array, which consists of several optical transmitting elements whose relative phase is adjusted to create a radiation pattern of constructive and destructive optical waves, forming a beam that can be electronically steered, by adjusting the phases of the individual optical transmitting elements. This phased array system is generally too expensive for use in the automotive environment. 
         [0005]    In another arrangement, aerosol LIDAR systems may be used to detect aerosol clouds that may include biological weapon agents. In this case, multiple laser sources are used, operating at different wavelengths, to generate a large set of optical scattering data that is used to develop a “signature” of the aerosol and ascertain its chemical content. However, present technologies, owing to the complexity and laser power levels required for aerosol LIDAR, are limited in range and not well-suited for an in-the-field, portable detection system. 
         [0006]    In these and other environments, therefore, a need remains for a LIDAR system that is relatively compact and portable, yet sufficiently precise for more complex applications. 
       SUMMARY OF THE INVENTION 
       [0007]    The need remaining in the art is addressed by the present invention, which relates to a “LIght Detection And Ranging” (LIDAR) system and, more particularly, to a compact, integrated LIDAR system utilizing SOI-based opto-electronic components to provide for lower cost and higher reliability as compared to current LIDAR systems. 
         [0008]    In one embodiment of the present invention, the various components of both a LIDAR transmitter and a LIDAR receiver (both optical components and electrical components) are integrated within a single module, based upon a silicon-on-insulator (SOI) arrangement. The SOI arrangement comprises a silicon substrate, an insulating layer formed over the substrate (the “buried oxide” layer), and a relatively thin (usually sub-micron in thickness) silicon surface layer (referred to in the art as the “SOI layer”) disposed over the buried oxide layer. The various optical and electrical components are formed utilizing portions of the SOI layer and applying well-known CMOS fabrication processes (e.g., patterning, etching, doping), including the formation of additional layer(s) over the SOI layer to provide the required devices. A laser source itself is attached to the SOI arrangement and coupled through an integrated modulation device (such as a Mach-Zehnder interferometer, i.e., MZI) to provide the scanning laser output signal (the scan controlled by, for example, an electrical (encoder) input to the MZI). The return, reflected optical signal is received by a photodetector integrated within the SOI arrangement, where it is thereafter converted into an electrical signal and subjected to various types of signal processing to perform the desired type(s) of signal characterization/signature analysis. 
         [0009]    In another embodiment of the present invention, the arrangement may be formed as a “multi-chip module”, with the different sub-systems and/or components integrated within separate silicon substrates, with the various silicon substrates mounted on a single, common substrate for optical and electrical interconnection. In one case, all of the transmitting elements may be formed on one “module”, with all of the receiving elements formed on another “module”; the two modules then supported on a common substrate and coupled to the required input and output optical/electrical signals. In another case, all of the electrical components (encoder, transimpedance amplifier and signal processor) may be formed on one substrate, with the active and passive optical devices formed as a separate module. 
         [0010]    A LIDAR transmitter of the present invention may include an optical splitter and/or optical combiner (integral with the SOI substrate) to allow for the creation of a plurality of separate laser output signals, all from a signal input laser source and all formed as a monolithic arrangement on a single SOI substrate. A number of these SOI substrates may be used together, providing multiple laser paths and multiple signal processors, as is required for automatic cruise control (ACC) applications. 
         [0011]    Other and further embodiments and advantages of the LIDAR system of the present invention will become apparent during the course of the following discussion and by reference to the accompanying diagrams. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Referring now to the drawings, 
           [0013]      FIG. 1  is an isometric view of an exemplary LIDAR system integrated within an SOI-based platform in accordance with the present invention; 
           [0014]      FIG. 2  illustrates an exemplary optical transmitting portion of the LIDAR system utilizing a discrete laser source and associated discrete collimating lens; 
           [0015]      FIG. 3  illustrates an alternative transmitting portion, utilizing a discrete laser source and an integrated collimating lens, formed as a portion of the SOI layer; 
           [0016]      FIG. 4  illustrates a portion of an SOI structure formed to include an exemplary Mach-Zehnder interferometer portion of the LIDAR system of the present invention; 
           [0017]      FIG. 5  is a top view of an exemplary integrated arrangement for a LIDAR transmitter formed in accordance with the present invention; 
           [0018]      FIG. 6  illustrates a portion of an exemplary SOI structure  12  utilized to form a portion of the LIDAR receiving arrangement; 
           [0019]      FIG. 7  illustrates an exemplary multi-module SOI-based LIDAR system formed in accordance with the present invention; 
           [0020]      FIG. 8  is an isometric view of an alternative multi-module LIDAR system of the present invention; 
           [0021]      FIG. 9  illustrates an exemplary wide field-of-view embodiment of the present invention; 
           [0022]      FIG. 10  illustrates the entire field of view that may be scanned with an arrangement as shown in  FIG. 9 ; 
           [0023]      FIG. 11  illustrates an alternative embodiment of an exemplary wide field-of-view arrangement that may be formed in accordance with the present invention; and 
           [0024]      FIG. 12  illustrates an exemplary automotive collision avoidance system with an integrated automatic cruise control arrangement utilizing an integrated LIDAR system of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  illustrates, in an isometric view, an exemplary LIDAR system  10  integrated within an SOI-based platform in accordance with the present invention. In this particular embodiment, the various components of LIDAR system  10  are integrated within a single SOI structure  12 . As will be discussed in other examples below, a “multi” module arrangement may also be utilized. Referring to  FIG. 1  in particular, however, SOI structure  12  is illustrated as comprising a silicon substrate  14 , an overlying insulating layer  16  (formed of a dielectric material, such as silicon dioxide and often referred to as the “buried oxide” layer), and a surface silicon layer  18  (hereinafter referred to as the “SOI layer”), where SOI layer  18  is generally of a sub-micron thickness. 
         [0026]    LIDAR system  10  includes a LIDAR transmitter  20  and a LIDAR receiver  30 , as shown in  FIG. 1 . LIDAR transmitter  20  includes a laser source  22 , a focusing lens  24 , an optical modulator  26  (such as, for example, a Mach-Zehnder interferometer), with an encoding/modulating electrical input from an encoder  25 , and an output collimating lens  28  for out-coupling the modulated optical output signal from SOI structure  10  into “free space”, or any other appropriate optical transmission medium. The optical output signal from LIDAR transmitter  20  is directed to a particular object (“target”) that is being analyzed. LIDAR receiver  30  includes a receiving, focusing lens  32  for collecting a sufficient portion of the returned, reflected “free space” optical signal from the target, a photodetector  34  for converting the received optical signal into an electrical representation, a transimpedance amplifier  36  for converting the electrical signal into digital form, and a signal processor  38  (a pre-configured, specialized microprocessor, for example) that is capable of analyzing the digital form of the returned signal and generating the desired return data (i.e., range calculation, speed, characterization of the targeted object, or the like). In some instances, the control signal input C applied to encoder  25  is also applied as an input to signal processor  38  to provide for proper synchronization between channel assignments (i.e., transmitted output signal for “channel 1” will be associated with reflected signal for “channel 1”, the channel assignments controlled by signal C). 
         [0027]    In most cases, laser source  22  will comprise a separate, discrete component that is mounted on top surface  40  of SOI structure  12  (either SOI layer  18 , or another layer formed thereover) and positioned (either through active or passive coupling operations) such that its output signal is directed through collimating lens  24 . Collimating lens  24  may itself be a discrete component, or formed within SOI layer  18 . The former arrangement is illustrated in  FIG. 2 , which illustrates an exemplary discrete laser source  22 -D and associated discrete collimating lens  24 -D. Discrete collimating lens  24 -D is shown as being fixed along a cavity  17  formed through SOI structure  12 , where lens  24 -D is adjustably positioned to couple the maximum amount optical energy into modulator  26 . 
         [0028]    The latter arrangement is illustrated in  FIG. 3 , which is a top view of a portion of LIDAR transmitter  20 , showing the use of discrete laser source  22 -D with a lens created directly within SOI structure  12 . As shown, collimating lens  24 -I is formed as an integral portion of SOI layer  18 . In this case, proper doping and electrical control of free carrier distribution within the selected portion of SOI layer  18  within the region of collimating lens  24 -I will achieve the desired degree of collimation of the output signal from the laser source. 
         [0029]    In similar form, modulator  26  may also be fabricated as an integral component of SOI structure  10 , where  FIG. 4  illustrates a portion of SOI structure  12  that includes an exemplary Mach-Zehnder interferometer  26 -I which comprises waveguiding regions formed within SOI layer  18 , with an overlying guiding structure comprising two separate materials: a thin oxide layer  19 , and a covering layer of polysilicon  21 . A plurality of electrodes  23  are disposed as shown, and coupled to encoder  25 -I, an “integrated” version of encoder  25  (see  FIG. 5 ), to provide the desired electrical input to the modulator structure. Instead of being directly incorporated into SOI structure  12 , modulator  26  may be fabricated on a separate chip, which is thereafter mounted on SOI structure  12  and electrically and optically coupled thereto. 
         [0030]      FIG. 5  is a top view of an exemplary integrated arrangement for LIDAR transmitter  20  of the present invention. As shown, discrete laser component  22 -D is used to provide the optical signal, which is thereafter passed through integral lens component  24 -I. The optical signal from the output of lens  24  is coupled into the input of modulator  26 -I. The electrical (“data”) input signal to modulator  26 -I is provided by encoder  25 -I, which is an electronic component that may be formed within SOI structure  12  utilizing well-known CMOS fabrication processes. The modulated output signal is thereafter collimated by an output integral lens  28 -I and is launched into “free space” (or any suitable optical transmission medium) toward a designated target. 
         [0031]    In similar fashion, the various components comprising LIDAR receiver  30  may be incorporated within SOI structure  12 , thus forming an extremely compact and efficient LIDAR system.  FIG. 6  illustrates a portion of SOI structure  12  utilized to form an exemplary focusing lens  32  and associated photodetector  34 . As with the case for LIDAR transmitter  20 , focusing lens  32  may comprise either a discrete component or, preferably and as shown in  FIG. 6 , an integral component of SOI layer  18 . In the formation of an exemplary (integrated) photodetector  34 , a layer  33  of germanium is disposed over a portion of SOI layer  18  in order to collector a substantial portion of the returned/reflected optical signal. A metal contact arrangement  35  is coupled to germanium layer  33 , where an electrical signal path is then provided from photodetector  34  to transimpedance amplifier  36  (not shown). Various other detector arrangements, including in-line detector arrangements, discrete photodetecting devices, or integrated arrangements utilizing other photosensitive materials, may be used in place of this exemplary germanium detector. 
         [0032]    As mentioned above, the various components forming LIDAR receiver  30  may be formed within the same substrate as that used to form LIDAR transmitter  20 . In an alternative embodiment, a multi-module arrangement may be implemented.  FIG. 7  illustrates an exemplary configuration of one such arrangement, where LIDAR transmitter  20  is formed within a first SOI structure  12 -T and LIDAR receiver  30  is formed within a second SOI structure  12 -R. SOI structures  12 -T and  12 -R are then mounted to a common substrate platform  120 . As shown in this particular embodiment, a separate LIDAR control system  50  is also mounted on substrate platform  120  and is utilized to both generate the input signals supplied to encoder  25  and analyze the return signals generated by signal processor  38 . The various modules may be interconnected using various known techniques well-known in the art, such as flip-chip attachment or direct wirebonding. 
         [0033]      FIG. 8  is an isometric view of an alternative multi-module LIDAR system of the present invention. In this particular embodiment, the input and output optical components (laser source  22 , lenses  24 ,  28  and  32 , modulator  26  and detector  34 ) are all formed within SOI layer  18 , using the arrangements discussed above and particularly illustrated in  FIGS. 5 and 6 . Hidden in this view is the location of various optical components associated with LIDAR transmitter  20 . In this embodiment, the various electronic elements required to complete the system are formed within a separate integrated circuit chip  200 . In particular, circuit chip  200  is formed to include encoder  25 , transimpedance amplifier  36  and signal processor  38 . As shown, circuit chip  200  is mounted (e.g., wirebonded or flip-chip attached) to a conducting substrate  210 , which provides electrical connections between SOI layer  18  of SOI structure  12  and circuit chip  200 . 
         [0034]    As mentioned above, an advantage of the arrangement of the present invention is the ability to integrate the various components onto a single substrate. This integration allows for a multiple number of such systems to be combined and form a multiple output unit that is still relatively compact and portable, yet is capable of covering a wide field of view.  FIG. 9  illustrates an exemplary wide field-of-view embodiment of the present invention that is capable of being integrated within a single SOI structure  12 . As with the arrangements discussed above, LIDAR transmitter  20  includes laser source  22  and associated collimating lens  24  (either discrete or integrated within SOI structure  12 ). In this particular embodiment, the output from lens  24  is passed through an optical processor  21  and applied as an input to a 1:N switch  23 . Optical processor  21  may comprise an electrical encoder (such as encoder  25 ) and an associated optical modulator (such as MZI  26 ), or any other suitable arrangement for applying “in-line” optical encoding to the output from laser source  22 . Indeed, one embodiment may utilize direct modulation of laser source  22  and thus eliminate the need for a separate optical processor element. 
         [0035]    In any of the variations of this embodiment, the encoded optical output signal is then applied as an input to 1:N optical switch  23 . As shown in  FIG. 9 , optical switch  23  is utilized to direct the generated optical signal into one of N available output ports. A plurality of N collimating lenses  28 - 1 ,  28 - 2 , . . . ,  28 -N are incorporated with SOI structure  12  and disposed along the separate waveguiding paths at the output of optical switch  23 . Optical switch  23  may comprise any well-known arrangement capable of providing optical switching (one arrangement comprises a plurality of cascaded interferometer elements), where by energizing the switches in sequence the appearance of the optical output signal may be switched among the various output ports. In one embodiment, a time division switching scheme may be employed so that the beam “sweeps” through the entire field of view in a controlled, sequential fashion. In such an arrangement, the control signal used to control the switching of the optical signal is also applied as an input to LIDAR receiver  30  so as to maintain a correlation between the individual transmitted beams and the individual reflected signals.  FIG. 10  illustrates the entire field of view that may be scanned with an arrangement as shown in  FIG. 9 . 
         [0036]      FIG. 11  illustrates an alternative embodiment of an exemplary wide field-of-view arrangement that may be formed in accordance with the present invention. In this case, LIDAR transmitter  20  includes a pair of laser sources, designated as  22 -P (“primary”) and  22 -B (“back-up”), where laser  22 -B is energized only upon failure of primary source  22 -P. Similar to the arrangements described above, each laser source  22  has an associated collimating lens  24  (either discrete or integrated within SOI structure  12 ). In this particular embodiment, the outputs from lenses  24 -P and  24 -B are applied as an input to a 1:N splitter  27 , where the single input optical signal is divided into a plurality of N separate signals, each applied as an input to a separate optical processor  21 , arranged as shown in  FIG. 11 . Each separate optical processor is utilized to “steer” the beam in a pre-defined direction, where by switching through the plurality of output beams, the arrangement as shown is capable of “sweeping” across a relatively wide field of view without requiring physical switching of a single beam, as is utilized in the embodiment of  FIG. 9 . Although not illustrated in particular, it is to be understood that a plurality of optical signals operating at different wavelengths may be utilized and associated with the plurality of separate beams, providing a wavelength diversity arrangement. 
         [0037]      FIG. 12  illustrates an exemplary automotive collision avoidance system with an integrated automatic cruise control arrangement utilizing an integrated LIDAR system of the present invention as described above. In this case, a plurality of separate LIDAR systems  10 - 1 , . . . ,  10 -N are utilized and positioned at various separate locations on a car. Inasmuch as the systems  10  are relatively small as a result of the integration advantages of the present invention, they do not require large spaces, or draw significant power from the car&#39;s battery. Each separate LIDAR system  10  constantly performs scanning operations, feeding the return information from signal processors  36  to a central processor  100  within the car. By comparing the returning data, along with input data from other sources, such as a radar system  105 , central processor  100  can perform a variety of functions, such as warning a driver about an impending collision through a human/machine interface  110 . When necessary, the information supplied to central processor  100  may be transmitted to a cruise controller module  120  to automatically disengage the cruise control process. Various other options are available and are considered to fall within the scope of the present invention. 
         [0038]    It is to be understood that the above-described arrangements are merely illustrative of the many possible specific embodiments which can be devices to represent application of the principles of the invention. Numerous and varied other arrangements can be devised in accordance with these principles by those skilled in the art without departing from the spirit and scope of the invention.