Patent Description:
LIDAR systems have been developed over the past few decades as a solution to range detection problems that could not be adequately addressed with traditional radio wave detection methods. Light detection systems employ various techniques for transmitting and receiving the reflected light and making a range calculation based on the difference between the transmitted and received light introduced by time of flight ("ToF") of the light and various techniques, such as measurement of doppler-shift, for determining velocity.

The emergence of high performance applications, such as autonomous vehicles, unmanned aerial systems, etc. have increased the demand for range detection systems, i.e., sensors. The capabilities of these new and traditional applications will be based at least in part on the performance of the various sensor systems providing data for the applications. As such, there is a growing demand for high performance range detection and other sensor systems that support the continued improvement in high performance applications.

<CIT> discloses a LIDAR system for determining the distance to a a target object. The system comprises a controller that generates a first reference signal; a transmitter including a laser that generates a base signal which is used as an optical carrier which is amplitude modulated by the first reference signal to create an output signal containing a chirp that is transmitted towards the target object which reflects a portion of the output signal back to the LIDAR system for processing by a receiver. The base signal is also used as an optical local oscillator signal for the receiver. The receiver processes the received signal with the optical local oscillator signal to generate an RF envelope. The RF envelope is then processed with a second reference signal to determine a difference frequency between the RF envelope and the second reference signal. The range is a function of the difference frequency caused by the propagation delay of the reflected light compared with the frequency change over that time caused by the chirp, for example, by using a frequency/range equation.

<CIT> discloses a LiDAR system with a signal generator that generates an output signal having a variable frequency. A modulation circuit receives the output signal from the signal generator and applies the output signal from the signal generator to an optical signal to generate an envelope-modulated optical signal having a frequency-modulated (FM) modulation envelope. An optical transmitter transmits the envelope-modulated optical signal into a region occupied by a target object. An optical receiver receives back a component of the optical signals that is reflected back from the target object. A signal processor uses quadrature detection to process the reflected optical signal and determine the range to the target object.

<CIT> discloses a LIDAR system with a transmitter laser whose output is intensity modulated with a chirp having a time-varying frequency, thereby applying a frequency modulation (FM). The output signal is used both for transmission to a target object and as an optical local oscillator signal for the receiver. The receiver uses an optical homodyne detection scheme and performs de-chirping with a photodetector.

The frequency difference between the chirp in the optical local oscillator signal and the chirp in the optical signal reflected from the target object is determined, this frequency difference being a measure of the transit time taken for the optical signal to travel to the target object and back. A signal processor determines the transit time, and hence the target distance, based on this frequency difference.

The present invention addresses the above noted needs by providing a system and method according to the claims that enable high performance range detection, optical time-domain reflectometry ("OTDR"), and other applications. The system may include homodyne and heterodyne detection receivers in combination with directly and externally modulated optical sources and bidirectional/ shared components that overcome the challenges of the prior art solutions to enable more compact and lower cost systems to be deployed in various applications.

The electrical reference signal may include analog and/or digital reference signals with or without reference identifiers as may be suitable for the response times and levels of precision desired. The optical-electrical converters are implemented with a bandwidth that accounts for the bandwidth of the reference signal and modulated light including variations including frequency chirp, and optionally also burst-mode spectral excursion, temperature, aging, etc. The local oscillator is not controlled, but rather merely selected, to enable efficient reception of reflected optical signal relative to the bandwidth of the receiver.

Accordingly, the present disclosure addresses the continuing need for range detection and object characterization systems and receivers with improved cost and performance.

The accompanying drawings are included for the purpose of exemplary illustration of various aspects of the present invention, and not for purposes of limiting the invention, wherein:.

<FIG> show exemplary systems embodiments and exemplary measurements.

In the drawings and detailed description, the same or similar reference numbers may identify the same or similar elements. It will be appreciated that the implementations, features, etc. described with respect to embodiments in specific figures may be implemented with respect to other embodiments in other figures, unless expressly stated, or otherwise not possible.

Systems <NUM> of the present invention may be employed in various configurations to detect target objects and determine various characteristics of the target objects relative to the system <NUM>. The system <NUM> may be a stand-alone fixed or mobile unit or associated with a host object that may be a stationary object, e.g., a pole, or a moving object, e.g., water, land, or air craft. The target objects being detected, measured, etc. may be very large, e.g., vehicles, or very small, e.g., particles, depending upon the particular application of the system <NUM>.

<FIG> illustrates system <NUM> of the present invention, which includes one or more optical transmitters (OTx) <NUM> to transmit output optical signals carrying a reference signal through a medium <NUM> and one or more optical receivers (ORx) <NUM> to receive input optical signals that include at least some of the output optical signals that have been reflected off a target object <NUM> back through the medium <NUM> to the optical receivers <NUM>. One of ordinary skill will appreciate that the medium <NUM> in many measurement and detection applications of the system <NUM> will be free space, i.e., non-waveguide, but may include a wide range of materials, e.g., air (gases), water (liquids), glass (solids), vacuums, etc., in various combinations depending upon the application and the light frequency(ies) used in the system <NUM>.

Since the optical transmitters <NUM> and optical receivers <NUM> generally may be co-located and, in some embodiments, part of the same unit, the transmitter <NUM> and receiver <NUM> may share components, such as lenses, combiners, splitters, signal generators, etc., as described herein and shown in the drawings. As noted below, it will be appreciated that while discrete components may be depicted in the drawings to facilitate explanation, the various components may be implemented and integrated in various combinations employing fiber, non-fiber waveguides, free-space, and photonic integrated circuit ("PIC") components and transmission media.

As shown in <FIG>, the system <NUM> includes an electrical reference signal generator <NUM>, which may be analog, such as a modulated radio frequency (RF) carrier from a RF source, or digital, such as a digital signal processor, to provide a reference signal or one or more electrical inputs configured to receive the reference signal from an external electrical signal generator. The reference signal may be split, or duplicated, inside or outside the system, such as via an electrical splitter into a transmit portion and a receive portion. The transmit portion may be used to directly modulate an optical source <NUM> in the optical transmitter <NUM> and/or externally modulate light output at a transmit frequency/ wavelength from the optical source <NUM> to produce modulated light. The modulated light is output from one or more optical output ports of the optical transmitter <NUM>, or transmit section of the system <NUM>, as an output optical signal.

The optical source <NUM> may include various types of lasers, such as a DFB, VCSEL, DBR, ECL or other type of laser, depending upon the particular performance and cost characteristics desired by the skilled artisan. The present invention generally enables the use of commercial off the shelf lasers for many applications, thereby enabling a low cost, robust platform. In other applications, it may be desirable to use an external modulator to impart the reference signal onto the output optical signal and/or to use one or more custom optical sources. For example, one or more lasers may be used as the optical source <NUM> in the optical transmitter <NUM> and as the local oscillator ("LO") <NUM> in the optical receiver <NUM>.

In various embodiments, one or more couplers <NUM> may be provided to couple the output optical signal from the optical transmitter <NUM> via one or more lenses <NUM> to the medium <NUM>. The lenses <NUM> may be a discrete lens and/or a lens fiber or other waveguide. The coupler <NUM> may also be used to split the output optical signal into multiple signals as further described below. As further described, the coupler <NUM> may be used bi-directionally as part of the optical receiver <NUM>.

The optical receiver <NUM> receives light from the medium <NUM> through one or more optical input ports which may include one or more lenses <NUM>, which may or may not be shared with the optical transmitter <NUM> for the output optical signal. The received light may include reflections of the output optical signal ("reflected optical signals") from the target object <NUM> and may likely also include other light present in the medium <NUM> and possibly reflections from objects other than the target object <NUM> that may represent noise in the input optical signal.

The optical receiver <NUM>, or receive section of the system <NUM>, includes:.

The reference signal may include analog and/or digital reference signals with or without reference identifiers, as may be suitable for response times and levels of precision desired by the skilled artisan. In various embodiments, transmit portion of the reference signal from the received reflection of the output signal is compared to the receive portion of the reference signal provided directly to the receiver to determine the time of flight of the reflected output optical signal and the distance of the target object <NUM> from the system <NUM>. The relative intensity of the transmitted and received optical signals at an instance and/or over time may be used to perform various calculations.

Multiple comparisons over time may be used to calculate the relative quantity, movement, speed/velocity of the object including the system <NUM> and the target object <NUM>, which may also be used in combination with other speed, or velocity, measurements of the host object including the system <NUM>. In various embodiments, the reference signal imparted to the output optical signal may include a time stamp or other markers that may be used in the optical receiver <NUM> to calculate the time of flight of the reflected output optical signal and the distance of the target object <NUM> from the system <NUM>. One or more of the above or other comparisons may be employed by the skilled artisan to perform detection, distance, and other calculations based on the time of flight and/or intensity of the reflections. In addition, the reference signal may be used to reduce the impact of noise in the input optical signal.

The optical-electrical converters <NUM> are implemented with a bandwidth sufficient to convert a wide range of bandwidths used for the reference signal and the modulated light and are selected to account for variations resulting from frequency chirp, and optionally also burst-mode spectral excursion, temperature, aging, etc., e.g., commercial off the shelf photodiodes and rectifiers may have a bandwidth of up to <NUM> or more. The local oscillator <NUM> is not controlled, but rather merely selected (i.e., not controlled), to enable efficient reception of reflected optical signal relative to the bandwidth of the converters <NUM>.

<FIG> embodiments may employ an electrically generated frequency-modulated continuous wave (EFMCW) generator to generate the reference signal as a sine-wave signal with a swept frequency (i.e., the amplitude of the sinusoidal modulation is kept constant/continuous and the frequency is swept/modulated). The frequency of the reference signal may be swept linearly up and down in a range within the bandwidth of the detection system. A modulation index of less than <NUM> may be used to allow for laser chirp to remain inside the receiver bandwidth. However, a higher amount of chirp may be tolerated compared to other coherent methods. The signal processing may utilize electrically homodyne or heterodyne detection. The reflected and recovered signal is then compared to the reference signal used to generate the transmit signal.

<FIG> embodiments are similar to the embodiments of <FIG> with the optical transmitter <NUM> including an optical source driver <NUM> to apply the reference signal to the optical source <NUM>. In the receiver <NUM>, the signal processor <NUM> may include an analog to digital ("A/D") converter <NUM> to convert the detection signal from an analog to a digital detection signal and a digital signal processor <NUM> to process the digital detection signal.

In these embodiments, an optical frequency-modulated continuous wave (OFMCW) optical signal may be created by control of the bias current of a directly modulated laser. The laser may be calibrated to obtain a linear frequency sweep up and down through control of the chirp versus bias. An alternative is to use an external modulator to create the sweep, or to use a temperature controller to modulate the temperature of the laser in order to introduce the desired frequency modulation.

<FIG> embodiments illustrate the use of an electrical splitter <NUM> to split the rectified detection signal into two rectified electrical signals, which may be mixed with the reference signal via two electrical mixers <NUM> and provided to a phase detector <NUM>.

<FIG> embodiments illustrate the coupling of a portion of the output optical signal with the reflected input optical signal and the local oscillator light and employing a high pass filter <NUM> to provide the detection signal. In these embodiments, light from the local oscillator <NUM>, reflected light, and transmission (fractional) light are all combine through one or more combiners <NUM> in the optical- electrical converter <NUM>. An offset in frequency of the local oscillator <NUM> from the average transmit frequency to approximately in the middle of the electrical frequency band (channel) may be used to create, by the optical-electrical converter <NUM>, the linear amplifier and high pass filter, a current I proportional to Elo * (Et + Er ), where Elo , Et , & Er denotes the electrical field of the local oscillator, transmitted light, and reflected light, respectively. This term is squared and rectified in the envelope detector/ rectifier <NUM>, creating a term Elo <NUM> * Et * Er , from which a signal containing a frequency change may be found after low-pass filtering and used to calculate the distance traveled by and / or velocity of the reflected optical signal relative to the reference signal. The high-pass filter <NUM> may be used to filter out the mixing signal of Et * Er , which may be small, from the output of the optical-electrical converter <NUM>.

The local oscillators <NUM> may generally include one or more fixed or tunable optical sources, such as lasers of various linewidths, to provide local oscillator light at one or more local oscillator frequencies, which may be offset from the frequency of the optical signal, i.e., the local oscillator frequency offset. The optical local oscillator laser <NUM> emits light at an optical frequency (Flo) which is offset from the signal center frequency (Fc) by frequency-offset, or frequency difference, (dF). As described above, the local oscillator(s) <NUM> may include one or more lasers, such as a VCSEL, DFB, DBR, ECL or other type of laser. The local oscillator <NUM> may be tuned to a frequency or a wavelength of the signal. This can either be an in-band or an out-of-band configuration. In an in-band configuration, the local oscillator <NUM> is tuned to a frequency or wavelength within a spectrum of the signal. In an out-of-band configuration, the local oscillator <NUM> is tuned to a frequency or wavelength outside a spectrum of the signal. In this way, wavelength selectivity may be achieved using the local oscillator <NUM>. Using the local oscillator <NUM> as a wavelength selector enables the system to operate with or without optical filters.

It will be appreciated that while the optical receiver embodiments described relative to <FIG> depict using the reception of the input optical signal, which includes the reflected output optical signal, with one optical-electrical converter <NUM>, the optical receiver <NUM> may include various embodiments involving multiple optical-electrical converters <NUM>. For example, <CIT>, published as <CIT>, describes various optical receiver embodiments including polarization diversity receivers that may be employed in the present invention. Other configurations utilizing multiple optical-electrical converters for further improvement of receiver sensitivity may include balanced receivers.

The foregoing disclosure provides examples, illustrations and descriptions of the present invention, but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. These and other variations and modifications of the present invention are possible and contemplated, and it is intended that the foregoing specification and the following claims cover such modifications and variations.

As used herein, the term component is intended to be broadly construed as hardware, firmware, and/or a combination of hardware and software. Thus, the operation and behavior of the systems and/or methods were described herein without reference to specific software code- it being understood that software and hardware can be designed to implement the systems and/or methods based on the description herein.

Various elements of the system may employ various levels of photonic, electrical, and mechanical integration. Multiple functions may be integrated on one or more modules or units in the system <NUM>.

Hardware processor modules may range, for example, from general- purpose processors and CPUs to field programmable gate arrays (FPGAs) to application specific integrated circuit (ASICs). Software modules (executed on hardware) may be expressed in a variety of software languages (e.g., , computer code), including C, C++, Java™, Javascript, Rust, Go, Scala, Ruby, Visual Basic™, FORTRAN, Haskell, Erlang, and/ or other object-oriented, procedural, or other programming language and development tools. Computer code may include micro-code or micro-instructions, machine instructions, such as produced by a compiler, code used to produce a web service, and files containing higher-level instructions that are executed by a computer using an interpreter and employ control signals, encrypted code, and compressed code.

Software may employ various input and output interfaces that may include one or more application programming interfaces and user interfaces to provide for data input and output. A user interface may include a graphical user interface, a non-graphical user interface, a text-based user interface, etc. A user interface may provide information for display. In some implementations, a user may interact with the information, such as by providing input via an input component of a device that provides the user interface for display. In some implementations, a user interface may be configurable by a device and/or a user (e.g., a user may change the size of the user interface, information provided via the user interface, a position of information provided via the user interface, etc.). Additionally, or alternatively, a user interface may be pre-configured to a standard configuration, a specific configuration based on a type of device on which the user interface is displayed, and/or a set of configurations based on capabilities and/or specifications associated with a device on which the user interface is displayed.

Claim 1:
A system (<NUM>) for determining distance to a target object (<NUM>), the system (<NUM>) comprising
an optical transmitter (<NUM>) having a laser (<NUM>) to transmit an optical signal;
an optical receiver (<NUM>) to receive back a reflection of the optical signal from a target object (<NUM>);
an electrical signal generator (<NUM>) to provide an electrical reference signal to both the optical transmitter and the optical receiver; and
a laser driver (<NUM>) to directly modulate the laser with the electrical reference signal, the optical receiver (<NUM>) including
a local oscillator (<NUM>) providing local oscillator light at a local oscillator frequency,
a combiner (<NUM>) to combine the reflection of the optical signal received by the receiver (<NUM>) with the local oscillator light to output a coupled optical signal,
an optical-electrical converter (<NUM>) to convert the coupled optical signal into a first electrical signal,
a rectifier (<NUM>) to rectify the first electrical signal and thereby provide a first rectified electrical signal, and
a signal processor (<NUM>) to receive the first rectified electrical signal from the rectifier and the electrical reference signal from the electrical signal generator (<NUM>), and to calculate a distance traveled by the optical signal based on the first rectified electrical signal and the electrical reference signal,
characterized in that
the optical-electrical converter is implemented with a bandwidth that accounts for the bandwidth of the reference signal and of the optical signal, including variations resulting from frequency chirp, and in that
the local oscillator frequency is merely selected and not controlled and acts as a wavelength selector relative to the bandwidth of the opto-electrical converter through selection of the local oscillator frequency to enable efficient reception of the reflected optical signal.