Patent ID: 12196889

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and some embodiments of the invention, examples of which are illustrated in the accompanying drawings.

Methods and systems for combining return signals from multiple channels of a LIDAR measurement system onto the input of a single channel of an analog to digital converter are described herein.

FIG.1depicts a multiple channel LIDAR measurement system120in one embodiment. LIDAR measurement system120includes a master controller190and N LIDAR measurement channels125A-N, where N is any positive, integer number. Each channel of LIDAR measurement system120includes a transmit channel (e.g., transmit channels160A-N) and a corresponding receive channel (e.g., receive channels130A-N).

As depicted inFIG.1, each LIDAR transmit channel160A-N includes an illumination source163A-N. An illumination driver of each transmit channel160A-N causes each corresponding illumination source163A-N to emit a measurement pulse of illumination light164A-N in response to a pulse trigger signal151A-N received from corresponding receive channel130A-N. Each measurement pulse of illumination light164A-N passes through mirror element121A-N and illuminates a volume of the surrounding environment. Each amount of return light136A-N reflected from object(s) at each illuminated location in the surrounding environment is incident on corresponding mirror elements121A-N. An overmold lens131A-N is mounted over each photodetector132A-N, respectively. Each overmold lens131A-N includes a conical cavity that corresponds with the ray acceptance cone of return light136A-N, respectively. Return light136A-N is reflected from mirrors121A-N to corresponding photodetectors132A-N, respectively.

As depicted inFIG.1, illumination light164A-N emitted from each channel of LIDAR measurement system120and corresponding return measurement light136A-N directed toward LIDAR measurement system120share a common optical path.

As depicted inFIG.1, each illumination source163A-N is located outside the field of view of each photodetector. Illumination light164A-N from illumination sources163A-N is injected into the corresponding detector reception cone through an opening in mirrors121A-N, respectively.

In some embodiments, each illumination source163A-N is laser based (e.g., laser diode). In some embodiments, each illumination source is based on one or more light emitting diodes. In general, any suitable pulsed illumination source may be contemplated.

Master controller144is configured to generate pulse command signals122A-N communicated to receive channels130A-N, respectively. In these embodiments, master controller144communicates a pulse command signal to each different LIDAR measurement channel. In this manner, master controller144coordinates the timing of LIDAR measurements performed by any number of LIDAR measurement channels. Each pulse command signal is a digital signal generated by master controller144. Thus, the timing of each pulse command signal is determined by a clock associated with master controller144.

In some embodiments, each pulse command signal122A-N is directly used to trigger pulse generation by transmit channels160A-N and data acquisition by each corresponding receive channels130A-N, respectively. However, transmit channels160A-N and receive channels130A-N do not share the same clock as master controller144. For this reason, precise estimation of time of flight becomes much more computationally tedious when a pulse command signal is directly used to trigger pulse generation and data acquisition.

In some other embodiments, each receive channel130A-N receives a pulse command signal122A-N and generates corresponding pulse trigger signals151A-N, in response to pulse command signals122A-N, respectively. Each pulse trigger signal151A-N is communicated to transmit channel160A-N and directly triggers an illumination driver associated with each transmit channel to generate a corresponding pulse of illumination light164A-N. In addition, each pulse trigger signal151A-N directly triggers data acquisition of return signals136A-N and associated time of flight calculations. In this manner, pulse trigger signals151A-N generated based on the internal clock of return signal receivers of each receive channel130A-N, respectively, are employed to trigger both pulse generation and return pulse data acquisition for a particular LIDAR measurement channel. This ensures precise synchronization of pulse generation and return pulse acquisition which enables precise time of flight calculations by time-to-digital conversion.

In one aspect, the outputs of each receive channel130A-N are electrically coupled (e.g., at voltage node140). In this manner, the outputs of receive channels130A-N are effectively summed at the input of the analog to digital converter143.

FIG.2depicts a more detailed view of the receive channels of LIDAR measurement system120in one embodiment. Like numbered elements described with respect toFIG.1are analogous to those illustrated inFIG.2, and vice-versa. As depicted inFIG.2, LIDAR measurement system120includes a number of analog receive channels130A-N, an analog to digital converter (ADC)143, and a master controller144.

As depicted inFIG.2, each analog receive channel130A-N includes a photodetector (e.g., an avalanche photodiode132A-N, or other photosensitive device) and a trans-impedance amplifier (TIA)133A-N. In addition, each analog receive channel includes one or more secondary amplifier stages134A-N. However, in general, secondary amplifier stages134A-N are optional.

In the embodiment depicted inFIG.2, incoming light136A is detected by APD132A. In response to an incoming return pulse of light136A, APD132A generates a current signal137A. TIA133A receives current signal137A and generates a voltage signal present at voltage node138A. In the embodiment depicted inFIG.2, TIA133A generates a single ended voltage output. However, in some other embodiments, TIA133A generates a differential voltage output. Amplifier134A amplifies the voltage signal at node138A and generates an output signal139A. In some embodiments the output of amplifier134A is a current signal. However, in some other embodiments, the output of amplifier134A is a voltage signal. As depicted inFIG.2, output signal139A is the output of receive channel130A generated in response to detected return pulse of light136A. Similarly, each receive channel130A-N generates an output signal139A-N indicative of the detected return pulse of light136A-N detected at each receive channel130A-N, respectively.

As depicted inFIG.2, the outputs of each receive channel130A-N are electrically coupled at voltage node140. In this manner, the outputs of receive channels130A-N are effectively summed. Combined output signal152is an analog signal indicative of the output of each receive channel130A-N in the same sequence as the sequence of laser pulse emission associated with each receive channel130A-N.

The summed signals are subsequently provided as input to a single channel of an analog to digital converter143, either directly, or after further processing (e.g., amplification by amplifier142). In the embodiment depicted inFIG.2, the summed output signal152is amplified by amplifier142. Amplified signal146is converted to a digital signal147by ADC143. Digital signal147is received by master controller144.

Alternatively, in the absence of amplifier142, the outputs of receive channels130A-N are effectively summed at the input of ADC143(e.g., as depicted inFIG.1). In general, amplifier142is optional.

In a further aspect, the electrical elements in each electrical path from a photodetector (e.g., APD132A-N) to ADC143are direct current (DC) coupled to one another. In other words, for each receive channel130A-N, there are no explicitly formed energy storage elements that act as DC signal blocking elements (e.g., capacitors, etc.) between any of APD132A-N, TIA133A-N, amplifier134A-N, amplifier142, and ADC143; only electrical conductors. In the embodiment depicted inFIG.2, each APD132A-N is DC coupled to a corresponding TIA133A-N. Each TIA133A-N is DC coupled to a corresponding amplifier134A-N. Each amplifier134A-N is DC coupled to amplifier142. Amplifier142is DC coupled to ADC143.

In another aspect, a DC offset voltage is provided at the output of the TIA associated with each receive channel.

In the embodiment depicted inFIG.2, master controller144communicates a command signal145to local controller190. Command signal145is indicative of a desired DC voltage offset at the output of each TIA of receive channels130A-N. Local controller190, in turn, communicates DC offset voltage signals148A-N to voltage nodes138A-N (via digital to analog converter191) at the outputs of TIA133A-N, respectively. In some embodiments, master controller144and local controller190are separate devices. However, in some other embodiments, a single device is employed to generate and communicate DC offset voltage signals to the output of each TIA. In some embodiments, master controller144is a field programmable gate array (FPGA) device and local controller190is a complex programmable logic device (CPLD). However, in general, any suitable computing device may be employed.

In some embodiments, master controller144generates command signal145based on the quality of measured signal147. In some examples, command signal145is generated to maximize the signal to noise ratio of the digital signals147generated by ADC143. In some examples, command signal145is generated to offset DC noise signals present in the operating environment of the LIDAR device. By offsetting DC noise, the full scale of ADC143is available for dynamic measurement. This increases signal to noise ratio.

In another aspect, the temperature associated with one or more receive channels is measured. In a further aspect, the measured temperature is employed to adjust a bias voltage supplied to each APD.

In the embodiment depicted inFIG.2, a temperature sensor module is located in close proximity to one or more elements of receive channels130A-N (i.e., elements of a receive subsystem including receive channels130A-N). In one example, temperature sensor module150is located within 40 millimeters of a receive channel (e.g., any of receive channels130A-N). However, in general, a temperature sensor may be located at any suitable distance from one or more receive channels. Temperature sensor module150measures temperature where module150is located and communicates a digital signal151indicative of the measured temperature to master controller144(e.g., over a serial peripheral interface). In response to the measured temperature, master controller communicates a command signal176to local controller190. Command signal176is indicative of a desired bias voltage provided to each APD of receive channels130A-N. Local controller190, in turn, communicates bias voltage command signals177A-N to APD bias power supplies131A-D, respectively (via digital to analog converter191). Each APD bias power supply131A-N adjusts a bias voltage signal135A-N provided to each APD132A-N, respectively.

In some embodiments, master controller144and local controller190are separate devices. However, in some other embodiments, a single device is employed to generate and communicate bias voltage signals to each APD bias power supply.

Master controller144generates command signal176based on the measured temperature associated with one or more receive channels. Command signal176is generated to save power and improve measurement consistency.

In another aspect, the temperature associated with one or more transmit channels is measured. In a further aspect, the measured temperature is employed to adjust a bias voltage supplied to each illumination source.

FIG.3depicts a more detailed view of the transmit channels of LIDAR measurement system120in one embodiment. Like numbered elements described with respect toFIG.1are analogous to those illustrated inFIG.3, and vice-versa.FIG.3depicts a set of N transmit channels160A-N (where N can be any positive integer number). Each transmit channel includes a power supply161A-N and an illumination source163A-N (e.g., a laser diode). Each illumination source163A-N emits a pulse of light164A-N. Light reflected from the surrounding environment is detected by a corresponding receiver channel (e.g., receiver channels130A-N depicted inFIG.2). The time of flight associated each pulse of light determines the distance between the LIDAR device and the detected object in the surrounding environment.

As depicted inFIG.3, a temperature sensor module165is located in close proximity to one or more elements of transmit channels160A-N (i.e., elements of a transmit subsystem including transmit channels160A-N). In one example, temperature sensor module165is located within 40 millimeters of a transmit channel160A-N. However, in general, a temperature sensor may be located at any suitable distance from one or more transmit channels. Temperature sensor module165measures temperature where module165is located and communicates a digital signal166indicative of the measured temperature to master controller144(e.g., over a serial peripheral interface). In response to the measured temperature, master controller144communicates a command signal167to local controller168. Command signal167is indicative of a desired bias voltage provided to each laser diode of transmit channels160A-N. Local controller168, in turn, communicates bias voltage command signals149A-N to power supply161A-D, respectively (via digital to analog converter169). Each power supply161A-N adjusts a bias voltage signal162A-N provided to each laser diode163A-N, respectively.

In some embodiments, master controller144and local controller168are separate devices. However, in some other embodiments, a single device is employed to generate and communicate bias voltage signals to each bias power supply.

In some embodiments, master controller144generates command signal167based on the measured temperature associated with one or more transmit channels and also the level of signal detected at each corresponding receive channel (e.g., signals139A-N).

In a further aspect, a multiplexer is disposed between multiple sets of receive channels and ADC143to enhance measurement throughput.

FIG.4depicts two sets of multiple receive channels of a multiple channel LIDAR measurement system in another embodiment. Like numbered elements described with respect toFIG.1are analogous to those illustrated inFIG.4, and vice-versa.FIG.4depicts receive channels130A-N and an additional set of receive channels170A-N. The outputs of receive channels130A-N are electrically coupled at voltage node140as described hereinbefore. Similarly, the outputs of receive channels170A-N are electrically coupled at voltage node171. In the embodiment depicted inFIG.4, a two channel multiplexer141receives the summed output signals140and171and generates multiplexed output145. Multiplexed output145is amplified by amplifier142. Amplified signal146is converted to a digital signal147by a single channel of ADC143. Digital signal147is received by master controller144. In this manner, the outputs of 2N receive channels are combined onto a single ADC channel.

In one embodiment, each receive channel is fabricated onto a single printed circuit board. A group of N boards are electrically coupled to another printed circuit board that includes multiplexer141, amplifier142, local controller190, DAC191, and temperature sensor module150. ADC143and master controller144are assembled on yet another printed circuit board. Similarly, each transmit channel is fabricated onto a single printed circuit board. A group of N boards are electrically coupled to another printed circuit board that includes temperature sensor module165, local controller168, and DAC169.

In some embodiments, illumination drivers, illumination sources163A-N, photodetectors132A-N, and return signal receivers are mounted, either directly or indirectly, to a common substrate (e.g., printed circuit board) that provides mechanical support and electrical connectivity among the elements.

In general, any of the power supplies described herein may be mounted to a separate substrate and electrically coupled to the various electronic elements in any suitable manner. Alternatively, any of the power supplies described herein may be integrated with other electronic elements in any suitable manner.

The power supplies described herein may be configured to supply electrical power specified as voltage or current. Hence, any electrical power source described herein as a voltage source or a current source may be contemplated as an equivalent current source or voltage source, respectively.

FIG.5depicts an illustration of the timing associated with the emission of a measurement pulse from an LIDAR measurement device and capture of the returning measurement pulse. As depicted inFIG.5, a measurement is initiated by the rising edge of pulse trigger signal122A generated, for example, by master controller144. A measurement window (i.e., a period of time over which collected return signal data is associated with a particular measurement pulse) is initiated by enabling data acquisition at the rising edge of pulse trigger signal122A. The duration of the measurement window, Tmeasurement, corresponds to the window of time when a return signal is expected in response to the emission of a measurement pulse sequence. In some examples, the measurement window is enabled at the rising edge of pulse trigger signal122A and is disabled at a time corresponding to the time of flight of light over a distance that is approximately twice the range of the LIDAR system. In this manner, the measurement window is open to collect return light from objects adjacent to the LIDAR system (i.e., negligible time of flight) to objects that are located at the maximum range of the LIDAR system. In this manner, all other light that cannot possibly contribute to useful return signal is rejected.

As depicted inFIG.5, return signal147includes three return measurement pulses147A-C that correspond with the emitted measurement pulse. Any of these instances may be reported as potentially valid distance measurements by the LIDAR system.

In another aspect, a master controller is configured to generate a plurality of pulse command signals, each communicated to different LIDAR measurement channels.

FIGS.6-8depict 3-D LIDAR systems that include multiple LIDAR measurement channels. In some embodiments, a delay time is set between the firing of each LIDAR measurement channel. In some examples, the delay time is greater than the time of flight of the measurement pulse sequence to and from an object located at the maximum range of the LIDAR device. In this manner, there is no cross-talk among any of the LIDAR measurement channels. In some other examples, a measurement pulse is emitted from one LIDAR measurement channel before a measurement pulse emitted from another LIDAR measurement channel has had time to return to the LIDAR device. In these embodiments, care is taken to ensure that there is sufficient spatial separation between the areas of the surrounding environment interrogated by each beam to avoid cross-talk.

FIG.6is a diagram illustrative of an embodiment of a 3-D LIDAR system100in one exemplary operational scenario. 3-D LIDAR system100includes a lower housing101and an upper housing102that includes a domed shell element103constructed from a material that is transparent to infrared light (e.g., light having a wavelength within the spectral range of 700 to 1,700 nanometers). In one example, domed shell element103is transparent to light having a wavelengths centered at 905 nanometers.

As depicted inFIG.6, a plurality of beams of light105are emitted from 3-D LIDAR system100through domed shell element103over an angular range, α, measured from a central axis104. In the embodiment depicted inFIG.5, each beam of light is projected onto a plane defined by the x and y axes at a plurality of different locations spaced apart from one another. For example, beam106is projected onto the xy plane at location107.

In the embodiment depicted inFIG.6, 3-D LIDAR system100is configured to scan each of the plurality of beams of light105about central axis104. Each beam of light projected onto the xy plane traces a circular pattern centered about the intersection point of the central axis104and the xy plane. For example, over time, beam106projected onto the xy plane traces out a circular trajectory108centered about central axis104.

FIG.7is a diagram illustrative of another embodiment of a 3-D LIDAR system10in one exemplary operational scenario. 3-D LIDAR system10includes a lower housing11and an upper housing12that includes a cylindrical shell element13constructed from a material that is transparent to infrared light (e.g., light having a wavelength within the spectral range of 700 to 1,700 nanometers). In one example, cylindrical shell element13is transparent to light having a wavelengths centered at 905 nanometers.

As depicted inFIG.8, a plurality of beams of light15are emitted from 3-D LIDAR system10through cylindrical shell element13over an angular range, β. In the embodiment depicted inFIG.8, the chief ray of each beam of light is illustrated. Each beam of light is projected outward into the surrounding environment in a plurality of different directions. For example, beam16is projected onto location17in the surrounding environment. In some embodiments, each beam of light emitted from system10diverges slightly. In one example, a beam of light emitted from system10illuminates a spot size of 20 centimeters in diameter at a distance of 100 meters from system10. In this manner, each beam of illumination light is a cone of illumination light emitted from system10.

In the embodiment depicted inFIG.7, 3-D LIDAR system10is configured to scan each of the plurality of beams of light15about central axis14. For purposes of illustration, beams of light15are illustrated in one angular orientation relative to a non-rotating coordinate frame of 3-D LIDAR system10and beams of light15′ are illustrated in another angular orientation relative to the non-rotating coordinate frame. As the beams of light15rotate about central axis14, each beam of light projected into the surrounding environment (e.g., each cone of illumination light associated with each beam) illuminates a volume of the environment corresponding the cone shaped illumination beam as it is swept around central axis14.

FIG.8depicts an exploded view of 3-D LIDAR system100in one exemplary embodiment. 3-D LIDAR system100further includes a light emission/collection engine112that rotates about central axis104. As depicted inFIG.8, a central optical axis117of light emission/collection engine112is tilted at an angle, θ, with respect to central axis104. 3-D LIDAR system100includes a stationary electronics board110mounted in a fixed position with respect to lower housing101. Rotating electronics board111is disposed above stationary electronics board110and is configured to rotate with respect to stationary electronics board110at a predetermined rotational velocity (e.g., more than 200 revolutions per minute). Electrical power and electronic signals are communicated between stationary electronics board110and rotating electronics board111over one or more transformer elements, capacitive elements, or optical elements, resulting in a contactless transmission of these signals. Light emission/collection engine112is fixedly positioned with respect to the rotating electronics board111, and thus rotates about central axis104at the predetermined angular velocity, ω.

As depicted inFIG.8, light emission/collection engine112includes an array of printed circuit boards114, each including a transmit channel (e.g., transmit channels160A-N). Light emitted from the illumination source associated with each of the transmit channels is directed toward a mirror (not shown). Light reflected from the mirror passes through a series of illumination optics115that collimate the emitted light into the array of beams of light105that are emitted from 3-D LIDAR system100as depicted inFIG.6. In general, any number of light emitting elements can be arranged to simultaneously, or substantially simultaneously, emit any number of light beams from 3-D LIDAR system100. In addition, any number of light emitting elements can be arranged to sequentially emit any number of light beams from 3-D LIDAR system100. In one embodiment, two or more light emitting elements are triggered to emit light substantially simultaneously, and then after a programmed period of time has elapsed, another two or more light emitting elements are triggered to emit light substantially simultaneously. Light reflected from objects in the environment is collected by collection optics116. Collected light associated with each illumination beam passes through collection optics116where it is focused onto each respective detecting element of an array of printed circuit boards113, each including a receive channel (e.g., receive channels130A-N). After passing through collection optics116, the collected light is reflected from a mirror (not shown) onto each detector element. In practice, crosstalk among each measurement channel limits the number of channels that can be triggered simultaneously. However, to maximize imaging resolution, it is desirable to trigger as many channels as possible, simultaneously, so that time of flight measurements are obtained from many channels at the same time, rather than sequentially.

FIG.9depicts a view of optical elements116in greater detail. As depicted inFIG.9, optical elements116include four lens elements116A-D arranged to focus collected light118onto each detector of the array of receive channels113. In the embodiment depicted inFIG.9, light passing through optics116is reflected from mirror124and is directed onto each detector of the array of receive channels113. In some embodiments, one or more of the optical elements116is constructed from one or more materials that absorb light outside of a predetermined wavelength range. The predetermined wavelength range includes the wavelengths of light emitted by the array of receive channels113. In one example, one or more of the lens elements are constructed from a plastic material that includes a colorant additive to absorb light having wavelengths less than infrared light generated by each of the array of receive channels113. In one example, the colorant is Epolight 7276A available from Aako BV (The Netherlands). In general, any number of different colorants can be added to any of the plastic lens elements of optics116to filter out undesired spectra.

FIG.10depicts a cutaway view of optics116to illustrate the shaping of each beam of collected light118.

In this manner, a LIDAR system, such as 3-D LIDAR system10depicted inFIG.7, and system100, depicted inFIG.6, includes a plurality of LIDAR measurement channels each emitting a pulsed beam of illumination light from the LIDAR device into the surrounding environment and measuring return light reflected from objects in the surrounding environment.

In some embodiments, such as the embodiments described with reference toFIG.6andFIG.7, an array of LIDAR measurement channels is mounted to a rotating frame of the LIDAR device. This rotating frame rotates with respect to a base frame of the LIDAR device. However, in general, an array of LIDAR measurement channels may be movable in any suitable manner (e.g., gimbal, pan/tilt, etc.) or fixed with respect to a base frame of the LIDAR device.

In some other embodiments, each LIDAR measurement channel includes a beam directing element (e.g., a scanning mirror, MEMS mirror etc.) that scans the illumination beam generated by the LIDAR measurement channel.

In some other embodiments, two or more LIDAR measurement channels each emit a beam of illumination light toward a scanning mirror device (e.g., MEMS mirror) that reflects the beams into the surrounding environment in different directions.

In a further aspect, one or more LIDAR measurement channels are in optical communication with an optical phase modulation device that directs the illumination beam(s) generated by the one or more LIDAR measurement channels in different directions. The optical phase modulation device is an active device that receives a control signal that causes the optical phase modulation device to change state and thus change the direction of light diffracted from the optical phase modulation device. In this manner, the illumination beam(s) generated by the one or more integrated LIDAR devices are scanned through a number of different orientations and effectively interrogate the surrounding 3-D environment under measurement. The diffracted beams projected into the surrounding environment interact with objects in the environment. Each respective LIDAR measurement channel measures the distance between the LIDAR measurement system and the detected object based on return light collected from the object. The optical phase modulation device is disposed in the optical path between the LIDAR measurement channel and an object under measurement in the surrounding environment. Thus, both illumination light and corresponding return light pass through the optical phase modulation device.

FIG.11illustrates a flowchart of a method200suitable for implementation by multiple channel LIDAR measurement system as described herein. In some embodiments, multiple channel LIDAR measurement system120is operable in accordance with method100illustrated inFIG.11. However, in general, the execution of method200is not limited to the embodiments of multiple channel LIDAR measurement system120described with reference toFIG.1. These illustrations and corresponding explanation are provided by way of example as many other embodiments and operational examples may be contemplated.

In block201, a measurement pulse of illumination light is emitted from each of a first plurality of LIDAR measurement channels.

In block202, an amount of return light reflected from a point in a three dimensional environment in response to each measurement pulse of illumination light is detected.

In block203, a return signal indicative of each amount of return light is generated.

In block204, an indication of each return signal is provided to a first shared output node of the first plurality of LIDAR measurement channels.

In block205, an indication of each return signal of the first plurality of LIDAR measurement channels is received at an input channel of an analog to digital converter.

A computing system as described herein may include, but is not limited to, a personal computer system, mainframe computer system, workstation, image computer, parallel processor, or any other device known in the art. In general, the term “computing system” may be broadly defined to encompass any device having one or more processors, which execute instructions from a memory medium.

Program instructions implementing methods such as those described herein may be transmitted over a transmission medium such as a wire, cable, or wireless transmission link. Program instructions are stored in a computer readable medium. Exemplary computer-readable media include read-only memory, a random access memory, a magnetic or optical disk, or a magnetic tape.

In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.