Time-multiplexing of lidar air-data optical channel

Abstract

To provide time-multiplexing of optical channels in an air-data sensor.SOLUTION: At least one switch outputs a reference optical signal, and each of a plurality of backscattered optical signals to at least one common optical path at a time. In other words, at least one common optical path sequentially receives the reference optical signal and at least one out of the backscattered optical signals, whereby a degree of systematic bias existing in at least one common optical path is compensated for and even reduced during sensor operation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] Vehicles such as aircraft are typically equipped with static pitot tubes. Such sensors are installed at one or more locations on the vehicle and are configured to determine environmental parameters describing various characteristics of the vehicle's environment, including the relative speed and wind direction with respect to the aircraft. Because pitot tubes require direct contact with the environment, they can suffer malfunctions due to icing conditions, blockages by particles, and the accuracy of the pitot tubes can be compromised due to the interaction of the air with the exterior of the aircraft. Malfunctioning of the pitot tubes can result in catastrophic accidents. Lidar-based sensors improve upon the shortcomings of pitot tubes. Similar to pitot tubes, these sensors can measure wind direction and relative speed with respect to the aircraft, but are not prone to malfunction and do not require direct contact with the environment. Additionally, lidar sensors can also measure air data parameters such as atmospheric particles and cloud composition in close proximity to the aircraft.

[0002] The lidar sensor includes a ferrule with multiple optical fibers for carrying both the reference signal and the backscattered signal received from the environment for processing and determining parameters. Each optical fiber corresponds to a specific set of signals (e.g., each of the reference signal and backscattered channels). However, when processing data from the optical signals, undesirable biases arise due to imperfections in the manufacturing of the ferrule and due to differences in optical path length for the various channels. Such biases due to the structure and material properties of the optical fibers are referred to herein as "systematic biases". Left unchecked, systematic biases can result in inaccurate environmental parameters, which risks reliance on erroneous data by other systems and / or vehicle operators during aircraft operations. Summary of the Invention

[0003] Details of one or more embodiments are set forth in the following description. Features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Thus, any of the various embodiments described herein may be combined to provide further embodiments. Aspects of the embodiments may be modified, if necessary, to employ concepts from the various patents, applications and publications identified herein to provide further embodiments.

[0004] In one embodiment, an air data sensor is disclosed. The air data sensor comprises a light source configured to generate a reference optical signal. The air data sensor comprises an optical transceiver coupled to the light source. The optical transceiver is configured to transmit the reference optical signal external to the air data sensor in a plurality of directions and responsively receive a backscattered optical signal from each of the plurality of directions. The air data sensor comprises at least one switch coupled to the optical transceiver. The at least one switch is configured to output at least one of the reference optical signal and the backscattered optical signal to at least one common optical path. In a first configuration, the at least one switch is configured to output the reference optical signal to the at least one common optical path. In a second configuration, the at least one switch is configured to output at least one of the backscattered optical signals to the at least one common optical path. The air data sensor comprises a detector coupled to the at least one switch via the at least one common optical path and configured to detect the reference optical signal and the backscattered optical signal received from the at least one switch. The air data sensor comprises at least one processor coupled to the detector and the at least one switch. At least one processor is configured to receive the reference optical signal and the backscattered optical signal and to set at least one switch to a first configuration or a second configuration.

[0005] In another embodiment, a system is disclosed. The system comprises a light source coupled to a vehicle and configured to generate a reference light signal. The system comprises an optical transceiver coupled to the light source. The optical transceiver is configured to transmit the reference light signal outside the vehicle in a plurality of directions and responsively receive a backscattered light signal from each of the plurality of directions. The system comprises at least one switch coupled to the optical transceiver. The at least one switch is configured to output the reference light signal and the backscattered light signal to at least one common light path. Each of the at least one common light path sequentially receives at least one of the reference light signal and the backscattered light signal. The system comprises a detector coupled to the at least one switch via the at least one common light path and configured to detect the reference light signal and the backscattered light signal received from the at least one switch. The system comprises at least one processor coupled to the detector. The at least one processor is configured to determine at least one parameter based on the reference light signal and the backscattered light signal.

[0006] According to yet another embodiment, a method is disclosed. The method includes generating a reference optical signal. The method includes transmitting the reference optical signal external to the vehicle in a plurality of directions. The method includes receiving a plurality of backscattered optical signals. The method includes outputting one of the reference optical signals and at least one of the plurality of backscattered optical signals to at least one common optical path at a time. The method includes determining a degree of systematic bias associated with the at least one common optical path. The method includes determining at least one parameter compensated for a degree of systematic bias associated with the at least one common optical path.

[0007] Other embodiments are also disclosed, as described below. [Brief description of the drawings]

[0008] Example embodiments will be described with additional specificity and detail through the use of the accompanying drawings, with the understanding that the drawings illustrate example embodiments only and therefore should not be considered limiting in scope. [Figure 1] FIG. 1 illustrates a block diagram of a system configured for air data sensing as described in one or more embodiments. [Diagram 2] 2 shows a block diagram of the system of FIG. 1 having three switches coupled to a four-channel ferrule as described in one or more embodiments. [Diagram 3] 2 illustrates a block diagram of the system of FIG. 1 having three switches coupled to a three-channel ferrule, as described in one or more embodiments. [Figure 4] FIG. 2 illustrates a block diagram of the system of FIG. 1 having a single switch coupled to a single channel ferrule, as described in one or more embodiments. [Diagram 5] FIG. 2 illustrates a block diagram of the system of FIG. 1 having a single switch coupled to a dual channel ferrule, as described in one or more embodiments. [Figure 6] 1 shows a block diagram of a system including a frequency shifter and three switches coupled to a four-channel ferrule, as described in one or more embodiments. [Figure 7] 1 shows a block diagram of a system including a frequency shifter and three switches coupled to a three-channel ferrule, as described in one or more embodiments. [Figure 8] FIG. 1 illustrates a block diagram of a system including a frequency shifter and a single switch coupled to a single channel ferrule, as described in one or more embodiments. [Figure 9] 1 illustrates a flow diagram of a method for time multiplexing optical channels as described in one or more embodiments.

[0009] According to common practice, the various features described are not drawn to scale but rather to emphasize particular features relevant to the exemplary embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which specific exemplary embodiments are shown by way of illustration. It should be understood, however, that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. Furthermore, the methods presented in the drawings and specification should not be construed as limiting the order in which individual steps may be performed. Accordingly, the following detailed description is not to be construed in a limiting sense.

[0011] The embodiments of the present disclosure utilize time multiplexing of optical channels when conveying optical signals to one or more channels of a ferrule. In doing so, systematic biases in the lidar sensor can be compensated for and further reduced during lidar sensor operation. As a result, the embodiments of the present disclosure improve the accuracy and reliability of sensor measurements during vehicle maneuvers.

[0012] 1 illustrates a block diagram of a system 100 configured for air data sensing in which embodiments of the present disclosure can be implemented. System 100 is, in some embodiments, a lidar sensor. System 100 may include other components and / or be coupled to other systems not explicitly shown in FIG. 1.

[0013] Although not explicitly shown, the system 100 is configured to be coupled to a vehicle, e.g., mounted to a vehicle. Use of the term "vehicle" is not intended to be limiting and includes all classes of vehicles within the ordinary meaning of the term, including, but not limited to, airborne mobile vehicles (e.g., commercial, non-commercial, or recreational aircraft), unmanned and / or spaceborne mobile vehicles (e.g., satellites, urban airborne mobile vehicles), waterborne mobile vehicles (e.g., ships, submarines), and ground mobile vehicles (e.g., automobiles, including cars, trucks, and motorcycles). Throughout this disclosure, a vehicle may further be referred to as an aircraft, with the understanding that the principles described herein apply to other vehicles where applicable.

[0014] The system 100 includes a laser source 102 configured to generate an optical signal. The laser source 102 can be any type of optical source generator, including any type of laser. The laser source 102 is coupled to an optical head 104 and at least one optical switch 106, for example, via one or more optical fibers. The optical signal generated by the laser source 102 is referred to as a reference signal because it serves as a reference for analyzing the backscattered signal received from the optical head 104. Parameters of the reference signal, including frequency / wavelength, optical power, etc., are known by the processor 112.

[0015] The optical head 104 receives a reference signal from the laser source 102. The optical head 104 is configured to transmit the reference signal in multiple directions to the outside of the system 100 (i.e., outside the vehicle). For example, the optical head 104 includes guidance optics (waveguides, beam splitters, reflectors, etc.) that separate the reference signal into components and direct each component to a different optical port of the optical head 104. Each optical port can be positioned on a portion of the vehicle to build a complete representation of the desired parameter. For example, in the case of velocity, each optical port of the optical head 104 is positioned differently to measure the x, y, and z components of the vehicle's velocity.

[0016] The optical head 104 functions as an optical transceiver that transmits a reference signal at each optical port and receives a backscattered optical signal corresponding to the reference signal. First, the optical head 104 transmits a reference signal from each optical port into the surrounding atmosphere. Then, the optical head 104 receives an optical signal corresponding to the light backscattered from the atmosphere. The difference between the reference signal and the backscattered signal can be used to determine an environmental parameter and / or a navigation parameter.

[0017] The system 100 includes an interferometer 107 comprising a ferrule 108 coupled to a detector 110. The interferometer 107 is generally configured to detect an optical path length difference between a reference signal and each of the backscattered signals received from the optical head 104. The ferrule 108 includes at least one optical channel that receives the reference signal and the backscattered signal. Each optical channel may be represented as an optical fiber or other waveguide that allows the reference optical signal and the backscattered optical signal to propagate to the detector 110. As shown in FIG. 1, the ferrule 108 includes four optical channels: Channel R (carrying a reference signal), Channel 1 (carrying a first backscattered signal), Channel 2 (carrying a second backscattered signal), and Channel 3 (carrying a third backscattered signal); however, the ferrule 108 may include more or fewer channels (including one channel).

[0018] The ferrule 108 provides the reference signal and each backscattered signal through each of its associated channels to the detector 110. The detector 110 detects interference between the reference signal and the backscattered signal, which may be represented as an interference pattern of fringes depending on the degree of constructive or destructive interference present in the superimposed signal. Such interference patterns may vary in characteristics based on the position of each channel within the ferrule 108, the optics (e.g., lenses, filters, etc.) used to provide the interference pattern to the detector, and the optical imaging of the detector 110. For example, the detector 110 may simultaneously receive output from each optical channel with the interference pattern between the reference signal and the backscattered optical signal corresponding to each channel projected onto different locations on a camera of the detector 110. A representation of the interference pattern is provided from the detector 110 to one or more processors 112 (described as a single processor for instructional purposes). In some embodiments, the detector 110 is configured to convert the optical interference pattern into a corresponding electrical signal based on the optical power of the interference pattern. The processor 112 then uses the electrical signals to determine one or more environmental and / or navigational parameters of the vehicle, which may be communicated to other systems onboard the vehicle and / or to the vehicle operator for use in steering.

[0019] In some lidar sensors, the reference signal is provided to the ferrule 108 on an optical channel separate from the optical channel used to carry the backscattered signal. This is done as a way to avoid contaminating the reference signal with the backscattered signal before superposition to the detector 110. However, the characteristics of the backscattered signal can change due to propagation in the optical channel as a result of imperfections in the optical channel. The resulting systematic bias is difficult to detect since it is perceived by the detector 110 as a property of the backscattered signal, and difficult to address since it is intrinsic to the properties of the optical channel. For example, the properties of the optical channel and any other optical system can change with time or environment (e.g., pressure, temperature, vibration, etc.), typically varying most strongly in the low frequency regime. Since both the reference and backscattered optical channels are spatially separated, variations in these properties can induce significant systematic biases in the sensor.

[0020] To compensate for and possibly reduce systematic bias present in the optical signal carrier, the system 100 includes at least one switch 106 coupled between the optical head 104 and the ferrule 108. The switch 106 is configured to output one of the reference signal and the backscatter signal (and optionally a separate reference signal) to one or more optical channels of the ferrule 108 at a time. In some embodiments, the switch 106 is represented as multiple optical switches in a switch array. Alternatively, the switch 106 can be implemented as a single optical switch. Various embodiments of the switch 106 are shown and described with respect to FIGS. 2-8.

[0021] The system 100 is configured to time multiplex the reference signal with each of the backscattered signals on at least one common optical path (e.g., the same optical channel) based on the configuration of the switch 106. As used herein, a "common optical path" refers to an optical path coupled between the optical head and the interferometer detector, the common optical path configured to receive the reference optical signal and at least one backscattered signal at different time periods. When time multiplexing the reference signal on the same optical channel used to carry the backscattered signal, the degree of systematic bias can be determined by the processor 112 and compensated for when determining the environmental parameters. The configuration of the switch 106 is set by the timing circuit 114. For example, the timing circuit 114 is configured to send a control signal that configures the switch 106 to output either the reference signal or the backscattered signal for a given optical channel. After a set time interval, the timing circuit 114 configures the switch 106 to change the output configuration to output a different optical signal to the same optical channel of the ferrule 108. The duration of the timing for each of the switch configurations is determined by the timing circuit 114 based on data provided by the processor 112. In some embodiments, the timing circuit 114 can be integrated with the processor 112 .

[0022] 2-8 show various embodiments of time multiplexing of optical signals to at least one optical channel. Referring to FIG. 2, the switch 106 includes three optical switches S1, S2, and S2, each of which is coupled to channels 1, 2, and 3, respectively, of the ferrule 108. The switch 106 is configured to receive both a reference signal from the laser source 102 and a backscattered signal from the optical head 104. Specifically, S1 receives the reference signal along with the first backscattered signal, S2 receives the reference signal along with the second backscattered signal, and S3 receives the reference signal along with the third backscattered signal. In the embodiment of FIG. 2, the ferrule 108 includes a separate reference channel R that receives only the reference signal from the laser source 102. In this embodiment, the switch 106 is configured to output the reference signal to the optical channel R regardless of the output to the optical channels 1, 2, and 3.

[0023] The switch S1 is configured to receive both the reference signal and the first backscattered signal and, based on control from the timing circuit 114, is configured to output one of the reference signal and the first backscattered signal to optical channel 1 of the ferrule 108. In a first configuration, the timing circuit 114 sets the switch S1 to output the reference signal to optical channel 1 of the ferrule 108. In a second configuration, the timing circuit 114 sets the switch S1 to output the first backscattered signal to optical channel 1 of the ferrule 108.

[0024] Switch S2 is configured to receive both the reference signal and the second backscattered signal and, based on control from the timing circuit 114, is configured to output one of the reference signal and the second backscattered signal to optical channel 2 of the ferrule 108. In a first configuration, the timing circuit 114 sets switch S2 to output the reference signal to optical channel 2 of the ferrule 108. In a second configuration, the timing circuit 114 sets switch S2 to output the second backscattered signal to optical channel 2 of the ferrule 108.

[0025] The switch S3 is configured to receive both the reference signal and the third backscattered signal, and is configured to output one of the reference signal and the third backscattered signal to optical channel 3 of the ferrule 108 based on control from the timing circuit 114. In a first configuration, the timing circuit 114 sets the switch S3 to output the reference signal to optical channel 3 of the ferrule 108. In a second configuration, the timing circuit 114 sets the switch S3 to output the third backscattered signal to optical channel 3 of the ferrule 108. The switching speed should preferably be set higher than the known time variation of the systematic bias of the optical channels of the ferrule 108. In some embodiments, switching is performed for each channel simultaneously, although each corresponding switch can also be switched sequentially to the receiving optical channel.

[0026] While optical channel R provides a reference signal to detector 110, optical channels 1, 2, and 3 are configured to provide either the reference signal or the respective first, second, and third backscatter signals to detector 110 depending on the output of switch 106. In this embodiment, optical channels 1, 2, and 3 comprise a common optical path. Thus, detector 110 receives either the reference signal or the respective backscatter signals from optical channels 1, 2, and 3 at a given time. Since the reference signals are expected to be identical between each of channels R, 1, 2, and 3, the difference between the reference signals in each of channels 1, 2, and 3 can be compared to the reference signal from channel R to determine the degree of systematic bias for a given optical channel. For example, if the optical path length of the reference signal corresponding to channel 1 is different from the optical path length of the reference signal of channel R, channel 1 is likely to suffer from some systematic bias, the degree of which can be determined by processor 112 based on the difference in optical path lengths detected by detector 110. The processor 112 may then take into account the degree of systematic bias (as represented by optical path difference, phase difference, or other parameters) when determining environmental and / or navigation parameters of the vehicle.

[0027] In some embodiments, the processor 112 determines the velocity of the vehicle based on the output of each of the optical channels, which may be done using speed measurement processing techniques. For example, a velocity component in each direction may be determined based on each of the outputs of optical channels 1, 2, and 3 as follows: Equation 1(a) OUT1 = Ref - S1 - ΔR1 Equation 1(b) OUT2=Ref-S2-ΔR2 Equation 1(c) OUT3=Ref-S3-ΔR3 where Ref is the reference signal from optical channel R, S1 is the backscattered signal from optical channel 1, and ΔR1 is the optical path difference in the reference signals from optical channel R and optical channel 1. Other quantities related to the outputs of channel 2 (OUT2 and 3 (OUT3) are similarly defined, as shown with respect to equations 1(b)-(c). Thus, the degree of systematic error in each channel is quantitatively represented as ΔR, which is used by processor 112 to determine corrected environmental and / or navigation parameters of the vehicle.

[0028] Alternative embodiments of the switch 106 and the ferrule 108 may also be used, such as the system 300 shown in FIG. 3. The system 300 operates similarly to that described with respect to FIGS. 1-2, except as otherwise described. In FIG. 3, the system 300 includes a switch array 106 having three optical switches S1, S2, S3, similar to that described with respect to the system 200. However, unlike the system 200, the ferrule 108 does not include a separate reference channel. Instead, a reference signal is provided to the ferrule 108 via each switch S1, S2, S3. Similar to that described with respect to FIG. 2, the switches S1, S2, and S3 are configured to output either the reference signal from the laser source 102 or the respective first (S1), second (S2), and third (S3) backscattered signals to the respective optical channel 1 (S1), optical channel 2 (S2), and optical channel 3 (S3) of the ferrule 108. In this embodiment, the common optical path is represented by optical channels 1, 2, and 3. The switching speed for changing each of the switches S1, S2, and S3 to different configurations is appropriately set by the timing circuit 114. In some embodiments, the switching speed of each switch is faster than the switching speed of the system 200 to accommodate the lack of a separate reference optical channel R.

[0029] To determine the output of each ferrule 108, the processor 112 can determine the relative systematic bias that exists between optical channels 1, 2, and 3. For example, optical channel 1 can be designated as the reference channel. In this example, the relative optical path length difference between the reference signals output from optical channel 1 and optical channel 2 can be used to determine the optical path length difference ΔR between optical channel 1 and optical channel 2, while the optical path length difference between the reference signals output from optical channel 1 and optical channel 3 can be used to determine the optical path length difference ΔR of optical channel 3. To determine the systematic bias of optical channel 1, the output of the reference channel can be compared between two successive switching periods.

[0030] FIG. 4 illustrates an exemplary embodiment of the system 100 shown and described with respect to FIG. 1. In the embodiment of FIG. 4, the system 400 includes a single switch 106, and the ferrule 108 includes a single optical channel 1. The switch 106 is configured to receive a reference signal from the laser source 102 and each of the backscattered signal components from the optical head 104. In this embodiment, the switch 106 is configured to output one of the reference signal, the first backscattered signal, the second backscattered signal, and the third backscattered signal on the same optical channel 1 at a time. That is, the switch 106 is configured to switch the output of each of the four optical signals. In this embodiment, the common optical path is shown as optical channel 1. The switching speed is appropriately set by the timing circuit 114. In some embodiments, the switching speed is higher than the switching speed of the switch 106 described with respect to FIGS. 2-3.

[0031] The ferrule 108 is configured to provide one of the reference signal, the first backscattered signal, the second backscattered signal, and the third backscattered signal at a time to the detector 110 via the optical channel 1. The processor 112 is configured to determine the degree of systematic bias of the optical channel 1 based on the reference signal output to the detector 110. Additionally, the processor 112 is configured to determine an environmental parameter and / or a navigation parameter based on the backscattered signal components, as previously described. The embodiment of FIG. 4 can reduce systematic bias by time multiplexing each of the optical signals on the same optical channel. By including a single optical channel, the signal projected to the detector 110 can occupy the entire detector camera, which can improve discrimination of interference patterns and subsequent data processing by the processor 112.

[0032] FIG. 5 illustrates an exemplary embodiment of the system illustrated in FIG. 1 and an alternative embodiment of the system 400 illustrated in FIG. 4. The system 500 operates similarly to the system 400, except as further described. In this embodiment, the ferrule 108 includes two optical channels, optical channel R and optical channel 1. The optical channel R receives a reference signal from the laser source 102. In addition, the optical channel 1 receives one of the reference signal, the first backscattered signal, the second backscattered signal, and the third backscattered signal at a time based on the configuration of the switch 106. In this embodiment, the common optical path is represented by optical channel 1. The ferrule 108 provides the reference signal from the optical channel R and the optical signal from the optical channel 1 to the detector 110. The processor 112 then determines the degree of systematic bias based on the phase difference between the reference signal provided from the reference channel R and the reference signal provided from the optical channel 1. The processor 112 can then compensate for the systematic bias present in the ferrule 108 by determining one or more environmental and / or navigational parameters (or components thereof) based on the degree of systematic bias. In this embodiment, the switching speed may be relaxed relative to the switching speed in the embodiment shown in FIG.

[0033] Figure 6 illustrates another exemplary embodiment of the system 100 shown and described with respect to Figure 1. The system 600 operates similarly as described with respect to the system 100, with additional features as further described. In the embodiment of Figure 6, the laser source 102 is coupled to a frequency shifter 116, which is configured to receive a reference optical signal and generate a known frequency shifted reference signal that is provided to the switch array 106. For example, the frequency shifter 116 can generate a Doppler shifted signal based on a defined phase shift, which can be a fixed frequency shift.

[0034] In this embodiment, the ferrule 108 comprises three optical channels coupled to each switch S1, S2, S3, respectively. Each switch is configured to output one of the reference signal from the laser source 102, the Doppler shift signal from the frequency shifter 116, and the respective backscatter signal from the optical head 104. For example, S1 is configured to receive the reference signal from the laser source 102, the Doppler shift signal from the frequency shifter 116, and the first backscatter signal from the optical head 104. S1 then outputs one of these signals at a time to optical channel 1 of the ferrule 108 according to the configuration set by the timing circuit 114. Switches S2 and S3 operate in a similar manner. The ferrule 108 also includes a reference optical channel R configured to receive a reference optical signal from the laser source 102. In this embodiment, optical channels 1, 2, and 3 comprise a common optical path.

[0035] To account for the systematic bias ΔR, the processor 112 can determine a compensated output corresponding to each optical channel indicative of a component of the environmental and / or navigation parameters. For example, looking at the output from optical channel 1, the systematic bias ΔR1 can be determined from the formula ΔR1=Ref-R1, where Ref is the optical path length of optical channel R and R1 is the optical path length of the reference signal of optical channel 1. The output from each optical channel can be demodulated by a scale factor determined based on the frequency shift generated by the frequency shifter 116. For optical channel 1, the scale factor can be determined by the formula SF=(Ref-DoppR1) / ω, where DoppR1 is the optical path length of optical channel 1 when the Doppler-shifted reference signal is output and ω is the frequency shift. Thus, the compensated output corresponding to optical channel 1 can be determined as follows: Equation 2 OUT1=(Ref-S1-ΔR1)*SF The power of the other optical channels 2 and 3 can be determined similarly.

[0036] FIG. 7 shows an exemplary embodiment of the system shown in FIG. 1 and an alternative embodiment of the system 600 shown in FIG. 6. The system 700 operates similarly to the system 600, except as further described. In this embodiment, the ferrule 108 comprises three optical channels 1, 2, 3 coupled to respective switches S1, S2, S3. In contrast to FIG. 6, the ferrule 108 does not include a separate optical channel R for the reference optical signal. The reference optical signal is distributed to each switch S1, S2, S3, respectively, along with the Doppler-shifted signal from the frequency shifter 116. As previously described, each switch S1, S2, S3 is configured to output one of the reference optical signal from the laser source 102, the Doppler-shifted signal from the frequency shifter 116, and the respective backscattered signal at a time to the corresponding optical channel. In this embodiment, the optical channels 1, 2, and 3 comprise a common optical path.

[0037] FIG. 8 illustrates an exemplary embodiment of the system shown in FIG. 1 and an alternative embodiment of the systems 600-700 shown in FIGS. 6-7. The system 800 operates similarly to the systems 600-700, except as further described. In this embodiment, the ferrule 108 includes only one optical channel 1 and a single switch 106. The switch 106 is configured to receive a reference optical signal from the laser source 102, a Doppler shift signal from the frequency shifter 116, and each backscatter signal from the optical head 104. The switch 106 outputs one of the reference optical signal, the Doppler shift signal, and each backscatter signal at a time to the optical channel 1. Each of these signals is then detected by the detector 110 and used both to determine the systematic bias in the optical channel 1 and to determine one or more environmental and / or navigation parameters adjusted for the determined systematic bias. In this embodiment, the common optical path is indicated by the optical channel 1.

[0038] 1-8 illustrate switching with respect to three backscattered signals, any number of backscattered signals may be used, and furthermore, any number of optical channels and switches may be used.

[0039] 9 illustrates a flow diagram of a method 900 for time multiplexing optical channels. The method 900 may be implemented via the techniques described with respect to FIGS. 1-8, but may also be implemented via other techniques. The blocks of the flow diagram are arranged generally sequentially for ease of explanation. However, it should be understood that this organization is merely exemplary, and that the processing associated with the methods described herein (and the blocks illustrated in the figures) may occur in a different order (e.g., at least some of the processing associated with the blocks is performed in a parallel and / or event-driven manner).

[0040] Method 900 includes, at block 902, generating a reference optical signal, for example by laser source 102 or other optical source. At block 904, method 900 transmits the reference optical signal external to the vehicle in a plurality of directions. In some embodiments, the reference optical signal is transmitted in three directions corresponding to a representation of a three-dimensional coordinate system. However, any number of directions may be used. This may be performed by optical head 104 or other optical transceiver. Method 900 then proceeds to block 906, where it receives a plurality of backscattered signals. Although three backscattered signals are shown and described with respect to FIGS. 1-8, any number of such signals may be used.

[0041] The method 900, at block 908, outputs the reference optical signal and one of each backscattered signal to at least one common optical path. This function can be performed by one or more optical switches, including any of the switches or switch arrays described in Figures 1-8. The output of each signal is done one at a time in a time multiplexed manner to at least one common optical path. For example, the at least one common optical path can be a single optical channel of the ferrule, or can be multiple optical channels of the ferrule. If multiple optical channels are used, each backscattered signal can be output to one of the multiple optical channels, along with the reference optical signal. For example, if three optical channels are used, the first optical channel can receive the first backscattered signal, the second optical channel can receive the second backscattered signal, and the third optical channel can receive the third backscattered signal, with each optical channel also configured to receive a reference optical signal. However, in some embodiments, several backscattered signals can be received on the same optical channel, along with the reference optical signal, one at a time. Optionally, the Doppler shifted reference signal may be output sequentially along with the other signals described.

[0042] Proceeding to block 910, the method 900 determines a degree of systematic bias associated with at least one common optical path. Such systematic bias may be expressed, for example, as an optical path difference or a phase difference between a reference signal output in a first optical channel and a reference signal output in a second optical channel. In some embodiments, the first optical channel is a channel dedicated to receiving a reference optical signal. In some embodiments, the systematic bias may be determined by a reference signal output from a single optical channel for a sufficiently high switching speed.

[0043] At block 912, the method 900 determines at least one parameter compensated for the degree of systematic bias. The at least one parameter may be an environmental parameter, a navigation parameter, or a component thereof. If a Doppler-shifted reference signal is used, the at least one parameter may be determined by utilizing an appropriate scale factor along with the degree of systematic bias for each optical channel.

[0044] The methods and techniques described herein may be implemented at least partially in digital electronic circuitry, or with a programmable processor (e.g., a special purpose processor or a general purpose processor such as a computer), firmware, software, or various combinations of each. Apparatus embodying these techniques may include suitable input and output devices, a programmable processor, and a storage medium tangibly embodying program instructions for execution by the programmable processor. Processes embodying these techniques may be performed by a programmable processor executing a program of instructions to perform a desired function by operating on input data and generating appropriate output. The techniques may be advantageously implemented in one or more programs executable on a programmable system including at least one programmable processor coupled to receive data and instructions from and transmit data and instructions to a data storage system, at least one input device, and at least one output device. In general, the processor receives instructions and data from a read-only memory and / or a random access memory. Suitable storage devices for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including, for example, semiconductor memory devices such as erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and flash memory devices, magnetic disks (internal hard disk or removable disk), magneto-optical disks, etc. Any of the foregoing may be supplemented by, or incorporated in, specially designed application-specific integrated circuits (ASICs).

[0045] Exemplary embodiments Example 1 includes an air data sensor, the air data sensor comprising: a light source configured to generate a reference optical signal; an optical transceiver coupled to the light source, the optical transceiver configured to transmit the reference optical signal in a plurality of directions external to the air data sensor and in response to receiving a backscattered optical signal from each of the plurality of directions; and at least one switch coupled to the optical transceiver, the at least one switch configured to output at least one of the reference optical signal and the backscattered optical signal to at least one common optical path, in a first configuration, the at least one switch configured to output the reference optical signal to the at least one common optical path, and in a second configuration, the at least one switch configured to output the reference optical signal to the at least one common optical path. In the configuration, the at least one switch includes at least one switch configured to output at least one of the backscattered optical signals to at least one common optical path; a detector coupled to the at least one switch via the at least one common optical path and configured to detect the reference optical signal and the backscattered optical signal received from the at least one switch; and at least one processor coupled to the detector and the at least one switch, the at least one processor configured to receive the reference optical signal and the backscattered optical signal and to set the at least one switch to a first configuration or a second configuration.

[0046] Example 2 includes the air data sensor of example 1, wherein the at least one common optical path comprises at least one optical channel of the ferrule.

[0047] Example 3 includes the air data sensor of any of Examples 1-2, wherein the at least one common optical path includes a single common optical path, and at least one switch is configured to output the reference optical signal in a first configuration, and at least one switch is configured to output each backscattered optical signal to the single common optical path in each separate configuration.

[0048] Example 4 includes the air data sensor according to any one of Examples 1 to 3, wherein at least one common optical path has a first common optical path and a second common optical path, and at least one switch is configured in a first configuration to output a reference optical signal to the first common optical path and the second common optical path, and at least one switch is configured in a second configuration to output a first backscattered optical signal to the first common optical path and output a second backscattered optical signal to the second common optical path.

[0049] Example 5 includes the air data sensor of any of Examples 1 to 4, wherein the at least one common optical path is part of a ferrule, the ferrule includes a reference optical channel, and the at least one switch is configured to output the reference optical signal to the reference optical channel in the first configuration and / or the second configuration.

[0050] Example 6 includes the air data sensor of any of Examples 1-5, further comprising a frequency shifter coupled to the at least one switch, the frequency shifter configured to generate a Doppler shifted reference signal, and the at least one switch configured to output the Doppler shifted reference signal to at least one common optical path in a third configuration.

[0051] Example 7 includes an air data sensor described in any of Examples 1 to 6, and the at least one switch includes a plurality of switches, a first switch of the plurality of switches configured to output the reference optical signal and the first backscattered optical signal to a first common optical path, and a second switch of the plurality of switches configured to output the reference optical signal and the second backscattered optical signal to a second common optical path.

[0052] Example 8 includes a system comprising: a light source coupled to a vehicle and configured to generate a reference optical signal; an optical transceiver coupled to the light source, the optical transceiver configured to transmit the reference optical signal to an exterior of the vehicle in a plurality of directions and in response to receive a backscattered optical signal from each of the plurality of directions; at least one switch coupled to the optical transceiver, the at least one switch configured to output the reference optical signal and the backscattered optical signal to at least one common optical path, each of the at least one common optical path sequentially receiving at least one of the reference optical signal and the backscattered optical signal; a detector coupled to the at least one switch via the at least one common optical path and configured to detect the reference optical signal and the backscattered optical signal received from the at least one switch; and at least one processor coupled to the detector, the at least one processor configured to determine at least one parameter based on the reference optical signal and the backscattered optical signal.

[0053] Example 9 includes the system of Example 8, wherein the at least one processor is configured to determine a degree of systematic bias for at least one common optical path, and the at least one processor is configured to determine at least one parameter based on the degree of systematic bias.

[0054] Example 10 includes the system of any of Examples 8 to 9, wherein at least one common optical path comprises a single optical path, and at least one switch is configured to sequentially output each of the reference optical signal and the backscattered optical signal to the single optical path.

[0055] Example 11 includes the system of any of Examples 8 to 10, wherein at least one common optical path comprises a first common optical path and a second common optical path, at least one switch is configured to sequentially output the reference optical signal and the first backscattered optical signal to the first common optical path, and at least one switch is configured to sequentially output the reference optical signal and the second backscattered optical signal to the second common optical path.

[0056] Example 12 includes the system of any of Examples 8-11, wherein the at least one common optical path is part of a ferrule, the ferrule includes a reference optical channel, and the at least one switch is configured to output a reference optical signal to the reference optical channel.

[0057] Example 13 includes the system of any of Examples 8-12, further comprising a frequency shifter coupled to the at least one switch, the frequency shifter configured to generate a Doppler-shifted reference signal, and the at least one common optical path configured to sequentially receive the Doppler-shifted reference signal along with at least one of the reference optical signal and the backscattered optical signal.

[0058] Example 14 includes the system of any of Examples 9 to 13, wherein to determine the degree of systematic bias, at least one processor is configured to determine an optical path length difference or a phase difference between a reference optical signal detected from the first common optical path and a reference optical signal detected from the reference optical channel.

[0059] Example 15 includes the system of any of Examples 9 to 14, wherein to determine the degree of systematic bias, at least one processor is configured to determine an optical path length difference or a phase difference between reference optical signals detected from the common optical path at two different times.

[0060] Example 16 includes a method, the method including generating a reference optical signal, transmitting the reference optical signal in a plurality of directions external to the vehicle, receiving a plurality of backscattered optical signals, outputting one of the reference optical signals and at least one of the plurality of backscattered optical signals to at least one common optical path at a time, determining a degree of systematic bias associated with the at least one common optical path, and determining at least one parameter compensated for the degree of systematic bias associated with the at least one common optical path.

[0061] Example 17 includes a method as described in Example 16, in which outputting one of the reference optical signals and at least one of the plurality of backscattered optical signals includes sequentially outputting the reference optical signal and the first backscattered optical signal to a first common optical path, and sequentially outputting the reference optical signal and the second backscattered optical signal to a second common optical path.

[0062] Example 18 includes the method of any of Examples 16-17, wherein outputting one of the reference optical signals and at least one of the plurality of backscattered optical signals includes sequentially outputting each of the reference optical signal and the plurality of backscattered optical signals to a single common optical path.

[0063] Example 19 includes the method of any of examples 16-18, including outputting the reference optical signal on a reference optical channel that is different from the at least one common optical path.

[0064] Example 20 includes the method of any of Examples 16 to 19, including generating a Doppler-shifted reference optical signal; and sequentially outputting at least one of the reference optical signal, the Doppler-shifted reference optical signal, and the plurality of backscattered optical signals to at least one common optical path.

[0065] Although specific embodiments have been illustrated and described herein, it will be understood by those skilled in the art that any configuration which is expected to achieve the same purpose may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.

Claims

1. 1. A system comprising: a light source coupled to the vehicle and configured to generate a reference light signal; an optical transceiver coupled to the light source, the optical transceiver configured to transmit the reference optical signal in a plurality of directions to an exterior of the vehicle and in response receive a backscattered optical signal from each of the plurality of directions; at least one switch coupled to the optical transceiver, the at least one switch configured to output the reference optical signal and the backscattered optical signal to at least one common optical path, each of the at least one common optical path sequentially receiving at least one of the reference optical signal and the backscattered optical signal; a detector coupled to the at least one switch via the at least one common optical path and configured to detect the reference optical signal and the backscattered optical signal received from the at least one switch; at least one processor coupled to the detector, the at least one processor configured to determine at least one parameter based on the reference light signal and the backscattered light signal.

2. 2. The system of claim 1, wherein the at least one processor is configured to determine a degree of systematic bias for the at least one common optical path, and the at least one processor is configured to determine the at least one parameter based on the degree of systematic bias.

3. 1. A method comprising: generating a reference optical signal; transmitting the reference light signal external to the vehicle in a plurality of directions; receiving a plurality of backscattered optical signals; outputting one of the reference optical signals and at least one of the plurality of backscattered optical signals onto at least one common optical path at a time; determining a degree of systematic bias associated with the at least one common optical path; and determining at least one parameter compensated for said degree of systematic bias associated with said at least one common optical path.

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