Method and system for determining a relative position to a target

Abstract

A method for determining the relative angular direction between a target and a transmitter. A generation of one or more light beams at the transmitter comprises diffracting broadband light in such a way that different optical frequency wavelengths are diffracted differently and a relative angular direction is detected by reading the optical frequency wavelength. A system is provided for determining the relative angular direction between a target and a transmitter and a system is provided for determining a relative position between a target and a transmitter in an area, wherein relative position is defined by the parameters: relative angular direction (1, 2), and distance.

Claims

1. A method for determining a relative angular direction between a target and a transmitter, the method comprising the following steps: producing one or more light beams, transmitting, by the transmitter, the one or more light beams, wherein a first light beam in the one or more light beams indicates a relative angular direction from the transmitter, receiving, by the target, one or more of the one or more light beams, wherein the generation of the one or more light beams comprises diffracting a broadband light in such a way that different optical frequency wavelengths are diffracted differently and a relative angular direction is detected by reading an optical frequency wavelength, wherein at least one light beam comprises at least two optical frequency combs or a dual frequency comb, comprising: a first optical frequency comb and a second optical frequency comb, the first and second frequency combs comprising a same .sub.0 and comprising respective .sub.r1 and .sub.r2 where .sub.r1 is different from .sub.r2, and wherein .sub.r1, .sub.r2 is the comb tooth spacing or mode repetition rate, .sub.0 is the carrier offset frequency.

2. A method according to claim 1 wherein the broadband light comprises discrete spectral lines or multimode light.

3. A method according to claim 2 wherein the broadband light or the multimode light comprises an optical frequency comb.

4. A method according to claim 1 wherein at least one light beam comprises two dual frequency combs comprising different repetition rates, said two dual frequency combs being transmitted in two different directions forming a grid in two angular directions.

5. A method according to claim 1 wherein the relative angular direction is determined by the target receiving the one or more light beams.

6. A method according to claim 1 wherein the relative angular direction is determined by the transmitter receiving a reflection of the one or more light beams from the target.

7. A method for determining a relative position between a target and a transmitter in an area, wherein relative position is defined by the parameters relative angular direction and distance, the method comprising the steps of: determining two or more relative angular directions 1, 2 between two or more receptors, comprised in the target and the transmitter, by respective methods comprising the steps of: producing one or more light beams, transmitting, by the transmitter, such one or more light beams, wherein a light beam indicates a relative angular direction from the transmitter, receiving, by the target, one or more of the light beams, wherein the generation of the one or more light beams comprises diffracting broadband light in such a way that different optical frequency wavelengths are diffracted differently and a relative angular direction is detected by reading the optical frequency wavelength, determining the distance between the target and the transmitter by triangulation, given a predetermined distance between the two or more receptors and the two or more relative angular directions 1, 2.

8. A system for determining the relative angular direction between a target and a transmitter configured to generate light beams, wherein the generation of the one or more light beams comprises diffracting broadband light in such a way that different optical frequency wavelengths are diffracted differently and a relative angular direction is detected by reading the optical frequency wavelength, comprising a transmitter comprising one or more broadband light sources, one or more diffraction gratings, configured to receive broadband light from the one or more broadband light sources, and a target comprising one or more receptors configured to receive one or more light beams generated by a method comprising the steps of: producing one or more light beams, transmitting, by the transmitter, such one or more light beams, wherein a light beam indicates a relative angular direction from the transmitter, receiving, by the target, one or more of the light beams, wherein the generation of the one or more light beams comprises diffracting broadband light in such a way that different optical frequency wavelengths are diffracted differently and a relative angular direction is detected by reading the optical frequency wavelength, and means in connection with the one or more receptors configured to determine the relative angular direction by reading the optical frequency wavelength according to the method.

9. The system according to claim 8 wherein the broadband light source comprises: a monomode light source, and one or more optical frequency comb generators, configured to receive the light from the monomode light source, and the optical frequency wavelength is related to an electronic frequency which is received by the one or more receptors.

10. The system according to claim 9 wherein the monomode light source comprises a laser light source.

11. The system according to claim 8 further comprising a grid generator.

12. The system according to claim 11 wherein the grid generator comprises two cylindrical lenses.

13. The system according to claim 8 further comprising an aircraft wherein the aircraft comprises the target.

14. The system according to claim 13 comprising a further aircraft wherein the further aircraft comprises the transmitter.

15. A system for determining a relative position between a target and a transmitter in an area, wherein relative position is defined by the parameters relative angular direction 1, 2 and distance, the system comprising a transmitter configured to generate light beams wherein the generation of the one or more light beams comprises diffracting broadband light in such a way that different optical frequency wavelengths are diffracted differently and a relative angular direction is detected by reading the optical frequency wavelength, the transmitter comprising one or more broadband light sources, one or more diffraction gratings, and a target comprising two or more receptors, means in connection with the two or more receptors, said means configured to determine the two or more relative angular directions 1, 2 by reading two or more optical frequency wavelengths by a method comprising the steps of: producing one or more light beams, transmitting, by the transmitter, such one or more light beams, wherein a light beam indicates a relative angular direction from the transmitter, receiving, by the target, one or more of the light beams, wherein the generation of the one or more light beams comprises diffracting broadband light in such a way that different optical frequency wavelengths are diffracted differently and a relative angular direction is detected by reading the optical frequency wavelength, and means configured to determine the distance between the target and the transmitter by triangulation, given a predetermined distance between the two or more receptors and the two or more relative angular directions 1, 2.

16. A system according to claim 13 wherein the broadband light source comprises: a monomode light source, and one or more optical frequency comb generators, configured to receive the light from the monomode light source, and the optical frequency wavelength is related to an electronic frequency which is received by the receptor.

17. The system according to claim 16 wherein the monomode light source comprises a laser light source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other characteristics and advantages of the invention will become clearly understood in view of the detailed description of the invention which becomes apparent from a preferred embodiment of the invention, given just as an example and not being limited thereto, with reference to the drawings.

(2) FIG. 1 shows a system according to the invention.

(3) FIG. 2 represents a diffraction grating and the principle of reflection of two parallel rays, and the influence of the wavelength of the incident light in the reflection angle.

(4) FIG. 3 shows the transmitter part of a system according to the invention.

(5) FIG. 4 represents the optical spectrum of the dual-comb source and the received frequency associated to the mixing of the superimposed lobes shown in the figure as f=.sub.r1.sub.r2<<.sub.r1,.sub.r2

(6) FIG. 5A shows a transmitter and an active detector according to the invention.

(7) FIG. 5B shows a transmitter and a passive detector according to the invention.

(8) FIG. 6 shows a system according to the invention where the distance is calculated by a method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) The examples below relate generally to a system for the determination of angular and relative positions between two objects, particularly between a target (1) and transmitter (2).

(10) Transmitter and Receiver

(11) FIG. 1 represents a transmitter 2, which may be installed on tanker aircraft, and a receiver (1).

(12) The transmitter (2) comprises

(13) a broadband light source (4) comprising

(14) a monomode light source (41),

(15) an optical frequency comb generator OFCG (42), configured to receive the light (10) from the monomode light source (41), and configured to generate the multimode light (5) or optical frequency comb (5).

(16) one or more diffraction grating (25), configured to receive the Optical Frequency Comb (5) from the OFCG (42).

(17) In a particular example, the transmitter (2) comprises the following features (in one axis):

(18) 35 cone coverage

(19) Angular resolution=0.005 to 30 meters (7000 lobes are estimated)

(20) Opening of the lobe in the orthogonal direction=35

(21) Transmission of signal in the optical domain, particularly in the infrared range used for optical communications (Wave length=1550 nm). This provides several benefits:

(22) Low cost associated to the use of communications components,

(23) High spatial resolution (angular) due to the low wavelength used,

(24) Wave length traditionally Eye-safe.

(25) The receiver (1) in FIG. 1 comprises

(26) a receptor (26), with the capacity to read the incident light wavelength (spectrometer) configured to receive one or more light beams (3) from one or more diffraction grating (25),

(27) means (29) for determining the relative angular direction by reading the incident light wavelength in connection with the receptor (26).

(28) The transmitter (2) is configured to produce of the one or more light beams (3) and at least two optical frequency combs in a dual Optical Frequency comb configuration:

(29) a first optical frequency comb and

(30) a second optical frequency comb,

(31) first and second frequency combs comprising the same fo and comprising respective .sub.r1 and .sub.r2 where .sub.r1 is different from .sub.r2, and

(32) wherein

(33) .sub.r1, .sub.r2 is the comb tooth spacing or mode repetition rate,

(34) .sub.0 is the carrier offset frequency.

(35) The described example uses a high-frequency modulation. The frequencies used in this example are:

(36) .sub.0=200 THz (=1500 nm, telecom wavelength).

(37) .sub.r1=10 GHz,

(38) .sub.r2=10.00001 GHz,

(39) Being such a small difference frequencies, the wavelengths of both combs are identical from the point of view of diffraction (/<<1) so the analysis for only one of them may be performed as follows, for example for a central wavelength of 1550 nm, and having regard of FIG. 2.

(40) In FIG. 2 a diffraction grating functioning in reflection is shown. Given a standard grating of 1000 lines/mm (d=1 mm), for the given central wavelength the grating equation indicates that d(sin +sin =); given c=*f; /, and f=.sub.r1.sub.r2=10 GHz results in 0.1 mrad. Therefore 0.1 mrad per line=0.005 per grid line. The fact that the separation between two lobes (m, m+1) is 0.1 mrad implies that 35/0.005=7000 lines are required at least to have a measurement range of 35. As the angular separation is given by .sub.r1 and .sub.r1 (that can be adjusted), the invention allows reducing the number of grid lines required by having =1 mrad, either changing .sub.r1 and .sub.r1 or using various gratings in cascaded to increase the divergence angle.

(41) Transmitter

(42) FIG. 3 shows a series of entities which may be comprised in a system according to the invention, in the transmitter (2). FIG. 3 shows:

(43) a light source (41),

(44) a dual optical frequency comb generator OFCG (42), configured to receive the light (10) from the light source (41),

(45) one or more diffraction grating (25), configured to receive one or more dual Optical Frequency Comb (5) from the OFCG (42),

(46) a grid generator (27), for example a couple of cylindrical lenses, from which a grid (9) is formed.

(47) Other Data for the Transmitter

(48) issued Power: 5 W

(49) Number of lines: 700

(50) losses in the optical: 10 dB

(51) divergence collimator: 0.047

(52) spot width in the orthogonal direction (35 to 30 m): 9.46 m

(53) output spot diameter: 12 mm

(54) spot size on detection: 769460 mm

(55) With these data, the power received in reception may be: Prec=75 nW.

(56) In a particular example, the transmitter may comprise an acousto-optic modulator in the OFCG in such a manner that it inserts an offset frequency, f.sub.AOM, so that in the direction =0 the detector would solve a positive frequency instead of a frequency of 0 Hz.

(57) Receiver

(58) In detection the two Optical Frequency Combs (5) are overlapped, or the wavelengths of both combs are identical from the point of view of diffraction (/<<1), so the actual electronic frequency detected (in the case of using an acousto-optic modulator) is fout=.sub.AOM+m (.sub.r1.sub.r2)=.sub.AOM+m 10 kHz. This is represented in FIG. 4, where m represents the modes or colors of the received light. For example, for m=0, the yellow color is obtained by detecting a frequency of fout=.sub.AOM, so that it would mean an angular position respective to yellow color. For m=1 the orange would be obtained, so it is possible to know the color and therefore the direction by detecting the frequency fout=.sub.AOM+m 10 KHz.

(59) The recovering of the electronica frequency (fout) will be implemented digitally using an FPGA with implementing FFTs.

(60) Extraction of Yaw and Roll.

(61) In a first approximation, there are two possible alternatives to implement a two-axis, i.e., to extract information uniquely yaw and roll.

(62) 1. Wavelength Division: In this case two combs may be used on two different wavelengths (1550 nm and 1310 nm to leverage standard communications components). This approach requires different listeners for each of the axes, which doubles the detection electronics.

(63) 2. Division in the frequency domain: In this case the two dual combs produce different outputs fout: fout=.sub.AOM+m (.sub.r1.sub.r2)=.sub.AOM+m 10 kHz. (10, 20, 30 KHz for the first dual comb or axis) and fout=.sub.AOM+5 kHz+m 10 KHz (15, 25 kHz for the second dual comb or axis) may be used. This would bring the following implications:

(64) same sensors and the same detection electronics may be used (no need to double the detection system);

(65) the detection electronics need to be modified slightly increasing its frequency resolution (larger FPGA), however this can help with aspects associated to noise bandwidth;

(66) it is highly desirable to synchronize the transmitter and receiver.

(67) FIG. 5A shows an example of the relative angular direction being determined by a target, an aircraft (28), receiving the one or more light beams (3). This is the case of having an active target in the aircraft (28), where the target is able to know its position and the position is forwarded by the active target or aircraft (28) to the transmitter (2), which may be a further aircraft, for both to know the position.

(68) FIG. 5B shows an example of the relative angular direction being determined by the transmitter (2) receiving the reflection of the one or more light beams (3) from the target (28). This allows the use of passive targets. This embodiment is opposite or complementary to the previous case. In the case of having a passive target in FIG. 5B, the target reflects the beam; a detector in the transmitter (2) receives the reflection of the passive target with no need of forwarding the beam (3) by any active target.

(69) Third Dimension (z).

(70) The proposed system is able to provide with two coordinates (yaw and roll), a third coordinate (distance) to be necessary to obtain the position of the object. This is represented in FIG. 6 where a system (30) for determining a relative position between a target (1) and a transmitter (2). In this example the relative position is defined by the parameters relative angular direction (1, 2) and distance (d).

(71) FIG. 6 shows a system (30) comprising

(72) a transmitter (2) and

(73) a target (1) comprising two receptors (7, 8), for example photodiodes.

(74) The system (30) in FIG. 5 further comprises

(75) means (31) in connection with the two or more receptors (7, 8), said means (31) configured to determine two or more relative angular directions 1, 2 by reading two or more electronic frequencies, and

(76) means (32) configured to determine the distance (d) between the target (1) and the transmitter (2) by triangulation, given a predetermined distance (6) between the two or more receptors (7, 8) and the two or more relative angular directions 1, 2.

(77) Advantages

(78) Some of the advantages of a method according to the invention are:

(79) quick measurements since an electronic frequency is to be detected instead of scanning a laser light; this entails that it is possible to detect several targets in a short period of time;

(80) possibility of working with passive receptors;

(81) It may allow guidance of an aircraft during the approach path to a tanker aircraft;

(82) The size of the detected object is no relevant in the case of an active detector;

(83) In the case of a passive target the receiver may comprise a retroreflector for avoiding the whole aircraft reflecting a wide area of beams (3). The retroreflector may be mounted, for example on the wings of the airplane to provide with the two locations to extract also the third dimension.

(84) While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.