Optical pulse radar for an automotive vehicle

• US 4,552,456 A
• Filed: 08/26/1982
• Issued: 11/12/1985
• Est. Priority Date: 10/31/1981
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Endo, Hiroshi
• Primary Examiner(s): Buczinski, S. C.
• Assistant Examiner(s): Sotomayor, John B.
• Application Number:
  US06/411,813
• Time in Patent Office: 1,174 Days
• Field of Search: 356/5, 356/28, 356/28.5, 343/9 PS, 343/10, 343/12 R
• US Class Current: 356/5.06
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4817 relating to scanning

Abstract

An optical pulse radar for an automotive vehicle of heterodyne detection-type which can detect an object ahead of the vehicle with an improved S/N radio even under the worst detection conditions in which sunlight or a strong headlight beam from a car is directly incident thereupon. The optical pulse radar according to the present invention comprises a laser system, a beam splitter for obtaining a carrier beam and a heterodyne beam, a beam deflector, a beam modulator, a beam mixer for obtaining a beat beam signal, a beam sensor and, a beat signal processing section, etc. An optical IC may incorporate the beam splitter and mixer, the beam modulator, and the beam deflector in order to miniaturize the system, while improving the sensitivity, reliability, massproductivity, and cost.

Claims

1. An optical pulse radar for an automotive vehicle for detecting an object outside of the vehicle, which comprises:

(a) beam transmitting means for generating a coherent beam, splitting the generated beam into a carrier beam B_C and a heterodyne beam B_H, deflecting the carrier beam B_C by a frequency f_o in response to a high frequency signal e_f to generate a deflected carrier beam B_F modulating the carrier beam B_F to a pulse laser beam B_T with a pulse width t_w in response to a pulse-modulating signal e_m, and transmitting the carrier beam B_T in a predetermined direction at a beam divergence angle B_T ;

(b) beam receiving means for receiving the beam transmitting from said beam transmitting means and reflected from the object and mixing the received beam B_R with the herterodyne beam B_H, and superheterodyning the mixed beam into a corresponding electrical interference beat signal e_b ;

(c) beat signal processing means connected to said beam transmitting means and said beam receiving means for amplifying the beat signal e_b falling within a predetermined frequency bandwidth to generate a detection signal e_d and calculating information with respect to the object on the basis of the trigger signal e_t and the detection signal e_d.

2. An optical pulse radar for an automotive vehicle as set forth in claim 1, wherein said beam transmitting means comprises:

(a) a laser system for generating a coherent beam with frequency f₁ ;

(b) a beam splitter connected to said laser system optically for splitting the coherent laser beam into a carrier beam B_C and a heterodyne beam B_H and outputting the carrier beam B_C and the heterodyne beam B_H, respectively;

(c) a high-frequency signal generator for outputting a high-frequency signal e_f with frequency f_o ;

(d) a beam deflector connected to said beam splitter optically and to said high-frequency signal generator electrically for deflecting the carrier beam B_C in response to the high-frequency signal e_f and outputting a transmission beam B_T with a frequency f_T =f₁ +f_o ;

(e) a pulse modulator for outputting a pulse-modulating signal e_m ;

(f) a beam modulator connected to said beam deflector optically and said pulse modulator electrically for modulating the carrier beam in response to the pulse-modulating signal e_m and outputting a pulsed transmission beam B_T ; and

(g) a beam transmitting device connected to said beam modulator optically for transmitting the transmission carrier beam B_T.

3. An optical pulse radar for an automotive vehicle as set forth in claim 1, wherein said beam transmitting means comprises:

(a) a laser system for generating a coherent beam with frequency f₁ ;

(b) a beam splitter connected to said laser system optically for splitting the coherent laser beam into a carrier beam B_C and a heterodyne beam B_H and outputting the carrier beam B_C and the heterodyne beam B_H ;

(c) a pulse modulator for outputting a pulse-modulating signal e_m ;

(d) a beam modulator connected to said beam splitter optically and said pulse modulator electrically for modulating the carrier beam in response to the pulse-modulating signal e_m and outputting a pulsed laser beam B_M ; and

(e) a high-frequency signal generator for outputting a high-frequency signal e_f with frequency f_o ;

(f) a beam deflector connected to said beam modulator optically and to said high-frequency signal generator electrically for deflecting the modulated carrier beam B_M in response to the high-frequency signal e_f and outputting a transmission carrier beam B_T with a frequency f_T =f₁ +f_o ;

(g) a beam transmitting device connected to said beam deflector optically for transmitting the transmission carrier beam B_T.

4. An optical pulse radar for an automotive vehicle as set forth in claim 1, wherein said beam receiving means comprises:

(a) a beam receiving device for receiving the beam reflected from the object;

(b) a beam mixer connected to said beam transmitting means and said beam receiving device optically for mixing the heterodyne beam B_H and the received beam B_R for interferometric processing; and

(c) a beam sensor connected to said beam mixer optically for transducing the mixed beam into a corresponding electrical beat signal e_b with frequency f_b =f_o +f_d.

8. An optical pulse radar for an automotive vehicle as set forth in claim 1, wherein said beat signal processing means comprises:

(a) an intermediate-frequency amplifier connected to a beam sensor, a central frequency f_o of which is the same as that of the high-frequency signal e_f, for amplifying the beat signal e_b and outputting signals corresponding thereto;

(b) a detector connected to said intermediate-frequency amplifier for detecting the amplified beat signal and outputting detection signal e_d corresponding thereto;

(c) a vehicle speed sensor for detecting an absolute vehicle speed and outputting a signal V_a corresponding thereto; and

(d) a data processing unit connected to said detector, said beam transmitting means, and said vehicle speed sensor for calculating a distance from the present vehicle position to an object, the relative vehicle velocity with respect to an object, and the direction to the object on the basis of the trigger signal e_t outputted from said beam transmitting means in synchronization with the pulse-modulating signal e_m, the detector signal e_d from said detector, and the absolute vehicle speed signal V_a, and outputting an audible alarm when the calculated distance between the vehicle and the object is below a predetermined reference value.

5. An optical pulse radar for an automotive vehicle for detecting an object outside of the vehicle, which comprises:

(a) beam transmitting means for generating a coherent beam, splitting the generated beam into a carrier beam B_C and a heterodyne beam B_H, modulating the carrier beam B_C to a pulse laser beam ^B T with a pulse width ^t w in response to a pulse modulating signal e_m, and transmitting the carrier beam ^B T in a predetermined direction at a beam divergence angle ^B T;

(b) beam receiving means for receiving the beam transmitted from said beam transmitting means and reflected from the object, deflecting the received beam B_R in accordance with a high-frequency signal e_f, mixing the deflected beam B_F with the heterodyne beam B_H, and superheterodyning the mixing beam into a corresponding electric beat signal e_b ; and

(c) beat signal processing means connected to said beam transmitting means and said beam receiving means for amplifying the beat signal e_b falling within a predetermined frequency bandwidth to generate a detection signal e_d and calculating information with respect to the object on the basis of the trigger signal e_t and the detection signal e_d.

6. An optical pulse radar for an automotive vehicle as set forth in claim 5, wherein said beam transmitting means comprises:

(a) a laser system for generating a coherent beam with frequency f₁ ;

(b) a beam splitter connected to said laser system optically for splitting the coherent laser beam into a carrier beam B_C and a heterodyne beam B_H and outputting the carrier beam B_C and the heterodyne beam B_H ;

(c) a pulse modulator for outputting a pulse-modulating signal e_m ; and

(d) a beam modulator connected to said beam splitter optically and said pulse modulator electrically for modulating the carrier beam in response to the pulse-modulating signal e_m and outputting a pulsed transmission beam B_T ; and

(e) a beam transmitting device connected to said beam modulator optically for transmitting the transmission carrier beam B_T.

7. An optical pulse radar for an automotive vehicle as set forth in claim 5, wherein said beam receiving means comprises:

(a) a beam receiving device for receiving the beam reflected from the object;

(b) a high-frequency signal generator for outputting a high-frequency signal e_f with frequency f_o ;

(c) a beam deflector connected to said beam receiving device optically and to said high-frequency signal generator electrically for deflecting the received beam B_R in response to the high-frequency signal e_f and outputting a frequency-converted beam B_F with frequency f_f =f₁ +f_o ;

(d) a beam mixer connected to said beam transmitting means and said beam deflector optically for mixing the heterodyne beam B_H and the frequency-converted received beam B_F for interferometric processing; and

(e) a beam sensor connected to said beam mixer optically for transducing the mixed beam into a corresponding electric beat signal e_b with a frequency f_b =(f_o +f_d).

9. An optical pulse radar for an automotive vehicle for detecting an object outside of the vehicle, which comprises:

(a) a laser system for generating a coherent beam with a frequency f₁ ;

(b) a pulse moderator for outputting a pulse-modulating signal e_m ;

(c) a high-frequency signal generator for outputting a high-frequency signal e_f with a frequency f_o ;

(d) a beam transmitting device for transmitting a transmission beam B_T in a predetermined direction;

(e) a beam receiving device for receiving the beam B_R transmitted from said beam transmitting device and reflected from the object ahead of the vehicle;

(f) a beam sensor for transducing a laser beam signal into a corresponding electrical signal;

(g) an optical integrated circuit connected to said laser system, said beam transmitting device, said beam receiving device, and said beam sensor optically and connected to said pulse modulator and said high-frequency signal generator electrically, for splitting the coherent laser beam outputted from said laser system into a carrier beam B_C and a heterodyne beam B_H, for deflecting the carrier beam B_C into a pulsed carrier beam B_M in response to a pulse-modulating signal e_m outputted from said pulse modulator, deflecting the pulsed carrier beam B_M with frequency f₁ into a pulsed transmission beam with frequency (f₁ +f_o) in response to the high-frequency signal e_f, for transmitting a pulsed transmission beam with frequency (f₁ +f_o) via said beam transmitting device in a predetermined direction, for receiving a beam B_R with frequency (f₁ +f_o +f_d) from said beam receiving device, for mixing the received laser beam B_R with the heterodyne beam B_H for interferometric processing, and for outputting the mixed beam to said beam sensor for superheterodyning the mixed beam into a corresponding electric signal e_b with a frequency (f_o +f_d), and

(h) a heat signal processing section connected to said beam sensor and said pulse modulator for amplifying the beat signal e_b falling within a predetermined frequency bandwidth, processing the amplified beat signal to generate a detection signal e_d and calculating a distance from the present vehicle position to an object, the relative vehicle velocity with respect to an object, and the orientation to the object on the basis of a trigger signal e_t outputted from said pulse modulator in synchronization with the pulse-modulating signal e_m, a detection signal e_d and the current vehicle speed V_a.

10. An optical pulse radar for an automotive vehicle as set forth in claim 9, wherein said optical integrated circuit comprises:

(a) a combined directional coupler-type beam splitter and beam mixer having;

(1) a first optical waveguide, one end of which is connected to said laser system optically to conduct the laser beam as the carrier beam B_C ;

(2) a U-shaped second optical waveguide, one straight portion of which is disposed adjacent parallel to said first optical waveguide with a predetermined distance therebetween for receiving part of the laser beam introduced to said first optical waveguide, to generate the heterodyne beam B_H ; and

(3) a third optical waveguide, one end of which is connected to said beam sensor and the other end of which is connected to said beam receiving device optically, the other straight portion of said U-shaped second optical waveguide being disposed near and parallel to said third optical waveguide with a predetermined distance therebetween for mixing the heterodyne beam B_H introduced to said U-shaped second optical waveguide with the received laser beam B_R introduced to said third optical waveguide via said beam receiving device to generate a beat beam;

(b) a beam modulator having;

(1) a fourth waveguide one end of which is connected to said first optical waveguide directly for receiving the carrier beam B_C ;

(2) a fifth waveguide disposed near and parallel to said fourth waveguide for transmitting the pulsed transmission beam B_T ;

(3) a planar electrode formed on said fourth waveguide;

(4) a grounded electrode formed on said fifth waveguide;

(5) a pair of conductors connected to said planar electrode at an appropriate distance therebetween and to said pulse modulator for applying the pulse-modulating signal e_m to said planar electrode, whereby transmission of transmitted beam B_T is prevented or passed in response to pulses of the pulse-modulating signal e_m ; and

(c) a beam deflector having;

(1) a thin film serving as an optical waveguide and a high-frequency acoustical signal medium;

(2) a transducer in contact with said thin film and connected to said high-frequency signal generator for transducing the high-frequency signal e_f with a frequency f_o into corresponding acoustical waves and transmitting the waves through said thin film; and

(3) a recessed waveguide formed at the center of said thin film for conducting a laser beam with frequency f₁ therethrough in a direction perpendicular to the propagation of the acoustical waves so as to convert the incident beam into a frequency-converted laser beam B_F1 with a frequency (f₁ +f_o); and

(4) a grating decoupler formed on said recessed waveguide for diffracting the frequency-converted laser beam B_F1.

11. A method of detecting an object ahead of an automotive vehicle, which comprises the following steps of:

(a) generating a coherent beam with frequency f₁ ;

(b) splitting the coherent laser beam into a carrier beam B_C and a heterodyne beam B_H ;

(c) deflecting the frequency of the carrier beam B_C in response to a high-frequency signal e_f with a frequency f_o into a frequency-converted beam B_F with frequency (f₁ +f_o);

(d) modulating the frequency-converted beam B_F in response to a pulse-modulating signal e_m into a transmission beam B_T ;

(e) transmitting the transmission beam B_T ;

(f) receiving the beam with a frequency (f₁ +f_o +f_d) after transmission and reflection from the object;

(g) mixing the received beam B_R with the heterodyne beam to obtain a beat beam;

(h) transducing the mixed beat beam into the corresponding electric beam signal e_b with frequency (f_o +f_d);

(i) calculating a distance to an object, the relative vehicle velocity with respect to the object, and a direction to the object on the basis of a trigger signal e_t outputted in synchronization with the pulse-modulated signal e_m, the transduced beat signal e_b, and the current vehicle speed V_a.

13. A method of detecting an object ahead of an automotive vehicle as set forth in claim 11, wherein the step of splitting the coherent laser beam into the carrier beam and the heterodyne beam and the step of mixing the received beam with the heterodyne beam are performed by means of optical directional coupling.

14. A method of detecting an object ahead of an automotive vehicle as set forth in claim 11, wherein the step of modulating the carrier beam into a pulsed transmission beam is performed by means of an electrooptical effect by which the refractive index of a medium through which the beam is travelling can be changed according to an intensity of an electric field applied to the medium.

15. A method of detecting an object ahead of an automotive vehicle as set forth in claim 11, wherein the step of deflecting the carrier beam is performed by means of an acoustooptical effect by which the refractive index of a medium through which the beam is travelling can be changed by surface compressional acoustical waves and thereby the beam incident upon the medium, at an angle satisfying Bragg condition is diffracted and boosted by a frequency equal to the frequency of the acoustical waves.

12. A method of detecting an object ahead of an automotive vehicle, which comprises the following steps of:

(a) generating a coherent beam with a frequency f₁ ;

(b) splitting the coherent laser beam into a carrier beam B_C and a heterodyne beam B_H ;

(c) modulating the the carrier beam B_C in response to a pulse-modulating signal e_m into a pulse-modulated transmission beam B_T ;

(d) transmitting the transmission beam B_T ;

(e) receiving the beam B_R with a frequency (f₁ +f_d) after transmission and reflection from the object;

(f) modulating the frequency of the received beam B_R in rsponse to a high-frequency signal e_f with frequency f_o into a frequency-converted beam B_F with frequency (f₁ +f_o +f_d);

(g) mixing the frequency-converted beam B_F with the heterodyne beam to obtain a beat beam;

(h) transducing the mixed beat beam into the corresponding electric beam signal e_b with frequency (f_o +f_d);

(i) calculating a distance to an object, the relative vehicle velocity with respect to the object, and a direction to the object on the basis of a trigger signal e_t outputted in synchronization with the pulse-modulated signal e_m, the transduced beat signal e_b, and the current vehicle speed V_a.