Abstract:
The optic coupling device comprises optic emitting elements arranged in a coating material to emit a first light signal to an optic duct, and optic receiving elements separated from the emitting elements to receive a second light signal from the optic device. To improve the efficiency and simplify manufacturing, the optic receiving elements receive the second light signal through the coating material. An optic probe comprises the optic coupling device, an optic sensor, and an optic duct joining the coupling device and the sensor to transmit a first light signal to the sensor and to receive a second light signal to the coupling device. The communication device comprises two stations connected by an optic duct and comprising coupling devices.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to an optic coupling device comprising optic emitting means arranged in a coating material to transmit a first light signal to an optic duct, and optic receiving means separated from the emitting means to receive a second light signal. 
   The invention also relates to an optic probe comprising an optic coupling device, an optic sensor, and an optic duct connecting the coupling device and the sensor to transmit a first light signal to the sensor and to send a second light signal back to the coupling device. 
   The invention also relates to a communication device comprising a first station and a second station joined by an optic duct and designed to transmit and receive information or data by light signals circulating in said optic duct. 
   STATE OF THE ART 
   A state-of-the art coupling device, notably used in probes, is represented in  FIG. 1 . It comprises emitting means  1  to transmit a first light signal  2  to a first optic fiber  3 , and receiving means  4  to receive a second light signal  5  from a second optic fiber  6 . The two fibers can be grouped together in a single duct  7  directed for example towards a sensor  8  reacting to the light signals. 
   Another state-of-the-art coupling device is represented in  FIG. 2 . It comprises emitting means  1  to transmit a first light signal  2  to an optic separator  9  and receiving means  4  to receive a second light signal  5  from the optic separator  9 . The optic signals  2  and  5  are carried by a fiber or an optic duct  10  directed towards a sensor  8 . The separator  9  generally comprises a semi-reflecting blade  11  allowing the first light signal coming from the emitting means to pass and the second light signal to be reflected to the receiving means. Thus, the first light signal is emitted by the emitting means  1 , passes through the separator  9  passing from the rear of the blade  11  to the front, then passes via the duct  10  to the sensor  8 . In return a second signal  5  is sent back by the sensor  8  to the duct  10  and separator  9 , then the signal  5  is reflected by the front face of the blade  11  to the receiving means  4 . 
   A probe comprising such optic coupling devices is described in Patent application EP-0,940,655. 
   State-of-the-art optic coupling devices require the light signal paths to be doubled up either by coupling of the optic fibers or by using an optic separator. These solutions are often difficult to implement efficiently. Furthermore, the optic efficiencies of the light signal transmission channels are very low. 
   Electro-optic components exist comprising emitting means and receiving means in a single housing, however the operating wavelengths of these components are often incompatible with uses in probes or with sensors. Choosing the wavelengths of the emitting means and receiving means is not possible on already associated components. Moreover, these specific components have low efficiencies due in particular to the dispersion of the optic beams on output of the fibers. They also require precise positioning of the fibers and sometimes the use of optic lenses to direct the beams towards the electro-optic components. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to provide an optic coupling device enabling an improved efficiency and avoiding the manufacturing problems of state-of-the-art devices. The object of the invention is also to achieve a probe and a communication device comprising such a coupling device. 
   In a coupling device according to the invention, the optic receiving means are arranged in such a way as to receive the second light signal through said coating material of the optic emitting means. 
   In a preferred embodiment, the optic receiving means, the optic emitting means, and an input of said optic duct are appreciably aligned. 
   Preferably, the coupling device comprises control means to control the optic emitting means and the optic receiving means alternately. 
   Advantageously, the optic emitting means are appreciably transparent to the wavelength of the second light signal, the optic receiving means being arranged to receive the second light signal through said coating material and through said optic emitting means. 
   Preferably, the optic emitting means and the optic receiving means are coated in the same material transparent to the wavelengths of said emitting means and of said receiving means. 
   In a preferred embodiment, the coupling device comprises a light guide arranged between the coating material and the optic receiving means to conduct the second light signal to the optic receiving means. 
   Advantageously, the light guide is made from the same material as the coating material of the optic emitting means. 
   In a preferred embodiment, the coupling device comprises an optic filter arranged between the coating material and the optic receiving means to filter the second light signal. 
   Preferably, the optic emitting means are arranged on a first face of a printed circuit and the optic receiving means are arranged on a second face of said printed circuit, said printed circuit comprising an opening between the optic emitting means and the optic receiving means. 
   Preferably, the optic emitting means and the optic receiving means operate by frequency modulation of the first optic signal and frequency demodulation of the second optic signal. 
   In a preferred embodiment, the coupling device comprises electronic filtering means connected between the optic receiving means and the control means to extract a variable signal from a carrier signal. 
   Advantageously, the optic receiving means comprise at least one receiver and the optic emitting means comprise at least two sequentially controlled emitters to emit at least two first signals having two different wavelengths. 
   For example, the at least two different wavelengths enable a color to be detected. 
   In an optic probe according to the invention comprising an optic coupling device, an optic sensor, and an optic duct joining the coupling device and the sensor to emit a first light signal to the sensor and to return a second light signal to the coupling device, the coupling device is a coupling device as defined above transmitting the first light signal to the sensor and receiving the second light signal from said sensor. 
   Advantageously, the optic duct is composed of a single optic fiber arranged between the sensor and the coupling device to conduct the first light signal and the second light signal. 
   In a preferred embodiment, the sensor is made of light-emitting material excited by the first light signal output from the optic duct and returning the second light signal to said optic duct. 
   For example, the sensor sends back to the optic duct a second optic signal of decreasing intensity after lighting by the first optic signal, the second signal having a different wavelength from the wavelength of the first signal. 
   Advantageously, the sensor returns to the optic duct a second optic signal modulated according to movement or vibration of said sensor. 
   In a preferred embodiment, the optic emitting means comprise at least two emitters to sequentially transmit to the sensor at least two first light signals having two different wavelengths to detect a color or a color change of said sensor, said sensor returning at least two second light signals in response to said two first light signals. 
   In a communication device according to the invention comprising a first station and a second station joined by an optic duct and designed to transmit and receive information or data by light signals circulating in said optic duct, the first station and the second station comprising at least one coupling device as defined above, a first optic signal emitted by emitting means of a first coupling device of the first station being received as a second optic signal by receiving means of a second coupling device of the second station, and a first optic signal emitted by emitting means of a second coupling device of the second station being received as a second optic signal by receiving means of a first coupling device of the first station. 
   Preferably, a first coupling device of the first station comprises a first optic filter arranged between the emitting means and the receiving means to let an optic signal emitted by emitting means of a second coupling device pass and to attenuate an optic signal having a wavelength equal or very close to the wavelength of a signal emitted by the emitting means of said first coupling device. 
   Preferably, a second coupling device of the second station comprises a second optic filter arranged between the emitting means and the receiving means to let an optic signal emitted by emitting means of a first coupling device pass and to attenuate an optic signal having a wavelength equal or very close to the wavelength of a signal emitted by the emitting means of said second coupling device. 
   Advantageously, at least one coupling device comprises modulating means to modulate in a first frequency band the first light signal designed to be emitted by the emitting means of said at least one coupling device and detecting means to detect a second light signal able to be received by the receiving means and modulated in a second frequency band. 
   Advantageously, the optic duct is an optic fiber connected between the first coupling device and the second coupling device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention given as non-restrictive examples only and represented in the accompanying drawings in which: 
       FIGS. 1 and 2  represent state-of-the-art optic coupling devices; 
       FIG. 3  represents a coupling device according to an embodiment of the invention; 
       FIG. 4  represents a coupling device according to an embodiment of the invention with an emitting diode and a receiving diode; 
       FIG. 5  represents a coupling device according to an embodiment of the invention with mounting on a printed circuit; 
       FIG. 6  represents a coupling device according to an embodiment of the invention with an optic guide; 
       FIG. 7  represents a coupling device according to an embodiment of the invention with an optic filter; 
       FIG. 8  represents different wavelengths of the optic signals; 
       FIG. 9  represents shapes of optic signals in a probe comprising a coupling device according to the invention; 
       FIG. 10  represents a vibration detection probe comprising a coupling device according to an embodiment of the invention; 
       FIG. 11  represents a color detection probe comprising a coupling device according to an embodiment of the invention; 
       FIGS. 12 and 13  represent communication devices comprising coupling devices according to embodiments of the invention; 
       FIGS. 14A and 14B  represent signals in communication devices comprising coupling devices according to embodiments of the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In an optic coupling device  14  according to an embodiment of the invention represented in  FIG. 3 , the emitting means comprise an emitter  1  to emit a first optic signal  2  having a first wavelength to an optic duct  12 , for example an optic fiber. The signal  2  passes through a coating material  13  of the emitter which enables the emitter  1  and optic fiber  12  to be kept in the optimum position for good efficiency. The coating material is preferably a solid and translucent broadband material enabling light signals of different color or wavelengths to pass through easily. The receiving means comprise a receiver  4  arranged so as to receive through said coating material  13  a second signal  5  generally of different wavelength from the first signal. This second signal  5  coming from the fiber  12  passes through the coating material  13  of the emitter and reaches the receiver  4 . For example the emitter and receiver are appreciably aligned or slightly offset for good coupling with the optic fiber. 
   When the device is used in a probe, the signal  2  is sent for example to a sensor  8  which returns a second signal  5  after having been excited by the signal  2 . The signal  5  returns through the fiber to the coating material  13  of the emitter, passes through said material and is detected by the receiver  4  with good efficiency. This device avoids doubling-up of the optic fibers and the use of semi-reflecting plates. 
   A control circuit  15  is connected to the emitter  1  and receiver  2  to control emission and receipt of the light signals. Preferably the emitter  1  sends the first signal  2  and the receiver  4  receives the second signal  5  in alternate manner. 
   Advantageously, the emitter is chosen from a component appreciably transparent to the wavelength of the second signal. In this case, the receiver is arranged in such a way as to receive the second light signal coming from the optic fiber through the coating material and through the emitter  1 . It is also possible to fit the receiver between the input of the optic fiber and the emitter. The receiver can then be transparent to the wavelength of the first light signal. 
   In  FIG. 4 , the emitter  1  is represented by an emitting diode  1  and the receiver  4  is represented by a light signal detection diode. These two components can be coated in the same coating material  13  to emit and receive the light signals  2  and  5 . 
     FIG. 5  shows a practical realization of a coupling device according to an embodiment of the invention. The emitter is a light signal emitting component such as a light-emitting diode  16  emitting in a preset wavelength. The emitting part  1  of the diode  16  is housed in a translucent or transparent housing acting as coating material  13 . The housing comprises an orifice  17  to keep the optic fiber in an aligned position close to the emitting part  1 . The diode  16  is arranged on a first face  18  of a printed circuit  19  comprising an opening  20  at the rear of the diode opposite the orifice  17 . The receiver is a photosensitive component  21  such as a diode or a phototransistor arranged on a second face  22  of the printed circuit  19  appreciably in the alignment of the optic fiber and the diode  16 . 
   The components  16  and  21  are preferably mounted and soldered on the faces of the printed circuit like surface-mounted components. To prevent the second signal  5  from being dispersed in the air between the component  16  and the component  21 , a small light guide  23  can advantageously be arranged between the two components  16  and  21 . The second signal  5  coming from the optic fiber  12  passes through the material  13  represented by the housing of the diode  16 , the passes through the guide  23  and reaches the component  21  comprising the receiver  4 . 
   In  FIG. 6 , the component  21  comprising the receiver  4  is arranged in remote manner. A light guide  24  is then arranged between the rear of the component  16  and the component  21  to conduct the second light signal from the material  13  of the housing of the component  16  to the component  21 . Preferably, the light guides  23  and  24  are made from the same material as the coating material  13 . 
   In  FIG. 7 , an optic filter  25  is arranged between the coating material  13  and the component  21  comprising the receiver  4  to let the second signal  5  pass and to stop signals having other wavelengths. Thus, the second signal returning from the sensor  8  is conducted by the optic fiber  12 , passes through the coating material  13 , passes through the optic filter  25  and reaches the receiver  4  of the component  21 . Stray light rays having different wavelengths from that of the second signal are thus stopped or attenuated. 
     FIG. 8  shows spectral curves of a first signal  2  and a second signal  5 . For example, the first signal  2  has a color or a main wavelength L 2  and a high amplitude, and the second signal  5  has a color or a main wavelength L 5  and a lower amplitude. The wavelengths L 2  and L 5  are different. The wavelengths L 2  and L 5  can be central or main frequencies of the signals  2  and  5  modulated in amplitude or frequency. For example, the emitting means can operate in frequency modulation and the receiving means can operate in frequency demodulation. Modulation and demodulation can also be performed with a centralized control circuit and/or associated electronic circuits. 
     FIG. 9  shows curves of a first signal  2  and a second signal  5  versus time. For example, the first signal  2  has a rectangular shape forming crenellations where a top part represents the presence of light, between times t 1  and t 2 , and the bottom part represents the absence of light, between the time t 2  and a time t 3 . In a sensor  8  made of light-emitting or fluorescent material, the second signal  5  has an intensity that increases in the presence of the first signal  2 , and an intensity that decreases when the signal  2  reaches zero or a very low value. In a temperature sensor where the sensor is for example ruby or alexandrite, the decreasing part of the signal  5  is representative of the value of the temperature. Thus, the control means command excitation of the sensor between the times t 1  and t 2  by emission of the signal  2 , and activate receipt and acquisition and/or measurement of the signal  5  to determine a temperature value, notably between the times t 2  and t 3 . 
     FIG. 10  represents a vibration detection probe comprising a coupling device  14 . The sensor  8  then enables mechanical vibrations to be detected, in particular sounds, ultra-sounds, pressures, or movements. The optic coupling device emits a signal  2  to the sensor and receives a second signal  5  to the receiver  4  modulated according to the vibrations detected. The sensor can have the form of a deformable membrane having a reflecting face. An electronic filter  26  connected between the receiver  4  and the control circuit  15  lets the useful signal representative of the detected vibrations pass and reduces the other signals. 
     FIG. 11  represents a color detection probe comprising a coupling device according to a particular embodiment. To detect a color, the emitting means comprise at least two emitters to emit two first signals having two different wavelengths. The emitters are preferably controlled sequentially. In the diagram of  FIG. 11 , the emitting means comprise three emitters  1 A,  1 B and  1 C to sequentially emit three first signals respectively  2 A,  2 B and  2 C to the duct or the optic fiber  12 . In return, the sensor sends back sequentially on a second signal  5  responses from said sensor or a signal representative of the color detected. The sensor can be an object on which a color has to be detected or determined. Analysis by a control circuit  15  of information sequences of the signal  5  enables a color to be determined. 
   The three emitters can be incorporated in a single electronic component for example integrating light-emitting diodes of red, green and blue color. It is also possible to detect a color by having a single emitter emitting for example white light and to have three receivers sensitive to different wavelengths or each comprising a different filter to determine the color of the sensor. 
     FIG. 12  shows a communication device  27  comprising a first station  28  and a second station  29  joined by an optic duct  12  and designed to emit and receive information or data by light signals  30  and  31  flowing in said optic duct. The first station  28  and second station  29  comprise at least one coupling device as defined in embodiments described above. A first optic signal  30  emitted by emitting means  1  of a first coupling device  14 A of the first station  28  is received as a second optic signal  5  by receiving means  4  of a coupling device  14 B of the second station  29 . A first optic signal  31  emitted by emitting means of a second coupling device  14 B of the second station  29  is received as a second optic signal  5  by receiving means  4  of a coupling device  14 A of the first station  28 . 
   To communicate efficiently, the first coupling device  14 A of the first station  28  comprises a first optic filter  32  arranged between the emitting means  1  and the receiving means  4  to let an optic signal emitted by emitting means  1  of a second coupling device  14 B pass and to attenuate an optic signal having a wavelength equal or very close to the wavelength of a signal emitted by the emitting means of the first coupling device  14 A. 
   Likewise, the second coupling device  14 B of the second station  29  comprises a second optic filter  33  arranged between the emitting means  1  and the receiving means  4  to let an optic signal emitted by emitting means of a first coupling device  14 A pass and to attenuate an optic signal having a wavelength equal or very close to the wavelength of a signal emitted by the emitting means of the second coupling device  14 B. 
   For example, the first emitting means of the first coupling device  14 A can be a light-emitting diode emitting in the green and the first emitting means of the second coupling device  14 B can be a light-emitting diode emitting in the red. Thus, the first optic filter  32  blocks the green light rays and lets the red light rays pass whereas the second optic filter  33  blocks the red light rays and lets the green light rays pass. Preferably, the light-emitting diodes emit in the red or green but comprise a transparent or colourless plastic housing. 
     FIG. 13  shows communication devices also able to operate without optic filters. In this case, for example a coupling device  14 A comprises a modulation circuit  34  to modulate the first light signal  30  designed to be emitted by emitting means  1  of said first coupling device  14 A in a first frequency band F 1  and detecting means  35  to detect a second light signal able to be received by the receiving means  4  and modulated in a second frequency band F 2 . The second coupling device  14 B comprises a modulation circuit  36  to modulate the second light signal  31  designed to be emitted by emitting means  1  of said second coupling device  14 B in the second frequency band F 2  and detecting means  37  to detect a first light signal  30  able to be received by the receiving means  4  and modulated in the first frequency band F 1 . 
     FIGS. 14A and 14B  illustrate frequency operating bands of the emitting, receiving and detecting means, and of the modulation or demodulation circuits. In  FIG. 14A , the first coupling device  14 A emits in a frequency band FBE tuned to the frequency F 1 , and receives on a frequency band FBR tuned to the frequency F 2 . In  FIG. 14B , the second coupling device  14 B emits in a frequency band FBE tuned to the frequency F 2 , and receives on a frequency band FBR tuned to the frequency F 1 . Advantageously, the frequency bands on receipt are broader than the frequency bands on emission. The frequencies are sufficiently far apart not to interfere in case of two-way communication. 
   The optic duct is preferably an optic fiber connected between the first coupling device and the second coupling device but other ducts or guides may be used. 
   The receiving means can notably be photodiodes, phototransistors or photoresistors. The emitting and receiving means can for example be housed in locally open or transparent plastic or metallic housings. The component housings forming the coating material of the emitting means may comprise reflecting walls to improve the efficiency of emission and receipt.