FIELD OF THE FINDING

The present invention refers to the field of transmitting optical radiation and in detail regards a system of data transmission by means of optical radiation.

The present invention also regards a method of data transmission by means of optical radiation.

The present invention also regards data transmission and reception devices which exploit the abovementioned method.

STATE OF THE ART

It is known to use the electromagnetic spectrum in the radio frequency field for the transmission of electronic data, such as images or audio. The transmission of electronic data over radio channels requires the attribution of a specific channel for each transmission, which can only be shared with multiplexing techniques.

The great diffusion of wireless transmissions for the diffusion of electronic data in broadcast mode, in simulcast mode or with transmissions selectively dedicated towards a portion of the users - especially with the increase of volume of electronic data to be exchanged that has developed in recent years - has quickly saturated the previously-available radio channels, forcing the technology community to seek new radio resources, and thus frequency bands, with increasingly high frequency, up to reaching the microwave spectrum, in order to allow the transmission of electronic data over radio channel employing wide band. The typical example is represented by radio transmission backbones for mobile telephone signals, DAB radio, high- definition television signals, which use frequency bands in the microwave region in order to have a plurality of channels adjacent to each other, each of which having sufficient band for the requested transmission type.

The massive use of wireless radio transmission for the transmission of electronic data has given rise to various problems. A first problem is given by the fact that radio transmissions often exploit radio channels that are overlapped, or in any case transmission spectra of adjacent channels interfere therewith, or other

- l - interference sources interfere therewith which are geographically situated in a position different from those of interest.

The use of radio transmissions with very high frequencies is also subjected to considerable atmospheric absorption, the latter actually being substantially increasing with the increase of the frequency for the radio frequency spectrum; consequently, in order to transmit electronic data over wide band with very high frequencies, it is typically necessary to employ very high transmission powers.

In addition, the use of particularly high radio frequencies especially for proximal transmissions and for consumer applications is currently the subject of debate regarding the harmfulness for the health.

The use of radio transmissions for transmitting electronic data is often limiting or entirely non-actuatable in specific environments in which the atmosphere is subject to risk of explosion. In particular, in the European Union, the applicant indicates that there is the directive AtEx 2014/34/UE for regulating apparatuses intended for use in zones with explosion risk.

The applicant has also observed that the range of a radio transmission cannot be precisely predicted; in other words, a user who decides to receive a radio transmission of electronic data is able (or not able) to have, in his/her receiver, a sufficient radio power only on the basis, as a non-limiting example, of a change of antenna. The unpredictability of the boundaries of radio transmissions is such that a WiFi network that the user would like to be only intended for his/her own home can in fact be picked up even outside the home thereof. This leads to privacy problems, presently resolved by means of encryption of the flow of electronic data transmitted in the networks; nevertheless, there are daily examples of violation of the WiFi network encryption protocols.

Transmissions of electronic data which employ light radiation are known. Such optical transmissions use an AM modulation, which has the limit of a direct transmission. In other words, the AM modulation employed for optical transmission of electronic data is such that if an optically opaque object is interposed between a photoemitter and a photoreceiver that are modulated in AM with an input signal, the photoreceiver substantially is unable to reproduce, as an output, a copy of the signal placed as an input to the photoemitter. In other words, the AM modulation of a data signal is direct. The object of the present invention is to describe a system and a method for transmitting electronic data by means of optical radiation which contribute to reducing the impact and preferably resolving the above-described drawbacks. SUMMARY OF THE INVENTION

Transmitter device

According to a first aspect of the invention is therefore realized a transmitter device (99) transmitting by means of optical radiation (108), said device being characterized in that it comprises at least one modulator stage (101 ) comprising: - an input (105) adapted to receive during use an electrical signal (s(t)) to be modulated, and

- an output (107) transmitting towards at least one photoemitter (100) a voltage or current driving signal (v7(t), i7(t)), for which said electrical signal (s(t)) represents a modulating signal, where said at least one photoemitter (100) transmits an optical radiation (108) with radiation intensity lr(t) variable in accordance with said driving signal (v7(t), i7(t)), and wherein, between said input and said output of said modulator stage (101 ), a cascade of a first AM modulator (102) and of a second FM modulator (103) is present, said FM modulator (103) being placed downstream of said AM modulator (102) and having an own output directly connected with the output (107) of said modulator stage (101 ), wherein said AM modulator (102) has an input directly connected to said input (105) of said modulator stage and is directly supplied by means of said electrical signal (s(t)) to be modulated and wherein said AM modulator (102) has an output on which it generates an intermediate signal (s2(t)) supplied as an input to said FM modulator (103).

According to a further non-limiting aspect, or second aspect, said intermediate signal (s2(t)) is directly supplied as an input to the FM modulator (103).

According to a further non-limiting aspect, or third aspect, the device comprises said at least one photoemitter (100), and said photoemitter is a photoemitter whose light intensity curve as a function of said driving signal (v7(t), i7(t)) is not constant and/or wherein said photoemitter (100) is configured to emit and/or during use emits an optical radiation variable in accordance with said driving signal (v7(t), i7(t)). According to a further non-limiting aspect, or fourth aspect, said photoemitter (100) has a pass band greater than the pass band of said driving signal (v7(t), i7(t)).

According to a further non-limiting aspect, or fifth aspect, said electrical signal (s(t)) is an audio signal and/or a base band signal.

According to a further non-limiting aspect, or sixth aspect, a driving stage

(104) is also present for said at least one photoemitter (100) interposed between said output (107) of said modulator stage (101 ) and said at least one photoemitter (100), wherein said driving stage (104) is configured to condition and/or process said driving signal (v7(t), i7(t)); optionally said driving stage (104) comprises means and/or a device for signal processing comprising at least one operating configuration such that said radiation intensity (lr(t)) variable in accordance with said driving signal comprises a first continuous part (I), independent of said driving signal and a second time variable part that is a direct function of said driving signal (v7(t), i7(t)), wherein said time variable part that is a direct function of said driving signal (v7(t), i7(t)) is lower in absolute value than the absolute value taken by said first continuous part.

According to a further non-limiting aspect, or seventh aspect, said driving stage (104) is configured to condition and/or process said driving signal (v7(t), i7(t)) and comprises processing means comprising at least one operating configuration in which it supplies said photoemitter (100) with an electrical signal having a first direct current or voltage signal component, of value independent of the value taken by said driving signal (v7(t), i7(t)), and a second time variable signal component, direct function of said driving signal, wherein said second time variable component is lower in absolute value than the absolute value taken by said first component and/or wherein the driving signal as an output from said driving stage (104) and supplied to said photoemitter (100) is always positive and/or greater than zero.

According to a further non-limiting aspect, or eighth aspect, dependent on the first or on the aforesaid second aspect, said intermediate signal (s2(t)) supplied as an input to said FM modulator (103) is a signal adapted to cause a variation of the instantaneous frequency that said driving signal (v7(t)), i7(t)) assumes at the output of said FM modulator (103).

According to a further non-limiting aspect, or ninth aspect, said device comprises at least one reference frequency generation stage (109), wherein said reference frequency generation stage (109) is electrically connected with a frequency reference input of said AM modulator (102) and generates at least one first reference frequency (fO) for said AM modulator.

As an alternative to the aforesaid ninth aspect, according to a further non- limiting aspect, or tenth aspect, said reference frequency generation stage (109) is electrically connected with a frequency reference input of said AM modulator (102) by means of an own first output (109f) and is further electrically connected with a frequency reference input of said FM modulator (103) by means of an own second output (109s).

According to a further non-limiting aspect, or eleventh aspect, said reference frequency generation stage (109) generates at least one first reference frequency (fO) for said AM modulator (102) and a second reference frequency (fc) for said FM modulator (103).

According to a further non-limiting aspect, or twelfth aspect, combinable with one or more of the preceding aspects, said modulator stage (101 ) is configured to be supplied with an analog signal and wherein upstream of said input (105) of said modulator stage (101 ), a digital/analog converter is present.

Method of modulation and transmission of the signal

According to a further and thirteenth aspect of the present invention, is described a method of modulation and transmission of a data signal (s(t)) by means of optical radiation (108) with even indirect reflection , said method being characterized in that it comprises:

- a first step of amplitude modulation of said data signal (s(t)) by means of an AM modulator (102), wherein following said amplitude modulation step, is generated an intermediate signal (s2(t)) of which said data signal (s(t)) is a modulating signal; - a second step of frequency modulation of said intermediate signal (s2(t)) by means of a FM modulator (103), wherein following said frequency modulation step, a voltage or current driving signal (v7(t), i7(t)) is generated;

- a step of adjusting the light radiation intensity (lr(t)) of said optical radiation (108) emitted by at least one photoemitter (107) by means of said driving signal (v7(t), i7(t)).

According to a further aspect of the invention, or fourteenth aspect, the data signal (s(t)) is a base band signal and/or an audio signal, and is directly supplied to the input of said AM modulator (102). According to a further aspect of the invention, or fifteenth aspect, said driving signal (v7(t), i7(t)) is directly generated following said frequency modulation step.

According to a further non-limiting aspect, or sixteenth aspect, in said step of adjusting the light radiation intensity, the radiation intensity lr(t) rendered variable in accordance with said driving signal comprises a first continuous part (I), independent of said driving signal and a second time variable part that is a direct function of said driving signal (v7(t), i7(t)).

According to a further non-limiting aspect, or seventeenth aspect, the method comprises a step of providing said driving signal (v7(t), i7(t)) to a photoemitter (100) whose light intensity curve as a function of said driving signal (v7(t), i7(t)) is not constant and/or wherein said photoemitter (100) is configured to emit and/or during use emits an optical radiation variable in accordance with said driving signal (v7(t), i7(t)).

According to a further non-limiting aspect, or eighteenth aspect, the method comprises a step of providing said driving signal (v7(t), i7(t)) to a photoemitter (100) which has a pass band greater than the pass band of said driving signal (v7(t), i7(t)).

According to a further non-limiting aspect, or nineteenth aspect, said time variable part that is a direct function of said driving signal (v7(t), i7(t)) is lower in absolute value than the absolute value taken by said first continuous part (I).

According to a further non-limiting aspect, of twentieth aspect, said method comprises a step of conditioning and/or processing of said driving signal (v7(t), i7(t)) in order to supply said photoemitter (100) with an electrical signal having a first direct current or voltage signal component, of value independent of the value taken by said driving signal (v7(t), i7(t)) and a second time variable signal component, direct function of said driving signal, wherein said second time variable component is lower in absolute value than the absolute value taken by said first component and/or wherein the driving signal as an output from said driving stage (104) and supplied to said photoemitter (100) is always positive and/or greater than zero.

According to a further non-limiting aspect, or twenty-first aspect, said method comprises a step of generating a first reference frequency (fO) for said amplitude modulation. According to a further non-limiting aspect, or twenty-second aspect, said method comprises a step of generating a first reference frequency (fO) for said amplitude modulation and a second reference frequency (fc) for said frequency modulation.

According to a further non-limiting aspect, or twenty-third aspect, the step of generating said first reference frequency and/or said first and said second reference frequency is performed by means of supplying an AM modulator (102) and/or an AM modulator (102) and a FM modulator (103) with a reference frequency generator (109).

According to a further non-limiting aspect, or twenty-fourth aspect, a step of converting an input signal from the numerical domain to the analog domain is present, following which the signal in said analog domain represents said data signal (s(t)).

According to a further non-limiting aspect, or twenty-fifth aspect, combinable with one or more of the preceding method aspects, a step of retrieving said data signal (s(t)) from a power grid is present.

According to a further non-limiting aspect, or twenty-sixth aspect, said data signal (s(t)) is filtered from an alternating component belonging to the network voltage present on said power grid.

Receiver device

According to a further and twenty-seventh aspect, a receiver device (199) for receiving optical radiation (108) can therefore be made, said device being adapted to cooperate with a transmitter device (99) according to one or more of the preceding aspects of the invention, said receiver device (199) being adapted to output a replication (s'(t)) of an electrical data signal (s(t)) by means of a hybrid AM/FM demodulation.

According to a further non-limiting aspect, or twenty-eighth aspect, combinable with said twenty-seventh aspect, said receiver device (199) is characterized in that it comprises at least one demodulator stage (201 ) comprising:

- an input (205) adapted to receive during use a voltage or current driving signal (v7(t), i7(t)) modulated and generated through a photoreceiver (200) connected thereto and receiving during use an optical radiation (108), also reflected, and - an output (207) transmitting an output replication signal (s'(t)) for which said electrical signal (s(t)) represents a modulating signal,

and wherein, between said input and said output of said demodulator stage (201 ), a cascade of a first FM demodulator (203) and of a second AM demodulator (202) is present, said FM demodulator (203) being placed upstream of said AM demodulator (202), wherein said AM demodulator (202) has an input directly connected to the output of said FM demodulator (203).

According to a further non-limiting aspect, or twenty-ninth aspect, said input (205) of said demodulator stage (201 ) is directly supplied by means of said driving signal (v7(t), i7(t)) produced as an output from said photoreceiver (200).

According to a further non-limiting aspect, or thirtieth aspect, the receiver device (199) comprises a filtering stage placed downstream of said photoreceiver (200), said filtering stage being adapted to filter and/or separate and/or eliminate a continuous electrical signal component produced as an output from said photoreceiver (200) from a variable electrical signal component produced as an output from said photoreceiver, said filtering stage being adapted to create as an output said driving signal (v7(t), i7(t)).

According to a further non-limiting aspect, or thirty-first aspect, said FM demodulator (203) has an output on which it generates an intermediate signal (s2'(t)) supplied in input to said AM demodulator (202).

According to a further non-limiting aspect, or thirty-second aspect, said at least one photoreceiver (200) supplies a driving stage (204) for said demodulator stage (201 ), said driving stage being interposed between said input (205) of said demodulator stage (201 ) and said at least one photoreceiver (200), wherein said driving stage (204), in generating said driving signal (v7(t), i7(t)), is configured to identify, in the variable radiation intensity lr(t) received during use from said photoreceiver (200), a first continuous part (I) and a second time variable part that is a direct function of said driving signal, and to generate said driving signal (v7'(t), i7'(t)) as a time variable signal, direct function of said second variable part.

According to a further non-limiting aspect, or thirty-third aspect, said intermediate signal (s2'(t)) supplied in input to said AM demodulator (202) is a signal adapted to cause a variation of the instantaneous amplitude that said replication signal (s'(t)) assumes at the output of said AM demodulator (202). According to a further non-limiting aspect, or thirty-fourth aspect, said device comprises at least one reference frequency generation stage (109), wherein said reference frequency generation stage (109) is electrically connected with a frequency reference input of said AM demodulator (202) and generates at least one first reference frequency (fO) for said AM demodulator.

As an alternative to the aforesaid thirty-fourth aspect, according to a further non-limiting aspect, or thirty-fifth aspect, said reference frequency generation stage (109) is electrically connected with a frequency reference input of said AM demodulator (202) by means of an own first output (109f) and is further electrically connected with a frequency reference input of said FM demodulator (203) by means of an own second output (109s).

According to a further non-limiting aspect, or thirty-sixth aspect, said reference frequency generation stage (109) generates at least one first reference frequency (fO) for said AM demodulator (202) and a second reference frequency (fc) for said FM demodulator (203).

According to a further non-limiting aspect, or thirty-seventh aspect, said demodulator stage (201 ) produces, as an output, an analog signal.

Method for demodulation and reception of the signal

According to a further and thirty-eighth aspect of the present invention, a method is described for demodulation and reception of a data signal (s(t)) by means of optical radiation (108) even with indirect reflection, said method being characterized in that it comprises:

- a step of receiving through at least one photoreceiver (200) of an optical radiation (108) with light radiation intensity (lr(t)) wherein through said at least one photoreceiver, a voltage or current driving signal (v7(t), i7(t)) is generated,

- a first step of frequency demodulation by means of a FM demodulator (203), wherein following said frequency modulation step, an intermediate signal s2'(t)) is generated, starting from said voltage or current driving signal (v7(t), i7(t));

- a second step of amplitude demodulation of said intermediate signal (s2'(t)) by means of an AM demodulator (202), wherein following said amplitude demodulation step, a replication signal of the transmitted data signal (s(t)) is generated.

According to a further non-limiting aspect, or thirty-ninth aspect, the radiation intensity lr(t) of said optical radiation (108) comprises a first continuous part (I) and a second time variable part modulated in a hybrid manner with an AM/FM modulation.

According to a further non-limiting aspect, or fortieth aspect, said time variable part is lower in absolute value than the absolute value taken by said first continuous part (I).

According to a further non-limiting aspect, or forty-first aspect, said method comprises a filtering step, in particular performed downstream of said photoreceiver (200), said filtering step being adapted to filter and/or separate and/or eliminate a continuous electrical signal component produced as an output from said photoreceiver (200) from a variable electrical signal component produced as an output from said photoreceiver, said filtering step being adapted to cause the creation of said driving signal (v7(t), i7(t)).

According to a further non-limiting aspect, or forty-second aspect, said method comprises a step of generating a first reference frequency (fO) for said amplitude demodulation

According to a further non-limiting aspect, or forty-third aspect, said method comprises a step of generating a first reference frequency (fO) for said amplitude demodulation and a second reference frequency (fc) for said frequency demodulation.

According to a further non-limiting aspect, or forty-fourth aspect, the step of generating said first reference frequency and/or of said first and said second reference frequency is performed by means of supplying an AM demodulator (202) and/or an AM demodulator (202) and a FM demodulator (203) with a reference frequency generator (109).

According to a further non-limiting aspect, or forty-fifth aspect, a step is present for converting a replication signal s'(t) from the analog domain to the numerical domain.

Powerline

According to a further non-limiting aspect, or forty-sixth aspect, a step of transmitting said replication signal (s'(t)) towards a power grid is present.

According to a further non-limiting aspect, or forty-seventh aspect, said data signal (s(t)) is filtered by an alternating component belonging to the network voltage present on said power grid. Pointing device

According to a further and forty-eighth aspect, is realized a reception system (300) comprising a receiver device (199) according to one or more of the preceding aspects, said system at its interior comprising an optically sensitive element (301 ) provided with a reception area (302) thereof and on which one or more photoreceivers (200) are installed, wherein said one or more photoreceivers (200) achieve a reception area (302) adapted to acquire at least one image in which a light variation lr(t) transmitted by a modulated photoemitter is present, said reception system (300) comprising means for selecting a part of the reception area (302) formed by the plurality of photoreceivers (200), configured to automatically select part of the reception area (302) in which a light variation lr(t) transmitted by a modulated photoemitter is present, and to cause the sending of a signal substantially corresponding to said light variation lr(t) towards said demodulator stage (201 ) of said receiver device.

According to a further and forty-ninth non-limiting aspect of the invention, the selection means are mechanical and are controlled by a data processing unit.

According to a further and fiftieth non-limiting aspect of the invention, alternative to the aforesaid forty-ninth aspect, the selection means are achieved via software.

According to a further and fifty-first non-limiting aspect of the invention, in both cases wherein the selection means are achieved via software or are of mechanical type, a predetermined algorithm analyzes the signal received by said one or more photoreceivers (200) of the reception area 302 in order to find a predetermined signal modulation scheme.

According to a further and fifty-second non-limiting aspect of the invention, in the system (300), a tracking algorithm is also performed through which said selection means are configured in order to find if the point of the reception area (302) or on the sub-portion of the reception area (302), in which said light variation lr(t) arrives, moves, and in order to perform an automatic pursuit thereof, hence without requiring intervention by of the user.

According to a further and fifty-third non-limiting aspect of the invention, dependent on said forty-first aspect, the search is without interruption of time continuity. For greater clarity, the following definitions are applied in the present description.

Pursuant to the present invention, by optical radiation it is intended an optical radiation comprised in the infrared spectrum and/or in the ultraviolet spectrum and/or in the visible spectrum.

Pursuant to the present invention, by direct optical radiation or direct optical transmission, it is intended a transmission of an optical signal in which between a source or photoemitter and a destination or photoreceiver optically opaque obstacles are not interposed and reflections are not present. In other words, in the direct optical radiation or direct optical transmission, the transmission of the signals occurs with said source or photoemitter and the destination or photoreceiver in optical range, i.e. mutually visible.

For the purpose of improved comprehension of the present invention, the following further definitions are applied:

- By "transparency" it is intended a characteristic such that the material under examination can make a radiation incident thereon pass along a preferential direction, independent of the attenuation that such radiation undergoes in the passage through said material.

- By "infrared" it is intended an electromagnetic radiation which has wavelength approximately comprised between 0.7 pm and 15pm.

- By "visible" or "visible spectrum" it is intended an electromagnetic radiation which has wavelength approximately comprised between 390 and 700nm.

- By "ultraviolet" it is intended an electromagnetic radiation which has a wavelength approximately comprised between 400nm and 10nm.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments and several aspects of the finding will be described hereinbelow with reference to the enclosed drawings, provided only as a non-limiting example in which:

- Figure 1 illustrates a block diagram of a modulator and of a demodulator of optical signals, operating with the hybrid AM modulation/FM according to the invention; - Figure 2 illustrates a block diagram of a multi-channel receiver demodulating an optical signal with the hybrid AM/FM demodulation, object of the invention;

- Figure 3 illustrates a block diagram of a reception device employing the demodulator, object of the invention; and

- Figure 4 illustrates a block diagram of a transmitter element and of a receiver element adapted to operate on an energy distribution power grid, in which the AM/FM modulation and demodulation, object of the invention, is used.

DETAILED DESCRIPTION OF THE INVENTION

The present invention first of all regards a method for transmitting electronic data by means of an optical signal. Such electronic data, preferably though not in a limiting manner, comprises an audio signal, hence an analog and continuous signal s(t), characterized by a predefined pass band.

In a preferred and non-limiting embodiment, the signal s(t) is a base band signal; the audio analog signal s(t), before being transmitted to a photoemitter 100 which preferably though not in a limiting manner comprises an LED diode, is subjected during transmission to a modulation step performed by a modulator stage 101 of analog and hybrid type. In a transmission module 99, which comprises the photoemitter 100, the modulator stage 101 comprises a plurality of modulators in series adapted to perform said hybrid modulation, and in detail, starting from its input 105 on which it receives the audio analog signal s(t), it first comprises an AM modulator 102 directly supplied from the aforesaid input 105, and a FM modulator 103 placed in series with the AM modulator 102 and directly supplied therefrom. The output 107 of the modulator stage 101 supplies an input of a driver stage 104 for said photoemitter 100.

In particular, the output 107 of the modulator stage 101 produces a voltage signal v7(t) or current signal i7(t) which is supplied through the driver 104 to the photoemitter 100 and which attains a driving signal. In particular if the photoemitter 100 is made from one or more LED diodes 100, it was found that the brightness of the diode is proportional to the voltage or current provided thereto as input. More in detail, the LED diode or generally the photoemitters 100 must be photoemitters whose light intensity curve as a function of the voltage or current, in particular of the driving signal, supplied thereto in input must not be constant. This signifies that the light intensity curve, and more generally the intensity of optical radiation, varies as a function of the voltage or current supplied to the photoemitter. More preferably, but not limiting, the light intensity curve of the voltage or current is substantially of linear type.

The voltage signal v7(t) or the current signal i7(t) produced as an output 107 from the modulator stage 101 are analog signals correlated with the audio input signal s(t) and, when supplied to the photoemitter 100, they produce a variation of the brightness lr(t) of the optical beam 108 transmitted by the photoemitter proportional to the variation of voltage or current, respectively of the voltage signal v7(t) or of the current signal i7(t).

More particularly, once the input signal s(t) has been given to the AM modulator 102, such AM modulator 102 produces as an output an intermediate signal s2(t) that assumes the following form:

s ₂ (t) = s(t)sin(27r/ot)

where fo is the carrier frequency of the AM modulation.

The FM modulator 103 attains a frequency modulation, such that its instantaneous frequency assumes the form:

wherein fc is the carrier frequency of the FM modulation.

The output signal v7(t) or i7(t) will therefore have the following form

The two carrier frequencies fO and fc respectively of the AM or FM modulation are actual predetermined values, which nevertheless can be modified by the user according to a technique that is known and hence not described herein. Conveniently in the device, object of the invention, a frequency generator 109 is also present, provided with a first output 109f supplying the AM modulator and a second output 109s supplying the FM modulator respectively with a sinusoidal frequency signal fO and with a cosinusoidal frequency signal fc. Such solution should be intended as non-limiting, since it is possible to make the device, object of the invention, in a manner such that the frequency generator 109 has a single output directed towards both the AM modulator 102 and the FM modulator 103, then giving the latter the task of generating the cosinusoidal frequency signal fc based on the signal fO generated by the frequency generator 109. The applicant has verified that the carrier frequency fc can also be zero. In such case, the hybrid modulation takes the form of a direct modulation. In addition, the applicant has observed that the carrier frequency fc can also be greater than 1 MHz; in particular when photoemitter is an LED diode, the carrier frequency fc for the FM modulator can as a non-limiting example be up to 10 MHz. Preferably though not limiting, the carrier frequency fc for the FM modulator 103 is greater than the carrier frequency fO for the AM modulator.

In order to avoid significant distortions of the optical beam 108 in terms of brightness variation lr(t), the applicant has observed that the band occupied by the brightness variation signal lr(t), and even more so the voltage signal v7(t) or current signal i7(t) supplied to the photoemitter 100, must not exceed its maximum pass band. In other words, the band occupied by the driving signal must be lower than the maximum pass band of the photoemitter 100 in order to not have distorsions. The absence of distorsions is important, especially since the signal placed as an input to the said signal modulator is an audio signal.

The applicant has observed that the data signal in input can also be a numerical signal. In such case, the applicant has conceived a second embodiment which differs from the first embodiment since it comprises an digital/analog converter 106 stage, placed between the input of the device and the input 105 of the modulator stage 101 , which provides to transform the input data signal into an analog signal suitably adapted in order to be analogically modulated through the modulators AM 102 and FM 103, as previously described. Since the digital/analog converter 106 belongs to the second embodiment and therefore is optional with respect to the first embodiment, representing an additional module with respect to the base system of the first embodiment, in figure 1 such digital/analog converter 106 is represented with dashed line, in order to highlight the optionality of the first embodiment and the association with the second embodiment.

The applicant has observed that the optical beam 108 obtained by means of the hybrid modulation as previously described is particularly adapted for being received even over indirect paths, i.e. by means of reflection or refraction caused by surfaces that are even micrometrically incoherent, such as a wall or the like. In figure 1 , there are two reflections but such number must not be intended as being limiting. In particular, the optical beam 108, as illustrated in figure 1 , is transmitted with one or more reflections 140, 141 as a non-limiting example over one or more walls M, towards a receiver device 199, which comprises at least one photoreceiver 200 which receives the reflected optical beam 108 and which transmits a voltage or current signal v7'(t) or i7'(t) - in accordance with the intensity as a function of time of said optical beam 108 - towards a demodulator stage 201 , which performs a step of hybrid demodulation of the received voltage or current signal. The demodulator 201 comprises a cascade of an FM demodulator 203 and of an AM demodulator 202, in which the input of the AM demodulator 202 is directly supplied from the output of the FM demodulator 203. The FM demodulator 203 has an input 205 on which said voltage or current signal v7'(t) or i7'(t) is supplied. As in the case of the transmission side, between the FM demodulator and the photoreceiver 200 a driver can be present that is adapted to generate the voltage or current signal v7'(t) or i7'(t), termed "driving signal" for the purposes of the present invention for the demodulator stage, in a manner such to separate the first continuous component I from the second variable component of the optical radiation, and only send the variable component to the input of the demodulator stage.

As in the case of the modulation side, also the receiver device 199 comprises a frequency generator 109, provided with a first output 109f supplying the AM modulator and a second output 109s supplying the FM modulator respectively with a sinusoidal frequency signal fo and with a cosinusoidal frequency signal fc. Such solution is not to be intended as limiting, since it is possible to make the device, object of the invention, in a manner such that the frequency generator 109 has a single output directed towards both the AM demodulator 202 and the FM demodulator 203, then giving the latter the task of generating the cosinusoidal signal with frequency fc based on the sinusoidal frequency signal fO generated by the frequency generator 109. The applicant has verified that the carrier frequency fc can also be zero. In such case, the hybrid demodulation takes on the form of a direct demodulation.

The demodulator stage 201 , as with the modulator stage 101 , can be made with hardware or with mixed hardware-software structure, or as SDR, hence only software, without such difference constituting a limitation for the purpose of the present invention. The receiver device 199 then produces, on its output 199u, a replication s'(t) of the input signal s(t) at the transmitter side.

In particular, the voltage or current signal v7'(t) or i7'(t) generated by the photoreceiver is first transmitted towards the FM demodulator 203 which extracts a copy s2'(t) of the intermediate signal s2(t) that is supplied to the input of the AM demodulator 202, which performs the actual conversion towards the replication signal s'(t) of the input signal s(t) at the transmitter side.

Advantageously, the applicant has observed that the hybrid modulation and demodulation performed as described above are particularly adapted for being used for transmitting an audio analog data signal, even with transmission by means of reflections, since it has been proven that the replication s'(t) of the audio analog input signal s(t) at the transmitter side is received without audible distortions, or in any case without distortions that are capable of significantly worsening the quality of the signal.

A further embodiment of the receiver 199, object of the invention, is advantageously described in the following portion of the text. Such embodiment of the receiver 199 is conceived so as to allow the reception of optical signals 108 over multiple channels simultaneously, hence realizing a multichannel receiver for optical signals.

The multichannel optical receiver described hereinbelow and reported in figure

2 comprises a plurality of demodulator stages 201 arranged in parallel and having the same structure as the above-described single-channel receiver 199 (reference being made to the description thereof), but it also integrates a filtering stage 210. Such filtering stage is positioned between the photoreceiver 200 and the demodulator stage 201 , and is conceived for causing the transmission of only part of the voltage signal v7'(t) or current signal i7'(t) in output from the photoreceiver, with a division by frequency bands.

In particular, the applicant has observed that, conveniently, the filtering stage 210 can integrate one or more band-pass filters 211 , each centered on a central frequency thereof ideally coinciding with each of the carrier frequencies fc of the FM modulator 103. In this manner, the filtering stage performs a procedure of selection of the sub-part of the spectrum to be transmitted to the various demodulators stages 201 , in a manner such that each of these can decode a channel thereof in an independent manner from the remaining demodulators 201 stages. The filtering stage 210 can be made of hardware, partially of software or entirely of software.

Advantageously the applicant has verified that the multichannel receiver described herein is particularly useful for the reception of data signals of audio type, since it allows distinguishing, as a non-limiting example, a left channel from a right channel, thus realizing a multichannel receiver adapted to be installed on a headset/earphone for the audio signal reception by means of optical transmission.

Such receiver device 199 is well-integrated in a transmission system that comprises a plurality of transmitters as described above, in which each i-th transmitter has its own FM modulator 103 operating with a carrier frequency f _C i different from the others, and in which the receiver 199 comprises a filtering stage 210 adapted such that it can be tuned or in any case divide the N carrier frequencies fc,, i=1 ... N of each of the transmitters towards one or more of the demodulators FM 203.

As an alternative to the above-proposed solution, the multichannel receiver described herein can be provided with a filtering stage 210 installed between the FM demodulator 203 and the FM demodulator 202, operating under the same principle as the preceding case. Nevertheless, in such case, the differentiation of the audio channels will only be given by the distinction of the carrier frequencies fO of the various modulators AM 103 on the transmitter side, hence taking care to maintain constant the carrier frequency fc of the modulators FM 103 of the system.

The filtering stage 210 may comprise selection means adapted to allow the manual selection of sub-parts, preferably one sub-part, of the various carrier frequencies fc, so as to select for example only one channel. Such solution is particularly advantageous for the applications of multilingual signal diffusion, since each i-th transmitter can employ its own carrier frequency fc, i=1 , ... ,N in the system in order to carry an audio signal, each in one language thereof, allowing the user to select the channel of interest by means of known selection means.

The method which is therefore carried out by the present invention, on the transmitter side, comprises a step of supplying an analog signal s(t) to a modulator stage 101 , which performs a step of modulation first comprising a step of amplitude modulation of said analog signal s(t) in order to produce, as an output from an AM modulator 102 thereof, an amplitude-modulated intermediate signal s2(t) and further comprising a step of supplying the intermediate signal s2(t) to a FM modulator 103 in order to obtain, as an output, a voltage or current signal v7(t), i7(t) supplied as an input to a photoemitter 100, wherein the step of supplying the voltage or current signal v7(t), i7(t) to said photoemitter 100 generates a light intensity variation lr(t) proportional to the voltage or current signal v7(t), i7(t).

Analogously, on the receiver side, said method comprises a step of receiving an optical beam 108 carrying electronic data modulated herein according to a predetermined modulation, wherein in the step of receiving at least one photoreceiver 200 it generates a voltage or current driving signal v7'(t), i7'(t) of amplitude proportional to the received light intensity lr(t), and wherein there is a step of demodulation performed by at least one demodulator stage 201 of a receiver 199 in which the at least one demodulator stage 201 first of all performs a frequency demodulation of said voltage or current driving signal v7'(t), i7'(t) generated by the at least one photoreceiver in order to produce an intermediate signal s2'(t) and wherein said method comprises a step of supplying said intermediate signal s2'(t) to the input of an amplitude demodulator 102 of said receiver 199, which performs an amplitude demodulation in order to extract an analog data signal s(t) from said intermediate signal s2'(t).

More in detail, since the signal being transmitted is modulated by means of the superimposition of a constant component and a variable component, also the output of the photoreceiver 200 generates an electrical signal comprising a first constant voltage or current component and a second voltage or current component variable in accordance with the modulation performed, and only the latter component is effective for the decoding of the signal s'(t). For such reason, a filtering stage can be present, downstream of the photoreceiver 200, which separates and/or eliminates and/or filters the constant component of said voltage or current signal, and produces as an output the voltage or current driving signal v7'(t), i7'(t) based on the single variable voltage or current component.

In the abovementioned method, during transmission as well as during reception, the modulations - respectively of frequency and amplitude - are sequential, and in particular: during transmission, the frequency modulation follows the amplitude modulation, while during reception the amplitude demodulation follows the frequency demodulation. During transmission, the intermediate signal s2(t) contributes to defining an instantaneous frequency of a signal which will be the object of a frequency modulation by means of the aforesaid intermediate signal s2(t).

The applicant has observed that, in the optical domain, the hybrid modulation formed by a cascade of a FM modulation of a signal previously modulated in AM renders the receivers particularly sensitive to detecting the presence of a power signal, even a very weak one.

The applicant has conceived a reception system 300, comprising a receiver 199 according to that described above, which is depicted in figure 3. Such reception system 300 integrates at its interior an optically sensitive element 301 provided with a reception area 302 thereof, on which one or more photoreceivers 200 are installed. In this case, even if such solution must not be intended as being limiting, preferably the photoreceivers 200 are of CCD type, and attain a matrix in the reception area 302. The reception area 302 therefore has relative size and can be adapted to acquire an image, as well as the light variation lr(t) transmitted by a modulated photoemitter. The assembly of the photoreceivers can therefore achieve a reception area 302 of a camera, of a video camera or of binoculars.

The receiver 199 in this case comprises means for selecting a part of the reception area 302 formed by the plurality of photoreceivers 200. Such selection means 303 are in particular configured for selecting part of the reception area 302 in which there is a light variation lr(t) transmitted by a modulated photoemitter.

In a first non-limiting embodiment, the selection means are mechanical, e.g. attained through micro-arms, while in a second non-limiting embodiment the selection means are attained via software; in both cases, a predetermined algorithm analyzes the signal received by the photoreceivers 200 of the reception area 302 in order to find a predetermined signal modulation scheme. The search can occur over all the photoreceivers 200 of the area or over a part thereof by means of the selection means. When such selection means are moved, electronically or mechanically, on the sub-portion of the area in which a signal is received with light variation lr(t) transmitted by a modulated photoemitter, the selection means perform a spatial filtering over the reception area 302 which allows more greatly isolating the light variation lr(t) transmitted by said modulated photoemitter from the optical noise otherwise captured on the remaining portion of the reception area 302; the light variation lr(t) transmitted by the photoemitter, which is an indication of an optical beam 108 modulated with the previously-described hybrid modulation, through the photoreceiver or the photoreceivers 200 of the abovementioned sub-portion is transformed into an electrical voltage or current signal v7'(t), i7'(t) which is sent as an input to a receiver as described above in a manner such to subsequently proceed with an extraction of the signal s(t) of interest.

According to a preferred aspect of the invention, in the system 300, a tracking algorithm is also performed through which the selection means are configured in order to find, preferably without interruption of time continuity, if the point of the reception area 302 or on the sub-portion of the reception area 302, in which said light variation lr(t) arrives, moves, and in order to perform an automatic pursuit thereof, hence without requiring intervention by the user.

The applicant has in particular observed that when such system 300 is installed on a camera, on a video camera or on binoculars - in particular if provided with enlarging or telephoto lenses - it can easily happen that during the pointing operation, especially if manual, the sought-after point can be subjected to movements over the reception area 302 due to accidental movements of the pointing axis of the lens or objective. Advantageously, the applicant has realized that by implementing the tracking algorithm on the video camera, camera or binoculars integrating the system 300, it is advantageously possible to transform the aforesaid camera, video camera or binoculars into a reception device for receiving signals transmitted over an optical channel and modulated by means of hybrid FM and AM modulation, which, even if able to capture an image in the visible spectrum, is also simultaneously able to receive a signal transmitted by an optical source present in said image, even if the source itself is - to the human eye - barely visible and/or even if the modulation of the brightness of the source might appear nonexistent to the human eye. For this particular aspect, the applicant has observed from its tests that an audio signal can be received even at a considerable distance, up to several kilometers, above all in non-foggy or cloudy weather conditions, through the light emission of one or more LEDs of conventional type, which, even if modulated, to the human eye appear to entirely lack light intensity variation.

In other words, a data signal and in particular an audio signal can be modulated on a photoemitter 100 or on multiple photoemitters 100 adapted for example to illuminate an environment, with a relative modulation of very low light intensity, even lower than 1/1000, without losing data and therefore without the human eye being able to perceive such modulation, not only due to its speed but also through the very limited variation of the amplitude between modulated or non-modulated signal peaks.

In particular the applicant has observed that it is convenient to allow the photoemitter 100 - in the absence of modulation - to have a constant non-zero light intensity I, on which a hybrid modulated signal is superimposed. In other words, the light radiation intensity lr(t) is given by two components according to the following formula:

/r(t) = I + kV ₇ (t)

where the first component I is the constant and/or continuous component and the second component kV ₇ (t) is that which follows the abovementioned law

Acos [(27r _c + 2nk _r s ₂ (t)^) tj. In order to prevent transitions to zero, in particular if the photoemitter is an LED diode, and in particular in order to work the aforesaid diode in a zone of linearity so as to prevent modulation distortions, the portion kV ₇ (t) would preferably (but not in a limiting manner), have to have an absolute value which is always maintained lower than the absolute value of the continuous component I. Such task is advantageously carried out by the driver stage 104. Therefore, the driver stage 104 processes and/or conditions the driving signal v7(t), i7(t), supplying, as an input to the photoemitter 100, an electrical signal which comprises a first direct current or voltage signal component, of value independent of the value taken by the driving signal v7(t), i7(t) and a second time variable signal component, direct function of the driving signal, in which the second time variable component is lower in absolute value than the absolute value taken by the first component; in other words, the signal in output from the driver stage 104 and supplied to said photoemitter 100 is always positive and/or greater than zero.

The applicant has also considered that operating the driver stage 104 in accordance with that specified above allows preventing the risk that, in the absence of signal s(t), the photoemitter 100 is driven with a zero or in any case overly low voltage such that it cannot be turned on or in any case not visibly turned on.

Through the hybrid modulation, object of the invention, the applicant has surprisingly found that even if the photoemitter 100 present or made to work in a region where the characteristic of optical radiation power or intensity as a function of the driving signal is non-linear, it is possible to obtain very accurate reproductions of the audio signal s'(t) when received.

The applicant has also observed that through the device, object of the present invention, it is possible to obtain a conveyed wave transmission system 400, comprising a transmitter element 401 and a receiver element 402, each of which connectable to the home power grid at an input 403 thereof. The transmitter element 401 comprises an output 404 in order to supply a photoemitter 100 while the receiver element integrates at least one photoreceiver 200.

The transmitter element 401 as in figure 4 integrates, at its interior, one or more modulator stages 101 with the previously-described characteristics, and also integrates at its interior an isolator stage 405, comprising at least one transformer therein adapted to separate the network voltage section from the rest of the circuitry, especially from the modulator stage 101 , whose characteristics are those described above (reference being made thereto). In the same manner, also the receiver element 402 comprises an isolator stage 405 therein in order to separate the demodulator stage 201 from the network voltage. During use, the user can inject, on the home network, a base band signal s(t). Such signal is diffused up to the transmitter element 401 , which modulates it through the aforesaid modulator stage 101 with a modulation of hybrid type, as previously described, and transmits it over its output 404 in order to supply a photoemitter 100 with such modulation. At another end of the room, however, the receiver element 402 receives the optical signal modulated in a hybrid manner as described above, and, with the same procedure, demodulates it and reconverts it into a replication s'(t). The applicant has verified that the conveyed wave system 400 as described above allows diffusing, through light signals, data signals s(t) which preferably though not in a limiting manner integrate audio signals, also over electrical lines that are decoupled from each other, with an optical transmission which also ensures that the aforesaid two electrical lines decoupled from each other are in perfect galvanic isolation with respect to each other.

The applicant has also verified that, in a particular embodiment, the transmitter element 401 can also integrate the photoemitter 100, thus realizing a photoemitter with integrated hybrid modulator, hence a kind of intelligent lamp capable of electronically processing a data signal s(t) superimposed on the network signal and causing the transmission thereof via light by means of a hybrid modulation, as previously described.

The applicant has also observed that it is convenient to introduce a filtering stage of the network frequency 406, which allows isolating the component of the data signal s(t) from the 50 Hz or 60 Hz signal typical of the network frequency. Advantageously, this contributes to preventing the network frequency component, which does not represent a useful signal, from entering into the modulation of the light intensity lr(t) transmitted by the photoemitter 100.

The applicant has observed that the advantages of the invention, especially in terms of indirect receivability, through the hybrid modulation and demodulation as described above are attained independently from the type of photoemitter 100, and in particular independent of whether the photoemitter is coherent - with "coherent" it being intended a monochromatic photoemitter such as a LASER - or incoherent, with "incoherent" it being intended a photoemitter that emits a polychromatic optical beam. The applicant in any case has observed that the use of coherent photoemitters improves the reception performances with respect to what could be obtained with an incoherent photoemitter.

Parts of the process described in the present invention can be - when possible - attained by means of a data processing unit, technically substitutable with one or more computers conceived for performing a software or firmware program portion that is predefined and loaded on a non-transient memory medium. Such software program can be written in any one programming language of known type. The computers, if there are two or more of these, can be connected together by means of a data connection such that their calculation powers are shared in any manner; the same computers can therefore be installed in positions that are even geographically different from each other.

The data processing unit can be a processor of general purpose type, especially configured through said software or firmware program in order to perform one or more parts of the method identified in the present invention, or be an ASIC or dedicated processor, specifically programmed for performing at least part of the operations of the method or process of the present invention. Finally, it is clear that additions, modifications or variations that are obvious for the man skilled in the art can be applied to the object of the present invention, without departing from the protective scope provided by the enclosed claims.