Reivindicaciones
1. A device for detecting a state condition of the surface of the roadway in a specific verification region (4.1), characterized in that it comprises - a first emitting group (1) in turn comprising ● a first laser source (1.1) emitting a beam (5.1) with a wavelength λ<1> in the operating mode, where this first laser source (1.1) has modulation means (1.1.2) modulating the intensity I1 at a frequency f1 in the operating mode, the value of the refractive index of the verification region (4.1) at wavelength λ<1> being indistinguishable when the verification region (4.1) is in one state condition or another; ● a second laser source (1.2) emitting a beam (5.2) with a wavelength λ<2> in the operating mode, where this second laser source (1.2) has modulation means (1.2.2) modulating the intensity I2 at a frequency f2 in the operating mode, where this frequency f2 is different from the frequency f1 , the value of the refractive index of the verification region (4.1) at wavelength λ<2> being different when the verification region (4.1) is in one state condition or another; - a second receiving group (2) in turn comprising: ● photodetector means (2.1) intended for receiving the reflected radiation (5.3) coming from the first and second laser source (1.1, 1.2) after striking the verification region (4.1) and comprising an output of the electrical signal S1 ; ● a first demodulation chain (2.2) supplied by the output of the electrical signal S1 from the photodetector means (2.1) and provided with an output of the demodulation signal A<1>; ● a second demodulation chain (2.3) also supplied by the output of the electrical signal S1 of the photodetector means (2.1) and provided with an output of the demodulation signal A2; where the first and second laser sources (1.1, 1.2) of the first emitting group (1) are oriented such that the radiation of the two laser beams (5.1, 5.2) strikes the verification region (4.1), and at least part of the reflected radiation (5.3) strikes the photodetector means (2.1) of the second receiving group (2) in the operating mode; and where the device additionally comprises a measuring module (3) which assesses the magnitudes A2 and A1 in the operating mode and compares their ratios with at least one set of values that reflect the variation of the refractive index in response to a local state condition of the roadway. 2. The device according to claim 1, characterized in that the first emitting group (1) has at least a third laser source emitting a beam with a wavelength λ<3> in the operating mode, where this third laser source: ● has modulation means modulating the intensity at a frequency f3 different from the frequencies f1 and f2 of the first and second laser sources in the operating mode, ● is oriented such that it strikes the verification region (4.1), and the reflected beam strikes the photodetector means (2.1) of the second receiving group (2) in the operating mode; and where the second receiving group (2) additionally comprises a third demodulation chain also supplied by the output of the electrical signal S1 of the photodetector means (2.1) and provided with an output of the demodulation signal A3 ; and where the device allows assessing the ratio between magnitudes A3 and A1 in the operating mode by means of the measuring module. 3. The device according to claim 1 or 2, characterized in that the laser sources (1.1, 1.2) as well as the photodetector means (2.1) are located in one and the same support. 4. The device according to any of claims 1 to 3, characterized in that it has guiding means or elements (1.3) which conduct the laser beams (5.1, 5.2) from the laser sources (1.1, 1.2) to an emitting point from where the emitting point is oriented towards the verification region (4.1). 5. The device according to any of claims 1 to 4, characterized in that at least one collimator (1.3.5) is provided for the collinear emission of beams towards the verification region (4.1). 6. The device according to any of claims 1 to 5, characterized in that the photodetector means (2.1) comprise a focusing lens (2.1.1) for focusing the reflected radiation (5.3) in the verification region (4.1). 7. The device according to any of claims 1 to 6, characterized in that the photodetector means (2.1) comprise a photodiode (2.1.3). 8. The device according to any of claims 1 to 7, characterized in that the photodetector means (2.1) comprise a preamplifier (2.1.4) between the photodiode (2.1.3) and the demodulation chains (2.2, 2.3). 9. The device according to any of claims 1 to 8, characterized in that at least one of the demodulators (2.2, 2.3) comprises a mixer (2.2.3, 2.3.3) wherein the electrical signal S1 is introduced in one of the inputs of the mixer (2.2.3, 2.3.3) and the signal of an oscillator (1.1.2, 1.2.2) at one of the modulation frequencies (f<1>, f<2>) is introduced in another one of the inputs of the mixer (2.2.3, 2.3.3), and the output of this mixer (2.2.3, 2.3.3) is introduced in a low-pass filter (2.2.4, 2.3.4) for detecting the phase-amplitude of the electrical signal S1 in phase with the local oscillator (1.1.2, 1.2.2). 10. The device according to any of claims 1 to 9, characterized in that at least one of the demodulation chains (2.2, 2.3) is implemented numerically by means of an analog-to-digital converter, an anti-aliasing filter and a logic device, such as a combination of DSP, microprocessor, microcontroller, DPS, FPGA, or another logic device suitable for detecting the phase-amplitude of the signal of the photodetector means (2.1) at a specific frequency. 11. The device according to any of claims 1 to 10, wherein the power of at least one of the laser sources (1.1, 1.2) is controlled by means of a power control system adjusted by a threshold power value P<i> and a power value proportional to the complex amplitude magnitude of |Ai | for any of the signals i=1, 2 , 3...n. 12. A detection method for detecting a state condition of the surface of the roadway in a specific verification region (4.1) comprising the steps of: - providing a first beam (5.1) with a wavelength λ<1>, wherein the value of the refractive index of the verification region (4.1) at wavelength λ<1> is indistinguishable when the verification region (4.1) is in one state condition or another, the intensity I1 of this first beam (5.1) being modulated at a frequency f1 ; and a second beam (5.2) with a wavelength λ<2>, wherein the value of the refractive index of the verification region (4.1) at wavelength λ<2> is different when the verification region (4.1) is in one state condition or another, the intensity I2 of this second beam (5.2) being modulated at a frequency f2 different from the frequency f1 ; and the radiation of both beams (5.1, 5.2) striking the verification region (4.1); - detecting the reflected radiation (5.3) in the verification region (4.1), comprising a component of wavelength λ<1> and a component of wavelength λ<2>, by means of photodetector means (2.1) transforming this reflected electromagnetic radiation into an electrical signal S1 ; - demodulating the electrical signal S1 at frequencies f1 and f2 providing the values of a first complex amplitude A1 at a frequency f1 and of a second complex amplitude A2 at a frequency f2 ; - comparing these values of the complex amplitude A1 , A2 with at least one complex amplitude reference value reflecting the variation of the refractive index at wavelength λ<2> when the verification region (4.1) is in said state condition. 13. The method according to claim 12, wherein the state condition is verified if the ratio between the moduli of the second complex amplitude |A2 | and of the first complex amplitude |A1 | is greater than a reference value RREF.
