93 results about "Frequency comb" patented technology

Disclosed herein is an optical frequency comb generator for a distributed acoustic anomaly detection system. The system can include a continuous wave frequency modulated laser source configured to generate a laser signal. The system can include an acousto-optical modulator configured to modulate the laser signal by altering an amplitude and / or frequency of the laser signal based on an RF drive signal applied to the AOM, and to output an optical pulse with multiple frequency sidebands based on the modulation. The output can form an optical frequency comb usable detecting and locating acoustic anomalies within a structure under observation.

The invention discloses a beat frequency comparison device mediated by an optical frequency comb. The beat frequency comparison device comprises the optical frequency comb, a first frequency stabilized laser, a first beat frequency device, a first frequency mixer, a first high-pass filter, a second frequency stabilized laser, a second beat frequency device, a second frequency mixer, a second high-pass filter, a DDS signal generator, a third frequency mixer and a low-pass filter. Frequency-stabilized lasers output by the first frequency-stabilized laser and the second frequency-stabilized laser and an optical frequency comb output by the optical frequency comb are subjected to beat frequency in the first beat frequency device and the second beat frequency device respectively, and first beat frequency and second beat frequency are obtained; the first beat frequency and the second beat frequency are mixed with the carrier envelope offset frequency of the optical frequency comb, and a first sum frequency and a second sum frequency are filtered out; the first sum frequency obtains a synthetic frequency through direct digital frequency synthesis; the second sum frequency and the synthetic frequency are mixed in the third mixer, and then the difference frequency is filtered out through the low-pass filter. According to the invention, beat frequency comparison of frequency-stabilized lasers with different wavelengths can be realized, and the influence of the stability of the optical frequency comb is avoided.

The invention provides a mid-infrared optical frequency comb. The mid-infrared optical frequency comb comprises a near-infrared optical frequency comb seed source of a polarization-maintaining all-fiber structure; the all-fiber nonlinear amplification and pulse compression module is connected with the near-infrared optical frequency comb seed source through a polarization maintaining fiber and is used for amplifying the power of the seed light and compressing the pulse width after generating a linear chirped pulse; the all-fiber nonlinear spectrum broadening module is connected with the all-fiber nonlinear amplification and pulse compression module through a polarization maintaining fiber and is used for broadening a laser spectrum; the difference frequency module is used for receiving the laser pulse processed by the all-fiber nonlinear spectrum broadening module and generating an intermediate infrared laser pulse through intra-pulse self-difference frequency; wherein the seed source, the all-fiber nonlinear amplification and pulse compression module and the all-fiber nonlinear spectrum broadening module are connected through a polarization maintaining fiber to form an all-fiber integrated structure. By adopting the scheme, the anti-interference capability of the system can be enhanced, miniaturization and high operation reliability are realized, the debugging process is simplified, and the difference frequency efficiency is improved.

The invention provides a terahertz frequency comb generation verification method and system based on an optical fiber microcavity optical frequency comb, and the method comprises the steps: injecting a continuous wave laser into an optical fiber microcavity resonator to generate a stable Kerr optical frequency comb, enabling the Kerr optical frequency comb to work in a single soliton state or a soliton crystal state, and obtaining an optical frequency reference with low phase noise. Furthermore, spectrum selection is performed on the optical frequency comb, multiple groups of optical comb tooth pairs comprising comb teeth of different orders are actively selected, and the optical frequency difference of each group of comb tooth pairs is directly converted into an electric signal in a terahertz frequency band by utilizing a beat frequency effect of a photoelectric detector. A plurality of terahertz electric signals generated by different comb tooth pairs are integrated to form a multi-channel terahertz frequency comb. The method allows a plurality of discrete and frequency-controllable terahertz signal channels to be generated in parallel on a single optical platform through one-time optical processing and photoelectric conversion, so that multichannel terahertz frequency comb generation is realized.

A metrology system may include a dual frequency comb source providing a first comb beam having a first repetition rate and a second comb beam having a second repetition rate; a beam splitter to generate one or more dual-frequency comb illumination beams from the first comb beam and the second comb beam; and a beam combiner to form a dual frequency comb illumination beam from the first comb beam and the second comb beam. The system may further include an illumination subsystem to illuminate a sample with the dual frequency comb illumination beam through an objective; a light collection subsystem to collect sample light from the sample with the objective lens; and a detector to capture a radio frequency signal based on the sample light. The system may further extract spectral measurement data associated with the sample from the radio frequency signal and generate a metrology measurement based on the spectral measurement data.

This invention provides a self-heterodyne detection system capable of stably and over long periods of time measuring broadband laser linewidths. [Solution] The present invention discloses a self-heterodyne detection system. The system may include a frequency comb light source that generates light, a photodetector that detects the light, an electrical spectrum analyzer connected to the photodetector that analyzes the frequency and wavelength of the light using the detection signal of the photodetector, an interferometer including an input coupler provided between the frequency comb light source and the photodetector to receive the light, a branch waveguide branched by the input coupler, and an output coupler connected to the branch waveguide, and a programmable filter provided in the branch waveguide to select the peak wavelength of the light.

The invention discloses a micro-cavity optical frequency comb and a structural parameter determination method thereof, relates to the technical field of optical frequency combs, and aims to solve the problems that in the prior art, a traditional optical frequency comb is limited in structural regulation dimension, and an existing design method is difficult to efficiently and accurately achieve matching of spectrum requirements and structural parameters. The micro-cavity optical frequency comb comprises an input / output waveguide and a grating-assisted nested micro-ring cavity. The input / output waveguide is coupled with the grating-assisted nested micro-ring cavity; the grating auxiliary nested micro-ring cavity comprises an outer micro-ring, an inner micro-ring and a grating; the grating is formed on the outer micro-ring or the inner micro-ring; the outer micro-ring and the inner micro-ring are coupled to form a nested resonant structure; structural parameters corresponding to the grating-assisted nested micro-ring cavity are obtained through light field steady-state verification based on trained reverse neural network prediction; the trained reverse neural network is obtained based on the forward neural network. The method is used for realizing efficient and accurate design of the microcavity optical frequency comb and meeting the target spectrum requirement.

The invention discloses a high-performance optical comb laser based on heterogeneous material integration and multi-effect fusion, belongs to the technical field of optical communication and laser devices, and aims to solve the problems that a traditional optical comb laser is difficult to start tuning, low in power efficiency, large in line width or limited in bandwidth and the like. A scheme of heterogeneous integration of a III-V group gain material, a low-loss Si3N4 waveguide and a high-electro-optical coefficient barium titanate (BTO) material is adopted, an outer cavity chip comprises a high-Q-value annular resonant cavity, an electro-optical comb is generated by modulating the annular resonant cavity, then a Kerr comb is excited, and the optical comb is amplified through gain. According to the invention, three mechanisms of electro-optical modulation, Kerr effect and semiconductor light amplification are fused, and based on device topological structure innovation and unit device optimization, the problems are solved, the on-chip frequency comb performance is significantly improved, and the optical comb laser with excellent starting and tuning performance, high power, large bandwidth and narrow line width is realized.

The application discloses a kind of fast quantitative distributed optical fiber vibration detection method and system based on frequency comb, belong to optical fiber sensing field technical field, method includes: S1, design target frequency comb, including the comb tooth interval Δf of the target frequency comb is designed C And the initial phase of the target frequency comb;S2, the target frequency comb is converted into time domain signal, and the time domain signal is modulated on probe light, obtains modulated time domain optical carrier signal;S3, the modulated time domain optical carrier signal is carried out optical domain frequency shift and probe pulse modulation, obtains modulated frequency comb pulse sequence;S4, the frequency comb pulse sequence is input to the optical fiber FUT to be measured, and quantitative distributed optical fiber vibration detection is carried out.The application realizes the modulation of target frequency comb on probe pulse, compresses single detection time, to improve the frequency response capability to external disturbance, can realize the high signal-to-noise ratio detection of dynamic signal.

A movement prediction apparatus including first and second light output devices, a light reception device, and a processor. The first light output device outputs output-light having a spectral component of a first optical frequency comb of which a frequency comb interval is a first interval. The second light output device outputs reference light having a spectral component of a second optical frequency comb of which a frequency comb interval is a second interval. The light reception device receives combination light that is a combination of the output-light, reflection light that is the output-light reflected by a flying object rotor wing, and the reference light, and measures a distance to the rotor wing based on the combination light. The processor calculates a rotation amount that represents a rotational speed of the rotor wing based on a change amount of the measured distance, and predicts a movement of the flying object.

LIDAR distance measuring device (10), comprising: a laser (12) for generating a laser beam, a frequency comb generator (14) configured to generate at least one optical frequency comb signal (37) based on the laser beam, a signal splitting unit (16) which is configured to split the optical frequency comb signal (37) into different optical signal channels (34), each of which is assigned a respective wavelength range, a channel matching unit (18) which is configured to change at least two optical signal channels (34) in their relative position to each other, a transmitting unit (20) which is configured to send light associated with the modified optical signal channels (36) as transmitting light (22) into a measuring area (24), a receiving unit (26) for receiving transmitted light reflected from objects (28) in the measuring range (24) as received light (30), and a signal processing unit (32) which is configured to determine a distance to the object (28) based on the received light (30) and in particular at least a part of the transmitted light (22).

The present disclosure provides a device suitable for generating a frequency-stable microcavity optical frequency comb, comprising: a light source part configured to emit a light beam; a beam splitting device configured to split the light beam emitted by the light source part into a plurality of first light beams; a light source frequency determination unit connected with a first output port of the beam splitting device, the adjustment frequency being determined based on the absorption of the first light beams by atoms in the light source frequency determination unit, and the light source part adjusting the frequency of the emitted second light beams based on the adjustment frequency; a resonant microcavity connected with the light source frequency determination unit, the second light beams generating a first microcavity optical frequency comb in the resonant microcavity; and a modulation unit arranged between a second output port of the beam splitting device and the resonant microcavity, configured to modulate the second light beams into third light beams with repetition frequency information based on the repetition frequency of the first microcavity optical frequency comb, and the third light beams generating a second microcavity optical frequency comb in the resonant microcavity.

Method for generating a frequency-modulated transmit signal (8) for a transmitting device (5) of a detection device (2) for transmitting the frequency-modulated transmit signal (8) into an environment (3) of the detection device (2), comprising the steps: - Generating a frequency comb (11) using an optical mode-locked source (10) of the transmitting device (5); - Filtering of at least one frequency line (12) in the generated frequency comb (11) by means of a first optical filter device (13) of the transmitting device (5); and - Generating the frequency-modulated transmit signal (8) by means of a photodiode (14) of the transmitting device (5) as a function of the filtered frequency comb (15), wherein the frequency-modulated transmit signal (8) is generated proportionally to the frequency difference to the filtered frequency line (12), wherein at least two frequency lines (12) are brought closer together by means of an optical dispersive element (18) of the transmitting device (5) or at least two frequency lines (12) are pulled further apart by means of an optical dispersive element (18) of the transmitting device (5), wherein the dispersive element (18) is arranged in the beam path after the first optical filter device (13) or the dispersive element (18) is arranged in the beam path before the first optical filter device (13).

The invention discloses a method for obtaining the thickness and refractive index of a film, a test system, a storage medium and application. The method for obtaining the thickness and the refractive index of the thin film comprises the following steps: obtaining an intermediate frequency signal carrying transmission phase information by using two groups of nonlinear transmission line terahertz frequency comb generators and a broadband mixer, and obtaining an actually measured phase curve based on the intermediate frequency signal; constructing an equivalent multi-optical-path interference model of the thin film, performing coherent superposition on multiple reflection components of a measured wave signal in the thin film in a complex field to obtain a complex phase of a total transmission field, and obtaining a phase-frequency change spectrum based on the complex phase as a model phase curve; and an error function of the model phase curve and the actually measured phase curve is constructed, and a parameter combination enabling the error function to take the minimum value is solved by scanning the parameter combination of the refractive index n and the thickness d of the thin film. According to the method, thermal drift or time drift of the phase is avoided, and then calculation errors caused by phase jump are avoided.

This invention provides an optical frequency comb frequency stabilization device and method. The device includes: a first optical filter configured to filter the optical frequency comb to obtain two comb teeth to be locked; an oscillation loop configured to oscillate based on the two comb teeth to be locked, generating an oscillation radio frequency signal at a first angular frequency and an oscillation radio frequency signal at a second angular frequency; and a feedback controller configured to perform mixing processing on the oscillation radio frequency signal at the first angular frequency, the oscillation radio frequency signal at the second angular frequency, and a radio frequency reference signal to extract a time-varying error signal, and output a control signal based on the error signal to lock the frequency of the optical frequency comb.

The application discloses a kind of background noise suppression systems of dual optical comb coherent raman spectrum of probe light delay control, by setting the laser that light frequency comb light source module is emitted into probe light and pump light by first beam splitter in probe light delay control module, and setting optical delay line is applied to the probe light with delay amount, utilize the characteristics that the decay time of coherent raman spectrum signal is longer than the decay time of background noise, probe using probe light with delay amount, realize the purpose of inhibiting background noise, it is beneficial to improve the signal-to-noise ratio of dual optical comb coherent raman spectrum measurement system, inhibits spectrum signal distortion.

According to the present invention there is provided optical assembly (1) comprising. a laser (2) which is operable to emit light: an optical wave guide (3) having an input (3a) and an output (3b). the input (3a) of the optical wave guide (3) being optically coupled to the laser (2) so that the laser (2) can input light to the wave guide (3): a resonator (5) which is optically coupled to the wave guide (3) between the input (3a) of the wave guide (3) and the output (3b) of the wave guide (3): and wherein the resonator (5) has a resonant frequency. and wherein the resonator (5) defines an optical path (11): and wherein the resonator (5) is configured so that said optical path (11) is a closed loop: and wherein the resonator (5) is configured to have a periodic change in optical characteristics along said optical path (11) so that the resonator (5) can provide a backreflection which is at the resonant frequency of the resonator: and wherein the periodic change in optical characteristics along said optical path (11) provide an amount of said backreflection, which will provide a first detuning range in which self-injection locking of the laser using said backreflection is achieved, and. a second detuning range wherein a multifrequency comb can be generated within the resonator (5): and wherein the first and second ranges at least partially overlap, so that both self-injection locking of the laser will occur and an optical resonator-based multifrequency comb is output from the wave guide (3), when the assembly (1) is in operation. There is further provided a corresponding method of providing a optical resonator-based frequency comb at an output of a waveguide, using said assembly (1).

The application provides a light frequency comb generation device and method based on a series double microcavity structure. The device comprises a pump laser, an optical amplifier, a polarization controller, a first tapered lens fiber, a series double microcavity structure and a second tapered lens fiber connected in sequence. The second tapered lens fiber is connected to a spectrum analyzer and an oscilloscope through a first coupler. The optical amplifier is used to amplify the power of the output laser of the pump laser to reach the power threshold required for microcavity light frequency comb generation. The polarization controller is used to adjust the polarization mode of the output laser of the optical amplifier so that the polarization mode of the laser is the same as the polarization mode of the microcavity light frequency comb to be generated. The series double microcavity structure comprises a bus waveguide and two microcavities coupled thereto and is used to generate a light frequency comb. The application can solve the technical problems of high pump power, low energy conversion efficiency and low parameter selection freedom of the existing light frequency comb based on a single microcavity structure.

The application provides a thin-film lithium niobate-based optical frequency comb generation device and method, and belongs to the technical field of optical frequency combs, and comprises a pumping unit for providing single / multi-frequency laser; a microwave modulation unit for performing electro-optic modulation on a normal dispersion double-micro-ring resonant cavity unit to generate modulation sidebands; and the normal dispersion double-micro-ring resonant cavity unit generates an optical frequency comb through normal dispersion, electro-optic effect and third-order nonlinear effect. The single / multi-frequency laser is coupled to the normal dispersion double-micro-ring resonant cavity unit based on thin-film lithium niobate, and the normal dispersion, electro-optic effect and third-order nonlinear effect are combined to realize optical frequency comb spectrum widening and spectrum envelope flattening.

The application discloses a kind of quantum cascade laser light frequency comb based on on-chip dispersion regulation and preparation method thereof, comprising: sequentially growing lower waveguide layer, passive waveguide layer, low-doped waveguide layer, high-doped waveguide layer, lower limiting layer, active region, upper limiting layer, upper waveguide layer, ohmic contact layer on substrate;SiO2 layer is grown on the surface of ohmic contact layer, and double-groove strip-shaped ridge structure is formed on the surface, and the etching depth reaches the lower waveguide layer;Fill half-insulating InP:Fe in double groove, remove residual SiO2 layer;Insulating layer is grown on the surface of ohmic contact layer;Surface of insulating layer is prepared front metal electrode window;Insulating layer surface and inside front metal electrode window, front metal electrode layer is grown;Thicken front metal electrode layer;Substrate is thinned and polished, back metal electrode layer is grown, annealing treatment, packaging, and quantum cascade laser light frequency comb is obtained.The dispersion problem of mid-infrared quantum cascade laser is solved, the yield is high, the cost is low, the process is simple, and the manufacturing demand of large-scale application is met.

The invention relates to the technical field of optical sensing and trace gas detection, in particular to an optical comb tooth space-time multiplexing photoacoustic spectrum detection device and method, and the device comprises a light source module, a modulation module, a dispersion light splitting module and an acoustic detection module. According to the device, a frequency comb is used as a light source, comb tooth light with different wavelengths is separated in parallel in space through intensity modulation and spatial dispersion light splitting, and multiple paths of light channels for synchronously exciting gas to be detected are formed. The acoustic detection module receives the excited photoacoustic signal and converts the photoacoustic signal into an electric signal. According to the invention, a traditional serial scanning or mechanical interference mode is innovated into parallel synchronous detection of multi-component gas, high-sensitivity and high-selectivity recognition of various trace gases is realized in single measurement, and the bottlenecks of the prior art in the aspects of detection efficiency, response speed and multi-component synchronous analysis capability are effectively solved.

An example apparatus, method, and system for determining a characteristic of a target gas in a fluid sample is provided. In some embodiments, the example apparatus includes a frequency comb illumination source configured to emit pulsed light having a plurality of frequency comb wavelengths. The apparatus also includes an optical cavity containing a fluid sample and exhibiting a plurality of cavity resonance modes. A frequency comb wavelength of the plurality of frequency comb wavelengths associated with the frequency comb illumination source is configured to align with a cavity resonance mode of the plurality of cavity resonance modes. A characteristic of the fluid sample is determined based on one or more optical characteristics of a transmitted light passing through the fluid sample within the optical cavity.

The invention discloses a method and a system for generating a tunable flat-topped spectrum based on a Flokey singular point. The method comprises the following steps: forming two types of supermodes alternately arranged on a frequency axis by using a pair of coupled optical ring resonators; applying periodic dynamic complex modulation including real and imaginary components to the resonator; configuring the modulation frequency to be matched with the super-mode interval so as to construct a periodically quenched non-Hermite frequency lattice on the synthetic frequency dimension; and adjusting modulation parameters, and driving the quasi-energy band of the crystal lattice to present a linear dispersion relationship at the singular point, thereby generating the flat-topped spectrum. According to the method, the intensity and the broadening speed of the flat-topped spectrum are linearly controlled by adjusting the imaginary part modulation amplitude, and the flat-topped frequency comb formed by a single supermode is obtained by extracting signals at a specific moment in a modulation period. According to the method, flexible electric control tuning of the spectrum form, the broadening speed and the modal component is realized, the system can work under the weak non-Hermite condition, and the practicability and integration of the system are improved.

To enable an increase in repetition rates of a passively mode-locked laser by a factor of up to 1000 up to a frequency range of 1 to 40GHz while maintaining comb characteristics of a harmonically mode-locked (HML) frequency comb laser.SOLUTION: The HML laser may include a reference cavity having a beam splitter that is common mode to the reference cavity and the main cavity, and is further configured to generate an output for the HML optical frequency comb. The bulk as well as the fiber reference cavities can be implemented with ultra-low expansion thermal expansion materials that enable the use of HML lasers as precision frequency references and frequency synthesizers for the microwave, millimeter wave, and optical frequency domains. HML dual-frequency combs with minimal differential noise between the two combs can reference both combs to the same reference cavity.SELECTED DRAWING: Figure 2A

Frequency comb generators are provided that include at least one of a closed loop formed of gain material, or a gain material section divided into two or more segments by one or more dividers, wherein at least one of the two or more segments is a tapered segment. A frequency comb generator is optically coupled to an output waveguide for providing frequency comb pulses generated by the frequency comb generator to one or more downstream elements.

The invention discloses an arc optical frequency comb device and system and communication equipment, and relates to the technical field of optical communication. According to the device, active or passive functional devices such as a wavelength division multiplexer, a gain waveguide, a microcavity structure, a delay tuning unit, a beam splitter and the like are all integrated on the same silicon nitride chip to form an on-chip laser resonant cavity, and the coupling alignment error of a discrete optical fiber and a spatial optical path is eliminated. The gain waveguide provides optical power amplification, and the microcavity structure forms a soliton state optical frequency comb based on a Kerr nonlinear effect; the delay tuning unit adjusts the detuning amount between the main cavity and the microcavity in real time by introducing accurate light delay, so that rapid excitation and stable locking of the soliton state optical frequency comb are realized, and traditional mechanical tuning is replaced. The beam splitter feeds back part of light to maintain oscillation, and the other part of light is output as a low-noise soliton optical frequency comb. The above structure solves the problems of large size, complex adjustment and poor stability of the existing system through the cooperation of all-on-chip integration and tuning and detuning.

The polarization multiplexing double-frequency comb laser with online polarization and mode locking belongs to the field of double-frequency comb lasers. The problems of large preparation difficulty of double-frequency comb optical system, instability of double-frequency comb output light source and uncontrollable power loss are solved. The passive mode locking is realized through the mode locker, and the circulating oscillation of the set direction of the resonant cavity is realized through the direction control component (polarization insensitive isolator or ring). Since the mode locker and the online polarizer are prepared by the side polished fiber, the preparation difficulty is small, the power loss is controllable, and the online polarizer is introduced to replace the traditional unstable polarization control. The online polarizer introduced makes the double-frequency comb more stable output. The present application is mainly used for generating stable double-frequency comb light.

A high-conversion-efficiency integrated frequency comb device (100; 200; 310a – 310c) comprises at least one micro-resonator (120; 220) configured to receive pump laser light from at least one pump laser source, convert at least partially the received pump laser light for generating a laser frequency comb, and output frequency comb light based on the produced laser frequency comb. The micro-resonator (120; 220) comprises at least one closed-circuit waveguide (122; 222) integrated in a semi-conductor topography of the micro-resonator (120; 220). The closed-circuit waveguide (122; 222) comprises at least one structure for producing periodic perturbation (124; 224) configured to produce mode hybridization via coupling of forwards and backwards travelling modes in the closed-circuit waveguide (122; 222) by means of rapid, in particular sub-wavelength, modulation of a propagation constant of light propagating in the closed-circuit waveguide (122; 222). The structure for producing periodic perturbation (124; 224) has been designed with respect to at least one of an intended width, in terms of comb lines, of the frequency comb and / or an intended intensity distribution within a target width, in terms of comb lines, of the frequency comb, based at least partially on the stipulation that a dispersion-loss operator to achieve an ideally flat microcomb according to an exact solution of a generalized Lugiato-Lefever Equation exists in the form [iD+K], and, as a function of resonator mode index μ, the dispersion-loss operator takes the following generic form: wherein a, b, c, d 3 ... d ∞ , h, p, q, r, s, u 3 , u ∞ are constants, and μ ≤ N / 2 for N being the number of intended comb lines apart from a potential comb line corresponding to the pump laser light.

Harmonically modelocked (HML) frequency comb lasers can allow an increase of the repetition rate of passively modelocked laser by up to a factor of 1000 to the frequency range of 1-40 GHz, while preserving their comb properties. An HML laser can include a reference cavity with a beam splitter that is a common mode to the reference cavity and a main cavity, while further configured for also producing an output for the HML optical frequency comb. Bulk as well as fiber reference cavities can be implemented with ultra-low expansion thermal expansion materials that allow the use of HML lasers as precision frequency references and frequency synthesizers for the microwave, mm wave and optical frequency domain. HML dual frequency combs with minimal differential noise between the two combs can reference both combs to the same reference cavity. Harmonic modelocking can also facilitate optical parametric oscillation inside the reference cavity.

The present disclosure provides a method comprising generating, by a dual-frequency comb source, a first optical frequency comb having a first repetition rate and a second optical frequency comb having a second repetition rate different from the first repetition rate. The method comprises directing one or more of the first optical frequency comb or the second optical frequency comb toward a material using one or more optical elements. The method comprises detecting, using a diode photodetector, optical signals from the first optical frequency comb and the second optical frequency comb after one or more of the first optical frequency comb or the second optical frequency comb interact with the material. The method comprises generating, using the diode photodetector, a radio frequency signal corresponding to the optical signals. The method comprises determining, based on the radio frequency signal, a thickness of the material.