52 results about "Kerr effect" patented technology

An optical metrology device includes a selectable pump arm that is used to produce a transient response in the target sample and a probe arm and may be configured to perform static Magneto-Optic Kerr Effect (MOKE) measurements or ellipsometry measurements when the pump arm is not selected, and time resolved (TR) MOKE measurements or ellipsometry measurements when the pump arm is selected. The optical metrology device may be further configured to perform opto-acoustic measurements when the pump arm is selected. A pulse shaper in the pump arm may be used to pulse duration, phase, or both, of the incident pump beam to enable measurement of the dependence of the magnetic dynamics on the pump pulse characteristics. The optical metrology device may be configured to operate at a single selectable wavelength or multiple wavelengths in a continuous or discontinuous spectrum.

The invention discloses a power distribution estimation method for optical performance monitoring of an optical communication system, and relates to the technical field of optical communication. A received signal is preprocessed to generate a complex value signal, the complex value signal is divided into two paths of signals, one path of signals is subjected to standard digital signal processing, the other path of signals is subjected to partial dispersion compensation, nonlinear compensation and residual dispersion compensation after dispersion reloading, absolute values of the two paths of signals are taken for related processing, and power is obtained; a power distribution diagram is obtained after repeated processing for n times, links of the power distribution diagram are changed, insertion losses are added to different link sections, then power is obtained by repeating the calculation method, multiple power distribution diagrams are obtained after repeated processing for n times, and all obtained power distribution diagram data are input into a deep neural network to train and recognize abnormal power distribution; according to the power distribution estimation method for optical performance monitoring of the optical communication system, the nonlinear Kerr effect of the optical fiber is utilized for longitudinal monitoring, and power distribution of multiple cross optical links is measured.

The invention discloses a magnetic detection device and method based on a four-quadrant detector, belongs to the technical field of magnetic detection, and is used for solving the problems that existing magneto-optical Kerr detection equipment cannot simultaneously detect a polar magneto-optical Kerr effect and a longitudinal magneto-optical Kerr effect through a set of optical paths, the same position of a detected object is difficult to align by using two sets of optical paths, and the detection precision is low. And the detection result is influenced. The device comprises a light source, a polarizer, a spectroscope, a lens assembly, an analyzer and a four-quadrant detector. A light beam with a preset width emitted from the light source is irradiated to a measured object through the spectroscope and the lens assembly; the polarizer is arranged in a light path between the light source and the spectroscope; the measured surface of the measured object is positioned on the focal plane of the lens assembly; light reflected by a detected object at least passes through the lens assembly, the spectroscope and the analyzer and then enters the four-quadrant detector.

Systems, devices, and methods are provided for all-optical reconfigurable activation devices for realizing various activations functions using low input optical power. The device and systems disclosed herein include a directional coupler comprising a first phase-shift mechanism and an interferometer coupled to the directional coupler. The interferometer comprises at least one microring resonator and a second phase-shift mechanism coupled to thereto. The interferometer and the directional coupler comprise waveguides formed of a first material, while the microring resonator comprises a waveguide formed of a second material and a third phase-shift mechanism. The second material is provided as a low-loss material having a high Kerr effect and large bandgaps, to generate various nonlinear activation functions. The first, second, and third phase-shift mechanisms are configured to control biases within the disclosed systems and devices to achieve a desired activation function.

A method includes acquiring and characterizing multiple laser beams. The method includes tracking the acquired laser beams. The method includes controlling a beam of the acquired laser beams. The method includes implementing an adaptive learning detection algorithm to identify and track a unique optical signature from at least one of the acquired laser beams. The method includes steering at least one laser beam towards a target based on the acquired laser beams. The method includes changing one or more optical properties of a beam steering unit to steer the at least one laser beam towards the target, including one or more of the following: inducing a Pockels effect on the at least one beam by applying an electric field; tuning Spatial Light Modulators; tuning a metamaterial structure; inducing a diffraction grating; and modifying an output angle of the at least one beam.

The invention relates to a miniature stress detector, which comprises a light emitting assembly, a detection head and a light receiving assembly, and is characterized in that the light emitting assembly is used for providing a scanning light beam for the detection head; the detection head is used for scanning the surface of the to-be-detected target after receiving the scanning light beam and generating a polar Kerr effect on the surface of the to-be-detected target; and the optical receiving assembly is used for receiving an optical signal fed back by the detection head under the polar Kerr effect and converting the optical signal into stress in the target to be detected. A stress detection method is provided. According to the invention, a light system is constructed by combining the light emitting assembly and the light receiving assembly, so that the detection head can detect the stress in a to-be-detected target by using the polar Kerr effect, the explosion risk is eliminated by using a non-electromagnetic sensing technology, the lift-off effect is overcome by using optical locality measurement, the size of the probe is reduced, and the detection precision is improved. An intrinsically safe and high-precision technical means is provided for rapid stress state scanning in a high-risk environment, and the safety of high-value targets in key industrial fields such as electric power, petrochemical engineering and aerospace is guaranteed.

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.

A method of separating a transparent workpiece comprises depositing a sacrificial layer onto a textured surface of the transparent workpiece, the sacrificial layer comprising a refractive index that is less than or equal to a refractive index of the transparent workpiece and greater than or equal to a refractive index of air. A defect-forming laser beam is generated via an optical assembly and used to form a plurality of defects in the transparent workpiece through sacrificial layer. The defect forming laser beam either comprises a pulsed laser beam forming a laser beam focal line in the transparent workpiece or an optical power of greater than or equal a critical power level to induce Kerr effect self-focusing in the transparent workpiece. The transparent workpiece is separated along the contour.

A kind of ultra-short pulse synchronization testing device and method based on optical Kerr effect. After the high-power density ultra-short pulse of multiple beams to be synchronized passes through optical Kerr medium, induced birefringence effect occurs, which instantaneously changes the polarization characteristics of the reference light beam, and the synchronization between multiple beams of ultra-short pulses is measured by the amplitude or phase change of the reference signal pulse. This method can realize the synchronization measurement of ultra-short pulses with large angle at the target point, and has the advantages of high measurement accuracy, good repeatability and high stability.

The present invention discloses a nanoparticle composite magneto-optical film, its preparation method, and its application, belonging to the technical field of magneto-optical film preparation and sensing applications. A CoFeB / W film is prepared on a silicon wafer using magnetron sputtering as a substrate. A gold-platinum nanoparticle layer, or a gold nanoparticle layer and a covering tungsten layer, is then spin-coated on the film. This method enhances the longitudinal magneto-optical Kerr effect of the CoFeB film by combining gold, which exhibits a surface plasmon effect, with platinum and tungsten, which exhibit a high spin-orbit coupling effect. This method utilizes the synergistic effect of these two effects to enhance the CoFeB film's longitudinal magneto-optical Kerr effect. As a sensitive element, the film has broad application potential in biomolecular sensors, as well as in the detection of viruses, bacteria, biofunctional molecules, and biological weapons.

The application discloses a kind of measurement system and method based on magneto-optical Kerr effect, belong to magnetic material measurement and imaging technical field, including three-dimensional displacement platform, optical path unit, electromagnetic unit and software control unit, three-dimensional displacement platform is in the magnetic field provided by electromagnetic unit;Optical path unit includes frame body and the laser generating device, focusing control device, differential signal measuring device and imaging device arranged in frame body interior;Linearly polarized light provided by laser generating device is focused to the sample surface fixed on three-dimensional displacement platform by focusing control device, sample surface reflects and returns focusing control device by reflected light, beam splitting obtains first reflected light and second reflected light, and the focusing control device can move up and down;Differential signal measuring device receives second reflected light to obtain electric signal, and transmit to software control unit;Imaging device receives first reflected light to realize the imaging of sample;Software control unit draws hysteresis loop according to the magnetic field intensity of the magnetic field and electric signal.

The invention provides a high-power femtosecond laser peak power multiplying device based on sheet self-compression. The high-power femtosecond laser peak power multiplying device is composed of a high-power femtosecond laser pulse, a thin lens, a fused quartz solid sheet set, a movable sliding rail, a convex reflector, a dielectric film reflector and a self-compression pulse in sequence in the direction of an incident light beam. The characteristic that negative dispersion can be generated due to the fact that femtosecond laser transmits the fifth-order nonlinear effect in quartz glass is utilized to be balanced with the Kerr effect and the positive dispersion of a quartz glass material, and the spectrum is broadened to achieve pulse self-compression under the condition that the quality of light beams is kept during transmission. Peak power multiplication of high-power femtosecond laser pulses can be achieved in a pulse self-compression mode, and the device has the advantages of being simple in structure, convenient to operate, stable, efficient and wide in application range. The device can be applied to the field of high-power femtosecond laser pulse compression and shaping, and can be better applied to application research of laser electron acceleration, higher harmonic generation and the like.

The utility model relates to the technical field of testing equipment for magneto-optical Kerr effect measuring instruments, in particular to a testing platform for a magneto-optical Kerr effect measuring instrument. The technical problem is that when a test platform for a magneto-optical Kerr effect measuring instrument is used and a measuring person needs to adjust a light test angle, the laser transmitter needs to be repeatedly dismounted and adjusted; according to the technical scheme, the testing platform for the magneto-optical Kerr effect measuring instrument comprises a testing platform body, a supporting assembly, a clamping assembly, a projection assembly, a moving assembly, a testing assembly and a control assembly. Compared with a traditional test platform for a magneto-optical Kerr effect measuring instrument, when a measuring person needs to adjust a light test angle, the laser emitter needs to be repeatedly dismounted and adjusted; the test platform for the magneto-optical Kerr effect measuring instrument can automatically adjust the laser transmitter according to a test angle required by a tester, does not need to be repeatedly disassembled, assembled and adjusted, and improves the test efficiency.

This invention provides a magnetic detection device based on diamond NV centers and the Kerr effect. It achieves the sharing of light sources and optical paths between magnetic detection technologies based on the magneto-optical Kerr effect and those based on NV centers, combining the two technologies and greatly simplifying the device structure. This increases the intensity of the optical signal received by the detection module, reduces noise interference in the signal, and thus improves the accuracy of magnetic detection. It can simultaneously meet the requirements of rapid and high-resolution detection, and improve the overall detection speed while ensuring detection accuracy.

A method of manufacturing a Kerr effect electro-optical modulator, comprising the steps of: a) using a substrate (1); b) forming a waveguide (2) on the substrate (1) so as to guide propagation of an electromagnetic wave, the waveguide (2) comprising: - a core (20), comprising a pn-type junction or a pin-type structure; - an optical cladding (21), surrounding the core (20); the core (20) and the optical cladding (21) having an interface (I); c) irradiating the interface (I) with ionizing radiation so as to trap at the interface (I) free carriers originating from the pn-type junction or the pin-type structure; d) polarizing the pn-type junction or the pin-type structure so as to apply an electric field within the core (20). Figure 3

The utility model discloses a magneto-optical Kerr effect measurement sample testboard in the technical field of sample testboards, which comprises a testboard main body and laser main bodies, two laser main bodies are arranged on the top surface of the testboard main body, and two cylinders are symmetrically fixed at the bottom end in the testboard main body. The irradiation table is fixed to the output end of the first servo motor, then the first servo motor drives the irradiation table to rotate, so that samples on different side faces of the irradiation table sequentially move to the front of the irradiation table, meanwhile, the air cylinder drives the lifting frame to move, and the height of the irradiation table is convenient to adjust; the problems that in the prior art, existing magneto-optical Kerr effect measurement samples often need to be independently placed in front of a laser device, different samples often need to be frequently arranged in front of the laser device when multiple samples are tested in the testing mode, the sample replacement process is tedious and complex, and the testing efficiency is high are solved. Therefore, the test efficiency of a plurality of samples is influenced.

A magnetic imaging device and imaging method based on diamond NV color center and Kerr effect, a spin-manipulated light source module provides a beam of incident laser light, which passes through a dichroic mirror system and is focused by a microscope objective lens and then irradiated onto the NV color center of a diamond probe, and the fluorescence generated by the NV color center returns to the dichroic mirror system through the microscope objective lens and enters the fluorescence detection module; a polarized light generating module generates polarized light, which passes through the dichroic mirror system through transmission and / or reflection, enters the microscope objective lens, and then irradiates onto a sample placed on a displacement stage, and after being reflected by the sample, part of the polarized light enters the microscope objective lens again, and then passes through the dichroic mirror system and enters the polarized light detection and imaging module. The present invention realizes high-resolution, global, and wide-field imaging of samples through compatibility design.

The invention relates to the technical field of magnetic measuring instruments, in particular to a magneto-optical Kerr effect-based magneton space imaging scanning device and method. The device comprises a transmitting assembly which comprises a laser, a beam expander, a beam splitter, a reflector, a first half-wave plate, a polarization beam splitting cube, a calcite polarizer, a first dichroscope, an objective lens, an LED light transmitting part, a convex lens and an achromatic doublet lens so as to focus an incident beam on an object to be measured; the scanning assembly comprises a second dichroscope, a second half-wave plate, a reflecting mirror, a beam splitter prism, a right-angle reflecting prism, an achromatic doublet lens, a photoelectric balance detector, a lock-in amplifier, a magnetic field applying part and a piezoelectric displacement table and is used for scanning an object to be detected; and the imaging assembly comprises a convex lens, a CMOS camera and a data processing component to generate a morphology image and a spin wave image. According to the invention, high-spatial-resolution, high-magnetic-sensitivity and wide-band spatial imaging measurement can be carried out on the spin wave and the magneton frequency comb.

Provided are: an optical modulation element that exhibits a Kerr rotation angle of at least 0.5°; a spatial light modulator comprising the optical modulation element; and a display device comprising the spatial light modulator. The optical modulation element comprises: a second electrode facing an incident surface on which light is incident; a ferromagnetic ferroelectric layer disposed on the incident surface side of the second electrode; and a ferromagnetic layer disposed on the incident surface side on the ferromagnetic ferroelectric layer. The thickness of the ferromagnetic ferroelectric layer is within the range of 20-100 nm; the thickness of the ferromagnetic layer is within the range of 3-20 nm; and the magnetization of the ferromagnetic ferroelectric layer and the ferromagnetic layer is controlled in accordance with an electrical polarization induced in the ferromagnetic ferroelectric layer by the application of a voltage to the ferromagnetic ferroelectric layer by the second electrode. A part of the incident visible light is transmitted through the ferromagnetic layer and is multiply reflected in the interior of the transparent ferromagnetic ferroelectric layer. The Kerr rotation angle is repeatedly changed in a fixed direction by the Kerr effect with each reflection at the lower surface of the ferromagnetic layer. When the visible light is finally transmitted through the ferromagnetic layer, the visible light exits from the ferromagnetic layer at a giant Kerr rotation angle. The spatial light modulator comprises the optical modulation element. The display device comprises the spatial light modulator.

A laser device (100) is provided with: a seed light source (10) that outputs pulsed light and is capable of controlling the repetition frequency of the pulsed light; an aberration generation unit (20) that applies an aberration caused by an optical Kerr effect to the pulsed light; a beam shaping optical system (30) that adjusts at least one of the beam diameter and the intensity distribution of the pulsed light; a solid-state amplifier (40) that amplifies the pulsed light and emits laser light; and arrangement adjustment units (21, 31) capable of operating at least one of the aberration generation unit (20) and the beam shaping optical system (30) in accordance with the repetition frequency of the pulsed light.

Electrically controllable optical element with a cell (D) filled with Kerr mixture (K) having two substrates (1a, 1b) and a conductive layer (2a, 2b) applied to the inner surface of each substrate (1a, 1b), wherein the Kerr mixture (K) comprises a mixture of rod-shaped molecules with a large dipole moment (5) and semi-mesogens (4) as active components, and wherein the Kerr mixture (K) forms a thin layer with a photopolymerization-produced, wide-mesh, anisotropic network (9) between a structured and / or planar conductive layer (2a, 2b) applied to a substrate (1a, 1b) in a thin-film cell (D), such thatthat, according to the electro-optical Kerr effect, the state of the active composites of semi-mesogens (4) and rod-shaped molecules with a large dipole moment (5) of the Kerr mixture (K) is isotropic without an electric field in the operating temperature range, and a change in the voltage-induced phase shift or refractive index shift in the optical element is generated by electrically continuous adjustment of the voltage U or by applying a constant voltage, characterized in that, in addition to the conductive layer (2a, 2b), an optically effective surface profile (O) is incorporated on the inner surface of a substrate (1a or 1b) or into the substrate (1a or 1b) or of both substrates (1a and 1b).

The application discloses an electromagnetic wave non-reciprocal transmission structure based on light-excited graphene and a transmission method thereof. The structure is composed of silicon rods with different widths placed on a silicon / silicon dioxide substrate, and large-area CVD graphene is transferred to the structure to form a graphene super surface structure. Due to the asymmetry of the structure and the excitation of the nonlinear Kerr effect, the transmission efficiency of electromagnetic waves is significantly related to the incident direction of signal light. By optimizing the structure parameters, the light-excited graphene super surface structure based on the light-excited graphene super surface structure shows a large positive and negative transmission ratio. The device structure is simple and compact, the required incident laser intensity is only 80kW / cm 2 , and is relatively easy to realize in experiments. By utilizing the optical adjustable function of graphene, the working frequency band of the non-reciprocal device can be effectively controlled, thereby flexibly realizing the optical isolation function.

The invention discloses an anti-interference differential polarimeter, which belongs to the technical field of optical measurement instruments, organically combines magneto-optical modulation with a polarization difference method for the first time, solves the problem of weak optical rotation signal detection in an open environment, has a lower glucose solution measurement limit of 0.020 g / mL, has greatly improved anti-interference capability compared with a traditional polarimeter, and has a wide application prospect. For solutions with different concentrations, the average error is maintained at a lower level of 3.25%, not only can light source fluctuation and ambient light interference be overcome and stable measurement be realized, but also subjective judgment of human eyes can be eliminated and objective quantitative reading can be realized. According to the invention, accurate measurement of a glucose solution in a range of 0.020-0.400 g / mL can be realized, automatic data acquisition and real-time concentration display are realized, and the system integrates electromagnetism, optics and information science, can be used as an ideal platform for college physical experiment and common physical experiment teaching, and has a wide application prospect. The method can also be popularized to measurement of physical quantities such as magneto-optical Kerr effect, weak magnetic field and micro displacement, and is wide in application prospect.

The invention discloses a nonlinear lens based on a transformation material and a Kerr effect and a design method, and belongs to the field of optical signal processing and transformation materials. The nonlinear lens is a rectangular lens and is made of a nonlinear material. The spatial refractive index distribution is designed by changing the optical principle, the path instability in a dynamic system is combined with the optical Kerr effect, and the circular lens is adjusted into the square lens with the unstable system path by utilizing the spatial distribution of special material parameters; the weak refractive index change is converted into violent offset of a light beam output position under the instability characteristic of a dynamic system, and under the specific refractive index distribution, the lens has a focusing effect on the light beam propagating in the lens, so that the light beam is enhanced in a local area, and then the nonlinear effect is enhanced; and an optical system with higher speed and lower energy consumption is realized on a simpler device. According to the invention, conformal transformation is adopted, the isotropy of a lens material is ensured, and manufacturing of a nonlinear lens is facilitated.

The application relates to the field of optical technology and discloses a second-order soliton trap transmission state regulation method based on an optical event horizon simulation, which comprises the following steps: preparing a second-order soliton pulse and an external probe pulse, wherein the second-order soliton pulse is generated through the balance of dispersion and nonlinearity in a nonlinear optical fiber, the external probe pulse is a weak power pulse, the group velocity parameter of the second-order soliton pulse and the external probe pulse is measured, and group velocity matching and group velocity mismatch conditions are set; through accurate setting of the group velocity matching and mismatch conditions and quantitative calculation of the refractive index change caused by the soliton pulse based on the Kerr effect, an equivalent event horizon is defined, definite physical parameter benchmarks and stable potential well environments are provided for transmission state regulation, the stability of a soliton potential well action boundary can be determined and ensured, the transmission state misjudgment problem caused by potential well drift and distortion is overcome, and the accuracy of the regulation process and the predictability of the result are ensured.

The invention discloses a magnetic skyrmion forming method and writing device based on femtosecond laser pulse regulation and control. The method comprises the following steps: acquiring a CoFeB nano-disk and placing the CoFeB nano-disk in a sample placing area of a magneto-optical Kerr effect microscope; pulse excitation is carried out on the CoFeB nanodisk by adjusting femtosecond laser thermal pulses, generation and annihilation of the Skyrmion of the CoFeB nanodisk in a preset area are controlled, and the number and position of the Skyrmion are obtained; and writing and reading data according to the generation and annihilation of the Skyrmion and the number and position of the Skyrmion. The device comprises a femtosecond laser pulser, a CoFeB nanodisk and a temperature sensor. According to the embodiment of the invention, the energy consumption can be reduced, the interference of external noise is avoided, and the precise control capability of the number and position of the skyrmion is improved. The method can be widely applied to the technical field of spintronics.

A method comprises providing an RFOG that includes a resonator in communication with a light source emitting a first signal at a first power level in a CW direction, and a light source emitting a second signal at a second power level in a CCW direction; adding a common intensity modulation to the first signal, to produce an intensity modulated CW signal; adding the same common intensity modulation to the second signal, to produce an intensity modulated CCW signal; introducing the intensity modulated CW signal into the resonator; introducing the intensity modulated CCW signal into the resonator; detecting modulated rate signals that are output from the resonator at a common intensity modulation frequency; and adjusting a power level ratio between the first and second power levels, to determine a modified power level ratio value where a Kerr effect bias instability due to an asymmetrical loss distribution is reduced or eliminated.

A method is provided for manufacturing a Kerr effect electro-optical modulator that includes using a substrate, forming a waveguide on the substrate so as to guide a propagation of an electromagnetic wave, irradiating the interface with an ionizing radiation so as to trap at the interface (I) free carriers originating from the p-n junction or from the p-i-n structure, and polarizing the p-n junction or the p-i-n structure so as to apply an electrical field within the core. The waveguide includes: a core, comprising a p-n junction or a p-i-n structure; and an optical sheath, enclosing the core. The core and the optical sheath have an interface.

The invention discloses a method and system for testing and analyzing magneto-optical parameters of a magnetic multilayer film, and belongs to the technical field of photoelectron data analysis, and the method comprises the following steps: carrying out an ellipsometry test on a to-be-tested magnetic multilayer film sample to obtain ellipsometry parameters of the sample; constructing an optical model according to the structure of the magnetic multilayer film sample to be tested, and performing fitting calculation by combining an optical theory and the ellipsometric parameters obtained by testing to obtain optical property parameters of each layer of film in the sample; the method comprises the following steps: carrying out a magneto-optical ellipsometry test on a to-be-tested magnetic multilayer film sample to obtain a reflection coefficient of the sample in an unmagnetized state and a magneto-reflection coefficient caused by a Kerr effect, deriving a total propagation matrix of light in the magnetic multilayer film sample, and calculating to obtain a Jones matrix of the sample; and calculating the magneto-optical coupling coefficient of each layer of film according to the Jones matrix, the reflection coefficient, the magneto-reflection coefficient and the optical property parameter of each layer of film. According to the invention, accurate characterization of magneto-optical parameters of magnetic multilayer films with various thicknesses, various materials and various layer numbers can be realized.

This application relates to a reconfigurable all-optical nonlinear activation function on a silicon integrated platform. This application provides systems, apparatuses, and methods for an all-optical reconfigurable activation device that implements various activation functions using low input optical power. The disclosed apparatus and system include a directional coupler comprising a first phase-shifting mechanism and an interferometer coupled to the directional coupler. The interferometer includes at least one microring resonator and a second phase-shifting mechanism coupled thereto. The interferometer and directional coupler include a waveguide formed of a first material, while the microring resonator includes a waveguide formed of a second material and a third phase-shifting mechanism. The second material is provided as a low-loss material with a high Kerr effect and a large bandgap to generate various nonlinear activation functions. The first, second, and third phase-shifting mechanisms are configured to control bias within the disclosed system and apparatus to achieve the desired activation function.