61 results about "Optical noise" patented technology

The invention discloses a photovoltaic glass defect detection method and system based on image recognition, particularly relates to the technical field of visual inspection, and is used for solving the problem that defect recognition is interfered by optical artifacts caused by a film layer interference effect on the surface of coated glass. The method comprises the following steps: extracting interference characteristics through a reflection image to generate an optical artifact distribution diagram, positioning an interference region in a transmission image frequency domain space, constructing a process response template in combination with a sedimentary pulse frequency, and executing polarization coherence screening and time-varying deconvolution collaborative filtering to eliminate artifacts; based on energy ratio dynamic decision reinspection or defect classification process implementation, inherent optical noise and real physical defects of a material are effectively separated, and the accuracy and reliability of coated glass defect detection are remarkably improved.

The invention provides an optical noise suppressor, a manufacturing method and application, the optical noise suppressor comprises a substrate, a piezoelectric driving structure and a top cover, the substrate is internally provided with a clearance space vertically penetrating through the substrate, the clearance space is internally provided with a grating structure, and the grating structure is connected with the substrate through a cantilever beam structure; the piezoelectric driving structure is located above the cantilever beam structure and comprises a bottom electrode metal layer, a piezoelectric film layer and a top electrode metal layer which are stacked from bottom to top; the top cover is located above the substrate and is in bonding connection with the substrate, a reflecting layer is arranged on the lower surface of the top cover, the projection of the reflecting layer on the substrate covers the grating structure, the piezoelectric driving structure can drive the cantilever beam structure to deform after applying voltage, and then the distance between the grating structure and the top cover is changed. The distance between the grating structure and the reflecting layer can be precisely regulated and controlled through voltage driving, the reference light intensity can be regulated and controlled and monitored in real time, and the advantages of full automation and high precision are achieved.

An optical multi-pass cell system, a gas absorption data detection method, and a terminal device. The optical multi-pass cell system comprises: an optical multi-pass cell (11), which comprises an input end (101) and an output end (102); and a driving mechanism (12), which is used for driving M sub-mirrors of the optical multi-pass cell (11) to perform periodic reciprocating motion in a Z-axis direction during each data collection process of a gas absorption data detection process, wherein the Z-axis direction is parallel to the optical axis of the optical multi-pass cell (11), M≥1, and the detection process comprises: when the optical multi-pass cell (11) is filled with a gas to be detected, a detection beam is inputted from the input end (101), is reflected multiple times in the optical multi-pass cell (11), and then forms an interference beam that is outputted from the output end (102). Optically noise-smoothed gas absorption data can be obtained, such that the sensitivity of detecting gas absorption data on the basis of an optical multi-pass cell system can be improved.

The invention provides a quartz enhanced photo-thermal spectral concentration data acquisition method and a light intensity correction method and device, and the light intensity correction method comprises the following steps: selecting data of non-absorption positions at two sides of an original 2f signal as base lines, and adjusting the value range of the base lines at the two sides according to an actually measured spectral signal; fourth-order polynomial fitting is carried out according to the base line, and a light intensity nonlinear response background signal in the whole spectral range is obtained through fitting; a background obtained by fourth-order polynomial fitting is deducted from the measured harmonic signal, and the peak-to-peak value of the signal is in direct proportion to the light intensity and the concentration of the gas to be measured; and dividing the peak-to-peak value of the 2f signal from which the background is deducted by the amplitude of the background signal to obtain a normalized peak-to-peak value of the 2f signal. According to the invention, light intensity correction of quartz enhanced photo-thermal spectrum concentration data is realized, light intensity jittering and drifting are prevented from introducing errors to system measurement, light noise can be inhibited, and the long-term stability of the system can be improved.

An example electronic system utilizing an optical ranging, proximity, and / or image sensor configured with retroreflective mechanisms to reduce unwanted optical noise at an optical radiation receiver are provided. The example ranging, proximity, and / or image sensor is configured to include a housing cap having a transmission opening and a receiving opening. The example sensor may further include an optical radiation source positioned to direct ranging optical radiation through the transmission opening toward a target object. An optical radiation receiver is positioned to receive ranging optical radiation reflected off the target object through the receiving opening. A retroreflective mechanism implemented on a surface of the housing cap directs unwanted optical noise back towards an unwanted optical noise source and away from the optical radiation receiver. Properties of the target object may be determined based on one or more properties of the ranging optical radiation received at optical radiation receiver.

The invention relates to the technical field of underwater wireless optical communication, in particular to optical communication equipment suitable for a deep sea underwater robot. The method comprises the following steps: a signal modulation unit loads a data signal needing to be transmitted to Gaussian laser generated by a laser, and loads a modulation signal to the Gaussian laser; the spatial light modulation unit converts the modulated Gaussian laser into a non-diffraction light beam; the optical transmitting unit is used for aligning and directionally transmitting non-diffraction light beams through a PI D control algorithm; the optical receiving unit collects the non-diffracting light beams transmitted from the optical transmitting unit and performs primary focusing on the non-diffracting light beams; the optical noise reduction unit uses a filtering module to remove scattered light of different wavebands, and uses a shading module to further eliminate noise in an area near a non-diffracting beam phase singular point; and the signal demodulation unit demodulates the modulation signal detected by the detector. The laser communication technology is adopted in the design, and the advantages of medium and long distance, high speed and miniaturization are simultaneously met under the condition of low power consumption.

The utility model belongs to the field of optical multi-pass pools, and provides an optical multi-pass pool system, comprising: an optical multi-pass pool comprising an input end and an output end; the driving mechanism is used for driving the M sub-reflectors of the optical multi-pass cell to periodically move back and forth in the Z-axis direction in each data acquisition process of the gas absorption data detection process, and the Z-axis direction is parallel to the optical axis of the optical multi-pass cell; wherein M is larger than or equal to 1, and the detection process comprises the steps that under the condition that the optical multi-pass cell is filled with gas to be detected, a detection light beam is input from the input end, and after multiple times of reflection in the optical multi-pass cell, an interference light beam is formed and output from the output end. According to the embodiment of the invention, the gas absorption data with smooth optical noise can be obtained, so that the sensitivity of detecting the gas absorption data based on the optical multi-pass cell system can be improved.

The invention discloses an intelligent monitoring method for slope deformation, particularly relates to the technical field of optical vision measurement, and is used for solving the problem that a deformation signal and optical noise are difficult to effectively separate due to the influence of atmospheric disturbance in an existing vision monitoring method. Collecting image data and point cloud data of the surface of the side slope through vision measurement equipment; analyzing high-order statistical characteristics of the data to identify abnormal components; analyzing cluster behaviors of abnormal components under different spatial scales to distinguish a random cluster from a structural cluster; marking according to cluster types or performing correlation analysis with atmospheric environment parameters; evaluating the comprehensive influence of the abnormal component on the deformation signal based on the analysis result; and finally, according to an evaluation result, adopting adaptive filtering to separate abnormal components and deformation signals, and outputting a monitoring result. Noise and real deformation signals caused by atmospheric disturbance can be effectively recognized and separated, and the accuracy and reliability of slope deformation monitoring are remarkably improved.

This invention proposes a dual-resonance coherent population trapping magnetometer and its implementation method, which can effectively suppress optical noise of lasers, improve sensitivity, and increase the lower limit of the measurement range. It includes: a first microwave source, a second microwave source, a first current source, a second current source, a first bias-T, a second bias-T, a first VCSEL laser, a second VCSEL laser, a first collimating lens, a second collimating lens, a first PBS, and a λ / 2 waveplate. 87 The system includes an Rb atom gas cell, a second PBS, a first photodiode, a second photodiode, a differential amplifier, and a dual-channel lock-in amplifier. The first VCSEL laser, the second VCSEL laser, the first collimating lens, the second collimating lens, the first PBS, and the λ / 2 waveplate are located at... 87 On the left side of the Rb atomic gas cell, the first VCSEL laser and the first collimating lens are located to the left of the first PBS, and the second VCSEL laser and the second collimating lens are located below the first PBS. The laser output from the second VCSEL laser is reflected by the first PBS and propagates towards the right atomic gas cell.

An estimation device 13 includes: a measurement unit 131 for measuring, for an optical transmitter and an optical receiver connected via a transmission path, a signal quality value for each received optical power in the optical receiver; a first calculation unit 132 for calculating a first signal distortion by the optical transmitter and the optical receiver dependent on the received optical power and a second signal distortion by the optical transmitter and the optical receiver independent of the received optical power by using the signal quality measurement value for each received optical power in the optical receiver; and a second calculation unit 133 for calculating a signal quality value for each optical noise amount by using the first signal distortion, the second signal distortion, and a third signal distortion by the transmission path calculated from the optical noise amount so as to calculate a relationship between the signal quality and the transmission quality of the optical transmitter and the optical receiver.

This application relates to the field of particle counters, and discloses a method, system, apparatus, and medium for calibrating the output signal of a particle counter. The method includes: acquiring the optical noise signal output by the particle counter to be calibrated, determining whether the optical noise signal meets preset conditions, and if not, transmitting the calibration signal to an optical power control circuit so that the optical power control circuit adjusts the input voltage of the laser in the particle counter to be calibrated, thereby calibrating the output signal of the particle counter. Therefore, the technical solution provided in this application, by acquiring the output signal of the particle counter and adjusting the input voltage of the laser based on the output signal to calibrate the particle counter's output signal, avoids the influence of factors such as temperature and the stability of the signal amplification circuit in the particle counter on the particle counter's output signal during the particle counter's processing of particle scattered light, such as reception, conversion, and amplification, thereby improving the particle monitoring accuracy of the particle counter.

The invention discloses a wavelength division isolation anti-interference method and system for a radio frequency optical network front return signal, and the method comprises the steps: introducing an interference monitoring system which represents the quality of a radio frequency signal and the power optical noise at the same time, and constructing a wavelength interference matrix of the normalized interference intensity between any wavelength channel pairs according to the interference monitoring system; carrying out topology analysis based on the matrix, calculating the interference degree and automatically dividing interference clusters of high-interference channels to realize global perception and quantitative description of a common-fiber link interference relationship; target wavelength configuration parameters of the central wavelength, the wavelength interval, the guard band width and the optical filter bandwidth of each channel are adaptively determined by using the interference matrix and the interference cluster result, and differential widening and frequency shift are performed on the channels in the interference cluster; and finally, by controlling the adjustable light source and the adjustable optical filter, the wavelength division configuration is dynamically reconstructed along with the interference environment. Therefore, in an ARoF + PoF common-fiber transmission scene, both the anti-interference capability of the radio frequency signal and the frequency spectrum utilization rate of the optical fiber can be considered.

The invention provides a method for improving the discrimination threshold of laser methane telemetering equipment, which comprises the following steps: in a dark environment, turning off a laser of the laser methane telemetering equipment, and measuring a first harmonic light intensity value I1c, a second harmonic light intensity value I2c and a fourth harmonic light intensity value I4c; selecting a central wavelength of a laser, and selecting a standard methane gas chamber with a remote measurement value of Wt; calculating a proportionality coefficient k21 considering the influence of the white noise, and calculating a telemetry measurement value W21 after the compensation of the electrical noise; calculating a proportionality coefficient k41 considering optical noise influence and an estimated value W41 of a telemetering value, and calculating a credibility criterion F '; selecting a confidence interval [b-1, b]; the standard methane gas chamber is slowly deflated, Wreal is calculated in real time, when the methane concentration is reduced to enable all the calculated Wreal to be zero, the methane concentration value Cmin at the moment is measured, and the identification threshold Wmin of the laser methane telemetering equipment is obtained through calculation. According to the method for improving the discrimination threshold of the laser methane telemetering equipment, electrical noise can be compensated, and part of optical noise can be filtered out.

The invention discloses a low-slow small moving target sample generation method based on a degradation model, and relates to the technical field of image processing, and the method specifically comprises the following steps: preparing a data set; obtaining an infrared target and a background sample; constructing an image degradation model; constructing a target pseudo sample generation model; performing a pseudo data set comparison detection experiment; and performing a pseudo data set sample contrast experiment. By simulating various degradation phenomena (such as motion blur, optical noise and illumination variation) in a real environment, high-quality training data is generated, a generative adversarial network with a controllable azimuth angle is constructed, a low-dimensional manifold of a target under a continuous azimuth angle is learned step by step, a target image with a specific azimuth angle is generated, and the target image with the specific azimuth angle is obtained. And through loss function adversarial training optimization, a high-quality false'low-slow-small 'moving target image is finally generated. Different degradation modes are constructed for a target and an infrared background, target motion characteristics and a background imaging mechanism are comprehensively considered, and a training sample conforming to an actual scene is generated.

The application discloses a photovoltaic glass defect detection method and system based on image recognition, and particularly relates to the technical field of visual detection, and is used for solving the problem of optical artifact interference defect recognition caused by film layer interference effect on the surface of coated glass; the optical artifact distribution map is generated by extracting interference characteristics from a reflection image, the interference area is positioned in the frequency domain space of a transmission image, a process response template is constructed in combination with a deposition pulse frequency, polarization coherence screening and time-varying deconvolution cooperative filtering are performed to eliminate artifacts; based on the energy proportion dynamic decision re-inspection or defect classification process implementation, the inherent optical noise of the material and the real physical defects are effectively separated, and the accuracy and reliability of the coated glass defect detection are significantly improved.

The invention provides an optical system for reducing optical noise, which is used in the field of laser gas analyzers, and comprises a doublet collimating lens, the doublet collimating lens is arranged on an emission light path of an infrared laser light source, the doublet collimating lens is used for shaping a laser beam emitted by the infrared laser light source, and the doublet collimating lens is used for outputting the shaped laser beam. And the obtained laser collimated light beam is a nearly flat-topped light beam with uniform energy, is freely propagated in the space and is received by a receiving end. According to the invention, a single-piece doublet lens is used as a core optical element, the free light laser beam of TO packaging is shaped to realize laser beam homogenization and collimation, the introduction of intensity noise caused by non-uniform light intensity distribution of the light beam after long-distance light beam transmission is reduced, and the optical interference noise frequency is increased in combination with the long-focal-length light path design, so that the optical interference efficiency is improved. The influence of optical interference noise is reduced through a filtering algorithm. And the structure is compact, the installation and adjustment are simple and convenient, the environmental adaptability is strong, and the application effect of the laser gas analyzer in the gas detection field is realized.

The utility model relates to the technical field of gas detection of laser sensing, in particular to a high-linearity low-noise semiconductor laser which comprises a laser body, and a semiconductor laser chip and an optical isolator are arranged in the laser body. The central axis of the optical isolator and the main optical axis of the semiconductor laser chip are in a coaxial state, a coaxial state but a rotation angle state or an inclined off-axis state, so that reflected light and stray light generated in a laser body and an optical link can be isolated and directionally scattered; light noise generated by reflected light and stray light in a laser body or an optical link is reduced, and the linearity of the laser body is improved. According to the utility model, the optical noise in the laser body and the optical link can be reduced, the precision, the stability and the reliability of the laser gas sensor are improved, and the applicability and the universality under various different environments and working conditions are realized.

The present invention discloses a gas detection method and system based on off-axis integrated output cavity enhanced photoacoustic spectroscopy. The method uses an off-axis integrated output cavity combined with a photoacoustic cell. The photoacoustic cell is placed inside the off-axis integrated output cavity structure. The laser forms an optical resonance in the off-axis integrated output cavity and at the same time interacts with the gas in the photoacoustic cell to generate a photoacoustic signal. Thus, the off-axis integrated output cavity increases the effective absorption path, the photoacoustic cell realizes the detection of the photoacoustic signal, reduces the influence of optical noise, and thereby improves the signal-to-noise ratio of the system. The system includes a laser controller, a laser, a collimator, an H-type photoacoustic cell, an off-axis integrated output cavity, a microphone module, a lock-in amplifier, a data acquisition card, and a host computer. This system has the advantages of being insensitive to optical noise, having a low detection limit, and high sensitivity.

This invention belongs to the field of electronic circuit technology, specifically relating to a true random number generation device based on a carbon-based chip, comprising: a broadband optical noise entropy source and an entropy collector. The broadband noise entropy source is used to generate a broadband chaotic noise signal. The entropy collector includes: a sample-and-hold circuit; a TIQ comparator for converting the sampling result into a digital signal output; a one-hot code generator for converting the digital signal output by the TIQ comparator into a one-hot code; and an encoder for converting the one-hot code into a binary code. In this invention, all parts of the entropy collector are designed using CNTFET technology, reducing power consumption.

The application discloses a built-in sound field measuring device for high-voltage electrical equipment and a spatial optimization arrangement method, and relates to the design of an internal fiber grating sound sensor and an external measuring loop for high-voltage electrical equipment and the design of a spatial optimization arrangement scheme, wherein the device comprises the internal fiber grating sound sensor and the external measuring loop. The detection frequency band of the fiber grating sound sensor is designed by the length of the grating area, and both ultrasonic waves and audible sound are considered. Polyimide is used as the coating material of the fiber grating, and the fiber grating has better high-temperature resistance and insulation performance. Glass fiber reinforced plastic is used as the packaging material of the fiber grating, and the fiber grating has higher mechanical strength and durability. A noise reduction device is designed by the interference principle to suppress the interference of optical noise in the measuring loop. By the design of the transfer function and the cutoff frequency, the band-pass filtering is transplanted into the data collector to suppress the influence of high-frequency and low-frequency interference during the collection of sound signals. A spatial optimization arrangement scheme is designed in combination with various constraint factors, and the engineering application value of the measuring device is improved.

The invention discloses a three-dimensional area light source light path magnetic control on-off device which comprises a first electromagnet (1), a second electromagnet (2), a third electromagnet (3), a first area light source (4), a second area light source (5), a third area light source (6), a magnetic fluid box (7), a first light intensity decision device (8), a second light intensity decision device (9) and a third light intensity decision device (10). As the light intensity transmissivity of the light beam transmitted into the magnetic fluid along the direction of the magnetic field is increased along with the increase of the external magnetic field within a certain range, when the light intensity transmissivity reaches a certain value, the light path of the light beam is determined to be on, otherwise, the light path is determined to be off, the magnetic field intensity generated by the three electromagnets is respectively adjusted, and the on-off of the three light paths can be realized; the optical on-off device has high environmental adaptability and optical noise interference resistance, and has good application potential in the technical field of optical communication and optical sensing.

The disclosure relates to an optical ranging sensor configured to determine proximity of a target object and an electronic system. The optical ranging sensor includes: a housing cover including a transmitting opening and a receiving opening; a light radiation source positioned to direct ranging light radiation through the emission opening toward the target object; an optical radiation receiver positioned to receive the ranging optical radiation reflected from the target object through the receiving opening; and a retroreflective mechanism implemented on a surface of the housing cover, where the retroreflective mechanism directs undesired optical noise back toward the undesired optical noise source and away from the optical radiation receiver; wherein the proximity of the target object is determined based on one or more attributes of the ranging light radiation.

The present disclosure relates to retroreflective mechanisms on optical ranging, proximity and image sensors for reducing optical noise from undesired sources. An example electronic system utilizes an optical ranging, proximity, and / or image sensor configured with a retroreflective mechanism to reduce undesired optical noise at an optical radiation receiver. An example ranging, proximity, and / or image sensor is configured to include a housing cover having a transmit opening and a receive opening. The example sensor may also include a light radiation source positioned to direct ranging light radiation through the emission opening toward the target object. The optical radiation receiver is positioned to receive the ranging optical radiation reflected from the target object through the receiving opening. A retroreflective mechanism implemented on the surface of the housing cover directs the undesired optical noise back toward the undesired optical noise source and away from the optical radiation receiver. Attributes of the target object may be determined based on one or more attributes of the ranging optical radiation received at the optical radiation receiver.

The utility model discloses an integrated fiber-optic gyroscope, which is characterized in that an optical signal emitted by a light source is firstly polarized by a polaroid and then enters a lithium niobate film chip, and is in countershaft coupling, so that the polarization extinction ratio of the optical signal transmitted in an optical waveguide of the chip is obviously improved (greater than 30dB). The improvement of the polarization degree is beneficial to improving the coherence degree of two beams of optical signals in the Sagnac waveguide ring and improving the signal-to-noise ratio. The optical signal output by the chip also needs to pass through the polaroid and then enters the tail fiber of the detector, and at the moment, the polaroid plays a role of a polarization analyzer to filter irrelevant polarization noise, so that the optical noise is further reduced, and the signal-to-noise ratio of the system is improved.

The invention provides a double-resonance coherent population trapping magnetometer and an implementation method thereof, which can effectively suppress optical noise of laser, improve sensitivity and increase a lower limit range of a measurement range. Comprising a first microwave source, a second microwave source, a first current source, a second current source, a first Bias-T, a second Bias-T, a first VCSEL laser, a second VCSEL laser, a first collimating lens, a second collimating lens, a first PBS, a lambda / 2 wave plate, an 87Rb atomic gas chamber, a second PBS, a first photodiode, a second photodiode, a differential amplifier and a two-way lock-in amplifier. The first VCSEL laser, the second VCSEL laser, the first collimating lens, the second collimating lens, the first PBS and the lambda / 2 wave plate are located on the left side of the 87Rb atomic gas chamber, the first VCSEL laser and the first collimating lens are located on the left side of the first PBS, the second VCSEL laser and the second collimating lens are located below the first PBS, and the lambda / 2 wave plate is located on the right side of the 87Rb atomic gas chamber. And the laser output by the second VCSEL laser is reflected by the first PBS and then propagates towards the right side atomic gas chamber.

The invention discloses an optical noise suppression difference method for an atom magnetometer, which belongs to the technical field of magnetic field measurement and weak signal detection, and comprises the following steps of: after acquiring double-optical-path optical signals of a main path and a reference path and converting the double-optical-path optical signals into voltage signals, separating alternating-current and direct-current components of the two paths of signals; the method comprises the following steps: respectively modulating and demodulating alternating current components of a main path and a reference path to obtain a main path demodulation signal containing magnetic field information and optical noise and a reference path demodulation signal only containing the optical noise, then calculating a dynamic gain coefficient based on two paths of direct current components, offsetting the optical noise through weighted difference operation, and outputting an effective magnetic field signal. According to the optical noise suppression difference method for the atom magnetometer, variable light intensity noise is effectively stripped, clinical landing enabling is carried out on the wearable SERF magnetometer, complex optical elements are not needed, interference resistance and adaptation integration are achieved, and the real-time measurement requirement of biological magnetic signals is met.

The application discloses a kind of all-fiber current sensor noise suppression method, light emitted by light source successively passes through coupler, polarizer, phase modulator, polarization maintaining optical fiber, 1 / 4 wave plate, sensing optical fiber and mirror, and the light reflected by mirror successively passes through sensing optical fiber, 1 / 4 wave plate, polarization maintaining optical fiber, phase modulator, polarizer and coupler, and then enters balanced photodetector positive port M, and the other outlet of coupler is electrically connected with balanced photodetector negative port N through optical attenuator.By adjusting the optical power of input light passing through coupler directly to photodetector through optical attenuator, and replacing common photodetector with balanced photodetector, the purpose of suppressing optical noise and photodetector common-mode noise is achieved, and the signal-to-noise ratio of output signal is improved.

This invention discloses a dual-laser synergistic high-temperature, high-speed rotating object axial vibration measurement device, relating to the field of vibration detection technology. It includes a main plate and a radiation-resistant plate mounted on the main plate. A drive motor is installed on the main plate. Measuring the dynamic characteristics, such as axial vibration, of a high-speed rotating object at high temperatures is a challenging problem. This device uses a dual-laser measuring instrument for measurement, and also features non-contact functionality. Furthermore, the dual lasers can compensate for light path disturbances caused by hot airflow. Specifically, one laser acts as the main measurement optical path, while the other acts as a reference optical path, specifically monitoring common path optical noise caused by hot airflow. Through differential calculations by a subsequent signal processor, environmental noise is subtracted from the main signal, thereby extracting the pure vibration signal of the measured turntable.

The utility model relates to a housing cap for an optical ranging sensor and an electronic system. A housing cap for an optical ranging sensor and an electronic system for transmitting and receiving optical radiation are provided while minimizing optical noise, such as ambient light, received at a reference sensor of the optical ranging sensor. An example housing cap of an optical ranging sensor may include a barrier wall defining a transmit cavity and a receive cavity. The emission cavity includes an optical radiation source positioned to direct the ranging optical radiation through the emission opening toward the target object, a reference sensor positioned to receive a portion of the ranging optical radiation, and an attenuation wall positioned between the optical radiation source and the reference sensor, an attenuation gap through which the portion of the ranging optical radiation passes is defined. The receiving cavity includes an optical radiation receiver positioned to receive the ranging optical radiation reflected from the target object through the receiver opening.

A method of making a grating coupler includes etching a first grating region into a substrate layer, wherein the first grating region comprises a first plurality of gratings having a first height and a first pitch between adjacent gratings of the first plurality of gratings. The method further includes etching a second grating region into the substrate layer, wherein the second grating region comprises a second plurality of gratings having a second height, different from the first height, and a second pitch between adjacent grating of the second plurality of gratings. The method further includes forming a cladding layer on the first and second grating regions, wherein the cladding layer has a different refractive index from the substrate layer.