Spatial modulation device

Abstract

A method for high frequency spatial modulation of electromagnetic radiation is provided, wherein the modulation is phase, polarization or direction of propagation. The method comprises a substrate carrying an ordered array of optical elements, the ordered array being in relative motion with an incident electromagnetic radiation beam to be modulated, and the relative motion is measured. The array comprises at least three optical elements and at least two different types of optical elements. At least some of the optical elements are formed of and integral with the substrate material. The optical elements may be fabricated on the substrate material by a thinning process. The electromagnetic radiation to be modulated is incident on an area of ​​the substrate referred to as an active area. As the substrate moves relative to the incident electromagnetic radiation, the active area also moves, and the designations of the individual optical elements also change.

Description

Technical Field

[0001] The present invention relates to a method and a device for high frequency spatial modulation of electromagnetic radiation. The modulation may be phase, polarization or propagation direction. Background Art

[0002] Multiplexed spectroscopy requires a means of spatially modulating the radiation field. In classical Fourier transform spectroscopy, an optical element is phase modulated along the optical axis, and the optical element is located in a plane perpendicular to the optical axis. In classical Hadamard spectroscopy, a code mask is placed in a plane intersecting the optical axis, and the incident radiation is transmitted or reflected in the direction of the detector. The modulation in these methods is usually spread out along a path. The present invention is preferably but not necessarily used in combination with high-efficiency multiplexing (HEMS) described in U.S. application Ser. No. 15 / 987,279 filed by the present applicant on May 23, 2018, which is consistent with PCT application Ser. No. PCT / CA2018 / 050599 published on November 29, 2018, as WO 2018 / 213923, the disclosure of which is incorporated herein by reference. HEMS is a multiplexing method that can improve the signal-to-noise ratio (SNR) of particle flux measurements by modulating particle flux along multiple paths. Therefore, the HEMS approach requires a new spatial modulator with multiple output directions, which is not required in the prior art. The present invention provides a modulation system suitable for use within a HEMS system. The following description includes some references to HEMS, and it should be understood that these are merely exemplary and that the present invention herein can be used with other approaches.

[0003] The number of spectral channels in a multiplexed spectrometer is proportional to the number of different modulation patterns N applied to the input radiation in the measurement series. The number of spectral channels can range from hundreds to thousands, depending on the spectral bandwidth and resolution required by the application. In high-throughput industrial inspection applications, hundreds to thousands of objects are inspected per minute, which requires data to be collected for each object in milliseconds. Taking these factors into consideration, the modulation rate needs to exceed 100kHz. Commercially available MEMS devices based on tunable micromirror arrays are able to maintain continuous modulation rates of about 5kHz and burst mode rates of about 50kHz. The maximum rate is limited by the inertia of the mirror relative to the (usually electrical) force provided to move the mirror. Higher rates can be achieved by reducing the size of the mirror and, in turn, the inertia of the mirror. However, as the size of the mirror approaches the wavelength λ of the incident radiation, diffraction effects from the edges of the mirror become increasingly important. The purpose of the present invention is to reduce edge diffraction effects by allowing the use of larger mirrors. The continuous modulation rate of micromirror arrays is limited by thermal factors. However, MEMS devices have the desirable feature of being able to dynamically change the pattern group in order to change the resolution or focus on the area of ​​interest. Therefore, there is a need for a new type of spatial modulator that can operate at rates exceeding 100 kHz, which rates are also dynamically adaptable.

[0004] Transitioning between different modulation modes can introduce undesirable convolution effects that degrade system performance. Conventionally, samples are acquired during the intervals when the spatial modulator configuration is close to a defined different modulation mode. In systems that require rapid transitions between spatial modulator configurations, a significant portion of the duty cycle may be used in transitions rather than collecting data, resulting in a reduction in the achievable SNR. Therefore, methods are needed to increase the duty cycle, the number of photons counted, and the SNR. Another object of the present invention is to improve the duty cycle by reducing the transition time. Summary of the invention

[0005] According to one aspect of the present invention, there is provided a method for spatially modulating electromagnetic radiation, comprising the following steps:

[0006] collecting electromagnetic radiation to be spatially modulated;

[0007] directing the radiation onto an ordered array of optical elements on a substrate;

[0008] translating the substrate so that at least two different optical elements engage incident radiation at two different times;

[0009] measuring a position of the substrate at the two different times;

[0010] and sending said location to a user;

[0011] The optical element array comprises at least three optical elements and at least two optical elements, and the at least three optical elements and the at least two optical elements modulate the radiation incident thereon differently.

[0012] According to one aspect of the present invention, there is provided a method for measuring displacement of a substrate, the method comprising the following steps:

[0013] directing the beam onto the substrate using a reflective or transmissive position indicator array;

[0014] moving the substrate relative to the light beam to transmit or reflect portions of the light beam from at least two different position marks at different times;

[0015] measuring the intensity of the transmitted or reflected light at intervals; and

[0016] The measured light intensity is analyzed a plurality of times to provide information about the position of the substrate.

[0017] According to one aspect of the present invention, there is provided a method for spatially modulating electromagnetic radiation, comprising the following steps:

[0018] collecting electromagnetic radiation to be spatially modulated;

[0019] directing the radiation onto an ordered array of optical elements on a substrate material;

[0020] translating the substrate material so that at least two different optical elements engage incident radiation at two different times;

[0021] At least some of the optical elements are formed from and integrally formed with the substrate material.

[0022] According to one aspect of the present invention, there is provided a method for spatially modulating electromagnetic radiation, comprising the following steps:

[0023] collecting electromagnetic radiation to be spatially modulated;

[0024] directing the radiation onto an ordered array of optical elements on a substrate;

[0025] translating the substrate so that at least two different optical elements engage incident radiation at two different times;

[0026] Wherein the substrate is a flexible strip forming a closed loop, wherein the strip translates around the loop, and the optical elements are arranged along the translation direction.

[0027] The invention comprises a substrate carrying an ordered array of optical elements in relative motion relative to an incident beam of electromagnetic radiation to be modulated and means for measuring the relative motion, wherein the array comprises at least three optical elements and at least two optical elements of different types. Preferably, at least some of the optical elements are formed from and integral with the substrate material. The optical elements may be fabricated on the substrate material by a thinning process such as etching, machining or laser cutting. The optical elements may be fabricated on the substrate material by an additive process such as deposition of a reflective layer.

[0028] The electromagnetic radiation to be modulated is incident on a region of the substrate called the active region. At least a portion of all optical elements in the active region is called active. All other optical elements are called passive. As the substrate moves relative to the incident electromagnetic radiation, the active region also moves and the designation of the individual optical elements changes. Preferably, the relative movement is periodic, resulting in each optical element falling inside and outside the active region at regular intervals.

[0029] The relative motion may be a translation, a rotation or a combination of translation and rotation, as long as such motion has the effect of causing the center of the beam of electromagnetic radiation incident on the substrate to impinge on each optical element in a defined order. The reference frame is chosen for convenience. For the present discussion the reference frame of the incident electromagnetic radiation is used. In this case the position of the source and the direction of propagation of the incident electromagnetic radiation are fixed and the substrate moves. The optical elements are assumed to be spaced α apart. In the case of a linear translation the number of optical elements impinged per second is referred to herein as the linear frequency V L = v / α, where v is the linear velocity of the substrate. In the case of rotation, the number of optical elements impacted per second is V L =α / rω, where ω is the angular velocity and r is the radius at which the optical element is located. The size of the optical element in the translational (or rotational) direction may be smaller than α, in which case there is a gap between the elements that does not direct incident electromagnetic radiation in the same direction as any of the optical elements. Preferably, the gap region (if any) is absorptive.

[0030] The means for measuring relative motion may be an optical or magnetic position encoder of conventional design attached to the substrate. Preferably, the means for measuring relative motion is intrinsic to the substrate. In a preferred embodiment, the substrate carries an array of reflective or transmissive position indicators placed along the translational or rotational direction of the substrate. Preferably, the array of position indicators has the same periodicity as the array of optical elements. Preferably, the array of position markers is parallel to and adjacent to the array of optical elements. Preferably, the size of the position marker is α / 2. Preferably, the substrate area between the position indicators is coated with an absorbing material. The position markers can reflect or transmit different parts of the probe beam intensity to convey more information. For example, a first type of position marker that reflects or transmits a first part of the probe beam intensity indicates the beginning of a sequence. A second type of position marker that reflects or transmits a second part of the probe beam intensity indicates a binary position marker. A third type of position marker that reflects or transmits a third part of the probe beam intensity indicates a binary zero. These three types of position markers are sufficient to uniquely mark each position of the array. A beam of probe radiation is linearly moved out from the incident radiation to be modulated and focused to an area that is less than or equal to the area occupied by one position indicator.

[0031] Probe radiation transmitted or reflected from each position indicator is directed to a detector, which may be, for example, a photodiode. When the probe beam and the first position indicator are aligned, a portion of the probe beam intensity characteristic of the first position mark type is incident on the detector. As the substrate displaces relative to the first position indicator, the portion of the probe beam returning to the detector decreases to zero and then rises to a portion characteristic of the second position mark type as alignment with the second position mark is approached. Thus, the intensity received at the detector periodically rises to a characteristic value when aligned with each position mark and drops to zero at the midpoint between the position marks. The intensity of the probe beam returning to the detector is varied at a rate at least 100% greater than the line frequency V L Four times higher sampling frequency V s Preferably, V s / V L > 20. The intensity measured by the detector is transmitted to a digital processor, and the digital processor calculates the position of the substrate relative to the center of the incident electromagnetic radiation to be modulated.

[0032] Each different type of optical element causes electromagnetic radiation incident on that element to leave the element in a different state than electromagnetic radiation incident on a different type of optical element. The different states may be associated with propagation direction, phase, or polarization. At any time, the ordered array is divided into an active region comprising a group of optical elements having at least some of the incident electromagnetic radiation to be modulated impinging thereon, and a passive region comprising a group of optical elements having no electromagnetic radiation to be measured impinging thereon.

[0033] One type of optical element is an aperture. In this case, the incident electromagnetic radiation leaves this type of optical element unchanged, except for diffraction effects from the edge of the aperture.

[0034] The second type of optical element is the transmissive type. In this case, the incident electromagnetic radiation passes through a transparent medium, where a phase change occurs, and the phase is proportional to the optical thickness of the transparent medium. Each different optical thickness results in a different phase change, and therefore corresponds to a different type of optical element.

[0035] The third type of optical element is the reflective type. In this case, the incident electromagnetic radiation leaves the optical element at a reflection angle equal to the angle of incidence. The orientation of the reflective element can be rotated relative to the direction of the incident electromagnetic radiation to give different angles of incidence. Each different angle of incidence causes the incident radiation to be reflected in a different direction, thus corresponding to a different type of optical element. Furthermore, the reflective optical element may be located in a plane perpendicular to the direction of the incident electromagnetic radiation and differ only in the distance from the average substrate surface. In this case, each distance from the average substrate surface causes a different phase change, thus constituting a different type of optical element.

[0036] A fourth type of optical element is a refractive type. In this case, incident electromagnetic radiation strikes a material having a different refractive index than one material and leaves the optical element at an angle dependent on the angle of incidence and the refractive index. Since both the angle of incidence and the refractive index can be varied to change the exit direction of the electromagnetic radiation, each combination of refractive index and angle of incidence constitutes a different type of optical element.

[0037] The fifth type of optical element is the diffractive type. In this case, the incident electromagnetic radiation strikes a set of diffraction grating lines that may vary in spacing and orientation. Each variation in spacing and orientation causes the incident electromagnetic radiation to diffract and constructively interfere in a different direction, so each combination of them constitutes a different type of optical element.

[0038] The sixth type of optical element is polarized. In this case, the incident electromagnetic radiation strikes the polarizing optics, which can have varying orientations, each of which causes the incident electromagnetic radiation to exit with a different polarization state. Thus, each polarizer orientation constitutes a different type of optical element.

[0039] The different types of optical elements listed above may be combined to produce other types of optical elements that alter at least one property of the incident radiation.

[0040] In some embodiments, the optical element is planar, while in other embodiments, the optical element has a curved surface. In particular, an optical element having a curved surface can be used to focus radiation incident on the surface to a detector location.

[0041] In a most preferred embodiment, the movable substrate is a flexible belt that translates an array of optical elements in a closed loop, wherein the belt is substantially flat for at least one region along the closed loop. Preferably, the belt loop is maintained in a rigid shape by two or more sprockets that engage the belt through drive holes to translate the belt at a controlled rate. The term "substantially flat" means that the belt surface is parallel to the line between the two sprockets with a tolerance of 2 degrees. The flat substrate surface so defined can correspond to the active area where the incident electromagnetic radiation interacts with the array of optical elements. Each type of optical element has the function of guiding electromagnetic radiation in the same direction. In HEMS applications, each type of optical element guides electromagnetic radiation onto a detector dedicated to that type. The optical element typically has a feature in a direction perpendicular to the flat substrate, where the flat substrate is larger than the standard deviation in the substrate surface.

[0042] In some embodiments, the strips contain regions of varying optical thickness, and the regions of varying optical thickness are arranged in close proximity to each other to alter the phase of the incident radiation flux to produce an interference pattern.

[0043] In some embodiments, the spacing of the diffractive features varies along the length of the ribbon. This feature can be used to change the free spectral range of the diffraction system, which alternates between, for example, broad spectral measurements at low spectral resolution of a spectral region of interest and high spectral resolution scanning of a spectral region of interest.

[0044] In a preferred embodiment, the movable substrate is a disk and the array of optical elements is arranged in a track near the periphery of the disk around a center of rotation, and a second concentric track near the array of optical elements contains an array of position marks having the same angular spacing as the optical elements.

[0045] In some embodiments, the movable substrate is an arc that undergoes harmonic motion relative to incident radiation, and the array of optical elements is arranged along an outer edge of the arc.

[0046] In some embodiments, the optical element can be switched between at least two different types of optical elements, and the switching occurs during the period of time when the optical element is in the passive region. This feature allows the spatial modulator of the present invention to dynamically change its modulation scheme without losing duty cycle due to the switching time. For example, the micromirror changes from a first fixed angle to a second fixed angle in the passive region.

[0047] In some embodiments, an optical element such as a micromirror on a spatial modulator can change orientation. When the element is in an inactive region, the orientation changes. For example, on a spinning disk spatial modulator with an active region between 0 and 10 degrees, the orientation of the optical element is fixed in the range 0-10 degrees. The transition occurs in the range 10-360 degrees. In this example, the required modulation rate is reduced by a factor of 36. This configuration combines the high line frequency of a translation modulator with the adaptability of a dynamically adjustable micromirror array.

[0048] In some embodiments, at least some of the optical elements are composed of a material that responds to an electro-optic effect, and the change in type is achieved by applying a voltage across the optical element. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a profile view of an enlarged section of a preferred embodiment of the present invention.

[0050] Figure 2 yes Figure 1 A schematic diagram of an embodiment showing a closed loop.

[0051] Figure 3 is another schematic diagram of a preferred embodiment showing a dynamically changing optical element.

[0052] FIG. 4 a is a schematic diagram of a pendulum embodiment of the present invention.

[0053] FIG. 4b is a schematic diagram of an embodiment of a disk of the present invention.

[0054] Figure 5 is a schematic diagram of a disc embodiment of the present invention showing different types of position marks.

[0055] Figure 6 The following are theoretical and noise waveforms from a series of position markers.

[0056] Figure 7 is a flow chart illustrating a method for measuring position. DETAILED DESCRIPTION

[0057] Figure 1 A perspective view of a preferred embodiment of the present invention is shown. A movable substrate 10 in the form of a strip is translated from left to right at a speed v along the direction indicated at 30 by incident electromagnetic radiation impinging on a region 200 on the substrate 10, which carries an array 40 of optical elements 111, including components 11, 12, 13, 14, 15, 16, 17, 19. This region 200 is designated as an active region, and an adjacent region 201 is designated as a passive region. The optical elements within the active region 200 modulate the incident electromagnetic radiation to an "on" state. The optical elements within the passive region 201 modulate the incident electromagnetic radiation to an "off" state. The segment shown is preferably part of a closed loop with a total length of L. The length of the active region 200 is A. The optical elements in the active region will direct the incident EM radiation in different directions specified by the type of optical element for a time of A / v, with a repeat period of L / v.

[0058] The optical element 11 is an aperture that allows incident EM radiation to pass substantially unchanged, except for diffraction effects due to the edges of the aperture. Diffraction effects are minimal if the sides of the aperture are much larger than the wavelength of the incident EM radiation. The aperture 11 is within the passive region 201, so no electromagnetic radiation passes through at the instant shown. However, when the substrate 10 is translated in the direction 30, the aperture 11 will enter the active region 200 at a later time. The modulation is achieved because transmission through the aperture 11 occurs only when the aperture 11 is in the active region 200.

[0059] The optical elements 12 and 13 are diffraction gratings with different pitches. The incident EM radiation of each wavelength is diffracted into several orders. For the 0th order, the diffraction gratings 12 and 13 reflect the EM radiation to the same direction. For orders other than the 0th order (i.e., + / -1), the diffraction gratings 12 and 13 diffract the incident EM radiation to different angles. The diffraction grating 12 is completely in the passive region 201, so no EM radiation is observed at the angle determined by the pitch of the diffraction grating 12. The diffraction grating 13 is partially located in the active region 200, so the incident EM is directed to the angle determined by the grating pitch, as long as the diffraction grating 13 remains in the active region 200. The optical elements 12 and 13 can be diffraction gratings composed of a dynamically adjustable micromirror array, which can change the pitch in the passive region 201 by changing the direction of the micromirror row.

[0060] Optical elements 14 and 15 are mirrors tilted at different angles to the EM radiation 100, so that the EM radiation is reflected at different angles when the mirrors 14 and 15 are within the active area 200. Detectors are placed at the appropriate angles of reflection, whereby each can observe the reflected EM radiation, the mere presence of which can represent, for example, a binary "1".

[0061] As substrate strip 10 translates in direction 30, optical element 15 will enter inactive region 201, and shortly thereafter optical element 15 will enter inactive region 201. The absence of reflected EM radiation may represent, for example, a binary "0." In some embodiments, the tilt angles of mirror elements 14 and 15 may be changed while the elements are in inactive region 201.

[0062] Optical elements 16 and 17 are mirrors parallel to the substrate surface. Each incident EM radiation is reflected at the same angle, but they have different phases due to the different elevations above the average substrate plane. Optical elements 16 and 17 can be, for example, part of a Fabry-Perot filter or interferometer. Optical elements 16 and 17 can be, for example, part of a step-scan Michelson interferometer. As shown, optical elements 16 and 17 are in active region 200. Optical elements 16 and 17 are translated along direction 30 into passive region 201, where, in some embodiments, the change in mirror height produces a different phase shift in the next repetition cycle of element L / v.

[0063] The optical element 19 is a dispersive prism with an adjacent buffer zone 18, both of which are located within the passive region 201. When the prism is located in the active region 200, the incident EM radiation is refracted into an angle determined by the geometry of the prism and the refractive index of the prism. In some embodiments, the buffer zone 18 is used to provide a clear optical path for adjacent optical elements. In some embodiments, the optical element does not abut the buffer zone.

[0064] An array of position indicators is shown at 20 adjacent and parallel to the array of optical elements 40. As shown, the position indicators are apertures that emit a probe beam when a portion of the aperture intersects the probe beam. A detector (not shown) measures the intensity of the emitted probe beam, and a computing device calculates the position of the substrate relative to the probe beam.

[0065] Figure 1 The examples shown in may be used, for example, in a multiplexed spectrometer as described in the HEMS application cited above.

[0066] Figure 2 Given Figure 1Schematic top view of the device shown. The belt substrate 10 forms a closed loop around the sprockets 51, 52 and 53. The belt carries optical elements, which include mirrors with different tilt angles shown at 14 and 15, and an aperture 11. The incident EM radiation 100 to be modulated is incident on the active area 200, which is essentially flat between the sprockets 51 and 53. In EMMS applications, the incident EM radiation can be dispersed on the active area 200, for example by wavelength. The modulated EM radiation from the aperture element 11 travels in the direction 31 and is observed at the detector 41. The modulated EM radiation from the mirror element 14 travels in the direction 34 and is observed at the detector 44. The modulated EM radiation from the mirror element 15 travels in the direction 35 and is observed at the detector 45. For illustration purposes, the detectors 44 and 45 are drawn in the plane of the belt substrate 10. In a preferred embodiment, the mirrors 14 and 15 are tilted in a direction perpendicular to the direction of belt movement and the detectors 44 and 45 are above and below the plane of the drawing. The probe beam 101 is generated by a light source 80 and the portion transmitted through a position indicator aperture (not shown) generates a beam 102 which is received by a photodiode 81 and converted into a digital amplitude by an analog-to-digital converter 82. The sequence of digital amplitudes is analyzed by a computing device 83 which outputs a digital representation of the substrate belt position 84 which is transmitted to a user. Position information is essential for the operation of optical instruments based on the spatial modulator of the apparatus of the present invention, as an operationally precise modulation configuration can be calculated based on the position information and knowledge of the geometry of the spatial modulator. In HEMS applications, the aperture 11 and the mirrors 14 and 15 may, for example, have a width of 50 microns along the direction of belt travel and a belt substrate speed of 50 m / s to give a modulation rate of 1 MHz. With the setup of this example, a spectrum with 1000 wavelength channels can be measured in 1 millisecond. By Figure 2 The settings can produce higher and lower modulation rates.

[0067] Figure 3 Given Figure 1 Schematic diagram of a tape substrate shown in FIG. Three types of optical elements 13, 14 and 15 (differently shaded) are arranged in a line along the tape axis running in the direction 30. The active area is indicated as 200. Optical element 14 is a movable mirror in an inactive area 201, the movable mirror being shown in an enlarged view, 24 pivoted about pivot 25 to a new position. Position indicators 20 are arranged in a row parallel to the array of optical elements 40. Figure 3 The two rows of holes 21 shown are Figure 2 The sprockets 51 , 52 , and 53 are shown engaged to translate the tape substrate 10 .

[0068] FIG4a shows another arrangement, in which Figure 1The array of optical elements 111 shown most clearly in FIG. 4 is mounted on a substrate 301 which is placed on a pendulum or rod 300 that performs harmonic motion. The rod can, for example, be excited to oscillate at a resonant frequency on a MEMS device. Oscillations are technically easier to achieve than linear translations for sub-millimeter MEMS devices. The optical elements can be mounted along an arc either in the plane swept by the pendulum arm or in a plane perpendicular to the pendulum axis. For example, the example shown in FIG. 4a can be used in a multiplexed spectrometer described in HEMS applications.

[0069] FIG4 b shows a perspective view of an embodiment in which an array of optical elements 111 is mounted around the circumference of a disk 112 perpendicular to the disk plane. In this arrangement, the optical elements have a constant radius and a preset constant width for the incident radiation. Optical elements arranged to fill the space in the disk plane are typically wedge-shaped, which distorts the resolution of the HEMS spectrometer. By increasing the radius at which the optical elements are located, the distortion can be reduced below a threshold.

[0070] Figure 5 A top view of a substrate 10 in the form of a disc 28 is shown, the disc 28 having an axis of rotation 27 and a direction of rotation 31. The active area is indicated as 200. The disc substrate 10 carries three types of optical elements 13, 14 and 15, which are different in shaded areas and are arranged to form a code sequence of length 10 in the active area 200. Three different types of position indicators with different radial dimensions are shown as 74, 75 and 76.

[0071] Position markers 74, 75 and 76 transmit probe beams of different amplitudes, such as Figure 2 . In the example shown, position mark 75 with the largest radial length indicates the start of the code sequence, while position marks 74 and 76 represent binary "0" and "1", respectively, for marking each sector of the code sequence. Position mark 76 differs from position mark 74 in that the radial length is larger. The values ​​assigned to position marks of different lengths can be interchanged, and there can be multiple lengths representing multiple values. In noisy environments, the binary level as shown is the most reliable. In the example shown, the sector labels in the active area are represented by position indicators 76 and 77 as binary "11". In the example shown, two binary digits are sufficient to uniquely mark all sectors. More binary digits can be used. The start and end points of the sector labels are referenced by the displacement relative to the index peak 75. The sector labels shown are adjacent to the index peak 75, but may appear anywhere between the index peaks. The sector label area between the first index peak and the second index peak is preferably closer to the first index peak, in which case the direction of the translation or rotation can be inferred. For example, it can be used in a multiplexed spectrometer described in a HEMS application Figure 5 The example shown in .

[0072] Figure 6 Shown by Figure 2 The theoretical waveform received by the detector 81 in (bottom curve) and the corresponding waveform with noise added (top curve). The main peak corresponds to a position indicator that marks the Figure 5 The start of the code sequence is shown at 75 and is designated as the index peak. The remaining peaks correspond to Figure 5 The position indicators 74 in the diagram. Some of the position markers 74 may be used as sector identifiers, in which case they all have the same value. When analyzed with a prior art comparator, the periodicity of the peak positions varies due to noise. When a threshold is reached, the comparator triggers. Noise in the signal will move the position of the threshold, and noise in the comparator may move the threshold itself. In the present invention, the position jitter caused by noise is greatly reduced by sampling the waveform from the position indicator at a frequency much higher than the waveform frequency to obtain at least 4 points and preferably more than 20 points per peak. In simulation, a higher sampling rate reduces the difference between the measured position and the actual position and better resists the effects of noise. The peaks are numbered consecutively starting from the index peak.

[0073] like Figure 7 As shown, once the approximate frequency and phase of the waveform are known, the approximate position of the minimum in the waveform relative to the index peak can be calculated and used as an integration limit to calculate the peak area and moment. The peak moment is calculated as the sum of the displacements from the index peak (in fractional peak width units) multiplied by the peak amplitude measured at each displacement between the approximate minimum displacements. The peak area is the sum of the peak amplitudes between the approximate minimum displacements. The peak center is calculated as the peak moment divided by the peak area. The positions of the N peak centers are obtained, and a least squares regression is then performed to relate the number of peaks to the peak centers. The slope and intercept of the regression give the frequency and phase, respectively. These improved approximations to the frequency and phase can be used to calculate the next set of minima. That is, with each iteration of the algorithm, the peak position measured in the presence of noise converges to the actual peak position. The position of the substrate can be calculated based on the frequency, phase, and number of clock ticks (measured at the ADC) since the last index peak. The accuracy achieved is about 20% of the transitions between ADC measurements, which is equivalent to about 1% of the size of the optical element when 20 measurements are made per line period.

Claims

1. A method for spatially modulating electromagnetic radiation, comprising the following steps: collecting electromagnetic radiation to be spatially modulated; directing the radiation onto an ordered array of optical elements on a substrate of a spatial modulator; translating the substrate so that at least two different optical elements engage incident radiation at two different times; wherein the array of optical elements of the spatial modulator has at least three optical elements and at least two different types of optical elements, the at least two different types of optical elements modulating the radiation incident thereon differently, and wherein each different type of optical element causes electromagnetic radiation incident on the element to leave the element in a different state than electromagnetic radiation incident on a different type of optical element; measuring a position of the substrate at the two different times; as well as The location is sent to the user.

2. The method according to claim 1, characterized in that The optical element of the spatial modulator produces at least two different phase changes in the electromagnetic radiation to be modulated.

3. The method according to claim 1, characterized in that The optical element of the spatial modulator produces at least three different phase changes in the electromagnetic radiation to be modulated.

4. The method according to claim 1, characterized in that: The optical element of the spatial modulator changes the polarization of the incident radiation to be modulated in at least two different ways.

5. The method according to claim 1, characterized in that: The optical element of the spatial modulator changes the polarization of the incident radiation to be modulated in at least three different ways.

6. The method according to any one of claims 1 to 5, characterized in that The optical elements of the spatial modulator are integral with the substrate material.

7. The method according to any one of claims 1 to 5, characterized in that The optical element is selected from the group consisting of an aperture, a mirror, a diffraction grating, a phase plate, a refractive wedge, a refractive prism and a polarizer.

8. The method according to any one of claims 1 to 5, characterized in that The optical element includes a mirror that can assume at least two different configurations, and wherein a transition from a first configuration to a second configuration occurs when the substrate is translated and the mirror is in an inactive region.

9. The method according to claim 8, characterized in that At least one of the mirrors changes configuration at least once, and the configuration change occurs when the mirror is not exposed to electromagnetic radiation to be modulated.

10. The method according to any one of claims 1 to 5, characterized in that The position measurement uses a component that is integral to the substrate and is proximate to the optical element.

11. The method according to any one of claims 1 to 5, characterized in that The substrate is a flexible strip forming a closed loop, wherein the strip translates about the loop and the optical elements are arranged along the translation direction.

12. The method according to claim 11, characterized in that The optical element is a diffraction grating, and the pitch of the diffraction grating varies along the length of the strip.

13. The method according to any one of claims 1 to 5, characterized in that The substrate is a rotating disk and the optical elements are arranged at a common radial distance from the axis of rotation.

14. The method according to any one of claims 1 to 5, characterized in that The substrate is an arc wherein it undergoes a periodic and / or reciprocating rotational motion about an axis of the arc, and the optical elements are arranged along the arc at a common radial distance from the rotational axis.

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