137 results about "Beam coupling" patented technology

The invention discloses a stress analysis method for bridge incremental launching construction, and particularly relates to the field of stress analysis. According to the method, a mechanical state matrix is generated by combining wavelet noise reduction and Kalman filtering through distributed optical fibers, a piezoelectric force sensor, a vibrating wire stress meter and other equipment and real-time data; a pushing system-temporary support-beam body coupling dynamic mechanical model is established, and a generalized alpha method is adopted for solving and Bayesian optimization calibration parameters are adopted; key parameters are identified on line through a three-level progressive framework, boundary conditions are dynamically updated in combination with a total station and a laser tracker, and supporting rigidity self-adaptive adjustment is achieved through fuzzy PID control. Model confidence evaluation adopts a residual norm-modal confidence criterion-Bayesian update three-level mechanism, finally, stress distribution, support reaction and displacement deviation are calculated based on a correction model, and a safety index, threshold alarm and risk analysis report is generated through a fuzzy comprehensive evaluation method and fed back to a construction control center in real time.

A method for assembling a photonic computing system includes attaching a photonic source to a support structure, and attaching a photonic integrated circuit to the support structure. The photonic source includes a first laser die on a substrate configured to provide a first optical beam, and a second laser die on the substrate configured to provide a second optical beam. The photonic integrated circuit includes a first waveguide and a first coupler coupled to the first waveguide, and a second waveguide and a second coupler coupled to the second waveguide. The method includes attaching a plurality of beam-shaping optical elements to the support structure, the substrate, or the photonic integrated circuit, in which the attaching includes aligning a first beam-shaping optical element during attachment so that the first optical beam is coupled to the first coupler, and aligning a second beam-shaping optical element during attachment so that the second optical beam is coupled to the second coupler.

Distances between photonic integrated circuits and multiport optical probes can be established by emitting an optical beam from a first optical port of the multiport optical probe so that the optical beam is coupled into a first waveguide section of a PIC. This optical beam portion is reflected from a surface of the multiport optical probe back to the PIC. At suitable PIC-probe distances, the optical beam is coupled by a second waveguide grating to propagate in a second waveguide section and is then emitted to a second optical port of the multiport optical probe by a third waveguide grating coupler and directed to a detector. The detector signal is used to determine or adjust PIC-probe separation.

The invention discloses a device and a method for detecting partial discharge in a gas chamber of a switch cabinet by using a closed-loop fluorescent optical fiber, and the device comprises a closed-loop fluorescent optical fiber transmission module and a photomultiplier, and the closed-loop fluorescent optical fiber transmission module comprises a fluorescent optical fiber. The two ends of the fluorescent optical fiber are connected with one end of the first transmission optical fiber and one end of the second transmission optical fiber through the first optical fiber adapter and the second optical fiber adapter respectively, and the other ends of the first transmission optical fiber and the second transmission optical fiber are connected with the input end of the photomultiplier. According to the invention, a closed-loop fluorescent optical fiber detection mode is provided, all-in-one signal processing and conversion can be carried out through the light beam coupling device, and the sensitivity and accuracy of partial discharge detection are effectively improved; the invention provides closed-loop fluorescent optical fiber detection to improve the sensitivity of fluorescent optical fiber detection so as to compensate the defects of normal open-loop fluorescent optical fiber detection. Interference received by fluorescent optical fiber detection is smaller than that received by other devices, and the device is suitable for remote or weak-signal partial discharge detection in equipment such as a switch cabinet and a transformer.

The invention provides a laser pulse width broadening device and a laser system. The laser pulse width broadening device comprises a first lens array, a plurality of optical fibers with different lengths, a second lens array and a focusing lens, the plurality of optical fibers with different lengths have the same incident plane and emergent plane; the first lens array divides the laser beam; the segmented laser beams are respectively transmitted in a plurality of optical fibers with different lengths, and the plurality of optical fibers with different lengths respectively emit a plurality of light beams with different delays based on the optical path difference of the plurality of optical fibers with different lengths; the second lens array collimates a plurality of light beams with different delays; and a plurality of light beams with different delays pass through the focusing lens and then are superposed to obtain uniformly distributed light beams with target sizes. The lens array can be used for segmenting light beams and coupling the light beams into optical fibers to improve the utilization rate of the light beams. The pulse width is broadened by using the optical path difference of the optical fibers with different lengths; the micro-lens array is used for collimating the light beams, the focusing lens is used for overlapping the light spots, small light spots are formed, and follow-up shaping and light beam coupling are facilitated.

Light guiding apparatuses include diffractive optics. A light guiding member includes a stack of layers and multiple interfaces between respective layers. The layers are arranged to enable light to be guided through the light guiding member via internal reflections. The apparatus also includes an in-coupling diffractive element configured to in-couple one or more input beams of light into the first layer of the light guiding member and an out-coupling diffractive element configured to out-couple the one or more beams of light from the light guiding member. The in-coupling diffractive element and the out-coupling diffractive element are provided on the first layer of the light guiding member. The light guiding member includes more than three layers and the refractive index of at least one of the respective layers or the respective interfaces decreases from the first layer through the stack of layers.

The invention belongs to the technical field of light beam coupling tracking and pointing, and particularly relates to a light beam coupling tracking and pointing method and device based on an automatic adjusting optical fiber coupling module, and the method comprises the steps: obtaining a cooperative target light beam, carrying out the shaping processing of the cooperative target light beam through an optical system, and carrying out the symmetric light splitting of the shaped cooperative target light beam through a spectroscope; the light beam is divided into a detection light path and a coupling light path; the position of a light spot on a detection light path is detected through a CMOS module, the center coordinate of the light spot is extracted, and the X-axis offset difference value and the Y-axis offset difference value of the center coordinate and the preset center position of the CMOS module are calculated; and calculating the adjusting quantity of the XYZ three-axis micro-motion execution mechanism through a closed-loop algorithm, controlling the micro-motion execution mechanism to drive the optical fiber coupling module to move in the corresponding axial direction, continuously collecting light spot position data of the CMOS module, and adjusting the adjusting parameters of the micro-motion execution mechanism in real time through data feedback. Therefore, the problems of high delay, limited accuracy and the like in the prior art are solved.

A display structure (1000), a display device, and a vehicle are disclosed. The display structure (1000) comprises a waveguide (1100); an in-coupling structure (1200) configured to couple a set of input beams (1020) into the waveguide (1100) as a set of in-coupled beams (1021), a diffractive exit pupil expansion structure (1300) configured to diffract the set of in-coupled beams (1021) to form at least three sets of guided beams (1030), and a diffractive retardation and out-coupling structure (1400) configured to receive from the exit pupil expansion structure (1300) a diffracted set of beams (1035) and comprising an out-coupling grating (1420). The retardation and out-coupling structure (1400) is configured to diffract the diffracted set of beams (1035) to form at least one returning set of beams (1040) guided towards the exit pupil expansion structure (1300).

The invention provides an ultrafast scanning interferometer. The interferometer comprises an ultrafast laser system, an interference module, a coupling module and a spectral measurement module which are sequentially arranged along a light path. The ultrafast laser system emits a laser beam, the interference module splits the laser beam into a reference beam and a detection beam, and the detection beam carries information of a detected optical element. The coupling module is connected with the spectral measurement module through an optical fiber, the coupling module couples the detection light beam into the optical fiber, and the spectral measurement module demodulates the detection light beam which is output by the optical fiber and carries the information of the detected optical element in real time and calculates the peak-valley value of the detected optical element. The interference module adopts a Michelson interferometer structure, and the spectral measurement module comprises a dispersion module, a high-speed photoelectric detector and a high-speed photoelectric signal acquisition and analysis module. According to the invention, continuous single-frame detection is carried out on the measured optical element in the form of the optical pulse string, and high-precision and high-efficiency measurement of the surface topography of the optical element is realized.

The invention discloses a medium-low speed magnetic levitation bearing rail beam design method based on vehicle rail beam coupling analysis, and belongs to the technical field of magnetic levitation rail traffic, and the method comprises the following steps: determining a bearing rail beam structure; determining the structural size of the bearing rail beam; carrying out vehicle rail beam road coupling analysis on the bearing rail beam, and determining an elastic supporting beam calculation model of the bearing rail beam; according to a structural mechanics principle, determining structural internal force and deformation; carrying capacity design and adaptability design are carried out according to structural internal force and deformation; carrying capacity design, adaptability design and structural size drawing design drawings. According to the method for designing the medium-low-speed magnetic levitation rail bearing beam based on the vehicle rail beam coupling analysis, the rail bearing beam form and the component size adapting to the vehicle load dynamic effect can be conveniently and rapidly designed, so that the rail bearing beam can resist the influence of vehicle vibration on the rail bearing beam, and it is ensured that the design result has good economical efficiency and reliability; and the construction cost of the maglev track can be reduced while the safety and comfort of a medium-low speed maglev traffic system are ensured.

A wavelength beam combining device includes: a plurality of laser light sources configured to emit a plurality of laser beams in a first direction and having mutually different peak wavelengths and central axes arranged in a second direction intersecting the first direction; a first diffraction grating disposed at a position where the plurality of laser beams are received, the first diffraction grating being configured to diffract the plurality of laser beams in different directions according to wavelengths of the laser beams to cause the diffracted laser beams to enter the second diffraction grating; a second diffraction grating configured to diffract the plurality of laser beams diffracted by the first diffraction grating to form a wavelength-combined beam, and to direct the wavelength-combined beam in the first direction; and an optical coupling unit configured to couple the wavelength-combined beam to an optical transmission fiber and to be movable in the second direction.

An eyepiece waveguide for an augmented reality display system may include a transparent substrate, an input coupling grating (ICG) region, a multi-directional pupil expander (MPE) region, and an exit pupil expander (EPE) region. The ICG region may receive an input light beam and couple the input light beam into the substrate as a guided light beam. The MPE region may include a plurality of diffraction features that exhibit periodicity along at least a first periodic axis and a second periodic axis. The MPE region may be positioned to receive the guided light beam from the ICG region and diffract the guided light beam in multiple directions to generate a plurality of diffracted light beams. The EPE region may be positioned to receive one or more diffracted light beams from the MPE region and couple the diffracted light beams out of the transparent substrate as output light beams.

The invention provides an automatic coupling device for a fast-axis beam of a micro-channel laser stack array, and relates to the technical field of semiconductor lasers. The device comprises an optical platform, and the optical platform is provided with a stack array adjusting subassembly, a power-up subassembly, a UV curing subassembly, a lens adjusting subassembly, a dispensing subassembly, a near-field detection subassembly and a far-field detection subassembly. The stack array adjusting part is used for installing the stack array, and the power-up part is used for powering up the stack array. And the UV curing subassembly is used for curing the ultraviolet glue. And the lens adjusting subassembly and the dispensing subassembly are respectively used for adjusting the position of the fast axis collimating lens and dispensing. The SAC lens is arranged on a sliding plate of the dispensing subassembly through a fixing rod, during coupling, laser emitted by the micro-channel laser sequentially passes through the fast axis collimating lens and the SAC lens and then is divided into a far-field light beam and a near-field light beam by the beam splitter prism, the near-field light beam enters the near-field detection subassembly, and the far-field light beam enters the far-field detection subassembly. The device effectively solves the problems of low production efficiency, poor coupling precision and the like in the existing coupling mode.

The invention relates to the field of photocuring additive manufacturing, in particular to a double-beam coupling pulse type photocuring additive manufacturing method and device.The method comprises the following steps that S1, a purple laser beam emitted by a purple laser sequentially passes through a purple DMD chip and a long-wave-pass dichroscope and then enters a focusing objective lens; patterning and projecting to photosensitive resin through a focusing objective lens to form an initial curing area with any section; s2, a red light laser beam emitted by a red light laser sequentially passes through a red light DMD chip and a short-wave-pass dichroscope to enter a focusing objective lens, and is projected to the boundary of the initial curing area in a patterning manner through the focusing objective lens, so that boundary modification is realized; s3, the purple laser beam and the red laser beam construct a complex three-dimensional micro-nano structure layer by layer in a double-beam coupling mode; and the defects of inaccurate boundary morphology, high residual stress and the like in the existing single-beam curing technology can be effectively overcome.

A waveguide sheet (100) and a preparation method thereof, an optical waveguide structure (200) and a preparation method thereof, and a display device (300), the waveguide sheet (100) comprising an optical waveguide body (101), the optical waveguide body (101) comprising a first main surface (101a) and a second main surface (101b) arranged opposite to each other, the first main surface (101a) being provided with a coupling-in grating (102) and a coupling-out grating (103), the second main surface (101b) being provided with a coupling-out grating (103), and the coupling-out grating (103) being provided with a coupling-in grating (102) and a coupling-out grating (103). And a polarization structure (104) disposed between the in-coupling grating (102) and the out-coupling grating (103); the coupling-in grating (102) is configured to couple a light beam into the optical waveguide body (101); the polarization structure (104) is configured to reflect light with a first polarization state included in the light beam, and enable the light with the first polarization state to be propagated in the optical waveguide body (101) in a total reflection mode; the coupling-out grating (103) is configured to couple the first color light transmitted to the coupling-out grating (103) out of the optical waveguide body (101), and the waveguide sheet (100) reflects the light with the first polarization state included in the light beam through the polarization structure (104) and makes the light with the first polarization state propagate in the optical waveguide body (101) in a total reflection mode. Therefore, the multilayer waveguide sheets (100) are arranged in a laminated manner, so that the problem of color cast caused by the response of the optical waveguide to the full wave band of visible light can be solved.

The invention discloses an angle continuously adjustable super-resolution microscope illumination device and method. The device comprises a light beam coupling assembly; an LED-DMD excitation light path and a digital micromirror array perform intensity modulation on Kohler illumination light according to a loaded intensity distribution reference pattern, a first light beam is reflected, and the first light beam is projected to a sample plane through a light beam coupling assembly and a conjugate light path in sequence; an SLM-Laser excitation / light control light path, a spatial light modulator performs phase modulation on parallel light according to a loaded phase distribution reference pattern to generate a second light beam, and the second light beam is coupled with the first light beam through a light beam coupling assembly and then is projected to a sample plane; the excitation mode switching module is used for switching a conjugate surface to realize TIRF illumination or spot scanning excitation; the control system realizes seamless switching between a preset light control imaging mode and a real-time light control imaging mode. The problems that a traditional super-resolution microscope is single in function, high in phototoxicity, poor in adaptability and the like are solved, and a more powerful imaging platform can be provided for biomedical research.

The invention discloses an up-conversion microscopic imaging rapid spot scanning method and device based on light-operated fluorescence erasure, and the device comprises an excitation light module, a loss light module, a double-beam coupling module, a laser spot scanning module, and a fluorescence detection imaging module. When the probe is lighted by the exciting light and the scanning passes, the following loss light acts on the probe which is emitting the fluorescence, and the fluorescence loss is quickly induced, so that the residual fluorescence is extinguished (the fluorescence lifetime is shortened) and the imaging brightness is not weakened. According to the method, the trailing phenomenon caused by overlong fluorescence lifetime in the up-conversion point scanning fluorescence microscope is solved, the limitation of the fluorescence lifetime on the point scanning imaging speed is broken through, and up-conversion rapid point scanning microscopic imaging without brightness loss and trailing can be realized.

The present invention provides an end capped optical fiber that can reduce the angular misalignment of the optical axis of a collimated light beam. [Solution] The optical fiber with an end cap comprises an optical fiber and an end cap having a first surface connected to the end face of the optical fiber, a second surface located opposite the first surface, and a side surface connecting the first and second surfaces. The end cap includes a convex lens, the second surface includes the convex lens surface, and the side surface includes an outer surface surrounding the optical axis of the convex lens. The angle formed by each of the two intersecting lines between the virtual plane containing the optical axis and the outer surface with respect to the optical axis changes as the virtual plane rotates once around the optical axis.

The invention relates to a coherent lidar imaging system (20) comprising: • a detection device (10, 10A) • a laser source (SL) configured to emit laser radiation (L) having a temporally modulated optical frequency (FL), • a splitter device (LS) adapted to spatially separate the laser radiation (L) into a beam called a reference beam (Lref) and into a beam called an object beam (Lo) directed towards a scene to be observed (Obj), • a coupling device (CD) configured to couple the reference beam to the integrated detector, • an optical imaging system (Im) producing an image of the scene by focusing a beam reflected by the scene (Lo,r) onto the detection device (10), • a processing unit (UT) configured to determine a distance of points of the scene imaged on the pixels of the integrated detector, from the beat frequency.

The application discloses a pump-repump-probe time-resolved spectrum system for measuring luminescence and absorption, comprising a laser beam splitting module, a probe light path construction module, a pump light path regulation module, a repump light path adjustment module, a double-channel signal acquisition module and a light path coupling and converging module. The same femtosecond laser is used to split a light beam, two-stage light splitting is performed to obtain initial light beams of pump, repump and probe light paths, and each light path is subjected to delay adjustment, wavelength conversion, focusing and other treatments, and then is precisely coupled at the same spatial position of a sample. The double-channel signal acquisition module synchronously captures luminescence signals and probe light transmission signals of the sample, and realizes data acquisition in combination with reference light path calibration. The test method acquires multidimensional dynamic information through light path optimization, light beam coupling, signal synchronous acquisition and analysis. The system realizes synchronous detection of luminescence and absorption signals under the same excitation condition, and solves the test error and single mode limitation of the traditional independent system.

Providing eyepiece waveguides for augmented reality display systems. [Solution] The eyepiece waveguide may include an optically transparent substrate with an input coupling grating (ICG) region. The ICG region can receive a beam of light and couple the beam into the substrate in the inductive propagation mode. The eyepiece waveguide may also include a combined pupil expander-extractor (CPE) grating region that receives a beam of light from the ICG region, modifies the direction of beam propagation using a first interaction, and externally couples the beam using a second interaction. The diffraction features of the CPE grating region may be arranged in alternating rows and columns of higher and lower quadrilateral surfaces, or the diffraction features may comprise rhombic raised ridges. The eyepiece waveguide may also include one or more recycler grating regions.

To improve coupling efficiency when coupling wavelength-coupled light beams with an optical transmission fiber. A wavelength beam coupling device couples a plurality of laser beams emitted from a laser light source and having mutually different peak wavelengths, and the central axes of the light beams emitted in a first direction are arranged in a second direction intersecting the first direction. The wavelength beam coupling device includes: first and second diffraction gratings, the first diffraction grating being disposed at a position receiving the plurality of laser beams and causing the plurality of laser beams to be diffracted in different directions according to wavelengths to be incident on the second diffraction grating, the second diffraction grating further diffracting the plurality of laser beams diffracted by the first diffraction grating to form wavelength-coupled light beams, and the wavelength-coupled light beams being emitted in the first direction; and an optical coupling unit coupling the wavelength-coupled light beams with the optical transmission fiber and configured to be movable in the second direction.

The invention discloses an inter-beam coupling signal decoupling judgment, decoupling and velocity measurement method in acoustic Doppler velocity measurement, and belongs to the technical field of coupling interference suppression in an underwater acoustic navigation technology. In order to solve the problem of signal cross coupling interference of phased array acoustic Doppler velocity measurement equipment, the method comprises the following steps: aiming at received velocity measurement beam echo signals, performing decoupling judgment on the beam echo signals by utilizing correlation between signals on a channel; and when it is judged that the speed measurement beam echo signal can be decoupled, performing preprocessing including whitening on the signal to obtain a signal, and processing a real part of the received signal by using a blind source separation algorithm to obtain a decoupled echo signal real part. And Hilbert transform is carried out on the obtained signal to obtain a complex signal for speed measurement.

The invention discloses an ultra-narrow band optical filter absolute frequency reference in-situ calibration device which comprises a hollow cathode lamp, the output end of the hollow cathode lamp is connected with one input end of a one-to-two optical fiber through a light beam coupling device, and the output end of a variable diaphragm is connected with the other input end of the one-to-two optical fiber through an optical fiber; light beams output by the one-to-two optical fiber are split, the first split beam is input to the second photoelectric detector, and the second split beam transmits the ultra-narrow band light filter and is detected by the first photoelectric detector; the invention further discloses an in-situ calibration method for the absolute frequency reference of the ultra-narrow band light filter, the center transmission wavelength of the etalon is calibrated through the absolute wavelength of the hollow cathode lamp, the etalon is accurately controlled at constant temperature and constant voltage, the center transmission wavelength of the etalon is calibrated, and the calibration of the center wavelength of the etalon is integrated with an external optical signal detection function; and through the automatic calibration process, the calibration efficiency is greatly improved, manual operation errors are avoided, and a high-precision calibration task can be completed in a short time.

Various aspects of the present disclosure generally relate to wireless communications. In some aspects, an apparatus may receive a first reference signal from a first transmit receive point (TRP) via a receive beam. The apparatus may receive a second reference signal from a second TRP via the receive beam. The apparatus may transmit an indication of a difference between a first measurement of the first reference signal and a second measurement of the second reference signal. Numerous other aspects are described.

An eyepiece waveguide for an augmented reality display system includes a substrate having a first surface and a second surface and a diffractive input-coupling element. The diffractive input-coupling element is configured to receive an input light beam and couple the input light beam into the substrate as a guided light beam. The eyepiece waveguide further includes a diffractive combiner pupil expander-extractor (CPE) element formed on or in the first surface or the second surface of the substrate. The diffractive CPE element includes a first portion and a second portion divided by an axis. A first set of diffractive optical elements is disposed in the first portion and oriented at a positive angle relative to the axis, and a second set of diffractive optical elements is disposed in the second portion and oriented at a negative angle relative to the axis.

The invention relates to a measuring device (10; 10a) for a machining system (12; 12a) for machining a workpiece (14; 14a) using a high-energy machining beam (16; 16a), wherein the measuring device (10; 10a) comprises a beam generating unit (18; 18a) configured to generate a sample beam (20; 20a) and a reference beam (22; 22a) that can be caused to interfere for the performance of optical interference measurements such as optical coherence tomography; a sample arm (24; 24a) that is optically connected to the beam generating unit (18; 18a) and in which the sample beam (20; 20a) is optically guided so that it can be projected onto the workpiece (14; 14a); a reference arm (26; 26a) that is optically connected to the beam generating unit (18; 18a) and in which the reference beam (22; 22a) is optically guided; and a measuring interface (28; 28a) that can be used to couple the sample beam (20; 20a) into the machining beam (16; 16a); the measuring device (10; 10a) comprising a base module (30; 30a) and an interchangeable module (32; 32a) that is connectable or connected thereto. The interchangeable module (32; 32a) comprises a beam guiding portion (48a) that includes optical components (50a) for guiding the sample beam (20a) and / or the reference beam (22a) and that is configured to form a central portion (52; 52a) of the sample arm (24; 24a) and / or the reference arm (26; 26a).The invention further relates to a system comprising a measuring device (10; 10a) and a plurality of interchangeable modules (32, 32′, 32″), a machining system (12; 12a) and a method for adjusting a measuring device (10; 10a).

The present application discloses a polarization-maintaining quantum frequency conversion device and a wavelength conversion method, relating to the technical field of optical modulation. The device includes: a polarization beam splitting device, an optical rotation device, a first off-axis parabolic mirror coated with a metal reflection film, a nonlinear crystal, and a second off-axis parabolic mirror coated with a metal reflection film; the polarization beam splitting device is configured to separate a pump light and a signal light into a first light beam and a second light beam; the optical rotation device is configured to flip the polarization direction of the light beam; the first off-axis parabolic mirror is configured to couple the first light beam into the nonlinear crystal, and collimate the second light beam and the output light and then input them into the polarization beam splitting device; the second off-axis parabolic mirror is configured to couple the second light beam into the nonlinear crystal, and collimate the first light beam and the output light and then input them into the polarization beam splitting device; the nonlinear crystal is configured to perform a nonlinear transformation on the first light beam or the second light beam to generate an output light.

The present disclosure relates to an optical device (1) for controlling light, the optical device (1) comprising: a first waveguide (2) for receiving a light beam from an external light source; at least a second waveguide (3); an optical coupler (4) for coupling the light beam from the first waveguide (2) to the second waveguide (3); a beam shaping structure (5) having a light emitting area (6) for emitting the light beam, wherein the second waveguide (3) is configured to guide the light beam coupled from the first waveguide (2) to the beam shaping structure (5), wherein the beam shaping structure (5) is configured to propagate the light beam received from the second waveguide (3) to the light emitting area (6) such that a beam divergence of the light beam emitted from the light emitting area (6) is lower than a beam divergence of the light beam received from the second waveguide (3).

Examples of the disclosure relate to optical apparatus, modules and devices for providing a more uniform output. The apparatus can comprise a light guiding member comprising a stack of layers and multiple interfaces between respective layers, wherein the respective layers are arranged to enable light to be guided through the light guiding member via internal reflections. The apparatus also comprises first in-coupling diffractive means configured to in-couple one or more input beams of light into the light guiding member, expanding diffractive means configured to expand the one or more input beams of light, and out-coupling diffractive means configured to out-couple the one or more beams of light from the light guiding member wherein the first in-coupling diffractive means and the out-coupling diffractive means are provided on a first layer of the stack of layers. The apparatus also comprises second in-coupling diffractive means configured to in-couple one or more input beams of light that has passed through the stack of layers into the light guiding member and wherein the second in-coupling diffractive means is provided on a different layer of the stack of layers to the first layer.