Diffractive Optical Element (DOE)
A Diffractive Optical Element (DOE) is an optical element which utilizs the diffraction phenomena of light. The general optical element like lenses controls the light such as focusing and diffusing by using the refraction of light at interface caused by the refractive index difference between air and optical element. On the other hand, DOE controls the light direction and intensity utilizing the diffraction pheonmena caused by the micro structures on the surface of the optical element. DOE can be used for a lot of applications. For example, it is used for a pattern generator to generate any desired diffraction image as Computer Generated Holograms (CGH), a beam shaper to change beam shapes of the laser beam, a spot generator to create many bright spots from a laser light, and giving optical functions on optics like chromatic aberration correction or temperature compensation.
Characteristics of NALUX Diffractive Optical Elements
We can:
- design and propose optimized CGH shapes using self-developed design software.
- design and mass-produce various profiles of diffractive structures like blazed (saw tooth shape) and staircase shape.
- design and process multi-level (multi steps) pattern.
- create diffractive structures on both surfaces of optical element
- directly process DOE on fused silica and also mass-produce the optical element by plastic injection molding.
- measure optical functions, such as spectro intensity and diffraction efficiency by self-deveoped functional measuring instrument in order to gurantee the quality.
Application examples DOE is applicable
- Amusement devices, Home appliances, Medical devices, Autotmotive, Robot etc.
(Applying DOE for motion capturing and AR/VR.) - Beam shapers and spot generators for laser processing equipment and communication devices and spectroscope etc.
(Applying DOE for beam shaping, spot generating and spectroscope.)
Actual DOE Application examples
Polymer Waveguide for Augmented Reality (AR)
Combination of AR, which displays digital information onto the real world, and smart glasses, wearable devices worn like eyeglasses, will enable us to overlay digital information on a user’s view of the real world. One of the expected applications is for maintenance and repair in the manufacturing industry, where AR glasses can guide technicians through complex tasks by displaying instructions or component layout onto their field of view, enhance work efficiency and reduce errors. Potential applications of AR glasses will expand further in the future in various industries including healthcare and gaming and entertainment.
Nalux diffractive waveguide for smart glasses has diffractive microstructure on the surface of lightweight resin plate with high level of safety, transmitting incident light by total internal reflection and projecting the light onto the human eye. Since plate flatness has a tremendous impact on the image resolution, it is essential to reduce Total Thickness Variation (TTV) to the maximum extent possible. Nalux waveguide offers low TTV and high resolution achieved by conducting injection molding of the microstructure, which is a unique technique in the industry.
Key Features of Nalux Diffractive Waveguide
- Reduced lead time in development: Nalux uses an optical software utilizing Rigorous Coupled-Wave Analysis (RCWA);
- Reducing luminance unevenness: Nalux high lithography technology sophisticatedly processes large-area and segmentally divided microstructure;
- Enhancing light efficiency and achieving brighter and clearer output: Nalux highly precisely processes a microstructure generating asymmetrical diffracted light at the light incidence part;
- Undistorted high image quality with lower cost: Nalux performs injection molding of a plate superior in flatness, to which microstructure with an aspect ratio of 1 or higher is transferred with high precision;
- Integrating design and functionality: Layout of incoupler, EPE and outcoupler can be freely customized.
Available in Monochrome-Color Display (Full color display is to be discussed)
Perfect for large diameter-spot light source
Currently, Nalux is offering waveguide only (protection and profile machining of waveguide is open to discussion).
Product testing under development is available.
Practical applications:
- Real-time display of translation from foreign language or transcription of conversation for people with healing loss.
- Display of emergency evacuation route in a disaster or navigation to destination
- Real-time measurement and display of heart rate, speed and altitude change during the exercise
Relevant Patents
- JP7309251
- Multiple patents pending or in the process of application
Computer-Generated Hologram (CGH)
Hologram is an optical element recording the interference fringes (2D phase information) generated by the ineterference between object light and reference light. Applying appropriate light to the hologram, the recorded object light image can be regenerated. on the other hand, CGH is an optical element created by calculating the phase information forming the desired diffractive image and modeling it as concave-convex structures. Applying the certain light to to such a CGH, the calculated diffractive image can be regeneraged. CGH is generally fine and very complicated structures. NALUX can produce various CGH products by our ultimate micro processing technologies like electron beam lithography and ultra precision injection molding.
Characteristics of NALUX CGH:
- Advanced optical design taking ghost and distorsion correction in to consideration by self developed design software.
- Fabrication of highly accurate microstructures by lithography technology using EB and etching.
- Materialization of sharply illuminated pattern by high transfer molding technology.
CGH Application examples:
- Pattern generators and target markers for barcode scanners in retail/logistics, attractions, and industrial devices
(Applying CGH for pattern generator and target markers.)
Chromatic aberration correction by DOE
The refractive index of the optical materials increases with shorter wavelength in and near the visible light range. So, for example, in the case of a condenser lens, the focal length varies depending on the wavelength and it's getting shorter with shorter wavelengths (Positive dispersion). In order to compensate this color aberration, it's well known to combine with a convex lens with small dispersion and a concave lens with large dispersion. However, the disadvantage of this method is that the number of lenses increases. On the other hand, a larger light diffraction angle can be obtained at longer wavelengths with a corrective DOE, depending on DOE structures (Negative dispersion). In other words, chromatic aberration can be corrected by combining a refractive lens and a corrective DOE structure and it can contribute to reduce the number of lenses. DOE structures can be applied on the flat surface of flat-convex lens and on the curved surface of the lens.
Application examples in actual use:
- Chromatic control of light distribution for head light lens
- Optical pick up lens
- Small imaging lens for mobile phone requiring high resolution
Example of Chromatic aberration improvement: Comparison on illumination pattern of LED lighting
Without DOE
With Chromatic aberration correction by DOE
Color control of light distribution by applying DOE (New Technology/Product Award at the 27th Small and Midium Enterprise Exhibition)
Related Patents
- Patents related to automotive headlight
- ・JP5315505
- ・JP5909419
- ・JP6849193
- Patents related to small imaging optics
- ・JP4317933
- ・JP4992004
- ・JP4798529
- ・JP4822033
- Patents related to pick-up optics (single objective lens for 3 wavelengths used for CD, DVD, and BD)
- ・JP4649572
Temperature compensated collimator
Temperature variation of refractive index in optical properties is one of the challenges in plastic lens design. For example, the refractive index decreases and the focal length increases as the temperature of the lens increases in collimator lenses used for laser beam printers. NALUX has materialized temperature-compensated optics by utilizing the temperature dependence of laser diode emission wavelengths and the characteristics of diffractive optical elements. This optical system suppresses focal length fluctuations of plastic lenses due to temperature by utilizing the characteristics of LD that the oscillation wavelength becomes longer as the temperature rises, and the characteristics of deffractive optical elements that the diffractive power becomes stronger at longer wavelengths. in this way, NALUX believes that it is possible to make better design proposals not only for the optical elements produced by us but also by understanding the entire product, including the light source, detector, assembly, usage, and application and by performing overall optimization by taking their characteristics into cosideration.
Application examples in actual use:
- Incident optical elements for laser beam printers (collimator and cylinder lens) and optical elements which has problems on operating temperature rgange.
