GB2607628A

GB2607628A - Wafer-level optics assembly with holographic optical element

Info

Publication number: GB2607628A
Application number: GB2108310.0A
Authority: GB
Inventors: Harel Oshrit; Sumarah Brandon
Original assignee: Metamaterial Technologies Canada Inc
Current assignee: Metamaterial Technologies Canada Inc
Priority date: 2021-04-01
Filing date: 2021-06-10
Publication date: 2022-12-14
Also published as: GB202104783D0; WO2022207784A1; GB202108310D0

Abstract

A method for manufacturing optical components comprising a volume holographic optical element comprises recording a volume holographic optical element (VHOE) in a photopolymer layer 20, bleaching the photopolymer layer to fix the recorded volume holographic optical element, forming a stack 40 including a wafer 10, the photopolymer layer 20 and one or more functional layers 30. Forming the stack includes bonding adjacent layers in the stack and cutting the stack into a plurality of optical components. The VHOE is arranged to function as one or more of a filter, a reflector, a diffuser, a lens, an optical waveguide, a redirector. The functional layer(s) may include a protective layer, a patterned CMOS layer, a MEMS layer, a photonics integrated circuit layer, a lens array layer, a spacer layer, an anti-reflective layer or a blacking layer. There is also provided an optical component comprising a volume holographic optical element and an apparatus for manufacturing the same. The photopolymer layer may be a liquid crystal photopolymer layer which may be applied onto the wafer as a liquid by spin-coating or inkjet printing.

Description

WAFER-LEVEL OPTICS ASSEMBLY WITH HOLOGRAPHIC OPTICAL ELEMENT

FIELD

The present disclosure relates to optical chip components, and methods and apparatus for manufacturing the same.

BACKGROUND

Wafer Level Optics (WLO) relates to optical products and components that are manufactured using semiconductor processes on wafers. WLO is been used to produce optical devices and highly structured surfaces for applications such as 3D sensors, lenses and lens arrays, gratings, light guides, beam shaping elements, refractive and diffractive optical elements (ROEs & DOEs), RE components, spacers, heat sinks and camera optics. WLO are used in a wide array of industries including electronics, display, spectroscopy and metrology, semiconductor, medical, aerospace and telecommunication.

In WLO, a micro-optics/ micro-electronic device (CMOS, MEMS, Photonics) can be built in semiconductor wafer to wafer processes, such as thin film deposition, lithography and imprinting, etching and metrology. Wafers are then assembled, for example by optical wafer bonding, to a full stack of additional wafers and layers, such as lens array elements, spacers and glass carriers, using high precision alignment. The full wafer stack is then singulated by dicing and packaged.

SUMMARY

According to a first aspect, a method for manufacturing optical components comprising a volume holographic optical element comprising: recording a volume holographic optical element in a photopolymer layer; bleaching the photopolymer layer to fix the recorded volume holographic optical element; forming a stack including a wafer, the photopolymer layer, and one or more functional layers, wherein the forming a stack includes bonding adjacent layers in the stack; and cutting the stack into a plurality of optical components.

The optical components may be optical chip components. The volume holographic optical element may be a volume holographic grating, either conformal or slant. The photopolymer may be RGB light-sensitive. The photopolymer may be flexible. The photopolymer may be a liquid crystal photopolymer, or a fluorescent photopolymer, etc. The wafer may be optical glass (e.g. BK7 etc.), a mirror, Silicon on insulator (SOO, etc. The cutting may comprise cutting the stack into three or more optical elements, four or more optical elements, or five or more optical elements.

The method may further comprise laminating the photopolymer layer onto the wafer. The laminating the photopolymer layer onto the wafer may be performed after the recording the volume holographic optical element in the photopolymer layer. The recording the volume holographic optical element in the photopolymer layer may be performed after the laminating the photopolymer layer onto the wafer.

The laminating the photopolymer layer onto the wafer may be laminating directly onto the wafer. Alternatively, the photopolymer layer may be laminated with an intermediate layer between the photopolymer layer and the wafer. Similarly, the surface of the wafer may be coated, and the photopolymer may be laminated onto the coated surface of the wafer. The laminating may be part of the forming a stack or may be performed separately.

The method may comprise applying the photopolymer onto the wafer as a liquid. The applying the photopolymer layer onto the wafer may be by spin-coating or inkjet printing.

The recording the volume holographic optical element in the photopolymer layer may be performed after the forming the stack.

The bleaching may be performed after the laminating the photopolymer layer onto the wafer or after the forming the stack, regardless of whether the recording is performed before or after the laminating or forming.

The recording may comprise producing an optical interference pattern of a first beam with a second beam in the photopolymer layer, wherein the second beam is a reflection off the wafer of the first beam. Alternatively, the second beam may be a reflection of the first beam off a reflective component (other than the wafer). The reflective component may be temporarily positioned next to the photopolymer layer for recording the volume holographic optical element and then removed before the photopolymer is formed into the stack.

The recording may comprise recording volume holographic optical elements in a plurality of photopolymer layers, wherein the stack includes the plurality of photopolymer layers. In other words, said photopolymer layer is a first photopolymer layer of the plurality of photopolymer layers which each have a respective volume holographic optical element recorded therein.

The plurality of photopolymer layers may be formed into a composite photopolymer layer wherein the volume holographic optical elements of the plurality of photopolymer layers may be recorded collectively at the same time. Alternatively, the volume holographic optical elements may be recorded individually in each of the plurality of photopolymer layers, optionally with the plurality of photopolymer layers formed into the composite photopolymer layer. The plurality of photopolymer layers may be adjacent layers in the formed stack.

A characteristic of the volume holographic optical elements may differ between volume holographic optical elements of respective photopolymer layers. The characteristic may be a spacing or a slant of a volume holographic grating, e.g. one photopolymer layer has a first slant angle and another photopolymer has a second slant angle. The characteristic may be a range of wavelengths and/or a range of angles for which the volume holographic optical element achieves a particular effect (e.g. filtering, diffusing, lensing, etc.). Multiple characteristics may vary between photopolymer layers in order to achieve a particular optical effect when light is incident on the volume holographic optical element.

At least one characteristic of the volume holographic optical element may vary across the photopolymer layer. For example, the volume holographic optical element may have a first characteristic at a first location or region and have a second characteristic at a second location or region. As mentioned above, the characteristic may be a spacing or a slant of a volume holographic grating or a range of wavelengths and/or a range of angles for which the volume holographic optical element achieves a particular effect. Varying a characteristic across the photopolymer layer can produce effects difficult to achieve otherwise. Hence the method of manufacturing has a versatility of types of optical components it can produce. As an example, spatially varying volume holographic optical elements can be designed to function as a lens or a curved mirror, or provide anomalous reflection, but having a flat form factor. This means the resulting optical component is smaller and simple to integrate with other components than using a normal lens or curved mirror etc. The at least one characteristic may vary periodically across the photopolymer layer to produce a repeat pattern of the volume holographic optical element. For example, the recorded volume holographic optical element may comprise a repeated contour pattern of a particular parameter (e.g. concentric contour rings of a slant angle, with outer contours having a higher slant angle). The cutting may comprise aligning cuts so that each optical component of the plurality of optical components comprises an integer multiple of the repeat pattern, optionally, a single repeat pattern. This improves the manufacturing speed and efficiency, as comparatively large areas of the photopolymer can have a volume holographic optical element recorded therein, with the result stack later cut into the individual optical components each having the required function of the repeat pattern.

The volume holographic optical element of the photopolymer layer may be arranged to function, for a wavelength or a range of wavelengths of optical radiation, as one or more of: a filter; a reflector; a diffuser; a lens; an optical waveguide; and a redirector. The particular properties of the resulting volume holographic optical element, e.g. the particular wavelengths it will work for, the angles it reflects/diffuses/redirects optical radiation, the focal length, etc. are determined by the characteristic(s) of the volume holographic optical element(s).

The method may comprise trimming the photopolymer layer before forming the stack, wherein the trimming comprises removing a peripheral portion of the photopolymer layer around the perimeter of the photopolymer layer. This protects the photopolymer layer from damage either during manufacture; in transport, or in use, as the periphery of the wafer shields the edge of the trimmed photopolymer layer.

The method may comprise applying a protective layer to the photopolymer layer before forming the stack. The protective layer may be glass, a hardcoat layer, or other material having a hardness higher than the photopolymer layer such that the photopolymer layer is protected from damage such as abrasions. The method may comprise edge sealing the photopolymer layer. The edge sealing may comprise applying tape or adhesive to the edges of the photopolymer layer to protect it. The protective layer and/or edge sealing can protect the photopolymer layer and volume holographic optical element therein from abrasions, extreme temperatures (especially high temperatures) or high humidity. The protective layer also protects against gases, fumes, or other chemical liquids/materials. In general, the protective layer may provide chemical and environmental protection.

The method may be performed such that a temperature of the photopolymer layer is maintained at no more than 150 degrees Celsius throughout the method. This protects the photopolymer from damage caused by overheating, such as melting, other deformation, or deteriorating the volume holographic optical element (for example, by affecting the refractive index).

The one or more functional layers may include one or more of: a patterned CMOS (i.e. a Complementary Metal-Oxide-Semiconductor) layer, a MEMS (Micro-Electromechanical System) layer, a photonics integrated circuit layer; a lens array layer, a spacer layer, an anti-reflective layer, and a blacking layer. In general, a CMOS layer or a MEMS layer is a wafer or stack of wafers which includes materials, patterns and components to achieve certain functions according to CMOS of MEMS techniques, respectively.

Bonding to form the stack may comprise applying a transparent adhesive between adjacent layers of the stack, wherein the refractive index of the adhesive matches the refractive index of the adjacent layers or is between the refractive indices of the adjacent layers. This improves the optical performance of the volume holographic optical element as stray reflections or deflections are reduced. Alternatively, the bonding may comprise activating, with a plasma treatment, a surface of one of a pair of adjacent layers in the stack so that the activated surface adheres to the other layer of the pair of adjacent layers.

The photopolymer layer may be positioned between two other layers in the stack. In other words, the photopolymer is not an outer layer but is sandwiched between wafers, functional layers, or a combination thereof.

According to an aspect an apparatus for manufacturing optical components comprising a volume holographic optical element is configured to perform any of the methods described above. The apparatus may comprise a laser assembly for recording the volume holographic optical element in a photopolymer layer as described above. The apparatus may comprise an optical radiation source for bleaching the photopolymer layer, wherein the optical radiation source may be configured to irradiate the photopolymer layer with ultra-violet or visible light to fix the recorded volume holographic optical element as described above. The apparatus may comprise a bonding tool for forming the stack as described above. The bonding tool may be configured to apply adhesive, UV bonding, plasma bonding, and optical bonding to form the stack and may also be configured to laminate the laminating the photopolymer layer onto the wafer. The apparatus may comprise a cutter for cutting the stack into a plurality of optical components as described above. The cutter may comprise a cutting laser, a waterjet, a computer numerical control (CNC) cutter, or a dicing saw.

According to an aspect, an optical component, comprising a volume holographic optical element, comprises a stack including: a wafer; a photopolymer layer, wherein the photopolymer layer comprises a volume holographic optical element; and one or more functional layers.

The optical component may have any of the features described above in relation to the method for manufacturing the optical component, including the following.

The optical component may be an optical chip component. The volume holographic optical element may be a volume holographic grating, either conformal or slant. The photopolymer may be RGB light-sensitive.

The optical component may comprise a plurality of photopolymer layers including the photopolymer layer, wherein each photopolymer layer comprises a respective volume holographic optical element. As described further above, a characteristic of the volume holographic optical elements may differ between volume holographic optical elements of respective photopolymer layers.

At least one characteristic of the volume holographic optical element may vary across the photopolymer layer, as described further above.

The volume holographic optical element of the photopolymer layer may be arranged to function, for a wavelength or range of wavelengths of optical radiation, as one or more of: a filter; a reflector; a diffuser; a lens; an optical waveguide; and a redirector, as described further above. The one or more functional layers may include one or more of: a protective layer configured to protect to the photopolymer layer (as described further above), a patterned CMOS layer, a MEMS layer, a photonics integrated circuit layer; a lens array layer, a spacer layer, an anti-reflective layer, and a blacking layer.

BRIEF DESCRIPTION OF THE FIGURES

Specific embodiments are now described by way of example and with reference to the accompanying drawings, in which: Figure 1 shows a diagram of a method for manufacturing optical chip components comprising a volume holographic optical element; Figure 2 shows a schematic view of layers of an optical chip component during a method of manufacturing Figure 3 shows a schematic view of layers of an optical chip component during a method of manufacturing; Figure 4 shows a schematic view of layers of an optical chip component during a method of manufacturing; Figure 5 shows two diagrams of how to record a volume holographic optical element; Figure 6 shows a stack of layers for cutting into optical chip components comprising a volume holographic optical element; Figure 7 shows a stack of layers with positioning of cuts shown; Figure 8 shows a stack of layers once cutting into the plurality of optical of components is complete; Figure 9 shows a stack of layers for cutting into optical chip components comprising a volume holographic optical element; and Figure 10 shows a diagram of an apparatus for manufacturing optical chip components comprising a volume holographic optical element.

DETAILED DESCRIPTION

Method for manufacturing optical chip components With reference to Figure 1, a method 100 for manufacturing optical components comprising a volume holographic optical element comprises: recording 110 a volume holographic optical element in a photopolymer layer; bleaching 120 the photopolymer layer to fix the recorded volume holographic optical element; forming 130 a stack including a wafer, the photopolymer layer, and one or more functional layers, wherein the forming a stack includes bonding adjacent layers in the stack; and cutting 140 the stack into a plurality of optical components.

With reference to Figure 2A, the wafer is a glass wafer 10. In alternative arrangements, the wafer is any substrate suitable for supporting the photopolymer layer, for example, fused silica and quartz, optical glasses such as B270, D263, Borofloat, Eagle XG, gorilla glass, soda lime glass, silicone, germanium, gallium arsenide, and epitaxial.

The photopolymer layer 20 is a photosensitive material which reacts to incident optical radiation, for example, changing refractive index according to an intensity pattern of the optical radiation in the material. Photopolymer layers by nature are generally thin and flexible and can be supported by a soft polymer substrate such as cellulose triacetate (TAC), polycarbonate (PC), and polyamide (PA). The flexible nature of photopolymer materials and their properties allow for integration with technologies historically not possible with rigid materials.

By using a photopolymer layer 20 rather than, say rigid materials, not only can the flexible property of a polymer material be utilised, but a broader range of volume holographic optical element types can be formed in the photopolymer layer 20. For example, spatially-varying volume holographic optical elements are possible or multiplexing, e.g. having multiple gratings at different levels within the photopolymer layer with varying properties. The speed at which a volume holographic optical elements can be recorded in a photopolymer layer exceeds other possible recording media, e.g. by using spool-to-spool recording of photopolymer layer 20.

A volume holographic optical element 25 can be recorded in the photopolymer due to the polymer's photosensitive property. A volume holographic optical element is the result of recording a particular profile or pattern in the photopolymer, which when receiving incident optical radiation, produces a particular effect. An example of a volume holographic optical element is a volume holographic grating (VHG), comprising a series of grating planes (i.e. lines of higher refractive index) spaced apart by a spacing. The grating planes may be peaks or troughs in a sinusoidal refractive index distribution. Conformal VHGs have the planes oriented parallel to the material surface. Slant VHGs have grating planes are oriented with an angle relative to the material surface, i.e. a slant angle. Slant gratings feature anomalous specular-like reflection within the spectral bandwidth of the grating that can be utilized to use them as in/out coupling optical elements for planar waveguides. Volume holographic optical elements may have more complicated or varying profiles, in order to reproduce the effect of a lens or a curved mirror on incident optical radiation. Some volume holographic optical elements may be multiplexed so that they diffract optical radiation into multiple different directions or diffract different spectral bands into different directions. Highly multiplexed holographic gratings can convert optical radiation incident from one direction into diffuse light with a well-defined range of output directions according to a desired shape (angle distribution). More generally, a volume holographic optical element is a volume hologram (wherein the thickness of the material is much larger than the recording wavelength of light, as opposed to a surface or 'thin' hologram) designed to produce a particular effect of incident optical radiation. In other words, the volume holographic optical element converts one input mode of light into an output mode of light by means of Bragg diffraction. The spatial structure of the modulation within the volume holographic optical element determines the shape and intensity of the output mode for a given input mode.

Once a volume holographic optical element has been recorded in the photopolymer, the photopolymer is bleached using a combination of ultra-violet and visible light to fix the volume holographic optical element and improve overall transmission. In simple terms, this is achieved by using up any unused chemistry in the photopolymer, not consumed by the recording process. Recipe parameters (i.e., wavelength range, intensity, dose) should be selected based on the specific photopolymer being used.

With reference to Figure 2A, the photopolymer layer is laminated onto the wafer 10 before the volume holographic optical element is recorded. In that case, wafer may be used as the recording plate for the recording of the volume holographic optical element, for example, the interference pattern produced in the photopolymer layer may be from a laser beam reflecting incident on the photopolymer layer and reflecting off the wafer. In other arrangements, the volume holographic optical element is recorded separately according to any suitable method and associated apparatus, before being laminated onto the wafer or otherwise formed into the stack.

Any suitable industrial technique may be used for lamination. Depending upon the alignment requirement, machines may be used offering various degrees of automation for providing lower or higher accuracies. Manual laminations commonly require physical markings or bump stops, while more sophisticated machinery commonly employs automated optical alignment with detailed feature recognition.

Depending on the recording method used, the bond strength of the lamination should be set accordingly. When recording using the wafer as the recording plate, the bond strength should be strong enough to survive downstream processing and meet overall product viability requirements, as it will become part of the final assembly. On the other hand, when recording on a separate recording plate before combining with the final wafer, the bond should be considered temporary. In this case, the photopolymer layer is removable from the recording plate without affecting optical properties. Depending on the photopolymer layer used, some will feature a low tackiness side protected by a cover-layer. This is ideal as the cover-layer may be removed and the photopolymer layer laminated, without the need for additional adhesives.

The wafer 10 and photopolymer layer 20 are formed into stack with one or more functional layers 30. The one or more functional layers may also be a wafer or otherwise include a wafer. With reference to Figure 2B, in an example there are two functional layers and there is a second wafer layer 10 positioned with the functional layers between the second wafer and the photopolymer layer 20.

Wafer level bonding for the stack may be performed using common industry methods for wafer alignment bonding including UV bonding, plasma bonding, and optical bonding. Volume holographic optical elements such as filters, diffusers, holographic optical elements, and waveguides may be integrated with functional layers such as MEMS, CMOS, photonics, LED, filters or other patterned chips or spacers, forming the stack. Functional coatings (e.g. anti-reflective and hard coating may also be applied depending on design requirements These may be an additional protective layer applied to the photopolymer layer before forming the stack or may be one of the functional layers of the stack. An anti-reflective coating reduces unwanted reflections, e.g. to improve the efficiency and image contrast by reducing light lost due to reflection and the elimination of stray light. These coatings may be used for single-wavelength operation for narrowband lasers to coatings functioning over very broad band spectral bands (i.e. visible and/or infrared). A hard coat, also referred to as a scratch resistant coating, provides increased durability to the surface. Polymer materials scratch more easily than glass and benefit from a durable hard coat to ensure longevity.

Another example of a functional layer which may be included in the stack, according to the design requirements, is a blacking layer. This may be a black silicon layer with low reflectivity and high absorption of visible and infrared light. Common applications include solar photovoltaic enabling greater light to electricity conversion efficiency and image sensing with greater sensitivity.

Another example of a functional layer which may be included in the stack, according to the design requirements, is a spacer layer. A spacer layer is used for patterning features with linewidths smaller than what can be achieved using standard lithography techniques. Generally, patterned features called mandrels are used, which define where the sidewall spacers are subsequently situated. The spacer material is deposited over the mandrel and etched such that the spacer portion covering the mandrel is removed. After removing the mandrel, only the spacer on the sidewall remains.

One option for bonding involves using liquid or film-based optically transparent adhesives between layers. Selecting the adhesive for material compatibility is relevant, especially in cases where it directly contacts the photopolymer layer comprising the volume holographic optical element. The adhesive can be selected in such a way that optical performance is maximized, whilst limiting potential holographic shifts due to improper material matchups. The refractive index (RI) of the layers can also be chosen to minimize unwanted reflection, refraction, diffraction, and rotations that occur at material interfaces within the multilayer stack.

It is advantageous for the physical forming of the various layers to be performed under clean, environmentally stable conditions. Again, depending on alignment requirements, manual or automated industrial techniques can achieve this. When using ultra-violet (UV) curable liquid adhesives in the example mentioned above, it is advantageous to perform the UV exposure with minimal time delay and absent movement between steps to limit the risk of layers translating with respect to one another causing misalignment.

Photopolymer layer are more sensitive to changes in environmental conditions as compared to traditional recording materials such as photosensitized glass. Accordingly, shifts in humidity, temperature, and cycling may be considered and tested for when designing a functional optical assembly. In some examples, safeguarding may be achieved through integration, e.g. the photopolymer layer may be cast to various form factors, encapsulating, and isolating from the external environment. Other functional coatings such as hard coat and edge sealing may also be used. Aside from improving the stability of the volume holographic optical element, integration is especially advantageous for polymer films, as they are inherently prone to scratching.

In some arrangements, if the volume holographic optical element has not already been recorded, the recording (and bleaching) may be performed after forming the stack. This can be achieved using the same principles as recording at any other time, except the beams to produce the interference pattern for producing the volume holographic optical element in the photopolymer layer travel through one or more of the other layers in the stack.

Once the stack is formed containing the volume holographic optical element and any other functional layers as required, the stack is cut 140 into individual optical components 50. Dicing may be performed using a variety of industry methods including laser, waterjet, CNC cutting, sawing etc. These techniques may be used to create any shape as required by the design. Finally, industrial used wafer-level packaging techniques may be used for packaging to final optical components.

By cutting the stack into a plurality optical components, the methods herein have the advantage of faster manufacturing, as the required volume holographic optical elements for many optical components can be recorded with one process, i.e. the recording in the photopolymer layer before cutting. This increases the speed and simplicity of manufacture compared to creating a volume holographic optical element in a separate photopolymer layer for each optical component individually.

Depending on the optical properties as dictated by the design of the system, the photopolymer layer may have homogeneous properties or vary across its area. With varying properties, dicing alignment is more important, requiring higher precision and control so that the desired sub-portion of the volume holographic optical element ends up in each optical component.

As an alternative to laminating the photopolymer layer as described above with reference to Figure 2, the photopolymer layer may be applied onto the wafer as a liquid, for example by spin-coating or inkjet printing thereby providing precise control of the location and shape of the photopolymer. In examples using a liquid photopolymer application, the method may also comprise curing the liquid photopolymer layer, or otherwise solidifying the liquid photopolymer layer (e.g. waiting for it to set). Once the photopolymer layer has been formed, the remaining features of the method may be performed as described above or according to any of the examples provided herein.

With reference to Figure 3, in some arrangements the method comprises trimming the photopolymer layer or stack. In the case of a sandwich stack with glass wafers on top and bottom, as shown in Figure 2, trimming the photopolymer layer slightly smaller than the wafer can help provide isolation from the external environment. When bonding the top glass, the adhesive may be used to fill the gap between the two glasses along the edge. Trimming may be performed by laser, or similar, where accuracy and cleanliness are key considerations when selecting an appropriate cutting method.

With reference to Figure 4, in some arrangements the photopolymer layer 20 is a composite photopolymer layer comprising three photopolymer layers 21, 22, 23. The rest of the features of the method for manufacturing optical components can be the same as described above, with the features of the photopolymer layer 20 applying to one, some, or all of the photopolymer layers 21, 22, 23 of the composite photopolymer layer 20. For example, the volume holographic optical element in each respective photopolymer layer may be recorded concurrently as the other photopolymer layers, or separately. Having multiple photopolymer layers 21, 22, 23 increases the possibilities of functions the volume holographic optical elements and resulting optical component can have. For example, in some arrangements, the volume holographic optical elements of different layers are different and effective for different wavelengths or angles of incident radiation, such as one photopolymer layer filters a first wavelength of radiation and another photopolymer layer filters a second wavelength of radiation. In some arrangements, rather than a single composite photopolymer layer 20, the plurality of photopolymer layers are not positioned adjacent to each other in the stack but at separate positions throughout the stack according to the required function.

While three photopolymer layers are shown in the composite photopolymer layer 20 of Figure 4, fewer (e.g. two photopolymer layers) or more (e.g. four or more photopolymer layers) may be used.

When using a liquid photopolymer as the starting material for the photopolymer layer, the composite photopolymer layer may be formed by applying successive layers of the photopolymer liquid. The successive layers may be cured or otherwise solidified between successive applications.

With reference to Figure 5, two examples of arrangement for recording a volume holographic optical element involve producing an optical interference pattern of a first beam with a second beam in the photopolymer layer, wherein the second beam is a reflection off the wafer of the first beam. The variation in amplitude of the electromagnetic field (or intensity of the radiation) in the photopolymer layer produces the hologram in the photopolymer layer. Because holograms record phase information in addition to intensity, they capture a large amount of information. This information is encoded in the micro-and nanostructure of the recording medium. To create volume holographic optical element, multiple beams of light are overlapped within a photosensitive medium that reacts to the interfering light beams. The medium records the areas of high and low light intensity as variations of its refractive index.

In general, there are two ways of capturing this interference pattern: (1) In reflection, whereby the interference pattern of the incident and reflected beams is captured; and (2) In transmission, whereby the interference pattern between two or more incident beams is captured. Periodic modulations in refractive index extend through the depth of the medium. These devices are known as volume phase holograms or volume holographic gratings (VHGs), a type of volume holographic optical element.

The term recording refers to the process of creating a VHG within the photopolymer recording medium. The resulting volume holographic optical element can perform several optical functions, each requiring specific recording geometries to create.

While Figure 5 shows having two incident beams and two corresponding reflected beams, there may be only one pair of incident and reflected beams, or only one pair of beams transmitted into photopolymer layer without reflection.

The processing of photopolymer layers for producing optical components differs fundamentally from rigid materials. Rigid materials utilize processes that require very high temperatures (e.g. annealing), which are not compatible with soft polymer material. For soft polymers, high temperatures tend to result in physical warping or distortions being induced in the films, having potentially severe effects on the hologram and overall optical properties. In the case of glass, annealing is commonly performed after forming processes, to relieve internal stresses within the material. Bonding multiple layers of rigid materials is also normally performed using high pressures and temperatures. In the case of photopolymer materials, the working temperature range must be kept much lower as compared to rigid materials. Accordingly, the working temperature can be chosen considering the glass transition temperature of the polymer and be based on quantitative test / survival data using recorded photopolymer. For example, keeping the temperature of the photopolymer layer 20 no more than 150 degrees Celsius throughout the manufacturing method will protect the photopolymer layer from damage. Alternatively, a different maximum temperature not to exceed may be chosen, e.g. 100 degrees Celsius, according to the photopolymer layer requirements. Outgassing can also be a consideration when using polymer materials, as it can lead to unwanted migration amongst material chemistries within a multi-layer stack, which can influence the volume holographic optical element(s). Pre-baking or thermal treatment of a substrate may also be used, for example before laminating the photopolymer.

Manufactured optical component With reference to Figure 6, a stack 40 is formed having a wafer 10, a photopolymer layer 20, comprising a volume holographic optical element and a functional layer 30. In some arrangements, there may be more than one functional layer as described above. The optical components resulting from the stack have the same layer composition and ordering as produced during the formation of the stack.

With reference to Figure 7, the cutting process (as described above) produces a series of cuts according the required design of the resulting optical components.

With reference to Figure 8, after cutting, the plurality of optical components 50 can be separated from each other and the stack 40. The optical components may then be processed or treated further, e.g. packaged for transportation.

With reference to Figure 9, the particular composition of optical components (or formed stacks ready to be cut into a plurality of optical components) can be selected according to the required functions of the resulting optical component.

With reference to Figure 9A, in an example, the optical component comprises two functional layers 30, a hardcoat layer 31 and an antireflecfion layer 32, as well as the wafer 10 and photopolymer layer 20 having a volume holographic optical element. The functional layers protect the photopolymer layer 20 from damage and reduce stray reflections.

With reference to Figure 9B, in an example, the optical component comprises two functional layers 30, which are both an antireflection layer 32, as well as two wafers 10 either side of the photopolymer layer 20 having a volume holographic optical element. This improves the optical performance of the optical component by reducing stray reflections either internally or off the surface of the optical component as light enters or leaves. This arrangement is advantageous for a filter optical component.

With reference to Figure 90, in an example, the optical component comprises three functional layers 30: an antireflection layer 32, a blacking layer 33 and a patterned layer 34; as well as the wafer 10 and photopolymer layer 20. This integrates the volume holographic optical element into an assembly with a patterned layer 34, which could have a variety of possible functions known in the field of patterned CMOS layers, MEMS layers, integrated photonics circuits etc. For example, the patterned layer 34 may be a photovoltaic layer and the optical component may be for a solar cell.

With reference to Figure 9D, in an example, the optical component comprises four functional layers 30: an antireflection layer 32, a blacking layer 33 and a patterned layer 34, and a spacer layer 35, as well as the wafer 10 and photopolymer layer 20. The spacer layer 35 has one or more gaps, e.g. air gaps, across the spacer layer. This may be used to separate portions of the photopolymer layer 20 from contact with other layers.

While Figures 9A to 9D show cylindrical optical components, other shapes are possible according to the specifics of the cutting of the stack into a plurality of optical components. For example, cubic or oblong optical components as shown in Figures 7 and 8.

In any of the above examples described above with reference to Figures 6 to 9, the photopolymer layer 20 may be a composite photopolymer layer comprising two or more photopolymer layers.

Apparatus for manufacturing optical components With reference to Figure 10, an apparatus 300 for manufacturing optical components according to the above description by the above methods includes a laser assembly 310 for recording the volume holographic optical element in a photopolymer layer 20 as described above. The apparatus also comprises an optical radiation source 320 for bleaching the photopolymer layer, wherein the optical radiation source may be configured to irradiate the photopolymer layer with ultra-violet or visible light to fix the recorded volume holographic optical element as described above, or any other type of bleaching as required by the particular material of photopolymer layer used. The apparatus also comprises a bonding tool 330 for forming the stack as described above. The bonding tool may be configured to apply adhesive, UV bonding, plasma bonding, and optical bonding to form the stack, or any other suitable bonding method and may also be configured to laminate the laminating the photopolymer layer onto the wafer. The apparatus also comprises a cutter 340 for cutting the stack into a plurality of optical components as described above. The cutter may comprise a cutting laser, a waterjet, a computer numerical control (CNC) cutter, or a dicing saw, or any other cutter suitable for cutting a stack into optical components. The optical components can then be packaged and integrated into larger optical assemblies.

Claims

CLAIMS1. A method for manufacturing optical components comprising a volume holographic optical element, the method comprising: recording a volume holographic optical element in a photopolymer layer; bleaching the photopolymer layer to fix the recorded volume holographic optical element; forming a stack including a wafer, the photopolymer layer, and one or more functional layers, wherein the forming a stack includes bonding adjacent layers in the stack; and cutting the stack into a plurality of optical components.
2. The method according to claim 1, wherein the method comprises: laminating the photopolymer layer onto the wafer.
3. The method according to claim 2, wherein the laminating the photopolymer layer onto the wafer is performed after the recording the volume holographic optical element in the photopolymer layer.
4. The method according to claim 2, wherein the recording the volume holographic optical element in the photopolymer layer is performed after the laminating the photopolymer layer onto the wafer.
5. The method according to claim 1, wherein the method comprises: applying the photopolymer layer onto the wafer as a liquid.
6. The method according to claim 5, wherein the applying the photopolymer layer onto the wafer is by spin-coating or inkjet printing.
7. The method according to any of claims 1, 2, 4, 5, or 6, wherein the recording the volume holographic optical element in the photopolymer layer is performed after the forming the stack.
8. The method according to any of claims 4 to 7, wherein the recording comprises producing an optical interference pattern of a first beam with a second beam in the photopolymer layer, wherein the second beam is a reflection off the wafer of the first beam
9. The method according to any preceding claim, wherein the recording comprises recording volume holographic optical elements in a plurality of photopolymer layers, wherein the stack includes the plurality of photopolymer layers.
10. The method according to claim 9, wherein a characteristic of the volume holographic optical elements differs between volume holographic optical elements of respective photopolymer layers
11. The method according to any preceding claim, wherein at least one characteristic of the volume holographic optical element varies across the photopolymer layer.
12. The method according to claim 11, wherein the at least one characteristic varies periodically across the photopolymer layer to produce a repeat pattern of the volume holographic optical element, wherein the cutting comprises aligning cuts so that each optical component of the plurality of optical components comprises an integer multiple of the repeat pattern, optionally, a single repeat pattern.
13. The method according to any preceding claim, wherein the volume holographic optical element of the photopolymer layer is arranged to function, for a wavelength or a range of wavelengths of optical radiation, as one or more of: a filter; a reflector; a diffuser; a lens; an optical waveguide; and a redirector.
14. The method according to any preceding claim, wherein the method comprises: trimming the photopolymer layer before forming the stack, wherein the trimming comprises removing a peripheral portion of the photopolymer layer around the perimeter of the photopolymer layer.
15. The method according to any preceding claim, wherein the method further comprises: applying a protective layer to the photopolymer layer before forming the stack.
16. The method according to any preceding claim, wherein the method comprises: edge sealing the photopolymer layer.
17. The method according to any preceding claim, wherein a temperature of the photopolymer layer is maintained at no more than 150 degrees Celsius throughout the method.
18. The method according to any preceding claim, wherein the one or more functional layers include one or more of: a patterned CMOS layer, a MEMS layer, a photonics integrated circuit layer; a lens array layer, a spacer layer, an anti-reflective layer, and a blacking layer.
19. The method according to any preceding claim, wherein the bonding comprises applying a transparent adhesive between adjacent layers of the stack, wherein the refractive index of the adhesive matches the refractive index of the adjacent layers or is between the refractive indices of the adjacent layers.
20. The method according to any preceding claim, wherein the photopolymer layer is positioned between two other layers in the stack.
21. The method according to any preceding claim, wherein the photopolymer layer is a liquid crystal photopolymer layer.
22. Apparatus for manufacturing optical components comprising a volume holographic optical element, the apparatus configured to perform the method of any preceding claim.
23. An optical component comprising a volume holographic optical element, wherein the optical component comprises a stack including: a wafer; a photopolymer layer, wherein the photopolymer layer comprises a volume holographic optical element; and one or more functional layers.
24. The optical component according to claim 23, comprising a plurality of photopolymer layers including the photopolymer layer, wherein each photopolymer layer comprises a respective volume holographic optical element.
25. The optical component according to claim 24, wherein a characteristic of the volume holographic optical elements differs between volume holographic optical elements of respective photopolymer layers.
26, The optical component according to any of claims 23 to 25, wherein at least one characteristic of the volume holographic optical element varies across the photopolymer layer.
27. The optical component according to any of claims 23 to 26, wherein the volume holographic optical element of the photopolymer layer is arranged to function, for a wavelength or range of wavelengths of optical radiation, as one or more of: a filter; a reflector; a diffuser; a lens; an optical waveguide; and a redirector.
28. The optical component according to any of claims 23 to 27, wherein the one or more functional layers include one or more of: a protective layer configured to protect to the photopolymer layer, a patterned CMOS layer, a MEMS layer, a photonics integrated circuit layer; a lens array layer, a spacer layer, an anti-reflective layer, and a blacking layer.
29. The optical component according to any of claims 23 to 28, wherein the photopolymer layer is a liquid crystal photopolymer layer.