Optical device

Abstract

The present disclosure relates to an optical device (1) comprising: a primary fan-out waveguide (3); at least one secondary fan-out waveguide (4); a fan-out optical coupler (5) for coupling a light beam between the primary fan-out waveguide (3) and the secondary fan-out waveguide (4); at least one bus waveguide (6) associated with the at least one secondary fan-out waveguide (4) and distinct from each secondary fan-out waveguide (4); wherein a reflection and coupling structure (7) connects the secondary fan-out waveguide (4) and the bus waveguide (6).

Description

Technical Field

[0001] This disclosure relates to an optical device comprising: a primary fan-out waveguide; at least one secondary fan-out waveguide; a fan-out optical coupler for coupling a light beam between the primary fan-out waveguide and the secondary fan-out waveguide; and at least one bus waveguide associated with and distinct from each of the at least one secondary fan-out waveguide. Background Technology

[0002] In the prior art, there are known devices that uniformly distribute light over a specific area or receive light from different channels distributed over a specific area. For certain applications, such as backlight units for LCDs, these devices need to be compact, particularly thin (in a direction orthogonal to the specific area), and include a minimum bezel around the specific (active) area.

[0003] Travis et al.'s paper "Collimated light from a waveguide for a display backlight" in Opt. Express 17, 19714-19719 (2009) demonstrates a classic approach to this type of backlight unit. In this method, light emitted from a point source fans out in a waveguide plate. The light is reflected off one side of the plate, essentially filling the entire area, and must then be emitted from the top surface of the plate. However, such devices are known to lack uniformity, efficiency, and compactness.

[0004] Ross, in his paper "Ion-exchanged glass waveguide sensors" published in Glass Integrated Optics and Optical Fiber Devices: A Critical Review, 102750C (July 25, 1994), demonstrates a method for sensing applications. The paper presents a sensor array with four parallel Mach-Zehnder interferometers. For this purpose, light is transmitted through a single-mode fiber coupled to an integrated optical chip and split into four waveguide channels guided to the four sensor elements. Fan-out to the four waveguide channels is achieved via a first splitter and two subsequent splitters. Subsequently, all beams are emitted from the side of the integrated optical chip opposite to the side to which they are coupled into the chip. However, such fan-out requires a large area, and if the area to be covered should, for example, be rectangular, this active area can only be provided after the fan-out is complete to achieve the full width and number of channels.

[0005] The main limitations of this fan-out are the length of the coupling / decoupling mechanism and the bending loss, which depends on the waveguide bending radius. The separated waveguides must be bent away from each other to achieve the required distance, such as pixel pitch in display applications.

[0006] An alternative approach is shown in WO 2007 / 046100 A2. In this approach, waveguides leading from the laser diode are coupled to subsequent waveguides, which are bent 90° toward the corresponding pixel row. While this may limit the fan-out length to the bending radius of the waveguides, it still requires the borders around the active region to be on the order of the bending radius, which is too large for some applications.

[0007] Alternatively, waveguides with two 90° bends can be used, such as those demonstrated by Van Acoleyen et al. in "Optical Retroreflective Marker Fabricated on Silicon-On-Insulator" published in IEEE Photonics Journal (Vol. 3, No. 5, October 2011), pp. 789-798. However, these do not allow for small bezels on all sides of the active region, and such bent waveguides introduce high optical loss. Summary of the Invention

[0008] One object of the present invention is to prevent or mitigate at least one disadvantage of the prior art. In particular, waveguide fan-out or fan-in to / from an active region should be implemented in a compact manner, and the border around such active region should be reduced. Optionally, optical loss caused by waveguide fan-out or fan-in should also be reduced.

[0009] This is achieved through an optical device as described at the beginning, which includes a reflection and coupling structure connecting the secondary fan-out waveguide and the bus waveguide.

[0010] By using a reflection and coupling structure connecting the secondary fan-out waveguide and the bus waveguide, light beams can be fanned out or fanned in a compact manner because a border around the active region (to be covered), with a bending radius limited by bending loss, is not required. Specifically, light can be fanned from the primary fan-out waveguide to the secondary fan-out waveguide, and the bus waveguide can guide light to areas not covered by the secondary fan-out waveguide due to the reflection and coupling structure. This area can, for example, be close to or adjacent to the primary fan-out waveguide preceding the fan-out optical coupler. Therefore, the primary fan-out waveguide and fan-out optical coupler can be partially or completely contained within the active region to be illuminated, and no border is needed around this region. Furthermore, by using different waveguides to fan out or fan in the beam, higher uniformity and lower loss can be achieved.

[0011] Fan-out refers to the distribution of light from one waveguide (or multiple waveguides) to another waveguide (or a further number of waveguides, preferably greater than the initial number). Optionally, the waveguide can be a single-mode waveguide. Optionally, the waveguide can have a low refractive index contrast (n2-n1<<1). Light can, but does not need to, be coupled out from the bus waveguide to multiple pixels. The optical device is primarily designed to cover certain areas with bus waveguides (or more bus waveguides) from which light can be coupled out to multiple pixels. This subsequent coupling out can be achieved by this optical device or in any other way, for example by another device not part of this disclosure.

[0012] The description in the fan-out context similarly refers to fan-in in the reverse operating mode, which can be used, for example, in sensing applications such as touch recognition devices. If the optical device is used for fan-in, then the primary fan-out waveguide, secondary fan-out waveguide, and fan-out coupler are also the primary fan-in waveguide, secondary fan-in waveguide, and fan-in coupler.

[0013] A reflection and coupling structure refers to a structure (e.g., via a directional coupler) that couples light between two waveguides, wherein the light beam is reflected at least at one point such that the beam is reversed along the propagation direction of at least one waveguide. Optionally, the reflection and coupling structure will:

[0014] -(Especially in the case of fan-out:) Couple the beam from the secondary fan-out waveguide to the bus waveguide such that the beam propagates in the bus waveguide in at least the opposite direction to its propagation in the secondary fan-out waveguide before coupling, or

[0015] - (Especially in the case of fan-in:) Coupling from the bus waveguide to the secondary fan-out waveguide causes the beam to propagate in the secondary fan-out waveguide in at least the opposite direction to its propagation in the bus waveguide before coupling. "Opposite" specifically refers to the portions of the secondary fan-out waveguide and the bus waveguide, where the two waveguides extend substantially side-by-side.

[0016] Optionally, the secondary fan-out waveguide and / or the bus waveguide includes a core surrounded by a cladding material and may provide at least one facet having a refractive index contrast greater than the refractive index contrast between the core and the cladding material. Therefore, sufficient reflection can be achieved even if the incident angle of the beam on this facet is not greater than the critical reflection angle at the core-cladding material boundary. Optionally, the beam is guided in at least one direction in a first portion of (at least) one of the bus waveguide and the secondary fan-out waveguide, and the beam is guided in at least the opposite direction in a second portion of the same one.

[0017] Optionally, the primary fan-out waveguide, secondary fan-out waveguide, and bus waveguide are different from each other. Optionally, the primary fan-out waveguide is different from the secondary fan-out waveguide and / or bus waveguide. Optionally, at least a portion of the bus waveguide is parallel to a portion of the secondary fan-out waveguide. Optionally, the fan-out optical coupler includes a portion in which the primary fan-out waveguide and the secondary fan-out waveguide extend close to each other and optionally extend close to each other at the coupling portion of each waveguide. Optionally, the length of the coupling portion of the primary fan-out waveguide and the secondary fan-out waveguide is less than 500 μm, more preferably less than 100 μm, and even more preferably less than 20 μm. The primary fan-out waveguide and the secondary fan-out waveguide extend in the coupling portion with a coupling distance between them, which is optionally less than 200 μm, more preferably less than 60 μm, and even more preferably less than 20 μm. Optionally, the coupling distance is at least 1 μm.

[0018] The optical device includes optionally at least 10, further optionally at least 100, further optionally at least 1,000, and further optionally at least 10,000 secondary fan-out waveguides, wherein each is provided with: a fan-out coupler for coupling a beam between a primary fan-out waveguide and a corresponding secondary fan-out waveguide or for coupling a beam between two secondary fan-out waveguides; at least one bus waveguide associated with and distinct from each secondary fan-out waveguide; and a reflection and coupling structure connecting each secondary fan-out waveguide and the corresponding at least one bus waveguide.

[0019] Optionally, the reflection and coupling structure is an interferometric structure, used to optionally couple a beam propagating in a secondary fan-out waveguide to a bus waveguide or vice versa, such that at least a portion of the coupled beam propagates in the opposite direction after leaving the interferometric structure. An interferometric structure refers to light being coupled from one of the secondary fan-out waveguides and the bus waveguide to the other, such that it interferes with light propagating in the other and light previously reflected in the other. Propagation in the opposite direction means that when the beam reaches the interferometric structure in one of the bus waveguides and the secondary fan-out waveguides, it leaves the interferometric structure waveguide in the other at an angle greater than 90° to its initial direction. Therefore, direction reversal is achieved efficiently and compactly without the disadvantages of using curved waveguides for this purpose. The interferometric structure optionally includes: a beam splitter, which may be an optical coupler for coupling light between the secondary fan-out waveguide and the bus waveguide, and / or a beam combiner, which may be an optical coupler for coupling light between the secondary fan-out waveguide and the bus waveguide, wherein, in particular, the beam splitter and the beam combiner are formed by the same optical coupler. The interferometric structure may be a Michelson interferometric structure (i.e., the beam is split and combined by the same element). Optionally, the interferometric structure is a balanced Michelson interferometric structure and / or a folded Mach-Zehnder interferometric structure. Optionally, the interferometric structure is passive, i.e., the optical path length in the interferometric structure is fixed. Optionally, the interferometric structure includes at least four arms, wherein two arms are formed by each of the secondary fan-out waveguide and the bus waveguide. One arm of each of the secondary fan-out waveguide and the bus waveguide is the input and output arm. The other arm of each of the secondary fan-out waveguide and the bus waveguide can be arbitrarily short. Alternatively, the optical path length is set such that for a beam entering the interferometric structure at one input and output arm, most of the beam (i.e., more than 50% intensity) exits the interferometric structure at the other input and output arm.

[0020] Reflection and coupling structures can have many different layouts. For example, each arm of a reflection and coupling structure or an interferometric structure can be redirected back to a reflection and coupling structure or an interferometric structure, i.e., it can be split back into an interferometer (with or without). Thus, the complexity can increase considerably.

[0021] Optionally, at least a portion of the bus waveguide extends alongside at least a portion of the secondary fan-out waveguide, particularly a portion substantially parallel to the secondary fan-out waveguide.

[0022] Optionally, the reflection and coupling structure includes an optical coupler (labeled "bus optical coupler") for coupling a beam between a secondary fan-out waveguide and a bus waveguide, wherein optionally substantially 50% of the beam is coupled between the secondary fan-out waveguide and the bus waveguide as it passes through the optical coupler in one direction. Optionally, the bus optical coupler includes portions in which the secondary fan-out waveguide and the bus waveguide are close to each other and optionally extend close to each other at the coupling portion of each waveguide. Optionally, the length of the coupling portions of the secondary fan-out waveguide and the bus waveguide is less than 500 μm, more optionally less than 100 μm, and even more optionally less than 20 μm. The secondary fan-out waveguide and the bus waveguide extend in the coupling portions at a coupling distance between them, which is optionally less than 200 μm, more optionally less than 60 μm, and even more optionally less than 20 μm. Both the bus waveguide and the secondary fan-out waveguide extend from the bus optical coupler in at least one direction. Optionally, they each extend from the optical coupler in two directions.

[0023] Optionally, the reflection and coupling structure includes a bus reflecting surface for at least partially reflecting a beam in the bus waveguide and a secondary fan-out reflecting surface for at least partially reflecting a beam in the secondary fan-out waveguide. Therefore, light coupled between the bus waveguide and the secondary fan-out waveguide in the reflection and coupling structure can be reflected in each waveguide, allowing it to be coupled again between the waveguides in the opposite direction, thus specifically causing an interference effect. Optionally, the optical paths between the bus optical coupler and the bus reflecting surface, and between the bus optical coupler and the secondary fan-out reflecting surface, are configured such that after the beam passes through the bus optical coupler once in the forward direction and once in the reverse direction, it propagates substantially in one of the bus waveguide and the secondary fan-out waveguide, in which the beam initially (before the bus optical coupler) did not propagate. The optical path can be arbitrarily shortened between the optical coupler and the bus reflecting surface and the corresponding secondary fan-out reflecting surface, thereby shortening the bus waveguide and the secondary fan-out waveguide. The bus reflector and / or secondary fan-out reflector can directly follow the bus optical coupler, meaning that the bus waveguide and secondary fan-out waveguide do not need to be separated before reflection occurs. This enables reflection and coupling structures with lengths less than 100 μm. Multiple layers can also be included, comprising more than one reflection at different facets for light distribution and, optionally, for monitoring or analyzing light along its path. This may slightly increase the thickness of the optics, but still eliminates the need for a border around the active region. For example, in addition to the two layers formed by the secondary fan-out waveguide and the bus waveguide, at least one additional layer can be present. That is, additional reflection and coupling structures can exist to connect the bus waveguide to another bus waveguide. This further reflection and coupling structure can be formed, for example, by an interface (e.g., the interface of a substrate mentioned below), which also includes an input surface where light can be coupled (e.g., from a light source) into the primary fan-out waveguide. This interface may include a reflective coating. Light can then be guided from the additional reflection and coupling structure through another bus waveguide in substantially the same direction as in the primary fan-out waveguide. Optionally, at the end of this additional bus waveguide, which may be on the same plane as the bus reflector and / or fan-out reflector, a detector, particularly a photodiode, may be positioned to measure optical power. In this case, if the bus reflector and / or fan-out reflector are provided by a reflective coating, that coating may optionally not be provided at that end of the additional bus waveguide. Another option is reflection from continuous surfaces, thus at 90° to each other.

[0024] Optionally, the optical path length between the optical coupler and the reflecting surface in the bus waveguide of the reflection and coupling structure is the same as the optical path length between the optical coupler and the reflecting surface in the secondary fan-out waveguide of the reflection and coupling structure. Generally, if the optical device is used with a light source, the optical path length modulo the wavelength of the light source is the same. Therefore, destructive interference can be achieved in the waveguide where the beam initially propagates (i.e., in which the beam is about to reach the reflection and coupling structure), and constructive interference can be achieved in another waveguide. Thus, a beam entering the reflection and coupling structure in one waveguide will exit the reflection and coupling structure in another waveguide, specifically in the opposite direction (i.e., in the opposite direction). Of course, this can also be achieved with other structures, particularly interferometric structures.

[0025] Optionally, secondary fan-out waveguides and bus waveguides are provided in a (particularly transparent) substrate, and further optionally, they are generated by femtosecond laser direct writing. This allows for particularly compact designs. By directly writing waveguides with femtosecond lasers, waveguides can be created at any depth within the substrate and can be bent in any direction. Due to this possibility of 3D waveguide tracing, more compact designs (i.e., high-density waveguides per volume) and waveguides with low optical loss can be achieved. Optionally, the substrate extends in three dimensions, wherein the extension of the substrate in one dimension (“depth”) is at least 1 / 5, and further optionally at least 1 / 10, of the extension of the substrate in the other two dimensions (“length” and “width”). Dimensions can be 25 x 25 x 0.5 mm. 3 Optionally, a portion of the substrate surface is an active region from which light will be illuminated or should be collected. Optionally, the active region is located on a surface of the substrate that defines the substrate in the depth direction. Optionally, a primary fan-out waveguide and / or any other waveguide of the optical device is also disposed in the transparent substrate. Optionally, the transparent substrate comprises aluminoborosilicate glass, such as Corning® Eagle XG®. Optionally, the bus waveguide is substantially parallel to the active region. Optionally, the bus waveguide is substantially parallel to the secondary fan-out waveguide and is spaced apart from the secondary fan-out waveguide in both the width and depth dimensions for most of its length, except near the reflection and coupling structures. At the reflection and coupling structures, the bus waveguide and the secondary fan-out waveguide can be at the same depth level; however, they can remain spaced apart in the width dimension. For coupling between the secondary fan-out waveguide and the bus waveguide, they can be close together in the width dimension to achieve coupling.

[0026] Femtosecond laser direct writing (FDLW, often also referred to as femtosecond laser direct etching) may optionally include one or more of the following steps:

[0027] - Provide a substrate containing a transparent dielectric material and / or containing glass, ceramic, polymer and / or crystalline materials;

[0028] - Use multi-photon (i.e., more than 2 photons) absorption, where the photon energy is below the band gap of the substrate material and / or where the pulse is a low- to mid-frequency femtosecond pulse, for example, between 20 kHz and 10 MHz, optionally between 80 kHz and 5 MHz, particularly between 100 kHz and 2 MHz, even more particularly between 500 kHz and 1.5 MHz, and / or where the pulse has a medium pulse width, for example, between 40 fs and 2 ps, optionally between 100 fs and 1 ps, particularly between 200 fs and 400 fs.

[0029] Another laser writing technology is 2PP (2-photon polymerization) laser writing, which can involve two-photon lithography or multi-photon lithography. Compared to femtosecond laser direct writing, it may include one or more of the following steps or properties:

[0030] - Use typical high-frequency (e.g., 80MHz) and low-pulse-width femtosecond pulses <100fs;

[0031] -Two-photon absorption is a third-order process for third-order magnetic susceptibility and a second-order process for light intensity;

[0032] - Provides a special photoresist (photosensitive material) that is highly transparent to photons with wavelength λ, but highly absorbent to photons with wavelength λ / 2.

[0033] Optionally, the bus reflective surface and / or the secondary fan-out reflective surface are provided by a (reflective) coating on the facets of the transparent substrate and / or the facets of the transparent substrate. The coating may include, for example, silver, aluminum, gold, and / or a dielectric coating.

[0034] Optionally, the optical device includes at least one pixel waveguide (or a pixel-specific waveguide) that receives or guides a light beam from at least one bus waveguide, wherein optionally, the pixel waveguide bends away from the bus waveguide. Optionally, more than one pixel waveguide (as described above) is provided associated with a bus waveguide, and more preferably, at least 10 pixel waveguides are provided associated with a bus waveguide. Optionally, the at least one pixel waveguide is formed in the substrate. Optionally, the at least one pixel waveguide bends from the bus waveguide toward the surface of the substrate, particularly toward the active region. A pixel optical coupler for coupling light between the bus waveguide and the pixel waveguide can be provided. Preferably, each pixel waveguide is associated with a pixel or color subpixel in the active region (or a pixel or color subpixel covering a liquid crystal layer in the active region, having an optional layer or film between the active region and the liquid crystal layer). Specifically, a one-to-one relationship may exist between each pixel waveguide and a pixel in the active region.

[0035] Light already emerging from the secondary fan-out waveguide can be coupled. Optionally, at least one additional pixel waveguide is provided that receives the beam from or guides the beam to at least one secondary fan-out waveguide, wherein, further optionally, the additional pixel waveguide is bent away from the secondary fan-out waveguide. Therefore, the average optical path length in the waveguide can be reduced, thereby reducing transmission loss.

[0036] Optionally, the optical device includes a phase adjustment element for adjusting the relative optical path lengths of the secondary fan-out waveguide and the bus waveguide in the reflection and coupling structure, wherein the phase adjustment element may also optionally include a phase shifter and / or a piezoelectric mirror. Therefore, the beam intensity in the bus waveguide, and subsequently the intensity of a portion of the active region, is adjustable. This is particularly useful for achieving localized dimming in display or sensing applications, such as when using optical devices in optical detection and ranging (LIDAR) systems or optical touch recognition.

[0037] Optionally, the optical device includes at least one additional bus waveguide associated with and different from each secondary fan-out waveguide, wherein reflection and coupling structures further connect the secondary fan-out waveguides and the additional bus waveguides. Therefore, each secondary fan-out waveguide can be used to couple a beam to more than one bus waveguide. That is, a greater number of bus waveguides can be achieved not only by providing more secondary fan-out waveguides as described above, but also by connecting more bus waveguides to each secondary fan-out waveguide. Thus, a compact layout is achieved.

[0038] Alternatively, these two measures can be combined. The reflection and coupling structure may include a tripper for coupling light between the secondary fan-out waveguide and the bus waveguide and another bus waveguide. Thus, a particularly compact design is achieved. Furthermore, the fan-out optical coupler can be a tripper, allowing the beam to be coupled from the primary fan-out waveguide to more than one secondary fan-out waveguide at a single point (or more precisely, one interaction length).

[0039] A splitter is specifically a power distribution device comprising one input waveguide and three output waveguides. Its function is to distribute optical power (light) from one or more input waveguides (input ports) to three output waveguides (output ports). This functionality can also be reversed. Its physical characteristics and operating principle are similar to a conventional directional coupler. A splitter allows optical power to be propagated to other waveguides within a smaller physical space, thus reducing the number of steps and waveguides. Optionally, the splitter distributes power substantially equally to each output port, i.e., substantially 33% at each output port. Optionally, cascading splitters can be used, where a primary fan-out waveguide is coupled to more than one secondary fan-out waveguide via a splitter, and these secondary fan-out waveguides are each connected to more than one additional secondary fan-out waveguide via a splitter. Experiments show that splitters with a splitting ratio variation of less than 5% can be achieved, where the interaction distance between wavelengths in the splitter is 5 μm and the interaction length is 140 μm. Typically, the interaction distance can range from the waveguide core size (e.g., at least 1 μm) to 30 μm and / or the interaction length is less than 300 μm. A cascade of four triode structures has been fabricated, resulting in 1x81 outputs. Therefore, an active region with an output pixel pitch of 50 μm and total output width and length dimensions of 4.05 mm and 21.31 mm, respectively, can be covered.

[0040] Optionally, the optical device includes:

[0041] Additional primary fan-out waveguide;

[0042] At least one additional secondary fan-out waveguide;

[0043] An additional fan-out optical coupler is used to couple the light beam between an additional primary fan-out waveguide and an additional secondary fan-out waveguide. Thus, light can be coupled in from different light sources or to different sensing devices. The optional features mentioned above in the context of the primary fan-out waveguide, (another) secondary fan-out waveguide, and fan-out coupler can also be used for the additional primary fan-out waveguide, at least one additional secondary fan-out waveguide, and the additional fan-out coupler. Therefore, multi-wavelength / color fan-out or fan-in can be achieved by stacking the secondary fan-out waveguides and additional secondary fan-out waveguides on top of each other and then interleaving them at the points where they must reach their respective bus waveguides (assuming the bus waveguides are arranged at the same depth below the active region). In this way, each reflection and coupling structure for each color remains independent of each other, thus operating at a single wavelength and achieving low optical loss.

[0044] Optionally, a primary fan-out waveguide is coupled to a light source for receiving a beam of light from the source. The light source can be a laser, particularly a single-mode laser diode. Optionally, the light source is configured to emit light with a center wavelength between 300 nm and 700 nm, and further optionally up to 2000 nm (particularly for sensing). More than one light source can be provided, with each source coupled to a different (additional) primary fan-out waveguide. Optionally, the light source (or a corresponding one of the light sources) is configured to emit light with a center wavelength of 460 nm, 530 nm, or 630 nm. More than one light source can emit light within the same range, particularly when the light source illuminates different areas of the active region. Optionally, if more than one light source illuminates the same area of ​​the active region (particularly sub-pixels of the same pixel but different colors), they emit light with different center wavelengths.

[0045] Furthermore, this disclosure relates to a backlight unit for a display, which includes optical devices according to any embodiment described herein. Thus, a compact, particularly flat, display is realized. The backlight unit can be used in LCD displays. Attached Figure Description

[0046] As examples, some selected embodiments shown in the accompanying drawings further explain this disclosure. However, these embodiments should not be considered as limiting the scope of this disclosure.

[0047] Figure 1 A top view of a prior art optical device is shown schematically.

[0048] Figure 2 A top view of another existing optical device is shown schematically.

[0049] Figure 3 A top view schematically illustrating an embodiment of the optical device according to this disclosure is shown.

[0050] Figure 4 It schematically shows the relationship with Figure 3 A side view of an embodiment of the same optical device.

[0051] Figure 5 A top view schematically illustrates another embodiment of the optical device according to this disclosure.

[0052] Figure 6 It schematically shows the relationship with Figure 5 A side view of an embodiment of the same optical device.

[0053] Figure 7 A top view schematically illustrates another embodiment of the optical device according to this disclosure.

[0054] Figure 8It schematically shows the relationship with Figure 7 A side view of an embodiment of the same optical device.

[0055] Figure 9 An estimated model of optical loss caused by the number of pixel waveguides is schematically shown.

[0056] Figure 10 The considerations regarding reflection and coupling structures are illustrated schematically.

[0057] Figure 11 A side view of another embodiment of the optical device is shown schematically. Detailed Implementation

[0058] Figure 1 A top view of a prior art optical device 101 for fan-out light is shown. The optical device 101 has a light source 102 that couples light to a fan-out waveguide 103. From there, the light is then coupled out in a cascaded manner to another fan-out waveguide 103. For coupling, the fan-out waveguides 103 must first propagate parallel to allow light to couple from the first fan-out waveguide 103 to the second fan-out waveguide 103. The second fan-out waveguide 103 then begins to bend away from the first fan-out waveguide to achieve the desired distance, e.g., pixel pitch in a display application. After fan-out to the full width of the optical device 101 is achieved, illumination of an active region 104 can begin. However, optical losses limit the minimum bending radius of the fan-out waveguides 103. Using a bending radius that still allows for low propagation loss, e.g., 10 mm, with a target distance of 100 μm (equivalent to the expected pixel pitch), the required propagation distance in the z-direction for an optical coupler is approximately 2 mm. Therefore, fan-out is impossible if there is no fairly large border 105 on at least one side of the active region.

[0059] Figure 2 A top view of an alternative prior art optical device 101 for fan-out light is shown. The light source 102 is oriented at 90° relative to the extension direction of the fan-out waveguide 103 over an active region 104. However, this still requires a bend radius of approximately 105 around the active region 104 on both sides of the display. This is particularly undesirable for mobile display applications.

[0060] Figure 3 An embodiment of the optical device 1 according to this disclosure is schematically shown in a top view (yz plane), and Figure 4The same embodiment is shown in a side view (xz plane). The optical device 1 includes a primary fan-out waveguide 3, two secondary fan-out waveguides 4, and a fan-out coupler 5 for coupling a light beam between the primary fan-out waveguide 3 and the secondary fan-out waveguides 4. In this embodiment, the fan-out coupler 5 is a tripper, allowing light to be coupled to both secondary fan-out waveguides 4 through a single coupler. However, the optical device 1 may also include only one secondary fan-out waveguide 4, and the fan-out coupler 5 need not be a tripper. Figure 4 This is a side view in the plane extending from the primary fan-out waveguide 3. However, it should be understood that the side view of the secondary fan-out waveguide 4 looks similar, except that its extension to the left in the z-direction will only reach the fan-out optical coupler 5, which can be as shown... Figure 3 As shown.

[0061] Furthermore, the optical device 1 includes a bus waveguide 6 associated with each secondary fan-out waveguide 4, and also provides a bus waveguide 6 associated with the primary fan-out waveguide 3. The optical device 1 includes a reflection and coupling structure 7 connecting each secondary fan-out waveguide 4 and the corresponding bus waveguide 6. A similar reflection and coupling structure also connects the primary fan-out waveguide 3 and the corresponding bus waveguide 6. As can be seen from the figure, a large portion of the bus waveguide 6 extends substantially parallel to a portion of the secondary fan-out waveguide 4, which accounts for more than 50% of the length of the secondary fan-out waveguide 4.

[0062] Each reflection and coupling structure 7 is an interferometric structure 8 for coupling a beam propagating in the secondary fan-out waveguide 4 to a corresponding associated bus waveguide 6 (or, particularly if the optical device 1 is used for sensing applications, coupling a beam propagating in the bus waveguide 6 to a corresponding associated secondary fan-out waveguide 4), such that at least a portion of the coupled beam propagates in the opposite direction after exiting the interferometric structure 8. The arrows near waveguides 4, 6 are idealized illustrations of the direction of beam propagation in the respective waveguides.

[0063] The reflection and coupling structure 7 includes an optical coupler 9 (labeled "bus optical coupler") for coupling a light beam between the secondary fan-out waveguide 4 and the bus waveguide 6 as it passes through the bus optical coupler 9 in one direction, wherein essentially 50% of the light beam is coupled between the secondary fan-out waveguide 4 and the bus waveguide 6 as it passes through the bus optical coupler 9 in one direction. The length of the bus optical coupler 9, which brings the secondary fan-out waveguide 4 and the bus waveguide 6 close to each other, can be less than 1 mm. Furthermore, the reflection and coupling structure 7 includes a bus reflecting surface 10 for at least partially reflecting the light beam in the bus waveguide 6 and a secondary fan-out reflecting surface 11 for at least partially reflecting the light beam in the secondary fan-out waveguide 4. The optical path length between the bus optical coupler 9 and the bus reflecting surface 10 is the same as the optical path length between the bus optical coupler 9 and the secondary fan-out reflecting surface 11. Thus, the reflection and coupling structure 7 forms a balanced Michelson interferometer structure and / or a folded Mach-Zehnder interferometer structure, and essentially all the light entering the reflection and coupling structure 7 in the secondary fan-out waveguide 4 leaves the reflection and coupling structure 7 in the opposite direction in the bus waveguide 6 (due to the constructive interference in the bus waveguide 6 when passing through the bus optical coupler 9 for the second time and the destructive interference in the secondary fan-out waveguide 4 when passing through the bus optical coupler 9 for the second time).

[0064] Primary fan-out waveguide 3, secondary fan-out waveguide 4, and bus waveguide 6 are disposed in the transparent substrate 12. They are generated by femtosecond laser direct writing, a method for realizing 3D waveguide trajectories. Figure 3 and Figure 4 As can be seen, the bus waveguide 6 and the secondary fan-out waveguide 4, or the primary fan-out waveguide, extend substantially parallel to each other along the z-direction, and most of their lengths are spaced apart from each other in the x and y directions. Therefore, there is no interference problem at their apparent intersection points in the top view. Near the reflection and coupling structure 7, they are at the same level in the x-direction, and at the bus optical coupler 9, they are also close to each other in the y-direction. The bus reflective surface 10 and the secondary fan-out reflective surface 11 are provided by the facets 13 of the transparent substrate 12.

[0065] The optical device 1 includes a plurality of pixel waveguides 14, each pixel waveguide 14 receiving a light beam from one of the bus waveguides 6 (or, particularly when the optical device 1 is used for sensing applications, directing the light beam to one of the bus waveguides 6). The pixel waveguides 14 are bent away from the corresponding bus waveguide 6 and towards the top surface 15 of the substrate 12, the top surface 15 including an active area to be illuminated by the optical device 1. If the optical device 1 is used as a backlight unit, each pixel waveguide 14 may illuminate, for example, a pixel or a color subpixel of a liquid crystal display (LCD). The pixel waveguides 14 may receive light from the corresponding bus waveguide 6 via an optical coupler, for example by bringing the pixel waveguide 14 close to the corresponding bus waveguide 6.

[0066] The optical device 1 includes a light source 2, from which a light beam is coupled into a primary fan-out waveguide 3, and then distributed to a pixel waveguide 14 via a secondary fan-out waveguide 4 and a bus waveguide 6. By using a reflection and coupling structure 7 to couple light between the secondary fan-out waveguide 4 and the bus waveguide 6, the entire extension of the substrate 12 in the y and z directions can be used for fan-out, the active region can substantially cover the entire top surface 15, and there is no need to set a border around the active region.

[0067] Figure 5 Another embodiment of the optical device 1 is schematically shown in a top view (yz plane), and Figure 6 The same embodiment is shown in a side view (xz plane). This embodiment is similar to... Figure 3 and Figure 4 The illustrated embodiment is the same; however, some pixel waveguides 14 are placed differently. Specifically, pixel waveguides 14 connected to the secondary fan-out waveguide 4 and the primary fan-out waveguide 3 are provided on both sides of the bus optical coupler 9. Therefore, even the region of the coupler can be part of the active region.

[0068] Figure 7 An embodiment of the optical device 1 is schematically shown in a top view (yz plane), and Figure 8 The same embodiment is shown in a side view (xz plane). The optical device 1 includes three light sources 2, each of which couples light into a different primary fan-out waveguide 3. Each light source 2 can be configured to emit different wavelengths, such as red, blue, and green light. From each primary fan-out waveguide 3 to the corresponding pixel waveguide 14 (… Figure 7 The beam distribution (not shown in the image) is aligned with the beam distribution in the image. Figure 3 and Figure 4 The same manner described in the context is employed. However, the primary fan-out waveguide 3 and secondary fan-out waveguide 4 of each light source 2 are located at different depth levels (x-axis) in the substrate 12 for most of their length (see [reference]). Figure 8 This allows them to be staggered. Specifically, the primary fan-out waveguide 3 and the secondary fan-out waveguide 4 are positioned at the same level just before the reflection and coupling structure 7. Therefore, the fan-out of each light source 2, especially the fan-out of each color light source 2, is independent of the other light sources 2, especially the other colors of light sources 2. Thus, the reflection and coupling structures 7 also remain independent for different light sources 2 and can operate at individual wavelengths (different wavelengths depending on which light source they are connected to). This achieves low loss while different colors are distributed across the active region.

[0069] Figure 9An estimated model of optical loss caused by the number of pixel waveguides is schematically illustrated. Waveguide loss in the coupling becomes significant when using a proposed architecture where many of these pixel waveguides are connected to a single bus waveguide. Small losses may occur due to the waveguides being very close together during evanescent coupling, and exponential power losses may occur if many of them occur sequentially. It will be shown below that these losses are low enough for this disclosure to be effective.

[0070] A typical pixel row consists of a power-carrying bus waveguide (i.e., a bus line) and multiple couplers (i.e., pixels) that remove / redirect a portion of the power carried by the bus line to the output facets of the substrate, particularly the glass. A simplified model for the following calculations is as follows: Figure 9 As shown.

[0071] In this arrangement, power P0 is coupled to the bus line and propagates from left to right. The bus line (from P0 to P...) bus The waveguide is coupled to a reference coupler and N couplers in series (i.e., pixels, in this case, straight diagonal parallel lines). After each coupler, a portion of the power carried by the bus line is removed. Furthermore, the reference waveguide coupled to the bus line terminates on the right-hand output facet (P). ref The reference waveguide is steered toward the output facet with a 50mm bend radius, high enough to negligible bend losses from this region and allowing for a faithful estimation of coupling C. Assuming no other power losses, the power (P) at the output of the bus line... bus ) is a function of the number of couplers (N) and their coupling coefficients C. Therefore, by understanding N and C, and by monitoring P... ref P can be calculated bus And estimate the losses caused by the evanescent coupling mechanism.

[0072] By fabricating multiple bus lines in the above arrangement and varying the number of couplers N, the presence of coupling loss can be identified and measured, thereby identifying and measuring optical transmission "t". A reference waveguide is used to characterize the coupling coefficient of the coupler and to verify the repeatability and stability of the fabrication process.

[0073] In this study, bus lines with N=1, 20, 40, and 80 couplers were fabricated (N=1 is a device with only a reference waveguide to evaluate the coupling coefficient, while the other devices consist of one reference waveguide and N-1 pixel waveguides). To obtain sufficient statistical data, 12 devices were fabricated for each N (4 devices per N achieve minimum statistical effectiveness). The coupler-waveguide was fabricated with an interaction distance of 7.75 μm, an interaction length of 0 μm, and a bending radius of 10 mm. The bending radii associated with the pixel waveguides and couplers should be in the range of 10 mm to 50 mm to maintain a low optical transmission loss of less than 0.2 dB.

[0074] Specifically, for a device with N=1, the coupling coefficient is measured as C=0.0132. For N=20, t avg =0.9800±0.0278, for N=40, t avg =0.9969±0.0113, for N=80, t avg =0.9968±0.0015. The results are consistent with each other and have higher statistical certainty for higher N values. All results are within t=1, so there does not appear to be significant optical power loss due to evanescent field coupling between waveguides.

[0075] Figure 10 The considerations regarding the reflection and coupling structure are schematically illustrated; however, they should not be considered as limiting the general concepts of this disclosure. An integrated directional coupler with a metallic coating on its output facet has been fabricated and characterized, corresponding to… Figure 3 and Figure 4 However, for ease of manufacturing, all waveguides are located in the same x-plane.

[0076] In particular, the interaction region of the coupler is located 1 mm from the output surface, making it insensitive to the amount of polishing material (300 μm to 600 μm) while demonstrating its compactness. The distance between the interaction region of the coupler and the output (coated and therefore reflected) surface can be less than 1 mm. With polishing as a post-processing step, the output surface thickness is less than 600 μm, thus avoiding this post-processing step.

[0077] The difference in length between the two arms leads to an imbalance in the optical power of the device, i.e., a reduction in power transfer from the forward waveguide to the reverse waveguide. For example, to transfer 90% of the input power to the reverse waveguide, the reflective facets can optionally be perpendicular with an accuracy of 0.1 degrees. Mechanical polishing processes can easily produce similar angles on the output facets. To minimize this effect, the coupler arms should be placed as close as possible. The distance between the coupler arms is typically set in the range of 15 μm to 100 μm. Simultaneously, the arms should not interact to maintain the behavior of the interferometer. To meet these requirements, the distance between the two arms of the coupler is set to 15 μm. It is worth noting that placing the arms close together reduces the overall length of the device. Assuming a perfectly perpendicular facet, the distance between the arms could potentially increase to, for example, 100 μm.

[0078] The optical circuit uses a 25 x 25 x 0.5 mm diameter. 3Aluminoborosilicate glass (Eagle XG, Corning) was fabricated using a technique called "femtosecond laser direct writing." This process utilizes the nonlinear interaction between a focused ultrashort light pulse and a dielectric substrate to create permanent modifications within the material. By adjusting the irradiation conditions of the sample, this method can fabricate single-mode waveguides with a core diameter of approximately 3 μm and a refractive index contrast of approximately 5 × 10⁻³. Measurements were performed at a wavelength of 638 nm, at which time these waveguides exhibited a mode field diameter of 4.2 μm, a propagation loss of 0.1 dB / cm, a bending loss of 0.45 dB / cm, and a bending radius of 10 mm.

[0079] The characterization process consists of two parts: First, the operation of the uncoated directional coupler is evaluated. In this stage, light is coupled through the fiber in one mode at the input facet, and the power distribution between the two output modes is measured using a power meter. The splitting ratio is then obtained.

[0080] Subsequently, reflection on the output facet was achieved through metallization: a gold plating layer with a thickness of approximately 50 nm was sputtered onto the side of the sample. Then, a microscope objective (NA = 0.20) was used to couple the light in one input mode and collect the optical power propagating back and forth through the device. A balanced external beam splitter was placed in front of the objective to isolate the output power from the input beam. Fresnel reflection on the input facet, overlapping with one of the two output modes, is measured and taken into account when evaluating the device's behavior.

[0081] In our tests, the relative power transferred from input mode to reflective coupling mode was 92.64%, with a standard deviation of 0.91% across 10 identical devices. This operating principle was also shown to be independent of arm spacing and length. Imbalance in the directional coupler (split ratio of 50.24%, standard deviation of 0.96%) hindered full power transfer, and tilting of the output facets more severely impaired it. The latter, randomly generated during polishing, results in different path lengths between the two arms, leading to imperfect device performance, which can be easily avoided by using more precise (currently available) polishing / cutting techniques, such as laser cutting.

[0082] Figure 11 A side view of another embodiment of the optical device 1 according to this disclosure is shown. This embodiment includes a multi-layer layout. The optical device 1 includes a light source 2 extending to the bus waveguide 6 and a pixel waveguide 14 leading to the top surface 15. Figure 11 (not shown in the image) between and in Figure 3 and Figure 4The manner described in the context of the illustrated embodiment works in essentially the same way (except that the x-dimensional shown is reversed). However, at the end of at least one bus waveguide 6, another reflection and coupling structure 7a is provided, specifically another interferometric structure, with another bus optical coupler 9a and reflection at another facet 13a. This other reflection and coupling structure 7a couples light between the bus waveguide 6 and another bus waveguide or detection waveguide 16. For simplicity, Figure 11 A bus waveguide 6 connected to the primary fan-out waveguide 3 is shown. However, this could also (or alternatively) provide at least one bus waveguide 6 connected to a corresponding secondary fan-out waveguide 4. The direction of light propagating in the respective waveguides is schematically shown by arrows. The intersection of the detection waveguide 16 with a corresponding one of the primary fan-out waveguide 3 or the secondary fan-out waveguide 4 is avoided by bypassing the primary fan-out waveguide 3 or the corresponding secondary fan-out waveguide 4 in the y-dimensional around point 17. The detection waveguide 16 leads to a corresponding detector 18, in particular a photodiode, which allows analysis of the light arriving there. This embodiment is particularly useful for touch sensing applications due to the proximity of the bus waveguide 6 to the top surface 15.

Claims

1. An optical device (1), comprising: Primary fan-out waveguide (3); At least one secondary fan-out waveguide (4); A fan-out optical coupler (5) is used to couple a light beam between the primary fan-out waveguide (3) and the secondary fan-out waveguide (4); and At least one bus waveguide (6) is associated with and different from the at least one secondary fan-out waveguide (4). A reflection and coupling structure (7) connects the secondary fan-out waveguide (4) and the bus waveguide (6). The reflection and coupling structure (7) therein is an interference structure (8) for coupling a beam propagating in the secondary fan-out waveguide (4) to the bus waveguide (6) or for coupling a beam propagating in the bus waveguide (6) to the secondary fan-out waveguide (4), such that at least a portion of the coupled beam propagates in the opposite direction after leaving the interference structure (8); The characteristic feature is that the reflection and coupling structure (7) includes a bus reflecting surface (10) for at least partially reflecting the light beam in the bus waveguide (6) and a secondary fan-out reflecting surface (11) for at least partially reflecting the light beam in the secondary fan-out waveguide (4).

2. The optical device (1) according to claim 1, characterized in that, At least a portion of the bus waveguide (6) extends side-by-side with at least a portion of the secondary fan-out waveguide (4).

3. The optical device (1) according to claim 2, characterized in that, At least a portion of the bus waveguide (6) extends substantially parallel to a portion of the secondary fan-out waveguide (4).

4. The optical device (1) according to any one of the preceding claims, characterized in that, The reflection and coupling structure (7) includes an optical coupler (9) for coupling a beam between the secondary fan-out waveguide (4) and the bus waveguide (6).

5. The optical device (1) according to claim 4, characterized in that, 50% of the beam is coupled between the secondary fan-out waveguide (4) and the bus waveguide (6) when passing through the optical coupler (9) in one direction.

6. The optical device (1) according to claim 4, characterized in that, The optical path length between the optical coupler (9) of the reflection and coupling structure (7) and the bus reflector (10) is the same as the optical path length between the optical coupler (9) of the reflection and coupling structure (7) and the secondary fan-out reflector (11).

7. The optical device (1) according to any one of claims 1-3, characterized in that, The secondary fan-out waveguide (4) and the bus waveguide (6) are disposed in the transparent substrate (12).

8. The optical device (1) according to claim 7, characterized in that, The bus reflective surface (10) and / or the secondary fan-out reflective surface (11) are provided by the facet (13) of the transparent substrate (12) and / or the coating of the facet (13) of the transparent substrate (12).

9. The optical device (1) according to any one of claims 1-3, characterized in that... At least one pixel waveguide (14) receives or directs a beam of light from or to the at least one bus waveguide (6), and the pixel waveguide (14) bends away from the bus waveguide (6).

10. The optical device (1) according to any one of claims 1-3, characterized in that... A phase adjustment element for adjusting the relative optical path lengths of the secondary fan-out waveguide (4) and the bus waveguide (6) in the reflection and coupling structure (7).

11. The optical device (1) according to any one of claims 1-3, characterized in that, At least one additional bus waveguide is associated with and different from each of the secondary fan-out waveguides (4), wherein the reflection and coupling structure (7) also connects the secondary fan-out waveguides (4) and the additional bus waveguides.

12. The optical device (1) according to claim 11, characterized in that, The reflection and coupling structure (7) includes a splitter for coupling a beam between the secondary fan-out waveguide (4), the bus waveguide (6) and the additional bus waveguide.

13. The optical device (1) according to any one of claims 1-3, characterized in that... Additional primary fan-out waveguide (3); At least one additional secondary fan-out waveguide (4); and An additional fan-out optical coupler (5) is used to couple a beam between the additional primary fan-out waveguide (3) and the additional secondary fan-out waveguide (4).

14. The optical device (1) according to any one of claims 1-3, characterized in that, The primary fan-out waveguide (3) is coupled to the light source (2) to receive the light beam from the light source (2).

15. The optical device (1) according to claim 7, characterized in that, The secondary fan-out waveguide (4) and the bus waveguide (6) are generated by femtosecond laser direct writing.

16. The optical device (1) according to claim 10, characterized in that, The phase adjustment element includes a phase shifter and / or a piezoelectric mirror.

17. A backlight unit for a display, characterized in that... The optical device (1) according to any one of the preceding claims.

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