WO2015116086A1

WO2015116086A1 - Optical modulation employing fluid movement

Info

Publication number: WO2015116086A1
Application number: PCT/US2014/013769
Authority: WO
Inventors: Gary Gibson; David A. Fattal
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2014-01-30
Filing date: 2014-01-30
Publication date: 2015-08-06

Abstract

One example includes an optical modulation system. The system includes a waveguide system comprising a waveguide to propagate an optical signal therethrough. The waveguide system further includes a grating separated from the waveguide via a cavity. The system further includes an optical coupling controller to selectively move a fluid with respect to the cavity in response to a control signal. The fluid can be moved with respect to the cavity from a first state to a second state to couple the optical signal to the grating to cause a portion of the optical signal to be diffractively redirected via the grating.

Description

OPTICAL MODULATION EMPLOYING FLUID MOVEMENT

BACKGROUND

[0001] Electro-optic modulators, such as light modulators, can be employed in a variety of applications ranging from optical communications to electronic displays. For example, light modulators may be employed to modulate light emitted by a backlight in many modern electronic displays. The light modulators may modulate the emitted light in discrete spatially separated regions of the electronic display representing pixels. For example, liquid crystal cells may be employed to modulate light from a backlight to produce pixels of an electronic display. Light emitted by the backlight is directed through and modulated by the liquid crystal cell to vary an intensity of the light emitted by the pixel, for example. Light modulators used in optical communications may employ any of a variety of means including, but not limited to, amplitude modulation, phase modulation and polarization modulation to encode information for transmission on an optical beam within an optical transmission line (e.g., a fiber optic cable).

[0002] Light modulators may be used to vary or modulate one or more of amplitude or intensity, phase and polarization of a light beam, for example. Light modulators that modulate light using amplitude modulation (e.g., optical amplitude modulators) are sometimes referred to as light valves. For example, amplitude modulation in a light valve may be accomplished through a change in transmission (e.g., a transmissive light valve) or a change in reflection (e.g., a reflective light valve). The change in transmission may result from a change in an absorption characteristic of the light valve, for example. A liquid crystal light valve can, for example, provide amplitude modulation through a change in a transmission characteristic accomplished using a polarization shift of light passing through the liquid crystal light valve. Reflection light valves may employ a change in direction of a light beam provided by a micromechanical mirror, for example, to affect amplitude modulation of the light beam. In addition, amplitude modulation may be

accomplished using phase changes in the optical beam such as in an interferometric light valve, for example. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] FIG. 1 illustrates an example of an optical modulation system.

[0004] FIG. 2 illustrates an example of a diagram of optical modulation

[0005] FIG. 3 illustrates an example of a waveguide system.

[0006] FIG. 4 illustrates another example of a waveguide system.

[0007] FIG. 5 illustrates an example of a display system.

[0008] FIG. 6 illustrates an example of a method for providing optical modulation in a waveguide system.

DETAI LED DESCRI PTION

[0009] FIG. 1 illustrates an example of an optical modulation system 10. The optical modulation system 10 can be implemented in a variety of optical applications, such as a display system. For example, the optical modulation system 10 can be implemented in a modulated backlight for an electronic display, for example. In another example, the optical modulation system 10 may provide a modulated light field (e.g., an array of modulated beams or beamlets) for a display such as, but not limited to, an autostereoscopic three-dimensional (3-D) display.

[0010] The optical modulation system 1 0 includes a waveguide system 12 that includes a waveguide 14, a grating 1 6, and a cavity 18 disposed between the waveguide 14 and the grating 16. The waveguide 14 is configured to propagate an optical signal OPT|_N therethrough. The optical signal OPT|_N can be provided from a variety of light source types, such as a light-emitting diode (LED) , fluorescent light source, or a laser. The waveguide 14 can be formed from a material having a predetermined refractive index (e.g., a high refractive index), such as to maintain propagation of the optical signal OPT|_N therein via internal reflection. The grating 16 can be any of a variety of optical gratings for diffractive redirection of the light, such as in a transverse direction with respect to the propagation of the optical signal

OPTIN. As an example, the grating 16 can be a diffraction grating that includes features, such as grooves, ridges, holes, and/or bumps that are arranged on a surface of the grating 1 6, such as in a pattern, sequence, or array. For example, the orientation and/or periodicity of the features of the grating 16 can be arranged in a predetermined manner to diffractively redirect a portion of the optical signal OPT|_N having a predetermined frequency band in a selected direction, such as to create a light field for a three-dimensional projexel application.

[001 1 ] The cavity 18 is disposed between a surface of the waveguide 14 and the grating 16, such as on a surface opposite the features of the grating. Thus, the cavity 18 can confine a volume therein between the waveguide 14 and the grating 16. In a first state, the cavity 18 can be substantially empty, such that the cavity can be filled with atmospheric gasses (i.e., "air"), a vacuum, or a low refractive index fluid. Therefore, in the first state, the cavity 18 can decouple the optical signal OPT|_N in the waveguide 14 from being provided to the grating 16 based on the surface of the waveguide 14 at the cavity maintaining an internal reflection of the optical signal OPTIN at the junction of the higher refractive index waveguide 14 relative to the atmospheric gasses or vacuum in the cavity 1 8.

[0012] In a second state, the cavity 1 8 can be filled with a fluid having a predefined refractive index relative to the refractive index of the waveguide 14 and the grating 16. As an example, the fluid can have a refractive index that is approximately equal to the refractive index of the waveguide 14 and the grating 16. As used herein, the term "approximately equal" means that while it is intended that the refractive indices be the same, due to processing variations, material differences, or other circumstances that some variation might exist (e.g., +/- 5% variation). As described herein, the term "fluid" describes one or more materials in a liquid state or gaseous state that is actively provided into the cavity 18. The fluid can be any of a variety of fluids having a refractive index that is selected to be approximately equal to the waveguide 14 and the grating 16. As an example, the waveguide 14 and the grating 1 6 can have a refractive index that is approximately equal. Thus, in the second state, the fluid that is provided into the cavity 18 can provide refractive coupling of the optical signal OPT|_N through the cavity 1 8 between the waveguide 14 and the grating 16 based on the fluid having an approximately equal refractive index with respect to the waveguide 14 and the grating 16. Therefore, the fluid can overcome total internal reflection of the waveguide 14 such that a portion of the optical signal OPT|_N is diffractively redirected via the grating 16. In the example of FIG. 1 , the portion of the optical signal OPT|_N that is diffractively redirected via the grating 1 6 is provided as an optical signal ΟΡΤουτ-

[0013] The optical modulation system 1 0 also includes an optical coupling controller 20 that is configured to move the fluid with respect to the cavity 1 8 to respectively couple and decouple the optical signal OPT|_N to and from the grating 1 6 to provide modulation of the optical signal OPT|_N as the optical signal ΟΡΤουτ- The fluid can be moved into or out of the cavity and/or it can be moved from one place to another within the cavity. For instance, the optical coupling controller 20 can include or be connected to a source of the fluid that is in fluid communication with the cavity 18, such that the controller can control the flow of such fluid into and out of the cavity. As another example, the optical coupling controller 20 can be configured to provide fluid transfer between high and low refractive index fluids with respect to the cavity 18, such that the optical coupling controller 20 can move (e.g., pump) a low refractive index fluid out of the cavity 18 and substantially concurrently or

sequentially move a high refractive index fluid into the cavity 18 in a switch from the first state to the second state. As yet another example, the optical coupling controller 20 can move the fluid from one location in the cavity 18 to another location in the cavity 18 to affect the refractive coupling of the optical signal OPT|_N with respect to the grating 1 6. In the example of FIG. 1 , the optical coupling controller 20 can provide the fluid FLD via at least one of electrowetting and micro-pumping (e.g., via a thermal micro-pump that can be driven by a resistive heating element). For example, the optical coupling controller 20 can be configured to control a voltage bias on at least one electrode in the example of electrowetting to affect movement of a polar fluid (e.g., water) relative to a non-polar fluid (e.g., a type of oil), or can be configured to control a current through a resistive heating element to drive a thermal micro-pump to affect movement of one of a variety of different types of fluids having respective known refractive indices. Thus, the movement of the fluid FLD can result from a controllable pressure and/or thermal gradient being provided to move the fluid into and out of the cavity 18. [0014] The optical coupling controller 20 receives a control signal CTRL that can initiate the movement of the fluid FLD into and out of the cavity 18. For example, the control signal CTRL can be provided from an image controller (not shown) that is configured to provide control signals to the optical coupling controller 20 of a plurality of optical modulation systems, including the optical modulation system 1 0, based on image data to form an image from respective optical signals OPTOUT- As a first example, the control signal CTRL can be a binary signal having a first state that indicates movement of the fluid FLD into the cavity 18 in its entirety to substantially match the refractive index of the cavity 1 8 with the waveguide 14 and the grating 16 to maximize a coupling of the optical signal OPT|_N to generate the optical signal OPTOUT- AS another example, the control signal CTRL can be analog or can have a plurality of states greater than two, such that the optical coupling controller 20 can control an amount of a mixture of the materials corresponding to the fluid FLD in the cavity 1 8 or can move a different type of fluid (e.g., with a lower index of refraction) of an available one or more additional fluids to control an intensity of the optical signal OPTOUT-

[0015] FIG. 2 illustrates an example of a diagram 50 of optical modulation. The diagram 50 demonstrates the waveguide 14, the grating 1 6, and the cavity 18 in each of a first state 52 and a second state 54. In the first state 52, the optical signal OPTIN is demonstrated as propagating in the waveguide 14 based on total internal reflection. The cavity 18 is demonstrated as empty in the first state 52, such that the cavity 18 can be filled with atmospheric gasses or can be a vacuum. Therefore, the cavity 18 separates a surface 56 of the waveguide 14 from the grating 16 to maintain total internal reflection of the optical signal OPT|_N, thus decoupling the optical signal OPTIN from the grating 16. As a result, the optical signal OPTOUT is not provided from the grating 16.

[0016] In the second state 52, the optical signal OPT|_N is demonstrated as propagating in the waveguide 14 based on total internal reflection. The cavity 18 is demonstrated as filled with one or more fluids in the second state 52, such that the cavity 18 can have a refractive index that is substantially the same as the waveguide 14 and the grating 16. Therefore, the surface 56 of the waveguide 14 does not provide internal reflection of the optical signal OPT|_N, thus coupling the optical signal OPTIN to the grating 16, as demonstrated by the dashed line 58. As a result, the optical signal ΟΡΤουτ is provided from the grating 16.

[0017] As described previously, the optical coupling controller 20 can be configured to control an amount, a type, and/or a relative mixture of materials corresponding to the fluid in the cavity 18. As an example, the optical coupling controller 20 can fill a portion of the cavity 18 with the fluid, as opposed to the entirety of the cavity 18. As a result, the volume of the fluid in the cavity 1 8 can be modulated to vary the refractive coupling of the optical signal OPT|_N with the grating 16 based on the non-filled portion of the cavity 18. As another example, the fluid can include a plurality of different fluid types, such as having different refractive indices. Thus, the optical coupling controller 20 can be configured to control a relative mixture of the plurality of different material types of the fluid to vary the refractive index of the cavity 18 relative to the waveguide 14 and the grating 1 6, and thus the refractive coupling of the optical signal OPT|_N with the grating 16. As a result, the optical coupling controller 20 can be configured to control an intensity of the optical signal ΟΡΤουτ that is diffractively redirected via the grating 16.

[0018] FIG. 3 illustrates an example of a waveguide system 100. The waveguide system 1 00 can correspond to the waveguide system 12 in the example of FIG. 1 . Therefore, reference is to be made to the example of FIG. 1 in the following description of the example of FIG. 3.

[0019] The waveguide system 100 includes a waveguide 1 02 and a plurality of gratings 104. Each of the gratings 104 is separated from the waveguide 1 02 via a respective plurality of cavities 106. One or more fluids can be selectively moved into each of the cavities 106 (e.g., via electrowetting or micro-pumping, similar to as described previously), such as via the optical coupling controller 20. Therefore, the cavities 106 can each have a refractive index that is selected to be equal to the atmospheric gasses, vacuum, or low refractive index fluid in a first state or approximately equal to the waveguide 102 and respective grating 1 04 in a second state, similar to as described previously in the example of FIG. 2. Therefore, the cavities 106 in the first state maintain total internal reflection of the optical signal OPTiN, thus decoupling the optical signal OPT|_N from the respective grating 104. However, the cavities 106 in the second state do not provide internal reflection of the optical signal OPT|_N, thus coupling a portion of the optical signal OPT|_N to the respective grating 104 and providing a respective optical signal ΟΡΤουτ, similar to as described previously in the example of FIG. 2. For example, the orientation and/or periodicity of the features of each of the gratings 104 can be arranged in a predetermined manner and differently with respect to each other to diffractively redirect respective portions of the optical signal OPT|_N having different frequency bands in selected directions, such as to create a light field for a three-dimensional projexel application.

[0020] Additionally, the optical coupling controller 20 can be configured to control an intensity of the optical signal ΟΡΤουτ provided from the respective gratings 104 individually. As an example, the optical coupling controller 20 can be configured to control an amount and/or a relative mixture of materials corresponding to the fluid in the respective cavities 106 individually. As an example, the optical coupling controller 20 can fill a portion of the cavities 106 with the fluid, as opposed to the entirety of the cavity 106, to vary the refractive coupling of the optical signal OPTIN to the respective grating 104. As another example, the fluid can include a plurality of different fluid types, such as having different refractive indices. Thus, the optical coupling controller 20 can be configured to control a relative mixture of the plurality of different material types of the fluid to vary the refractive index of the cavity 106 relative to the waveguide 102 and the respective grating 104. As a result, the optical coupling controller 20 can be configured to selectively control an intensity of the optical signal ΟΡΤουτ that is diffractively redirected via the respective grating 104.

[0021] FIG. 4 illustrates an example of a waveguide system 150. The waveguide system 1 50 can correspond to the waveguide system 12 in the example of FIG. 1 . Therefore, reference is to be made to the example of FIG. 1 in the following description of the example of FIG. 4.

[0022] The waveguide system 150 includes a waveguide 1 52 and a plurality of gratings 154. Each of the gratings 154 is separated from the waveguide 1 52 via a single cavity 156. One or more fluids can be selectively moved into the cavity 156 (e.g., via electrowetting or micro-pumping), such as via the optical coupling controller 20. In the example of FIG. 4, sets of electrodes 1 58 associated with each respective grating 1 54 are disposed within the cavity 156. While the sets of electrodes 1 58 are demonstrated as located substantially inline with the respective gratings 154, it is to be understood that the electrodes 158 can be located opposite each other along the sides of the cavity 156, as opposed to opposite each other on the top and bottom of the cavity 156. Other electrode configurations can also be implemented. As an example, the optical coupling controller 20 can be configured to selectively apply electrical biases to the sets of electrodes 158 associated with the respective grating 154 to control a location of the fluid with respect to the gratings 1 54. For example, the fluid can include a polar fluid that can be responsive to an electric field resulting from the electrical bias, such that the electrical field can be implemented to position the fluid between the waveguide 152 and the respective grating 1 54 or away from a space between the waveguide 152 and the respective grating 154 to provide coupling or non-coupling, respectively, of the optical signal OPT|_N to the respective grating 1 54. For example, the orientation and/or periodicity of the features of each of the gratings 1 54 can be arranged in a predetermined manner and differently with respect to each other to diffractively redirect respective portions of the optical signal OPTIN having different frequency bands in selected directions, such as to create a light field for a three-dimensional projexel application.

[0023] Additionally, as another example, the cavity 156 can be filled with a plurality of liquids. Therefore, the optical coupling controller 20 can implement coupling and/or intensity control of the respective optical signals ΟΡΤουτ individually based on a combination of the movement of the liquids relative to each other based on application of the electrical bias via the sets of electrodes 158. Accordingly, the optical modulation of the optical signal OPT|_N can be implemented in a variety of ways.

[0024] FIG. 5 illustrates an example of a display system 200. As an example, the display system 200 can be implemented to control any of a variety of display devices, such as a monitor or three-dimensional image display that implements projexel control. The display system 200 includes one or more optical sources 202, such as laser(s) or LED(s), which are configured to generate one or more optical signals OPT|_N. The display system 200 also includes an image controller 204 configured to generate a plurality of control signals CTRL based on image data. The display system 200 further includes a plurality N of optical modulation systems 206, where N is a positive integer. Each of the plurality of optical modulation systems 206 can be configured substantially similar to the optical modulation system 10 in the example of FIG. 1 . Thus, each of the optical modulation systems 206 includes a waveguide system 208 and an optical coupling controller 210. The waveguide system 208 can correspond to the waveguide system 1 2 in the example of FIGS. 1 through 4, and thus includes at least one grating that is separated from an

associated waveguide via a cavity.

[0025] The optical signal OPT|_N can be provided in a waveguide of each of the waveguide systems 208, and the plurality of control signals CTRL are provided to the optical coupling controller 210 in the respective plurality of optical modulation systems 206. Thus, the optical coupling controllers 210 can selectively move a fluid in the one or more cavities in each of the waveguide systems 208 to optically modulate the optical signal OPT|_N via the respective gratings to generate sets of image signals, demonstrated in the example of FIG. 5 as image signals IMd through IMG_N. As an example, each of the image signals IMGi through IMG_N can correspond to a given row or column of an associated visual content to be displayed by the display system 200. Thus, the control signals CTRL can be provided based on image data to control the coupling of and/or the intensity of a portion of the optical signal OPT|_N that is diffractively redirected via each grating in each of the waveguide systems 208 in each of the optical modulation systems 206 to generate the image signals IMGi through IMG_N. Accordingly, the image signals IMGi through IMG_N can be provided to form an image (e.g., on a display or in three-dimensional space based on the emission of light beams in different directions and/or at different wavelengths).

[0026] In view of the foregoing structural and functional features described above, an example method that can be implemented will be better appreciated with reference to FIG. 6. While, for purposes of simplicity of explanation, the methodology of FIG. 6 are shown and described as executing serially, it is to be understood and appreciated that the method is not limited by the illustrated order, as some aspects could, in other embodiments, occur in different orders and/or concurrently with other aspects from that shown and described herein. Moreover, not all illustrated features may be required to implement a method.

[0027] FIG. 6 illustrates a method 250 for providing optical modulation in a waveguide system (e.g., the waveguide system 12). At 252, an optical signal (e.g., the optical signal OPT|_N) is provided into a waveguide (e.g., the waveguide 14). At 254, a fluid (e.g., the fluid FLD) is moved with respect to a cavity (e.g., the cavity 18) that is formed between the waveguide and a grating (e.g., the grating 1 6) from a first state to a second state in response to a control signal (e.g., the control signal CTRL) to couple the optical signal to the grating to emit a portion of the optical signal (e.g., the optical signal ΟΡΤουτ) from the grating. The fluid can have a refractive index that is approximately equal to a refractive index of a material from which the waveguide and the grating are formed. At 256, the fluid is moved with respect to the cavity from the second state to the first state in response to the control signal to decouple the optical signal from the grating to substantially prevent emission of the optical signal from the grating.

[0028] What have been described above are examples. It is, of course, not possible to describe every conceivable combination of components or methods, but one of ordinary skill in the art will recognize that many further combinations and permutations are possible. Accordingly, the invention is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims. Additionally, where the disclosure or claims recite "a," "an," "a first," or "another" element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements. As used herein, the term "includes" means includes but not limited to, and the term "including" means including but not limited to. The term "based on" means based at least in part on.

Claims

CLAIMS What is claimed is:

1 . An optical modulation system comprising:

a waveguide system comprising a waveguide to propagate an optical signal therethrough, the waveguide system further comprising a grating separated from the waveguide via a cavity; and

an optical coupling controller to selectively move a fluid with respect to the cavity in response to a control signal, the fluid being moved with respect to the cavity from a first state to a second state to couple the optical signal to the grating to cause a portion of the optical signal to be diffractively redirected via the grating.

2. The system of claim 1 , wherein the waveguide and the grating are formed from respective materials having a predetermined refractive index, and wherein the fluid has a refractive index that is approximately equal to the predetermined refractive index.

3. The system of claim 1 , wherein the optical coupling controller is to variably control an intensity of the portion of the optical signal being diffractively redirected via the grating based on at least one of an amount of the fluid being moved with respect to the cavity, a type of fluid being moved with respect to the cavity, and a relative mixture of a plurality of materials corresponding to the fluid being pumped into the cavity.

4. The system of claim 1 , wherein the optical coupling controller is to move the fluid based on one of electrowetting and micro-pumping.

5. The system of claim 1 , wherein the waveguide system comprises a plurality of gratings, wherein the optical coupling controller is to move the fluid in response to the control signal to selectively couple the optical signal to the plurality of gratings.

6. The system of claim 5, wherein the plurality of gratings are separated from the waveguide by a respective plurality of cavities, wherein the optical coupling controller is to selectively move the fluid into and out of each of the plurality of cavities in response to the control signal to selectively couple the optical signal to the

respective plurality of gratings.

7. The system of claim 5, wherein the plurality of gratings are separated from the waveguide by a single cavity comprising a plurality of sets of electrodes associated with the respective plurality of gratings, wherein the optical coupling controller is to individually control a location of the fluid in the single cavity in response to the control signal to selectively couple the optical signal to the respective plurality of gratings.

8. A display system comprising a plurality of optical modulation systems of claim 1 , each of the plurality of optical modulation systems being to provide respective portions of a respective plurality of optical signals to be distributed across a display surface.

9. A method for providing optical modulation in a waveguide system, the method comprising:

providing an optical signal into a waveguide;

moving a fluid with respect to a cavity that is formed between the waveguide and a grating from a first state to a second state in response to a control signal to couple the optical signal to the grating to cause a portion of the optical signal to be diffractively redirected via the grating, the fluid having a predefined refractive index relative to a refractive index of a material from which the waveguide and the grating are formed; and

moving the fluid with respect to the cavity from the second state to the first state in response to the control signal to decouple the optical signal from the grating to substantially prevent emission of the optical signal from the grating.

10. The method of claim 9, wherein moving the fluid with respect to the cavity comprises controlling an amount, a type, or a relative mixture of a plurality of materials corresponding to the fluid that is moved with respect to the cavity via the control signal to variably control an intensity of the portion of the optical signal being diffractively redirected via the grating.

1 1 . The method of claim 9, wherein moving the fluid with respect to the cavity comprises applying an electrical bias to a set of electrodes in the cavity to control a location of the liquid in the cavity via the control signal to variably control an intensity of the portion of the optical signal being diffractively redirected via the grating.

12. The method of claim 9, wherein moving the fluid with respect to the cavity comprises moving the fluid based on one of electrowetting and micro-pumping.

13. An optical modulation system comprising:

an optical coupling controller to selectively move a fluid with respect to the cavity in response to a control signal, the fluid being moved with respect to the cavity from a first state to a second state based on one of electrowetting and micro- pumping to couple the optical signal to the grating to cause a portion of the optical signal to be diffractively redirected via the grating and to variably control an intensity of the portion of the optical signal being diffractively redirected via the grating based on at least one of an amount of the fluid being moved with respect to the cavity, a type of fluid being moved with respect to the cavity, and a relative mixture of a plurality of materials corresponding to the fluid being moved with respect to the cavity.

14. The system of claim 13, wherein the waveguide and the grating are formed from respective materials having a predetermined refractive index, and wherein the fluid has a refractive index that is approximately equal to the predetermined refractive index.

15. The system of claim 13, wherein the waveguide system comprises a plurality of gratings, wherein the optical coupling controller is to move the fluid in response to the control signal to selectively couple the optical signal to the plurality of gratings.