Patent Application
20130315527
The invention relates generally to optical devices, and more particularly, to photocarrier-injecting variable optical attenuators.
The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Optical attenuators are used to reduce the intensity of light signals. These attenuators can employ optical waveguides to confine light signals to particular regions. An optical waveguide is generally defined by a channel or a ridge extending from a slab of a light transmitting medium. Optical attenuators associated with optical waveguides often achieve light signal attenuation by free carrier absorption. Existing practice employs a diode structure to inject free carriers electrically from at least two electrodes in forward bias condition. The concentration of free carriers by the electrical injection method is limited by diode injection efficiency, whereas high operating power and long device lengths are often required to achieve considerable attenuation.
Exemplary embodiments are illustrated in the referenced figures. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.
One skilled in the art will recognize many methods, systems, and materials similar or equivalent to those described herein, which could be used in the practice of the present invention. Indeed, the present invention is in no way limited to the methods, systems, and materials described.
Embodiments of the present invention are directed to systems and methods for attenuating optical signals by providing a photocarrier-injecting variable optical attenuator. In general, the optical attenuators of the present invention operate by injecting photocarriers into a light transmitting waveguide from a second, injection light source. In some embodiments, the light transmitting waveguide is defined by a ridge extending from a slab of a light transmitting medium. The optical attenuators generally include the second light source, wherein light emitted therefrom is optically absorbed by the waveguide medium to introduce photocarriers in a plurality of configurations.
The injected photocarriers are a form of free carriers, which provide optical absorption of the signal light in the originally transparent waveguide. The optical absorption thus provides optical attenuation of the signal light. The second light source, which provides light that is absorbed by the waveguide, may include, but is not limited to, lasers, light emitting diodes, thermal emitters, etc. The optical energy of the second or injection light source is partially or completely absorbed by the light transmitting waveguide medium, thereby providing the optical attenuation.
In this embodiment, the second or injection light source chip 110 is placed upside-down on top of the waveguide 101 by flip-chip bonding technology. The second light source chip 110 may comprise one light source, an array of light sources, or a plurality of light source chips. The light source chip 110 comprises a light output aperture 111 that faces downward towards a section of the top surface 101B of the waveguide 101 with accurate alignment provided by the flip-chip bonding process. The light output aperture 111 emits the injection light downward into the waveguide 101 and the light is absorbed by the waveguide medium. The wavelength of the light emitted from the light output aperture 111 may be at, but is not limited to, wavelengths between 400 nm to 1400 nm, e.g. 633 nm, 850 nm, 980 nm, 1064 nm, etc. The optical attenuation of the light signal passing between the input interface 130 and the output interface 132 of the optical attenuator 80 may be selectively adjusted by adjusting the optical power of the second light source 110 (e.g., using a suitable controller). That is, increasing the photocarriers injected into the waveguide 101 provides increased optical absorption and thus provides increased optical attenuation of the signal light. The optical absorption of the injection light in the medium of the waveguide 101 is typically greater than 1000/cm so that it can be efficiently absorbed to generate photocarriers, while the optical absorption of the light signals in the medium of the waveguide 101 is typically less than 1/cm (i.e., transparent).
A plurality of spacers 103 are each formed by a ridge extending upward from the slab medium 112. The spacers 103 provide mechanical support and precise height control for the flipped second light source chip 110. As shown in
In this embodiment, a plurality of metal solder bumps 120 are included to provide strong bonding between the light source chip 110 and the attenuator chip 100 during the flip-chip bonding process. The metal solder bumps 120 also provide electrical connections between metal pads of the light source chip 110 and metal lines of the attenuator chip 100 such that electrical current may be applied from the metal lines on the attenuator chip 100 to the light source chip 110 to operate the injection light source. The optical power of the light source 110 is controlled by the selectively applied electrical energy through the metal lines.
The distance between each of the angled mirror structures 104 and the sidewalls 101A of the waveguide 101 is also related to the efficiency of the light reflected into the waveguide 101. A suitable distance between the angled mirror structures 104 and the waveguide 101 may be a distance that is approximately the same as the radius of the light output aperture 148. Generally, the angled mirror structures 104 are most useful when the size of the light source aperture 148 is larger than the width of the waveguide 101 between the sidewalls 101A. In this instance, a portion of the light emitted from the light source aperture 148 does not directly enter the waveguide 101. The additional mirror structures 104 operate to reflect the portion of the light to the sidewalls 101A of the waveguide 101 such that additional light is absorbed by the waveguide medium to provide greater optical attenuation.
In some embodiments, the second or injection waveguide 220 is made of a different medium than the medium of the optical waveguide 101. In this case, the injection waveguide 220 may be made of a medium that does not absorb the injection light from the injection light source 221. As shown, a first portion 220A of the injection waveguide 220 extends from the light source 221 at a position on the attenuation chip 100 spaced apart from the optical waveguide 101. The injection waveguide 220 bends towards the first waveguide 101 that carries the light signal. The injection light is coupled or “leaked” from the injection waveguide 220 into the optical waveguide 101 when a second portion 220B of the second waveguide comes in close proximity to the first waveguide 101 for a certain distance. Suitable spacing between the two waveguides 101 and 220 at the coupling region includes, but is not limited to, from less than 1 μm to 10 μm, e.g. 0.2 μm, 0.5 μm, 1 μm, 2 μm, etc.
In the embodiment shown, the injection waveguide 220 is positioned above the waveguide 101 so that the second portion 220B is disposed directly over the waveguide 101 to couple the injection light into the waveguide 101. In this embodiment, the waveguide 101 may be covered by a layer 105 that is planarized before making the injection waveguide 220 thereon. In this case, the spacing between the two waveguides 101 and 220 is provided by the thickness of the layer 105. In other embodiments, the injection waveguide 220 may be disposed at the same horizontal level as the first waveguide 101.
In some embodiments, the injection waveguide 300 is made of a different medium from that of the waveguide 101. When the injection waveguide 300 is made of a medium that does not absorb the injection light, a structure 302 may be provided adjacent the waveguide 101 at the location where injection waveguide 300 would cross or “intersect” the waveguide 101. The structure 302 is wider than the width of the elongated waveguide 101 between the sidewalls 101A and extends from the opposite sidewalls of the waveguide 101. The structure 302 acts as a “connector” between the waveguide 101 and the waveguide 300 to minimize the disturbance of the light signal optical mode inside the waveguide 101 when passing the intersect region. Without the structure 302, the light signal optical mode may be disturbed by the intersecting waveguide 300 due to its different medium and dimensions. The length L of the waveguide 300 may be relatively long since the medium of the injection waveguide 300 does not absorb the injection light.
In other embodiments, the injection waveguide 300 is made of the same medium as the optical waveguide 101. In this instance, because the medium absorbs injection light, the length L of the injection waveguide 300 should not be very large. Suitable lengths for the length L of the injection waveguide 300 include, but are not limited to, lengths between 1 μm and 100 μm, etc.
Suitable materials for the substrate 100 may include silicon, indium phosphide, etc. Suitable materials for the lower cladding layer 102 may include silicon dioxide, indium gallium phosphide, etc. Suitable materials for the angled structure 104 may include silicon, indium phosphide, etc. Suitable materials for the coating on the angled surfaces 150 may include metal (e.g. aluminum, gold, etc.) and dielectric multi-layers composed of silicon dioxide, silicon nitride, aluminum oxide, etc.
The foregoing described embodiments depict different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality.
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. Furthermore, it is to be understood that the invention is solely defined by the appended claims. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.).
It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations).
