1. Field of the Invention
The present invention relates generally to optical waveguides, and more particularly to an optical waveguide that changes the depth of propagation of the photons in the waveguide.
2. Description of the Prior Art
Optoelectronic integrated circuits (OEICs) have found significant applications in a number of fields including communications and optical interconnects of computing. However, those concerned with designing OEICs have recognized the meed for developing improved optical interconnects capable of transmitting light between active devices that form these integrated circuits. Conventional OEICs usually employ optical waveguides as device interconnects. Specifically, circuit fabricators have used thin films of various materials to form optical waveguides directly on the surface of OEIC structures.
Typically, active devices or electronic logic elements such as those employed in electronic computer systems do not directly interface with optical information processing and communications systems. Therefore, in a typical system interface involving both electronic and optical techniques, photons must be detected and converted to electrical energy of commensurate signal information, the signal processing operations must then be performed electronically, and that procedure followed by reconversion of the electrical signals to photons.
Various techniques and fabrication methods have been utilized to construct OEICs that provide control over the in plane direction of the path of photons in an OEIC. For example, waveguide bends, waveguide junctions and directional couplers have been used to assist in controlling the direction of the path of the photons; however, often the current methods are difficult or expensive to fabricate and often result in optical loss or leakage. In addition, these devices do not address out of plane or the depth of optical coupling.
Embodiments described herein include a waveguide that will redirect photons propagating in the waveguide in a direction substantially perpendicular to the propagation axis of the waveguide.
Various embodiments also provide for inter-planar propagation of a wave front disposed in a waveguide and allow control over the amount of photons directed to select regions of an OEIC.
In general, in one aspect, the invention features a waveguide including: a first photon propagating material having a first index of refraction (n1) and having a pinch disposed therein, the pinch having a second index of refraction (n1′); and a second photon propagating material disposed in optical communication with the first photon propagating material and having a third index of refraction (n2); wherein n1′<n1, n1′<n2, and the pinch redirects at least a portion of the photons from the first photon propagating material to the second photon propagating material.
In general, in another aspect, the invention features an optical apparatus including: a first photon propagating material having a first index of refraction (n1) and having a pinch disposed therein, the pinch having a second index of refraction (n1′); and a second photon propagating material disposed in optical communication with the first photon propagating material and the second photon propagating material having a target region disposed therein and the target region having a third index of refraction (n2); wherein n1′<n1, n1′<n2, and the pinch redirects at least a portion of the photons from the first photon propagating material to the second photon propagating material in at least the target region.
In general, in still another aspect, the invention features an optical apparatus including: a first photon propagating material having a first index of refraction (n1) and having a pinch disposed therein, the pinch having a second index of refraction (n1′); a second photon propagating material disposed in direct contact with the first photon propagating material and the second photon propagating material having a target region disposed therein and the target region having a third index of refraction (n2); and a photon source for supplying photons to the first photon propagating material; wherein n1′<n1, n1′<n2, and the pinch redirects at least a portion of the photons from the first photon propagating material to the second photon propagating material in at least the target region.
In general, in still yet another aspect, the invention features a waveguide including: a first photon propagating material having a first index of refraction (n1) and having a first pinch disposed therein, the pinch having a second index of refraction (n1′); and a second photon propagating material disposed in direct contact with the first photon propagating material and having a third index of refraction (n2), the second photon propagating material having a second pinch oriented opposite that of the first pinch in an axial direction; wherein n1′<n1, n1′<n2, and the first and second pinches redirect at least a portion of the photons from the first photon propagating material to the second photon propagating material.
Other objects and features of the invention will be apparent from the following detailed description.
The invention will be described in conjunction with the accompanying drawings, in which:
A waveguide is provided, comprising a first photon propagating material having a first index of refraction (n1) and having a pinch disposed therein, the pinch having a second index of refraction (n1′); and a second photon propagating material disposed in optical communication with the first photon propagating material and having a third index of refraction (n2); wherein n1′<n1, n1′<n2, and the pinch redirects at least a portion of the photons from the first photon propagating material to the second photon propagating material.
Turning now to
IA, a top view of a waveguide 100 is illustrated. As may be seen, waveguide 100 has three distinct regions. The first region is an upstream region 110. Next is a pinch region 112. Finally, there is a downstream region 114. It should be appreciated that the terms upstream and downstream are utilized to provide axial location with respect to pinch region 112 in the direction of the propagation of light 116 as illustrated by the associated line. As may be seen, waveguide 100 has an axial length L. In the described embodiment, L will be about 20 micrometers or less. The selection of the length L is non-trivial in that prior art inter-planar couplers are on the order of 100 micrometers or more. Thus, prior art waveguides can be a factor of 10 times larger than the currently described embodiment. It should also be understood that waveguides having a length of greater than 20 micrometers are within the scope of the teachings of the present invention.
Waveguide 100 has a lateral width of W1. In the described embodiment, width W1 of waveguide 100 is some fraction of the wavelength of light 116 propagating through waveguide 100. Generally, width W1 would be defined by the equation: W1≦λ2, where λ is the free space wavelength of light 116 propagating within waveguide 100. In the described embodiment, W1 is less than or equal to ½ a micrometer, when λ=1.5 μm. The selection of width W1 is non-trivial in that prior art waveguides have widths that are on the order of 2λ or greater. Thus, prior art waveguides can be a factor of 4 times wider than the currently described embodiment. It should be appreciated that waveguides 100 having a width of greater than λ/2 are within the scope of the teachings of the present invention.
Turning now to
Disposed above substrate 118 is an interaction layer 120. In the described embodiment, interaction layer 120 is formed from a uniform layer of III-V, IV, and/or II-VI semiconductor material selected from the group comprising: GaAs, InP, AlAs, etc., or any combination thereof. A portion of interaction layer 120 could comprise an active material and have an active region 124 disposed in target region 128. It should be appreciated that target region will have an index of refraction n2′ which is different than layer 120 outside of target region 128, i.e., have an index of refraction n2. Typically, n2′>n2. In some embodiments, interaction layer 120 will be at least partially optically transparent. The index of refraction (n2′) for target region 128 will be between 3.4 and 3.6 (e.g. 3.5) while n2 for interaction layer 120 will be between 1 and 3.4. It should be appreciated that interaction layer 120 may be non-uniform with respect to the index of refraction in an axial, lateral, and/or transverse direction outside of target region 128. For example, the index of refraction for interaction layer 120 may be different in regions 110, 112, and/or 114. While no intermediate layers are illustrated between substrate 118 and interaction layer 120, it should be appreciated that the presence or absence of these intermediate layers are within the scope of the teachings of the present invention.
It is also contemplated that in various embodiments interaction layer 120 will comprise distinct sub-layers which may or may not be constructed from the same material. It should be appreciated that interaction layer 120 may be non-uniform with respect to the index of refraction in an axial, lateral, and/or transverse direction. For example, the index of refraction for interaction layer 120 may be different in regions 110, 112, 114, and/or 128. For simplicity, we will refer to interaction layer 120 having an index of refraction n2, whether it is uniform or if that is the average or index of refraction for interaction layer 120 outside of target region 128.
Disposed above interaction layer 120 is a confinement layer 122. In the described embodiment, confinement layer 122 is formed from a uniform layer of III-V, IV, and/or II-VI semiconductor material selected from the group comprising: Si, GaAs, InP, AlAs, etc., or any combination thereof. In at least some embodiments, confinement layer 122 will at least partially optically transparent. It should be appreciated that confinement layer 122 may be multimode or single mode. In the described embodiment, the index of refraction (n1) for confinement layer 122 will be between 3.4 and 3.6 (e.g. 3.49). It should be appreciated that confinement layer 122 may be non-uniform with respect to the index of refraction in an axial, lateral, and/or transverse direction. For example, the index of refraction for confinement layer 122 may be axially different in regions 110, 112, and/or 114 as well as laterally different within any of the regions 110, 112, and/or 114. For simplicity, we will refer to confinement layer 122 having an index of refraction n1, whether it is uniform or if that is the average index of refraction for confinement layer 122 in regions 110 and 114. Confinement layer 122 has an index of refraction n1′, whether it is uniform or if that is the average index of refraction for confinement layer 122 in region 112. While no intermediate layers are illustrated between interaction layer 120 and confinement layer 122, it should be appreciated that the presence or absence of these intermediate layers are within the scope of the teachings of the present invention.
Pinch region 112 is illustrated as tapering or “pinching” from a width W1 to a width W3 and then expanding to a width W4. In the described embodiment, the change in pinch region 112 is uniform and symmetrical. A goal of designing pinch region 112 is to eliminate as many discontinuities as possible and to remove any sharp corners that may adversely effect wave propagation. In the described embodiment, the change in width is also smooth, i.e., the first derivative would be a continuous as illustrated in the numerous embodiments in the figures. The specific goal of the pinch is to reduce waveguide 100 to a width W3. Typically, W3 is be small enough to prevent any modes from existing downstream of the narrowest point 126 of pinch region 112. Thus, W3 is between 0 and W1, depending on the particular wavefront propagating in waveguide 100. It should be appreciated that pinch region 112 may have any shape, such as a quadric, cosine, polynomial series, and/or any other shape specifically illustrated in
Pinch region 112 is illustrated as expanding from a width W3 to a width W4, downstream of point 126. It should be appreciated that width W4 may be greater than W1 or may be less than W3, i.e., pinch region 112, downstream of point 126, may either expand or contract further, depending on the specific downstream result required in region 114. We will now discuss the specific widths for downstream region 114 with respect to the width W4, in the table, below.
It should be appreciated that while pinch region 112 has been illustrated as a two dimensional taper, it may in fact, be desirable to have pinch region 112, upstream of point 126, taper in three dimensions, i.e. provide a change in n1′ in the axial, lateral and transverse directions.
Waveguide 100 may be maintained in free space or may be enclosed in a protective material such as glass (SiO2). The enclosing material or free space will have an effective index of refraction of n0. In the described embodiment, n1 is greater than n0, e.g. n1 is 2 times greater than n0.
While
It should be appreciated that while light 116 is illustrated as penetrating “down” into interaction layer 120 which is disposed below confinement layer 122, it may be advantageous to have light propagate “up” above confinement layer 122. To accomplish this, one would have to assure that in some region above confinement layer 122, the index of refraction for that region would be greater than n1′.
While it has been illustrated that regions 112 are in axial alignment, it should be appreciated that the alignment of region 112 in layer 118 is not critical. The alignment of region 112 in layers 120 and 122 has some criticality in that region 112 in layer 122 should have some overlap with region 112 in layer 120. In the described embodiment, region 112 in layer 122 would start before region 112 starts in layer 120. Also, typically, region 112 in layer 122 would end after region 112 ends in layer 120. That would assure photon interaction with target region 124.
The relationship of the index of refraction of confinement layer 122 and interaction layer 120 are important in determining the confinement of light 116 to a particular layer 120,122 in regions 110, 112, and 114, i.e., the creation of a low velocity channel for light 116 to propagate in. The following table illustrates this concept.
Thus, by appropriately designing the width of regions 110, 112, and 114 with the appropriate index relationship, one is able to create a unique set of low velocity channels for light 116 to propagate in waveguide 100. While the above table provide a desired Δ between n1 and n2, it should be appreciated that this is illustrative.
The photon source may be any suitable source for providing photons to a waveguide, such as a laser, optical fiber, etc. In particular, the teachings herein may be combined with the teachings of U.S. Provisional Patent Application No. (T.B.D.), entitled “Semiconductor Laser” filed on Nov. 14, 2005; or U.S. Provisional Patent Application No. (T.B.D).), entitled “Semiconductor Device Having A Laterally Injected Active Region” filed on Nov. 14, 2005, to allow optical propagation in the active layer or region disclosed in these applications.
Various specific examples will now be described.
Turning now to
As the photons continue to propagate axially down waveguide 600, pinch 630 begins to push the photons into layer 610 due to the indicies of refraction between layers 630 and 610. As may be seen in
Photons may be made to contact a laser diode either by redirecting photons from a waveguide via interaction with a pinch, or by directing photons that continue to propagate along the longitudinal axis of the waveguide in region 603 into a laser diode or photon source. When contacting the laser diode or photon source, the photons are at or below a threshold level such that the photons will not cause the laser diode or photon source to lase. However, contacting a laser diode or photon source with this level of photons greatly decreases the amount of time necessary for the laser diode or photon source to overcome the threshold such that the laser diode or photon source will lase. Thus, by controlling the level of photons contacting the laser diode or photon source, the laser diode or photon source may be maintained in a state of readiness.
A double pinch can be used to control the level of photons entering a laser diode. A top view of an exemplary double pinch arrangement is shown in
Photon redirection may also be controlled by methods, such as layer doping and cladding. For example, the waveguide, including the pinch, may be clad with any suitable cladding material, such as glass, silicon oxynitride or a polymer, to confine photons within the waveguide. The various layers of the OEIC may be doped to achieve desired indices of refraction for each layer.
Redirected photons may be directed to any suitable device or layer. For example, photons may be redirected to another waveguide. Redirected photons may also be redirected into a target region. In an embodiment of the present invention, the target region may be active layer 620. The target region or active layer may, for example, contain a photodiode (photon detector) that interacts with photons to produce current or may be a laser (photon source) and thus form an optical amplifier. The target region or active layer may contain a variety of optoelectronic devices, logic devices, etc.
In addition, a pinch may be fabricated in a waveguide in combination with a reduction in the top or upper surface of the waveguide. In other words, a waveguide may be tapered or may contain a vertical or transverse pinch in any shape described above for a lateral pinch. Thus, various combinations of pinches are contemplated within the present invention and may be utilized for various applications by one of ordinary skill in the art based on the present disclosure.
Waveguides mentioned herein may be of any suitable material. Suitable materials include germanium, silicon, indium-phosphide (InP), gallium-arsenide (GaAs), aluminum-arsenide (AlAs), indium-arsenide (InAs), and/or SiO2 polymers, etc.
Insulating layers mentioned herein may be of any suitable material. Suitable materials include silicon dioxide (SiO2) and/or nitrides, etc.
Dielectric layers mentioned herein may be of any suitable material. Suitable materials include SiO2, Si3N4, Al2O3, CaF2, and/or nitrides, etc.
Active layers mentioned herein may be of any suitable material. Suitable materials include, but are not limited to, II-V, IV, and/or II-VI, such as INAlGaAs and InGaAsP.
Suitable materials for substrates mentioned herein include, but are not limited to, III-V, IV, and/or II-VI, such as InP, GaAs, aluminum-gallium-arsenide (AlGaAs), silicon, SiO2, and sapphire.
Waveguides mentioned herein may be fabricated by any known method. Suitable methods include thin film deposition, dry etching, wet etching, reactive ion etching, epitaxial techniques such as molecular beam epitaxy, lithography such as photolithography and E-beam lithography.
Other suitable fabrication methods and materials are described in U.S. Pat. Nos. 6,051,445; 5,917,967; 5,838,870; 5,559,912; 5,514,885; 5,354,709; 5,163,118; 4,996,575; 4,877,299; and 4,789,642, the entire disclosures of which are hereby incorporated by reference.
Other embodiments are within the following claims.
This application claims the benefit of U.S. Provisional Patent Application No. 60/736,202, entitled “Pinch Waveguide” filed on Nov. 14, 2005. This application makes reference to co-pending U.S. Provisional Patent Application No. 60/736,480, entitled “Semiconductor Device Having A Laterally Injected Active Region” filed on Nov. 14, 2005, and U.S. Provisional Patent Application No. 60/736,201, entitled “Semiconductor Laser” filed on Nov. 14, 2005, the contents of both of which are incorporated herein by reference.
Number | Date | Country | |
---|---|---|---|
60736202 | Nov 2005 | US | |
60736201 | Nov 2005 | US |