News Column

Patent Issued for Micromechanically Aligned Optical Assembly

July 16, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Pezeshki, Bardia (Menlo Park, CA); Heanue, John (Boston, MA), filed on November 30, 2012, was published online on July 1, 2014.

The patent's assignee for patent number 8768119 is Kaiam Corp. (Newark, CA).

News editors obtained the following quote from the background information supplied by the inventors: "The invention relates generally to the fiber optic communications, and more particularly to optical packaging techniques used to align laser sources to optical fibers and other types of waveguides.

"Optical fiber communications has generally replaced electrical links over long distances in the past few decades. In more recent past, optical links are being used at shorter distances to connect servers to switches and for datacenters. In the future it is expected as data rates increase and costs of optics decreases that optics will diffuse into computers and the connections within a machine or between processors will be optical. (see for example Kash et al. SPIE Photonics West conference 2009 and references cited therein, the disclosures of which are incorporated by reference herein)

"A challenge of fiber optics has been that packaging and alignment processes are considerably more difficult than electrical wiring. The advantages are the greater bandwidth and reduced degradation of the signal with distance. At 10 Gb/s data rates, for the signal to travel more than 100-300 m in a fiber, single mode fiber is generally needed, with a typical mode size of about 8 microns. Laser sources typically have a mode size of only a few microns. Thus the alignment between the laser and the fiber through the intermediate optics generally has to be very high precision, and tolerances on the order of a tenth of a micron are typically required. One great advantage of single mode fiber is that multiple wavelengths can be coupled simultaneously to get a parallel link through a single fiber. Thus a 100 Gb/s signal can be sent through a single mode fiber for many kilometers by using ten channels of 10 Gb/s each, with every lane at a different wavelength.

"As an alternative, when distances are on the order of 100 m or less, multimode fiber and multimode vertical cavity lasers are often used. In this case the core size in the fiber is much larger, at about 50 um, and tolerances can be substantially looser. However, the reach is limited as different modes of the fiber travel at different speeds and it is becomes more difficult to transmit multiple wavelength simultaneously.

"As bandwidth requirements increase, there is increased parallelism in both single mode and multimode fiber links. In single mode systems, parallel channels can be obtained easily by adding wavelengths to the same fiber. In multimode systems, additional fibers generally are added to form a fiber ribbon. Parallel ribbon fibers are of course quite expensive and connectors with 24 fibers inside are complicated to make, even if they use multimode fiber with looser alignment tolerance.

"There has been considerable work in the industry on different techniques of loosening the alignment tolerance in single mode systems. However, none is very effective, especially if multiple sources are coupled into the same fiber. In these cases there are multiple single mode alignments that occur in the same package.

"The simplest way to loosen the tolerances slightly is to fabricate a laser with a bigger optical mode. The technique most commonly used is to have a tapered section at the output of the laser where the optical mode is expanded. This makes the laser mode roughly the same size as the optical fiber or waveguide mode and the alignment tolerance increases from about a quarter micron to about a micron. The disadvantage of this technique is that the fabrication of the laser or semiconductor source becomes more complex, raising the cost. There is also some sacrifice in the performance of laser. In addition, the effect of a laser with a slightly larger optical mode is not that dramatic. One micron alignment tolerance is better than a quarter of a micron, however, it is still not amenable to low cost packaging techniques.

"Another technique is to etch the facet of the laser and add a passive silica waveguide. The laser is bonded upside down to a planar lightwave circuit (PLC) that has waveguides built in. The passive waveguide in the laser source and the waveguide in the PLC are matched in effective index, and with a slight taper, all the power can theoretically transfer from the laser source into the single mode waveguide underneath. This loosens the tolerance in the die bonding process to about 5 um, allowing the use of some standard packaging and diebonding equipment. The issue with this technique is that the laser chips become tremendously more complicated. One has to etch a facet and through epitaxial and lithographic processes, align a passive waveguide to the semiconductor waveguide. Such lasers are highly customized and there is an unavoidable optical loss between the laser waveguide and the passive waveguide formed next to it.

"MEMS with active rather than passive alignment has also been used to align lasers and waveguides. Alignment may be performed with a MEMS mirror with alignment maintained by a control loop. However, the feedback loop has to be maintained during operation, requiring that the high voltage control electronics outside of the package stay active during operation.

"There have been some proposals of MEMS active alignment techniques for switches and alignment of arrays. Some have moving waveguides (E. Ollier, '1\.times.8 Micromechanical Switches based on Moving Waveguides.' in Proc. 2000 IEEE/LEOS Int. Conf. Opt. MEMS Kauai, HI, August 2000, pp. 39-40.), some have torsional mirrors (MEMS optical switches, Tze-Wei Yeow; Law, K. L. E.; Goldenberg. A. Communications Magazine, IEEE Volume 39, Issue 11, November 2001 Page(s):158-163) and some with lenses on an x-y stage (MEMS packaging for micro mirror switches, Long-Sun Huang; Shi-Sheng Lee; Motamedi. E.; Wu, M. C.; Kim, C.-J. Electronic Components & Technology Conference, 1998. 48th IEEE Volume, Issue, 25-28 May 1998 Page(s):592-597) (all of which are incorporated by reference herein). However, all of these approaches are complex and difficult to apply, for example, to PLCs."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "In some aspects the invention provides a structure containing multiple lasers of different wavelengths, a planar lightwave circuit that can combine the different wavelengths into a single waveguide, and set of lenses whose position can at least initially be adjusted using micromechanical means all mounted on a submount where the lasers and the planar lightwave circuit are soldered onto the submount lens holders are an integral part of the submount and are initially adjustable

"A structure as above where the lens holders are on a lever, thereby demagnifying the motions used to adjust their positions.

"A structure as above where the submount contains a region of predeposited solder that can be reflowed with an integrated heater, and where the solder can lock down the position of the lens with electrical means

"The structure as above where actuators are formed on the submount, as an integral part of the submount, and where the actuators move the lenses to optimize the coupling without external mechanical motion

"In some aspects the invention provides a structure of at least one laser, one output waveguide, and a microlens, whereby the microlens can be moved by electromechanical means and locked down after optimizing the coupling.

"In some aspects the invention provides a structure comprising of multiple lasers of different wavelengths, a planar waveguide circuit that can combine the different wavelengths into a single waveguide, a set of lenses for collimating and focusing the beam, and a set of micromirrors, whose deflection can adjust the position of the beam and the focusing of the beam into the waveguide.

"The structure as above where the lasers are mounted ontop of the planar lightwave circuit and emit the optical beam through the microlens onto to adjustable micromirror.

"In one aspect of the invention, the invention provides a micromechanically aligned optical assembly, comprising: a first waveguide on a substrate; a second waveguide on the substrate; a lens for focusing light of the first waveguide into the second waveguide; and a lever holding the lens, the lever having at least one point fixed with respect to the substrate, the lever holding the lens at a position such that movement of the lever will result in demagnified movement of the lens in at least directions other than an optical axis of light of the first waveguide, the lever moveable so as to position the lens to focus light of the first waveguide into the second waveguide.

"In one aspect of the invention, the invention provides the assembly of claim 1,

"further comprising: a plurality of further first waveguides on the substrate; a plurality of second waveguides on the substrate; a plurality of further lenses, each of the plurality of further lenses for focusing light of a corresponding one of the further first waveguides into a corresponding one of the further second waveguides; and a plurality of further levers, each of the further levers holding a corresponding one of the plurality of further lenses, each of the further levers having at least one point fixed with respect to the substrate, each of the further levers holding the corresponding further lens at a position such that movement of each of the further levers will result in demagnified movement of the corresponding lens in at least directions other than an optical axis of light of the corresponding one of the further first waveguides.

"In one aspect of the invention, the invention provides an optical device, comprising: a first optical component configured to provide light; a second optical component configured to receive light; and a third optical component in an optical path between the first optical component and the second optical component, the third optical component mounted on an arm with a length along an axis substantially parallel to an axis defined by the optical path between the first optical component and the third optical component.

"In one aspect of the invention, the invention provides a method of making an aligned optical assembly, comprising: manipulating a lever holding a lens to position the lens to focus light from a first waveguide into a second waveguide, the first waveguide and the second waveguide, being physically coupled to a substrate and the lever having a fulcrum fixed in position with respect to substrate, the lever demagnifying movement of the lens in other than an optical axis of the light.

"In one aspect of the invention, the invention provides a method of making an aligned optical assembly, comprising: moving a lever holding a lens to position the lens to focus light from a first waveguide into a second waveguide, the first waveguide and the second waveguide being physically coupled to a substrate, with the lever having a point fixed with respect to the substrate and the lever having a length substantially parallel to an optical axis of the light from the first waveguide to the lens; and fixing position of the lever with the lens focusing light from the first waveguide into the second waveguide.

"In one aspect of the invention, the invention provides a micromechanically aligned optical device, comprising: a first waveguide coupled to a substrate; a second waveguide coupled to the substrate; a lens for focusing light from the first waveguide into the second waveguide, the light having an optical axis substantially parallel to a planar base of the substrate; a holder for holding the lens, the holder physically coupled to the substrate; at least one electrically actuated actuator at least partially coupled to the holder, the actuator configured to cause movement of the holder in at least one direction absent application of means for effectively fixing position of the holder; and means for effectively fixing position of holder.

"In one aspect of the invention, the invention provides a method of aligning an optical assembly, comprising: providing light from a first waveguide physically coupled to a substrate; providing an electric signal to an actuator to move a lens to focus light from the first waveguide into a second waveguide, the lens on a holder physically coupled to the first substrate, the actuator fixedly physically coupled to the holder; determining that the lens is focusing light from the first waveguide into the second waveguide; and fixing position of the holder.

"In one aspect of the invention, the invention provides an aligned optical device, comprising: an input waveguide physically coupled to a substrate; an output waveguide physically coupled to the substrate; a lens configured to focus light from the input waveguide into the output waveguide; an arm holding the lens, the arm having a longitudinal length substantially parallel to an axis defined by a linear path from the input waveguide to the output waveguide, the arm being fixed in position with respect to the substrate.

"In one aspect of the invention, the invention provides an aligned optical device, comprising: an input waveguide physically coupled to a substrate; an output waveguide physically coupled to the substrate; a lens configured to focus light from the input waveguide into the output waveguide; an arm holding the lens, the arm having a longitudinal length substantially parallel to an axis defined by a linear path from the input waveguide to the output waveguide, and means for fixing position of the arm with respect to the substrate.

"In one aspect of the invention, the invention provides an optical device, comprising: an input waveguide; an output waveguide; a convex mirror mounted in a holder, the mirror moveable, in the absence of application of means to effectively fix position of the mirror, to reflect light from the input waveguide into the output waveguide; an arm physically coupled to the mirror, the arm having a moveable free end distal from the mirror; and means for effectively permanently fixing position of the mirror.

"In one aspect of the invention, the invention provides an optical device, comprising: a plurality of input waveguides physically coupled to a substrate; a plurality of output waveguides physically coupled to the substrate; a plurality of lenses configured to focus light from each of a corresponding one of the input waveguides into a corresponding one of the output waveguides, the plurality of lenses mounted in a holder; a plurality of arms physically coupled to the holder, the further arms moveable, in the absence of application of means to effectively permanently fix position of the arms with respect to the substrate, so as to cause focus of light from each of the corresponding ones of the input waveguides into the corresponding ones of the corresponding output waveguides; and means for effectively permanently fixing position of the arms with respect to the substrate.

"These and other aspects of the invention are more fully comprehended upon review of this disclosure."

For additional information on this patent, see: Pezeshki, Bardia; Heanue, John. Micromechanically Aligned Optical Assembly. U.S. Patent Number 8768119, filed November 30, 2012, and published online on July 1, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8768119.PN.&OS=PN/8768119RS=PN/8768119

Keywords for this news article include: Electronics, Kaiam Corp., Semiconductor.

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Source: Electronics Newsweekly


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