US 11,501,097 B2

3

FIG. 1 shows a barcoded end facet printed photonic chip,
according to some embodiments, in plan view in panel A and
an end view in panel B

FIG. 2 shows a bareoded photonic chip, according to
some embodiments, in plan view in panel A, an end view in
panel B, and in a configuration for on-axis printing of a
barcode-guided direct laser written optical coupling in panel
c

FIG. 3 shows a barcode-guided direct laser writer for
barcode-guided direct laser writing of an optically transpar-
ent direct laser writing substrate in a configuration for
transverse printing of a barcode and waveguide in panel A
and in a configuration for on-axis printing of a barcode-
guided direct laser written optical coupling in panel B,
according to some embodiments.

FIG. 4 shows a photonic chip with alignment marks in
plan view in panel A, an end view in panel B, and in a
configuration for transverse printing in panel C.

FIG. 5 shows that direct laser writing on the facet of a

conventional photonic chip can be blocked or obfuscated 2

when done from an off-axis perspective with a direction
propagation of direct write laser light mainly orthogonal to
a transverse waveguide writing surface and parallel to a
facet surface of an optically transparent direct laser writing
substrate. (a) A device in a conventional photonic chip can
include a high refractive index waveguide core surrounded
by a lower refractive index cladding on a high refractive
index substrate. The waveguide core is tapered down to a
small width at the facet to create an input/output (IO) port
with improved mode matching, and hence optical coupling,
to a single-mode optical fiber. (b) With off-axis printing, the
lithography beam referred to the direct write laser light from
the DLW system is partially obstructed by the cladding when
printing an optical structure at the facet surface, and the
working distance of the objective limits the size and depth
of the printable area. The influence of this obstruction
becomes more significant if the cladding refractive index is
larger or if a reflective layer (e.g., metal) is present. (c)
Rotating the relative orientation of chip presented to the
direct write laser light for on-axis printing provides the
primary axis of the port to be presented co-linear with the
axis of the lithography beam to prevent obstruction of direct
write laser light and enable printing with an objective of any
working distance, regardless of the specific material stack
comprising the photonic chip, according to the Example.
FIG. 6 shows a results from off-axis and on-axis perspec-
tives of viewing conventional waveguides (a) and wave-
guides with adjacent optically visible bulk impregnated
barcode (b). From the off-axis perspective (a, i). features like

labels or waveguides are easily identifiable. From the on- 5

axis perspective (a, ii-iv), only the cross section of the
waveguide can be imaged, hence, the waveguide becomes a
small dot (a, ii) that can be confused with dust (a, iii) or
spurious reflections (a, iv) from surface imperfections. The

optically visible bulk impregnated barcode in (b) provides a

fiducial that can be read from both orientations with high
visibility and tolerance to surface imperfections due to its
large spatial extent. While in image (b, ii) the waveguide is
visible, in image (b, iii) the waveguide is not visible, and
reflections from contaminant particles are present. The cen-
ter of the waveguide is inferred after detection of barcode
members of the optically visible bulk impregnated barcode.
In panel (b, i), a DLW-printed micro-lens is printed at the
facet surface of the optically transparent direct laser writing
substrate, according to the Example.

FIG. 7 shows machine vision results with a optically
visible bulk impregnated barcode to determine the center of

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the waveguide that are more reliably than if the optically
visible bulk impregnated barcode is absent, even when
subject to imaging/facet imperfections, (a) An image from a
DLW system, with a optically visible bulk impregnated
barcode and a tapered Si,N, waveguide at its center. The
contrast in the image is determined by the index contrast
between the various materials and the illumination condi-
tions, (b) The uninterrupted high-contrast edge between the
underlying SiO, and Si layers is observed in the binary
output of a Canny edge detection algorithm. A Hough
transform is used to identify straight lines from Si—SiO,
and SisN,—SiO, edges in the Canny image. The detection
of the Si—SiO, edge and its angle @ with respect to
horizontal is overlaid on the original image in panel (c).
Barcode members are read by taking a 1D line scan along
the average of the top and bottom Si;N,—SiO2 edges,
according to the Example,

FIG. 8 shows the rectangle in (c, FIG. 7) that identifies a
region of interest that will be further processed using a
pre-generated binary template (a) that matches the region
(the tapered waveguide itself is omitted from the template,
since its presence in the original image is not assured, e.g.,
if imaging conditions are poor). The template is rotated by
the same angle 6 extracted from the Si—SiO, line. A
sub-pixel peak search in the cross correlation (b) between
the original image (a, FIG. 7) and the adjusted binary pattern
(a) determines the center of the waveguide (circle in (b)).
The final output of the process (c) determines the location of
the waveguide (circle), but neither the edge detection nor the
cross correlation assume the presence of a waveguide signal,
only a barcode signal. (d) Off-axis optical microscope image
of four lenses printed on the facet of waveguides surrounded
by the barcode pattern, according to the Example.

FIG. 9 shows results from an on-axis method for arrays of
micro-optic structures well-aligned to on-chip waveguides
that are printed with high yield. Elliptical lenses were
printed at the input facet of photonic chips with an optical
microscope image of twenty-one such lenses shown in (a).
Ascanning electron microscope image of one representative
lens is shown in (b) with the location of a Si,N, IO
waveguide in the plane of the chip, wherein the Si,N, is
located underneath 3 jum of SiO,, and the len: isposed on
the chip. The nominal design of the lens is shown in (c),
according to the Example.

FIG. 10 shows a fiber-to-chip coupling performance of
lenses as characterized with the configuration shown in (a),
wherein a 1550 nm fiber-coupled laser with polarization
control (pc) is optimally-coupled to the chip via one of three
fiber-based methods: lensed fibers, cleaved fibers, and
cleaved fibers with micro-optics on the facet of the chip
(referred to as “micro-optic method”). A zoom-in of the
coupling section for the three methods is shown in panel (b).
The output is collected through a lensed SMF-28e fiber in
each case. Once optimally coupled, the insertion losses are
measured, and the coupling sensitivity to misalignment is
assessed by displacing the input fiber in the x and y
directions to create excess-loss profiles. For TE polarization,
the electric field points along the x-axis, pm=polarization-
maintaining, according to the Example.

FIG. 11 shows misalignment tolerance and insertion loss
of the micro-optic coupling approach as measured and
compared against other end-fire coupling options. Two-
dimensional maps of the excess losses were generated for
each of the three cases shown in FIG. 9(c), with each case
averaged across 10 waveguides, according to the Example.

FIG. 12 shows excess loss maps (TE and TM polariza-
tions) for the case of the micro-optic show smooth, circular



U.S. Patent Nov. 15, 2022 Sheet 12 of 16 US 11,501,097 B2

-10 5

-10 5
Displacement (um)

“Micro Optic Cleaved Fiber Lensed Fiber.

FIG. 12


US 11,501,097 B2

11

In an embodiment, barcode-guided direct laser writing
includes receiving, by laser controller 220 of analyzer 212
that is in communication with direct write laser 207 and
processor 225 of analyzer 212, laser data 221 from processor
225; producing, by laser controller 220, direct write control
signal 219; communicating, from laser controller 220 to
direct write laser 207, direct write laser 207; producing, by
direct write laser light 214, direct write laser light 214 under
control of direct write control signal 219; receiving, by
imaging controller 222 of analyzer 212 that is in commu-
nication with light sensor 210 that acquires image 224 and
in communication with processor 225, image data 223 from
light sensor 210; communicating image data 223 from
imaging controller 222 to processor 225; and receiving, by
laser-substrate position controller 208 of analyzer 212 in
communication with translation stage 217 and in commu-
nication with processor 225, position control signal 213
from processor 225; producing, by laser-substrate position
controller 208, position control signal 213 and communi-
cating position control signal 213 from laser-substrate posi-
tion controller 208 to translation stage 217; and moving, by
translation stage 217, optically transparent direct laser writ-
ing substrate 201 relative to direct write laser light 214 under
control of position control signal 213.

In an embodiment, barcode-guided direct laser writing
includes receiving, by optically transparent direct laser writ-
ing substrate 201, direct write laser light 214 from direct
write laser 207, forming three-dimensional optical structures
in optically transparent direct laser writing substrate 201 in
response to receiving direct write laser light 214, and
forming integrated photonic chips comprising the three-
dimensional optical structures. Barcode-guided direct laser
written optical coupling 206 can include a lens for receiving
a laser light and optically coupling the laser light into or out
of the waveguide 202.

It should be appreciated that barcode-guided direct laser
writing includes direct laser writing of micro-optics (or other
structures) on facets of nanophotonic chips. Although con-
ventional approaches may rely on the approach shown in
FIG. 4, where a lithography beam is perpendicular to
transverse waveguide writing surface 205 in an off-axis
orientation. This leads to several limitations that can include
any of the following: the size or location of the object to be
printed are limited by the working distance of the lithogra-
phy objective; material compatibility is reduced due to the
strong absorption/reflectivity of certain materials (e.g. Si);
optical access to the input port of a chip may be obscured by
the chip itself or other structures on the device. This causes
a shadow to form along the optical path and leads to

distortions at the focal point, and thus in whatever device is 5

to be printed. Without correction, such distortions can cause
device performance degradation. Some conventional tech-
nologies compensate the shadowing effect using electro-
magnetic simulations that result in a structure-dependent and

spatially non-uniform exposure dose. However, such cor- 5

rections may not be universally applicable, for example, if
the layers of the photonic chip that partially obscure the
beam are highly absorbing or reflective.

Barcode-guided direct laser writing overcomes these
problem independently of structure and material by printing
directly on-axis with the device layer of a photonic chip on
facet surface 204 as shown in FIG. 3c. Printing in the on-axis
orientation involves accurate determination of the locations
at which elements are to be printed and is harder in the
on-axis orientation than the off-axis orientation because less
information is observable in an image taken from the on-axis
orientation from facet surface 204. That is, when printing in

20

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conventional off-axis orientation, the entire plane of the
device layer provides location information using, e.g., align-
ment mark 226. When viewed from facet surface 204, this
plane is contracted to a line, rendering conventional align-
ment mark 226 effectively useless, limiting the accuracy or
precision of localization techniques, and becoming sensitive
to imperfections on the chip facet.

Barcode-guided direct laser writing and barcoded end
facet printed photonic chip 200 provide edge-based local-
ization by presence of optically visible bulk impregnated
barcode 203 in the device layer of barcoded end facet printed
photonic chip 200. Optically visible bulk impregnated bar-
code 203 do not require any additional processing steps and
can be design changes to the mask used when fabricating
barcoded end facet printed photonic chip 200. Optically
visible bulk impregnated barcode 203 provide a distinct
pattern of barcode members 215 in on-axis imaging from
facet surface 204 that is robust to imperfections and con-
tamination of facet surface 204. Advantageously, controlling
barcode-guided direct laser writing with machine vision
processing robustly detects and identifies optically visible
bulk impregnated barcode 203 using image-processing tech-
niques and can accelerate commercialization of nanopho-
tonic devices. Furthermore. such provides new packaging
techniques that are not provided by off-axis printing such as
the interconnect that bridges two photonic chips that are
vertically stacked shown in FIG. 16. This type of connection
can form dense assemblies of optically-connected photonic
chips that otherwise would be very challenging to fabricate
via the off-axis printing orientation. Moreover, barcode-
guided direct laser writing aids automation of direct laser
writing for packaging of optical devices into more complex
systems for automatically printing micro-optic structures
that couple on-chip light to off-chip fibers or vice-versa.
Beneficially, barcode-guided direct laser writing avoids the
shadowing effect, removes size restrictions, and improves
material compatibility even in an absence of sophisticated
modeling tools that would otherwise be used when a new
structure is written. It will be appreciated that different types
of optical coupling elements can be fabricated with barcode-
guided direct laser writing. Moreover, barcoded end facet
printed photonic chip 200 can be made of various elements
and components that are microfabricated.

The articles and processes herein are illustrated further by
the following Example, which is non-limiting,

EXAMPLE

Automated On-Axis Direct Laser Writing of Coupling
Elements for Photonic Chips

Direct laser writing can create versatile micro-optic struc-
tures that facilitate photonic-chip coupling, like free-form
lenses, free-form mirrors, and photonic wire bonds. How-
ever, at the edges of photonic chips, the top-down/off-axis
printing orientation typically used limits the size and com-
plexity of structures and the range of materials compatible
with the DLW process, To avoid these issues, we develop a
DLW method, referred to as barcode-guided direct laser
writing. in which the photonic chip’s optical input/output
(10) ports can be co-linear with the axis of the lithography
beam (on-axis printing). Alignment automation and port
identification are enabled by a one-dimensional barcode-like
pattern that is fabricated within the chip’s device layer and
surrounds the IO waveguides to increase their visibility. We
demonstrate passive alignment to these markers using stan-
dard machine vision techniques, and print single-element
elliptical lenses along an array of 42 ports with a 100%



U.S. Patent Nov. 15, 2022 Sheet 3 of 16 US 11,501,097 B2

(Cy) 26 1



US 11,501,097 B2

5

profiles, as expected from axially-symmetric lenses. White
dashed lines on the maps indicate the -1 dB and -3 dB
contours, and black dashed lines indicate the location of x
and y line-scans used to compare the three coupling tech-
niques. The top (bottom) two line scan plots correspond to
data from the TE (TM) polarization, in which the electric
field points in the x (y) direction. Light-colored markers
indicate data from the ten waveguides, dark-colored markers
correspond to averages of the data, and dark-colored lines
correspond to Gaussian fits of the averaged data. These
line-scans show that the micro-optic approach has the great-
est misalignment tolerance, according to the Example.

FIG. 13 shows measurement results from per-facet inser-
tion losses, wherein the micro-optic method has on average
~2 dB more loss than lensed fibers, according to the
Example.

FIG. 14 shows 1 dB and 3 dB diameters for the micro-
optic method are around four times greater for the micro-

optic technique than they are for the lensed-fiber technique, 2

according to the Example.

FIG. 15 shows on-axis direct laser writing provides novel
chip-to-chip interconnects for stacking two photonic chips.
Printing at the edge of this system would be challenging in
the off-axis orientation because the top Si substrate is highly
absorbing at the wavelength of a 780 nm wavelength lithog-
raphy beam and is thicker than the working distance of the
objective, according to the Example.

FIG. 16 shows results from on-axis 3D printing of a
chip-to-chip photonic wire bond formed using an optically
visible bulk impregnated barcode in each waveguide layer
for alignment and guiding of the printing.

DETAILED DESCRIPTION.

A detailed description of one or more embodiments is
presented herein by way of exemplification and not limita-
tion.

Integrated photonic chips are used for a wide range of
applications. For many of these applications, coupling light
on and off of the photonic chip and into single optical fibers
or optical fiber arrays and coupling light from one photonic
chip to another photonic chip are desirable. Direct laser
writing (DLW) of micro-optic structures can provide such
optical coupling structures. The optical coupling structures
can include lenses, mirrors, and other optics that are created
in a polymer photoresist material by scanning of a focused
laser beam in three dimensions in a direct laser writing
process. These optical couplers are referred to as free-form

because an arbitrary three-dimensional (3D) structure can be s

created as long as it is mechanically stable and within
resolution limits of the DLW system. When printed directly
‘on a facet of a photonic chip, the micro-optic elements
provide an optical fiducial to print optical couplings that

overcomes misalignment and can be used for single fiber

coupling, fiber array coupling, and chip-to-chip coupling.
Printing micro-optic elements on the facets of photonic
chips presents technical challenges. A common configura-
tion for printing is with a microscope objective of the DLW
system oriented normal to the chip surface (off-axis) so that
printing occurs at a transverse waveguide writing surface.
With this orientation, it is easy to determine where the
printing should take place because the photonic chip ele-
ments are viewable, but the photonic chip obscures the direct
write laser light, impacting the quality of the micro-optic
element to be formed. The degree to which this is an issue
depends on many factors, including the material of the

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photonic chip, size of the micro-optic element, and depth
below transverse waveguide writing surface where that
element is to be centered.

If the photonic chip, referred to as the optically transpar-
ent direct laser writing substrate, is rotated so that the
microscope objective is oriented parallel to the chip surface
(referred to as being on-axis), the obfuscation of the direct
write laser light is overcome. But locating the specific
position for forming the micro-optic elements to be written
is removed if using conventional processes that involve a
conventional alignment mark that are typically viewable in
the off-axis orientation from transverse waveguide writing
surface and are not viewable in the on-axis orientation as
observed from the facet surface of the optically transparent
direct laser writing substrate.

Embodiments herein overcome the above problem by a
optically transparent direct laser writing substrate that
includes an optically visible bulk impregnated barcode dis-
posed proximate to the waveguide layer and that enables
on-axis printing at specified locations (i.e., the waveguide
inputs/outputs) with high accuracy and precision. The bar-
code members of the optically visible bulk impregnated
barcode are viewable from the facet surface in the on-axis
orientation of the optically transparent direct laser writing
substrate and can be detected, e.g., in an automated process
with machine vision, with a barcode-guided direct laser
writer.

Optical micro-machining with direct write laser light is a
direct-laser-write and rapid prototyping process for making
integrated photonic chips. Strong focusing of direct write
laser light into optically transparent direct laser writing
substrate can induce positive refractive index modifications
within the material and without surface damage. Direct laser
writing provides flexible 3D structuring of various glasses
and makes optical devices with selectively tailorable wave-
guides, couplers, Bragg gratings, wavepiates, and the like
are building blocks for 3D optical circuits.

Direct-laser-writing can confine strong nonlinear optical
interactions that may induce, e.g., positive or negative
refractive index changes in bulk transparent materials for
creating optical waveguides (WGs). The mechanisms by
which direct-laser-write modifications occur include, but are
not limited to, multiphoton ionization, avalanche ionization,
electron-atom collisions, plasma interactions, thermal
effects (e.g. diffusion, heat accumulation), energy dissipa-
tion, and material cooling leading to inhomogeneous solidi-
fication. For direct-laser-writing waveguides, waveguide
performance can be tuned and optimized by, but not limited
to, the properties (pulse duration, pulse temporal shape,
bandwidth and shape, pulse repetition rate, wavelength,
polarization, and beam spatial shape) of the direct write laser
light and the focusing conditions (lens numerical aperture,
air/liquid immersion, translation direction and speeds, and
the like)

Direct laser writing forms integrated photonic chips with
micro-optic and photonic waveguide chip-to-chip and fiber-
to-chip connections. However, conventional approaches, in
which the laser lithography beam is oriented perpendicular
to the chip surface, i.e., at the transverse waveguide writing
surface rather than the facet surface, are limited in that they
cannot write structures at any depth on chip facets and have
to be concerned with specific materials included in the
photonic chip. Moreover, conventional direct laser writing
can involve complicated, structure-dependent simulations.
Barcode-guided direct laser writing described herein
involves an optically visible bulk impregnated barcode to
locate the position of photonic waveguides when observed



US 11,501,097 B2

17

inspection revealed that the algorithm was able to success-
fully locate, align to, and print lenses on 42 out of 42 10
waveguides, on a single chip, from the on-axis perspective
(100% fabrication yield). Twenty-one of these lenses are
shown in FIG. 9(a). After localization, each lens took
approximately 20 seconds to polymerize from IP-Dip pho-
toresist. About half of the write time was occupied by the
auto focus procedure of the DLW system, The geometric
accuracy of the lenses was verified using scanning electron
microscope imaging (SEM). A representative SEM image of
one of the lenses is shown in FIG. 9(). Note that the lens
is well-aligned to the IO waveguide. For comparison, the
model of our design is illustrated in FIG. 9(c). From these
figures it is evident that the produced lens closely resembles
the model.

The accuracy of the alignment is limited by the mechani-
cal stability and imaging resolution of the DLW system. For
example, repeatedly using the autofocus function of the

DLW system returned slightly different values for the focal 2

point, and leaving the system alone for periods of several
minutes caused the mechanical stages to drift. Since the
micro-optic structures in this study printed in 20 seconds or
less, the errors due to the slow drift can be neglected. As
DLW systems become increasingly sophisticated, we expect
these errors to shrink. Depending on the application, it may
also be possible to design micro-opties that are tolerant to
miscalculation of the focal plane.

Ona second chip, ten waveguides were selected, with no
particular pre-screening, to verify that the on-axis printing
method was not introducing unexpected errors in either the
DLW process or the micro-optics themselves. Lenses that
decrease the sensitivity of fiber-to-chip coupling to fiber
misalignment were chosen to benchmark the fidelity of our
‘on-axis machine-aligned DLW process. The coupling effi-
ciency into each waveguide and its sensitivity to misalign-
ment was measured using the set-up shown in FIG. 10(a),
where a 1550 nm (polarization maintaining) fiber-coupled
laser was coupled into the on-chip waveguides using the
three methods highlighted in FIG. 10(6). The lensed fiber
method can be used in an end-fire technique due to its ability
to realize low insertion losses because of the small, focused
spot size it achieves (~2.5 jum mode field diameter) and its
natural compatibility with single mode optical fiber. How-
ever, it suffers from a high sensitivity to misalignment
because of the small size of this focused spot as well as the
small size of the mode at the optical waveguide facet. The
cleaved fiber method increases the mode field diameter
(MED) of the input fiber (nominally to ~10.5 jy), so this

method is expected to have a greater misalignment tolerance s

but also greater insertion losses due to the mode-size mis-
match between the fiber and the on-chip waveguide. The
micro-optic method attempts to bridge these extremes by
using an ellipsoidal lens as an intermediary mode-size

converter. In effect, this transfers the mode overlap problem

from fiber-to-chip to micro-optic-to-chip, with the latter
benefiting from the high positioning resolution of the DLW
system and the permanent adhesion of the micro-optic to the
chip.

Fach of the ten waveguides was tested with the three
coupling methods in both the TE and TM polarizations,
where TE (TM) polarization is defined as having the electric
field pointed along the x (y) axis of the device facet, based
on the coordinate system shown in FIG. 5(6) and FIG. 10.
Measurements included two-dimensional excess-loss_pro-
files created by displacing the input fiber along the x and y
directions in steps of dx and dy.

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18

The micro-optic structures selected for this examination
were ellipsoidal lenses with minor radii of 9.3 jum and focal
lengths of 20 um, SiN, waveguides were 550 nm thick,
tapered down to a 200 nm width at the chip facet, and had
a nominal mode field diameter of 2.5 jyum. The facets were
created by dicing and polishing with a nominal surface
roughness of 100 nm. Away from the facet, the waveguides
are | jim wide to reduce propagation losses.

FIG. 11 shows the excess loss profiles for the TE and TM
polarizations (averaged across all ten waveguides) of the
micro-optic coupling method with displacement steps
dx=dy=0.5 yim. The dashed white lines in the figure cor-
respond to the -1 dB and -3 dB contours, which are smooth
and circular as expected due to the axial symmetry of
elliptical lenses. The excess loss profiles are normalized with
respect to the averaged peak efficiency of the coupling
method, the explicit values of which are listed in the scatter
plots of FIG. 13.

‘To compare the three coupling techniques, FIG. 12 shows
line-scans along the x and y axes for each configuration. In
this image the light-colored markers correspond to the data
from the ten waveguides, and the dark-colored markers
correspond to averages of the data. The dark-colored lines
correspond to Gaussian fits of the averaged data. The data

5 show the expected trend: coupling methods that overlap

large optical modes are more tolerant to displacement, and
the micro-optic method (in which the fiber and lens both
have large modes) has the greatest amount of displacement
tolerance. This trend is quantified in FIG. 14, where the -1
dB and -3 dB diameters are reported. The uncertainty in
these measurements is the standard deviation of the diam-
eters about their average, and the leading source of mea-
surement error is laser power fluctuations while the leading
source of variation from waveguide to waveguide is likely
the lens quality.

The insertion loss (FIG. 13) for each coupling technique
was measured for each of the ten waveguides in both
polarizations, where we have assumed that all losses are due
to facet coupling. From initial calculations, we expected the
micro-optic method to perform on par with the lensed fiber
method, but the micro-optics introduced an insertion loss
penalty as small as ~1 dB and ~2 dB on average. 3D FDTD
simulations show that errors in the micro-optic placement
would need to be at the 1 pum level (far greater than the
maximum placement error we observe experimentally (e.g.
FIG. 9(4)) to account for the discrepancy between measured
and simulated insertion losses. We believe that the added
loss is likely due to imperfections in the lens fabrication,
resulting from an un-optimized lithography process. For the
specific DLW system we use, a transition from the current
fast printing mode to a slower printing mode is expected to
come with an improvement in micro-optic surface quality.

The on-axis printing of barcode-guided direct laser writ-
ing reads barcode patterns and aligns to waveguides from
the on-axis perspective for configurations in chip-to-chip
interconnects. While photonic wire bonding has achieved
great success in realizing low loss interconnection between.
laterally adjacent photonic chips, the lateral footprint can be
limited, and stacks of chips can be made. For the stack of
two chips shown in FIG. 15, Chip B is identical to Chip A
(besides its upside down orientation), but this need not be
the case. Instead, the chips could be composed of completely
different layer stacks. Such chip stacking might be useful for
increasing the density of photonic devices or for combining
the properties of otherwise incompatible materials. One
possible solution would be to make a chip-to-chip intercon-
nect that utilizes the barcode patterns in each chip (FIG. 15)



US 11,501,097 B2

9

printing orientation (panel A, FIG. 3) or an on-axis printing
orientation (panel B, FIG. 3) with respect to direct write
laser 207; direct write laser 207 in optical communication
with optically transparent direct laser writing substrate 201
and that produces direct write laser light 214; optical objec-
tive 209 in optical communication with optically transparent
direct laser writing substrate 201 and that receives image
224 of optically transparent direct laser writing substrate
201; light sensor 210 in optical communication with opti-
cally transparent direct laser writing substrate 201 via opti-
cal objective 209 and that receives image 224 from optical
objective 209 and produces image data 223 from image 224;
analyzer 212 in electrical communication with direct write
laser 207, light sensor 210, and translation stage 217 and
that: controls direct write laser 207 so that direct write laser
207 produces direct write laser light 214 under the control of
analyzer 212; receives image data 223 from light sensor 210
and controls direct write laser 207 and translation stage 217
based on image data 223; determines a position of wave-
guide 202 in optically transparent direct laser writing sub-
strate 201 relative to optically visible bulk impregnated
barcode 203 disposed in optically transparent direct laser
writing substrate 201; and controls translation stage 217 so
that translation stage 217 positions optically transparent
direct laser writing substrate 201 relative to direct write laser
207 under control of analyzer 212 to make barcode-guided.
direct laser written optical coupling 206 on facet surface 204
of optically transparent direct laser writing substrate 201 to
form barcoded end facet printed photonic chip 200 from
optically transparent direct laser writing substrate 201 via
barcode-guided direct laser writing, wherein optically trans-
parent direct laser writing substrate 201 forms barcode-
guided direct laser written optical coupling 206 in response
to receipt of direct write laser light 214 from direct write
laser 207 at facet surface 204, and optically transparent
direct laser writing substrate 201 includes: transverse wave-
guide writing surface 205 that receives direct write laser
light 214 when disposed on translation stage 217 for off-axis
direct write laser printing and facet surface 204 that receives
direct write laser light 214 when disposed on translation
stage 217 for on-axis direct write laser printing of barcode-
guided direct laser written optical coupling 206 on facet
surface 204; waveguide 202 disposed in optically transpar-
ent direct laser writing substrate 201 and in optical commu-
nication with facet surface 204; and optically visible bulk
impregnated barcode 203 disposed in optically transparent
direct laser writing substrate 201 arranged proximate to
waveguide 202 and in optical communication with facet
surface 204.

In an embodiment, analyzer 212 includes: laser controller 5

220 in communication with direct write laser 207 and in
communication with processor 225 and that receives laser
data 221 from processor 225 and produces direct write
control signal 219 that is communicated from laser control-

ler 220 to direct write laser 207, such that direct write laser 5

207 produces direct write laser light 214 under control of
direct write control signal 219; imaging controller 222 in
communication with light sensor 210 and in communication
with processor 225 and that receives image data 223 from
light sensor 210 and communicates image data 223 to
processor 225; and laser-substrate position controller 208 in
communication with translation stage 217 and in commu-
nication with processor 225 and that receives position con-
trol signal 213 from processor 225 and produces position
control signal 213 that is communicated from laser-substrate
position controller 208 to translation stage 217, such that
translation stage 217 moves optically transparent direct laser

20

&

&

10

writing substrate 201 relative to direct write laser light 214
under control of position control signal 213.

In an embodiment, optically transparent direct laser writ-
ing substrate 201 receives direct write laser light 214 from
direct write laser 207, forms three-dimensional optical struc-
tures in optically transparent direct laser writing substrate
201 in response to receiving direct write laser light 214, and
forms integrated photonic chips including the three-dimen-
sional optical structures.

In an embodiment, a process for barcode-guided direct
laser writing of optically transparent direct laser writing
substrate 201 includes: receiving optically transparent direct
laser writing substrate 201 on translation stage 217 so that
facet surface 204 of optically transparent direct laser writing
substrate 201 is in optical communication with direct write
laser 207, optically transparent direct laser writing substrate
201 includes: transverse waveguide writing surface 205 that
receives direct write laser light 214 when disposed on
translation stage 217 for off-axis direct write laser printing
and facet surface 204 that receives direct write laser light
214 when disposed on translation stage 217 for on-axis
direct write laser printing of barcode-guided direct laser
written optical coupling 206 on facet surface 204; wave-

5 guide 202 disposed in optically transparent direct laser

writing substrate 201 and in optical communication with
facet surface 204; and optically visible bulk impregnated
barcode 203 disposed in optically transparent direct laser
writing substrate 201 and arranged proximate to waveguide
202 and in optical communication with facet surface 204;
producing direct write laser light 214 by direct write laser
207; acquiring image 224 of facet surface 204 with optically
visible bulk impregnated barcode 203 and waveguide 202
observable in image 224; analyzing the image to determine
the position of waveguide 202 relative to optically visible
bulk impregnated barcode 203; positioning optically trans-
parent direct laser writing substrate 201 relative to direct
write laser light 214 from direct write laser 207 so that direct
write laser light 214 is received at facet surface 204 on-axis
at a position corresponding to waveguide 202 in optically
transparent direct I: writing substrate 201; and forming,
in response to receiving direct write laser 207 at facet
surface 204, barcode-guided direct laser written optical
coupling 206 on facet surface 204 on-axis at the position
corresponding to waveguide 202 in the optically transparent
direct laser writing substrate 201 to form barcoded end facet
printed photonic chip 200 from optically transparent direct
laser writing substrate 201.

Tn an embodiment, analyzing the image to determine the
position of waveguide 202 relative to optically visible bulk
impregnated barcode 203 includes: controlling direct write
laser 207 so that direct write laser 207 produces direct write
laser light 214 under the control of direct write control signal
219; controlling direct write laser 207 and translation stage
217 based on image 224 of optically transparent direct laser
writing substrate 201; determining a position of waveguide
202 in optically transparent dire r writing substrate 201
relative to optically visible bulk impregnated barcode 203
disposed in optically transparent direct laser writing sub-
strate 201; and controlling translation stage 217 so that the
translation stage 217 positions optically transparent direct
laser writing substrate 201 relative to direct write laser 207
to make barcode-guided direct laser written optical coupling
206 on facet surface 204 of optically transparent direct laser
writing substrate 201 to form barcoded end facet printed
photonic chip 200 from the optically transparent direct laser
writing substrate 201.



U.S. Patent Nov. 15, 2022 Sheet 16 of 16 US 11,501,097 B2

FIG. 16


U.S. Patent Nov. 15, 2022 Sheet 8 of 16 US 11,501,097 B2

Omrotation artifact no waveguide in templat

vA

a

(a)

FIG. 8


US 11,501,097 B2

23

6. The barcoded end facet printed photonic chip of claim
5, wherein the barcode members are distributed laterally
with respect to the waveguide as observed from the facet
surface.
7. The barcoded end facet printed photonic chip of claim
1, wherein the optically transparent direct laser writing
substrate comprises a polymer, glass, or a combination
comprising polymer and glass.
8. The barcoded end facet printed photonic chip of claim
1, wherein the facet surface is arranged at an oblique angle
to the transverse waveguide writing surface.
9. A barcode-guided direct laser writer for barcode-guided
direct laser writing of an optically transparent direct laser
writing substrate, the barcode-guided direct laser writer
comprising:
a translation stage that receives an optically transparent
direct laser writing substrate in an off-axis printing
orientation or an on-axis printing orientation with
respect to a direct write laser;
a direct write laser in optical communication with the
optically transparent direct laser writing substrate and
that produces direct write laser light;
an optical objective in optical communication with the
optically transparent direct laser writing substrate and
that receives an image of the optically transparent
direct laser writing substrate;
a light sensor in optical communication with the optically
transparent direct laser writing substrate via the optical
objective and that receives the image from the optical
objective and produces image data from the image;
an analyzer in electrical communication with the direct
write laser, the light sensor, and the translation stage
and that:
controls the direct write laser so that the direct write
laser produces the direct write laser light under the
control of the analyzer;

receives the image data from the light sensor and
controls the direct write laser and the translation
stage based on the image data;

determines a position of a waveguide in the optically
transparent direct laser writing substrate relative to
an optically visible bulk impregnated barcode di
posed in the optically transparent direct laser writing
substrate; and

controls the translation stage so that the translation
stage positions the optically transparent direct laser
writing substrate relative to the direct write laser
under control of the analyzer to make a barcode-

guided direct laser written optical coupling ona facet 5

surface of the optically transparent direct laser writ-
ing substrate to form a barcoded end facet printed
photonic chip from the optically transparent direct
laser writing substrate via barcode-guided direct
laser writing,
wherein the optically transparent direct laser writing
substrate forms a barcode-guided direct laser written
optical coupling in response to receipt of the direct
write laser light from the direct write laser at the facet
surface, and
the optically transparent direct laser writing substrate
comprises:

a transverse waveguide writing surface that receives the
direct write laser light when disposed on the trans-
lation stage for off-axis direct write laser printing and
the facet surface that receives the direct write laser
light when disposed on the translation stage for

20

0

4

4

35

0

5

24

on-axis direct write laser printing of the barcode-
guided direct laser written optical coupling on the
facet surface;

a waveguide disposed in the optically transparent direct
laser writing substrate and in optical communication
with the facet surface; and

the optically visible bulk impregnated barcode dis-
posed in the optically transparent direct laser writing
substrate arranged proximate to the waveguide and
in optical communication with the facet surface.

10. The barcode-guided direct laser writer of claim 9,

wherein the analyzer comprises:

a laser controller in communication with the direct write
laser and in communication with a processor and that
receives laser data from the processor and produces a
direct write control signal that is communicated from
the laser controller to the direct write laser, such that the
direct write laser produces the direct write laser light
under control of the direct write control signal;

an imaging controller in communication with the light

sensor and in communication with the processor and

that receives the image data from the light sensor and
communicates the image data to the processor; and
laser-substrate position controller in communication
with the translation stage and in communication with
the processor and that receives a position control signal
from the processor and produces a position control
signal that is communicated from the laser-substrate
position controller to the translation stage, such that the
translation stage moves the optically transparent direct
laser writing substrate relative to the direct write laser
light under control of the position control signal.

11. The barcode-guided direct laser writer of claim 9,

ey

wherein the optically visible bulk impregnated barcode
comprises a plurality of barcode members.

12. The barcode-guided direct laser writer of claim 11,

wherein the barcode members are distributed laterally with
respect to the waveguide as observed from the facet surface.

13. The barcode-guided direct laser writer of claim 9,

wherein the barcode-guided direct laser written optical cou-
pling comprises a lens for receiving a laser light and
optically coupling the laser light into or out of the wave-
guide.

14. The barcode-guided direct laser writer of claim 9,

wherein the optically transparent direct laser writing sub-
strate receives the direct write laser light from the direct
write laser, forms three-dimensional optical structures in the
optically transparent direct laser writing substrate in
response to receiving the direct write laser light, and forms
integrated photonic chips comprising the three-dimensional
optical structures.

15. The barcode-guided direct laser writer of claim 9,

wherein the facet surface is arranged at an oblique angle to
the transverse waveguide writing surface.

16. A process for barcode-guided direct laser writing of an

optically transparent direct laser writing substrate, the pro-
cess comprising:

receiving an optically transparent direct laser writing
substrate on a translation stage so that a facet surface of
the optically transparent direct laser writing substrate is
in optical communication with a direct write laser, the
optically transparent direct laser writing substrate com-
prises:

a transverse waveguide writing surface that receives
direct write laser light when disposed on the trans-
lation stage for off-axis direct write laser printing and
the facet surface that receives the direct write laser


US 11,501,097 B2

Sheet 5 of 16

Novy. 15, 2022

U.S. Patent

(A)

201

202

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US 11,501,097 B2

Sheet 4 of 16

Novy. 15, 2022

U.S. Patent

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US 11,501,097 B2

1
BARCODED END FACET PRINTED
PHOTONIC CHIP AND BARCODE-GUIDED
DIRECT LASER WRITING

CROSS REFERENCE TO RELATED
APPLICATIONS,
This application claims the benefit of U.S. Provisional

Patent Application Ser. No. 63/078,550 (filed Sep. 15, 2020),
which is herein incorporated by reference in its entirety.

MENT REGARDING FEDERALLY
SPONSORED RESEARCH

This invention was made with United States Government
support from the National Institute of Standards and ‘Tech-
nology (NIST), an agency of the United States Department
of Commerce. The Government has certain rights in this
invention.

BRIEF DESCRIPTION

Disclosed is a barcoded end facet printed photonic chip
comprising: an optically transparent direct laser writing
substrate comprising a transverse waveguide writing surface
to receive a direct write laser light for off-axis direct write
laser printing and a facet surface to receive the direct write
laser light for on-axis direct write laser printing of a barcode-
guided direct laser written optical coupling on the facet
surface; a waveguide disposed in the optically transparent
direct laser writing substrate and in optical communication
with the facet surface; and an optically visible bulk impreg-
nated barcode disposed in the optically transparent direct
laser writing substrate arranged proximate to the waveguide
and in optical communication with the facet surface.
Disclosed is a barcode-guided direct laser writer for
barcode-guided direct laser writing of an optically transpar-
ent direct laser writing substrate, the barcode-guided direct
laser writer comprising: a translation stage that receives an
optically transparent direct laser writing substrate in an
off-axis printing orientation or an on-axis printing orienta-
tion with respect to a direct write laser; a direct write laser
in optical communication with the optically transparent
direct laser writing substrate and that produces direct write
laser light; an optical objective in optical communication
with the optically transparent direct laser writing substrate
and that ives an image of the optically transparent direct
laser writing substrate; a light sensor in optical communi-
cation with the optically transparent direct laser writing

substrate via the optical objective and that receives the s

image from the optical objective and produces image data
from the image; an analyzer in electrical communication
with the direct write laser, the light sensor, and the transla-
tion stage and that: controls the direct write laser so that the

direct write laser produces the direct write laser light under s

the control of the analyzer; receives the image data from the
light sensor and controls the direct write laser and the
translation stage based on the image data; determines a
position of a waveguide in the optically transparent direct
laser writing substrate relative to an optically visible bulk
impregnated barcode disposed in the optically transparent
direct laser writing substrate; and controls the translation
stage so that the translation stage positions the optically
transparent direct laser writing substrate relative to the direct
write laser under control of the analyzer to make a barcode-
guided direct laser written optical coupling on a facet
surface of the optically transparent direct laser writing

20

&

&

0

2

substrate to form a barcoded end facet printed photonic chip
from the optically transparent direct laser writing substrate
via barcode-guided direct laser writing, wherein the opti-
cally transparent direct laser writing substrate forms a bar-
code-guided direct laser written optical coupling in response
to receipt of the direct write laser light from the direct write
laser at the facet surface, and the optically transparent direct
laser writing substrate comprises: a transverse waveguide
writing surface that receives the direct write laser light when
disposed on the translation stage for off-axis direct write
laser printing and the facet surface that receives the direct
write laser light when disposed on the translation stage for
on-axis direct write laser printing of the barcode-guided
direct laser written optical coupling on the facet surface: a
waveguide disposed in the optically transparent direct laser
writing substrate and in optical communication with the
facet surface; and the optically visible bulk impregnated
barcode disposed in the optically transparent direct laser
writing substrate arranged proximate to the waveguide and
in optical communication with the facet surface.

Disclosed is a process for barcode-guided direct laser
writing of an optically transparent direct laser writing sub-
strate, the process comprising: receiving an optically trans-
parent direct laser writing substrate on a translation stage so
that a facet surface of the optically transparent direct laser
writing substrate is in optical communication with a direct
write laser, the optically transparent direct laser writing
substrate comprises: a transverse waveguide writing surface
that receives direct write laser light when disposed on the
translation stage for off-axis direct write laser printing and
the facet surface that receives the direct write laser light
when disposed on the translation stage for on-axis direct
write laser printing of the barcode-guided direct laser written
optical coupling on the facet surface; a waveguide disposed
in the optically transparent direct laser writing substrate and
in optical communication with the facet surface; and an
optically visible bulk impregnated barcode disposed in the
optically transparent direct laser writing substrate and
arranged proximate to the waveguide and in optical com-
munication with the facet surface. producing direct write
laser light by the direct write laser; acquiring an image of the
facet surface with the optically visible bulk impregnated
barcode and the waveguide observable in the image; ana-
lyzing the image to determine the position of the waveguide
relative to the optically visible bulk impregnated barcode;
positioning the optically transparent direct laser writing
substrate relative to the direct write laser light from the
direct write laser so that the direct write laser light is
received at the facet surface on-axis at a position corre-
sponding to the waveguide in the optically transparent direct
laser writing substrate; and forming, in response to receiving
the direct write laser at the facet surface, a barcode-guided
direct laser written optical coupling on the facet surface
on-axis at the position corresponding to the waveguide in the
optically transparent direct laser writing substrate to form a
barcoded end facet printed photonic chip from the optically
transparent direct laser writing substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description cannot be considered limiting
in any way. Various objectives, features, and advantages of
the disclosed subject matter can be more fully appreciated
with reference to the following detailed description of the
disclosed subject matter when considered in connection with
the following drawings, in which like reference numerals
identify like elements.


U.S. Patent Nov. 15, 2022 Sheet 7 of 16 US 11,501,097 B2

tapered waveguide

FIG. 7


US 11,501,097 B2

13

fabrication yield. These lenses improve fiber-to-chip m
alignment tolerance relative to other fiber-based coupling
techniques. The 1 dB excess loss diameter increases from
~2.3 um when using a lensed fiber to ~9.9 jum when using
the DLW printed micro-optic and a cleaved fiber. The
insertion loss penalty introduced by moving to this misalign-
ment-tolerant coupling approach is limited, with an addi-
tional loss (in comparison to the lensed fiber) as small as ~1
dB and ~2 dB on average. On-axis printing can accommo-
date a variety of multi-element free-space and guided wave
coupling elements, without requiring calibration of printing
dose specific to the geometry of the 3D printed structure or
to the materials comprising the photonic chip. It also enables
interconnection between chips such as in a 3D photonic wire
bond between two vertically stacked photonic chips.

Nanophotonic devices created in photonic chips have
ushered in significant advances in computer and data com-
munications, sensing, nonlinear optics, and quantum optics.
Even so, efficient and robust optical coupling between
‘on-chip devices and the outside world remains a challenging
problem. As the exciting applications of nanophotonic tech-
nologies continue to mature, the importance of robust and
cost-effective packaging methods will become a pressing
priority, given that they already present a significant bottle-
neck in the commercialization of photonic integrated circuits
(PICS).

Fiber-to-chip coupling can include end-fire approaches,
wherein inverse tapered Waveguides can be implemented to
improve efficiency, End-fire techniques, such as the use of
lensed optical fibers that easily produce a focused optical
spot from a standard single mode fiber input, offer a large
coupling bandwidth and ease of use, but often suffer from a
high sensitivity to misalignment. Depending on the on-chip
waveguide geometry, a lensed fiber may have a 1 dB
misalignment tolerance of +0.5u+0.5 um to #l+l jum,
which is difficult to satisfy using passive alignment. In
contrast, grating couplers can extend this tolerance signifi-
cantly, but (in general) they suffer from smaller coupling
bandwidths and often require additional fabrication steps to
achieve high efficiency coupling,

Direct laser writing provides miniaturization of linear
optical elements for versatility in the nanophotonics plat-
form. DLW can be used to create free-form lenses, total-
internal-reflection mirrors, and photonic wire bonds that
improve fiber-to-chip coupling for photonic chips. The flex-
ibility of DLW systems permits creation of plug-and-play-
type solutions and broadband out-of-plane coupling, Despite
the tremendous progress made with DLW, its implementa-
tion is still challenging in some contexts. Specifically, this

includes the ability to write structures at any depth on the

chip facets, without regard to the specific materials com-
prising the chip, and without the need for complicated,
structure-dependent simulations.

In this Example, barcode-guided direct laser writing

involves machine vision with barcode-like patterns to over- 5

come the aforementioned fabrication challenges associated
with printing micro-optic elements on chip facets (i.c.,
input/output (IO) ports). Conventional DLW methods have
lithography beams that get obstructed when printing at the
edge of the chip, reducing the size and optical quality of the
printed micro-optics and limiting the materials compatible
with the DLW process. To solve these issues, barcode-
guided direct laser writing orients photonic chips so that the
lithography beam can access the IO facet of a photonic chip
without obstruction. Printing from this orientation can
include labeling and detection of very small features 200 nm
length scale), which are problems simultaneously solved by

20

4

&

14

incorporating high-visibility information-encoding barcode-
like markers. A machine-vision process can include image
processing techniques that reliably detects, reads, and
aligns-to the barcode patterns. Using barcode-guided direct
laser writing, micro-optic lenses were formed along an array
of waveguides as well as a photonic wire bond between
vertically stacked chips.

Challenges with Off-Axis Printing

Printing micro-optic elements on facets of photonic chips
was done conventionally with top-down (off-axis) printing,
resulting in challenges due to the orientation of the chip with
respect to the lithography beam. Consider the photonic chip
schematically depicted in FIG. (a), where a waveguide core
is embedded in a lower refractive index cladding on top of
an opaque substrate. The waveguide core can be made of
materials like Si, Si,N,, or GaAs, and the cladding can be
SiO,. The IO ports of the waveguide employ an inverse taper
geometry, which improves coupling to optical fibers by
better matching the mode profile of the waveguide to that of
the fiber.

Attempting to print on the IO port of such a typical chip
in the conventional manner, from the top-down (off-axis)
perspective shown in FIG. 5(b), can limit the micro-optic
structure. The size and depth of the structure can be limited

5 by the working distance of the objective. The waveguiding

layer is just a few micrometers below the chip surface so that
this is not a practical limitation, and there are scenarios in
which this is not the case, including 3D assemblies of chip
stacks or highly integrated systems in which metallic layers
associated with control electronics lie above the photonics.
Near the facet, the lithography beam will partially overlap
with the chip, as shown in FIG. 5(b), causing aberrations that
distort the focal point. This is known as the shadowing
effect, and previous studies indicate that it can decrease the
effective dose at the focal point and deteriorate the quality of
the focused beam. One can dynamically adjust the power of
the beam so that the effective dose remains constant, but this
requires dispersion simulations for each micro-optic design
and still suffers from decreased focal spot quality. It may be
assumed that the layers of the photonic chip are transparent
at the wavelength of the lithography beam, so that the
primary effect is dispersive. The photonic chip can contain
reflective and absorptive layers like metallic traces or silicon
layers which absorb commonly used lithography wave-
lengths (e.g., 780 nm), These layers would cause a signifi-
cant distortion of the lithography beam and would be hard to
compensate.

On-Axis Printing with Barcode Patterns

To circumvent the issues associated with off-axis printing,
we propose writing structures in the on-axis orientation
shown in FIG. 5(c), so that the IO facet of a chip is
perpendicular to the lithography beam. This change in
orientation removes limitations on the micro-optic size set
by the working distance of the objective, avoids any obstruc-
tion of the lithography beam, and reduces the possibility of
unwanted absorption/reflections since the lithography beam
interacts only with the facet of the device, rather than each
boundary in the layer stack. On the other hand, orienting the
chip for on-axis printing introduces a new set of challenges,
primarily related to the ability to image the facet well
enough for high-accuracy localization of the waveguide
terminations (IO ports). We note that this challenge is
distinct from that faced in previous implementations of
DLW in on-axis configurations, where, for example, struc
tures have been written on the facets of optical fibers. In such.
instances, injection of laser light into the fiber could enable
its active alignment to the lithography beam, while passive



United States Patent

US011501097B2

(12) (0) Patent No.: US 11,501,097 B2
Srinivasan et al. (45) Date of Patent: Nov. 15, 2022
(54) BARCODED END FACET PRINTED (58) Field of Clas: n Search
PHOTONIC CHIP AND BARCODE-GUIDED CPC ... .. GO6K 7/1408; GO6K 7/10742
DIRECT LASER WRITING See application file for complete search history.
(71) Applicant: Government of the United States of (56) References d
America, as represented by the
Seeretary of Commerce, Gaithersburg, U.S. PATENT DOCUMENTS
MD (US) 5,018,813 A * 5/1991 Roddy HOAN 1/1911
385/16
(72) Inventors: Kartik Arvind Srinivasan, Rockville, 9,933,574 BI® 4/2018 Zhang ceennn. GO2B 6/4239
MD (US); Edgar F. Perez, College
Park, MD (US) OTHER PUBLICATIONS
(73) Assignee: GOVERNMENT OF THE UNITED Billah, M.R., et al., “Hybrid integration of silicon photonics circuits
STATES OF AMERICA, AS and InP lasers by photonic wire bonding”, Optica, 2018, p. 876-883,
REPRESENTED BY THE vol. 5 No. 7.
SECRETARY OF COMMERCE, Dietrich, P-1, et al., “In situ 3D nanoprinting of free-form coupling
elements for hybrid photonic integration”, Nature Photonics, 2018,
Gaithersburg, MD (US) cee wt
(*) Notice: Subject to any disclaimer, the term of this (Continued)
want by Oda under 35 yimary Examiner — Jamara A Franklin
(74) Attorney, Agent, or Firm — Office of Chief Counsel
(21) Appl. No.: 17/476,020 for National Institute of Standards and ‘Technology
(22) Filed: Sep. 15, 2021 67) ABSTRACT
‘A barcoded end facet printed photonic chip includes: an
(65) Prior Publication Data optically transparent direct laser writing substrate including
US 2022/0083755 Al Mar. 17, 2022 a transverse waveguide writing surface to receive a direct
. a write laser light for off-axis direct write laser printing and a
Related U.S. Application Data facet surface to receive the direct write laser light for on-axis
; : direct write laser printing of a barcode-guided direct laser
(60) Provisional application No. 63/078,550, filed on Sep. _written optical coupling on the facet surface; a waveguide
15, 2020. disposed in the optically transparent direct laser writing
, substrate and in optical communication with the facet sur-
(51) Int. Cl. face; and an optically visible bulk impregnated barcode
GOK 7/14 (2006.01) disposed in the optically transparent direct laser writing
06K 7/10 (2006.01) substrate arranged proximate to the waveguide and in optical
(52) U.S. CL communication with the facet surface.
cpc G06K 7/1408 (2013.01); GO6K 7/10742

(2013.01)

20 Claims, 16 Drawing Sheets

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US 11,501,097 B2

Sheet 10 of 16

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U.S. Patent Nov. 15, 2022 Sheet 9 of 16 US 11,501,097 B2

FIG. 9


US 11,501,097 B2

25

light when disposed on the translation stage for
on-axis direct write laser printing of the barcode-
guided direct laser written optical coupling on the
facet surface;

a waveguide disposed in the optically transparent direct
laser writing substrate and in optical communication
with the facet surface; and

an optically visible bulk impregnated barcode disposed
in the optically transparent direct laser writing sub-
strate and arranged proximate to the waveguide and
in optical communication with the facet surface;

producing direct write laser light by the direct write laser;

acquiring an image of the facet surface with the optically
visible bulk impregnated barcode and the waveguide
observable in the image;

analyzing the image to determine the position of the

waveguide relative to the optically visible bulk impreg-

nated barcode;

positioning the optically transparent direct laser writing

substrate relative to the direct write laser light from the
direct write laser so that the direct write laser light is
received at the facet surface on-axis at a position
corresponding to the waveguide in the optically trans-
parent direct laser writing substrate; and

forming, in response to receiving the direct write laser at

the facet surface, a barcode-guided direct laser written

optical coupling on the facet surface on-axis at the
position corresponding to the waveguide in the opti-
cally transparent direct laser writing substrate to form

a barcoded end facet printed photonic chip from the

optically transparent direct laser writing substrate.

17. The process of claim 16, wherein analyzing the image
to determine the position of the waveguide relative to the
optically visible bulk impregnated barcode comprises

controlling the direct write laser so that the direct write

laser produces the direct write laser light under the
control of a direct write control signal;

controlling the direct write laser and the translation stage

based on image of the optically transparent direct laser

writing substrate:

determining a position of the waveguide in the optically

transparent direct laser writing substrate relative to the

optically visible bulk impregnated barcode disposed in
the optically transparent direct laser writing substrate:
and

controlling the translation stage so that the translation

stage positions the optically transparent direct laser

writing substrate relative to the direct write laser to
make the barcode-guided direct laser written optical

0

4

26

coupling on the facet surface of the optically transpar-
ent direct laser writing substrate to form the barcoded
end facet printed photonic chip from the optically
transparent direct laser writing substrate.
18. The process of claim 17, further comprising:
receiving, by a laser controller of an analyzer that is in
communication with the direct write laser and a pro-
cessor of an analyzer, laser data from the processor;

producing, by the laser controller, a direct write control
signal;

communicating, from the laser controller to the direct

write laser, the direct write laser;

producing, by the direct write laser light, the direct write

laser light under control of the direct write control
signal;

receiving, by an imaging controller of the analyzer that is

in communication with a light sensor that acquires the
image and in communication with the processor: the
image data from the light sensor;

communicating the image data from the imaging control-

ler to the processor; and

receiving, by a laser-substrate position controller of the

analyzer in communication with the translation stage
and in communication with the processor, a position
control signal from the processor;

producing, by the laser-substrate position controller, a

position control signal and communicating the position
control signal from the laser-substrate position control-
ler to the translation stage: and

moving, by the translation stage, the optically transparent

direct laser writing substrate relative to the direct write
laser light under control of the position control signal.

19. The process of claim 16, wherein the optically visible
bulk impregnated barcode comprises a plurality of barcode
members that are distributed laterally with respect to the
waveguide as observed from the facet surface.

20. The process of claim 16, further comprising receiving,
by the optically transparent direct laser writing substrate, the
direct write laser light from the direct write laser, forming
three-dimensional optical structures in the optically trans-
parent direct laser writing substrate in response to receiving
the direct write laser light, and forming integrated photonic
chips comprising the three-dimensional optical structures,

wherein the barcode-guided direct laser written optical

coupling comprises a lens for receiving a laser light and
optically coupling the laser light into or out of the
waveguide.



U.S. Patent Nov. 15, 2022 Sheet 6 of 16 US 11,501,097 B2

(a) Conventional photonic chip without barcode

off-axis “on-axis

(b) Waveguide + Barcode

206

204

x03 fe dust — \

202 _ .

on-axis
FIG. 6


US 11,501,097 B2

7

on-axis via facet surface. Accordingly, barcode-guided
direct laser writing is fast and scalable for on-axis, facet-
based DLW that can operate autonomously and overcome
aforementioned issues and technical deficiencies of conven-
tional direct laser writing.

Embodiments provide for optical packaging, fabrication,
and optical packages that are compatible with integration of
optoelectronic components. Certain embodiments employ a
three-dimensional direct-write lithography system (referred
to as a barcode-guided direct laser writer) for writing
deeply-buried, localized index structures into a diffusion-
mediated photopolymer. Barcode-guided direct laser writ-
ing, the barcoded end facet printed photonic chip, and the
barcode-guided direct laser writer described herein provide
advantages that include greater flexibility in the writing
media (e.g., optically transparent direct laser writing sub-
strate) and the use of low power, inexpensive, continuous-
wave lasers. Index structures are written both parallel and
perpendicular to the writing beam in different types of
photopolymers, providing control over the feature size and
shape. Embodiments provide systems that can be fully
automatic, compact, mechanically robust, and inexpensive
to operate for both large and small production volumes.
Certain embodiments provide low cost and short processing
cycles. Optical circuit components can be assembled with
selective tolerances that can include fiber pig tailing or
external packaging, producing an apparatus or article that is
ready to ship after it comes off of the machine.

Conventional two-dimensional lithographic processing of
photonic chips can include fiducial markings for sighting or
alignment of etching and patterning of features in a single
direction of exposure in a mainly planar arrangement
through use of lithographic masks and etching with depo-
sition through processes such as chemical vapor deposition.
However, as noted above, these conventional process do not
provide high-fidelity facet production of optical elements,
and the barcode-guided direct laser writing, the barcoded
end facet printed photonic chip, and the barcode-guided
direct laser writer overcome the limitations of such con-
strained printing geometry of just direct write laser light
directed at transve eguide writing surface 205.

In an embodiment, with reference to FIG. 1, FIG. 2, and
FIG. 3, barcoded end facet printed photonic chip 200
includes: optically transparent direct laser writing substrate
201 including transverse waveguide writing surface 205 to
receive direct write laser light 214 for off-axis direct write
laser printing and facet surface 204 to receive direct write
laser light 214 for on-axis direct write laser printing of
barcode-guided direct laser written optical coupling 206 on

facet surface 204; waveguide 202 disposed in optically s

transparent direct laser writing substrate 201 and in optical
communication with facet surface 204; and optically visible
bulk impregnated barcode 203 disposed in optically trans-
parent direct laser writing substrate 201 arranged proximate

to waveguide 202 and in optical communication with facet

surface 204.

In an embodiment, barcoded end facet printed photonic
chip 200 includes barcode-guided direct laser written optical
coupling 206 disposed on facet surface 204 in response to
on-axis direct write laser printing by direct write laser light
214,

In an embodiment, optically visible bulk impregnated
barcode 203 includes a plurality of barcode members 215.
The barcode members 215 can be distributed laterally with
respect to waveguide 202 as observed from facet surface
204. Although barcode member 215 is shown, e.g., in FIG.
1, as being an elongate strip, other shapes, formats, and sizes

20

&

&

8

are contemplated including dots, meanders, regular shapes
(e.g., polygons such as parallelepipeds, tetrahedrons, poly-
hedrons, and the like), or arbitrary shapes that may or may
not involve symmetry. The number of barcode members can
be selected for a particular application and can be, e.g., 1, 2,
3, or as many as desired. The spacing (e.g., pitch) of adjacent
bar code members 215 can be identical or not. The material
of the barcode member 215 can be formed from the optically
transparent direct laser writing substrate 201 (e.g., by direct
laser writing) or disposed chemically (¢.g., by a chemical
growth mechanism), mechanically, or optically in optically
ansparent direct laser writing substrate 201 and has a
different refractive index than the optically transparent direct
laser writing substrate 201 to provide a machine vision
discernable index for referencing the position of waveguide
202.

Although waveguide 202 is shown, eg., in FIG. 1, as
being an elongate strip, other shapes, formats, and sizes are
contemplated including dots, meanders, regular shapes (e.g...
polygons such as parallelepipeds, tetrahedrons, polyhe-
drons, and the like), or arbitrary shapes that may or may not
involve symmetry as well as different optical formats that
allow electromagnetic storage such as an optical resonator or
optical cavity. The number of waveguides can be selected

5 for a particular application and can be, e.g.. 1, 2. 3, or as

many as desired. The spacing of waveguides 202 can be
selected as desired. The material of the waveguide 202 can
be formed from the optically transparent direct laser writing
substrate 201 (eg., by direct laser writing) or disposed
chemically (eg., by a chemical growth mechanism),
mechanically, or optically in optically transparent direct
laser writing substrate 201 and has a different refractive
index than the optically transparent direct laser writing
substrate 201.

Optically transparent direct laser writing substrate 201
includes a polymer, glass, or a combination comprising
polymer and glass but is not so limited so long as the
maierial when subjected to direct laser writing forms bar-
code-guided direct laser written optical coupling 206 or
other optical features. In addition to the waveguide layer and
upper and lower cladding as illustrated in FIG. 2, this can
include additional waveguiding and cladding layers, as well
as opaque or reflective layers. The shape and size of opti-
cally transparent direct laser writing substrate 201 is arbi-
trary and can be compatible with integrated photonic chips.
In an embodiment, facet surface 204 is arranged at an
oblique angle to transverse waveguide writing surface 205.

Barcode-guided direct laser written optical coupling 206
can include various optical elements such as lenses, mirrors,
gratings, and the like. In an embodiment, barcode-guided
direct laser written optical coupling 206 includes a lens for
receiving a laser light and optically coupling the laser light
into or out of the waveguide 202.

In an embodiment, optically transparent direct laser writ-
ing substrate 201 receives direct write laser light 214, forms
three-dimensional optical structures in optically transparent
direct laser writing substrate 201 in response to receiving
direct write laser light 214, and forms integrated photonic
chips including the three-dimensional optical structures. In
this manner, optical circuits can be made with barcode-
guided direct laser written optical coupling 206 formed on
facet surface 204.

In an embodiment, with reference to FIG. 3, barcode-
guided direct laser writer 216 for barcode-guided direct laser
writing of optically transparent direct laser writing substrate
201 includes: translation stage 217 that receives optically
transparent direct laser writing substrate 201 in an off-axis



US 11,501,097 B2

19

to link a specific waveguide in Chip A to a specific wave-
guide in Chip B. Since the methodology that we have
developed above is suitable for such an endeavor, we
fabricated a proof-of-concept interconnect (FIG. 16) that
connects a Si,N,, 1O port from one of the chips to that in the
other. In this case, the chips were bonded to each other using
SU-8 photoresist, and the two-chip stack was transferred to
the DLW system as a pre-assembled unit. Since the inter-
connect was fabricated using on-axis lithography, no sig-
nificant modifications to the methods outlined in the previ-
ous sections were needed. The design of the interconnect
shown FIG. 15 may not be suitable for low loss intercon-
nection but was designed so that all of the features of the
2-chip stack could be captured in one image. The bending
radius can be increased by laterally displacing the wave-
guides to be connected, or adding a thick layer of photoresist
between the two chips. With these practical concerns related
to loss addressed, the interconnect then be designed to
control for properti
Such a stack of chips would be hard to address through
off-axis DLW because the distance between the waveguide
layers and the top surface (>500 jum, exceeding the objective
working distance) as well as the absorption of the lithogra-
phy beam by the top silicon substrate can be significant
obstacles.

On-axis DLW via barcode-guided direct laser writing
overcomes technical deficiencies and issues with printing of
micro-optics on chip facets, including beam obstruction (the
shadowing effect) and material incompatibilities. To enable
high-accuracy localization of the waveguide ports, barcode-
guided direct laser writing uses a optically transparent direct
laser writing substrate 201 with optically visible bulk
impregnated barcode 203 (in the device layer) that can be
read from the on-axis perspective from facet surface 204.
The optically visible bulk impregnated barcode 203 was
read and aligned-to using image processing tools. We
printed an array of elliptical lenses that improve fiber-to-
chip misalignment tolerance and fabricated a concept 3-di-
mensional photonic wire bond to bridge optical ports on
vertically stacked chips, which might be incompatible with
off-axis DLW.

Fabrication

The lenses were printed with a DLW system configured
with a 63x objective with a 1.4 numerical aperture. The
system was operated in the dip-in laser lithography (DiLL)
mode to print on the facet of the chip, and only reflective
illumination was used. The system uses a 780 nm femto-
second laser as its source, which is rastered with a speed of

10 mm/s, repetition rate of 80 MHz, and with an average 5

power of 20 mW entering the aperture of the objective. The
raster distances between subsequent lines and between sub-
sequent layers were set to 200 nm and 300 nm respectively.
The system was operated locally (i.e., not in server mode)
although server mode could be used as well.

IP-Dip was the photoresist used in this study, due to its
physical and optical properties being known. Losses might
0.78 dB/mm at 1550 nm through IP-Dip. Length of our
lenses was approximately 20 jyim, corresponding to
approximately 0.02 dB, and some losses occurred due to
absorption of laser light by the resist. Lenses were made to
benchmark the on-axis fabrication method, and recipe devel-
opment can improve surface quality.

To hold the samples in the correct orientation for on-axis
DLW, a sample mount was made, The mount was a rectan-
gular sheet with a cutout near its middle at a default location
of the objective. Approximately 6 mm long chips were

like polarization and mode shape. 2

&

&

s

20

disposed against walls of this cutout with the bottom portion
of the chip in contact with the wall and held in place with a
nylon-tipped setscrew.

Lens Design

The lenses were axially symmetric ellipsoids with minor
diameters of 18.6 jum and focal lengths of 20 jm. An
ellipsoid focuses light of a single wavelength without spheri-
cal aberrations. To increase adhesion between the lens and
the surface of the photonic chip, the bottom half of the
ellipse was embedded in a cylinder of the same radius, This

ipse-with-cylindrical-base geometry is what gives the
in FIG. 9(b) and FIG. 9(c) a bullet-like shape. The
equation for the curve of the ellipsoid is

wo

wherein r=9.3 um is the design’s minor radius; z is the
distance away from the apex of the ellipse in microns,
yonair/nresisty-nair/nresist, nair-1.00029nair=1.00029 is
the index of refraction of air, y-M,,/t,,,i,7~1-48922 is the
index of refraction of IP-Dip as calculated from Cauchy
coeflicients, and B=0.443166 is a constant defined by

B-YO=yT+-
Using r as a free parameter, 3D FDTD simulations opti-

5 mized r for the 200 nm width inverse tapers at the IO facet

of our chips.

‘The processes described herein may be embodied in, and
fully automated via, software code modules executed by a
computing system that includes one or more general purpose
computers or processors. The code modules may be stored
in any type of non-transitory computer-readable medium or
other computer storage device. Some or all the methods may
alternatively be embodied in specialized computer hard-
ware. In addition, the components referred to herein may be
implemented in hardware, software, firmware, or a combi-
nation thereof.

Many other variations than those described herein will be
apparent from this disclosure. For example, depending on
the embodiment, certain acts, events, or functions of any of
the algorithms described herein can be performed in a
different sequence, can be added, merged, or left out alto-
gether (¢.g., not all described acts or events are necessary for
the practice of the algorithms). Moreover, in certain embodi-
ments, acts or events can be performed concurrently, e.g.,
through multi-threaded processing, interrupt processing, or
multiple processors or processor cores or on other parallel
architectures, rather than sequentially. In addition, different
tasks or processes can be performed by different machines
and/or computing systems that can function together.

Any logical blocks, modules, and algorithm elements
described or used in connection with the embodiments
disclosed herein can be implemented as electronic hardware,
computer software, or combinations of both. To clearly
illustrate this interchangeability of hardware and software,
various illustrative components, blocks, modules, and ele-
ments have been described above generally in terms of their
functionality. Whether such functionality is implemented as
hardware or software depends upon the particular applica-
tion and design constraints imposed on the overall system.
The described functionality can be implemented in varying
ways for each particular application, but such implementa-
tion decisions should not be interpreted as causing a depar-
ture from the scope of the disclosure.

The various illustrative logical blocks and modules
described or used in connection with the embodiments
disclosed herein can be implemented or performed by a
machine, such as a processing unit or processor, a digital


U.S. Patent Nov. 15, 2022 Sheet 2 of 16 US 11,501,097 B2

ut ais 2s) US ats
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263 203

{C} on-axis printing

264
Upper Cladding

Lower Cladding



U.S. Patent Nov. 15, 2022 Sheet 13 of 16 US 11,501,097 B2

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U.S. Patent Nov. 15, 2022 Sheet 15 of 16 US 11,501,097 B2

FIG. 15


U.S. Patent Nov. 15, 2022

Sheet 1 of 16 US 11,501,097 B2

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US 11,501,097 B2

15

alignment has also been pursued. However, passive on-axis
alignment to fiber facets is a qualitatively different challenge
from the one addressed here, on-axis alignment to nanopho-
tonic waveguides, due to the ‘al feature sizes encoun-
tered. Whereas the core diameter of a typical single mode
fiber for 1550 nm operation is ~9 jum, a photonic waveguide
at a chip facet may be just a couple hundred nanometers in
width. Since the waveguides themselves are used as align-
ment features, it is more challenging to align to an inversely
tapered on-chip waveguide than an optical fiber. A second
challenge associate with on-axis printing is the absence of
traditional labels, which provide information about the
device connected to a given IO port.

FIG. 6 shows off-axis and on-axis images of a waveguide
device in a photonic chip. This specific chip is comprised of
a 550 nm thick silicon nitride (Si,N,) waveguide core
surrounded by ~6 uum of silicon dioxide (SiO.) cladding (~3
jm above and below the waveguide), all on a silicon (Si)
substrate, The waveguides are 1 um wide, and are tapered

down to a nominal width of 200 nm at the facet. Such a 2

relatively thick Si;N, layer is consistent with our recent
demonstrations of nonlinear optical functionality in this
platform. From the off-axis perspective, the entire plane of
the device layer can be clearly imaged (FIG. 6(a-b, i).
which provides easy-to-see labels and unmistakable wave-
guides. From the on-axis perspective (FIG. 6(a, ii-iv) and
ii)), on the other hand, the information in the
ce layer (ie., markers, labels, and wave-
guide locations) is reduced to the 1D intersection of the
device layer with the edge of the photonic chip. As shown
in FIG. 6(a, i) and FIG. 6(4, i), a waveguide that appears as
a long line from the off-axis perspective is reduced to a small
spot when viewed from the on-axis perspective (FIG. 6(a,
ii)), and labels are no longer visible. FIG. 6(a, i’) shows an
example of an ideal situation, where the imaging/facet
quality is such that the waveguide termination at the facet is
clearly visible. Such images suggest that a blob-finding
algorithm could be applied to determine the waveguide
center, enabling aligned lithography of a micro-optic ele-
ment. Clean images are highly sensitive to illumination
conditions and can be atypical since reflections from con-
taminants and surface imperfections, which can be common
(and dependent on facet preparation), are difficult to differ-
entiate from the waveguide itself (FIG. 6(a, iii-iv)).

‘To address the visibility and information losses associated
with on-axis imaging, we introduce barcode patterns (FIG.
6(6)), which transfer information from the device-layer
plane to the device-layer edge while providing high-visibil-
ity markers that can be read and aligned-to from the on-axis

perspective. These barcodes consist of a simple series of 5

stripes that run parallel to the waveguide and extend all the
way to the chip facet, so that they are visible when the chip
is oriented in the on-axis position. The markers can encode
information in the number, spacing, and width of the bars

well as in binary encoding (bar/no bar). For example, the 5

waveguide in FIG. 6(4, i) has a barcode consisting of three
bars to the left and four bars to the right of the waveguide,
but all the bars are of equal width. Furthermore, the cross-
section of the markers, viewed on-axis in FIG. 6(}, ii-iii), is
large enough to reduce sensitivity to spurious reflections
Moreover, even if the waveguide is itself not easily imaged,
the barcode pattern is, and the waveguide center can be
inferred from the location of the barcode elements. It is
important to note that the barcode stripes have sufficient
separation from the IO waveguide (~2 jum on each side) to
avoid deterioration of its optical mode or undesired coupling
to slab modes.

&

&

16

Machine Vision Using Barcode Patterns

Ahigh-visibility barcode like that in FIG. 7(a) signals the
location of a waveguide in a way that cannot be disturbed by
random dust or surface impurities, given its unique signature
that can be readily detected. In general, the quality of the
image that the DLW system captures depends on the clean-
liness of the device, the surface roughness, and the index
contrast between the waveguide core material and the clad-
ding material. We found that Si,N, (refractive index n=2)
buried in SiO, cladding (n=1.5) provides a sufficient index
contrast for pattern localization, and we expect the image
ality to improve with higher-contrast waveguides, such as
in SiO,.

To use the barcode pattern for waveguide identification
and localization, we use machine vision techniques. The
machine vision processing includes a Canny filter, a Hough
transform, a binary template, and a cross correlation;
together, this enables alignment without coupling a visible
laser through the waveguide (i.e., without active alignment).
In the machine vision processing a medium-to-high contrast
image like that shown in FIG. 7(a) is captured. Because of
the long spatial extent of the barcode, medium contrast is
sufficient, but high contrast is preferred. A Canny filter
detects edges by searching for the peaks in the gradient of

5 the 2D image. Its output (FIG. 7(6)) includes a binary map

of edge points that are then used to compute the Hough
transform of the image. The Hough transform identifies the
location of straight lines, not just edges, in the binary map
and determines their angles with respect to the horizontal
axis of the image. This information is used to determine the
location of the interface between the Si and SiO, layers, and
its angle (6) shown in FIG. 7(c). At this point, the informa-
tion encoded in the barcode can be retrieved from a 1D
line-scan of the code, whose position is determined by
interpolating between the top and bottom edges of the Si,N,
device layer. The extracted angle 0 is then applied to a binary
template (FIG. 8(a)) so that the template and the original
image overlay at the same angle. Finally, the template and
the image are cross correlated (FIG. 8(5)), and a sub-pixel
peak-search determines the position of the waveguide,
depicted as the center of a small red circle in the figure.
Neither the line-scans nor the templates assume the presence
of the waveguide itself (i.e., there is no small dot at the
center of the template), meaning that even in cases of low
waveguide-visibility, the barcode pattern is sufficient to
determine the precise location of the small (200 nm wide)
tapered-down waveguide termination. FIG. 8(c) overlays the
output of this algorithm (circles centered about the detected
waveguide position) on the original image, and shows that
the waveguide location determined by machine vision is
consistent with the position one could derive directly if they
had a high-visibility image of the waveguide at the facet.
Application of this localization algorithm to adjacent wave-
guides (with a micro-lens printing step after each localiza-
tion) results in the array of devices shown in FIG. 8(d).
Exemplary Configuration.
Machine vision processing was implemented in the
Python programming language using NumPy and scikit-
image libraries. Different Python packages or other pro-
gramming languages can provide different performance. The
localization technique takes about two minutes to detect
each waveguide. The printing process is executed on a
port-by-port basis, meaning that a port is detected, aligned
to, and printed on before the next port is analyzed. The
machine vision processing can be applied successively to
check for errors, since a second execution should determine
that no more adjustments in position are needed. Visual



US 11,501,097 B2
Page 2

(56) References Cited

OTHER PUBLICATIONS,

‘Thomas, R., et al., “In situ fabricated 3D micro-lenses for photonic
integrated circuits”, Optics Express, 2018, p. 13436-13642, vol. 26
No. 10.

Bogucki, A., et al., “Optical fiber micro-connector with nanometer
positioning precision for rapid prototyping of photonic devices”,
Optics Express, 2018, p. 11513-11518, vol. 26 No. 9

* cited by examiner


US 11,501,097 B2

21

signal processor (DSP), an application specific integrated
circuit (ASIC), a field programmable gate array (FPGA) or
other programmable logic device, discrete gate or transistor
logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein.
A processor can be a microprocessor, but in the alternative,
the processor can be a controller, microcontroller, or state
machine, combinations of the same, or the like. A processor
can include electrical circuitry configured to process com-
puter-executable instructions. In another embodiment, a
processor includes an FPGA or other programmable device
that performs logic operations without processing computer-
executable instructions. A processor can also be imple-
mented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunc-
tion with a DSP core, or any other such configuration.
Although described herein primarily with respect to digital

technology, a processor may also include primarily analog. 2

components. For example, some or all of the signal pro-
cessing algorithms described herein may be implemented in
analog circuitry or mixed analog and digital circuitry. A
computing environment can include any type of computer
system, including, but not limited to, a computer system
based on a microprocessor, a mainframe computer, a digital
signal processor, a portable computing device, a device
controller, or a computational engine within an appliance, to
name a few.

The elements of a method, process, or algorithm
described in connection with the embodiments disclosed
herein can be embodied directly in hardware, in a software
module stored in one or more memory devices and executed
by one or more processors, or in a combination of the two
A software module can reside in RAM memory, flash
memory, ROM memory, EPROM memory, EEPROM
memory, registers, hard disk, a removable disk, a CD-ROM,
or any other form of non-transitory computer-readable stor-
age medium, media, or physical computer storage known in
the art. An example storage medium can be coupled to the
processor such that the processor can read information from,
and write information to, the storage medium. In the alter-
native, the storage medium can be integral to the processor.
The storage medium can be volatile or nonvolatile.

While one or more embodiments have been shown and
described, modifications and substitutions may be made
thereto without departing from the spirit and scope of the
invention. Accordingly, it is to be understood that the present
invention has been described by way of illustrations and not
limitation. Embodiments herein can be used independently
or can be combined.

All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are independently combinable with each
other. The ranges are continuous and thus contain every

value and subset thereof in the range. Unless otherwise s

stated or contextually inapplicable, all percentages. when
expressing a quantity, are weight percentages. The suflix (s)
as used herein is intended to include both the singular and
the plural of the term that it modifies, thereby including at
least one of that term (e.g., the colorant(s) includes at least
‘one colorants). Option, optional, or optionally means that
the subsequently described event or circumstance can or
cannot occur, and that the description includes instances
where the event occurs and instances where it does not. As
used herein, combination is inclusive of blends, mixtures,
alloys, reaction products, collection of elements, and the
like.

&

0

&

50

22

As used herein, a combination thereof refers to a combi-
nation comprising at least one of the named constituents,
components, compounds, or elements, optionally together
with one or more of the same class of constituents, compo-
nents, compounds, or elements.

All references are incorporated herein by reference.

The use of the terms “a,” “an,” and “the” and similar
referents in the context of describing the invention (espe-
cially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by con-
text. It can further be noted that the terms first, second,
primary, secondary, and the like herein do not denote any
order, quantity, or importance, but rather are used to distin-
guish one element from another. It will also be understood
that, although the terms first, second, etc. are, in some
instances, used herein to describe various elements, these
elements should not be limited by these terms. For example,
a first current could be termed a second current, and,
similarly, a second current could be termed a first current,
without departing from the scope of the various described
embodiments. The first current and the second current are
both currents, but they are not the same condition unless
explicitly stated as such.

The modifier about used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by
the context (eg., it includes the degree of error associated
with measurement of the particular quantity). The conjune-
tion or is used to link objects of a list or alternatives and is
not disjunctive; rather the elements can be used separately or
can be combined together under appropriate circumstances.

What is claimed is:
1. A barcoded end facet printed photonic chip comprising:
an optically transparent direct laser writing substrate
comprising a transverse waveguide writing surface to
receive a direct write laser light for off-axis direct write
laser printing and a facet surface to receive the direct
write laser light for on-axis direct write laser printing of
a barcode-guided direct laser written optical coupling
on the facet surface;
waveguide disposed in the optically transparent direct
laser writing substrate and in optical communication
with the facet surface; and
an optically visible bulk impregnated barcode disposed in
the optically transparent direct laser writing substrate
arranged proximate to the waveguide and in optical
communication with the facet surfac
2. The barcoded end facet printed photonic chip of claim
1, further comprising the barcode-guided direct laser written
optical coupling disposed on the facet surface in response to
on-axis direct write laser printing by direct write laser light.
3. The barcoded end facet printed photonic chip of claim
2, wherein the barcode-guided direct laser written optical
coupling comprises a lens for receiving a laser light and
optically coupling the laser light into or out of the wave-
guide.
4. The barcoded end facet printed photonic chip of claim
2, wherein the optically transparent direct laser writing
substrate receives the direct write laser light, forms three-
dimensional optical structures in the optically transparent
direct laser writing substrate in response to receiving the
direct write laser light, and forms integrated photonic chips
comprising the three-dimensional optical structures.
5. The barcoded end facet printed photonic chip of claim
1, wherein the optically visible bulk impregnated barcode
comprises a plurality of barcode members.

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Sheet 14 of 16

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