US 10,599,007 B2

9

Visual Interface (DVI), 802. 11a/b/g/n/x, cellular, etc.). Net-
work interfaces 650 may be in communication with the
network 630. Through the network 630, the tool 600 may be
accessible to remote terminal devices 620. Network inter-
faces 650 may use various wired and wireless connection
protocols such as, direct connect, Ethernet, wireless connec-
tion such as IEEE 802.11a-x, and the like.

Examples of network 630 include the Internet, Local Area
Network (LAN), Metropolitan Area Network (MAN), a
Wide Area Network (WAN), wireless network (e.g., using
Wireless Application Protocol WAP), a secured custom
connection, and the like. The network interfaces 650 can
include a firewall which can, in some aspects, govern and/or
manage permission to access/proxy data in a computer
network, and track varying levels of trust between different
machines and/or applications. The firewall can be any num-
ber of modules having any combination of hardware and/or
software components able to enforce a predetermined set of
access rights between a particular set of machines and
applications, machines and machines, and/or applications
and applications, for example, to regulate the flow of traflic
and resource sharing between these varying entities. The
firewall may additionally manage and/or have access to an
access control list which details permissions including, for
example, the access and operation rights of an object by an
individual, a machine, and/or an application, and the cir-
cumstances under which the permission rights stand. Other
network security functions performed or included in the
functions of the firewall, can be, for example, but are not

limited to, intrusion-prevention, intrusion detection, next- 3

generation firewall, personal firewall, etc., without deviating
from the novel art of this disclosure.

Storage interfaces 655 may be in communication with a
number of storage devices such as, storage devices 690,

removable disc devices, and the like. The storage interfaces 3

655 may use various connection protocols such as Serial
Advanced Technology Attachment (SATA), IEEE 1394,
Ethernet, Universal Serial Bus (USB), and the like.

User input devices 605 and peripheral devices 610 may be
connected to I/O interface 645 and potentially other inter-
faces, buses and/or components. User input devices 605 may
include card readers, finger print readers, joysticks, key-
boards, microphones, mouse, remote controls, retina read-
ers, touch screens, sensors, and/or the like. Peripheral
devices 610 may include antenna, audio devices (e.g.,
microphone, speakers, etc.), cameras, external processors,
communication devices, radio frequency identifiers
(RFIDs), scanners, printers, storage devices. transceivers,
and/or the like. Co-processor devices 615 may be connected
to the tool 600 through interface bus 635, and may include
microcontrollers, processors, interfaces or other devices.

Computer executable instructions and data may be stored
in memory (e.g., registers, cache memory, random access
memory, flash, etc.) which is accessible by processors.
These stored instruction codes (e.g., programs) may engage
the processor components, motherboard and/or other system
components to perform desired operations. The tool 600
may employ various forms of memory including on-chip
CPU memory (e.g., registers), RAM 680, ROM 685, and
storage devices 690. Storage devices 690 may employ any
number of tangible, non-transitory storage devices or sys-
tems such as fixed or removable magnetic disk drive, an
optical drive, solid state memory devices and other proces-
sor-readable storage media. Computer-executable instruc-
tions stored in the memory may include one or more
program modules such as routines, programs, objects, com-
ponents, data structures, and so on that perform particular

S

3

40

&

10

tasks or implement particular abstract data types. For
example, the memory may contain operating system (OS)
component 695, modules and other components, database
tables, and the like. These modules/components may be
stored and accessed from the storage devices, including from
external storage devices accessible through an interface bus

The database components can store programs executed by
the processor to process the stored data. The database
components may be implemented in the form of a database
that is relational, scalable and secure. Examples of such
database include DB2, MySQL, Oracle, Sybase, and the
like. Alternatively, the database may be implemented using
various standard data-structures, such as an array, hash, list,
stack, structured text file (e.g., XML), table, and/or the like.
Such data-structures may be stored in memory and/or in
structured files.

The design tool 600 may be implemented in distributed
computing environments, where tasks or modules are per-
formed by remote processing devices, which are linked
through a communications network, such as a Local Area
Network (“LAN”), Wide Area Network (“WAN”), the Inter
net, and the like. In a distributed computing environment,
program modules or subroutines may be located in both
local and remote memory storage devices. Distributed com-
puting may be employed to load balance and/or aggregate
resources for processing. Alternatively, aspects of the design
tool 600 may be distributed electronically over the Internet
or over other networks (including wireless networks). Those
skilled in the relevant art(s) will recognize that portions of
the system may reside on a server computer, while corre-
sponding portions reside on a client computer. Data struc-
tures and transmission of data particular to aspects of the
design tool 600 are also encompassed within the scope of the
disclosure.

CONCLUSION,

Unless the context clearly requires otherwise, throughout
the description and the claims, the words “comprise,” “com-
prising,” and the like are to be construed in an inclusive
sense, as opposed to an exclusive or exhaustive sense; that
is to say, in the sense of “including, but not limited to.” As
used herein, the terms “connected,” “coupled,” or any vari-
ant thereof means any connection or coupling, either direct
or indirect, between two or more elements; the coupling or
connection between the elements can be physical, logical, or
a combination thereof. Additionally, the words “herein,”
“above,” “below,” and words of similar import, when used
in this application, refer to this application as a whole and
not to any particular portions of this application. Where the
context permits, words in the above Detailed Description
using the singular or plural number may also include the
plural or singular number respectively. The word “or,” in
reference to a list of two or more items, covers all of the
following interpretations of the word: any of the items in the
list, all of the items in the list, and any combination of the
items in the list.

The above Detailed Description of examples of the tech-
nology is not intended to be exhaustive or to limit the
technology to the precise form disclosed above. While
specific examples for the technology are described above for
illustrative purposes, various equivalent modifications are
possible within the scope of the technology, as those skilled
in the relevant art will recognize. For example, while
processes or blocks are presented in a given order, alterna-
tive implementations may perform routines having steps, or
employ systems having blocks, in a different order, and


US 10,599,007 B2

Sheet 3 of 7

Mar. 24, 2020

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US 10,599,007 B2

1
SYSTEMS AND METHODS FOR EFFICIENT
OPTICAL FREQUENCY CONVERSION
WITH INTEGRATED OPTICAL SYSTEMS

CROSS-REFERENCE TO RELATED
APPLICATIONS

This application claims priority to U.S. Provisional Appli-
cation Ser. No. 62/699,423 filed Jul. 17, 2018, which is
incorporated herein by reference in its entirety for all pur-
poses.

STATEMENT REGARDING FEDERALLY
SPONSORED RESEARCH

This invention was made with government support under
grant number 70NANB18H006 awarded by NIST. The
government has certain rights in the invention.

TECHNICAL FIELD

Various embodiments of the present technology generally
relate to waveguides. More specifically, some embodiments
of the present technology relate to provide a novel archi-
tecture for efficient optical frequency conversion with inte-
grated optical systems.

BACKGROUND

Efficient second harmonic generation (SHG) is desired for 3

stabilizing octave-spanning frequency combs with the self-
referencing technique. The low pump power level from a
single (or a few) comb lines typically requires an amplifier
before the SHG conversion to produce sufficient second-
harmonic light for the self-referencing technique. Bulk SHG
crystals are often used with free-space input and output
beams. For example, many traditional systems use periodi-
cally-poled crystals for quasi phase-matching of the pump
and signal light.

Recent developments have integrated similar SHG
devices in waveguides, rather than free-space. Waveguides
allow for a dramatic increase of the pump light intensity due
to the smaller effective area of the optical mode, leading to
a greater efliciency. These waveguide SHG devices gener-
ally are implemented with a straight waveguide section and
facet couplers at the input and output. Some traditional
systems have used a repetition of bends with alternating
bend radius sign with the intent to broadening the conver-
sion efficiency spectrum while decreasing the peak efli-
ciency or used a bend meander to increase the interaction
length, though the bends have the same waveguide width as
the straight sections. Unfortunately, these traditional sys-
tems suffer from a phase-mismatch in the straight and bend
sections and as a result, the conversion efficiency is very
low.

SUMMARY

Various embodiments of the present technology generally
relate to waveguides. More specifically, some embodiments
of the present technology relate to provide a novel archi-
tecture for efficient optical frequency conversion with inte-
grated optical systems. For example, some embodiments
provide for a waveguide comprising multiple sections. The
first section can have an input to receive pump light that
generates a signal light throughout the waveguide. The
pump light and signal light can be phase matched within the

S

2

8

3

40

&

3!

3

2

first section. The second section can be connected to the first
section. The second section (e.g., a bended section) can be
formed with a phase matched bend. The second section have
a geometry that allows for a phase mismatch with the first
section such that the phase output of the second section
matches the phase of the input to the second section. The
waveguide may be applied to phase-sensitive nonlinear
optical processes, including, but not limited to, sum-fre-
quency generation and difference-frequency generation.

In some embodiments, the phase matched bend can have
an/2 angle to create either a x or 2m phase-shift between the
pump light and the signal light depending on a sign-change
of a second order nonlinear susceptibility at the 2/2 angle.
The second portion can include a non-phase-matched wave-

5 guide geometry to introduce a desired phase shift. For

example, the non-phase-matched waveguide geometry can
include modal dispersion for a specific bending radius,
through a different waveguide width, or both.

Some embodiments of the waveguide may have a wave-
guide core (e.g.. gallium arsenide) and one or more cladding
layers (eg., silicon dioxide) that include a uniform or
composite material. For example, the cladding layers may
include sub-layers of quantum wells that form an effective
medium. In some embodiments, the waveguide core and/or

cladding layers may be formed by deposition techniques

(e.g., epitaxial growth or chemical-vapor deposition, or by
wafer bonding techniques). The waveguide core may have a
higher refractive index than the waveguide cladding in
various embodiments. The cladding surrounding the wave-
guide may include a gaseous medium, such as air, or vacuum
in some embodiments. In addition, the waveguide may be
suspended via mechanical tethers that are the same material
or a different material as the core.

The waveguide may include an intermediate layer formed
between the waveguide core and the waveguide cladding,
The waveguide core layer formed by direct bonding or
adhesive bonding from a secondary substrate material to a
primary substrate material. In addition, the waveguide core
layer may be formed using selective die, selective area
bonding, or full wafer-scale bonding.

In some embodiments, the waveguide may include non-
linear materials that are uniform along the length of the
waveguide to support modal or birefringent phase matching
or periodically poled to support quasi phase-matching. The

5 waveguide core, in some embodiments, may include gallium

arsenide, indium phosphide, silicon nitride, aluminum gal-
lium arsenide, gallium phosphide, silicon, tantalum pentox-
ide, lithium niobate, and/or aluminum nitride. The wave-
guide cladding, in various embodiments, may include
silicon dioxide, silicon nitride, tantalum pentoxide, alumi-
num nitride, calcium fluoride, aluminum gallium arsenide,
silicon oxynitride, and/or aluminum oxide.

While multiple embodiments are disclosed, still other
embodiments of the present invention will become apparent
to those skilled in the art from the following detailed
description, which shows and describes illustrative embodi-
ments of the invention. As will be realized, the invention is
capable of modifications in various aspects, all without
departing from the scope of the present invention. Accord-
ingly, the drawings and detailed description are to be
regarded as illustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS.

Embodiments of the present technology will be described
and explained through the use of the accompanying draw-
ings.


U.S. Patent Mar. 24,2020 Sheet 5 of 7 US 10,599,007 B2

470

FIG. 4B



U.S. Patent Mar. 24,2020 Sheet 4 of 7 US 10,599,007 B2

400

f

410

420

430

FIG. 4A


U.S. Patent Mar. 24,2020 Sheet 7 of 7 US 10,599,007 B2
O
i aN
User input Peripheral Co-processor Terminal — a] S
devices 605 devices 610 devices 615 HAN
620 L\\
wane)
*
| Users 625
- _——
> Networks 630 ‘
\ ; 7
Ne ae
Interface Bus 635
Processor interface VO interface Network interface Storage interface
640 645 650 655
Storage device 690
System Bus 660
Modules and
engines
Co-
Clock CPU
665 670 Processor Operating System
675 695
RAM ROM
680 685
DESIGN TOOL 600

FIG. 6


a2 United States Patent

Stanton et al.

US010599007B2

(10) Patent No.: US 10,599,007 B2

(54) SYSTEMS AND METHODS FOR EFFICIENT
OPTICAL FREQUENCY CONVERSION
WITH INTEGRATED OPTICAL SYSTEMS

(71) Applicant: The Regents of the University of
Colorado, a body corporate, Denver,
co (Us)

(72) Inventors: Erie Stanton, Boulder, CO (US);
Jeffrey Chiles, Boulder, CO (US)

(73) Assignees: The Regents of the University of
Colorado, a body corporate, Denver,
CO (US); Government of the United
States of America, as represented by
the Secretary of Commerce National
Institute of Standards and
‘Technology, Gaithersburg, MD (US)

(*) Notice: Subject to any disclaimer, the term of this

patent is extended or adjusted under 35
U.S.C, 154(b) by 0 days

(21) Appl. No.: 16/514,620
(22) Filed: Jul. 17, 2019

(65) Prior Publication Data
US 2020/0026148 Al Jan. 23, 2020
Related U.S. Application Data

(60) Provisional application No. 62/699,423, filed on Jul.
17, 2018

(51) Int. Cl

(45) Date of Patent: Mar. 24, 2020
(52) U.S. Ch
CPC esses GO2F 1/377 (2013.01); GO2B 6/1223

(2013.01); G02F 1/3558 (2013.01); GO2F
1/365 (2013.01): G02F 1/383 (2013.01): G02B
2006/12078 (2013.01); GO2B 2006/12178
(2013.01)
(58) Field of Classification Search
CPC nen severe GOZE 1/365; GO 1/377
See application file for complete search history.

(56) References Cited
U.S. PATENT DOCUMENTS

5,109,462 A * 4/1992 Watanabe GO2F 1/377
359/328
8,873,133 B2* 10/2014 Vermeulen GO2F 1/395
359/327

(Continued)

Primary Examiner — Daniel Petkovsek

(7) ABSTRACT

Various embodiments of the present technology provide a
novel architecture for optical frequency conversion in a
waveguide which can be applied to any suitable nonlinear
waveguide material and any wavelength. In accordance with
some embodiments, phase-matched bends can be used to
increase the nonlinear interaction length. For example, the
device can begin with a straight waveguide section with a
width designed for phase-matching. When the straight
waveguide section approaches the end of the chip, a bending
waveguide section allows the waveguide to meander back in
the opposite direction. Various embodiments of the bend can
have a wider or narrower width to eliminate phase-matching
for second harmonic generation (SHG) and instead provide
a 2n phase-shift between the pump and signal light. There-
fore, at the end of the bend, the pump and signal light are
in-phase and a phase-matched width will continue the SHG

21 Claims, 7 Drawing Sheets

L

190

GO2F 1/37 (2006.01)
GO2F 17377 (2006.01)
GO2F 1/383 (2006.01)
GOK 1/7355 (2006.01) process
GO2B 6/122 (2006.01)
(Continued)
120
L
RA 4600
1108, 60D.

]Outpat



US 10,599,007 B2

5

of a second order nonlinear susceptibility at the x/2 angle.
The second portion 110A can include a non-phase-matched
waveguide geometry to introduce a desired phase shift. For
example, the non-phase-matched waveguide geometry can
include modal dispersion for a specific bending radius,
through a different waveguide width, or both.

The waveguide width w, is designed to provide phase-
matching between the pump wavelength transverse electric
(TE) mode and the signal wavelength transverse magnetic
(TM) mode. The bending waveguide width w, can be
designed to create a 2x phase shift between the pump and
signal modes. A linear taper 160A-160D can transition the
waveguide between widths of w, and w3. An offset of d
increases the transmission from the straight waveguide
mode to the bending waveguide mode. The taper transition
can be designed by traditional waveguide propagation meth-
ods, including but not limited to the finite difference time
domain method, the beam propagation method, or the eigen-
mode expansion method. This taper is only necessary to
provide efficient coupling between these two sections. Other
methods to provide efficient coupling between waveguides
of different cross-sectional sizes can be used enable efficient
coupling between these two waveguides,

In accordance with various embodiments, a phase-
matched condition can be solved when the parameter, y, is
equal to unity. The formulation for this parameter is

40 An
Ay!

where 0 is the angle of the bend, @ is the relative phase shift

between the pump and signal light, An is the difference in ;

refractive index between the pump and signal light, and A,,
is the pump wavelength.

Consider, in accordance with various embodiments, the
design of a gallium arsenide (GaAs) waveguide with silicon
dioxide cladding where 0=n, $=2n, »,=2.0 ym, and An is
found by solving the effective refractive indices of the
waveguide. In this example, a channel waveguide with a
core height of 135 nm and nominal width of 1085 nm was
selected.

FIG. 2 provide a top view of a diagram of a waveguide
200 that may be used in various embodiments of the present
technology. In the embodiments illustrated in FIG. 2, wave-
guide 200 is a planar optical waveguide with input 210 to
accept light from one or more pumps. The light can travel
through the various sections 220A-220Q to output 230.
Sections 220A-220Q can include differing combinations of
straight and bended waveguides connected in series, that is,
the output of one is connected to the input of the next. The
pump light and signal light can be phase matched within the
first section 220A. Then each subsequent section can be
designed to have a geometry that allows for a phase mis-
match with the immediately previous section such that the
phase output (of the current section) matches the phase of
the input (to that section). In some cases where the nonlinear
coefficients of the waveguide change sign when the direction
of propagation changes, then the relative phase shift
between sections may need to be adjusted to maximize the
continuation of the nonlinear process.

In FIG. 3A, a simulation shows the phase-matched con-
dition parameter (y) for a Aw=-25 nm and varying bend
radii. The phase-matched condition, plotted on the left axis
with the solid line, indicates the relative phase between the

40

&

g

6

pump and signal light after propagating through the bend
section, scaled such that “1.0” corresponds to a 2x phase
shift

Assuming an offset of d=0 nm, the transmission of the
pump and signal light is plotted in blue. For this waveguide
material and geometry, an offset is not necessary since the
transmission for both pump and signal light is greater than
99.5%. This calculation can be performed for varying values
of Aw and the bend radius where y=1.0 is plotted in FIG. 3B.
The black circle shown in FIG. 3A corresponds to the black
circle shown in FIG. 3B.

In FIG. 3B, the radius corresponding to a 2x phase shift
is plotted for varying values of Aw. The black circle corre-
sponds to the black circle in (a). In 3B, the green circle
shows that for Aw=-S0 nm, there is less sensitivity to
variations in Aw and this smaller radius allows for a smaller
device footprint while still allowing high transmission
greater than 99.8%.

‘An experimental study may be necessary to determine the
optimal Aw that would support a reproducible phase-
matched bend with high transmission and a small size.
Smaller bend radii result in a smaller size and reduced
transmission of the pump and signal light. As stated previ-
ously though, an offset (d) can be introduced to minimize
this bend-to-straight transition loss. However, in the regime
presented here, the waveguides are strongly single-mode
and transmission loss to the bend modes is therefore very
low.

Various embodiments of the proposed architecture can
have other advantages that make it desirable for commer-
cialization. With this approach, a waveguide can be created
in a smaller chip area than an equivalent straight waveguide,
which could normally span several centimeters. In contrast,
a maximum length ofa few millimeters is sufficient with this
novel approach. This allows greater yield in production and
minimizes the effects of epitaxial layer nonuniformity that is
present at longer length scales.

The phase matching method used in this example is form
birefringence between the fundamental TE mode of the
pump and the fundamental TM mode of the signal. Other
methods of phase matching may also be used in conjunction
with a bending section to preserve phase matching around a
bend. For example, other types of form birefringence may be
used by matching the phase between some combination of
higher order modes or by using a TM polarized pump. Direct
birefringence or a combination of direct and form birefrin-
gence is also possible using a birefringent crystal for one or
multiple of the waveguide materials. Also, quasi-phase
matching could be used by periodically poling a material
such as lithium niobate or orientation patterning a material
such as GaAs or AlGaAs. Quasi-phase matching can also be
achieved using periodically bent waveguides, which are
separate from the phase-preserving bend sections. Other
methods for phase-matching can also be used with these
phase-preserving bends.

FIG. 4A is a cross-sectional view of a waveguide 400 in
accordance with various embodiments of the present tech-
nology. As illustrated in the embodiments shown in FIG. 4,
waveguide 400 may include cladding 410 surrounding
waveguide core 420 built on a substrate 430. Some embodi-
ments of the waveguide 400 may have a waveguide core 420
(e.g., gallium arsenide) and one or more cladding layers
(e.g., silicon dioxide) that include a uniform or composite
material. For example, the cladding layers 410 may include
sub-layers of quantum wells that form an effective medium.
There are many other embodiments of a nonlinear wave-
guide in which this technology can be implemented.



US 10,599,007 B2

3

FIG. 1 provides a top view of a diagram of a waveguide
that may be used in various embodiments of the present
technology.

FIG. 2 provide a top view of a diagram of a waveguide
that may be used in various embodiments of the present
technology.

FIG. 3A shows a simulation shows the phase-matched
condition parameter (y) for a Aw=-25 nm and varying bend
radii.

FIG. 3B shows a plot of varying values of Aw and the
bend radius where y=1.0.

FIGS. 4A-4B are cross-sectional views of waveguides
that may be used in accordance with various embodiments
of the present technology.

FIG. 5 is a flowchart illustrating an example of a set of
operations for designing a waveguide according to one or
more embodiments of the present technology.

FIG. 6 illustrates an example of a computer system that
may be used in one or more embodiments of the present
technology.

The drawings have not necessarily been drawn to scale.
Similarly, some components and/or operations may be sepa-
rated into different blocks or combined into a single block
for the purposes of discussion of some of the embodiments
of the present technology. Moreover, while the technology is
amenable to various modifications and alternative forms,
specific embodiments have been shown by way of example
in the drawings and are described in detail below. The
intention, however, is not to limit the technology to the

particular embodiments described. On the contrary, the 3

technology is intended to cover all modifications, equiva-
lents, and alternatives falling within the scope of the tech-
nology as defined by the appended claims.

DETAILED DESCRIPTION

Various embodiments provide a novel architecture for
optical frequency conversion in a waveguide. Some embodi-
ments provide an increase in the conversion efficiency
compared to existing architectures. The architecture used in
various embodiments can be applied to any suitable nonlin-
ear waveguide material and any wavelength.

In accordance with some embodiments, phase-matched
bends can be used to increase the nonlinear interaction
length. The device can begin with a straight waveguide
section with a width designed for phase-matching. When the
straight waveguide section approaches the end of the chip,
a bending waveguide section allows the waveguide to mean-
der back in the opposite direction. Various embodiments of
the bend can have a wider or narrower width to eliminate
phase-matching for second harmonic generation (SHG) and
instead provide a 2m phase-shift between the pump and
signal light. Therefore, at the end of the bend, the pump and
signal light are in-phase and a phase-matched width will
continue the SHG process. The necessary width difference
between the straight and bending sections (Aw=w,-w,) is
generally small (<100 nm) so the taper length (L) can be
very short (~5 jm long).

Various embodiments of the present technology enable
significantly more efficient nonlinear optical frequency con-
version to be obtained for any given constraints in chip size
or pump power. Consequently, this makes it valuable for
numerous applications where nonlinear optical frequency
conversion is required. For example, any system requiring
optical second harmonic generation would benefit from the
higher efficiency, allowing smaller chips or lower pump
powers to be used. Other more elaborate systems could

S

2

8

3

40

&

4

benefit from this invention, such as optical frequency combs,
which often require a second-harmonic generation module
in order to allow direct detection of the comb’s carrier
envelope offset frequency. By using various embodiments of
the present technology, the power budget of the overall
system can be substantially reduced, and potentially the
footprint as well. One can also envision applications where
commercial laser light sources are available at some specific
frequencies but are not mature at others such as the second
harmonic frequency, or the difference frequency of two
initial laser sources. In these cases, some embodiments can
be used to efficiently convert light from one or more
conventional light sources to new frequencies where other
applications may benefit (e.g., spectroscopy, materials pro-

5 cessing, LIDAR, and others).

Various embodiments of the present technology provide
for a wide range of technical effects, advantages, and/or
improvements to computing systems and components. For
example, various embodiments include one or more of the
following technical effects, advantages, and/or improve-
ments: 1) efficient nonlinear optical frequency conversion;
2) use of wider or narrower width to eliminate phase-
matching for second harmonic generation (SHG) and instead
provide a 2x phase-shift between the pump and signal light;
3) increased efficiency in nonlinear optical frequency con-
version for any given constraints in chip size or pump
power; and/or 4) decrease the bandwidth of a nonlinear
frequency conversion to promote one frequency conversion
process over another.

In the following description, for the purposes of expla-
nation, numerous specific details are set forth in order to
provide a thorough understanding of embodiments of the
present technology. It will be apparent, however, to one
skilled in the art that embodiments of the present technology
may be practiced without some of these specific details.

The phrases “in some embodiments,” “according to some
embodiments,” “in the embodiments shown,” “in other
embodiments,” and the like generally mean the particular
feature, structure, or characteristic following the phrase is
included in at least one implementation of the present
technology, and may be included in more than one imple-
mentation. In addition, such phrases do not necessarily refer
to the same embodiments or different embodiments.

FIG. 1 provides a top view of a diagram of a waveguide
100 that may be used in various embodiments of the present
technology. In the embodiments illustrated in FIG. 1, each
waveguide bend 110A-110B has identical dimensions. The
first section 120 can have an input 130 to receive pump light
that generates a signal light throughout the waveguide. The
pump light and signal light can be phase matched within the
first section 120. The second section has a waveguide bend
110A and is connected to the first section 120 which is
straight in the embodiments illustrated in FIG. 1. The second
section (e.g., a bended section) can be formed with a phase
matched bend. The second section 110A can have a geom-
etry that allows for a phase mismatch with the first section
120 such that the phase output of the second section 110A
matches the phase of the input to the second section.
Additional sections, such including waveguide bend 110B
and section 140 may be included before output 150 is
provided. The waveguide may be applied to phase-sensitive
nonlinear optical processes, including, but not limited to,
sum-frequency generation and difference-frequency genera-
tion.

In some embodiments, the phase matched bend can have
an/2 angle to create either a x or 2x phase-shift between the
pump light and the signal light depending on a sign-change


U.S. Patent Mar. 24,2020 Sheet 6 of 7 US 10,599,007 B2

f

500

510
SELECT WAVEGUIDE MATERIALS

y

520
DESIGN STRAIGHT SECTION OF WAVEGUIDE

y

530
SOLVE FOR PHASE MATCHED CONDITION

y

540
IDENTIFY PARAMETERS FOR BEND IN
WAVEGUIDE

FIG. 5


US 10,599,007 B2

Sheet 2 of 7

Mar. 24, 2020

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US 10,599,007 B2

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some processes or blocks may be deleted, moved, added,
subdivided, combined, and/or modified to provide alterna-
tive or subcombinations. Each of these processes or blocks
may be implemented in a variety of different ways. Also,
while processes or blocks are at times shown as being
performed in series, these processes or blocks may instead
be performed or implemented in parallel, or may be per-
formed at different times. Further any specific numbers
noted herein are only examples: alternative implementations
may employ differing values or ranges.

The teachings of the technology provided herein can be
applied to other systems, not necessarily the system
described above. The elements and acts of the various
examples described above can be combined to provide
further implementations of the technology. Some alternative
implementations of the technology may include not only
additional elements to those implementations noted above,
but also may include fewer elements.

These and other changes can be made to the technology
in light of the above Detailed Description. While the above
description describes certain examples of the technology,
and describes the best mode contemplated, no matter how
detailed the above appears in text, the technology can be
practiced in many ways. Details of the system may vary
considerably in its specific implementation, while still being
encompassed by the technology disclosed herein. As noted
above, particular terminology used when describing certain
features or aspects of the technology should not be taken to
imply that the terminology is being redefined herein to be

restricted to any specific characteristics, features, or aspects 3

of the technology with which that terminology is associated.
In general, the terms used in the following claims should not
be construed to limit the technology to the specific examples
disclosed in the specification, unless the above Detailed

Description section explicitly defines such terms. Accord- 3

ingly, the actual scope of the technology encompasses not
only the disclosed examples, but also all equivalent ways of
practicing or implementing the technology under the claims.

To reduce the number of claims, certain aspects of the
technology are presented below in certain claim forms, but
the applicant contemplates the various aspects of the tech-
nology in any number of claim forms. For example, while
only one aspect of the technology is recited as a computer-
readable medium claim, other aspects may likewise be
embodied as a computer-readable medium claim, or in other
forms, such as being embodied in a means-plus-function
claim. Any claims intended to be treated under 35 U.S.C. §
112(f) will begin with the words “means for”, but use of the
term “for” in any other context is not intended to invoke
treatment under 35 U.S.C. § 112(f). Accordingly, the appli-
cant reserves the right to pursue additional claims after filing
this application to pursue such additional claim forms, in
either this application or in a continuing application.

What is claimed is:
1. A waveguide comprising:
a first section to receive pump light that generates a signal
light throughout the waveguide,
wherein within the first section the pump light and the
signal light are phase matched; and
a second section connected to the first section,
wherein the second section is formed with a phase
matched bend; and
wherein the second section has a phase mismatch with
the first section such that the phase output of the
second section matches the phase of the input to the
second section.

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2. The waveguide of claim 1, wherein the phase matched
bend has a 2/2 angle to create either a x or 2x phase-shift
between the pump and the signal light depending on a
sign-change of a second order nonlinear susceptibility at the
a/2 angle.

3. The waveguide of claim 1, wherein the phase matched
bend has a x angle to create either a x or 2x phase-shift
between the pump and the signal light.

4. The waveguide of claim 1, wherein the second section
includes non-phase-matched waveguide geometry to intro-
duce a desired phase shift

5. The waveguide of claim 4, wherein the non-phase-
matched waveguide geometry includes modal dispersion for
a specific bending radius, through a different waveguide
width, or both.

6. The waveguide of claim 1, further comprising a wave-
guide core and cladding layers that include a uniform or
composite material.

7. The waveguide of claim 6, wherein the cladding layers
include sub-layers of quantum wells that form an effective
medium.

8. The waveguide of claim 6, wherein the waveguide core
and the cladding layers are formed by deposition techniques

9. The waveguide of claim 8, wherein the deposition
techniques include epitaxial growth or chemical-vapor
deposition, or by wafer bonding techniques.

10. The waveguide of claim 1, further comprising non-
linear materials that are uniform along the length of the
waveguide to support modal or birefringent phase matching
or periodically poled to support quasi phase-matching.

11. The waveguide of claim 1, further comprising a
waveguide core of gallium arsenide and a cladding layer of
silicon dioxide.

12. The waveguide of claim 1, further comprising a
waveguide core with a higher refractive index than a wave-
guide cladding.

13. The waveguide of claim 12, wherein the waveguide
core comprises gallium arsenide, indium phosphide, silicon
nitride, aluminum gallium arsenide, gallium phosphide, sili-
con, tantalum pentoxide, lithium niobate, or aluminum
nitride.

14. The waveguide of claim 12, wherein the waveguide
cladding comprises silicon dioxide, silicon nitride, tantalum
pentoxide, aluminum nitride, calcium fluoride, aluminum
gallium arsenide, silicon oxynitride, or aluminum oxide.

15. The waveguide of claim 12, further comprising an
intermediate layer formed between the waveguide core and
the waveguide cladding

16. The waveguide of claim 1, further comprising a
waveguide core layer formed by direct bonding or adhesive
bonding from a secondary substrate material to a primary
substrate material.

17. The waveguide of claim 16, wherein the waveguide
core layer is formed using selective die bonding, full wafer-
scale bonding, or selective area bonding.

18. The waveguide of claim 1, further comprising a
cladding surrounding the waveguide, wherein the cladding
includes a gaseous medium or vacuum, and wherein the
waveguide is suspended via mechanical tethers that are the
same material or a different material as a core.

19. The waveguide of claim 1, applied to phase-sensitive
nonlinear optical processes for sum-frequency generation
and difference-frequency generation.

20. An optical waveguide comprising:

a first section to receive pump light that generates a signal

and idler light throughout the waveguide,


U.S. Patent Mar. 24,2020 Sheet 1 of 7 US 10,599,007 B2

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US 10,599,007 B2

Page 2
(51) Int. CL
G02F 1/365 (2006.01)
GO2B 6/12 (2006.01)
(56) References Cited
U.S. PATENT DOCUMENTS
9,470,956 B2* 10/2016 Mazur GO2F 1/355
9,915,852 B2* 3/2018 Vermeulen GO2F 1/3544
2017/0256277 Al* 9/2017 Peng GILIB 5/4866,

* cited by examiner


US 10,599,007 B2

7

In some embodiments, the waveguide core 420 and/or
cladding layers 410 may be formed by deposition techniques
(e.g., epitaxial growth or chemical-vapor deposition, or by
wafer bonding techniques). The waveguide core 420 may
have a higher refractive index than the waveguide cladding
410 in various embodiments. The cladding 410 surrounding
the waveguide may include a gaseous medium, such as air,
or vacuum in some embodiments. In addition, the wave-
guide may be suspended via mechanical tethers that are the
same material or a different material as the waveguide core.

In some embodiments, the waveguide may include an
intermediate layer (not shown) formed between the wave-
guide core 420 and the waveguide cladding 410. The wave-
guide core layer 420 formed by direct bonding or adhesive
bonding from a secondary substrate material to a primary
substrate material. In addition, the waveguide core layer 420
may be formed using selective die, selective area bonding,
or full wafer-scale bonding.

FIG. 4B is a cross-sectional view of a waveguide 450 in
accordance with various embodiments of the present tech-
nology. In the embodiments illustrated in FIG. 4B, wave-
guide layer 460 which waveguide core 470 may be built on
substrate 480 and suspended in air trench 490. The following
reference, which is hereby incorporated by reference in its
entirety for all purposes, describes examples of suspended
silicon-membrane ridge waveguides that may be used in
some embodiments: Chiles, Jeff & Khan, Saeed & Ma, Jichi
& Fathpour, Sasan. (2013). High-contrast, all-silicon wave-

guiding platform for ultra-broadband mid-infrared photon- 3

ics. Applied Physics Letters. 103. 151106-151106. 10.1063/
1.4824771. In some embodiments a thin membrane of some
waveguide material can be fused to a bulk substrate such as
silicon using direct bonding methods. The bulk substrate

may be pre-patterned with trenches, forming highly compact 3

suspended membranes. Waveguides can then be formed by
standard lithographic techniques on the membranes.

In some embodiments, the waveguide may include non-
linear materials that are uniform along the length of the
waveguide to support modal or birefringent phase matching
or periodically poled to support quasi phase-matching. The
waveguide core, in some embodiments, may include gallium
arsenide, indium phosphide, silicon nitride, aluminum gal-
lium arsenide, gallium phosphide, silicon, tantalum pentox-
ide, lithium niobate, and/or aluminum nitride. The wave-
guide cladding, in various embodiments, may include
silicon dioxide, silicon nitride, tantalum pentoxide, alumi-
num nitride, calcium fluoride, aluminum gallium arsenide,
silicon oxynitride, and/or aluminum oxide.

FIG. 5 is a flowchart illustrating an example of a set of
operations 500 for designing a waveguide according to one
or more embodiments of the present technology. These
operations may be performed by waveguide design tool
running on a computer. The waveguide design tool may
present various graphical user interfaces having drop down
options, boxes for entering design constraints (e.g., values,
materials, dimensions, etc.). As illustrated in FIG. 5, selec-
tion operation 510 allows the user to select a waveguide
material. For example, the waveguide core material may be
selected from gallium arsenide, indium phosphide, silicon
nitride, aluminum gallium arsenide, gallium phosphide, sili-
con, tantalum pentoxide, lithium niobate, and/or aluminum
nitride. The waveguide cladding may be selected to be
silicon dioxide, silicon nitride, tantalum pentoxide, alumi-
num nitride, calcium fluoride, aluminum gallium arsenide,
silicon oxynitride, aluminum oxide, and/or other appropriate
material.

3

40

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8

Design operation 520 can use the properties of the
selected materials and information about the pump light to
design a first section of the waveguide. The first section may
be a straight section in which case design operation 520
computes the dimensions of the first section so that the phase
of the pump light and signal light are matched. For each
subsequently connected section, computation operation 530
solves for a phase match condition and uses identification
operation 540 to identify parameters for a bend in the
waveguide. In some embodiments, the design tool can
simulate the design and create a design file for manufacture
of the waveguide.

Exemplary Computer System Overview
‘Aspects and implementations of waveguide design tool of

s_ the disclosure have been described in the general context of

various steps and operations. A variety of these steps and
operations may be performed by hardware components or
may be embodied in computer-executable instructions,
which may be used to cause a general-purpose or special-
purpose processor (e.g., in a computer, server, or other
computing device) programmed with the instructions to
perform the steps or operations. For example, the steps or
operations may be performed by a combination of hardware,
software, and/or firmware.

FIG. 6 isa block diagram illustrating an example machine
representing the computer systemization of the waveguide
design tool. The tool 600 may be in communication with
entities including one or more users 625 client/terminal
devices 620, user input devices 605, peripheral devices 610,
an optional co-processor device(s) (e.g., cryptographic pro-
cessor devices) 615, and networks 630. Users may engage
with the tool 600 via terminal devices 620 over networks
630.

Computers may employ central processing unit (CPU) or
processor to process information. Processors may include
programmable general-purpose or special-purpose micro-
processors, programmable controllers, application-specific
integrated circuits (ASICs), programmable logic devices
(PLDs), embedded components, combination of such
devices and the like. Processors execute program compo-
nents in response to user and/or system-generated requests.
One or more of these components may be implemented in
software, hardware or both hardware and software. Proces-
sors pass instructions (e.g., operational and data instruc-
tions) to enable various operations.

The tool 600 may include clock 665, CPU 670, memory
such as read only memory (ROM) 685 and random access
memory (RAM) 680 and co-processor 675 among others
These controller components may be connected to a system
bus 660, and through the system bus 660 to an interface bus
635. Further, user input devices 605, peripheral devices 610,
co-processor devices 615, and the like, may be connected
through the interface bus 635 to the system bus 660. The
interface bus 635 may be connected to a number of interface
adapters such as processor interface 640, input output inter-
faces (I/O) 645, network interfaces 650, storage interfaces
655, and the like.

Processor interface 640 may facilitate communication
between co-processor devices 615 and co-processor 675. In
one implementation, processor interface 640 may expedite
encryption and decryption of requests or data. Input output
interfaces (I/O) 645 facilitate communication between user
input devices 605, peripheral devices 610, co-processor
devices 615, and/or the like and components of the tool 600
using protocols such as those for handling audio, data, video
interface, wireless transceivers, or the like (e.g., Bluetooth,
IEEE 1394a-b, serial, universal serial bus (USB), Digital


US 10,599,007 B2

13
wherein within the first section the pump light and
signal and the idler light are phase matched; and
a bended section connected to the first section,
wherein the bended section has a phase mismatch with
the first section such that the phase output of the
bended section matches the phase of the input to the
bended section.
21. An optical waveguide comprising:
a first section to receive pump light that generates a signal
light throughout the waveguide,
wherein within the first section the pump light and the
signal light are phase matched; and
one or more additional sections interconnected and at
least one of the one or more additional sections having
phase matched bends to create either a desired phase-
shift between the pump light and the signal light via a
phase mismatch between the one or more additional
sections having bends.

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14