Patent Application Publication Feb. 2, 2023 Sheet 19 of 21. US 2023/0032022 Al

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Patent Application Publication Feb. 2, 2023 Sheet 13 of 21. US 2023/0032022 Al

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US 2023/0032022 Al

by a chip waveguide of the photonic bolometer, communi-
cating the primary probe light from the chip waveguide to a
photonic temperature sensor of the photonic bolometer;
receiving incident radiation light by a photon absorber of the
photonic bolometer; increasing the temperature of the pho-
ton absorber in response to receiving the incident radiation
light; communicating heat from the photon absorber to the
photonic temperature sensor; receiving, by the photonic
temperature sensor, the heat from the photon absorber and
increasing a temperature of the photonic temperature sensor
in response to receiving the heat from the photon absorber:
changing a resonance frequency of the photonic temperature
sensor in response to increasing the temperature of the
photonic temperature sensor due to absorption of the inci-
dent radiation light by the photon absorber; producing, by
the photonic temperature sensor, bolometer light from the
primary probe light based on the change of the resonance
frequency due to heating the photonic temperature sensor:
communicating the bolometer light from the photonic tem-
perature sensor to the chip waveguide; and determining the
temperature change of the photonic temperature sensor due
to the absorption of the incident radiation light by the photon
absorber from the bolometer light to perform broadband
high-absorption photonic bolometry.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The following description cannot be considered
limiting in any way. Various objectives, features, and advan-
tages of the disclosed subject matter can be more fully
appreciated with reference to the following detailed descrip-
tion of the disclosed subject matter when considered in
connection with the following drawings, in which like
reference numerals identify like elements.

[0007] FIG. 1 shows perspective views of photonic
bolometers that include an array of photonic bolmetric
pixels in panels (A), (B), and (C) along with insets for a
corresponding single photonic bolometric pixel, according
to an embodiment.

[0008] FIG. 2 shows an SEM of a photonic bolometer,
according to an embodiment

[0009] FIG. 3 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment.

[0010] FIG. 4 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment

[0011] FIG. 5 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment

[0012] FIG. 6 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment.

[0013] FIG. 7 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment

[0014] FIG. 8 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment.

[0015] FIG. 9 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment.

[0016] FIG. 10 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment.

Feb. 2, 2023

[0017] FIG. 11 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment.

[0018] FIG. 12 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment.

[0019] FIG. 13 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment.

[0020] FIG. 14 shows a perspective view of a photonic
bolometer and cross-sections of the photonic bolometer,
according to an embodiment.

[0021] FIG. 15 shows a perspective view of a photonic
bolometer that includes an array of photonic bolometer
pixels and cross-sections of the photonic bolometer, accord
ing to an embodiment.

[0022] FIG. 16 shows a perspective view of a photonic
bolometer that includes an array of photonic bolometer
pixels and cross-sections of the photonic bolometer, accord
ing to an embodiment.

[0023] FIG. 17 shows steps involved in making a photonic
bolometer, according to an embodiment.

[0024] FIG. 18 shows a plan view of a photonic bolometer
and indicates reception of incident radiation light by a
photon absorber, wherein the photon absorber produces heat
that flows from the photon absorber to a photonic tempera-
ture sensor, as well as communication of primary probe light
and bolometer light in the photonic bolometer, according to
an embodiment.

[0025] FIG. 19 shows a photonic bolometry system,
according to an embodiment.

[0026] FIG. 20 shows a photonic bolometry system,
according to an embodiment.

[0027] FIG. 21 shows a photonic bolometry system,
according to an embodiment.

DETAILED DESCRIPTION,

[0028] A detailed description of one or more embodiments
is presented herein by way of exemplification and not
limitation.

[0029] Conventional microbolometers use  thermistors
materials such as vanadium oxide or amorphous silicon to
read out temperature electrically. Such materials are incom-
patible with high temperature processes. In a departure from
conventional articles, photonic bolometer 200 described
herein overcomes this technical deficiency of conventional
microbolometers and senses changes in temperature of a
bolometer element that absorbs incident radiation, e.g., by
vertically aligned carbon nanotubes (VACNTS). It is con-
templated that VACNTs withstand high temperatures and
can be made at 800° C. Advantageously, VACNTs are highly
photon absorbing (>99%) and extremely broadband (e.
from 0.2 um to 200 um), unlike traditional microbolometer
interference filters that are narrow band (typically 8-14 jun).
Beneficially, photonic bolometer 200 can include a photonic
temperature sensor that is compatible with 800° C. VACNT
growth and provides easy integration of carbon nanotube
absorbing elements in a microbolometer array for the first
time. Moreover, photonic bolometer 200 provides thermal
imaging beyond 20 jum, which is currently not possible. Past
attempts at developing such a bolometer array have been
hindered by incompatibility of conventional thermistor tech-
nology with the 800° C. growth temperature of VACNTs.



Patent Application Publication Feb. 2, 2023 Sheet 4 of 21 US 2023/0032022 Al

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Patent Application Publication Feb. 2, 2023 Sheet 20 of 21. US 2023/0032022 Al

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FIG. 20


US 2023/0032022 Al

HfO,, SnO,, In,O;, Zn,SnO,, Ga;05, Al,O,, and the like.
In an embodiment, oxide dielectric 205 is produced by
oxidation of a portion of substrate 204 to produce the
semiconductor oxide. According to one embodiment, oxide
dielectric 205 is a product of rapid thermal oxidation of
substrate 204 so that the oxide (the dielectric layer) is
derived from substrate 204, In another embodiment, the
oxide dielectric 205 is a product of low temperature oxida-
tion of substrate 204 to produce an oxide. In a further
embodiment, oxide dielectric 205 is a product of depositing
the oxide on substrate 204, which may or may not involve
oxidation of substrate 204. Moreover, oxide dielectric 205
can be bonded to substrate 204. In an embodiment, oxide
dielectric 205 includes SiO, as the oxide, which is a product
of oxidation of substrate 204 that includes Si. In some
embodiments, oxide dielectric 205 includes a semiconductor
oxide, a ceramic (e.g, ZrO2, AI203, SiC, Si3N4, BN,
BaTiO3, and the like), a glass, a polymer, or a combination
thereof. In some embodiments, the dielectric oxide includes
an organic compound such as a polymer, e.g., cellulose,
poly(methy! methacrylate), and the like.

[0047] A thickness of oxide dielectric 205 can be from
0.25 um to 10 um, specifically from 0.5 um to 5 jum, and
more specifically from 1 jum to 3 jum.

[0048] Cladded dielectric 206 can include the same com-
position, properties and function as oxide dielectric 205.
Moreover, the cladded dielectric 206 can be an encapsula-
tion layer that seals photonic temperature sensor 216 from
environmental factors such as humidity and moisture, dust,
chemical depositions that can change the effective refractive
index of photonic temperature sensor 216, and the like.
Furthermore, cladded dielectric 206 can optically isolate
photonic temperature sensor 216 from photon absorber 217
grown over cladded dielectric 206, directly on top of pho-
tonic temperature sensor 216. In an embodiment, cladded
dielectric 206 includes a product of depositing the oxide on
substrate 204. Moreover, cladded dielectric 206 can be
bonded to photonic temperature sensor 216.

[0049] Waveguide 215 receives primary probe light 238
and bolometer light 244 in communication with photonic
temperature sensor 216. Waveguide 215 guides light along
a path and can be a structure on or over a substrate which
guides light along the axial direction and confines it in the
transverse directions. Exemplary waveguides 215 include
rib waveguides and ridge waveguides. Moreover, waveguide
215 can include coupling elements to light into and out of
the waveguide 215, such as Bragg grating couplers or
inverse tapers, and the like. A size, Le., a transverse cross-
section dimension relative to a propagation path of primary
probe light 238 in waveguide 215, can be from 20 nm to 20
tum, specifically from 50 nm to 5 um, and more specifically
from 200 nm to 1 um, A transmission loss of waveguide 215
can be from 0.1 dB/cm to 50 dB/cm, specifically from 0.5
dB/em to 10 dB/em, and more specifically from 1 dB/em to
4 dB/em at a wavelength from 500 nm to 10 um, specifically
from 750 nm to 4 jun, and more specifically from 1 jum to
2.5 mm. In an embodiment, waveguide 215 guides light
along a path; can have dimensions from 300 nm to 1 jum
width, 200 nm to 500 nm height; can include silicon and
similar materials; and can operate at a wavelength from 1 um
to 2.5 um

Feb. 2, 2023

[0050] Photonic temperature sensor 216 can be formed
according to methods described in US patent 220/
0103594A1, which is incorporated by reference herein in its
entirety.

[0051] The thermally isolated area 202 has a very weak
thermal link to photonic chip 201 by weak thermal link 250
and can include thin suspended membrane 207 that is
thermally isolated from the bulk of chip 201 and supported
by tethers or legs that act as weak thermal links 250 to the
bulk of chip 201. Moreover, the thermally isolated area 202
can be a portion/surface area on a chip that is surrounded by
isolation trenches 203. These isolation trenches 203 are a
weak thermal link to chip 201. The thermal isolation area
202 supports both a photonic thermometer 216, VACNTs
217, and a portion of the waveguide 215. Furthermore,
thermally isolation area 202 can include etch cavity 208,
wherein etch cavity 208 is etched in substrate 204. Further-
more, thermally-isolated member 202 can include undercut
209 so that photonic temperature sensor 216, wherein pho-
tonic temperature sensor 216 is suspended over undercut
209.

[0052] VACNTs in photon absorber 217 absorb incident
radiation light 236 that can be, e.g., from ultraviolet (~0.2
jum) to long-range infrared (~200 pm) and transform it into
heat that is sensed by photonic temperature sensor 216
fabricated from silicon-on-insulator (or other photonics
semiconductor materials, e.g. silicon nitride, AIN, III-V, and
the like), and is thermally disconnected from the photonic
chip 201 by suspending it with legs or on cladded dielectric
206.

[0053] Isolation trench 209 can be a gap between ther-
mally-isolated member 202 and photonic chip 201 that is
empty (e.g., an air gap) or filled with a thermally insulating
material so that thermally-isolated member 202 is thermally
isolated from photonic chip 201. Accordingly, when ther-
mally-isolated member 202 is heated due to electrical cur-
rent causing Joule heating of photon absorber 217, even
though thermally-isolated member 202 is heated, photonic
chip 201 maintains its temperature without a temperature
increase or having an insignificant increase in temperature.
[0054] In an aspect, photonic temperature sensor 216 has
an optical resonance frequency that is sensitive to tempera-
ture. The temperature rise sensed by photonic temperature
sensor 216 is determined using frequency metrology. The
photonic temperature sensor 216 can be encapsulated,
shielding it from the environment effects such as humidity.
Moreover, photonic temperature sensor 216 can be fabri-
cated from silicon, silicon nitride (silicon- or silicon nitride-
on-insulator platform), AIN, TiO,, GaAs, or other semi-
conductive materials.

[0055] Photonic bolometer 200 can be made of various
elements and components that are microfabricated, micro-
fabricated or nanofabricated. Elements of photonic bolom-
eter 200 can be various sizes and can be made of a material
that is physically or chemically resilient in an environment
in which photonic bolometer 200 is disposed. Exemplary
materials include a metal, ceramic, thermoplastic, glass,
semiconductor, and the like. Some of the elements of
photonic bolometer 200 can be made of the same or different
material and can be monolithic in a single physical body or
can be separate members that are physically joined.
[0056] Photonic bolometer 200 can be made in various
ways. It should be appreciated that photonic bolometer 200
includes a number of optical, electrical, or mechanical



US 2023/0032022 Al

PHOTONIC BOLOMETER AND

PERFORMING BROADBA!

HIGH-ABSORPTION PHOT¢
BOLOMETRY

ite

CROSS REFERENCE TO RELATED,
APPLICATIONS

[0001] This application is a continuation in part of U.S
patent application Ser, No. 17/486,852 (filed Sep. 27, 2021).
which claims the benefit of U.S. Provisional Patent Appli-
cation Ser. No. 63/083,218 (filed Sep. 25, 2020), which are
herein incorporated by reference in their entirety. This
application claims the benefit of U.S. Provisional Patent
Application Ser. No. 63/251,186 (filed Oct. 1, 2021), which
is herein incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY
SPONSORED RESEARCH

[0002] This invention was made with United States Gov-
ernment support from the National Institute of Standards and
‘Technology (NIST), an agency of the United States Depart-
ment of Commerce. The Government has certain rights in
this invention

BRIEF DESCRIPTION

[0003] Disclosed is a photonic bolometer for performing
broadband high-absorption photonic bolometry, the pho-
tonic bolometer comprising: a photonic chip; a weak thermal
link disposed on and in mechanical communication with the
photonic chip; a thermally-isolated member disposed on the
weak thermal link and in mechanical communication with
the weak thermal link, such that the weak thermal link is
interposed between the thermally-isolated member and the
photonic chip, and the weak thermal link thermally isolates
the thermally-isolated member from the photonic chip; a
photonic temperature sensor disposed on the thermally-
isolated member and comprising a resonance frequency
from which a temperature of the thermally-isolated member
is determinable and that varies with temperature of the
thermally-isolated member, wherein the photonic tempera-
ture sensor receives primary probe light from a chip wave-
guide and produces a bolometer light from the primary
probe light; the chip waveguide disposed on the thermally-
isolated member in optical communication with the photonic
temperature sensor and that communicates the primary
probe light to the photonic temperature sensor and that
monitors transmission and storage of the primary probe light
by the photonic temperature sensor, wherein the chip wave-
guide receives the bolometer light from the photonic tem-
perature sensor to determine the temperature of the ther-
mally-isolated member via a change in resonance frequency
of the photonic temperature sensor; and a photon absorber
disposed on the thermally-isolated member in thermal com-
munication with the photonic temperature sensor and that
receives incident radiation light, increases temperature due
to absorption of the incident radiation light, heats the pho-
tonic temperature sensor in response to receipt of the inci-
dent radiation light, and changes the resonance frequency of
the photonic temperature sensor in response to receiving the
incident radiation light.

[0004] Disclosed is a photonic bolometry system, com-
prising: a chip probe light source that receives a control light
signal and produces a primary probe light based on the

Feb. 2, 2023

control light signal; a photonic bolometer in optical com-
munication with the chip probe light source and that receives
the primary probe light from the chip probe light source,
receives incident radiation light, and produces ref a244 from
the ref a206 in response to receiving the incident radiation
light, the photonic bolometer comprising: a photonic chip; a
weak thermal link disposed on and in mechanical commu-
nication with the photonic chip; a thermally-isolated mem-
ber disposed on the weak thermal link and in mechanical
communication with the weak thermal link, such that the
weak thermal link is interposed between the thermally-
isolated member and the photonic chip, and the weak
thermal link thermally isolates the thermally-isolated mem-
ber from the photonic chip; a photonic temperature sensor
disposed on the thermally-isolated member and comprising
a resonance frequency from which a temperature of the
thermally-isolated member is determinable and that varies
with temperature of the thermally-isolated member, wherein
the photonic temperature sensor receives primary probe light
from a chip waveguide and produces a bolometer light from
the primary probe light; the chip waveguide disposed on the
thermally-isolated member in optical communication with
the photonic temperature sensor and that communicates the
primary probe light to the photonic temperature sensor and
that monitors transmission and storage of the primary probe
light by the photonic temperature sensor, such that the chip
waveguide receives the primary probe light from the chip
probe light source, receives the bolometer light from the
photonic temperature sensor, and communicates the bolom-
eter light to a photodetector; and a photon absorber disposed
on the thermally-isolated member in thermal communica-
tion with the photonic temperature sensor and that receives
incident radiation light, increases temperature due to absorp-
tion of the incident radiation light, heats the photonic
temperature sensor in response to receipt of the incident
radiation light, and changes the resonance frequency of the
photonic temperature sensor in response to receiving the
incident radiation light; a photodetector in optical commu-
nication with the photonic bolometer and that receives the
bolometer light from the chip waveguide of the photonic
bolometer and produces photodetector signal in response to
receiving the bolometer light from the photonic bolometer;
a phase sensitive detector in electrical communication with
the photodetector and that receives the photodetector signal
from the photodetector, receives a reference frequency sig-
nal, and produces a lock signal based on the photodetector
signal with reference to the reference frequency signal; a
local oscillator in electrical communication with the phase
sensitive detector and a servo controller and that produces
the reference frequency signal and communicates the refer-
ence frequency signal to the phase sensitive detector and the
servo controller; the servo controller in electrical commu-
nication with the phase sensitive detector and the local
oscillator and that receives the lock signal from the phase
sensitive detector, receives the reference frequency signal
from the local oscillator, produces control light signal in
response to receiving the lock signal and the reference
frequency signal, and communicates the control light signal
to the chip probe light source, wherein the temperature of the
thermally-isolated member is determined via a change in
resonance frequency of the photonic temperature sensor.

[0005] Disclosed is a process for performing broadband
high-absorption photonic bolometry with a photonic bolom-
eter, the process comprising: receiving primary probe light


Patent Application Publication

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Patent Application Publication Feb. 2, 2023 Sheet 9 of 21 US 2023/0032022 Al

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US 2023/0032022 Al

18. A photonic bolometry system, comprising:

aprobe light source that receives a control light signal and
produces a primary probe light based on the control
light signal;

a photonic bolometer in optical communication with the
probe light source and that receives the primary probe
light from the probe light source, receives incident
radiation light, and produces ref a244 from the ref a206
in response to receiving the incident radiation light, the
photonic bolometer comprising:

a photonic chip;

a weak thermal link disposed on and in mechanical
communication with the photonic chip;
thermally-isolated member disposed on the weak
thermal link and in mechanical communication with
the weak thermal link, such that the weak thermal
link is interposed between the thermally-isolated
member and the photonic chip, and the weak thermal
link thermally isolates the thermally-isolated mem-
ber from the photonic chip;
photonic temperature sensor disposed on the ther-
mally-isolated member and comprising a resonance
frequency from which a temperature of the ther-
mally-isolated member is determinable and that var-
ies with temperature of the thermally-isolated mem-
ber, wherein the photonic temperature sensor
receives primary probe light from a chip waveguide
and produces a bolometer light from the primary
probe light;
the chip waveguide disposed on the thermally-isolated
member in optical communication with the photonic
temperature sensor and that communicates the pri-
mary probe light to the photonic temperature sensor
and that monitors transmission and storage of the
primary probe light by the photonic temperature
sensor, such that the chip waveguide receives the
primary probe light from the probe light source,
receives the bolometer light from the photonic tem-
perature sensor, and communicates the bolometer
light to a photodetector; and
photon absorber disposed on the thermally-isolated
member in thermal communication with the pho-
tonic temperature sensor and that receives incident
radiation light, increases temperature due to absorp-
tion of the incident radiation light, heats the photonic
temperature sensor in response to receipt of the
incident radiation light, and changes the resonance
frequency of the photonic temperature sensor in
response to receiving the incident radiation light;

a photodetector in optical communication with the pho-
tonic bolometer and that receives the bolometer light
from the chip waveguide of the photonic bolometer and
produces photodetector signal in response to receiving
the bolometer light from the photonic bolometer;

a phase sensitive detector in electrical communication
with the photodetector and that receives the photode-
tector signal from the photodetector, receives a refer-
ence frequency signal, and produces a lock signal based
on the photodetector signal with reference to the ref-
erence frequency signal:

a local oscillator in electrical communication with the
phase sensitive detector and a servo controller and that
produces the reference frequency signal and commu-

cy

s

»

Feb. 2, 2023

nicates the reference frequency signal to the phase
sensitive detector and the servo controller;

the servo controller in electrical communication with the
phase sensitive detector and the local oscillator and that
receives the lock signal from the phase sensitive detec-
tor, receives the reference frequency signal from the
local oscillator, produces control light signal in
response to receiving the lock signal and the reference
frequency signal, and communicates the control light
signal to the probe light source,

wherein the temperature of the thermally-isolated mem-
ber is determined via a change in resonance frequency
of the photonic temperature sensor.

19. A process for performing broadband high-absorption

photonic bolometry with a photonic bolometer, the process
comprising:

receiving primary probe light by a chip waveguide of the
photonic bolometer;

communicating the primary probe light from the chip
waveguide to a photonic temperature sensor of the
photonic bolometer;

receiving incident radiation light by a photon absorber of
the photonic bolometer;

increasing the temperature of the photon absorber in
response to receiving the incident radiation light;

communicating heat from the photon absorber to the
photonic temperature sensor;

receiving, by the photonic temperature sensor, the heat
from the photon absorber and increasing a temperature
of the photonic temperature sensor in response to
receiving the heat from the photon absorber,

changing a resonance frequency of the photonic tempera-
ture sensor in response to increasing the temperature of
the photonic temperature sensor due to absorption of
the incident radiation light by the photon absorber;

producing, by the photonic temperature sensor, bolometer
light from the primary probe light based on the change
of the resonance frequency due to heating the photonic
temperature sensor;

communicating the bolometer light from the photonic
temperature sensor to the chip waveguide; and

determining the temperature change of the photonic tem-
perature sensor due to the absorption of the incident
radiation light by the photon absorber from the bolom-
eter light to perform broadband high-absorption pho-
tonic bolometry.

20. The process for of claim 19, wherein the photonic

bolometer comprises:

a photonic chip;

a weak thermal link disposed on and in mechanical
communication with the photonic chip;

a thermally-isolated member disposed on the weak ther-
mal link and in mechanical communication with the
weak thermal link, such that the weak thermal link is
interposed between the thermally-isolated member and
the photonic chip, and the weak thermal link thermally
isolates the thermally-isolated member from the pho-
tonic chip;

the photonic temperature sensor disposed on the ther-
mally-isolated member and comprising a resonance
frequency from which a temperature of the thermally-
isolated member is determinable and that varies with
temperature of the thermally-isolated member, wherein
the photonic temperature sensor receives primary probe


US 2023/0032022 Al

include power meter, photodiodes, and photoreceivers.
Examples of photodetector 225 include InGaAs and or Si
photodiode. The bandwidth of the photodetector 225 can be
between 0 Hz and 10 GHz, specifically between 100 Hz and
5 GHz, and more specifically between 1 kHz and 1 GHz.
[0070] Voltage amplifier 226 can include electronic cur-
rent or voltage amplifier that amplifies signal from a pho-
todetector 225 by a factor in the range from 2 to a factor to
10000. Exemplary amplifiers 226 include differential ampli-
fier and transimpedance amplifier.

[0071] Filter 227 can include a low pass electrical filter
that cuts off high-frequency component of the electrical
signal. Filter 227 can be used with phase sensitive detector
229. In an embodiment, filter 227 includes a low pass with
high-frequency cutoff in the range from 1 kHz to 10 MHz,
specifically from 2 kHz and 1 MHz, and more specifically
between 10 kHz and 100 kHz.

[0072] Phase sensitive detector 229 can include mixer, low
pass filter, local oscillator 228 and voltage amplifier 226.
Exemplary phase sensitive detector 229 includes lock-in
amplifier. Moreover, lock-in amplifier can discriminate sig-
nal in noisy environment. In an embodiment, phase sensitive
detector 229 includes mixer, low pass filter, local oscillator,
and amplifier. These components can be packaged together
in the form of lock-in amplifier that is used to detect small
changes in the phase of the laser light. Photodetector signal
245 is converted to lock signal 247 by photodetector 225.
Lock signal 466 can include an electronic signal. An elec-
tronic signal of lock signal 426 can be from 1 nV to 100 V,
specifically from 1 uV to 20 V, and more specifically from
ImV to 10V.

[0073] Local oscillator 228 can include microwave source,
and or radio frequency source that produces a known
frequency in the microwave and or radio frequency range.
Exemplary local oscillator 228 includes a signal generator.
Moreover, the frequency produced is coherent, and located
in the band from 1 Hz to 10 GHz, specifically from 10 Hz
to 1 GHz, and more specifically from 100 Hz to 100 MHz.
In an embodiment, local oscillator 228 includes a signal
generator with a phase control and operating radio frequency
range. Local oscillator 228 produces oscillating electric
signal reference frequency signal 246. Reference frequency
signal 246 can include a signal from a signal generator or
from a lock-in amplifier. Moreover, reference signal 624 can
be a signal in the range from 10 Hz to 10 HGz. A reference
frequency signal 246 can be from 1 Hz to 10 GHz, specifi-
cally from 10 Hz to 1 GHz, and more specifically from 100
Hz to 100 MHz. Reference frequency signal 246 can be used
to control electro-optic phase modulator 318. The reference
frequency signal 246 is within the range of operation of
electro-optic phase modulator 318.

[0074] Servo controller 230 can include an electronic
instrument that can be used for feedback control applica-
tions. In embodiment, servo controller 230 is used for
adjusting the frequency of the probe light source 218 (laser).
Exemplary servo controllers 230 include instrument that
feeds the error signal back to the transducer 231 that
modulate the probe light source 218. In an embodiment,
servo controller 230 includes three stages differential ampli-
fier stage that generates an error signal, PID filter stage that
filter error signal to generate feedback signal, and output
stage that provides the control light signal 248. Moreover, in
embodiment, PID filter stage adjust the control light signal
248 to use keep an error signal at zero. In embodiment, servo

Feb. 2, 2023

controller 230 produces control light signal 248. Control
light signal 248 can include dither error signal, Pound-
Drever-Hall error signal, and the like. Moreover, the band-
width of the servo controller 230 can be from 100 Hz to 1
GHz, specifically from 1 kHz to 500 MHz, and more
specifically from 10 kHz to 100 MHz. The control light
signal 248 can be from -20 V to +V, specifically from -15
V to +15 V, and more specifically from -10 V to +10V.
[0075] Electro-optic phase modulator 232 is a fiber-
coupled or a free space device, whose refractive index
changes with applied voltage with a fast response time on
the order of a nanosecond. The result of voltage modulation
on 232 leads to frequency modulation of probe light source
218. Exemplary electro-optic phase modulators 232 include
fiber-based electrooptic crystal driven to phase modulate
light travelling though the fiber, Moreover, elector-optic
phase modulator 232 can include lithium-niobate crystal. In
an embodiment, electro-optic phase modulator 232 includes
electro-optic crystal that modulate phase of light. Phase
modulation depth generated by electro-optic phase modula-
tor 5232 18 can be from 0.001 to 0.1, specifically from 0.005
to 0.1, and more specifically from 0.01 to 0.1.

[0076] Mixer 234 can include a non-linear device for
generating an error signal, that goes into the servo controller
230 to generate a control signal to adjust the frequency of
probe light source 218.

[0077] A process for making photonic bolometer 200 can
include various steps to form features thereof such as
vertically aligned carbon nanotubes and photonic tempera-
ture sensor 216 in an array disposed in photonic bolometric
pixel 252. Various fabrication methods can be used, includ-
ing fabrication from silicon, silicon nitride (“silicon-” or
“silicon nitride-on-insulator” platform), AIN, TiO, GaAs,
and other semiconductor or dielectric materials. In an
embodiment, a process for making photonic bolometer 200
includes growing single pixel bolometric detectors with
carbon nanotubes over or adjacent to photonic temperature
sor 216 so that photonic bolometer 200 can determine
responsivity to incident radiation 236. In an embodiment,
with reference to FIG. 17, a process for making photonic
bolometer includes: providing substrate 204 (e.g., a silicon-
on-insulator, silicon nitride-on-insulator, lithium-niobate-
on-insulator, and the like) that includes silicon; forming
oxide dielectric 205 on substrate 204 by thermal growth,
chemical vapor deposition or plasma-enhanced chemical
vapor deposition; forming device layer 212 (e.., silicon,
silicon nitride, aluminum nitride, lithium niobate and the
like) on the oxide dielectric 205 by smart cut, wafer bonding,
thin film deposition, epitaxial growth, as shown on panel A
of FIG. 17. Forming soft (resist) or hard (dielectric or metal)
layer 210 on device layer 212 by spin-coating on device
layer 212 as shown in panel B of FIG. 17. As shown in panel
C of FIG. 17, resist mask 213 is made from layer 210 by
lithography (¢.g., photolithography, electron beam lithogra-
phy, nanoimprint lithography). As shown in panel D of FIG.
17, a portion of device layer 212 that is unprotected by resist
mask 213 is etched, and a selected portion of device layer
212, that is protected by resist mask 213, forms waveguides
215 and photonic temperature sensor 216. As shown in panel
E of FIG. 17, resist mask 213 is dissolved in a solvent, or
selectively etch away in plasma, to expose waveguides 215
and photonic temperature sensor 216. As shown in panel F
of FIG. 17, a cladded dielectric 206 is formed by depositing
an insulating layer such as silicon dioxide on top of wave-



Patent Application Publication Feb. 2, 2023. Sheet 6 of 21 US 2023/0032022 Al

(B) 200

203

204



Patent Application Publication Feb. 2, 2023. Sheet 5 of 21 US 2023/0032022 Al

217

202

216 203

A-A 200 202
200 215 2"
207 250 4 250 216

n i Pans MN oe Px ll i T = — 06
Ht aH
r= — =
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aed
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rsok-2-b-4-~---

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Patent Application Publication Feb. 2, 2023 Sheet 18 of 21 US 2023/0032022 Al

IN
io

238 / 252

|
i=
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| Heat
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rz ( ; leg \ _ — 250
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Patent Application Publication Feb. 2, 2023 Sheet 8 of 21 US 2023/0032022 Al

215252

Ww
203 215 246 J

202 —j

\ O5

204

NJ
\



US 2023/0032022 Al

However, the photonic temperature sensor allows for inte-
gration of carbon nanotube absorbers in photonic bolometer
200.

[0030] _Ithas been discovered that photonic bolometer 200
measure radiation incident upon photon absorber 217 of
photonic bolometer 200 over a broad frequency range, ¢.g..
from ultraviolet wavelengths (~0.2 jm) to far infrared
wavelengths (~200 um) of the radiation. Photon absorber
217 produces heat from the incident radiation. The heat is
sensed by a photonic temperature sensor (or quantum stan-
dard) that can be fabricated from silicon-on-insulator (or
other photonics semiconductor materials, e.g., silicon
nitride, AIN, a III-V semiconductor, and the like). Advan-
tageously, photonic bolometer 200 can include a plurality of
chip-scale. single photonic bolmetric pixels 252 that are
multiplexed and arranged in a multi-pixel array, wherein in
addition to sensing the incident radiation, the array can
image the extent of the incident radiation over, e.g., a
two-dimensional surface area.

[0031] Photonic bolometer 200 performs broadband high-
absorption photonic bolometry. In an embodiment, with
reference to FIG. 1, FIG, 2, FIG. 3, FIG. 4, and FIG. 5, FIG.
6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, FIG, 12, FIG.
13, FIG. 14, FIG. 15, FIG. 16, and FIG. 18, photonic
bolometer 200 includes: photonic chip 201; weak thermal
link 250 disposed on and in mechanical communication with
photonic chip 201; thermally-isolated member 202 disposed
on weak thermal link 250 and in mechanical communication
with the weak thermal link 250, such that weak thermal link
250 is interposed between thermally-isolated member 202
and photonic chip 201, and weak thermal link 250 thermally
isolates thermally-isolated member 202 from photonic chip
201; photonic temperature sensor 216 disposed on ther-
mally-isolated member 202 and including a resonance fre-
quency from which a temperature of thermally-isolated
member 202 is determinable and that varies with tempera-
ture of thermally-isolated member 202, wherein photonic
temperature sensor 216 receives primary probe light 238
from chip waveguide 215 and produces bolometer light 244
from primary probe light 238; chip waveguide 215 disposed
on thermally-isolated member 202 in optical communication
with photonic temperature sensor 216 and that communi-
cates primary probe light 238 to photonic temperature sensor
216 and that monitors transmission and storage of primary
probe light 238 by photonic temperature sensor 216,
wherein chip waveguide 215 receives bolometer light 244
from photonic temperature sensor 216 to determine the
temperature of thermally-isolated member 202 via a change
in resonance frequency of photonic temperature sensor 216;
and photon absorber 217 disposed on thermally-isolated
member 202 in thermal communication with photonic tem-
perature sensor 216 and that receives incident radiation light
236, increases temperature due to absorption of incident
radiation light 236, heats photonic temperature sensor 216 in
response to receipt of incident radiation light 236, and
changes the resonance frequency of photonic temperature
sensor 216 in response to receiving incident radiation light
236.

[0032] In an embodiment, photonic bolometer 200
includes isolation trench 203 bounded by photonic chip 201
and thermally-isolated member 202, such that isolation
trench 203 is interposed between photonic chip 201 and
thermally-isolated member 202. In an embodiment, isolation
trench 203 surrounds the thermally-isolated member 202.

Feb. 2, 2023

[0033] In an embodiment, photonic bolometer 200
includes a reference phonic thermometer disposed on pho-
tonic chip 201 to measure a temperature of substrate 204
without measuring the temperature of thermally-isolated
member 202.

[0034] In an embodiment, weak thermal link 250
mechanically interconnects thermally-isolated member 202
and photonic chip 201.

[0035] In an embodiment, photonic bolometer 200
includes undercut 209 arranged between substrate 204 and
thermally-isolated member 202, e.g., as shown in FIG. 16. In
an embodiment, undercut 209 spaces apart substrate 204 and
thermally-isolated member 202 so that chip waveguide 215,
photonic temperature sensor 216, and photon absorber 217
are suspended above and relative to substrate 204, with chip
waveguide 215 extending from opposing portions of oxide
dielectric 205, which are interposed between chip wave-
guide 215 and substrate 204, over substrate 204, and photon
absorber 217 is disposed on photonic temperature sensor
216.

[0036] Various arrangements of chip waveguide 215, pho-
tonic temperature sensor 216, and photon absorber 217 in
thermally-isolated member 202 are contemplated. In an
embodiment, photonic temperature sensor 216 is interposed
between chip waveguide 215 and photon absorber 217. In an
embodiment, photonic temperature sensor 216 and photon
absorber 217 are disposed proximate to chip waveguide 215,
and photon absorber 217 is disposed on photonic tempera-
ture sensor 216 so that photonic temperature sensor 216 is
interposed between photon absorber 217 and thermally-
isolated member 202.

[0037] In an embodiment, photonic chip 201, thermally-
isolated member 202, and weak thermal link 250 indepen-
dently comprise a semiconductive material. In an embodi-
ment, photonic temperature sensor 216 includes a
semiconductive material. In an embodiment, photonic tem-
perature sensor 216 includes a photonic crystal cavity, a ring
resonator, or a disk resonator, such that the resonance
frequency of photonic temperature sensor 216 is sensitive to
temperature. In an embodiment, photon absorber 217
includes vertically aligned carbon nanotubes.

[0038] In an embodiment, photonic bolometer 200
includes cladded dielectric 206 disposed on photonic tem-
perature sensor 216, such that photonic temperature sensor
216 is interposed between cladded dielectric 206 and sub-
strate 204.

[0039] In an embodiment, weak thermal link 250, ther-
mally-isolated member 202, photonic temperature sensor
216, and photon absorber 217 are arranged as a single
photonic bolometric pixel 252 in photonic bolometer 200. In
an embodiment, photonic bolometer 200 further includes
additional photonic bolometric pixels 252 arranged in an
array. In an embodiment, chip waveguide 215 extends along
photonic bolometer 200 so that chip waveguide 215 is in
optical communication with each photonic temperature sen-
sor 216 in each photonic bolometric pixel 252 and: com-
municates primary probe light 238 to each photonic tem-
perature sensor 216 in each photonic bolometric pixel 252;
and receives bolometer light 244 from each photonic tem-
perature sensor 216 in each photonic bolometric pixel 252,
such that the at least a two-dimensional temperature map is
obtained across photonic bolometer 200 from bolometer
light 244 from each photonic temperature sensor 216 in each
photonic bolometric pixel 252. The temperature map can be



as) United States
a2) Patent Application Publication co) Pub. No.: US 2023/0032022 Al

300320224

Klimov et al. (43) Pub. Date: Feb. 2, 2023
(54) PHOTONIC BOLOMETER AND Publication Classification
PERFORMING BROADBAND (51) Int.
OoNeR TION PHOTONIC GOI 5/58 (2006.01)
GOLT 5/0818 (2006.01)
(71) Applicant: Government of the United States of ean Seen
America, as represented by the O14 i )
Secretary of Commerce, Gaithersburg, 2) , .
MD (Us) . . GOLT 5/58 (2013.01); GOLF 5/0818
(2013.01); GOLJ 5/0853 (2013.01); GOIT 5/20
(72) Inventors: Nikolai Nikolaevich Klimov, Ellicott (2013.01)
City, MD (US); Nathan Andrew
Tomlin, Boulder, CO (US); .
Christopher Shing-Yu Yung, 6n ABSTRACT
Louisville, CO (US) .
‘A photonic bolometer includes: a photonic chip; a weak
(21) Appl. No: 17/957,817 thermal link; a thermally-isolated member, and the weak
thermal link thermally isolates the thermally-isolated mem-
(22) Filed: Sep. 30, 2022 ber from the photonic chip; a photonic temperature sensor;
a chip waveguide in optical communication with the pho-
Related U.S. Application Data tonic temperature sensor; and a photon absorber that
- coti receives incident radiation light, increases temperature due
(65) _ Continua ton-n-pan of application No. 17486852. ig absorption of the incident radiation light, heats the pho-
Sep. 27, 2021. tonic temperature sensor in response to receipt of the inci-
(60) Provisional application No. 63/083,218, filed on Sep. _ dent radiation light, and changes the resonance frequency of

25, 2020, provisional application No. 63/251,186,
filed on Oct. 1, 2021.

the photonic temperature sensor in response to receiving the
incident radiation light.



Patent Application Publication Feb. 2, 2023 Sheet 11 of 21 US 2023/0032022 Al

200

(C)

201 215 252

217 //
203

202

216

“A 200 7"

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fe ee 206
tt fata al ra ——
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_ 7 205

20
B-B 200
215
203 202

207
205
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204



Patent Application Publication Feb. 2, 2023 Sheet 10 of 21

201 215 252

217 Ww)
- 203

216

202

US 2023/0032022 Al

\ eo <p sos
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US 2023/0032022 Al

embodiments. The first current and the second current are
both currents, but they are not the same condition unless
explicitly stated as such.

[0087] The modifier about used in connection with a
quantity is inclusive of the stated value and has the meaning
dictated by the context (e.g., it includes the degree of error
associated with measurement of the particular quantity). The
conjunction 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 photonic bolometer for performing broadband high-
absorption photonic bolometry, the photonic bolometer
comprising:

a photonic chip;

a weak thermal link disposed on and in mechanical

communication with the photonic chip;

a thermally-isolated member disposed on the weak ther-
mal link and in mechanical communication with the
weak thermal link, such that the weak thermal link is
interposed between the thermally-isolated member and
the photonic chip, and the weak thermal link thermally
isolates the thermally-isolated member from the pho-
tonic chip:

a photonic temperature sensor disposed on the thermally-
isolated member and comprising a resonance frequency
from which a temperature of the thermally-isolated
member is determinable and that varies with tempera-
ture of the thermally-isolated member, wherein the
photonic temperature sensor receives primary probe
light from a chip waveguide and produces a bolometer
light from the primary probe light;

the chip waveguide disposed on the thermally-isolated
member in optical communication with the photonic
temperature sensor and that communicates the primary
probe light to the photonic temperature sensor and that
monitors transmission and storage of the primary probe
light by the photonic temperature sensor, wherein the
chip waveguide receives the bolometer light from the
photonic temperature sensor to determine the tempera-
ture of the thermally-isolated member via a change in
resonance frequency of the photonic temperature sen-
sor; and

a photon absorber disposed on the thermally-isolated
member in thermal communication with the photonic
temperature sensor and that receives incident radiation
light, increases temperature due to absorption of the
incident radiation light, heats the photonic temperature
sensor in response to receipt of the incident radiation
light, and changes the resonance frequency of the
photonic temperature sensor in response to receiving
the incident radiation light.

2. The photonic bolometer of claim 1, further comprising
an isolation trench bounded by the photonic chip and the
thermally-isolated member, such that the isolation trench is
interposed between the photonic chip and the thermally-
isolated member.

3. The photonic bolometer of claim 2, wherein the isola-
tion trench surrounds the thermally-isolated member.

4. The photonic bolometer of claim 1, further comprising
a reference phonic thermometer disposed on the photonic
chip to measures a temperature of the substrate.

Feb. 2, 2023

5. The photonic bolometer of claim 1, wherein the weak
thermal link mechanically interconnects the thermally-iso-
lated member and the photonic chip.

6. The photonic bolometer of claim 1, further comprising
an undercut arranged between the substrate and the ther-
mally-isolated member

7. The photonic bolometer of claim 6, wherein the under-
cut spaces apart the substrate and the thermally-isolated
member so that the chip waveguide, the photonic tempera-
ture sensor, and the photon absorber are suspended above
and relative to the substrate, with the chip waveguide
extending from opposing portions of an oxide dielectric,
which are interposed between the chip waveguide and the
substrate, over the substrate, and the photon absorber is
disposed on the photonic temperature sensor.

8. The photonic bolometer of claim 1, wherein the pho-
tonic temperature sensor is interposed between the chip
waveguide and the photon absorber.

9. The photonic bolometer of claim 1, wherein the pho-
tonic temperature sensor and the photon absorber are dis-
posed proximate to the chip waveguide, and the photon
absorber is disposed on the photonic temperature sensor so
that the photonic temperature sensor is interposed between
the photon absorber and the thermally-isolated member.

10. The photonic bolometer of claim 1, wherein the
photonic chip, the thermally-isolated member, and the weak
thermal link independently comprise a semiconductive
material.

11. The photonic bolometer of claim 1, wherein the
photonic temperature sensor comprises a photonic crystal
cavity, a ring resonator, or a disk resonator, such that the
resonance frequency of the photonic temperature sensor is
sensitive to temperature.

12. The photonic bolometer of claim 1, further comprising
a cladded dielectric disposed on the photonic temperature
sensor, such that the photonic temperature sensor is inter-
posed between the cladded dielectric and the substrate.

13. The photonic bolometer of claim 1, wherein the
photonic temperature sensor comprises a semiconductive
material.

14. The photonic bolometer of claim 1, wherein the
photon absorber comprises vertically aligned carbon nano-
tubes.

15. The photonic bolometer of claim 1, wherein the weak
thermal link, the thermally-isolated member, the photonic
temperature sensor, and the photon absorber are arranged as
a single photonic bolometric pixel in the photonic bolom-
eter.

16. The photonic bolometer of claim 15, further compris-
ing additional photonic bolometric pixels arranged in an
array.

17. The photonic bolometer of claim 16, wherein the chip
waveguide extends along the photonic bolometer so that the
chip waveguide is in optical communication with each
photonic temperature sensor in each photonic bolometric
pixel and:

communicates primary probe light to each photonic tem-

perature sensor in each photonic bolometric pixel; and
receives bolometer light from each photonic temperature
sensor in each photonic bolometric pixel,

such that the at least a two-dimensional temperature map

is obtained across the photonic bolometer from the
bolometer light from each photonic temperature sensor
in each photonic bolometric pixel.



US 2023/0032022 Al

guides 215 and photonic temperature sensor 216 by chemi-
cal vapor deposition or plasma-enhanced chemical vapor
deposition, atomic layer deposition. As shown in paned G of
FIG. 17 a bottom resist layer is deposited on the substrate
204 by spin-coating. As shown in panel H of FIG. 17, resist
mask 214 is made from layer 211 by lithography (e.g.,
photolithography, electron beam lithography, nanoimprint
lithography). As shown in panel I of FIG. 17, a portion of
substrate 204 that is unprotected by resist mask 214 is
etched, and a selected portion of substrate 204, that is
protected by resist mask 214, forms etched cavity 208 or
membrane 207. As shown on panel J of FIG. 17 after
forming etch cavity 208 or membrane 207, the bottom etch
mask 214 is dissolved in solvent. Also, a top resist layer 210
is spin-coated on top of cladded dielectric 206. shown on
panel K of FIG. 17 the etch mask 115 for isolation trench
203 is made from layer 210 by lithography (¢.g., photoli-
thography, electron beam lithography, nanoimprint lithog-
raphy). As shown on panel L of FIG. 17 areas of cladded
dielectric 206 that are not protected by etch mask 115 are
etched to form isolation trench 203. Following the formation
of isolation trench 203, resist mask 115 is dissolved in
solvents or selectively etched away in plasma (as shown on
panel M of FIG. 17). As shown in panel N of FIG. 17
VACNTS are grown over thermally-isolated member 202 to
form photon absorber 217

[0078] Single-pixel photonic bolometers can be made into
photonic bolometer arrays by multiplexing a single pixel
bolometer into a plurality of bolometers, coupled to the
common waveguide 215.

[0079] Photonic bolometer 200 has numerous advanta-
geous and unexpected benefits and uses. In an embodiment,
a process for performing broadband high-absorption pho-
tonic bolometry with photonic bolometer 200 includes:
receiving primary probe light 238 by a chip waveguide 215
of the photonic bolometer 200; communicating the primary
probe light 238 from the chip waveguide 215 to a photonic
temperature sensor 216 of the photonic bolometer 200;
receiving incident radiation light 236 by a photon absorber
217 of the photonic bolometer 200; increasing the tempera-
ture of the photon absorber 217 in response to receiving the
incident radiation light 236; communicating heat from the
photon absorber 217 to the photonic temperature sensor 216;
receiving, by the photonic temperature sensor 216, the heat
from the photon absorber 217 and increasing a temperature
of the photonic temperature sensor 216 in response to
receiving the heat from the photon absorber 217; changing
‘a resonance frequency of the photonic temperature sensor
216 in response to increasing the temperature of the pho-
tonic temperature sensor 216 due to absorption of the
incident radiation light 236 by the photon absorber 217;
producing, by the photonic temperature sensor 216, bolom-
eter light 244 from the primary probe light 238 based on the
change of the resonance frequency due to heating the
photonic temperature sensor 216; communicating the
bolometer light 244 from the photonic temperature sensor
216 to the chip waveguide 215; and determining the tem-
perature change of the photonic temperature sensor 216 due
to the absorption of the incident radiation light 236 by the
photon absorber 217 from the bolometer light 244 to per-
form broadband high-absorption photonic bolometry.
[0080] Advantageously, photonic bolometer 200 uses sili-
con photonics and carbon nanotubes with a silicon wave-
guide that are compatible with carbon nanotube growth and

Feb. 2, 2023

processing. It is contemplated that the bolometer can include
unsuspended high-Q optical resonators with or without
carbon nanotubes to measure differential response, a sus-
pended (or supported by a thermally isolation area/mem-
brane) high-Q optical resonator, or a linear array of elements
for multiplexed read out.

[0081] Integrated silicon waveguides and associated sili-
con photonic devices such as photonic crystal cavities, ring
resonators, and the like can include carbon nanotubes. A’
high temperature growth process (800° C.), thin film catalyst
(Fe, Ni, Co or other transition metal), and support catalyst
(aluminum oxide, aluminum nitride, or other metal oxide/
nitride) do not degrade waveguide performance as indicated
by transmission measurement of power through a selectively
patterned region with grown carbon nanotubes is not notice-
ably attenuated. A scanning electron microscope image is
shown for VACNTs grown on top of photonic thermometer
in FIG. 2.

[0082] _ 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.

[0083] 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 other-
wise stated or contextually inapplicable, all percentages,
when expressing a quantity, are weight percentages. The
suffix (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 option-
ally means that the subsequently described event or circum-
stance 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.

[0084] As used herein, a combination thereof refers to a
combination comprising at least one of the named constitu-
ents, components, compounds, or elements, optionally
together with one or more of the same class of constituents,
components, compounds, or elements.

[0085] All references are incorporated herein by reference.

[0086] The use of the terms “a,” “an,” and “the” and
similar referents in the context of describing the invention
(especially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
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



Patent Application Publication Feb. 2, 2023. Sheet 7 of 21 US 2023/0032022 Al

(B) 200

203

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Patent Application Publication

(A)2

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Feb. 2, 2023 Sheet 21 of 21

US 2023/0032022 Al

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FIG. 21


US 2023/0032022 Al

components, wherein such components can be intercon-
nected and placed in communication (e.g., optical commu-
nication, electrical communication, mechanical communi-
cation, and the like) by physical, chemical, optical, or
free-space interconnects. The components can be disposed
on mounts that can be disposed on a bulkhead for alignment
‘or physical compartmentalization. As a result, photonic
bolometer 200 can be disposed in a terrestrial environment
or space environment. Elements of photonic bolometer 200
can be formed from silicon, silicon nitride, and the like
although other suitable materials, such ceramic. glass, or
metal can be used. According to an embodiment, the ele-
ments of photonic bolometer 200 are formed using 3D
printing although the elements of photonic bolometer 200
can be formed using other methods, such as injection
molding or machining a stock material such as block of
material that is subjected to removal of material such as by
cutting, laser oblation, chemical vapor deposition, etching,
and the like. Accordingly, photonic bolometer 200 can be
made by additive or subtractive manufacturing. In an
embodiment, elements of photonic bolometer 200 are selec-
tively etched to remove various different materials using
different etchants and photolithographic masks and proce-
dures. The various layers thus formed can be subjected to
joining by bonding to form photonic bolometer 200.

[0057] Bolometer light 244 Produced by photonic tem-
perature sensor 216 can be communicated to photonic
bolometry system 251 for determine of the temperature
increase of photon absorber 217 caused by incident radiation
light 236 as well as properties of incident radiation light 236.
In an embodiment, with reference to FIG. 19, FIG. 20, and
FIG. 21, photonic bolometer 200 performs performing
broadband high-absorption photonic bolometry and can
include various optical and electrical features to determine
temperature, optical resonance shifts, and the like. Here,
incident radiation light 236 is received by photonic bolom-
eter 200; probe light source 218 receives control light signal
248 and produces, based on control light signal 248, primary
probe light 238 that includes primary wavelength 239 and
primary power 243. Photonic bolometer 200 is in commu-
nication with probe light source 218 and includes chip
waveguide 215, photonic temperature sensor 216, and pho-
ton absorber 217. Waveguide 215 is in communication with
photonic temperature sensor 216 and receives primary probe
light 238; photonic temperature sensor 216 in communica-
tion with waveguide 215 and: interacts with primary probe
light 238 from waveguide 215, and stores primary probe
light 238 when primary wavelength 239 matches resonance
frequency 240 of photonic temperature sensor 216, such that
‘an amount of primary probe light 238 stored in photonic
temperature sensor 216 includes absorption power 242.
Waveguide 215 receives primary probe light 238 after
primary probe light 238 has interacted with photonic tem-
perature sensor 216. Bolometer light 244 includes transmis-
sion power 241 that is indirectly proportional to absorption
power 242 of primary probe light 238 stored in photonic
temperature sensor 216. Photodector 225 is in communica-
tion with photonic bolometer 200 and receives bolometer
light 244 from photonic bolometer 200; and produces pho-
todetector signal 245 from bolometer light 244. Phase sen-
sitive detector 229 is in communication with photodetector
225 and receives photodetector signal 245 from photode-
tector 225; receives reference frequency signal 246: and
produces lock signal 247 from photodetector signal 245,

Feb. 2, 2023

based on reference frequency signal 246. Local oscillator
228 is in communication with phase sensitive detector 229
and produces reference frequency signal 246. Servo con-
troller 230 is in communication with phase sensitive detector
229 and local oscillator 228 and receives lock signal 247
from phase sensitive detector 229; receives reference fre-
quency signal 246 from local oscillator 228; and produces
control light signal 248 from lock signal 247 and reference
frequency signal 246 such that absorption power 242 is
maximized through wavelength control of probe light source
218 by control light signal 248.

[0058] In photonic bolometry system 251, transducer 231
can be electrically interposed between and in communica-
tion with light source 218 and servo controller 230. Trans-
ducer 231 receives control light signal 248 from servo
controller 230; produces transduction control signal 249
based on control light signal 248; and communicates trans-
duction control signal 249 to probe light source 218 to
control production of primary wavelength 239 by light
source 218. Wavelength meter 220 is in communication with
light source 218 and receives primary probe light 238 from
probe light source 218 and determines a wavelength of
primary wavelength 239. Optical isolator 221, optical
attenuator 222, polarization controller 223, or a combination
of at least one of the foregoing optical elements is in
communication with probe light source 218 and receives
primary probe light 238 and varies a property of primary
probe light 238. The property of primary probe light 238 that
is varied can include a broadband light or a coherent light
with a narrow linewidth to provide primary probe light 238
to photonic bolometer 200. Optical power meter 224 is in
communication with photonic bolometer 200 and receives
bolometer light 244 from photonic bolometer 200 and
determines transmission power 241.

[0059] In photonic bolometry system 251, bolometer light
244 can be controlled by control light signal 248. It is
contemplated that transducer 231 can change the frequency
of the probe light source 218 and can include piezo actuator
that changes the cavity length. Exemplary transducers 231
include a piezo actuation element, current transducer, Peltier
heater and or cooler. In an embodiment, transducer 231
includes piezo actuator that changes the cavity length.
[0060] Probe light source 218 produces primary probe
light 238. Primary probe light 238 can include light a
broadband source or a coherent light source with a narrow
linewidth to provide primary probe light 238 to photonic
bolometer 200, and can be a light emitted diode, and arc
lamp, an infrared laser, a visible laser, and ultraviolet laser,
and the like. Exemplary primary probe lights 608 can be
tunable diode lasers. Moreover, in the embodiment, primary
probe light 238 is emitted form a C-band tunable laser. A
wavelength of primary probe light 238 can be from 200 nm
to 10 um, specifically from 400 nm to 3 um, and more
specifically from 500 nm to 2 A power of primary probe light
238 can be from of primary probe light 238 can be from 10
nW to 100 mW, specifically from 50 nW to 50 mW, and
more specifically from 100 nW to 10 mW. In an embodi-
ment, primary probe light 238 includes light from C-band
tunable laser in a wavelength from 1520 nm to 1570 nm and.
a laser power from 0.1 mW to 20 mW.

[0061] Primary probe light 238 is converted to bolometer
light 244 in photonic bolometer 200. Bolometer light 244
can include light transmitted along waveguide 215 with a
reduced transmission at the resonant frequency of the pho-


Patent Application Publication Feb. 2, 2023. Sheet 3 of 21 US 2023/0032022 Al

200
(A)

4

of ape.

=
1
Fa

2415 217

200 203 a
207 202 +

216
iS 206

204

208]



Patent Application Publication Feb. 2, 2023 Sheet 14 of 21 US 2023/0032022 Al

In

(D)

202

203

A-A 200

204

215
203

205

204



Patent Application Publication Feb. 2, 2023 Sheet 16 of 21 US 2023/0032022 Al

2 21 pe 252
7 Z 201
A“ aM
\d
iM ‘s
217 —_]
209
A-A 200
216
209
205
. 205
204
a °
B-B 200 206 215
205
7
a TM 204

FIG. 16


Patent Application Publication Feb. 2, 2023 Sheet 2 of 21 US 2023/0032022 Al

217

In
IS

215

216

215

216 Reference thermometer

FIG. 2


US 2023/0032022 Al

a spatial map of incident radiation light 236 that is absorbed
by the plurality of photon absorbers 217 disposed in the
array of photonic bolometric pixels 252.

[0040] In an embodiment, photonic bolometer 200 can
include additional layers. Such layers can include oxide
dielectric 205, dielectric membrane 207, dielectric mem-
brane 207 among others that can be used for electrical
insulation or selective conduction, optical or thermal isola-
tion and the like. It should be appreciated that an order of the
layers and a number of repeats of any of these layers in a
stacked structure can occur based on a desired application or
environment of operation of photonic bolometer 200. For
example, with reference to FIG. 3, dielectric membrane 207
can be interposed between photon absorber 217 that is
disposed on photonic temperature sensor 216. Photonic chip
201 can include substrate 204 and oxide dielectric 205
disposed on substrate 204. The thermally-isolated member
202 has a very weak thermal link to photonic chip 201 and
can include dielectric membrane 207, etch cavity 208,
undercut 209, or isolation trench 203. Further, photonic
temperature sensor 216 can be, e.g., a photonic crystal
cavity, ring resonator, or disk resonator, such that the reso-
nance frequency thereof is sensitive to temperature. Since
photonic temperature sensor 216 is disposed on thermally-
isolated member 202. the temperature rise sensed by pho-
tonic temperature sensor 216 is determined using optical
frequency metrology. In an embodiment, photonic tempera-
ture sensor 216 is coated, e.g., top-covered, with cladded
dielectric 206.

[0041] Probe light 237 is coupled to and from photonic
temperature sensor 216 via chip waveguide 215 disposed
proximate to photonic temperature sensor 216. Vertically
aligned carbon nanotubes (VACNTs) can be grown as pho-
ton absorber 217 over photonic temperature sensor 216,
providing for an isothermal pixel structure, wherein incident
radiation light 236 is absorbed by photon absorber 217 and
converted therewith to heat. VACNTs in photon absorber
217 absorb incident radiation light 236 (e.g., light) and
transform it into heat, raising the temperature of thermally-
isolated member 202 (but not ref a201) and sensed by
photonic temperature sensor 216.

[0042] Inan embodiment, an additional photonic tempera-
ture sensor 216 (referred to herein as a reference photonic
thermometer) and chip waveguide 215 can be disposed on
photonic chip 201, external to thermally-isolated member
202, wherein the reference phonic thermometer measures a
bulk or substrate (reference) temperature of photonic chip
201. The temperature difference between the reference pho-
tonic temperature sensor 216 and photonic temperature
sensor 216 give the temperature rise solely due to absorbed
incident radiation light 236, illumination temperature fluc-
tuation of the surrounding environment where photonic chip
201 is located.

[0043] Substrate 204 can include a material that can be
processed (e.g., micromachined, including lithography and
the like) to form a support structure for photonic temperature
sensor 216. Exemplary substrates 204 include wafers or dies
of silicon, sapphire, silicon carbide or III-V materials. A
thickness of substrate 204 can be from 100 jum to 10 mm,
specifically from 250 pm to 1 mm, and more specifically
from 550 jum to 680 uum. In an embodiment, substrate 204
includes a semiconductor. An exemplary semiconductor is
an element from group 11, 12, 13, 14, 15, or 16 (UPAC
nomenclature, which respectively is identical to group I, II,

Feb. 2, 2023

III, IV, V, or VI) of the periodic table such as a Si, Ga, Ge,
‘As, In, Sn, Sb, Te, At, Hf, Zn, and the like, or a combination
thereof. According to an embodiment, substrate 204 is a
compound semiconductor such as SiC, SiGe, GaN; a group
13-15 (also referred to as a group III-V) semiconductor such
as AISb, AlAs, Aln, AIP, BN, GaSb, GaAs, GaN, GaP, InSb,
InAs, InN, InP, and the like; a group 12-16 (group II-VI)
semiconductor such as CdSe, CdS, CdTe, ZnO, ZnSe, ZnS,
ZnTe, and the like; a group 11-17 (group I-VII) semicon-
ductor such as CuCl and the Ii group 14-16 (group
TV-VI) semiconductor such as PbS, PbTe SnS, and the like;
a layer semiconductor such as PbI,, MoS,, GaSe, and the
like; an oxide semiconductor such as CuO, Cu,O, and the
like; (Al,Ga)N, (Al,Ga)As, (In,Ga)As, (Al,Ga)$b, (In,Ga)
Sb, as well as nitride, arsenide, antimonide quaternary II]-V
alloys, or a combination comprising at least one of the
foregoing. Examples of II-VI alloys include, but are not
limited to CdSe, CdTe, CdS, ZnSe, and combinations
thereof. Examples of Group III-V ternary alloys include, but
are not limited to, (Ga,Al)As, (In,Ga)As, and combinations
thereof. Exemplary Group III-V quaternary alloys include
(Ga,In)(As.P), (In, Al,Ga)Sb, and the like. Exemplary Group
Ill-nitride alloys include (Ga,ADN, (Ga,In)N, (ALIn)N, Ga,
AL In)N, and combinations thereof. Quaternary alloys of the
above may also be employed.

[0044] Substrate 204 also can include a supplemental
element such as C, H, N, Li, Na, K, Mg, Ca, Sr, Ba, Bi, B,
Al, P, S, O, and the like in an amount typically less than an
amount of the semiconductor. In an embodiment, common,
substrate 204 includes silicon, and the silicon is optionally
doped. According to an embodiment, the semiconductor is
an intrinsic semiconductor or an extrinsic semiconductor
doped with a selected dopant, e.g., a p-dopant or an n-dop-
ant. In one embodiment, the substrate includes a p-dopant.
In another embodiment, substrate 204 includes an n-dopant.
Ina particular embodiment, substrate 204 is p-doped Si. In
one embodiment, substrate 204 is n-doped Si. Substrate 204
can be produced from, e.g. commercially available semi-
conductor grade p-doped Si having a particular crystalline
orientation, e.g., having Miller indices <111>, <100>, and
the like, Substrate 204 can be amorphous, polycrystalline, or
a single crystal. In an embodiment, substrate 204 has a
stacked structure that includes a plurality of semiconductor
layers such as by forming films as SiGe/Si/SiGe/Si on a Si
substrate. In some embodiments, substrate 204 includes
crystalline domains among amorphous material.

[0045] In an embodiment, substrate 204 includes a glass,
Pyrex, sapphire, polymer, ceramic, or an electrically con-
ductive material, e.g., a metal. Substrate 204 can be elec-
trically conductive, semiconductive, or electrically insulat-
ing. Substrate 204 can include a plurality of layers such
oxide dielectric 205 and top-cladded dielectric oxide 206 on.
a base layer, e.g., of silicon.

[0046] Oxide dielectric 205 can be disposed on substrate
204 to isolate the photonic temperature sensor 216 from
substrate 204. The oxide dielectric 205 can include an oxide
of an clement deposited on substrate 204 or independently
can be an oxide of a semiconductor material such as SiO,.
In an embodiment, substrate 204 includes Si, and oxide
dielectric 205 includes silicon dioxide (SiO,), Additional
oxide dielectric 205 materials include gallium oxide (GaO,),
aluminum oxide (A1,O,), or alloys thereof, oxides of com-
pounds from Groups III and V or alloys thereof, and the like.
Exemplary oxides in oxide dielectric 205 also include ZnO,



Patent Application Publication Feb. 2, 2023. Sheet 1 of 21 US 2023/0032022 Al

200

217

202

216 203

216

202
202

203

FIG. 1


US 2023/0032022 Al Feb. 2, 2023
12

light from a chip waveguide and produces a bolometer
light from the primary probe light:

the chip waveguide disposed on the thermally-isolated
member in optical communication with the photonic
temperature sensor and that communicates the primary
probe light to the photonic temperature sensor and that
monitors transmission and storage of the primary probe
light by the photonic temperature sensor, wherein the
chip waveguide receives the bolometer light from the
photonic temperature sensor to determine the tempera-
ture of the thermally-isolated member via a change in
resonance frequency of the photonic temperature sen-

sor; an

the photon absorber disposed on the thermally-isolated
member in thermal communication with the photonic
temperature sensor and that receives incident radiation
light, increases temperature due to absorption of the
incident radiation light, heats the photonic temperature
sensor in response to receipt of the incident radiation
light, and changes the resonance frequency of the
photonic temperature sensor in response to receiving
the incident radiation light.

+e eee


US 2023/0032022 Al

tonic bolometer 200. A wavelength of bolometer light 244
can be from 200 nm to 10 um, specifically from 400 nm to
3 jum, and more specifically from 500 nm to 2 um. A power
of bolometer light 244 can be from 10 nW to 100 mW,
specifically from 50 nW to 50 mW, and more specifically
from 100 nW to 10 mW. In an embodiment, bolometer light
244 includes light from C-band tunable laser in a wave-
length range from 1520 nm to 1570 nm and laser power from
0.1 mW to 20 mW which passed through the photonic
bolometer 200.

[0062] Optical beam splitter 219 can split or combine
light. Exemplary beam splitters 219 include a waveguide-
based splitter that couples incoming light flux propagating
through an incoming waveguide to two or more waveguides.
Moreover, beam splitter 219 is optionally used to provide a
portion of the light to a wavelength meter 220, an optical
power meter 224, and or photodetector 225, and the like.
Moreover, beam splitter 219 is optionally used to provide a
portion of the light to an optical power meter 224, and or a
wavelength meter 220, and the like. In an embodiment,
beam splitter 219 provides 10% of primary probe light 238
to wavelength meter 220, and 90% of light incident from
light source is directed to photonic bolometer 200. More-
over, in an embodiment, beam splitter 219 provides 50% of
bolometer light 244 to an optical power meter 224, and 50%
of bolometer light 244 to photodetector 225.

[0063] Optical circulator 235 is three- or four-port non-
reciprocal optical device designed that light entering any
port exits from the next port. Optical circulator 235 allows
light to travel in only one direction. In embodiment, optical
circulator 235 is fiber optics circulator, which is non-recip-
rocal optics device, in which the properties of light passing
through the device are not revered when light changes
direction from forward to backward. Exemplary optical
circulator 235 can separate propagating forward in fiber
optics light and reflected backward in fiber optics light.
Exemplary optical circulator is based on Faraday rotator. In
embodiment optical circulator 235 is single mode fiber or
polarization maintaining fiber optics device.

[0064] Wavelength meter 220 an element that determines
wavelength of light incident of it. Exemplary wavelength
monitors 220 diffraction grating, spectrometer, spectrum
analyzer, an etalon, wavelength sell, and frequency combs,
and the like. Moreover, the wavelength meter 220 produces
a wavelength signal that can include a voltage of other
electric or photonic signal whose characteristics are deter-
mined by the measured wavelength and a specified calibra-
tion. Exemplary wavelength signals include DC voltages,
the frequency of AC voltages, DC electric currents, micro-
wave signals, and spectra dispersed by a diffraction grating.
Moreover, the wavelength meter 220 can determine the
frequency of light incident on it. In an embodiment, wave-
length meter 220 produces analog DC voltage signal, and the
wavelength value displayed on a computer.

[0065] Optical isolator 221 can include a magneto-optic
device that only allows light to travel in forward direction,
and prevent the transmission of light in backward direction.
Exemplary optical isolators 221 are Faraday effect isolators.
Moreover, optical isolator can operate in infrared, visible,
and or UV frequency range. In an embodiment, optical
isolator 221 includes fiber-optic, fiber coupled with single-
mode and or polarization maintaining single-mode fiber, and

Feb. 2, 2023

optical isolation between 10 dB and 100 dB, specifically
between 20 dB and 80 dB, more specifically between 30 dB
and 60 dB.

[0066] Optical attenuator 222 can include a free space, and
or fiber-optic device, that produce attenuation of optical
power of incident light. Exemplary optical attenuators 222
include single mode, multimode, polarization-maintaining
optical attenuator, Moreover, optical attenuator 222 can
operate in infrared, visible, and UV frequency range. Fur-
thermore, optical attenuator 222 can be of fixed attenuation,
and of variable attenuation. In an embodiment, optical
attenuator 304 includes fiber-optic variable or fixed attenu-
ator with attenuation range between 1 dB and 100 dB,
specifically between 2 dB and 80 dB, more specifically
between 3 dB and 60 dB.

[0067] Polarization controller 223 can include a free-space
or fiber-optic device that manipulates the polarization of
light. Exemplary polarization controllers 223 include bire-
fringent crystals and calcite polarizers. Moreover, polariza-
tion controller 223 utilizes fiber-optic stress-induced bire-
fringence device that can convert between linear, circular,
and elliptical polarization of light. In an embodiment, polar-
ization controller 223 include fiber-optic device that
utilizes stress-induced birefringence to create two or three
independent fractional wave plates to alter the polarization
in single mode fiber. Moreover, in an embodiment, polar-
ization controller 223 can include in-line polarization con-
troller that can transform an arbitrary input polarization of
light to arbitrary output polarization of light using a sing a
quarter-wave, half-wave, and another quarter-wave plate.
[0068] Optical power meter 224 can include an element to
absorb incident light and another element to quantify the
effect of this absorption, which is proportional to the amount
of the light absorbed. Exemplary optical power meter 224
includes photodiodes and bolometers. Moreover, a device
with a response that is proportional to the power of light
incident upon it may be incorporated into a power meter.
Output signal from optical power meter 224 produces power
signal that can include DC voltages and DC currents. In an
‘embodiment, an optical power meter 224 includes a germa-
nium-based photodiode, when a light is absorbed in the
photodiode, an electron-hole pair is formed within the
device, and a voltage is developed across the photodiode
junction, measuring a photocurrent between photodiode
terminals provides a measure of the optical power incident
upon a detector.

[0069] Photodector 225 can include an element to receives
incident light from which it produces frequency signal,
photodetector signal 245. Exemplary photodetectors 225
includes InGaAs and Si photodiodes. In an embodiment,
photodetector 225 is an element that produces a measurable
voltage or current that can be quantified, in response to
incident light. Thermometer light 420 is converted to pho-
todetector signal 245 by photodetector 225. Photodetector
signal 245 can include a measurable voltage or current
signal that is proportional to incident light. Moreover, a
photodetector signal 245 can include a voltage or other
electric signals. In embodiment, photodetector signal 245
can be produced by a germanium-based photodiode, when a
light is absorbed in the photodiode, an electron-hole pair is
formed within the device, and a voltage is developed across
the photodiode junction, measuring a photocurrent between
photodiode terminals provides a measure of the optical
power incident upon a detector. Exemplary photodetectors



Patent Application Publication Feb. 2, 2023 Sheet 12 of 21 US 2023/0032022 Al

(D

202
203
AL 200
217
12 «~TaL 216
250 B 250
Hi ne pec Lo
ott yt
yl ee ee fy a
_/ eZ ae 204
208 205
B-B 200
215
203

{ 4
7 i 204
= 205
208


Patent Application Publication

Feb. 2, 2023 Sheet 15 of 21. US 2023/0032022 Al

200 215 216

216
_ 205
204
B-B 200 238
206 216
eas
ia
204
i °

FIG. 15