US 11,422,101 B2

7

photonic dew sensor 210 by an amount from 0.1° C. to 200°
C., specifically from 1° C. to 100° C., and more specifically
from 10° C. to 50°C. A size (eg., a longest linear dimen-
sion) of heater 230 can be from | jm to I mm, specifically
from 10 um to 500 jm, and more specifically from 100 um
to 200 um. Moreover, the thickness of the heater 230 can be
from 10 nm to 10 um, and more specifically from 100 nm to
2 wm. In an embodiment, heater 230 includes Pt or Cr film
‘of 200 nm thickness and 50 jm in the longest linear
dimension.

Sensor cover 220 can include a sealed membrane or cap
to isolate photonic temperature sensor 212 and optom-
echanical temperature sensor 214 and can be an impervious
material that prevents the analyte from reaching each of
photonic temperature sensor 212 and optomechanical tem-
perature sensor 214, Exemplary sensor covers 220 include
silicon, silicon dioxide and borosilicate glass. Moreover, the
sensor may incorporate a metal film or polyimide film
deposited over silicon dioxide, borosilicate glass, and the
like. A size (e.g., a longest linear dimension) of sensor cover
220 can be from 2 um to 1000 um, specifically from 5 um
to 500 um, and more specifically from 10 um to 100 jum.
Cavity 222 is a spacing between sensor cover 220 and each
of photonic temperature sensor 212 and optomechanical
temperature sensor 214. Cavity 222 can be a spacing from
0.2 um to 100 um, specifically from 0.5 um to 25 jm, and
more specifically from 1 jum to 10 um. In an embodiment,
sensor cover 220 includes a layer of silicon dioxide depos-
ited over temperature sensor 212 and optomechanical tem-
perature sensor 214 by plasma-enhanced chemical vapor
deposition (PE-CVD). In another embodiment, sensor cover
220 includes borosilicate wafer bonded to temperature sen-
sor substrate 218 over cavity 222.

Photonic dew sensor 210, photonic temperature sensor
212, and optomechanical temperature sensor 214 indepen-
dently include waveguide 232 to guide light along a path and
can be a structure on or over a substrate which transmits
light along the axial direction and confines it in the trans-
verse directions. Exemplary waveguides 232 include rib
waveguides and ridge waveguides. Moreover, the wave-
guide may contain coupling elements to bring light into and
out of the waveguide, such as Bragg couplers or inverse
tapers. A size, ie., a transverse cross-section dimension
relative to a propagation path of primary light 234 in
waveguide 232, can be from 20 nm to 20 um, specifically
from 50 nm to 5 um, and more specifically from 200 nm to
1 um. A transmission loss of waveguide 232 can be from 0.1
dB/em to 50 dB/em, specifically from 0.5 dB/cm to 10
dB/cm, and more specifically from 1 dB/cm to 4 dB/cm at

a wavelength from 500 nm to 10 um, specifically from 750s

nm to 4 um, and more specifically from 1 um to 2.5 mm. In
an embodiment, waveguide 232 includes guides light along
a path; can have dimensions from 300 nm to I ym width, 200
nm to 500 nm height; can include silicon and similar

materials; and can operate at a wavelength from 1 jum to 2.5

yum.
Photonic dew sensor 210, photonic temperature sensor
212, and optomechanical temperature sensor 214 indepen-
dently include resonator 236 that independently can include
a structure with narrow width temperature dependent, fre-
quency dependent dispersion to measure temperature and
can be a photonic structure exhibiting this property. Exem-
plary resonators 236 include ring resonator 246, disk reso-
nator 248, photonic crystal 250, Bragg waveguide 252,
photonic nanobeam 244 over trench 240, and the like. A size
of a width, i.e., a transverse cross-section dimension relative
to a propagation path of primary light 234 in resonator 236,

20

&

&

8

can be from 20 nm to 10 um, specifically from 50 nm to 5
jum, and more specifically from 200 nm to 1 im. A size for
a thickness, i.e., a transverse cross-section dimension rela-
tive to a propagation path of primary light 234 in resonator
236, can be from 50 nm to 5 jum, specifically from 100 nm
to 3 um, more specifically form 200 nm to I jum. The optical
resonator and waveguide independently can be made from a
same or different material as the substrate. In some embodi-
ments, the optical resonator includes sapphire, silicon, silica,
silicon nitride, diamond, silicon carbide, group III-V semi-
conductors, or a combination thereof. Exemplary group
IlI-V semiconductors include AN, GaN, InN, TIN, BP, AIP,
GaP, InP, TIP, BAs, AlAs, GaAs, InAs, TIAs, BSb, AISb,
GaSb, InSb, TISb, BBi, AIBi, GaBi, InBi, TIBi, or a com-
bination thereof. The material for forming the optical reso-
nator can be selected based on a resonant wavelength for the
optical resonator, e. ilicon for devices a resonant fre-
quency in a near infrared region (c.g., up to 2 jum wave-
length), silicon nitride or aluminum nitride for a visible
wavelength, sapphire for a terahertz wavelength, and the
like.

The resonant frequency of the optical resonator includes
a wavelength from 200 nm to 10 um, specifically 400 nm to
3 um, and more specifically 500 nm to 2 um. The output light

5 of the thermometer includes a reduced transmission of the

resonant frequency with respect to the input light. A free
spectral range of the optical resonator is greater than 0.001
nm and specifically from 0.1 nm to 20 nm. A bandwidth of
the optical resonator is from 0.0001 nm to 1 nm. A quality
factor (Q-factor) of the optical resonator is from 1 to 10° and
specifically from 100 to 100,000. It is contemplated that the
optical resonator can have an increased Q-factor by includ-
ing a Bragg waveguide.

Ring resonator 246 is an is an optical resonator that
includes a ring structure separated from waveguide 234. A
size, i.e., a transverse cross-section dimension relative to a
propagation path of primary light 234 in ring resonator 246,
can be from 50 nm to 10 um, specifically from 100 nm to 5
jum, and more specifically from 500 nm to 2.5 jm. A ring
resonator radius can be from 1 ym to 1 mm, specifically,
from 2 um to 500 um, more specifically from 5 jum to 50 pm.
The separation of the ring resonator 246 from the waveguide
246 can be from 20 nm to 3 um, specifically, from 50 nm to
1 um, more specifically, from 100 nm to 500 nm. In an
embodiment, ring resonators 246 has a radius of 10 jum with
transverse dimensions 220 nm in height and 600 nm in width
and is separated from waveguide 234 by 130 nm. Moreover,
the ring resonator has a free spectral range of 9.2 nm at 1550
nm, Q-factor of 50000, and estimated group index of 4.

Disk resonator 248 is an optical resonator comprising a
disc structure that is separated from waveguide 234. A
thickness of a disk resonator 248, can be from 50 nm to 5
4m, specifically from 100 nm to 3 um, more specifically
form 200 nm to 1 um. A radius of a disk structure can be
from 1 jum to 1 mm, specifically, from 2 jum to 500 jum, more
specifically from 5 jm to 50 um. The separation of the disk
resonator 248 from the waveguide 234 can be from 20 nm
to 3 um, specifically, from 50 nm to 1 jum, more specifically,
from 100 nm to 500 nm.

Photonic crystal 250 can include periodic or aperiodic
perturbation of an effective index of refraction through
apertures of different shape disposed therein. In some
embodiments, a plurality of apertures 306 is distributed
along a length axis of a photonic crystal 250. In certain
embodiments, the plurality of apertures 306 have a diameter
of the same size. In an embodiment, some of the plurality of
apertures 306 have different size diameters. According to an



U.S. Patent Aug. 23, 2022 Sheet 12 of 14 US 11,422,101 B2

BIg

Drive off accumulated moisture using integrated microheater,
then turn off heater

Y

Cool sensor using temperature controlled stage while monitoring
temperature sensor and dew sensor

1

When dew sensor registers onset of dew, stabilize temperature
such that dew has formed, but does not completely cover device

4

The temperature read from the temperature sensor will be taken
as the dew (or frost) point

t— 320)

4 322

L—~ 396

Figure. 12


US 11,422,101 B2

15

ously measured by wavelength meter 282. A fraction of
primary light 234 from splitter 280 is communicated via an
optical fiber to wavelength meter 282. Wavelength signal
286 and power signal 288 can be acquired from a commu-
nication interface such as an SMG connector and coaxial
cabling. In this manner, a measured wavelength of some
characteristic feature of device response, e.g., a wavelength
measured when transmitted power is at a maximum can be
determined. A value of wavelength of that feature depends
‘ona presence of dew of analyte 228 or temperature, wherein
photonic dew sensor 210 and photonic temperature sensor
212 sense temperature.

Optomechanical temperature sensor 214 can be subjected
to heterodyne detection as shown in FIG. 7. Output light 238
and primary light 234.3 is detected in heterodyne by an
optical local oscillator frequency, shifted by frequency
shifter 290 that can be fiber-coupled between laser 278 and
‘optomechanical temperature sensor 214.

Regarding a response of photonic dew sensor 210 and
photonic temperature sensor 212, optical responses can be
acquired from wavelength signal 286 and power signal 288
respectively from wavelength meter 282 and power meter
284 to determine transmission spectrum 270, temperature
curve 272, or dew curve 274 as shown in FIG. 9. Panel A
shows transmission spectrum 270 for photonic dew sensor
210, photonic temperature sensor 212, or optomechanical
temperature sensor 214. Resonance wavelength, 2.0, corre-
sponding to a peak center in transmission spectrum 270 is
determined. Panel B shows a temperature curve 272 for a
dependence in temperature of 2.0 in absence of condensation
of analyte 228 on photonic dew sensor 210. As temperature
is decreased, a positive thermo-optic coefficient results in a
decrease of effective refractive index and a decrease of
resonance wavelength. Panel C show dew curve 274 for
dependence of resonance wavelength 40 when analyte 228
accumulates on photonic dew sensor 210 at a fixed tem-
perature. An increasing layer of analyte 228 on photonic dew
sensor 210 increases an effective refractive index of pho-
tonic dew sensor 210. As a result, resonance wavelength 20
increases as the coverage of analyte 228 on photonic dew
sensor 210 increases.

In an embodiment, with reference to FIG. 10, process 302
for calibrating photonic temperature sensor 212 includes
stabilizing a temperature of photonic temperature sensor 212
by thermoelectric member 254 or cooling member 258 to
stabilize, as substantially constant, resonant wavelength A0
of photonic temperature sensor 212. Output light 238 from
optomechanical temperature sensor 214 is subjected to het-
erodyne detection, e.g.. as shown in FIG. 7, wherein output

light 238 is combined with frequency shifted light 290 to s

produced combined light 300.1 and 300.2, which are
detected using detectors 292.1 and 292.2. That is, average
spectral features or correlations of the detected light are
computed to ascertain a scale of thermally excited, Brown-

ian motion of the mechanical element and a fundamental s

scale of quantum noise in the optomechanical system. Using
ratios of spectral features or correlations, the thermody-
namic temperature is computed according to a fundamental
governing equation. As a result, a primary measurement of
thermodynamic temperature from optomechanical tempera-
ture sensor 214 is determined from which the temperature of
photonic temperature sensor 212 is calibrated. Here, process
302 for calibrating can include measuring temperature with
photonic temperature sensor 212 by measuring temperature
induced wavelength shift (step 304); controlling a tempera-
ture of common substrate 226 by controlling a temperature
of thermoelectric member 254 or cooling member 258 with

20

&

&

16

the measured temperature of photonic temperature sensor
212 as a process control variable for thermoelectric member
254 or cooling member 258 (step 306); and, when the
measured temperature of photonic temperature sensor 212 is
stable, calibrating photonic temperature sensor 212 to mea-
sured temperature of optomechanical temperature sensor
214 (step 308). Calibration can be repeated at multiple
different stable temperatures to increase the calibration
accuracy over a range of temperatures.

In an embodiment, with reference to FIG. 11, process 310
for determining an onset of formation of dew of analyte 228
is determined through measurements initiated above the dew
point of analyte 228, wherein process 310 includes simul-
taneously monitoring the optical responses of photonic dew
sensor 210 and photonic temperature sensor 212 (step 312);
decreasing the temperature of common substrate 226, in
thermal contact with photonic dew sensor 210 and photonic
temperature sensor 212, with thermoelectric member 254 or
cooling member 258 (step 314); determining a change in
temperature of photonic dew sensor 210 and photonic tem-
perature sensor 212 with temperature curve 272 by measur-
ing temperature induced wavelength shift; and determining
a change in photonic dew sensor 210 due to an amount of
analyte 228 on photonic dew sensor 210 once the dew point

s of analyte 228 is reached (step 316). When the optical

responses of photonic dew sensor 210 and photonic tem-
perature sensor 212 diverge as determined by a sudden
increase in the difference of the resonant frequencies of the
photonic sensor and the photonic temperature sensor, dew of
analyte 228 has formed on photonic dew sensor 210. A
temperature at which the dew forms on photonic dew sensor
210 is the dew point of analyte 228.

In an embodiment, with reference to FIG. 12, process 318
for determining the dew point includes: removing moisture
from photonic dew sensor 210 prior to determining the dew
point of analyte 228, by heating photonic dew sensor 210
with heater 230 (step 320); terminating heating of photonic
dew sensor 210 with heater 230; supplying electrical current
to thermoelectric member 254 or supplying cooling fluid to
cooling member 258 and cooling photonic dew sensor 210
and photonic temperature sensor 212 (step 322); monitoring
the optical responses of photonic dew sensor 210 and
photonic temperature sensor 212 (step 322); performing
process 310 to determine when dew condenses; when dew
condenses, terminating cooling and actively controlling
thermoelectric member 254 and cooling member 258 by a
difference in the optical responses from photonic dew sensor
210 and photonic temperature sensor 212 as the process
control variable to thermoelectric member 254 and cooling
member 258 to stabilize temperature of thermoelectric mem-
ber 254 and cooling member 258 at a temperature where
moisture of analyte 228 is present on photonic dew sensor
210 but does not completely cover photonic dew sensor 210
(step 324); once the optical response from photonic tem-
perature sensor 212 stabilizes, determining that temperature
reading from photonic temperature sensor 212 as the mea-
sured dew point of analyte 228 (step 708).

In an embodiment, with reference to FIG. 13, process 328
for removing dew from photonic dew sensor 210 includes
achieving reliable and repeatable measurements of dew
point by removing residual moisture from photonic dew
sensor 210 before measuring the dew point of analyte 228 by
heating photonic dew sensor 210 to a temperature greater
than the temperature of the dew point with heater 230;
monitoring output light 238 of photonic dew sensor 210
(step 330); maintaining power supplied to thermoelectric
member 254 and cooling member 258 at a constant level


U.S. Patent Aug. 23, 2022 Sheet 3 of 14 US 11,422,101 B2

ko
[S

“Ta

poceee EZEFH=EEI-FP To PEE ET-EPTI-FH

244

244 236

COT eer rr

(| ns

.
|
(

40

bo

Figure. 3


US 11,422,101 B2

9

embodiment, the plurality of apertures 306 have different
size diameters such that apertures 306 are arranged sym-
metrically with respect to the center of photonic crystal 250
with largest diameter apertures 306 located proximate to
waveguide 232 and smallest diameter apertures 306 located
distal to waveguide 232. Exemplary photonic crystals 250
include apertures circular in shape disposed therein. The size
of apertures can be from 20 nm to 3 jim, specifically from
50 nm to 1 jm, more specifically from 100 nm to 800 nm.

dimension relative to a propagation path of primary light
234 in photonic crystal 250, can be from 50 nm to 10 jum,
specifically from 100 nm to 5 um, and more specifically
from 500 nm to 2.5 jum. In an embodiment, photonic crystal
250 includes circular apertures of diameters ranging from
100 nm to 270 nm, aperture depth of 220 nm, and aperture
period of 335 nm.

Bragg waveguide 252 can include a periodic (as shown on

FIG. 2D) or aperiodic perturbation of an effective index of 2

refraction in optical resonator 236. In an embodiment, the
perturbation causes reflection of light (propagating in Bragg
waveguide 252) for a wavelength of light that satisfies a
Bragg condition. Light at other wavelengths that does not
satisfy the Bragg condition is substantially unaffected by
Bragg waveguide 252. Exemplary Bragg waveguides 252
include square wave modulation of the width of waveguide
232 with modulation period ranging from 50 nm to 5 jum,
specifically from 100 nm to 2.5 jim, more specifically from
200 nm to | jum. Moreover, the modulation width depth can
be from 10 nm to 2 um, specifically from 20 nm to 500 nm,
more specifically from 50 nm to 100 nm. A size, ie, a
transverse cross-section dimension relative to a propagation
path of primary light 234 in Bragg waveguide 252, can be
from 50 nm to 10 um, specifically from 100 nm to 5 jum, and
more specifically from 500 nm to 2.5 um. In an embodiment,
Bragg waveguide 252 includes.

Photonic nanobeam 244 can include periodic or aperiodic
perturbation of an effective index of refraction through
apertures of different shape disposed therein. Photonic nano-
beam 244 can be disposed on a substrate. Photonic nano-
beam 244 can also be suspended over a trench. In some
embodiments, a plurality of apertures is distributed along a
length axis of a photonic nanobeam 244. In certain embodi-
ments, the plurality of apertures has a diameter of the same
size. In an embodiment, some of the plurality of apertures
have different size diameters. According to an embodiment,
the plurality of apertures has different size diameters such
that apertures are arranged symmetrically with respect to the

center of photonic nanobeam 244 with largest diameter 5

apertures located proximate to waveguide 232 and smallest
diameter apertures located distal to waveguide 232. Exem-
plary photonic nanobeam 244 include apertures circular in
shape disposed therein. The size of apertures can be from 20

nm to 3 yim, specifically from 50 nm to 1 jum, more s

specifically from 100 nm to 800 nm. The depth of apertures
can be equal or less than the thickness of the waveguide. A
size, i.e., a transverse cross-section dimension relative to a
propagation path of primary light 234 in photonic nanobeam
244, can be from 50 nm to 10 wm, specifically from 100 nm
to 5 um, and more specifically from 500 nm to 2.5 um. In an
embodiment, photonic nanobeam 244 includes circular aper-
tures of diameters ranging from 100 nm to 270 nm, aperture
depth of 220 nm, and aperture period of 335 nm.

Photonic nanobeam 244 is disposed and suspended over
trench 240 that is disposed in temperature sensor substrate
218 and bounded by wall 242. A size, e.g., a longest linear

&

&

10

dimension and smallest linear dimension, of trench 240 can
be from 500 nm to 2 mm, specifically from 1 jum to 200 um,
and more specifically from 10 jum to 50 um. The depth of
trench 240 can be from 500 nm to 1 mm, specifically from
1 um to 200 um, more specifically from 2 1m to 20 pm. In
an embodiment, trench 240 has depth of 3 um, shortest linear
dimension of 10 um, and longest linear dimension of 50 um.

Primary light 234 can include light from laser 278 trans-
mitted to waveguide 232. Exemplary primary light 234 can
be light emitted from diode, an arc lamp, an infrared laser,
a visible laser, an ultraviolet laser, and the like. Moreover, in
the embodiment, primary light 234 is emitted from a C-band
tunable laser. A wavelength of primary light 234 can be from
200 nm to 10 pm, specifically 400 nm to 3 ym, and more
specifically 500 nm to 2 um. A power of primary light 234
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, primary light 234 includes light from C-band
tunable laser in a wavelength range from 1520 nm to 1570
nm and laser power from 0.1 mW to 20 mW.

Output light 238 can include light transmitted along
waveguide 232 with a reduced transmission at the resonant
frequency of the resonator 236. A wavelength of output light
238 can be from 200 nm to 10 um, specifically 400 nm to 3

5 im, and more specifically 500 nm to 2 um. A power of

output 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 embodiment, output light 238 includes light
from C-band tunable laser in a wavelength range from 1520
nm to 1570 nm and laser power from 0.1 mW to 20 mW
which has passed through the dew sensor 200.

Thermoelectric member 254 can include a Peltier element
to transfer heat into or out of thermal conductor 256 and can
move heat from one of its faces to the other. Exemplary
thermoelectric members 254 include bulk Peltier module
and planar Peltier module. Thermoelectric member 254 can
remove heat from common substrate 226 to cool photonic
dew sensor 210 by from 1° C, to 100° C., specifically from
10° C, to 80° C., and more specifically from 40° C. to 70°
C. Asize (e.g., a longest linear dimension) of thermoelectric
member 254 can be from 0.1 mm to 100 mm, specifically
from | mm to 20 mm, and more specifically from 3 to 10
mm. In an embodiment, thermoelectric member 254
includes a bulk Peltier cooling stage with wire leads sol-
dered in place and with a metalized cold-plate surface. In
another embodiment, thermoelectric member 254 includes a
Peltier cooling stage fabricated by thin-film or thick-film
techniques. In yet another embodiment, thermoelectric
member 254 includes a planar Peltier cooling stage.

Cooling member 258 can include compressed gas con-
fined to channels and one or more orifices through which the
gas may expand to provide cooling and can be made from a
material that is formed or machined such as silicon, glass,
metal, and the like. Exemplary cooling members 258 include
micromachined Joule-Thomson cryocoolers. Cooling mem-
ber 258 can remove heat from dew sensor substrate 216 to
cool photonic dew sensor 210 to a temperature below the
environment by up to from 1 C to 300 C, specifically from
10 C to 200 C, and more specifically from 50 C to 150 C.
A size (e.g., a longest linear dimension) of cooling member
258 can be from 1 mm to 100 mm, specifically from 5 mm
to 50 mm, and more specifically from 10 mm to 20 mm. In
an embodiment, cooling member 258 includes a Joule-
Thomson cryocooler micromachined from a silicon wafer
with high pressure nitrogen gas introduced through tubing
epoxied to the wafer and expelled into the environment
through the orifices built into the structure.



US 11,422,101 B2

21

wherein an intensity of the output light is substantially
lower than an intensity of the primary light when a
wavelength of output light is at a resonance of the
resonator.
18. The relative humidity sensor of claim 11, further
comprising:
a thermoelectric member disposed on the dew sensor
substrate.
19. The relative humidity sensor of claim 18, further
comprising:
a thermal conductor interposed between the dew sensor
substrate and the thermoelectric member.

20. The relative humidity sensor of claim 19, further
comprising:
a cooling member disposed on the thermoelectric mem-
ber,

wherein a second thermal conductor is interposed
between the cooling member and the thermoelectric
member.

22


US 11,422,101 B2

13

shift in frequency can be from 1 kHz to 20 GHy, specifically
from 1 MHz to 1 GHz, and more specifically from 1 MHz
to 250 MHz. In an embodiment, frequency shifter 290
includes a fiber-coupled acousto-optic modulator driven by
a frequency source at the selected frequency through which
a portion of primary light 234 passes. Moreover, shifted
primary light 234.3 can interact with output light 238 to
produce combined light 300.1 and combined light 300.2.
The light signals can be combined with optical element
(280.2) that can include a beam splitter, a set of optical
elements acting as a beam splitter, a fiber-optic coupler, or
other combination of optical elements.

Detectors (292.1, 292.2) independently receive combined
light (300.1, 300.2) from which is produced frequency
signals (296.1, 296.2). Examples of detectors (292.1, 292.2)
include InGaAs or Si photodiodes. Frequency signals
(296.1, 296.2) occur at differences in oscillation frequencies
of components of combined light (300.1, 300.2)

Receiver 294 receives frequency signals (296.1, 296.2)
and can include electronic amplifiers, filters, transformers,
and subtraction circuitry to produce receiver signal 298.
Exemplary receivers 294 include differential amplifiers and
transimpedance amplifiers. Receiver signal 298 can include
information from amplitude and phase modulation on light
that passed through dew point sensor 200. These modula-
tions can arise from interaction of light with optomechanical
temperature sensor 214 in dew point sensor 200. Receiver
signal 298 can be processed with analog and digital signal
processing to compute spectral features and correlations of
the arising amplitude and phase modulations or a linear
combination thereof to calculate the device temperature.
Furthermore, measurements with different frequencies of
shifted primary light 234.3 can be made to reduce depen-
dence of the measurement on a frequency response of
detectors (292.1, 292.2) or receiver 294.

Photonic quantum dew point sensor 200 can be made in
various ways. In an embodiment, with reference to FIG. 8,
a process for making photonic quantum dew point sensor
200 includes: providing common substrate 226 (e.g., a
silicon-on-insulator, silicon nitride-on-insulator, and the
like) that includes silicon; forming an insulator layer (dew
sensor substrate 216 and temperature sensor substrate 218)
‘on common substrate 226 by thermal growth, chemical
vapor deposition or plasma-enhanced chemical vapor depo-
sition; forming device layer 266 (¢.g., silicon, silicon nitride,
and the like) on the insulator layer by smart cut, wafer
bonding, thin film deposition, epitaxial growth; and forming
resist layer 264 on device layer 266 by spin-coating on
device layer 266 as shown in panel A of FIG. 8. As shown

in panel B, resist mask 268 is made from resist layer 264 by s

lithography (¢.g., photolithography, electron beam lithogra-
phy, nanoimprint lithography). As shown in panel C, a
portion of device layer 266 that is unprotected by resist mask
268 is etched, and a selected portion of device layer 266

forms sensor (210, 212, or 214) that is protected by resist s

mask 268. As shown in panel D, resist mask 268 is dissolved
in a solvent to expose sensor (210, 212, or 214). Sensor
cover 220 is formed by depositing an insulating layer such
as silicon dioxide on sensor (212 or 214) as shown in panel
E by chemical vapor deposition or plasma-enhanced chemi-
cal vapor deposition, atomic layer deposition, or as shown in
panels F and G, by bonding sensor cover 220 with cavity 222
such that cavity 222 is aligned with photonic temperature
sensor 212 and optomechanical temperature sensor 214
before bonding. Bonding can be performed by wafer bond-
ing sensor cover 220 to temperature sensor substrate 218 by
laser welding of a glass sinter, anodic bonding, thermal

20

3

&

&

14

compression. Thermoelectric member 254 or cooling mem-
ber 258 can be disposed on dew sensor substrate 216 by
soldering to dew sensor substrate 216 or common substrate
220 if the bottom of the substrate is first metalized, or by
epoxying to the bottom of the substrate. Secondary tempera-
ture sensor 262 can be disposed in communication a digital
meter, microprocessor of other system that is also in com-
munication with photonic quantum dew point sensor 200 to
allow a measurement of relative humidity.

In an embodiment, with reference to FIG. 6, sensor
system 276 includes light source 266 to provide input
primary light 234 to photonic dew point sensor 200. Light
source 278 is a broad band source (e.g., a lamp), a laser, or
a combination thereof. Beam splitter 280 is optionally used
to provide a portion of the input light to a wavelength meter
282 to measure the wavelength of the input light, a photo-
diode, a power meter, and the like. It is contemplated that a
wavelength of the input is measured using, e.g., a wave-
length meter, an etalon, a spectrometer, a wavelength cell, a
spectrum analyzer, and the like. The other portion of light
from laser 278 is directed to photonic dew point sensor 200
Output light from photonic dew point sensor 200 is sent to
second detector 284, which is, e.g., a light detector such as
a photo-diode, charge coupled device, semiconductor detec-

stor (e.g., InGaAs), photomultiplier tube, and the like.

In an embodiment, sensor system 276, as shown in FIG.
7, is made by assembling fiber optic components into a
configuration described for elements (234, 280.1, 234.1,
234.2, 234.3, 290, 238, 280.2, 300.1, 300.2). Elements
(300.1, 300.2) are connected to a balanced photoreceiver
containing elements (292.1, 292.2, 296.1, 296.2, 294),
which output signal 298 into an analog or digital electronics
to compute the temperature.

Photonic quantum dew point sensor 200 has numerous
advantageous and unexpected benefits and uses. Photonic
dew sensor 210 has a property such as resonant frequency,
quality factor, or transmission that changes with an amount
of analyte 228 such as water present ona surface of photonic
dew sensor 210. Photonic temperature sensor 212 has a
property such as resonant frequency that changes with a
change in temperature. Optomechanical temperature sensor
214 includes photonic nanobeam 244 suspended over trench
240, wherein an amplitude of a mechanical oscillation of
photonic nanobeam 244 can be directly related to thermo-
dynamic temperature and measured using a cavity-enhanced
optical probe such as photonic crystal cavity, wherein opto-
mechanical temperature sensor 214 can be a temperature
standard as well as a sensor.

It is contemplated that dew sensor substrate 216 and
temperature sensor substrate 218 can be fabricated on the
same or different components in photonic quantum dew
point sensor 200, wherein dew sensor substrate 216 and
temperature sensor substrate 218 can be thermally bonded
onto common substrate 226. Moreover, heater 230 is proxi-
mate to photonic dew sensor 210 so that a current passed
through heater 230 locally heats photonic dew sensor 210 to
desorb analyte 228 on photonic dew 210.

Sensor (¢.g,, 210, 212, or 214) can be interrogated with
wavelength scanning as shown in FIG. 6, wherein primary
light 234 from tunable laser 278 is communicated to sensor
(e-g., 210, 212, or 214). A fiber-coupled laser 278 can be
used and fiber-coupled to an input port of waveguide 232.
An output port of waveguide 232 can be fiber-coupled and
connected to power meter 284. A power of output light 238
(eg., a transmitted signal of primary light 234 from the
sensor), is recorded from power meter 284 as power signal
288. A wavelength of primary light 234 can be simultane-



US 11,422,101 B2

3

dew point sensor can have a scalable size, and a selected size
of the photonic quantum dew point sensor can be miniature
with a size of about 1 cm*, including micron-sized sensing
elements, that combine fast response speed, highly sensitive
response, precision, and stability greater than conventional
apparatus such as a chilled mirror dew point hygrometer.
The photonic quantum dew point sensor provides rapid
changes in temperature of an optical sensor at a low frost
point, e.g., less than -50° C., and determination of a dew
point in seconds instead of tens of minutes. The photonic
quantum dew point sensor determines dew point for a frost
point temperatures as low as -100° C. in an absence of a
bulky refrigeration system present in conventional chilled
mirror hygrometers. The photonic quantum dew point sen-
sor also has sub-second readout speed with high precision,
e.g, greater than | milliKelvin (mK) to 10 mK.

Photonic quantum dew point sensor 200 determines a dew
point of analyte 228. In an embodiment, with reference to
FIG. 1, photonic quantum dew point sensor 200 includes
common substrate 226; photonic dew sensor 210 disposed
on common substrate 226 and exposed for direct contact
with analyte 228; photonic temperature sensor 212 disposed
‘on common substrate 226; optomechanical temperature sen-
sor 214 disposed on common substrate 226; dew sensor
substrate 216 disposed on common substrate 226 and inter-
posed between photonic dew sensor 210 and common
substrate 226; heater 230 disposed on dew sensor substrate
216 proximate to photonic dew sensor 210 to heat photonic
dew sensor 210 above a dew point of analyte 228; tempera-
ture sensor substrate 218 disposed on common substrate 226
and interposed between common substrate 226 and each of
photonic temperature sensor 212 and optomechanical tem-
perature sensor 214; and sensor cover 220 disposed on
photonic temperature sensor 212, optomechanical tempera-
ture sensor 214, and temperature sensor substrate 218 to
cover photonic temperature sensor 212 and optomechanical
temperature sensor 214 to prevent direct contact between
analyte 228 and each of photonic temperature sensor 212
and optomechanical temperature sensor 214. It should be
appreciated that analyte 228 can directly contact photonic
dew sensor 210. But, due to presence of sensor cover 220
disposed on photonic temperature sensor 212 and optom-
echanical temperature sensor 214, analyte 228 cannot not
directly contact photonic temperature sensor 212 and cannot
directly contact optomechanical temperature sensor 214.

Tn an embodiment, with reference to FIG. 2, photonic dew
sensor 210 and photonic temperature sensor 212 indepen-
dently includes waveguide 232. It is contemplated that
waveguide 232 receives primary light 234; communicates

primary light 234 to resonator 236; receives output light 238 s

from resonator 236; and communicates output light 238
therefrom. In an embodiment, resonator 236 is in optical
communication with waveguide 232 and receives primary
light 234 from waveguide 232; produces output light 238

from primary light 234; and communicates output light 238. 5

to waveguide 232. An intensity of output light 238 is
substantially lower than an intensity of primary light 234
when a wavelength of output light 238 is at a resonance of
resonator 236, e, is shown in panel A of FIG. 9. According
to an embodiment, resonator 236 includes ring resonator 246
(panel A, FIG. 2), disk resonator 248 (panel B, FIG. 2),
photonic crystal 250 (panel C, FIG. 2), or Bragg waveguide
252 (panel D, FIG. 2).

In an embodiment, with reference to FIG. 3, optom-
echanical temperature sensor 214 includes waveguide 232
that receives primary light 234; communicates primary light
234 to resonator 236; receives output light 238 from reso-

20

&

&

4

nator 236; and communicates output light 238 therefrom.
Optomechanical temperature sensor 214 also includes reso-
nator 236 in optical communication with waveguide 232.
Resonator 236 receives primary light 234 from waveguide
232; produces output light 238 from primary light 234; and
communicates output light 238 to waveguide 232. An inten-
sity of output light 238 is substantially lower than an
intensity of primary light 234 when a wavelength of output
light 238 is at a resonance of resonator 236, e.g., as shown
in panel A of FIG. 9. According to an embodiment, resonator
236 includes photonic nanobeam 244 disposed over trench
240, wherein trench 240 is disposed in temperature sensor
substrate 218 and bounded by wall 242 of temperature
sensor substrate 218.

In an embodiment, with reference to FIG. 4, photonic
quantum dew point sensor 200 includes thermoelectric
member 254 disposed on dew sensor substrate 216, as
shown in panel A. In some embodiments, photonic quantum
dew point sensor 200 further includes thermal conductor 256
interposed between dew sensor substrate 216 and thermo-
electric member 254. Photonic quantum dew point sensor
200 can include cooling member 258 disposed on thermo-
electric member 254, wherein a second thermal conductor
256 is interposed between cooling member 258 and ther-

5 moelectric member 254, as shown in panel B.

In an embodiment, with reference to FIG. 5, relative
humidity sensor 260 includes photonic quantum dew point
sensor 200 and secondary temperature sensor 262 in com-
munication with photonic quantum dew point sensor 200.

In an embodiment, with reference to FIG. 6, sensor
system 276 includes laser 278 in optical communication
with photonic quantum dew point sensor 200, wherein laser
278 provides primary light 234. Splitter 280 is optically
interposed between laser 278 and photonic quantum dew
point sensor 200 and optically splits primary light 234 from
laser 278 into primary light 234.1 that is communicated from
splitter 280 to photonic quantum dew point sensor 200; and
primary light 234.2 that is communicated from splitter 280
to wavelength meter 282. Wavelength meter 282 receives
primary light 234.2 and produces wavelength signal 286
from primary light 234.2. Photonic quantum dew point
sensor 200 receives primary light 234.1, produces output
light 238 from primary light 234.1, and communicates
output light 238 to power meter 284 that produces power
signal 288 from output light 238.

In an embodiment, with reference to FIG. 7, sensor
system 276 includes laser 278 in optical communication
with photonic quantum dew point sensor 200, wherein laser
278 provides primary light 234. Splitter 280.1 is optically
interposed between laser 278 and photonic quantum dew
point sensor 200 and optically splits primary light 234 from
laser 278 into primary light 234.1 that is communicated from
splitter 280.1 to photonic quantum dew point sensor 200;
and primary light 234.2 that is communicated from splitter
280.1 to frequency shifter 290. Frequency shifter 290
receives primary light 234.2 and produces shifted primary
light 234.3 from primary light 234.2. Photonic quantum dew
point sensor 200 receives primary light 234.1, produces
output light 238 from primary light 234.1, and communi-
cates output light 238 to splitter 280.2. Splitter 280.2
receives output light 238 from photonic quantum dew point
sensor 200 and shifted primary light 234.3 from frequency
shifter 290; produces combined light 300.1 that is received
by detector 292.1; and produces combined light 300.2 that is
received by detector 292.2. Detector 292.1 produces fre-
quency signal 296.1 from combined light 300.1, and detec-
tor 292.2 produces frequency signal 296.2 from combined


U.S. Patent Aug. 23, 2022 Sheet 8 of 14 US 11,422,101 B2

(A)
264
I 266
— 261, 218
> 226
(B) (E) 212,214
268 (
I 266 co 20
I 216, 218 218
> 226, yo 226
«) () 212, 214
Pi r ( 222
t 210, 212, 214 a 95
47 | 4 220
J 216, 218 =} 218
L— 226 4 216
()

7~ 210, 212, 214

+ 216, 218.

4 226

Figure. 8


U.S. Patent Aug. 23, 2022 Sheet 5 of 14 US 11,422,101 B2

+> 262

200—TM

v

Figure. 5


U.S. Patent Aug. 23, 2022 Sheet 4 of 14 US 11,422,101 B2

re %
&8 8 8 &
a a ( nN (

7 Hs J
i)

Figure. 4

47254

4-226
4-256

(A)



US 11,422,101 B2

5
light 300.2. Heterodyne receiver 294 is in electrical com-
munication with detector 292.1 and detector 292.2; receives
frequency signal 296.1 and frequency signal 296.2; and
produces receiver signal 298 from frequency signal 296.1
and frequency signal 296.2.

In photonic quantum dew point sensor 200, common
substrate 226 can include a material that can be processed
(e.g., micromachined, including lithography and the like) to
form a support structure for dew sensor substrate (e.g., 216)
and temperature sensor substrate (e.g., 218). Exemplary
substrates 226 include wafers or dies of silicon, sapphire,
silicon carbide or III-V materials. A thickness of common,
substrate 226 can be from 100 um to 10 mm, specifically
from 250 um to 1 mm, and more specifically from 550 um
to 680 pm. In an embodiment, common substrate 226
includes a semiconductor. An exemplary semiconductor is
an element from group 11, 12, 13, 14, 15, or 16 (TUPAC
nomenclature, which respectively is identical to group I, II,
IIL, 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, common substrate
226 is a compound semiconductor such as SiC, SiGe, GaN;
a group 13-15 (also referred to as a group III-V) semicon-
ductor 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-VID)
semiconductor such as CuCl and the like; a group 14-16
(group IV-VI) semiconductor such as PbS, PbTe SnS, and
the like; a layer semiconductor such as PbI,, MoS,, GaSe,
an oxide semiconductor such as CuO, Cu,O,
(ALGa)N, (AL.Ga)As, (In,Ga)As, (Al,Ga)Sb,
(In,Ga)Sb, as well as nitride, arsenide, antimonide quater-
nary ITI-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
Il-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.

Common substrate 226 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 226 includes silicon, and the silicon is optionally
doped. According to an embodiment, the semiconductor is

an intrinsic semiconductor or an extrinsic semiconductor 5

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 226 includes an n-dopant.
In a particular embodiment, common substrate 226 is

p-doped Si. In one embodiment, common substrate 226 is

n-doped Si. Common substrate 226 can be produced from,
e.g., commercially available semiconductor grade p-doped
Si having a particular crystalline orientation, e.g., having
Miller indices <111>, <100>, and the like. Common sub-
strate 226 can be amorphous, polycrystalline, or a single
crystal. In an embodiment, common substrate 226 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, common substrate 226
includes crystalline domains among amorphous material.
In another embodiment, common substrate 226 includes a
glass, Pyrex, sapphire, polymer, ceramic, or an electrically

20

&

6

conductive material, e.g., a metal. The substrate can be
electrically conductive, semi-conductive, or electrically
insulating.

A thermal conductance of common substrate 226 can be
selected by choice of a composition of common substrate
226 as well as a geometrical shape or size of common
substrate 226. A thermal conductivity of common substrate
226 can be from 0.1 to 5000 W/mK, specifically from 0.5
W/mK to 100 W/mK and more specifically from 1 W/mK to
5 W/mK

In photonic quantum dew point sensor 200, dew sensor
substrate 216 can be disposed on common substrate 226 to
isolate dew sensor 210 from common substrate 226. In an
embodiment, the dielectric layer insulates dew sensor sub-
strate 216 from common substrate 226. The dielectric layer
can include an oxide of an element in dew sensor substrate
216 or independently can be an oxide of a semiconductor
material such as SiO,. According to an embodiment, the
dielectric layer is an oxide such as an oxide that includes an
element from dew sensor substrate 216, e.g., an oxide of the
semiconductor (also referred to herein as a semiconductor
oxide). In an embodiment, dew sensor substrate 216
includes Si, and dielectric layer 323 includes silicon dioxide
(SiO,). Additional dielectric layer materials include gallium

5 oxide (GaO;), aluminum oxide (Al,O;), or alloys thereof,

oxides of compounds from Groups III and V or alloys
thereof, and the like. Exemplary oxides in the dielectric
layer also include ZnO, HfO,, SnO,, In,O,, Zn,SnO,,
Ga,O,, Al,O,, and the like. In an embodiment, the dielectric
layer is a product of oxidation of a portion of dew sensor
substrate 216 to produce the semiconductor oxide. Accord-
ing to one embodiment, the oxide is a product of rapid
thermal oxidation of dew sensor substrate 216 so that the
oxide (the dielectric layer) is derived from dew sensor
substrate 216. In another embodiment, the oxide is a product
of low temperature oxidation of dew sensor substrate 216 to
produce an oxide. In a further embodiment, the oxide is a
product of depositing the oxide on dew sensor substrate 216,
which may or may not involve oxidation of dew sensor
substrate 216. Moreover, the dielectric layer may be bonded
to the dew sensor substrate 216. In a certain embodiment, the
dielectric layer includes SiO, as the oxide, which is a
product of oxidation of dew sensor substrate 216 that
includes Si. In some embodiments, the dielectric layer
includes a semiconductor oxide, a ceramic (eg., Z1O>,
‘Al,O3, SiC, Si;N;, BN, BaTiO,, and the like), a glass, a
polymer, or a combination thereof. In some embodiments,
the dielectric layer includes an organic compound such as a
polymer, ¢.g., cellulose, poly(methyl methacrylate), and the
like.

A thickness of dew sensor substrate 216 between photonic
dew sensor 210 and common substrate 226 can be from 0.25
jum to 10 jum, specifically from 0.5 um to 5 um, and more
specifically from 1 pm to 3 jm. A thermal conductivity of
dew sensor substrate 216 can be from 0.1 W/mK to 1000
IK, specifically from 0.5 W/mK to 100 W/mK, and more
lly from 1 to 5 WimK.

In photonic quantum dew point sensor 200, temperature
sensor substrate 218 can have the same composition, prop-
erties and function as dew sensor substrate 216.

In photonic quantum dew point sensor 200, heater 230 can
include a resistive element to deposit heat into the dew
sensor substrate 216 and can be composed of metal or a
doped or undoped semiconductor. Exemplary heaters 230
include a film of n- or p-type doped Si, a metal film of
aluminum, gold, platinum or chromium, and the like. Heater
230 can provide heat to photonic dew sensor 210 to heat



US 11,422,101 B2

Sheet 7 of 14

Aug. 23, 2022

U.S. Patent

L eansty

f
z008 \ j
° e'PEZ )
z'082 062

BEG “VES
j J 002

L666

—
be
2
a

b6G



US 11,422,101 B2

17

before the removal cycle was initiated while maintaining
electrical power to heater 230 at a constant level (step 904);
obtaining a steady state of output light 238 of photonic dew
sensor 210 (step 334) so that all dew of output light 238 is
removed and the temperature of optomechanical tempera-
ture sensor 214 is stabilized; and terminating heating by
heater 230 (step 336)

In an embodiment, with reference to FIG. 14, process 330
for measuring relative humidity includes determining a
temperature of the external environment such as the air
surrounding photonic dew point sensor 200 by a secondary
thermometer 262 (step 332); determining the dew point
temperature of analyte with photonic dew point sensor 200;
combining the dew point measurement and temperature of
the external environment by reading both values into a
microprocessor 318 (step 334); and determining a relation-
ship between the air temperature and dew point by the
known dew point—vapor pressure relationship, ie., the

coexistence curve of the analyte, (step 336) to determine the 2

relative humidity by dividing the inferred analyte vapor
pressure by the saturated analyte vapor pressure at the
environmental temperature measured by secondary ther-
mometer 262 (step 338).

Photonic quantum dew point sensor 200 and processes
disclosed herein have numerous beneficial uses, including
precise dew point measurement, rapid humidity measure-
ment, and embedded sensing. Advantageously, photonic
quantum dew point sensor 200 overcomes limitations of
technical deficiencies of conventional articles such as slow
response of conventional chilled-mirror dew point hygrom-
eters, instability of capacitive and resistive hygrometers and
the requirement of frequent calibration for all hygrometers.
Further, the sensor is interrogated using photonic tech-
niques, and it resists to electro-magnetic interference.

Moreover, photonic quantum dew point sensor 200 and
processes herein have numerous advantageous properties. In
an aspect, the small size of the sensor makes the sensor light
and portable, allowing installation in locations with tight
dimensional constraints. In another aspect, the solid state,
impervious material from which photonic quantum dew
point sensor 200 is constructed leads to a mechanically and
chemically robust sensor compatible with use in a wide
range of environments and conditions. In yet another aspect,
the small size leads to low power requirements, allowing
‘operation of the dew point sensor with less power dissipa-
tion that conventional dew point sensors.

Photonic quantum dew point sensor 200 is precise (pro-
vides relative humidity precision corresponding to dew point

precision of about 0.1° C.), fast (provides a response time 5

measured in seconds), and compact (includes sensors that
are less than 1 cm in size).

Photonic quantum dew point sensor 200 and processes
herein unexpectedly, by including a quantum temperature

sensor 214 in dew point sensor 200, the dew point sensor 5

may be installed permanently since it may be self-calibrated
using this quantum temperature sensor 214. By ensuring
traceability through on-chip calibration against quantum
temperature sensor 214, dew point sensor 200 becomes
embeddable in its measurement environment, during initial
construction of that environment or anytime thereafter. Fur-
thermore, embedded dew point sensors 200 may be com-
bined into a distributed sensor network.

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

&

&

0

18

invention has been described by way of illustrations and not
limitation. Embodiments herein can be used independently
or can be combined.

All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are independently combinable with each
other. The ranges are continuous and thus contain every
value and subset thereof in the range. Unless otherwise
stated or contextually inapplicable, all percentages, when
expressing a quantity, are weight percentages. The
suflix “(s)” as used herein is intended to include both the
ngular and the plural of the term that it modifies, thereby
including at least one of that term (eg., the colorant(s)
includes at least one colorants). “Optional” or “optionally”
‘means that the subsequently described event or circumstance
can or cannot occur, and that the description includes
instances where the event occurs and instances where it does
not. As used herein, “combination” is inclusive of blends,
mixtures, alloys, reaction products, and the like.

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.

All references are incorporated herein by reference.

The use of the terms “a” and “an” and “the” and similar
referents in the context of describing the invention (espe-
cially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by con-
text. “Or” means “and/or.” It should 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 distinguish one element from another. The
modifier “about” used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by
the context (eg., it includes the degree of error associated
with measurement of the particular quantity). The conjune-
tion “or” is used to link objects of a list or alternatives and.
is not disjunctive; rather the elements can be used separately
or can be combined together under appropriate circum-
stances

What is claimed is:

1. A photonic quantum dew point sensor for determining
a dew point of an analyte, the photonic quantum dew point
sensor comprising:

a common substrate;

a photonic dew sensor disposed on the common substrate

and exposed for direct contact with the analyte;

a photonic temperature sensor disposed on the common
substrate;

an optomechanical temperature sensor disposed on the
common substrate;

a dew sensor substrate disposed on the common substrate
and interposed between the photonic dew sensor and
the common substrate;

a heater disposed on the dew sensor substrate proximate
to the photonic dew sensor to heat the photonic dew
sensor above a dew point of the analyt

a temperature sensor substrate disposed on the common
substrate and interposed between the common substrate
and each of the photonic temperature sensor and the
optomechanical temperature sensor; and

a sensor cover disposed on the photonic temperature
sensor, the optomechanical temperature sensor, and the
temperature sensor substrate to cover the photonic
temperature sensor and the optomechanical tempera-
ture sensor to prevent direct contact between the ana-



United States Patent

US

(12) (0) Patent No: US 11,422,101 B2
Herman et al. (45) Date of Patent: Aug. 23, 2022
(54) PHOTONIC QUANTUM DEW POIN (56) References Cited
SENSOR
U.S. PATENT DOCUMENTS
(71) Applicant: Government of the United States of -
America, as represented by the 4,392,362 A 7/1983. Little ,
Secretary of Commerce, Gaithersburg, 6,164,817 A 12/2000 Trainer ON *
MD (US) (Continued)
(72) Inventors: Tobias K. Herman, Clarksburg, MD
(US); Nikolai N. Klimov, Ellicott City, FOREIGN PATENT DOCUMENTS
MD (US); Thomas P. Purdy,
> 9 EP 2444769 AL 4/2012
Gaithersburg, MD (US) wo 2016190816 Al 12/2016
(73) Assignee: GOVERNMENT OF THE UNITED
STATES OF AMERICA, AS OTHER PUBLICATIONS
REPRESENTED BY THE
SECRETARY OF COMMERCE, Purdy, T-P., et al., “Quantum correlations from a room-temperature
Gaithersburg, MD (US) optomechanical cavity”, Science, 2017, 1265-1268, vol. 356
(Continued)
(*) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35 Primary Examiner — Paul M. West
USC. 154(b) by 528 days. (74) Attorney, Agent, or Firm — Office of Chief Counsel
for National Institute of Standards and Technology
(21) Appl. No.: 16/527,209
(57) ABSTRACT
(22) Filed: Jul. 31, 2019 A photonic quantum dew point sensor determines a dew
(65) Prior Publication Data point of an analyte and includes a common substrate: a
photonic dew sensor on the common substrate and exposed
US 2020/0041431 Al Feb. 6, 2020 for direct contact with the analyte; a photonic temperature
Related U.S. Application Data sensor on the common substrate; an optomechanical tem-
perature sensor on the common substrate; a dew sensor
(60) Provisional application No. 62/713,109, filed on Aug. substrate interposed between the photonic dew sensor and
1, 2018. the common substrate; a heater on the dew sensor substrate
| proximate to the photonic dew sensor; a temperature sensor
(51) Int. Cl. substrate interposed between the common substrate and each
GOIN 25/68 (2006.01) of the photonic temperature sensor and the optomechanical
GOIN 21/17 (2006.01) temperature sensor; and a sensor cover on the photonic
(52) U.S. temperature sensor, the optomechanical temperature sensor,
CPC ..... GOIN 25/68 (2013.01); GOIN 2021/1723 and the temperature sensor substrate to cover the photonic
(2013.01); GOIN 2021/1731 (2013.01); GOIN temperature sensor and the optomechanical temperature
2021/1763 (2013.01) sensor to prevent direct contact between the analyte and
(58) Field of Classification Search each of the photonic temperature sensor and the optom-

CPC ... GOIN 25/68; GOIN 2021/1731; GOIN
2021/1723; GOIN 2021/1763

See application file for complete search history.

echanical temperature sensor.

20 Claims, 14 Drawing Sheets



U.S. Patent Aug. 23, 2022 Sheet 10 of 14 US 11,422,101 B2

Measure temperature using temperature sensor 212 4 304

}

Use measured temperature as proces

variable for the

temperature controlled stage 7 808
When stable, calibrate temperature sensor 212 to measured
47> 308

temperature of optomechanical temperature sensor 214

Figure. 10


U.S. Patent Aug. 23, 2022 Sheet 9 of 14 US 11,422,101 B2

2
of
=
g
z
g
g
=
&
g
4
3) Oy YASuapoarm aoueuOsoy
£ fon)
8
E ©
x aed
a
Fa =]
D
& woe
= oy YISUIpIABM goURUOSOY

Wa velength

4

(A)


U.S. Patent

Aug. 23, 2022

b> 234.2

Sheet 6 of 14

~~ 282

b> 286

US 11,422,101 B2

Figure. 6


US 11,422,101 B2

11

Thermal conductor 256 can include a conductive material
to allow heat to flow out of common substrate and into the
cold-plate of the thermoelectric element 254 and can be a
solid, a liquid, or a combination thereof such as a paste or
emulsion. Exemplary thermal conductors 256 include sol-
der, thermally conductive greases and thermally conductive
epoxies. Thermal conductor 256 can provide heat transfer
via thermal conduction from thermoelectric member 254
and common substrate 226 as well as from cooling member
258 and thermoelectric member 254. A size, e.g., a thickness
of thermal conductor 256 between thermoelectric member
254 and common substrate 226 can be from | jum to 10 mm,
specifically from 20 um to 1 mm, and more specifically from
50 jum to 400 uum. In an embodiment, thermal conductor 256
includes pure metals such as indium or gallium, alloys such
as gallium-indium-tin, silver loaded epoxy or thermally
conductive grease.

In photonic quantum dew point sensor 200, secondary
temperature sensor 262 can include a sensor element in
thermal equilibrium with the environment to report the
temperature of that environment and can be an element that
reproducibly reports the environmental temperature. Exem-
plary secondary temperature sensors 262 thermistors, ther-
mocouples, resistance thermometers, thermocouples, diode
thermometers, liquid-in-glass-thermometers, photonic ther-
mometers, acoustic thermometers, radiation thermometers,
and colorimetric thermometers. In an embodiment, second-
ary temperature sensor 262 includes a wire-wound 100-ohm
platinum resistance thermometer measured using an ohm-
meter. In another embodiment, secondary temperature sen-
sor 262 includes a ceramic thermistor measured using an
ohmmeter. In yet another embodiment, secondary tempera-
ture sensor 262 includes a type K thermocouple measured
using a voltmeter. In a further embodiment, secondary
temperature sensor 262 includes a photonic thermometer
similar in form and function to photonic temperature sensor
212.

Photonic dew sensor 210, photonic temperature sensor
212, optomechanical temperature sensor 214, secondary
temperature sensor 262 independently attenuate primary
light 234 in a wavelength dependent fashion, wherein a
minimum power of transmitted light 238 occurs at the
wavelength which is resonant with the resonator 236 in each
of these components. Moreover, the resonant frequency of
the resonator provides a measurement of the relevant quan-
tity, such as the presence or absence of dew, or the tem-
perature.

In photonic quantum dew point sensor 200, laser 278 can
include a broadband source or a coherent light source with

a narrow linewidth to provide primary light 234 to photonic

dew sensor 210, photonic temperature sensor 212, or opto-
mechanical temperature sensor 214 and can be a light
emitting diode, an arc lamp, an infrared laser, a visible laser,
an ultraviolet laser, and the like. Exemplary lasers 278

include tunable diode lasers. In an embodiment, laser 278 5

includes C-band tunable laser.

Presence of analyte 228 is detected by photonic dew
sensor 210. Analyte 228 can include a fluid that exists as
vapor that can be in equilibrium with its solid or liquid form
at some characteristic pressure and temperature and can be
either a pure fluid or a mixture of two or more fluids.
Exemplary analytes 228 include water, a hydrocarbon,
ammonia, and the like. Moreover, the analyte condenses on
the dew sensor when the temperature of the dew sensor is
below a characteristic temperature for the analyte when
present in vapor form at some concentration. A dew point of
analyte 228 can be from -120° C. to 95° C., specifically

20

3

4

45

at

6:

12

from -100° C. to 75° C., and more specifically from -90° C.
to 45° C, at a temperature from -100° C. to 100° C.,
specifically from -70° C. to 80° C., and more specifically
from -50° C. to 50° C. In an embodiment, analyte 228
includes water vapor which condenses as liquid or solid
water on to the photonic dew sensor 210 when the tempera-
ture of the photonic dew sensor 210 is at or below the dew
point of water corresponding to that concentration of water
vapor.

Beam splitter 280 split or combine light. Exemplary
splitters 280 include a waveguide-based splitter that couples
incoming light flux propagating through an incoming wave-
guide to two or more outgoing light fluxes in two or more
waveguides. Moreover, beam splitter 280 is optionally used
to provide a portion of the light to a photodetector 272 and
or a wavelength meter 270 and the like. In an embodiment,
beam splitter 280 provides 10% of incident light from laser
278 to wavelength meter 270 and 90% of light incident from
laser 278 is directed toward dew point sensor 210.

Wavelength meter 282 can include an element that deter-
mines wavelength of light incident on it. Exemplary wave-
length meters 282 include diffraction grating, spectrometers,
spectrum analyzer, an etalon, wavelength cell, and fre-
quency combs. Moreover, the wavelength meter communi-

5 cates the measured wavelength as an electronic or photonic

signal. Wavelength meter 282 produces wavelength signal
286 that can include a voltage or other electric or photonic
signal whose characteristics are determined by the measured
wavelength and a specified calibration. Exemplary wave-
length signals 286 include analog DC voltages, the fre-
quency of AC voltages, DC electrical currents, microwave
signals, and spectra dispersed by a diffraction grating. More-
over, wavelength meter 282 can determine the frequency
light incident on it. In an embodiment, wavelength signal
286 analog DC voltage signal, and wavelength value dis-
played on a computer.

Power meter 284 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 light
absorbed. Exemplary power meters 284 include 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. Power signal 288 produces
power signal 288 that can include a voltage or other electric
signal whose characteristics are determined by the measured
wavelength and a specified calibration. Exemplary power
signals 288 include DC voltages and DC currents. In an
embodiment, power signal 288 includes 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 mea-
sure of the optical power incident upon on a detector.

For balanced heterodyne detection in photonic quantum
dew point sensor 200, frequency shifter 290 can include a
modulator that shifts the oscillation frequency of a portion of
primary light 234 and can be accompanied by additional
optical filtering or amplification, or producing frequency
shifted light can be accomplished by providing a separate
laser system that operates at a frequency different from that
of primary light 234. Frequency shifter 290 produces a laser
beam, wherein some or all of the light oscillates at a
frequency different from the oscillation frequency of pri-
mary light 234. Exemplary frequency shifters 290 include
acousto-optic modulators and electro-optic modulators. Fre-
quency shifter 290 can provide a frequency shift to primary
light 234 to produce shifted primary light 234.3, wherein a



US 11,422,101 B2

Sheet 2 of 14

Aug. 23, 2022

U.S. Patent

9¢¢——
887NA
vee

GE6——]

a»

ves

@

Bee

PES

Z ‘OINSIyY

ica

PES

98Z

88S

De

98Z



U.S. Patent Aug. 23, 2022 Sheet 13 of 14 US 11,422,101 B2

28

Monitor dew sensor signal 4 330

Y

Apply constant power to integrated microheater and keeping the
power supplied to the thermoelectric cooler in the temperature
controlled stage constant

1

When dew sensor signal stabilizes, dew is no longer present and
sensor temperature has reached a steady state

4

Turn off microheater and resume normal measurement = ~}-~ 336

4 332

t— 334

Figure. 13


US 11,422,101 B2

1
PHOTONIC QUANTUM DEW POINT
SENSOR

CROSS REFERENCE TO RELATED,
APPLICATIONS

‘The application claims priority to U.S. Provisional Patent
Application Ser. No. 62/713,109 filed Aug. 1, 2018, the
disclosure of which is incorporated herein by reference in its
entirety.

STATEMENT REGARDING FEDERALLY,
SPONSORED RESEARCH

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

invention. Licensing inquiries may be directed to the Tech- >,

nology Partnerships Office, NIST, Gaithersburg, Md
20899; voice (301) 301-975-2573; email tpo@nist.gov; ref-
erence NIST Docket Number 18-057USI.

BRIEF DESCRIPTION

Disclosed is a photonic quantum dew point sensor for
determining a dew point of an analyte, the photonic quantum,
dew point sensor comprising: a common substrate; a pho-
tonic dew sensor disposed on the common substrate and
exposed for direct contact with the analyte; a photonic
temperature sensor disposed on the common substrate; an
‘optomechanical temperature sensor disposed on the com-
mon substrate; a dew sensor substrate disposed on the
common substrate and interposed between the photonic dew
sensor and the common substrate; a heater disposed on the
dew sensor substrate proximate to the photonic dew sensor
to heat the photonic dew sensor above a dew point of the
analyte; a temperature sensor substrate disposed on the
common substrate and interposed between the common
substrate and each of the photonic temperature sensor and
the optomechanical temperature sensor; and a sensor cover
disposed on the photonic temperature sensor, the optom-
echanical temperature sensor, and the temperature sensor
substrate to cover the photonic temperature sensor and the
optomechanical temperature sensor to prevent direct contact
between the analyte and each of the photonic temperature
sensor and the optomechanical temperature sensor.

Disclosed is a relative humidity sensor comprising: a 5

photonic quantum dew point sensor; and a secondary tem-
perature sensor in communication with the photonic quan-
tum dew point sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description should not be considered lim-
iting in any way. With reference to the accompanying
drawings, like elements are numbered alike.

FIG. 1 shows, in panel A, a plan view of a photonic
quantum dew point sensor; in panel B, a cross-section along
line A-A of the photonic quantum dew point sensor shown
in panel A that includes a cover in direct contact with a
temperature sensor; and in panel C, a cross-section along,
line A-A of the photonic quantum dew point sensor shown
in panel A that includes a cavity between a cover and a
temperature sensor;

0

&

&

2
FIG. 2 shows a waveguide in optical communication with
a ring resonator in panel A, a disk resonator in panel B, a
photonic crystal in panel C, and a Bragg waveguide in panel

FIG. 3 shows a waveguide in optical communication with
a photonic nanobeam disposed over a trench;

FIG. 4 shows a dew sensor substrate disposed on a
thermoelectric member in panel A and a cooling member in
panel B;

FIG. 5 shows a relative humidity sensor;

FIG. 6 shows a sensor system;

FIG. 7 shows a sensor system;

FIG. 8 shows structures formed in making a photonic
quantum dew point sensor;

FIG. 9 shows, in panel A, a graph of transmission versus
wavelength for a transmission spectrum; in panel B, a graph.
of resonance wavelength versus temperature for a tempera-
ture curve: and in panel C, a graph of resonance wavelength
versus analyte coverage for a dew curve;

FIG. 10 shows steps in calibrating a photonic temperature
sensor;

FIG. 11 shows steps in identifying onset of forming dew
on a photonic dew sensor;

FIG. 12 shows steps in determining a dew point of an
analyte;

FIG. 13 shows steps in removing dew from a photonic
dew sensor; and

FIG. 14 shows steps in operating a relative humidity
sensor.

DETAILED DESCRIPTION,

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

Some conventional transducers measure a property such
as capacitance across a membrane or resistance of a material
in which the response of the conventional transducer
changes with humidity but such response depends on a
material property of a sensing element that changes with
time or environmental history so that the conventional
transducer involves frequent calibration. Moreover, a con-
ventional dew point hygrometer directly measures dew point
at a humidity and moisture rather than a moisture sensitive
property of a material, and the conventional dew point
hygrometer directly probes thermodynamics of water vapor
so that when the conventional dew point hygrometer is
clean, the conventional dew point hygrometer provides a
measurement of dew point that depends on an accuracy and
stability of an embedded temperature sensor. A conventional
chilled mirror dew point hygrometer measures reflection of
light off a chilled metal mirror that involves a bulky and
expensive instrument and having mirrors that are relatively
large metal structures for thermal contact with an internal
temperature probes but that disadvantageously have a slow
thermal time constant that takes over a minute or longer to
stabilize at a new dew point if humidity changes.

It has been discovered that a photonic quantum dew point
sensor described herein overcomes technical limitation of
conventional apparatus in determination of a dew point of an
analyte. Moreover, the photonic quantum dew point sensor
includes a quantum temperature standard that provides zero
chain traceability to a photonic dew point sensor and elimi-
nates a future calibration. The photonic quantum dew point
sensor directly measures dew point that overcomes conven-
tional transducers measure of humidity-dependent behavior
that involves frequent calibration. The photonic quantum


U.S. Patent

(A) 200 210

Aug. 23, 2022

Sheet 1 of 14

US 11,422,101 B2

216

230 7_

(B) 200
210

ann

p> 220

216

4 218

L

1 226

210

216

Figure. 1


US 11,422,101 B2

19

lyte and each of the photonic temperature sensor and
the optomechanical temperature sensor.
2. The photonic quantum dew point sensor of claim 1,
wherein the photonic dew sensor comprises:
a waveguide that:
receives a primary light;
communicates the primary light to a resonator;
receives an output light from the resonator; and
communicates the output light; and
the resonator in optical communication with the wave-
guide and that:
receives the primary light from the waveguide;
produces the output light from the primary light; and
communicates the output light to the waveguide,

« . « . . . 1
wherein an intensity of the output light is substantially

lower than an intensity of the primary light when a
wavelength of output light is at a resonance of the
resonator.

3. The photonic quantum dew point sensor of claim 2,
wherein the resonator comprises a ring resonator, a disk
resonator, a photonic crystal, or a Bragg waveguide.

4. The photonic quantum dew point sensor of claim 2,
wherein the resonator comprises photonic nanobeam dis-
posed over a trench that is disposed in temperature sensor
substrate and bounded by a wall of temperature sensor
substrate.

5. The photonic quantum dew point sensor of claim 1,
wherein the photonic temperature sensor comprises:

a waveguide that:

receives a primary light:

communicates the primary light to a resonator;
receives an output light from the resonator; and
communicates the output light; and

the resonator in optical communication with the wave-

guide and that:
receives the primary light from the waveguide;
produces the output light from the primary light; and
communicates the output light to the waveguide,
wherein an intensity of the output light is substantially
lower than an intensity of the primary light when a
wavelength of output light is at a resonance of the
resonator.

6. The photonic quantum dew point sensor of claim 5,
wherein the resonator comprises a ring resonator, a dis
resonator, a photonic crystal, or a Bragg waveguide.

7. The photonic quantum dew point sensor of claim 1,
wherein the optomechanical temperature sensor comprises:

a waveguide that:

receives a primary light:

communicates the primary light to a resonator;
receives an output light from the resonator; and
communicates the output light; and

the resonator in optical communication with the wave-

guide and that:
receives the primary light from the waveguide:
produces the output light from the primary light; and
communicates the output light to the waveguide,
wherein an intensity of the output light is substantially
lower than an intensity of the primary light when a
wavelength of output light is at a resonance of the
resonator.

8. The photonic quantum dew point sensor of claim 1,
further comprising:

a thermoelectric member disposed on the dew sensor

substrate.

3

20

45

35

0

65

optomechanical temperature sensor comprises:

20

9. The photonic quantum dew point sensor of claim 8,

further comprising:

a thermal conductor interposed between the dew sensor
substrate and the thermoelectric member.
10. The photonic quantum dew point sensor of claim 9,

further comprising:

a cooling member disposed on the thermoelectric mem-
ber,

wherein a second thermal conductor is interposed
between the coding member and the thermoelectric
member.

11. A relative humidity sensor comprising:

the photonic quantum dew point sensor of claim 1; and

a secondary temperature sensor in communication with
the photonic quantum dew point sensor.

12. The relative humidity sensor of claim 11, wherein the

photonic dew sensor comprises:

a waveguide that:
receives a primary ligh
communicates the primary light to a resonator;
receives an output light from the resonator; and
communicates the output light; and

the resonator in optical communication with the wave-

guide and that:
receives the primary light from the waveguide;
produces the output light from the primary light; and
communicates the output light to the waveguide,
wherein an intensity of the output light is substantially
lower than an intensity of the primary light when a
wavelength of output light is at a resonance of the
resonator.

13. The relative humidity sensor of claim 12, wherein the
resonator comprises a ring resonator, a disk resonator, a
photonic crystal, or a Bragg waveguide.

14. The relative humidity sensor of claim 12, wherein the
resonator comprises photonic nanobeam disposed over a
trench that is disposed in temperature sensor substrate and
bounded by a wall of temperature sensor substrate.

15. The relative humidity sensor of claim 11, wherein the

photonic temperature sensor comprises:

a waveguide that:
receives a primary light;
communicates the primary light to a resonator;
receives an output light from the resonator; and
communicates the output light; and

the resonator in optical communication with the wave-
guide and that:
receives the primary light from the waveguide;
produces the output light from the primary light; and
communicates the output light to the waveguide,

wherein an intensity of the output light is substantially
lower than an intensity of the primary light when a
wavelength of output light is at a resonance of the
resonator.

16. The relative humidity sensor of claim 15, wherein the

resonator comprises a ring resonator, a disk resonator, a
photonic crystal, or a Bragg waveguide.

17. The relative humidity sensor of claim 11, wherein the

a waveguide that
receives a primary ligh
communicates the primary light to a resonator:
receives an output light from the resonator; and
communicates the output light; and

the resonator in optical communication with the wave-
guide and that:
receives the primary light from the waveguide;
produces the output light from the primary light; and
communicates the output light to the waveguide,



US 11,422,101 B2
Page 2

(56) References Cited
U.S. PATENT DOCUMENTS.
9,726,553 B2

2013/0248167 AL
2018/0164236 AL

8/2017 Ahmed et al.
9/2013 Lerou
6/2018 Tao et al

OTHER PUBLICATIONS,

‘Tao, J., et al., “An Ultahigh-accuracy Miniature Dew Point Sensor
based on an Integrated Photonics Platform”, Nature Scientific
Reports, 2016.

Limodehi, H.E., et al., “Fiber optic humidity sensor using water
vapor condensation”, Optics Express, 2017, 15313, vol. 25 No. 13
Mathew, J., et al., “Photonic Crystal Fiber Interferometer for Dew
Detection”, Journal of Lightwave Technology, 2012, 1150-1155,
vol. 30 No.8.

Ascorbe, J., et al., “Recent Deveopments in Fiber Optics Humidity
Sensors”, Sensors, 2017, 893, vol. 17

Kolpakov, S.A,. et al., “Toward a New Generation of Photonic
Humidity Sensor: Sensors, 2014, 3986-4013, vol. 14.

Nie, J., et al., “Dew point measurement using dual quartz crystal
resonator sensor”, Sensors and Actuators B Chemical, 2017, 792-
799, vol. 246.

Jachowiez, R.S., et al, “A MEMS-based super fast dew point
hygrometer-construction ans medical applications”, Measurement
Science and Technology, 2009, 124008, vol. 20.

Fenner, R., et al., “Micromachined Water Vapor Sensors: A Review
of Sensing Technologies”, IEEE Sensors Journal, 2001, 309-317,
vol. 1 No. 4.

Derking, J.H., et al., “A miniature Joule-Thomson cooler for optical
detectors in space”, Review of Scientific nstruments, 2012, 045117,
vol. 83.

Tao, J., et al, “A Novel Photonic Dew-Point Hygrometer with
Ultra-High Accuracy”, IEEE, 2016, 893-896.

Purdy, T.P,, et al., “Observation of Optomechanical Quantum Cor-
relations at Room Temperature”, 2016, DOI: arXiv:1605.05664.
Purdy, TP, et al., “Thermometry with Optomechanical Cavities”,
Optical Society of America, 2016.

* cited by examiner


U.S. Patent Aug. 23, 2022 Sheet 11 of 14 US 11,422,101 B2

Monitor dew sensor 210 and
temperature sensor 212 signal

}

Cool devices using temperature controlled stage 4-314

Y

When dew sensor signal exhibits behavior that is distinct from
temperature sensor, dew has formed

4 S12.

> 316

Figure. 11


US 11,422,101 B2

Sheet 14 of 14

Aug. 23, 2022

U.S. Patent

88S J

Aupramy oareyoy

pL eansty

aossaooadoaory
i

)

986

amyeaaduray yurod mag,

P~ PEE

Suipeoer
amnyetaduiay (are) Peuaorxg

Okt