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US 10,718,872 B2

11

In some embodiments, the optical resonator includes a
ring resonator, a concave disk resonator, a photonic wave-
guide, disk resonator, a microsphere resonator, a photonic
crystal cavity, a photonic array, or a combination comprising
at least one of the foregoing. As such, the optical resonator
can be a ring, disk, or spherical structure disposed at a
selected distance from a waveguide. A radius of the optical
resonator is selected so an effective length of a circumfer-
ence is an integer of a resonant wavelength. In some
embodiments, the optical resonator is the ring resonator that
has a substantially uniform width with respect to a radial
dimension of the ring resonator, e.g., substantially uniform
width W1 between outer diameter OD and inner diameter ID
as in FIG. 18C.

According to an embodiment, input light is coupled into
the thermometer from a light source, coupled from the
thermometer to a detector, or a combination thereof. In an
embodiment, the waveguide comprises a Bragg coupler, an
end coupler, or a combination comprising at least one of the
foregoing disposed at a terminus of the waveguide. As
shown in FIG. 30A (top view of compensation waveguide
238) or FIG. 30B (cross-section along line A-A of FIG.
30A), compensation waveguide 238 includes Bragg coupler
336 disposed at a terminus thereof. Bragg coupler 336
includes a plurality of protrusions 337 and depressions 338
alternatingly disposed on substrate 210. With reference to
FIG. 30C (an alternate embodiment for a Bragg coupler
corresponding to a cross-section along line B-B in FIG.
30A), depressions 338 are blind with respect to substrate 210
relative to through features as shown in FIG. 30B. In one
embodiment, depressions 338 include blind depressions
338, through depressions, or a combination thereof. Here,
“through” refers to expose substrate 210 through depres-
sions 338, and “blind” refers to covering substrate 210 by

depressions 338 such that substrate 210 is not exposed. It is 3

contemplated that a Bragg coupler uses a grating structure
(e.g,, protrusions 337 and depressions 338) to couple input
light into the thermometer and to couple output light out of
the thermometer. In an embodiment, coupling light by
compensation waveguide 238 is evanescent coupling via
Bragg coupler 336.

In an embodiment, as shown in FIG. 31, compensation
waveguide 238 includes edge coupler 339 disposed at a
terminus of compensation waveguide 238. Edge coupler 339
couples light in and out by, e.g., a pigtailed fiber optic, which
is connected, e.g., adhered, to substrate 210.

Temperature compensator 234 includes substrate 210.
Substrate can include any material that can effectively be
processed (e.g., micromachined, including lithography and
the like) to form a support structure for optical resonator
(e.g., 236), thermal member 314, waveguide (e.g., 238), or
other components thereof.

In a particular embodiment, substrate 210 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, Il, 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 210 is a compound semicon-
ductor 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) semiconductor such as CuCl and
the like; a group 14-16 (group IV-VI) semiconductor such as
PbS, PbTe Sn, and the like; a layer semiconductor such as

30

40

&

0

12

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)Sb, (In,Ga)Sb, as well as_ nitride,
arsenide, antimonide quaternary III-V alloys, or a combina-
tion 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 IIL-nitride alloys include
(Ga,AD)N, (Ga,In)N, (Al.In)N, (Ga,ALIn)N, and combina-
tions thereof. Quaternary alloys of the above may also be
employed.

Substrate 210 also can include a supplemental element
such as C, H, N, Li, Na, K, Mg, Ca, Sr, Ba, Bi, B, Al, P, 8,
O, and the like in an amount typically less than an amount
of the semiconductor. In an embodiment, substrate 210
includes silicon, and the silicon is optionally doped. Accord-
ing 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-dopant. In one
embodiment, the substrate includes a p-dopant. In another
embodiment, substrate 210 includes an n-dopant. In a par-
ticular embodiment, substrate 210 is p-doped Si. In one
embodiment, substrate 210 is n-doped Si. Substrate 210 can
be produced from, e.g., commercially available semicon-
ductor grade p-doped Si having a particular crystalline
orientation, e.g.. having Miller indices <111>, <100>, and
the like. Substrate 210 can be amorphous, polycrystalline, or
a single crystal. In an embodiment, substrate 210 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 210 includes
crystalline domains among amorphous material.

In another embodiment, substrate 210 includes a glass,
Pyrex, sapphire, polymer, ceramic, or an electrically con-
ductive material, e.g., a metal. The substrate can be électri-
cally conductive, semiconductive, or electrically insulating,

A thermal conductance of substrate 210 can be selected by
choice of a composition of substrate 210 as well as a
geometrical shape or size of substrate 210.

A dielectric layer can be disposed on substrate 210 to
generally isolate substrate 6 from, e.g., contamination or
deterioration during formation of compensation resonator
236. In an embodiment, the dielectric layer electrically
insulates substrate 210 from thermal member 314. The
dielectric layer can include an oxide of an element in
substrate 210 or independently can be an oxide of a semi-
conductor material such as SiO. According to an embodi-
ment, the dielectric layer is an oxide such as an oxide that
includes an element from substrate 210, e.g., an oxide of the
semiconductor (also referred to herein as a semiconductor
oxide). In an embodiment, substrate 210 includes Si, and

5 dielectric layer 323 includes silicon dioxide (SiO,). Addi-

tional dielectric layer materials include gallium oxide
(GaO,), aluminum oxide (AI,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,O3, Zn,$nO,, Ga,O,, Al,O;,
and the like. In an embodiment, the dielectric layer is a
product of oxidation of a portion of substrate 210 to produce
the semiconductor oxide. According to one embodiment, the
oxide is a product of rapid thermal oxidation of substrate 210

5 so that the oxide (the dielectric layer) is derived from

substrate 210. In another embodiment, the oxide is a product
of low temperature oxidation of substrate 210 to produce an


US 10,718,872 B2

7

compensation waveguide 238 and includes an optical reso-
nance and receives, from compensation waveguide 238,
resonant frequency 240 corresponding to the optical reso-
nance and produces secondary compensation output light
244 in response to receipt of resonant frequency 240.
Thermal isolator 262 on which radiation absorber 268 is
disposed thermally isolates radiation absorber 268 from heat
loss by thermal transfer due to physical contact by an object.
Here, temperature compensator 234 changes the optical
resonance of compensation resonator 236 in response to a
change in temperature of radiation absorber 268 due to
absorption of ionizing radiation 254 by radiation absorber
268.

In an embodiment, photonic calorimeter 300 further
includes substrate 210 on which thermal isolator 262 is
disposed. In this configuration, thermal isolator 262 is
interposed between substrate 210 and radiation absorber
268, and radiation absorber 268 is thermally isolated from
substrate 210 by thermal isolator 262

In an embodiment, with reference to FIG. 15, photonic
calorimetric array 402 includes a plurality of photonic
calorimeter 300, e.g., 300A, 300B, ... , 300N, wherein N is
an integer number of photonic calorimeters 300 that can be,
e.g., thousands of photonic calorimeters 300. In an embodi-
ment, photonic calorimeters 300 are laterally disposed on
thermal isolator 262 as shown in FIG. 15. In an embodiment,
photonic calorimeters 300 are stackedly disposed on thermal
isolator 262. Moreover, individual photonic calorimeter 300,
eg. 300A, 300B . 300N, independently can be

addressed and optically communicate with light members 3

256.

In an embodiment, with reference to FIG. 16, photonic
dosimeter array 400 is subjected to ionizing radiation 254
from radiation source 404. Sensing elements can be 10

micrometers to 100 micrometers length, 500 nanometers to 3

1000 nanometers width, and 200 nanometers to 500 nano-
meters depth; the sensing element can be disposed proxi-
mate to a waveguide to which it evanescently couples, with
a gap separating the two elements of 100 nm to 900 nm;
sensing elements are separated by at least 1 micrometer.
Accordingly, photonic dosimeter array 400 can be subjected
to ionizing radiation 254 in vitro. In some embodiments,
photonic dosimeter array 400 is implanted in head 406 of a
person, wherein photonic dosimeter array 400 is subjected to
ionizing radiation 254 in vivo. In an embodiment, with
reference to FIG. 17, photonic calorimeter 300 is subjected
to ionizing radiation 254 from radiation source 404, wherein
radiation absorber 268 absorbs ionizing radiation 254 and
converts ionizing radiation 254 to heat that changes the
optical resonance of individual photonic calorimeter 300,
e.g., 300A, 300B, ..., 300N, in photonic calorimetric array
402, wherein an amount of change depends upon a position
of the photonic calorimeter 300, e.g., 300A, 300B, . . . ,
300N, relative to the an incident position of photonic calo-
rimeter 300, e.g., 300A, 300B, ... . , 300N, in the array as
irradiated by ionizing radiation 254. In this manner, photonic
dosimeter array 400 or photonic calorimetric array 402 are
position sensitive detectors with respect to a position of
incidence of ionizing radiation 254 on photonic dosimeter
array 400 or photonic calorimetric array 402.

With reference to FIG. 18A (top view of temperature
compensator 234, also referred to as thermometer herein,
e.g., thermometer 332 and the like), FIG. 18B (cross-section
along line A-A of FIG. 18A), and FIG. 18C (cross-section
along line B-B in FIG. 18A), in an embodiment, temperature
compensator 234 includes compensation resonator 236 (also
referred to herein as optical resonator, e.g., optical resonator

0

2

40

60

8

328, that can be. e.g., a ring resonator) disposed on substrate
210. Compensation waveguide 238 (also referred to herein
as waveguide, e.g., waveguide 334) is disposed on substrate
210 proximate to compensation resonator 236. Compensa-
tion resonator 236 has an optical resonance and is configured
to receive resonant frequency 240 corresponding to the
optical resonance. Compensation waveguide 238 is config-
ured to receive primary compensation input light 242 (also
referred to herein as input light), to communicate the reso-
nant frequency 240 to compensation resonator 236, and to
transmit primary compensation output light 246 (also
referred to herein as output light). Temperature compensator
234 is configured to change the optical resonance in
response to a change in temperature of compensation reso-
nator 236. Distance D separates compensation resonator 236
and compensation waveguide 238. Compensation resonator
236 has outer diameter OD, inner diameter ID, thickness H1,
and width W1. Compensation waveguide 238 has thickness
H2 and width W2.

According to an embodiment shown in FIG. 19A (top
view of temperature compensator 234), FIG. 19B (cross-
section along line A-A of FIG. 19A), and FIG. 19C (cross-
section along line B-B in FIG. 19A), temperature compen-
sator 234 includes thermal member 314 disposed on
substrate 210 opposing compensation resonator 236.
According to an embodiment shown in FIG. 20A (top view
of temperature compensator 234), FIG. 20B (cross-section
along line A-A of FIG. 20A), and FIG. 20C (cross-section
along line B-B in FIG. 20A), temperature compensator 234
includes thermal member 314 disposed in substrate 210
opposing compensation resonator 236. Thermal member
314 is configured to change or maintain a temperature of
compensation resonator 236. In some embodiments, thermal
member 314 increases a temperature of compensation reso-
nator 236. In an embodiment, thermal member 314
decreases a temperature of compensation resonator 236.

With reference to FIG. 20B, over layer 315 can be
interposed between thermal member 314 and compensation
resonator 236. Over layer 315 can be made of a same or
different material as substrate 210. In an embodiment, over
layer 315 includes a material that efficiently communicates
thermal energy between thermal member 314 and compen-
sation resonator 236.

According to an embodiment shown in FIG. 21A (top
view of temperature compensator 234), FIG. 21B (cross
section along line A-A of FIG. 21A), and FIG. 21C (cro:
section along line B-B in FIG. 214), temperature compen-
sator 234 includes thermal member 314 disposed on
compensation resonator 236 opposing substrate 210. An
over layer (e.g,, 315, not shown) can be interposed between
compensation resonator 236 and thermal member 314.

Besides ring resonator indicated as compensation resona-

‘5. tor 236, various other optical resonators can be used in the

thermometer. In an embodiment, as shown in FIG. 22A (top
view of temperature compensator 234), FIG. 22B (cross
section along line A-A of FIG. 22A), and FIG, 22C (cro:
section along line B-B in FIG. 22), temperature compen-
sator 234 includes first intermediate member 321 interposed
between disk resonator 316 and substrate 210. Additionally,
second intermediate member 322 is interposed between
compensation waveguide 238 and substrate 210. Although
first intermediate member 321 and second intermediate

5 member 322 are shown as having a frustoconical shape, first

intermediate member 321 and second intermediate member
322 can have any shape (e.g,, cylindrical, square, rectangu-


US 10,718,872 B2

19

In an embodiment, the thermometer is configured to
measure a temperature from 300 milliKelvin (mK) to 500 K,
specifically 300 mK to 450 K, and more specifically 300 mK
to 325 K. According to an embodiment, the thermometer is
configured to measure a temperature, wherein an uncertainty
in a measured temperature is less than or equal to 10 mK. In
certain embodiments, the thermometer has a temperature
resolution greater than or equal to 1 mK. The thermometer
has a temperature-dependent shift in a resonance wavelength
from (picometers per Kelvin (pmV/K) to 150 pnV/K. Accord-
ing to an embodiment, for resolving a temperature differ-
ence, the thermometer has a resolution greater than or equal
to 1 mK (ie., the thermometer resolves a temperature
difference of at least 1 mK), specifically greater than or equal
to 80 K, and more specifically greater than or equal to 10
K.

The thermometer has advantageous optical properties. In
an embodiment, the input light to the thermometer includes
a wavelength from 200 nm to 10 um, specifically 400 nm to
3 um, and more specifically 500 nm to 2 pm. The resonant
frequency of the optical resonator includes a wavelength
from 200 nm to 10 jum, specifically 400 nm to 3 pm, and
more specifically 500 nm to 2 um. The output light 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 106 and

specifically from 100 to 100,000. It is contemplated that the 3

optical resonator can have an increased Q-factor by includ-
ing a Bragg reflector.

In an embodiment, a group index is from 1 to 5, specifi-
cally from 1.5 to 4.7. The thermometer operates over a wide

range of input light power provided the resonant wavelength 3

can be communicated from the waveguide to the optical
resonator. Moreover, the power can be as large as a damage
threshold of the optical resonator or waveguide. e.g., greater
than or equal 10 microwatts (W), specifically greater than
20 W, and more specifically 50 pW up to the damage
threshold.

The thermometer has numerous advantages and benefits.
The thermometer is useful to detect a temperature with a
sub-mK resolution. The thermometer has a low noise level
and low thermal mass. Moreover, the thermometer is sub-
stantially unaffected by electromagnetic interference and has
applications wherever a thermometer can be used provided
light can be coupled into the thermometer with transmission
from the waveguide to the optical resonator. Exemplary
areas of application include, but are not limited to, medicine,
aerospace, analytical instrumentation, microfluidic, and the
like,

The thermometer leverages frequency metrology to
achieve mechanical and environmental stability. A silicon-
based thermometer that includes the optical resonator
resolves temperature differences of 1 mK using, e.g., by
scanning the input wavelength over the resonant frequency
of the optical resonator, and a noise floor of 80 1K or better
is achieved for measuring a temperature difference, e.g., by
using a side-of-fringe method where constant power input
light is incident at the waveguide as discussed below.

Additionally, while certain conventional thermometers
such as a platinum resistance thermometer is sensitive to
mechanical shock, the thermometer herein has a response
that is substantially independent of mechanical shock such
that the thermometer is configured to operate stably in a
presence of a perturbing vibration and can be disposed on a

S

2

40

20

plurality of actively vibrating articles, e.g., airplanes, satel-
lites, automobiles, buildings, shoes, and the like. Moreover,
the thermometer can be inexpensively manufactured com-
pared to many current commercially available thermom-
eters.

The thermometer beneficially includes an optical resona-
tor that has a periodic notch filter-like thermal response
where the resonant wavelength shows a temperature-depen-
dent change due to thermal expansion or thermo-optic effect.

Advantageously, a resonance frequency of the thermom-
eter does not vary over a wide range of relative humidity
levels, e.g., a relative humidity greater than 17 percent
relative humidity (% RH), and more specifically 26% RH,
based on amount of water vapor in a gas surrounding the
optical resonator. As such, a change in resonance frequency
is due to a temperature change, which does not depend on a
change in humidity of an environment in which the ther-
mometer is disposed.

The thermometer has numerous uses. In an embodiment,
the thermometer has a temperature response such that the
output light from the waveguide depends on a temperature
of the optical resonator. For the optical resonator that
includes the ring resonator, a change in the resonant fre-

5 quency (corresponding to resonant wavelength 2,,) arises

from a change in refractive index (n) of the optical resonator
or a change of a physical dimension of the optical resonator
that occurs in response to a change in temperature of the
optical resonator. The resonance wavelength i, for a mode
number (m) of a ring resonator is 4,(m)=[n,(A.T,)xL(T,)/
m, where is a vacuum wavelength; n,y is an effective
refractive index of the ring resonator; m is a mode number;
Lis a ring perimeter; and T,, is a temperature of the optical
resonator. A change in the resonant wavelength of the optical
resonator is given by formula (1)

where group index n, is given by

neg

Jn,
ng = tag — Ie

With reference to FIG. 32, in an embodiment, a process
for acquiring a temperature from the thermometer includes
providing the thermometer that includes the optical resona-
tor and that has first transmission curve C1 at first tempera-
ture T1, second transmission curve C2 at second temperature
T2, and third transmission curve C3 at third temperature T3.
The optical resonator has first resonant wavelength 2.1 at
first temperature T1, second resonant wavelength M2 at
second temperature T2, third resonant wavelength 413 at
third temperature T3. The input light at wavelength 40 is
provided to the waveguide and transmission of the output
light at wavelength 40 is detected as the thermometer is
subjected to a temperature change that includes first tem-
perature T1, second temperature T2, and third temperature
T3. In this manner, the output light detected at wavelength
0 establishes an intensity curve as shown in FIG. 33 for a
graph of intensity versus temperature of the thermometer.
Here, the output has first transmission intensity I1, second


US 10,718,872 B2

27

radiation-transport with the change in response of dosimeter
from prime state to dosed state to convert dosimeter
response to the energy absorbed per unit mass can include
combining the absorbed energy predicted by the Monte
Carlo model with the absorber mass input into the model to
determine absorbed energy per unit mass corresponding to
various responses of the temperature compensator.

In the process for performing dosimetry, logging a tem-
perature history of photonic dosimeter 200 by receiving, by
compensation waveguide 238, primary compensation input
light 242 and can include monitoring the frequency response
of a compensation resonator that can be located near the
dosimatrix.

In the process for performing dosimetry, producing, by
compensation waveguide 238, secondary compensation out-
put light 244 which can be transmitted to the compensation
resonator 236. In a particular embodiment, light in the
waveguide is evanescently coupled to the optical resonator.

In the process for performing dosimetry, receiving, by
compensation resonator 236, resonant frequency 240 can be
transmitted to the compensation waveguide 238. In a par-
ticular embodiment, light in the optical resonator is evanes-
cently coupled to the waveguide.

In the process for performing dosimetry, producing by
compensation waveguide 238, primary compensation output
light 246 is communicated to light detector 258. In an
embodiment, output light is communicated to a detector
using a fiber optic cable.

In the process for performing dosimetry, monitoring pri-
mary compensation output light 246 as a function of time to
log the temperature history of photonic dosimeter 200 can
include measuring peak frequency, linewidth, intensity. In
an embodiment, this involves locking a laser to the optical
resonator, and its frequency can be monitored using a
wavemeter.

In the process for performing dosimetry, in changing
prime state 230 to dosed state 232, changing a physical
property or a chemical property of active element 224 by
ionizing radiation 254 can include changes in temperature,
strain, density, oxidation and refractive index. In an embodi-
ment, dosing will result in frequency changes in the reso-
nator, and these changes are combined with the response of
a dosimatrix to improve the calculation by accounting for
temperature-induced frequency changes.

In an embodiment, photonic calorimeter 300 provides a
response to receipt of ionizing radiation 254, wherein radia-
tion absorber 268 produces heat from absorption of ionizing
radiation 254 as shown in FIG. 36. Here, photonic calorim-
eter output signal (e.g., primary compensation output light
246) changes as a function of an amount of ionizing radia-
tion 254 received by radiation absorber 268. Accordingly,
photonic calorimeter 300 can be used multiple times, can be
used over differing amounts of ionizing radiation 254, can be
used over an arbitrary period, or can be subjected to con-
tinuous or intermittent presence of ionizing radiation 254.
With reference to FIG. 38, panel A shows an optical trans-
mission of compensation resonator 236 versus frequency of
resonant frequency 240 at a first temperature of radiation
absorber 268. Here, compensation resonator 236 has optical
transmission I0 at frequency FO that increases to optical
transmission 14 at frequency F2. At the first temperature,
compensation resonator 236 has an optical resonance at first
resonant frequency FR1 with intensity 11. Compensation
resonator 286 has optical transmission 10 at final frequency
FN. When subjected to ionizing radiation 254, radiation
absorber 268 absorbs ionizing radiation 254 and converts
ionizing radiation 254 to heat. Accordingly, the temperature

30

40

&

g

0

28

of radiation absorber 268 increases from the first tempera-
ture to a second temperature, wherein the second tempera-
ture is greater than the first temperature. With reference to
panel B of FIG, 38, at the second temperature, the optical
resonance of compensation resonator 286 decreases to sec-
ond resonance frequency FR2. In this manner, photonic
calorimeter 300 optically associates a shift in optical reso-
nance of compensation resonator 236 with heat produced by
radiation absorber 268 in response to absorption of ionizing
radiation 254 by radiation absorber 268. Moreover, since the
optical resonance of compensation resonator 236 changes as
a function of temperature, secondary compensation output
light 244 and primary compensation output light 246 like-
wise change as a function of temperature so that detector 258
outputs a signal indicative of an amount of ionizing radiation
254 received by radiation absorber 268, an amount of heat
produced by radiation absorber 260, or a temperature of
radiation absorber 268.

Photonic calorimeter 300 has numerous advantageous and
unexpected benefits and uses, including performing calo-
rimetry. In an embodiment, a process for performing calo-
rimetry with photonic calorimeter 300 includes: receiving,
by compensation waveguide 238, primary compensation
input light 242; producing, by compensation waveguide
238, secondary compensation light 244 from primary com-
pensation input light 242; receiving, by compensation reso-
nator 236, secondary compensation light 244 from compen-
sation waveguide 238; producing, by compensation
resonator 236, resonant frequency 240 output light; receiv-
ing, by compensation waveguide 238, resonant frequency
240 output light from compensation resonator 236; produc-
ing, by compensation waveguide 238, primary compensa-
tion output light 246 from secondary compensation output
light 244; subjecting radiation absorber 268 to ionizing
radiation 254; producing, by radiation absorber 268, heat
from ionizing radiation 254; communicating the heat to
compensation resonator 236; and changing the optical reso-
nance of compensation resonator 236 in response to pro-
ducing heat from ionizing radiation 254 by radiation
absorber 268 to perform calorimetry. The process for per-
forming calorimetry further can include determining a first
calorimeter response based on primary compensation output
light 246 prior to subjecting radiation absorber 268 to
ionizing radiation 254. The process for performing calorim-
etry further can include determining a second calorimeter
response based on primary compensation output light 246
afer subjecting radiation absorber 268 to ionizing radiation
254. The process for performing calorimetry further can
include determining an amount of ionizing radiation 254
absorbed by radiation absorber 268 from the first calorimeter
response and the second calorimeter response. It is contem-
plated that determining the amount of ionizing radiation 254
absorbed by radiation absorber 268 can include performing
an inverse Monte Carlo conversion from a temperature
change of radiation absorber 268 due to absorption of
ionizing radiation 254; and determining an energy absorbed
per unit mass of radiation absorber 268 from heating with
the inverse Monte Carlo conversion. In the process for
performing calorimetry, the first calorimeter response and
the second calorimeter response can differ in a resonance
frequency, an amount of transmission, or a combination
including at least one of the foregoing differences.

In the process for performing calorimetry, receiving, by
compensation waveguide 238, primary compensation input
light 242 can include physical or evanescent coupling of
input light 242 with compensation waveguide 238.


US 10,718,872 B2

3

FIG. 21 shows a thermometer including a heater disposed
on an optical resonator in panels A, B, and C:

FIG. 22 shows a thermometer in panels A, B, and C;

FIG. 23 shows a thermometer including an optical reso-
nator having a conical shape in panels A, B, and C;

FIG. 24 shows a thermometer including a waveguide
having a plurality of apertures in panels A, B, and C;

FIG. 25 shows a thermometer including an aperture;

FIG. 26 shows a thermometer including a plurality of
waveguides in panels A, B, and C;

FIG. 27 shows a thermometer including an optical reso-
nator having a Bragg grating in panels A, B, C, and D;

FIG. 28 shows a thermometer including a plurality of
optical resonators and a plurality of waveguides in panels A,
B, and C;

FIG. 29 shows a thermometer including a waveguide in
panels A and B;

FIG. 30 shows a waveguide including a Bragg grating in
panels A, B, and C:

FIG. 31 shows a waveguide including an end coupler:

FIG. 32 shows a graph of transmission versus wavelength
for a plurality of temperatures;

FIG. 33 shows a graph of intensity versus temperature in
panel A and a graph of resonant wavelength versus tem-
perature in panel B;

FIG. 34 shows a thermometer system in panel A and a
thermometer system in panel B;

FIG. 35 shows a thermometer system in panel A and a
system to detect temperature of an article in panel B;

FIG. 36 shows a graph of state versus cumulative dose in 3

panel A and a graph of state versus cumulative dose in panel

FIG. 37 shows a graph of photonic calorimeter output
versus amount of ionizing radiation;

FIG. 38 a graph of transmission versus frequency prior to 3

subjecting a photonic dosimeter to ionizing radiation in
panel A and after subjecting the photonic dosimeter to
ionizing radiation in panel A;

FIG. 39 shows a micrograph of a thermometer:

FIG. 40 shows a graph of transmission versus wavelength
at a plurality of temperatures in panel A and a graph of
normalized transmission versus wavelength at a plurality of
temperatures in panel B;

FIG. 41 shows a graph of wavelength versus temperature
in panel A and a graph of wavelength versus temperature in
panel

FIG. 42 shows a graph of wavelength versus dose:

FIG. 43 shows a graph of wavelength versus temperature;

FIG. 44 shows a graph of power versus wavelength;

FIG. 45 shows a graph of Q and change in wavelength
versus date;

FIG. 46 shows a graph of residual and peak wavelength
versus temperature;

FIG. 47 shows cross-sections of pedestal and chip; and

FIG. 48 shows a graph of positions for a gamma-ray field.

DETAILED DESCRIPTION

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

The National Institute of Standards and Technology
(NIST) uses water calorimetry as a primary standard for
absorbed dose for which the SI unit is the gray (Gy), wherein
a radioactive cobalt-60 (Co-60) source irradiates a volume
of water, and the energy received is calculated from the rise
in water temperature as measured by immersed thermistors

3

40

&

3

4

to determine an estimated depth-dose profile. However,
there is an urgent and growing interest in making dosimetry
measurement at a smaller scale than provided by this pri-
mary standard. To this point, no conventional method
directly measures radiation dose in such dimensions, and
this capability is needed for medical and industrial applica-
tions such as microbeam therapy, microelectronics, and
cellular dosimetry.

The NIST on a Chip (NOAC) program is researching a
solution based on silicon chip fabrication and telecommu-
nications technology. The goal is micro-scale calorimetry
with photonic thermometers that are in the form of a fiber
Bragg grating or silicon ring resonators embedded in a
radiation-resistant substrate. These could be arranged to
perform real-time dose measurements in a phantom, and
eventually even in vivo.

Described here is a photonic dosimeter and photonic
calorimeter that overcome limitations of conventional
devices and provide photonic dosimetry and photon calo-
rimetry that expand uses of photonic dosimetry and calo-
rimetry. It is contemplated that arrays of miniaturized sen-
sors of the photonic dosimeter and photonic calorimeter are
multiplexed in an array separately or together on a chip
measure radiation. These chips can be arranged to determine
perform real-time absorbed-dose levels in a phantom and
provide dosage tailored sensors for individual patients.

The photonic dosimeter and photonic calorimeter herein
provide increased sensitivity, spatial resolution, optical read-
out, and multiplexing in devices. The photonic dosimeter
and photonic calorimeter reduce dependence on Co-60
sources, include new portable sensors, and provide measure-
ment articles for quantitative nuclear medicine. The pho-
tonic dosimeter and photonic calorimeter independently
provide response of thousands of photonic thermometers
through a single fiber optic interface. NIST research into
fabricating the photonic dosimeter and photonic calorimeter
shown that the photonic dosimeter and photonic calorimeter
withstand exposure to ionizing radiation so that the photonic
dosimeter and photonic calorimeter can be used harsh envi-
ronments, such as space or energy-generation. Although a
more detailed discussion follows, the photonic dosimeter
and photonic calorimeter can be a silicon photonic device
that can be irradiated with up 1 MGy of gamma radiation
and 250 kGy of beta radiation, which is 10,000 times higher
than medical radiation treatment levels, with little to no
damage to the photonic devices and provide baseline drift in
individual exposure over time that is negligible.

The photonic dosimeter and photonic calorimeter can
include a photonic thermometer that is highly sensitive and
resistant to change in response due to a physical impact.
Moreover, the thermometer is useful as self-calibrating or
self-diagnosing thermometer. The thermometer has an inte-
grated optical resonator with a resonant frequency that
changes with temperature due to thermal expansion or a
thermo-optic effect of the optical resonator. The thermom-
eter can include a thermal member to provide a selected
temperature change to the optical resonator, Advanta-
geously, the thermometer is to calibrate or determine a
performance of an article, e.g., remotely. Further, the ther-
mometer has a robust physical construction and is small, yet
scalable. The thermometer also is rugged, does not require
frequent, expensive, time-consuming re-calibration, and has
a small thermal mass that does not rely upon voltage
measurement for temperature determination. The thermom-
eter can be fabricated in bulk quantities in a mass production
environment. Beneficially, the thermometer involved tem-
perature dependent light transmission and is resistant to


U.S. Patent Jul. 21, 2020 Sheet 22 of 48 US 10,718,872 B2

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U.S. Patent

Jul. 21, 2020 Sheet 40 of 48

US 10,718,872 B2

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US 10,718,872 B2

Sheet 3 of 48

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Sheet 21 of 48

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Figure 34


U.S. Patent Jul. 21, 2020 Sheet 16 of 48 US 10,718,872 B2

Figure 16


US 10,718,872 B2

23

swept over the resonance frequency of the optical resonator.
The resonance frequency is determined. The process also
includes providing an amount of electrical power to the
thermal member, changing the temperature of the optical
resonator, and changing the wavelength of the input light,
wherein a wavelength range includes the resonance fre-
quency. The resonance frequency is determined by detecting
from the output light. In an embodiment, a plurality of
heating events delivers a plurality of different amounts of
electrical power to the thermal member. For a single mea-
surement, a change in resonance frequency provides a
change in the resonant frequency corresponding to a first
temperature and a second temperature. For the plurality of
heating events, the process also includes determining
whether a change in the resonance frequency is linear with
respect to a change in temperature. In an embodiment, an
alert signal is communicated, e.g., to a user, in response to
the change in resonant frequency being nonlinear with
respect to temperature change. Such nonlinear behavior may
be associated with operation of the thermometer in a non-
calibrated fashion. Thus, the self-diagnosing behavior of the
thermometer provides a way to perform a self-check service
by a user or an automatic drive (e.g., an electronic controller
such as programmed computer) to determine if the ther-
mometer is performing within an acceptable parameter.
According to an embodiment, the thermometer is sub-
jected to temperature-wavelength calibration to determine
the response (e.g., a wavelength shift) determined at a
plurality of temperatures that includes an operation tempera-
ture. A mathematical function (e.g., a polynomial) is fit to
calibration data to create a conversion for a measured
resonant wavelength (or wavelength shift) to a temperature.
In an embodiment, a process for self-calibrating a ther-
mometer includes providing a thermometer (including a

waveguide and optical resonator disposed on a substrate), 3

determining the resonant frequency of the optical resonator,
and providing a stable input light tuned to a longer wave-
length side of the resonant frequency to cool the resonator
(e.g., a detuned laser). A spectrum analyzer can be used to
determine the frequency and intensity of the output light.
Under a laser cooling condition, the spectrum analyzer
displays a signal corresponding to the wavelength of the
detuned laser (e.g... a frequency and intensity) and a plurality
(e.g., two) side bands that occur, e.g., equidistantly from the
detuned laser frequency. The self-calibration process further
includes determining an area of each side band and deter-
mining phonon occupancy number P. Phonon occupancy
number P is determined from the data by using a phonon
occupancy equation such as P=1/[(A(LF)/A(HF))-1], where
Pis the phonon occupancy number; A(LF) is an area ofa low
frequency side band, and A(HF) is an area of a high
frequency side band. The temperature of the optical reso-
nator is determined from phonon occupancy number P by
applying Boltzmann’s law. In a particular embodiment, a
thermodynamic temperature is determined from phonon
occupancy number P to eliminate a temperature artifact such
as a triple point water such as that used in temperature
standards, e.g., the International Temperature Scale of 1990
(ITS-90), to approximate a thermodynamic temperature.
Photonic dosimeter 200 can be made in various ways. In
an embodiment, a process for making photonic dosimeter
200 includes forming dosimatrix 220 on a silicon-on-insu-
lator substrate (SOI). The substrate can include a stacked
structure having a first silicon layer (e.g., 220 nm thick) and
a buried silicon dioxide layer (BOX, e.g., 2 um thick)
interposed between the first silicon layer and a bottom
silicon layer (e.g., 670 jim thick). The SOI can be a wafer or

30

40

24

die. A positive or negative tone electron beam resist is spin
coated on the SOI substrate and baked at a temperature
above a glass transition temperature of the resist. The
substrate is subjected to electron beam to provide the optical
resonator. During development of the resist from an exposed
resist (e.g,, the positive tone electron beam resist) or an
unexposed resist (e.g. the negative tone electron beam
resist), portions of the first silicon layer are removed by a
solvent post lithography to form an etch mask. The resulting
structure is subjected to dry etching by, e.g., an inductively
coupled plasma reactive ion etch where an unmasked por-
tion of the first silicon layer is etched through to the BOX
layer. The etch mask is dissolved in a solvent to provide the
dosimeter. In some embodiment, the dielectric layer (e.g., a
polymer coating, such as a polyimide or polyvinyl alcohol)
is disposed on the dosimeter by spin coating or drop casting
to provide, e.g., a 2 jum thick layer of the dielectric poly-
meric layer.

In an embodiment, a process for making photonic calo-
rimeter 300 includes: embedding temperature compensator
234 in radiation absorber 268 (such as graphite, polymeth-
ylmethacrylate, water) thermal isolator 262 (material,
removal of material), thermal compensator 234 include
compensation resonator 236 and a compensation waveguide
238, embedded in radiation absorber 268 while ensuring
thermal isolation achieved by inserting a gap between the
radiation absorber 268 and the substrate or other absorbers
for a multiplexed embodiment 402.

The thermometer provides an optical response as a func-
tion of temperature, e.g., as shown in FIG. 32 and FIG. 33.
It is contemplated that photonic dosimeter 200 provides a
response to cumulative dose of ionizing radiation 254 via
conversion from prime state 230 to dosed state 232 as shown
in panel A of FIG. 36. Here, at first cumulative dose C1 of
dosimatrix 220, active element 224 is in first state S1
corresponding to prime state 230, wherein dosimatrix 220
has an optical resonance at first wavelength L1. As photonic
dosimeter 200 is subjected to increasing cumulative dose of
ionizing radiation 254, dosimatrix 220 obtains cumulative
dose C2, and active element 224 converts from prime state
230 to dosed state 232, wherein dosimatrix 220 has an
optical resonance at second wavelength L2. As a result,
without changing a wavelength of primary input light 214
received by waveguide 212, primary output light 222 from
waveguide 212 changed due to a change in secondary output
light 216 because of the shift in wavelength of the optical
resonance of dosimatrix 220 caused by increasing cumula-
tive dose of ionizing radiation 254 received by dosimatrix
220 that converted from prime state 230 to dosed state 232.
Panel B of FIG. 36 shows a continuous conversion of state
of active element 224 from S1 at cumulative dose C1 with
wavelength L1 of optical resonance of dosimatrix 220, to S2
at cumulative dose C2 with wavelength L2 of optical
resonance of dosimatrix 220, to S3 at cumulative dose C3
with wavelength L3 of optical resonance of dosimatrix 220,
to S4 at cumulative dose C4 with wavelength L4 of optical
resonance of dosimatrix 220, and to S5 at cumulative dose
C5 with wavelength LS of optical resonance of dosimatrix
220. With regard to prime state 230 and dosed state 232 of
dosimatrix 220, any state at a selected cumulative dose (e.g.,
C2) can be selected as a primary state, and any state at a
cumulative dose (e.g., C8, which'is not shown in panel B of
FIG. 36 but would be greater than C5) greater than the
selected cumulative dose can be a dosed state. Accordingly,
photonic dosimeter 200 can be used multiple times, can be
used over differing amounts of cumulative dose, can be used


US 10,718,872 B2

Sheet 8 of 48

Jul. 21, 2020

U.S. Patent

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U.S. Patent Jul. 21, 2020 Sheet 31 of 48 US 10,718,872 B2

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US 10,718,872 B2

37

a proportional-integral-derivative controller that drove a
thermoelectric cooler. The first stage minimizes global tem-
perature fluctuations inside the enclosure to +1 K, and the
second stage minimized temperature variations at the ther-
mometer to less than 17 mK over 24 hours. A relative
humidity (% RH) inside the enclosure was monitored by a
humidity meter. Relative humidity levels were changed
inside the enclosure by varying a flow rate of air saturated
with water.

The wavelength of the input light from the laser was
scanned, and the transmission spectrum was recorded. A
center frequency of the transmission spectrum was deter-
mined. From a calibration curve, the center frequency was
converted to temperature. Thereafter, the temperature of the
thermometer was changed from 288 K and 306 K.

As shown in FIG. 40B, the thermometer had a resonant
frequency that changed with temperature at 77 pm/K, and
the thermometer resolved a temperature difference of 1 mK.
FIG. 22 shows a graph of resonance wavelength versus
temperature for the thermometer.

‘A second thermometer having a ring resonator with a
radius of 11 jum was prepared per Example 1 and subjected
to testing. For the second thermometer, a graph of transmis-
sion versus wavelength is shown in FIG. 40B with a graph
of resonance wavelength versus temperature being shown in
FIG. 40B.

Example 3

FIG. 41A shows a graph of the resonance wavelength vs.
temperature calibration curve for a fiber Bragg grating.

Example 4

FIG. 41B shows a graph of the resonance wavelength vs.
temperature calibration curve for a fiber Bragg grating.

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.

Reference throughout this specification to “one embodi-
ment,” “particular embodiment,” “certain embodiment,” “an
embodiment,” or the like means that a particular feature,
structure, or characteristic described in connection with the
embodiment is included in at least one embodiment. Thus,
appearances of these phrases (e.g., “in one embodiment” or
“in an embodiment”) throughout this specification are not
necessarily all referring to the same embodiment, but may.
Furthermore, particular features, structures, or characteris-
tics may be combined in any suitable manner, as would be
apparent to one of ordinary skill in the art from this
disclosure, in one or more embodiments.

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
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). “Optional” or “optionally”
means that the subsequently described event or circumstance
can or cannot occur, and that the description includes

S

20

30

40

45

3!

38

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.” Further, 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.
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 (e.g., it
includes the degree of error associated with measurement of
the particular quantity).

What is claimed is:

1. A photonic dosimeter to accrue cumulative dose, the
photonic dosimeter comprising:

a substrate;

a waveguide disposed on the substrate and that:

receives a primary input light;

transmits secondary input light from the primary input
light to a dosimatrix;

receives a secondary output light from the dosimatrix;
and

produces primary output light from the secondary out-
put light;

the dosimatrix disposed on the substrate and in optical

communication with the waveguide and that:

receives the secondary input light from the waveguide;

produces the secondary output light that is communi-
cated to the waveguide; and

comprises an active element that undergoes conversion
from a prime state to a dosed state in response to
receipt, by the active element, of a dose of radiation
such that a wavelength of an optical resonance of the
dosimatrix depends on the prime state and the dosed
state, wherein the optical resonance of the dosimatrix
changes due to conversion from the prime state to the
dosed state; and

a cover layer disposed on waveguide and the dosimatrix

2. The photonic dosimeter of claim 1, further comprising
a cladding disposed on the dosimatrix such that:

the dosimatrix is interposed between the substrate and the

cladding; and

the cladding is interposed between the dosimatrix and the

cover layer.

3. The photonic dosimeter of claim 1, further a tempera-
ture compensator disposed on the substrate and that com-
pensates for a temperature change of the photonic dosimeter
as a function of time during which the active element
accrues cumulative dose and undergoes conversion from the
prime state to the dosed state in response to receipt, by the
active element, of the dose of radiation.

4. The photonic dosimeter of claim 3, wherein the tem-
perature compensator comprises:


U.S. Patent Jul. 21, 2020 Sheet 28 of 48 US 10,718,872 B2

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US 10,718,872 B2

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a2 United States Patent
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US010718872B2

US 10,718,872 B2
Jul. 21, 2020

(10) Patent No.:
(45) Date of Patent:

(54) PHOTONIC DOSIMETER AND PROCESS
FOR PERFORMING DOSIMETRY

(71) Applicant: Government of the United States of
America, as represented by the

Secretary of Commerce, Gaithersburg,
MD (US)

(72) Inventors: Ronald Tosh, Frederick, MD (US);
Zeeshan Ahmed, Washington, DC
(US); Ryan P. Fitzgerald, Washington,
DC (US); Nikolai Klimoy, Ellicott City,
MD (US)

(73) Assignee: GOVERNMENT OF THE UNITED
STATES OF AMERICA, AS
RESPRESENTED BY THE
SECRETARY OF COMMERCE,
Gaithersburg, MD (US)

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

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

(21) Appl. No.: 16/276,932

(22) Filed: Feb. 15, 2019

(65) Prior Publication Data
US 2019/0293808 Al Sep. 26, 2019
Related U.S. Application Data
(60) Provisional application No. 62/647,515, filed on Mar.

23, 2018
(51) Int. Ch
GOIT 1/02 (2006.01)
GOIT 7/00 (2006.01)
(Continued)
(52) US.CL
CPC verssseteee GOIT 1/12 (2013.01); GOIT 1/026
(2013.01); GOT 7/00 (2013.01); GO2B 6/124
(2013.01);
(Continued)

209

(58) Field of Classification Search
CPC .. GOIT 1/12; GOIT 1/026; GOIT 7/00; GO2B
2006/12107; GO2B 6/124; GO2B 6/29338;
G02B 6/29323

See application file for complete search history.

(56) References Cited
U.S. PATENT DOCUMENTS

9,726,553 B2
2012/0156763 Al*

8/2017 Ahmed et al.

6/2012 Wikswo. GOIN 33/5005

435/287.1
(Continued)

OTHER PUBLICATIONS

De Leonardis, F., et al., “Modeling of Radiation Effects in Silicon
Photonic Devices”, IEEE Transactions on Nuclear Science, 2015,
2155-2168, vol. 62, No. 5.

(Continued)

Primary Examiner —‘Taeho Jo
(74) Attorney, Agent, or Firm — Ofiice of Chief Counsel
for National Institute of Standards and Technology

(67) ABSTRACT

A photonic dosimeter accrues cumulative dose and includes:
a substrate; a waveguide disposed on the substrate and that:
receives a primary input light; transmits secondary input
light from the primary input light to a dosimatrix; receives
a secondary output light from the dosimatrix; and produces
primary output light from the secondary output light: the
dosimatrix disposed on the substrate and in optical commu-
nication with the waveguide and that: receives the secondary
input light from the waveguide; produces the secondary
output light that is communicated to the waveguide; and
includes an active element that undergoes conversion from
a prime state to a dosed state in response to receipt, by the
active element, of a dose of radiation; and a cover layer
disposed on waveguide and the dosimatrix.

16 Claims, 48 Drawing Sheets



US 10,718,872 B2

Sheet 46 of 48

Jul. 21, 2020

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Jul. 21, 2020 Sheet 9 of 48 US 10,718,872 B2

200A 2008

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US 10,718,872 B2

21

transmission intensity 12, third transmission intensity 13
respectively at first temperature T1, second temperature T2,
and third temperature T3.

Furthermore, first resonant wavelength Arl at first tem-
perature T1, second resonant wavelength r2 at second
temperature T2, third resonant wavelength 213 at third
temperature T3 can be detected using a detector, e.g., a
wavemeter. Such results are shown in FIG. 14C for a graph
of resonant wavelength versus temperature. Information in
the graph shown in FIG. 14C and knowledge of intensity
data provides determination of an unknown temperature of
temperature change of the thermometer. According to an
embodiment, a process for determining an unknown tem-
perature or change in temperature includes detecting an
intensity of output light at a wavelength and comparing an
intensity of output light at the wavelength to an intensity
curve to determine the temperature, temperature change, or
combination thereof.

According to an embodiment, the thermometer includes
the thermal member to change a temperature of the ther-
mometer by providing a controlled and defined heat source
to the thermometer, e.g., the optical resonator. The change in
resonant frequency of the optical resonator is measured and
a transmission response of output light is detected to deter-
mine if the thermometer is responding as expected based on
either a theoretical response curve or a calibration curve for
the thermometer.

In an embodiment, a process for determining a thermal
property includes providing a thermometer that includes a
substrate, an optical resonator disposed on the substrate and
comprising an optical resonance and a waveguide disposed
on the substrate proximate to the optical resonator. The
process also includes subjecting the optical resonator to a
first temperature, receiving (by the waveguide) an input light

comprising a wavelength having a first transmission inten- 3

sity through the waveguide at the first temperature, receiving
(by the optical resonator from the waveguide) a first amount
of the wavelength at the first temperature, subjecting the
optical resonator to a second temperature, receiving (by the
optical resonator from the waveguide) a second amount of
the wavelength at the second temperature, changing the first
transmission intensity to a second transmission intensity
corresponding to the second amount, and analyzing the first
transmission intensity and the second transmission intensity
to determine the thermal property that includes the first
temperature, the second temperature, a difference between
the first temperature and the second temperature, or a
combination comprising at least one of the foregoing.

According to an embodiment, the process for determining
the thermal property further includes subjecting the optical
resonator to a temperature change that includes the first
temperature and the second temperature by applying an
amount of electrical power to a thermal member disposed on
the substrate to achieve the first temperature, the second
temperature, or a combination comprising at least one of the
foregoing; and comparing a change in the first transmission
intensity and the second transmission intensity, the differ-
ence between the first temperature and the second tempera-
ture, or a combination comprising at least one of the
foregoing to a reference value for the amount of electrical
power.

In an embodiment, with reference to FIG. 34A, thermom-
eter system 340 includes light source 341 to provide primary
compensation input light 242 to thermometer 345. Light
source 341 is a broad band source (e.g., a lamp), a laser, or
a combination thereof. Optical filter 342 (e.g. a Fabry-Perot
cavity) is optionally disposed in a path of the input light to

0

0

30

40

0

3

22

select a narrow bandwidth of input light to be communicated
to thermometer 345. Beam splitter 343 is optionally used to
provide a portion of the input light to first detector 344, e.g.,
a wavemeter to measure the wavelength of the input light, a
photodiode, a power meter, and the like. It is contemplated
that a wavelength of the input is measured using, e.g., a
wavemeter, an etalon, a spectrometer, a wavelength cell, a
spectrum analyzer, and the like. Output light from thermom-
eter 345 is sent to second detector 346, which is, e.g., a light
detector such as a photo-diode, charge coupled device,
semiconductor detector (e.g., InGaAs), photomultiplier
tube, and the like.

According to an embodiment, with reference to FIG. 34B,
thermometer system 340 includes thermometer 345 having
an add-drop arrangement of an optical resonator and wave-
guides. Here, optional optical filter 342 is absent due to the
self-filtering behavior of an auxiliary waveguide in combi-
nation with the optical resonator.

In an embodiment, with reference to FIG. 35A, thermom-
eter system 340 includes thermometer 345 to receive input
light from first light source 347 (e.g., a read-out laser) or
second light source 348 (e.g., a cooling laser) via combiner
349 (e.g., a multiplexer or lock-in amplifier). Output light
from thermometer 345 is directed to optical amplifier 350
and detected by detector 351 (e.g.. a spectrum analyzer)
Here, the side bands of second light source 348 are detected,
and a ratio of an area of a side band or intensity is
determined to calculate phonon occupancy, which is used in
a Boltzmann’s law calculation to provide temperature of the
thermometer.

According to an embodiment, with reference to FIG. 35B,
thermometer system 340 includes controller 353 (e.g., a
microprocessor, computer, and the like) in communication
with light source 354 that provides input light to splitter 355
and control thermometer 356, including a plurality of ther-
mometers, e.g., first thermometer 357 and second thermom-
eter 358 to provide a thermal calibration response for control
thermometer 184, Output light from control thermometer
356 is sent to first detector 359 whose output signal is
communicated to controller 353. A plurality of test ther-
mometers (including the thermometer herein), e.g., first test
thermometer 361, second test thermometer 362, and third
test thermometer 363 are disposed in thermal contact with
article 360 (e.g... airplane, automobile, surgical patient, desk
clock, aquarium, and the like), and input light from beam
splitter 355 is directed in series (or parallel) to first test
thermometer 361, second test thermometer 362, and third
test thermometer 363, which provide output light to second
detector 364. An output signal is directed to the controller
353. Output signals from test thermometers (202, 204, 206)
can be compared to reference signals from control thermom-
eter 356.

In some embodiments, the thermometer is a self-diagnos-
ing thermometer that includes a thermal member such that
the thermometer is remotely interrogated after installation in
an article. Here, the thermal member provides a known heat
load to the optical resonator and output light is collected to
determine if a change in the resonant frequency has occurred
with respect to an expected value of change in the resonant
frequency for the known heat load.

According to an embodiment, a process for self-diagnos-
ing a thermometer includes disposing a thermal member
proximate to an optical resonator of the thermometer, pro-
viding an input light to the waveguide, detecting output light
from the waveguide, and measuring transmission intensity.
The thermometer is at a first temperature, and a wavelength
of the input light is changed such that the wavelength is


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US 10,718,872 B2

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A C-band laser was swept over the sensor resonance. Ten
percent of laser power was immediately picked up from the
laser output for wavelength monitoring while the rest was
evanescently coupled to the photonic device under test using
an optical fiber held within a few microns of the chip
surface. The photonic chip was mounted on a Peltier assem-
bly atop a 3-axis stage. Input from a platinum resistance
thermometer (measurement accuracy +0.1° C.) was com-
municated to a proportional-integral-derivative controller
that controlled a thermoelectric cooler and maintained the
temperature to within 0.02° C. of the set value. Photonic
chips were fabricated using complementary metal-oxide-
semiconductor (CMOS) technology. Three of the represen-
tative chips from the batch were systematically exposed to
varying levels of y-ray radiation at the NIST high-dose
dosimetry laboratory, while a fourth chip, used as a control,
was never exposed to radiation, though it traveled with the
other three chips between the photonics testing facility and
the radiation facility.

Photonic sensors were irradiated with y-rays in the NIST
high-dose dosimetry laboratory. Three °°Co irradiators were
used with dose rates between 0.2 kGy/h and 3.9 kGy/h. Most
of the irradiations were done using irradiator number
GC207, which contained a nominal activity of 1.76*10"* Bq
on a reference date and delivered an absorbed dose rate to
water, determined using alanine dosimetry, of R=1.08 Gy/s
on the reference date, with an expanded uncertainty of about
2%. This amounts to a dose rate per “Co activity of
D=6.12*10"'> Gy/s/Bq.

Monte Carlo simulations were performed and calculated
dose to the silicon devices based on measured dose to
alanine calibration pellets. A geometry for the GC 220 was
created based on the irradiator specification sheet. The 1 cm

diameter “Co rods were simulated as a single cylindrical 3

shell. Aluminum and steel shells of 2 mm thickness were
implemented between sources and exposure chamber. The
©°Co emission spectrum included two 1.25 MeV y-rays.

‘Two irradiation geometries were simulated—the chamber
calibration and chip irradiation, shown in FIG. 47, a cross-
sectional side-view of the simulated geometry for the cali-
bration pedestal (left) and chip in beaker geometry (right).
The radiation absorber material in the model was varied
among water, silicon, and silica. The calibration geometry
used to transfer calibration from the primary standard of
absorbed dose to water included 5-mm diameter alanine
pellets stacked inside a polystyrene cylinder (pedestal) of
wall thickness 3.7 mm. For the chip irradiation, one chip at
a time was placed inside a glass beaker of diameter and wall
thickness of 30.5 mm and 1.3 mm, respectively. Although
the chip device layer was only a few um thick, the simulated
dose to the chip was averaged over the top 100 um of the
chip, to achieve adequate Monte Carlo statistics.

For the calibration geometry, the simulated result was
D=6.23-10"!S Gy/s/Bg, which is 2% higher than the nominal
calibrated value. For the chip geometry, the result was
D=5.42:10"-!* Gy/s/Bq. The ratio of the calculated dose for
the chip geometry to the calibration geometry was 0.870,
with a total Monte Carlo uncertainty of about 3%.

Scaling the calibrated value for R by the ratio of the
calculated D values for the chip geometry to the calibration
geometry resulted in a dose rate to the chip of 0.94 Gy/s with
an expanded uncertainty of 7% (k=2).

An approximate gamma-ray field map was calculated by
numerically solving an integral representing the y-ray flux,
F, inside a chamber consisting of a thin, radiating, cylindri-
cal shell,

S

20

40

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0

36

pinch pe , w
Fo = | i Toe more” &

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wherein L=210 mm is the shell length, =105 mm is the shell
radius, and (x, h) is the test position within the chamber. No
interactions were considered. The field map, relative to the
value in the center of the chamber, is shown in FIG. 48 that
shows normalized, simulated gamma-ray field, F(x.h/F(0.0)
for cylindrical shell source. Contours represent a change in
field of about 2% of the central value. Along the vertical axis
of the chamber (x=0), the field changes by -1% at z=+18
mm. Along the midplane of the chamber (h=0), the field
changed by +1% at x=+14 mm. The ~5 mm positioning
accuracy of the chip did not affect absorbed dose beyond the
Monte Carlo and calibration accuracy.

Regarding transient charged particle equilibrium (TCPE),
a Monte Carlo model was constructed for a version of the
chip geometry. A 1.25 MeV y-ray source was incident from
the side of the chip, aligned with the center of the top layer,
which was 200 um thick and was thicker than the actual
device layer, but not thick enough to achieve TCPE. Only
about 1 out of 50 y-rays interact with the chip. Of those that
do, about 80% produced Compton-scattered electrons that
escaped into the air from the top layer. Since there was not
an equal energy flux of electrons produced in the air that pass
into the top Si layer, TCPE was not achieved. Therefore, the
absorbed dose to the chip was not calculated based on the
relative linear-energy transfer and density of silicon relative
to water. Rather, full Monte Carlo simulations were per-
formed.

Example 1. Thermometer

A thermometer was fabricated using CMOS techniques on.
a silicon on insulator (SOT) wafer with a 220 nm thick layer
of silicon on top of a 2 um thick buried oxide layer that
isolates an optical mode and prevents loss to the substrate.
The fabrication of silicon devices was performed through
microfabrication and nanofabrication. Masks were made
using ultraviolet light at 193 nm for photolithography and
were etched to from a waveguide and Bragg coupler. The
Bragg coupler provided free space coupling of light in or out
of the thermometer at, e.g., 4 dB per Bragg coupler. The
thermometer was subjected to thermal oxidation to form a
10 nm thick SiO, layer thereon to reduce a surface rough-
ness.

FIG. 39 shows a micrograph of the thermometer 365 that
included ring resonator 367 and waveguide 366. The micro-
graph was acquired by a scanning electron microscope. Ring
resonator 367 had 10 jm radius and was separated from
waveguide 366 by 130 nm. The thermometer had a free
spectral range of 9.2 nm at 1550 nm, Q-factor of 52000, and
estimated group index of 4.2.

Example 2. Temperature Response of Thermometer

The thermometer from Example 1 was subjected to ther-
mal response testing. A tunable laser provided input light to
the ring resonator. A portion of the input light was picked up
from the laser output for wavelength monitoring while the
balance of the input light, after passing through the ther-
mometer, was detected by a power meter. The thermometer

5 was mounted on a two-axis stage in a two-stage tempera-

ture-controlled enclosure. Input from a platinum resistance
thermometer from each stage was fed to an input channel of


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US 10,718,872 B2

17

protons that cause ionization when the ionization radiation
interacts with a material. Radiation source 404 is a material
that produces ionizing radiation 254, e.g., radioactive mate-
rial such as Co-60 or an accelerator-based source.

Light member 248 contains a light source and a light
detector. In an embodiment, it contains light source 250 and
light detector 252. Light member 256 contains a light source
and a light detector. In an embodiment, it contains light
source 260 and light detector 258. Light source 250 is a
source of light. In an embodiment, light source 250 is a laser.
Light source 258 is a source of light. In an embodiment, light
source 258 is a laser. Light source 341 is a source of light
In an embodiment, light source 341 is a laser. First light
source 347 is a source of light. In an embodiment, light
source 347 is a laser. Second light source 348 is a source of
light. In an embodiment, light source 348 is a laser. Light
source 354 is a source of light. In an embodiment, light
source 354 is a laser. Primary input light 214 is light
transmitted from a light member (in an embodiment, light
source 250) to a waveguide (in an embodiment, waveguide
212). Secondary output light 216 is light transmitted from
dosimatrix 220 to waveguide 212. Secondary input light 218
is light transmitted from waveguide 212 to dosimatrix 220.
Primary output light 222 is light transmitted from a wave-
guide (in an embodiment, waveguide 212) to a light member
(in an embodiment, light member 248). Primary compensa-
tion input light 242 is light transmitted from a light member
(in an embodiment, light source 258) to a waveguide (in an
embodiment, temperature-compensating waveguide 238).

Secondary compensation output light 244 is light transmit- 3

ted from a waveguide (in an embodiment, temperature-
compensating waveguide 238) to a compensation resonator
(in an embodiment, compensation resonator 236). Primary
compensation output light 246 is light transmitted from a

waveguide (in an embodiment, temperature-compensating 3

waveguide 238) to a light member (in an embodiment, light
source 258). Resonant frequency 240 is the frequency of
light transmitted from a compensation resonator 236 to
compensation waveguide 238.

Light detector 252 produces a measurable voltage or
current that can be quantified, in response to incident light.
Light detector 260 produces a measurable voltage or current
that can be quantified, in response to incident light First
detector 344 produces a measurable voltage or current that
can be quantified, in response to incident light Second
detector 346 produces a measurable voltage or current that
can be quantified, in response to incident light Detector 351
produces a measurable voltage or current that can be quan-
tified, in response to incident light. First detector 359
produces a measurable voltage or current that can be quan-
tified, in response to incident light Second detector 364
produces a measurable voltage or current that can be quan-
tified, in response to incident light

Optical filter 342 removes a portion of the frequency
spectrum of the incident light. Beam splitter 343 divides
incident light flux into two or more paths. Combiner 349
combines multiple light paths into one output light path.
Optical amplifier 350 increases the intensity of the primary
light (an embodiment is an erbium-doped fiber amplifier)
Controller 353 is an electronic device that controls other
elements such as light members and optical amplifiers.
Splitter 355 divides incident light flux into two or more
paths.

In an embodiment, thermometer is produced by forming
the optical resonator (e.g., a ring resonator) on a silicon-on-
insulator substrate (SOI). The substrate can include a
stacked structure having a first silicon layer (e.g. 220 nm

S

2

40

3

18

thick) and a buried silicon dioxide layer (BOX, e.g.. 2 um
thick) interposed between the first silicon layer and a bottom
silicon layer (¢.g., 670 uum thick). The SOI can be a wafer or
die. A positive or negative tone electron beam resist is spin
coated on the SOI substrate and baked at a temperature
above a glass transition temperature of the resist. The
substrate is subjected to electron beam to provide the optical
resonator. During development of the resist from an exposed
resist (e.g., the positive tone electron beam resist) or an
unexposed resist (e.g. the negative tone electron beam
resist), portions of the first silicon layer are removed by a
solvent post lithography to form an etch mask. The resulting
structure is subjected to dry etching by, e.g., an inductively
coupled plasma reactive ion etch where an unmasked por-

s tion of the first silicon layer is etched through to the BOX

layer. The etch mask is dissolved in a solvent to provide the
thermometer. In some embodiment, the dielectric layer (e.g.,
silicon dioxide) is disposed on the thermometer by plasma-
enhanced chemical vapor deposition to provide, e.g... a2 um
thick silicon dioxide dielectric layer.

According to an embodiment, the Bragg grating or Bragg
coupler can be formed by irradiating the optical resonator or
the waveguide with an ultraviolet light (e.g., from an ultra-
violet laser such as ArF or KrF) to modify an index of

5 refraction of the illuminated material. An angle between an

ultraviolet light beam and optical resonator (or waveguide)
can determine a period of protrusions and depressions of the
Bragg grating or coupler and thus the Bragg wavelength. A
plurality of ultraviolet laser beams can be used to create a
periodic phase mask (photomask) in a phase mask tech-
nique, e.g., by using two first-order diffracted ultraviolet
laser beams. A non-periodic phase mask can be used to
obtain other patterns of the Bragg grating or coupling. In
another embodiment, a point-by-point Bragg grating or
coupler is created by point-by-point writing a pattern with a
focused laser beam. In some embodiments, an infrared light
having intense femtosecond pulses is used to produce the
Bragg grating or coupler.

According to an embodiment Bragg grating is fabricated
on a silicon-on-insulator substrate (SOI) that includes the
topmost silicon layer (e.g. 220 nm thick), thick buried
silicon dioxide layer (BOX) e.g. 3 um thick. and the sup-
porting bottom silicon layer (e.g. 670 tm thick). The SOI
can be wafer or die. A positive or negative tone electron
beam resist is spin coated on the SOI substrate, and the
resultant structure is baked at a temperature greater than a
glass transition temperature of the resist. The substrate is
subjected to electron beam exposure to provide the Bragg
grating. Electron beam lithography defines the structure of
Bragg grating and is an etch mask. A subsequent dry etch
process such an inductively coupled plasma reactive ion etch
where an unmasked portion of the first silicon layer is etched
through to the BOX layer. The etch mask is dissolved in a
solvent to provide the thermometer. In some embodiments,
the dielectric layer (e.g., silicon dioxide) is disposed on the
thermometer by plasma-enhanced chemical vapor deposi-
tion to provide, e.g.. a 2 um thick silicon dioxide dielectric
layer.

A physical size or material of the thermometer is selected
based on a wavelength range of the input light, output light,
or resonant frequency of the optical resonator. The optical
resonator can have an outer diameter from 9 jum to 900 um,
specifically 9 um to 700 um, and more specifically from 9
jum to 150 jm. A distance between the optical resonator and
the waveguide can be less than or equal to 300 nm, specifi-
cally 10 um to 200 jum, and more specifically from 20 nm to
150 nm.


US 10,718,872 B2

31

dose from low-energy radiation sources. Photonic calorim-
eter 300 overcomes this limitation by providing sub-milli-
meter-resolution dosimetry, with the option of embedding
networks of photonic calorimeters.

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

EXAMPLES

Example 1. Radiation Hardness of Fiber Bragg
Grating Thermometers

Photonic sensing is tolerant to harsh environments where
conventional sensing technologies fail. With regard to tol-
erance to radiation, the impact of gamma-ray exposure on
the temperature response of fiber Bragg gratings is
described. At 25° C., exposures leading to an accumulated
dose of up to 600 kGy result in complex dose-dependent
drift in Bragg wavelength, increasing uncertainty in tem-
perature measurements obtained if appreciable dose is deliv-
ered over the measurement interval. Temperature sensitivity
is not severely impacted by integrated dose, wherein devices
measure relative changes in temperature.

Photonic sensing involves exploiting sensitivity of the
device to changes in the refractive index of the host material.
For example, in a fiber Bragg grating (FBG), the resonant
condition is directly proportional to the refractive index of
the waveguide. A small change in the refractive index e.g.,
due to a rise in temperature, leads to a significant change in

resonance wavelength which has been exploited for pho- 3

tonic thermometry. Radiation induced damage causes local
point defects, dislocations, and formation of color centers
that contribute to local changes in refractive index that might
degrade measurement sensitivity and accuracy of a sensor.

In radiation environments, with dose rates ranging from a 3

few Gy/h to a few kGy/h, devices function over years of
exposure to radiation and aggregate dose accumulations
exceeding 1 MGy. Optical fibers show increased attenuation
with accumulated dose, and drifts in Bragg resonances
occur, wherein resonance wavelength redshifts with increas-
ing dose rate for accumulated doses below about 25 kGy. A
blue shift of magnitude (<0.1 nm) might occur at aggregate
doses approaching 0.5 MGy. Many industrial irradiation
processes deliver doses ranging from 10 Gy to 1 MGy, and
dose-related shifts in Bragg wavelength contribute 10 K
systematic uncertainty to in situ temperature measurements.

Devices herein correlate the shift with dose and dose rate
over irradiation conditions.

FBG thermometers were exposed to gamma (y)-rays, and
the thermometers were systematically exposed for FBG
thermometers that included Ge-doped silica fibers with two
cladding materials—polyimide and ORMOCER (Organic
Modified Ceramics)—to varying levels of radiation, leading
up to 600 kGy of absorbed dose. A dose-dependent change
occurred in the Bragg resonance, wherein a magnitude and
direction of wavelength shift vary over the dose range. The
experimental measurement apparatus includes the FBG sen-
sors that were probed with a C-band laser that was swept
over the sensor resonance. Ten percent of the laser power
was immediately picked up from the laser output for wave-
length monitoring (absolute accuracy=0.16 pm) while the
rest, after passing through an optical circulator, was injected
in the FBG. Six FBG devices (three with polyimide clad-
ding, labelled FBG 1-3, and three with ORMOCER clad-
ding, labelled FBG 4-6) were exposed to multiple dose
fractions of y-radiation to achieve dose levels ranging from
0.1 Gy to 600 kGy (1 Gy=100 rad) in the NIST high dose

2

40

32
irradiation facility. The absorbed dose to SiO, in the FBG
core was calculated from dose-to-water standards by Monte
Carlo simulation of the FBG irradiation geometry.

The impact of dose on resonance peak position is shown
in FIG. 39 for FBGs 1 through 6, in which wavelength shift
vs. absorbed dose is determined relative to the peak position
obtained at an absorbed dose of 0.1 kGy. Our results indicate
a distinct difference in response of the two groups of FBGs
within the initial 0.1 kGy of absorbed dose, with the ORMO-
CER-coated devices (FBGs 4-6) showing a dramatic redshift
of ~0.75(15) nm, whereas the polyimide-coated fibers
(EGBs 1 through 3) exhibit small shifts that are comparable
in magnitude to experimental uncertainties (1 standard
deviation) as determined by reproducibility of measure-
ments (for which representative error bars are provided on a
few of the data points). For absorbed doses above 0.1 kGy,
clear differences in response of the two groups of fibers are
no longer discernible—all six fibers exhibited a weak ten-
dency to blueshift with absorbed doses between 0.1 kGy and
1 kGy, while all but one showed a tendency to redshift as the
accumulated dose grows to 300 kGy. The total shift in peak
center for the two fibers that received 300 kGy dose, 135 pm
and 165 pm, is the equivalent of ~13.5° C. and ~16.5° C.
spurious increase in temperature, respectively (i.e. as would
be registered by each device in normal thermometric moni-
toring). However, when FBG 3 was exposed to another 300
kGy dose, for a total integrated dose of 600 kGy, the peak
center blue-shifted by 119 pm. The origins of this non-linear
dose dependence of the peak center are not presently under-
stood.

We also investigated the effect of radiation dose on
temperature sensitivity of three other FBGs by measuring
temperature dependence of the resonance wavelength before
and after delivering a single dose fraction of 250 kGy. As
shown in FIG. 43, temperature scans acquired after radiation
exposure exhibit a net redshift of ~120 pm, comparable to
what is shown for FBGs 1, 3 and 6 in FIG. 1 (i.e., all FBGs
in the initial batch of six which had received as much dose),
but the temperature sensitivity (slope of plots in FIG. 2) of
the FBG is not as significantly impacted by radiation dose.
Hence, in view of accumulated dose, such devices provide
for relative temperature measurements such as tracking
temperature rise while a reactor is operating,

Example 2. Assessing Radiation Hardness of
Silicon Photonic Sensors

Silicon photonic platforms provide optical communica-
tion. It is contemplated that such devices can be deployed in
photonics-based communication and science instruments in
harsh environments such as outer space, where radiation
damage can occur. The impact of cobalt-60 y-ray radiation
up to 1 megagray (MGy) absorbed dose on silicon photonic
devices is described, wherein systematic impact of radiation

5 on passivated devices is absent such that passivated silicon

devices were durable under harsh conditions.

Silicon photonic sensors are sensitive to external stimuli
that produce changes in refractive index of a host material
In photonic devices, small changes in temperature can
produce measurable changes in resonance peak wavelength
for photonic thermometry and similar applications. This
sensitivity to refractive index is geometrically increased in
resonant devices such as a ring resonator or photonic crystal
cavity, where refractive index sensitivity grows with quality

5 factor. Radiation induced damage produces dislocations and

other defects in crystalline structure that affect refractive
index.


U.S. Patent Jul. 21, 2020 Sheet 37 of 48 US 10,718,872 B2

Photonic Colorimeter Output Signal

Amount of Ionizing Radiation ———»

Figure 37


U.S. Patent Jul. 21, 2020 Sheet 38 of 48 US 10,718,872 B2

(a)

Transmission ————>

(B)

Transmission ————>

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13 4-

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Frequency §=———>

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Figure 38


US 10,718,872 B2

9

lar, ellipsoidal, parallelpiped, and the like) effective to
separate substrate 210 from disk resonator 316 or compen-
sation waveguide 238.

In one embodiment, as shown in FIG. 23A (top view of

temperature compensator 234), FIG. 23B (cross-section 5

along line A-A of FIG. 23A), and FIG. 23C (cross-section
along line B-B in FIG. 23), temperature compensator 234
includes concave resonator 317 disposed on substrate 210.
Concave resonator 317 includes base 319 proximately dis-
posed to substrate 210, concave portion 318, and protuber-
ance 320. Concave portion 318 has width W3 and depth H4,
and protuberance 320 has width W4 at a top surface thereof.
Thickness H3 is a thickness of concave resonator 317. Width
W4 of protuberance 320 optionally can be absent in some
embodiments.

According to an embodiment, as shown in FIG. 24A (top
view of temperature compensator 234), FIG. 24B (cross-
section along line A-A of FIG. 24A), and FIG. 24C (cross-
section along line B-B in FIG. 24A), temperature compen-
sator 234 includes compensation waveguide 238 having an
aperture 324 disposed therein. In some embodiments, a
plurality of apertures 324 is distributed along a length axis
of compensation waveguide 238. In certain embodiments,
the plurality of apertures 324 have a diameter of the same
size. In an embodiment, some of the plurality of apertures
324 have different size diameters. According to one embodi-
ment, the plurality of apertures 324 have different size
diameters such that apertures 324 are arranged symmetri-
cally with respect to compensation resonator 236 with

largest diameter apertures 324 located distal to compensa- 3

tion resonator 236 and smallest diameter apertures 324
located proximate to compensation resonator 236.

In an embodiment, as shown in FIG. 25A (top view of
temperature compensator 234), FIG. 25B (cross-section

along line A-A of FIG. 25A), and FIG. 25C (cross-section 3

along line B-B in FIG. 25), temperature compensator 234
includes aperture 325 interposed between compensation
resonator 236 and substrate 210. Aperture 325 has a size in
a dimension (e.g., depth, width, or height) effective to
mechanically or optically decouple compensation resonator
236 and substrate 210 such that compensation resonator 236
and substrate 210 independently support a mechanical mode
or an optical mode. In this manner, without wishing to be
bound by theory, it is believed that a mechanical mode or an
optical mode of compensation resonator 236 is not quenched
by substrate 4.

According to an embodiment, as shown in FIG. 26A (top
view of temperature compensator 234), FIG. 26B (cross-
section along line A-A of FIG. 26A), and FIG. 26C (cross-
section along line B-B in FIG. 26A), temperature compen-
sator 234 includes auxiliary waveguide 326 disposed on
substrate 210 opposing compensation waveguide 238,
wherein compensation resonator 236 is interposed between
compensation waveguide 238 and auxiliary waveguide 326
Accordingly, temperature compensator 234 includes a drop-
add arrangement of compensation resonator 236

In an embodiment, as shown in FIG. 27A (top view of
temperature compensator 234), FIG. 27B (cross-section
along line A1-A1 of FIG. 27A), and FIG. 27C (cross-section
along line B-B in FIG. 27A), temperature compensator 234
includes optical resonator 328 (e.g., a ring resonator as
shown) disposed on substrate 210 proximate to compensa-
tion waveguide 238. Optical resonator 328 includes a Bragg
grating 327 integrally disposed in optical resonator 328.
Bragg grating 327 includes a plurality of regions having a
different refractive index from each, e.g., alternating first
region 329 (having a first index of refraction) and second

3

40

&

10

region 330 (having a second refractive index). The first or
second index of refraction can be the same or different as an
index of refraction of a remainder of material of optical
resonator 328.

According to an embodiment, Bragg grating 327 is a
periodic (as shown in FIG. 27D, which is a cross-section
along line A2-A2 of FIG. 27A) or aperiodic perturbation of
an effective index of refraction in optical resonator 328. In
an embodiment, the perturbation causes reflection of light
(propagating in optical resonator 328) for a wavelength of
light that satisfies a Bragg condition. Light at other wave-
lengths that does not satisfy the Bragg condition is substan-
tially unaffected by Bragg grating 327.

In some embodiments, as shown in FIG. 28A (top view of
temperature compensator 234), FIG. 28B (cross-section
along line A-A of FIG. 28A), and FIG. 28C (cross-section
along line B-B in FIG. 28A), temperature compensator 234
includes auxiliary optical resonator 331 (e.g., a ring reso-
nator as shown) disposed on substrate 210 proximate to
auxiliary waveguide 326 and spaced apart therefrom by
distance D2. Distance D3 separates auxiliary optical reso-
nator 331 and compensation resonator 236. Although, two
optical resonators (236, 331) are shown, some embodiments

s include a plurality of optical resonators coupled and inter-

posed between compensation waveguide 238 and auxiliary
waveguide 326. In one embodiment, the plurality of optical
resonators includes different types for optical resonators,
e.g., a ring resonator, disk resonator, concave resonator, or a
combination thereof. Such combination of coupled optical
resonators (236, 331) provide a narrow bandwidth of fre-
quencies communicated to auxiliary waveguide 326 from a
broader band of frequencies transmitted by compensation
waveguide 238 via optical resonators (236, 331).
According to an embodiment, as shown in FIG. 29A (top
view of thermometer 332) and FIG. 29B (cross-section
along line A-A of FIG. 29A), thermometer 332 includes
waveguide 334 disposed on substrate 333. Aperture 335 is
present in substrate 333 and is interposed between a portion
of waveguide 334 and substrate 333. Aperture 335 has width
W and thickness H, a dimension of each of which indepen-
dently can be varied during formation to form various
shapes (¢.g., circular, square, polygonal, and the like) and
aspect ratios of length L, width W, and thickness H. In some

5 embodiments, waveguide 334 includes a Bragg grating 327

(see FIG. 27C) in a position proximate to aperture 335.

In some embodiments, the thermometer includes the
substrate and the waveguide disposed on the substrate to
receive input light and to transmit output light such that the
aperture is interposed between the substrate and the wave-
guide. The waveguide is configured to change an intensity of
the output light at a wavelength in response to a change of
a temperature of the waveguide.

In an embodiment, the thermometer includes a substrate;

‘5 an optical resonator disposed on the substrate and including

an optical resonance. The optical resonator is configured to
receive the resonant frequency corresponding to the optical
resonance. The thermometer also includes a waveguide
disposed on the substrate proximate to the optical resonator
to receive input light, to communicate the resonant fre-
quency to the optical resonator, and to transmit output light
with an aperture is interposed between the substrate and the
optical resonator, the substrate and the waveguide, or a
combination comprising at least one of the foregoing. Fur-

5 ther, the thermometer is configured to change the optical

resonance in response to a change in temperature of the
optical resonator.


U.S. Patent

(A) 234

Jul. 21, 2020

Sheet 26 of 48

238 —~|

US 10,718,872 B2

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a

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326 —T_
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(c) 234 236
326
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Figure 26


US 10,718,872 B2

15

index of refraction can be the same or different as an index
of refraction of a remainder of material of optical resonator
328. According to an embodiment, Bragg grating 327 is a
periodic or aperiodic perturbation of an effective index of
refraction in optical resonator 328. In an embodiment, the
perturbation causes reflection of light (propagating in optical
resonator 328) 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,
grating 327.

Bragg coupler 336 an end coupler, or a combination
comprising at least one of the foregoing disposed at a
terminus of the waveguide. As shown in FIG. 31A (top view
of waveguide 238) or 31B (cross-section along line B-B of
FIG. 30A), waveguide 238 includes Bragg coupler 336
disposed at a terminus thereof. Bragg coupler 336 includes
a plurality of protrusions 337 and depressions 338 alternat-
ingly disposed on substrate 210. With reference to FIG. 30C
(an alternate embodiment for a Bragg coupler corresponding
to a cross-section along line B-B in FIG. 30A), depressions
338 are blind with respect to substrate 210 relative to
through features as shown in FIG. 30B. In one embodiment,
depressions 338 include blind depressions, through depres-
sions, or a combination thereof. Here, “through” refers to
expose substrate 210 through depressions 338, and “blind”
refers to covering substrate 210 by depressions 338 such that
substrate 210 is not exposed. It is contemplated that a Bragg
coupler uses a grating structure (e.g., protrusions 337 and
depressions 338) to couple input light into and output light

out of the optical resonator, e.g. optical resonator 328. In an 3

embodiment, coupling light by waveguide 238 is free-space
coupling via Bragg coupler 336.

Ring resonator 367 is an optical resonator that includes a
ring structure having a 10 um radius and is separated from

waveguide 366 by 130 nm. The ring resonator has a free 3

spectral range of 9.2 nm at 1550 nm, Q-factor of 52000, and
estimated group index of 4.2.

The optical resonator and waveguide independently can
be made from a same or different material as the substrate.
In some embodiments, the optical resonator incudes sap-
phire, silicon, silica, silicon nitride, aluminum nitride, dia-
mond, silicon carbide or a combination thereof. The material
for forming the optical resonator can be selected based on a
resonant wavelength for the optical resonator, e.g., silicon
for devices a resonant frequency in a near infrared region
(e.g., up to 2 um wavelength), silicon nitride or aluminum
nitride for a visible wavelength, sapphire for a terahertz
wavelength, and the like.

Cladding 226 includes a dielectric material disposed on
photonic elements, such as a waveguide (e.g. waveguide
212) or dosimatrix 220. In an embodiment, cladding 226 is
interposed between the dosimatrix 220 and the cover layer
228. In an embodiment, the dielectric layer electrically
insulates substrate 210 from thermal member 314. The
dielectric layer can include an oxide of an element in
substrate 210 or independently can be an oxide of a semi-
conductor material such as SiO,. According to an embodi-
ment, the dielectric layer is an oxide such as an oxide that
includes an element from substrate 210, e.g., an oxide of the
semiconductor (also referred to herein as a semiconductor
oxide).

Cover layer 228 can include a material to undergo a
thermophysical or chemical change (e.g. strain, temperature,
density, volume, conductivity, dielectric constant) or alters
the ionizing radiation 254. In an embodiment, cover layer
228 communicates or enhances changes to dosimatrix 220
that influence the change from prime state to dose state in

0

2

40

&

16

dosimatrix 220. In an embodiment, cover layer 228 is
composed of polymers (eg., free-radical polymerization
products), water, graphite, SiO2, diamond, SiN, air, Si, and
the like.

Thermal isolator 262 thermally isolates radiation absorb-
ers (e.g., radiation absorber 268) from heat loss or gain by
thermal transfer due to physical contact by an object (e.g.,
substrate 210). Thermal isolator 262 can include material
with low thermal conductivity, e.g., air, vacuum, or a
mechanical element that can include a standoff made of
structured materials or partial removal of a substrate, such as
substrate 210.

In photonic calorimeter 300, radiation absorber 268
absorbs ionizing radiation 254 and converts ionizing radia-

$s tion 254 to secondary radiation that is absorbed, thermal-

ized, and conducted as heat to the compensating resonator
236. Radiation absorber 268 includes outer surface 264 and
interior material 266 disposed in and bounded by outer
surface 264. Interior material 266 can be a solid, fluid, or
combination thereof. When interior material 266 includes a
fluid, the fluid is contained inside outer surface 264 that is
a solid material that entraps the fluid to prevent the fluid
from loss out of radiation absorber 268. When interior
material 266 is a solid, outer surface 264 can be a same solid

Sas interior material 266 or a different solid than interior

material 266. Interior material 266 absorbs ionizing radia-
tion 254 and converts ionizing radiation 254 to heat. outer
surface 264 can be transparent to ionizing radiation 254 or
can absorb and convert to heat ionizing radiation 254.
Exemplary fluids include water, fluoropolymers, blood,
blood plasma, alcohols, oils, water, and the like. Exemplary
solids include graphite, silicon, silica, sapphire, alanine,
diamond, polymers (such as polymethylmethacrylate, poly-
vinyl alcohol, polydimethylsiloxane), hydroxyapatite, and
graphite, and the like.

Thermal member 314 measures temperature. In various
embodiments, thermal member 314 includes a metal layer.
The metal layer can be disposed on substrate 210, on the
dielectric layer, or disposed on substrate 210 and covered by
a dielectric layer interposed between thermal member 314
and compensation resonator 236. Exemplary conductive
materials include a metal such as a transition metal, alkaline
earth metal, alkali metal, rare earth metal, metal carbide,
metal oxide, metal sulfide, or a combination thereof. Exem-
plary metals include Zr, Hf, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,
Zn, Nb, Mo, Te, Ru, Rh, Pd, Ag, Cd, Ta, W, Re, Os, Ir, Pt,
‘Au, Li, Na, K, Be, Mg, Ca, Sr, Ba, Gd, and the like. Thermal
member 314 can include the metal layer, a non-metal (e.g.
graphene, carbon nanotubes, carbon black, and the like), or
a combination thereof.

Cover layer 315 is made of material(s) that may undergo
a thermophysical and/or chemical change (e.g. strain, tem-
perature. density, volume, conductivity, dielectric constant)
or alters the ionizing radiation 254 and, in an embodiment,

5 communicates and/or enhances changes to the dosimatrix

220 that influence the change from prime state to dose state
in the dosimatrix 220. In an embodiment, cover layer 315 is
composed of polymers (e.g. free-radical polymerization
products), water, graphite, SiO2, diamond, SiN, air, Si.

Intermediate members (321, 322) can include materials
described for the substrate, waveguide, or a combination
thereof. Dielectric layer 323 includes a dielectric material
that provides dielectric separation of elements disposed on
dielectric layer 323.

Tonizing radiation 254 is radiation that can include x-rays,
gamma rays, or particles. In some embodiments, ionization
radiation includes electrons, alpha particles, positrons, or


US 10,718,872 B2

33

In silicon-on-insulator (SOI) based electronic devices,
trapped charges and local changes in bond structure are a
cause of device failure. Here, changes in the refractive index
due to changes in free carrier population and damage to the
Si lattice can significantly degrade the measurement sensi-
tivity and accuracy of a photonic sensor. Unpassivated Si
ring resonator devices exposed to relatively low levels of
ionizing radiation (<9 kGy) show a blue shift in resonance
wavelength that was not observed for passivated devices
exposed to «1.5 kGy of ionizing radiation. A photonic sensor
operating in a high radioactivity environment such as a
nuclear power plant is expected to receive about 1 MGy of
dose per year. Under such conditions, sensor performance
can be negatively impacted by changes in refractive index,
covalent bond breaking, radiation induced densification, or
changes in surface chemistry that can result in increased
propagation losses, resulting in lower quality factors and
drift in resonance wavelength of resonant devices

Impact of y-radiation up to a cumulative dose of | MGy
(1 Gy=100 Rad) from ©Co y-ray radiation on silicon ring
resonators and Bragg waveguides across multiple devices
and chips was studied. Dose absorbed by such chips was
modelled using a radiation transport Monte Carlo simulation
based on engineering drawings of the source and previous
measurements of the radiation field. Silicon photonic
devices withstood high cumulative doses without degrada-
tion in performance.

Bragg waveguides and ring resonators were exposed to
levels of y-ray radiation and did not show changes in spectral

characteristics. A typical Bragg waveguide transmission 3

spectrum, shown in FIG. 44, does not show any systematic
changes in either the peak center or the bandwidth of the
Bragg waveguide rejection window. Here, the Si ring reso-
nator and Bragg waveguide (insert) showed no significant

changes in spectral characteristics as absorbed dose is 35

increased from 0 Gy to 1048 kGy. The variation in peak
center observed between the different dose spectra is found
to be 8 pm and was not correlated with dose (R*=0.28).
Similarly, variation in linewidth (2.6 pm) was poorly cor-
related with dose (R*=0.54) and was within the measure-
ment uncertainty of +7 pm. The linewidth in a Bragg device
was directly proportional to the refractive index contrast
between the waveguide and etched step regions (where the
evanescent field interacts with the surrounding oxide mate-
rial, sampling an effectively lower refractive index than the
unetched waveguide region). A lack of change in Bragg
linewidth indicated the oxide layer immediately next to the
Si does not suffer any significant changes such as bond
breaking or densification of the oxide layer due to radiation
exposure. Similarly, a lack of significant change in peak
isolation indicated the devices did not have damage to the Si
surface or lattice.

In ring resonators, where spectral consequences of small
changes in device characteristics, such as refractive index,
can increase due to recirculation of light in the ring structure,
significant dependence on absorbed dose was not observed.
We examined impact of radiation in several ring resonator
devices with quality factors (Q-factors) ranging from 5,000
to 30,000 at room temperature. As shown in FIG. 45 and
FIG. 46, ring resonator devices did not show dose-dependent
change in the free spectral range (FSR), Q-factor, and peak
position. The FSR was uncorrelated with dose (R?=0.08),
with a standard deviation for the 4 doses of 2.5 pm (0.031%).
FIG. 45 shows Q-value (top) and peak position (bottom) of
a ring resonance across three different irradiated chips (plus
control chip #4) was not significantly impacted by radiation
dose, wherein a number next to the symbols refer to dose

8

34

(kGy) delivered on that particular date. The Q-factor
decreased over time, but the decrease was the same for the
control chip as for the irradiated chips and thus cannot be
unambiguously ascribed to dose (see top of FIG. 45). The
observed decrease of ~12% in Q-factor was correlated with
peak input power and was reproduced when input power
was doubled and indicated the observed effect was due to the
device undergoing self-heating during the laser scan, not
radiation damage. The small variation in absolute peak
position observed for Chips 1-3 between irradiations (aver-
age standard deviation of [13+13] pm) was statistically
indistinguishable to changes observed in the control chip
This small variability was found to be random, with the most
stringent test coming from the peak position at 20° C.
(measured at 0 Gy dose), which was found to be uncorre-
lated to dose, with R?=0.01. The four chips were made in the
same batch and contained the same devices. The control chip
traveled with other chips to and from the photonics lab to the
radiation facility but was never exposed to radiation itself.

FSR of the devices did not show any significant changes
and indicated that neither the group index nor the dispersion
(parameters important in communication systems) was
affected by radiation exposure. Examination of the tempera-
ture-dependent response of ring resonator devices showed
temperature sensitivity was not impacted by radiation dose.
FIG. 46 shows temperature response of silicon ring resona-
tor, wherein a top plot shows residuals from a common fit to
all the data, and propagated uncertainty due to temperature
measurement is shown for one point. For the data shown in
FIG. 46, the average and standard deviation of the three
responses was (76.9+0.2) pm/° C. A linear regression of
response as a function of dose returned a slope of

pm

—4£2)-104
(422104

which was not significant at the 95% level (t=-1.8, p=0.32).
The slight offset variability observed between doses (residu-
als shown in FIG. 46 insert) was within the limited precision
of the thin film resistance thermometer (+0.1° C.) when
employed using nominal coeflicients.

Regarding, impact of ionizing radiation on silicon pho-
tonics devices, devices were irradiated within a self-con-
tained, commercially produced Co irradiator, and deliv-
ered doses were estimated using Monte Carlo analysis
Measurement of device characteristics such as peak center,
peak width, FSR and temperature sensitivity did not show
dose-dependent changes and indicated that the characteristic
group index. dispersion and thermo-optic coefficient
remained constant for aggregate doses up to 1 MGy (the
maximum absorbed dose delivered in this study). These
results contrasted with those of FBG-based sensors, where
radiation induced changes in Bragg resonance result in
significant drift in device characteristics. Accordingly, sili-
con photonics can be used to develop communication and
sensor platforms for operating in harsh environments, such
as industrial sterilization of health care products or radiation
processing systems where doses can be in the range 15 kGy
to 300 kGy, or nuclear power plants where dose rates of 10
kGy/h occur. Precision photonic sensors can be used in
instrumentation used in radiotherapy clinics or space-based
systems, where much lower aggregate doses (<100 Gy) are
more commonplace but high reliability and accuracy are
involved.


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US 10,718,872 B2

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compensation waveguide disposed on the substrate

proximate to a compensation resonator and that:

receives primary compensation input light;

communicates a resonant frequency based on the pri-
mary compensation input light to the compensation
resonator;

receives secondary compensation output light from the
compensation resonator; and

transmits primary compensation output light that is
based on the secondary compensation output light;
and

acompensation resonator disposed on the substrate proxi-

mate to the compensation waveguide and the dosima-

trix and that:

comprises an optical resonance;

receives, from the compensation waveguide, the reso-
nant frequency corresponding to the optical reso-
nance; and

produces the secondary compensation output light in
response to receipt of the resonant frequency, and

the temperature compensator changes the optical reso-

nance of the compensation resonator in response to a

change in temperature of the dosimatrix.

5. The photonic dosimeter of claim 1, wherein the active
element comprises a compound semiconductor comprising a
group semiconductor.

6. The photonic dosimeter of claim 4, wherein the com-
pensation resonator comprises an element from

2

group I of the periodic table (IUPAC group 11), group II,

of the periodic table (IUPAC group 12), group III of the
periodic table (IUPAC group 13), group IV of the
periodic table (IUPAC group 14), group V of the
periodic table (IUPAC group 15), or group VI of the

periodic table (IUPAC group 16) in an absence of a

compound semiconductor comprising a group III-V
semiconductor.

7. The photonic dosimeter of claim 6, wherein the active
element comprises a compound semiconductor comprising a
group III-V semiconductor.

8. The photonic dosimeter of claim 6, wherein the active
element comprises AIN, GaN, InN, TIN, BP, AIP, GaP, InP,
TIP, BAs, AlAs, GaAs, InAs, TIAs, BSb, AlSb, GaSb, InSb,
TISb, BBi, AIBi, GaBi, InBi, TIBi, or a combination com-
prising at least one of the foregoing compounds.

9. A process for performing dosimetry with the photonic
dosimeter of claim 1, the process comprising:

receiving, by the waveguide, primary input light;

producing, by the waveguide, secondary input light from.

the primary input light;

receiving, by the dosimatrix, the secondary input light

from the waveguide;

producing, by the dosimatrix, secondary output light from.

the secondary input light;

receiving, by the waveguide, the secondary output light

from the dosimatrix:

producing, by the waveguide, primary output light from

the secondary output light;

S

8

2

50

35

40
subjecting the dosimatrix to ionizing radiation; and
changing the active element from the prime state to the
dosed state in response to receiving ionizing radiation
by the dosimatrix to perform dosimetry.
10. The process for performing dosimetry of claim 9,
further comprising:
determining a first dosimeter response based on the sec-
ondary output light prior to subjecting the dosimatrix to
the ionizing radiation.
11. The process for performing dosimetry of claim 10,
further comprising:
determining a second dosimeter response based on the
secondary output light after subjecting the dosimatrix
to the ionizing radiation.
12. The process for performing dosimetry of claim 11,

5 further comprising:

determining a dose of the ionizing radiation absorbed by
the dosimatrix from the first dosimeter response and the
second dosimeter response.

13. The process for performing dosimetry of claim 12,
wherein determining the dose comprises:

performing an inverse radiation-transport simulation; and

determining an energy absorbed per unit mass of dosi-

matrix from changing the active element from the
prime state to the dosed state.

14. The process for performing dosimetry of claim 12,
wherein the first dosimeter response and the second dosim-
eter response differ in a resonance frequency, an amount of
transmission, or a combination comprising at least one of the
foregoing differences.

15. The process for performing dosimetry of claim 12,
further comprising logging a temperature history of the
photonic dosimeter by:

receiving, by the compensation waveguide, primary com-

pensation input light;

producing, by the compensation waveguide, resonant

frequency from the primary compensation input light;
receiving, by the compensation resonator, the resonant
frequency from the compensation waveguide;
producing, by the compensation resonator, secondary
compensation output light from the resonant frequency;
receiving, by the compensation waveguide, the secondary
compensation output light from the compensation reso-
nator;
producing, by the compensation waveguide, primary
compensation output light from the secondary compen-
sation output light; and

monitoring the primary compensation output light as a

function of time to log the temperature history of the
photonic dosimeter,

wherein the primary compensation output light changes as

a function of temperature of the compensation resona-
tor.

16. The process for performing dosimetry of claim 9,
wherein changing the prime state to the dosed state com-
prises changing a physical property or a chemical property
of the active element by the ionizing radiation.

+ * RR Oe


U.S. Patent Jul. 21, 2020 Sheet 13 of 48 US 10,718,872 B2

300
234
—_
236 ¢
A
262
264 266
—-—
268

Figure 13


US 10,718,872 B2

13

oxide. In a further embodiment, the oxide is a product of
depositing the oxide on substrate 210, which may or may not
involve oxidation of substrate 210. In a certain embodiment,
the dielectric layer includes SiO, as the oxide, which is a
product of oxidation of substrate 210 that includes Si. In
some embodiments, the dielectric layer includes a semicon-
ductor oxide, a ceramic (e.g., ZrO, Al;03, SiC, SisN,, 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, e.g., cellulose,
poly(methyl methacrylate), and the like.

Substrate 333 can have the same composition, properties
and function as substrate 210.

Photonic dosimeter 200 accrues cumulative dose for
performing dosimetry, and photonic calorimeter 300 con-
verting ionizing radiation dose to heat for performing calo-
rimetry. Photonic dosimeter 200 includes waveguide 212. In
an embodiment, waveguide 212 guides light along a path;
can have dimensions from 300 nm to 1 micrometer width,
200 nm to 500 nm height; can include silicon and similar
material; and can be operable at a wavelength from 1 micron
to 2.5 microns. The waveguide can contain a coupling
element to communicate light into the waveguide. Exem-
plary coupling elements include a Bragg coupler, inverse
taper, and the like. The waveguide can include an optical
resonator to measure temperature, strain, or radiation dose.

Compensation waveguide 238 guides light along a path;
has dimensions of: 300 nm to 1 micrometer width, 200 nm

to 500 nm height; is composed primarily of materials like 3

silicon and works over the range of 1 micron to 2.5 microns
wavelength of light; the waveguide may contain coupling
elements to bring light into the waveguide, such as Bragg
couplers or inverse tapers; the waveguide may include
optical resonators to enable measurement of temperature.

Aperture 324 has a diameter from 25 nm to 500 nm, more
specifically 50 nm to 300 nm, in compensation waveguide
238. In an embodiment, a plurality of apertures 324 have
different size diameters. According to one embodiment, the
plurality of apertures 324 have different size diameters such
that apertures 324 are arranged symmetrically with respect
to compensation resonator 236 with largest diameter aper-
tures 324 located distal to compensation resonator 236 and
smallest diameter apertures 324 located proximate to com-
pensation resonator 236.

Aperture 325 is an opening interposed between compen-
sation resonator 236 and substrate 210. Aperture 325 has a
size in a dimension (e.g., depth, width, or height) effective
to mechanically or optically decouple compensation reso-
nator 236 and substrate 210 such that compensation reso-
nator 236 and substrate 210 independently support a
mechanical mode or an optical mode.

Auxiliary waveguide 326 is similar in construction and
function to the compensation waveguide 238. Ina particular
embodiment, auxiliary waveguide 326 transmits light from
the compensation resonator 236 to light detector 260.

Waveguide 334 is similar in construction and function to
compensation waveguide 238.

Aperture 335 is an opening interposed between a portion.
of waveguide 334 and substrate 333. Aperture 335 has width
W and thickness H, a dimension of each of which indepen-
dently can be varied during formation to form various
shapes (e.g., circular, square, polygonal, and the like) and
aspect ratios of length L, width W, and thickness H.

Edge coupler 339 is disposed at the terminus of a wave-
guide. Edge coupler 339 couples light in and out of a
waveguide, in a particular embodiment by, ¢.g., a pigtailed

S

2

40

45

3

14

fiber optic, which is connected, e.g., adhered, to substrate
333, brings light into and out of a compensation waveguide
238.

Waveguide 366 is a waveguide that transmits light to (or
receives light from) an optical resonator (e.g. optical ring
resonator 367). Waveguide 366 has similar construction and
function to compensation waveguide 238.

In photonic dosimeter 200, dosimatrix 220 is an array of
photonic resonators that changes resonant frequency in
response to received dose. Photonic dosimeter 200 includes
active element 224. Active element 224 interacts with ion-
izing radiation 254, whereupon active element 224 under-
goes conversion from prime state 230 to dosed state 232 in
response to receipt, by active element 224, of a dose of

s ionizing radiation 254. Active element 224 can include a

compound semiconductor that is a group III-V semiconduc-
tor. Exemplary group III-V semiconductors include AIN,
GaN, InN, TIN, BP, AIP, GaP, InP, TIP, BAs, AlAs, GaAs,
InAs, TIAs, BSb, AlSb, GaSb, InSb, TISb, BBi, AIBi, GaBi,
InBi, TIBi, or a combination thereof. It is contemplated that
besides active element 224, dosimatrix 220 can include
materials mentioned above in addition to silicon dioxide,
II-V materials coated in silver, titanium, gold or copper and
polymers synthesized using free-radical polymerization. In

san embodiment, dosimatrix 220 consists essentially of active

element 224.

To determine accrued dose of ionizing radiation 254 by
active element 224, active element 224 undergoes conver-
sion from prime state 230 to dosed state 232. Exemplary
conversions include frequency change, changes in linewidth
or intensity. In undergoing conversion from prime state 230
to dosed state 232, active element 224 experiences a change
in refractive index brought on by changes in temperature,
stress, chemical or physical characteristics such as density or
volume/geometry resulting in frequency change. In under-
going conversion from prime state 230 to dosed state 232,
resulting in changes in linewidth or intensity, active element
224 experiences changes in light transmission, reflectivity
that results in increased optical losses resulting in lower
quality factors or greater linewidths. Accordingly, prime
state 230 can be the frequency, linewidth or intensity of the
resonance before dosing. Further, dosed state 232 can be the
frequency, linewidth or intensity of the resonance after
dosing.

In an embodiment, compensation resonator 236 com-
prises an element from group I of the periodic table (TUPAC
group 11), group II of the periodic table (IUPAC group 12),
group III of the periodic table (IUPAC group 13), group IV
of the periodic table (IUPAC group 14), group V of the
periodic table (IUPAC group 15), or group VI of the periodic
table (TUPAC group 16) in an absence of a compound
semiconductor that includes a group III-V semiconductor.

Disk resonator 316 is an optical resonator that can include
materials such as those in optical resonators 328 or com-

5 pensation waveguide 238. Ina particular embodiment, a disk

resonator consists of a circular structure with radius R,
thickness T, sitting on a pedestal 321 composed of substrate
210.

Concave resonator 317 includes a base 319 proximately
disposed to substrate 210, concave portion 318, and protu-
berance 320. Concave portion 318 has width W3 and depth
H4, and protuberance 320 has width W4 at a top surface
thereof. Thickness H3 is a thickness of concave resonator
317. Width W4 of protuberance 320 optionally can be absent

5 in some embodiments.

Bragg grating 327 includes a plurality of regions having
a different refractive index from each. The first or second


US 10,718,872 B2

25

over an arbitrary period of dosing, or can be subjected to
continuous or intermittent dosing with ionizing radiation
254.

Photonic dosimeter 200 has numerous advantageous and
unexpected benefits and uses, including performing dosim-
etry In an embodiment, a process for performing dosimetry
with photonic dosimeter 200 includes: receiving, by wave-
guide 212, primary input light 214; producing, by wave-
guide 212, secondary input light 218 from primary input
light 214; receiving, by dosimatrix 220, secondary input
light 218 from waveguide 212; producing, by dosimatrix
220, secondary output light 216 from secondary input light
218; receiving, by waveguide 212, secondary output light
216 from dosimatrix 220; producing, by waveguide 212,
primary output light 222 from secondary output light 216;
subjecting dosimatrix 220 to ionizing radiation 254; and
changing active element 224 from prime state 230 to dosed
state 232 in response to receiving ionizing radiation 254 by
dosimatrix 220 to perform dosimetry. The process for per-
forming dosimetry further can include determining a first
dosimeter response based on secondary output light 216
prior to subjecting dosimatrix 220 to ionizing radiation 254.
‘Additionally, the process for performing dosimetry can
include determining a second dosimeter response based on
secondary output light 216 after subjecting dosimatrix 220
to ionizing radiation 254. In some embodiment, the process
for performing dosimetry includes determining a dose of
ionizing radiation 254 absorbed by dosimatrix 220 from first
dosimeter response and second dosimeter response. It is

contemplated that determining the dose includes performing 3

an inverse radiation-transport simulation; and determining
an energy absorbed per unit mass of dosimatrix 220 from
changing active element 224 from prime state 230 to dosed
state 232. Moreover, the first dosimeter response and the

second dosimeter response can differ in a resonance fre- 3

quency, an amount of transmission, or a combination of the
foregoing differences. The process for performing dosimetry
also can include logging a temperature history of photonic
dosimeter 200 by: receiving, by compensation waveguide
238, primary compensation input light 242; producing, by
compensation waveguide 238, resonant frequency 240 from
primary compensation input light 242; receiving, by com-
pensation resonator 236, resonant frequency 240 from com-
pensation waveguide 238: producing, by compensation reso-
nator 236, secondary compensation output light 244 from
resonant frequency 240; receiving, by compensation wave-
guide 238, secondary compensation output light 244 from
compensation resonator 236; producing, by compensation
waveguide 238, primary compensation output light 246
from secondary compensation output light 244; and moni-
toring primary compensation output light 246 as a function
of time to log the temperature history of photonic dosimeter
200. Here, primary compensation output light 246 changes
as a function of temperature of compensation resonator 236.
According to an embodiment, in the process for performing
dosimetry, changing prime state 230 to dosed state 232
includes changing a physical property or a chemical prop-
erty of active element 224 by ionizing radiation 254.

In the process for performing dosimetry, primary light 214
is transmitted from a light member 248 and can originate
from a light source 250 and receiving, by waveguide 212,
primary input light 214 can include is transmitted into
dosimeter 200. In a particular embodiment, primary light
from a laser is swept over a wavelength range and trans-
mitted to the waveguide on a dosimeter via fiber optic.

In the process for performing dosimetry, producing, by
waveguide 212, secondary input light 218 from primary

S

40

26

input light 214 can be transmitted to the dosimatrix 220. In
a particular embodiment, light in the waveguide is coupled
to the optical resonator.

In the process for performing dosimetry, receiving, by
dosimatrix 220, secondary input light 218 from waveguide
212 can interact with the dosimatrix 220 and the active
element 224. In a particular embodiment, frequencies of
light resonant with the optical resonator are trapped in the
resonator; transmitted light will show intensity changes
around the resonant frequencies.

In the process for performing dosimetry, producing, by
dosimatrix 220, secondary output light 216 from secondary
input light 218 can be transmitted to the waveguide 212. In
a particular embodiment, light in the optical resonator is
coupled into the waveguide.

In the process for performing dosimetry, producing, by
waveguide 212, primary output light 222 from secondary
output light 216 can be transmitted to a light member 248,
and subsequently transmitted to a light detector 252. In an
embodiment, light is transmitted from the waveguide to the
detector by fiber optic cable.

In the process for performing dosimetry, subjecting dosi-
matrix 220 to ionizing radiation 254 can change the state of
dosimatrix 220 from the prime state to the dosed state. In an
embodiment, the dosimatrix is placed under a source of
ionizing radiation and exposed to ionizing radiation.

In the process for performing dosimetry, changing active
element 224 from prime state 230 to dosed state 232 in
response to receiving ionizing radiation 254 by dosimatrix
220 can include changes in resonance frequency, intensity
and linewidth that are transmitted to the secondary light.

In the process for performing dosimetry, determining a
first dosimeter response based on secondary output light 216
prior to subjecting dosimatrix 220 to ionizing radiation 254
can include measuring and recording spectral characteristics
of output light 216. In an embodiment, the frequency
characteristics of the output light are measured.

In the process for performing dosimetry, determining a
second dosimeter response based on secondary output light
216 after subjecting dosimatrix 220 to ionizing radiation 254
can include measuring and recording spectral characteristics
of output light 216. In an embodiment, the frequency
characteristics of the output light are measured

In the process for performing dosimetry, determining a
dose of ionizing radiation 254 absorbed by dosimatrix 220
from first dosimeter response and second dosimeter response
can include determining differences in the responses. In an
embodiment, the frequency responses before and after expo-
sure to ionizing radiation are compared; changes to fre-
quency characteristics are functionally correlated to
absorbed dose.

In the process for performing dosimetry, performing an
inverse radiation-transport simulation (e.g., using Monte
Carlo methods) can include modeling of electromagnetic

5 interactions of radiation (e.g. photons, charged particles and

neutrons) with the dosimeter for multiple input parameters
of ionizing radiation using a radiation transport Monte Carlo
software (¢.g., Geant4) by inputting the dosimeter physical
characteristics into the model and running the model for
multiple (e.g., millions) of ionizing radiation particles or
photons, producing model results for the absorbed energy in
the dosimatrix and temperature increase in the active ele-
ment.

In the process for performing dosimetry, determining an

5 energy absorbed per unit mass of dosimatrix 220 from

changing active element 224 from prime state 230 to dosed
state 232 can include combining the results of the inverse


U.S. Patent Jul. 21, 2020 Sheet 15 of 48 US 10,718,872 B2

264 '
2684
266

Figure 15


US 10,718,872 B2

Sheet 1 of 48

Jul. 21, 2020

U.S. Patent

T omsty

Tp 6ls



U.S. Patent Jul. 21, 2020 Sheet 36 of 48 US 10,718,872 B2

(A)

of ~
5

232

State
Wavelength of Optical Resonance

Si

co C1

Cumulative dose ———>

(B)

Wavelength of Optical Resonance

| { | {
I i i ij
co Cl C2 C3 C4

Cumulative dose ———»

Figure 36


U.S. Patent Jul. 21, 2020 Sheet 24 of 48 US 10,718,872 B2

(A) 234

mH O00 60 0 C8

210
236
(B) 234
236 ‘A
210 to
(©) 234 324
236

238 ~y }->}—p “a
210 To

Figure 24


US 10,718,872 B2

Page 2
(51) Int. CL

GOIT 1/12 (2006.01)

GO2B 6/12 (2006.01)

GO2B 6/124 (2006.01)

GO2B 6/293 (2006.01)
(52) US. CL

CPC ...... GO2B 6/29323 (2013.01); GO2B 6/29338
(2013.01); G02B 2006/12107 (2013.01)

(56) References Cited
U.S. PATENT DOCUMENTS

2016/0258942 Al* 9/2016 Scherer GOIN 21/41
2018/0045835 Al* 2/2018 Kher GOIT 1/02
2020/0041508 Al* 2/2020 Scherer GOIN 33/4373

OTHER PUBLICATIONS

Grillanda, S., et al., “Gamma radiation effects on silicon photonic
waveguides”, Optics Letters, 2016, 3053-3056, vol. 41 No. 13.
Desrosier, M., CIRMS Meeting, IAME Breakout Session II, “The
Electronic Gray”, http://cirms.org/pdficirms2016/CIRMS-2016-
Desrosiers.pdf (conceptual art on I slide), Apr. 18, 2016
Dusautoy, A.R., “The UK primary standard calormeter for photon-
beam absorbed dose measurement”, Phys. Med. Biol., 1996, 137-
151, vol. 41, UK.

* cited by examiner


U.S. Patent Jul. 21, 2020 Sheet 48 of 48 US 10,718,872 B2

EO

Figure 48


U.S. Patent Jul. 21, 2020 Sheet 32 of 48 US 10,718,872 B2

5 ms
3

g

a

g C3

=

g T2
2

3g

g

a

5 C2

a

g Tl
A

a

g

2 C1

S

£

B

Art Ar2 Ard 20
Wavelength

Figure 32


U.S. Patent

(A) 1849.26

Jul. 21, 2020 Sheet 41 of 48 US 10,718,872 B2

1849.25

T

1849.24

T

1649.23

v

1549.22

7

1849.24

A, Wavelength

1849.2

v

1542.19

7

1549.18

.

t

1549.45

(B) 1554

je4a 3046 G48 205
Temperature (K)

3043 305.2

1553.5

1553

d, Wavelength

1552.5 -

a
oa y = 0.0753x + 1530.7
vo R? = 0.9974

1552

285.00

295.00 305.00

Temperature (K)

Figure 41


U.S. Patent Jul. 21, 2020 Sheet 27 of 48 US 10,718,872 B2

(A) 234

238 ——T

Al

7 Ny) — e

210 Ds
B) 234 ~
210 — Tt
© 234
<ri— 1) 328
238 ~~ 7 a
210 -—T_
(D) 234 327
329 330 J
] _| — 528
210 ——T

Figure 27


US 10,718,872 B2

Sheet 11 of 48

Jul. 21, 2020

U.S. Patent

Figure 11



US 10,718,872 B2

29

In the process for performing calorimetry, producing, by
compensation waveguide 238, secondary compensation
light 244 from primary compensation input light 242 can
include transmission of light through waveguide 238.

In the process for performing calorimetry, receiving, by
compensation resonator 236, secondary compensation light
244 from compensation waveguide 238 can include physical
or evanescent coupling of secondary compensation light 244
to compensation resonator 236.

In the process for performing calorimetry, producing, by
compensation resonator 236, resonant frequency 240 output
light can include transmission of light through compensation
resonator 236.

In the process for performing calorimetry, receiving, by
compensation waveguide 238, resonant frequency 240 out-
put light from compensation resonator 236 can include
physical or evanescent coupling of light to compensation
waveguide 238.

In the process for performing calorimetry, producing, by
compensation waveguide 238, primary compensation output
light 246 from secondary compensation output light 244 can
include transmission of light through waveguide 238.

In the process for performing calorimetry, subjecting
radiation absorber 268 to ionizing radiation 254 can produce
secondary radiation, which can include photons and elec-
trons, that transfer energy to the radiation absorber 268 in the
form of heat can include placing radiation absorber 268 in
the path of a radiation beam.

In the process for performing calorimetry, producing, by 3

radiation absorber 268, heat from ionizing radiation 254 can
be communicated from the radiation absorber 268 to the
compensation resonator 236 by processes including thermal
thermalization of electrons and thermal conduction to com-
pensation resonator 236.

In the process for performing calorimetry, communicating
the heat to compensation resonator 236 can change its
optical resonance by processes including thermal variation
of index of refraction of the compensator resonator 236.

In the process for performing calorimetry, changing the
optical resonance of compensation resonator 236 in response
to producing heat from ionizing radiation 254 by radiation
absorber 268 can indicate a temperature change in the
temperature compensator 234 by processes including the
thermal variation of index of refraction of the temperature
compensator 234.

In the process for performing calorimetry, determining a
first calorimeter response based on primary compensation
output light 246 prior to subjecting radiation absorber 268 to
ionizing radiation 254 can indicate temperature of the tem-
perature compensator 234 for the prime state by methods
including determining the calorimeter response without ion-
izing radiation 254 incident.

In the process for performing calorimetry, determining a
second calorimeter response based on primary compensa-
tion output light 246 afier subjecting radiation absorber 268
to ionizing radiation 254 can indicate temperature of the
temperature compensator 234 for the dosed state by methods
including determining the calorimeter response after ioniz-
ing radiation 254 has been incident on radiation absorber
268 for a finite amount of time.

In the process for performing calorimetry, determining an
amount of ionizing radiation 254 absorbed by radiation
absorber 268 from the first calorimeter response and the
second calorimeter response can include determining differ-
ences in the responses by subtracting the second calorimeter
response from the first calorimeter response.

3

40

&

30

In the process for performing calorimetry, in determining
the amount of ionizing radiation 254 absorbed by radiation
absorber 268, performing an inverse Monte Carlo conver-
sion from a temperature change of radiation absorber 268
due to absorption of ionizing radiation 254 can include
modeling of electromagnetic interactions of radiation (e.g.
photons, charged particles and neutrons) with the calorim-
eter 300 for multiple likely input parameters of ionizing
radiation 254 using a radiation transport Monte Carlo sofi-
ware by inputting the photonic calorimeter 300 physical
characteristics into the model and running the model for
multiple (e.g. millions) of ionizing radiation 254 particles or
photons, producing model results for the absorbed energy in
the radiation absorber 268 and temperature increase in the
compensation resonator 236.

In the process for performing calorimetry, determining an
energy absorbed per unit mass of radiation absorber 268
from heating with the inverse Monte Carlo conversion can
combining the results of the inverse radiation-transport with
the change in response of temperature compensator from
prime state to dosed state to convert temperature compen-
sator response to the energy absorbed per unit mass can
include combining the absorbed energy predicted by the
Monte Carlo model with the absorber mass input into the
model to determine absorbed energy per unit mass corre-
sponding to various responses of the temperature compen-
sator.

In the process for performing calorimetry, with regard to
the first calorimeter response and the second calorimeter
response, differing in a resonance frequency can include
change in resonance frequency due to heating of the tem-
perature compensator 234. It is contemplated that differing
in an amount of transmission can include differing in the
transmission of the temperature compensator 234.

The process for performing calorimetry further can
include calibration of the temperature compensator 234 by
comparing its response to temperature to the response of a
calibrated temperature compensator or thermometer.

Photonic dosimeter 200, photonic calorimeter 300 and
processes disclosed herein have numerous beneficial uses,
including imaging of dose for industrial and medical appli-
cations. Advantageously, photonic dosimeter 200 or pho-
tonic calorimeter 300 can measure absorbed dose over a
wide range of spatial scales down to 100 nm, radiation types
(photons, particles), intensities and energy scales. Further,
individual or groups of devices can be embedded in photonic
and electronic devices, construction materials, soft materials
(such as polymerics), composite materials, additively manu-
factured materials.

Moreover, photonic dosimeter 200 and processes herein
have numerous advantageous properties. In an aspect, pho-
tonic dosimeter 200 provides real-time data acquisition with
ca, microsecond time resolution.

Photonic dosimeter 200 unexpectedly overcomes prob-
lems with conventional technologies and testing, wherein
the size of the conventional dosimeter is too large to resolve
dose from low-energy radiation sources. Photonic dosimeter
200 overcomes this limitation by providing sub-millimeter-
resolution dosimetry, with the option of embedding net-
works of photonic dosimeters.

Moreover, photonic calorimeter 300, and processes herein
have numerous advantageous properties. In an aspect, pho-
tonic calorimeter 300 provides real-time data acquisition
with ca. microsecond time resolution.

Photonic calorimeter 300 unexpectedly overcomes prob-
lems with conventional technologies and testing, wherein
the size of the conventional dosimeter is too large to resolve


US 10,718,872 B2

1
PHOTONIC DOSIMETER AND PROCESS
FOR PERFORMING DOSIMETRY

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 17-024US1

BRIEF DESCRIPTION

Disclosed is a photonic dosimeter to accrue cumulative
dose, the photonic dosimeter comprising: a substrate; a
waveguide disposed on the substrate and that: receives a
primary input light; transmits secondary input light from the
primary input light to a dosimatrix; receives a secondary
output light from the dosimatrix: and produces primary
output light from the secondary output light; the dosimatrix
disposed on the substrate and in optical communication with
the waveguide and that: receives the secondary input light
from the waveguide; produces the secondary output light
that is communicated to the waveguide; and comprises an
active element that undergoes conversion from a prime state

to a dosed state in response to receipt, by the active element, 3

of a dose of radiation; and a cover layer disposed on
waveguide and the dosimatrix.

‘A process for performing dosimetry with the photonic
dosimeter, the process comprising: receiving, by the wave-

guide, primary input light; producing, by the waveguide, 3

secondary input light from the primary input light; receiv-
ing, by the dosimatrix, the secondary input light from the
waveguide; producing, by the dosimatrix, secondary output
light from the secondary input light; receiving, by the
waveguide, the secondary output light from the dosimatrix;
producing, by the waveguide, primary output light from the
secondary output light; subjecting the dosimatrix to ionizing
radiation; and changing the active element from the prime
state to the dosed state in response to receiving ionizing
radiation by the dosimatrix to perform dosimetry.

A photonic calorimeter for converting ionizing radiation
dose to heat, the photonic calorimeter comprising: a radia-
tion absorber comprising a radiation absorber and a radiation
absorber disposed in the radiation absorber and bounded by
the radiation absorber such that the radiation absorber:
receives ionizing radiation; and converts the ionizing radia-
tion into heat; a temperature compensator disposed within
the radiation absorber and comprising: a compensation
waveguide disposed in optical communication with a com-
pensation resonator and that: receives primary compensation
input light; communicates a resonant frequency based on the
primary compensation input light to the compensation reso-
nator; receives secondary compensation output light from
the compensation resonator; and transmits primary compen-
sation output light that is based on the secondary compen-
sation output light; and a compensation resonator disposed
in optical communication with the compensation waveguide
and that: comprises an optical resonance; receives, from the
compensation waveguide, the resonant frequency corre-
sponding to the optical resonance; and produces the second-
ary compensation output light in response to receipt of the
resonant frequency; a thermal isolator on which the radiation

S

2

40

45

2

absorber is disposed and that thermally isolates the radiation
absorber from heat loss by thermal transfer due to physical
contact by an object, and the temperature compensator
changes the optical resonance of the compensation resonator
in response to a change in temperature of the radiation
absorber due to absorption of the ionizing radiation by the
radiation absorber.

A process for performing calorimetry with the photonic
calorimeter, the process comprising: receiving, by the com-
pensation waveguide, primary compensation input light;
producing, by the compensation waveguide, resonant fre-
quency from the primary compensation input light; receiv-
ing, by the compensation resonator, the resonant frequency
from the compensation waveguide: producing, by the com-
pensation resonator, secondary compensation output light
from the resonant frequency; receiving, by the compensation
waveguide, the secondary compensation output light from
the compensation resonator; producing, by the compensa-
tion waveguide, primary compensation output light from the
secondary compensation output light; subjecting the radia-
tion absorber to ionizing radiation; producing, by radiation
absorber, heat from the ionizing radiation; communicating
the heat to the compensation resonator; and changing the

S_ optical resonance of the compensation resonator in response

to producing heat from the ionizing radiation by the ionizing
radiation to perform calorimetry.

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 a plan view of a photonic dosimeter;

FIG. 2 shows a cross-section along line A-A of the
photonic dosimeter shown in FIG. 1;

FIG. 3 shows a plan view of a photonic dosimeter;

FIG. 4 shows a cross-section along line A-A of the
photonic dosimeter shown in FIG. 3;

FIG. 5 shows a plan view of a photonic dosimeter;

FIG. 6 shows a cross-section along line A-A of the
photonic dosimeter shown in FIG. 5;

FIG. 7 shows a plan view of a photonic dosimeter;

FIG. 8 shows a cross-section along line A-A of the
photonic dosimeter shown in FIG. 7;

FIG. 9 shows a perspective view of a photonic dosimeter
includes a plurality of waveguides and dosimatrixes;

FIG. 10 shows a plan view of the photonic dosimeter
shown in FIG. 9;

FIG. 11 shows a perspective view of a photonic dosimeter
includes a plurality of waveguides and dosimatrixes;

FIG. 12 shows a plan view of the photonic dosimeter
shown in FIG. 11:

FIG. 13 shows a photonic calorimeter;

FIG. 14 shows a cross-section along line A-A of the
photonic calorimeter shown in FIG. 13

FIG. 15 shows a perspective view of a photonic calorim-
eter includes a plurality of temperature compensators;

FIG. 16 shows an array of photonic dosimeters subjected
to ionizing radiation;

FIG. 17 shows a photonic calorimeter subjected to ion-
izing radiation;

FIG. 18 shows a thermometer in panels A, B, and C;

FIG. 19 shows a thermometer including a heater disposed
on a substrate in panels A, B, and C;

FIG. 20 shows a thermometer including a heater disposed
in a substrate in panels A, B, and C;



US 10,718,872 B2

5

electromagnetic interference. Additionally, the thermometer
is deployable in harsh environments and supplants calibra-
tion of on-board temperature sensors.

In an embodiment, with reference to FIG. 1 and FIG. 2,
photonic dosimeter 200 accrues cumulative dose and
includes substrate 210; waveguide 212 disposed on substrate
210. Waveguide 212 receives primary input light 214, trans-
mits secondary input light 218 from primary input light 214
to dosimatrix 220; receives secondary output light 216 from
dosimatrix 220, and produces primary output light 222 from
secondary output light 216. Photonic dosimeter 200 also
includes dosimatrix 220 disposed on substrate 210 and in
optical communication with waveguide 212. Dosimatrix 220
receives secondary input light 218 from waveguide 212 and
produces secondary output light 216 that is communicated to
waveguide 212. Dosimatrix 220 includes active element 224
that undergoes conversion from prime state 230 to dosed
state 232 in response to receipt, by active element 224, of a
dose of radiation from being subjected to ionizing radiation
254; and cover layer 228 disposed on waveguide 212 and
dosimatrix 220. In an embodiment, light member 248
includes light source 250 that provides primary input light
214 to waveguide 212 and light detector 252 that receives
primary output light 222 from waveguide 212. Communi-
cation of primary input light 214 or primary output light 222
between light member 248 and waveguide 212 can be
propagation through free space or propagation through a
condensed optical medium such as a fiber optic cable,
wherein a first fiber optical cable can interconnect light

source 250 to waveguide 212, and a second fiber optical 3

cable can interconnect light detector 252 to waveguide 212.
It should be appreciated that communication of secondary
input light 218 from waveguide 212 to dosimatrix 220 and
that communication of secondary output light 216 from

dosimatrix 220 to waveguide 212 is due to evanescent 3

coupling between waveguide 212 and dosimatrix 220 in a
presence of light, e.g., primary input light 214 in waveguide
212

In an embodiment, with reference to FIG. 3 and FIG. 4,
photonic dosimeter 200 includes cover layer 228 disposed
on dosimatrix 220 such that dosimatrix 220 and waveguide
212 are interposed between substrate 210 and cover layer
228.

In an embodiment, with reference to FIG. 5 and FIG. 6,
photonic dosimeter 200 includes cladding 226 disposed on
dosimatrix 220 such that dosimatrix 220 is interposed
between substrate 210 and cladding 226, and cladding 226
is interposed between dosimatrix 220 and cover layer 228.

In an embodiment, with reference to FIG. 7 and FIG. 8,
photonic dosimeter 200 includes temperature compensator
234 disposed on substrate 210. Temperature compensator
234 compensates for a temperature change of photonic
dosimeter 200 as a function of time during which active
element 224 accrues cumulative dose and undergoes con-
version from prime state 230 to dosed state 232 in response
to receipt, by active element 224, of the dose of radiation
from ionizing radiation 254. Temperature compensator 234
includes compensation waveguide 238 disposed on substrate
210 proximate to compensation resonator 236. Compensa-
tion waveguide 238 receives primary compensation input
light 242, communicates resonant frequency 240 based on
primary compensation input light 242 to compensation
resonator 236, receives secondary compensation output light
244 from compensation resonator 236, and transmits pri-
mary compensation output light 246 that is based on sec-
ondary compensation output light 244, Temperature com-
pensaior 234 includes compensation resonator 236 disposed

S

3

40

&

5 radiation 254 into heat

6

on substrate 210 proximate to compensation waveguide 238
and dosimatrix 220 such that compensation resonator 236
and compensation waveguide 238 are in optical communi-
cation via evanescent coupling. Compensation resonator 236
has an optical resonance and receives, from compensation
waveguide 238, resonant frequency 240 corresponding to
the optical resonance and produces secondary compensation
output light 244 in response to receipt of resonant frequency
240. Temperature compensator 234 changes the optical
resonance of compensation resonator 236 in response to a
change in temperature of dosimatrix 220.

In an embodiment, light member 256 includes light detec-
tor 260 that provides primary compensation input light 242
to compensation waveguide 238 and light source 258 that

5 receives primary compensation output light 246 from com-

pensation waveguide 238. Communication of primary com-
pensation input light 242 or primary compensation output
light 246 between light member 256 and compensation
waveguide 238 can be propagation through free space or
propagation through a condensed optical medium such as a
fiber optic cable, wherein a first fiber optical cable can
interconnect light detector 260 to compensation waveguide
238, and a second fiber optical cable can interconnect light
source 258 to compensation waveguide 238. It should be

S appreciated that communication of resonant frequency 240

from compensation waveguide 238 to compensation reso-
nator 236 and that communication of secondary compensa-
tion output light 244 from compensation resonator 236 to
compensation waveguide 238 is due to evanescent coupling
between compensation waveguide 238 and compensation
resonator 236 in a presence of light, e.g., primary compen-
sation input light 242 in compensation waveguide 238.

In an embodiment, with reference to FIG. 9 and FIG. 10,
photonic dosimeter array 400 includes a plurality of pho-
tonic dosimeter 200 (e.g., 200A, 200B, . . . , 200N, wherein
N is an integer number of photonic dosimeters 200 that can
be, e.g., thousands of photonic dosimeters 200) and option-
ally temperature compensator 234. In an embodiment, pho-
tonic dosimeters 200 are laterally disposed on substrate 210
as shown in FIG. 9 and FIG. 10. In an embodiment, photonic
dosimeters 200 are stackedly disposed on substrate 210 as
shown in FIG. 11 and FIG. 12. Moreover, individual pho-
tonic dosimeters 200 (e.g., 200A, 200B, . . . , 200N)
independently can be addressed and optically communicate

5 with light members 248.

While photonic dosimeter 200 accrues cumulative dose
from ionizing radiation 254 for performing dosimetry, pho-
tonic calorimeter 300 converts a dose of ionizing radiation
254 to heat for performing calorimetry. In an embodiment,
with reference to FIG. 13 and FIG. 14, photonic calorimeter
300 includes radiation absorber 268 that has outer surface
264 and interior material 266 disposed in interior material
266 and bounded by outer surface 264. Radiation absorber
268 receives ionizing radiation 254 and converts ionizing
Photonic calorimeter 300 also
includes temperature compensator 234 disposed within
radiation absorber 268. Temperature compensator 234
includes compensation waveguide 238 disposed in optical
communication with compensation resonator 236. Compen-
sation waveguide 238 receives primary compensation input
light 242, communicates resonant frequency 240 based on
primary compensation input light 242 to compensation
resonator 236, receives secondary compensation output light
244 from compensation resonator 236, and transmits pri-

5 mary compensation output light 246 that is based on sec-

ondary compensation output light 244. Compensation reso-
nator 236 is disposed in optical communication with


U.S. Patent Jul. 21, 2020 Sheet 14 of 48 US 10,718,872 B2

234

je
IS

a
236 © 238

T ~~ 266
268
iM 264

> 262

Figure 14