Photophoretic Optical Trapping (POT) is a relatively new concept in the field of optics which has potential application in 3D display. The POT is realized by confining a particle within a very small location of the optical system, mostly around the focus. The particle, if captured by the beam, has the potential to print visible 3D images in free space. Our POT system is encapsulated by an acrylic enclosure, which also incorporates a biconvex lens as well as a laser module with an adjustable focus. Particles are released around the top of the lens’ focal point until the captured particle can be seen. First, by implementing varying sizes of biconvex lenses, we are able to measure the capture rates of different focal length ranging from 60 to 200mm and extract the maximum capture rates of the system. The capture rates give us an accurate representation of the system limitations which demonstrates if the particle can and cannot be captured efficiently. From our data, we found that the most efficient capture is produced between the focal length around 80 to 160mm for a 405nm laser source. The range of 60 to 200mm will be used to reevaluate the wavelength of 405nm as well as 532nm and 630nm against one another to determine which yields the highest efficiency or rate of captures. The wavelength-dependence study experimentally reveals the relationship between wavelengths of light source and trapping capability which is novel and important for future photophoretic optical trapping applications.
Free Space Optics (FSO) has the potential to offer fast broad-bandwidth communication, but experiences signal loss due to atmospheric attenuation. Our study assesses the performance of different lens configurations to mitigate the fog scattering loss in a low-cost visible-band FSO communication system. We built a fog-testing chamber and novel transmitter board to evaluate our FSO link at four different visible-band wavelengths and three different lens configurations. We also analyze the receiver signal strength to determine the fog-induced attenuation and compare each lens performance in the system. To design and evaluate the optimum lens system, several novel transmitterreceiver lens configurations are analyzed and compared: plano-convex to plano-convex (P-P), bi-convex to planoconvex (B-P), and bi-convex to bi-convex (B-B). We observe that the visible-band wavelength can minimizes the amount of fog-induced signal loss. The lens configuration in conjunction with the most optimal visible-band wavelength is then analyzed with various fog levels. We determine the most efficient double-lens configuration in the FSO system with fog-induced noise. On average, the biconvex-planoconvex system performed 63.85% better than the planoconvex-planoconvex system and 50.42% better than the biconvex-biconvex system. These results can be attributed to the spherical aberration from the transmitter lens and will be discussed in the paper.
Free Space Optical (FSO) Communications data link offers high data rates with low system complexity but atmospheric attenuation, such as fog, alters signal integrity. In the paper, we present a novel low-cost visible band FSO system design and its performance evaluations in foggy conditions. Using LTSPICE design tools, we proposed a low-cost transmitter and receiver circuits. We built a fog-testing chamber and FSO systems to measure different transmitter sources by analyzing DC carrier powers and digital AC signals at 1MHz. A He-Ne laser at 630nm was used to calibrate chamber fog density and measure the steady state performance. Concurrently, we developed a CAD model of our FSO systems using Synopsys Optsim and obtained FSO system performance at different foggy levels to compare with our experimental results. The red laser diode (LD) at 658nm has the best performance in foggy environments with experimental attenuation of -0.20dB and simulated attenuation of -0.63dB. The green LD at 520nm and violet LD at 405nm experience experimental attenuation of -0.35dB and -0.53dB respectively. Despite beam divergence, the red LED at 615nm has good performance in foggy environments with experimental attenuation of -0.33dB and simulated attenuation of -5.2dB. The yellow LED at 590nm, green LED at 522nm, and blue LED at 470nm experience an experimental attenuation of -0.51dB, -2.2dB, and - 0.72dB respectively.
Epitaxial lateral overgrowth can be implemented using patterned sapphire substrates (PSS) and SiO2 nanorod arrays (NR). Both PSS and SiO2 arrays are fabricated using nanoimprint lithography. In this paper, we study patterned sapphire substrate width and period and SiO2 nanorod array z position to optimize GaN LED light extraction and improve the device efficiency. First, we compare our simulation with pervious experimental data from other group. The simulation results match the experimental results in the trend. Second, we investigate PSS design and optimization, and find that by setting the period and width of PSS to 2μm and 1.3μm respectively, the light extraction can be increased by 47.9%. We also optimize the z-position of the SiO2 nanorod array to 7.1μm increases the light extraction by 51.8%, which is much better improvement prediction compared to the published experimental data. Finally, we find that the appearance of the reflection layer has major effects on light extraction. Ag layer can increase or decrease the light extraction efficiency. From these simulations we find a maximum increase in light extraction of 128% for a l LED with an Ag reflection layer compared to a conventional LED.
We study nano-scale ITO top transmission gratings to improve light extraction efficiency using finite difference
time domain (FDTD) method. Our study deals with a LED model with triangular-gratings and square-gratings. We
achieve a 165.67% improvement for triangular ITO grating. Our study for square-gratings shows that it also can
improve the total light extraction efficiency. Thus far, we have only achieved a 7.16% improvement with an ITO
layer thickness of 230nm, a 230nm grating width and 10% duty cycle. We will present our comparison in further
detail which will include various ITO layer thicknesses, grating widths and duty cycles.
We study nano-scale ITO top transmission gratings to improve light extraction efficiency (LEE).
We use the finite difference time domain (FDTD) method to measure light extraction from a
device with various grating structures and layer thicknesses. We simulate our device using a twodimensional
model with top triangular-gratings in a crystal lattice arrangement described by
grating cell period (Α), grating cell height (d), and grating cell width (w). We also define ITO
layer thickness (L) as the layer between the p-type GaN and the ITO surface layers. Simulation
models vary in grating period, grating width, and ITO layer thickness. Our simulations monitor
the amount of light emitted from the top, bottom, and sides of the LED model. We calculate the
total light extraction and determine which grating duty cycle maximizes LEE. We found that
adding a nano-scale grating with optimum duty cycle can achieve 165.67% and 136.77% LEE
improvement, respectively, for ITO layer thickness of 230nm and 78nm.
We study nano-grated surface GaN LED to improve light extraction efficiency by optimizing the device parameters. Our study is based on rigorous coupled wave analysis (RCWA) to obtain total transmission across a device. Our simulation results allow us to optimize the device parameters to maximize light extraction efficiency. We simulate our device using a two-dimensional model with square-grating cells in a crystal lattice arrangement whose parameters we define as follows: grating cell period (Λ), grating cell height (d), and grating cell width (ω). We also define grating layer location (L) as the distance between the multi-quantum wells (MQW) source and the grating surface layer. Each simulation varies in grating cell period, grating cell width, and grating layer location and provides a result of total transmission across the device. These results are used to calculate improvement over the non-grated surface GaN LED. Our preliminary study focused on 50% fill factor and showed that location of the grating as well as the grating period both strongly effect the total transmission across the device. In addition, we noticed that optimizing the surface grating location might affect the total transmission. Our study allowed us to improve the light extraction efficiency of nano-grated GaN LED by an average of 133% when fill factor is 50%. We also present our study in detail which includes fill factors ranging between 0 to 100%.
The paper presents the optical power absorption simulation in a silicon solar cell utilizing single and double diffraction gratings at varying locations (depths) within the device. The solar cell under discussion consists of a rectangular top grating, P-type Si, N-type Si, a rectangular bottom grating, and a reflective material on the bottom. We use 3D finite differential time domain (FDTD) simulations to calculate the power at the solar cell PN interface at wavelengths ranging from 300nm to 1100nm. Throughout simulation, the structure of the gratings remains unchanged – only its location within the device varies, which is accomplished by varying the thickness of the P and N regions. The spectrum of incident solar light and the photo-responsivity of silicon are also took into account to obtain a total weighted power factor, allowing comparison between all simulated cases. We find an increase in weighted power absorption (compared to the non-grating case) ranging from 42% to 72% across all simulated grating locations. Overall, our simulations show that varying the location of the grating(s) changes the amount of power absorbed, and that certain device thicknesses correspond to increased power absorption and are preferred in the design.
Today’s advanced technology allows engineers to fabricate GaN LEDs with various heights, widths, shapes, and materials. Total internal reflection is a key factor in GaN LED design, because all light that is created inside the LED is lost unless it approaches the chip to air interface at an angle less than 23.58° with respect to the normal. The narrow range of angles at which light can successfully escape the chip is a result of the large difference in refractive indices between GaN and air. Adding a layer of ITO to the GaN reduces the difference in refractive indices between steps and increases the critical angle to 28.4°. Transmitting from ITO into epoxy reduces this difference in refractive indices again, bringing the critical angle to 47.9°. Because a higher critical angle should allow more light to escape the LED, we focus on enhancing light extraction efficiency of GaN LED's that utilize an ITO to epoxy interface using FDTD simulations. The simulation results show us that increasing the critical angle to 47.9° improves light extraction by 40%, proving that the critical angle does play a significant role in light extraction. From this initial result, we then compare light extraction efficiencies of ITO and GaN gratings over varied grating periods, and show that adding an Ag reflection layer improves overall efficiency. Finally, we show that the light extraction for LED's utilizing an Ag reflection layer is highly dependent on the sapphire substrate thickness.
This study concentrates on solar light absorption power in a silicon solar cell using a double diffraction triangular
nano-grating. The first grating is located on top of the solar cell and the second grating is located on bottom of the
solar cell above a reflective metallic substrate of Ar (Si3 N4 ) (Argon gas mixed with Silicon Nitride). We simulate the
solar cell behavior over varying grating parameters as it absorbs sunlight and compare the average power output
absorbed at the center of the solar cell. Each case simulates a period (At ) that varies from 100nm to 800nm in 100nm
interval for the top lattice, while maintaining the bottom lattice at a constant period (Ab ). We repeat this procedure
for the bottom lattice, changing the lattice period from 100nm to 800nm in 100nm interval in order to find the
optimized case. We also consider solar spectrum irradiation under wavelengths ranging from 300nm to 1100nm in
50nm intervals. The total power absorption improvement is about 170% compared to the non-grating case, occurring
in the weighted solar cell simulation with top grating period greater than 300nm and bottom grating period of
500nm.
This study analyzes optical confinement factor and light emitting mode order for three different GaN LEDs:
a conventional LED, thin Film LED, and thin Film LED with a photonic crystal (PhC) grating. For the first
structure, we increase the thickness of AlxGa1-xN from 0 to 600nm, alter the x composition in AlxGa1-xN
from 0.05 to 0.2 in steps of 0.05, and adjust the p-GaN and n-GaN thicknesses each from 0 to 200nm. For
the second structure, we alter the n-GaN substrate thickness from 300-1000nm in steps of 100nm and 1000-
4000nm in steps of 1000nm. These simulations show that increasing the substrate thickness causes the light
emitting mode order to increase. The higher the mode, the more current is needed to make the device emit
light. Higher current leads to shorter device lifetime. The last structure contains a photonic crystal grating
with a period T = 100nm, 230nm, 460nm, 690nm, 920nm, 1500nm, 2000nm, 3000nm and 50% duty cycle.
For each grating period, we display the effects on optical confinement factor and optical field intensity. The
results show that changing the grating period does not affect the mode order, but does affect the optical
field intensity. A larger grating period corresponds to lower optical field intensity. Maximizing optical field
intensity increases the brightness of the device. The simulation method above can be used to improve the
efficiency, brightness, and lifetime of GaN LEDs by reducing the effects of transverse mode coupling and
maximizing the optical field intensity.
In this paper, we use a Finite-Difference Time-Domain GaN LED model to study constant wave (CW)
average power of extracted light. The structure simulated comprises of a 200nm-thick p-GaN substrate,
50nm-thick MQW, 400nm-thick n-GaN substrate, and a 200nm n-GaN two-dimensional Photonic
Crystal(2PhC) grating. We focus on optimizing three design parameters: grating period (A), grating height
(d), and fill factor (FF). In the primary set of simulations, we fix the fill factor at 50% and simulate ten
different grating periods (100 to 1000nm in steps of 100nm) and four different grating heights (50 to
200nm in steps of 50nm), and calculate the average power output of the device. The results from these
simulations show that for both conical and cylindrical gratings, the maxmium light extraction improvement
occurs when A =100nm. In the second set of simulations, we maintain a constant grating period A = 100nm
and sweep the fill factor from 25 to 75%. The results of these simulations show that the fill factor affects
clyindrical and conical gratings differently. As a whole, we see that the nano-structure grating mostly
depends on period, but also depends on height and fill factor. The grating structure improves light
extraction in some cases, but not all.
We study solar-cell designs using nano-grating on both top (transmission) and bottom (reflection) of the
solar cell. First, we perform simulations based on rigorous coupled wave analysis (RCWA) to evaluate
the diffraction top gratins. In RCWA method, we calculate up to 20 harmonics, and sweep the launch
angle of incident light from 0 to 90 degree. The incident light varies from100nm to 1200nm wavelength.
Triangular grating can achieve higher light absorption compared to the rectangular grating. The best top
grating is around 200nm grating period, 100nm grating height, and 50% filling factor, which responses to
37% improvement for triangular grating and 23% for rectangular grating compared to non-grating case.
Then, we use Finite-Difference Time-Domain (FDTD) to simulate transmission/reflection double grating
cases. We simulated triangular-triangular (top-bottom) grating cases and triangular-rectangular (top-bottom)
grating case. We realize solar cell efficiency improvement about 42.4%. For the triangular-triangular
(top-bottom) grating case, the 20% efficiency improvement is achieved. Finally, we present
weighted-light simulation for the double grating for the first time and show the best grating can achieve
104% light improvement, which is quite different from traditional non-weighted calculation.
We study the top transmission grating's improvement on GaN LED light extraction efficiency. We use the finite
difference time domain (FDTD) method, a computational electromagnetic solution to Maxwell's equations, to measure
light extraction efficiency improvements of the various grating structures. Also, since FDTD can freely define
materials for any layer or shape, we choose three particular materials to represent our transmission grating: 1) non-lossy
p-GaN, 2) lossy indium tin oxide (ITO), and 3) non-lossy ITO (α=0). We define a regular spacing between unit
cells in a crystal lattice arrangement by employing the following three parameters: grating cell period (Α), grating cell
height (d), and grating cell width (w). The conical grating model and the cylindrical grating model are studied. We
also presented in the paper directly comparison with reflection grating results. Both studies show that the top grating
has better performance, improving light extraction efficiency by 165%, compared to that of the bottom reflection
grating (112%), and top-bottom grating (42%). We also find that when grating cells closely pack together, a
transmission grating maximizes light extraction efficiency. This points our research towards a more closely packed
structure, such as a 3-fold symmetric photonic crystal structure with triangular symmetry and also smaller feature sizes
in the nano-scale, such as the wavelength of light at 460 nm, half-wavelengths, quarter wavelengths, etc.
In this paper, we present an analysis of gallium nitride (GaN) quantum-well (QW) laser diode (LD) by numerical
simulation. Here we discuss three aspects that are crucial to our analysis. First, the transverse mode pattern is studied,
and our current GaN diode laser structure is discussed with optical waveguide mode analysis. Then we compare the QW
design of the laser and maximize laser modal gain. Finally, we report the influence of the electron block (e-block) layer
on lasing performance of our design.
The Gallium Nitride (GaN) Light-Emitting-Diode (LED) bottom refection grating simulation and results are
presented. A microstructure GaN bottom grating, either conical holes or cylindrical holes, was calculated and
compared with the non-grating (flat) case. A time monitor was also placed just above the top of the LED to measure
both time and power output from the top of the LED. Many different scenarios were simulated by sweeping three
parameters that affected the structure of the micro-structure grating: unit cell period (Α) from 1 to 6 microns, unit
cell width (w) from 1 to 6 microns, and unit cell grating height (d) from 50 to 200nm. The simulation results show
that the cylindrical grating case has a 98% light extraction improvement, and the conical grating case has a 109%
light extraction improvement compared to the flat plate case.
The paper discusses a low power consumption, light weight and low cost 10MHz free-space optical communication
(FSO). The system is designed for mounting on mobile platforms, with effective range of at least 50 meters. Light-Emitting Diodes (LEDs) and Laser diodes (LDs) are used in the transmitter for comparison for their relative performance
in the system. The receiver features a beam splitter that feeds part of the data link optical signal to a quadrant
photodetector and controls a tracking/stabilization system using microcontroller. Since almost all commercial FSO
systems are mounted on fixed positions such as buildings, the paper explores the possibility and challenges of designing
a FSO system for a mobile system such as remotely operated-vehicles or between ships.
California Polytechnic State University (Cal Poly) is one of 23 campuses comprising the California State University, the nation's largest four-year comprehensive public undergraduate university system. Cal Poly has a photonics program, photonics student club, and photonics laboratory within the Electrical Engineering Department that dates back to 1985. This laboratory is dual-use for both teaching and as a photonics center of excellence for the newly established Project-Based Learning Institute (PBLI) (http://pbl.calpoly.edu/). Our photonic education program at Cal Poly emphasizes four main educational tools. A. Lecture Classes. B. Photonics Laboratory Classes C. Student Photonics Club, and D. PBLI Design Projects. In this paper, we will describe the above four aspects with emphasizing on our new initiatives for part B and D.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.