Blu-ray Wavelength Read/Write Device for
Multilayer Polymer Data Storage
Adam Rych
2 May 2012
Abstract
The production of optical data storage systems that possess storage
capacities above a terabyte are increasing in demand every day. In order to meet the demands of
consumers, scientists and engineers have to start to look at three dimensional optical storage
systems for an increased capacity. Currently there are several different approaches for increasing
the storage capacity via 3D, or even higher dimensional optical storage devices, such as:
holographic optical storage, multidimensional optical storage as a bulk materials, and
multilayered fluorescent optical data storage systems. The most economically feasible approach
appears to be a multilayered fluorescent optical data storage system.
A multilayered fluorescent optical storage disc can be easily massproduced at low cost and could store over half a terabyte of data. The key to unlocking this
terabyte-level storage discs is the development of a reliable 3D optical data drive apparatus that
can both read and write data from a polymer multilayered fluorescent system (PMFS). We
propose here a device that can utilize this PMFS to create an economically viable 3D optical
storage drive. Having mobility in the z-direction as well as the x and y directions is essential to
accessing the many layers in a PMFS. Using this apparatus along with a single-photon
absorption technique, we plan to use photobleaching as a means of writing on such a polymer.
Then using a confocal microscope setup we plan to be able to read data from individual layers of
the PMFS.
2 Contents
Abstract
…...………………………………………...2
Acknowledgements
…………………………….……………….4
List of Figures
…….……………………………………….5
1. Review of Previous Works
1.1 2D Optical Data Storage
1.2 Ultra-high Density Data Storage
……………………………………………..6
……………………………………………..6
……………………………………………..9
2. Introduction
…………………………………………....13
3. Objectives
……………………………………………15
4. Materials & Methods
4.1 Photobleaching
4.2 Confocal Microscope
4.3 Construction
……………………………………………16
……………………………………………16
……………………………………………17
……………………………………………18
5. Results
……………………………………………22
6. Future Work
……………………………………………24
References
……………………………………………26
3 Acknowledgments
Firstly, none of this would have been possible without the time and guidance of Cory
Christenson and Kenneth Singer. Cory Christenson has been an endless source of knowledge and
assistance throughout the past two semesters. Kenneth Singer was the inspiration behind this
whole project as well as a great PI. Again I couldn’t have done any of this without both of you.
Thank you both for everything.
Secondly, I’d like to give a thank you to all the graduate students in the optics lab for
their assistance in the construction of my project. Thank you all.
4 List of Figures
1
2D Optical Disc Drive Design12
……………………..6
2
Table of Physical Specs of CD, DVD, & Blu-ray Discs
……………………..9
3
Holographic Recording & Reading Processes13 ……………………10
4
Simplified Representation of 4D Optical Data Storage2
……………………11
5
Cross-Sectional View of a Multilayered Fluorescent Disc14
……………………12
6
Cross-Sectional View of the Pits & Lands of a CD & DVD15
……………………13
7
Top & Side View of our Multilayered Fluorescent Sample
……………………14
8
Examples of Micro-Sized Photobleached Designs
……………………16
9
Simplified Representation of a Confocal Microscope16
……………………17
10 Theoretical Design of our Apparatus
……………………18
11 Mounted Laser Sled & Track
……………………19
12 3-Dimension Sample Holding Translation Stage Setup
……………………19
13 Detector Stage of our CAD Designed Apparatus
……………………20
14 Our Completed Experimental Apparatus
……………………22
15 Results of Intensity vs. Position of a 23-Layered Polymer
……………………24
5 Review of Previous Works
2D Optical Data Storage
Most widely known and used optical data storage technology today is a two-dimensional
reading and writing system. The two dimensions that are being used are the rotation of the disc
and the radial movement along the discs radius. 2D optical data storage technology has been
around since the 1970s. 2D
optical data storage technology
has three distinct generations.
The first generation of 2D
optical data storage came about
in the early 1980s with the
commercial introduction of the
Compact Disc (CD). The second
generation of 2D optical data
storage came about in the
Figure 1: Typical 2D optical disc drive design.
mid 1990s with the arrival of the Digital Video Disc (DVD). The third and final generation of the
2D optical data storage technology installation came about in the mid 2000s with the release of
the first Blu-ray Disc (BD). All three generations of the 2D optical data storage discs share the
same basic physical features such as: data track that consists of lands (flat smooth segments in
the track) and pits (indentations in the track) spiraling outward to create a 12cm wide disc that is
approximately 1.2mm in thickness. Figure 1 above gives a simplistic view of how a typical 2D
optical disc drive is setup and works.
6 In 1982 Philips launched the first commercially available CDs and CD players.1 The
physical specifications for a CD data track are listed below in Table 1. CDs have a track pitch
(distance between neighboring tracks) of 1600nm.1 CDs use infra red lasers to read and write
information (pits and lands) on the spiral data track.1 An objective lens is used to converge the
laser beam down to a single spot that is in the range of a couple microns or less in diameter. The
way the objective lens is categorized is by its numerical aperture (NA), which is used to describe
the angle at which the laser beam will converge. The larger the NA value means the smaller the
angle of convergence. The rotational speed of a CD drive is approximately 200-500 rotations per
minute (rpm). CDs data transfer rates are approximately 1.41 Megabytes per second (Mbps). The
maximum data capacity that the first generation 2D optical data storage system could store was
approximately 650-700 Megabytes (Mb).2 The total information stored in a CD only occupies
approximately 0.01% of the discs entire volume.2 Therefore, 99.99% of a CDs volume is wasted
space, making CDs highly inefficient.
In an attempt to make the CD more efficient, Sony and Philips set out to create the DVD.
The Japanese company, Toshiba, was the first company to manufacture commercially the DVD
and the DVD drive in early 1996. With the introduction of the DVD into the market came the
second generation of 2D optical data storage systems. The DVD was a much greater success than
its predecessor the CD due to three significant modifications: larger numerical aperture objective
lens, a lower wavelength laser beam, and dual layers of information. The resolution at which
information, pit, can be written and read can be characterized by the following equation:
𝑟 = 0.61× 𝜆 𝑁𝐴 , where 𝑟 is the resolution of the laser, 𝜆 is the wavelength of the laser beam,
and 𝑁𝐴 is the numerical aperture value.2 Therefore, since the DVDs have a NA value of 0.6 and
its typical wavelength is 650nm, this allows the DVD to have a much greater resolution than that
7 of the CD.2 A standard single-sided single-layered DVDs physical specifications can be found
below in Table 1. The DVD drive has a rotational speed of approximately 570-1600rpm, and a
data transfer rate of 11.08Mbps. The third significant modification of the CD was the
introduction two layers of data on a single side of the disc and having data stored on both sides
of the disc. DVDs consist of two 0.6mm thick discs combined to form a standard 1.2mm disc.3
The maximum storage capacity for a DVD is found in the double-sided dual-layered disc that has
approximately 17.08 Gigabytes (Gb). But having two 0.6mm thick discs manufactured and
combined to form one disc wasn’t highly cost effective.3
In February of 2002 a large group of companies set forth to create the next generation of
2D optical data storage technology, they called the project Blu-ray Disc. It wasn’t until April of
2003 that the first Blu-ray consumer device became commercially available, Sony BD-RE
recorder for $3,800 only made available in Japan. The advantages that Blu-ray drives have over
DVD drives are the increased NA value, and an even shorter wavelength, which is why the “Blu”
is in Blu-ray.4 The increased NA value and decreased λ allows for Blu-ray drives to have a
higher resolution at reading and writing data off the BD disc. Blu-ray drives laser spot size is
approximately 19% of the laser spot size in DVD drives.5 This increased resolution leads to the
improved BD physical specification found below in Figure 2. Blu-ray drives are capable of
transferring data at a rate of approximately 36Mbps.3 BDs have only a 0.1mm layer of protective
lacquer on the surface of the disc separating the data layer from the surface, while DVDs have a
0.6mm layer of protection separating its data layer from the surface.5 With BDs the data layer is
much closer to the laser lens which allows for less distortions resulting in much greater tolerance
of precision.4 BD come in both single-layered and dual-layered with storage capacities of 25Gb
and 54Gb respectively.3 Blu-ray is currently the most efficient 2D optical data storage device
8 available on the market, but with the 3D optical data storage devices on the horizon Blu-ray will
become obsolete.
CD1
DVD4
Blu-ray6
Pit
Length
830nm
440nm
150nm
Pit
Width
600nm
320nm
130nm
Pit
Depth
160nm
160nm
60nm
Track
Pitch
1600nm
740nm
320nm
Laser
Wavelength
780nm
650nm
405nm
Numerical
Aperture
0.45
0.6
0.85
Maximum
Capacity
0.7Gb
17Gb
54Gb
Figure 2: Table of the physical specs of a CD, DVD, and Blu-­‐ray discs. Ultra-high Density Optical Data Storage
For a little over a decade scientists have been conducting research on the next generation
of optical data storage technology that produces a higher density of data storage capabilities. The
first three generations of optical data storage technology dealt with only using the x – y space,
which left much of the discs z – space empty. With the addition of an axial dimension, allowing
data to be read and written in the x – y – z space, comes the opportunity to create CD sized discs
that have the potential to store data in the multi-Terabyte level. Optical data storage technology
involving the use of all three spatial dimensions is referred to as 3D optical data storage
technology.2 There are several different approach of research being done with 3D or higher
dimensional optical data storage technology. One such technique is done by using a multi-photon
process to write individual bits in a bulk material.2 Another approach to ultra-high density data
storages is done by using multilayered discs and writing data on individual layers. There are also
competing approaches to multidimensional optical data storage for a higher-density optical data
storage technology. One of the most notable alternate approaches is holographic data storage.
Holographic data storage devices open a whole new door to ultra-high density data
storage along with a faster rate of data transfer. With conventional 2D optical data storage
9 devices data, known as bits, are written one bit per flash of light, while with holographic data
storage you are able to write over a thousand bits of data in a single flash of light.7 With
thousands of bits of data from a single flash of light this will enable holographic data storage
drives to transfer data at rates around hundreds of thousands of bits per second.7 Holographic
data storage is done by splitting a
single laser beam into two beams: a
signal, which is the data-carrying
beam, and a reference beam. The
data that is to be encoded onto the
holographic disc is arranged into
pages or large arrays.7 The binary
data on the large arrays are
converted into pixels on a spatial
light modulator that either block or
Figure 3: Holographic recording and reading processes. (a) Recording process, data is digitized, formed into p ages of data with which the signal beam is modulated to write on the storage medium. (b) Reading process, reference beam shines onto the storage medium and the modulation of the diffracted light is detected to reconstruct the original d ata.
transmit the light.7 The signal light
then travels through the modulator
and is therefore encoded with the
checkerboard-like pattern of the data page.7 Finally, the encoded beam then interferes with the
reference beam through volume of the holographic disc thereby storing the digital data pages.7
The process of reading off data is done with an interference pattern inducing regulations in the
refractive index of the recording material producing diffractive volume gratings.7 Using the
reference beam during the reading process it is possible to diffract off the recorded gratings,
reconstructing the stored data arrays of bits then projecting them onto a pixilated detector that
10 reads the data of in parallel.7 The parallel reading of the data is what enables holographic data
storage to have such high data transfer rates.7 By being able to store an enormous amount of bits
of data into a single array in a single pulse of light is what allows holography to have terabyte
level storage capacities. The only downfall to using holographic data storage technology is that a
holographic disc drive will cost you roughly $15,000 and each holographic disc will cost about
$200.8
Multidimensional optical data storage on a bulk material has been opening new ideas into
ultra-high storage capacities. The idea behind multidimensional optical data storage comes from
the ability to write data in different physical dimensions within the writing beam and then read
off the disc individually. Data is written in the spectral dimension, which is the heart of 3D
optical data storage. Data can also be written in the same spectral dimension but with a different
polarization. In 2007 it was
reported in Optics Letters that
the first erasable 4D optical data
storage device was created.2 This
4D optical device was the first to
use a polarization-encoding
technique which allowed the
two-state information to be
multiplexed in the two
polarization states of the laser
Figure 4: A simplified representation of the 4D optical data storage device first introduced in Optical Letters in 2007. Showing how several different layers of information can b e stored over top one and other but at different polarizations. writing beams.2 Using a 2 photon-induced re-orientation of a dye inside of a photopolymer,
researchers were able to write a polarization-sensitive refractive-index change in the volume of
11 the recording polymer and then were able to retrieve back the information they had encoded.2
The advantage of writing multiple sets of data on a bulk material such as a photopolymer is that
it allows for a drastic increase in storage capacity. It is theorized that a 5-dimensional optical
storage device could hold up to a petabyte, a petabyte is equivalent to a 1,000 terabytes, of data.2
Unfortunately 5D optical storage technology probably won’t be commercially available for
another decade and even then it will probably be pretty expensive.
Multilayered optical data storage technology is a fairly popular approach to ultra-high
density optical data storage devices. Using a multilayered fluorescent polymer along with a twophoton absorption technique it is possible to create a 3D optical data storage device capable of
generating a higher storage
capacity than what is currently
available.9 Two-photon
absorption is the simultaneous
absorption of two photons of
either identical or different
frequencies in order to excite a
Figure 5: Side view of a multilayered fluorescent disc. Laser light shining through the many fluorescent layers of the disc. molecule from one state to a
higher energy electronic state. Starting with a blocking gel containing monomers and a twophoton active photoinitiator in a multilayered fluorescent polymer then applying a focused laser
on the blocking gel will result in polymerization. Using the two-photon absorption technique is
how this polymerization is done which is how data is encoded on multiple layers of a fluorescent
polymer. Data retrieval is done by using a confocal microscope system.2 The confocal
microscope is used to essentially filter out the interference of unwanted data from neighboring
12 layers. A multilayered fluorescent optical data storage device that uses a two-photon absorption
technique does show promising results for increasing the storage capacity of a typical DVD sized
disc up to around 300GB. The only downfall to this 3D optical data storage system is the
complexity and high cost of using a two-photon writing process.
Introduction
All 2D optical data storage discs have the same method of storing and retrieving data.
Generally, the 2D optical data storage disc has only one single layer, except in special cases like
a double-layered Blu-ray and DVD. The single layer is made up of a single track of data that is
wrapped radially outward from the center of the disc. The data track is made up of these things
called pits and lands, as seen on the right
in Figure 6. When data is written onto the
disc it is essentially engraved onto the
data track and this is what the pits are.
The non-engraved spaces between the pits
on the data track are the lands. The pits
and lands represent binary information.
When a laser shines onto a land it gets
reflected back to a sensor and registers the
information as a 1. Alternatively, when
Figure 6: Cross-­‐sectional view of pits and lands on a CD (top) and DVD (bottom).
laser light is shined onto a pit that light will scatter and have a decreased intensity that is
collected by the sensor and cause it to register as a 0. This is a very effective way of reading data
13 of a disc but it is limited to primarily that surface layer of the disc in which leaves a lot of wasted
space in the thickness of the disc.
In 3D optical data storage systems such as multilayered fluorescent discs (MFD) there are
many layers on which data can be stored in a data track. Just as in the 2D optical data storage
disc, information on a MFD is stored in binary. Instead of having lands and pits a MFD has
fluorescing and non-fluorescing bits that are interpreted into binary information. The nonfluorescing bits are normal
fluorescent material that has
been photobleached. When a
laser is shined onto a desired
Figure 7: Two neighboring layers of our polymer multilayerd fluorescent sample that have been photobleached with data.
layer it will cause that layer,
and neighboring layers, to
fluoresce. The fluorescing light is collected by a sensor and registers this information as a 1.
Then when a laser is shined onto the photobleached bits the sensor will detect a drastic decrease
in light intensity and register this information as a 0. A multilayered fluorescent disc allows for a
much greater capacity of data storage because it makes use of the depth of the disc instead of just
a single surface layer.
The Center for Layered Polymer System (CLiPS) at Case Western Reserve University
has developed a co-extrusion of two or more alternating polymers to form a sheet of tens to
thousands of layers.10 Furthermore, CLiPS has demonstrated the feasibility of using a 22-layered
polymer substrate for storing data. The substrate that we used is created through a co-extrusion
process that produces alternating layers of active and buffer material. The active material
contains a bleachable fluorophore. The polymer substrate that we used can be made in great
14 quantities, very quickly, at a very inexpensive price. This makes our polymer substrate an ideal
choice for a potential ultra-high density optical data storage material.
Using this multilayered polymer substrate of alternating active and buffer layers we are
attempting to study the feasibility of using it as an ultra-high density optical storage material. To
do this we have designed, created, and tested an apparatus capable of reading and writing on
multiple layers of the aforementioned polymer substrate. What we have built is very similar to
that of fluorescent multilayered disc drives. There are many different techniques to writing on a
multilayered co-extruded polymer substrate, but we focused on one specific technique called
photobleaching. In order to read off the data from the polymer substrate we had to construct and
use a device similar to that found in confocal laser scanning microscopy.
Objectives
We intended to design, construct, and test an automated reading and writing apparatus
that could be used to the study our polymer multilayered fluorescent sample. In the process of
creating this apparatus, we had to design and construct a mobile lens that translates along the zaxis. A mobile z-axis lens will allow our apparatus to read and write over to 22 layers of data
onto our polymer multilayered fluorescent sample. In addition to the mobile z-axis lens we had
to design and construct a collocated confocal microscope reading system. Using confocal laser
scanning microscopy system adjoined to our mobile z-axis lens our apparatus will be able to read
specific layers of data without interference from neighboring layers. After the construction of our
apparatus is completed we will need to develop the software to allow us to read/write on our
polymer multilayered fluorescent sample.
15 Materials & Methods
Photobleaching
The way our apparatus is able to encode data onto our polymer multilayered fluorescent
sample is through a single-photon absorption technique known as photobleaching.
Photobleaching occurs when a fluorophore permanently loses the ability to fluoresce due to
photon-induced chemical damage. The way we achieved photobleaching of our polymer
multilayered fluorescent sample is by exposing the sample to short pulses of increased intensity
from our Blu-ray laser. The high intensity of the laser causes the destruction of the fluorophore
in our sample. We are able to
program the current that is
being supplied to the Blu-ray
laser from a power generator
such that we can expose the
sample to a very high intensity
of light in millisecond pulses.
Since we are using a Blu-ray
disc drive laser system we are
Figure 8: Examples of micron-­‐scale sized designs that our department has been able to create using photobleaching.
able to write data on our polymer multilayered fluorescent sample at the same size as data
written onto a typical Blu-ray disc, refer back to Figure 2 for dimensions of Blu-ray data size.
We are able to photobleach with extreme precision onto our sample, as seen in Figure 8 on the
right.
16 Confocal Microscope
When laser light is shone onto the polymer multilayered fluorescent sample it will cause
the other undesired layers to fluoresce along with the specific desired layer. For us to be able to
read each layer independently of the other ones we had to construct a confocal microscope
system. In order for us to be able to read off data from individual layers had to filter out the noise
caused by the fluorescence of the neighboring layers, this is what a confocal microscope does for
us. When light is shone
onto the sample many
layers will fluoresce and
each one of these layers
will have a linearly spaced
apart focal point. Using a
pinhole situated at the
exact focal point of the
desired layer we are then
Figure 9: Simplified schematic representation of a confocal microscope being used on a multilayered fluorescent material.
able to filter out the
unwanted fluorescent light of neighboring layers of data. Our setup used a 50µm diameter
pinhole to filter out the out of focus fluorescent emission. Once the pinhole is perfectly aligned
with the desired layer’s focal point we are able to move freely to any layer and read off data from
that layer only. There is no need to adjust the pinhole’s positioning for each individual layer of
the sample because the focal length will be the same for each layer. Figure 9 on the left gives a
clear image of how a confocal microscope works in a polymer multilayered fluorescent system.
17 Construction
The apparatus was broken up into three primary sections: laser stage, polymer sample
stage, and a detector stage. Each of the three sections will be on separate platforms and move
independently of each other. Using SolidWorks CAD designing software I was able to make a
theoretical 3D model of how we initially designed our apparatus to look like, this CAD design is
illustrated below in Figure 10.
Figure 10: SolidWorks CAD theoretical design of our apparatus.
I shall go through each of the three sections on full detail describing the function and purpose of
all materials below. Each of the individual sections will be mounted together to a single
stationary platform.
The first section of our apparatus is the laser stage. This section is where we mount the
LG WH12LS30 12X SATA Blu-ray Burner Internal Drive’s laser to the stationary platform. In
order to keep our setup simple, we kept the sled unit that housed the Blu-ray laser on the track
18 that it originally would move radially inwards and outwards scanning a Blu-ray disc, as seen in
Figure 11. Powering the Blu-ray laser is a Keithley power generator that allows us to control the
voltage and current that is being supplied to the laser
diode. I had to solder wires to the positive and negative
ends of the laser diode in order to attach it to the power
generator. Through a GPIB cable we are able to program
the current that is being supplied to the laser. The laser
stage is where we actually do the photobleaching, writing,
of data. While we read data off the polymer multilayered
Figure 11: Laser sled mounted onto the track that is attached to the stationary platform.
fluorescent sample we typically keep the laser’s current at 40mA and voltage at 5V. We’ve
determined that long exposure to the sample at these settings doesn’t seem to have any
noticeable effects on it.
The second section of our apparatus is the polymer sample stage. This section is where
the polymer multilayered fluorescent sample is mounted to our apparatus. This section is distinct
from the other sections because this section is the only one that
is designed to move on a regular basis. It is constantly moving
so as to read and write data from our sample’s many layers.
Since our sample is a 3D polymer we require translation stages
to move our sample in the xyz-axis. We used three linear
translation stages powered by three Newport LTA-HS actuators
to create our xyz-axis translation stage setup, as seen on the left
in Figure 12. A Newport Universal Motion Controller/Driver
Figure 12: XYZ-­‐axis translation stage setup of our apparatus.
controls our high-speed actuators allowing us extremely fine
19 movement in the xyz-axis. We control the Newport Universal Motion Controller/Driver through
the use of GPIB cables from our lab computer. Attached to the top translation stage is our
polymer multilayered fluorescent sample holder.
The third and final section of our apparatus is the detector stage. The detector stage
houses the confocal microscope system that allows us to read data off of our polymer sample and
interpret it into binary information. The detector stage is where most of the optical components
in our apparatus can be found.
Figure 13: Detector stage of the theoretical apparatus design.
Referring to Figure 13 above, I shall explain what each component is and what it is used for
starting from the left and working our way to the right. The first piece of optical equipment is an
objective lens that has a magnification of x44. This objective lens is used to collect and slows
down the divergence of the fluorescing light from the sample and transmits it to the following
lens in the system. Without the objective lens the fluorescing light would diverge far to quickly
for any data to be collected. The second piece of optical equipment in Figure 13 is a planoconvex lens. This plano-convex lens causes the fluorescent light to be slowly convergent in the
direction of the detector. Without this first plano-convex lens the fluorescent light would diverge
20 before it reaches the pinhole. The third piece of optical equipment is a filter. This filter is
specifically designed to block out the Blu-ray laser wavelength that still passes through our
sample and only transmits the fluorescent wavelengths of light. Without this filter our detector
would continuously be reading a light intensity from the laser’s wavelength and not that of the
fluorescent sample. In the middle of the detector stage setup is a beam splitter. This beam splitter
is used to reflect a small portion, less than 10%, of the fluorescent light upwards into an
observable eyepiece setup while still transmitting the majority of the light onward to the detector.
To the right of the beam splitter is a pinhole iris. The pinhole is essential to our ability to read off
data from individual layers. It filters out the out of focus fluorescent emission. After the pinhole
is a second plano-convex lens that is used to focus the pinhole filtered fluorescent light into a
light detector. Without this second lens the light from the pinhole would diverge before it reaches
the detector. The last piece of optical equipment in my theoretical apparatus design is the
photodetector. The photodetector collects all the fluorescent emissions from the desired layer of
the polymer multilayered fluorescent sample. Without the photodetector our system wouldn’t be
able to read anything. The light collected from the photodetector determines intensity
measurements. The whole detector stage part of my apparatus is mounted a top a linear
translation stage so I am able to adjust the whole confocal microscope system as a single piece if
I need to at some point down the road. Above the beam splitter are two lenses aligned one behind
the other. These two lenses are used for us to be able to see the actual individual layers of our
sample. We are able to tell where on each layer there has been photobleaching. This allows us to
keep track of the data being read by the detector with the physical observation of the
photobleached bits. The microscope system acts as a way of checking our data that is being read.
21 Results
Throughout the construction process of our apparatus we decided to make some
alterations to the theoretical design. Figure 14 is a photograph of our actual apparatus.
Figure 14: This is the experimental apparatus that I built. It is capable of reading and writing on our polymer multilayered fluorescent sample.
The first alteration from the theoretical design to the actual apparatus is the placement of the
filter. The filter is now located directly after the objective lens on the same mount. This was done
just out of convenience and doing this took up less space overall. The next change was the
position of the first plano-convex lens. We rearranged this first lens to be located after the beam
splitter (glass slide) in order for us to be able to see the individual fluorescent layers through the
22 microscope setup with greater ease. If we hadn’t moved this lens to come after the beam splitter
it would’ve caused us to have more lenses in the microscope setup to magnify the smaller image.
The final alteration from theoretical to actual apparatus is the addition of a second plano-convex
lens directly after the first one. Using only one plano-convex lens caused the focal length of the
fluorescent emission to be far greater than our setup allowed for. The addition of this second
identical plano-convex lens causes the image to converge much quicker, a shorter focal length.
The rest of the experimental apparatus remained the same as the theoretical CAD design.
Due to time constraints, I was unable to complete the alignment of the pinhole to the
exact focal point of the in focus fluorescent emission from our sample. All the necessary
components are there for our apparatus to function it just needs to have the pinhole precisely
aligned in order to filter out the out of focus fluorescent emissions so as to be able to read data.
Upon the completion of the alignment of the pinhole our apparatus will work as anticipated.
As a result on our apparatus not being aligned we were unable to acquire any data. Once
the pinhole is aligned we intend to program the apparatus to make measurements of intensity as a
function of the position of the polymer multilayered fluorescent sample. As we move the sample
layers through the focal point of the Blu-ray laser our photodetector will record the intensity.
Through this simple experiment we will be able to identify the accuracy of our apparatus. We
know the approximate thickness of the layers, so as the laser moves through the alternating
active and buffer layers of the sample we should see a plot of intensity as a function of position
similar to that of Figure 15.
23 Figure 15: Plot of intensity vs position of a 23-­‐layered polymer fluorescent material.
Figure 15, courtesy of Cory Christenson, is an actual measurement of fluorescent light
intensity as a function of position through a 23-layered polymer of alternating layers of active
and buffer substrates similar to the polymer we used in our apparatus.
Future Work
Since I was unable to complete the alignment of our device it’ll have to be finished up by
another student. There is plenty of work that still needs done on our apparatus before we can start
using it for regular data storage. First and foremost, the student that picks up after me will have
to get the pinhole perfectly aligned such that it is in focus with the desired layer’s focal point.
Upon the alignment of the pinhole our device should be able to read and write on all 22 layers as
we had hoped it would. Once the device is completely aligned the student will have to work on
the designing and programming of the software that will operate the apparatus that we’ve built.
After the completion of aligning and programming the apparatus is done there is still
plenty of work that needs to be done on our device as well as research on the polymer that we are
using. Future work on the completed apparatus itself will be dealing with making it more
24 compact and efficient than what it currently is. Research into using other types of fluorescent
materials is needed as well. The fluorescent material that we are currently using in our device
becomes photobleached in a linear fashion. This means that after a long period of repeated
exposure to the laser from simply reading the multilayered fluorescent sample will cause it to
slowly become photobleached. Work is currently being done on creating a multilayered
fluorescent polymer that doesn’t photobleach linearly but rather that is only able to be
photobleached above a specific intensity, essentially threshold intensity. Once we have a
multilayered fluorescent material that isn’t photobleached linearly we will have created a device
that could be the next economically feasible approach to data storage technology. If this device
does make it to production and become commercially available it’ll be the first in affordable
terabyte-level data storage technology.
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