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1.Analysis of replacing an optical fiber core with polymer

Kevin H. Smith, Richard H. Selfridge, Stephen M. Schultz, Douglas J.
Markos, and Benjamin L. Ipson
Department of Electrical Engineering, Brigham Young University, Provo, Utah 84602
khs9@ee.byu.edu
Abstract: This paper presents the analysis of a 2 cm long in-fiber polymer
waveguide formed on the platform of a D-shaped optical fiber. Numerical
simulations provide an understanding of the major loss mechanisms for feasible
in-fiber polymer waveguide geometries. The primary loss mechanism
is determined to be excitation of slab modes on the flat surface of the fiber
with transition geometry being the next major contribution to loss.
© 2004 Optical Society of America
OCIS codes: (060.2310) Fiber optics; (130.2790) Guided waves; (130.3120) Integrated optics
devices; (060.5060) Phase modulation
References and links
1. R. Mears, L. Reekie, I. Jauncey, and D. Payne, “Low noise erbium-doped fiber amplifier aperating at 1.54 µm,”
Electron. Lett. 23, 1026–1028, (1987).
2. K. O. Hill and G. Meltz, “Fiber Bragg grating technology fundamentals and overview,” IEEE J. Lightwave
Technol. 15, 1263–1276 (1997).
3. S. Tseng and C. Chen, “Side-polished fibers,” Appl. Opt. 31, 3438–3447, (1992).
4. D. J. Welker, J. Tostenrude, D. W. Garvey, B. K. Canfield, and M. G. Kuzyk, ”Fabrication and characterization
of single-mode electro-optic polymer optical fiber,” Opt. Lett. 23, 1826–1828 (1998).
5. D. J. Markos, B. L. Ipson, K. H. Smith, S. M. Schultz, R. H. Selfridge, T. D. Monte, R. B. Dyott, and G. Miller,
“Controlled core removal from a D-shaped optical fiber,” Appl. Opt. 42, 7121–7125 (2003).
6. K. H. Smith, D. J. Markos, B. L. Ipson, S. M. Schultz, R. H. Selfridge, J. P. Barber, K. J. Campbell, T. D. Monte,
and R. B. Dyott, “Fabrication and analysis of a low-loss in-fiber active polymer waveguide,” Appl. Opt. 43,
933–939 (2004).
7. S. Mononobe and M. Ohtsu, “Fabrication of a pencil-shaped fiber probe for near-field optics by selective chemical
etching,” J. Lightwave Technol. 14, 2231–2235 (1996).
8. S. Garner, “Three dimensional integration of passive and active polymer waveguide devices,” Ph. D. dissertation,
Dept. Elect. Eng., Univ. of Southern California, Los Angeles, CA, 1998.
9. BeamPROP™User’s Guide, RSoft Inc., 200 Executive Blvd., Ossining, NY 10562.
10. J. D. Love,W. M. Henry,W. J. Stewart, R. J. Black, S. Lacroix, and F. Gonthier, “Tapered single-mode fibres and
devices,” IEE Proc. J. 138, 343–354, Oct. 1991.
1. Introduction
In-fiber devices have received attention because they allow optical signals to be generated and
manipulated entirely in the optical fiber domain. Existing in-fiber devices such as erbium-doped
fiber amplifiers and Bragg gratings have demonstrated these advantages [1, 2]. Side-polished
fibers are another variety of in-fiber device used in some applications [3], although they limit
device length and only permit interaction with the evanescent field of the fiber. In-fiber devices
have also been constructed using fiber made completely out of polymer [4].
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 354
#2985 - $15.00 US Received 4 September 2003; revised 3 November 2003; accepted 4 November 2003
Prior work in our laboratory [5, 6] demonstrated how to etch an arbitrary length of D-fiber
to remove the core of the fiber and then replace that section of the core with another optical
material. Possible applications for such in-fiber waveguides include amplitude and phase
modulation, fiber sensors, tunable filters, frequency converters, etc.
Previous papers [5, 6] focused on the experimental techniques used to produce such devices.
However, there is a need to examine the major loss mechanisms associated with this new in-
fiber polymer waveguide section. This paper provides a detailed investigation into the major
loss mechanisms and exploits the graphical capabilities of this journal. Section 2 provides an
overview of the fabrication of in-fiber polymer waveguides and Section 3 presents the analysis
of primary loss mechanisms in these waveguides.
2. Background
2.1. D-fiber platform
Figure 1 is an illustration of a D-shaped optical fiber composed of a germania-doped core, a
fluorine-doped cladding, and an undoped supercladding. The protective jacket is not shown in
the figure. The core of the fiber is approximately 2 x 4 µm in size and is located roughly 10 µm
from the flat side of the D-fiber. The fiber manufacturing process results in a small undoped
section in the center of the core.
Undoped silica, nsi
Germania doped core, ncore
Fluorine
doped cladding, nclad
Fig. 1. The elliptical germania doped D-fiber core is surrounded by a lower index fluorine
doped cladding region.
The differential doping of the fiber allows for selective chemical etching with hydrofluoric
(HF) acid [7]. In a previous paper [5] we show how to use this selective chemical etching
to controllably remove a portion of the core of the D-fiber while leaving the fluorine doped
cladding intact, preserving the structural integrity of the fiber. Figure 2 shows a movie of the
core etch, demonstrating the differential etch rates of the core and cladding. The etch depth
is chosen to allow for the formation of a single mode polymer waveguide near the center of
the fiber. Figure 3 is a cross-sectional scanning electron microscope (SEM) image of an etched
D-fiber with a groove along the flat side of the fiber into which polymer is deposited.
2.2. Polymer waveguide
The polymer is deposited by spin casting and forms a waveguide that is contiguous with the core
of the unetched portion of the fiber. In this research we use polymethyl methacrylate (PMMA)
as the host polymer with DR1-azo dye as the guest chromophore. After the polymer is deposited
on the fiber, the fiber is spun in a standard commercial spinner, forming a polymer waveguide
in the groove left by the wet etch.
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 355
#2985 - $15.00 US Received 4 September 2003; revised 3 November 2003; accepted 4 November 2003
Fig. 2. (452 KB) Movie of the cross-section of the fiber as it is etched in HF acid.
Fig. 3. SEM images of a D-fiber and a typical etch profile. The cladding has been etched
only slightly while about half of the core has been removed.
As demonstrated in an earlier paper [6], polymer waveguide thickness can be changed by
varying the polymer viscosity. Figure 4 shows cross-sectional SEM images of polymer waveguide
sections with increasing viscosities. These images show that a layer of polymer in the
groove is accompanied by a layer of polymer on the flat surface. Figure 4(a) shows that the
polymer in the groove is substantially thicker than the polymer layer on the flat surface when
a low viscosity polymer is applied. Figures 4(b) and 4(c) show that once polymer viscosity is
above a certain point, further increases in viscosity cause the thickness of the polymer in the
groove and on the flat to increase at the same rate.
The transmission loss of the approximately 2 cm long polymer waveguides shown in Figs.
(a) - (c) were measured at a wavelength of 1550 nm to be respectively 1.6 dB, 36 dB, and too
high to measure. Experiments demonstrated that waveguides with a thick layer of polymer on
the flat surface of the fiber have high loss. Of the three samples shown in Fig. 4, only sample
(a) is suitable for many applications because of the high loss of the other two.
3. Loss analysis
Several factors affect transmission loss as light travels through the polymer waveguide section.
First, the electro-optic polymer has a higher bulk absorption coefficient than the germaniadoped
glass. In particular, DR1-azo dye doped PMMA has a bulk absorption coefficient of
about 1 dB/cm at a wavelength of 1300 nm [8]. Light scattering along the length of the polymer
waveguide is another source of loss. This source of loss can be avoided by keeping fibers free
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 356
#2985 - $15.00 US Received 4 September 2003; revised 3 November 2003; accepted 4 November 2003
1131nm
1165nm
(c)
709nm
177nm
(a)
1060nm
695nm
(b)
Fig. 4. Cross-sectional SEM images of polymer waveguides with polymer viscosities increasing
from (a) to (c). The white lines were added to show the interface between the glass
and polymer.
of contamination between the core removal step and the polymer application step.
As noted above there is a strong relationship between the polymer thickness on the flat surface
of the fiber and transmission loss. This loss is attributed to the excitation of slab modes
in the polymer on the flat side of the fiber. Also, there is transmission loss associated with the
mismatch between the mode supported by the unetched fiber section and that supported by the
polymer waveguide. Such losses can be reduced by forming a gradual transition to and from
the polymer waveguide section. We performed numerical simulations to analyze these sources
of loss.
All numerical simulations of waveguides were performed at a wavelength of 1550 nm using
the beam propagation method (BPM) in the commercial software package BeamPROP™.
BPM is based on the paraxial approximation to the Helmholtz equation [9]. To simulate threedimensional
propagation, the fundamental mode of the unetched fiber is computed via the imaginary
distance beam propagation method and then launched into the fiber. BeamPROP™then
simulates the propagation of light through the polymer waveguide. The computed electric field
distribution at regular intervals along the propagation axis is stored and used to calculate loss
in the waveguide as a function of propagation distance.
3.1. Slab modes
Experiments consistently demonstrate that waveguides with thick polymer layers on the flat
surface of the fiber have high transmission loss. These thick polymer layers on the flat result in
high loss because they behave like slab waveguides, allowing light to couple out of the polymer
waveguide in the core region and into slab modes on the flat side of the fiber.
nclad=1.441
ncore=1.476
npolymer=1.54
1.0 µm 0.2 µm
(a) thin (b) thick
Fig. 5. The cross-sections of the two polymer waveguides that were analyzed.
BeamPROP™’s three-dimensional simulation capabilities model light propagation through
the transition from the unetched fiber core to the polymer waveguide. Figure 5(a) shows a
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 357
#2985 - $15.00 US Received 4 September 2003; revised 3 November 2003; accepted 4 November 2003
model of a waveguide with a thin layer of polymer on the flat surface of the fiber, similar to
the cross-sectional image shown in Fig. 4(a). Figure 5(b) shows a waveguide with a thick layer
of polymer similar to the cross-section shown in Fig. 4(c). All indices of refraction are given
at a wavelength of 1550 nm and absorption loss in the polymer has been neglected in these
models. If thick enough, polymer layers on the flat surface of the fibers behave as asymmetric
slab waveguides. The polymer layer on the flat of the fiber in Fig. 5(a) is too thin to support a
slab mode, but that in Fig. 5(b) does support a slab mode [6]. The full three-dimensional model
assumes a butt-coupled transition between the unetched section of optical fiber and the polymer
waveguide sections illustrated in Fig. 5.
Fig. 6. Top view of the three-dimensional simulation of light propagating from unetched
fiber into polymer waveguide for thin (a) and thick (b) polymer layers.
Figure 6 shows the top view of the simulations of light propagating from the unetched core
into the polymer waveguide section. The abrupt transitions from unetched core to polymer
waveguide occur at the longitudinal position of z = 10µm. At the transition, any power that is
not coupled into the polymer layer quickly radiates away from the core. In addition to this loss
from mode mismatch, a thick layer of polymer also results in continuous radiation of light away
from the core region along the length of the fiber. Even though more power is coupled from the
unetched fiber into the polymer waveguide when the polymer is thicker, the total transmission
loss is substantially higher because the power that couples into slab modes does not couple
back into the optical fiber core. Figure 7 shows full simulations of light propagating through
the abrupt transition from unetched fiber to polymer waveguide. The green ellipse in the figure
shows the location of the elliptical core (before etching). The top half of Fig. 7 is a simulation of
the thin-polymer waveguide in Fig. 4(a) and the bottom half is a simulation of a thick-polymer
waveguide as in Fig. 4(c). Power continuously couples out of the core region along the length of
the waveguide in the simulation of the thick polymer waveguide. The simulated thick polymer
waveguide loses about 1.5 dB/mm to slab modes, whereas the thin polymer waveguide loses no
power to slab modes.
The cutoff thickness for different polymer indices gives an estimate of the upper bound on the
thickness of the polymer on the flat side of the optical fiber. The cutoff thickness is defined as
the point where the effective index of refraction of the fundamental mode falls below the index
of the substrate. To ensure that no slab modes were supported, the thickness of the polymer on
the flat needs to be kept below 0.4 µm [6].
3.2. Transition loss
The mode supported by the unetched optical fiber is different than the mode supported by the
polymer waveguide. This mode mismatch contributes to the transmission loss of the device.
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 358
#2985 - $15.00 US Received 4 September 2003; revised 3 November 2003; accepted 4 November 2003
Fig. 7. (1.27 MB) Simulations of light propagating through a transition from unetched fiber
to thin (top) and thick (bottom) polymer waveguides.
Butt-coupled transitions can result in a total transmission loss of about 3 dB [6]. The loss
associated with mode mismatch is decreased by a gradual transition between the unetched core
and the polymer waveguide [10].
Light propagation through transitions from fiber core to polymer waveguide and back into
the fiber core was modeled using BeamPROP™. The transition length was varied in order to
quantify its effect on transmission loss. The model consists of a short unetched length of fiber
followed by a transition region, a 2500 µm section of polymer waveguide, another transition,
and a final length of unetched fiber 2500 µm long. Figure 8 is a movie of a cross-sectional
view of the fiber along the z-direction. This movie shows the transitional geometry from the
unetched fiber into the polymer waveguide.
Fig. 8. (322 KB) Video of the index profile of the fiber with 110 µm long transition regions
as a function of z.
Figure 9 shows the relationship between loss and propagation distance for waveguides with
different transition lengths. The 1100 µm transition fiber performs best, having only 0.5 dB of
loss. The plot shows that the overall loss is approximately evenly divided between the transitions
to and from the polymer waveguide.
0 2000 4000 6000 0
1
2
3
z-Position (microns)
Loss in dB
Transition Length
110 microns
560 microns
1100 microns
Fig. 9. Plot of loss as light propagates through transitions of different lengths.
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 359
#2985 - $15.00 US Received 4 September 2003; revised 3 November 2003; accepted 4 November 2003
4. Summary and conclusions
Insertion of a polymer that is contiguous with an optical fiber presents a new means of launching
into and guiding light in a variety of materials. Using experiment and numerical simulations,
we have designed and analyzed a low-loss in-fiber polymer waveguide.
The simulations and experiments discussed above provide bounds on the waveguide dimensions
in order to achieve low transmission loss. An in-fiber polymer waveguide must have a
very thin layer of polymer on the flat side of the fiber for the waveguide to have low loss. Numerical
results indicate that a polymer waveguide of index 1.54 must have a flat thickness less
than 0.4 µm to avoid excitation of slab modes. The transition length from unetched fiber to
polymer waveguide should also be greater than 1 mm to ensure low loss.
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 360
#2985 - $15.00 US Received 4 September 2003; revised 3 November 2003; accepted 4 November 2003

lottie · 发表于 2004-2-16 00:24:00

Thin liquid-crystal display backlight system with
highly scattering optical transmission polymers

Akihiro Tagaya, Michio Nagai, Yasuhiro Koike, and Kazuaki Yokoyama
We describe an advanced highly scattering optical transmission HSOT polymer backlight system that
has shown twice the brightness of a conventional transparent system in spite of its having a thinner
backlight. The HSOT polymer that contains optimized heterogeneous structures produced homogeneous
scattered light with forward directivity and sufficient color uniformity. Although it was thought
that polymers for light-guide plates LGPs must be transparent to minimize scattering, we have come
to the conclusion that the HSOT polymer, which is not an absorping medium but a scattering medium,
is a more suitable medium for LGPs. © 2001 Optical Society of America
OCIS codes: 230.3720, 120.2040, 290.4210, 290.7050.
1. Introduction
Liquid-crystal displays LCDs have been widely
used as an important human interface with typical
portable devices such as notebook-type computers.
Many researchers have worked toward developing a
more efficient backlight, which would lead to longer
battery lifetimes for portable devices; typical
notebook-type computers have a poor battery lifetime,
typically 1–2 h. The energy consumption of a
typical LCD module is more than 50% of the total
energy consumption of a typical portable device, and
the energy consumption of a typical backlight, which
is an area light source that illuminates a LCD panel
from behind, accounts for more than 60% of the typical
LCD module’s energy consumption.
A light-guide plate LGP, which is typically a
wedge-shaped polymer plate, has been widely used in
the backlights for LCDs of portable devices. A LGP
guides light from a cold fluorescent lamp and radiates
it homogeneously from all over its output surface.
In other words, the LGP is a device that converts a
linear light source or a point light source into an area
light source. Conventionally, all LGPs have been
made from transparent polymers, and it was believed
that polymers for the LGPs must be transparent,
with no contaminants, because a contaminant would
absorb and scatter light. Even if the contaminant
were transparent, it would scatter light, leading to a
decrease in brightness. However, we had some
doubt whether a conventional transparent LGP is the
brightest achievable plate. For illumination media
this point is of considerable importance but so far has
not been investigated in depth. We believed that
LGPs made from polymers that contain a great
amount of a contaminant would be the brightest obtainable
plates. Under the circumstances, we proposed
a highly scattering optical transmission
HSOT polymer and applied it to LCD backlights,1–3
in which injected light is multiply scattered to maintain
its directivity as a result of the optimized amount
of contamination and then homogeneously emerges
in a specific direction. The HSOT backlights showed
approximately twice the brightness of a conventional
backlight and high uniformity, which disproved the
suggestion that illumination media must be transparent
because color dispersion caused by scattering
degrades the color uniformity of an illumination medium.
In recent backlight technology, the angle of
the wedge decreased with a decrease in the thickness
of the wedge-shaped LGPs for thinner backlights,
which generally lowered the efficiency of backlights
that use wedge-shaped LGPs. In this paper we propose
a thinner and more efficient HSOT backlight
system. In this advanced HSOT backlight system
the HSOT polymer LGP has prism structures at the
bottom to achieve higher luminance and efficiency in
spite of its being a thinner system. In addition, we
A. Tagaya bzz13624@nifty.ne.jp, M. Nagai, and Y. Koike are
with the Faculty of Science and Technology, Keio University,
3-14-1, Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan. K.
Yokoyama k-yokoyama@enplas.co.jp is with Enplas Laboratories,
Incorporated, 2-38-5, Namiki, Kawaguchi City, Saitama 332-
0034, Japan.
Received 25 July 2000; revised manuscript received 18 July
2001.
0003-693501346274-07$15.000
© 2001 Optical Society of America
6274 APPLIED OPTICS Vol. 40, No. 34 1 December 2001
describe the advantages of the advanced HSOT backlight
system based on its comparison with conventional
backlights that use transparent LGPs with dot
patterns.
2. Scattering Phenomenon in the HSOT Polymer
A structure with a different refractive index from
that of the surrounding homogeneous medium scatters
light. In this paper we define such a structure
as a heterogeneous structure. Light injected into
the HSOT polymer is multiply scattered and homogenized
because the structure is heterogeneous and
then emerges as a directive illuminating light, as
shown in Fig. 1a. However, injected light just
passes through a typical transparent bulk polymer,
as shown in Fig. 1b. The heterogeneous structure
was theoretically designed by the HSOT-designing
simulation program described in this section to produce
the desired performance.
A. Single Scattering
The scattering property of a medium that contains a
heterogeneous structure depends on the relative refractive
index, size, and form of the heterogeneous
structure and on the distance by which the heterogeneous
structures are separated from one another.
The HSOT polymer contains some types of transparent
spherical particles of which the heterogeneous
structures that cause scattering are formed. The
light-scattering intensity profile and the scattering
efficiency of a single particle can be calculated from
the following equations:
I, m, 2i1 i282, (1)
K, m 2
22r2
1

2 1a2 b2, (2)
i1
1

2 1
1 a
P
1cos
sin
b
dP
1cos
d 2
,
i2
1

2 1
1 b
P
1cos
sin
a
dP
1cos
d 2
, (3)
a
m mm
m
mm

,
b
mm m
mm
m

, (4)
2rnm0, (5)
m nsnm, (6)
which are derived from Mie scattering theory,4,5
where I, m, and K, m are scattering intensity
and scattering efficiency, respectively, is a size parameter,
m is the relative refractive index between
particle ns and matrix nm, r is the particle radius,
and is the wavelength of incident light in the matrix.
P
lcos is a Legendre polynomial and and

are the first two orders of the Ricatti–Bessel functions.
According to Mie scattering theory,4,5 there
are two important properties of the scattering phenomenon
caused by the spherical heterogeneous
structure: 1 As size of the heterogeneous structure
becomes larger, the ratios of forward and backward
scattering intensity to total scattering intensity become
higher and lower, respectively; this effect was
remarkable when the size of the heterogeneous structure
was comparable with or greater than a wavelength.
2 Although the scattering efficiency was
described to be inversely proportional to the fourth
power of the wavelength based on Rayleigh scattering
theory,5 the actual scattering efficiency has a
more-complex relation to wavelength. We refer to
these properties as Mie scattering properties MSP
in this paper to distinguish them from those that can
be described based on Rayleigh scattering theory.
Fig. 1. Bulk HSOT polymer and conventional transparent bulk
polymers. a Light injected into the HSOT bulk polymer is multiply
scattered and homogenized because of the heterogeneous
structures of the HSOT and then emerges as a directive illuminating
light. b Injected light simply passes through conventional
transparent bulk polymer.
1 December 2001 Vol. 40, No. 34 APPLIED OPTICS 6275
Single-scattering profiles calculated based on Mie
scattering theory are shown in Fig. 2. For scattering
profiles in the forward direction 0°–90° and in the
backward direction 90°–180°, Mie scattering theory,
which is applicable to a spherical heterogeneous
structure with any size, gives asymmetric singlescattering
profiles. Although scattering has been
thought to distribute light in all directions, one can
achieve a forward-directional single-scattering pro-
file in which scattered light is concentrated in a forward
small angle by controlling the heterogeneous
structure. As a result, injected light can be guided,
multiply scattered while directivity is maintained,
and homogeneously radiated in a specific direction
from its surface.
Scattering-efficiency curves of the diameter of a
spherical heterogeneous structure at 615, 545, 435
nm, which correspond to red, green, and blue light,
are shown in Fig. 3. Generally, we tend to think,
based on Rayleigh scattering theory, that blue light is
always scattered more strongly than red light.
However, such is not always true and depends on the
size of the heterogeneous structure. By injecting
white light from a typical cold fluorescent lamp or a
white LED into the scattering medium that contains
the heterogeneous structure, curve A, we obtained
yellowish transmitted light with a lower color temperature
because blue light was scattered more
strongly than red light. This is the same phenomenon
as is responsible for the red sunset. However,
bluish transmitted light with a higher color temperature
was obtained in the scattering medium that
contained the heterogeneous structure, curve B, because
red light was scattered more strongly than blue
light. By controlling the diameter of the heterogeneous
structure to give almost the same scattering
efficiencies for red, green, and blue light, one can
obtain output light with almost the same color temperature
as that of injected light.
However, there were no materials and devices that
used the MSP effectively, because none provided the
precise control of the form and size of the heterogeneous
structure and of the distance of the heterogeneous
structures from one another that was
necessary. Scattered light from each spherical
structure interferes when the distance is small. Under
these circumstances the scattering form does not
follow Mie scattering theory. Thus we have proposed
using the HSOT polymer, which will enable us
to utilize the MSP. We formed the heterogeneous
structure in the HSOT polymer precisely by doping
transparent particles with a narrow distribution of
diameter sizes. When the distance among particles
is approximately or slightly larger than 100 times the
wavelength, single-scattering behavior of each particle
approximately follows Mie scattering theory.
Heterogeneous structures in conventional materials
such as polymer blends and copolymers had not been
optimized to utilize the MSP.
B. Multiple Scattering
We analyzed the light-homogenization effect caused
by multiple scattering in the HSOT polymer by using
the HSOT design simulation with the Monte Carlo
method6 based on Mie scattering theory.4,5 We
doped polymer particles to introduce the microscopic
heterogeneous structure. We used the Monte Carlo
method to analyze random and repeating processes
in the multiple-light-scattering phenomenon because
the Monte Carlo method is a powerful method with
which to solve problems that have no immediate
probabilistic interpretation.
By the Monte Carlo method we can define scattering
angle , expected photon path length L,
Fig. 2. Calculated single-scattering profiles based on Mie scattering
theory. The vector from the origin of the coordinates to each
curve is proportional to the logarithmic intensity scattered at the
corresponding angle. Size parameters, 1.7, 11.5, 69.2; relative
refractive index, m 0.965.
Fig. 3. Scattering efficiency curves of a single particle for 435-,
545-, and 615-nm wavelengths. Typical cold fluorescent lamps
have spectral peaks near these wavelengths. Relative refractive
index, m 0.965. A, B Particle diameters for heterogeneous
structures A and B, respectively.
6276 APPLIED OPTICS Vol. 40, No. 34 1 December 2001
probability-density distribution function F of scattering
angle, and extinction coefficient as
0

0

r2nar f K, mdrd, (7)
L lnrandom1, (8)
F
0

2Isin d
0

2Isin d
, (9)
F1random2, (10)
where nar is the particle concentration, f is the
probability-density distribution function of a wavelength,
random1 and random2 are uniform random
numbers generated from 0 to 1, and I is the scattering
intensity profile. Here, scattering is analyzed in a
polar coordinate system. After polar angle was determined,
the other polar angle was determined randomly
because the scattering intensity caused by
nonpolarized light was uniform with respect to polar
angle . Here, “photon” means an imaginary particle
with which to analyze the multiple-scattering process.
The multiple-scattering process in the HSOT polymer
was analyzed by this Monte Carlo simulation method.
3. Advanced HSOT Backlight
A. Structure of the Advanced HSOT Backlight and the
Conventional Transparent Backlight
In the conventional backlight system shown in Fig.
4a, the LGP was made from a transparent polymer
such as an acrylic polymer. Light from a cold fluorescent
lamp is injected from the edge of the LGP.
Injected light is scattered by dot patterns at the bottom
of the LGP and then emerges. The dot patterns
are typically formed by white ink or microscopic uneven
structures. The density of the printed dot patterns
increases relative to distance from the lamp
homogenize the luminance in the output surface. In
addition, a diffuser film and two prism films are
Fig. 4. Schematic diagrams of LCD backlighting systems. a
Conventional transparent backlight system, in which the LGP is
made from a transparent polymer. b Advanced HSOT polymer
backlight system, in which the LGP is made from HSOT polymer.
Fig. 5. Definition of angles and to describe the angular distribution
of luminance. Vector A, which is the projection of luminance
vector A, lies in the y–z plane at an angle from the z axis.
Fig. 6. Schematic diagram of the prism structures at the bottom
of the LGP and definition of prism angle . Filled circles, points of
reflection and refraction.
1 December 2001 Vol. 40, No. 34 APPLIED OPTICS 6277
placed on the output surface to hide the dot patterns
and to collect scattered light. In the advanced
HSOT polymer backlight system shown in Fig. 4b, a
wedge-shaped LGP is made from HSOT polymer.
Only one prism film is placed on the HSOT polymer
LGP. There are microscopic prism structures at the
bottom of the HSOT LGP in the y direction to achieve
high luminance and efficiency by gathering light scattered
in the direction parallel to the incident surface.
B. Simulation of Illuminating Properties of the Advanced
HSOT Backlight
We optimized the angle of the prism structures by
using a three-dimensional 3-D HSOT designing program
that was originally developed for precise design
based on the method described in Section 2. Angles
and were defined as shown in Fig. 5 to describe
3-D angular distribution of luminance. Vector A,
which is the projection of luminance vector A, lies in
the y–z plane at an angle from the z axis. Figure
6 is a schematic diagram of a part of the prism structure
at the bottom of the LGP and definition of the
prism angle . Simulated 3-D profiles of luminance
from the HSOT LGP with prism angles of 90°, 100°,
110°, and 180° are shown in Fig. 7. The prism angle
significantly affects the shape of 3-D luminance pro-
files and the peak value. These results show the
light-gathering effect of the prism structures, which
leads to higher luminance, greater efficiency, and a
more nearly symmetric shape of the luminance pro-
Fig. 7. Simulated 3-D profiles of luminance from the HSOT LGP. Prism angles are indicated. Here, “photon” means an imaginary
particle with which to analyze the multiple-scattering process. The photon number is proportional to the luminance; the various colors
are related to the number of photons as shown in the scale at the right of each figure.
Fig. 8. 3-D luminance profile of the 10.4-in. HSOT LGP without
a prism film.
6278 APPLIED OPTICS Vol. 40, No. 34 1 December 2001
file. At a prism angle of 100°, a symmetric profile
with the highest peak value was obtained.
C. Luminance Properties of the HSOT Backlight
The advanced HSOT backlight with optimized prism
structures was prepared by injection molding. The
3-D luminance profile for the 10.4-in. 26.4-cm
HSOT LGP that we obtained is shown in Fig. 8 without
the prism film. The angle of the illuminating
light should be converted into the vertical angle to the
output surface by the prism film, as shown in Fig. 9,
because the luminance profile had a peak at an angle
of 70°. The actual 3-D luminance profile of the
advanced HSOT backlight with the prism film and
that of a transparent backlight with dot patterns under
the same conditions are shown in Fig. 10. The
advanced HSOT backlight shows approximately
twice the luminance of the transparent backlight
with the dot patterns.
4. Discussion
In this section we discuss the difference in brightness
between the advanced HSOT backlight and the
conventional transparent backlight. The injected
light is guided and scattered but has enough directivity
in the HSOT polymer because of the forwarddirected
single scattering caused by the optimized
heterogeneous structures. This scattered light is
reflected in the advanced HSOT polymer LGP and
finally emerges beyond critical conditions. Diffusion
of multiple-scattered light in the z direction
was restricted because of the presence of total re-
flection and internal reflection, and in the x direction
it was controlled by the prism structures at the
bottom surface. As a result, output light from the
LGP has directivity at 70° from the vertical direction
to the output surface, as shown in Fig. 11, and
there is little light scattered backward and in another
direction that does not contribute to brightness.
Therefore, high efficiency is achieved by
conversion of the angle of the light to a vertical
direction. However, scattered light that results
from the dot patterns in the conventional system is
distributed in a wide range of angles and does not
have sufficient directivity. Furthermore, the diffuser
film placed on the LGP scatters light further
to hide the dot patterns and produces widely diffused
light, as shown in Fig. 11; then the two prism
films collect the diffused light. However, efficiency
is low compared with that of the advanced HSOT
polymer backlight because there is a great deal of
light that cannot be utilized. To scatter light is
necessary to realize a homogeneous area light
source, because the image of the lamp is reflected
and overlapped multiply in a transparent LGP that
has a smooth bottom surface without any dot patterns.
With respect to color, we achieved a homogeneous
color temperature by optimizing the heterogeneous
structures, as shown in Fig. 12. The HSOT polymer
was the first polymer for which there was no color
dispersion of scattered light in such a long interactive
distance. Here we have shown that the HSOT polymer
is an innovative material for use as an illumination
medium, and the conventional transparent LGP
backlight system is not the brightest system.
Its thickness is one of the most important factors of
Fig. 9. Typical locus of a ray in the prism film optimized for the
advanced HSOT LGP. The illuminating light is refracted and
reflected and finally emerges in a direction vertical to the output
surface through the prism.
Fig. 10. 3-D luminance profiles of a the advanced HSOT backlight
with the prism film and b a transparent backlight with dot
patterns under the same conditions. Lamp current, 3.0 mA; lamp
voltage, 573 V rms.
1 December 2001 Vol. 40, No. 34 APPLIED OPTICS 6279
backlight because backlights that are as thin as possible
are desirable for recently developed thin LCDs.
The minimum thickness of a typical LGP is restricted
by the dimensional stability of the material against
humidity and temperature during operation. When
the total thickness of the advanced HSOT backlight is
equal to that of the conventional transparent backlight,
the advanced HSOT backlight can use an approximately
0.3-mm-thicker LGP than can the
conventional backlight, because the conventional system
requires three films on the output surface but the
advanced HSOT backlight system requires only one
prism film. In recent thin-backlight technology, a
0.3-mm margin for thickness is significant advantage
in terms of dimensional stability. When the thickness
of a LGP in the advanced HSOT backlight system
is equal to that of a conventional plate the
advanced HSOT backlight system is approximately
0.3 mm thinner than the conventional system.
5. Conclusions
We have proposed an advanced highly scattering optical
transmission backlight system that was designed
with a HSOT designing simulation program
that exhibits twice the brightness of the conventional
transparent system in spite of its having a thinner
backlight. The HSOT polymer that contains the optimized
heterogeneous structures have produced homogeneous
scattered light with forward directivity.
Therefore the scattered light in the advanced HSOT
backlight can be controlled by the prism structures at
the bottom of the LGP, resulting in higher luminance
in the vertical direction to the output surface. In
addition, the optimized heterogeneous structures
achieved sufficient color uniformity. Previously it
had been thought that polymers for LGPs must be
transparent to minimize scattering. On these
grounds, however, we have come to the conclusion
that the HSOT polymer is a more suitable material
for LGPs.
The authors thank Eizaburo Higuchi, Suguru Ishii,
and Masahiro Horiguchi for their useful comments
and for encouraging discussions.
References
1. A. Horibe, M. Izuhara, E. Nihei, and Y. Koike, “Brighter backlights
using highly scattered optical transmission polymer,” SID
J. 3, 169–171 1995.
2. A. Horibe, M. Baba, E. Nihei, and Y. Koike, “High-efficiency and
high-quality LCD backlight using highly scattering optical
transmission polymer,” IEICE Trans. Electron. E81-C, 1697–
1702 1998.
3. A. Tagaya and Y. Koike, “Highly scattering optical transmission
polymers for liquid crystal display,” in Design, Fabrication, and
Characterization of Photonic Devices, M. Osinski, S. J. Chua,
and S. F. Chichibu, Proc. SPIE 3896, 214–222 1999.
4. G. Mie, “Beitra¨ge zur Optik truber Medien, speziell kolloidaler
Metallo¨sungen,” Ann. Phys. Leipzig 25, 377–445 1908.
5. M. Kerker, The Scattering of Light and Other Electromagnetic
Radiation Academic, San Diego, Calif., 1969.
6. I. Lux and L. Koblinger, Monte Carlo Particle Transport Methods:
Neutron and Photon Calculations CRC Press, Boca Raton,
Fla., 1991.
Fig. 11. Luminance profiles for the advanced HSOT LGP and the
conventional transparent LGP with a diffuser film relative to angle
. Here 0.
Fig. 12. Uniformity of color in the output surface of the advanced
HSOT backlight. A backlight for a color LCD is a white-light
source. A slight difference in color, for example, bluish white or
yellowish white, for a white-light source is indicated by color temperature.
Color temperature is almost constant in the output
surface area.
6280 APPLIED OPTICS Vol. 40, No. 34 1 December 2001

lottie · 发表于 2004-2-16 00:32:00

All-optical AND gate at 10 Gbit/s based
on cascaded single-port-coupled SOAs
Xinliang Zhang, Ying Wang, Junqiang Sun, Deming Liu,
and Dexiu Huang
Department of Optoelectronic Engineering, Huazhong University of Science and Technology,
Wuhan, Hubei, 430074, China
xlzhang@mail.hust.edu.cn
Abstract: An all-optical logical AND gate at 10 Gbit/s based on cross-gain
modulation (XGM) in two cascaded semiconductor optical amplifiers
(SOAs) is demonstrated. Single-port-coupled SOAs are employed and
specially designed to improve the output extinction ratio as well as the
output performance of the logic operation. The output signal power and
extinction ratio from the first-stage wavelength converter are critical to
achieving all-optical logical AND operation.
© 2004 Optical Society of America
OCIS codes: (250.5980) Semiconductor optical amplifiers; (200.3760) logic-based optical
processing.
References and links
1. C. Bintjas, M. Kalyvas, G. Theophilopoulos, T. Stathopoulos, H. Avramopoulos, L.Occhi, L. Schares, G. Guekos,
S. Hansmann, and R. DALL’Ara, “20Gb/s All-optical XOR OPERATION with UNI Gate,” IEEE Photon. Technol.
Lett. 12, 824-836 (2000).
2. T. Fjelde, D. Wolfson, A. Kloch, B. Dagens, A. Coquelin, I. Guillemot, F. Gaborit, F. Poingt, and M. Renaud,
“Demonstration of 20Gbit/s all-optical logic XOR in integrated SOA-based interferometric wavelength converter,”
Electron. Lett. 36, 1863-1864 (2000).
3. J. H. Kim, Y. M. Jhon, Y. T. Byun, S. Lee, D. H.Woo, and S. H. Kim, “All-optical XOR OPERATION gate using
semiconductor optical amplifiers without additional input beam,” IEEE Photon. Technol. Lett. 14, 1436-1438
(2002).
4. A. Hamie, A. Sharaiha, M. Guegan, and B. Pucel, “All-optical logic NOR gate using two-cascaded semiconductor
optical amplifiers,” IEEE Photon. Technol. Lett. 14, 1439-1441 (2002).
5. A. J. Poustie, K. J. Blow, A. E. Kelly, and R. J. Manning, “All-optical full adder with bit-differential delay,” Opt.
Commun. 156(11), 22-26 (1998).
6. A. J. Poustie, K. J. Blow, A. E. Kelly, and R. J. Manning, “All-optical parity checker with bit-differential delay,”
Opt. Commun. 162, 37-43 (1999).
7. H. Avramopoulos, “Optical TDM devices and their applications,” in Optical Fiber Communication (OFC 2001),
Vol. 54 of OSA Trends in Optics and Photonics Series (Optical Society of America, Washington, D.C., 2001),
Tutorial paper.
8. M. N. Islam, “All-optical component tasks (originally proposed in SAMMI project),”
http://www.eecs.umich.edu/OSL/Islam/DODN-Router.pdf.
9. H. Soto, C. A. Díaz, J. Topomondzo, D. Erasme, L. Schares, and G. Guekos, “All-optical AND gate implementation
using cross-polarization modulation in a semiconductor optical amplifier,” IEEE Photon. Technol. Lett. 14,
498-500 (2002).
10. D. Nesset, M. C. Tatham, and D. Cotter, “High-bit rate operation of an all-optical AND gate by using FWM in an
SLA with degenerate input signals,” in Optical Fiber Communication (Optical Society of America, Washington,
D.C., 1995), Paper TuD2.
11. Y. Maeda and L. Occhi, “All-optical triode based on a tandem wavelength converter using reflective semiconductor
optical amplifier,” IEEE Photon. Technol. Lett. 15, 257-259 (2003).
12. X. L. Zhang, J. Q. Sun, D. M. Liu, and D. X. Huang, “A novel scheme for XGM wavelength conversion based
on single-port-coupled SOA,” Chin. Phys. 10, 124-127 (2001).
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 361
#3421 - $15.00 US Received 2 December 2003; revised 29 December 2003; accepted 14 January 2004
13. Y.Wang, X. L. Zhang, and D. X. Huang, “Novel all-optical AND gate based on XGM in cascaded semiconductor
optical amplifiers,” Chin. J. Laser (to be published).
14. A. D. Ellis, A. E. Kelly, D. Nesset, D. Pitcher, D. G. Moodie, and R. Kashyap, “Error free 100Gbit/s wavelength
conversion using grating assisted cross-gain modulation in 2mm long semiconductor amplifier,” Electron. Lett.
34, 1958-1959 (1998).
15. T. Durhuus, B. Mikkelsen, C. Joergensen, S. L. Danielsen, and K. E. Stubkjaer. “All-optical wavelength conversion
by semiconductor optical amplifiers,” IEEE J. Lightwave Technol. 14, 942-954 (1996).
1. Introduction
All-optical signal processing is expected to have many applications in communications and
computation because it can handle large bandwidth signals and large information flows. Alloptical
logic gates are key functional elements in all-optical signal processing and have received
increasing attention in recent years [1–4] for addressing, demultiplexing, regenerating,
and switching. The all-optical AND gate is one of the fundamental logic gates because it is able
to perform on-the-fly bit-level functions such as address recognition, packet-header modification,
and data-integrity verification. Until now, all-optical AND gates reported in the literature
[5–10] could be achieved with a semiconductor laser amplifier loop mirror (SLALOM), a semiconductor
optical amplifier- (SOA-) based Mach-Zehnder interferometer (SOA-MZI), a SOAbased
ultrafast nonlinear interferometer (UNI), cross-polarization modulation, and four-wave
mixing (FWM) in SOAs. These schemes have been shown to have some advantages, but they
are difficult to control or construct and polarization states or random phase changes are critical
for their output performance. Maeda [11] reported an all-optical triode at 5 GHz based on crossgain
modulation (XGM) in tandem wavelength converters by use of a SOA with bulk material.
Based on a similar structure, a simple scheme for an all-optical AND gate is presented in this
paper, and a 10-Gbit/s all-optical logical AND gate is experimentally demonstrated for random
bit sequences by proper control of the signal power. To improve the output performance, singleport-
coupled SOAs [12, 13] with multi-quantum-well (MQW) materials are specially designed
for a large output extinction ratio in the first-stage wavelength converter. Identical with XGM
wavelength conversion [14, 15], this scheme has the potential advantages of high operation
speed, simple implementation, large wavelength span, high power efficiency, and easy of use.
In Section 2, the experimental setup and principle of operation are described. In Section 3, experimental
results and related discussion are presented. Finally, conclusions are summarized in
Section 4.
Fig. 1. Experimental setup diagram for all-optical logical AND operation based on cascaded
single-port-coupled SOAs.
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 362
#3421 - $15.00 US Received 2 December 2003; revised 29 December 2003; accepted 14 January 2004
Fig. optical AND gate at 10 Gbit/s based
on cascaded single-port-coupled SOAs
Xinliang Zhang, Ying Wang, Junqiang Sun, Deming Liu,
and Dexiu Huang
Department of Optoelectronic Engineering, Huazhong University of Science and Technology,
Wuhan, Hubei, 430074, China
xlzhang@mail.hust.edu.cn
Abstract: An all-optical logical AND gate at 10 Gbit/s based on cross-gain
modulation (XGM) in two cascaded semiconductor optical amplifiers
(SOAs) is demonstrated. Single-port-coupled SOAs are employed and
specially designed to improve the output extinction ratio as well as the
output performance of the logic operation. The output signal power and
extinction ratio from the first-stage wavelength converter are critical to
achieving all-optical logical AND operation.
© 2004 Optical Society of America
OCIS codes: (250.5980) Semiconductor optical amplifiers; (200.3760) logic-based optical
processing.
References and links
1. C. Bintjas, M. Kalyvas, G. Theophilopoulos, T. Stathopoulos, H. Avramopoulos, L.Occhi, L. Schares, G. Guekos,
S. Hansmann, and R. DALL’Ara, “20Gb/s All-optical XOR OPERATION with UNI Gate,” IEEE Photon. Technol.
Lett. 12, 824-836 (2000).
2. T. Fjelde, D. Wolfson, A. Kloch, B. Dagens, A. Coquelin, I. Guillemot, F. Gaborit, F. Poingt, and M. Renaud,
“Demonstration of 20Gbit/s all-optical logic XOR in integrated SOA-based interferometric wavelength converter,”
Electron. Lett. 36, 1863-1864 (2000).
3. J. H. Kim, Y. M. Jhon, Y. T. Byun, S. Lee, D. H.Woo, and S. H. Kim, “All-optical XOR OPERATION gate using
semiconductor optical amplifiers without additional input beam,” IEEE Photon. Technol. Lett. 14, 1436-1438
(2002).
4. A. Hamie, A. Sharaiha, M. Guegan, and B. Pucel, “All-optical logic NOR gate using two-cascaded semiconductor
optical amplifiers,” IEEE Photon. Technol. Lett. 14, 1439-1441 (2002).
5. A. J. Poustie, K. J. Blow, A. E. Kelly, and R. J. Manning, “All-optical full adder with bit-differential delay,” Opt.
Commun. 156(11), 22-26 (1998).
6. A. J. Poustie, K. J. Blow, A. E. Kelly, and R. J. Manning, “All-optical parity checker with bit-differential delay,”
Opt. Commun. 162, 37-43 (1999).
7. H. Avramopoulos, “Optical TDM devices and their applications,” in Optical Fiber Communication (OFC 2001),
Vol. 54 of OSA Trends in Optics and Photonics Series (Optical Society of America, Washington, D.C., 2001),
Tutorial paper.
8. M. N. Islam, “All-optical component tasks (originally proposed in SAMMI project),”
http://www.eecs.umich.edu/OSL/Islam/DODN-Router.pdf.
9. H. Soto, C. A. Díaz, J. Topomondzo, D. Erasme, L. Schares, and G. Guekos, “All-optical AND gate implementation
using cross-polarization modulation in a semiconductor optical amplifier,” IEEE Photon. Technol. Lett. 14,
498-500 (2002).
10. D. Nesset, M. C. Tatham, and D. Cotter, “High-bit rate operation of an all-optical AND gate by using FWM in an
SLA with degenerate input signals,” in Optical Fiber Communication (Optical Society of America, Washington,
D.C., 1995), Paper TuD2.
11. Y. Maeda and L. Occhi, “All-optical triode based on a tandem wavelength converter using reflective semiconductor
optical amplifier,” IEEE Photon. Technol. Lett. 15, 257-259 (2003).
12. X. L. Zhang, J. Q. Sun, D. M. Liu, and D. X. Huang, “A novel scheme for XGM wavelength conversion based
on single-port-coupled SOA,” Chin. Phys. 10, 124-127 (2001).
#3421 - 15.00 Received
output bit stream is 0100 as shown in Fig. 2(d). Because bits 0 and 1 in channel C correspond
to bits 1 and 0 in channel A, respectively, the truth table for this logic operation is as shown
in Table 1. From the truth table we can conclude that the all-optical logical AND gate could be
achieved with this scheme.
Table 1. Truth table for all-optical logical AND operation.
A C B Pout = A•B
1 0 1 1
1 0 0 0
0 1 1 0
0 1 0 0
In this scheme, single-port-coupled SOAs are employed to achieve good output performance.
The extinction ratio in channel C is critical for all-optical logical AND operation, and the large
power difference between the mark and space signal in channel C is helpful for achieving the
large gain difference in SOA2. As we know, extinction ratio degradation always exists in XGM
wavelength conversion with ordinary SOAs. However, owing to double-pass gain in the singleport-
coupled SOA and transmission loss in its rear facet, output extinction ratio performance
could be improved in XGM wavelength conversion with single-port-coupled SOAs [12], and
good logical AND output performance could be achieved with single-port-coupled SOAs. Theoretical
analysis results [12] showed that low rear facet reflectivity is helpful for improving
extinction ratio. Therefore, the rear facet reflectivity of the SOA is specially designed to be of
the order of 10−2. The SOAs are fabricated with InGaAsP/InP MQW materials and a vertical
cavity; the length of its active cavity is 400 mm, and the net gain for −10 dBm@1550-nm input
signal is 13 dB at 150-mA biased current.
Fig. 3. Optical spectra for input signals before SOAs: (a) before SOA1; (b) before SOA2.
3. Results and discussion
Figure 3(a) represents the spectrum of the input signal before SOA1, and Fig. 3(b) represents
the spectrum of the input signal before SOA2. The input cw signal wavelength is 1549.5 nm,
and the pump signal wavelength is 1542.6 nm. In SOA1, the signal power in the pump channel
is −1.4 dBm, and the signal power in the cw probe channel is −11.6 dBm. After wavelength
conversion and optical amplification, the signal power in channel C is 2.4 dBm, and the signal
power in channel B is −12.4 dBm. By use of the single-port-coupled SOA, the output extinction
ratio after the first-stage wavelength converter is larger than 10 dB.
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 364
#3421 - $15.00 US Received 2 December 2003; revised 29 December 2003; accepted 14 January 2004
Output
B
A
60µW
0
200 200ps
Fig. 4. Waveforms for different channels in this scheme for all-optical AND gate.
The signal waveforms for different channels are shown in Fig. 4, which are direct screen
captures from the CSA. Among these waveforms, two upper waveforms, labeled R2 and R3,
are recalled from the temporary memory in the CSA. For clear contrast they have been upshifted
from their original locations, and their power scales and zero levels are different from those of
the lowest waveform. The upper waveform represents the signal in channel A, whose bit stream
is 1100. The second waveform represents the signal in channel B, in which the time delay is
controlled to be (n400+100) ps, and the bit stream is 0110. The lowest waveform represents
the output signal from the TBF2 with the wavelength of 1542.6 nm, and the bit stream changes
to be 0100, which is precisely the logical AND operation result of the above two waveforms.
We may conclude that all-optical logical AND operation was achieved on the basis of XGM in
two cascaded single-port-coupled SOAs.
Fig. 5. All-optical logical AND output performance versus input signal power in channel C.
In experimental study, the signal power in channel C is found to be critical to output performance
of logical AND operation. If this signal power is not high enough, the signal in channel
C would be amplified to some extent, the amplified signal and the logical AND operation result
would be superposed together, and the output signal would be an incomplete logical AND operation
result. To quantify the logic operation output performance, a parameter R is introduced,
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 365
#3421 - $15.00 US Received 2 December 2003; revised 29 December 2003; accepted 14 January 2004
and R=P01/P11, where P11 is the output power for bit 1 in channel A and bit 1 in channel B, P01
is the output power for bit 0 in channel A and bit 1 in channel B. The smaller of the parameter
A is, the better output performance would be. As shown in Fig. 5, the parameter R versus the
signal power in channel C is presented, in which the signal power in channel B is −12 dBm,
and the bit stream in channel A is 1110. In Fig. 5, the output waveform is an incomplete logical
AND result, which corresponds to −0.4 dBm input signal power in channel C. It can be shown
that the ratio would decrease as the input signal power increases, and then the output performance
would be better and better. It should be noted the average output power would decrease
as the signal power increased. There is a trade-off between output performance and average
output power.
Although all-optical logic AND operation is achieved only at 10 Gbit/s because of experimental
conditions, but this scheme still has the ability to achieve higher-speed logic operation.
As we know, wavelength conversion based on XGM in SOAs has been demonstrated experimentally
at 100 Gbit/s [14] with 2-mm-long SOA. Operating with the same XGM principle,
all-optical logic operation based on this scheme also has the potential to be demonstrated at
100 Gbit/s. Large input signal power and long SOA biased at large current should be exploited
in order to shorten the effective carrier lifetime during operation at higher bit rates. In this case,
the temperature of the SOAs should be autoregulated to prevent thermal damage. Simultaneously,
this scheme has the same advantages as XGM wavelength conversion in SOAs [15], such
as simple implementation, easy of control, large wavelength span, and high power efficiency.
The logical AND operation could be polarization-insensitive if polarization-independent SOA
is used in this scheme.
4. Conclusions
An all-optical logical AND gate at 10 Gbit/s was demonstrated by use of cross-gain modulation
(XGM) in cascaded single-port-coupled SOAs. Owing to double-pass gain in the single-portcoupled
SOA and transmission loss in its rear facet, a high-output extinction ratio could be
achieved in wavelength conversion based on single-port-coupled SOAs, and thus good logical
AND operation output performance could be obtained. Output performance versus the input
signal power was investigated experimentally. Large-input signal power is helpful for achieving
improved output performance, and an incomplete logical AND operation result will be obtained
when the input signal power is not large enough. Operating with the same principle, the scheme
has characteristics identical with those of XGM wavelength conversion in SOAs.
Acknowledgments
Related research on SOA has been funded by the High Technology Development Project (863-
2002AA312160), the National Great Foundation Project (973-G2000036605), theWuhan Great
Special Project (2002100513013), and theWuhan Youth Chenguang Project (2003500201602).
(C) 2004 OSA 9 February 2004 / Vol. 12, No. 3 / OPTICS EXPRESS 366
#3421 - $15.00 US Received 2 December 2003; revised 29 December 2003; accepted 14 January 2004

rose22mary · 发表于 2004-2-16 02:10:00

能直接发E-mail给我吗，rose22mary@126.COM

lottie · 发表于 2004-2-17 01:20:00

可以的啊，你要哪一篇？

rose22mary · 发表于 2004-2-18 05:27:00

都要可以吗？我上班不能上网的，但是查字典看文件又很方便，谢谢你啊！

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