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Results and Discussion
Switching time is an important parameter in designing of optical
switch and it depends on coupling
length, which in turn depends on physical parameters (waveguides
separation, structure of grating, gratingheight and RIs of film and
substrate). Parameters considered in simulation are RI of film (n
f=1.723) and
substrate (ns=1.711), waveguide spacing (g= 4 m), and grating
height (h = 2.5 m). For complete power
transfer from port 1 to port 4 (Fig. 2), switching time found
for waveguide grating structures is: rectangular,
0.77; triangular, 1.3; and trapezoidal, 0.235 ps (picoseconds).
Trapezoidal waveguide grating structureprovides less switching time
than other grating structures, and also much less than reported
technologies
(optical MEMS switches4,5
, thermal optical switches6,7
and PLZT electro optic switches8,9
).As waveguide spacing (varied between 3-7 m; step size, 0.25m)
is reduced, the switching time
reduces (Fig. 3a). Also, trapezoidal grating structure gives
lower switching time than other structures. While
looking into performance of switch as a function of grating
height, trapezoidal grating structure has fastest
switching speed (0.23 ps) for an optimized grating height of 2.5
m as compared to other gratings (Fig. 3b).Also, looking into
performance of switch with operating voltage, trapezoidal grating
provides lowest
switching time (0.2 ps) as compared to other gratings (Fig. 3c).
Simulation results show that trapezoidalgrating structure provide
faster switching taking into account all device parameters. So,
this structure was
considered for the design of wavelength independent EO
switch.
Looking into switching characteristics for 2x2 EO waveguide
switch (Fig. 4), crosstalk is found < -79
dB at bar state. With electrode voltage of 8.5 V, switching
state is in cross state (< -77dB). This switchexhibits
relatively very low crosstalk. Transmission power from input port
to output port as a function of RIchanges due to EO effect (Fig.
5). With zero index contrast, power is maximum in port 3, which is
bar state of
switch. As index contrast increases, there is a gradual transfer
in power from port 3 to port 4. When index
contrast is 0.0065, there is maximum power in port 4, which
represents cross state of switch. Thus this switch
exhibits a bar-state switching at zero voltage with zero RI
contrast.Switching characteristics of a trapezoidal waveguide
grating switch [RI of film layer (1.73) and
substrate (1.711); waveguide separation, 4 m; grating height,
2.5 m; and electrode thickness, 1 m] areshown (Fig. 6). When no
voltage is applied to electrodes, signal launched in port 1 comes
out of port 3, which
is bar state of the switch. As voltage applied to electrode is
increased, RI contrast between waveguides
increases, causing a gradual shift of power from port 1 to port
4, thus representing cross state of the switch at adrive voltage of
8.5 V. Driving voltage makes an index difference of 0.0065, which
makes power launched in
port 1 coupled to port 4 (coupling length, 81 m; and switching
time, 0.47 ps). As switching time is very less,
this switch is very much useful in protection application, so
that in the event of failure, network can berecovered soon very
quickly without any loss in data. Proposed PEOW grating switch has
very low switching
time and wavelength independency (Table 1) when compared with
other types of switches.
Conclusions
In proposed PEOW switch, coupled mode theory was used to study
switching characteristics with
device parameters (waveguide spacing, grating height, grating
structure and electrode thickness). This study
analyzed rectangular, triangular and trapezoidal waveguide
structures for the design of optical switch.
Trapezoidal grating structure was found with high speed
switching (0.47 ps) and also device length (81 m)makes device
compact. Proposed switch is found to be wavelength independent
beyond 1400 nm. Thus
trapezoidal grating is optimized structure for faster protection
in intelligent optical network.
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Fig. captionsFig.12x2 optical waveguide grating switchFig.
2Power transfer from port 1 to port 4 (n f= 1.723, ns=1.711)
Fig. 3Switching response of different grating profiles with: a)
waveguide spacing; b) grating height; and c) wavelengthFig.
4Switching characteristics as a function of drive voltage
Fig. 5Transmission power as a function of index contrastFig.
6Switching characteristics of a trapezoidal grating electro-optic
switch
![Annual Report G V Sethuraman, Enfab Industries Pvt. Ltd., Plot No. 138-A, IDA Mallapur, Hyderabad 500 076, Andhra Pradesh, [O] (040) 2782-4343, 2782-0010/2782-3073, [R] (040) 2733-4321/5363,](https://img.dokumen.tips/doc/110x75/5ab10c627f8b9a7e1d8be79f/annual-g-v-sethuraman-enfab-industries-pvt-ltd-plot-no-138-a-ida-mallapur.jpg)
