Recent Advances of Wide Band Magneto-Optical Modulators in Advanced High Speed Optical Communications Systems

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Volume 1, No.1, March – April 2012
International Journal of Advanced Trends in Computer Science and Engineering
Available Online at www.warse.ijatcse.current

Recent Advances of Wide Band Magneto-Optical Modulators In
Advanced High Speed Optical Communication Systems
Ahmed Nabih Zaki Rashed
Electronics and Electrical Communications Engineering Department
Faculty of Electronic Engineering, Menouf 32951, Menoufia University, EGYPT
ahmed_733@yahoo.com

ABSTRACT polarization sensitive beam deflectors, switches, and
isolators. In spite of these benefits, MO device technology is
The technology involves a new type of compact device still in its infancy and has not yet been fully explored for
based on magneto-optics in a fiber micro modulator. This integrated high-speed optical technology. Magneto photonic
type of modulator allows the user to inter manipulate and devices to date have relied on the propagation of light waves
control the propagation of the incoming light. The operation through the MO material. As the light beam travels through
mechanism uses external magnetic field to manipulate Fe the MO medium, its plane of polarization is rotated
micro particle in order to cause modulation of an optical according to the Faraday effect [5], resulting in a
signal that propagates along an optical waveguide. This polarization modulation. However, the transmission
paper has presented Yttrium Iron Garnet (YIG) and lithium arrangement presents difficulties associated with the MO
niobate (LiNbO3) which are examined for use as a wideband material such as optical absorption of the light beam as it
magneto-optic modulator. A wideband YIG modulator has propagates through the interaction region, as well as inherent
recently been developed which represents a great birefringence. To observe a maximum MO effect, it is
improvement over other magneto -optic modulators. desirable to have a MO material with large Faraday rotation,
negligible birefringence, and very little absorption. Of the
Keywords: Magneto-optic Modulation, Faraday Rotation Effect, various MO materials available, bismuth-substituted yttrium
LiNbO 3, YIG, Ultra Fast Magnetic Field. iron garnet (Bi-YIG) is often chosen for the backbone of a
variety of MO devices as it has a very large MO interaction
1. INTRODUCTION [6].

Over the last several years, the demand for high bandwidth Optical modulators have become indispensible in many
networking has dramatically increased, encouraging the applications or optical instruments. Light interacts with
continued development of high-speed electrical and optical matters in various macroscopic ways. The most commonly
devices. In particular, the realization of high bandwidth, low known phenomenon include Electro-Optical (EO) effect,
power, efficient modulators plays a fundamental role in the Acousto-Optical (AO) effect, and Magneto-Optical (MO)
improvement of integrated optical systems and networks. effect. AO modulators and EO modulators have already
Contemporary optical modulation devices rely primarily on found many applications, and state-of-the-art modulators are
Electro-Optic (EO) interaction in nonlinear materials. By already commercially available. However, AO modulator
exploiting the Pockels effect, the electric field associated inherently suffers from slow modulation speed. Although
with a high-speed electrical signal is employed to modulate EO modulator is capable of fast modulation [7], it requires a
an optical beam. However, in recent years, there has been an relatively high accuracy on the alignment in free-space
emergence of a new class of photonic devices based on the applications. MO effect, on the other hand, finds its
magneto-optic (MO) effect [1][2]. These devices utilize the application only as an optical isolator so far. Although there
Faraday effect, in which the magnetic field associated with have been many researches on MO modulators in integrated
an electrical signal modulates an optical beam. Such optics [8], the possibility of a free-space MO modulator has
magneto-photonic devices offer high bandwidth modulation not been widely investigated. The MO modulator can not
and switching capabilities comparable to those based on the only work as an intensity modulator when combined with
EO effect. The recent interest in such technology is two linear polarizer, but can also work as a polarization
stimulated by current advances in the growth of a variety of rotator alone.
MO materials, namely rare-earth iron garnets [3]. High-
quality magnetic garnet films are readily available in a In the present study, magneto-optic materials have unique
variety of forms and can be grown by epitaxial or sputter physical properties that offer the opportunity of constructing
methods for particular applications. Such films have a large devices with many special functions not possible from other
Faraday rotation, low absorption in the near infrared, and a photonic devices. The most significant of these properties
low saturation magnetization. Furthermore, their optical are that the linear magneto-optic effect can produce circular
properties can be easily manipulated by doping, such as the birefringence and that, unlike other optical effects in
substitution of bismuth in yttrium iron garnets [4]. Research dielectric media, it is nonreciprocal. All practical magneto-
into the application of rare-earth iron garnets has resulted in optic devices exploit one or both of these two properties.
the development of a variety of unique MO photonic Important applications of these devices include polarization
devices, such as resonant/non resonant modulators,

© 2012, IJATCSE All Rights Reserved 1
Ahmed Nabih Zaki Rashed, International Journal of Advanced Trends in Computer Science and Engineering, 1 (1), March – April, 1-8

control, optical isolation, optical modulation, and magneto- Where V is the Verdet constant for the material. The Verdet
optic recording. The basic principles of magneto-optic constant is both temperature and wavelength dependent. The
modulator effects are considered in this study. Faraday Effect is similar to optical activity. The difference is
that optical activity doesn’t require an externally applied
2.MAGNETO-OPTICAL MODULATOR SCHEMATIC magnetic field to rotate the light polarization and it only
VIEW depends on the traveling length and material concentration.
The modulation depth, Mp can be expressed in terms of
As the internet and modern communications becomes pulse duration τ in psec, and angle of rotation θ in degree, by
increasingly prevalent across the globe, all-optic networks. using MATLAB curve fitting program as the following
In recent years, for the sake of satisfying high speed formula [12]:
transmission and exchange of optical-message through fiber-
optic networks, optical switch has been significantly M p  0.1021  0.0765 x105 (  )  0.0032 x108   2 (2)
improved as an important element for optical
communication by continuous widely research [9].
The transmittance of MO modulator Tm, can be expressed as
follows:
Tm  cos 2 0.5     (3)

The signal to noise ratio (SNR) of MO modulator can be
expressed as the following formula [13]:
2  P0 r 
SNR  10 log , (4)
q BWe
Figure. 1: Basic Construction of MO Modulator under study
Where r is the reflection coefficient, BWe is the electrical
As shown in Figure 1, the proposed structure of MO bandwidth, P0 is the laser power, q is the electron charge,
modulator based on a microwave micro strip line with a and  is the its modulator responsivity. The bit error rate
polarization sensitive MO active medium and fiber optic (BER) essentially specifies the average probability of
continuous wave (CW) light delivery. As the requirement incorrect bit identification. In general. The higher the
from the optical communication technique, it should be received SNR, the lower the BER probability will be. The
characterized as low crosstalk, low insert loss, short bit error rate (BER) is related to the signal to noise ratio
switching time and low polarization sensitivity together with (SNR) as follows [12] [13]:
special requirement on extinction ratio, switch scale and   SNR  
dimension. As the factors that will affect the optical switch BER  0.5 1  erf   , (5)
  2 2 
parameters, it consists of the quality of separate units   
technical index (transmissivity, rotation angle etc.) and also
the quality of units final assembly and adjusting1. So far, a Moreover the refractive index of the LiNbO3, and YIG are
variety of optical switches have been developed. In cast under the Sellemier equation as the following [14] [15]:
comparison to the various other optical switches, the
magneto-optic switch based on Faraday rotation effect for B3  B4M B B M
light consists of special optical route including a type of n2  B1  B2M   7 8  B102
2  (B5  B6M)2 2  B92
high-quality magneto-optic material YIG crystal, a novel
switch of generating pico second-order electrical pulses and (6)
Faraday rotator configuration with ultrafast magnetic field. It
is featured as low insertion loss, low crosstalk, high The set of parameters is dimensionally adjusted for LiNbO3
switching speed and small bulky size. Using the polarization as: B1Li=5.35583, B2Li=4.629x10-7, B3Li=0.100473,
and Faraday Effect of magneto-optic crystal, the magneto-
-8
B4Li=3.862x10 , B5Li=0.20692, B6Li=-0.89x10-8, B7Li=100,
optic switch can hold the function of all-optical switching, B8Li=2.657x10-5, B9Li=11.34927, B10Li=0.015334, and M=(T-
which is needed in all-optical communication networks [10]. T0)(T+570.82). While the set of parameters is dimensionally
adjusted for YIG as: B1YIG=0.00987, B2YIG=1.43567x10-11,
3. THEORETICAL MODEL ANALYSIS B3YIG=0.10765x10-3, B4YIG=0.00532x10-8, B5YIG=0.0541,
B6YIG=10.4329x10-9, B7YIG=1234, B8YIG=0.05437x10-7,
When a transparent material is placed in a magnetic field B9YIG=14927, B10YIG=0.00384, and M=(T-T0)(T+590.54).
and linearly polarized light is passed through it along the Thus the previous equation can be simplified as the
direction of the magnetic field, the emerging light is found to following formula:
remain linearly polarized, but with a net rotation θ in degree, B34 B78
n2  B12    B102 (7)
of the plane of polarization that is proportional to both the 2  B 2 2  B 2
56 9
thickness d in mm, of the sample and the strength of the
magnetic field B in Tesla, along traveling direction, Where B12=B1+(B2M), B34=B3+(B4M); B56=B5+(B6M), and
according to the empirical relation [11]: B78=B7+(B8M). In the general case, if the device operation
efficiency, η  1, the inductance L and internal electrical
180 B V d
 , Degree (1) resistance Re of MO modulator, we have [16]:


© 2012, IJATCSE All Rights Reserved 2
Ahmed Nabih Zaki Rashed, International Journal of Advanced Trends in Computer Science and Engineering, 1 (1), March – April, 1-8

 2
L (8) v) As shown in Figs. (11, 12) have assured that
c 2 Lm  0 n 6 modulator inductance and resistance decrease with
increasing MO modulator length for both materials
  based MO modulator devices. As well as we have
Re  (9) observed that YIG MO modulator has presented
c Lm  0 n 6
lower resistance and inductance compared to LiNbO3
MO modulator at the same operating conditions.
Where Lm is the modulator length, c is speed of light, μ0 is
the free space permeability, Δλ is the spectral linewidth of Table 1: Proposed operating parameters for magneto-optical
the laser diode, and n is the refractive index of the selected modulators
material based MO modulator.
Parameter Definition Value and unit
4. SIMULATION RESULTS AND PERFORMANCE T=T0 Ambient 300 K
ANALYSIS temperature=room
temperature
τ Pulse duration 100 psec
We have deeply investigated the recent advances of wide
d Modulator 5 mm —25 mm
band magneto optical modulators in advanced high speed thickness
optical communication systems over wide range of the B Magnetic field 0.1 web/mm2—1
affecting operating parameters as shown in Table 1. intensity web/mm2
 Operating signal 1.3 μm
Based on the model equations analysis of MO modulator, wavelength
assumed set of the operating parameters, and the set of the Verdet constant 4.54x10-6 rad/A
V
series of the Figs. (2-12), the following facts are assured: for LiNbO3
Verdet constant 5.65x10-6 rad/A
i) Figs. (2-4) have assured that angle of rotation for YIG
q Electron charge 1.6x10-19C
increases with increasing MO modulator thickness
BWe Electrical 1 MHz
and applied magnetic field intensity for both materials bandwidth
based MO modulator devices. We have indicated that P0 Laser power 1 mWatt
YIG MO modulator has presented higher angle of  Modulator 0.4 A/Watt
rotation than LiNbO3 MO modulator at the same responsivity
operating conditions. r Reflection 0.55 at λ=1.3 μm
ii) Figs. (5-7) have demonstrated that modulation depth coefficient
increases with increasing MO modulator thickness Δλ Spectral linewidth 0.1 nm
and applied magnetic field intensity for both materials of optical source
based MO modulator devices. As well as we have
observed that YIG MO modulator has presented c Speed of light 3x108 m/sec
higher modulation depth compared to LiNbO3 MO Lm Modulator length 50 mm —100 mm
modulator at the same operating conditions. μ0 Free space 4πx10-7 H/m
iii) As shown in Fig. 8 has indicated that modulator
permeability
transmittance increases with increasing MO
modulator thickness and applied magnetic field η Device operation 0.9
intensity for both materials based MO modulator efficiency
devices. We have indicated that YIG MO modulator
has presented higher transmittance than LiNbO3 MO
modulator under the same considerations.
iv) Figs. (9, 10) have demonstrated that SNR increases
and BER decreases with increasing MO modulator
thickness and applied magnetic field intensity for both
materials based MO modulator devices. As well as we
have observed that YIG MO modulator has presented
higher SNR and lower BER compared to LiNbO3 MO
modulator at the same operating conditions.

© 2012, IJATCSE All Rights Reserved 3
Ahmed Nabih Zaki Rashed, International Journal of Advanced Trends in Computer Science and Engineering, 1 (1), March – April, 1-8

© 2012, IJATCSE All Rights Reserved 4
Ahmed Nabih Zaki Rashed, International Journal of Advanced Trends in Computer Science and Engineering, 1 (1), March – April, 1-8

© 2012, IJATCSE All Rights Reserved 5
Ahmed Nabih Zaki Rashed, International Journal of Advanced Trends in Computer Science and Engineering, 1 (1), March – April, 1-8

© 2012, IJATCSE All Rights Reserved 6
Ahmed Nabih Zaki Rashed, International Journal of Advanced Trends in Computer Science and Engineering, 1 (1), March – April, 1-8

REFERENCES
5. CONCLUSION
1. Abd El-Naser A. Mohammed, Ahmed Nabih Zaki
The Faraday effect or Faraday rotation is a magneto-optical Rashed, and Mohamoud M. A. Eid. Rapid Progress of
phenomenon, or an interaction between light and a magnetic A Thermal Arrayed Waveguide Grating Module for
field. The rotation of the plane of polarization is proportional Dense Wavelength Division Multiplexing
to the intensity of the component of the magnetic field in the Applications, Advanced Science Letters, Vol. 5, No. 1,
direction of the beam of light. It is observed that the pp. 56-63, Jan. 2012.
increased applied magnetic field intensity and MO thickness, 2. S. E. Irvine and A. Y. Elezzabi. Modeling of High
resulting in the increased angle of rotation, modulation Speed MO Beam Deflection, IEEE J. Quantum
depth, transmittance, signal to noise ratio, and the decreased Electron., Vol. 38, No. 2, pp. 1428–1435, Oct. 2002.
bit error rate for both materials based MO modulators under 3. D. Young and C. S. Tsai, “GHz Bandwidth Magneto
the same considerations. It is theoretically found that YIG Optic Interaction in Yttrium Iron Garnet Gadolinium
based MO modulator has presented the highest angle of Gallium Garnet Waveguide Using Magnetostatic
rotation, modulation depth, transmittance, and signal to Forward Volume Waves,” Appl. Phys. Lett., Vol. 53,
noise ratio, and the lowest bit error rate, inductance and No. 3, pp. 1696–1698, 1988.
resistance circuit values under the same operating 4. Abd El-Naser A. Mohammed, Gaber E. S. M. El-
conditions. Therefore this made YIG based MO modulator is Abyad, Abd El-Fattah A. Saad, and Ahmed Nabih Zaki
the best candidates selected materials for wide bandwidth Rashed. High Transmission Bit Rate of A thermal
and high speed applications in advanced optical Arrayed Waveguide Grating (AWG) Module in
communication systems. Passive Optical Networks, IJCSIS International
Journal of Computer Science and Information Security,
Vol. 1, No. 1, pp. 13-22, May 2009.

© 2012, IJATCSE All Rights Reserved 7
Ahmed Nabih Zaki Rashed, International Journal of Advanced Trends in Computer Science and Engineering, 1 (1), March – April, 1-8

5. H. Dötsch, P. Hertel, B. Lührmann, S. Sure, H. P. 13. Abd El-Naser A. Mohammed, Ahmed Nabih Zaki
Winkler, and M. Ye. Applications of Magnetic Rashed, and Mohammed S. F. Tabour.
Garnet Films in Integrated Optics, IEEE Trans. Transmission Characteristics of Radio over
Magn., Vol. 28, No. 3, pp. 2979–2984, Sept. 1992. Fiber (ROF) MillimeterWave Systems in Local
6. S. E. Irvine and A. Y. Elezzabi. A miniature Area Optical Communication Networks,
Broadband Bismuth Substituted Yttrium Iron International Journal of Advanced Networks and
arnet Magneto Optic Modulator, J. Phys. D, Vol. Applications, Vol. 2, No. 6, pp. 876-886, May/June
36, No. 3, pp. 2218–2221, 2003. 2011.
7. Prabhakar and D. D. Stancil. Wideband Optical 14. M. Caldwell and E. Yeatman. Surface Plasmon
Modulation Via the Magneto Optic Interaction Spatial Light Modulators Based On Liquid
in A bismuth-Luetriu Iron Garnet Film, Appl. Crystal, Appl. Opt., vol. 31, pp. 3880–3891, 1992.
Phys. Lett., Vol. 71, No. 2, pp. 151–153, 1997. 15. Abd El-Naser A. Mohammed, Abd El-Fattah A.
8. S. Tsai. Integrated Acousto Optic and Magneto Saad, and Ahmed Nabih Zaki Rashed. Estimated
Optic Devices for Optical Information Optimization Parameters of Arrayed Waveguide
Processing, Proceedings of IEEE, Vol. 84, No. 3, Grating (AWG) for C-Band Applications,
pp. 853–869, June 1996. International Journal of Physical Sciences, Vol. 4,
9. F. Zhou, H. Lu, Z. Cao, and Q. Shen. Electro No. 4, pp. 149-155, April 2009.
Optic Polymer Light Modulator Based on 16. Abd El-Naser A. Mohammed, Abd El-Fattah A.
Attenuated Total Reflection, Proceedings of Saad, and Ahmed Nabih Zaki Rashed. Thermal
SPIE, Vol. 49, No. 5, pp. 395–398, 2002. Sensitivity Coefficients of the Fabrication
10. J. Bremer, V. Vaicikauskas, F. Hansteen, and O. Materials Based A thermal Arrayed Waveguide
Hundrei. Influence of Surface Plasmons on the Grating (AWG) in Wide Area Dense
Faraday Effect in Bismuth Ssubstituted Yttrium Wavelength Division Multiplexing Optical
Iron Garnet Films, J. Appl. Phys., Vol. 89, No. 1, Networks, International Journal of Engineering and
pp. 6177–6182, 2001. Technology (IJET), Vol. 1, No. 2, pp. 131-139,
11. Abd El-Naser A. Mohammed, Abd El-Fattah A. June 2009.
Saad, and Ahmed Nabih Zaki Rashed. Matrices of 17. Ahmed Nabih Zaki Rashed. Ultra High Speed
the Thermal and Spectral Variations for the LiNbO3 and Polymer Electrooptic Modulators in
fabrication Materials Based Arrayed Waveguide Lightwave Optical Access Communication
Grating Devices, International Journal of Physical Networks, International Journal of Advanced
Sciences, Vol. 4, No. 4, pp. 205-211, April 2009. Science and Technology, Vol. 35, pp. 41-60, Oct.
12. Abd El-Naser A. Mohammed, Mohamed A. 2011.
metawe’e, Ahmed Nabih Zaki Rashed, and Amina
E. M. El-Nabawy. Unguided Nonlinear Optical
Laser Pulses Propagate in Waters With Soliton
Transmission Technique, International Journal of
Multidisciplinary Sciences and Engineering
(IJMSE), Vol. 2, No. 1, pp. 1-10, March 2011.