**7. References**


ensure in this case the BER value of 10-9. From the measurement results it follows that the 25 GHz channel interval ensures a good signal quality and that the signal eye-pattern does not

At 10 Gbit/s HDWDM transmission the channel interval should be 37.5 GHz to ensure the signal quality with the BER value of 10-9, which fits well the previous simulation results.

It is established that the operators of telecommunication networks, when creating the HDWDM communication systems, raise the total transmission speed step-by-step in response to the increased request for the data volume. As a result, a mixed HDWDM system is formed, with different transmission speeds (2.5 Gbit/s or 10 Gbit/s), coding formats (NRZ, RZ or Duobinary) and frequency intervals (12.5 GHz, 25 GHz, 50 GHz, 100 GHz). Therefore, in order to ensure stabile functioning (i.e. BER < 10-9 for each signal) of a mixed HDWDM system the channel interval should exceed 25 GHz at a 2.5 Gbit/s transmission speed per channel. In turn, for stabile operation of a mixed 10 Gbit/s WDM system the

The Duobinary technique for signal coding ensures a better protection of the transmitted signals against Kerr effects as compared with the RZ coding. This allows a highly compact NRZ-Duobinary-NRZ system to be formed with the 12.5 GHz frequency interval and 2.5 Gbit/s transmission speed per channel. In turn, in the case of a 10 Gbit/s transmission speed

Abbou, F., Chuah, T., Hiew, C. and Abid, A, (2008), Comparison of RZ-OOK and RZ-DPSK

Belai, O. V., Shapiro, D. A. and Shapiro, E. G., (2006), Optimisation of a High-Bit-Rate

Bhamber, R., Turitsyn, K., Mezentsev, V., (2007), Effect of carrier reshaping and narrow

Bierlaire, M., Bolduc, D. and McFadden, D., (2007), Characteristics of generalized extreme

Binh, Le Nguyen, (2008), Photonic Signal Processing: Techniques and Applications, CRC

Bobrovs, V., Ivanovs, G., (2008), Comparison of different modulation formats and their

Bobrovs, V., Ivanovs, Ģ., (2009) Investigation of Minimal Channel Spacing in HDWDM

Binh, Le Nguyen, (2009), *Digital Optical Communications,* CRC Press, Boca Raton.

Systems, *Electronics and Electrical Engineering*, Vol.4(92), pp. 53-56.

Agrawal, G.P. (2001), *Nonlinear Fiber Optics,* 3rd edition, Academic Press, California.

in Dense OTDM-WDM Systems Using Q Factor Models, *Journal of Russian Laser* 

Optical Communication Link with a Non ideal Quasi-Rectangular Filter. *Quantum* 

MUX-DEMUX filtering in 0.8 bit/s/Hz WDM RZ-DPSK transmission, Optical

compatibility with WDM transmission system, *Latvian Journal of Physics and* 

overlap with the mask.

**7. References** 

frequency interval should be raised to 50 GHz.

*Research*, Vol.29, pp. 133-141.

*Electronics*. Vol.36(9), pp. 879-882.

value distributions. *Technical report.*

*Technical Sciences*, Vol.2, pp. 6-21.

Press, Boca Raton.

per channel it is possible to use an 18.75 GHz frequency interval.

Azadeh, M. (2009), *Fiber Optics Engineering.* Springer, New York.

Quantum Electronics, Vol.39. pp. 687-692.


**9** 

*Iran* 

Kiazand Fasihi *Golestan University* 

**Design and Modeling of WDM Integrated** 

Recently, photonic crystals (PCs) have attracted great interests due to their potential ability of controlling light propagation with the existence of photonic bandgap (PBG), and the possibilities of implementing compact nanophotonic integrated circuits. Some of the most successful structures are based on planar PCs. In such structures, the optical field is confined, horizontally, by a PBG provided by the PC and, vertically, by total internal reflection due to refractive index differences. Various PC components, such as, waveguides, bends, Y splitters, directional couplers, low crosstalk intersections and all-optical switches have already been realized. These basic building blocks can be combined to realize complete circuits with various optical functions within an extremely small area. One of the most important fields for ultra-dense integrated circuits is optical communications. A key component in modern optical communications systems is a wavelength division multiplexer (WDM). This component is needed to divide and combine different wavelength channels each carrying an optical data signal. Traditionally, WDM components are realized using thin-film filters, fiber Bragg gratings (FBG), or arrayed waveguide gratings. However, such devices are not convenient for ultra-dense integration. Various concepts for realizing a WDM component utilizing the extraordinary properties of PCs have recently been proposed. These ideas include optical micro-cavities, multimode self-imaging waveguides, and superprisms, but we focus on the components which are based on the interaction of the

The chapter is organized as follows: In Section 2, the hybrid waveguides are introduced and analyzed using coupled-mode theory (CMT) and the finite-difference time-domain (FDTD) methods. First, the resonance frequencies and the field distribution of the resonance modes have been analyzed, then the hybrid waveguides are introduced and analyzed using FDTD and CMT methods, and the conditions which lead to quasi-flat and Lorentzian transmission spectrum will be presented. Finally, the Fundamental approach to low cross-talk and wideband intersections design which is based on the orthogonal hybrid waveguides is presented and analyzed using CMT and FDTD methods. It will be shown that when the phase-shift of the electromagnetic waves traveling between two adjacent PC coupled

be achieved. In addition it will be shown that simultaneous crossing of ultra-short pulses is

the best performance for the intersection can

**1. Introduction** 

PC micro-cavities with the waveguides.

cavities is approximately equal to ( 1/2) , *k*

**Devices Based on Photonic Crystals** 

Venghaus, H., (2006), *Wavelength Filters in Fibre Optics,* Springer, Berlin.

Voges, E. and Peteramann, K., (2002), *Optische Kommunikationstechnik - Handbuch für Wissenschaft un Industrie* Springer-Verlag, Berlin.
