**1. Introduction**

146 Optical Communications Systems

Rohit, A., Albores-Mejia, A., Calabretta, N., Leijtens, X., Robbins, D.J., Smit, M.K. &

Saha, D., Rajagopalan, B. & Bernstein, G. (2003). The optical network control plane: state of

Shen, G. & Tucker, R.S. (2007.) Translucent Optical Networks: The Way Forward. *IEEE* 

Shuto, Y., Yanagi, S., Asakawa, S., Kobayashi, M. & Nagase, R. (2004). Fiber Fuse

*Electronics*, Vol. 40, No. 8, (August 2004), pp. (1113-1121), ISSN 0018-9197 Skorin-Kapov, N., Chen, J. & Wosinska, L. (2010). A New Approach to Optical Networks

Stanic, S. & Subramaniam, S. (2011). Fault Localization in All-Optical Networks with User

*Communications (ICC 2011)*, ISBN 978-1-61284-232-5, Kyoto, Japan, June 2011 Tzanakaki, A., Zacharopoulos, I. & Tomkos, I. (2004). Broadband Building Blocks [Optical

Vaez, M.M. & Lea, C.-T. (2000). Strictly Nonblocking Directional-Coupler-Based Switching

Way, I.W., Chen, D., Saifi, M.A., Andrejco, M.J., Yi-Yan, A., von Lehman, A.& Lin, C. (1991).

Witcher, K. (2005). Fiber Optics and its Security Vulnerabilities. SANS Institute, Available from: <http://www.sans.org/reading\_room/whitepapers/physcial/> Wu, T. & Somani, A.K. (2005). Cross-Talk Attack Monitoring and Localization in All-Optical

Zsigmond, S. (2011). External Report on Physical-Layer Attacks in Optical Networks.

No. 2, (February 2000), pp. (316-323), ISSN 1036-6692

ISBN 978-1-4577-0213-6

pp. (32-37), ISSN 8755-3996

pp.(1390-1401), ISSN 1036-6692

Education and Sports, Croatia, 2011

0163-6804

0013-5194

(August 2003), pp. (S29-S34), ISSN 0163-6804

Williams, K. (2011). Fast Remotely Reconfigurable Wavelength Selective Switch, *Proceedings of Optical Fiber Communication Conference* (OFC 2011), Los Angeles, USA,

the standards and deployment. *IEEE Communications Magazine*, Vol. 41, No. 8,

*Topics in Optical Communications*, Vol. 45, No. 2, (February 2007), pp. (48-54), ISSN

Phenomenon in Step-index Single-mode Optical Fibers. *IEEE Journal of Quantum* 

Security: Attack-Aware Routing and Wavelength Assignment. *IEEE/ACM Transactions on Networking*, Vol. 18, No. 3, (June 2010), pp. (750-760), ISSN 1063-6692

and Supervisory Lightpaths. *Proceedings of IEEE International Conference on* 

Networks]. *IEEE Circuits and Devices Magazine*, Vol. 20, No. 2, (March/April 2004),

Networks Under Crosstalk Constraint, *IEEE Transactions on Networking*, Vol. 48,

High Gain Limiting Erbium-Doped Fiber Amplifier With Over 30 dB Dynamic Range, *IEEE Electronic Letters*, Vol. 27, No. 3, (January 1991), pp. (211-213), ISSN

Networks, *IEEE/ACM Transactions on Networking*, Vol. 13, No. 6, (December 2005),

Technical report, project SAFE (http://www.fer.unizg.hr/tel/en/research/safe), supported by the Unity through Knowledge Fund (UKF), Ministry of Science, According to the explosive popularization of the internet, the infrastructure for a broadband optical network becomes very important. The most serious problem, however, for a broadband network is large energy consumption of the infrastructure. For example, over 1% of generated energy is consumed in Japan, and in the near future it will become over 10 %. An energy-saving measure, therefore, is energetically promoted in all of Japan including the government, industry and universities. Namely, an effort to save energy in homes is important, because about 50 million families are living in Japan. With the spread of "fibre to the home (FTTH)", in the future, several services such as high definition television (HDTV), will use the Internet, which will become a larger energy consumer in homes. Equipment for FTTH, which include electrical-switched devices, such as HUBs and Routers, are on standby for communication. If the energy consumption in every home decreased by 10%, it will bring about surprising energy savings.

An optically gated optical switch without any electric parts is composed of several lenses and a dye-dissolved high-boiling-point solvent, where the absorbance of the dye for the signal light is lower than 0.1 and for the gating light is over 3. The most versatile advantage of this system is easy selection of the wavelengths for both the gating light and the signal light. The signal light, which is transparent to the dye-solution, is refracted by a temporally formed microscopic thermal-lens (region with lower refractive index) that is locally heated around a focal point by the irradiation of the gating light (Tanaka et al., 2007; Tanaka et al., 2010, Ueno et al., 2003, Ueno et al., 2007, Tanaka et al., 2010).

Here, we have developed a local telecommunications system for FTTH using an optically gated optical switch composed of only optical parts. This system is suitable for a local-area network within a home. An optical-fibre line from a telephone office is directly connected to a 1x7 optically gated optical switch (Fig. 1). A terminal unit (optical interface; Opt-I/F) of the present system connected directly between a 1x7 optically gated optical switch (all-optical switch) and a PC, TV, IP-phone and so on, plays the role of a controller of 1x7 optically gated optical switch for the light-path switching of a PC, and so on. This unit sends a command to another terminal unit for negotiation among the terminal units using a 980 nm line. All terminal units connected to a 1x7 optically gated optical switch via a reflection-type optical star coupler in a 980 nm line can establish completely independently collision-free communication among the terminal units.

The Least Stand-By Power System Using a 1x7 All-Optical Switch 149

light. All of the collecting optical fibre is for the signal light (details of these fibres are explained in section 2.1.3). The 2nd is a dye cell made of quartz filled with a high-boilingpoint solvent and a dissolved dye for the absorbing gating light. The medium for operating an optical switch is perfectly dehumidified and deoxygenated, which brings long-life operation, even under light-irradiation (details of preparation are explained in section 2.1.2). The 3rd is a prism of a hexagonal truncated pyramid, located between a collecting lens for the dye-cell and a collimating lens for the collecting fibre. This prism brings a higher coupling efficiency to the collecting fibre. The 4th are lenses focusing both the signal light and the gating light from an incidence optical fibre to a dye-cell. Another two pairs of lenses collect signal light from the dye-cell, and focuses it to the collecting

Fig. 2. An external view of 1x7 optically-gated optical switch.

configurations under a gating light power of 20~35 mW.

The typical performance of the present 1x7 optically gated optical switch is summerized in Table 1. Both the insertion loss and the crosstalk are the mean value of the 7 exit ports.

**Parameters Specifications**  Wavelength 1310-1490 nm Gating light 980 nm Insertion loss 6.5 dB min. Crosstalk 34 dB min. Dimension 95×30×12mm Table 1. Typical performance of a 1x7 optically gated optical switch using different axis

optical fibre.

Fig. 1. Block diagram of the present system. The solid line is the optical fibre for data communication (wavelength of 1310-1550 nm), and the dashed line is the optical fibre for the control of a 1x7 all-optical switch (wavelength of 980 nm). The 1x7 optically gated optical switch (1x7 all-optical switch) is connected directly to the optical interface (Opt-I/F).
