Power Budget Analysis OPTICAL INTERCONNECTION NETWORK FOR

OPTICAL PACKET SWITCHES 326 Ž . used to perform faster switching ; 100 ps in multiple wavelength levels instead of the SOA gates in the proposed OIN. To compensate for the high coupling loss caused by the EAM, higher-power EDFAs or EAMs integrated w x with semiconductor optical amplifiers will be necessary 59 . Here, the SOA-based OIN is considered because the SOA can provide high gain and Ž . fast switching ; 1 ns simultaneously.

11.4.6.2 Interconnection Complexity

As a representative interconnec- tion complexity, the interconnection between the electronic controller and the 256 = 256 OIN is evaluated. The interconnection complexity of the proposed 256 = 256 OIN is determined by the number of the SOA gates in the OOMs. The types of tunable filters and the number of wavelengths applied to the OIN are two dominant factors of the interconnection complex- ity, because they determine the number of SOA gates in the OOMs. Because the interconnection complexity with type-I and type-II tunable filters is the same, only type-II and type-III tunable filters are considered in this regard. Figure 11.40 shows the interconnection complexity for different wave- Ž . lengths W s 8, 16, 32, and 64 and different types of tunable filters, where X is the complexity introduced by the switching fabrics, Y is the complexity represented by the tunable filters, and X q Y gives the total interconnection complexity. Type-I and type-II tunable filters have the same interconnection complexity. For example, if W s 16, X s Y s 256 = 4 when using type-I -II, or -III tunable filters. As shown in Figure 11.40, the total interconnection complexity, X q Y, is equal to 256 = 8, and is independent of the wavelength number and the type of tunable filter used in the OIN.

11.4.7 Power Budget Analysis

Power loss in the OIN, which is due to splitting loss, depends on the number of wavelengths and the size of the switching fabric of each OOM. To compensate for power loss in the OIN, optical amplifiers, such as EDFAs Fig. 11.40 Interconnection complexity of the 256 = 256 OIN for different types of tunable filter and different wavelength numbers W. OPTICAL INTERCONNECTION NETWORK FOR TERABIT IP ROUTERS 327 and SOA gates, have to provide wide bandwidth to accommodate multiple wavelengths with uniform gain in the 1550-nm window. At each IOM, to avoid the problems introduced by direct modulation of lasers, such as large Ž . frequency chirp, an external modulator EM is used to obtain an optical Ž . on᎐off keying OOK signal. Figure 11.41 shows the optical signal path through the OIN with type-II tunable filters and W s 16. All the optical components are represented with their gains or losses. For simplicity of modeling and analysis, the OIN is assumed to be fully loaded and all the possible connections between the input᎐output pairs established. Second, optical signals are represented by their optical power corresponding to bit mark᎐space data signals. Third, frequency chirp due to the EM and dispersion effects of all the components are not taken into consideration since signals are transmitted only in the Fig. 11.41 Power budget of the 256 = 256 optical interconnection network with 16 Ž . Ž . wavelengths and type-II tunable filters: a before and b after power compensation by EDFA. OPTICAL PACKET SWITCHES 328 short-length fibers in the OIN. Finally, all the light reflections in the system are ignored and all the passive components are assumed to be polarization- insensitive. Ž . Figure 11.41 a shows that, without power compensation, the received power is only y30.5 dBm, much less than required sensitivity of about y20 Ž . y 12 dBm at the bit error rate BER of 10 for signals at 10 Gbitrs. To increase the received optical power, optical amplifiers are necessary to provide sufficient gain to compensate for the power loss in the OIN. In the proposed OIN, there are two kinds of optical amplifiers to perform the power compensation function. One is the SOA and the other is the EDFA. Ž . As shown in Figure 11,41 b , an EDFA with 10.5-dB gain at each IOM is used to amplify 16 wavelengths simultaneously, so that the sensitivity at the receiver is increased to y20 dBm. Note that the gain provided by the EDFA needs to be increased to 20 dB if the AWG, which is near the output link of type-II tunable filter, is replaced by a 16 = 1 combiner.

11.4.8 Crosstalk Analysis