**4. Conclusions**

SOAs saturates and the conversion process is less efficient, which reduces the output mean

**Figure 19.** Left—Input sequence "1110010010101100"; Right—Phase and power output, with SOA input current ISOA

We have presented a method to perform optical phase modulation, from an all-optical XOR gate configuration. We measure the influence of input CW power and SOAs bias current on the signal phase at the MZI-SOA output port. We verify that an increase in the SOA bias current produces higher values of the mean power and the phase span of the output signal, but SOAs gain saturation has an inverse result on the same output signal. Overall, the experimental results show the viability of the MZI-SOA as device capable of all-optical modulation and

Higher order all-optical modulation formats can be generated using the phase modulator setup of **Figures 15** and **16** as a building block. For example, all-optical OOK to quadrature phase shift keying (QPSK) converter can be constructed with nested amplitude to binary phase shift keying (BPSK) converter pairs [23]. When the overall phase difference between the two nested BPSK pairs is set to /2 rad, a QPSK signal is generated. Kang et al. [24] demonstrate

Furthermore, one may build a modulator for generating even higher order modulation formats, including quadrature amplitude modulation (QAM), following a similar method by which the amplitude to QPSK format converter is constructed [25]. Other methods of all-optical format conversion techniques using MZI-SOA are subject of further research in

the viability of this conversion scheme to generate a QPSK signal with 173 Gbps.

power and phase span [9].

182 Optical Interferometry

*3.1.2. Summary*

format conversion.

Ref. [26].

equal to 150 mA and input laser power PCW equal to 0 dBm.

**3.2. Other advanced format conversions techniques**

A MZI-SOA is a compact semiconductor device capable of performing many different alloptical modulations format conversion and generation functions. Its use has a building block for future all-optical networks can avoid the electronic bottleneck affecting opaque optical network nodes. It is estimated that 80% of the traffic flowing into a node is a pass-through traffic, with a destination located in another node of the network [27]. It is then particularly efficient to maintain that traffic flow in the optical domain, without optoelectronic conversion or packet processing. Transparent optical systems have the advantage of contributing to more energy-efficient networking without decreasing flexibility and agility. This clear and challenging objective is mandatory to cope with the traffic increase, while maintaining the cost and energy of the transported bit at an acceptable level.
