We experimentally demonstrate the ultrafast and high-repetition capabilities of a polarization-discriminating symmetric Mach-Zehnder (PD-SMZ) all-optical switch. This switch, as well as an original symmetric Mach-Zehnder (SMZ) all-optical switch, is based on a highly efficient but slowly relaxing band-filling effect that is resonantly excited in a passive InGaAsP bulk waveguide. By using a mechanism that cancels out the effect of the slow relaxation, ultrafast switching is attained. We achieve a switching time of 200 fs and demultiplexing of 1.5 Tbps, showing the applicability of the SMZ or PD-SMZ all-optical switches to optical demultiplexing of well over 1 Tbps for the first time. High-repetition capability, which is another important issue apart from the switching speed, is also verified by using control pulses at a repetition rate of 10.5 GHz. We also discuss the use of nonlinearity in a semiconductor optical amplifier to further reduce the control-pulse energy.

Research and development of a multi-degree colorless, directionless and contentionless reconfigurable optical add-drop multiplexer (CDC-ROADM) has recently been attracting a lot of attention. A large-scale transponder aggregator (TPA) is indispensable for providing high-capacity flexible connections to optical networks. In this paper, we report our study of the requirements for the TPA, which is a key technology for achieving flexible optical networks. To meet the requirements, we have developed an 848 TPA prototype based on Si photonics technology. This prototype was made with a few 88 Si optical switches and designed to be used with a commercial ROADM system. The 88 Si optical switches are made by integrating 152 Mach Zehnder (MZ) Thermo Optoelectronic (TO) 22 optical switch elements. A double gate structure is introduced to achieve the high extinction ratio (ER) required for optical communication. To the best of our knowledge, this is the world's first Si-TPA that can be used with a commercial ROADM system. By evaluating the basic optical characteristics utilizing real-time 100 Gbps digital coherent detection as one of today's practical technologies and a 4.4 THz spectral bandwidth 20 Tbps super-channel with digital coherent detection, as a promising future technology, we have confirmed that our prototype Si-TPA has the potential for practical use and future extensibility.

Symmetric Mach-Zehnder (SMZ) type all-optical swit-ches are discussed. The SMZ type all-optical switches feature the so-called differential phase modulation scheme to achieve a speed unrestricted by efficient, thus usually slow nonlinearities. In these switches, semiconductor optical amplifiers (SOAs) are often used to realize low optical power switching. We discussed SOAs from a view point of all-optical switch applications, rather than amplifier applications. Finally, all-optical signal processing experiments are discussed with the SMZ type all-optical switches. These include ultrafast demultiplexing of 336 Gb/s signal pulses and random operations at 42 Gb/s for all-optical logic operation and wavelength conversion.

Control scheme for accurately optimizing (and also automatically stabilizing) the interferometer phase bias of Symmetric-Mach-Zehnder (SMZ)-type ultrafast all-optical switches is proposed. In this control scheme, a weak cw light is used as a supervisory input light and its spectral power ratio at the switch output is used as a bipolar error signal. Our experimental result at 168-Gb/s 16:1 demultiplexing with a hybrid-integrated SMZ switch indicates the feasibility and the sensitivity of this control scheme.

Silicon photonic devices based on silicon photonic wire waveguides are especially attractive devices, since they can be ultra-compact and low-power consumption. In this paper, we demonstrated various devices fabricated on silicon photonic wire waveguides. They included optical directional couplers, reconfigurable optical add/drop multiplexers, 12, 14, 18 and 44 optical switches, ring resonators. The characteristics of these devices show that silicon photonic wire waveguides offer promising platforms in constructing compact and power-saving photonic devices and systems.

We experimentally demonstrate the ultrafast and high-repetition capabilities of a polarization-discriminating symmetric Mach-Zehnder (PD-SMZ) all-optical switch. This switch, as well as an original symmetric Mach-Zehnder (SMZ) all-optical switch, is based on a highly efficient but slowly relaxing band-filling effect that is resonantly excited in a passive InGaAsP bulk waveguide. By using a mechanism that cancels out the effect of the slow relaxation, ultrafast switching is attained. We achieve a switching time of 200 fs and demultiplexing of 1.5 Tbps, showing the applicability of the SMZ or PD-SMZ all-optical switches to optical demultiplexing of well over 1 Tbps for the first time. High-repetition capability, which is another important issue apart from the switching speed, is also verified by using control pulses at a repetition rate of 10.5 GHz. We also discuss the use of nonlinearity in a semiconductor optical amplifier to further reduce the control-pulse energy.

We propose a cyclic sleep control technique for backup resources in reconfigurable optical add/drop multiplexer (ROADM) systems to simultaneously achieve power savings and high-speed recovery from failures. Processes to check the reliability of backup resources, backup transponders and paths, are also provided in the control technique. The proposed technique uses sleep mode where backup transponders are powered down to minimize power for power savings. At least one of the backup transponders is always activated after self-checking using the loopback fiber connection in the ROADM and it becomes a shared backup for working transponders to enable high-speed recovery from failures. This activated backup transponder is powered down again after the next transponder is activated. These state transitions are cyclically applied to each backup transponder. This “cyclic” aspect of operation enables network operators to continuously monitor the reliability for all backup resources with the sleep mode. The activated backup transponders at both ends of the path are used in checking the reliability of backup paths. Therefore, all backup resources, both transponders and paths, can be regularly checked with the sleep mode to ensure data are stably forwarded. We estimated the power consumption with this technique under various conditions and found a trade-off between power reduction and the recovery capabilities from failures. We achieved more than 34% power saving of backup transponders maintaining the failure recovery time within 50ms in experiments. Furthermore, we confirmed the reliability of backup paths in experiments using backup transponders with the cyclic sleep control technique. These results indicated that the proposed control technique is promising in dramatically and reliably reducing the power consumption of backup resources.

A newly developed hybrid-integrated Symmetric Mach-Zehnder (HI-SMZ) all-optical switch is reported. For integration, we chose the Symmetric Mach-Zehnder (SMZ) structure rather than the Polarization-Discriminating Symmetric Mach-Zehnder (PD-SMZ) structure which is similar to SMZ but more often used in experiments using discrete optical components. We discuss advantages and disadvantages of SMZ and PD-SMZ to show that SMZ is more suitable for integration. We also discuss about the use of SOAs as nonlinear elements for all-optical switches. We conclude that, although the ultrafast switching capability of SMZ is limited by the gain compression of SOAs, the very low switching energy is more important for practical devices. We then describe the HI-SMZ all-optical switch. This integration scheme has advantages which include low loss, low dispersion silica waveguides for high speed operation and ease in large scale integration of many SMZs with other optical, electrical, and opto-electrical devices. We show that a very high dynamic extinction ratio is possible with HI-SMZ. We also examine HI-SMZ with 1 ps pulses to show its ultrafast capability. Finally, we describe a 168 to 10.5 Gbps error-free demultiplexing experiment which is to our best knowledge the fastest experiment with an integrated device.