Device design for unitraveling-carrier photodiodes (UTC-PDs) and their derivative structures is reconsidered from the point of view of terahertz (THz) applications. A key design procedure for maximizing their bandwidth is optimization by incorporating hybrid absorbers. The effect of quasi-field in p-type absorber is carefully examined. It has been shown that the initial velocity transient must be taken into account to evaluate the effective average velocity. Photomixers integrating a hybrid-absorber UTC-PD and a bow-tie antenna were fabricated and characterized. THz-wave generation by the photomixers in a frequency range of up to around 2.5 THz was confirmed. The observed THz-wave output exhibits significant changes with bias voltage, where the decrease in the output with increasing negative bias voltage is more pronounced at higher frequencies. This output behavior is due to the change in electron velocity in the diode depletion layer associated with the overshoot effect. From the dependence of the output power on frequency, effective electron velocity is found to be as high as 6 × 10 7 cm/s at optimum bias voltage of −0.4 V. Index Terms-Photodiode (PD), uni-traveling-carrier photodiode (UTC-PD), transient electron velocity, velocity overshoot, terahertz (THz), photomixer, antenna integrated photomixer.1077-260X

Elastic Optical Networking (EON) is a solution that promises to improve infrastructure utilisation by implementing flexible spectrum allocation with small spectrum slots instead of the rigid 50-GHz fixed grid of current DWDM deployments. This new EON flexible grid supports Bandwidth Variable Transponders (BVT) that can tune their bit rate and bandwidth dynamically with a trade off between reach and capacity. However, when BVTs need to transmit at low bit rates, part of their capacity is wasted. Therefore, the Sliceable Bandwidth Variable Transponder (SBVT) has been proposed, which can provide even higher levels of elasticity and efficiency to the network. SBVTs enable transmitting from one point to multiple destinations, changing the traffic rate to each destination and the number of destinations on demand. The aim of this work is to identify the target cost of 400 Gb/s and 1 Tb/s SBVTs to reduce, by at least 30%, transponder costs in a core network scenario. This target cost is calculated in relation to estimations for non-sliceable transponders of 400 Gb/s and 1 Tb/s. In light of our results, cost savings of 30% are feasible for 1 Tb/s transponders in the next nine years with a higher cost than non-sliceable transponders. Savings of 30% for 400 Gb/s case are possible in the short-term before 1 Tb/s SBVTs can appear in the market. Feasibility of such savings with a target cost higher than current non-sliceable transponder shows that SBVT can be a reality.

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We describe experimental demonstration of spectrum-sliced elastic optical path network (SLICE) architecture. We employ optical orthogonal frequency-division multiplexing (OFDM) modulation format and bandwidth-variable optical cross-connects (OXC) to generate, transmit and receive optical paths with bandwidths of up to 1 Tb/s. We experimentally demonstrate elastic optical path setup and spectrally-efficient transmission of multiple channels with bit rates ranging from 40 to 140 Gb/s between six nodes of a mesh network. We show dynamic bandwidth scalability for optical paths with bit rates of 40 to 440 Gb/s. Moreover, we demonstrate multihop transmission of a 1 Tb/s optical path over 400 km of standard single-mode fiber (SMF). Finally, we investigate the filtering properties and the required guard band width for spectrally-efficient allocation of optical paths in SLICE.

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