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We propose and experimentally demonstrate a reconfigurable ultrawideband (UWB) pulse generation scheme by using a dual-drive Mach-Zehnder modulator (DDMZM). In the proposed method, two phase modulators of the DDMZM are respectively driven by properly designed electrical signals. By carefully setting the parameters of the two electrical signals and the bias voltage of the DDMZM, different UWB pulses can be achieved at the interference output of the DDMZM. A proof-of-concept experiment verifies the feasibility of the proposed method. Photonic generations of UWB monocycle, doublet, triplet, and quintuple pulses have been successfully demonstrated, with central frequencies of 4.69, 4.69, 5.47, and 6.25 GHz and fractional bandwidths of 150%, 133%, 186%, and 75%, respectively.

We propose and experimentally demonstrate a dynamic encryption method to realize physical layer security for orthogonal frequency division multiplexing passive optical network (OFDM-PON). In our scheme, encryption of the downstream signal is obtained by applying exclusive or (xor) operation between optical network units' (ONUs') downstream signals and received upstream signals at the optical line terminal side. The upstream signals are used as secure keys for corresponding ONUs. Then the encrypted downstream signals are sent to the ONU sides, where the downstream signal can be retrieved by applying xor operation again between the encrypted downstream signal and the stored upstream signal. Since each ONU cannot obtain the upstream signals of other ONUs, only the ONU itself can recover its downstream signal from the encrypted downstream signal. Moreover, the secure key is dynamically changing along with the upstream signal, significantly improving the security of the downstream signal for the OFDM-PON system. A 5-Gb/s 16-quadrature amplitude modulation OFDM signal with xor-based encryption has been successfully implemented over a 25-km standard single-mode fiber. Experimental results verify that the encryption scheme can effectively prevent eavesdropping by malicious users.

In this paper, we propose and demonstrate an all-optical second-order differentiator based on a two-stage self-coupled optical waveguide on a silicon-on-insulator platform. The transmission spectrum of the fabricated device has a parabola-like filtering notch with a 3-dB bandwidth of up to ~ 100 GHz and a depth of ~ 12 dB. Experiments are carried out for 10-, 20-, and 40-Gb/s optical time-domain multiplexing (OTDM) picosecond pulse trains, and the second-order differentiations are achieved using the fabricated device.

We experimentally demonstrate a push-pull optical nonreciprocal transmission (ONT) mechanism induced by thermo-optic effect in cascaded silicon microring resonators (MRRs). A nonreciprocal extinction ratio of up to 27 dB and an operation bandwidth larger than 0.15 nm are achieved in the proposed ONT system. The device can operate with a resonance mismatch between the two cascaded MRRs from 0.14 nm to 0.55 nm. The proposed ONT device could potentially find applications in optical diodes and bidirectional control of light in future on-chip all-optical information processing systems.