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All-optical modulation has been regarded as an effective method to solve the electrical bandwidth bottleneck problems existing in the current telecommunication network. By taking advantage of high photothermal conversion of two-dimensional (2D) MXene, a high-performance all-optical modulator is demonstrated. The polarization-dependent all-optical modulator exhibits a broadband intensity modulation behavior with a modulation depth of 15 dB. The response time of such all-optical modulator is approximately ten times than that of fiber-type MZI/MI-assisted all-optical modulator based on the thermal-optic effect. Besides, an all-optical information loading with a bit rate of 400 bit s−1 is successfully achieved. Therefore, it is anticipated that the all-optical modulator with the advanced optical structures and excellent 2D materials has extraordinary potentials for future optical information processing.

Although thulium-doped fiber lasers operating at 2 ?m have been intensively investigated, lasers with high repetition rate (up to several tens of gigahertz) and tunable output characteristics are difficult to achieve at this band. In this paper, an all-optical actively mode-locked fiber laser is proposed for this purpose. By employing a section of specially-designed highly nonlinear group-velocity-matched tellurite photonic crystal fiber as the mode-locker, the proposed thulium-doped fiber laser can easily produce stable pulses with tunable pulse width and repetition rate up to 40 GHz. Moreover, through investigating the pulse dynamics in the cavity, a transfer-limited soliton pulse is successfully achieved. The proposed laser can find application in future optical fiber communication systems at 2 ?m.

On the basis of the phase transition between an insulator and a metal in vanadium dioxide (VO2), we propose ultracompact and broadband lower- and higher-order mode pass filters (LOMPF and HOMPF, respectively) for a multimode silicon waveguide supporting two transverse electric (TE) modes. Good performance of mode filtering can be maintained over a wavelength range of 100 nm. In addition, the two filters can be cascaded to achieve reconfigurable operation for both TE00 and TE01 modes, including TE00-pass, TE01-pass, all-pass, and all-block. The reconfigurable response of the proposed on-chip mode filter is helpful for flexible mode-division multiplexing applications.

We present the fabrication of fiber Bragg gratings (FBGs) in a trench-assisted heterogeneous multicore fiber (MCF). Two obviously different Bragg reflection peaks are obtained due to the slight difference of refractive indices between the center core and the outer cores. To investigate the reflections of the two FBGs simultaneously, only a segment of multimode fiber is inserted between the lead-in single mode fiber and the MCF. The experimental results confirm that the curvature sensitivity of the FBG in the outer core is a sinusoidal function of the bending orientation angle. The maximum linear curvature sensitivity is about 0.128 nm/m?1. The cross sensitivity to temperature or externally applied axial strain can be eliminated by discriminating the different responses of FBGs inscribed in outer cores and the center core. Thus this MCF with FBGs can be utilized as a directional bending sensor. Moreover, the proposed sensor offers several advantages, such as low cost and flexibility in fabrication.

A center frequency-tunable multi-tap bandpass microwave photonic filter (MPF) is proposed and experimentally demonstrated, with reconfigurable capability by electronic control. A Mach–Zehnder modulator-based optical frequency comb (OFC) is used as an optical source, and its output is optically shaped before introducing a time delay by 70 km single-mode fiber (SMF) transmission. After an optical-to-electronic conversion, the frequency response in terms of central frequency and passband bandwidth can be electronically reconfigurable by varying either the input microwave frequency of the OFC or the waveshaper configuration without modification of the optical configuration. The experimental results show that more than a 35 dB out-of-band rejection ratio and at least a 3 GHz continuously tuning range of passband center frequency without any DC response can be successfully achieved.

Mode division multiplexing (MDM) transmission based on few-mode fibers (FMFs) appears to be an alternative solution for overcoming the capacity limit of single-mode fibers (SMFs). A FMF coupler-based mode division multiplexer/demultiplexer (MMUX/DeMMUX) is proposed and theoretically investigated after the fabricated FMF is characterized. MMUXs/DeMMUXs with a mode contrast ratio (MCR) of more than 20 dB can be obtained for two-mode multiplexing and three-mode multiplexing over a wavelength span of 60 and 10 nm, respectively. We numerically verify the proposed MMUX/DeMMUX which has the advantages of high MCR, easy fabrication and maintenance, and low wavelength dependence.

We experimentally demonstrate simultaneous 4???10?Gb?s?1 all-optical wavelength multicasting and non-return-to-zero (NRZ)-on-off-keying (OOK) to return-to-zero (RZ)-OOK format conversion with a tunable duty cycle using nonlinear polarization rotation in a semiconductor optical amplifier (SOA). The experimental results show that the duty cycle of four converted RZ-OOK signals can be tuned by adjusting the orientation of a polarizer placed at the SOA output. Four-channel NRZ-OOK-to-RZ-OOK conversion with a full width at half maximum of 33?67?ps can be simultaneously obtained with an extinction ratio over 10?dB. Moreover, it is experimentally verified that such a wavelength multicasting scheme with simultaneous NRZ-OOK-to-RZ-OOK conversion is insensitive to the wavelength of the input signal, indicating that such a scheme can be operated in the whole C-band with less than 0.18?dB power penalty at a bit error ratio level of 10?9. The device can facilitate the cross-connection between optical transmission networks employing different modulation formats.