Shangjian Zhang

Ultrafast erbium-doped fiber laser mode-locked by a CVD-grown molybdenum disulfide (MoS2) saturable absorber.

We demonstrate an erbium-doped fiber laser passively mode-locked by a multilayer molybdenum disulfide (MoS(2)) saturable absorber (SA). The multilayer MoS(2) is prepared by the chemical vapor deposition (CVD) method and transferred onto the end-face of a fiber connector. Taking advantage of the excellent saturable absorption of the fabricated MoS(2)-based SA, stable mode locking is obtained at a pump threshold of 31 mW. Resultant output soliton pulses have central wavelength, spectral width, pulse duration, and repetition rate of 1568.9 nm, 2.6 nm, 1.28 ps, and 8.288 MHz, respectively. The experimental results show that multilayer MoS(2) is a promising material for ultrafast laser systems.

8 × 8 × 40 Gbps fully integrated silicon photonic network on chip

We demonstrate a fully integrated photonic network-on-chip circuit with wavelength division multiplexing transceivers on silicon. The total transmission capacity is up to 8×8×40 Gbps for intra- and inter-chip interconnections.

Self-calibrating measurement of high-speed electro-optic phase modulators based on two-tone modulation

We propose a self-calibrating method for high-frequency response measurement of electro-optic phase modulators based on two-tone modulation. The method utilizes the electrical domain measurement of heterodyning spectrum between the two-tone modulation optical signal and the frequency-shifted optical carrier, and eliminates the need to correct the responsivity fluctuation in the photodetection. High-frequency modulation depth and half-wave voltages are measured and compared to those with the traditional optical spectrum analysis method in the experimental demonstration. The proposed method enables calibration-free and accurate frequency response measurement of electro-optic phase modulators by using high-resolution electrical spectrum analysis.

Graphene decorated microfiber for ultrafast optical modulation.

With a convenient and controllable evanescent-field-induced transfer method, graphene flakes were deposited on the surface of a 1-μm-diameter microfiber, which can be used for ultrafast optical modulation based on its distinct saturable absorption.

Optical Frequency-Detuned Heterodyne for Self-Referenced Measurement of Photodetectors

A self-referenced frequency response measurement of high-speed photodetectors (PDs) is proposed and demonstrated based on optical frequency-detuned heterodyne method. Our method provides a narrow linewidth and wide-bandwidth optical stimulus consisting of acoustooptic frequency shifting and two-tone phase modulation in a Mach-Zehnder interferometer, and achieves the self-referenced frequency response measurement of high-speed PDs without the need for correcting the power variation of optical stimulus. Moreover, it allows multiplied measuring frequency range and avoids any bias drifting problem. Frequency responses are experimentally measured for a commercial PD, which agree well with the results obtained by the conventional methods.

Extinction-ratio-independent electrical method for measuring chirp parameters of Mach-Zehnder modulators using frequency-shifted heterodyne

An extinction-ratio-independent electrical method is proposed for measuring chirp parameters of Mach-Zehnder electric-optic intensity modulators based on frequency-shifted optical heterodyne. The method utilizes the electrical spectrum analysis of the heterodyne products between the intensity modulated optical signal and the frequency-shifted optical carrier, and achieves the intrinsic chirp parameters measurement at microwave region with high-frequency resolution and wide-frequency range for the Mach-Zehnder modulator with a finite extinction ratio. Moreover, the proposed method avoids calibrating the responsivity fluctuation of the photodiode in spite of the involved photodetection. Chirp parameters as a function of modulation frequency are experimentally measured and compared to those with the conventional optical spectrum analysis method. Our method enables an extinction-ratio-independent and calibration-free electrical measurement of Mach-Zehnder intensity modulators by using the high-resolution frequency-shifted heterodyne technique.

Calibration-free measurement of high-speed Mach-Zehnder modulator based on low-frequency detection.

A calibration-free electrical method is demonstrated for measuring the frequency response of high-speed Mach-Zehnder modulators (MZMs) based on low-frequency detection. The method achieves the high-frequency modulation index and half-wave voltage measurement of MZMs by the low-frequency electrical spectrum analysis of the two-tone and bias-modulated optical signal. Moreover, it eliminates the need for correcting the responsivity fluctuation in the photodetector through setting a specific frequency relationship between the two-tone and bias modulation. Both absolute and relative frequency response of MZMs are experimentally measured with our method and compared with those obtained with conventional methods to check for consistency.

Compact noise-like pulse fiber laser and its application for supercontinuum generation in highly nonlinear fiber

We report on supercontinuum generation in a highly nonlinear fiber (HNLF) pumped by noise-like pulses (NLPs) emitted from a compact fiber ring laser. The compact erbium-doped fiber ring laser is constructed by using an optical integrated component and mode-locked by the nonlinear polarization rotation technique. The laser produces NLPs with a 3-dB spectral bandwidth of 60.2 nm, repetition rate of 9.36 MHz, and pulse energy of 2.8 nJ. Numerical simulations reproduce the generation of NLPs in the experiment. The NLPs are then launched into a 110-m-long HNLF and a supercontinuum with a 20-dB spectral width over 500 nm is obtained. Such a simple and inexpensive supercontinuum-generation system is a potential alternative for various practical applications.

Calibration-Free Electrical Spectrum Analysis for Microwave Characterization of Optical Phase Modulators Using Frequency-Shifted Heterodyning

A novel calibration-free electrical spectrum analysis method for microwave characterization of electrooptic phase modulators is proposed and experimentally demonstrated based on frequency-shifted optical heterodyning. The method achieves the electrical domain measurement of the modulation efficiency of phase modulators without the need for correcting the responsivity fluctuation in the photodetection. Moreover, it extends double the measuring frequency range through setting a specific frequency relationship between the driving microwave signals. Modulation depth and half-wave voltage of phase modulators are experimentally extracted from the heterodyning spectrum of two phase-modulated signals with and without frequency shifting, and the measured results are compared to those obtained with the traditional optical spectrum analysis method to check the consistency. The proposed method provides calibration-free and accurate measurement for high-speed optical phase modulators with the high-resolution electrical spectrum analysis.

Broadband linearization in photonic time-stretch analog-to-digital converters employing an asymmetrical dual-parallel Mach-Zehnder modulator and a balanced detector

A broadband linearization scheme for time-stretch analog-to-digital converters (TS-ADCs) is proposed based on an asymmetrical dual-parallel Mach-Zehnder modulator and a balanced detector. The theoretical and simulation results indicate that, compared with the differential and arcsine operation method generally employed in TS-ADCs, the proposed scheme has a superior performance on enhancing the spur-free dynamic range and suppressing the even-order distortions and the third-order spurs even under a large modulation depth. Additionally, the proposed scheme realizes online linearization. Therefore, it has the potential to enhance the dynamic range of a broadband TS-ADC in real time.