Zhichao Wu

• PhD
• Professor at China University of Geosciences

Temporal cavity solitons, the temporal counterparts of Kerr frequency combs in the spectral domain, have found extensive applications over the past decade, ranging from integrated optical clocks to low‐noise microwave generation. These localized waveforms present as ultra‐narrow bright pulses in the anomalous dispersion regime and as dip‐embedded d...

The bright and dark cavity solitons (CSs) are typical stable nonlinear states that can be preserved in Kerr resonators. However, due to the distinct forming mechanisms, the generation of the two kinds of CSs requires different dispersion conditions and thus they are difficult to be produced by individual resonator, simultaneously. In this paper, we...

A low-complexity multi-subcarrier pulse generation scheme is proposed to suppress the interference fading in a phase-sensitive optical time-domain reflectometer (Φ-OTDR) based distributed acoustic sensor (DAS) with heterodyne coherent detection. The multi-subcarrier pulse is generated in the digital domain based on the proper clipping operation of...

This chapter explores the advancements in magnetic field sensors based on optical fibers and advanced multi-material fibers. Traditional optical fibers face challenges in directly sensing magnetic fields due to their insulating properties against electromagnetic interference. To overcome this limitation, transduction materials and modified structur...

Cavity solitons are persistent light pulses arising from the externally driven Kerr resonators. Thanks to the passive parametric gain, cavity soliton has been endowed with the natural advantage of the chip-scaled integration since it was first experimentally generated in the fiber-based platform. Deterministic single soliton with smooth spectrum is...

In this paper, an interference fading mitigation method based on subband phase-shift transform in coherent phase-sensitive optical time-domain reflectometer ( $\Phi$ -OTDR) is proposed. The operation principle of the subband phase-shift transform with complementary amplitude characteristic is presented. The phase shift transform is performed in th...

The Kerr microresonators have aroused widespread interests for their ultrahigh integration, compatible fabrication and ultralow energy consumption. Similar to the traditional mode-locked fiber lasers, the microresontors can sustain the generation of dissipative solitons called cavity solitons relying on the double balance of gain and loss as well a...

We use the linear optical sampling with ultra-high equivalent sampling rate to achieve characterization of dual, triple and quadruple bound state optical solitons. The spectral and temporal resolution are both better than conventional measurement devices.

Cavity solitons are shape-preserving waveforms infinitely revolving around a cavity, which have numerous applications from spectroscopy to telecommunications. Although the cavity solitons have been widely studied for their special time-frequency characteristics over the past decade, the spectral flatness will be a large limitation in some applicati...

Recent researches have demonstrated that pulsed driving is an effective method to increase the temporal overlap between cavity soliton (CS) and pump field, thereby increasing the pump-to-comb conversion efficiency. The amplitude-modulated inhomogeneity of the background wave causes the solitons to drift toward edges of the driving pulse. To elimina...

Magnetic field sensing plays an important role in many fields of scientific research and engineering applications. Benefiting from the advantages of optical fibers, the optical fiber-based magnetic field sensors demonstrate characteristics of light weight, small size, remote controllability, reliable security, and wide dynamic ranges. This paper pr...

We report the interaction between orthogonal components of three types of vector solitons which are generated in a passively mode-locked fiber laser. By adjusting pump power and cavity birefringence, single, dual and bound state vector solitons can be selectively acquired, while all the types of vector solitons reveal energy exchange phenomenon on...

To support large transmission and reduce inter-mode crosstalk, we designed a polarization-maintaining few-mode fiber (PM-FMF) with a separated-circles-formed elliptical ring core and two stress rods. This fiber can support ten different polarization modes with tunable chromatic dispersion. With the stress-rods-induced birefringence and the high ref...

The multimode waveguide is essential for future mode-division-multiplexing optical interconnection systems to further improve data capacity. However, the complex waveguide design process based on numerical methods is time consuming and requires a lot of computational effort. By using machine learning trained models, one can find the rules from the...

In this chapter, the multiplexed dissipative soliton fiber lasers including bidirectional multiplexing, wavelength multiplexing, polarization multiplexing are discussed. In bidirectional multiplexed soliton lasers, the features of various saturable absorbers are introduced. For wavelength multiplexed ones, balancing the gain competition by filter,...

Nonlinear Fourier transform (NFT) is a powerful tool for characterizing optical soliton dynamics, which, however, suffers from fundamental limitations that ultra-wide bandwidth photodetectors and ultra-high sampling rate analog-to-digital converters should be used when accessing the full-field information of an ultrafast optical pulse. Herein, we r...

We report on the numerical simulation results of vector soliton molecules (VSMs) manipulation based on the extra-cavity projected super-position technique. The VSMs are generated in a passively mode-locked fiber laser, and their time separations can be flexibly adjusted by applying different birefringence parameters. Moreover, along the laser outpu...

Soliton manipulation is considered as an effective way to generate complicated and controllable vector solitons. Here, we experimentally acquire flexible vector solitons deriving from standard scalar solitons by route-assisted and birefringence-enhanced structures along the laser output port. These vector solitons with weak interaction between two...

Two frequency combs emitting from a single cavity are of great potential in the field of dual-comb spectroscopy because they are mutually coherent and therefore the common mode noise can be suppressed naturally. However, it is difficult to fully and flexibly control the repetition frequency difference in most of the all-optical schemes. In this pap...

The Kerr microresonators have aroused widespread interests for their ultrahigh integration, compatible fabrication and ultralow energy consumption. Similar to the traditional mode-locked fiber lasers, the microresontors can sustain the generation of dissipative solitons called cavity solitons relying on the double balance of gain and loss as well a...

We report numerical simulation on the Kerr cavity solitons (CSs) manipulation based on projected super-position technique. The CSs are generated in a fiber-based Kerr resonator. The positions and amplitudes of these CSs can be adjusted by setting intra-cavity parameters. By introducing a polarization controller (PC) and an inline polarization beam...

Soliton manipulation is considered as an effective way to generate complicated and controllable vector soliton molecules (VSMs). With the help of projected super-position technique, we have successfully obtained a series of novel and stable VSMs from fundamental 1-1-2 VSMs to more complex 2-2-4 VSMs. Moreover, we have investigated that vector solit...

Nonlinear Fourier transform enabled soliton distillation is experimentally verified for the first time, where the full-field information of 1.71 ps ultrashort pulse delivered from a fiber laser can be accessed by linear optical sampling technique.

MoSe2 is a layered transition-metal dichalcogenide (TMD) with outstanding electronic and optical properties, which is widely used in field-effect transistor (FET). Here the structural evolution and phase transition of MoSe2 under high pressure are systematically studied by CALYPSO structural search method and first-principles calculations. The stru...

Dissipative cavity solitons (CSs) in a Kerr resonator have wide applications from optical communications to spectroscopy due to their the broad bandwidth. Although the broadband spectrum ultrashort pulses are easy to be generated in a high-Q microresonator, such kinds of solitons in the macroscopic fiber ring resonator are difficult to be obtained....

In this paper, an on-chip refractive index (RI) sensor based on the asymmetric Mach–Zehnder interferometer (MZI) is proposed for sensitivity enhancement. The outstanding sensing performance is obtained by achieving the dispersion turning point (DTP). We analyze the necessary conditions for DTP formation, the transmission spectrum characteristics, a...

In this paper, a compact and stable Q-switched erbium-doped fiber laser operating at around 1600 nm by employing a segment of 1-cm thulium-doped fiber saturable absorber (TDF-SA) is proposed. When the pump power is adjusted between 28 and 71 mW, the Q-switched operation can be maintained stably, and the output power increases from 74 µW to 2.6 mW....

Linear optical sampling (LOS) is a powerful technique to circumvent the electronic bottleneck arising in optical modulation analyzer (OMA). To extend the range of operation wavelength for the LOS-based OMA, the fiber optical frequency comb (FOFC) is proposed to replace the mode-locked fiber laser (NMFL) as an optical sampling source. However, this...

Dissipative Kerr solitons based on microresonators have wide applications from optical communications to optical ranging for the high-repetition rate and broad bandwidth. Restricted by the bending losses and dispersion control of the optical waveguide, it could be hard to further realize ultrahigh-repetetion rate reaching several terahertz by simpl...

We investigate polarization-locked vector solitons (PLVSs) arising in an all-polarization-maintaining (PM) soliton fiber laser mode-locked by a carbon nanotube. The laser can operate stably in both Q-switched and mode-locked states with different pump power. Under the PLVS condition, we observe a string of peak-dip-pair sidebands after polarization...

We report robust vector soliton bunches arising in a passively mode-locked fiber laser based on carbon nanotube (CNT). By introducing a polarization-route-assisted module (PRAM) and finely adjusting the cavity birefringence, the soliton bunches can be flexibly manipulated to operate with controllable soliton numbers and positions. Moreover, the pot...

Dissipative Kerr solitons based on microresonators have wide applications from optical communications to optical ranging for the high-repetition rate and broad bandwidth. Restricted by the bending losses and dispersion control of the optical waveguide, it could be hard to further realize ultrahigh-repetetion rate reaching several ter-ahertz by simp...

Linear optical sampling is proposed to obtain the full-field information of ultrafast laser pulse and nonlinear Fourier transform is applied to calculate its eigenvalues, providing an alternative solution for eigenvalue analysis of fiber laser radiation.

Temporal cavity solitons (CS)s are pulses that can maintain and circulate indefinitely in a resonant cavity under coherently driving. The approach for writing, erasing, and moving of CSs have significant ramifications for optical signal processing such as buffering. Previous work mainly focused on the manipulation of scalar CSs while conventional m...

Polarization-maintaining (PM) all-fiber cavity is always essential to realize stable ultrafast-pulse generation. With the help of five sections of PM fibers with independently specific splicing angles, we successfully obtain a femtosecond pulse output from a PM Ytterbium-doped fiber laser (YDFL) mode-locked by the nonlinear polarization evolution (...

We investigate various patterns of vector solitons arising in a passively mode-locked fiber laser based on semiconductor saturable absorber mirror (SESAM). By properly adjusting the cavity parameters including the pump power and intra-cavity birefringence, the fundamental vector solitons, vector soliton molecules, and macroscopic vector solitons ca...

A reconfigurable multiwavelength erbium-doped fiber laser based on an all-fiber multimode interferometer (MMI) is proposed and experimentally demonstrated. The interferometer is constructed by sandwiching a section of highly germanium-doped fiber (HGDF) between two sections of single-mode fiber. The insertion loss of the interferometer is as low as...

We report the peak-power-clamping (PPC) effect in a polarization-maintaining (PM) Q-switched mode locking fiber laser. The laser cavity with a compact and stable all-PM fiber configuration can clearly demonstrate three different output states including normal Q-switching, PPC Q-switching, and PPC Q-switched mode-locking (QML) with the increasing pu...

In this paper, we propose a photonic crystal fiber (PCF) with broadband ultra-flattened normal dispersion at 2 μm. In this fiber, a subwavelength air hole in the core region and air holes arrangement in the cladding region are used to control the property of dispersion. With optimized design, the dispersion of the proposed ultra-flattened normal di...

We demonstrate femtosecond dissipative solitons generated from an all-PM Ytterbium-doped fiber laser. The simplified fiber ring cavity has been shown to reliably self-start and provides a route to a robust platform for future development.

Although thulium-doped fiber lasers operating at 2 μm 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...

Details of various composites of the projections originated from a fundamental group-velocity-locked vector dissipative soliton (GVLVDS) are both experimentally and numerically explored. By combining the projections from the orthogonal polarization components of the GVLVDS, a high-order vector soliton structure with a double-humped pulse profile al...

Although the linear optical sampling (LOS) technique is powerful enough to characterize various advanced modulation formats with high symbol rates, the central wavelength of a pulsed local oscillator (LO) needs to be carefully set according to that of the signal under test, due to the coherent mixing operation. Here, we experimentally demonstrate w...

In this paper, we have achieved a high repetition rate and tunable pulse generation near ∼2 μm through an all-optical actively mode-locked fiber laser. The performances of the fiber laser have been systematically investigated through numerical simulations. The thulium-doped fiber laser cavity is modulated by the optical injection at 1.55 μ m via...

Linear optical sampling is a promising characterization technique for advanced modulation formats, together with digital signal processing (DSP) and software-synchronized algorithm. We theoretically investigate the acquisition of optical sampling, when the high-speed signal under test is either periodic or random. Especially, when the profile of op...

Vector solitons are for the first time generated in a fiber laser mode-locked by the nonlinear polarization rotation technique. Coexistence of scalar and vector solitons are found in the laser.

We experimentally demonstrate switchable temporal soliton generation from a thulium-doped fiber laser (TDFL), using carbon nanotubes as the mode-locker. With the help of residual polarization dependent loss of a wavelength division multiplexer, a weak nonlinear polarization rotation (NPR) effect can be achieved within the laser cavity, which may pr...

Vectorial nature of dissipative solitons (DSs) with high repetition rate is studied for the first time in a normal-dispersion fiber laser. Despite the fact that the formed DSs are strongly chirped and the repetition rate is greater than 100 MHz, polarization locked and polarization rotating group velocity locked vector DSs can be formed under 129.3...

We report a passively mode-locked fiber laser by nonlinear polarization rotation (NPR), where both vector and scalar soliton can co-exist within the laser cavity. The mode-locked pulse evolves as a vector soliton in the strong birefringent segment and is transformed into a regular scalar soliton after the polarizer within the laser cavity. The exis...

We experimentally demonstrate switchable dual-wavelength mode-locking of thulium-doped fiber laser (TDFL), using single-wall carbon nanotubes as saturable absorber. Due to the cavity birefringence-induced comb filter, switchable mode-locking can be individually realized for the proposed TDFL among three wavelengths of 1947, 1945, and 1943 nm, with...

A switchable passively mode-locked fiber laser is experimentally demonstrated by using single-wall carbon nanotubes as saturable absorber. The mode-locked fiber laser can be operated at the central wavelengths of 1947nm, 1945nm and 1943nm, individually.

Vectorial nature of dissipative solitons (DSs) with high repetition rates is studied for the first time in a normal-dispersion fiber laser. Despite the fact that the formed DSs are strongly chirped and the repetition rate is greater than 100 MHz, polarization locked and polarization rotating group velocity locked vector DSs can be formed under 129....

The dynamics of dissipative solitons (DSs) are explored in a high repetition rate normal-dispersion erbium-doped fiber laser for the first time. Despite of the high fundamental repetition rate of 129 MHz and thus the low pulse energy, a DS train with a dechirped pulse width of 418 fs, period-doubling of single and dual DSs, as well as 258 MHz 2nd-o...

The dynamics of dissipative solitons (DSs) are explored in a high repetition rate normal-dispersion erbium-doped fiber laser for the first time. Despite of the high fundamental repetition rate of 129 MHz and thus the low pulse energy, a DS train with a dechirped pulse width of 418 fs, period-doubling of single and dual DSs, as well as 258 MHz 2nd-o...

Manipulation of group-velocity-locked vector solitons (GVLVSs) is numerically proposed and experimentally demonstrated. A pseudo-high-order GVLVS could be generated from a fundamental GVLVS with the help of a polarization-resolved system. Specifically, a pseudo-high-order GVLVS with a two-humped pulse along one polarization and a single-humped puls...

We report numerical simulations on the high-order group-velocity-locked vector soliton (GVLVS) generation based on the fundamental GVLVS. The high-order GVLVS generated is characterized with a two-humped pulse along one polarization while a single-humped pulse along the orthogonal polarization. The phase difference between the two humps could be 18...

A simple and compact configuration of multiwavelength pulse generator is proposed and experimentally demonstrated, using a SESAM-based passively mode-locked fiber laser together with fiber Fabry–Perot filter. By optimizing the dispersion of fiber ring cavity, a flat rectangular optical spectrum with 3 dB bandwidth of 8.1 nm is obtained, with power...

A SESAM based continuously wavelength-tunable erbium-doped passively mode-locked fiber ring laser is proposed and demonstrated. The dissipative solitons possess almost fixed spectral characteristics and repetition rates, after the optimization of polarization-dependent loss within the ring cavity.

We propose and experimentally demonstrate switchable operation of dissipative solitons (DSs) in an erbium-doped fiber laser. By managing normal dispersion of laser cavity, the 3-dB spectral bandwidth up to 8.1 nm can be obtained with the help of a semiconductor saturable absorber mirror. Using an inline polarizer, the fiber laser can be separately...

A liquid level optical fiber sensor based on all-fiber single-mode-multimode-no-core-single-mode (SMNS) structure is proposed, which possesses a water level sensitivity of 215.98 pm/mm by monitoring the wavelength shift, and −0.109 dB/mm of the power attenuation.

We report an experimental observation of bound states of group-velocity locked vector solitons (GVLVSs) in a passively mode-locked fiber laser. Bound states of GVLVSs with various soliton separations are demonstrated for the first time.