Tigang Ning

Single-polarization, switchable dual-wavelength erbium-doped fiber laser with two polarization-maintaining fiber Bragg gratings

An improved erbium-doped fiber laser configuration for achieving single-polarization, switchable dual-wavelength of orthogonal polarizations oscillations at room temperature is proposed. For the first time, two fiber Bragg gratings (FBGs) directly written in a polarization-maintaining (PM) and photosensitive erbium-doped fiber (PMPEDF) as the wavelength-selective component are used in a linear laser cavity. Due to the polarization hole burning (PHB) enhanced by the polarization-maintaining FBG (PMFBG), the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller (PC). Each lasing line shows a single polarization with a polarization extinction ratio of >25 dB under different pump levels. The optical signal-to-noise ratio (OSNR) is greater than 50 dB. The amplitude variation with 16 times scans in nearly one and half an hour is less than 0.5 dB at both operating wavelength.

Performance Analysis of a Photonic-Assisted Periodic Triangular-Shaped Pulses Generator

We propose and analyze a photonic-assisted periodic triangular-shaped pulses generator, in which a continuous wave (CW) laser is connected to a dual electrode Mach-Zehnder modulator (De-MZM), and then the De-MZM is connected with a normal dispersion fiber or element. A radio frequency (RF) sinusoid directly drives the De-MZM to obtain optical subcarrier modulation with optical carrier suppression. By carefully setting the physical parameters, the generated harmonics of optical intensity can be corresponding to the Fourier components of typical periodic triangular pulses. Numerical simulations reveal that modulation index must be set to 2.305 and bias voltage drift must be within a range from from the minimum transmission of the De-MZM. In addition, the dispersion must be set correctly to suppress the primary distortion of 4th order harmonics.

Polarization Effects in Tilted Fiber Bragg Grating Refractometers

The polarization effects in tilted fiber Bragg grating (TFBG) refractometers are investigated theoretically. The polarization effects may degrade the sensor performance greatly, and should be considered to achieve high-precision surrounding refractive index (SRI) measurement. The possible paths to reduce the influence of polarization effects are discussed. For large SRI changes, the cutoff resonance wavelength can be used as sensing parameter to achieve a polarization insensitive SRI measurement with linear sensitivity of ~500 nm/u.r.i and SRI uncertainty of ~10-3 over SRI range of 0.1; for tiny SRI changes the measurement can be refined by monitoring proper individual resonance (close to the cutoff resonance wavelength) with accuracy approaching 2.5 × 10-5 over a SRI range of 0.001.

Photonic-Assisted Periodic Triangular-Shaped Pulses Generation With Tunable Repetition Rate

An optical triangular-shaped pulses generator with tunable repetition rate is proposed and analyzed. Using optical carrier suppression modulation and active polarization control, the optical intensity with its expression corresponding to the Fourier expansion of typical triangular-shaped waveform can be generated. It is also found that the pulses repetition rate is only dependent on the driving frequency of local oscillator. Thus, by changing it, continuous tunability of repetition rate is obtained. The mechanism is first analyzed by theory and then verified by simulation. Continuous tunability of the repetition rate (20–40 GBps) is obtained by using one 50/100-GHz optical interleaver. The proposal might be attractive since tuning the repetition rate requires only one frequency-tunable oscillator.

Photonic generation of triangular waveform signals by using a dual-parallel Mach-Zehnder modulator.

A photonic approach to generate triangular waveform signals is proposed and analyzed. With active bias control, two sub-MZMs (MZ-a and MZ-b) of a dual-parallel Mach-Zehnder modulator (DP-MZM) operate at minimum transmission point, leaving the main MZM (MZ-c) at quadrature transmission point. Triangular waveform can be observed by a parameter setting of modulation index. The proposal is first analyzed and then validated by simulation. The key significance of the scheme is that it is capable of generating triangular waveform signals via a sinusoid local oscillator.

Millimeter-wave radio-over-fiber system based on two-step heterodyne technique

We theoretically demonstrate an improved two-step-heterodyne-based, millimeter-wave, radio-over-fiber system. With the millimeter-wave mixer and a fiber Bragg grating located in the base station, two-step heterodyne is achieved. The proposed scheme has the merit of good system performance and high suppression of unwanted frequency tones, which is verified by numerical simulations.

Liquid level measurement by applying the Mach–Zehnder interferometer based on up-tapers

A novel scheme for liquid level detection using an all-fiber Mach-Zehnder interferometer, based on two up-tapers, is proposed and experimentally investigated. The effective refractive indices of the axisymmetric modes LP(0n) are analyzed while it is partly immersed in liquid. The sensitivity of the sensor is greatly dependent on the fiber length between the two up-tapers, as well as the order of the cladding modes through the calculation. The experimental results show that the sensitivity of the Mach-Zehnder interferometer reaches a 22.5 nm wavelength shift per meter of level change with the middle fiber length of 14.3 cm. The proposal might be attractive since the up-tapered liquid level sensor could easily be fabricated and used for a large measuring range.

An Improved Radio Over Fiber System With High Sensitivity and Reduced Power Degradation by Employing a Triangular CFBG

We propose and demonstrate a prototype for an improved intensity modulation direct detection (IMDD)-based radio over fiber (RoF) system by employing a homemade triangular chirped fiber Bragg grating (CFBG). In the scheme, an intensity modulator first modulates the lightwave with millimeter-wave driving signals to realize optical double-sideband (DSB) modulation, and then the output DSB signals pass though a triangular CFBG. Because the triangular CFBG is with a negative slop in spectrum, the lower sideband experiences higher attenuation than the upper sideband, which means the optical single sideband with carrier (OSSB+C) modulation can be easily implemented. The process of triangular CFBG also improves the link performance by balancing optical carrier-to-sideband ratio. As our scheme only uses a commercially used intensity modulator and homemade triangular CFBGs, the system is guaranteed with cost-effective architecture and good performance.

Dumbbell-Shaped Mach–Zehnder Interferometer With High Sensitivity of Refractive Index

We proposed and fabricated a dumbbell-shaped Mach-Zehnder interferometer (MZI) on a single mode fiber using a revised program of the fusion splicer. To the best of our knowledge, it is the first time one has produced and applied the MZI of this configuration to detect liquids refractive indexes. The dumbbell shape has a length of 1.9 mm and a minimum waist diameter of 63 μm. The wavelengths shift with the changing of surrounding refractive indexes, and the refractive index sensitivity is as high as 251 nm per refractive index unit with the linear range of 1.333-1.391 that is tens of times higher than the MZI based on two fiber tapers.

60 GHz millimeter-wave generator based on a frequency-quadrupling feed-forward modulation technique

We propose and analyze a prototype of a 60 GHz millimeter-wave (mm-wave) generator. In the scheme, two lasers with a 70 GHz frequency interval serve as sources. Then a frequency-quadrupling feed-forward modulation technique is employed to generate two phase correlated sidebands with a 60 GHz interval. The desired sidebands can be selected by using standard optical interleavers. In our work, a 60 GHz mm-wave signal free of phase noise can be achieved. The employed technique can also be extended to frequency 8-tupling.