Linghao Cheng

An exact analytical model for dispersive transmission in microwave fiber-optic links using Mach-Zehnder external modulator

A new exact analytical model is presented to analyze the dispersive transmission in microwave fiber-optic links using a dual-drive Mach-Zehnder external modulator (DD-MZM). The model is very general and can be applied to almost all operating conditions of DD-MZM, such as bias point, drive level, phase shift, and modulation index difference between DD-MZM drives. The model results in simple new closed-form expressions for output power spectrum, permitting an accurate and fast analysis of such links. Expressions for two special cases, double sideband and single sideband modulation, are included, together with a novel presentation of some new results on power fading of fundamental and second harmonic.

Linear photonic radio frequency phase shifter using a differential-group-delay element and an optical phase modulator

We demonstrate a stable and linear photonic radio frequency (RF) phase shifter based on a differential-group-delay element and the polarization sensitive effect of an optical phase modulator. The phase shift can be tuned continuously over 360 degrees for RF signals over 40GHz with an electrical control voltage from -7.5 to +7.5V.

Signed chromatic dispersion monitoring of 100Gbit/s CS-RZ DQPSK signal by evaluating the asymmetry ratio of delay tap sampling

In this paper, we theoretically and experimentally demonstrated the residual chromatic dispersion (CD) monitoring of 100-Gbit/s carrier suppress return-to-zero differential quadrature phase shift keying (CS-RZ DQPSK) signals by evaluating the asymmetry ratio of delay tap asynchronous sampling. This scheme can easily differentiate the positive and negative residual CD of the fiber link. The resolution of this scheme is better than 8 ps/nm and the measurable range is around +/- 24 ps/nm for 100 Gbit/s CS-RZ DQPSK signals. We can also simultaneously realize both signed CD monitoring and demodulation of CS-RZ DQPSK signal based on only one demodulator.

PMD and chirp effects suppression in RF tone-based chromatic dispersion monitoring

We investigate the effects of polarization-mode dispersion (PMD) and chirp on radio-frequency tone-based chromatic dispersion (CD) monitoring method, and show that the PMD and chirp induce significant CD monitoring errors. We propose a CD monitoring technique to suppress these effects. Experiment results show that the CD monitoring errors induced by PMD and chirp fluctuation are greatly suppressed.

Tunable photonic microwave bandpass filter using phase Modulation and a chirped fiber grating in a Sagnac loop

We propose a novel all-optical microwave bandpass filter configuration, which uses phase modulation and a linearly chirped fiber grating in a Sagnac loop. The free spectral range (FSR) of the filter can be tuned continuously by tuning the grating. We also derive an expression for the filter transfer function. Calculated and measured results, which agree well, are presented to show a large notch rejection and an easily tunable FSR.

Ampere force based magnetic field sensor using dual-polarization fiber laser.

A magnetic field sensor is proposed by placing a dual-polarization fiber grating laser under a copper wire. With a perpendicular magnetic field applied, an electrical current flowing through the copper wire can generate Ampere force to squeeze the fiber grating laser, resulting in the birefringence change inside the laser cavity and hence the change of the beat note frequency. When an alternating current is injected into the copper wire, the magnetic field induced beat note frequency change can be discriminated from environment disturbances. A novel fiber-optic magnetic field sensor is therefore demonstrated with high sensitivity and inherent immunity to disturbances.

NRZ-DPSK and RZ-DPSK Signals Signed Chromatic Dispersion Monitoring Using Asynchronous Delay-Tap Sampling

In this paper, we demonstrated a signed chromatic dispersion (CD) monitoring method of 10 GHz nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) and return-to-zero differential phase-shift keying (RZ-DPSK) signals by using asynchronous delay-tap sampling and an imperfect tuned delay interferometer. This method could monitor not only the value but also the polarity of residual CD. The demodulated signals show amplitude shoulders on the rising edge or the trailing edge with CD accumulation. Delay-tap sampling scatter plots could reflect this signal distortion by a unique characteristic and realize the signed CD monitoring. The monitoring range can be up to plusmn400 and plusmn720 ps/nm for NRZ-DPSK and RZ-DPSK signals, respectively. Simulation and experimental results are also proposed.

Generalized analysis of subcarrier multiplexing in dispersive fiber-optic links using Mach-Zehnder external modulator

A new exact analytical model is presented to analyze the dispersive transmission in subcarrier multiplexing (SCM) fiber-optic links using dual-drive Mach-Zehnder external modulator (DD-MZM). The model is very general and can be applied to almost all operating conditions of DD-MZM, such as bias point, drive level, phase shift, and modulation index difference between DD-MZM drives. The model results in simple, new, and closed-form expressions for output power spectrum, permitting an accurate and fast analysis of such links. Two special cases, double sideband (DSB) and single-sideband (SSB) modulation, are studied in detail. Some important system parameters, such as 1-dB compression point, the input third-order intercept point (IIP3), and the system capacity, are derived for the first time. Measured results for system capacity and intermodulation products of different orders match very well with the calculated results.

Chromatic Dispersion Monitoring Based on Variance of Received Optical Power

For lightwave transmission systems employing advanced modulation formats such as phase-shift keying (PSK) and quadrature-amplitude modulation (QAM), chromatic dispersion monitoring based on average variance of optical power has been demonstrated. Theoretical analyses are verified by simulations, and experiment results show that the variance of optical power at the receiver is a simple and effective statistical parameter to monitor the residual chromatic dispersion of a transmission link.

Hydrostatic Pressure Measurement With Heterodyning Fiber Grating Lasers: Mechanism and Sensitivity Enhancement

In this paper, dual-polarization fiber grating lasers are exploited as heterodyning sensors for hydrostatic pressure measurement. The laser is formed by photo-inscribing two highly reflective wavelength-matched Bragg gratings over a short section of Er-doped fiber. The measurement is carried out by monitoring the beat frequency between the orthogonally polarized laser output. The pressure sensitivity of a bare sensor is -0.59 MHz/MPa. Theoretical analysis suggests that the pressure response is dominantly determined by the change in intra-cavity birefringence, which is associated with the geometrical imperfection of the fiber core. The effects of differences in elastic properties between fiber core and cladding on the pressure response are examined. We found that the differences in Youngs modulus and Poissons ratio are mainly responsible for the pressure sensitivity. The pressure sensitivity can be significantly enhanced by packaging the laser into a polymer incorporated with a steel rod. Due to the difference in elastic properties between materials, an additional birefringence is introduced into the laser cavity under hydrostatic pressure. The sensitivity has been enhanced by 228 times, to 170 MHz/MPa. The minimal detectable pressure change of the packaged sensor is about 0.01 MPa. We further demonstrate a miniature packaged sensor with a cross-sectional dimension of only 1.42 mm and a pressure sensitivity of 53.9 MHz/MPa towards practical applications.