Minghua Chen

A Photonic Microwave Frequency Quadrupler Using Two Cascaded Intensity Modulators With Repetitious Optical Carrier Suppression

We theoretically analyzed and experimentally demonstrated a novel 4- to 40-GHz frequency quadrupler for radio-over- fiber systems. By using an optical carrier suppression modulation scheme in two cascaded intensity modulators, four-fold microwave or millimeter wave signals are optically generated without the need for an optical and electrical notch filter to remove the residual carrier components. Moreover, the limitation of high drive voltage is greatly reduced through tandem intensity modulation with pi/2 phase shift between two driving signals.

Methods for Ultra-Wideband Pulse Generation Based on Optical Cross-Polarization Modulation

Optical methods for different type ultra-wideband (UWB) pulse generation based on cross-polarization modulation (CPM) are proposed and demonstrated in this paper. Two polarity-reverse pulses can be obtained by CPM and birefringence time delay to form a monocycle pulse. A semiconductor optical amplifier (SOA) is placed after the monocycle pulse process for doublet pulse generation. These two kinds of pulses can be employed in single-band impulse radio UWB (IR-UWB) systems. Two kinds of multi-band UWB pulses can be generated based on monocycle pulse train with proper apodization profiles, realized by hybrid photonic microwave filter and synchronous polarization modulation respectively. Experimental results show that these pulses can be used in multi-band UWB (MB-UWB) over fiber systems.

Optical ultra-wide-band pulse bipolar and shape modulation based on a symmetric PM-IM conversion architecture

A simple and feasible technique for ultra-wide-band (UWB) pulse bipolar modulation (PBM) and pulse shape modulation (PSM) in the optical domain is proposed and demonstrated. The PBM and PSM are performed using a symmetric phase modulation to intensity modulation conversion architecture, including a couple of phase modulators and an optical bandpass filter (OBPF). Two optical carriers, which are separately phase modulated by two appropriate electrical pulse patterns, are at the long- and short-wavelength linear slopes of the OBPF spectrum, respectively. The high-speed PBM and PSM without limit of chip length, polarity, and shape are implemented in simulation and are also verified by experiment.

A Novel Composite Method for Ultra-Wideband Doublet Pulses Generation

A novel composite approach to generate ultra-wideband (UWB) doublet pulses in optical domain through an electrical Gaussian pulse is proposed and demonstrated in this letter. Two pulses with reversed polarity generated by polarization modulation are fed into a differential group delay device and a semiconductor optical amplifier (SOA) wherein the optical pulse profile is modified. Doublet pulses are obtained after optical-electrical detection due to gain saturation and recovery mechanism in the SOA. The fractional bandwidth of doublet pulses exceeds 180%, fulfilling the UWB requirements.

Slow-light delay enhancement in small-core pure silica photonic crystal fiber based on Brillouin scattering

We demonstrate that we realize large-delay slow light based on stimulated Brillouin scattering in a short length of our fabricated small-core photonic crystal fiber (PCF). The cavity effect from the partially reflective splices in the end of the PCF enhances slow-light delay significantly. Our experiments show that large slow-light delay can be easily realized in a very short length of the PCF with a moderate pump power. Up to a one-half pulse-width delay is achieved in only 50 m of PCF in a single pump segment.

Gigabit/s Photonic Generation, Modulation, and Transmission for a Reconfigurable Impulse Radio UWB Over Fiber System

We propose and demonstrate a flexible and high-speed impulse radio ultrawideband (IR-UWB) over fiber system using various modulation schemes. Two kinds of fully Federal Communication Commission (FCC) compliant UWB pulses are produced, which is based on the incoherent summation of multiple monocycle pulses with inverse polarities, proper time delays, and different weights. Theoretically, their spectral power efficiency can achieve 33.9% and 47.4%, respectively, which is much higher than that of the conventional monocycle and doublet pulses. A good agreement between the theoretical and experimental results for the generation of designed UWB pulses is also observed. Moreover, electrically reconfigurable multiple modulation formats such as on-off keying (OOK) modulation, binary phase shift keying (BPSK) modulation, pulse shape modulation (PSM), and pulse position modulation (PPM) are implemented experimentally. Furthermore, the UWB signals with OOK, BPSK, and PPM are transmitted over a combined wired (single-mode fiber) and wireless link. The transmission performance of the newly generated UWB pulses is then evaluated by electrical spectra, eye diagrams, and bit-error-rate measurements. For all the modulation formats, a forward-error-correction (FEC)-limit error-free operation is obtained, and the power penalties of transmission are less than 1 dB.

60-nm-Wide Tunable Single-Longitudinal-Mode Ytterbium Fiber Laser With Passive Multiple-Ring Cavity

A broadband tunable, single-longitudinal-mode (SLM) ytterbium fiber laser based on a passive multiple-ring cavity (MRC) technique is proposed and demonstrated experimentally for the first time to our knowledge. Two different short ring cavities are inserted into the main ring cavity and serve as wideband mode filters to ensure SLM oscillation. With 1-m ytterbium-doped fiber as the gain medium, the SLM operation is achieved with over 60-nm wavelength tuning range at 100-mW pump power. The laser is very stable with output power of 6 dBm and an optical signal-to-noise ratio of higher than 53 dB in all the 60-nm tuning range.

High-Spectral-Purity Millimeter-Wave Signal Optical Generation

In this paper, novel approaches for millimeter-wave signal generation using double-sideband suppressed-carrier modulation and four-wave mixing are proposed and demonstrated. The millimeter-wave signal is generated at a photodetector by beating the optical sidebands, which are gained from intensity modulation and after semiconductor optical amplifiers. In the proposed methods, the generated millimeter-wave signal has a frequency that is double, quadruple, sextuple, 12 times, or even 18 times higher than the microwave drive signal. And, it has quite good gain flatness with extremely high-spectral-purity and stability. The phase noise performance of the generated millimeter wave is investigated. The 3-dB linewidth of the millimeter wave has no broadening after propagating through 20-km standard single-mode fiber.

Optically tunable multiband UWB pulse generation.

A novel tunable multiband ultra-wide band (MB-UWB) pulses generation method using synchronously-apodized polarization modulation and birefringence time delay is proposed and demonstrated in this letter. Proper apodization profile is used to get MB-UWB pulses with spectra sidelobes suppression over 20dB. Five bands of MB-UWB pulses are generated by tuning the modulation frequency and transmitted over wireless channel. The central frequencies are from 4GHz to 6GHz and bandwidths larger than 500MHz. This method can be used in multiband modulation UWB over fiber systems.

Bit error rate analysis of OTDM system based on moment generation function

The performance of optical time division multiplexing (OTDM) system is limited by a complex combination of noise. In this paper we present a theoretical framework for the optical receiver in OTDM system based on the moment generation function. The proposed receiver model is showed to be more accurate in predicting the bit error rate (BER) performance than the former ones. Its validity is also verified by the experimental results.