Tangjun Li

Analytical theory of pulse broadening due to polarization mode dispersion and polarization-dependent loss

The interaction of polarization mode dispersion (PMD) with polarization-dependent loss (PDL) and their combined effects on pulse broadening are investigated in detail. The relation between PMD vector and PDL vector in optical links is described analytically. In presence of PMD and PDL, we derive a precise analytical expression of pulse broadening in optical fibers, and the chromatic dispersion, chirping are also considered simultaneously.

Simultaneous measurement of strain and temperature using dual-period fiber grating

This paper demonstrates a novel dual-period fiber grating sensor which can measure strain and temperature simultaneously. The dual-period fiber grating consists of a long-period fiber grating (LPG) and a fiber Bragg grating (FBG) which are written in the same section of an uncovered hydrogen-loaded fiber orderly. As is known, the Bragg wavelength of LPG and that of FBG have the different sensitivity of strain and temperature, then strain and temperature can be determined simultaneously by measuring the two transmitted Bragg wavelengths of the dual-period fiber grating. The accuracy of the sensor in measuring strain and temperature is estimated to be +/- 16 (mu) (epsilon) in a range from 0 to 1700 (mu) (epsilon) and +/- 0.8 degree(s)C from 20 to 120 degree(s)C, respectively.

Simultaneous Clock Enhancing and Demultiplexing for 160-Gb/s OTDM Signal Using Two Bidirectionally Operated Electroabsorption Modulators

We demonstrate a technique for performing optical time-division simultaneous clock enhancing and demultiplexing using two bidirectionally operated electroabsorption modulators (EAMs). The performance of the proposed setup is verified experimentally in a 160-Gb/s 100-km transmission system. The 10-GHz clock component is enhanced before launching into the clock recovery module. The recovered 10-GHz clock signal is featured with low timing jitter ( <;300 fs) and error-free transmission is achieved with the power penalty of ~ 0.9 dB. The proposed setup has merits of simultaneously enhancing base clock component and demultiplexing.

Tunable PMD compensator based on highbirefringence.

The simple structure of a tunable polarization mode dispersion (PMD) compensator based on a cantilever beam and a high-birefringence linearly chirped fiber Bragg grating is proposed. A cantilever structure is used to introduce a linear strain gradient on the grating, and we can tune the compensated differential group delay (DGD) at a fixed signal wavelength just by changing the displacement at the free end of the beam. Based on numerical simulations, the performance of the cantilever structure as a PMD compensator is assessed for 10-Gbits/s nonreturn-to-zero transmission systems with a large DGD. With this compensator, a significant improvement of system performance can be achieved in the eye pattern of a received signal.

Analytical theory for polarization mode dispersion of spun and twisted fiber

We derive an analytical expression for differential group delay of spun and twisted fibers, which should provide valuable guidance for optimization of such parameters to produce low polarization mode dispersion fiber.

Polarization independent 4-stage OTDM multiplexer using plated GRIN lens

In this paper, a 4-stage optical time domain multiplexing (OTDM) multiplexer based on plated graded index (GRIN) lens is proposed and experimentally demonstrated. A 10Gbit/s return-to-zero (RZ) signal is upgraded to 160Gbit/s. The time-domain accuracy of the multiplexer is evaluated by analyzing the multiplexed 160Gbit/s signal. Experimental results validate the stability of the optical multiplexing behavior and the polarization insensitivity of the proposed multiplexer. The results also show the advantages of our OTDM multiplexer such as the flexible output signal speeds at the output of different stages, the low insertion loss and the temperature and wavelength stability.

Dispersion compensation experiment on 19 ps pulse width over 133 km single mode fiber with tunable chirp and wavelength gratings

A novel method utilizing a cantilever beam to tune the center wavelength and the linear chirp of fiber gratings is presented. Based on this method, the center wavelength and the chirp of a 10 cm uniform fiber grating are tuned to compensate for the dispersion of 19 ps pulse width after 133 km transmission. Experimental results show that the effect of dispersion compensation is favorable.

All‐optical correlator based on modal dispersion in multimode fiber

Abstract. We propose and demonstrate an all‐optical correlator based on modal dispersion in a multimode fiber. Many of the modes can be excited in a large core high numerical aperture step‐index multimode fiber under overfilled launching. The incident optical signal is copied into different modes and a time delay is introduced by the modal dispersion. We use a mask with slits as a space filter to select the modes needed. A correlator of the mask and input signal is achieved at the output end. Thanks to the use of modal dispersion, the correlator is nearly independent of the wavelength and bandwidth of the input signal. By adjusting the slits on the mask, the target patterns of the correlator can be changed easily. A radio frequency signal detection is also experimentally demonstrated with this construction.

Method of improving bandwidth efficiency for OTDM transmission systems

Spectrum compression based on filters for improving bandwidth efficiency is presented and demonstrated experimentally in 40Gb/s OTDM system. Even after 100km transmission, demultiplexing and clock recovery can be implemented successfully, and the data rate-to-bandwidth ratio has been improved to 4 times.

FBGs-based dispersion compensators and EDFA gain equalizators

32 chirped FBGs (fiber Bragg gratings)-based dispersion compensators and EDFA (Er-Doped Fiber Amplifier) gain-equalizators is demonstrated. Dispersion compensation of 600km G652 fiber and limiting amplification of 16 wavelength signals with low power penalty of<2dB can be obtained at a 10GHz/s optical communication system.