Li Tangjun

FTTH - a promising broadband technology

With the extraordinary increase of bandwidth requirement nowadays, service providers are compelled to push fiber deeper into the access networks in order to be able to offer the emerging services that customers are demanding. Fiber-to-the-home (FTTH) networks have always been the ultimate solution to a future broadband access network. In recent years, several technological developments have brightened the outlook on FTTH. The paper highlights these changes, and presents architectures that may be successfully deployed in the near future. The author estimates the value of FTTH and the foreground of its application and development in the world market.

Novel B/Ge codoped photosensitive fiber and dispersion compensation in an 8×10 Gbit/s DWDM system

We used the Modified Chemical Vapor Deposition (MCVD) method to fabricate a B/Ge codoped fiber with a depressed cladding in which boron and germanium were also doped, the depressed cladding was photosensitive, which can greatly suppress the cladding mode coupling. The transmission spectrum of written grating in this fiber made by the phase mask method verified its larger photosensitivity and great suppression of the cladding mode coupling. We then analyzed the Bragg wavelength tuning theory in the phase mask method in detail which gave us a more exact equation. The ultra-violet (UV) exposure system was modified, and eight cascaded Fiber Bragg Gratings (FBG) centered at different wavelengths were written in this photosensitive fiber successfully using a 248 nm KrF excimer laser and one piece of 1067 nm phase mask. Each channel spacing was 100 GH according to the Densed Wavelength Division Multiplexing (DWDM) standards of the International Telecommunication Union (ITU-T). At the same time, we also wrote in chirp in each grating by tilting the phase mask to realize dispersion compensation. The dispersion in 44 km SMF was successfully compensated by the cascaded chirped gratings in the eight channel WDM system with each channel being 10 Gbit/s.

A Simple Loop for Simultaneous OTDM Demultiplexing and Clock Recovery

A simple and stable loop consisting of a pair of concatenated electroabsorption modulators (EAMs) and 10 GHz clock recovery module is presented and demonstrated experimentally for simultaneous demultiplexing and clock recovery for OTDM networks. The 10Gb/s demultiplexed signal and 10 GHz recovered clock are successfully implemented from 80 Gbit/s and 160 Gbit/s OTDM signals utilizing the loop. The loop based on EAM-PLL can provide excellent tolerance range (> 5 dB) of the OSCR of the source laser, and the recovered clock signal exhibits low rms jitter over a dynamic input optical power range of 15 dB.

A Clock Enhanced Loop for Simultaneous Error-Free Demultiplexing and Clock Recovery of 160 Gb/s OTDM Signal Single-Channel Transmission over 100 km *

A simple clock enhanced loop of cascaded electro-absorption modulators (EAMs) and 10 GHz clock recovery modules is presented. The intensity of harmonic of clock-frequency component is analyzed theoretically and verified experimentally in a 160 Gb/s OTDM 100 km transmission system. The 10 GHz clock component is enhanced obviously before launching into the clock recovery module and the recovered clock signal exhibits low rms jitter of < 400 fs. Moreover, completely error-free (10−12) transmission is observed for more than two hours without using forward error correction technology. The power penalty is about 3.6 dB. The proposed loop has merits of enhancing base clock component, simultaneously de-multiplexing and clock recovery, which make the performance of this loop more stable and high suppression of non-target channels.

Dynamic Polarization-Mode-Dispersion Compensation for 160 Gbit/s OTDM Systems

We report on 160 Gbit/s RZ (return-to-zero) code transmission experiments including a dynamic polarization mode dispersion (PMD) compensation. The 2.5-ps first-order and 15-ps2 second-order PMD are compensated for. The PMD compensation time is within 24 ms. The experimental results show that a significant improvement of system performance can be achieved by auto-correlative curves.

20 Gb/s optical time division multiplexing signal generation by fiber coupler loop-connecting configuration

Connecting an input port and an output port of a single-mode fiber coupler to form a fiber-loop, and making the time delay of the fiber-loop odd times half-period of the input optical pulse stream, we can obtain a pulse stream with multiplying repetition rate at the other output port of the coupler. Utilizing three loop-connecting fiber couplers concatenated, a pulse stream with eight times the repetition rate is achieved.

Compensating the first-order PMD by using a novel tunable compensator

With increasing bit-rate PMD (polarization mode dispersion) is becoming major system impairment. As the birefringence of a fiber changes randomly along a fiber link and the state-of-polarization (SOP) of an optical signal changes, with environmental conditions, PMD effects on the data signal are stochastic and time varying. Consequently, compensation of PMD, especially for the first-order PMD is necessary to maintain adequate performance in long-haul systems at a high bit rate of 10 Gbit/s or beyond. In this paper, we successfully demonstrated automatic and tunable compensation for first-order polarization-mode dispersion. Furthermore, we reported the statistical assessment of this tunable compensator at 10 Gbit/s. Experimental results, including bit error rate measurements, are successfully compared with theory, therefore demonstrating the compensator efficiency at 10 Gbit/s. The first-order PMD was max 274 ps before PMD compensation, and it was lower than 7ps after PMD compensation.

Erbium Doped Fiber Amplifier Gain Flattening Using Long-Period Fiber Gratings

Based on theoretical and experimental studies on the optical properties of long-period gratings (LPGs), an erbium doped fiber amplifier (EDFA) gain equalizer was fabricated by writing three long period gratings with designed properties in hydrogen-loaded standard single-mode fibers. The LPGs were written by a KrF excimer laser at 248 nm with amplitude masks. The gain variation of ±3 dB in the EDFA is reduced to ±0.3 dB with a bandwidth of 30 nm and the total insertion loss of the device is less than 0.3 dB.

Optimization scheme for complete second-order PMD compensation

Based on the structure of the three-stage complete second-order polarization mode dispersion (PMD) compensator, the combination of the DIRECT algorithm and the Hooke & Jeeves algorithm is advanced as the optimization scheme for the control parameters of it. The optimization scheme is validated by the simulation of the measurement values of the degree of polarization (DOP) in the optimization process. A 16×10-Gb/s optical time-division-multiplexing (OTDM) transmission system with home-made dynamic polarization mode dispersion (PMD) compensator is demonstrated experimentally.

The study of multifunctional intelligent fiber amplifier

In this paper, a kind of multifunctional intelligent fiber amplifier with gain flattening, automatic gain control (AGC), automatic power control (APC), chromatic dispersion compensation, amplified spontaneous emission (ASE) noise filtering is developed by using long-period fiber grating (LFG), uniform Bragg grating, chirp fiber grating and APC circuit. This amplifier have a variety of applications in optical communication system