Mar 2013, Volume 6 Issue 1

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    Jian WANG
    Wei JIN, Jian JU, Hoi Lut HO, Yeuk Lai HOO, Ailing ZHANG

    This paper reviews different types of air-silica photonic crystal fibers (PCFs), discusses their novel properties, and reports recent advances in PCF components and sensors as well as techniques for splicing PCFs to standard telecomm fibers.

    Sigang YANG, Kenneth K. Y. WONG, Minghua CHEN, Shizhong XIE

    The development of fiber optical parametric oscillators (FOPO) based on highly nonlinear dispersion-shifted fiber is reviewed in this paper. Firstly, the background and motivation are introduced, and it is pointed out that the FOPO is promising to act as optical source in non-conventional wavelength bands. Subsequently, the context focuses principally on the problem of inherent multiple-longitudinal-mode characteristic of FOPO and the corresponding solutions to it. The primary technique is by locking the phase of multiple longitudinal modes. The first reported actively mode locked FOPO is also presented in this article. However, it is not probable to realize passively mode locked FOPO because of the random phase dithering of the pump required for suppressing stimulated Brillouin scattering. Furthermore, a regeneratively mode locked FOPO is demonstrated, which can generate wide band tunable radiation in non-conventional wavelengths. Besides mode locked FOPO, the single-longitudinal-mode FOPO is also introduced. Finally, potential future directions are discussed.

    Xiang ZHOU

    This paper reviewed the recent progress in transmission of 400 Gb/s, wavelength-division-multiplexed (WDM) channels for optical networks based on the standard 50 GHz grid. We discussed the enabling modulation, coding, and line system technologies, as well as the existing challenges. It is shown that, 400 Gb/s per channel signal can be transmitted on the standard 50 GHz ITU-T grid at 8.4 b/ds/Hz net spectral efficiency (SE) over meaningful transmission reach for regional and metropolitan applications. However, further studies are needed to fully understand the potential for meeting the requirements of long-haul transmission applications.

    Zhengxuan LI, Lilin YI, Weisheng HU

    In this paper, key technologies, system proposals and future directions of next generation passive optical networks stage 2 (NG-PON2) are reviewed. We first discuss the potential solutions for NG-PON2 standardization. Then we focus on time and wavelength division multiplexed PON (TWDM-PON), which is the primary solution selected by Full Service Access Network (FSAN). The key technologies in TWDM-PON configuration are analyzed, including how to improve the bandwidth capacity and power budget of the system, and choose upstream tunable transceiver, etc. Several system proposals are illustrated as candidates for NG-PON2 configuration.

    Li HUO, Qiang WANG, Yanfei XING, Caiyun LOU

    In this paper, we review our recent works in 100 Gb/s signal generation and processing. A high-speed 100 Gb/s system with on-off keying (OOK) modulation format is implemented by using optical time division multiplexing (OTDM) method. As modifications of this system, simultaneous multicolor optical signal generation and 100 Gb/s return-to-zero (RZ)-to-non-return-to-zero (NRZ) format conversion are presented. We also demonstrate basic all-optical signal processing functions of 100 GHz clock recovery and 100 Gb/s all-optical 2R generation based on semiconductor optical amplifiers (SOAs).

    Claudio PORZI, Giovanni SERAFINO, Sergio PINNA, An NGUYEN, Giampiero CONTESTABILE, Antonella BOGONI

    Semiconductor optical amplifier-Mach-Zehnder interferometer (SOA-MZI) is a technologically mature optical device that can be exploited for a wide range of operations on both amplitude and phase modulated signals, with performance limited by the carrier lifetime in the SOAs. Recent advances on SOA structures have demonstrated their suitability for high quality, ultra-fast photonic signal processing, making SOA-MZI a good candidate for elaborating signals in new generation high-capacity optical networks. Dynamic wavelength switching/routing and add/drop operations are expected to bring benefits in future optical networks in terms of improved system flexibility and efficiency. The capability of performing such operations directly in the optical domain can significantly reduce the number of opto/electrical and electro/optical conversions in the routing nodes, reducing their power consumption and their latency time. Moreover, since phase-shift keying (PSK) formats or other advanced modulation formats involving both amplitude and phase modulation, start to coexist in optical communication systems with the conventional on-off keying (OOK) modulation format, the availability of a single device, suitable for processing all these different signals, is mandatory. The SOA-MZI fits all these requirements for both OOK and constant-envelope phase-modulated signals, providing a compact and flexible solution. Here we review on the use of the SOA-MZI for carrying out all-optical switching operations, by realizing wavelength conversion and add/drop functionalities, both for OOK and differential binary phase shift keying (DPSK) signals up to 40 Gb/s. Power penalties lower than 2 dB are demonstrated in all cases.

    Chaotan SIMA, James C. GATES, Michalis N. ZERVAS, Peter G. R. SMITH

    This paper reviews the demonstrations of photonic Hilbert transformers (PHTs), describing their progress and recent developments. The physical operating principles of PHTs including fractional Hilbert transformers are discussed, together with device applications in all-optical signal processing. Versatile approaches to realize PHTs are discussed, e.g., discrete free space optics, fiber-based schemes and integrated planar geometry. The numerical designs and experimental performances of these PHTs are analyzed in terms of spectral quality, operating bandwidth, system integration, and mechanical and thermal stability. Recent developments of the monolithically integrated photonic Hilbert transform (HT) devices include directional couplers and planar Bragg gratings which allow all-optical single-sideband (SSB) suppression and sideband switching.

    Thomas G. BROWN, Amber M. BECKLEY

    Spatial inhomogeneities in the polarization of a light field can show fascinating effects in focusing, propagation, illumination, and imaging. This paper provides examples of these effects and describes how deterministic stress on the periphery of an optical element can be used in fundamental studies of beam propagation, as well as applications such as polarimetry.

    Xia GUO, Xinxin LUAN, Wenjuan WANG, Chunwei GUO, Guangdi SHEN

    Scalabilities of light-emitting diodes (LEDs) and vertical-cavity surface-emitting lasers (VCSELs) with tunnel-regenerated multi-active-region (TRMAR) structure were investigated. It was found that the output optical power and quantum efficiency of these new LEDs with TRMAR increased with the number of its active regions, but the threshold gain and threshold current density decreased. However, for VCSELs with TRMAR, the differential quantum efficiency and optical power increased with the number of the active region. The results suggest that LEDs and VCSELs with the TRMAR structure have some potential advantages over the conventional LEDs or VCSELs in high internal quantum efficiency, low heat generation, high round-trip gain, and so on. These advantages will make TRMAR LEDs or VCSELs more attractive for the industrial application.

    Muhammad Idrees AFRIDI, Jie ZHANG, Yousaf KHAN, Jiawei HAN, Aftab HUSSEIN, Shahab AHMAD

    The performance of colorless wavelength-division multiplexing passive optical network (WDM-PON) systems suffers from transmission impairments due to Rayleigh backscattering (RB). A single feeder fiber colorless WDM-PON architecture was modeled, simulated and analyzed at 25 km distance that sustained the noise induced by RB. We analytically compared the performances between single feeder and dual feeder WDM-PON architectures based on array waveguide gratings (AWGs). For single feeder WDM-PON, the high extinction ratios in both return-to-zeros (RZ)-shaped differential phase shift keying (DPSK) downstream and intensity remodulated upstream data signals helped to increase the tolerance to the noise induced by RB. However, a cost effective colorless system in dual feeder WDM-PON architecture was achieved without any optical amplification and dispersion compensation, low power penalty. These results illustrate that single feeder fiber architecture was cost effective in terms of deployment having a power penalty, while dual feeder fiber had lower power penalty thereby with better performance. Simulation results show that downstream and upstream signals achieved error-free performance at 10-Gbps with negligible penalty and enhanced tolerance to the noise induced by RB over 25 km single mode fiber.

    Kambiz ABEDI, Habib VAHIDI

    In this paper, structure and microwave properties of a substrate removed GaAs/AlGaAs traveling wave electro-optic modulator structure were analyzed and simulated by using the finite element numerical technique for lower loss, simultaneous matching of optical and microwave velocities and impedance matching with 50 Ω. The effects of core layer thickness, claddings thicknesses, and width of the modulator on the microwave effective index nm were investigated, the characteristic impedance ZC, the microwave losses α, and the half-wave voltage-length product VπL were calculated. The results of the simulation suggest that the electrical bandwidth of 22 GHz and the optical bandwidth of 48 GHz can be obtained for fully matched, lower loss structure, which correspond to a 13 V·cm drive voltage.

    Diqiu HUANG, Xiangbin ZENG, Yajuan ZHENG, Xiaojin WANG, Yanyan YANG

    This paper presents the influence of process parameters, such as argon (Ar) flow rate, sputtering power and substrate temperature on the band gap of Al-doped ZnO film, Al-doped ZnO thin films were fabricated by radio frequency (RF) magnetron sputtering technology and deposited on polyimide and glass substrates. Under different Ar flow rates varied from 30 to 70 sccm, the band gap of thin films were changed from 3.56 to 3.67 eV. As sputtering power ranged from 125 to 200 W, the band gap was varied from 3.28 to 3.82 eV; the band gap was between 3.41 and 3.88 eV as substrate temperature increases from 150°C to 300°C. Furthermore, the correlation between carrier concentration and band gap was investigated by HALL. These results demonstrate that the band gap of the Al-doped ZnO thin film can be adjusted by changing the Ar flow rate, sputtering power and substrate temperature, which can improve the performance of semiconductor devices related to Al-doped ZnO thin film.