Dec 2010, Volume 3 Issue 4

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    Wei CHEN, Shiyu LI, Peixiang LU, Dongxiang WANG, Wenyong LUO

    Dispersion compensation was originally proposed to equalize pulse distortion. With the development of wavelength division multiplexing (WDM) techniques for large capacity optical communication systems, dispersion compensation technologies have been applied into the field. Fiber-based dispersion compensation is an attractive technology for upgrading WDM communication systems because of its dispersion characteristics and good compatibility with transmission optical fibers. Dispersion compensation fibers and the modules are promising technologies, so they have been receiving more and more attention in recent years.

    In this work, high performance dispersion compensation fiber modules (DCFMs) were developed and applied for the 40 Giga bit-rate systems. First, the design optimization of the dispersion optical fibers was carried out. In theory, the better the refractive index profile is, the larger the negative dispersion we could obtain and the higher the figure of merit (FOM) for the dispersion optical fiber is. Then we manufactured the fiber by using the plasma chemical vapor deposition (PCVD) process of independent intellectual property rights, and a high performance dispersion optical fiber was fabricated. Dispersion compensation fiber modules are made with the dispersion compensating fibers (DCFs) and pigtail fibers at both ends of the DCFs to connect with the transmission fibers. The DCFMs present the following superior characteristics: low insertion loss (IL), low polarization mode dispersion, good matched dispersion for transmission fibers, low nonlinearity, and good stability for environmental variation.

    The DCFMs have the functions of dispersion compensation and slope compensation in the wavelength range of 1525 to 1625 nm. The experiments showed that the dispersion compensation modules (DCMs) met the requirements of the GR-1221-CORE, GR-2854-CORE, and GR-63-CORE standards. The residual dispersions of the G.652 transmission lines compensated for by the DCM in the C-band are less than 3.0 ps/nm, and the dispersion slopes are also compensated for by 100%. With the DCFMs, the 8×80 km unidirectional transmission experiments in the 48-channel 40 Gbps WDM communication system was successfully made, and the results showed that the channel cost was smaller than 1.20 dB, without any bit error.

    Jing HUANG, Deming LIU

    A signal remodulation scheme of 10-Gb/s differential phase-shift keying (DPSK) downstream and 10-Gb/s on-off keying (OOK) upstream using a semiconductor optical amplifier (SOA) and a Mach-Zehnder intensity modulator (MZ-IM) at the optical networking unit (ONU) side for wavelength division multiplexed passive optical network (WDM PON) is proposed. Simulation results indicate that error-free operation can be achieved in a 20-km transmission, and the receiver sensitivity of return-to-zero differential phase-shift keying (RZ-DPSK) is higher than nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) in the proposed scheme.

    Shangjian ZHANG, Lei XU, Yong LIU, Yongzhi LIU

    A novel clock distribution concept based on in-band phase-modulated pilot insertion is demonstrated. This method avoids the need for an ultrafast phase comparator and a phase-locked loop in the receiver. Experimental results show that the clock can be successfully extracted from 160 Gbit/s optical time-division multiplexing (OTDM) data signal and employed for demultiplexing of 40 Gbit/s tributaries. The in-band clock distribution introduces 1.5 dB of power penalty with an error-free performance.

    Bin LI, Fengguang LUO, Zhihua YU, Weilin ZHOU, Liangjia ZONG

    A novel architecture of optical code (OC) label generation and recognition for optical packet switching (OPS) by using super structured fiber Bragg grating (SSFBG) is proposed. The OC label is generated and recognized by a label generator and recognizer, respectively. The label generator is composed of N encoders in parallel, and it can generate 2N kinds of serial optical code labels (SOCLs) for indicating 2N network routing information. The label recognizer can decode SOCLs by N decoders in parallel and provides label information to the switching control unit so that clock information is not required during the decoding process. In the switch nodes, handling of the high-speed information payload stream and the recognition of the OC label are performed in the optical domain, while processing of the routing information remains in the electrical domain. This approach could be a promising solution for an OPS network with high capacity, good quality of service (QoS), multi-service function and high security. In this experiment, we demonstrate 40 Gbps 256 label optical packet switching that employs clockless SOCL processing.

    Li PEI, Chunhui QI, Tigang NING, Song GAO, Jing LI

    Microwave photonic filter (MPF) as one of the key devices in the radio-on-fiber (ROF) system has attracted much interest recently. Some key technologies of MPF including the coherence, quality factor (Q) and reconfigurability are introduced. The difference between the incoherent and coherent MPF (ICMPF and CMPF) is given, and the methods to realize an ICMPF are also introduced. Higher Q factor MPF can be developed with more taps, and it is proved by simulation. Then the methods of finite and infinite impulse response MPF (FIRMPF and IIRMPF) are both given. At last, the reconfigurability is verified by four kinds of window functions.

    Shijuan WU, Baojian WU, Kun QIU, Chongzhen LI

    According to the symmetry of transmission matrix for non-uniform magneto-optic fiber Bragg gratings (MFBGs), the simulation model of the non-uniform MFBGs with bidirectional injection of light has been presented for the Optisystem software. The simulation model is verified by comparing with the Matlab numeric results using the piecewise-uniform MFBG model. As an example, the polarization-dependent loss (PDL) of an MFBG-based Sagnac interferometer (MSI) is analyzed in detail. Simulation results indicate that the magnetic field sensitivity of the MSI system can be improved by optimizing the coupling coefficient of the coupler, and the maximum of peak PDL is up to three times that of the single MFBG structure. The simulation model proposed in the paper is useful for the design of MFBG-based optical information devices.

    Yan LIU, Bo LIU, Hao ZHANG, Yinping MIAO

    In this paper, a novel simple but effective method is presented to construct compact all-fiber Mach-Zehnder (M-Z) interferometer based on CO2-laser-machined micro-notches in single mode fibers. Interference fringes are obtained, and temperature, force, and bending characteristics of the interferometer have been experimentally investigated. Such a compact fiber component with acceptable sensing performances makes it a good candidate for the measurement of numerous physical parameters.

    Xin WU, Sihai CHEN, Xiaogang XIONG, Benyi SHI, Wei CHEN

    The optical scanner is one of the most important components in free-space optical communications, airborne and space-based lidars, adaptive optics, and so on. The performance of an optical scanner is frequently limited by the presence of mechanical resonances. This paper presents an analog notch filter with adjustable function to reject the mechanical resonances of the optical scanner. First of all, the structure and work principle of the piezoelectric optical scanner are introduced. Furthermore, the frequency sweep method based on virtual instrumentsβis used to gain the natural frequency of the piezoelectric optical scanner. Then, the notch filters in series are used to reduce the oscillation of the scanner at the resonance frequencies. A variety of scanning experiments were carried out. After the introduction of the notch filter, the non-linearity was reduced to±1.1% from±2.1%. The linearity performance was greatly improved.

    Saeed OLYAEE, Samaneh HAMEDI, Zahra DASHTBAN

    Noncontact displacement measurement is generally based on the interferometry method. In the semiconductor industry, a technique for measuring small features is required as circuit integration becomes denser and the wafer size becomes larger. An interferometric system known as a three-longitudinal-mode heterodyne interferometer (TLMI) is made of two main parts: optical setup and electronic sections. In the optical part, the base and measurement signals having 500-MHz frequency are produced, resulting from interfering three longitudinal modes. The secondary beat frequency to measure the displacement in the TLMI is about 300 kHz. To extract the secondary beat frequency, wide-band amplifiers, double-balanced mixers (DBMs), band-pass filters (BPFs), and low-pass filters (LPFs) are used. In this paper, we design the integrated circuit of a super-heterodyne interferometer with total gain of 56.9 dB in size of 1030 μm×1030 μm.

    Yunpeng FENG, Xiaoyan QIAO, Haobo CHENG, Yongfu WEN, Ya GAO, Huijing ZHANG

    During the testing of aspherical mirrors through the null compensation method, structural parameters observe changes which affect the test results of interference pattern. Several errors are induced due to the maladjustment among compensator, interferometer and the mirror under test. It is important for optical manufacturing, testing and the actual alignment process to distinguish between the aberrations arising from both surface errors and maladjustment of the null compensation testing system. The purpose of this paper is to obtain the real aspheric surface errors during the optical polishing process. In this work, we have established an error separation model to the least square method to separate the errors caused by the maladjustment of the testing system from the test results. Finally, the analysis and simulation results show that high precision figure errors can be obtained by separating the maladjustment errors.

    Lei DING, Fanghui ZHANG, Qian JIANG, Honggang YAN, Dinghan LIU

    This paper is based on the analysis of white organic electroluminescent device electroluminescent spectrum to explain the regular pattern of carrier radiation distribution. It has proved electron that is injected from cathode is satisfied with the regularity of radiation distribution on the organic emitting layer. This radiation distribution is related to several factors, such as electron injection capabilities, applied electrical field intensity, carrier mobility, etc. The older instruction design is ITO/2-TNATA/NPB/ADN:DCJTB:TBPe/Alq3/cathode. Get to change electron injector capabilities through using different cathode and also find electroluminescent spectrum to produce significant changes. Simultaneously, electron radiation quantity has some limitation, and electroluminescent spectrum reflects that spectral intensity does not change anymore when the ratio of cathode dopant reaches a value, namely, the quantity of electron’s radiation distribution gets to a saturated state on the organic emitting layer. It also shows the same spectrum variational phenomenon while changing the applied electrical field intensity. To put forward of the carrier radiation distribution is good for organic light emitting diode (OLED) luminescence properties analysis and research.

    Feng CAO, Duan LIU, Jiang LIN, Bichun HU, Deming LIU

    The absorption coefficient of methane is very important for measuring the concentration of methane. We theoretically analyzed the general expression of methane absorption coefficient for a given condition, at room temperature of 296 K, and we simulated the relationship between the absorption and the wavelength of the light source. The experimental results we obtained are consistent with the simulation. The discrepancy between the experimental results and the simulation results is also discussed.

    Hongbin SHEN, Gang LI, Han ZHANG, Wengang HU, Bing ZHOU, Bingqi LIU

    The optical elements’ maladjustment is a potential threaten in optical systems, thus, the transmission feature of laser beams passing through a misaligned optical system is widely studied. By using approximate expansion of circle diaphragm and generalized Huygens-Fresnel diffraction formula, a universal analytic expression is deduced for the flat-topped multi-Gaussian beams passing through a misaligned optical system with two-lens and two-diaphragm. The study on the propagating property of fundamental-mode Gaussian beams and a flat-topped multi-Gaussian beam is carried out accordingly. The expansion of complex Gauss function of misaligned optical circle diaphragm is given, as well as a group of new parameter values of the expansion of complex Gauss function. By using the new parameter values, the influence of disadjust parameters on output intensity distribution is analyzed numerically. The result shows that the diaphragms’ offset can make the beams offset or covered, and the second diaphragm influences more; the angle deflection of diaphragms can make light beams compressed in the deflection direction, and the first diaphragm influences more; the offset of the first lens can weaken light intensity in the same direction of the lens offset, and the offset of the second lens can weaken light intensity in the opposite direction of the lens offset; the angle deflection of the first lens can make light beams move to the opposite direction, and the angle deflection of the second lens has no influence; when all the diaphragms and the lenses are disadjust, the angle deflection of the first lens has a vital influence to the output intensity distribution.

    Haobo CHENG, Yunpeng FENG, Tan WANG, Zhichao DONG

    This research is aimed at the development of computer-aided polishing technology for optical surfaces using magnetorheological (MR) fluid as medium. The mechanism of a dual-axis polishing wheel and the mathematical model combined with a symmetrical tool function are demonstrated. The effects of speed, gap, time and geometric parameters of the tool have been experimentally evaluated by polishing a parabolic BK7 mirror in 120 mm diameter. The surface topography presented an obvious amelioration, and the shape accuracy decreased to 0.067λ from 0.519λ (λ=632.8 nm, RMS) after 75 min finishing.

    Juan ZHAO, Junsheng YU, Wen WEN, Yadong JIANG

    Organic light-emitting devices (OLEDs) were constructed with a structure of indium tin oxide (ITO)/N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) (50-x nm)/bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2′] iridium (acetylacetonate) [(t-bt)2Ir(acac)] (d nm)/NPB (x nm)/2,2′,2′′(1,3,5-benzenetriyl)tris-(1-phenyl-1H-benzimidazole) (TPBI) (30 nm)/Mg:Ag (200 nm). A thin blue emission material of NPB was used as a separating layer, and the (t-bt)2Ir(acac) yellow phosphorescent dye was acted as an ultrathin light-emitting layer. TPBI acted as both hole-blocking and electron-transporting layer. By changing the location (x) and the thickness (d) of the phosphor dye, the variation of device performance were investigated. The results showed that all the devices had a turn-on voltage of 2.8 V. In the case of d=0.2 nm and x=5 nm, the OLED had a maximum luminance of 18367 cd/m2 and a maximum power efficiency of 5.3 lm/W. The high performance is attributed to both direct charge carrier trapping of iridium phosphor dye and the thin NPB separation layer, which effectively confines the recombination zone of charge carriers.

    Jian LIU, Hao ZHANG, Bo LIU

    Based on the interferences between core modes and cladding modes in photonic crystal fiber (PCF), a novel temperature sensor is presented and experimentally demonstrated. The peak wavelength of the interference spectrum linearly increased with an increase in temperature. A measurement sensitivity of 10.38 pm/°C was experimentally achieved for temperatures ranging from 30°C to 100°C. Experimental results also indicate that the curvature and transverse load do not have a distinguishable influence on the transmission spectrum of the proposed fiber sensor, which ensures its applicability for practical applications.

    Khaleel S. ALTOWIJ, Abdulsalam ALKHOLIDI, Habib HAMAM

    Free space optical (FSO) communication is one of the most recently developed modes of wireless communication. FSO is a technique used to convey data carried by a laser beam through the atmosphere. While FSO offers a broadband service, it requires a line of sight communication between the transmitter and receiver. The atmosphere has effects on the laser beam passing through it. For instance, the quality of data received is affected by the scattering and atmospheric turbulence. The atmospheric turbulence is caused by both temporary and special random fluctuations of the refractive index along the optical propagation path. Clear air turbulence impairs the performance of the FSO due to the fluctuation in the intensity of the laser beam. By referring to the two criteria, namely bit error rate (BER) and signal to noise ratio (SNR), this work includes analysis of the effect of atmospheric turbulence on FSO systems in Yemen by using an appropriate model.