KEYWORDS: Dispersion, Microwave radiation, Telecommunications, Signal processing, Digital signal processing, Signal detection, Sensors, Transmitters, Fiber optic communications, Optical amplifiers
A feasible and cost-effective online chromatic dispersion (CD) monitoring scheme for high speed optical communication system is demonstrated in this paper. Based on the formerly verified theoretical model, the output electrical power of a specific frequency band is tested to reflect the residual chromatic dispersion online. Thus the microwave devices are selected to form the electrical power detecting circuit, which consists of a PIN photodiode, a microwave power filter and a power detector in tandem. In the experiments, frequency band center were chosen at 5 GHz for the 10 Gbit/s system and 12 GHz for the 40 Gbit/s system. Then the output voltage of the detector was processed and converted to digital signal and the signal was processed to obtain the amount of the chromatic dispersion of the tested systems. For the 40 Gbit/s system, the maximum detectable chromatic dispersion was around 130-ps/nm and a resolution of 5-ps/nm/db was achieved at the chosen frequency band centered at 12 GHz. Performance of the microwave devices and comparison of the experimental results at different frequency bands are also discussed, which verified that the chosen center frequency was suitable for detection of CD in optical communication system beyong 10 Gbit/s speed.
A white light Michelson interferometer is designed to measure the distributed polarization mode coupling in High birefringence polarization-maintaining fibers (HiBi-PMFs). Using a Michelson interferometer to compensate the optical path difference induced by the modal birefringence of PMF, both power coupling intensity and position of the coupling point can be acquired. Traditionally, this technique requires only one polarization mode in the PMF to be exited or both polarization modes to be exited with equal intensity. This needs precise alignment of the polarization direction with the principal axis of the PMF. In practice, it's not easy to realize. In this paper, the influence of the incident polarization extinction ratio (PER) on the measurement result was evaluated theoretically and experimentally. A polarization state adjusting mechanism is designed. An analyzer can be oriented at any angle of the PMF's principle axes. By alternating this angle between 0o, 90o and 45o, the incident PER can be calculated and the measurement can be carried out with random exited polarization mode. An instrument was designed and implemented to verify this scheme. Spatial resolution better than 7cm and coupling strength sensitivity less than -75dB are realized.
A high-performance switched optical interconnection network is designed. The top layer of optical fiber ring network builds upon wavelength division multiplexing and hardware routing technologies. The bottom layer of star network has a throughput of 10 Gbit/s based on an 8-channel digital cross-point switch. Two types of optical network interface cards are developed to meet the requirements of interconnection bandwidth and support PCI bus full bandwidth of 1.056 Gbit/s and 4.224 Gbit/s, respectively. Field programmable gate array (FPGA) is adopted for frame head analysis, hardware routing and dynamic switch configuration. By adding a subnet to enlarge the network, the maximal delay increment is only 1.5 μs.
A microstructure inspection endoscope, based on directly imaging, is proposed. It is designed for detecting defects on the surface of optical fiber end. It is matched with FC or SC female fiber connector. The inspection head of the endoscope can be put into a 2.5-millimeter-diameter micro-pore. Its numerical aperture is not restricted by tiny dimension of object lenses. System resolution is increased to 600 line-pairs per millimeter. The endoscope consists of object lenses, scanner slab and kohler illumination system. The design provides possibility of various utilities such as aiming at a smaller subject by micro optical scanner and modeling the surface by tri-dimensional vision. And the optical system includes low-magnification lenses and high-magnification zoom lenses. Rough observation at low-magnification and particularly inspection at high-magnification are provided. The instrument has the advantages of high identification, compact configuration and flexible manipulation.
The numerical aperture (NA) of the double beam interferometers (DBI) can affect the accurate measurement of surface profiles. Based on the double beam interference microscope imaging theory, the fringe spacing will vary wide nonlinearly with the increasing of numerical aperture. The double beam interferometers require oblique incidence illumination, including Michelson, Mirau and Linnik types. The intensity distribution of the illumination across its stop is constant so the correction factor depends mainly on the NA in the Michelson and Linnik interferometers. The correction factor expression is derived in the Michelson interferometer. The reference surface is a central obscuration in the beam, which will reduce the effective numerical aperture in the Mirau interferometer. At the same numerical aperture, larger central obscuration has a much effect on the correction factor. The correction factor expression is determined by considering the influence of central obscuration and oblique incidence in the Mirau interferometer.
Both hardware and software are optimized simultaneously to improve the bus throughput of node computer in cluster computing network. A cost effective optical interconnection ring network is established using off-the-shelf PCs with windows operating system. A network adapter card ONIC is developed. Using ETDM and field program technique, the full bandwidth of the 32bit×33MHz PCI bus is reached in physical layer. In order to overcome the hardware and software data bottlenecks induced by using of general purpose platform such as PCs and Windows 2000 system, several methods are adopted to maximum the bus throughput of node computer. A user-level interface is designed to blur the kernel/user mode boundary of the software system, and bypass the OS overhead. Zero-copy DMA is realized. The bandwidth in application level using PIO and DMA transfer mode is improved 17 and 26 times respectively. The sustained bandwidth in application layer can reach 437.6Mbit/s. It’s also shown theoretically and experimentally that the selection of main board chipset, using memory space map, reasonable using of PIO and DMA transfer mode, using polling and large MTU will also improve the bus throughput of node computer considerably.
In this paper, a white light interferometer has been designed to measure the distributed polarization coupling in high birefringence fibers. The limitations to the measurement accuracy have been analyzed. The main structure is a Michelson interferometer. A superluminescent diode (SLD) has been adopted as the broadband source in the white light interferometer. Corner mirrors have been adopted to reflect the light beams in both arms of the Michelson interferometer. To enlarge the measurement range, the light beam in the scanning arm of the Michelson interferometer is reflected three times. Thus the scanning range of the interferometer is doubled for a certain linear motion rail. The full width half maximum (FWHM) spectrum of the SLD is 50 nm, and its central wavelength is 1300 nm. If the modal birefringence of the HBF is 6 X 10-4, a spatial resolution of 56 mm can be achieved. A high sensitivity photo detector and a high-resolution analog to digital converter (ADC) have been adopted. These devices are capable of testing a coupling point with accuracy up to -80 dB.
White light interferometry has been adopted to measure the distributed polarization coupling in high birefringence fibers. A superluminescent diode is adopted as the optical source in the white light interferometer. To enlarge the measurement range, the light beam in the scanning arm of the Michelson interferometer is reflected three times. Thus the scanning range of the interferometer is doubled. The full-width half-maximum spectrum of the SLD is 50 nm, and the central wavelength is 1300 nm. If the modal birefringence of the HBF is 5×10-4, a spatial resolution of 70 mm can be achieved. A high sensitivity photo detector and a high-resolution analog to digital converter have been adopted. The polarization coupling intensity measurement accuracy can be up to -75 dB.
In this paper, a novel method to measure the distributed polarization mode coupling in polarization-maintaining (PM) fibers is introduced. The measurement system is based on white light interference. A super luminescent diode is used as the broadband light source in the system. The whole test system is working on 1300nm wavelength. There are two main parts of the measurement equipment: polarization adjustment and a scanned Michelson interferometer. In order to improve the accuracy, a piezoelectric transducer (PZT) is applied in the scanned Michelson interferometer. The maximum length of tested polarization-maintaining fiber is one kilometer, and the spatial resolution of this method reached 60 mm along the tested PM fiber. The degree of polarization mode coupling that could be detected is —75dB.
We present a new device for determining the state of polarization (SOP) during the measurement of spatial distribution of mode coupling in high birefringent. polarization-maintaining (PM) fibers. The linear polarization light can be randomly rotate to obtain the best experimental result through it. And we draw a conclusion that in the distributed polarization coupling analyzer (DPCA) the fringe contrast is equal to 0.943 when the amplitude ratio is equal to 1. It can be widely used in the PM fiber testing and linearly polarized light interference system.
In this paper, an apparatus has been designed to inspect the end surface of fiber optic connectors. A white-light high-brightness light emitting diode has been adopted to offer enough light power. Zoom lenses comprise field lens and achromatic lens with a large range of magnification from 1.25 to 60. They can be used to inspect not only the whole ferrule but also the details of the core. The illumination system has two modes: perpendicular and oblique. In oblique illumination, the relation on the maximum length of shadow
along the incident direction and the angle of oblique illumination is disclosed and the curvature of shadow is drawn. Fiber undercut and protrusion can be judged whether they are satisfied the tolerance with the curvature.
A noncontact system for detecting and monitoring the grain and contour of optical connector end face based on Mirau-type interferometer is proposed in this paper. In this system, phase shift technique has been adopted. A five steps algorithm is presented. By this algorithm, the computer can analyze the interference pattern and unwrapped the phase information of the detected surface. Then we can get the differential height of every point on the surface. This
method is capable of measuring fiber height to ±0.003 microns and radius of curvature and offset of polish to ±0.30 mm and ±2.0 microns respectively. So we can get not only 2-D and 3-D topography of testing surface, but also the evaluation parameters of surface roughness.
In this paper, we overview the research and development of optical interconnection network from 1993 to 2001 in Tianjin University. These works are divided into two categories. One is optical interconnection network for massively parallel processing systems. Another is optical interconnection technique for computer clusters. In the former, we have designed a massively parallel processing system that consists of 64 processors, which are interconnected by optical fiber links. In the later, we have developed giga-bitls optical links, hardware-routing optical rings and wavelength-routing dual rings. The optical layer data transmission speed has been improved from 20 Mbit/s in the massively parallel processing system to 1.25 Gbit/s in the computer clusters. Meanwhile, the communication latency has been reduced to 200 ns adopting hardware-routing technique. To further reduce the data packet routing-latency, wavelength routing technique has been implemented in a dual-wavelength ring. Finally, we have designed some novel network structures for tera-bit/s optical interconnection network.
A multi-pipeline optical interconnection network for distributed computing system has been designed. Each sub-layer network is connected to the ring with an access node (AN), which can transmit data at every wavelength with a tunable laser diode. The data transmission speed at each wavelength is 1.25 Gbit/s. With 8 wavelengths, a total bandwidth of 10 Gbit/s can be obtained. Each AN only receives a certain wavelength. With a band pass filter, the desired optical signal can be dropped down. Pipelining data transmission is achieved among different wavelengths. This network is a multi-pipeline structure. So the communication latency and communication overheads can be decreased. Meanwhile, the ring topology has good scalability. The scale of the network can be expanded adopting more wavelengths at each access node.
A high-performance metropolitan area network has been designed with the combination of coarse wavelength division multiplexing (CWDM) and electrical time division multiplexing (ETDM) techniques. The network consists of n access nodes with each node transmitting and receiving m wavelengths. Virtual multi-channel (VMC) has been achieved at each wavelength via ETDM technique to minimize the data blocking possibility. This network structure has high bandwidth, low communication latency and high performance-to-cost ratio. A prototype network of 6 access nodes has been implemented with 4 virtual channels at each wavelength. The data transmission speed at each wavelength is 1.25 Gbit/s. It can be upgraded to 2.5 Gbit/s. The network has high flexibility and scalability. To further expand the network capacity, multi-wavelength window CWDM technique can be adopted at 1300 nm and 1550 nm simultaneously.
This paper presented an optical interconnection multiple PC system connected by a ring network. This multiple PC system uses Linux Operating system, and the standard communication protocol of complying with Ethernet specification. This paper studied the factors that influence the interconnection performance among multiple computers, including the effect of the buffer size of OLI on the bandwidth of network layer, and the effect of retransmission method on the performance. The results of ping-pong test show that optical fiber link is able to provide high-bandwidth and low-latency communication for a multi-PCs system. We found that the performance of the interconnection network can be improved by improving the interface match between the optical fiber link and computer bus input/output. Besides, the development of a chip to implement network interface and a part of network protocol, such as developing with FPGA device in this paper, could result in the higher performance of the interconnection.
KEYWORDS: Data transmission, Field programmable gate arrays, Clocks, Human-machine interfaces, Data communications, Interfaces, Local area networks, Switching, Computer networks, Time division multiplexing
A giga-bit per second optical ring has been designed. The data link layer bandwidth of the network is 1.5 Gbit/s. Hardware routing has been achieved by field programmable gate array (FPGA) to minimize the communication latency. As a result, the point-to-point communication latency between adjacent node computers is less than 300 ns. To reduce the data communication latency and have a more efficient usage of the data link layer bandwidth, virtual multi-channel transmission mechanism has been achieved with hardware. The network supports a maximum of four virtual channels for each physical data link. Time slots can be dynamically assigned to each virtual channel. The length of each time slot can also be dynamically selected based on the length of each data packets. Zero wait time has been achieved for the switching between different virtual channels. The relationship between the network performance and the number of virtual channels has also been analyzed in this paper.
In this paper, high-density and large-capacity parallel data reliable transmission has been accomplished in high electro-magnetic interference environments via virtual- parallel optical transmission technique. Through time division multiplexing (TDM), all the parallel data signals and control signals are converted to high-speed serial data stream. Each bit is transmitted in a time slot during a frame period Thus, the parallel signals can be transmitted using only one opto-electronic device. Each optical transmission channel consists of two optical fibers, can achieve full-duplex transmission of 24 bits parallel signals. The maximum frame rate is 75 MHz. This data transmission card can be expanded to 6 channels, has a maximum data throughput of 15 Gbps. This optical data transmission link can work properly for a wide range of supply voltage. When the supply power voltage varied from 4.2 to 7.0 volts, the bit error rate (BER) is still below 10E-12.
A hybrid opto-electronic optical fiber inspection system based on a quasi-joint transform correlator is proposed. The system can overcome the drawback of the overall small size of the joint transform spectrum in a conventional JTC. Experiment results show the system can successfully perform the defect detection of optical fibers. Furthermore, it has higher discrimination comparing with the conventional JTC.
In this paper, some study results to apply fiber link to a computer cluster are presented. The research is based on a ring network topology for a cluster system, which is connected by gigabit/s virtual parallel optical fiber link (VPOFLink) and its driver is for Linux Operating System, the transmission protocol of VPOFLink is compliant with Ethernet standard. We have studied the effect of different types of motherboard on transmission rate of the VPOFLink, and have analyzed the influence of optical interconnection network topology and computer networks protocol on the performance of this optical interconnection computer cluster. The round-trip transmission bandwidth of the VPOFLink have been tested, and the factors that limit transmission bandwidth, such as modes of forwarding data packets in the optical interconnection ring networks, and the size of the link buffer etc., are investigated.
In this paper, a communication protocol has been designed for the two-layer scalable optical interconnection network (TSOINet) designed in Tianjin University. The communication protocol has been designed based on TCP/IP (transmission control protocol/internet protocol) protocol. But it is more efficient than TCP/IP for data transmission in TSOINet. An auxiliary channel has been introduced in TSOINet for transmission of the communication status messages among the sub-layer rings. Many network management functions, such as flow control, hand shaking, etc., can be achieved via the auxiliary channel, so the communication overheads can be decreased. The performance of the communication protocol has been evaluated compared to TCP/IP protocol for data transmission in TSOINet.
A hybrid opto-electronic correlator for detecting defects in optical fibers is proposed. After the light from a He-Ne laser being expanded and filtered, it is not collimated but directly passes a Fourier transform lens and illuminates a fiber to be detected and a perfect fiber as reference one at the input plane. The Fourier transform spectrum of the fiber pair is obtained at the rear focal plane of the lens, where it is sampled via a CCD array connected with a computer through a frame grabber. The computer performs filter, inverse Fourier transform and setting threshold operation on classification. Under specific conditions, the system is an equivalent of joint transform correlator with a Fourier lens of long focal length. We analyze the conditions in terms of theory and show the experiment results corresponding to optical fibers having incoordinate defects. The results indicate that the system can be used for fiber defects detection, and it has the advantages of high identification, compact configuration, easy adjustment and flexible manipulation.
In this paper, we present a low cost fiber-optic data link for the computing cluster. The link is a 32 bit-virtual- channel fiber-optic computer bus used only a pair of OE devices and fibers. The link is integrated with the popular PCI Bus interface in order to make the link hold the same bandwidth as that of the PCI Bus, and it can operate under managed by PCI Bus. Our research addresses how to match accessing bandwidth between computer bus and high-speed optical interconnections, and how to make low overhead and latency interfaces between optics and electronics, and integrates fiber optic link into computing system designs.
This paper describes the two-layer scalable wavelength routing optical interconnection network being developed in Tianjin University. The top layer of the network is multi- wavelength bi-directional optical bus, which has high bandwidth and low latency. The optical bus is made up of passive components, no wavelength-tunable devices have been sued. As a result, the optical bus has low communication latency that is mainly decided by the optical fiber length. The sub-layer of the network is single-wavelength ring, which has low communication latency and high-scalability. In each ring, a wavelength routing node is used for data transmission between the ring and the optical bus. Each node computer is connected to the ring using an optical network interface card, which is based on peripheral component interconnect bus. The communication latency inside the ring is decreased using synchronous pipelining transmission technique. The scale of the ring is mainly limited by the efficient bandwidth required by each node computer. The number of rings is mainly decided by the optical power of the laser diodes and the sensitivity of the optical detectors. If Erbium doped fiber amplifier is used in the optical bus, the scale of the network can be further developed.
In this paper, wavelength routing technology is applied to computer interconnection network. By analyzing the relationship between wavelength and networks routing, we describe a concept of wavelength being used as network address, and propose a wavelength routing topology to extend the scale of networks and realize scalability of networks. A twin-wavelength ring network to implement and test the function of wavelength routing is presented, and the main units of the twin-wavelength ring network are presented as well. In addition, we put forward tow methods to implement it. The design method of physical link driver software for Linux, which uses optical interconnection interface as network interface for parallel computing, is also introduced.
Joint transform correlation systems are proposed for detecting defects in optical fibers. When joint transform spectrum of the reference and the signal fibers is sampled, off focus operation has been adopted. The corresponding influence on detection results is discussed in theoretical analysis, computer simulation and experimental comparison. In addition, a correlation processor is demonstrated, in which after the light from a He-Ne laser being expanded and filtered via a spatial light filter, it passes a Fourier transform lens without being collimated. This processor is actually an equivalent of joint transform correlator with long focal length Fourier transform lens. The experiment results of detecting defects in fibers are also given, which indicate that joint transform correlation systems can be used for automatic fiber defects detection.
The investigations on GaAs/AlGaAs multiple quantum well self electro-optic effect device (SEED) arrays for optoelectronic smart pixels are reported. The hybrid integration of GaAs/AlGaAs multiple quantum well devices flip-chip bonding directly over 1 micrometers silicon CMOS circuits are demonstrated. The GaAs/AlGaAs multiple quantum well devices are designed for 850 nm operation. The measurement result under applied biases show the good optoelectronic characteristics of elements in SEED arrays. The 4 X 4 optoelectronic crossbar structure consisting of hybrid CMOS- SEED smart pixels have been designed, which could be potentially used in optical interconnects for multiple processors.
It is well known that a wavelength can be regarded as an address code of a packet in the optical interconnection network. In our scheme, we use wavelength as a part of an address to build a multiple wavelengths optical interconnection ring network. The network consists of double layer rings, the routing inside a ring is electronic, and wavelength routing technology is applied to switch between rings. Two wavelength are used in the network, one is for transmitting data inside local ring, another is for switching to another ring. The detail of the network is described in this paper. Besides, a low-cost virtual parallel optical link and optical interconnection interface, which is bound up with the multiple-wavelengths network, is presented.
In this paper, the design idea and application of an optoelectronic hybrid interconnection network are presented. In this network, the programmable electronic device is used for reconfiguring the topologies, and the optical fiber are used for transmitting the flows of data and instructions.
A forward scattering particle image velocimetry is presented in which a low power cw laser and a band pass filter are used. The experimental results measuring the rising velocities of oil droplets of low density are given.
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