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 vertical-shaft-type Mirau white-light phase-shifting interferometer is designed based on white-light phase-shifting interference microscopy in this paper. The interferometer is composed of an illumination and interference imaging part, a piezoelectric transducer in the vertical direction, a two-dimensional scanning part in the test surface, image collection and interferograms analysis part. The light illuminates the sample and the test surface uniformly, and the interferogram is formed. In order to get phase-shifting, the move of the objective is driven by PZT. The three-dimensional scanning system consists of a two-dimensional horizontal motorized stage and a vertical piezoelectric transducer. Multi-aperture stitching extends the measurement range in the test surface. A new pixel divided phase-extracting algorithm was put forward in combination with a residues-pretreatment phase-unwrapping algorithm based on image segmentation. The algorithm is used to minimize the phase-shifting error and nonlinearity error of the detector. The surface profile of a fiber connector with fiber inserted was measured. Mean value of the protrusion between fiber and fiber connector was measured to be 45.7nm, with 0.9 nm error. The mean height of a spot on the end surface of fiber connector was measured to be 23.6nm, with 0.7nm error.
A multichannel bidirectional dynamic data transmission system (DDTS) through a rotary interface with one fiber is designed based on a fabricated single pass fiber optic rotary joint. The feasibility of transmission system is tested at both 1310- and 1550-nm wavelength bands. The performance of this DDTS was measured using optical spectrum analyzer and lightwave multimeter. The insertion losses of DDTS were 1.55 and 1.20 dB at 1310- and 1550-nm wavelength bands, respectively. The total bandwidth of the DDTS is more than 170 nm.
An 8-channel switching node with routing function is designed in this paper using a high-performance digital cross-point switch. The throughput of the 8-channel routing node is 10 Gbit/s. Combined with time division multiplexing (TDM) technique, a high-speed optical interconnection network was designed. Using Optical Network Interface Cards (ONIC) and the designed routing node, a two-layer optical interconnection network with structure of ring and star topology is designed. Based on circuits cascading technique, the network can be expanded to meet the request of large scale data communication with low communication latency.
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.
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.
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.
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