Time-interleaved photonic analog-to-digital converter (TIPADC) is a promising candidate to process ultra-wideband signals. In a TIPADC, quantization is electrical in order to obtain large effective number of bits (ENOB). In this paper, we study the issues on the signal sampling and reconstruction in the TIPADC from the systematic point of view. The sampling output and frequency response of the system are derived using a model that includes the photonic sampling, demultiplexing, photo detecting, electronic quantizing and digital processing. The signal sampling and reconstruction mechanism of TIPADC with a uniform system sampling rate and matched channels are illuminated with the spectrum of signal in each processing step. The effect of the sampling pulse and back-end electronics on the system frequency response is analyzed in detail. The feasible regions of the system for alias-free sampling in terms of system frequency response, and a set of sampling criteria on bandwidth of the sampling pulse and back-end electronics are presented for the TIPADC. We find that the analog bandwidth of TIPADC can be much higher than the bandwidth of back-end electronics due to the weighted summing introduced by the multichannel time-interleaved photonic sampling. The proposed model and sampling criteria are validated by simulations under different parameter configurations.
We propose a one-point to multipoint distributed time transfer through passive optical networks using a time division multiple access (TDMA) based two-way time transfer. The clock at each clock user node is, in turn, compared with the high-precision reference clock at a master node by a two-way time transfer during assigned subperiods. The corresponding TDMA control protocol and time transfer units for the proposed scheme are designed and implemented. A 1×8 experimental system with a 20 km single-mode fiber in each subpath is demonstrated. The results show that a standard deviation of <60 ps can be reached in each comparison subperiod.
KEYWORDS: Computing systems, Passive optical networks, Network architectures, Optical engineering, Reliability, Time division multiplexing, Field programmable gate arrays, Telecommunications, Data transmission, Control systems
A passive optical network (PON) based real-time Ethernet (PONRTE), which can take advantage of PON features such as broad bandwidth, high reliability, and easy maintenance to satisfy the determination and real-time requirements of high performance industrial applications, is proposed. The protocol model and network architecture having a compatible physical layer and MAC layer with Ethernet passive optical network are presented for the proposed PONRTE. A fixed periodic time slot allocation mechanism including a synchronic time division multiplexing transmission and an asynchronic data transmission is adopted to guarantee the determination and real-time of the communication. A simple and easy to implement time synchronization approach, where the starting time of the first transmission slot of an access node is synchronized by a relative time synchronization while the starting time of subsequent slots is determined by the fixed period and a dynamic time synchronization, is designed to support the fixed time slot allocation mechanism and avoid the collision in PONRTE. A 100 Mb/s PONRTE experimental testbed with 16 access nodes and a time allocation period of 240 μs is demonstrated. The results show that the experimental PONRTE can work stably and reliably with a frame loss ratio less than 10 −7 .
Optical burst switching (OBS) is more efficient and feasible solution to build terabit IP-over-WDM optical network by employing relatively matured photonic and opto-electronic devices and combining the advantage of high bandwidth of optical transmission/switching and high flexibility of electronic control/processing. Channel scheduling algorithm is one of the key issues related to OBS networks. In this paper, a class-based scheduling algorithm is presented with emphasis on fairly utilizing the bandwidth among different services. A maximum reserved channel numbers and a maximum channel search times is introduced for each service based on its class of services, load and available bandwidth resource in the class-based scheduling algorithm. The performance of the scheduling algorithm is studied in detail by simulation. The results show that the scheduling algorithm can allocate the bandwidth more fairly among different services and the total burst loss ratio under high throughput can be lowered with acceptable expense on delay performance of services with lower delay requirement. Problems related with burst loss ratio and the delay requirement of different services can be well solved simultaneously.
The first optical burst switching (OBS) system has been demonstrated in China, which includes three edge routers and one core-node. A kind of fast wavelength selective optical switching was used in the system. The core OBS node consists of a kind of wavelength selective optical switch we developed. It consists of two SOA switches and one wavelength selective thin film filter with centre wavelength at one wavelength. There are one input optical fiber and two output fibers, each fiber carries two wavelengths. The Dell PE2650 servers act as the edge OBS routers. The wavelength of each data channel is located in C-band and the bit rate is at 1.25Gbps. The control channel uses bit rate of 100Mbps at wavelength of 1310 nm. A novel effective scheme for Just-In-Time (JIT) protocol was proposed and implemented. OBS services, such as Video on Demand (VOD) and file transfer protocol (FTP), have been demonstrated. Assembling and scheduling methods that are capable to guarantee the QoS (quality of service) of the transported service are studied.
Optical burst switching (OBS) has been emerging as a promising technology that can effectively support the next generation IP-oriented transportation networks. JIT signaling protocol for OBS is relatively simple and easy to be implemented by hardware. This paper presented an effective scheme to implement the JIT protocol, which not only can effectively implement reservation and release of optical channels based on JIT, but also can process the failure of channel reservation and release due to loss of burst control packets. The scheme includes: (1) a BHP (burst head packet) path table is designed and built at each OBS node. It is used to guarantee the corresponding burst control packet, i.e. BHP, BEP (burst end packet) and BEP_ACK (BEP acknowledgement), to be transmitted in the same path. (2) The timed retransmission of BEP and the reversed deletion of the item in BHP path tables triggered by the corresponding BEP_ACK are combined to solve the problems caused by the loss of the signaling messages in channel reservation and release process. (3) Burst head packets and BEP_ACK are transmitted using “best-effort” method. Related signaling messages and their formats for the proposed scheme are also given.
We have developed an optical probe for local determination of tissue optical properties using a small source-detector separation (<1mm). A 1310nm LED (25 μW) coupled to a fiber with 62.5 μm diameter was used as the light source and multiple detector fibers were employed to achieve spatially resolved reflectance measurement. Each detector fiber has a diameter of 62.5 μm and apart away 125 μm from each other. Pin detectors and continuous wave detection
scheme were performed to obtain a sensitivity of 4x109V/W and 82dB dynamic range. Applied to the normal human skin in the forearm, 63dB signal to noise ration can be achieved with a time resolution less than 1 second. The absorption and scattering coefficientions of tissue can be calculated by generalized diffusion approximation with measured reflective intensity. In this paper, we discussed the design of the system in general, and then described our
instrument, along with the technique issues that influenced its design. Phantom experimental was performed to analyze the relationship between the reflectance light and the optical properties (μa, μs). The results showed that this optical probe could be used for local determination of tissue optical properties.
Optical burst switching (OBS) is a promising solution for realizing IP over WDM since it combines the advantages of optical circuit switching and optical packet switching (OPS) while overcoming their shortages. In this paper, the mechanisms to implement burst assembly and scheduling in an OBS edge router are discussed. The performance of the output traffic from the edge router, e.g. traffic shape and delay, is analyzed with simulation results. The results show that the traffic shape and the delay are affected by maximum delay specified by different classes of services, the maximum length of the burst, the burstiness of the traffic, and the mechanisms of burst assembly and scheduling. By properly designing, the traffic shape can be improvement while the delay keeping in the bounds.
In long haul wavelength division multiplexing (WDM) optical transmission systems, fiber Raman amplifier will become an important subsystem because of its unique advantages. This paper is concentrated on one kind of noise in fiber Raman amplifiers—amplified spontaneous emission (ASE) noise induced by parametric gain (PG). When a strong optical wave (pump) propagates along a fiber, it creates a spectral region around it where a small optical wave (noise) may experience gain. This phenomenon is known as parametric gain (PG). Although the noise generated by PG around signal wavelength is very small, Raman effects under high pump power can amplify it to a relatively high level. It interacts with the signal and affects the system performance. In this paper, PG induced ASE noise in the optical fiber Raman amplifier is analyzed and the related expressions are present, including single pumping and WDM pumping. The ASE noise in a 5 pumps, 64 channels and gain-flattened fiber Raman amplifier systems is also calculated.
A phase modulation spectroscopy system was designed to monitor the dynamic changes of optical properties of rat liver at various constant temperatures. The experimental results show the Frequency-Resolved Spectroscopy can be applied in non-invasive monitoring of process of thermotherapy.
In this paper, the theoretical studies, considering the formation of boundary layer, have been performed to describe RF discharges in annular CO2 lasers with diffusion-cooling. Such characteristic parameters as spatial distributions of electron density, electric field, RF power density and discharge mixture temperature have been evaluated, which can be used to explain some experimental properties of RF discharges very well.