The conventional measurements of the speed of light were performed before the early twentieth century. Only few used extraterrestrial sources and got the result with large uncertainty. We design a transmitter to modulate the rays from the local infrared light source and the extraterrestrial sources simultaneously into pulses. Both are received by a distant receiver. We have the white light travelling exactly along the path of the starlight pulses for calibration. It is found that the travel times of Aldebaran and Capella pulses are longer than that of Vega pulses. The results indicate that the speeds of starlights are different.
The speed of light is an important physical parameter. Currently it is a common belief of the constance of the speed of light regardless of the relative velocity between the source and the observer. Because the speed of light is very fast, if the relative velocity is small compared with the speed of light, it is difficult to detect the effect of the relative velocity on the measurement of the speed of light. In this paper we present a method of comparing the speeds of starlight and the light emitting from a terrestrial source. We use a telescope to collect the light from the star having significant relative velocity with respect to the earth, e.g. Capella. Then we modulate the starlight and the light emitted from the local source into pulses i.e. these pulses leave the modulator simultaneously. After travelling 4.2 km, these pulses are detected by a receiver. If the starlight and the terrestrial light have the same speed, then these pulses must arrive at the receiver at the same time. Our results show that the arrival times of the pulses of starlight are different from that of the local light. For example, the Capella is leaving away from the earth. The Capella pulses arrive later than the local light pulses. It indicates that the speed of Capella starlight is slower than the common believed value, c. The presented method uses one clock and one stick, so the clock synchronization problem and any physical unit transformation can be avoided.
In this paper, we study the impact of noise constraints due to the accumulated Amplified Spontaneous Emission (ASE) noise for partially shared buffering (PSB) optical packet switches under self-similar traffic. Noise constraints have a severe impact on the performance of PSB optical packet switches. We then propose a new priority switching algorithm that can effectively alleviate the performance degradation caused by the noise constraints on re-circulation limits in WDM PSB type OPS.
Survivability is an important issue in communication networks. Protection and restoration are two mechanisms to provide the survivability. Conventional restoration scheme is classified into link and path restoration. This paper proposed a new hybrid restoration scheme that combines link and path restoration methods using priority wavelength strategy. This new method provides better recovery blocking probability than the conventional link/path restoration method. Due to the characteristics of protection methods, which must reserve spare capacity and is stiff to variable traffic, we further proposed a dynamically adjusted protection scheme that can have more flexible usage of network resource and gives better recovery blocking probability. We simulate the performance and compare with the conventional protection/restoration schemes. The results show that the proposed methods have better recovery blocking probability than others.
A novel and simple design of all-optical encoder/decoder utilizing variable length orthogonal spreading sequences is proposed. The proposed encoder/decoder is applicable to fiber-optic WDMA/CDMA networks which combine wavelength division multiple access (WDMA) and code division multiple access (CDMA) techniques to provide large system capacity. Because when traffic is light, the subscriber can shorten the spreading sequence, and the utilization of network can be further increased.
In this paper, we utilize the embedded hybrid fiber-optic/coaxial CATV network for wireless bidirectional communications with a star-ring fiber-optic network to distribute broadcasting cable TV programs and simultaneously to provide bidirectional transmission of wireless signals. At the head end, there are two lasers: the downlink laser is split into two parts (one as the local oscillator for the uplink coherent detection and the other being externally modulated by the combined TV and wireless signals); the uplink laser connects to the ring network with the cascaded phase modulators schemes. For the star-ring topology, the total hub number are limited by the CNR of TV signals and the radius between head end and hub as: the total hub number of this system to be 14 and 20 for r of 5 km and 1 km, respectively, with the CNRU and CNRD larger than 15 dB together with CNRTV larger than 50 dB.
A microcellular system with radio signals transmitted over a passive optical network is proposed. External amplitude- and phase-modulation are employed in the base station (BS) and the radio port (RP), respectively. A remodulation scheme is used at RPs to eliminate the need of active optical source. An optical local oscillator is employed at BS receiver for heterodyne detection to eliminate the distortions caused by remodulation. Theoretical analysis is carried out and the system capacity is also estimated. It shows that two 200 mW and 25 mW and 25 mW Nd:YAG lasers can serve 16 microcells and provide a total number of 1600 channels for a macrocell with radius 5 km.
The coplanar electrode for lithium niobate automatic polarization controller is superior to other approaches proposed in many aspects. We have analyzed the half-wave voltages for the automatic polarization controller with regard to the design parameters of the coplanar electrode. The numerical analysis using combined FD-CM method is proposed. The optimal electrode design for approach minimum control voltages is analyzed. The numerical method can reduce calculation time compared with using FDM method only.
KEYWORDS: Radio optics, Modulators, Optical fibers, Oscillators, Active optics, Modulation, Radio over Fiber, Denoising, Semiconductor lasers, Photodetectors
A common optical local oscillator scheme for distributing radio signals over fiber in a microcellular system is proposed. Remodulation scheme is used at the radio port to eliminate the need of active optical source. Theoretical analysis and experiment prove that the suitable IF frequency can prevent uplink radio signal from the additional distortions caused by remodulation. The system capacity is also calculated, where the linearization of amplitude modulator and the thermal noise reduction technique are employed to enhance the capacity.
Polymer waveguide exhibits an easy connection with a fiber optic network and low coupling loss. Due to the large bandwidth and short signal delay time, polymer optical interconnects are gradually replacing metal interconnections. This paper presents a roof-shape polymer waveguide by using embossing method. The propagation characteristic of polymer roof-shape waveguide is analyzed by triangular-element finite-element method. The experimental fabrication shows a promising result to develop roof-shape organic polymer optical interconnection by using embossing method.
In this paper, synchronous fiber-optic code division multiple access (S/CDMA) networks using matrix code are presented. The algorithm for constructing the S/CDMA matrix code from the modification of the modified prime sequence code is described, and the error probability is also derived. In comparison with the modified prime sequence code, the matrix code can greatly relax the laser pulse width requirement for the S/CDMA network.
Recently, subcarrier multiplexing method combined with the conventional microwave techniques provides high capacity multichannel optical fiber communication. But as the microwave frequency gets higher, the carrier generation and carrier recovery circuits are more difficult to implement by using traditional microwave technology. This paper proposes a way to generate many subcarriers using only a single reference tone by deep phase modulation method. Tunabilities of operating band and carrier spacing are presented in experimental results. It is found that the optimum phase modulation index is 3.1 for minimum power deviation to generate 7 carriers. Those generated subcarriers can operate from dc to K-band that can be used in transmitting end or receiving end.
A study of the multichannel coherent CPFSK communication system employing Reed-Solomon codes is reported. The crosstalk between adjacent channels, the impact of the laser phase noise, and selection of the optimum code rate are investigated. By applying a suitable coding scheme, the laser linewidth can be greatly relaxed, and the receiver sensitivity will be remarkably improved. A 100 Mb/s system is used to verify the coding benefit. The results show that the impact of the laser linewidth can be largely alleviated by applying a (255, 223) Reed-Solomon code. When the linewidth is fixed ((Delta) (upsilon) T equals 2%), this code can improve the receiver sensitivity by more than 15 dB.
This paper analyzes an optical wavelength division multiplexing system (WDM) with subcarrier multiplexing (SCM). The pump laser is tuned to amplify the corresponding optical carrier by fiber Brillouin amplification (FBA) in WDM for the desired group of SCM signals and then a microwave tuner is used to select the desired channel in this group. This system has the benefits of eliminating the need of polarization control, the ability of phase noise cancelling due to the 'squaring' photodetection process of the selected optical carrier together with its SCM channels, and enhancement of optical receiver sensitivities by amplification of the carrier.
The Bit Error Rate (BER) performance of optical phase diversity FSK receivers of both single filtered (LPF1 in Fig. 1) and dualfiltered version (LPF1 and LPF2 in Fig. 1) is analyzed. The effects of several key system parameters (e. g. the bandwidth of LPF1 the amount of laser phase noise the frequency deviation employed the delay time r in the frequency discriminator etc. ) on receiver performance are investigated in detail. Clear system design guide rules have also been obtained. The analysis has been focused on obtaining expressions for the probability distribution functions (pdf''s) of the signal v at the sampler output. The derivation does not use Gaussian approximations and is therefore more accurate. The results are valid for any value of delay time r.
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