Showing papers on "Optical Carrier transmission rates published in 1983"

Fm modulator for semiconductor laser

Abstract: PURPOSE:To stabilize the optical carrier frequency, by inserting a Fabry-Pe rot etalon to a negative feedback circuit of an FM modulator using a semiconductor laser. CONSTITUTION:A bias DC is applied to a laser 4 from a terminal 5, a signal S1 and an output of a differential amplifier 6 of a negative feedback loop are inputted to a synthesis circuit 7, and the output is inputted to the laser 4 to perform FM modulation corresponding to the change in the signal S1. A part of the output of the laser 4 is collected at a lens 8 and a Fabry-Pe rot etalon FPE11 is inserted into an optical path 9. The intensity of light is changed according to the frequency fluctuation of the FM signal changed at the FPE11 and the transmitted light is detected at a photodetector 13 via a lens 12. The optical signal of an optical path 10 is detected at a photodetector 16 via a lens 15. The output of the detectors 13 and 16 is inputted to a differential amplifier 14 to input a signal S2 proportional to the difference of the optical paths and an input signal S'1 having the equal amplitude with the signal S2 to the amplifier 6, then the output of the amplifier 6 is zero. If the frequency of the laser 4 is changed due to temperature change, the amplifier 6 generates an output cancelling the frequency change to stabilize the laser frequency.

Optical signal transmitter

Abstract: PURPOSE:To decrease the number of transmission lines and to increase the amount of transmission, by providing a plurality of light emitting and detecting device having a peak at different wavelengths respectively for each terminal station. CONSTITUTION:In turning on a terminal device 43, a microprocessor 31 converts a code of the device 43 and the control content of ''ON'' into prescribed signals and transmits them in a fiber 35 by using an optical carrier wave, lambda1 of wavelength. A branching filter 33 branches the carrier wave, lambda1 of wavelength and the device 43 receives this optical signal. Since the reception signal is provided with a code designating the terminal device 43, the content of control succeeding to the code is decoded and the terminal device 43 is turned on. Although a branching filter 34 branches the optical carrier wave, lambda1 of wavelength, since no code designating a terminal device 44 exists, the terminal device 44 is not actuated. Similarly, the transmission system having the optical carrier wave, lambda2 of wavelength is used for other controls to the same terminal device.

High Capacity Optical Systems For Trunk Networks

Abstract: IntroductionSince the culmination of early work on 140 Mbit /s optical systems, a number ofexperimental links have been installed. The first, a nine kilometre link between Stevenageand Hitchin just north of London, in 1977, was chosen to demonstrate the suitability ofoptical communications for trunk networks. In 1979 British Telecom awarded contracts forthe first phase of proprietary optical line systems, (POLS 1) for installation in the UKnetwork between 1980 and 1982. POLS 2 and POLS 3 awards included seventy 140 Mbit /ssystems, mainly using multimode optical fibre cables.This paper describes the component and equipment technology used and the installation andperformance of 140 Mbit /s systems.Principal system featuresSTC's 140 Mbit /s systems provide a transmission link for digitally encoded information inthe CCITT 140 Mbit /s format thereby meeting the requirements for a high quality broadbandsystem of international standard. Traffic capacity is 1920 channels, or two broadcastquality television channels, or 140 Mbit /s of any digital data.The 140 Mbit /s system uses a semiconductor light source operating at a nominal wavelengthof 850nm over one pair of graded -index multimode optical fibres, with one fibre being usedfor each direction of transmission. An avalanche photodiode (APD) is used to detect thelight at the receiver. With these a repeater spacing of 10km can be achieved.Intermediate repeaters can be power fed over the phantom circuits of metallic pairswhich run parallel to the optical fibres; alternatively the repeaters may obtain powersupplies locally.The metallic pairs are also used by the supervisory and engineering speaker systems whichform part of a major trunk transmission system. Four pairs of conductors provide thesefacilities for two complete optical transmission systems.The properties of the 7B8B line code make it possible to detect errors at the receiveterminal and at all intermediate repeaters without interrupting the flow of traffic,because the received data stream is inspected for code violations. The supervisory systemis under the control of a microprocessor and includes an EPROM (Erasable Programmable ReadOnly Memory). This is programmed to contain route information and the error messages to betransmitted to peripheral devices such as printers or visual display units.The route identification data eliminates the need for a station route directory, andallows the repeater housing number or surface station address to be displayed directly asthe location of the fault. The error messages can be programmed to the needs of thecustomer, thus allowing foreign languages to be used.The engineering order wire (EOW) system uses dual tone, multi- frequency key padsignalling facilities for selective calling between stations. A portable speaker which hasselective calling, is available for use at dependent repeater sites, any of which may becalled from any station.System planningA number of different combinations of fibre type and electro -optic devices can be used tofulfil the requirements for an 8 to 10km repeater spacing.The use of an 850nm laser, low loss graded index multimode fibre, and an APD receivergives the lowest cost alternative using commercially available devices. The power budgetallocation for the system is shown in Table 1. The mean transmitted power of -3dBm is setto be compatible with long laser life. Demountable connectors are used to connect the lineequipment to the system fibre. The fibre in the connector is cenEred in a tapered ferruleby using three ball bearings positioned around the outside diameter of the fibre.Alignment is by the tapered ferrules in a biconical adaptor. These connectors will