摘要:

The reflectivity of the end facet of a 3-D dielectric waveguide can be easily calculated, in case of weak guidance, by replacing the waveguide with a homogeneous medium of refractive indexneqwhile the incident electric (or magnetic) field remains that of the guided mode. The calculation is done through a plane-wave expansion of the incident field; a practical algorithm is given to cope with multidielectric coatings. This process naturally emerges when exact equations are expanded in terms of powers of the weak guidance parameter and it leads to a 1st-order approximation of the reflectivity (i.e. within 2nd-order error) whenneqis suitably chosen. The facet can be normal or angled with respect to the waveguide axis.

DOI:10.1049/ip-j.1990.0033

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Numerical results are presented about the operation of polarisation insensitive 2-layer AR coatings deposited on normal facets. Operation with less than 1 dB gain ripple and with 25 dB internal gain would require the fabrication process to be better than 0.5% accurate on refractive indices and thicknesses for the deposited layers.

DOI:10.1049/ip-j.1990.0034

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The authors report that erbium doped Al2O3−P2O5−SiO2based fibres can be used as efficient optical amplifiers provided the concentration of erbium is kept low. Small signal gains of 35 dB at 1.55 μm and a 3 dB bandwidth of 35 nm have been measured using 70 mW pump power at 1.475 μm. Even when driven heavily into saturation, 16 dB gain was achieved with a resultant signal output power of 15.6 dBm.

DOI:10.1049/ip-j.1990.0035

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper describes a scheme for frequency conversion of optical data signals with use of NDFWM in travelling wave semiconductor laser amplifiers. The frequency conversion range is limited by the gain bandwidth of the optical amplifier, which is about 4000 GHz in the considered case. The experimental arrangement of the conversion scheme is described and a theoretical analysis is presented. Finally the advantages and disadvantages of this scheme are discussed.

DOI:10.1049/ip-j.1990.0036

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A study has been made of the factors influencing crosstalk in twin-guide laser amplifier switches. Theoretical analysis indicates that both crosstalk and wavelength tolerance can be improved by the use of anti-reflecting (AR) coatings. Preliminary experimental results on a low-reflectivity twin-ridge device have verified this prediction and yielded a measured crosstalk as low as −15 dB. The experimental measurements also examined the sensitivity of the crosstalk to wavelength, polarisation and temperature. Means to reduce the crosstalk still further have been identified.

DOI:10.1049/ip-j.1990.0037

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Two distinct operating regimes for Raman amplification are identified. In the first case, distributed Raman gain in standard system fibre is used to improve the end-to-end system performance, as demonstrated with the reduction of the loss of a 100 km link of dispersion-shifted fibre from 21 dB to only 13 dB. In the second case, high index difference small core optical fibres have been developed for use as discrete Raman amplifiers, such as transmitter power amplifiers in transmission systems. The saturation performance of the amplifier has been investigated and shows promise for high efficiency high power operation.

DOI:10.1049/ip-j.1990.0038

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Novel optical transmission system configurations which use remotely pumped fibre amplifiers are proposed to increase repeater spacings. The configurations and properties of major optical components, such as the Er-doped fibre pre-amplifier and booster amplifier, developed for this system, are described. Also Raman amplification for a dispersion shifted fibre and its high power optical signal handling capacity are evaluated. Finally, fibre transmission was demonstrated at 1.8 Gb/s over 310.3 km with a 62 dB repeater gain in a direct detection repeater system.

DOI:10.1049/ip-j.1990.0039

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The performance of optical communication systems employing multilongitudinal mode laser and semiconductor laser preamplified receiver combinations is investigated theoretically, emphasis being placed on the influence of mode partition noise (MPN). Two types of MPN are considered in the analysis: one owing to wavelength-dependent fibre dispersion and the other owing to the wavelength-dependent attenuation mechanism associated with both the amplifier gain and optical filter transmission characteristics. To reduce the influence of amplifier gain ripple and to ensure high receiver performance the mode spacing and the centre mode wavelength of the laser source may need to match closely those of the amplifier, especially for high internal amplifier gains and substantial facet reflectivity. For example, for 1% amplifier facet reflectivity, 30 dB internal optical gain, and 3 nm half-spectral-width laser the receiver sensitivity degrades by 5.1 dB when the lengths of the laser and the amplifier differ by 5%. In contrast with 0.1 and 0.01% reflectivity this reduces to 1.95 dB and 0.4 dB, respectively. We also show that for multimode laser operation there is an optimum bandwidth for the bandpass optical filter at which the required detectable optical power for a given bit error rate (BER) is minimum. Operating with filter bandwidth less than this optimum value will degrade dramatically the sensitivity and may, even in the absence of fibre dispersion, lead to a BER floor in the presence of MPN. The analysis presented here may be used to provide guidelines for the design of optical systems based on laser amplifiers and multimode or nearly single mode laser sources.

DOI:10.1049/ip-j.1990.0040

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Previously, the transmission line laser model (TLLM) has been used to predict the pulse response of semiconductor laser amplifiers. This paper shows that it can also be used to find the magnitude and spectral properties of internally amplified spontaneous emission noise in TWLA, FPLA and DFB laser amplifiers.

DOI:10.1049/ip-j.1990.0041

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Interfering echoes in semiconductor amplifier cascades can cause severe BER degradations in optical transmission systems. We describe an experimental investigation of the effect in a coherent system, and report results in good agreement with theoretical predictions. It is concluded that interfering echoes will severely limit the minimum interamplifier attenuation, which will in turn limit the number of semiconductor laser amplifiers that can be cascaded without optical isolation.

DOI:10.1049/ip-j.1990.0042

出版商:IEE    

年代:1990

数据来源: IET