CATV Applications Research Articles

Performance Analysis of Flat Gain Wideband Raman Amplifier for S+C and C+L Band DWDM System

Raman amplifier is an open area of research in telecommunication field. This paper discusses the performance of 64 channels of 10 Gbps WDM systems with backward multipump Raman amplifier. The main goal of this paper is the optimization of Raman amplifier to minimize its gain variation without using any gain flattening techniques. To increase the transmission capacity of DWDM system, Raman amplifier with backward multipump configuration is implemented. The optimized parameters such as pump power and frequencies are used to deliver both ground and excited state absorption for amplification in S+C and C+L band region. The pump power and frequencies are optimized through multitarget and multiparameter optimization tool available in OptiSystem software. Gain ripple was achieved <0.5 dB for this simulation setup. The maximum flat gain achieved is 8.6 dB and noise figure of <8 dB was achieved for this wide bandwidth without using gain flattening techniques. This amplifier design will be helpful for CATV applications and telecommunication networks.

PDG Characterization of an EDFA Developed for CATV Application DOI: 10.14209/jcis.2002.2

Results for the Polarization Dependent Gain (PDG) of an Erbium-Doped Fiber Amplifier, aimed to cable television distribution networks (CATV), are described. PDG measurements are done by switching the state of polarizarion of the launched signal between two orthogonal states, for several wavelengths and signal input powers. The obtained results show that the amplifier has very low PDG. 0.0279 ± 0.0012 dB.

Linearised integrated SOA-EA modulator for long-haul and FTTH CATV applications at 1.55 [micro sign

The 78-channel CATV performance of a packaged amplified electroabsorption modulator with high optical modulation index of 4.2%, CSO of −69 dBc, CTB of −38.5 dBc with no predistortion, measured at a CNR of 50 dB with −6.5 dBm received power, is presented. The device showed output power of >8.5 dBm and a low RIN of −162 db/Hz at the operating conditions.

PDG Characterization of an EDFA Developed for CATV Application

Results for the Polarization Dependent Gain (PDG) of an Erbium-Doped Fiber Amplifier, aimed to cable television distribution networks (CATV), are described. PDG measurements are done by switching the state of polarizarion of the launched signal between two orthogonal states, for several wavelengths and signal input powers. The obtained results show that the amplifier has very low PDG. 0.0279 ± 0.0012 dB.

High-power CW-DFB laser diode modules for CATV applications operating at 1550 nm

Investigation of the correlation between longitudinal photon density distribution and spectral linewidth re-broadening, in conjunction with carefully designed coupling optics, enable laser modules that simultaneously achieve very high fibre-coupled power of 175 mW and very narrow linewidth <1 MHz even at ∼120 mW of output power to be successfully fabricated.

1.3-μm uncooled DFB lasers with low distortion for CATV application

Strained-layer multiquantum-well distributed-feedback (MQW-DFB) lasers at a wavelength of 1.3 /spl mu/m operating from -40/spl deg/C to 85/spl deg/C without any coolers are demonstrated. Extremely low threshold current of 17 mA at 85/spl deg/C and operation current of 37 mA at 5 mW and 85/spl deg/C are obtained. To the best of our knowledge, each of them is the lowest value so far reported in InGaAsP-InP based DFB lasers. The lasers also realize low distortion of less than -50 dBc at 65/spl deg/C in 78-channel composite second order distortion (CSO) measurements. An experimental estimation of the leakage current in buried heterostructure presents that the distortion at high temperatures is mostly dominated by the carrier overflow from an active layer, not by the leakage current flowing through current blocking layers. On the basis of the leakage current analysis, a laser structure including the active layer and the current blocking layer is chosen to achieve low distortion over a wide-temperature-range. The uncooled distributed-feedback (DFB) laser we have developed is very useful for several channel transmission in CATV systems.

Design of efficient optical fiber communication systems for CATV/HDTV distribution

We present an efficient design of intensity-modulation direct-detection optical fiber communication systems with erbium-doped fiber amplifiers to support future CATV/HDTV distribution and broadcasting. We consider three system configurations for CATV applications. The first one is the in-line amplifier scheme. The second scheme is based on a passive optical power splitter and optically-preamplified receivers, while the third scheme uses hybrid passive and active optical power splitters. The receiver sensitivity is also analyzed for various system parameters. The schemes are compared in terms of the number of HDTV subscribers and the superiority of the third scheme over the second scheme is demonstrated.

Limiting distortion of CATV lasers

Recent research indicates that carrier heating effects resulting from coherent radiation and input current inherently limits the linearity of CATV lasers. This limitation on the linearity was estimated to limit the carrier-to-second order distortion ratio per channel to about 62 dB for an 80 channel CATV system operating in the frequency band 60-540 MHz with a total root-mean-square (rms) modulation index /spl mu/=0.19. Since this level of distortion is near the tolerance limit of present subcarrier multiplexing CATV systems, this new source of nonlinearity is of some concern. Prevailing practice now attributes the limiting distortion to laser clipping rather than to the linearity of the laser. However, it is known that laser clipping alone cannot account for this border-line level of distortion. The limiting distortion also applies to optical fiber interconnections of RF signals as, for example, between a cellular base station and its remote antenna sites, especially for implementing microcells. The purpose of this paper is to apply an exact method based on noise theory applied to a fully loaded system in order to evaluate the joint distortion resulting from both laser clipping and the nonlinearity introduced by the carrier heating effects. All orders of distortion are treated and compared with the corresponding cases when the carrier heating effects are suppressed. The resulting carrier-to-nonlinear distortion ratios per channel are presented in graphical form as a function of /spl mu/ and I/sub b/, the laser bias current. The results also confirm an earlier finding that in the vicinity of /spl mu/=0.19, second-order distortion limits the performance per channel rather than laser clipping. However, when second order distortion is suppressed, laser clipping again limits the performance per channel. Based on the composite second order (CSO) and composite triple beat (CTB) distortions, it is shown that the optimal total rms modulation index is about /spl mu/=0.25 for subcarrier multiplexed CATV applications.

High power Er-Yb linear optical fibre amplifier for CATV applications with gain tilt window over 11 nm and integrated dispersion pre-compensation

An Er-Yb fibre amplifier has been constructed with dispersion compensation and gain tilt correction. Gain tilt has been minimised within 0.2 dB/nm for the spectral width of 11 nm and input power range of 0–4 dBm. A noise figure of 5 dB and output power of 21 dBm has been obtained for this operating range. Tests using a 77 channel NTSC signal show its compatibility to CATV applications.

Nonlinear distortions and compensations of DFB laser diode in AM-VSB lightwave CATV applications

The nonlinear distortions of a directly modulated laser diode applied to AM-VSB lightwave CATV systems are studied from the viewpoint of rate equations. A simple method for calculating composite second-order distortion (CSO) is proposed, which is called the quasidynamic approach. The contribution to nonlinearity from fiber dispersion and laser chirping is also discussed. The dependences on the variations of parameters of rate equations are investigated to determine the dominant factor for CSO degradation. This approach explains quite well the experimental results and suggests a method for constructing a predistortion circuit with at least 10 dB improvement.

Wide-temperature-range operation of 1.3 [micro sign]m DFB lasers with low distortion for CATV application

Low-distortion 1.3 /spl mu/m DFB lasers operating from -40 to 85/spl deg/C without any coolers are demonstrated. Extremely low threshold current of 17 mA at 85/spl deg/C is obtained. The lasers also realise low distortion <-50 dBc at 65/spl deg/C in 78-channel CSO measurements.

Influence of imbalance on distortion in optical push-pull frontends

The influence of imbalance on second-order intermodulation distortion (IMD2) in optical push-pull frontends for subcarrier multiplex CATV applications is investigated theoretically and experimentally. The investigation focuses on imbalance introduced in either the photodiode, the push-pull amplifier, or the output balun, and expressions describing the overall IMD2 cancellation efficiency are derived. The developed theory is used to predict the IMD2 cancellation behavior of an optical push-pull frontend. Commercially available PIN photodiodes for CATV purposes and ferrite core transformers are characterised for phase and amplitude balance up to 1 GHz. The overall IMD2 cancellation efficiency of an optical push-pull frontend based on the best of these devices is calculated. The theory is finally verified experimentally with an optical push-pull frontend designed with the characterised photodiode and transformer. The improvement in IMD2 suppression obtained with the push-pull structure relative to a single-ended structure is in average 29 dB across the band from 47-862 MHz. The total IMD2 suppression obtained for the frontend is between 60 dBc and 79 dBc at an average optical input power of 1 mW and with an optical modulation index (OMI) of 35 percent per carrier in a two-tone setup,.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimum range for DFB laser chirp for fiber-optic AM video transmission

Simple expressions for the impact of the distributed feedback (DFB) laser chirp on the system noise and distortion specifications of AM CATV fiber links are derived. These expressions are found to agree well with measured results. There is a narrow range of chirp for which the degradation of both noise and distortion is low. 1310-nm lasers are found to have chirp within the acceptable range. 1550-nm lasers are found to have chirp that is unacceptably large for most CATV applications.

Transmission characteristics of DFB laser modules for analog applications

In this paper analog transmission characteristics of highly linear 1.3- and 1.55-μm distributed feedback (DFB) laser modules are described. To obtain high-power and high-performance DFB lasers, the bias dependence of distortion characteristics is discussed. The carrier-to-noise ratio, the composite second-order distortion, and the composite triple beat of the DFB laser module which is developed for analog CATV applications are presented. The analog transmission characteristics, such as CNR degradation, after fiber transmission, dispersion-induced distortion, and the influence of reflection, have been made clear. The stable high linearity of the DFB laser also has been confirmed by the composite distortion measurement under an accelerated aging test.

Semiconductor lasers versus external modulators: a comparison of nonlinear distortion for lightwave subcarrier CATV applications

Second- and third-order distortion measurements performed on various buried-heterostructure InGaAsP DFB (distributed feedback) lasers and on LiNbO/sub 3/ external modulators are discussed. It is shown that by optimally biasing the external modulator, the second-order distortion can be eliminated but the third-order distortion is 25 dB greater than that of direct modulation. It is also shown that these discrete two-tone measurements can be used to predict the system performance of a 42-channel CATV trunk system. The increased composite-triple beat and lower carrier-to-noise ratio, due to modulator loss, are the disadvantages of the external modulator. If it is possible to improve third-order distortion by modifying the structure of the modulator or by electronic compensation without increasing the second-order distortion, then these modulators may be useful for CATV applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Long-wavelength single-mode WDM for CATV applications

A two ‘colour’ wavelength-division-multiplexing system based on GRIN rod lenses and interference filters and operating at λ = 1.2 μm and 1.3 μm has been developed for use with single-mode fibre, and exhibits a single-mode MUX loss of −1.4±0.2 dB.

VHF Tuner IC for Use in Television Receivers and CATV Receivers

A single chip VHF Tuner IC will be described with a frequency range covering the entire VHF band up to 440 MHz. The development of this new component was based on the increasing demands for additional transmitting and cable channels. At the same time, these requirements increased selectivity, temperature and operating stability. CATV applications profited from these new developments as well. The ASBC technology is especially suited for high frequencies, enabling the the develop-ment and mass production of this VHF Tuner IC.

Reliability Considerations in CATV Hybrids

The construction of broadband thin-film hybrid amplifiers for CATV applications is described. Failure modes and reliability considerations of the major components of the hybrid are discussed. The effects of environmental constraints unique to CATV amplifier service are analyzed and the results of recent analysis and testing done on hybrids designed for resistance to voltage transients are presented.

High Frequency Distortion Analysis of a Semiconductor Diode for CATV Applications

Intermodulation distortion generated in a semiconductor diode in series with a resistor is analysed using a Volterra series representation. The equivalent circuit of a diode includes the nonlinear junction conductance, nonlinear junction capacitance, series resistance and series inductance. Nonlinear terms up to and including the fifth order are considered. It is shown that for the VHF range of frequencies the diode capacitance can significantly affect the magnitude and phase of the total distortion at a given product frequency.

Time-Domain Reflectometer Measurement of Random Discontinuity Effects on Cable Magnitude Response

Time-domain reflectometry (TDR) is used to specify the structural return loss and structural transmission loss that are caused by the randomly spaced electrically short structural defects that are present in commercially available coaxial cables. The theory for the statistical prediction of these effects is presented and TDR methods for making measurements are described. The results should be of particular interest in telephony and CATV applications.