Ko-ichi Suto

Signal distortion and noise in AM-SCM transmission systems employing the feedforward linearized MQW-EA external modulator

In subcarrier multiplexing (SCM) optical video distribution systems, the nonlinear signal distortion generated by the combined action of laser chirp and fiber dispersion limits the transmission distance. This paper for the first time shows that low-chirp MQW (multiquantum well)-EA (electroabsorption) external modulators are applicable to AM-SCM transmission systems. The feedforward linearization technique is used to compensate the signal distortion due to the nonlinearity in the modulators L-V (light power versus voltage) characteristic. The effectiveness of this type of modulator for suppressing dispersion-induced distortion is clarified experimentally. A feedforward linearized transmitter with composite second order (CSO) intermodulation distortion 50.5 dB is successfully constructed. It is shown that the transmitter can achieve a CSO 49.5 dB for a 32 channel AM signal and 10 km transmission. Furthermore, estimations of the signal distortion cancellation and the noise characteristic achieved with feedforward circuit modeling are shown. The results obtained here emphasize that MQW-EA external modulators are applicable to AM-SCM transmission systems. >

Erbium-doped fiber amplifier for video distribution networks

The possibility of an application of Er-doped fiber amplifiers to AM-FDM (frequency division multiplexing) or FM-FDM video distribution networks is discussed. The measured noise and modulation distortion properties of ER-doped fiber amplifiers are good enough to meet even the severe quality standards set for trunk lines. A carrier-to-noise ratio (CNR) of 57 dB for an AM-FDM transmission was measured. A second-order harmonic distortion (HD2) of less than -56 dB was measured by the monotone method (modulation depth m=50%), and a cross modulation distortion (XM) of less than -63 dB was measured by the two-tone method (m=25%*channel). On the basis of these values, composite second-order distortion (CSO) and XM in a 40-channel transmission were estimated as less than -57 dB and -73 dB, respectively. Significant reduction of noise and modulation distortion is made possible by optimizing the length of Er-doped fiber amplifiers and using input- and output-port isolators. >

Reduction of dispersion-induced distortion in SCM transmission systems by using predistortion-linearized MQW-EA modulators

The application of low-chirp MQW (multiquantum well)-EA (electro-absorption) modulators to subcarrier multiplexing (SCM) optical transmission systems is studied. The authors show that a third-order predistortion circuit is feasible for compensating the nonlinearity of this type of modulator. The degree of frequency chirping per optical intensity modulation depth of the modulator is theoretically determined to be about 1.4 MHz. A 42-channel AM-SCM signal transmitter with the predistortion circuit realizes both composite second-order distortion (CSO) and composite triple beat distortion (CTB) values under -57 dBc after 200-km-long transmission. The authors confirm dispersion-induced distortion of the MQW-EA modulator is as small as that of the LiNbO/sub 3/ modulator. Carrier-to-noise ratios (CNRs) of 45.2 dB for channel 1 and 43.8 dB for channel 42 were measured after 100 km transmission. It is found that the deterioration of a CNR is caused by the cascaded erbium doped fiber amplifiers (EDFAs), Rayleigh backscattered power and the optical phase noise. Theoretical CNRs show that the output power of the modulator should be higher to improve CNR.

A Super Wideband Optical FM Modulation Scheme for Video Transmission Systems

A novel super wideband optical FM modulation scheme that employs an optical heterodyne detection technique is proposed and demonstrated. The experimental results show that applying this scheme to 40-channel AM video transmission expands the power budget by approximately 10 dB at a carrier- to-noise ratio (CNR) of 42 dB. The feasibility of the scheme is also discussed from the viewpoints of connector reflectivity and fiber-dispersion.

Super-wide-band optical FM modulation scheme and its application to multichannel AM video transmission systems

A novel super-wide-band optical FM modulation scheme employing an optical heterodyne detection technique is proposed and demonstrated. Experimental results show that by applying this scheme to 40-channel AM video transmission, the power budget is expanded by approximately 10 dB at a CNR of 42 dB.

All-fiber video distribution (AFVD) systems using SCM and EDFA techniques

this paper describe the design and performance of all-fiber video distribution (AFVD) systems based on AM/FM FDM subcarrier multiplexing (SCM) and erbium-doped fiber amplifiers (EDFAs). The impact of applying EDFAs to SCM analog video distribution systems is investigated. AM/FM hybrid systems, which can simultaneously distribute 11 AM TV channels and 50 FM TV channels are proposed and discussed. Four-stage amplifier-branch transmission experiments are introduced. The construction and performance of a newly designed 50-channel FM tuner are also presented.

Fully engineered multi-channel FM-SCM video distribution systems

This paper reports the design and performance of a multi-channel FM-SCM video distribution system that can be placed into practical use. Fifty FM video channels can be delivered to more than 10 000 customers through three-cascaded erbium-doped fiber amplifiers, and wideband/low-noise analog SCM links. As the outdoor plant is completely passive, reliability and easy maintenance can be expected. An evaluation of fabricated equipment shows good transmission quality and stable operation. >

Intermodulation distortion in 48 TV channel FM-FDM optical transmission

The effect of dispersive fibers on multichannel FM video transmission characteristics is experimentally investigated. A directly modulated 1.5 mu m distributed feedback laser diode (DFB-LD) and a LiNbO/sub 3/ external modulator with a continuous-wave (CW) 1.55 mu m DFB-LD are used as optical signal sources. When the 1.3 mu m single-mode fiber (SMF) is used, directly modulated DFB-LDs suffer from second-and third-order intermodulation distortion (IMD). The external modulator realizes good transmission characteristics irrespective of the fibers dispersion value. This means that external modulators can realize multichannel FM television signal transmission systems that use the standard 1.3 mu m SMF already installed in fiber optic subscriber loops.<<ETX>>

Polarization dependent distortion in AM-SCM video transmission systems

The second-order intermodulation distortion product, namely composite second-order (CSO) distortion, of an AM-SCM video transmission system can be caused by the optical isolators, cascaded fiber amplifiers, or the fiber transmission cable employed. Moreover, the absolute distortion value depends on the polarization angle of light input to the optical isolators, cascaded fiber amplifiers, and fiber transmission line. The degraded distortion values are measured and their mechanisms are clarified. >

New MMIC's for tuners in multichannel video distribution systems using optical fiber networks

New MMICs have been developed for an ultra-broadband FM video tuner in a multi-channel video distribution system using optical fiber networks. The MMICs provide both frequency synthesis and up-conversion. They are integrated on two GaAs MMIC chips and one Si LSI chip. The chips are mounted in a flat package to form a tunable block up converter, By combining the MMICs with currently available consumer product type components, a low cost FM video tuner with a 2 GHz tuning bandwidth was achieved in hardware. Successful tuning performance is obtained over the whole tuning frequency range. >