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Subcarrier multiplexed transmission using wavelength division multiplexing and optical amplifier
Electronics Letters
Abstract
Measured bit-error-rate performance is reported for a wavelength-division-multiplexed subcarrier-multiplexed transmission experiment. Six digital channels were carried over two wavelengths in the 1.5 mu m wavelength region and amplified using a semiconductor laser amplifier which gave a 12 dB increase in tolerable path loss with no noticeable penalty.
This paper analyzes the coherent optical wavelength division and subcarrier multiplexing (WDM-SCM) system employing fiber Brillouin amplifiers (FBA). The FBA with the pump laser and the external modulator is used to amplified the desired group of SCM signals and to select the channel in this group. This system has the benefits of eliminating the need of polarization control, reducing the impact of phase noise, enhancing the receiver sensitivities by amplification of the carrier, and selecting channel by the FBA without the microwave tuner.
Many of the time-honoured techniques developed during the sixty-year history of microwaves are now being adopted for optical fibre applications. Until comparatively recently, optical systems were more akin to the early wireless spark transmitters rather than the now sophisticated and ubiquitous radio systems. However, with the advent of coherent optics and photonic amplifiers based on semiconductor laser structures and pumped non-linear undoped/doped fibre, the next generation of optical systems looks set to ape modern microwave radio. The use of optical heterodyne techniques and the arrival of intermodulation distortion are the first indication of a symbiotic relationship, with radio using thousands of electrons/bit in comparison with optics which requires <100 photons/bit. In this paper we explore the migration of optical system development and the future complementary role of microwave radio.
A subcarrier multiplexing based optical wavelength division
multiplexing system with fibre Brillouin amplification (FBA) is
analysed. In the optical domain, a pump laser is tuned to amplify the
corresponding optical carrier by FBA for the desired group of SCM
signals. In the electrical domain, a microwave tuner is used to select
the desired channel in the selected SCM group. This system has the
benefits of eliminating the need for polarisation control, the ability
to cancel phase noise due to the squaring photodetection process of the
selected optical carrier together with its SCM channels, and enhancement
of optical receiver sensitivity by amplification of the carrier.
Comparisons with other systems are also presented
The authors present theoretical and experimental results for
coherent subcarrier multiplexed (SCM) systems using a novel architecture
that shares both the transmitter and local oscillator (LO) laser among
multiple optoelectronic receivers. The ability to share both lasers
significantly reduces the cost and complexity compared to a multichannel
coherent frequency division multiplexed (FDM) system. Experimental
results confirm that the system performance can be greatly enhanced by
inserting an inline optical amplifier so that many receivers can share
one transmitter and LO laser. For example, with an amplifier chip gain
of 24 dB, increasing the optical power at the input to the amplifier by
3 dB from -27.6 to -24.5 dBm, the number of receivers can be increased
from 2 to 32
The use of a 1.3 ¿m InGaAsP constricted mesa laser to transmit microwave subcarriers at frequencies from 3 GHz to 16 GHz is described. The subcarriers are phase-modulated at 2 Gbit/s and the error rate is measured for transmission over 34 km. The effect of laser intensity noise on the system transmission is described.
Multi chennel TV transmission using frequency modulation
- D M Fuller
- W H Powell