There are a number of parametric challenges in designing transmit optical amplifiers for the current deployment of optical communication constellations. Constellations are often aligned to channel wavelengths defined by the Space Development Agency (SDA) Tranche 1 Optical Communications Terminal Standard, which requires duplex operation at 1536.61 and 1553.33nm. We present an experimental characterisation supported by numerical modelling, of duplex operation up to 10W at both channel wavelengths and discuss performance limits. The characterisation includes power, out-of-channel amplified spontaneous emission (ASE) content and in-channel ASE content / noise figure determined from time-domain extinction measurements. For an output power of 10W, stimulated Brillouin scattering (SBS) can readily limit the delivery of optical power over relatively short fiber lengths. We also present the growth of a Stokes wave as a function of output power, delivery fiber length and fiber type experimentally. These results showing good agreement with theory, and set design limits on peak power transmission. These peak power considerations being of particular interest for pulse position modulation (PPM) encoding which are required in both the SDA and Consultative Committee for Space Data Systems (CCSDS) 142.0-B-1 standards. The CCSDS and SDA standards both require a sinusoid amplitude modulated tracking tone. We present the limits of the design space of achievable modulation depth, as function of amplifier design, modulation condition and operating wavelength & power. A good agreement between experimental and numerical results is found.
Satellite free-space optical communication offers higher data rates, lower power consumption and mass savings compared to traditional RF and microwave technologies that are currently more widely deployed. Data rates are quickly increasing; with higher data throughputs enabled if higher power optical amplifiers are available. In this paper submission, G&H discuss initial scoping work performed in project EPOS (Extremely Powerful Optical Sources), a European Space Agency (ESA) funded development programme to significantly increase the optical power available from C-Band optical amplifiers. The project will develop a 100W amplifier for spaceborne use and a 1000W combined amplifier source for ground that will be enabling components in Tbit/s links.
The recent emergence of bismuth-doped fiber amplifiers (BDFAs) enables the reach extension of high-speed O-band communication links. In this work, our recent efforts on amplified O-band direct-detection (DD) transmission using BDFAs are reviewed. We first present the performance of a four-channel O-band coarse wavelength-division multiplexed (CWDM) transmission over 50-km length of single-mode fiber (SMF), showing that the chromatic dispersion (CD) which has long been neglected in O-band transmission, will degrade the transmission performance of dispersive O-band channels. In this context, we quantify the relative benefits of different DD formats at 50 Gb/s over up to 70-km length of SMF in a BDFA pre-amplified O-band system. The considered formats include Nyquist on-off keying (OOK), Nyquist 4-ary pulse amplitude modulation (PAM4), and Kramers–Kronig (KK) detection assisted subcarrier modulation using quadrature phase-shift keying (QPSK), and they are evaluated over both the low CD 1320-nm wavelength and the more dispersive 1360-nm wavelength. It is demonstrated that OOK exhibits the best receiver sensitivity over all distances up to 70 km at the 1320-nm channel, whereas KK-QPSK achieves the optimal transmission performance at the 1360-nm wavelength when the reach is extended beyond 50 km. We consider that our results provide useful insights into possible future implementations of longer-reach O-band WDM systems.
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