Combining the capabilities of photonic and microwave technologies, radio-over-fiber
(RoF) has emerged as a promising solution for the next generation wireless communication
systems. In RoF, an optical carrier is modulated by a subcarrier microwave signal,
which is then transmitted between the central office and remote base stations through optical
fibers. RoF has the attractive advantages of centralizing high-speed electronics, low
signal attenuation, large bandwidth, immunity to radio frequency interference, and high
cell density. In this thesis, RoF uplink transmission based on the nonlinear dynamics of
an optically injected semiconductor laser is investigated. A master laser at the central
office optically injects a slave laser at the base station. The slave laser exhibits nonlinear
dynamical period-one (P1) oscillation such that the output intensity is modulated at a microwave
frequency, which is regarded as the RoF subcarrier frequency. When the slave
laser receives an uplink current modulation in tune with the P1 oscillation frequency, it
is double-locked by both the optical injection and the current modulation. Uplink microwave
phase-shift keying (PSK) signal is converted to optical PSK signal accordingly,
which allows both electrical and optical demodulations at the central office. The approach
offers large tunability of the subcarrier frequency through optical injection, bandwidth
enhancement beyond the relaxation resonance frequency, and elimination of high-speed
electronics. Experimentally, RoF uplink transmission is demonstrated at 16 GHz using
simply a 2.5-Gbps-grade single-mode semiconductor laser. By employing an optical
delay-line interferometer, differential demodulations into non-return-to-zero (NRZ) and
return-to-zero (RZ) signals are achieved. The bit-error rate (BER) remains below 10-9 with a temperature tolerance of at least 10°C through compensations of optical injection. In order to investigate the feasibility of operating at the 60-GHz window, numerical simulations
are conducted using the well-established rate-equation model. The characteristics
of double-locking are quantified by the associated phase variance as the modulation index
and the modulation frequency vary. Compared to stable locking, the double-locked P1
oscillation requires a smaller modulation index for low BER due to bandwidth enhancement.
With a moderately strong injection strength of 0.25, uplink transmission with BER
below 10-10 at 60 GHz is possible by optimizing the injection detuning frequency. The
results illustrate the capability of using double-locked semiconductor lasers for optically
controlled RoF uplink transmissions.
Date of Award | 4 Oct 2010 |
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Original language | English |
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Awarding Institution | - City University of Hong Kong
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Supervisor | Sze Chun CHAN (Supervisor) |
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- Wireless communication systems
- Semiconductor lasers
Radio-over-fiber uplink transmission using semiconductor laser dynamics
CUI, C. (Author). 4 Oct 2010
Student thesis: Master's Thesis