We propose and demonstrate a long-reach wavelength division multiplexed-passive optical networks (WDM-PON) based on reflective semiconductor optical amplifiers (RSOAs) with easy maintenance of the optical source. Unlike previous studies the proposed WDM-PON uses two RSOAs: one for wavelength-selected light generation to provide a constant seed light to the second RSOA, the other for active external modulation. This method is free from intensity-fluctuated power penalties inherent to directly modulated single-RSOA sources, making long-reach transmission possible. Also, the wavelength of the modulated signal can easily be changed for the same RSOA by replacing the external feedback reflector, such as a fiber Bragg grating, or via thermal tuning. The seed light has a high-side-mode suppression ratio (SMSR) of 45 dB, and the bit error rate (BER) curve reveals that the upstream 1.25-Gb/s nonreturn-to-zero (NRZ) signal with a pseudo-random binary sequence (PRBS) of length of 215−1 has power penalties of 0.22 and 0.69 dB at BERs of 10−9 after 55-km and 110-km transmission due to fiber dispersion, respectively.
Fiber Bragg grating (FBG) sensor networks have been intensively researched in optical sensor area and it developed in
wavelength division multiplexing (WDM) and time division multiplexing (TDM) technologies which was adopted for its
interrogating many optical sensors. In particular, WDM technology can be easily employed to interrogate FBG sensor
however, the number of FBG sensors is limited. On the other hand, the TDM technique can extremely expand the
number of sensor because the FBG sensors have same center wavelength. However, it suffers from a reduced sensor
output power due to low reflectivity of FBG sensor. In this paper, we proposed and demonstrated the FBG sensor
network based on code division multiple access (CDMA) with a rapid response and wide spectral dynamic range. The
reflected semiconductor optical amplifier (RSOA) as a light source was directly modulated by the generated
pseudorandom binary sequence (PRBS) code and the modulated signal is amplified and goes through FBG sensors via
circulator. When the modulated optical signal experienced FBG sensor array, the optical signal which was consistent with
center wavelength of FBGs is reflected and added from each sensors. The added signal goes into dispersion
compensating fiber (DCF) as a dispersion medium. After through the DCF, the optical signal is converted into electrical
signal by using photodetector (PD). For separate individual reflected sensor signal, the sliding correlation method was
used. The proposed method improves the code interference and it also has advantages such as a large number of sensors,
continuously measuring individual sensors, and decreasing the complexity of the sensor network.
We report an integrated all-fiber variable optical attenuator (VOA) for dynamic control of a device by achieving optimized taper and axial compression of an index-guiding holey fiber. We experimentally demonstrate a VOA device with dynamic ranges of 18 dB over the spectral range from 1450 to 1650 nm and a low insertion loss of 0.5 dB.
A Q-switched all-fiber laser application based on a novel micro-optical waveguide (MOW) on micro-actuating platform (MAP) light modulator is presented. A fused biconical taper (FBT) coupler acts as MOW, mounted on an electromechanical system, MAP, where an axial stress over the waist of FBT coupler is precisely controlled. The axial stress induced refractive index changes caused the coupling efficiency to result in modulation of optical power. The light modulator was implemented in a laser cavity as a Q-switching element. Q-switching of Yb3+-doped fiber laser was successfully achieved with the peak power of 192mW at 4.1W pump power and 699mW at 5.2W at the repetition rate of 18.6kHz. Further optimization of switching speed and modulation depth could improve the pulse extraction efficiency and the proposed structure can be readily applied in all-fiber Q-switching laser systems for marking applications.
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