We have demonstrated a silicon traveling wave Mach-Zehnder modulator adopting the single-drive push-pull scheme. The traveling wave electrode is made of coplanar stripline structure. Several key parameters have been optimized to get a high-speed modulator. It is shown that using the coplanar stripline electrode, group velocity matching and impedance matching are achieved by careful design. After optimization, the VπL of the modulator is calculated to be 2.23 V·cm with the phase shifter length of 4.2 mm. The insertion loss of the modulator excluding the grating couplers loss is 3.4 dB. The 3 dB electro-optic bandwidth of the modulator is simulated to be 32 GHz at 0 V reverse bias. A modulation speed of 70 Gbps under the driving voltage of 1 Vpp is realized with an extinction ratio of 4.9 dB. A higher data transmission capability can be get when high modulation formats such as PAM-4, together with digital signal processing is implemented. Such high-speed silicon modulator can be utilized for next generation communication networks.
We have proposed and demonstrated a nanosecond square-wave fiber laser working in the 1060nm band. The passively
mode-locked fiber laser based on the nonlinear optical loop mirror has a peak power clamping effect which leads to the
generation of nanosecond square-wave pulses. To investigate the spectrum width of the nanosecond square-wave pulse
laser, we added couplers with different coupling ratio to the bidirectional ring of the figure-8 fiber laser and analyzed the
laser output. The results show that a higher output coupling ratio leads to stronger peak power clamping effect, and the
peak power of the square-wave pulse gets lower and the corresponding spectrum band width is narrower.
A stable mode-locked fiber laser employing graphene as a saturable absorber is presented. One
monolayer graphene can obtain mode-locking when the cavity is around 12m, but when the cavity
decreases to 6m, no stable pulses can be formed. In order to solve this problem, cascade of two
monolayer graphenes is used and stable mode locked pulses with a frequency of 44.53MHz, a
bandwidth of 2.4nm, a pulse width of 43.89ps and an average power of 19.10mW have been directly
obtained from the laser. Our results show the atomic-layer graphene may be a promising satrurable
absorber for stable pulses formation of fiber laser.
This paper designs and implements one kind of automatic mode-locked system. It can adjust a passively mode-locked
fiber laser to keep steady mode-locked states automatically. So the unsteadiness of traditional passively mode-locked
fiber laser can be avoided. The system transforms optical signals into electrical pulse signals and sends them into MCU
after processing. MCU calculates the frequency of the signals and judges the state of the output based on a quick
judgment algorithm. A high-speed comparator is used to check the signals and the comparison voltage can be adjusted to
improve the measuring accuracy. Then by controlling two polarization controllers at an angle of 45degrees to each other,
MCU extrudes the optical fibers to change the polarization until it gets proper mode-locked output. So the system can
continuously monitor the output signal and get it back to mode-locked states quickly and automatically. States of the
system can be displayed on the LCD and PC. The parameters of the steady mode-locked states can be stored into an
EEPROM so that the system will get into mode-locked states immediately next time. Actual experiments showed that,
for a 6.238MHz passively mode-locked fiber lasers, the system can get into steady mode-locked states automatically in
less than 90s after starting the system. The expected lock time can be reduced to less than 20s after follow up
improvements.
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