Yu-Chan Lin

50 fs soliton compression of optical clock pulse recovered from NRZ data injected SOAFL

Mode-locking of semiconductor optical amplifier fiber laser (SOAFL) with 50 fs pulses by extracting the clock of an optical non-return-to-zero (NRZ) data injection is demonstrated. The efficiency of mode-locking in the SOAFL is improved by increasing the seeding power of the large-duty-cycle NRZ data from 3 to 8 dBm into the SOA driven at biased current of 350 mA. After linear dispersion compensation, the mode-locked SOAFL pulsewidth can be further shortened from 20 to 3 ps by increasing the DCF length up to 110 m. By using a booster the EDFA to enlarge the average power of mode-locked SOAFL pulse to 1.3 W, the shortest soliton pulse is occurred after propagating through a 12-m-long SMF. The amplified SOAFL pulse can be compressed to 50 fs after nonlinear compression with its spectral linewidth broadening to 64 nm. Nearly transform-limited time-bandwidth product of 0.436 and the maximum pulse compressing ratio of 400 are reported to date.

Peak equalization of rational-harmonic-mode-locking fiberized semiconductor laser pulse via optical injection induced gain modulation

Optical injection induced gain modulation of a semiconductor optical amplifier (SOA) is demonstrated to equalize the peak intensity of pulses generating from the rational-harmonic-mode-locking (RHML) SOA based fiberized semiconductor laser. This is achieved by adjusting the temporal shape of the injected optical signal generated from a Mach-Zehnder intensity modulator, in which the DC biased level exceeding Vpi and the electrical pulse amplitude of 1.5Vpi are concurrently employed. Numerical simulation on the injected optical signal profile and the SOA gain during the inverse-optical-pulse injection induced gain modulation process are also demonstrated. After a peculiar inverse-optical-pulse injection, each pulse in the 5th-order RHML pulse-train experiences different gain from temporally varied SOA gain profile, leading the pulse peak to equalize one another with a minimum standard deviation of 2.5% on the peak intensity variation. The optimized 5th-order RHML pulse exhibits a signal-to-noise suppression ratio of 20 dB and a reduced variation on temporal spacing from 11 to 4 ps. The clock amplitude jitter is compress from 35.3% to 7.3%, which is less than the limitation up to 10% for 5th order RHML generation.

Nonlinear dependence between the surface reflectance and the duty-cycle of semiconductor nanorod array

The nonlinear dependence between the duty-cycle of semiconductor nanorod array and its surface reflectance minimization is demonstrated. The duty-cycle control on thin-SiO2 covered Si nanorod array is performed by O(2-) plasma pre-etching the self-assembled polystyrene nanosphere array mask with area density of 4 × 10(8) rod/cm(-2). The 120-nm high SiO2 covered Si nanorod array is obtained after subsequent CF4/O2 plasma etching for 160 sec. This results in a tunable nanorod diameter from 445 to 285 nm after etching from 30 to 80 sec, corresponding to a varying nanorod duty-cycle from 89% to 57%. The TM-mode reflection analysis shows a diminishing Brewster angle shifted from 71° to 54° with increasing nanorod duty-cycle from 57% to 89% at 532 nm. The greatly reduced small-angle reflectance reveals a nonlinear trend with enlarging duty-cycle, leading to a minimum surface reflectance at nanorod duty-cycle of 85%. Both the simulation and experiment indicate that such a surface reflectance minimum is even lower than that of a uniformly SiO2 covered Si substrate on account of its periodical nanorod array architecture with tuned duty-cycle.

Compression of 200GHz DWDM channelized TDM pulsed carrier from optically mode-locking WRC-FPLD Fiber Ring at 10 GHz

The compression of 200GHz DWDM channelized optically mode-locking WRC-FPLD fiber ring pulse of at 10 GHz is performed for high-capacity TDM application. To prevent temporal and spectral cross-talk, the duty-cycle of the DWDM channelized WRC-FPLD FL pulse needs to be shortened without broadening its linewidth. With dual-cavity configuration induced DWDM channelization, a shortest single-channel WRC-FPLD FL pulsewidth of 19 ps is generated, which can be linearly compensated to 10 ps and fifth-order soliton compressed to 1.4 ps. Under a maximum pulsewidth compression ratio up to 14 and a +/-100 m tolerance on compressing fiber length, the single-channel pulsewidth remains <2 ps (duty-cycle <2%) with spectral linewidth only broadening from 0.29 nm to 0.8 nm. In comparison, a typical SOAFL without intra-cavity TBF in fiber ring broadens its spectral linewidth from 2.4 to 3.8 nm after compressing its mode-locked pulsewidth from 21 to 2.1 ps. The duty-cycle of the DWDM channelized WRC-FPLD FL pulsed carrier is approaching 1% to satisfy at least 256 optical TDM channels.

Chirp-Compensated Multichannel Hybrid DWDM/TDM Pulsed Carrier From Optically Injection-Mode-Locked Weak-Resonant-Cavity Laser Diode Fiber Ring

The multichannel chirp compensation of a hybrid pulsed carrier with dense wavelength division multiplexing/ time-division multiplexing (DWDM/TDM), generated from a mode-locked weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) fiber ring under 10-GHz dark-optical-comb injection, is demonstrated with a DWDM channel spacing of 200 GHz. This was implemented by selecting the least-common-multiple repetition frequency in the WRC-FPLD and fiber ring dual cavity. With a chirp parameter of for the WRC-FPLD-based fiber ring, the absolute value of the negative frequency chirp could be linearly suppressed from to with the pulse duration varying from 27 to 20 ps. By using a tunable band-pass filter, nine DWDM channels located between 1533.4 and 1546.2 nm were selected for dispersion compensation within a 55-m long diode fiber ring segment. The original pulsewidth varied from 21.7 to 17 ps for different channels. After chirp compensation, an auto-correlation diagnosis showed that the all-channel pulsewidths of mode-locked WRC-FPLD fiber ring laser changed only from 7.8 to 9.1 ps. The single-channelized WRC-FPLD pulsewidth after linear dispersion compensation and fifth-order soliton compression could be to shortened to 7.8 and 1.4 ps, respectively.

Electron–Hole Plasma-Induced Spectral Blueshift of Optical-Data Injection Mode-Locked Semiconductor Optical Amplifier Fiber Laser

Under an optical nonreturn-to-zero (NRZ) data injection at 10 Gbit/s, the 10-GHz mode-locking and pulsed return-to-zero (RZ) clock extraction from a semiconductor optical amplifier (SOA) based fiber ring is investigated in this paper. The diagnoses on gain and intracavity-power-controlled anomalous blueshifted spectrum and subpicosecond timing jitter are demonstrated. By increasing the injecting power of the optical NRZ data from -3 to 8 dBm into the SOA bias at different currents, the mode locking is completed with a dc level greatly decreasing from 480 to 50 ¿W (only 1.5% of the mode-locked pulse power at 3 mW), corresponding to a pulse/dc amplitude contrast ratio up to 18 dB. Increasing the SOA bias current up to 350 mA significantly suppresses the timing jitter from 1.8 ps to 345 fs, and the extracted RZ clock pulse is shortened from 55 to 27 ps. The pulsewidth of the amplified SOAFL is compressed from 11 ps to 836 fs after dispersion compensation. At constant data injection level, the increasing SOA bias or gain oppositely redshifts the mode-locked SOA fiber ring laser (SOAFL) spectrum by 5 nm. The amplifier spontaneous emission of SOA at short wavelength region ( ~ 1520 nm) is eliminated with increasing NRZ data power, whereas the mode-locking gain peak arises and blueshifts from 1558 to 1552 nm due to the band-filling effect. Such a blueshift in mode-locking spectrum becomes more significant in SOA at lower bias (or gain) condition. A theoretical model interprets the correlation between the nonlinear gain suppression-induced variation of electron-hole plasma in SOA and the blueshifted mode-locking SOAFL spectrum, which is occurred when the gain saturation condition for the SOA becomes more pronounced.

Temperature dependences of quantum-dot laser thresholds under simultaneously three-state or two-state lasing operations

Three-state lasing in quantum-dot lasers is demonstrated for the first time in this work. The individual threshold currents corresponding to different states are measured as a function of temperature, respectively. Their correlations will be discussed.

Optical injection mode-locking and DWDM channeling of the weak-resonant-cavity FPLD-based fiber ring lasers

10-GHz optical injection mode-locking of a weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) with 10%-end-facet reflectivity based fiber ring with an intra-cavity power controlled wavelength shift and a reducing chirp linewidth at high intra-cavity coupling ratio condition is demonstrated. Both the strong dark-optical comb and strong feedback coupling contribute to the red shift of mode-locking spectrum. The wavelength shift from 1536 to 1542 nm of the WRC-FPLD based fiber ring associated with its pulsewidth and linewidth also reduced from 27 to 19 ps and from 10 to 6 nm, respectively, can be observed. The peak-to-peak frequency chirp reduced from 3.5 to 1.8 GHz was caused by the shrink of linewidth. The WRC-FPLD exhibits relatively weak cavity modes and a gain profile covering > 33.5 nm. The least common multiple of the WRC-FPLD and the fiber-ring mode-spacing is tunable by adjusting length of the fiber ring cavity to approach intracavity mode spacing of 1.6 nm. Up to 12 lasing modes naturally and a mode-locking pulsewidth up to 19 ps can be observed. With an additional intracavity bandpass filter, the operating wavelength can further extend from 1520 to 1553.5 nm. After channel filtering and linear dispersion compensating, the pulsewidth can be further compressed to 8 ps with corresponding chirp reducing from 9.7 to 4.3 GHz. Such a mode-spacing tunable pulsed fiber laser matching ITU-T DWDM channels can be employed as a novel optical carrier to integrate the OTDM function into the DWDM system with a channel spacing tunable from 50 to 200 GHz.

Optical OC-192 NRZ injection induced 540-fs wavelength converted clock pulse recovery from SOA fiber ring

Wavelength converted 10GHz clock pulse recovery induced by injecting optical OC-192 NRZ data into SOA fiber-ring is demonstrated to obtain a 540-fs RZ clock pulse with duty-cycle of 0.5% after chirp compensation and compression.