Jung-Jui Kang

Manipulation of operation states by polarization control in an erbium-doped fiber laser with a hybrid saturable absorber

We propose an operation switchable ring-cavity erbium-doped fiber laser (EDFL) via intra-cavity polarization control. By using a semiconductor saturable absorber mirror in the EDFL cavity, stable Q-switching, Q-switched mode-locking, continuous-wave mode-locking, pulse splitting, and harmonic mode-locking pulses can be manipulated simply by detuning a polarization controller while keeping the pump power at the same level. All EDFL operation states can be obtained under the polarization angles detuning within 180 degrees. Continuous-wave mode-locking of EDFL with 800-fs pulsewidth repeated at 4 MHz has been obtained, for which the output pulse energy is 0.5 nJ and the peak power is 625 W. Interaction between solitons and the accompanied non-soliton component will lead to either pulse splitting or 5th-order harmonic mode-locking at repetition rate of 20 MHz.

High-order rational harmonic mode-locking and pulse-amplitude equalization of SOAFL via reshaped gain-switching FPLD pulse injection

The 40-GHz rational harmonic mode-locking (RHML) and pulse-amplitude equalization of a semiconductor optical amplifier based fiber-ring laser (SOAFL) is demonstrated by the injection of a reshaped 10-GHz gain-switching FPLD pulse. A nonlinearly biased Mach-Zehnder modulator (MZM) is employed to detune the shape of the double-peak pulse before injecting the SOA, such that a pulse-amplitude equalized 4th-order RHML-SOAFL can be achieved by reshaping the SOA gain within one modulation period. An optical injection mode-locking model is constructed to simulate the compensation of uneven amplitudes between adjacent RHML pulse peaks before and after pulse-amplitude equalization. The indirect gain compensation technique greatly suppresses the clock amplitude jitter from 45% to 3.5% when achieving 4th-order RHML, and the amplitude fluctuation of sub-rational harmonic modulating envelope is attenuated by 45 dB. After pulse-amplitude equalization, the pulsewidth of the optical-injection RHML-SOAFL is 8 ps, which still obeys the trend predicted by the inverse square root of repetition rate. The phase noise contributed by the residual ASE noise of the RHML-SOAFL is significantly decreased from -84 to -90 dBc/Hz after initiating the pulse-amplitude equalization, corresponding to the timing jitter reduction from 0.5 to 0.28 ps.

Rational harmonic mode-locking pulse quality of the dark-optical-comb injected semiconductor optical amplifier fiber ring laser.

We study the rational harmonic mode-locking (RHML) order dependent pulse shortening force and dynamic chirp characteristics of a gain-saturated semiconductor optical amplifier fiber laser (SOAFL) under dark-optical-comb injection, and discuss the competition between mode-locking mechanisms in the SOAFL at high-gain and strong optical injection condition at higher RHML orders. The evolutions of spectra, mode-locking and continuous lasing powers by measuring the ratio of DC/pulse amplitude and the pulse shortening force (I(pulse)/P(avg)(2) ) are performed to determine the RHML capability of SOAFL. As the rational harmonic order increases up to 20, the spectral linewidth shrinks from 12 to 3 nm, the ratio of DC/pulse amplitude enlarges from 0.025 to 2.4, and the pulse-shortening force reduces from 0.9 to 0.05. At fundamental and highest RHML condition, we characterize the frequency detuning range to realize the mode-locking quality, and measure the dynamic frequency chirp of the RHML-SOAFL to distinguish the linear and nonlinear chirp after dispersion compensation. With increasing RHML order, the pulsewidth is broadened from 4.2 to 26.4 ps with corresponding chirp reducing from 0.7 to 0.2 GHz and linear/nonlinear chirp ratio changes from 4.3 to 1.3, which interprets the high-order chirp becomes dominates at higher RHML orders.

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.

Passively mode-locked lasers using saturable absorber incorporating dispersed single-wall carbon nanotubes

Passively mode-locked lasers using saturable absorber incorporating dispersed single-wall carbon nanotubes (SWCNTs) is demonstrated. The peak absorption wavelength of saturable absorber can be engineered within the gain band-width of erbium-doped fiber (EDF) centered at 1550 nm. The mean diameter of SWCNTs and the linear optical absorption of SWCNTs-polyvinyl alcohol (PVA) film are verified by Raman spectroscopy and UV-Visible-NIR spectrophotometer. By integrating the SWCNTs-PVA film into EDF ring laser (EDFL) centered at 1550 nm, we observed three pulse mode operations, Q-switching, mode-locking, and 5th-order harmonic mode-locking. The measured pulsewidths of the mode-locking and 5th harmonic mode-locking EDFL are 4.2 ps and 2.7 ps, respectively

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.

Second-order fractional Talbot effect induced frequency-doubling optical pulse injection for 40 GHz rational-harmonic mode-locking of an SOA fiber laser

A second-order fractional Talbot effect induced frequency-doubling of a 10 GHz optical pulse-train is demonstrated to backward injection mode-lock a semiconductor optical amplifier fiber laser (SOAFL) for 40 GHz rational-harmonic mode-locking (RHML). That is, a real all-optical gain-modulation of the SOAFL can be created by injecting such a time-multiplexed but pseudo-frequency-doubled pulse-train into the cavity. The time-multiplexing pulse-train can thus be transformed into a frequency-multiplied pulse-train via cross-gain modulation (XGM). The optical pulse-train at 10 GHz is generated by nonlinearly driving an electro-absorption modulator (EAM), which experiences the second-order fractional Talbot effect after propagating through a 4 km long dispersion compensation fiber (DCF). The DCF not only plays the role of frequency-doubler but also compensates the frequency chirp of the 10 GHz optical pulse-train. The pulsewidth broadening from 22 to 60 ps for initiating the time-domain Talbot effect is simulated by the nonlinear Schrodinger equation. With careful detuning of the RF modulation power of the EAM at 5 dBm, the generated 20 GHz optical pulse-train exhibits a positive frequency chirp with minimum peak-to-peak value of 2 GHz, and the peak-amplitude fluctuation between adjacent pulses is below 1.4%. In comparison with the SOAFL pulse-train repeated at 40 GHz generated by the fourth-order purely RHML process, the optimized second-order fractional Talbot effect in combination with the second-order RHML mechanism significantly enhances the modulation-depth of RHML, thus improving the on/off extinction ratio of the 40 GHz SOAFL pulse-train from 1.8 to 5.6 dB. Such a new scheme also provides a more stable 40 GHz RHML pulse-train from the SOAFL with its timing jitter reducing from 0.51 to 0.23 ps.

Chirp Evolution Algorithm of a Dark-Optical-Comb Injection Mode-Locked SOA Fiber Laser Pulses During Soliton Compression

The chirp evolution of a dark-optical-comb injection harmonic mode-locked (HML) semiconductor optical amplifier fiber ring laser (SOAFL) with a nonlinearly driven electro-absorption modulator is demonstrated. The dispersion compensation of the 10-GHz HML-SOAFL pulse with a 100-m-long dispersion compensation fiber is performed to shorten the pulsewidth from 29 to 2.9 ps with a compression factor of 10, and a time bandwidth product (TBP) of 0.5. The soliton compression with a 10-m-long single-mode fiber is employed to deliver the amplified 10-GHz HML-SOAFL soliton pulse with a peak power of 38.2 W and a pulsewidth of 1.6 ps, while the spectrum is broadened from 1.4 to 2.3 nm with a TBP of 0.45. To monitor the dynamic chirp evolution, a second-harmonic generation frequency-resolved optical gating (SHG-FROG) is used to retrieve the amplitude and phase contour profile of the HML-SOAFL. The phase fitting result distinguishes the linear chirp from the nonlinear chirp associated with the HML-SOAFL pulse, which are 0.016 ps2 and 0.002 ps3. The Schrödinger equation assists to retrieve the phase evolution of the 10-GHz HML-SOAFL with negative group velocity dispersion. Disregarding the linear dispersion compensation and soliton compression, the original 10-GHz HML-SOAFL pulse with a negative GDD of -5 ps2 is quantified.

Competition of Rational Harmonic Mode-Locking and Continuous-Wave Lasing in Semiconductor Optical Amplifier Fiber Laser Under Optical Pulse Injection

Twentieth-order rational harmonic mode-locking (RHML) semiconductor optical amplifier fiber laser (SOAFL) pulses are demonstrated by using 1-GHz backward dark-optical comb injection. Maximum frequency detuning range of plusmn 300 Hz, broadened pulsewidth of 35 ps, and highest average power of 0.4 muW for twentieth-order RHML-SOAFL pulse are characterized. The extraordinary phenomena on the red-shifted wavelength from 1535.5 to 1541.5 nm and the corresponding spectral linewidth reduced from 12 to 3 nm are observed with the RHML order increasing to 8 or higher. Such a less pronounced RHML mechanism at higher orders occurred in the optically injection mode-locked SOAFL is mainly attributed to the weak mode-locking strength at high RHML orders as compared to continuous-wave lasing mechanism.

200GHz DWDM channel pulsed optical carrier generated by 10ghz mode-locking of weak-resonant-cavity Fabry-Perot laser diode fiber ring

A novel optical TDM carrier with 200 GHz DWDM channel spacing from optically injection-mode-locked weak-resonant-cavity Fabry-Perot laser diode with 10%-end-facet reflectivity is demonstrated with chirp and pulsewidth dispersion compensated to 5.4 GHz and 8.5 ps, respectively.