Super-mode Suppression Ratio Research Articles

Wavelength tunable actively mode-locked Tm3+ doped fiber laser with GHz repetition rate

Using a phase modulator to synchronize the longitudinal modes in an all-fiber cavity, we demonstrate a wavelength tunable (1955–2045 nm) diode pumped actively mode-locked Thulium doped fiber laser with tunable repetition rate up to 10 GHz with the shortest measured pulse width of 42 ps and average output power of 5 mW. We have performed a detailed analysis of the stable mode-locking regimes, including the self mode-locking condition that challenges the harmonic mode-locked operation. We demonstrate a supermode suppression ratio of > 50 dB across the entire wavelength band of operation while maintaining a pulse width and timing jitter of < 50 ps and < 1 ps, respectively.

10 GHz regeneratively mode-locked thulium fiber laser with a stabilized repetition rate.

GHz pulsed thulium-doped fiber laser with stabilized repetition rate can enable a wide range of applications. By employing regenerative mode-locking and cavity stabilization technique, we have for the first time demonstrated a 10 GHz polarization-maintaining thulium-doped fiber laser, which has a long-term repetition-rate stabilization and picosecond timing-jitter. In our experiment, a RF circuitry is designed to extract the 10 GHz longitudinal clock signal so that stable regenerative mode-locking is achieved. A piezo actuator-based phase-lock-loop is used to lock the regeneratively mode-locked pulses to a local reference synthesizer. The regeneratively mode-locked pulses with picosecond pulse width exhibit a high super-mode suppression ratio of 60 dB. In addition, the repetition rate of the laser shows good long-term stability with a variation of 8 Hz in 8 hours, corresponding to a cavity free spectral range fluctuation of less than 16 mHz. Meanwhile, the Allan deviation of the stabilized 10 GHz regeneratively mode-locked pulses is measured to be as low as 2 × 10-12 over 1000 s average time, which is only limited by the stability of the reference synthesizer. Such an ultra-stable 10 GHz pulsed thulium fiber laser may find potential application in 2 µm optical communication, material processing and spectroscopy.

Harmonically mode-locked Er-doped fiber laser at 1.3 GHz using a V2AlC MAX phase nanoparticle-based saturable absorber

We experimentally demonstrate a harmonically mode-locked erbium (Er)-doped fiber laser using a V2AlC-based saturable absorber (SA) at the 1.55 μm wavelength region. The prepared SA was fabricated using a side-polished fiber with V2AlC MAXphase nanoparticles via liquid-phase exfoliation (LPE). The derived saturation intensity and modulation depth of the V2AlC-based SA were approximately 63 MW/cm2 and 18%, respectively. The repetition rate was tuned from 14.98 MHz to 1.3 GHz (86th harmonic) by adjusting the pump power. The 86th harmonic mode-locked pulses at approximately 1.3 GHz repetition rate were generated with a temporal width and supermode suppression ratio of approximately 863 fs and 30 dB, respectively. These results demonstrate the application of the V2AlC MAX phase in giga-hertz frequency ultrafast fiber lasers.

2.5 GHz harmonic mode locking from a femtosecond Yb-doped fiber laser with high fundamental repetition rate.

We experimentally demonstrated a high repetition rate harmonic mode-locked fiber laser with a high signal-to-noise ratio (SNR) and super mode suppression ratio. A novel approach using a laser with a high fundamental repetition rate and low harmonic order was presented. 2.5 GHz harmonic mode-locking from an Yb-doped fiber laser was realized with a short cavity length corresponding to a 167 MHz fundamental repetition rate. The laser operated at anomalous net dispersion regime and generated soliton-like pulses at 1050 nm. At the harmonic order of 15th, the laser had a stable output of 773 fs at 2.5 GHz with the average power of 48 mW under a subwatt pump power of 406 mW, and the time jitter was 2 ps. A high RF SNR over 70 dB was measured. A super mode suppression ratio was confirmed larger than 60 dB. This is, to the best of our knowledge, the highest SNR and super mode suppression ratio achieved in harmonic mode-locked fiber lasers with an over 2 GHz repetition rate.

Nonlinearity managed passively harmonic mode-locked Er-doped fiber laser based on carbon nanotube film.

We examine the implication of intracavity nonlinearity for harmonic mode locking (HML) by exploiting highly nonlinear fiber in a carbon nanotube film mode-locked Er-doped fiber laser. It is found that the reasonably large nonlinearity is of benefit to increase the extent of harmonic order while the excessive nonlinearity leads to some peculiar multi-pulse patterns such as noise-like pulse and soliton rain. Via appropriate nonlinearity management, nearly 4 GHz repetition rate pulses at the 91st harmonic with 936 fs pulse duration are delivered under the pump power of 280 mW. The pulse stability is evidenced by the super-mode suppression ratio of 35.6 dB. To the best of our knowledge, it is the highest repetition rate yet reported for a passively HML fiber laser based on a film-type physical saturable absorber. Furthermore, the laser exhibits steep pumping efficiency slope of ${\gt}{19}\;{\rm MHz/mW}$, which is also a record among all of the passively HML fiber lasers.

Intracavity birefringence-controlled GHz-tuning range passively harmonic mode-locked fiber laser based on NPR.

We experimentally demonstrate a harmonic-order controllable L-band Er-doped passively mode-locked fiber laser based on nonlinear polarization rotation (NPR). Distinct from all previous reports, we find that the intracavity birefringence is able to control the harmonic order of a passively mode-locked fiber laser. Experimentally, under a constant pump power of 704 mW, the harmonic order can be tuned from 113th to 39th monotonically by adjusting the polarization controller orientation only. The corresponding repetition rate changes from 2.21 to 0.77 GHz simultaneously. Remarkably, the super-mode suppression ratio of each harmonic order we observed is higher than 29 dB with a maximum of 36.5 dB. Simulated transmission spectra of NPR prove that the changed transmission plays an important role in controlling the harmonic order.

L-Band GHz Femtosecond Passively Harmonic Mode-Locked Er-Doped Fiber Laser Based on Nonlinear Polarization Rotation

Via using an L -band optimized in-fiber polarizing grating device, a GHz L -band femtosecond passively harmonic mode-locked Er-doped fiber laser based on nonlinear polarization rotation is first demonstrated. In total, 4.22 GHz pulses with the duration of 810 fs and super-mode suppression ratio (SMSR) of 32 dB are obtained under the pump power of 712 mW corresponding to 215th harmonic order. The central wavelength of 4.22 GHz pulses is 1581.7 nm with 10.1 nm 3 dB bandwidth. Furthermore, under this fixed pump power, higher harmonic orders can also be attained by rotating the polarization controllers properly. The highest repetition rate we obtained is 7.41 GHz with the SMSR of 20.7 dB.

Pulse-repetition-rate tuning of a harmonically mode-locked fiber laser using a tapered photonic crystal fiber.

Strong enhancement of optoacoustic interactions in the micrometer-sized core of a photonic crystal fiber (PCF) enables stable, harmonic mode locking of a soliton fiber laser at GHz frequencies. Here we report that by tapering the PCF during the draw, the optoacoustic gain bandwidth can be broadened to ∼47 MHz, more than 3 times wider than in the untapered fiber. This made possible broad pulse-repetition-rate tuning over 66MHz (from 2.042 to 2.108GHz) of an optoacoustically mode-locked soliton fiber laser. Within this tuning range, the harmonically mode-locked pulse trains at the laser output were observed to be quite robust, with better than 40dB supermode suppression ratio, sub-ps pulse timing jitter, and <0.2%relative intensity noise. This gigahertz-rate, near-infrared soliton fiber laser has remarkable pulse-rate tunability and low noise level, and has important potential applications in frequency metrology, high-speed optical sampling, and fiber telecommunications.

20 GHz actively mode-locked thulium fiber laser.

A high repetition-rate actively mode-locked thulium fiber laser is demonstrated where an electro-optic lithium niobate phase modulator is used to synchronize the longitudinal modes in the cavity. The repetition rate of the actively mode-locked laser is tunable from 14.6 MHz to 19 GHz, where the 19 GHz pulses exhibit a super-mode suppression ratio of 46 dB. Furthermore, the output pulse width could be manipulated through finely controlling the detuning frequency or repetition rate. We have also experimentally observed rational harmonic mode-locking in the laser and obtained 14 GHz and 21 GHz repetition rate pulses using a 7 GHz modulating signal. To the best of our knowledge, we have improved the repetition-rate of actively mode-locked thulium fiber laser by more than one order of magnitude. Such a high repetition source can be readily synchronized to a master clock, which makes it very suitable for high speed optical data processing, communication and remote sensing.

A Coupled Optoelectronic Oscillator With Performance Improved by Enhanced Spatial Hole Burning in an Erbium-Doped Fiber

A coupled optoelectronic oscillator (COEO) with performance improved by the enhanced spatial hole burning (SHB) effect in an unpumped erbium-doped fiber (EDF) is proposed and demonstrated. In the proposed COEO, a strong standing-wave forming structure is incorporated to enable large SHB effect in the unpumped EDF, which significantly improves the supermode suppression ratio of the generated optical pulse, and the sidemode suppression ratio and phase noise performance of the generated electrical signal. A 10-GHz COEO is established. A stable optical pulse train is successfully generated with a supermode suppression ratio as high as 75 dB. The system is observed in the lab environment for 1.5 h with no significant variation. Without introducing any long fiber or multiloop structure in the optoelectronic oscillator loop, the sidemode suppression ratio of the 10-GHz RF output reaches 90 dB and the phase noise is about −130 dBc/Hz at 10-kHz offset. The influence of the optical power injected into the EDF, and the effects of the absorption coefficient and length of the EDF on the key parameters of the COEO are investigated and discussed.

Passively harmonic mode-locked erbium-doped fiber laser at a 580 MHz repetition rate based on carbon nanotubes film

We propose and demonstrate a passively harmonic mode-locked erbium-doped fiber laser (EDFL) using carbon nanotubes polyvinyl alcohol (CNTs-PVA) film. The laser allows generation of the pulses with a repetition rate of 580 MHz, which corresponds to the 22nd harmonics of a 26.3 MHz fundamental repetition rate under 323 mW pump power. A particularly noteworthy feature of the pulses is the super-mode suppression ratio (SMSR), which is over 40 dB, indicating a stable operation.

Polarization-maintained coupled optoelectronic oscillator incorporating an unpumped erbium-doped fiber

A polarization-maintained coupled optoelectronic oscillator (COEO) with its performance significantly improved by a short-length unpumped erbium-doped fiber (EDF) is reported and experimentally investigated. A 10 GHz optical pulse train with a supermode suppression ratio of 61.8 dB and a 10 GHz radio frequency signal with a sidemode suppression ratio of 94 dB and a phase noise of ?121.9 dBc/Hz at 10 kHz offset are simultaneously generated. Thanks to saturable absorption of the 1 m unpumped EDF, which introduces relatively large cavity loss to the undesired modes and noise, the supermode suppression ratio and the phase noise are improved by 9.4 and 7.9 dB, respectively.

Ultra-High Repetition Rate Harmonic Mode-Locking Generated in a Dispersion and Nonlinearity Managed Fiber Laser

Stable pulses with a 22.132-GHz repetition rate are successfully obtained by managing the dispersion and nonlinearity in a passively soliton erbium-doped single-mode fiber laser, which is as high as the 2192nd order of the fundamental frequency of 10.096 MHz. The super-mode suppression ratio beyond 40 dB is observed under only 485 mW pump power.

Tunable passively harmonic mode-locked Yb-doped fiber laser with Lyot-Sagnac filter.

A novel passively harmonic mode-locked dissipative soliton Yb-doped fiber laser with all normal dispersion is proposed and experimentally demonstrated based on a semiconductor saturable absorption mirror and tunable Lyot-Sagnac filter. By only tuning the bandwidth of the filter at fixed pump power, the repetition rate of 9.87 to 167.8MHz (corresponding to 17th-order harmonic) is obtained. This is the highest repetition rate and harmonic order for a passively harmonic mode-locked dissipative soliton Yb-doped fiber laser with all-normal dispersion to the best of our knowledge. The signal-to-noise ratio and super-mode suppression ratio for all harmonic orders are higher than 65 and 35dB, respectively, which shows the high stability of the fiber laser.

1484-nm two-cascaded Raman fiber laser mode-locked by an intermode-beating mode-locking technique

We demonstrate a 1484-nm two-cascaded Raman mode-locked fiber laser based on the intermode-beating mode-locking (IBML) technique. Through the two-cascaded Raman shifts of P2O5 in a phosphosilicate fiber, the continuous-wave (CW) 1064-nm Raman pump can be transferred to the 1484-nm second-order Stokes. When the intermode-beating frequency of the 1064-nm pump source matches with the 1484-nm Raman-cavity frequency, the IBML condition is satisfied, and the harmonic mode-locking at 1484-nm occurs to stably emit nanosecond pulse trains. By properly adjusting the 1484 nm Raman-cavity length, we have further realized the tuning of the mode-locking harmonic order. The 472nd- and 757th-order harmonic mode-locking operations with repetition rates of 72.728 and 116.292 MHz have been obtained, respectively. The IBML operation is stable with a radio-frequency (RF) supermode suppression ratio of 33.9 dB and RF signal-to-noise ratio of 51.8 dB.

A Dual-Wavelength Rational Harmonic Mode-Locked Fiber Ring Laser With Different Repetition Frequencies

A dual-wavelength rational harmonic mode-locked fiber ring laser with different repetition frequencies is theoretically analyzed and experimentally demonstrated. In this scheme, two wavelength channels are inserted into the laser loop to form two resonant cavities. By tuning the length of each channel, required rational harmonic mode-locking conditions can be achieved, and dual-frequency mode-locked signals are simultaneously generated at different wavelengths. In addition, the supermode suppression ratio is further improved due to the mode competition caused by this dual-cavity configuration. In the experimental demonstration, when the fourth-order (or fifth-order) harmonic mode-locked signal is generated in Cavity 1, the first-, second-, and third-order (or fourth-order) harmonic mode-locked signals, respectively, can be generated in Cavity 2 by tuning its length. The measured radio frequency spectra and waveforms show that the signals have high quality. Compared with a conventional rational harmonic mode-locked laser (RHMLL), more than 10 dB supermode suppression ratio improvement is obtained. Since this system can flexibly implement multiwavelength and multifrequency signal generation without adding much cost, it may have wide applications in optical communication system, photonic microwave signal generation, and optical waveform synthesizers.

All Fiber Actively Mode-Locked Ytterbium-Doped Laser With Large Range Temporal Tunability

An all-fiber ytterbium-doped laser widely tunable in duration and repetition rate is reported, which is actively mode locked based on a high speed in-cavity intensity modulator. The laser can generate a stable pulse train with a duration adjustable from 31 to 910 ps, and a repetition rate ranging from 13.12 MHz to 6.2 GHz (from the basic to the 475th-order harmonic) without changing the cavity construction. The cavity supermode suppression ratio is as good as 45 dB, and the signal-to-noise ratio is better than 48 dB at the 475th-harmonic mode locking. To the best of our knowledge, it is the highest order (475th) harmonic mode locking achieved in an all-normal-dispersion ytterbium-doped fiber laser, with the widest tuning range of repetition rate and pulsewidth.

Flexible picosecond thulium-doped fiber laser using the active mode-locking technique.

An all-fiber actively mode-locked thulium-doped fiber laser (AML-TDFL) based on a 10 GHz bandwidth electro-optic intensity modulator (EOM) providing flexible picosecond pulses at 1980 nm is presented. The EOM is driven by electrical pulses rather than traditional sine-wave signals. The repetition rate of output pulses was 21.4 MHz at fundamental mode-locking, which could be scaled up to 1.498 GHz through the 70th order harmonic mode-locking, and the shortest measured output pulse width was 38 ps. Furthermore, the output pulse width could be tuned by either adjusting the modulation frequency with small detuning or changing the width of these driving electrical pulses without frequency detuning. In our work, the stability of these mode-locked pulses obtained from the AML-TDFL was superior; for instance, the measured supermode suppression ratio of 1.498 GHz pulses train was up to 48 dB.

Tunable Active Harmonic Mode-Locking Yb-Doped Fiber Laser With All-Normal Dispersion

We report tunable active harmonic mode-locking of a dissipative soliton ytterbium-doped fiber laser based on a high-speed intensity modulator with all-normal-dispersion (ANDi) cavity. Adjusting the working frequency and the data length of radio driving signals for the dissipative soliton pulses shaping, the repetition rates can be facilely and accurately scalable from 20.33 to 609.84 MHz corresponding to the harmonic order from the fundamental rate to 30th, which is higher than the passive harmonic mode-locking (HML) fiber laser in an all-fiber and ANDi cavity. The cavity supermode-suppression ratio is suppressed up to 50 dB, and the signal-to-noise ratio is better than 57 dB at the 30th HML.

Wavelength switchable multiwavelength actively mode-locked fiber-ring laser based on highly nonlinear photonic crystal fiber and multimode fiber Bragg grating

A wavelength switchable multiwavelength actively mode-locked fiber-ring laser based on highly nonlinear photonic crystal fiber (PCF) and polarization-dependent mode coupling to multimode-fiber Bragg grating (MMFBG) is proposed. Twenty meters of highly nonlinear dispersion-shifted PCF (DS-PCF) is inserted into the fiber ring cavity to suppress gain competition through the four-wave-mixing (FWM) effect. A mode scrambler is attached to the multimode fiber (MMF) to introduce a polarization-dependent mode coupling to the MMFBG. Through changing polarization in the cavity, stable and switchable one-wavelength, two-wavelength (wavelength spacing of 0.8 and 2.4 nm), and three-wavelength simultaneously actively mode-locked optical pulse trains at a repetition rate of 5 GHz are obtained. We show that high nonlinearity introduced by the nonlinear PCF in the cavity can improve significantly supermode suppression ratio (SMSR) of the multiwavelength pulses generated and a sidemode suppression ratio (SMSR) of 58 dB is realized.