Nonlinear Polarization Rotation Research Articles

All-normal-dispersion nonlinear polarization rotation mode-locked Tm:ZBLAN fiber laser.

We demonstrated an all-normal-dispersion nonlinear polarization rotation mode-locked Tm:ZBLAN fiber laser in the 2 μm wavelength band. All fibers in the experiment were ZBLAN fibers with normal dispersion in the wavelength band. An average power of 63 mW with a characteristic cat-ear shaped optical spectrum of an ANDi laser was obtained. The center wavelength and the spectral bandwidth were 1880 nm and ~80 nm, respectively. The repetition rate was 70.6 MHz and the corresponding pulse energy was 0.9 nJ. The pulse duration directly from the oscillator was 860 fs and it was compressed to 107 fs.

Observation of sub-400fs, wavelength-switchable stretched pulse and bound-state pulse in Tm-doped fiber laser.

We report on the experimental observation of wavelength-switchable stretched pulse and bound-state pulse in a dispersion-managed Tm-doped laser. At a pump power of 572 mW, a stretched pulse with a pulse duration of 389 fs can be first obtained at 1961 nm. By increasing the pump power and appropriately adjusting the cavity polarization state, the mode-locking wavelength can be switched from 1961 nm to 1980 nm caused by the birefringence filtering effect based on nonlinear polarization rotation, and the corresponding pulse duration is 371 fs. Meanwhile, loosely bound states of two pulses and three pules at 1980 nm can be observed with appropriate cavity parameters.

Improvements of Soliton Pulse Energy and Peak Power in Thulium-Doped Fiber Laser

We report on improvements of mode-locked soliton pulse energy and peak power in a thulium-doped fiber laser. At the pump power of 370 mW, conventional soliton can be first generated using nonlinear polarization rotation technology. By increasing the pump power to 550 mW and appropriately adjusting cavity polarization state, the conventional soliton pulse can be converted into the Gaussian pulse. Due to dispersion management, excess accumulation of nonlinear phase shifts in the cavity can be avoided. In this case, the pulse energy and peak power can be increased from 77 pJ to 1.38 nJ and from 106.9 W to 2.67 kW, respectively. These improvements indicate that the Gaussian pulse operation can effectively enhance the pulse energy and peak power of the thulium-doped fiber laser.

Vector Nature of Dissipative-Soliton-Resonance Pulses in Fiber Lasers Mode-Locked by Nonlinear Polarization Rotation Technique

The vector nature of dissipative-soliton-resonance (DSR) pulses is numerically investigated in an all-normal-dispersion Yb-doped fiber laser mode-locked by the nonlinear polarization rotation technique. We calculate the polarization ellipses of the DSR pulse throughout the cavity, which shows that the polarization state varies during the propagation. The features of pulse polarization are also displayed on the Poincare sphere. The impact of nonlinear birefringence on the polarization evolution is analyzed. Furthermore, we find that the polarization state is not uniform across a DSR pulse at a fixed intra-cavity position. The flat-top part of the pulse has a nearly fixed polarization, while its leading and trailing edges feature polarization states that vary with time. The peak power ratio of the two orthogonal polarization components in the pulse is limited in the range from 4 to 31. Our simulation results offer insight into the polarization properties of DSR pulses in mode-locked fiber lasers containing polarization discrimination devices.

High-power supercontinuum generation by noise-like pulse amplification in Yb-doped fiber amplifier operating in a nonlinear regime.

In this paper, we report on a supercontinuum generation by amplifying noise-like pulses (NLPs) in a nonlinear Yb-doped fiber amplifier. The NLP source is a homemade Yb-doped all-fiber ring oscillator based on nonlinear polarization rotation mode-locking method. NLPs possess a repetition rate of 11.57MHz, energy of 16.5nJ, and 3dB spectral bandwidth of 42nm. The intensity autocorrelation function of NLPs has a broad pedestal and a narrow central spike. The pedestal and the spike have temporal widths of 63ps and 92fs, respectively. The NLPs are amplified by a Yb-doped fiber nonlinear power amplifier to achieve output power of 7.5W. Nonlinear effects in the amplifier drastically broaden the spectrum of NLPs and generate high-power supercontinuum light with 10dB spectral bandwidth of 1130nm (from 1037 to 2167nm). The presented supercontinuum generation system is an all-fiber compact structure and has the advantage of not requiring long single-mode, nonlinear, or photonic crystal fibers.

Long cavity ring fiber mode-locked laser with decreased net value of nonlinear polarization rotation.

We investigate a new configuration of a mode-locked fiber laser by using a nonlinear polarization rotation-based design to generate soliton pulses with low repetition rate. Unlike with previously reported configurations, we introduce a Faraday mirror after the first half of the cavity length to counteract the nonlinear polarization rotation effects. The total cavity length is 437 m including a 400-m long twisted SMF-28 fiber. The fiber was twisted to cancel the linear birefringence and to ensure that the polarization ellipticity is not altered as the pulse travels along the fiber. The strict control of polarization yields a stable relation between the polarization state of the pulses propagating in the cavity and the regimes of generation. Depending on the polarization state we observed three different emission regimes, the single soliton regime (SR), conventional noise-like pulses (NLP) and noise-like square-waveform pulse (NLSWP). In the SR, a 467.2 kHz train of solitons was obtained with pulse duration of 2.9 ps at 1558.7 nm.

Multiwavelength operation in praseodymium fiber laser using polarization maintaining fiber and nonlinear polarization rotation in ring cavity

A multiwavelength praseodymium fiber laser (MWPFL) operating at the 1300-nm region is proposed and demonstrated. The MWPFL incorporates a polarization maintaining fiber acting as a Lyot birefringence filter, and when combined with the nonlinear polarization rotation effect, generates the desired multiwavelength output. Careful adjustment of the polarization controller at different angles allows for the generation of up to five channels above a power level of −3.4 dBm and a spacing of 0.2 nm. The peak power fluctuation and wavelength shifts of these lasers are measured to be less than 2.1 dB and 0.04 nm, respectively, over an observation period of 60 min. The demonstrated MWPFL shows good stability combined with a simple structure for generating a multiwavelength output at the 1300-nm wavelength region.

Observation of Soliton Molecules in NPR Mode-Locked Er-Fiber Laser via Birefringence Management

We have experimentally demonstrated that soliton molecules can be achieved from an Er-doped fiber laser oscillator via polarization dispersion management in the anomalous dispersion regime. In the laser oscillator, selective high-birefringence (HIBI) fibers were cross-spliced twice to counteract the linear polarization dispersion, which could highlight the role of the accumulated nonlinear phase shift and thus ensure the stable generation of mode-locking pulses by means of nonlinear polarization rotation (NPR). Depending on the length of the HIBI fibers, the angle of waveplates, and the pumping power, different types of soliton, such as single-pulse soliton and soliton molecules in tightly and loosely bound state, are observed.

All-fiber polarization interference filter based uniform multiwavelength erbium-doped fiber laser

We demonstrate a compact and stable room-temperature multiwavelength erbium doped fiber laser by employing 45° tilted fiber gratings based on an all-fiber polarization interference filter. Benefiting from the filter, the channel number, linewidth, uniformity and stabilization of the multiwavelength laser are greatly improved. The filter also works as a functional polarizing device in a nonlinear polarization rotation, leading to the multiwavelength operation. Instead of a highly nonlinear fiber, the single mode fiber is used to provide enough linearity and to reduce the splice loss. More than 80 wavelengths (within a 3 dB bandwidth), lasing with a linewidth of 0.03 nm and a signal-to-noise ratio of 33 dB, are obtained. The wavelength spacing of 0.164 nm agrees with the channel spacing of the filter, and can be flexibly controlled by adjusting the length of the filter.

Numerical Study on the Soliton Mode-Locking of the Er3+-Doped Fluoride Fiber Laser at ~3 μm with Nonlinear Polarization Rotation

Recent interest in the application of mid-infrared (mid-IR) lasers has made the generation of ~3 µm ultrafast pulses a hot topic. Recently, the generation of femtosecond-scale pulses in Er3+-doped fluoride fiber lasers has been realized by nonlinear polarization rotation (NPR). However, a numerical study on these fiber lasers has not been reported yet. In this work, the output properties of the NPR passively mode-locked Er3+-doped fluoride fiber ring laser in ~3 µm have been numerically investigated based on the coupled Ginzburg–Landu equation. The simulation results indicate that stable uniform solitons (0.75 nJ) with the pulse duration of femtosecond-scale can be generated from this fiber laser. This numerical investigation can provide some reference for developing the high energy femtosecond soliton fiber lasers in the mid-IR.

Formation of Various Soliton Molecules in a 2-<inline-formula> <tex-math notation="LaTeX">$\mu$ </tex-math> </inline-formula>m Anomalous-Dispersion Mode-Locked Fiber Laser

We report on the experimental observations of stable single soliton and soliton molecules in an anomalous-dispersion thulium-doped passively mode-locked fiber laser by using the nonlinear polarization rotation technology. The stable single soliton operation can convert to the soliton pair operation by cautiously adjusting the PCs, at the pump power of 350 mW. It is experimentally demonstrated that the formation of stationary soliton pairs is related to the interaction between solitons and dispersive waves. By appropriately adjusting the cavity parameters, more complex soliton molecules composed of three, four, and five bound solitons can be observed. Meanwhile, we experimentally analyze complex nonlinear dynamics of soliton molecules around 2- ${\mu }\text{m}$ .

High repetition-rate passively mode-locking Tm-doped fiber laser based on narrow bandwidth filtering

Abstract We propose and demonstrate a high repetition-rate passively mode-locking Tm-doped fiber laser. Mode-locking operation is achieved by using a conventional nonlinear polarization rotation (NPR) structure. Fundamental frequency soliton laser is obtained with the repetition-rate of 5.05 MHz and the pulse width of 54.7 ps. 3-dB bandwidth and signal and noise ratio (SNR) are 3.1 nm and 53.03 dB, respectively. In order to improve repetition-rate of the mode-locking pulse, a narrow band filter is adopted. In this case, maximum repetition-rate of the output pulse can be up to 7.75 GHz (1534 orders). Pulse width and 3-dB bandwidth of mode-locking laser are compressed to 67.2 ps and 0.2 nm, respectively, and SNR is 19.71 dB. In addition, the laser center wavelength can be tuned from 1882 nm to 1925 nm by adjusting the filter.

Passive harmonic mode-locked ytterbium-doped fiber laser with chirped pulse amplification

A passive harmonic mode-locked ytterbium-doped fiber laser with all-normal dispersion has been demonstrated. The mode-locking mechanism of the laser is based on the interaction between semiconductor saturable absorber mirror and nonlinear polarization rotation. The repetition rate of the laser is adjustable from 7.91 MHz to 31.65 MHz. Via the chirped pulse amplification, the 1 ps mode-locked pulse at the fundamental repetition rate of 7.91 MHz is compressed to 720 fs with single pulse energy of 12.6 nJ.

Analysis of nonlinear polarization rotation by an ultrashort optical pump and probe pulse in a strained semiconductor optical amplifier

In this paper, a comprehensive dynamic model is used to study the nonlinear polarization rotation (NPR) of a probe signal in the presence of a copropagating pump signal in a strained semiconductor optical amplifier (SOA). Pump and probe signals are Gaussian pulse with 200 fs pulse width, propagating in a 500 μm SOA. In the present model, the effects of carrier dynamics on the SOA gain and phase are considered and the NPR of the probe signal is measured by the ellipticity angle using the Stokes vector and Mueller matrices. The effects of several important factors on the NPR of the probe signal are investigated. These factors include pump signal energy, free carrier absorption and two-photon-absorption nonlinear effects, tensile/compressive strain, pump-probe pulse width, and pump-probe delay time. The results show that the pulse width and strain have a considerable effect on the ellipticity angle deviation (EAD); we especially see that the tensile strain increases the EAD, and the compressive strain reduces the EAD compared to the no strain structure. For a specific range of pulse width (here 0.2 ps to 1 ps), the EAD increases noticeably with the pulse width. It is also shown that, for the pump-probe delay time, the maximum EAD is obtained when the delay time is 0.1 ps.

Theoretical approach of developing a frequency-encoded reversible optical arithmetic and logic unit using semiconductor optical amplifier-based polarization switches

The reversible logic gate is a great choice for designing various types of optical processors due to so many advantageous aspects of it; such as low power consumption and the ability of data recovery. At first, the optical circuit of Fredkin gate, a universal reversible logic gate, is designed theoretically using a semiconductor optical amplifier (SOA)-based polarization switch, and the performance of the circuit is studied using simulated results. The frequency-encoded binary data are used to execute the operations. Subsequently, we propose the techniques of developing NOT, AND, OR, EX-OR, EX-NOR gates, and full adder circuit using reversible Fredkin gates. Finally, we develop an optical arithmetic logic unit using the proper combination of reversible Fredkin gates. The theory of nonlinear polarization rotation of the probe beam in the presence of the pump beam in SOA is adopted here. The simulated input–output spectra of the optical circuits enhance the admissibility of the proposed concept.

Investigation of mid-infrared parabolic pulse evolution in a mode-locked Er-doped fiber laser based on the nonlinear polarization rotation technique

The parabolic pulse evolution in a mode-locked Er-doped fiber laser operating at 2.8 μm has been numerically investigated by utilizing the nonlinear polarization rotation technique. In this work, the parabolic pulse evolution has been investigated by utilizing a segment of chalcogenide dispersion-decreasing bandgap fiber and a piece of Er-doped ZBLAN around 2.8 μm, whose total dispersion is in normal dispersion regime. Stable parabolic pulses can be obtained in the soft-glass fiber resonator when the polarizing angles changes from 0.356 to 0.4 π and the net group velocity dispersion from 0.006 to 0.03 ps2, respectively. Through optimizing the dispersion (i.e. net dispersion is 0.014 ps2), the pulse with 7.35 ps duration and 1.7 nJ pulse energy fits quite well with the parabolic profile. The ratio of maximum to minimum pulse width in the cavity is about 10. The pulse energy and K parameter increase with the increase of the net dispersion. As the net dispersion increases to 0.03 ps2, the pulse energy can reach up to 2.5 nJ. These results can be regarded as guidance when designing a wave-breaking-free fiber laser in the mid-infrared region.

Nonlinear polarization dynamics of Kerr beam self-cleaning in a graded-index multimode optical fiber.

We experimentally study polarization dynamics of Kerr beam self-cleaning in a graded-index multimode optical fiber. We show that spatial beam cleaning is accompanied by nonlinear polarization rotation and a significant increase of the degree of linear polarization.

L-Band Efficient Dissipative Soliton Erbium-Doped Fiber Laser With a Pulse Energy of 6.15 nJ and 3 dB Bandwidth of 47.8 nm

Here, an efficient dissipative soliton mode-locked fiber laser in the L-band using nonlinear polarization rotation technology is demonstrated. With a maximum pump power of 495.3 mW and polarization state optimization, the fiber laser delivers a maximum output power of 68.6 mW with an 11.16 MHz repetition rate and corresponding single pulse energy of 6.15 nJ. The dissipative soliton spectrum is centered at 1599.6 nm with a 3 dB bandwidth of 47.8 nm. The full width at half maximum of the compressed pulse is 156 fs. To the best of our knowledge, this is the highest single pulse energy reported so far for an L-band passively mode-locked all-fiber laser.

High-order mode lasing in all-FMF laser cavities

We experimentally demonstrate two kinds of all few-mode fiber (FMF) ring lasers with high-order mode (HOM) oscillation in the laser cavity. One kind is a switchable-wavelength all-FMF HOM laser with an output of tunable optical vortex beams (OVBs); the other is a Q-switched all-FMF HOM laser with an output of pulsed cylindrical vector beams (CVBs). The lasers are composed of all-FMF components and few-mode erbium-doped fiber. A Sagnac interferometer made of a 3 dB FMF coupler functions as the wavelength selector, and switchable multiwavelength tunable OVBs are experimentally realized. Carbon nanotube-based saturable absorbers and the nonlinear polarization rotation technique are used to achieve Q-switched CVB lasers. This is the first report, to our knowledge, on the generation of switchable-wavelength and Q-switched HOM beams in all-FMF laser cavities.

Wavelength tunable noise-like pulse generation from an erbium-doped fiber laser

We demonstrated a wavelength tunable mode-locked erbium-doped all-fiber ring cavity laser with the nonlinear polarization rotation technique. By adjusting the polarization states of the ring cavity, the laser can deliver noise-like pulses with wavelength tunable from 1568 nm up to 1610 nm. For a 1610 nm center wavelength, we could obtain an output with a pulse repetition rate of 1.67 MHz and pulse energy of 19.2 nJ. In addition, as we know, the 1610 nm is the reported longest wavelength for noise-like pulses operation with erbium’s gain in the L-band.