Intracavity Modulator Research Articles

Spatial-mode switchable EDF laser based on low modal-crosstalk mode MUX/DEMUX

We report an all-fiber ring laser that emits three linearly polarized (LP) modes based on the intracavity mode multiplexer/demultiplexer (MUX/DEMUX). The low modal-crosstalk all-fiber mode MUX/DEMUX consisting of cascaded mode-selective couplers (MSCs) multiplex/demultiplex multiple spatial modes. The output mode lasing of the Erbium-doped fiber (EDF) laser can be switched among the three LP modes by employing combination of a mode MUX and a simple N × 1 optical switch. The slope efficiencies, optical spectra and mode profiles are investigated.

Nickel nanoparticles‐based saturable absorber: Toward compact multiwavelength Yb‐doped fiber pulsed lasers near 1 μm region

AbstractWe experimentally demonstrate a compact pulsed dual‐wavelength Ytterbium‐doped fiber laser (YDF) based on Nickel nanoparticles (Ni‐NPs) as a Q‐switcher and optical stabilizer. By integrating the Ni‐NPs saturable absorber (SA) in the cavity, and adjust the 975 nm diode pump power to 185 mW, a self‐starting passively Q‐switched was generated at a central wavelength of 1038.5 nm. By exploiting the extra high nonlinearity of Ni‐NPs, the homogenous gain broadening of the YDF oscillator can be suppressed. Consequently, at a pump power of 195 mW, a stable dual‐wavelength passively Q‐switching laser has been generated at room temperature without any intracavity spectral filters or modulation elements. As increases the pump power up to the maximum value of 288 mW, the Ytterbium‐doped fiber laser observed that the smallest pulse width, the maximum repetition rate, and the maximum pulse energy of 1.44 μs, 100.1 kHz, and 4.45 nJ, respectively. The Ni‐NPs SA proof its potential in generating multiwavelength pulsed laser in the 1 μm region for different photonic applications.

Frequency stabilization of an injection seeded Nd:YAG ring oscillator by ramp-fire technique with a RbTiOPO4 modulator

We report on an injection seeded Q-switched Nd:YAG zigzag slab ring oscillator with pulse energy of 67 mJ and pulse duration of 19 ns at repetition rate of 20 Hz. With a RbTiOPO4 (RTP) electro-optic crystal as the intra-cavity phase modulator, stable single frequency operation is achieved using the ramp-fire technique with a 10 µs linear voltage ramp sweeping 2.5 free spectral ranges. Frequency jitter of output pulse at 1064 nm is measured to be 2.0 MHz over 7 min. The beam quality factor is $$ M_{x}^{2} = 1.38 \pm 0.03, M_{y}^{2} = 1.29 \pm 0.02 $$ in seeded operation, which is improved from that of $$ M_{x}^{2} = 1.67 \pm 0.01, M_{y}^{2} = 1.35 \pm 0.01 $$ in free oscillation. The measured linewidth of the output is 27 MHz, which is 1.2 times Fourier-transformed-limited. Based on the RTP crystal as the modulator, the ramp-fire technique with a high ramp speed is capable of achieving high frequency and timing stability.

Vortex laser by transforming Gaussian mode with an interferometric output coupler.

Generation of vortex beams directly from the laser source can be limited in power and efficiency, or to specific pump sources and gain media. Here, we propose a new high power and high efficiency vortex laser methodology with interferometric mode transformation as output coupling, which uses high power handling and low loss optics that have wavelength versatility. Experimental demonstration is made in a diode-pumped Nd:YVO4 laser using an imbalanced Sagnac interferometer as output coupler producing high quality vortex output beams (M2 = 2.07) with fully selectable control of handedness whilst the intracavity mode is maintained as a fundamental Gaussian. Vortex output power >3W is produced with only small reduction in efficiency compared to the equivalent TEM00 laser. Continuous variation of vortex output coupling transmission and the quality of the vortex is investigated experimentally showing good agreement with theory. This work reveals a new approach to high power structured laser radiation direct from the source through interferometric spatial mode transformations.

Robust lasing modes in coupled colloidal quantum dot microdisk pairs using a non-Hermitian exceptional point

Evanescently coupled pairs of microdisk lasers have emerged as a useful platform for studying the non-Hermitian physics of exceptional points. It remains an open question how scalable and versatile such phenomena can be when carried over to other designs. Here we have studied the effect of gain/loss modulation in an evanescently coupled pair of microdisk optical resonators fabricated from solution-processed colloidal quantum dots. The emission spectra of these structures are sensitive to small imperfections, which cause frequency-splitting of the whispering gallery modes. Despite this inherent disorder, we found that when spatially modulating the optical pump to vary the gain differential between the coupled microdisks, the coupling drives the split parasitic intra-cavity modes into coalescence at an exceptional point of the resulting three-mode system. This unusual behavior is rationalized via a Hamiltonian that incorporates the intra-cavity coupling as well as the anisotropic inter-cavity coupling between modes in the microdisk pair.

Localized patterns in star networks of class-B lasers with optoelectronic feedback

We analyze how a star network topology shapes the dynamics of coupled CO\textsubscript{2} lasers with an intracavity electro-optic modulator that exhibit bistability. Such a network supports spreading and stationary activation patterns. In particular, we observe an activation spreading where the activated periphery turns on the center element, an activated center which drifts the periphery into the active region and an activation of the whole system from the passive into the active region. Pinned activation, namely activation localized only in the center or the peripheral elements is also found. Similar dynamical behavior has been observed recently in complex networks of coupled bistable chemical reactions. The current work aims at revealing those phenomena in laser arrays, giving emphasis on the essential role of the coupling structure in fashioning the overall dynamics.

Hybrid two-qubit gate using a circuit QED system with a triple-leg stripline resonator

We theoretically propose a circuit QED system implemented with triple-leg stripline resonator (TSR). Unlikely from linear stripline resonator, the fundamental intra-cavity microwave modes of the TSR are two-fold degenerate. When a superconducting qubit is placed near one of the TSR legs, one fundamental mode is directly coupled to the qubit, while the other one remains uncoupled. Our system closely resembles an optical cavity QED system, where an atom in a cavity couples only to the incident photon with a specific polarization by placing a polarization beamsplitter in front of the optical cavity. Using our circuit QED system, we have theoretically studied a two-qubit quantum gate operation in a hybrid qubit composed of flying microwave qubit and superconducting qubit. We have demonstrated that for the hybrid qubit, the quantum controlled phase flip (CPF) gate can be reliably implemented for the experimentally available set of parameters.

All-in-fiber SESAM based comb oscillator with an intra-cavity electro-optic modulator for coherent high bandwidth stabilization.

We demonstrate the stabilization of an all-in-fiber polarization maintaining semi-conductor saturable absorber mirror (SESAM) mode locked frequency comb oscillator with an intra-cavity waveguide electro-optic phase modulator (EOM) to a narrow linewidth HeNe laser over 46 hours. The high feedback bandwidth of the EOM allows a coherent optical lock with an in-loop integrated phase noise of 1.12 rad (integrated from 10 Hz to 3 MHz) from the carrier signal. No piezo fiber stretcher was required to guarantee long-term stabilization, preventing mechanical degradation of the optical fibers and enabling a long lifetime of the oscillator. As an application a hybrid stabilization scheme is presented, where a comb tooth is phase locked to a longitudinal mode of the large ring laser "G" located at the Geodatic Observatory Wettzell. The hybrid stabilization scheme describes the optical lock of the frequency comb to the G laser and the simultaneous compensation of the ring laser frequency drift by comparing the comb repetition rate against an active H-maser reference. In this context the ring laser reached a fractional Allan deviation of 5 · 10-16 at an integration time of 16384 s.

Dual-cavity digital laser for intra-cavity mode shaping and polarization control.

In this paper, we present a digital laser for on-demand modes with polarization control based on a single intra-cavity spatial light modulator (SLM). We employ a phase-only SLM as the back reflector in a dual-cavity resonator. We prove that we can digitally control and switch lasing modes with desired linear polarization at video rates. Moreover, we experimentally generate vector beams based on the selection and coherent summation of two orthogonally polarized Hermite-Gaussian (HG) beams inside the resonator.

Rate-equation theory of a feedback insensitive unidirectional semiconductor ring laser.

For our recently designed continuous-wave and single-frequency ring laser with intra-cavity isolator, we have formulated a rate-equation theory which accounts for two sources of mutual back-scattering between the clockwise and counterclockwise modes, i.e. induced by side-wall irregularities and due to inversion-grating-induced spatial hole burning. With this theory we first confirm that for a ring laser without intra-cavity isolation, from sufficiently large pumping strength on, the inversion-grating-induced bistable operation (i.e. either clockwise or counterclockwise) will overrule the back-reflection-induced coupled-mode operation (i.e. both clockwise and counterclockwise). We then analyze the robustness of unidirectional operation in case of intra-cavity isolation against the intra-cavity back-reflection mechanism and grating-induced mode coupling and derive for this case an explicit expression for the directionality in the presence of external optical feedback, valid for sufficiently strong isolation. The predictions posed in the second reference remain unaltered in the presence of the mode coupling mechanisms here considered.

Single-Frequency TEA CO2 Laser for Experiments on Non-Resonant Radiation Interaction with Matter

The design philosophy and output radiation parameters of single frequency TEA CO2 laser with bleaching intracavity longitudinal modes selector (cell filled with SF6) are described. At cavity tuning to 10P(16) line and choosing optimum SF6 pressure in the cell the stable single frequency lasing is realized with scatter of radiation peak power in a series of “shots” less than ±7% of average value. The radiation energy density and intensity gradually tuned in the ranges 0.36–12.5 J/cm2 and 2.9–100 MW/cm2 correspondingly were realized in the focal plane of a lens with f = 127 mm.

Carrier-Envelope Offset Frequency Stabilization of a Fiber Laser by Cross Gain Modulation

We present the first carrier-envelope offset (CEO) frequency stabilization of a fiber laser by cross gain modulation. The Yb-doped fiber laser is mode-locked by nonlinear polarization evolution and emits 32-nm wide dissipative solitons at a repetition rate of 125 MHz with 150 mW of average output power. A continuous wave laser signal at a wavelength of 1025 nm is used as an intracavity power modulator. A low power of only 200 μW of modulator signal is coupled into the fiber laser and amplified in the gain segment. This signal cross modulates the laser gain, achieving 40 times larger modulation bandwidth of the intracavity laser power than with standard pump-current control. A tight CEO lock is demonstrated with 361 mrad of residual integrated phase noise (from 1 Hz to 1 MHz). The method allows easy implementation in many existing fiber laser frequency combs based on various saturable absorbers and fiber configurations.

Topologically Controlled Intracavity Laser Modes Based on Pancharatnam-Berry Phase

Incorporation of a metasurface that involves spin-orbit interaction phenomenon into a laser cavity provides a route to the generation of spin-controlled intracavity modes with different topologies. By utilizing the geometric phase, Pancharatnam-Berry phase, we found a spin-enabled self-consistent cavity solution of a Nd:YAG laser with a silicon-based metasurface. Using this solution we generated a laser mode possessing spin-controlled orbital-angular momentum. Moreover, an experimental demonstration of a vectorial vortex is achieved by the coherent superposition of modes with opposite spin and orbital angular momenta. We experimentally achieved a high mode purity of ∼95% due to laser mode competition and purification. The photonic spin-orbit interaction mechanism within a laser-cavity can be implemented with multifunctional shared-aperture nanoantenna arrays to achieve multiple intracavity topologies.

Improving the accuracy of a dual-comb interferometer by suppressing the relative linewidth

We present a compact system of synchronization for two fiber-based optical frequency comb lasers. We use a free-running continuous wave laser as an intermediary to obtain the relative noise of two combs and employ an intra-cavity electro-optic modulator (EOM) to achieve active phase feedback for fast synchronization. The EOM bandwidth is 150 kHz and the relative linewidth is suppressed markedly from 300 kHz to sub-hertz values. The relative effective timing jitter of the two pulse trains is also decreased from 680 fs to 25 fs. The proposed method shows promise for developing a high-performance, low-cost, fiber-based dual-comb interferometer for ranging or spectroscopy.

Amplitude noise suppression by intracavity phase modulation in a harmonically mode-locked laser

A fiber coupled semiconductor ring laser that employs both an amplitude and a phase modulator was built and actively harmonic mode-locked at a repetition rate of 10 GHz. The phase modulator was driven at the cavity fundamental frequency and its effects on the optical spectrum and the optical pulse train were analyzed. The intracavity phase modulation at the cavity fundamental frequency resulted in 40% lower optical pulse amplitude fluctuations and improved the stability of the optical spectrum.

Dual-wavelength passively Q-switched ytterbium-doped fiber laser using Fe3O4-nanoparticle saturable absorber and intracavity polarization

We have experimentally demonstrated the operation of a dual-wavelength passively Q-switched ytterbium-doped fiber laser by using a saturable absorber (SA) based on Fe3O4 nanoparticles in a magnetic fluid. The SA was fabricated by depositing magnetic fluid at the end of an optical fiber ferrule. By performing adjustments to the pump power and polarization controller state in the cavity, a stable dual-wavelength lasing operation was generated without intracavity spectral filters or modulation elements. The Q-switched laser output was achieved at a pump threshold of 80 mW with a maximum output pulse energy of 38.8 nJ, a repetition rate of 73.4 kHz and a minimum pulse width of 3.4 µs. To the best of the authors’ knowledge, this is the first demonstration of a dual-wavelength passively Q-switched fiber laser using Fe3O4 nanoparticles as the SA in the 1.0 µm operation region.

Time and Fourier domain jointly mode locked frequency comb swept fiber laser

Fourier domain mode locked (FDML) fiber lasers enable megahertz wavelength sweeping rate but suffer from the short coherent length. Discretization of the swept spectrum by a comb filter was demonstrated effective to enhance the coherent length. In this paper, we propose a novel discretization method of the FDML signal with an intracavity intensity modulator. We propose and successfully demonstrate a time and Fourier domain jointly mode locked fiber laser with a Fabry-Perot comb filter and an intensity modulator in the cavity. A 50 GHz free spectral range comb filter in the Fourier domain mode locked fiber swept laser slices the spectrum into a series of comb lines and chops the swept signal into short pulses in time domain. The temporal signal is detected by a photodetector to generate a series of ultrashort pulses to drive the intensity modulator to further polish the intracavity pulses. We experimentally realized the proposed time and Fourier domain jointly mode locked fiber laser. Discrete wavelength swept laser output with a wavelength spacing of ~0.4 nm in a 41 nm sweeping range has been achieved.

Steering optical comb frequencies by rotating the polarization state

We demonstrate a new approach to steer the frequencies of a nonlinear polarization-rotation mode-locked laser, where a specially designed intrcavity electro-optic modulator tunes the polarization state of the laser signal. This approach not only results in the broadband associated with high performance, but also results in a large dynamic range associated with good robustness. Our experimental results show that frequency control dynamic ranges are at least one order of magnitude larger than those of the previous ultra-fast frequency control techniques, reaching hundreds of hertz and hundreds of megahertz for repetition rate (fr) and carrier-envelope-offset frequency (fceo), respectively.

Pure antimony film as saturable absorber for Q-switched erbium-doped fiber laser

This paper reports on the use of Antimony (Sb) polymer film to generate stable Q-switching pulses in Erbium-doped fiber laser (EDFL) cavity. The SA is fabricated by coating a thin layer of Sb on a polyvinyl alcohol (PVA) film through physical vapour deposition (PVD) process. A 1 × 1 mm area of the film SA is cut and integrated into between two fiber ferrules inside the laser cavity for intra-cavity loss modulation. Self-starting and stable Q-switched pulses are obtained within a pump power range from 60 to 142 mW. Within this range, the repetition rate increases from 70.82 to 98.04 kHz, while pulse width decreases from 7.42 to 5.36 μs. The fundamental frequency signal-to-noise ratio of the pulse signal is 74 dB, which indicates the excellent stability of the pulses. The maximum output power and pulse energy are 8.45 mW and 86.19 nJ, respectively. Our demonstration shows that Sb film SA capable of generating stable pulses train operating at 1.55-micron region.

Quasi-regenerative mode locking in a compact all-polarisation-maintaining-fibre laser

A novel technique of mode locking in erbium-doped all-polarisation-maintaining-fibre laser has been developed and preliminary investigated. The proposed quasi-regenerative technique combines the advantages of conventional active mode locking (when an intracavity modulator is driven by an independent RF oscillator) and regenerative mode locking (when a modulator is driven by an intermode beat signal from the laser itself). This scheme is based on intracavity intensity modulation driven by an RF oscillator being phase-locked to the actual intermode frequency of the laser. It features also possibilities of operation at multiple frequencies and harmonic mode-locking operation.