Intra-cavity Electro-optic Modulator Research Articles

Ultra-narrow linewidth laser system based on intra-cavity electro-optic crystal frequency stabilization of external-cavity diode laser

An external-cavity diode laser based on an intra-cavity electro-optic modulator tuning is developed in this paper. Electro-optic crystal lithium niobate (LiNbO3), with no hysteresis effect and high response speed, is used to replace the traditional tunable part piezoelectric transducer (PZT). The linewidth of this laser at free-running mode is about 133 kHz. In addition, in the ultra-narrow linewidth laser system, the error signal is fed back to the driving voltage of LiNbO3 to realize laser locking, which can avoid the problem of laser output power fluctuation caused by feeding back to the laser injection current. The self-developed crystal-tuned laser has been successfully used in an ultra-narrow linewidth laser system, and the experimental results show that the linewidth of its beat frequency signal is about 1.5 Hz.

High-efficiency coupled-cavity optical frequency comb generation

We present a high efficiency source of picosecond pulses derived from a dual cavity optical frequency comb generator. This approach overcomes the limitations of single cavity comb generators that are restricted to efficiencies of a few percent. We achieve picosecond pulses with GHz repetition rates offering over a hundred times higher output efficiency than a single cavity design and demonstrate tuning of pulse width by varying the modulation depth of the intra-cavity electro-optic modulator. These results provide a wavelength-agnostic design with a compact footprint for the development of portable picosecond pulsed laser systems for timing, metrology, and LIDAR applications.

High bandwidth frequency modulation of an external cavity diode laser using an intracavity lithium niobate electro-optic modulator as output coupler

We present a novel approach to high bandwidth laser frequency modulation. A lithium niobate chip is used as an intracavity electro-optic modulator in a tunable cateye external cavity diode laser. The modulator is conveniently integrated with the cateye output coupler, providing a unique approach to high bandwidth frequency stabilization and linewidth narrowing. The intracavity modulator feedback was successfully operated below 1 V and achieved superior frequency noise suppression compared to conventional feedback through diode injection current modulation. A closed loop bandwidth of 1.8 MHz was demonstrated, and the laser linewidth reduced to around 1 Hz as measured by the heterodyne measurement.

Ultrashort Pulse Generation in Modeless Laser Cavity

We demonstrate experimentally that random phase modulation of an erbium-doped fiber ring-laser by an intra-cavity electro-optic phase modulator did not inhibit ultrashort-pulse operation. Stable and self-starting ultrashort-pulse operation with a single pulse circulating in the cavity was achieved even when the phase modulator was driven with random sequences sufficiently fast and strong to render the laser cavity modeless, in the sense that heterodyning of the laser output did not show any spectral lines corresponding to a mode spectrum. No significant change in measured pulse characteristics was observed, compared to conventional mode-locking in the unmodulated cavity. The insensitivity to the random phase modulation is expected, given the lack of phase-sensitive elements in the cavity.

Delay-Spectral Focusing Dual-Comb Coherent Raman Spectroscopy for Rapid Detection in the High-Wavenumber Region

Rapid multiplex coherent anti-Stokes Raman scattering (CARS) spectroscopy in the high-wavenumber (HW) region shows great advantages in real-time dynamic process visualizations, clinical diagnosis, abundant microplastic assessment, etc. Fourier transform CARS (FT-CARS) improves the acquisition speed of multiplex CARS to the order of tens of kHz, yet typical approaches to utilize the intrinsic coherence of ultrabroadband pulses notably impede the attainable Raman vibrations in the HW region. Here, a novel delay-spectral focusing dual-comb (DC) CARS scheme is proposed for rapid HW Raman detection based on two fiber combs with 100 MHz repetition rates. By combining the particular advantages of DC asynchronous optical sampling and spectral focusing instantaneous single molecular vibration excitation, the Raman spectrum directly maps to DC relative delay, releasing the coherence constraint of excitation sources. Thus, an Er comb and a Yb comb, as pump and Stokes excitation pulses, respectively, flexibly match the Raman vibration in the HW region. Further, a rapid delay focusing method with intracavity electro-optic modulation is applied to actively control the DC relative delay scanning in the Raman shift region of interest. With these efforts, the spectral acquisition rate is improved more than 1000-fold up to 40 000 spectra/s, while keeping spectral resolution (∼10 cm–1) and the signal-to-noise ratio (∼260) stable along with active acquisition rate tuning. Combined with a microfluidic device, high-speed measurement in the HW region of 15 μm microbeads in flow is demonstrated by the system, reaching a high throughput of around 2150 events/s and more than 99% classification consistency. The prospect of rapid acquiring multiplex CARS spectra without the sacrifice of spectral resolution or the need for the coherence of the pulse sources offers huge potential in rapid monitoring circumstances, such as flow cytometry and microspectroscopic imaging in biomedicine.

Variable Repetition Rate Picosecond Master Oscillator for Photoelectron Gun

In this work, aiming at the master oscillator of the photoelectron gun with a variable repetition rate of electron bunches, a picosecond solid-state laser subject to delayed optoelectronic feedback and RF loss modulation is studied. Loss modulation is performed using an electro-optical modulator with zero bias at the second accelerator frequency subharmonic. Optoelectronic negative feedback uses an intracavity electro-optical modulator and a fast high-voltage photodiode mounted as close as possible to the modulator crystal. An analytical formula is obtained for the pulse duration, and estimates are given for Nd and Yb based media and L, S, C and X-band used in modern linear accelerators. Numerical simulation proves that the control is suitable for pulse-repetitive operation. The proposed approach solves the problem of laser pulse shortening and locking the master oscillator, and therefore, electron bunches in photoelectron guns, to the high-stable RF generator controlling accelerator functioning.

Ultrashort pulse generation from continuous-wave driven degenerate optical parametric oscillators

Degenerate <inline-formula><tex-math notation="LaTeX">$\chi ^{(2)}$</tex-math></inline-formula> optical parametric oscillators (OPOs) pumped by continuous-wave (cw) lasers in bulk or integrated format represent a promising platform for the study of classical as well as quantum phenomena, enabling interesting applications such as squeezing and random number generation. When subjected to phase modulation, such devices can generate ultrashort output pulses. In this report, we study pulse generation and spectral broadening in degenerate OPOs with intracavity electro-optic modulator (EOM). We numerically investigate ultrashort pulse generation from a cw-driven degenerate OPO based on MgO:PPLN as the nonlinear gain medium. The phase sensitive gain provided by the quadratic nonlinear medium in a detuned cavity and the inherent self-phase-locking of the degenerate field with that of the pump govern the signal amplification. Using high-performance computing tools, we study the full intracavity complex field evolution over 10000 round trips, as the OPO reaches the steady state. Taking advantage of the high nonlinear gain and low threshold of degenerate OPO, and using an intracavity EOM synchronized to the free-spectral-range of the cavity in combination with spectral filtering, we show that a stable, uniform, and periodic train of picosecond pulses of <inline-formula><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula>5 ps duration with FWHM spectral bandwidth of 0.4 THz can be generated. The results of our theoretical model are valid for <inline-formula><tex-math notation="LaTeX">$\chi ^{(2)}$</tex-math></inline-formula> OPOs in bulk and integrated format.

Multi-branch erbium fiber-based femtosecond optical frequency comb for measurement of cavity ring-down spectroscopy

&lt;sec&gt;In this paper, we demonstrate an optical frequency comb (OFC) based on an erbium-doped-fiber femtosecond laser, for the measurement of cavity ring-down spectroscopy (CRDS) with wavelengths of 1064, 1083, 1240, 1380, 1500, 1600, 1750 and 2100 nm. We adopt a multi-branch structure to produce high power at the specific wavelengths to meet the requirement for application in the spectral measurement. The OFC is developed by using a mode-locked fiber ring laser based on the nonlinear amplifying loop mirror mechanism. The laser is self-starting by introducing a nonreciprocal phase bias in the cavity and insensitive to the environmental perturbation. Using the chirped pulse amplification and highly nonlinear fibers, the broad spectra at the specific wavelengths are obtained. By optimizing the parameters of the pulses, the power of per mode at each target wavelength is greater than 300 nW.&lt;/sec&gt;&lt;sec&gt;The&lt;i&gt; &lt;/i&gt;&lt;i&gt;f&lt;/i&gt;&lt;sub&gt;rep&lt;/sub&gt; is obtained by detecting the output of the femtosecond laser directly, while the&lt;i&gt; &lt;/i&gt;&lt;i&gt;f&lt;/i&gt;&lt;sub&gt;ceo&lt;/sub&gt; is detected by &lt;i&gt;f&lt;/i&gt;-2&lt;i&gt;f&lt;/i&gt; interference. The signal-to-noise ratio of the&lt;i&gt; &lt;/i&gt;&lt;i&gt;f&lt;/i&gt;&lt;sub&gt;ceo&lt;/sub&gt; is about 35 dB with a 300-kHz resolution bandwidth. By controlling the intra-cavity electro-optic modulator and piezoactuator , the &lt;i&gt;f&lt;/i&gt;&lt;sub&gt;rep&lt;/sub&gt; is stabilized with high bandwidth and large range (about megahertz bandwidth and 3 kHz range). The &lt;i&gt;f&lt;/i&gt;&lt;sub&gt;ceo&lt;/sub&gt; is stabilized by using feedback to the pump current of the femtosecond laser dynamically. The in-loop frequency instability degree of the &lt;i&gt;f&lt;/i&gt;&lt;sub&gt;ceo&lt;/sub&gt;, evaluated by the Allan deviation, is approximately 4.95 × 10&lt;sup&gt;–18&lt;/sup&gt;/&lt;i&gt;τ&lt;/i&gt;&lt;sup&gt;1/2&lt;/sup&gt; at 1 s and integrates down to 10&lt;sup&gt;–20&lt;/sup&gt; level after 2000 s, while that of the &lt;i&gt;f&lt;/i&gt;&lt;sub&gt;rep&lt;/sub&gt; is well below 5.85 × 10&lt;sup&gt;–13&lt;/sup&gt;/&lt;i&gt;τ&lt;/i&gt;. The all polarization-maintaining erbium fiber-based femtosecond optical frequency comb with multi-application branches we demonstrate in this paper is efficient and reliable for many other applications including optical frequency metrology and optical atomic clocks.&lt;/sec&gt;

Er:fiber-based femtosecond frequency comb stabilized to an Yb+ single-ion optical frequency standard

An erbium fiber-based femtosecond optical frequency comb stabilized to an Yb+ single-ion optical frequency standard was created. For the first time, a combination of an extra-cavity acousto-optic frequency modulator with fiber outputs and an intracavity electro-optic phase modulator based on a KTP crystal were used to stabilize offset frequency and one of the optical components of the Er:fiber femtosecond comb. As a result a locking bandwidth of 30 kHz for the optical comb offset frequency has been obtained. It is shown that the relative instability introduced by the stabilization and measurement systems into the output radio frequencies (in addition to the instability of the reference optical signal) is no worse than 5 × 10−14 for averaging times of 1 s and 2 × 10−16 for averaging times of 400 s.

Analysis of Self-Starting Harmonic Mode-Locking in an Electro-Optic-Feedback Laser

The concept of the self-starting harmonic mode-locking (SSHML) by electro-optical feedback in a solid-state laser is studied. Such an operational mode with m equidistant pulses in a laser cavity is controlled by a delayed single negative electro-optical feedback loop which comprises an intracavity electro-optical modulator and a fast high-voltage photodiode mounted directly on it. Analytical expressions for the feedback delay time and the short pulse duration are derived depending on laser parameters. The build-up time of the SSHML process and the limiting gain values are assessed by a high-resolution numerical simulation. For the purposes of accelerator physics, the pulse duration estimations for a set of the widely used Nd and Yb active media are provided. Robustness, high limiting gain and low sensitivity to gain level make SSHML laser an attractive platform for future multi-bunch photoinjector design.

Chirp-compensated pulsed titanium-sapphire laser system for precision spectroscopy.

Active frequency-chirp control for a narrowband pulsed titanium-sapphire laser oscillator-amplifier laser system is demonstrated using an intra-cavity electro-optic modulator, resulting in improved spectral resolution and stability. Beat-note measurements of its output to a continuous-wave laser locked to an optical frequency comb yields an Allan deviation of 5×10-11 (at 10 s). Correction of residual chirp from a comparison with the fourth-harmonic upconverted pulsed output to a molecular H2 two-photon resonance delivers a value for the uncertainty contribution due to frequency chirp below the 1.5×10-10 level.

An Yb-fiber frequency comb phase-locked to microwave standard and optical reference**Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDA1502040404 and XDB21010400) and the National Natural Science Foundation of China (Grant Nos. 91850209 and 11774234).

We present a fully stabilized Yb-fiber frequency comb locked to a microwave standard and an optical reference separately. The carrier-envelope offset frequency is generated by a standard f –2f interferometer with 40 dB signal-to-noise ratio. The offset frequency and the repetition rate are stabilized simultaneously to the radio frequency reference for more than 30 hours, and the fractional Allan deviation of the comb is the same as the microwave standard of 10−12 at 1 s. Alternatively, the comb is locked to an ultra-stable optical reference at 972 nm using an intracavity electro-optic modulator, exhibiting a residual integrated phase noise of 458 mrad (1 Hz–10 MHz) and an in-loop tracking stability of 1.77 × 10−18 at 1 s, which is significantly raised by six orders comparing to the case locked to the microwave frequency standard.

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.

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.

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.

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.

Repetition rate stabilization of an optical frequency comb based on solid-state laser technology with an intra-cavity electro-optic modulator.

The repetition rate stabilization of an optical frequency comb based on diode-pumped solid-state laser technology is demonstrated using an intra-cavity electro-optic modulator. The large feedback bandwidth of such modulators allows disciplining the comb repetition rate on a cavity-stabilized continuous-wave laser with a locking bandwidth up to 700 kHz. This surpasses what can be achieved with any other type of actuator reported so far. An in-loop integrated phase noise of 133 mrad has been measured and the PM-to-AM coupling of the electro-optic modulator has been investigated as well.

Long-Term Stabilization of an Actively Mode-Locked Er-Doped Fiber-Ring Laser via Dynamic Intracavity Loss Feedback

We demonstrate a long-term stabilized all-fiber actively mode-locked laser (AMLL) by locking the optical pulse train to a mode locker. By dynamically controlling the bias voltage of the intracavity electrooptical modulator, we established an optoelectronic phase-locked loop and achieved long-term phase stabilization of the AMLL. With the help of an optical-microwave phase detector, sensitive phase error signal is obtained and used for the phase stabilization. With this approach, the AMLL achieved long-term stable operation, and the residual fractional frequency stability is significantly improved from 1.8 × 10−13 to 2.8 × 10−15 at 1 s and from 2.1 × 10−16 to 6.8 × 10−19 at 4000 s.

Application of optoelectronic negative feedback to ordering of the temporal structure of the diode-pumped Nd:YLF laser radiation

The conditions of the generation of radiation with ordered temporal structure are determined for a solid-state laser with external negative feedback. Experiments are performed based on the Nd:YLF laser longitudinally pumped by a high-power diode array. Lasing was controlled using an intracavity electro-optic modulator based on a lithium tantalate crystal. Intensity smoothing and self-mode-locking regimes with generation of several short pulses in the axial interval are implemented by varying the delay in the feedback circuit. Under conditions of amplification above the stability boundary, the secondary electro-optic effect manifestation was detected in the lithium tantalate crystal.

Attosecond-Resolution Er:Fiber-Based Optical Frequency Comb**Supported by the National Natural Science Foundation of China under Grant Nos 91336101 and 61127901, and the West Light Foundation of the Chinese Academy of Sciences under Grant No 2013ZD02.

Highly stable frequency-controlled optical frequency combs are key elements of many applications in time-frequency and optical-metrology domains. In this work, we demonstrate a highly stable frequency-controlled erbium-fiber-based optical frequency comb system. Its repetition rate is phase-stabilized to a continuous-wave laser with both an intra-cavity electro-optic modulator and a piezo-transducer; while the carrier-envelope-offset frequency is phase-locked to a radio-frequency signal generator by controlling the pump power. In-loop relative frequency stabilities of the comb are below 1 × 10−16 at 1 s, and integrate down to low 10−20 level at 104 s. The corresponding timing uncertainties are 100–200 as over the full measurement range.