Pump Wavelength Tuning Research Articles

Observation of deterministic double dissipative-Kerr-soliton generation with avoided mode crossing

Dissipative Kerr solitons (DKSs) in microresonators have boosted the development of the chip-scale ultrastable microcomb sources, and thrived in both fundamental physics and a wide range of applications. Among various DKS states, single DKS, double DKS, and a perfect soliton crystal could be identified simply based on the optical spectrum. Especially, the double DKS state, due to its two-pulse-interference nature, has recently found its own application in microwave photonics, such as reconfigurable rf filters. However, the traditional method to generate double DKS usually yields stochastically relative positions of the DKS in the cavity, which limits the versatility of the application. Here a method to deterministically generate double DKSs with fixed relative positions assisted by the dual-pump driven scheme in a 97-GHz ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ microresonator is demonstrated. Via the dual-pump scheme, not only has the single soliton been repeatably generated, double DKS with deterministic relative positions has also been realized through backward tuning. The effects of pump wavelength tuning and pump power on the relative positions are investigated. A direct bridge between the relative positions and the avoided mode crossing induced modulated cw background is established. This work not only provides insight to DKS dynamics in a dual-pump scheme, but also improves the versatility of double-DKS based applications in microwave photonics.

Dual-mode microresonators as straightforward access to octave-spanning dissipative Kerr solitons

The Kerr soliton frequency comb is a revolutionary compact ruler of coherent light that allows applications from precision metrology to quantum information technology. The universal, reliable, and low-cost soliton microcomb source is key to these applications. As a development and extension of the direct creation of a soliton microcomb with the dual-mode scheme in an aluminum nitride microresonator, this paper thoroughly presents the design strategy to reliably attain such dual-modes in the silicon nitride (Si3N4) platform, separated by ∼10 GHz, which stabilizes soliton formation without using additional auxiliary laser or RF components. We demonstrate the deterministic generation of the refined single-solitons that span 1.5-octaves, i.e., near 200 THz, via adiabatic pump wavelength tuning. The ultra-wide soliton existence range up to 17 GHz not only suggests the robustness of the system but will also extend the applications of soliton combs. Moreover, the proposed scheme is found to easily give rise to multi-solitons as well as the soliton crystals featuring enhanced repetition rate (2 and 3 THz) and conversion efficiency greater than 10%. We also show the effective thermal tuning of mode separation to increase the possibility to access the single-soliton state. Our results are crucial for the chip-scale self-referenced frequency combs with a simplified configuration.

Femtosecond optical parametric oscillator continuously tunable across 3.6-8 μm based on orientation-patterned gallium phosphide.

We report a synchronously-pumped femtosecond optical parametric oscillator (OPO) based on orientation-patterned gallium phosphide (OP-GaP), providing continuously tunable mid-infrared (mid-IR) idler radiation across 3570-7892nm (2801-1267 cm-1), by exploiting pump wavelength tuning. We generate up to 54mW of output average power at 80MHz, and quantum conversion efficiencies up to 28.9% are achieved by use of synchronized pump retroreflection. With the inclusion of intracavity dispersion compensation in an OP-GaP OPO, near-transform-limited signal pulse durations of 112fs at 1288nm are measured, and peak powers up to 3kW in the mid-IR are inferred. Finally, evidence of three-photon absorption is observed and characterized near the pump wavelength.

Single-Stage Ti:Sapphire-Pumped Deep-Infrared Optical Parametric Oscillator Based on CdSiP2

We report a high-repetition-rate femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on the nonlinear optical crystal, CdSiP2 (CSP), pumped directly by a Ti:sapphire laser, for the first time. By pumping CSP at μ m, we have achieved practical output powers at the longest wavelengths generated by any Ti:sapphire-pumped OPO. Using a combination of pump wavelength tuning, type-I critical phase matching, and cavity delay tuning, we have generated continuously tunable radiation across 6654–8373 nm (1194–1503 cm−1) at 80.5-MHz repetition rate, providing up to 20 mW of average power at 7314 nm and >7 mW beyond 8000 nm, with idler spectra exhibiting bandwidths of 140–180 nm across the tuning range. Moreover, the near-IR signal is tunable across 1127–1192 nm, providing up to 37 mW of average power at 1150 nm. Signal pulses, characterized using intensity autocorrelation, have durations of ∼260–320 fs, with corresponding time-bandwidth product of Δ υ Δ τ ∼ 1. The idler and signal output exhibit a TEM00 spatial profile with single-peak Gaussian distribution. With an equivalent spectral brightness of ∼6.68 × 1020 photons s−1 mm−2 sr−1 0.1% BW−1, this OPO represents a viable alternative to synchrotron and supercontinuum sources for deep-IR applications in spectroscopy, metrology, and medical diagnostics.

Pump-tuned deep-infrared femtosecond optical parametric oscillator across 6-7 μm based on CdSiP2.

We report on a high-power femtosecond optical parametric oscillator (OPO) at 80 MHz repetition rate, tunable across 6318-7061 nm in the deep-infrared (deep-IR) using pump wavelength tuning. The OPO, based on CdSiP2 (CSP), is synchronously pumped by a commercial Ti:sapphire-pumped femtosecond OPO in the near-IR, enabling rapid static tuning of the CSP OPO with minimal adjustments to its cavity length. The deep-IR CSP OPO provides as much as 32 mW of average idler power at 6808 nm with spectral bandwidth >1000 nm (at -10 dB level) across the tuning range. By implementing intracavity dispersion control, near-transform-limited signal pulses of ∼100 fs duration with smooth single-peak spectrum are achieved at 1264 nm, corresponding to an idler wavelength at 6440 nm. To the best of our knowledge, this is the first time such practical idler powers in the deep-IR have been generated from a dispersion-compensated CSP femtosecond OPO at sub-100 MHz repetition rate.

Investigation of a terahertz-wave parametric oscillator using LiTaO3 with the pump-wavelength tuning method

We investigate theoretically the performance of a terahertz parametric oscillator (TPO) using LiTaO3 (LT) with the pump-wavelength tuning method. The frequency tuning accuracy of the LT-TPO is potentially superior to that of a TPO using LiNbO3 (LN) under the same conditions. The variation of the radiation angle of THz waves coupled from the Si prism of the LT-TPO is up to about 20° lower than that for the LN-TPO for a pump-wavelength tuning range of 0.4–1.6 μm. Although the THz-wave parametric gain characteristics of LiTaO3 are somewhat unsatisfactory compared with those of LiNbO3, the LT-TPO with pump-wavelength tuning can still show potential for high-performance operation, with the excellent optical properties of the LiTaO3.

Tunable single-to-dual channel wavelength conversion in an ultra-wideband SC-PPLN

We experimentally demonstrate tunable dual channel broadcasting of a signal over the C-band for wavelength division multiplexed (WDM) optical networks. This is based on cascaded χ(2) nonlinear mixing processes in a specially engineered, 20-mm-long step-chirped periodically poled lithium niobate with a broad 28-nm second harmonic (SH) bandwidth in the 1.55-μm spectral range. A 10-GHz picosecond mode-locked laser was used as a signal along with a CW pump to generate two pulsed idlers, which are simultaneously tuned across the C-band by detuning of the pump wavelength within the broad SH bandwidth. Variable-input, variable-output scheme of tuned idlers is successfully achieved by tuning the signal wavelength. Pump or signal wavelength tuning of ~10 nm results in the idlers spreading across 30 nm in the C-band.

Multiple Raman Pump Assisted Fiber Optical Parametric Amplifiers

We studied the use of multiple Raman pumps to assist fiber optical parametric amplifiers (FOPAs). We derived a theoretical model to describe the performance of multiple Raman pump assisted FOPAs. We demonstrated that the over 40 nm flat gain bandwidth provided by the multiple Raman pumps can be used to support the parametric gain bandwidth of Raman-assisted FOPAs (RA-FOPAs). We also found that if indirect Raman gain contribution dominates, by using dispersion-flattened highly nonlinear fiber with small dispersion slope and polarization-mode dispersion effect, broadband FOPA with broad parametric pump wavelength tuning range can be obtained by using multiple Raman pump assistance. On the other hand, if direct Raman gain contribution dominates, the parameters of the multiple Raman pumps have to be chosen carefully to ensure that the Raman gain bandwidth matches the parametric gain bandwidth in order to achieve a flat gain with broad gain bandwidth in the RA-FOPAs.

Transparency pump intensity and differential gain in resonantly pumped W optical pumping injection cavity lasers

We report the results of a cavity length characterization of a W optical pumping injection cavity (OPIC) laser with a room temperature emission wavelength of 3.2 μm using pump wavelength tuning to achieve resonant optical pumping. Devices with cavity lengths ranging from 312 to 2030 μm are characterized to determine geometry-independent figures of merit. The measurements yield transparency pump intensities Itr that range from 230 W/cm2 at 100 K to 7.8 kW/cm2 at 300 K, as gain per unit pump intensity (differential gain) decreases from 0.17 cm/W at 100 K to 0.011 cm/W at 300 K. The characteristic temperature of the transparency pump intensity is 55.6 K, while the gain per unit pump intensity demonstrates an exponential decay with a characteristic temperature of 67.9 K. Compared to other optically pumped type-II W lasers and electrically injected interband cascade lasers, there is less reduction in the differential gain with increasing temperature, consistent with the high temperature operation of these OPIC devices.

Investigation of a novel frequency-tuning method for terahertz-wave parametric oscillators

A novel frequency tuning scheme for terahertz-wave parametric oscillators (TPOs) is proposed. We demonstrate that the generation of the tunable terahertz wave can be realized by continuously varying the incident pump wavelength at a fixed angle of incidence of pump relative to the TPO resonator axis, based on the variation of noncollinear phase-matching conditions between the pump and Stokes/THz waves in the process of simulated polariton scattering. Combined with the angle-tuning method, this potential pump-wavelength tuning technique can further extend the TPO tuning range, especially in low-frequency THz region. However, the stability of the output direction of THz waves from the Si prism under this tuning method has yet to be further improved. The characteristics of THz-wave parametric gain involved in this frequency tuning scheme are also studied.

Pump Wavelength Tuning of Optical Pumping Injection Cavity Lasers for Enhancing Mid-Infrared Operation

ABSTRACTRecent efforts to improve the performance of mid-infrared antimonide-based semiconductor lasers have focused on enhancing the absorption of the pump beam to maximize power conversion efficiencies and minimize threshold intensities. One successful approach has been the optical pumping injection cavity (OPIC) laser, in which a type-II W active region is enclosed between distributed Bragg reflector (DBR) mirrors in order to achieve multiple passes of the pump beam and thereby to enhance absorption.Previously, fixed wavelength sources have been used for optical pumping of OPIC laser structures, with limited tuning available by adjusting the incident angle. By tuning the pump wavelength using an optical parametric oscillator, we demonstrate minimum threshold intensities and maximum slope efficiencies at the resonance of the DBR cavity surrounding the active region, further demonstrating the potential of OPIC lasers. A 3.2 μm OPIC laser operated at 350 K in pulsed mode (at the highest operating temperature of the dewar), with a characteristic temperature of 50 K. The power conversion efficiency for a single facet at 300 K was the highest ever observed in the mid-IR, at approximately 4%.Results are presented for two OPIC samples (emitting at ∼3.2 μm and 4.3 μm at high temperature), one of which was designed with a broadened cavity resonance, suitable for pumping with a multi-mode source. Threshold intensities and slope efficiencies measured as a function of pump wavelength demonstrate the strong resonance effect, and that the “broadened OPIC” does in fact manifest a much wider resonance than the non-broadened resonance cavity design.

Bandwidth and tunability enhancement of wavelength conversion by quasi-phase-matching difference frequency generation

Abstract Bandwidth and tunability enhancement of difference frequency generation (DFG)-based wavelength conversion by introducing various distributing formats of π-phase shifting domains into the quasi-phase-matching (QPM) gratings is demonstrated, and the concise expressions describing the tuning curves in these cases are obtained for the first time. The results show not only the pump and signal bandwidth can be obviously broadened and flattened, but also diverse comblike pump–wavelength tuning curves with controllable channel spacing can be achieved by introducing periodically distributed π-phase shifting domains into the QPM gratings, which would greatly improve the tunability and practibility of DFG-based wavelength converters.

Transparent wavelength conversion in fibre with 24 nm pump tuning range

A transparent continuous wave-pumped highly nonlinear fibre wavelength converter (WC) with a conversion bandwidth of 61 nm and a pump wavelength tuning range of 24 nm, the largest ever reported for fibre-based WCs, is demonstrated. The conversion quality is confirmed by bit error rate measurements showing < 1.4 dB power penalty at 10 Gbit/s data transmission.

A continuous-wave tunable solid-state blue laser based on intracavity sum-frequency mixing and pump-wavelength tuning

We report on continuous-wave tunable blue-light generation from a Nd:Y3Al15O12 laser by intracavity sum-frequency mixing of its fundamental laser line at 946 nm with the pump light from a tunable Ti:sapphire laser by use of cadmium–mercury–thiocyanate nonlinear crystal. The tunable range of the blue light was 434.4–437.5 nm, and the maximum output power at 436 nm was measured to be 310 μW.

Single-crystal sum-frequency-generating optical parametric oscillator

We report a synchronously pumped optical parametric oscillator that generates the sum frequency of the pump and the signal wavelengths. A single KTiOPO4 (KTP) crystal is used for both parametric generation and sum-frequency generation in which these two processes are simultaneously phase matched for the same direction of propagation. The parametric oscillator, pumped by a femtosecond Ti:sapphire laser at a wavelength of 827 nm, generates a blue output beam at 487 nm with 43% power-conversion efficiency. The polarization geometry of simultaneous phase matching requires rotation of the pump polarization before the cavity. Adjusting the group delay between the two orthogonally polarized pump components to compensate for the group-velocity mismatch in the KTP crystal increases the photon-conversion efficiency more than threefold. Angle tuning in conjunction with pump wavelength tuning provides output tunability in the 484–512-nm range. A plane-wave model that takes group-velocity mismatch into account is in good agreement with our experimental results.

Near- to mid-infrared picosecond optical parametric oscillator based on periodically poled RbTiOAsO_4

We describe a Ti:sapphire-pumped picosecond optical parametric oscillator based on periodically poled RbTiOAsO(4) that is broadly tunable in the near to mid infrared. A 4.5-mm single-grating crystal at room temperature in combination with pump wavelength tuning provided access to a continuous-tuning range from 3.35 to 5microm , and a pump power threshold of 90 mW was measured. Average mid-infrared output powers in excess of 100 mW and total output powers of 400 mW in ~1-ps pulses were obtained at 33% extraction efficiency.

Near-infrared optical parametric oscillation in an organomineral crystal

Efficient singly resonant oscillation near 1.3 μm and pump wavelength tuning are demonstrated for what is believed to be the first time in an organomineral crystal. An oscillation threshold of 6 MW cm-2 and a total conversion efficiency of 8% are achieved in a doubly noncritical configuration with respect to the crystal orientation and the signal wavelength. The performance and buildup time of the optical parametric oscillator have been considered and have been shown to benefit from injection seeding.

Femtosecond optical parametric oscillator based on periodically poled KTiOPO_4

We report a femtosecond optical parametric oscillator based on a periodically poled KTiOPO(4) crystal for which quasi-phase matching is achieved with a 24-microm poling period. The singly resonant parametric oscillator, synchronously pumped by a Ti:sapphire laser at a wavelength of 758 nm, generates a signal at 1200 nm and an idler at 2060 nm. The maximum signal power conversion efficiency of the device is 22% with a pump depletion of 69%. We tune the signal wavelength over a 200-nm band by changing the cavity length. In addition, pump wavelength tuning provides output tunability in the 1000-1235-nm range.

Phase-matched self-doubling optical parametric oscillator

We report a synchronously pumped intracavity frequency-doubled optical parametric oscillator that employs a single KTiOPO(4) crystal for both parametric generation and frequency doubling. Both nonlinear processes are phase matched for the same direction of propagation in the crystal. The parametric oscillator, pumped by a femtosecond Ti:sapphire laser at a wavelength of 745 nm, generates a green output beam at 540 nm with a 29% power conversion efficiency. Angle tuning in conjunction with pump wavelength tuning provides output tunability in the 530-585-nm range.

Broadband pump wavelength tuning of a low threshold N-(4-nitrophenyl)-L prolinol near infrared optical parametric oscillator

We report the pump wavelength tuning of a low threshold N-(4-nitrophenyl)-L-prolinol based nanosecond pulsed optical parametric oscillator in the near infrared. A broad tuning range from 1 to 1.5 μm corresponds to a limited pump wavelength excursion from 583 to 590 nm and a record low oscillation threshold of the order of 0.5 MW cm−2.