Idler Power Research Articles

Spectral programmable mid-infrared optical parametric oscillator

A spectral programmable, continuous-wave mid-infrared (MIR) optical parametric oscillator (OPO), enabled by a self-developed high-power spectral tailorable fiber laser, was proposed and realized. While operating at a single-wavelength, the maximum idler power reached 5.53 W at 3028 nm, with a corresponding pump-to-idler conversion efficiency of 14.7%. The wavelength number switchable output was available from one to three. The single idler was tunable in a range of 528 nm (2852–3380 nm). In a dual-wavelength operation, the interval between two idlers could be flexibly tuned for 470 nm (53–523 nm), and the intensity of each channel was controllable. Triple-wavelength idler emission was realized, meanwhile exhibiting spectral custom-tailored characteristics. Furthermore, we balanced the parametric gain through the pre-modulating broadband multi-peak pump spectra, enabling a 10 dB bandwidth adjustment of the idler emission from 20 to 125 nm. This versatile mid-infrared laser, simultaneously featuring wide tuning, multi-wavelength operation, and broad bandwidth manipulation, has great application potential in composition detection, terahertz generation, and speckle-free imaging.

Highly efficient and widely tunable Si3N4 waveguide-based optical parametric oscillator.

We demonstrate an efficient and widely tunable synchronously pumped optical parametric oscillator (OPO) exploiting four-wave mixing (FWM) in a silicon nitride (Si3N4) waveguide with inverted tapers. At a pump pulse duration of 2 ps, the waveguide-based OPO (WOPO) exhibited a high external pump-to-idler conversion efficiency of up to -7.64 dB at 74% pump depletion and a generation of up to 387 pJ output idler pulse energy around 1.13 μm wavelength. Additionally, the parametric oscillation resulted in a 64 dB amplification of idler power spectral density in comparison to spontaneous FWM, allowing for a wide idler wavelength tunability of 191 nm around 1.15 μm. Our WOPO represents a significant improvement of conversion efficiency as well as output energy among χ3 WOPOs, rendering an important step towards a highly efficient and widely tunable chip-based light source for, e.g., coherent anti-Stokes Raman scattering.

Over 3.8 W, 3.4 µm picosecond mid-infrared parametric conversion based on a simplified one-to-many scheme

In this paper, we demonstrate a simplified one-to-many scheme for efficient mid-infrared (MIR) parametric conversion. Such a scheme is based on a continuous wave (CW) single longitudinal mode master oscillator power-amplifier (MOPA) fiber system as the signal source and a picosecond pulsed MOPA fiber system, exhibiting multiple longitudinal modes, as the pump source. The signal and pump beams are combined and co-coupled into a piece of 50-mm long 5% MgO-doped PPLN crystal for the parametric conversion. As high as ∼3.82 W average power at a central idler wavelength of ∼3.4 µm is achieved when the launched pump and signal powers are ∼41.73 and ∼11.45 W, respectively. Above some threshold value, the delivered idler power shows a roll-over effect against the signal power and saturation-like effect against the pump power. Consequently, the highest conversion efficiency is observed at such a threshold pump power. To the best of our knowledge, our result represents the highest average power produced from any single-pass parametric conversion source with >3 µm idler wavelength feeding with a CW signal. Moreover, our proposed scheme can simplify the design of parametric conversion system significantly and meanwhile make the system more robust in applications. This is attributed to two main aspects. Firstly, the scheme’s one-to-many feature can reduce wavelength sensitivity remarkably in the realization of quasi-phase-matching. Secondly, for moderate power requirement it does not always require a high peak power synchronized pulsed signal source; a CW one can be an alternative, thereby making the system free from complex time synchronization and the related time jitter.

Inter-/intra-pulse dual-wavelength-operated mid-infrared optical parametric oscillator.

We demonstrate a pulsed mid-infrared (MIR) optical parametric oscillator (OPO) with both inter-pulse and intra-pulse dual-wavelength operation capability. A fiber master oscillator power amplifier incorporating an acousto-optic tunable filter (AOTF) was employed as the pump for the OPO. By finely adjusting the drive wave packets for the AOTF, dual-wavelength pump can be realized within each pulse or between two adjacent pulses. These special temporal-spectral behaviors of the pump can be transferred to MIR via an OPO. In the proof-of-principle experiments, two pump wavelengths at ∼1065 and ∼1076 nm were generated and amplified to ∼31.2 W with equivalent spectral intensities for both pulsation modes. At the highest pump power, total idler power of ∼3.5 W was achieved at ∼3.45 and ∼3.55 µm under both pulsation modes. To the best of our knowledge, this is the first demonstration of both inter-pulse and intra-pulse dual-wavelength MIR generation via an OPO with an identical configuration. It is believed that our design may provide a promising solution to many practical applications including differential absorption lidar and tunable terahertz wave generation.

High power widely tunable mid-IR (5–7.2 μm) ZnGeP2 optical parametric oscillator pumped by a 2.09 μm laser

A high-power widely tunable nanosecond (ns) mid-infrared (mid-IR) optical parametric oscillator (OPO) in a ZnGeP2 crystal has been demonstrated. The OPO is pumped by a Q-switched 2.09 μm Ho: YAG laser with 10 kHz repetition frequency. Based on optimizing the parameters of ZGP-OPO system, a maximum idler power as high as 5.47 W is achieved at 5.05 μm with photon conversion efficiency of up to 46.4 %. By rotating the angle of the ZGP crystal, the idler tuning region across from 5 to 7.2 μm is realized, with >1 W of idler power over almost the entire tuning region. The idler operation displays high pulse stability with peak to peak amplitude fluctuation less than ±2.8 % in near-Gaussian spatial mode.

High–Efficiency, Widely Tunable MgO: PPLN Optical Parametric Oscillator

We report on the investigation of a high–efficiency, widely tunable femtosecond optical parametric oscillator (OPO) based on a multi–period MgO–doped periodically poled lithium niobite (MgO: PPLN) crystal, pumped by an all–solid–state femtosecond mode–locked Yb: KGW laser at 1030 nm providing 100 fs pulses. With 6 W pump power, the OPO generates 2.68 W of signal power at 1540 nm and 1.2 W of idler power at 3110 nm, which corresponds to the total conversion efficiency adding up to 67.4%. To the best of our knowledge, this is the highest conversion efficiency of a femtosecond OPO. Meanwhile, in order to obtain a broad optical spectrum range, both the grating period and working temperature are tuned, resulting in tunable signals of 1.43–1.78 µm and idlers of 2.44–3.68 µm. This source will be used to generate a femtosecond mid–infrared laser of wavelength range 3.7–6.5 µm and tens milliwatts average power through difference frequency generation (DFG).

Performance improvement factors in quantum radar/illumination

In this study, we exploit quantum information processing, the research field focusing on quantum two-mode squeezed (QTMS) radar and quantum illumination (QI), to investigate the qualitative behaviors of entanglement, the entropy of formation, and squeezing in these protocols. We use logarithmic negativity to investigate entanglement between the signal and idler and propose strategies to maintain entanglement at room temperature in both protocols. We also calculate the entanglement, squeezing, and entropy for the QTMS radar when the target is present and the signal is transmitted to the target. In addition, by controlling the squeezing parameter which is a tool to control entanglement, entropy, and squeezing, the performance of the QTMS radar can be improved, so this work shows how it is implemented in practice. In both protocols, entanglement is maintained by considering conditions. Since the squeezing parameter controls both signal and idler power and the correlation between them, therefore, the qualitative behavior of squeezing in the QTMS radar and QI is also studied in this research. The significant result obtained from the QI is that the entanglement maintains at high power, low temperature, and high correlation between signal and idler. In contrast, in the QTMS, the entanglement survives when the correlation and power are low, even at room temperature.

High-performance Kerr microresonator optical parametric oscillator on a silicon chip

Optical parametric oscillation (OPO) is distinguished by its wavelength access, that is, the ability to flexibly generate coherent light at wavelengths that are dramatically different from the pump laser, and in principle bounded solely by energy conservation between the input pump field and the output signal/idler fields. As society adopts advanced tools in quantum information science, metrology, and sensing, microchip OPO may provide an important path for accessing relevant wavelengths. However, a practical source of coherent light should additionally have high conversion efficiency and high output power. Here, we demonstrate a silicon photonics OPO device with unprecedented performance. Our OPO device, based on the third-order (χ(3)) nonlinearity in a silicon nitride microresonator, produces output signal and idler fields widely separated from each other in frequency ( > 150 THz), and exhibits a pump-to-idler conversion efficiency up to 29 % with a corresponding output idler power of > 18 mW on-chip. This performance is achieved by suppressing competitive processes and by strongly overcoupling the output light. This methodology can be readily applied to existing silicon photonics platforms with heterogeneously-integrated pump lasers, enabling flexible coherent light generation across a broad range of wavelengths with high output power and efficiency.

Design and demonstration of an efficient pump rejection filter for silicon photonic applications.

Photon pair generation via spontaneous four-wave mixing in silicon waveguides/microring resonators integrated with a high extinction pump rejection filter is very much in demand for futuristic large-scale integrated quantum photonics circuits. Ideally, a distributed Bragg reflector (DBR) can be designed to offer desired pump rejection. However, fabricated DBRs suffer degradation in pump extinction due to roughness-induced unwanted scattering waves in the forward direction around the Bragg wavelength. It is therefore inferred that the roughness-induced forward scattering can be reduced significantly by integrating a DBR structure in one of the sidewalls (instead of two sidewalls) of a multimode rib waveguide (instead of a single mode strip waveguide). Therefore, we studied a single-stage DBR filter with this design which exhibits a significantly higher stop band extinction (∼63 dB), in comparison with that of earlier reported results (<50 dB). To validate the pump rejection efficiency of such fabricated devices in quantum photonic applications, we have carried out on-chip stimulated four-wave mixing experiments and shown that the pump laser within the rejection band could be attenuated to the level of idler power.

Compactly Efficient CW 3 to 4.5 μm Wavelength Tunable Mid-Infrared Laser in Optically Pumped Semiconductor Laser With Intracavity OPO

An efficient continuous-wave (CW) mid-infrared laser with a tunable wavelength range from 3 to 4.5 μm is demonstrated by using intracavity optical parametric oscillator (ICOPO). An optically pumped semiconductor laser (OPSL) is applied as the parent pumped laser gain medium to eliminate self-modulation effect caused by Nd-doped gain medium with ICOPO for fulfilling true CW emissions. Simultaneously, the OPSL gain chip with flip-chip packaging method can avoid mode hopping resulted from internal heat spreader etalon when strong depletion in ICOPO was achieved. The diode pump criteria of the OPSL is first investigated to prevent thermal roll over. By observing the spectral and temporal dynamics of the parent pumped OPSL with and without OPO operation, the true CW and mode-hop-free quality of the laser is verified. A low diode pump threshold of 2.67 W is obtained for the mid-IR idler emission and a total extracted idler power is 250 mW at a diode pump power of 8 W. Finally, the wavelength tunability is confirmed by adjusting the horizontal location of the multiple channel MgO:PPLN crystal, which indicated the feasibility of practical application in such a compact configuration.

A 515-nm laser-pumped idler-resonant femtosecond BiB3O6 optical parametric oscillator

We report on an idler-resonant femtosecond optical parametrical oscillator (OPO) based on BiB3O6 (BiBO) crystal, synchronously pumped by a frequency-doubled, mode-locked Yb:KGW laser at 515 nm. The idler wavelengths of OPO can be tuned from 1100 nm to 1540 nm. At a repetition rate of 75.5 MHz, the OPO generates as much as 400 mW of idler power with 3.1 W of pump power, the corresponding pulse duration is 80 fs, which is 1.04 times of Fourier transform-limited (FTL) pulse duration at 1305 nm. In addition, the OPO exhibits excellent beam quality with M 2 < 1.8 at 1150 nm. To the best of our knowledge, this is the first idler-resonant femtosecond OPO pumped by 515 nm.

Thermo-Optic Effects in Congruent-LiTaO 3 Based Continuous-Wave Optical Parametric Oscillator

We present an experimental study on single-frequency, singly-resonant optical parametric oscillator (SRO) comprised of 50 mm long congruently-grown, 8-mol%-doped, periodically-poled LiTaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (MgO:cPPLT) crystal. The SRO is pumped by a single-frequency, fiber laser pumped green laser. Our observations reveal that the SRO output (idler) scales linearly with the pump power ( P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ) near the SRO threshold ( P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p(th)</sub> ). However, the SRO idler power ( P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> ) exhibits strong saturation at pump power ≈ 1.5P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p(th)</sub> which eventually switches-off the SRO operation on further pump-power enhancement. By coarsely tuning the MgO:cPPLT crystal temperature from 50 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> C to 170 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> C, the SRO idler wavelength is varied from 1810-1920 nm wavelength band. A maximum idler power P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> =583 mW was obtained when the input pump power was ≈ 3.1 W. The idler power saturation is accompanied by discernible distortion in idler beam profile. An early onset of saturation in MgO:cPPLT is essentially a consequence of strong linear absorption exhibited by MgO:cPPLT at pump wavelength, its high thermo-optic coefficient as well as low thermal conductivity. The results are theoretically analyzed by solving the heat conduction equation which provides a deeper insight about the impact of pump-induced thermo-optic effects on a three-wave interaction process.

Seeded optical parametric generation in CdSiP2 pumped by a Raman fiber amplifier at 1.24 µm.

We report a seeded optical parametric generator (OPG) producing tunable radiation from 4.2-4.6 µm. The seeded OPG employs a 13 mm long CdSiP2 (CSP) crystal cut for non-critical phase-matching, pumped by a nanosecond-pulsed, MHz repetition rate Raman fiber amplifier system at 1.24 µm. A filtered, continuous-wave fiber supercontinuum source at 1.72 µm is used as the seed. The source generates up to 0.25 W of mid-infrared (MIR) idler power with a total pump conversion of 42% (combined signal and idler).

Green-pumped continuous-wave parametric oscillator based on fanout-grating MgO:PPLN.

We report the first green-pumped continuous-wave (cw) optical parametric oscillator (OPO) based on MgO:PPLN in a fanout grating design. Pumped by a single-frequency cw laser at 532 nm, the OPO provides tunable radiation across 813-1032 nm in the signal and 1098-1539 nm in the idler by simple mechanical translation at a fixed temperature of 55°C. By deploying a 25-mm-long crystal to minimize thermal effects and using output coupling for the signal wave, we generate a total output power of up to 714 mW at 30% extraction efficiency in excellent Gaussian beam quality with M2<1.1 and high output stability. Simultaneous measurements of signal and idler power result in passive stability of 2.8% and 1.8% rms, respectively, over 1 h. Strong thermal effects contribute to the high stability and excellent beam quality, while linear and green-induced infrared absorption limit the power scaling capabilities of the OPO. The output signal is single-mode with an instantaneous linewidth of ∼3MHz and frequency stability of ∼84MHz over 72 s.

Wavelength tunable picosecond pulse bunch laser around 3 µm through PPMgLN –based DFG with temperature insensitive high power scaling

We report a bunch-mode-operated, wavelength-tunable, temperature-insensitive high power, mid-infrared (MIR) laser based on difference frequency generation (DFG) in a periodically poled Magneoisum-oxide doped Lithium Niobate (PPMgLN) chip. Two synchronized fiber lasers each with master oscillator power amplifier (MOPA) structures are utilized as pump and signal sources for the DFG. The pump laser is seeded by a mode-locked Yb fiber laser around 1030 nm with fundamental repetition rate of 16.32 MHz and pulse duration of 8.5 ps. Each pulse of the pump seed is multiplied by a factor of 16, forming the pulse bunch, and then amplified to 27.8 W. A super-luminescent light emitting diode (SLED) around 1580 nm is triggered by the first pulses of the pump bunch and adopted as the signal seed, which is amplified to 4 W afterwards. The pulse duration and spectral bandwidth of the signal are ~ 5 ns and 50 nm, respectively, covering the total duration of the pump bunch in the time domain and signal wavelength tuning range in the spectral domain, respectively, enabling wavelength-tuning DFG with temperature-insensitive power scaling. High power pulse bunch MIR laser can always be realized within the crystal temperature range from 25 to 95 °C with corresponding idler wavelength from 3.03 μm to 2.84 μm. The highest idler power of 4.6 W is achieved at 3.0 μm with pump-to-idler conversion efficiency of ~ 16.5%. It is believed that such a bunch-mode-operated, mid-infrared ps laser source with high output power within the whole temperature-wavelength tuning range are of great value to the evaluation of wavelength dependent laser bio-ablation.

Influence of linear coupling and group delay fluctuations on intermodal four wave mixing in few mode fiber

We present numerical and experimental study on the origin of fluctuations in the idler power in partially degenerate intermodal four wave mixing in a 1 km long few mode graded index fiber where both the fundamental and higher order modes are excited in both pump and signal wavelengths. Numerical simulation is carried out in the presence of different types of mode coupling processes and group delay fluctuations in order to independently predict the influence of these phenomena by considering the appropriate statistics of the corresponding processes. We propose a quasi-distributed model by choosing the locations of specific coupling events statistically, in correspondence to their correlation lengths. Idler conversion efficiency is experimentally evaluated for different detuning frequencies between the signal and pump through multiple trials, and it is found that even though distinct features of maxima and minima are retained, there are fluctuations in frequencies corresponding to maxima and minima. These experimental results are compared with those from numerical simulations in order to identify the origin of fluctuations.

Green-pumped optical parametric oscillator based on fan-out grating periodically-poled MgO-doped congruent LiTaO3.

We report a green-pumped optical parametric oscillator (OPO) based on periodically poled MgO-doped congruent lithium tantalate (MgO:cPPLT). Pumped at 532nm by a frequency-doubled Q-switched Nd:YAG laser, and using a fan-out grating structure, the singly-resonant OPO provides continuous tuning across 689-1025nm in the signal and 1106-2336nm in the idler at room temperature by simple mechanical translation of the crystal. The tuning range can be further extended to 677nm and 2479nm in the signal and idler, respectively, by temperature tuning the crystal to 200°C. With a 29-mm-long crystal, the OPO generates 131mW of average idler power at 1476.5nm for an input pump power of 1.8W at 25kHz repetition rate, with a slope efficiency of 11.3%. Bulk damage in the MgO:cPPLT crystal has been observed for pump powers above ∼1.8 W, and at pump powers beyond ∼1.4 W under long-term operation. The passive power stability of the generated idler is 3.9% over 30min, in a Gaussian spatial profile.

Frequency downconversion of low-power Raman laser using intracavity difference frequency mixing

We report efficient frequency downconversion of a continuous-wave low-power Raman laser using intracavity difference frequency mixing in a periodically poled lithium niobate (PPLN)-adopted optical parametric oscillator (OPO). The Raman laser was obtained using a 1060-nm fiber laser and 137-m passive fiber. Its central wavelength was fixed at 1111 nm with the power ranging from 320 mW to 5.984 W. The 1060- and 1111-nm pump beams were incident into the OPO at the same time. The high-power 1060-nm pump beam built parametric oscillation first, and the difference frequency generation (DFG) occurred between the low-power Raman laser and intracavity signal laser. The PPLN temperature was properly controlled at 45°C to ensure both the OPO and DFG processes synchronously satisfy phase matching conditions. Benefiting from intracavity high signal power, the Raman laser was successfully converted to the 3560-nm midinfrared radiation under every investigated pump power level. The maximum 3560-nm idler power reached 1.026 W, indicating a 17.4% pump-to-idler slope efficiency and about 15% optical-to-optical conversion efficiency. The comparative experiments also verified that the phase matching conditions were satisfied maximally at 45°C.

A multi-layer platform for low-loss nonlinear silicon photonics

We demonstrate four-wave mixing (FWM) interactions in a-Si:H waveguides in a multilayer integrated silicon photonic chip. The a-Si:H waveguides are accessed through interlayer couplers from waveguides composed of SiNx. The interlayer couplers achieve a coupling of 0.51 dB loss per transition at the target wavelength of 1550 nm. We observe greater idler power extraction and conversion efficiency from the FWM interaction in the interlayer-coupled multilayer waveguides than in single-material waveguides.

91.1 kW, 5.3 ns compact mid-infrared optical parametric amplification based on PPMgLN

We report a compact mid-infrared optical parametric oscillator (OPO) seeded optical parametric amplifier (OPA) based on PPMgLN. The pump for the OPO and OPA is a split 1064 nm electro-optical Q-switched Nd:YAG laser with a pulse width of 11.7 ns and a pulse repetition frequency of 2 kHz. The idler power of 116 mW of the OPO is used for the OPA seed. Under the incident pump power of 7.36 W and the crystal temperature of 30 °C, the idler power of the OPA is 966 mW with a pulse width of 5.3 ns, corresponding to a conversion efficiency of 11.5% and a calculated peak power of 91.1 kW. The central wavelength of the OPA idler is 3731.2 nm with a linewidth of 8.8 nm at 30 °C, and decreased from 3748.8 nm to 3704.0 nm when the crystal is heated from 20 to 45 °C. The beam quality factors of the OPA are 3.4 and 3.7 in the horizontal and vertical directions, respectively.