Single Pump Wavelength Research Articles

Multimodality integrated microresonators using the Moiré speedup effect.

High-Q microresonators are indispensable components of photonic integrated circuits and offer several useful operational modes. However, these modes cannot be reconfigured after fabrication because they are fixed by the resonator's physical geometry. In this work, we propose a Moiré speedup dispersion tuning method that enables a microresonator device to operate in any of three modes. Electrical tuning of Vernier coupled rings switches operating modality to Brillouin laser, bright microcomb, and dark microcomb operation on demand using the same hybrid-integrated device. Brillouin phase matching and microcomb operation across the telecom C-band is demonstrated. Likewise, by using a single-pump wavelength, the operating mode can be switched. As a result, one universal design can be applied across a range of applications. The device brings flexible mixed-mode operation to integrated photonic circuits.

Performance improvement of dual-GSA-wavelength pumped heavily-doped 3 μm Er:YSGG laser by using wing-pumping method

The dual-GSA-wavelength pumping combined with wing-pumping method has been successfully used to improve the output performance of a 30 at.% Er:YSGG laser at 3 μm. According to the GSA spectrum of 4I15/2→4I9/2 transition at 0.8 μm, two pump wavelengths of 785 and 798 nm are used to verify the effectiveness of dual-GSA-wavelength pumping, with 798 nm overlapping an absorption peak, while 785 nm deviating from the absorption peak of Er:YSGG crystal. With regard to the 798/976 nm dual-wavelength pumping, the output power fails to maintain a continuous growth trend with the dual-wavelength pump power in comparison with the single-wavelength pumping at 976 nm. This indicates the influence of thermal effects on the heavily erbium-doped material is more severe, resulting in a significant reduction in the available pump power range. When the 785 nm with weak absorption is used for dual-wavelength pumping, the output power achieves a nearly linear increase within a larger range of dual-wavelength pump power. The achievable maximum output power is 662 mW for the 785/976 nm dual-wavelength pumping, respectively increased by 13.2 % and 64.7 % compared to the achievable maximum output power obtained in 976 nm single-wavelength and 798/976 nm dual-wavelength pumping. It is also found that the introduction of 785 nm pump light would lower the threshold for achieving dual-wavelength laser output for the Er:YSGG laser. The dual-GSA-wavelength pumping combined with wing-pumping method provide an effective solution for improving the performance of heavily erbium-doped lasers at 3 μm.

976 nm and 808 nm dual-GSA-wavelength pumped 3 µm erbium-doped solid-state laser.

A dual-wavelength pumping scheme at 976 nm and 808 nm is proposed to improve the performance of 3 µm Er:YAP laser. 976 nm and 808 nm correspond to the ground state absorption processes of 4I15/2→I11/2 and 4I15/2→I9/2, respectively. The experimental results indicate that the introduction of 808 nm pumping not only increases the total inversion population, but also can adjust the population distribution among the sublevels in the upper and lower manifold, thus supporting higher output power and multiple wavelengths emissions. Under the single-wavelength pumping, the maximum output powers of 1.192 W and 0.223 W are obtained for 976 nm and 808 nm pumping, respectively. With regard to the 976/808 nm dual-wavelength pumping, the achievable maximum output power is 1.398 W, increased by 17.3% compared to the case of single-wavelength pumping at 976 nm. The dual-wavelength pumped Er:YAP laser can also operate in a state of multi-wavelength emissions at 2.79 µm, 2.82 µm and 2.92 µm with different dual-wavelength pump power combinations. Considering the broadband absorption characteristics of ground state absorption and the convenience of obtaining near-infrared laser diodes pumping sources, the proposed dual-wavelength pump scheme shows great potential to realize high-power, high-efficiency 3 µm erbium-doped solid-state lasers with better cost-effectiveness and more compact structure.

Modeling and simulation of erbium-ytterbium co-doped optical waveguide amplifiers with dual-wavelength pumping at 980 nm and 1480 nm

With the rapid development of silicon photonic chips and integrated photonic circuits, erbium-doped optical waveguide amplifiers have received more and more attention in order to compensate for the transmission and coupling losses caused by the integration of optical devices on a chip. Pumping wavelength and pumping efficiency directly affect the gain and noise figure of the amplifier. In this paper, we propose an innovative dual-wavelength pumping method based on an erbium-ytterbium co-doped optical waveguide amplifier with simultaneous pumping at 980 nm and 1480 nm. A relaxation method based on the fourth-order Range-Kutta method is used to solve the rate and propagation equations and simulate the gain characteristics of the dual-wavelength pumping method for different ytterbium-erbium ion concentration ratios, erbium ion concentrations and ratio K between the 980 nm and total pump power. From the simulation results, it can be seen that the gain of the dual-wavelength pumping method is higher than that of the single-wavelength pumping methods when the erbium ion concentration exceeds 3 × 1026 m−3. At higher erbium ion concentrations, the dual-wavelength pumping method can provide higher gain for optical waveguide amplifiers, and may be able to become a new choice of pumping method for optical waveguide amplifiers.

Asymmetry Optimization for 10 THz OPC Transmission over the C + L Bands Using Distributed Raman Amplification.

An optimized design for a broadband Raman optical amplifier in standard single-mode fiber covering the C and L bands is presented, to be used in combination with wideband optical phase conjugation (OPC) nonlinearity compensation. The use of two Raman pumps and fiber Bragg grating reflectors at different wavelengths for the transmitted (C band) and conjugated (L band) WDM channels is proposed to extend bandwidth beyond the limits imposed by single-wavelength pumping, for a total 10 THz. Optimization of pump and reflector wavelength, as well as pump powers, allows us to achieve low asymmetry across the whole transmission band for optimal nonlinearity compensation. System performance is simulated to estimate OSNR, gain flatness and nonlinear Kerr distortion.

Bandwidth Extension in a Mid-Link Optical Phase Conjugation

In this paper, we investigate various designs of distributed Raman amplifier (DRA) to extend amplification bandwidth in mid-link optical phase conjugation (OPC) systems and compare bands 191–197 THz and 192–198 THz giving a total bandwidth of 6 THz using a single wavelength pump. We demonstrate the use of highly reflective fiber Bragg grating (FBG) to minimize gain variation across a WDM grid by optimizing forward and backward pump powers as well as the wavelength of FBGs for original and conjugated channels. Finally, we also simulate OSNR and Kerr nonlinear reduction as a product of signals asymmetry and nonlinear phase shift (NPS) for all channels.

Dual-comb photothermal spectroscopy

Dual-comb spectroscopy (DCS) has revolutionized optical spectroscopy by providing broadband spectral measurements with unprecedented resolution and fast response. Photothermal spectroscopy (PTS) with a pump-probe configuration offers a highly sensitive gas sensing method, which is normally performed using a single-wavelength pump laser. The merging of PTS with DCS may enable a spectroscopic method by taking advantage of both technologies, which has never been studied yet. Here, we report dual-comb photothermal spectroscopy (DC-PTS) by passing dual combs and a probe laser through a gas-filled anti-resonant hollow-core fiber, where the generated multi-heterodyne modulation of the refractive index is sensitively detected by an in-line interferometer. As an example, we have measured photothermal spectra of acetylene over 1 THz, showing a good agreement with the spectral database. Our proposed DC-PTS provides opportunities for broadband gas sensing with super-fine resolution and high sensitivity, as well as with a small sample volume and compact configuration.

Pump-efficient flattop O+E-bands bismuth-doped fiber amplifier with 116 nm –3 dB gain bandwidth

We report on a new record in the field of broadband BDFA in the O+E spectral range. Using only 250 mW single wavelength pump at 1256 nm and a low-OH bismuth-doped fiber containing two types of bismuth active centers, we achieved >23 dB gain from 1325 nm to 1441 nm with flatness <3 dB and a NF of <6.8 dB. Three different pump wavelengths were considered: 1230, 1256, 1270 nm. Pumping at the shortest wavelength enabled wider gain bandwidth – 125 nm but required pump power up to ∼620 mW, whereas the longest one provided higher pump efficiency but narrower gain bandwidth. We also studied multiple wavelength amplification effects in the BDFA to reveal potential problems with simultaneous broadband signal amplification in such amplifiers.

Broadband femtosecond spectroscopic ellipsometry.

We present a setup for time-resolved spectroscopic ellipsometry in a pump-probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer-sample-compensator-analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump-probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV-3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues.

GSA and ESA dual-wavelength pumped 2.3 μm Tm:YLF laser on the 3H4→3H5 transition

The population trapping effect of the F34 level is an important factor limiting the power scaling of the 2.3 μm thulium (Tm) laser on the H34→H35 transition. In this Letter, we demonstrate a novel scheme of ground state absorption (GSA) (H36→H34) and excited state absorption (ESA) (F34→H34) dual-wavelength pumped 2.3 μm Tm lasers. Introducing an ESA pumping process can accurately excite the Tm3+ ions accumulated in the F34 level to the H34 level, constructing a double populating mechanism for the upper laser level H34. A proof-of-principle experimental demonstration of the GSA (785 nm) and ESA (1470 nm) dual-wavelength pumped 2.3 μm Tm:LiYF4 (Tm:YLF) laser was realized. A maximum continuous-wave output power of 1.84 W at 2308 nm was achieved under 785 and 1470 nm dual-wavelength pumping, increased by 60% compared with the case of 785 nm single-wavelength pumping under the same resonator condition. Our work provides an efficient way to achieve higher output power from 2.3 μm Tm-doped lasers on the H34→H35 transition.

Numerical Analysis of 3.92 μm Dual-Wavelength Pumped Heavily-Holmium-Doped Fluoroindate Fiber Lasers

The 3.92 μm laser pumped by 888 and 962 nm sources in a high concentration holmium-doped InF3 fiber is predicted and verified by simulation for the first time. Most parameters involved in the numerical model are taken from published results about the fundamental properties of holmium in fluoroindate glasses. The remaining unknown parameters are estimated from published 888 nm single-wavelength pumping experimental data. Simulated results indicate that the dual-wavelength pumping system can give a more powerful output than the single-wavelength pumping system when the total launched power is at the same level. The laser output as a function of the power of each source, as well as several macro factors such as fiber length and output coupler reflectivity, are investigated to find the best condition for higher output. To evaluate the importance and influence of the known interionic energy transfer processes, we analyze the corresponding laser output and changes of population densities of laser upper and lower levels by isolating each process. This investigation gives a preliminary insight into the 3.92 μm laser performance and interionic dynamics of the dual-wavelength pumping system in holmium-doped InF3 fibers.

Determination of metastable state lifetimes of a high-concentration erbium-doped fiber under population inversion conditions at 980 nm pump and 1.5 µm probe wavelengths

We report two-wavelength pump-probe measurements of the metastable state lifetime in a high-concentration erbium-doped fiber (EDF). The lifetimes under population inversion conditions are measured using a 980 nm pump laser and a 1.5 µm probe laser. The lifetime variation from the lifetime under low excitation conditions to that of a highly inverted population are calculated using a model derived from the rate equations. To confirm the validity of our method, we compare the results obtained with those for temporally resolved spontaneous emissions in the perpendicular direction and those measured using a 1.5 µm single-wavelength pump–probe technique in our previous work.

Gain investigation of Perylene-Red-doped PMMA for stimulated luminescent solar concentrators.

Luminescent solar concentrators (LSCs) utilizing stimulated emission by a seed laser are a promising approach to overcome the limitations of conventional LSCs, with a significant reduction of the photovoltaic material. In our previous work, we demonstrated the principle of a stimulated LSC (s-LSC) and correspondingly developed a model for quantifying the output power of such a system, taking into account different important physical parameters. The model suggested Perylene Red (PR) dye as a potential candidate for s-LSCs. Here, we experimentally investigate the gain of PR-doped polymethyl methacrylate (PMMA) required for s-LSCs using a single pump wavelength (instead of the solar spectrum) as a proof of principle. The results found from the experiment are well matched with the previously developed numerical model except for gain saturation, which occurs at a comparatively small seed laser signal power. To investigate the gain saturation, two approaches were taken: investigating (i) spectral hole burning and (ii) triplet state absorption. Experimental investigation of spectral hole burning with PR dyes showed a small effect on the gain saturation. We developed a general state model considering triplet state absorption of the PR dyes for the second approach. The state model suggests that the PR dyes suffer from significant triplet state absorption loss, which obstructs the normal operation of the PR-based s-LSC system.

Efficient All-Optical Transistor Action in Short-Length Multimode Optical Fibers

The quest for realizing an all-optical transistor while fulfilling desired criteria has been around since long time. Various schemes have been put forward over the years to achieve it; however, almost all techniques make use of at least two different laser sources. Optical event horizon principle has also been employed to see transistor action in glass fibers using two different frequency sources. In this paper, we report an optical transistor action in short-length, tailor-made multimode optical fibers through a single pump only. The higher order mode properties of the fiber and intermodal nonlinear interaction (mainly cross-phase modulation) are used to achieve efficient transistor action. Both the soliton and a weak dispersive pulse are excited in $ LP_{02}$ and $ LP_{01}$ modes of the fiber, respectively, with a certain temporal delay set by the sign of the differential group delay between the modes. We believe that the scheme has potential to improve system performance owing to the fact that only a single-wavelength pump source is required as opposed to the optical-transistor devices available till date that essentially require two-color pumping.

Low-temperature intracenter relaxation times of shallow donors in germanium

The relaxation times of localized states of antimony donors in unstrained and strained germanium uniaxially compressed along the [111] crystallographic direction are measured at cryogenic temperatures. The measurements are carried out in a single-wavelength pump–probe setup using radiation from the Novosibirsk free electron laser (NovoFEL). The relaxation times in unstrained crystals depend on the temperature and excitation photon energy. Measurements in strained crystals are carried out under stress bar S > 300, in which case the ground-state wavefunction is formed by states belonging to a single valley in the germanium conduction band. It is shown that the application of uniaxial strain leads to an increase in the relaxation time, which is explained by a decrease in the number of relaxation channels.

Degenerate Four-Wave Mixing in a Multiresonant Germanium Nanodisk

Dielectric nanoantennas excited at Mie resonances are becoming suitable candidates for nonlinear optical effects due to their large intrinsic nonlinearity and capability to highly confine electromagnetic fields within subwavelength volumes. In this work, we show that a single Ge nanodisk, recently demonstrated as an efficient source of third-harmonic generation (THG), can also be exploited for four-wave mixing (FWM) phenomena. The high field enhancement inside the disk yields effective third-order susceptibilities as high as 2 × 10–8 esu (2.8 × 10–16 m2/V2), which were determined by single pump wavelength THG measurements tuned to high-order Mie modes. A similar nonlinear optical response is observed in the case of degenerate FWM where two different pump wavelengths are coupled to a single high-order resonant mode. However, when the two pump wavelengths are coupled to different high-order modes, the FWM process is partially suppressed due to a diminished near-field spatial overlap of the mixed wavelengths...

Broadband silica-based thulium doped fiber amplifier employing multi-wavelength pumping.

A multi-wavelength pumped thulium doped fiber amplifier is investigated to extend the spectral gain coverage of the amplifier in the 1.7-1.9μm wavelength range. Through the use of a combination of 791 nm, 1240 nm, and 1560 nm laser diode pumping, the amplifier gain can be improved significantly and overall gain bandwidth enhancement of ~47% as compared to single-wavelength pumping achieved. A nominal gain of 15 dB is achieved over a bandwidth of more than 250 nm spanning from 1700 to 1950 nm with a maximum gain of 29 dB and a noise figure of less than 5 dB.

Energetic mid-IR femtosecond pulse generation by self-defocusing soliton-induced dispersive waves in a bulk quadratic nonlinear crystal.

Generating energetic femtosecond mid-IR pulses is crucial for ultrafast spectroscopy, and currently relies on parametric processes that, while efficient, are also complex. Here we experimentally show a simple alternative that uses a single pump wavelength without any pump synchronization and without critical phase-matching requirements. Pumping a bulk quadratic nonlinear crystal (unpoled LiNbO(3) cut for noncritical phase-mismatched interaction) with sub-mJ near-IR 50-fs pulses, tunable and broadband (∼ 1,000 cm(-1)) mid-IR pulses around 3.0 μm are generated with excellent spatio-temporal pulse quality, having up to 10.5 μJ energy (6.3% conversion). The mid-IR pulses are dispersive waves phase-matched to near-IR self-defocusing solitons created by the induced self-defocusing cascaded nonlinearity. This process is filament-free and the input pulse energy can therefore be scaled arbitrarily by using large-aperture crystals. The technique can readily be implemented with other crystals and laser wavelengths, and can therefore potentially replace current ultrafast frequency-conversion processes to the mid-IR.

Effect of dip in refractive index profile on fiber Raman gain amplifier performance

We have studied and reported the effect of practically possible linear dips in the inner core of a coaxial fiber Raman gain amplifier having step index inner and outer cores in the structure on the amplifier performance. In this work, we have used single pump wavelength of 1.465µm. A variation of dip depth beyond 0.25% of maximum refractive index and that of dip width beyond 25% of the inner core radius deteriorate the gain performance of characteristics of this amplifier significantly along with an appreciable shift of phase matching wavelength. Within these limits, the amplifier resembles closely the behavior of an ideal one. These prescribed limits of dip depth and dip width are also valid limits above which there will be valid ground in their effect to modulate Raman gain performance and dispersion. The present study should find wide attention of system designers.

Flexible single pump hybrid fiber amplifier for the S+C bands

This work proposes optical amplification in the S+C bands using a hybrid optical fiber amplifier (HFA) that uses a single wavelength pump. Its configuration is based on an erbium doped amplifier (EDFA) to provide gain over the C band and a distributed Raman fiber amplifier (RFA) to attain gain over the S band. Moreover, the proposed amplifier uses standard commercially available fibers. The HFA was numerically characterized and its optimal configuration was calculated using optimization procedures based on genetic algorithms. A flexible HFA configuration was achieved allowing a span length up to 100km.