Minwan Jung

A femtosecond pulse fiber laser at 1935 nm using a bulk-structured Bi 2 Te 3 topological insulator

We experimentally demonstrate a femtosecond mode-locked, all-fiberized laser that operates in the 2 μm region and that incorporates a saturable absorber based on a bulk-structured bismuth telluride (Bi(2)Te(3)) topological insulator (TI). Our fiberized saturable absorber was prepared by depositing a mechanically exfoliated, ~30 μm-thick Bi(2)Te(3) TI layer on a side-polished optical fiber platform. The bulk crystalline structure of the prepared Bi(2)Te(3) layer was confirmed by Raman and X-ray photoelectron spectroscopy measurements. The modulation depth of the prepared saturable absorber was measured to be ~20.6%. Using the saturable absorber, it is shown that stable, ultrafast pulses with a temporal width of ~795 fs could readily be generated at a wavelength of 1935 nm from a thulium/holmium co-doped fiber ring cavity. This experimental demonstration confirms that bulk structured, TI-based saturable absorbers can readily be used as an ultra-fast mode-locker for 2 μm lasers.

Mode-locked, 1.94-μm, all-fiberized laser using WS₂ based evanescent field interaction.

We demonstrate the use of an all-fiberized, mode-locked 1.94 μm laser with a saturable absorption device based on a tungsten disulfide (WS2)-deposited side-polished fiber. The WS2 particles were prepared via liquid phase exfoliation (LPE) without centrifugation. A series of measurements including Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) revealed that the prepared particles had thick nanostructures of more than 5 layers. The prepared saturable absorption device used the evanescent field interaction mechanism between the oscillating beam and WS2 particles and its modulation depth was measured to be ~10.9% at a wavelength of 1925 nm. Incorporating the WS2-based saturable absorption device into a thulium-holmium co-doped fiber ring cavity, stable mode-locked pulses with a temporal width of ~1.3 ps at a repetition rate of 34.8 MHz were readily obtained at a wavelength of 1941 nm. The results of this experiment confirm that WS2 can be used as an effective broadband saturable absorption material that is suitable to passively generate pulses at 2 μm wavelengths.

Mode-locked pulse generation from an all-fiberized, Tm-Ho-codoped fiber laser incorporating a graphene oxide-deposited side-polished fiber

An in-depth experimental investigation was conducted into the use of a graphene oxide-based saturable absorber implemented on a side-polished fiber platform for femtosecond pulse generation in the 2 μm region. First, it was experimentally shown that an all-fiberized thulium-holmium (Tm-Ho)-codoped fiber ring laser with reduced cavity length can produce stable femtosecond pulses by incorporating a graphene oxide-deposited side-polished fiber. Second, the measurement accuracy issue in obtaining a precise pulse-width value by use of an autocorrelator together with a silica fiber-based 2 μm-band amplifier was investigated. It showed that the higher-order soliton compression effect caused by the combination of anomalous dispersion and Kerr nonlinearity can provide incorrect pulse-width information. Third, an experimental investigation into the precise role of the graphene oxide-deposited side-polished fiber was carried out to determine whether its polarization-dependent loss (PDL) can be a substantial contributor to mode-locking through nonlinear polarization rotation. By comparing its performance with that of a gold-deposited side-polished fiber, the PDL contribution to mode-locking was found to be insignificant, and the dominant mode-locking mechanism was shown to be saturable absorption due to mutual interaction between the evanescent field of the oscillated beam and the deposited graphene oxide particles.

A Mode-Locked 1.91 µm Fiber Laser Based on Interaction between Graphene Oxide and Evanescent Field

The use of a graphene oxide (GO)-deposited D-shaped fiber as a saturable absorber for mode locking of a thulium-doped fiber laser is experimentally demonstrated. By using the evanescent field interaction of an oscillating beam with GO, a passive mode locking operation at a wavelength of ~1.91 µm is shown to be achievable from a ring cavity. Stable picosecond pulses are readily obtained at a repetition rate of 15.9 MHz. This demonstration confirms that GO is a cost-effective saturable absorber applicable for ~2 µm ultrafast pulse generation.

Passively Q-Switched 1.89-μm Fiber Laser Using a Bulk-Structured Bi 2 Te 3 Topological Insulator

We experimentally demonstrate that a bulk-structured Bi2Te3 topological insulator (TI) film deposited on a side-polished fiber can act as an effective Q-switch for a 1.89-μm laser. Our bulk-structured Bi2Te3 TI film with a thickness of ~31 μm, was prepared using a mechanical exfoliation method, and the fabricated film was transferred onto a side-polished SM2000 fiber to form a fiberized saturable absorber based on evanescent field interaction. By incorporating the saturable absorber into a thulium (Tm)-holmium (Ho) co-doped fiber-based ring cavity, it is shown that Q-switched pulses with a minimum temporal width of ~1.71 μs can readily be produced at a wavelength of 1.89 μm. The output pulse repetition rate was tunable from ~35 to ~60 kHz depending on the pump power. The maximum output pulse energy was ~11.54 nJ at a pump power of 250 mW. The output performance of our laser is compared to that of the 1.98-μm Q-switched fiber laser based on a nanosheet-based Bi2Se3 TI demonstrated previously by Luo et al.

A band-separated, bidirectional amplifier based on erbium-doped bismuth fiber for long-reach hybrid DWDM-TDM passive optical networks

We propose a band-separated, bidirectional amplifier based on a bismuth-based erbium-doped fiber for use in long-reach hybrid dense wavelength division multiplexing-time division multiplexing passive optical networks (DWDM-TDM-PONs). We also propose a long-reach hybrid DWDM-TDM-PON architecture in which the proposed amplifier can be effectively used. The feasibility of using the proposed amplifier for long-reach hybrid DWDM-TDM-PONs is experimentally investigated by performing a series of signal transmission experiments with an exemplary PON configuration having a total reach of 75 km and 8 split users. Error-free bidirectional signal transmission at a line rate of 10 Gbit/s is successfully demonstrated. A theoretical investigation also shows that the reach/split limitation issue associated with an insufficient WDM signal gain in the experimental demonstration can be easily solved by optimizing the amplifier.

Self-Q-switching of a bismuth-doped germanosilicate fiber laser operating at 1.46 μm

A self-Q-switched bismuth-doped germanosilicate fiber laser operating at 1463 nm is demonstrated. This letter experimentally shows that stable Q-switched pulses with a temporal width of ~1.8 μs at a repetition rate of ~65 kHz can be obtained from a simple, all-fiberized Fabry–Perot-type cavity without using a saturable absorber. The tuning capability of the temporal characteristics of the output pulses depending on pump power is also investigated.

Combined effect of pump excited state absorption and pair-induced quenching on the gain and noise figure in bismuth oxide-based Er 3+ -doped fiber amplifiers

The impact that pump excited state absorption (ESA) and pair-induced quenching (PIQ) have on the gain and noise figure (NF) performance of a bismuth oxide-based erbium-doped fiber amplifier (EDFA) is investigated in both theoretical and experimental manners. The gain and the NF performance are shown to significantly degrade due to the combined effect of the pump ESA and PIQ when 980 nm pumping is employed. It is shown that the use of 980 nm pumping does not provide any significant NF benefit relative to 1480 nm pumping in highly doped bismuth oxide-based EDFAs with non-negligible PIQ, contrary to the common wisdom regarding pump wavelength-dependent NF performance. The reason turns out to be associated with a considerable population decrease in the I13/24 state, caused by the mutual stimulation effect between the pump ESA and PIQ. From this investigation the better of the two pump wavelengths is found to be 1480 nm when the signal gain and NF are considered together.

Actively Q-switched, thulium–holmium-codoped fiber laser incorporating a silicon-based, variable-optical-attenuator-based Q switch

An actively Q-switched thulium-holmium-codoped fiber laser incorporating an Si-based variable optical attenuator (VOA) is experimentally demonstrated. It has been shown that an Si-based VOA with a response time of hundreds of nanoseconds can be used as a cost-effective 2 μm Q switch due to its extremely wide operating bandwidth from 1.5 to 2 μm, and low electrical power consumption. In our study, the lasers slope efficiency was measured to be ~17% at an operating wavelength of 1.89 μm. The repetition rate tuning range was from 20 to 80 kHz, which was limited by the optical damage threshold and the response time. The minimum temporal pulsewidth was measured to be ~184 ns at a modulation frequency of 20 kHz, and the corresponding maximum peak power was ~10 W.

A Theoretical and Experimental Investigation into Pair-induced Quenching in Bismuth Oxide-based Erbium-doped Fiber Amplifiers

The pair-induced quenching (PIQ) effect in a highly doped bismuth oxide-based erbium-doped fiber amplifier (EDFA) was theoretically and experimentally investigated. In the theoretical investigation, the bismuth oxide-based EDFA was modeled as a 6-level amplifier system that incorporated clustering-induced concentration quenching, cooperative up-conversion, pump excited state absorption (ESA), and signal ESA. The relative number of paired ions in a highly doped bismuth oxide EDF was estimated to be ~6.02%, determined by a comparison between the theoretical and the experimentally measured gain values. The impacts of the PIQ on the gain and the noise figure were also investigated.