Thulium-fiber-laser-pumped, high-peak-power, picosecond, mid-infrared orientation-patterned GaAs optical parametric generator and amplifier.

We report a high-peak-power, picosecond, mid-infrared optical parametric generator (OPG) and optical parametric amplifier (OPA) based on orientation-patterned gallium arsenide pumped by a thulium:fiber master-oscillator-power-amplifier employing direct diode-seeded amplification. An OPG tuning range of 2550-2940 nm (signal) and 5800-8300 nm (idler) is demonstrated with peak powers as high as 3 (signal) and 2 kW (idler), and with pulse energies of 0.26 and 0.16 µJ, respectively. When seeded with a 0.6 cm-1 linewidth tunable Cr:ZnSe laser, the OPA idler linewidth is narrowed to 1.4 cm-1 and a small-signal parametric gain of 60 dB is achieved. A maximum peak power of 13.3 (signal) and 3.2 kW (idler) is obtained at an overall conversion efficiency of 36%. The corresponding maximum pulse energies for the signal and idler are 1.07 and 0.26 µJ, respectively.

Radially and azimuthally polarized nanosecond Yb-doped fiber MOPA system incorporating temporal shaping.

We report an Yb-doped fiber master-oscillator power-amplifier (MOPA) system with the capability of selectively generating doughnut-shaped radially and azimuthally polarized beams with user-defined temporal pulse shapes. The desired output polarization was generated with the aid of a nanograting spatially variant half-waveplate (S-waveplate). The latter was used to convert the linearly polarized fundamental (LP01) mode output from the preamplification stages to a doughnut-shaped radially polarized beam prior to the power amplifier stage. A maximum output pulse energy of ∼860 µJ was achieved for ∼100 ns pulses at 25 kHz with user-defined pulse shape for both radial and azimuthal polarization states. The polarization purity and beam propagation factor (M2) were measured to be >12 dB and 2.2, respectively.

Exploiting the short wavelength gain of silica-based thulium-doped fiber amplifiers.

Short wavelength operation (1650-1800 nm) of silica-based thulium-doped fiber amplifiers (TDFAs) is investigated. We report the first demonstration of in-band diode-pumped silica-based TDFAs working in the 1700-1800 nm waveband. Up to 29 dB of small-signal gain is achieved in this spectral region, with an operation wavelength accessible by diode pumping as short as 1710 nm. Further gain extension toward shorter wavelengths is realized in a fiber laser pumped configuration. A silica-based TDFA working in the 1650-1700 nm range with up to 29 dB small-signal gain and noise figure as low as 6.5 dB is presented.

100 Gbit/s WDM transmission at 2 µm: transmission studies in both low-loss hollow core photonic bandgap fiber and solid core fiber.

We show for the first time 100 Gbit/s total capacity at 2 µm waveband, using 4 × 9.3 Gbit/s 4-ASK Fast-OFDM direct modulation and 4 × 15.7 Gbit/s NRZ-OOK external modulation, spanning a 36.3 nm wide wavelength range. WDM transmission was successfully demonstrated over 1.15 km of low-loss hollow core photonic bandgap fiber (HC-PBGF) and over 1 km of solid core fiber (SCF). We conclude that the OSNR penalty associated with the SCF is minimal, while a ~1-2 dB penalty was observed after the HC-PBGF probably due to mode coupling to higher-order modes.

Fiber-laser-pumped, high-energy, mid-IR, picosecond optical parametric oscillator with a high-harmonic cavity.

We demonstrate the generation of high-energy, mid-IR, picosecond pulses in a high-harmonic-cavity optical parametric oscillator (OPO) that has a relatively compact cavity with a length that is a small fraction of that required to match the pump repetition rate. The OPO, based on an MgO-doped periodically poled LiNbO3 crystal, is pumped by a fiber master-oscillator-power-amplifier system employing direct amplification and delivering 11-µJ, 150-ps pulses at 1035 nm. For a 1.554-m-long OPO cavity, resonating near-infrared signal pulses with a repetition rate that is the 193rd harmonic of the 1-MHz pump are demonstrated. The mid-infrared idler output pulses, tunable from 2300 nm to 3500 nm, are generated at a 1-MHz repetition rate and have energies as high as 1.5 µJ.

Dense WDM transmission at 2 µm enabled by an arrayed waveguide grating.

We show, for the first time, dense WDM (8×20 Gbit/s) transmission at 2 µm enabled by advanced modulation formats (4-ASK Fast-OFDM) and the development of key components, including a new arrayed waveguide grating (AWGr) at 2 µm. The AWGr shows -12.8±1.78 dB of excess loss with an 18-dB extinction ratio and a thermal tunability of 0.108 nm/°C.

Few-mode multi-element fiber amplifier for mode division multiplexing.

We experimentally demonstrate a few-moded cladding-pumped multi-element fiber amplifier, comprising 4 Er/Yb co-doped signal fibers and 1 multimode pump-delivery fiber all of which are drawn together in a common polymer coating, providing a total spatial path multiplicity of 12. An average WDM signal gain of 18.3 dB and differential modal gain of 1.1 dB were achieved in the spectral range of 1542-1560 nm.

Cladding pumped few-mode EDFA for mode division multiplexed transmission.

We experimentally demonstrate a few-mode erbium doped fiber amplifier (FM-EDFA) supporting 6 spatial modes with a cladding pumped architecture. Average modal gains are measured to be >20dB between 1534nm-1565nm with a differential modal gain of ~3dB among the mode groups and noise figures of 6-7dB. The cladding pumped FM-EDFA offers a cost effective alternative to core-pumped variant as low cost, high power multimode pumps can be used, and offers performance, scalability and simplicity to FM-EDFA design.

First demonstration of a 2µm few-mode TDFA for mode division multiplexing.

We report the first demonstration of an inline few-mode thulium doped fiber amplifier (TDFA) operating at 2µm for mode division multiplexed transmission. Similar gain and noise figure performance for both the LP(01) and LP(11) modes are obtained in a cladding pumped 2-mode group TDFA. A maximum gain of 18.3dB was measured at 1970nm with a 3dB gain bandwidth of 75nm while the average noise figure was measured to be between 7 and 8dB for wavelengths longer than 1970nm.

20 × 960-Gb/s Space-division-multiplexed 32QAM transmission over 60 km few-mode fiber.

We show transmission of 20 wavelength-division-multiplexed (WDM) × 960-Gb/s space-division-multiplexed 32QAM modulated channels (spectral efficiency (SE) of 15 bits/s/Hz) over 60 km of few-mode fiber (FMF) with inline few-mode EDFA (FM-EDFA). Soft-decision FEC was implemented and used to achieve error-free transmission.

High-energy diode-seeded nanosecond 2 µm fiber MOPA systems incorporating active pulse shaping.

We report on high-energy nanosecond-pulsed fiber master oscillator power amplifier (MOPA) systems seeded by semiconductor laser diodes at 2 µm incorporating arbitrary pulse-shaping capabilities. Two MOPA systems, one based on direct diode modulation and the second using additional electro-optic modulator (EOM) based shaping, are investigated, with up to 0.5 mJ (25 kHz) and 1.0 mJ (12.5 kHz) pulse energies achieved, respectively, for 100 ns pulses with user-defined pulse shapes. Our results indicate that further energy scaling with shaped output pulses is primarily limited by the maximum pulse peak power available from the seed laser diode and the dynamic range offered by the first generation of EOMs at 2 µm.

Optical chopper-based re-circulating loop for few-mode fiber transmission.

An optical chopper-based re-circulating loop is presented for emulating long-haul transmission using few-mode fiber (FMF). A proper functioning of the loop is verified by transmission of three-mode-division multiplexed × 128 Gb/s DP-QPSK over more than 1000 km of FMF.

Diode-pumped wideband thulium-doped fiber amplifiers for optical communications in the 1800 - 2050 nm window.

We present the first in-band diode-pumped TDFAs operating in the 2 µm wavelength region and test their suitability as high performance amplifiers in potential future telecommunication networks. We demonstrate amplification over a 240 nm wide window in the range 1810 - 2050 nm with up to 36 dB gain and noise figure as low as 4.5 dB.

Mid-infrared ZBLAN fiber supercontinuum source using picosecond diode-pumping at 2 µm.

We present the first demonstration of mid-IR supercontinuum generation directly pumped with picosecond pulses from a Thulium fiber-amplified gain-switched laser diode at 2 µm. We achieve more than two octaves of bandwidth from 750 - 4000 nm in step-index ZBLAN fiber with Watt-level average power and spectral flatness of less than 1.5 dB over a 1300 nm range in the mid-IR from 2450 - 3750 nm. The system offers high stability, power-scaling capability to the 10 W regime, and demonstrates an attractive route towards relatively inexpensive, versatile and practical sources of high power broadband mid-IR radiation.

Dual mode fused optical fiber couplers suitable for mode division multiplexed transmission.

We experimentally demonstrate 2 × 2 and 3 × 3 fused fiber couplers made from dual mode fiber. A unique mode dependent power transfer characteristics as a function of pulling length is obtained that support various optical functionalities. Exploiting this we demonstrate several devices of interest for mode division multiplexed data transmission including LP11 mode filter, LP11 mode tap coupler, and 50:50 power splitter for both LP01 and LP11 modes.

Thulium-doped fiber amplifier for optical communications at 2 µm.

We report the first experimental realization and detailed characterization of thulium doped fiber amplifiers (TDFAs) specifically designed for optical communications providing high gain (>35 dB), noise figure as low as 5 dB, and over 100 nm wide bandwidth around 2 µm. A maximum saturated output power of 1.2 W was achieved with a slope efficiency of 50%. The gain dynamics of the amplifier were also examined. Our results show that TDFAs are well qualified as high performance amplifiers for possible future telecommunication networks operating around 2 µm.

Three mode Er3+ ring-doped fiber amplifier for mode-division multiplexed transmission.

We successfully fabricate three-mode erbium doped fiber with a confined Er(3+) doped ring structure and experimentally characterize the amplifier performance with a view to mode-division multiplexed (MDM) transmission. The differential modal gain was effectively mitigated by controlling the relative thickness of the ring-doped layer in the active fiber and pump launch conditions. A detailed study of the modal gain properties, amplifier performance in a MDM transmission system and inter-modal cross-gain modulation and associated transient effects is presented.

Field demonstration of mode-division multiplexing upgrade scenarios on commercial networks.

We demonstrate three possible scenarios for upgrading current single-mode transmission networks with high capacity few-mode fiber technology using mode-division multiplexing (MDM). The results were obtained from measurements over a number of field-deployed single-mode fiber links with an additional experimental in-line amplified few-mode fiber link. The results confirm the viability of employing MDM using few-mode fiber technology to gradually replace legacy optical systems.

Demonstration of amplified data transmission at 2 µm in a low-loss wide bandwidth hollow core photonic bandgap fiber.

The first demonstration of a hollow core photonic bandgap fiber (HC-PBGF) suitable for high-rate data transmission in the 2 µm waveband is presented. The fiber has a record low loss for this wavelength region (4.5 dB/km at 1980 nm) and a >150 nm wide surface-mode-free transmission window at the center of the bandgap. Detailed analysis of the optical modes and their propagation along the fiber, carried out using a time-of-flight technique in conjunction with spatially and spectrally resolved (S2) imaging, provides clear evidence that the HC-PBGF can be operated as quasi-single mode even though it supports up to four mode groups. Through the use of a custom built Thulium doped fiber amplifier with gain bandwidth closely matched to the fiber's low loss window, error-free 8 Gbit/s transmission in an optically amplified data channel at 2008 nm over 290 m of 19 cell HC-PBGF is reported.

All-fiber, ultra-wideband tunable laser at 2 µm.

We report a direct diode-pumped all-fiber tunable laser source at 2 µm with a tuning range of more than 250 nm. A 3 dB power flatness of 200 nm with a maximum output power of 30 mW at 1930 nm was achieved. The laser has a high optical signal-to-noise ratio (OSNR) of more than 40 dB across the whole tuning range.