Enhanced carrier-carrier interaction in optically pumped hydrogenated nanocrystalline silicon

A femtosecond pump-probe setup was used to measure the time resolved reflectivity of hydrogenated amorphous silicon containing crystalline silicon nanoparticles at eight different incidence angles. Results fitted with the Drude model found a scattering rate of G = 2-1+1.2×1015?s-1 at a corresponding carrier concentration of ~ 1020?cm-3. The observed scattering rate is attributed to enhanced carrier-carrier interaction in optically pumped nanocrystals.

Optically pumped chirped grating for tunable chromatic dispersion compensation

We demonstrate a novel optically tunable dispersion compensator based on pumping a chirped grating made in Er/Yb co-doped fiber. The dispersion was tuned from 900 to 1900ps/nm and also from-600 to-950ps/nm in the experiment. © 2010 Optical Society of America.

1.2-μm semiconductor disk laser frequency doubled with periodically poled lithium tantalate crystal

In this letter, we demonstrate an optically pumped semiconductor disk laser frequency doubled with a periodically poled lithium tantalate crystal. Crystals with various lengths were tested for intracavity frequency conversion. The semiconductor disk laser exploited GaInNAs-based active region with GaAsAlAs distributed Bragg mirror to produce emission at 1.2- μm wavelength. The frequency doubled power up to 760 mW at the wavelength of 610 nm was achieved with a 2-mm-long crystal. © 2010 IEEE.

Self-mode-locked quantum-dot vertical-external-cavity surface-emitting laser

We present the first self-mode-locked optically pumped quantum-dot semiconductor disk laser. Our mode-locked device emits sub-picosecond pulses at a wavelength of 1040 nm and features a record peak power of 460 W at a repetition rate of 1.5 GHz. In this work, we also investigate the temperature dependence of the pulse duration as well as the time-bandwidth product for stable mode locking. © 2014 Optical Society of America.

High-power quantum-dot vertical-external-cavity surface-emitting laser exceeding 8 W

We report on a record-high output power from an optically pumped quantum-dot vertical-external-cavity surface-emitting laser, optimized for high-power emission at 1040 nm. A maximum continuous-wave output power of 8.41 W is obtained at a heat sink temperature of 1.5 °C. By inserting a birefringent filter inside the laser cavity, a wavelength tuning over a range of 45 nm is achieved. © 2014 IEEE.

High-power operation of quantum-dot semiconductor disk laser at 1180 nm

In this letter, we report on a high-power operation of an optically pumped quantum-dot semiconductor disk laser designed for emission at 1180 nm. As a consequence of the optimization of the operation conditions, a record-high continuous-wave output power exceeding 7 W is obtained for this wavelength at a heat-sink temperature of 2 °C. A wavelength tuning over a range of 37 nm is achieved using a birefringent filter inside the cavity.

Unrepeatered DP-QPSK transmission over 352.8 km SMF using random DFB fiber laser amplification

Unrepeatered 100 Gbit/s per channel wave-divisionmultiplexed dual-polarization-QPSK transmission with random distributed feedback fiber laser-based Raman amplification using fiber Bragg grating is demonstrated. Transmission of 1.4 Tb/s (14 × 100 Gbit/s) was possible in 352.8 km link and 2.2 Tb/s (22 × 100 Gbit/s) was achieved in 327.6 km without employing remote optically pumped amplifier or speciality fibers.

Periodically poled lithium tantalate crystals for efficient SHG generation

In this paper, we investigate SHG efficiency dependency on crystal length. Four periodically-poled MgSLT crystals (PPMgSLT) of 2, 4, 11 and 25 mm in length were used, for intracavity frequency doubling of an optically-pumped GalnNAs semiconductor disk laser.

Intracavity generation of 610nm light by periodically poled near-stoichiometric lithium tantalate

Intracavity frequency doubling of an optically pumped GaInNAs semiconductor disk laser by a periodically poled near-stoichiometric lithium tantalate crystal has been investigated. Stable second-harmonic generation at 610nm has been achieved with an output power of 730mW, limited only by the spectral acceptance range and Fresnel losses of the crystal. Spectral tuning of 8nm was realised with a Fabry-Pérot etalon. © The Institution of Engineering and Technology.

Quantum dot-based terahertz photoconductive antennas

We present novel Terahertz (THz) emitting optically pumped Quantum Dot (QD) photoconductive (PC) materials and antenna structures on their basis both for pulsed and CW pumping regimes. Full text Quantum dot and microantenna design - Presented here are design considerations for the semiconductor materials in our novel QD-based photoconductive antenna (PCA) structures, metallic microantenna designs, and their implementation as part of a complete THz source or transceiver system. Layers of implanted QDs can be used for the photocarrier lifetime shortening mechanism[1,2]. In our research we use InAs:GaAs QD structures of varying dot layer number and distributed Bragg reflector(DBR)reflectivity range. According to the observed dependence of carrier lifetimes on QD layer periodicity [3], it is reasonable to assume that electron lifetimes can be potentially reduced down to 0.45ps in such structures. Both of these features; long excitation wavelength and short carriers lifetime predict possible feasibility of QD antennas for THz generation and detection. In general, relatively simple antenna configurations were used here, including: coplanar stripline (CPS); Hertzian-type dipoles; bow-ties for broadband and log-spiral(LS)or log-periodic(LP)‘toothed’ geometriesfor a CW operation regime. Experimental results - Several lasers are used for antenna pumping: Ti:Sapphire femtosecond laser, as well as single-[4], double-[5] wavelength, and pulsed [6] QD lasers. For detection of the THz signal different schemes and devices were used, e.g. helium-cooled bolometer, Golay cell and a second PCA for coherent THz detection in a traditional time-domain measurement scheme.Fig.1shows the typical THz output power trend from a 5 um-gap LPQD PCA pumped using a tunable QD LD with optical pump spectrum shown in (b). Summary - QD-based THz systems have been demonstrated as a feasible and highly versatile solution. The implementation of QD LDs as pump sources could be a major step towards ultra-compact, electrically controllable transceiver system that would increase the scope of data analysis due to the high pulse repetition rates of such LDs [3], allowing real-time THz TDS and data acquisition. Future steps in development of such systems now lie in the further investigation of QD-based THz PCA structures and devices, particularly with regards to their compatibilitywith QD LDs as pump sources. [1]E. U. Rafailov et al., “Fast quantum-dot saturable absorber for passive mode-locking of solid-State lasers,”Photon.Tech.Lett., IEEE, vol. 16 pp. 2439-2441(2004) [2]E. Estacio, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures. Appl.Phys.Lett., vol. 94 pp. 232104 (2009) [3]C. Kadow et al., “Self-assembled ErAs islands in GaAs: Growth and subpicosecond carrier dynamics,” Appl. Phys. Lett., vol. 75 pp. 3548-3550 (1999) [4]T. Kruczek, R. Leyman, D. Carnegie, N. Bazieva, G. Erbert, S. Schulz, C. Reardon, and E. U. Rafailov, “Continuous wave terahertz radiation from an InAs/GaAs quantum-dot photomixer device,” Appl. Phys. Lett., vol. 101(2012) [5]R. Leyman, D. I. Nikitichev, N. Bazieva, and E. U. Rafailov, “Multimodal spectral control of a quantum-dot diode laser for THz difference frequency generation,” Appl. Phys. Lett., vol. 99 (2011) [6]K.G. Wilcox, M. Butkus, I. Farrer, D.A. Ritchie, A. Tropper, E.U. Rafailov, “Subpicosecond quantum dot saturable absorber mode-locked semiconductor disk laser, ” Appl. Phys. Lett. Vol 94, 2511 © 2014 IEEE.

Mode-locked semiconductor disk lasers

This paper will review the recent advances in the field of ultrashort pulse generation from optically pumped vertical-external-cavity surface-emitting lasers (OP-VECSELs). In this review, we will summarize the most significant results presented over the last 15 years, before highlighting recent breakthroughs related to mode-locked VECSELs by different research groups. Different mode-locking techniques for OP-VECSELs are described in detail. Previously, saturable absorbers, such as semiconductor saturable absorber mirrors—external, or internal as in mode-locked integrated external-cavity surface emitting lasers (MIXSEL)—, and recently, novel-material-based carbon-nanotube and graphene saturable absorbers have been employed. A new mode-locking method was presented and discussed in recent years. This method is referred to as self-mode-locking or saturable-absorber-free operation of mode-locked VECSELs. In this context, we particularly focus on achievements regarding self-mode-locking, which is considered a promising technique for the realization of high-power, compact, robust and cost-efficient ultrashort pulse lasers. To date, the presented mode-locking techniques have led to great enhancement in average powers, peak powers, and repetition rates that can be achieved with passively mode-locked VECSELs.

THz emission from quantum dot-based THz antennas pumped by a tunable quantum-dot laser diode

The THz optoelectronics field is now maturing and semiconductor-based THz antenna devices are becoming more widely implemented as analytical tools in spectroscopy and imaging. Photoconductive (PC) THz switches/antennas are driven optically typically using either an ultrashort-pulse laser or an optical signal composed of two simultaneous longitudinal wavelengths which are beat together in the PC material at a THz difference frequency. This allows the generation of (photo)carrier pairs which are then captured over ultrashort timescales usually by defects and trapping sites throughout the active material lattice. Defect-implanted PC materials with relatively high bandgap energy are typically used and many parameters such as carrier mobility and PC gain are greatly compromised. This paper demonstrates the implementation of low bandgap energy InAs quantum dots (QDs) embedded in standard crystalline GaAs as both the PC medium and the ultrafast capture mechanism in a PC THz antenna. This semiconductor structure is grown using standard MBE methods and allows the device to be optically driven efficiently at wavelengths up to ~1.3 µm, in this case by a single tunable dual-mode QD diode laser.

Optically controlled tunable dispersion compensators based on pumped fiber gratings

We demonstrate optically tunable dispersion compensators based on pumping fiber Bragg gratings made in Er/Yb codoped fiber. The tunable dispersion for a chirped grating and also a uniform-period grating was successfully demonstrated in the experiment. The dispersion of the chirped grating was tuned from 900 to 1990 ps/nm and also from -600 to -950 ps/nm in the experiment.

Time resolved bit error rate analysis of a fast switching tunable laser for use in optically switched networks

We investigate the use of different direct detection modulation formats in a wavelength switched optical network. We find the minimum time it takes a tunable sampled grating distributed Bragg reflector laser to recover after switching from one wavelength channel to another for different modulation formats. The recovery time is investigated utilizing a field programmable gate array which operates as a time resolved bit error rate detector. The detector offers 93 ps resolution operating at 10.7 Gb/s and allows for all the data received to contribute to the measurement, allowing low bit error rates to be measured at high speed. The recovery times for 10.7 Gb/s non-return-to-zero on–off keyed modulation, 10.7 Gb/s differentially phase shift keyed signal and 21.4 Gb/s differentially quadrature phase shift keyed formats can be as low as 4 ns, 7 ns and 40 ns, respectively. The time resolved phase noise associated with laser settling is simultaneously measured for 21.4 Gb/s differentially quadrature phase shift keyed data and it shows that the phase noise coupled with frequency error is the primary limitation on transmitting immediately after a laser switching event.

High-power diode-pumped fiber laser operating at 3 μm

A high-power diode-cladding-pumped Ho-doped fluoride glass fiber laser operating in cascade mode is demonstrated. The 5|6 -> 5|7 and 5|7 -> 5|8 laser transitions produced 0:77W at a measured slope efficiency of 12.4% and 0:24Wat a measured slope efficiency of 5.2%, respectively. Using a long fiber length, which forced a large threshold for the 5|7 -> 5|8 transition, a wavelength of 3:002 µm was measured at maximum output power, making this system the first watt-level fiber laser operating in the mid-IR.