Search

We study gain switching of the broad-stripe InAs/GaAs quantum dot lasers and show that the ratio of ground and excited states emission varies with the lateral position at the laser facet.

We demonstrate a record low threshold current density of 250 A/cm2 in a quantum dot microdisk laser with a 31-μm diameter operating at room temperature in continuous wave regime without temperature stabilization. This low threshold current density is very close to the transparency current density estimated in broad-area edge-emitting lasers made of the same epitaxial wafer.

Microdisk injection lasers on GaAs substrates, with a minimum diameter of 15 μm and an active region based on InAs/InGaAs quantum dots, are fabricated. The lasers operate in the continuous-wave mode at room temperature without external cooling. The lasing wavelength is around 1.27 μm at a minimum threshold current of 1.6 mA. The specific thermal resistance is estimated to be 5 × 10–3 °C cm2/W.

We analyze, experimentally and theoretically, the pulsed generation in quantum well laser simultaneously operating from the ground (GS) and the excited (ES) states. We find that an exponential increase in the output power at the GS laser turn-on noticeably changes its timescale when the laser turns on at the ES wavelength, indicating extremely fast dynamical interaction between the lasing states.

The linewidth enhancement factor (LEF) of an InAs/InGaAs quantum dot Fabry-Perot laser in a wide wavelength range from 1110 to 1300 nm, including ground state (GS) and exited state (ES) bands, is studied. LEF spectra were derived from amplified spontaneous emission spectra measured below the threshold in the pulse regime. The ES optical transition is characterised by significantly lower values of the LEF (≤0.54) as compared to the GS (≥1.21). Moreover, a zero LEF is observed within the ES spectral band. At sufficiently high currents, a near-zero LEF (|α| ≤ 0.1) is achieved in a wide spectral interval from 1146 to 1175 nm, in which the optical gain is not less than 9 cm−1.

The spectral analysis of amplified spontaneous emission is used to determine the linewidth enhancement factor (α-factor) in lasers based on InAs/InGaAs quantum dots (QDs) in a wide spectral range near the ground-state optical transition energy. The effect of the pump current and number of QDs on the spectral dependences of the α-factor is examined. The temperature dependence of the spectra of the α-factor is experimentally determined for the first time for lasers with InAs/InGaAs QDs. An explanation is suggested for the observed anomalous decrease in the α-factor with increasing temperature.

Microring cavities (diameter D = 2.7–7 μm) with an active region based on InAs/InGaAs quantum dots are fabricated and their characteristics are studied by the microphotoluminescence method and near-field optical microscopy. A value of 22 000 is obtained for the Q factor of a microring cavity with the diameter D = 6 μm. Lasing up to room temperature is obtained in an optically pumped ring microlaser with a diameter of D = 2.7 μm.

We demonstrate the possibility to use a fractional order of poling period of nonlinear crystal waveguides for tunable second harmonic generation. This approach allows one to extend wavelength coverage in the visible spectral range by frequency doubling in a single crystal waveguide.

In this work, electrically-injected microdisk lasers with diameter varied from 15 to 31μm based on an InAs/InGaAs QD active region have been fabricated and tested in continuous wave regime. At room temperature, lasing is achieved at wavelength around 1.26…1.27 μm with threshold current density about 900 A/cm 2 . Specific series resistance is estimated to be about 10 -4 Ohm•cm 2 . The lasers were tested at elevated temperatures. Lasing is achieved up to 100°C with threshold current of 13.8mA and lasing wavelength of 1304nm in device with 31μm diameter. To the best of our knowledge, this is the highest CW lasing temperature and the longest lasing wavelength ever reported for injection QD microdisk/microring lasers on GaAs substrates. Emission spectrum demonstrates single-mode lasing with side mode suppression ration of 24dB and dominant mode linewidth of 35pm. The far field radiation pattern demonstrates two narrow maxima off the disk plane. A combination of device characteristics achieved (low threshold, long wavelength, operation at elevated temperatures) makes them suitable for application in future optoelectronic circuits for optical interconnect systems.

Quasi-phase-matching is an important and widelyused technique in nonlinear optics enabling efficient frequency up-conversion. However, since its introduction almost half a century ago, this technique is well developed for near infrared (IR) but is intrinsically limited in spectral tunability in the visible range by the strict conditions set by the spatial modulation which compensates the momentum mismatch imposed by the dispersion. Here, we provide a fundamental generalization of quasi-phase-matching based on the utilization of a significant difference in the effective refractive indices of the high- and low-order modes in multimode waveguides. This concept enables to match the period of poling in a very broad wavelength range and opens up a new avenue for an order-ofmagnitude increase in wavelength range for frequency conversion from a single crystal. Using this approach, we demonstrate an all-room-temperature continuous-wave (CW) second harmonic generation (SHG) with over 60 nm tunability from green to red in a periodically-poled potassium titanyl phosphate (PPKTP) waveguide pumped by a single broadly-tunable quantumdot laser diode.

The lasing spectra and light-current (L-I) characteristics of an InAs/InGaAs quantum dot laser emitting in the simultaneous lasing mode at the ground- and excited-state optical transitions are studied. Lasing and spontaneous emission spectra are compared. It is shown that ground-state quenching of lasing is observed even in the absence of active region self-heating or an increase in homogeneous broadening with growth in the current density. It is found that the intensities of both lasing and spontaneous emission at the ground-state transition begin to decrease at a pump intensity that significantly exceeds the two-level lasing threshold. It is also found that different groups of quantum dots are involved in ground- and excited-state lasing.

The concept of a diffraction optical filter is used for prevention of high-order mode oscillation in a design of stripe laser diodes with an active region based on InAs/InGaAs quantum dots emitting in the 1.3-μm wavelength range grown on GaAs substrates. Incorporation of such a filter made it possible to increase the width of the stripe and obtain an output power as high as 700 mW with retention of a single-spatial-mode character of lasing.

980-nm VCSELs based on submonolayer growth show for 20-Gbit/s large-signal modulation clearly open eyes without adjustment of the driving conditions between 25degC and 120degC. To access the limiting mechanism for the modulation bandwidth, a temperature-dependent small-signal analysis is carried out on these devices. Single-mode devices are limited by damping, whereas multimode devices are limited by thermal effects, preventing higher photon densities in the cavity.

A novel GaAs–AlGaAs vertical-cavity surface-emitting laser (VCSEL) design based on the coupled cavities and all-epitaxial non-transparent filter section (F-VCSEL) was proposed. The key point of this approach is that the absorption filter selectively provides the high losses for off-resonance optical modes and relatively narrow transparency window (∼1.3 nm). The broad area (100 μm×500 μm) F-VCSEL devices with a metal contact grid on the top demonstrate the 0.85 μm range narrow line emission and the Gaussian-like far-field patterns, which confirm the possibility of the achievement of the surface-emitting lasing by using the all-epitaxial wavelength-selective filter concept. Single-mode operation in wide pump current range in F-VCSEL was achieved at the larger oxide current aperture (3 μm) as compared with that for the conventional oxide-confined VCSEL (1 μm).

980 nm vertical-cavity surface-emitting lasers based on submonolayer growth of quantum dots show clearly open eyes and operate error free with bit error rates better than 10 at 25 and 85degC for 20 Gb/s without current adjustment. The peak differential efficiency only reduces from 0.71 to 0.61 W/A between 25 and 85degC; the maximum output power at 25degC is above 10 mW.

We present a compact, all-room-temperature continuous-wave laser source in the visible spectral region between 574 and 647 nm by frequency doubling of a broadly tunable InAs/GaAs quantum-dot external-cavity diode laser in a periodically poled potassium titanyl phosphate crystal containing three waveguides with different cross-sectional areas (4 × 4, 3 × 5, and 2 μm × 6 μm). The influence of a waveguide's design on tunability, output power, and mode distribution of second-harmonic generated light, as well as possibilities to increase the conversion efficiency via an optimization of a waveguide's cross-sectional area, was systematically investigated. A maximum output power of 12.04 mW with a conversion efficiency of 10.29% at 605.6 nm was demonstrated in the wider waveguide with the cross-sectional area of 4 μm × 4 μm.

Low-threshold (3.7 mA) high-power (150 mW) ridge-waveguide lasers based on 1.3 µm self-organized quantum dots were fabricated and studied at and above room temperature. The output power spectrum of these lasers consists of two components, which correspond to the ground-state (~1.29 µm) and the excited-state (~1.22 µm) optical transitions. The ground-state component of the lasing mode saturates with increase in the drive current and then persists. Further growth of the total output power is due to the excited-state component. Design criteria of quantum-dot lasers, which maximize the ground-state output power, are considered by solving the carrier-photon rate equations. Current-induced ground-to-excited-state lasing transition is due to a combination of slow carrier capture/relaxation to and efficient thermoionic emission from the ground-state level.

Near-1.3-μm lasers based on multiple layers (2, 5 and 10) of InAs/InGaAs/GaAs quantum dots with high performance have been grown by molecular beam epitaxy. A record differential efficiency as high as 88% was achieved in laser based on 10 QD layers. Threshold current density of 100–150 A/cm2 and differential efficiency of 75–80% were achieved simultaneously in the same device. Characteristic temperature of 150 K in 20–50°C temperature range was demonstrated for the laser based on 5 QD layers. A steep increase in internal loss with decreasing cavity length was found to limit the highest mirror loss possible for ground state lasing.

Long-wavelength (1.29 μm ) lasers grown on GaAs and based on several planes of self-organized quantum dots in an external quantum well demonstrate significant improvement of the external differential efficiency (88%) and the characteristic temperature (150 K ) . This is due to suppression of carrier pile-up in the waveguide region in combination with extended range of optical loss in which the ground-state lasing survives.

A comparative analysis is made of laser diodes based on Stranski-Krastanow (SK) and sub-monolayer (SML) InAs/GaAs quantum dots, emitting at about 940 nm. Owing to the better uniformity of sub-monolayer quantum dots, the SML QD laser surpasses the SK QD one in power characteristics. A maximum output power of 3.9 W and a peak power conversion efficiency of 59% have been achieved for SML QD 100 µm wide lasers at 10 °C.

Data are presented on the threshold and power characteristics and their dependence on the quantum dot (QD) surface density for QD diode lasers. The active region is based on the dense array of composite InAs/InAlAs self-organized QDs. The 3.5 W output power, limited by catastrophic optical damage, and a peak conversion efficiency of 45% were achieved at 10°C in 100-μm-wide diodes with uncoated facets.

A passive mode-locked Cr:forsterite laser with electronically controlled pulse duration is demonstrated. A DC voltage controlled p-n junction quantum-dot semiconductor saturable absorber mirror is presented. Output pulse durations varying from 17.4 to 6.4 ps were obtained by applying a DC voltage between 0 and -4.5 V. No dispersion compensation was used.

A 31 µm in diameter microdisk laser with an InAs/InGaAs quantum dot active region has been tested in the continuous-wave regime at elevated temperatures. Lasing is achieved up to 100°C with a threshold current of 13.8 mA. The emission spectrum demonstrates single-mode lasing at 1304 nm with a side mode suppression ratio of 24 dB and a dominant mode linewidth of 35 pm.

In this paper, we study experimentally the generation of picosecond short optical pulses with an improved peak power of 42 W at a repetition rate of 16 GHz and an associated pulse width of 1.4 ps. Pulses from a tapered quantum dot laser emitting at 1250 nm are amplified using a tapered quantum dot optical amplifier without any pulse post-compression. We specifically investigate the amplification behavior of this master-oscillator power-amplifier configuration with a focus on the pulse peak power, pulse width, average power and amplified spontaneous emission towards improving the figure of merit for two photon excitation microscopy.

We report on GaAs-based broad area (100 µm) 1.3 µm quantum dot (QD) lasers with high CW output power (5 W) and wall-plug efficiency (56%). The reliability of the devices has been demonstrated beyond 3000 h of CW operation at 0.9 W and 40 °C heat sink temperature with 2% degradation in performance. P-doped QD lasers with a temperature-insensitive threshold current (T0 > 650 K) and differential efficiency (T1 = infinity) up to 80 °C have been realized.

DBR stabilized InAs/GaAs quantum dot comb laser diode is demonstrated. It generates 4+ low-noise comb lines within the temperature range 25-65°C. The DBR section improves comb spectrum stability in the changing operating conditions.

We propose a model for operation of mode-locked (ML) quantum-well semiconductor laser consisting of a reverse biased saturable absorber and a forward biased amplifying section. To describe the dynamics of this laser we use the traveling wave model. Numerical simulations performed for the InGaAs/InGaAlAs laser structure emitting at 1,55 um.

We present high average power femtosecond VECSELs based on both quantum dot (QD) and quantum well (QW) gain with extremely low dispersion. 1.05 W in 784-fs pulses could be achieved from a QD-VECSEL modelocked by a QDSESAM with fast recovery dynamics. A similar QW-gain structure modelocked by the same SESAM enabled stable 480-fs with an average output power of 300 mW at a repetition rate of 7 GHz. Furthermore, we investigated repetition rate scaling by changing the cavity length. We demonstrated fundamentally modelocked pulses over a tuning range from 6.5 GHz to 11.3 GHz. Without any realignment of the cavity over the whole tuning range, the pulse duration remained nearly constant around 625 fs (±3.5%) while the output power was 169 mW (±6%). The center wavelength changed only about ±0.2 nm around 963.8 nm. A tunable repetition rate can be of interest for various metrology application such as optical sampling by laser cavity tuning.

A broadly tunable master-oscillator power-amplifier (MOPA) picosecond optical pulse source is demonstrated, consisting of an external cavity passively mode-locked laser diode with a tapered semiconductor amplifier. By employing chirped quantum-dot structures on both the oscillator's gain chip and amplifier, a wide tunability range between 1187 and 1283 nm is achieved. Under mode-locked operation, the highest output peak power of 4.39 W is achieved from the MOPA, corresponding to a peak power spectral density of 31.4 dBm/nm.

We present λ=1.26 μm all quantum-dot (QD) master-oscillator-power-amplifier (MOPA) system with a pulse energy of 321 pJ, and peak power of 30.3 W at a repetition rate of 648 MHz for nonlinear bio-imaging applications.

Semiconductor lasers with broad tunability of the pulse repetition rate in the range of MHz to GHz are very useful for non-linear imaging techniques, especially in the bio-medical field. In our previous work, we demonstrated a quantum-dot external-cavity passively mode-locked lasers (QD-ECMLL) incorporating a QD semiconductor saturable absorber mirror (SESAM) [1], generating pulses at repetition rates ranging from 1.5 GHz to 350 MHz. In a more recent investigation [2], a QD-ECMLL is demonstrated with pulse repetition rate as low as 310 MHz and corresponding harmonics up to 4 GHz (based on a fundamental frequency of ∼1 GHz). We have demonstrated very recently the generation of high-peak-power picosecond pulses with repetition frequency from 2.4 GHz to 1.14GHz [3] using an external cavity output coupler of 96% transmissivity.

Wavelength bistability between 1245nm and 1295nm is demonstrated in a multi-section quantum-dot laser, controlled via the reverse bias on the saturable absorber. Continuous-wave or mode-locked regimes are achieved (output power up to 25mW and 17mW).

Passively modelocked VECSELs continue to improve their performance in terms of output power, repetition rate and pulse duration. Recently, up to 6.4 W of average power in 28-ps pulses have been achieved from a modelocked VECSEL with an integrated saturable absorber (MIXSEL, [1]). The shortest pulse duration generated by a VECSEL was 60 fs and below 35 mW of average output power in harmonic modelocking [2]. To date, femtosecond VECSELs were based on quantum well (QW) gain structures and the average output power has been limited to

In recent years, there has been a growing interest in the development of broadly tunable compact coherent sources emitting in the visible spectral region at around 550 nm – 650 nm, which are of interest for a wide range of applications, such as photodynamic therapy, biophotonic applications and laser projection displays. An attractive approach for the implementation of such laser sources is frequency doubling of infrared light, particularly into the orange spectral region, for which compact and efficient sources are relatively scarce [1]. In this respect, quantum dot materials have shown a great promise for development of a new generation of optoelectronics devices, due to the temperature insensibility and the broad gain bandwidth. The wide tunability offered by the quantum-dot external cavity diode laser (QD-ECDL) [2] is very promising for the development of a tunable green-yellow-orange-red source based on a single laser device and a single waveguide.

In recent years, quantum-dot (QD) mode-locked semiconductors lasers have shown great potential as ultrashort pulse laser sources [1]. For instance, the generation of ultrashort transform-limited pulses with pulse durations of 360 fs has been previously demonstrated in tapered index-guided mode-locked quantum-dot lasers without any dispersion compensation - however, peak power reached only 2.25 W, for a typical average power of 15.6 mW [2]. In our recent work, we have shown that output average/peak power and pulse energy can be greatly increased using a tapered (or flared) gain-guided structure [3]. In [3], two-section devices incorporating 5 or 10 QD layers with a total length of ∼2.78mm were used, resulting in pulse repetition rates of the order of 14.6 GHz. With an absorber-to-gain lengths ratio of 1∶7, the highest peak power achieved was 3.6W from both QD structures. On the other hand, a maximum average power of 209 mW corresponding to 14.2 pJ pulse energy with 6-ps pulse duration was achieved for the 5-layer QD laser. The generation of high-peak-power pulses is vital for a variety of applications such as biomedical nonlinear microscopy and imaging, where a combination of high peak power and average power (up to the limit tolerable by the bio-sample) are most effective in enhancing the nonlinear effects required. In this paper, we report the highest peak power (to our knowledge) of 15 W directly from a monolithic quantum-dot tapered laser, with sub-picosecond pulse width.

Results of a photoluminescence and electroluminescence study of vertically coupled In0.5Ga0.5As/GaAs quantum dot?(QD) structures with an extended waveguide (1.24??m thick) are presented. Spectra of spontaneous and stimulated near-infrared (?1??m) emission as well as spectra of spontaneous mid-infrared?(MIR) (?12??m) emission are obtained under optical and electrical pumping. It is shown that the observed MIR emission is connected with intraband electron optical transitions in the QD structures.

With a fully gain guided quantum-dot tapered laser diode we demonstrate stable low beam divergence, high beam quality together with a record peak power of 2.6W under passive mode locking.

We demonstrate an instantaneous all-optical manipulation of optical absorption in InGaAs/GaAsquantum dots (QDs) via an electro-absorption effect induced by the electric field of an incidentfree-space terahertz signal. A terahertz signal with the full bandwidth of 3 THz was directly encodedonto an optical signal probing the absorption in QDs, resulting in the encoded temporal features asfast as 460 fs. The instantaneous nature of this effect enables femtosecond all-optical switching atvery high repetition rates, suggesting applications in terahertz-range wireless communicationsystems with data rates of at least 0.5 Tbit/s.

Record broadly tunable high-power external cavity InAs/GaAs quantum-dot diode laser is demonstrated. A maximum output power of 455mW and a side-mode suppression ratio >45dB in the central part of the tuning range are achieved.

Conventional optically pumped semiconductor disk lasers (SDLs) are able to produce laser light at a wide range of wavelengths across the visible and near infra-red spectrum with high output power and diffraction limited beam whilst allowing the advantages of various intracavity techniques to be exploited [1]. Recently the SDL architecture has been combined with quantum dots (QDs) based gain materials [2, 3] to explore their advantages provided by three dimensional carrier confinement, like temperature insensitivity and broad gain bandwidth, supported by inhomogeneous broadening [4]. In this paper the gain bandwidth supported wavelength tuning in QD based SDLs is in focus. We report wavelength tuning results of two QD SDLs at 1040 nm and 1260 nm. Broad tunability, of respectively 50 nm and 35 nm is observed. The results show QD based SDLs have wider tunability range than most conventional quantum well (QW) based their counterparts [5, 6] and make QD SDL potentially as a broadly tuneable continuous wave light source.

Continuous-wave operation near 1.3 /spl mu/m or a diode laser based on self-organized quantum dots (QD's) on a GaAs substrate is demonstrated. Multiple stacking of InAs QD planes covered by thin InGaAs layers allows us to prevent gain saturation and achieve long-wavelength lasing with low threshold current density (90-105 A/cm/sup 2/) and high output power (2.7 W) at 17/spl deg/C heatsink temperature. It is thus confirmed that QD lasers of this kind are potential candidates to substitute InP-based lasers in optical fiber systems.

Strong frequency up-chirping is observed in light pulses generated by passively mode-locked, multi-sectional InGaAs quantum dot lasers. Using a dispersive compressor, sub-picosecond pulses with >1 W peak power are obtained at the 1st (5 GHz) and 8th (40 GHz) harmonic.

So far, long wavelength Stranski-Krastanow (SK) quantum dots (QDs) have been failed to provide enough differential gain and temperature stability, required for high speed VCSEL -the fastest modulation bandwidth of a SK QD-VCSEL is only 3 GHz. In contrast, InGaAs quantum dots, grown at low temperatures of ~400 degC (LTQDs), demonstrate the possibility to reach simultaneously long wavelengths and a high QD density with an exciton-like recombination mechanism. LTQDs allow a high modal gain, avoid temperature depletion and gain saturation effects. Thus they are suitable for high-speed vertical-cavity surface-emitting lasers (VCSELs).

We report on the generation of femtosecond pulses in the 1-μm and 1.3-μm spectral regions from Yb:KYW and Cr:forsterite lasers, respectively, where InAs/InGaAs quantum dot based saturable absorber mirrors (QD-SAMs) have been utilised. For the experimental observations reported here, cw Yb:KYW and Cr:forsterite lasers pumped by a tapered 980nm laser diode and a Nd:YVO4 laser at 1064nm, respectively, were constructed and evaluated. Highly asymmetric Z-fold laser cavities were configured for both laser systems. During continuous wave operation the Yb:KYW laser produced an output power of 2W (3.5W incident power) at 1047nm and 250mW of average power (6W incident power) was generated by Cr:forsterite laser at 1270nm.

Efficient passive mode locking of a diode-pumped Yb3+:KY(WO4)2 laser using a quantum-dot saturable absorber is demonstrated. Pulses of 114 fs centered around 1040 nm were generated with an average output power of 0.5 W.

We report on a quantum dot laser having an emission spectrum as broad as 74.9 nm at 25 degrees C in the 1.2-1.28 wavelength interval with a total pulsed output power of 750 mW in single lateral mode regime and the average spectral power density of10 mW/nm. A significant overlap and approximate equalization of the ground-state and the excited-state emission bands in the laser's spectrum is achieved by means of intentional inhomogeneous broadening of the quantum dot energy levels.

In this paper, we demonstrate, experimentally and theoretically, that in a mode-locked two-section quantum-dot laser, the pulsewidth decreases with temperature. The primary cause is the increase of carrier capture rate with temperature, leading to a faster absorption recovery

In this paper, we demonstrate for the first time to our knowledge, an external cavity quantum-dot laser, mode-locked using a quantum-dot semiconductor saturable absorber mirrors (SESAM). The laser exhibits high-average power of up to 27 mW and RF linewidth of 10 Hz

For the first time hybrid and passive mode-locking jitter performance is investigated in 40GHz quantum-dot mode-locked lasers. Record low passive mode-locking jitter of 219fs is presented, along with promising hybrid mode-locking results of 124fs.

Beam profiling of broad area quantum-dot VCSEL is presented with 10Gb/s data transmission over 300m of MMF. Single mode-performance with SMSR of 35dB is achieved with no significant impairment of the modulation performance.