Showing papers on "Semiconductor optical gain published in 2016"

Optical gain in GaAsBi/GaAs quantum well diode lasers

Abstract: Optical gain, absorption and spontaneous emission spectra for GaAs 0.978 Bi 0.022 /GaAs laser diodes are measured experimentally and compared with theory. Internal optical losses of 10–15 cm−1 and peak modal gain of 24 cm−1 are measured at threshold. The results of calculations showed excellent agreement with the experiment, key for future laser design.

Semiconductor membrane external-cavity surface-emitting laser (MECSEL)

Abstract: Optically pumped semiconductor disk lasers are an important class of solid state lasers. Despite all their advantages, however, they suffer from heat incorporation into the active region caused by the excess energy of the pump photons. To overcome the limits of common methods in thermal management, we realized a semiconductor membrane external-cavity surface-emitting laser (MECSEL) consisting of a diamond heat spreader sandwiched active region design without a monolithically integrated distributed Bragg reflector (DBR). This diamond-sandwich approach improves the heat dissipation out of the active region and makes generally low-heat conductive DBRs obsolete. In an AlGaInP-based system, we demonstrate 595 mW output power at a wavelength of 657 nm and heatsink temperature of 10°C. The MECSEL enables a variety of new material combinations for new laser wavelengths and further potential for power scaling.

Experimental demonstration of change of dynamical properties of a passively mode-locked semiconductor laser subject to dual optical feedback by dual full delay-range tuning.

Abstract: In this contribution we experimentally demonstrate the change and improvement of dynamical properties of a passively mode-locked semiconductor laser subject to optical feedback from two external cavities by coupling the feedback pulses back into the gain segment. Hereby, we tune the full delay-phase of the pulse-to-pulse period of both external cavities separately and demonstrate the change of the repetition rate, timing jitter, multi-pulse formation and side-band suppression for the first time for such a dual feedback configuration. In addition, we thereby confirm modeling predictions by achieving both a good qualitative and quantitative agreement of experimental and simulated results. Our findings suggest a path towards the realization of side-band free all-optical photonic oscillators based on mode-locked lasers.

Improvement of the quasi-continuous-wave lasing properties in organic semiconductor lasers using oxygen as triplet quencher

Abstract: We demonstrate quasi-continuous-wave lasing in solvent-free liquid organic semiconductor distributed feedback lasers based on a blend containing a liquid 9-(2-ethylhexyl)carbazole host doped with a blue-emitting heptafluorene derivative. The liquid gain medium is bubbled with either oxygen or nitrogen in order to investigate the role of a triplet quencher such as molecular oxygen on the quasi-continuous-wave lasing properties of organic semiconductor lasers. The oxygenated laser device exhibits a low threshold of 2 μJ cm−2, which is lower than that measured in the nitrogenated device and is independent of the repetition rate in a range between 0.01 and 4 MHz.

Theoretical estimation of optical gain in Tin-incorporated group IV alloy based transistor laser

Abstract: We have calculated the electronic band structure and polarization dependent optical gain in a strain balanced SixGeySn1−x−y/GezSn1−z based transistor laser (TL) with GezSn1−z single quantum well (QW) in the base. Design consideration for QW is also addressed to ensure moderate carrier and optical confinement. A significant TE mode optical gain is obtained in mid infra red region for the transition of Г valley conduction band to heavy hole valence band. Optical gain in the QW plays an important role in determining the optical characteristics of Tin (Sn) incorporated group IV material based TL.

80 nm tunable DBR-free semiconductor disk laser

Abstract: We report a widely tunable optically pumped distributed Bragg reflector (DBR)-free semiconductor disk laser with 6 W continuous wave output power near 1055 nm when using a 2% output coupler. Using only high reflecting mirrors, the lasing wavelength is centered at 1034 nm and can be tuned up to a record 80 nm by using a birefringent filter. We attribute such wide tunability to the unique broad effective gain bandwidth of DBR-free semiconductor disk lasers achieved by eliminating the active mirror geometry.

Thermally insensitive determination of the linewidth broadening factor in nanostructured semiconductor lasers using optical injection locking.

Abstract: In semiconductor lasers, current injection not only provides the optical gain, but also induces variation of the refractive index, as governed by the Kramers-Kronig relation. The linear coupling between the changes of the effective refractive index and the modal gain is described by the linewidth broadening factor, which is responsible for many static and dynamic features of semiconductor lasers. Intensive efforts have been made to characterize this factor in the past three decades. In this paper, we propose a simple, flexible technique for measuring the linewidth broadening factor of semiconductor lasers. It relies on the stable optical injection locking of semiconductor lasers, and the linewidth broadening factor is extracted from the residual side-modes, which are supported by the amplified spontaneous emission. This new technique has great advantages of insensitivity to thermal effects, the bias current, and the choice of injection-locked mode. In addition, it does not require the explicit knowledge of optical injection conditions, including the injection strength and the frequency detuning. The standard deviation of the measurements is less than 15%.

Type-II vertical-external-cavity surface-emitting laser with Watt level output powers at 1.2 μm

Abstract: Semiconductor laser characteristics based on type-II band-aligned quantum well heterostructures for the emission at 1.2 μm are presented. Ten “W”-quantum wells consisting of GaAs/(GaIn)As/Ga(AsSb)/(GaIn)As/GaAs are arranged as resonant periodic gain in a vertical-external-cavity surface-emitting laser. Its structure is analyzed by X-ray diffraction, photoluminescence, and reflectance measurements. The laser's power curves and spectra are investigated. Output powers at Watt level are achieved, with a maximum output power of 4 W. It is confirmed that laser operation only involves the type-II transition. A blue shift of the material gain is observed while the modal gain exhibits a red shift.

Semiconductor mode-locked lasers with coherent dual-mode optical injection: simulations, analysis, and experiment

Abstract: In this paper, we study the dynamics of a passively mode-locked semiconductor laser with dual-frequency coherent optical injection. The locking regions, where the laser pulse repetition rate is synchronized to the separation of the two injected frequencies, were calculated numerically using a delay differential equation model and measured experimentally. Asymptotic analysis performed in the limit of the small injection field amplitude revealed the dependence of the locking regions on the model parameters, such as optical bandwidth, absorber recovery time, and linear losses.

On-Chip Multiple Colliding Pulse Mode-Locked Semiconductor Laser

Abstract: We report for the first time to the best of our knowledge, an on-chip multiple colliding pulse mode-locked semiconductor laser source. The device structure is fully integrated, replacing cleaved facet mirrors by using multimode interference reflectors; this allows us to precisely control the location of the saturable absorbers within the cavity length, which is critical to achieve the multiple colliding regime. In this paper, we succeeded to achieve this regime generating a repetition rate at four times the fundamental round-trip frequency, demonstrating a repetition rate within the millimeter wave frequency range, at 100 GHz using a 25 GHz resonator cavity length. We also demonstrate the advantage of having the signal on-chip including a boost semiconductor optical amplifier in order to increase the output optical power. This novel structure was fabricated on a generic InP photonic integrated technology through a multi-project wafer run.

Optical Injection Effects in Nanolasers

Abstract: The response of nanolasers subject to optical injection has been analyzed. Calculations have been performed using rate equations, which include the Purcell cavity-enhanced spontaneous emission factor F and the spontaneous emission coupling factor I². In the analysis, the influence of F and I² is evaluated for varying the injection strength and frequency detuning between the master and slave laser. It is observed that, in general, increased F and I² increases the stable locking region and have only a few regions of dynamic instability as compared with conventional semiconductor lasers over a large frequency detuning. It is also found that for larger F, the modulation bandwidths of 90 GHz can be achieved.

Effect of External Optical Feedback on Tunable Micro-Ring Lasers Using On-Chip Filtered Feedback

Abstract: We experimentally and numerically study the influence of external optical feedback on semiconductor ring lasers, which are wavelength tunable using on-chip filtered optical feedback. We investigate the dynamics in the laser’s intensity due to the conventional optical feedback and how this dynamics is changed by adding filtered optical feedback. Experimental observations show that the filtered optical feedback shifts the onset of the feedback-induced dynamics to larger values of the feedback rate. We are able to numerically reproduce the experimental observations using a rate equations model.

First Monolithically Integrated Dual-Pumped Phase-Sensitive Amplifier Chip Based on a Saturated Semiconductor Optical Amplifier

Abstract: For the first time, a monolithically integrated photonic phase-sensitive amplification chip is fabricated and demonstrated based on an InP/InGaAsP platform. Different semiconductor optical amplifiers have been fabricated as well for characterization. On the chip, two tunable laser pumps that are coherently injection-locked, respectively, from two first-order sidebands of an externally modulated tone are generated to enable signal-degenerate dual-pumped phase-sensitive amplification in a saturated semiconductor optical amplifier. Experiments on different chips are conducted to successfully demonstrate phase-sensitive amplification with approximately 6.3 and 7.8 dB extinction of phase-sensitive on-chip gain. Theoretical simulations are performed and agree well with experimental results. The additive noise properties of the phase-sensitive amplification chip are also investigated.

Measurements of nonlinear lensing in a semiconductor disk laser gain sample under optical pumping and using a resonant femtosecond probe laser

Abstract: Accurate characterizations of the nonlinear refractive index of semiconductor disk laser (SDL) gain samples are of critical importance for understanding the behavior of self-mode-locked SDLs. Here we describe measurements of nonlinear lensing in an SDL gain sample for a wide range of optical pump intensities and using a probe which is on resonance with the quantum wells in the SDL gain sample and whose intensity, pulse duration, and spot size are chosen to be similar to those reported in self-mode-locked SDLs. Under these conditions, we determine an effective value of the nonlinear refractive index, n2 = −6.5 × 10−13 cm2/W at zero pump intensity, and find that the value of n2 changes by less than 25% over the range of pump intensities studied. The nonlinear refractive index is measured using a variation on the well-established z-scan technique, which was modified to make it better suited to the measurement of optically pumped samples.

Tunable single-frequency fiber laser based on the spectral narrowing effect in a nonlinear semiconductor optical amplifier.

Abstract: A wavelength-tunable single-frequency fiber laser based on the spectral narrowing effect in a nonlinear semiconductor optical amplifier (NL-SOA) is proposed and experimentally demonstrated. The single-frequency operation is achieved based on the spectral narrowing effect resulted from the inverse four-wave mixing in a NL-SOA. By incorporating the NL-SOA in the fiber laser cavity, single-frequency lasing is achieved. The lasing frequency can be tuned by tuning the center wavelength of a tunable filter (TF) incorporated in the laser cavity. The proposed wavelength-tunable single-frequency fiber laser is experimentally evaluated. Stable single-frequency oscillation with a side-mode suppression ratio (SMSR) as high as 55 dB and a spectral linewidth of less than 10.1 kHz over a wavelength tuning range of as wide as 48 nm is demonstrated.

Gain spectroscopy of a type-II VECSEL chip

Abstract: Using optical pump–white light probe spectroscopy, the gain dynamics is investigated for a vertical-external-cavity surface-emitting laser chip, which is based on a type-II heterostructure. The active region of the chip consists of a GaAs/(GaIn)As/Ga(AsSb)/(GaIn)As/GaAs multiple quantum well. For this structure, a fully microscopic theory predicts a modal room temperature gain at a wavelength of 1170 nm, which is confirmed by the experimental spectra. The results show a gain buildup on the type-II chip that is delayed relative to that of a type-I chip. This slower gain dynamics is attributed to a diminished cooling rate arising from the reduced electron–hole scattering.

Organic Semiconductor Laser Biosensor: Design and Performance Discussion

Abstract: Organic distributed feedback lasers can detect nanoscale materials, and are, therefore, an attractive sensing platform for biological and medical applications. In this paper, we present a model for optimizing such laser sensors, and discuss the advantages of using an organic semiconductor as the laser material in comparison to dyes in a matrix. The structure of the sensor and its operation principle are described. Bulk and surface sensing experimental data using oligofluorene truxene macromolecules and a conjugated polymer for the gain region are shown to correspond to modeled values and is used to assess the biosensing attributes of the sensor. A comparison between organic semiconductor and dye-doped laser sensitivity is made and analyzed theoretically. Finally, experimental and theoretical specific biosensing data are provided, and methods for improving sensitivity are discussed.

Emergence of resonant mode-locking via delayed feedback in quantum dot semiconductor lasers.

Abstract: With conventional semiconductor lasers undergoing external optical feedback, a chaotic output is typically observed even for moderate levels of the feedback strength. In this paper we examine single mode quantum dot lasers under strong optical feedback conditions and show that an entirely new dynamical regime is found consisting of spontaneous mode-locking via a resonance between the relaxation oscillation frequency and the external cavity repetition rate. Experimental observations are supported by detailed numerical simulations of rate equations appropriate for this laser type. The phenomenon constitutes an entirely new mode-locking mechanism in semiconductor lasers.

Synchronization properties of two mutually delay-coupled semiconductor lasers

Abstract: This paper reports a detailed numerical study of the synchronization properties of two mutually delay-coupled semiconductor lasers in the framework of the Lang–Kobayashi model. By computing high-definition stability diagrams, we predict the complex distribution of periodic and chaotic laser oscillations on the coupling versus detuning control parameter plane. Such diagrams provide details concerning the behavior of the laser intensities, quantify objectively the synchronization between their electric fields, and display in-phase and out-of-phase laser behavior. In addition, we also describe the presence of a conspicuous abrupt change in the optimal shift for the greatest value of the cross-correlation function when varying the detuning between the optical angular frequencies of the lasers.

Dynamics of Hybrid III-V Silicon Semiconductor Lasers for Integrated Photonics

Abstract: The dynamics of hybrid III-V/Si lasers are studied for the first time under a combination of two optical feedbacks. A cleaved fiber placed about 20 μm away from the laser creates a short feedback cavity. The effect of this short feedback is studied on a Fabry–Perot laser and reveals the sensitivity of the device to such perturbation, as well as the presence of sub-cavities in the Si waveguides. The dynamics of the laser subjected to additional feedback from a 70-m fiber cavity show that the long-feedback dynamics are governed by the sub-cavities. This behavior is confirmed using a complex tunable III-V/Si laser.

Effective Linewidth of Semiconductor Lasers for Coherent Optical Data Links

Abstract: We discuss the implications of using monolithically integrated semiconductor lasers in high capacity optical coherent links suitable for metro applications, where the integration capabilities of se ...

Reliability of high power laser diodes with external optical feedback

Abstract: Direct diode laser systems gain importance in the fields of material processing and solid-state laser pumping. With increased output power, also the influence of strong optical feedback has to be considered. Uncontrolled optical feedback is known for its spectral and power fluctuation effects, as well as potential emitter damage. We found that even intended feedback by use of volume Bragg gratings (VBG) for spectral stabilization may result in emitter lifetime reduction. To provide stable and reliable laser systems design, guidelines and maximum feedback ratings have to be found. We present a model to estimate the optical feedback power coupled back into the laser diode waveguide. It includes several origins of optical feedback and wide range of optical elements. The failure thresholds of InGaAs and AlGaAs bars have been determined not only at standard operation mode but at various working points. The influence of several feedback levels to laser diode lifetime is investigated up to 4000h. The analysis of the semiconductor itself leads to a better understanding of the degradation process by defect spread. Facet microscopy, LBIC- and electroluminescence measurements deliver detailed information about semiconductor defects before and after aging tests. Laser diode protection systems can monitor optical feedback. With this improved understanding, the emergency shutdown threshold can be set low enough to ensure laser diode reliability but also high enough to provide better machine usability avoiding false alarms.

Optical net gain measurement in n-type doped germanium waveguides under optical pumping for silicon monolithic laser.

Abstract: Silicon (Si) monolithic lasers are key devices in large-scale, high-density photonic integrated circuits. Germanium (Ge) is promising as an active layer due to the complementary metal-oxide semiconductor process compatibility with Si. A net optical gain from Ge is essential to demonstrate lasing operation. We fabricated Ge waveguides and investigated the n-type doping effect on the net optical gain. The estimated net gain of the n-Ge waveguide increased from −2200 to −500/cm, namely reducing loss, under optically pumped condition.

Invited Article: Four-mode semiconductor optical amplifier

Abstract: We demonstrate the first few-mode semiconductor optical amplifier (FM SOA) that supports up to four waveguide modes. We show that each of the modes are confined to the waveguide, overlapping the quantum wells with approximately the same amount, leading to equalized gain for each of the four waveguide modes.

Tunable narrow linewidth AlGaInP semiconductor disk laser for Sr atom cooling applications.

Abstract: We report a frequency-stabilized semiconductor disk laser based on AlGaInP and operating at 689 nm, a wavelength of interest for atomic clocks based on strontium atoms. With a gain structure designed for emission at around 690 nm, more than 100 mW of output power are generated in single-frequency operation. We show that the source can be tuned over 8 nm with pm precision. By servo-locking the frequency to the side of fringe of a reference cavity, we demonstrate rms frequency noise of 5.2 kHz.

A Dual-Grating InGaAsP/InP DFB Laser Integrated With an SOA for THz Generation

Abstract: We report a dual-mode semiconductor laser that has two gratings with different periods below and above the active layer. A semiconductor optical amplifier (SOA), which is integrated with the dual-mode laser, plays an important role in balancing the optical power and reducing the linewidths of the emission modes. A stable two mode emission with the 13.92-nm spacing can be obtained over a wide range of distributed feedback and SOA injection currents. Compared with other types of dual-mode lasers, our device has the advantages of simple structure, compact size, and low fabrication cost.