Browsing by Subject "Semiconductor lasers"

Now showing 1 - 10 of 10

Open Access
915 nm pumped 1018 nm Yb-doped all-fiber high power fiber laser system
(Institute of Electrical and Electronics Engineers Inc., 2019) Midilli, Yakup; Efunbajo, O. Benjamin; Şimşek, Bartu; Ortaç, Bülend
Fibers lasers have attracted great attention in the last decades and the power scaling has reached tens of kW levels. Especially with the tandem pump configuration, pumping the active medium with a pump laser light instead of a diode laser, has made a breakthrough and so many research has been conducted about 1018 nm fiber laser systems [1]. Decreasing the quantum defect, the slope efficiency could be increased up to 90 % levels; on the other hand, due to the emission cross section of the Ytterbium (Yb), to operate the laser in the 1018 nm wavelength region is very challenging because of the presence of the ASE about the 1030 nm region. However, in the literature by using 976 nm pump diodes multi-hundred watts level 1018 nm fiber lasers could be demonstrated [2, 3].
Open Access
Facet cooling in high-power InGaAs/AlGaAs lasers
(Institute of Electrical and Electronics Engineers Inc., 2019) Arslan, Seval; Gündoğdu, Sinan; Demir, Abdullah; Aydınlı, A.
Several factors limit the reliable output power of a semiconductor laser under CW operation, such as carrier leakage, thermal effects, and catastrophic optical mirror damage (COMD). Ever higher operating powers may be possible if the COMD can be avoided. Despite exotic facet engineering and progress in non-absorbing mirrors, the temperature rise at the facets puts a strain on the long-term reliability of these diodes. Although thermoelectrically isolating the heat source away from the facets with non-injected windows helps lower the facet temperature, data suggests the farther the heat source is from the facets, the lower the temperature. In this letter, we show that longer non-injected sections lead to cooler windows and biasing this section to transparency eliminates the optical loss. We report on the facet temperature reduction that reaches below the bulk temperature in high power InGaAs/AlGaAs lasers under QCW operation with electrically isolated and biased windows. Acting as transparent optical interconnects, biased sections connect the active cavity to the facets. This approach can be applied to a wide range of semiconductor lasers to improve device reliability as well as enabling the monolithic integration of lasers in photonic integrated circuits.
Open Access
Green stimulated emission boosted by nonradiative resonant energy transfer from blue quantum dots
(American Chemical Society, 2016) Gao, Y.; Yu, G.; Wang Y.; Dang C.; Sum, T. C.; Sun, H.; Demir, Hilmi Volkan
Thanks to their tunability and versatility, the colloidal quantum dots (CQDs) made of II-VI semiconductor compound offer the potential to bridge the "green gap" in conventional semiconductors. However, when the CQDs are pumped to much higher initial excitonic states compared to their bandgap, multiexciton interaction is enhanced, leading to a much higher stimulated emission threshold. Here, to circumvent this drawback, for the first time, we show a fully colloidal gain in green enabled by a partially indirect pumping approach assisted by Förster resonance energy transfer process. By introducing the blue CQDs as exciton donors, the lasing threshold of the green CQDs, is reduced dramatically. The blue CQDs thus serve as an energy-transferring buffer medium to reduce excitation energy from pumping photons in a controlled way by injecting photoinduced excitons into green CQDs. Our newly developed colloidal pumping scheme could enable efficient CQD lasers of full visible colors by a single pump source and cascaded exciton transfer. This would potentially pave the way for an efficient multicolor laser for lighting and display applications.
Open Access
High-energy femtosecond photonic crystal fiber laser
(2010) Lecaplain, C.; Ortaç, B.; MacHinet G.; Boullet J.; Baumgart, M.; Schreiber, T.; Cormier, E.; Hideur, A.
We report the generation of high-energy high-peak power pulses in an all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. The self-starting chirped-pulse fiber oscillator delivers 11 W of average power at 15:5 MHz repetition rate, resulting in 710 nJ of pulse energy. The output pulses are dechirped outside the cavity from 7 ps to nearly transform-limited duration of 300 fs, leading to pulse peak powers as high as 1:9 MW. Numerical simulations reveal that pulse shaping is dominated by the amplitude modulation and spectral filtering provided by a resonant semiconductor saturable absorber. © 2010 Optical Society of America.
Open Access
Low-threshold optical gain and lasing of colloidal nanoplatelets
(IEEE, 2014-10) Keleştemur, Yusuf; Güzeltürk, Burak; Olutaş, Murat; Delikanlı, Savaş; Demir, Hilmi Volkan
Semiconductor nanocrystals, which are also known as colloidal quantum dots (CQDs), are highly attractive materials for high performance optoelectronic device applications such as lasers. With their size, shape and composition tunable electronic structure and optical properties, CQDs are highly desired for achieving full-color, temperature-insensitive, low-threshold and solution-processed lasers [1, 2]. However, due to their small size, they suffer from the nonradiative multiexciton Auger Recombination (AR), where energy of a bound electron-hole pair is transferred to a third particle of either an electron or a hole instead of radiative recombination. Therefore, CQDs having suppressed AR are strongly required for achieving high quality CQD-based lasers. To address this issue, CQDs having different size, shape and electronic structure have been synthesized and studied extensively [3-5]. Generally, suppression of AR and lower optical gain thresholds are achieved via reducing the wavefunction overlap of the electron and hole in a CQD. However, the separation of the electron and hole wavefunctions will dramatically decrease the oscillator strength and optical gain coefficient, which is highly critical for achieving high performance lasers. Therefore, colloidal materials with suppressed AR and high gain coefficients are highly welcomed. Here, we study optical gain performance of colloidal quantum wells [6] of CdSe-core and CdSe/CdS core/crown nanoplatelets (NPLs) that demonstrate remarkable optical properties with ultra-low threshold one- and two-photon optical pumping. As a result of their giant oscillator strength, superior optical gain and lasing performance are achieved from these colloidal NPLs with greatly enhanced gain coefficient [7]. © 2014 IEEE.
Open Access
Memory effect by charging of ultra‐small 2‐nm laser‐synthesized solution processable Si‐nanoparticles embedded in Si–Al2O3–SiO2 structure
(Wiley-VCH Verlag, 2015) El-Atab, N.; Rizk, A.; Tekcan, B.; Alkis, S.; Okyay, Ali Kemal; Nayfeh, A.
A memory structure containing ultra-small 2-nm laser-synthesized silicon nanoparticles is demonstrated. The Si-nanoparticles are embedded between an atomic layer deposited high-κ dielectric Al2O3 layer and a sputtered SiO2 layer. A memory effect due to charging of the Si nanoparticles is observed using high frequency C-V measurements. The shift of the threshold voltage obtained from the hysteresis measurements is around 3.3V at 10/-10V gate voltage sweeping. The analysis of the energy band diagram of the memory structure and the negative shift of the programmed C-V curve indicate that holes are tunneling from p-type Si via Fowler-Nordheim tunneling and are being trapped in the Si nanoparticles. In addition, the structures show good endurance characteristic (>105program/erase cycles) and long retention time (>10 years), which make them promising for applications in non-volatile memory devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Photoluminescence from a VCSEL structure a-SiNx:H microcavity
(IEEE, 1999) Serpengüzel, A.; Darici, Y.
Microcavity effects on the photoluminescence (PL) of porous Si has already been reported. Recently, we have observed visible and near infrared (IR) PL from hydrogenated amorphous Si nitride (a-SiNx:H) grown by low temperature PECVD. We have also reported the enhancement and inhibition of PL in an a-SiNx:H microcavity formed with metallic mirrors. The a-SiNx:H used in the microcavity was grown both with and without ammonia (NH/sub 3/). For the Si rich a-SiNx:H grown without NH/sub 3/, the PL is in the red-near IR. For the N rich a-SiNx:H grown with NH/sub 3/, the PL is in the blue-green. In this paper, we report on the bright and spectrally pure PL of a-SiNx:H in a VCSEL structure microcavity.
Open Access
Single-mode operation of electrically pumped edge-emitting lasers through cavity coupling of high order modes
(SPIE, 2022-03-04) Şeker, Enes; Şengül, Serdar; Dadashi, Khalil; Olyaeefar, Babak; Demir, Abdullah
The output power of a typical single-mode semiconductor laser is limited by its narrow waveguide width required to cut off high-order spatial modes. Conventional techniques rely on engineering the waveguide without introducing higherorder modes. In contrast, this work utilizes the concept of coupled-cavity (CC) structures. A single-mode lasing is achieved by employing a multi-mode and a neighboring single-mode waveguide. The CC approach is based on the resonant coupling of the high-order mode in the wide waveguide to the fundamental mode of a narrower lossy waveguide. First, geometrical dispersion of the CC lasers, such as their width, spacing, and their sensitivity to the resonance, was investigated. After optimizing the design, edge-emitting-lasers were fabricated using high-efficiency GaAs-based structures. Optical mode control and single-mode operation of the design are demonstrated through fundamental optical characterization measurements. The output power curves for the single and CC designs show similar slope efficiencies suggesting the proposed method as a promising approach towards high-power single lateral mode operation of edge-emitting lasers.
Open Access
Sub-80 fe dissipative soliton large-mode-area fiber laser
(2010) Baumgartl, M.; Ortaç, B.; Lecaplain, C.; Hideur, A.; Limpert J.; Tünnermann, A.
We report on high-energy ultrashort pulse generation from an all-normal-dispersion large-mode-area fiber laser by exploiting an efficient combination of nonlinear polarization evolution (NPE) and a semiconductor-based saturable absorber mode-locking mechanism. The watt-level laser directly emits chirped pulses with a duration of 1 ps and 163 nJ of pulse energy. These can be compressed to 77 fs, generating megawatt-level peak power. Intracavity dynamics are discussed by numerical simulation, and the intracavity pulse evolution reveals that NPE plays a key role in pulse shaping. © 2010 Optical Society of America.
Open Access
Ultralow-threshold up-converted lasing in oligofluorenes with tailored strong nonlinear absorption
(Royal Society of Chemistry, 2015) Guzelturk, B.; Kanibolotsky, A.L.; Orofino-Pena, C.; Laurand, N.; Dawson, M.D.; Skabara P.J.; Demir, Hilmi Volkan
Nonlinear optical response in organic semiconductors has been an attractive property for many practical applications. For frequency up-converted lasers, to date, conjugated polymers, fluorescent dyes and small organic molecules have been proposed but their performances have been severely limited due to the difficulty in simultaneously achieving strong nonlinear optical response and high performance optical gain. In this work, we show that structurally designed truxene-based star-shaped oligofluorenes exhibit strong structure-property relationships enabling enhanced nonlinear optical response with favorable optical gain performance. As the number of fluorene repeat units in each arm is increased from 3 to 6, these molecules demonstrate a two-photon absorption cross-section as high as 2200 GM, which is comparable to that of linear conjugated polymers. Tailored truxene oligomers with six fluorene units in each arm (T6) show two-photon absorption pumped amplified spontaneous emission with a threshold as low as 2.43 mJ cm-2, which is better than that of the lowest reported threshold in organic semiconductors. Furthermore, we show a frequency up-converted laser using the newly designed and synthesized star-shaped oligomer T6 with a threshold as low as 3.1 mJ cm-2, which is more than an order of magnitude lower than that of any conjugated polymer. Thus, these oligomers with enhanced nonlinear optical properties are highly attractive for bio-integrated applications such as photodynamic therapy and in vivo bio-sensing. © The Royal Society of Chemistry 2015.