Control of light polarization using optically spin-injected vertical external cavity surface emitting lasers

<sec> The vertical external cavity surface emitting laser (VECSEL) is one of the hottest research fields of semiconductor lasers, due to its high power and good beam quality. However, there are few reports about how to systematically design the active region of VECSEL. In this paper, the gain design of quantum wells, which are the most important region within the VECSEL, is carried out. </sec><sec> To achieve low power consumption under high temperature condition, epitaxial structure of the VECSEL is optimized by using the commercial software PICS3D. Firstly, the relationship between the structure of quantum well and the gain is simulated by the <i>k</i>·<i>p</i> method. Then, the gain spectra of quantum wells at different carrier densities and temperatures are compared with each other, and the optimal composition and thickness of quantum well are thus determined. The temperature drift coefficient is 0.36 nm/K, obtained by simulating the drift of the gain peak wavelength at the working temperature. Finally, the gain spectra of quantum wells with five different barriers are compared with each other. The slight blue shift of the gain peak in the quantum well with five different barriers accommodates the different emission thermal drifts of the quantum well at high temperature operation. With the GaAsP barriers on both sides of quantum well the gain characteristics of quantum wells can be improved efficiently. </sec><sec> The designed structure is deposited by the MOCVD system. According to the reflection spectrum of the gain chip, measured by ellipsometer, the stop-band over 100 nm is centered at the about 970 nm wavelength, confirming accurate growth of the VECSEL. The 808 nm pump laser is focused on the surface of VECSEL chip at an incident angle from 30° to 50°. The VECSEL light-light characteristics are tested under the output coupling mirror with different reflectivity. The output power of VECSEL with a 97.7% reflectance output coupling mirror reaches 9.82 W at the pumping power of 35 W, without saturating the power curve. By using the external mirrors with different reflectivity, there appears the wavelength shift with the pumping power changing from 0.216 nm/W to 0.16 nm/W. Thus, the internal heating effects are different for VECSEL with different mirrors. The divergence angles at two orthogonal directions are 9.2° and 9.0°, respectively. And the circle profile of optical field shows good symmetry. </sec>

We report on the design, fabrication and optical performance of gain mirrors in single crystal diamond substrates for vertical external cavity surface emitting lasers (VECSELs). VECSELs have gained attention recently due to their potential for high emission power in single mode with low beam divergence, yet their maximum output power remains typically limited due to thermal roll-over resulting from insufficient heat dissipation. In order to increase the heat transfer, we exploit the excellent thermal conductivity of single crystal diamond, which is assembled in direct contact with the active structure. The optical cavity is hereby defined by an output coupler and a high reflection grating structure etched into the diamond surface. We here present the design and microfabrication of a diffraction grating that was optimized to reflect light into the 0th order, therefore combining the role of a gain mirror and a heatsink at the same time. Our process involved metal mask deposition onto the diamond surface, e-beam lithography and reactive ion etching. Characterization showed reflection above 95% at a center wavelength of 1550 nm, potentially allowing the integration of the diamond mirror into a vertical external cavity surface emitting laser.

Laser technology is finding applications in areas such as high resolution spectroscopy, radar-lidar, velocimetry, or atomic clock where highly coherent tunable high power light sources are required. The Vertical External Cavity Surface Emitting Laser (VECSEL) technology [1] has been identified for years as a good candidate to reach high power, high coherence and broad tunability while covering a wide emission wavelength range exploiting III-V semiconductor technologies. Offering such performances in the Near- and Middle-IR range, GaAs- and Sb-based VECSEL technologies seem to be a well suited path to meet the required specifications of demanding applications. Built up in this field, our expertise allows the realization of compact and low power consumption marketable products, with performances that do not exist on the market today in the 0.8-1.1 μm and 2-2.5 μm spectral range. Here we demonstrate highly coherent broadly tunable single frequency laser micro-chip, intracavity element free, based on a patented VECSEL technology, integrated into a compact module with driving electronics. VECSEL devices emitting in the Near and Middle-IR developed in the frame of this work [2] exhibit exciting features compared to diode-pumped solid-state lasers and DFB diode lasers; they combine high power (>100mW) high temporal coherence together with a low divergence diffraction limited TEM00 beam. They exhibit a class-A dynamics with a Relative Intensity Noise as low as -140dB/Hz and at shot noise level reached above 200MHz RF frequency (up to 160GHz), a free running narrow linewidth at sub MHz level (fundamental limit at Hz level) with high spectral purity (SMSR >55dB), a linear polarization (>50dB suppression ratio), and broadband continuous tunability greater than 400GHz ( Those devices surpass the state of the art commercial technologies thanks to a combination of power-coherence-wavelength tunability performances and integration.

High power, tunable two color lasers are highly suitable for the new wavelengths generation thanks to various nonlinear conversion phenomena. Vertical external cavity surface emitting lasers (VECSELs) are of special interest due to the access to the high intracavity circulating power and wavelength control. We report a novel VECSEL cavity design, which can deliver high power, tunable two color emission. The VECSEL setup is based on a two-chip T-shape cavity configuration which utilizes a polarizing beam splitter to combine two VECSEL cavities. This allows for two-color orthogonally polarized high-power collinear outputs. The two color emission of this kind is ideal for type II nonlinear frequency conversion. A high-Q folded T-cavity is utilized to achieve the combined beams circulating power in excess of 175 W. Intracavity birefringent filters are used to facilitate tunability and wavelength separation between two colors. A configuration of this type is used for high power intracavity type II sum frequency generation, which resulted in tunable blue emission with above 750 mW output, and in the second case a tunable green emission with more than 1.4 W output was obtained. A signal around 1 THz was achieved through type II difference frequency generation in tilted periodically poled lithium niobate. Lastly, a silver thiogallate was utilized to generate mid-IR wavelength around 5.36 μm through type II difference frequency generation.

We developed and tested a miniature optical bench to implement a cesium CPT clock based on a Vertical External Cavity Surface Emitting Laser (VECSEL) that provides two orthogonally polarized frequencies separated by a difference of 9.2 GHz. This work presents characterizations of the miniature optical power stabilization set-up as well as preliminary investigations of the VECSEL properties.

We report on a picosecond pulse source delivering near transform-limited pulses in the 1.55 µm wavelength region, based on an optically pumped InP-based mode locked Vertical External Cavity Surface Emitting Laser (VECSEL). The cavity combines two semiconductor elements, a gain structure which includes six strained InGaAlAs quantum wells and a hybrid metal-metamorphic Bragg bottom mirror bonded onto a CVD diamond substrate, and a single quantum well GaInNAs SEmiconductor Saturable Absorber Mirror (SESAM). The laser operates at a repetition frequency of 2 GHz and emits near-transform-limited 1.7 ps pulses with an average output power of 15 mW at room temperature, using 1.7 W pump power at 980 nm. The RF line width of the free running laser has been measured to be less than 1 kHz.

We report a passively mode-locked vertical external cavity surface emitting laser (VECSEL) producing 400 fs pulses with 4.35 kW peak power. The average output power was 3.3 W and the VECSEL had a repetition rate of 1.67 GHz at a center wavelength of 1013 nm. A near-antiresonant, substrate-removed, 10 quantum well (QW) gain structure designed to enable femtosecond pulse operation is used. A SESAM which uses fast carrier recombination at the semiconductor surface and the optical Stark effect enables passive mode-locking. When 1 W of the VECSEL output is launched into a 2 m long photonic crystal fiber (PCF) with a 2.2 µm core, a supercontinuum spanning 175 nm, with average power 0.5 W is produced.

Lead-chalcogenide Vertical External Cavity Surface Emitting Lasers (VECSEL) employing PbSe, PbTe and PbSnTe as active layers have recently been described [1–4]. Here we present PbSe quantum well (QW) VECSEL covering a wavelength-range from 3.3 to 5.0 µm. Several PbSe QW structures were made, which differ in: • PbEuSe or PbSrSe host material • λ or λ/2 thick active layer (λ is the optical thickness) • different numbers of QW

Investigation of thermal management in optically pumped, antimonide VECSELs

Recent developments in technology and active layer design for the realization of high-power (GaIn)As-based VECSEL, applying a specific MOVPE growth process, with cw output powers in excess of 100 W will be presented and discussed.

Summary form only given. Vertical cavity surface emitting lasers (VCSELs) are efficient sources of red and near IR light that often produce near-Gaussian spatial profiles. Optically-pumped vertical, external cavity surface emitting lasers (VECSELs) have been shown to be efficient sources of higher power (>100 mW) near IR light with near-Gaussian spatial profiles. VECSELs replace the upper distributed Bragg reflector (DBR) with an external, spherical mirror that is used for output coupling and for controlling the transverse mode of the laser. VECSEL output couplers, like those of VCSELs, can have very high reflectivity. The low output coupling produces high intracavity power ideal for intra-cavity frequency doubling. We have obtained blue light with a near Gaussian spatial profile from the intracavity doubled VECSEL.

Self-assembled quantum dots (QDs) as active media for ultrafast semiconductor disk laser offer large gain bandwidths, fast gain dynamics, and high temperature stability. We report on the shortest pulses and the highest pulse peak power from an optically pumped vertical external cavity surface emitting laser (VECSEL) based on QDs and optimized for passive modelocking at 1035 nm using a semiconductor saturable absorber mirror. We demonstrate 216-fs pulses with an average output power of 269 mW at a pulse repetition rate of 2.77 GHz and 396 W peak power. At a lower pulse repetition rate of 1.67 GHz, we achieve 193-fs pulses with 112 mW of average output power. We remark a higher optical-to-optical pump efficiency compared to our previous QW VECSELs in the sub-300-fs regime. This is further confirmed by a comparative analysis of the saturation recovery which reveals longer carrier lifetimes for the QD compared to QW VECSELs.

We demonstrate a VECSEL (vertical external cavity surface emitting laser) based degenerate source with an adjustable degree of spatial coherence that is electrically pumped, mechanically compact and supports continuous-wave emission. The laser operation can be switched between a large number of mutually incoherent spatial modes and few-mode operation at little power loss. This technology allows multimodality imaging, where low spatial coherence illumination is used for traditional high-speed video-microscopy and high spatial coherence illumination is used to extract dynamic information of flow processes. The initial demonstration is performed on imaging embryo heart function in Xenopus, which is an important animal model for human heart disease.

The CO2 absorption spectrum in the 2.3 µm transparency window by high sensitivity CRDS: (I) Rovibrational lines

We present an experimental and theoretical study of the intensity noise correlation between the two orthogonally polarized modes in a dual frequency Vertical External Cavity Surface Emitting Laser (VECSEL). The dependence of the noise correlation spectra on the non-linear coupling between the two orthogonally polarized modes is put into evidence. Our results show that for small coupling the noise correlation amplitude and phase spectra remain nearly flat (around -6 dB and 0° respectively) within the frequency range of our interest (from 100 kHz to 100 MHz). But for higher values of the coupling constant the low frequency behaviors (below 1-2 MHz) of the correlation amplitude and phase spectra are drastically changed, whereas above this cut-off frequency (1-2 MHz) the correlation spectra are almost independent of coupling strength. The theoretical model is based on the assumptions that the only source of noise in the frequency range of our interest for the two modes are pump noises, which are white noises of equal amplitude but partially correlated.