Tunable Vertical Cavity Research Articles

Design Optimization of Mechanical Support Structures in Tunable Vertical Cavity Surface Emitting Lasers

Design Optimization of Mechanical Support Structures in Tunable Vertical Cavity Surface Emitting Lasers

Temperature-Stabilized and Widely Tunable Vertical External Cavity Surface-Emitting Laser With a Simple Line Cavity

We designed and demonstrated a temperature-stable, wide-tuned, high-power Vertical External Cavity Surface-emitting Laser (VECSEL) with a simple linear cavity. The quantum well is optimized by using the commercial PICS3D software to obtain wide gain and good thermal performance. The curve of BF has also been optimized, and a birefringent filter (BF) with a thickness of 1mm is selected as the tuning element. Then, we obtained a continuously adjustable range cover from 1044.5 nm to 1092.1 nm, 8 W of output power, and temperature-stable VECSEL, which verifies the feasibility of the design. Based on the experimental results, we concluded that the gain intensity corresponding to the tuning range should be at least greater than 163 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">26</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> before the growth process ensures a wide tuning range. For the first time, to the best of our knowledge, we designed and obtained the tuning result of VECSEL in the linear cavity, and this is of great significance to the design of VECSEL with wide-tuning, high-power, and good temperature stability.

Coaxial laser absorption and optical emission spectroscopy of high-pressure aluminum monoxide.

This work advances laser absorption spectroscopy with measurements of aluminum monoxide (AlO) temperature and column density in extreme pressure (P > 60 bar) and temperature (T > 4000 K) environments. Measurements of the AlO A2Πi-X2Σ+ transition are made using a microelectromechanical system, tunable vertical cavity surface emitting laser (MEMS-VCSEL). Simultaneous emission measurements of the AlO B2Σ+-X2Σ+ transition are made along a line of sight that is coaxial with the laser absorption. Absorption temperature fits agree with emission spectra for a T = 3200 K, P = 9 bar case. In cases with T > 4000 K, P > 60 bar, absorption fits match the ambient temperature while emission fits over-estimate it, owing to high optical depths. These data juxtapose passive and active spectroscopic methods and demonstrate the versatility of AlO laser absorption in high-pressure and high-temperature environments where experimental data remain scarce, and engineering models will benefit from refined measurements.

Indirect stress and air-cavity displacement measurement of MEMS tunable VCSELs via micro-Raman and micro-photoluminescence spectroscopy

We employ micro-Raman spectroscopy to optically infer the stress experienced by the legs of a bridge-type microelectromechanical systems (MEMS) used in high contrast gratings tunable vertical cavity surface emitting lasers (VCSELs). We then employ micro-photoluminescence (PL) spectroscopy to indirectly measure the air cavity displacement of the same MEMS structure. Results from micro-Raman showed that electrostatically actuating the MEMS with a DC bias configuration yields increasing residual stress on the endpoints of the MEMS with values reaching up to 0.8 GPa. We simulated a finite element model via Comsol Multiphysics which agrees with the trend we observed based on our micro-Raman data. Our micro-PL spectroscopy showed that change in the air cavity of the VCSEL structure resulted in a change in the full width of the PL peak emitted by the layer consisting of four pairs of distributed Bragg reflectors. The change in the full width of the PL peak was due to the change in the optical cavity induced by displacing the MEMS via externally applied bias and agrees with our transfer matrix convolution simulation. These optical characterization tools can be used for failure analysis, MEMS design improvements, and monitoring of MEMS tunable VCSEL devices for mass production and manufacturing.

MEMS–VCSEL design method using a diffraction loss map

The micro–optical resonator of the microelectromechanical system(MEMS) tunable vertical cavity surface emitting laser(VCSEL), which is a gain–guided laser, consists of two mirrors fabricated on semiconductor chips of different materials. To understand the relationship between the curvature radius of the concave mirror and the diameter of the tunnel junction forming the active region, the diffraction loss map was obtained. The Fox–Li method was used with the integral kernel of the Rayleigh–Sommerfeld diffraction to simulate an optical resonator with a large Fresnel number. We derived the guideline for the actual bonding process of the different material chips by simulating with each parameter.

Liquid crystal tunable vertical cavity surface emission laser with inner cavity sub-wavelength grating

With the rapid development of information technology, a wavelength-tunable vertical cavity surface emitting laser (VCSEL) is urgently needed as an optical signal source in dense wavelength division multiplexing (DWDM). Liquid crystal tunable VCSEL realized by utilizing the birefringence characteristics of liquid crystal has the advantages of stable polarization, high reliability, continuous wavelength tuning. In this paper, a liquid crystal tunable VCSEL structure based on intracavity sub wavelength grating is designed, and the influence of liquid crystal layer and sub wavelength grating on the wavelength tuning characteristics of VCSEL are analyzed and studied in depth. The results show that the thickness of the liquid crystal layer in the tunable VCSEL structure not only affects the wavelength tuning range, but also determines the mode hopping in the tuning process. In addition, an effective refractive index antireflection layer is formed by designing the subwavelength grating structure, and the refractive index difference between the liquid crystal layer and the semiconductor layer is optimized to further improve the wavelength tuning range and tuning efficiency. When the center wavelength is 980 nm, the tuning range is increased by 42%, reaching 41 nm, and the wavelength tuning efficiency is increased by 41%. It provides a new method of designing the VCSEL laser with high beam quality and continuous wavelength tuning.

基于导模共振滤波器的波长可调谐垂直腔面发射激光器的研究

基于导模共振滤波器的波长可调谐垂直腔面发射激光器的研究

Frequency domain diffuse optical spectroscopy with a near-infrared tunable vertical cavity surface emitting laser.

We present an approach for performing frequency domain diffuse optical spectroscopy (fd-DOS) utilizing a near-infrared tunable vertical cavity surface emitting laser (VCSEL) that enables high spectral resolution optical sensing in a miniature format. The tunable VCSEL, designed specifically for deep tissue imaging and sensing, utilizes an electrothermally tunable microelectromechanical systems topside mirror to tune the laser cavity resonance. At room temperature, the laser is tunable across 14nm from 769 to 782nm with single mode CW output and a peak output power of 1.3mW. We show that the tunable VCSEL is suitable for use in fd-DOS by measuring the optical properties of a tissue-simulating phantom over the tunable range. Optical properties were recovered within 0.0006mm-1 (absorption) and 0.09mm-1 (reduced scattering) compared to a broadband fd-DOS reference system. Our results indicate that tunable VCSELs may be an attractive choice to enable high spectral resolution optical sensing in a wearable format.

Stress Optimization for a MEMS Multilayer Fixed-Fixed Beam

Micro-Electro Mechanical System (MEMS) based multi-layer fixed-fixed beams are used as suspensions to support the suspended membranes in tunable Fabry-Pérot Filters and tunable Vertical Cavity Surface Emitting Lasers. The electrical and optical performance of these devices depends highly on the parallelism of the suspensions holding the membrane in place. However, the residual stress in the suspension layer(s), upon relaxation, results in bending of the suspensions, which in turn results in displacement of the membrane. Therefore, the stress induced bending in the free-standing suspensions holding the membrane in place, must be minimized. A novel stress optimized multi-layer suspension system consisting of a fixed-fixed beam is designed in this work, whereby a tensile stressed material is sandwiched between two compressively stressed material films; such that the suspension layer system has an overall tensile film force, while an additional stress less layer is used to balance the clock-wise and counter clock-wise moments. The displacement of the central portion of the fixed-fixed beam is reduced from several micrometers to a mere 1.63nm using this technique.

A signal impairment-aware scheme for next-gen flexible spectrum in 10 Gb/s VCSEL metro-access optical fibre networks

We experimentally characterized and optimized link performance of a multi-node flexible spectrum network. The cheap and low power consuming and wavelength tunable vertical cavity surface-emitting lasers (VCSELs) have been used to create colourless and wavelength selective flexible transmitters to enable up to 10Gb/s per channel/wavelength signals. With a −3.8dBm VCSEL optical power and chromatic dispersion mitigation, a 25km multi-node network has been experimentally demonstrated with a transmission penalty range of 0.2–3.2dB. Moreover, an impairment-aware mathematical model has been created to predict signal continuity for crosstalk and dispersion penalties for a hop-to-hop signal transmission and a bit error-rate (BER) evaluation at the 10-9 threshold level. This study is vital for creating routing and network algorithms for the next-generation optical fibre networks.

亚波长光栅对微机电系统波长可调谐垂直腔面发射激光器的影响

亚波长光栅对微机电系统波长可调谐垂直腔面发射激光器的影响

Volumetric cutaneous microangiography of human skin in vivo by VCSEL swept-source optical coherence tomography

We demonstrate volumetric cutaneous microangiography of the human skin in vivo that utilises high-speed swept-source optical coherence tomography (SS-OCT). The swept source is based on a micro-electro-mechanical (MEMS)-tunable vertical cavity surface emission laser (VCSEL) that is advantageous in terms of long coherence length over and spectral bandwidth, which enables the visualisation of microstructures within a few mm from the skin surface. We show that the skin microvasculature can be delineated in 3D SS-OCT images using ultrahigh-sensitive optical microangiography (UHS-OMAG) with a correlation mapping mask, providing a contrast enhanced blood perfusion map with capillary flow sensitivity. 3D microangiograms of a healthy human finger are shown with distinct cutaneous vessel architectures from different dermal layers and even within hypodermis. These findings suggest that the OCT microangiography could be a beneficial biomedical assay to assess cutaneous vascular functions in clinic.

Space-division multiplexing optical coherence tomography

High speed, high resolution and high sensitivity are desirable for optical coherence tomography (OCT). Here, we demonstrate a space-division multiplexing (SDM) technology that translates long coherence length of a commercially available wavelength tunable laser into high OCT imaging speed. We achieved an effective 800,000 A-scans/s imaging speed using a 100,000 Hz tunable vertical cavity surface-emitting laser (VCSEL). A sensitivity of 94.6 dB and a roll-off of < 2 dB over ~30 mm imaging depth were measured from a single channel in the prototype SDM-OCT system. An axial resolution of ~11 μm in air (or ~8.3 μm in tissue) was achieved throughout the entire depth range. An in vivo, 3D SDM-OCT volume of an entire Drosophila larva consisting of 400 x 605 A-scans was acquired in 0.37 seconds. Synchronized cross-sectional OCT imaging of three different segments of a beating Drosophila larva heart is demonstrated. The SDM technology provides a new orthogonal dimension for further speed improvement for OCT with favorable cost scaling. SDM-OCT also preserves image resolution and allows synchronized cross-sectional and three-dimensional (3D) imaging of biological samples, enabling new biomedical applications.

Swept source optical coherence microscopy using a 1310 nm VCSEL light source

We demonstrate high speed, swept source optical coherence microscopy (OCM) using a MEMS tunable vertical cavity surface-emitting laser (VCSEL) light source. The light source had a sweep rate of 280 kHz, providing a bidirectional axial scan rate of 560 kHz. The sweep bandwidth was 117 nm centered at 1310 nm, corresponding to an axial resolution of 13.1 µm in air, corresponding to 8.1 µm (9.6 µm spectrally shaped) in tissue. Dispersion mismatch from different objectives was compensated numerically, enabling magnification and field of view to be easily changed. OCM images were acquired with transverse resolutions between 0.86 µm - 3.42 µm using interchangeable 40X, 20X and 10X objectives with ~600 µm x 600 µm, ~1 mm x 1 mm and ~2 mm x 2 mm field-of-view (FOV), respectively. Parasitic variations in path length with beam scanning were corrected numerically. These features enable swept source OCM to be integrated with a wide range of existing scanning microscopes. Large FOV mosaics were generated by serially acquiring adjacent overlapping microscopic fields and combining them in post-processing. Fresh human colon, thyroid and kidney specimens were imaged ex vivo and compared to matching histology sections, demonstrating the ability of OCM to image tissue specimens.

3–4.5 μm continuously tunable single mode VECSEL

We present continuously tunable Vertical External Cavity Surface Emitting Lasers (VECSEL) in the mid-infrared. The structure based on IV–VI semiconductors is epitaxially grown on a Si-substrates. The VECSEL emit one single mode, which is mode hop-free tunable over 50–100 nm around the center wavelength. In this work, two different devices are presented, emitting at 3.4 μm and 3.9 μm, respectively. The lasers operate near room temperature with thermoelectric stabilization. They are optically pumped, yielding an output power >10 mWp. The axial symmetric emission beam has a half divergence angle of <3.3∘.

Automatic identification of wavelength range of VCSEL-based gas sensor using ratios of gas absorption lines

In this paper a method for identifying the wavelength range of a tunable vertical cavity surface-emitting laser (VCSEL) is introduced. The measuring technology is wavelength modulation spectroscopy (WMS). The laser is tuned over its wavelength by applying a temperature ramp using the onboard Peltier element. During this ramp the 2f absorption lines are recorded. After finishing the temperature ramp and collecting the lines, a ratio-compare algorithm calculates the theoretical amplitudes of selected predefined lines. Then it compares the measured 2f line amplitudes iteratively with the theoretical ones. If the error of the ratios of the calculated and the measured lines is below a predefined limit, the searched lines and hence the emission wavelength are identified.

10 Gbit/s transmission over 50 km of SMF using MEMS tunable VCSEL

A widely tunable vertical cavity surface emitting laser (VCSEL) with an integrated mirror has been externally modulated in transmission experiments demonstrating error-free transmission over 50 km in singlemode optical fibre at 10 Gbit/s over a 30 nm tuning range. A penalty of 0.2 dB was measured when compared with a tunable external cavity laser which was due to residual membrane movement in the unpackaged VCSEL.

Tunable Vertical-Cavity Surface-Emitting Lasers Integrated with Two Wafers

A novel two-wafer concept for micro-electro-mechanically tunable vertical cavity surface emitting lasers (VCSELs) is presented. The VCSEL is composed by two wafers: one micro-electromechanical-system membrane wafer with four arms to adjust the cavity length through electrostatic actuation and a “half-VCSEL" wafer consisting of a fixed bottom mirror and an amplifying active region. The measurement results of the electricity pumped tunable VCSEL with more than 9 mW output power at room temperature over the tuning range prove the feasibility of the proposition.

Micro-nano-optical machine system tunable wavelength vertical cavity surface emitting lasers with wide tunable range

The stucture of tunable vertical cavity surface emitting laser is obtained based on the micro-nano-mechanical technology. The DBR reflector with Al0.8Ga0.2As sacrificial layer consisted the micro-nano reflector systerm, which combines with the multi-well active region coupled structure. In addition, the structure of micro-nano-optical machine system is not only the DBR reflector, but also serves to tune the wavelength of lasing by the electrostatic force. Good laser characteristics are obtained with continuous tuning ranges over 18.8 nm near 968.8 to 950 nm for 0—7 V tuning bias.

Continuously tunable singlemode VECSEL at 3.3 [micro sign]m wavelength for spectroscopy

A singlemode tunable vertical external cavity surface emitting laser (VECSEL) has been realised. The VECSEL can be tuned continuously over more than 80 nm from ∼3.22 to 3.3 µm wavelength. Tuning is performed by changing the cavity length with a piezoelectric driver. Covering this wavelength range allows various potential applications, especially for gas spectroscopy of organic compounds. The VECSEL is optically pumped, and emits a maximum output power of 20 mWp when cooled with a Peltier element to −20°C. The active medium consist of PbSe quantum wells embedded in Pb1−xSrxSe (x=0.08) barrier layers and is grown on a Si-substrate.