There has been increased interest in vertical-cavity surface-emitting lasers (VCSELs) for illumination and sensing in the consumer market, especially for 3D sensing ("gesture recognition") and 3D image capture. For these applications, the typical wavelength range of interest is 830 similar to 950nm and power levels vary from a few milli-Watts to several Watts. The devices are operated in short pulse mode (a few nano-seconds) with fast rise and fall times for time-of-flight applications (ToF), or in CW/quasi-CW for structured light applications. In VCSELs, the narrow spectrum and its low temperature dependence allows the use of narrower filters and therefore better signal-to-noise performance, especially for outdoor applications. In portable devices (mobile devices, wearable devices, laptops etc.) the size of the illumination module (VCSEL and optics) is a primary consideration. VCSELs offer a unique benefit compared to other laser sources in that they are "surface-mountable" and can be easily integrated along with other electronics components on a printed circuit board (PCB). A critical concern is the power-conversion efficiency (PCE) of the illumination source operating at high temperatures (> 50 deg C). We report on various VCSEL based devices and diffuser-integrated modules with high efficiency at high temperatures. Over 40% PCE was achieved in broad temperature range of 0-70 degrees C for either low power single devices or high power VCSEL arrays, with subnano- second rise and fall time. These high power VCSEL arrays show excellent reliability, with extracted mean-time-to-failure (MTTF) of over 500 years at 60 degrees C ambient temperature and 8W peak output.

High power 808 nm vertical-cavity surface-emitting laser (VCSEL) arrays were used to end-pump diffusion-bonded composite laser rods consisting of an Nd:YAG gain medium and a Cr:YAG saturable absorber. The laser pulse energy, q-switch delay time, and optical efficiency of a passively Q-switched monolithic solid state laser in a compact rugged package were measured as a function of VCSEL power for various heatsink temperatures. Up to 19 mJ laser pulse energy was produced with 13% optical efficiency.

Vertical-cavity surface-emitting lasers (VCSELs) are attractive for many pumping and direct-diode applications due to combined advantages in low cost, high reliability, narrow and thermally stable spectrum, high power scalability, and easy system integration, etc. We report our progress on electrically pumped, GaAs-based, high- power high-brightness VCSELs and 2D arrays in the infrared wavelength range. At 976nm, over 5.5W peak CW output and 60% peak power conversion efficiency (PCE) were demonstrated with 225um oxide-confined device. For 5x5mm arrays, peak PCE of 54% and peak power of >450W at 976nm, peak PCE of 46% and peak power of >110W at 808nm were achieved respectively under QCW conditions. External cavity configuration was used to improve the VCSEL brightness. Single mode output of 280mW and 37% PCE were realized from 80um device. For large 325um device, we obtained single mode (M2=1.1) CW output of 2.1W, corresponding to a brightness of 160MW/cm2*sr. Three major areas of applications using such VCSELs are discussed: 1. High brightness fiber output; 2. High power, high efficiency green lasers from 2nd harmonic generation. 3.34W green output with 21.2% PCE were achieved; 3. Pumping solid state lasers for high energy pulse generation. We have demonstrated Q-switched pulses with 16.1mJ at 1064nm and 4.9mJ with 1W average power at 473nm.

We report on a Q-switched VCSEL side-pumped 946 nm Nd: YAG laser that produces high average power blue light with high pulse energy after frequency doubling in BBO. The gain medium was water cooled and symmetrically pumped by three 1 kW 808 nm VCSEL pump modules. More than 1 W blue output was achieved at 210 Hz with 4.9 mJ pulse energy and at 340 Hz with 3.2 mJ pulse energy, with 42% and 36% second harmonic conversion efficiency respectively. Higher pulse energy was obtained at lower repetition frequencies, up to 9.3 mJ at 70 Hz with 52% conversion efficiency.

We have achieved a 21.2% wall-plug efficiency green laser at 532 nm based on an electrically pumped vertical externalcavity surface emitting laser (VECSEL) through intracavity second harmonic generation. The continuous-wave green output power was 3.34 W. The VECSEL gain device is cooled by using a thermoelectric cooler, which can greatly benefit packaging. Both power and efficiency can be further scaled up by optimizing external-cavity design and improving the performance of VECSEL gain device.

We have demonstrated a compact, 4.7 W green laser based on an electrically pumped vertical external-cavity surface emitting laser through intracavity frequency doubling. The overall wall-plug efficiency (electrical to green) was 18.3%. The power fluctuations were measured to be ±1.4% over a 2 h time period.

High power, kW-class, 808 nm pump modules based on the vertical-cavity surface-emitting laser (VCSEL) technology were developed for side-pumping of solid-state lasers. Two 1.2 kW VCSEL pump modules were implemented in a dual side-pumped Q-switched Nd:YAG laser operating at 946 nm. The laser output was frequency doubled in a BBO crystal to produce pulsed blue light. With 125 μs pump pulses at a 300 Hz repetition rate 6.1 W QCW 946 nm laser power was produced. The laser power was limited by thermal lensing in the Nd:YAG rod.

Dissipative solitons from an all-fiber Thulium-doped fiber (TDF) ring oscillator are generated by using optically deposited single-wall carbon nanotubes as the saturable absorber (SA) and high numerical aperture (NA) fiber of measured normal dispersion is introduced to produce large net normal dispersion at 1.9 m. (C) 2013 Optical Society of America

A compact UV pulsed laser pumped by high-power two-dimensional arrays of vertical-cavity surface-emitting lasers (VCSELs) was presented. A passively Q-switched 1064-nm Nd:YAG laser was side-pumped by kW-class 808-nm VCSEL pump modules and the output pulses were frequency quadrupled to 266-nm. 10-ns, 0.68-mJ UV pulsed output was obtained at 1.33k-Hz repetition rate. The average UV power is > 0.9-W. This VCSEL pumped high power UV laser source provides a reliable, low-cost and low-profile solution for military and commercial applications including remote sensing, laser processing and spectroscopy.

This Letter presents distributed Bragg reflector (DBR) fiber lasers for high-temperature operation at 750°C. Thermally regenerated fiber gratings were used as the feedback elements to construct an erbium-doped DBR fiber laser. The output power of the fiber laser can reach 1 mW at all operating temperatures. The output power fluctuation tested at 750°C was 1.06% over a period of 7 hours. The thermal regeneration grating fabrication process opens new possibilities to design and to implement fiber laser sensors for extreme environments.

An ultrafast thulium-doped fiber laser with large net normal dispersion has been developed to produce dissipative soliton and noise-like outputs at 1.9 μm. The mode-locked operation was enabled by using single-wall carbon nanotubes as saturable absorber for all-fiber configuration. Dissipative soliton in normal dispersion produced by the fiber laser oscillator was centered at 1947 nm with 4.1-nm FWHM bandwidth and 0.45 nJ/pulse. The output dissipative soliton pulses were compressed to 2.3 ps outside the laser cavity.

An all-fiber passively mode-locked thulium-doped fiber ring oscillator is constructed using optically deposited few layer graphene micro-sheets as the saturable absorber (SA). The mode-lock operation was achieved by 130-mW pump power at 1.5-μm. The fiber oscillator produces 2.1-ps soliton pulse output with 80-pJ per pulse energy. The 3-dB bandwidth of the laser output was measured as 2.2-nm. The RF signal-to-noise ratio of 50-dB and sub 20-Hz 3-dB bandwidth of the laser output confirms the stable laser operation with low time jittering. This paper shows that graphene can be an effective saturable absorber for the development of mid-IR fiber mode-locked laser.

We present thermally regenerated fiber Bragg gratings in air-hole microstructured fibers for high-temperature, hydrostatic pressure measurements. High-temperature stable gratings were regenerated during an 800 °C annealing process from hydrogen-loaded Type I seed gratings. The wavelength shifts and separation of grating peaks were studied as functions of external hydrostatic pressure from 15 to 2400 psi, and temperature from 24 °C to 800 °C. This Letter demonstrates a multiplexible pressure and temperature sensor technology for high-temperature environments using a single optical fiber feedthrough.

This letter reports a fully distributed hydrogen sensing technique using Rayleigh backscattering in palladium (Pd) and copper (Cu) coated optical fiber. The local in-fiber strain changes due to Pd hydrogen absorptions are interrogated spatially resolved optical frequency domain reflectrometry measurements of the Rayleigh signals. Electrical power is used to induce heating in the Pd coating, which accelerates both the hydrogen response and the sensor recycling. This technique promises an inexpensive and truly distributed fiber solution for continuous hydrogen leak detection with centimeter spatial resolution at room and low temperatures.

A graphene-based saturable absorber was fabricated by optically depositing layers of graphene onto the end tip of single mode fiber, and it was used to passively Q-switch thulium-doped fiber laser at 2 μm pumped by EDFA. The spectrum of the graphene Q-switched thulium-doped fiber laser and the relationship between the output power, repetition rate and pump strength are studied and presented.

We present a continuous liquid level sensing system for both room temperature and cryogenic fluids with millimeter spatial resolution. Change of in-fiber Rayleigh backscattering signal from the distinct thermal response of the heated sensing fiber in liquid and in air were interrogated and spatially resolved using the optical frequency domain reflectometry. Both electrical and optical heating techniques were investigated for cryogenic liquid applications at 4 K, 77 K, and the room temperature. The successful combination of self-heated fiber and wavelength-swept Rayleigh scattering interferometry provides, for the first time to our best knowledge, a truly distributed fuel gauge with high spatial resolution for cryogenic fuel storage, transportation, and management on ground and in space.

We report distributed sensing with active control using self-heated optical fibers. The heat loss profile along the fiber is spatially interrogated with OFDR Rayleigh backscattering signals to perform gas flow and liquid level sensing measurements.

An optical hot-wire flow sensing grid is presented using a single piece of self-heated optical fiber to perform distributed flow measurement.The flow-induced temperature loss profiles along the fiber are interrogated by the in-fiber Rayleigh backscattering, and spatially resolved in millimeter resolution using optical frequency domain reflectometry (OFDR).The flow rate, position, and flow direction are retrieved simultaneously.Both electrical and optical on-fiber heating were demonstrated to suit different flow sensing applications.