Oleg V. Smolski

Volume-chirped Bragg gratings: monolithic components for stretching and compression of ultrashort laser pulses

Abstract. An innovative type of optical component—a volume Bragg grating—has recently become available commercially and has found wide applications in optics and photonics due to its unusually fine spectral and angular filtering capability. Reflecting volume Bragg gratings, with the grating period gradually changing along the beam propagation direction (chirped Bragg gratings—CBGs) provide stretching and recompression of ultrashort laser pulses. CBGs, being monolithic, are robust devices that have a footprint three orders of magnitude smaller than that of a conventional Treacy compressor. CBGs recorded in photo-thermo-refractive glass can be used in the spectral range from 0.8 to 2.5 μm with the diffraction efficiency exceeding 90%, and provide stretching up to 1 ns and compression down to 200 fs for pulses with energies and average powers exceeding 1 mJ and 250 W, respectively, while keeping the recompressed beam quality M2<1.4, and possibly as low as 1.1. This paper discusses fundamentals of stretching and compression by CBGs, the main parameters of the gratings including the CBG effects on the laser beam quality, and currently achievable CBG specifications.

High efficiency surface-emitting laser with subwavelength antireflection structure

We report on a high efficiency tapered grating surface-emitting laser with an antireflection-structured (ARS) substrate. A 64% improvement of the device efficiency is obtained by monolithic integration of a sawtooth-shaped ARS on the GaAs substrate. Slope efficiencies of 0.82 W/A were measured at 975 nm in pulse pumping and are mainly limited by free-carrier absorption in the n-doped GaAs substrate. A maximum peak power of 25 W was obtained without coating the devices cleaved facet. The symmetry of the near-field intensity profile along the grating coupler is improved by varying the grating duty cycle from 20% to 55%.

Integrated wavelength stabilization of in-plane semiconductor lasers by use of a dual- grating reflector

We summarize a novel integrated wavelength-stabilization scheme for broad stripe surface-emitting lasers. The method is based on two gratings fabricated on opposite sides of a device in which the first grating disperses light through the substrate to the opposite side, where the second surface has a feedback grating that operates under total internal reflection and in the Littrow condition to provide feedback into the gain medium. Experimental results have been obtained for both high power and a narrow linewidth, showing a CW slope of 0.85 W/A.

Crossed-beam superluminescent diode

We investigate a novel surface-emitting superluminescent diode configuration that uses two detuned grating outcouplers to suppress lasing. This device exhibits a shaped beam with a peak power of 1.5 W quasi-continuous wave with an 11 nm bandwidth centered on 970 nm.

Multiwavelength Blue Light Source Based on MgO : PPLN SHG Using Vertically Stacked Grating-Coupled Surface-Emitting Lasers

In this letter, we present the first experimental results of frequency doubling the output of vertically stacked grating coupled surface-emitting laser/dual-grating reflector devices with different emitting wavelengths. We used a multigrating 5% magnesium-oxide-doped periodically poled lithium niobate (MgO : PPLN) crystal as the nonlinear conversion medium. In pulse operation, 0.6 W of multiwavelength total second-harmonic peak power was obtained. The individual emitter output is focused into each channel of the crystal by diffractive beam shaping optical element array to minimize the footprint area of the whole setup.

High efficiency dual-wavelength surface-emitting laser incorporating integrated dual-grating reflector

We present a high-power monolithically integrated dual-wavelength emission source employing a dual-grating reflector. The basic structure and fabrication of this device are described. The operational characteristics of this device are presented, including a light-current characteristic slope of 0.86 W/A for dual-wavelength emission separated by 2 nm

Compact Vertically Stacked Master Oscillator Power Amplifier Based on Grating Coupled Laser Diodes

A new design of hybrid master oscillator power amplifier (MOPA) has been proposed and realized by vertically stacking laser diodes with optical coupling provided by identical in-plane integrated gratings. Low beam divergence, large emitting and input areas of the grating coupled devices simplify the assembling technique over the fabrication of MOPA devices based on edge-emitting laser diodes. The master oscillator also incorporates a dual-grating reflector providing a wavelength-selective feedback resulting in a narrow emission spectrum of 0.2 nm at a wavelength of 975.4 nm. The power amplifier is a tapered chip with two integrated grating couplers. The operational characteristics of the MOPA were evaluated in the pulse regime demonstrating an output peak power of 32 W with a total amplification factor of 9.3dB

Picosecond pulse generation using a saturable absorber section of grating-coupled surface-emitting laser

We report on a passively and hybridly mode-locked grating-coupled surface-emitting laser (GCSEL) using the unpumped section of the GCSEL as a saturable absorber. We obtain 8.8-ps full-width at half-maximum (FWHM) autocorrelation pulses in passive mode-locked operation and an FWHM pulse duration of 3.4 ps in hybrid mode-locked operation, which are the shortest pulses from a GCSEL external cavity. With hybrid mode-locking, a peak power of 0.26 W and a spectral bandwidth of 0.6 nm are obtained. These results demonstrate the potential of multisegment GCSELs in ultrashort pulse generation.

Blue Light Source Based on a ppKTP SHG Using a Grating-Coupled Laser Diode

In this letter, we present the first experimental results of a single-pass second-harmonic (SH) generation from a grating-coupled surface-emitting laser (GCSEL) with integrated dual-grating reflector. In pulse operation, the maximum SH peak power was obtained at 0.66 W, yielding a normalized conversion efficiency of 0.6times10-3 W-1. A high-level monolithical integration of the GCSEL device led to a compact blue light source, which was based on a frequency-doubled near-IR laser diode.

Master oscillator power amplifier 3D assemblies based on grating coupled laser diodes

We report on novel architectures of the hybrid master oscillator power amplifier (MOPA) assemblies incorporating vertically stacked surface-emitting laser diodes. Optical coupling between the MO and the PA is provided by nonresonant grating couplers integrated on both of the devices. The MOPA consists of a MO chip with dual grating reflector for single wavelength operation and a flared PA chip with two grating outcouplers. Optical peak power over 100W and spectral bandwidth of 0.2nm were achieved from the single MOPA while the MO operated in the gain-switching regime and the PA operated as a traveling wave amplifier. New designs of coherent MOPA arrays are proposed based on a phase locked MO bar and a single transverse mode PA bar. This MOPA assembly requires an optical cross-coupling between the bars provided by tilted gratings which have been developed and experimentally evaluated.