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 M 2 <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.
We present a method of designing a grating outcoupler to obtain the desired two dimensional-intensity profile and improved field distribution of the optical beam emitted by a grating coupled surface-emitting laser. The method is based on variation of the periodicity, the duty cycle, and the groove tilt angle of the grating. Grating design involves numerical analysis of the optical field propagated through the grating by applying the rigorous coupled wave approach method. Experimental evaluation of the designed grating components was done by fabrication and testing the broad area semiconductor lasers with the monolithically integrated grating outcouplers. We present a grating design that provides the spreading of a single optical output into multibeams at different outcoupling angles in the emitting plane. We also present an approach to provide uniform optical intensity profile from the grating outcoupler based on varying duty cycle.
KEYWORDS: Optical design, Etching, Near field optics, Waveguides, Wave propagation, Semiconductor lasers, Beam shaping, Broad area laser diodes, Optical fabrication equipment, Near field
We present a method of designing a grating outcoupler to obtain the desired 1D- and 2D-intensity profile of the optical
beam emitted by a grating coupled surface emitting laser. The method is based on variation of the periodicity, duty
cycle, and the groove tilt angle of the grating. Grating design involves numerical analysis of the optical field propagated
through the grating, by applying the Rigorous Coupled Wave Approach method. Experimental evaluation of the
designed grating components was done by fabrication and testing the broad area semiconductor lasers with the
monolithically integrated grating outcouplers. We also present a grating design which provides the spreading of a single
optical output into multi-beams at different outcoupling angles in the emitting plane.
Second harmonic generation (SHG) from near infrared (IR) diode lasers is an attractive solution for blue-light sources with high peak power and narrow linewidth. IR sources based on broad stripe devices with narrow linewidth makes it possible to achieve a wide range of wavelengths throughout the blue region. This paper summarizes recent results utilizing a configuration of external dual grating reflector coupled surface emitting laser array for blue light generation.
Recent achievements in second harmonic generation (SHG) from mid-IR diode lasers have made the realization of
compact blue-light sources with high power a reality. Moreover, narrow linewidth control of IR sources based on broad
stripe high power devices makes it possible to achieve a wide range of wavelengths throughout the blue region. This
paper summarizes recent results utilizing a novel Master Oscillator Power Amplifier configuration for blue light
generation.
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.
A dual grating reflector is a scheme for wavelength stabilization of laser diodes. The fabrication of a dual grating reflector involves the fabrication of a grating coupler on the p-side of a laser diode and a feedback grating on the n-side of the same device. The basic theory of the dual grating reflector is presented, along with the methods used to determine the required tolerances for near optimum performance. The fabrication processes used to obtain the required tolerances needed for a dual grating reflector are presented.
A hybridly modelocked grating-coupled surface-emitting laser (GCSEL) with pulse duration 2.8psec at 980nm is demonstrated. The unpumped grating section of the GCSEL is used as a saturable absorber to generate pulses with a 535MHz repetition rate. The peak power of 0.31W and a spectral bandwidth of 1.1nm are obtained.
We demonstrate an external cavity, active mode-locked GCSEL. The optical pulse duration from the actively mode-locked oscillator is 22.6ps and a 3 dB optical spectrum bandwidth is 0.07nm at 976nm. The average power from the oscillator is 0.72mW and its peak power is 108mW. The amplification characteristics of a GCSOA, optically injected with a continuously operated external cavity GCSEL, are also demonstrated. Despite the observation of lasing from the device, injection locking can be performed using an external source. At 4A peak current injection, 375mW output is achieved with 12mW injection.
We have demonstrated a 60 nm-tunable, 160 psec-width, optical pulses from a 980 nm Grating Coupled Surface Emitting Laser (GCSEL) in an external cavity under nanosecond pump pulses. GCSEL is in-plane laser monolithically integrated with grating outcoupler. The grating was detuned from second order Bragg condition and it served as an efficient interface between planar waveguide and free space. Wavelength tuning was simply achieved by tilting an external flat mirror provided wavelength selective feedback to the GCSEL chip. Gain switched pulses with wavelength linewidth less than 0.1 nm and peak power of 200 mW have been obtained. In our experiments we measured a shortest optical pulses by reducing a distance between external mirror and laser diode chip. This corresponded with decreasing the effective laser cavity length and the cavity round-trip time as well.
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