J. P. Hohimer

Single‐frequency continuous‐wave operation of ring resonator diode lasers

We report continuous‐wave room‐temperature operation of a semiconductor ring resonator diode laser with a single Y‐junction outcoupling waveguide. This device with a 150 μm radius and 8‐μm‐wide etched‐rib waveguide has a threshold current of 72 mA and emits up to 1 mW of single‐frequency output. The side‐mode‐rejection ratio of this laser exceeds 22 dBm over a ≳50 mA current range corresponding to a stable operating mode of the laser. Studies of the emission behavior in this and other similar ring lasers suggest that the ring is lasing in ‘‘whispering gallery’’ modes, and also that the Y junction is affecting mode selection in the ring.

Single‐channel injection locking of a diode‐laser array with a cw dye laser

We report injection‐locking studies on a gain‐guided diode‐laser array using a single‐frequency cw tunable dye laser master oscillator. By injecting a single end element, both the spatial and spectral emission characteristics of the entire ten‐element array could be controlled. The injection‐locked array produced over 100 mW output in a single‐lobed far‐field beam ( 60 GHz wide. Furthermore, by varying the injection frequency, the far‐field emission angle of the array could be continuously scanned over several degrees at a rate of 2.3×10−2 deg/GHz.

Comprehensive modeling of diode arrays and broad-area devices with applications to lateral index tailoring

A numerical model for calculating the emission characteristics of diode laser arrays and broad-area devices operating well above threshold is discussed. This model uses the beam propagation technique for determining the field intensities for several lateral modes, while simultaneously and self-consistently solving for the two-dimensional current flow through the laser structure and the subsequent carrier diffusion in the active region. The active-region temperature distribution is also computed in a self-consistent manner, based on the flow of heat generated in the active region through the layered device structure to a constant-temperature heat sink. The model is applied by investigating the sensitivity of the lasing modes of a broad-area diode laser to variations in the lateral temperature distribution. >

Unidirectional operation in a semiconductor ring diode laser

We report the first demonstration of a unidirectional ring diode laser based on the use of an active crossover waveguide. The crossover waveguide introduces both a nonreciprocal loss and gain into the ring cavity to promote unidirectional lasing in the clockwise ring direction. Up to 95% of the continuous‐wave lasing output of 3.5 mW (at 150 mA ring current) is emitted from this preferred lasing direction. Unidirectional operation of the ring diode laser is also shown to increase the linearity of the light‐vs‐current curves, eliminating kinks otherwise occurring from gain competition in the ring cavity.

Passive mode locking of monolithic semiconductor ring lasers at 86 GHz

We report the development of monolithic passively mode‐locked semiconductor ring lasers. These direct‐waveguide‐coupled lasers with a ring radius of 150 μm emit a continuous train of 1.3 ps transform‐limited lasing pulses at 86 GHz repetition rate with a peak power of 10 mW/pulse at the laser output facet. We also observe, under certain conditions, the presence of a second pulse in the ring cavity doubling the pulse repetition rate to 172 GHz.

Modeling of injection-locking phenomena in diode-laser arrays

We report the first self-consistent numerical model to our knowledge of the injection-locking process in a gain-guided diode-laser array. This model reproduces two essential features of device behavior seen in recent experiments: (1) the single-lobed far-field output beam that results from injecting a single end-element of the array and (2) the linear dependence of the far-field beam angle on injection frequency. This angular scanning of the far-field beam angle can be understood on the basis of a simple plane-wave picture in which a change in the injection frequency leads to a tilt of the wave front in the diode-laser array in order to maintain the Fabry–Perot resonance condition.

Picogram detection of cesium in aqueous solution by nonflame atomic fluorescence spectroscopy with dye laser excitation

The determination of trace cesium in aqueous solution by nonflame atomic fluorescence spectroscopy using dye laser excitation is reported. Using a nonflame atomization system and direct‐line fluorescence detection, the limit of detection was found to be 1.2 pg in a 20‐pg/ml sample solution.

Unidirectional semiconductor ring lasers with racetrack cavities

We report the development of racetrack‐cavity semiconductor ring lasers that operate unidirectionally by means of an active crossover waveguide. These racetrack‐cavity lasers show improved performance over previous circular‐cavity unidirectional ring lasers with continuous‐wave single‐frequency output powers of ≥10 mW, and with up to 99% of the lasing output emitted from the preferred ring direction.

Improving the performance of semiconductor ring lasers by controlled reflection feedback

We report a tenfold increase in the lasing output of single‐output Y‐junction semiconductor ring lasers by reducing the end‐facet reflection feedback. Controlled reflection feedback is also shown to be a means for promoting unidirectional lasing in dual‐output ring lasers. Finally, we show that the counterpropagating ring modes are strongly coupled by gain competition.

All optical millimeter-wave electrical signal generation using an integrated mode-locked semiconductor ring laser and photodiode

The first monolithic photonic integrated circuit for all-optical generation of millimeter (mm)-wave electrical signals is reported. The design integrates a mode-locked semiconductor ring diode laser, an optical amplifier, and a high-speed photodetector into a single optical integrated circuit. Signal generation is demonstrated at frequencies of 30, 60, and 90 GHz.