R. J. Helkey

Short pulse generation using multisegment mode-locked semiconductor lasers

Mode-locked semiconductor lasers which incorporate multiple contacting segments are found to give improved performance over single-segment designs. The functions of gain, saturable absorption, gain modulation, repetition rate tuning, wavelength tuning, and electrical pulse generation can be integrated on a single semiconductor chip. The optimization of the performance of mode-locked lasers in terms of material parameters, waveguiding parameters, electrical parasitics, and segment length is discussed experimentally and theoretically. >

ULTRAFAST DYNAMICS IN FIELD-ENHANCED SATURABLE ABSORBERS

Absorption recovery dynamics of GaAs/AlGaAs field‐enhanced waveguide saturable absorbers are studied by pump‐probe differential transmission measurements. We compare the response of bulk and single quantum well absorbers at different reverse bias levels and pump powers, and find an ultrafast transient in the response, followed by a slower rise before the final recovery. The absorption fully recovers after a few picoseconds, which is an important result for mode‐locked lasers.

Dynamic detuning in actively mode-locked semiconductor lasers

The authors describe a new limit on the achievable pulsewidth from actively mode-locked semiconductor lasers which is due to dynamic detuning. Dynamic detuning sets a higher limit on pulsewidth than the effects of finite gain bandwidth and dispersion, agreeing with experimental results which show pulsewidths much longer than expected if dynamic detuning is neglected. The dynamic detuning mechanism gives rise to the multiple-pulse output seen for all measurements of subpicosecond pulses and can lead to an unstable output waveform if a perfect antireflection coating is used. The analysis uses the traveling-wave rate equations to include a spatial variation in carrier and photon densities along the laser cavity and also includes the nonzero reflectivity on the antireflection-coated facet. The effects of phase at the antireflection-coated facet and dynamic carrier heating are included in the model. >

Suppression of multiple pulse formation in external-cavity mode-locked semiconductor lasers using intrawaveguide saturable absorbers

Imperfect antireflection coatings in external-cavity mode-locked semiconductor lasers can cause multiple output pulse generation. The incorporation of an intrawaveguide saturable absorber segment into the laser suppresses this problem. Single pulse outputs of less than 2.8 ps and 0.7 pJ of energy are obtained using such devices with both quantum well and bulk active regions.<<ETX>>

HIGH-POWER MODE-LOCKED SEMICONDUCTOR LASERS USING FLARED WAVEGUIDES

We describe the use of flared waveguide diode lasers for obtaining increased output power under mode‐locked operation. The flared waveguide expands the optical mode from a narrow region which gives a single lateral optical mode, to a wider multimode region for higher pulse saturation energy. Flared gain and flared absorber section geometry devices are compared to devices with conventional uniform waveguides. Using flared gain section devices, improvements in both pulse energy (6.8 pJ) and pulsewidth (3.3 ps) were measured compared to uniform waveguide devices. Peak powers of over 2 W are obtained, which, to our knowledge, is the highest peak power obtained directly from mode‐locked single stripe diode lasers.

Microwave and millimeter wave signal generation using mode-locked semiconductor lasers with intra-waveguide saturable absorbers

The authors consider electrical and optical signal generation techniques using passively and hybridly mode-locked semiconductor lasers with intra-waveguide saturable absorbers. Microwave and millimeter-wave signals can be generated using mode-locked semiconductor lasers with the intra-waveguide saturable absorbers. Monolithic and external cavity devices optimized for electrical and optical signal generation are discussed along with measurements of amplitude noise, phase noise, output power, and repetition rate tunability.<<ETX>>

Partial-integration method for analysis of mode-locked semiconductor lasers

A new, computationally efficient semiconductor-laser model has been developed for subpicosecond mode-locked laser analysis. It consists of a set of infinitesimal laser sections resulting from longitudinal integration of the laser rate equations. The model is used to predict the response of an actively mode-locked semiconductor laser for various pulsed-current drives.

Self-Mode-Locking of a Semiconductor Laser Using Positive Feedback

A new mode‐locking technique, self‐mode‐locking, is described which uses the detected optical pulses from the mode‐locked laser as the active driving source. This technique forms narrow‐width mode‐locked optical pulses at low repetition rates without the use of a microwave synthesizer.

Mode-locked multisegment resonant-optical-waveguide diode laser arrays

The first mode-locked operation of resonant optical waveguide (ROW) semiconductor laser arrays is reported. The well-behaved emission patterns of such arrays allow coupling to external cavities with efficiencies comparable to those achieved by using single-element lasers. Single- and multisegment lasers are employed to achieve active, passive, and hybrid mode-locking. The use of an arrayed gain region is effective in increasing the saturation energies of gain and absorber segments, resulting in high pulse energies. Pulses are generated that have well-suppressed secondary pulsations, with pulsewidths as short as 5.6 ps and peak powers of over 3 W in a collimated beam with a single main lobe.<<ETX>>

Actively mode-locked external-cavity semiconductor lasers with transform-limited single-pulse output.

We describe the use of split-contact semiconductor laser diodes to suppress multiple-pulsing phenomena in actively mode-locked external-cavity lasers. The laser-diode length is critical for the elimination of multiple-pulse output. With a grating installed in the external cavity, 11.5-ps pulses are generated that have a time–bandwidth product of only 0.30, an important property for use in soliton transmission systems. By using a broadband mirror in place of the grating, nearly transform-limited single pulses of 1.4-ps duration are generated at a 3-GHz repetition rate.