Thomas Schrans

Broad-band wavelength tunable picosecond pulses from CW passively mode-locked two-section multiple quantum-well lasers

Wavelength tunable CW (continuous-wave) passive mode-locking of a two-section quantum-well laser coupled to an external cavity is demonstrated. A tuning range of 26 nm is achieved with typical autocorrelation full widths at half maximum of 4.5 ps. The pulses are not transform limited, having a typical time-bandwidth product of 2.5.<<ETX>>

Supermodes of high-repetition-rate passively mode-locked semiconductor lasers

We present a steady-state analysis of high-repetition-rate passively mode-locked semiconductor lasers. The analysis includes effects of amplitude-to-phase coupling in both gain and absorber sections. A many-mode eigenvalue approach is presented to obtain supermode solutions. Using a nearest-neighbor mode coupling approximation, chirp-free pulse generation and electrically chirp-controlled operation are explained for the first time. The presence of a nonzero alpha parameter is found to change the symmetry of the supermode and significantly reduce the mode-locking range over which the lowest order supermode remains the minimum gain solution. An increase in absorber strength tends to lead to downchirped pulses. The effects of individual laser parameters are considered, and agreement with recent experimental results is discussed.

Semiconductor lasers with uniform longitudinal intensity distribution

Power‐dependent nonuniform longitudinal intensity distribution leading to spectral and spatial instabilities is a major problem in semiconductor lasers. It is shown theoretically that a proper choice of the longitudinal distribution of the gain as well as that of the magnitude of the grating coupling coefficient will lead to a uniform intensity distribution in distributed feedback lasers. We also show that the widely used phase, rather than magnitude, control of the coupling coefficient cannot lead to a uniform intensity distribution when the facet reflectivities are zero.

Timing jitter and pulse energy fluctuations in a passively mode‐locked two‐section quantum‐well laser coupled to an external cavity

Stability of pulse energy and timing in a passively mode‐locked two‐section quantum‐well laser is measured. Spectral analysis of the 546‐MHz pulse train reveals rms timing jitter of 5.5 ps above 50 Hz and rms pulse energy fluctuations of <0.52% above 200 Hz.

Tunable active chirped-corrugation waveguide filters

A novel tunable semiconductor waveguide reflection filter is proposed and analyzed. The filter is based on spatially selective gain pumping of a chirped‐corrugation waveguide. This active chirped‐corrugation waveguide filter (ACF) is considered for monolithic broadband tuning of semiconductor lasers.

Wavelength tunable source of subpicosecond pulses from CW passively mode-locked two-section multiple-quantum-well laser

A wavelength-tunable passively-mode-locked semiconductor laser source of subpicosecond pulses is demonstrated. The system includes a two-section multiple-quantum-well laser which is coupled to an external grating for tuning and is followed by an external grating pair for pulse compression. A tuning range of 16 nm round 846 nm is obtained, resulting in compressed pulse widths as short as 260 fs and pulse widths shorter than 600 fs for all wavelength values within this tuning range. Time-bandwidth products are one to two times the transform limit.<<ETX>>

Pulse characteristics of passively mode-locked diode lasers

For the first time to our knowledge, asymmetric pulse shapes and the linear and nonlinear chirp from a passively mode-locked semiconductor laser are directly measured. For the laser tuned to various center wavelengths, fall-time-to-rise-time ratios of 2.0 to 2.5 are measured. With the laser tuned to the shorter-wavelength side of its tuning range, a significant quadratic chirp of -60 fs/nm(2) is measured, along with a linear chirp of -800 fs/nm. The nonlinear chirp is responsible for the asymmetrically shaped compressed pulses that produce long-tailed autocorrelations.

High Performance MEMS-Based Micro-Optic Assembly for Multi-Lane Transceivers

Advanced transceivers generally require a multi-lane approach, which necessitates the integration of multiple subcomponents. The use of mature, generally available, and low-cost single element components such as electro-absorption modulated lasers, silica planar lightwave circuits, and direct-modulated distributed feedback lasers, integrated in a hybrid fashion and optically aligned with micro-electromechanical systems provides a practical solution. Standard bonding tools with positioning tolerances of approximately ten micrometers are used to populate a silicon microbench that incorporates micro-adjustable elements with various optical components. After diebonding, the positions of coupling microlenses are adjusted to correct for the poor diebond accuracy, and then these movable elements are fixed in place with built-in heaters and solder. The net result is highly uniform, manufacturable, and low loss coupling between the optical elements, with typically 1 to 2 dB of loss. Using this packaging technique, we demonstrate a 40 Gb/s four-channel (4 × 10 Gb/s) DML-based transceiver and a 100 Gb/s ten-channel (10 × 10 Gb/s) EML-based transceiver for 10 and 80 km reach respectively.

High speed, high performance laser module

We will present the performance data and discuss a few pertinent design details of a cooled directly modulated laser (DML) module that is targeted for use in several SONET OC-192 applications and capable of addressing 10G Ethernet requirements. The intent of the presentation is to demonstrate the performance potential of the module operating at 1310 nm wavelength for these applications. The four primary technical areas of focus are: (1) the ability to continuously operate in adverse environmental conditions, i.e. 85/spl deg/C case temperature, (2) demonstrate transmission up to 80 km is achievable via use of, (3) a high efficiency optical coupling design, and (4) ease of RF interface due to low RF return loss and high bandwidth. These all assume that the lasers intrinsic design is properly specified and well matched to the package design. The regime of engineering design is approaching the practical limits and diminishing returns in terms of RF and optical coupling efficiencies. This suggests that further substantial improvements require a change in the underlying technology.

Effects of nonuniform current injection on the spectral dynamics of multisection distributed feedback lasers

The effects of nonuniform current injection on the linewidth enhancement factor (α) and the adiabatic chirp in a multielectrode distributed feedback laser are measured through a FM/AM modulation technique. This technique measures the adiabatic chirp due solely to carrier density effects and excludes the contributions of current induced temperature changes. The effects are shown to be a function of the pumping ratio between two active sections in the laser. The adiabatic chirp is enhanced by as much as a factor of 3 and the α parameter is reduced from a value of approximately 4 to 2.