A. Vainionpaa

Self-starting stretched-pulse fiber laser mode locked and stabilized with slow and fast semiconductor saturable absorbers

A self-starting stretched-pulse mode-locked erbium-doped fiber laser that uses fast and slow semiconductor saturable absorbers is described. By using two absorbers, we obtained reliable operation at a fundamental repetition rate with 250 pJ of pulse energy without multiple-pulse breakup. External chirp compensation was used to compress the highly chirped pulses to durations of 135 fs.

Broadband semiconductor saturable absorber mirrors in the 1.55-/spl mu/m wavelength range for pulse generation in fiber lasers

Broadband low-loss semiconductor saturable absorber mirrors (SESAMs) in the 1.55-/spl mu/m wavelength range were monolithically grown by solid source molecular beam epitaxy using a Burstein-Moss blue-shifted Ga/sub 0.47/In/sub 0.53/As-InP distributed Bragg reflector. Absorbers with fast and slow temporal responses were used to start up and to stabilize a stretched pulse mode-locked fiber laser. Reliable operation at a fundamental repetition rate was obtained without multiple pulse break-up with pulse energy of over 250 pJ.

Semiconductor mirror for optical noise suppression and dynamic dispersion compensation

We report on a monolithic Gires-Tournois semiconductor interferometer used for both suppression of low-intensity spontaneous noise in a high-power fiber amplifier and to generate a tunable delay. The potential of the noise suppression technique was demonstrated using a two-stage amplifier system. Gain improvement by a factor of five illustrates the capability of semiconductor gates to greatly enhance energy extraction from optical amplifiers. We demonstrate also that controllable saturable absorption in an optically pumped multiple-quantum-well semiconductor reflector provides promising means for rapidly changing the group delay of the reflector and represents a new form of dynamic dispersion compensator.

Vertical-cavity saturable-absorber intensity modulator

We propose and demonstrate a reflection-type optical modulator, with surface-normal architecture, that exploits the optical saturation of absorption in semiconductor quantum wells. The modulation section of the modulator, which is composed of quantum wells placed within a Fabry–Perot cavity, is optically controlled by an intensity-modulated beam generated by an in-plane laser integrated monolithically on the same wafer and grown in a single epitaxial step. The modulation section and the in-plane laser share the same medium; therefore, efficient coupling between the control beam and the signal beam is achieved. The device was successfully used for active mode locking of an erbium-doped fiber laser.

Saturable absorber intensity modulator

We propose and demonstrate a reflection-type optical modulator, with surface-normal architecture that exploits saturation of absorption in semiconductor quantum wells pumped optically. The modulation section, composed of quantum wells placed within a Fabry-Perot cavity, is exposed to an intensity-modulated beam generated by an in-plane laser integrated monolithically on the same wafer. Since the modulation section and the in-plane laser share the same medium, an efficient coupling between the control beam and the signal beam is achieved. Design guidelines and device performance are presented. We demonstrate that the modulator provides an efficient light modulation mechanism that is sufficient to actively mode-lock an erbium-doped fiber laser.

Metamorphic growth of long-wavelength saturable absorber on GaAs substrates

The metamorphic growth of InP on GaAs induces high density of the dislocations near GaAs/InP interface . In this study, it is demonstrated that the lattice-mismatch induced imperfections can be used to tailor the device properties. Particularly, the growth imperfections in semiconductor saturable absorber mirror (SESAM) is investigated as a mechanism for decreasing the recovery time of the absorption.

Self-starting mode-locked fiber laser using biased semiconductor absorber mirror

We present an erbium-doped fiber laser mode-locked using a reverse-biased InGaAsP multiple quantum-well saturable absorber. We have examined the performance of a p-type-intrinsic-n-type (PIN) structured semiconductor absorber mirror both in starting the pulse operation and in pulse shaping. We have also found that applying a reverse bias is a useful means to suppress the Q-switching instability. By varying the reverse bias voltage applied to the absorber mirror, we could change the recovery time of the device owing to the electric-field-induced carrier sweep-out. Through the sweep-out process we were able to control the mode-locking start-up capability and the pulse duration of the fiber laser. In the experiment the mode-locked pulse duration could be reduced from 50 to 20 ps by application of an 80 kV/cm sweep-out field in the intrinsic region of the PIN absorber. The equivalent spectral broadening by a factor of 2.5 was observed as well.

Passively mode-locked erbium fiber laser synchronized to clock using vertical-cavity semiconductor modulator driven optically with the 1.54-/spl mu/m laser diode

Robust synchronization of a passively mode-locked fiber laser to an optical clock based on gain-switched semiconductor laser diode has been achieved. Owing to high nonlinear response of vertical-cavity semiconductor reflecting modulator, the locking mechanism is efficient and would allow for reliable synchronization of passively mode-locked laser at high harmonics. The clock is built entirely of standard telecom-grade components

Actively mode-locked fiber laser with semiconductor all-optical modulator

In this paper, we report on an actively mode-locked 1.56-mum erbium fiber laser using all-optical surface-normal semiconductor modulator. The 1.56-mum modulator is a purposely-designed semiconductor modulator mirror (SEMM) exploiting saturable absorption in the multiple quantum-well structure with enhanced modulation depth. Conceptually, the SEMM structure is very similar to the absorber mirrors used for passive mode-locking, except for higher values of saturation fluence and recovery time as compared to typical parameters for SESAMs

Surface-normal saturable absorber intensity modulator

We present a surface-normal semiconductor intensity modulator based on optically pumped saturable absorber mirror. The modulation section consists of quantum wells placed within a Fabry-Perot cavity. A laser integrated monolithically within the modulator structure generates the control beam used to pump the absorber. Since the modulation section and the in-plane laser share the same medium, an efficient coupling between the control beam and the signal beam is achieved. The modulator provides an efficient light modulation mechanism that is sufficient to actively mode-lock an Er-doped fiber laser.