Malcolm W. Wright

Injection locking dynamics of vertical cavity semiconductor lasers under conventional and phase conjugate injection

Stable phase locking of an electrically pumped vertical cavity surface-emitting semiconductor laser (VCSEL) was demonstrated experimentally by injecting light from an edge-emitting master laser into the slave laser VCSEL cavity within a large detuning range (/spl sim/80 GHz). By varying the injected power and frequency detuning, a variety of interesting nonlinear behavior was observed. A theoretical model based on two-field rate equations is presented and compared with experiment, showing good agreement.

Spectral properties of angled-grating high-power semiconductor lasers

We study the spectral properties of angled-grating high-power semiconductor lasers, also known as /spl alpha/ distributed feedback (DFB) lasers. We have derived a closedform expression to describe the cavity resonance. The results of this model are shown to compare favorably with experimental data. Intrinsic device parameters such as coupling coefficient and grating period are shown to be correlated to spectral and nearfield characteristics. The formulations and insights developed in this paper allow one to calculate these critical design parameters for optimum performance.

Dynamic instabilities in master oscillator power amplifier semiconductor lasers

We investigate theoretically the master oscillator power amplifier using a semiconductor laser model that is fully time and space (laterally and longitudinally) resolved. We numerically examine the stability of the device and identify the nature of the different instabilities. These can arise from undamped relaxation oscillations, beating between the longitudinal modes of any of the cavities that comprise the device, or lateral filamentation.

Yb-doped fiber amplifier for deep-space optical communications

A custom-developed high-power laser based on a Yb-doped amplifier is characterized as a transmitter for deep-space optical communications. The key requirements are high peak power at moderate data rates with good beam quality. The transient pulse dynamics are modeled via a simple rate equation approach and reveal a qualitative agreement with the pulsed performance. Peak powers were obtained up to 8 kW for a 22-ns pulsewidth at a 3.5-kHz repetition rates. The peak power dropped significantly as the repetition rate was increased to 50 kHz.

Injection locking semiconductor lasers with phase conjugate feedback

Abstract Phase conjugate injection locking is shown to couple coherently two semiconductor lasers through a double phase conjugate mirror geometry. The mutual coherence and stability of the lock band are characterized from the visibility and relative intensity noise measurements for various levels of phase conjugate coupling and frequency detunings. Side mode phase conjugate injection locking is demonstrated by high mutual coherence with visibility ∼0.93 and detunings up to nine longitudinal mode spacings at injection levels of −22 dB. Central mode phase conjugate injection locking with high mutual coherence is also possible for feedback levels of −36 dB and exhibiting an asymmetric stable locking region of 350 MHz bandwidth within the locking band. The phase locking is unstable though, the reasons for which are discussed. Increased phase conjugate feedback extends the lock band to greater detunings and asymmetry as in direct injection locking with only a small region showing high mutual coherence. Intensity noise measurements are also discussed.

Adaptive optics correction into single mode fiber for a low Earth orbiting space to ground optical communication link using the OPALS downlink.

An adaptive optics (AO) testbed was integrated to the Optical PAyload for Lasercomm Science (OPALS) ground station telescope at the Optical Communications Telescope Laboratory (OCTL) as part of the free space laser communications experiment with the flight system on board the International Space Station (ISS). Atmospheric turbulence induced aberrations on the optical downlink were adaptively corrected during an overflight of the ISS so that the transmitted laser signal could be efficiently coupled into a single mode fiber continuously. A stable output Strehl ratio of around 0.6 was demonstrated along with the recovery of a 50 Mbps encoded high definition (HD) video transmission from the ISS at the output of the single mode fiber. This proof of concept demonstration validates multi-Gbps optical downlinks from fast slewing low-Earth orbiting (LEO) spacecraft to ground assets in a manner that potentially allows seamless space to ground connectivity for future high data-rates network.

Midinfrared Interband Cascade Laser for Free Space Optical Communication

A free space optical (FSO) link utilizing midinfrared (mid-IR) interband cascade lasers has been demonstrated in the 3- to 5-¿m atmospheric transmission window with data rates up to 70 Mb/s and bit-error rate (BER) less than 10-8. The performance of the mid-IR FSO link has been compared with the performance of a near-IR link under various fog conditions using an indoor communication testbed. These experiments demonstrated the lower attenuation and scintillation advantages of a mid-IR FSO link.

Temporal dynamics and facet coating requirements of monolithic MOPA semiconductor lasers

Dynamics of temporal instabilities in tapered broad-area InGaAs SQW semiconductor master oscillator/power amplifier lasers are experimentally investigated. Multigigahertz self-pulsations are evident in the optical and temporal spectra along with coupled-cavity modes due to the finite output-facet reflectivity. From a previously developed time-dependent coupled-wave model, it is shown that by adjusting the grating strength in the distributed Bragg reflector (DBR) section of the master oscillator the antireflection facet coating requirements can be relaxed. Increased stable operation at high powers is then possible.

Improved optical communications performance combining adaptive optics and pulse position modulation

A free-space optical communication channel suffers degraded performance due to blurring and scintillation of the received signal caused by atmospheric turbulence. Adaptive optics (AO) improves the communication performance of such a channel by concentrating the received power on the detector. The degree of improvement with AO correction depends on the modulation format, and on the modulation order when pulse position modulation is utilized. Gains of up to 6 dB with AO have been experimentally validated in a laboratory test bed under simulated atmospheric conditions involving turbulence and background light. The fade statistics of the turbulent atmospheric channel have also been analyzed with and without AO correction.

Qualification and reliability testing of a commercial high-power fiber-coupled semiconductor laser for space applications

A compact microchip laser pumped by a single fiber-coupled semiconductor diode laser is developed for a space-borne scanning laser radar instrument. A commercial off-the-shelf component is used for the pump laser and undergoes a rigorous qualification approach to meet the requirements for the space-borne application. The qualification and testing process for the commercial pump laser is derived based on a nonstandard piece part screening plan and is presented along with the test results. These tests include mechanical, vibration, thermal cycling, and radiation tests as well as a full destructive parts analysis. Accelerated lifetests are also performed on the packaged device to demonstrate the ability to meet an operational lifetime of 5000 h. The environmental testing approach would be applicable to space qualification of a variety of commercial photonic systems, particularly in cost-constrained missions.