Saeed Mahmud Ullah

GaInAsP/InP distributed reflector laser with phase-shifted DFB and quantum-wire DBR sections

A low-threshold-current distributed reflector laser consisting of phase-shifted distributed feedback (DFB) grating and quantum-wire distributed Bragg reflector (DBR) sections was realized. The device with a DFB length of 150µm, a DBR length of 240µm and a stripe width of 1.5µm achieved a threshold current as low as 1.2mA and a differential quantum efficiency of 13% from the front facet under RT-CW conditions. A good single-mode operation was also realized at a mode determined by the phase-shifted grating.

Low-Threshold-Current Operation of High-Mesa Stripe Distributed Reflector Laser Emitting at 1540 nm

A sub-mA-threshold-current operation (as low as 0.8 mA) of a high-mesa stripe geometry distributed reflector (DR) laser with a wirelike active distributed feedback (DFB) section and passive distributed Bragg reflector (DBR) section was realized under room-temperature continuous-wave conditions utilizing a narrow laser stripe (2.1 µm) and a large index coupling coefficient of 570 cm-1.

DFB Lasers With Deeply Etched Vertical Grating Based on InAs–InP Quantum-Dash Structures

Distributed feedback lasers with first-order vertical grating based on AlInGaAs-InAs-InP quantum-dash lasers were fabricated by electron beam lithography and Cl2-Ar reactive ion etching with an electron cyclotron resonance source. Low threshold currents and single-mode operation with sidemode suppression ratios of 48 dB and a direct modulation bandwidth of 5.5 GHz were demonstrated

GaInAsP/InP Distributed Reflector Lasers and Integration of Front Power Monitor by Using Lateral Quantum Confinement Effect

By using lateral quantum confinement effect, a sub mA threshold current operation of a long wavelength GaInAsP/InP distributed-reflector (DR) laser, consisting of wide and narrow wirelike active regions, was demonstrated for the first time under room-temperature continuous-wave (RT-CW) condition. Eye-patterns have been studied for back-to-back as well as 10-km optical fiber transmission line. Even though devices had broad contact electrodes, clear eye opening was observed up to 2 Gbps pseudo random bit sequence (PRBS; 231 - 1) data. A monolithic integration of a power monitor (PM) at the front side of the DR laser was also demonstrated for the first time. Almost linear photocurrent characteristic with very high isolation resistance of 60 MΩ was obtained by separating the PM section by a narrow (500 nm) and deep groove filled with benzocyclobutene (BCB).

Bit-error-rate measurement of GaInAsP/InP distributed reflector laser with wirelike active regions

Dynamic characteristics of 1.55 mum wavelength distributed reflector (DR) lasers with wirelike active regions were examined for the first time. BER measurements over a wide temperature range were performed. 10 km error-free transmission at 10 Gbit/s was confirmed by using a dispersion-shifted fiber.

Very High Electric Isolation Resistance between Distributed Reflector Laser and Front Power Monitor through Deeply Etched Narrow Groove

The monolithic integration of a distributed reflector (DR) laser with a front power monitor was realized for the first time, where quantum wirelike active regions were used to obtain the partial absorption necessary for monitoring the photodetector. The electrical isolation between the laser and power monitor sections was realized by deep (3.8 µm) and narrow (500 nm) groove etching, and a moderately high optical transmittivity of about 95% and a very high isolation resistance of 60 MΩ were achieved.

Bragg Wavelength Detuning in GaInAsP/InP Distributed Feedback Lasers with Wirelike Active Regions

By adopting a relatively large amount (54 nm) of Bragg wavelength detuning from the gain peak wavelength of active regions, temperature dependences of threshold current density and differential quantum efficiency were markedly improved in a GaInAsP/InP distributed feedback laser with wirelike active regions emitting at 1600 nm. A stable single-longitudinal-mode operation with a sub-mode suppression ratio of 51 dB (at a bias current of 2 times the threshold) was obtained at room temperature. Variations of threshold current density and differential quantum efficiency between 10 and 85 °C were reduced to as low as ±19 and ±24%, respectively; hence, the variation of the operating current required for a certain output power in this temperature range was reduced to 1/2 to 1/3 of that without Bragg wavelength detuning.

Sub-Milliampere Operation of 1540 nm Wavelength Distributed Reflector Laser with Wirelike Active Regions

Sub-mA threshold current operation (as low as 0.8 mA) of distributed reflector (DR) lasers with wirelike active DFB section and passive DBR section was realized at room temperature continuous wave condition utilizing narrow laser stripe (2.1 mum) and strong index coupling coefficient of 450 cm-1.

Integration of Front Power Monitor with Distributed Reflector Laser Through Deep Etched Narrow Groove Isolation

Monolithic integration of a distributed reflector (DR) laser with a front power monitor has been fabricated, where quantum wire-like active regions have been used as a photo detector for the first time. The electrical isolation between the laser and power monitor sections has been realized by deep (3.8 mum) and narrow (500 nm) groove etching while moderately high optical transmittivity of about 95% and a very high isolation resistance of 60 MOmega have been achieved. Almost linear photocurrent output has been observed with increasing the optical output power.

Improved Temperature Dependences of GaInAsP/InP DFB Lasers with Wirelike Active Regions by Bragg Wavelength Detuning

By adopting Bragg wavelength detuning into DFB lasers with wirelike active regions, the changes of threshold current densities and differential quantum efficiencies as low as plusmn19% and 24%, respectively, were obtained between 10degC and 85degC.