We have fabricated a photonic integrated circuit (PIC) that had two GaAs distributed Bragg reflector (DBR) laser diodes (LD) and a Y-branch coupler integrated by means of the compositional disordering of a quantum well. Using this PIC as an optical heterodyne sweeper, frequency characteristics of a GaAs Schottky photodiode were measured.
AlGaAs tunable distributed Bragg reflector (DBR) laser diodes (LD's) with a lasing wavelength of 780 nm were fabricated by means of electron beam (EB) lithography, ion implantation, and two-step metalorganic vapor phase epitaxy (MOVPE). Active and passive waveguides were monolithically integrated by using silicon ion implantation for compositional disordering of quantum-well heterostructures. The optimum single-quantum-well (SQW) structure, with low threshold current and low internal loss, is about 5 nm thick and has an Al mole fraction of 0.06. The graded-index separate-confinement heterostructure (GRIN-SCH) with a carrier-blocking layer was also used to improve the characteristic temperature of a two-step-growth LD. A Iinewidth as narrow as 690 kHz and a frequency tuning of more than 1.7 THz were obtained.
Fully integrated PICs for measurement have been successfully fabricated for the first time. The device is implemented with waveguide grating components, a GRIN-SCH-SQW-DFB LD and PDs. Special care is taken to prevent direct optical coupling between integrated LDs and PDs in order to detect feeble sensing light. An interference signal is actually detected as photocurrent modulation of ∼1-nA amplitude by this integrated structure.
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