Optoelectronic oscillators can provide low noise oscillators at radio frequencies in the 0.5-40 GHz range and in this
paper we review two recently introduced approaches to optoelectronic oscillators. Both approaches use an optical fibre
feedback loop. One approach is based on passively modelocked laser diodes and in a 40 GHz oscillator achieves up to 30
dB noise reduction. The other approach is based on resonant tunneling diode optoelectronic devices and in a 1.4 GHz
oscillator can achieve up to 30 dB noise reduction.
A 1.55-μm ridge DFB laser and electroabsorption modulator monolithically integrated with a buried-ridge-stripe dual-waveguide spot-size converter at the output port for low-loss coupling to a cleaved single-mode optical fiber was fabricated by means of selective area growth, quantum well intermixing and dual-core technologies. These devices exhibit threshold current of 28 mA, side mode suppression ratio of 38.0 dB, 3-dB modulation bandwidth of 12.0 GHz, modulator extinction ratios of 25.0 dB dc. The output beam divergence angles of the spot-size converter in the horizontal and vertical directions are as small as 8.0°×12.6°, respectively, resulting in 3.2 dB coupling loss with a cleaved single-mode optical fiber.
We have demonstrated an electroabsorption modulator and semiconductor optical amplifier monolithically integrated with novel dual-waveguide spot-size converters (SSC) at the input and output ports for low-loss coupling to planar light-guide circuit silica waveguide or cleaved single-mode optical fiber. The device was fabricated by means of selective-area MOVPE growth, quantum well intermixing and asymmetric twin waveguide technologies with only a three steps low-pressure MOVPE growth. For the device structure, in SOA/EAM section, double ridge structure was employed to reduce the EAM capacitances and enable high bit-rate operation. In the SSC sections, buried ridge structure (BRS) were incorporated. Such combination of ridge, ATG and BRS structure is reported for the first time in which it can take advantage of easy processing of ridge structure and the excellent mode characteristic of BRS. At the wavelength range of 1550~1600nm, lossless operation with extinction ratios of 25 dB dc and more than 10 GHz 3-dB bandwidth is successfully achieved. The beam divergence angles of the input and output ports of the device are as small as 8.0°×12.6°, resulting in 3.0 dB coupling loss with cleaved single-mode optical fiber.
A 1.60-µm laser diode and electroabsorption modulator monolithically integrated with a dual-waveguide spot-size converter output for low-loss coupling to cleaved single-mode optical fiber is demonstrated. The devices emit in a single transverse and quasi-single longitudinal mode with a side mode suppression ratio of 25.6 dB. These devices exhibit a 3-dB modulation bandwidth of 16.0 GHz, and modulator extinction ratios of 16.2 dB dc. The beam divergence angle is about 7.3×10.6 deg, resulting in 3.0-dB coupling loss with cleaved single-mode optical fiber.
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