F.G. Johnson

Very high-order microring resonator filters for WDM applications

High-order microring resonators having from 1 to 11 coupled cavities are demonstrated. These filters exhibit low loss, flat tops, and out-of-band rejection ratios that can exceed 80 dB. They achieve performance that is suitable for commercial applications.

All-optical nonlinear switching in GaAs-AlGaAs microring resonators

In this paper, we demonstrate all-optical nonlinear switching in compact GaAs-AlGaAs microring resonators at the 1.55-/spl mu/m wavelength. Switching is accomplished in the pump-and-probe configuration in which the pump-and-probe signals are tuned to different resonance wavelengths of the microring. Refractive index change in the microring due to free carriers generated by two photon absorption is used to switch the probe beam in and out of resonance. Measured transient responses of the pump and probe through the microring show good agreement with theoretical predictions based on nonlinear pump-probe interaction due to two photon absorption.

Parallel-cascaded semiconductor microring resonators for high-order and wide-FSR filters

We demonstrate an optical channel dropping filter (OCDF) using three parallel-cascaded vertically coupled microrings with improved rolloff, bandpass flattening, and wide free spectral range (FSR) compared to a single-ring OCDF using single-mode tightly confined waveguides in both GaAs-AlGaAs and GaInAsP-InP. We achieve FSRs of 30 nm for GaAs-AlGaAs and 40 nm for GaInAsP-InP devices, which are three and four times greater, respectively, than those for single rings. The rolloff is 2.8 times faster than that for a single ring.

Fully programmable ring-resonator-based integrated photonic circuit for phase coherent applications

A novel ring-resonator-based integrated photonic chip with ultrafine frequency resolution, providing programmable, stable, and accurate optical-phase control is demonstrated. The ability to manipulate the optical phase of the individual frequency components of a signal is a powerful tool for optical communications, signal processing, and RF photonics applications. As a demonstration of the power of these components, we report their use as programmable spectral-phase encoders (SPEs) and decoders for wavelength-division-multiplexing (WDM)-compatible optical code-division multiple access (OCDMA). Most important for the application here, the high resolution of these ring-resonator circuits makes possible the independent control of the optical phase of the individual tightly spaced frequency lines of a mode-locked laser (MLL). This unique approach allows us to limit the coded signals spectral bandwidth, thereby allowing for high spectral efficiency (compared to other OCDMA systems) and compatibility with existing WDM systems with a rapidly reconfigurable set of codes. A four-user OCDMA system using polarization multiplexing is shown to operate at data rates of 2.5 Gb/s within a 40-GHz transparent optical window with a bit error rate (BER) better than 10/sup -9/ and a spectral efficiency of 25%.

Vertically coupled microring resonators using polymer wafer bonding

A new technique is presented to make vertically coupled semiconductor microring resonators that eases the fabrication process with devices more robust to ring-to-waveguide misalignments. Single-mode microring optical channel dropping filters are demonstrated for the first time in this configuration with Qs greater than 3000 and an on-resonance channel extinction greater than 12 dB. A 1/spl times/4 multiplexer/demultiplexer crossbar array with second-order microrings was also made and exhibited channel-to-channel crosstalk lower than 10 dB.

High-power broad-band superluminescent diode with low spectral modulation at 1.5-/spl mu/m wavelength

A 1.5-/spl mu/m wavelength superluminescent light source operating at a heat sink temperature of 13/spl deg/C with the following properties was realized: 20-mW continuous wave output power, 130-nm spectral bandwidth, and 0.2-dB spectral modulation. This light source consists of an angled facet single-mode waveguide with a rear absorption region. These results were obtained by optimizing the epitaxial design, the waveguide design, and the device mounting.

Compact mode expanded lasers using resonant coupling between a 1.55-μm InGaAsP tapered active region and an underlying coupling waveguide

We demonstrate a novel expanded mode laser for enhanced laser-fiber coupling based on resonant coupling between a tapered active waveguide and an underlying coupling waveguide. This device was grown in a single standard epitaxial growth and was processed using conventional fabrication techniques, thus making it attractive for low-cost manufacturing. The total taper length required for mode transformation was 200 /spl mu/m and the excess transformation loss was 0.6 dB indicating the compact, low-loss mode transformation. Far-field divergence angles (13/spl deg//spl times/24/spl deg/) and improved coupling to cleaved single-mode fibers (3.8-dB coupling loss), were achieved.

Dependence of the light-current characteristics of 1.55-μm broad-area lasers on different p-doping profiles

We have investigated the dependence of the light-current characteristics of broad-area lasers with different p-doping profiles for a two-step separate-confinement heterostructure (SCH) 1.55-/spl mu/m InGaAs-InP laser. A sizable increase of the optical output power is observed in a structure with delta doping at the heterointerfaces and moderate doping in the thick SCH layer. It is also shown that the characteristic temperature (T/sub 0/) of the structure with delta doping at the heterointerfaces and moderate doping at the thick SCH layer is almost constant as the measurement temperature is increased. Such an improvement in device performance is attributed to a reduction of carrier leakage to the SCH layer.

Lossless 1 x 2 optical switch monolithically integrated on a passive active resonant coupler (PARC) platform

We demonstrate a lossless 1/spl times/2 optical switch utilizing resonant vertical coupling between an active and a passive waveguide. Optical power is coupled into the passive waveguide and split into two ports using a 3-dB Y-junction splitter. The mode is then coupled up to a 1-mm-long active waveguide where gain is provided. A 100-/spl mu/m-long taper is utilized in each arm for coupling the mode from the passive to the active waveguide. Internal gain greater than 22 dB is obtained in each arm of the integrated splitter. High yield and good uniformity of devices are obtained over multiple processing runs.

1.9-W quasi-CW from a near-diffraction-limited 1.55-μm InGaAsP-InP tapered laser

1.9-W quasi-CW output power with about 80% of the power in the central lobe is obtained from a 1.55-/spl mu/m wavelength InGaAsP-InP MQW tapered unstable resonator laser. This power is found to be emitted in a near-diffraction-limited beam.