Abstract:

The goal of this work is to demonstrate integratable devices that constitute the reconfigurable optical add-drop multiplexer (ROADM) and to consolidate them into a single device---monolithically integrated reconfigurable optical add-drop multiplexer (MI-ROADM). The devices are based on InGaAsP material growth and integration method employed is re-growth free asymmetric twin-guide technology (ATG). The devices include high linearity bulk and multi-quantum well tapered photodetectors with saturation current density in excess of (2.8?0.3)kA/cm 2 for the former and that of (1.2?0.1)kA/cm2 for the latter. The multi-quantum well tapered photodiode is further integrated with a semiconductor optical amplifier to form a SOA-PIN device which employs the same active layer for detection as well as amplification. The SOA-PIN has a peak external responsivity of (8.2?0.4)A/W (~ 9dB fiber-to-detector gain), and a 3dB RF bandwidth of (11?1)GHz, equivalent to a 265 GHz gain-bandwidth product and an optical bandwidth ~30nm.

A balanced photodiode (BPD) integrated with a multi-mode interference coupler is also demonstrated and used in a coherent heterodyne RF FM optical link with wideband-rectifier-narrowband-amplifier (WIRNA) architecture. The BPD exhibits a bandwidth of (15?1)GHz at optical wavelength ?=1.55?m with a responsivity of (0.32?0.02)A/W. The balance is within 0.5dB, minimum dark current of 5nA, linearity up to +3dBm optical power and rejection ratio of (34?2)dB. A comparison of the links employing BPD and a single photodiode is presented, with the conclusion that the BPD based directly modulated link has the best performance with noise figure (NF) of (20?1)dB and a spurious-free-dynamic-range (SFDR) of (102?2)dB/Hz2/3 .

A compact 2x2 optical switch with an operational wavelength range from 1520nm to 1580nm used to route signal between the add and drop ports of a ROADM is demonstrated with on-off contrast ratio within (21?2)dB over the temperature range from 16?C to 64?C, the polarization sensitivity <2dB, and the propagation loss of (3?2)dB in both the ON and OFF states.

Finally, the first two generations of MI-ROADM circuit are demonstrated that employ an arrayed waveguide grating (AWG) for demultiplexer/multiplexer operation, an array of optical switches and multi-quantum well tapered photodetectors for signal routing and detection, and a SOA for gain. These lay the groundwork for next generation of the MI-ROADM, provided the challenges of loss and high cross talk in the AWG, arising in most part due to contact lithography, are overcome.