Kuen-Ting Shiu

Compact polarization-insensitive InGaAsP-InP 2 × 2 optical switch

We demonstrate a simple, compact, high-contrast ratio, and low-loss polarization-insensitive InGaAsP-InP 2 /spl times/ 2 optical switch with an operational wavelength range from 1520 to 1580 nm. The switch is 1.3 mm long by 160 /spl mu/m wide. The on-off contrast ratio is within (21/spl plusmn/2) dB over the temperature range from 16/spl deg/C to 64/spl deg/C, the polarization sensitivity is <2 dB, and the propagation loss is (3/spl plusmn/2) dB in both the ON and OFF states, making it potentially useful for optical cross-connects, delay lines, and add-drop multiplexers.

Evidence of cascaded emission in a dual-wavelength quantum cascade laser

This letter reports on a quantum cascade laser that exhibits simultaneous dual-wavelength emission from two consecutive optical transitions in each active region. These “cascaded” transitions—a second-excited state to first-excited state and a first-excited state to ground state—yield light at ∼9.5 and ∼8.2μm, respectively, in good agreement with simulations. The two lasing wavelengths have similar thresholds at the leading edge of a current pulse.

A simple monolithically integrated optical receiver consisting of an optical preamplifier and a p-i-n photodiode

We demonstrate a monolithic optical receiver consisting of the integration of a semiconductor optical amplifier and a p-i-n photodetector based on asymmetric twin-waveguide technology. Multiple quantum wells with 1% compressive strain are used for both optical amplification and detection. The device has a peak external responsivity of 8.2/spl plusmn/0.4 A/W (/spl sim/9-dB fiber-to-detector gain), and a 3-dB optical bandwidth of 11/spl plusmn/1GHz, equivalent to a 265-GHz gain-bandwidth product. The efficient coupling of light between individual optical components is achieved by a lateral adiabatic taper that reduces the fabrication complexity. This work represents a considerable simplification over previously demonstrated high-performance integrated optical receivers.

An InP-Based Monolithically Integrated Reconfigurable Optical Add–Drop Multiplexer

We demonstrate an InP-based monolithically integrated reconfigurable optical add-drop multiplexer consisting of an array waveguide grating, a semiconductor optical amplifier, four 2x2 Mach-Zehnder optical switches, and four PIN photodetectors using the asymmetric twin waveguide technology. The total chip size is 10 x 6 mm, and each of the components in the circuit exhibited performance similar to that achieved in a discrete form. The add-drop functionality of the chip is demonstrated via the routing of the signal from the add port to the drop/output port.

Integratable High Linearity Compact Waveguide Coupled Tapered InGaAsP Photodetectors

We investigate high linear response tapered photodiodes composed of bulk and multiquantum-well absorption layers based on the integratable asymmetric twin waveguide architecture. The tapered shape reduces space-charge induced nonlinearities, enhancing the saturation current densities at high input optical powers. The 1-dB compression current density for an InGaAsP bulk active layer photodiode (BPD) is in excess of (2.8 plusmn 0.3) kA/cm2, compared to quantum-well photo- diodes (QWPD) in the same materials system that saturate at (1.2 plusmn 0.1) kA/cm2. We find that the limited density of states of QWPDs leads to the early onset of current saturation. The BPD has a polarization sensitivity of SPol = (1.0 plusmn 0.5) dB and responsivity R = (0.3plusmn0.03) A/W at a wavelength of 1.55 mum, whereas the QWPD has SPol = (7plusmn1) dB and R = (0.55plusmn0.05) A/W, while both have a bandwidth of (11 plusmn 1) GHz.

Integratable High Linearity and High Bandwidth Compact Tapered Photodetector

We demonstrate a compact, high linearity, tapered photodiode based on the asymmetric twin guide (ATG) architecture. The photodiode has a 1-dB compression current density >2.8 kA/cm2, a bandwidth of (11plusmn1) GHz, a responsivity of (0.30plusmn0.03) A/W, and polarization sensitivity les(1.0plusmn0.5) dB. The tapered shape of the detector reduces space-charge induced nonlinearities at high current density. The linearity current density, to the best of our knowledge, is the highest reported for an integratable, edge-illuminated, polarization-insensitive p-i-n photodetector. The ATG architecture makes the device suitable for monolithic integration with active and passive optical elements such as amplifiers, lasers, modulators, arrayed waveguide gratings, and multimode interference couplers

A monolithic, reconfigurable optical add-drop multiplexer using asymmetric twin waveguide technology

An InP-based monolithically integrated optical add-drop multiplexer (ROADM) is demonstrated with the asymmetric twin waveguide (ATG) technology. Its add/drop functionality has been measured and shows > 20 dB drop extinction ratio.

An integratable high bandwidth high linearity polarization insensitive compact tapered photodetector

We demonstrate an integratable, high linearity (>15 dBm optical power), high bandwidth ((11plusmn1) GHz), polarization insensitive tapered photodetector with a peak responsivity of (0.25plusmn0.03)A/W. The tapered photodiode of this work consists of a lower passive guide for enhanced fiber coupling, with the active absorption region grown on the waveguide surface.

Dual-Wavelength Quantum Cascade Laser with Two Optical Transitions in Each Active Region

We report on a novel quantum cascade laser design that utilizes wide active region quantum wells to create a lasing transition between the second- and first-excited states of the constituent wells. Electroluminescence and lasing spectra confirm the presence of the optical transition at the expected energy, but also show the conventional transition between energy levels resulting from excited and ground states of the original quantum wells. As a result, the laser produces simultaneous dual-wavelength emission at 8.2 µm and 9.3 µm.

A Simple, Monolithically Integrated Optical Receiver

A monolithic integrated optical receiver is demonstrated by using the asymmetric twinwaveguide (ATG) technology. This device shows a peak responsivity of 8±0.2 A/W, and a 3dB optical bandwidth of 10±1 GHz, equivalent to a 265 GHz gain-bandwidth product.