In this paper, we demonstrate a regrowth-free monolithically integrated photonics circuit which consists of a tunable, single-frequency, low-linewidth 1x2 multimode-interferometer laser diode (MMILD) and two waveguide devices connected with the two arms of the laser and electrically isolated by deep etched slots. In this photonic integrated circuit (PIC), the 1x2 MMILD showed similar tuning and single frequency performance as the discrete 1x2 MMILD, with more than 30dB side mode suppression ratio (SMSR). The integrated waveguide devices could be used as semiconductor optical amplifiers, photodiodes or electro-absorption modulators, thus the integrated circuit could be used for different functions. The integrability of the MMI lasers indicates its potential applicability in more advanced low-cost topological PICs.
In this paper, we present a novel 1x2 multi-mode-interferometer-Fabry-Perot (MMI-FP) laser diode, which demonstrated tunable single frequency operation with more than 30dB side mode suppression ratio (SMSR) and a tuning range of 25nm in the C and L bands, as well as a 750 kHz linewidth. These lasers do not require material regrowth and high resolution gratings; resulting in a simpler process that can significantly increase the yield and reduce the cost.
In this paper, we demonstrate a novel InGaAlAs/InGaAlAs quantum well multimode-interferometer-Fabry-Perot laser
diode (MMI-FP LD) in which a 1x3 multimode interferometer is inserted into the conventional FP laser waveguide to
generate single wavelength emission. The designed and fabricated laser diode shows a single longitudinal mode lasing
with side mode suppression ratio (SMSR) of 25dBm at a wavelength of 1567nm with driving current of 170mA and can
be tuned over a certain range by adjusting the driving current. A laser diode incorporating a 1x3 MMI and three single
mode waveguide outputs is also proposed which could be potentially used to generate a 3-channel single longitudinal
mode coherent source using injection locking. The simple structure of this single longitudinal mode laser significantly
eases the fabrication processing enabling an increase in the yield and a reduction in the cost compared with the
traditional single mode lasers.
In this paper, a single facet slotted Fabry-Perot (FP) laser is demonstrated to provide tunable, single mode operation and
has been monolithically integrated into a photonic integrated circuit (PIC) with semiconductor optical amplifiers and a
multimode interference coupler. These lasers are designed by incorporating slots into the ridge of traditional FP cavity
lasers to achieve single mode output, integrability and tunability. With the feature size of the slots around 1μm, standard
photolithographic techniques can be used in the fabrication of the devices. This provides a time and cost advantage in
comparison to ebeam or holographic lithography as used for defining gratings in distributed feedback (DFB) or
distrusted Bragg reflector (DBR) lasers, which are typically used in PICs. The competitive integrable single mode laser
also enables the PIC to be fabricated using only one epitaxial growth and one etch process as is done with standard FP
lasers. This process simplicity can reduce the cost and increase the yield.
In this paper, the composition profiles within intermixed AlInGaAs-based multiple quantum wells structure are analyzed
by secondary ion mass spectrometry and the bandgap blue shift is found to be mainly attributed to the interdiffusion of In
and Ga between the quantum wells and barriers. Based on these results, AlInGaAs-based single quantum well structures
with various compressive strain (CS) levels are then investigated and we report an enhancement of the bandgap shift by
increasing the compressive strain level in the SQW. For instance, at an annealing temperature of 850°C, the
photoluminescence blue shift can reach more than 110 nm for the sample with 1.2%-CS SQW, but only 35 nm with
0.4%-CS SQW. The indium composition ratios are designed to be 0.59 and 0.71 for the 0.4% and 1.2%-CS quantum
wells, respectively, as opposed to 0.53 for the lattice-matched barrier. This relatively larger atomic compositional
gradient between the CS quantum well and barrier is expected to facilitate the atomic interdiffusion and lead to the more
pronounced bandgap shift.
The photodiode (PD) is a key component in optical transmission and optical measurement systems which receive optical
signals and convert them into electric signals. High speed, high responsivity, high power and low dark current are
desirable attributes of the PD in these applications, but also a simple fabrication process for high yield and low cost is
essential for industry production. In this paper, an undercut-air-bridge high speed InGaAs/InP PIN structural photodiode
is presented. By utilizing the crystal orientation dependent wet etching of InP material and designing the arms of the
bridge with proper angle, the air bridge was easily obtained, which greatly eased the fabrication. The fabricated devices
with 120μm×3μm ridge waveguides work robustly up to 30GHz in the measurements and potentially faster with
The packaging aspect of the high-speed TO laser module has been investigated in this paper. A conventional TO 56
package is employed for compact and low cost high-speed applications. In the TO header, a special designed RF
substrate is developed to minimize the RF reflection and insert loss. The influence of the feedthrough and the TO leads
on signal transmission is analyzed using the electromagnetic (EM) method. A testing interface PCB based on the tapered
coplanar waveguide (CPW) transmission line is proposed, and simulation results indicate that the coaxial type TO
package has an insert loss of 1.5dB at 10GHz. In order to improve the electronic performance of the TO module, the
equivalent circuit is built and a bandwidth compensation circuit is introduced, and results show that the 3dB bandwidth
of the TO package can extend to 16.3GHz.
Photodiode (PD) is a key component in optical transmission and optical measurement systems. In this paper, we present
the design and fabrication of traveling-wave edge-coupled Unitraveling Carrier (UTC) PD. The fabricated UTC PD with
40μm×5μm waveguide shows 3dB bandwidth 13GHZ and 32GHz under 0 biases and -1V respectively. In parallel, PIN
PD was also fabricated for comparison and only shows 4GHz and 18GHz under same bias conditions. This indicates the
UTC PD is superior to the PIN PD for higher speed operation, especially in application of system without power supply.
We report on quantum well intermixing of AlInGaAs-MQWs using the impurity-free vacancy diffusion method with
dielectric capping layers which has potential for realization of photonic integrated circuits. The extent of the bandgap
shifts with respect to different dielectric capping layers and alloy temperatures are investigated. The intermixing inhibitor
and promoter are then integrated using combination of SiO<sub>2</sub> and SiN<sub>x</sub> dielectric capping layers which shows a
differential photoluminescence wavelength more than 110 nm. Based on this developed intermixing technique, we have
fabricated AlInGaAs-InP based material stripe lasers emitting at two different wavelength ranges centered at 1519 nm
and 1393 nm respectively. Characterizations including the current-voltage and electroluminescence measurements show
that the integration of two-bandgaps can be achieved and furthermore a differential wavelength in lasing spectra up to
120 nm is demonstrated.
Electroabsorption modulator has been widely used in modern optical fiber communication system and analog RF link system. In this paper, the design of a high-performance EAM with low coupling loss, high saturation power and high speed was demonstrated, which include the waveguide, active core and electrodes. A novel EAM with large optical cavity (LOC) waveguide structure, intrastep quantum well (IQW) active core and traveling wave electrodes was presented and fabricated successfully. Our results show that the LOC waveguide effectively improved the optical profile of EAM and reduced the coupling loss. The obtained traveling wave EAM achieved 21dBm saturation power and 23GHz 3-dB bandwidth.