Photonic Integrated Circuits (PICs) enable photons as data carriers at a very high speed. PIC market opportunities call for reduced wafer dimensions, power consumption and cost as well as enhanced reliability. The PIC technology development must cater for the latter relentless traits. In particular, monolithic PICs are sought as they can integrate hundreds of components and functions onto a single chip. InGaAsP/InP laterally-coupled distributed feedback (LC-DFB) lasers stand as key enablers in the PIC technology thanks to the compelling advantages their embedded high-order surface-gratings have. The patterning of the spatial corrugation along the sidewalls of the LC-DFB ridge, has been established to make the epitaxial overgrowth unnecessary thereby reducing the cost and time of manufacturing, and ultimately increasing the yield. LC-DFBs boast a small footprint synonymous of enhanced monolithic integrate-ability. Nonetheless, LC-DFBs suffer from the adverse longitudinal spatial hole burning (LSHB) effects materialized by typically quite high threshold current levels. Indeed, the carrier density longitudinal gradient- responsible for modes contending for the available material gain in the cavity- may be alleviated somewhat by segmenting the LC-DFB electrode into two or three reasonably interspaced longitudinal sections. In this work we report on the realization and performance of various electrode partition configurations. At room temperature, the experimental characterization of many as-cleaved LC-DFB devices provides ample evidence of superior performance such as a narrow linewidth (less than 400 kHz), a wide wavelength tune-ability (over 4 nm) and a hop-free single mode emission (side mode suppression ratio (SMSR) exceeding 54dB).
A time-domain traveling wave algorithm is extended to investigate high-order quantum dot based laterally-coupled distributed feedback semiconductor lasers. The effect of radiation modes in laser performance is included via Streifer’s terms. We calculate the optical gain spectra based on a coupled set of rate equations and taking into account both inhomogeneous broadening due to dot size fluctuation and homogeneous broadening due to polarization dephasing. It was found that, for third-order quantum dot based laterally-coupled distributed feedback lasers; a stable single mode operation with high SMSR can be achieved by means of fine tuning of the grating duty cycle
There has been much interest in developing low-cost laser sources for applications such as photonics integrated circuits
and advanced coherent optical communications. The ultimate objectives in this development include wide wavelength
tunability, a narrow linewidth, and an ease of integration with other devices. For this purpose, semiconductor surface
grating distributed feedback (SG-DFB) lasers have been introduced. SG-DFB manufacturing consists of a unique
sequence of planar epitaxial growth resulting in a major simplification to the fabrication process. SG-DFB lasers are
highly monolithically integrate-able with other devices due to their small footprint.
The segmentation of the built-in top electrode helps to alleviate the adverse spatial-hole burning effects encountered in
single-electrode devices and brings hence significant enhancements to the laser performance. For the first time, we report
here on the design, fabrication, and characterization of InGaAsP/InP multiple-quantum-well (MQW) SG-DFB lasers
with uniform third-order surface grating etched by means of stepper lithography and inductively-coupled reactive-ion.
The uncoated device reported here is 750 μm-long SG-DFB laser whose central and lateral top electrodes are 244 μmlongs
each, separated by two 9 μm-long grooves. The experimental characterization shows stable single mode operation
at room temperature under uniform and non-uniform injection. High side mode suppression ratios (SMSRs) (50-55dB)
under a wide range of injection current have been discerned as well. A relatively broad wavelength tuning (<4nm) has
also been observed. Moreover, a narrow linewidth (<300 kHz) has been recorded for different injection currents.
Laterally-coupled distributed feedback (LC-DFB) lasers offer compelling advantages over standard DFB lasers. The use
of surface grating on the ridge waveguide sidewalls in LC-DFB devices avoids any epitaxial overgrowth. This provides a
considerable simplification in the fabrication process, reducing cost and time of manufacturing, and ultimately increasing
yield. It offers also the potential for monolithic integration with other devices; paving the way towards low-cost and
mass-production of photonics integrated circuits. In this work, we report on the realization of high-order grating
InGaAsP/InP multiple-quantum-well (MQW) LC-DFB lasers at 1.55 μm by means of stepper lithography and
inductively-coupled reactive-ion as well as wet chemical etching. Third-order rectangular-shaped grating has been
lithographically defined on the ridge waveguide sidewalls with a relatively deep etching along the laser cavity. The
preliminary experimental characterization shows interesting results for as-cleaved devices tested in room temperature
under CW operation. A fabricated 1500 μm-long cavity LC-DFB laser shows stable single-mode operation with a side
mode suppression ratio as high as 50 dB. The tested device can emit at power as high as 9 mW, and the measured
threshold current is around 80 mA at room temperature. Moreover, the measured linewidth has been found to be as
narrow as 178 kHz using the delayed self-heterodyne interferometric technique.
In this work, we numerically study the effect of high-orderλ /4 phase-shift grating in laterally-coupled distributed
feedback (LC-DFB) lasers performance. It is well known that single-mode operation is improved by introducing λ/4
phase-shift grating in conventional DFB lasers. However, introducing λ/4 phase-shift region increases the optical
intensity around this region and results in strong longitudinal spatial-hole burning (LSHB). To flatten the longitudinal
carrier density distribution, we have numerically studied the effect of the radiation modes on high-order LC-DFB lasers
using a modified time-domain travelling-wave algorithm. It is shown that, the degree of LSHB can be effectively
reduced when considering high-order LC-DFB lasers with grating duty-cycle tailored to optimal values. LC-DFB laser
cavity with high-order grating shows a strong non-uniformity of the carrier density distribution. However, as we finely
engineer grating features, LSHB is highly reduced and high single mode suppression ration can be achieved.
We report here on the design, fabrication and performance characteristics of 1310 nm laterally coupled distributed-feedback (LC-DFB) semiconductor lasers. We describe the epidesign of these InGaAsP/InP quantum-well ridge waveguide LC-DFB lasers, which were fabricated in a single epitaxial growth step using stepper lithography and inductively-coupled reactive-ion as well as wet chemical etching. Such a DFB fabrication process avoids the commonly required regrowth steps in conventional DFB laser fabrication processes. The lithographic tolerance has been enhanced by employing higher order gratings, yielding lasers more amenable to mass-manufacturing. In this work, uniform third-order gratings have been lithographically patterned out of the waveguide ridge built on an epitaxial structure conceived for 1310 nm lasing wavelength. We now report on L-I measurements, threshold determination and sidemode suppression ratios (SMSR) for a broad distribution of devices. These fabricated lasers achieve stable single mode lasing with SMSR as high as 54 dB under CW operation at room temperature, albeit with thresholds higher than anticipated.
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