Optical Confinement Factor Research Articles

High Performance Electrically‐Injected InGaN Microdisk Lasers through Simultaneous Enhancement of Optical Confinement and Overlap Factor (Laser Photonics Rev. 18(8)/2024)

High Performance Electrically‐Injected InGaN Microdisk Lasers through Simultaneous Enhancement of Optical Confinement and Overlap Factor (Laser Photonics Rev. 18(8)/2024)

Theoretical analysis of passively mode-locked semiconductor ring lasers

In this paper, the theoretical analysis of the passive mode-locked semiconductor ring lasers (PML-SRLs) is investigated based on a travelling wave model. It is found that both the optical confinement factor and the injection current make great contributions to the operation regime and the performance of PML-SRLs. All operation regimes of PML-SRLs are governed by the transient gain-loss balance. Such balance is closely associated with the relationship among the stimulated rate in the semiconductor optical amplifier (SOA), the carrier lifetime in the saturated absorber (SA), and the roundtrip time of the ring resonator. Furthermore, our investigation indicates that the mode-locked state of such PML-SRLs is independent of the passive waveguide, but the performance degrades with the increased waveguide loss or the shortened waveguide length, once the material bandwidth is wide enough. Another discovery is that it is possible to achieve the high energy pulse in the PML-SRL with shortening the passive length and narrowing the gain spectrum meanwhile. Overall, such investigations should benefit designing the required PML-SRLs and achieving the high performance.

Fabrication of high power 1.5 µm wavelength InGaAsP/InP BH lasers having dilute waveguide structure

1.5 µm wavelength high power buried heterojunction (BH) semiconductor lasers having dilute waveguide structure have been fabricated. The optical field is dragged down toward the n side of the device by the dilute waveguide layer, lowering the optical confinement factor of the p doped material and active material, which helps to enlarge the laser output light power. Compared with thick InGaAsP cladding layer, the dilute waveguide material is easy to be grown and has higher thermal conductivity. The slope efficiency of the obtained dilute waveguide BH lasers is notably higher than that of the BH lasers having no dilute waveguide. Our studies show that the dilute waveguide structure is promising for the fabrication of high power BH lasers.

High Performance Electrically‐Injected InGaN Microdisk Lasers through Simultaneous Enhancement of Optical Confinement and Overlap Factor

AbstractDespite the considerable research interest in InGaN‐based microdisk lasers, owing to their unique circular geometry distinct from vertical cavity surface‐emitting lasers (VCSEL) or edge‐emitting lasers, commercial products remain scant due to deficient performance under electrical injection. This study proposes an innovative method integrating a thin‐film configuration with a metallic undercut, significantly augmenting optical confinement, overlap factor, and thus lasing performance. This approach results in a diminished lasing threshold from 1500 to 670 Wcm−2 and a record high quality (Q) factor of 10100 under electrical injection. Strain relaxation in the metallic undercut, identified via scanning near‐field optical microscopy (SNOM), beneficially mitigates the Quantum Confined Stark Effect (QCSE), boosting the internal quantum efficiency of the laser. Furthermore, a beneficial blue‐shift in the emission spectrum aligns with the lasing peak, strengthening the Q factor. A tactfully implemented recessed top contact enables electrical injection lasing without optical performance compromise. The study provides invaluable insights for future microdisk laser technology advancements, potentially leading to specialized functionalities, including quantum optics, thereby opening new avenues for research and applications in this field.

III-Arsenide separate confinement heterostructure infrared laser diodes with engineered the cladding layers

In this work, III-Arsenide laser diodes (LDs) show better optoelectronic properties when the aluminum (Al) concentration in the cladding layer is increased up to 95 % in a separate confinement heterostructure (SCH). These laser diodes show their peak gain the infrared lasing wavelength of ∼840 nm. Enhancing the Al in the n- and p-cladding layers, both separately and simultaneously in LDs, shows that the optoelectronic properties are reasonably improved. The output light power has been increased to 50 mW at a current density of 13 × 104A/cm2, with 95 % aluminum in both the n- and p-claddings. The modal field intensity has increased by 5 %, and the optical confinement factor (OCF) has improved from 0.0102 to 0.0105 in the proposed device. Consequently, the engineered cladding design, incorporating varied aluminum concentrations, is recognized as pivotal for optimizing the performance of arsenide laser diodes.

Design and analysis of Si photonic NaCl sensors based on suspended microdisk resonators

In this paper, two optical refractive index sensors, respectively based on a suspended microdisk resonator (SMDR) and a sub-wavelength Bragg grating suspended microdisk resonator (SWG-SMDR) have been designed on a silicon on insulator (SOI) platform, and their optical and sensing performances have been analyzed using the three-dimensional finite-difference time-domain method. It has been shown that the Bragg grating increases the optical confinement factor in the sensing region and, consequently, improves the light–matter interaction and sensitivity. Considering concentrations of 0 to 25% for the NaCl dissolved in the deionized water, the enhanced sensitivity and FOM of the SWG-SMDR sensor with the miniaturized optimal geometrical dimensions are 163.77 nm RIU−1 and 10.81 RIU−1, respectively. This compact optical sensor enhances the sensitivity and FOM by combining effects of the Bragg grating and suspension configuration in improving the light–matter interaction.

Developing Deep Ultraviolet Laser Diode: Design and Improvement of Al0.62Ga0.38N/Al0.68Ga0.32N Quantum Wells on AlN Substrates for 266 nm DUV Emission

A deep ultraviolet (DUV) laser diode is a compact and efficient semiconductor device that emits laser light in the deep ultraviolet range. Its unique properties make it suitable for a wide range of applications in fields such as manufacturing, research, and healthcare. In this research we propose two Al-graded Electron Blocking Layer (EBL) and quantum barriers (QBs) to improve the performance of AlGaN-based Deep UV-LDs. The electrical properties and optical properties of three structures containing conventional EBL, composition graded increased EBL, and liner graded increased of EBL and QBs were numerically investigated. It was found that the structure-C with linear graded increased EBL and QBs significantly improved the Optical Confinement Factor (OCF) 21%, gain 1600 cm-1, emission power 0.060 W, raised the carrier concentration in the MQWs region, enhanced the stimulated recombination rate and reduced the carrier leakage, of the laser diode (LDs). But at a 100-mA injection current, the threshold current and voltage were reduced to 43 mA and 5.00 V, valance barrier height 270 meV respectively. In compare to the conventional structure, introducing a graded design for both EBL and Quantum Barriers (QBs) with increased aluminum content significantly enhanced the performance of the laser diode (LD). This improvement is essential for advancing Deep Ultraviolet Laser Diodes (DUV-LD) technology.

Low-threshold AlGaN-based deep ultraviolet laser enabled by a nanoporous cladding layer.

We demonstrated an AlGaN-based multiple-quantum-well (MQW) deep ultraviolet (DUV) laser at 278 nm using a nanoporous (NP) n-AlGaN as the bottom cladding layer grown on the sapphire substrate. The laser has a very-low-threshold optically pumped power density of 79 kW/cm2 at room temperature and a transverse electric (TE)-polarization-dominant emission. The high optical confinement factor of 9.12% benefiting from the low refractive index of the nanoporous n-AlGaN is the key to enable a low-threshold lasing. The I-V electrical measurement demonstrates that an ohmic contact can be still achieved in the NP n-AlGaN with a larger but acceptable resistance, which indicates it is compatible with electrically driven laser devices. Our work provides insights into the design and fabrication of low-threshold lasers emitting in the DUV regime.

Optical Gain Spectrum and Confinement Factor of a Monolayer Semiconductor in an Ultrahigh-Quality Cavity.

Two-dimensional (2D) semiconductors have attracted great attention as a novel class of gain materials for low-threshold, on-chip coherent light sources. Despite several experimental reports on lasing, the underlying gain mechanism of 2D materials remains elusive due to a lack of key information, including modal gain and the confinement factor. Here, we demonstrate a novel approach to directly determine the absorption coefficient of monolayer WS2 by characterizing the whispering gallery modes in a van der Waals microdisk cavity. By exploiting the cavity's high intrinsic quality factor of 2.5 × 104, the absorption coefficient spectrum and confinement factor are experimentally resolved with unprecedented accuracy. The excitonic gain reduces the WS2 absorption coefficient by 2 × 104 cm-1 at room temperature, and the experimental confinement factor is found to agree with the theoretical prediction. These results are essential for unveiling the gain mechanism in emergent, low-threshold 2D-semiconductor-based laser devices.

Evaluating the performance of an AlGaN based deep ultraviolet laser diode using graded waveguide layer and graded cladding layer

To improve the output power and reduce electron leakage of a deep ultraviolet laser diode and optimize its performance,in this paper, the graded waveguide layer was first applied to a traditional AlGaN based deep ultraviolet laser diode, and four different combinations of the waveguide layer structure were simulated. Then a graded cladding layer structure with reduced thickness was added. Finally, the carrier concentration, energy band diagram, P-I curve, and optical confinement factor were numerically analysed and studied. The results demonstrate that, by using an Al-graded waveguide layer/p-cladding layer structure, the optical confinement factor of a laser diode with an emission wavelength of 267 nm, was 29.34%, and the maximum power was 89.81 mW at 100 mA current.

On-chip Mach-Zehnder interferometer sensor with a double-slot hybrid plasmonic waveguide for high-sensitivity hydrogen detection.

An on-chip Mach-Zehnder interferometer (MZI) hydrogen sensor, applying a double-slot hybrid plasmonic (DSHP) waveguide composed of a Si waveguide and two Pd disks on both sides as the sensing arm, is designed. The optical confinement factor of the sensing area can be up to 87%. For the MZI hydrogen sensor with a DSHP waveguide of 14 µm, the sensitivity can be as high as 11.935 nm/%, corresponding to a free spectral range (FSR) of 15 nm. Furthermore, the sensor sensitivity is influenced by the MZI structure parameters, which is highly adjustable. The extinction ratio of the interference spectra can reach over 30 dB. A feasible solution is provided in this paper for highly sensitive hydrogen detection.

Hybrid silica and thin-film lithium niobate waveguides and Y-junctions

Silica (SiO2) strip-loaded waveguides and Y-junctions on lithium niobate (LN) thin film were designed, fabricated and experimentally investigated. We first studied the optical confinement factor distribution in strip-loaded waveguides. The Simulations showed that most of the power (>82%) was confined in the LN layer, and the dimensions of the SiO2 loading strip had a relatively small influence on the optical confinement factor distribution. The SiO2 film was deposited with the magnetron sputtering method. The deposited SiO2 layer approached stoichiometric SiO2, and a smooth surface was obtained. A group of waveguides with widths of 2–5 μm were fabricated using lift-off technology. The 2 μm-wide waveguide displayed low propagation losses of 0.2 dB/cm for the quasi-TE (q-TE) mode and 0.8 dB/cm for the quasi-TM (q-TM) mode at the wavelength of 1550 nm. Y-junctions with small sizes were designed and fabricated based on the low-loss waveguides. The transmission could reach 70–80%, and the splitting ratio maintained at a stable level near 1:1 for the Y-junctions S1 and S4. The low-loss strip-loaded waveguides and Y-junctions offer the possibility of combining SiO2 and LN materials for integrated optics. Additional high-performance photonic devices and circuits using this method are expected in the future.

88×nm High-Efficiency Narrow Divergence Angle Laser Diodes With Coupled Waveguide Photonic Crystal

88x nm laser diodes with coupled waveguide photonic band crystal (CPBC) are designed and fabricated. By optimizing the optical confinement factor in the lightly doped coupled waveguide, the internal loss reduces to 0.52 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The CPBC lasers achieve maximum power conversion efficiency of 65.57% under a continuous wave (CW) mode condition at room temperature, which is the highest reported value to our knowledge at 88x nm. The corresponding vertical divergence angel is 19.8°.

Reverse compositional strategy of multiple quantum wells for the AlGaN-based deep-ultraviolet laser diodes

Due to the high activation energy/ionization energy as Mg increases, Al-rich AlGaN-based deep-ultraviolet (DUV) laser diodes have a structure that is difficult to perform Mg p-doping. The performance of this type of laser diode is affected by the content of Al in the quantum barriers of multiple quantum wells, and reducing the Al content in the laser diodes may simplify its structure and make Mg p-doping less difficult. The proposed device can be improved by adopting the reverse compositional strategy of multiple quantum wells with the Al content of quantum barriers 10% lower than that of quantum wells as opposed to the reference device where the Al content of the quantum barriers is 10% higher than that of the quantum wells. The simulation results have been observed theoretically in terms of the performance parameters such as band diagrams, optical confinement factor, peak gain, emitted power, stimulated recombination rate, and carrier concentration. Two deep ultraviolet laser diode devices have been analyzed in this study within the wavelength range of 267 nm. The proposed device has superior performance with a larger optical confinement factor and increased output power with reduced injection current.

WMS-based near-infrared on-chip acetylene sensor using polymeric SU8 Archimedean spiral waveguide with Euler S-bend

SU8 is a cost-effective polymer material that is highly suitable for large-scale fabrication of waveguides. However, it has not been employed for on-chip gas measurement utilizing infrared absorption spectroscopy. In this study, we propose a near-infrared on-chip acetylene (C2H2) sensor using SU8 polymer spiral waveguides for the first time to our knowledge. The performance of the sensor based on wavelength modulation spectroscopy (WMS) was experimentally validated. By incorporating the proposed Euler-S bend and Archimedean spiral SU8 waveguide, we achieved a reduction in the sensor's size by over fifty percent. Leveraging the WMS technique, we evaluated the C2H2 sensing performance at 1532.83 nm for SU8 waveguides of lengths 7.4 cm and 13 cm. The limit of detection (LoD) values were 2197.1 ppm (parts per million) and 425.5 ppm, respectively, with an averaging time of 0.2 s. Furthermore, the experimentally obtained optical power confinement factor (PCF) closely approximated the simulated value, with a value of 0.0172 compared to the simulated value of 0.016. The waveguide loss is measured to be 3 dB/cm. The rise time and fall time were approximately 2.05 s and 3.27 s, respectively. This study concludes that the SU8 waveguide exhibits significant potential for high-performance on-chip gas sensing in the near-infrared wavelength range.

Micro-Transfer-Printed Membrane Distributed Reflector Lasers on Si Waveguide Modulated With 50-Gbit/s NRZ Signal

In this work, we fabricate directly modulated membrane distributed reflector (DR) lasers on a Si waveguide by utilizing micro-transfer printing method. Micro-transfer printing enables low-loss coupling between the lasers and the silicon photonics circuit, and since it is a back-end process, we can test the lasers prior to integration. A membrane laser is as thick as the Si waveguides, which makes optical coupling between the two quite easy. In addition, membrane lasers with a lateral <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-i-n</i> diode structure have low capacitance and a large optical confinement factor, which means they can achieve a low threshold current and high-speed modulation operation with low energy consumption. The fabricated membrane DR laser integrated with a 220-nm-thick Si waveguide exhibits a low threshold current of 1.2 mA and single-mode operation at 1535 nm with a side-mode suppression ratio (SMSR) of about 40 dB at the bias current of 14 mA. It also achieves the E-O bandwidth of over 25 GHz and 50-Gbit/s non-return-to-zero (NRZ) signal modulation with an extinction ratio of 2.5 dB.

Uncooled 100-GBaud Directly Modulated Membrane Lasers on SiC Substrate

We investigate the temperature dependence of the dynamic characteristics of a 1.3-μm InGaAlAs-based directly modulated membrane laser on a SiC substrate. The laser is fabricated by combining direct wafer bonding of SiC and InP substrates using a very thin (∼10 nm) oxide layer and epitaxial regrowth of a membrane InP layer on the InP/SiC template. The membrane laser structure on SiC with a high thermal conductivity (490 Wm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) and a moderate refractive index (∼2.6) ensures both high thermal dissipation and a large optical confinement factor in the active region, which are ideal for increasing the relaxation oscillation frequency even at high operating temperatures. We further leverage the optical feedback effect from the output facet of a waveguide to enhance the bandwidth and enable signal modulation at 100 GBaud and beyond. Owing to the high relaxation oscillation frequency and the photon-photon resonance effect, it is possible to obtain a flat frequency response at temperatures ranging from 25 to 85°C. The fabricated membrane laser on SiC with an active-region length of 50 μm exhibits 3dB bandwidths of >110, 97, and 74 GHz at 25, 55, and 85°C, respectively. We successfully demonstrate 2-km transmissions of 100-Gbit/s NRZ signals under uncooled conditions (25 to 85°C). Furthermore, the laser is capable of 112-Gbit/s NRZ modulation at 85°C.

Effect of AlGaN quantum barrier thickness on electron-hole overlapping in deep-ultraviolet laser diode

AlGaN deep ultraviolet (DUV) with the high induced polarization emitters effect degrades the performance of the laser diode (LD) and brings a higher injection current density, resulting in reduced laser gain. Quantum barriers (QB) play a vital role in carrier flow (electrons, holes) in multiple quantum well (MQW). This work investigates the quantum barrier thickness effect on the performance of DUV LDs. Furthermore, the performance of DUV LD is enhanced by working on overlapping electrons and holes in the active region. The theoretically analyzed results illustrate that by minimizing the thickness of the AlGaN quantum barrier (QB), the electron-hole overlapping can be improved. Higher overlapping increases the rate of stimulated recombination. Compared with the reference structure AlGaN QB with 3 nm thickness, the emitted power can be increased by 11%, the optical confinement factor (OCF) by 71%, the electron-hole overlapping by 55%, and the laser gain by 149%. But selecting 12 nm QBs, power starts decreasing along with OCF, electron-hole overlapping, and laser gain. When the AlGaN QB is thicker, the height of the conduction band barrier diminishes, which boosts electron leakage coming from MQM, and when the valance band barrier's height is elevated, which reduces the efficiency of hole injection toward the MQW. Thus, it is concluded the below 12 nm QB thickness, the thinner the quantum barriers, the more carrier flows toward MQW, improving performance.

Wideband SOA fiber-to-fiber gain and saturation output power in the C-band: impact of characteristic parameters

Semiconductor Optical Amplifiers (SOAs) have numerous attractive characteristics; for example: minimum power usage, broadband, flexible wavelength, wide dynamic range and significant nonlinearities. In this study, we present a comprehensive model of output saturation power and fiber-to-fiber gain of wideband SOAs. Furthermore, we investigate the impact of optical confinement factor, bias current, input signal power, temperature, and amplifier length on the fiber-to-fiber gain spectrum in the C-band. The obtained numerical results are approved by comparison with simulation results showing a fair agreement. The results reveal that output saturation power is improved by decreasing the optical confinement factor. Additionally, when input signal power rises, the maximum fiber-to-fiber gain value declines. Furthermore, as the temperature rises, the fiber-to-fiber gain decreases. Moreover, the maximum fiber-to-fiber gain is obtained at shorter amplifier lengths. Additionally, the effect of carrier density on the spectrum of coefficient of material gain is investigated, showing an increase in its value when increasing the carrier density, with a peak near 1550 nm.

Symmetric longitudinal Mach-Zehnder modulator using lithium niobate

There are many problems that restrict the work of the Mach-Zehnder modulator (MZM), including the lack of using various windows of wavelengths, the large half-wave voltage, and the small optical confinement factor. In this paper, a mathematical model for MZM based on lithium niobate (LN) is designed to solve these problems. In this model, a wide window of optical wavelength from visible-to-infrared (632.8-to-1560 nm) was utilized. Moreover, it achieved a better modulation with lower attenuation and a lower dispersion by the window (1550-1560) nm. The other window of optical wavelength is about (632.8-to-634 nm), and (646-to-647 nm) which can be used for short-haul applications to reduce attenuation and dispersion. Furthermore, a small length of the arm, about 2-3 mm, was utilized to accomplish a large change of the refractive index and lower applied voltage of up to 250 V. The small operation half-wave voltage achieved about 1.2 V leading to better switching of the MZM. In addition, a large optical confinement factor of ≤1 unitless was obtained. Even better performance of MZM was attained by using a suitable length arm of MZM of about 2 mm, along with an electric field of about 175 V/mm and 233 V/mm using poling at 100 V.