Ridge Waveguide Research Articles

Dual-color upconversion luminescence emission from Er:LiNbO3 on-chip ridge waveguides

Dual-color upconversion luminescence of Er3+-doped (0.1% mol) lithium-niobate-on-insulator (Er:LNOI) on-chip ridge waveguides is observed under the excitation of a continuous-wave 980-nm semiconductor laser, emitting both blue (at 450 nm) and green (at 528.3 nm) fluorescence emissions. The on-chip waveguides, with a propagation loss of around 3 dB/cm at 1550 nm, are fabricated by diamond blade dicing technique. The experimentally observed waveguiding modal profiles are in fairly good agreement with simulation results, indicating good quality of the fabricated waveguides. We believe this work will benefit the development of LiNbO3-based integrated photonics.

Birefringence phase-matched direct third-harmonic generation in a ridge optical waveguide based on a KTiOPO4 single crystal

Birefringence phase-matched third-harmonic generation at 1594 nm is performed for the first time in a KTiOPO4 single crystal micrometric ridge waveguide. The energy conversion efficiency reaches 3.4% for a pump energy as low as 2 µJ over a pulse duration of 15 ps at a repetition rate of 10 Hz. Strong agreements between theory and experiments for both phase-matching and conversion efficiency is obtained, which let us envision future triple photon generation quantum experiments.

Efficient generation of ultra-broadband parametric fluorescence using chirped quasi-phase-matched waveguide devices.

We present a highly efficient photon pair source using chirped quasi-phase-matched (QPM) devices with a ridge waveguide structure. We developed QPM waveguide devices with chirp rates of 3% and 6.7%. Spectrum measurements reveal that the generated photons have bandwidths of 229 nm and 325 nm in full width at half maximum (FWHM), alternatively, 418 nm and 428 nm in base-to-base width for the 3% and 6.7% chirped devices, respectively, which are much broader than the bandwidth of 16 nm in FWHM observed with a non-chirp device. We also evaluate the generation efficiency of photon pairs from coincidence measurements using two superconducting single photon detectors (SSPDs). The estimated generation efficiencies of photon pairs were 2.7 × 106 pairs/s·µW and 1.2 × 106 pairs/s·µW for the 3% and 6.7% chirped devices, respectively, which are comparable to the generation efficiency for the non-chirp device of 2.7 × 106 pairs/s·µW. We also measured the frequency correlation of the photon pairs generated from the 6.7% chirped device. The experimental results clearly show the frequency correlation of the generated broadband photon pairs.

High efficiency, small size, and large bandwidth vertical interlayer waveguide coupler

Since the advent of three-dimensional photonic integrated circuits, the realization of efficient and compact optical interconnection between layers has become an important development direction. A vertical interlayer coupler between two silicon layers is presented in this paper. The coupling principle of the directional coupler is analyzed, and the traditional method of using a pair of vertically overlapping inverse taper structures is improved. For the coupling of two rectangular waveguide layers, a pair of nonlinear tapers with offset along the transmission direction is demonstrated. For the coupling of two ridge waveguide layers, a nonlinear taper in each layer is used to achieve high coupling efficiency. The simulation results show that the coupling efficiency of the two structures can reach more than 90% in a wavelength range from 1500 nm to 1650 nm. Moreover, the crosstalk is reduced to less than –50 dB by using multimode waveguides at intersections. The vertical interlayer coupler with a nonlinear taper is expected to realize the miniaturization and dense integration of photonic integrated chips.

Suspended nanocrystalline diamond ridge waveguides designed for the mid-infrared

A comprehensive study and design of air-clad suspended ridge diamond waveguides for operation across the 2.5–16 µm spectral range is presented, specifically targeting nanocrystalline diamond (NCD) thin films directly grown on silicon substrates. Three film thicknesses of 520, 1000 and 2000 nm are considered, to cover overlapping sub-bands of 2.5–5, 4–9 and 8–16 µm, respectively. Within each sub-band, the waveguide dimensions for single mode quasi-TE operation are found and the waveguide material losses and bending losses are estimated at each design point. In addition, in each case the minimum required undercut depth and etch hole placement for optical isolation of the waveguide mode from the silicon substrate is also quantified. We also estimate the losses associated with scattering from surface roughness, which is an unavoidable byproduct of the NCD thin film growth process. Our results indicate that despite the relatively low film thickness-to-wavelength ratio, mechanically stable waveguides with good optical confinement and low material and bending losses can be realised to cover the full 2.5–16 µm range. In addition, scattering loss estimations predict a drastic drop in roughness-induced scattering losses above 6 µm, even for relatively rough films. In addition to highlighting the utility of suspended NCD as a versatile platform for mid-infrared integrated photonics, the approaches and results presented here can be used to inform the design of suspended air-clad waveguides in other material platforms.

783 nm wavelength stabilized DBR tapered diode lasers with a 7 W output power.

Wavelength stabilized distributed Bragg reflector (DBR) tapered diode lasers at 783 nm will be presented. The devices are based on GaAsP single quantum wells embedded in a large optical cavity leading to a vertical far field angle of about 29° (full width at half maximum). The 3-inch (7.62 cm) wafers are grown using metalorganic vapor phase epitaxy. In a full wafer process, 4 mm long DBR tapered lasers are manufactured. The devices consist of a 500 µm long 10th order surface DBR grating that acts as rear side mirror. After that, a 1 mm long ridge waveguide section is realized for lateral confinement, which is connected to a 2.5 mm long flared section having a full taper angle of 6°. At an injection current of 8 A, a maximum output power of about 7 W is measured. At output powers up to 6 W, the measured emission width limited by the resolution of the spectrometer is smaller than 19 pm. Measured at 1/e2 level at this output power, the lateral beam waist width is 11.5 µm, the lateral far field angle 12.5°, and the lateral beam parameter M2 2.5. The respective parameters measured using the second moments are 31 µm, 15.2°, and 8.3. 70% of the emitted power is originated from the central lobe.

Power scaling of continuous-wave second harmonic generation in a MgO:PPLN ridge waveguide and the application to a compact wavelength conversion module.

The power scaling of continuous-wave (CW) second harmonic generation (SHG) in a MgO:periodically poled lithium niobite (PPLN) ridge waveguide is investigated. The nonlinear coefficient and propagation loss factors of the MgO:PPLN waveguide are verified for future reference. The MgO:PPLN waveguide structure is determined according to a practical fiber coupling configuration, as well as the theoretical model of output power characteristics. Utilizing the designed MgO:PPLN waveguide, the 775 nm SHG power successfully reaches up to 4.02 W at an incident power of 7 W with overall conversion efficiency of 58%. Finally, a compact all-fiber waveguide conversion module is demonstrated for verifying the feasibility of commercial applications.

RF and Microwave Ion Sources Study at Institute of Modern Physics

Intense ion beam production is of high importance for various versatile applications from accelerator injectors to secondary ion mass spectrometry (SIMS). For these purposes, different types of ion beams are needed and, accordingly, the optimum plasma to produce the desired ion beams. RF-type plasma features a simple structure, high plasma density and low plasma temperature, which is essential for negative ion beam production. A very compact RF-type ion source using a planar coil antenna has been developed at IMP for negative molecular oxygen ion beam production. In terms of high-intensity positive ion beam production, 2.45 GHz microwave power-excited plasma has been widely used. At IMP, we developed a 2.45 GHz plasma source with both ridged waveguide and coaxial antenna coupling schemes, tested successfully with intense beam production. Thanks to the plasma built with an external planar coil antenna, high O2− production efficiency has been achieved, i.e., up to 43%. With 2.45 GHz microwave plasma, the ridged waveguide can support a higher power coupling of high efficiency that leads to the production of intense hydrogen beams up to 90 emA, whereas the coaxial antenna is less efficient in power coupling to plasma but can lead to attractive ion source compactness, with a reasonable beam extraction of several emA.

Tunable polarization mode conversion using thin-film lithium niobate ridge waveguide.

Lithium niobate on insulator (LNOI) waveguides, as an emerging technology, have proven to offer a promising platform for integrated optics, due to their strong optical confinement comparable to silicon on insulator (SOI) waveguides, while possessing the versatile properties of lithium niobate, such as high electro-optic coefficients. In this paper, we show that mode hybridization, a phenomenon widely found in vertically asymmetric waveguides, can be efficiently modulated in an LNOI ridge waveguide by electro-optic effect, leading to a polarization mode converter with 97% efficiency. Moreover, the proposed device does not require tapering or periodic poling, thereby greatly simplifying the fabrication process. It can also be actively switched by external fields. Such a platform facilitates technological progress of photonics circuits and sensors.

A low‐loss Ka‐band waveguide to substrate integrated waveguide transition based on ridged stepped‐impedance transformer

A low-loss Ka-band transition from waveguide to substrate integrated waveguide (SIW) is presented based on ridge waveguide stepped-impedance transformer. This novel transition can operate across a full Ka-band (26.5 to 40 GHz) with an insertion loss lower than 0.59 dB and return loss over 14.2 dB. Furthermore, compared to existing transitions the introduction of ridges reduces the metal usage, resulting in weight reduction and offering an encouraging application for weight-sensitive satellite communications (SatComs).

Design and development of a compact ion implanter and plasma diagnosis facility based on a 2.45GHz microwave ion source.

A project on developing a 2.45GHz microwave ion source based compact ion implanter and plasma diagnostic facility has been taken up by the Central University of Punjab, Bathinda. It consists of a double-wall ECR plasma cavity, a four-step ridge waveguide, an extraction system, and an experimental beam chamber. The mechanical design has been carried out in such a way that both types of experiments, plasma diagnosis and ion implantation, can be easily accommodated simultaneously and separately. To optimize microwave coupling to the ECR plasma cavity, a four-step ridge waveguide is designed. Microwave coupling simulation for the ECR plasma cavity has been performed at different power inputs using COMSOL Multiphysics. An enhanced electric field profile has been obtained at the center of the ECR plasma cavity with the help of a four-step ridge waveguide compared to the WR284 waveguide. The magnetic field distribution for two magnetic rings and the extraction system's focusing properties have been simulated using the computer simulation technique. A tunable axial magnetic field profile has been obtained with a two permanent magnetic ring arrangement. The dependency of the beam emittance and beam current on accelerating voltages up to 50 kV has been simulated with different ions. It shows that ion masses have a great impact on the beam emittance and output current. This facility has provision for in situ plasma diagnosis using a Langmuir probe and optical emission spectroscopy setups. This system will be used for ion implantation, surface patterning, and studies of basic plasma sciences.

Photonics Rib Waveguide Dimension Dependent Charge Distribution and Loss Characterization

The simulation of behaviour of the charge distribution and the loss characteristic for rib-waveguide is demonstrated by using silicon-on-insulator (SOI). In this simulation, the rib waveguide is designed at a core width of 450nm, core height of 250nm, rib height of 50nm and buried oxide height of 100nm. These dimensions are set as reference. The aspiration of designing rib waveguide instead of other type of waveguide such as ridge waveguide is from the higher light confinement that can be accomplished by rib waveguide as the refractive index difference is huge and the designing of an active device can be realized. In this analysis, free carrier-injection effect was implemented in the first part of the simulation to study the distribution charges of rib-based waveguide structure based on basic dimensions. In this analysis, electrical voltage was varied from 0V to 1.2V in steps of 0.2V for the analysis of distribution of electron. In the second part of the simulation, four design parameters had been amended which included the core width and height, rib height and buried oxide height. Physical dimensions of the waveguide were altered to achieve smaller device footprint with optimized performance affecting large Free Spectral Range (FSR) and high Q-factor. With proper waveguide physical dimensions design, a good performance Micro-Ring Resonator (MRR) exhibits the principles of wide FSR and Q-factor can be achieved.

Reconfigurable and low-power consumption polarization rotating beam splitter with EIT-like effect based on SOI ridge waveguide

Polarization rotating beam splitter (PSR) is a key component of an on-chip polarization diversity system. However, a conventional PSR is usually designed for a specific use case, which limits general-purpose applications since its polarization rotation and beam splitting ratio are fixed. In this paper, this theoretical modeling, numerical simulations, and experimental results on the reconfigurable PSR with arbitrary beam splitting ratio is proposed for the silicon on insulator (SOI) platform. The device includes a polarization rotation region and a beam splitting region. The polarization rotation region is composed of multi-segment tapered waveguides, and the beam splitting region consists of a racetrack resonator with a heater. By changing the voltage applied to the heater, the beam splitting ratio can be changed. Measured results show that when the incident light is TM0 mode, it will be converted to TE0 mode and output from two output ports. The beam splitting ratio of the two output ports can be adjusted from 9:1 to 1:9. Furthermore, in order to optimize the thermal tunability of the PSR, we introduce an asymmetric embedded racetrack resonator with electromagnetically induced transparency (EIT)- like effect in beam splitting region, which can reduce the power consumption dramatically from 27.5 mW to 1.8 mW. The proposed integrated PSR suggests great potential for reconfigurable, fully programmable photonic polarization diversity circuits. In addition, we believe such an embedded racetrack resonator with EIT-like effect could find its applications in chip-scale sensor, modulator, switch, etc.

Watt-level SHG in undoped high step-index PPLN ridge waveguides

Nonlinear quadratic waveguides are key components to obtain efficient frequency conversion. In this paper we present the performances of highly multimode periodically poled lithium niobate (PPLN) ridge waveguides for high power CW SHG are presented. We report the generation of 1 W of second harmonic on the fundamental guided mode with a conversion efficiency of 56% at telecom wavelengths. A stable nonlinear process is obtained despite use of an undoped congruent LiNbO3 crystal. The input damage threshold of the ridge waveguide is found to set the maximum usable power.

Converting the guided-modes of Bloch surface waves with surface pattern.

The guided-modes of Bloch surface waves, such as the transverse electric modes (TE00 and TE01 modes), can simultaneously exist in a low-refractive-index ridge waveguide with subwavelength thickness that are deposited on an all dielectric one-dimension photonic crystal. By using the finite difference frequency domain method, coupled mode theory and finite-difference time-domain method, the conversion between the guided-modes has been investigated. This conversion can be realized in a broadband wavelength with surface pattern of this low-index ridge. This conversion is useful for developing lab-on-a-chip photonic devices, such as a mode converter that can maintain the output mode purity over 90% with working wavelength ranging from 590 to 680 nm, and a power splitter that can maintain the splitting ratio over 8:2 with wavelength ranging from 530 to 710 nm.

High-power narrow spectrum GaSb-based DBR lasers emitting near 2.1 µm

Stable high-power narrow-linewidth operation of the 2.05-2.1 µm GaSb-based diode lasers was achieved by utilizing the sixth-order surface-etched distributed Bragg reflector (DBR) mirrors. The DBR multimode devices with 100 µm wide ridge waveguides generated ∼850mW in the continuous wave (CW) regime at 20°C. The device CW output power was limited by thermal rollover. The laser emission spectrum was defined by Bragg reflector reflectivity at all operating currents in a wide temperature range. The devices operated at DBR line with detuning from gain peak exceeding 10 meV.

Low loss ridge-waveguide grating couplers in lithium niobate on insulator

The conventional ridge waveguides and grating-couplers in x-cut single-crystal lithium niobate on insulator (LNOI), have been designed, fabricated and characterized. All the device structures patterned on the sample were monolithically defined by one step of the electron-beam lithography process, followed by dry-etching. A low insertion loss (IL) of −6.3 dB/coupler for transverse-electric (TE) polarization inputs at the wavelength of 1543 nm was measured in the fabricated best device with the tapered structures, and exhibited a broad 3-dB optical bandwidth of more than 90 nm. This work may pave the way towards the future research of high-efficiency photonic waveguide components in thin-film LNOI.

Frozen mode in coupled silicon ridge waveguides for optical true time delay applications

We propose a simple photonic waveguide structure that exhibits light propagation modes with vanishing group velocity via mode degeneracy. This enables stationary inflection point dispersion leading to the frozen mode and a true time delay device suitable for ultra-wide-band beamforming for millimeter wave (mmWave) phased arrays. The structure consists of three silicon ridge waveguides in proximity with periodic gaps introduced in the outer waveguides to create a band gap. The structure is complementary metal–oxide–semiconductor compatible with a very small footprint of only about 56 µ m 2 and more resilient to fabrication uncertainties as compared to the previously studied structures. Simulation results show transmission of 70% of the incident wave for the frozen mode at the 1.55 µm (193.6 THz) wavelength through the waveguide. It also enables a delay-bandwidth product of 6.75 along with unprecedented frequency independent bandwidth of about 0.5 THz for RF-mmWave–terahertz beamforming.

High power GaN-based blue superluminescent diodes with low spectral modulation

We present high-power GaN-based blue superluminescent diodes (SLDs) with bend waveguides. The devices were grown on a c-plane GaN free-standing substrate by metal–organic chemical vapor deposition. Studies on waveguide design were conducted to increase the output power of SLDs. Low spectral modulation had been obtained by optimizing the bend angle of the ridge waveguide. An output power as high as 510 mW had been obtained for SLDs emitting at 441 nm with a full width at half maximum of 4.4 nm.

Monolithic DWDM source with precise channel spacing

We report a low-cost manufacturing approach for fabricating monolithic multi-wavelength sources for dense wavelength division multiplexing (DWDM) systems that offers high yield and eliminates crystal regrowth and selective area epitaxy steps that are essential in traditional fabrication methods. The source integrates an array of distributed feedback (DFB) lasers with a passive coupler and semiconductor optical amplifier (SOA). Ridge waveguide lasers with sampled Bragg side wall gratings have been integrated using quantum well intermixing to achieve a fully functional four-channel DWDM source with 0.8 nm wavelength spacing and residual errors < 0.13 nm. The output power from the SOA is > 10 mW per channel making the source suitable for use in passive optical networks (PONs). We have also investigated using multisection phase-shifted sampled gratings to both increase the effective grating coupling coefficient and precisely control the channel lasing wavelength spacing. An 8-channel DFB laser array with 100 GHz channel spacing was demonstrated using a sampled grating with two π-phase-shifted sections in each sampling period. The entire array was fabricated by only a single step of electron beam lithography.