Temperature-dependent Wavelength Shift Research Articles

Low-cross-talk and thermo-insensitive CWDM (de)multiplexer assisted with compact MZIs and slot waveguides.

A low-cross-talk and thermo-insensitive 1×4 coarse wavelength-division multiplexing device is proposed on the silicon-on-insulator platform with the help of compact Mach-Zehnder interferometers (MZIs) and slot waveguides. The compact MZIs are used to achieve wavelength-insensitive power splitting. In the phase shifters, the trade-off between the opposite thermo-optical coefficients of the Si core and SU8 cladding in the slot waveguide is used to overcome the strong thermo-optic effect of silicon. The simulated results show that the cross talk is less than -20d B at central wavelengths and the temperature-dependent wavelength shift is reduced to ∼4.7p m/∘ C. For the four channels, the 1-dB and 3-dB bandwidths are ∼14n m and ∼18n m, respectively.

Compact thermo-optic modulator based on a titanium dioxide micro-ring resonator.

Thermo-optic (TO) modulators with the ability of working from the visible to the infrared spectrum are promising for many emerging applications. However, current technologies suffer from either a limited operating spectrum range or weak TO effect. In this work, we present an effective TO modulator based on a titanium dioxide TiO2 micro-ring resonator with solgel SiO2 as the cladding. Taking advantage of the large negative TO coefficients of TiO2 and solgel SiO2, the fabricated device demonstrates a temperature-dependent wavelength shift of 58.3 pm/°C and a π-shift power consumption of 7.8 mW. Since both TiO2 and solgel SiO2 have a broad transmission window, the demonstrated device will have wide applications in integrated optics from the visible to the infrared wavelength range.

Silicon-coupled tantalum pentoxide microresonators with broadband low thermo-optic coefficient.

Stable microresonators are important integrated photonics components but are difficult to achieve on silicon-on-insulator due to silicon intrinsic properties. In this work, we demonstrate broadband thermally stable tantalum pentoxide microresonators directly coupled to silicon waveguides using a micro-trench co-integration method. The method combines in-foundry silicon processing with a single step backend thin-film deposition. The passive response of the microresonator and its thermal behavior are investigated. We show that the microresonator can operate in the overcoupled regime as well as near the critical coupling point, boasting an extinction ratio over 25 dB with no higher-order mode excitation. The temperature dependent wavelength shift is measured to be as low as 8.9 pm/K and remains below 10 pm/K over a 120 nm bandwidth.

1.4 million Q factor Si3N4 micro-ring resonator at 780 nm wavelength for chip-scale atomic systems.

A silicon nitride micro-ring resonator with a loaded Q factor of 1.4 × 106 at 780 nm wavelength is demonstrated on silicon substrates. This is due to the low propagation loss waveguides achieved by optimization of waveguide sidewall interactions and top cladding refractive index. Potential applications include laser frequency stabilization allowing for chip-scale atomic systems targeting the 87Rb atomic transition at 780.24 nm. The temperature dependent wavelength shift of the micro-ring was determined to be 13.1 pm/K indicating that a minimum temperature stability of less than ±15 mK is required for such devices for wavelength locking applications. If a polyurethane acrylate top cladding of an optimized thickness is used then the micro-ring could effectively be athermal, resulting in reduced footprint, power consumption, and cost of potential devices.

Athermal third harmonic generation in micro-ring resonators

Nonlinear high-harmonic generation in micro-resonators is a common technique used to extend the operating range of applications such as self-referencing systems and coherent communications in the visible region. However, the generated high-harmonic emissions are subject to a resonance shift with a change in temperature. We present a comprehensive study of the thermal behavior induced phase mismatch that shows this resonance shift can be compensated by a combination of the linear and nonlinear thermo-optics effects. Using this model, we predict and experimentally demonstrate visible third harmonic modes having temperature dependent wavelength shifts between -2.84 pm/℃ and 2.35 pm/℃ when pumped at the L-band. Besides providing a new way to achieve athermal operation, this also allows one to measure the thermal coefficients and Q-factor of the visible modes. Through steady state analysis, we have also identified the existence of stable athermal third harmonic generation and experimentally demonstrated orthogonally pumped visible third harmonic modes with a temperature dependent wavelength shift of 0.05 pm/℃ over a temperature range of 12 ℃. Our findings promise a configurable and active temperature dependent wavelength shift compensation scheme for highly efficient and precise visible emission generation for potential 2<em>f</em>-3<em>f</em> self-referencing in metrology, biological and chemical sensing applications.

Monolithic Integration of CMOS Temperature Control Circuit and Si3N4 Microring Filters for Wavelength Stabilization Within Ultra Wide Operating Temperature Range

Microring resonators are widely used for both active and passive devices for their small footprint and low- power consumption. However, it is very challenging to achieve precise control of stability of the resonant wavelength, as the microring is very sensitive to fabrication imperfections and temperature variations. In this paper, we propose and demonstrate a new method of monolithic integration of complementary metal-oxide-semiconductor (CMOS) temperature control circuit and Si3N4 microring filters for resonant wavelength stabilization. Through CMOS back-end process, Si3N4 photonic layer is formed vertically above the CMOS circuit chip. Due to the automatic temperature control, the integrated Si3N4 microring filters are almost immune to environment temperature change. The temperature-dependent wavelength shift (TDWS) is decreased from 21.43 pm/°C to 1.43 pm/°C with the environment temperature tuning range from 30 °C to 65 °C.

A thermal-sensitive design of a 3D torus-based optical NoC architecture

In order to overcome limitations of traditional electronic interconnects in terms of power efficiency and bandwidth density, optical networks-on-chip (NoC) based on silicon photonics have been proposed as an emerging on-chip communication architecture for chip multiprocessors (CMPs) with large core counts. However, due to thermo-optic effects, wavelength-selective silicon photonic devices such as microresonators suffer from temperature-dependent wavelength shift. In this work, we propose a thermal-sensitive design of a 3D torus-based optical NoC architecture. For the 3D torus-based optical NoC architecture, we propose a hybrid optical-electronic router architecture with a fully-connected 7 × 7 optical switching fabric. Besides, a thermal-sensitive routing algorithm is proposed to optimize the optical power loss in the presence of on-chip temperature variations. Simulation results show that for a set of synthetic traffic patterns, the proposed 3D torus-based optical NoC with the thermal-sensitive routing reduces the average thermal-induced optical power loss by 14.3% and 17% respectively as compared to the matched 3D torus-based optical NoC and the 3D mesh-based optical NoC with the traditional XYZ routing. For a set of real applications, the proposed 3D torus-based optical NoC with the thermal-sensitive routing reduces the worst-case optical power loss by 7.9% and 14.6% respectively as compared to the matched 3D torus-based optical NoC and the 3D mesh-based optical NoC with the traditional XYZ routing.

Optimization of size uniformity and dot density of InxGa1−xAs/GaAs quantum dots for laser applications in 1 µm wavelength range

This work reports on growth and characterization of self-assembled InxGa1−xAs quantum dots grown on GaAs (1 0 0) substrate designed to emit at 1030 nm. All structures were grown by molecular beam epitaxy and investigated by photoluminescence (PL) spectroscopy and atomic force microscopy. The growth parameters, such as the growth temperature, QD layer thickness and indium content were changed systematically. A strong reduction in PL linewidth from 54 meV down to 26 meV measured at 10 K for a single QD layer was achieved as the result of a more uniform QD size distribution. Additionally, a correlation between the linewidth and the temperature dependent wavelength shift of the PL peak was found.

Temperature dependence of microhole-based fiber Fabry–Perot interferometric sensors fabricated by excimer laser

A miniature in-fiber Fabry–Perot interferometric (FPI) sensor is demonstrated. Through manufacturing microhole in a single-mode fiber with excimer laser, a single microhole FPI sensor and a dual microhole FPI sensor are fabricated, and the temperature sensing characteristics of them are investigated experimentally. The results show that the spectra of two sensors shift to short wavelength with an increase in the temperature, and the relationships between wavelength shift and temperature change have better linearity in temperature range of 30°C to 85°C. The temperature sensitivity of single microhole FPI sensor is 0.160 nm / ° C, and the dual microholes FPI sensor has two temperature sensitivities corresponding to different FP cavities. Furthermore, the temperature sensitivity can be adjusted by changing the distance between two microholes. When increasing the distance from 1 to 2 mm, the higher temperature sensitivity can be changed from 0.176 to 0.192 nm / ° C, and the temperature-dependent wavelength shift still keeps a good linearity. Compared with conventional fiber Bragg grating temperature sensor, this kind of FPI sensor has not only different dual temperature sensitivities but also higher sensitivity and stability, so that this kind of microhole FPI sensor can be used in many fields.

Polymer resonators sensors for detection of sphingolipid gel/fluid phase transition and melting temperature measurement

This work describes a low-cost biophotonic sensor shaped by way of cheap processes as hybrid silicon/silica/polymer resonators able to detect biological molecule gel/fluid phase transition as lipids at very low concentration (sphingomyelin). The photonic structure is composed of specific amplified deep UV photoresist-polymer waveguides coupled by a sub-wavelength gap with racetrack microresonators allowing a low temperature-dependent operation ranging from 16 to 42°C. The temperature dependent wavelength shift and the thermo-optic coefficient characterizing the quantified resonances and opto-geometric properties of the device have been evaluated, highlighting an enough low thermal features of the whole system for such application. With an appropriate vesicle lipid deposition process specific in biology associated to an apt experimental bio-thermo-photonic protocol (made of serial optical resonance spectra acquisitions with statistical treatments), the dynamic evolution of the sphingomyelin lipid phase transition was assessed: then, the ability to detect their own gel/fluid transition phase and melting temperature has been demonstrated with a mass product factor 107 lower than that of more conventional methods The equilibrium of the regime of the resonators was highlighted as being broken by the dynamic of the sphingomyelin and its own phase transition prior relevant detection.

Highly Sensitive Nonlinear Temperature Sensor Based on Modulational Instability Technique in Liquid Infiltrated Photonic Crystal Fiber

A highly sensitive nonlinear temperature sensor, which is based on modulational instability (MI) process, is theoretically demonstrated for the first time using a CS2-filled photonic crystal fiber (CSPCF). The proposed novel temperature sensor works on the principle of measurement of a temperature-dependent wavelength shift of generated Stokes and anti-Stokes MI Sidebands. Based on the notion of MI dynamics, the performance of the proposed temperature sensor is studied in both anomalous and normal dispersion regimes of an appropriately designed CSPCF. It is found that the sensitivity of the proposed nonlinear temperature sensor is very low when the CSPCF is pumped in the anomalous dispersive region. However, the sensitivity is enhanced by more than 66 times using Stokes line in the normal dispersion regime. The proposed sensor is optimized by varying the structural parameters and pump parameters, such as pitch, air-hole diameter, pump wavelength, and pump power. The proposed nonlinear temperature sensor, which is made up of an appropriate structure of CSPCF having a length of 13 cm exhibits a sensitivity of −82 nm/°C using Stokes line and 435 nm/°C using anti-Stokes line while pumped with a power of 100 W in the normal dispersive region.

Silicon nitride O-band (de)multiplexers with low thermal sensitivity.

In this paper, four-channel cascaded Mach-Zehnder interferometer-based wavelength (de)multiplexers in the O-band are demonstrated experimentally by utilizing silicon nitride (SiN) optical waveguides. By reference to the commonly used 100 Gigabit Ethernet standards, two types of (de)multiplexer devices with different channel spacings are designed and fabricated. Both the devices exhibit low insertion loss and flat passbands. The lower thermo-optical coefficient provided by SiN brings benefits of reduction in thermal sensitivity. The fabricated (de)multiplexers show a temperature-dependent wavelength shift of about 18.5 pm/°C, which is reduced by 75% compared to the standard silicon-based devices.

Wavelength division multiplexed light source monolithically integrated on a silicon photonics platform.

We demonstrate monolithic integration of a wavelength division multiplexed light source for silicon photonics by a cascade of erbium-doped aluminum oxide (Al2O3:Er3+) distributed feedback (DFB) lasers. Four DFB lasers with uniformly spaced emission wavelengths are cascaded in a series to simultaneously operate with no additional tuning required. A total output power of -10.9 dBm is obtained from the four DFBs with an average side mode suppression ratio of 38.1±2.5 dB. We characterize the temperature-dependent wavelength shift of the cascaded DFBs and observe a uniform dλ/dT of 0.02 nm/°C across all four lasers.

Low-threshold room-temperature AlGaAs/GaAs nanowire/single-quantum-well heterostructure laser

Near-infrared nanowire lasers are promising as ultrasmall, low-consumption light emitters in on-chip optical communications and computing systems. Here, we report on a room-temperature near-infrared nanolaser based on an AlGaAs/GaAs nanowire/single-quantum-well heterostructure grown by Au-catalyzed metal organic chemical vapor deposition. When subjects to pulsed optical excitation, the nanowire exhibits lasing, with a low threshold of 600 W/cm2, a narrow linewidth of 0.39 nm, and a high Q factor of 2000 at low temperature. Lasing is observed up to 300 K, with an ultrasmall temperature dependent wavelength shift of 0.045 nm/K. This work paves the way towards ultrasmall, low-consumption, and high-temperature-stability near-infrared nanolasers.

Athermal and flat-topped silicon Mach-Zehnder filters.

Athermal and flat-topped transmissions are the two main requirements for a silicon WDM filter. A Mach-Zehnder (MZ) filter which simultaneously satisfies these two requirements has been experimentally demonstrated in this paper. A combination of strip waveguide and hybrid strip-slot waveguide is introduced for athermalization, and two-stage interference is utilized for flat-topped transmission. The temperature dependent wavelength shift is measured to be ~-5 pm/K while the best 1 dB bandwidth is 5.5 nm with 14.7 nm free spectral range (FSR). The measured minimum insertion loss is only 0.4 dB with a device dimension of 170 μm × 580 μm. Moreover, Such a MZ filter is compatible with the state-of-art CMOS-fabrication process and its minimum feature size is as large as 200 nm.

Highly sensitive optical temperature sensor based on a SiN micro-ring resonator with liquid crystal cladding.

This work develops a sensitivity-enhanced optical temperature sensor that is based on a silicon nitride (SiN) micro-ring resonator that incorporates nematic liquid crystal (NLC) cladding. As the ambient temperature changes, the refractive index of the NLCs, which have a large thermal-optical coefficient, dramatically varies. The change in the refractive index of the NLC cladding that is caused by the temperature shift can alter the effective refractive index of the micro-ring resonator and make the resonance wavelength very sensitive to the ambient temperature. The temperature-sensitivity of the device with 5CB cladding for TM-polarized light was measured to be as high as 1nm/°C between 25 and 33 °C and over 2nm/°C at temperatures close to clearing temperature of the 5CB cladding. The temperature-sensitivity of the proposed device is at least 55 times that of the micro-ring resonator with air cladding, whose temperature-dependent wavelength shift for TM-polarized light is 18pm/ °C.

Athermal and High-Q Hybrid TiO2–Si3N4 Ring Resonator via an Etching-Free Fabrication Technique

In this work, we have demonstrated a hybrid TiO2–Si3N4 ring resonator with a high-Q and a temperature-insensitive resonance. The waveguide consists of a thermo-optic positive Si3N4 slab and a negative TiO2 overcladding. The TiO2 layer has a shallow ridge structure, which has been designed to realize an athermal operation and maintain a low scattering loss. During the fabrication of this waveguide, there was no need to utilize the dry-etching process. The method affords a straightforward fabrication and a precise control over the waveguide dimensions. As a result, the ring resonator exhibits a high Q value of 1.55 × 105, a low propagation loss of 0.4 dB/cm, and a small temperature-dependent wavelength shift of 0.14 pm/°C between 25 and 60 °C.

Influence of titania cladding on SOI grating coupler and 5 μm-radius ring resonator

Titania cladding is deposited on a 5μm-radius silicon-on-insulator ring resonator and grating couplers which are patterned by deep-ultraviolet lithography. The influence of titania cladding is studied by measuring the transmission spectra of the ring resonator coupled to a pair of single-mode fibers through the grating couplers. Temperature dependent wavelength shift of TE-like mode through the ring resonator is reduced to −20 to +20pm/K from 74pm/K without a noticeable degradation of insertion loss through the ring and the transmission peak of grating coupler is shifted at about 50nm by the addition of titania cladding.

Narrow Linewidth 1550 nm Corrugated Ridge Waveguide DFB Lasers

We report on the design and characterization of InP-based multiple quantum well corrugated ridge waveguide distributed feedback diode lasers operating at 1550 nm. Third-order gratings have been etched along the sidewalls of the ridge waveguide using the standard I-line stepper lithography technique with an inductively coupled reactive ion etching process. An as-cleaved 1500-μm-long laser diode shows stable continuous wave single-mode operation at 1550 nm with high side-mode suppression ratios (>50 dB), a temperature-dependent wavelength shift dλ/dT ~0.095 nm/°C, and output powers ≥7 mW at 25 °C. Linewidth determination has been carried using the delayed self-heterodyne interferometric technique. Narrow linewidths (≤250 kHz) have been observed for a wide range of current injection, with a minimum of 184 kHz at 300 mA.

Theoretical investigation on the temperature characteristics of liquid-cladding micro/nanofiber Bragg grating

Based on the functions of the effective refractive index of fundamental mode in step-index fiber, a theoretical mode about the Bragg wavelength shift of micro/nanofiber Bragg grating (MNFBG) is presented. The numerical simulation results demonstrate, for a MNFBG with given radius, the Bragg wavelength shifts to short wavelength as ambient temperature increases, and the reason results from the effective index decreasing with the increase of ambient temperature. Moreover, with the reduction of fiber-core radius, as well as the increase of ambient index and its thermo-optic coefficient, the temperature sensitivity, linearity and linear response range of the temperature-dependent Bragg wavelength shift are improved obviously. Especially for a MNFBG with fiber radius smaller than 0.5 μm, the linearity of Bragg wavelength shifting with temperature will be close to the theoretical limit, and the temperature sensitivity is proportional to the thermo-optic coefficient of the ambient liquid. Compared with the temperature properties of conventional fiber Bragg grating (FBG), all the results will provide much theoretical guides for FBG applied in fiber sensing and communication.