A novel dual-channel thermo-optic locking method for the whispering gallery mode microresonator

Mode locking can be effectively achieved by using the thermo-optic effects in the whispering gallery mode(WGM)optical microcavity,without the help of external equipment.Therefore,it has the advantages of small size,low integration costs,and self-locking,which shows great potential for application.However,the conventional single-channel microcavity thermal-locking method that relies solely on internal thermal balance will inevitably be disturbed by the external environment.This limitation affects the locking time and stability.Therefore,in this paper,we propose a new method for closed-loop thermal locking of a dual-channel microcavity.The thermal locking of the signal laser and the thermal regulation of the control laser are carried out respectively by synchronously drawing a dual-path tapered fiber.The theoretical model of the thermal dynamics of the dual-channel microcavity system is established,and the influence of the control-laser power on the thermal locking of the signal laser is confirmed.The deviation between the locking voltage of the signal laser and the set point value is used as a closed-loop feedback parameter to achieve long-term and highly stable mode locking of the signal laser.The results show that in the 2.63 h thermal-locking test,the locking stability is an order of magnitude higher than that of the single tapered fiber.This solution addresses the issue of thermal locking being disrupted by the external environment,and offers new possibilities for important applications such as spectroscopy and micro-optical sensor devices.

Towards electronic-photonic-converged thermo-optic feedback tuning

As Moore’s law approaching its end,electronics is hitting its power,bandwidth,and capacity limits.Photonics is able to overcome the performance limits of electronics but lacks practical photonic register and flexible control.Combining electronics and photonics provides the best of both worlds and is widely regarded as an important post-Moore’s direction.For stability and dynamic operations considerations,feedback tuning of photonic devices is required.For silicon photonics,the thermooptic effect is the most frequently used tuning mechanism due to the advantages of high efficiency and low loss.However,it brings new design requirements,creating new design challenges.Emerging applications,such as optical phased array,optical switches,and optical neural networks,employ a large number of photonic devices,making PCB tuning solutions no longer suitable.Electronic-photonic-converged solutions with compact footprints will play an important role in system scalability.In this paper,we present a unified model for thermo-optic feedback tuning that can be specialized to different applications,review its recent advances,and discuss its future trends.

Design of Thermo-Optic Variable Optical Attenuator Based on Quartz Substrate

In this paper, we designed a thermo-optic variable optical attenuator (VOA) based on quartz substrate, which consists of a Mach-Zehnder interferometer (MZI) and a thin film heater above the phase-modulation arm. The transmission properties of the waveguide and attenuation characteristics of the device have been simulated by beam propagation method (BPM), and the simulated results illustrated that the designed VOA had good performance.

Study on the thermo-optic properties of DR1/PMMA composite

This paper reports that the thermo-optic coefficient （dn/dT） as well as thermal expansion coefficients （β） of DR1/PMMA polymer film are measured for both TE （transversal electric） and TM （transversal magnetic） polarizations by using an attenuated total reflection configuration at the wavelengths of 832nm. The thermo-optic coefficients of DR1/PMMA are negative and as high as the order of 10^-4/℃. The influences of dopant concentration, poling process and photobleaching process on the thermo-optic properties of DR1/PMMA are also investigated.

Compact, submilliwatt, 2 × 2 silicon thermo-optic switch based on photonic crystal nanobeam cavities

We propose and experimentally demonstrate a 2×2 thermo-optic(TO) crossbar switch implemented by dual photonic crystal nanobeam(PCN)cavities within a silicon-on-insulator(SOI)platform.By thermally tuning the refractive index of silicon,the resonance wavelength of the PCN cavities can be red-shifted.With the help of the ultrasmall mode volumes of the PCN cavities,only～0.16 mW power is needed to change the switching state.With a spectral passband of 0.09 nm at the 1583.75 nm operation wavelength,the insertion loss(IL)and crosstalk(CT)performances were measured as IL(bar)=-0.2 dB,CT(bar)=-15 dB,IL(cross)=-1.5 dB,and CT(cross)=-15 dB.Furthermore,the thermal tuning efficiency of the fabricated device is as high as1.23 nm/mW.

Vertically Integrated Thermo-Optic Waveguide Switch Using Optical Polymers

We propose and fabricate a vertically integrated thermo-optic waveguide switch. It controls the optical path between two vertically stacked waveguides using the thermo-optic effect of optical polymer. The measured crosstalk is less than -10 dB.

Fast response 2×2 thermo-optic switch with polymer/silica hybrid waveguide

A polymer/silica hybrid 2×2 multimode-interference switch is designed and fabricated. Instead of polymer Mach-Zehnder interferometer thermo-optic （TO） silica is used as under-cladding to accelerate heat release because of its large thermal conductivity. The developed switch exhibits low power consumption of 6.2 mW, low crosstalk of about 28 dB, and short response time. The rise and fall times of 103 and 91 its for this hybrid switch are shortened by 40.8% and 52.4%, respectively, compared with those of the fabricated TO switch （174 and 191 μs） using polymer as both upper- and under-claddings.

Thermo-optic phase shifters based on silicon-on-insulator platform: state-of-the-art and a review

Silicon photonic platforms offer relevance to large markets in many applications,such as optical phased arrays,photonic neural networks,programmable photonic integrated circuits,and quantum computation devices.As one of the basic tuning devices,the thermo-optic phase shifter(TOPS)plays an important role in all these applications.A TOPS with the merits of easy fabrication,low power consumption,small thermal time constant,low insertion loss,small footprint,and low crosstalk,is needed to improve the performance and lower the cost of the above applications.To meet these demands,various TOPS have been proposed and experimentally demonstrated on different foundry platforms In this paper,we review the state-of-the-art of TOPS,including metal heater,doped silicon,silicide,with silicon substrate undercut for heat insulation,folded waveguide structure,and multi-pass waveguide structure.We further compare these TOPSs and propose the directions of the future developments on TOPS.

A Fiber Optic Temperature Sensor Based on the Combination of Epoxy and Glass Particles With Different Thermo-Optic Coefficients

This paper describes the development and function of an optical fiber temperature sensor made out of a compound of epoxy and optical glass particles. Because of the different thermo-optic coefficients of these materials, this compound exhibits a strong wavelength and temperature dependent optical transmission, and it therefore can be employed for fiber optic temperature measurements. The temperature at the sensor, which is integrated into a polymer optical fiber （POF）, is evaluated by the ratio of the transmitted intensity of two different light-emitting diodes （LED） with a wavelength of 460nm and 650rim. The material characterization and influences of different sensor lengths and two particle sizes on the measurement result are discussed. The temperature dependency of the transmission increases with smaller particles and with increasing sensor length. With glass particles with a diameter of 43 Bm and a sensor length of 9.8 mm, the intensity ratio of the two LEDs decreases by 60% within a temperature change from 10℃ to 40℃.

9.4 nm Tunable Vertically Coupled Microring Resonator Filter by Thermo-Optic Effect

A wide range (9.4nm) tuning of vertically coupled microring resonator filter was demonstrated utilizing a large TO coefficient of polymer. The power consumption was about 60m W and no degradation of filter response was observed.

Design and fabrication of wavelength tunable AWGs based on the thermo-optic effect

In this Letter, a 16 channel 200 GHz wavelength tunable arrayed waveguide grating（AWG） is designed and fabricated based on the silicon on insulator platform. Considering that the performance of the AWG, such as central wavelength and crosstalk, is sensitive to the dimension variation of waveguides, the error analysis of the AWG with width fluctuations is worked out using the transfer function method. A heater is designed to realize the wavelength tunability of the AWG based on the thermo-optic effect of silicon. The measured results show that the insertion loss of the AWG is about 6 d B, and the crosstalk is 7.5 d B. The wavelength tunability of 1.1 nm is achieved at 276 m W power consumption, and more wavelength shifts will gain at larger power consumption.

Thermo-optic characterization of KDP single crystals by a modified Snarmont setup for electro-optic modulation system

For our KDP crystal orientation, various tbermo-optic （TO） and relevant temperature-dependence param- eters are defined, presented, and studied in the framework of a transverse and a longitudinal electro-optic （EO） modulation systems. This study is based on the concept of the so-called opto-electrical bias （~） ap- plied to the system. For both of the above EO-modulation systems, a set of original equations is extracted and investigated with regard to each of the more important TO or temperature coefficients. Using these equations, for these parameters the role of the transverse configuration is examined in comparison with its corresponding longitudinal configuration. A comparison is done with other orientation of the same KDP crystal.

Analysis of the thermo-optic effect in lateral-carrier-injection SOI ridge waveguide devices

The thermo-optic effect in the lateral-carrier-injection pin junction SOI ridge waveguide is analyzed according to the thermal field equation.Numerical analysis and experimental results show that the thermo-optic effect caused by carrier injection is significant in such devices,especially for small structure ones.For a device with a 1000μm modulation length,the refractive index rise introduced by heat accounts for 1/8 of the total effect under normal working conditions.A proposal of adjusting the electrode position to cool the devices to diminish the thermal-optic effect is put forward.

Fabrication of 2×2 Thermo-Optic Switches with Organic-Inorganic Hybrid Materials Prepared by Sol-Gel Technique

2×2 Mach-Zehnder interferometric thermo-optic switch was fabricated with organic/inorganic hybrid materials by sol-gel technique and direct UV patterning. The switching time of device was measured to be 4.2 ms and switching power 9.3 mW.

基于硅基微环谐振器的Fano共振线型产生和调谐研究进展

Fano共振的线型具有明显不对称特征,在光学通信、调制和传感等领域中极具应用潜力。首先对微环谐振器的各种线型进行了介绍,强调了Fano共振线型的独特优势,其次依据结构分类梳理了国内外基于硅基微环谐振器产生Fano共振的研究现状,然后介绍了基于热光效应的Fano共振调谐的研究进展,最后展望了硅基微环谐振器的Fano共振的发展及应用。

二氧化硅平面波导集成光开关器件研究

基于二氧化硅平面光波导平台,设计并制作了一种多模干涉马赫曾德型的低功耗热光开关。该器件结合了多模干涉耦合器的稳定性及二氧化硅波导和热光开关的低损耗等优势。经仿真,对器件参数进行了优化,并讨论了金属层与波导的间距对传输光强及功耗的影响。测试结果表明,该器件的结构稳定,偏振依赖小,插入损耗低于2 dB,能实现开关的转换,功耗为450 mW左右,开关响应时间为103µs和113µs,在1564 nm工作波长下消光比超过16 dB,尺寸为2.30 cm×0.25 mm。该器件不仅与互补金属氧化物半导体工艺相兼容,同时与光纤之间也有较好的兼容性。二氧化硅波导光开关器件具有成本低,产量大,性能稳定的优势,能给光通信及光计算的未来发展提供可靠的基础。

基于半导体制冷的光模块高低温测试系统

5G网络建设和大规模数据中心建设带来了大量光模块需求。在光模块生产制造中,为了保障光模块在环境温度变化情况下能够长时间正常工作,需要检测模块在不同温度下的性能,而进行高低温测试。高低温测试在光模块制造成本中占了很大比重。设计了一种基于半导体制冷器(Thermo Electric Cooler)的光模块高低温测试系统,相较传统基于热流仪的方案,不需要压缩空气,能够大幅降低功耗、噪声和整体成本,且能够实现与热流仪相当的升降温时间。该系统对于节能减排、降低光模块制造成本有重要意义。

In-fiber photoelectric device based on graphene-coated tilted fiber grating

Graphene and related two-dimensional materials have attracted great research interests due to prominently optical and electrical properties and flexibility in integration with versatile photonic structures.Here,we report an in-fiber photoelec-tric device by wrapping a few-layer graphene and bonding a pair of electrodes onto a tilted fiber Bragg grating(TFBG)for photoelectric and electric-induced thermo-optic conversions.The transmitted spectrum from this device consists of a dense comb of narrowband resonances that provides an observable window to sense the photocurrent and the electrical injection in the graphene layer.The device has a wavelength-sensitive photoresponse with responsivity up to 11.4 A/W,allowing the spectrum analysis by real-time monitoring of photocurrent evolution.Based on the thermal-optic effect of electrical injection,the graphene layer is energized to produce a global red-shift of the transmission spectrum of the TF-BG,with a high sensitivity approaching 2.167×10^(4)nm/A^(2).The in-fiber photoelectric device,therefore as a powerful tool,could be widely available as off-the-shelf product for photodetection,spectrometer and current sensor.

Four-stage cascaded variable optical attenuator with large attenuation range for quantum key distribution

A four-stage cascaded variable optical attenuator(VOA)with a large attenuation range is presented.The VOA is based on a Mach–Zehnder interferometer(MZI)and fabricated in a silica-based planar lightwave circuit(PLC)platform.The thermo-optic effect is used to achieve intensity modulation.The measured maximum attenuation of the four-stage cascaded VOA is 88.38 d B.The chip is also tested in a quantum key distribution(QKD)system to generate signal and decoy states.The mean photon number after attenuation of the four-stage cascaded VOA is less than 0.1,which can meet the requirement of QKD.

光学电压传感器温度响应特性分析与实验研究

光学电压传感器面临温度稳定性问题。本文以BGO晶体的Pockels效应模型为基础,结合热光效应等推导出光学电压传感器在多物理场作用下的温度响应模型,并对输出信号进行频谱分析,得到温度对传感器输出的影响规律,即由温度引起的输出漂移属于低频分量。在卡尔曼滤波降噪的基础上,提出了一种基于频谱分析的高通滤波温度补偿方法,通过滤除低频分量提高温度稳定性,并进行标定实验和温度响应特性实验。实验结果表明,传感器在[0℃,50℃]温度范围内输出电压测量精度优于±1.79%,与同平台下BP神经网络温度补偿方法进行对比,该方法易于实现且有效地抑制了温度漂移的影响。