Experimental Study on One-mirror-inclined Three-mirror-cavity Photodetectors

Research on the one-mirror-inclined three-mirror-cavity (OMITMiC) photodetectors in the laboratory is reported. In the structure of photodetectors, it is the inclined-mirror that makes the filtering cavity and the absorption cavity decoupled, thus narrow spectral response linewidth, wavelength-tunable and high quantum efficiency can be achieved simultaneously. On the basis of the theoretical analysis and experimental verification on the principle with separated optical components, the vertical taper structure, the key part in the whole integrated device was realized, by dynamic etch mask technique. Moreover, the first integrated device of this type was fabricated. A spectral linewidth less than 6 nm and a quantum efficiency of 52.6% have been achieved experimentally.     

Ultranarrow band and high-quantum-efficiency photodetector with waveguide-grating structure and inclined top mirror

A new type of one-mirror inclined waveguide-grating photodetector, which combines a waveguide-grating filter and an inclined top mirror is proposed. Greatly improved spectral response is achieved by the integration of waveguide-grating into classical thin-film homogeneous layers. Comparison between the grating filter and Fabry-Perot filter demonstrates that this structure has two advantages over other photodetector devices. First, the inclined mirror can decouple the quantum efficiency from response speed and spectral response linewidth. Second, comparing the traditional photodetector with Fabry-Perot filter, this type of photodetector with the same materials requires significantly fewer layers while maintaining the same linewidth response, high peak efficiency and remarkably low sideband reflectivity. Thus, this type of photodetector device represents basic new optical features with a significant potential for practical applications.     

背照射和正照射p-i-n结构GaN紫外探测器的i-GaN和p-GaN厚度设计

研究了i-GaN和p-GaN厚度对背照射和正照射p-i-n结构GaN紫外探测器响应光谱的影响。模拟计算发现:对于背照射结构, 适当地减小i-GaN厚度有利于提高探测器的响应, 降低i-GaN层的本底载流子浓度也有利于提高探测器的响应;p-GaN的欧姆接触特性好坏对探测器的响应影响不大, 适当地增加p-GaN厚度可以改善探测器性能。而正照射结构则不同, i-GaN厚度对探测器的响应度影响不大, 但欧姆接触特性差将严重降低探测器的响应, 适当地减小p-GaN厚度可以大幅度改善探测器的响应特性。能带结构和入射光吸收的差别导致了正照射和背照射探测器结构中i层和p层厚度的选择和设计不同。     

Narrow line-width resonant cavity enhanced photodetectors operating at 1.55 μm

A method for fabrication of long-wavelength narrow line-width InGaAs resonant cavity enhanced (RCE) photodetectors in a silicon substrate operating at the wavelength range of 1.3-1.6 μm has been developed. A full width at half maximum (FWHM) of 0.7 nm and a peak responsivity of 0.16 A/W at the resonance wavelength of 1.55 μm have been accomplished by using a thick InP layer as part of the resonant cavity. The effects of roughness and tilt of the InP layer surface, and its free carrier absorption, as well as the thickness deviation of the mirror pair on the resonance wavelength shift and the peak quantum efficiency of the RCE photodetectors are analyzed in detail, and approaches for minimizing them toward superior performance are suggested.     

A smile insensitive method for spectral linewidth narrowing on high power laser diode arrays

To eliminate the smile effect in spectral linewidth narrowing on high power laser diode arrays, we have introduced a plane reflective mirror into a common Littrow configuration external cavity to enhance the correlation among emitters. By this way, we obtained uniform spectral distribution among emitters of a 64-elements laser diode array with 35 GHz linewidth and 41 W output laser power.     

Continuous wave, 30 W laser-diode bar with 10 GHz linewidth for Rb laser pumping

A laser-diode bar incorporated into an external cavity with a volume Bragg mirror produced 30 W of cw output power within a 20 pm (10 GHz) spectral linewidth (FWHM) centered at 780 nm. The device output power exceeded 90% of that for the free-running laser-diode bar. The emission wavelength was tuned over a 400 pm range without broadening laser spectrum width. Absorption of 90% of the laser radiation by a 25 mm vapor cell containing Rb that has been pressure broadened with 300 torr of ethane was demonstrated.     

顶部反射镜对GaN基共振腔发光二极管性能的影响研究

本文在Ga N基共振腔发光二极管(RCLED)顶部设计制备了高反膜结构分布式布拉格反射镜(DBR)和滤波器结构DBR,对比分析了两种反射镜的反射率曲线特征以及对应的RCLED器件的光输出纵模模式、光谱线宽和输出光强等性能差异,详细研究了顶部反射镜的光反射特性对RCLED器件输出光谱性能的影响机理.研究结果表明,顶部反射镜是RCLED的重要组成部分,其反射率曲线特征决定器件的光输出性能.常规高反膜结构DBR顶部反射镜的反射率曲线具有较宽的高反射带,将其作为顶部反射镜可有效压窄RCLED发光纵模线宽,但是发光光谱仍呈现多纵模光输出特征.滤波器结构DBR顶部反射镜的反射率曲线在中心波长处具有较窄的透光凹带,利用透光凹带对输出光的调制作用,器件可实现单纵模光输出,在光通信、光纤传感等领域展示了广阔的应用前景.通过进一步设计RCLED顶部反射镜结构,可以改变其反射率曲线特性,进而优化RCLED器件的输出光谱特性,以满足器件在多个领域的应用需求.     

不同谐振腔分步合成法制备的固态染料P567可调谐激光器

利用新型分步合成法制备的激光染料P567掺杂有机改性凝胶玻璃,建立了基于全息光栅的两种不同腔型可调谐激光器.采用光栅零级作为输出的激光器,调谐范围近70nm (543～610nm), 获得的最高斜效率为17%;采用腔镜耦合输出方式,调谐范围超过30 nm (553～585 nm),获得的最高斜效率为9.7%.并对激光器的可调谐范围、阈值、斜效率及线宽等参数进行了深入的分析比较.     

Dual-wavelength distributed Bragg reflector semiconductor laser based on composite resonant cavity

We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector (DBR) composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase section, and an active gain section. The gain section facet is cleaved to work as a laser cavity mirror. The other laser mirror is the DBR grating, which also functions as a wavelength filter and can control the number of wavelengths involved in the laser action. The reflection bandwidth of the DBR grating is fabricated to have an appropriate value to make the device work at the dual-wavelength lasing state. We adopt the quantum well intermixing (QWI) technique to provide low-absorption loss grating and passive phase section in the fabrication process. By tuning the injection currents on the DBR and the gain sections, the device can generate 0.596 nm-spaced dual-wavelength lasing at room temperature.     

Multilayer resonances sharpened by grating waveguide resonance

A multilayer planar structure comprising a highly reflective multilayer dielectric mirror and a corrugated waveguide is proposed for use as a narrow passband optical filter. The proposed filter has a much narrower linewidth than a usual Fabry–Perot cavity with two multilayer dielectric mirrors. It is shown that the narrowing of the linewidth is due to the strong spectral dependence of the phase of the wave reflected from the waveguide grating mirror. The shape of the pass band can be made symmetrical by a proper choice of the grating groove profile.     

Dual-wavelength distributed Bragg reflector semiconductor laser based on a composite resonant cavity

We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector (DBR) composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase section, and an active gain section. The gain section facet is cleaved to work as a laser cavity mirror. The other laser mirror is the DBR grating, which also functions as a wavelength filter and can control the number of wavelengths involved in the laser action. The reflection bandwidth of the DBR grating is fabricated to have an appropriate value to make the device work at the dual-wavelength lasing state. We adopt the quantum well intermixing (QWI) technique to provide low-absorption loss grating and passive phase section in the fabrication process. By tuning the injection currents on the DBR and the gain sections, the device can generate 0.596 nm-spaced dual-wavelength lasing at room temperature.     

4.4 μm中红外激光外差光谱探测技术研究

在国内首次报道以窄线宽的4.4 μm外腔量子级联激光(QCL)作为本地振荡光源,黑体作为辐射光源的激光外差光谱实验装置的建立和测量工作。激光外差光谱是一种高灵敏度的光谱探测技术,并可以用于发展一种小型的光谱探测系统,进行地基或星载的地球大气或天文观测。介绍了激光外差的基本理论、装置的建立和实验测量工作。此激光外差光谱实验装置采用4.4 μm外腔量子级联激光,出光功率高达180 mW,在4.38～4.52 μm间连续可调,具有很宽的光谱调谐范围,能实现CO₂,CO和N₂O等大气重要分子的同时测量。通过开展不同压力下CO₂气体的激光外差光谱测量,对激光外差光谱实验装置的性能进行了评估。目前该激光外差系统的信噪比达到86,低于散粒噪声极限条件的理论计算值287,系统的光谱分辨率约为0.007 8 cm-1,能满足较窄线宽条件下的高分辨率激光外差光谱的测量。分析结果表明,中红外激光外差光谱系统具有很高的瞬态信噪比及光谱分辨率,在高精度测量大气温室气体的柱浓度和温室气体垂直廓线分布方面具有广阔的应用前景。     

High-power flat L-band erbium-doped fiber ASE source using dual forward-pumping scheme

We experimentally investigate a high output power L-band (1565–1605 nm) erbium-doped fiber amplified spontaneous emission (ASE) source using dual forward-pumping configuration. Such configuration allows high pumping-power operation and enhances the pumping efficiency. The high pumping efficiency of 36.1% is achieved for such ASE source with a mirror reflectance of 30%. The output power of about 72.2 mW and a linewidth of 40.8 nm with a power ripple of 0.7 dB are obtained without using any external spectral filters.     

Resonant cavity enhanced (RCE) photodetectors with flat-top and steep-edge spectral response

Flat-top and steep-edge spectral response of photodetectors is important for dense wavelength-division-multiplexed system. Realization of the flat-top and steep-edge response is very challenging. In the last two decades many methods have been proposed, but the spectral response linewidth is not acceptable to wavelength-division-multiplexes system. In this paper a novel RCE photodetector with flat-top and steep-edge spectral response is presented. Using the step shaped structure, designing multiple-step-type p-type In_0.67Ga_0.33As_0.7P_0.3 contact layer and adjusting the thickness of the absorption layer, a design with good flat-top performance is demonstrated such that the quantum efficiency is 51.161% in the flat-top passband, 0.5 and 3 dB bandwidths are 0.26 and 0.4 nm, respectively.     

Single-longitudinal-mode lasing of Tm,Ho:GdVO<Subscript>4</Subscript> using a filter of Fabry-Perot etalon and volume Bragg grating

In this letter, we report a diodepumped CW Tm, Ho:GdVO₄ laser at 77 K with a volume Bragg grating (VBG) instead of the conventional mirror. Inserting a Fabry-Perot etalon into the cavity, a singlelon-gitudinal-mode of Tm, Ho:GdVO₄ laser which I s operating at 2038.387 nm with output power 64 mW is obtained. The slope efficiency of 4.68% and a narrow linewidth about 45 pm FWHM are achieved. And appropriate cavity length is about 75 ± 5 mm.     

Influence of anomalous dispersion mirror properties on quantum efficiency of InGaAs/GaAs resonant cavity photodetector

We present a theoretical analysis of the quantum efficiency of a resonant cavity enhanced InGaAs/GaAs p-i-n photodetector (PD) for the ultrashort optical connections. The numerical method of calculation of quantum efficiency combining a transfer matrix method and an energy conservation law is offered. Using anomalous dispersion (AD) mirror, flat-topped QE spectrum has been obtained. Conditions for ideal flat-topped spectral response have been received. A design with a maximum QE of 93.5% and 3-nm bandwidth at 0.02 dB below the peak is presented.     

External-cavity quantum cascade lasers with fast wavelength scanning

Fast wavelength scanning of an external-cavity quantum cascade laser (EC-QCL) has been developed using a modified Littrow-type cavity configuration. Scan rates up to 5 kHz and tuning ranges up to 7 cm⁻¹ have been realized using folded cavity arrangement with a fast piezoactuated intracavity mirror to vary the effective diffraction grating angle. High-resolution molecular spectroscopy, limited primarily by the effective laser linewidth, has been demonstrated in pulsed and CW mode using direct absorption spectroscopy of ammonia and ethylene in the 10-μm wavelength region. A high-resolution broadband spectral scan employing mode-hop-free tuning of a set of discrete laser modes within the fast frequency scan has been developed. The method has been demonstrated by performing high-resolution broadband spectrum of ethylene under atmospheric and reduced pressures.     

三种半导体阵列光谱组束结构的输出特性

基于光谱光束组合技术,利用光栅的衍射和外腔的反馈,并通过加入光束整形系统,将标准的半导体激光阵列的发光单元锁定在窄线宽的不同波长上,以近似平行光束沿组合方向输出,以实现半导体激光阵列输出光束质量的改善和线宽的压窄。实验中采用发光单元宽度100μm,周期500μm,由19个单元构成的标准阵列,分别对快、慢轴准直后光谱组束、光束整形后光谱组束和线宽压窄外腔组束进行了实验验证,实现了组合光束与单个发光单元近似的光束质量,同时得到了较窄的线宽输出,并对实验结果进行了分析。     

Single mode operation of a continuously tunable TE CO2 laser using a three mirror resonator

An analysis and experimental results for spectral narrowing and mode-control of a continuously tunable TE CO₂ laser using a three mirror resonator is reported. Single mode operation of a 10 atmosphere device has been obtained with an estimated linewidth of ?0.5 GHz.     

Cavity phase matching via an optical parametric oscillator consisting of a dielectric nonlinear crystal sheet

We experimentally demonstrate cavity phase matching for the first time using a sheet optical parametric oscillator which is made of an x-cut KTiOPO(4) crystal sheet. This microcavity presents 220 kW peak power capability for near-frequency-degenerate parametric outputs with up to 23.8% slope efficiency. It also features unique spectral characteristics such as single-longitudinal-mode and narrow linewidth. These attractive properties predict broad applications of such a mini-device, such as terahertz generation, photonic integration, spectroscopy, and quantum information, etc.