Narrow-band vertically stacked filters in InGaAlAs/InP at 1.5 μm

A narrow-band wavelength filter in InGaAlAs/InP has been modeled, fabricated, and tested. A highly asymmetrical, vertically coupled directional coupler operating near the band-edge is formed by a narrow ridge and a wide strip-loaded waveguide. The results of numerical simulation, performed by employing the spectral index method, effective-index method, and a modified coupled-mode theory, are used to fabricate a filter structure with a prescribed filter response. Operation at a center wavelength around 1.5 μm with a bandwidth of 18 Å and transfer efficiency of ~46-68% is achieved. Excellent agreement between the. Designed and measured bandwidth is demonstrated. A multichannel filter device based on an array of individual filters that is capable of extending the usable spectral range is analyzed     

Characteristics of dispersion free single-mode fiber in the 1.5 µm wavelength region

Characteristics of dispersion free single-mode fibers in the wavelength regions 1.5 and 1.3 μm are compared experimentally and theoretically. We consider the influence of the refractive index profile on dispersion, the tolerance limits of structure parameters for minimum dispersion, attainable fiber bandwidth, and transmission loss including splicing and bending losses. For a fiber designed for minimum dispersion at 1.5 μm, the measured fiber loss was less than 1 dB/km and bandwidth was 250 GHz. km. nm. The achievable minimum loss estimation shows the advantage of dispersion free fibers at the 1.5 μm wavelength over dispersion free fibers at 1.3 μm.     

Single and multimode fiber bandwidth measurements with single and multilongitudinal mode lasers operating at 0.8-, 1.3-, and 1.5-µm wavelength

The bandwidth characteristics of single and multimode optical fibers have been investigated with single and multilongitudinal mode laser sources operating at 0.8, 1.3, and 1.5 μm. It is shown that single-mode fiber with a cutoff wavelength of 1.3 μm can support 1 Gb/s transmission over at least 7.5 km with a 0.8-μm laser source.     

High-speed electrooptic modulation in GaAs/GaAlAs waveguide devices

A figure of merit is constructed for broad-band electrooptic modulators which compares bandwidth with launched generator voltage standardized to a common wavelength. Comparison of various published results in terms of this figure shows that a lumped-element III-V semiconductor device performance may be no more than a factor of two below that of typical (i.e., LiNbO3) traveling wave devices and are probably easier to implement-especially in an integrated format. Accurate modeling, which incorporates all transit time and velocity match effects, is described and found to agree well with experimental results. Experimental GaAs/GaAlAs modulators have been made, using a Mach-Zehnder interferometer configuration. At a wavelength of 1.15 μm and with unterminated drive a bandwidth of 6.5 GHz was obtained with Vpiof 17.3 V. A shorter (34.6-v) device was ∼ 1.25-dB down at 8.4 GHz. The corresponding figures of merit are close to the maximum expected for the configurations used.     

Dispersion and bandwidth spectra in single-mode fibers

Bandwidth spectra of single-mode fibers are calculated from experimentally obtained chromatic-dispersion-versus-wavelength curves. Results include second-order effects on bandwidth which depend on the curvature of the dispersion curves. Examples illustrate how bandwidth spectra change as a function of source power spectra. They also show how small changes in fiber dimensions and refractive-index differences can cause significant bandwidth changes at 1.3 μm wavelength.     

A novel integrated acoustooptic frequency shifter

An integrated optical frequency shifter that utilizes guided-wave acoustooptic Bragg diffractions in cascade from two tilted- and counterpropagating-surface acoustic waves is reported. The doubly and frequency-shifted diffracted light propagates in a fixed direction, but spatially resolved from the incident light, irrespective of the magnitude of frequency tuning. A device fabricated in a Y-cut LiNbO₃ planar waveguide has demonstrated desirable characteristics, including single-sideband suppressed-carrier properties, a frequency shift centered at 1 GHz, a tunable bandwidth of 165 MHz, a linear dynamic range greater than 41 dB, and high efficiency at the optical wavelength of 0.63 μm. These preliminary results suggest that a compact integrated acoustooptic frequency shifter module capable of multigigahertz center frequency and gigahertz bandwidth can be realized in a common LiNBO₃ substrate 0.2 cm×1.0 cm×1.5 cm in size     

Fabrication of 7×6 multimode optical fiber gratingdemultiplexer-star coupler using a single GRIN-rod lens

A multimode optical fiber grating demultiplexer-star coupler having seven demultiplexing channels and six fan-out channels is demonstrated. This device consists of an input-output fiber array, in which 42 output fibers are aligned radially around an input fiber, a single gradient-index (GRIN)-rod lens and a multifacet blazed reflection grating. In this device, the incident light beam is split into six beams, each of which is diffracted at the multifacet grating and couples to the output fibers. The device has a working band from 0.62 to 0.88 μm, channel separation from 36 to 45 nm and 3 dB bandwidth from 13 to 24 nm. We also evaluate the unevenness in the center wavelength and the minimum excess loss among the fan-out channels and discuss the relationship between the unevenness and the fabrication accuracy of the optical components in detail     

一种新型光纤光栅波长与带宽独立调谐的方法

提出了一种新型的光纤光栅的中心波长与带宽独立调谐的方法。将光纤布拉格光栅(FBG)粘贴于圆环形薄壁截面梁的外表面,通过旋转圆环形薄壁截面梁,即相当于改变光纤光栅的位置来实现中心波长与带宽的独立调谐。实验上得到了6.706 nm准无啁啾的中心波长调谐和5.368 nm的准无中心波长漂移的最大带宽调谐,并且此中心波长和带宽调谐均与拉力呈线性关系,实验结果与理论分析一致。     

Silicon Photonic Wire Filter Using Asymmetric Sidewall Long-Period Waveguide Grating in a Two-Mode Waveguide

We demonstrate a silicon photonic wire filter using asymmetric sidewall long-period waveguide gratings for the first time. The proposed device consists of single-mode waveguide sections, a two-mode section with corrugated gratings, and taper sections to connect them. The operation of this device is based on the codirectional coupling between two core modes. By adopting a high refractive index contrast waveguide, the period and depth of grating are given as 4.44 m and 5 nm, respectively. Thus, the total length of long-period grating is significantly reduced to 260 m. The measured maximum attenuation at the center wavelength is about 13 dB. The bandwidth of the transmission dip is 15 nm. Finally, issues on the design and the performance of our device are discussed.     

InGaAs/InGaAsP MQW optical amplifier integrated withgrating-assisted vertical-coupler noise filter

A photonic integrated circuit with an InGaAs/InGaAsP multiple-quantum-well (MQW) traveling-wave optical amplifier and a grating-assisted vertical-coupler filter as a noise filter have been demonstrated. A fiber-to-amplifier/filter gain of ~0.5 dB and a 3-dB filter bandwidth (FWHM) of ~70 Å at 1.56 μm filter center wavelength have been achieved. This photonic circuit is potentially suitable as a building-block for preamplifier lightwave receivers or high-gain, high-power optical amplifiers which are essential for optical communication systems and lightwave networks     

Ultra-High speed InGaAsP/InP DFB lasers emitting at 1.3 µm wavelength

A bandwidth of 13 GHz has been attained in a 1.3 μm DFB laser at 25 °C. A mesa structure was introduced to reduce the parasitic capacitance and the lasing wavelength was detuned from the gain peak to increase the differential gain. This bandwidth is the widest so far reported in 1.3 μm DFB lasers.     

Linear interferometric modulators in Ti:LiNbO3

Measurements are described on asymmetric interferometric channel waveguide modulators in Ti:LiNbO3at 0.83-μm wavelength. Modulation voltages and device transmissions are compared forX-, Y-andZ-cut substrates. An interferometer intrinsic phase bias ofsimpi/2allows linear modulation and we have observed linearity over 67 dB for a 3-kHz bandwidth. This dynamic range is limited by optical damage effects, of which the photovoltaic effect is the most critical.     

硅基竖直耦合三环谐振波分复用器的特性

对1×N信道硅基竖直耦合三环谐振波分复用器的传输特性进行了分析,给出了光学传递函数的公式.在中心波长1550.918nm、波长间隔1.6nm的情况下,对其振幅耦合比率、波谱响应、分光光谱、插入损耗、信道间的串扰进行了数值模拟.计算结果表明,该器件具有以下良好性能:若取小环与信道间的振幅耦合比率为0.27,小环与大环间的振幅耦合比率为0.06,该器件具有箱形波谱响应,输出光谱中的次峰值已被抑制到-25dB,谐振峰平坦且陡峭,3dB带宽约为0.28nm,每条输出信道的插入损耗及串扰较小,插入损耗小于0.71dB,串扰可降至-53dB以下.     

High-speed picosecond optical pulse compression from gain-switched 1.3-µm distributed feedback-laser diode (DFB-LD) through highly dispersive single-mode fiber

Picosecond optical pulse compression characteristics of chirped pulses from gain-switched distributed feedback-laser diodes (DFB-LD) transmitting through highly dispersive media are studied theoretically and experimentally. It is clarified theoretically that gain-switched chirped pulses can be compressed to about a 0.7-time bandwidth product by normal dispersion of the dispersive media and that the optimum dispersion value to obtain a minimum compressed pulse is proportional to the square of original pulsewidth. Through a dispersion, shifted single-mode fiber with -48-ps/nm normal dispersion at a 1.3-μm wavelength, gain-switched 30-ps (FWHM) pulses from a directly modulated 1.3-μm DFB-LD at a 4.4-GHz repetition rate have been successfully compressed to 6.4-ps optical pulses with a 0.86-time bandwidth product. Experimental results agree with the theoretical analysis.     

Bandwidth enhancement for p-end-illuminated InP/InGaAs/InP p-i-nphotodiodes by utilizing symmetrical doping profiles

This paper shows that the bandwidth of a p-end-illuminated planar InP-InGaAs-InP heterojunction p-i-n photodiode can be promoted by using a rather symmetrical doping profile that is produced through diffusion depth control. Caused by extra-depleted InP region in the end of p-InP, the device with symmetrical doping profile has additional series capacitance and thus has a smaller total capacitance than conventional asymmetrical doping profile. Such devices with 0.3 μm depleted InP cap region, together with 1 μm depleted InGaAs absorption region and 0.3 μm depleted InP buffer region, having the capacitance as small as those devices with 1.6 μm depletion region, while have the carrier transit time as short as those devices with 1.3 μm depletion region. Under appropriate bias condition, which is required for getting rid of the heterointerface effects, the symmetrical device as stated with 40 μm junction diameter can have a 3 dB bandwidth exceeding 17 GHz without inductance optimization. For device with conventional asymmetrical doping profile, that is, the p-n junction locating at ~0.1 μm deep in the InGaAs layer, only a bandwidth of about 15 GHz can be obtained. Due to the same thickness of InGaAs absorption layer, both devices have similar responsivity of ~0.8 A/W at -5 V at 1.3 μm wavelength. However, the heterointerface exposed in the depletion region results in several detrimental effects in symmetrical devices, such as interface-generation current, which leads to slightly increased dark current, and barrier/traps for hole transport, which lead to inferior photoresponse at low biases     

Design of ultra-compact wavelength splitter based on lithium niobate nanowire optical waveguides

A wavelength splitter with ultra-compact and simple structure is proposed and analyzed by using both plane wave expansion(PWE) method and finite difference time domain(FDTD) method.The device is based on directional coupling between two parallel lithium niobate(LiNbO3,LN) nanowire optical waveguides.The wavelength splitter with a coupling region length of 5 μm can separate 1.31μm and 1.55 μm wavelengths for corresponding outputs with transmittance higher than 97%.     

Transmission bandwidth of the two-mode fiber link

The transmission bandwidth of the two-mode fiber link is investigated both experimentally and theoretically. It is shown that the experimental bandwidth as a function of wavelength is accurately predicted by using the individual fiber transfer functions and the mode conversion matrix at a splice. The bandwidth is maximized at the wavelength where the overall group delay time difference between the LP01and LP11modes becomes zero, showing the so-called modal equalization effect. It is experimentally certified that the 3 dB bandwidth over 2 GHz is obtained in the wide two-mode-propagation spectral region around 1.3 μm for 5.2 km long two-mode fiber link for the maximum output power launching condition, due to the relatively large attenuation of the LP11mode after long propagation.     

Integrated optical devices of InGaAsP/InP heterojunction phototransistor and inner stripe light-emitting diode

New integrated optical devices combining an InGaAsP/InP HPT and an inner-stripe LED are proposed and their fabrication processes are described. The device functions of light amplification, optical bistability, and optical switching are demonstrated in the 1-μm wavelength region.     

High-speed InGaAlAs/InAlAs multiple quantum well optical modulators

High-speed modulation over 22 GHz for waveguided InGaAlAs/InAlAs multiple quantum well (MQW) optical modulators is described. A large on/off ratio of over 25 dB is demonstrated with a low-drive voltage (6 V) operating in the 1.55-μm wavelength region. The design and characteristics of MQW p-i-n modulators are discussed. The causes of large-insertion loss and the required drive voltage bandwidth figure of merit for the MQW modulator are discussed. The frequency response measurements show that the response speed is limited by the RC time constant of the device. This suggests that the speed can be further enhanced by decreasing the size and capacitance of the device     

Transmission characteristics of long spliced graded-index optical fibers at 1.27µm

Transmission characteristics of graded-index fibers at 1.27 μm are investigated. Bandwidth measurements are made in the frequency domain by using a CW GaInAsP laser diode modulated by a sinusoidal signal. For a germanium pbosphosilicate fiber, the optimum index profile at 1.27 μm is determined as 1.98. It is shown that optimum profile at 0.83 μm is 2.08 and there exists a large profile dispersion effect: for example, the experimental maximum 3-dB bandwidth at 1.27 μm decreases to one-third at 0.83 μm. Length dependence of bandwidth is investigated for 48 km long spliced graded-index fibers at 1.27 μm. It is verified that using a simplified transmission model in which mode conversion is assumed at splicing points, the bandwidths of long spliced fibers are predicted with satisfactory accuracy in terms of unit fiber transfer functions.