Mach-Zehnder interferometer with a uniform wavelength period

We have realized a first optical filter composed of optical delay lines and couplers that has a periodic response with respect to wavelength, whereas a conventional optical filter is known to have a periodic response to relative optical frequency. This new filter can be constructed by using a phase-generating coupler (PGC) that supplies the optical delay lines with a wavelength-dependent nonlinear phase. The PGC, which is also composed of optical delay lines and couplers, can simultaneously provide a desired phase and an arbitrary amplitude coupling ratio. We applied our transformation method to a conventional Mach-Zehnder interferometer (MZI) as an example of an optical frequency filter and converted it to an optical wavelength filter. We fabricated the designed MZI on a silica-based planar lightwave circuit and successfully realized what is believed to be the first MZI with a uniform wavelength period.     

Design of a spectrum-expanded polymer Mach�CZehnder interferometer electro-optic switch using two-phase generating couplers

A novel structure, thorough analysis and design technique are presented for a kind of polymer Mach?CZehnder Interferometer (MZI) electro-optic (EO) switch consisting of two-phase generating couplers (PGCs). By optimizing the PGCs structure, the output spectrum of the two PGCs based MZI EO switch is greatly expanded to almost six times of that of the traditional MZI EO switch with two 3?dB directional couplers. Under a central wavelength of 1550 nm, the driving voltages of the designed switch are as low as about 0 (ON state) and ±0.925?V (OFF state) with an EO region length of 5000???m. A wide spectrum more than 350 nm (1380??1730?nm) is achieved, and within this wavelength range, the crosstalk is less than ?30?dB, and the insertion loss is less than 5.91?dB which is larger than that of the traditional MZI EO switch due to the longer waveguide length by introducing two PGCs. The design technique on the two PGCs based MZI EO switch is supported to be reasonable compared with the beam propagation method (BPM). The proposed structure shows potential wide applications especially in optical cross-connect (OXC) and optical add-drop multiplexing (OADM) systems.     

Design of wide-spectrum polymer Mach-Zehnder interferometer electro-optic switches using two symmetric N-th order phase-generating couplers

To enlarge the output spectrum, a novel reasonable structure of one kind of Mach-Zehnder interferometer (MZI) electro-optic (EO) switches containing two symmetric N-th order phase generating couplers (PGCs) is presented, and thorough model, analysis and design technique are proposed. A non-linear least square method is investigated for optimizing the PGC structure to eliminate the phase difference error caused by the wavelength variation. Under the central wavelength of 1550 nm, optimization and simulation are performed on three MZI EO switches using two first, second and third order PGCs, respectively. The switches exhibit a low switching voltage of 1.156 V with an active region length of 4 mm. The output spectrums covering the whole S-C-L bands are as wide as 320, 390 and more than 435 nm, respectively, the insertion loss are less than 5.57, 5.98 and 7.90 dB, respectively, and the crosstalk is less than −30 dB over the wide wavelength ranges, for the three designed switches. The design technique is supported to be feasible by the comparison with beam propagation method (BPM).     

Analysis of tunable codirectional vertical couplers with liquid crystal overlays for integrated dye lasers

We propose a guided-wave dye laser using a grating-assisted codirectional vertical coupler as an intracavity tunable filter. A liquid crystal overlay is designed to attain a phase-matching wavelength shift in the vertical coupler and a tunable range of over 60 nm is calculated at a center wavelength of 590 nm with a coupling efficiency of more than –1 dB. The tunable range is limited by the coupling length mismatch rather than by the refractive index variation in the liquid crystal overlay. Sidelobe level in the filter response is increased when the phase-matching wavelength is shifted to the long-wavelength side; nevertheless, the weighted coupling keeps the sidelobe-suppression ratio at more than 30 dB over a spectral span of 100 nm.     

Optimal design and analysis of a high-speed, low-voltage polymer Mach-Zehnder interferometer electro-optic switch

Detailed model, analysis and design technique are presented for simulating a high-speed polymer Mach-Zehnder interferometer (MZI) electro-optic switch with push-pull dual driving electrodes and rib waveguides. The novel formulas of the time-domain response are derived. Thorough optimization and simulation for the designed device are performed. The total length of the basic function unit of the switch is about 5049 μm, the push-pull switching voltage is 2.23 V, the switching time is 18.1 ps, and the insertion loss and crosstalk are less than 2.64 and −30 dB, respectively, within the range of the operation wavelength from 1534 to 1566 nm. These results are in good agreement with those obtained from the beam propagation method (BPM).     

Compact optical short-pass filters based on microfibers

We demonstrate a compact short-pass filter fabricated by integrating a microfiber (approximately 1 microm in diameter) with a low-index substrate. By varying the interaction length (from 0.65 to 3 mm) between the microfiber and the substrate for wavelength-dependent evanescent leakage, the cutoff wavelength has been tuned over a wide range of 400 nm. Typical rejection loss is higher than 40 dB with insertion loss as low as 0.3 dB. The fiber-diameter-dependent cutoff is also investigated, suggesting that the filter can be applied over a wide spectral range from 600 to 1500 nm. The microfiber-based short-pass filters demonstrated show advantages of compact size, wideband applicability, simple structure, high rejection loss, and compatibility with miniaturized fiber devices.     

Design of a spectrum-periodized polymer optical filter using arc-type Mach–Zehnder interferometer and <Emphasis Type="Italic">N</Emphasis>th order phase-generating couplers

We proposed a kind of polymer arc-type Mach–Zehnder interferometer (MZI) optical filter by employing two parallel cascaded Nth-order phase-generating couplers (PGCs). To realize periodic spectrum response with low insertion loss, a nonlinear least square method was investigated for optimizing PGC structure to satisfy periodic phase compensation (PPC) and insertion loss compensation (ILC) conditions. With the needed wavelength period of 24 nm, design and simulation on five Nth-order PGCs-based filters were performed as N changes from 0 to 4. When N=3, the optimized filter exhibits the most favorable uniform periodic response with the maximum period shift less than 0.3 nm, which is about 1/10 times of that of the traditional filter when N=0, and the insertion loss at the central wavelength of each channel is 1.39–9.98 dB. The PGC’s order N should be properly selected for low optical loss, uniform wavelength period, and feasible optimization complexity. The proposed technique can also be used to design such PGCs-based arc-type MZI filters with any other uniform wavelength period by altering the radius-difference between two arc-type MZI waveguides for CWDM networks.     

利用倾斜光纤光栅的可开关双波长光纤激光器

报导了一种在四波混频作用下利用倾斜光纤布拉格光栅进行波长选择的可开关双波长掺铒光纤激光器。通过将倾斜光纤光栅与单模光纤进行横向错位焊接,使光栅的反向LP01和LP11两个模式具有相近的有效反射率,从而可以用来进行激光器的双波长选择。接入腔内的一段高非线性光子晶体光纤引入的四波混频效应克服了模式竞争,使得双波长激光在室温下稳定振荡。腔内起偏器和偏振控制器的联合作用可产生依赖于波长的损耗,以补偿光纤光栅两反射峰峰值的大小差异。基于以上原理,通过调节腔内的偏振态,该激光器实现了室温下稳定的双波长输出,也实现了在两波长之间的转换。两波长激光均有超过45 dB的信噪比,最大的功率波动为0.8 dB     

Integrated-Optics Multimode-Interference Wavelength Division Multiplexer for Optical Communication

An integrated-optics multimode-interference 1.3 1.55-mum wavelength division mul tiplexer demultiplexer for optical communication is reported. We have found that the device length can be reduced by adopting a restricted-resonance multimode-interference scheme and a lower beat length ratio. The former allows the device length to be 3 times shorter, and the latter has been found to be able to avoid the wavelength insensitivity of the multimode-interference effects. Modal propagation analysis was used to investigate transmission characteristics of the device. Simulation results show that a demultiplexer with contrasts of 40 dB at 1.3-mum wavelength and 34.5 dB at 1.55 mum can be achieved at an optimum coupler length of 435.5 mum. We have also discussed the fabrication and operation tolerances of the wavelength multiplexer and the effect of the wavelength-dependent refractive index.     

Tunable filter based on a pair of special long-period fiber gratings and its application in fiber ring laser

A filter based on a Mach-Zehnder interferometer (MZI) formed by cascading a pair of longperiod fiber gratings (LPFGs) written by CO₂ laser in a twisted single-mode fiber is proposed. The transmission spectrum of the filter is tuned by modifying the bending curvature of the MZI, and thus wavelength tuning is achieved. And a tunable erbium-doped fiber (EDF) ring laser employing the filter as a wavelengthselection component is experimentally demonstrated. The laser can be tuned continuously from 1573.05 to 1595.75 nm with a side-mode suppression ration of ∼50 dB over the total tuning range.     

Mach-Zehnder Interferometer Based on Coupled Dielectric Pillars

We propose a Mach-Zehnder interferometer （MZI） based on coupled dielectric pillars. It is composed of single-row pillar coupled waveguide modulating arms and three-row pillar waveguide 3 dB couplers. The slow light property and transmission loss of the single-row pillar modulating arm are optimized by the plane wave expansion method. A short 3dB coupler is designed based on the modes transformation in three-row pillar waveguide. Finite difference time domain simulations prove the validity of this MZI and show that it has low insertion loss of 1.1 dB and high extinction ratio of 〉 12 dB.     

82-channel multi-wavelength comb generation in a SOA fiber ring laser

We demonstrate a multi-wavelength semiconductor optical amplifier (SOA) fiber ring laser with a dual-pass Mach-Zehnder interferometer (MZI) filter. Two SOAs with different gain spectra provide sufficient gain and a wider gain spectrum to facilitate multi-wavelength lasing. The dual-pass MZI, configured by adding an optical isolator to the two outputs of the conventional MZI, serves as comb filter for multi-wavelength operation, and its extinction ratio can be enhanced to twofold as that of the conventional MZI in the same parameters. To investigate the influences of a dual-pass MZI filter and a conventional MZI filter on multi-wavelength operation, two different cavity configurations are presented and compared, including a single-SOA ring cavity and a double-SOA ring cavity. Stable simultaneous operation at 82 wavelengths, with a wavelength spacing of 40 GHz and a power deviation of 5 dB, and with a minimum optical signal-to-noise ratio (OSNR) of 28 dB, is observed from the double-SOA ring cavity using a dual-pass MZI filter.     

Polarization beam splitter using a binary blazed grating coupler

A novel polarization beam splitter using a two-layer grating coupler is proposed and demonstrated. It can directly couple the normally incident light from fiber into two separate waveguides according to their polarization states while splitting them. It realizes high coupling efficiency and a good extinction ratio by using binary blazed grating couplers. The coupling length is less than 14 microm. The extinction ratio is better than 20 dB for both polarizations over a 40 nm wavelength range, and the coupling efficiencies for the two layers are 58% and 50%.     

High-performance SOA-based multiwavelength fiber lasers incorporating a novel double-pass waveguide-based MZI

In this paper, using a direct double-pass and a novel isolator-assisted double-pass waveguide-based Mach-Zehnder interferometer (MZI), high-performance SOA-based multiwavelength fiber lasers (MFL) are proposed and demonstrated experimentally. The filtering characteristics of the proposed isolator-assisted double-pass MZI are analyzed and examined theoretically in comparison with those of the single-pass and direct double-pass MZI. Using a direct double-pass waveguide-based MZI with the single-pass free spectral range (FSR) of 43 GHz, up to 115- and 104-channel simultaneous oscillations spaced at 21.5 GHz in the L-band and C-band are obtained, respectively, with a power non-uniformity of less than 3 dB and an extinction ratio of ∼30 dB. To the best of our knowledge, it is the highest lasing-channel count that has been achieved from an SOA-based MFL. To enhance the extinction ratio while maintaining the FSR, the proposed isolator-assisted double-pass MZI is then utilized in the laser cavity, and a stable 55-wavelength simultaneous oscillation spaced at 43 GHz is accordingly achieved in C-band with an extinction ratio of higher than 50 dB. Compared with the lasing linewidth of 0.058 nm with the conventional single-pass MZI, narrower linewidths of 0.038 and 0.028 nm are obtained with the isolator-assisted and direct double-pass MZI configurations, respectively. The lasers are stable with a maximum power fluctuation per channel of less than 0.8 dB during an hour’s test.     

Novel Fused Taper 1x4 Star Coupler for Full-Band Operation

A novel fused taper 1x4 coupler for full-band operation is proposed. Wavelength flattened characteristics and excellent branching uniformity less than 0.4 dB have been achieved in wavelength range from 1200 nm to 1700 nm.     

Highly sensitive Si nanowire-based optical sensor using a Mach-Zehnder interferometer coupled microring

A Mach-Zehnder interferometer (MZI) coupled microring is demonstrated experimentally to obtain a high sensitivity as well as a large range for measuring change in refractive index. For the present MZI-coupled microring, there is a major resonance wavelength with a high extinction ratio (16-36 dB) in a very large wavelength span. Consequently, a very large quasi-free spectral range (>120 nm) is achieved, which helps to obtain a large measurement range. The MZI-coupled microring sensor is used for measuring the change of the ambient refractive index ranging from 1.0 to 1.538, and the sensitivity is as high as 111 nm/refractive index unit.     

一种定向耦合器型高聚物光开关设计

本文提出了一种基于定向耦合器型的高分子聚合物波导光开关设计,其突出特点是极低的波长相关性和耦合区几何尺寸敏感度,可采用橡胶成型工艺(Rubber Molding Process)实现高聚物波导在硅基底上的快速转印成型.利用BPM方法进行了器件的波导结构设计及性能模拟,插入损耗为0.4-0.6 dB,串扰<-32 dB,偏振相关损耗约为0.08 dB,电光系数r33＝14 pm/V时,器件的开关电压为42 V.     

Power Analysis and Experimental Study of the Fiber Null Coupler with an Acousto-optic Device

A single-mode fiber acousto-optic (AO) switch based on a null coupler at wavelength of 1.55 μm is reported.According to the coupled mode theory,power distribution of the null coupler with the acoustic-wave is formulated for general case.Excess loss of 0.1 dB and the schematic graph of throughput and coupled power are obtained experimentally.     

反相电极聚合物定向耦合电光开关的优化设计

为了消除单节电极定向耦合电光开关的工艺误差对器件性能的不良影响,应用耦合模理论、电光调制理论、保角变换及镜像法,优化设计了一种两节交替反相电极聚合物定向耦合电光开关.模拟结果表明,该器件具有良好的开关性能:在1 550 nm的工作波长下,器件耦合区的长度为4 753.5 μm,交叉态电压为1.22 V,直通态电压为2.65 V,插入损耗小于2.21 dB,串扰小于-30 dB.通过微调状态电压,可以很容易地消除工艺误差对器件性能产生的不良影响.本文方法的设计结果与光束传播法的仿真结果符合得很好.     

Tunable optical add-drop multiplexer based on long-period fiber gratings for coarse wavelength division multiplexing systems

We propose and experimentally demonstrate a voltage-controllable add-drop multiplexer with a tunable coupler based on long-period fiber gratings (LPFGs). The tunable coupler is based on cladding mode coupling between two parallel LPFGs with divided coil heaters, which controls the resonant wavelength positions of the two LPFGs. The wavelength tunability of the tunable coupler is measured to be -0.45 nm/degrees C in the temperature range from 20 to 120 degrees C. The large tuning range of optical signals (approximately 50.54 nm) from 1502.32 to 1552.86 nm, which covers both the short (S) and the conventional (C) bands, is achieved. The channel isolation is as high as approximately 40 dB. It has several advantages, including a broad tuning range of wavelength in both the S- and C-bands, high channel isolation, no backreflection, and so on.