Polarization mode converter with polyimide half waveplate insilica-based planar lightwave circuits

A TE/TM polarization mode converter, with an excess loss of 0.26 dB, is constructed by inserting a polyimide half waveplate into a groove formed in a silica-based single mode waveguide. The polarization dependence of an arrayed-waveguide grating multiplexer is completely eliminated with this mode converter     

Birefringence control of silica waveguides on Si and itsapplication to a polarization-beam splitter/switch

A novel polarization-beam splitter/switch with a Mach-Zehnder interferometer configuration was fabricated using a silica-based planar lightwave circuit (PLC) on a silicon substrate. The polarization-beam splitter/switch was realized by accurately controlling the waveguide birefringence and the phase state by laser trimming two kinds of stress-applying amorphous silicon film with widths of 50 μm and 95 μm. Fiber-waveguide-fiber insertion loss of 0.5 dB and crosstalk attenuations of over 25.6 dB were attained     

Mode evolution type polarization splitter on InGaAsP/InP

A new type of mode-evolution polarization-splitter based on InGaAsP/lnP has been designed and realized. The component uses the large waveguide birefringence of the first-order TE and TM modes in a ridge waveguide made in a heterostructure, In the input section an asymmetric Y-junction acts as a mode converter in order to inject first-order TE- and TM-modes in a polarization-splitting section, which consists of a Y-junction formed by a bimodal and a monomodal waveguide. In the output section a third Y-junction is connected to the bimodal waveguide to couple the first-order mode to a monomodal output waveguide. Components that are 6-mm long and show polarization splitting at a wavelength of 1.55 μm have been realized. The best splitting ratios are close to -20 dB, which is in agreement with BPM simulations. Excess losses are below 1 dB     

Elimination of PD-/spl lambda/ at all output ports of silica-based AWG

It is shown that the polarisation dependent wavelength shift (PD-/spl lambda/) of a silica-based arrayed waveguide grating (AWG) is proportional to its output port location as a result of the birefringence in a slab waveguide. This PD-/spl lambda/ was eliminated to less than 0.01 nm by inserting a half waveplate across the slab waveguide.     

Polymeric waveguide polarization splitter with a buriedbirefringent polymer

A waveguide polarization splitter is demonstrated based on a low-loss polymer waveguide and a birefringent polyimide. Crosslinkable fluorinated polymers with an excellent stability and a low absorption loss are utilized for the device. The polyimide is buried under one branch of the Y-branch waveguide to enhance the birefringence between the TE and TM modes. By the adiabatic mode evolution, the TE mode is coupled to the branch with the polyimide strip, while the TM mode propagates through the other branch without the polyimide. For the device with a branch angle of 1/400 rad, we obtained a crosstalk less than -20 dB and a fiber-to-fiber insertion loss of 3.8 dB     

一种太赫兹波段宽带反射型极化变换器

提出了一种由表层矩形金属周期图案、聚酰亚胺薄膜基底和金属反射面组成的新型反射型极化变换器。为了降低极化变换器对基底厚度的敏感度,增大工作带宽,该设计采用将传统反射型极化变换器表层金属线栅开口截断和增大金属线栅宽度的方法,引进了表层金属图案对两正交极化方向电磁场的等效电容电感效应,进行相位调制。仿真结果表明中心频率为500 GHz时,工作带宽可达到140 GHz,插入损耗小于0.5 dB,并且在一定基底厚度条件下误差在一定范围内,整体性能几乎无变化。仿真表明该极化变换器有效增大了工作带宽,并降低了对基底厚度敏感度。提出了薄膜光刻工艺来对设计的极化变换器进行加工制作。     

ARROW-type polarizer utilizing form birefringence in multilayerfirst cladding

A waveguide polarizer using an ARROW (antiresonant reflecting optical waveguide) structure, of which the first cladding consists of three thin layers, is proposed. Theoretical calculation shows that this polarizer can achieve isolation over 30 dB/cm with an insertion loss of 0.01 dB/cm at 1.3 μm. Isolation of 83 dB/cm with insertion loss of 4.3 dB/cm was experimentally obtained at 0.633 μm. This structure is suitable for the integration of a polarization splitter and photodetector     

Integrated-Optic Polarization Controlling Devices Using Electro-Optic Polymers

Integrated-optic polarization controlling devices such as polarizers, polarization splitters, and polarization converters, are proposed and demonstrated in nonlinear optic polymers. Poling-induced birefringence in electro-optic polymers is exploited to fabricate the devices. The polymeric waveguide polarizers show low excess losses, and extinction ratios of 20.7 dB and 17.1 dB for TM-pass and TE-pass polarizers, respectively. The polymeric waveguide polarization splitters exhibit TE-TM mode splittings with crosstalk of 14.2 dB and 10.1 dB for TM and TE mode splittings, respectively. The polymeric waveguide polarization converters show successful TE/TM polarization mode conversion with conversion efficiencies of higher than 30 dB. The device employs poling-induced waveguides which have slowly rotating azimuth angle of optic axis along the light propagation direction. The novel polarization converter is insensitive to wavelength and easier to fabricate than the other polarization converters containing periodic structures.     

ARROW-B type polarization splitter with asymmetric Y-branchfabricated by a self-alignment process

We have proposed and demonstrated a polarization splitter based on an ARROW-B type waveguide. This device has an asymmetric Y-branch configuration, connecting a waveguide with a large modal birefringence to a low-birefringent waveguide which is channeled by a stripe lateral confinement structure. The device can achieve a high extinction ratio without precise mask alignment, since these two waveguides are connected by a self-alignment process. In addition, a low insertion loss is achieved because of adiabatic Y-branching. We designed this device at the wavelength of 1.55 μm and fabricated it using RF sputtering. As a result, high extinction ratios of -19.4 dB for TE mode and -19.0 dB for TM mode were achieved     

Circularly Polarized External Cavity Laser Hybrid Integrated With a Polyimide Quarter-Wave Plate on Planar Lightwave Circuit

We propose and demonstrate a circularly polarized external cavity laser (ECL) hybrid integrated on a planar lightwave circuit (PLC). The ECL is composed of a spot-size converter integrated laser diode, a UV-written grating, and a polyimide quarter-wave plate on the PLC using hybrid-integration technology. The polyimide quarter-wave plate of an 8.8-mum thickness was inserted in a trench with a 20-mum width and a 300-mum depth on the PLC platform, and fixed with a UV-curable adhesive. The ECL hybrid integrated with the polyimide wave plate becomes highly circular-polarized with a degree of circular polarization of 0.992. This circularly polarized ECL operated with a sidemode suppression ratio of >50 dB at ~1550 nm.     

Measurement of depolarization ratio and ultimate limit ofpolarization crosstalk in silica-based waveguides by using a POLCR

A polarization optical low coherence reflectometer (POLCR) is described that enables us to excite only the transverse electric (TE) mode of a test waveguide and to measure its Rayleigh backscatter signal distributions in the TE and transverse magnetic (TM) modes at a spatial resolution of 0.3 mm. The depolarization ratios of silica-based waveguides with relative refractive index differences of Δ=0.45 and 0.75% are obtained as 0.14 and 0.10, respectively, by measuring the bias in the ratio between the distributions in the TM and TE modes of each waveguide. By using the depolarization ratios and the Rayleigh backscatter signal levels, we calculate the ultimate polarization crosstalks to be -53 and -51 dB over 1 km, respectively. The actual polarization crosstalks of previously fabricated waveguides are about 50 dB higher than their ultimate limits for the same length of fiber     

A hybrid integrated waveguide isolator on a silica-based planarlightwave circuit

La and Ga substituted yttrium iron garnet single-mode buried channel waveguides, prepared using liquid-phase-epitaxial growth and Ar ion beam etching, have been successfully applied as 45° nonreciprocal waveguide rotators (NRWR) for hybrid integrated waveguide isolators at λ=1.55 μm. The optical and magneto-optical properties of the prepared 45° NRWRs and the epitaxial films are investigated in detail. We describe the assembly procedure and present optical measurement results for the hybrid integrated waveguide isolators. The hybrid isolators are composed of a 45° NRWR, a half-wave plate sheet, thin film-type polarizers, a thin plate-type permanent magnet and a silica-based waveguide on a silicon substrate. We obtained good waveguide isolators with low insertion losses (<3.2 dB) and high isolation (>25 dB) in the 1.5 μm wavelength band     

Fluorinated polyimide waveguides with low polarization-dependentloss and their applications to thermooptic switches

Fluorinated polyimide waveguides with low polarization dependent loss (PDL) and thermooptic (TO) switches made from them were demonstrated. The waveguides showed loss of less than 0.3 dB/cm at the wavelength of 1.3 μm and 0.6 dB/cm at 1.55 μm for both TE and TM polarizations. The PDL's were less than 0.1 dB/cm. Extinction ratios of Y-branching-type TO switches fabricated from these waveguides were larger than 20 dB when over 160 mW of electric power was applied at 1.3 μm, and over 150 mW at 1.55 μm. The switching speed was faster than 8 ms     

Hybrid polyimide/Ta2O5/polyimide antiresonantreflecting optical waveguides

A hybrid polyimide/Ta₂O₅/polyimide antiresonant reflecting optical waveguide (ARROW) is presented. The ARROW consists of fluorinated polyimide and tantalum pentoxide hybrid layers deposited on Si substrates. The propagation losses of the device are 0.6 and 2.6 dB/cm at 1.3 μm for TE and TM polarised lights, respectively     

Fabrication of LiTaO3 optical waveguides by Ni diffusionbelow the Curie temperature

Using Ni diffusion into LiTaO₃ below the Curie temperature for the fabrication of optical waveguides was presented for the first lime. Ordinary and extraordinary polarization waveguide modes were obtained. The index distribution profiles of both modes were measured by a prism coupler. Loss in planar waveguides at 0.6328 μm is 0.7±0.1 dB/cm for the ordinary mode and 1.3±0.2 dB/cm for the extraordinary mode. Moreover, a Mach-Zehnder interferometer was fabricated by this method for electrooptic characterization. The measured half-wave voltage is 5.5 V and the extinction ratio is greater than 29 dB     

Novel micromirror for vertical optical path conversion formed insilica-based PLC using wettability control of resin

A novel technique has been developed for fabricating a micromirror in a single-mode silica-based planar lightwave circuit (PLC), in which the flat slope for the mirror is made of resin by utilizing wettability control and the surface tension effect. It was shown that the mirror could be designed by numerical calculation based on the equation of Young and Laplace for a liquid surface. A controllable mirror angle range from 30 to 60° was achieved experimentally by changing the position of the boundary line between high and low wettability regions using oblique evaporation. The characteristics of a fabricated 45° mirror installed in a silica-based PLC were evaluated by coupling it vertically to a single-mode fiber. The obtained coupling losses between waveguides and a fiber were 0.60-1.15 dB for mirrors with widths of more than 200 μm, and 0.92 1.62 dB for 190 μm wide mirrors, at a wavelength of 1.55 μm. The experimental minimum losses of 0.6 and 0.92 dB coincided with the calculated values     

Theoretical and experimental studies of a spot-size transformerwith integrated waveguide for polarization insensitive opticalamplifiers

The simple fabrication technology of an active waveguide for polarization insensitive optical amplifiers, integrated with tapers and a passive waveguide for fiber coupling, is presented. The spot size transformation along the taper, yielding a mode expansion factor of more than 9 in horizontal direction and about 2 in vertical direction, is experimentally verified and the results are compared to theoretical computations. Using a cleaved single mode fiber, the coupling loss is as low as 2.6 dB with -1-dB positional tolerances of 2.2 μm and 1.5 μm in vertical and horizontal directions. Besides relaxing on fiber coupling, the large spot size transformation in horizontal direction allows for a drastic reduction of the reflection coefficient to less than 10^-3 at a facet tilted by 4° with respect to the waveguide axis     

Incoupling waveguide hologram with reduced polarization sensitivity

An incoupling waveguide hologram (IWGH) with significantly reduced polarization sensitivity was designed and fabricated in InP for 1550 nm wavelength. The IWGH couples the light from an optical fiber, irrespectively of the state of polarization, into the InP waveguide and simultaneously focuses it to a desired position in the waveguide. Conventional IWGHs are strongly polarization sensitive with a measured 19 dB difference in the incoupling efficiency between the TE and TM mode. In contrast, although some design parameters turned out to be slightly in error, the fabricated IWGHs designed for reduced polarization sensitivity exhibited a 3.1 dB difference in the incoupling efficiency between the TE and TM modes     

Integrated polarisation beam splitter using waveguide birefringencedependence on waveguide core width

A novel integrated polarisation beam splitter on a silica-based planar lightwave circuit that utilises the waveguide birefringence dependence on waveguide core width is proposed. It was successfully confirmed that the fabricated splitter has a polarisation extinction ratio of >21 dB over a wide wavelength range of 1530 to 1620 nm     

Low-loss and thermally stable TE-mode selective polymer waveguide using photosensitive fluorinated polyimide

A low-loss, thermally stable TE-mode selective optical waveguide was fabricated using a photosensitive fluorinated polyimide. The polymer undergoes photocrosslinking under UV exposure, thus changing its refractive index. The photocrosslinking-induced refractive index change was utilized to form channel waveguides. The propagation losses of the photosensitive fluorinated polyimide waveguides were less than 0.3 and 0.5 dB/cm for TE polarization at wavelengths of 1.3 and 1.55 /spl mu/m, respectively. The measured polarization extinction ratio was higher than 29 and 28 dB at wavelengths of 1.3 and 1.55 /spl mu/m, respectively. The refractive index of fluorinated polyimide film remains almost constant after being stored at 150/spl deg/C for 600 min.