Athermalised monolithic VMUX employing silica arrayed waveguide grating multiplexer

The realisation of a monolithic athermalised variable-optical-attenuator-integrated multiplexer (VMUX) implemented in silica-on-silicon waveguide technology is reported. The VMUX incorporates an athermal arrayed waveguide grating, providing <0.05 nm of peak transmission wavelength shift over 20-70/spl deg/C operating ambient independent of attenuator settings.     

Design and fabrication of zinc oxide thin-film ridge waveguides on silicon substrate with ultraviolet amplified spontaneous emission

Zinc oxide (ZnO) thin-film ridge waveguides have been designed and fabricated on n-type (100) silicon substrate. A filtered cathodic vacuum arc technique is used to deposit high-crystal-quality ZnO thin films on lattice-mismatched silicon substrates at 230/spl deg/C. A ridge waveguide of width /spl sim/2 /spl mu/m and height /spl sim/0.1 /spl mu/m is defined on the ZnO thin film by plasma etching. Room-temperature amplified spontaneous emission is observed with peak wavelength at /spl sim/385 nm under 355-nm optical excitation. It is found that the net optical gain of the ZnO thin-film ridge waveguides can be as large as 120 cm/sup -1/ at a pump intensity of /spl sim/1.9 MW/cm/sup 2/.     

Widely tunable long-period gratings fabricated in polymer-clad ion-exchanged glass waveguides

Long-period-grating filters were fabricated in polymer-clad ion-exchanged BK7 glass waveguides. The transmission spectra of the filters exhibited strong polarization dependence. A contrast as high as 25 dB at the resonance wavelength was obtained. The temperature sensitivity of the filters was measured to be /spl sim/9.0 nm//spl deg/C, which allows potential wavelength tuning over the entire S+C+L band of /spl sim/180 nm with a temperature control over a range of /spl sim/20/spl deg/C.     

A two-step laterally tapered 1.55-/spl mu/m SSC DFB laser fabricated by using a nonselective grating process

We demonstrate a two-step laterally tapered 1.55-/spl mu/m spot size converter distributed feedback laser diode (SSC DFB LD) having a planar buried heterostructure-type active waveguide and a ridge-type passive waveguide fabricated by using a nonselective grating process. Unlike conventional SSC DFB LDs, where a selective grating is employed, this SSC DFB LD employed a nonselective grating over the entire device region in order to make its fabrication much simpler than that of the conventional SSC DFB LDs. The two-step laterally tapered SSC is effective in removing an unwanted wavelength peak originating from the SSC section having a multiquantum well and a grating under it. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far field pattern in horizontal and vertical directions of 13.4/spl deg/ and 19.5/spl deg/, respectively.     

Athermalisation of silica arrayed waveguide grating multiplexers

Successful athermalisation of a silica arrayed waveguide grating (AWG) multiplexer using compensating longitudinal strain is reported. Peak wavelength shift of <0.04 nm is recorded over 5-70/spl deg/C in a 40/spl times/100 GHz device, representing a 95% reduction on standard silica AWGs, without introduction of birefringence or compromise of optical crosstalk.     

Reducing the thermal dependence of silica-based arrayed-waveguide grating using inorganic-organic hybrid materials

This study demonstrates the application of a temperature-independent arrayed-waveguide grating (AWG) using a simple hybrid waveguide structure composed of silica core/inorganic-organic hybrid material overcladding layer. The thermooptic effect of the hybrid materials varies over a wide range of temperature and provides athermal characteristics in an AWG. The temperature dependence of the AWG was reduced through the precision control of the thermooptic coefficient of the hybrid materials (/spl Delta//spl lambda/=/spl sim/3pm//spl deg/C).     

Two-step laterally tapered spot-size converter 1.55-/spl mu/m DFB laser diode having a high slope efficiency

We demonstrate a two-step lateral tapered 1.55-/spl mu/m spot-size converter distributed feedback laser diode (SSC DFB LD) having slope efficiencies as high as 0.457 and 0.319 mW/mA measured at 25 /spl deg/C and 85 /spl deg/C, respectively. The SSC DFB LD fabricated by using a nonselective grating process has a double core waveguide structure including a planar buried heterostructure type active waveguide and a ridge type passive waveguide. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far-field pattern in horizontal and vertical directions of 7.3/spl deg/ and 11.6/spl deg/, respectively.     

Arrayed waveguide gratings based on perfluorocyclobutane polymers for CWDM applications

Compact wavelength-division multiplexers based on arrayed waveguide grating structures have been designed and fabricated for short-haul communication network applications using low-loss perfluorocyclobutane-containing polymers. The devices exhibit high thermal stability and low on-chip losses. The average on-chip loss was <6 dB, including the fiber-to-chip coupling loss. The output uniformity across five channels was typically /spl plusmn/0.5 dB, and the thermal sensitivity of the central wavelength was 0.045nm//spl deg/C. Optimization of devices through material properties and fabrication process parameters is discussed.     

A broad-band waveguide grating coupler with a subwavelength grating mirror

A new diffractive device for light coupling between a planar optical waveguide and free space is proposed. The device utilizes a second-order waveguide grating to diffract the fundamental waveguide mode into two free propagating beams and a subwavelength grating (SWG) mirror to combine the two free propagating beams into a single beam. The finite-difference time-domain (FDTD) simulations show that the SWG mirror improves the coupling efficiency of the waveguide fundamental mode into the single out-coupled beam from about 30% to 92%. A high efficiency (>90%) is predicted for a broad wavelength range of 1520-1580nm. The proposed device is compact (/spl sim/80 /spl mu/m in length) and it eliminates the need for blazing the waveguide grating.     

SiC thin-film Fabry-Perot interferometer for fiber-optic temperature sensor

Polycrystalline SiC grown on single-crystal sapphire substrates have been investigated as thin-film Fabry-Perot interferometers for fiber-optic temperature measurements in harsh temperatures. SiC-based temperature sensors are compact in size, robust, and stable at high temperatures, making them one of the best choices for high temperature applications. SiC films with thickness of about 0.5-2.0 /spl mu/m were grown at 1100/spl deg/C by chemical vapor deposition (CVD) with trimethylsilane. The effect of operating temperature on the shifts in resonance minima, /spl Delta//spl lambda//sub m/, of the SiC/sapphire substrate has been measured in the visible-infrared wavelength range. A temperature sensitivity of 1.9/spl times/10/sup -5///spl deg/C is calculated using the minimum at /spl sim/700 nm. Using a white, broadband light source, a temperature accuracy of /spl plusmn/3.5/spl deg/C is obtained over the temperature range of 22/spl deg/C to 540/spl deg/C.     

Widely tunable polymer long-period waveguide grating with polarisation-insensitive resonance wavelength

A long-period waveguide grating in a polymer channel waveguide, which consisted of a benzocyclobutene core and an epoxy cladding, has been fabricated. By changing the stress in the waveguide through etching of the cladding width, a polarisation-insensitive resonance wavelength thermo-tunable from 1520 to 1610 nm with a temperature range of only 8/spl deg/C was achieved.     

Lossless electroabsorption modulator monolithically integrated with a semiconductor optical amplifier and dual-waveguide spot-size converters

Semiconductor optical amplifier and electroabsorption modulator monolithically integrated with dual-waveguide spot-size converters at the input and output ports is demonstrated by means of selective area growth, quantum-well intermixing, and asymmetric twin waveguide technologies. At the wavelength range of 1550/spl sim/1600 nm, lossless operation with extinction ratios of 25-dB dc and 11.8-dB radio frequency and more than 10-GHz 3-dB modulation bandwidth is successfully achieved. The output beam divergence angles of the device in the horizontal and vertical directions are as small as 7.3/spl deg//spl times/10.6/spl deg/, respectively, resulting in 3.0-dB coupling loss with cleaved single-mode optical fiber.     

High-finesse laterally coupled organic-inorganic hybrid polymer microring resonators for VLSI photonics

We produced laterally coupled optical microring resonators having high finesse (F/spl sime/17 at 1.5-/spl mu/m wavelength) using a two-step patterning technique based on optical photolithography. The technique used allows us to separately control the height of both ring and port waveguides and structure submicrometer gaps. The resonance spectrum of microrings with radii of 50 /spl mu/m made of an organic-inorganic hybrid polymer have an extinction ratio of about 12 dB and a filter bandwidth /spl delta//spl lambda//spl sime/0.28 nm (full-width at half-maximum) at a wavelength /spl lambda/=1547.78 nm. We show that the resonances can be thermooptically tuned by 0.2 nm//spl deg/C, thus allowing us to modulate the transmission of the through port signal.     

Wideband quantum-dash-in-well superluminescent diode at 1.6 /spl mu/m

We demonstrate broadband superluminescent diode at /spl sim/1.6-/spl mu/m peak emission wavelength using InAs-InAlGaAs quantum-dash-in-well structure on InP substrate. The fabricated device exhibits the close-to-Gaussian emission with a bandwidth of up to 140 nm. The device produces a low spectrum ripple of 0.3dB and an integrated power of 1.7 mW with the corresponding bandwith of 110 nm measured at 20 /spl deg/C under 8 kA/cm/sup 2/.     

MEMS tunable resonant leaky mode filters

A tunable double-grating resonant leaky mode microelectromechanical-type element is introduced. A significant level of tunability is demonstrated by adjusting mechanically the structural symmetry of the grating profile. Tuning is also possible by variation of the thickness of the resonant layer. For a particular example silicon-on-insulator structure treated, it is shown that the resonance wavelength can be shifted by /spl sim/300 nm with a horizontal movement of /spl sim/120 nm within the 1.4-1.7-/spl mu/m wavelength band. Additionally, the reflectance can be varied from /spl sim/10/sup -3/ to 1 at central wavelength of 1.55 /spl mu/m with a vertical movement of /spl sim/200 nm. These results demonstrate new possibilities in design of tunable optical devices.     

A 310/spl deg//3.6-dB K-band phaseshifter using paraelectric BST thin films

Ferro- and para-electric BaSrTiO/sub 3/ (/spl epsiv//sub r//spl sim/350 and tg/spl delta//spl sim/5/spl times/10/sup -2/ at 0V) thin films were deposited by low-cost sol-gel techniques. Subsequently, the films were used for fabricating coplanar waveguide phaseshifters using tunable finger-shaped capacitors. A 310/spl deg/ phaseshift was obtained at 30GHz and 35V of tuning voltage with 3.6dB of insertion loss yielding a figure of merit of 85/spl deg//dB.     

Waveguide microcavity based on photonic microstructures

A waveguide based microcavity exhibiting a quality factor Q/spl ap/2500 has been realized by incorporating a /spl lambda//4 phase shift into a 1-D photonic microstructure. The microstructure has an overall length of 3 /spl mu/m, consists of a deeply etched grating with very narrow (75 nm) air-gaps and exhibits a third-order stop band in the 800-900 nm wavelength regime. A comparison between measurement and simulation suggests that there is a thin (approximately 18 nm) skin of oxidized material at the etched semiconductor-air interfaces.     

Low-threshold narrow-linewidth InGaAs-GaAs ridge-waveguide DBR lasers with first-order surface gratings

The design and operation of InGaAs-GaAs ridge-waveguide distributed Bragg reflector (DBR) single quantum-well lasers with first-order surface gratings fabricated using only a single growth step are presented. Uncoated devices exhibit CW threshold currents as low as 6 mA with slope efficiencies of 0.46 W/A. By varying the period of the first-order DBR grating, a wavelength range of 540 /spl Aring/ (/spl sim/15.2 THz) is obtained with the threshold currents and slope efficiencies remaining below 10 mA and above 0.40 W/A, respectively, over the entire wavelength range. High characteristic temperature, T/sub 0/, values of 450 K, as measured between T=10/spl deg/C and 40/spl deg/C, are obtained for devices with Bragg wavelengths positively detuned from the peak gain wavelength. The spectral linewidth minimum of these devices is below 25 kHz, which is the resolution limit of the self-heterodyning system used to measure the spectral linewidth.     

Polysiloxane optical waveguide layer integrated in printed circuit board

A hybrid electrical-optical circuit board is demonstrated using polysiloxane as low-loss and high-temperature stable waveguide material system. After board lamination at 180/spl deg/C for two hours and a subsequent annealing at 230/spl deg/C for 5 minutes the waveguide insertion loss is 0.05 dB/cm at 850 nm wavelength.     

Integration of a multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides

We demonstrate the integration of a 3-dB multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides by direct electron beam writing. Both transmission and reflection spectra of the Bragg grating are measured through this integrated device directly. We use the thermooptic effect to tune the integrated waveguide grating, achieving a tuning range of 6.2 nm and a bandwidth variation of 0.3 nm within a temperature change of 62/spl deg/C.