Monolithic integration of an ARROW-type demultiplexer andphotodetector in the shorter wavelength region

A monolithic integration of an antiresonant reflecting optical waveguide (ARROW)-type demultiplexer and photodetector is discussed. The isolation was theoretically calculated to be -21.6 dB between the wavelengths of 0.78 and 0.88 μm, with a maximum detecting efficiency of 58% in a short demultiplexing/photodetecting length of 100 μm. The fundamental characteristic was demonstrated experimentally. This type of device can be applied to a wavelength division multiplexing (WDM) system with comparatively wide wavelength separation, e.g. 1.3- and 1.55-μm wavelengths     

High-isolation demultiplexing in bend-tuned twin-core fiber

By applying a cantilever bend to a twin-core optical fiber wavelength division demultiplexer, isolations of >30 dB have been achieved between channels at 1.33-1.54 μm. These bend-tuned TCF's exhibit ⩾20 dB isolation over a bandwidth of 32 and 21 nm in the two wavelength windows, respectively. This is significantly better than that typically offered by commercially available, single-stage, tapered coupler demultiplexers. The bend-tuning mechanism is demonstrated experimentally and described theoretically using a coupled local-mode analysis     

High-performance compact optical WDM transceiver module for passivedouble star subscriber systems

High-performance transceiver-type optical WDM interface modules with a volume of only 36 cc have been developed for PDS subscriber systems. The new module comprises an optical WDM sub-module, hybrid-integrated transmitter and receiver circuits. In the WDM sub-module, a planar lightwave circuit chip was hermetically sealed together with laser and photodiode chips in order to minimize the size of the transceiver module. The lightwave circuit was formed on an optical-waveguide chip by adopting a high-silica based optical-waveguide technology. The circuit has a 3-dB directional coupler for bi-directional transmission with a 1.3-μm wavelength through a single fiber and a wavelength division multiplexer between both 1.3-μm and 1.55-μm wavelengths. The overall characteristics of the fabricated WDM sub-module achieved were a responsitivity of 0.25±0.05 A/W, an insertion loss approximately 3 dB at 1.55 μm and an isolation of 35 dB between both wavelengths. Optical output power of the fabricated transceiver module was -3.8 dBm. Also, receiver sensitivity of less than -35 dBm with an overload of over -14 dBm were obtained by introducing high-speed automatic gain and threshold control techniques. Thus, an allowable span loss of over 30 dB and an optical dynamic range of over 20 dB were attained. The preamble bit length required to reach stable receiver operation was confirmed to be within three bits     

Fused taper/filter hybrid single-mode wavelength divisionmulti/demultiplexer

A low loss and low crosstalk single-mode wavelength division multi/demultiplexer was successfully fabricated by embedding an interference filter in each output arm of a fused taper coupler. The insertion loss was around 1.5 dB at the wavelengths of 1.3 μm and 1.55 μm, and both near-end and far-end crosstalks were less than -50 dB     

AWG-based device for a WDM overlay PON in the 1.5 μm band

A novel concept has been developed for overlaying a power-splitting passive optical network (PON) in one wavelength band with a wavelength-division-multiplexed (WDM) PON in another wavelength band. An eight-channel device fabricated in silica technique shows an insertion loss of 3.5 dB and a crosstalk of -23 dB for the WDM channels around 1.55 μm wavelength. The 1 to 8 splitting function at 1.50 μm wavelength has an additional penalty of -1 dB and a uniformity of ±0.5 dB     

Four-channel tunable optical notch filter using InGaAsP/InPreflection gratings

A new tunable optical notch filter for use in wavelength division multiplexing (WDM) transmission system has been fabricated in the InGaAsP/InP material system for use at 1.55 μm. The device uses tunable reflection gratings in a waveguide to control the channels (4 in this case). Crosstalk levels between 9 dB and 20 dB have been measured, depending on the channel. System experiments at 150 Mb/s show less than 1 dB crosstalk penalty at 10^-9 bit-error rate     

Crosstalk characteristics of a 100 km-long splicedpolarisation-maintaining optical fibre

Crosstalk of -10.1 dB in a 100 km-long spliced polarisation-maintaining optical fibre has been achieved at 1.56 μm wavelength. The fibre has been constructed from 14 125 μm-diameter PANDA fibres, with an average modal birefringence of 4.8×10^-4 , by conventional arc-fusion splice techniques. An average transmission loss of 0.37 dB/km, including the splice loss, has been obtained at 1.56 μm wavelength     

Monolithic GaInAs/InP photodetector arrays for high-densitywavelength division multiplexing (HDWDM)

Monolithic arrays of interdigitated GaInAs/InP photodetectors have been fabricated for high density wavelength division multiplexing (HDWDM) applications. The detectors typically exhibit a reverse leakage current of 400 nA, capacitance of less than 70 fF and a responsivity of 0.5 A/W at -5 V bias. An optical crosstalk of -33.4 dB has been measured between adjacent detectors in an experimental grating demultiplexer system. Preliminary electrical crosstalk measurements in the frequency range of 1-500 MHz indicate signal isolation of the order of 46 dB     

Crosstalk Analysis of a Fiber Laser Sensor Array System Based on Digital Phase-Generated Carrier Scheme

A detailed study on analyzing the crosstalk in a wavelength division multiplexed fiber laser sensor array system based on a digital phase generated carrier interferometric interrogation scheme is reported. The crosstalk effects induced by the limited optical channel isolation of a dense wavelength division demultiplexer (DWDM) are presented, and the necessary channel isolation to keep the crosstalk negligible to the output signal was calculated via Bessel function expansion and demonstrated by a two serial fiber laser sensors system. Finally, a three-element fiber laser sensor array system with a 50-dB channel-isolation DWDM was built up. Experimental results demonstrated that there was no measurable crosstalk between the output channels.     

In-line single-mode wavelength division multiplexer/demultiplexer

A single-mode fibre optic wavelength division multiplexer/demultiplexer at 1.32 ?m and 1.55 ?m, constructed from a fused evanescent wave coupler, is described. This device has an insertion loss of less than 0.05 dB and a wavelength isolation of 16 dB at 1.32 ?m and 18 dB at 1.55 ?m.     

Low-loss phased-array based 4-channel wavelength demultiplexerintegrated with photodetectors

A 4-channel phased-array wavelength division demultiplexer with 1.8 nm channel spacing at 1.54 μm has been monolithically integrated with photodetectors in InP/InGaAsP. On chip losses are 3.5 to 4.5 dB. These are the lowest losses reported so far for demultiplexers monolithically integrated with photodetectors. Nearest neighbor crosstalk ranges from -12 to -21 dB     

26 km-long polarisation-maintaining optical fibre

The letter describes the development of a long-length and large-diameter preform for polarisation-maintaining optical fibres. The preform was 470 mm in length and 48 mm in diameter. As a result, a 26 km-long PANDA fibre is developed. This fibre achieves crosstalk of ?22 dB, corresponding to h = 2.4 × 10-7m-1 and a transmission loss of 0.3 dB/km at a wavelength of 1.56 ?m. These fibres will be useful for future high-speed and medium-span coherent optical communications.     

Reconfigurable wavelength add-drop filtering based on a Banyannetwork topology and ferroelectric liquid crystal fiber-optic switches

This paper presents a modular optical implementation of a Banyan network by using the physical flexibility of the optical fiber to form the interconnections between compact switching stages based on bulk polarization optics. Specifically, these switching stages use total internal reflection (TIR) prisms with ferroelectric liquid crystal (FLC) polarization rotators to form compact modules. Using this Banyan network implementation, a reconfigurable multiwavelength add-drop filter for wavelength division multiplexed (WDM) applications is proposed. Experimental results for our fiber connected 2 in-2 out FLC-based bulk-optic switching stage gives a ~6.7 dB optical insertion loss and a ~-40 dB optical interchannel crosstalk level. A low 2 dB optical insertion loss design number is expected with optimized components, realizing high (e.g., 35 μs) switching speed and low crosstalk switching networks     

1.5 μm two-section Fabry-Perot wavelength tunable optical filter

A 1.5 μm two-section Fabry-Perot wavelength tunable optical filter is studied. As opposed to DFB filters, this wavelength tunable optical filter has the advantage that the wavelength tuning range and the transmission bandwidth can be designed independently. This two-section Fabry-Perot filter also controls the transmissivity (gain) and the transmission wavelength independently by current injection and the constant-gain and constant-bandwidth wavelength tuning is achieved. The wavelength tuning range is as wide as 188 GHz (15 Å), the constant-gain is as high as 23 dB and the constant-bandwidth is as narrow as 5 GHz during wavelength tuning. A 25-channel wavelength selection with less than -10 dB crosstalk is expected with this filter     

Multiplexing of fibre optic intensity sensors using fused biconicalwavelength selective couplers

Fused biconical wavelength division multiplexers have been used to replace standard couplers in an intensity-sensor multiplexing network. The wavelength-selective power splitting and the low insertion losses of these devices (<0.2 dB) improve the power budget, while providing network overall optical isolations >30 dB. With this isolation, crosstalk effects in the network are proven to be negligible     

A highly dispersive wavelength division demultiplexer inInGaAlAs-InP for 1.5 μm operation

A novel integrated optical wavelength division demultiplexer in InGaAlAs-InP is described. It uses interference between the fundamental (zeroth) and second-order modes in a symmetric waveguide structure. Experimental results show that this device is twice as dispersive as two-mode interference (TMI) devices based on interference between the fundamental and antisymmetric modes. Channel spacings between 15 μm and 40 nm were obtained with channel isolation in excess of ±10 dB     

Spectral slicing WDM-PON using wavelength-seeded reflective SOAs

A method of implementing wavelength division multiplexed-passive optical network (WDM-PON) upstream channels based on spectral slicing with wavelength-seeded travelling-wave reflective semiconductor optical amplifier (SOA) modulators is described. A dense WDM comprising eight 1 nm slices, each modulated at a data rate of 1.25 Gbit/s are shown to operate over 25 km of standard fibre with negligible crosstalk and <1 dB dispersion penalty     

2×2 optical waveguide switch with bow-tie electrode based oncarrier-injection total internal reflection in SiGe alloy

Based on the total internal reflection and the plasma dispersion effect of SiGe alloy, a 2×2 intersectional rib optical waveguide switch with bow-tie electrode has been proposed and fabricated for the wavelength of 1.3-μm operation. The thickness of the SiGe layer is 2.6 μm and the width is 9 μm. The branch angle of the switch is 2° and the bow-tie angle is 1.5°. The on-state crosstalk is -19.6 dB, the off-state extinction ratio is 38.5 dB and the off-state insertion loss is less than 1.70 dB. The switching time is about 180 ns     

Polarisation insensitive semiconductor optical amplifier withintegrated electroabsorption modulators

The authors demonstrate a 1.55 μm wavelength multiquantum well semiconductor optical amplifier, integrated with bulk layer electroabsorption modulators and passive waveguide beam expanders at the input and output ports. The device has a fibre to fibre gain of 9 dB, an extinction ratio of 15 dB per modulator, a spectral range >35 nm, and polarisation sensitivity <1 dB     

Design techniques for subcarrier multiplexed broadcast opticalnetworks

Design techniques which enable the performance of subcarrier multiplexed FM broadcast optical networks to be optimized at the planning stage are described. At the transmitter node, criteria for maximizing the subscriber carrier-to-noise ratio (CNR) are presented. At the subscriber node, it is shown that under the majority of circumstances, the optimum direct detection receiver consists of a low-noise III-V avalanche photodiode and high-impedance front-end preamplifier. Sensitivities approaching -40 dB (1 mW) for 16.5 dB CNR in 36 MHz subscriber bandwidth are predicted for a 60-channel system. Preliminary experimental tests on an optical-feedback subcarrier receiver showed -34 dB (1 mW) sensitivity at 1.55 μm from 16.5 dB CNR in a 36 MHz bandwidth centered on 1.2 GHz with a 12% modulation index single-channel FM test signal