FDM-FSK star network with a tunable optical filter demultiplexer

An optical frequency-division-multiplexed star network is analysed and demonstrated experimentally using two 45Mbit/s frequency-shift-keyed laser channels at 1.5 ?m. A tunable fibre Fabry?Perot filter is used as demultiplexer. The analysis predicts and experiment supports a minimum channel spacing of about six times bit rate B for a single FFP and 3B for a tandem FFP.     

1.2 Gb/s closely-spaced FDMA-FSK direct-detection star network

For the frequency-division-multiple-access-frequency-shift-keying (FDMA-FSK) network, the FSK signal is converted to amplitude-shift-keyed (ASK) format by a tunable fiber Fabry-Perot (FFP) filter that acts simultaneously as a demodulator and demultiplexer. Frequency-tunable two-electrode distributed-feedback (DFB) laser transmitters produce distorted FSK spectra due to nonuniform FM response for modulation frequencies above ~200 Mb/s. The frequency-domain properties of the laser are related directly to the time-domain properties of the transmitted data stream. The critical dependence on the FFP passband width and center frequency location for undistorted signal recovery is shown. By optimizing these parameters, the data transmission rate can be increased while keeping the power penalty due to signal distortion below 1 dB     

A tunable wavelength demultiplexer using logarithmic filter chains

This paper proposes a novel wavelength division multiplexer (WDM) demultiplexer design for dense WDM networks. The proposed demultiplexer consists of rectangular shaped periodic frequency filters connected in series. These rectangular filters can be formed with an apodized one-dimensional (l-D) photonic crystal structure on a ridged semiconductor waveguide. A design example is given for such filters. In such designs, we can use a moderate refractive index contrast, in discrete groups of many layers, to achieve the same stop-band width that we would get with a large contrast. Apart from being compact in size, to demultiplex an arbitrary wavelength from N wavelengths, only log₂ N switches and filter stages are required. This type of filter has a large potential to be used in integrated photonic implementation and packet switched dense WDM applications     

DBR-based tunable optical filter

A device structure for implementing a continuously tunable optical filter is described. The proposed filter relies on the creation of a resonant optical cavity between a high-reflectivity mirror and a periodic grating, with a phase control section in between. The filter has only one transmission peak over the entire frequency range, can be tuned in a few nanoseconds, and is suitable for integration with the receiver in a photonic circuit     

Electrically tunable narrowband optical filter

A narrowband optical filter of the Sole type is made from a twisted stack of birefringent plates between polarisers. If the plates are replaced by homogeneously aligned liquid-crystal cells whose retardation is controllable, the transmitted wavelength of the filter can be varied over the visible spectrum. The characteristics of a rudimentary device of this type agree with predictions.     

Use of LD-pumped erbium-doped fiber preamplifiers with optimalnoise filtering in a FDMA-FSK 1 Gb/s star network

An erbium-doped fiber amplifier was implemented in a closely spaced FDMA-FSK (frequency-division-multiple-access-frequency-shift-keyed) optical star network with a signaling rate of 1 Gb/s per channel. The fiber preamplifier, which is laser-diode pumped, increases the sensitivity of the direct-detection avalanche photodiode (APD) receiver by 14 dB, allowing for an increased number of network users. This enhanced sensitivity nearly corresponds to all of the available gain of the amplifier. Furthermore, the amplifier noise is optimally filtered by means of a wide band interference filter cascaded with a narrow band fiber Fabry-Perot filter     

Integrated-optic acoustically tunable infra-red optical filter

Demonstrates a narrowband (≈1 nm) LiNbO₃ acoustically tunable optical filter with a tuning range adequate to span the 1.3-1.55 μm wavelength range, exploiting the considerable advantages of an unconventional x-cut design     

5 GHz-spaced, eight-channel optical FDM transmission experimentusing guided-wave tunable demultiplexer

A 5 GHz-spaced, eight-channel optical FDM transmission experiment using a guided-wave tunable demultiplexer is presented. 400 Mbit/s intensity-modulated optical carriers are multiplexed and transmitted through 13 km single-mode fibre. One of the carriers is selected by the tunable demultiplexer and directly detected     

Simple star multihop optical network

A new multihop wavelength division multiplexed (WDM) optical network with two wavelengths per node that can give the maximum throughput and minimum delay is proposed. It is called a “simple star” multihop network. This network has good characteristics in traffic balance and minimum average number of hops. Furthermore, unlike most existing networks, it does not impose an upper limit to the number of nodes     

WDM coherent optical star network

The results obtained with a fiber-optical star network using densely-spaced wavelength division multiplexing (WDM) and heterodyne detection techniques are reported. The system consists of three lasers transmitting at optical frequencies around 234000 GHz, spaced at a frequency interval of 300 MHz. The lasers are frequency-shift-key (FSK) modulated at 45 Mb/s. A 4×4 optical star coupler combines the three optical signals. The WDM signals received from one of the four outputs of the star coupler are demultiplexed by a heterodyne receiver. The minimum received optical power needed to obtain a bit-error rate of 10^-9 is -61 dBm or 113 photon/bit, which is 4.5 dB from the shot noise limit. The degradation caused by co-channel interference was measured and found to be negligible when the channels, modulated at 45 Mb/s, are spaced by more than 130 MHz in the IF domain. These results indicate that a WDM coherent optical star network of this type has a potential throughput of 4500 Gb/s     

A combined tunable optical filter and tunable MQW ring laser

A dual-purpose, grating-based tunable optical filter/ring laser is described for accurate wavelength selection and generation at customer terminals. The device selects a single-wavelength channel from a HDWDM multiplex with 1 nm channel spacing, and simultaneously generates an identical wavelength as part of a tunable ring laser. The device is tunable over a 125 nm wavelength range, centered in the 1.5 μm low-loss fiber window     

Integrated optical, acoustically tunable wavelength filter

A TM/TE convertor is combined with a TE-pass polariser on a common LiNbO/sub 3/ chip to obtain an integrated optical, acoustically tunable wavelength filter. Its tuning range is 1.45-1.57 mu m wavelength with a filter half-width of 2.8 nm. Due to the combined acoustical/optical strip guide structure used in the mode convertor, a very low acoustic drive power of only 9 mW is required.<>     

Two-stage integrated-optic acoustically tunable optical filter with enhanced sidelobe suppression

Demonstrates a two-stage integrated-optic acoustically tunable infra-red optical filter with subnanometre bandwidth and -19 dB sidelobe suppression. This configuration also eliminates the optical frequency shift of one-stage devices.<>     

Analysis of a tunable multichannel two-mode-interferencewavelength-division-multiplexer/demultiplexer

An integrated optical multichannel wavelength-division multiplexer/demultiplexer for a single-mode fiber system is investigated by the beam propagation method (BPM). Important wavelength characteristics of dual-channel two-mode-interference (TMI) multiplexer/demultiplexer waveguide with and without electrode are studied and general design guidelines for realizing multichannel multiplexer/demultiplexer are given. Design and simulation of four-channel TMI multiplexer/demultiplexer are discussed     

Broad-passband-width optical filter for multi/demultiplexer using a diffraction grating and a retroreflector prism

The letter describes the experimental results of a novel optical filter for a multi/demultiplexer using a diffraction grating and a retroreflector prism. A broader passband width, which is proportional to the difference between the prism base length and the input fibre core diameter, is obtained. The minimum insertion loss is 2.2 dB.     

Quadro-Star: a high performance optical WDM star network

This paper proposes an original approach to controlling WDM Passive optical stars, termed queuing arrivals for delayed reception operation (Quadro). In WDM stars the fundamental problem of receiver conflicts leads to severe performance degradation. In current solutions conflicts are prevented by scheduling transmissions or resolved by retransmissions. Both approaches waste bandwidth and involve electronic processing and buffering. The proposed approach is conceptually different in introducing a local conflict resolution mechanism at each receiver incorporating delay lines. This solution brings optical star networks a step closer to an all-optical realization. In addition, it allows an almost total utilization of the channels, as obtainable until now only by TDM control. Contrary to TDM, however, the proposed solution does not suffer performance degradation under heterogeneous traffic conditions and increasing number of nodes. It is thus unique in offering the potential of an all-optical solution providing at the same time high throughput, low delay, small buffer requirements, and robustness under all traffic conditions     

Variable bandwidth and tunable centre frequency filter usingtransversal-form programmable optical filter

The authors report the realisation of an integrated-optic variable bandwidth and tunable centre frequency filter using a transversal-form programmable optical filter with 32 taps. The bandwidth is varied from 44 to 84 GHz with a fixed centre frequency. Also, the centre frequency is tuned over 105 GHz with a fixed bandwidth     

Narrow-band light source with acoustooptic tunable filter for optical low-coherence reflectometry

An electrically-tunable narrow-band light source with no moving parts is constructed for jaggedness-free optical low coherence reflectometry. The source incorporates a double-path acoustooptic tunable bandpass filter module whose two passbands automatically agree to within 0.2 nm during wavelength tuning from 1529-1568 nm. The source emits narrow-band light with an FWHM of 1.8/spl plusmn/0.1 nm, a power of >0 dBm and a suppressed background spectrum. The entire wavelength range can be swept electrically within 100 ms by using a variable RF source.     

Densely spaced WDM coherent optical star network

An optical WDM star network consisting of three lasers transmitting at about 234 000 GHz, spaced by 300 MHz, has been used to demonstrate dense packing of WDM signals. The three optical signals, FSK-modulated at 45Mbit/s, are multiplexed by a 4 × 4 star coupler and demultiplexed by a balanced heterodyned receiver. Receiver sensitivity is -61dBm for a BER of 10?9, or 113 photons/bit, which is 4.5dB from the shot noise limit and represents the best sensitivity yet reported for FSK modulation. The results indicate that 100 000 users in a 10km radius could be interconnected with such a system.     

可调谐光滤波器的发展及其DWDM应用

可调谐光滤波器是未来全光网络中的核心光器件,在DWDM系统中发挥着重要的作用.对几种常用并极具发展潜力的可调谐光滤波器的工作原理、结构、性能以及最新进展分别进行了介绍,指出了各自的功能和缺陷.最后给出了可调谐光滤波器在可重构光分叉复用和光性能监测方面的应用.