Technology advances for ECOC
ECOC 2002: Technology preview
Ahead of ECOC 2002 - Europe's major industry conference and exhibition - Lightwave Europe has collected some of the key technology announcements to give a taste of what will be on show in Copenhagen.
By Matthew Peach
This year's European Conference on Optical Communications takes place in Copenhagen from 8-12 September and, as usual, will represent the main showcase in Europe for emerging technologies in optoelectronic components and optical subsystems. Below, we profile selected exhibitors and their technologies on show.
Anritsu will be demonstrating its newly developed family of Lightning Vector Network Analysers (VNA) that enable the measurement of domain-transfer devices such as optical modulators, photodiodes and photoreceivers. The technique enables the measurement of electrical-to-optical and optical-to-electrical transfer function in terms of bandwidth, flatness and phase linearity. With frequency coverage to 65GHz, it is ideally suited for characterising devices used in 2.5, 10 and 40Gbit/s transmission systems.
The technique relies on a fully characterised O/E transfer standard, typically a photodiode. A suitable laser source completes the set-up. For E/O measurements, first a normal 12-term RF calibration is performed over the frequency range of interest to create an electrical measurement reference plain. Then the response of the transfer standard is de-embedded from the overall VNA measurement of the E/O, O/E back-to-back configuration. This has the effect of moving the measurement reference plain to the electrical input and optical output of the device under test. For O/E measurements, the transfer standard is used to characterise a "golden" E/O standard (for example, a modulator) whose response is then de-embedded in a similar way.
The new procedure is standard on all Lightning microwave VNAs and existing units can be upgraded to incorporate the new functionality. The de-embedding software is internal to the VNA and provides full on-screen direction, simplifying calibration and speeding measurement throughput.
Bookham Technology will be showing the hybridisation of a Linear Optical Amplifier (LOA) chip on its ASOC platform, having debuted the technology at OFC 2002. This development brings together two powerful technologies: what the company describes as the world's most advanced platform for multiple active/passive optical integration and the first semiconductor WDM amplifier on a chip. Applications include loss-less components, metro amplification and advanced optical switching and signal processing. The demonstration was performed with an LOA from Genoa Corp, the first single-chip amplifier which can handle multiple wavelengths and data rates with low crosstalk.
Bookham is demonstrating a typical metro configuration of power grooming, multiplexing and amplification - a combination which previously needed multiple discrete devices but now can be achieved by low-cost, small-footprint integration. VP of Business Development Robert Green said, "ASOC has demonstrated integration leadership through products such as single-chip Mux-VOA and multiple active transceivers. The amplification function adds an extra dimension to the technology and opens up new opportunities to develop low-cost integrated sub-systems with our customers."
Most optical patchcord manufacturers use operators for the final visual inspection of the polishing and cleanliness of the end-face of the optical fibres. They must identify and analyse defects such as scratches, chips and dirt located on the surface of the optical fibre and, depending on their size and location with respect to the optical core, decide whether the patchcord is acceptable. However, Data Pixel will highlight its development of automated visual inspection software based on computer vision technology.
Defect Inspector works in conjunction with a video microscope and can accept most video input signal types. Before use, the software loads a customised template of pass/fail criteria. Then, once a connector is placed in the inspection microscope, a simple mouse click delivers the verdict within a few seconds as well as an Excel report with endface image and highlighted detected defects.
Data Pixel is a French company, created in May 2001. It manufactures optical instruments dedicated to metrology for the fibre-optic industry - for measurement of different parameters like concentricity and index for fibre-optic connectors (tuning applications) and bare ferrules. Customers include NetTest, Radiall, and Tyco.
A key aim of communications companies is to reduce the need for amplification and regeneration in optical networks. Swiss company Giga Tera believes that the Return to Zero (RZ) pulse format provides better transmission properties such as a higher resilience to PMD and chromatic dispersion. The company has developed a new pulse laser (pictured above) that lowers the cost and increases the performance of pulse generation, and thus enables the broader implementation of RZ transmission systems.
Hitherto, actively mode-locked fibre and semiconductor lasers have been used to create short RZ optical pulses for high-data-rate transmission experiments. However, both these approaches have limitations that hinder their wider deployment in telecom networks: fibre lasers have a large footprint, consume high power and are expensive; semiconductor mode-locked lasers have a small footprint, but generally produce low output power and therefore require costly amplification.
Passive mode-locked lasers are able to improve the economics of RZ transmission by eliminating the need for pulse modulators and modulator drivers, while increasing system performance.
GigaTera's Ergo pulse generating laser (PGL) combines small footprint and high average power within a simple, low-cost design. The ERGO PGL employs a proprietary saturable absorber to generate a stable, constant amplitude train of high-repetition-rate (10 and 40GHz) RZ pulses with high average power (>10mW) and extremely low timing jitter (of the order of <150fs RMS).
Modular test instrumentation platforms will play a prominent role in reducing cost of ownership and capital expenditures.
JDS Uniphase Instrumentation is taking a leading role through its Multiple Application Platform (MAP) to drive convergence of both physical optical controls with time domain analysis tools.
These two test categories have existed separately on several different platforms. In the case of data communications and telecommunication transmission module test, the effect has been to force more complex software efforts and made production scaling, automation and software reuse a challenge.
By driving these two functions together in one platform, software development is dramatically simplified, test rack space is minimised and engineers can re-deploy previously purchased test modules. Typical lab set-ups can be automated by adding two fibre optic switches in available slots, while leveraging previously developed software. As a result, time to market, cost of test and capital budgets can be flexibly managed to match the current business and competitive environment.
At both September's ECOC and NFOEC 2002, JDS Uniphase Instrumentation will be showing test applications for telecom and datacom transmission modules that demonstrate standards-compliant configurations at reduced size and complexity. Through the incorporation of switches, the demonstrations will highlight the ability to easily scale for pilot or full production.
Stocker Yale spin-off Optune believes that reliable WDM filtering is the fundamental building block of next generation, ultra-high-bandwidth, recofigurable, all-optical network equipment. To this end, the company will be demonstrating its latest tunable optical filter (TOF) subsystem enables reliable WDM filtering.
With one or more proprietary optical interferometers controlled by a digital signal processor (DSP), the external interface presented by the TOF subsystem is simple: unfiltered optical input, filtered optical output, and an interface to the network control layer.
The TOF's combination of high-performance optics and digital signal processing control brings several advantages to the subsystem:
- an interface to the network control layer;
- continuous tuning to any wavelength;
- power, wavelength and SNR monitoring without disturbing the optical signal; and
- automatic compensation for wavelength drift.
TOF provides a tuning range of over 220nm and a passband as narrow as 0.2nm. It covers the entire 1550nm ITU grid, and can select a single optical channel from a composite signal with 100, 50 or even 25MHz channel spacing. Closed-loop DSP control (with a lock range of 0.1% of the passband) ensures that the filter remains tuned to the selected channel, regardless of carrier drift.
The core of the tunable optical filter is a proprietary multiple-beam interferometer without a resonant cavity, which acts as the wavelength selection element. The interferometer exhibits Fabry-Pérot characteristics: as the passband is narrowed, more peaks appear in the tuning range (which can be as wide as 220nm). The set of peaks and the distance between them can be continuously adjusted across the tuning range, with the major parameters (passband, insertion loss, and rejection ratio) remaining constant.
Lightconnect predicts that at this year's ECOC there will be significant advancements in MEMS-based optical component technology as the market prepares for the successful emergence of the second-generation intelligent dynamic optical network.
While still in its infancy, a new way of transmitting voice and data information will soon replace the current network architecture in the following ways: from point-to-point configuration to mesh, from a static to dynamic state, from fixed bandwidth allocation to fluid, on-demand capabilities and from truck roll to automated service provisioning.
For those companies developing second-generation systems or subsystems based on the meshed architecture of reconfigurable networks, the effective and efficient management of wavelengths with varying power levels is a critical challenge.
Dynamic Channel Equalisers (DCEs) apply filters on each wavelength to attenuate or block light, replacing a mux/demux and any number of Variable Optical Attenuators (VOAs) along the way. More than 100 wavelengths are manageable with this one component by using software to block or control the output power of channels coming through the equaliser. In this dynamic environment, designers are free to create any configuration desired - from routing available channels, eliminating channels, or changing power levels - all in real-time.
Rohde & Schwarz
Rohde & Schwarz will present the new Chirp Test Set Q7607 from Advantest, which was specially developed for the new requirements of broadband high-speed networks. The test set allows chirp measurements up to a data rate of 50Gbit/s and can be used in the development of active optical components, such as direct modulators, systems and subsystems, as well as in the production of such systems.
Particularly for the transition from the current-generation 10Gbit/s DWDM systems to future 40Gbit/s systems, parameters such as chirp have become an important bandwidth-limiting factor. Therefore, measures must be taken to ensure that this chirp does not impair signal quality and data transmission.
Terahertz Photonics will be showing its latest polymer, Truemode Backplane, intended for the emerging optical backplane market enables high-speed optical interconnections within high-performance computer and switch systems.
Terahertz is addressing the need for increased backpanel bandwidth with what it claims is "the only waveguide material that has low loss temperature stability and photosensitivity". This combination of properties means that the polymer has both high optical performance and also works with techniques used to make electrical PCBs.
CTO Dr Frank Tooley said, "It was a natural progression to extend the use of the Truemode polymer to backplane applications. Major players in the high-end PCB expressed interest and we saw that we could be the first to market with a waveguide material that truly does what is required."
Challenges facing the fabrication of optical backplanes include that waveguides must be optically written as the boards are about 1m in size. This requires a photosensitive waveguide material. Also, waveguides must withstand temperatures of 280°C during the solder reflow process. Tooley continued, "The first optical backplanes to be widely adopted will have a combination of electrical tracks and optical waveguides. Telecom and datacom system designers will be excited not only by the extra speed of optics but also by the design freedom it provides."
Kamelian Ltd launched its initial 1550nm semiconductor optical amplifier products at OFC 2002 and will announce several key breakthroughs in SOA performance at ECOC.
The noise figure (NF) of an optical amplifier has a strong effect on system performance. An SOA's NF is high due to inefficient coupling between input fibre and semiconductor chip. Through innovative chip design and enhanced coupling efficiency, Kamelian can now offer much-improved NF values, reduced from the 9dB routinely available to <6dB.
A further disadvantage has been the large variation in polarisation-dependant gain, typically 1.5-2dB. Kamelian can now offer as low as 0.5dB. This, coupled with the SOA's inherent advantages of low cost and small footprint will expand the applications space for SOAs