Electro-optic sensors made of lasers or photodetectors assemblies can be associated with a window interface. In order to
use these sensors in an avionics application, this interface has to be set on the periphery of the aircraft. This creates
constraints on both the position/access of the associated electronics circuit card and the aircraft fuselage. Using an
optical fiber to guide the light signal to a sensor being situated inside the aircraft where electronics circuit cards are
deployed is an obvious solution that can be readily available. Fiber collimators that adapt to circular TO-can type
window sensors do exist. However, they are bulky, add weight to the sensor and necessitate regular maintenance of the
optical interface since both the sensor window and the collimator end-face are unprotected against contamination. Such
maintenance can be complex since the access to the electronics circuit card, where the sensor is sitting, is usually
difficult. This interface alignment can also be affected by vibrations and mechanical shocks, thus impacting sensor
As a solution to this problem, we propose a highly-hermetic feedthrough fiber pigtailed circular TO-can package. The
optical element to optical fiber interface being set inside the hermetic package, there is no risk of contamination and
thus, such a component does not require any maintenance. The footprint of these sensors being identical to their window
counterparts, they offer drop-in replacement opportunities. Moreover, we have validated such packaged electro-optic
sensors can be made to operate between -55 to 115°C, sustain 250 temperature cycles, 1500G mechanical shocks,
20Grms random vibrations without any performance degradations. Their water content is much smaller than the 0.5%
limit set by MIL-STD-883, Method 1018. They have also been verified to offer a fiber pigtail strain relief resistance over
400g. Depending on the electronics elements inside these sensors, they can be made to have a MTBF over 50 000h at
Harsh environment avionics applications require operating temperature ranges that can extend to, and exceed -50 to
115°C. For obvious maintenance, management and cost arguments, product lifetimes as long as 20 years are also sought.
This leads to mandatory long-term hermeticity that cannot be obtained with epoxy or silicone sealing; but only with
glass seal or metal solder or brazing. A hermetic design can indirectly result in the required RF shielding of the
component. For fiber-optics products, these specifications need to be compatible with the smallest possible size, weight
and power consumption. The products also need to offer the best possible high-speed performances added to the known
EMI immunity in the transmission lines.
Fiber-optics transceivers with data rates per fiber channel up to 10Gbps are now starting to be offered on the market for
avionics applications. Some of them are being developed by companies involved in the "normal environment"
telecommunications market that are trying to ruggedize their products packaging in order to diversify their customer
base. Another approach, for which we will present detailed results, is to go back to the drawing boards and design a new
product that is adapted to proven MIL-PRF-38534 high-reliability packaging assembly methods. These methods will
lead to the introduction of additional requirements at the components level; such as long-term high-temperature
resistance for the fiber-optic cables. We will compare both approaches and demonstrate the latter, associated with the
redesign, is the preferable one.
The performance of the fiber-optic transceiver we have developed, in terms of qualification tests such as temperature
cycling, constant acceleration, hermeticity, residual gaz analysis, operation under random vibration and mechanical
shocks and accelerated lifetime tests will be presented. The tests are still under way, but so far, we have observed no
performance degradation of such a product after more than 1050 hours of operation at 95°C.
Optical LADARs require high sensitivity near 1 nanowatt while also having fast recovery to overloads as high as
100W. Fast recovery is required in order to detect a secondary target from behind a bright target. In the current work,
we have created a new family of LADAR receivers having a higher gain bandwidth product than most commercially
available receivers. While maintaining the receiver bandwidth, a 4.8 × increase in responsivity can now be achieved.
With cooling of the APD, these new receivers are offering more than a twofold time reduction of the NEP, allowing
longer range coverage of the LADAR system. In addition, a new feature is the improvement of the overload recovery
to 93ns from an laser pulse of 56mW, allowing close secondary target detection.
In this presentation we will present a new passive alignment method used to obtain highly efficient optical fibre coupling from VCSELs (vertical-cavity surface-emitting lasers). This method is compatible with low-cost, high-yield volume production of compact transceivers for applications in rugged environments. Coupling efficiencies larger than 94% have been obtained using this visually-aided passive alignment method for the coupling between a rounded-tip, 50μm core graded-index fibre and an 850nm VCSEL having an emission area diameter of approximately 25&mgr;m. Our alignment procedure was used to make compact, high-speed (2Gbps) transceivers that can work from -50 to 105oC. They have shown to be able to resist to mechanical shocks of more than 200g. They have also shown to maintain a constant coupling efficiency while being submitted to 35Grms random vibration tests around 200Hz.
The RISQ (Réseau d'Informations Scientifiques du Québec) research and education network has been a trail-blazer in the development of privately owned fiber networks, by implementing an optical fiber owner model. This model allows RISQ to have a gracefully upgradable network that is at the forefront of the large bandwidth optical communications technology. It also allows RISQ to offer a parallel network that can be used as a test equipment for the R&D community, in universities, research institutions or the industry; a real in-the-field fiber optic network test bench.
RISQ is in a privileged situation to influence optical communications R&D work. It is aware of the real needs of the telecommunications industry. It is also aware of the technological needs of the next-generation networks. RISQ suggests that telecommunications R&D should be focused on increasing network reliability and decrease network operations and capital expanses, rather than on increasing their capacity. A key to decreasing expanses would be to avoid SONET network management on long-haul trunks, without affecting the transmission quality of service. IP over optics should thus be reinstalled as a priority in the telecom R&D world. RISQ thinks optical 3R might be the solution that will allow IP over optics. As for the next-generation networks: flexibility, reconfigurability, in order to offer lightpaths of adjustable bandwidth to the user; while wasting a minimum of the valuable network bandwidth, is where we believe efforts should be concentrated on.
Cladding mode coupling loss below 0.1 dB for a 30 dB fiber Bragg grating are reported for a wide range of H2 treatment pressure up to 1500 psi. Extension of the photosensitive region into the clading was used for reducing the cladding mode coupling. It is shown that to take proper advantage of this, one must use a wider laser scan beam. Otherwise, the cladding mode coupling loss may increase as the H2 pressure treatment is raised. The benefit of a properly matched photosensitivity obtained by matching the Ge concentration in the core and cladding regions is also highlighted. The fiber was also designed to match a standard single-mode fiber in order to lower the average splicing loss below 0.03 dB and the attenuation to about 0.2 dB/km at 1550 nm.
Cobalt-doped high attenuation fibers were tested in terms of temperature, humidity, and optical power. The maximum attenuation variation recorded was less than 3% for temperatures between -40 to + 65°C under uncontrolled humidity. When the humidity was controlled, the maximum attenuation variation was less than 3% under the worst case: +85°C and 85% R.H. Optical power test were carried out at 1W and 1550 nm over 12 minutes without any recorded damage to the fibers.
Since the beginning of optical fiber communications, many fiber designs, driven by the desire to extend the fiber limited performances, have been proposed. In the last decade, the most innovative concept that came out is probably the HF (Holey Fibre). This new fiber design consist of a pure silica fiber with a periodic array of air holes running along the length of the fiber. Usually, the air holes forming the cladding region are arranged in an hexagonal lattice and the introduction of a defect, absence of a hole, in the center of this periodic structure creates the core of the fiber. Over the past few years, impressive possibilities offered by this new type of fiber have been demonstrated in various fields of optical fiber technology such as single-mode fiber, high optical power guidance, polarization control, dispersion compensation, soliton propagation, continuum generation, fiber lasers and amplifiers, remote sensing, etc. In this paper, we review the technology and present our design, fabrication capability, as well as some results obtained with our HFs.
WDM systems require some means to lock the gain of surviving channels when one or several channels are added or
dropped. The pump loss method is particularly interesting but, to our knowledge, has not been applied to multiplestage
amplifiers. This paper reports on a modified pump loss technique for the gain locking of dual-stage amplifiers.
Gain equalization of an amplifier is performed by introducing spectrally designed Bragg gratings in the
mid-stage of a dual-stage erbium-doped fiber amplifier. The long-haul performances of the amplifier are
evaluated using a 50 km recirculating loop. The results show a clear improvement of the transmission
quality when equalizing the gain.
In this paper, we show that Bragg gratings can greatly contribute to enhance the performances of today's optical amplifiers.
some of the applications of Bragg gratings in optical amplifiers such as gain equalization, gain stabilization and dispersion
compensation will thus be reviewed.
For high data rate (greater than 1 Gbps) Optical Inter- Satellite Link (OISL), a compact laser transmitter with high power and good efficiency is required. A trade-off analysis between the technologies such as the mature 840 nm laser diodes, 1064 nm diode-pumped solid state laser and the more recent 1550 nm Erbium Doped Fiber Amplifier (EDFA) is used to find the optical solution. The Si-APDs are preferred for their large detector areas and good noise figures which reduce the tracking requirements and simplify optical design of the receiver. Because of significant amount of power needed to close the link distance up to 7000 km (LEO-LEO), use of 840 nm diodes is limited. In this paper, we present an alternative system based on a system concept denoted as the SLYB (Semiconductor Laser Ytterbium Booster). The SLYB uses a polarization maintaining double-clad ytterbium fiber as a power amplifier. The device houses two semiconductor diodes that are designed to meet telecom reliability: a broad-area 917 nm pump diode and a directly modulated FP laser for signal generation. The output signal is in a linearly polarized state with an extinction ratio of 20 dB. The complete module (15 X 12 X 4.3 cm3) weighs less than 0.9 kg and delivers up to 27 dBm average output power at 985 nm. Designed primarily for direct detection using Si APDs, the transmitter offers a modulation data rate of at least 1.5 Gb/s with a modulation extinction ratio better than 13 dB. Total power consumption is expected to be lower than 8 W by using an uncooled pump laser. Preliminary radiation testing of the fiber indicates output power penalty of 1.5 dB at the end of 10 years in operation. We are presently investigating the fabrication of an improved radiation-hardened Yb-fiber for the final prototype to reduce this penalty. For higher data rate the design can be extended to a Wavelength Division Multiplexing (WDM) scheme adding multiple channels.
Gain equalization of an EDFA is performed by introducing spectrally designed all-fiber filters in the mid-stage of a dual-stage fiber amplifier. Two types of filters are studied: a cascade of narrow-band Bragg gratings for discrete equalization of a finite number of channels and a wide-band Bragg grating performing equalization over the whole 1539 nm to 1557 nm range. In future work, it is planned to use the discrete Bragg grating configuration to simultaneously perform Dispersion compensation (D), Equalization (E) and Stabilization of gain (S) and Channel dropping (C) in a dual-stage EDFA. Integration of these functions will result in a high performance amplifier called the DESC-EDFA.
The prospect of using optical fiber amplifiers made of rare- earth doped glasses other than the very familiar silica glass opens new applications and new amplifications windows. A literature survey has been conducted in order to assess the current situation in regards to these alternative technologies. Clearly, despite the amount of efforts, the 1.3 micrometers spectral region is still looking for a more efficient candidate. So far, Pr3+-doped ZBLAN is the technology of choice, offering quantum efficiencies of about 1.5 percent only. On the other hand, the current 1.55 micrometers fiber amplifiers offer nearly unbeatable performances. Other than rare-earth silica fiber amplifiers, only fluoride and tellurite glasses rare-earth doped fiber amplifiers applications is currently in a prospective state, although the potential of these technologies is undeniable. In these cases, the huge step between bulk glass and fiber fabrication remains to be made and/or optimized.
A miniaturized, planar-grating optical spectrometer for the 2 to 6 micrometer range has been designed and fabricated. This has entailed development of a slab waveguide structure suitable for the infrared, a broad-band optical grating structure and fiber-based, IR input/output optics. Broad- band light is coupled into the spectrometer through a pig- tailed IR fiber and is subsequently dispersed into its spectral components and can be focused either onto a thermo- electrically (TE) cooled HgCdZnTe detector array or an IR fiber array. Integration of the optics and detector provides exceptional optical alignment and a very compact package that is suitable for various airborne and terrestrial applications.
The index change induced by two-photon absorption of green light in Ge-doped optical fiber is partly anisotropic. We review the experimental facts that form the basis for a physical model of bleachable oriented defects. We also describe how a density matrix formalism, based on a simili three-level system, can be used to determine the tensorial properties of the photoinduced index change.