نوشته شده توسط : sunprince

Optical fiber may be the medium of choice for high capacity digital transmission systems and speed local area network. Besides these applications, optical fiber is also used to transmit microwave signals for cable tv, cellular radio, WLAN and microwave antenna remoting. To deliver microwave over optical fiber, the microwave signal is converted into optical form in the input from the fiber and at the creation of the fiber, it’s converted back to electrical signal. The benefit of fiber transmission of microwave is reduced losses in accordance with metallic media (e.g. copper coaxial cable). This leads to longer transmission distance without signal amplification or utilization of repeaters.

There are two approaches to optical signal modulation and recovery. The very first type is IMDD (Intensity Modulation Direct Detection) and also the second type is Coherent Detection. In IMDD, the optical source intensity is modulated through the microwave signal and also the resulting intensity modulated signal passes through the optical fiber to a photodiode where the modulation microwave signal is converted to electrical domain. In Coherent Detection, the optical source is modulated in intensity, frequency or phase by the microwave signal. The modulated signal goes through the optical fiber towards the receiver where it is mixed with the creation of a local oscillator (LO) laser. The combined signal is converted to electrical domain using a photodiode. This produces an electric signal dedicated to the main difference frequency between the optical source and the LO laser (i.e. intermediate frequency). This signal is further processed to recuperate the analog microwave signal.

RFoG (Radio Frequency over Glass) is the cable operators’ implementation of microwave transmission over optical fiber where the coax portion of the HFC (Hybrid Fiber Coax) is substituted with a single fiber, passive optical network architecture (PON). RFoG allows cable operators to deploy fiber connectivity to customer premises (FTTP) while keeping its existing HFC and DOCSIS infrastructure. Such as the HFC architecture, video controllers and knowledge networking services are fed through a CMTS/edge router.

These electrical signals are then converted to optical and transported via a 1550 nm wavelength via a wavelength division multiplexer (WDM) and a passive optical splitter to a R-ONU (RFoG Optical Network Unit) located at the customer premises. R-ONUs terminate the fiber connection and convert the traffic to RF for delivery over the in-home network. Video traffic could be fed over coax to a set-top box, while voice and knowledge traffic could be delivered to an embedded multimedia terminal adapter (eMTA), The return path for voice, data, and video visitors are on the 1310 nm or 1590 nm wavelength to some return path receiver, which converts the optical signal to RF and feeds it back into the CMTS and video controller.

The benefit of radio-over-fiber technologies are that it centralizes the majority of the transceiver functionality by transmitting the microwave signals within their modulated format over fiber. This reduces the number of access suggests antennas with amplifiers and frequency converters. In-building passive picocell for GSM or UMTS is implemented using radio-over-fiber. Wireless base stations are located in a central communications room as well as their outputs/inputs fed through RF multiplexers to lasers/photodiodes contained within the optical transceiver hub. The modulated optical signals are linked to/from the remote antenna units (AUs) within the building using single-mode optical fiber. The bottom station utilizes a combined detector/optical modulator, that is directly coupled to the antenna, to ensure that no electrical amplification or any other processing is needed.

Source: http://www.fiberstore.com/



:: برچسب‌ها: fiber transmission , optical splitter , optical transceiver ,
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تاریخ انتشار : دو شنبه 16 ارديبهشت 1392 | نظرات ()
نوشته شده توسط : sunprince

With the recovery of optical fiber communication industry and the development of FTTX, the spring of fiber optic splitter market is coming.

There are two types of optical splitter, which are Fused fiber splitter and PLC splitter. PLC splitter is a hot research today, with a good prospect of application. PLC splitter package, however, is the difficulty in manufacturing.

The PLC splitter Package refers to the planar waveguide splitter on the light guide path (waveguide) with the fiber in the fiber array aligned one by one, and then stick with specific adhesive (such as epoxy glue) together with the technology. Wherein the alignment accuracy of the PLC splitter and an optical fiber array is the key technology. PLC splitter package involves a six-dimensional optical fiber array and optical waveguides in close alignment difficult. When the manual, the drawback is the low efficiency, poor reproducibility, human factors and is difficult to achieve large-scale production.

PLC splitter Production
PLC splitter using semiconductor technology (lithography, etching, developing technology) production. Multi-channel optical fiber array and the optical waveguide array is located on the upper surface of the chip, branching function is integrated on-chip is a chip on the splitter 1,1; Then, the ends of the chip, respectively coupling the input terminal and an output terminal package.

Compared with Fused Splitter, PLC splitter has these advantages: (1) loss wavelength is not sensitive to light, to meet the different wavelengths of the transmission needs. (2) spectroscopic uniform signal can be uniformly allocated to the user. (3) compact structure, small size, can be installed directly in the various existing junction box, without leaving a lot of space for installation. (4) only a single device shunt channel can achieve much more than 32 channels. (5) The multi-channel, low cost, stars ones more and more obvious cost advantages.

At the same time, the main drawback of the PLC splitter: (1) device fabrication process complexity, high technical threshold, the chip by several foreign companies to monopolize the domestic bulk package produced by very few companies. (2) relative to the higher cost of Fused Splitter more at a disadvantage, especially in the low channel splitter.

PLC splitter Packaging Technology
PLC splitter package process includes coupling alignment and bonding operations. Coupling of the PLC splitter chip and the optical fiber array is aligned with both manual and automated, and they depend on the hardware with the six-dimensional precision trimming frame, the light source, power meter, microscopic observation system, while the most commonly used are self-aligned , it is through the optical power feedback closed-loop control is formed, and therefore high coupling efficiency docking accuracy and docking.

PLC splitter has 8 channels and each channel must be accurately aligned to ensure that the relative position between the respective channels due to the manufacturing process of the waveguide chip and an optical fiber array (FA), so only the PLC splitter and the first channel of the FA and 8-channel simultaneous alignment can ensure that other channel aligned, thus reducing the complexity of the package. The most important in the packaging operation at the technical difficulty is the highest coupling alignment operation, it comprises two steps First Harmonic precise alignment. First tune the purpose is to enable the waveguide to light through; the purpose of precise alignment is precise positioning of the completion of the preferred optical power of the coupling point, and it is realized by the program to search the maximum optical power.



:: برچسب‌ها: fiber optic splitter , optical splitter , PLC splitter ,
:: بازدید از این مطلب : 653
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تاریخ انتشار : دو شنبه 2 ارديبهشت 1392 | نظرات ()

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