data transfer in optical fiber

[neptune]

hi,
As we all know data speed of a single optical fiber is from 1 Gbps to 10 Gbps
but how are these in-coming bits are stored in memory , because we dont have any type of memory units working at speed of 1 Gbps to 10 Gbps.
thanx

 

[MrAl]

Hi,

That's Gbps not GBps right? That means there is a receiver that converts the serial data into parallel data at a much slower speed something like 10 times less, but there's also the chance that it converts it to a wider data path that would be even slower.

 

[neptune]

but still we dont have any memory type which is working in range of 10 Ghz ?
at max SRAM can work at 2-3Ghz but it is very expensive memory, which can not be used to gega bytes of data

 

[MrAl]

Hi,

Well im just guessing here. To deal with very fast signals sometimes the memory is interleaved. That means you store one bit in one memory bank and the next bit in another memory bank using buffers. For 16 bits you would have 16 separate chips for example. Once the 16 bits are stored they are then transferred to the slower memory. The slower memory only has to be 1/16 times as fast as the fastest buffer. Interleaving those 16 bits into 32 bits means you use one bank then the next bank then back to the first bank.
I actually had to do this with a design for a digital storage scope one time where i wanted to use low cost memory. The memory banks were accessed by their own address counters with each address count being 1/2 clock away from the other.

 

[neptune]

ok so if we use separate 16 memory banks then each one has speed of 1/16.
then we would need 1 to 16 decoder to send the bits into 16 separate paths, and the counter of decoder would have to run at a speed of 10 Ghz same as that of incoming bits speed. but do we have decoders or even transistors available that can switch on 10 Ghz speed ?

 

[misterT]

From wikipedia https://en.wikipedia.org/wiki/Fiber-optic_communication

"Wavelength-division multiplexing (WDM) is the practice of multiplying the available capacity of optical fibers through use of parallel channels, each channel on a dedicated wavelength of light. This requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer (essentially a spectrometer) in the receiving equipment. Arrayed waveguide gratings are commonly used for multiplexing and demultiplexing in WDM. Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as 160 channels[6] to support a combined bit rate in the range of terabits per second."

So, all that (10Gbps) data is not processed by one receiver.. it is split to multiple receivers.

 

[MrAl]

Hi,

Thanks for the post misterT. That's the way Fios does it.

 

[neptune]

From wikipedia (**broken link removed**

"Wavelength-division multiplexing (WDM) is the practice of multiplying the available capacity of optical fibers through use of parallel channels, each channel on a dedicated wavelength of light. This requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer (essentially a spectrometer) in the receiving equipment. Arrayed waveguide gratings are commonly used for multiplexing and demultiplexing in WDM. Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as 160 channels[6] to support a combined bit rate in the range of terabits per second."

So, all that (10Gbps) data is not processed by one receiver.. it is split to multiple receivers.

your link doesn't work.
if 10 Gbps is split into 8 channels, 8 channels for 8 bit of parallel data for parallel optical fiber which in all gives us 1 byte. then we still would need 1 Ghz of memory unit. which is very expensive and is of less capacity.

One more Question is if we are detecting light in Ghz of range, So is there transistor fast enough to switch in Ghz of range ? if there are whats there name

 

[misterT]

Something strange happened with the parentheses and the link, fixed.

if 10 Gbps is split into 8 channels, 8 channels for 8 bit of parallel data for parallel optical fiber which in all gives us 1 byte. then we still would need 1 Ghz of memory unit. which is very expensive and is of less capacity.

The answer to that is.. more channels!
Apparently there can be as much as 160 channels.

I also found this: http://www.chipestimate.com/tech-talks/2010/07/20/MoSys-High-Speed-Serial-Memory-Interfaces

One more Question is if we are detecting light in Ghz of range, So is there transistor fast enough to switch in Ghz of range? if there are whats there name

I don't know much about this one either, but I found this device. Maybe if you google some key words from the product description and read the datasheet you'll find more info.
**broken link removed**

 

[neptune]

**broken link removed**

11.3 Gbps :-O !!
i wonder how do they connect this thing to any of the circuitry ?

 

[neptune]

do you have any idea of which electrical components they use for Ghz speed range ? diode or triode

 

[koolguy]

May be Schottky diode...!!

 

[ChrisP58]

do you have any idea of which electrical components they use for Ghz speed range ? diode or triode

I'm sure the actual hardware is an ASIC, but if you want to make your own, you might start with and FPGA. Altera claims their Stratix V line can do 28G.

Application Specific Integrated Circuit
Field Programmable Gate Array
https://www.altera.com/devices/fpga/stratix-fpgas/about/stx-about.html

 

[crutschow]

Microwave transistors (typically GaAs devices) can operate at GHz speeds. But it requires transmission line (micro strip) type wiring of the circuitry.

 

[neptune]

Microwave transistors (typically GaAs devices) can operate at GHz speeds. But it requires transmission line (micro strip) type wiring of the circuitry.

cool, they need stub matching i suppose

 

[crutschow]

cool, they need stub matching i suppose

Stub matching is usually used with RF antennas and such. I don't think it's used much in microwave circuitry.