[Laser] A first look at RT5-2354DTS-C2 photodiodes

[KY1K]

At 10:05 AM 3/27/2006, you wrote:
>I received a lot of RT5-2354DTS-C2 photodiodes I purchased off Ebay 
>and had a chance to take a quick look at them this weekend. They 
>have a standard 5mm clear molded plastic lens and short leads cut 
>for PC mounting. The mounting of the diode inside the case is 
>strange though. The diode is offset to one side so is not centered 
>when looking in to the lens.  I put the diode in place of the 
>SFH-203  in my receiver and saw about  a 7dB reduction in 
>sensitivity to the 120 Hz signal from a light maybe 1/2 mile 
>away.  I also just as a comparison pointed both the RT5 and the 
>SFH-203 bare diodes at the sun and measured the maximum current. The 
>RT5 has about 1/2 the output current of the SFH-203 which has 
>1/4  the area.  I need to confirm the optical beam width of the RT5 
>but believe it is 70 deg total. These are certainly functional for 
>getting stared in optical communications but maybe not as good as 
>the some of the other diodes mentioned that I and  others are 
>using.  If anyone wants to run some tests on these, I'll be happy to 
>send some off.
>  - Kerry N6IZW -

Kerry,

The units that come in plastic LED type packages are NOT good. If you 
want to use the bare diode without an external lens, they are fine.

When using them with an external lens to collect more light, they are 
not good. The problem is that the package does not focus the light on 
the photodiode unless the light striking the package is parallel. SO, 
the losses are quite large when used with an external collector lens 
because the focal point will then fall quite short of the photodiode 
surface itself.

Years ago, I worked out a procedure to correct the problem though. I 
ground the bubble lens away till it was flat, then polished the front 
surface (with Comet and water on a small piece of glass). Having a 
front face that is flat and relatively smooth made a lot of 
difference when used with an external lens.

Regards,

Art