# Presentation: 551042

## ODU Status, QC of some ODUs, Grease Tests

- Howard Budd
- University of Rochester
- PMG Meeting
- Feb 14 2007

## ODUs Optical Decoder Units

- ODU – Optical Decoder Unit (CMS term)
- Takes light from the cable to the PMT
- The ODU is made like an optical cable with DDK connectors on both ends
- Its is 50 long
- But a cable must be made light tight - light tight boot
- ODUs are cut 2 by PMT box factory
- Installed by PMT factory in the PMT boxes
- 4 ODUs/PMT box, 8 optical connectors/PMT box

## ODUs and Cables

- ODUs and optical cables are made using  the same same techniques & same groups
- This was the same philosophy as CMS had
- All the techniques that are applied to making ODUs can be applied to making cables
- Polishing technique – Eileen Hahn – Lab 7
- Lab 7 & Lab 8 group have done a lot of work in getting excellent polishes
- Lab 7 understands the polishing tolerance
- Run through the same QC apparatus as cables
- This will be shown in this talk

## Toward ODU Production

- The DDK connectors contain fiber glass
- Fiber glass is very hard on the polishing diamonds
- In MSU technique, the fiber glass is not polished
- The front face of the connectors are cut back with a carbide bit
- The fibers are glued in with the front face pointing down
- The epoxy flows through the holes and forms a pool on the front face
- The epoxy should surround all the fibers
- The connectors are polished about .2 mm from the fiber glass part of the connector leaving .2 mm of epoxy on the front face
- The polished fiber sticks has no epoxy cover
- Saves diamonds and we get a better finish

## Debris on the Edge of the Hole

- Problem was the facing off of the connectors left debris on the front of the hole
- With the glass fiber in the hole, epoxy doesn’t consistently flow out to the front face
- Some fibers had very little epoxy encapsulating them
- Cladding would get ripped in polishing
- Epoxy flowing out was the technique that seemed to work the best from earlier R&D and we were reluctant to give it up
- We needed to remove the material from the hole
- But it is held by fiber glass and doesn’t come off easily

## Debris on the Edge of the Hole

- We tried a variety of techniques to remove the material
- Dremel 3.2 mm cutting tool bit
- Slightly countersink of fiber holes by hand
- Visually this seem to worked best
- Connectors are blown with dry N2 after reaming
- This is our default technique

## Transmission QC Device 

- LED on Calibration Pin Diode and WLS pigtail
- Calibration Pin Diode just in front of LED
- WLS fiber -> jumper-> cable->jumper->pigtail->pin diode
- Cable Measurement
- Measure without cable
- Direct Measurement
- Transmission =  (Cable Measurement / Direct Measurement)

- Pin Diodes

- Jumper

- Tested Cable

- Jumper

- LED

- WLS Pigtail

## Measuring Transmission

- Measure transmission through ODU by starting off with a measurement of the jumpers connected directly together
- We call this the direct measurement
- There  is a direct measurement at the beginning of the measurement and the end of the measurement
- For this we use the direct measurement at the end.
- I discovered during the connector acceptance tests that the transmission across a connection depends on how you inject light into the fiber
- Therefore,  the transmissins shown here might not be the transmissions for the ODUs in the experiment
- A test using an apparatus which simulates the detector would have to be done to determine the transmission in the experiment

## Transmission QC Device

- The pin diodes are connected to a switcher
- A picoammeter  readouts the switcher
- Switcher goes one fiber to another
- Lab View controls the readout

## QC of ODUs

- We insert the cables between the jumpers and measure the ratio of the measurement/direct measurement
- This is the transmission of the 0.5 m cable including one connector transmission
- One would like to know the connector transmission
- However, we have only measured fiber attenuation using PMTs not pin diodes and the spectral response of pin diodes are different
- For example, the transmission of 0.5 m fiber using 8 m attenuation length is 0.94
- The maximal connectors transmission we expect is .92
- The numbers shown include the loss from the 0.5 m cable and the additional connector connection
- A maximal transmission we might expect is .865

- We will show the QC plots from the QC programs
- Transmission
- Individual fibers
- We have used 2 sets of jumpers
- These are all the connectors from the 2d set of jumper
- For the 1st set of jumpers there was high rms, especially high transmissions, for one set of measurements
- Not sure of  the physical mechanism

- Individual fibers normalized to 1

- Previous plots put on one graph
- Lit/conn and cable plot show whether the RMS is due to the individual fibers or cables
- Old polishing 5 cables
- Av=79.0%
- RMS=1.5%

- Top plot gives transmission cable average
- Bottom plot sets total average to 1

- Transmission for individual fibers with fiber numbers coded by symbol and color

- Averaged to 1
- Program prints out outlying fibers
- Bad fiber file
- The CMS ODU cut was  nor lit > 0.9 for all fibers in an ODU
- 10 out 156 ODUs fail this cut
- Most of these at beginning of production
- 3 close to the cut
- The CMS cable cut was 0.88

- Earlier set of ODUs
- Transmission using the first set of jumpers
- Showing the fiber glass polishing technique (traditional technique) Cables 81-85

## ODU & Cable QC

- For ODUs
- Pass transmission test
- Look at them with ×20 magnifying glass
- Excel file that lists QC status
- For Cable
- Pass transmission test
- Look at them with ×20 magnifying glass
- Pass light tight test with light leak checker
- Box with PMT in it connected to picoammeter
- Check the fiber order is OK in cable
- Box with multicolored LEDs
- Excel file to list QC status

## Cable Status

- Cable are made like ODUs, but we need to make them light tight
- A polyurethane boot is put at the connectors
- The boot mold and the mold procedure have been developed at Rochester
- We have tested the mold at FNAL
- We have made a set of suggestions
- Mold is continuing to be tested at Rochester
- We will retest it at FNAL in the beginning of March
- We expect to be able to start producing cables at the beginning of March.

## What about greasing the connection

- No Grease/grease
- Measured with cable QC program
- The increase of light from grease appears to be independent of how the light is injected in the fiber
- Ave=.924
- With old technique = .86
- With optical grease we get an increase of light of 1% over old technique, consistent with 0
- The optical grease fills in the imperfections due to the cutting of the fiber glass

## Grease Stable over a Month

## Conclusions

- We have QCed 86 connectors using the nominal countersinking technique and they look OK
- Some of these which the epoxy could have flowed better
- We have already produced something like 146 ODUs which look fine according to the QC program
- Although the front face isn’t covered quite as well I think they should be but they are probably OK  ODUs
- An additional 25 wait QC for a total of 171 out of a total of 400 needed for tracking prototype
- Grease still looks OK
- With grease the transmission appear to be independent of the polishing technique