This device is used to drive acousto-optic mode lockers for laser systems running in the range 60MHz to 110MHz. The device uses a phased locked loop configuration to drive the mode locker synchronously with a signal derived from the light output of the laser. Prior to lasing the unit scans over a preset frequency range looking for enough output signal to enable the unit to lock the output to the input.

Once such a signal is found the scanning stops and the output is locked to the input.The unit has controls for input gain, output level, "Q", loop delay. In addition the start and stop frequencies and sweep speed of the unlocked drive frequency can be set using a built in frequency meter. There are indicators for locked, sweep direction, input signal strength and modulator over heat; (this requires that the moulator be fitted with a thermistor). In addition to the main output (at half the laser frequency) there is an auxillary output at the laser frequency. The unit has a fibre optic input (SMA) and comes with a 2 meter length of 200µm fibre and an input beam focussing lens.

 

Specifications:-

1. Frequency coverage, 60MHz to 110MHz input, the main output is half of these values.
2. Output power ~1 watt into 50Ω (the amplifier delivers 2 watts but there is a reverse terminating network which reduces this to ~1 watt).
3. Input sensitivity, approximately 4µW will lock the unit. (The unit needs about 2µwatts in the fundamental frequency).
4. Max sweep width, 665kHz @ 60MHz, 530kHz @ 80MHz and 677kHz @ 110MHz.
5. Sweep speed, will go from many seconds for the sweep to a fraction of a second.
6. Minimum sweep width is nominally zero but the unit actually just sweeps very fast around a value. The width is then similar to the oscillator bandwidth.
7. Adjustable Q, 5,7,10,15,20,50, 70 &100.
8. Delay 10 steps of 2.5ns plus fine delay between steps.
9. Input gain adjustment 40dB refered to the diode output voltage, i.e. 20dB on the light input.
10. The output can be adjusted and also an attenuator can be switched in to give both a lower output and improved reverse termination. This is particularly useful for operating on the resonance of the mode locker.
11. There is a frequency meter with six active digits, 1kHz resolution is used.
12. There is an indicator of the locked and sweep conditions. When it is sweeping slowly the indicator tells you which way it is sweeping.
13. There are controls for the sweep rate, start frequency and range of sweep when it is scanning the drive and looking for a signal on which to lock. The frequency meter can be used to set these parameters up.
14. Ancillary output, approx 2 volts into 50Ω at the frequency of the local oscillator. This output does not go through the delay circuitry and is intended as an additional metering point.
15. There is an output inhibit, both manual and external. The latter is intended for use with a thermistor. There is a potentiometer to set the threshold level. This can be used to stop the driver when the mode locker overheats.
16. Mains input is universal.
17. The unit has an optical input to keep pick up on the signal input down. We supply 2 metes of 200µm fibre and in input coupling lens.
18. Size 330mm wide, 140mm high, 250mm deep.
19. Connectors, Input fibre optic (2 meter x 200µm SMA cable provided with input lens). Main output SMA, ancillary outputs BNC. Thermal trip input, Lemo "00". Power IEC (Lead supplied, please specify country or mains plug type.)