LDTC-LAB datasheet(22/31 Pages) WAVELENGTH

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ENABLE THE LASER DRIVER

Press the

LDD ENABLE button on the front panel to enable

current to the laser. Once enabled, the button will glow red.

This occurs after the requisite time delay (adjustable via

remote commands, see ONDELAY or LASer:ONDELAY).

EXTERNAL MODULATION

(EXT MOD) BNC

NOTE: The modulation bandwidth is different in Constant

Current and Constant Power modes see

Electrical

Specifications for details.

This is the external modulation input. The voltage input on

this BNC sums with the DC value on the screen if the unit is

configured to allow external modulation. To enable or disable,

use the remote command LASer:MOD. The input impedance

is 2.5 kΩ. To calculate the external modulation signal voltage,

see the next section for the transfer function, and use the

following equation:

EXT_MOD =

ISETPOINT

Transfer Function

Note that I

SETPOINT is the laser diode current setpoint, whether

operation mode is CC or CP.

If the external modulation input causes the driver to reach the

current limit, the output signal will be clamped at the limit level

but will not switch off.

The bandwidth of the Current Monitor is lower than the

bandwidth of the output. To monitor the actual output waveform

at frequencies greater than 300 kHz, connect an oscilloscope

across the output pin on the MONITOR D-SUB, Pin 10

(positive) and Pin 12 (ground) while using the resistor test

load.

CAUTION: Connect the oscilloscope across

the monitor pins only — never connect the

oscilloscope across the laser or in series with it.

EXTERNAL MODULATION BNC

TRANSFER FUNCTIONS

The external modulation transfer function depends on the

LDTC LAB instrument model and is as follows:

MODEL NUMBER

TRANSFER FUNCTION

LD250mTC5

50 mA / V

LD2TC5 LAB

0.4 A / V

LD5TC10 LAB

1 A / V

Table 5. Model-dependent external modulation transfer

functions.

The input range is always -5 V to +5 V. Damage will occur

at ±6 V input.

ADDITIONAL CAPABILITIES

ANALOG CURRENT MONITOR

(PINS 10 & 12)

This signal is the sum of the DC setpoint as shown on the

screen and the external modulation input. To monitor the

analog current level:

1. Connect the Analog Output Current Monitor (Pin 10) on

the LDD/MONITOR D-SUB to an oscilloscope.

2. Connect Analog Monitor Ground (Pin 12) to oscilloscope

ground.

This measurement gives the current through the laser diode,

whether operation is CC or CP. See

Table 6 for the transfer

function.

LASER DIODE SETPOINT CURRENT

MONITOR (PINS 11 & 12)

To monitor the setpoint current:

1. Measure the voltage on the Analog Setpoint Monitor

(Pin 11).

2. Ground for the measurement is the Analog Monitor

Ground (Pin 12).

The setpoint current monitor gives the laser diode current

setpoint whether operation mode is CC or CP. In CP mode,

LD current setpoint is calculated after output is enabled.

The setpoint monitor and analog current monitor transfer

functions depend on the LDTC LAB instrument model and are

given below:

MODEL NUMBER

TRANSFER FUNCTION

LD250mTC5

50 mA / V

LD2TC5 LAB

0.4 A / V

LD5TC10 LAB

1 A / V

Table 6. Analog current and setpoint monitor transfer functions.

The range is 0-5 V where 5 V is full scale current.

ENABLE STATUS INDICATOR

(PINS 6 & 8)

This is a +5 V TTL indicator. If current to the LD output is

enabled, the voltage between Pin 6 and Pin 8 on the

MONITORS D-SUB will be low. It will be high if current is

disabled.

ENABLE STATUS INPUT (PINS 7 & 8)

This is a TTL signal that will override the front panel ENABLE

button. The default polarity is ENABLE HIGH. Use 0 V to

disable the output regardless of the front panel enable button.

An internal 100 kΩ pull-up resistor means no external voltage

is required for front panel operation with the default polarity.

The polarity can be changed by remote command.

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