EM650 Series

This fiber-coupled high-power DFB laser package represents a precision OEM solution, operating with excellent frequency stability, narrow linewidth, low noise, and stable polarization. The module contains a high‐power DFB laser, optical isolator, single‐mode fiber pigtail, thermoelectric cooler, thermistor, and monitor detector integrated with a laser current source, temperature controller, and monitor detector readout amplifier.

The entire module operates from a single +5 V supply and provides a bi‐directional power adjust input that may be used for SBS prevention, for constant power operation in conjunction with the monitor detector readout signal and an external control loop, or for finely adjusting the laser oscillation frequency via chirp. The unit also incorporates a bi‐directional temperature adjust input for coarse tuning of the laser oscillation frequency. The module is designed and built using our high‐reliability platform for defense components and incorporates an advanced ultra‐low noise laser current source.

Absolute Maximum Ratings

Stresses beyond those listed may cause permanent damage to the device. These are stress ratings only and operation of the device at these or conditions beyond these is not implied. Exposure to absolute maximum ratings for extended periods of time may affect device reliability.

Electrical Connector

NOTES

WARNINGS: several of the parameters listed in the specifications above are denoted with a warning. These warnings are covered by the following notes, which should be understood before operating the device.

Mounting

The EM650 is conductively cooled through its base and needs to be mounted using a thermal interface material to a customer supplied heatsink. G&H recommends Panasonic PGS series pyrolitic graphite sheets, available in the US from Digi‐Key Corporation. Care should be taken to keep the base temperature of the module between ‐10 and 60° C at all times during operation.

Noise suppression

The EM650 is a no‐compromises low‐noise integrated laser solution; the temperature controller output is class AB linear, there are no DC/DC converters in the module, the lowest noise components and architectures available are used along with heavy filtering and EMI shielding. Nevertheless, power supply ripple and noise should be minimized and the cable shield should be connected to the EM650 connector shield and tied to the appropriate signal at the power supply end of the cable.

Power Adjust (PA)

The EM650 is designed to run in constant current mode with the drive current set for the as‐ordered output power to achieve the highest possible performance. However, some applications require fine tuning of the laser bias current. The PA input provides this functionality, but its use carries an amount of risk.

If bias adjustment is not required this input should be left open. Use of this input carries the potential to overdrive the laser and/or circuitry with the ability to destroy or drastically reduce the device lifetime. No internal protections on this input are provided, but the user is encouraged to clamp or otherwise limit the voltage and current that may be applied to this input.

The default operating power corresponds to an input of 2.05V. For maximum reliability it is recommended that power only be reduced, although if required it can be driven as high as 2.2V (corresponding to a 10% boost in output power). The safest method of using this input is to pull the voltage down using an external resistor or potentiometer to ground. Applying a resistance to ground will create a voltage divide circuit between the external resistance and an internal resistance of 1K to the 2.05V reference. Damage due to overdrive will not be covered under warranty. Use of this input will likely decrease the performance of the EM650 by bypassing its internal ultra‐low noise voltage
reference.

The PA input must never be shorted directly to Vcc, which would cause circuit malfunction or rapidly destroy the DFB laser.

Temperature Adjust (TA)

The EM650 is designed to operate the laser chip at a constant temperature holding the output frequency within 5 GHz of the ordered frequency. However, some applications require coarse tuning of the output frequency via temperature. In these cases, the laser may be tuned using the TA input. Temperature deviations of more than a few degrees (50 GHz in laser frequency) from the as‐ordered setpoint may result in decreased stability and increases the likelihood of the laser experiencing a longitudinal mode‐hop. The achievable tuning range will depend on the specific laser chip, the ambient temperature, and the thermal resistance to the ambient.

Use of this input carries the inherent potential of overdriving the TEC. The TA input is clamped to Vcc through integrated protection diodes. If Vta is established before Vcc these clamp diodes will conduct. The input current should always be limited to ≤3.5mA to prevent destruction of the clamp diodes.

The safest method of driving this input is with a tri-state output whose output is current limited when active, maintained at high‐impedance until Vcc is established, and whose output returns to high‐impedance before Vcc is removed. The device warranty will not be honored for lasers with overdriven TECs. Use of this input also carries the likelihood of decreased frequency stability as it bypasses the internal ultra‐low noise voltage reference.

The TA input must never be shorted directly to Vcc or ground which would cause circuit malfunction or rapidly destroy the DFB laser.

Grounding

Care must be taken with grounding, cabling, and connections due to the amount of current the module consumes. Make sure that the voltage on pins PA/TA reference ground as close to the EM650 as possible if either input is connected.

DO NOT connect the cable shield to ground at both ends of the cable to avoid producing a ground loop. #

DO NOT connect the EM650 housing to ground to avoid producing a ground loop.

Startup Considerations

The EM650 consumes a considerable amount of current in the startup phase and when operating at temperature extremes. A voltage source plus cabling able to deliver the maximum specified current at no less than the minimum voltage is therefore needed. Current limiting below the specified maximum during the startup phase will result in an internally measured drive voltage lower than specified. This condition can result in permanent, non‐warrantable damage to the device.

If the user fails to sequence the supplies as described in the Power and Temperature adjust sections of this document and Applications Note DS‐7047, the device will immediately suffer non‐warrantable damage or destruction.

Applications Information

Be sure to check this website for the latest applications information for this device. Application note DS‐7047 (in Downloads) covers general usage of the EM650 along with information particular to tuning via temperature or chirp. If you plan to tune this device, it is highly recommended that you read this app note.