ILX Lightwave LDX-3620 – Ultra Low-Noise Current Source

The ILX Lightwave LDX-3620 is a battery-powered, ultra-low-noise current source for precision laser diode testing and characterization. It delivers stable, low-noise current output with operating modes for constant current (low and high bandwidth) and constant optical power, plus comprehensive laser diode protection.

Technical Specifications

• Laser diode current range: 0 to 200 mA or 0 to 500 mA


• Compliance voltage: < 5 V


• Output noise/ripple: < 600 nA rms (standard); < 100 nA rms in battery mode


• Current noise density: 815 pA/√Hz


• Wideband current noise: 850 nA rms


• Output stability: < 10 ppm over one hour; < 50 ppm over 24 hours; < 4 ppm over 5 minutes


• Temperature coefficient: < 20 ppm/°C


• Floating output: Fully floating relative to earth ground Operating Modes


• Constant current (low bandwidth): Stable DC with minimum noise


• Constant current (high bandwidth): DC or modulated control up to 1 MHz


• Constant optical power: Closed-loop optical power regulation Modulation & Control


• Internal programmable ramp generator


• Two external modulation inputs (fine and coarse), AC or DC coupled


• High bandwidth mode: DC to 1 MHz (3 dB)


• Low bandwidth mode: 10 kHz (3 dB)


• AC coupled: 100 Hz to 1 MHz


• Transfer functions: 2 mA/V or 5 mA/V (primary input, depending on range); 100 mA/V or 250 mA/V (external modulation, depending on range) Protection


• Adjustable current limit with transient protection


• Slow-start turn-on circuits


• Shoring relays across output


• IEC surge and electrically fast transient (EFT) tested


• Error indicators for open circuit and power-limit conditions Display & Power


• 4.5-digit display


• AC input: 100–120 VAC (±10%, 47–63 Hz) or 210–250 VAC


• Maximum current draw: 1.6 A (100–120 VAC)


• Internal lead-acid battery: 4.5 A·h (standard); optional long-life battery available


• Battery operation: Up to 16 hours at full charge

Key Features

• Ultra-low noise output (< 100 nA rms battery mode) for spectroscopy and coherent communications


• Excellent short-term and long-term stability across temperature


• Dual-range current capability (200 mA or 500 mA)


• Multiple modulation inputs with programmable waveform generation


• Comprehensive laser diode overstress protection

Typical Applications

• Narrowlinewidth laser characterization


• Coherent optical communications testing


• Spectroscopic applications requiring stable laser wavelength


• Research and development of semiconductor laser sources

Compatibility & Integration Fully floating output allows flexible circuit integration. Dual modulation inputs (fine and coarse) support both AC and DC coupling schemes. Four-and-a-half digit display provides direct current and power readout.