RLMR3 1310 nm 4 mW 3 GHz Coaxial Analogue DFB Laser (Return Path)

The module is specified for CATV return-path and RF-over-fibre applications, combining 1310 nm emission with a 3 GHz bandwidth. Its analogue performance figures include IMD2 of no more than -50 dBc and IMD3 of no more than -57 dBc under rated-power, 25 °C, 10% optical modulation index and two-tone test conditions. Relative intensity noise is specified at no more than -145 dB/Hz from 5 to 300 MHz. These figures provide a basis for initial noise and linearity calculations, although the distortion test conditions do not establish identical performance across the entire 3 GHz bandwidth. The complete transmitter, fibre path and receiver should therefore be validated against the intended channel plan and optical loss budget.

The y = 4 option defines an optical output-power class of at least 4 mW rather than an exact 4 mW operating value. In the complete RDLMR3-A-1-4-FU code, A selects the Type A pinout, 1 specifies a single optical isolator, 4 identifies the ≥4 mW class and FU specifies the FC/UPC interface. The electro-optical specifications link operating power to this model code without stating an upper output limit. Link budgets should therefore use 4 mW as the specified minimum rather than assuming a fixed launch power. Applications with a strict maximum transmitter power should confirm that requirement separately before final selection.

The laser is intended for uncooled operation and has a specified operating temperature range of -20 to +85 °C. Threshold current can reach 15 mA at 25 °C and 40 mA at 85 °C, while operating current can reach 90 mA across the stated temperature range. The laser driver must also accommodate an operating voltage of up to 2.1 V. Its internal monitor photodiode, with a stated response range of 10 to 2,000 μA, can be incorporated into an automatic power-control loop. In practice, the bias circuit should have sufficient adjustment range to maintain the required optical output as threshold current and device behaviour change with temperature.

The module contains a single internal optical isolator with at least 30 dB isolation, which can reduce optical feedback reaching the DFB laser. It also provides a minimum side-mode suppression ratio of 30 dB for the stated operating condition. These characteristics support stable analogue operation, but they do not eliminate the need to manage reflections elsewhere in the fibre path. The FC/UPC receptacle should be connected to a clean, compatible FC/UPC fibre interface, and an FC/APC connector should not be directly mated to it. Reflective components, poor connector end faces and multiple open interfaces should be assessed during system-level testing because an allowable reflected-power limit is not defined.

The maximum ratings are stress limits and should not be treated as normal operating targets. Forward DC laser current is limited to 100 mA continuously, compared with a maximum stated operating current of 90 mA, while reverse DC voltage across the laser must not exceed 1 V. The monitor photodiode reverse-voltage limit is 10 V continuously or 15 V for no more than 60 seconds. Its dark current is specified at up to 0.2 μA when the laser operating current is zero. The driver design should include current limiting, reverse-voltage protection and transient control, with operating margins that prevent start-up or fault conditions from approaching these limits.

The Type A arrangement assigns pin 1 to PD+, pin 2/GND to LD+, pin 3 to LD- and pin 4 to PD-. The pin 2/GND notation means that the grounding and laser-driver topology must be reviewed carefully rather than applying a generic laser-diode footprint. Monitor photodiode polarity must also be observed if its current is used in an automatic power-control loop. The stated monitor response range of 10 to 2,000 μA means that the feedback amplifier should provide a suitable input range and calibration adjustment. PCB documentation should clearly identify both the electrical pin orientation and the optical receptacle orientation before the assembly is released for production.

Mechanical interchangeability should not be assumed solely from the coaxial package description. Compatibility depends on the mounting flange, fixing-hole positions, receptacle projection, pin clearance, panel arrangement and available space around the fibre connector. A mechanical outline is supplied for checking these details, but its dimensions are presented only within the drawing and are not reproduced as tabulated values here. The optical interface is FC/UPC, while the electrical connection uses the four-position Type A configuration. Before finalising the enclosure or PCB, the complete outline should be checked against mounting hardware, panel thickness, fibre bend requirements and the selected laser-driver layout.