Active Alignment

The need to align devices down to nanoscale accuracy is arising in many fields. Optical components such as the lenses or lens assemblies in small cameras, or even the CCD chip itself, need to be positioned with ever more precision. In Silicon Photonics, fiber optic devices need to be aligned to optimize optical throughput before testing or packaging can begin. Sometimes multiple channels, or interacting inputs and outputs, need to be aligned and optimized for the characterization of devices, or in test and packaging procedures.

Power Metrology

Optimizing the Optical Power Transmission

Common to all applications is the need to optimize the optical power transmission. For example, as is the case in Silicon Photonics applications, light from a fiber is coupled into a silicon substrate or vice versa. The coupling profile is very narrow-shaped which results in an equally narrow peak of power distribution.

Logarithmic Scaling of the Output Signal

Using a logarithmic response provides a much larger dynamic range for optical power metrology than a linear response. This is especially important for capture of small signals, e.g. when far from optimum alignment.

The fast alignment routines in PI’s controllers, such as E-712, preferably use a logarithmic power signal. The logarithmic response flattens the steep sides of the typically Gaussian-like coupling profile, allowing a smoother approach to maximum with less risk of overshoot.

Calculation of Optical Power

To obtain real power values it is necessary to convert the logarithmic signal. PI’s F-712 fast alignment systems, namely the E-712 controllers, provide an automatic conversion to power via software command.

To accurately compare these real power values with other measurement results, we recommend using a calibrated power meter, such as PI’s F-712.PM1.

Using the F-712.PM1 Power Meter with F-712 High-Precision Fast Alignment Systems

The versatility of F-712 Fast Alignment Systems is enhanced by using the F-712.PM1 Optical Power Meter for power metrology in both the visible and infrared range. In addition, a current input can be used to connect a photodiode.

Independently from the source, the output signal is an analog, logarithmic voltage signal. This allows to take advantage of logarithmic scaling and measure optical power accurately over a wide range of input powers.

A simple software command inside the E-712 controller allows an automatic conversion of the logarithmic response signal to power.

Features

Large signal bandwidth of 20 kHz
High dynamic range
Wavelength range 400 to 1550 nm
Current input range to 1 mA
Logarithmic output
Calibrated power meter