940 lpmm Grating Testing Procedure

We have received a lot of very good feedback from a number of companies that are independently testing Wasatch Photonics' Dickson^TM gratings. Based upon this feedback and to help you test and evaluate our gratings, we provide the information below.

Dickson^TM Gratings Considerations

	These are small production quantity DicksonTM gratings (possibly with less than optimal AR coatings). Once these gratings go into production, the insertion loss will be lower and the coatings better.
	These DicksonTM gratings are generally centered at wavelengths of 1545nm.  The packaging containing each grating will be marked with the specific CWL for which it was tuned.
	These particular DicksonTM grating samples are designed with the angle of incidence (AOI) equal to the angle of diffraction (AOD).  Going away from the optimum angle, the Bragg angle, will have effects shown on this graph 940 Bragg Angle Sensitivity.
	Use the grating equation to approximate angle.  If for instance your grating is marked as 940 lpmm, then with lambda=2d sin theta, you can approximate the correct angle for 1545 nm by arcsin(1.545 x .940)/2 = 46.56 degrees.

	Place a meter in front of a collimated source
	Insert the grating at about 45-47 degrees and rotate it through 44-48 range until you find the lowest zero order reading. This should be about 1% of the incident light at the best angle in either polarization. P polarization is more sensitive to angular error (than S polarization) so it may be the preferred polarization for optimizing the angle.

The standard optics definition for P & S polarizations is shown in the diagram below. Note: For some reason, companies that make ruled and surface relief gratings define P & S polarizations as just the opposite of this.  The standard optics definition is: Es = When the electric field vector is perpendicular to the plane of incidence, the light is said to be S-Polarized (TE). Ep = When the electric field vector is parallel to the plane of incidence, the light is said to be P-Polarized (TM).

	Alternatively, the diffracted beam may be used to optimize the angle while looking for the most output.
	Samples are centered around 1545nm unless otherwise noted.  Perform tests for PDL and diffraction efficiencies over a wide wavelength range (maybe 1480-1600) if possible and should produce results similar to this 940 Transmission.

We are confident this will help you test and evaluate Wasatch Photonics' Dickson^TM gratings more easily. Please contact us with any questions and/or test results