Frequently Asked Questions
Can you also provide near 100% reflectivity?
We’ve made filters with > 99.99% reflectivity. But it does depend on the thickness of the grating.
Do you offer low power (100 mW) laser diodes in the near infrared (800 – 900 nm) that are frequency stabilized using VBG?
Currently we offer broad-area single emitters on C-mounts that are 1, 2 or 3 Watts in output power and are wavelength-stabilized. Wavelengths are from around 750 nm to upper 900’s of nm. Single-mode lasers with lower power are also available. Typical packaging options are 9 mm and 5.6 mm TO cans and free-space butterfly package. In either case the lasers are available with circular beam output.
How big are the wafers you can produce with your technology?
Glass wafers with sizes of up to 80×80 mm can be produced right now. In the future larger wafer sizes will become available.
How should I determine the optimum reflectivity of the VBG when I use it for wavelength stabilization?
We don’t have an exact formula for this. We can tell you that with fast axis collimation only and focal length of that lens ranging from 0.1 mm to 0.9 mm it is sufficient to have a VBG with approximately 30 – 40% intrinsic reflectivity (i.e. measured with light collimated on both axis). When slow axis is collimated as well it may be sufficient to use VBG with 10 – 20% reflectivity. Please note that the result will strongly depend on the characteristics of the laser diode.
How stable is the grating on the temperature? What is the usable temperature range
VBGs have been tested to 200C for up to several weeks without measurable degradation in performance.
Is there a big price difference for various reflectivities?
Not until about 90% reflectivity. There may be a price premium for gratings with higher than 90% reflectivity.
Is there a possibility to tune the reflectivity peak by changing the temperature or other parameters? What is the dLambda/dTemp coefficient?
Yes. The easiest thing is to tune by temperature. The temperature tuning coefficient for our VBG elements is 0.01 nm/K. It is also possible to tune the wavelength in much wider range by rotation. In addition, please note also that we offer gratings with transverse wavelength “chirp” where the Bragg wavelength of the grating varies across its clear aperture. These gratings can be used very efficiently for wavelength tuning.
s there any angular dependence of the peak wavelength? If yes, please give details.
The peak wavelength changes with angle as follows: λ = λc*sqrt(1-sinθ^2/n^2), where λc is the cut-off wavelength, θ is the angle of incidence in air and n is the refractive index of glass.
What is the damage threshold and long-time stability for these VGBs (example: laser diode bar with emitter 1 umx10 mm, power 50 W)?
The gratings have been tested with ~ 50 MW/cm2 cw power density at 1064 nm without any damage. They have also been shown to survive when operating at ~ 200 MW/cm2 with Q-switched (ns pulse duration) lasers.
What is the optimum reflectivity when used for the above purpose (stabilizing the wavelength of laser diodes used in pumping solid-state lasers)?
It depends on the front facet coating, the design of the laser chip as well as the collimation optics.
What is the typical thickness of the VGB itself in the glass wafer in order to achieve the near 100% reflectivity?
The Bragg grating penetrates the entire volume of glass. So the entire 1 mm of glass thickness is the Bragg grating. In 1 mm of glass we have achieved approximately 93% reflectivity at around 800 nm. We recommend gratings with thickness of > 4 mm in order to achieve reflectivity of > 99.5%.
What is the typical thickness of the wafers?
For wavelength stabilization of the high-power laser diodes and arrays the typical thickness of the VBG element is from 0.5 to 2 mm.
What is the useful range of wavelengths?
In general, it is anywhere between 350 and 3000 nm, depending on how much loss you are willing to tolerate. As part of the research, we have actually made recordings at wavelengths from 480 nm to the 1550 nm range. Our wavelength locking products, however, are offered in the 630 to 1064 nm range. There are some standard wavelengths in that range that are offered with faster delivery times and at lower prices then others: 785 nm, 808 nm, nm and 976 nm.
What was the thickness of your samples with 99.9% reflectivity?
It was upwards of 4 mm, depending on the operating wavelength.
Fiber Optic Packaging FAQs
Can I send you a laser to package?
We will package customer supplied lasers as long as they are in a sealed TO-can and are received with the lasers specifications.
Can I supply my own fiber for pigtailing?
We will accept customer supplied fiber.