FAQs

What is the length of the gain medium of the 795 DBR lasers we purchased from you previously? It is a 120mW diode.

The gain ridge length of the 795DBR laser is 1.5mm. The total DBR laser chip is 2mm in length, with 500um being the passive DBR grating. The effective cavity length is around 1.6 to 1.65mm.

I am interested in a 795 DBR diode such as the PH795DBR180TS. The online spec sheet gives a quite broad linewidth compared with the 780 DBR. Is it possible to get one that has <1 MHz linewidth?

Yes the typical linewidth of most of our DBR lasers are under 1MHz. At the time of the product bulletin was produced, we did not have all wavelengths and packages linewidth measured. We now offer PH795DBR180TS with less than 1MHz line width.

We have a 780nm laser diode and before hooking it up to our laser diode controller we had a question about how the laser is hooked up. Are the laser and photodiode hooked up independently? If not then is the laser anode grounded or is the laser cathode grounded?

The laser anode and cathode leads are both floating, ie, isolated from the case, as are the pins for photodiode, TEC and thermistors. The customer has the flexibility to configure different polarities she chooses.

I need to modulate the laser, so I will add a Bias-Tee in the current feed of the laser; do you know the specifications that I should have in the Bias-Tee to do this? Can I achieve a modulation of 30 MHz?

For amplitude modulation, the diodes show a RIN peak at around 3.5GHz; however the TO8 packages are not optimized for RF design. The wire bonds and feed-troughs will add parasitics that can limit modulation, as well as any constrains from the drivers. Theoretically, the TO8 package is comparable to the butterfly package, where our customers have done sub-nsec pulses routinely as in the reference.
http://www.photodigm.com/picosecond-pulsed-laser-diode-nanosecond For frequency tuning, tuning coefficient with current at low frequencies is generally around ~ 2nm / A for all wavelengths. The thermal cutoff is around 100 KHz.

Typical:

The current tuning coefficient of a typical DBR laser is around 0.002nm/mA at low frequencies with the thermal cutoff around 10kHz-100KHz. So if the application requires frequency modulation, then +/-4.8GHz is doable. Although 350KHz rate is a little on the high side.

For amplitude modulation, the diodes show a RIN peak at around 3.5GHz, however the TO8 packages are not optimized for RF design. The wire bonds and feed-throughs will add parasitics that can limit modulation, as well as any constrains from the drivers.

The laser diodes are anode grounded or cathode grounded? (TO-8 pkg)

The laser anode and cathode leads are both floating, i.e., isolated from the case, as are the pins for the photodiode, the TEC and thermistors. You have the flexibility to configure different polarities as you
choose.

It is ok to wire the diode with the cathode as common?

Yes, it is OK to wire the diode with the cathode as common, as long as the current flows from laser anode to laser cathode.

Do you have the conversion table of the diode from resistance to temperature?

The current tuning of the laser is around 0.06nm/C. The actual spectral measurement is shown on the second plot in the data sheet that is shipped with the device.

What are the values of the temperature that the mount of the diode can reach in a normal use of the laser diode?

Depending on the thermal load, the embedded TEC can cool the laser down to close to 0C and heat up to higher than 50C. However, we recommend operating the device within 10-40C. The lower temperature is constrained by the TO8 package which is epoxy sealed. Operating the device under dew point will result in condensation. The higher temperature is constrained by laser life time, which follows the Arrhenius equation.

Do you have the conversion table of the diode from resistance to temperature?

The current tuning of the laser is around 0.06nm/C. The actual spectral measurement is shown on the second plot in the data sheet.

Could you please give me a comparison between DBR laser and ridge waveguide diodes?

Ridge waveguide diodes are essentially Fabry-Perot FP Lasers. They are typically single spatial mode, but multi-spectral mode. FP lasers are fairly inexpensive, but the wide linewidth and spectral instability limit their use in certain applications. DBR lasers are both single spatial mode and single frequency, which make them a simple to use instruments in many high precision applications.

We are evaluating the DBR laser against ECDL laser for a new system. I need to find compelling reasons for changing to DBR lasers.

Please check this application note; it has a fairly detailed description on the performance comparisons of ECDL versus DBR/DFB lasers. http://www.vescent.com/technology/short-cavity-lasers/ . We believe that in most hyperfine spectroscopic applications, Photodigm's DBR lasers can be applied in place of an ECDL thanks to the DBR's excellent stability and narrow line width. The following is another table comparing ECDL and DBR.

780nm	ECDL	DBR
Power	50mW	300mW
Linewidth	<200kHz	<500kHz
Tuning range	765-781 nm	779.5-781.5
Mode hop free tuning	15nm	2nm
Size	2,650 cm3	<1cm3
Scalable	No	Yes, monolithic
Price	Mid-range	Volume discount

Can you tell me something about the current and temperature tuning rates and ranges for the 852nm/240mW DBRs?

Current tuning rate is ~0.002nm/mA, temperature tuning rate is ~0.06nm/°C

PH976DBR280TS - On the data sheets you applied ~0.4 A of current to get to the spec'd 280mW, but on the general datasheet it says absolute max current is 250mA. So is it still safe to apply 0.4 A of current to these DBR's for long periods (>10hrs)? Does the data sheet I attached simply refer to a different model?

Yes it is safe to apply 0.4 A of current to the DBR's for long periods (>10hrs) as long as the lasers are properly temperature controlled. The general product bulletin is for the standard devices and the two parts customer received are of longer cavity and higher power; they can be operated at higher drive current reliably.

PH780DBR180XX. These are mostly 100mW avg. power CW, we’re looking for something pulsed with an avg. power of 100mW plus. What pulse energies can be achieved with these lasers?

Our highest power rating for 780nm DBR is 180mW. With gain switching, the laser can be pulsed at ~100ps. Although the laser can be pushed to higher output at pulse mode without thermal rollover, it could possibly suffer catastrophic optical damage at above 250mW.

I need the exact laser beam specifications for the Mercury package (diameter or waist size and position, beam diversion, emission position on package) as well as the details of the package dimension and connector for the controller.

Beam diversion: typical 6° FWMH slow axis (horizontal) and 28° FWMH fast axis (vertical) Waist size: Our wave-guide software generated beam size is defined different from conventional, so we normally estimate the near field beam waist through the far field divergence measurement. With the FWHM divergence at 6 and 28 degrees for slow and fast axis, the estimation will be 6.7um and 1.4um 1/e2 beam waist for the 795nm DBR and 7.2um and 1.5um 1/e2 beam waist for the 852nm DBR.

Emission position: An aperture sits in the middle point of the TOSA window, i.e., 2.6mm from the base of package and 2.9mm from the side of package. In the direction of light emission, the aperture is 1.05 mm max from the outer edge of package.

Connection: The TOSA flex cable is compatible with ZIF connectors such as Digi-Key Part #WM6762CT-ND. Our TOSA heat sink mount provides conventional Dsub D9 and D15 connector to laser driver and temperature controller.

What is Photodigm's recommendation for a current controller for this laser?

For a typical application such as magneto-optical trapping (MOT), a servo system for locking is necessary. The current resolution of a commercial digital controller is not quite adequate for stabilizing the wavelength and will not be as fast. Other than Vescent, and Toptica, Stanford Research Systems may also offer servos. The choice of controller and stabilization scheme highly depends on the application's line width target.

Could you clarify, this laser can be used as a seed laser (CW ) for Q-switched Nd: YAG generator?

Yes our 1064 diode can be used as a seed laser in a Nd:YAG system. More in the MOPA configuration than Q-switch since our diode has very good linewidth.

Can you please recommend an alternative package that suits our purpose along with any optics that is required for beam collimation and polarization?

Our TOSA package is ideal for various applications. For simple lensing, we see a decent beam using a fast aspheric (NA of .55 or better) such as these, please follow link provided.

http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3811

The slow axis beam divergence is 6° FWHM typical, 8° maximum. The fast axis beam divergence is 28deg FWHM typical, 32° maximum. The laser facet to the outer edge of the TOSA package is 1.35mm maximum. In addition, the DBR laser is polarized with ER around 20dB. The polarization of the E field is horizontal by design (looking into the laser ridge from front facet, p side up, n side down).