Actually the laser diode current also alters the refractive index of the laser diode chip.
Usually, an external cavity is used to stabilise and tune the diode laser operating wavelength in such applications. A cateye ECDL with a tilt tuned narrow bandwidth filter is easier to construct than either Littrow or Littman-Metcalf EDL's using tilt tuned gratings.

If the cavity is reanonably compact then a single oven design similar to that used by the E1938A would perhaps be a better choice.
However laser diode temperature controllers usually employ a TEC to cool the diode rather than a heater.

Whilst some FP laser diodes will operate in single transverse and single longitudinal mode without an external cavity and associated band select filter achieving this together with operation at the desired wavelength can be problematic.
I have a single transverse mode, single longitudinal mode FP laser diode that uses a TEC to control the diode temperature along with a low noise current drive. Both the temperature and operating current are selected so that mode hopping doesnt ocurr in temperature and current island of stability.

Bruce

Hi

Simple answers (and likely not much help):

Thermal gain on a single oven is likely in the 300 to 600 range.

Double oven boosts that by 10 to 30X

Thermal gain in this case: take the ambient change divide it by the thermal gain
and you get the oven temperature change.

Long term stability:

low enough that it does not impact aging. ( = that’s how you test it). Since that gets back
to the specific thermistor being used, you are into the ‘likely not much help” range.

Best guess info: The crystal + circuit is < 1x10^-9 / C in the vicinity of the turn. The operating
point is offset from turn to minimize the combination of crystal + circuit. Just what the net
is ….

Still, if you can “see” aging at the parts in the (low?) 10^-11 range, it sort of kind of gets
you to a number. Maybe 0.01C / day.

Since you are canceling the circuit with the crystal, if things got to far off, a year later the
temperature performance would not be any good. That likely gets you to something
in the < 1C per year range.

Bob

The DFB lasers you use for this typically has a thermistor and
termoelectical cooler to form a control loop with external components,
just as for any other DWDM DFB laser. Tune the setpoint of this to lock
the laser to the rubidium. The laser becomes warm, so you stabilize it
by how much you cool it.

Further, it has a photodiode to set a loop to stabilize the current and
thus the intensity of the laser, which often is of interest to stabilize
for clock transitions.

Add modulation to the laser for sidebands if that is relevant.

One DFB datasheet I found had typical 0.06 nm / K in temperature
sensitivity and typ 0.003 nm / mA in current sensitivity. Thus, it could
be wise to "leak" the current-steering to the temperature to compensate
for current effect in feed forward rather than indirect lock.

Look at the available DFB lasermodules, I think it should become fairly
clear quite quickly as you look at datasheets etc. Exactly which laser
to use depends on power and bandwidth that fit a particular use, so it
boils down to what you end up needing it to do.

Cheers,
Magnus

On 2023-03-31 00:16, Gerhard Hoffmann via time-nuts wrote:

Linear technology made a thermoelectric full H bridge temperature controller. At the time, I’d like to say it came as a lot of two components. The second was an op-amp that may have been selected or trimmed unless there was a good reason to include it with samples (maybe less commonly available).

It was supposed to be able to achieve 10 millikelvin stability easily, and with more care in design, 1 millikelvin stability was supposed to be not too difficult to achieve.

It was a moderately expensive part…about $20 for the two components. A handful of passives and a a pair of N-channel and a pair of P-channel MOSFETs were required.

If memory serves correctly it was also switched mode rather than linear.

Get Outlook for iOShttps://aka.ms/o0ukef

From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Thursday, March 30, 2023 6:01:55 PM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: Temperature accuracy / repeatability / drift of double ovens

Hi

Simple answers (and likely not much help):

Thermal gain on a single oven is likely in the 300 to 600 range.

Double oven boosts that by 10 to 30X

Thermal gain in this case: take the ambient change divide it by the thermal gain
and you get the oven temperature change.

Long term stability:

low enough that it does not impact aging. ( = that’s how you test it). Since that gets back
to the specific thermistor being used, you are into the ‘likely not much help” range.

Best guess info: The crystal + circuit is < 1x10^-9 / C in the vicinity of the turn. The operating
point is offset from turn to minimize the combination of crystal + circuit. Just what the net
is ….

Still, if you can “see” aging at the parts in the (low?) 10^-11 range, it sort of kind of gets
you to a number. Maybe 0.01C / day.

Since you are canceling the circuit with the crystal, if things got to far off, a year later the
temperature performance would not be any good. That likely gets you to something
in the < 1C per year range.

Bob

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Hi

There are a lot of ways to rate this sort of thing. One is to look at the level of control
at the temperature sensor. It might be a thermistor, it could easily be something else.
For a long time OCXO designers tossed around this as their “control level”.

You would look at the variation on the thermistor bridge over some period. Convert
the volts to resistance and then to C, F, or K. Folks would get numbers like “12 micro
kelvin” as a result.

A fairly simple step back, scratch head, and think about it sort of analysis ultimately
showed this to be a bit useless or any sort of real performance evaluation.

What matters is the level of temperature control over some volume ( the inside of
an OCXO or ….). Real world devices are not completely located at a single point.
It’s a bit amazing just how much things change over a CM or so of distance in an
enclosure. Toss in variable heat sources and it really gets wild.

One route down this rabbit hole:

http://www.karlquist.com/oven.pdf

One also might note that the author is floating around here on the list.

Bob

Hi,

There is a few things which differs. The oven for crystals is quite
different from the cooling of DFB lasers. You regulate your built in
Peltier element. Also, the temperature gradient over the crystal blank
isn't the same as the temperature of the DFB laser diode.

So, there is a bit difference in these rabbit holes.

Cheers,
Magnus

On 2023-03-31 21:03, Bob Camp via time-nuts wrote:

Hi

Since we started the thread with a question about double ovens …. I’m guessing that the
structure being considered is some sort of oven in a oven sort of thing. In that case, you
are right into a very similar rabbit hole as the OCXO.

Bob

I  believe that IC went out of production decades ago.

Rick

On 3/31/2023 11:13 AM, Ed Marciniak via time-nuts wrote:

On 3/31/23 4:04 PM, Richard (Rick) Karlquist via time-nuts wrote:

https://www.analog.com/en/products/ltc1923.html#product-overview

High Efficiency Thermoelectric Cooler Controller

Example circuit is 0.01degree.

Eval boards available too DC388C and DC491A

Looks like a $40 part, with a $150 eval board.