Questions and Answers Wavemeter.pdf

QUESTIONS AND ANSWERS

Salient Characteristics

1) self-referenced optical frequency comb centered at 16501560 nm, based on Er doped fiber laser

2) expandable to four other laser frequency outputs (wavelength extensions) throughout visible and NIR

3) comb spacing 100 or 200 MHz

4) frequency stability at least (better than) two parts in 10^16

5) capable of lock to external 10 MHz reference input

6) capable of lock to heterodyne beatnote of an external laser

7) phase lock servo offset up to 9 GHz

8) 19 inch rack mounted unit

9) water cooling not needed

10) various fiber optics to send laser beams in and out

11) computer control interface

Question: Regarding #1): is 1650 nm correct? Typically, Er doped fiber lasers typically operate at 1560 nm. Just want to make sure there is no typo.

Response: This is a typo. The wavelength stated should be 1560 nm, which is the standard Er fiber laser wavelength.

Regarding #2): what other four frequencies are needed; if the wavelengths are not known yet, will it be sufficient to configure the system with four additional outputs that can later be upgraded with additional amplifiers for future wavelength extensions?

Response: The other four wavelengths are not known yet, but the wavelengths will most likely be 630 nm, 780 nm, 993 nm, and 1008 nm. It is sufficient to configure the system with four additional outputs that can later be upgraded with additional amplifiers for future wavelength extensions.

Regarding #4): is relative frequency stability between an optical reference and the comb output meant by this?

Response: Essentially, yes. We mean the achievable accuracy or stability of the comb mode spacing, in 100s. It should be less than on the order of a few x 1e-16.

Regarding #6): can the wavelength of the external laser be specified?

Response: In a word, no; but to be more expansive, the wavelength of the external laser would be in the range from 400 to 1100 nm, and it would be one of the comb output wavelengths which are not yet determined for sure, but will probably be 630, 780, 993, 1008 nm.

Regarding #7): what reference would be used in this implementation?

Response: A Rb/GPS disciplined frequency reference would be used to lock the comb.

However, the Government would like to have an external stabilized single frequency laser locked to the nearest one of the comb teeth, at an adjustable offset of up to 9 GHz. The external laser would have its own locking circuitry and fast photodiode.

Would it be an optical or an RF reference?

Response: RF or optical, see above.

What would be the frequency of the RF reference?

Response: 10 MHz

Can a frequency range be specified for RF reference?

Response: Just right at 10 MHz

Would it be correct to assume that the repetition rate of the comb would needed to be phase locked to the RF reference?

Response: Yes.

Regarding #10): can the frequency of the laser beams be specified? For example would an external laser, i.e. an optical reference at 1542 nm, be used to lock the comb to? Or would other references also be implemented?

Response: It would be one of the output wavelengths which are not yet determined, but will probably be 630, 780, 993, 1008 nm.

What are the specific target wavelengths for the desired four extensions throughout the visible and NIR?

Response: It would be one of the output wavelengths which are not yet determined for sure, but will probably be 630, 780, 993, 1008 nm.

Does the optical comb need to provide 10^-16 frequency stability at all times, or does it need to meet this requirement with the proper optical reference?

Response: We mean the achievable accuracy or stability of the comb mode spacing, in 100 s. It should be less than on the order of a few x 1e-16. It should meet this requirement being locked to a GPS frequency reference, relative to that GPS frequency reference.

Does the vendor need to provide the fast photodiode to demonstrate a 9 GHz offset between two beat notes?

Response: No.

Can you elaborate on the requirements for “phase lock servo offset up to 9 GHz”?

Response: The Government would like to have an external stabilized single frequency laser locked to the nearest one of the comb teeth, at an adjustable offset of up to 9 GHz. The external laser would have its own locking circuitry and fast photodiode.

What are the requirements for the optical comb when it is RF referenced to GPS?

Response: The optical comb should be phase locked to the 10 MHz reference frequency standard output from the GPS disciplined frequency standard, with the same fractional absolute error as the GPS standard.

Additional Information:

In addition to all the above, the Government can clarify that item 3 the 100 or 200 MHz comb spacing means one or the other, not both, and not switchable between. The Government realizes that it cannot be switched from one to the other. It should be 100 MHz only, or it could be 200 MHz only.

The Government can clarify that item 6 means that the external laser can be locked to the nearest comb tooth by a heterodyne beatnote of the external laser to the comb tooth. The external laser will have its own locking circuitry and fast photodiode.