OSA's Digital Library

Optics Express

Optics Express

  • Editor: J. H. Eberly
  • Vol. 5, Iss. 5 — Aug. 30, 1999
  • pp: 114–119
« Show journal navigation

Self-injection-locking of a CW-OPO by intracavity frequency-doubling the idler wave

D.-H. Lee, M. E. Klein, J.-P. Meyn, P. Groß, R. Wallenstein, and K.-J. Boller  »View Author Affiliations


Optics Express, Vol. 5, Issue 5, pp. 114-119 (1999)
http://dx.doi.org/10.1364/OE.5.000114


View Full Text Article

Acrobat PDF (100 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We report on the observation of self-injection-locking of the signal wave of an optical parametric oscillator (OPO) with the intracavity frequency doubled idler wave. The two-mirror OPO is based on a periodically poled LiNbO3 (PPLN) crystal and pumped with a grating stabilized, continuous-wave (CW) single-frequency diode master-oscillator power-amplifier (MOPA) system. Simultaneous quasi-phase-matching (QPM) of OPO and second harmonic generation (SHG) is provided in the same crystal which carries two different domain gratings. The beat of the signal wave and the frequency-doubled idler wave is suppressed within a 500-kHz wide frequency range centered around zero as expected for self-injection- locking. The measurements prove the feasibility of optically phase-stabilized by-three-division of an optical frequency with CW-OPOs using cascaded nonlinearities.

© Optical Society of America

Phase coherent division of optical frequencies by two and three is of high interest for precision metrology spanning wide optical ranges [1

1. N. C. Wong, “Optical frequency counting from the UV to the near IR,” Opt. Lett. 17, 1155 (1992). [CrossRef] [PubMed]

]. Promising candidates for phase coherent division with high efficiency are continuous-wave (CW) optical parametric oscillators (OPOs). Division by two or by three of the pump laser frequency is, e.g., achieved with the idler frequency at one half or one third of the pump frequency. An exact ratio of 1:2 as required for phase coherent by-two-division can be maintained by electronically phase-locking the signal-idler beat note to zero (or the frequency of a stable radio-frequency oscillator) via a piezo or electro-optic servo control of the OPO cavity length [2

2. D. Lee and N. C. Wong, “Tunable optical frequency division using a phase-locked OPO,” Opt. Lett. 17, 13 (1992). [CrossRef] [PubMed]

]. By-three-division requires that one frequency-doubles the idler wave before a radio-frequency (RF) beat with the signal wave can be observed and used for a servo control [3

3. T. Ikegami, S. Slyusarev, and Shin-ichi Ohshima, “Realization of a 3:1 optical frequency divider using a CW optical parametric oscillator,” in Conference on Lasers and Electro-Optics, OSA Technical Digest (Optical Society of America, Washington DC, 1999), pp. 10–11.

]. Although electronic phase-locking is a well established technique [4

4. H. R. Telle, D. Meschede, and T. W. Hänsch, “Realization of a new concept for visible frequency division: phase locking of harmonic and sum frequencies,” Opt. Lett. 15, 532 (1990) [CrossRef] [PubMed]

], there are also disadvantages. These are the shot noise and electronic noise associated with any beat measurement [5

5. I. Andonovic and D. Uttamchandani, Principles of modern optical systems (Artech House, Norwood, 1989), Chap. 5.

], and the approximately 1-GHz bandwidth limit of photodetectors, electronic circuits, and amplifiers required for electronic phase-locking.

To avoid such disadvantages and reduce the residual phase noise, frequency division is of interest which solely relies on optical methods to stabilize the phase of the OPO output waves with respect to each other. Such optically phase-locked by-two-division has, in fact, been observed with a type-I CW-OPO at degeneracy [6

6. C. D. Nabors, S. T. Yang, T. Day, and R. L. Byer, “Coherence properties of a doubly-resonant monolithic optical parametric oscillator,” J. Opt. Soc. Am. B 7, 815 (1990). [CrossRef]

], where optical injection-locking of the signal by the idler wave (and vice versa) stabilized the phase difference of these waves, which is similar to injection-locking of lasers [7

7. A. E. Siegman, Lasers (University Science Books, Mill Valley, 1986), Chap. 29.

]. This also stabilized the signal and idler phase with respect to that of the pump laser, which is equivalent to parametric oscillation in one of their two phase eigenstates. Recently, also a type-II OPO (with the signal and idler polarization perpendicular to each other) was used for frequency by-two-division, where an intracavity half-wave-plate was used to gradually vary the signal-idler injection efficiency and thus the optical locking range [8

8. E. J. Mason and N. C. Wong, “Observation of two distinct phase states in a self-phase-locked type II phase-matched OPO,” Opt. Lett. 23, 1733 (1998). [CrossRef]

]. A phase coherent frequency by-three-division using solely optical techniques has not been reported so far. Such division should be possible using a CW-OPO whose idler frequency is set to about one third of the pump frequency. The idler frequency is then simultaneously frequency-doubled inside the OPO cavity in order to injection-lock the signal frequency for phase coherent oscillation. In this contribution we report, for the first time to our knowledge, on the observation of such self-injection-locking of a CW-OPO.

Fig. 1. Experimental setup for self-injection locking of a CW-OPO with its idler frequency set to a third of the pump frequency (FR: Faraday rotator, EOM: electro-optical modulator, PD: photodiode, PZT: piezo transducer, FPI: confocal scanning Fabry-Perot interferometer).

The OPO consists of two mirrors with 30-mm radius of curvature each, in a distance of 77 mm, with the PPLN crystal placed at the beam waist. The free spectral range (FSR) of the OPO resonator is 1.2 GHz. The pump input mirror, M1, is coated for a power transmission of 3 % at the pump wavelength and for high reflectivity at the signal and idler wavelengths. The signal output mirror, M2, is coated for high reflectivity at the pump and idler wavelengths and for 90 % transmission at the signal wavelength. The pump beam is mode-matched to the OPO cavity with a spherical lens of 100-mm focal length. The beam radius in the crystal is 35 µm. The observed maximum pump input coupling is 80 % at a pump power below the OPO threshold and 50% at the maximum pump power of 350 mW. To provide a CW output from the OPO, the cavity length is stabilized to the pump wavelength using the Pound-Drever-Hall (PDH) technique [10

10. R. W. P. Drever, J. L. Hall, F. V. Kowalski, J. Hough, G. M Ford, A. J. Munley, and H. Ward, “Laser phase and frequency stabilization using an optical resonator,” Appl. Phys. B 31, 97 (1983). [CrossRef]

]. The required frequency modulation (FM) side bands (at 32.5 MHz) are generated with an electro-optic modulator placed between the diode oscillator and the diode amplifier. The PDH error signal is obtained by detecting the AC component in the reflected pump light from the OPO cavity with a Si-diode (bandwidth of 100 MHz) and demodulating this signal with a balanced mixer. The mixer output is filtered (low-pass <1 MHz) and amplified to control the resonator length via a piezo transducer at M2. The servo bandwidth of the PDH loop is about 500 Hz as limited by the piezo transducer. Fig. 2 shows the power output characteristic of the OPO. The pump power at threshold is 150 mW and the maximum signal wave output power (behind M2) is 46 mW at a pump power of 350 mW. The maximum output power of the frequency-doubled idler is about 1 mW. The maximum idler wave output is less than 1 mW due to the high reflectivity of the OPO mirrors at the idler wavelength. The signal wave is single-frequency as monitored with a confocal scanning Fabry-Perot interferometer (FPI) of 1-MHz resolution.

Fig. 2. Signal wave output power of the OPO with a crystal temperature of 167 °C as a function of pump power. The pump, signal, and idler wavelength are 812 nm, 1218 nm, and 2436 nm, respectively.

During temperature tuning of the signal wavelength close to the frequency-doubled idler wavelength we observe the OPO spectrum with a double grating optical spectrum analyzer (OSA, Ando AQ-6315A) with a resolution of 100 GHz and, in addition, with a confocal scanning FPI with a FSR of 7.5 GHz and a resolution of 250 MHz. Fig. 3 shows emission spectra of the OPO near 1218 nm recorded with the OSA for three different values of the crystal temperature. At about 167 °C the two nonlinear processes (OPO and idler-SHG) are simultaneously phase-matched. At a temperature of 167.12 °C the signal wavelength coincides with the wavelength of the frequency-doubled idler radiation within the 100-GHz resolution interval of the OSA and also within the 250-MHz resolution interval of the FPI.

Fig. 3. Output of the OPO (on a logarithmic scale) vs. wavelength for different crystal temperatures. The emission peaks show the signal wavelength and one-half of the idler wavelength.

Continuous tuning of the OPO frequencies via the pump frequency is then used to further reduce the beat frequency, until the beat frequency is close to zero. The observation of near zero beat frequencies is now performed at the upper FM sideband such that indicated frequencies are higher by 32.5 MHz compared to the actual beat frequency. This technique is commonly used to move out of the typically 10 kHz to 1 MHz wide noise band of analogue RF analyzers around zero frequency. The observation interval of the beat signal is about 5 MHz centered at 32.5 MHz. As in Fig. 4, the beat frequency is seen to randomly fluctuate within this interval. A measurement with the RF analyzer in the max-hold mode (integration time of over 2 minutes) is shown in Fig. 5 as the black trace. The trace shows a flat distribution of the beat signal over most of the 5-MHz interval except a small interval around 32.5 MHz. The sharp peak at 32.5 MHz is caused by electronic pick-up from the FM driver as can be seen also from the red trace obtained with the photodiode blocked. In addition, however, the black trace shows a significant dip (approximately 10 dB) centered at 32.5 MHz, extending over a width of about 500 kHz. This dip proves that beat signals within the 500-kHz frequency interval around zero do not occur with the same strength or probability, as do beat signals outside this interval. It is also observed in this interval that the beat is pulled in frequency to zero and simultaneously suppressed in amplitude. This is exactly what is expected from injection-locking of the signal wave by the frequency-doubled idler wave: at sufficiently close proximity of the two frequencies, injection-locking suppresses the free running signal and idler frequencies (as they would be observed without idler-SHG) and replaces them by oscillation at the same frequency such that the beat frequency becomes zero. Thus the 500-kHz wide range of beat suppression should correspond to the locking range of the OPO. The measured range is in good agreement with the locking range we calculate by numerically integrating the coupled amplitude equations of the OPO with cascaded SHG using known experimental parameters. A detailed analysis of the experimental and theoretical OPO locking ranges is currently under investigation.

Fig. 4. RF beat frequency of the signal and the frequency-doubled idler wave as recorded with an RF spectrum analyzer. For details, see text.
Fig. 5. Signal-idler beat recorded around the upper sideband in the max-hold mode (integration time of over 2 minutes, black trace). For reference, the red trace is recorded with the photodiode blocked.

In conclusion the experimental data show, to our knowledge, the first evidence of self-injection-locking of a CW-OPO by using a cascaded SHG nonlinearity. This is the most important step for the experimental realization of all-optical phase coherent by-three-division. Further work should investigate in detail the degree of phase coherence, e.g., by beating the frequency-tripled idler wave with the pump wave.

Acknowledgments

The authors thank S. Marzenell for his assistance to characterize the phase-matching properties of the crystal, and the Deutsche Forschungsgemeinschaft (DFG) for support. Two of the autors, D.-H. L. and P. G., acknowledge support through the Graduiertenkolleg of the DFG.

References and links

1.

N. C. Wong, “Optical frequency counting from the UV to the near IR,” Opt. Lett. 17, 1155 (1992). [CrossRef] [PubMed]

2.

D. Lee and N. C. Wong, “Tunable optical frequency division using a phase-locked OPO,” Opt. Lett. 17, 13 (1992). [CrossRef] [PubMed]

3.

T. Ikegami, S. Slyusarev, and Shin-ichi Ohshima, “Realization of a 3:1 optical frequency divider using a CW optical parametric oscillator,” in Conference on Lasers and Electro-Optics, OSA Technical Digest (Optical Society of America, Washington DC, 1999), pp. 10–11.

4.

H. R. Telle, D. Meschede, and T. W. Hänsch, “Realization of a new concept for visible frequency division: phase locking of harmonic and sum frequencies,” Opt. Lett. 15, 532 (1990) [CrossRef] [PubMed]

5.

I. Andonovic and D. Uttamchandani, Principles of modern optical systems (Artech House, Norwood, 1989), Chap. 5.

6.

C. D. Nabors, S. T. Yang, T. Day, and R. L. Byer, “Coherence properties of a doubly-resonant monolithic optical parametric oscillator,” J. Opt. Soc. Am. B 7, 815 (1990). [CrossRef]

7.

A. E. Siegman, Lasers (University Science Books, Mill Valley, 1986), Chap. 29.

8.

E. J. Mason and N. C. Wong, “Observation of two distinct phase states in a self-phase-locked type II phase-matched OPO,” Opt. Lett. 23, 1733 (1998). [CrossRef]

9.

M. Scheidt, B. Beier, K.-J. Boller, and R. Wallenstein, “Frequency-stable operation of a diode-pumped continuous-wave RbTiOAsO4 optical parametric oscillator,” Opt. Lett. 22, 1287 (1997). [CrossRef]

10.

R. W. P. Drever, J. L. Hall, F. V. Kowalski, J. Hough, G. M Ford, A. J. Munley, and H. Ward, “Laser phase and frequency stabilization using an optical resonator,” Appl. Phys. B 31, 97 (1983). [CrossRef]

OCIS Codes
(190.2620) Nonlinear optics : Harmonic generation and mixing
(230.4320) Optical devices : Nonlinear optical devices

ToC Category:
Research Papers

History
Original Manuscript: August 4, 1999
Published: August 30, 1999

Citation
Dong-Hoon Lee, Marvin Klein, Jan-Peter Meyn, P. Grob, Richard Wallenstein, and Klaus Boller, "Self-injection-locking of a CW-OPO by intracavity frequency-doubling the idler wave," Opt. Express 5, 114-119 (1999)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-5-5-114


Sort:  Journal  |  Reset  

References

  1. N. C. Wong, "Optical frequency counting from the UV to the near IR," Opt. Lett. 17, 1155 (1992). [CrossRef] [PubMed]
  2. D. Lee, N. C. Wong, "Tunable optical frequency division using a phase-locked OPO," Opt. Lett. 17, 13 (1992). [CrossRef] [PubMed]
  3. T. Ikegami, S. Slyusarev, Shin-ichi Ohshima, "Realization of a 3:1 optical frequency divider using a CW optical parametric oscillator," in Conference on Lasers and Electro-Optics, OSA Technical Digest (Optical Society of America, Washington DC, 1999), pp. 10-11.
  4. H. R. Telle, D. Meschede, T. W. H�nsch, "Realization of a new concept for visible frequency division: phase locking of harmonic and sum frequencies," Opt. Lett. 15, 532 (1990) [CrossRef] [PubMed]
  5. I. Andonovic, D. Uttamchandani, Principles of modern optical systems (Artech House, Norwood, 1989), Chap. 5.
  6. C. D. Nabors, S. T. Yang, T. Day, R. L. Byer, "Coherence properties of a doubly-resonant monolithic optical parametric oscillator," J. Opt. Soc. Am. B 7, 815 (1990). [CrossRef]
  7. A. E. Siegman, Lasers (University Science Books, Mill Valley, 1986), Chap. 29.
  8. E. J. Mason, N. C. Wong, "Observation of two distinct phase states in a self-phase-locked type II phase-matched OPO," Opt. Lett. 23, 1733 (1998). [CrossRef]
  9. M. Scheidt, B. Beier, K.-J. Boller, R. Wallenstein, "Frequency-stable operation of a diode-pumped continuous-wave RbTiOAsO4 optical parametric oscillator," Opt. Lett. 22, 1287 (1997). [CrossRef]
  10. R. W. P. Drever, J. L. Hall, F. V. Kowalski, J. Hough, G. M Ford, A. J. Munley, H. Ward, "Laser phase and frequency stabilization using an optical resonator," Appl. Phys. B 31, 97 (1983). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited