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Scientific Reports

Determination of blue-light-induced infrared absorption based on mode-matching efficiency in an optical parametric oscillator

Yajun Wang, Wenhai Yang, Zhixiu Li, Yaohui Zheng

Published Feb 1, 2017• 5 citations
Publisher

Abstract

Non-classical squeezed states of light at a compatible atomic wavelength have a potential application in quantum information protocols for quantum states delaying or storaging. An optical parametric oscillator (OPO) with periodically poled potassium titanyl phosphate (PPKTP) is the most effective method for generating this squeezed state. However, it is a challege for the nonlinear interaction in PPKTP crystal at the D1 line of rubidium atomic, due to a strong blue-light-induced infrared absorption (BLIIRA). In this paper, we report an indirect measurement method for the BLIIRA through measuring the mode-matching efficiency in an optical parametric oscillator. In contrast to previous works, our method is not limited by the absolute power variation induced from the change of frequency conversion loss and the impedance matching originated from the change of absorption loss. Therefore, the measurement process is performed at the phase-matching condition. The measured results show that BLIIRA coefficient is quadratic dependence of blue light intensity below 1 kW per square centimeter in our PPKTP device, which will provide important basis for optimizing squeezed state generation at 795 nm.

DOI
10.1038/srep41405

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In this experiment we use periodically poled potassium titanyl phosphate (PPKTP) as the nonlinear crystal in an optical parametric oscillator (OPO) for the generation of squeezed light on the D1 line of rubidium which lies at 795 nm. Although OPOs have long been used as sources of squeezed light, the shorter wavelengths required for atomic interactions have always been a challenge due to a limited choice of nonlinear crystals. PPKTP is a new material that has recently been shown to be highly effective over a very wide range of optical frequencies (Akamatsu, 2006).

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Abstract. We report on the generation of more than 5 dB of vacuum squeezed light at the Rubidium D1 line (795 nm) using periodically poled KTiOPO4 (PPKTP) in an optical parametric oscillator. We demonstrate squeezing at low sideband frequencies, making this source of non-classical light compatible with bandwidth limited atom optics experiments. When PPKTP is operated as a parametric amplifier, we show a noise reduction of 4 dB stably locked within the 150 kHz-500 kHz frequency range. This matches the bandwidth of Electromagnetically Induced Transparency (EIT) in Rubidium hot vapour cells under the condition of large information delay. Squeezed light at the Rubidium D1 line 2 The control of quantum states of light is of great interest for quantum communication purposes. Many quantum information protocols rely on the possibility of coherently delaying and storing the information carried by a laser beam. This can for example be achieved using Electromagnetically Induced Transparency (EIT). Experimental and theoretical studies have shown that information can be delayed within a narrow bandwidth when light interacts with atoms in a lambda configuration [2, 3, 4, 5]. One step further is the delay of quantum information, carried by squeezed

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Squeezed light for bandwidth-limited atom optics experiments at the rubidium D1 line

Gabriel Hetet, O Glöckl, K A Pilypas +4 more

We report on the generation of more than 5 dB of vacuum squeezed light at the Rubidium D1 line (795 nm) using periodically poled KTiOPO$_{4}$ (PPKTP) in an optical parametric oscillator. We demonstrate squeezing at low sideband frequencies, making this source of non-classical light compatible with bandwidth limited atom optics experiments. When PPKTP is operated as a parametric amplifier, we show a noise reduction of 4 dB stably locked within the 150 kHz-500 kHz frequency range. This matches the bandwidth of Electromagnetically Induced Transparency (EIT) in Rubidium hot vapour cells under the condition of large information delay.

arXiv:quant-ph/0611204•Journal of Physics B Atomic Molecular and Optical Physics•Dec 20, 2006•62 citations
Non-classical squeezed states of light at a compatible atomic wavelength have a potential application in quantum information protocols for quantum states delaying or storaging. An optical parametric oscillator (OPO) with periodically poled potassium titanyl phosphate (PPKTP) is the most effective method for generating this squeezed state. However, it is a challege for the nonlinear interaction in PPKTP crystal at the D1 line of rubidium atomic, due to a strong blue-light-induced infrared absorption (BLIIRA). In this paper, we report an indirect measurement method for the BLIIRA through measuring the mode-matching efficiency in an optical parametric oscillator. In contrast to previous works, our method is not limited by the absolute power variation induced from the change of frequency conversion loss and the impedance matching originated from the change of absorption loss. Therefore, the measurement process is performed at the phase-matching condition. The measured results show that BLIIRA coefficient is quadratic dependence of blue light intensity below 1 kW per square centimeter in our PPKTP device, which will provide important basis for optimizing squeezed state generation at 795 nm.
In this experiment we use periodically poled potassium titanyl phosphate (PPKTP) as the nonlinear crystal in an optical parametric oscillator (OPO) for the generation of squeezed light on the D1 line of rubidium which lies at 795 nm. Although OPOs have long been used as sources of squeezed light, the shorter wavelengths required for atomic interactions have always been a challenge due to a limited choice of nonlinear crystals. PPKTP is a new material that has recently been shown to be highly effective over a very wide range of optical frequencies (Akamatsu, 2006).
The non-classical light resonance on the cesium D1 (894.6 nm) line has important applications in solid-state quantum information networks due to its unique advantages. The cesium D1 line has a simplified hyperfine structure and can be used to realize a light-atom interface. In our previous work, we demonstrated 2.8-dB quadrature squeezed vacuum light at cesium D1 line in an optical parametric oscillator(OPO) with a periodically poled KTP(PPKTP) crystal. However, the squeezing level is relatively low, and the tunability that has practical significance for squeezed light has not been further investigated. Theoretically, the increase of the transmittance of output mirror and the decrease of the intra-cavity loss of the OPO can improve the squeezing level. Here, we use super-polished and optimal coating cavity mirrors to improve the nonlinear process in OPO. We prepare 447.3 nm blue light from 894.6 nm fundamental light by a second harmonic generation cavity (SHG). The SHG is a two-mirror standing-wave cavity with a PPKTP crystal as the nonlinear medium. The power of generated blue laser is 32 mW when the incident infrared power is 120 mW. Using the blue light to pump an OPO, we achieve quadrature squeezed vacuum light at cesium D1 line. The OPO is a two-mirror standing-wave cavity with a PPKTP crystal. The threshold of OPO is reduced to 28 mW. The squeezing level of generated quadrature squeezed vacuum light is increased to 3.3 dB when the pump power is 15 mW. Taking into account the overall detection efficiency, the actual squeezing reaches 5.5 dB. We inject a weak signal beam into the OPO cavity to act as an optical parametric amplifier (OPA), and test the tunability of squeezzed light. The blue light and the squeezed light are tuned by using a low-frequency triangular wave signal to scan the Ti: sapphire laser. Gradually increasing the amplitude of the scanning triangle wave signal, the generated bright squeezed light can be continuously tuned over a range around 80 MHz without losing the stability of the whole system. The generated squeezed light offers the possibility for the efficient coupling between the non-classical source and solid medium in the process of quantum interface.
The field of squeezed state is an important quantum resource in the study of quantum optics. In the application of quantum information, the spectrum bandwidth of the squeezed light field is an important index to limit the information transmission capacity. Currently, the optical parametric oscillator (OPO) is one of the most efficient ways to generate high squeezed non-classical optical fields. In this paper, the degenerate singly-resonant and doubly-resonant OPO structures are introduced. Both OPOs are composed of concave mirrors and periodically poled potassium titanyl phosphate crystals (PPKTP). The length of PPKTP crystal is 10 mm. The curvature radius of the curved surface is 12 mm, and it has high reflectivity at 1550 nm and 775 nm. The plane surface is coated with anti-reflection coating. The air gap length is 21 mm. The concave mirror is an output coupling mirror, and its radius of curvature is 25 mm. In the singly-resonant OPO, only the signal light resonates in the cavity, and the pump light passes through the nonlinear crystal twice and then outputs out of the cavity. The reflectivity of OPO output coupling mirror to the wavelength of 1550 nm is 88%. The linewidth of the corresponding fundamental frequency wave is 77.4 MHz. For doubly-resonant OPO, both the signal light and the pump light resonate simultaneously in the cavity. The reflectivity of OPO output coupling mirror to 1550 nm and 775 nm is 85% and 97.5%, respectively. The linewidth of the corresponding fundamental frequency wave and harmonic is 97.1 MHz and 15.6 MHz, respectively. Then the threshold of OPO is calculated. The threshold pump power of OPO increases with signal light transmittance increasing, but the threshold value of doubly-resonant OPO is obviously smaller than that of singly-resonant OPO. After that, the variation of the squeezing bandwidth of the squeezed light field generated by OPO with the transmittance of the signal is analyzed. Finally, we complete the design of quantum squeezer with low threshold (18 mW), broadband (84.2 MHz) and high stability (the standard deviation of locking baseline is 0.32 MHz) experimentally. The results show that compared with the singly-resonant optical parametric oscillator, the doubly-resonant cavity has the characteristics of low threshold and high stability, which is more suitable for the preparation and practical application of broadband squeezed light field.
Abstract. We report on the generation of more than 5 dB of vacuum squeezed light at the Rubidium D1 line (795 nm) using periodically poled KTiOPO4 (PPKTP) in an optical parametric oscillator. We demonstrate squeezing at low sideband frequencies, making this source of non-classical light compatible with bandwidth limited atom optics experiments. When PPKTP is operated as a parametric amplifier, we show a noise reduction of 4 dB stably locked within the 150 kHz-500 kHz frequency range. This matches the bandwidth of Electromagnetically Induced Transparency (EIT) in Rubidium hot vapour cells under the condition of large information delay. Squeezed light at the Rubidium D1 line 2 The control of quantum states of light is of great interest for quantum communication purposes. Many quantum information protocols rely on the possibility of coherently delaying and storing the information carried by a laser beam. This can for example be achieved using Electromagnetically Induced Transparency (EIT). Experimental and theoretical studies have shown that information can be delayed within a narrow bandwidth when light interacts with atoms in a lambda configuration [2, 3, 4, 5]. One step further is the delay of quantum information, carried by squeezed
We report on the generation of more than 5 dB of vacuum squeezed light at the Rubidium D1 line (795 nm) using periodically poled KTiOPO4_{4}4​ (PPKTP) in an optical parametric oscillator. We demonstrate squeezing at low sideband frequencies, making this source of non-classical light compatible with bandwidth limited atom optics experiments. When PPKTP is operated as a parametric amplifier, we show a noise reduction of 4 dB stably locked within the 150 kHz-500 kHz frequency range. This matches the bandwidth of Electromagnetically Induced Transparency (EIT) in Rubidium hot vapour cells under the condition of large information delay.