Narrow linewidth squeezed state light generator

Abstract

To provide a system and a method for a narrow linewidth squeezed state light generator.SOLUTION: A system includes a pump optical signal source which emits a pump optical signal at a first frequency. Further, the system includes a resonator, and the pump optical signal is coupled so as to propagate in a first direction within the resonator. In addition, the first frequency is a first resonance frequency of the resonator, and stimulated Brillouin scattering (SBS) within the resonator generates an SBS optical signal having a second frequency at a second resonance frequency of the resonator to propagate in a second direction opposite to the first direction within the resonator. Also, the SBS optical signal generates a squeezed optical signal according to spontaneous emission four-wave mixing. Moreover, the system includes an output optical transmission medium for outputting the squeezed optical signal generated within the resonator.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] Sensors are essential to technology, serving as an interface between the physical world and electronic systems. Some sensors use light to gather information about the relationship between electronic systems and the physical world. Specifically, light can propagate through optical resonators to probe the environment, analyze materials, and perform other operations. Because high-power light can create problems such as nonlinearity, material damage, and measurement contamination, it is often desirable to keep the light output as low as possible during sensor operation. However, at lower power levels, shot noise, the statistical fluctuations in light intensity, affect the accuracy of sensor measurements and place lower limits on the input light output. By using photons with superior spectral and quantum properties to classically generated light, such as reduced shot noise, sensors can achieve the same sensitivity level while using fewer photons. Summary of the Invention

[0002] A system and method for a narrow-linewidth squeezed-state optical generator. In a specific embodiment, the system includes a pump optical signal source configured to emit a pump optical signal at a first frequency. The system further includes a resonator, the pump optical signal coupled to propagate in a first direction within the resonator. Additionally, the first frequency is a first resonant frequency of the resonator, and stimulated Brillouin scattering (SBS) within the resonator generates an SBS optical signal having a second frequency at a second resonant frequency of the resonator, propagating in a second direction within the resonator opposite the first direction. The SBS optical signal also generates a squeezed optical signal by spontaneous emission four-wave mixing. The system further includes an output optical transmission medium configured to output the squeezed optical signal generated in the resonator. [Brief explanation of the drawings]

[0003] The figures illustrate only some embodiments that are relevant to the claims that follow this specification. Therefore, the described and illustrated embodiments should not be considered limiting in scope. The accompanying drawings and specification describe exemplary embodiments and their features with additional specificity and detail. [Figure 1] FIG. 1 is a block diagram of a system for generating narrow linewidth squeezed-state light, according to one aspect of the present disclosure. [Figure 2] 1 is a graph of optical frequency in a system for generating narrow linewidth squeezed-state light according to one aspect of the present disclosure. [Figure 3] FIG. 1 is a block diagram of a system for generating narrow linewidth squeezed-state light using a grating, according to one aspect of the present disclosure. [Figure 4] FIG. 1 is a block diagram of a system for generating narrow linewidth squeezed-state light, according to one aspect of the present disclosure. [Figure 5] FIG. 1 is a flowchart diagram of a method for providing narrow linewidth squeezed-state light according to one aspect of the present disclosure.

[0004] According to common practice, the drawings do not show the various features described to scale, but rather illustrate features to emphasize their relevance to exemplary embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0005] The following detailed description refers to the accompanying drawings, which form a part hereof. The drawings show, by way of example, specific exemplary embodiments. However, it is to be understood that other embodiments may be used and logical, mechanical, and electrical changes may be made.

[0006] Described herein are systems and methods for generating narrow-linewidth squeezed-state light. Specifically, a pump optical signal propagates within a resonator, and the frequency of the pump optical signal is the resonant frequency of the resonator. As the pump signal propagates around the resonator, stimulated Brillouin scattering (SBS) generates a counter-propagating SBS optical signal. The counter-propagating SBS optical signal generates two squeezed optical signals through spontaneous emission four-wave mixing and squeezed quadrature noise, and either the phase uncertainty or the amplitude uncertainty of the squeezed photon state can be lower than either the phase uncertainty or the amplitude uncertainty of the pump photon. Furthermore, the system can employ additional nested resonators coupled to or formed within the resonator, which create resonance splitting to prevent the SBS optical signal from generating multiple additional higher-order SBS optical signals that can interfere with the generated squeezed optical signal. Thus, the systems and methods described herein generate optical signals with increased frequency stability and squeezed quadrature noise.

[0007] As mentioned above, the effects of shot noise become increasingly problematic as the power of an optical signal decreases. This shot noise arises due to the discrete nature of photons in a given optical signal. The quantized, stochastic nature of photons causes random fluctuations in the number of photons detected or measured over a period of time. Shot noise can adversely affect the operation of optical sensors. Specifically, low-power optical signals are often desirable for sensor operation because high-power optical signals can produce undesirable nonlinear effects that can bias or interfere with measurements. However, shot noise imposes lower signal-to-noise ratio (SNR) limitations on low-power levels of the optical signal.

[0008] Sensors can overcome the lower limit imposed by shot noise by using squeezed optical signals generated by the systems described herein. Squeezed optical signals are a state of light in quantum optics in which quantum noise in one property can be reduced below the standard quantum limit at the expense of increased noise in the complementary property. For example, reducing the phase uncertainty increases the amplitude uncertainty. Nonlinear optical effects are often used to generate squeezed light. For example, squeezed light can be created using parametric down-conversion, four-wave mixing, and other nonlinear optical effects.

[0009] When four-wave mixing is used to generate squeezed light, a nonlinear optical process occurs in which lasers with two or three different frequencies interact in a medium with nonlinear properties (such as an optical fiber) to generate a new optical field. In four-wave mixing, the interaction can involve mixing input photons to generate new photons with different frequencies, one photon referred to as the signal optical signal and the other photon referred to as the idler optical signal. In some implementations, the four-wave mixing can be spontaneous emission four-wave mixing. Quantum fluctuations in the nonlinear medium cause the optical signals to interact, generating the signal optical signal and the idler optical signal.

[0010] In the embodiments described herein, a signal optical signal and an idler optical signal are generated within a resonator, and squeezed light is provided as an output from the resonator for use in other systems. A coupler couples a pump optical signal into the resonator to generate the squeezed light. The pump optical signal is an optical signal with a frequency equal to one of the resonant frequencies of the resonator. As the pump optical signal propagates around the resonator, SBS causes an SBS optical signal to propagate in the opposite direction of the pump optical signal. The SBS optical signal will be at a resonant frequency of the resonator that is different from the resonant frequency of the pump optical signal.

[0011] In a further embodiment, the resonator can be coupled to a nested resonator to suppress cascaded SBS lasers. Specifically, light propagating within the resonator can be coupled into the nested resonator to perform resonance splitting. Resonance splitting shifts the resonator frequency of higher-order SBS lasers from the SBS gain profile. Thus, resonance splitting can suppress cascaded SBS lasers, preventing any cascaded SBS lasers from clamping the first-order SBS output and interfering with the generated signal and idler optical signal.

[0012] Once squeezed optical signal and idler optical signals are generated within the resonator, a coupler combines the signal and idler optical signals from the resonator. Optical waveguides and other optical elements coupled to the resonator carry the signal and idler optical signals to other systems capable of optical sensing. When the signal and idler optical signals are squeezed, other systems can use the squeezed signals to perform sensing at lower power levels without being adversely affected by shot noise.

[0013] FIG. 1 is a diagram of a system 100 for generating narrow-linewidth squeezed light. As shown, the system 100 includes a pump optical signal source 101 that generates and emits a pump optical signal. The pump optical signal source 101 includes a device capable of generating light at a particular frequency. For example, the pump optical signal source 101 may include a laser diode, such as, but not limited to, a distributed feedback laser diode or other laser light generating device. As shown, the pump optical signal source 101 is coupled to an optical transmission medium 107 to provide the pump optical signal generated by the pump optical signal source 101 to other optical elements in the system 100. The optical transmission medium 107 may include an optical waveguide, an optical fiber, a free-space optical element, etc.

[0014] The system 100 may also include an optical coupler 111 and a resonator 103. The optical transmission medium 107 carries a pump optical signal to the optical coupler 111, which couples a portion of the pump optical signal to the resonator 103, where the coupled portion of the pump optical signal propagates around the resonator 103. As described herein, a resonator, such as the resonator 103, may refer to a closed optical path in which an optical signal having a particular frequency resonates. For example, the resonator 103 may be an optical fiber resonator having one or more turns of an optical fiber coil. The resonant frequency of an optical fiber coil is based on the constructive interference condition; therefore, optical waves that traverse the coil different times will constructively interfere at any point within the coil. Due to this constructive interference, an optical wave having a wavelength λ is said to be “on-resonance” when the round-trip resonator path length is equal to an integer multiple of the wavelength.

[0015] In certain embodiments, when a pump optical signal propagates within the resonator 103, it generates a counter-propagating stimulated Brillouin scattering (SBS) optical signal that propagates in the opposite direction to the pump optical signal. Stimulated Brillouin scattering is an effect that occurs when an incident optical wave propagating through a medium, such as an optical fiber, in the resonator 103 reaches a threshold power that induces acoustic waves within the fiber. This acoustic wave excitation changes the refractive index of the glass fiber, causing scattering of the incident light. The scattered light propagates in the opposite direction to the pump optical signal and is sometimes referred to as an SBS optical signal.

[0016] In an additional embodiment, the system 100 may include a nested resonator 105. As shown, an optical coupler 113 may couple the nested resonator 105 to the resonator 103. Specifically, the optical coupler 113 couples a portion of the light propagating within the resonator 103 to the nested resonator 105. Brillouin lasers offer some of the narrowest and most stable spectral characteristics, but their use at a single optical frequency is often required. Furthermore, Brillouin lasers typically exhibit high-order cascade lasing above a certain power threshold. To suppress high-order lasing in a Brillouin laser, the nested relationship of the nested resonator 105 to the resonator 103 can suppress high-order lasing without affecting the first-order SBS lasing. Specifically, a pump optical signal propagates within the larger resonator 103 at the resonant frequency of the resonator 103. Light in the larger resonator 103 couples to the smaller nested resonator 105, and when the light resonates in the nested resonator 105, the resonance of the larger resonator 103 is split into two resonances. The original resonance of the stand-alone resonator 103 is suppressed and split into two separate resonances. The separation depends on the coupling efficiency and free spectral range of the cavity 103. This suppression can be used to suppress higher-order Brillouin lasing in the larger resonator 103. For example, resonances corresponding to first-order Brillouin lasing can be designed to be unsuppressed, while resonances corresponding to second-order and higher-order Brillouin lasing can be designed to be suppressed. Thus, the optical signal propagating in the resonator 103 includes the pump optical signal and the counter-propagating SBS optical signal, but not the higher-order Brillouin SBS optical signal.

[0017] In a further embodiment, the SBS optical signal induces spontaneous four-wave mixing (SFWM) to produce two-state squeezing in the signal and idler optical signals. Specifically, SFWM is a nonlinear optical process in which the SBS optical signal acts as a degenerate pump light in the resonator 103, which is a nonlinear medium. SFWM results in the annihilation of two SBS photons and the simultaneous creation of two new photons, a signal photon and an idler photon. This phenomenon relies on the conservation of both energy and momentum (phase matching) in the medium: the combined energy of the signal and idler photons is equal to the energy of the two colliding photons, and their combined momentum is also conserved.

[0018] In certain embodiments, the signal and idler photons propagating around the resonator 103 are coupled out of the resonator 103 by an optical coupler 111. The optical coupler 111 can couple the signal and idler photons from the resonator 103 into an optical transmission medium 109. The optical transmission medium 109 transports the signal and idler photons out of the system 100 for use by other systems. Because the signal and idler photons are squeezed light, the signal and idler photons allow for sensing at lower power levels with less shot noise.

[0019] FIG. 2 is a graph illustrating different optical signal frequencies that can propagate within the resonator 103. As illustrated, the horizontal axis represents the optical signal frequency. Within the resonator 103, a pump optical signal 221 propagates at the resonant frequency of the resonator 103. As the pump optical signal 221 propagates around the resonator 103, the pump optical signal 221 can induce a counter-propagating SBS optical signal 223. As illustrated, the counter-propagating SBS optical signal 223 is generated at a frequency corresponding to an SBS gain curve 229. As used herein, the SBS gain curve 229 corresponds to the frequency range in which the SBS optical signal is generated. Thus, the resonator 103 can be designed, and the frequency of the pump laser can be selected, such that the pump optical signal 221 and the gain curve 229 for generating the first-order SBS optical signal 223 match the resonance of the resonator 103.

[0020] In a further embodiment, to prevent the counter-propagating SBS optical signal 223 from producing higher-order cascaded SBS optical signals, a portion of the optical signal propagating within the resonator 103 may be coupled to the nested resonator 105. The nested resonator 105 then produces a resonance splitting 225 around the gain curve 231, which causes the higher-order SBS gain curve 231 to be mismatched with the resonance frequency of the resonator 103. Because the resonator frequency and the higher-order SBS gain curve are mismatched with each other, higher-order SBS optical signals are not generated within the resonator 103.

[0021] In certain embodiments, due to the effect of SBS on pump optical signal 221, pump optical signal 221 and counter-propagating SBS optical signal 223 counter-propagate within resonator 103. SBS optical signal 223 interacts within resonator 103 by spontaneous emission four-wave mixing to generate signal optical signal 233 and idler optical signal 235. As shown, pump optical signal 221 has a pump frequency f p and the SBS optical signal 223 is at an SBS frequency f SBS After the interaction, the signal optical signal 233 has a near-resonant frequency f SBS -FSR, and the idler optical signal 235 has a frequency f higher than the SBS frequency. SBS +FSR. The signal optical signal 233 and the pump optical signal 221 may be used for other sensing devices.

[0022] Figure 3 is a diagram of a portion of a system 300, similar to system 100 of Figure 1, for generating narrow-linewidth squeezed light. However, system 300 differs from system 100 in that system 300 includes a nested resonator 305 implemented using a Bragg grating, as compared to the coupled nested resonator 105 shown in Figure 1. As shown, system 300 receives a pump optical signal via an optical transmission medium 307, similar to optical transmission medium 107.

[0023] The system 300 may also include an optical coupler 311 and a resonator 303. The optical transmission medium 307 carries a pump optical signal to the optical coupler 311, which couples a portion of the pump optical signal into the resonator 303, with the coupled portion of the pump optical signal propagating around the resonator 303. As described above, as the pump optical signal propagates within the resonator 303, the pump optical signal generates a counter-propagating stimulated Brillouin scattering (SBS) optical signal that propagates in a direction counter to the pump optical signal.

[0024] In certain embodiments, system 300 includes a nested resonator 305 implemented as a Bragg filter or grating integrated into a portion of the optical path of resonator 303. Specifically, nested resonator 305 includes a first reflector 306-1 and a second reflector 306-2 on the optical path of the resonator. First reflector 306-1 and second reflector 306-2 are partial reflectors that reflect a portion of the light in nested resonator 305 back into the nested resonator 305. For example, first reflector 306-1 reflects a portion of the light in nested resonator 305 toward second reflector 306-2, and second reflector 306-2 reflects a portion of the light in nested resonator 305 toward first reflector 306-1. Thus, a portion of the light propagating in resonator 303 will also resonate in nested resonator 305, resulting in resonance splitting at the junction of resonator 303 and nested resonator 305. Nested resonator 305 thus performs a resonance splitting function similar to that described above with respect to nested resonator 105 of FIG. 1, and nested resonator 305 suppresses higher-order SBS optical signals.

[0025] Furthermore, the first-order SBS optical signal undergoes spontaneous four-wave mixing (SFWM) to generate a signal optical signal and an idler optical signal. Furthermore, the signal optical signal and the idler optical signal propagating around the resonator 303 are coupled out of the resonator 303 by an optical coupler 311. The optical coupler 311 can couple the signal optical signal and the idler optical signal from the resonator 303 to an optical transmission medium 309. The optical transmission medium 309 carries the signal photons and idler photons out of the system 300 for use by other systems. Because the signal photons and idler photons are squeezed light, the signal photons and idler photons enable sensing at lower power levels with less shot noise.

[0026] 4 is a block diagram of a system 400 for generating squeezed light. As shown, the system 400 includes a pump optical signal source 401, an optical transmission medium 407, a resonator 403, a nested resonator 405, and an optical transmission medium 409. The pump optical signal source 401, the optical transmission medium 407, the resonator 403, the nested resonator 405, and the optical transmission medium 409 function similarly to the pump optical signal source 101, the optical transmission medium 107, the resonator 103, the nested resonator 105, and the optical transmission medium 109 described above in connection with FIG.

[0027] In an additional embodiment, system 400 includes pump filter 411. Pump filter 411 is a filter placed on a reflection port to admit a pump optical signal from optical transmission medium 409 into frequency control loop 413.

[0028] In further embodiments, frequency control loop 413 includes components for maintaining the frequency of the pump optical signal at the resonant frequency of resonator 403. For example, frequency control loop 413 may include a photodetector for detecting the pump optical signal and electronics for controlling the pump optical signal generated by pump optical signal source 401. In some implementations, frequency control loop 413 is a Pound-Drever-Hall loop for maintaining the frequency of the pump optical signal.

[0029] In an exemplary embodiment, frequency control loop 413 may include one or more processors to assist in controlling the frequency of the pump optical signal generated by pump optical signal source 401. The one or more processors execute instructions that direct the processor to control the frequency. The processor may be a single processor or may be a device including a combination of a general-purpose processor, a multi-core processor, multiple processors, special-purpose circuitry, etc. The functions performed by the processor may be implemented using software, firmware, hardware, or any suitable combination thereof. Processors and other computing devices may be supplemented by, or incorporated in, specially designed application-specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs). Processors and other computing devices may also include or be functioning by software programs, firmware, or other computer-readable instructions for performing various process tasks, calculations, and control functions used in the present methods and systems.

[0030] The methods may be implemented by computer-executable instructions, such as program modules or components, that are executed by processors and other computing devices. Generally, program modules include routines, programs, objects, data components, data structures, algorithms, and the like that perform particular tasks or implement particular abstract data types.

[0031] In addition to the processor, the processor may also be interfaced with memory. The memory may be any suitable computer-readable storage medium, including, for example, semiconductor memory devices such as random access memory (RAM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM), or flash memory devices; magnetic disks, such as internal hard disks or removable disks; optical storage devices, such as compact discs (CDs), digital versatile discs (DVDs), Blu-ray discs, or other media capable of carrying or storing desired program code as computer-executable instructions or data structures.

[0032] 5 is a flowchart of a method 500 for generating narrow-linewidth squeezed light. Method 500 proceeds to 501, where a pump optical signal is generated at a first frequency. Method 500 then proceeds to 503, where the pump optical signal is coupled into a resonator. Method 500 then proceeds to 505, where an SBS optical signal having a second frequency is generated in the resonator at a second resonant frequency of the resonator, and the SBS optical signal propagates through the resonator in a second direction opposite the first direction. Method 500 then proceeds to 507, where a squeezed optical signal is generated by four spontaneously emitted optical waves launched by the SBS optical signal. Method 500 then proceeds to 509, where the squeezed optical signal is output via an output optical transmission medium.

[0033] Illustrative Embodiments Example 1 includes a system comprising: a pump optical signal source configured to emit a pump optical signal at a first frequency; a resonator, the pump optical signal coupled to propagate in a first direction within the resonator, the first frequency being a first resonant frequency of the resonator; stimulated Brillouin scattering (SBS) within the resonator generating an SBS optical signal having a second frequency at a second resonant frequency of the resonator, propagating in a second direction within the resonator opposite to the first direction, the SBS optical signal generating a squeezed optical signal by spontaneous emission four-wave mixing; and an output optical transmission medium configured to output the squeezed optical signal generated in the resonator.

[0034] Example 2 includes the system of example 1, wherein the resonator is an optical fiber resonator.

[0035] Example 3 includes the system according to any one of Examples 1 and 2, further including a nested resonator, wherein a portion of a second-order spontaneous Brillouin scattering (SpBS) optical signal propagating within the resonator is coupled to the nested resonator, and the nested resonant frequency of the nested resonator and the resonant frequency of the resonator are hardly ever matched.

[0036] Example 4 includes the system of example 3, wherein the nested resonator is a nested optical fiber resonator coupled to the resonator.

[0037] Example 5 includes the system of any of examples 3-4, wherein the nested resonator is along the optical path of the resonator.

[0038] Example 6 includes the system of any of Examples 1-5, further comprising an optical coupler that couples a pump optical signal to the resonator.

[0039] Example 7 includes the system of example 6, wherein an optical coupler couples a portion of the pump optical signal to the output optical transmission medium.

[0040] Example 8 includes the system of Example 7, further comprising a pump optical signal filter configured to couple the pump optical signal from the output optical transmission medium to the frequency control loop, wherein the frequency control loop maintains the first frequency of the pump optical signal source at the first resonant frequency.

[0041] Example 9 includes a method, the method including: generating a pump optical signal at a first frequency; coupling the pump optical signal to a resonator, the pump optical signal propagating in a first direction at a first resonant frequency of the resonator; generating a stimulated Brillouin scattering (SBS) optical signal in the resonator, the SBS optical signal having a second frequency at a second resonant frequency of the resonator, the SBS optical signal propagating in the resonator in a second direction opposite to the first direction; generating a squeezed optical signal by spontaneous emission four-waves launched by the SBS optical signal; and outputting the squeezed optical signal via an output optical transmission medium.

[0042] Example 10 includes the method of example 9, wherein the resonator is an optical fiber resonator.

[0043] Example 11 includes the method of any of Examples 9 to 10, further including coupling a portion of the SBS optical signal propagating within the resonator to the nested resonator, wherein the nested resonant frequency of the nested resonator and the resonant frequency of the resonator are not substantially matched.

[0044] Example 12 includes the method of example 11, wherein the nested resonator is a nested optical fiber resonator coupled to the resonator.

[0045] Example 13 includes the method of any of Examples 11-12, wherein the nested resonator is along the optical path of the resonator.

[0046] Example 14 includes the method of any of Examples 9-13, wherein an optical coupler couples the pump optical signal and a portion of the squeezed optical signal to the output optical transmission medium.

[0047] Example 15 includes the method of example 14, further including coupling a pump optical signal from the output optical transmission medium to a frequency control loop, the frequency control loop maintaining the first frequency at the first resonant frequency.

[0048] Example 16 includes a system comprising: a pump optical signal source configured to emit a pump optical signal at a first frequency; a resonator, wherein the pump optical signal is coupled to propagate in a first direction within the resonator, the first frequency being a first resonant frequency of the resonator, and wherein stimulated Brillouin scattering (SBS) within the resonator generates an SBS optical signal having a second frequency at a second resonant frequency of the resonator and propagates in the resonator in a second direction opposite to the first direction, the SBS optical signal generating a squeezed optical signal by spontaneous emission four-wave mixing; a nested resonator, wherein a portion of the SBS optical signal propagating in the resonator is coupled to the nested resonator, and wherein the nested resonant frequency of the nested resonator and the resonant frequency of the resonator are rarely matched; and an output optical transmission medium configured to output the squeezed optical signal generated in the resonator.

[0049] Example 17 includes the system of example 16, wherein the nested resonator is a nested optical fiber resonator coupled to the resonator.

[0050] Example 18 includes the system of any of examples 16-17, wherein the nested resonator is along the optical path of the resonator.

[0051] Example 19 includes the system of any of Examples 16-18, further comprising an optical coupler configured to couple a portion of the pump optical signal to the output optical transmission medium.

[0052] Example 20 includes the system of Example 19, further comprising a pump optical signal filter configured to couple the pump optical signal from the output optical transmission medium to the frequency control loop, wherein the frequency control loop maintains the first frequency of the pump optical signal source at the first resonant frequency.

[0053] Although specific embodiments have been illustrated and described herein, those skilled in the art will recognize that any configuration which is expected to achieve the same purpose may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.

Claims

1. 1. A system comprising: a pump optical signal source (101) configured to emit a pump optical signal at a first frequency; a resonator (103), wherein the pump optical signal is coupled to propagate in a first direction within the resonator (103); the first frequency is a first resonant frequency of the resonator (103), and stimulated Brillouin scattering (SBS) in the resonator (103) generates an SBS optical signal having a second frequency at a second resonant frequency of the resonator (103) and propagating in the resonator (103) in a second direction opposite to the first direction; a resonator (103) for generating a squeezed optical signal by spontaneous four-wave mixing of the SBS optical signal; an output optical transmission medium (109) configured to output the squeezed optical signal generated in the resonator (103).

2. 2. The system of claim 1, further comprising a nested resonator (105), wherein a portion of the second spontaneous Brillouin scattering (SpBS) optical signal propagating within the resonator (103) is coupled into the nested resonator (105), and wherein a nested resonant frequency of the nested resonator (105) and a resonant frequency of the resonator (103) are not substantially matched.

3. generating a pump optical signal at a first frequency; coupling the pump optical signal into a resonator (103), the pump optical signal propagating in a first direction at a first resonant frequency of the resonator (103); generating a stimulated Brillouin scattering (SBS) optical signal in the resonator (103) having a second frequency at a second resonant frequency of the resonator (103), the SBS optical signal propagating in the resonator (103) in a second direction opposite to the first direction; generating a squeezed optical signal by four spontaneously emitted optical waves emitted by the SBS optical signal; and outputting the squeezed optical signal via an output optical transmission medium (109).

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