JP-7856927-B2 - Optical devices and optical amplification devices

Inventors

• 阿部 真志
• 梅木 毅伺
• 風間 拓志

Assignees

• ＮＴＴ株式会社

Dates

Publication Date

20260512

Application Date

20221205

Claims (6)

1. A first polarization beam splitter (PBS) and a second PBS that reflect the linearly polarized light of an incident first polarization component and transmit the linearly polarized light of a second polarization component perpendicular to the first polarization component, wherein the first PBS is arranged such that it reflects the linearly polarized light of the first polarization component toward the first path of the first and second paths between the first PBS and the second PBS, and the second PBS is arranged such that it reflects the linearly polarized light of the first polarization component toward the second path, A first polarization rotor and a second polarization rotor are arranged in the first path described above, An optical element that transmits only linearly polarized light of the third polarization component, positioned between the first polarization rotor and the second polarization rotor, An optical device comprising, The first polarization rotator is a Faraday rotator configured to rotate the polarization direction by an angle less than 45°, The second polarization rotator is a Faraday rotator configured to rotate the polarization direction by 45°, The optical element is a third PBS configured to transmit only polarization components with a polarization angle of 135° that have passed through the first polarization rotor, and to reflect polarization components with a polarization angle other than 135° that have passed through the first polarization rotor. An optical device further comprising a photodetector into which the polarization component reflected by the third PBS is incident .
2. The optical device according to claim 1, wherein, of the light incident on the first PBS and emitted from the second PBS, the light that is incident on the second PBS again does not incident on the first PBS.
3. A third polarization rotor and a fourth polarization rotor are arranged in the second path described above, An optical element that transmits only the linearly polarized light of the third polarization component, disposed between the third polarization rotor and the fourth polarization rotor, The optical device according to claim 1, further comprising the above.
4. An optical device according to any one of claims 1 to 3 , A first wavelength converter equipped with a first optical parametric amplification (OPA) module, A second wavelength converter equipped with a second OPA module, A polarization-maintaining fiber connecting the first PBS and the first wavelength converter of the optical device, and the second PBS and the second wavelength converter of the optical device, An optical amplification device equipped with this device.
5. The first wavelength converter is an optical parametric amplifier further comprising a first second harmonic generator (SHG) module, The optical amplification apparatus according to claim 4 , wherein the second wavelength converter is an optical parametric amplifier further comprising a second SHG module.
6. The system further comprises a fifth PBS that reflects the first polarization component of the signal light and transmits the second polarization component, The optical amplification device according to claim 4, wherein the first polarization component is incident on the first wavelength converter, the second polarization component is incident on the second wavelength converter, and the fifth PBS transmits the optical signal output from the first wavelength converter and reflects the optical signal output from the second wavelength converter.

Description

This invention relates to optical devices and optical amplification devices. Conventionally, the C-band wavelength range of 1530 nm to 1565 nm has been widely used in long-distance optical communication. To date, wavelength division multiplexing (WDS) and high-speed, multi-level modulation (LDS) technologies have been researched, developed, and put into practical use, leading to significant increases in optical communication capacity. While this capacity increase is expected to continue, WDS technology has reached a plateau because it already utilizes the entire C-band wavelength range. Therefore, in recent years, to further increase the capacity of 5G and beyond communications, expanding the communication wavelength range to the adjacent S-band (1460 nm to 1530 nm) and L-band (1565 nm to 1625 nm) has been considered (see, for example, Non-Patent Document 1). Expanding the communication wavelength band in this way requires the use of existing communication equipment, thus necessitating wavelength converters. Wavelength converters using optical nonlinear effects have been proposed. Nonlinear media include highly nonlinear fiber types and nonlinear crystals (for example, periodically polarized inverted LiNbO3 (Periodically Poled Lithium Niobate: PPLN) crystals). Unless otherwise specified, this document describes wavelength converters using nonlinear optical crystals. Figure 1 shows a schematic configuration of a wavelength converter using a nonlinear optical crystal. The wavelength converter 3 shown in Figure 1 converts the wavelength of signal light input via the optical fiber 1. The wavelength converter 3 comprises an erbium-doped fiber amplifier (EDFA) 4 for amplifying excitation light from the excitation light device 2, an SHG module 7 for second harmonic generation (SHG), and an OPA module 6 for optical parametric amplification (OPA) of the signal light using the second harmonic. Each SHG module 7 is equipped with a PPLN 5. The SHG module 7 has two lenses and a dichroic mirror on its input side to transmit only excitation light of a desired wavelength and couple it to the PPLN5. Only the excitation light of the desired wavelength from the excitation light focused by the first lens onto the dichroic mirror is focused by the second lens and coupled to the PPLN5. Furthermore, the SHG module 7 has two lenses and a dichroic mirror on its output side to separate and output only the second harmonic of a desired wavelength. Only the desired second harmonic from the output of the PPLN5, focused by the first lens onto the dichroic mirror, is focused by the second lens and coupled to an external optical fiber. The SHG module 7 can also be configured to have only lenses for focusing light on one or both of its input and output sides, i.e., without dichroic mirrors. The OPA module 6 has three lenses and a dichroic mirror on its input side for coupling signal light and the second harmonic from the SHG module 7 to the PPLN 5. Only the signal light of the desired wavelength, focused by the first lens and transmitted through the dichroic mirror, and the desired second harmonic, focused by the second lens and reflected by the dichroic mirror, are focused by the third lens and coupled to the PPLN 5. On the output side of the OPA module 6, there are two lenses and a dichroic mirror for separating and outputting only the signal light that has been frequency-converted to the desired frequency. Only the signal light that has been frequency-converted to the desired frequency, focused by the first lens and transmitted through the dichroic mirror, is focused by the second lens and coupled to the external optical fiber. Polarization-independent optical amplification is used to increase the capacity of optical communication. The wavelength converter 3 equipped with a PPLN shown in Figure 1 is the basic configuration for amplifying polarization-independent optical amplification. The wavelength converter 3 is also called an optical parametric amplifier. Since the wavelength converter equipped with a PPLN exhibits polarization dependence, polarization-independent optical amplification corresponding to polarization-independent optical amplification has been proposed and demonstrated (see, for example, Non-Patent Document 2). Figures 2 and 3 show a schematic configuration of a polarization-independent optical amplification device. The polarization-independent optical amplifier 20 shown in Figure 2 separates the signal light incident through the optical fiber 1 into polarization components using a polarizing beam splitter (PBS) 21-1. The linear polarization of the first polarization component (S-polarization component) is optically parametric amplified by a wavelength converter 3-2, and the linear polarization of the second polarization component (P-polarization component), which is orthogonal to the first polarization component, is independently optically parametric amplified by a separate wavelength converter 3-1. The two polarization