WO2021223148A1

WO2021223148A1 - Optical isolator core in between fiber and collimator lens

Info

Publication number: WO2021223148A1
Application number: PCT/CN2020/088952
Authority: WO
Inventors: Jian Chen; Chang Xiao; Xia Hong; Fangdong ZHAO
Original assignee: Lumentum Operations Llc
Priority date: 2020-05-07
Filing date: 2020-05-07
Publication date: 2021-11-11
Also published as: WO2021223361A1

Abstract

An optical device may include an optical fiber having an input leg and an output leg, a collimating lens, and an optical isolator core positioned between the optical fiber and the collimating lens. The optical isolator core may include birefringent crystals, a Faraday rotator, a halfwave plate, and/or the like. The optical isolator core may laterally displace a portion of a light beam. In some implementations, the optical isolator core may be a single stage isolator core, a dual stage isolator core, and/or the like. The optical device may include a wavelength-division multiplexing filter, another collimating lens, and a pump chip.

Description

OPTICAL ISOLATOR CORE IN BETWEEN FIBER AND COLLIMATOR LENS

Some implementations described herein provide an optical isolator core and/or optical devices including an optical isolator core. For example, some implementations provide a displacement walk-off isolator core positioned in between a fiber and a collimator lens to enable a same side input/output fiber, 980 nanometer (nm) /1550 nm wavelength-division multiplexing (WDM) function, self-compensated polarization mode dispersion (PMD) , self-compensated polarization dependent loss (PDL) , and/or the like.

Conventional optical isolator designs include an optical isolator core that deflects a collimated light beam with a small angle, which may be used in a collimated light beam application. Some implementations described herein provide an optical isolator core design that may not deflect the beam and may create a lateral displacement walk-off (e.g., using an yttrium orthovanadate (YVO ₄) birefringent crystal) so that light from an output side of an optical fiber may not be coupled into an input side of the optical fiber, which may achieve optical isolation.

In some implementations, the optical isolator design may conserve space by utilizing space between the optical fiber and a collimating lens. In some implementations, the optical isolator design may enable 1550 nm input and output on a same side of an optical fiber with the optical isolator. In some implementations, the optical isolator design may enable an integrated 980 nm/1550 nm WDM function.

In some implementations, the optical isolator design may provide flexibility to place the optical isolator core on an input leg, an output leg, or both the input and the output legs. For example, a forward pump erbium doped fiber amplifier (EDFA) may include 980 nm pump light coupling through a WDM filter into the output leg, where the optical isolator core is in the input leg (e.g., because the optical isolator core may block 980 nm light) . As another example, a reverse pump EDFA may include 980 nm pump light coupling through a WDM filter into the output leg, where the optical isolator core is in the output leg. In some implementations, the optical isolator design may achieve an input optical fiber and an output optical fiber on a same side, which may enable integration with a 980 nm pump laser chip and/or a monitor photodiode.

Some implementations may include cascaded two stage optical isolator cores to achieve high isolation and self-compensated low PDL and/or low PMD. In some implementations, one or more of the optical isolator cores may include three birefringent crystal plates (e.g., YVO ₄) and a Faraday rotator (e.g., garnet) . Rotating two of the three birefringent crystal plates may create freedom to tune the optical isolator to improve performance and/or compensate a material manufacturing tolerance. For example, a first YVO ₄ plate (e.g., YVO ₄-1) and a garnet plate may be fixed, and a second YVO ₄ plate (e.g., YVO ₄-2) and a third YVO ₄ plate (e.g., YVO ₄-3) may be tuned. As another example, the second YVO ₄ plate (e.g., YVO ₄-2) and the garnet plate may be fixed, and the first YVO ₄ plate (e.g., YVO ₄-1) and the third YVO ₄ plate (e.g., YVO ₄-3) may be tuned. In some implementations, an optical isolator design may include cascading similar and/or identical optical isolator cores with orientations and directions such that a material tolerance and an assembly tolerance (e.g., for each optical isolator core) cancel with each other to achieve low PMD, PDL, and/or insertion loss (IL) .

Fig. 1 is a diagram of an example implementation 100 including a real package design (e.g., a highly integrated packaging and processing (HIPP) design) for an integrated module with a pump laser, a 980 nm/1550 nm WDM filter, and an isolator core (e.g., an optical isolator core) . As shown in Fig. 1, the integrated module may include a 1550 nm isolator core in between an optical fiber (e.g., a dual fiber pigtail) and a first collimated A-lens, a 980 nm/1550 nm WDM filter (e.g., 980 nm transmission and 1550 nm reflection) , a second collimated A-lens, and a pump laser chip. Fig. 2 is an optical pass schematic of the example implementation 100 of Fig. 1.

Fig. 3 is a diagram of an example implementation 300 of a single stage isolator core showing a signal stage core single pass. As shown in Fig. 3, the single stage isolator core may include three pieces (e.g., plates) of birefringent YVO ₄ crystal (e.g., YVO ₄-1, YVO ₄-2, YVO ₄-3) and a garnet piece (e.g., plate) , which are bonded together (e.g., by epoxy) . Fig. 3 also shows a single pass of O-light and E-light (e.g., through the single stage isolator core) .

In some implementations, a single stage isolator core (e.g., the single stage isolator core shown in Fig. 3) may have a design with characteristics as shown in Table 1, where α, β, and γ are azimuth angles of the optical axes of each crystal.

Table 1

Fig. 4 is a diagram of an example implementation 400 of an optical isolator design with a single stage core and a 1550 nm signal path. As shown in Fig. 4, an isolator core and a compensator may be positioned between a pigtail optical fiber having an input leg and an output leg, which may achieve optical isolation of more than 18 decibels (dB) . In some implementations, the compensator may compensate the optical path between the input leg and the output leg (e.g., because the input leg and the output leg are on a same side of the optical isolator design) .

In some implementations, an optical isolator design may include a fiber core of the input leg and a fiber core of the output leg having a fiber-core-to-fiber-core distance of 460 microns (μm) , an A-lens with a 2.7 millimeter (mm) focal length, and a 980 nm/1550 nm WDM filter. For example, the input leg and the output leg may be a thermal expanding core (TEC) which expands fiber mode diameter from 6 μm to 9 μm, such as a CORNING HI 1060 FLEX fiber. In this way, an optical isolator device having the optical isolator design may have a diameter of less than 3.0 mm.

Fig. 5 is a diagram of an example implementation 500 of an optical isolator design with a dual stage isolator core and a 1550 nm signal path. The optical isolator design of example implementation 500 may be similar to the optical isolator design of example implementation 400 shown in Fig. 4; however, instead of the compensator of example implementation 400 shown in Fig. 4, the optical isolator design of example implementation 500 may include a second isolator core and one or more half wave plates (HWPs) . In some implementations, such an optical isolator design may achieve optical isolation of more than 30 dB.

Fig. 6 is a diagram of an example implementation 600 of a dual stage isolator core including a schematic diagram of O-light and E-light traveling on a 1550 nm signal path. As shown in Fig. 6, the dual stage isolator core includes two stages, one for the input leg and another for the output leg, where each stage includes YVO ₄, garnet, and an HWP. For example, the lower stage of the dual stage isolator core includes two YVO ₄ plates, YVO ₄-11 and YVO ₄-12, as well as HWP 1 and a garnet plate (garnet 1) positioned between the two YVO ₄ plates. The upper stage of the dual stage isolator core includes two YVO ₄ plates, YVO ₄-21 and YVO ₄-22, as well as HWP 2 and another garnet plate (garnet 2) positioned between the two YVO ₄ plates.

Fig. 7 is a diagram of an example implementation 700 of a dual stage isolator core including a schematic diagram of O-light and E-light traveling on a 1550 nm isolation path. In some implementations, the dual stage isolator core of example implementation 700 may be similar to the dual stage isolator core of example implementation 600 shown and described with respect to Fig. 6. As shown in Fig. 7, backlight from the output leg to the input leg is separated into O-light and E-light by the dual stage isolator core, and the O-light and/or the E-light may not be coupled into the input leg, thereby achieving high isolation.

Fig. 8 is a diagram of an example implementation 800 of an optical isolator design with a dual stage isolator core in one leg and a 1550 nm signal path. As shown in Fig. 7, the optical isolator design includes two isolator cores (e.g., a dual self-compensated isolator core) on the input leg, a collimating A-lens, a WDM filter, and a compensator on the output leg. In some implementations, the compensator may be used to compensate for an optical path difference between the input leg and the output leg.

Fig. 9 is diagram of an example implementation 900 of a dual stage isolator core (e.g., the dual self-compensated isolator core of Fig. 8) including a schematic diagram of O-light and E-light traveling on a 1550 nm signal path. As shown in Fig. 9, the dual stage isolator core includes two stages, where each stage includes YVO ₄, garnet, and an HWP. For example, a first stage of the dual stage isolator core includes two YVO ₄ plates, YVO ₄-11 and YVO ₄-12, as well as HWP 1 and a garnet plate (garnet 1) positioned between the two YVO ₄ plates. The second stage of the dual stage isolator core includes two YVO ₄ plates, YVO ₄-21 and YVO ₄-22, as well as HWP 2 and another garnet plate (garnet 2) positioned between the two YVO ₄ plates.

Fig. 10 is a diagram of an example implementation 1000 of a dual stage isolator core including a schematic diagram of O-light and E-light traveling on a 1550 nm isolation path. In some implementations, the dual stage isolator core of example implementation 1000 may be similar to the dual stage isolator core of example implementation 900 shown and described with respect to Fig. 9. As shown in Fig. 10, backlight from the output leg to the input leg is separated into O-light and E-light by the dual stage isolator core, and the O-light and/or the E-light may not be coupled into the input leg, thereby achieving high isolation.

In this way, an optical device may include an optical isolator core design where the optical isolator core laterally displaces a portion of a light beam. For example, the optical isolator core may include at least two birefringent crystals to create a lateral displacement walk-off, and the birefringent crystals may be tuned to achieve low PMD, PDL, and/or IL.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the implementations.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of possible implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of possible implementations includes each dependent claim in combination with every other claim in the claim set.

No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more. ” Furthermore, as used herein, the term “set” is intended to include one or more items (e.g., related items, unrelated items, a combination of related and unrelated items, etc. ) , and may be used interchangeably with “one or more. ” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has, ” “have, ” “having, ” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.

Claims

An optical device, comprising:

an optical fiber having an input leg and an output leg;

a collimating lens; and

an optical isolator core positioned between the optical fiber and the collimating lens.
The optical device of claim 1, wherein the optical isolator core comprises at least two birefringent crystals and a Faraday rotator.
The optical device of claim 2, wherein the birefringent crystals comprise yttrium orthovanadate.
The optical device of claim 2, wherein the Faraday rotator comprises garnet.
The optical device of claim 1, wherein the optical isolator core comprises a half wave plate.
The optical device of claim 1, wherein the optical isolator core laterally displaces a portion of a light beam.
The optical device of claim 1, wherein the optical isolator core is a single stage isolator core.
The optical device of claim 1, wherein the optical isolator core is a dual stage isolator core.