Aspherical fiber coupling lens

BACKGROUND OF THE INVENTION

The present invention relates to a fiber coupling lens that is applied to a photoelectric coupling module for efficiently collecting and focusing light from a semiconductor laser to be transmitted by optical fiber.

Optical communication is one of promising industries in recent years. In optical communication elements, a photoelectric coupling module includes a light source such as laser diode or LED, a fiber coupling lens and an optical fiber. A data light beam emitted from the laser diode passes the fiber coupling lens, then converges at the optical fiber for transmission. Refer to FIG. 1, due to small diameter of the optical fiber ranging from several microns to decades of microns and small size of the fiber coupling lens, not only precise alignment in directions (X-directions) perpendicular to the optical direction of the laser beam in the optical fiber is required, but also accurate alignment in the direction (Z-direction) of the optical axis is required.

Conventional fiber coupling lens may be formed by a single-piece of lens or multiple-piece lens. The fiber coupling lens formed by the multiple-piece lens collects maximum amount of light and has good focusing effect. However, single-piece type fiber coupling lens is more competitive in the market. As to short focal length (from a light source to focus point) single-piece type fiber coupling lens, a bi-convex design is the most common used, as shown in U.S. Pat. Nos. 5,764,838, 4,932,763, 5,293,269, and JP62059912. Generally, the diameter of the fiber coupling lens is quite small so that diffraction may happen when the distance to the focus point is relative long. Besides the problem of diffraction, alignment accuracy and coupling efficiency of the lens should also be required, as disclosed in U.S. Pat. No. 5,642,233, US2003/012496, JP09-061665, JP63-010119, JP05-273463, JP62-108217, JP02-150816, and JP07-128616 etc. Moreover, while the data light from a laser source of the photoelectric coupling module passing through the fiber coupling lens, the temperature of the lens will be increase. In order to avoid deformation of the fiber coupling lens caused by a long term heat exposure, the fiber coupling lens is made of glass by glass molding, as shown in JP63-297233, US2002/114085, TW240706, and TWD 076092 etc.

In order to achieve optimal effects of the fiber coupling unit (module), the fiber coupling lens has optical features such as small focal point, high coupling efficiency, and large numbers of apertures on objective side. In order to achieve above effects, conventional fiber coupling lens is designed to be formed by diffraction lens, as shown in WO2007145118, JP2006-227366, and US2003/0012496 etc. Yet such design also increases difficulties in manufacturing so that the cost is difficult to be reduced. Thus there is a need to develop a fiber coupling lens having simple optical surface with low cost and made by glass molding technique for enhancing development of optical communication industries.

SUMMARY OF THE INVENTION

Therefore it is a primary object of the present invention to provide a fiber coupling lens which is a bi-convex lens with positive refraction power having a first aspherical optical surface and a second aspherical optical surface and its optical features satisfy the following conditions:

$\begin{matrix} 0.5 < \frac{d_{2}}{f} < 1.5; & (1) \\ 1.0 < \frac{R_{1} - R_{2}}{R_{1} + R_{2}} < 2.0; & (2) \\ 1.2 < (\frac{1}{R_{1}} - \frac{1}{R_{2}}) \cdot f < 2.2; & (3) \\ 0.001 < \frac{(N_{d} - 1)}{R_{1}} \cdot \frac{f}{N_{d}} < 0.15; & (4) \\ 0.2 < (N_{d} - 1) \frac{d_{2}^{2}}{f^{2}} < 1.2; & (5) \end{matrix}$

wherein f is effective focal length of the lens, d₂is thickness of the lens on optical axis, N_dis refraction index of the lens, R₁, R₂respectively are curvature radiuses of the first optical surface and the second optical surface of the lens on optical axis. Thereby the focusing as well as localization precision is effectively improved, the coupling efficiency is high and the number of apertures on objective side is large. The lens has simple structure and the manufacturing cost is low. Therefore, applications of the fiber coupling lens are broadened.

It is another object of the present invention to provide a fiber coupling lens made of glass by precision glass molding technique and refraction index thereof satisfies the following conditions:

70<N_d·ν_d (6)

wherein N_dis refraction index of the lens and ν_dis Abbe number of the lens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing showing the structure of an embodiment of a fiber coupling lens according to the present invention;

FIG. 2 is a drawing showing optical path of a fiber coupling lens according to the present invention and light path;

FIG. 3 is a wavefront aberration of an embodiment according to the present invention;

FIG. 4 shows wavefront aberration of an embodiment according to the present invention;

FIG. 5 shows wavefront aberration of another embodiment according to the present invention;

FIG. 6 shows wavefront aberration of a further embodiment according to the present invention;

FIG. 7 shows wavefront aberration of a further embodiment according to the present invention;

FIG. 8 shows wavefront aberration of a further embodiment according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Refer to FIG. 1, an embodiment according to the present invention is applied to a photoelectric coupling module 1, along an optical axis Z of a fiber coupling lens 2, having a light source 3 which is a semiconductor laser emitting data light with wavelength of 1310 nm, a cover glass 4 and an aperture 5 that is a middle-positioned aperture disposed between the cover glass 4 and the fiber coupling lens 2. After the data light passing through the cover glass 4 and the aperture 5, it is focused onto a focal point 6 by the fiber coupling lens 2 and being received and transmitted by the optical fiber (not shown in figure). There is no restriction on range of wavelength of the semiconductor laser. There is also no limit on the distance between the light source 3 and the focal point 6.

Refer to FIG. 2, the fiber coupling lens 2 is an aspherical bi-convex lens with an aspherical first optical surface R₁and an aspherical second optical surface R₂, made of glass or plastic material with the refraction index N_dthat is higher than 1.5 and the Abbe number ν_dthat is larger than 46 while the optical properties of the lens satisfy the following conditions:

$\begin{matrix} 0.5 < \frac{d_{2}}{f} < 1.5; \\ 1.0 < \frac{R_{1} - R_{2}}{R_{1} + R_{2}} < 2.0; \\ 1.2 < (\frac{1}{R_{1}} - \frac{1}{R_{2}}) \cdot f < 2.2 \\ 0.001 < \frac{(N_{d} - 1)}{R_{1}} \cdot \frac{f}{N_{d}} < 0.15; \\ 0.2 < (N_{d} - 1) \frac{d_{2}^{2}}{f^{2}} < 1.2; \end{matrix}$

wherein f is the effective focal length of the lens, d₂is thickness of the lens on optical axis, N_dis refraction index of the lens, R₁, R₂respectively are curvature radiuses of the first optical surface and the second optical surface of the lens on optical axis.

The aspherical surface formula of the first optical surface R₁and the second optical surface R₂is as shown in equation (7):

$\begin{matrix} Z = \frac{{ch}^{2}}{1 + \sqrt{(1 - (1 + K) c^{2} h^{2})}} + A_{4} h^{4} + A_{6} h^{6} + A_{8} h^{8} + A_{10} h^{10} + A_{12} h^{12} & (7) \end{matrix}$

wherein c is curvature radius,

h is height of the lens,

K is conic constant, and

A₄{grave over ( )}A₆{grave over ( )}A₈{grave over ( )}A_l0{grave over ( )}A₁₂respectively are the 4^th, 6^th, 8^th, 10^th, 12^thorder aspherical coefficients.

In accordance with above structure, the focusing and the localization precision are effectively improved, the coupling efficiency is high and the number of apertures on objective side is large. Thus the simple structure and the low manufacturing cost of the lens are achieved. Therefore, applications of the fiber coupling lens and the related module are improved.

The following embodiments are described in details. The list (1) to list (6) include the radius of curvature R (unit: mm) on the Z optical axis of the first optical surface R₁and the second optical surface R₂, the thickness d₂(unit: mm) of the fiber coupling lens 2, the effective focal length f of the lens, the thickness d₂of the lens, the refraction index n_Fof the lens, the number of aperture on objective side NA_O, the number of aperture on image side NA_I, and the fiber coupling efficiency η.

The First Embodiment

The fiber coupling lens 2 in this embodiment is made of glass material with the refraction index N_dof 1.583, and the Abbe number ν_dof 59.4.

TABLE ONE

f = 1.182 nF = 1.590

d₂
N_d
ν_d

The first optical surface

R₁
3.747745
1.200
1.583
59.4

K
4.656747

A₄
0.118695

A₆
0.740645

A₈
−0.027967

A₁₀
−3.62406

A₁₂
4.828305

The second optical surface

R₂
−0.724872

K
−0.380312

A₄
−0.325224

A₆
5.726254

A₈
−24.500778

A₁₀
52.185614

A₁₂
−40.830891

η = 69.20%

NA_O= 0.4
NA_I= 0.23

the following results are obtained through the table one:

$\frac{d_{2}}{f} = 1.0156;$

$\frac{R_{1} - R_{2}}{R_{1} + R_{2}} = 1.4796;$

$(\frac{1}{R_{1}} - \frac{1}{R_{2}}) \cdot f = 1.9453$

$\frac{(N_{d} - 1)}{R_{1}} \cdot \frac{f}{N_{d}} = 0.1161;$

$(N_{d} - 1) \frac{d_{2}^{2}}{f^{2}} = 0.6014;$

$N_{d} \cdot v_{d} = 94.04$

The above results satisfy equation (1), equation (2), equation (3) equation (4), equation (5) and equation (6).

When the light source 3 emits laser light with wavelength of 1310 nm, the laser light is collected and focused onto the focusing point 6 by the fiber coupling lens 2 because the wavefront of the laser light is a spherical wave. The wavefront of the focusing point 6 is shown in FIG. 3. Through this figure, root mean square of Wavefront Aberration is obtained and is equal to 0.0321λrms. This proves that the embodiment has features of small focus, compact volume and high coupling efficiency so that the applications are improved.

The Second Embodiment

The fiber coupling lens 2 in this embodiment is made of glass material with the refraction index N_dof 1.583, and the Abbe number ν_dof 59.4.

TABLE TWO

f = 1.258 nF = 1.590

d₂
N_d
ν_d

The first optical surface

R₁
3.747745
1.513
1.583
59.4

K
4.913352

A₄
0.118695

A₆
0.740645

A₈
−0.027967

A₁₀
−3.62406

A₁₂
4.828305

The second optical surface

R₂
−0.756071

K
−0.389121

A₄
−0.075934

A₆
2.520131

A₈
−8.903683

A₁₀
16.115097

A₁₂
−10.30923

η = 76.70%

NA_O= 0.4
NA_I= 0.25

the following results are obtained through the table two:

$\frac{d_{2}}{f} = 1.2023;$

$\frac{R_{1} - R_{2}}{R_{1} + R_{2}} = 1.5054;$

$(\frac{1}{R_{1}} - \frac{1}{R_{2}}) \cdot f = 1.9996$

$\frac{(N_{d} - 1)}{R_{1}} \cdot \frac{f}{N_{d}} = 0.1236;$

$(N_{d} - 1) \frac{d_{2}^{2}}{f^{2}} = 0.8430;$

$N_{d} \cdot v_{d} = 94.04$

The above results satisfy equation (1), equation (2), equation (3), equation (4), equation (5) and equation (6).

When the light source 3 emits laser light with wavelength of 1310 nm, the laser light is collected and focused onto the focusing point 6 by the fiber coupling lens 2. The wavefront of the focusing point 6 is shown in FIG. 4. Through this figure, root mean square of Wavefront Aberration is obtained and is equal to 0.0225λrms. This proves that the embodiment has features of small focus, compact volume and high coupling efficiency so that the applications are improved.

The Third Embodiment

The fiber coupling lens 2 in this embodiment is made of glass material with the refraction index N_dof 1.514, and the Abbe number ν_dof 63.7.

TABLE THREE

f = 1.167 nF = 1.522

d₂
N_d
ν_d

The first optical surface

R₁
141.839324
1.000
1.514
63.7

K
44818.240

A₄
0.356

A₆
1.404

A₈
5.221

A₁₀
−23.444

A₁₂
21.081

The second optical surface

R₂
−0.587845

K
−0.28625

A₄
−0.520486

A₆
8.75882

A₈
−28.193085

A₁₀
38.519421

A₁₂
10.633482

η = 63.00%

NA_O= 0.4
NA_I= 0.22

the following results are obtained through the table three:

$\frac{d_{2}}{f} = 0.8569;$

$\frac{R_{1} - R_{2}}{R_{1} + R_{2}} = 1.0083;$

$(\frac{1}{R_{1}} - \frac{1}{R_{2}}) \cdot f = 1.9935$

$\frac{(N_{d} - 1)}{R_{1}} \cdot \frac{f}{N_{d}} = 0.0028;$

$(N_{d} - 1) \frac{d_{2}^{2}}{f^{2}} = 0.3776;$

$N_{d} \cdot v_{d} = 96.46$

The above results satisfy equation (1), equation (2), equation (3) equation (4), equation (5) and equation (6).

When the light source 3 emits laser light with wavelength of 1310 nm, the laser light is collected and focused onto the focusing point 6 by the fiber coupling lens 2. The wavefront of the focusing point 6 is shown in FIG. 5. Through this figure, root mean square of Wavefront Aberration is obtained and is equal to 0.0563λrms. This proves that the embodiment has features of small focus, compact volume and high coupling efficiency so that the applications are improved.

The Fourth Embodiment

The fiber coupling lens 2 in this embodiment is made of glass material with the refraction index N_dof 1.58313, and the Abbe number ν_dof 59.4.

TABLE FOUR

f = 1.127 nF = 1.590

d₂
N_d
ν_d

The first optical surface

R₁
4.264219
0.000
0.000
0.0

K
62.694834

A₄
0.002634

A₆
1.442488

A₈
2.768814

A₁₀
−6.456358

A₁₂
−44.02713

The second optical surface

R₂
−0.761144

K
−0.350427

A₄
−0.334724

A₆
5.580306

A₈
−24.597471

A₁₀
53.153555

A₁₂
−40.022299

η = 76.00%

NA_O= 0.4
NA_I= 0.25

the following results are obtained through the table four:

$\frac{d_{2}}{f} = 1.3539;$

$\frac{R_{1} - R_{2}}{R_{1} + R_{2}} = 1.4345;$

$(\frac{1}{R_{1}} - \frac{1}{R_{2}}) \cdot f = 1.7457$

$\frac{(N_{d} - 1)}{R_{1}} \cdot \frac{f}{N_{d}} = 0.0974;$

$(N_{d} - 1) \frac{d_{2}^{2}}{f^{2}} = 1.0689;$

$N_{d} \cdot v_{d} = 94.04$

The above results satisfy equation (1), equation (2), equation (3), equation (4), equation (5) and equation (6).

When the light source 3 emits laser light with wavelength of 1310 nm, the laser light is collected and focused onto the focusing point 6 by the fiber coupling lens 2. The wavefront of the focusing point 6 is shown in FIG. 6. Through this figure, root mean square of Wavefront Aberration is obtained and is equal to 0.0278λrms. This proves that the embodiment has features of small focus, compact volume and high coupling efficiency so that the applications are improved.

The Fifth Embodiment

The fiber coupling lens 2 in this embodiment is made of glass material with the refraction index N_dof 1.583, and the Abbe number ν_dof 59.4.

TABLE FIVE

f = 1.148 nF = 1.590

d₂
N_d
ν_d

The first optical surface

R₁
31.884136
1.000
1.583
59.4

K
1963.124

A₄
0.196

A₆
1.258

A₈
3.527

A₁₀
−14.940

A₁₂
12.330

The second optical surface

R₂
−0.659849

K
−0.363483

A₄
−0.487625

A₆
7.111876

A₈
−26.371641

A₁₀
46.812404

A₁₂
−20.709032

η = 64.00%

NA_O= 0.4
NA_I= 0.22

the following results are obtained through the table five:

$\frac{d_{2}}{f} = 0.8711;$

$\frac{R_{1} - R_{2}}{R_{1} + R_{2}} = 1.0422;$

$(\frac{1}{R_{1}} - \frac{1}{R_{2}}) \cdot f = 1.7757$

$\frac{(N_{d} - 1)}{R_{1}} \cdot \frac{f}{N_{d}} = 0.0133;$

$(N_{d} - 1) \frac{d_{2}^{2}}{f^{2}} = 0.4425;$

$N_{d} \cdot v_{d} = 94.04$

The above results satisfy equation (1), equation (2), equation (3) equation (4), equation (5) and equation (6).

When the light source 3 emits laser light with wavelength of 1310 nm, the laser light is collected and focused onto the focusing point 6 by the fiber coupling lens 2. The wavefront of the focusing point 6 is shown in FIG. 7. Through this figure, root mean square of Wavefront Aberration is obtained and is equal to 0.0502λrms. This proves that the embodiment has features of small focus, compact volume and high coupling efficiency so that the applications are improved.

The Sixth Embodiment

The fiber coupling lens 2 in this embodiment is made of glass material with the refraction index N_dof 1.731, and the Abbe number ν_dof 40.5.

TABLE SIX

f = 1.130 nF = 1.743

d₂
N_d
ν_d

The first optical surface

R₁
7.974495
1.000
1.731
40.5

K
58.054

A₄
0.108

A₆
0.041

A₈
4.877

A₁₀
7.254

A₁₂
−51.368

The second optical surface

R₂
−0.843268

K
0.783698

A₄
−0.431282

A₆
8.248266

A₈
−30.200965

A₁₀
51.605569

A₁₂
−6.379389

η = 58.00%

NA_O= 0.4
NA_I= 0.2

the following results are obtained through the table six:

$\frac{d_{2}}{f} = 0.8849;$

$\frac{R_{1} - R_{2}}{R_{1} + R_{2}} = 1.2365;$

$(\frac{1}{R_{1}} - \frac{1}{R_{2}}) \cdot f = 1.4817$

$\frac{(N_{d} - 1)}{R_{1}} \cdot \frac{f}{N_{d}} = 0.0598;$

$(N_{d} - 1) \frac{d_{2}^{2}}{f^{2}} = 0.5723;$

$N_{d} \cdot v_{d} = 70.09$

The above results satisfy equation (1), equation (2), equation 3) equation (4), equation (5) and equation (6).

When the light source 3 emits laser light with wavelength of 1310 nm, the laser light is collected and focused onto the focusing point 6 by the fiber coupling lens 2. The wavefront of the focusing point 6 is shown in FIG. 8. Through this figure, root mean square of Wavefront Aberration is obtained and is equal to 0.0502λrms. This proves that the embodiment has features of small focus, compact volume and high coupling efficiency so that the applications are improved.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Aspherical fiber coupling lens

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