JPS5945412A - Coupling method of semiconductor laser and optical fiber - Google Patents

Abstract

PURPOSE:To suppress the reflected return light without decreasing coupling efficiency by propagating the output light of a semiconductor laser in an optical fiber in parallel with the optical axis thereof without making said output light incident perpendicularly to the incident surface of the optical fiber or the wedge- shaped block mounted thereon. CONSTITUTION:The incident face 7 and exit face 5 of a wedge-shaped block 16 mounted to an optical fiber 3 are respectively inclined by theta0, theta3 relatively with the optical axis of the light of a semiconductor laser 1 emitted from a lens 2. The angles theta0, theta3 and the refractive index of the block 16 are so determined that the light past the block 16 propagates in the fiber 3 in parallel with the optical axis of the fiber 3. The reflected return light in the incident part of the optical fiber is thus suppressed without the decrease in the coupling efficiency between the laser 1 and the fiber 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a coupler or a method for coupling a semiconductor laser and an optical fiber to efficiently couple excavation light from a semiconductor laser to an optical fiber.

[Description of prior art]

In recent years, the coupling efficiency of semiconductor laser and optical fiber couplers has been improved by improving the lens system. However, with the improvement of the coupling efficiency, the ray beam reflected from the input end face of the optical fiber returns to the active layer of the semiconductor laser 77! 'i'l self has increased (7. Semiconductor laser's firing flaw +'1, for example, deterioration of the firing spectrum, modulation waveform, noise, etc.) has become impossible to ignore. As the Hals waveform fluctuates, ffi and waveforms are known to cause deterioration of C/N during analog signal transmission.
To explain all conventionally known convenient methods, the first one is shown in Figure 1, which uses glass with a reflective anti-corrosion coating (A 11. = 11.) applied to the entrance surface of the optical fiber. This is the method of putting up a board. This method is based on the output of a semiconductor laser) (using L k lens thread 2,
: When guiding the fiber 1 to the core 4 of the fiber 3, a glass plate coated with a glass plate 6 and a glass plate 6 can be pasted onto the end face 5 of the optical fiber 3. It is necessary to attach the fiber to the radiation surface 5 using a contact λ'1 agent, and -
However, it is difficult to match the Jilt 41r ratio of the optical fiber, glass, and adhesive, and it is difficult to suppress the residual reflection on the contact surface. . Ma/
This, during reflection+! =, )l^/171i 1. Regarding the reflection from the body, when the reflection is complete, it is +1-. Illλka(l icf (', ka, l ko(D reflection)Y;
ld) Y; Reflection amount in the axial direction ＼11ru/kod), reflection ゛) Y, imaging position d Exit side of the semiconductor laser! 'Although shifted from the Inj plane, reflection) Y, and) 1. Coupling with the conductor laser t
, 1. There were unavoidable drawbacks.

f'1'-211 of the conventional method, as shown in FIG.
,[,Since the input end face of the optical fiber is tilted from the plane perpendicular to the optical axis, the light beam entering the fiber is refracted 11,)'t, and enters at a certain angle with the optical axis of the fiber. become. Therefore, in order to suppress reflection as much as possible, the inclination of the incident surface must be increased, and the incident angle within the optical fiber becomes too large, resulting in poor coupling efficiency with the optical fiber.

[Purpose of the invention]

The present invention aims to eliminate these drawbacks and to provide a coupler that suppresses the rate of reflected light returning to the semiconductor laser without impairing the coupling efficiency.

[Characteristics of the invention]

In the present invention, the output light of the semiconductor laser is fully valved in the lens system.
In the direction of coupling to the fiber, the input end face of the optical fiber is jY: 1h
The input surface is formed at an angle θ3 with respect to l+, and the input surface is inclined at an angle θ0 with respect to a plane perpendicular to the optical axis of the output light of the lens system if1 (~, the output surface is formed at an angle θ0 with respect to the plane perpendicular to the optical axis of the output light of the lens system 17). A transparent wedge-shaped block having a diameter of Q'4 and a refractive index of n1 is interposed between the lens system and the optical fiber so as to be in close contact with the end face, and -1- closing angle and each refractive index Q,
[, +11nj is characterized in that tζ-selects t·1'. , fc fr', L When the refractive index nD of air is 1, the direction of light qlt becomes parallel to the incident surface and the exit surface of the haptic block r1.

[General 11. W theory, clear] In general, in a lens system that couples the half iq: body 1/-the one Y to the optical core I,
To the waist &1z) subotoriise r<) 2 V/
, , After lens conversion and fiber subsotorization, I used E-12W2.2wn and "4",
The large coupling efficiency for j' is wo = V/.

That is, the subotorization of the 31' conductor relay is
/W+ (-' rllnpl) Is it 1 when you do double shi\J? Lane 2). Normally, J'::, 11tm, W
O-,-,5pm--1CI pm-Ca7-, (7
) T,”n)11: k13 < In(1(
, O to 10. This ++1,1111. t,
By changing the ratio of the lens focal length, the focal length NIP of the introduction lens, and the distance between the semiconductor laser and the lens system,
1 will be given. In such an R-appropriate coupling state, in order to suppress reflection from the input end face of the optical fiber, it is conceivable to lower the reflectance from the input face and to shift the reflection direction by an angle θ from the optical axis direction. I'm hooked!Beano where you can narrow down the reflection position with a lens\distance 11 from the waist position! I#Z
It is also effective to shift the In this ζ, if we evaluate how much the reflected light matches the incident light by the angle θ and the distance KfZ, we can find that the reduction due to the angle θ and the distance 2,
lfj 1ll11 possible.

The following formula k is the coupling efficiency of the reflected light and the incident light with respect to this angle θ and the distance *(fz).
n, v+ata.

Rem i CON d, 11 CtOr ia
Day Or I: o ai, nglθ-mOt3e f
ibercoupl(+r,” Appl, Dpt,
, vow,, 18. pp, 1847-H(5
A.

1979] has a detailed description.

...-...(1) /ξtoe(!, 1 2-easy(tln Wn-5μIII's!q A =
6.8×H)ゝ. Jin's equation is incidence) r; and 1V
, beam) Y, and the beam waist is n in distance d.
This equation 19 shows the efficiency when the angle θ is shifted by −1°.
To reduce the return efficiency of reflected light by 206-13) J, Z
= 0, it becomes θ-10 degrees.

In other words, if the incident angle θ3 of the light beam is set to 5 degrees, the return efficiency can be suppressed by TdB. Also, Z = 8
If 0n//jQ, then θ=n l6dr3
, θ-3f19 yields a return efficiency reduction of 20 dB. Due to the following, the reflection at the position t' of the semiconductor 1/-the beano ga Hayabusa)', and the angle 11.
The return efficiency is sufficient if there is no 7 for the junior high nine)) 1 is not available, but the foul side is Beano, from the waist') Y; 11 + 1
11 No.j direction 11r Reflection from the damaged surface 1d J+
The 1-minute return efficiency is extremely low at a relatively small angle of 11 degrees.
I understand.

[Acid 4 Light According to Examples] The details of the 19 raccoon dog and 1 corporal of the present invention will be explained using 11 drawings.

/'l'+3Figure t'' is a diagram showing the configuration of 11 examples of wood inventions.

1 is a semiconductor laser 9', a two-piece lens system, and 3 is a nine optical fiber to be coupled. 16) Y is a transparent wedge-shaped block attached to the input surface of the fiber. This block has an incident surface 0, an incident direction 7, and an exit surface 5, forming a wedge shape, and as shown in 1-1, it is a lens.
For those perpendicular to the axis, θ0 and θS are 11:i, respectively.
It's just me.

On the other hand, the entrance surface of the optical fiber 3 has a difference of 06, similar to the exit surface 5 of Block 6. At the exit surface 5, the end face of the optical fiber 3 is brought into close contact with block 16.

With this configuration, the angle at which the Y2 pinion passing through the block 16 is incident on the optical fiber core 4 is also estimated as η. In order not to deteriorate the coupling efficiency from the semiconductor laser 1 to the optical fiber 3, it is preferable to make the direction of incidence into the fiber (Vl, as described above) parallel to the (-fiber) Y; tea+.

Next, in this configuration, conditions are derived such that the beam emitted from the lens system 2 is refracted at the entrance surface 7 and the exit surface 5 of the lens 16 and becomes an optical fiber (Y:Q1+) in line 817. The refractive index in the air is 1141, and the refractive index of block 16 is 0.
1,) Y, 711 (47+ index of fiber optic f4 is 02. The refraction angle θ1 at the entrance surface 7 of the block 1G is expressed by a linear expression. However, it is assumed to be 7, nn-1.

minθTl = nl n+, nθ+
-, -(force 1 +,, button 1 and 9"
C, if the incident angle at the interface with the fiber is 02, then the refraction angle θ3't'' ■10tinθ2-1+7 R11) to θ'
・ −・・・(4) becomes. here −C, '+Il 'I
When the li angle 03' becomes 17 to θ, )Y, f
The incidence angle 1 into the fiber is 1C, the fiber iY: +
It becomes parallel to fil+, and the optimal coupling condition becomes 1 (1, et.
) ...I in (5)? I can see it. Jzo”
From the second equation, /10.1θ%-, nf-'[day1nθn/nI]-L
R1n'-"Cn71'li, nθg/r++]...
...((+) when)
It can be seen that it is parallel to 7-i IhajYdoor1+11.

Figure 54 shows the angles θ0 and 05 [section 91] r7 tsuku16
1, where) Y, the refractive index n2kt of the fiber core 4 is
Ishi Moe; Fiber protection>i21. , and n2=1. /l'+. In the figure, the angle fi9In and the direction of θ3 and 4 are rE
,': 1. .

Tebru.

Next, consider the angular deviation between the reflected light from the entrance surface 7 and exit surface 5 ((&) of the block and the incident Y:.

This is a diagram showing each color 18' on the incident surface 7 and the exit surface 5. The reflected light that falls on the incident surface 7 is 2θ from the optical axis of the human beam. only angle il
In this case, if the thickness of the block 16 is d and the length J is increased by 6-f, the return efficiency can be significantly reduced as is clear from equation (1).

On the other hand, an angular deviation of 2θ2 occurs due to the traveling direction of the reflected light ej (in the block 16) Y: on the output surface 5 of the block 16 (in particular, the fiber input direction). In order to reduce the return efficiency from this point 5, IrJ, θ2-03+(
It is better to make θ0-01) possible or large. Generally, θ0. 〉θ
1, so the condition of θ, ゛〉n is a morphism)'(: length J i('i, as V
Sat 1 roux! -I can see that According to the results in Figure 4, θ3
> 0 is nl (5, +17), so a material TI having a lower refractive index than monosilica glass is suitable as the block 16. Hookah lithium (
T, , i F, n --138), then the angle -θ3t, and the results in Figures 1 to 4 are '#,;!
Let i be represented by A.

This stand, θ. Choose -2pa and get θ3-54°.

-F, θ21t, l:=r: (:0, use (r+) θ7-!i, 4°l-(,2'-4,45°)-5
, 95°. From ) Y, T - (the amount of reduction in reflected light at the incident 1711 is 28 dB by substituting 2θ2 = 12° into equation (1) as the effect of angular shift.
is obtained. Furthermore, it goes without saying that the Fresnel reflection between the fiber core 4 and the air can be reduced by a Fresnel reflection level of 1 between the +17 -L 1 optical fiber and the above-mentioned material.

Combining the above, the return light from the vertical end face of the optical fiber is 28-+-51-14,6=44.4 (dJl) using this method.
It can be seen that this can be reduced. The efficiency of the return light from the entrance surface 7 of the block is determined by the angle of the reflected light tl''2θo==4° and the distance between the beam wastes 2 due to the thickness d of the block 16.
22 d/n 1 is added and real 12. Bolt 1: Due to angular misalignment, axis misalignment also occurs.
The coupling efficiency of the returned light can be sufficiently suppressed.

FIG. 6 illustrates the relationship between the person #'4)Yl, the emitted light, and the reflected light regarding the block 16.

FIG. 7 shows a structural diagram of an embodiment of an optical coupler according to the method of the present invention. A semiconductor laser 1d is attached to a laser mount 10 of a so-called TO type heat sink 8. The condensing lens system is 2FD metallized and integrated with the window IJ.
Qi ■ 1 blockade and spear). i, optical fiber 3 is core 1
3), and is fixed to the heat sink 8 using the optical fiber fixing jig 12. Furthermore, the oscillation state of the semiconductor laser 1 can be monitored by taking out the rear output of the laser through the window 9.

Jukikatsu, t in the clear drawing, 1 (external shape of the rust-shaped block) Y,
Matches the outer shape of the fiber t Z, J: As shown in Figure 1, the outer shape of the wedge block can be any shape as long as the output surface has a larger area than the input end surface of the fiber. It's okay.

[[Moving piece hg, 1lIIJ Jtl-1iW, 'l'l 1. , raise ((-1 "+i-") According to Akira, the output γ(,ga) of the semiconductor Ray
'+': It is arrogant compared to 1- of the input surface.

+ip should not be directly incident on the attached wedge-shaped hook v1, and in the optical fiber -\J (1011 [ray output after entering at 7) Y: & must be incident on the optical fiber core and line 1'. By devising this method, it is possible to sufficiently suppress the influence of the reflected light from the input section of the fiber without deteriorating the coupling efficiency between the conductor 11' and the optical fiber.

The present invention can be applied to all couplers that connect semiconductor lasers and optical fibers. -In the optical coupler, the actual M111-bar:l
IIr characteristics are shown.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are explanatory diagrams of a conventional coupling system with eleven reflection countermeasures. Figure 1 to Figure 3 shows the structure of the present invention and its II+11 principle. A diagram showing the relationship between the tilt angles θ0 and 03 of 11 and output (llll). A diagram showing the relationship between each angle on both sides of the 5th block. Figure 6 shows the incident light, output light, and reflected light of the block.゜Figure 7 shows +IIJ of the optical coupler in which the method of the present invention is implemented.
FIG. 9 is a diagram showing an example of 9i. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Coupling J1' (lens system, 3... Optical fiber, 4... Core of optical fiber, 5...
...Optical fiber entrance end face, 6...Glass plate, 7...
Block incidence plane, 8...The heat sink, 9...
Glass L 10... Laser mount, 11... Laser airtight window, 12... Optical fiber fixing jig, ] 3... Core, 14... Optical fiber holster, 16... Wedge-shaped block. 111 people, 111 people, F1 Honichi, Telephone and Telephone Public Corporation representative.''
(Patent Attorney Ide rN Takashi 1 Figure 2 Figure 3 3 RoX几(rad) Tsuta 4 l To------a---12,5rg

Claims (1)

[Claims] (1) The output light of the semiconductor j/-ν" is passed through a lens system,
In the method of coupling to an optical fiber whose refractive index is r)2, the input end face of the optical fiber is
zt to lhb and form it to ear the fishing θ (2
, the incident surface is earth R+': the output 9Y of the I/lens system, )Y
7-C angle Jf5θ0
2. A transparent wedge-shaped block with a refractive index n1 arranged so that the output tn1 is in close contact with the incident end face of the fiber is placed between the lens system and the 1'5 fiber. A method for coupling a semiconductor laser and an optical fiber, characterized in that the above-mentioned negative angle ``j-'' and each) FBI refractive index V'' are selected so that the following relationship holds true.