WO2009128317A1 - 光学モジュール及び光学ユニット - Google Patents
光学モジュール及び光学ユニット Download PDFInfo
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- WO2009128317A1 WO2009128317A1 PCT/JP2009/055134 JP2009055134W WO2009128317A1 WO 2009128317 A1 WO2009128317 A1 WO 2009128317A1 JP 2009055134 W JP2009055134 W JP 2009055134W WO 2009128317 A1 WO2009128317 A1 WO 2009128317A1
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- Prior art keywords
- lens
- light
- optical
- semiconductor laser
- light source
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/42—Coupling light guides with opto-electronic elements
- G02B6/4201—Packages, e.g. shape, construction, internal or external details
- G02B6/4204—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms
- G02B6/4207—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms with optical elements reducing the sensitivity to optical feedback
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
- H01S5/0064—Anti-reflection components, e.g. optical isolators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/0225—Out-coupling of light
- H01S5/02251—Out-coupling of light using optical fibres
Definitions
- the present invention relates to an optical module and an optical unit that couple light from a laser light source to an optical fiber, emit light to a space, or perform processing such as modulation and wavelength conversion on the light.
- a semiconductor laser used as a light source of an optical module is easily affected by return light.
- the return light returns to the active layer in the oscillation state of the semiconductor laser by any path, the return light also induces stimulated emission, thereby reducing the laser gain, and the relationship between the input current and the laser output and the state of the oscillation spectrum are within the normal characteristics range. The phenomenon of collapse from occurs. Therefore, in order to suppress the oscillation state of the semiconductor laser within the range of the normal characteristics, it is necessary to suppress the incident return light as much as possible.
- Patent Document 1 As a countermeasure against return light for an optical module using a semiconductor laser, one disclosed in Patent Document 1 is known.
- An optical component that constitutes a coupling optical system in an optical module in which a laser mounted on a substrate, an optical fiber, and a coupling optical system that causes laser light to enter an incident opening on one end face of the optical fiber are integrally formed.
- the optical axis of the lens closest to the laser is configured so that the optical axis of the laser light does not coincide. By doing so, the light intensity of the return light from the lens to the laser can be reduced, so that the operation of the laser can be stabilized and the characteristics of the optical module can be stabilized.
- JP 11-295559 A JP 11-295559 A
- An object is to provide an optical module and an optical unit.
- An optical module having a laser light source and at least one lens on which light emitted from the laser light source is incident, wherein the optical axis of the laser light source and the optical axis of the lens are approximately coincident, and the light emitted is incident Among the lenses, the lens on which the outgoing light first enters (hereinafter referred to as the first lens) has an optical surface having a convex surface facing the light source.
- the optical module according to any one of 1 to 6, A waveguide structure for coupling and emitting laser light emitted from the optical module;
- An optical unit comprising:
- the return light reflected from the optical surface to the light source side is diverged, and the amount of light incident on the light source exit aperture is very small. Accordingly, the influence of the return light on the oscillation characteristics of the semiconductor laser can be greatly reduced without requiring a highly accurate and costly positioning adjustment step.
- FIG. 6 is an explanatory diagram showing the lens shape of Example 4.
- FIG. 10 is an explanatory diagram showing the lens shape of Example 5.
- the present invention will be described based on an embodiment, but the present invention is not limited to the embodiment.
- the optical module 1 shown in FIG. 1 has a function of coupling outgoing light from the semiconductor laser 11 to an optical fiber 13 using a lens 12.
- the optical module 2 shown in FIG. 2 has a function of emitting light emitted from the semiconductor laser 11 to the external space as collimated light using the collimating lens 21.
- the optical unit 3 shown in FIG. 3 uses the optical module shown in FIG. 1 to couple the light emitted from the semiconductor laser 11 to the waveguide 31 via the lens 12, and modulate the waveguide 31. After wavelength conversion, the collimator lens 21 is used to emit light to an external space.
- the waveguide represents a waveguide structure having a function of confining and transmitting light in a direction perpendicular to the light transmission direction, and other examples of the waveguide structure include an optical fiber.
- a waveguide type SHG (Second Harmonic Generation) device as a device equipped with a waveguide.
- a lens 41 (also referred to as a first lens) into which divergent light emitted from the semiconductor laser 11 as a light source first enters has a concave optical surface directed toward the semiconductor laser 11 side.
- the divergent light emitted from the semiconductor laser 11 is reflected so as to converge on the optical surface.
- a large amount of light returns to the light emission aperture of the semiconductor laser 11, so that a large amount of light enters the laser oscillation resonator, which induces stimulated emission in the laser gain medium, and oscillates the laser beam.
- instability causes instability.
- Mode competition which is a mode hop in which the longitudinal mode of the laser shifts to another mode due to instability of the oscillation operation of the laser beam, transition from a single longitudinal mode to multiple modes, and fluctuations in light intensity between multiple modes
- an unfavorable state occurs as a semiconductor laser.
- the first lens 51 has the convex optical surface facing the semiconductor laser 11
- the light reflected by the optical surface is reflected by the semiconductor laser. 11 diverges more than the diverging light emitted from the light source 11. If it does so, the light intensity of the return light to the output opening of the semiconductor laser 11 will become very small, and the influence on the oscillation operation
- the light emitted from the semiconductor laser includes light emitted from the semiconductor laser via the waveguide structure as described above.
- the divergent light emitted from the semiconductor laser is reflected by the optical surface on the semiconductor laser side of the first incident lens to become return light, but the intensity of the return light incident on the emission opening of the semiconductor laser is flat on the reflection surface. In this case, it decreases as the distance between the semiconductor laser and the lens increases.
- the light intensity modulation of laser light is generally performed at a high frequency, but the return light changes the light intensity of the laser light and deteriorates the controllability of the light intensity of the laser light. Bring.
- the light intensity of the return light that does not change the light intensity of the laser light is said to be about 70 dB smaller than the intensity of the emitted light.
- a non-reflective coating generally applied to the surface of the optical surface of the lens is frequently used.
- the non-reflective coating forms multiple layers on the optical surface of the lens that reflect the incident light by shifting the phase by half a wavelength, cancels the reflected light reflected by each layer, and comprehensively reflects the light intensity of the reflected light. Is reduced. If a non-reflective coating is used, the reflected light can be almost eliminated. However, in actuality, incident light has a certain wavelength width, and the coating is not uniform. Reduction of light intensity is said to be the limit. Then, in order to reduce the light intensity of the return light by 70 dB, it is necessary to further reduce it by 40 dB.
- the light intensity of the return light mainly depends on the shape of the exit aperture of the semiconductor laser, the distance WD (WORKING DISTANCE) between the exit aperture of the semiconductor laser and the lens surface on the semiconductor laser side, the surface shape of the optical surface of the lens, etc. .
- the shape of the emission aperture of the semiconductor laser does not depend on the semiconductor laser and has a width of about several ⁇ m.
- the surface shape of the lens on the semiconductor laser side is almost flat. Considering the conditions of these optical systems, it can be said that the light intensity of the return light mainly depends on WD. Therefore, the value of WD that reduces the light intensity of the return light by 40 dB was obtained by calculation.
- the light emitted from the emission aperture of the semiconductor laser is a Gaussian beam
- the cross-sectional shape of the emission aperture is a circle having a radius of 5 ⁇ m
- the beam waist radius of the Gaussian beam is 5 ⁇ m.
- WD is the distance between the exit aperture of the semiconductor laser 11 and the optical surface of the first lens 71 on the semiconductor laser 11 side as described above.
- the vertical axis represents the logarithm of the ratio of the light intensity of the return light to the light intensity of the emitted light. From this calculation result, it can be seen that the WD to be reduced by 40 dB is 8 mm.
- the optical surface of the first lens is a flat surface, WD of 8 mm is required, and when the optical surface of the first lens is a convex surface, the return light to the semiconductor laser 11 is reduced, so that the WD is 8 mm.
- the optical surface of the first lens on the side of the semiconductor laser 11 is a convex surface and non-reflective coating is applied, and the WD is 8 mm or less, whereby the light intensity of the return light can be reduced by 70 dB, and the oscillation characteristics of the semiconductor laser. Can be stabilized.
- the radius of curvature r As the radius of curvature r is smaller, the light emitted from the semiconductor laser is more divergent on its optical surface, so that the intensity of the light incident on the exit aperture is reduced and the influence on the laser oscillation is small.
- the generation of spherical aberration increases as the radius of curvature r decreases, it is necessary to take measures to suppress spherical aberration, such as making the optical surface an aspherical surface.
- the value of the curvature radius r needs to be larger than a certain value. From the above, it can be said that there is a lower limit for the value of the curvature radius r.
- the focal length f the longer the focal length f, the longer the distance between the semiconductor laser and the first lens, and the return light from the optical surface of the first lens on which the divergent light emitted from the semiconductor laser is incident spreads to the exit aperture in order to spread widely. Since the incident light intensity is reduced, the influence on the laser oscillation is reduced.
- the focal length f has a certain upper limit value.
- the index r / f has a lower limit value, and when a value equal to or higher than the lower limit value is adopted, the influence of the return light can be reduced while suppressing the spherical aberration generated in the lens. It can be downsized.
- a combination of 1.2 as the lower limit value of r and 2.5 as the upper limit value of f is considered appropriate, and the lower limit value of the index r / f is preferably about 0.5.
- the upper limit value of the index r / f will be described below.
- the smaller the focal length f the shorter the distance between the semiconductor laser and the lens, which can meet the demand for miniaturization of the optical module.
- the difficulty of assembly adjustment increases as the size is reduced. Therefore, there is a lower limit value for the focal length f.
- the focal length f is short, the intensity of return light from the lens to the semiconductor laser increases.
- the value of the curvature radius r increases, the light intensity of the return light from the optical surface of the lens increases. Therefore, the value of the curvature radius r needs to be smaller than a predetermined value. Therefore, there is an upper limit for the value of the radius of curvature r.
- the light emitted from the emission aperture of the semiconductor laser is a Gaussian beam. It is assumed that a Gaussian beam is emitted from an emission opening having a circular cross section, and the beam waist radius is 2 ⁇ m.
- the emitted light is reflected by the surface of the first lens on the semiconductor laser side, the light intensity of the return light incident on the exit aperture of the semiconductor laser is calculated.
- the reflectance on the optical surface of the lens is 100%.
- the optical surface shape of the lens is assumed to be an aspherical shape.
- the wavelength of the emitted light is 1.06 ⁇ m
- the refractive index is 1.58
- the axial thickness of the lens is 1.5 mm
- the focal length f is 1.5 mm.
- the above calculation condition is referred to as calculation condition 1.
- the calculation results are shown in FIG.
- the index r / f as the horizontal axis
- the light intensity of the return light coupled to the exit aperture is based on the light intensity when the optical surface of the lens is a plane, and the ratio to the reference.
- the light intensity ⁇ of the returned light is represented on the vertical axis.
- the vertical axis is a logarithmic display.
- the index r / f is about 6.
- the index r / f is about 6 when the allowable value of the light intensity ⁇ of the return light is ⁇ 1 dB. Therefore, regardless of the focal length f, the index r / f for which the allowable value of the light intensity ⁇ of the return light is ⁇ 1 dB is about 6.
- the value r / f is qualified as an index representing the amount of the return light beam coupled to the exit aperture of the semiconductor laser. Therefore, when the value of the index r / f is constant, the amount that the light intensity of the return light is coupled to the emission aperture of the semiconductor laser is constant regardless of changes in the values of the radius of curvature r and the focal length f. It shows that it becomes. Assuming that the same calculation condition 1 as described above is adopted and the amount of coupling of the return light intensity to the exit aperture of the semiconductor laser is 2 dB down (when ⁇ is ⁇ 2 dB), the focal length f and the curvature An example of calculating the relationship of the radius r is shown in FIG. From FIG.
- the radius of curvature r and the focal length f are substantially directly proportional, and the index r / f is substantially constant. Therefore, it can be said that the value r / f is suitable as an index representing the amount of the intensity of the return light coupled to the exit aperture of the semiconductor laser.
- d is the axial thickness of the lens
- f is the focal length of the lens.
- the focal length f when the focal length f is large, the optical module becomes large. Accordingly, in order to meet the demand for downsizing of the optical module, the focal length f needs to be set smaller than a predetermined value. Therefore, it can be said that there is an upper limit value for the focal length f.
- the index d / f has a lower limit in terms of adopting a manufacturable lens while achieving downsizing of the optical system.
- a combination of 1 as the lower limit value of d and 2.5 as the upper limit value of f is considered appropriate, and the lower limit value of the index d / f is preferably 0.4.
- the upper limit value of the index d / f will be described below.
- the focal length f becomes a constant value
- the optical surface of the lens on the semiconductor laser side approaches the semiconductor laser, so that WD decreases.
- the focal length f becomes smaller, the distance between the semiconductor laser and the lens becomes shorter, which can meet the demand for miniaturization of the optical module.
- the difficulty of assembly adjustment increases as the size is reduced. Therefore, there is a lower limit value for the focal length f.
- the index d / f has an upper limit value in consideration of simplification and downsizing of the assembly adjustment of the optical module.
- a combination of 1.5 as the upper limit value of d and 1.2 as the lower limit value of f is considered appropriate, and the index d / f is preferably about 1.3.
- the optical module according to the present embodiment is used when collimating and using light emitted from a light source or when making light incident on another optical component.
- a collimating lens is used to collimate the light emitted from the semiconductor laser.
- one lens can be designed and used.
- the light emitted from the semiconductor laser can be used for other optical components with one lens. In the case of coupling to a component, it is difficult to adjust the assembly of the semiconductor laser, the lens, and other optical components.
- the adjustment axes of the lenses can be distributed to the two lenses, so that each axis can be adjusted separately. Adjustment of each axis becomes easy. Furthermore, when a collimating lens is used as the first lens, the light emitted from the collimating lens is collimated, so that the lens on which the emitted light enters next can be arranged with a loose positioning accuracy in the optical axis direction.
- the return light can be reduced by increasing the curvature of the vicinity of the optical axis by increasing the aspheric coefficient, but in this case, the optical surface of the lens above the optical axis is abruptly changed. Therefore, the lens is difficult to remove aberration. For this reason, it is desirable that the absolute value of the aspheric coefficient A4 of the optical surface on the light source side of the lens closest to the light source is 5 or less.
- a spherical lens is preferable to an aspherical lens.
- an aspheric lens as shown in FIG. 11, a shape in which the normal of the optical surface is directed to the exit aperture of the semiconductor laser is assumed, and the return light increases.
- the return light to the semiconductor laser can be reduced by using a spherical lens for the first lens.
- Example 1 The first embodiment will be described below. The embodiment corresponds to all of the first to fifth embodiments described above.
- the wavelength of the semiconductor laser is 1.31 ⁇ m used in optical communication
- the light source mode radius of the optical fiber exit aperture is 2 ⁇ m.
- E represents a power of 10
- 3.0E-01 represents 0.3.
- the aspherical sag amount Z (h) in such a lens can be expressed by the following equation 1 where the optical axis direction is the X axis and the height perpendicular to the optical axis is h.
- k is a conic coefficient and A 2i is an aspheric coefficient.
- the on-axis spherical aberration of the designed lens has a practically sufficient value as a collimating lens for optical communication with 1 m ⁇ rms.
- an aspheric lens was used as the lens, either a spherical lens or an aspheric lens may be used as the lens to be adopted. If the optical axes of the light source and lens are approximately the same, the light that is reflected by the optical surface of the lens and returns to the exit aperture of the optical fiber to recombine is mainly light that is reflected near the optical axis whose lens shape is close to a spherical surface. It is because it causes.
- An aspherical lens is preferably used when it is necessary to reduce the aberration caused by the refraction of the lens, such as when the light beam emitted from the lens is coupled to the waveguide.
- the curvature radius r is a positive value of 0.8 mm
- the focal length f is 1.5 mm and 8 mm or less
- the axial thickness of the lens is 1.3 mm.
- the index r / f is 0.53
- the index d / f is 0.87
- the return light coupling efficiency is ⁇ 53.2 dB
- ⁇ is The effect of reducing the coupling efficiency of -10 dB and returning light entering the exit aperture was confirmed.
- the light source mode radius represents the radius of the cross section of the light beam at the exit aperture from which light exits.
- the light source is a semiconductor laser
- the radius at which the light intensity attenuates from the maximum light intensity to a value of 1 / e 2 is represented.
- a radius at which the light intensity is attenuated from the maximum light intensity to a value of 1 / e 2 in the intensity distribution in the optical axis vertical section of the light emitted from the emission opening of the optical fiber Represents.
- the light source NA represents NA obtained from the light emission angle at which the light intensity of the emitted light attenuates from the maximum light intensity to a value of 1 / e 2 .
- the return light coupling efficiency ⁇ represents the rate at which the light emitted from the exit aperture is reflected by the optical surface of the lens and returned to the exit aperture when the light emitted from the exit aperture is reflected by the optical surface of the lens.
- Example 2 The second embodiment will be described below.
- the embodiment corresponds to all of the first to fifth embodiments described above.
- the light emitted from the semiconductor laser is reflected by the optical surface of the first lens and returns to the optical fiber.
- the optical system specifications shown in Optical system specification data 2 were assumed.
- the mode radius of the exit aperture of the semiconductor laser is 2 ⁇ m in the X direction and 3 ⁇ m in the Y direction.
- the mode radius also differs between the X direction and the Y direction.
- the wavelength of the light source is 1.06 ⁇ m in the near infrared.
- a collimating lens was designed, and the design results shown in paraxial data 2 and conic coefficient / aspheric coefficient data 2 were obtained.
- the radius of curvature r is a positive value of about 0.9 mm, the focal length f is 1.3 mm and 8 mm or less, and the axial thickness of the lens is 1.2 mm.
- the index r / f is 0.69, the index d / f is 0.92, satisfies the conditional expressions (1) and (2), and the return light coupling efficiency is ⁇ 44.0 dB, ⁇ is The effect of reducing the coupling efficiency of -7 dB and returning light entering the exit aperture was confirmed.
- Example 3 A third embodiment will be described below. The embodiment corresponds to all of the first to fifth embodiments described above.
- the optical system specifications shown in Optical system specification data 3 were assumed.
- the wavelength of the light source is 1.31 ⁇ m used in optical communication, and the mode radius of the optical fiber exit aperture is 10 ⁇ m.
- the light emitted from the optical fiber is reflected by the optical surface of the first lens and returns to the optical fiber.
- a spherical collimating lens was designed, and the design results shown in paraxial data 3 and conic coefficient / aspheric coefficient data 3 were obtained.
- the on-axis spherical aberration of the designed lens is 1 m ⁇ rms, which is a practically sufficient value as a collimating lens for optical communication.
- the curvature radius r is a positive value of about 2.5 mm
- the focal length f is 4.7 mm and 8 mm or less
- the axial thickness of the lens is 3.0 mm.
- the index r / f is 0.53 and the index d / f is 0.63, which satisfies the conditional expressions (1) and (2).
- Example 4 A fourth embodiment will be described below.
- the embodiment corresponds to all of the first to fifth embodiments described above.
- the optical system specifications shown in Optical system specification data 4 were assumed.
- the design results shown in paraxial data 4 and conic / aspheric coefficient data 4 were obtained.
- the shape of the designed lens is shown in FIG.
- the radius of curvature r is a positive value of about 1.0 mm, the focal length f is 1.2 mm and 8 mm or less, and the axial thickness of the lens is 1.5 mm.
- the index r / f is 0.83 and the index d / f is 1.25, which satisfies the conditional expressions (1) and (2).
- the return light coupling efficiency is ⁇ 42.2 dB
- ⁇ is ⁇ 3.4 dB, confirming the effect of reducing the coupling efficiency of the return light entering the exit aperture.
- the index d / f is close to the upper limit value of the conditional expression (2), and the effectiveness of the upper limit value of the conditional expression (2) was confirmed.
- Example 5 The fifth embodiment will be described below.
- the embodiment corresponds to all of the first to fifth embodiments described above.
- the optical system specifications shown in Optical system specification data 5 were assumed.
- the design results shown in paraxial data 5 and conic / aspheric coefficient data 5 were obtained.
- the shape of the designed lens is shown in FIG.
- the radius of curvature r is a positive value of about 4.0 mm, the focal length f is 3.5 mm and 8 mm or less, and the axial thickness of the lens is 1.5 mm.
- the index r / f is 1.15 and the index d / f is 0.43, which satisfies the conditional expressions (1) and (2).
- ⁇ is ⁇ 4.8 dB, confirming the effect of reducing the coupling efficiency of the return light entering the exit aperture.
- the index d / f is close to the lower limit value of the conditional expression (2), and the effectiveness of the lower limit value of the conditional expression (2) was confirmed.
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Abstract
Description
0.50<r/f<6.0 (1)
4.前記第1レンズの軸上厚をd、前記第1レンズの焦点距離をfとしたときに、次の条件式を満たすことを特徴とする前記1から3のいずれかに記載の光学モジュール。
0.40<d/f<1.3 (2)
5.前記第1レンズはコリメートレンズであることを特徴とする前記1から4のいずれかに記載の光学モジュール。
前記光学モジュールから出射したレーザ光を結合させ、かつ出射させる導波構造と、
を有することを特徴とする光学ユニット。
11 半導体レーザ
12,41 レンズ
21 コリメートレンズ
13 光ファイバ
31 導波路
51、62、71 第1レンズ
61 導波構造
0.50<r/f<6.0 (1)
条件式(1)の妥当性を以下に説明する。最初に指標r/fの下限値について以下に説明する。曲率半径rが小さいほど半導体レーザから出射した光はその光学面で大きく発散するので、出射開口に入射する光強度は少なくなり、レーザ発振に与える影響は少ない。しかし、曲率半径rが小さくなると球面収差の発生が大きくなるので、光学面を非球面にするなど、球面収差を抑える対応策が必要となる。しかし、光学面を非球面にして球面収差の発生を抑えようとしても限界がある。従って、第1レンズで発生する球面収差を実使用に耐えうる値に抑えるためには、曲率半径rの値は一定の値以上に大きくする必要がある。以上より曲率半径rの値には下限値があると言える。
0.40<d/f<1.3 (2)
条件式(2)の妥当性を以下に説明する。最初に指標d/fの下限値について説明する。dはレンズの軸上厚であるので、小さくすればするほど、レンズを小型化することになり、光学モジュールの小型化の要請に応えることができる。しかし、レンズの軸上厚dを小さく作製するにも製造技術上の限界がある。また、一定の焦点距離fの値を得つつ、厚みを小さくすると、レンズ全体の形状を小さくすることになり、入射光の光束径も小さくなってしまう。以上から軸上厚dには下限値が存在すると言える。
以下に第1の実施例を説明する。上記の第1の実施の形態から第5の実施の形態の全てに該当する実施の形態となっている。光学系諸元については、光学系諸元データ1に示すような値を採用し、半導体レーザの波長は光通信において用いられている1.31μm、光ファイバ出射開口の光源モード半径は2μmとする。例えば、光ファイバからの出射光が第1レンズの光学面で反射して光ファイバに戻る場合が想定できる。このような場合に、コリメートレンズを設計し、近軸データ1とコーニック係数・非球面係数データ1に示す設計結果を得た。ここで、Eは10のべき乗を表しており、例えば3.0E-01は0.3を表している。かかるレンズにおける非球面形状のサグ量Z(h)は、光軸方向をX軸、光軸に垂直な方向の高さをhとするとき次の数1で表せる。但し、kをコーニック係数、A2iを非球面係数とする。
面番号 曲率半径r 軸上厚d 硝材 備考
1 ∞ 1.7196 光源
2 0.80000 1.3000 BAF5 レンズ
3 3.29573 0.0000
4 ∞ 0.0000
コーニック係数・非球面係数データ1
第2面
k=0.00000E+00,A4=-4.74793E-01,A6=9.97793E-01,A8=-1.62894E+00,
A10=0.00000E+00
第3面
k=-1.90063E+02,A4=6.11252E-01,A6=-2.04715E+00,A8=1.81598E+01,
A10=-2.83363E+01
光学系諸元データ1
波長 1.31μm
光源モード半径 2μm
光源NA 0.21
レンズ焦点距離f 1.5mm
r/f 0.53
d/f 0.87
設計結果データ1
軸上球面収差(NA=0.21) 1mλrms
戻り光結合効率η -53.2dB
Δη -10dB
Δηとは、出射開口からの出射光が反射するレンズの光学面が平面であると仮定して算出した戻り光結合効率を基準とした場合に、算出された本実施例の戻り光結合効率の比率を表す。
以下に第2の実施例を説明する。上記の第1の実施の形態から第5の実施の形態の全てに該当する実施の形態となっている。例えば、半導体レーザからの出射光が第1レンズの光学面で反射して光ファイバに戻る場合が想定できる。光学系諸元データ2に示した光学系諸元を前提とした。光の進行方向をZ方向とした場合に、半導体レーザの出射開口のモード半径はX方向が2μm、Y方向が3μmであるとする。なお、半導体レーザでは、X方向とY方向とで光の閉じ込め効果が異なるのでモード半径もX方向とY方向とで異なってくる。光源の波長は近赤外の1.06μmとする。このような場合に、コリメートレンズを設計し、近軸データ2とコーニック係数・非球面係数データ2に示す設計結果を得た。
面番号 曲率半径r 軸上厚d 硝材 備考
1 ∞ 1.2000 光源
2 0.89588 1.2000 BK7 レンズ
3 -1.36725 0.0000
4 ∞ 6.6719 集光点位置
コーニック係数・非球面係数データ2
第2面
k=0.00000E+00,A4=-2.55945E-01,A6=1.56560E-01,A8=0.00000E+00,
A10=0.00000E+00
第3面
k=-5.40704E+00,A4=-2.47221E-02,A6=4.01418E-01,A8=9.21886E-02,
A10=0.00000E+00
光学系諸元データ2
波長 1.06μm
光源モード半径(X) 2μm
光源モード半径(Y) 3μm
光源NA 0.21
レンズ焦点距離f 1.3mm
r/f 0.69
d/f 0.92
設計結果データ2
軸上球面収差(NA=0.21) 0mλrms
戻り光結合効率η -44dB
Δη -7dB
設計結果データ2に示すように、設計したレンズの軸上球面収差は解消されている。曲率半径rは約0.9mmと正の値であり、焦点距離fは1.3mmと8mm以下であり、レンズの軸上厚は1.2mmである。指標r/fは0.69、指標d/fは0.92であり、条件式(1)と条件式(2)を満たし、戻り光結合効率が-44.0dBであるところを、Δηは-7dBと戻り光が出射開口に入射する結合効率を減少させる効果を確認できた。
以下に第3の実施例を説明する。上記の第1の実施の形態から第5の実施の形態の全てに該当する実施の形態となっている。光学系諸元データ3に示した光学系諸元を前提とした。光源の波長は光通信において用いられている1.31μm、光ファイバ出射開口のモード半径は10μmとする。例えば光ファイバからの出射光が第1レンズの光学面で反射して光ファイバに戻る場合が想定できる。このような場合に、球面のコリメートレンズを設計し、近軸データ3とコーニック係数・非球面係数データ3に示す設計結果を得た。
面番号 曲率半径r 軸上厚d 硝材 備考
1 ∞ 5.1478 光源
2 2.50000 3.0000 BAF5 レンズ
3 13.00000 0.0000
4 ∞ 0.0000
光学系諸元データ3
波長 1.31μm
光源モード半径 10μm
光源NA 0.04
レンズ焦点距離f 4.7mm
r/f 0.53
d/f 0.63
設計結果データ3
軸上球面収差(NA=0.04) 1mλrms
戻り光結合効率η -34.5dB
Δη -9.7dB
設計結果データ3に示すように、戻り光結合効率が-34.5dBであるところを、Δηは-9.7dBと戻り光が出射開口に入射する結合効率を減少させる効果を確認できた。
以下に第4の実施例を説明する。上記の第1の実施の形態から第5の実施の形態の全てに該当する実施の形態となっている。例えば、半導体レーザからの出射光が第1レンズの光学面で反射して光ファイバに戻る場合が想定できる。光学系諸元データ4に示した光学系諸元を前提とした。近軸データ4とコーニック係数・非球面係数データ4に示す設計結果を得た。設計したレンズの形状を図12に示す。
面番号 曲率半径r 軸上厚d 硝材 備考
1 ∞ 0.5523 光源
2 1.00000 1.5000 BAL35 レンズ
3 -1.01762 0.0000
4 ∞ 0.0000
コーニック係数・非球面係数データ4
第2面
k=-5.69047E-01,A4=-7.50264E-01,A6=1.88681E+00,A8=0.00000E+00,
A10=0.00000E+00
第3面
k=-1.16292E+00,A4=-2.92320E-02,A6=7.63141E-02,A8=-1.47254E-01,
A10=4.25234E-01
光学系諸元データ4
波長 1.06μm
光源モード半径 1.5μm
光源NA 0.22
レンズ焦点距離 1.2mm
r/f 0.83
d/f 1.25
設計結果データ4
軸上球面収差(NA=0.21) 0mλrms
戻り光結合効率η -42.2dB
Δη -3.4dB
設計結果データ4に示すように、設計したレンズの軸上球面収差は解消されている。曲率半径rは約1.0mmと正の値であり、焦点距離fは1.2mmと8mm以下であり、レンズの軸上厚は1.5mmである。指標r/fは0.83、指標d/fは1.25であり、条件式(1)と条件式(2)を満たしている。戻り光結合効率が-42.2dBであるところを、Δηは-3.4dBと戻り光が出射開口に入射する結合効率を減少させる効果を確認できた。指標d/fについては、条件式(2)の上限値に近い値となっており、条件式(2)の上限値の有効性を確認することができた。
以下に第5の実施例を説明する。上記の第1の実施の形態から第5の実施の形態の全てに該当する実施の形態となっている。例えば、半導体レーザからの出射光が第1レンズの光学面で反射して光ファイバに戻る場合が想定できる。光学系諸元データ5に示した光学系諸元を前提とした。近軸データ5とコーニック係数・非球面係数データ5に示す設計結果を得た。設計したレンズの形状を図13に示す。
面番号 曲率半径r 軸上厚d 硝材 備考
1 ∞ 2.9526 光源
2 4.03290 1.5000 BAL35 レンズ
3 -3.50000 0.0000
4 ∞ 0.0000
コーニック係数・非球面係数データ5
第2面
k=3.37771E+00,A4=-4.18685E-02,A6=2.53548E-02,A8=-3.59249E-03,
A10=0.00000E+00
第3面
k=-1.86480E+01,A4=-5.92018E-02,A6=3.45907E-02,A8=-1.14758E-02,
A10=3.01092E-03
光学系諸元データ5
波長 1.06μm
光源モード半径 1.5μm
光源NA 0.22
レンズ焦点距離 3.5mm
r/f 1.15
d/f 0.43
設計結果データ5
軸上球面収差(NA=0.21) 10mλrms
戻り光結合効率η -57.7dB
Δη -4.8dB
設計結果データ5に示すように、設計したレンズの軸上球面収差は解消されている。曲率半径rは約4.0mmと正の値であり、焦点距離fは3.5mmと8mm以下であり、レンズの軸上厚は1.5mmである。指標r/fは1.15、指標d/fは0.43であり、条件式(1)と条件式(2)を満たしている。戻り光結合効率が-57.7dBであるところを、Δηは-4.8dBと戻り光が出射開口に入射する結合効率を減少させる効果を確認できた。指標d/fについては、条件式(2)の下限値に近い値となっており、条件式(2)の下限値の有効性を確認することができた。
Claims (7)
- レーザ光源と、前記レーザ光源からの出射光が入射する少なくとも一つのレンズを有し、前記レーザ光源の光軸と前記レンズの光軸が凡そ一致する光学モジュールであって、前記出射光が入射するレンズの中で、前記出射光が最初に入射するレンズ(以下第1レンズと称す)は光源側に凸面を向けた光学面を有することを特徴とする光学モジュール。
- 前記レーザ光源の出射開口と、前記第1レンズの前記レーザ光源側の光学面までの距離は8mm以下であることを特徴とする請求の範囲第1項に記載の光学モジュール。
- 前記第1レンズの光源側の光学面の近軸曲率半径をr、前記第1レンズの焦点距離をfとしたときに次の条件式を満たすことを特徴とする請求の範囲第1項または第2項に記載の光学モジュール。
0.50<r/f<6.0 (1) - 前記第1レンズの軸上厚をd、前記第1レンズの焦点距離をfとしたときに、次の条件式を満たすことを特徴とする請求の範囲第1項から第3項のいずれか一項に記載の光学モジュール。
0.40<d/f<1.3 (2) - 前記第1レンズはコリメートレンズであることを特徴とする請求の範囲第1項から第4項のいずれか一項に記載の光学モジュール。
- 前記第1レンズの光源側の光学面は球面であることを特徴とする請求の範囲第1項から第5項のいずれか一項に記載の光学モジュール。
- 請求の範囲第1項から第6項のいずれか一項に記載の前記光学モジュールと、
前記光学モジュールから出射したレーザ光を結合させ、かつ出射させる導波構造と、
を有することを特徴とする光学ユニット。
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Citations (3)
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JPS62172767A (ja) * | 1986-01-24 | 1987-07-29 | Mitsubishi Electric Corp | 光半導体装置 |
JPH08139397A (ja) * | 1994-01-19 | 1996-05-31 | Konica Corp | レーザダイオード光源の駆動装置 |
JP2008053346A (ja) * | 2006-08-23 | 2008-03-06 | Konica Minolta Opto Inc | 光モジュール装置 |
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JP3435311B2 (ja) * | 1997-06-19 | 2003-08-11 | 松下電器産業株式会社 | 情報読み取り装置 |
US6075650A (en) * | 1998-04-06 | 2000-06-13 | Rochester Photonics Corporation | Beam shaping optics for diverging illumination, such as produced by laser diodes |
JP2002076440A (ja) * | 2000-08-28 | 2002-03-15 | Stanley Electric Co Ltd | 発光装置及び光空間伝送装置 |
JP2003172874A (ja) * | 2001-12-05 | 2003-06-20 | Samsung Electro Mech Co Ltd | 光照射装置とそれを備えた光ピックアップ装置及び光照射装置の調整方法 |
JP2004020720A (ja) * | 2002-06-13 | 2004-01-22 | Olympus Corp | コリメートレンズ |
US6768593B1 (en) * | 2003-06-24 | 2004-07-27 | Suganda Jutamulia | Fiber-coupled laser diode having high coupling-efficiency and low feedback-noise |
US7511880B2 (en) * | 2005-10-14 | 2009-03-31 | Konica Minolta Opto, Inc. | Semiconductor light source module |
JP3926380B1 (ja) * | 2006-12-07 | 2007-06-06 | マイルストーン株式会社 | 撮像レンズ |
ATE456071T1 (de) * | 2007-02-13 | 2010-02-15 | Konica Minolta Opto Inc | Optische kopplungslinse und lichtquelle |
KR100867950B1 (ko) * | 2007-04-25 | 2008-11-11 | 삼성전기주식회사 | 조명 광학 장치 |
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JPS62172767A (ja) * | 1986-01-24 | 1987-07-29 | Mitsubishi Electric Corp | 光半導体装置 |
JPH08139397A (ja) * | 1994-01-19 | 1996-05-31 | Konica Corp | レーザダイオード光源の駆動装置 |
JP2008053346A (ja) * | 2006-08-23 | 2008-03-06 | Konica Minolta Opto Inc | 光モジュール装置 |
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