JP3287599B2 - Light beam separation device and optical information device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam separating device for separating a light beam of each wavelength by using a semiconductor laser having a plurality of oscillation wavelengths as a light source and an optical information device using the same.

[0002]

2. Description of the Related Art In recent years, the technology in the fields of optical memory, optical measurement, and optical information processing has been remarkably advanced. With the multiplexing of wavelengths and the improvement of spatial resolution, high-performance wavelength tunable has been required as a function required for semiconductor lasers. Function has become important.

[0003] In these fields, optical communication mainly uses temporal parallelism, but it is characterized by achieving higher multiplexing by simultaneously using spatial parallelism.

Therefore, for the purpose of tuning the wavelength, we have proposed the following semiconductor laser structure and driving method.

That is, the semiconductor laser active layer is composed of a plurality of quantum well layers each having a different quantum level, and the oscillation wavelength can be changed by changing the magnitude of the injection current (see Japanese Patent Application Laid-Open (JP-A) No. 2002-112686). 1988
787).

FIG. 4 shows a current-light output characteristic of a semiconductor laser having an example of this structure.

In this example, an AlGaAs semiconductor laser is composed of an 80 ° GaAs well and a 60 ° Al _0.12 Ga _0.88 As.
The wells consist of a structure separated by a 300ÅAl _0.36 Ga _0.64 As barrier, λ ₁ = 830 nm and λ ₂ = 780
The two wavelengths of nm switch with respect to the current change as shown in FIG. That is, the light oscillates in wavelength lambda ₁ at a current I _1, the wavelength lambda ₂ of light in current I ₂ will oscillate.

Such a light source that emits two wavelengths of laser light from almost the same light emitting position does not need to accurately align the optical axes of the independent lasers and the array lasers, and is therefore compact. -Very advantageous in lightness and stability.

In such a system in which the optical axes of a plurality of wavelengths of laser beams are made to coincide with each other, beams are separated for each wavelength, and information is added to each beam without crosstalk, In many cases, it is necessary to detect information inside.

As a means for this, conventionally, a method of spatially separating beams of each wavelength by using a wavelength dispersion element such as a wavelength filter using interference such as a diffraction grating, a prism, and an etalon is used.

[0011]

As described above, as described above,
In a system in which light beams of a plurality of wavelengths are made to coincide with each other, a light beam is separated for each wavelength, information is added to each light beam without crosstalk, and information in each light beam is detected by a conventional diffraction grating. A method of spatially separating beams of each wavelength by using a wavelength dispersion element such as a wavelength filter using interference such as a prism, an etalon, or the like.

However, with such a conventional device,
In order to reduce the crosstalk between wavelengths, for example, it is only necessary to improve the chromatic dispersion characteristics.However, it is necessary to further strictly control the number of longitudinal modes of the light source and the wavelength stability, thereby reducing the manufacturing and adjustment. There is a problem that it becomes difficult, and it takes time and cost for that.

[0013]

According to the present invention, as a means for solving the above-mentioned problems, a light source for emitting light of a plurality of wavelengths, a light source provided in a light beam of the plurality of wavelengths and having a specific wavelength are provided. On the other hand, there is an optical path length difference of about a half wavelength, an optical path length difference of about an integral multiple of wavelengths with respect to other wavelengths, and a stepped edge for separating the light flux of the specific wavelength and the light flux of another wavelength. And an optical element having the same.

A light source for emitting light of a plurality of wavelengths;
An optical system that forms an image of the light beams of the plurality of wavelengths as a light spot, and is provided in the light beams of the plurality of wavelengths, has an optical path length difference of about a half wavelength with respect to a specific wavelength, and has a difference in other wavelengths. An optical element having a step-shaped edge that has an optical path length difference of approximately an integral multiple of wavelength and at least a light amount distribution of the light spot of a specific wavelength and is asymmetric in a direction perpendicular to the edge line of the edge. A light beam separation device characterized by the above feature is used as the means.

The optical element separates at least a light beam having a specific wavelength into at least two light spots having different light amounts in a scanning direction of the recording medium, and the light sources are different from each other. It is an object of the present invention to solve the above-mentioned problem by a light beam separating device, which is a stacked semiconductor laser including an active layer including a plurality of light emitting layers having energy levels.

[0016]

According to the present invention, in an optical information device using a light source having a plurality of wavelengths, a stacked semiconductor laser including an active layer composed of a plurality of light emitting layers having mutually different energy levels is used as a light source. In an optical system for imaging a light beam of a wavelength into a minute spot, a stepped edge in which the optical path length difference is approximately λ / 2 for a specific wavelength λ and the optical path length difference is approximately an integral multiple of λ for other wavelengths. By providing an optical element having the above, by at least asymmetrically distributing the light amount distribution of the spot of the specific wavelength, by separating from the light flux of other wavelengths, a light flux separation device resistant to wavelength fluctuation and its use The optical information device is provided.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic structural view of an embodiment of an optical information device using the light beam separating device of the present invention.

In this embodiment, the present invention is applied to an optical memory system, and FIG. 1 is a schematic diagram showing a configuration of an optical head of an optical memory. In the figure, 1 is a magneto-optical disk, 2 is an achromatic pickup lens, 3 is a polarization beam splitter, 4 is a phase element as an optical element having a stepped edge shape, 5 is an achromatic beam shaping prism, and 6 is achromatic. Collimator lens, 7 is a two-wavelength semiconductor laser, 8
Is a dichroic prism, 9 is a beam splitter, 1
0 is a λ / 2 plate, 11 is an RF sensor lens, 12 is an RF polarization beam splitter, 13 and 14 are two-split RF sensors,
21 is an information input / output terminal, 22 is a controller, 23 is a modulation unit, 24 is a semiconductor laser driver, 25 is RF
A sensor amplifier, 26 is a demodulation unit, and 27 is a comparator.

In FIG. 2, light (wavelengths λ ₁ and λ ₂ ) from a two-wavelength semiconductor laser 7 described later is converted into a parallel beam by a collimator lens 6, and the beam shape is shaped into a substantially perfect circle by a prism 5. after, the phase element 4 will be described later, giving a spatial phase difference distribution on lambda ₁ of the beam.

Λ ₁ transmitted through the polarizing beam splitter 3,
The light having two wavelengths of λ ₂ is connected by the pickup lens 2 to the recording surface of the magneto-optical disk 1 so that λ ₂ connects a normal minute spot and λ ₁ connects a spot having an asymmetric light amount distribution as described later. .

The P-polarized light component and the S-polarized light component contained in the reflected light from the optical disk 1 are reflected by the polarizing beam splitter 3 by about 30% and 100%, respectively, guided to the detection optical system, and further, the dichroic prism 8 By
The beam 15 at λ ₂ is reflected and the beam at λ ₁ passes through 8.

The beam of λ ₁ is further converted by an RF beam splitter 9 into a beam 16 of an AT / AF detection system (not shown).
(Transmission) and an RF detection system (reflection). The RF detection system beam is operated and detected by a λ / 2 plate 10, a lens 11, a polarizing beam splitter 12, and split sensors 13 and 14.

The two-wavelength semiconductor laser 7 used here is
A laser with an active layer consisting of quantum well layers of two different compositions or different widths.

FIG. 2 is a diagram schematically showing an energy band diagram in the vicinity of an active layer in one embodiment of a two-wavelength semiconductor laser.

Referring to FIG.
And the 60 ° Al _0.12 Ga _0.88 As well 302
ÅAl _0.36 Ga _0.64 As barrier separated by 500 Å GRINAl _0.3 Ga _0.7 As-Al
_0.5 Ga _0.5 As optical / carrier confinement layer (SCH
Layer) 304, 305.

Further, FIG. 3, in the film structure of a two-wavelength semiconductor laser that shown schematically, n ⁺ -GaAs substrate 310
On top of this, a 0.5 μm n ⁺ -GaAs buffer layer 308,
1.5 μm n-AlGaAs lower cladding layer 306,
SCH layer 304, well layer 301, barrier layer 303, well layer 302, SCH layer 305, 1.5 μm p-Al _0.5 G
a _0.5 As upper cladding layer 307, _0.5 μm p ⁺ −
A GaAs cap layer 309 is laminated by molecular beam epitaxy, and an Au / Cr electrode 311 on the p side,
An Au-Ge / Au electrode 312 is vapor-deposited on the n-side, and is made into an alloy with an ohmic contact.

304, 301, 303, 3 near the active layer
Nos. 02 and 305 are not doped.

Next, the principle of light emission of the two-wavelength semiconductor laser will be described with reference to FIG.

When a current is applied between the electrodes 312 and 311 shown in FIG. 3, electrons e are injected into the first light emitting layer 302 and the second light emitting layer 301, and first, the electrons e are positively charged in the first light emitting layer 302. Recombination with the hole h occurs, and stimulated emission of light having a wavelength of λ ₁ = 830 nm.

Next, when the injection current is increased, recombination of electrons e and holes h occurs even in the second light emitting layer 301, and light having a wavelength of λ ₂ = 780 nm is induced and emitted. When the injection current is further increased, the oscillation of the wavelength λ ₁ stops, and only the light of the wavelength λ ₂ is emitted.

FIG. 4 schematically shows the current-light output characteristics as described above.
Shown in In FIG. 4, I indicates a current, and P ₁ and P ₂ indicate outputs of light of wavelengths λ ₁ and λ ₂ , respectively. As the current I increases, the wavelength λ ₁ at the first threshold current I = I + h
Then, the light having the wavelength λ ₂ oscillates at the second threshold current I = I ₁ . As the current further increases, I
= I ₂ , the light of wavelength λ ₁ stops oscillating, and only the light of wavelength λ ₂ oscillates.

Therefore, when the reproduction is performed with the light of λ _1, the injection current for obtaining the reproduction light output P _R is _IL , but λ ₁ and λ ₂
Also in the current I _H which There has been co-oscillation, the light output of lambda ₁ is reproduced light output P _R. At the injection current I _H ,
The optical output of λ ₂ becomes P _W and can be used for writing. In other words, during recording, binary information to be recorded, two-level I _L of the injection current, in correspondence with I _H, when modulating the laser, lambda ₁ of the optical output P _R for reproduction, depending on the modulation of the recording Instead, it is always obtained as a constant output.

FIG. 5 shows an example of an injection current waveform and an optical output waveform.

In FIG. 1, the data to be recorded, which has been input to the terminal 21, is recognized as recording data by the controller 22, and a seek mechanism (not shown) is used to access an optical spot to an area on the optical disc 1 where data is to be recorded. Then, the physical address and the logical address on the optical disk 1 and whether or not recording is possible are confirmed.

The controller 22 sends the data to the modulation unit 23, converts the data into an optical disk format, adds a header, ECC, and the like, and according to the determined modulation method,
The information is converted into a modulated binary signal, and a waveform as shown in FIG.

This waveform is converted by the laser driver 24 into an injection current waveform (FIG. 5B) to drive the laser 7.

As a result, as described above, the recording optical output waveform of λ ₂ modulated by the optical outputs O and P _W corresponding to the data to be recorded (FIG. 5D), constant reproduction output P _R a is lambda ₁ of the output waveform (FIG. 5 (c)) can be obtained.

The light λ ₁ from the laser undergoes a phase shift by the phase element 4 and becomes a spot on the disk 1 having an asymmetric light quantity distribution in the track direction.

The phase element 4 is an optical element having a stepped edge as shown in Japanese Patent Application No. 2-64305. For example, in this embodiment, as shown in FIG. A structure in which a transparent dielectric 402 is deposited on 401 is used. Here, assuming that the refractive index of the dielectric 402 with respect to the wavelengths n ₁ and n ₂ is n ₁ and n ₂ and the thickness is d, 2π (n ₁ −1) d / λ ₁ = (2m ₁ +1) π ( _{1) 2π (n 2 -1)} d / λ 2 = 2m 2 π ... (2) (m 1, m 2 = 0,1,2,3, ...) is as.

Accordingly, the wavefront of λ ₁ transmitted through the phase element 4 undergoes a shift of the phase difference π in these regions 403 and 404, but the wavefront of λ ₂ receives a relative phase difference of 0 in the two regions 403 and 404. Becomes

When examining the diffraction of the wavefront having undergone the phase shift due to the step edge, the light spot shape of λ on the optical disk 1 has a light amount distribution 405 as shown in FIG.
Becomes That is, the spot 40 which does not receive the phase shift
6 is more asymmetric in the direction perpendicular to the edge (partition line),
The dip position has a light amount distribution shifted from the optical axis. In scalar Fourier optics, which includes approximations such as Kirchhoff's boundary conditions, analysis results are obtained in which the dip falls down to zero with symmetrical results. According to the above method, the light amount distribution is as shown in FIG.

FIG. 6D schematically shows a two-dimensional spot shape. The spot 409 which is not subjected to the phase shift is divided into two large and small spots 407 and 408.

This method is less affected by wavelength fluctuations than the conventional spot separation method using a wavelength dispersion element. Accordingly, spots 408 and 407 of λ ₁ shifted in the track direction are obtained with respect to spots 409 of λ ₂ where the relative phase difference of the wavefront is 0.

Therefore, data is written on the track of the optical disk 1 at the preceding spot 409 of λ ₂ , and the subsequent written light spot 407 of λ ₁ reads the directly written data to determine whether the data has been written correctly. Confirmation, that is, verification operation can be performed in one pass. This is one spot, and the total throughput of the writing speed is greatly improved, and a high transfer rate and a high speed access are achieved, as compared with the normal method of switching between writing and verifying every rotation.

The separation of the two spots 407 and 408 is as follows:
As shown in FIG. 1, this is possible with the two-divided sensors 13 and 14 divided in the track direction.

The spot 408 preceding the recording spot 409 provides a pilot spot function for confirming a state before writing, such as confirmation of a defect on a recording medium and erasure of previous data, and a preheat function for preheating. , It is also possible to use.

When the detection is unnecessary, the two-divided sensors 13 and 14 are used as non-divided sensors, and crosstalk is reduced by optimizing the shape and size of the light-shielding mask and the sensor. It is possible to detect only

The verify signal read in this manner is subjected to waveform shaping such as photocurrent-voltage conversion, differential common-mode noise removal, amplification and filtering by the sensor amplifier 25, and is binarized. E by 26
Through a normal reproduction process such as CC decode check, the information is decoded to the original information and reproduced.

Further, the data and the data to be written are compared by a comparator 27, and a signal indicating whether the writing has been completed normally or needs to be rewritten is returned to the controller 22 depending on the type and level of the error, and the controller 22 performs necessary processing. Execute.

During normal reproduction only, the modulation is stopped by the signal from the controller 22 and the modulation unit 2
The output of the demodulation unit 26 may be output from the terminal 21 without performing the verifying operation via the comparator 27, with the output of _{No. 3} being kept at the “Low” level and emitting only λ ₁ . (Other Embodiment) FIG. 7 shows a second embodiment of the present invention. The phase element 4 shown in FIG. 6 has improved mass productivity as compared with the above-described embodiment. In contrast to the embodiment shown in FIG. 6 in which the thickness of the phase difference is formed by vapor deposition, in this embodiment, An integrated step element is formed by a glass mold. The step satisfies the expressions (1) and (2), where n ₁ and n ₂ are the refractive indexes of the glass.

It should be noted that as long as the birefringence is small, it can be manufactured even with a resin mold.

In this embodiment, the step is not vertical but is inclined so that the mold can be easily removed. This reduces the asymmetry of the spot. Studies have shown that it has no significant effect.

As a method of controlling the asymmetry, one method is to select the angle of the step edge portion, and the angle of the slope in the direction opposite to that of FIG. 7 may be selected. Alternatively, a method of depositing a conductor such as a metal only on the slope portion can be adopted.

Further, in the above embodiment, an example was described in which a phase difference π, ie, a step λ / 2, was added to the wavefront of λ ₁ as shown in equation (1). asymmetric spot formation method using, as compared to the method of separating the lambda ₁ and lambda ₂ of the beam by using a wavelength dispersion element such as a prism or a diffraction grating, Features that influence of wavelength variation of the light amount distribution of the spot is small Yes, this means that the steps and the phase difference are not so precisely created, and the cost advantage of the phase element 4 is improved as compared with the prism and the diffraction grating.

Further, in the above embodiment, an example is shown in which the step of the phase element 4 is made coincident with the optical axis.
As a result of the study, it was found that even if the position is shifted on the order of 00 μm, the obtained spot shape does not largely change. In other words, the accuracy at the time of assembly adjustment is more advantageous than the method using a prism or a grating.

Strictly speaking, λ ₂ shown in the equation (2)
The phase difference of an integral multiple of 2π given to the wavefront of
Asymmetry of the spot shape of λ ₂ occurs, but there is no particular problem since it can be regarded as substantially symmetric near the optical axis.

[0058]

As described above, in a luminous flux including a plurality of wavelengths, an optical path length difference of about a half wavelength is given only for a specific wavelength, and about an integral multiple for other wavelengths. Providing a step edge optical element that gives a difference in the optical path length of the wavelength, creating an asymmetric light quantity distribution at least in the light flux and spot of a specific wavelength, and separating the light flux and spot of other wavelengths from each other, thereby causing a wavelength variation. Light beams and light spots can be separated with little influence and reduced crosstalk between wavelengths.

Therefore, the longitudinal mode characteristic of the oscillation wavelength of the light source,
The management of the wavelength stability can be relaxed, and the accuracy in assembling and adjusting can be performed with lower accuracy than the conventional one.

[0060] For this reason, it is possible to obtain the effects that the production becomes easy, the cost can be reduced, and the reliability can be improved.

Further, unlike the dispersive element, there is no need to spread the light beam in the angle direction, so that there is an effect that the size and weight can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head unit of an optical information device using a light beam separation device of the present invention.

FIG. 2 is a schematic view of an energy band of a semiconductor laser.

FIG. 3 is a diagram showing a film configuration of a semiconductor laser.

FIG. 4 is a diagram showing injection current-optical output characteristics of a semiconductor laser;

FIG. 5 is an explanatory diagram of an injection current waveform and an optical output waveform of a semiconductor laser.

FIG. 6 is an explanatory diagram of a structure and a light spot shape of a phase element according to an embodiment.

FIG. 7 is a diagram illustrating the structure of a phase element according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magneto-optical disk (optical recording medium) 2 Achromatic pick-up lens 3 Polarizing beam splitter 4 Phase element (optical element having stepped edge) 5 Achromatic beam shaping prism 6 Achromatic collimator lens 7 Two-wavelength semiconductor laser (light source) 8 Dichroic prism 9 Beam splitter 10 λ / 2 plate 11 RF sensor lens 12 RF polarization beam splitter 13, 14 Split RF sensor 21 Information input / output terminal 22 Controller 23 Modulation unit 24 Semiconductor laser driver 25 RF sensor amplifier 26 Demodulation unit 27 Comparator 405-409 light spot

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomohiro Ikeda 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Canon Inc. (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 27 / 10 G11B 7/135

Claims (7)

(57) [Claims] A light source that emits light of a plurality of wavelengths; a light source provided in the light beam of the plurality of wavelengths, having an optical path length difference of about one-half wavelength with respect to a specific wavelength, and substantially with respect to other wavelengths. An optical element having an optical path length difference of an integral multiple wavelength and having an optical element having a stepped edge for separating the light beam of the specific wavelength from the light beam of another wavelength. 2. A light source that emits light of a plurality of wavelengths; an optical system that forms an image of the light of the plurality of wavelengths as a light spot; and a light source that is provided in the light of the plurality of wavelengths and has a specific wavelength. There is an optical path length difference of approximately one-half wavelength, having an optical path length difference of approximately an integral multiple of the wavelength with respect to other wavelengths, at least the light intensity distribution of the light spot of a specific wavelength, perpendicular to the edge line of the edge An optical element having a step-shaped edge that is asymmetric in a direction. 3. The light beam separating apparatus according to claim 2, wherein the optical element separates at least a light beam having a specific wavelength into at least two light spots having different light amounts. 4. The semiconductor laser according to claim 1, wherein the light source is a stacked semiconductor laser including an active layer including a plurality of light emitting layers having different energy levels.
3. The light beam separation device according to claim 1. 5. The step-shaped edge-shaped optical element is formed by depositing a transparent dielectric on a part of the surface of a transparent substrate to form the step-shaped edge. 3. The light beam separation device according to claim 1. 6. The light beam separation device according to claim 1, wherein the step-shaped edge-shaped optical element is a transparent glass formed in a step-shaped edge shape. 7. An optical information device comprising: the light beam separation device according to claim 1; and an information recording medium that connects a light spot generated by a light beam passing through the light beam separation device.