JPH0491485A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To make it possible to radiate laser light which has stabilized wavelength and excellent mono-chromaticity by installing a semiconductor laser device, a photodiode which monitors the intensity of laser light radiated from the semiconductor laser device, and an optical modulator which modulates the intensity of laser light on the same stem. CONSTITUTION:A DFB type semiconductor laser device 101, which is a light source, is installed to a stem 103. Then, a photodiode 102 to monitor radiated light is installed so that it may come into contact with the radiation end face. To supply current to the semiconductor laser device 101, an interconnection is made between a surface electrode of the semiconductor laser device 101 and a stem rear side electrode 109. An interconnection is made from another electrode of the photodiode 102 to a stem rear side electrode 110 where a stem electrode 114 is further installed. The stem is covered with a stem cap 108. A liquid shutter 104, which serves as an optical modulator, is installed to the stem cap 108 so that it may come into contact with the forward radiating end face of the semiconductor laser device 101.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device, and more specifically,
The present invention relates to a semiconductor laser device that can obtain laser light with excellent wavelength stability even when driving methods with different degrees of modulation are used.

(Prior Art) Semiconductor laser elements are very small and can produce light with high intensity, so they are used, for example, as a light source for reading information in optical disk devices, a light source for laser printers, or in the field of optical communications. It is widely used as a light source in In particular, laser printers are currently applied exclusively to office equipment such as computer printers, electronic copying machines, and facsimile machines. But in the future.

Considering that these devices will become widespread in general households, it is expected that the demand for semiconductor laser devices will increase significantly.

Laser printers currently in practical use mainly include:
A method is adopted in which the laser beam is deflected using a polygon mirror. However, this type of laser printer has various problems. For example, many steps are required to process a polygon mirror, which increases the cost of laser printers. Furthermore, since the polygon mirror needs to be rotated at high speed, a large amount of noise is generated.

Recently, in order to solve such problems.

As an optical means for deflecting laser light.

A method using a hologram instead of a polygon mirror is being actively studied. This hologram method allows for mass production using a stamp method, so the cost of laser printers can be reduced. Moreover, the member used is disk-shaped.

31 It has the advantage of almost no noise during rotation.

Furthermore, the conventional one-type polygon mirror has the advantage that it does not require an Fθ lens that is used after deflecting the laser beam.

FIG. 4 is a schematic diagram of a holographic laser printer system. Here, the printing principle of this laser printer will be explained.

A laser beam 402 with a wavelength of about 780 nm emitted from a semiconductor laser element 401 serving as a light source passes through a collimator lens 4.
06, deflected and scanned by the hologram disk 403, and passed through the cylindrical lens 407.

The surface of the photoreceptor drum 404 is irradiated with light. At this time.

As the photoreceptor drum 404 rotates, the light emission intensity of the semiconductor laser element 401, which is the light source, is modulated using a drive current direct modulation method according to the pattern to be printed.
This pattern is drawn on the surface of the photoreceptor drum 404. The wavelength of the laser light emitted from the semiconductor laser element 401 is set within a range in which the photosensitive layer formed on the surface of the photosensitive drum 404 has sufficient sensitivity. Only the photosensitive portions of the photosensitive drum 404 that have been exposed to light according to the pattern are charged and attract toner (not shown). The toner adsorbed in the pattern comes into contact with the surface of the paper 405 as the photosensitive drum 404 rotates, and the pattern to be printed is transferred onto the paper 405. Next, the paper 405 onto which the pattern has been transferred is heat-treated by a heating means (not shown) to fix the toner, and is then ejected from the printer. By repeating this series of operations, a desired pattern can be continuously printed on plain paper.

The above-mentioned technique of polarizing laser light using a hologram utilizes the phenomenon of light diffraction.

Its principle is "optical integrated circuit" (Hiroshi Nishihara, Masamitsu Haruna).

Co-authored with Toshiaki Suhara, published by Ohmsha, 1985, No. 67~
lot page). What is the deflection direction of the laser beam?

It changes depending on conditions such as the rotation period of the hologram, its shape, the incident direction of the laser beam, and the wavelength of the laser beam.

In order to print no f turns with appropriate precision in a laser printer, an error of approximately 50 μm is required on the photoreceptor drum 404.
The pattern must be formed with an accuracy of m. Therefore, the deflection direction of the laser beam must be set strictly.
The conditions mentioned above must be kept constant. Among them,
It is particularly important to suppress fluctuations in the wavelength of the laser light irradiated onto the hologram disk 403 to 5 Å or less. Therefore, the one-distribution feedback type (
DFB type) semiconductor laser device, Bragg reflection type (DBR type)
Semiconductor laser devices having a wavelength stabilizing structure, such as type) semiconductor laser devices and composite resonator semiconductor laser devices, are preferred. This is because semiconductor laser elements having these wavelength-stabilized structures oscillate in a single longitudinal mode and have excellent monochromaticity even when pulse-driven by supplying a driving direct current in pulses.

The structure of these semiconductor laser devices is based on “optical communication device engineering.”
(Yasuharu Suematsu, published by Ohmsha, 1984.

Chapter 12).

(Problems to be Solved by the Invention) FIG. 5(a) is a graph diagram showing an example of a current nozzle signal when modulating the intensity of laser light using a conventional semiconductor laser device. (b) is a graph diagram showing the wavelength fluctuation of the laser light pulse signal emitted from the semiconductor laser device in response to the above-mentioned no-time reply signal.

When actually printing by modulating laser light with a laser printer that uses the semiconductor laser device as described above as a light source, the modulation signal applied to the semiconductor laser device is
As shown in FIG. 5(a), the current pulse signal has nine different widths.

Theoretically, when such a current pulse signal is applied, a pulse signal of laser light of a constant wavelength can be obtained in immediate response to changes in the signal.

In reality, since the semiconductor laser element generates heat while current is flowing, the wavelength of the laser light varies depending on the width of the applied current pulse signal and the current density. Therefore, when a current Noculus signal as shown in FIG. 5(a) is applied to a semiconductor laser element, a Noculus signal of a laser beam with a disordered wavelength as shown in FIG. 5(b) is obtained. There are many.

Especially in the case of FIG. 5(b).

Since the wavelength of the laser light emitted during the first current pulse signal varies by more than 5, it is not possible to obtain a printed pattern with adequate precision.

The present invention solves the above-mentioned conventional problems, and its purpose is to provide a device with stable wavelength and excellent monochromaticity, regardless of the length of the applied current pulse or current density. An object of the present invention is to provide a semiconductor laser device capable of emitting laser light.

(Means for Solving the Problems) The present invention includes a semiconductor laser device, a photodiode that monitors the intensity of laser light emitted from the semiconductor laser device, and an optical modulator that modulates the intensity of the laser light. The present invention is a semiconductor laser device provided on a stem, thereby achieving the above object.

Preferably, an electrode for supplying a drive current to the semiconductor laser element, an electrode for extracting a monitor current from the photodiode, an electrode for applying a drive voltage to the optical modulator, and a common voltage level is supplied to each of these elements. The electrode is drawn out from the stem.

The semiconductor laser element used in the semiconductor laser device of the present invention has a single distribution feedback structure and a single distribution reflection structure.

At least one selected from the group consisting of a composite resonator structure using a light reflecting part installed inside or outside the element.
It is preferable to have two wavelength stabilizing structures.

In addition, the above-mentioned luminous intensity: A device is 2, for example, an optical shutter using liquid crystal, a solid magneto-optic effect element.

and solid electro-optic effect elements. An optical modulator that constitutes a window provided in the stem may also be used.

(Function) In the semiconductor laser device of the present invention, the current density of the drive current applied to the semiconductor laser element is kept constant, and by applying a voltage pulse signal to the optical modulator, light is emitted from the semiconductor laser element. modulates the laser beam. In this way, when the current density of the current supplied to the semiconductor laser element is constant, the temperature of the semiconductor laser element is kept constant, so fluctuations in the wavelength of the laser light due to temperature changes are suppressed. be done.

(Example) An embodiment of the present invention will be described below.

FIG. 1 is a sectional view showing a semiconductor laser device which is an embodiment of the present invention.

A DFB type semiconductor laser element 101 serving as a light source is provided on the stem 103, and a photodiode 102 for monitoring emitted light is provided facing the rear emitting end face thereof. Both of these are fixed to the stem with n-type solder material on each electrode surface.

In order to supply current to the semiconductor laser device 101, the stem back electrode 10 is connected from the front surface electrode of the semiconductor laser device lot.
9, and is wired from the other electrode of the photodiode 102 to the stem back electrode 110 in order to monitor the emitted laser light. moreover.

A stem electrode 114 is provided on the stem. The stem is covered with a stem cap 108, and a liquid crystal shutter 104, which is an optical modulator, is provided on the stem cap 108, facing the front emission end face of the DFB type semiconductor laser element 101. LCD shutter 10
4 is a laser beam exit window, which has a structure in which a liquid crystal material 105 is sandwiched between two polarizing plates 106 and 107 provided with transparent electrodes. Either the transparent electrode provided on the polarizing plate 107 on the light input side or the transparent electrode provided on the polarizing plate 106 on the light output side is connected to the stem, and the other is connected to the cap provided on the stem cap 108. Electrode 112. and is led out to the back electrode 111 of the stem 103 via the cap electrode receiver 113.

A twisted nematic method was adopted as a method for modulating laser light with a voltage signal using the liquid crystal shutter 104. This is done by applying a voltage to an electrode provided in contact with the liquid crystal material to change the alignment state of the liquid crystal contained in the liquid crystal material.

This method modulates the intensity of transmitted light by utilizing the principle of controlling the polarization direction of light transmitted through a liquid crystal material.

By combining this liquid crystal material and a polarizing plate,
The intensity of transmitted light can be modulated. This principle is explained in the ``Applied Physics Handbook'' (edited by Japan Society of Applied Physics, published by Maruzen Co., Ltd.).

1990, p. 50). In the semiconductor laser device of the present invention, the light emitted from the DFB type semiconductor laser element 101 is generally TE mode polarized light, and the polarization plane is between the stem 103 and the semiconductor laser element 101.
parallel to the joint surface with Therefore, the polarizing plate 106 on the light output side is provided so that its polarization direction is parallel to the bonding surface between the stem 103 and the semiconductor laser element 101, and a glass plate is used instead of the polarizing plate 107 on the light input side. You can.

Such an optical modulator used in the present invention is adjusted to transmit light only when a voltage signal is applied.

The semiconductor laser element 101 of the above-described semiconductor laser device was continuously driven by passing a direct current through it. After a short period of time after startup, the heat generation and heat dissipation caused by the drive current of the semiconductor laser device 101 reached an equilibrium state, and the temperature of the device became stable. Open the liquid crystal shutter 104 to emit forward light 11
After confirming that the light 5 is emitted, the rear emitted light 116
While monitoring using the photodiode 102, the wavelength of the laser beam was adjusted to 780 nm. Then, when the fluctuation width of the wavelength of the laser beam was measured, the wavelength fluctuation width was 2 Å or less.

FIG. 2(a) is a graph diagram showing an example of a voltage pulse signal when the intensity of emitted light is modulated using the semiconductor laser device of the present invention, and FIG. 2(b) corresponds to the voltage pulse signal described above. FIG. 2 is a graph diagram showing wavelength fluctuations of a laser light pulse signal emitted from a semiconductor laser device.

The liquid crystal shutter 104 is as shown in FIG. 2(a).

A voltage pulse signal corresponding to the printed pattern was applied. Only while the voltage was applied, the liquid crystal shutter 104 was opened to emit laser light, and a pulse signal of laser light with a stable wavelength as shown in FIG. 2(b) was obtained. The maximum modulation speed was 100 μs.

9 In this example, DF is used as the semiconductor laser element.
Although a B-type semiconductor laser device is used, similar results can be obtained even if a Bragg reflection type laser device or a composite resonator type semiconductor laser device is used instead.

As a way to obtain faster modulation speed.

It is conceivable to use a ferroelectric type liquid crystal material as the liquid crystal material used in the optical modulator, and to use a solid magneto-optic effect element in the optical modulator.

This solid magneto-optic effect element is GGG (Gado
Magnetic garnet thin film (5 μm thick) of iron bismuth on a transparent substrate of liniumGallium Garmet
It has been established. The thin film exhibits the Faraday effect and has the property of rotating the plane of polarization of transmitted light depending on the direction of the magnetic field applied thereto. The magnetic field is generated by passing a current through the thin film, and in order to change the direction of the generated magnetic field, a heat pulse is applied to the thin film using a heating resistor. An optical modulator is obtained by sandwiching this solid magneto-optic effect element between two polarizing plates.

When this optical modulator is used in the semiconductor laser device of the present invention, it is used for passing current through the thin film, or.

It is necessary to newly provide the stem with a wiring electrode used to pass current through the heating resistor.

A solid electro-optic effect element may be used in the optical modulator. In this case as well, it becomes possible to perform optical modulation at relatively high speed.

A typical example of a solid-state electro-optic effect element is Ga
An example is an element having a multiple quantum well structure of As and AlGaAs. This device is fabricated as shown below.

Figure 3 shows a typical example of a solid-state electro-optic effect element.
1 is a cross-sectional view of an element having a multiple quantum well structure of As and AlGaAs.

First, on the n-GaAs substrate 301, n-Al
GaAs layer 302. A high resistance multiple quantum well layer 303 made of a GaAs layer and an AlGaAs layer. Then, a p-AlGaAs layer 304 is sequentially grown using molecular beam epitaxial method. Next.

By partially etching and removing the substrate, a light incidence part 306 is provided, and finally, an ohmic electrode 308 is formed on the back surface of the substrate, and an ohmic electrode is formed on the surface of the p-AlGaAs layer 304 except for the light propagation part 307. 309 is provided.

In the figure, the arrow indicates the forward emitted light 115 from the semiconductor laser element.
shows the state in which light is transmitted through this solid-state electro-optic effect element.

When using the solid electro-optic effect element manufactured in this way as an optical modulator, ohmic electrodes 308 and 309
By applying a voltage to and changing the light absorption rate of the multiple quantum well layer 303, the forward emitted light 115 is modulated.

Regarding the principles of the light modulation method described above, see 9.
"Physics and Applications of Semiconductor Superlattices" (edited by the Physical Society of Japan, published by Baifukan, 1984). In a semiconductor laser device using this solid-state electro-optic effect element, n
Modulation speeds on the order of s can be obtained relatively easily. This optical modulator has an extinction ratio inferior to that of a liquid crystal shutter, but since the sensitivity of the photoreceptor to light intensity changes nonlinearly, the on/off characteristics of the optical modulator can be adjusted.

There are no problems with printing characteristics.

As an optical modulator of the semiconductor laser device of the present invention.

In addition to this, it also has a multiple quantum well structure.

An etalon-type optical modulator or the like that changes the refractive index of transmitted light by stiffening the voltage can be used.

The semiconductor laser device of the present invention can emit various laser beams with wavelengths other than the laser beam with a wavelength of 780 nm, such as 670 na+ and 830 rv.

Furthermore, it can be used not only as a light source for laser printers, but also as a light source for any system that requires a stable wavelength of emitted light. For example, if a semiconductor laser device with an output light of 1.3 μm band or 1.55 μm band is used, it is optimal as a light source for an optical LAN (optical local area network) system.

(Effects of the Invention) In the semiconductor laser device of the present invention, the current density of the current applied to the semiconductor laser element is kept constant, and the laser light is modulated by applying a voltage pulse signal to the optical modulator. Even when laser light is modulated by pulse signals of various different lengths, laser light pulses with stable wavelengths can be obtained.

4,' 1. Figure 1 is a cross-sectional view showing an example of the semiconductor laser device of the present invention, and Figure 2 (a) is an example of a voltage pulse signal when modulating the intensity of emitted light using the semiconductor laser device of the present invention. FIG. 2(b) is a graph showing the wavelength fluctuation of the laser light pulse signal emitted from the semiconductor laser device in response to the voltage pulse signal, and FIG. 3 is a representative of the solid-state electro-optic effect element. FIG. 4 is a schematic diagram of a holographic laser printer system, and FIG. FIG. 5(b) is a graph showing an example of a current pulse signal when the intensity of the laser light is modulated by using the current pulse signal. FIG.

101...DFB type semiconductor laser element, 102.
...Photodiode, 103...Stem, 104...
・LCD shutter 108... Stem cap,
109, 110, 111... stem back electrode.

114... Stem electrode.

that's all

Claims (1)

[Claims] 1. A semiconductor laser element, a photodiode for monitoring the intensity of laser light emitted from the semiconductor laser element, and an optical modulator for modulating the intensity of the laser light are provided on the same stem. Semiconductor laser equipment. 2. An electrode for supplying a drive current to the semiconductor laser element, an electrode for extracting a monitor current from the photodiode, an electrode for applying a drive voltage to the optical modulator, and supplying a common voltage level to each of these elements. The semiconductor laser device according to claim 1, wherein the electrode is drawn out from the stem. 3. The semiconductor laser element has at least one wavelength stabilizing structure selected from the group consisting of a distributed feedback structure, a distributed reflection structure, and a composite resonator structure using a light reflecting section installed inside or outside the element. The semiconductor laser device according to claim 1, having a structure. 4. The light modulator includes an optical shutter using liquid crystal;
The semiconductor laser device according to claim 1, wherein the semiconductor laser device is selected from the group consisting of a solid-state magneto-optic effect element and a solid-state electro-optic effect element. 5. The semiconductor laser device according to claim 4, wherein the optical modulator constitutes a window provided in the stem.