JP2000056185A - Laser diode module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily improve wavelength stability by adjusting the temperature of a laser diode, controlling the transmission wavelength and bringing the laser diode and an optical wavelength filter into thermal contact so as to keep both at an almost equal temperature. SOLUTION: A laser diode 1 inside a module package outputs the laser beam of a prescribed transmission wavelength and an optical fiber 9 is optically coupled to the laser diode 1 and leads out the laser beam outputted from the laser diode 1 to the outside. An optical wavelength filter 3 is provided with a cut-off wavelength almost same as the transmission wavelength of the laser diode 1. One or more photodiodes for wavelength control transmits or reflects a part of the light output of the laser diode 1 to the optical wavelength filter, then, receives it and outputs the received light level. Then, a Peltier element 6 controls the transmission wavelength of the laser diode 1. Further, a thermal contact means brings the laser diode 1 and the optical wavelength filter 3 into thermal contact so as to keep both at the almost same temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode module, and more particularly to a laser diode light source module used for optical communication and measurement, and more particularly to a laser diode module used when precise wavelength accuracy is required. is there.

[0002]

2. Description of the Related Art In recent years, with the development of wavelength multiplexing transmission technology,
Wavelength (frequency) accuracy on the order of 0.1 nm is required, and DFB-LD (Distributed Feed Back-
Simply controlling the laser diode at a constant temperature cannot compensate for the wavelength variation due to the aging of the element, so the accuracy has become insufficient. Conventionally, as an LD light source whose wavelength is controlled with high precision, as shown in FIG. 6, there is a configuration in which a specific wavelength is locked by using a fiber grating.

In FIG. 1, reference numeral 61 denotes an LD module having a built-in temperature control element, 62 denotes an optical splitter, 63 denotes a fiber grating, 64 denotes a PD (Photo Diode) module, 65 denotes an automatic frequency control (AFC) circuit, and 66 denotes It is a thermostat for fiber grating. In this case, L
A part of the output light of the D module 61 is introduced into the fiber grating by the optical splitter 62, and the reflected light takes a peak value for a specific wavelength.
4 and the AFC circuit 65 detects the LD module 61
The oscillation wavelength is stabilized by feedback to the LD temperature.

However, in this configuration, it is impossible to arbitrarily output wavelengths other than the initially set wavelength. Therefore, in order to output a large number of wavelengths by wavelength multiplexing or the like, the wavelengths are precisely adjusted for each wavelength. Fiber grating is required. Further, in order to obtain a wavelength stability of 0.1 nm or less in a wide operating temperature range of 0 to 60 ° C., even a fiber grating has a temperature dependency of about 0.005 nm / ° C., so that temperature stabilization is required. However, there is a problem that the configuration becomes complicated.

On the other hand, as shown in FIG. 7, a steep cut-off region of an optical wavelength filter using a dielectric multilayer film is used to
There is also a configuration in which a part of the output light of D is passed through an optical wavelength filter, and the temperature and drive current of the LD are adjusted so that the ratio between the transmitted power and the reflected power becomes constant. In FIG.
1 is an LD module having a built-in temperature control element, 72 is a beam splitter, 73 is an optical wavelength filter, 74 is a PD module, 75 is an AFC circuit, and 76 is an optical wavelength filter 7
3 is a constant temperature device, 77 is a collimating optical system, and 78 is an incident angle control mechanism of the optical wavelength filter 73.

In this case, after the output light of the LD module 71 is collimated by the collimating optical system 77, a part thereof is taken out by the beam splitter 72 and introduced into the optical wavelength filter 73, and its transmission power (reflection power and transmission and reflection) is obtained. Is sometimes sensitively changed depending on the wavelength. Therefore, it is detected by the PD module 74, and the LD module 71 of the LD module 71 is detected by the AFC circuit 75.
The oscillation wavelength is stabilized by adjusting the temperature.

The optical wavelength filter 73 used here
May use a bypass, a low-pass, or a band-pass filter because only the cut-off region is used.
In this configuration, by utilizing the effect that the center wavelength of the filter is shifted by mechanically changing the incident angle of the filter by the incident angle control mechanism 78, a wide range of wavelength tuning can be performed with one type of filter, and the transmission ( By selecting the power ratio of (reflection), there is an advantage that the wavelength can be finely adjusted electrically.

[0008]

However, in such a conventional laser diode module, the wavelength accuracy depends on the stability of an optical wavelength filter using a dielectric multilayer film, and the optical wavelength filter is also a fiber grating. Therefore, there is a problem that temperature control is indispensable over a wide operating temperature range. In addition, there is a problem that the space factor is poor because each module is composed of an individual module, the optical system is complicated, and the cost is high. An object of the present invention is to solve such a problem, and an object of the present invention is to provide a compact, low-cost laser diode module having good wavelength stability.

[0009]

In order to achieve the above object, a laser diode module according to the present invention includes a laser diode for outputting a laser beam having a predetermined oscillation wavelength in a module package, and an optical element for the laser diode. An optical fiber that couples the laser light output from the laser diode to the outside, an optical wavelength filter that has a cutoff wavelength that is almost the same as the oscillation wavelength of the laser diode, and a part of the optical output of the laser diode to the optical wavelength filter One or more wavelength controlling photodiodes that receive light after being transmitted or reflected and output the received light level, a Peltier element that controls the oscillation wavelength of the laser diode by adjusting the temperature of the laser diode, Heat-contact both so that the optical wavelength filter is kept almost isothermal. Those comprising a thermal contact means for. Therefore, the optical wavelength filter is substantially equal in temperature to the laser diode whose temperature is adjusted to be substantially constant by the Peltier element, and the temperature is stabilized.

[0010]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a laser diode module according to a first embodiment of the present invention. In the figure, 1 is an LD (Laser Diode) element, 2 is an optical beam splitter, 3 is an optical wavelength filter using a dielectric multilayer film, 4A, 4B and 4C are PDs having PD (Photo Diode) elements mounted on the end faces. Carrier.

Reference numeral 5 denotes an AFC circuit; 6, a Peltier element for controlling the temperature of the LD; 7, a lens for converging light from the back of the LD; 9, an optical fiber; A lens for coupling, 11 is an LD carrier on which an LD is mounted, 12 is a metal substrate on which the optical wavelength filter 3 and PD carriers 4A to 4C are mounted, 13 is an LD module package, and 14 is a sleeve for holding and fixing the fiber.

In this embodiment, the output light from the back surface of the LD is focused by the lens 7 and divided by the beam splitter 2 for power monitoring and wavelength control, and is received by the PDs of the PD carriers 4A to 4C. In FIG. 1, 4A is a PD carrier for power monitoring, and 4B and 4C are PD carriers for wavelength control. The PD carrier 4C is placed at a position where the light reflected by the optical wavelength filter 3 can be transmitted through the beam splitter 2 and received.

To assemble this, first, the LD element 1 is mounted on the LD carrier 11, and the lens 10 is fixed to the LD carrier 11 by YAG laser welding. After that, the Peltier element 6 and the LD carrier 11 are placed in the LD module package.
Is fixed by soldering, the fiber 9 is centered at an optimum coupling position via a sleeve, and fixed by YAG laser welding.

Next, the lens 7 is fixed to the LD carrier 11 by YAG welding, low-temperature solder or adhesive, while
The PD carriers 4A to 4C, the optical wavelength filter 3, and the beam splitter 2 are fixed to the metal substrate 12 with solder or an adhesive. Then, the LD element 1 is made to emit light after being connected to the package terminal with a longer gold wire, and the light receiving currents of the wavelength controlling PD carriers 4B and 4C are substantially equal when the desired wavelength is obtained.
In addition, the angle and the position of the metal substrate 12 with respect to the LD carrier 11 are adjusted so that the light receiving current of the power monitoring PD carrier 4A becomes as large as possible, and the metal substrate 12 is fixed with a YAG laser from above.

The required accuracy (tolerance) at the time of fixing mainly depends on the light receiving area of the PD. However, since a large-area PD for a low speed can be used here, the tolerance is loose and there is no problem with the axis deviation during YAG welding. Here, if the metal substrate 12 is made of a material having a low thermal conductivity such as stainless steel, the weldability with the YAG laser is good, and even when the temperature of the LD element 1 changes instantaneously due to circuit noise or the like. Since the temperature change becomes gentle, there is an advantage that tolerance for noise is increased.

Basically, the temperature dependency coefficient of an optical wavelength filter using a dielectric multilayer film is much smaller than that of an LD (about 0.1 nm / ° C. in a normal DFB-LD). Therefore, there is no need to control the temperature so precisely and quickly.
Even if the thermal conductivity is somewhat low, it is sufficient because it is stabilized at a constant temperature in the long term.

In this embodiment, automatic power adjustment (APC) for keeping the output power constant when the temperature is changed
In order to make the circuit independent, a power monitoring PD (PD carrier 4A) is provided exclusively. However, APC and A
If the FC circuit is devised and integrated, the wavelength control PD
It is also possible to perform APC control with the light receiving current of the (PD carriers 4B, 4C).

This is because if the light receiving current ratio between the two wavelength controlling PDs (PD carriers 4B and 4C) is determined to be constant, the light receiving current flowing at that time is proportional to the power.
However, in the present embodiment, when the AFC circuit 5 is not used, there is an advantage that the AFC circuit 5 can be used as a normal LD module in a normal APC circuit. Further, the fixing means and the assembling order of each part do not need to be limited to the above description, and may be changed according to the conditions of the apparatus and members.

Further, in FIG. 1, each PD carrier is drawn at a position perpendicular to the incident light, but in practice, the optical axis and the end face are slightly angled to avoid the reflected light returning to the LD. Needless to say, it is better to arrange them.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a configuration diagram illustrating a laser diode module according to a second embodiment.
In this figure, the same or equivalent parts as those described above (see FIG. 1) are denoted by the same reference numerals, and 5A is a control circuit for both AFC and APC.

In the present embodiment, the wavelength control PD can be simplified to one, and the width of the module package 13 can be reduced by placing the optical wavelength filter 3 in the optical axis direction of the LD element 1. Is the feature. The assembling method is almost the same as that of the first embodiment, but since the wavelength controlling PD is only the PD carrier 4B, the light receiving current is fixed at about half the maximum value at the specified wavelength. .

In actual use, the LD carrier temperature is at most 5
In the structure in which the optical wavelength filter 3 and the wavelength control PD are temperature-stabilized, it is possible to sufficiently stabilize only one of the PDs. However, the AFC circuit 5
In A, it is necessary to control the current ratio between the monitor PD and the wavelength control PD to be constant. At the same time, in order to perform the APC operation, the AFC circuit 5A needs to incorporate a LD drive circuit for the APC. Become.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a configuration diagram showing a laser diode module according to the third embodiment.
In the figure, the same or equivalent parts as those described above (see FIGS. 1 and 2) are denoted by the same reference numerals.

In the present embodiment, the assembly is simplified by bonding the beam splitter 2 and the optical wavelength filter 3 or integrating them by double-side deposition. P
Due to the arrangement of the D carriers 4A and 4B, the angle of incidence on the optical wavelength filter 3 must be increased. Therefore, a film design corresponding to this is necessary. However, there is basically no problem. , Are almost the same as those of the second embodiment, and a description thereof will be omitted.

Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 4 is a configuration diagram illustrating a laser diode module according to a fourth embodiment.
In the figure, the same or equivalent parts as those described above (see FIGS. 1 to 3) are denoted by the same reference numerals, and 15 is a half-wave plate.

In this embodiment, by using a normal glass plate as the beam splitter 2, the detection sensitivity is improved by utilizing the difference in the reflectance of the polarization component with respect to the incident angle. Here, BK7 (refractive index =
Assuming that the incident angle is 56.5 degrees (Brewster's angle) using 1.51), the reflectance for the polarized light of the parallel component with respect to the incident surface is about 15%, while the reflectance for the vertical component light is almost 0%.
%.

Since the LD element 1 normally performs TE mode oscillation (in the case of the arrangement shown in FIG. 4, vertical polarization at the incident angle), a half-wave plate 15 is inserted between the LD element 1 and the beam splitter 2, and
If rotated by 0 degrees, the TM component of the LD element 1 (spontaneous emission light mainly including a wide wavelength component) does not come to the wavelength detection PD, so that there is an advantage that the noise level of wavelength detection can be reduced.

Incidentally, even if the incident angle of the glass plate actually has an error of about ± 5 degrees, it is sufficiently effective for polarization separation.
There is no problem in angle adjustment at the time of wavelength adjustment. 1/2 wave plate 1
Except for the addition of 5, the assembling method and the method of use are almost the same as those of the second embodiment, and a description thereof will be omitted.

Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a configuration diagram illustrating a laser diode module according to a fifth embodiment.
In the figure, the same or equivalent parts as those described above (see FIGS. 1 to 4) are denoted by the same reference numerals, and 3A is an optical wavelength filter fixed to a metal member in advance.

This embodiment has the same optical configuration as the second embodiment, but is different from the second embodiment in the assembly procedure. That is, a metal substrate 12 on which a beam splitter and a PD are mounted in advance is attached to the LD carrier 11 by each PD (P
DAGs 4A and 4B) are aligned and fixed to YAG so that the light receiving current is maximized.

Finally, the optical wavelength filter 3 is positioned (mainly at an angle), and the metal part is fixed by YAG at a place where the light receiving current of the wavelength controlling PD (PD carrier 4B) becomes about half of the maximum value. And assemble. According to such an assembling method, although the number of steps is increased, the accuracy of each part can be relaxed, so that improvement in yield and optimization of characteristics can be expected.

In each of the above-described embodiments, the wavelength of the light emitted from the back surface of the LD element 1 is used exclusively for the wavelength detection. It is also possible to use it by taking it out with a half mirror or the like.

[0033]

As described above, according to the present invention, a laser diode for outputting a laser beam having a predetermined oscillation wavelength and a laser beam optically coupled to the laser diode and output from the laser diode are provided in a module package. Optical fiber, an optical wavelength filter with a cut-off wavelength that is almost the same as the laser diode's oscillation wavelength, and a part of the laser diode's optical output that is transmitted or reflected by the optical wavelength filter and then received. One or more wavelength controlling photodiodes that output laser light, a Peltier element that controls the oscillation wavelength of the laser diode by adjusting the temperature of the laser diode, and a laser diode and an optical wavelength filter that are kept substantially isothermal. Thermal contact means for bringing the two into thermal contact with each other. Therefore, since the optical wavelength filter is almost isothermal with the laser diode whose temperature is controlled to be substantially constant by the Peltier element, the temperature is stabilized, so that the excellent wavelength stability can be achieved without separately providing a thermostat. The laser diode light source having the above characteristics can be realized compactly and at low cost with a single module.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a laser diode module according to a first embodiment.

FIG. 2 is a configuration diagram illustrating a laser diode module according to a second embodiment.

FIG. 3 is a configuration diagram showing a laser diode module according to a third embodiment.

FIG. 4 is a configuration diagram showing a laser diode module according to a fourth embodiment.

FIG. 5 is a configuration diagram showing a laser diode module according to a fifth embodiment.

FIG. 6 is a configuration diagram showing a conventional laser diode module.

FIG. 7 is a configuration diagram showing another conventional laser diode module.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... LD element, 2 ... Beam splitter, 3 ... Optical wavelength filter, 4A ... PD carrier (for power monitor), 4B,
4C: PD carrier (for wavelength control), 5: AFC circuit,
5A: AFC / APC circuit, 6: Peltier element, 7: Lens (for back light), 9: Optical fiber, 10: Lens (for front light), 11: LD carrier, 12: Metal substrate, 13
... Module package, 14 ... Sleeve, 15 ... 1 /
Two-wave plate.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Isao Nishi 20-1 Sakuragaoka-cho, Shibuya-ku, Tokyo F-term in NTT Electronics Corporation (reference) 2H037 AA01 BA03 BA12 DA03 DA04 DA05 DA06 DA38 5F073 BA02 EA03

Claims (6)

[Claims] A laser diode for outputting a laser beam having a predetermined oscillation wavelength; an optical fiber optically coupled to the laser diode for guiding the laser beam output from the laser diode to the outside; An optical wavelength filter that has a cutoff wavelength that is almost the same as the oscillation wavelength, and one or more wavelength controls that output a part of the optical output of the laser diode after being transmitted or reflected by the optical wavelength filter and output the received light level A photodiode, a Peltier element for controlling the oscillation wavelength of the laser diode by adjusting the temperature of the laser diode, and a thermal contact means for thermally contacting the laser diode and the optical wavelength filter so that the two are maintained at substantially equal temperatures. A laser diode module comprising: 2. A laser diode for outputting a laser beam having a predetermined oscillation wavelength, an optical fiber optically coupled to the laser diode for guiding the laser beam output from the laser diode to the outside, and a laser diode. An optical wavelength filter having a cut-off wavelength substantially equal to the oscillation wavelength, a beam splitter for splitting a part of the optical output of the laser diode into two, and transmitting or reflecting one of the spectral outputs of the beam splitter to the optical wavelength filter. One or more wavelength controlling photodiodes that receive light after receiving the light, and output the light receiving level; a power monitoring photodiode that receives the other of the spectral output of the beam splitter and output the light receiving level; and a temperature of the laser diode. The oscillation wavelength of the laser diode by adjusting The laser diode module comprising: the Peltier element, and a thermal contact means for thermally contacting the two so that the laser diode and the optical wavelength filter is kept substantially isothermal. 3. The laser diode module according to claim 2, wherein the thermal contact means is provided with an optical wavelength filter, each photodiode and a beam splitter in advance, and a laser is provided so that the light receiving level of the power monitoring photodiode is maximized. A laser diode module which is aligned with a diode and fixed by YAG laser welding. 4. The laser diode module according to claim 2, wherein the thermal contact means has a photodiode and a beam splitter mounted in advance, and is positioned and fixed so that the light receiving level of the power monitoring photodiode is maximized. The optical wavelength filter is fixed to the thermal contact means after the fixing by YAG laser welding so that the light receiving level of the wavelength controlling photodiode becomes a predetermined value. Laser diode module. 5. The laser diode module according to claim 1, wherein said thermal contact means comprises a metal substrate having a low thermal conductivity. 6. The laser diode module according to claim 1, wherein the optical wavelength filter and the beam splitter are integrally formed.